Metal founding – Process – With measuring – testing – inspecting – or condition determination
Reexamination Certificate
2002-08-12
2003-12-23
Elve, M. Alexandra (Department: 1725)
Metal founding
Process
With measuring, testing, inspecting, or condition determination
C164S113000, C164S455000
Reexamination Certificate
active
06666259
ABSTRACT:
TECHNICAL FIELD
The present invention relates generally to a method for manufacturing a mold for a hot-runner injection molding machine, and more particularly, to a method for manufacturing a mold for a hot-runner injection molding machine for injection molding of metal having a higher melting point and a higher thermal conductivity than resin.
BACKGROUND ART
Due to its capability of molding products without runners and sprues, the runnerless injection molding method has a remarkable advantage over the cold-runner system injection molding. Such a runnerless injection molding is suited to injection molding of resin having a relatively low melting point and a low thermal conductivity. The runnerless injection molding method is thus in wide use for the resin injection molding.
FIG. 9
is a sectional view of a mold for a hot-runner injection molding machine making use of induction heating.
The mold comprises a fixed mold plate
3
′ having thereon mounted a nozzle
1
′ and a manifold
2
′, and a movable mold plate
4
′ having a cavity
4
a
′ shaped correspondingly to the shape of products. The cavity
4
a
′ is formed in a heat-resistant metallic core
6
′ attached to the movable mold plate
4
′, whilst a metallic core
5
′ corresponding to the metallic core
6
′ is attached to the fixed mold plate
3
′.
A back plate
8
′ is mounted behind (upper side in
FIG. 9
) the fixed mold plate
3
′, with the manifold
2
′ being arranged in a space
7
′ that is defined between the back plate
8
′ and the fixed mold plate
3
′. The fixed mold plate
3
′ and the metallic core
5
′ are formed with a nozzle fitting hole
3
a
′ extending from the space
7
′ toward the cavity
4
a
′ of the movable mold
4
′. The nozzle
1
′ is inserted from the space
7
′ into the nozzle fitting hole
3
a
′.
A coil (not shown) is wound around the nozzle
1
′ so that the material within the nozzle
1
′ is heated by induction heating by the coil.
By the way, the above mentioned mold of the hot-runner injection molding machine is exclusively used for resin injection molding, although it would theoretically be applicable also to injection molding of metals such as magnesium alloy, aluminum alloy and zinc alloy.
For example, Japan Patent Laid-open Publication No. Hei 9-85416 proposes a hot-runner mold capable of injection molding of metal materials such as magnesium alloy, aluminum alloy and zinc alloy.
In characteristics, however, the above metals have a melting point of 400° C. to 700° C. which is fairly higher than that of resin, and have a fairly higher thermal conductivity than that of resin.
Accordingly, direct application to molten metal injection molding of the existing mold of the hot-runner injection-molding machine for use with resin will pose problems, which follow.
(1) Due to an extremely large difference in temperature between the high-temperature molten metal (material) and the mold, simultaneously with the injection molding the heat of the material is rapidly absorbed by the mold in contact with the nozzle and by the product solidified in the cavity. Thus, for solidifying, the temperature of the material in the gate cut portion drops to the vicinity of the mold temperature, which is fairly lower than the melting point of that material. For this reason, in order to melt the material in the gate cut portion to open the gate cut portion for the next injection, the material in the nozzle runner needs to be heated up to several hundred degrees or above. This means that much time is spent on opening the gate, and it may disturb the high-cycle operation.
(2) Meanwhile, upon the mold opening after the injection molding, the temperature of the material within the gate cut portion and the nozzle in proximity thereto needs to be dropped to a sufficiently low level for solidifying. Otherwise, the molten material may leak out of the nozzle tip or molten material lying behind the gate cut portion may be ejected from the nozzle tip.
(3) In the invention as recited in Japan Patent Laid-open Publication No. Hei 9-85416 described above, the gate is formed with a 0.1 to 0.5 mm diameter circular hole or slit so that the flow resistance of the molten metal passing through the gate becomes higher than the residual pressure of the molten metal material existing in the flow passage, to thereby prevent the molten metal from leaking out of the gate.
Due to the constant exposure of the molten material from the gate, however, any leakage of the molten material is apt to occur upon the mold opening.
From the above reasons, in spite of its higher material yield and productivity, the metal injection molding by the hot-runner injection molding machine was extremely difficult to practice in actuality.
The present invention has been conceived in order to solve the above problems and to provide a method for manufacturing the hot-runner injection molding applicable to metals as well. It is therefore an object of the present invention to provide a method of manufacturing a mold for a hot-runner injection molding machine suitable for the injection molding of molten metal such as molten magnesium alloy and capable of injecting metal by securely blocking the gate cut portion with solidified metal upon the mold opening and by rapidly opening the gate cut portion upon the next injection molding.
SUMMARY OF THE INVENTION
The above object is attained by providing a mold having a gate cut portion whose position has been selected in an appropriate manner.
According to the present invention, there is provided a mold for a hot-runner injection molding machine, the mold being provided with a movable mold plate having a cavity and with a fixed mold plate having a nozzle for injecting molten metal into the cavity and having heating means for heating metal existing in the nozzle, the mold comprising temperature measurement means arranged in the vicinity of a gate cut portion where gate cutting is performed, for measuring the temperature of metal in the gate cut portion; heating control means for providing a control of heating of the nozzle effected by the heating means, on the basis of the result of measurement by the temperature measurement means; the gate cut portion formed on the nozzle at a predetermined position thereof; and heat insulation means arranged on the nozzle so as to cover at least an area where the gate cut portion is formed.
The temperature measurement means detects the temperature of the gate cut portion and sends the result of detection to the heating controller. The heating controller compares for example a preset temperature with the detected temperature, and if it is judged that the temperature of the gate cut portion is lower than the preset temperature, outputs a command signal to the heating means so as to heat the nozzle. This allows the temperature of metal in the gate cut portion to be kept at a certain level or more, making it possible to rapidly melt the metal in the gate cut portion by a slight heating upon the next injection molding, rendering the metal injectable.
The heat insulation means reduces the quantity of heat migrating from the gate cut portion to the mold. The reason for the provision of such heat insulation means is as follows.
If the gate cut portion and the gate portion near the gate cut portion are in contact with the mold, then a greater quantity of heat will be radiated from the metal in the gate cut portion to the mold. For this reason, even though the heating means applies heat to the nozzle to keep the temperature of the metal in the gate cut portion at a certain level or more, a lot of quantity of heat will be migrated toward the mold, making it difficult to keep the temperature at a certain level. Additional thermal energies will be needed for heating. Particularly, even in the cases where a remarkably increased difference exists between the temperature of metal within the nozzle runner and the temperature of metal in the gate cut port
Mizushima Takashi
Sekiguchi Ryoichi
Shibata Itsuo
Elve M. Alexandra
Ju-Oh Inc.
Kanesaka & Takeuchi
Tran Len
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