JPS6147689B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a method and apparatus for manufacturing hollow hemispheres used for ping pong balls, flush toilet floats, fishing floats, toys, etc.

(Prior Art) Conventional techniques for producing hollow spheres using resin include blow molding, sheet homing to produce hemispheres and then fitting them together, and rotational molding.

(Problems to be Solved by the Invention) According to the first blow molding method, uneven thickness during molding is unavoidable, and burrs are generated at the joints of the molds, and processing is required to remove these burrs. This has the disadvantage that the strength of the joint is reduced.

According to the so-called pressure forming method in which the hemispheres are manufactured by forming the second sheet and then fitted together, this also applies to the first sheet.
Similar to the blow molding method described above, uneven thickness occurred, and a ball with roundness could not be obtained, and there were also problems in workability during fitting and bonding.

According to the third rotational molding method, this
Although this method does not cause uneven thickness reduction and can produce a spherical object with roundness, there are limitations in terms of materials suitable for rotary molding, and there is also a problem with the occurrence of burrs on the mold joint surface and the possibility of mating adhesion. Problems still remain regarding workability.

In particular, ping pong balls are manufactured by the second method using celluloid sheets, but they still have the problems of the second method described above.

That is, in the method of forming a hemisphere from a sheet, it is impossible in principle to obtain a uniform film thickness over the entire spherical surface, and therefore uneven thickness tends to occur.

If there is uneven thickness on the membrane surface, it will not be possible to obtain the proper bounce required for a ping pong ball.

In addition, since the hemispheres are cut out from the sheet and joined together, the shape of the cut surface can only be a simple cut surface, which makes the bonding work using dove cement in the subsequent process extremely difficult. It was not possible to obtain a ping pong ball with extremely roundness.

Furthermore, since the dove cement bonding method uses the same material as the material to be bonded as a solvent, the solvent acts on the cellulose base material, causing internal distortion and strength deterioration, or even causing negative causes such as shrinkage. ing.

(Means for Solving the Problems) As a result of intensive research, the inventors of the present invention devised a method of creating a hollow hemisphere using a new injection method, and were able to solve the above-mentioned problems.

That is, the present invention provides an injection mold for injection molding, which consists of a cavity and a core, while rotating either the cavity or the core, or the inside of the mold through a gate provided at a position offset from the central axis of rotation of the mold. Molten resin is injected to form a hollow hemisphere, and the resin is compressed while the mold is rotating, or the mold is further rotated in the opposite direction after the mold rotation has stopped. , the first invention is a method for manufacturing a hollow hemisphere characterized by forming a three-layer structure in the resin layer of the hollow hemisphere, and a mold cavity with a gate located at a position offset from the central axis of rotation. Alternatively, the second invention is a hollow hemispherical injection molding device in which one or both of the cores is constructed of an injection molding die having a rotation function.

(Effects of the Invention) According to the manufacturing method and device according to the present invention, a hollow hemisphere is made by an injection molding method, that is, an injection molding method. It is possible to obtain a perfectly round hollow hemisphere with a fleshy texture, and it is also possible to create a more flexible shape compared to the conventional method of making hemispheres using pressure molding and fitting and bonding them, where the shape of the joint surface is limited. Not only can you improve workability, bond strength, and roundness accuracy by improving the applicator, but you can also freely select the adhesive, and resin The decrease in strength due to internal strain caused by the flow of water is eliminated by rotating either the cavity or the core of the mold, or both, to effectively create a three-layer structure between the membrane layers, resulting in high tensile strength and burst resistance. It has the characteristic of being able to produce a perfectly circular hollow hemisphere with high impact resistance.

In any case, the most distinctive feature of the present invention is that injection molding is performed by virtually rotating either or both of the cavity and core of the mold, which has a gate at a position offset from the central axis of rotation. It is in.

Generally, due to the characteristics of injection, resin flows from the gate into the space between the cavity and the core.
At this time, it is common knowledge that internal strain occurs along the flow of the resin. Normally, this internal strain is removed by annealing in a heating chamber, etc., but in the present invention, when resin is injected from the gate into the space between the cavity and the core, the mold cavity or core is removed. By rotating either or both of the
The molten resin that has entered the space between the cavity and the core causes a turbulent flow and at the same time the mold surface is cooled, creating a temperature difference between the surface that directly contacts the mold surface and the intermediate layer. The membrane rotates as it develops, thereby effectively forming a three-layer structure, which provides high strength against tearing and tension.

However, since the resin is injected from the gate located at a position offset from the center of the mold, turbulent flow occurs throughout the entire molten resin, making it possible to obtain a resin structure randomly oriented in multiple directions. I can,
Furthermore, more efficient molding can be achieved by compressing the resin while rotating the mold, or by rotating the mold in the opposite direction after stopping the mold rotation.

