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!

 

[roydm]

A couple of ideas.
Motor load missalignment, this should show as a high temperature of the bearing under load. I have seen this on sleeve bearing motors driving a conveyor via a gearbox. When the conveyor is empty the bearing runs cool but once loaded the bearing overheats.
Or
Current circulating in the motor via the bearing which causes pitting. Many large motors have one bearing insulated from the frame and a grounding brush at the other bearing to short circuit any stray current.
No doubt others can add to this.

Roy

 

[waross]

Is this direct drive? Is the coupling solid or resilient? Have you checked for vibration? Is it possible that thermal expansion of the roll may be affecting the motor?

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

 

[itsmoked]

I think bad loading too. 40 ton rolls.. Whew.

Any chance you could change to a roller driven by chain with the motor offset a few inches. Then the motor would have no aberrant loading issues, nor be shock abused by loading and unloading of paper rolls.

Is the current to the motors modulated in any fashion?

Keith Cress
kcress -

http://www.flaminsystems.com

 

[ScottyUK]

I had a long and unhappy history with a DC motor mounted in a similar frame. Motor was approx 3/4 tonne, 280 frame. Bearing failure was almost accepted as inevitable. I lost count of the arguments I had with the mechanical people who said the mounting was strong enough, which it was in terms of load bearing capability but not in terms of rigidity. I would agree that the most likely cause of your problems is the relatively low mass and resilient mounting on the steel frame.


----------------------------------

If we learn from our mistakes I'm getting a great education!

 

[stantomas]

Hi,
Thanks for all the replies. Your comments are in the same general area as mine have been. Now I need to try to prove out the root cause.

Here's some more info to answer some of the questions in your replies.

-The motor is connected to a gear box by a dodge coupling, its a boot style size 140.

-The rolls are "speed match" controlled by a SAF (Brock solutions in Kitchner Ontario) scr drive-each roll motor uses tachometer feedback to confirm the motor speed. The rolls get pressed together, then the drive control system "speed matches" the top and bottom rolls so they run at same speed. The rolls are same size, approx 30 feet long by 4 ft diameter and again are 44 tons each. At start up you can see the amps for each motor oscilating up and down...i.e. the top will rise in amps , taking the bulk of the load, while the bottom roll motor will lower in amps. Then this reverses. This occurs from start up until the paper machine is running at full line speed of typical 2100 feet per minute. Might the motors see strange electrical stresses while the rolls are again pressed together and the drive controls are trying to balance the load and eventually resulting in each motor amps at abotu the same...ramp takes about 10 minutes to line out.

-I also thought of circulating currents; looking into grounding.
- we have inhouse vibration people but they never see anything wrong! bearings also not hot.

Any further comments much appreciated. I am looking for best way to rule in or out the various possible root causes.

Thanks again!
stan

 

[edison123]

What sort of bearings, sleeve or anti-friction ? As a rewinder, I can vouch GE/Reliance motors are very good products.

As others, I would suspect the motor mounting arrangement.

Could you possibly post some pictures of the motor mounting arrangement ?

 

[ozmosis]

I may be "stating the obvious" but the simple fact that this motor is the only one mounted on a steel frame and this is the one with significant problems tends to give a clue.

 

[MotorVib]

Take a look at the bearings they will tell you a lot on how they failed. Your SKF or NTN rep can help you out on this. They can take the bearing apart and tell you how it failed. Or if they are not will to help or you can do it you self.

My only word of wisdom is to disassembly the cage and push outer race in a vice to get the balls out. Please don't cut the outter race, it is harder to find there root cause that way. See the below web page

http://www.alliedbearings.com/downloads/skf_bearing_failureandcauses.pdf

Chris

"In this house, we obey the laws of thermodynamics." Homer Simpson

 

[ScottyUK]

A vice for the bearings from a 300HP motor...


----------------------------------

If we learn from our mistakes I'm getting a great education!

 

[stantomas]

Hello,
Thanks again for the many replies. Someone asked for pics of the installation. I think I was successful in uploading 3 pics. One shows the lower motor on a 3.5 ft or so tall stand. The other two show the higher motor frame. One pic shows the frame, the other shows the motor on top- motor has an orange cover on it- keeps it dry

Bearings on the drive end 6218, 6216 opposite end.

Havent doen a thorough bearing analyses because we all thought the problem was the Reliance motor design...but now that the GE is failing in similar manner, I am having bearings looked at.

Our vibration on site people check things often and find no out of ordinary vibrations,heat,etc.

Anyone familiar with controls schemes to "speed match" two rolls that are run from separate motors and scr drives? I am thinking our start up is not best. We run the rolls "pressed" together (hydraulic presses them together)from 0 to 2000 Feet per minute. What should the control system be doing as far as driving the 2 motors during this time? Should one be pulling the other?

