GB2222653A

GB2222653A - Hollow tubular structures of fibre reinforced plastics material and method for their production

Info

Publication number: GB2222653A
Application number: GB8820981A
Authority: GB
Inventors: John Coppendale
Original assignee: TI Corporate Services Ltd
Current assignee: TI Corporate Services Ltd
Priority date: 1988-09-07
Filing date: 1988-09-07
Publication date: 1990-03-14
Also published as: GB8820981D0

Abstract

Composite tubes of non-circular cross-section, e.g. a box section, are formed by providing a thin, circular section plastics or metal (e.g. aluminium) tube (2) with an uncured GRP coating (1), reshaping the cross-section of the tube e.g. in a die and the applied uncured coating, and curing the reshaped coating with the tube still in situ. The GRP coating (1) may be applied by wrapping or drawing a sleeve over the tube (2). <IMAGE>

Description

HOLLOW TUBULAR STRUCTURES OF FIBRE REINFORCED PLASTICS MATERIAL AND METHODS FOR THEIR PRODUCTION This invention relates to hollow tubular structures of fibre reinforced plastics material, e.g. glass and carbon fibre reinforced plastics (GRP), and methods for their production.

As is well known, GRP and other fibre reinforced plastics have an extremely high strength:weight ratio, and advantage is taken of this in many applications: boat hulls, vehicle bodies, reactor vessels and pipes. Traditional methods of laying up GRP and other fibre reinforced plastics, however, do not lend themselves easily to the production of hollow tubular structures, particularly hollow tubular structures of complex, varying crosssection, and/or of considerable length.

Hollow GRP and other fibre reinforced plastic bodies can be produced by techniques such as: laying up two complementary mating halves of GRP in a female shell mould, curing the two halves, and subsequently bonding the two halves together; laying up the GRP on a collapsible mandrel, curing the GRP and removing the mandrel; and by centrifugal casting, but such methods are of limited application.

It is also known to lay up GRP and other fibre reinforced plastics on a mandrel moulded from an expanded plastics foam, e.g. foamed polystyrene or foamed polyurethane, but in such cases the mandrel remains a permanent part of the structure which cannot them be used as ducting for other pipework or for control lines, electrical power cables, electrical or optical communication cables etc.

In many applications, particularly in the automobile and aerospace industries, it would be desirable to have hollow, lightweight tubular structures of GRP or other fibre reinforced plastics, often of considerable length, and often of complex configuration and/or cross-section, and where advantage can be taken of the hollow interior for the running of such cables, power and/or communication lines, etc.

In accordance with this invention this object is achieved by laying up the GRP or other fibre reinforced plastic on a thin walled tubular mandrel, preferably of light weight aluminium or aluminium alloy, which mandrel becomes an integral part of the structure, but which serves no or substantially no purpose beyond that, i.e. it does not materially contribute to, nor detract from, the strength and weight characteristics of the composite structure which are essentially those of the fibre reinforced plastic.

In one method of producing such a structure, a possibly pre-impregnated web of fibre reinforcement, e.g. of glass or carbon fibres, is spirally wrapped around the preformed tubular mandrel, impregnated with a curable resin composition, e.g. a heat curable unsaturated polyester resin, as necessary, and which is then cured in situ on the mandrel.

In another method, a possibly pre-impregnated sleeve of fibre reinforcement material, is drawn over the tubular mandrel preferably so as to be a close tight fit therearound, further impregnated, if necessary with the, or with additional, curable resin, and which is then cured in situ.

In a particular method according to the invention, particularly suited to the production of polygonal, e.g. box section, tubular composite structures, a circular section, hollow tubular mandrel, e.g. of aluminium, is provided with a wrapping of resin impregnated fibre reinforcement material by either of the two methods described above, and is then shaped into a box, or other section, either along its entire length, or at one or more spaced locations therealong, for example, by the technique disclosed in EP-A0195157 or its US counterpart, US Patent No. 4,567,743, and to which reference should be made for full details, that shaping taking place before final cure of the resin impregnated wrapping.Indeed, in some cases it may be preferable to shape the tubular mandrel into the desired box section, either before the wrapping is applied, or after the wrapping has been applied, but before impregnation with the resin.

Broadly speaking, the technique diclosed in EP-A-0 195 157, and which may be applied to the shaping either of the wrapped or unwrapped mandrel, but preferably to the wrapped mandrel, comprises initially collapsing opposite sides of the circular section tube, in those regions which are to form the opposed parallel faces of the box section, and re-expanding those collapsed regions by the application of internal fluid presure to the collapsed tube whilst in a die having a die cavity conforming. to the desired final box section of the tube.In a variation of that process, which as described is esentially a two step process involving an initial collapsing of opposite sides of the tube in a first die, and the subsequent re-expansion of those collapsed sides in a second die, the tubular mandrel used in accordance with this invention, and either before or after wrapping with the fibre reinforcement, but in any case before final cure of the impregnating resin, can be given a desired cross-section at one or more locations along its length, by the progressive collapse and shaping of the tube in a single die having a cavity of the desired section, that progressive collapse and shaping being brought about by the gradual closing of the two halves of the die about the tube, and controlling the progressive collapse and shaping of the tube by the die by means of fluid pressure applied inside the tube during the shaping thereof by the die.

