GB2191440A - Fibre reinforced plastics structure - Google Patents

Abstract

A hollow, fibre (14, 15, 16) reinforced plastics structure is made by making a resin impregnated, fibre reinforced flat structure (11) incorporating a flattened impervious tube member (12) and expanding the tube member and the resin impregnated structure whilst flexible under fluid pressure to the inside of the tube member. The method can be used for making pipe. <IMAGE>

Description

SPECIFICATION Fibre reinforced plastics structure This invention relates to the manufacturers of fibre reinforced plastics structures, and particularly to making hollow such structures.

Coventionally, the production of hollow, fibre reinforced structures involves one of two different approaches. In one technique, reinforcement fibre, such as glass or carbon fibre, is mixed with a liquid resin and the resultant mixture cast or moulded to whatever shape is required. In another technique, a reinforcement fabric or web is laid up in the required shape, and the resin is then applied by painting or dipping. The latter method uses the reinforcement fibres to better effect inasmuch as there is already strength in the fabric or web, which would remain even if the resin could be dissolved away, whereas the technique is, however, expensive and labour intensive, not lending itself readily, especially for more complicated shapes, to mechanisation.And difficulties are often encountered in ensuring an even and proper application of resin, especially with larger objects, where the resin might well change its properties during the application so that it will have different viscosities while being applied to different parts of the structure.

The present invention provides a method for making a hollow, fibre reinforced plastics structure which ensures that the best conditions for a uniform and thorough application of resin can be availed of, and which permits of mechanisation resulting in considerable reduction of labour costs and ecconomies of production. Novel, inherently strong structures can be produced, which can replace conventional structural materials such as concrete and steel with considerable improvement in performance, saving in weight and greatly reduced resistance to attack by rust and other corrosive agents and reduced maintenance requirements.

The invention comprises a method for making a hollow, fibre reinforced plastics structure, comprising making a resin impregnated, fibre reinforced flat structure incorporating a flattened impervious tube member and expanding the tube and the resin impregnated structure whilst flexible under fluid pressure to the inside of the tube member.

The fibre reinforced flat structure may comprise opposed laminar sections disposed either side of the flattened tube member and seamed together at the edges.

The fibre reinforcement may comprise warp and/or weft threads and cushioning fibres.

The cushioning fibres may comprise a fleece, such as a cross folded card web, stitchbonded fabric or needle felt. Cushioning fibre may be disposed between warp threads and weft threads.

At least one weft thread may be continuous and may be wound around the structure.

The fibre reinforced structure may also comprise woven or knitted fabric.

Elongate textile structures such as threads, ribbons or tapes may be wrapped around the structure in opposite directions in such manner as to result in helically extending such textile structures oppositely inclined in the expanded structure.

The fibre reinforcement may be impregnated by a vacuum-pressure technique. Such is facilitated by impregnating the structure in a flat condition as it may be carried out on the surface of a resin bath maintained in a state of low viscosity in an evacuable and pressurisable container through which the flat structure, produced on a continuous basis, may pass, dwelling while the chamber is evacuated and the resin level elevated to cover the structure followed by the application and then release of pressure, the impregnated structure then passing out of the chamber between squeeze rollers removing excess resin and defining the fibre/resin weight ratio, at the same time drawing the next section of structure in to the chamber for treatment.

For the production of pipe, the impregnated structure, after drying off, may be cut into pipe lengths before expanding. Expanding may be effected by warming the flat length so that it is flexible and inserting conical end seals and clamping the pipe ends thereto, introducing pressure air through one or both end seals. Expansion may be effected in a tube defining the outer diameter of the finished pipe. The resin is then cured as appropriate.

The method can also produce articles with cavities, however, by suitably pocketing the tube member, which may be supplied as individual pockets or connected pockets for continuous feeding from a roll. The impregnated structure will be cut into lengths appropriate to the pocket arrangement. pockets may be conveniently provided with a connecting piece for an air line by which they may be expanded, and as with pipes, the flat structure may be expanded into form means such as a mould determining the shape of the finished structure.

Embodiments of hollow, fibre reinforced plastics structures and methods for making the same according to the invention, will now be described with reference to the accompanying drawings, in which: Figure 1 is a diagrammatic elevation of one form of machinery for making the structures.

