Friction and wear characteristics of lead and its compounds filled polytetrafluoroethylene composites under oil lubricated conditions

The friction and wear properties of Pb, PbO, Pb3O4, or PbS filled polytetra fluoroethylene (PTFE) composites sliding against GCr15 bearing steel under both dry and liquid paraffin lubricated conditions were studied by using an MHK-500 ring-block wear tester. The worn surfaces and the transfer films o f these PTFE composites formed on the surface of GCr15 bearing steel were t hen investigated by using a scanning electron microscope (SEM) and an optic al microscope, respectively. Experimental results show that filling Pb, PbO , Pb3O4, or PbS to PTFE can greatly reduce the wear of the PTFE composites, but the wear reducing action of Pb3O4 is the most effective. Meanwhile, Pb S increases the friction coefficient of the PTFE composite, but Pb and Pb3O 4 reduce the friction coefficients of the PTFE composites. However, the fri ction and wear properties of lead or its compounds filled PTFE composites c an be greatly improved by lubrication with liquid paraffin, and the frictio n coefficients of the PTFE composites can be decreased by one order of magn itude. Optical microscope investigation of transfer films shows that Pb, Pb O, Pb3O4 and PbS enhance the adhesion of the transfer films to the surface of GCr15 bearing steel, so they greatly reduce the wear of the PTFE composi tes. However, the transfer of the PTFE composites onto the surface of GCr15 bearing steel can be greatly reduced by lubrication with liquid paraffin, but the transfer still takes place. SEM examination of worn surfaces shows that the interaction between liquid paraffin and the PTFE composites create s some cracks on the worn surfaces of the PTFE composites; the creation and development of the cracks reduces the load-carrying capacity of the PTFE c omposites, and this leads to deterioration of the friction and wear propert ies of the PTFE composites filled with lead or its compounds under higher l oads in liquid paraffin lubrication. (C) 1998 Elsevier Science Lid. All rig hts reserved.