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Rolling Bearing Performance and Film Formation Behavior of Four Multiply Alkylated Cyclopentane (MAC) Base Greases for Space Applications

Four multiply alkylated cyclopentane (MAC)-based greases, used for space applications, were used for rolling contact fatigue tests employing thrust ball bearings. These greases were R2000, ML, MU, and 5200 and were made from the same base oil 2001A. Each grease had a different thickener, which were sodium soap, Li soap, urea, and polytetrafluoroethylene (PTFE), respectively. The effect of the grease thickener on the ball bearings' fatigue life in vacuum and atmospheric environments was investigated via testing. For the greases R2000, MU, and ML it was found that the oil film formation in the experiments performed under vacuum conditions declined remarkably in comparison to under atmospheric conditions. For the 5200 grease, the oil film formation was almost the same as under atmospheric conditions. These results were supported by the occurrence of cage wear in the ball bearing fatigue tests. In the absence of sufficient films, high wear rates were measured.