GB2179263A - Sports racquet assembly - Google Patents

Abstract

A sports racquet has a frame with a head 13 joined to a shaft by a throat. The frame is moulded out of reinforced plastics material and the head 13 has a wholly convex profile in cross-section. A bumper strip 50 is fitted to the head and has an array of holes 57 registering with string holes 70 in the head and a peripheral groove 53 joining the outer ends of the holes 57 to ensure that the strings 71 do not project radially beyond the surface of the bumper strip 50. The racquet is strung by threading the strings 71 through the holes in both the head and the bumper strip. <IMAGE>

Description

SPECIFICATION Sports racquet assembly Introduction This invention relates to sports racquets and more particularly relates two moulded racquet frames for squash, tennis or badminton.

PriorArt There has been a recent trend towards the manu facture of squash, tennis and badminton racquets moulded in reinforced plastics. A variety of plastics and reinforcements have been used to provide the desired weight and inherent mechanical properties that the racquet requires in use. However, it has been discovered that, due to a number of problems, the failure rate in such racquets is high. Poor moulding techniques, badly applied reinforcements and poor design ofthe cross-sectional shape ofthe racquet frame have been found to contribute to the incidents of racquet failure.

Summary ofthe invention It is the object of this invention to provide an aesth etically pleasing racquet frame construction that provides the required mechanical properties of weight and balancewhilstatthe sametime reducing the in cidence offailure.

According to the present invention there is prov ided a racquet frame comprising a frame including a shaft joined to one end of a head by a throat, the other end ofthe head defining acrown,theframebeing moulded in reinforced plastics so that the cross section through the head oftheframe presents a whollyconvex profileto the exterior,the head having a peripheral array of spaced apart string holes exten ding radially through the cross-section ofthe head;; and a bumper strip having a concave inner surface that fits closely on the convex exterior ofthe crown of the head, the bumper strip having an array of radially extending holes spaced to correspond to the spacing ofthe string holes in the head, the exterior surface of the bumper strip including a groove or grooves that extends over the holes so that in use the racquet frame assembly is strung bythreading the racquet strings through the holes in the frame and the bumperstripwith the groove or grooves in the bumper strip ensuring that the strings do not project radially outside the exterior surface of the bumper strip.

The term "wholly convex" as used herein is understood to embrace an outwardly curved or planar surface unbroken by indentations, grooves or slots ex cept string holes that extend radially through the cross-section ofthe racquet head.

Preferably the bumper strip is provided with integrallyformed grommets extending radially from the inner surface of the strip to line the string holes.

In a preferred embodiment the cross-sectional profile ofthe racquet frame varies from one portion of the frame to another. The shaft is preferably ofcir- cular cross-section for a flexible orwhippy racquet and is preferably of a rounded square cross-section fora stiffor rigid racquet. The throat, shoulders and crown of the racquet frame are preferably ofelliptical cross-section with the cross-section of the crown being aflatterellipsethanthecross-section ofthe throat and shoulders.

Description ofthe drawings One embodiment ofthe present invention will now be described by way of example only with reference to the accompanying drawings in which: Figure lisa plan view of a squash racquetframe illustrating areas of localized reinforcement; Figure2a and 2b are cross-sectional views of parts ofthe head ofthe racquet frame; Figure 3a and 3b are cross-sectionai view of altern ativeshaftsforthe racquet; Figure 4 is a perspective view illustrating reinforcements of the racquet shaft; Figure 5 is a cut-away perspective view illustrating one example of laminate reinforcements ofthe racquet frame;; Figure 6is a plan view a strung racquet with a bumper strip attached to the crown of the racquet frame; and Figure 7 is a cross-sectional view of the crown of the racquet head illustrating the bumper strip attached to the racquet head.

