Sliding Friction Characteristics of MAC Greases under Vacuum Condition

Abstract

Even though solid lubricants or low-volatile greases are used for lubrication of mechanical equipments in space satellites, the life of grease is longer than that of solid lubricants because of the hydrodynamic effects and replenishment. New grease using multiply alkylated cyclopentane (MAC) as base oil was developed for space applications. In this paper, the lubrication characteristics of the new grease have been investigated by experiments using the basic friction tester under high vacuum condition. The results clearly show that the difference of thickener influences the lubrication characteristics even if the greases consist of the same base oil, and MAC grease used with non-soap urea thickener was superior to the others.

Investigation of decomposition of hydrocarbon oil on the nascent surface of steel

“…Especially in outer space, many moving mechanical assemblies (MMAs) for space applications rely on a small, initial charge of lubricant for the entire mission lifetime, often in excess of 5 years [14]. The lubricants used in this field are synthetic hydrocarbon oils with low vapor pressure [15][16][17]. Tribological failure of MMAs occurs when the lubricant degrades or evaporates and therefore loses its ability to lubricate tribological contacts, for example raceways contacting with bearing balls.…”

Effect of Lubricant Additives on Tribochemical Decomposition of Hydrocarbon Oil on Nascent Steel Surfaces

“…Consequently, additives effective under mild conditions are likely to be polar compounds such as fatty acids and phosphates, whereas additives effective under severe conditions are likely to be non-polar compounds such as organic sulfides, according to Pearson's hard and soft acids and bases (HSAB) principle 14) . The advantage of MACs over more conventional lubricants for vacuum applications such as PFPEs is the compatibility with currently available hydrocarbon-based additives 15) . Therefore, one possible method to decrease the decomposition of lubricants during the friction process is to reduce the surface activity by introducing additives.…”