This worm gear was running 245 degF, at the pair of tapered bearings, normally below 180. We split to look inside, one spall spot on radial bearing drive end of worm, hard to see the tapered bearings. My question at moment is the wear at lead in on the worm, and none opposite? This is located by the tapered bearings stopped by housing wall and can not move to drive end without shimming bearing by shaft shoulder. Shouldn't the wear be more centered on worm, as most are?
DSCF0407.jpg (624 Kb, 38 downloads)
This is a shot of the wormwheel wear, don't like the pits, but vertical alignment seems centered.
DSCF0405.jpg (574 Kb, 41 downloads)
one more, I don't like the way this is loaded on one point at start. 4 point start on worm by the way. Seems like it looses contact after first tooth? 460 worm gear lube, heat may be part of problem, but from alignment???Any thoughts appreciated.
DSCF0412.1.jpg (618 Kb, 33 downloads)
That looks like damage to me as opposed to normal wear. I would be suspicious of the preload on the tapered roller bearing too.
Was this recently worked on? Was the increased temp of sudden onset? Any vibe data?
You might want to move this to the vibration section to get the attention of John from Pa.
He knows more about gears than Og, the caveman that invented them.
billw, some keys things needed in failure analysis of worms gears isn't clear from the pictures. However, based on what I see/read the history (as requested by Danny Harvey) might prove to be helpful. For one thing 245 deg F temperature would be very unusual unless there were some environmental considerations that might explain a temp that high (you say normal is 180). I would be looking for things that might cause high temperatures...480 oil, can you clarify exactly what oil is being used? Also, what is the chance that the oil might have been mixed with something incompatible with a worm gear. Oil for worm gears typically have "compound" somewhere in their name as they have an additive package specifically for applications that have high degrees of sliding. Oil level is also critical. What is the history of oil being added to this machine - is it a leaker? Could it have been run low for some period of time?
On tooth contact...I have attached a few pages from a reputable Japanese manufacturer on setting up worm gear contact. For your application you need to identify what is approach and recess and then note that contact should be set to favor slightly the recess portion of the contact. This is to insure that the lubricant is "pulled" into the mesh to provide adequate lubrication and cooling. Backlash is also important, again to insure that a proper amount of lubricant is pulled into the mesh and that thermal expansion isn't an issue. Once a good contact pattern is obtained the gear should be run at about 1/4 load for a few hours, then increase the load in 1/4 steps with an inspection between load points. If good access is available then the gearing should be blued betwen load runs and careful observation should be made relative to how the pattern is spreading across the mesh. Worm gears do have to wear in; very often the worm and gear are lapped to each other at the factory.
techsec19.pdf (380 Kb, 63 downloads)
Danny, this is all i can post for the vib data.
John, I couldn't open the file; we use a PAG synthetic oil for worm gear; oil level was ok. 680 was changed to 460 due to heat in other unit with mfg recommendation. This sat idle, 2yr, was flushed and then put in service, with a few days use to test, and this was found. No "known" issues prior to use. Leaker yes, and that may have been the main contributor. Hot bearing made us check it out for crud in oil channel possibly not getting oil to outer bearing. Thermal expansion is a thought as well adding to it, others do run 180 -sure dont' like it. I'm looking into the rest of drive train, as well as loading, <90%FLA of 50 HP motor.
h4vib.png (88 Kb, 13 downloads)
I've redone the attachment since some people had trouble with the previous.
More on worm gear lubricants...
One type of lubricant type commonly used with worm gears is mineral-based, industrial extreme pressure (EP) gear oils. This will give you problems with a brass or bronze worm gear at elavated temperatures. Your 180 deg that you state is normal is too high for this type of oil. There is also a group PAO gear lubricants that work well in worm gear applications but again, since these often have an EP additive package, the same cautions about a bronze or brass gear may apply. Best thing is to go back to the OEM recommendations.
techsec19.pdf (948 Kb, 34 downloads)
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