Electrical Erosion (Fluting)
Current passing through the bearing causing fluted washboard damage to raceways.
Symptoms
Washboard or "fluted" pattern of dark bands across the raceway, often with corresponding marks on rolling elements. In early stages, localised melt marks or craters; advanced stages show regular fluting visible to the eye.
Likely causes
Stray electrical current passing through the bearing — common with variable-frequency drives (VFDs), electric motors with inadequate grounding, or static discharge. Current arcs across the lubricant film, locally melting and damaging the raceway.
Prevention
Ensure proper motor grounding and bonding. Use insulated bearings (ceramic-coated or ceramic balls) on VFD-driven motors. Install shaft grounding rings. Check VFD cabling and grounding. Reduce high-frequency common-mode currents.