It depends on the mode of failure. Possible materials with pros and cons are:-
1)Ultra High Molecular Weight Poly Ethylene. This is soft tough an slippery, but has a very low melting point. It is good for low load or low speed bearings in a hostile and dirty environment. It is ductile and has quite a lot of compliance for a plastic. It is very similar to the High Molecular Weight Polyethylene used in cutting boards
2) Acetal (Delrin, Celcon, Ultraform, Tenax etc). This makes a hard stable very high load bearing bearing. It does not tolerate dirt well due to its lack of ductility, and it only has a moderate melting point. It responds well to silicone oil and PTFE (Teflon, Fluon Hostaflon etc) additives. Silicone and PTFE are synergistic in their actions as additives to Acetal.
3) Polyurethanes have extremely good ductility, and moderate bearing properties. Probably not for this application.
4) Nylon 6.6 (Nylatron, Zytel, Ultramid, Vydene, Maranyl etc etc etc) Nylon 6.6 is used extensivly as barstock for the higher load or speed sector of the plastic bearing market, often graphite and Molibdimum DiSulphide filled. These molly filled nylon 6.6s are also used almost exclusivly as original equipment timeing chain guides and tensioners. Other Nylon options are Bronze filled nylon 12 and nylon 4.6 (Stanly). Nylon 4.6 gives generally 3 times t6he life of molly filled 6.6 in timeing chain tensioner applications as it has the same frictional properties, but substantially higher softening and melting points.
I would use Nylon 4.6 for this application, if "burning" or melting is the mode of failure.
Regards
pat
Please see FAQ731-376 for tips on how to make the best use of Eng-Tips Fora.