Wear and friction of PTFE seals

Abstract

Radial lip seals made from PTFE-compounds are used more and more frequently for the sealing of crank shafts in the automotive industry. Due to wear the seal loses material and finally fails. State-of-the-art is the experimental determination of the tribological behaviour on a test rig with pin-on-disc apparatus with the help of which the wear behaviour of sealing systems, especially of PTFE seals, can be predicted. Because of the non-linear elasto-viscoplastic material properties of the sealing material the history-dependent seal mounting process has to be followed in the finite element analysis (FEA). A new FEA procedure is presented which can meet these demands. It is based on a modified iterative `rezoning' procedure. Under the assumption that the lip wears out according to the magnitude of the contact stress (maximum wear at maximum contact stress) the node coordinates of the seal contact surface are modified according to the node contact forces. Comparisons between numerical simulations and long-term service seals are made. The experiments also indicate under which radial load the seal can withstand insufficient lubrication which occurs in practical use without much wear.