Abstract
White Etch Cracking (WEC) is a severe and unpredictable failure mode affecting bearings in various industrial sectors. In this work, accelerated WEC laboratory tests have been performed using FE8 type test rigs with ceramic rollers to test the WEC resistance of different bearing materials, materials quality and roughness. It is demonstrated that the test method can reliably and consistently provoke WEC in commercially available washers. Tests using washers with different roughness values did not show significant changes in the time to failure. Tests of through hardened bearing steel with a low content of inclusions resulted in a significantly longer time to failure compared to the baseline. Through hardened washers with a black oxide coating did not improve the WEC life as the coating was worn away during testing. Tests with two types of carbo-nitrided washers gave significantly longer time to failure, of which one type in particular showed high resistance towards WEC formation.
Highlights
White Etch Cracking (WEC) is a well known cause of premature failures in wind turbine gearbox bearings, resulting in macro-pitting
All tests failed in a similar manner with spalling on the washer raceway, see Fig. 3a, with ultrasound measurements showing presence of extensive subsurface cracks, which was confirmed to be WEC by optical microscopy
During this work an accelerated WEC test setup with FE8 type test rigs and ceramic rollers was used for determining the WEC lifetime of different washer bearing materials, materials quality and roughness
Summary
White Etch Cracking (WEC) is a well known cause of premature failures in wind turbine gearbox bearings, resulting in macro-pitting. Some preventive measures have been imple mented by bearing, gearbox and wind turbine manufacturers, typically using new bearing types or bearing configurations based on best prac tice. Several WEC resistant bearing materials based on surface treat ments are currently available, including carburization, induction hardening and black oxide coating as well as bearings made from high-end expensive nitrogen rich steels. Either these solutions do not offer 100 % guarantee against WEC or are significantly more expensive than current standard bearings [22,23,24]
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