RU95620U1 - WEAR-RESISTANT BRAKE SHOES WITH INCREASED FRICTION FACTOR FOR SPEED MOVEMENT (OPTIONS) - Google Patents

Abstract

 1. Wear-resistant brake shoe with a high coefficient of friction for high-speed movement of a locomotive is a structure consisting of a continuous working surface and a solid ridge shaped groove, characterized in that N cuts are made on the working surface of the shoe at a distance L from each other with depth Hpr at an angle α to reduce the complexity of determining the residual life of the pads and ensure timely replacement, designed to reduce the intensity of wear of the brake pads per second even removal of wear products from the friction zone and improving the temperature regime (heat removal) of the pads and wheels. ! 2. Wear-resistant brake shoe with a high coefficient of friction for high-speed movement of a locomotive according to claim 1, characterized in that the continuous figured groove is replaced by three hooks, which reduce the force effect on the working surface of the wheel flange and the formation of thermal cracks. ! 3. A wear-resistant brake shoe with a high coefficient of friction for high-speed movement of a car is a structure consisting of a continuous working surface, characterized in that N slots are made on the working surface of the shoe at a distance L from each other with a depth of Hpr at an angle α, which reduces the complexity of determining the residual life of the pads and to ensure its timely replacement, designed to reduce the wear rate of brake pads by removing wear products from the tren zone ia and improving the temperature regime of work (heat sink) pads and wheels.

Description

The invention relates to rail vehicles, in particular to locomotives and wagons, relates to part of the Executive (friction) mechanism of the brake linkage.

Brake pads (lining) are the most important element of the mechanical part of the brake, providing the necessary friction when they are pressed against the wheel for the formation of braking torque on the wheelset. The effectiveness of braking depends on them, and, consequently, traffic safety - this causes a number of requirements for their quality and characteristics:

- the presence of a stable and high coefficient of friction in a wide range of speeds and pressing forces;

- minimal wear per unit of braking distance to reduce the amount of work on replacing pads on rolling stock;

- the possibility of prolonged braking without loss of frictional properties;

- the absence of unacceptable thermal and other influences on the wheelset or wheel damaging their surface;

- the invariability of frictional characteristics when moisture enters the pads;

- ease of installation when replacing due to wear or changing the type of brake pads;

- elimination of occurrence of non-conductive inclusions on the wheel surface (third body), as well as reducing its coefficient of adhesion to rails;

- the absence of wear products harmful to humans and the possibility of spontaneous combustion of pads [1].

Reducing braking distances, increasing speeds and driving safety depends on the quality and design of brake pads. Brake pads should have a high coefficient of friction, which does not depend on speed, high wear resistance and work stably in different climatic conditions [2].

In the form of execution on a rolling stock, the most widespread are ridge 1 (Fig. 1) and ridge 2 (Fig. 2) cast-iron standard brake pads.

Combless pads are used on freight and passenger cars. On locomotives, crest pads are mainly used, as because of the traction equipment, it is impossible to connect them in pairs with triangles or brake beams, eliminating the displacement of the pads from the surface of the wheels, as is done on cars. Since the surface of the wheels has a conical shape and when you press the block, in addition to normal force, there is also lateral force, the ridge block is kept on the wheel from slipping with the help of a special figured groove 3 (figure 2), which rests on the wheel flange, and does not intended to create an additional inhibitory effect [1].

In the process of braking the train, its kinetic energy is converted into other types: thermal, electric, etc. During frictional braking, the heat generated heats the rubbing parts and dissipates in the environment. The operational experience of brake systems, especially with an increase in the speed of movement, shows that the thermal stress of the braking processes affects the durability and damage of friction units.

When braking, the friction process of the brake pads and wheels occurs at the points of their actual contact. The total area of these contacts is only an insignificant amount of the geometric area covered by the brake shoe. Heat is released only at the points of actual contact, the density of heat fluxes and temperature flashes in them can reach large values, which, with poor heat removal, causes the friction surface to glow and the metal to transition to a plastic state at these points. In this case, the metal is deformed or rapidly deteriorates, and the place of the temperature flash moves in accordance with the change in contact specific pressures. Due to the small area of actual contact, insufficient heat removal from the friction zone and temperature flashes, higher average temperatures occur on the friction surface of the blocks than on the wheel, at which the strength of the block material is further reduced, and the metal is subjected to intense plastic deformations [6]. In such conditions of friction, rapid thermal wear of the surfaces of the wheel and pads occurs. Moreover, the wear rate is determined by the occurrence and development of high temperature in the friction zone.

In this regard, the main problem is that cast-iron blocks wear out quickly, this reduces the safety of the train moving along the run (descent) and increases the cost of their maintenance in operation when replacing and manufacturing them. Cast iron microparticles formed during the wear process in the friction zone of the block and wheel are relatively large, which has the additional effect of increasing the wear rate in the brake block "Wheel-Wheel", and their movement in the friction zone of the block and wheel during movement reduces the coefficient of friction of the block on the surface skating wheels. This affects the decrease in the effectiveness of mechanical braking and increase the braking distance. For example, on steep, long descents, the wear of cast-iron blocks per run is 7–9 mm [2]. The presence of a curly groove on the ridge block additionally contributes to an increase in the wear rate of the working surface of the wheel ridge and the formation of thermal cracks on the ridge surface resulting from sudden braking with a large pressing of the block on the wheel ridge [4, 5]. All this happens as a result of poor-quality adjustment of the brake linkage and not maintaining the technology for the production of new pads.

