GB2245525A

GB2245525A - Sheet reinforcing material

Info

Publication number: GB2245525A
Application number: GB9108246A
Authority: GB
Inventors: Norman Yates
Original assignee: BTR PLC
Current assignee: BTR PLC
Priority date: 1990-04-24
Filing date: 1991-04-17
Publication date: 1992-01-08
Anticipated expiration: 2011-04-17
Also published as: GB9009210D0; GB9108246D0; GB2245525B

Abstract

Sheet material for use in reinforcing a conveyor belt comprises at least one ply of a woven textile material having a plurality of substantially co-planar weft elements interwoven by warp elements which have a higher percentage of crimp than the weft elements, the weft elements each being substantially bereft of twist and comprising at least one synthetic monofilament having a diameter in the range 0.1 to 1.00 millimetres, and the monofilaments being provided at a sett in the range 60 to 180 filaments per centimetre.

Description

IMPROVEMENTS IN AND RELATING TO ShEET MATERIAL This invention relates to sheet material of a kind more resistant to flexing in a first direction than in a direction perpendicular thereto, to a conveyor belt incorporating the sheet material of the invention and to apparatus such as a shot blasting cabinet which incorporates said conveyor belt.

The invention relates in particular, though not exclusively, to sheet material for use as the reinforcement of a conveyor belt to provide the belt with transverse rigidity and in which longitudinal traction or other tensile forces are withstood bv additional layers of reinforcement. The conveyor belt may be of the kind used in a shot blasting cabinet to support and tumble products within the cabinet, such a belt being provided with a large number of perforations through which shot may pass and with transversely extending bars to assist the tumbling of products.

For both sheet material and conveyor belts for use in certain applications (such as in a shot blasting cabinet) there is a requirement that the material or belt shall be less flexible in one direction than in a direction perpendicular thereto. In the case of a conveyor belt it may be required that the belt is relatively rigid in a transverse direction so as not to sag unduly between its supported edges under the weight of products carried by the belt but relatively flexible in the longitudinal direction so as to be able to pass easily around end drums.Desirably the transverse rigidity should be attained without any adverse effect on longitudinal flexibility so that the belt is able to pass easily around end drums or edge rollers of a relatively small diameter and thus allow provision of a compact coeor installatior..

It is well known that transverse rigidity may be imparted to a conveyor belt by providing therein a pair of spaced apart reir.fcrcer..~nt layers each comprising transversely extending and individually flexible metal cords. This is described for example in Patent Specification GB 974131. The provision of metal cords suffers the disadvantage of weight and cost; also in the case of a belt which requires perforation the presence of cords of metal causes difficulty in undertaking perforation.

In the case of conveyor belt of the edge supported type and in which the embedded reinforcement for providing tranverse rigidity (herein referred to as rigidifying reinforcement) is not designed to withstand substantial tensile load in the longitudinal direction it is known from the patent specification of GB 1445567 that a reinforcement may be constructed from synthetic, non-metallic material. In GB 1445567 it is taught that a belt may be reinforced by a pair of spaced apart fabric sheets each of which sheets is of a thick solid woven construction comprising two interwoven plies of transversely extending filaments.

The present invention seeks to provide a sheet material, suitable for use in the reinforcement of conveyor belts and in particular though not exclusively edge supported type conveyor belts, in which relatively greater rigidity in a first direction than in a direction perpendicular thereto is attained without requiring that the material be unduly thick, and with an efficient use of relatively low weight reinforcing material which preferably is of a kind which does not hinder the provision of perforations.

In accordance with one of its aspects the present invention provides sheet material comprising at least two superimposed reinforcement layers of woven textile material, an intervening layer of polymeric material which is adhered to each of the reinforcement layers of woven textile material and maintains said layers in a spaced apart superimposed relationship, at least one of said reinforcement layers being a rigidifying reinforcement layer comprising over at least a part of its length at least one ply of woven material comprising a plurality of weft elements all of which are arranged in a substantially co-planar manner and a plurality of warp elements arranged in a woven relationship with the weft elements and having a higher percentage of crimp than the weft elements, each weft element being substantially bereft of twist and comprising at least one synthetic monofilament having a diameter in the range 0.1 to 1.00 millimetres and the monofilaments being provided at a sett in the range 60 to 180 filaments per centimetre in each said ply.

