PRODUCTION OF WARP/WEFT SHEET

Abstract: A warp sheet (5) comprising individual warp yarns is fed forward. A plurality of weft yarns (9) are laid over the warp sheet. These weft yarns (9) are trapped between filamentary elements (12) and the outer warps of the warp sheet (5). By directing the elements (12) and outer warps outwardly with respect to the remainder of the sheet (5) the weft yarns are tensioned prior to the yarns being introduced into a layer of adhesive. The adhesive is cured to form the material layer.

Description: PRODUCTION OF WARP/WEFT SHEET This invention relates to the production of warp/weft sheets which can be used in the production of reinforced sheet material. According to one aspect of the present invention,there is provided a method of producing a warp/weft sheet comprising the steps of forming a warp sheet and laying weft yarns to extend transversely across the warp sheet, characterised by trapping the weft yarns at each edge of the warp sheet between filamentary elements extending in the same direction as the warp sheet and moving the said filamentary elements at opposite edges of the warp sheet apart to tension the trapped weft yarns. According to another aspect of the present invention, there is provided a machine for producing a warp/weft sheet comprising means for supplying a warp sheet comprising a plurality of warp yarns extending in substantially the same direction, characterised by means for supplying filamentary elements extending in the same general direction as the warp sheet on opposite sides respectively thereof, means for laying weft yarns to extend transversely across the warp sheet and means for controlling the filamentary elements relative to the warp sheet to trap the weft yarns at opposite ends thereof and to tension them. The invention includes a machine comprising means for carrying out the steps set out above and warp/weft sheets made by the above method, or such machines, and further includes reinforced sheet material in which the• reinforcement comprises such a warp/weft sheet. The invention will be further described with reference to the accompanying drawings in which:- Figure 1 is a diagrammatic side view of a machine for producing a warp/weft sheet according to the invention, Figure 2 is a diagrammatic section on the line II—II of Figure 1, and Figure 3 is a diagrammatic side view of an alternative form of machine to that shown in Figures 1, and Figure 4 is a modification of a part of the machines of Figures 1 and 3. The machine shown in the drawings comprises a part of a larger machine for producing reinforced plastics sheet material. Referring to Figure 1, a warp sheet 5, that is a set of parallel warp yarns 6 (Figure 2), is led from a supply (not shown) over a roller 7 and beside and below a set of six air jets 8 each adapted to fire a weft yarn 9 (Figure 2) to lay it to extend transversely across the warp sheet 5. The air jets 8 will normally be operated together so that, in this case, six weft yarns will be laid across the warp sheet 5 at once and after the warp sheet has moved on far enough, six more weft yarns will be laid and so on so that evenly spaced weft yarns are laid across the warp sheet. Two edge yarns 12 from the warp sheet 5, one at each edge of the warp sheet, are separated from the warp sheet by being lead over the roller 13 to the roller 14 and thus pass above the track of the weft yarns 9 across the warp sheet 5. The edge warp yarns 12 are recombined with the warp yarns 6 at a roller 15 from which the warp/weft sheet 18 comprising the warp sheet 5 together with the weft yarns 9 is guided onto a support 16 continuously moving in the direction of the arrow 17 in Figure 1. Upon the support 16, which may be an endless belt or a length of release paper, is carried a layer 19 of synthetic plastics material, for example polyvinyl chloride, in a paste-like condition in which it is sufficiently viscous to form a coherent layer, but sufficiently fluid to allow entry into it of the warp/weft sheet 18 and to completely surround the warp/weft sheet, advantageously, but not necessarily, so that it completely envelopes each warp yarn 6 or 12 and each weft yarn 9 so that in the reinforced plastics sheet material eventually produced each reinforcing yarn is preferably separated from its neighbours by plastics material. Each edge warp yarn 12 and its immediate neighbouring yarn 6 in the warp sheet is guided, as it leaves the roller 15, by an associated shallow guide channel 22, which may be made of ceramic material. The two channels 22 have an outwardly curved shape so that they diverge from one another in the direction of longitudinal movement of the warp/weft sheet 18 past the channels. Guiding the edge warp yarn 12 and the adjacent warp yarn 6 at each edge of the warp/weft sheet 18 in the associated channel 22 brings these warp yarns to the configuration shown in Figure 2 in which a yarn 12 is in each case below the adjacent yarn 6 and the ends of the weft yarns 9 are trapped at each edge of the warp/weft sheet 18 between the yarn 12 and the adjacent yarn 6. The path of the warp yarns 12 and 6 from the roller 15 onto the support 16 is such that these warp yarns are under tension and each warp yarn 12 is positioned close against the adjacent warp yarn 6 so as effectively to trap the weft yarns 9. This is achieved, partly due to the configuration of the support 16 in the machine. As seen in Figure 1, the support 16 (carrying the plastics layer 19) rises in the direction of movement 17 to a roller 