Warp lock wire carrier

Abstract

 A wire carrier (10) has an uncoated wire weft formed into a zig-zag configuration including a plurality of generally parallel limbs (11,13,15,17) interconnected at alternate ends by connecting regions (19,21,23). The wire weft is reinforced by a plurality of warps (25,27,29), each warp (25,27,29) having a first thread having a first melting temperature, and a second thread having a second higher melting temperature, so that when the wire carrier is heated to a temperature sufficient to melt the first thread and below a temperature that melts the second thread, the second thread is bonded to the weft by the first thread.

Description

[0001] This invention relates to a knitted wire carrier with the warp threads locked to the wire weft.

[0002] Knitted wire carriers are well known, and one such carrier is disclosed in U.S. Patent No. 3,467,423. Basically, such carriers comprise a continuous wire formed into a sinuous formation or zig-zag, with substantially parallel limbs interconnected by arcuate regions at each side edge of the zig-zag (thus providing loops) which limbs provide a plurality of wefts, into which is knitted a plurality, usually at least six, of warp threads. These threads can be of small gauge wire, or a synthetic resinous filament or a natural fiber, such as cotton.

[0003] Such wire carrier is widely used mainly as a frame for extruded polymer products, such as vehicle door and other seals and the like. Accordingly, during the manufacture of the seals, the carrier has to be passed through an extruder, which requires at least one handling operation beforehand. This means that there is a real tendency for the warp threads to shift laterally on the wire wefts.

[0004] Normally, wire carriers are made by knitting the wire wefts together with the warp threads under uniform warp tension. However, as soon as the warp threads shift laterally, this results in a change in warp tension at the point where the thread shifts and consequently creates in the carrier a non-uniform stress distribution of the warp. This can result in breakage of the warps or non-uniform performance of the seal in which the carrier is incorporated.

[0005] One attempt to solve the problem of lateral warp shifting formed the adjacent wefts, i.e. each loop, into a propeller or banana shape, but this is difficult to control, and has been found to have little controlling effect on lateral warp shifting.

[0006] In a further attempt to overcome the above problem, the knitted carrier is run through a latex bath and then heated to cure the latex, but this process is costly both in latex and in energy consumption, and often results in webs of latex forming windows in the square defined by a pair of adjacent wefts and a pair of adjacent warp threads, which then cause problems in the subsequent extrusion process.

[0007] In a still further attempt to solve the problem, Beck and Holmes, in published EPO Application Serial No. 0,175,818 have suggested to provide a knitted wire carrier comprising a wire folded into a zig-zag configuration so as to have a plurality of substantially parallel limbs forming wefts interconnected at alternate ends by arcuate regions which define side edges of the zig-zag, and a plurality of warp threads knitted into the wefts so that there is a knitted knot at each junction between a warp thread and a weft, and wherein the location of each junction is fixed by means of an elastomer weld or fusion of the wefts to the warp threads, to provide a locking grid within the carrier.

[0008] To achieve the welds or fusions, the weft is partly formed of a polymeric material or coated with a polymeric material which is compatible with the warps, which themselves may be formed partly or entirely of a polymeric material, or preferably coated with a polymeric material. Alternatively, the wefts may comprise two threads in side-by-side relationship, one of which is wire and the other is formed at least with a coating of, or impregnated with, a polymeric material, but which is preferably formed entirely of such a material. It was also suggested that the warps could be formed of two such materials, and that the polymeric material be thermosetting, and preferably thermoplastic.

[0009] In one preferred construction, it was suggested that the wefts comprise wire and, alongside the wire, a vinyl coated polyester yarn thread, and that the warp threads be formed of another vinyl coated polyester thread. For example, the weft may be of 300 denier and the warp threads of 1000 denier.

[0010] To form the welds or fusions, the knitted carrier was subjected to a heating step immediately after the knitting operation. Ideally, a hot air stream was used, but a heated roller or bar or even induction heating of the wire were suggested.

[0011] It is already known to incorporate heat fusible materials in woven products, for example to assist in the adhesion of another polymeric material to the woven material (see U.S. Patent Specifications No. 4,288,482/3 and 2,070,335).

[0012] Furthermore, it is also known to prevent fraying of cut selvages of woven fabric by incorporating thermoplastic strands in the fabric adjacent the cuts, and causing the strands to melt prior to cutting (see U.S. Patent No. 3,515,623).

[0013] Also, it has been proposed in U.S. Patent No. 3,829,048 to form a wire fabric of sets of longitudinal strands and cross strands, and to prevent slippage by arranging for one of the sets of strands to be gripped frictionally by the strands of the other set, either by off-setting the strands of one set, or piercing them with the other set, at the strand junctions.

