GB2112689A

GB2112689A - Manufacture of composite tube

Info

Publication number: GB2112689A
Application number: GB08232987A
Authority: GB
Inventors: Raymond Charles Houghton
Original assignee: Bristol Composite Materials Engineering Ltd
Current assignee: Bristol Composite Materials Engineering Ltd
Priority date: 1981-11-25
Filing date: 1982-11-18
Publication date: 1983-07-27
Also published as: GB2112689B

Abstract

A method of fabricating a fibre reinforced composite tube, e.g. a driveshaft, having a mating unit capable of attachment to high torque loads in which a sleeve 2 having a tapered end portion is positioned on a mandrel 1 and a resin/ fibre composition 4 layed over the mandrel and sleeve to bond the sleeve to the tube. The cured resin/ fibre composition is machined from part of the sleeve to allow a second similar tapered sleeve 5 to be positioned co-axially over the first sleeve, the tapered portion of the second sleeve overlapping and being bonded by adhesive to the composite tube. The sleeves are connected rigidly together, e.g. by welding, bonding or riveting. <IMAGE>

Description

SPECIFICATION Composite tube The present invention relates to composite tubes and more particularly to the connection of composite tube to mating items.

Composite tubes such as those fabricated from fibre glass and resin have advantages of e.g. cost, weight over metal tubes. However they are not as susceptible to connection to mating items e.g. gear boxes, axles, as their metal equivalents which can be joined in a variety of ways e.g. by use of bolts, screws, welds. This is particularly the case when it is required to transfer high torque loads into and out of composite tubes.

One means of connection comprises fabricating the composite tube by conventional winding technique and continuing the winding over a metal sleeve so that, upon curing of the tube, the metal sleeve becomes bonded to the inside of the composite tube. End fittings such as a universal joint or other unit may then be attached to the metal sleeve.

A method of joining metal and pottery pipes is described in US Patent No. 332754. In this method, one pipe is formed with its end having a surrounding circumferential recess or annulus capable of accommodating another pipe. The connection between the pipes is made by pouring a molten metal, adhesive or the like into the recess so that upon setting a seal is formed. Also there is described in GB 2026651A an assembly of a universal joint and a shaft having a plurality of superimposed layers of material in which there is an adhesive bond between axially interfitting parts of the shaft and universal joint, the adhesive bond being established with more than one of the layers of material of the shaft to overcome a tendency to disruption of the layers of the shaft on torque transmission.

The present invention relates to a connecting means for composite tubes or pipes having advantages over previously used connecting means.

Thus according to the present invention there is provided a method of fabricating a fibre reinforced composite tube having a mating unit capable of attachment to high torque loads comprising the steps of positioning a first sleeve having an end portion upon the surface of mandrel, laying fibrous material and non-solidified resinous material over the mandrel and the sleeve, and curing the fibrous material and resinous material to form a composite tube characterised in that cured material is removed to expose at least a part of the surface of the sleeve so as to enable a further second co-axial sleeve having an end portion to be located around the first sleeve and to about the composite tube, the end portions of the first and second sleeves forming a projection or recess, the projection or recess mating with a complementary recess or projection on the composite tube the further co-axial sleeve being bonded to the composite tube and the sleeves being rigidly connected together.

Typical fibrous materials for forming the composite tube are glass fibre, aramid fibre and carbon fibre and a typical resinous material is an epoxy resin. The resinous material may be curable in one or more ways e.g. heat cured. The mandrel may be coated with a release agent to facilitate removal of the cured tube subsequent to fabrication.

In one preferred embodiment of the invention, the first and second sleeves are oriented so that the end portions diverge to form an annular recess. In a second preferred embodiment of the invention, the first and second sleeves are oriented so that the end portions overlap to form an annular projection.

The end portion of the sleeves are preferably tapered in the form of an annular wedge of triangular cross-section. The preferred angle of taper of the wedge is from 1.5 to 5 degrees.

