GB2241464A

GB2241464A - Moulding rackets

Info

Publication number: GB2241464A
Application number: GB9004567A
Authority: GB
Inventors: Steven Andrew Jordan; Matthew Emmett Sayer; David Jones
Original assignee: Cinpres Ltd
Current assignee: Cinpres Ltd
Priority date: 1990-03-01
Filing date: 1990-03-01
Publication date: 1991-09-04
Also published as: GB9004567D0

Abstract

A racket frame is manufactured using a mould 28 having a mould cavity 29 defining the required frame, the cavity extending along a first handle forming portion 15 around a head forming portion 13 and along a second handle forming portion 16 extending alongside the first handle forming portion 15. Plastics material and fluid (gas or liquid) are injected into the handle forming portion 15 to fill the handle forming portion 15, the head forming portion 13 and the second handle forming portion 16 with plastics material having a fluid filled core, to form a plastics moulded frame. The head may include a separately moulded or an integrally moulded throat member to complete the perimeter of the head. The fluid may be injected simultaneously with the plastics material or sequentially thereto. <IMAGE>

Description

THE MANUFACTURE OF RACKETS AND RACKET FRAMES This invention relates to the manufacture of rackets and frames therefor.

A racket for ball games such as tennis, rackets, squash, badminton and the like comprises a racket frame having a head strung with cat-gut or nylon and a handle. The frame was generally formed of wood, but is now more normally formed of metal or carbon fibre filled polymer.

By conventional injection moulding, it would not be possible to mould a racket frame which combines the required cross-sectional dimensions and strength.

An object of the invention is to mould a racket frame by the technique of fluid assisted injection moulding.

According to the invention there is provided a method of manufacturing a racket frame comprising the step of using a mould having a mould cavity defining the required frame, the cavity extending along a first handle forming portion around a head forming portion and along a second handle forming portion extending alongside the first handle forming portion, the method further comprising the step of injecting plastics material and fluid into the first handle forming portion of the mould cavity to fill the first handle forming portion, the head forming portion and the second handle forming portion of the mould cavity with plastics material having a fluid filled core, to form a plastics moulded frame. The fluid may be introduced simultaneously with or sequentially to the introduction of the plastics material into the mould cavity.

Preferably the fluid is a gas, e.g. nitrogen.

The method may include the step of venting or draining the core before opening the mould to remove the moulded frame.

The plastics material and the fluid may be introduced into the first handle forming portion through the same or separate inlets therein. The or each inlet is preferably at or adjacent the end of the first handle forming portion which is remote from the head forming portion.

The two handle parts may be fixed together after removal of the moulded frame from the mould cavity. Alternatively, the two handle parts may be moulded to a common insert within the mould cavity whereby the handle parts are fixed together during the moulding process.

In one embodiment of the invention the moulded frame is assembled with a separately moulded throat member which completes the perimeter of the head.

Alternatively the moulded frame head may include an integrally moulded throat member which completes the perimeter of the head, the throat member being moulded in two portions of the mould cavity, which are connected respectively to opposite sides of the head forming portion, the two parts of the throat member being interconnected either during the moulding process or after removal of the moulded frame from the mould cavity.

Preferably the plastics material is a fibre filled polymer.

The invention also provides a racket frame moulded by a process as defined above.

The two handle parts preferably include interconnecting means for at least locating one part relative to the other part.

The interconnecting means may be a snap fit or held together by, for example, pins or adhesive, or by a sleeve surrounding both parts.

The two handle parts may have a cushioning member therebetween to which the handle parts are attached or moulded.

Preferably the handle parts have an outer covering of strip material wound thereon.

The invention further provides a racket comprising a racket frame as defined above including stringing holes around the periphery of the head and being strung through said holes.

