Plastic and nonmetallic article shaping or treating: processes – With measuring – testing – or inspecting
Patent
1997-06-26
1998-08-18
Heitbrink, Jill L.
Plastic and nonmetallic article shaping or treating: processes
With measuring, testing, or inspecting
264 405, 2643281, 26432819, 425145, 425147, 425558, B29C 4554, B29C 4576
Patent
active
057955093
DESCRIPTION:
BRIEF SUMMARY
TECHNOLOGICAL FIELD
The present invention relates to a method of injection molding using a preplasticization type injection molding machine. More specifically, the present invention relates to an injection method using a preplasticization type injection molding machine that feeds molten resin which has been plasticized in a plasticization chamber to an injection chamber where the molten resin is measured, and injects the molten resin in the injection chamber by means of a plunger.
TECHNOLOGICAL BACKGROUND
Precision molded parts have been manufactured by means of injection molding. In this field, it is essential that the geometry of the mold die cavities be exactly transferred to the molded parts, and that the physical properties of the material be stable. For this purpose, it is important that the molding resin material be stably plasticized (or molten) in terms of its physical properties, that the molten resin be accurately measured in accordance with a predetermined volume, and that the filling volume be accurately controlled, preventing the cushion amount (i.e., the amount of molten resin needed for replenishing the contraction volume of the molded parts upon cooling provided by storing some molten resin in the tip of the injection chamber under high pressure shortly after filling) from varying when maintaining the appropriate pressure.
Performing this type of injection molding with a preplasticization type injection of molding machine, i.e., a machine in which the synthetic resin material is plasticized in the plasticization chamber and is injected from the injection chamber, has the advantage that no leakage of the molten resin takes place except for a minute amount of the resin from between the plunger and the injection cylinder, resulting in little variation in filling volume. The reason is that injection is done by the plunger which is not equipped with a check valve. Therefore, the variation in cushion amount between injection shots can be minimized provided that the molten resin is substantially accurately measured.
Applicant has disclosed, in Toku-Kai-Hei 6-170900 technology for injection molding by a screw preplasticization type of injection molding machine. After the measuring process is completed, the plasticization screw is moved forward to close (hereinafter referred to as "blocking") the connection passage between the plasticization chamber and the injection chamber, followed by injection. Since blocking is done by moving the screw forward, the molten resin in the injection chamber increases slightly in amount. This incremental change in position (hereinafter referred to as "position movement caused by blocking") from the position of the plunger where the completion of measurement is detected (hereinafter referred to as "measurement detection position") to the position of the plunger when the plunger moves backward by means of the blocking operation is calculated so as to correct the next measurement detection position where the measurement is completed. Over the short-term, the resin material is almost continuously plasticized for each molding shot, and therefore, the physical properties of the molten resin does not vary between molding shots. On the other hand, during continuous operations over a longer period of time, the situation may gradually vary. In this case, the position movement caused by blocking will gradually vary. Therefore the measurement detection position corrected by this position movement caused by blocking may be measured with little variation.
However, the molten resin fed to the injection chamber may contain a small amount of resin-dissolved gas, such as bubbles which were not expelled at the time of plasticization. This presence of the bubbles in the molten resin may cause the density of the molten resin to vary, leading to slight variations in the volume of the resin measured. The reason is that, for improved plasticization efficiency, the pressure acting on the molten resin in the injection chamber (which is controlled by the back-pressure acting on the plunge
REFERENCES:
patent: 5258147 (1993-11-01), Yokota
patent: 5260010 (1993-11-01), Yokota
patent: 5266247 (1993-11-01), Yokota
patent: 5500166 (1996-03-01), Sasaki et al.
patent: 5665282 (1997-09-01), Nakamura
Fujikawa Misao
Otowa Hirotsugu
Heitbrink Jill L.
Sodick Co. Ltd.
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