Preferred embodiment Asquash racquetframe loins illustrated in Figure 1 manufactured from reinforced plastics. The racquet 10 comprises a grip 11 with a projecting shaft 12 that joins a head 13 via a throat 14. The head 13 is joined to the throat 14via shoulders 15 and terminates in a crown 16. Thethroat 14joins the shoulders 15 and theshaft 12 bymeansofa pairof bifurcated arms 17 and 18. The racquet is moulded to a shape that isdic- tated by the sport and the aesthetic demands of the user. In a preferred embodiment the technique used to produce the racquet comprises positioning a preform into a steel mould cavity conforming to the desired shape ofthe racquet.The preform comprises a thin film of plastic tube that runs up the shaft 12 ofthe racquet, along arm 18 and around the head 13, down the second arm 17 and then in a parallel array down the shafttothe grip 11. In Figure4the ends 20 and 21 of the tube are illustrated at the end ofthe shaft 12 showing the parallel passes of the tube. A variety of reinforcing fibres impregnated with a suitable epoxy resin are then wrapped aroundthetube to form a composite laminate structure. The material, physical properties, and orientation ofthe reinforcements vary from racquet to racquet but are specifically des igned to produce the desired strength to resist localized stresses that the racquet will be subjected to in use.It is further understood that the reinforcing must alsofulfil the requirements of weight and balance.

The portion ofthethroat 14(a) atthe baseofthe head 13 - known as the bridge - is formed by positioning resin preimpregnatedfibrous reinforcing, wrapped around a strip of plasticsfoam, into the mould cavity and blending the ends into the major structure of the racquet frame. The mould is then closed off by means of joining a secondary steel plate to the steel mould incorporating the racquet cavity.

The plastic tube inside the mould is then inflated to force the resin into homogenous contact with the mould surfaces, the layers of reinforcement and the tube surface. The mould is simultaneously heated to curethe resin. After the resin has cured, the mould is cooled and the racquet frame removedfortrimming, chamfering and final preparation. It is at this stage thatthe radially extending string holes are drilled through the racquet frame.

The method described above is the conventional method for moulding reinforced plastics racquet frames. This invention relates to the design and consideration that has gone into the selection ofthe cross-sectional area of various parts ofthe racquet as well as of the selection and positioning of reinforcementto improve the quality and characteristics ofthe racquet. It has been found by experimentation that the most effective cross-sectional shapeforthe racquet head and throat is either a circularorellipti- cal cross-section. It is important that this crosssection presents a convex surface to the exterior and does not include depressions, indentations or grooves.In particular it has been discovered that it is important that there is no groove extending around the external periphery ofthe racquet head, that is a groove ofthe kind used in conventional racquets into the base of which is positioned the array of closely spaced string holes. By moulding the cross-section ofthe racquet in circular or el liptical form, the occur- rence of voids and delamination is substantially reduced. The pressure within the plastics tube can be used to exert a uniformly distributed force on there- inforcing structure to improve the homogeneous intimate contact between the reinforcing structure and the resin. The uniformity of this force is not possible when the cross-section ofthe racquet is interrupted bya groove.The use of a plain elliptical shape without a groove or rebate allows a greater amount ofstructural reinforcing material to be used without effecting the weight of balance ofthe racquet. The cross-sectional shape ofthe racquet head is important, notonlyfromthe point of view of inherent mechanical stiffness and strength but also, as discussed above, in relation to the mouldability,thereby reducing the problems of reinforcing orientation and pressure distribution during the moulding cycle. In considering ultimate strength and stress distribution as well as mouldability a circular cross-section is considered most desirable.However, this has to be tempered by an aesthetic or cosmetic appeal as well as the wind resistance or drag on the racquet as it is swung through the air.

After extensive experimentation it has been discovered that a preferable cross-section forthe racquetheadforsquash isforthethroatandshoul- ders of the racquet to have an elliptical cross-section that can be defined as a 12 mm. 600 ellipse with a 1:1.15 ratio (Figure 2a) and the crown portion ofthe head to be formed as a 12 mm. 45" ellipse with a 1:1.41 ratio (Figure 2b). In both casestheelliptical cross-section presents a wholly convex surface to the exterior with no grooves or indentations.