Figure 2 is a cross section of a flat structure produced during the production on the machinery of Figure 1.

Figure 3 is a part cut-away face view of the flat structure shown in Figure 2.

Figure 4 is a diagrammatic end elevation of a modification to the machinery illustrated in Figure 1.

Figure 5 is a plan view of the machinery illustrated in Figure 4.

Figure 6 is a side elevation of the machinery of Figures 4 and 5.

Figure 7 is a face view of a flat structure which may be produced by the machinery of Figures 4, 5 and 6.

Figure 8 is a face view of another flat structure which may be produced by the machinery of Figures 4, 5 and 6.

Figure 9 is a cross-section of the structure of Figure 7.

Figure 10 is a cross-section of the structure of Figure 8.

Figure 11 is an illustration showing how a flat structure is expanded into pipe.

Figure 12 is a cross-section of a pipe expanded from the structure of Figures 2 and 3.

Figure 13 is a cross-section of a pipe expanded from the structure of Figures 7 and 9.

Figure 14 is a cross-section of a pipe expanded from the structure of Figures 8 and 10.

Figure 15 is a part cut-away elevation of the pipe of Figure 13.

Figure 16 is a part cut-away part sectional elevation of the pipe of Figure 14.

Figure 17 is a face view of another flat structure adapted for the production of articles with cavities.

Figure 18 is a view of an expanded article produced from the structure of Figure 17.

Figure 19 is a perspective view of a shaped hollow square section. and Figure 20 is a perspective view of a piece of an airfoil section produced according to the invention.

The drawings illustrate the production of hollow, fibre reinforced plastics structures by making a resin impregnated, fibre reinforced flat structure 11 incorporating a flattened, impervious tube member 12 and expanding the tube member 12 and the resin impregnated structure 11 whilst flexible under fluid pressure to the inside of the tube member 12.

The structure 11 comprises opposed laminar sections 1 la, 1 1b disposed either side of the flattened tube member 12. The sections 1 la, 11 b are shown seamed together at the edges in Figures 2 and 3 by rows of chain stitches 13.

The fibre reinforcement of the laminar sections 1 1 a, 1 1 b comprises warp threads 14, weft threads 15 and cushioning fibres 16. The fibres 16 may be in the form of a fleece such as a cross-folded card web, which comprises aligned fibres and has enough coherence to withstand the handling operations during as sembiy of the structure, or a stitch bonded fabric, which may be a fleece stitch bonded fabric such as may be produced without stitching yarn on an Arabeva or Maliviless machine, or a needle felt. It serves to embed the warp and weft threads and form a matrix which can absorb the resin and be squeezed down to a required thickness to achieve a predetermined resin/fibre weight ratio.The cushioning fibres may serve also to protect brittle warp and/or weft thread, if such are used, against snapping at crossing points under pressures used to consolidate the structure.

The fibre reinforcement may be of any fibre type depending on the end use of the structures. Cushioning fibres may comprise natural or regenerated cellulose or other natural fibres or synthetic fibres of linear polymers such as polyamides, polyesters, arcylics, polyvinyl chloride and aramids such as Nomex (RTM) and Kevlar (RTM) or even ceramic fibres such as Saffil (RTM) or metal wire or glass fibres.

Warp and weft thread where such strength is required, such as Kevlar (RTM) and carbon fibres. Warp threads, which do not need to bend very much, can be quite thick, even up to the weight of ropes in heavy duty structures on a large scale, or as fine as, say, 100 denier weaving yarns for smaller structures.

The manner of assembly is illustrated in Figure 1. A flattened tube member 12 of impervious material such for example as polyethylene or polyester film is run from a supply roll 12a thereof. Cushioning fibre layers 17a, 17b are fed either side of the member 12 extending beyond the edges thereof. Next, warp threads 14 are fed from beams 18 to become upper and lower thread warps 14a, 14b. Further cushioning fibre layers 17c, 17d are added from reels 19, all coming together in feed rollers 21.

