EP0055184A1 - Racket frame, particularly for tennis, made from polymeric synthetic material strengthened with reinforced fibres, and method for its manufacture - Google Patents

Abstract

Racket frame of the essentially reinforced box-structure type, characterised in that at least its two plane faces parallel to the plane of the stringing have been formed from panels (3, 5, 6, 7) of preimpregnated reinforced fibres (4), cut out from layers (1) of such fibres (4) and which, after polymerisation and finishing, are joined without an interruption of continuity to the lateral sides or edges (8, 9) of the said structure. <IMAGE>

Description

The present invention relates first of all to a racket frame, in particular for tennis game, made of polymerized synthetic material reinforced with resistant fibers, and more particularly a frame of the type with a resistant structure essentially in a box, with or without internal reinforcement ribs. , this frame being of the general type comprising a basket intended to receive a taut rope, and a handle connected to the basket by an intermediate part or core.

By "essentially box-like resistant structure" is meant to indicate that the resistant part of the racket frame structure is hollow, that is to say tubular, with or without internal reinforcing ribs.

Tennis rackets are already known, the frame of which is constituted in this way, with, in particular, as resistant fibers, glass fibers. To make the tubular structure in question, there is in a mold, and depending on the shape of the outline to be given to the racket, sheaths or tubular braids of fibers, containing an inflatable tube, after which the mold is closed, of the synthetic material Compressed air is injected into the inflatable tubes to impregnate the braids, to expel the excess synthetic material, and finally this is heated to ensure the polymerization of the synthetic material. There are thus obtained frames of the general type mentioned at the beginning, that is to say composite frames made of a synthetic material - epoxy resin or the like, impregnating reinforcing fibers - glass fibers, carbon fibers, boron fibers, etc.

Snowshoes of this type give good results, but the resistant fibers do not have the optimal direction at any point of the frame. Indeed, the braided sheaths are made of fibers which always have the same orientation relative to the general axis of the sheath; when they cross at 90 °, they make an angle of 45 ° with respect to said axis. Now, this axis follows exactly the shape of the contour of the racket, and therefore follows an oval course in the part constituting the basket, and a course also curved, concave, in the intermediate part connecting this basket to the handle, which constitutes the only straight part. As a result, in the parts of the racket which are the most critical, in terms of mechanical strength, that is to say which undergo the greatest stresses during the game, the fibers follow very diverse directions , which are found only fortuitously and rarely correspond to the optimal direction in the considered zone of the frame, which leads to the frequent appearance of micro-cracks.

Thus, for an equal weight of reinforcing material, such a racket will not have the ideal mechanical qualities, such as could be obtained with a racket in which the resistant fibers are oriented in an adequate manner at all points.

The same kind of drawbacks arise with rackets of a different type, in which a woven or non-woven strip of reinforcing fibers is wound in a helix around an inflatable tube; the orientation of the fibers is then quite different, but it is just as diverse as in the case of braided sheaths, and the fibers, there either, do not have the optimal orientation in every respect.

One of the aims of the invention is to remedy these drawbacks of known snowshoes, and to control, to a large extent, the orientation of the fibers in the different areas of the frame.

The object of the present invention is also to obtain a simplified manufacturing process, allowing production in large series and at lower cost; it is also, in general, to obtain rackets, in particular for tennis, which have qualities of mechanical resistance notably increased, without increase in weight, and which make it possible to obtain a better striking of the ball, with greater accuracy of the trajectory, as well as a reduction in vibrations and fatigue of the player.

To this end, in accordance with the invention, at least for the most part, the faces or sides of the box constituting the resistant structure by cutting panels or strips of suitable shapes from a sheet of resistant prepreg fibers. It will then suffice to position these panels or bands in the mold to constitute the hollow resistant structure, around inflatable tubes, then to implement the known operations of inflating said tubes, then of polymerization, with however the economy of the operation. for introducing synthetic material into the mold.

By operating the cuts in directions determined relative to that (s) in which or which extend said fibers in the web, it will be possible to obtain different panels or cut strips whose fibers are oriented in the optimal direction, depending on the positioning panels or strips in the frame. We are thus in control of the orientation of the fibers at each location of the frame, and we can therefore freely choose the optimal orientation of the fibers according to the type of force or vibration undergone by the frame at this location.

