Non-lubricated friction of polybutylene terephthalate (PBT) sliding against polyoxymethylene (POM)

The purpose of this work is to study dry sliding frictional properties of a polymer pair consisting of two commonly used engineering polymers: polybutylene terephthalate (PBT) blended with PTFE and polyoxymethylene (POM). A reciprocating pin-on-flat tribometer was employed to measure the maximum initial and dynamic friction coefficients (COF). All the specimens were used as obtained from injection molding, without any abrasive pretreatment. A sufficient repeatability of the results was achieved by using a PBT pin with a spherical tip. The influence of the applied load (1, 5, 10 and 20 N) and the sliding speed (10, 30 and 50 mm/s) on the frictional performance of PBT+PTFE pin sliding against POM was examined. Frictional heating was measured with an infrared camera and the obtained temperature rises were compared with the values predicted by three analytical frictional heating models. The results showed that both the maximum initial and dynamic friction coefficients were strongly affected by the applied load. Up to 50% reduction in the values of COFs was observed by increasing load from 1 to 20 N. The electron microscopy results of the worn surfaces indicated that the decrease in friction at higher loads could be due to softening of the PBT pin by frictional heating.