Hi Eduardo,

Do I understanding correctly that you spaced every other idler 2.5 m and then 3.5 m to try and avoid the possibility of belt flap? But now the 2.5 m is a distance that would cause belt flap in the primary mode shape? What changed? Why don't you use a constant idler spacing of 3 m?

Generally if you are really concerned about belt flap on the return run you may have different, but locally consistent, idler spacing as the tension changes along the return run - higher tension portion versus a lower tension portion.

Does your calculus show you will have problems along the entire return run or only in an isolated area.

Are your return idlers flat or v-returns (2 roll idlers)?

The belt flap is very dependent on several factors including the belt mass, belt modulus, local tension, idler configuration, roller quality, spacing and even the structure and idler diameters. Your belt "might" flap at different locations during transients as the tension changes in the system during starting/stopping or load changes on the belt. A lot will depend on the profile and how responsive your take-up is. I've seen conveyors where the belt flaps only when certain sections of the belt pass through specific areas at specific tensions.

The location of the belt flap may move as the belt mass changes (from belt wear). Belt flap can lead to shorter idler life in the area where the belt flap is occurring.

Lots of conveyors have been designed and built without any consideration for belt flap. I wouldn't expect too much dangerous misbehavior from the belt due to this. There a much bigger items to be concerned about.

Best regards,

Andrew Hustrulid ■

Dear Mr.E.Finke,

Hope this link may be interesting to you.

https://forum.bulk-online.com/showth...ight=belt+flap

Thanks & regards, ■

Hi Eduardo,

Does your belt flap calculation take into account that you have the v returns? This makes a big difference.

Are these steel rollers or rubber disk return rollers? Rubber disk return rollers will be more of an issue over time as they wear and can pick up an oval shape.

Even on a flat conveyor the tension changes enough on the return that if you do get some resonance it should be localized and not the "entire" return strand.

What is the critical tension for mode 1 belt flap with a 2.5 m spacing? What is the critical tension for mode 1 belt flap with a 3.0 m spacing? What is your T2 tension? What is your tail tension?

With alternating idler spacings along the return it might be that you have doubled your chances of having issues with belt flap. Now you have two critical tensions to worry about.

Is this conveyor on the ground or up in the air - such as a mobile bridge conveyor?

Best regards,

Andrew Hustrulid ■

Hi Eduardo,

Do you know if the belt flap calculations take into account the V shape? There is a big difference in the mode shapes and critical tensions between flat returns and v-shaped.

Is the drive and take-up on the ground or up in the gallery?

It won't make a huge difference but I'm wondering if the tension rises slightly from the TU tension of 118kN to the tail tension of 126kN (the TU is at ground level)

OR

the tension drops from the TU tension of 118kN to an even lower tension and then rises once the belt is running horizontally along the ground? (the TU is in the gallery)

How do you get to the 133kN max tension on the return? With a gravity take-up your return tensions, during running should be more or less constant. Is the 133kN coming from "low temperature" calculations or ??

With the above assumptions the area to watch would be near the tail, on the ground mounted structure, as the belt approaches the tail.

What does the program consider the "range" for mode 1? 158kN +/- what? It's looking like a very small portion of the return tensions would fall into the range.

Best regards,

Andrew Hustrulid

Originally Posted by Eduardo Finke

Hi Andrew,

The rollers are V 10° metallic without rubber

the critical tension is 158KN for mode 1 at 2,5 m, I have 133 KN (max) in running condition. Still inside range for mode 1

the critical tension is 218 KN for mode 1 at 3,0m.

T2 and take up belt line tension = 118KN

tail tension = 126KN

The conveyor starts horizontal at the ground and elevates 34,4m to discharge in a silo. The final section is a gallery with 50m with the last 19m hanging.

Best Regards,

Eduardo Finke

■

Hello,

The earlier respondents have already given good information on the subject. I add some information as below.

The natural frequency of transverse vibration at specific location of particular belt conveyor, changes with the span of return idlers (idlers pitch), because other particulars influencing the natural frequency are constant in such situation. In case of adjacent idlers, the belt tension would be practically same at both the locations (at each place on conveyor).

Above implies that belt flapping natural frequency for adjacent idlers would be different according to their pitch i.e. vibration natural frequency for 2.5 m and 3.5 m pitch adjacent zones will never be equal at any location on belt conveyor, and they together cannot create (amplify / spread) the resonance. So, questioners hidden answer appears to be on right track. Better get to know the reason from supplier.

The suppliers approach is worthy of analyses by engineers regularly concerned with the subject. The differing pitch needs to be chosen such that not to make the conveyor construction difficult.

Regards,

Ishwar G. Mulani

Author of Book: ‘Engineering Science And Application Design For Belt Conveyors’. Conveyor design basis ISO (thereby book is helpful to design conveyors as per national standards of most of the countries across world). New print Nov., 2012.

Author of Book: ‘Belt Feeder Design And Hopper Bin Silo’

Advisor / Consultant for Bulk Material Handling System & Issues.

Pune, India. Tel.: 0091 (0)20 25871916

Email: conveyor.ishwar.mulani@gmail.com

Website: www.conveyor.ishwarmulani.com ■