Shh--shh-shhaker feeder...
Shh--shh-shhaker feeder...
(OP)
We recently installed a shaker feeder on a 48' dropdeck trailer for a customer of ours. This was done so that they can take the conveyor on the road and demonstrate the capabilities of their system. It was a decent idea in theory but not so great in practice. The motors on the conveyor have speed controls that adjust the power from 0 Hz to 50 Hz. At certain frequencies you would think that the trailer is going to fall to shambles. Now they want us to come up with a solution to the problem. Does anyone have any ideas on how to dampen the vibration of the trailer without compromising the effectiveness of the conveyor. We can adjust the counterweights but I think that it has more to do with the frequecy, than the amplitude, which we are kind of limited to. The frame of the conveyor is now rigidly attached to the frame of the trailer. We might try some damping mounts but we can't afford to lose any performance from the convyors. Any ideas?





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Good luck
Regards
Dave
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Garland E. Borowski, PE
Borowski Engineering & Analytical Services, Inc.
www.borowskiengineering.com
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This might help you out in the short term.
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Regards
Dave
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It is difficult to say exactly which direction I need my force. The shaker pan is mounted on an incline, probably about 5 degrees. I can adjust the weights to cancel out forces in certain directions but I still have the harmonic frequencies to deal with, right? There was specialty sliderbed conveyor also on the trailer and we were able to isolate the vibrations from the trailer, to the conveyor, amazingly well with spring mounts. I'm afraid if we try this on the shaker it will dance like a mexican jumping bean. Modifying the trailer seems like it would just be a stab in the dark guess and check game. I would never hear the end of it if it didn't work, but would never hear a word if it did. Avoiding the certain frequencies seems like a good idea but unfortunatly the equipment works best at the higher frequecies which also correspond to the worst resonance. I might try to adjust the counterweights all of the way out and try to achieve a larger amplitude at lower frequecies.
RE: Shh--shh-shhaker feeder...
I'm in Nascar country where guys LOVE playing with vehicle suspension systems...unfortunately, I'm not one of them. Find a good automotive guy and explain to him that you don't need to avoid the 1Hz frequency that makes people sick, but would rather avoid the band of frequencies that are causing excitation problems. Another option may be one of the West Coast earthquake engineers...I don't think altering the suspension system would be as difficult as you seem to think.
My 2 cents.
Garland E. Borowski, PE
Borowski Engineering & Analytical Services, Inc.
www.borowskiengineering.com
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http://ww
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I assumed that for the vibratory shaker feeder only vibrated in one direction; the horizontal. Apparantly it is supposed to vibrate in at least two directions. That complicates the problem because now you are dealing with not only interactions but different resonant frequencies.
Is this correct, can you post a photo or drawing?
Out of curiosity what are the resonant frequencies?
If you phase the weights and get only - say horizontal vibration, that should reduce the vertical vibration.
If the device is hard mounted to the trailer, you may want to consider isolation mounts, either springs or elastomeric, with dampers. Conversely if it is only setting on the trailer, you may want to consider hard mounting it.
I am envisioning a full length flat bed trailer. Is this correct or is this a smaller utility type trailer? If it is the utility type you may want to consider going to a larger, more rugged trailer.
I sympathize with you plight of hearing only about errors and not about accomplishments. It is sad to see that management continues to be their same egocentric self.
Good Luck
Regards
Dave
RE: Shh--shh-shhaker feeder...
You should be able to get >> 10 dB attenuation across the mounts.
What frequency range does your shaker run at? What frequencies are causing you problems?
To be honest for a one off that is probably the most cost effective, 5 tons of steel and you are done.
Cheers
Greg Locock
Please see FAQ731-376 for tips on how to make the best use of Eng-Tips.
RE: Shh--shh-shhaker feeder...
If the problem is actually with the suspension, why not just take it out the picture when the equipment is running. Maybe outriggers like used to stabilize a wheeled crane.
You cannot mount a shaker table on isolation mounts unless the mass of the parts that are supposed to stay still is VERY MUCH greater than the mass of the parts that are supposed to shake. Something about equal and opposite forces....
And yes, shaker tables need to move in two axis, otherwise they don't move the product.
RE: Shh--shh-shhaker feeder...
"You cannot mount a shaker table on isolation mounts unless the mass of the parts that are supposed to stay still is VERY MUCH greater"
That's a fascinating observation. The vibration on the surface of an engine is up to 20g. The virbation of the body near the engine mount will be much less than 1 g. The effective mass of the body is less than that of the engine.
I think you are ignoring the attenuation seen after the first resonance.
Cheers
Greg Locock
Please see FAQ731-376 for tips on how to make the best use of Eng-Tips.
RE: Shh--shh-shhaker feeder...
How much does your combined shaker and trailer currently weigh?
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Second: careful with damping, as damping means destruction of usefull energy. Too much damping and you will not be able to meet the specifications.
The best thing to do is establish the mode shape at resonance (if correct, deflections are in the plane of excitation only), and increase stiffness in areas where you see or expect deflections. You will have to increase stiffness, preferably shifting resonances upwards and away from exciting forces. These forces are related to unbalance, so exciting frequencies are relatively low. Don't be shy on adding stiffness. Too much isn't a bad thing.
if you need more info:
rmooij@technofyscica.nl
web: www.technofysica.nl
best
rob
RE: Shh--shh-shhaker feeder...
Isolation mounts will work very will to prevent the vibration energy from getting to the trailer. However the shaker table won't work correctly.
Typically shaker tables are driven by eccentric masses rotating on shafts to provide the driving force. The goal is to get most of that force into the table. However if the shaker's base is free to move, than the force will be equally happy to shake the base pretty much in the opposite phase of the table. The whole thing will jiggle around quite impressively, but the product won't move.
To continue with your engine analogy, the table would be the pistons, the base would be the block and the carbody would be the trailer.
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The plates and/or brackets to attach these to the frame may already exist from the trailer manufacturer, and if successful, when the landing gear is no longer needed, the brackets and landing gear sets can be removed from the trailer frame so that it can be returned to normal service.
Since it is a drop deck, you might run into dimensional problems, because landing gear is normally sized for frame heights normally associated with fifth wheel heights, not drop deck heights, but, there are single landing gear towers that are built for smaller (less capacity) trailers that have much lower frame heights than tractor/trailer equipment. Individual (rather than paired) landing gear points along the trailer length may offer advantages as well, as I can't imagine these locations where it is being used as being real even surfaces.
rmw
RE: Shh--shh-shhaker feeder...