• How:

    1. 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.
  • Possible source of voltage and current:

    1. External: With encoder、frequency converter etc.
    2. Unbalance: Gap unequal between rotor and stator,cause shaft voltage (shaft current) during operation.
    3. Static electricity: Running belt、belt etc. cause triboelectric.
  • Performance after the electrical pitting:

    1. Grease discoloration (turn to dark), discharge cause overheating.
    2. Pit (slight)、wave (severe) trace on the raceway.



  • Countermeasures:

    1. Conduct: (1) Conductive grease (contain with Carbon or Molybdenum disulfide). (2) Earth bolt or carbon brush etc. at the circuit.
    2. Insulate: (1) Replace the rolling element to ceramic ball. (2) Ceramic layering on the bearing.

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