We will also obtain great flexibility as to the ability to provide reinforcements or extra thicknesses in certain particularly stressed areas. It will suffice to have in these areas several thicknesses of panels or strips.

It should be clarified here that by the term "panels" is meant above all to designate parts cut from a sheet of fibers, and which may have a particular shape, for example substantially the shape, seen in plan, of a racket. or a part of a tennis racket, these panels therefore being intended to constitute, in whole or in part, the upper and lower faces of the racket, parallel to the plane of the string. The term "bands" is intended to denote above all elements with parallel edges, of fibers -woven or not more particularly intended to constitute the edges or sides of the racket, that is to say to extend, according to the sides of the cabinet, perpendicularly to said panels; these strips can also be cut from sheets of pre-impregnated fibers, or be made up properly of strips delivered as is, therefore precut. With such bands, we can anyway also perform on the edges of the frame, and in the most stressed places, localized thicknesses.

That said, a racket frame according to the invention can therefore be essentially characterized in that at least its two flat faces parallel to the plane of the rope were made from panels of strong prepreg fibers, cut from sheets of such fibers and which, after polymerization and finishing, are connected without solution of continuity to the lateral sides or edges of said structure.

In accordance with the above, it can at the same time be characterized in that the edges of said structure were formed from narrow plies or strips of resistant prepreg fibers, or from strip-shaped panels cut from plies of such fibers.

Such a frame can also be distinguished in that the panels and / or strips of fibers are arranged in several layers.

Some of said layers, at determined locations in the structure, may only extend along part of it, the structure thus being with localized reinforcements.

These reinforcements will in principle be located in particular in said intermediate part between the basket and the handle and possibly at the top of the basket and towards the free end of the handle, locations which are usually the most stressed during the game.

It will be even more particularly advantageous to provide, in accordance with the invention, that the frame comprises, as resistant fibers, unidirectional fibers, in particular as regards said faces parallel to the plane of the rope. It will then be particularly appropriate to ensure, at the time of cutting, that said faces parallel to the plane of the rope comprise panels of strong unidirectional fibers parallel to the axis of the handle (general axis of the frame).

This will give a racket frame having a very high resistance to longitudinal bending, that is to say with respect to the forces which are exerted essentially in the plane of axial symmetry perpendicular to the plane of the rope. Indeed, then, all the fibers of the upper and lower faces of the racket, and whatever their location, will be oriented parallel to the axis of the handle, that is to say to the general axis of the frame, and will thus be able to oppose, in an entirely optimal manner, the deformations in the direction of said efforts. In this way, the high modulus of elasticity of the resistant fibers currently on the market, in particular glass fibers, carbon, boron, kevlar, etc., is ideally used.

We will get at the same time a racket frame whose flexural vibrations, during the game, will be of considerably reduced amplitude, which will decrease the fatigue of the player, and the usual unpleasant impression felt in the elbow. of these vibrations.

As with these panels of the upper and lower faces of the frame, provision may also be made for the side edges or sides of the resistant box structure to have unidirectional resistant fiber bands or panels extending in planes parallel to said plane of the rope. .

Again, this is a provision that was never encountered in the rackets of the prior art, as is apparent from the explanations given at the start.

This arrangement is also extremely advantageous, in that it gives the racket frame, in particular the oval or basket part, a very high rigidity with respect to static (tension of the rope) and dynamic (vibrations to the impact of the balls), in the plane of the rope, along the two main axes of the basket, as a result of the hoop effect, exerted by the continuous fibers of the edges, along the entire periphery of the frame. Again, all the fibers work in the optimal direction. This will give you a racket whose contractions during the game and alternative basket elongations, in the plane of the rope, will be considerably reduced, which will reduce the amplitude of the vibrations of the rope, therefore will increase the speed of the balls, and will give them a more precise trajectory.