Said synthetic monofilaments forming at least a part of the weft of the or each ply of a rigidifying reinforcement layer may be provided singly or in groups forming threads which preferably each comprise between 5 and 25 and more preferably 7, 14 or 21 monofilaments.

Where the monofilaments are grouped into the form of weft element threads, the threads may have a nominal twist (generally less than one turn per 2 centimetre) to assist in handling and weaving but otherwise are to be substantially bereft of twist. Preferably the monofilaments of the weft elements are provided at a sett in the range 80 to 160 per centimetre.

Where the monofilaments of the weft are provided grouped in threads, preferably each filament has a diameter in the range 0.1 to 0.5 millimetres, the number of filaments per 1 centimetre being in the range 80 to 160. If the monofilaments are provided singly their diameter may be in the range 0.1 to 1.0 millimetres.

In the case where the synthetic monofilaments forming the weft are not grouped into threads, it will be appreciated that in order for the monofilaments to be substantially co-planar in the sheet material the product of the sett of the filaments per centimetre and diameter of each filament in millimetres (or in the case of weft monofilaments of different diameters the total of the diameters of each of the filaments in the sett) cannot exceed 10. To allo for interweaving of the warp elements that product should be less than 8, but preferably greater than 5 so as to attain an adequately uniform reinforcing effect.

Preferably the synthetic monofilaments forming the weft are monofilaments of polyethylene terephthalate, a particularly suitable material being Macrofil (ex-Nymofil).

The monofilaments of the weft preferably each have a modulus of elasticity of at least 10,000 and more preferably at least 12,000 MPa. In constructions in which the weft monofilaments are arranged in groups and provided with a nominal twist the modulus of elasticity of each group preferably is at least 8,000 and more preferably at least 10,000 MPa, the corresponding effective modulus figures of the groups when embedded in and adhered to the polymeric material of the intervening layer of the sheet material being at least 6,000 and more preferably at least 8,000 MPa.

The warp elements interwoven with the weft elements may be formed from a conventional textile yarn material such as a polyester, a polyamide such as nylon, a natural material such as cotton or a reconstituted material such as rayon.

The warp elements may be formed from continuous or discontinuous fibres, and may be woven with the weft elements for example in a plain weave.

Particularly in the case of sheet material for use as the rigidifying reinforcement of a conveyor belt which has one or more additional layers of reinforcement to provide reinforcement and tensile strength in the longitudinal direction of the belt, said warp elements (which extend longitudinally of the conveyor belt) do not need to provide longitudinal reinforcement strength and are required essentially only to maintain the required orientation of the weft elements of the rigidifying reinforcement especially during handling, coating and other operations forming part of the technique for manufact#ring the sheet material of the invention.In accordance with the present invention it is preferred that the total weight of the warp elements shall be less than 5E and more preferably less than 1% of the total weight of the weft elements in each ply.

The ply of woven material containing said weft of synthetic monofilamentary material may extend continuously over the length of the sheet material.

Alternatively the synthetic monofilamentary material may be provided in longitudinal sections of the ply which are spaced apart by intervening portions provided with weft elements of metallic material; the weft elements of metallic material preferably are interconnected in groups, between successive ply portions of synthetic monofilamentary material, by warp elements and said warp elements may be the same as those of the ply portions of synthetic monofilamentary material. The weft elements of metallic material may be provided over between one tenth and one quarter of the longitudinal length of the sheet material.

Suitable metallic material for the weft elements includes metal wires of a multi-filamentary form and of conventional twist levels. The wires may be of a cord or cable construction and may comprise groups of filaments of S twist and groups of Z twist.

