NL8502514A - Producing playing balls, quoits etc. - comprises joining moulded half shells to form hollow cores, positioning core in mould, injecting settable material etc. - Google Patents

Abstract

Method comprises producing thin-walled part-shells (half-shells,) injection-moulding, connecting such shells to form enclosed hollow cores, positioning each core in a mould cavity complementary with the shape of the complete object, filling the space between core and cavity wall with settable material, allowing this to set, and removing the complete object. Connection of the half-shells (and moulding the complete object) may be carried out in an enclosed pressurised space.

Description

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Method and device for manufacturing a hollow object such as a ball.

The invention relates to a method for manufacturing a hollow object such as a ball.

According to a known method of this kind, the hollow object is built up of two or more parts, which are joined together, for example, by gluing. The connecting seam can form a weak spot in the finished article and generally has in any case deviating properties, for example in terms of elasticity. In certain applications, such as for instance in a sports hall, this is very undesirable. In the case of a ball with an internal increased pressure, a leak can occur quickly at the location of the seam and therefore pressure loss, making it unusable.

According to another known method of the above-mentioned kind, the object is completely molded. In the open mold form, the appropriate material, which may be thermoplastic or thermoset, is introduced. After closing the die, it is rotated about two axes to ensure a good distribution of the material. Even with such a combined rotational movement, an equal centrifugal force does not occur everywhere on the periphery of the mold cavity, so that an uneven wall thickness results. This is also undesirable.

The object of the invention is to provide a method for manufacturing a spherical object which does not have the above-mentioned drawbacks.

This object is achieved in the method according to the invention by manufacturing a number of thin-walled partial shells; connecting the partial shells together into a closed, hollow core shell; positioning the core shell in a mold cavity, with a shape complementary to the shape of the object; filling a space bounded by the hard cavity material by the wall of the mold cavity and the core shell; curing the curable material, and removing the molded hollow * * -? 5 f V_ "^" J *> 2 le object. An object is hereby obtained with a precisely controlled, and thus, if desired, precisely uniform wall thickness. Since the core shell is thin-walled, the influence of the core on the final properties of the object can be very small, so that any inhomogeneities in the core shell at the location of the joint therein can have only a correspondingly very small influence.

The method according to the invention is particularly suitable for manufacturing a sports ball. A sports ball manufactured in this way has very uniform properties over the circumference, in particular very uniform elasticity. In addition, the center of gravity of the ball is centered within narrow limits. This is essential for a good "loop" 15 or "flight".

A further development of the invention is achieved when the sub-shells are joined together in a gastight closed hollow core shell in a space with a pressure higher than atmospheric pressure. In this way, a final article is obtained which is stiffer and harder. When used for the manufacture of a ball, this results in a ball with better bounce properties. By a suitable combination of the above-atmospheric pressure in the core shell and the pressure under which the curable material is supplied in the mold cavity, in combination with a suitable choice of material for both the core shell and the curable material, a very wide variety of properties can be reached. These properties include hardness, elasticity, bounce properties, etc.

A further development of the method according to the invention, in which the object to be manufactured is a ball, is obtained in that two hemispherical partial shells with a circular end edge are used, which are connected to each other by inserting into a partial shell. an amount of flowable, hardenable material, placing the part shells with the end edges together, rotating about the axis through: the spherical center and perpendicular to the plane through the end edges of the placed part shells to evenly distribute the hardenable material. 8502514 s. * - 3 rial, joining the end edges and curing the curable material. As a result, the connection seam of the partial shells can be formed with great precision in terms of material distribution. In this way, any imbalance in the formed ball is avoided.

A favorable embodiment of this further development is obtained when the curable material is supplied in the form of a granulate of thermoplastic material and heat is supplied during rotation at the level of the end edges for a certain period of time.

The invention also relates to and provides an apparatus for manufacturing a hollow object such as a ball. This device comprises a device for manufacturing thin-walled partial shells; a device for connecting partial shells together; a mold-forming device comprising a frame movably guided between an open and a closed position and mold parts connected to the frame, which in the closed position define a mold cavity with a shape complementary to the shape of the object, arranged on the mold parts the mold cavity excellent core shell support means and supply means for supplying hard hair material.

