At present, asbestos material is widely used as automobile brake pad. Although its load-bearing capacity is not as good as that of powder metallurgy materials, its friction coefficient is higher and its dynamic and static friction coefficients are close to each other, which can make braking smooth, noise low and the price low. The application of powder metallurgy friction materials has been found in almost all fields except automobiles. It can work normally under high load and high temperature, especially with stable friction coefficient and good wear resistance. Therefore, it is used as brake pad for aircraft landing, ball screw friction pad for heavy load and clutch pad for motor mechanism. In transport machinery such as automobiles, ships and trains, in bulldozers, mine lifts, excavators and tractors, large and medium-sized construction machinery, agricultural machinery and light industrial machinery, various specifications and types of powder metallurgy friction pads and brake pads can not only perform excellent clutching and braking functions, but also reduce energy consumption and improve transmission accuracy. With the development of modern science and technology, the demand for high performance friction materials is more urgent.
Carbon-carbon composites, which appeared in the late 1970s, are promising friction materials. They have stable high temperature friction properties, long life and light weight. Now they have been successfully used in the braking devices of Concorde and Boeing aircraft, but they are expensive and affect the widespread application. Graphite-based friction materials with good properties under medium load, low temperature and wet friction conditions are also promising new materials. It has almost all the advantages of asbestos and powder metallurgy materials at present, and its price is cheap. It is an ideal friction material.