RU2090578C1 - Polymer friction composition (variants) - Google Patents

Abstract

FIELD: production of asbestos-free friction materials for coatings of braking units which operate in heavily loaded friction devices. SUBSTANCE: polymer friction composition comprises, mas.%: resol phenol-formaldehyde resin, 13-15; butadiene acrylonitrile rubber, 3-5; aramide fiber, 2.5-3.0; basalt fiber which surface is modified by 3-4 mass % of polyorganohydride siloxane, 8-10; wollastonite which surface is modified by 2-10 mass % of carbon modifier, 10-12; alumina, 4-8; graphite, 1-2; copper powder, 10-15; bronze chips, 10-15; barite, up to 100. According to the second variant similar to the first one wollastonite which surface is modified by 3-4 mass % of polyorganohydride siloxane is proposed for using. Composition is prepared by mixing at 90 C within 15-18 min, the process is carried out in rubber mixer. After sustaining within 1-7 days thus prepared material is ground and formed initially in cold mold and then in hot mold at 190 C and at 30-40 MPa. Article is affected by heat treatment at 200 C, the process is carried out within 2-3 h in furnace. EFFECT: improved physical and mechanical characteristics, increased wear resistance. 3 cl, 2 tbl

Description

 The invention relates to the field of producing asbestos-free friction materials for brake linings operating in heavily loaded friction units (automotive equipment and hoisting machines).

 Known friction composition based on phenol-formaldehyde resin and fiber [1] of the following composition, wt. h

Phenol formaldehyde resin 20-35
Asbestos 30-45
Barite 1-18
Wollastonite 15-33
Oleic acid 1-2
The disadvantages of the material include the use of asbestos as a fibrous filler, which is currently banned in many countries for environmental reasons due to the carcinogenic properties of asbestos dust.

 Known friction composition [2] based on a combination of fibers and phenol-formaldehyde resin of the following composition, wt.

Fiber 20-33
Metal particles or oxides 4-22
Organic Modifiers (Cashew Nut Powder) 0-7
Inorganic Modifier 7-24
Carbon or graphite particles 18-34
Phenolic resin 8-14
The disadvantages of this material include the use of fiberglass in the fibrous filler, which is low-tech and leads to the loss of frictional properties in the event of oil getting into the friction zone, as well as the use of an organic modifier (cashew nut powder), which significantly reduces the maximum working temperature of the material, which does not allow use it in heavily loaded friction units, and also leads to a decrease in physical and mechanical properties.

 Also known is a friction composition [3] based on a combination of fibers and phenol-formaldehyde resin of the following composition, wt.

Phenol formaldehyde resin 30-60
Hexamethylenetetramine 5-22
Graphite 1-5
Iron oxide 1-3
Tribromobenzoic acid 0.2-4
Silicon fluoride basic aluminum 0.3-3
A mixture of basalt and glass fiber 4-10 / 1-2
The main disadvantage of this composition is the use of too much phenol-formaldehyde resin, which leads to its intense burnout at high temperatures (400-500 ^o C) and lower strength characteristics of the material. The disadvantages of this material can also include the use of fiberglass, which has low processability and loss of frictional properties in the event of oil.

 Known polymer friction composition [4] of the following composition, wt.

Modified Phenol-Formaldehyde Resin 13-16
Nitrile butadiene rubber 2-4
Barite concentrate 10-20
Alumina 8-15
Metal powder 10-19
Graphite 1-5
Diammonium phosphate 0.5-2
Fibrous filler
In this case, asbestos (up to 50 wt. Of the entire composition) and up to 10 wt. basalt fiber and mineral wool.

 The disadvantages of the material include the use of asbestos as a fibrous filler, which is currently banned in many countries for environmental reasons due to the carcinogenic properties of asbestos dust.

 The closest in technical essence is a polymer friction composition [5] which includes, by weight.

Phenol-formaldehyde resin 10-12
Nitrile butadiene rubber with a content of bound nitrile-acrylic acid 27-30 2-3
Basalt fiber 17-25
Glass fibers 3-10
Carbon fiber 1-2
Barite concentrate 16-21
Alumina 6-10
Copper powder 5-10
Bronze chips 12-20
Graphite 1-3
Three Sulfur Antimony 3-7
This composition has increased wear resistance due to the use of carbon fibers in its composition, as well as increased adhesion of the pads to the pad at normal and elevated temperatures, provided by the introduction of antimony.

