In many products, plastic bearing surfaces are used on metal contact surfaces. Plastic bushings are resistant to corrosion and attack by many chemicals, and do not transfer heat to other areas of the mechanical assembly. Some plastics can be self-lubricating, therefore reducing failures due to a lack of maintenance.
Plastics commonly used as bushings include: Polyoxymethylene (POM) such as DuPont Delrin, Nylon, Acetal, Ultra High Molecular Weight Polyethylene (UHMWPE), and PPS (Polyphenylene Sulfide). It is important to understand the limitations of plastics for use as bearings including the maximum loading, maximum surface speed, and maximum service temperature. For applications such as vehicles, ATVs, motor cycles, etc. it is important to look at the engineering specs for the materials to be used and satisfy yourself that they will be safe for your application.
For general hobby projects where failure of a bushing will not result in injury or death, here are some suggestions to test:
Polyoxymethylene (POM) such as DuPont Delrin is used for inexpensive bearings in a wide variety of automotive, appliance, and industrial applications. It is useful in wet environments because it resists wet abrasion well and is stable.
Nylon is another good choice for bearings because they are quite abrasion resistant, wear slowly, and are easily molded or machined to tight tolerances. Nylon can be used in applications up to 170°F, but by adding lubricating solids such as graphite and/or molybdenum disulfide, Nylon to be used up to approximately 275°F.
Ultra High Molecular Weight Polyethylene (UHMWPE) is a low cost, easily moldable and machinable plastic that resists abrasion, provides a smooth, low-friction surface, and is often used as a replacement for Acetal, Nylon, or PTFE materials.
Acetal is an ideal choice for many industrial applications due to its mechanical properties and fatigue endurance, high tensile strength, creep resistance, low moisture absorption, chemical resistance to hydrocarbons, solvents & neutral chemicals, ease of machining, temperature range (air): -50°F to 180°F, and it meets FDA standards for contact with food.
PPS (Polyphenylene Sulfide) is an amazing semi-crystalline engineering thermoplastic that is useful for many applications. It has the best resistance to chemicals of any advanced engineering plastic! There are no known solvents that affect PPS under 392ºF and it is inert to steam, strong bases, fuels, and acids. It is ideal for precise tolerance machined components because it has minimal water absorption, has a very low coefficient of linear thermal expansion, and is stress-relieving manufactured. PPS is also a great option for structural applications, corrosive environments, and a lower temperature replacement for Polyether ether ketone (PEEK). At moderate temperatures, PPS offers great dimensional stability and strength.