RU2647338C2 - Method for evaluating external and internal parameters of friction units when tested in bench conditions - Google Patents

Abstract

FIELD: machine building; measurement technology.

SUBSTANCE: invention relates to methods for evaluating external and internal parameters of friction units of brake devices in bench conditions, in particular, pairs of friction of belt-block brakes of drilling winches. Method for estimating external and internal parameters of friction units is proposed for testing in bench conditions, in which the mechanical systems of the object and model structure, consisting of subsystems, at their contact-pulse electrothermomechanical frictional interaction of subsystems, which is in interaction with design features, linear or polynomial laws of change of tachograms of a frictional metal element of a friction pair, as well as with speed, power, electrical, thermal and chemical characteristics of the friction unit, which make up its single field of energy interaction, that between the external and internal parameters of the “object” and “model” provide the necessary relationships.

EFFECT: increase in reliability of the results of determining the operating parameters of friction pairs is achieved.

1 cl, 12 tbl, 57 dwg

Description

The invention relates to methods for evaluating the external and internal parameters of friction assemblies of brake devices in bench conditions, in particular friction pairs of tape-shoe brakes of drawworks.

A known method for determining operational parameters with a quasilinear regularity of their change in the band brake of the drawworks consists in the fact that when the brake pulley rotates from a steady value to zero when the loaded elevator is lowered, the operational parameters reduced to the first group of the band brake are determined in the following sequences: evaluate the rotation mode of the brake pulley, then determine the braking time, the tension of the oncoming branch of the brake belt, maximum and minimum specific loads in friction pairs, braking torque developed by friction units; safety factor of braking torque, energy consumption of friction units, efforts exerted by a driller to a brake control lever; brake efficiency. Then, successively determine the operational parameters, summarized in the second (safety factor of the cross section of the brake tape and the deformation of its branches; the deformation of the friction lining; the general deformation of the elements of the brake system), the third (heat, temperature and their distribution over the thickness of the rim of the brake pulley; heat transfer intensity ; distribution coefficient of heat fluxes between tribojoint elements; thermal deformations of the brake pulley rim and friction lining) and the fourth (wear o-friction properties of the friction pairs) band as applied to the belt drum brakes drawworks. It is possible to determine operational parameters with a quasilinear pattern of their change in band brakes with the interconnected power, thermal and wear-friction properties of their friction pairs and limiting permissible limitations of the speed, dynamic and thermal conditions that ensure the working state of the winch brake system (1, analog , Russian patent No. 2507423 C2, CL F16D 49/08 for 02.20.2014).

The disadvantage of this method is that it did not consider the internal parameters of friction friction pairs, namely: the work function of the electrons and ions; Fermi levels; charge density; Debye shielding length; various kinds of electric currents, electron affinity, various types of contacts, etc.

It is known that for modeling external friction the method of dimensional analysis and similarity theory was used, which made a number of significant refinements. Four submodels were considered:

- macrocontact taking into account K _OT (coefficient of mutual overlap);

- macroheat formation, thermal conductivity and heat transfer;

- microcontacting spots of protrusions of friction pairs;

- heat generation on rough surfaces.

At the same time, the main parameter was introduced into consideration - the complex of geometric dimensions Kg, through which all operating parameters of model tests were determined. It is shown that the sizes of the elements of the friction pair and the friction path of the microprotrusions affect the friction process in different ways and it is necessary to characterize them with a specific dimension. It is also shown that the same dimensional quantities for the first, second element and the environment must be taken into account. As a result, a number of criteria were obtained (thermophysical, heat transfer, physical and mechanical), the observance of which ensures the identity of the friction and wear processes on the model and in kind during dry friction (2, prototype, A.V. Chichinadze. Practical implementation of thermal dynamics and friction modeling and wear during dry and boundary friction / A.V. Chichinadze // Practical Tribology. World experience. Volume I. - M .: Center: Science and technology. - 1994. - S. 67-72).

The proposed method for modeling external friction has the disadvantage that the submodel includes parameters that relate to different fields of frictional interaction with a significantly different nature. In addition, such complex criteria, which have a different physical nature due to the parameters included in them, significantly distort the arising fields during electrothermomechanical friction and do not make it possible to form them into a single field of friction interaction in the tribosystem.

Compared with analog and prototype, the proposed technical solution has the following advantages:

- declared contact-pulsed electrothermomechanical friction, in which the patterns of change in the normal force over time were studied by the method of pulsed pairs during oscillatory processes of microprotrusions of the pulley rim for pulsed moment circuits, i.e. "negative-positive" and "positive - negative";

- regularities of changes in the lines of currents of the force, electric, thermal and chemical fields, which are characterized by internal and external parameters, in interaction with the lines of the currents of the velocity field of the washing media, obeying the wave nature in phase and described both by simplexes and criteria that enter into the functional dependencies;

- considered several different standard criteria at the micro level, on the basis of which one of the main "non-standard" criteria was obtained, establishing a relationship between the thermophysical parameters of friction elements and washing them with high-speed currents of air and mixture, not only in the gaseous, but also in the liquid state;

- the static and dynamic coefficients of mutual overlap of the multi-pair friction units of the tape-block brake are introduced, which make it possible to control the pulsed specific loads on the on and off surface of its brake pulley;

- the concepts of the rates of heating and forced cooling of the surface and subsurface layers of the rims of the brake pulleys with pulsed and continuous heat supply are introduced and the surface and volume temperature gradients are determined;

- it was found that the electrothermal resistance of discrete contacts with different energy activities of micro-capacitors and - thermoelectric batteries with their instantaneous switching when changing both the area of the spots and the types of contacts of the microprotrusions and the gradient of mechanical properties, as well as the penetration rate of the interacting pulses of electric and thermal currents affect the intensity of wear of microprotrusion during repolarization, leading to the destabilization of the dynamic coefficient of friction of metal fields ernyh friction pairs;

- the total thermal stresses acting on the rim of the brake pulley are determined, taking into account its design parameters and the features of the mounting protrusion associated with the rim surface that is not working.

The aim of the present invention is to increase the reliability of the results of determining the external and internal operational parameters of metal-polymer friction pairs of tape-shoe brakes of drawworks in bench conditions.

This goal is achieved in that the patterns of change in the lines of the currents of the force, electric, thermal and chemical fields, characterized by internal and external parameters, in interaction with the lines of the currents of the velocity field of the washing media obey the wave nature with a phase shift and are described by the corresponding dependencies, subject to the following relations :

- the ratio of the height of the microprotrusions of the friction surfaces of the object (H) and the model (h) is H / h = C _H = 1,0;

- the ratio of the length of the microprotrusions of the fictitious surfaces of the object (L _m ) and the model (l _m ) is equal to L _M / l _M = C _Lm = 1,0;

- the ratio of the areas of the spots of contacts of the microprotrusions of the friction surfaces of the object (A _o ) and the model (A _m ) is equal to A _o / A _m = C _Ao = 1.0;

- the ratio of the impulse normal forces of the object (N) and model (n) is N / n = C _N = 1,0;

- the ratio of the linear sliding velocities of the object (V _CK ) and the model (v _ck ) is equal to V _CK / v _ck = C _V = 1,0;

- the ratio of the pulsed friction forces of the object (F _t ) and the model (f _t ) is F _t / f _t = С _Ft = 1,0;

- the ratio of the pulsed dynamic coefficients of friction of the object (f _o ) and the model (f _m ) is equal to f _o / f _m = C _fo = 1,0;

- the ratio of the pulsed specific loads of the object (r _o ) and model (r _m ) is equal to r _o / r _m = C _Po = 1,0;

- the ratio of the impulse braking moments of the object (M _o ) and the model (M _m ) is equal to M _o / M _m = C _Mo = 1.0;

- the compliance ratio of the joints of the subsystem "brake tape - non-working surfaces of the linings" of the object (P _o1 ) and model (P _o2 ) is equal to P _o1 / P _o2 = C _Po1 = 1.0;

- the ratio of the amplitudes of the oscillations of the bonds of the mechanical subsystems and the deformations of the microroughness of the object (A) and model (a) is equal to A / a = C _A = 1.0;

- the ratio of the energy levels of the surface layers of the object (E ' _o ) and the model (E' _m ) is equal to E ' _o / E' _m = C _E'o = 1.0;

- the ratio of the currents of the speeds of the washing air of the object (V _B ) and the model (v _B ) is equal to V _B / v _B = C _Vt = 1>0;

- the ratio of the velocity currents of the components of the washing media of the object (V _c ) and the model (v _c ) is equal to V _c / v _c = C _Vc = 1.0, and in this case, not only surface temperatures, but also chemical equalities are observed in an open thermodynamic tribo-conjugation system potentials in forced convective heat transfer of its subsystems:

- “the outer surface of the pulley rim - high-speed currents of cooling air”;

- "the inner surface of the pulley rim - high-speed currents of the components of the washing medium";

- “the surface and the surface layer of the polymer lining - high-speed currents of the components of the washing medium”, and the interaction of the subsystem “brake pulley rim - mounting protrusion - winch drum flange” is carried out by conductive heat exchange due to variable temperature gradients along their thickness, after which measurements and parameters are made tribological conjugation with simultaneous monitoring and fixing of areas of the spots of contacts of microprotrusions in real time because the electrothermal resistance of the disc contacts with different energetic activity of microcapacitors and thermal batteries with their instantaneous switching when the contact areas of the microprotrusions change, subject to the conditions at the first stage of frictional interaction (A _f <A _n ), based on the fact that the actual contact area (A _f ) is small in comparison with a nominal value (A _n ) and at the same time, the components of the generated currents are summed, and under the condition A _n = A _f , the triboEMF is fixed in conjunction with the variable gradients of the mechanical properties of its materials. The penetration rate of the interacting pulses of electric and thermal currents affects the wear rate of the microprotrusions during repolarization, and the values of the thermal currents on the surfaces of the contact stains of the microprotrusions are determined using the hypothesis of summing the surface temperatures taking into account the generated electric currents

A bulk temperature (ϑ _v1 ) is formed in the body of the metal friction element, caused by the action of the first two temperature components, as well as from the Joule heat; temperature ϑ _{v1 is} determined from the condition of the action of two heat sources (electric and frictional) in the friction zone

Flash point ϑ _vsp is determined by the type:

The volumetric temperature of the metal friction element (ϑ _v1 ) is determined from the condition that the heat fluxes on the contact surface are equal, taking into account the friction and electric components, as well as taking into account the velocity of the washing medium from the polished surface:

Subsequently, the energy levels of the surface and subsurface layers of tribo-conjugation elements are estimated from the above temperatures. After that, the maximum compressive stresses σ _1max in the pulley rim are determined analytically

которое характеризует темп нагревания обода шкива, а в зависимость вместо

которая характеризует температурные градиенты по толщине рассматриваемых элементов, а зарождение и развитие трещин на рабочей поверхности ободов тормозных шкивов оценивается коэффициентом сопротивления тепловому ударуBut while for more accurate determination of components σ ₁ and σ ₂ dependent instead of (θ ₁ -θ _'1) substitute the term

which characterizes the heating rate of the pulley rim, and instead of dependence

which characterizes the temperature gradients along the thickness of the elements under consideration, and the nucleation and development of cracks on the working surface of the rims of the brake pulleys is estimated by the coefficient of resistance to thermal shock

и

- нумерация зазоров между накладками; на фиг. 31 представлена классификации податливости фрикционных стыков при формировании их контактно-импульсного взаимодействия; на фиг. 32а, б проиллюстрирована зависимость импульсной нормальной нагрузки, вызывающей деформации микровыступов фрикционной накладки при их параллельном соединении в блок (а) и их модель (б): 1 - участок фрикционной накладки: П_п -податливости микровыступов (2); 3 - металлическая пленка на рабочей поверхности шкива; на фиг. 33 изображена закономерность изменения деформаций микровыступов металлополимерных пар трения ленточно-колодочного тормоза от импульсных удельных нагрузок при разных площадях пятен их контактирования; на фиг. 34а, б, в, г, д, е проиллюстрировано влияние коэффициентов перекрытия К_вз (б, в, г, д) и температурного градиента по поверхности (∂ϑ_n/∂l) [а, г, е] на динамический коэффициент трения f (а, б), интенсивность изнашивания и_р.п. (д, е) и среднюю температуру поверхностей трения ϑ (в); на фиг. 35а, б показана схема модельного ленточно-колодочного тормоза с подвижными фрикционными накладками, установленными с постоянным (а) и переменным (б) шагами (бандаж составленный из четырех накладок): 1 - тормозной шкив; 2 - тормозная лента; 3 - фрикционные накладки: 4 - кольцевые цилиндрические стержни; 5 - цилиндрические пружины; 6 - стопорная планка; на фиг. 36 показаны зависимости динамического (а, б) и статического (в, г) коэффициентов взаимного перекрытия внешних (1) и внутренних (2) пар трения фрикционных узлов тормоза с подвижными накладками на первой и третей стадиях торможения; на фиг. 37 проиллюстрирован фрагмент изменения нормального усилия в контакте пары трения «шкив-накладка» при импульсном взаимодействии (1 - положительном: 2 - отрицательном) ленточно-колодочного тормоза буровой лебедки по времени торможения; на фиг. 38а, б изображены закономерности изменения нормального усилия во времени, исследуемого методом импульсных пар, при колебательных процессах микровыступов обода тормозного шкива для схем моментов: а - «отрицательный-положительный» б - «положительный-отрицательный»; на фиг. 39 показана расчетная схема фрикционного узла тормоза для определения усилий растяжения в тормозной ленте; на фиг. 40 изображена расчетная схема для определения усилий растяжения участка ленты и нормального контактного усилия на поверхности трения шкива; на фиг. 41 показаны закономерности изменения импульсных нормальных усилий N по длине фрикционной накладки L_н при скоростях скольжения V_ck=2,5 м/с в модельном ленточно-колодочном тормозе; на фиг. 42 представлена расчетная схема фрикционного узла ленточно-колодочного тормоза: 1 - тормозная лента; 2 - фрикционная накладка; 3 - тормозной шкив; на фиг. 43 проиллюстрированы закономерности изменения тормозных моментов по длине ленты ленточно-колодочного тормоза буровой лебедки (R_ш=0,725м; ϕ=9,8°; S_c=50,0кH) при разных динамических коэффициентах трения в паре «тормозной шкив - фрикционная накладка»: 1 - f=0,2; 2 - f=0,25; 3 - f=0,3; 4 - f=0,35; на фиг. 44 приведена зависимость изменения динамического коэффициента трения фрикционного узла «шкив-накладка» (материал 35ХНМ - ФК-24А) в стендовых условиях при удельных нагрузках 0,6 МПа и поверхностных температурах 200°С (кривая 1) и 400°С (кривая 2) от скорости скольжения; на фиг. 45 представлена схема узла трения в сборе с барабаном лебедки при торможении во взаимодействии со скоростными токами омывающего воздуха: 1, 2, 3 - тормозной шкив с крепежным выступом и с ребордами; 4 - тормозная лента; 5 - фрикционная накладка; 6, 7 - фланец барабана лебедки; 8 - подъемный вал; на фиг. 46а, б показана зависимость коэффициентов теплоотдачи (α) лучеиспусканием матовых (а) и полированных (б) поверхностей металлических фрикционных элементов от температуры нагревания (ϑ) при различных значениях отношения диаметров поверхности трения к площадям поверхностей (d/A); на фиг. 47 проиллюстрировано зависимость напряжений сопротивлению трещинообразования (σ₀) от объемной температуры обода шкива (ϑ_об) и величины сопротивления тепловому удару (К_С); на фиг. 48а, б, в, г приведены закономерности изменения величин безразмерных термонапряжений обода тормозного шкива от относительного времени торможения: фрикционного нагревания (а, б) и естественного охлаждения (в, г) при различных значениях критерия Био: а,

б,

; на фиг. 49а, б, в, г, д, е представлены усовершенствованные модели электротермомеханического трения и износа фрикционных материалов (первоначально разработанные А.В. Чичинадзе и Э.Д. Брауном) применительно к типичному трибологическому сопряжению; на фиг. 50 показана структурная развивающаяся модель реального сложного многоуровневого трибологического сопряжения фрикционного узла тормоза; на фиг. 51 представлена трибосистема (фрикционного узла) ленточно-колодочного тормоза и ее подсистемы различного порядка; на фиг. 52а, б, в, г, д, е, ж представлены общий вид ленточно-колодочного тормоза с многопарными фрикционными узлами и их графические модели: 1 - тормозная лента; 2, 4 - фрикционные накладки с отверстиями; 3 - тормозной шкив; 5, 6 - цилиндрические стержни и пружины; физические модели сцепления внешних («внутренняя поверхность тормозной ленты - внешние поверхности фрикционных накладок») (б, в, г) и внутренних («внутренние поверхности фрикционных накладок - рабочая поверхность тормозного шкива») (д, е, ж) пар трения его фрикционных узлов; на фиг. 53 приведена блок-схема основного расчетного модуля; на фиг. 54 проиллюстрированны закономерности изменения во времени (τ) динамического коэффициента трения (f) для пары «металл - полимер» (при р=0,3 МПа, V_CK=0,6 м/с); 1,2 - высокочастотная и низкочастотная составляющие «сухого» трения; 3 - кривая при «мокром» трении; 4 - систематизированная синусоидальная кривая; на фиг. 55 показан массоперенос материала между фрикционными накладками и рабочей поверхностью обода тормозного барабана при поляризации рабочих поверхностей накладок: 1 - анодной; 2 - катодной; на фиг. 56 представлена связь между режимами разряда и износом пары трения «полимер - металл»: 1 - тлеющий разряд; 2 - искровой; на фиг. 57 проиллюстрированы этапные изменения динамического коэффициента трения материала «Ретинакс» ФК-24А в функции температуры поверхности трения по зонам: I - 200-250°С; II - 250-400°С; III - 400-550°С; IV - 550-800°С; V - 800-1000°С.In FIG. 1 shows a contact diagram of metal-polymer friction pairs: 1 - friction pad; 2 - a brake pulley; in FIG. 2 illustrates the classification of microroughnesses in height h and pitch S _{m of} microprotrusions of metal-polymer friction pairs: 1 - macroscopic deviations; 2 - waviness; 3 - roughness; 4 - sub-roughness; in FIG. Figure 3 shows typical reference curves constructed in relative (I) and absolute (II) coordinates (distribution of materials [ a , b, c] along the height of the rough layer) according to the Abbot method (A); in FIG. 4 is a diagram illustrating the transition to a temporarily constant speed (А _ф1 ) of elementary contact pads during running-in (I) and steady-state (II) mode; in FIG. 5 a , b, c shows the contact-pulse interaction of the microprotrusions of the “polymer (1) - metal (2)” friction pair at different microprotrusion loads: a - 0.1N; b - 0.5N; in - 1.0N; in FIG. Figure 6 illustrates computational models for evaluating the characteristics of the interaction of contact spots with different diameters ( a _n , a _n1 , a _n2 ) of a metal (1) polymer (2) pair when generating: a - pulse electric currents; b, c - pulse temperature currents: flashes; superficial; in FIG. Figures 7a and 7b show the change in the electrochemical potential of metallic ( a ) and nonmetallic (b) friction surfaces during loading of a friction pair in the region of: I, II — natural films of oxides (primary structures) and their destruction; IV - dynamic equilibrium and automatic regulation of the processes of formation and destruction of secondary structures; I - patterns for a metal friction element; 2, 3, 3 '- patterns for the surface and near-surface layers of friction linings up to, in the zone and above the permissible temperature for their materials; in FIG. Figure 8 shows the patterns of change in the electrification currents in time (τ) of the forward ("block - disk") ( a ) and reverse ("disk - disk") (b) friction pairs at different sliding speeds (V _CK ) and specific loads (p) : a -V _CK = 0.3 m / s (1); V _CK = 0.8 m / s (2); V _CK = 1.5 m / s (3); V _CK = 2.0 m / s (4) at p = 0.15 MPa; ↑ - the moments of destruction of the surfaces of polymer blocks are indicated; in FIG. 9 a, b, c shows the temperature field of the surface layer of the metal (1) element (s) and the change in thermal current (2) and the diagrams temperature therein (b) and in the surface layer of the polymer (3) of element (a) in FIG. 10 a , b shows the distribution of surface temperature ϑ _n and heat flux q at the contact spot at: a -ϑ _n = const; b-q = const; in FIG. 11 a , b illustrates the lines of the electric field between the opposite ( a ) and the same (b) charges; in FIG. 12 a, b, c, d show patterns of changes in the surface temperature (θ _n, curve 1) in the temperature range below and above the permissible (θ _d) for the materials of the polymer lining and the electron work function (curve 2) and ions (curve 3) working surfaces of metal-polymer friction pairs (W _M , W _P ) from specific loads (p) during frictional interaction of various types of contacts: a - blocking (W _M > W _P ); b - neutral (W _M = W _P ); c, d - ohmic for ϑ _d <ϑ _n and ϑ _d > ϑ _n (W _M <W _P ); I, II, III - the region of deformation of the surface layers of friction elements: elastic and plastic; in FIG. 13 a , b, c, d illustrate thermograms of temperature change along the layers of the friction lining with its thickness ϑ _n = 25 mm in the intervals: a - 253.2-78.9 ° C; b - 330.5-92.6 ° C; c - 450.1-98.6 ° C; g - 535.6-160.0 ° C; in FIG. 14 a , b, c, d show the thermograms of temperature change along the layers of the pulley rim (1) and its mounting protrusion (2) in the intervals: a - 1 - 253.2-235.9 ° C; 2 - 204.8-136.6 ° C; b - 1 - 329.5-310.2 ° C, c - 1 - 450.4-432.5 ° C; 2 - 400.8-295.7 ° C; g - 1 - 535.2-52.2 ° C; 2 - 492.6-403.7 ° C; in FIG. 15 a , b, c illustrates the energy levels of various types of contacts during frictional interaction of the spots of microprotrusions of metal-polymer friction pairs: a - neutral; b - ohmic; in - blocking; in FIG. 16 shows an energy diagram of a metal-polymer friction pair; in FIG. 17 a , b presents a qualitative picture of the energy zones in the "metal - polymer" system with normal impulse forces acting on the polymer film: a - N <N _C ; b - N> N _C ; in FIG. 18 illustrates a band diagram of a three-layer structure "metal 1 - polymer - metal 2"; in FIG. 18 illustrates a band diagram of a three-layer structure of metal 1 - polymer - metal 2 "; in FIG. 19 a , b, c, d, d, e are diagrams of the directions of the components of electric currents in metal-polymer friction pairs at temperatures up to ( a ) and above (b-d) of the polymer lining permissible for materials; e is a vector diagram of electric currents and directions in the surface layers of the polymer lining; in FIG. 20 a , b shows the equivalent circuit (a) and the vector diagram (b) of parallel substitution of the surface layer of the polymer lining; in FIG. 21 a , b illustrates the polarization of the working surface of the polymer lining at fast (a) and slow (b) frequencies of influence on the processes; in FIG. 22 a , b shows the kinematic diagram of the tape-shoe brakes ( a , b) and their friction unit (c) of the U2-5-5 winch: 1 - control lever; 2, 4 - brake tapes and pulleys; 3 - friction pads; 5 - drum; 6, 9, 10 - crank crankshaft necks; 7 - driller crane; 8 - pneumatic cylinder; 11 - balancer; in FIG. 23 a , b, c, d shows a general view of the stand with a model band brake ( a ), a loading device (b), DC and AC motors (c) and a brake band with friction linings (d): 1 - I-beams ; 2 - a brake tape; 3 - friction pads; 4 - a brake pulley; 5 - a shaft with bearings; 6 - shaft support; 7, 8 and 9 - electric motors: direct and alternating current; 10 - finger coupling; 11 - load device; 12 - motor shaft; in FIG. 24 a , b, c, d, d, the energy balance of the tape brake shoe parts with various frictional characteristics is given: a - linear (1) and nonlinear (2); b - movement of parts during vibrations; c, d - diagrams of the work of parts in an oscillatory process; d is the dependence of the energy of vibration of the parts on the amplitude; in FIG. 25 shows the dependence of the dynamic coefficient of friction on the surface temperature for the friction pair FK-24A - steel 35KHNL; in FIG. 26 shows the work diagrams of the friction pair FK-24A - steel 35KHNL in the temperature range: 1 - up to 200 ° C; 2 - 200-350 ° C; 3 - 350-500 ° C; in FIG. 27 illustrates the dependence of the tension of the running branch of the brake belt on the amplitude of the radial vibration resistance of the adjustments for the running (1) and runaway (2) branches of the tape; in FIG. 28 a , b show the amplitude spectra of the radial vibration resistance of the friction pairs: a - at a specific load of 0.2 and 2.0 MPa (curves 3.4, and 1.2) and sliding speeds of 5 and 15 m / s (curves 3.4 , and 1,2); b - from the runaway branch of the tape to the runaway (the numbers correspond to a decent lining number) with a specific load of 2.0 MPa on the runaway branch of the tape; in FIG. 29 a , b, c shows the force patterns acting: in the “pad-tape” assembly ( a ); on the tape section above the i-th pad (b); when determining the deformations of the tape sections (c); 2 - a brake tape; 3 - friction lining; in FIG. Figure 30 shows the patterns of change in the relative deformations of sections of the brake belt when the friction linings are located on the arc of its girth with constant (1, 1 ') and variable (2, 2') steps: calculated (1, 2) and experimental (1 ', 2') data:

and

- numbering of gaps between overlays; in FIG. 31 presents the classification of the flexibility of friction joints during the formation of their contact-pulse interaction; in FIG. 32 a , b illustrates the dependence of the pulsed normal load causing deformation of the microprotrusions of the friction lining when they are connected in parallel to the block ( a ) and their model (b): 1 - section of the friction lining: P _{n -} compliance of the microprotrusion (2); 3 - a metal film on the working surface of the pulley; in FIG. 33 shows the pattern of change in the deformations of the microprotrusions of the metal-polymer friction pairs of the tape-shoe brake from impulse specific loads at different areas of their contact spots; in FIG. 34 a, b, c, d, e, f illustrates the effect of _substituting the overlap coefficients K (b, c, d, e) and temperature gradient along the surface (∂θ _n / ∂l) [a, d, f] to the dynamic coefficient friction f ( a , b), wear rate and _r.p. (e, f) and the average temperature of the friction surfaces ϑ (c); in FIG. 35 a , b shows a diagram of a model tape-shoe brake with movable friction linings installed with constant ( a ) and variable (b) steps (a band made up of four linings): 1 - brake pulley; 2 - a brake tape; 3 - friction pads: 4 - annular cylindrical rods; 5 - coil springs; 6 - a lock level; in FIG. 36 shows the dependences of the dynamic ( a , b) and static (c, d) coefficients of mutual overlap of the external (1) and internal (2) friction pairs of friction brake assemblies with movable pads in the first and third stages of braking; in FIG. Figure 37 illustrates a fragment of a change in the normal force in the contact of a friction pair “pulley-slip” during pulsed interaction (1 - positive: 2 - negative) of the drawworks brake of the drawworks over the braking time; in FIG. 38 a , b show the patterns of change in the normal force over time, studied by the method of impulse pairs, during oscillatory processes of microprotrusions of the rim of the brake pulley for torque patterns: a - “negative-positive” b - “positive-negative”; in FIG. 39 shows a design diagram of a brake friction assembly for determining tensile forces in a brake belt; in FIG. 40 is a design diagram for determining tensile forces of a belt portion and normal contact force on a friction surface of a pulley; in FIG. 41 shows the patterns of change in the normal impulse forces N along the length of the friction lining L _n at sliding speeds V _ck = 2.5 m / s in a model tape-shoe brake; in FIG. 42 presents the design scheme of the friction unit of the tape-shoe brake: 1 - brake tape; 2 - friction lining; 3 - a brake pulley; in FIG. 43 illustrates the patterns of change in braking moments along the length of the tape of the drawbar brake of the drawworks (R _w = 0.725m; ϕ = 9.8 °; S _c = 50.0kH) for different dynamic friction coefficients in the pair “brake pulley - friction lining” : 1 - f = 0.2; 2 - f = 0.25; 3 - f = 0.3; 4 - f = 0.35; in FIG. Figure 44 shows the change in the dynamic coefficient of friction of the friction unit “pulley-pad” (material 35XHM - FK-24A) in bench conditions at specific loads of 0.6 MPa and surface temperatures of 200 ° C (curve 1) and 400 ° C (curve 2) from sliding speed; in FIG. 45 is a diagram of a friction assembly complete with a winch drum during braking in conjunction with high-speed washer air currents: 1, 2, 3 — a brake pulley with a mounting protrusion and with flanges; 4 - a brake tape; 5 - friction lining; 6, 7 - winch drum flange; 8 - a lifting shaft; in FIG. 46 a , b show the dependence of the heat transfer coefficients (α) by radiating the matte ( a ) and polished (b) surfaces of metal friction elements on the heating temperature (ϑ) for various values of the ratio of the friction surface diameters to surface areas (d / A); in FIG. 47 illustrates the dependence of stresses on cracking resistance (σ ₀ ) on the volumetric temperature of the pulley rim (ϑ _vol ) and the value of thermal shock resistance (K _C ); in FIG. 48 a , b, c, d shows the regularities of the change in the dimensionless thermal stresses of the rim of the brake pulley from the relative braking time: frictional heating ( a , b) and natural cooling (c, d) for various values of the Bio criterion: a ,

b

; in FIG. 49 a , b, c, d, e, f presents improved models of electrothermomechanical friction and wear of friction materials (originally developed by A.V. Chichinadze and E.D. Brown) as applied to a typical tribological conjugation; in FIG. 50 shows a structurally evolving model of a real complex multi-level tribological coupling of the brake friction assembly; in FIG. 51 shows a tribosystem (friction unit) of a tape-block brake and its subsystems of various orders; in FIG. 52 a , b, c, d, d, f, f, general view of the tape brake with multi-pair friction units and their graphic models: 1 - brake tape; 2, 4 - friction pads with holes; 3 - a brake pulley; 5, 6 - cylindrical rods and springs; physical models of external clutch (“the inner surface of the brake band - the outer surfaces of the friction linings”) (b, c, d) and internal (“the inner surface of the friction linings - the working surface of the brake pulley”) (e, f, g) of friction pairs of its friction nodes; in FIG. 53 is a block diagram of a basic calculation module; in FIG. 54 the regularities of the change in time (τ) of the dynamic coefficient of friction (f) for the metal-polymer pair (at p = 0.3 MPa, V _CK = 0.6 m / s) are illustrated; 1,2 - high-frequency and low-frequency components of the "dry"friction; 3 - curve with "wet"friction; 4 - systematized sinusoidal curve; in FIG. 55 shows the mass transfer of material between the friction linings and the working surface of the rim of the brake drum with polarization of the working surfaces of the linings: 1 - anode; 2 - cathodic; in FIG. 56 shows the relationship between discharge modes and wear of a polymer-metal friction pair: 1 - glow discharge; 2 - spark; in FIG. 57 illustrates the step-by-step changes in the dynamic coefficient of friction of the Retinax FC-24A material as a function of the temperature of the friction surface in the zones: I - 200-250 ° С; II - 250-400 ° C; III - 400-550 ° C; IV - 550-800 ° C; V - 800-1000 ° C.

At the first stage of modeling, the geometric parameters of microprotrusions, the energy levels of contact spots and their surface and subsurface layers during electrothermomechanical frictional interaction in metal-polymer friction pairs at nanoscale and microlevels are considered.

In the process of frictional interaction of metal-polymer friction pairs, i.e. when the microprotrusions slip, the metal friction element receives micropulses from the microprotrusions of the stationary counterbody, which is the working surface of the polymer lining (direct friction pair). In reverse friction pairs, everything happens the other way around. In multi-pair friction units of the tape-shoe brake, at different stages of braking, reverse friction pairs are observed, and then direct ones. Impulse fluctuations in the magnitude of the normal force acting on the side of the brake band are determined by the rigidity of the friction joint.

In FIG. 1 a, b illustrated contact-pulse interaction at different microprojections "polymer - metal" pair of brake friction stage during its loading normal force N. N different quantities at each of steps proportional braking contact area. At the first stage of contacting (Fig. 1 a ), a pulsed interaction of microprotrusions occurs, which contributes to the generation of an elementary electric current. Subsequently, in the second stage (Fig. 1b), the electric current is supposedly extinguished, and turns into accumulated heat. At the third stage of interaction of microprotrusions, the pulsed normal force N is maximum (Fig. 1c), the area of the contacting surfaces increases, and, consequently, an increase in the triboeffect is observed, i.e. surface contact temperature. The summation of elementary electric currents generated at microprotrusions (the first stage of braking) made it possible to form an electric field on the interacting contact surfaces. The generated thermal field at the second and third stages develops with growth, and as a result, leads to an increase in thermal currents.

Between the areas of actual contact are micro- and macrocavities, interconnected and filled with liquid, formed due to burnout of the binder components of the polymer overlays, wear products. These cavities have constrictions and extensions in height. During the rotation of the metal friction element, the intermediate medium is carried away by its sliding surface and hydrodynamic wedges form in the places of narrowing. The effect of the latter is summarized and can lead to the emergence or rise of one surface above another.

As the microroughness bodies rise up, contact deformation decreases and part of the normal impulse load, perceived by the total supporting surfaces of the microprotrusions, contributes to a simultaneous increase in the part of the normal normal impulse load attributable to the liquid layer of the patch.

The observed elastoplastic deformation of the surface layers at the actual contact areas, leading to their gradual embrittlement due to electropulse flashing of the waviness and roughness of the surfaces, as well as to dispersion, allows us to imagine the wear process as surface cycle materials in the form of low-cycle fatigue located in the deformation zone.

For a short time, the destruction of the friction surface and the separation of wear particles, i.e. there is a latent phase, but this leads to the accumulation of energy, microdefects, the development and evolution of secondary structures. Upon reaching the limit state of the materials of the surface layer due to the appearance of a certain concentration of microdamage, the stage of destruction of the surface layer begins.

Under the influence of the normal impulse load, individual microprotrusions enter into contact (Fig. 2 a , b). The latter are microroughnesses that are located at the tops of the waves of contacting spots. In this regard, the following contact areas are distinguished: nominal, contour and actual.

The nominal contact area (A _n ) is the geometric location of all possible actual contact areas. This area is limited by the size of the interacting metal-polymer friction pairs.

Contour area of contact (A _k ) - is formed as a result of deformations of microroughness of interacting contact spots. On the contour area are the actual contact areas. Depending on the relief of the contacting surfaces of the metal-polymer friction pairs and the external action on each of them of pulsed normal force, the contour area can be up to ten percent of the entire nominal contact area. The area of individual contour sections varies from one to tens of square millimeters. When two wavy friction surfaces interact, the contour areas of the contacts change over time. This is due to a change in the surface microrelief; action of pulsed normal forces and pulsed unit loads; thermophysical and physico-mechanical properties of materials in a stress-strain state; instability of thermoelastic contact under the influence of pulsed specific loads, pulsed electric and thermal currents, wear and other factors. The classification of microroughnesses in height h and pitch S _{m of} metal-polymer friction pairs of a band brake shoe is illustrated in FIG. 3.

при этом возможны и другие комбинации отношений площадей контакта взаимодействующих металлополимерных пар трения.The nominal, contour, and actual area of interaction in the metal-polymer friction pairs of the tape brake shoe, taking into account the cross-sectional shape, can be reduced to a geometric figure (square, circle, rectangle, etc.). In this case, the area of the contact spots of the interaction surfaces is reduced to a circle, which allows us to determine their ratio through the ratio of squares of radii, So, for example,

while other combinations of the relationship of the contact areas of the interacting metal-polymer friction pairs are possible.

The microprotrusions shown in FIG. 4 a , b, c had the following geometric characteristics for the material FK-24A (to scale): a -h = 32.5 mm; z ₁ = 10 mm; z = 17.0 mm; l = 60.0 mm; b-h = 32.5 mm; l = 61.0 mm; h = 31.0 mm; l _S = 60.0 mm.

The surface topography of the microprotrusions was evaluated on the basis of processing a limited number of profilograms (zi = 10). To construct the curve of the supporting surface for three types of characteristic microprotrusions, the method proposed by Abbot was used.

The actual contact area ( _AF ) is formed by the action of microprotrusions of the friction surfaces and is of the greatest interest due to the fact that microprotrusion deformation and generation of electric currents occur in the actual contact areas, and as a result, thermal currents are formed and wear occurs. The actual contact area of these friction pairs varies in a wide range: from hundredths to units of percent of the nominal surface area of the friction.

Reference curves (I, I ', I''), consisting of three sections (1, 2 and 3), shown in FIG. 4 are variable. Moreover, the function t _p (ε _max ) in the range from 0 to 1.0 shows what proportion of the material is above a given level. The physical meaning of each reference curve obtained expresses the probability that the profile material is above the level of ε _max , i.e. it characterizes the distribution of material along the height of the rough layer.

The reference curves constructed in relative values make it possible to evaluate not only the surface topography, but also its area according to Table. one.

The summation of the areas of elementary contacts and the achievement of a steady-state value of A _{f1 are} illustrated in FIG. 5.

This process proceeds gradually and takes several hours in time, depending on the operating conditions of the friction brake band brake shoe. The value of A _{1 is} determined by the electro- and thermodynamic friction regimes and can be quite wide depending on the intensity of specific loads (activation level) and the composition of the washing media (passivation level) during contact-pulse interaction of metal-polymer brake friction pairs.

In the interaction of metal-polymer friction pairs of brake devices, the contact is discrete due to the constant change of its elementary sections. The latter are foci of "electrical" and "thermal" irregularities. “Electric” foci contribute to the generation of electric currents using the formed microthermobatteries with various properties of materials and therefore they operate in the microthermoelectric generator and microthermoelectric refrigerator mode. Some areas are heated, while others are cooled. “Thermal” foci are heated by the triboelectric effect. Subsequently, more heated sections of the friction surface as a result of thermal expansion and ductility rise above the rest of the surface and therefore begin to perceive the entire applied load. This will continue until local wear of this section leads to a decrease in its level, after which again the load will be redistributed, which will be applied to other parts of the surface.

The surface layer must be considered as a synergistic self-regulating system, which is capable of internal changes when the internal energy of the system reaches a certain threshold value - activation energy.

A study of the interaction processes occurring at nano, micro, and macroscopic levels allows us to establish the relationship between the occurrence of wear cycles and kinetic phase transitions of the mechanisms of energy dissipation that occurs as a result of self-organization and evolution of dissipative-dislocation substructures.

In FIG. 6 a , b, c show the proposed calculation models for evaluating the characteristics of the interaction of contact spots with different diameters of the metal-polymer friction pair when generating electric and accumulating thermal currents.

It should be noted that with an increase in the area of contact spots of microprotrusions, an increase in charged particles on their surfaces is observed.

The formation of double electric layers occurs at the interphase boundary of two media with different characteristics of electronic conductivity (friction metal element) and ionic (surface and near-surface layers of the lining in different thermodynamic states). The surface and near-surface layers of friction linings are multicomponent structures, i.e. heterogeneous system in which consideration of their models must be carried out from the point of view of chemical kinetics of the reaction oscillations. The chemical potential depends on the concentration of the components in the pad. In FIG. 7 a and b illustrates the change in the electrochemical potential of the metal (a) and nonmetal (b) a pair of surfaces under friction loading in the region of their various structural and thermal condition. It was found that the chemical potential (curve 3 ', see Fig. 7 a ) increases in the temperature zone exceeding the allowable for the lining materials, because on its surface there are islands of electrolyte.

The presence of chemical potential is accompanied by the accumulation of charges of the opposite sign and the manifestation in the contact zone of the characteristics of each phase: ions in the surface and near-surface layers of the lining and electrons (holes) in the metal friction element. In other words, physical contact between the above media leads to the appearance and formation of a double electric layer.

In the latter, the charges are localized at a very small distance, the layer thickness in most cases of which is in the range 4.0-7.0 A.

The appearance of an electrochemical cylindrical capacitor is possible under conditions that ensure reliable spatial separation of charges on its shells and polarization of the space charge in the surface layers of friction pads. Such conditions are “perfectly polarized”, and the corresponding shell in the given electrolytic systems and certain potential limits is polarized. Their nature is such that, upon polarization of the working surface of the metal friction element, Faraday processes do not occur on it, which are associated with mass transfer of the patch material through the phase boundary.

Let us consider at the nanotribological level the generated electric currents in friction pairs of various types.

The diagram of the current change in a direct ("block-disk") friction pair (Fig. 8 a ) obtained on the SMC-2 friction and wear machine in laboratory conditions showed that the currents are unstable (curves 1 and 2). These curves originate with the same negative direction of currents, and then curve 2 under loading of 2.0 N goes into the zone of positive current direction. The form of curve 3 differs significantly from curves 1 and 2. The specified curve begins at the maximum value of the negative current direction (- 9.7 nA), crosses the abscissa axis of the coordinate system at a load of 1.35 N and rises to the maximum value of the positive current direction (5 , 2 nA). In the loading range from 4.5 N to 7.3 N, an almost aperiodic change in the direction of the current takes place. At 7.3 N, the value from the positive current direction (4.5 nA) changes to negative (-11.75 nA). A change in the direction of the current (curve 3) occurs at a sliding velocity V _CK = 1.5 m / s.

The kinetics diagram in the reverse friction pair (Fig. 7b) shows that at low friction speeds (curve 1), the magnitude of the electrification current in the initial period of friction increases, and then remains almost unchanged. We can assume that the system is in an unstable state. With an increase in the sliding speed (curves 2-4), the direction (inversion) of the electrification current changes (respectively, with a force F, which was 10.5, 3.0, and 2.0 N), while it had the nature of multiple manifestations. With an increase in the sliding velocity, the number of current inversions also increases, and for direct and reverse friction pairs (see Figs. 8 a and b), it shows that in both cases both positive and negative values of the electrification currents are observed depending on the braking mode.

Let us analyze the heat load of the surface and near-surface layers of friction elements of metal-polymer pairs.

According to the classical theory, in the immediate vicinity of the contact points of the friction pair “metal (1) - polymer (2)” (Fig. 9 a ), separate hemispherical isothermal surfaces form, merging into a common surface at a certain depth of materials. The location of the isothermal surfaces is characterized by the magnitude of the temperature gradient. In the general case, the temperature field in the metal and polymer friction elements related, respectively, to their surface and subsurface layers is shown in FIG. 9b, c. It can be seen from the latter that the following temperatures take place in the interaction zone: friction arising in the deformation zone of the micro-sections of the working surface; contact arising at contact points; superficial, arises on macro-sections of friction surfaces; volumetric, occurs in the body of the friction element below the deformation zone.

In FIG. 10 shows the distribution of temperature (ϑп) and heat flux (q) on the contact spot at: а -ϑ _n = const; b-q = const. However, such an ideal distribution of temperature (ϑ) and heat flux (q) on the contact spot in friction pairs is impossible due to the inversion of currents between interacting zones, as well as electric field lines between unlike (a) and homonymous (b) charges (see Fig. . 11 a , b).

In the case of contact-pulse interaction of the microprotrusions of the friction surfaces of metal-polymer pairs of brake devices, the friction elements experience an electrothermomechanical stress-strain state and the distribution of electric and thermal fields near the contact interaction zone occurs. At the macro level (external parameters), these are operational parameters (sliding speed; flexibility of the elements of a friction pair and its contact joint; coefficients of (static and dynamic) mutual overlap; normal forces; specific loads; dynamic coefficient of friction; braking torque; temperatures: flashes, surface , volumetric, etc.), which are determined taking into account the known conditions of interaction and microforms of rubbing surfaces. At the micro level (internal parameters), these are actually pulsed: normal forces, specific loads, deformations, mechanical and thermal stresses, electric and thermal currents and the fields generated by them, temperatures in the surface layers, etc., which are determined on the basis of the theory of a single interaction field . At the nanoscale - conditions of equilibrium are considered at energy levels during the operation of the polymer lining (its working surface layer) in the temperature zone below and above the permissible level for its materials; potential barriers in equilibrium during contact-pulse interaction of thermoelements of microthermal batteries in friction pairs; contacts between the microprotrusions of the metal friction element and the semiconductor films of the polymer lining; pn type transitions in microthermobatteries of a friction metal element and semiconductor films of polymer overlays; the interaction of electric and thermal fields, etc.

The concept of the interaction state of contact spots of microprotrusions of metal-polymer friction pairs includes the stress-strain state and the generated electric and accumulated thermal currents on their surfaces and in the surface layers.

At the macro level, these are nominal characteristics determined taking into account the known conditions of interaction in the macro form of surfaces. At the micro level, these are actual pulsed specific loads, actual mechanical electric, thermal and chemical fields in the surface and near-surface layers washed by high-speed currents, in which the absolute value of the electrification current increases in the initial period of operation. In this case, it is necessary to analyze current diagrams of media components that have arisen on the surfaces of the contact spots of microprotrusions during their interaction.

The destruction of materials during friction is due to contact-pulse interaction, accompanied by the combined action of mechanical, electrical and thermal loads. This causes an increase in surface temperatures and temperature gradients, which leads to significant thermal stresses in the metal friction element.

The thermal stresses arising in the elements of the friction pair of the brakes are the result of thermal shock caused by a rapid increase in temperature. This phenomenon is accompanied by structural changes in the materials of the friction pair.