According to a favorable embodiment of the device according to the invention, the supporting means are formed by pins protruding into the mold cavity over precisely determined distances. These pins can abut the surface of the core shell and fix it during the feeding of the curable material.

The pins are preferably retractable.

After the hardening of the curable material has begun, the pins can be withdrawn and the remaining voids in the wall of the article can be filled, for instance by pressing hard hair material into the mold. In the case of the curable material being foam-forming material, the pins can be retracted before foam formation is completely finished, so that the remaining spaces are automatically filled.

A further development is obtained by the fact that the 3302514 4 pins are hollow and concentrically arranged around these bases, with the cavity in each pin and the cylindrical jacket-shaped space between each pin and the bus extending and draining means for a gas 5 underneath. pressure are connected. The fixation of the core in the mold is hereby not achieved by physical contact with the core, but by the gas flowing out of the hollow pins.

Instead of centering the core in the mold 10 by means of pins protruding in the mold cavity, this can also be done in a simple manner by forming projections on the core which, when the mold is closed, can abut the wall of the mold cavity.

It should be noted that the invention is not limited to a method and device for manufacturing balls. Torus-shaped objects, for example, can also be advantageously manufactured using the present invention. Non-rotationally symmetrical hollow objects can also be manufactured with the invention. In particular in those cases where good control of the wall thickness of such a more or less arbitrary object is desired, the invention can be advantageously applied.

The invention will be further elucidated in the following description of embodiments shown in the figures.

Fig. 1 schematically shows a device according to the invention for carrying out a method according to the invention.

Fig. 2 schematically shows the device for manufacturing thin-walled partial shells of FIG. 1.

Fig. 3 shows the device for connecting the partial shells of FIG. 1 to one another.

Fig. 4 shows part-shells connected to each other to form a closed, hollow core shell.

FIG. 5 shows schematically and partly cut through the mold-forming device of FIG. 1.

Fig. 6 is an enlarged partial sectional view of one showing the arrangement of FIG. 3 core shell manufactured at the connection seam.

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Pig. 7 shows another die-forming device for manufacturing a toroidal hollow object.

Fig. 8 shows an alternative embodiment of support means for a core shell.

The device 1 schematically shown in fig. 1 is intended for manufacturing hollow balls with the method according to the invention. Generally, the device 1 comprises a device 2 for manufacturing thin-walled partial shells, in the form of hemispherical shells, a device 103 for connecting two partial shells in each case into a spherical core shell, and a mold-forming device 4. In the mold-forming device, each spherical core shell is received in a mold space, after which a remaining space between the core shell and the wall of the mold space is filled with hardenable material by a feed device 5. After the material has hardened, the mold is opened and the finished ball is removed from the mold.

The different parts of the device 1 are controlled by a control device 6, which communicates with the said different parts via control lines 7, only a few of which are shown.

The device 1 and the said devices forming part thereof will be described in more detail below.

The partial scale manufacturing device 2 is shown schematically, partly in longitudinal section in Fig. 2. The device 2 comprises a frame 10 in which two mold parts 11 and 12 are received. The mold part 11 is fixedly connected to the frame part 10, while the mold part 12 is movable by means of guides 13 and a cylinder 15 in the direction of the arrow 14 and opposite from the open position shown in Fig. 2 to the closed position. position, wherein the mold parts 11 and 12 contact each other with contact surfaces and define a mold cavity in the form of a thin-walled hemispherical shell.

The device 2 further comprises an injection molding unit 16. Thermoplastic plastic in granulate form is introduced into the hopper 17. From this hopper 17, the granulate is fed in known manner with a transport screw 19 driven by the motor 3502514 6 tor to a nozzle 20 which communicates with the mold cavity. On the way, the granulate is heated to a plastic state, in which state a portion of plastic is injected into the mold cavity each time. After the injected plastic has hardened sufficiently by cooling, the mold parts 12, 11 are moved into the open position shown, after which the molded part-shell 25 can be removed from the mold by means of a removal device 25 shown in Fig. 1.