Note that U.S. Patent No. 340970 describes a device that rotates the mold during injection molding, but this is for molding a container, and the corners of the bottom of the container are not rounded. Since the molten resin tends to stagnate at an angle and does not create uniform turbulence, it is not possible to obtain a molded product with good orientation.Furthermore, since the gate is provided in the center of the mold, the molten resin remains stationary in this area. However, in the present invention, since a hollow hemisphere is molded and the molded product is rounded as a whole, the gate is shifted from the center of the mold. Combined with this, there are no drawbacks such as those mentioned above.

As the resin used in the present invention, any resin that can be injection molded can be used, such as phenol resin, urea resin, melamine resin, cellulose acetate, polyvinylidene chloride, and methacrylic resin. , polyolefins such as polyamide, polyethylene or polypropylene,
Polystyrene, styrene-acrylonitrile copolymer, acrylonitrile-butadiene-styrene copolymer, fluororesin, polycarbonate, polyether, saturated polyester, etc. are used.

(Example) The present invention will be specifically described below with reference to the drawings.

As the injection molding machine used in the method and apparatus according to the present invention, a general-purpose molding machine is used in consideration of materials, precision, etc. Regarding the mold, consideration is given to precision, roundness, etc., and the shape and surface of the joint surface. A mold is manufactured taking into consideration the condition and other factors.

However, since it is necessary to rotate either the cavity or the core, or both, the ones shown in FIGS. 1 to 4 are used.
However, the illustrated one rotates the core.

FIG. 1 is a cross-sectional view of the mold portion, and FIG. 2 is a diagram showing the molds arranged in a quadruple arrangement. Cavity 1 of the injection mold is fixed side mold plate 2
The device is equipped with a gate 3, which is the same as a conventional device, through which resin is injected into the space between the cavity and the core.

The rotating core 4, which forms a hemispherical space together with the cavity 1 as described above, is integrally formed with a main shaft 6 that is rotatably mounted on the movable mold plate 5, and the rear end of the main shaft 6 is attached to a pressure bearing. It is thrust supported by a receiving plate 8 via a ring 7.

9 and 10 are thrust roller bearings.

A sprocket 11 driven via a chain from a motor (not shown) installed on the movable mold 5 drives a drive shaft 12, whose gear 13 meshes with the gear 14 of each main shaft 6. As a result, each main shaft 6 is driven and the rotating core 4 is rotated.

The rotating core 4 is mushroom-shaped, and its constriction is supported by another core 4a, which together with the thrust roller bearings 9 and 10 described above are made to withstand injection pressure sufficiently. Note that 15 is a stripper plate, and a stripper bush 16 is provided on this plate.

In addition, there are a runner and a stripper plate 17 between the fixed side mold plate 2 and the fixed side mounting plate 2a, and the movable mold moves with respect to these fixed side molds.
is adapted to form a molding space together with the cavity 1. The other part 18 is a fixed side mounting plate.

In the above mold, cavity 1 is the rotating core 4.
When a molding space is formed, the core 4 is rotated from the drive shaft 12 via the gears 13 and 14 and the main shaft 6, and resin is injected into the molding space from the gate 3.

At this time, the molten resin entering the molding space from the gate 3 located at a position offset from the center of the mold causes turbulence as the rotating core 4 rotates, and at the same time, as the mold is being cooled, the molten resin enters the molding space. Since the film rotates while creating a temperature difference between the part that is in direct contact with the mold and the intermediate layer that is not in direct contact with the mold, the film is molded while effectively forming a three-layer structure. At this time, the molten resin is injected into the molding gap from the gate 3 located at a position offset from the center of the mold, causing a turbulent flow of the entire molten resin, forming a hollow hemisphere oriented randomly in multiple directions. compress the resin while rotating the mold, or
Alternatively, by further rotating the mold in the reverse direction after the mold rotation has stopped, more rational molding can be performed.

When the molding is completed, the rotary core 4 stops rotating and the molded product that leaves the cavity 1 is cut out by the strip plate 15.

For example, the injection molding conditions described above are as follows.

Clamping force 10ton or more Injection pressure 500Kg/ ^cm2 or more Core rotation speed 50rpm~1000rpm Rotational torque 1Kgm~20Kgm Mold temperature 15℃ or more Injection time 0.2~3sec Injection pressure 500~600Kg/ ^cm2 Injection rate 100~300c.c ./S Screw rotating machine of extruder 10-300rpm The shape of the core is a straight round rod shape following a spherical part as shown in Figure 4, or a straight round bar shape following a spherical part as shown in Figure 3. It is conceivable that the core be formed into a conical shape, but since the core must rotate while receiving considerable injection pressure, a shape as shown in FIG. 1 is preferable.