Electrothermomechanical friction in highly loaded metal-polymer pairs of the drawworks brake of the drawworks is carried out at variable sliding speeds and specific loads, under the conditions of generated electric and accumulated heat currents with uneven heating of the surface layers of metal-polymer friction pairs. Moreover, the processes, phenomena and effects occurring in the surface layers of friction pairs are very complex. Thus, the surface of each of the bodies in a pair is characterized by a high level of heterogeneity of materials and structural defects, the scales of which are commensurate with the sizes of contact spots, which affects electrothermomechanical friction. Assessment of the energy loading of friction surfaces and its influence on the main processes, phenomena and effects are necessary in solving problems of ensuring the reliability of friction units by increasing the resource of both polymer linings and the working surfaces of metal elements.

Particle exit work from microprotrusions of metal-polymer conjugation. Let us dwell on the work of the exit of electrons and ions from the friction interaction surfaces of metal-polymer conjugation.

Consider the relationship between the work function of electrons and ions from the working surfaces of metal-polymer friction pairs and their surface temperature from pulsed specific loads acting on contact spots of microprotrusions (Fig. 12 a , b, c, d). In this case, the surface temperatures of the polymer linings were lower (Fig. 12 a , b, c) and higher (Fig. 12 g) acceptable for their materials, despite the fact that the temperatures in the interaction contacts were the same.

Let us analyze the temperatures occurring on the surfaces of the spots of microprotrusions during various types of contact in the process of frictional interaction (Fig. 12). Section I corresponds mainly to the region of elastic deformation of the surface layers of materials of friction elements, and sections II and III to the region of plastic deformation of processes without and with a saturated dislocation density.

Section I in FIG. 12c is shifted to the left, and in fig. 12g section I is generally absent, while expanding in section II. This is explained by the fact that in the first case, destructive processes of burning out the binder components of materials in the surface layers of the polymer lining begin and liquid stains form on its surface, and in the second case, destructive processes end with an increase in the number of liquid stains on the working surface of the polymer lining. The third section in all the figures is characterized by a dynamic equilibrium between the processes of propagation and angulation of defects with the formation of micropairs and microcracks in the surface layers of metal-polymer friction pairs. Moreover, the thickness of the thermal layer at high pulsed specific loads in metal-polymer friction pairs is one to two orders of magnitude greater than the thickness of the surface and subsurface layers of their elements.

We illustrate how the above three sections affect the change in surface temperature, specific loads and the work function of the electrons and ions from the working surfaces of metal-polymer friction pairs. The last parameter is decisive and significantly affects the first two parameters. In section I (Fig. 12 a ), an increase in the work function of both electrons and ions is observed with an increase in specific impulse loads. As a result of changes that occur on the working surfaces of metal-polymer friction pairs, the work function of the electrons and ions from the friction surfaces decreases (Fig. 12 a ). As for the graphical dependencies shown in FIG. 12c, d, the presence of a liquid phase causes an increase in specific loads in friction pairs. The work function of the ions on them is greater than the work function of the electrons in connection with the effect of affinity for the electron (the conversion of electrons into ions). As can be seen from FIG. 12 a, b, c, d the surface temperature increases monotonically in the range of unit loads, and does not correlate with the extrema of the electron work function and ions.

However, in the III sections (Fig. 12b, d) with W _M = W _P and W _M <W _P in the temperature range, respectively, below and above the allowable temperature for the polymer lining materials, a constant and thermal stabilization temperature occurred. The first occurs when, for a short time, the amount of heat generated on the friction surfaces is removed from the matte surfaces of the metal friction element into the environment. The thermal stabilization state of a metal friction element occurs for a long time when the temperature gradient is minimal in thickness of its polished surface. To confirm the foregoing in FIG. 13 a , b, c, d, and 14 a , b, c, d show thermograms of temperature changes in layers, respectively, of the friction lining (ϑ _Н = 25.0 mm) and the brake pulley (δ _Н = 20.0 mm) the interval of their thermal state, respectively, from 535.6 to 160.0 ° C and from 535.2 to 52.2 ° C.

Energy levels of various types of contacts of microprotrusions of metal-polymer friction pairs. In polymer overlays composed of inhomogeneous materials, there are amorphous and crystalline phases, a different kind of capture occurs - at interphase boundaries. The accumulation of charges at the boundaries is due to the difference in the conductivities of the phases under consideration (Maxwell-Wagner effect). During the electrification of such a material, carriers will collect near a given interphase boundary, or vice versa, leave it, depending on which of the two conductivity currents is greater: flowing to the charge boundary or departing from it. Differences in local conduction currents also lead to dissipation of charges during the subsequent conduct of a thermally stimulated discharge, since in this case the currents flow in the opposite direction.

For the processes of charge neutralization, the properties of the working surface of the metal friction element also play an important role. The relationship between energy levels is determined by the frictional contact interaction of the microprotrusions of friction pairs.

In the table. Figure 2 illustrates a detailed approach to the energy levels of contact spots of microprotrusions of friction pair elements during electrothermomechanical frictional interaction.

In FIG. 15 a , b, c conventionally shows the difference between neutral, ohmic and blocking contacts.

Let us consider the occurrence of neutral contacts at the microprotrusions of metal-polymer friction pairs according to FIG. 15 a .

The first case relates to the surface temperatures of the polymer lining, which have their values below the permissible for its materials. According to FIG. 15 a, the work function of the exit of electrons and ions from metallic and nonmetallic frictional elements is equal to each other. A large increase in the work function of the exit of ions from the surface layer of the patch gives an affinity for the electron. The latter is the ability of some atoms and molecules to attach an additional electron and turn into positive ions. A measure of electron affinity is the energy released in this process. The purposeful reorientation of electrons to ions and thus allows due to this effect to achieve equality of the work function of the particles.

The second case. When the working surface of the polymer lining reaches a temperature higher than that acceptable for its materials, burnout of the binder components occurs in the surface and subsurface layers, which leads to the formation of liquid islands on the surface of the lining. When the working surface of the metal friction element is in contact with the liquid, the phenomena of the transition of ions from metal to liquid are observed (see Fig. 15 a , curve 1).

A metal enters the solution in the form of either positive ions or complex negative ions if it interacts with a liquid solution. In this case, the metal surface acquires a certain specific potential, which establishes an equilibrium between the process of ion separation and deposition. This potential depends both on the nature of the metal and on the concentration of ions in the liquid. At a certain value of acidity (pH), the metal does not send ions to the solution, but rather takes them from the solution, acquiring charges before the onset of electrical equilibrium.

As you know, metals are arranged in an electrochemical series with respect to the positive hydrogen ion H ⁺ . When immersed in a liquid of two different metals, each of them has a certain potential with respect to the liquid. When metals come into contact, an electric current occurs until all metal or solution ions are exhausted in the solution. Electric currents can also flow between different points of the same metal surface, if it is charged and heterogeneous.

In addition to the chemical mechanism of electrical phenomena in the contact of metal and liquid, another mechanism is also possible - the electrification of metal and liquid surfaces during the movement of the latter, since a layer of liquid, moving away, carries away an ionic charge. Calculations show that a significant accumulation of charges during the movement of a liquid occurs at a specific resistance above 10 ⁹ Ohm⋅cm. It is believed that in this case a double electric layer forms on the surface of the metal in contact with the liquid. The metal surface as a result of loss or capture of ions acquires an insignificant chemical potential, and a certain charge is distributed over it. The opposite charge is in the liquid. The charge distribution in the liquid can be characterized by a potential ϕ _e , which varies with distance from the surface in accordance with the electrostatic forces and the Boltzmann distribution (Fig. 15 a ). An analytical expression for calculating the potential ϕ _{e is} obtained by solving the Poisson equation under the assumption of the existence of a shielding double layer [3]:

Thus, under the conditions of electrothermomechanical friction of metal-polymer friction pairs, the energy load of the working surface of the polymer lining plays a decisive role in the formation of a neutral contact in the friction interaction zone.

Most often, in metal-polymer friction pairs [in relation to two-layer (“metal-polymer”)] structures of braking devices, an ohmic (injecting) contact occurs (Fig. 15c).

In FIG. 16 shows the zone diagram of the contact "metal - conductive polymer" [3]. A feature of this diagram is the presence of a narrow electrically conductive zone in the middle of the polymer gap. According to one hypothesis, it is precisely such a narrow zone that can be responsible for the transport properties of thin dielectric films. Changes in the position of the Fermi level of the metal in the region of its phase transition relative to a narrow zone in the polymer provide the conditions for injection from the metal into the polymer and thereby characterize the change in the conductivity of the system as a whole.

In FIG. 17 a , b presents a model of energy zones in the metal-polymer system stimulated by pulsed normal forces injection of current carriers from the metal into the polymer conduction band. According to this model, polymer compression causes the decay of surface states playing the role of electron acceptors. It is also possible that due to an increase in the polarizability of the friction interaction surfaces, the bottom of the polymer conduction band decreases simultaneously. As a result, at a certain value of N = N _{C, the} structure of energy bands near the metal – polymer interface is favorable for carrier injection, although at N <N _C this process either does not occur at all or has an extremely low efficiency.

In FIG. 18 is a simplified zone diagram of a three-layer metal-1-polymer-metal-2 structure. The solid bold line in the polymer layer shows the shape of the potential barrier for the charge when d is greater than the depth of penetration of the surface charge, the dashed curve corresponds to the case when d is less than the depth of penetration of the surface charge, the electronic states are indicated by shading. A contact option was chosen in which both metals are the same, the electron work functions from the metal and polymer are also the same. This is the so-called case of direct zones, and when using a polymer in this structure, it is most often possible to obtain an ohmic contact. We will not dwell on the details of the mechanism of establishing electrical contact. We only state the fact that the presence of a dielectric between two metal electrodes with a large band gap can prevent the charge from flowing between the electrodes in the case when the thickness of the dielectric layer is large. In this case, the dielectric layer plays the role of a rectangular rectangular potential barrier, the height of which is determined by the difference between the work function of the metal and the electron electron affinity of the polymer.

With a decrease in the thickness of the polymer film, a situation may arise when charges concentrated near the opposite boundaries of the contact in question begin to interact with each other, leading to a distortion of the shape of the potential barrier. The largest film thickness at which the interaction of boundary charges begins, can be considered the double value of such a contact parameter as the depth of penetration of the surface charge. The interaction of surface charges can lead to the formation of a local minimum in the middle of the barrier, which in principle can lead to the intersection of the curve describing the envelope of the potential barrier with the Fermi level.

With this hypothetical option, new electronic states can arise in the middle of the barrier at the Fermi level, which increase its permeability to electrons. If you learn to manage such states, then in fact it will mean the creation of a fundamentally new electronic hybrid nanostructured metal-polymer material.

At the same time, the issue of controlling the "metal 1 - polymer - metal 2" system by switching the charge-inducing effect in a polymer film in which the regions of change in electrical conductivity are spatially separated becomes of great importance. For studies, switching in the system was chosen due to a change in the boundary conditions in the three-layer structure “metal - polymer - metal”, which led to the melting of one of the electrodes. As a result, the surface charge is redistributed in the near-contact region of the polymer due to a sharp change in the effective work function of the electrons of the metal near the critical temperature. Thus, the transition of the polymer to a highly conductive state is caused by a change in the position of the Fermi level of the metal (the effective work function of the electrons) at the point of phase transition. A similar result can be achieved if another metal is placed between the metal undergoing a phase transition and the polymer film, which is stable in a given temperature range, in such a situation, all structural and mechanical changes (changes in the state of aggregation, strictive phenomena, etc.) in the first metal can be suppressed using a second metal, i.e. by technological solution. It is worth noting another important feature of the ohmic (injecting) contact on the microprotrusions of the metal element, whose behavior resembles a heated cathode, even in the absence of a field on the surface, it is possible to spontaneously inject carriers into the surface layer of the polymer overlay. The cloud of space charge that arises in front of the electrode ultimately completely blocks the emission from the electrode, unless, of course, the cloud is resolved by the action of the applied field. The boundary conditions at the injection electrode are reduced to E (0, t) = 0 and charge density ρ _З (0) = ± ∞, and the polarity is determined by the sign of the injected carriers.

The behavior of the microprotrusions of the polymer lining strongly depends on the material of the microprotrusions of the metal friction element. Typically, the contact spots of the last microprotrusions are coated with films, at weak and intermediate field strengths are blocking contacts (Fig. 15 a ). This contact prevents the transfer of charge carriers from the electrode into the surface and subsurface layers of the polymer lining, while at the same time, it itself can receive carriers from the above layers.

In a dielectric with blocking contacts, which does not contain charge carriers at all, the flow of a stationary current is obviously impossible. If there are carriers of both signs in the dielectric, and with very different values of their mobilities, then a Schottky barrier forms near the contact spots of the microprotrusions of the metal friction element, the sign of which coincides with the sign of more mobile carriers. The polarization of the contact spots of the microprotrusions of the patch arising under these conditions is due precisely to the presence of electrodes. This situation is quite easily explained in the limiting case when there is no mobility in carriers of any one polarity (for example, electrons) and there is no further generation of free carriers. In this case, the applied field removes the positive carriers from the contact spots of the microprotrusions of the patch (anodes located, say, at x = 0).

и не зависит от приложенного электрического поля.Since this electrode is not able to transfer positive charges to materials, a cloud of negative space charge with a density ρ is formed near it in a layer of thickness δ _s between the planes x = 0 and x = δ _s . After the space charge layer has been fully formed, the voltage u initially applied over the entire thickness of the metal microprotrusion will now become applied to the layer with a thickness of δ _s . As a result, the current will go to zero. The length of the layer is determined by the formula

and does not depend on the applied electric field.

For example, with a density of stationary (captured) carriers ρ _s = 110 ^-4 C / cm ³ , ε = 2⋅10 ^-13 F / cm and u = 1.0 V. The layer thickness δ _s is 1.25⋅10 ^-3 see. So, the use of blocking contacts prevents the complete removal of mobile carriers from the dielectric, and regardless of the value of their mobility.

The presence of a non-conductive layer of finite thickness between the dielectric and the electrode can cause the formation of barrier polarization. True, the molecular dimensions of the resulting double layer of positive and negative carriers do not allow it to be detected in ordinary external measurements, for example, compensation charges on the electrode. In addition, the formation of a double electric layer does not lead to a blocking effect.

Thus, if the contacts are blocked, neutralization must occur inside the metal friction element, regardless of the type of contact (is it electron-injecting or blocking). It depends only on which of the work functions of the electrons or ions is greater: a metal or polymer friction element. If the work function of the first element is greater than the second, a blocking barrier is formed. The presence of the latter makes it possible to study semi-insulators and semiconductors, which are characterized by high conductivity currents, by the method of thermally stimulated discharge. Blocking contacts act in the opposite way: they prevent both injection and charge neutralization.

Contact-pulse interaction of microprotrusions of friction units with various gradients of electric potential and temperature. The gradient theory of solids and at the boundaries of interfacial layers in the range of surface temperatures lower and higher than the polymer lining acceptable for the material of the polymer lining will provide an answer to the question of providing a positive gradient of mechanical properties in the surface layers of metal-polymer friction pairs of brake devices. However, the gradients of the electric potential and temperature on the interacting surfaces of the contact spots of the microprotrusions of the polymer-metal friction pairs and along their depth have a significant effect.

In the table. Figure 3 shows six cases of contact-pulse interaction of microprotrusions of friction surfaces with different gradients of the electric potential and temperature under given boundary conditions.

We briefly analyze each of the cases presented in table. 3.

The first case. Asymmetry is observed in separate zones where the distance r from the contact is large compared to the radius a _{n of the} contact spot of microprotrusions A _k , which in this case has the shape of a circle.

It has been established that the potential gradient in the contraction zone decreases as the distance from the contact increases, approximately as 1 / a t _n ² . Moreover, the total spatial charge in individual zones of contraction is almost the same in magnitude as the charges in the immediate vicinity of the contact spot (see Fig. 11 a , b). Consequently, the effect of specific charges on the electric field in the contraction zone is negligible. Similar considerations hold true for the thermal field.

Thus, the asymmetry does not violate the law of the dependence of the form ϕ _e -ϑ in the narrowest parts of the contraction, since the temperature and stress gradients in them are large, and the asymmetry in individual zones does not affect the general stress and contraction and the temperature difference in the contact surface of the interaction spot .

The second case is characteristic of metal-polymer friction pairs. When heating the microprotrusions of the contact surface, the conditions (dϕ _e / dn) _E = 0 and (dϑ / dn) _E = 0 are not observed, since there is a temperature difference between the interacting contact spots. In this case, the heat flux is divided into two parts: longitudinal (part X) and transverse (part Y). The heat flux along Y will cause the deviation of the calculation results according to dependence (23) (see Table 3) by approximately (W _X / W _Y ) 100,%. The components of equation (23) are determined by dependencies (21) and (22). After the calculations, based on the values of the parameters, the deviation of the heat flux W _X / W _Y <0.05 was obtained, which can be neglected.

The third case is characteristic of intensive mass transfer from microprotrusions of contacting surfaces according to the “polymer-metal” scheme and vice versa. It determines the energy levels of interaction of the microprotrusions of the contact spots according to dependences (24) and (25).

The fourth case differs from the third case with gradients (gradϕ _e ) _Aph1 and (gradϕ _e ) _Aph2 , since the energy levels of the metals included in the bimetal are different.

Fifth case. The surface of the contact spot of the microprotrusions А _ф0 satisfies the boundary conditions, but does not satisfy the condition (dϕ _e / dn) _Af0 , since А _{ф0 is} intersected by a heat flux whose density is proportional to the electric current density j. As a result, we obtain Yj, where Y has a unit of voltage. Since the heat flux is proportional to j, it does not change the system of elementary streamlines.

As a result of transformations of a number of dependences, expression (28) was obtained for estimating the heat flux in the temperature range 0-ϑ and when the temperature changes from ϑ to θ [expression (29)]. Part of the Peltier heat (P ₁ ) goes into the investigated contact spot and makes up the heat flux P ₁ J, and is the tension of the contraction zone on it.

An analysis of dependence (29) shows that for small values and characteristic of metal-polymer friction pairs, the Peltier effect causes a noticeable deviation of u from a dependence of the form ϕ _e -ϑ.

The sixth case is characterized by the transfer of electric current by heat carriers from a more to a less heated zone of the contact spot lying on the path of its movement. This is done through the Thompson effect, the intensity of which depends on the Thompson coefficient (σ _t ). Having written down the amount of heat (30) coming from the cross section of the microprotrusion with the temperature ϑ + dϑ to the neighboring section with the temperature 3 taking into account the boundary conditions, and using the dependence of the form (32), after the final integration, we obtained expression (33).

Subsequently, applying the condition that at high temperatures of the metal friction element σ _{t is} proportional to T in the final form, we obtain the dependence (34). The latter connects the parameters of the electric and thermal fields, the currents of which penetrate the contact spots of the microprotrusions of the rubbing surfaces.

With short-term braking in the absence of heat transfer from the matte surfaces of the pulley, intense heat accumulation occurs, which can lead to the ultimate thermal state of its rim. For a simplified consideration of the problem of heat conduction, we neglect heat transfer to the environment.

The rate of flow of pulses of electric and thermal currents in the microprotrusion of friction pairs. Let us consider the rate of flow of pulses of electric and thermal currents in the microprotrusions of the friction surfaces of metal-polymer pairs.

Let us dwell on the electric and thermal currents arising in metal-polymer friction pairs. In the table. Figure 4 shows the calculated dependences that describe the electrical and heat transfer processes during the operation of metal-polymer friction pairs [4].

Темп накопления и рассеивания теплоты

использован в зависимостях: (35), описывающей протекание электрического тока; (37) и (38), относящихся к конвективному и излучательному вынужденному охлаждению.Depending on the thermal conductivity (36), the thermal current flow rate is applied

The rate of accumulation and dissipation of heat

used in dependencies: (35), which describes the flow of electric current; (37) and (38), related to convective and radiative forced cooling.

Electrodynamics of contact interaction in tribological conjugation. Volchenko A.I. a method is proposed for determining the components of the generated electric currents in metal-polymer friction pairs based on experimental calculation data, implemented in five stages, each of which was determined [5]:

- total thermal current (I _T );

- the total current that occurs due to sliding friction and contact of interacting macro-sections of surfaces (I _CK );

- the component of the total current that occurs due to sliding friction (I _TC );

- component of the total current formed by the movement of charged particles of mass transfer (I _M );

- the total current due to sorption-desorption processes in the surface layers of the lining, which are at a temperature higher than permissible for its materials (I _D ).

The components of the above currents depending on the direction of rotation of the brake pulley are presented in the form of a vector diagram in FIG. 19 a .

The method for determining the directions of the components of the generated electric currents in the polymer-metal friction pairs, based on the dependence of the yield of electrons and ions from the metal and polymer friction elements, respectively, is as follows [6]. Ultimately, the experimentally recorded total current (I _C ) of electrification, taking into account the directions of the component currents, has the form

In FIG. 19b, c, d, e illustrates the directional diagrams of the constituent electric currents in metal-polymer friction pairs at a temperature higher than the allowable polymer lining materials. In FIG. 19b, f shows the currents I _M1 and I _M2 caused by the movement of charged particles of mass transfer according to the "polymer-metal" and "metal-polymer" schemes.

Let us dwell on the electrodynamics of the surface layer of the polymer lining. Since active I _a and reactive I _r currents flow in the surface layer of the polymer pad (Fig. 20b), which are replaced by an equivalent electrical circuit containing ideal resistances R 'and capacitance C _p , which allow these currents to flow. The ideal R ′ and C _{p are} connected in parallel (FIG. 20 a ).

The conditions for the equivalence of the equivalent circuit to the real surface layer of the polymer lining is the equality [7]:

- phase shift between current I and voltage u in the real layer and in the equivalent circuit;

- power allocated in the equivalent circuit, losses in the surface layer in a real polymer patch.

Let us consider a parallel equivalent circuit, since in assessing the compliance of the friction joint of the metal-polymer friction pair, the microprotrusions are connected in parallel. The vector diagram of currents and voltages for a parallel equivalent circuit (Fig. 20b) allows us to calculate tanδ ₁ and the power lost in the surface layer of the polymer overlay.

According to the vector diagram (Fig. 20b) for a parallel equivalent circuit, we have

,

и

,

and

From (40) it follows

Since the power lost in the surface layer of the patch is determined only by the active component of the current, taking into account (41) we obtain

It follows from (42) that for this equivalent circuit, the power loss is proportional to tanδ ₁ , ω, and u ² . Therefore, it is legitimate to characterize the losses in the surface layer in the polymer patch with the quantitative parameter tanδ ₁ . For layers with a small resistance value R, i.e. with large leakage currents and, consequently, large losses, it is necessary to use the inequality tanδ ₁ <5.0-10 ^-2 .

When the surface layers of polymer overlays are in an alternating electric field, the vector diagram has the form shown in FIG. 20b.

