Another perspective: False brinelling and fretting corrosion

cle [1] on false brinelling and fretting corrosion provided an excellent discussion of both wear mechanisms. This article presents observations and conclusions regarding fretting wear derived from investigations of gearbox failures. WIND TURBINES As pointed out by Godfrey, a wind turbine gearbox is susceptible to fretting wear. Figure 1 shows the high-speed pinion from a modern wind turbine. With the highspeed pinion stopped by the brake, and the rotor buffeted by the wind, the mating gear rocks back and forth through small amplitude motion. The four faint lines in Figure 1 are false brinelling that occurred when the wind turbine was parked for a short time under light winds. The three prominent red lines are fretting corrosion that occurred when the wind turbine was parked for an extended period under heavy winds. Figure 2 shows the outer raceway of a rolling-element bearing, also from a wind turbine, which suffered false brinelling and fretting corrosion when the wind turbine was parked. Fretting corrosion also can occur when a wind turbine is rotating. It occurs on components such as splines or blade pitch bearings that are subjected to small-amplitude, vibratory motion. Splines are especially vulnerable to fretting corrosion because, unlike gears, whose rotation entrains lubricant between mating gear teeth, splines have small sliding motion with essentially no motion to entrain lubricant between mating spline teeth. Blade pitch bearings are susceptible to fretting wear if the blades remain at one pitch angle for too long, and the lubricant is not replenished by movement of the rolling elements. Another Perspective: False Brinelling and Fretting Corrosion