The validity of experimental simulation of ball-bearing lubrication by a rolling-disk apparatus has been scrutinized mathematically, with specific attention to films generated for thickness measurements by X-rays. Emphasis was given to distinctive ball-bearing features, such as surface slip and related thermal effects alterable by geometric expansion. For a representative ball bearing, rigorous simulation demanded unattainble disk speeds and hampered X-ray measurements of film thickness, but experiments were made feasible through acceptable relaxation of carefully chosen details. Several experiments were performed under fairly severe combinations of load, speed, and temperature. Specific results with a synthetic paraffinic oil under maximum pressure of 200,000 psi at high speeds showed films about 20 microin. thick at 200 F but indicated only about one microin. at 600 F. Even the thin films allowed little surface contact, though they may have increased susceptibility to damage from sliding.

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