Thanks again,

stan

 

[stantomas]

Looks like you can only post one pic at a time. The one in previous post is the upper motor. I'll add the lower motor next, then a lower view of the upper motor framework.

thx

 

[stantomas]

And the last pic...

 

[Kigif]

Stan,

I am assuming this is a press section. Typically the primary drive will be run in speed, the other driven rolls will be run in torque mode as helpers. If Brock did the integration, I would doubt that your problem is the control scheme, those guys are very good with web applications.

If I understand correctly, motor is close coupled to a gear box and the ODE bearing is failing? Only thing I can think of is alignment and I'm sure you have already checked.

We do put all our motors on steel frames encased in concrete. Good Luck.

 

[itsmoked]

Welcome to Eng-Tips Kigif.



Keith Cress
kcress -

http://www.flaminsystems.com

 

[LaffeyDD724]

Concerning the 300 HP press roll motor loosing opposite shaft end bearings. I have had some experience with loosing opposite shaft end bearings. Electric motor applications with belted load transmission require a tapered cone roller bearing on the shaft end, other wise the side loading will cause the opposite shaft end bearing to fail. I have had this to happen and the result was bearing failure on the opposite end. Now I say this to bring up what I think might be a point. Some have stated that they lean toward misalignment and I do also, for this reason,you stated that the frame work was somewhat weak. That makes me think that the weakness of the mounting framework could be contributing to misalignment and if the misalignment is causing side thrust then it may cause the same problem as a ball bearing on the shaft end in a belted load application.
You could install a tapered cone roller bearing on the front end and see what happens. I know about these things and how difficult it is to get mechanical to buy into the fact that they may have a problem that is effecting your motor. You could change the shaft end bearing without a lot of fuss. Even if the allignment is corrected chances are it will not stay corrected due to the weakness of the supporting framework. If a different bearing on the front end of the motor would solve the problem it would be more economical than reworking the framework, if that is in fact the source of the trouble.
Tom

None of us is as smart as all of us.

 

[itsmoked]

LaffeyDD724; Don't you have to preload tapered roller bearings? How would he do that in his present setup?

Keith Cress
kcress -

http://www.flaminsystems.com

 

[waross]

Hi Keith;
One method of preloading is to use back to back bearings and shims in the bearing cap.
Stan. One thing that may help and may be an easier sell to the mechanical side is plating the supports.
I would consider stiffening the supports with 1/2 in sheet steel. Fill in the openings in the stand with welded in place sheet.
I would try first filling all openings at right angles to the motor shaft. The top and bottom welds will be the ones that do the job. The welds on the side will tend to deflect the sides of the support members under load and may still allow overall deflection and vibration.

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

 

[LaffeyDD724]

Keith, I cannot answer that question authortativly, so I won't try. I have always used a motor shop to change bearings on large motors unless it was a dire emergency. It has been a while since I have had to confront this type of problem, but to the best of my memory the work was done in the field and it was no big deal for my crew and the motor shop to accomplish. If the gentleman thinks that this theory has merrit then I would suggest that he contact a reputable motor shop to assist his crew with the changing of the bearing style and first get their opinion on this,they may say that this is not the way to go for this application.I know, for a fact that belted applications do require a tapered roller bearing on the shaft end of an electric motor due to the side loading. If it is not there then someone will be in for a lot of bearing replacements on the opposite end bearing. I learned this fact the hard way, I had a belted application that was driving me mad loosing opposite end bearings, just as the gentleman has with his problem. If a plant has a motor poole for spare motors then it is not difficult for a motor that is not suitable for the application to get into place, like at 2:00 am with a skeleton crew performing the work to get back up and running. It would not be a big deal to change it, it could be done on a routine maintenance outage and we are not talking a whole lot of money. If it were mine I would stick my neck out and try anything that I thought, after careful consideration would do no harm and had enough merrit to give it a try. Nothing ventured nothing gained. I would not do this if the problem could be solved with standard procedures but sometimes that is not feasible because of lack of cooperation, competition and capital. Edison once said, when questioned about didn't he become discouraged after he did and experiment that failed and he replied "no, now I know that this is just another way it won't work".
Tom

None of us is as smart as all of us.

 

[LaffeyDD724]

Keith, just after I made the last post I got to thinking that I may be wrong on the tapered part of the roller bearing but it definitely would have to be a roller bearing, that much I am sure of. When I wrote my first post on this I was thinking tapered roller but now I am not sure about the tapered part, it may be just roller. But the gentleman can find out the correct bearing type for a belted load should he be interested and it will be some sort of roller bearing.
Tom

None of us is as smart as all of us.