1250 Hp. Reliance motor oscillating while running

Do you have any competent people on site that can help with checking the drive settings?  Forget vibration analysis.  Use a current clamp with an AC output and watch the output of the drives.  You are watching the tail instead of the dog wagging it.  You couldn’t possibly have a mechanical issue with all three motors doing the same thing. 

Ron Brook posted:

You couldn’t possibly have a mechanical issue with all three motors doing the same thing. 

Ron, good comments.  But there is one mechanical fault that could cause a low frequency "beat" type phenomenon in all three drives, that being a tooth repeat frequency in the gearbox.  Hence the reason I have asked on three occasions for the tooth combination so the potential cause can be ruled out, or possibly supported to the extent that further investigation is justified.  I also can not see through this thread that an inspection of the gearing has even occured, something that should be, IMO, step 1 if the machine can be shut down and an inspection port exists.

To elaborate, I have seen a few instances where drive had both pinion and gear shrunk onto a shaft with a single key.  The keys were improperly fitted and essentially were "topping" because they were too high.  This caused an area in the gear teeth that had an area of localized pitch line runout.  Being on both the gear and pinion, it was a perfect setup to generate a tooth repeat frequency. 

Early on in the thread, the OP stated "I have been doing vibration on this belt line for a year now. I have always heard a noise from the gearbox, but until now I never knew where it was coming from."  It is apparent that the sound has been there for quite some time. 

 

Sledder posted:

I run the conveyor today at 90%. The RPM's ranged from 1607 on the motor in question and the other two motors were at 1617 RPM. The oscillation is still present...

Did you take any data at that speed? Or videos of the coupling?

If so, did it show anything different?

Thanks,

Ralph

 

Ralph,

I did take a video of it and it pretty much looked the same and it sounded the same. I did not take data on it because I was running the belt empty and I like to take data on a loaded belt.

Ron,

We have a competent electrical group. Are they drive experts? They can troubleshoot them, but they not drive engineers. 

Input - 21 teeth / Intermediate - 88 / 17 teeth / L/S - 92 teeth. FALK - M1230 gearbox

 

Thanks for the help

Sledder

Sledder posted:

Ralph,

I did take a video of it and it pretty much looked the same and it sounded the same. I did not take data on it because I was running the belt empty and I like to take data on a loaded belt.

Ron,

We have a competent electrical group. Are they drive experts? They can troubleshoot them, but they not drive engineers. 

Input - 21 teeth / Intermediate - 88 / 17 teeth / L/S - 92 teeth. FALK - M1230 gearbox

 

Thanks for the help

Sledder

Sledder,

Can you post the video? Be nice for us to be able to compare the oscillation frequency with the first one you posted.

Thanks and Have a Great Day,

Ralph

With an input speed of 1783, the tooth repeat frequency for the 1st reduction (21 x 88 teeth) is 20 cpm.  That is sufficiently removed from what Walt Strong established earlier by using the original audio/video which "...yielded a frequency of about 1.6 Hz or 95 cpm."  The 2nd reduction (17 x 92 teeth) tooth repeat frequency is much lower than 20 cpm since the rotor speeds are quite low.  The output speed of the gearbox, again with an input of 1783, is 79 RPM, somewhat close to the 95 cpm measured by Walt.  

I suggest that the OP verify the 95 cpm by counting out the beat frequency while in proximity to the gearbox.

Walt Strong posted:

John, 79-rpm is 1.3-Hz and this is in the ball park (now baseball season) of the 1.6-Hz that I guesstimated from the very short video.

Walt

Walt, I already say that!

John from PA posted:

The output speed of the gearbox, again with an input of 1783, is 79 RPM, somewhat close to the 95 cpm measured by Walt.  

I suggest that the OP verify the 95 cpm by counting out the beat frequency while in proximity to the gearbox.

 

Sledder,

Why not humor me and have your drive technicians check the drives setting for rpm accuracy and have them de-tune it slightly and see if the oscillation is alleviated.  My terminology may not be correct.  The setting controls how wide of a speed variation the drive will tolerate before it compensates by forcing the rpm change in the other direction.   So, what you end up with is a rotation that is always hunting, back and forth.  Sound familiar?

 

Ron,

What you are saying makes sense to me, that is exactly what it seems to be doing. The motor is just doing what is being told to do. I will pass this on to the electricians, they will think I'm more nuts than I already am. You know how that goes.

I did take another video while running at 90%, it's not as clear as the last one, but you will get the picture.

The output shaft RPM is 89 according to my records at 1800 RPM input.

 

Thanks

Attachments

Videos (1)
CV 2  sw motor 1606 rpm
Sledder posted:
The output shaft RPM is 89 according to my records at 1800 RPM input.

 

Thanks

Hmmm, do you have a cross sectional drawing?

By my math, and your previous tooth combination, (21/88 x 17/92) x 1800 = 79 RPM.  Ignore rotation arrows in my attached graphic as they are from previous work.

 

Untitled

 

Attachments

Photos (1)

Couple articles on possible low frequency causes:

B&K motor vibration discussing beat frequency - could be normal.

https://www.bksv.com/media/doc/BO0269.pdf

Gear hunting tooth frequency - my recommendations for review is attached. The gear in question may not have as accurate gears as the other two. Gears could be checked for backlash etc. Look for uneven wear. If not hunting tooth could rotate bull or pinion to have different teeth in contact.

 

Attachments

FRANKO posted:

 

Gear hunting tooth frequency - my recommendations for review is attached. The gear in question may not have as accurate gears as the other two. Gears could be checked for backlash etc. Look for uneven wear. If not hunting tooth could rotate bull or pinion to have different teeth in contact.

 

I suspect that much of the content of the "gear hunting tooth frequency" article is from my BN Orbit article dating to June 1991.  The "gear hunting tooth frequency" mentions the term Na but with minimal explanation.  Should anyone desire better explanations I refer you to Component Identification of Gear Generated Spectra

Yes John From Pa is correct. That summary used equations from his article when he was with Bently Nevada. It was written back then for my emphasis to use a hunting tooth. So often it's easy for design to have a prime number for one of the gears.

Thanks for all the information relating to "gear hunting tooth frequencies". We are running 4 of these Falk gearboxes on our overland conveyor. The belt with 3 motors is driving a 2 mile long belt line (CV 2). The belt feeding CV 2  is 1 mile long and is running the identical motor and gearbox (CV 1). The RPMs' of CV 1 is spot on at 1800 RPM, nothing unusual what so ever. So, with that said I still think it has to do with the drive more than anything. 

A problem we have is that other than a down day we can't take this belt down to experiment with the drives, it's running constantly and on a down day the belt line is being worked on and not able to run it. I know results on my side have been slow, but it's on our radar.

Thanks 

 

Franko,

No rotor bar issues have been showing up in any of the vibration data I have taken. The other two motors are basically tied together through the drive pulley, so I am thinking that's why their speeds are always constant. '

I will check out the link you provided.

 

Thanks

Sledder

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