The characteristics of the bearing material are: small friction coefficient, sufficient fatigue strength, good running-in and good corrosion resistance. Commonly used bearing materials include bearing alloy (Babbitt alloy), copper alloy, powder metallurgy, gray cast iron and wear-resistant cast iron.
There are three main categories of non-lubricated bearing bush materials: polymer, carbon graphite and special ceramics.
1. Polymers
Polymers are also called organic polymer materials and engineering plastics. Commonly used materials include phenolic resin, nylon, polytetrafluoroethylene (PTFE), etc. Non-lubricated bearings made of plastic (such as PTFE) can resist strong acids and weak alkali, and have good embedded type, wear reduction and wear resistance. Stamping polytetrafluoroethylene sheets into lip seals, bearing bushes, piston rings and gaskets are used in equipment such as belt conveyors, typewriters, sewing machines, record players, water pumps, textile machinery and agricultural machinery.
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. Its moisturizing and anti-wear properties depend on the amount of adsorbed water vapor, but it loses its lubricity when the humidity is very low. Applying a wear-resistant coating can improve the wear resistance of carbon graphite. Carbon-graphite can also be used as a water-lubricated bearing material.
Graphite can not only be used as a solid lubricant, but can also be added to resins, metals, ceramics and other materials to increase the friction reducing properties of these materials. It can also be used directly as friction material, such as papermaking, wood processing, etc. Bearings, high-temperature sliding bearings, sealing rings, piston rings, scrapers, etc. used in oil-free places such as textiles and food. The "class" symbol of carbon graphite materials used in mechanical engineering is M, and there are 4 series: carbon graphite materials, electrochemical graphite materials, resin carbon composite materials and metal graphite materials.
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.
The performance of ceramics is largely determined by their microstructure, including grain size and distribution, the composition and content of the glass phase, and the nature, content and distribution of impurities. The microstructure is determined by raw materials, composition and manufacturing process. The unique characteristics of ceramics are high hardness and compressive strength, high temperature resistance, wear resistance, oxidation resistance, corrosion resistance, brittleness, impact resistance and no ductility.
Ceramic is a newer bearing material for non-lubricated bearings, especially SiC and Si3N4. Their strength, heat resistance and corrosion resistance are very good, and their tribological properties are also very good.