GB2283196A - Fibre reinforced parison for moulding tennis racquet frames - Google Patents

Abstract

Method for embodying a tennis racquet frame by moulding a tubular flexible element impregnated with resin, which comprises the following steps: - impregnating reinforcing fibers with resin; - winding said impregnated reinforcing fibers around a flexible sheath placed onto a rigid rotary-driven mandrel, caracterised in that: &cirf& the flexible tubular element has a length L1 comprised between 1200 and 1800 mm, &cirf& the impregnated reinforcing fibers windings laid over the flexible sheath have a total weight P comprised between 150 and 250 g, and are laid with angles contained between 18 DEG and 42 DEG with relation to the mandrel axis. The weights and lengths of the windings on the sheath are comprised within values indicated in the following table: Layers Length of layers Coefficients Percentage of the a, b, c/L1 total P weight of impregnated fibers L1 L1 58 % to 70 % L2 L2 = L1 x a 72% </= a </= 85% 12 % to 26 % L3 L3 = L1 x b 50% </= b </= 62% 8 % to 20 % L4 L4 = L1 x c 16% </= c </= 33% 2 % to 8 % In the preferred embodiment the finished tubular element is removed from the mandrel placed in a mould and inflated to take the form of the mould (i.e. a tennis racquet frame). <IMAGE>

Description

- Method for embodying a tennis racket frame from a tubular flexible element of resin impregnated fibers to be moulded.

The present invention concerns a method to manufacture flexible tubular elements from resin impregnated fibers, these flexible elements are to be moulded to form a tennis racket frame, the mechanical characteristics of which vary along all points to be adapted to the player's desires.

The purpose of this invention is to offer a specifically rapid low cost method since it can be used repeatedly from a filamentary winding on machine with digital control.

The process presents both the method and the values within which the windings of impregnated fibers must be performed : their lengths, their weights and their angles with the longitudinal axis of the mandreL The invention provides a method which consists of winding by superimposed layers whose number vary inside certain weight values, impregnated reinforcing fibers of glass, carbon, aramid or any other fibers impregnated with synthetic hardening resins around a flexible sheath which covers a rigid mandrel to be subsequently removed after the filamentary winding operation has been carried out on an automatic machine. If desired, the synthetic resins used may be tinted in different colours.

Indeed, the inventor has discovered that, surprisingly, to obtain after a moulding operation according to the mentioned method, a tennis racket frame adapted to the most various conditions of use, the manufacturing parameters must compulsorily obey to the following conditions: - the flexible tubular element must have a length L1 comprised between 1200 and 1800 mm, - the impregnated reinforcing fibers windings laid over the flexible sheath must have a weight P comprised between 150 and 250 g, - the impregnated fibers windings must be laid over with angles contained between 180 and 420 with relation to the mandrel axis.

The said impregnated fibers windings must be such as: a first winding is performed over the said L1 length of the tubular flexible element and has a weight contained between 58 % and 70 % of the total P weight, a second winding is performed over a L2 length, symmetrical to the middle of the L1 length of the tubular flexible element, comprised between 72 % and 85 % of L1, the said second winding having a weight comprised between 12 % and 26 % of the total P weight, a third winding is performed over a L3 length, symmetrical to the middle of the L1 length of the tubular flexible element, contained between 50 % and 62 % of L1, the said third winding having a weight comprised between 8 % to 20 % of the total P weight, and a fourth winding is performed over a L4 length, symmetrical to the middle of the L1 length of the tubular flexible element, comprised between 16 % and 33 % of L1, the said fourth winding having a weight comprised between 2 % and 8 % of the total P weight.

Thus, the method makes it possible to wind according to variable angles preimpregnated fibers with resins tinted in different colours. Finally, the flexible tubular element made of polychrome impregnated fibers is separated from the mandrel and introduced into a mould cavity.

In the latter case, air or a neutral gas is then introduced under high pressure into the inflatable flexible element for plating the impregnated fibers onto the sides of the mould and then heated so as polymerize the pre-impregnated resin.

It shall be observed that the method of the invention makes it possible to vary at will repetitively and cheaply the bending and/or resistance qualities on crushing of the tubular element.

In fact, in this instance it is possible to determine the winding pitches, their number, length and superposition and the nature of the impregnated fibers. A strip of unidirectionnal fibers forming an undirectionally oriented strip of fibers may be placed along the generating line of the sheath thus providing this line with greater rigidity after the resin has solidified.

The above-mentioned object and advantages of the invention, as well as other advantages, shall be readily understood on reading the following description given by way of non-restrictive example with reference to the accompanying drawings in which: - figures 1 to 3 show a diagrammatical view of various embodiments of the method for preparing a flexible tubular element according to the invention, and - figure 4 shows very diagrammatically an example of a tubular flexible fibers element obtained according to the invention by successive windings in order to realise a tennis racket frame; - figure 5 is a view similar to figure 4 showing another example of tubular flexible fibers element obtained according to the invention to realise a tennis racket frame, and - figure 6 is a flat view of the figure 4 flexible fibers element.

