Plastic article or earthenware shaping or treating: apparatus – Female mold and charger to supply fluent stock under... – With means to evacuate mold or provide controlled environment
Patent
1994-05-09
1994-12-20
Chiesa, Richard L.
Plastic article or earthenware shaping or treating: apparatus
Female mold and charger to supply fluent stock under...
With means to evacuate mold or provide controlled environment
425564, 425566, 425812, 425DIG224, B29C 4520, B29C 4534
Patent
active
053741811
DESCRIPTION:
BRIEF SUMMARY
FIELD OF THE INVENTION
This invention relates to an injection molding nozzle device for use in injection molding of synthetic resin. More particularly, this invention relates to an injection molding nozzle device to be used in molding a shaped article containing a cavity formed by dint of a fluid, such as a gas, by injecting molten synthetic resin and the fluid into the mold cavity of a mold.
DESCRIPTION OF THE PRIOR ART
Among conventional injection molding nozzle devices of the class adapted to injecting molten synthetic resin and a fluid into the mold cavity of a mold, one known version comprises a nozzle body with a needle valve reciprocated by the force of an external drive mechanism to open and shut a resin passage. Provided in the central part of this needle valve is a fluid passage fitted with a check valve [Japanese Patent Application Disclosure (KOKAI) No. 119,063/1976]. In this injection molding nozzle device, when the needle valve is advanced, the leading terminal of the needle valve is pressed against the periphery of an opening of the front part of the nozzle body which communicates with the resin passage, consequently shutting off the resin passage. The needle valve is provided at the front part thereof with a needle valve opening which communicates with the fluid passage. While the resin passage is kept in its shut state, the fluid can be injected via the needle valve opening and the nozzle body opening into the mold cavity. Conversely, when the needle valve is retracted, the tight contact is terminated between the periphery of the nozzle body opening and the front part of the needle valve and the nozzle body opening is opened into the resin passage. In this manner, the molten synthetic resin will be injected via the nozzle body opening into the mold cavity.
In this conventional injection molding nozzle device, however, once the fluid is injected into the mold cavity, it no longer can be recovered or discharged through the fluid passage because the fluid passage is provided with a check valve adapted to prevent the molten synthetic resin from flowing back into the fluid passage during injection of the molten synthetic resin into the mold cavity. The discharge of the fluid so injected into the mold cavity, therefore, is attained by separating the mold and the nozzle body from each other and consequently allowing direct release of the fluid from the mold. This procedure, however, not only makes fluid recovery and reuse difficult but also can cause some defects in the shaped article because the pressure of the fluid inside the mold cavity cannot be controlled, for example, by gradually lowering.
The problem will be described in more detail below.
Generally, the pressure of the fluid which is injected into the mold cavity is required; (a) to overcome that of the molten synthetic resin at the injection inlet, (b) to be capable of causing flow of the molten synthetic resin to be expelled to the gate and the mold cavity when the fluid is injected into the sprue and the runner and used therein in forming a hollow part, (c) to pass through the gate part, and (d) to enable flow inside the mold cavity of the molten synthetic resin when the fluid forms a hollow part inside the mold cavity. The magnitude of this pressure is fixed by such factors as the viscosity of the molten synthetic resin, the design of the mold, and the amount of the molten synthetic resin needed to fill the mold cavity.
After a hollow part has been formed or after the molten synthetic resin admitted into the mold cavity has been cooled to the extent of failing below the flowing temperature and undergoing solidification, the fluid injected into the central part of the molten synthetic resin in the mold cavity, presses the resin layer enveloping the hollow part and prevents a sink mark. If the pressure of the fluid is unduly high, it produces residual strain in the resin layer enveloping the hollow part. Particularly, this residual strain occurs concentrically in the boundary surface between the hollow part and the solid part when
REFERENCES:
patent: 2940123 (1960-06-01), Beck et al.
patent: 3947177 (1976-03-01), Eckardt
patent: 4106887 (1978-08-01), Yasuike et al.
patent: 4942006 (1990-07-01), Loren
patent: 4944910 (1990-07-01), Hendry
patent: 5022846 (1991-06-01), Schmidt
No. JP4089220, Publication Date Mar. 23, 1992.
Patent Abstracts of Japan, vol. 016, No. 314 (M-1278), Jul. 9, 1992.
Horikoshi Maki
Matsumoto Hiroyuki
Watanabe Mitsuo
Yamaji Teppei
Asahi Kasei Kogyo Kabushiki Kaisha
Chiesa Richard L.
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