I have a dual drive conveyor that is starting to puzzle me.  One side has always had a bit of a resonance, but lately, when the belt is unloaded and first staring up I'm starting to get a pretty violent shudder on the motor and platform.  There is one Vibe sensor on the input of the gearbox that shuts the system down at .6 In/Sec.

The vibe sensor has been tripping during start ups.  Haven't seen any drastic difference in line frequencies to the motors during these occurrences.  The shudder settles out after about 30 seconds or so.  Peak amplitude has gotten up to 1.6 In/Sec.  Right now, the vibe sensor is jumped during start up an then put back online within a minute of the belt being fully loaded.  There are no bearing fault frequencies on the motor or gearbox. 

Could the fluid coupling be going bad...slipping?  Oil was checked at the proper angle and both were found to be filled to proper level.

Any thoughts would be greatly appreciated.



Original Post

What other data to you have to offer for diagnosis? Vibe, oil, IR, amps, speed? New/old, has it done this same thing in the past? Equipment sketch/pic?

A slipping fluid coupling I don't believe will normally vibrate, unless you are near a natural frequency from 0 rpm to max input/output rpm or there is a bearing fault, misalignment, bent/cracked shaft, worn coupling elements etc...

 Have you looked closely at the supporting structure of your drive assemblies? Belt screw or drag conveyor? Broken structural steel/welds under drive assemblies? Has it been running slower acting weird? What kind of shape are the conveyor drive drums, tracking of the belt? Is the oil in fluid coupling burnt/smell bad?

A "normal" machine should never vibrate above 1.0 in/sec/pk. Sounds like you have an "exciter" at some speed during start up. Have you verified if the vibration is input or output related? A true mechanical defect should be present across the entire speed range, not just at start up. A violent shudder is never good. Have you done a quick shaft lift check on motor, gbx in, gbx output shafts to see if there is excessive shaft play? Have seen the sprocket meshing frequency on a drag conveyor excite the mounting support of the conveyor, 1.3 in/sec/pk. Have seen worn bearings on output shaft do the same thing that you describe above.


Thanks for the reply Dave.  A lot of good questions, some I can answer.  I have given the surrounding structure around the motor and gearbox a thorough once over looking for loose bolts or cracked welds. Nothing there.  We cut out part of the coupling guard and put some expanded steel (mesh) over it and hit the drive with a strobe.  I was able to freeze the motor and coupling at 1798.  The Driven end hub past the coupling I could not get to freeze, it was about 5 RPM slower, but had a distinct back and forth motion, again that I could not freeze.  I'm waiting for the results of the oil sample, but it did smell kind of burn.  Thinking of just draining the fluid and replacing and see if that has an effect.  What are your thoughts about running a 68 weight hydraulic oil in it?  Presently, we are running a 46 weight.  I'll post more about what I'm getting on vibe later today.  That too, is pretty interesting, with no solid conclusions.  No Bearing issues at all though.



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