rotor fell out of 185Kw motor 1

[Feg]

Hi
Can anyone offer advice on the following. We had a rotor fall out today on a WEG 185Kw 4pl in Vertical position shaft pointing down. The motor is 3 years old, is fitted to a Barmac crusher with approx 10 inch 8 groove pulley on the shaft no flange fitted mounted by the feet. The roller bearing came through the bearing cap.The bearings don't seem to have been the fault as they look prety good and are monitored.
Regards
Feg

 

[electricpete]

Can you tell by examination whether it was a vertical or horizontal force which pulled it apart.

If vertical... maybe the setup of the bearings did not allow proper expansion and axial expansion

If horizontal... maybe extreme belt force. I imagine that 8 10" belts could produce quite a lot?

Either of the above I would have thought you would have seen some earlier warning. Maybe just weak bearing housing?

 

[rbulsara]

What kind of rotor is it? Wound or squirrel cage?
What type of starter?

And what is meant by rotor falling out? What kind of protective devices opened? Is stator burnt?

 

[Mendit]

Your most likely cause, NDE bearing overheated, lost fit to the shaft. This size of motor probably did not have a locknut or retaining ring to keep the bearing on. With the roller at the DE and no bearing holding it at the top, what keeps holding it in. Did you ask WEG before you made this installation?

 

[Feg]

Thanks Guys

electricpete
As it is very noisy in the area with the crusher bearing noise cannot be heard normaly. The force seems to be vertical, belt tension seemed ok.

rbulsara
A squirrel cage rotor. Control Techniques Soft start. Rotor came out of its position in the bearing journals and broke through bearing end cap & droped about 4 inches.
Yes Stator burnt.The circlip seems to have opened.
Mendit
Yes WEG said motor was ok for this position,but i have seen other motors in this position with a flange at DE.

 

[electricpete]

Mendit's comments make sense. The weight should be supported by upper bearing. Roller bearing on bottom wouldn't be capable of taking any axial/weight load. At some point there must have been a failure of the upper bearing.... inner ring separating from shaft sounds most plausible way to release the whole shaft. Is it possible to inspect the condition of that bearing?

 

[Mendit]

The circlip opened only after the fit between the bearing and the shaft became loose, either by temperature (loss or lack of lubrication most likely). Point to note Vertical motors with grease lubricated bearings should be greased at half the interval of horizontal motors in the same service. Or, contamination. You said a crusher application (dusty I bet) again calls for additional greasing.
If you install a similar motor the upper bearing should be retained with a lock nut and washer and lubricate with an Auto greaser.

 

[busman1]

Hi Feg,
I am the Agent for TECO electric motors in South Africa. We have had similar installations with our motors and if it is a vertically mounted motor then the standard roller bearings can not handle the upward and downward thrust therefor for all of these type of installations we have changed the bearings to angular contact bearings thus relieving the stress on the bearings and bearing housing. Maybe this was the problem. I am interested to find out how it goes.
Andrew Bussey