With reference to figure 1, two juxtaposed impregnated fibers of different colours are wound, the first 10a being made of black carbon impregnated with resin, the second lOb being made of glass fiber whose impregnated resin is tinted in red making fibers red.

This first winding is embodied around a sealed inflatable cellophane hose 11 first introduced onto a hollow driving mandrel 12 and to be subsequently removed after several layers of fibers 10a and lOb have been wound and superimposed.

To facilitate the operation for uncovering the hollow mandrel 12, the latter is perforated with holes a allowing air under pressure to pass releasing the inflatable casing plated by the pressure of the wound threads 10a and 10b.

With reference to figure 2, it can be seen that on the tubular element being prepared, the fibers 15 are placed at 15a, 15b and 15c according to the various angles obtained by solely varying the rotational speed of the driving hollow mandrel 12, whereas the presentation of the fibers along the mandrel is effected at constant speed.

This figure also shows unidirectional fibers 14, made of carbon for example, which have been placed after the winding up operation has stopped, and which are clamped onto the cellophane sheath between the fibers 13 and the fibers 15 wound after the winding has stopped. The unidirectional fibers 14 are thus kept in place along the complex and, after polymerization, shall have specific mechanical characteristics.

Figure 3 shows a preferred embodiment variant having the largest number of advantages of the method of the invention. Thus, the hollow mandrel 16, perforated with holes a intended to be used to uncover the composite tubular element is covered with a resistant flexible sheath 17 made of cellophane or polypropylene for example, two juxtaposed fibers 18, 19, one of which being made of carbon and the other tinted glass, are wound around the mandrel 16. The fibers 19 are wound onto one central portion of the complex during four to-and-fro passages.

The rotational speed of the mandrel 16 has varied so that the angles at which the fibers 18, 19 are deposited with respect to the axis of the mandrel 16 are different, as specified on figure 2.

When being superimposed on the winding of the fibers 18, fibers 20 are wound all along the sheath so as to finish the composite tubular element. It can be seen that in this instance the mechanical characteristics at the extremities of the tubular element differ from those at its centre.

This disposition of fibers superimposed at certain locations of the tubular element and moreover according to different angles, is particularly advantageous, in manufacturing a tennis racket, so as to vary the resistance according to the zones as all the points of the racket frame are not stressed by comparable forces.

Thus to produce tennis rackets of which mechanical, weight, aspect and prices characteristics will cover as a whole the users' wishes, one may advantageously use the process according to the following examples: Example 1: In view to manufacturing a light and very stiff tennis racket, carbon fibers are impregnated with epoxyde resin so that 38 % of the total weight carbon fibers epoxyde resin is made of resin, then a 200 g tubular flexible fibrous element is realised before being moulded to produce a tennis racket frame. These 200 grammes include the weight of terminal windings which are wound perpendicularly to the axis to prevent impregnated fibers from sliding along the sheath. These terminal windings which are situated at the extremity of the racket handle will be trimmed after moulding.

A tubular flexible element is obtained in winding around a mandrel the said impregnated fibers over an inflatable polyamide 6.6 type sheath having a 60 micro thickness, weighing 4,5 g/m with a 19 mm diameter and a 1650 mm length. To that end, as represented on figures 4 and 6, a first winding under a 250 angle with relation to the mandrel axis is made so that 130 g of impregnated fibers are laid over the L1 length of the sheath that is to say 65 % of the total 200 g weight of the tubular element to be obtained. Then, over the first winding, under a 220 angle with relation to the mandrel axis, over a L2 length equal to 80 % of L1, that is to say 1320 mm, and spread over symetrically to the middle of the L1 length, a second winding is laid until reaching 30 g that is to say 15 % of the total 200 g weight. Then over the second winding, under a 270 angle over a L3 length equal to 910 mm corresponding to 55 % of L1, a third winding is wrapped until it reaches 34 g that is to say 17 % of the total 200 g weight.

Then over this third winding, under a 220 angle, over a 300 mm L4 length equal to 18 % of L1, is laid a fourth winding weighing 6 g corresponding to 3 % of the total weight.

Finally, after injecting air into the inflatable sheath, the tubular flexible element is separated from the mandrel.

On the following synoptic table n 1 the caracteristics of each successive layer of continuously wound carbon-resin filaments forming the flexible tubular element are presented.

