Increasing the longitudinal flexity will increase power to pull the belt axially.

Increasing the deformation of rubber and fabric will increase the internal hysteresis in the flexible region. More flex = more strain = more energy loss from flexure. This type of energy loss is called a flexure hysteresis of the carcass.

Read all the recent publications on low rolling resistant rubbers and their effect on belt power such as: Hager, Nordell, Spaan, Wheeler, et al in BSH.

Why would you do it?

You can make the response more effective with a better internal rubber and/or polymer fabric. However, the fabric should be stiffer, when bending in the vertical plane not more flexible, if you desire to lower the power consumption. ■

There are many ways to increase the longitudinal flexibility in an EP belt, the easiest way is to change the weave pattern but why would you do this. For the last 40 years we have been working in the opposite direction for very sound reasons one of which is as Larry says, power consumption. I think you need to explain the problems you are trying to overcome in more detail.

Col Benjamin

Gulf Conveyor Systems P/L ■

You may try by increasing the crimp of the warp in the fabric?

Regards

SD ■

The intermediate elongation of the fabric may increase by a percent . The growth of the belt in service may not get affected. But it has to be seen. Can not be guranteed at this moment. I do not think it will be advisable to mix EP and NN in the same belt. If any one has done the same before, they can share their experience. It will be a learning for me too.

Regards

SD ■

Hi Bol

A few pointers..

The more plies you have, the stronger the splice using conventional methods. So 2 plys are a bit of a non starter in this direction.

You only need worry about flexibility for the higher classes of belt. In such cases you could opt for steelcord belt.

You cannot mix EP with NN in the warp .. so forget it

The crimp of a warp is normally around 2.5% in practice. this also gives 2.5% elongation at 10% rated tension for the good old EP. Any more than this value of crimp and you will get time based creep.. so it must be avoided.

When a belt goes round a pulley, the top cover elongates. In so doing it heats up. This is called the "Bragg effect" and can be demonstrated by pulling a rubber band hard and putting it on your forehead.. feel the heat.

If you let the rubber band contract it will immediately cool down. (Try it on you r forehead again)

The trouble is a rubber band is made of natural rubber. Belting is made of SBR which is horrible stuff. Once SBR has been stretched you actually have to compress the last bit to get it back to the same length as it started, therefore doing more work on it. This takes a bit of power.

It is therefore the covers that are the main culprit as they are thicker than the carcass and behave badly.

In the words of Michael Cane ..."Not many people know that.."

Regards

LSL Tekpro ■

Hi,

It is of no use just changing the crimp in the weave of the belt as the belt in time will stretch permanently taking out this additional crimp. Any process that you use to achieve this additional longitudinal flexibility MUST logically mean the belt will stretch more and have more dynamics during start and this must be factored into any system design eg take up. If you want to maintain this additional fexibility over time the safest option is to use a polyamide (nylon) as the warp or longitudinal tension member. Overall this problem needs to be addressed directly to one of the major belt manufacturers as there are a lot of options and only they can tailor what you want to achieve into a commercially available product.

All the best

Col Benjamin

Gulf Conveyor Systems P/L ■

Dear BoF,

I do not concur with your comment on lower damping means lower elasticity. They are independent. Elasticity is set by the rubber's dynamic modulus while the damping is set by the loss modulus.

Dear Graham,

Most modern, welll designed belts, do not use significant amounts of SBR. NR , BR and other ingridients are more dominant.

On cheaper belt designs, SBR can be a lower cost option depending on the price of NR and is therefore used for commercial gain. It is used to stabilize against the sun in moderate amounts.

SBR is a poor choice if designing for low rolling resistance.

Fillers and other materials play a significant role in establishing the dynamic and loss modulii. ■

Hi Larry

Here in the sticks of South Africa we use SBR a lot.

In what is left of Zimbabwe at General Beltings in Bulawayo its the same story. I made many belts there myself (special U-Cons) I could have SBR or SBR a la Spriggs.. so I experimented till I got a blend that could roll into a U-con shape flex open and roll back again without self destructing.

Oh and same story in Italy at Cigo.

Oh and incidentally Colin.

We never use Nylon warps any more. Since we stopped using them we now do not have problems with the belts rolling into pipes, and no more take-ups creeping to the bottom overnight.

Cheers

LSL Tekpro ■

Hi Graham,

Thanks for your replies, I know the issues you talk about with nylon in the warp of belts and these issues have well and truely been overcome by most quality manufacturers of fabric belts. We still see a lot of NN belts in high impact applications although I agree polyester has taken over as the preferred yarn in the warp direction. My suggestion was only in response to the desire for additional flexibility, not a recommendation.

Col Benjamin ■

High elastic (recoverable) stretch is not necesarrily associated with with high energy loss, if the stress-strain curve is very linear and the rebounding curve follows the path of the ascending curve. Energy loss and dampening are related to hysteresis; the area between the ascending and rebounding paths of the stress-strain curve. The best solution for a high stretch belt with minimal dampening is to select a high stretch fabric in straight warp construction, imbeded in a high quality (natural grade 1) rubber. The high stretch fabric is nylon not polyester. The elastic characteristics are improved as the belting is run in and permanent elongation is taken up. Operating tension range also effects the losses and dampening, with higher losses occuring at the lower tensions.

Joseph A. Dos Santos ■