According to the vector diagram, the reactive current I _r = I _o + I _{Pr is} ahead of the voltage u by 90 °. Active current I _a = I _cn + I _{P a} coincides in phase with the voltage u. The total current I is achieved relative to the applied voltage with a shift by an angle ϕ. The angle δ ₁ , complementary to the phase angle ϕ between the current and voltage of 90 °, is called the dielectric loss angle. The dielectric loss tangent characterizes the losses in the surface layer of the polymer lining, which are easy to understand from the vector diagram tanδ ₁ = I _a / I _r . The greater the active current I _a , heating the surface layer of the polymer lining, the greater δ ₁ and tan δ ₁ and, consequently, the greater the loss. Using the value of tanδ ₁ , the quality of the surface layer of the polymer overlay is estimated: the higher it is, the more heating of the surface layer of the overlay will be, and consequently, the larger the area of the contact-pulse interaction spots and the lower the specific load on the contact spots. Rational values should be provided tgδ ₁ ≤10 ^-4 .

Conductivity phenomena in the surface layers of a polymer patch. The processes of internal charge relaxation in the polymer pad control the phenomena of conductivity. The latter are determined by such characteristics: carrier mobility and their concentration; conditions for the injection of charges on contact spots, etc.

In polymer materials capable of retaining a charge for a long time, carrier capture centers are present whose mobility is suppressed by the capture processes. Capture also affects conduction processes. In addition to intrinsic charge carriers, foreign materials are also present in the polymer material, injected electrons into the body of the microprotrusion of the contact of the metal-polymer friction pair.

In the study of contact conductivity, it is necessary to distinguish between transient processes and stationary processes on the spot of frictional interaction. This is because when studying the conductivity or mobility of carriers, it is not possible to simultaneously monitor over time the charge distributions both in the body of the polymer patch and on its working surface. The imprint on the problem of the conductivity of the polymer material is imposed by the absence of its structural uniformity and purity.

The mobility of charge carriers in a polymer material is affected by the presence of various states in it - free (delocalized) and associated at shallow and deep trapping levels located along the thickness of the patch. The movement of ions with energy near the surface of the contact spot (conduction band) is a quantum-mechanical tunneling between delocalized states located on an energy scale above the mobility edge. This process occurs without any thermal activation, and the corresponding charge mobilities turn out to be relatively high - about 10 cm ³ / (V⋅s). For the movement of a charge captured by a shallow level located in energy below the edge of mobility, a certain amount of thermal energy is needed, converted from electric pulse energy during friction. The process of motion of such charges becomes thermally activated and reduces to successive jumps between localized states. In this case, the mobility of the charges is less [about 10 ² cm ² / (V⋅s)] than in the first case. Finally, the carrier capture time at a deep level is very large, and their mobility, taking into account such capture, becomes extremely small [10 ^-10 -10 ^-17 cm ² / (V /s)] [3].

In many polymeric materials that do not have energetically strong carriers, they can be created by injection through a contact spot from a metal friction element. If the influx of carriers due to injection exceeds the flow of particles transported through the polymer film of the patch, then the currents are limited by the field of the forming space charge. In the opposite case, the currents are determined by the intensity of injection from the metal films of the contact spot.

The energy balance of the surface layer of the polymer lining in the formation of the regime of metal-polymer friction pair.

The dielectric loss in the surface layer of the polymer patch located in an alternating electric field during friction is the dissipated power, i.e. energy generated by an electric field.

There are two reasons for the irreversible loss of energy of the electric field in the surface layer of the polymer overlay:

- heating currents through conductivity;

- delayed types of polarization.

According to the Joule-Lenz law, the flow of through conductivity leads to the release of heat in the surface layer of the patch, and there are irreversible losses of the external field energy.

Polarization processes are characterized by polarization R _P and also lead to irreversible loss of energy of the external field. The polarization P _{P is} numerically equal to the electric dipole moment M _d unit volume of the surface layer of the lining.

If the polarization processes have time to monitor the change in the external field, then there is no phase shift between the field strength ξ and the polarization P _P (Fig. 21 a ). In this case, during the first quarter of the period, the field orients the bound charges in the direction, completing the work. The directions of the field ξ and the electric dipole moment M _d coincide. The kinetic energy of bound charges grows, which is equivalent to an increase in their temperature, i.e. heating the surface layer of the polymer lining, and with it the metal-polymer friction pair, which is characteristic of a single mode of braking.

In the second quarter of the period, the direction of the field ξ remains the same, and the polarization Р _П decreases, i.e. due to a decrease in ξ, bound charges begin to return to their original state, giving up the accumulated kinetic energy, which leads to a decrease in their temperature, i.e. cooling the surface layer of the polymer lining.

During the period, heating is compensated by cooling and, thus, irreversible energy losses are absent. This state of the surface layer of the polymer lining is called steady due to the fast types of polarization.

In the case of slow types of polarization, a lag in polarization from a change in the external field is observed (Fig. 21b). Due to the phase shift between the tension ξ and the polarization Р _П , the heating time of the surface layer of the polymer lining turns out to be longer (long braking mode), i.e., the kinetic energy accumulation time is longer than the time of its removal to the metal-polymer friction pairs.

Therefore, the surface layer of the polymer lining is heated, or irreversible losses of the external field energy are observed in it. The energy loss on the orientation of the bound charges is equivalent to the fact that an active current flows in the surface layer, as it were, due to polarization processes that lag behind changes in the external field.

At the second stage, the dynamic and thermal similarity of the subsystem of the friction pairs of the band brake shoe is analyzed.

During frictional interaction, which has a contact-pulse nature, the working surfaces of metal-polymer friction pairs proceed complex non-linear processes, phenomena and effects that contribute to affect their subsurface layers, as well as the state of the metal friction element. During electrothermomechanical friction of metal-polymer friction pairs, processes, phenomena and effects exert external and internal effects on their surface and subsurface layers, thereby contributing to the appearance of mechanical, electric, thermal and chemical fields.

The listed fields interact with each other, while being in a single energy field, and for their description it is necessary to use an inhomogeneous system of nonlinear functional dependencies. The type of differential equations depends not only on which friction materials are used in the friction unit, at what impulse loads and sliding speeds they contact each other, what heat input is realized in friction pairs, what is the heat fractional distribution between friction elements, what external control action is realized in the tribosystem, but also in what mechanical and thermal field the friction unit functions. Theoretical dynamic and thermal calculation of tribosystems is a very complex process, since according to A.V. Chichinadze includes more than 50 parameters, with many assumptions, simplifications, and linearization of dynamic and thermal processes. As a result of this, calculation results are often obtained that are inadequate to the actual operating conditions due to the inconsistency of various evaluation methods, based on a huge number of models (up to a million or more) and their inconsistency with the results of experimental studies in laboratory (bench) and operational (industrial) conditions. However, all of the foregoing is ultimately impossible due to a violation of the principle of superposition ("mechanical tension - mechanical compression", "thermal expansion - thermal compression", "polarization - depolarization", "heating - cooling", "restoration - destruction", etc. .) for nonlinear tribosystems.

Thus, it is practically impossible to solve the problem theoretically by making an effective optimization of the design and operational parameters of friction pairs. The most appropriate way to implement the optimization of the friction pairs of the tape-shoe brake is to use experimental data obtained in laboratory conditions on brake stands based on the methods of physical similarity and modeling using elements of the theory of a systems approach.

A correct physical model of a metal-polymer friction pair is more accessible for research than a real object. Moreover, the model should accurately reflect the behavior of the tribosystem under certain restrictions, which will allow to obtain a solution that reflects its adequate state with respect to the real tribosystem.

As an object of research, friction assemblies of the tape and shoe brake of the U2-5-5 winch are used.

Serial tape brake shoe.

According to the kinematic scheme (see Fig. 22 a , b), the friction linings 3 are mounted on the brake belts 2, which are attached to the balancer 11 at one end [from the side of the runaway branch (II) of the belt] and the other [from the side of the branch running along it (I )] - to the crank necks 6 and 9 of the crankshaft 10.

Serial tape-shoe brakes of a drawworks operate as follows. By moving the handle 1, the crankshaft 10 is rotated, as a result of which the driller tightens the brake belts 2 with friction linings 3 and they sit on the brake pulleys 4. The tape-block brake is characterized by the following stages: initial (first), intermediate (second) and final (third). Let us dwell on each of the stages separately.

At the initial stage of braking, the friction linings 3 located in the middle part of the brake belt 2 interact with the working surface of the brake pulley 4. The front of interaction extends towards the friction linings 3 of the running branch (I) of the brake belt 2.

The intermediate stage of braking is characterized by the further spread of the interaction front towards the friction linings 3 of the runaway branch (II) of the brake belt 2.

The final stage of braking is characterized by the fact that almost all the fixed pads 3 of the brake belt 2 interact with the working surface of the rotating pulley 4. During braking, the sequence of friction surfaces coming into contact is repeated. The full braking cycle is completed by stopping the brake pulleys 4 with the drum 5. The control of the winch brake is also carried out by supplying compressed air through the driller's valve 7 to the pneumatic cylinder 8, the rod of which is connected to one of the crank crankshaft necks 10 of the brake. The pressure value of the compressed air in the pneumatic cylinder 8 is regulated by turning the crane 7 of the driller.

When uneven wear of the friction linings 3 mounted on the belts 2, the balancer 11 at the time of braking slightly deviates from the horizontal position and evens the load on the runaway branch (II) of the brake belts 2, while ensuring uniform and simultaneous girth of the brake pulleys 4. Thanks to ball joints the implementation of the loads from the brake bands 2 to the balancer 11 is not changed.

The weakest link in the brake assembly is the friction linings. They are made in the form of individual parts, which can be attached in various ways (for example, using antennae) to a relatively flexible steel tape. Friction linings with constant and variable pitch are installed along the arc of grasping with the brake belt of the pulley. When installing overlays with a constant pitch on the tape, their number is always even (12; 16; 18; 20; 22; 26) (see Fig. 23g). With a variable step, this number may be odd.

The total number of friction linings on the brake belt depends on their geometrical parameters, as well as on what angle of rotation of the brake pulley of the brake pulley working surface is realized in the given drawbar brake of the drawworks.

Model tape brake shoe. The main nodes of the brake stand are mounted on two I-beams 4 (Fig. 23 a , b, c), which, in turn, are anchored to the concrete base with anchor bolts. The model brake has a brake band 2. At the same time, one end of the brake band 2 is fixedly mounted, and a load device 11 is located on its second end. The inner surface of the band 2 interacts with the non-working surfaces of the polymer linings 3. The linings 3 are attached to the belt 2. The brake pulley 4 is installed on the shaft 5 with bearings located in bearings 6. The shaft 5 is connected through a flexible finger coupling 10 to the shaft 12 of the DC motor 7. In this case, a DC motor of the 2PN225MU4 brand with a power of 15.0 kW is used. The use of an engine of this brand made it possible to smoothly control the rotational moment on the drive shaft 12 and maintain it stable when the rotational speed of the shaft 5 changes. The force to press the idle and working surfaces of the friction linings 3, respectively, to the inner surface of the brake belt 2 and the working surface of the brake pulley 4 was regulated by device 11.

The traction motor 7 of the brake pulley 4 (DPT) is supplied with direct current with a rated voltage of the armature winding (YA) 110V, a similar DC motor 8 (GPT) was used as its power source, which worked in the generator mode. The generator shaft 10 was rotated by an asynchronous three-phase alternating current motor 9 (DPT). Direct currents were applied to the excitation windings of the generator (OVG) and the motor (OZD), which were rectified on diode bridges composed of VD1-VD4 and VD5-VD8 diodes, and were controlled by laboratory autotransformers LATR-1M and LATR-2M.

In the table. Figure 5 shows the main parameters of the friction pair of the model tape-shoe brake.

The research objectives, test conditions and real possibilities determined the test object - a physical model of drawworks brake brakes with a scale:

- geometric similarity for its main dimensional parameter - the radius of the brake pulley

m _l = 2, 2.45 i 2.9 for R _W = 500, 612.5 i 725 mm, respectively,

where l _H and l _M are the radii of the brake pulley of nature and model (l _H = R _w , l _m = 250 mm);

- dynamic similarities

where S _H and S _m - the tension force of the incident sections of the brake belt of nature and model, kN.

Note that the scale of similarity changes if the parameters of the nature or model, for example, the tension of the branch of the tape, change.

For testing, the model was equipped with:

толщиной δ_Л=2,0, 3,0 и 3,7 мм (m_δ=2,0, 1,67 и 1,62 для толщины ленты натуры 4,0, 5,0 i 6,0 мм, соответственно), с длиной промежутка 2L_n участка ленты между накладками (L_n=30,0-90,0 мм, m_Ln=1,0);- brake bands made of steel 50.0 with a width of 200.0 mm

thickness δ _L = 2.0, 3.0 and 3.7 mm (m _δ = 2.0, 1.67 and 1.62 for the thickness of the tape of nature 4.0, 5.0 and 6.0 mm, respectively) , with a gap length of 2L _n of the tape section between the plates (L _n = 30.0-90.0 mm, m _Ln = 1.0);

шириной B_H=230,0 мм

и длиной L=120 мм

- friction linings from retinax FC-24A with a thickness of δ _H = 15.0 mm

width B _H = 230.0 mm

and length L = 120 mm

при V_H=20,0 м/с; при других значениях скорости на тормозных шкивах буровых лебедок m_V уточняется).- the brake pulley rotated with the highest frequency of 200 min ^-1 , which provided the highest linear speed of the pulley relative to the linings V _W = 5.236 m / s (

at V _H = 20.0 m / s; for other values of speed on the brake pulleys of drawworks m _{V is} specified).

Energy balance of friction brake assemblies. Fluctuations in the main parts of the tape-shoe brake lead to additional dynamic loads, which affects the stability of its output parameters and, as a result, leads to uneven wear of the mating friction surfaces.

As you know, the occurrence of vibration of the tape brake shoe parts is due to the working processes in the friction units, i.e. a change in the patterns of contacting the microprotrusions of friction pairs, as well as unequal deformations of the branches of brake bands.

In FIG. 24 a , b linear and non-linear frictional characteristics are presented depending on the pulsed specific load acting in the friction pairs of the brake. We assume that when vibrations occur, the contact areas of the pads will move according to a sinusoidal law (Fig. 24b) and based on the graphical dependencies (Fig. 24 a , b) we will construct diagrams of the disturbing force.

If the phase of the forced oscillations coincides with the disturbing force, the operation diagram of the disturbing force is a straight line (straight line 1) with a linear change in the friction force of the pulsed specific load (Fig. 24c) and a curve in the case of a nonlinear change (curve 2) [Fig. 24c], and the work of the disturbing force in the latter case is zero.

However, the phases of the forced oscillations and the action of the disturbing force may not coincide. At resonance, when the largest amplitude of oscillations is observed, the phase difference is π / 2. This case is depicted in FIG. 24c, d, curves 2, i.e. the work diagram is depicted as an ellipse.

Since the energy supplied to the oscillatory system by the disturbing force is proportional to the area of the diagram, it changes in a single cycle according to a linear law. On the other hand, the energy dissipated by the oscillatory system is proportional to the square of the amplitude.

Thus, the introduced and scattering energies will be equal only at the intersection of the function curves for both types of energy and characterize the steady state of the tribosystem.

In FIG. 24d shows graphical dependencies characterizing the change in the introduced vibrational energy on the runaway (E _c ) and oncoming (E _n ) branches of the tape and energy damping the oscillations R _e and R _{n by the} indicated branches of the tape.

Since the loading of the oncoming branch of the tape is greater than the runaway, the introduced energy on the oncoming branch of the tape will be greater than on the runaway. However, the scattering energy on the oncoming branch is greater than on the oncoming branch, and the scattering energy grows faster than the introduced energy. As a result, the amplitude of oscillations on the runaway branch of the tape is greater than on the runaway.

Consider the change in the magnitude of the perturbing energy and the scattering energy when the surface temperature of the friction pairs fluctuates. In FIG. 25 shows the dependence of the dynamic coefficient of friction on the surface temperature for a retinax FK-24A friction pair - 35KHNL steel. The figure shows that in the temperature range up to 200 ° C the dynamic coefficient of friction of this pair varies slightly. In the operation diagram (Fig. 26, curve 1), this case corresponds to the largest friction force and the smallest vibration amplitude.

In the temperature range 200 ° C-350 ° C, a decrease in the dynamic coefficient of friction is observed due to the intensive development of plastic deformation of the friction material of the lining. In this case, there was a decrease in the dissipation energy, while the value of the disturbing energy remained almost constant. As a result, the intersection point of the curves R _{n, s} and E _{n, s} (Fig. 24e) has shifted to the right for both the incoming and the running branches of the tape, i.e. the amplitude of the oscillations increased. However, due to the softening of the surface layer of the linings, the damping properties of the tape branches are improved and the growth of the amplitude of the oscillations slows down (Fig. 26, curve 2).

In the temperature range 350 ° C-450 ° C, the dynamic coefficient of friction is stabilized, while the amplitude of the oscillations continues to decrease due to further softening of the surface layer of the pads (Fig. 26, curve 3).

In the surface temperature range 450 ° С-600 ° С, a further decrease in the amplitude of oscillations was observed, caused by a slight increase in the dynamic coefficient of friction (see Fig. 25).

Thus, the greatest vibrations occur on the runaway branch of the brake belt due to the action of much smaller pulsed specific loads in the friction pair compared to the runaway branch, which contributes, in turn, to the development of the nonlinear characteristics of the tribosystem friction pairs.

Let us analyze the vibrations developing in the metal-polymer friction pairs of a tape-brake shoe. In FIG. 27a, b shows the patterns of change in the tension of the running branch of the tape when changing the amplitude of the radial vibrational velocity of the plates on the runaway (a) and oncoming (b) branches of the tape and the forces on the loading device 100 N and 300 N.

An analysis of the graphical dependencies showed that with an increase in the amplitude of the radial vibration velocity, the tension of the incident branch of the tape decreases with constant tension of its running branch. An increase in the amplitude of the radial vibration velocity on the runaway branch of the tape leads to a decrease in the tension of its oncoming branch by only 2–3%, regardless of the pulling force of the runaway branch. An increase in the amplitude of the radial vibration velocity on the incident branch of the tape leads to a more significant (5–8%) decrease in the tension of its running branch, regardless of tension.

This is explained by the fact that the total impulse braking moment created by the difference in tension between the on-ram and on-ram branches is realized by friction linings on the on-ram branch of the belt, 2-4 times greater than the total impulse braking moment on the on-ram branch of the belt. It was found that a decrease in the impulse force as a result of dynamic processes in friction pairs by approximately the same value on the incoming and outgoing branches of the belt causes a different decrease in the tension force of their branches.

Thus, in the process of experimental studies it was found that the amplitude of the radial vibration velocity of the patch sections on the runaway branch of the tape is on average 1.5-2 times greater than on its oncoming branch. However, an increase in the radial vibration velocity of the patch sections on the running branch of the tape leads to a decrease in the tensile force by 3-5 times more than a similar increase on the branch running off of it.

In FIG. 28 a , b show the amplitude spectra of sections of tapes with overlays obtained with various types of pulsed loading and the rotation speed of the brake pulley. An analysis of the obtained spectra showed that frictional vibrations occurred in areas in all friction pairs, regardless of the operating mode. The maximum oscillation amplitudes were observed in the frequency range 300–1000 Hz, depending on the loading mode and the degree of wear of the patch sections. The greatest modification of the spectra occurred when the pulsed specific loads changed. If at the minimum pulsed specific load (0.1-0.2 MPa) one pronounced peak was observed in the frequency range 800-1000 Hz, then with an increase in the pulsed specific load, the amplitude of the vibration velocity at these frequencies decreased, while the low-frequency component relatively increased vibration velocities in the frequency range 300-500 Hz, and at maximum load, the amplitude of the vibration velocities at these frequencies reached a maximum value. Such a tendency was observed from the tape running down to the running branch with a constant load loading. Thus, the largest oscillation amplitude at small pulsed specific loads was observed on the first friction lining (the runaway end of the brake band) lying in the frequency range 800-1000 Hz, and at maximum pulsed specific loads - on the moving end of the belt (eighth friction lining) in the frequency range 250-500 Hz. When replacing unworn linings with worn ones, the indicated growth trend of the low-frequency component of the vibration velocity changed with an increase in the pulsed specific load, due to an increase in the amplitude of oscillations by an average of 20-30%.

An increase in the sliding velocity from 5.0 to 15.0 m / s led to a shift of the maximum oscillation amplitudes to the higher frequency region by approximately 10-30%. At the same time, the maximum oscillation amplitudes both in the high-frequency and low-frequency regions slightly increased (by an average of 9-15%). So, if at a sliding speed of 5.0 m / s and a pulsed specific load of 0.2 MPa at the running end of the tape, the maximum vibration velocity amplitude was observed at a frequency of 810 Hz and amounted to 11.1 mm / s, then with an increase in the sliding speed to 15.0 m / s, the maximum amplitude of the vibration velocity shifted along the frequency axis to 1050 Hz and amounted to 12.7 mm / s.

A similar picture was observed at large pulsed specific loads in the frequency range 250–500 Hz. If for a sliding speed of 5.0 mm / s and a pulsed specific load of 1.0 MPa, a maximum amplitude of radial vibration velocity of 9.4 mm / s at a frequency of 260 Hz was recorded on the incident branch of the tape, then with an increase in sliding speed to 15.0 m / with the maximum amplitude of the vibration velocity was 11.6 mm / s at a frequency of 380 Hz.

Safety factor of the cross section of the brake tape. The safety factor (n _T ) of the cross section of the brake tape is determined by the dependence of the form [8]

The maximum voltage in the cross section of the brake tape is determined by the type

Moreover, the permissible value of the safety factor of the brake tape was [n _T ] = 2.

Deformation of the brake tape. The expression for determining the complete elongation of the brake band when the friction lining with a variable pitch is located on the arc of its girth has the following form [1]

For a brake tape with a uniform spacing of the pads, when β ₁ = β ₂ = ... = β _n-1 = β, equation (46) takes the following form [1]

In FIG. 29 a , b, c shows the force patterns acting: in the knot of the patch-strip, the tape section above the i-th patch; when determining the deformation of sections of the tape; 1 - a brake tape; 2 - friction lining.

и

- нумерация зазоров между накладками представлены на фиг 30.Patterns of change in the relative deformations of sections of the brake band when the friction linings are arranged along the arc of its girth with a constant (1, 1 ') and a variable (2, 2') step: calculated (1, 2) and experimental (1 ', 2') data,

and

- the numbering of the gaps between the plates is presented in FIG. 30.

Compliance of the frictional joint of metal-polymer friction pairs. By the compliance of the frictional joint we understand the cyclic process of contact-pulse interaction of its microprotrusions, which includes the elastic deformation of the elements and their return to some initial position in the pauses between these interactions (Fig. 31).

The flexibility of the joints of the friction pairs largely depends on the elasticity of the microprotrusions of the polymer lining. The magnitude of the compliance of the microprotrusions during the braking process is variable. Compliance P _{n of} elastic elements, which are microprotrusions under the action of normal impulse loads acting on microcontacts, i.e. on contact spots, characterizes the limit of the ratio of the increment of deformation to the change in the pulsed normal load that caused this increment:

The dependence of the normal impulse load causing deformation of the microprotrusions of the friction lining when they are connected in parallel to the block is shown in FIG. 32 a .

