Brake pads are called brake shoes in railway terminology. The brake shoes are located on the tread of the wheels. When braking is required, the two brake shoes at the front and rear of the wheels clamp the wheels together through the action of a brake lever, achieving the purpose of parking. During the operation of a train, braking is required. Friction is generated when the train comes into contact with the wheel tread, converting the train's kinetic energy into thermal energy and dissipating it into the atmosphere. The braking components that directly rub against the wheels to stop the train are the brake shoes. A tile shaped brake pad made of cast iron or other materials, which holds the wheel tread tightly during braking and stops the wheel from rotating through friction. Brake shoes can be divided into two types based on their materials: cast iron brake shoes and synthetic brake shoes.
Composite brake shoes. Also known as non-metallic brake shoes, they are made by hot pressing asbestos and other fillers mixed with resin or rubber as adhesive. Synthetic brake shoes also need to be reinforced with steel backs. If the brake shoe is pressed into a sheet shape for disc braking, it is called a brake pad. Synthetic brake shoes were first used on London Underground vehicles in 1907. Since the 1950s, applications have become increasingly common. Synthetic brake shoes are lightweight, wear-resistant, and have almost no sparks during braking. The variation of the friction coefficient between it and the steel wheel with increasing speed is small, which is basically consistent with the variation of the braking adhesion coefficient between the wheel and rail. Therefore, it can better utilize the adhesion effect, improve braking performance, and shorten the parking braking distance. Synthetic brake shoes can be classified into high friction coefficient and low friction coefficient. The friction coefficient of high friction coefficient composite brake shoes is about twice that of cast iron brake shoes, and smaller diameter brake cylinders and auxiliary air cylinders can be used to reduce the weight of the basic braking device and save compressed air, with many advantages. Low friction coefficient synthetic brake shoes can directly replace cast iron brake shoes and are suitable for retrofitting old cars. The disadvantage of synthetic brake shoes is poor thermal conductivity, and the heat generated by friction increases the temperature of the wheel tread, even causing local high temperatures on the tread and leading to thermal cracking. In recent years, synthetic brake shoes free of harmful substances such as asbestos and lead have been increasingly adopted to avoid environmental pollution. So how does it actually work?
The principle of train brake shoe braking: During the braking process of a train, the braking device needs to convert enormous kinetic energy into thermal energy and dissipate it into the atmosphere. The quality of this braking effect mainly depends on the ability to dissipate frictional heat energy. When using this braking method, the friction area of the brake shoes is small, and most of the heat load is borne by the wheels. The higher the train speed, the greater the thermal load on the wheels during braking. If cast iron brake shoes are used, the temperature can melt the brake shoes; Even with advanced synthetic brake shoes, the temperature can reach up to 400-450 ℃. When the temperature of the wheel tread increases to a certain extent, it will cause wear, cracking or peeling of the tread, which not only affects the service life but also affects driving safety. It can be seen that traditional tread brake shoes cannot meet the needs of high-speed trains.
