Rob,

Wow … a lot of problem for a quick answer but let's hav a go …

1)It is not possible to make much comment on the trailer without drawings and detailed analysis, but if spans are long and their natural frequency is close to operating frequency of the feeder, then struts or braces can be used to reduce the effective span and thus increase their natural frequency.

2)If the Rosta rocker arm mounts that you are using are type AU, AR, AS-P, or AS-C then these are intended for crank shaft driven feeders which have a reciprocating motion, and they will have VERY poor dynamic load isolation when used on circular (or linear motion) vibratory feeders.

For circular (or linear) motion feeders Rosta mounts AB or AB-D should be used, and when selected properly they should have excellent dynamic load isolation properties (better than Marsh Mellow albeit at greater $'s).

3)The Rosta recommended acceleration of 1.6 ‘g’ is only for their rocker arm mounts, and would not apply for their AB or AB-D oscillating mounts. The recommended acceleration of 4’g’ that you mention is debatable, but would only have validity when talking about grizzly feeders which are attempting to screen as well as feed. For a straightforward feeder the acceleration may be dropped as low as possible while still achieving required capacity.

4)It is hard to give a recommended throw/frequency set up without knowing what transportation speed you are aiming for, but in this case I would tend towards a smaller throw and higher speed - rather than slower speed and higher throw. i.e.: perhaps a 6 pole rather than 8 pole motor???

5)When selecting mounts for maximum isolation, the greater the spring compression under static load, the more efficient will be the isolation efficiency - and the lower the feeder operating frequency the greater will be the compression required to achieve the same isolation result.

Hope this gobbledegook is of some help ■

Rob:

1. Trailer appears to be built too light for shaker. When we build portable screen chassis. We just had a customer with same problem on which we lost the order to fabricate. Competitor was much cheaper ours was much heavier beam.

2. Blocking the trailer may help reduce the transmission of shaking when wheels are not on the ground. We block all portables when running for this reason.

3. Could check beams with REED METER to determine IF cross bracing is needed. Or just X BRACE a few spots.

4.MECHANICAL CONVEYOR: not really a vibrating screen correct?

You are just moving from feed end to discharge end into shredder? Stroke on this type is typically around 1"

5. A change in speed may help create greater distance between the feeder freq and the trailer freq. When we have multiple screeners in a row we find a lot of ramping or sympathetic vibration caused by units being closed together at the same operating rpm. We change speeds on motors by plus minus 50 rpm to rectify this extra vibration. We quite often must throw a few XBRACES into the structure also.

6. Using a small electromagnetic feeder would elimate all vibrationcompletely and handle the job easily and eliminate the trailer vibration situation.

7. TYPE or make of the feeder now using?

8. Going to MARSHMELLOWS should do nothing in my opinion, the trailer design is key culprit here, I think.

Happy New Years........ ■

Rob,

To respond to your questions:

1)I would go along with your strategy of not placing priority on altering the trailer in the first instance. You may (or may not) have a natural frequency problem there, but I think it is safe to say that there IS a MAJOR support mount problem, which should be resolved first.

2)I agree that the AU rocker arms should be replaced. Replacing them with Rosta AB mounts will most likely give the best possible isolation, but if you want to save dollars you could use soft coil springs (which if selected properly should be satisfactory).

3)My comment about " low as possible acceleration force' was based on the following thinking:

High acceleration forces are detrimental to the structural integrity of screens and feeders, and it is obvious that lower acceleration is to be preferred. However in the case of vibrating screens if the ‘intensity’ of vibration is too low the particles will clog the apertures (peg) and the finer particles will not work their way down through the bed (and the courser particles work their way up), and this stratification is essential for good sizing. It follows therefore that in the case of vibrating screens there is a lower as well as upper limit of acceleration forces (g).

In the case of a vibrating feeder the material only has to shuffle down the pan. The stroke and speed set up (acceleration) will determine how fast the particles are transported, but there is no detrimental effect in low acceleration - provided that required capacity is maintained.

4)If you don’t have any capacity requirement I would suggest you change to 60 Hz (900 rpm?) and adjust the motors to give about 8mm throw (about 3.6 ‘g’).

5)There are practical limits to how soft the support springs can be. First of all the compression should not be so much as to pose any danger of bottoming out during the period if increased resonance at stop/start. Usually an additional allowance of about three times the screen throw will cover this. Secondly the degree of isolation improvement will decrease the further the spring is compressed. Usually if you can get a static spring compression of say 65 mm you will achieve good results.

6)George raises a good question in his bullet point (4). He is assuming that you have a reciprocating feeder (backwards and forwards stroke), and your description of a “one mass shaker” supports this. But I am assuming from your previous posts, and also because you are using a single unbalanced motor, that you are trying to achieve a circular motion. This is crucial to any recommendations – can you confirm???.

I also agree with George’s bullet point (6) whereas a small electromagnetic feeder would do the job.

Finally in your previous post you suggested that your customer wants to add another unbalanced motor to generate a linear motion. While a linear motion feeder would have better feeding ‘adjustment’ than circular motion – it would not have any better (less) dynamic load transmission to the trailer.

Happy New Year ■

Wishing both health, wealth and success to all of your challenges.

Nice discussion.

Sincerely,

George ■

Thanks for the clarification Rob.

It was important to establish that the beast is a mechanical shaker conveyor (where the material slides rather than micro jumps along the pan), and I guess that my incorrect assumption that it was a circular motion unit made some of my comments pretty confusing!!!!

Lets go back a couple of steps:

For your one mass mechanical shaker conveyer the Rosta AU mounts are in principle OK, but the dynamic forces must be kept low (hence the Rosta limit of 1.6 'g' for conveyor acceleration), and even then this type of mount should be installed on a very sturdy base frame.

You say that you now plan to change to Rosta AB mounts and add a second unbalanced motor. From this I can I assume your intention is to convert to a linear motion conveyor? My concern with this would be the structural integrity of the tray (at 1m x 14 metres long !!!). i.e.: a vibrating node and antinode (wave) effect.

Have you definitely established that the present set up is not acceptable if it is limited to 1.6 'g'. ■

I don't know if the problem is solved. Otherwise we are working on a similar problem now. We are consulting engineers and the actual job is vibration control of a 1,000 t frame with frequencies from 1 Hz to maybe 1000 Hz. There are not very difficult and expensive solutions who are very efficent.

If you are intereted in know more about or get it calculated and designed - send a mail. ■

Greetings from my corner of the "Frozen Eastern Wildernesss" @1140 feet above mean sea level.

It sounds like you need to mount the unit on an air bag suspension as this would isolate it completely and solve the problem.

Contact Goodyear or Aeroquip to look at industrial air spring suspensions.

I think that will help you a lot.

<www.goodyear.com> ■