Plastic and nonmetallic article shaping or treating: processes – With measuring – testing – or inspecting – Positioning of a mold part to form a cavity or controlling...
Patent
1990-01-05
1991-10-15
Heitbrink, Jill L.
Plastic and nonmetallic article shaping or treating: processes
With measuring, testing, or inspecting
Positioning of a mold part to form a cavity or controlling...
2643287, 425145, 425147, 425150, 425562, B29C 4576
Patent
active
050572555
DESCRIPTION:
BRIEF SUMMARY
TECHNICAL FIELD OF THE INVENTION
The present invention relates to an injection-compression molding machine for plastic resins, and more particularly to a molding apparatus including a valve which is disposed in a flow passageway of molten resin provided between an injection unit and a metal mold of an injection-compression molding machine to perform blocking and change of a cross-section area of the aforementioned flow passageway, as well as the molding method.
BACKGROUND TECHNIQUE OF THE INVENTION
In the prior art, for instance, as disclosed in the respective specifications and drawings of Laid-Open Japanese Patent Specifications 60-21225 (1985) and 60-110419 (1985), a molding method by means of a compression molding method is achieved through the steps of pouring resin material to be molded into a heated metal mold, actuating the molding machine to press the material at a low pressure, after the molten resin material to be molded has been filled within the metal mold, once opening upper and lower metal molds a little to remove a gaseous component in the material, again pressing the material at a high pressure, continuing the pressing and the heating until the material has finished to be hardened, and thereafter taking out a molded ariticle by opening the mold. On the other hand, in injection-compression molding, when molten resin material is injected into a metal mold, an injection flow rate and an injection flow velocity of the molten resin are controlled by a moving speed of a screw and a pressing force of the screw.
However, in the above-described compression molding method in the prior art, due to the fact that the pressing is effected as divided into low-pressure pressing and high-pressure pressing, a lot of man-hours are necessitated.
In addition, in the injection-compression molding, since molten resin is injected into a metal mold as varying a speed and a pressure of a screw, depending upon viscosity and elasticity of the molten resin, the responsibility would become an issue, and furthermore, in molding at a low flow resistance such as injection-compression molding, a time of injecting molten resin into a metal mold or an amount of molten resin to be molded cannot be stabilized, so that defects (short-sits, shrinks and warps) would arrive in the molded articles.
Moreover, in the case where compression is commenced during injection, a flow resistance of molten resin would increase gradually, hence in the injection method in the prior art, an amount of injection would vary depending upon viscosity and elasticity of the molten resin, resulting in surplus or shortage in the amount of injection, and so, there is a shortcoming that burrs or short-sits are generated.
SUMMARY OF THE INVENTION
The present invention has been worked out in view of the aforementioned circumstance, and an object of the invention is to provide a molding method which can obtain stable products within a short period of time by carrying out preliminary pressing within an injection unit before injecting molten resin into a metal mold in order to make a density of the molten resin uniform and subsequently carrying out pressing of the molten resin within the metal mold during injection or after injection in an injection-compression molding machine provided with a value between an injection unit and a metal mold, and a molding apparatus for achieving the above-mentioned molding method.
In order to achieve the aforementioned object, according to a first aspect of the present invention, there is provided a molding method in an injection-compression molding machine including a valve disposed in a flow passageway of molten resin provided bewteen an injection unit and a metal mold for effecting blocking and change of a cross-section area of the above-mentioned flow passageway, which method consists of the steps of carrying out preliminary pressing on the molten resin within the injection unit under a closed condition of the aforementioned valve in order to make a density of the molten resin uniform, thereafter injecting a preset a
REFERENCES:
patent: 3787159 (1974-01-01), Bielfeldt
patent: 4421467 (1983-12-01), Richmond
patent: 4855095 (1989-08-01), Sato
patent: 4932854 (1990-06-01), Matsuda et al.
patent: 4952364 (1990-08-01), Matsuda et al.
Fujimoto Satoshi
Higuchi Makoto
Nogawa Makoto
Sasaki Yosuke
Sato Kan'ichi
Heitbrink Jill L.
Kabushiki Kaisha Komatsu Seisakusho
Kananen Ronald P.
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