GB2219240A - Fibre reinforced racquet frame - Google Patents

Abstract

A method of making a fibre-reinforced moulded racquet frame comprises placing a core comprising a polyethylene foam core member encased in the reinforcing fibres in a mould, and injecting a methacrylate resin into the mould around the core. In a preliminary step, the core is formed by weaving the fibres around the foam core member.

Description

RA=ErS This invention relates to racquets for use in games such as tennis, squash, racquet-ball and the like. The invention is more particularly concerned with methods of making fibre-reinforced moulded racquet frames.

It is known to mould racquet frames in fibre-reinforced thermoplastics material, with the fibre reinforcement taking the form of continuous filamentary material woven into a fabric or braid. However, currently available methods of producing such moulded racquet frames suffer from a number of disadvantages. For example, they are rather time-consuming, firstly because the fibres normally have to be pre-impregrated with the epoxy or polyester resin into which they are to be moulded. The pre-impregnated fibres are then laid in the mould, which is closed and heated to an elevated temperature while further epoxy or polyester resin is injected and allowed to cure (or set).This process typically takes over an hour, erring which at least same resin usually exudes from the mould. As a result of this, and of the fact that the resin is fairly viscous, the surface finish of racquet frames made by the known methods is usually rather poor, so that, on removal from the mould, further surface finishing operations such as deflashlng, filling voids and holes, polishing an4/or coating are necessary to render the appearance of the frames acceptable.

Additionally, it can be difficult to provide frames moulded by these methods with stringing holes or other string-supporting structures.

It is therefore an object of the present invention to provide methods of making fibre-reinforced moulded racquet frames in which some or all of the abovementioned disadvantages are alleviated.

According to one aspect of the invention, there is provided a method of making a fibre-reinforced moulded racquet frame, the method comprising placing at least one core including the reinforcing fibres in a mould shaped to define the frame, and injecting a plastics material into the mould around the core, wherein said core is produced by weaving a tube of reinforcing fibres around an elongate plastics foam core member.

The plastics foam is preferably polyethylene foam, and the core member is preferably formed by extrusion.

Advantageously, the msthod comprises suocessively weaving a plurality of layers of reinforcing fibres around the core member, forming on said plurality of layers a further layer of reinforcing fibres which extend parallel to each other and substantially longitudinally of the core member, and then weaving at least one outer layer of reinforcing fibres around the layer of longitudinally extending fibres.

The or each layer of woven reinforcing fibres is preferably woven as a braid.

The reinforcing fibres can be carbon fibres, boron fibres, glass fibres, silicon carbide fibres or aramid fibres of the kind available under the trade name Kevlar, or any combination of these.

Where the tube of reinforcing fibres is woven into a braid, it is preferably woven in at least two ccrtrasting colours, for example by using black carbon fibres and yellow Kevlar fibres. This has the effect of producing a striking finished aç}l#uolnce for for the frame, as will became apparent hereinafter.

The invention also includes a racquet frame made by the method of the inventian, and a racquet incorporating such a frame.

the invention will now be described, by way of example only, with reference to the aoocmpanying drawings, of which: Figure 1 is an exploded view of a mould for making a fibre-reinforced moulded racquet frame by a method in accordance with the present irwertion; Figure 2 is a detailed sectional view of the part of the racquet frame being moulded in the mould of Figure 1, at an early stage in the moulding process; and Figure 3 is a plan view of part of the finished racquet frame moulded in the mould of Figure 1, but with the string-securing wire omitted for the sake of simplicity.

The e mould shown in Figure 1 is designated generally by reference 10, and is intended for moulding a racquet frame of the kind shown at 11. As can be seen in Figure 1, the mould 10 comprises four principal parts, namely upper and lower complementary mould plates 12 and 14, which together define the basic mould cavity 16 in which the racquet frame 11 is moulded, and llzPat and lower locating member 18,20. The e locating members 18,20 together define a cassette for precisely locating and supporting a one-piece sinuous titanium wire string-securing member 21 which is to be moulded into the racquet frame 11.The mould 10, the string-securing member 21 and the way the latter is located and supported with respect to the mould 10 are substantislly as described in United Kingdom Patent Application No. 8426226 (Publication No. 2 148 133A). However, the racquet frame 11, and the precise method by which it is moulded in the mould 10 differ from the frame and method described in that applicatian in several important respects, as follows.

