300 HP GE motor

[stantomas]

Hi,
Looking for any specific application info or general thoughts. This is a long standing problem. We had a Reliance 300 HP DC motor driving a "jumbo" roll on a paper machine. The motors would fail every 2-6 months. Failure was non driven end bearing housing would work itelf loose, then motor would fail. The "theory" was the motor was of poor design. So we changed to GE 300 HP DC motor. These motors are having similar failures: occurring every 2-4 months, had at least 1 of 4 failures was the same non driven end bearing failed, one failure was a motor warranty issue. It is my belief that since the problem seems to be not dependent on manufacturer, and similar failures are happening, that the root cause is more the application and/or the design of the motor mounting. The motor is on steel support some 6 ft in the air driving 40 ton tolls. All our other motors are on concrete slabs and they dont fail at this frequency.
I realize there isnt enough info to have a definite answer but possibly someone has previous similar motor application experience, knows of issues with GE or Reliance motors, or agrees the lack of solid mass for motor mounting is probably a no brainer!?
The problems is long standing here and it has long been viewed as a motor problem....
Thank you for any and all comments!

 

[itsmoked]

Thanks LaffeyDD724. Waross has it. You could use two bearings reversed and shimmed.

Would seem to me that the opposite,(from drive end), bearing would be better as the roller bearing since it's going to have the larger side loading.

But then this is all fairly moot since this is a direct drive situation. Though a bearing change might still help.

Keith Cress
kcress -

http://www.flaminsystems.com

 

[waross]

With a direct drive, a very small deflection of the mount structure may develop even more side thrust than belt loading.

Bill
--------------------
"Why not the best?"
Jimmy Carter

 

[LaffeyDD724]

Keith,
It has been a while since I ran into that problem, to tell you the truth I cannot remember the bearing specs except that it was a roller bearing my first impulse was tapered roller and first impulses are usually correct, but the more it was discussed the more doubt I had about the accuracy of my recollection. It may have been a double tapered roller installed on the front end (Drive end). If the gentleman is interested in the theory and feels it worth investegating it, he would be well advised to contact an electric motor manufactures rep. and find out from him exactly what type of bearing should be used for a belted load and while he is talking with them discuss the present motor problem with them and get their recomendations. If it were me in that predicament I would have already gotten them involved and I would not let them sell me a bill of goods on the issue, I would keep pressing until I got a satisfactory answer and solution to this delima.
Tom

None of us is as smart as all of us.

 

[LionelHutz]

It looks like the base is basically 2 square posts under each end of the motor. If so, I'd agree with the others that the base is lacking in side-side support and it is likely "torquing over" causing your failures. Vibrational analysis won't show a problem because it is not a vibration.

Does the motor current go above the rated current during that start-up you describe? If so, the extra forces during the start-up could be hurting too.

 

[stantomas]

Hello,

Thanks all for the many excellent replies.
I am digesting the info and agree the problem is somewhere in the motor stands (steel) causing loading affects that are damaging the bearings prematurely.
I am also looking at the way we start up the two motors that are supposed to work together via the controls. We may have made change in start up operation that is causing stresses that the motor bearing is seeing.Thsi may not be the root cause but may be contributory.
We do have a motor shop that has worked onthis issue for many years. Unfortunately a theory was presented by an employee here and belived byall, that the previous motor (Reliance) had an inherant design flaw, which we all believed. Since we tried the new GE motors and are seeing same failures, we realize the theory was not accurate. During all the previous bearing failure w/ Reliance motor, it appears no one did any bearing analyses. I am now doing that with the latest failure!

I believe the root cause is in the motor mounting/alignment/startup controls ....it can't be much else!

Thaksn again.
stan

 

[Compositepro]

It seems to me that any misalignment or excess radial loads on the motor shaft would primarily affect the drive-side bearing. An axial thrust load on the motor shaft, however, could affect only the back-end bearing. That or currents circulating through the bearing. You ought to be able to diagnose the problem by analyzing the bearing.

 

[Ray39836]

If you are experiencing bearing failures every two months my suggestion would be to remove the bearings in one month and have them analyzed by a bearing manufacturer. They should be well on their way to failing but not enough to destroy any evidence.

 

[edison123]

Stan

Bearings on the drive end 6218, 6216 opposite end

Since both of them are ball bearings, one of them (usually the ODE) must be free to move axially to accommodate thermal expansion. The bearing cups of this nolocating bearing should not touch the bearing.

Another thing - Bearings seem undersized for a 300 HP motor. What is the motor speed ?

 

[LaffeyDD724]

I did some research and found that a tapered roller bearing, that is typically used for belted loads would not be suitable for a coupling application. The reason given is that the tapered roler bearing requires side loading to keep it healthy. If that type of bearing were to be installed on a coupling application there would not be sufficient side loading to keep the bearing functioning properly and skipping would occur and that would result in bearing failure.

Tom

None of us is as smart as all of us.

 

[itsmoked]

Thanks LaffeyDD724. More fodder for the memory banks.

Keith Cress
kcress -

http://www.flaminsystems.com