Dear Woody,

Yes, there are some publications on the matter. I believe if you search for Alex Harrison's publications you will find his work on plate (belt) theory. There are factors in his work which are hard to obtain witrhout serious lab tests.

Another more conventional approach is to use string theory. The answer lies in between for coupling resonance between idler spin frequency and belt modal resonance.

There is yet another you did not mention. Compliance of the support frame and its modes. This includes structures and idler stringers.

For all of the above, the desire is to operate outside of their modal frequencies and to operate where they do not couple or have the same resonance. As they approach common resonance, they force a syncopation and amplify the resonance. THis can be seen in product coalescence to form volcanoes or strong structural vibrations.

In addition to the above, idler roll and bearing failures are significantly increased.

Conveyor Dynamics, Inc. does provide a means of evaluating the first four idler rotating and belt string vibration modes and multiplication factor interations in our BELTSTAT program. THe program provides a safe region and warning region for these modes.

We have also applied the plate theory of Dr. Harrison, but find it is less accurate unless major testing is done on the belt flexural modulus orthotropic properties.

Frame analysis must be accomplised by finite element analysis due to the complexity of the steel shapes. This is not trivial. Some try to find the vibration transfer function of the frame by field or lab testing.

The belt and idler resonance does not force product segration. This is mainly due to support resonance. Maybe fine wet product will be less effected due to its viscous shear strength. ■

Dear Woody,

I wonder if your first initial is "J"? Are you in Perrh? If so, I had hoped to have this conversation Friday, but time did not permit it. Maybe next week?

We were able to isolate the vibration problem with Cape Lambert, Eastern Range, and other non-Australian installations. We will be happy to show the method and results. The vibration is not induced as a belt flap mode even though it appears as such. ■

Hello Woody..

For what it is worth, I noticed that the conveyors that I have installed fitted with Plastic Rolls from one supplier, do not promote any belt flap to speak of.

The rolls are light and therefore keep still, especially as the concentricity is excellent.

I also have some simple formlars for calculating resonance which have served me well. I will dig them out.

Regards

LSL Tekpro ■

Dear Woody,

Please note that my earlier responses to this question indicated that the actions at Cape Lambert and Eastern Range were do to idler transom and support structure compliance.

At Cape Lambert, the correction was to stiffen the support system and problem ceased.

At Eastern Range, the correction was to place a few additional idlers to cut the span length at one critical point which produces a similar correction.

THese examples are not the coupling problem addressed in BELTSTAT. BELTSTAT calculates the belt and idler spin modal coupling frequencies for the first four vibration modes. ■

Woody,

On second thought, Eastern Range was a support frame compliance excitation brought about from the idler and belt resonance at one tension under one load at one belt speed. BELTSTAT showed a slight propensity to couple.

We did not believe it would resonate the structure. We did not design the structure. We have since made this analysis are can see the affect. ■

Hi Woody

The plastic rolls don't actually "absorb" the belt flap, they simply run so concentrically that they do not excite the belt in the first place. Stuff doesn't tend to stick to the rolls either.

So instead of the usual "Ching-ching-ching-flap-flap flap" noise from steel rolls and belt, you get a nice gentle constant whisper and no flap.

All very nice, and they don't corrode either.

We had a set of steel rolls in the horizontally curved section of one of our conveyors which had clay build up on the ends of the wing rolls. The areas between the clay and the steel rolls turned out to be an ideal environment for anaerobic bacterial corrosion to take place. They corroded right through just under the ring of clay.

So we replaced with plastic rolls, (and are testing galvanised ones as well).

So..I like the plastic ones. No noise, no flap, no corrosion, and far less risk to the belt.

Regards

LSL Tekpro ■

Mr. Graham,

A plastic idler probably will present lower vibrations because of its lower weight, reducing the effects of its eventual unbalance.

Do you have more information about your idlers?

Also, reference lists, including belt speeds, forming, width and capacities?

Thanks

Regards.

Alexandre

. ■

Hi Alexandre..

The Plastic rolls are actually not my ones... I simply buy them from the suppliers.

In this case it is usually Rulmeca (previously Melco) . Get them at www.melcoconveyors.com.

There are also many other suppliers.

Cheers

LSL Tekpro ■

Thank you very much, Graham.

Alexandre. ■