Nissei Plastic Industrial Co., Ltd.

Hisato Shimizu

Kiyoto Takizawa

Masashi Suganuma

Yoshitoshi Yamagiwa

Takayoshi Shioiri

Hiroshi Koizumi

Kazutoyo Kobayashi

An unstable weighing due to the plunger sliding resistance in a prepla type injection molding machine is prevented by dividing control of the plunger retraction movement for the weighing into speed control and pressure control. A plastic resin supply start position and a forced retraction release position are set along the way of the plunger retraction stroke by reference to a weighing start position. A plunger is moved from the weighing start position after injection and pressure-keeping to a weighing stop retraction position. Plastic resin is supplied to the forward portion of the injection cylinder when the plunger attains the supply start position from the weighing start position. The plunger is moved by forced retraction up to the forced retraction release position by speed control; the weighing is stabilized by changing the speed control to the pressure control once the plunger attains the forced retraction release position.

Weighing method in prepla type injection molding machine

In a method for controlling an injection molding machine, a screw is advanced from an injection start position by means of velocity control, and when the screw reaches a control changeover point, pressure control is effected in place of the velocity control to apply pressure to the screw. Preliminary molding is performed to obtain an acceptable product; a total charged amount of resin during the preliminary mold is obtained on the basis of a movement distance over which the screw has moved before reaching the control changeover point during the preliminary mold; and the total charged amount is stored as a changeover target value. During ordinary molding, a total charged amount of resin is obtained on the basis of a movement distance over which the screw advances from the injection start position; and pressure control is started when the total charged amount reaches the changeover target value. Thus, the total amount of resin charged into a mold cavity in each molding cycle becomes constant without being affected by the charging pressure and temperature of the resin.

Method for controlling injection molding machine

A preplasticizing type injection apparatus having an injection cylinder internally provided with an injection plunger and a plasticizing cylinder provided in the inside with a plasticizing screw or plunger, the injection and plasticizing cylinders being arranged in juxtaposition and held in communication with each other by way of a resin conduit connecting an inlet path of the injection cylinder arranged at the front end thereof and defining the limit of advancement of the plunger and an outlet path of the plasticizing cylinder arranged at the front end thereof so that a front end portion of the injection cylinder is charged with resin molten in the plasticizing cylinder and the resin in the front end portion of the injection cylinder is injected into a mold by the plunger, characterized in that the resin conduit is realized in the form of a small metal pipe having an inner diameter between 5 and 10 mm and a length at least five times and preferably twenty to forty times greater than the inner diameter of the pipe and provided on the outer periphery with temperature control element is provided. With such a conduit, resin passing therethrough can be more kneaded to improve the distribution of heat and plasticity before it gets to the injection cylinder.

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Nagano-ken, Japan

Hisato Shimizu