The metal wires preferably are co-planar with synthetic monofilamentary material which forms other weft components of the same ply.

The wires may be comprised of individual filaments each having a diameter in the range 0.15 to 0.40 millimetres, the filaments typically being provided at a sett in the range 3 to 140 filaments per centimetre length in each ply over that part of the ply containing metal wires.

The wires preferably each comprise between 9 and 30 individual filaments twisted together to provide ease of processing and suitable final properties.

The individual filaments may be brass-coated high tensile steel and preferably each multi-filament wire has a modulus of elasticity of at least 100,000 MPa.

An assembly of wires may be coated with polymeric material, e g in a rubberising operation, to facilitate subsequent processing to construct the sheet material.

To promote adhesion between the polymeric interlayer and the warp and weft elements of the rigidifying and any additional reinforcement layers a bonding agent such as resorcinol formaldehyde latex may be used.

Suitable materials for the polymeric interlayer include flexible elastomeric material such as natural and synthetic rubbers and also flexible thermoplastic materials such as polyvinyl chloride. Preferably the polymeric material of the interlayer is caused to penetrate interstices of any groups of weft filaments during manufacture or groups of weft elements may be pre-impregnated with polymeric material.

The present invention requires a minimum of one woven reinforcement ply in one or each of the superimposed and spaced apart reinforcement layers of the sheet material. One or each of the reinforcement layers may, however, be provided with at least one additional woven rigidifying reinforcement ply the construction of which preferably is in accordance with the construction of the at least one ply of woven material as recited herein in respect of the sheet material of the present invention. Preferably all plies of each reinforcement layer containing two or more plies are of substantially identical construction.

In a rigidifying reinforcement layer comprising two or more woven plies it is preferred that the plies should not be in direct contact; it is preferred that they be separated by and adhered to a thin lave of polymeric material which may be of the same polymeric material as that of the interlayer between the two reinforcement layers.

In the sheet material of the present invention each of the spaced apart reinforcement layers may be of a construction corresponding to that of the recited rigidifying reinforcement layer thereby to provide a material which resists deformation to a concave or convex shape at either surface as considered in a plane containing a weft element. Alternatively only one reinforcement layer may be a rigidifying reinforcement layer; the other reinforcement layer may comprise for example tension resisting elements such as of metal wire or of Kevlar and which are not necessarily arranged to resist longitudinal compression. In this case a surface of the resulting sheet will be free to deform to either one of a concave or a convex shape as considered in a cross-sectional plane containing the reinforcement element.

The present invention further provides a conveyor belt having a reinforcement structure comprised by sheet material of the present invention arranged with the said elements extending transversely relative to the direction of the length of the belt.

The conveyor belt of the present invention may be adapted for use in a shot blast cabinet. It may have transversely extending stirrer strips secured at intervals to a face of the belt with intervening portions of the length of the belt being apertured for the passage of shot therethrough. In a belt of this type the or each rigidifying reinforcement layer may comprise weft elements of synthetic monofilamentary material in said perforated intervening portions and weft elements of metallic material at portions, such as those underlying the stirrer strips, which are not perforated. Where additional rigidity is desired between stirrer strips, metal weft elements may be provided in said intervening portions and preferably in positions clear of perforations.If only one reinforcement layer is a rigidifying reinforcement layer of a kind as recited in accordance with the present invention, preferably it is arranged to be the reinforcement layer which lies closest to the surface carrying the stirrer strips.

Embodiments of the present invention will now be described, by way of example, with reference to the accompanying drawings in which: Figure 1 is a diagrammatic longitudinal sectional view of a piece of sheet material in accordance with the present invention; Figure 2 is a plan view of part of a piece of a woven textile reinforcement layer of the sheet material of Figure 1; Figure 3 is a perspective view, part cut away, of an end portion of a piece of edge supported type conveyor belt reinforced by the sheet material of Figure 1; Figure 4 is a longitudinal sectional view of a conveyor belt for a shot blasting cabinet, and Figure 5 is a perspective view of part of the belt of Figure 4 as in situ in a shot blasting cabinet.

