Damage from shaft currents, often driven by variable frequency drives, discharging through the thin lubricant film of a running bearing. Each discharge melts a micro-crater, and over time the craters organize into evenly spaced gray flutes across the raceway, making the bearing noisy. The grease near the track turns black and burnt. Shaft grounding rings, insulated or ceramic-ball bearings and proper cable grounding are the fixes.
Motor's on a VFD and the outer race looks like a washboard, that's electrical fluting, get a grounding ring on it.
Also heard as
- fluting
- washboarding
- EDM damage
Related terms
False brinelling
Dents in bearing races caused by vibration while the machine sits still, not by impact.
Spalling
Flaking of large chunks from a bearing race or gear tooth after fatigue cracks below the surface link up.
Running hot
Shop phrase for a bearing, gearbox or motor operating above its normal temperature.
Grease
Semi-solid lubricant made of oil held in a thickener sponge, usually with additives.