10 The choice of material for the partial shells depends on the intended application. A fairly soft polyvinyl chloride, a mixture of polypropylene and polyethylene and the like may be suitable.

As can be seen from Fig. 1, the part-scale connecting device 3 and the mold-forming device 4 are placed in a chamber 23 which is kept under a higher pressure by atmosphere than a compressor 22. The partial shells 24 manufactured with the partial shell manufacturing device 2 are brought into a lock 20 with the take-out device 25.

Any suitable device can be used for the removal device 25. The extraction device 25 does not form part of the invention and is therefore not described in detail.

The lock 26 is shown here in the simple form of a tube, in which the partial shells 24 can be slid slidingly. The sub-shells 24 thus form the closure themselves. At the end of the lock 26, which is located inside the chamber 23, a random extraction device 27 is again placed, which in each case takes a shell part 24 out of the lock and places it in the partial shell connection device 3.

The partial scale connecting device 3 shown in more detail in Fig. 3 comprises a frame 30 in which two cups 31,32 are mounted concentrically. Each cup 31,32 comprises a cavity 33 facing the other, in which a holder 34 for a partial shell 24 is received. The holders 34 are pivotally mounted in the cavities 33 such that in the moved position of the cups 31, 32, which are moved apart, the holders 34 pivot more or less in the lying position.

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The partial shells 24 are arranged in this position. Via a filling nozzle 37, granulate 33 is introduced from a storage funnel 40 via a metering slide 41 into the partial tray 24 into a container 34. After this, the cup 31 in fig. 3 is moved to the right, by means of the piston-rod 44 of the cylinder unit 43, until the end faces of the cups 31,32 lie against each other. Centering pins 35 and centering holes 36 are provided in these end faces. During the movement towards each other, the holders 34 also come into contact with each other, which thereby pivot with their connecting surface in a vertical position. Motor 45 is then switched on, causing the whole to rotate, as indicated by arrow 46.

A heating element 39 is arranged in the cups 31,32 near the end surfaces thereof, that is to say near the connection point between the shell parts 24. Due to the heat supply via the heating elements 39, the material of the partial shells 24 and of the granulate at the location of the connecting seam becomes liquid, so that a connection is formed. After cooling, an entire spherical core shell 48 is thus obtained.

Pig. 6 shows the connection seam in cross-section. In this embodiment, each of the part sides is provided on the inside with a bevel 42, so that in the assembled position a V-shaped groove is formed at the location of the connecting seam. This groove is filled with the granulate which, after the described heating, connects in one piece with the shell parts 24.

The spherical core shell 48, which, as shown in Fig. 4, is composed of two sub-shells 24 in the manner described, is then fed to the mold forming device 4. This device comprises a lower mold part 52 and an upper mold part 51. The upper mold part 51 is facing the lower mold part 52 and movable therefrom by means of a piston rod 55 of a cylinder 54. In the opened position of the mold parts 51, 52 shown in Fig. 1, a core shell 48 is introduced into the mold cavity 59 of the lower mold half 52. Subsequently, the cylinder 54 is activated whereby the upper mold part 51 is closed at the bottom part 52 at 9302514 3.

Retractable pins 53 are mounted in the mold parts 51 and 52 and can be moved into the mold cavity by a movement device (not shown in greater detail). The core shell is centered in the mold cavity 59 by moving the pins 58 inward. In this state, curable material is introduced into this mold cavity 59 by the feed device 5 comprising a pump 53 in a conduit 56 which opens via a nozzle 57 into the mold cavity 59. The feed device 5 can be an injection molding device known per se.

After the hardenable material has hardened to a sufficient strength, the pins 58 are retracted and any openings left thereby as a result can still be filled in the curable material, for instance by post-pressing of curable material. If the pins 58 are made thin, this is unnecessary. After further curing, the mold can be opened and the finished ball can be taken out of the mold cavity by a removal device 65 (not further described). The take-out device 65 again places the formed balls 61 in a lock 66, which here too is designed as a tube with an inner diameter corresponding to the outer diameter of the balls 61, so that the balls 61 themselves form the closure.

