Investigation of porous polyimide lubricant retainers to improve the performance of rolling bearings under conditions of starved lubrication

The current work examines the lubricant retaining effect of porous polyimide (PI) on the performance of rolling bearings under starved lubrication conditions. PI with four different porosities were prepared by cold pressing and sintering processes. The oil-containing and oil-supply properties as well as frictional properties were investigated. Then, PI was used as the retainer for a commercial thrust ball bearing with a race diameter of 18.7 mm. Room temperature tests of retainer performance were conducted with an axial load of 500 N under starved lubrication, in which only residual oil on and in the retainer could work for lubrication. Experimental results show that oil-containing porous PI can easily release oil mainly by thermal expansion rather than centrifugation. Lubrication failure happened quickly with a compact retainer at starved lubrication whereas the bearings with oil-containing porous retainers operated smoothly for 12 h at 800 rpm and 5 h at 1200 rpm. Friction reduction and cooling effects are even more obvious with increased porosity.