Similar techniques can be employed to the production of a wide variety of tubular composites having a variety of different cross-sections, e.g. elliptical, ovate, polygonal, such composites having either a uniform cross-section along their entire length, or of varying cross-section, such sections being obtained by shaping the tubular mandrel either before or after application, but before cure, of the resin impregnated fibre wrapping.

Similarly, the invention permits the construction of straight and curved tubular composite structures, including complex curved structures.

Such curved or complex curved structures may be obtained by wrapping the tubular mandrel in the manner described with the resin impregnated fibrous wrapping, the mandrel being bent into the required curved or complex curve either before or after the application of the wrapping, but in any case before the final cure of the impregnating resin.

Since the function of the tubular mandrel is substantially entirely to support the resin impregnated fibre reinforcement during the lay up and curing process, and contributes substantially nothing to the weight and strength characteristics of the final structure, the mandrel should be as thin as possible, consistent with supporting the resin impregnated fibre reinforcement in the desired section during the lay up and curing process. In certain instances it can be envisaged that the tubular mandrel can be temporarily stiffened or strengthened during the laying up and curing process by a temporary filling material, e.g. a water soluble or low melting point solid material, which can be removed at the end of the curing process.

Alternatively the thin walled mandrel can be temporarily held in shape by the application of internal fluid pressure.

Whilst thin-walled metal, e.g. aluminium or aluminium alloy mandrels, are preferred, other thin-walled mandrels, e.g. of plastics material, may be used. These may be of thermoset plastics material, at least in those cases where the mandrel is not reshaped after laying up the resin impregnated fibre thereon but before final cure of the resin. Alternatively, where the mandrel is to be reshaped a thermoplastics mandrel may be used.

For the final curing of the resin impregnated fibre reinforcement in situ on the mandrel, various techniques may be employed. For smaller items, this may simply involve oven heating. For larger items other possibilities exist, for example, passing hot gas through the mandrel, or electrical resistance or induction heating of the mandrel itself.

The principles of the present invention are illustrated by the accompanying drawings in which: Figure 1 shows a section through a fibre reinforced plastic tubular structure in accordance with the invention and having a circular crosssection; Figure 2 shows a section through a similar tubular structure, but having a box section; Figures 3a, 3b and 3c show progressive stages in the formation of a box section structure as shown in Figure 2.

Figure 1 illustrates the principle of the invention applied to a tubular structure having a simple circular cross-section. Basically this structure consists quite simply of a thin-walled inner tube (2) of light weight metal or alloy, preferably aluminium or aluminium alloy, and an outer, generally thicker annulus (1) of resin bonded fibre reinforcement, e.g. resin bonded glass fibre GRP, which gives the structure its basic characteristics of high strength and stiffness, but low in weight.

The structure is formed by taking a thin walled tube, e.g. of extruded aluminium, and using that tube as a mandrel to lay up a resin impregnated glass (or carbon or other suitable fibre) reinforcement annulus around the mandrel, either by spirally wrapping the mandrel in a glass fibre web, or by inserting the mandrel into a close fitting woven glass fibre sleeve, and impregnating the glass fibre annulus with a heat curable resin, before finally curing the resin impregnated fibre reinforcement in situ on the mandrel, the mandrel thus becoming an integral part of the final tubular structure. It will be appreciated that that principle can be applied to tubular mandrels of any desired cross-section, e.g. elliptical, ovate or polygonal, not just circular, so that the invention permits the construction of tubular composites virtually of any desired cross-section.

Figure 2 represents a similar structure, but having a box rather than circular cross-section. The structures of both Figure 1 and Figure 2 can have a uniform cross-section along their respective lengths, or the cross section may vary along the length of the structure, some sections of the structure having a circular section, and others a box section for example.

One method of forming a box section structure, either extending along the whole length of the structure, or just in selected sections thereof, the remainder being circular, is illustrated by Figures 3a, 3b and 3c.

In this method, which is essentially the same as that described in EP A-0 195 157, one starts with a uniform circular section tubular metal mandrel (2), which may be a straight length of tube, or it may have a simple or complex curved confirguration. This is then wrapped, for example by spiral winding, with one or more layers of woven fibre reinforcement material (1).

Alternatively, a close fitting woven sleeve of fibre reinforcement, e.g. a woven glass or carbon fibre sleeve, is drawn onto the mandrel, Figure 3a.

