No abstract

A common application for grease-lubricated oscillating rolling element bearings is, e.g., rotor blade bearings in wind turbines. These bearings mainly operate under conditions that are prone to starvation. If the grease is unable to provide enough inlet lubricant supply for the contact between rolling element and bearing raceway, wear in the form of False Brinelling and thus premature bearing failure is possible. Bearing experiments with different lithium complex model greases, which differ mainly in their base oil viscosity and oil separation rate, were carried out to show the influence of the grease parameters on wear initiation. The results show that the ability of the grease to release a high amount of base oil with high mobility into the track of the rolling element is a crucial mechanism to prevent wear, especially at small oscillation angles. For oscillation angles larger than a critical angle, a secondary replenishment mechanism may prevent early wear initiation. The experimental results are used to validate a starvation model proposed in earlier work (Wandel et al. in Tribol Int 165:107276, 2022).

Rotor blade bearings enable 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 oscillation 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 this paper was to identify the dominant wear mechanisms and their consequences for the operation of oscillating bearings. Oscillating experiments with an increasing number of cycles on the angular contact ball bearings of two different sizes (types 7208 and 7220) show that the damage initiation starts with adhesive and corrosive wear mechanisms, which result in a sharp increase in 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 were evaluated and classified using an energy-wear approach according to Fouvry.

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.

A common application for grease-lubricated oscillating rolling element bearings are, e.g., rotor blade bearings in wind turbines. These bearings mainly operate under low-velocity conditions leading to starvation. If the grease is unable to provide enough inlet lubricant supply for the contact between rolling element and bearing raceway, wear in the form of False Brinelling and thus premature bearing failure is possible. Bearing experiments with different lithium complex model greases, which differ mainly in their base oil viscosity and oil separation rate, were carried out to show the influence of the grease parameters on wear initiation. The results show that the ability of the grease to release a high amount of base oil with high mobility into the track of the rolling element is a crucial mechanism to prevent wear, especially at small oscillation angles. For oscillation angles larger than a critical angle, a secondary replenishment mechanism may prevent early wear initiation. The experimental results are used to validate a starvation model proposed in earlier work [1].