Depending on the height of the microprotrusion and the location between the microprotrusion adjacent to it on the working surface of the friction lining, we assume that each of them is loaded with a variable pulsed normal force, and, therefore, also has a variable flexibility.

When parallel connection in blocks of elastic elements with different characteristics (Fig. 32b), given that their deformations are different and equal to the total deformation, we have

Consequently, the forces acting on each elastic element in a parallel block are inversely proportional to their compliance

where from

In this case, the compliance of the block is

Thus, with the parallel connection of elastic elements into blocks, their total compliance decreases as microprotrusions wear out, and the total stiffness of the block is equal to the sum of their stiffnesses

However, the flexibility of joints of metal-polymer direct and reverse friction pairs in tape-shoe brakes is affected by the peculiarities of their design and deformation of elements, in particular brake bands.

The research results establishing patterns of changes in the deformations of microprotrusions of metal-polymer friction pairs of a tape-shoe brake from impulse specific loads at different areas of their contact spots are shown in FIG. 33.

Coefficient of mutual overlap of metal-polymer friction pairs. Studies have established that the geometry of micro- and macrocontacts has a significant effect on the temperature field during frictional interaction of friction pairs. A.V. Chichinadze introduced into consideration the coefficient of mutual overlap K _b for single-pair friction units. This coefficient is the ratio of the product of the contact areas of friction of both friction elements of the pair A _k1 and A _k2 to the square of the total area A ₀ .

This coefficient significantly affects the values of: pulsed normal loads N in the contact zone of microprotrusions generated by electric and accumulated heat currents, dynamic friction coefficients, sliding speeds, longitudinal (on the surface) and transverse (thickness) temperature gradients, thermal stresses in friction bodies, intensity wear of friction working surfaces, impulse braking torque. In addition, this parameter, along with the factors listed above, takes into account heat transfer conditions when determining the distribution coefficients of heat fluxes between friction pairs.

и

, соответственно, на поверхности обода шкива и по его толщине.The value of K _b determines the average temperature of the friction surface ϑ _n1,2 , volumetric temperature ϑ _v1,2 , and temperature gradients

and

, respectively, on the surface of the pulley rim and in its thickness.

. Этот эффект достигается при нормальной удельной нагрузке p=const и скорости скольжения V_ck=const. Следствием этих изменений является возрастание динамического коэффициента трения f и снижение интенсивности изнашивания u_p.n [9]. В данных исследованиях не было четкого разграничения температурных градиентов по поверхности пары трения и по толщине цилиндрического кольца. Такие исследования следует отнести к выполненным на микроуровне.In experiments to study the temperature field during friction with the ends, the universal friction machine “Unitrib” was used. In this standard model used ring samples (d _N = 28.0 mm, d _ext = 20,0MM, h _n = 15.0 mm) corresponding to the friction polymeric material and gray cast iron SCH15. As a result of studies of the relationship of overlap K coefficient of friction _taken from the process parameters were set to: K _taken reduction reduces the average surface temperature θ _n and ascending temperature gradient

. This effect is achieved at normal specific load p = const and slip velocity V _ck = const. The consequence of these changes is an increase in the dynamic coefficient of friction f and a decrease in the wear rate u _pn [9]. In these studies, there was no clear distinction between temperature gradients along the surface of a friction pair and the thickness of a cylindrical ring. Such studies should be attributed to those performed at the micro level.

On real physical models in industrial and bench conditions (material of a friction pair “steel 35KHNL - FK-24A”) when studying the temperature field during electrothermomechanical friction, subject to the condition that Δϑ _n > Δϑ _v on a serial and model tape-shoe brake as a result of research the mutual overlap coefficient K _b with the parameters of the friction process, from which the normal pulse N is extracted, depending on the thermal condition of the rim of the brake pulley, it was found (Fig. 34 a , b, c, d, e, e):

и

; увеличение К_вз способствует возрастанию

и

;- a decrease in _Kb leads to a decrease in the average surface temperature ϑ _n , and as a result, the volumetric temperature ϑ _v and a decrease

and

; an increase in K _v promotes an increase

and

;

;

;- a decrease in K _b causes an increase in the dynamic coefficient of friction; as for the dynamic coefficient of friction, it increases (f) due to a decrease in K _b and

;

;

;

способствует увеличению интенсивности износа u_p.n.- To increase and _taken

;

contributes to an increase in the wear rate u _pn .

и

изменяются больше от К_вз, чем от

и

:For friction pairs of a tape-shoe brake (in bench conditions), a decrease in K _b during friction work W _T = const leads to a high and stable dynamic coefficient of friction, as well as to minimal wear, only when the functions

and

To change over from _taken than from

and

:

A.I. Volchenko introduced the static and dynamic coefficients of overlap K multipair _taken for friction units.

In FIG. 35 a , b, c depicts a diagram of a tape-shoe brake with movable friction pads installed with constant (a) and variable (b) steps (a bandage made up of four pads) [10].

In the brake, the lining 3 is interconnected by springs 5 in a flexible ring - a bandage, which is fitted with an interference fit on the working surface of the brake pulley 1. In this case, external and internal friction units are formed. In this regard, the following stages of braking are distinguished: initial (I), when the inner surface of the brake belt 2 interacts with the outer surface of the lining 3, stationary relative to the pulley 1; intermediate (II), when the work of friction is performed by the external and internal surfaces of the linings 3, moving relative to the pulley 1 and the belt 2. During this stage, the load is transferred from the external to the internal friction brake assemblies, and it is transitional and a very short period of time continues; and the final (III), during which the internal surfaces of the fixed plates 3 interact with the working surface of the brake pulley 1. It is during the third stage that the brake performs its main work.

Two surfaces of one friction lining, the outer surface of which is movable when interacting with the inner surface of the brake band (at the first stage of braking, a variable coefficient of mutual overlap takes place) with an increase in the pulling force of the brake band. The mutual overlap coefficient of external friction pairs increases all the time and reaches its maximum value until the completion of the first stage of braking. After which it remains constant even with a further increase in the tightening force of the brake band. At the third stage of braking, the quasi-stationary internal surfaces of the linings interact with the moving working surface of the brake pulley. In this case, the mutual overlap coefficient increases until an interference between the inner surface of the last bandage lining and the pulley occurs. In the future, the coefficient of mutual overlap of the internal friction pairs of the friction units is constant until the end of the third stage of braking. Due to the fact that the friction units of the tape-shoe brake with movable pads work alternately, i.e. first external and then internal, and also for a clear understanding of the stages of braking, we introduce the concept of “static” and “dynamic” mutual overlap coefficients for their friction pairs.

Thus, in a first step the braking dynamic coefficient of mutual overlapping of external friction nodes (. Figure 36, line 1 a) is variable in time and static coefficient of mutual overlapping of internal friction nodes (Figure 36, line 2i.) - it is constant in time. In the third stage of braking, the static coefficient of mutual overlap of the external friction units (Fig. 36, line 1, c) is a constant value in time, and the dynamic coefficient of mutual overlap of the internal friction units (Fig. 36, line 2b) is a variable in time until until there is a breakdown of the interference of the last lining of the bandage. After that, the dynamic coefficient of mutual overlap of the internal friction units becomes static (Fig. 36, line 2d) and keeps constant in time until the completion of the third stage of braking. In FIG. 36 dashed lines show the possible changes in the static and dynamic coefficients of the mutual overlap of the external and internal friction pairs in time at the first and third stages of braking.

The dynamics of the braking process are inextricably linked with the frictional properties of materials of direct (internal) and reverse (external) friction pairs, which, in turn, depend on the speed, load and temperature conditions of frictional contacts, as well as environmental influences.

The influence of these factors on the dynamic coefficient of friction for different materials is different. This is due to the physicomechanical properties of materials, the nature and intensity of processes, phenomena and effects occurring on frictional contacts and in volumes of materials.

Knowing the mutual overlap coefficients in the friction pairs of brake devices allows you to adjust the static specific loads in the mates. Especially, this is evident in the works of D.A. Volchenko as applied to tape-shoe brakes, assembling friction linings with variable and constant pitch on the branches of the brake belt.

The pulsed nature of the change in normal forces during frictional interaction of nodes. In the energy aspect, friction is the process of transforming the mechanical energy entering the system into electrical, thermal and other types of energy. The redistribution of energy flows on the surfaces of friction pairs of braking devices is observed only in the processes of friction itself, and therefore it is necessary to develop and use in-situ research methods.

The contact-pulse interaction of metal-polymer friction pairs of the tape-shoe brake, expressed by the pattern of change in the normal force with respect to the braking time, is shown in FIG. 37. It follows from the latter that the pattern of change in the normal time impulse effort has a wave nature and approaches the quasi-sinusoidal law of its change.

The interaction of microprotrusions in the metal-polymer friction pair is discrete, due to the different heights of microroughness it is realized simultaneously in levels and in time. The resulting pulses are characterized by amplitude (height), duration (width), aperiodic repetition and the position of the pulse within the period (time shift or phase of the pulse).

It is known that the displacement of microprotrusions of mass m _{m of the} pulley rim under the action of a variable normal force N, given as a function of time τ, is determined by the following dependence

)

)

Accepting the integration limits from 0 to T and using the Cauchy formula for converting an n-fold integral to a single, we write the equation for the projection of the path traveled in time T:

The integral in this expression is the static moment of the area of the pulses formed by the force N (t) in the time interval from 0 to T relative to the straight line, the position of which is determined by the equation

t = T.

In this case, the static moment refers to the algebraic sum of the static moments of positive and negative areas relative to the straight line, therefore, equation (56) is written in the following form

Opening the brackets in equation (47), we obtain

- мгновенное изменение скорости i-ой массы m_м микровыступов под действием импульсов A_i.Where

- instantaneous change in the speed of the i-th mass m _{m of} microprotrusions under the action of pulses A _i .

For oscillatory processes, an alternation of positive and negative impulses is usually characteristic. In [11], a method for analyzing such vibrational motions with the help of pulsed pairs is described, the essence of which is as follows. We divide the normal force curve N (τ) into sections for which the equality

которые назовем приведенными импульсными парами. Тогда путь массы m_м микровыступа обода шкива согласно выражениям (46) и (47) можно изобразить в виде ломаной линии, абсциссы точек излома которой будут соответствовать точкам приложения фиктивных мгновенных импульсов, а ординаты определяются из уравнения, которое показывает абсолютное изменение величины пути микровыступа обода шкива под действием приведенной импульсной пары, т.е.Therefore, on each spot of contact of the microprotrusions “metal-polymer” there are two pulses (pulse pair), and the pulse modules are equal. Replacing the actual impulses with equal fictitious ones applied at the centers of gravity of the microcontact areas, we obtain impulse pairs formed by instantaneous impulses

which we call reduced impulse pairs. Then the path weight m _m microprojection rim of a pulley according to expressions (46) and (47) can be represented as a broken line, the abscissa points of which fracture will correspond to points of application dummy instant pulses and ordinates determined from the equation that shows the absolute change in the way of the rim microprojection pulley under the action of a reduced impulse pair, i.e.

The presented method for evaluating vibrational processes using pulsed pairs was used to study metal-prolimer microprotrusions during the interaction of their contact spots during braking.

Taking into account the pulses A _y and A ₀ acting on the microprotrusion of the pulley rim at the moment of its interaction with the microprotrusions of the polymer overlay, write

It follows that the O-O axis (Fig. 38a, b, fragments from Fig. 37 are taken) divides the loading cycle of the microcontacts into two zones satisfying condition (61 and 62). In this case, we have two impulse pairs, one of which acts from the side of the metal-polymer microprotrusions, and the second from the side of the polymer-metal microprotrusions. When these pairs interact, a phenomenon of displacement of microprotrusions is observed. Pulsed pairs are replaced by the given ones. Then the path of the microprotrusion of the pulley rim, covered during the duration of the reduced impulse pair (at V ₀ = 0), is equal to the moment of the pair divided by the mass of the microprotrusion of the pulley rim

The pulley rim micro-protrusion path graph plotted using the pulsed pair method is depicted by a broken line 0-1-2-3-4, which coincides with the actual path graph at points of greatest interest. In the spaces between them, the actual curve is constructed approximately by rounding the corners of the polyline. Each impulse pair corresponds to a portion of the path graph characteristic of oscillatory processes. Points with zero speed A ', B' and 4 (0, A '' and B '') correspond to the boundaries of the pulse pairs. In this case, the maximum speed of the microprotrusion of the pulley rim is achieved at the moment of sign reversal when the microprotrusion of the lining and the reaction force are shifted (point B on the track graph).

Thus, during the interaction of microprotrusions "metal-polymer" two identical in magnitude, but different in the direction of the moment are formed. As a result of this, the interaction of the microprotrusions of the metal-polymer friction pairs is as if balanced. It follows from dependences (61) and (62) that the sum of the areas of positive impulses is equal to the sum of the areas of negative impulses, and the center of gravity of the area of positive impulses lies on the same vertical as the common center of gravity of all areas of negative impulses.

The pulsed nature of the interaction of microprotrusions of friction pairs “metal-polymer” leaves an imprint on the change in the pulsed normal forces on their contact spots, and as a result, on the patterns of change in pulsed specific loads.

One of the main operational parameters of the tape brake shoe is the tension of the branches of the brake tape. The difference between the tension of the running and running branches of the brake belt determines the pulsed friction force acting in the friction pairs of the brake.

It is known that the efficiency and durability of metal-polymer friction pairs of a tape-shoe brake depends on its design parameters. The latter, in turn, affect the operational parameters of the brake. We proceed to their definition. In FIG. 39 is a diagram of a tape-shoe brake for determining the tension forces in the brake belt.

. Считаем

и, пренебрегая величиной второго порядка малости

, получаемWe compose the equation of equilibrium of the elementary section of the tape with the overlay

. We consider

and neglecting the magnitude of the second order of smallness

we get

; откуда

(65)

; where from

(65)

; или

откудаFrom (64) and (65) we obtain

; or

where from

Wherein

Determining the tension of the running branch of the brake band by setting the value of the tension of the running branch allows you to go on to assess the definition of normal, impulse contact force in the friction pair "pad-pulley".

First, we consider the contact problem of interacting with a pulley of a system of friction linings pivotally connected to a steel tape under the action of static forces S _n and S _c at the ends of the tape. Following the work [12], we replace the pads with dots, and take the central angles as variables (Fig. 40), based on the fact that the uniform arrangement of the pads along the arc around the tape leads to an uneven distribution of the pulsed normal load on them, and as a result, to uneven wear their work surfaces.

We compose the equilibrium equation of the i-th lining. We denote by F _i and N _i , the friction force and normal force the contact points acting on the tape, by S _i-1 , S _i , S _{i + 1} the tension forces of the sections of the tape acting on the three selected plates along the chords. Projecting these forces along the tangent and normal, we get:

If there is a slip at the contact point, the Coulomb friction condition is satisfied (f is the dynamic coefficient of friction)

Using condition (68), we obtain

In formulas (67, 69), S _i , β ₀ , and β _n are considered given values. In particular, if we put β ₀ = β ₁ = β ₂ = ... = β _n = β, then from relation (69) (after excluding S _i (i = 1, 2, 3 ... n-1), we obtain the formula used at 10]:

When deriving relation (70), it was assumed that at all contact points of the pads with a pulley slip occurs, i.e. condition (68) is satisfied.

Using dependences (69) - (70), it is possible to find the values of the brake belt tension and choose the angles β _j so that the normal forces at the contact points of the pads with the pulley are evenly distributed. In this case, the friction materials of the linings will be used more rationally.

The calculation results of pulsed normal forces according to dependence (67) are illustrated in FIG. 41.

The patterns of pulsed change in the contact normal force in the friction pair “pulley-pad” of the tape-shoe brake along the length of the pad in different zones of its width ( a ) of interaction showed the following. The overlay in width was divided into three zones: the first ( a ₁ = 30.0 mm); the second ( a ₂ = 60.0 mm) and the third (a ₃ = 90.0 mm). The first and second zones of the lining were located on its running part, and the third zone was located on the runaway part of the lining. The maximum normal forces occurred in the first and second zones (curves 1 and 2), and the minimum ones in the third zone (curve 3). If we consider the change in normal forces along the length of the friction lining, then from the non-clamped edge of the rim of the pulley about one third of its length was observed quasi-equalization of normal forces.

The braking torque developed by the friction brake assemblies.

In most cases, it is very difficult to analyze and evaluate in detail the dynamic parameters of metal-polymer friction pairs of the drawworks brake of the drawworks during braking due to their contact-pulse interaction. The pulsed nature of the interaction of microprotrusions of metal-polymer friction pairs leaves an imprint on the patterns of change in contact of normal forces, dynamic coefficient of friction, friction forces and other operational parameters, and as a result, one of the most important parameters is the braking torque developed by the drawbar brake of a drawworks.

The design diagram of the friction brake assembly is shown in FIG. 42.

Braking torque developed by brake friction pairs

"Pulley lining"

"Overlays tape"

Dependence (72) is used to determine the braking torque in the case when the friction linings are fitted with an interference fit on the working surface of the brake pulley and rotate with it. In this case, the brake band is free of friction linings.

Let us analyze the patterns of change in braking moments along the length of the brake band, which is divided into three zones: from the 1st to the 7th; from the 7th to the 15th; from the 15th to the 22nd overlay (Fig. 43). In each zone, bursts of braking moments are observed, which have maximum values on the third, eleventh (with f = 0.2, the maximum is shifted to the 12th pad) and the nineteenth pad. Relative to the last lining, the displacement of the maximum values of the braking moments at f = 0.2; 0.25 and 0.3 are on the twentieth pad.

In the table. Figure 6 shows the torque characteristics of the brake linings at their minimum and maximum values.

We give an analysis of the values of braking moments separately for each zone of the brake band section for specific friction linings when the dynamic coefficient of friction changes from 0.2 to 0.35. First, we determine the ratio of the dynamic coefficients of friction 0.25 / 0.2 = 1.25; 0.3 / 0.25 = 1.2 and 0.35 / 0.3 = 1.16, i.e. their values are decreasing. At the same time, with the minimum values of the braking moments, their ratios in the zones of the brake belt are: in the first, 1.564; 3.23 and 2.27; in the second, 1.16; 1.8 and 1.08; in the third, 1.27; 1.22 and 1.19 (with the above ratios of the dynamic coefficients of friction). The most stable are the ratios of the minimum braking moments in the third zone, since they are almost equal to the ratios of the dynamic friction coefficients. In the second zone, the ratios of the minimum braking moments vary from 1.08 to 1.8, and in the first zone, from 2.24 to 15.6.

As for the ratios of maximum braking moments, they vary in the areas of brake bands as follows: in the first - 2.68; 1.40 and 1.211; in the second - 0.745; 2.02 and 1.25; in the third - 1.25; 1.69 and 1.49. The closest ratios in relation to the dynamic coefficients of friction are the ratios of the maximum braking moments developed by the overlays of the third zone of the tape.

Thus, the ratio of the minimum and maximum braking moments developed by the third zone of the brake band (located on the oncoming branch of the band) are quasistable values.

Analysis of the values of the gradients of braking moments developed by the third pad (the first zone of the tape), according to the table. 6, shows that there is a fluctuation in their values from 62.1 to 166.8 kNm / m, and the ratios vary from 0.745 to 2.686. The most stable ratio values are the braking torque gradients developed by the twentieth plate (third zone of the tape), which are 1.21; 1.25 and 1.23 with ratios of dynamic friction coefficients 1.25; 1.2 and 1.16.

Using a new operational parameter, which is the gradient of the braking moments developed by the friction pairs “brake pulley - friction lining” allows us to evaluate their values for each friction lining of the brake belt.

Sliding speed of brake friction pairs. When the specific friction power fpV _ck is realized by the friction pairs of the band brake, the specific loads p and the dynamic friction coefficient f developed on the contact spots of their microprotrusions depend to a large extent on the sliding speed V _ck . So, at the initial stage of braking at a high sliding speed V _ck, when microprotrusions of friction pairs interact, electric currents are generated at their vertices at high specific loads p at the contact spots with markedly decreased values of the dynamic friction coefficient f. With a further increase in the areas of contact spots of microprotrusions due to their deformation and wear, the sliding speed V _ck and the pulsed specific loads p decrease, and as a result, the dynamic friction coefficient f increases. In this case, an increase in the surface temperature ϑ _n is observed at the contact spots of the microprotrusions of the friction pairs.

Thus, a change in the sliding velocity V _ck and pulsed specific loads p significantly less affects the change in the dynamic friction coefficient f and the wear rate than the effect of the temperature of the friction surface ϑ _n .

Between the sliding speed and the temperature of the surface layer of the metal friction element, ceteris paribus, there is a dependence according to the Eger formula, the temperature increase is proportional to the root of the sliding speed. At a temperature of 100 ... 200 ° C, when the surface and subsurface layers of the metal friction element are heated, due to the discreteness of the contact of their microprotrusions in the general stress-strain state of the surfaces, they increase and the contact impulse specific loads decrease. Melting microprotrusion of contact spots, i.e. surfaces of active mass transfer leads to a change in their shape, which in the general case is accompanied by an increase in the actual area of contact spots and a proportional decrease in contact pulse specific loads. In that place, the temperature during electrothermomechanical friction does not change from this, i.e. the deep temperature gradient in the rim of the metal friction element is independent of pulsed specific loads and is completely determined by the sliding speed and the friction work performed. Temperature peaks are almost completely realized in the active microvolume of the microprotrusions of the metal friction element. At a temperature at the contact spots of microprotrusions of 800 ... 1000 ° С, the volumetric temperature of the remaining material of the rim of the metal friction element will be 200 ... 250 ° С and significantly differs from the environment (20 ... 40 ° С). This suggests a large surface temperature gradient, as well as the temperature gradient of the active microvolume of microprotrusions. The duration of the temperature peak and the period of transition from heating to cooling and vice versa according to the principle of superposition is estimated by the rates of heating and cooling.

The magnitude of the active microvolume of the microprotrusions of the metal-polymer friction pair depends on the physicomechanical characteristics, as well as on the parameter pV _ck (the product of the relative slip velocity and the specific impulse load) and is limited by the penetration depth of the thermal pulse, on which the effect of temperature on the physicomechanical properties The material of the rim of the metal friccin element are tangible.

In fig. 44 shows the results of an experimental study of a “pulley-slip” friction pair (material 35KHNL-FK-24A steel) under bench conditions at specific loads of 0.6 MPa and surface temperatures of 200 ° C and 400 ° C, depending on the dynamic coefficient of friction on sliding speed. An analysis of the graphical dependencies indicated indicates the following: with an increase in the sliding speed of friction pairs at levels below (curve 1) and above (curve 2) of the permissible temperature of the lining materials, a change in the dynamic coefficient of friction is expressed by falling curvilinear dependencies. In this case, the deviation of the values of the dynamic friction coefficients is 0.015 at V _ck = 1.0 m / s and 0.041 at V _ck = 6.0 m / s, i.e. with an increase in the sliding speed by six times, and the surface temperature increases only twice with constant specific loads p = 0.6 MPa. As for the dynamic coefficient of friction, its magnitude of change increased by 2.8 times.