By way of example, specific embodiments in accordance with the invention will be described with reference to the accompanying drawings in which: Figure 1 shows a tennis racket in accordance with the invention; Figure 2 illustrates diagrammatically the moulding of the main frame of the racket of Figure 1 within a mould cavity by gas-assisted injection moulding; Figures 3 and 4 are sections along the lines 3-3 and 4-4 respectively in Figure 1; Figure 5 is a section through the handle of the racket frame along line 5-5 in Figure 1; Figure 6 is a section through the throat member of the racket frame along line 6-6 in Figure 1; Figures 7 to 10 show alternative sections to Figures 3 and 4; Figures 11 and 12 are sectional views through different handle constructions; Figure 13 illustrates an integrally moulded throat member; and Figure 14 is a section along line 14-14 in Figure 13.

Referring to Figures 1 to 6 of the drawings, a tennis racket 10 comprises a main frame 11 having a head 13 which is strung with cat-gut or nylon stringing 14 in known manner, and a straight handle 12.

The main frame 11 is a moulding of thermoplastics material and includes the head 13 and the handle 12 which is divided longitudinally into two parts 15, 16, or in this embodiment halves, extending alongside one another, each half being joined separately to the head 13. The head 13 has transverse stringing holes 17 at the required intervals around its periphery and an external longitudinally extending groove 18 for protection of the stringing during use of the racket. The two basic cross-sections of the main frame 11 in and between the locations of the stringing holes 17 are shown in Figures 3 and 4 respectively. From these cross-sectional views, it will be appreciated that the moulded frame is hollow and contains a continuous internal channel 19 which will be referred to in detail below.It will also be appreciated that the cross-section around the periphery of the head 13 and in the two lengths of the frame joining the handle halves 15, 16 respectively to the head 13, may be variable. For example, there may be smooth variations or stepped variations in cross-sectional area. Indeed, it may be desirable that the crosssectional area of the moulded lengths interconnecting the head and the handle halves is generally greater than that around the periphery of the head of the frame.

In this embodiment, the two halves 15, 16 of the handle 12 have an interlocking tongue and groove construction 20 which snap fit together (Figure 5).

At the end of the handle is a cap member 25. In addition, an external strip 23, e.g. of leather or towelling material, is wound spirally around the handle and attached thereto at each end by a band of sticky tape 24 or other convenient means.

A curved throat member 26 completes the perimeter of the head 13. In this embodiment, the throat member 26 is a separately moulded member of solid cross-section (Figure 6) except for the stringing holes 17, which at each end has a joint connection with the adjacent part of the head 13 of the frame 11. Thereby, when the handle halves 15, 16 are fixed together, the throat member 26 is rigidly locked into the main frame 11 and is unable to move longitudinally of the racket 10 in either direction.

To manufacture the racket 10, the main frame 11 is moulded from any desirable thermoplastics material by employing the technique of fluid assisted injection moulding. By means of this technique, in this embodiment, gas, e.g. nitrogen, under pressure is injected into plastics material introduced into a mould cavity 29 of a split mould 28 to create a gas filled core 19 within the plastics material (Figure 2). The gas applies an internal pressure within the plastics material which serves to cause the plastics material to fill the mould cavity 29 and which is maintained to hold the plastics material positively against the interior mould surfaces as the plastics material solidifies and cools until the moulding can itself sustain the form dictated by the mould surfaces. The core 19 is then vented before the mould 28 is opened to remove the hollow moulded frame 13. Alternatively, the fluid may be a liquid which is injected under pressure into the plastics material to create a liquid filled core. The core would then be drained before the mould is opened. The fluid, whether gas or liquid, may be introduced simultaneously with or sequentially to the introduction of the plastics material into the mould cavity 29.

In this embodiment the plastics material is a fibre filled polymer. Maximum strength resulting from the reinforcing presence of the fibres is achieved when the fibres are directed longitudinally of the mould cavity. Weak points in the moulded frame are also caused by any weld lines or solid sections resulting from plastics material meeting after flowing together from opposite directions, and at the entry point of the fluid. It is thus desirable to concentrate these weak points within the handle portion 12, and as near its free end as possible, which is the portion of the racket frame least vulnerable to fracture during use of the racket. By the process of the invention such weak points are kept away from the head 13 of the frame.

