Corrosion (Rust) in Rotor (electric motor)
Corrosion (Rust) in Rotor (electric motor)
(OP)
Dear Friends,
3 years ago we purchased 200 numbers of 3 phase induction motors. Due to some reason, we did not use the motors and was in our ware house. Now we want to use the motors. Before assembling it on the machine, we opened one motor and found corrosion in rotor.
I request motor experts view on this.
1) Can we use the rest of the motors?
2) If there is corrosion on rotor, what are the effects of it during operation?
Thanks,
An
3 years ago we purchased 200 numbers of 3 phase induction motors. Due to some reason, we did not use the motors and was in our ware house. Now we want to use the motors. Before assembling it on the machine, we opened one motor and found corrosion in rotor.
I request motor experts view on this.
1) Can we use the rest of the motors?
2) If there is corrosion on rotor, what are the effects of it during operation?
Thanks,
An





RE: Corrosion (Rust) in Rotor (electric motor)
Keith Cress
kcress - http://www.flaminsystems.com
RE: Corrosion (Rust) in Rotor (electric motor)
RE: Corrosion (Rust) in Rotor (electric motor)
Keith Cress
kcress - http://www.flaminsystems.com
RE: Corrosion (Rust) in Rotor (electric motor)
Bill
--------------------
"Why not the best?"
Jimmy Carter
RE: Corrosion (Rust) in Rotor (electric motor)
There is only superficial rust on your pic.
Should be ok.
RE: Corrosion (Rust) in Rotor (electric motor)
RE: Corrosion (Rust) in Rotor (electric motor)
Will the long storage impact the grease in the ball bearings.
Two Ball bearings used are sealed type. Will the long storage degrade the grease and impact the function of motor?
What type of test is done to check the quality of grease in the bearing?
thanks,
Ana
RE: Corrosion (Rust) in Rotor (electric motor)
If you're not happy with that then a bearing change is certainly an option although the labour costs may approach the value of a new motor if these are small types.
RE: Corrosion (Rust) in Rotor (electric motor)
They should run quiet and smooth.You will soon hear if the bearings need changing.
There's not a lot of grease in sealed bearings usually.Just enough to lubricate.
RE: Corrosion (Rust) in Rotor (electric motor)
Is this OK?
what is the allowable range?
RE: Corrosion (Rust) in Rotor (electric motor)
If your Windings read better than one hundred megohms after drying, then I would regard the motors as good as new.
Keith's consensus seems to be "connect and run - no probs".
Gunnar Englund
www.gke.org
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Half full - Half empty? I don't mind. It's what in it that counts.
RE: Corrosion (Rust) in Rotor (electric motor)
Keith Cress
kcress - http://www.flaminsystems.com
RE: Corrosion (Rust) in Rotor (electric motor)
http://www.stle.org/assets/document/Environmental_...
RE: Corrosion (Rust) in Rotor (electric motor)
But, how did you measure the water contents? And what are your error margins?
And, why do you think that there is a problem with water or corrosion? is the warehouse damp?
Gunnar Englund
www.gke.org
--------------------------------------
Half full - Half empty? I don't mind. It's what in it that counts.
RE: Corrosion (Rust) in Rotor (electric motor)
It looks to me that the paper discusses bearings immersed in oil with dissolved water. Grease is a different situation. Grease is supposed to be a little better at excluding moisture. I don't think grease absorbs water as readily as oil. I have seen from motors stored in bad conditions, rust occurred in the bearing only at locations where grease was not present.
The run and check strategy is pretty good in my view. Modern vibration equipment and techniques are s very sensitive to the tiniest of defects (you need to look at more than just the overall level). If you get a good vib check I feel good about the bearing. The small reservation I might have is condition of the lubricant. It is a tricky question, the bearing manufacturers, lubricant manufacturers and even motor manufacturers tend to have very strict recommendations regarding storage. Something like 2 - 8 years storage life even in good conditions and with periodic rotation. Experience suggests those limits are overly conservative, but it's up to your comfort level how to approach it.
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(2B)+(2B)' ?
RE: Corrosion (Rust) in Rotor (electric motor)
I think that it is important to have an answer to my question about how the OP measured the water contents of the grease and how wide the measuring tolerances are. You may be worrying about something that has no significance at all.
Gunnar Englund
www.gke.org
--------------------------------------
Half full - Half empty? I don't mind. It's what in it that counts.
RE: Corrosion (Rust) in Rotor (electric motor)
RE: Corrosion (Rust) in Rotor (electric motor)
Personally, I would use the motors for all but the most demanding purposes (like critical applications in nuclear plants).
Gunnar Englund
www.gke.org
--------------------------------------
Half full - Half empty? I don't mind. It's what in it that counts.
RE: Corrosion (Rust) in Rotor (electric motor)
Also the motor bearings are sealed for life. I guess, the "sealed for life bearings" do not need any re-greasing. They are moisture protected by their construction.
Why not take the no load trail for few hours satisfy before putting them into service.
RE: Corrosion (Rust) in Rotor (electric motor)
To follow up on the comment about condition of lubricant itself following storage in possibly non-ideal ideal conditions:
http://www.reliancebearing.ie/wp-content/uploads/2...
Whatever concern for the bearing itself can be evaluated from a test run, but the concern articulated in paragraph above is that the lubricant itself may have degradedduring storage. You can find similar sentiment echo'd in literature from motor manufacturers, bearing manufacturers, lubricant manufacturers. For them it's an easy way to CYA and it costs them nothing to make that recommendation. You could easily argue the other way since many iinstalled motor have had grease in the bearings for decades, sometimes combination of running/standby service and sometimes in poor conditions. If we watch the housing temperature upon installation and have a regular vibration monitoring program, one would think we could catch any consequence of the degraded grease before it starts to threaten the equipment reliability. Depends on your circumstances, experience and opinions.
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(2B)+(2B)' ?
RE: Corrosion (Rust) in Rotor (electric motor)
Based on the motor manufacturing year, we decided to scrap some motors and not take risks.