White etching cracks and white structure flaking failures have afflicted bearings in wind turbine gearboxes. Research has not led to a definitive root cause, but lubricant additives, roller skidding, lubricant breakdown, impact/impulsive loadings, hydrogen formation, water in oil, hydrogen content of bearing steel and electrical currents are thought to be contributors. It is also not known whether WEC/WSF formation is surface or sub-surface initiated. The role of non-metallic inclusions is highlighted when WEC/WSF crack formations are not surface-breaking.
In the first of a series, solutions offered by bearing manufacturer SKF are explored. They principally conclude that surface initiation dominates and have developed technical solutions to reduce or avoid WEC/WSF. These solutions are a special black oxide passivation of the bearing components, steel of higher cleanliness by reduction or size and number of non-metallic inclusions that act as stress raisers near the surface and a deep strengthening process that induces residual compressive stress in the near surface.
Click here to view the technical paper by Stadler and Stubenrauch