Although the advantage of the invention is, as we have just demonstrated, particularly clear when using unidirectional fiber panels or strips, cut from sheets of prepreg fibers, it cannot be excluded that, in in some cases, for all or part of the frame, and possibly in combination with unidirectional fibers, woven fiber panels or strips are used, the woven prepreg fiber sheets being at present cheaper than the unidirectional prepreg fiber sheets .

In such a case, provision could advantageously be made for said faces parallel to the plane of the rope to include panels of resistant woven fibers extending at an angle of 45 °, or of a similar value, relative to the axis of the handle ( general axis of the frame).

Similarly, it will also be advisable to provide that said edges of the structure comprise strips or panels of resistant woven fibers extending at an angle of ^± 45 °, or of a similar value, relative to the plane of the rope.

In both cases, an effect will be obtained which, although perhaps less marked than with unidirectional fibers, will be broadly of the same nature, since the effects resulting from the forces exerted along the length of the fibers will be directed essentially in the same directions as with said unidirectional fibers.

In any case, it should be noted that, here again, the woven fibers of the cut panels and constituting the faces of the frame parallel to the plane of the rope may have a constant direction, independent of their position in the frame.

• - la figure 1 est une vue en plan d'une nappe de fibres résistantes préimprégnées unidirectionnelles, montrant, dans le cas de la fabrication d'une raquette de tennis ou analogue, le contour et l'orientation des découpes pour les panneaux des faces du cadre et pour les bandes de ses chants
• - la figure 2 est une vue en plan du même genre, dans le cas où l'on effectue les découpes en question dans une nappe de fibres résistantes préimprégnées tissées, et ceci selon une orientation générale à 45° par rapport aux deux directions orthogonales des fibres ;
• - la figure 3 montre en plan différentes formes possibles de panneaux découpés, par exemple dans une nappe de fibres préimprégnées unidirectionnelles, pour la constitution de tout ou partie des faces du cadre qui sont parallèles au plan du cordage ;
• - la figure 4 est une vue schématique de profil, montrant un exemple possible de superposition de ces différents panneaux pour la constitution desdites faces du cadre qui sont parallèles au plan du cordage, et l'obtention de renforcements localisés ;
• - la figure 5 est une vue en plan schématique d'un cadre de raquette élaboré conformément à l'invention, et montrant un exemple possible de répartition de bandes de renforcements localisés sur les chants ;
• - la figure 6 est une vue schématique en perspective, montrant la disposition, dans un moule de polymérisation, de panneaux et bandes découpés, pour l'élaboration d'un cadre de raquette conforme à l'invention ; et
• - la figure 7 est une vue en coupe transversale du moule supposé fermé, au niveau du manche de la raquette.

An embodiment of the invention will now be described below by way of nonlimiting example, with reference to the figures of the appended drawing, in which

• - Figure 1 is a plan view of a sheet of strong unidirectional prepreg fibers, showing, in the case of the manufacture of a tennis racket or the like, the outline and the orientation of the cutouts for the panels of the faces of the frame and for the bands of his songs
• - Figure 2 is a plan view of the same kind, in the case where the cutouts in question are made in a sheet of resistant pre-impregnated woven fibers, and this in a general orientation at 45 ° relative to the two orthogonal directions of fibers;
• - Figure 3 shows in plan different possible forms of cut panels, for example in a sheet of unidirectional prepreg fibers, for the constitution of all or part of the faces of the frame which are parallel to the plane of the rope;
• - Figure 4 is a schematic profile view, showing a possible example of superposition of these different panels for the constitution of said faces of the frame which are parallel to the plane of the rope, and obtaining localized reinforcements;
• - Figure 5 is a schematic plan view of a racket frame developed in accordance with the invention, and showing a possible example of distribution of reinforcement strips located on the edges;
• - Figure 6 is a schematic perspective view, showing the arrangement, in a polymerization mold, of cut panels and strips, for the development of a racket frame according to the invention; and
• - Figure 7 is a cross-sectional view of the mold assumed to be closed, at the level of the handle of the racket.

