Bearing noise due to overgreasing ?

[edison123]

Two 3000 KW, 6 Pole, 994 RPM sq. cage motors driving reciprocating gas compressors have NU 244M + 6244C3 bearings on DE and NU 244M bearing on ODE. Motor OEM (Hyundai) specified to charge grease (Alvania 2) every six months of continuous running with 2100 gms in DE and 1000 gms in ODE, which is the original total grease quantity for a new motor.

After regreasing as per above OEM schedule and quantity, we hear a high frequency squeal from both the motors. This noise is cyclic with a 3-4 second duration between peaks like a beat. No such noise before regreasing. We do not have any SPM or other noise measuring devices at present. No abnormal vibrations and the bearing temps not more than 60 deg C.

1. Did regreasing introduce this noise and if so, how ?
2. Normally, for such slow speed machines, regreasing amount is small and interval is large. Why in this case, the OEM has recommended a full grease replenishment within six months of continuous running?
3. After regreasing the above entire quantity, not a bit of old grease came out of grease outlet. What happened to all the old grease (3 kilos) ?
4. Do we need to open up this motor immediately and check the bearings, grease etc?
5. Finally, is it not abnormal to use rolling element bearings for such a large capacity of 3 MW ?

 

[steamboat444]

Although it sounds like this is not the problem it might come in handy in the future.

I was taaught many years ago that overgreasing a ball, and presumably a roller, bearing retards the movement of the ball/roller in the race. This causes the balls or rollers to "collide" with each other as the bearing rotates. This is evidenced by gauling on the ball/roller. It is noisey and the increased friction of the balls rubbing together would add to the load current of the motor in time with the noise caused.

Hope this helps.

 

[electricpete]

steamboat - What if the bearing has a cage?