RU2357131C2 - Method for determination of zone of initial interaction of friction pairs in belt-block brakes of draw works - Google Patents

Abstract

FIELD: machine building.

SUBSTANCE: invention is related to the field of machine building and may be used in belt-block brakes of draw works. Method consists in the fact that brakes with even number of friction pads that are fixed on wrapping arc of brake wheel working surface brake belt, angle β is defined, which specifies position of arbitrary radius-vector p_i relative to axis of abscissas, i.e. point of their contact, and then surface of pad contact with wheel, with the help of dependence of

type, where δ_p -

thickness of friction pad; R_P - radius of non-working surface of friction pad. Calculations are made provided that material of pad has not achieved value of permissible wear.

EFFECT: provides for possibility to assess performance parameters of every pad with section of belt above it as separate brake device.

4 dwg

Description

The invention relates to mechanical engineering and can be used in tape-shoe brakes of drill hoists.

It is indicated that during the initial interaction of friction pairs in the drawbar brake of the drawworks, the first pad, which touches the working surface of the pulley, is one of the linings of the oncoming branch of the brake band [1, analog]. However, it is not specifically indicated which of the pads according to the serial number of the brake belt touches the working surface of the brake pulley.

It is indicated that the moment of time when the initial working surface of the lining touches the surface of the brake pulley is taken as the start of braking in the brake device and braking ends after the friction surfaces open [2, prototype]. However, it is not noted that for this pad the braking time will be the largest in magnitude.

The aim of the present invention is to develop a method for analytically determining the initial contact of the working surface of the friction lining of the running branch of the brake band with the surface of the brake pulley of the drawbar brake of a drawworks.

The goal is achieved by the fact that for a given design scheme of the tape-shoe brake with an even number of friction linings, motionlessly mounted on the arc of the brake belt to cover the working surface of the brake pulley, determine the angle β, indicating the position of an arbitrary radius vector ρ _i relative to the abscissa axis, t. e. the touch point, and then the touch surface of the lining with a pulley, using the dependence of the form

,

,

where δ _H is the thickness of the friction lining; R _H is the radius of the idle surface of the friction lining; and according to this formula, calculations are performed provided that the lining material has not reached the allowable wear value.

Compared with the analogue and prototype, the proposed method has the following distinctive features: analytical determination of the point of contact of the working surface of the lining of the running branch of the belt pulley surface allows you to have: the start of the braking time; the heaviest loaded surface of the lining; specific load propagation front; maxima and minima of the dynamics of changes in the coefficient of friction; maximum wear of the working surface of the lining.

Figure 1 shows the kinematic diagram of a drawworks with a tape-shoe brake; figure 2 is a kinematic diagram of a tape-shoe brake; figure 3 is a section along aa figure 2 is a transverse section of the friction unit; figure 4 illustrates the design scheme of the tape-shoe brake. Legend: R _Ш - radius of the working surface of the brake pulley; S _H , S _C - tension of the running and running branches of the brake belt; ω is the angular speed of rotation of the pulley; r is the radius of the crank of the crankshaft; F _P - the force exerted by the driller to the brake control lever; 1, 2, 3 ... 11, 12 - serial number of overlays on a tape; l ₁ , l ₂ , l ₃ - the length of the sections of the brake tape; R ₀ is the radius indicating the position of the point O ₁ with respect to the geometric center of the brake belt and the friction unit pulley located at an angle φ ₀ to the abscissa axis; ρ _i - arcs of circles of given radii (describe the points of the friction surface of the friction linings) moving at small angles δ _i ; φ _i is the current angle indicating the position of an arbitrary radius vector ρ _i ; α is the angle of coverage of the brake belt of the pulley; R _H is the radius of the idle surface of the friction lining; δ _H is the thickness of the friction lining; y ₀ , x ₀ are the segments on the ordinate and abscissa, which are equal to the segments AO ₁ and AO ₂ , respectively.

According to the kinematic scheme (see Fig. 1), the friction linings 3 are mounted on brake bands 2, which are attached to the balancer 11 at one end (from the side of the runaway branch II of the belt 11) and to the crank necks 6 from the side of the branch of the branch I) and 9 crankshaft.

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 braking process with a tape-block brake (see figure 2) 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 initial 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 wear of their working surfaces.

According to figure 3, the position of an arbitrary point on the surface of the friction lining is determined by the magnitude and direction of the radius vector ρ _i drawn from the center of rotation of the brake band - point O ₁ . Before contact of the friction linings of the brake belt with the mating surface, i.e. the working surface of the pulley, the tape will rotate around point O ₁ , and the points of the friction surface of the plates describe arcs of circles of radii ρ _i , which move at small angles δ _i . The essence of the method is to find the initial contact point of the surface of the friction lining, which first will interact with the friction surface of the pulley.