Firstly, the frame 11 is reinforced by continuous woven reinforcing fibres, preferably a combination of carbon fibres for tensile and flexural strength and Kevlar fibres for impact resistance. The carbon fibres are black, while the Kevlar fibres are yellow, and respective bundles of both fibres are preferably woven together into a multi-layer tubular braid 24 having a strikingly zig-zag striped appearance of the kind shown in Figures 2 and 3. The braid 24 forms part of a core 26, which is produced by weaving successive layers of fibres, each layer containing both kinds of fibres, onto an extruded polyethylene foam core member 28, until a braided tube, four or five layers thick, is woven onto the core member.

The weaving technique involved is knawn per se, eg for the weaving of boot- or shoe-laces on a fibre core, and involves pulling the core-membar 28 along the centre line or ails of a mLlti-spindle braiding machine while weaving the first layer therearourd, then passing the core member with the first layer of braid on it through the same braiding machine again to weave the second layer therearound, and so on. To give added tensile strength, a layer of longitudinally-extending fibres is applied to the core 26, preferably between the penultimate and the final braided layers.

The e weaving of the braid 24 Otto the core member 28 ensures an extremely tight fit therebetween, so that the braid and core member form an almost integral structure with significantly greater integration between the braid and the core member than can be achieved by simply inserting the latter into the former after weaving (particularly bearing in mind that if the braid were separately woven to be such a tight fit on the core member, it would probably not then be possible to insert the core member into it).

It will be appreciated that the core 26 can be continously produced as described above to form considerable continuous lengths thereof, which are typically wound onto drums. Then, when required, any desired length of core 26 is sim-ply unwound and cut from the drum.

To mould the racquet frame 11, a first cut length 26a of core 26 is placed in the portion of the mould cavity 16 in the mould plate 12, and a second cut length 26b of core 26 is placed in the portion of the mould cavity in the lower mould plate 14: the walls of the mould cavity are previously sprayed with a releasing agent, and it has been found that this assists in holding the cores 26a and 26b in their respective halves of the mould cavity.The string-securing member 21 is then mounted in the cassette defined by the locating neXkeLS 18, 20, as described in the aforementioned UK patent application, and a bundle of reinforcing fibres (preferably carbon fibres) may, if desired, be interwoven with the portions 22 of the stringseouring member 21 protruding from the cassette (ie the portions intended to be disposed in the mould cavity 16). The mould 10 is then assembled, ie closed, as also described in the aforementioned UK patent application, with the result that the portions 22 of the member 21 disposed within the mould cavity 16, and the reinforcing fibres woven therearound, are trapped between the cores 26a and 26b, as shown in Figure 2.As the mould 10 is closed, the cores 26a and 26b tend to be compressed against each other and around the portions 22 of the member 21, which ensures that the member 21 is firmly keyed into the moulded frame 11 as will become apparent hereinafter.

Once the mould 10 is asseebled in its closed condition, a low viscosity, low temperature setting plastics material in the form of a methacrylsts-based resin is injected into the mould cavity 16 under pressure. We have found that a particularly suitable resin is that available fran the division of ICI under the trade 'çdar 835", which is a high molecular weight methacrylate-based resin in methyl methacrylate solution.It has a viscosity of 40 ops at 20 C. The resin is typically injected at a pressure of 30 p.s.i. (2.1 kg per square cm) and maintained at a taperature of about 200C during curing (or setting), under which conditions it sets, and the mould 10 can be opened to remove the moulded frame 11, in about four minutes. oever, if the resin is maintained at the higher temperature of about 85 C, it sets in about one mite.