Whilstan elliptical cross-section is the preferred form ofthe racquet head the invention also relates to other cross-sections with straight line or planar port- ions. Such cross-sections include rectangular,tri- angular and combinations of straight and curved sided forms, all of which present an exterior surface unbroken by grooves, slots and indentations save the radially extending string holes. The crosssectional shape of the shaft varies according to the flexibility ofthe racquet. For a stiff racquet the crosssectional area is almost square with rounded sides as illustrated in Figure 3b. Four a more flexible orwhippy racquet the cross-sectional area is circular as illustrated in Figure3a.

In Figure 5 there is illustrated an example ofthe typical laminate structure used to mould a racquet frame. The number and direction of the layers may vary depending upon the desired structural or playing characteristics of the racquet. However, in general the laminate structure comprises reinforce mentsextending longitudinally, or diagonally ofthe racquet frame as well as woven or braided layers.

The orientation and sequence ofthefibre layers is important in determining the ultimate strength ofthe racquet and can vary depending on the racquet and the material used as reinforcement. The ratio offibre reinforcements to resin and the interlaminate adhesion of the fibre layers controlled by the tightness of the wrapping or preforming ofthe layers before cur ing is also important as isthe pressure used to inflate the plastic tube in the moulding cycle to ensure mould uniformity.

In the throat and headoftheracquetwherethe frame is subjected to torsional,tensile and compressive loads it is importantthatthe laminate composition is balanced to counteract these stresses.

In Figure 4a portion of the shaft 1 2 is illustrated in which the reinforcing fibres are mainly unidirectional with the outer layer 40 being used to bind the assembly. The construction absorbs the tensile and compressive loads that the shaft is normally subjected to.

As illustrated in Figure 1 localized areas of reinforcement may be added to portions ofthe racquet that are subjected to a particular high stress and wear namelythethroat 14, the bifurcated arms 17 and 18 of the shoulders 15 and the crown 16. These reinforcements may consist of bias ply laminations of graphite fibres and are positioned as illustrated in Figure 1.

It is understood that the fibres used for reinforcement are extensive and include graphite, fibreglass, KEVLAR (Registered T.M.) and other commonly used reinforcing fibres. The exact composition and con tent ofthese materials may bevaried to dictate quali- ties of stiffness, vibration dampening, weight and balance.

By moulding the racquet head to assume a circular or elliptical cross-sectional that presents a wholly convex surface to the exteriorthere is introduced a problem in respect of protection for the strings. As shown in Figures 6 and 7 the racquet head is provides with a plurality of closely spaced string holes 70 arranged equally spaced in an arrayaroundtheper- ipheryofthe racquet head. The string holes 70 extend radiallythrough the cross-section ofthe racquet and are conventionally lined with a grommet. When the racquet is strung the strings 71 are threaded through adjacent holes.To protect the portion of the string 71 that extends from one hole to anotherexter nally of the racquet it is conventional to provide a groove in the outer surface ofthe racquet of sufficient depth so thatthe strings are within the groove. However the wholly convex exterior of the racquet head precludes the use of a groove and thus the strings project outwardly ofthe racquet head. It is in the area of the crown 13 of the racquet head that the strings are most proneto damage and thus a bumper strip 50 shown in Figures 6 and 7 is specifically designed to protectthestringsinthatregion. In the remaining regions of the racquet head no protection is provided forthestrings7l and they project outwardly of the elliptical cross-section ofthe frame.Suitable grommets line the string holes 70 in these noncritical areas.

