David,
Most of the gear coupling problems we experienced was that the PM did not take place timely enough and the grease became very stiff or baked. In one unit that we followed with vibration the stiffness did not allow the coupling to move freely and our axial vibration increased. Our normal monthly vibration trending caught the obvious increase and we looked at the coupling first as nothing else had changed from a repair stand point. This unit operated 24/7 for emissions control (baghouse fan). Motor is sleeve bearing and fan had pillow block roller bearings. Our PM crew would take the opportunity to change bearing oil but the coupling breakdown/clean and re-lube would take to long and basically not be followed up later. PM's were completed in the future on schedule.

Just to mention we have had PM personnel that would lube the coupling and do it improperly by hand packing then purging through the ports for until grease came out then for good measure seal the purge opening and give a couple of extra shots (more is better?) from each side. This too locked the coupling. You would think the seal would blow but it didn't.

Proper PM will definitely limit coupling failures.

I've had to do a lot of arm twisting and offer help to get gear couplings clean before regreasing. Couplings can and do last a long time if well maintained. Not every plant has good coupling maintenance procedures. Not every coupling in a plant is in the best of condition, so a good method of fault detection is needed. Ultrasound is the best single tool available to assess coupling condition.

Walt

quote:

Originally posted by Walt Strong:
Ultrasound is the best single tool available to assess coupling condition.

Walt,

I'm not really arguing against it. I just wonder whether or not the US measuremnt will be affected by the air borne noise coming even from the same coupling (generated by things like sticking out bolts, etc.)? Also, other nearby US sources, such as motor, may influence readings.

David

Walt,
You can dial in frequencies? You may not have the same frequency each time but that could help in limiting the background noise, correct?

Not all machine installations are suitable or easy for ultrasound monitoring of couplings. Some issues include:
1) Hostile or unsafe environment for personnel -- consider remote sensors
2) Coupling inaccessible inside guard -- consider temporary guard removal, guard modification (hole) for sensor, remote or flexible sensor
3) High ultrasound background -- consider reducing background, waiting for background to reduce, blocking sound (with body or object), changing measurement locations, or sensor type

It may take some creativity, extra work, or extra cost (for accessories or modifications) to make a good measurement, but the results can be worthwhile.

I use a fixed-frequency meter. If you use a tunable frequency meter, then keep the same frequency to compare data. Changing frequency settings can alter dB level and audible sound characteristic, and that is not good for accurate evaluation. This is a major reason why folks struggle with coupling and bearing measurements!

Walt