An arbitrary radius vector is determined from Δ O ₁ OB

- радиус, указывающий положение точки О₁ по отношению к геометрическому центру ленты и шкива тормоза;

- угол, определяющий положение радиуса ρ_i по отношению к оси абсцисс (фиг.3); φ_i - текущий угол, показывающий положение произвольного радиуса-вектора ρ_i.Where

- a radius indicating the position of the point O ₁ with respect to the geometric center of the belt and the brake pulley;

- the angle determining the position of the radius ρ _i with respect to the abscissa axis (Fig.3); φ _i is the current angle showing the position of an arbitrary radius vector ρ _i .

From dependence (1) we find

where β = φ _i -φ ₀ ; b = R ₀ ² —R _L ² ; R _L - the radius of the inner surface of the brake tape.

Let the radius vector ρ _i prior to contact with the friction lining tape running path pulley rotated by a small angle δ _i given that the clearance between the friction σ ₃ pairs compared to the radius R _W of the pulley is very small.

Then from ΔО ₁ OS the radius of the pulley R _{W is} expressed as follows

or

.

.

For small angles δ _{i it is} true that cosδ _i ≈1 and sinδ _i ≈δ _i . As a result, we obtain

In order to determine the minimum angle δ _{i, we} equate to zero the first derivative δ _i from the expression (4)

.

.

After algebraic transformations, we obtain the equation for the angle φ _i = β + φ ₀ .

Equation (5) after substituting z = cos ² β and the corresponding transformations will be cubic

The discriminant of equation (6) is equal to

.

.

Therefore, equation (6) has one real and two imaginary roots. It is not necessary to determine the latter, and therefore we will find the actual root of interest to us

and

, а вместе с тем и положение радиуса-вектора ρ_i, указывающего точку поверхности фрикционной накладки тормозной ленты, которая первой вступит в контакт с поверхности трения шкива.The resulting expressions (7) and (8) allow you to accurately determine the angle

and at the same time the position of the radius vector ρ _i indicating the point on the surface of the friction lining of the brake belt, which first comes into contact with the friction surface of the pulley.

связано с большим объемом вычислительных операций, что не совсем удобно в инженерной практике, и поэтому упростим в границах 5-7% ошибки вычисления

.However, the use of expressions (7) and (8) to determine

due to the large volume of computational operations, which is not very convenient in engineering practice, and therefore simplify the calculation error within 5-7%

.

Due to the fact that R ₀ differs from R _Ш by a relatively small amount, then R ₀ ≈R _Ш and expressions (1) and (2) are transformed to the following form:

Solving expressions (9) and (10) together, we obtain

.

.

Where from

.Where

.

The minimum values of the angle φ _{i are} determined from the expression

.

.

In this way

We transform the value of b ₁ , given that R _H = R _W + δ _H ,

.

.

We neglect the quantity δ _H / 2R _H because of its smallness and we obtain

.

.

Then expression (12) takes the following form:

.Since δ _H / R _H ≤8, it is necessary to determine the actual value from the expression

.

Using dependence (13), we determine the angle β, showing the position of an arbitrary radius vector ρ _i relative to the X axis, i.e. the specified point, and then the contact surface of the friction lining with the belt brake pulley of the U2-5-5 winch with the following initial data: δ _H = 0.004 m; R _H = 0.729 m. Then we get that the angle β = 7 ° 15 'and the radius vector ρ _i indicates the second overlay of the oncoming branch of the tape-shoe brake, the first in contact with the friction surface of the pulley.

Thus, the knowledge of the moment when the second lining of the running branch (see Fig. 2) touches the working surface of the winch brake pulley allows one to further evaluate the operational parameters of each lining with the belt section above it, as a separate brake device.

Information sources

1. Volchenko A.I., Volchenko D.F., Rybin G.P. and others. Brake mechanisms. - Lugansk: Lugansk worker, 1995 (p. 80, fig. 5.1) [analog].

2. Alexandrov M.P. Braking devices in mechanical engineering. - M.: Engineering, 1965 (pp. 353-354) [prototype].

Claims (1)

The method for determining the zone of initial interaction of friction pairs of tape winch brakes of a winch containing a winch drum resting on a lifting shaft, and brake pulleys are installed from the ends of the drum, the working surfaces of which envelope the brake belts with friction linings mounted on their circumference arc with a uniform pitch, divided between each other by spacer bars, while the ends of the runaway branches of the brake bands through the rods are attached to the balancer, and the ends of the runaway branches to the crank crankshaft of the shaft, which is connected through the transmission device to the brake control lever, characterized in that the brakes with an even number of friction linings fixedly mounted on the arc of the brake band of the brake pulley working surface determine the angle β indicating the position of an arbitrary radius vector ρ _i relative to the axis abscissa i.e. the point of their contact, and then the surface of contact of the lining with a pulley, using the dependence of the form

,
where δ _H is the thickness of the friction lining; R _H is the radius of the non-working surface of the friction lining, and according to this formula, calculations are performed provided that the lining material has not reached the allowable wear value.

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