[0014] In U.S. Patent No. 3,904,847, there is disclosed a grid-like heating structure for embedding in concrete pavements and the like to melt snow and ice, which is formed of a thermoplastic-coated heating wire formed into a zig-zag formation, the spaced sections of which are interconnected by a plurality of parallel spaced strands of thermoplastic material which are laid over the zig-zag formation, and fused to it. Such a structue is formed by laying out the zig-zag formation on a board, with the aid of pegs, and is of large dimensions commensurate with its use. A knitting setp is not disclosed.

[0015] U.S. Patent No. 4,343,845 shows a wire carrier with selectively located warp threads formed from degradable material, such as thermally degradable material. When the trim strip is heated or subjected to other degrading conditions, the degradable warp threads are weakened to the point that they break when the trim strip is flexed, thus increasing the flexibility of the trim strip in certain areas, while maintaining its longitudinal stability.

[0016] French Patent specification No. 2378117 relates to stitched and/or knitted fabrics of glass fiber, wherein special stitching threads are used, which can be fused together under thermal treatment, to prevent disintegration of the fabric when it is cut up.

[0017] None of the above described prior art constructions provides an entirely satisfactory structure for a wire carrier having warp threads attached to a wire weft. The structure suggested by Beck and Holmes comes closest, but suffers from several important disadvantages. It is difficult and/or expensive to provide either the coated wire weft or the combination of an uncoated wire weft with a second weft thread fed to the knitting machine with the wire. Furthermore, the use of vinyl coated polyester warp threads also increases the cost of the wire carrier. These disadvantages, though they were not insurmountable technically, increased the cost of the carrier enough, so that it could not be used in commercial product.

[0018] Accordingly, it an object of this invention to provide a wire carrier having warp threads attached to an uncoated wire weft, to prevent shifting of the warps with respect to the wefts.

[0019] It is another object of this invention to provide such a wire carrier that can be constructed from inexpensive readily available materials.

[0020] It is still another object of this invention to provide such a wire carrier that may be constructed using existing manufacturing equipment, without the need for substantial modification.

[0021] Briefly stated, in accordance with the presently preferred embodiment of this invention, a wire carrier is provided having an uncoated wire weft formed into a zig-zag configuration including a plurality of generally parallel limbs interconnected at alternate ends by connecting regions, the wire weft being reinforced by a plurality of warps, each warp comprising a first thread having a first melting temperature, and a second thread having a second higher melting temperature, so that when the wire carrier is heated to a temperature sufficient to melt the first thread and below a temperature that melts the second thread, the second thread is bonded to the weft by the first thread.

[0022] While the novel aspects of the invention are described with particularity in the appended claims, the invention itself, together with further advantages thereof, may be more readily understood by reference to the following description of the presently preferred embodiment of the invention, taken in conjunction with the accompanying drawing, in which:

Figure 1 shows a wire carrier in accordance with this invention.

[0023] Referring now to Figure 1, a knitted wire carrier in accordance with a presently preferred embodiment of this invention is shown in a schematic plan view of the carrier. The carrier designated generally at 10 includes a length of wire 11 formed into a zig-zag serpentine configuration to form the weft of the knitted carrier. Preferably the wire 11 is an uncoated length of about .030 inch diameter steel wire. As formed into the weft of the wire carrier, wire 11 has a plurality of generally parallel limbs 13, 15 and 17, interconnected at alternate ends by arcuate portions 19, 21 and 23 respectively, which define the side edges of the weft. A multiplicity of warps 25, 27, and 29, for example, is knitted or preferably lock stitched onto the weft to reinforce the weft and prevent distortion during extrusion.

[0024] The wire carrier as thus far described can be manufactured in a manner known to those skilled in the art utilizing known wire carrier knitting equipment.

[0025] In order to attach the warps to the generally parallel limbs of the weft at the points where the warps and weft intersect, the warps 25, 27, and 29 in accordance with this invention, each comprise two threads, a first thermoplastic, preferably polyester thread, and a second thermoplastic preferably polypropylene thread. The melting temperature of the polypropylene thread is lower than the melting temperature of the polyester thread.

[0026] Preferably, polypropylene threads having a denier of approximately 300 and a melting temperature in the range of 350-400° F, and polyester threads having a denier of approximately 1,000 and a melting temperature in the range of 510-515°F are used to manufacture the wire carrier in accordance with this invention.

