Howzit Andrew,

I am a S.A living in the U.K.

Are you the Demco that does polyester moulding ?. If so, you already deal with a division of our company called Eli-Dough DMC.

Anyway, we can offer you a repair system for the damaged length of belt otherwise adhesives for cold bonding / splicing.

Please visit :

www.elichem.co.uk

and view the Eli-Flex and Eli-Bond pages.

Regards,

Aram Friedrich

Eli-Chem Resins U.K Limited

aram@elichem.co.uk ■

Hello Andrew Woollon,

Fancy meeting you here.

Belt Construction:

Manufacturers have different methods of conditioning the fabric denier. Some manufacturers condition nylon to minimize stretch and stablize the yarn behavior. Some polyester also have special treatment. These are usually the better suppliers. Their tensile strength and splice dynamic fatigue strength is superior. So, what do you have? The problem with some nylons is they cold flow if not treated. Thus, over time, nylon can continue to grow. A belt in service for a reasonable length of time, will already be ironed out or prestretched, so to speak. This is better than placing two new belts togther. Therefore, putting a new EP to an old nylon is better than the reverse.

Splice:

How many plies you got? What are you going to use for the splice pattern? In general, the differential stretch, applying the EP to nylon belt should not effect the belt rating. As a rule, the more stretchy fabric causes the problem. As the splice step grows in length from loading, the rubber interface gum is non-linearly loaded. The shear stress and strain displacement grows towards the ends of the step from the splice lap center. Thus, the center has a lower shear stress and the splice step ends a higher shear stress. The higher shear stress or strain will fail first. You could draw a general conclusion that the EP will help. However, the patttern and trreatment of the fabric should be considered.

Take-up Motion:

Yep. You should see a subtle difference in motion of the take-up, if the modulus of the two materials differ to a significant degree as the 200m section works its way to the high tension end. This motion should, of itself, not be a problem. You have already got plenty of takeup to accomodate the nylon.

Load Sharing of Mulitple Drives:

You probably dont have dual pulley drives. If you did, this might be more of a problem, with the differential stretch.

I think I answered in the general and gave note on need for a little more info. to be more factual.

Merry Christmas and Practice a Lot of Holiday Cheering. See You in the New Year.

Lawrence Nordell

Conveyor Dynamics, Inc.

www.conveyor-dynamics.com - but you already know it. ■

Mr. Woollon,

Splicing saddle sections of dissimilar carcass materials is a fairly common practice. As Mr. Nordell has indicated, there should not be a problem with the take-up or the splice strength.

When splicing together belts with different carcass materials, but the same belt specification, the following splicing practices should be followed:



(1) If there is a difference in recommended step length, use the longer.

(2) If there is a difference in tie gum thickness, use the thicker.

(3) If one of the belts appears to have a light RF coating on the fabric, apply a primer or use an extra coat of cement.

(4) Before splicing, check to ensure that the splice materials are compatible with both belts. If not, don't do it!

With regard to the take-up issue, the EP carcass has a lower stretch factor than the NN. As such, the total amount of take-up travel required will be lower. Therefore, the take-up will not be an issue. When installing the saddle, splice the section in so that the take-up pulley is between the first 1/4 point and midway point of the allowable take-up travel. This will allow for stretch of the new belt section and still provide some start-up and loading bounce space in the take-up. (Note: the NN carcass is already at its stretched length and the only belt stretch you have to contend with is with the saddle piece -- assuming that you do not allow the existing belt to relax before or during the saddle insertion process.

Hope this helps.

Regards, ■

Andrew - A Second Comment

Take care when removing the steps between plies. As I stated earlier, the fabric is treated, to enhance bonding. If you remove the interlayer rubber so that you see fabric, you need to prime it. Furthermore, if you see fabric it may indicate a cheap belt. A good splicer will take special care to maintain the core gum interply rubber. With cheap belt, it may not be possible to maintain the bond.

Caveat -- you get what you pay for.

LKN

Conveyor Dynamics, Inc. ■

Happy New Year Andrew,

As you know the lapped splice works by transferring shear force through the rubber between plies. The step lengths are determined for this while taking care that the steps are not too long, in which case poor stress distribution results with low stresses at the step's mid length and high stresses at the ends. I digress from the main point however. An increased bias angle will help to create a great splice that reduces the stresses at the splice (just do the geometry of the forces and you will see this, if not call me), is forgiving of flaws, and better distributes the splice exposure over pulleys, convex curves and transitions. In our DSI Snake manuals we always require a 45 degrees bias angle. We don't always get it.

In sandwich belt conveyors there have been several inadvertant occassions of EP belts being spliced successfully to NN belts. Of course the splices were the only success as the higher modulus polyester caused radius constraint violations.

I hope this helps a little. ■

If you want to splice two belts with 2 differents textile quality you should use the very innovative "super-screw fasteners" of the company MINET of France (see www.minet.fr).



Formed like an “H”, the “Super-Screw fastener” has the same consistence as the conveyor belts themselves. With a multiply synthetic textile structure and rubber as cover material, the “Super-Screw“ meets the requirements of abrasion resistance and tensile strength. You will install this flexible fastener by placing the belt between the top and bottom of the fastener and fixing them with self taping screws and a good power screw-driver with Prozidriv bit’s. Metal pieces inside the Super-Screw held the screws in position.

Unlike traditional metalic fasteners, the “Super-Screw” is compatible with scrapers by skiving the top belt cover, to limit the fasteners over thickness on the belt and by installing it in biais.

This solution allows you to install a splice regardless of weather conditions and accessibilty and allow joining different belts (old and new one, different textile quality etc.) ■

From conveyor design consideration; the gradual conversion from NN to EP belt (by gradual increase of EP length as a consequence of replacement) will need to examine following aspects :

1) EP Belt needs somewhat bigger pulleys

2) EP Belt needs less length of take-up stroke (so existing take-up length for NN belt will also suit EP Belt)

If conversion happens to be in reverse order, the above issue will also have implication of opposing nature.

If NN & EP belt fabric strength are close-by, possibly vulcanised joint may not pose problems, however, the belt manufacturers will be in better position to provide dependable answer. What about thickness of two belts? If these are dissimilar, its consequences around pulley and at scrapers may be examined. ■