Does anyone have pictures of a coupling lock up on a shim pack coupling? I'm not sure what to look for.
I took a fan down last week and the coupling was installed wrong and the shims had separated. After fixing it and restarting, the vibration is still higher than I'd like, but it is not consistent. It is mainly in the axial direction on both sides of the coupling.
I've seen lock up on gear couplings but not on shim packs.
Thanks!
Peggy T.

Coupling lock-up when referring to a gear tooth coupling means that the gear teeth on the hub no longer are able to flew when meshed with the teeth on the sleeve.

Given that, I'm not sure how a shim pack coupling could be "locked-up".

It sounds like you may have a good degree of misalignment. Has it been properly aligned? Look at the coupling with a tunable strobe and look for distortion of the shims under load.

Good Luck,

did you replace the coupling altogether, or did you reinstall the existing coupling? there may have been damage to the existing coupling.

the only "lock-up" in shim-pack couplings i have experienced is when the alignment between driver and driven has been adjusted without relieving and resecuring the coupling bolts after the alignment. and this wasn't something you could really see.

quote:

Look at the coupling with a tunable strobe and look for distortion of the shims under load.

i like this idea too.

Peggy,
Check the axial positioning of the couplings to be sure that there is no preload on the shims. If the drive and driven machine is fixed axially ensure proper hub spacing. If the motor is sleeve bearing type, ensure running magnetic center before setting hub gap. Let us know what you find..

Peggy,
PS, take collect phase angles.

oh yeah. Take phase readings across the coupling.

I am getting phase readings tomorrow afternoon and I can post them tomorrow evening. I rechecked alignment when we changed the shims and it was not good. The axial spacing in the old shim packs was not correct, and we corrected this as well as the alignmnet.
Thanks!
Peg

Peggy,

Here are a few things to look for during a shutdown or with a strobe light:

1) Excessive or wavy gap between disks
2) Line-up of match marks for shaft hubs and spool piece
3) Drilled holes or other indications that coupling was balanced as an assembly
4) Missing or dissimilar bolts, nuts, and washers
5) Added washers, possibly used for rotor trim balance
6) Limited end-float button or disk, if needed

If the coupling was incorrectly assembled once, then it should be reassembled "by the book" to avoid the same or different mistakes. It would be a good idea to inspect all disks for cracks with dye penetrant. A torque wrench should be used to achieve uniform/correct torque on all bolts.

If adequate time is not available to do the job correctly, then how is there enough time to do it over again?

I finally got the phase readings and some other answers to your questions. I'll put the data out here. I have some ideas now that I know some more history. I am pretty sure what I have is secondary damage because of poor assembly.
This is a large centerhung fan that moves about 40,000 scfm.
In January 2002, the outboard fan bearing was replaced. In September 2002, both fan bearings were replaced as well as the motor. In October 2002, the motor was replaced again because the rebuilt one put in the month before had a bad bearing. In December 2004, the outboard fan bearing was replaced and it ran ok for 6 months.
Vibration readings and spike energy went up in late May this year and on the PM, we checked the alignment and coupling which were both bad. The alignment was .010" out at the coupling face. The coupling pack was wavy due to heavy loading. The picture of the coupling showed that one shimpack had a spacing of 1-5/8 between the faces and the other coupling had only 1-1/4" between the faces. As a result, the bolt installation created an S shaped shimpack which didn't have any flexibility. The shim pack eventually cracked and separated. This is when the vibration increased from "normal".
We replace the coupling shimpacks and realigned to within .002" at the coupling centers. So this is not really "lock up" but poor installation added to the misalignment made the assembly pretty rigid.
There were no signs of the wrong bolts or balancing of the coupling.
The readings today show some high peaks at 1x with harmonics. A new peak appeared on yesterdays' vibration spectrum that is outer race defect on the inboard fan bearing. The spike energy is pretty high on the motor bearing.
I am thinking right now that the rigid shimpacks put a lot of thrust forces on the motor and fan bearings and did some damage to them.
Here are the amplitude and phase readings. The amplitudes are lower than they have been in the last week, but I think that is because the process is running a bit differently. The patterns are the same.

b10_scrubber.xls (16 Kb, 43 downloads) scrubber fan

Word of caution: it make me cringe - these couplings can and do fly apart. Stand clear and out of the path. I've seen too many imbedded in walls and ceilings.

They are a great coupling and many use a model that isn't designed exactly for their application which will give the 4X component. Axial positioning is always a consideration and necessary.

Make sure you have the right coupling for the given application and alignment is tight: at running speed and all operational conditions met (thermal, etc.) specs might look like this:
+/- 2 mils parallel w/ zero degrees zero minutes and 15 seconds angle. Write for exacts for your application and/or a tolerance chart.

With the history of this drive, I would suggest that the coupling hubs be checked for runout or other damage too. It sounds like they have had a pretty rough life.

Like Sam said, make sure htat you are using the right coupling. I think that this type of coupling has a very low end float allowance. Make sure that it and the motor are compatible.

Good Luck

Is there only one shim pack?
A single one is radially very stiff and will not tolerate parallel misalignment.

Gotta have 2 with a spool/spacer.
http://www.gbmcoupling.com/images/products/disk_coupling.gif

Peggy,
Assuming that the phase readings are direction compensated, the angles appear to be basically in phase across the coupling (both axially and radially). Misalignment doesn't appear to be a problem source.
1x phase readings @1781 on the motor OB???? I'm unsure if phase was taken at two different speeds or if the "@3562" is the 2x component reading.
There also appears to be an approximate 180 degree phase shift on the IB and OB fan bearings in the axial direction (@3562). Please clarify whether 3562 is running speed or the 2nd order of running speed.
If you haven't found all of the problems with this fan, you certainly have found a major one with the coupling gap. Hopefully, others here will look at the phase readings and shed some light on the phase change between IB and OB fan bearings.... Good luck.

Thanks to all! This confirms my suspicions.
Sid,
The 3562 is the 2nd mode of the ODS, not an actual running speed.
I'll be keeping an eye on things. We'll be down again in September and will do some more work then, unless something crops up in the mean time.
Peggy T.