The most important parameter of the temperature regime of friction and wear is the surface and deep temperature gradients of the metal friction element. Temperature gradients affect the gradient of the mechanical properties of the contacting materials, and hence the dynamic coefficient of friction and wear.

Energy load of metal-polymer brake friction pairs.

Band brake shoes have heavily loaded friction units, in which the temperature in the contact zones can reach 1000 ° C and higher, which leads to the melting of metal spots of contacts of microprotrusions and the decomposition of the surface layer of the polymer lining. The strain rate and temperature of the surface and subsurface layers are reduced, and temperature gradients in such conditions can reach 800-1000 ° C / cm along the surface and 80-100 ° C / mm deep.

If harmonic temperature fluctuations in the working layer of the rim of the brake pulley of the tape-shoe brake are expressed as a sinusoid, then we obtain the equation

For a given curve, the angle ϕ 'depends on the initial time reference; for this moment (τ = 0) from equation (73) it follows

We obtain the maximum temperature at τ _k equal to

Equation (74) describes the temperature fluctuation over time near a certain constant temperature, which is taken as zero at the counting of the oscillations.

Harmonic fluctuations in heat fluxes (kW / m ² ) are expressed by a similar equation. During their oscillations, heat fluxes have directions either in the direction of wave motion or in the opposite direction. We consider the first direction positive, and the second negative.

During harmonic oscillations, the positive heat flux during the half-cycle transfers heat to the direction of wave motion, and during the next half-cycle, the same amount of heat is in the opposite direction.

The distribution of heat flux in the material of friction pairs of brake devices is determined by the dependence

The temperature difference on a surface area of length l _uch is defined as

In view of (77), the temperature difference in the surface area is defined as

The parameter R _λ (78) is called the thermal resistance of the surface area

In formulas (78) and (79), an analogy is observed from the relations for linear electric circuits, in particular, formula (78) is an analog of Ohm's law, where the temperature drop on the surface area выступает _l acts as a voltage drop. The temperature ϑ _l corresponds to the electric potential, and the heat flux q is an analog of the current. Formula (79) is an analogue of the well-known ohmic resistance formula, in which the value 1 / λ _Uch acts as the resistivity [13].

The heat flux passing through any part of the interacting surfaces of the friction pairs of the brake is determined from the expression

The last parameter is determined by the formula

The above formula (81) is based on a calculated contact model based on generally accepted assumptions of the theory of mechanical contacting surfaces. This theory was developed by N.M. Demkim, according to which it is supposed to determine the total conductivity of the contact 1 / R ' _K as the sum of the conductivities of the actual contact 1 / R' _λ and the contact medium 1 / R ' _C. It is especially important to know the last term when the brake drum rim enters the thermal stabilization state.

The penetration of heat into the body of the pulley rim and the friction lining during prolonged and pulsed loading conditions.

The calculation results for the above dependencies, taking into account changes in the coefficients of thermal diffusivity at temperatures of 150; 300 and 450 ° C allowed us to analyze the data obtained under pulsed and continuous heat supply modes, which indicate the following:

pulsed (pulley rim)

- when changing a _w within (0.87-1.08) 10 ^-5 , m ² / s - the penetration depth of heat ranged from 0.051 mm to 0.22 mm, i.e. the surface layer of the pulley rim was warmed up;

long (pulley rim)

- when changing a _w within (0.87-1.08) 10 ^-5 , m ² / s, the penetration depth of heat ranged from 5.1 mm to 22.02 mm, i.e. the thickness of the pulley rim was completely warmed up;

pulsed (pad)

- when changing a _n in the range (0.2-0.6) 10 ^-6 , m ² / s, the penetration depth of heat was from 0.008 mm to 0.052 mm, i.e. the surface layer of the lining was warmed up;

long (overlay)

- when changing a _n in the range (0.2-0.6) 10 ^-6 , m ² / s, the penetration depth of heat was from 0.77 mm to 5.19 mm, i.e. the working layer of the lining was warmed up.

In the calculations, the time changed as follows: when applying heat: pulsed - from 0.0001 s to 0.0015 s; long - from 1.0 s to 14.0 s.

Thus, the energy load of the rim of the brake pulley is such that the effective penetration depth of the thermal currents is obviously greater than its nominal thickness under long-term thermal load conditions.

The energy load of metal-polymer friction pairs of braking devices largely depends on their forced cooling.

In FIG. 45 illustrates a heat transfer scheme from surfaces of friction assemblies of a drawbar brake of a drawworks. In heat exchange take part: brake pulley 1 with flanges 3 and protrusion 2; brake belt 4 with friction linings 5. The accumulator of thermal energy in this type of brake is a pulley 1. Friction linings 5 are a kind of heat insulator between the brake pulley 1 and the brake belt 4. The heat exchange from the surfaces of the latter is negligible and therefore its effectiveness can be neglected. The polished surface of the brake pulley 1 is its working (outer) surface. The frosted surfaces of the brake pulley 1 are; the inner and end surfaces of its rim, as well as its outer surface, which is in contact with the flange 6 of the winch drum 7. The polished surface of the brake pulley 1 is heated, and its matte surface is cooled.

At surface temperatures of metal friction elements, which are brake pulleys and drums made of various materials, above 150-200 ° C, the intensity of forced convective heat transfer decreases sharply, and heat transfer by radiation is noticeably increased. According to the Stefan-Boltzmann law, heat transfer coefficient by radiation [14]

In FIG. 46 a , b presents the results of calculations by the formula (82) of the heat transfer coefficients by radiating the matte and polished surfaces of metal friction elements from the temperature of their heating.

However, there is a peculiarity in that the emissivity for a matte and polished surface for cast iron and steel have different values. In addition, with respect to the emissivity of the matte surface to the polished one, which is equal to the ratio of the area of the cooled surface to the area of the heated surface of the metal friction element, it is possible to judge the steady-state thermal state of the metal friction element. In the form of relations we obtain:

for drum brake

(brake drum made of cast iron)

for tape brake

(brake pulley made of steel)

In this case, the heat exchange surface areas are considered: the rear brake drum of the KrAZ-250 motor vehicle (Table 7) and the brake pulley of the drawbar brake of the U2-5-5 winch (Table 8). The percentage discrepancy between the ratio values for various types of braking devices is: 11.5% - for the first case; 23.0% - for the second.

If we assume that 15.5% of the heat is compensated by forced convective and conductive heat exchanges from the surfaces of the brake drum of a motor vehicle, then this option of a steady thermal state is possible in the range of low temperatures, i.e. 15-125 ° C. For a belt brake pulley, a variant of its steady state of heat is not possible up to the permissible temperature of the friction lining material.

Thus, a method for determining the surface areas of metal friction elements with different energy intensity in the brake devices is proposed.

Temperature gradients in a metal friction friction element. The process of electrothermomechanical friction, implemented by a braking device (tape-disk-drum-shoe), can be both short (single braking) so long and long (cyclic and long braking). The duration of the process depends on the generated currents on the friction surface of the friction units, the amount of accumulated heat and the penetration depth of thermal waves through the thickness of the metal friction element. Based on the foregoing, it is proposed to consider a pulsed and long-term supply of heat to the elements of tribological conjugation.

The relationship between the heating rate of the pulley rim and the temperature gradient along its thickness is established using the control function [4]

However, in dependence (83), it is necessary to introduce the quantity δ, i.e. the thickness of the surface and near-surface layers of friction elements for a more accurate assessment of their heating. To do this, we use the substitution a = λ / (сρ) (where ρ is the density of the friction materials) and ν = А _m δ _ш (where ν is the volume of the friction material). As a result of substitutions and transformations, we obtain

Let us analyze the dependence (84) by parameters. An increase in the working (polished) area of the pulley rim promotes an increase in its metal consumption, since its thickness also increases, and as a result, the moment of inertia. Moreover, the thickness of the rim (δ _W ) of the brake pulley is determined through its regulated moment of inertia (I _{in W} )

The diameter of the brake pulley is determined from the condition that the tape-shoe brake reaches the moment that allows the drill string to run at maximum weight, as well as the ability to keep them on weight.

то можно установить связь между темпом нагревания

и градиентом температуры

имеющим место на рабочей поверхности обода шкива.An increase in the thermal conductivity coefficient, and in the place with it the thermal diffusivity of the pulley rim materials, causes a quick warm-up over its thickness, and as a result, a decrease in the temperature gradient. If we denote the constant term

then you can establish a connection between the heating rate

and temperature gradient

taking place on the working surface of the pulley rim.

(для обода шкива) и

(для полимерной накладки) для определения эффективной глубины проникновения теплоты в тело обода и накладки при длительном и импульсном режимах.As for the dependence (84), here is a slightly different picture. The value of the pattern of change in the coefficient of thermal diffusivity of the pulley rim materials as a function of temperature, as well as the time that heat penetrates into the layers of the pulley rim, allows one to more accurately determine the ratio ( a _w / b _w ) than in the first case. In this case, the dependence proposed by A.V. Chichinadze, species

(for pulley rim) and

(for polymer lining) to determine the effective depth of penetration of heat into the body of the rim and lining for continuous and pulsed modes.

Thermal stresses in the rim of the brake pulley. Let us dwell on the determination of the components of compressive stresses acting on the working surface of the pulley rim during tripping operations. The maximum compressive stresses σ _1max in the pulley rim will be on its working surface and they are equal to the algebraic sum of the components

Let us evaluate the magnitude of thermal stresses arising in the rim of the brake pulley, which are the result of the peculiarities of its thermal loading.

According to the energy theory of strength, the maximum equivalent stress arising in the rim of the pulley at the junction of it with the mounting protrusion is determined by the dependence of the form

Processing of statistical data on cutting edges of three new rims of brake pulleys showed that they converged by 1.0-2.0 mm, i.e. there was an action of compressive stresses in them. After cutting 12 spent pulleys, their edges diverged by 40.0-50.0 mm. Consequently, significant residual tensile stresses in the rim of the brake pulley were formed only in the processes of frictional interaction of the friction pairs of the brake during their heating and forced cooling during tripping.

As can be seen from the table. 9, compressive stresses in the rim of the brake pulley are created mainly due to stresses from a significant temperature gradient on the surfaces of the rim of more than 74.0% of the total stresses, as well as from the location of the mounting protrusion in the middle of the rim (see Fig. 22c). From the table. 9 and formulas (7-9) it follows that such compressive stresses in the pulley σ ₁ could be formed when the temperature difference exceeds 38.5 ° C; a temperature difference below 22.5 ° C does not lead to the formation of residual stresses.

In the process of cooling the elements of the brake pulley after the descent of the tool due to different intensities of heat transfer from

redistribution of the polished and dull surfaces results in a redistribution of the heat flux currents, as a result of which temperature gradients of the opposite sign appear along the thickness of the rim layers due to their recharge by heat fluxes coming from the mounting protrusion, as well as due to the destruction processes occurring in the surface and subsurface layers of the friction lining, which are forced to cool the working surface of the pulley rim. In this case, the surface temperature of the latter becomes lower than the temperature of the rim layers (see Fig. 22 a , c). Stresses on the surface of the rim of the brake pulley in this case coincide with the residual stresses. Their value is determined by the dependence

For the investigated design of the brake pulley, even under the most adverse conditions, i.e. when working on serial friction pairs throughout the descent of the tool to the bottom, these stresses amounted to less than 5% of the residual tensile stresses. The temperature gradient of the opposite sign was 10 ° C.

The data obtained make it possible to determine the maximum equivalent stress arising in the pulley rim from mating with the mounting protrusion as a result of the action of the temperature gradient over their thickness, using dependence (8). In this case, when braking for the pulley rim, the temperature gradient with respect to the mounting protrusion is 65.0 ° C, and the calculated voltage in this case reaches σ ₀ = 147.5 MPa.

Therefore, temperature stresses in the pulley rim can reach unregulated values, especially in summer, when the surface temperature gradient is large. Repeated application of pulsed normal forces, electric and thermal currents leads to the appearance of residual stresses in the pulley rim body. During operation, shrinkage occurs in the brake pulleys, which generates a force on the centering surface that causes tensile stress. This explains the fact that spent pulleys made of steels of all grades, provided there were no cracks in them, had to be cut with autogenes during dismantling, while the ends at the cut points diverged by 40-50 mm.

The decisive factor in the initiation and development of cracks on the working surface of the rims is the ratio of the resistance to cracking (σ ₀ ) to the maximum thermal stress (σ ')

If K _C > 1.0, the surface and subsurface layer of the pulley rim material does not collapse.

In FIG. 47 illustrates the dependence of stresses of resistance to cracking (σ ₀ ) on the volumetric temperature of the pulley rim (ϑ _rev ) and the value of resistance to thermal shock (K _C ). In the range of volume temperatures from 50.0 to 200.0 ° C of the pulley rim, the total residual thermal stresses vary from 100.8 to 299.0 MPa and at K _C = 1.0 they are equal to the stresses of cracking resistance (σ ₀ ). At K _C = 0.2-0.8, the stresses of resistance to cracking vary from 20.2 to 239.2 MPa, which will contribute to the nucleation and development of microcracks on the working surface of the pulley rim.

Based on the foregoing, improving the efficiency of the rims of the pulley of the tape-shoe brake of a drawworks is achieved by:

- reducing residual thermal stresses in the pulley rim, as by reducing the surface allowable temperatures for the materials of the friction lining to prevent the occurrence of destructive processes and the network of cracks on the working surfaces of the pulley rims;

- reducing the metal consumption of the rims of the brake pulleys by: reducing their thickness; the implementation of collapsible or their elimination from the process of electrothermomechanical friction.

To assess the relative stress at any thickness (normal to the friction surface) of the rim of a brake pulley operating in aperiodic cyclic mode, we use the obtained relations for:

, т.е. на поверхности обода тормозного шкиваwhen heated

, i.e. on the surface of the rim of the brake pulley

free cooling when

Based on the obtained expressions (90) - (93), graphical dependences of the relative thermal stresses during heating and natural cooling were constructed for one heat supply cycle (Fig. 48 a , b, c, d).

Analysis of the graphical dependences (see Fig. 48 a , b, c, d) show that the relative thermal stresses (when heated) on the working surface of the pulley rim are almost ten times higher than the thermal stresses arising in its layers. Relative stresses reach a maximum when the process occurs on the heat-insulated matte surfaces of the pulley (Bi = 0) and are equal to zero when the heat transfer is infinite (Bi → ∞). The Bi criterion has a significant effect on natural cooling. Moreover, with an increase in the duration of the braking process, its effect on natural cooling increases.

From the analysis of the graphical dependencies (see Fig. 48 a , b, c, d) it follows that during natural cooling the relative thermal stresses on the polished surface, which is the source of radiation heat transfer, are almost five times greater than in the pulley rim layers. Moreover, the relative stresses reach a maximum when intense heat exchange occurs (Bi → ∞) and has a maximum value when the matte surfaces are thermally insulated (Bi = 0).

The calculations showed that the highest thermal stresses are experienced on the polished surfaces of the pulley rim due to the large surfaces of temperature gradients. In addition, the superposition principle manifests itself in the processes of “heating - cooling” of the pulley rim layers, which contribute to their thermal expansion and contraction, since there is uneven heating of the pulley rim layers.

High-speed currents of media and their components washing friction units. The qualitative and quantitative composition of the washer fluid currents in the gaps between the microprotrusions of the metal-polymer friction pairs significantly affects their tribological characteristics. It has been established that the composition of the currents of the washing media also has a significant effect on the processes, phenomena and effects that occur on the contact spots of the microprotrusions of friction pairs and their wear, in particular, friction materials based on Fe working in tandem with a metal counterbody. When working in such washing media containing O ₂ , oxide films are formed on the spots of friction contacts, which ensure work in frictional contacts in the mode of oxidative wear, which excludes setting.

Currents washing the media must be considered from the standpoint of gas dynamics, nonstationary diffusion and chemical kinetics of the active components and consumption environment as between microprotrusions do not interact at the moment and the lateral surfaces of the microprotrusions, are contacting with the proviso that the coefficient of mutual overlap K _substituting <1.0 .

The area of the friction zone, free from direct contact and available for chemical interaction with the active components of the washing medium, is determined by the dependence

The gas-dynamic model of the contact gap is a cavity in which the flow of currents of the washing medium containing active components takes place. The nature of the currents of the washing medium is evaluated by the Knudson criterion

A contact gap of height h _eff must be considered as a chemical nanoreactor, on the walls of which heterogeneous chemical reactions occur with the formation of oxide films. During friction (during braking), the regeneration of oxide films instead of worn ones is carried out by unsteady chemical consumption of active components of the currents of the washing medium by the walls of microprotrusions with their subsequent delivery from the outside to the intercontact gap.

However, it is necessary to take into account the condition of thermal equilibrium, which, as is well known, requires, along with the constancy of temperature, the constancy of the sum μ _xn + U along the medium. In this case, we are talking about equilibrium with respect to electrons, so that by μ _xn we need to understand their chemical potential, a U = -еϕ _e . Accordingly, the electric current j ₁ and the dissipative energy flux q 'vanish simultaneously only under the conditions q ₁ = const, μ-eϕ _e = const, i.e. for ∇ϑ ₁ = 0, ∇μ _xn + еЕ _е = 0. The expression for j ₁ and q 'is written in the form of the following relations satisfying the specified condition

, вычтенная из полного потока энергии, представляет собой плотность конвективного потока энергии. Последнюю и необходимо учитывать при оценке термостабилизационного состояния металлического фрикционного элемента в тормозных устройствах.The relation between the coefficients ∇ϑ ₁ in (96) and j ₁ in (97) is a consequence of the Onsager principle. Value

subtracted from the total energy flux, is the density of the convective energy flux. The latter and must be taken into account when assessing the thermal stabilization state of a metal friction element in brake devices.

The indicated stabilization thermal state of the pulley rim is supported by the appearance in the elementary volumes of the surface layers of friction elements of a multitude of microthermobaths that create external and internal electric fields with different double electric layers and operating in the modes of microthermoelectric generators and microthermoelectric refrigerators, and when the internal electric field predominates, the surface inverts from currents pulley in the surface layers of the linings.

At the third stage of modeling are considered: tribological conjugation, tribosystem, similarity criteria and the main operational parameters of the friction unit of the brake device [11; 15-19].

By tribological conjugation is meant the frictional interaction of two bodies having different mechanophysical properties.

The general tribological conjugation model has the following submodels at the nano, micro, and milli levels: kinematic; electrothermal; contacting; electrical formation and behavior of the contacting layers of materials, taking into account the discrete nature of the contact; multilayer formation on the surface due to frictional interaction; defects in the materials of the elements of the friction pair (see Fig. 49 a , b, c, d, e, e).

Let us dwell briefly on submodels, which are necessarily taken into account when decomposing the general model and modeling the processes of electrothermomechanical friction and wear at various test facilities:

1) the kinematic submodel (see Fig. 49 a ), reproducing the coefficient of mutual overlap of the full-scale object and the direction of movement of the elements of the friction pair, the parameters of which are the coefficient of mutual overlap K _b <1, load p, area: nominal (A _n1,2 ) and ventilated (A _σ1,2 ) friction surfaces; mass of friction pair elements m _c1,2 ; volumes of a friction pair ν _1.2 ; friction work W _TP ; sliding speed V _ck ; angular velocity ω; acceleration w and time τ (duration of friction);

2) the macro thermal model (Fig. 49b), taking into account the distribution of heat fluxes, the parameters of which are the volumetric temperatures of the elements of the friction pair ϑ _v1,2 ; external heat transfer coefficients α _T1,2 ; ambient temperature ϑ ₀ ; thermal conductivity of materials λ _1,2 ; specific heat of materials c _1.2 ; the density of the materials of the friction pair and the environment ρ _m1,2,3 ; dynamic viscosity of the environment η ₃ ;

3) a contact submodel (Fig. 49c), which clearly shows the relationship between the nominal, contour and actual contact areas;

4) a micromodel of electrical heat generation and the behavior of the contacting layers of the material, taking into account the discrete nature of the contact (Fig. 49d), the parameters of which are the average radii of the individual protrusions of the rough surfaces of the elements of the friction pair r _1.2 , the height of the individual irregularities h _1.2 , the shear resistance of thin surface elements (film) of the pair of friction τn _1,2, generated pulsed electrical currents I, the bulk temperature of the elements the pair of friction θ _v1,2, flash point of tangency on the actual spot θ _aux coefficients r ploprovodnosti λ _1,2, c _1,2 specific heat and density ρ _m1,2 pair of friction materials, the modulus of elasticity E _1.2 and hardness HB _1,2 materials, dynamic viscosity η _1,2 tribological materials;

5) a multilayer formation on the surface (Fig. 49d) due to frictional interaction with six layers — adsorbed, boundary, lubricant, oxides, textured and starting materials;

6) defects in the material of the element of the friction pair that arise during friction (Fig. 49f) (1 - dislocations, 2 and 3 micro- and macrocracks).

The general model of external friction fully takes into account two fundamental triads of external friction proposed by I.V. Kragelsky and A.V. Chichinadze, as well as the basic principles of tribosystem compatibility developed by N.A. Boucher [9].

Modeling is the ability to represent a system with a finite set of models, each of which reflects a certain facet of its essence.

The latter property has found application in the development of a rational tribological test cycle. Instead of creating a complete model for complex tribotechnical pairing, a number of sequential models are used that make it possible to establish the boundaries of the use of a friction pair. Then, within these boundaries, in relation to a given operating mode, the output characteristics of the tribo-conjugation (temperature ϑ, dynamic friction coefficient f, wear rate u _pn and) are revealed and, finally, the degree of influence of the design of the friction units of the machine on the same characteristics is established.

Creating a complete model for complex tribo-conjugation is generally useless, since according to Turing's theorem, such a model will be as complex as the tribo-conjugation itself and unsuitable for detailed study.

When developing a finite set, one should take into account (or understand) which properties of the subsystem suppress or enhance the general system properties, for example, the insufficient rigidity of the subsystem contributes to the manifestation of fretting.

The hierarchical model corresponding to the graphical model shown in FIG. 49 is shown in FIG. 50. The graphic model of the tribological interface - the friction unit has five levels: geometric, electric, thermal, power and information, in addition to these levels, the initial properties of materials and the functional properties of the system are taken into account.

It should be borne in mind that due to heat generation, which is amplified by the generated currents (level three), the initial properties of materials, geometric and power levels change. The researcher receives information about all these changes at the information level: dynamic effects include the dynamic coefficient of friction, instability of friction and frictional heating, and local damage to the material includes wear at individual points on the surface.

