Do sealed bearings need lube?

[Egoy]

We are having problems with a marmon herrington transfer case. (MVG 1600 LD) where a roller bearing (MVG16-1028)located just behind the idler shaft cover is failing in a most spectacular way(taking the idler shaft with it and scattering itself throughout the transfer case).

MH has been no help and nobody seems to be using this case under the same conditions as we are (heavy duty six wheel drive snow plow with dump body).

I have considered all the typical methods of bearing failure and the only things I am left with are brinelling (either due to transportation of the bearings or the vibrations of the plow when it is plowing) contamination (it is in a transfer case and is an open bearing) or improper lubrication (splash lubrication).

My problem is it is impossible for me to inspect an worn but not destroyed bearing because A)it is mid january and the plows are very busy, B)I am a student on a coop work term, and C)it's a government organization so taking apart equipment that isn't bronken just isn't done.

Would a sealed bearing need lubrication often? if so putting it in a transfer case is a bad idea and I'm stuck with fixing the transfer case to get more lube to the bearing, and keep contamination to a minimum.

I appreciate any thoughts.

 

[Tmoose]

Even the spectacularly broken parts (rollers, inner and outer races, cages) might offer some clues.

Could you grab some oil analysis samples, or some up-in-hte air idling vibration analysis (or listening with a stethoscope) testing ?

A sealed bearing is pre-charged with grease, and usually has a lower speed rating than an oil lube bearing. Running one in oil might invites eventual "oil contamination" of the grease with probably less than optimum lubrication.

Brinneling is denting from overload.
Vibration "false brinnels" a non-rotating bearing with micromotions shivering thru the lube film.
If the bearing is spinning while plowing the lube should be continually re-distributed, thus precluding false brinneling.

A pattern of dents/lines should exist on either brinelled or false brinelled races, with spalling originating from the dents if the bearing was in service for a while. When first brinelled or false brinelled the bearing howls, but can still run a very long time.

 

[electricpete]

I am not familiar with your application... just throwing out my perspective working mostly on electric motor bearings.

If it is truly sealed, there is no way to effectively lubricate it, unless there are some special provisions for getting grease in.

If it is double-shielded there is a debate whether it can be relubricated (depends on who you talk to).

Grease does have a fixed lifetime in revolutions depending on application (speed, bearing size, etc), although in some cases far beyond the life of the equipment.



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[plasgears]

1. I suspect that the bearing is running on an insufficiently HT shaft. I always specified HT shafts when running needle bearings on them. Another approach is a HT sleeve upon which the bearing runs.

2. Another possibility is unexpected overload on this idler shaft. In a typical speed reducer, as you progress from the input to the high torque output:

- shaft size increases,
- gear face width increases,
- gear diameter increases,
- gear pitch reduces,
- increased size bearings.

Any violation of these trends will be suspect.

 

[rmw]

Even sealed bearings under high load and high temperatures can "push" the lube out from under the seals. (I assume you are referring to a double sealed "lubed for life" type bearings.) The seals are not air tight, as the bearing has to 'breath' as it heats up and cools off.

If it is operating in a condition where it is pushing the grease out, (altitude changes can do the same thing) there is no way for the bearing to become relubricated.

A roller or ball bearing works by 'pumping' the grease in and out of the bearing while in operation as the grease heats up, and flows in and out and around and through the bearing, carrying heat away with it, to be replaced by new grease from a nearby resorvoir, or, by regreasing, or by oil flow into the bearing, in the case of splash lubrication.

I once in an emergency (weekend outage) carefully removed the seals from a high speed ball bearing with a pocket knife, being super careful not to damage them, and manually relubricated the bearing with litium EP-2 grease, and carefully pressed the seals back into place. The device ran for several years before I had to replace the bearing with a new one, but it sure got me out of a pinch.

I was surprised in that instance, upon initially removing the bearing, to find the ball bearing still inside it's seals in a bone dry condition. I don't know where all the grease went to, but it was not in the bearing, and it was making a gosh awful racket.

If your application is such that you are finding these types of sealed bearings bone dry after the failures you are experiencing, you need to use some other kind of bearing, such as the type that can be regreased, or one that get splash lubrication from the gear case.

rmw