Maintenance
Insulated Bearings
One or both bearings may be insulated to prevent shaft currents from pitting bearing surfaces. The insulation is located at the joint between the bearing housing or bracket and the bearing. Insulated bearings are designated by an instruction plate on the bearing housing.
Check periodically to be sure the insulation has not been weakened or destroyed.
The bearing insulation can be checked using an ohmmeter or circuit test light. For sleeve bearing motors with one bearing insulated, the shaft must be raised a few mils at the
Antifriction Bearings
Antifriction bearings are selected to give long service when they are given proper maintenance. Bearing failure can be caused by too little or too much lubrication, contamination, excessive bearing load, improper installation, alignment, or vibration.
The symptoms of antifriction bearing failure are excessive vibration, noise, and excessive heat generation. The races and balls should be periodically inspected for damage. Any damage requires replacement of the bearing.
Sleeve Bearings
Check sleeve bearings daily to be sure the oil rings are turning properly. See motor outline drawing to determine proper oil level. Add oil through the oil ring sight glass opening or oil inlet pipe, if so equipped. Be careful not to overfill.
Drain the oil reservoir by removing pipe plug. Clean and flush with solvent and refill with fresh filtered oil every three months to one year, depending on severity of service. Use a high grade turbine oil having a viscosity of
In addition, seasonal oil changes are desirable if unit is subject to wide variations in temperature.
Bearing babbitt temperatures that exceed 90°C (194°F) or a sudden rise in temperature should be investigated.
Common causes of hot bearings are:
1.Lack of oil.
2.Incorrect viscosity.
3.Poor quality oil.
4.Inoperative oil ring.
5.Misalignment of couplings or bearings.
6.Insufficient bearing clearance.
7.Oil seal rubbing on shaft.
8.Shaft or bushing rough spots.
9.Plugged oil passages on circulating oil systems. (Note that circulating oil systems include a filter in the oil line to strain the oil after it leaves the pump. Check and clean or replace filter when necessary.)
10.End thrust on bearing face.
Sleeve bearings are bored to an even dimension and shaft journals are slightly smaller to obtain running clearance. Side reliefs are provided to distribute oil axially and reduce friction. During normal operation, the shaft is supported on an oil film 0.001 to 0.005 inch thick, depending on speed, load and viscosity. Unless adverse conditions exist which tend to break down the oil film, metallic contact occurs only during starting and stopping. Under normal circumstances, bearing wear is very small.
Oil Rings
Inspect oil level and oil ring operation frequently. Oil ring operation can be observed through the oil sight glass. Oil rings should be perfectly round, free of burrs or rough edges, turn at a constant speed, and carry a noticeable amount of oil to the top of the bearing journal. Failure of the oil ring to turn freely may be caused by:
1.Ring out of round - rings should be round within 0.062 inch.
2.Fouling on a projection of the bearings, bushing, or housing.
3.Ring not balanced (heavy side will tend to remain down).
4.Adhesion to guide slot (trapezoidal section reduces adhesion).
5.Oil too cold, too viscous, or oil level too high.
6.Shaft not level – oil rings tend to bind.
7.Vibration causing oil ring to bounce and slow down.
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