EP3016721B1 - Racket or club consisting of magnesium - Google Patents

Description

The present invention relates to a method of manufacturing a frame for a ball game racket comprising magnesium.

As a material for the frame of a ball game racket, especially a tennis racket, the most diverse materials have already been proposed. However, technically enforced after initial wooden clubs only aluminum rackets whose frame is bent from an aluminum profile, and glass fiber reinforced rackets and in particular carbon fiber reinforced rackets whose frame is formed from one or more so-called prepreg hoses.

Furthermore, for example, from the US 3,874,667 known to use magnesium as a material for the frame of ball game rackets. The Indian US 3,874,667 revealed racket consists of a massive metal frame. Such a massive metal frame can not meet the requirements of today's weight and playability of a ball game racket. In the US 2003/0054908 A1 ball rackets made of fiber-reinforced synthetic resin are described, the frames are reinforced in sections with aluminum or magnesium strips. Furthermore, in the US 5,551,689 B1 Ball game rackets made of various materials, including magnesium, and various production methods described.

If, however, as is customary today, the frame for a ball game racket in the blown from prepregs made, so it is extremely challenging to vary the wall thickness of the frame specifically to influence the local stiffness of the frame and the weight distribution of the same. On the other hand, if the frame is bent from an aluminum hollow profile, the wall thickness of the frame profile is usually constant, since aluminum profiles with a constant cross-section are used.

The present invention has as its object to provide a method of manufacturing a frame for a ball game racket, which allows to selectively optimize the rigidity of the frame locally on the variation of the wall thickness and to achieve optimum weight distribution, keeping the total weight of the racket as low as possible shall be.

This object is achieved by a method for producing a frame for a ball game racket according to claim 1. The frame produced according to the invention for a ball game racket, in particular for a tennis racket, has a head section and a grip section. The frame is designed as a hollow profile and has magnesium, wherein the wall thickness of the hollow profile varies along a cross section through the frame hollow profile.

The term "hollow profile" is understood in the context of the present invention, a real hollow profile, which is formed only by a frame wall which surrounds a cavity, said cavity is free of additional walls, struts and the like. In other words, according to the invention, mechanical properties such as bending stiffness and natural frequencies are determined essentially exclusively by the variable wall thickness of the hollow profile, without, for example, requiring additional stabilization struts.

It has been found within the scope of the invention that magnesium or magnesium alloys can be used for a frame hollow profile for a ball game racket. The manufacturing techniques used in this case advantageously allow a targeted variation of the wall thickness of the hollow profile, in particular also along a cross section through the frame hollow profile. In the context of the present invention, the section through the frame hollow profile is understood to mean a section perpendicular to the contour of the frame profile. Targeted variation of the wall thickness along such a cross-section through the frame hollow profile is virtually impossible with the aid of the generally customary blow-molding method since the prepreg layers are generally wound to extend along such a cross-section through the frame hollow profile. Usually only different cross-sectional shapes and / or dimensions can be realized in the blow-molding process.

According to the invention, the frame is produced by means of magnesium injection molding techniques according to the so-called thixotropic method. Using this technique, wall thickness can be easily achieved
appropriate training of the injection mold specifically vary. Particularly preferred is the so-called melt-core technique, in which an injection mold core is melted after the molding of the frame.

It is further preferred that the wall thickness of the hollow profile varies not only along a cross-section through the frame hollow profile, but additionally also in the longitudinal direction of the frame, i. varies along the frame contour. Thus, the wall thickness in the heart region or in the transition between bridge and head section of the frame is preferably greater than in the remaining head section.

According to a preferred embodiment, the variation of the wall thickness along at least one transverse and / or longitudinal section relative to the minimum wall thickness is at least 25%, preferably at least 50%, more preferably at least 75% and particularly preferably at least 100%.

Using magnesium and / or magnesium alloys, particularly thin wall thicknesses can be achieved with the help of magnesium injection molding in particular. Thus, according to a preferred embodiment, the wall thickness of the frame according to the invention is thinner in sections than 1 mm, preferably thinner than 0.8 mm, more preferably thinner than 0.7 mm and particularly preferably thinner than 0.6 mm.