The wear of the pads under operating conditions significantly depends on their pressing force, material, type and duration of braking, the presence of a third body (wear products of the brake pads and wheels), the adjustment of the linkage, the position of the pads relative to the surface of the wheel, both in the brake and in the traction mode, temperature regime of the braking process and a number of other factors.

The temperature regime of the braking process is characterized by the heat flux density and the resulting temperatures depending on the initial braking speed, decelerations, the magnitude of the braking forces, the material of the rubbing pairs and the conditions of heat transfer to the environment. At high speeds in braking mode, special attention is always paid to the conditions of heat transfer in the friction zone of the shoe and wheel. Since there is a fast and intense heating of the wheel's rolling surface, which on the one hand causes a redistribution of stresses in the wheel rim, its weakening and subsequent possible rotation relative to the wheel center (with the retaining structure) due to the unevenness of the temperature field, and on the other hand, significant compression stresses appear, which can exceed the elastic limit and cause plastic deformation of the rolling surface. After cooling, in such cases, tensile stresses of the metal occur. Repeated loading with alternating stresses leads to thermal fatigue cracks on the surface of the ride, progressively developing in the depth of the wheel, especially when moving to a zone with tensile stresses. All this serves as a criterion of permissible braking performance and the type of brake system at high braking speed.

Therefore, maintaining the temperature regime on the friction surface of the brake system without changing its design with increasing speed requires lengthening the braking distance in proportion to the speed cube [6].

In operation, cast-iron brake pads of locomotives and wagons wear out rather quickly to a critical thickness, which leads to the need for their replacement [1]. However, in modern conditions of operation of brake pads of locomotives and wagons, it is impossible to provide visual control of its wear, and consequently, their timely replacement.

Thus, the closest prototype is the cast iron brake pad of a locomotive and a car [1, 3].

Currently, the thickness of the brake pads is controlled by the assistant to the driver with a ruler or vernier caliper in the parking lot of the locomotive, which causes a lot of time and is very labor intensive.

It is proposed to modify the design of the brake pads of cars 4 (FIG. 3) and locomotives 4 (FIG. 4), by making N slots on the working surface N at a distance L from each other with a depth H _pr up to the maximum wear rate (which depends on the operating conditions of the rolling stock and set by local regulations) at an angle α. The presence of slots will allow you to visualize the residual resource and provide less time for identifying worn blocks in operation without additional measuring tools, thereby ensuring their timely replacement and increasing the safety of train traffic.

The expression of the wear pad ΔH of the brake pad over the thickness for the case of emergency braking for a time t _in until it stops, is determined by the formula [6]

where α _to is the distribution coefficient of the heat flux, shows what part of the heat generated by friction has entered the block;

In _t - braking force;

Δh is the average destructible height of the protrusions of the actual contact;

υ ₀ - initial braking speed;

A is the mechanical equivalent of thermal work;

χ is the coefficient of the actual contact area;

F _k - geometric contact area of the pads and wheels;

Δτ _max - increase in temperature to a value at which the destruction of the roughness protrusions occurs (depends on the material of the block and is constant);

_{Δτ psr} - the average increase in the working surface of the friction pads;

λ is the coefficient of thermal conductivity;

γ is the specific gravity of the heated wheel;

C is the specific heat of the wheel.

From the formula (1) it can be seen that the proposed design promotes the effective removal of the third body (cast iron wear microparticles) from the friction zone 7 (Fig. 5), which reduces the average destructible height of the protrusions of the actual contact Δh during braking, thereby reducing the wear rate of the pads and its friction coefficient increases, increasing braking efficiency.

The average increase in the working surface of the friction pads can be determined by the following formula

where Δτ _p is the excess surface temperature on which heat is generated.

Temperature change (Δτ _p ) at time t caused by the amount of heat q (t) dt released on a surface unit

Given the heat transfer from the friction surface to the environment, we have

where q _a is the amount of heat released on a surface unit per unit time (heat flux density) at the beginning of the temperature increase process;

α is the heat transfer coefficient from the friction surface to the environment.

The heat transfer coefficient from a heated surface to the environment is determined as the sum of the heat transfer coefficients by convection α _to and radiation α _l

The coefficient of heat transfer by radiation α _l depends on the reduced degree of tone of the color gamut (dark, light) of the radiating surface of the block, the absolute temperature of the block and the ambient temperature. In the modified design of the block, the heat transfer coefficient of radiation α _{l is} not considered, since it slightly affects the wear of the block, because a weak heat removal from the friction zone of the wheel and shoe surfaces is organized into the environment.

The convective heat transfer coefficient α _{k is} calculated depending on the Reynolds criteria Re and Prandtl Pr [6].