[0027] Knitting is preferably carried out on a conventional knitter with the warp threads pretensioned to 20-30 pounds, preferably 26 pounds.

[0028] In accordance with this invention, the first and second warp threads need not be twisted together prior to knitting. Twisting the threads will not adversely affect the invention, but may unnecessarily increase the cost. For example, in accordance with the presently preferred embodiment of the invention, the first and second warp threads are fed to the knitter from first and second cones. As the threads are drawn from the cones into the knitter, each thread tends to ply by turning and twisting during the knitting operation. As the knitting progresses, the two threads become intermeshed to some extent, without the need for a separate operation twisting the threads together. Thus, in accordance with the invention, the formation of a wire carrier as described is especially easy to accomplish, requiring no more than feeding the first and second warp threads to the knitter directly from their supply cones.

[0029] After the wire carrier has been knitted, but before it is handled in any operation that tends to displace the warps, the carrier is heated. This may be carried out in line with the knitting operation, or in a separate batch operation. Preferably the carrier is heated by exposing it to a flow of heated air in the range of 480° to 495°F, for 17-25 seconds, preferably 22 seconds, to at least partially melt the polypropylene to attach the polyester warps to the uncoated wire.

[0030] While a stream of hot air is the preferred method of heating the wire carrier of this invention, the carrier may also be heated by other known methods, such a heated roller or bar, by induction heating of the wire, or by subjecting it to infrared heating at 25-30 watts/inch² for about 7 seconds.

[0031] Wire carriers in accordance with this invention exhibit significantly reduced warp shift, without the need for thermoplastic weft yarns as have been heretofore required.

[0032] While the presently preferred embodiment of this invention utilizes 1,000 denier polyester and 300-400 denier polypropylene to form the warps, other suitable materials could also be used, such as thermoplastic materials of the types known to those skilled in the art, in combination with polyester or other suitable reinforcing threads.

[0033] While knitting is the presently preferred method of manufacturing a carrier in accordance with this invention, those skilled in the art will appreciate that other methods such as stitching may also be used.

[0034] Where reference in this specification has been made to generally parallel wefts, it should be understood that this is intended to include wefts which diverge or converge to some extent, or are slightly curved, e.g. are of a banana or propeller shape, as known in the art.

[0035] Accordingly, while the invention has been described in accordance with a presently preferred embodiment thereof, those skilled in the art will recognize that these and other modifications and changes may be made without departing from the true scope of the invention which is defined in the appended claims.

Claims

1. A wire carrier comprising a weft consisting of an uncoated wire formed into a zig-zag configuration having a plurality of generally parallel limbs interconnected at alternate ends by connecting regions, and a plurality of warps, each warp comprising a first thread having a first melting temperature and a second thread having a second, higher, melting temperature, whereby when the wire carrier is heated to a temperature above said first melting temperature and below said second melting temperature, said second thread is attached to said weft by said first thread.

2. A wire carrier according to claim 1 wherein said first thread comprises a thread of polymeric material.

3. A wire carrier according to claim 2 wherein said polymeric material is thermoplastic.

4. A wire carrier according to claim 1, 2 or 3 wherein said first thread comprises polypropylene.

5. A wire carrier according to claim 1, 2, 3 or 4 wherein said second thread comprises polyester.

6. A wire carrier according to any one of claims 1-5 wherein said first and second threads are disposed in adjacent side-by-side relationship.

7. A wire carrier according to any one of claims 1-6 wherein said warps are lock stitched on said weft.

8. A wire carrier according to any one of claims 1-6 wherein said warps are knitted on said weft.

9. A wire carrier according to any one of claims 1-6 wherein said warps are stitched on said weft.

10. A method of manufacturing a wire carrier comprising the steps of forming an uncoated wire into a serpentine weft, feeding first and second threads directly from first and second supply cones to a knitter, said first and second threads being characterized by first and second different melting points respectively, simultaneously knitting first and second warp threads onto said weft to form a wire carrier, and heating said wire carrier to a temperature sufficient to attach said second thread to said wire carrier.

11. The method of claim 10 wherein said heating step comprises heating said carrier with infrared radiation.

12. The method of claim 11 wherein said heating step comprises heating said carrier with infrared radiation at between 25-30 watts inch² for about seven seconds.

13. The method of claim 10 wherein said heating step comprises heating said carrier in an oven.

14. The method of claim 13 wherein said heating step comprises heating said carrier in an oven at between about 480°F and 495°F for between about 17 and 25 seconds.

15. The method of claim 10 wherein said heating step comprises passing said carrier over a heated roller.

Drawing