The large and small bushes (bearing bushes) play the role of cooling the bearings and ensuring liquid lubrication in the engine. When the sliding bearing is working, a thin layer of oil film is required between the bearing bush and the rotating shaft for lubrication. If the lubrication is poor, there will be direct friction between the bearing bush and the rotating shaft, and the friction will generate very high temperatures. Although the bearing bush is made of a special high-temperature resistant alloy material, the high temperature generated by direct friction is still enough to burn it out.
Thick-walled bearing bushes can be cast. In order to improve friction performance, a layer of bearing alloy (called a bearing lining) can be cast on the inner surface of the bearing bush. In order to make the bearing alloy and the bearing bush adhere well, various forms of tenons, grooves or threads are often made on the inner surface of the bearing bush. Thin-walled bearing bushes can be mass-produced using bimetal plate continuous rolling and other processes. Powder metallurgy mixes basic materials such as powdered iron or copper with graphite, then presses and sinters them into shape. Its pores can store lubricating oil.
Extended information
Bearing materials mainly include polymers, carbon graphite and special ceramics:
1. Polymers
Polymers have the characteristics of light weight, insulation, friction reduction, wear resistance, self-lubrication, corrosion resistance, simple molding process, and high production efficiency. Compared with metal materials, their tribological properties are sensitive to ambient temperature and humidity, and have significant viscoelastic properties, so the gap between the bearing bush and the journal is larger. In addition, due to its low mechanical strength, small elastic modulus, and poor adsorption of lubricating oil, the working speed and pressure value of the bearing are limited.
2. Carbon-graphite
Carbon-graphite material bearings can be used in harsh environments. The more graphite content, the softer the material and the smaller the friction coefficient.
Carbon graphite generally has good electrical conductivity, heat resistance, wear resistance, self-lubrication, good high temperature stability, strong chemical corrosion resistance, higher thermal conductivity than polymers, and small linear expansion coefficient. The friction coefficient and wear rate with chrome-plated surfaces are very low under atmospheric and room temperature conditions.
3. Ceramics
Ceramics are made from inorganic non-metallic natural minerals or artificial compounds as raw materials, which are crushed, shaped and sintered at high temperatures. They are composed of countless inorganic non-metallic small crystals and Non-metallic materials composed of glass phase.
Traditional ceramics are made from inorganic non-metallic natural minerals, such as clay, feldspar, quartz, etc.; special ceramics are made from artificial compounds. Ceramics used in mechanical engineering are generally special ceramics made from man-made compounds such as aluminum oxide, magnesium oxide, zirconium oxide, lead oxide, titanium oxide, silicon carbide, boron carbide, silicon nitride, boron nitride, etc.