It is fairly common to see proper equipment maintenance get neglected, especially when plants are concentrating on maximizing production. Reductions in maintenance staffs add to the challenge. Yet neglecting to maintain equipment properly can cost money.

One of the more costly aspects of maintaining a motor is turning and undercutting of the commutator, which can run into thousands of dollars -- not to mention the costly downtime when the motor is out of service.

Typical commutator problems include: streaking (shown), threading, bar edge burning, grooving, slot bar marking, photographing, and copper drag. Streaking may be caused by low or unequal spring pressure, low current loads, contaminated atmosphere, high humidity, or copper particle pickup from the commutator.

Causes of threading include low or unequal spring pressure, low current loads, contaminated atmosphere, high humidity, and uneven current distribution. Bar edge burning may result from low or unequal spring pressure, incorrect brush alignment / off neutral, wrong brush grade, sparking caused by commutation problems, or incorrect interpole strength.

Grooving arises from low or unequal spring pressure, contaminated atmosphere, low humidity and temperature, and abrasive brush grade; slot bar marking, from uneven current distribution in armature windings, unequal number of windings in adjacent slots, and inconsistency in armature windings related to the number of coils, slots, and commutator bars.

Causes of photographing include high humidity, high resistance area at the same point of rotation, or a mechanical problem that causes a jolt on the brushes and interruption of contact or electrical spike at the same point in rotation. Copper  drag  is caused by low or unequal spring pressure, excess vibration, wrong brush grade, overheated and softened commutator, and high friction.

Solutions to these problems may include:

• Increasing and equalizing spring tension
• Upgrading the brush holders to constant pressure type
• Applying the brush grade best suited for the current load
• Removing brushes on lightly loaded machines
• Reconditioning of the collector including turning the commutator and /or undercutting the slots and chamfering the commutator bars.

An aid to reducing maintenance and downtime, extending carbon brush life, and increasing the longevity of the motor is Helwig Carbon’s Commutator Condition Guide. The Guide is designed to help you spot possible problems before they cause serious damage by comparing the condition of your commutator to one of the pictures. Seven of the most common conditions with possible causes are illustrated in the foldout brochure, along with a chart showing recommended spring pressures on typical applications and the formula for calculating spring pressure. Also included are step-by-step instructions for proper carbon brush installation.

Request a copy of the guide.