Plastic bearings are very popular for use on metal surfaces. Plastics offer many advantages over other common bearing materials. Plastics are extremely corrosive resistant and most are chemically resistant. Plastic bearings do not transfer heat to other areas of the mechanical assembly. Many plastics are even self-lubricating and therefore eliminate the possibility of failures from lack of maintenance.
Although many different types of plastics have properties which make them suitable for bearing applications, the most commonly used are phenolics, acetals, Teflon (PTFE), ultra high molecular weight polyethylene (UHMWPE), and nylon. The major limitations involved in the use of plastics have to do with high temperatures and possible cold flow under heavy loads.
1) Phenolics: The compatibility of the phenolics makes them easily lubricated by various fluids. They have replaced metal bearings in such applications as propeller and rubber-shaft bearings in ships and electrical switch-gear, rolling-mill, and water-turbine bearings. In small instruments and clock motors, laminated phenolics serve as structural members as well as a bearing material. They have excellent strength and shock resistance coupled with resistance to water, acid, and alkali solutions. Phenolic plastic bearings work well in heavily loaded systems provided sufficient clearance and cooling is provided.
2) Nylon: Although the phenolics have predominated in heavy-duty applications, they are frequently replaced by nylon, which has the widest use in plastic bearings. Nylon bushings exhibit low friction and require no lubrication. Nylon is quiet in operation, resists abrasion, wears at a low rate, and is easily molded, cast, or machined to close tolerances. Improvement in mechanical properties, rigidity, and wear resistance is obtained by adding fillers such as graphite and molybdenum disulfide to nylon. While the maximum recommended continuous service temperature for ordinary nylon is 170°F, and 250°F for heat-stabilized compositions, filled-nylon parts resist distortion at temperatures up to 300°F. As mentioned in some of our other posts, nylon is also very inexpensive.
3) Teflon (PTFE): Teflon is a great material for bearings for several reasons. It has an exceptionally low coefficient of friction and high self-lubricating characteristics, immunity to almost all types of chemical attack, and ability to operate over an extremely wide temperature range (-330 to 360°F continuous, to 550°F short-term). PTFE’s load capacity depends on construction and reinforcing material. PTFE is a great choice for applications that include exposure to weather, chemicals, or vapors which can attack metals, lubricants, and some plastics. Teflon bearings are also ideal for applications like sluice gates that involve the need to operate smoothly, reliably, and without sticking after prolonged idle periods. Other applications for PTFE include those with low rpm, oscillatory or intermittent service, or where reliable service without lubrication is vital. The major drawback to using Teflon is that the cost of PTFE is high relative to plain metal or other resins.
4) Acetal (Delrin): Delrin is a popular material for inexpensive bearings in a wide variety of automotive, appliance, and industrial applications. Delrin is particularly useful in wet environments because of its stability and resistance to wet abrasion.
5) Ultrahigh-molecular-weight polyethylene (UHMWPE): UHMWPE bearings resist abrasion and have a smooth, low-friction surface. UHMWPE is often an ideal replacement material for parts typically made from acetal, nylon, or PTFE materials.
5 not enough? Here’s a few more!
Polyimide, polysulfone, polyphenylene sulfide: These are high-temperature materials with excellent resistance to both chemical attack and burning. With suitable fillers, these moldable plastics are useful for PV factors to 20,000 to 30,000. Polyimide molding compounds employing graphite as a self-lubricating filler show promise in bearing, seal, and piston ring applications at temperatures to 500°F.
What materials do you prefer for bearings? Let us know in the comment section below!
Need more information on engineering plastics? Check out our High Performance Plastics Material Guide!