23, passes v n th n fo o xi a horizontal course. The warp/weft sheet 18 enters the layer 19 in the proximity of the roller 23 and moves forward with the layer 19 on the support 16. The weft yarns 9 are thus trapped at each edge of the warp sheet 5 between filamentary elements constituted by the edge warp yarn 12 and the adjacent warp yarn 6 and the guide channels 22 cause these filamentary elements at opposite edges of the warp sheet to move apart thus tensioning the weft yarns 9. Thus, as the warp/weft sheet 18 thus formed approaches the layer 19, the weft yarns 9, at this stage located beneath the warp yarns 6, are maintained approximately horizontal and clear of the layer 19 along the whole of their length until they enter the layer, pressed in by the warp yarns 6. Each weft yarn 9 thus enters the layer 19 at the same moment along the whole of its length and there is only a small risk of the central part of the weft yarn drooping below the ends of the weft yarn and entering the layer 19 first. This could lead to distortion of the weft yarns from a straight line configuration which would be undesirable. The tension required in the weft yarns is only a few grams, for example 2-10 gm, and this can be achieved by guiding the edge warp yarns in grooves in the channel members 22 which are semi-circular in cross-section and a few millimetres, for example 2-3mm deep. The splay of the channel members 22 is such that the edge warp yarns are moved apart by a few millimetres, for example 2-6mm, in their passage along the channel members. The support 16 is carried over guide and driving rollers, not shown, to bring it to the machine shown in the present Figures and it passes from the machine to an oven (not shown) for curing the synthetic plastics material 19 so as to form a reinforceed sheet material in which the reinforcement is constituted by the warp/weft sheet 18. The source of supply for the warp yarns 6 and 12 may be a warp beam, and guide and driving rollers, not shown, may be used to bring the warp yarns from the supply to the machine shown in the Figures. The filamentary elements arranged to trap the end of the weft yarns 9 may be elements other than normal warp yarns 6. For example yarns with a rough outer surface and of greater diameter than the other warp yarns may be used. Or filamentary elements with a flat configuration and thus of tape-like form may be used. It may be sufficient that the edge warp yarns 12 have this different configuration or in some cases the adjacent warp yarns 6 may have the different configuration as well, so as to enable sufficient tension to be imparted to the weft yarns 9 without risk of their ends slipping from between the edge warp yarns. More than one warp yarn may be maintained above the air jets 8 at each end of the warp sheet so that more than one warp yarn is available to grip the weft yarns at the sides of the warp sheet. By guiding alternate warp yarns at each edge of the warp sheet above the air jets 8 and leaving the intermediate yarns in the warp sheet 5 and subsequently guiding all the edge yarns into close proximity an interlacing effect akin to a woven structure can be produced at each edge of the warp sheet to grip the ends of the weft yarns. Referring to Figure 3, in an alternative machine to that shown in Figure 1, the weft yarns are laid across the warp sheet 5 by means of a weft traversing mechanism 38. This mechanism receives, for example, six weft yarns 8 and drawn them back and forth across the warp sheet 5 by performing a reciprocating motion. As with the air jets, the speed of the traverse is geared to the speed of the warp sheet so that sets of six wefts 8 are progressively laid on the warp sheet 5. At the end of each traverse, the weft yarns are drawn around pins (not shown) to restrain them as the traversing unit changes direction. As the weft yarns enter the nip formed between yarn 12 and roller 15 the loops in the wefts at each end are cut to enable the wefts to be removed from the pins and permit their speed to be matched to that of the warp yarns. In other respects the machine is the same as that of Figure 1 and equivalent parts bear the same reference numerals. Instead of the channels 22, swivel mounted pulleys 40 may be mounted on opposite sides respectively of the warp sheet. The degree of divergence imparted to the filamentary elements 12 and associated warps 6 can be varied by adjusting the degree of swivel by means of the bolts 41. One such pulley is shown in Figure 4. The numbers of warp yarns and weft yarns shown in the drawings (which as mentioned are diagrammatic) is illustrative only and does not necessarily indicate the number of warp and weft yarns in an actual reinforced sheet material. It will be appreciated that the above embodiments have been described by way of example only and that many variations are possible without departing from the scope of the invention. For example, each channel 22 could extend further around roller 15 to provide greater guidance for the associated warp yarn 12. Also, different yarns may require different tension and different channel dimensions than those specified above. Furthermore, by using yarn coated with adhesive in either or both the warp or weft and pressing the warp and weft yarns together and not introducing the arrangement so formed into a layer of material a net rather than a sheet may be formed. If desired the adhesive may be activated by passing the coated yarn over a heated roller. alternatively, pressure sensitive adhesive may be used.

