Mixing oil and grease in a gearbox 4

[paintballJim]

Not sure if this is the correct place for this but the Petroleum engineer section seemed to be for exploration so here goes.
We have a gear box that we have been using for a while now. We had been using oil in it but the manufacturer suggested using grease. We switched to the grease he suggested and started seeing bearing failure. We are planning to go back to oil but are wondering if there is a problem leaving the grease in there with the oil, or if the grease needs to be cleaned out. The thought is that there should be no problem with them both in there together but I have not been able to find anything to confirm or deny that idea.
Can someone point me in the right direction?

Thank you

 

[Tmoose]

What does the OEM O&M manual have to say about // how // to run with grease lube, beyond a chart or table containing rpm?

 

[paintballJim]

Manual? We don't need no stinkin Manual.
At least that appears to be the opinion for the manufacturer.
The closest would come with this portion of the dimensional drawing we were provided. There is little there other than the shaft with two bearings. And there is a grease zerk shown in the top of the manufacturer's drawing mid-way between the two bearings which are about 3" apart. In correspondence they indicate they pack the bearings before sending the unit to us. The units that failed never had oil in them, When we made the switch we started with new production units and simply used the manufacturer recommended grease to fill the housing rather than the oil we had been using.

 

[1gibson]

If it ain't broke...

 

[MikeHalloran]

In correspondence they indicate they pack the bearings before sending the unit to us. The units that failed never had oil in them, When we made the switch we started with new production units and simply used the manufacturer recommended grease to fill the housing rather than the oil we had been using.

Well, that's interesting. A grease gun can easily develop enough pressure to blow the seal right out of a one-side sealed bearing, and/or displace the bearing itself, depending on the details of the assembly, so far not in evidence.
That's the sort of bearing one might specify for an oil-lubricated gearbox, or one might pre-pack for use with grease.
... but if the gearbox is intended to be filled with grease through a zerk fitting, it should have one-side shielded bearings, or one-side sealed bearings plus some aperture through which excess grease can be forced out without pressurizing the cavity.

Of course zerk fittings and grease extruding everywhere is sort of a last-century or earlier fashion; more modern assemblies might use double-sealed bearings, pre-greased for life at assembly.

Just out of curiosity, how long has this unidentified OHLA manufacturer been in business?





Mike Halloran
Pembroke Pines, FL, USA

 

[paintballJim]

As to:
If it ain't broke, Believe it or not sometimes you need to reduce manufacturing steps to keep your costs in line. We had been providing a small oil reservoir with hose lines to keep oil in this unit. Going to grease the way the manufacturer was suggesting would reduce quite a bit of cost and time. We thought going to how the manufacturer recommended would save cost, guess not in the long run.

And I checked, the manufacturer which shall remain nameless has been in business 68 years.

 

[Artisi]

Has the nameless manufacturer been approached for comment as to why the bearings failed?

It is a capital mistake to theorise before one has data. Insensibly one begins to twist facts to suit theories, instead of theories to suit facts. (Sherlock Holmes - A Scandal in Bohemia.)

 

[tbuelna]

MikeHalloran brings up a great point about proper design of the re-lubrication provisions for grease lubed rolling element bearings. It is not a simple matter of installing a zerk fitting at some convenient location near the bearing and squirting in some random quantity of new grease. First, the bearing installation should have an arrangement of shields/deflectors/cavities/etc that retain the correct volume of grease around the bearing both during and after operation, but also allow excess grease to be expelled within the housing enclosure where it won't create a problem. Second, the circuit for applying new grease should control the flow so that it efficiently displaces the old grease from the bearing space. The old grease is usually full of debris and contaminants, and simply adding some new grease to the old grease is not that helpful.

 

[Lnewqban]

Being intended for grease, how did you add and remove the oil prior to replacing it with grease?

Are all the adaptors working in horizontal position?

How did you measure the amount of grease that was injected in each overhung load adaptor?
Because it is a relatively small cavity, the manufacturer usually recommends a max/min volume.

How frequently is the removing and repacking of grease recommended by the manufacturer?

"Where the spirit does not work with the hand, there is no art." - Leonardo da Vinci