Hello all, I have 3-1250 Hp. Reliance drive motors on an overland conveyor. One of the motors seems to be oscillating when running, this is creating noise in the gear train due to the oscillations. I have strobed the H/S coupling at 1800 RPM and it appears the motor is trying to stop. When you look at the attached video you can hear the gearmesh noise when the coupling drops down. I have strobed the other 2 motors and you can see the same thing with the coupling and slightly hear some...
Old machine or new machine? Has the issue always been there or is this something relatively new? I have generally found that if this is a new problem and at some former time the machine was OK, then a careful investigation of the VFD is justified.
Always difficult to analyse without any spectra and detailed info but I suspect this noise frequency is somehow related with the gearbox output rotation. Check it. If so, you could have some output shaft issues (eccentricity, damaged bearing, something is breaking the conveyor, belt is oscilating etc...). This unconstant load could lead to some VFD issues or mechanical issues. For detailed source you should measure and attach as much vibration data as possible.
Any way you can shut down and get a look inside the GB through an inspection opening? The opens aren’t alway obvious; in a fabricated steel housing they tend to be a bolted on plate. In cast housings I have seen bolted on plates and sometimes a good sized pipe plug.
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. This belt line has been in service since 2007.
I don't have the time at the moment to analyze your audio track. Have you confirmed the source of the high pitch frequency (gears or electrical)? Have you measured the modulating frequency, and confirmed it is same as visual frequency? Have you looked for this frequency in the conveyor drive and slack/tension take-up rollers? Walt
Sledder, I am inclined to think it might be electrical, possibly like Dave mentioned, rotor bar. Can you take a low fmax 200 Hz high resolution spectrum, at least 3200 lines, and see what the sidebands, if any, are riding on 1x, 2x, 3x, etc. and then calculate the Line Frequency feeding it at the time of the data collection? Just a thought. Thanks and Have a Great Day, Ralph
I have seen a VFD have a torsional problem where the gear teeth could be heard unloading and loading - as Walt says, this cannot be ruled out. If you know the torsional natural frequencies you can check the vibration data to see if these frequencies (one of these frequencies) is excited.
Maybe the gear has the issue and is causing the motor oscillation, instead of the other way around as you've described it. Tooth repeat frequency comes to mind. It is a low frequency phenomenon that is the result of errors that exists in both the gear and pinion. When the two areas simultaneously "pass" through mesh, noise and vibration are at a maximum. Then, relatively speaking, a considerable amount of time may pass before these areas again come into mesh. The time interval can be so slow...
I've worked with Toshiba VFDs for over 30 years and have seen oscillations similar to the one in your video many times. Before doing a lot of mechanical troubleshooting check the speed reference into the VFD to see if it's fluctuating slightly. An easy test is to take manual control of the VFD and set it for 60 Hz and then check with your strobe light. Please let us know what u find.
JVOITL, Thanks for the response with a troubleshooting idea. I checked the RPMs' on each motor the other day and this is what I come up with. S.W. motor - 1783 rpm ( the motor in question) S.E. motor - 1796 rpm N.E. motor - 1796 rpm Ralph, I looked at the data again and can't find issues with the rotor bars. I will take a 200 HZ reading and see if there is anything there.. Thanks Mark
Similar to jvoitl , I have seen VFDs cause torsional oscillations to the point of hearing the gear teeth unload and load. I've seen this being sensitive to load and speed, too - exciting (self-exciting) a torsional natural frequency. One can see (generally) when torsional frequencies are excited from the vibration at the gears.
Check the VFD settings. Speed control may be set to 'hot'. In other words, the controller is trying to maintain too tight of a speed control. This can cause modulation in the motor. Usually the speed control settings from the factory, if not changed, are not realistic for some field applications.
Interesting sites with torsional oscillations and VFDs: http://industrial.embedded-com...-industrial-blowers/ http://www.engdyn.com/images/u...nal_-_turbo_2008.pdf https://oaktrust.library.tamu....ce=1&isAllowed=y
Barry, The guys were getting a fault on one of the 3 tach drives yesterday. He changed it out and one of the electricians said it made no difference on the test run, but the plant has been down all day today so I could take look at it myself. Thanks for the links William, I will check them out. Thanks Mark
Our guys sent a 3 roll vinyl mill out three time for repair and the third time they sent the motor to the shop. They called me on the third start up to check it. Me first guestion was the tack drive checked. As it turned out the only repair it needed was the tack drive coupling replaced.
Sledder, Can the motors be decreased in speed, say 300 rpm, to see if the problem goes away or maybe better yet, can you check it on a slow startup to see if the problem is there at lower rpms and where (what rpm) does it appear? BTW. Do you use CSI analyzer and Software? Thanks and Have a Great Day, Ralph
Thanks for the reply Sledder. Can you take a Peakvue data set (acquired off route)with a, 1K HP Filter, 1K Fmax, 6400 lines and a 2K HP Filter with a 1K Fmax 6400 lines spectrum and waveform on this motor at the bearing point where the highest 1x amplitude is showing and post them here? Or you may already be taking route Peakvue data, if so, are they at or close to these setting I suggested? Edit: You would not happen to know the rpm when you took your video, would you? Thanks and Have a...
Getting back to the OP: A rough stopwatch measurement of the audible sound modulation (amplitude modulation) yielded a frequency of about 1.6 Hz or 95 cpm. The visual change of shaft rotation by strobe-light may or may not be at the same frequency as the audible sound amplitude modulation. A longer video saved in video file format would be helpful for analysis. If the strobe-light was simply set as a fixed frequency, and not triggered from vibration, then the shaft speed has to be speeding...
Ralph, I'm not exactly sure what the RPM was the day of the video. The most recent RPM taken was 1783 RPM with the same type of oscillation. The other 2 motors were running 1796 RPM. I am currently running the following for my P vue setting. 1K Hz HP filter / 100 Hz Fmax / 1600 lines / 1 average I will give your settings a try. The plants have not been running much lately due to the flooding in Nebraska, the trains aren't coming like they should be. Walt, The Electricians have been checking...
Thanks Sledder, Can you post the spectrum in velocity with out an autoscale vertical, but make the 1x be 75% of full scale? Can you zoom in on the 3x rpm in Velocity also? Did you take any Peakvue 6400 Lines, with the HP Filter of 1K Hz and Fmax of 1K Hz and also a 200 Hz Fmax and 2K HP Filter with a 2K Fmax? Thanks, Ralph
Here's the spectrum taken on the rotor bars. 1X is coming in at 1785, I put the strobe light on it last week and that's where it was running. It looks like the timewave form is showing the oscillations I am seeing with the strobe light. Thanks
Have you monitored the " oscillating" when the power is "cut" to see if it disappears instantly? Or have you changed speeds or monitored a slow start up to see when it might start oscillating? No, I have not done this. Still wanting to change speed to see if it goes away. 3200 lines Thanks
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, 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,...
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...
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?
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
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.
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