When the speed reducer brakes the rolling stock, countless high-pressure lubrication areas will be formed between the frictional contact surface of the brake rail and the wheel, and the contact surfaces will be forced to separate under the action of high pressure. At this time, friction cannot be directly generated between the surfaces of the friction pair, but friction between the lubricating films, which causes the friction coefficient μ to drop sharply (less than 1/5 of the original value), resulting in a sharp drop in the braking force of the reducer, or even loss. Make the braked vehicle exceed the constant speed control accuracy range of the control system at the exit of the reducer, resulting in overspeed connection.
The compressive elastic modulus of composite materials is 2 to 3 orders of magnitude smaller than that of steel rails, which can significantly increase the friction contact area between the wheel and the brake beam; the thermal conductivity of composite materials is 2 orders of magnitude lower than that of steel, which can make the surface fluid film heated. The viscosity decreases and the lubrication effect is reduced. The composite material can contain various types of fibers and granular fillers, which are mixed between the surface fluids after falling off, showing a certain abrasive wear and adhesive wear state, increasing the friction coefficient; the composite material can make the medium from the fluid lubrication state to the boundary lubrication state Transition destroys the high-pressure fluid between the friction interfaces and keeps the friction braking force stable or reduces less; the stability of the friction coefficient of the composite material is better.
The flash from the rolling process of the wheel will cut the composite material, resulting in a shorter service life of the composite brake pad. In contrast, metal materials have high hardness and good cutting resistance, and the anti-overspeed performance of the reducer can be significantly improved by adjusting the composition, organization, and structure of the metal material.
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Link to this article：Discussion on the Life of Composite Materials in Wheel Braking
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