Bearings are very important machine elements that we use in the mechanical design of different structures. They are very important dynamic elements for power transmission and motion transmission. So, in the design of bearings, a dynamic approach is very important. Because of that, we need to select the proper material for bearings. Here, you will see the general types of bearing materials in detail. Among these materials we mention, are plastic bearings, metal bearings, and ceramic bearings.
What are the General Types of Bearing Materials?
There is a wide variety of bearing materials that they use in the machines. But the use of metallic materials is more common in bearing applications if we compare it with other materials. So, it will be better to separate the bearing materials into metallic bearing materials and nonmetallic bearing materials.
Metallic Bearing Materials
There are different kinds of metals and metal alloys for different types of applications. Metals, especially steels are very good both for structural and dynamical applications. They withstand both dynamic loads and static loads. This is the biggest advantage of metals in bearing materials.
Steels
Carbon steels without chrome contents in them are one of the cheapest bearing materials. Carbon content in steels can be up to 2.1% and with the increasing amount of carbon, the hardness increases but the ductility decreases. Also with the increasing amount of carbon content, the bearing speed increases, and load-carrying capacity increases.
In general, carbon steel bearings are used in the bike wheels and wheels of shopping charts.
Chrome content in the steel provides very high resistance to chemical reactions and chemical attacks. High load-carrying capacity is one of the biggest advantages of chrome steel.
Stainless steels are also very common as a bearing material. They are very resistant to corrosion and chemical attacks.
The most important drawback of the steel applications is the very high requirement for lubrication and very heavy construction.
Tin-Lead Alloys as Bearing Materials
Tin-lead alloys are very common in bearing applications. In general, these alloys are used in lubricated bearings.
Tin-lead alloys generally have low load-carrying capacities. But if there are good backing materials such as cast irons or steels, the load-carrying capacity of the tin-lead alloys will be better.
The temperature has a significant effect on the mechanical characteristics of tin-lead alloys. Also, increasing or decreasing the alloying elements in tin-lead alloys may have significant effects. For example with the increasing alloying elements such as copper or antimony, the hardness and tensile strength of the tin-lead alloys increase but the ductility decreases.
So, the use of tin-lead alloys is very common because of these properties in bearing lining applications.
Copper-Lead Alloys
In the bearing applications, they use these materials in heavy-duty applications. Also, the fatigue resistances of copper-lead alloys are superior if we compare them to other materials. The lead content in the copper-lead alloys provides very good bearing surfaces. So, the frictions between the bearing surfaces are very low. But the corrosion resistance decreases with the increasing amount of lead.
Copper lead alloys are very common in the lining applications of steel-backed bearings. The general alloying elements in copper-lead alloys are tin, lead, and aluminum.
Bronzes
Bronzes are copper-tin alloys that they extensively use in bearing applications. They have very good structural properties that we use in bearing applications without backing materials. Also, they use lead content in bronzes to obtain better mechanical properties. Load carrying capacity and fatigue resistances are increased with the lead content. In the bearing applications of pumps, diesel engines, and train cars, we use bronze materials generally.
Also, designers use tin content in bronzes up to 20% to obtain heavy-duty applications.
Non-Metallic Bearing Materials
Also, there are other types of materials in the bearing applications. Among these materials, they use polymers, ceramics, and other materials. Let’s take a look at the other bearing materials.
Use of Polymers in Bearings
The biggest advantage of polymer materials in bearing applications is the very low frictions. Because of this property, there is no lubrication requirement for plastic bearings.
The most important polymers in bearing applications are; nylon and Teflon. They have very good low friction capabilities to use in bearing applications.
The most important drawback of polymers in bearing applications is the low mechanical properties compared with metals. We use polymer-based bearings in low loads. Because the mechanical strength of these materials is low. Also, they are suitable for low-speed bearing applications.
Nylons
The main advantage of nylon is its good abrasion resistance which is very important for bearing applications. Also, a good wear rate and good embed abilities make the nylon polymer is very useful material in bearing applications. In addition to these properties, nylon has a creep disadvantage under loads.
The most important application of nylon bearings is the kitchenware where low loads on the stage.
Teflon
The most important characteristic of Teflon is the resistance to chemical attacks and we can use Teflon materials up to very high temperatures. But the most important disadvantages of Teflon are low stiffness, very high thermal expansion coefficient, and poor wear resistance. These disadvantages of Teflon can be eliminated with the addition of glass, ceramics, and metal powders.
Phenolics
Phenolics are the thermoseting polymers that they use in bearing applications. We use phenolic resin sheets and bronze journals to obtain good resistance to wear. The most important drawback of phenolics in bearing applications is the low capability of dissipating the heat rise. Because of this reason, they tend to fail due to the heat rise in bearing frictions.
Use of Ceramics as Bearing Materials
The most important example of ceramics is graphite. The use of graphite material in bearing applications is very common. This is because of the very good low-friction capability of graphite. Also graphite material is very resistant to high temperatures and chemical attacks.
With the use of graphites, very low viscosities of lubricants can be used. But we need to use them in low-speed applications.
The most important applications of graphite as bearing applications; are pump shaft bearings, propeller rings of centrifugal pumps, and other pump bearing applications. In general, they use graphite lining with steel backings.
Conclusion
Bearings has very common application areas in machinery and mechanical engineering. Because of this reason, they use a wide range of materials in the design of bearing materials. For different kinds of applications, we use different kinds of bearing materials.
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