Modeling is considered as a process of comparing the results of model and field experience based on similar transformations (similarity analysis). Thus, modeling means the implementation in some way of displaying or reproducing reality in order to study the objective laws existing in it. By similarity is meant a one-to-one correspondence between two objects, in which the transition functions from the parameters characterizing one of the objects to the other parameters are known, and the mathematical description of these objects can be converted into identical ones.

In FIG. 51, a tribosystem is illustrated, in which the tape brake shoe of a U2-5-5 winch is represented, and the tribosystem is examined from a first-order subsystem to an eighth-order subsystem.

In FIG. 52 a , b, c, d, d, f, f, g shows a general view of the tape-shoe brake with multi-pair friction units and their graphic models.

Similarity criteria for modeling tribosystem processes.

Критерий гомохронности сформирован из параметров V_ck, τ и l, то даже если не один из них не входит в число базисных, имеем основные параметры фрикционного взаимодействия микровыступов металлополимерных пар трения.The homochronism criterion characterizing the homogeneity of processes in time V _ck ⋅τ / l = idem, in the implemented simulation we obtain if

The homochronism criterion is formed from the parameters V _ck , τ, and l, then even if not one of them is not among the basic ones, we have the basic parameters of the frictional interaction of the microprotrusions of metal-polymer friction pairs.

The remaining criteria used in the simulation were obtained in the same way as the criterion H _O. Moreover, their interpretation corresponds to the nano- and microlevels of the development of tribology.

Let us consider several different “standard” criteria, based on which we obtain one of the main “non-standard” criteria, establishing a relationship between the thermophysical parameters of friction pairs and washing their high-speed air currents, and the mixture not only in a gaseous, but also in a liquid state.

Bio Criterion

The Biot criterion can be considered as the ratio of cooling processes when high-speed components are used to wash the mixture of the medium to the processes of conductive heating of the brake pulley layers when thermal currents reach the specified rim depth.

Fourier test

The Fourier criterion can be considered as the ratio of the braking time τ to the restructuring time of the energy _{load of the} working layers of the brake pulley b ² _sh.eff / a , proportional to the square of their thickness and inversely proportional to the thermal diffusivity of the material of its rim.

Nusselt criterion

The resulting expression can be considered as the ratio of the heat flux density transferred during the heat transfer from the polished and matte surfaces of the brake pulley when they are washed with high-speed currents of the medium mixture to the thermal current density through its layers of thickness h due to their thermal conductivity.

Peclet criterion

The numerator contains the value of the heat flux carried by the washing fluid flows of the components of the medium mixture circulating in the gaps with variable cross sections between the microprotrusions of the friction pairs, and the denominator shows the heat flux flashing the layer with thickness h _C due to their thermal diffusivity. In this form, the Peclet criterion can be considered as a measure of the relative role of molar and molecular heat transfer.

Ratio of criteria

An analysis of the ratio of criteria from a conceptual approach from the perspective of synergetics and fractals in tribology [20] made it possible to propose the Volchenko criterion for assessing the state of a cooled working surface of a brake pulley rim and the energy load of its surface and subsurface layers.

The resulting ratio can be considered as the product of the thermal resistance of the surface and subsurface layers of the rim of the brake pulley to the surface of which the layers of washer air allegedly “stick” at the surface temperature of the polymer lining below the allowable for its friction materials. If the surface of the polymer lining gets into the zone above the permissible temperature, the binding components burn out of its materials. The components of the latter are mixed with circulating layers of air. Subsequently, islands of liquid appear on the surface of the lining, which supposedly stick to the working surface of the pulley rim. Thus, the control action for the thermal resistance of the surface layer of the polymer lining is its state (solid, liquid, gaseous). For the surface and subsurface layers of the rim of the brake pulley, the control action for thermal resistance is their energy load. Knowing the values of the components of the Volchenko criterion makes it possible to predict the energy loading of surface and subsurface layers of microprotrusions of metal-polymer friction pairs.

Features of computer simulation of energy loading of metal-polymer brake friction pairs. The initial assumptions of the model are as follows: the materials of the contact patch of the microprotrusions are homogeneous and isotropic; the contact is discrete in nature and occurs along the vertices of individual microprotrusions of roughness, the deformation of the microprotrusions is elastic and is described by the Hertz dependence for the contact of two curvilinear smooth bodies with the initial contact at a point; the sizes of individual contact spots are small in comparison with the dimensions of the interaction zone and the radii of curvature of the microprotrusions at the point of contact; in the contact zone, only pulsed normal forces and friction forces act; the distribution of contact spots on the surface of the friction pairs is uniform. The initial data for the calculation are the characteristics of the surface microgeometry - the maximum height of the protrusions above the middle profile line h _max and the maximum radius of curvature of the protrusions r _max ; physico-mechanical characteristics of the material - elastic modulus (Young's modulus) E, Poisson's ratio μ, electrical resistivity of the material ρ; performance, pulsed normal force, compressive contact.

The computer model is practically implemented as a windows application, written in C ++ using the Borland class library. The program model is included in the main calculation module, which includes an assessment of the external and internal parameters of metal-polymer friction pairs at the macro, micro, and nanoscale levels.

In addition to the main one, there is an additional module responsible for the convenience of presenting data and the user interface. The result of the work is the operational characteristics of the contact, presented in the form of a table. For greater clarity, on the basis of the proposed formulas, it is possible to construct graphs of the dependences of the contact characteristics on external factors, which are the currents of the washing air and the components of the mixtures.

In the table. 10 shows the main dependences for calculating the characteristics of a single contact of two spherical microprotrusions of the contact spot [21].

Within the framework of a computer model, the calculation of the contact characteristics is as follows. A pair of random numbers is generated, distributed according to a given law, corresponding to the height and radius of the protrusion of the rough surface. The logic of the program is illustrated by the block diagram of the main calculation module for the parameters of the mechanical, electric and thermal fields (Fig. 53).

The program is connected with the MS Access database, which consists of two tables, each of which includes 33 fields. The first table contains the values of the initial intermediate data, and the second contains the values of the results. Tables are used for plotting.

At the same time, the first field of each table is reserved for the checked initial combination of initial parameters and is used only at the beginning of work and only for reading. First of all, the program reads the initial combination of source parameters from the database and supplements these fields with the source data fields. Then the user edits them, performs the calculation, after which the table of values is filled in and a graph is built on it.

The adequacy of the model was checked by comparing the simulation results with data from other authors obtained on the basis of analytical models for some special cases.

Using computer simulation was determined:

- patterns of changes in the hardness of metallic and nonmetallic material from specific loads and the relative value of the ratio 2 a _n / l;

- patterns of changes in microcurrents at the contact patch of microprotrusions of the tribo-conjugation, depending on the surface temperature and its gradient along the length of the contact patch, and at various pulsed normal loads;

- patterns of changes in the deformations of the microprotrusions of metal-polymer friction pairs of the drawworks brake of the drawworks from pulsed specific loads at different surface areas of their contact spots;

- patterns of change in the area of contact spots of metal microprotrusions and their number from the acting pulsed normal forces.

The software of the model brake stand includes a special program for recording and processing signals from sensors of microprotrusions of metal-polymer friction pairs of the tribosystem.

The program sets:

- sampling frequency - the maximum frequency depends on the clock frequency of the computer, the technical characteristics of the analog digital converter (ADC) and is selected experimentally (for example, 1.2 kHz);

- sampling duration - sets the recording time in seconds. Recording starts from the moment you press the START key and continues until the time specified in this paragraph expires or until you press the STOP key. The recording time is limited only by the size of the computer's hard drive;

- calibration - the levels that are currently set are considered zero (a zero offset is selected).

The recorded signals are used for their software processing, for example, MATLAB. System. MATLAB was developed by The Math Works, Inc. (USA, Natic, Massachusetts) and is an interactive system for performing engineering and scientific calculations, focused on working with data arrays. The system uses a mathematical coprocessor and allows access to programs written in FORTRAN, C and C ++.

The software determines the frequency transfer function based on the results of processing the signals of pulsed normal loads and the friction force, and based on the analysis of the frequency transfer function, the dynamic state of the contact spots of the microtubes of the tribosystem is analyzed, and its stability is checked according to the stability criteria of Nyquist, Lyapunov, etc. [22].

We give some theoretical information.

Let the output signal of the friction node y (k) represent the sum (with weight coefficients) of a certain number of previous output samples, depending on a number of input samples u (k) (including the last). If we group the obtained terms in such a way that there are only input samples on the one side of the equal sign, and only weekend samples on the other, then we get a notation form called the difference equation:

The structure of the difference equation is similar to the structure of the differential equation of the analog system, but instead of the differentiation operation, the delays of the discrete signal sequences appear in the formula.

The output signal, based on the linearity and stationarity of the system in question, should be a linear combination of impulse responses, i.e. normal and friction forces

A convenient analysis of discrete sequences is the z-transform. Its meaning is that the sequence of numbers {u (k)} is associated with the function of the complex variable z.

Knowing the impulse response of a discrete system allows you to analyze the passage through it of any signal and find its internal state. Applying the z-transformation to the equations of the discrete system (111), we obtain its system function or transfer function (transfer function)

Applying the z - transformation to both sides of the difference equation (112), we obtain

From here it is easy to obtain the form of the transfer function of a discrete system:

Thus, the transfer function of a physically feasible discrete system shows how the complex amplitude of a sinusoid with frequency ω changes when passing through the system and can be represented as the ratio of polynomials in negative powers of the variable z. The numerator polynomial characterizes the external impact on the friction unit, and the denominator polynomial (characteristic polynomial) is the result of this effect on the contact spots of the microprotrusions of the tribosystem.

входного и выходного сигналов, дальше рассчитывается взаимный спектр входного и выходного сигналов, представляющий собой произведение их спектральных функций, одна из которых подвергнута комплексному сопряжению:Knowing the spectra * (* the spectrum is a representation of the analyzed signal not in the time domain of the study, but in the frequency domain), and the signal is converted from the temporary domain of research into the frequency domain by the fast Fourier transform algorithm according to the expression

input and output signals, then the mutual spectrum of the input and output signals is calculated, which is a product of their spectral functions, one of which is subjected to complex conjugation:

If the signal u (τ _p −τ _s ) is an even function, then the spectrum will be purely real (it will be an even function). If u (τ _p −τ _s ) is an odd function, then the spectral function S (ω) will be purely imaginary (and odd).

Thus, if the spectra of the signals do not overlap, then their mutual spectrum is equal to zero at all frequencies and the mutual correlation function of these signals will also be equal to zero for any time shifts τ. Therefore, signals with non-overlapping spectra are uncorrelated.

From the obtained expression (114), the complex transmission coefficient of the discrete system is determined

The mathematical models of the dynamics of real tribosystems are mainly non-linear and in many cases cannot be linearized due to the possibility of losing the characteristic dynamic properties due to the fundamental non-linearity of the dynamics equations. However, with some limitations, the frequency transfer function of tribology is linearized by the criterion of the minimum dispersion of the output signal of the Dirac pulse function. The optimal order of the polynomials of the numerator and denominator is the order of the polynomials of the numerator (m) and the denominator (n) of the transfer function (115), in which the dispersion of the output pulse signal will be minimal.

The result of the analysis of amplitude-phase-frequency characteristics (AFC) is the ability to check the stability of the internal space of the system states and the value of the complex dynamic coefficient of friction acting in the zone of frictional loading of contact spots of microprotrusions of metal-polymer friction pairs

- характеристики динамического коэффициента трения: амплитудно-частотная; фазочастотная; вещественная частотная и мнимая частотная.Where

- characteristics of the dynamic coefficient of friction: amplitude-frequency; phase-frequency; real frequency and imaginary frequency.

Consider the process of changing the dynamic coefficient of friction during electrothermomechanical frictional interaction of contact spots of microprotrusions of metal-polymer friction pairs in time (Fig. 54).

The study of this dynamic process was performed on a model tape-shoe brake with a normal impulse load of N = 0.3 kN on the eighth pad of the running branch of the brake belt with respect to the linear dimensions of the pulley rims

and the scale factor of the normal load C _N = C ₁ = 8.12 kN and the sliding velocity V _ck = 0.6 m / s and the object of study V = 1.71 m / s.

Structural changes and the redistribution of energy flows on the surfaces of the contact spots of the microprotrusions of metal-polymer friction pairs of the band brake can be observed only in the processes of electrothermomechanical friction, which must be developed and used in-situ research methods.

The wear and tear properties of polymer-metal friction pairs in braking devices.

The study over time of the dependences of the dynamic coefficient of friction of the friction assemblies of the brake devices (Fig. 55) allows us to state a dynamic picture of the overall balance of the energy supplied and allocated to the tribosystem.

External work, applied to the tribosystem, is spent on elastic and plastic deformation of the surface layers and on the formation of microthermobatteries, which operate in microthermoelectric generators and microthermal refrigerators, and, as a result, direct heating and cooling of the surface and surface layers of friction pairs of brake devices. Other types of transformation of mechanical energy at low sliding speeds of the friction pairs of the brakes are insignificant (for example, radiation). The work of friction depends on the area of actual contact and on the physicomechanical and chemical properties of the surface and subsurface layers of materials of friction pairs of brake devices, which harden and soften relatively slowly. Therefore, part of curve 2 (Fig. 54) of the dynamic coefficient of friction, which is described by the low-frequency component, is associated with the mechanical energy entering the tribosystem. The latter is spent on its redistribution and maintenance of the microthermal batteries, which generate electrical energy with its subsequent transformation into thermal energy in the surface layers of the elements of the friction assemblies of the brake devices.

The nature of the high-frequency component (curve 1 in Fig. 54) is related to the discreteness of the contact, and the high-frequency peaks of the dynamic coefficient of friction correspond to instantly occurring energy processes in the contacting surface layers, which are a source of heat and cold, due to the generation of forward and reverse currents in them. Curves 1, 2, and 3 (Fig. 54) contain information on the influence of the direction of the current generated in the polymer – metal friction pairs on the value of the dynamic coefficient of friction. When direct microcurrents pass from the contacting surfaces of the rim of the brake pulley to the working surfaces of the polymer linings (anode-polarized surfaces of the linings) f is always larger (see Fig. 54 time intervals (510-520) s and (550-570) s for curves 1 and 2) than at the cathode-polarized sections of the surfaces of the tape linings, the material of which is at temperatures above the permissible temperature, and in this case reverse microcurrents occur (see Fig. 54 time interval (510-580) s for curve 3). Moreover, in all cases, f decreases with increasing current density j at the contact of the friction pairs of the brake devices. The dynamic coefficient of friction of the cathode-polarized sections of the polymer plates is always less than the dynamic coefficient of friction of their anode-polarized sections, i.e. (f _a > f _k ), as j increases, it varies differently for friction materials.

Thus, the repolarization of the friction lining sections in the friction pairs of the brake devices causes inversion of microcurrents and a change in their values, and as a result, a change in the dynamic coefficient of friction characterizing the energy processes in their surface and near-surface layers of friction pairs.

The wear characteristic determines the durability and many other operational parameters of friction pairs of brake devices. If the work of friction pairs occurs at temperatures below the allowable for friction lining materials, then it can be argued that the wear of their working surfaces and metal friction elements is the sum of the mechanical (fatigue) u _pnm and electrical (erosion) and _{rn.e wear} (Fig. 55).

Assessment of the contribution u _pnm to the total wear gives from 1/2 to 3/4 depending on the polarity of the working surfaces of the polymer linings. Mechanical wear of the working surface of the rim of the metal friction element is 5-10% of the wear of the working surface of the polymer linings.

The calculation of the electrical wear component u _pne depends on a combination of factors (current direction, discharge mode between contact elements). The amount of transported material from the working surfaces of the rims of the metal friction element, and therefore the wear, depends on the direction of the current and its magnitude. The dependence of the amount of transported substance from unequally polarized sections of the surfaces of the polymer plates on the working surface of the rim of a metal friction element obtained by the radioactive isotope method is shown in FIG. 55. It can be seen that the transfer from the anode-polarized sections of the surfaces of the polymer overlays is more intense.

The dependency diagram, which makes it possible to evaluate the effect of the discharge mode during the operation of sections of the working surfaces of the plates with sparking on wear, is shown in FIG. 56. Any form of self-sustained discharge in ionized gases between friction pairs during their interaction is accompanied by erosion of the micro-sites. In the case of a glow discharge, wear of the working surface of the rim of the metal friction element predominates, and spark discharge leads to wear of the working surfaces of the polymer linings. The transition of a discharge from one form to another is always accompanied by an inversion of the electrical component of the wear of the interacting microareas of friction surfaces.

The energy load of the discrete contact of the microprotrusions of the metal-polymer friction pairs of the tribosystem is based on FIG. 57 with the involvement of the percentage ratio of the components of the gas mixture formed in the intercontact space of the friction pair (table. 11). The energy load of the discrete contact of the microprotrusions of metal-polymer friction pairs of tribosystems is given in table. 12.

Thus, an example of a change in the dynamic coefficient of friction depending on the energy loading of contact spots of microprotrusions of metal-polymer friction pairs in the interconnection of their external and internal parameters illustrates the implementation of various energy levels of the surface and subsurface layers of friction units.

CONVENTIONS

Dimensions

And _f , A _to , And _n - the area of frictional interaction: actual; contour line; nominal, mm ² ;

ΔA _f , ΔA _to - elementary area: a single actual spot of touch; contour area of friction, mm ² ;

And _α1 , And _α2 , And _α3 - the surface area of heat transfer, m ² ;

A _q is the cross-sectional area through which the heat flux Q _λ , m ²

η _r is the relative actual contact area; η _r = A _f / A _n ;

And ₁ , And ₂ - the area of positive and negative impulses, mm ² ;

And ₃ ... A _n

And _in , And _f - the cross-sectional area of the mounting protrusions of the rim and the flange of the drum, m ² ;

A _n , A _m - surface area of the metal element: polished, matte friction, m ² ;

d _cp , d _n - diameter of the contact spot: average, reduced, mm;

b _W , δ _W - the width and thickness of the pulley rim, m;

L _n , In _N and δ _N - the dimensions of the friction lining: length, width and thickness, m;

δ ₁ , δ ₂ , δ _cf - thickness: mounting protrusion; drum flange; their average value, m;

δ _L , V _l , V _P , - design parameters of the brake tape: thickness,

A _L , R _l and R ₀ width, groove width, cross-sectional area, radius of the tape and its middle surface, m;

R _W , R _B and r _W - the radii of the pulley rim: outer, inner and current, m;

a _n is the radius of the contact spot, microns;

ν _{1, 2, 3} - volumes, m ³ ;

e '- the gap between the outer surfaces of the friction linings and the inner surface of the brake tape in the open friction brake assembly, mm;

h, h _max , r _max and S _m - protrusion microroughness: current and greatest height, radius of curvature, step, microns;

h _C is the thickness of the layers of high-speed currents of the washing medium, m;

d is the thickness of the layer firmly bound to the surface of the polymer lining, mm;

l _k is the contact length, mm;

r is the distance from the contact spot, microns;

h _eff - the height of the contact gap, microns;

s is the air gap between the spots of contacts, microns;

l _C and l _H - the length of the runaway and oncoming branches of the tape, m;

l ₀ - the distance traveled by the microprotrusion of the pulley rim to the beginning of its movement, microns;

l _n is the mean free path of the molecules of the currents of the washing media, μm;

l is the friction path of the microprotrusion, mm;

z is a certain distance from the line of microprotrusions relative to the section profile of lines parallel to the average, microns;

t _p = l _i / l is the ratio of the reference length of the microprotrusion to its base length;

ε is the average value of the relative approximation of the surfaces;

z _T - coordinate along the width of the pulley rim, mm;

l _ci is the shoulder of the static moment created by the action of the reduced impulse pair, microns;

ϕ is the central lining angle, °;

β _i is the angle between the ends of adjacent friction linings, °.

Mass, energy

m _c , m _m - mass: layers of the friction element, microprotrusion, kg;

m is the mass of the rim of the brake pulley, kg;

g - gravity acceleration, m / s ²

γ, ρ * is the specific gravity of the pulley rim material, kg / m ³ ;

G is the weight of the drill pipe string, N;

u _pn — wear of working surfaces, mg;

E _C , F _M (E _F ) - energy levels: critical motion, metal and F _P (Fermi), polymer;

E _C1 , E _P1 - energy zones: the bottom of the conductivity and the valence ceiling of the polymer, J;

W _M , W _P - work function of electrons and ions from metal and polymer, J;

ΔQ is the change in thermal energy, J;

δ ₀ - the thickness of the enriched and depleted electronic layers, microns;

E _with , E _n - energy from oscillations on the branches of the tape: runaway, running, J;

I _in - the moment of inertia of the brake pulley, kg⋅m ² ;

U is the energy of particles in an external electric field, J.

Dynamic parameters

- значение мгновенного фиктивного импульса, Н;

is the value of the instantaneous fictitious impulse, N;

ΣA _M , ΣA _P - total pulses created by the microprotrusions of the metal-polymer friction pair;

N, dN - pulse normal force and its increment, kN;

F, dF — impulse friction force and its increment, kN;

∂N - normal reaction of the pulley rim, kN;

∂F _T is the elementary friction force in a pair of "slip-pulley", kN;

Q _p is the reaction of the metal microprotrusion, kN;

S, S + ΔS - tension of the ends of the tape section, kN

S _H , S _C - tension of the running and running branches of the brake belt, kN;

p - pulse specific load, MPa;

M _from , M _from + dM _from - bending moments in the lining sections and their increment, kNm;

M _T - braking torque, kNm;

C is the rigidity of the friction joint;

P _n - the compliance of the microprotrusion, microns;

D - deformation of the polymer microprotrusion, microns;

ε _D - the relative deformation of the sections of the brake tape;

σ _1max , σ _k , σ ₁ , σ ₂ - maximum compressive stresses and stresses in the pulley rim from the action: specific loads in friction pairs; temperature gradients of the working surface; volumetric temperature: mounting protrusion (ϑ _c ) and pulley rim (ϑ _r ) provided (ϑ _r > ϑ _c ), MPa;

σ ₀ , σ '- stress: resistance to cracking; maximum thermal, MPa;

σ _a , σ _max - amplitude and maximum stress of the cycle, MPa;

τ _kn - shear stress, MPa

σ _-1 is the fatigue limit of the material with a symmetric loading cycle, MPa;

σ _B is the compressive strength of a plastically deformable material, MPa;

E - elastic modulus (Young), MPa;

HB - Brinell hardness of contact materials, MPa.