As shown in Fig. 8, instead of pins 58 which come into direct contact with the core shell 48, hollow pins 68 can also be used. A bush 69 is arranged concentrically around each hollow pin 68. Air under pressure can now be supplied through the cavity 70 into the pin 68, which air is again discharged via the cylinder-jacketed cavity 71 between the pin 68 and the sleeve 69. The core shell 43 can thus be fixed in the mold cavity without being physically Contact.

Although the invention has been described with reference to an application and embodiment for manufacturing balls, it is also useful for manufacturing hollow objects of a different rotationally symmetrical shape or of any desired shape.

A die-forming device that can be used in the manufacture of toroidal objects such as casting rings is shown in Fig. 7. This mold-forming device 75 comprises two mold parts 76 and 77 which together define a mold cavity 73 with a toroidal shape. A core shell 79 can also be accommodated in this mold cavity 73, which is itself also toroidal and can be composed of two identical half toruses. The mold parts 76 and 77 are also provided with support means for the core shell 79 in the form of pins 80. In contrast to the embodiment of fig. 5, 10 wherein the pins 53 extend radially with respect to the mold cavity, lying pins 30 in planes perpendicular to the. symmetry axis of the mold cavity 73.

The curable material can also be selected again according to the ultimate desired properties of the hollow object to be manufactured. For example, a suitable thermoplastic plastic, whether or not in foamed form, can be used.

In another application of the method and device according to the invention, the partial shells can be manufactured from a natural or synthetic rubber and the curable material to be applied in the mold-forming device can also be a natural or synthetic rubber. After vulcanization in the mold-forming device, a homogeneous rubber ball is thus obtained.

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Claims (11)

1. Method for manufacturing a hollow object such as a ball / characterized by: manufacturing a number of thin-walled sub-shells, connecting the part-shells together into a closed, hollow core shell, placing it in a mold cavity, with a mold of the article complementary shape, positioning the core shell, filling a space bounded by the wall of the mold cavity and the core shell with a curable material, allowing the curable material to harden, and removing the formed hollow from the mold object. 2. A method according to claim 1, characterized in that the sub-shells are connected to one another in a gastight closed hollow core shell in a space with a pressure higher than atmospheric pressure. 3. Method according to claim 1 or 2, wherein the object is a ball, characterized in that two hemispherical partial shells with a circular end edge are used, which are connected to each other by introducing a quantity of flowable material into a partial shell, hardenable material, placing the partial shells with the end edges against each other, rotating the part shells placed against each other perpendicularly to the plane through the end edges, for an even distribution of the hardenable material, with the end edges bonding and curing of the curable material. A method according to claim 3, characterized in that the curable material is supplied in the form of a granulate of thermoplastic material and that heat is supplied during rotation at the level of the end edges for a certain period of time. 5. Device for manufacturing a hollow object such as a ball, characterized by: 8502514 a device for manufacturing thin-walled part-shells, a device for connecting part-shells together, a mold-forming device comprising a frame, movable between mold parts guided in an open and closed position and connected to the frame, which in the closed position define a mold cavity with a shape complementary to the shape of the object, arranged on the mold parts, supporting means for a core shell and supply means in the mold cavity for feeding hard hair material. 6. Device according to claim 5, characterized in that at least the device for connecting the partial shells together is placed in a lockable space and that the space is connected to a source of a gas mixture under pressure. 7. Device as claimed in claim 5 or 6, characterized in that the partial shell connecting device comprises a partial shell holder rotatably mounted in a frame and coupled to a motor. 8. Device as claimed in claim 7, characterized by granulate supply means and heat supply means. 9. Device as claimed in any of the claims 5-8, characterized in that the supporting means are formed by pins protruding over accurately determined distances in the mold cavity. 10. Device as claimed in claim 9, characterized in that the pins are hollow and concentrically arranged around these sleeves, wherein with the cavity in each pin and the cylinder-jacketed space between each pin and the sleeve extending and discharging around it. for a gas under pressure. 11. Device according to claim 9 or 10, characterized in that the pins are retractable. 8502314 ---;