Performance of P.T.F.E. Based Piston Rings in an Unlubricated Reciprocating Compressor

Abstract

Published data on the wear of non-metals is usually based on tests using a sliding disc on a rotating drum, with atmospheric air surrounding the equipment. Although this type of test gives a fair indication of the relative merits of the materials, it is impossible to accurately estimate the wear of piston rings under working conditions. Tests have therefore been carried out on various filled polytetrafluorethylene (P.T.F.E.) materials in an un-lubricated reciprocating compressor. The materials were tested as piston rings with helium as the working gas. The gas was used in two conditions:

1. (1)

‘Wet’ where the moisture content was approximately 200 parts per million (p.p.m.) by volume.

(2)

‘Dry’ where the moisture content was approximately 7 p.p.m.

The fillers used were carbon, glass fibre and molybdenum disulphide and it was found that the carbon filled materials had the lowest wear rate in the wet gas. Using the dry gas the glass fibre filled materials gave the lowest wear rates.

All the materials showed a tendency to local decomposition of the P.T.F.E. to carbon and fluorine and this is thought to be due to local hot spots formed by the relative movement of the ring in its groove.