Weft threads 15a, 15b are added next, applied by a traversing device 15c after the fashion of a weft-laying device of a Malimo machine. This is not strictly a weft, of course, since it does not weave with the warp thread after the manner of regular shuttle weaving, rather it is a laid-in or laid-on thread which extends across the warp threads. A further cushioning layer 17e, 17f is added on each side from reels 22, the whole passing between further feed rollers 23. The weft is held on pegs on moving bands (not shown) travelling with the structure up until a stitching head 24 where the rows 13 of stitches (which may be chain stitches or lock stitches are preferably-overlock stitches) are sewn in using conventional sewing equipment 24. The stitches are made in between the warp and weft threads, the sewing equipment being suitably aligned, and synchronised with the weft insertion device so as not to damage the warp and weft threads but to hold the weft threads in place so that the pegs can be withdrawn therefrom.

The thus assembled structure is then fed a length at a time into a vacuum-pressure impregnation chamber 25 having a hood 26 connectible to evacuating and then pressurising means (not shown) which is raisable and lowerable into sealing engagement with a bath 27 containing liquid resin 28 which is elevatable through a hot screen 29 to cover the fibre reinforcement structure. First, the lid is sealed down over the structure, then the chamber is evacuated. Resin 28 is elevated to cover and penetrate the fibrous structure, then the chamber is pressurised to force the resin into the voids of the structure.Pressure is released and the resin level lowered, the treated fibrous structure being then fed out through squeeze rollers 29 preset to a given spacing which determines the thickness of the structure (which is of course compressible on account of the cushioning fibres) leaving the impregnation unit and hence determines the resin/fibre weight ratio. According to the use to which the finished product will be put, the ratio can be typically 60% by weight resin to 40% by weight fibre to 40% resin to 60% fibre.

The squeezed, impregnated assembly is then dried so as to render it handleable but not so as to cure the resin in an oven 31 from which it is removed by feed rollers 32 and cut up as by a guillotine device 33 into lengths as required.

Vacuum and pressure cycles for the impregnation stage will be similar as regards pressures and times to these which apply to such impregnation methods for the insulation of windings for rotating electric machinery.

After cutting up into lengths the dried, impregnated structure may be further consolidated and compressed in a press similar to one used for laminating pre-preg to make conventional board materials such as electrical board for making printed circuits, say.

The variation shown in Figures 4, 5 and 6 involves a feed system 41 for laying threads, tapes, ribbons or like textile filamentary structures in what will, in the finihed product, become a helical configuration.

Supports 42 for spools 43 of tape, thread, ribbon or the like 44 are mounted on a track 45 extending all the way around the assembling fibrous structure. The track 45 is mounted in the place of the weft insertion arrangement 1 sic of Figure 1. The supports 42 revolve the spools 43 continuously around the travelling assembly so that the threads are fed alternately above and below the web.

As shown in Figures 5 and 6, such tracks 45 can be provided so that helixes of opposite hand can be wound simultaneously. The threads need not be under much tension while being wound-conventional positive feed means may be provided synchronised with the rate at which the assembling fibrous structure is moving through the arrangement and the rate at which the spools 43 are traversed, so as to lay exactly the right amount of thread or ribbon.

Figures 7 and 9 show a flat structure resulting from using one only of the tracks 45 with multiple spools 43. Unidirectional 'helically' wound threads 71 are incorporated into the structure. Figures 8 and 10 show how the two tracks 45 operating in opposite senses lay a criss cross pattern of reinforcing fibre threads ribbons or tubes 81, 82.

Whatever the precise arrangement of fibres, threads, ribbons, tapes even fabrics, for woven or knitted fabrics can be incorporated in place of or in addition to any of the individual components described so far of the fibre reinforcement-what is produced is a cut length of essentially flattened prep-preg with the capability of being blown up to make a hollow structure.

So far, we have described in detail only structures with a continuous flattened tube of polymeric material such as polythene or polyester fibre in the middle. Such is useful for making pipe, as illustrated in Figure 11.

At length 111 of the flat pre-preg product is warmed to soften it and the ends opened out and penetrated by conical inserts 112, 112a.

As shown, the right hand insert 112a is blind.

But the left hand insert 113 is bored and has a connection 114 for a pressure hose by which pressure air (or water or hydraulic fluid) may be introduced. The ends of the pre-preg 111 are clamped to the inserts 112, 112a by clamp means 115 and the warmed, softened structure blown up into a circular section tube by admitting the pressure fluid.

