Silicon nitride products have high mechanical strength, and the friction coefficient of silicon nitride ceramics is small. Under the conditions of high temperature and high speed, the increase of friction coefficient is also small, so it can ensure the normal operation of the mechanism. This is its outstanding advantage. When silicon nitride ceramics begin to grind, the sliding friction coefficient reaches 1.0 to 1.5. After precision running in, the friction coefficient decreases greatly, Kept below 0.5, silicon nitride ceramics are considered to be self-lubricating materials. The main reason for this self-lubricating property, which is different from graphite, boron nitride and talc, lies in the scale layered structure of the material structure. Under the action of pressure, the friction surface decomposes slightly to form a thin gas film, so as to reduce the sliding resistance between the friction surfaces and increase the smoothness of the friction surface. In this way, the greater the friction, the smaller the resistance, and the wear amount is particularly small. After continuous friction, most materials tend to gradually increase the friction coefficient due to surface wear or softening due to temperature rise. In terms of machinability, silicon nitride ceramics can achieve the required shape, accuracy and surface finish by machining.