Mixing oil and grease in a gearbox
Mixing oil and grease in a gearbox
(OP)
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
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





RE: Mixing oil and grease in a gearbox
More important, did you find out from the manufacturer WHY he wanted you to change to grease, and what the advantage was supposed to be? Clearly, you have introduced some warrantee issues - because of that recommendation. Slow speed gear lube is usually grease, high speed at high loads is usually pressurized oil. Medium speed with low loads can work with "splashed" oil from the sump.
RE: Mixing oil and grease in a gearbox
To see what I mean, place a pea size glob of grease on sheet of brown paper (like grocery bag) and wait for a week to see what is left of the original pea size. You can also look at the spec for the grease or call the maker to determine what the thickener is, but the visual evidence is more informative for the nature of the material.
RE: Mixing oil and grease in a gearbox
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.)
RE: Mixing oil and grease in a gearbox
also you can find grease lubricated gears in agricultural equipment and some industrial applications.
you did not mention what type of grease you used in the gearbox. given the fact that you observed bearing damage, the grease might have been to viscous. standard lubricating grease has a consistency of NLGI 2, for gear lubrication usually a much less consistent grease is used, like NLGI 0 or NLGI 00. those thinner greases will more or less be semifluid and thus can flow back into bearings once a rolling element has passed.
RE: Mixing oil and grease in a gearbox
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.)
RE: Mixing oil and grease in a gearbox
RE: Mixing oil and grease in a gearbox
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.)
RE: Mixing oil and grease in a gearbox
RE: Mixing oil and grease in a gearbox
RE: Mixing oil and grease in a gearbox
> How did the manufacturer envision the grease distributing correctly within the bearing? Were there recommendations that were missed or not presented to you?
> Ostensibly, it was the lack of grease that caused the failures. BUT, the issue is how close to failure are the remaining units and ought you not rebuild and repack the bearings to make sure? Dry running the bearings would imply the possibility of metal particles getting generated, and if they aren't removed, the oil will ensure that they go to where they'll do the most damage.
TTFN (ta ta for now)
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RE: Mixing oil and grease in a gearbox
RE: Mixing oil and grease in a gearbox
There is obviously no problem with thoroughly cleaning out all the grease.
There might be a problem with the mixture.
So the safe and easy course of action is clean them.
Beyond that, everyone is speculating and guessing because of a near complete lack of information.
For example. Are the bearings actually grease lubricated? There is a whole world of oil-lubed gearboxes that use oil lubricated bearings. There are features in the casting that catch the splashed oil and port it into the bearing cavities. If these gearboxes are of this type then the expected result of draining the oil and throwing in grease would be failed bearings in short order.
Grease can be finicky. Too fast or too slow and the film doesn't form right. Too hot or too cold and the oil doesn't come out to do its job. Running "well below listed speed" is not necessarily a good thing.
RE: Mixing oil and grease in a gearbox
If that is what needs to be done so be it,there are only 6 of them to do, we were just hoping the answer to the original question would be something along the lines of " No there is no problem leaving some grease in the housing when switching to oil. The grease and oil will mix to produce a thicker oil and thinner grease." The thought there was that since we have gone several years using oil in the same units with no problem we would be able to provide better bearing lubrication by going back to the oil that had been successful. Then possibly if the grease did thicken the oil somewhat it would still have the viscosity that would allow it to flow to the bearing as needed.
RE: Mixing oil and grease in a gearbox
TTFN (ta ta for now)
I can do absolutely anything. I'm an expert! https://www.youtube.com/watch?v=BKorP55Aqvg
FAQ731-376: Eng-Tips.com Forum Policies forum1529: Translation Assistance for Engineers Entire Forum list http://www.eng-tips.com/forumlist.cfm
RE: Mixing oil and grease in a gearbox
Thank you all.
RE: Mixing oil and grease in a gearbox
RE: Mixing oil and grease in a gearbox
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.)
RE: Mixing oil and grease in a gearbox
RE: Mixing oil and grease in a gearbox
Dik
RE: Mixing oil and grease in a gearbox
RE: Mixing oil and grease in a gearbox
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.
RE: Mixing oil and grease in a gearbox
RE: Mixing oil and grease in a gearbox
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
RE: Mixing oil and grease in a gearbox
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.
RE: Mixing oil and grease in a gearbox
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.)
RE: Mixing oil and grease in a gearbox
RE: Mixing oil and grease in a gearbox
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