As shown in Figures 6 and 7the bumper strip 50 comprises a piece of flexible plastics or rubber hav ingan inside surface 51 ofsuitablearcuatecross- section so that the strip can closely engage the external surface of the cross-section ofthe crown 13 of the racquet head. The exterior surface 52 of the bumper strip 50 is provided with a centrally positioned groove 53 having walls 54 and 55 and a base 56. A plurality, preferably 30, of equally spaced holes 57 are positioned in the base ofthe groove 53 in posi tions that correspond to the array of string holes 70 in the racquetframe.A similar number of rubber grommets 58 in the form of cylindrical pipes 59 are formed integrally with the bumper strip to each extend radially downwardly from the hole 57 in the base of the groove 53 to extend through the string hole 70 in the cross-section ofthe racquet frame. In this mannerthestrings71 ofthe racquet extend through the grommets 58 and across from one hole to another in the bumper strip 50 to thus hold the bumperstrip in positive and firm engagementonthe frame. The depth of the groove 53 in the bumper strip is greaterthan the height of the strings 71 sothatthe bumper strip acts to protect the strings from damage in use. The bumper strip 50 is also provided with overlapping side portions 60 and 61 that serve to add further protection to exposed surfaces ofthe racquet.

In this mannerthe strings 71 are protected in the area where they are most proneto damage in use, without detrimentally affecting the strength and mouldability of the racquet frame.

Although the preferred embodiment is described in relation to squash racquets it is understood that this invention applies to all types of moulded sports racquets especially squash and tennis. It is further understood that although the preferred embodiment is described with reference to a conventional mould ing technique it is understood that the invention is also applicable to the manufacture of racquets by injection moulding.

Claims (9)

1. Aracquetframe assembly comprising aframe including a shaftjoined to one end of a head buy a throat, the other end of the head defining a crown, the frame being moulded in reinforced plastics so that the cross-section through the head of the frame presents a wholly convex profile to the exterior, the head having a peripheral array of spaced apart string holes extending radially through the cross-section of the head; and a bumper strip having a concave inner surface that fits closely on the convex exterior ofthe crown ofthe head, the bumper strip having an array of radially extending holes spaced to correspond to the spacing of the string holes in the head, the ex terior surface ofthe bumper strip including a groove or grooves that extends overthe holes, so that in use the racquet frame assembly is strung by threading the racquet stringsthrough the holes in the frame and the bumper strip with the groove or grooves in the bumper strip ensuring that the strings do not pro ject radially outside the exterior surface of the bumper strip.

2. Theracquetframeassemblyaccordingto Claim 1,wherein the bumper strip is provided with integrally formed grommets extending radiallyfrom the innersurface ofthe strip to line the string holes in the racquet frame.

3. The racquet frame assembly according to either Claim 1 or 2, wherein the cross-section of the head and throat oftheframe is circular orelliptical.

4. The racquetframe assembly according to Claim 3, wherein the head and throat, ofthe racquet are of elliptical cross-section with the cross-section ofthe crown being a flatter ellipse than the crosssection ofthe remainderofthe head and thethroatof the racquet frame.

5. The racquet frame assembly according to any one of the preceding claims, wherein the crosssection ofthe shaft is either circular or a rounded square cross-section.

6. The racquet frame assembly according to any one of the preceding claims, wherein the frame comprises a plurality of superimposed layers of reinforcing fibres impregnated and moulded in a suitable epoxy resin.

7. The racquet frame assembly according to Claim 6, wherein localized reinforcement is positioned in the throat, crown and shoulders ofthe racquet frame.

8. A sports racquet comprising a frame including a shaft joined to one end of a head by a throat, the other end ofthe head defining a crown, the frame being moulded in reinforced plastics so that the cross-section through the head oftheframe presents a wholly convex profile to the exterior, the head having a peripheral array of spaced apart string holes extending radially through the cross-section of the head; a bumper strip having a concave inner surface fitting closely on the convex exterior of the crown of the head, the bumper strip having an array of radially extending holes spaced to correspond to the spacing of the string holes in the head, the exterior surface of thebumperstrip including agrooveorgroovesthat extends over the holes, and racquet strings threaded through the holes in the frame and the bumper strip with the groove or grooves in the bumper strip ensuring that the strings do not project radially outside the exterior surface of the bumper strip.

9. A racquet frame assembly substantially as described herein with reference to and as illustrated in the accompanying drawings.