The sheet material 10 comprises two superimposed reinforcement layers 11,12 of woven textile maintained spaced apart by an intervening layer 13 of natural rubber whereby said reinforcement layers 11,12 serve as rigidifying layers which co-operate (by virtue of their spacing) to provide resistance to flexing in a first direction. A layer 21 of conventional woven reinforcement is provided between the rigidifying layers to withstand longitudinal tensile loads.

Each rigidifying reinforcement layer (see Figure 2) comprises a single ply of warp and weft elements 14,15 interwoven in a plain weave such that the weft elements are all substantially co-planar.

The weft elements 15 are formed from monofilaments of polyethylene terephthalate (e g Macrofil ex-Nymofil) of a diameter 0.25 millemetres. Each weft element is in the form of a pair of threads each comprising 21 monofilaments, and on average 6.6 such threads are provided per centimetre in the warp direction to give an average weft element sett of 138.6 filaments per centimetre. Each thread has a diameter of approximately 1.5 millimetres. The threads and the filaments in each thread are substantially bereft of twist, there being just sufficient nominal twist in the threads as necessary to maintain together the filaments of a thread during weaving.

Each of said weft element monofilaments has a modulus of elasticity in the order of 10,000 MPa, a breaking stress in the order of 800 MPa and an elongation at break of between 12 and 28%, the elongation at break being a function of yarn elongation at break and the thread crimp.

The warp elements 14 are formed from yarns of continuous rayon filaments arranged as lacing strands of a strength and at a sett sufficient to facilitate satisfactory processing and adequate longitudinal strength during handling. The total weight of the warp elements is 0.7% of the weight of the weft elements in the fabric shown in Figure 2.

In each rigidifying woven ply the weft threads have a crimp of only 1.5% whilst the lacing strands have a substantially greater degree of crimp, the crimp of the lacing strands being in the order of 23%.

The two reinforcement layers 11,12 are treated with resorcinol formaldehyde latex during manufacture to facilitate attaining a good bond to the rubber of the interlayer 13. In consequence the interlayer is well able to transmit forces from the weft element threads 15 of one reinforcement layer to those of the other reinforcement layer. By virtue of the substantially untwisted nature of the weft threads the rubber of the interlayer may be caused readily to fully infiltrate into the interstices of the threads during manufacture thereby to further assist in effective transmission of forces.

The interlayer of this embodiment of the invention has a thickness of 4 millimetres.

To provide the conveyor belt of Figure 3 the sheet material of Figure 1 is provided in the form of a long length reinforcement strip with the weft element threads 15 lying transverse relative to the direction of the length of the strip and the warp strands 14 parallel with the length of the strip.

Cover layers 16,17 of natural rubber are then moulded and bonded over the outer surfaces of the reinforcement layers 11,12, edge formations 18 being formed by moulding in a conventional manner for engagement, in use of the finished belt, by means to support the belt.

The finished belt, exclusive of the edge formations, has a thickness of approximately 13 millimetres.

A conveyor belt for use in a shot blast cabinet is shown in Figures 4 and 5. The belt 40 comprises two superimposed rigidifying reinforcement layers 41,42 spaced apart by an intervening layer 43 of natural rubber. Two layers 54 of conventional woven reinforcement are provided between the rigidifying layers 41,42. The belt has cover layers 46,47 The belt 40 therefore is of a construction generally similar to that described above with reference to Figure 3. However, it differs in that one face 50 has secured thereto, by bonding, a plurality of transversely extending rubber stirrer strips 51. These are provided at approximately 300 millimetre intervals and each has a width, in the longitudinal direction of the belt, of approximately 25 millimetres. The stirrer strips each contain a reinforcing wire 52.