Because of its low viscosity, the methacrylate resin not only penetrates the weave of the reinforcing fibres of the cores 26a and 26b and of the fibres woven round the portions 22 of the string-securing member 21, but also forms a thin layer between the cores on the one hand and the walls of the cavity 16. The penetration of the resin ensures that the string-securing member 21 is firmly keyed into the resulting moulded racquet frame 11 by the various reinforcing fibres.Additionally, the aforementioned formation of a thin layer of resin has the result that, when the mould 10 is opened, the resulting moulded racquet frame requires little or no further surface finishing to enhance its appearance. In fact, the moulded frame 11 has the rather striking appearance shown in Figure 3, with a snoth finish and the regular yellow and black zig-zag pattern of the braid clearly visible through the transparent resin: consequently, little or no further surface finishing is necessary.All that remains to complete the racquet, therefore, is fitting a suitable grip (not shown) on the handle part 30 of the moulded frame 11, and securing the stringing (not shown) to the string-securing member 21.

It will be appreciated that the above described method of making the racquet frame 11 has a number of advantages. Primarily, it is relatively fast and clean, and produces a racquet frame that needs little or no further surface finishing and can if desired have a striking appearance. Additionally, the use of carbon and Kevlar reinforcing fibres means that the racquet frame 11 is light and strong, with a good impact resistance. Mcst importantly, tests have shown that even without the further bundle of reinforcing fibres round round the string-securing member 21, the force required to pall this member fran the moulded frame 11 was extremely ly large, so large in fact that, on occasions, the wire simply brake before it cculd be pulled out.

Many modifications can be made to the above-described method of making the racquet frame 11. For example, reinforcing fibres other than carbon and Fsvlar can be used, eg glass fibres, silicon carbide fibres or boron fibs, either on their own or in combination with each other. Various different weaving patterns and colour combinations can also be used, to produce different visual effects or patterns in the surface of the finished frame, eg diamond patterns, E*Tlx3rmanl-salt patterns and so on. Also, the cores 26a and 26b can be formed with hollow inflatable core members in place of the foam core member 28, each inflatable core member being inserted into the braid 24 while unffflated or only partially inflated, and then fully inflated during the moulding process.

other ather suitable low temperature curing, low viscosity resins or like plastics materials can be used in place of the specific methacrylate resin cited, including other resins in the tbRxlar range of resins offered by ICI. Indeed, a thermosetting plastics material can also be used, butt in that case, sate of the advantages of the above-described method of making the racquet frame 11 would be lost.

Another modification which can be made is to replace the single string-securing member 24 with a plurality of individual stringing loops, which can take any convenient form and need not be made fran wire: all that is required is a first portion to define a loop or eye for the stringing and a second or root portion shaped to be entedded in the moulded frame 11.

This application has been divided out of United Kingdnm patent Application No. 8506351 (2 172 238A).

Claims (9)

1. A method of making a fibre-reinforced moulded racquet frame, the method comprising placing at least one core including the reinforcing fibres in a mould shaped to define the frame, and injecting a plastics material into the mould around the core, wherein said core is produced by weaving a tube of reinforcing fibres am und an elongate plastics foam core member.

2. A method as claimed in claim 1, wherein said plastics foam is polyethylene foam.

3. A method as claimed in claim 1 or claim 2, wherein the core member is formed by extrusion.

4. A method as claimed in any one of the preceding claims, comprising successively weaving a plurality of layers of reinforcing fibres around the core member, forming on said plurality of layers a further layer of reinforcing fibres which extend parallel to each other and substantially longitudinally of the core member, and then weaving at least one otter layer of reinforcing fibres around the layer of longitudinally extendirsg fibres.

5. A method as claimed in any one of the preceding claims, wherein the or each layer of woven reinforcing fibres is woven as a braid.

6. A method as claimed in any one of the preceding claims, wherein the reinforcing fibres are selected and woven as tows of two contrasting colarrs.

7. A method as claimed in any one of the pceing claims, wherein the reinforcing fibres are carbon fibres, boron fibres, glass fibres, silicon carbide fibres or aramid fibres of the kind available under the trade name Kevlar, or any catbination of these.

8. A moulded racquet frame made by a method in accordance with any one of claims 1 to 7.

9. A racquet incorporating a racquet frame according to claim 8.