GB2053696A

GB2053696A - Carbon fibre laminated sports equipment

Info

Publication number: GB2053696A
Application number: GB7925002A
Authority: GB
Original assignee: GRAYS OF CAMBRIDGE INTERNATION
Current assignee: GRAYS OF CAMBRIDGE INTERNATION
Priority date: 1979-07-18
Filing date: 1979-07-18
Publication date: 1981-02-11

Abstract

A carbon fibre reinforced, laminated sports equipment shaft (15) comprises a wooden core (19), opposed layers (18) of carbon fibre laminated on opposite faces of the core and a woven carbon fibre outer sheath (16) wrapped around and bonded to the carbon fibre laminated core (19) by curing the carbon fibre in a mould, preferably by impregnation with epoxy resin. One end of the shaft is sandwiched between two layers of hardwood, cut to a taper, and bonded to a head using epoxy resin. A handle is fitted to the other end of the shaft. Glass fibre or carbon and glass fibre tape is used to reinforce the head and handle connections. <IMAGE>

Description

SPECIFICATION Carbon fibre laminated sports equipment This invention relates to carbon fibre laminated sports equipment, and is particularly, but not exclusively, concerned with the construction of sports equipment shaft assemblies.

The advantages of a laminated construction for a variety of sports equipment have long been recognised, by virtue of the strength imparted for a low weight penalty. Various laminated constructions have been proposed employing laminations of a variety of materials to achieve particular characteristics of strength, weight and flexibility or torsional stiffness, necessary to impart desired playing characteristics to the sports equipment in use. Such criteria are particularly important in the case of sports equipment in which playing or striking head is mounted at one end of a support or handle shaft and in which the implement as a whole is swung in the hand to strike a playing piece such as- a ball, with the playing head.Primary examples of such equipment are rackets, clubs and bats, in which the shaft and some or all of the head assemblies are commonly laminated and in which the playing head is at one end and the handle or gripping region at the opposite end. This configuration imposes severe loading on the intermediate shaft assembly between the handle and head and the characteristics of the shaft under load, in particular impact with the ball upon the head, may be crucial to the characteristics of the implement as a whole and thus its suitability for use in playing a game successfully. At high levels of professional skill, the characteristics of the playing implement become all the more crucial.

With laminated constructions generally, problems are encountered in fabrication, because the laminations must be bonded together and this typically involves a heating and curing step and the equipment must be shaped and finished, and in particular the head and handle constructions must be completed without imparing the strength of the intervening shaft.

Since the advent of carbon fibre technology, it has been proposed to use the potential of carbon fibre reinforcement in laminated sports equipment construction and in this respect attention is drawn to our UK patent 1,311,287. However, with a carbon fibre reinforced wood laminated construction, problems are encountered in bonding the carbon fibre reinforcement to the wooden iaminates and heating and curing the assembly to achieve the desired integrally bonded whole without detriment to the wood structure.

According to one aspect of the present invention, a method of fabricating sports equipment, comprises fabricating a shaft assembly separately from a wooden core, applying opposed layers of carbon fibre laminate on opposite faces of the core, wrapping a woven carbon fibre outer sheath around the laminated core and curing the carbon fibre in a mould to bond the core, carbon fibre laminations and carbon fibre sheath integrally together, and subsequently mounting a playing head assembly upon one end of the shaft and fitting a handle portion to the other end of the shaft.

The invention also provides a shaft assembly produced by the foregoing method and an item of playing equipment comprising such a shaft assembly with a handle and head fitted at opposite ends.

There now follows a description of a particular embodiment of the invention, by way of exampleonly, with reference to the accompanying diagrammatic drawings, in which: Figure 1 shows a shaft assembly; Figure 2 shows one end of the shaft assembly of Figure 1 with a handle portion fitted thereupon; Figure 3 shows the opposite end of the handle portion shown in Figure 1 with a mounting for a playing head; Figure 4 shows the subsequent fabrication step for the playing head mounting shown in Figure 3; and Figure 5 shows a shaft assembly with a playing head mounted thereupon.