 However, such indicators of physical and mechanical properties as impact strength and strength are not high enough for heavily loaded friction units due to the weak connection of individual fibrous components with the polymer matrix. So, the impact strength of such a material is about 2.5 kgf / cm2, tensile strength 20 MPa, compression 15 MPa, which is lower than even asbestos-containing analogues. In addition, the composition of the composition includes fiberglass, which is low-tech and leads to the loss of frictional properties in the event of oil getting into the friction zone, and the use of antimony compounds in the composition affects the ecological purity of the material.

 The objective of the invention is the creation of an environmentally friendly polymer friction composition with improved physicomechanical characteristics and increased wear resistance for operation under conditions of heavily loaded friction units.

 This object is achieved in that the polymer friction composition containing rezol phenol-formaldehyde resin, nitrile butadiene rubber, fibrous fillers and dispersed fillers - alumina, graphite, copper powder, bronze shavings and barite, as fibrous fillers it contains aramid fiber and basalt fiber, the surface of which modified 3-4 wt. polyorganohydridesiloxane, and as a dispersed filler it additionally contains wollastonite, the surface of which is modified 2-10 wt. carbon modifier in the following ratio of components of the composition, wt.

Resol phenol-formaldehyde resin 13 15
Nitrile butadiene rubber 3 5
Aramid fiber 2.5 3.0
Basalt fiber, the surface of which is modified 3-4 wt. organopolysiloxane 8 10
Wollastonite, the surface of which is modified 2-10 wt. carbon modifier 10 12
Alumina 4 8
Graphite 1 2
Copper Powder 10 15
Bronze chips 10 15
Barite Else.

 The task according to the second embodiment is achieved in that the polymer friction composition containing rezol phenol-formaldehyde resin, nitrile butadiene rubber, fibrous fillers and dispersed fillers - alumina, graphite, copper powder, bronze shavings and barite, it contains aramid fiber and basalt as fibrous fillers whose surface is modified 3-4 wt. polyorganohydridosiloxane, and as a dispersed filler, it additionally contains wollastonite, the surface of which is modified 3-4 wt. polyorganohydridosiloxane, in the following ratio of components of the composition, wt.

Resol phenol-formaldehyde resin 13 15
Nitrile butadiene rubber 3 5
Aramid fiber 2.5 3.0
Basalt fiber, the surface of which is modified 3-4 wt. organopolysiloxane 8 10
Wollastonite, the surface of which is modified 3-4 wt. organopolysiloxane 10 12
Alumina 4 8
Graphite 1 2
Copper Powder 10 15
Bronze chips 10 15
Barite Else
Introduction to the composition of the composition of alumina (aluminum oxide) in a finely dispersed state allows to increase the friction coefficient and wear resistance of the material, improve braking efficiency, reduce the curing time of the resin binder by 30-50 %.At the same time, the properties of alumina as an abrasive material are not manifested due to the high dispersion of particles.

 Bronze shavings (ground) are introduced in order to increase thermal conductivity in order to reduce the developing high temperatures in the contact zone of rubbing bodies, which contributes to increase the wear resistance of the friction material.

 The use of wollastonite as a filler makes it possible to stabilize the friction-wear properties of the composition due to the high coefficient of friction inherent in materials such as pyroxenes, as well as to increase the strength of the material due to the needle structure of its particles, similar to the strengthening effect of fibers in the composition.

 The use of a mixture of basalt and aramid fibers allows you to obtain the necessary properties of the composition, such as strength, impact strength, hardness, stability of the coefficient of friction in a wide temperature range, high wear resistance, necessary for the normal operation of the friction material and thereby eliminate asbestos from its composition.

 The use of a carbon and organosilicon modifier of fibrous and dispersed fillers allows the creation of active centers on their surface that improve the dispersibility of fillers and increase the degree of structuring of the polymer matrix due to the formation of a chemical bond between the hybrid polymer base and the filler surface, and thereby further increase the physicomechanical properties of the composite.

Butadiene nitrile rubber of the SKN-26M brand (GOST 7738-79) is a product of high-temperature copolymerization of butadiene and acrylic nitrile (NAC) acid in an aqueous emulsion under the influence of free radical initiators. The content of NAC is 27-30%; the mass-average molecular weight is 200-300 thousand. Rubber is amorphous. The density of 960-980 kg / m ³ . Available in the form of elastic briquettes of light brown color.

