Experimental investigation of the chemical degradation of lubricating grease from an energy point of view

Abstract

Abstract The chemical degradation/oxidation of lubricating grease is investigated experimentally from an energy point of view. A Pressure Differential Scanning Calorimeter (PDSC) is used to measure the activation energies of two lithium-complex greases and to monitor their chemical degradation through induction time. For this purpose, an experimental setup consisting of a heating chamber, a temperature controller and an energy meter is designed, built, and calibrated to heat up grease samples and measure pure energy absorption during the chemical degradation at different test temperatures. A relationship between the energy absorption of the grease and its chemical degradation is established that is independent of the testing time and temperature. It is shown that the energy absorption of the grease approaches to an identical maximum value in a shorter time in high temperatures and a longer time in low temperatures. The maximum energy absorption depends on the grease type and experimental results reveal that it can be used to estimate the grease chemical life. A roller tester rig is used to measure and compare the lubrication ability of two chemically degraded grease samples and to validate the results of the research. To gain further insight, experimental results are presented to examine the flow characteristics of a chemically degraded grease in an elastohydrodynamic (EHL) line contact with a comparison to that of the fresh grease.