GB2320699A - Production of a composite hollow article - Google Patents

Abstract

A method of producing a hollow article at least partially from a base material composed of continuous, relatively inelastic fibres extending in at least one direction and a binder material for retaining the fibres in a desired orientation in which at least one layer (5) of base material is placed within a hollow former with the fibres (6) of the material extending peripherally to form a closed formation, the peripherally extending fibres being divided so that, during outward expansion of the material in a moulding operation to produce the hollow article, the fibres and binder move outwardly together. The article may also include a layer (7) in which the fibres extend longitudinally, and inner and/or outer plastics layers (1) and (3).

Description

HOLLOW ARTICLE PRODUCTION This invention relates to a method of producing hollow articles from material composed of continuous, relatively inelastic fibres of a material, such as glass fibre, extending in at least one direction therein, and a binder material usually of thermoplastics, for retaining the fibres in a desired orientation. Such a material will be referred to broadly as a base material, for the purpose of this specificati on .

It is known to form a hollow article from mouldable material using a hollow former on which an internal moulding surface has the form of the article to be created, by applying the mouldable material to the internal moulding surface and, after hardening of the material, separating the article and mould. In order to achieve the desired homogeneity in the moulded article, it can be advantageous to apply pressure to the material in an outward direction prior to hardening thereof. When this process is applied to the aforesaid base material a problem can arise if the continuous fibres are arranged to follow the curvature of the hollow former. Because their lack of elasticity limits their capacity for outward expansion, the applied outward pressure can result in the binder moving relative to the fibres, leading to partial separation of the fibres and binder and a potential lack of integrity in the finished article.

An object of the present invention is to provide an improved method of producing hollow articles using the aforesaid base material, in which the aforesaid problem is minimised or avoided.

According to the present invention, a method of producing a hollow article at least partially from the aforesaid base material comprises placing a layer of the material in moulding relationship with the internal surface of a former such that the fibres of the material extend peripherally of the surface to form a substantially closed formation, the peripherally extending fibres being divided in such a manner that, during outward expansion of the material in a moulding operation to produce the hollow article, the fibres and binder move outwardly together.

In one convenient arrangement, the fibres are divided in a direction generally transverse to the peripheral direction.

Preferably, at least one additional layer of base material is applied transversely of the peripheral direction with its fibres extending continuously through each additional layer.

Conveniently, the method includes applying a layer of thermoplastics material to form the outermost and/or innermost surface of the hollow article.

In a typical form of the method, the layers forming the article are assembled together outside the former and subsequently laid against or adjacent the internal surface thereof, being thereafter urged against the surface by the application of pressure, preferably at a raised temperature.

The invention will now be described, by way of example, with reference to the accompanying drawings in which: Figure 1 illustrates diagrammatically one form of cylindrical hollow article made by the method of the invention; Figure 2 illustrates the performance of a series of steps in carrying out the method of the invention; Figure 3 illustrates a portion of base material prepared in an alternative manner for use in the method; Figure 4 is a diagrammatic representation of part of an apparatus for carrying out the method of the invention, and Figures 5 and 6 illustrate respective alternative profiles which may be made using the method of the invention.

One form of an article in the form of a cylindrical pipe made by the method of the invention is illustrated in Figure 1 of the drawings and has an inner layer of plastics material 1 surrounded by a composite layer of base material 2, which material is composed of continuous, relatively inelastic fibres extending in at least one direction therein and a binder material for retaining the fibres in a desired orientation. The composite layer, in the case illustrated, contains a plurality of layers of base material arranged in different ways, as will be described hereafter. A further layer 3 of plastics material overlies the composite material, forming the outer layer in the finished article. The plastic layers 1 and 3 contribute to the structural strength and integrity of the pipe, the outer layer in particular providing protection against damage to the composite material and possibly providing colour coding indicating the type and/or qualities of the pipe for example.

The pipe of Figure 1 may conveniently be manufactured by pre-constructing the basic shape of the finished article prior to inserting it into a main former for the performance of a final moulding operation. The pre-construction is carried out by applying layers of material to the outer surface of a suitable preformer which is used to provide support for the applied based material until such time as this is sufficiently self-supporting to be independently handled and inserted into the main former. Alternatively, the base material may be applied directly to the moulding surface of the main former, the layers being temporarily held in place, if required, by local heating or spot welding.

