Our Paper mill has recently experienced several coupling failures on Paper machine drives and Disc refiners. The couplings in use are Falk gearflex style and are lubricated with multipurpose grease as recommended by our lube supplier. The mode of failure is severe wear on both hub teeth and cover teeth resulting in a locked coupling and increased motor vibration. Alignment is probably not an issue as all our installations are laser aligned to spec.Is anybody having better success using multipurpose grease in this style of coupling?

In my experience gear type coupling failures are usually traceable to misalignment or a lubrication issue, or a combination of the two factors. Misalignment causes increased sliding velocity along the tooth flanks and with any given lubricant, there is an upper limit.

You state that misalignment is "probably not an issue as all our installations are laser aligned". Can you make that statement with 100% assurance? Have you personally watched an alignment and walked away satisfied or just get a hard copy of the numbers. If you can, since it seems to be multiple machines and perhaps multiple instances of failure I would be looking carefully at the lubricant. Ask yourself if these failures can be traced back to a lubricant type change or even to a formulation change in the grease. Even though names don't change, sometimes due to environmental issues the formulation might change. Instead of placing reliance with the lubricant supplier (salesperson) pull the coupling manuals out or go back to the coupling manufacturer and get their current recommendation. Often times a brand "X" GL-2 may appear to be equivalent to a brand "Z" GL-2 but the OEM may have had bad experiences with a product. I can recall many years ago while employed by an OEM that we had fits with end users that used a certain turbine oil in high speed gearboxes - we could almost bet that foaming would be excessive.

John from PA

I second John's advice about finding out what grease the coupling OEM recommends versus what the Lube supplier recommends. Note that there are speciality coupling greases that maybe a better fit than a mulitpurpose grease.

Falk recommends using their special coupling grease because of the tendency of bearing greases to centrifuge separating the soap from the oil.

The bigger diameter and faster turning speed of the coupling, the worse the effect.

In addition, Walt Strong has had good results in diagnosing coupling wear from air-borne ultrasonics.

Do a search of the vibration forum and you will find his comments.

Thanks to all for your replies. Our latest failure was on a Disc Refiner. 400 H.P. motor rotating at 900 rpm. The motor was aligned to spec at installation 18 months ago. I saw the alignment results myself. A preliminary alignment check before the damaged coupling was removed found the motor coupling .017" low, indicating the motor had moved. Further investigation found the support foundation to be in very poor condition. Cracked welds on the transition base allowed the motor to run in a misaligned condition, even though the motor had been aligned to spec at installation. Just a tip to clean and check the foundation condition and don't assume that everything is solid under your machine bases. As to the other coupling failures, I've talked management into changing to the recommended coupling grease rather than using multipurpose grease in this style of coupling. Thanks again for your input.

David, It is possible that the laser has not been mounted properly. Although you have seen the results, check that the alignment gear is on the shafts and not the coupling assembly. I speak from experience!
Regards
Joe Mc Cormack

Yes; a lot of very poor alignment is accomplished via laser alignment. It appears you do have a lube issue with the wrong lubricant.

Also many of the refiners have an axial setting that must be an exact and I've found problems with setup there - may want to check axial dimensions.

David,
The comments already made pretty well sum it up!

Correct foundation
Correct spacing (shaft & coupling)
Correct alignment (per coupling manufacturer's spec's)
Correct lube (to prevent speration)

Had a lot of experience with these on refiner app's. (Falk/Waldron, Koppers, etc.).

Also, need to be careful not to over fill lubricant to avoid hydraulic effect.

Hi David,
You may be the victim of too good alignment. These couplings rely on a small misalignment to lubricate the gear teeth. If you read the installation instructions, I think they mention this. I would have a dialog with the coupling manufacturer to verify this. I haven't installed one of these for quite a while.

Good morning David we had the sme problem with some of our refiners, the alignment was very good but we lost couplings. the problem was solved when we changed from grease to oil in our couplings hope this helps

Regards and
Merry Christmas
Don

David,

In the 1980's we experienced several failures of Zurn Amerigear couplings in a nuclear power plant. Our alignment was good, but there was speed variation, or "hunting", as the turbine drive varied speed to respond to reactor level. This loaded and unloaded the coupling, and had a tendency to squeeze the grease out of the contact. In addition to the correct grease (a formulation with specific gravity of the thickener and the oil being very close to prevent separation), we found that grease quantity was very important. Too much grease, and it can be slung unevenly in the coupling and cause imbalance. Too little, and the grease can be squeezed out of the contacts and result in inadequate lubrication. In our case, the mechanics were measuring out a precise amount of grease per the procedure to apply to the gears, but when they were assembled, some was being squeezed out and wiped away as excess, causing underlubrication. We also had good success using infrared thermography to discover hotspots on the coupling surface prior to failure, and were able to identify damage and take proactive measures to avoid tripping off. Infrared, ultrasound and vibration I think can all work together very effectively to monitor coupling health of these type of coupling. We also had good experience in analyzing the grease when the equipment was shutdown. That helped us to identify a fretting wear issue that was being caused by the underlubrication. Grease analysis would also help to confirm separation of the oil from the grease.

Nice work finding the base issues. That sounds like it may be your root cause, but if not, or for others reviewing this posting for their own situation, the other mentioned considerations and monitoring tools here should be helpful.

Rich Wurzbach
MRG Power Labs

I would suspect grease as the main problem. We have had a large population of lubricated couplings and found that coupling grease as requested by the coupling supplier to be the best lubricant. As stated earlier the grease has to adhere to the teeth and hub to lubricate the coupling. Multipurpose grease will not do a good job and will normally even leak out the coupling seals. I would suggest trying the recommended grease in a couple applications. We have been running for over 60 years and our machinists found out long ago that multipurpose grease (just because convenient) would not normally last.

Have you ever considered going to a coupling style that doesn't need lubrication?
The benefits of disc couplings are many, however, ease of inspection is probably one of the most consequential. Being aware of change of condition before failure will save you the most money.
I've replaced gears with discs with excellent results, give Lovejoy a call.

I have worked at several large industrial facilities. In each one that used "multi-purpose" grease in their couplings, the failures were what could be considered premature. The biggest difference between a grease specified for coupling use and the other greases is the "tacky" additive. This, along with a heavy base oil, keeps the grease from seperating and also from being squeezed out from between the tooth surfaces. Most major lubricant suppliers sell grease specified as coupling grease. Most of them are very similar to Falk's LTG that comes with the coupling.

If allignment is not a problem then I would suspect the grease. I have had similar problems and switched to a over base calcium grease. The one I used is made by VIP Lubricants in Timmins Ont. Also works well in wet conditions and high temp locations. I also suggest you trend your rotating equipment with ultra sound. You will be amaized with what you learn using ultrasound and trending.

Thanks for all your interest in our coupling problems. I feel that coupling issues are generally ignored and we focus on bearing and motor issues. Coupling installation errors and poor maintenance have a huge effect on machine reliability, causing excessive loads and vibration in both driver and driven machines.We're presently monitoring machine condition with vibration analysis and thermal imaging, but I'm interested in how to trend ultrasound measurements on our couplings. In have a SDT 170 M ultrasound detector for leak detection. Any hints would be appreciated.

The OEM lubricant as mentioned is LTG please see: http://pt.rexnord.com/Products...ts/LTG-couplings.asp

I strongly recommend using it.

The correct quantity is also very important because if too much is used it can hydraulically place axial forces on the driven and driving equipment which can be very detrimental. The correct procedure is not to pump it until it comes out the hole on the other side of the coupling shell. There is a set amount specified by Falk and it is available on their nice website in the coupling info sheets.