Bearing Fatigue Life Tests in Advanced Base Oil and Grease for Space Applications

Abstract

Two synthetic base oils (815Z and 2001A) and two greases (601EF and R2000) used for space applications have been studied at ground level. Rheological tests were performed in order to characterize the behavior of each of the base oils versus the pressure and the temperature. Next, the effect of base oils and greases on ball bearing fatigue life was carried out using thrust ball bearings. The results of L 10 life tests showed a bearing life order from the highest to the lowest of grease 601EF (blended with base oil 815Z), base oil 2001A, grease R2000 (blended with the base oil 2001A) and, the lowest, the base oil 815Z. The general tendency of the base oils and the greases shows that the bearing life increases with the EHL film parameter. However, the anticipated beneficial effect of an apparently high film parameter for the base oil 815Z was not seen due to permanent viscosity loss in the EHL contact. The results showed that the viscosity of the base oil 815Z, which contains the acetal group , was decreased by mechanical shear at the high shear rate in the EHL conjunction and the EHL oil film was thinner than expected. Hydrogen fluoride is released with the decomposition of the acetal group. As a result, the permanent viscosity loss at high Hertzian pressure and the hydrogen fluoride generation shortened bearing life with the 815Z base oil. In the case of grease 601EF with base oil 815Z, the permanent viscosity loss did not occur in ball bearings and the bearing life is extended.

The Effect of Plasma Nitriding on the Tribology of Perfluoropolyether Grease-Lubricated 2Cr13 Steel Couples in Vacuum

“…10. This formation mechanism of carboxylic acids is consistent with the reference [38]. On the other hand, FTIR spectrum of the used grease taken from the surfaces of the unnitrided disks under 90 N exhibits little changes, comparing to the virgin grease, indicating that little or no degradation of the PFPE grease occurs in this case.…”

Effect of Tribochemical Reaction on Transfer-Film Formation by Poly(tetrafluoroethylene)

“…A hydrogen fluoride molecule is liberated by this reaction and, in fact, has been detected in a previous friction experiment on fluorocarbon lubricant. 27 The geometries of the products were constructed and optimized by DFT, and the TS geometry was then optimized on the basis of the superimposed structure between the reactant and product geometries. Single-point-energy calculations were subsequently performed to obtain electronic energy for reactant, TS, and product.…”

Effect of Environmental Gas on Surface Initiated Rolling Contact Fatigue

“…Tamada and Tanaka [7] suggested that the hydrogen generated by decomposition of lubricant affected the formation of white structure which caused reduction in rolling contact fatigue life. More recently, Ohno et al [8,9] showed that fatigue cracks similar to those in hydrogen embrittlement were developed in a rolling contact fatigue test with two synthetic base oils and two greases for space applications. They demonstrated that a perfluoropolyethers base oil in atmospheric conditions reduced rolling contact fatigue life through permanent viscosity loss at high Hertzian pressure and hydrogen fluoride generation.…”