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

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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

 

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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.

 

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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

Sledder,

one question.  Besides the fear of a gear box problem, does the oscillation cause any production issues?  If not, why worry?

your situation wouldn’t be the first time the ‘experts’ begged off.

please have someone check the two signals the the drive is comparing.  There should be a reference signal and a feedback signal.

our situation wouldn’t be the first time the ‘experts’ begged off.

Also, it would not be the first time that a vendor pointed the finger away from themselves.  Personally, I would never think a vendor would dismiss a complaint from a good customer.  Vendors have your best interest in mind - way in the back somewhere.

Was this all the data that the vendor reviewed.  If the oscillation is at 1.6 Hz (or even somewhat higher), the oscillation would have be occurring in the data analyzed.  The resolution one gets with only 3 cycles - as the data shows - will not be good enough to see the low frequency; you need longer data samples.

 

Ron,

This issue doesn't affect production at all. What I am seeing are some major bearing failures on several pulleys that are in the vicinity of the drive pulley that is being driven by this motor.

We just changed a bearing out last week on #7 pulley, heavily worn outer race. We changed out the other bearing out on #7 in October 2018, it had a broken inner race and major damage on the outer race. 

We have replaced one of the drive pulley bearings out late last year. This drive pulley is connected to the motor / gearbox that oscillates. This bearing had major outer race damage.

I have a video of what the belt looks like coming off this drive pulley. There is a lot of belt slap as it's going to and coming away from the take up pulley. I need to take a shorter video so I can e-mail it.

Here is my theory; The oscillating motor is like hitting the brakes and causing and causing a ripple affect with the belt line. For instance, put 3 locomotive nose to tail and have the guy in the back engine continually tap the brakes as the front two are trying to pull. 

We are planning to un-couple the 3rd motor/gearbox from the belt and see if we still have the belt slap with the 3rd motor out of the loop.

I will mention the reference and feedback signals to our guys.

William, Yes, this is all the data they looked at.

Thanks

 

 

The pictures of the bad bearings are from pulley #7. You can see #7 behind the screen. Both outer races were extremely worn. The bearing and block you see in the picture had a cracked inner race and a worn and broken out outer race.

The video will show the belt slap as it goes to and comes off the take up pulley. Yes, I do have some lagging missing on pulley #7,  I have never seen an issue like this due to missing lagging on a pulley. If you listen to the video and watch the belt slap it it matches the whine in the gearbox (backlash noise).

Thanks

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IMG_2753

is 95 RPM the speed of the belt?  I imagine the belt has counterweight rolls to keep it tight.  May have an issue their causing the belt to tug and relax.  This would be seen in all of your drives.  Also something that would cause uneven loading or feeding of the belt.

Ron,

The drive pulleys turns at 89 RPM. The loading point of the belt is around 10,000 feet away. You don't see anything like this anywhere else on the belt line. All this action is is near the drive pulley of the motor with the oscillations. The loading of the belt is generally smooth and even. 

Our next step is to un-hook the low speed coupling from this drive and run it with the the other 2 motors and see if we still have the belt slap. The drive for this motor will be disabled, hopefully we can run the belt on 2 motors.. We need to try something outside the box.

 

Thanks

Sledder, any updates on this issue?

Read majority of the posts on this thread, the last video, longest one, shows what appears to be a partial splice going over the drum on right hand side of video. It appeared to me the noise coincided with this splice leaving the drum. Wouldn't this splice cause a beat of load and unload? Seems like a big bump on the belt....

Dave

No new updates on the issue with the oscillations. We are planning to run the belt on 2 motors sometime in June to see if we still have the belt slap. 

Yes, there is some rubber lagging missing on one of the bend pulleys in the video. That might be causing some of the slap, but IMO, not as much as we are getting. Will keep everybody informed when I know something.

 

Thanks

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