Referring to the drawings, an item of sports equipment and in particular a racket, such as a tennis, squash or bandminton racket, is fabricated from a separate shaft assembly upon which a playing head is subsequently mounted at one end and to which a handle portion is fitted at the opposite end. The separate fabrication of the shaft assembly by a carbon fibre reinforced laminated wooden construction enables the necessary high strength, durability and flexibility to be incorporated without detriment to the wooden structure, without the encumberance of the less durable handle portions and playing head, which are fitted subsequently, but in a manner which ensures the desired integrity of the assembled racket.

Referring to Figure 1, a shaft assembly 15 forms the basis of the racket construction and comprises an elongate wooden core 19 of rectangular section.

Preferably the wood employed is ash to impart the desired natural wood flexibility resilience and strength characteristics to the laminated construction as a whole. Two strips or laths of unidirectional (that is all the fibres in one direction) high modulus carbon fibre material, which may conveniently be of a proprietary strip or sheet material, are applied to the wider opposite faces of the ash core 19. The dimensions of the core 19, and thus the spacing of the strips 18 and indeed the thickness of the strips 18 themselves are determined by quantative testing to achieve the desired degree of overall flexure or stiffness.

The laminated core 19 is then covered by a sheath 16 of diagonally woven carbon or carbon and glass fibre fabric again a proprietary material in which the strands cross one another and lie inclined to the general longitudinal axis of the shaft assembly 15.

This outer woven layer 16 improves the torque characteristics of the shaft assembly as a whole.

The sheathed laminated core is then cured at a high temperature to bond the carbon fibre strips or laths, the ash wood core and the outer woven sheath 16 into an integral assembly. This curing can be effected without fear of damage to more delicate parts of the racket which will be added later as subsequently described. Indeed the fabrication of the shaft assembly can be carried out separately from the reminder of the racket construction and this affords great production flexibility.

By curing the sheath and the core laminations at one and the same time, a uniform bonding is achieved of three separate elements, namely the ash core 19, the opposed carbon fibre laminations 18 and the outer carbon fibre woven sheath 16. In the resultant assembly the carbon fibre strands are orientated in different directions to achieve the required strength in those directions.

The curing of the shaft assembly is effected in a mould by impregnation of the assembly under pressure with an epoxy or polyester resin which upon the application of heat cures the outer carbon fibre or carbon glass fibre woven sheath 16 at the necessary elevated temperature without damage to the ash core 19.

The resulting shaft assembly 15 has the desired high strength properties at a very low weight penalty and is both stronger and lighter than an equivalent wood shaft of comparable dimensions, but with betterflexural and torque characteristics.

The subsequent fabrication stages, in which the shaft assembly 15 is incorporated into a racket construction, as shown in Figures 2 through 5, a playing head is mounted to one end and a handle portion at the opposite end. Prior to these stages, the cured shaft assembly 15 is degreased to remove any residual release fluid from the mould curing stage and the end three inches of the shaft faces are then lightly sanded, degreased again and pieces 25 of hardwood, of width corresponding to the width of the shaft assembly 15, are bonded to opposite sides of the shaft assembly 15 with an epoxy resin. This bonded end assembly is then machined to a taper 26, as shown in Figure 4 to a dimension of approximately 1/8" width at the far end ready for assembly into a playing head 30 shown in Figure 5.The latter is bonded to the tapered end of the shaft assembly 15, with epoxy resin, and may be fabricated itself in a conventional laminated manner. Thus the end of the carbon fibre reinforced shaft is surrounded by hardwood itself bonded to a wooden laminated head, thereby ensuring a correct bond. For additional strength, the lower portion of the tapered throat of the playing head or frame 30 at its junction with the tapered end of the shaft assembly 15 is wrapped around in glass fibre or carbon glass tape and bonded thereto with epoxy resin.

