GB2056364A - Method of joining pieces of sheet material - Google Patents

Abstract

Pieces of rubber or other polymeric or polymer coated flexible sheet material 30, 32 for forming connected tube sections, e.g. of an inflatable structure, have to be joined along curved edges 34, 36. For this a tube 14 of material is sleeved, as a flattened tube, onto a laminar former 18 and the margins 40, 42 of the sheets to be joined are bonded to opposite faces of the flattened tube 14, after which the former 18 is removed and the tube 14 is cut along its edge further from the join line, and opened out. Preferably the tube 14 is formed by temporarily joining opposite edges of a tape 12, notably by stitching 16 which is later cut out or ripped out to open out the tube 14. The channel 50, Fig. 6, may be filled with a hot melt composition or a rubber strip. If thermoplastics are to be joined, radio frequency welding may be used with the metal former 18 acting as an electrode. <IMAGE>

Description

SPECIFICATION Method of joining pieces of sheet material The invention concerns the joining of the edges of pieces of flexible sheet material. It relates both to the method of joining and to produces made thereby.

The material may consist of a reinforcing or support material, notably a woven or knitted textile fabric, coated on one or both sides with rubber or other polymer, or may simply be a polymer in flexible sheet form.

There are a number of applications notably in the manufacture of flexible inflatable structures in which pieces of such sheet material are used to form adjoining curved surfaces, the join between two pieces of material forming the join between different curved surfaces. These curved surfaces may be the surfaces of adjoining tubular or parttubular sections. When the pieces of sheet material are seen in flat form the edges to be joined are curved, and as the join is formed the pieces can no longer lie flat. It can be difficult to form such a join without wrinkles developing, and a wrinkle in one of two adhered surfaces can provide a path for leakage, so that the joint is not airtight or watertight.

At present, to avoid the formation of wrinkles when a join is being made using adhesives, wrinkles are eliminated as they are formed, by repeated use of a hand roller; when a join is being made by heat welding (which is employed with thermoplastics-coated material) the weld must proceed in short steps with tension progressively applied.

According to the present invention there is provided a method of joining two pieces of flexible sheet polymeric or polymer-coated material comprising drawing a tube of such material onto a laminar former which is of width sufficient to hold the tube in flattened condition, and which has an edge of corresponding shape to the edges to be joined, sandwiching said former with the tube thereon between the margins of the pieces to be joined, bonding the material margins to the flattened tube and thereafter removing the former and slitting the tube along its length opposite the edges of the pieces to allow the join to be opened out. It is desirable that the material of the tube should have some ability to stretch, although this is not essential for the pieces of sheet material which are joined.

The tube may be formed in an initial step by folding a length of tape about its longitudinal centre line and joining the edges in a manner permitting their separation later. This may for instance be done by sewing and the stitching later cut. It may be done by sewing using a stitch which can readily be ripped out by pulling one thread. It may be done by means of a heat sensitive adhesive, so that the edges can be released from each other by heating.

The invention is particularly applicable when the edges to be joined are exact mirror images.

Then when the former with the tube on it is sandwiched between the margins of the pieces the edge of the flattened tube can be aligned with the pieces' edges being joined.

The invention will now be explained further with reference to the accompanying drawings. In these drawings: Fig. 1 is a perspective view of part of an inflatable life raft, and Fig. 2 shows a typical pair of curved surfaces to be joined, and Fig. 2a being a cross-section of a conventional overlapping join, and Fig. 2b being a cross-section of a conventional butt join.

The remaining Figures illustrate a method embodying the invention: Figs 3 and 4 are respectively a perspective view and a cross-section of pieces about to be joined, diagrammatically illustrating the formation of a sandwich structure, and Fig. 5 is a cross-section of the sandwich when the join is made, and Fig. 6 is a cross-section of the completed join as it is being opened out, and Fig. 7 is a cut-away perspective view when the joined pieces have been formed into tubular sections, showing part of the join formed by the method illustrated by the preceding Figures, at the region where it meets the overlaps which run along the tubular sections.

