BRUSH LIFE:

With a surface speed up to 3,940 ft./min., the mechanical wearing life of the brush is approximately 10,000 hrs. This life will increase with a decrease in the rubbing velocity.

POSITIVE BRUSH:

If the positive brush is continuously passing current at 3,940 ft./min. and rated current, the expected life will be 1,000 hrs. At this time, the slip ring would start to show evidence of wear, signified by gray spots on the slip ring.

If the brush is allowed to run idle (not carrying current) for a period of 15 to 30 minutes every 1,000 hrs., the surface condition of the slip ring would be restored and another 1,000 hrs. of operation under continuous current could be realized and this procedure can be repeated up to the expected life of 10,000 hrs.

On applications where the clutch is revolving only when current passes through the brush, it is necessary to place another brush on the slip ring which is not connected to any source of current. This idle brush will polish the slip ring and the 10,000 hr. life will be approached.

The brush on single slip ring clutches should always be connected to the positive side of the power supply. Otherwise, electrolysis may shorten both slip ring and brush life.

On high speed applications, eccentricities can cause brush bounce and arcing. The arcing can be reduced by using two brushes spaced ninety degrees apart.

BRUSH MOUNTING:

The brushes must be mounted in such a manner that the support is rigid and will not vibrate. The brushes also must be mounted so that the recommended mounting dimension for proper spring loading on the brushes is held within the tolerance of + .010. The brushes can have a tolerance of plus or minus 8° on either side of a radial line from the center of the shaft. Oil of the proper viscosity as recommended should always be used since heavy oil will cause a brush to be lifted and thereby cause arcing between the brush and the slip ring which is very detrimental to the life of the slip ring. This condition can be improved by adding a second brush close to the original brush to act as a wiper. The slip ring finish should be between 8 to 12 micro inches and, if possible, the slip ring should be ground after the unit has been mounted on a shaft to keep the concentricity within .0008" T.I.R.

When replacing brushes the slip rings should be checked and reground if they show evidence of wear. Care should be taken not to grind any more off the diameter than necessary to clean it up.