Material Analysis of Cam Bearings

Metal materials of cam bearing:

(1) The main alloy components of bearing alloys (also known as Babbitt alloys or white alloys) are tin, lead, antimony, and copper. Antimony and copper are used to improve the strength and hardness of the alloy. According to national standards, Babbitt alloys can be divided into two types: tin-based alloys and lead-based alloys. The strength and hardness of lead-based alloys are lower than those of tin-based alloys, and their corrosion resistance is also poor. Therefore, when using Babbitt alloy, tin-based alloy is usually used, and its commonly used grades are ZSnSb11Cu6, ZSnSb8Cu4, etc. Although the performance of lead-based alloys is not as good as that of tin-based alloys, it is still selected to be used under the required working conditions because it is more economical. Its commonly used grades are ZPbSb16Sn16Cu2 and so on. However, most of the bearing alloy elements have low melting points, so they are suitable for working conditions below 150 °C.

(2) Copper-based alloys have higher thermal conductivity and better wear resistance than steel. And the copper-based alloy has good machinability and lubricity, and its inner wall can be finished, and it is in contact with the smooth surface of the shaft. Copper-based alloys used as sliding bearing materials mainly include: brass with copper and antimony as the main components; bronze with copper and tin as the main components; and copper-lead alloys (also known as lead bronze). Copper-based alloys have high strength, good thermal conductivity and wear resistance, and allow higher operating temperatures than babbitt alloys, but are inferior to babbitt alloys in compliance, embedding and friction compatibility. The commonly used tin bronze containing tin and phosphorus is suitable for bearings with medium speed, heavy load or impact load; tin bronze containing tin, zinc and lead is suitable for medium speed and medium load bearings.

Non-metallic materials for cam bearings:

(1) PTFE: It has excellent self-lubricating properties and high thermal stability. Its friction coefficient is small, it does not absorb water, is not sticky, is not flammable, and can be used under the condition of -180~250°C. But there are also disadvantages such as large linear expansion coefficient, poor dimensional stability, and poor thermal conductivity. In order to improve its performance, it can be filled and strengthened with metal particles, fibers, graphite and inorganic substances.

(2) Graphite: It is a good self-lubricating material, and because it is easy to process and smoother with grinding, it is the preferred material for bearings. However, its mechanical properties are poor, and its impact resistance and load bearing capacity are poor, so it is only suitable for light load occasions. In order to improve its mechanical properties, some fusible metals with good wear resistance are often impregnated. The commonly used impregnation materials are Babbitt alloy, copper alloy and antimony alloy. Babbitt alloy-impregnated graphite bearing allowable temperature is 120~180°C, copper-impregnated graphite alloy-impregnated bearing allowable temperature is 300°C, antimony-impregnated alloy graphite bearing allowable operating temperature can reach 500°C.

(3) Rubber: It is a polymer made of elastomer, which has good elasticity and shock absorption. However, its thermal conductivity is poor, processing is difficult, the allowable operating temperature is below 65°C, and it needs circulating water to lubricate and cool continuously, so it is rarely used.

(4) Carbide: It has a series of excellent properties such as high hardness, wear resistance, good strength and toughness, heat resistance, corrosion resistance, etc. Therefore, the sliding bearing processed with it has high precision, stable operation, high hardness and good strength , durable, but expensive.

(5) Silicon carbide: It is a new type of artificially synthesized inorganic non-metallic material. The hardness is inferior to that of diamond. It has excellent chemical corrosion resistance, wear resistance, high temperature resistance, high mechanical strength, good self-lubricating performance, high temperature creep resistance, small friction factor, high thermal conductivity, and low thermal expansion coefficient. It can be widely used Used in petroleum, metallurgy, chemical industry, machinery, aerospace and nuclear energy and other fields, it is often used as the friction pair material of sliding bearings and mechanical seals. A large number of tests have shown that silicon carbide is the best material in the friction pair at present, especially the pressureless sintered SiC and hot-pressed sintered SiC have the best performance.