Reynolds criterion for the rolling surface of a rotating wheel is determined from the expression

where γ _in , Z is the specific gravity and absolute viscosity of the air flowing around the wheel;

υ is the air velocity (directly depends on the speed of the rolling stock).

Prandtl criterion depends on the characteristics of the air flowing around the wheel

where c _p is the specific heat of air (at constant pressure);

λ _in - coefficient of thermal conductivity of air.

The physical characteristics of air included in the Prandtl and Reynolds criteria are taken at the temperature of the surface to be cooled.

The formula for calculating the heat transfer coefficient by forced convection (υ> 0) has the form

To use formula (8) as applied to cooling bodies of various geometric shapes, it is convenient to transform it by substituting the value of the Reynolds criterion to the form

The presence of slots of the proposed block design reduces the intensity of their wear ΔН, especially at high speeds, by improving the temperature regime by increasing the efficiency of heat removal from the friction zone to the environment. In the process of movement, the cold air pumped under the shoe 8 (Fig. 5) is heated and efficiently released into the environment through slots on the working surface of the shoe 6 (Fig. 5), as a result of which the convective radiation coefficient α _k increases, which reduces the average friction temperature of the working the surface of the pad _{Δτ psr} , thereby increasing the time to reach the maximum temperature Δτ _max at which the protrusions of the actual contact are destroyed, according to formula (1). In a typical block, with an increase in the initial braking speed, the intensity of its heating increases.

The decrease in the average temperature in the friction zone also reduces the likelihood of the rotation of the brace relative to the wheel center and the formation of surface stresses in the brace, which is very important for high-speed movement of the rolling stock.

To eliminate thermal cracks and reduce the wear rate of the working surface of the wheel flange, it is further proposed to modify the locomotive ridge pad by replacing the solid curly groove of the block 3 (Fig. 2) with three hooks 5 (Fig. 4). The hooks will perform the same function as a continuous figured groove, but the force exerted on the working surface of the ridge will be significantly lower. This is possible due to the fact that the figured groove of the pad does not create additional braking forces.

Thus, there are two options for the implementation of wear-resistant brake pads for high-speed movement, in the first case for a locomotive (figure 4), in the second for a car (figure 3).

The technical result of the proposed design options for the pads of a locomotive and a wagon in operation is achieved by:

- increasing the safety level of train traffic, by increasing the reliability of braking, in connection with the timely replacement of extremely worn blocks;

- reducing the intensity of wear of the brake pads due to the timely removal of wear products and improving the temperature regime of the pads;

- material savings in the manufacture of new pads;

- the possibility of applying the design of the pads in high-speed movement without increasing the braking distance of the locomotive;

- increasing the braking efficiency and reducing the intensity of wear of the pads due to the timely removal of the products of frictional wear from the contact area of the pads and the surface of the wheel;

- reducing the probability of turning the brace relative to the wheel center and the formation of stresses on its surface;

For the embodiment of the design of the locomotive pads, an additional technical result is achieved:

- reduction of wear on the flanges of the wheelsets;

- reducing the likelihood of thermal cracks on the working surface of the wheel flange.

Bibliography:

1. Automatic brakes of rolling stock / V.R. Asadchenko-Moscow: Route, 2006. - 392 p.

2. Automatic brakes of rolling stock / V.I. Krylov, V.V. Krylov - Moscow: Transport, 1983. - 360 p.

3. GOST 1205-73 Cast-iron, brake shoes for wagons and tenders, broad gauge railways “Design and main dimensions”

4. Brakes of railway rolling stock: Questions and Answers / VG Inozemtsev M .: Transport, 1987. - 207 p.

5. The mechanical part of the electric rolling stock / DK Minov - Moscow, 1959 - 384. p.

6. The theoretical basis for the design and operation of auto brakes. / V.M.Kazarinov, V.G. Inozemtsev, V.F.Yasentsev - Moscow: Transport, 1968, 400 p.

Claims (3)

1. Wear-resistant brake shoe with a high coefficient of friction for high-speed movement of the locomotive is a structure consisting of a continuous working surface and a solid ridge shaped groove, characterized in that N slots are made on the working surface of the shoe at a distance L from each other with a depth of H _cr at an angle α, allowing to reduce the complexity of determining the residual life of the pads and to ensure timely replacement, designed to reduce the wear rate of brake pads for Thu removal of wear of the friction zone and improving temperature operation (heat sink) and the wheel block. 2. Wear-resistant brake shoe with a high coefficient of friction for high-speed movement of a locomotive according to claim 1, characterized in that the continuous figured groove is replaced by three hooks, which reduce the force effect on the working surface of the wheel flange and the formation of thermal cracks. 3. A wear-resistant brake shoe with a high coefficient of friction for high-speed movement of a car is a structure consisting of a continuous working surface, characterized in that N cuts are made on the working surface of the shoe at a distance L from each other with a depth of H _cr at an angle α, which reduces the complexity determine the residual life of the pads and ensure its timely replacement, designed to reduce the wear rate of brake pads by removing wear products from the tren zone ia and improving the temperature regime of work (heat sink) pads and wheels.