Next, the hollow hemispheres obtained by injection molding as described above are bonded together at their opening edges to form a hollow sphere, and the joining method is as shown in Figures 5 and 6. is used. That is, as shown in FIG.
The hemispherical molded bodies a and b are bonded to 9 and 20 so that they fit together.

Perforated disk surfaces 19a, 20 of holders 19, 20
Since the boxes a are formed in the same hemispherical shape, they can be easily absorbed by the perforated discs 19a and 20a by evacuating the boxes 19b and 20b in the holders 19 and 20 through a pipe from a vacuum pump.

Each holder 19, 20 also has its shaft 21,
Since it is rotatable at 22 and also movable up and down, a certain amount of adhesive, such as cyanoacrylate, is applied from a needle-shaped applicator 23 to either one of the opening edges of the hollow hemisphere while rotating the shafts 21 and 22. is dropped, and then either or both of the shafts 21 and 22 are brought close to each other to join the opening edges. In this case, more uniform bonding can be achieved by changing the rotation.

The one shown in FIG. 6 uses an endless belt-shaped coating device instead of the injection needle-shaped coating device shown in FIG.

24 is an endless belt stretched between rotating rollers 25 and 26, a part of which is immersed in an adhesive tank 27, and as the belt rotates, the part coated with adhesive is applied to the opening edge of the hemisphere. It can be applied by direct contact.

Hemispheres can be joined as described above to form a hollow sphere, but in addition to the above-mentioned adhesive application joining method, there is also a method in which the shape of the joining surface can be freely designed on the mold. The spin welding method, high-frequency joining method, ultrasonic joining method, and dove cement joining method are used, and the optimal method is freely selected taking into consideration the material, purpose, strength, workability, etc. .

As for the shape of the bonding surface, any shape as shown in FIG. 7 A to E is selected.

In Figure 7B, there are burrs and notches on the outside, but it can still be used. However, in consideration of adhesive strength, shapes C, D, and E in FIG. 7 are preferable.

Regarding other adhesive application bonding methods, if the adhesive uses a solvent, the influence of the solvent on the material will be large, so a solvent-free type is preferable.

When the hemispheres are joined as described above and a hollow sphere is completed, for example, in the case of adhesive application joining method,
Since the adhesive protrudes from the joint, it is removed in the subsequent burr process.In addition to the method using a polisher, grinding with a cutting tool is also used to remove the burr.

The final surface finishing of the sphere is also performed as a post-treatment, and a sandblasting method or wrapping method is employed.

Generally, there are no Japanese industrial standards for ping pong balls, and although the International Table Tennis Federation specifies that they are made of plastic, the material has not yet been determined.

However, based on the diameter of the ball (37.7 m/m ± 0.5), the weight of the ball (2.46 ± 0.06 g), and the repulsive force of the ball (dropped from 30.5 cm above the standard board, it rebounds from 23.5 to 25.5 cm). When a ping pong ball was manufactured according to the method of the present invention by using ABS resin while taking into consideration the specific gravity and film thickness of the resin, as well as workability with adhesives, it was found that it was extremely resistant to tearing and tension. A ping pong ball with high strength was obtained.

Furthermore, when observing a ping pong ball with a polarizing plate,
A very remarkable orientation phenomenon was observed.

[Brief explanation of the drawing]

FIG. 1 is a cross-sectional view of the mold of the present invention, FIG. 2 is an embodiment diagram showing an arrangement method of the mold of the present invention, FIGS. 3 and 4 are diagrams of modified embodiments of the mold different from FIG. 1, 5th and 6th
The figures show different embodiments of the joining device, and FIGS. 7A and 7E show modified embodiments of various joining surfaces. 1...Cavity, 3...Gate, 4...Rotating core, 6...Main shaft.

Claims (1)

[Scope of Claims] 1. While rotating either the cavity or the core of an injection mold consisting of a cavity and a core, or both, a gate provided at a position offset from the central axis of rotation of the mold Injecting molten resin into a mold to mold a hollow hemisphere, and compressing the resin while rotating the mold, or after stopping rotation of the mold, further rotating the mold in the reverse direction. A method for manufacturing a hollow hemisphere, characterized by forming a three-layer structure on the resin layer of the hollow hemisphere. 2. An injection mold consisting of a cavity and a core is one in which either the cavity or the core, or both, can rotate, and the injection mold has a mold located at a position offset from the central axis of rotation. , a hollow hemisphere manufacturing device characterized by having a molten resin gate.