GB2245536A - A conveyor belt - Google Patents

Abstract

A conveyor belt has different stretch characteristics across its width such that the sides thereof have a lower modulus of elasticity than the central portion.

Description

A CONVEYOR BEST The present invention relates to a conveyor belt, and more particularly, to a conveyor belt for use In a belt conveyor system capable of transporting fluent materials over relatively steep inclines.

Because material on a conveyor belt has a tendency to slip when the belt is operated over inclines greater than 180, it is necessary to construct underground roadways with shallow gradients to accommodate a series of belts over the required vertical distance. As will be readily understood this entails considerable expense.

Belt conveyor systems have been proposed which are capable of operating on gradients steeper than 18 , but these systems tend to have major operating limitations inherent in their design and are thus restricted to a narrow range of special limitations.

One example of such a system is the so-called tube conveyor which comprises a continuous conveyor belt which is shaped by rollers carried by a support structure to form a tubular portion between the feed and discharge ends of the belt. A tube conveyor is capable of transporting material uphill at angles of 50 to 55 .

However, to operate effectively at this angle of incline the material must be generally uniform in size and must fill the tube. Moreover, a tube conveyor can only operate to transport material downhill at an angle of less than 189 - at angles greater than this the tube conveyor simply becomes a chute and all the material slides to the bottom.

Another example of a known conveyor system capable of operating at relatively steep angles of incllne is the bucket elevator. This comprises a continuous belt or chain which carries a plurality of buckets spaced along its length. Each bucket is filled with material as it passes a material feed point and is then raised through the required vertical distance on the continuous belt.

At the top of the continuous transport system the bucket is tipped up to discharge the material and the bucket is then lowered back to the bottom where it is filled with material again. This system is capable of operating at very steep angles of incline, but unfortunately it has a relatively low capacity, is very noIsy in operation and requires considerable maintenance.

A belt conveyor system is known which seeks to overcome the problems associated with transporting material over relatively steep inclines as well as horizontal sectIons. This comprises a troughed conveyor belt running in parallel with a chain conveyor. Attached to the chain are flights or paddles whIch are so shaped as to match the profile of the belt and which serve to drive both the belt and the bulk material thereon up or down the incline as required. By relaying on the paddles and the bulk material friction with the belt to drive the belt the system avoids the complication of separate drives for the chain and the belt, and also ensures synchronlsed motion between the two.

Unfortunately, it has been found that conveyor belts manufactured in accordance with conventional fabrication techinques are not capable of operating effectively in this particular system. At the upper end of the belt the belt must negotiate a convex curve of approximately 10 metres radius whilst troughed and fully loaded as the belt levels off to a horizontal section from its steeply inclined section. Throughout this curve the belt must maintain a trough, the sides of which are approximately 455 to the floor or base thereof. This requirement is totally alien to conventional belt conveyor systems which are rarely inclIned to negotiate curves of less than 50 metres radius - this being the typical radii of the curved section between a belt inclined at 180 and its horizontal section.

In addition the belt must have sufficient weft frigidity to bridge the gap between the idlers which support the belt on each side.

It is an object of the present invention to provide a conveyor belt which is suitable for use in conveyor belt systems transporting fluent materIals over relatively steep inclines as well as horizontal sectIons.

According to a first aspect of the present invention there is provided a conveyor belt having different stretch characteristics across its width, such that the sides thereof have a lower modulus of elasticity than the central portion thereof.

The differential elasticity allows the belt to negotiate tight convex curves formed between the steeply inclined sections of the conveyor system run and the horlzontal sections thereof.

Preferably, the conveyor belt comprises a central region having a relatively high modulus of elasticity and an outer or side region on each side of the central region having a relatively low modulus of elastIcity.

Preferably, m lntermediate region 15 provided between the central region and each side region, whlch intermediate regions have progressively decreasing modulii of elasticity across their widths towards the side regions.

According to a second aspect of the present invention there is provided a conveyor belt system comprIsing a conveyor belt in accordance with the first aspect of the present invention.

The conveyor belt may be fabrIcated with either a plied or solid woven constructIon.

The differential stretch characteristics are required across the width of the belt to give a lower modulus of elasticity at the belt edges than within the load carrying centre portion. Yarns with differIng stress/strain properties can be employed in bands to match the changes in stretch considered necessary across the width.

An embodiment of the present invention will now be described, by way of example, with reference to the accompanying drawings, in which: Fig. 1 shows a section through a troughed conveyor belt supported on idlers; and Fig. 2 shows a side view of a section of conveyor belt supported at intervals along its length on idlers.

Referring to Figs. 1 and 2, as will be appreciated on a convey curve, the side sections 1 of the belt will effectively have to travel a longer distance than the central sections 2. In this respect consider for example the case where: R2 = 10.00 Metres R1 = 10.20 Metres and the Curvature C = 300 At R2 = 10.00 Metres the belt will travel 90 x 2.#.10 Metres 360 5.237 Metres At R1 = 10.20 Metres the belt will travel 30 x 2 x # x 10.2 360 5.341 Metres As can be seen from this simple example the slde sections 1 are effectively stretched: : 5.341 - 5.237 x 100 = 1.98% 5 .237 more than central section 2; thus in a conventional belt there is a tendency (because of this increased elongation) for the tension to be greater in the side sections 1 than the centre sections 2. Because of the angle of trough the side sections 1 tend to want to pull in towards the centre section 2 In order to equalise the induced tensions by running at the same effective radius.

This cannot occur and results In a situation known as the "" formation which can rapidly result in belt failure.

By making the side sections of the belt with a lower elastic modulus than the centre section 2 so that it is capable of running at the same tension as the centre section 2, even whilst extended between 2 and 5 more this problem can be overcome.

An example of a continuous belt conveyor fabrlcated in accordance with the present inventIon is as follows: Weave 2 ply 4 shaft interweave employing polyester filament yarns folded with polyester textured yarns and nylon filament folded with textured nylon. These combInations can be varied according to the ratios of stretch required.

Yarns employed Nylon Total denier approximately 7500 made up of filament and textured nylon.

Polyester Total denier approximately 8000 made up of filament and textured polyester.

Weave 4 ends per repeat of weave.

Warp Repeats across width of belt.

Nylon Nylon/Polyester Polyester Nylon/Polyester Nylon 100 36 80 36 100 Blended Blended (8N4PE6N6PE4NSP) (8 4 6 6 4 8) The carcass of the belt is woven with textured nylon weft at 5 picks/cm.

The carcass can then be impregnated with rubber, PVC or some other polymers and covered according to specific operating requirements. In all cases the belt must be held after completion of the gel/cure time under the same stretch and pressure conditions until cool in order to retain the belt configuration.

In one preferred embodiment of the present invention, the central section of the belt is comprised of polyester and the side sections are each comprlsed of nylon. Between the central section and each side section there is an intermediate region where the polyester gradually gives way to nylon. These intermediate regions have a graded modulus of elasticity which progressively decreases from the high modulus central section to the low modulus side section.

Claims (5)

1. A conveyor belt having different stretch characteristics across its width, such that the sides thereof have a lower modulus of elasticity than the central portion thereof.

2. A conveyor belt according to claim 1, wherein the central region has a relatively high modulus of elasticity and each of the outer or side regions has a relatively low modulus of elasticity.

3. A conveyor belt according to claim 2, wherein an intermediate region is provided between the central region and each side region, each of which intermediate regions has a progressively decreasing modulii of elasticity across its width towards the side region.

4. A conveyor belt according to any preceding claim which is fabricated with either a plied or solid woven construction.

5. A conveyor belt system comprising a conveyor belt in accordance with any of the preceding claims.