Reibungsbedingte WEC-Bildung bei hohen Lasten

Abstract

Rolling bearings can fail in rare cases far ahead the calculated rating life due to White Etching Cracks (WECs). Prerequisites for WEC formation are the so called additional loads (electrical current, high friction, etc.) acting besides the Hertzian rolling contact stresses as the main load. Currently, it is being discussed in the literature whether a high pressure at the beginning of operation can be sufficient to initiate WECs. To address this question, recently performed as well as published WEC tests on bearing test rigs and basic tribometers working with high Hertzian pressures and various levels of internal friction energy are reviewed and discussed. It could be obtained from ball and roller bearing tests that high Hertzian pressures in conjunction with low specific friction energy do not lead to WEC formation. So, evaluating simple tribometer tests, it can be assumed that a combination of high pressure and a minimum proportion of slip (leading also to friction energy ingress) is required to trigger an accelerated WEA formation. In contrast, WECs occur in angular contact ball bearings and spherical roller bearings if they are subjected to high contact pressures and high specific friction energy at the same time. Additionally, the failure location indicates that the friction energy was the main trigger. A frictional WEC lifetime m odel, which was derived from a large number of bearing tests (FE8, R4G) before, provides an explanation for these different failure behaviors in the WECtests.