Characteristics And Applications Of Commonly Used Bearing Materials

We all know that there are many types of bearing materials in the market, and our common bearing materials are divided into three categories: metal materials, porous metal materials, and non-metal materials.

Metallic material

Bearing alloys, bronze, aluminum-based alloys, zinc-based alloys, etc. are all considered metal materials. Among them, bearing alloys, also known as white alloys, are mainly alloys of lead, tin, antimony or other metals, which can have low strength under heavy load, high speed, etc. The reason is because of its characteristics, good wear resistance, high plasticity, good running-in performance, good thermal conductivity, good glue resistance and good adsorption with oil. However, because it is more expensive, it must be cast on the bearing bush of bronze, steel strip or cast iron to form a thinner coating when it is used.

(1) Bearing alloy (commonly known as babbitt or white metal)

The bearing alloy is an alloy of tin, lead, antimony and copper. It uses tin or lead as the matrix and contains hard grains of antimony tin (Sb-Sn) and copper tin (Cu-Sn). The hard grains play an anti-wear effect, and the soft matrix increases the plasticity of the material. The elastic modulus and elastic limit of the bearing alloy are very low. Among all bearing materials, its embedment and frictional compliance are the best, it is easy to run in with the journal, and it is not easy to stick to the journal. However, the strength of the bearing alloy is very low, and the bearing pad cannot be made alone. It can only be attached to the bronze, steel or cast iron bearing pad as a bearing lining. Bearing alloys are suitable for heavy loads, medium and high speeds, and are expensive.

(2) Copper alloy

Copper alloys have higher strength, better friction reduction and wear resistance. Bronze performs 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 running-in and embedment, and is suitable for heavy-duty and medium-speed occasions. Lead bronze has strong anti-adhesion ability and is suitable for high-speed and heavy-duty bearings. Aluminum bronze has high strength and hardness, and poor anti-adhesion ability, which is suitable for low-speed and heavy-duty bearings.

(3) Aluminum base alloy

Aluminum-based bearing alloys have fairly good corrosion resistance, high fatigue strength, and good friction properties. These qualities have enabled aluminum-based alloys to replace more expensive bearing alloys and bronze in some areas. Aluminum-based alloys can be made into single-metal parts (such as bushings, bearings, etc.), and can also be made into bimetallic parts. Bimetallic bearing bushes use aluminum-based alloys as bearing linings and steel as 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 ductile iron, can be used as bearing materials. After the flake or spherical graphite in this type of material is covered on the surface of the material, it can form a layer of graphite that acts as a lubricating layer, so it has certain anti-friction and wear resistance. In addition, graphite can adsorb hydrocarbons and help 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 and poor running-in properties of cast iron, it is only suitable for occasions with light load, low speed and no impact load.

Non-metallic material

The most widely used non-metallic materials are various plastics (polymer materials), such as phenolic resin, nylon, polytetrafluoroethylene, etc. The characteristics of the polymer are: it does not react with many chemical substances, and the corrosion resistance is particularly strong; it has a certain self-lubricating property, can work under non-lubricated conditions, and has a certain lubricating ability under high temperature conditions; good embedment; Friction and wear resistance are relatively good.

When selecting polymers as bearing materials, the following issues must be paid attention to: Since the thermal conductivity of polymers is only a few percent of that of steel, the dissipation of frictional heat must be considered, which strictly limits the working speed and speed of polymer bearings. Pressure value. Because the coefficient of linear expansion of polymer is much larger than that of steel, the gap between the polymer bearing and the steel journal should be larger than that of the metal bearing. In addition, polymer materials have low strength and yield limits, so they can withstand limited loads during assembly and operation. 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 adverse environments. The more graphite content, the softer the material and the smaller the friction coefficient. Metal, PTFE 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 friction-reducing properties depend on the amount of water vapor adsorbed. Carbon-graphite has an affinity with lubricants containing hydrocarbons, and adding lubricants helps to improve its boundary lubrication performance. In addition, it can also be used as a water-lubricated bearing material.

Rubber is mainly used in places where water is used as a lubricant and the environment is dirty.

Wood has a porous structure and fillers can be used to improve its properties. Filled polymers can improve the dimensional stability of wood and reduce moisture absorption, and increase strength. Bearings made of wood to work in extremely dusty conditions.

Porous metal material

This is a bearing material made of different metal powders by pressing and sintering. This material has a porous structure, with pores accounting for about 10% to 35% of the volume. Before use, the bearing bush is immersed in hot oil for several hours, so that the pores are filled 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 journal rotation and the expansion effect of the oil when the bearing heats up, the oil enters the friction surfaces to play a lubricating role; For a long time, it can work well even without lubricating oil. It works better if it is supplied with oil on a regular basis. However, due to its low toughness, it is suitable for stable non-impact loads and low and medium speeds. Commonly used are porous iron and porous bronze. Porous iron is often used to make mill bushings, machine tool oil pump bushings, internal combustion engine camshaft bushings, etc. Porous bronze is often used to make the bearings of record players, electric fans, textile machinery and automobile generators. There are factories specializing in the manufacture of oil-impregnated bearings in my country, which can be selected according to the design manual when necessary.

Powder metallurgy material is porous metal is a kind of powder material, it has a porous structure, if it is immersed in lubricating oil, the micropores are filled with lubricating oil, and it becomes an oil-impregnated bearing with self-lubricating properties. Porous metal materials have low toughness and are only suitable for stable non-impact loads and medium and small speeds.