Effect of lubricant base stock on rolling-contact fatigue life

Thomas L. Carter
Feb 1958

Five lubricants of different base stock were tested using groups of 1/2-inch air-melt AISI M-1 tool-steel balls under rolling-contact fatigue conditions in the fatigue spin rig. A methyl silicone, a mineral oil, a glycol, a sebacate, and an adipate were used. The particular fluids chosen all had about the same atmospheric pressure viscosity (10 centistokes) at the test temperature of 100 degrees F. Other test conditions such as ball loading were held constant. Ball loading was held at that level necessary to produce a maximum theoretical Hertz stress of 725,000 pounds per square inch in compression at the contacting surfaces and 225,000 pounds per square inch in shear at a depth of 0.009 inch below the surfaces. This investigation studies the effect of lubricant base stock upon rolling-contact fatigue life and correlates any observed differences in life results with unique properties of the different base-stock fluids. The tests showed differences in rolling-contact fatigue life for the five different base-stock fluids tested. The observed lives appeared to correlate with the pressure-viscosity coefficients of lubricants of the same base stock. Lubricants whose viscosities were increased the greatest by pressure produced the longest fatigue lives. However, other lubricant properties, such as bulk modulus and chemical activity, may well influence fatigue life, and more data are required to determine their relative importance. Chemical activity did not appear to be significant in these tests, and the spalls obtained in all tests compared closely with those obtained in full-scase bearings. Metallurgical transformation in the material was consistent for all test runs.

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