Atthis stage, or if desired before the head assembly is mounted, the opposite end of the shaft assembly 15 is fitted with a handle portion by sanding the bottom 61/2" of the shaft assembly 15 to improve the adhesive bond degreasing and gluing specially shaped side and handle pieces 20 to that end of the shaft to form a handle of desired oval cross section. The handle assembly is then sanded down two size with shaping or moulding at the inner end 21 to flow the shape of the handle into the shaft with the correct taper, as shown in Figure 2. This tapered end of the handle may also be reinforced by wrapping a layer of glass fibre or carbon and glass fibre tape therearound and bonding with epoxy resin.

The completed racket comprising shaft assembly 15 with the handle portion fitted to one end and the playing head mounted at the other end may be finished in the conventional manner, for example by spraying with the desired finishing paint of lacquer.

The final application of gripping material to the handle, stringing of the head is performed in the conventional manner.

Claims

1. A method of fabricating a sports equipment shaft assembly comprising the steps of applying strips of carbon fibre laminate to opposite faces of a wooden core, wrapping around the laminated core with a carbon fibre woven sheath and curing the carbon fibre sheathed and laminated core to form an integrally bonded carbon fibre reinforced assembly.

2. A method of fabricating a sports equipment shaft assembly, as claimed in Claim 1, comprising effecting curing of the carbon fibre sheathed and laminated core in a mould with the application of epoxy resin adhesive to penetrate and bonded the interstitial spaces of the woven sheath.

3. A method of fabricating a sports equipment shaft assembly, substantially as herein before described, with reference to Figure 1 oftheaccom- panying drawings.

4. Amethod of fabricating sports equipment, comprising initially fabricating a shaft assembly by the method as claimed in any of the preceding claims, and mounting a prefabricated head assembly at one end and a handle portion at the opposite end.

5. A method of fabricating sports equipment, as claimed in Claim 4, including applying wood strips to opposite faces at one end of the shaft assembly, tapering said one end by machining the alternate intervening opposed faces thereof, fitting theta- pered end into a correspondingly shaped recess in a prefabricated playing head assembly, and adhesively bonding the shaft assembly thereto.

6. A method of fabricating sports equipment, as claimed in Claim 5, including reinforcing the join between the head and shaft assemblies by wrapping therearound with carbon fibre tape and bonding thereto with epoxy resin.

7. A method of fabricating sports equipment, as claimed in any of Claims 4to 6, including fitting a handle portion by applying and adhesively bonding shaped-section strips to one end ofthe shaft assembly, machining the bonded strips to form the desired combined handle cross-section and tapering the handle portion inner end to form a neck join with the handle assembly.

8. A method of fabricating sports equipment substantially as hereinbefore described with reference to, and as shown in Figures 2to 5 of the accompanying drawings.

9. A carbon fibre reinforced laminated sports equipment shaft assembly comprising a wooden core, opposed layers of carbon fibre laminate on opposite faces of the core and a woven carbon fibre outer sheath wrapped around and bonded to the carbon fibre laminated core by curing the carbon fibre in a mould.

10. A sports equipment shaft as claimed in Claim 9, in which the assembly is impregnated with epoxy or polyester resin which when heat treated, cures and bonds the outer carbon fibre sheath to form an integral carbon fibre reinforced assembly.

11. A shaft assembly as claimed in either of the preceding Claims, in which the core is made of ash wood.

12. A shaft assembly as claimed in any of the preceding Claims, in which the woven carbon fibre sheath comprises intersecting strands of fibre running diagonally in relation to the length and breadth of the sheath.

13. A shaft assembly according to any of claims 9 to 12, attached to a separately fabricated head by means of a tapered end, exposing the flanks of the wooden core bonded to the head material by epoxy resin and with the throat region of attachment at the taper wrapped around with adhesively bonded carbon fibre woven fabric.

14. A shaft assembly as claimed in any of Claims 9to 13 incorporating at one end a handle formed by moulded additional pieces adhesively bonded to opposite sides of the one end of the shaft.

15. A carbon fibre reinforced laminated shaft assembly, substantially as herein before described with reference to, and as shown in, Figure 1 of the accompanying drawings.

16. Carbon fibre reinforced laminated sports equipment, in particular a racket, substantially as hereinbefore described with reference to, and as shown in, the accompanying drawings.