The aforesaid preconstruction process will now ben described in relation to Figure 2. The first stage in this process is the application of a plastic inner layer 1 around the outer surface of a cylindrical pre-former 4. This may conveniently be done by winding plastic sheet around the former to produce the necessary layer thickness, which may be up to about 20% of the thickness of the finished article. The next step is to commence building up the composite layer 2 of base material by applying successive individual layers one on top of the other. A first layer 2A is laid over the plastic inner layer 1 and is composed of a plurality of strips or sections 5 of base material laid around the pre-former with their fibres 6 extending peripherally of the former.

The sections 5 are in the form of discrete tiles so that the peripherally extending fibres 6 are interrupted at the junctions of the tiles and do not extend continuously around the periphery of the article. This facilitates the formation of the article from the base material, as will become apparent hereafter.

The pre-construction process is continued by the application of successive layers 2B, 2C of base material tiles, again with peripherally extending fibres, the successive layers being laid over each other, as illustrated. It is convenient to arrange these layers with their tiles 5 staggered peripherally of the preformer in order to increase the strength and integrity of the assembly.

It is very convenient to provide the tiles 5 in strips, in which the individual tiles are interconnected by small inserts of unfilled thermoplastic material, such as polypropylene or polyethylene for example. Alternatively, the tile strips may be formed by mounting tiles on an interconnecting thermoplastic sheet.

Such strips may be more quickly and accurately put in place than individual tiles and therefore facilitate the manufacturing process, although the use of individual tiles is not excluded.

The final layer 2D is composed of strips 7 of base material arranged adjacent each other around the periphery of the pre-former with their fibres 6 extending longitudinally of the latter. The proportions of tiles 5 and strips 7 in the finished article is chosen to provide the desired balance between high compressive/bursting strength and longitudinal flexibility. A high proportion of tiles leads to high compressive/bursting strength and vice versa. A typical example of a burst-resistant article, such as a pipe, includes 70% of circumferentially extending tiles and 30% of longitudinally extending strips, although it will be understood that these proportions may be varied, as desired, according to requirements.

The pre-construction process is completed by the application of the outer plastic layer 3, again conveniently by winding plastic sheet around the superposed layers of base material until the required thickness is produced.

This may again be typically about 25% of the pipe wall thickness, although this may be varied to suit requirements.

Instead of using discrete tiles for the layers having circumferentially extending fibres 6, it is possible to use an arrangement, such as that illustrated in Figure 3, in which a sheet of base material is provided along its length with a series of slits 10, each of which extends from an extreme edge of the sheet to a location beyond the sheet centre line, with alternate slits extending from opposite extreme edges of the sheet. It is found that such a sheet, when wound peripherally around the pre-former to form one of the layers 2A, 2B, 2C, may be expanded outwardly without disturbing the fibres 6.

The next stage in the method is to insert the preconstructed article within a main former, within which a final consolidation and finishing stage is carried out thereon. An example of an apparatus useful for this purpose is illustrated in diagrammatic form in Figure 4 and includes an outer cylindrical metal support 11 lined with a radially expandible finishing element 1 2 providing a high quality smooth or textured moulding surface. This element is required to expand radially outwardly during the moulding operation and may be of thin steel or similar material or, alternatively, a high temperature release fabric.

The preconstructed article is illustrated at 8 lying against the element 12 and, inserted within the article 8 is an inner radially expandible moulding element 13, again conveniently of thin steel or high temperature release fabric, providing a high quality moulding surface adjacent the article 8.