The frame profile of the frame according to the invention preferably has in the head portion an outer portion facing outward, an inner portion facing inwardly to the fabric, and two side portions, wherein at least partially the wall thickness of the inner and / or outer portion is thicker than the wall thickness of side sections. In this case, the frame profile does not have to be rectangular. Rather, further sections can form a flowing transition from the inner or outer section to the two side sections, so that a polygon, a rectangle with rounded corners or the like is formed. According to an alternative preferred embodiment, the wall thickness of the inner or outer portion is at least partially thinner than the wall thickness of the side portions. Additionally or alternatively, at least in sections, the wall thickness of the inner portion may be thinner or thicker than the wall thickness of the outer portion.

The frame preferably has at least 50 wt%, more preferably at least 80 wt%, even more preferably at least 90 wt%, and most preferably at least 95 wt% magnesium. According to a preferred embodiment, the frame comprises a magnesium alloy, preferably a fiber- or particle-reinforced alloy, particularly preferably SAE SiC / AZ91. Particularly preferably, substantially the entire frame is made of such an alloy. In addition, the frame may be locally reinforced with carbon and / or fiberglass material. Such a reinforcement is preferably provided in the region of the transition between the head section and the grip section.

According to the invention, the magnesium or magnesium alloy content does not have to be evenly distributed over the ball game racket frame. Rather, it is also preferred that the frame has a frame portion having magnesium, wherein the wall thickness of the hollow profile varies along a cross section through this frame portion. In this case, preferably, the frame in this frame portion has at least 50% by weight, more preferably at least 80% by weight, even more preferably at least 90% by weight and most preferably at least 95% by weight of magnesium. In this preferred embodiment, one or more components may be made separately from magnesium or a magnesium alloy, in particular injection molded. These components can then be placed together with the prepreg layers in a Schlauchblasform and pressed together with the prepreg layers. These separate components may be individual sections of the head section or handle section. However, according to the invention, a separate heart region, which consists of magnesium or has magnesium or magnesium alloys, is particularly preferably provided, since particularly advantageous effects can be achieved in this region with a corresponding variation of the wall thickness.

The magnesium-containing frame section preferably consists of two frame section halves, which are welded together, pressed and / or glued. If the entire frame has magnesium, then preferably the entire frame consists of two frame halves which are welded together, pressed and / or glued together. The frame halves or frame portion halves are preferably identical, with each of the two Frame halves or frame portion halves is formed asymmetrically with respect to the frame longitudinal axis or frame portion longitudinal axis. In this way, using the injection molding process, two identical halves can be produced in a particularly simple manner, which then interlock when connecting.

The present invention further relates to a method of manufacturing a frame portion for a ball game racket. The frame produced by the method according to the invention is preferably a frame with the properties described above. According to a preferred embodiment of the method according to the invention for producing a frame or frame section, an injection mold and a core are provided, wherein the core is preferably made of a material having a melting temperature below the melting temperature or heat resistance temperature of the frame material. Preferably, the melting temperature of the core material is less than 400 ° C, more preferably less than 370 ° C. It is further preferred that the melting temperature of the core material is above 190 ° C, more preferably above 200 ° C. The frame (or frame member) is then molded between the injection mold and the core, preferably by the thixotropic method, by introducing a material comprising magnesium. The core material is chosen so that during the molding of the frame not enough heat energy is introduced into the core in order to melt this, with a slight softening may be tolerated. After the frame has been molded, removed from the mold, and cooled to keep its shape stable, the core is melted, preferably by heating the entire racket above the melting temperature of the core, such that the core material is formed from the cavity formed by the frame can escape. At this time, the heat-resistant temperature of the frame is preferably not exceeded.

The core material preferably comprises one or a combination of the following materials or consists of one or a combination of the following materials: tin-based alloys (preferably at least 50% tin and optionally zinc, bismuth, antimony, copper, silver, lead, indium), Bismuth based alloys (preferably at least 50% bismuth and optionally tin, silver, germanium), lead based alloys (preferably at least 50% lead and optionally tin, antimony, bismuth, silver, indium), zinc based alloys (preferred at least 50% zinc), die-cast zinc alloys such as ZnAl4, ZnAl4Cu1, ZnA14Cu3, indium-based alloys, glass, plastic with or without glass-fiber reinforcement such as polyamide. Particularly preferred are metallic integral foam cores based on these low-melting alloys. These can be produced, for example, by die casting. The addition of a propellant results in an integral foam with closed outer skin. The relative density may be, for example, 50% to 100% of the absolute material density. Thus, by using a foam, for example, only half the amount of material is needed compared to a solid core.