Tablen0l

Layers Length of layers (mm) I Angles of fibers layer Weight of fibers layers g %ofthetotal L1 1650 =L1 250 130 65 % L2 1310 = L1 x 80 % 220 30 15 % L3 910 = L1 x 55 % 27 34 17 % L4 300 =L1x 18 % 220 6 3 % 200 100 iso Example 2 To realise a less rigid but heavier tennis racket frame (250 g weight including weigh of the terminal windings as seen in example nO 1) the flexible tubular element is made from simultaneously wound impregnated carbon fibers with glass fibers also embedded in an epoxy resin. These glass fibers are tinted with green colour to endow the racket with an original cosmetic to that end, as represented on figure 5, over an inflatable sheath comparable to the sheath used in example 1 but having a 1620 mm length, a first carbonglass-resin winding is wound over the total L1 length with a starting 270 angle regularly varying to reach 180 in the middle of the sheath and coming back to 270 when reaching the second end of the inflatable sheath. This first winding of impregnated fibers weighs 150 g corresponding to 60 % of the total 250 g.

Then a second winding of the same carbon-glass-resin composite is realised under a 360 angle over a 940 mm = L3 length corresponding to 58 % of the L1 length until reaching 45 g that is to say 18 % of the total 250 g weight.

As shown on figure 12, this second winding is made of two symmetric parts, L3a and L3b, directly wound over the first winding and of a central L3C part which, as described further, will be wound around the external L4b part belonging to a third winding of fibers. Then over the first L1 central part winding an inside part L4a of the third winding such as L4a + L4b = L4 is wound under a 240 angle over a 535 mm length (33 % of L1) weighing 10 grammes that is to say 4 % of the total 250 grammes weight.

Then a fourth winding always of the same composit is performed, under a 24 angle, over a 1361 mm length (24% of L1) weighing 45 grammes that is to say 18 % of the total weight.

Over this fourth winding the L4b complementary third L4a winding part is wound, then over this last one the complementary L3C part to the second L3a and L3b parts of the second winding is performed.

The following table sums up the weights, lengths, angles repartitions of the various windings.

Table n 2

Layers Length of layers (mm) Angles of fibers layers Weight of fibers layers g % of the total L1 1620 = L1 180to270 150 60 % L2 1361 = L1 x 84 % 240 45 18 % L3a+L3b+ L3c + L3d 940 = L1 x 58 % 360 45 18% L4a + L4b 535 = L1 x 33 % 230 10 4% 250 100 % In this last example it is clear that the various windings forming the different layers are interwoven similar experiences have been performed on very numerous examples so that it has been demonstrated that to realise a tennis racket frame of good quality made of impregnated composite fibers it was enough to realise a plurality of fibers windings weighing between 150 grammes and 250 grammes under angles contained between 180 and 420 with relation to the longitudinal axis of the mandrel, these windings having weights and covering the lengths indicated in the following table nO 3.

Table n03

Layers Length of layers Coefficients Percentage of the total P a, b, c / L1 weight of impregnated fibers L1 L1 58 % to 70 % L2 L2 =L1xa 72% < a < 85% 12 % to 26 % L3 L3 = L1 x b 50 % # b # 62 % 8 % to 20 % L4 L4 =L1xc 16 % # c # 33 % 2% to 8%

Claims (5)

1. Method for embodying a tennis racket frame by moulding a tubular flexible element impregnated with resin, which comprises the following steps: - impregnating reinforcing fibers with resin; - winding said impregnated reinforcing fibers around a flexible sheath placed onto a rigid rotary-driven mandrel, caracterised in that: the flexible tubular element has a length comprised between 1200 and 1800 mm, the impregnated reinforcing fibers windings laid over the flexible sheath have a weight P comprised between 150 and 250 g, the impregnated fibers windings are laid over with angles contained between 18 and 420 with relation to the mandrel axis.

The said impregnated fibers windings comprising: a first winding performed over the said L1 length of the tubular flexible element and having weight contained between 58 % and 70 % of the total P weight, a second winding performed over a L2 length, symmetrical to the middle of the L1 length of the tubular flexible element, comprised between 72 % and 85 % of L1, the said second winding having a weight comprised between 12 % and 26 % of the total P weight, a third winding performed over a L3 length, symmetrical to the middle of the L1 length of the tubular flexible element, contained between 50 % and 62 % of L1, the said third winding having a weight comprised between 8 % to 20 % of the total P weight, and a fourth winding performed over a L4 length, symmetrical to the middle of the L1 length of the tubular flexible element, comprised between 16 % and 33 % of L1, the said fourth winding having a weight comprised between 2 % and 8 % of the total P weight.

2. Method according to claim 1, caracterised in that, at least one of said windings is divided into several parts which are differently interwoven between other windings.

3. Method according to claim 1, caracterised in that prior to winding the impregnated reinforcing fibers, the latter are coated with resins tinted in different colours giving the obtained tubular flexible element a woven multicoloured appearance.

4. Method according to claim 1, caracterised in that a strip of contiguous fibers oriented along a generating line of said flexible sheath is cramped between the latter and the windings of the impregnated reinforcing fibers, thus forming a punctual reinforcement of the tubular flexible element.

5. Tennis racket frame caracterised in that it is obtained with the method according to any one of claims 1 to 4.