Effects of Thermal Degradation on the Lubrication Properties of Fluids

Abstract

Fluids representative of nine chemical types of base stocks that have been considered promising for use in high-temperature hydraulic systems were examined for anti-wear properties at 167 F, before and after exposure at 650 F and 750 F. A number of mixtures of these fluids were similarly evaluated. Significant thermal effects on anti-wear properties measured at 167 F were frequently found for the high-temperature base fluids and their mixtures after thermal stress at 650 F and 750 F. Fluids that formed large amounts of volatile decomposition products often showed poorer anti-wear properties after thermal stress. The polysiloxane fluid appeared to have a protective effect on steel when this fluid was combined in mixtures with other fluids that were corrosive at high temperatures. The ester and silicate fluids were better lubricity additives for the unstressed polysiloxane than were the chlorinated biphenyl and phosphate fluids. Differences were noted between the 1- and 40-kg load wear test results as they monitored thermal effects on wear properties, and several fluids showed such effects most frequently at one of the two loads.