The profile of the cured tube is machined preferably to accurately interfit with the second co-axial sleeve. The second coaxial sleeve and the cured fibrous material of the tube are preferably bonded together by an adhesive preferably using a hot or cold curing resin system. The optimum length of the bond is typically of the order 50 mms.

The inner and outer sleeves are preferably positively attached to each other by a suitable method e.g. welding, bonding, rivetting etc.

The outer sleeve preferably extends over the outer surface of the composite tube to a position equivalent to the inner sleeve and is bonded peripherally to the tube. Thus the inner sleeve may be bonded automatically with the resin employed in the composite tube.

Preferably the internal surface of the composite tube is flush with the internal surface of the inner sleeve.

The sleeves are preferably manufactured from plain tube with a gradual taper at the end, the tapered area being the length of the adhesive bond.

Preferably the outer sleeve is not split and it is slid over the outside diameter of the composite tube after it has been machined. The optimum form of the outer sleeve is of a tapered geometry as this provides the gradual transfer of load from composite tube to metal sleeve. The design could be reversed by producing tubes in a centrifuge where the outer sleeve is the first item to be 'wound in', this being located inside an outer mould and the composite tube lay up being held in position by centrifugal force by rotating the mould until it is cured. It is possible that tubes could be made by laying fibres with an alternative process other than winding e.g. hand lay up or injection etc.

There is also provided according to the invention a fibre reinforced composite tube in which one end of the tube is mated to a unit capable of attachment to high torque loads characterised in that the unit comprising a pair of co-axial sleeves and the tube mate by means of a complementary recess and projection, the complementary recess or projection being formed by the end portions of a pair of co-axial sleeves, the inner sleeve being bonded by the cured fibrous and resinous material of the tube and the outer sleeve being bonded to the cured reinforced fibres, the inner and outer sleeves being rigidly connected together.

The invention will now be described by way of example only and with reference to Figs. 1 to 3 of the accompanying drawings.

Figure 1 shows a vertical section through a tubular rotational driveshaft, the inner and outer sleeves being welded together.

Figure 2 shows a similar driveshaft using a flange to connect the inner and outer sleeves.

Figure 3 shows a vertical section through a driveshaft having an alternative arrangement of the tapered portions of the sleeves.

A mandrel 1 of circular cross-section is mounted with a metal sleeve 2 also of circular cross-section, the sleeve 2 having tapered an end portion 3 which is adjacent to the mandrel 1. The mandrel is coated with a release agent capable of resisting the adherence of resin or adhesive. Layers of resin wetted fibre glass are applied circumferentially or axially onto the mandrel until a layer of desired thickness is obtained. The laying is continued over the tapered portion 3 of the inner sleeve 3 and along part of the rest of the sleeve 2.

After the resin wetted fibre glass has been applied, the resin is cured. The resin may be cured in several ways depending upon its formulation e.g. self curing, heat curing. The mandrel 1 is then removed leaving a composite shaft or tube 4 bonded to the sleeve 2.

The outer surface 4 of the cured resin is then machined away to expose a length of the non tapered portion of the sleeve 2. A second outer metal sleeve 5 having a tapered portion 6 is then located on the outer circumference of the first inner sleeve 2. The tapered portion 6 of the second outer metal sleeve overlaps and is bonded by adhesive to the composite shaft 4 so that a wedge shaped recess between the tapered portions of the inner and outer sleeves is engaged or mated by a complementary projection 7 of the composite shaft 4.

After curing, the inner and outer sleeves 2, 5 5 are positively attached to each other by a suitable technique such as welding, bonding, rivetting etc. Fig. 1 shows an annular welded joint 8 connecting the sleeves.

The metal sleeves shown in Fig. 1 are connected to a universal joint 9 leading to a high torque load 10 such as the drive from an engine or gear box.

The arrangement is believed to allow a gradual transition from the tube to the sleeve connector thereby reducing the high stress concentration at the beginning of the joint and therefore allowing a greater load to be transmitted .

With the present arrangement, the bonding faces are accessible for cleaning and abrading to give optimum bonding surfaces using conventional techniques.

