Plastic and nonmetallic article shaping or treating: processes – Direct application of fluid pressure differential to... – With internal application of fluid pressure
Patent
1996-04-19
2000-02-01
Timm, Catherine
Plastic and nonmetallic article shaping or treating: processes
Direct application of fluid pressure differential to...
With internal application of fluid pressure
B29C 4500
Patent
active
060199350
DESCRIPTION:
BRIEF SUMMARY
The invention relates to a method of injection molding of articles made of a thermoplastic material and having walls which enclose a hollow space, in which a predetermined amount of a plastic material melt is injected into a cavity of a mold and is subjected, simultaneously or subsequently, to an action of a fluid pressure medium, in particular gas, so that, with the formation of the hollow space, the plastic material melt is distributed along and is set against the cavity walls.
The invention also relates to a mold for effecting this method and in which the fluid pressure medium, in particular gas, can be fed into the mold cavity through an injection nozzle of the injection unit connected to the mold gate, or through an injection device located adjacent to the mold gate.
The injection molding of articles is often effected by injecting into mold cavity a predetermined amount of a thermoplastic material melt, which corresponds to the volume of the article, through an injection nozzle of an injection unit connected to the mold gate, with simultaneous or subsequent feeding into the cavity of the fluid pressure medium, in particular gas.
This manufacturing technique is designed for manufacturing objects which, while having relatively large dimensions, should be manufactured with as small amount of a plastic material as possible and, therefore, have an inside hollow space.
It is important that the articles have a certain wall thickness distribution, dependent on their geometry and the plastic material used for their manufacture, to thereby insure their necessary stability in accordance with the purpose of their use.
At the conventionally available manufacturing conditions, their influence on the wall thickness and, in particular, on the minimum wall thickness of an article is very small. That is the temperature of the thermoplastic material, the temperature of the mold walls, the injection speed, and the pressure of the fluid pressure medium, in particular gas, injected into the mold cavity for acting on the thermoplastic material, cannot guarantee an optimal wall thickness distribution and the minimum wall thickness in critical locations of a respective article.
Often it is important or it is required to produce an injection-molded article in which the minimum wall thickness in certain regions should not be reduced under any circumstance, in particular when these regions are regularly subjected to a high load.
The manufacturing of such articles up to the present was effected in the following manner, the mold cavity was completely filled with the thermoplastic material melt, and then a fluid pressure medium, in particular gas, was fed into the plastic material melt or into the cavity containing the same, in order to force out a portion of the liquid plastic material melt.
With such manufacturing of plastic articles, the portion of the thermoplastic material, which was forced out of the mold cavity with the fluid pressure medium, is either returned to the ante-chamber of the injection unit or is pushed into an overflow chamber adjacent to the mold cavity.
The problem with this consists in that the gate of the mold, which communicates with the injection unit, should remain open until the excess plastic material is forced out from the cavity by the action of the fluid pressure medium. Thereby, the course of each separate injection process would be adversely affected.
In another case, an outside control of the flow into the overflow chamber is absolutely necessary, i.e., the costs of producing and operating the mold increase. Namely, in addition, to the mold cavity itself, after each injection process, the adjacent overflow chamber should be cleared from the excess plastic material therein.
A drawback of both know techniques consists in that the portion of the thermoplastic material, which is delivered from the mold cavity to the ante-chamber of the injection unit or to the overflow cavity, can vary from shot to shot, and their results in a too large deviation of the weight of the finished article and in the accomp
REFERENCES:
patent: 4106887 (1978-08-01), Yasuike et al.
patent: 5118455 (1992-06-01), Loren
patent: 5135703 (1992-08-01), Hunerberg et al.
patent: 5204050 (1993-04-01), Loren
patent: 5612067 (1997-03-01), Kurihara et al.
patent: 5759479 (1998-06-01), Gotterbauer
Abstract for Japanese Publication 4-168,017, Patent Abstracts of Japan, Jun. 1992.
Eckardt Helmut
Ehritt Jurgen
Lusebrink Klaus
Renger Michael
Hattenfled GmbH
Timm Catherine
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