I've seen a few instances on some of our larger gear couplings where coupling lock up occurs from a dry lube situation on the motor side of the coupling, always on the motor side. The driven is gear boxes. The grease looks great on the gear box side of the coupling. There is no divider plate between the two hubs of the coupling, so each side shares the same grease. There is no water splash at all around these either. The lube is coupling grease. I know that with using oil, we would need a "no leak situation" with a good coupling flanged hubs gasket and o-rings with the centrifugal force going on. Just wanting to see who prefers to use grease as a lube compared to oil. With the last "dry" one found, maintenance has increased the PM frequency to clean, inspect, and repack.

On the gear couplings, there's basically two types: the normal one flanged in the middle and one where the third member is one piece (no middle connection). The later is for high speed application and/or where better balance is needed plus it takes away the worry of gasket leakage or cracked gasket. On some hi-HP units I've used EP-1 grease and checked 8 years later and the coupling looked as new but I knew exactly where the alignment was and it stayed the same over time. Remember, we're not lubing as in bearing lubrication but rather chassi lube. The basic need is not to break through the lube film. Oil could be a nightmare to retain.

Don,

I have never seen a gear-tooth coupling lubed with oil. I have attached a page out of Falk's SPC88 catalog the deals with oil lube of geartooth couplings. The 88 means 1988, so you might want to see if anything has changed while I call my Falk guy to get some more recent stuff.

With the kind of redundant failure you are experiencing there has to be some cause. What hp and speed are you dealing with? What is the manufacturer and designation of the coupling? What type of motor bearings? If sleeve bearings, is the motor hunting for it's axial center? Are your alignment procedures adequate? Is thermal growth compenstaed for?

That came out kinda big. How can I make it smaller?

Good Luck,

Lots of gear type couplings are lubricated with a continuous spary of oil. These are commonly used in high speed applications and are designed to provide a path for the oil that insures it passes over the teeth prior to excaping. Unfortunately this also turns the coupling into a decent centrifuge with the crud collecting in the teeth and thus causing lock-up. Hence the market for dry type couplings, now preferred over continuous lube, since they aren't a maintenance headache for routine cleaning.

John

Sam, I feel the same way you do on keeping the oil in. Talk about really messing some stuff up!

quote:

Oil could be a nightmare to retain.

Danny, rpm usually runs around 700 - 850 rpm, variable. 750 hp motors, AF motor bearings. Couplings are Amerigear, size 203 1/2. If I remember right, motor shaft was 3.249". Alignment is good and thermal growth accounted for. We have some good craftsmen here that you can trust.

Don,

It's always nice to work with craftsman that you can trust.

Gear tooth couplings should be bored for an interference fit of .0005" to .003". If they and the shaft are to spec, it usually takes about 275 deg F to enlarge the hub enought to fit it on the shaft. I'm sort of doubt if that small an opening could allow all the grease to seep out, but I guess it is a possibility if the motor shaft is under and the gearbox isn't.

How is the speed varied? Is there a possibility of shaft current? More often, high shaft current will harden the coupling grease rather than burn it, though. I have seen cases where the grease had to be chiseled out, but none where it was gone from just one half of the coupling.

Don, have you checked the drive-end motor bearing temperature while it is running? I use an Exergen infrared thermometer that has a detached probe that will get right up against the inboard motor bearing. You can also check the shaft temperature where it exits the endbell. Typically the inboard motor bearing temperature will run about 50 F hotter than the hottest motor frame temperature. If you have a motor that runs 'hot', say around 185 F, then the bearing temperature can be well over 200F and the shaft will approach 190F as well. You could just be cooking the grease in the motor side.