 Phenol-formaldehyde resin brand SF-342A (GOST 18694-80) is an oligomeric product of the polycondensation of phenol with formaldehyde in the presence of a catalyst. Belongs to the class of thermosetting resins and is a solid product in the form of pieces of irregular shape of light yellow color, which has high thermal and water resistance, chemical resistance, mechanical strength and dielectric properties.

Aramid fiber was used ultra-high modulus fiber (CBM), TU 6-06-31-554-86, having the following main characteristics:
linear density, tex 0.84
breaking load, cN / tex ≥ 30
cutting length, mm 0,110
tensile elongation ≥ 7
linear density deviation, ± 7
humidity not less than 5
pH 6-8
Chopped basalt fiber made of glass basalt complex thread RB-9, TU 88 USSR 023.004-01 (valid until 01.01.96)
The diameter of the elementary fiber, μm 9 ± 1
Monofilament length, mm 0.5-10
Wollastonite is a crystalline mineral (chain silicate), TU-14-1-112-71, a powder of light gray color, odorless. It is a mixture of metal oxides (Ca, Si, Ti, Fe, Mo, Al, Mn). The density of 2.9 g / cm ³ . The chemical formula of CaSiO ₃ . Melting point 1540-1598 ^o C.

 Possessing a simple crystalline chain structure that provides close packing of structural elements, wollastonite has high strength and chemical resistance. No carcinogenic properties.

 The crystals have a needle structure with an average ratio of length to average diameter of about 15. The mineral has low moisture absorption, good physical and mechanical properties.

 Alumina is an inert filler (GOST 6912-80). The raw materials are bauxite, nepheline, kaolin and other aluminum-containing products.

Alumina grades G-00 to G-4 were used, the alumina content of which is at least 30%
Graphite is a crystalline modification of carbon, has a strong anisotropy of physical properties.

 In the production of friction products, graphites were used: crystalline foundry GL (GOST 5279-74) and cryptocrystalline GLS (GOST 5420-74) of the following grades GL-1, GL-2, GLS-1, GLS-2, GLS-3.

 The main properties include: high chemical resistance and heat resistance, low coefficient of linear expansion, low specific gravity, porosity, developed surface of the particles, providing good mechanical adhesion of the components in the composition.

 PMS-1 copper powder (GOST 4960-73), metal filler in the form of a red-brown powder.

 Bronze shavings in accordance with GOST 1639-78 from bronze grade BrS-30. It has high thermal conductivity, it is resistant to shock loads. Tensile strength 5.8 MPa, hardness HRC 25.

Barite (heavy spar) is a natural mineral that contains mainly anhydrous barium sulfate BaSO ₄ (80-94%). Most often, the impurities are quartz (SiO ₂ ), CaCO ₃ , dolomite (CaCO ₃ • MgCO ₃ ) and hematite (Fe ₂ O ₃ ). We used a barite concentrate according to GOST 4682-74 class A, white with a particle size of 5.6-6.0 microns of the following grades: KB-1, KB-2, KB-3, KB-5, KB-6.

The carbon modifier was obtained by deposition on the surface of wollastonite particles from the gas phase in the form of a black coating at a temperature of 600-100 ^° C. Methane (TU 51841-78) and carbon tetrachloride (GOST 20288-74) were used to obtain it.

As an organosilicon modifier, polyorganohydride siloxane of the general formula (RSiHO) n, grade 136-41 according to GOST 10834-76, which is a polymer of ethyl hydrosiloxane, was used. It is a colorless or slightly yellow liquid with a T flash of 75 ^o C, T self-ignition. 280 ^o C, density at 20 ^o C 0.995-1.003 g / cm ³ , T fast. below 60 ^o C.

 As a result, the use of alumina in the composition due to the high hardness of its particles results in a significant increase in the wear resistance of the composite material, and a well-developed surface and the presence of alumoxane and hydroxyl surface groups ensure the effective interaction of alumina particles with a polymer matrix and, as a result, improve the physicomechanical characteristics of the material .

 Bronze chips contribute to the creation of an intermediate layer, which is a semi-solid lubricant that is produced from the material itself.

