In addition to the physical appearance of the surface of the commutator, the skin or patina is of equal importance for the good running of the carbon brushes. Each carbon brush builds a characteristic patina which is affected by operating and ambient conditions.
The patina consists mainly of copper oxides, graphite deposits and adsorbed water, and its appearance is of importance when assessing the most suitable brush grade.
The following pictures show typical appearances of commutation surfaces. The pictures are not of an international standard specification but are used by carbon brush manufacturers and users of brushers as a guide to
assist in judging the operation of carbon brushes.
Normal Skin or Patina Formation
P2, P4 and P6 are examples of normal skin or patina formation. When a machine runs well, the patina or skin on a commutator will be even, slightly shiny and coppery brown to black in colour.
There may be appearance of greyish, blueish and reddish hues. but of importance is the evenness of the skin formation and not its colour.
The above link is for computer users who need to obtain and use FREE Adobe Reader software. (Previously known as "Adobe Acrobat Reader" software.)