Conveyor Belt Induced Truss Vibration

[pmleow]

My company is providing Construction Administration services for a project were several coal conveyors are being constructed. A recent test run of one conveyor has revealed some vibrations within the middle span of the conveyor gallery induced by the return belt which appears to have a harmonic vibration.

The truss vibrations in my opinion are small but noticable. The Structural Engineer of Record is currently formulating a response. General thought is that the vibrations are not a structural concern however we would like to please our client by reducing them if possible.
What could be causing these vibrations? Does anyone have any suggestions to help minimize the vibrations?

The take-up weight cannot be reduced significantly because it would result in slipage at the drive pulley.

 

[civilperson]

Change the diameter of the rollers under the return belt. Make them as differing as possible for vibration produced by one revolution. Even at the same location, different sizes will help if not tied together at the axle.

 

[fratrowie]

how about adding roller under the return belt at the section where the vibration is noticable induced?


fratrowie

 

[JStephen]

I can visualize a long belt bouncing up and down on the bottom side. If that's the case, then putting additional support pulleys under it ought to help.

I can visualize a roller or pulley being off-center, unbalanced, or whatever, and that causing the vibration.

It would help to know if it was at the frequency of the rotation of the pulleys, or at the natural frequency of the truss, or what.

 

[pmleow]

Adding additional idlers was my first thought as well. I will need to consult with my mech. engineer to more closly determine opperating belt speed and the EOR for the natural frequency of the truss. Thanks for everyones help.

 

[evelrod]

Increasing the weight in the take up pulley, within bearing and/or belt limitations, will alter the frequency. Ballasting the truss section in question may also alter the frequency. That and perhaps a concerted effort at alignment of the return rollers and, if all else fails, a couple of additional rollers.

I am assuming this is not an asymmetrical load or drive induced vibration (belt, chain etc.) or a worn out belt. This is a new application, is it not?

Rod

 

[pmleow]

Yes, this is a new application, new equipment, new structure. The drive is shaft mounted and properly alligned. The pulleies have all been check and are within acceptable specs for run-out. The belt is lighter than the one used for a similar system on site due to the project constraints.

Already investigated the possibility of altering the take-up weight but the system limits modifying the take-up significantly.

Also have been experiencing belt wobble at the top of the gallery where the conveyor rises off of the rollers to a traveling tripper.

I will report back what changes were made and to what affect.