When there is a need for cleaning the contact surfaces of commutators and slip rings with brushes, emery cloth with aluminum oxide is NOT recommended, as conductive abrasive particles will cause arcing and damage to the surface. Many times, stone cleaning, garnet paper and machining are not a convenient, sufficient, or cost-effective option for machines as the priority is to keep the downtime to a minimum. This is when the carbon brush can be designed to clean up the contact surface.

This video shows the proper procedure for seating carbon brushes in a DC machine.

When working with DC machines, it’s not uncommon to find a customer who runs different products requiring a range of armature current. Unlike other conductors, where lower current is a good thing, carbon brushes are designed for a narrow range of current density. A unique aspect of carbon brush life is that brushes operating at a much lower current density than they are designed for do not last nearly as long as expected.

Al trabajar con máquinas de CC, no es raro encontrar un cliente que fabrica diferentes productos que requieren un rango de corriente de armadura. A diferencia de otros conductores, donde una corriente más baja es algo bueno, las escobillas de carbón están diseñadas con poco margen de densidad de corriente.

This video shows how to adjust the brush neutral position of a DC machine to prevent sparking at the brushes at full load.

One of the more mundane things we as repairers must be concerned with is motor storage. For many of us, storing large motors for major customers is its own profit center. For all of us, being aware of how our customers store the motors we repair and send to them is critical to customer satisfaction. A poorly stored motor is likely to suffer winding or bearing failure, and we don’t want unrealistic warranty claims over something outside our control.

The worn carbon brush face indicates the operating conditions. Therefore, it can be utilized by brush experts as a highly effective diagnostic tool for troubleshooting and determination of root causes. If these warning signs shown at the brush face can be identified and proactively addressed in a timely manner, then major unexpected expensive catastrophic failures like flashover or repair of the contact surface can be avoided.

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The lowly brush is underrated and misunderstood. The brush grade, brush pressure and spring tension, as well as the effect of load and humidity are each important to brush performance in DC machines, wound rotor motors, and synchronous machines.