PTFE is used in bearings due to its extremely low friction and inherent lubricity (Fig.) Compounded with graphite, bronze powder, or other fillers to reduce creep and improve wear resistance, PTFE is molded or machined into bearings for unlubricated service. PTFE offers unusual performance in bearings because its static coefficient of friction is lower than its dynamic coefficient.
Example of PTFE bridge bearing:
Therefore, PTFE bearings do not exhibit “stick-slip”; the jerking action that occurs in overcoming a higher static coefficient before movement begins. In motion against a PTFE surface, a metal component causes fairly rapid initial wear. After a time, the rate of wear diminishes. That is because PTFE transfers to the metal surface so that the contact is PTFE against PTFE, a combination that produces little wear. Bearings of PTFE usually require the added support of metal structures because PTFE lacks mechanical strength and stiffness. Compared with metal bearings, PTFE bearings are suitable only for relative low loads and velocities.
PTFE bearings are used in instruments, aircraft and aerospace vehicles control systems, office machines, and other applications where lubrication is difficult or undesirable. Slide bearings called bearing pads are used in support systems for bridges and some buildings to accommodate thermal and seismic movement without damage to the structures they support. Compared with similar elastomeric supports, they allow greater range of movement, and compared with lubricated metal bearings, PTFE bearing pads require no lubrication and are highly resistant to moisture and chemical attack. Designs often have stainless steel plates riding against a PTFE sheet surface. As for other bearings, the PTFE is usually compounded to improve creep performance.