Oil exchange between ball bearings and porous polyimide ball bearing retainers

The kinetics of the absorption of lubricating oils and moisture from air into porous polyimide, as well as the exchange of oil between porous polyimide retainers and oil baths or operating bearings, have been measured. Oil absorption into porous polyimide is much faster than into cotton-phenolic. Water is absorbed by oil-impregnated polyimide, but little or no oil is lost during the process. Oil is absorbed by air-equilibrated polyimide at a slower rate than by dry polyimide. Porous polyimide is much easier to impregnate with oil than cotton-phenolic, and is also much more tolerant of storage in air once impregnated. Oil within a porous polyimide ball bearing retainer exchanges slowly with oil in a bath in which the retainer is placed. The exchange is due to diffusion of the oils, and the diffusion coefficient is determined to be 3 X 10(-9) cm(2)/s for the oils used in these experiments. Oil is exchanged quickly between polyimide retainers and well-lubricated operating bearings. The exchange is faster than a diffusion process, and is probably driven by bearing action. In these experiments, the authors could detect no net gain or loss of oil from the retainer or the bearing parts. Only about one-half of the oil originally supplied to the parts is available to the retainer; the rest remains elsewhere in the bearing.