The problem with which the invention is concerned is exemplified in the making of inflatable life rafts such as shown, in part, in Fig. 1.

Such rafts have a polygonal rim consisting of a number (usually six or eight) of tubular sections. A life raft is by no means the only product in which the invention can be used, however.

These sections are each formed from a flat piece of polymer-coated textile fabric (generally a square woven fabric coated on both sides with rubber).

Two opposite sides of each piece are joined along the length of the piece to form the piece into a length of tube. Each piece is joined to the next at an edge which is curved to form a join 10 of the life raft rim. Customarily the pieces are joined together before they are formed into tube and each piece of the completely closed loop of joined sections is finally folded over and joined so that a polygon of tubular sections is formed.

The join 10 must of course be air- and watertight. The pieces' curved edges which are to be joined are mirror-images, as seen in Fig. 2 which shows part of two pieces 30, 32 whose curved edges 34, 36 are to be joined. Conventionally, the pieces may be joined by overlapping or butt joins, as shown in Figs. 2a, 2b, and in either case there is a tendency for wrinkling to occur in the margins of the sections. These wrinkles may form air passages through the join and must therefore be eliminated, typically by repeated application of a hand roller, requiring increased time and effort to produce an airtight and watertight join.

In Figs. 3 to 7 there is illustrated an embodiment of the method of the invention.

The pieces 30,32 to be joined are shaped as shown in Fig. 2. A tape 12 consisting of a strip of rubber-coated woven textile material is folded lengthways and made into a tube 14 by stitching 16 along the edges opposite the fold. This tube is drawn onto a laminar former 1 8 which is a strip of sheet material whose edge 19 corresponds in shape to the curved edges which are to be joined (see Fig. 3), such that the fold 20 in the tape lies along the edge 19 of the metal former and the stitching 16 lies along the opposite edge.

The former 18 must be of width sufficient to maintain the tube 14 flattened, and therefore free of large wrinkles, although small wrinkles may be tolerated since these can be removed fairly readily after the sandwich has been formed. On the other hand the former should not be so wide that the tube cannot easily be drawn onto the former. The former is suitably of metal but may be of some other material for example the low friction material polytetrafluoroethylene to reduce the friction between the former and the inside of the tube when the tube is drawn onto the former. This friction may also be reduced by lubricating the inside of the tube for example with powdered chalk.

The flat surfaces of the tube 14, on both sides of the former 18, between the stitching 16 and the fold 20, are coated with a cross linking adhesive 29 such as Bostik 2402 (The word "Bostik" is a registered Trade Mark). Adhesive is also applied to the margins 40, 42 of one surface of each of the pieces 30, 32 which are to be joined.

The join is assembled by applying the margin 40, 42 of each of the pieces 30, 32 to one side of the flattened tube 14 on the former 18, as shown by Figs. 3 and 4, so that a sandwich is formed as shown in Fig. 5, with the folded edge 20 of the tube 14 coincident with the edges 34, 36 of the pieces being joined.

The margins of the pieces 30, 32 may be pressed against the tube 14 by application of a hand roller, and the sandwich may be consolidated by clamping in a press, if desired. At this stage any small wrinkles can be eliminated fairly easily by the application of pressure.

The join is completed by removing the former and slitting through the stitching 1 6 by means of a hook-bladed knife inserted into the tube 14. The join can then be opened out as shown in Fig. 6. In some cases the tube 14 may be split open before the former is removed. The edges 34, 36 may touch each other in the finished join or there may be a narrow channel 50 between them.

After the joins between pieces such as the pieces 30, 32 have been made each piece is formed into a tubular section by the conventional method of lapping one of its straight side edges over the other; adhesive being applied to the contacting surfaces. Fig. 7 shows part of the join between two pieces 30, 32 and also shows the meeting of this join with the overlaps by which each piece is formed into a tubular section. The side edges of the tape 12 are indicated by reference numeral 55.

When the pieces 30, 32 are formed into tube sections their edge portions which adjoin their straight side edges 52 overlap their opposite edge portions which adjoin their straight side edges 54.

