A uniform and light surface skin or patina formation on the commutator indicates that the machine and brushes are working well. This film can be damaged in service resulting in a commutator with raw grooved or streaked surface, flat spots, ridges, copper dragging, burning, bar marking or patchiness. These can be caused by many conditions including overloading, contamination, vibration, incorrect brushes, brushgear settings or commutator brush surface diameter.
Once the film has been damaged, the brushes do not operate correctly and sparking with rapid brushwear can occur resulting in a premature machine failure.
When we refurbish or repair a DC machine, the commutator will be skimmed and undercut to return it to its original condition ready to lay down a new film or patina in service. We fit new brushes , which are carefully bed-in with new tension springs if needed or required.