Motor Bearing Grease Plug

[KenRad]

I have a new clean room air handling unit with a direct drive fan attached to a 40 HP TEFC motor. Because the fan wheel is mounted to the motor shaft with very little clearance between the wheel and the front of the motor, it is very difficult to access the grease plug on the bottom of the bearing housing. And because this clean room operates 24/7, I need to be able to grease this motor without shutting it down. I've extended the grease fittings to the outside of the fan housing so this can be done.

As for the grease plugs, does anyone know of a good reason why I shouldn't run the motor with the plugs removed? I have not been able to get the motor manufacturer to bless the idea (Toshiba), but that doesn't surprise me. If this was a high temperature or very dirty environment, I could see the need for keeping the plugs in place. But this motor is in a very clean airstream that is cool year-round, and it operates at no higher than 1200 RPM. The grease should never get hot enough to run out of the drain.

Any input? I'm posting this in the HVAC forum as well.

---KenRad

 

[ischgl99]

Why not just put an extension on the grease plug far enough that you can get at it and then keep it plugged when not greasing? A short run of tubing with a cap on the end should work fine unless there is not any room to get it past the coupling. Mike Bensema

http://www.dutchmenservices.com

 

[acmotorengineer]

to KenRad

It is not a good idea to remove the drain plug. When the motor is shut off the bearing temperaure cools down very slowly. Since there is a temperature differential between the bearing and the surrounding ambient the bearing decreasing internal air volume will suck in surrounding air, contaminants and all. It does this even with the plug in, however the restricted flow path will filter out most of the particulates.

It is also not a good idea to re-lubricate with the plug in. Overgreasing is a common cause of bearing failure due to overheating.

Mike had the best solution.

 

[busbar]

From motor end-bell bearing housings, pairs of tubing routed external to air-handler enclosures--terminated in Zerk fittings--has probably been standard practice for at least 60 years.

 

[jOmega]

I'm surprised that you are allowed to have regreasable bearings in a clean room environment.

Why not go with sealed, non-regreasable bearings and preserve the clean room standards ?

Hmmmm.

 

[electricpete]

For the drain plug, you can buy a grease relief for a buck or two which will prevent foreign material entry and will allow any excess grease to discharge immediately after greasing (so you don't have to walk away for an hour after greasing and then come back and put the drain plug in).

The use of a drain grease relief is a standard practice which I'm sure Toshiba and the bearing manufacturers approve of.

 

[PUMPDESIGNER]

In response to jOmegas suggestion:
Sealed bearings are a great idea on smaller motors because they last a very long time. However, the shaft diameter on a 40 hp motor has a shaft diameter too large for sealed bearings to provide reliable long term service (although they are available), you need greasable bearings to obtain long term reliability.

One large utility did a long term study and obtained excellent results by piping the vent and leaving it open. The excess grease fills the vent piping and plugs it so that contamination cannot cannot get in. Whenever the bearing was greased the excess old used grease simply came out the vent opening and was wiped up. The old used grease is waxy and stiff so it does not usually run easily. In your case pipe the vent to the same position as the grease zerk, then pipe it upwards so that the old grease does not run out easily. When they grease just catch the excess coming out with a rag. This "grease plug" can move in and out slightly so that air with contamination does not have to enter the bearing as the bearing goes through heating and cooling stages.

Richard Neff
pump@shadow.com Richard Neff
Irrigation Craft

 

[electricpete]

pumpdesigner - I am intrigued by your statement that 40hp motor has shaft too large to use sealed bearings at 1200rpm. Can you provide any reference to support that?

 

[jlhmaint]

when i worked in a plastic factory in the powder room were they ground up plastic pellets we had 3 75hp and 3 50hp motors all had sealed bearings because of plastic dust and powder and they ran fine and performed well for long periods of time.

 

[jbartos]

Suggestion: Visit

http://www.leroy-somer.com/alternateur/DOCS/PARTNER/Catalogues/3363d_GB.pdf

for the bearing choice for machines from 5kVA to 2700kVA
Also, I am surprised the same as JOmega is that the clean room would allow some grease, leaks if the machines are actually located in the clean room considering the statement that "...this motor is in a very clean airstream that is cool year-round, and it operates at no higher than 1200 RPM. The grease should never get hot enough to run out of the drain." in the original post.

 

[PUMPDESIGNER]

Here is the reference to answer the question about motor size. I incorrectly left out the RPM question which may be why some were confused, my fault in not asking the RPM first.

"Basic Lubrication Knowledge Challenged"
By - Heinz P. Bloch, P.E., Process Machinery Consulting

"Sealed bearings are preferred in continuous duty applications as long as the product of the bearing bore diameter ”D”, in mm, and speed “N”, in RPM, does not exceed 80,000. (“Seals” are elastomeric disks fitted to the bore of the bearing outer ring and making rubbing contact with the outer periphery of the bearing inner ring. Sealed bearings are factory pre-filled with grease and cannot be regreased)."

I have personally found the above idea correct through experience. However all that experience is based on 3500 rpm machines. Again, I apologize for the mistake.

Richard Neff
Richard Neff
Irrigation Craft