According to a further preferred embodiment of the method according to the invention for producing a frame, an injection mold and a core are provided, wherein the core consists of a salt. The frame (or frame member) is then molded between the injection mold and the core, preferably by the thixotropic method, by introducing a material comprising magnesium. After the frame has been molded, removed from the mold, and cooled enough to stably retain its shape, the core is washed out by introducing water into the cavity formed by the frame.

According to a further preferred embodiment of the method according to the invention for producing a frame, the core can also be made of an acid-soluble material, e.g. glass base, so that the core can be removed from the frame after forming the frame with the help of an acid.

According to a further preferred embodiment of the method according to the invention for producing a frame, first two frame halves are cast from a material which comprises magnesium. This is preferably done using the so-called thixotropic method. Subsequently, the two frame halves are connected to form a frame.

In the method according to the invention of this second embodiment for producing a frame section, first two frame section halves of a material comprising magnesium are cast, and then the two frame section halves are firstly cast Frame section connected. In order to produce a frame for a ball game racket from this first frame section, a second frame section is provided and the first and second frame sections are connected to form a frame. According to the invention, the second frame section may be an unfinished section, for example a prepreg tube, so that the finishing of the second frame section and the connection of the second frame section to the first frame section occur in one method step.

The injection molding of the magnesium-containing material is preferably carried out at temperatures between 500 ° C and 800 ° C, more preferably at temperatures between 550 ° C and 700 ° C. The injection of the material into the mold is preferably carried out in less than 80 ms, more preferably in less than 60 ms and particularly preferably in less than 50 ms.

The step of connecting the two frame halves or frame section halves preferably comprises welding and / or pressing and / or gluing. Furthermore, the two frame halves or frame section halves are preferably identical, wherein each of the two frame halves or frame section halves is formed asymmetrically with respect to the longitudinal axis.

The frame according to the invention for a ball game racket has a number of technical advantages over the prior art. Although magnesium has higher density, lower specific stiffness, and lower specific strength than conventional prepreg materials, a frame for a magnesium or magnesium magnesium racket can be better optimized for stiffness and strength at the same weight, as the wall thickness can be reduced to simple Way can be optimally designed. The use of magnesium injection molding allows automated production with short cycle times of approx. 35 seconds. A pre- and post-processing, which are often done manually by conventional Perpregverfahren, accounts for virtually completely. Injection molding also allows excellent production stability and allows to produce exactly the desired structure using a defined injection mold.

Fig. 1

eine perspektivische Ansicht des erfindungsgemäßen Rahmens;

Fig. 2

eine perspektivische Ansicht einer Rahmenhälfte des Rahmens gemäß Figur 1;

Fig. 3

eine vergrößerte perspektivische Ansicht des Herzbereichs des Rahmens gemäß Figur 2;

Fig. 4

eine perspektivische Ansicht des Übergangs vom Griffabschnitt in den Herzbereich des Rahmens gemäß Figur 2;

Fig. 5

eine perspektivische Ansicht eines Abschnitts des Kopfabschnitts des Rahmens gemäß Figur 2;

Fig. 6

einen perspektivischen Querschnitt durch den Kopfabschnitt des Rahmens gemäß Figur 1;

Fig. 7

einen perspektivischen Querschnitt durch die Brücke des Rahmens gemäß Figur 1;

Fig. 8

einen perspektivischen Längsschnitt durch den Griffabschnitt des Rahmens gemäß Figur 1;

Fig. 9

eine Draufsicht auf ein separates Bauteil für einen Rahmen gemäß einer bevorzugten Ausführungsform der vorliegenden Erfindung;

Fig. 10

eine Seitenansicht betrachtet von der Bespannungsebene auf das Bauteil aus Figur 9;

Fig. 11

eine Seitenansicht von einer Figur 10 gegenüberliegenden Seite auf das Bauteil gemäß Figur 9;

Fig. 12

eine perspektivische Ansicht des Bauteils gemäß Figur 9; und

Fig. 13

eine weitere perspektivische Ansicht des Bauteils gemäß Figur 9.

