Motor Bearings

[session88]

We have two 150 HP 480 VAC motors that had bad bearings that cooked/fused themselves to the motor shaft. Our local motor shop had to cut, heat and pull the internal bearing races off the shaft. This damaged the shaft pulling some of the shaft off in the process of pulling.

My question is: If we have our local machine shop build up the damaged motor shafts by welding and turn (lathe)the built up weld back down will these motors still be reliable? Our local motor repair shop is telling us they will not be reliable after this shaft repair.

These motors are running a critical process that need very reliable motors 24/7 - 365.

 

[BrianE22]

If the existing shaft material is a high strength steel, the high temperature from welding might adversly affect the strength of the steel.

Another possibility for repair is to chrome plate and grind or build up the area with a metal coating process that's machinable with lathe tools.

 

[electricpete]

The cost of new motors is probably comparable to cost of repair. If the people you would trust to do the repair aren't prepared you stand behind the repair.....seems like new motor is the way to go........unless there is a schedule constraint and this is a unique motor that can't be purchased in time.

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(2B)+(2B)' ?

 

[petronila]

Hello Session 88,

What they damage? The inner bearing fit?

If yes, the shop most verify the shaft straightness, if is OK you can repair that fit by Welding and machinning process,this practice is common and I don´t see the problem,the only is the shop most use the correct tolerance for the bearing fit.


Regards

Carlos

 

[wayne440]

This-

Our local motor repair shop is telling us they will not be reliable after this shaft repair. These motors are running a critical process that need very reliable motors 24/7 - 365.

- is what you should base your decision on. You are not in a good position if you are the one that decides it is OK to repair this motor.

Why? If you repair the motor anything that later goes wrong will be blamed on that repair. And you will have little defense, because the motor shop told you so, etc.

 

[DOsul]

Lots of Qs.
Had the ball/roller bearings spun on the shaft, if not what where your repairers doing to trash the shafts. (remove bearing cage, drop out balls/rollers and off with the outer track. ready with extractor for inner track, add lube to fit and torch inner track with oxy-acet. lube. extract some, cool shaft, heat track, lube, torch, lube, extract an-on.)other wise grind off (a flat)on inner track to break interference fit, then remove.)

As the shafts are shaged, check rotor all over for run out between centers (dont worry about shaged bearing fits), if ok consider repair.
Possible repair is skim shaft,sprayed metal build up and grind to correct fit or PRECISION turned, mounted in bored soft jaws and a center or between centers.( no bruised centers in shaft !!)
All in all could put you out of action for a bit, If you can stretch to it some new motors and repaired and tested motors in hand. Coffee Please !

Dom

 

[burnt2x]

Lots of Qs.
Had the ball/roller bearings spun on the shaft, if not what where your repairers doing to trash the shafts. (remove bearing cage, drop out balls/rollers and off with the outer track. ready with extractor for inner track, add lube to fit and torch inner track with oxy-acet. lube. extract some, cool shaft, heat track, lube, torch, lube, extract an-on.)other wise grind off (a flat)on inner track to break interference fit, then remove.)

As the shafts are shaged, check rotor all over for run out between centers (dont worry about shaged bearing fits), if ok consider repair.
Possible repair is skim shaft,sprayed metal build up and grind to correct fit or PRECISION turned, mounted in bored soft jaws and a center or between centers.( no bruised centers in shaft !!)
All in all could put you out of action for a bit, If you can stretch to it some new motors and repaired and tested motors in hand. Coffee Please !

Yep. That's how we do it. Once, we even skimmed a few mm off the shaft and force-fitted a nice sleeve on then have it turned precisely to original bearing inside diameter (with proper radial clearance).

 

[ozmosis]

I would also be looking at cause of bearing failure and also your maintenance activities to assess bearing performance on critical applications.
I agree with the other comments about trusting the repair agent. If they are reputable, trust them and act on it accordingly.

 

[bartb102]

Any thought as to cause of failure? Excessive shaft currents due to bearing insulation failure?

 

[session88]

The motor shop did not see any piting on the bearings that would indicate current leakage. The bearings might have failed to do improper bearing greasing. The bearing grease vent port has a cap that needs to be pulled before greasing and this might not have been done in the past on these motors. Thanks for all of the responses.

 

[electricpete]

Linked below is vibration case study on bearing spinning on shaft, which evolved to discussion of shaft repair methods on pages 2 and 3:

http://maintenanceforums.com/eve/forums/a/tpc/f/3751089011/m/54620207663/p/2

Also here is a previous eng-tips thread on similar subject:
thread248-49516


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(2B)+(2B)' ?