motor bearing high temperature?

[kmg1983]

I'm having trouble diagnosing what may be causing the top motor bearing on a 5-stage vertical, centrifugal pump to shutdown on high temperature alarm. The motor was sent off for inspection. The following was returned on the inspection report:

Prior to disassembly, a no load run test was done. The upper bearing temperature stabilized after two hours at 148 degrees F. The bottom bearing leveled at 115 degrees F. Vibration levels did not exceed .004 inch/sec in any direction. All parameters appeared to be normal. Total end play was found to be .012 inch.

Inspection of the upper bearing revealed that the rollers had been loading hard on the top edge of the outer race which had a dark blue color from overheating. The reason for the overloading could not be determined but can possibly be a defective bearing or caused by defective components in the pump.
The failed bearing will be sent to the bearing manufacturer for a failure analysis.

Meanwhile the motor will be reassembled and no load tested with a new bearing. If the test is satisfactory the motor will be returned to the site. Once it is reinstalled the amp draw should be closely monitored, if above normal it could be an indication of a problem with the pump.

Does anybody have any input or suggestions on what to look for?

 

[dickon17]

Does the pump dicharge head contain its own thrust bearing and a flexible coupling or does the motor bearing take all the thrust load?

 

[electricpete]

In addition to questions above.... Is there a temperature trend available prior to the shutdown? What ist he normal temperature? What is the trip temperature? How fast did it increase? Any lower bearing tempearture data avaialble? Any vibration data? I assume the upper bearing is oil lubricated? Is there any cooling water coil in the upper bearing? Was the pump operating in an unusual lineup?

On the surface, it sounds like the high temperature condition was a result of thrust from the pump (since you didn't have a high temperature during uncoupled run later). One possibility could be high pump thrust compared to bearing rating.


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[electricpete]

On the other hand "loading hard on the top edge of the outer race" doesn't exactly sound like thrust. Are you talking about the top/outer edge of the lower/outer race on a spherical roller bearing?

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[kmg1983]

I do not believe that the pump doscharge head contains its own thrust bearing, although I'm not really sure what you mean by that, dickon17.

Electricpete, yes a temperature trend is available prior to shutdown and it should a steady increase in temp., not an instantaneous spike. The normal operating temperature is about 175 deg. While the trip temperature, I believe, is 200 deg. The pump was operating as it always has as far as service. The lower motor bearing operated under normal conditions with no apparent rise in temperature. Vibrations at the motor bearings were not significant. The upper bearing is oil lubricated with no internal water cooling.

 

[dickon17]

Is the elecrtic motor a "hollow shaft" design allowing the turbine shaft to pass through and out the top of the motor where it is locked in place?

 

[kmg1983]

Yes. That is correct. It is a hollow shaft

 

[Artisi]

" ..........if above normal it could be an indication of a problem with the pump."

As it is a hollow shaft motor and I assume the top bearing is carrying the hydraulic thrust and rotating component weight I cannot see how this can be a "pump problem" - it sounds like a bearing problem either a faulty fit in the housing, wrong bearing rating for the load or a fault with lubrication. What does the report from the bearing manufacturer say.

 

[dickon17]

A) Check with the pump manufacturer for actual downthrust load from this pump when operating at your duty conditions.
B) Check with the electric motor manufacturer for maximum allowable bearing thrust load.
C) Compare A with B.

 

[dickon17]

If bearing loads are acceptable, check VERY carefully that the correct shaft setting has been made when adjusting the pump clearances from the motor bearing end. Follow the pump manufacture's instructions exactly.

 

[electricpete]

Artisi - who/what were you quoting? I can't find the context.

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[Artisi]

"electricpete (Electrical) 19 Sep 07 19:49
Artisi - who/what were you quoting? I can't find the context."

I was quoting the last sentence from the OP

 

[unclesyd]

What I've done numerous times with similar situations with bearings is to change the grease or oil to higher quality product with some additional additives.
I have found this method to be quite effective especially in basket case bearing failures. If nothing else it gives one more time to analyse the problem and possible elimination of one data point.

I have used these peoples products with excellent results on many a bearing problem.

http://www.le-inc.com/index.jsp

 

[Tmoose]

http://www.bardenbearings.com/scan pdf/Bearing Failure Brochure.pdf

What oil is recommended? What was the oil level, and how was that measured? How did the oil look? Clear or murky? I'd probably invest $50 oil analysis to confirm the right oil was installed, and it was not water contaminated.

These guys would run at least an ISO 32 oil in a high thrust motor with ball thrust bearing, and at least ISO 68 in a motor with spherical roller bearings, and an ISO 150 (!!) if the room temp was consistently 80 F.

Viscosity is one of the most important characteristics of oil ( and grease ). If the oil viscosity is just plain low it takes a heap of fancy additives to save my neck.