Lubrication characteristics of oils and greases applied to ball bearings for use in vacuo

Three experiments were conducted to evaluate the long-term running performance in vacuo of ball bearings lubricated by a synthetic oil and grease. The first experiment was carried out using ball bearings of a shielded deep-groove type (no. 6204) filled with a grease containing perfluoropolyalkylether (PFPAE) as a base oil and TFE as a thickener. Tests were done at room temperature in a vacuum of 10−4∼10−5 Pa mainly at a rotational speed of 2,000 r/min under an axial load of 50N. The bearings were successfully run for a period of 24,400 h, which corresponds to 3 × 109 revolutions. About 10% in weight of the grease was lost during the test. An inspection of the running accuracy of the bearings tested showed negligible change. The degradation of the grease inspected by FTIR was found to be negligible. A change in the molecular weight distribution of the grease was not observed during the test. The second experiment was conducted with angular-contact-type ball bearings (no. 7204), with retainers impregnated with PFPAE oils. Exploratory work was done using full-component-type ball bearings (no. 7204), lubricated by a heat-cured PFPAE oils, both in vacuo and in an air environment. The bearings were run for 280 h (5.0 × 106 revolutions) in air at a speed of 300 r/min under an axial load of 50 N, but failed to operate afer 25 h (4.5 × 105 revolutions) in a vacuum.