This is shown in Fig. 7 and it can be seen that the end 56 of the tape 12 overlaps the corner regions 57 of the pieces 30, 32 and hence also overlaps the end 58 of the tape 12.

Inthe embodiment shown, when the join between the pieces 30 and 32 is made, the tube 14 of tape 12 does not extend fully to the edge 52 of the pieces 30, 32 but stops short, leaving a small corner area 60. When the pieces are formed into tubular sections the area 60 of each piece 30, 32 lies over the corner region 57 of the same piece and is adhered onto it. This blocks any path for leakage through the overlap which might otherwise be formed at 66 along the side edges 55 of the tape 12. A blob of sealant is inserted into the channel 50 at the position indicated by numeral 64, adjacent the end 58 of the tape, to prevent leakage through the overlap along the channel 50.

After the pieces 30, 32 have been formed into tubular sections, the appearance of the join between the pieces 30, 32 may be improved by filling the channel 50 with a hot melt composition or covering it over with a strip of plain rubber.

The material of the tape 12 may not be the same as that of the pieces 30, 32. It may be coated with rubber or other polymer on both sides or only on the side which becomes the outer side of the tube 14. if the tape is cut from a sheet material formed by coating an ordinarly squarewoven fabric it has been found desirable for it to be cut on the bias to give enhanced flexibility and extensibility. A coated knitted fabric is advantageous because of the flexibility and extensibility conferred by the knitted fabric. Such material need not be cut on the bias and the tape could be cut from a sheet either with or across the grain of the fabric (which is more economical).It is envisaged that if the tape was of a coated squarewoven fabric, but the fabric was one formed of elastic thread such as LYCRA (registered Trade Mark), cutting on the bias could again be dispensed with.

In the foregoing the invention is described as employed for making the corner of a hexagonal tubular structure. It can of course be employed for corners with different angles, and notably the right angled corners of a square tubular structure.

Material which is itself tubular may be used rather than making a tube from tape, in which case it is the material of the tube itself which must be slit after the sandwich has been formed in order to open out the join.

As described above, the sandwich of material piece, tape-covered former and material piece may be joined by a crosslinked adhesive. In cases where thermoplastics are to be joined, radio frequency welding can be employed, in which case a metal former can be employed as an electrode for the welding.

Claims (11)

1. A method of joining two pieces of flexible sheet polymeric or polymer-coated material comprising drawing a tube of such material onto a laminar former which is of width sufficient to hold the tube in flattened condition, and which has an edge of corresponding shape to the edges to be joined, sandwiching said former with the tube thereon between the margins of the pieces to be joined, bonding the material margins to the flattened tube and thereafter removing the former and slitting the tube along its length opposite the edges of the pieces to allow the join to be opened out.

2. A method according to claim 1 including an initial step of folding a length of tape about its longitudinal centre line and joining the edges to form the said tube, the joining being performed in a manner which permits separation of the edges later.

3. A method according to claim 2 wherein the edges of the tape are joined by sewing.

4. A method according to claim 2 wherein the edges of the tape are joined by an adhesive which makes only a temporary bond between them.

5. A method accordng to any one of the preceding claims wherein the material of the tape and/or tube is a woven fabric coated with rubber or other polymer on at least one side.

6. A method according to claim 5 as appendant to claim 2 wherein the fabric is square woven and the tape is cut on the bias.

7. A method according to claim 5 wherein the fabric is square woven using elastic thread, and the longitudinal direction of the tape or tube is along or perpendicular to the grain of the fabric.

8. A method according to any one of claims 1 to 4 wherein the material of the tape and/or tube is a knitted fabric coated with rubber or polymer on at least one side.

9. A method according to any one of the preceding claims wherein the material of the tube or tape is more extensible than the pieces of sheet material which are joined.

10. A method of joining two pieces of flexible sheet polymeric or polymer-coated material substantially as herein described with reference to Figs. 3 to 7 of the drawings.

11. A flexible inflatable structure incorporating connected tube sections formed from respective pieces of flexible sheet material joined by the method of any one of the preceding claims.