What is Bearing Fluting?

Fluting is damage caused to bearing due to an electrical current flow on the shaft of a VFD (Variable Frequency Drive) machine.

Current flow from shaft -> Inner Race -> Rolling Elements -> Outer Race

  • Attaching picture of outer race damage due to fluting.

Diagnosing Bearing Fluting

High frequency vibration is generated - a series of BPFO, BPFI or BSF sidebands will appear in spectrum between 100K & 180K CPM.

Two ways to fix fluting: "The electrical current must be redirected"

  • If a machine is rated at less than 100 HP, a carbon fiber brush may be attached to a shaft grounding ring (also called a split ring, solid ring, or a press fit) and installed on the drive side of the shaft.

This will effectively redirect the current to ground and will avoid electrical arcing.

  • If a machine is rated at 100 HP or more, a non-conductive ceramic bearing may be attached to the opposite side of the shaft in addition to the carbon fiber brush.

The ceramic bearing prevents the NDE of the motor from becoming another path for current discharge to ground.