Larry..

I have not seen a steelcord belt roll into anywhere near as much as a pipe configuration, as I have for fabric ones.

We had some Korean belts which were delivered incorrectly with Nylon warp (longitudinal) as well as Nylon weft (transverse), and these rolled into almost closed pipes especially in the concaves.

The effect was noticed after a couple of days of varying load.

It looked like the varying load worked on pushing the belts into the troughs, and effectively rolled them into a pipes.

(Incidentally, these belts never stoped stretching, and the supplier had to replace them. I believe that the additional stretch in the bottom of the trough in the concave sections has a direct bearing on the pipe shape formation, as the unstretched edges want to take the shortest route instead of the middle bit)

I have not had anything like this effect on the less stretchy EP warp and Nylon weft.

It therefore follows that the higher the modulus of the warp, the less of a pipe you get. Therefore with St of 10 times the modulus, you get 10 times less pipe shape I suppose.

Have a good weekend

LSL Tekpro ■

Hi Larry,

a) Are the tensions in the cords equal?

b) Are the top and bottom cover compounds the same?

c) If you fillet off the top and bottom cover individually does the cupping go away?

d) Are the coords alternating S and Z?

Regards,

Andrew Hustrulid

Sandvik Mining & Construction ■

G'day Larry,

If the amount the rubber compound shrinks or grows while the rubber cures and crosslinking increases is significantly different between the top and bottom cover then I would expect to see some level of cupping. However with "light but normal cover gauge" this should be negligable.

Regarding the long life - I've never seen belt cupping improve significantly until the top cover is worn away!

I'm still seeing the sights here in Australia. Hope to get back to Chile before the kids forget their Spanish.

Regards,

Andrew Hustrulid

Sandvik Mining & Construction ■

Dear Lawrence,

I have seen quite a few steelcord belts curling.

Two main sources for the problem:

- presence of discontinued weft layers

- manufacturing process.

What is thecover thickness? and what is the rating?

Kind Regards

John Paul ■

Dear Lawrence:

prevous curled Steelcord belt:

- TXI Texas

- Copetro Argentina

- SPCC Peru

- Norilsk Russia

- Paksteel Pakistan

Not all to the same grade.

Kind Regards

JP ■

Hi

Can someone explain what is meant by S & Z lay of the cords?

Shane ■

S and Z cords is a code use internationally by steel cord manufacturers to specify the direction of the twist of the filaments within the cable.

In a steel cord belt, each second cord has to be twisted to the right (and same to the left) in order to keep the belt straight.

So one cord is "S", the next one is "Z" and so on.

This is one of the way to ensure a balance between the remaining tensions in the cords after cure.

When you order steel cord for your belt production, the supplier automatically provide 50% S and 50% Z, unless you specify otherwise.

Best Regards ■

Hi Larry,

For what it is worth I have seen this happen before but not to the extent you describe. The cause was the compounding or lack thereof and the problem got worse as the top cover was exposed to heat/sun. Essentially what we found was that the rubber lost a great deal of its elasticity and basically shrank. Test the top cover now for physicals against what the original spec for the compound and particularly if the elastic elongation and tensile has dropped off then you can focus on the compounding.

Regards

Col Benjamin

Gulf Conveyor Systems Pty Ltd ■

Colin,

you are right.

If there is no weft reinforcements, the curling problem probably comes from the compound. What you describe is a compound where the Pentaeritrithyl Diphosphate is missing. Some manufacturers save money on this expensive but essential additive.

If your hypothesis is right, then cracks on the cover exposed to the sun or the air (ozone) should appear. If not, then the construction of the belt, is the source of the problem.

Best Regards ■