Plastic and nonmetallic article shaping or treating: processes – With measuring – testing – or inspecting
Patent
1991-09-13
1993-11-02
Heitbrink, Jill L.
Plastic and nonmetallic article shaping or treating: processes
With measuring, testing, or inspecting
264 405, 425145, 425149, B29C 4576
Patent
active
052581470
DESCRIPTION:
BRIEF SUMMARY
FIELD OF THE INVENTION
The present invention relates to a method of detecting the amount of plasticized synthetic resin injected from the cylinder of an injection molder to fill the cavity of a mold.
BACKGROUND OF THE INVENTION
For continuous production of desired moldings by an injection molder, plasticized synthetic resin is injected from the cylinder of the molder through the nozzle into the cavity of a mold connected to the nozzle. In such continuous molding, it is essential to inject plasticized synthetic resin by the amount corresponding precisely to the inside capacity of the cavity, in other words, the volume of an intended product. If the injected amount is greater than required, the resin is forced out through the parting line of the mold to form flash. On the other hand, if the injected amount is less than required, recesses or sinks are formed on the molded surface, resulting in a defective product.
Conventionally, for continuous production of moldings with a stable quality, the amount of plasticized synthetic resin injected to fill the mold cavity is detected on the basis of the position of the screw in the injection molder, as described in the following:
i) The injected amount is detected on the basis of the screw position before the plasticized synthetic resin is injected into the mold cavity. ii) The injected amount is detected on the basis of the following screw position upon completion of dwelling after the plasticized synthetic resin is injected into the mold cavity. dwelling is completed.
However, both of these conventional methods have a problem that the detection may not be accurate because of the following reasons:
Method of i)
The resin pressure of the plasticized synthetic resin in the cylinder of the injection molder is not controlled nor monitored until immediately before the plasticized synthetic resin is injected through the injection molder nozzle into the mold cavity. Therefore, the compressible plasticized synthetic resin does not always provide a constant resin pressure. Particularly when the screw is retreated forcibly to reduce the resin pressure in the cylinder for preventing the resin from leaking through the injection molder nozzle, the resin pressure fluctuates due to the air drawn through the nozzle end.
Furthermore, the check valve provided at the front end of the screw is open before the injection process because pressure is not applied to the screw. Consequently, when pressure is applied to the screw for injection, small amount of the resin flows back as the check valve is closed. This also results in the poor detection accuracy.
Method of ii)
Based on the position 1)
The dwelling pressure is varied to meet various molding conditions for products. The compression amount of compressible plasticized synthetic resin varies depending upon the dwelling pressure, thus hampering the detection accuracy.
High detection accuracy could be achieved if the resin amount in the cylinder of the injection molder was compared under a fixed dwelling pressure. However, since the dwelling pressure is one of the essential molding conditions determining the shape and dimensions of a product, it is impracticable to use a fixed dwelling pressure.
Based on the position 2)
After the screw stops applying the dwelling pressure on the resin in the cylinder, the resin is released from the pressure, taking different times depending on the kind and temperature of the plasticized synthetic resin. Therefore, it is difficult to know whether or not the pressure has been removed completely. This uncertainty also leads to the poor detection accuracy.
Although it takes time for the resin to be released from the dwelling pressure, in general, only short time is assigned for this purpose in the actual production, to avoid reduction in the productivity.
To solve these problems, the object of the present invention is to provide a method of detecting the injected amount of an injection molder, which permits accurate detection, on the injection molder side, of the amount of plasticized synthetic res
REFERENCES:
patent: 3693946 (1972-09-01), Merritt
patent: 3767339 (1973-10-01), Hunkar
patent: 3822057 (1974-07-01), Wheeler
Heitbrink Jill L.
Komatsu Ltd.
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