Life-Limiting Wear of Wind Turbine Gearbox Bearings: Origins and Solutions

摘要

Brittle flaking, micropitting, and smearing are life-limiting wear modes of critical bearing positions in wind turbine gearboxes. Whereas micropitting and smearing are caused by roller/raceway sliding in thin film lubricant conditions, the origins of brittle flaking are less understood. Bearings experiencing low load conditions at high speeds and rapid accelerations are more at risk of smearing, while bearings operating for extended periods of time at low loads, slower speeds, and in boundary layer lubrication are more at risk of micropitting. It is argued here that brittle flaking of critical gearbox bearings is not due to hydrogen embrittlement but is instead attributed to the creation of near-surface butterflies at non-metallic inclusions due to very high transient stress. It is therefore postulated that the risk of brittle flaking can be reduced by using bearing steels with higher fracture strengths and smaller densities of non-metallic inclusions than bearing steels currently used. Although black oxide surface treatments may delay the onset but will not eliminate the risk of micropitting, they will provide no protection against smearing. On the other hand, more technologically advanced surface treatments applied to the rolling elements of bearings eliminate micropitting and greatly reduce the risk of smearing. Additionally, bearings with advanced engineered surfaces are about ten times more resistant to damage from lubricant interruption, have more than a 3.5 times greater low-lambda fatigue life, have about 15% less frictional torque, and are twice as resistant to damage from gearbox debris than bearings with untreated rollers.