Hereinafter, preferred embodiments of the frame according to the invention are described in detail with reference to FIGS. Show it:

Fig. 1

a perspective view of the frame according to the invention;

Fig. 2

a perspective view of a frame half of the frame according to FIG. 1 ;

Fig. 3

an enlarged perspective view of the heart region of the frame according to FIG. 2 ;

Fig. 4

a perspective view of the transition from the handle portion in the heart region of the frame according to FIG. 2 ;

Fig. 5

a perspective view of a portion of the head portion of the frame according to FIG. 2 ;

Fig. 6

a perspective cross section through the head portion of the frame according to FIG. 1 ;

Fig. 7

a perspective cross section through the bridge of the frame according to FIG. 1 ;

Fig. 8

a perspective longitudinal section through the handle portion of the frame according to FIG. 1 ;

Fig. 9

a plan view of a separate component for a frame according to a preferred embodiment of the present invention;

Fig. 10

a side view viewed from the clothing plane on the component FIG. 9 ;

Fig. 11

a side view of one FIG. 10 opposite side on the component according to FIG. 9 ;

Fig. 12

a perspective view of the component according to FIG. 9 ; and

Fig. 13

a further perspective view of the component according to FIG. 9 ,

FIG. 1 shows in perspective view a frame for a ball game racket according to a preferred embodiment of the present invention. The frame is formed as a hollow profile and has a head portion 1 for receiving a fabric, not shown, a handle portion 2 and a heart portion 3, which has two arms 4a and 4b and a bridge 5. The scope of this preferred embodiment is composed of two identical frame halves, with respect to the frame longitudinal axis are formed asymmetrically. One of these two identical frame halves is in perspective view in FIG. 2 shown.

As in FIG. 2 can be seen, the asymmetry of the frame half is provided so that the two frame halves can join each other during assembly. In the enlarged section of FIG. 3 that make up the heart area 3 of the frame half FIG. 2 For example, the protruding webs 5a of the bridge 5 can engage with the step-shaped sections 5b of the bridge 5 of the respective other frame half. This allows a flush connection of the two frame halves to a frame. Similarly, the head portion (see. FIG. 5 ) Areas with projecting webs 1a and stepped portions 1b.

In the illustrated preferred embodiment, the step forms a kind stop for the second frame half and web and stage can be welded or glued together, for example. Alternatively or additionally, the frame halves may also, for example, projections and grooves or similar areas, which allow to lock the two frame halves together.

In FIG. 6 is a cross section through the frame hollow profile of the frame FIG. 1 represented in the region of the head section 1. As in FIG. 6 can be clearly seen, the wall thickness of the frame hollow profile according to the invention vary quite considerably along a cross section through the frame hollow profile. In the illustrated preferred embodiment, the frame profile in the region of the head portion on an outer portion 7, an inner portion 6 and two side portions 8a and 8b, wherein in the illustrated cross section, the wall thickness of the inner portion 6 and the outer portion 7 is considerably larger than the wall thickness of the two side portions 8a and 8b. In this case, there is a continuous or gradual transition from the wall thickness of the inner or outer section to the two side sections. Such a finely tuned cross-sectional profile could not be achieved using the conventional bubble-blowing process. However, if magnesium or a magnesium alloy is injection-molded, such a cross-sectional profile can be designed in a simple manner by appropriate design of the injection mold, wherein the cross-sectional profile can additionally vary along the frame contour in the longitudinal direction.

In FIG. 7 is a cross section through the hollow profile in the region of the bridge 5 is shown. Again, the wall thickness of the hollow profile varies, although the variation is not as pronounced as in the example of FIG. 6 ,

An additional variation of the wall thickness in the longitudinal direction of the frame, ie along the frame contour, is in FIG. 8 to see a longitudinal section through the handle section 2 of the frame FIG. 1 shows. As can be clearly seen here, the wall thickness of the frame hollow profile increases significantly in the region of the transition to the arm 4b.

