Investigation on the lubricity of self-lubricating ball bearings for cryogenic turbine pump

The lubricity of newly designed self-lubricating 70-mm-bore angular contact ball bearings was tested using a special bearing tester under thrust load of about 20 kN and speed of about 20000 r/min in liquid nitrogen. The test bearing was characterized with the pure polytetrafluoroethylene (PTFE) retainer coupled with the Ag-based lubricant film initially deposited on bearing raceways. After running for 1200 and 2400 s respectively, the states of the PTFE transfer films on the surfaces of the balls and raceways as well as the wear state of the Ag-based solid lubricant film for each tested bearing were analyzed mainly by scanning electron microscopy and X-ray photoelectron spectroscopy. The results indicated that good lubricating conditions were obtained for all tested bearings. The newly designed self-lubricating ball bearing could run steadily for more than 2400 s under high speed, heavy load and at cryogenic temperature conditions. The formation and the evolution of PTFE transfer films with bearing operation are mainly discussed according to the relevant analysis.