Current leakage erosion (fluting)

A low, steady current draws washboard ridges across the track. Urgency

Current passing through the bearing, arcing across the oil film and cratering the steel.

What current leakage erosion (fluting) looks like

• Evenly spaced ridges across the raceway like a washboard (fluting), on the rings and often on the rollers
• In the early stage, a dull grey frosting on balls and tracks made of thousands of shallow craters
• Grease turned dark, hard or burnt, especially on the cage bars

Rotec AI schematic illustration. It shows the typical pattern and is not a photograph of a real bearing.

How current leakage erosion (fluting) develops

A small current passes continuously, typically from inverter-induced shaft voltage, discharging across the oil film. Each discharge leaves a tiny crater; over time the craters line up into flutes. The steel under them turns brittle or soft, and the grease carbonises and stops lubricating, so the bearing finishes by fatigue or seizure, usually humming first.

How fast it progresses: Slow but relentless. A new steady rumble from an inverter-fed motor is an early warning.

Causes of current leakage erosion (fluting)

Environment & sealing

• Inverter (VFD) drives; poor grounding; asymmetric or unshielded motor cabling

Design & seats

• Rotor and stator misalignment; no current path around the bearings

How to confirm it is current leakage erosion (fluting)

• Fluting plus an inverter-drive history is close to conclusive
• Balls look uniformly dull grey; grease has gone black
• Check shaft voltage if you can, and the earthing arrangement

How to fix and prevent current leakage erosion (fluting)

• Fit shaft grounding (brush or ring) and make sure the motor and drive are properly bonded
• Use symmetric, shielded motor cabling
• Use an insulated (coated) or hybrid bearing on the non-drive end, and the drive end in severe cases
• Check the stator-to-rotor alignment

Easily confused with

• Excessive current erosion: Excessive current gives a few big craters from one event; leakage gives a fine pattern that builds up.
• Overload deformation (true brinelling): Fluting is evenly spaced ridges across the whole track; overload dents are separate and deeper.

Catching current leakage erosion (fluting) early

Fluted bearings often announce themselves with a steady hum or rumble at a fixed pitch long before spalling. If a drive-fed motor develops a new rumble, check for current damage before anything else.

Other electrical modes

Questions about current leakage erosion (fluting)