What is meant by light load and what effect does it have on carbon brushes?
When a grade operates with insufficient average current density the filming process is inhibited, friction increases, and brushes wear faster mechanically. The usual methods to address light load are to increase the current density through appropriate removal of brushes or to use a grade which can film at lower current density.
An oversized motor was installed for reliability, potential future load increase, and long life. Why are the brushes wearing out rapidly?
When brushes operate at less than recommended current density, there will be inadequate low-friction film formation and increased mechanical wear. It would be best to submit nameplate data, operating current, brush size, and number of brushes per set to our technical staff for a recommendation on increasing current density or changing the brush grade.
The brush is wearing too fast. Should the spring force be decreased?
The first step would be to make measurement of the present spring force, calculate spring pressure, and compare value to recommended standards. In most situations it has been determined that the spring forces are inadequate. This results in poor brush contact, excess electrical wear, and a wide variety of maintenance problems.
Is this an exact cross to the OEM# xxxxx?
Unless Helwig manufactures the brushes for the OEM, our brushes will always be an equivalent to the OEM brush. No manufacturer can exactly duplicate another manufacturer due to varying quality standards, production capabilities and differences in raw materials.
Can you supply a brush like number xxxxx, except in grade xxxx?
Complete nameplate information should accompany this statement to determine if the new grade would actually improve the commutation or improve the existing problem.
The brush writes like a #2 pencil. What grade is it?
This will make it difficult to determine the correct grade. Complete nameplate information should be included with the description of the brush.
Do you have a brush that does not dust?
No. Dusting occurs as the brushes carry current at levels below that required for the formation of a film on a commutator. The operation of brushes on a raw material surface has a very high coefficient of friction. Consequently, this results in a mechanical abrasion of carbon particles from the brush face or dusting. Some grades may dust less under different situations. Complete nameplate and operating information must be obtained for proper recommendations.
My brushes are wearing out too fast. Would a harder brush work more effectively?
Hardness does not have a direct effect on brush life or brush wear. If the commutators are out of round or have high spots, a harder brush will actually have a tendency to bounce more and leave the commutator surface, potentially causing greater problems than before. Light loads, light spring force and poor commutator conditions are the usual causes of rapid brush wear.
My commutator is grooving. Would a softer brush be a solution?
Grooving occurs when there is poor electrical contact, resulting in a high resistance at the brush face with the ring or commutator. This may be due to roughness on the surface or vibration. Light loads, light spring force and poor commutator conditions are the usual causes of rapid brush wear.
Steps in Identifying a Carbon Brush:
- Check the brush for markings such as:
- Helwig Part Number
- OEM Part Number
- Grade Marking
- Customer part number
- Any other markings, numbers, or special stamping
- Measure the brush dimensions (best done with digital calipers)
- Start with the thickness of the brush
- Next measure the width of the brush
- Third, measure the length of the brush and note if the brush is used or new
- Describe unique features of the brush
- Does the brush have a pad or hammerplate on the top of the carbon?
- Is there one solid piece of carbon or is it a multiflex brush with 2+ pieces of carbon?
- Note if there are any shoulders, slots, wearlines, or inserts in the brush
- Take note of the shunt features
- Is the wire connection tamped or riveted?
- Measure the shunt wires from the top of the carbon or Redtop pad to the middle of the terminal. Also measure the diameter of the wire.
- Count the number of wires
- Note if the shunt is copper or tin colored
- Does the shunt have any sleeving or insulation?
- Note the shunt/s location coming out of the brush
- Get details on the terminal connection
- Popular terminal styles include: spade, flag, yoke, stamped, pressed tube, plug, or HQD (Helwig Quick Disconnect)
- Measure dimensions of the opening
- Use a protractor to measure the degree to which the terminal is bent (if any)
- Check the bottom and top of the brush for bevels and concave radiuses
- Use a protractor to measure the degree of the bevel
- Describe the application
- What is the brush used in: a motor, generator, tachometer, etc.?
- What is the duty cycle of the equipment?
- Describe the environment the brush will be in: normal industrial, high altitude, plastic extrusion, etc.
If possible please supply all of the information from the motor’s nameplate, or provide pictures of the nameplate and the brush itself. It is also helpful to know how many brushes are used in the equipment.