With some structures, and depending also upon the cut length, the pipe maybe well formed without any additional support. However, it will with longer pipes and many structures be necessary to contain the structure in a circular mould (indicated at 118) during the expanding operation, and this will enable high pressures to be developed. The mould and/or the expanding fluid may be heated to a curing or setting temperature for the resin.

The appearance of the flat structures shown in Figures 2 and 3, Figures 7 and 9 and Figures 8 and 10 after expansion is shown in Figures 12 to 16.

Figures 12 is a cross section of the expanded product of Figures 2 and 3. Visible in this cross-section are the tube member 12, the various layers of cushioning fibres 17, the warp threads 14 and the weft threads 15.

The stitches 13 are shown at opposite ends of a diagonal. The seams have been essentially incorporated into the general tubular geometry of the structure.

Figures 13 and 15 show the product of expansion of the structure of Figures 7 and 9.

Visible are the tube member 12, the various layers of cushioning fibres 17, the warp threads 14 and the helically disposed threads 71. Clearly, in this arrangement, no seaming is necessary at the edges of the flat structure.

Figures 14 and 16 show the equivalent view of the product of expansion of the structure of Figures 8 and 10. Here the criss-cross components are shown as ribbons 81, 82.

Hollow structures which are not tubes but which have cavities (either open or closed) can be produced by suitably shaping pockets in the tube member 12. Such a pocket 171 is shown in Figure 17, defined by heat or ultrasonic or like welding of seams 173 in the film of which the member 12 is made. As shown the pocket 171 has a bottle shape with a narrow neck 172. When such is processed, a container 181 as shown in Figure 18 is produced, the narrow neck portion 172 being used to introduce expanding gas into the structure to expand the same against a suitable mould.

Figures 19 and 20 show the effect of expanding the flat structure into shaped moulds.

Figure 19 illustrates a square hollow section.

Figure 20 shows an airfoil secton suitable for use as a wing or a helicopter blade.

The vacuum-pressure impregnation system describe facilitates the use of solventless resin systems, which do not suffer the problems associated with solvent retention and are easier to work with than solvented resins.

Among resin systems which can be used in the above described operations may be included polyimide, silicone, epoxy, isophthalate, polyester, phenolic, acrylic, melamine and polyurethane resins or blends thereof.

Claims (17)

1. A method for making a hollow, fibre reinforced plastics structure, comprising making a resin impregnated, fibre reinforced flat structure incorporating a flattened impervious tube member and expanding the tube member and the resin impregnated structure whilst flexible under fluid pressure to the inside of the tube member.

2. A method according to claim 1 in which the fibre reinforced flat structure comprises opposed laminar sections disposed either side of the flattened tube member and seamed together at the edges.

3. A method according to claim 1 or claim 2, in which the fibre reinforcement comprises warp and/or weft threads and cushioning fibres.

4. A method according to claim 3, in which the cushioning fibres comprise a fleece, stitch bonded fabric or needle felt.

5. A method according to claim 3 or claim 4, in which cushioning fibres are disposed between warp threads and weft threads.

6. A method according to any one of claims 1 to 5, in which at least one weft thread is continuous.

7. A method according to claim 6, in which said continuous weft thread is wound around the structure.

8. A method according to any one of claims 1 to 7, in which the fibre reinforced structure comprises woven or knitted fabric.

9. A method according to any one of claims 1 to 8, in which threads are wrapped around the structure in opposite directions in such manner as to result in helically extending threads oppositely inclined in the expanded structure.

10. A method according to any one of claims 1 to 9, in which the fibre reinforcement is impregnated by a vacuum-pressure technique.

11. A method according to any one of claims 1 to 10, in which the structure after impregnation is squeezed between rollers to eliminate excess resin and define a fibre/resin weight ratio.

12. A method according to any one of claims 1 to 11, in which the structure is dried to a pre-preg state after impregnation but prior to expansion.

13. A method according to any one of claims 1 to 12, for producing pipe in which the impregnated structure is cut into required lengths before expanding.

14. A method according to any one of claims 1 to 12, for producing articles with cavities, in which the tube member is pocketed.

15. A method according to any one of claims 1 to 14, in which the impregnated structure is expanded into form means defining the external shape of the finished structure.

16. A method substantially as hereinbefore described with reference to the accompanying drawings.

17. A hollow, fibre reinforced plastics structure made by a method according to any one of claims 1 to 16.