Long-Term Operation of Si3N4 Ball Bearings at Temperatures up to 650°C in Ultra-High Vacuum©

Abstract

Si3N4 bearings were tested for more than 1400 hours at temperatures up to 650°C in a vacuum on the order of 10−7 to 10−6 Pa. The bearings were lubricated with a precoated sputtered MoS2 film and a self-lubricating composite retainer. The test bearings were 20 mm-bore angular contact ball bearings (7204 size). The tests were carried out at a rotational speed of 600 rpm under a thrust load of 50 N. The Si3N4 bearings exhibited low fractional torque throughout the operations for 4200 hours at 500° C and for 1400 hours at 650°C in vacuum. Little wear was found on the balls and races after the tests, and little deterioration in running accuracy was observed. The bearings also showed excellent tribological performance at ambient temperature in vacuum. Full-complement-type Si3N4 bearings lubricated with only a precoated MoS2 film showed severe wear at 500°C in vacuum. On the other hand, Si3N4 bearings with the retainer and without a precoated MoS2 film were successfully operated with little wear for 1400 hours at 500°C. This study suggested that a transfer film from the retainer was responsible for the long-term lubrication of the bearings with the excellent tribological performance at high-temperature in a vacuum. Presented as a Society of Tribologists and Lubrication Engineers paper at the ASME/STLE Tribology Conference in San Francisco, California, October 13–17, 1996