Claims: CLAIMS 1. A method of producing a warp/weft sheet comprising the steps of forming a warp sheet and laying weft yarns to extend transversely across the warp sheet, characterised by trapping the weft yarns at each edge of the warp sheet between filamentary elements extending in the same direction as the warp sheet and moving the said filamentary elements at opposite edges of the warp sheet apart to tension the trapped weft yarns. 2. A method as claimed in claim 1, in which the warp sheet with the tensioned weft yarns is introduced into a layer of settable material. 3. A method as claimed in claim 2, in which the material has a paste-like condition which is sufficiently viscous to form a coherent layer, but sufficiently fluid to allow entry into it of the warp sheet and trapped weft yarns. . A method as claimed in claim 3, in which the warp sheet and trapped weft yarns are introduced such that and the consistency of the layer of material is such that the material completely envelops each individual warp and weft yarn. 5. A method as claimed in claim 3, in which the layer of material is laid on an endless belt. 6. A method as claimed in claim 3, in which the layer of material is laid on release paper. 7. A method as claimed in any preceding claim, in which the weft yarns are laid by means of air jets. 8. A method as claimed in any of claims 1 to 6, in which the weft yarns are laid by means of a reciprocatable device which traverses the warp sheet. 9. A method as claimed in claim 1, in which adhesive is applied to the warp or weft yarns or to both to enable the warp and weft to be adhered together to form a net. 10 A machine for producing a warp/weft sheet comprising means for supplying a warp sheet comprising a plurality of warp yarns extending in substantially the same direction, characterised by means for supplying filamentary elements extending in the same general direction as the warp sheet on opposite sides respectively thereof, means for laying weft yarns to extend transversely across the warp sheet and means for controlling the filamentary elements relative to the warp sheet to trap the weft yarns at opposite ends thereof and to tension them. 11. A machine as claimed in claim 10,in which the means for controlling the filamentary elements comprises guide means by which the filamentary elements are initially guided at a distance spaced away from the warp yarns to enable the weft yarns to be laid between the filamentary elements and the warp yarns and then brought together with the warp yarns to trap the weft yarns therebetween. 12. A machine as claimed in claim 10 or 11 in which the means for controlling comprises guide members for directing the filamentary elements and adjacent outer yarns of the warp sheet outwardly in relation to the remainder of the warp sheet to tension the weft yarns trapped between those elements and the warp sheet. 13. A machine as claimed in claim 11, in which the guide means comprise rollers over which the filamentary elements run in operation of the machine. 14. A machine as claimed in claim 12, in which the guide members comprise guide channels of outwardly curved shape in the direction of forward movement of the warp sheet. 15. A machine as claimed in any of claims 10 to 14, in which a support is provided for a layer of settable material into which the yarns may be introduced during operation of the machine. 16. A machine as claimed in claim 15, in which the support comprises an endless belt. 17. A machine as claimed in claim 15, in which the support comprises a length of release paper. 18. A machine as claimed in claim 15, 16 or 17, in which the support and warp sheet follow convergent paths in the direction of movement of the warp sheet. Q 19. A machine as claimed in any of claims 10 to 18, in which the means for laying weft yarns comprises a plurality of air jets disposed to insert weft yarns between the filamentary elements and the warp sheet. 5 20. A machine as claimed in any of claims 10 to 18, in which the means for laying weft yarns comprises a reciprocatable device disposed to traverse the warp sheet. 21. Reinforced sheet material made by the method of any 0 of claims 1 to 9 or the machine of any of claims 10 to 20. 5

Inventors: BRITTON ARTHUR, BRITTON, ARTHUR
Applicants: COURTAULDS PLC
Application year: 1988
Main classification: D04H3
IPC codes: B29C70, D04H3