It should first of all be noted that the plies of resistant prepreg fibers 1 and 2, shown respectively in FIGS. 1 and 2, can be single plies, but preferably are to be considered as the top ply of a pile containing a certain number of layers, for example of the order of several units or several tens, the cutting tool, of the cookie cutter type or of any other type, then being suitable for making cuts at once over the entire height of said stack. This allows, of course, to obtain by a single cutting operation a large number of panels or strips of prepreg resistant fibers, cut to the desired shape.

In FIG. 1, the lines of the various panels or bands which are intended to be cut from a stack of plies of resistant fibers, for example carbon fibers, prepreg of a synthetic material, have been represented by lines in dashed lines. heat-polymerizable, for example of the epoxy resin type, said fibers being unidirectional.

The contours of panels intended to constitute, over their entire surface, part of the thickness of the upper and lower faces of the resistant box-shaped structure of a snowshoe frame, the general axis of said frames is thus referenced in 3. contours 3 (axis of the handle) being oriented exactly in the direction of the unidirectional fibers which, in order not to overload the design, are represented, in the sheet, only in certain locations, such as 4.

We have also shown, in 5, 6 and 7, other contours for the constitution of localized reinforcement panels of the two aforementioned faces of the frame. It can be seen in FIG. 1 that the contour 5 is intended to constitute a reinforcement panel for the lower part of the basket and the intermediate part between the latter and the handle, that the contour 6 is intended for constituting a reinforcement panel, only of this intermediate part, and that the contour 7 is intended to constitute a reinforcement panel for the top of the basket. We see that these contours 5 to 7 also have a general orientation coinciding with the direction of the unidirectional fibers 4.

Finally, the contours of different bands intended to constitute all or part of the edges of said box structure of the frame have been referenced at 8. It can be seen that provision has been made in the sheets 1 for cutting strips of different lengths, the longest being intended to constitute the outer edge of the box, that is to say to extend along the entire periphery of the frame, from one side to the other of the end of the handle, after having bypassed the basket, as well as 'to constitute the inside edge of the basket, while the shorter strips 9 (see transverse cutting lines 10) are intended to constitute localized reinforcements of said edges, either inside the basket or outside the frame, or even possibly, in the case of a hollow heart frame, the inner edge of this heart.

A frame produced from such panels and strips all cut so that their general orientation co-coincides with the direction of the fibers, will have the advantage of requiring only very reduced finishing operations, given that said fibers, of this done, connect extremely well, without a solution of continuity, according to the different edges of the frame, namely at the junction between the edges and the surfaces parallel to the plane of the rope; deburring operations can therefore be, if not eliminated, at least reduced to a strict minimum.

In Figure 2, there is shown, analogously to the case of Figure 1, different contours of elements to be cut from webs 2 of woven prepreg fibers. The contours similar to those of FIG. 1 have been identified by the same references.

It can be seen that in this case, provision has been made in the sheets 2 for cutouts oriented so that the general direction of the panels and strips of fibers are oriented at 45 ° with respect to the two orthogonal directions of the woven fibers which, in this figure , have been shown only in certain areas, as in FIG. 1, and have been referenced at 12. It goes without saying that, here again, these woven fibers 12 have not been represented over the entire extent of the upper ply 2, so as not to overload the drawing.

In this way, and as already explained above, it will be possible to obtain a racket frame having largely the same qualities as an ela frame. borated from unidirectional fibers.

In FIG. 3, various panels have been shown on a larger scale, referenced 3a, 5a, 6a and 7a cut from a sheet of unidirectional prepreg fibers 1 according to the contours respectively referenced in this last figure in 3, 5, 6 and 7.

FIG. 4 shows in profile how these various panels 3a to 7a can be superimposed, to constitute, on the one hand the upper face of the frame and, on the other hand, its lower face. These different panels are shown on either side of a central part 11 which diagrams the hollow internal space of the box.

We see in this Figure 4 that there are provided on each side two superimposed panels such as 3a, to form the upper and lower faces of the frame over their entire extent (from the free end of the handle 13 to the top of the basket 14) , two superimposed panels such as 5a, for reinforcing said faces in the intermediate part 15 of the frame (substantially between half the length of the handle and half of the basket), two superimposed panels such as 7a, for reinforcing the top of the basket and, finally, a panel such as 6a to further reinforce the intermediate part or core, but to a smaller extent than that of the panels 5a.

