What factors affect the friction coefficient of brake shoes?

The friction coefficient of brake shoes is influenced by various factors,mainly including the following aspects:

Brake shoe material

Brake shoes made of different materials have different coefficients of friction.Generally speaking,the friction coefficient of composite brake shoes is relatively stable and varies little under different working conditions.The friction coefficient of cast iron brake shoes is influenced by factors such as alloy elements and graphite morphology in the material.For example,the friction coefficient of high phosphorus cast iron brake shoes is to some extent higher than that of ordinary cast iron brake shoes.

Braking speed

Usually,as the braking speed increases,the friction coefficient between the brake shoes and the wheels will decrease.This is because during high-speed braking,the contact time between the brake shoe and the wheel surface is shortened,and heat is generated rapidly,resulting in an increase in the temperature of the friction surface and a decrease in the friction coefficient.

brake pressure

The braking pressure has a significant impact on the friction coefficient.Within a certain range,as the brake pressure increases,the positive pressure between the brake shoe and the wheel increases,and the friction coefficient will also increase.But when the pressure exceeds a certain value,due to the deformation and wear of the brake shoe material,as well as the temperature rise of the friction surface,the friction coefficient may gradually decrease.

Friction surface temperature

An increase in the temperature of the friction surface will cause a change in the friction coefficient of the brake shoe.In general,when the temperature is low,the friction coefficient is relatively stable;When the temperature rises to a certain level,the friction coefficient will gradually decrease with the increase of temperature.This is because high temperatures can cause changes in the properties of brake shoe materials,such as resin softening in synthetic brake shoes and changes in the metallographic structure of cast iron brake shoes,which can affect friction performance.

Wheel tread condition

The roughness,hardness,and presence of oil and water stains on the surface of the wheel tread can all affect the friction coefficient of the brake shoe.When the tread roughness is moderate,it is conducive to the meshing between the brake shoe and the wheel,and the friction coefficient is relatively high;When the tread surface is too smooth or has oil or water stains,it will significantly reduce the friction coefficient.In addition,changes in the hardness of the wheel tread can also have a certain impact on the friction coefficient.

environmental condition

Environmental humidity and temperature have a certain impact on the friction coefficient of brake shoes.When the humidity is high,a layer of water film will form on the surface of the brake shoe and the wheel,providing lubrication and reducing the friction coefficient.The change in ambient temperature can also affect the performance of brake shoe materials,thereby affecting the friction coefficient,but this effect is relatively complex and related to the characteristics of brake shoe materials.