A vacuum pressure bag 14 is arranged internally of the element 13, with the laminated article 8 sandwiched between the two finishing elements 12 and 13, the bag extending beyond the ends of the article 8 and being sealingly secured at end locations 1 4A to the support 11. A space 1 5 exists between the bag and the internal surface of the support 11, so that vacuum applied to this space via a connection 1 SA has the effect of forcing out of the pre-constructed article 8 any bubbles or pockets of entrapped air, as well as compressing the article against the finishing surfaces of the elements 12 and 1 3 in the direction indicated by the arrows A. During this process, heat from a suitable source, such as an infra-red or radiant source, represented by arrows B, is applied to the mould to maintain the article in soft mouldable condition so that its inner and outer surfaces may be finished to the required degree of smoothness or by the provision of a texture thereon, as a result of the application of vacuum pressure via the bag 10. Heating may alternatively be carried out by placing the entire apparatus in an enclosure, represented at 16, and circulating therein air heated to the desired temperature. It is during this outward expansion step applied to the closed formation formed by the article 8 that the use of discrete portions of peripherally extending base material becomes important, since it enables these portions to move outwardly, carrying the embedded substantially inextensible fibres with them, without substantial radial relative movement between the binder and fibres of the material. This enables the fibres to assume the required shape of the former, whilst maintaining the essential integrity of the structure. Once the required expansion and finishing of the article has been achieved, the heating is interrupted and cooling effected whilst maintaining the vacuum pressure to ensure that no deformation of the article can occur during tooling, following which the hardened structure becomes self-supporting.

It is possible to apply the method of the invention to many forms of hollow articles, two examples of which are illustrated respectively in Figures 5 an 6.

Tiles similar to those used in the cylindrical article are again arranged peripherally or transversely of the main axis of the hollow article, again enabling the aforesaid structural integrity to be obtained whilst using the base material containing relatively inelastic fibres. These tiles are used in conjunction with continuous strips of material extending generally along the article and providing the necessary flexibility, as previously. A similar effect may be achieved by using material similar to that shown in Figure 3.

It will be understood that the base material may be in the form of a woven fabric in which fibres extend in at least two directions at right angles. The tiles extending peripherally of the article may be applied other than at right angles to the longitudinal direction of the article, the angle of application varying, if required, between individual layers of tiles. Any convenient number of layers of base material may be used, including a single layer and layers of material having peripherally extending fibres may be interspersed with layers having longitudinally extending fibres in any combinations according to the required properties of the finished article. The layer or layers having longitudinally extending fibres may be omitted, particularly in an article, such as the one illustrated, in which the plastic layers may provide the required longitudinal strength and flexibility.

One or more layers having peripherally extending fibres may be in a single cylindrical piece having free adjacent or overlapping longitudinal edge portions permitting some radially outward expansion without a substantial disturbance of the fibres within the binder.

The invention can be applied to hollow articles of conical and many other shapes and also to part-hollow articles.

Claims (11)

1. A method of producing a hollow article at least partially from a base material composed of continuous, relatively inelastic fibres extending in at least one direction therein, and a binder material for retaining the fibres in a desired orientation, comprising placing a layer of the material in moulding relationship with the internal surface of a former such that the fibres of the material extend peripherally of the surface to form a substantially closed formation, the peripherally extending fibres being divided in such a manner that, during outward expansion of the material in a moulding operation to produce the hollow article, the fibres and binder move outwardly together.

2. A method according to Claim 1, wherein the fibres are divided in a direction generally transverse to the peripheral direction.

3. A method according to Claim 1 or Claim 2, wherein at least one additional layer of base material is applied transversely of the peripheral direction with its fibres extending continuously therethrough.

4. A method according to any one of the preceding claims, wherein a layer of thermoplastics material is applied to form an outermost and/or innermost layer of the hollow article.

5. A method according to any one of the preceding claims, wherein the layers forming the article are assembled together outside the former and subsequently laid against or adjacent the internal surface of the latter being thereafter urged against the surface by the application of pressure.

6. A method according to any one of Claims 1 to 4, wherein the layers forming the article are built up within the former, being thereafter urged against the internal surface of the latter by the application of pressure.

7. A method according to Claim 5 or Claim 6, wherein the layers are urged against the surface under raised temperature conditions.

8. A method according to any one of Claims 1 to 7, wherein the base material with its fibres extending peripherally of the former is in a plurality of discrete portions.

9. A method substantially as hereinbefore described.

10. A method substantially as hereinbefore described, with reference to Figures 2 to 4 of the accompanying drawings.

11. A hollow article made by performing the method of any one of Claims 1 to 10.