In Figure 5, there is shown in a similar manner, but in plan, a possible arrangement for the different strips of unidirectional (or woven) prepreg fibers intended to constitute the edges of the frame.

It can thus be seen that two outer bands 8a have been provided superimposed along the outline of the frame from one side to the other of the free end of the handle 13, these bands 8a being themselves partially covered by bands 9a more short, to reinforce the top of the basket, the intermediate part or core 15 of the frame and the end of the handle 13, this of course symmetrically with respect to the axial longitudinal plane perpendicular to the plane of the rope.

Reinforcement strips 9a are also provided, superimposed on the main strip 8a inside the basket 14, in particular to reinforce the top of the basket and its opposite part, which is located near the. heart 15, and finally, as regards, according to the exemplary embodiment shown, the production of a racket with a hollowed-out heart (reference 16), reference is also made to 9a a band constituting the inner edge of the song of the hollow heart 15.

It goes without saying, of course, that these various arrangements of panels and strips, for the constitution of the faces and edges of the box of resistant structure, have been given in the foregoing only for explanatory purposes and in no way limitative, and that it would be possible to envisage many variants, in particular as a function of the type of racket that it is desired to obtain, its weight, its cost price, the nature of the fibers used, etc.

In Figure 6, there is shown schematically and partially a mold for shaping and polymerization of a frame, in particular for tennis rackets, produced in accordance with the invention. There is shown in particular and referenced in 17 a bottom plate of the mold, in 18 a middle plate for lateral closure, in 19 a removable core (positioning pins 20) corresponding to the internal shape of the racket basket, and in 21 a also removable core (positioning pins 22) corresponding to the hollowed out part of the heart of the racket (of course, this core is not necessary when it is desired to make a racket with a full heart).

That said, we first put on the bottom plate 17 (the middle plate 18 and the cores not yet in place) the various cut panels intended to constitute the underside of the frame (this will be successively panels 7a, 6a, 5a and 3a).

Then, the cores 19 and 21 are put in place on the bottom plate 17, the corresponding bands 8a and 9a are applied to the edges 23 of these cores, for example according to the type of configuration shown in FIG. 5, then similarly in place the median lateral closure plates 18 and the edges 24 are applied other bands 8a and 9a, intended to constitute the outer edges of the frame also, for example, according to the configuration of FIG. 5.

The inflatable tubes can then be placed in the mold housing thus formed. This is for example a first inflatable tube 25 starting from the end of the mold housing which corresponds to the end of the handle of the racket, which goes around the core 21 and then returns to this same end of the mold; it is also a second inflatable tube 26 likewise starting from the end in question of the mold housing, going around the core 19 and also returning towards this same end. As can be seen in FIG. 7, the parts of the first tube 25 which extend along the handle of the racket are thus placed between the corresponding parts of the second tube 26.

Next, the panels 3a, 5a, 6a and 7a intended to constitute the upper face of the frame are put in place, superimposed as shown in FIG. 4, after which the mold can be closed by means of a closing plate 27 , then proceed to inflate the tubes 25 and 26, which plates the various panels and edges of resistant fibers impregnated against the walls of the mold, and finally proceed to the polymerization of the reinforced synthetic material, by heating the mold.

It should be noted here that the inflation of the tubes allows said panels and strips to be pressed perfectly against the walls of the mold, since these panels and strips are free to move slightly relative to one another. This constitutes a very important advantage compared to the processes in which, as indicated at the beginning, braided sheaths are used, since these sheaths are in no way elastic, and whatever the pressure of the fluid injected into the tubes, there is no it is never possible to flatten these sheaths perfectly on said walls, which makes appear, in particular on the edges of the structure, masses of synthetic material not impregnating the sheath.

Unmolding will directly obtain a racket frame having an excellent appearance and requiring very few finishing operations.

