Wear Development in Oscillating Rolling Element Bearings

Rotor blade bearings enable the rotor blades to pivot about their longitudinal axis and thus control the power output and reduce the loads acting on the wind turbine. Over a design period of 20 years, rolling bearings are exposed to frequent oscillating movements with amplitude ratios of x/2b>1, especially due to new control concepts such as Individual Pitch Control, which can lead to wear and a reduction in service life. The objective of the paper is to identify the dominant wear mechanisms and their consequences for the operation of oscillating bearings. Oscillating experiments with increasing number of cycles on angular contact ball bearings of two different sizes (type 7208 and 7220), show that the damage initiation starts with adhesive and corrosive wear mechanisms, which result in a sharp increase of the torque as well as the wear volume on the bearing raceway. As the number of cycles increases, an abrasive mechanism occurs, resulting in a lower slope of the wear curve and a smoothing of the resulting wear depressions. The wear and torque curves are evaluated and classified using an energy-wear approach according to Fouvry.