Paper 16: Recent Developments in Polytetrafluorethylene-Based Dry Bearing Materials and Treatments

The addition of bronze or certain phosphates to lead/polytetrafluorethylene (p.t.f.e.) mouldings can produce a high degree of wear resistance. Similar performance can be obtained from porous bronze or phosphated steel surfaces impregnated with lead/p.t.f.e. The effectiveness of lead or lead oxides in these ternary compositions is related to an exothermic reaction with p.t.f.e. It is postulated that during rubbing the reaction takes place at local hot spots and results in the formation of a chemically bonded p.t.f.e. layer on the mating surface.

Polyethylene compositions have similar wear properties to p.t.f.e. compositions, but the response of polymers to the bronze+lead type of addition decreases as the molecular structure of the polymer deviates from the simple CF₂ or CH₂ type.

The optimum bronze/lead ratio for maximum wear resistance depends on the rubbing conditions. For instance, it is not possible to combine in a homogeneous composition maximum dry wear resistance, when a low bronze content is required, and maximum wet wear resistance, which requires a higher bronze content.