Controlling method of injection through injection molding machine

A method for controlling the injection of a molten resin through an in-line screw type injection molding machine equipped with a check ring for permitting the injection of the molten resin, which is stored on a front side of a free end portion of a screw, by an advancement of the screw through a heating cylinder in an injection stroke and also for preventing the molten resin from flowing backward from the front side of the free end portion of the screw to the rear side of the screw during the injection stroke, which comprises the following consecutive strokes:

• rotating the screw in a normal direction to knead and plasticize a resin material and to feed the resultant molten resin to the free end portion of the screw and then retracting the screw to meter and store a predetermined amount of the molten resin adjacent to the free end portion of the screw;
• rotating the screw in reverse direction to make the pressure of the molten resin on the rear side of the check ring lower than the pressure of said predetermined amount of the molten resin on the front side of the check ring;
• retracting the screw to reduce the pressure of the resin on the front side of the check ring, thereby performing a decompression stroke;
• and
• advancing the screw to inject the molten resin, which is stored on the front side of the check ring, into a mold.