Concentricity of sleeves relative to the tube is governed by the location of the sleeve on the manufacturing mandrel and the subsequent laying of the tube on that mandrel makes an integral component of the composite tube and inner sleeve.

Fig. 2 shows an alternative arrangement in which the composite tube 11 is bonded to inner and outer sleeves 12, 13, the sleeves being further connected to or fabricated in the form of a flange 14.

Fig. 3 shows an alternative form of joint geometry. The outer sleeve 15 is tapered on its inside diameter and the inner sleeve 16 is tapered on its outside diameter to produce a matching taper on the inside and outside of the tube at the joining zone. When the outer sleeve 16 and tube 17 are assembled with an adhesive, they meet at this taper 18 giving a zero adhesive gap.

Claims

1. A method of fabricating a fibre reinforced composite tube having a mating unit capable of attachment to high torque loads comprising the steps of positioning a first sleeve having an end portion upon the surface of a mandrel, laying fibrous material and nonsolidified resinous material over the mandrel and the sleeve, and curing the fibrous material and resinous material to form a composite tube characterised in that cured material is removed to expose at least a part of the surface of the sleeve so as to enable a further second co-axial sleeve having an end portion to be located around the first sleeve and to overlap the composite tube, the end portions of the first and second sleeves forming a projection or recess, the projection or recess mating with a complementary recess or projection on the composite tube, the further coaxial sleeve being bonded to the composite tube and the sleeves being rigidly connected together.

2. A method according to claim 1 in which the end portion of the sleeves comprises an annular wedge of triangular crosssection.

3. A method according to claim 2 in which the taper angle of the triangular wedge is from 1.5 to 5 degrees.

4. A method according to any of claims 1 to 3 in which the fibrous and resinous ma terials are circumferentially laid on the mandrel.

5. A method according to any of the preceding claims in which the fibrous material is carbon fibre, aramid fibre or fibre glass.

6. A method according to any of the preceding claims in which the resinous material is an epoxy resin.

7. A method according to any of the preceding claims in which the first and second sleeves are oriented so that the tapered portions diverge to form an annular recess.

8. A method according to any of claims 1 to 6 in which the first and second sleeves are oriented so that the tapered portions overlap to form an annular projection.

9. A method according to any of the preceding claims in which the tapered portion of the further sleeve is bonded by an adhesive to the cured fibrous material.

10. A method according to any of the preceding claims in which the sleeves are connected together by welding, bonding or rivetting.

11. A method of fabricating a fibre reinforced composite tube having a mating unit capable of attachment to high torque loads as hereinbefore described and with reference to Figs. 1 to 3 of the accompanying drawings.

12. Fibre reinforced composite tube in which one end of the tube is mated to a unit capable of attachment to high torque loads characterised in that the unit comprising a pair of co-axial sleeves and the tube mate by means of a complementary recess and projection, the complementary recess or projection being formed by the end portions of a pair of co-axial sleeves, the inner sleeve being bonded by the cured fibrous and resinous material of the tube and the outer sleeve being bonded to the cured reinforced fibres, the inner and outer sleeves being rigidly connected together.

13. Fibre reinforced composite tube according to claim 12 in which the tapered portions of the co-axial sleeves diverge to form an annular recess interfitting with a complementary projection formed by the tube.

14. Fibre reinforced composite tube according to claim 12 in which the tapered portions of the co-axial sleeves overlap to form an annular projection interfitting with a complementary annular recess formed in the tube.

15. Fibre reinforced composite tube according to any of claims 12 to 14 in which the tapered portion of the sleeves comprises a wedge of triangular cross-section.

16. Fibre reinforced composite tube according to claim 15 in which the angle of taper is from 1.5 to 5 degrees.

17. Fibre reinforced composite tube according to any of claims 12 to 16 in which the fibres are carbon fibre, aramid fibre or glass fibre.

18. Fibre reinforced composite tube according to any of claims 12 to 17 in which the outer sleeve is bonded to the composite tube by an epoxy adhesive.

19. Fibre reinforced composite tube as hereinbefore described and with reference to Figs. 1 to 3 of the accompanying drawings.