We recently overhual a motor that had high vibration due to inner race defect frequency at motor inboard bearing. Bearing replacement was done on the motor and during test run, the inner race peak was still domimant. The peak was at 3 mm/sec and remain steady at that level for about 2 hours of running. Then the peak started to increased steady from 3 mm/sec to 12 mm/sec with another 2 hours of running. The motor was stopped when it reach 12 mm/sec.

The high vibration was in the axial direction at motor inboard bearing. The radial vibration remain stable through out the test run.

The motor is coupled to a screw compressor and during the test run the load was constant. The vibration on the compressor and motor outboard bearing remain stable during the test run. Only the vibration at motor inboard bearing in axial direction showed the increased in vibration level.

From past data showed that the vibration on the motor inboard bearing was around 2 to 3 mm/sec with the domimant peak at motor 1x speed.

Could a coupling problem create this extra axial load on the motor bearing and cause the vibration to inceased? or some other problems

any help?

Will try to attach trend and spectrum data later. And also the photo of the first defected bearing.

Regard
Adam

Ive experienced that when there are sheet metal broken in coupling it produce high 1X, wich you can see with a stroboscopy lamp in service but there isnt your case. When you send historic data please indicate characteristic of bearing

Attached is the vibration trend and spectra for the motor bearing.

Regards
Adam

Y050428_Motor_Bearing_Trouble.doc (314 Kb, 79 downloads)

What was seen inside the old bearing, as far as an inner race defect is concerned?

Adam,

What type of compressor is this? Are you certain that this is an inner race frequency and not a harmonic of gas pulse frequency?

Good Luck,

Adam,

What type of compressor is this?

Are you certain that what you are looking at is inner race related and not a harmonic of gas pulse frequency?

Good Luck,

Miguel,
The coupling used on this unit is Thomas disc coupling. The coupling was found to be in good condition visually. The "N" value was slightly out of the manufacture tolerance. Will attached the "N" value later and photo of the coupling.

Ralph,
There was flaking seen on the inner race. The spacing of the flaking was about the two balls distance. Suspected high axial load caused the defect.
Will attach some bearing photo once I get back to the office.
Thank
Regards
Adam

Adam, you said this motor is coupled to a screw compressor. I've taken data on many Sullair rotary screw compressors. Most of them have a high 7.2x in the axial direction caused by the compressor rotor gear mesh. Oddly enough, the highest reading was usually on the motor outboard end. Screw compressors do have an axial load.

Don
The frequency is from motor inner race defect frequency. Past data showed that the motor compressor had very low axial vibration at motor inboard bearing.

Attached is the defect bearing when the vibration hit over 50 mm/sec.

Attached also the coupling inspection data for the "N" value of the Thomas coupling series 71. The "N"value was out of the manufacter tolerance.
How critical is the "N" value?
Could coupling axial gap cause this problem?

Regards
Adam

Y050415_Motor_Inner_Race_Defect.doc (496 Kb, 59 downloads)

Good pictures.

Looks like the "bad" bearing was loaded in the axial direction. In fact it looks like both bearings were loaded in the axial direction.
Where were the loaded areas located, facing the coupling end or the opposite end of the motor. By any chance were the loaded areas facing each other or both facing the same way?

Adam,

With that much difference in the n values on the coupling it seems like there has to be either some misalignment or the coupling is not assembled properly. Were the measurements taken with the coupling in place or removed from the machine?
Have you looked for distortion in the shimpacks while running with a tunable strobe?

Ralph,
Both bearing were loaded in tha axial direction and both facing the coupling end.
Danny,
The alignment look ok, we suspect the center piece of the coupling was mot the original assembled position. Will tried to look at the shimpacks while running.

Thank
Regards
Adam

Adam,
Looking at the last picture of the coupling the right side shim pack appears to be deformed. Is it actually deformed or is this just an optical illusion.
We have several machine with this type coupling and lately have had a rash of problems with axial vibration being high. When checked we are finding that the mechanics are not getting the coupling spacing correct when reinstalling hte couplings. We have had a large turn over here in the past year due to retirements and alot of the knowledge went with them.
It sometimes feels like we are starting over from scratch.
Back to the subject. If the disc pack was deformed maybe this coupling was assembled with the improper coupling spacing causing an axial push.