Brake Shoe

The brake shoe contacts the wheel tread and generates friction, converting the train's kinetic energy into heat energy and dissipating it into the atmosphere, achieving the purpose of slowing down or stopping the train. Brake shoes can be divided into two categories according to their materials: cast iron brake shoes and synthetic brake shoes.

Composite brake shoe history

Synthetic brake shoes, also known as non-metallic brake shoes, are made by hot pressing asbestos and other fillers mixed with resin or rubber as adhesives. Synthetic brake shoes should also be reinforced with steel backs. If the brake shoe is pressed into a sheet for disc brakes, it is called a brake pad. Synthetic brake shoes were first used on London Underground vehicles in 1907.

Since the 1950s, their application has become increasingly common. Synthetic brake shoes are light in weight, wear-resistant, and basically spark-free when braking. The friction coefficient between them and the steel wheel changes little with increasing speed, and is basically consistent with the change in the braking adhesion coefficient between the wheel and the rail, so that the adhesion effect can be better utilized to improve braking performance and shorten the parking brake distance. Synthetic brake shoes are divided into high friction coefficient and low friction coefficient. The friction coefficient of high friction coefficient synthetic brake shoes is about twice that of cast iron brake shoes. Smaller diameter brake cylinders and auxiliary air cylinders can be used, thereby reducing the weight of the basic braking device and saving compressed air. It has many advantages. Low friction coefficient synthetic brake shoes can directly replace cast iron brake shoes and are suitable for the reconstruction of old vehicles. The disadvantage of synthetic brake shoes is that they have poor thermal conductivity. The heat generated by friction increases the temperature of the wheel tread, and even causes local high temperature on the tread, resulting in thermal cracking. In recent years, in order to avoid environmental pollution, synthetic brake shoes without asbestos, lead and other harmful substances have been increasingly adopted.

Cast Iron brake shoe history

Cast iron brake shoes. It has been used for more than 100 years. In the early days, it was gray cast iron brake shoes with a phosphorus content of about 0.2%. The friction coefficient dropped rapidly with the increase of speed, and the wear resistance was also very poor. Switching to medium-phosphorus brake shoes (phosphorus content of 0.7% to 1.0%) can improve performance, but it is easy to generate sparks and cause fires during braking. High-phosphorus brake shoes (phosphorus content of more than 2.5%) produce fewer sparks and are safer, but they are brittle and easy to break, and steel tile backs must be added during casting. The use of high-phosphorus cast iron brake shoes is becoming more and more common.