A study of grease lubricants under wind turbine pitch bearing conditions

• Published in: Wear 2020-08, Vol.454-455, p.203335, Article 203335
• Main Authors: Schwack, Fabian, Bader, Norbert, Leckner, Johan, Demaille, Claire, Poll, Gerhard
• Format: Article
• Language: English
• Subjects: Blade bearing; False brinelling; Grease; Pitch bearing; Wear; Wind energy
• ISSN: 0043-1648; 1873-2577; 1873-2577
• DOI: 10.1016/j.wear.2020.203335

Pitch bearings in wind turbines are affected by reciprocating motion due to pitch control. The combination of oscillating operation, high loads, and mixed lubrication often leads to wear. Grease lubricants in wind turbine pitch bearings should be designed to avoid such wear. Due to different available grease lubricants, the anti-wear properties are investigated under downscaled wind turbine pitch bearing conditions. The downscaling is accomplished by load simulation for a pitch bearing and analysis of the pitch movements for a 7.5 MW reference turbine. The operational conditions of the four point contact ball bearing with 5 m outer diameter are scaled to angular contact ball bearings of the size 7208. The investigations are concluded with contact model experiments. Six Industrial grease lubricants for wind turbine pitch bearings are tested that follow very different compositions. The investigations reveal, that none of the tested grease lubricants was able to reduce wear for all tested conditions. After 250000 cycles certain conditions lead to severe wear. Therefore, the pitch controller should avoid such conditions if possible. Nevertheless, grease lubricants with low base oil viscosities and high bleeding rates are best on average for the tested conditions. Furthermore, the results of the bearing experiments are comparable to the model experiments. [Display omitted] •Operating behaviour considered of pitch bearings under individual pitch control.•Method for scaling the operating behaviour to test rig conditions.•Experimental investigations on six commercial greases used in pitch bearings.•None of the greases was able to show satisfactory wear protection for all conditions.•Greases with low base oil viscosities and high bleeding rates showed the least wear.