Lubricant Additive Effects Upon Bearing Metal Fatigue. Ii. Effects in Multi-Purpose Soap Thickened Greases

摘要

To determine if additives in greases have effects upon bearing fatigue life overriding thickener and oil effects, greases of the Military Specification MIL-G-10924B type were made, with and without additives, using low viscosity naphthenic or paraffinic mineral oils thickened with calcium or lithium 12-hydroxystearate. They were tested in the rolling contact adaptation of the Four Ball Extreme Pressure Tester with 52100 steel balls at 1,200,000 psi. Hertz load and ambient temperatures. Fatigue life improvement over the oils was greater using calcium soap instead of lithium soap as the grease thickener. Nonylphenoxyacetic acid was relatively ineffective for improving fatigue life in all greases except the lithium base paraffinic oil grease. The insoluble crystalline additives with good lubricating properties, molybdenum disulfide and molybdenum dibutyldithiocarbamate, were very effective for improving fatigue life in greases of both thickener types. The oil miscible molybdenum dibutyldithiophosphate in the calcium base paraffinic oil grease was nearly as effective as the latter, which was the best fatigue inhibiting additive tested, but was less effective than either of the above additives in the lithium soap paraffinic oil grease. With the less effective tricresyl phosphate the relative improvement of fatigue life in these two greases was reversed. (Author)