MASSEY TECHNICAL SERVICE LLC 10-Millbrook Rd. Bridgeport WV. 26330 Phone:304-842-6948

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09/11/2001

 

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Bearing Preloading

I will try to update the readers of this newsletter with new information as we discover and solve machine maintenance problems. I will accomplish this with newsletters that pertain to real case histories, as the one that follows.

CASE HISTORY #23. "300SL Bearing Pre-loading"

by Larry Massey

During 2000, while checking vibration on a rebuilt gear case at the repair facility. We found a definite bearing problem on the output bearing. The spectrum below shows bearing inner race defects with sidebands of running speed. The sidebands are an indication of a serious problem. This problem was found in an Enveloped Gs spectrum. We did not find any problems using the velocity or acceleration readings.

The bearing was removed and it was found that only a glazing was visible on the inner race. The bearing cover plate was examined and found to be to thick. It was removed and machined to give additional clearance. It was determined that pre-loading was affecting the bearing. The bearing was replaced and the machined cover installed. 

The spectrum waterfall below shows the before and after spectrums. Notice that only running speed and itsí harmonics are evident on the follow up spectrum.

I have found, during previous inspections, where pre-loading of a bearing can cause inner race defects or outer race defects. During the previous inspections, the problem could not be found using velocity and acceleration readings. The use of the SKF Enveloped Gs spectrum is a powerful tool in the diagnostic health care of rotating equipment. This also provides us more reliability and a better look at the health condition of the units tested, under no load conditions.

This is one of many examples of vibration analysis uncovering a problem before the unit is shipped and installed. In the next newsletter I will illustrate a different case study of vibration analysis, that detects a problem and verification of the problem when investigated. If you have any questions please contact us. Feed back is very important to us.

 

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