What are the common materials for bearings?
Bearing steel is used to make balls, rollers and bearing rings. Bearings are subjected to extreme pressure and friction during operation, so bearing steels are required to have high and uniform hardness and wear resistance, as well as high elastic limits. The requirements for the uniformity of the chemical composition of bearing steel, the content and distribution of non-metallic inclusions, and the distribution of carbides are very strict, and it is one of the most stringent steel types in all steel production.
Bearing steel material performance requirements
In order to meet the above requirements for the performance of dynamic bearings, the following basic performance requirements are proposed for bearing steel materials:
(1) High contact fatigue strength,
(2) After heat treatment, it should have high hardness or hardness that can meet the performance requirements of bearings,
(3) High wear resistance, low friction coefficient,
(4) High elastic limit,
(5) Good impact toughness and fracture toughness,
(6) Good dimensional stability,
(7) Good anti-rust performance,
(8) Good cold and hot processing performance.
Different materials for bearing
Bearing alloys are widely used. They usually come in two types: tin-based bearing alloys and lead-based bearing alloys. They have the characteristics of fast running-in and it is easy to make the surface very smooth. They are usually attached to the steel bearing base as a bearing lining. The babbitt alloy bearing has good adaptability, and has the characteristics of automatic adjustment for smaller misalignment or defective shafts. Because the appropriate amount of dust or foreign debris that enters the lubricant can be absorbed by this soft material to prevent the shaft from gluing and breaking, this embeddability makes them excellent bearing materials. The journal material can be mild steel, hard steel or cast iron.
Bronze bearings are suitable for low-speed and heavy-load applications where the shaft and bearings are neutral and can be made from a variety of alloy components to obtain various physical properties.
The bearing capacity of this kind of bearing is higher than that of bearing alloy, and its adaptability is poor, so it is used in occasions where the shaft has good rigidity and good neutrality.
Cast iron bearing materials are widely used in less stringent occasions. The hardness of the journal must be higher than the hardness of the bush. The working surface should be carefully run-in with a mixed gum of graphite and oil. It is required that the journal and the bearing must be well aligned.
First, the metal powder is sintered, and then immersed in oil to make a so-called “self-lubricating” or “porous” bearing. Bronze of various compositions is widely used in porous bearings, but less iron. Since the porous bearing has self-lubricating properties, it is mainly used in situations where it is difficult or impossible to obtain reliable lubrication when the general lubrication method is used.
Carbon and plastic
In high temperature occasions, or when traditional lubrication methods cannot be used, pure carbon bearings can achieve satisfactory results. Teflon is a very common plastic. The bearing made of it has a very low coefficient of friction, and is used in oil-free lubrication, it can work under low-speed or intermittent swing and heavy load conditions. Experiments have shown that some combinations of materials work well together, while others cannot. Material combinations that do not work well together will cause excessive wear.
Bearing alloy material performance requirements
Bearing alloy is used as the material of sliding bearing. The structure of the bearing alloy is that the hard phase particles are evenly distributed on the soft phase substrate, or the soft phase particles are evenly distributed on the hard phase substrate. Bearing alloys should have the following properties:
①Good wear resistance and wear reduction performance;
②Have a certain compressive strength and hardness, and have sufficient fatigue strength and bearing capacity;
③Good plasticity and impact toughness;
④ Has good anti-bite resistance;
⑥Good mosaic property;
⑦ Must have good thermal conductivity, corrosion resistance and small coefficient of thermal expansion.
The main alloy components of bearing alloys are tin, lead, bromine and copper. Gold and copper are used to improve the strength and hardness of the alloy. The representative composition (mass fraction) of tin-based babbitt alloy is: antimony 3% ~ 15%, copper 2% ~ 6%, cadmium <1%, tin balance.