 The intermediate layer promotes smooth braking, prevents the setting of contacting surfaces, and also prevents the appearance of scoring on the counterbody, due to which the wear resistance of the material is significantly increased.

 Natural wollastonite has a characteristic asymmetry of particles of the order of 15, which is mainly preserved during grinding.

 This circumstance determines the behavior of wollastonite in the composition as a reinforcing material, similar to the action of fibers, which gives the composition enhanced physical and mechanical properties. It provides higher strength in bending and stretching, and is characterized by high water resistance.

 In addition, it helps to increase heat resistance, stiffness and surface hardness, which improves the wear resistance of friction products.

 When creating fiber-reinforced composites, it is important to take into account the ratio of the thermophysical characteristics of the material components. High temperatures developing in high-temperature friction pairs lead to uneven wear and uneven destruction of the surface layers in the friction zone, causing increased wear of the material.

 Slowing down this process and increasing the physicomechanical characteristics of the composite can be achieved by modifying the surface of reinforcing fillers with substances similar in properties to both the binder and the filler and entering into chemical interaction with both, and thereby contributing to a significant improvement in the adhesion between fillers and the polymer.

 The carbon modifier deposited from the gas phase onto the surface of wollastonite includes spatially branched regions of the graphite-like type and regions of disordered carbon containing surface functional groups such as carboxyl, carbonyl, phenolic hydroperoxide, lactone, which include carbon, oxygen and hydrogen, capable of reacting with chain fragments polymer matrix. At the same time, when a carbon modifier is deposited on the surface of wollastonite, carbon chemisorption occurs as a result of reactions of primary active center-silanol and siloxane groups with carbon tetrachloride and methane vapors. In this way, a bond is ensured both between the carbon modifier and the filler surface, and between the modifier and the polymer matrix. In this case, the optimal concentration of the carbon modifier on the surface occurs during the final filling of the primary active centers.

 A further increase in concentration does not lead to an improvement in the properties of the material and unjustifiably increases its cost.

 For wollastonite with a particle size of about 20-60 microns, the optimal content of the carbon modifier on the surface corresponds to 2-10% by weight of the filler.

 However, not all materials used as reinforcing fillers can be subjected to high-temperature processing necessary for the synthesis of a carbon modifier on their surface. So, basalt fibers undergo a significant change in the internal structure, as a result of which their strength and wear resistance are sharply reduced, which is unacceptable.

 In this regard, for the modification of basalt fibers, as well as, as an option, and for the modification of wollastonite, an organosilicon modifier was used, the application technology of which does not require high-temperature processing.

 The action of the organohydride siloxane used in this case is based on the interaction of the Si-H reactive bond with primary active centers, for example, hydroxyl or hydroperoxide, of the surface of the fillers. As a result, a spatially oriented polymer is formed on the surface of the material particles, which has good adhesion to the material due to the condensation of hydrosiloxane fragments and the formation of a siloxane bond with the surface. On the other hand, the remaining Si – H bonds will be those secondary active centers that form chemical bonds with the components of the polymer matrix during compounding and subsequent heat treatment.

 Thus, the action of both modifiers is based on one mechanism, namely, the creation of a buffer layer on the surface of the filler particles, which has equally high adhesion to both the surface of the filler and the polymer binder.

 The result is a significant improvement in the thermophysical and physico-mechanical properties of the material.

 Strength, toughness, and wear resistance of the friction material are increased.

 The use of polyaramide fibers in the proposed technical solution as a reinforcing filler allows one to obtain a significant improvement in such physical and mechanical properties of the material as impact strength and strength due to the good combination of fiber with a hybrid polymer matrix and a fibrillated structure, which gives it reinforcing properties.

 At the same time, aramid fibers have high hardness and significantly reduce material wear when introduced into the composition.

 For comparison, it is necessary to compare with the same positions and the composition described in the prototype.

 In the case of the prototype [5], the composition does not contain aramid fiber, which gives the material high strength characteristics.

 The absence of wollastonite in the prototype worsens the stability of the friction-wear properties of the composition, and also precludes the possibility of increasing the strength of the material due to the reinforcing properties of wollastonite.

 In the case of the prototype, the surface modification of the particles of reinforcing fillers was not used, which did not allow to further improve almost all the properties of the filled compositions as a result of improving the dispersibility of the filler and its adhesive interaction with the polymer matrix.

