Typically, excessive belt edge flap or vibration is caused when the idlers spin frequency, divided by the belt's natural modal frequency, reaches a ratio of 1st ,2nd, or 3rd vibration response modes.

There are other, most complex vibration issues and culprits. Structural stiffness, idler transom stiffness, idler bracket support compliance, et al can induce vibrations. If your problem is of the spin/belt modes types above, you may eliminate the unwanted vibration by moving (opening or closing) the idler spacing by forward or aft displacement ~200-400 mm as a trial to see if the local fit goes away. Maybe just add another idler mid-span in the vibration field. Note, it may then appear in another location nearby

There are many ways to knowingly protect against the former vibration cases. Change belt tension, change idler diameter and/or spacing. However, there are more difficult cases to control such as large compliance of idler supports which can induce extreme mode syncopation of many idlers in synchronized vibration that can resonate major structures such as elevated steel trusses et al. These larger vibrations can be brought about from random events that initiate the calamity.

Another type of vibration may occur from idler ovality syncopatation, from pulley ovality in the take-up system, from wind buffeting, and so on. ■

Morning Coenraad..

You could try putting in plastic idler rolls where you get the flap.

Make sure you use a good make that has been machined perfectly concentric like the Roman Roller for this application. (The Africa roll would probably also do the job.)

They run like weigh-class rolls

Cheers

LSL Tekpro ■

I have designed a 37m long 1050mm wide conveyor at 15deg using an off-the-shelf design package.

It is indicating that I would get resonance / belt flap on the carry side if the idlers spacing is between 0.9m and 1.2m.

I would have thought that a 1m spacing was pretty normal, but that falls directly within this range. If I move the idler spacing to 1.5m, I need a much higher tension to reduce sag to below 2%, and this seems excessive.

My understanding is that belt flap is more of a problem on the return belt - can it really occur on the curry section, and do I really need to change the spacing away from 1m?

Thanks

Richard ■

Looked at that, though one of the details that I left out is that we're going to use a refurbished conveyor, hence the width is fixed ad hence to get the throughput the speed is fixed. And the vendor already has the idlers, so changing those would chase up the costs, which is why I'd rather play with the spacings. ■

The 37 m carry flap is a no-issue. The belt is too short to manifest damaging coalescence. I don't think a 1m spacing would be a problem in any case.

What are the parameters of your query on the vibration:

1. belt normal operating tension range carry & return - 15 degrees slope?

2. belt mass kg/m

3. belt elastic modulus in N/mm or total N

4. belt speed in m/s

5. idler diameters carry & return in mm

6. type and belt tension at take-up ■

Originally Posted by nordell

The 37 m carry flap is a no-issue. The belt is too short to manifest damaging coalescence. I don't think a 1m spacing would be a problem in any case.

What are the parameters of your query on the vibration:

1. belt normal operating tension range carry & return - 15 degrees slope?

2. belt mass kg/m

3. belt elastic modulus in N/mm or total N

4. belt speed in m/s

5. idler diameters carry & return in mm

6. type and belt tension at take-up

Thanks Lawrence,

I am not sure if I am too concerned with the conveyor self destructing, but more if the potential resonance would interfere with the belt weigher reading. belt weigher is due to be installed about 12m from the head pulley.

I think I understand your questions and the answers are as follows:

1 - carry 16.4 to 28.3kN; return 15.9 to 18,4kN; the conveyor has a vertical curve from 10deg at the feed chute to 15deg at the head pulley.

2 - belt mass is 23.4kg/m

3 - modulaus is 2.070N/mm

4 - belt speed is 2.5m/s

5 - carry and return idlers are both 127mm diameter

6 - screw takeup with 18.33kN tension required

Regards

Richard ■

Can you also note the belt width, tonnage, and material density? ■

no problem.

its a 1050 belt designed for 900 tonnes per hour with material density ranging from 1.2 to 1.5 tonnes per cubic meter.

Regards

Richard ■