As illustrated in Figure 2, the mould cavity 29 of the mould 28 (one part of which is shown) has in the direction of flow which is described below a first handle forming portion defining handle half 15 leading into a head forming portion defining the head 13 and a second handle forming portion leading from the head forming portion and defining the other handle half 16, the second handle forming portion extending alongside the first handle forming portion. The plastics material and the fluid are introduced together or sequentially at the same location or at different locations into the first handle forming portion of the mould cavity 29 defining the handle half 15, for example, at one of the arrowed positions at or adjacent the end of the first handle forming portion of the mould cavity which is remote from the head forming portion.

Indeed it will be appreciated that the fluid may be introduced at a different position from the position at which the plastics material is introduced into the mould cavity. In this case, when the plastics material has filled the mould cavity at least to the extent of passing the fluid introduction position, the fluid may be injected into the plastics material to create the core therein. The two handle forming portions of the mould cavity 29 essentially preclude the passage of fluid therebetween. A thin web of plastics material may be allowed to be formed to join the handle halves 15, 16 together but the entry of fluid into such a junction is to be avoided, the web thereby remaining solid plastics material.

By this design of mould cavity 29, the plastics material and fluid enter separately or together the first handle forming portion defining the handle half 15, then each flow simultaneously or sequentially in the same direction shown by the arrows in Figure 2 around the head forming portion defining the head 13, and finally fill the second handle forming portion defining the other handle half 16. If the fluid is introduced at one of the arrowed positions spaced from the end of the first handle forming portion which is remote from the head forming portion, the resultant fluid containing channel 19 will be created in both directions from the fluid entry position and may conveniently be intended to extend to a similar distance from the free end of the second handle forming portion. Alternatively, the fluid may enter the first handle forming portion through its free end.Likewise, the fluid containing channel 19 may extend to the free end of the second handle forming portion by permitting, during the moulding process, plastics material to be emitted through the free end of the second handle forming portion. If the plastics material is introduced through the free end of the first handle forming portion, the fibres will advantageously extend longitudinally of the moulded frame throughout its length for maximum strength.

The stringing holes 17 are formed by cores during the moulding process.

The moulded main frame 13 is assembled with the separately moulded throat member 26 and the two handle halves 15, 16 are snap fitted together. The frame is then complete. Subsequently, the cap member 25 is attached to the free end of the handle 12, and the handle is bound by the strip 23,the ends of which are held by the tape 24. The frame is then strung in conventional manner ready for use.

Alternative cross-sections of the head 13 of the frame 11 are illustrated in Figures 7 to 10. In the embodiment of Figures 7 and 8, the external groove 18 is omitted, but the general cross-section remains rectangular. Figures 9 and 10 concern an embodiment in which at least the head of the frame 11 has a generally oval cross-section. In each embodiment, in a similar manner ta the cross-sections of Figures 3 and 4, the cross-sectional area may vary at different positions around the periphery of the head and in the lengths joining the handle halves to the head.

If desired, instead of snap-fitting the handle halves 15, 16 together, the handle halves may be fixed together by adhesive or pins pushed through transverse aligned holes formed by cores during the moulding process. Additionally or alternatively, the handle halves 15, 16 may have a cushioning spacer member 21 therebetween which is glued to each half of the handle or which comprises an insert member in the mould around which the handle halves are moulded during the moulding process (Figure 11). In a further embodiment (Figure 12), the two handle halves 15, 16 are held together by an external sleeve 22 which has tongue and groove connections 27 with the handle halves and which is pushed over the moulded handle portion from its free end. Conveniently, the sleeve 22 would have an integral end wall so that a separate end cap member 25 is unnecessary.The sleeve 22 is slid over the handle halves 15, 16 prior to the application of the outer strip 23.

Alternatively, in another embodiment not shown, the two handle halves 15, 16 may be held together by an external sleeve which is moulded over the handle halves in a subsequent moulding operation.

