Extended Roller Bearing Outage

[AardWurk]

I have to restart a large number of industrial electric motors and fans which have not run in 5 years. I'm concerned about the roller bearing and ball bearings in the equipment. The project cannot afford to replace the bearings and I want to give the equipment the best possible chance of success. All the bearings are grease lubricated and are inside protected from the environment.

I can't do anything to reverse any fretting damage, but any tips that people can offer to give the equipment the best chances on start-up are appreciated.

 

[MikeHalloran]

Barring them through a revolution or two should help to identify the ones that are going to be problematic. That should expose cracked belts that will need to be replaced before startup.

I hesitate to recommend greasing anything unless your crew has the discipline to not overdo it.

An example of overdoing it would be pumping grease in until it comes out somewhere. The somewhere is too often a lip seal blowing out in one expensive way or another.

I would recommend removing the dust/crud from the nameplates and taking geolocated photographs for the maintenance database you will need to build if you didn't inherit one.



Mike Halloran
Pembroke Pines, FL, USA

 

[1gibson]

Have they been periodically rotated by hand to prevent the balls settling into the races? Can you come up with a procedure to slowly rotate and either measure shaft runout with dial indicator, try to feel by hand, or watch for repeatable preferred stopping position that might indicate indentions in the races? On that last one, depending on the equipment type, it could just be showing you the unbalance of the rotor, but those will swing back and forth across the preferred position. Indentations in the races will stop more abruptly, and the period of swinging back and forth will be shorter.

And the real question, if you can't afford to replace them now, can you afford the alternative? Make an assessment for each piece of equipment and decide if you should roll the dice or not.

 

[MintJulep]

You are trusting your luck.

So what you really need to do is try to limit the consequences when your luck runs out.

Start with the advice from Mike and 1gibson above.

Then start each machine and get some immediate recordings of bearing condition - vibration, sound, temperature.

For the first week you should probably have a crew CONSTANTLY moving from machine to machine checking for things going south. Shut it down immediately when a problem is detected.

After that once a day might suffice for a week. And after that you are probably out of the woods.

Some good info:

http://www.skf.com/group/products/c...asic-condition-monitoring-products/index.html

 

[3DDave]

Even if you can't replace them, it would be valuable to remove, examine, clean, carefully examine, repack, and reinstall a few representative bearings.

That will give you an idea on the first examination what the condition of the grease is and on the careful examination what the condition of the rollers, balls, seals, and races is. It will also give you an idea of the quality of the maintenance crew that may be responsible for the rest of the motors.

If one assumes it's all good and it is all good, then it's a little time and money. If one assumes it's all good and none of it is, then it provides some planning cushion instead of allowing the installation to head into unexpected disaster.

 

[3DDave]

MJ - You type faster than I do - excellent suggestions on monitoring.

 

[tbuelna]

AardWurk-

The most problematic issue with grease lubed rolling element bearings that have been sitting idle for extended periods is moisture that has condensed and collected on the race surfaces. After 5 years of sitting idle, even a tiny droplet of moisture sitting on a bearing race surface will produce corrosion pitting. If the corrosion pitting is located on a loaded sector of the race surface, it will quickly produce more serious spalling damage. Without removing the bearings and inspecting them for surface corrosion, there is no sure way to know if you have such a problem. And there is no way to mitigate the further damage the corrosion will produce.

Good luck to you.
Terry

 

[romke]

there is no substitute for dismantling, cleaning, inspecting and correct regreasing of the bearings if you want to assess their condition. if that is out of the question, you can try turning over the motors a few times and then start them. if they are fitted with grease nipples you can also give them just a few shots of grease. when they run watch temperature and noise - when excessive you better exchange the bearing before further damage occurs.

corrosion might well be your biggest problem - when stationary very little moisture can be catastrophic. they might well start though, but you will likely notice increased and increasing noise. if that is the case they should be exchanged.

 

[Tmoose]

The grease condition is an issue. No grease manufacturer is going to say 5 year old grease is any good, even if kept in a sealed container.
Some motors have purge plugs that permit a certain amount of heavy re-greasing while assembled.

I'd expect a ball or roller bearing with rust damage or false brinneling from sitting to have evidence in a vibration "signature/spectrum/FFT . Taken with the motor idling, so the outer race load zone is at 6:00 o'clock position.

I think some motor folks would also want to assess the insulation for dampness/etc with a "megger" test.

 

[tbuelna]

Per the OP, if you cannot afford the cost of replacing the bearings then the discussion is mostly academic. Simply re-grease any bearings that you can access and hope for the best. Even if you determine that a bearing is damaged, there is nothing you can do about it since you can't afford the replacement cost, right?

Don't worry too much. In reality, grease lubed rolling element bearings used in commercial applications like electric motors and fans are typically designed quite conservatively. So they tend to experience rather benign failure events over long periods of operation. Just keep a close eye on the equipment.