What is Patina?

About Carbon Brushes:
1. Carbon Brush	2. Why Carbon is Selected as the medium?
3. Current Density in Carbon Brush	4. Why Carbon Brushes are split?
5. What is Patina?

Patina is also know as film or skin over DC motor commutator. It is mainly copper oxide that formed on a commutator surface as a result of reaction among copper, graphite, oxygen and other free particles in some range of temperature. Patina is a very thin film and can easily damaged.

Patina is very helpful in commutation, it makes commutation smooth. So during maintenance extra care should be taken to preserve patina.

Patina color

Normally in good condition patina formed all over the commutator evenly. And the color of patina can be slightly shinny, coppery brown to black. But keep in mind that the color of patina is not that important thing, the important thing is whether they are forming evenly or not.

Bad patina indicates some abnormality of the environment or the motor. Such as high humidity, presence of oil and grease particles, uneven commutator surface, uneven current distribution, low load operation, commutation problem, high resistance problem, raised mica, vibration etc.