Wear Studies on Moldings of Polytetrafluoroethylene Resin. Considerations of Crystallinity and Graphite Content

Abstract

The wear of molded bearings of polytetrafluoroethylene resin has been investigated in relation to crystallinity and filler content (graphite) as factors effecting changes in selected mechanical properties. In a homogeneous, unfilled resin molding, the rate of wear increases in direct proportion to the modulus in flexure and inversely with yield strain. A useful, simple expression is proposed to describe this relationship. In a heterogeneous, graphite-filled molding at a low filler content, the rate of wear initially approximates that of the homogeneous unfilled system and then decreases with time; at moderate, filler content, the wear rate is constant at levels below that of the unfilled resin. The rate of wear is also proportional to the applied load at low loading under conditions where bearing temperature remains reasonably constant; the wear data indicate the importance of removing frictional heat especially at high bearing loads. Practical suggestions are included for design for efficient bearings.