Excessive current erosion
A tiny arc-weld at every contact. Urgency
Current passing through the bearing, arcing across the oil film and cratering the steel.
What excessive current erosion looks like
- Craters in the raceway and on rolling elements, often fairly large (up to about half a millimetre) with melted-looking edges
- Burn marks, sometimes in zig-zag or bead-like lines on ball bearing tracks
- Discoloured spots where steel has been tempered or re-hardened
Rotec AI schematic illustration. It shows the typical pattern and is not a photograph of a real bearing.
How excessive current erosion develops
When a high current passes from ring to ring through the rolling elements, each contact behaves like a spot weld: high current over a tiny area. The steel melts, then breaks away as the element rolls on. It is usually a single event (welding current, an earthing fault) rather than continuous leakage.
How fast it progresses: The craters are permanent and roughen the track, so noise and vibration follow and fatigue is quick to start.
Causes of excessive current erosion
Environment & sealing
- Welding on or near the machine with the return current finding a path through a bearing
- Poor or missing earthing; electrical faults; static discharge
How to confirm it is excessive current erosion
- Large, isolated craters or zig-zag burns, often on only a few contacts
- Ask: was there welding or an electrical fault around the failure date?
- Check the earth connections and the current path
How to fix and prevent excessive current erosion
- Make earth connections correct and low in resistance
- Never weld with the return path through a bearing; clamp the earth next to the weld
- Use insulated or hybrid ceramic-element bearings where stray currents are likely
Easily confused with
- Current leakage erosion (fluting): Leakage erosion is many shallow craters that evolve into fluting; excessive current gives fewer, larger craters.
Other electrical modes
Questions about excessive current erosion
What causes excessive current erosion in a bearing?
Welding on or near the machine with the return current finding a path through a bearing.
How do you fix or prevent excessive current erosion?
Make earth connections correct and low in resistance. Never weld with the return path through a bearing; clamp the earth next to the weld. Use insulated or hybrid ceramic-element bearings where stray currents are likely.
What does excessive current erosion look like?
Craters in the raceway and on rolling elements, often fairly large (up to about half a millimetre) with melted-looking edges. Burn marks, sometimes in zig-zag or bead-like lines on ball bearing tracks.