 The combination of these properties makes the friction composition in the case of the prototype less effective than the claimed, which has significantly higher strength characteristics.

 Analysis of the friction compositions known from the prior art has shown that some features introduced into the claimed solution are known.

 Thus, the known composition [6] is obtained by mixing organic fiber and an inorganic filler treated with 0.1-5% by weight of a filler of a silane sizing, with combining the resulting mixture with paper impregnated with a thermosetting resin (phenolic and melamine resins, ES, etc.) with subsequent curing of the finished composition.

 Despite the use of a silane dressing in the specified composition, the maximum effect of its action is not achieved due to the application of the modifier only to the dispersed filler, and not to the reinforcing fibrous components.

 In addition, the use of a carbon modifier is more effective than organosilicon due to the higher adhesion of the first to the surface of the reinforcing fillers and the great diversity and activity of surface functional groups that form chemical bonds with fragments of the polymer matrix.

 As a result, in both variants of the claimed composition, a significantly greater effect of increasing the physicomechanical properties and the associated wear resistance characteristics is achieved than in the known case under consideration.

 In addition, in the known embodiment, only organic fiber and paper are used as reinforcing fillers, which does not allow to obtain the wear resistance and heat resistance of friction products necessary for working in heavily loaded friction pairs.

 This allows us to conclude that the proposed solution meets the criterion of "inventive step".

The composition is prepared in a rubber mixer with oval rotors by mixing for 15-18 minutes at a temperature of 90 ^o C. After aging for 1-7 days, the material is crushed and molded first in a cold, and then in a hot mold at 190 ^o C, pressure 30 -40 MPa at the rate of 1.5 min / mm thickness. The finished product is heat treated in an oven for 2-3 hours at 200 ^o C.

Before mixing the components in a rubber mixer, the surface of wollastonite in the first embodiment is preliminarily modified with a carbon modifier from a mixture of methane vapor and carbon tetrachloride at a temperature of 600 ^o C for 30 min to a content of 2-10 wt.

 An organosilicon modifier treats the surface of basalt fiber, as well as the surface of wollastonite in the second embodiment.

Weighed portions of the fillers are placed on a metal baking sheet and treated with a grade 136-41 polyorganohydride siloxane prepared by GOST 10834-76, then dried in air for 2 hours and in a thermostat for 15 minutes at a temperature of 145-150 ^o C.

 An example of a specific implementation.

A weighed portion of wollastonite weighing 413 g is placed in a flow reactor and heated to a temperature of 600 ^o C, and then treated with a gas mixture of methane and carbon tetrachloride for 30 minutes As a result of processing, the surface of the wollastonite particles is modified by carbon. The mass of material after processing 440 g includes 6% carbon modifier.

A sample of basalt fibers weighing 385 g is placed on a metal baking sheet and treated at room temperature with 136-41 polyorganohydride siloxane liquid by dipping, after which the fibers are dried in air for 2 hours, and then in an thermostat for 15 minutes at a temperature of 145-150 ^o C. Mass of material after treating 400 g includes 3.5% polyorganohydride siloxane modifier.

 Next, the components are loaded into the rubber mixer in the following sequence: rubber, phenol-formaldehyde resin, fibrous and dispersed fillers.

The composition is prepared on a rubber mixer with oval rotors of the VN4003A brand with a mixing chamber volume of 2.0 l with a total load of 4 kg and the following weighed components, g:
Rubber 160
Phenol-formaldehyde resin 560
Aramid Fiber 120
Basalt fiber, the surface of which is modified 4.5 wt. organopolysiloxane 400
Wollastonite, the surface of which is modified 6 wt. carbon modifier 440
Alumina 240
Graphite 60
Copper Powder 500
Bronze shavings 500
Barite 1020
Total 4000 g
The mixture displacement time in the rubber mixer is 15-18 minutes.

The temperature of the mixing process is regulated by cooling the walls of the rotors of the mixer with water and should not be more than 90 ^o C in the compounding process.

The duration of the aging mixture in the container at an air temperature of 20 ± 5 ^o C for at least a day and no more than 7 days.

