Michiharu Naka

Effects of urea grease composition on the seizure of ball bearings

The authors tested various urea greases to examine grease leakage, oil separation, degradation by oxidation, wear and seizure life. Presented as a Society or Tribologists and Lubrication Engineers paper at the World Tribology Congress in London, United Kingdom, September 8–12, 1997

Particle Generation by Solid-Lubricated Bearings and Ball Screws in Vacuum Environments©

Rolling bearings used for transporting wafers and liquid crystals in the film-forming process of semiconductor and LC panel manufacturing are required to minimize the particles (originating from both lubricant and bearing material) they generate while in operation. The research reported in this paper focuses on the particle generation under different rotational conditions of ball bearings and ball screws coated with various solid lubricants and operating in a vacuum environment. The results of the tests indicated that a specially composed and applied polytetrafluoroethylene (PTFE) coating was superior in minimizing particle generation by ball bearings and ball screws. Observation of the bearing interior surfaces indicated that particle generation is primarily caused by wear of cage-pocket surfaces, while sudden and large increases in wear are the result of the balls making direct surface-to-surface contact with the raceways and cages due to erosion of the solid lubricant coatings. Presented at the 53rd An...

Evaluation of Tribological Properties of Synthetic Lubricants under High Temperature and High Speed Conditions

Tribological properties of synthetic lubricants of a dipentaerythritol ester (DiPE), a tripentaerythritol ester (TriPE), and a five-ring polyphenol ether (5P4E) were evaluated using a unique oxidation stability tester and a high-temperature, high-speed ball/disc tribotester. The test conditions simulated a high-temperature (300° C) high-speed (60 m/s) bearing. As for oxidative stability, 5P4E showed superior oxidative stability for all parameters evaluated except for deposition. The oxidative stability of ester-based lubricants TriPE and DiPE was much superior to that of an oil specified by MIL-L-23699E (MIL), though less than that of5P4E. DiPE and 5P4E showed a high traction coefficient even at 300° C and its dependency on temperature was high. In contrast, TriPE showed a low traction coefficient under many of the test conditions and the temperature dependency was less. Overall oxidative stability and traction property results suggest TriPE may be a more suitable high-temperature and high-speed bearing l...