The wrapped mandrel, either before or after impregnation of the fibre reinformement material with the curable resin composition, is then placed in a first die and the opposite sides of the tube, which correspond to the opposite flat faces of the eventual box section, are deformed inwardly, Figure 3b. This may be done over the whole length of the mandrel, or just in selected regions thereof. The inwardly deformed tubular mandrel with its fibre wrapping is then placed in a second die having a cavity of the desired box section, and the inwardly deformed regions of the mandrel re-expanded outwardly to conform to the die cavity by the application of internal fluid pressure to the mandrel, Figure 3c. In the final step or steps, fibre wrapping around the now box sectioned mandrel is impregnated with the curable resin, if not pre-impregnated, and heated to effect the cure.

Instead of going from Figure 3a to 3c in two distinct steps, a single die forming step can be used in which the wrapped circular section mandrel of Figure 3a can be progessively shaped into a box section under control of a pressurised fluid applied inside the mandrel to control the collapse and simultaneous reshaping of the mandrel.

By either of the latter methods complex curved hollow tubular structures of fibre reinforced plastics can be created.

Claims

1. A hollow tubular fibre reinforced plastics structure comprising an outer annulus of fibre reinforced plastics material formed about a thin walled light weight tubular mandrel, said mandrel forming an integral part of the structure.

2. A tubular structure according to claim 1, which is of a non-circular cross-section along at least part of its length.

3. A tubular structure according to claim 2, which is of a polygonal cross-section along at least part of its length.

4. A tubular structure according to claim 3, which is of a box section along at least a part of its length.

5. A tubular structure according to any one of claims 1 to 4, which is of a uniform cross-section along its length.

6. A tubular structure according to any one of claims 1 to 4, the crosssection of which varies along the length of the tube.

7. A tubular structure according to any one of the preceeding claims, which is curved along at least part of its length.

8. A tubular structure according to claim 7, which is uniformly curved along its length.

9. A tubular structure according to claim 7, which has a complex curved configuration comprising a multiplicity of curves spaced along its length.

10. A tubular structure according to any one of claims 1 to 9, wherein the thin-walled light weight tubular mandrel is of metal.

11. A tubular structure according to claim 10, wherein the thin-walled light weight tubular mandrel is of aluminium or aluminium alloy.

12. A method of forming hollow tubular structures of fibre reinforced plastics material, which comprises laying up one or more layers of fibre reinforcement material on a thin walled light weight tubular mandrel, impregnating said material with a curable resin composition, and curing the resin impregnated fibre reinforcement in situ on the mandrel whereby the mandrel becomes and remains an integral part of the final structure.

13. A method according to claim 12, wherein the fibre reinforcement material is spirally wound about the mandrel.

14. A method according to claim 13, wherein the fibre reinforcement material is in the form of a close fitting woven sleeve of fibre reinforcement material which is drawn onto the mandrel.

15. A method according to any one of claims 12 to 14, as applied to the manufacture of a tubular structure having a cross-section and/or configuration as required by any one of claims 2 to 9.

16. A method according to claim 15, wherein the tubular mandrel is shaped to the desired configuration and/or cross-section before laying up the fibrous reinforcement material thereon.

17. A method according to claim 15, wherein the tubular mandrel and the fibrous reinforcement material are shaped to the desired configuration after laying up the fibrous reinforcement material on the mandrel, but before curing the impregnating resin.

18. A method according to claim 17, wherein a thin-walled tubular metal mandrel is used.

19. A method according to claim 18, wherein the mandrel is of aluminium or aluminium alloy.

20. A method according to claim 17, 18 or 19, as applied to the manufacture of a box section tubular structure, wherein the box section is formed by the steps of initially inwardly deforming the opposite sides of a circular section mandrel in those region(s) which are to correspond with the opposite faces of the box section, and subsequently re-expanding those inwardly deformed regions to conform to a die cavity having the desired box section by the application of fluid pressure inside the mandrel whilst positioned in said die cavity.

21. A method according to claim 20, wherein the box section is formed by progressively shaping those region(s) of a circular section mandrel which are to be given said box section in a die having a die cavity having the desired box section, the progressive shaping of those regions by said die taking place under control of a pressurised fluid applied inside the mandrel.

22. A method according to claim 20 or 21, wherein said box section(s) is or are formed after laying up the fibre reinforcement material on the tubular mandrel, but before curing the impregnating resin.

23. A method according to any one of claims 11 to 16, wherein the tubular mandrel is of metal.

24. A method according to claim 23, wherein the mandrel is of aluminium or aluminium alloy.

25. A method according to any one of claims 12 to 24, wherein the resin is cured by heating the structure in an oven.

26. A method according to any one of claims 12 to 24, wherein the resin is cured by passing a hot fluid through the tubular mandrel after laying up the fibrous reinforcement material thereon and impregnating the fibrous reinforcement material with the resin.

27. A method according to any one of claims 18, 19, 23 and 24, wherein the structure is cured by induction heating of the mandrel.