Figures 13 and 14 concern an embodiment in which the racket frame has an integrally moulded throat member 30. As shown, the throat member is divided centrally into two parts 31, 32. Each part is joined to the respective side of the head 13, and interlocking tongue and groove connecting means 33 between the parts are snap-fitted together when the handle halves 15, 16 are interconnected. In another embodiment, the throat member parts 31, 32, like the handle halves 15, 16 of Figure 11, may be moulded around an interconnecting member during the moulding process. The throat member parts 31, 32 in a further embodiment, may be joined together, subsequent to the moulding operation, by a clip which may be moulded or formed of metal. In each case, the mould cavity 29 includes two separate throat forming portions which are connected respectively to opposite sides of the head forming portion of the mould cavity (Figure 13). Fluid within the plastics material will only create a core or channel 19 in each throat forming portion extending from the respective side of the head forming portion of the mould cavity. The two fluid filled cores or channels 19 are unable to meet due to the division between the throat forming portions. The fluid cannot thus enter the far side of the head forming portion via the throat forming portions of the mould cavity.

The invention is not restricted to the specific details of the embodiment described above. For example, the method of manufacture and the construction of racket frame and racket is equally applicable to rackets for other uses, e.g. rackets, squash, badminton and like sports.

Claims

1. A method of manufacturing a racket frame comprising the step of using a mould having a mould cavity defining the required frame, the cavity extending along a first handle forming portion around a head forming portion and along a second handle forming portion extending alongside the first handle forming portion, the method further comprising the step of injecting plastics material and fluid into the first handle forming portion of the mould cavity to fill the first handle forming portion, the head forming portion and the second handle forming portion of the mould cavity with plastics material having a fluid filled core, to form a plastics moulded frame.

2. A method as claimed in Claim 1, wherein the fluid is a gas.

3. A method as claimed in Claim 1 or Claim 2, including the step of venting or draining the core before opening the mould to remove the moulded frame.

4. A method as claimed in any one of the preceding claims, wherein the plastics material and fluid are introduced into the first handle forming portion through the same or separate inlets therein.

5. A method as claimed in Claim 4, wherein the or each inlet is at or adjacent the end of the first handle forming portion which is remote from the head forming portion.

6. A method as claimed in any one of the preceding claims, wherein the two handle parts are fixed together after removal of the moulded frame from the mould cavity.

7. A method as claimed in any one of Claims 1 to 5, wherein the two handle parts are moulded to a common insert within the mould cavity whereby the handle parts are fixed together during the moulding process.

8. A method as claimed in any one of the preceding claims, wherein the moulded frame is assembled with a separately moulded throat member which completes the perimeter of the head.

9. A method as claimed in any one of Claims 1 to 7, wherein the moulded frame head includes an integrally moulded throat member which completes the perimeter of the head, the throat member being moulded in two portions of the mould cavity, which are connected respectively to opposite sides of the head forming portion, the two parts of the throat member being interconnected either during the moulding process or after removal of the moulded frame from the mould cavity.

10. A method as claimed in any one of the preceding claims, wherein the plastics material is a fibre filled polymer.

11. A racket frame moulded by a method in accordance with any one of the preceding claims.

12. A racket frame as claimed in Claim 11, wherein the two handle parts include interconnecting means for at least locating one part relative to the other part.

13. A racket frame as claimed in Claim 12, wherein the interconnecting means are a snap fit.

14. A racket frame as claimed in Claim 12, wherein the handle parts are held together by pins or by adhesive.

15. A racket frame as claimed in Claim 12, wherein the two handle parts are held together by a sleeve surrounding both parts.

16. A racket frame as claimed in Claim 11, wherein the two handle parts have a cushioning member therebetween to which the handle parts are attached or moulded.

17. A racket frame as claimed in any one of Claims 11 to 16, wherein the handle parts have an outer covering of strip material wound thereon.

18. A racket comprising a racket frame as claimed in any one of Claims 11 to 17, including stringing holes around the periphery of the head and being strung through said holes.

19. A method of manufacturing a racket frame or racket substantially as hereinbefore described.

20. A racket frame or racket substantially as hereinbefore described with reference to and as shown in the accompanying drawings.