The amount of PTFE in perfluoropolyether grease by the enthalpy of fusion

摘要

Lubricating greases used for extreme-environment applications such as: temperatures above 200℃, temperature below -54℃, or contact with oxygen and other highly aggressive chemicals are often based on perfluoropolyether fluids thickened with various grades of polytetrafluoroethylene. Since approximately 20 w/w percent or more of PTFE is required to achieve an NLGI Grade 2 consistency, the rheology of PFPE greases is extremely vulnerable to changes in the fluid thickener ratio. This paper describes a thermodynamic test procedure based on the enthalpy of fusion to detect PTFE levels in PFPE grease. The method is expected to be a valuable addition to procedures used to monitor grease serviceability in rolling element bearings. A major advantage of the procedure is that only milligram quantities of grease are required.