We did Vibration Analysis on a newly Overhauled Motor (3000KW 1800RPM) in our Electrical Workshop. The vibration levels were low but we got clear peaks at Outer race bearing fault frequency from both the DE & NDE bearings(NU234E). The Motor was running at no-load condition with half coupling and the bearings were new. There was no abnormal sound during testing and the bearings were sufficiently greased. We are confused about the signature that whether it is because of bearing mounting problem or skidding of the bearings during no-load testing or some real problem in the bearings. If anybody could give a comment on this subject is highly appreciated.

This message has been edited. Last edited by: Jenish,

Vibration_Report-3000_KW_DCK_2003-_Mtr___960023008-(22-02-06).pdf (155 Kb, 38 downloads) Vibration Report

Newly installed bearings may show BPOR due to race pinching but vibration pattern in this case will be heavy on low BPOR harmonics.

In your case, IMHO, defect is real from the spectrum and it is ringing all over the frame. This is also supported by the TWF pattern. I suggest taking PeakVue reading to see the real amplitude of impacting. Please post it.

I agree with David. And I will say this bearing is defective and should be replaced. I can see no way it can be considered 'as new'.

What kind of bearing, how much sand and how big was the hammer?

Do you have any unloaded spectra from the motor prior to rebuild?

I would recommend that before you either replace the bearings (and maybe have the same problem) or pass the motor and hope it is skidding, you find some way to load test it.

If you can't do it in your shop, I would consider transporting it to a facility that can. I would think that even a small load would tell the truth about these bearings.

Nothing more to add, Jenish, just adding to statistics. Now four are of the same opinon.

I'll jump on the bandwagon, too. For me, seeing that much action in the waveform is enough to replace it.

Jenish,
I read the report and found it curious that you would recommend sending motor from repair shop into service and expect plant personnel to "monitor" it. Why should the bearing problem not be resolved in the shop? How can running the motor under load improve the bearing situation? The bearing itself may not be deffective. It could be loose on shaft or loose in housing or have insufficient preload. Some motors have belville spring washers to apply an axial preload to bearings. I would not accept the motor with 6-g's vibration, loaded or not!

Walt

Thanks for all your comments...
Unfortunatley we don't take peakvue readings for newly Overhauled Motors. I think the real amplitude of impacting can be viewed from the waveform itself. I agree with Walt that the bearing may not be properly mounted. But it is difficult to change the mentality of some people here.