Diagnosing Brush Face Conditions
When carbon brushes wear quickly, it is common to assume that the problem lies with the brush grade. However, inspecting the face of the brush can provide insight and tell a story about the operating conditions. Analysis performed by carbon brush experts can be utilized as a diagnostic tool to conduct a root cause analysis. If the earning signs presented by abnormal brush wear can be identified and proactively addressed in a timely manner, unexpected and expensive failures, such as flashover, can be avoided.
What exactly is happening at the brush face when it is making contact with the commutator or slip ring? At a microscopic level, the two surfaces are never making full contact. Unlike in theory, practical current density is always higher. Current flows through few but constantly changing contact points based on quality of contact. The amount of contact points depends on current level, surface finish, TIR, spring force, vibration, etc. Often referred as brush track, patina will vary for different grades, current density, humidity, and other atmospheric conditions. Typically the patina is desired to reduce friction and extend life of both contacts.
While there are many different markings or patterns that could develop on the brush face due to operating conditions, the following are the most common.
It would be premature to blame the brushes or the carbon grade for fast wear problems. The appearance of the worn carbon brush is telling you a story about operation conditions. Instead of throwing away used brushes, take clear pictures of some or save a few that best represents all of the other brushes.
Involve a carbon brush specialist, preferably one who knows how different carbons are made at the composition level.
Contact a Carbon Brush Specialist: (800) 962- 4851 or email [email protected]