Thermodynamic parameters

Q is the amount of heat accumulated on the surfaces of metal-polymer brake friction pairs, kJ;

P ₁ - Peltier heat;

q is the heat flux on the contact surface, taking into account the electric and frictional component, W / m ² ;

W _x , W _Y - thermal resistance of parts of the flows, referred to the axes of the coordinates X and Y

b _sh.ef - effective depth of heat penetration into the pulley rim body, m;

ϑ ₁ , ϑ ' ₁ and ϑ ₂ are the temperatures of the pulley rim: the working and inner surfaces, the surface layer, ° С;

_n θ, Δθ _P1, θ _ν1 and θ _aux - Temperature: Surface and its increment, and volumetric flash, ° C;

ϑ _in , ϑ _about , ϑ _f - volumetric temperature: mounting protrusion; pulley rim, ° С; volumetric temperature of the flange of the drum, ° C;

Δϑ, Δϑ _υ - temperature difference: surface in the studied area; volumetric between the rim of the pulley and its mounting protrusion, ° C;

ϑ _f , ϑ _k , ϑ _n , ϑ _ν , ϑ _d - temperature: friction pairs, contact, surface on the interaction micro-sites; volumetric below the deformation zone; permissible for polymer lining materials, ° С;

ϑ _max - maximum temperature at the contact spot of microprotrusions, ° С.

θ, ϑ and ϑ ₀ are temperatures: differences on the contact spot; metal surface and environment, ° С;

,

- температуры поверхностей трения: номинальной; контурного участка, °С;

,

- temperature of friction surfaces: nominal; contour plot, ° C;

ϑ _N is the temperature of the surface of the metal friction element, ° K;

ϕ _to - the initial phase angle of temperature fluctuations, degrees; ϕ '= 90-ϕ _k ;

And _to - the amplitude of temperature fluctuations, ° C;

dϑ / dn - temperature gradient, ° С / mm

ΔQ / Δτ and Δϑ / Δτ are the rates of change in the amount of heat (J / s) and temperature (° C / s);

W _TD - the level of thermal deformation and stress;

C is the specific heat, J / (kg ° C);

R ' _K , R' _c , R ' _m - thermal resistance: contact; intercontact medium; actual contact, ° C / W;

R ₁ , R ₂ - thermal resistance: layers of the pulley rim; layers of a circulating medium or in a liquid state between the microprotrusions of the contact spots, ° C / W;

μ _xn is the chemical potential of particles, J / kg.

Electrical parameters

I is the generated current on the microprotrusion of friction pairs, mA;

I _o and I _Pr , I _cn , I _{P a} - currents: reactive, caused by fast and slowed-down types of polarization; through conductivity; slow, due to delayed types of polarization, mA;

I _T , I _CK , I _D - total currents: thermal; arising due to sliding friction and contact interaction; due to sorption-desorption processes in the surface layers of the lining at a temperature higher than permissible for its materials, mA;

I _TC , I _M - components of the total current: arising due to sliding friction; formed by the movement of charged particles of mass transfer, mA;

I _P , I _a , I _r - currents: pulse (discharge), active, reactive, mA;

j is the electric current density, mA / mm ² ;

- плотность заряда поверхностного слоя, Кл/мм²;

- charge density of the surface layer, C / mm ² ;

q _n is the total space charge, C / mm ³ ;

u is the total tension tension, mV;

ϕ _e is the electric field potential, mV;

dϕ / dn — gradients of electric potential, mV / mm;

R _P - polarization of the friction interaction surfaces, (Kl⋅m) / m ³ ;

R 'is the electrical resistance of the contacts of the microprotrusion, Ohm;

ρ, ρ '- resistivity: contact materials; films on the contact, (Ohm⋅mm ² ) / m;

σ _en - electrical conductivity of the medium, Ohm ^-1 ;

ε is the dielectric constant of the liquid, f / m;

ξ is the electric field strength, V / m;

M _∂ - electric dipole moment, Kl⋅m;

With _p - capacity of electric current, F.

Similarity criteria

But - a criterion of homochronism;

Re - Peclet criterion;

Bi - Biot criterion;

F _O - Fourier criterion;

Nu - Nusselt criterion;

V _O - Volchenko criterion.

Mathematical parameters

G (x) is the distribution of injected electrons in the polymer film;

N (τ) is the variable in time and the magnitude of the pulsed normal force acting over time τ;

w (k) is the impulse response of a discrete dynamic system;

z ^-k is a discrete filter memory element delaying a discrete sequence of clock cycles (z ^-k = e ^-rT );

u (k) - samples of the input signal;

U (z) -z is the conversion of the input signal;

Y (z) and - conversion of the output and input signals;

U (z) - z

W (k) is the impulse response of the system from the k-th sample of the input signal;

- комплексное сопряжение спектральной плотности входного сигнала;

- complex conjugation of the spectral density of the input signal;

- энергетический спектр входного сигнала, автоспектр;

- energy spectrum of the input signal, auto-spectrum;

W (ω) is the complex transmission coefficient of the system;

u (τ _p ) is the input signal arriving at the friction unit (change in the pulse normal load), N;

y (τ _p ) is the output signal obtained as a result of friction (pulsed tangential friction force), N;

- основная функция ошибки.

- The main function of the error.

Odds

By _substituting - coefficient of mutual overlapping outer and inner surfaces;

f is the dynamic coefficient of friction;

α _TP1 - distribution coefficient of heat fluxes;

λ _uch , λ, λ _З , λ _С - coefficient of thermal conductivity: surface area, materials of friction pairs, air gap between contacts, layers of high-speed currents of the washing medium, W / (m⋅ ° С);

a , a _C - thermal diffusivity: materials of friction pairs, layers of a mixture of medium, m ² / s;

α is the coefficient of linear expansion;

α _m is the thermoelectric coefficient.

μ is the Poisson's ratio;

K _C - coefficient of resistance to thermal shock;

α _T - heat transfer coefficient, Wt / (m ² ⋅ ° C);

l / k is the Debye screening coefficient;

χ is the coefficient of electrical conductivity of the contacting materials;

σ _t , γ - coefficients: Thompson, proportionality;

k _δ is the effective stress concentration coefficient;

Ψ _σ is a coefficient depending on the material of the brake tape;

ε _p and β _L are coefficients that take into account the dimensions of the cross section of the tape and the cleanliness class of its working surface.

m _З - fill factor of the roughness profile with materials for various types of machining;

With _L - emissivity (Stefan-Boltzmann constant), W / (m ² ⋅K ⁴ );

a _j , b _i are real coefficients.

Different

k is the reference number;

e ₁ is a dimensionless number varying from 0 to 1.0;

m _P - the number of grooves in the cross section of the brake tape;

z ₁ is the minimum number of microprotrusions;

ε _max = z / H _max is the relative level of microprotrusions;

τ, τ ₁ and τ ' ₁ - time: braking; reaching temperatures ϑ ₁ and ϑ ' ₁ , s;

- относительное время торможения;

- отношение времени цикла к максимально возможной его величине;

- relative braking time;

- the ratio of cycle time to its maximum possible value;

τ ₁ , τ ₂ , τ ₃ ... τ _n - time intervals that determine the position of the centers of gravity of the pulse areas to a straight line, relative to which is the algebraic sum of static moments, s;

τ _to - time counted from some given initial moment, s;

z _to - period of oscillations, s;

τ _p - recorded time, s;

τ _s - time shift of the output signal relative to the input, s;

A _ν is the amplitude of the radial vibration velocity of the branches of the brake tape, mm / s;

V ₀ - the initial velocity of the microprotrusion of the pulley rim, m / s;

V _CK , V - speed: slip; washing mixture currents, m / s;

ω _p - the recorded frequency of the signals (0 ... 0.5 f _L ), Hz;

t _D - sampling frequency of the analog-to-digital Converter.

Information sources

1. RF patent No. 2507423 C2, class. F16D 49/08 A method for determining operational parameters in the case of a quasilinear regularity of their change in band-brake brakes of drawworks. - 02.20.2014. Bull. No. 5. - 39 p. (analogue).

2. Chichinadze A.V. The practical implementation of thermal dynamics and modeling of friction and wear during dry and boundary friction / A.V. Chichinadze // Practical tribology, world experience. Volume 1. - M .: Center: science and technology. - 1994. - S. 67-72 (prototype).

3. Friction interaction in electric and thermal fields of metal-polymer friction pairs / A.Kh. Dzhanakhmedov, A.I. Volchenko, E.S. Pirverdiyev [et al.] // Bulletin of the Azerbaijan Engineering Academy. - Baku. - 2014. - No. 6 (2). - S. 30-54.

4. The rate of heating of metal-polymer friction pairs during a pulsed and continuous heat supply in a tape-brake brake / A.Kh. Dzhanakhmedov, A.I. Volchenko, D.A. Volchenko, N.A. Volchenko, N.M. Stebeletskaya // Scientific and Technical. Journal / - Kiev: NAU. - No. 2 (61). - 2013 .-- S. 20-30.

5. Patent 2459986 C2 of the Russian Federation F16D 65/82, F16D 51/10. A method for determining the components of electric currents in the polymer-metal friction pairs of a drum-shoe brake when they are heated in bench conditions (options). / Volchenko A.I., Volchenko N.A., Volchenko D.A., Bachuk I.V., Gorbey A.N., Polyakov P.A .; applicant and patent holder Ivano-Frankivsk, national, tech. un-t oil and gas. - No. 201007170/11; declared 02/26/2010; publ. 08/27/2012, Bull.No. 25. - 14 p.

6. Patent 2462628 C2 of the Russian Federation F16D 65/82, F16D 51/10. A method for determining the directions of the components of electric currents in the polymer-metal friction pairs of a drum-shoe brake when they are heated in bench conditions / Volchenko A.I., Volchenko N.A., Volchenko D.A., Bachuk I.V., Gorbey A.N., Polyakov P.A .; applicant and patent holder Ivano-Frankivsk, national, tech. un-t oil and gas. - No.2010115528 / 11; declared 04/19/2010; publ. 10/27/2011, Bull. No. 30. - 27 p.

7. Patent 2502900 C2 of the Russian Federation F16D 49/08. The method of electrodynamic study of the laws of changes in the operational parameters of metal-polymer friction pairs of tape and shoe brakes of a drawworks. / Volchenko A.I., Volchenko N.A., Volchenko D.A., Polyakov P.A., Vozny A.V .; applicant and patent holder Ivano-Frankivsk, national, tech. un-t oil and gas. - No. 20125664/11; declared 02/20/2012; publ. 12/27/2013, Bull. Number 36. - 11 p.

8. Timoshenko S.P. Material Mechanics / S.P. Tymoshenko, J. Gere. - M .: Mir, 1976 .-- 669 p.

9. Friction, wear and lubrication (tribology and tribotechnology) / Under the general. edited by A.V. Chichinadze. - M.: Mechanical Engineering, 2003 .-- 575 p.

10. Volchenko N.A. Dynamics of multi-pair friction units / N.A. Volchenko. - Rostov-on-Don: North Caucasian scientific. center, higher Schools, 2005 .-- 238 p.

11. Brown E.D. Models of friction and wear in cars / E.D. Brown, Yu.A. Evdokimov, A.V. Chichinadze. - M.: Machine Stand, 1982, - 191 p.

12. Tape-shoe braking devices. Monograph (scientific publication) in 2 vol. T. 2 / [N.A. Volchenko, D.A. Volchenko, S.I. Kryshtopa, D.Yu. Zhuravlev, A.V. Vozny]. - Kubansk. states, technologist, un-t. - Krasnodar - Ivano-Frankivsk, 2013 .-- 441 p.

13. Shlykov Yu.P. Contact thermal resistance / Yu.P. Shlykov, E.A. Ganin, SI. Tsarevsky. - M.: Energy, 1977 .-- 328 p.

14. Tribology (electrothermomechanical foundations, analysis and synthesis at the nano-, micro- and milli-levels and technical applications): textbook. allowance. [A.I. Volchenko, M.V. Kindrachuk, D.A. Volchenko and others.]. - Kiev - Krasnodar, 2015 .-- 371 p.

15. Berdinsky V.A. Static modeling of friction-contact interaction processes during external friction / V.A. Berdinsky, V.V. Zaporozhets // Reliability and durability of machines and structures, - M, 1984, No. 5. S. 80-84.

16. Gukhman A.A. Introduction to the theory of similarity / A.A. Guhman. - M.: Higher School, 1963, 254 p.

17. Sedov L.I. Methods of similarity and dimensions in mechanics / L.I. Sedov. - M .: Nauka, 1967, 438 p.

18. Shapovalov V.V. Complex modeling of dynamic loaded knots of machine friction / V.V. Shapovalov // Friction and wear. - M., 1985. No. 3. S. 451-457.

19. Buckley D. Surface phenomena during adhesion and frictional interaction / D. Buckley: Per. from English / Ed. A.I. Sveridenka. M .: Mir, 1986, 294 p.

20. Djanakhmedov A.Kh. Synergetics and fractals in tribology / A.Kh. Dzhanakhmedov, O.A. Dyshin, M.Ya. Javadov // Baku: Apostrophe: 2014 .-- 504 p.

21. Computer simulation of the energy load of metal-polymer pairs of friction of the tape-shoe brake of drawworks (part one) / D.Yu. Zhuravlev, S.I. Kryshtopa, I.O. Bekish et al. // Scientific and Technical. Journal. - Kiev: NAU. - No. 4 (65). - 2014 .-- S. 47-59.

22. Patent 2343450 C2 of the Russian Federation, IPC G01N 3/56. Test method for friction units / Shapovalov V.V., Chelokhyan A.V., Lubyagov A.M. and etc.; Applicant and patent holder Vladimir Vladimirovich Shapovalov. - No. 2006121024/28; declared 06/13/06; publ. 01/10/09, Bull. No. 1. - 31 p.

23. Chichinadze A.V. Wear resistance of friction polymer materials / Chichinadze A.V., Belousov V.Ya., Bogatchuk I.M. / Lviv. - Higher school, 1989. - 114 p.

24. The diploma No. 444 for the opening of the "Phenomenon of thermal stabilization in metal-polymer friction pairs" dated January 18, 2013 by A.I. Volchenko, M.V. Kindrachuk, D.A. Volchenko, N.A. Volchenko. - M .: International, Acad. authors of scientific open, and invented. - Examination of the application for opening No. A-588 of 09/05/2012

Claims (53)

A method for evaluating the external and internal parameters of friction units during testing under bench conditions, in which mechanical systems of an object and model structure, consisting of subsystems, with their contact-pulse electrothermomechanical frictional interaction, interacting with structural features, linear or polynomial laws of change of metal tachograms friction element of a friction pair, as well as with high-speed, power, electrical, thermal and chemical characteristics of friction unit I, constituting its single field of energy interaction, provided that between the external and internal parameters of the “object” and “model” provide the following relationships: - the mass ratio of the object (M) and model (m) is M / m = C _m = C ² _L ; - the ratio of the linear dimensions of the object (L) and the model

equal to geometric scale similarity

; - the ratio of the polished areas of the object (S _n) and the model (s _n) is equal to S _n / s _{n Sn} = C = C ² _Ln; - the ratio of the matte areas of the object (S _m ) and the model (s _m ) is S _m / s _m = C _Sm = C ² _Lm , - the ratio of physical and mechanical parameters of materials: thermal conductivity and thermal diffusivity, temperatures and their gradients, heat transfer coefficients; hardness, elastic modulus, tensile strength, shear resistance of an object (Ф) and model (f) is equal to Ф / ф = С _ф = 1,0; - the ratio of external forces acting on the elements of the friction pair, object (F) and model (f) is F / f = C _F = C ² _L ; - the ratio of the duration of the studied processes, phenomena and effects in the object (ζ) and model (τ) is ζ / τ = С _τ = 1,0, which are observed for the following admissible external parameters: - the ratio of the tension of the running branch (S _H ) and the tension of the running branch (S _C ) of the brake belt is S _H / S _C ≤ [n]; - specific loads (p) do not exceed the permissible value for the materials of the friction lining; - change in the dynamic coefficient of friction (f) ranges from 0.2 to 0.5; - surface temperatures of the friction lining do not exceed the allowable for its materials; - the pulley rim does not fall into the zone of thermostabilization state, characterized in that the patterns of change in the lines of the currents of the force, electric, thermal and chemical fields are characterized by internal and external parameters, in interaction with the lines of the currents of the velocity field of the washing media they obey the wave nature with a phase shift and are described by the corresponding simplexes subject to the following relations: - the ratio of the height of the microprotrusions of the friction surfaces of the object (H) and the model (h) is H / h = C _H = 1,0; - the ratio of the length of the microprotrusion of the friction surfaces of the object (L _m ) and model

equally

; - the ratio of the areas of the spots of contacts of the microprotrusions of the friction surfaces of the object (A _o ) and the model (A _m ) is equal to A _o / A _m = C _Ao = 1.0; - the ratio of the impulse normal forces of the object (N) and model (n) is N / n = C _N = 1,0; - the ratio of the linear sliding velocities of the object (V _SK ) and the model (v _SK ) is equal to V _SK / v _SK = C _V = 1,0; - the ratio of the pulsed friction forces of the object (F _t ) and the model (f _t ) is F _t / f _t = C _Ft = 1,0; - the ratio of the pulsed dynamic coefficients of friction of the object (f _о ) and the model (f _m ) is equal to f _о / f _m = C _fо = 1,0; - the ratio of the pulsed specific loads of the object (r _o ) and model (r _m ) is equal to r _o / r _m = C _Po = 1,0; - the ratio of the impulse braking moments of the object (M _o ) and the model (M _m ) is equal to M _o / M _m = C _Mo = 1.0; - the compliance ratio of the joints of the subsystem "brake tape - non-working surfaces of the linings" of the object (P _o1 ) and model (P _o2 ) is equal to P _o1 / P _o2 = C _Po1 = 1.0; - the compliance ratio of the joints of the subsystem “working surface of the lining - the surface of the pulley rim” of the object (P _o3 ) and model (P _o4 ) is equal to P _o3 / P _o4 = C _Po3 = 1.0; - the ratio of the amplitudes of the oscillations of the bonds of the mechanical subsystems and the deformations of the microroughness of the object (A) and model (a) is equal to A / a = C _A = 1.0; - the ratio of the oscillation frequencies of the object (Ω) and the model (ω) is Ω / ω = C _Ω = 1,0; - the ratio of the energy levels of the subsurface layers of the object (E ' _o ) and the model (E' _m ) is equal to E ' _o / E' _m = C _E'o = 1.0; - the ratio of the currents of the speeds of the washing air of the object (V _in ) and the model (v _in ) is equal to V _in / v _in = C _Vt = 1,0; - the ratio of the velocity currents of the components of the washing media of the object (V _c ) and the model (v _c ) is equal to V _c / v _c = С _Vс = 1,0 and at the same time, in an open thermodynamic tribo-conjugation system, not only the equality of surface temperatures, but also the equality of chemical potentials in forced convective heat transfer of its subsystems: - “the outer surface of the pulley rim - high-speed currents of cooling air”; - "the inner surface of the pulley rim - high-speed currents of the components of the washing medium"; - "the surface and subsurface layer of the polymer lining - high-speed currents of the components of the washing medium", and the interaction of the subsystem "brake pulley rim - mounting protrusion - winch drum flange" is carried out by conductive heat exchange due to temperature gradients along their thickness, after which the tribo-conjugation is measured and determined with simultaneous monitoring and fixing of areas of spots of contacts of microprotrusions in real time, since the electrothermal resistance of discrete contacts in with different energetic activity of microcapacitors and thermal batteries with their instantaneous switching when changing the areas of contact spots of microprotrusions under the conditions at the first stage of friction interaction (A _f <A _n ), that the actual contact area (A _f ) is small compared to the nominal (A _m ), the components of the generated currents are summed, and at A _n = A _{f, the} triboEMF is fixed in conjunction with the variable gradients of the mechanical properties of its materials and the penetration rate of the interacting between of pulses of electric and thermal currents affects the intensity of wear of microprotrusions during repolarization, and the values of thermal currents on the surfaces of the spots of contacts of microprotrusions are determined using the hypothesis of summing the temperatures on the surface taking into account the generated electric currents

where ϑ _P is the surface temperature from friction and contact resistance caused by the generated currents on the contact spots of the microprotrusions, as well as the friction component; Δϑ _П1 - increase in surface temperature from the flash point caused by discharge currents between microprotrusions; ϑ _pop - flash point caused by discharge currents between microprotrusions; in this case, a volumetric temperature (ϑ _υ1 ) is formed in the body of the metal friction element caused by the action of the first two components, it is determined from the condition of the action of two heat sources (electric and frictional) in the friction zone

Where

- heat flux on the contact surface, taking into account the electric and frictional component, W / m ² ; And _f is the actual area of contact, mm ² ; I is the generated current in friction pairs, A; ρ - resistivity of contact materials, (Ohm⋅mm ² ) / m; HB - Brinell hardness of the contact materials, MPa; N - normal impulse force acting in the contact zone of materials, N; ρ 'is the resistivity of the films at the contact, (Ohm⋅mm ² ) / m; ƒ - dynamic coefficient of friction; V _SK - sliding speed, m / s; α _TP1 - distribution coefficient of heat fluxes; λ is the reduced coefficient of thermal conductivity of materials of friction pairs, W / (m⋅ ° С); d _cp is the average diameter of the contact spot, determined taking into account its real roughness, mm; flash point ϑ _vsp is determined by the type

where Re = (V _SC d _cp ) / a is the Peclet criterion; a is the reduced coefficient of thermal diffusivity of materials of friction pairs, m / s ² , and the volumetric temperature of the metal friction element (ϑ _ν1 ) is determined from the condition of equal heat fluxes on the contact surface taking into account the friction and electric components and which is diverted from its polished surface to high-speed currents washing Wednesday:

subsequently, from the above temperatures, the energy levels of the surface and subsurface layers of the tribojunction elements are estimated, and then the maximum compressive stresses σ _1max in the pulley rim are estimated by the dependence of the form

where σ _k , σ ₁ , σ ₂ - stress in the pulley rim from the action: specific loads in friction pairs; temperature gradients on its working surface; volumetric temperature: mounting protrusion (ϑ _in ) and pulley rim (ϑ _about ) under condition (ϑ _about > ϑ _in ),

where To _b - the coefficient of mutual overlap of friction pairs; b _W , δ _W - width and thickness of the pulley rim,

where α is the coefficient of linear expansion; E is the modulus of elasticity; ϑ ₁ , ϑ ' ₁ - temperature of the working and inner surface of the pulley rim; μ is the Poisson's ratio,

where ϑ _in , ϑ _f - volumetric temperature of the mounting protrusion and the flange of the drum; And _in , And _f - the cross-sectional area of the mounting protrusions of the rim and the flange of the drum; but at the same time, for a more accurate determination of the components σ ₁ and σ _{2, the} term is substituted instead of (ϑ ₁ -ϑ ' ₁ ) by the term

(where τ is the braking time; τ ₁ , τ ' ₁ is the time to reach temperatures ϑ ₁ and ϑ' ₁ ), which characterizes the heating rate of the pulley rim, and instead of the dependence

(where δ ₁ , δ ₂ , δ _cf are the thicknesses of the mounting protrusion; drum flange; their average value), which characterizes the temperature gradients along the thickness of the elements under consideration, and the nucleation and development of cracks on the working surface of the brake pulley rims is evaluated by the coefficient of resistance to thermal shock

where σ ₀ , σ '- stress: resistance to cracking; maximum thermal.

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