The mixture is crushed in a disintegrator or manually and briquetted in a cold mold, after which the briquette is subjected to hot molding in a mold at a temperature of 190 ± 5 ^o C, specific pressure 30-40 MPa and holding time at the rate of 1.5 min per 1 mm thickness of the finished product. After pressing, the product is subjected to final heat treatment in an oven at 200 ± 5 ^o C for 2-3 hours

 The compositions of the polymer friction compositions are presented in table 1.

 Barite compensates for the missing to 100% share, while its content ranges from 23.8-30.8 wt.

 It was established that a change in the concentration of barite (inert filler) within the indicated limits does not affect the properties of the friction material.

 Friction-wear characteristics (Table 2) were obtained when determining the frictional heat resistance according to the standard method RD-50-662-88 on a universal friction machine 2168 UMT.

 Samples in the form of cylindrical rings simulating a friction pair of an iron-polymer friction composition, with an outer diameter of 28 mm, an inner diameter of 20 mm, and a height of 15 mm are brought into contact on end surfaces at a certain load and friction speeds.

где

средняя величина коэффициента трения на данной ступени испытания;

среднее значение момента трения на данной ступени испытания;
P нагрузка на образцы при испытаниях
Величина и стабильность интенсивности изнашивания композиции

Интенсивность массового энергетического износа фрикционной композиции определяли по формуле:
I_Gi = Δm_i/W_тi = Δm_i/L_i•f•P
где Δm_i = m_i-1 - m_i величина массового износа;
m_i; m_i-1 масса образца i-й и i-1 ступени;
W_ti работа трения i-й ступени испытаний (Дж);
P нагрузка (H);
L_i путь трения (м) L = 2πr_ср•N;
N число оборотов образца на данной ступени испытаний;
r_ср. средний радиус образца.To compare the materials, the following criteria were selected:
The value and stability of the coefficient of friction
α _st.f = f / f _max .
The value of the coefficient of friction was determined by the formula:

Where

the average value of the coefficient of friction at this stage of the test;

the average value of the friction moment at this stage of the test;
P test load
The magnitude and stability of the wear rate of the composition

The intensity of mass energy wear of the friction composition was determined by the formula:
I _Gi = Δm _i / W _ti = Δm _i / L _i • f • P
where Δm _i = m _i-1 - m _{i the} amount of mass wear;
m _i ; m _{i-1 is the} mass of the sample of the i-th and i-1 stages;
W _ti friction work of the i-th test stage (J);
P load (H);
L _i friction path (m) L = 2πr _sr • N;
N is the number of revolutions of the sample at this test stage;
r _cf. average radius of the sample.

Maximum allowable temperature V _pre. ( ^o C)
The beginning of a sharp monotonous increase in wear intensity.

 As can be seen from table 2, the optimal composition is for a polymer friction composition containing components within the claimed limits.

Introduction to the composition of butadiene rubber less than 3 wt. does not provide a sufficiently high coefficient of friction, and higher concentrations, over 5 wt. lead to a decrease in the limiting temperature (V _pred. ^o C), after which the wear rate sharply monotonously increases.

 The use of phenol-formaldehyde resin due to its high heat resistance allows you to increase the maximum operating temperature of the composition, while the introduction of the resin is less than 13 wt. does not provide the specified effect, and with the introduction of more than 15 wt. there is a significant decrease in the coefficient of friction of the composition, due to the fact that the resin itself has a low coefficient of friction.

 The decrease in the content of aramid fiber having good reinforcing properties up to 2 wt. does not allow to achieve optimal values of hardness, toughness and strength of the material, and with an increase in its concentration of more than 3.5 wt. there is a decrease in the limiting operating temperature and an increase in the wear of the composition due to the low heat resistance of the aramid fiber.

 Introduction to the composition of basalt fiber below the claimed limit (less than 8 wt.) Leads to a decrease in strength, hardness, wear resistance and maximum operating temperature. The high content of basalt fiber (more than 10 wt.) Reduces the impact strength and compressive strength. The material becomes brittle and cannot be used for friction linings.

 With a decrease in the concentration of wollastonite below 9 wt. no effective increase in strength, toughness, and friction coefficient is observed.

 The content of wollastonite is more than 12 wt. leads to a significant increase in the coefficient of friction and, as a consequence, overheating and high wear of the material and counterbody.

 As noted above, the presence of alumina in the composition gives it good strength and anti-wear properties, however, with a low content (less than 4 wt.) Its effect is not effective enough. There is increased wear, the absence of a strengthening effect.

