Electrical Pitting Causes and Countermeasures
2020-10-16
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How:
- Grease isolate the O/R、I/R and ball after uniform distribution in the bearing, but under some circumstance electric potential difference would cumulative, the current force to pass O/R and I/R instantaneous when it reach critical value, cause the spark inside the bearing, make the surface of raceway and rolling elements into molten state, it is electrical pitting.
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Possible source of voltage and current:
- External: With encoder, frequency converter, etc.
- Unbalance: Gap unequal between rotor and stator, cause shaft voltage (shaft current) during operation.
- Static electricity: Running belt, belt etc. cause triboelectric.
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Performance after the electrical pitting:
- Grease discoloration (turn to dark), discharge cause overheating.
- Pit (slight), wave (severe) trace on the raceway.
Pit(Slight)
Wave(Severe)
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Countermeasures:
- Conduct: (1) Conductive grease (contain with Carbon or Molybdenum disulfide). (2) Earth bolt or carbon brush etc. at the circuit.
- Insulate: (1) Replace the rolling element to ceramic ball. (2) Ceramic layering on the bearing.