Induction Motor Failure Autopsy

[adddy]

Hi all.

Can you help please?A Jeary SD14/039/57 30Lbs/ins. ST rating 59 RPM with right angle worm/gear box stopped working in my absence. Replaced bearings and seal 6 months ago after the bearings became rough/stiff and the motor kept overheating and seizing after a short run. The bearings and seal where replaced and new oil in the box. Now the seal is loose on shaft and from housing. One bearing is seized and oil is everywhere and the coils cooked. Motorman, can you you help diagnose the sequence of events that led to it's demise? Can you recommend a source for rewind or replacement? It also has a gear to drive a castellated rubber belt. Question-If jammed, do (why)the coils heat up?
Thanks

 

[itsmoked]

First check whatever the "belt" is driving. Has that load somehow changed? Angle of conveyor? Thicker mix? Its bearings are failing?

You say "motor kept overheating and stalling". This only needs to happen one time to damage the motor. You should prevent that from EVER happening. Where is your overload protection for your motor?(Which also can prevent your facility from burning down.)(And is required by NEC)

After seal replacement you're right back in the same place again. This is all pointing at what the belt is driving.... The load has increased past the gear box's rating or the normal heat generating losses of the gear box have now greatly increased from scuffing gear teeth, rough surfaces, and violated lubricant.

Keith Cress
kcress -

http://www.flaminsystems.com

 

[adddy]

Thanks IS, It's a very light load and it's hardly changed in 10 years.
Well, it became hot and there was a smell once and I tested it again to check for myself. It worked but I felt it was hot and investigated and repaired.
It was an in house installation when I arrived and there is no dedicated trip. Point taken...thanks.
I think the dry gear box originated it's demise and possibly age , the bearings?
I am there again tomorrow and they will be seeking my advice and hopeful of a solution.
I ponder as to whether the seal failed and allowed oil past the still working bearing and onto the windings and caused a short or the bearing seized and caused the heat which damaged the seal and let in oil or whatever.
Question-If jammed, do the coils heat up and why?
Thanks

 

[itsmoked]

If jammed and there is no overload protection the motor will draw 8 to 12 times the normal current it should and its windings are sized for. Also with the motor not turning its fan is doing nothing. This all results in the insulation system (varnish/whatever) breaking down. That destroys the motor. Usually in seconds..

So yes the 'coils', we call them windings, do heat up, and generally in a spectacular fashion.


If your seal failed and let out the oil then the gear box bearings, shafts, and gears could/would die.

You show up and replace the oil and the seal. But now the part of the shaft the seal rubs on can be ever so slightly rougher. After a few thousand revolutions the new seal again dies. Step and repeat.. It's a possibility.

Keith Cress
kcress -

http://www.flaminsystems.com

 

[adddy]

Thanks again,
No fan at all and totally sealed.
I would never have deduced that the old seal could roughen the shaft rather than polish it!
There is another clue to the problem in that the starter cap. needed help with a push on the load to get it going, but once going, if disconnected and reconnected soon after, it worked.
However, if unplugged and then replugged, it started.
I assumethe switch was single pole and that 2 pole and earth connection made the difference.
So, sometimes it was not prodded into start and that's when the coils eventually cooked.
I can only wonder why the cap. start failed after renovation.
Cheers

 

[MikeHalloran]

Sealed motors usually have a fan inside the sealed perimeter, often in the form of fins on the rotor, just to keep the air moving around inside the enclosure, which conducts heat away from the moving air.

Unless the air flow stops, which happens when the rotor stops.



Mike Halloran
Pembroke Pines, FL, USA

 

[ccjersey]

Capacitor start may have failed from:
bad capacitor
bad centrifugal switch mechanism
bad centrifugal switch contact(s)

Internal motor problem:
Motor bearings failed
Start winding insulation failure

Overload on output of motor
from gearbox problem
from load problem

Low voltage supply to motor

It's not that the seal will roughen the shaft in most cases, instead the groove worn in the shaft by the seal lip typically decreases the lip tension and allows oil to leak. It's also very likely the bearings failed first and then the seal could no longer contain the oil as the shaft was oscilating back and forth.

 

[adddy]

thanks. I am now not positive I oiled the seal lips. Would that increase drag enough to add damaging load?

 

[itsmoked]

No.

Keith Cress
kcress -

http://www.flaminsystems.com

 

[crthompson]

You may also want to check the voltage source feeding the motor... It could be low or if it is a 3 phase motor, you may have lost a phase.