Plastic and nonmetallic article shaping or treating: processes – With measuring – testing – or inspecting
Patent
1991-11-04
1993-11-09
Heitbrink, Jill L.
Plastic and nonmetallic article shaping or treating: processes
With measuring, testing, or inspecting
264 405, 425145, 425147, 425148, 425149, B29C 4576
Patent
active
052600084
DESCRIPTION:
BRIEF SUMMARY
FIELD OF THE INVENTION
The present invention relates to a method for detecting the resin property of plasticized synthetic resin in an injection molder which has a flow path opening/closing mechanism in the passage between the cylinder of the molder and the cavity of a mold so as to block the resin flow between the cylinder and the cavity, and to an injection control method for controlling the weight of the plasticized synthetic resin injected from the cylinder of the injection molder to fill the cavity of the form, on the basis of the detected resin property.
BACKGROUND OF THE INVENTION
In the conventional injection molding of plasticized synthetic resin by an injection molder, the weight of the injected plasticized synthetic resin varies with the molten resin pressure, the molten resin specific volume or the molten state of the resin indicated by the molten resin temperature etc. (including the influence of the disturbance on the molding system). Therefore, it is difficult to form products of a constant quality. To cope with this problem, a number of proposals, so-called adaptive control, have been made. The art disclosed in the Japanese Patent Laid Open Publication No. 84932 of Showa 56 (the year 1981) is an example.
Basically, in the adaptive control method, when the influence of a disturbance on the molding system and change in the molten resin pressure, molten resin temperature or mold temperature are detected, a controllable molding condition (pressure, time, etc.) other than the detected factors are changed into a control factor, thereby assuring the constant product quality.
However, this control method has the following disadvantages: correlation between the detected factor according to the mold and the product quality and between the control factor and the product quality. detected factor and the product quality and between the control factor and the product quality varies greatly depending on the mold. Therefore, the study and analysis described in the item 1 above must be repeated each time the mold is changed.
Injection molding process is generally described in view of the plasticized synthetic resin property such as the PVT property [molten resin pressure-molten resin specific volume-molten resin temperature (=molten state)]. Based on this fact, some proposals have been made to control the molding process by the PVT property, such as described on the pages 11 and 12 of Modern Plastics International, October 1989. This PVT property-based control method also has the following problems:
(i) To control the molding process by the PVT property, the PVT property must be given or determined in advance for practical use. Determination of the PVT property requires accurate measurement using a special measurement instrument in a test facility.
(ii) Various kinds of plasticized synthetic resins are used in actual injection molding and, in many cases, new plasticized synthetic resins are introduced one after another. Therefore, if the PVT property of certain type of plasticized synthetic resin can be obtained experimentally to provide the experimental determination of the PVT property of all the plasticized synthetic resins to be used would involve enormous time and expense and is not feasible.
(iii) Moreover, for the same plasticized synthetic resin, the experimentally determined PVT property does not always coincide with the PVT property in an injection molder actually used at the injection molding site because of the following reason. In an experimental equipment, the plasticized synthetic resin is heated only externally. In an actual injection molder, in contrast, the thermal history and extremely large shearing force during the melting process of the plasticized synthetic resin cause slight change in the molecular distribution of the resin. Consequently, the melting behavior of the resin in the actual injection molder may be different from that in the experimental equipment.
(iv) Furthermore, for recycled use of waste resin material, the actual injection molding may use reclaimed plasticized syn
REFERENCES:
patent: 3767339 (1973-10-01), Hunkar
patent: 3822057 (1974-07-01), Wheeler
patent: 4066725 (1978-01-01), Boettner
patent: 4240996 (1980-12-01), Hunkar
patent: 4816197 (1989-03-01), Nunn
patent: 5057255 (1991-10-01), Sato et al.
Article from Plastics Engineering, "Processing-A Deductive Approach to Process Control" Feb., 1989, pp. 45-47.
Article from Plastverarbeiter, Oct., 1989, pp. 43, 44, 46, 47.
Heitbrink Jill L.
Komatsu Ltd.
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