According to the invention does not have the entire frame magnesium. Rather, according to the invention, the frame can also have a section or a separate component made of magnesium or a magnesium alloy. A preferred embodiment of such a separate component of magnesium alloy is in the FIGS. 9 to 13 shown. This is a section of the heart area, namely the bridge 5 and sections of the arms 4a and 4b and in the transition of the heart area in the head section. The stress on this frame part during the game is particularly complex, so that in this area by means of a variation of the wall thickness of the hollow profile, the greatest effect can be achieved. According to the invention, however, other insert components such as, for example, the grip section or regions of the head section can likewise be made of magnesium or a magnesium alloy and inserted into the frame according to the invention. This is preferably done by the separate magnesium component is pressed with the prepreg layers of the rest of the frame in the tube blowing process. For example, in the side view of FIG. 10 can be seen, the injection molding process can be controlled so well with the aid of the method according to the invention that even the string openings 10 for the passages of strings forming the stringing can be manufactured without an additional step of drilling being required.

Claims (12)

1. A process for producing a frame or a frame portion for a ball-game racket comprising a head portion (1) and a handle portion (2), wherein at least a part of the frame is configured as a hollow profile and comprises magnesium and wherein the wall thickness of the hollow profile varies along a cross-section through the hollow frame profile, wherein the process comprises the following steps:

   providing an injection mold and a core, wherein the core consists of a material having a melting temperature below 400°C;

   casting the frame or the frame portion by means of the thixo process by inserting a material comprising magnesium between the injection mold and the core; and

   melting the core by heating the frame or frame portion including the core to above the melting temperature of the core, wherein the heat resistance temperature of the frame or frame portion is not exceeded.
2. The process according to claim 1, wherein the frame material comprises at least 50% (by weight), preferably at least 80% (by weight), more preferably at least 90% (by weight), particularly preferably at least 95% (by weight) of magnesium.
3. The process according to claim 1 or 2, wherein the frame material comprises a magnesium alloy, preferably a fiber-reinforced or particle-reinforced alloy, particularly preferably SAE SiC/AZ91.
4. The process according to any one of the preceding claims, wherein the core material comprises or consists of one of or a combination of the following materials: an alloy on the basis of tin, an alloy on the basis of bismuth, an alloy on the basis of lead, an alloy on the basis of zinc, an alloy on the basis of indium, glass, plastics with or without glass-fiber reinforcement, polyamide.
5. The process according to any one of the preceding claims, wherein further the wall thickness of the hollow profile varies in the longitudinal direction of the frame or frame portion.
6. The process according to any one of the preceding claims, wherein the variation in the wall thickness along at least one cross-section and/or longitudinal section relative to the minimum wall thickness is at least 25%, preferably at least 50%, more preferably at least 75%, particularly preferably at least 100%.
7. The process according to any one of the preceding claims, wherein the wall thickness of the frame or frame portion in sections is thinner than 1 mm, preferably thinner than 0.8 mm, more preferably thinner than 0.7 mm, particularly preferably thinner than 0.6 mm.
8. The process according to any one of the preceding claims, wherein the frame profile of the frame comprises an outer portion (7), an inner portion (6) and two side portions (8a, 8b) in the head portion (1), and wherein the wall thickness of the inner and/or outer portion at least in sections is thicker than the wall thickness of the side portions and/or wherein the wall thickness of the inner and/or outer portion at least in sections is thinner than the wall thickness of the side portions.
9. The process according to any one of the preceding claims, wherein the frame profile of the frame comprises an outer portion (7), an inner portion (6) and two side portions (8a, 8b) in the head portion (1), and wherein the wall thickness of the inner portion at least in sections is thinner than the wall thickness of the outer portion.
10. The process according to any one of the preceding claims, wherein the frame is locally reinforced with carbon fiber material and/or glass fiber material, wherein preferably the frame is reinforced with carbon fiber material and/or glass fiber material in the area of the transition between the head portion (1) and the handle portion (2).
11. The process according to any one of the preceding claims, wherein the frame or frame portion comprises two frame halves or frame portion halves which are welded to each other, pressed together and/or bonded to each other, wherein preferably the two frame halves or frame portion halves are identical and wherein preferably each of the two frame halves or frame portion halves is asymmetrical with respect to the longitudinal axis of the frame or the frame portion.
12. The process according to any one of the preceding claims, wherein the frame comprises a frame portion comprising magnesium, and wherein the wall thickness of the hollow profile varies along a cross-section through this frame portion, wherein preferably the frame in said frame portion comprises at least 50% (by weight), more preferably at least 80% (by weight), more preferably at least 90% (by weight) and particularly preferably at least 95% (by weight) of magnesium, and/or wherein preferably said frame portion comprises two frame portion halves which are welded to each other, pressed together and/or bonded to each other.

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