OPERATION OF INJECTION MOLDING MACHINE

PURPOSE:To make the back pressure of a material smaller when metered, to decrease the damage of glass fibers and to carry out the metering rapidly, by retreating a screw or a plunger in such a way that an empty space having a specified ratio to a predetermined metering quantity is produced at an apex side of the screw or the plunger. CONSTITUTION:An injection molding machine, in the barrel of which a screw or plunger being capable of going back and forth and rotating is provided, is used. In the method for storing a specified amt. of a material at an apex side of said screw or plunger in the barrel and carrying out injection by forwarding the screw or the plunger, said screw or plunger is kept backward in advance so that an empty space being 30-99% of the specified amt. of the material can be formed at the apex side. Too much increase of a pressure acting the resin material in a metering process can be thereby avoided and an injection molding can be done with less degradation of materials such as glass fibers, etc. It is thereby possible to obtain a molding having excellent characteristics such as impact strength, etc. Metering capacity also increases and the productivity is improved.