Grease Life Prediction for Sealed Ball Bearings

Abstract

Sealed ball bearings are used widely for electric motors and automotive components. Appropriate grease is selected for the each application, considering grease life, bearing torque, sound characteristics, etc. Recently, as these components have become progressively more compact, the sealed ball bearings are required to operate at higher temperatures and rotational speeds. In such cases, grease life has become more critical in determining the bearing's overall life. Therefore, it is important to estimate grease life in order to select the appropriate grease and predict the life of the final product. In this paper, the grease life formulas for both urea and lithium soap greases were generated. The formulas were derived from grease life data generated on 6204 bearings with inner ring rotation. The formulas were composed of temperature, rotational speed and applied load terms. These terms were obtained, based on the test results, the temperatures from 100 °-180 °C, the rotational speeds from 10,000–20,000 revolutions per minute (rpm) and the axial loads from 67-670 N, respectively. The grease life formulas were further improved to be applicable to outer ring rotation bearings. It was found that the grease life in bearings with outer ring rotation was shorter than for bearings with inner ring rotation. The difference in cage rotational speed was found to affect the grease life. By adding a correction factor for outer ring rotation to the rotational speed term, the same grease life formula, independent of rotational type, can be utilized. Presented as a Society of Tribologists and Lubrication Engineers Paper at the ASME/STLE Tribology Conference in Seattle, Washington, October 1–4, 2000