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
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