Rheological evaluations of solidified lubricating greases and their base oils under very high pressure

Abstract

Some of high-pressure rheology of solidified lubricating greases and their base oils were estimated up to 3.5 GPa by metal microsphere deformation analysis in a diamond-anvil pressure cell (DAC) under the quasi-static compression condition. From aluminum sphere deformation in the greases, the solidification pressures of lithium greases were obtained and were almost the same as those of their base oils. Whereas, the solidification pressures of urea greases were slightly higher than those of their base oils and lithium greases. The solidification pressure was about 0.6 GPa for the traction grease, whereas it was 1.5-1.8 GPa for both PAO greases and MAC greases (space lubricants). Estimated traction coefficients from copper sphere deformation were 0.06-0.07 at 0.6 GPa-2.5 GPa for the traction grease and 0.03-0.04 around 3 GPa for both PAO greases and MAC greases and few difference was found out between greases and their base oils for all the lubricants. Copyright © 2013 Japanese Society of Tribologists.