The belt differs from that of Figure 2 in two other aspects. One is that the rigidifying reifcrin layers 41,42 each comprise transversely extending weft elements in the form of metal wires at longitudinal positions 58 which lie in register with the stirrer strips. The wires extend over a 50 millimetre length of belt in the region of each stirrer strip 51; a typical wire construction is an arrangement of a group of three individual wires of 0.20 millimetre diameter surrounded by a group of six wires of 0.38 millimetre diameter, the wires of the two groups lying at opposite twist directions.

The other aspect of difference is that the portions of the belt between stirrer strips are perforated, typically with an array of 500 circular apertures 60 (see Figure 5) between successive stirrer strips.

Claims

CLAIMS:

1. Sheet material comprising at least two superimposed reinforcement layers of woven textile material, an intervening layer of polymeric material which is adhered to each of the reinforcement layers of woven textile material and maintains said layers in a spaced apart superimposed relationship, at least one of said reinforcement layers being a rigidifying reinforcement layer comprising over at least a part of its length at least one ply of woven material comprising a plurality of weft elements all of which are arranged in a substantially co-planar manner and a plurality of warp elements arranged in a woven relationship with the weft elements and having a higher percentage of crimp than the weft elements, each weft element being substantially bereft of twist and comprising at least one synthetic monofilament having a diameter in the range 0.1 to 1.00 millimetres and the monofilaments being provided at a sett in the range 60 to 180 filaments per centimetre in each said ply.

2. Sheet material according to claim 1 wherein said weft elements comprise groups of said synthetic monofilaments.

3. Sheet material according to claim 2 wherein each group comprises between 5 and 25 monofilaments.

4. Sheet material according to any one of the preceding claims wherein the or each said weft element has no more than a nominal degree of twist.

5. Sheet material according to any one of the preceding claims wherein the monofilaments of said weft elements are provided at a sett in the range 80 to 160 per centimetre.

6. Sheet material according to claim 1 wherein the monofilaments of said weft have a diameter in the range 0.1 to 1.0 millimetres.

7. Sheet material according to claim 2 or claim 3 wherein the monofilaments of said weft have a diameter in the range 0.1 to 0.5 millimetres.

8. Sheet material according to any one of the preceding claims wherein the monofilaments of said weft have a modulus of elasticity of at least 10,000 MPa.

9. Sheet material according to claim 8 wherein the monofilaments of said weft have a modulus of elasticity of at least 12,000 MPa.

10. Sheet material according to any one of the preceding claims wherein the monofilaments of said weft are monofilaments of polyethylene terephthalate.

11. Sheet material according to any one of the preceding claims wherein the total weight of said warp elements in each ply is less than 5% of the weight of said weft elements in that ply.

12. Sheet material according to claim 11 wherein the total weight of warp elements in each ply is less than 1% of the weight of the weft elements in that ply.

13. Sheet material according to any one of the preceding claims wherein said rigidifying reinforcement layer comprises at least two plies of said woven material.

14. Sheet material according to any one of the preceding claims wherein said rigidifying layer comprises weft elements of synthetic monofilamentary material over the whole of its length.

15. Sheet material according to any one of claims 1 to 13 wherein weft elements of metallic material are provided at intervals along the length of the sheet.

16. Sheet material according to claim 15 wherein groups of weft elements of metallic material and of synthetic monofilamentary material are interconnected by common warp elements.

17. Sheet material according to claim 15 or claim 16 wherein the weft elements of metallic material are provided over between one tenth and one quarter of the length of the sheet.

18. Sheet material constructed and arranged substantially as hereinbefore described with reference to Figures 1 and 2 of the accompanying drawings.

19. A conveyor belt comprising a rigidifying reinforcement structure comprised by sheet material according to any one of the preceding claims arranged with the weft elements extending transversely relative to the direction of the length of the belt.

20. A conveyor belt according to claim 19 when dependent on any one of claims 15 to 17 wherein a surface of the belt is provided with stirrer strips at the positions which lie in register with weft elements of metallic material.

21. A conveyor belt according to claim 20 wherein the belt is perforated between said stirrer strips.

22. A conveyor belt constructed and arranged substantially as hereinbefore described with reference to the accompanying drawings.