Moreover, to perfect the surface appearance of the racket, it is possible to interpose between the walls of the mold and the elements of prepreg fibers, in particular the panels, a sheet of a material such as cellophane, cut to the corresponding shape. , and that it will be easy to remove after demolding, such a material not adhering to the polymerized synthetic material.

Finally, it should be noted that preferably, provision is made on the edges of the median lateral closure plates 18, as well as on the edges of the cores 19 and 21, for grooves such as those which have been referenced at 28 for the plate 18, in FIG. 6. If provision has been made to cut from the plies of prepreg fibers panels (generally referenced as 29 in FIG. 7) of a width slightly greater than that of the upper and lower faces of the frame the racket, it will be possible to accommodate the edges of these panels, protruding from the edges, in these grooves 28, which will in all cases ensure continuity between said faces and the edges of the frame.

As FIG. 7 also shows, the width of the prepreg fibers can also be provided slightly greater than that of the edges of the racket frame, which allows the edges to be folded inwards, between said panels 29 Such bands have been generally referenced at 30 in FIG. 7 and their edges folded at 31. It should be emphasized that the increase in width of the panels and bands has been deliberately exaggerated in this figure to make this arrangement clearer. . In order not to complicate the drawing, we have not drawn the grooves such as 28 which can also include the edges of the cores 19 and 21.

As goes without saying, and as it already follows from the above, the invention is in no way limited to those of its modes of application and embodiments which have been more particularly envisaged; on the contrary, it embraces all its variants.

Claims (12)

1. Racquet frame, in particular for tennis game, in polymerized synthetic material reinforced with resistant fibers _/ of the type with resistant structure essentially in box, with or without internal reinforcement ribs, this framework being of the general type comprising a basket intended for receive a stretched rope, and a handle connected to the basket by an intermediate part or heart, characterized in that at least its two flat faces parallel to the plane of the rope were formed from panels of strong prepreg fibers, cut from sheets such fibers and which, after polymerization and finishing, are connected without solution of continuity to the lateral sides or edges of said structure. 2. Frame according to claim 1, characterized in that the edges of said structure were formed from narrow plies or strips of resistant prepreg fibers, or from strip-shaped panels cut from sheets of such fibers. 3. Frame according to claim 1 or 2, characterized in that the panels and / or strips of fibers are arranged in several layers. 4. Frame according to claim 3, characterized in that some of said layers, in determined locations of the structure, extend only along a part thereof, the structure thus being localized reinforcements. 5. Frame according to claim 4, characterized in that said reinforcements are located in particular in said intermediate part between the basket and the handle and possibly at the top of the basket and towards the free end of the handle. 6. Frame according to any one of the preceding claims, characterized in that it comprises, as resistant fibers, unidirectional fibers, in particular as regards said faces parallel to the plane of the rope. 7. Frame according to claim 6, characterized in that that said faces parallel to the plane of the rope comprise unidirectional resistant fiber panels parallel to the axis of the handle (general axis of the frame). 8. Frame according to claim 6 or 7, characterized in that said edges of the structure comprise bands or panels of unidirectional resistant fibers extending in planes parallel to said plane of the rope. 9. Frame according to any one of the preceding claims, characterized in that it comprises, as resistant fibers, woven fibers. 10. Frame according to claim 9, characterized in that said faces parallel to the plane of the rope comprise panels of resistant woven fibers extending at an angle of - 45 °, or of a similar value, relative to the axis of the handle (general axis of the frame). 11. Frame according to claim 9 or 10, characterized in that said edges of the structure comprise strips or panels of resistant woven fibers extending at an angle of ± 45 °, or of a similar value, relative to the plane rope. 12. A method of manufacturing a racket frame with a resistant box structure, according to any one of the preceding claims, characterized in that it consists in cutting from a sheet or a stack of sheets of resistant fibers preimpregnated with synthetic material. polymerizable, and according to a determined orientation, panels and strips having the shape of all or part of the upper and lower faces and of the edges of the box, to arrange these cut elements in a mold, around one or more inflatable tubes, according the configuration chosen, in particular for the location of localized reinforcements of the frame, then to close the mold, to inflate the said tube or tubes, and to cause in said mold the polymerization of the synthetic material impregnating the fibers.

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