Common used bearing materials and characteristics
Everyone knows about bearing materials. There are many types of market applications, and our common bearing materials include three types of metal materials, porous metal materials, and non-metal materials.
metallic material
Bearing alloys, bronze, aluminum-based alloys, zinc-based alloys, etc. are all made of metallic materials. Among them, bearing alloys, also known as white alloys, are mainly alloys of lead, tin, antimony or other metals. It can be of low strength under heavy load, high speed, etc. The reason is because of its characteristics, good wear resistance, high plasticity, good running performance, good thermal conductivity, good resistance to glue and good oil absorption. However, because of its relatively high price, when it is used, it must be cast on the bush of bronze, steel strip or cast iron to form a thinner coating.
(1) Bearing alloy (commonly known as Babbitt alloy or white alloy)
The bearing alloy is an alloy of tin, lead, antimony, and copper. It uses tin or lead as a matrix and contains hard grains of antimony tin (Sb-Sn) and copper tin (Cu-Sn). Hard grains play an anti-wear role, while soft matrix increases the plasticity of the material. The elastic modulus and elastic limit of the bearing alloy are very low. Among all the bearing materials, its embedment and friction compliance are the best, it is easy to run in with the journal, and it is not easy to bite with the journal. However, the strength of the bearing alloy is very low, and the bearing bush cannot be made separately, and can only be attached to the bronze, steel or cast iron bearing bush as the bearing lining. Bearing alloy is suitable for heavy load, medium and high speed occasions, the price is more expensive.
(2) Copper alloy
Copper alloy has higher strength, better friction reduction and wear resistance. Bronze is better than brass and is the most commonly used material. Bronze includes tin bronze, lead bronze and aluminum bronze, among which tin bronze has the best friction reduction and is widely used. However, tin bronze has higher hardness than bearing alloys, poor run-in and embeddability, and is suitable for heavy load and medium speed occasions. Lead bronze has strong anti-adhesion ability and is suitable for high-speed, heavy-duty bearings. Aluminum bronze has high strength and hardness, and poor anti-adhesion ability. It is suitable for low speed and heavy load bearings.
(3) Aluminum-based alloy
Aluminum-based bearing alloys have fairly good corrosion resistance and high fatigue strength, as well as good friction properties. These qualities have made aluminum-based alloys replace expensive bearing alloys and bronzes in some areas. Aluminum-based alloys can be made into single metal parts (such as bushings, bearings, etc.), or bimetal parts. The bimetallic bearing bush is made of aluminum-based alloy as the bearing lining and steel as the backing.
(4) Gray cast iron and wear-resistant cast iron
Ordinary gray iron or wear-resistant gray cast iron with nickel, chromium, titanium and other alloy components, or nodular cast iron can be used as bearing materials. The flake or spherical graphite in this kind of material can form a graphite layer for lubrication after covering on the surface of the material, so it has certain friction reduction and wear resistance. In addition, graphite can adsorb hydrocarbons, which helps to improve the boundary lubrication performance. Therefore, when gray cast iron is used as the bearing material, lubricating oil should be added. Due to the brittleness of cast iron and poor run-in, it is only suitable for occasions with light load and low speed and without impact load.
Non-metallic materials
The most widely used non-metallic materials are various plastics (polymer materials), such as phenolic resin, nylon, and polytetrafluoroethylene. The characteristics of the polymer are: it does not react with many chemical substances, and its corrosion resistance is particularly strong; it has a certain self-lubricity, can work under no lubrication conditions, and has a certain lubricating ability under high temperature conditions; good embedment; Friction and wear resistance are better.
When choosing a polymer as the bearing material, you must pay attention to the following problems: Since the thermal conductivity of the polymer is only a few percent of that of steel, the dissipation of frictional heat must be considered. It strictly limits the working speed of the polymer bearing and Pressure value. Because the linear expansion coefficient of the polymer is much larger than that of steel, the gap between the polymer bearing and the steel journal should be larger than the gap between the metal bearings. In addition, the strength and yield limit of polymer materials are low, so the load that can be withstood during assembly and work is limited. And because the polymer material will creep under normal temperature conditions, it is not suitable for making bearings with strict clearance requirements.
Carbon-graphite can be used as a bearing material in a bad environment. The more graphite content, the softer the material and the smaller the friction coefficient. Metal, polytetrafluoroethylene or molybdenum disulfide components can be added to the carbon-graphite material, and liquid lubricants can also be impregnated. Carbon-graphite bearings are self-lubricating, and their self-lubricating and anti-friction properties depend on the amount of water vapor adsorbed. Carbon-graphite and lubricants containing hydrocarbons have an affinity, and the addition of lubricants can help improve their boundary lubrication properties. In addition, it can also be used as a bearing material for water lubrication.
Rubber is mainly used for water as a lubricant and the environment is dirty.
Wood has a porous structure, and fillers can be used to improve its performance. Filled polymer can improve the dimensional stability of wood and reduce moisture absorption, and improve strength. Bearings made of wood can work under extremely dusty conditions.
Porous metal material
This is a bearing material made by pressing and sintering different metal powders. This material is porous, with pores accounting for about 10% to 35% of the volume. Before use, the bearing pad is immersed in hot oil for several hours to fill the pores with lubricating oil, so the bearing made of this material is usually called an oil bearing.
It is self-lubricating. When working, due to the suction effect of the rotation of the journal and the expansion of the oil when the bearing heats up, the oil enters the friction surface for lubrication; when not working, the oil is sucked back into the bearing due to the capillary action, so For a long time, it can work well even without lubricating oil. If the oil is supplied regularly, the effect is better. However, due to its low toughness, it is suitable for stable and no impact load and low and medium speed conditions. Commonly used are porous iron and porous bronze. Porous iron is commonly used to make milling machine bushings, machine tool oil pump bushings, internal combustion engine camshaft bushings, etc. many
Porous bronze is commonly used to make bearings for record players, electric fans, textile machinery and automobile generators. China already has a factory specializing in the manufacture of oil-bearing bearings, which can be selected according to the design manual when needed.
Powder metallurgy material is porous metal is a kind of powder material, it has a porous structure, if it is immersed in lubricating oil, so that the pores are filled with lubricating oil, it becomes an oil bearing, with self-lubricating properties. The porous metal material has a low toughness and is only suitable for stable, non-impact loads and medium and small speeds.