 The increase in its concentration above 8 wt. reduces specific impact strength and compressive strength and tensile strength.

 The formation of an intermediate lubricant layer of graphite between the friction material and the counterbody helps prevent increased wear of the composite and stabilizes the friction coefficient, but with a graphite content of less than 1 wt. its effect is subtle. At the same time, with a high concentration of graphite above 2 wt. its lubricating effect is too high, which leads to an unjustified decrease in the coefficient of friction, loss of braking efficiency.

 The use of copper powder in the composition is associated with the need for good heat removal from the friction zone.

 The decrease in the boundary value of the concentration of copper powder is less than 10 wt. helps to reduce thermal conductivity, the rapid development of high temperatures and, as a consequence, increase wear, and an increase in powder content (above 15 wt.) worsens the toughness and strength of the material.

 The concentration of bronze chips below 10 wt. It does not allow to provide the necessary values of thermal conductivity, and also to sufficiently realize the effect of lubricating the friction surface with a metal layer, which prevents the setting of surfaces.

 At the same time, the limiting operating temperature is reduced and the wear of the material increases. Too much chip content of more than 15 wt. already begins to strongly affect the stability and value of the coefficient of friction, at the same time, such material properties as strength and toughness deteriorate.

 The effectiveness of the use of surface modifiers for reinforcing fillers is determined by improving such physical and mechanical properties of the material as tensile and compressive strength, impact strength.

 The formation of chemical bonds in the filler-modifier and modifier-polymer systems also makes it possible to increase the wear resistance of the composition, since significantly more friction work is required to overcome the energy of chemical bonds than if unmodified fillers are used.

 When studying the effect of modifiers on the above characteristics of the material, it was found that the concentration of 2-10 wt. for carbon modifier and 3-4 wt. for organopolysiloxane. The research results are given in table.2.

 When the content of modifiers is less than the lower limit of concentrations, their effect is not effective enough, since the primary functional groups of the surface remain largely free and do not participate in fixing the modifier molecules.

 Exceeding the upper concentration limit leads to the fact that the deposition of the modifier occurs no longer on the functional groups of the surface with the formation of chemical bonds, but by layers, the bond between which is much weaker and breaks much easier.

 As a result, the effect of the modification is significantly attenuated.

 Thus, the proposed composition of the polymer friction composition has improved physical and mechanical characteristics and increased wear resistance and can be used to work in conditions of heavily loaded friction units.

Claims (1)

 1. The polymer friction composition containing resole phenol-formaldehyde resin, nitrile butadiene rubber, fibrous fillers and dispersed fillers alumina, graphite, copper powder, bronze shavings and barite, characterized in that it contains aramid fiber and basalt fiber, the surface of which is modified 3 to 4 wt. polyorganohydridosiloxane, and as a dispersed filler, it additionally contains wollastonite, the surface of which is modified 2 to 10 wt. carbon modifier, in the following ratio of components of the composition, wt. Resol phenol-formaldehyde resin 13 15
Nitrile butadiene rubber 3 5
Aramid fiber 2.5 3.0
Basalt fiber, the surface of which is modified 3 to 4 wt. organopolysiloxane 8 10
Wollastonite, the surface of which is modified 2 10 wt. carbon modifier 10 12
Alumina 4 8
Graphite 1 2
Copper Powder 10 15
Bronze chips 10 15
Barite Else
2. Polymeric friction composition containing cutting phenol-formaldehyde resin, nitrile butadiene rubber, fibrous fillers and dispersed fillers alumina, graphite, copper powder, bronze shavings and barite, characterized in that it contains aramid fiber and basalt fiber, the surface of which is modified 3 to 4 wt. polyorganohydridosiloxane, and as a dispersed filler, it additionally contains wollastonite, the surface of which is modified 3 to 4 wt. polyorganohydridosiloxane, in the following ratio of components of the composition, wt. Resol phenol-formaldehyde resin 13 15
Nitrile butadiene rubber 3 5
Aramid fiber 2.5 3.0
Basalt fiber, the surface of which is modified 3 to 4 wt. organopolysiloxane 8 10
Wollastonite, the surface of which is modified 3 to 4 wt. organopolysiloxane 10 12
Alumina 4 8
Graphite 1 2
Copper Powder 10 15
Bronze chips 10 15
Barite Rest

Images