Plastification and injection device for an injection molding machine

A plastification and injection device for an injection molding machine, comprising a screw housing having an inlet for granular plastic material and an outlet nozzle, an injection screw mounted within said housing and having a tip end spaced from said outlet nozzle to therewith define a plasticizing chamber, means for axially rotating said screw in one direction for thereby plasticizing the material fed into said housing, a hydraulic piston and cylinder unit for axially shifting said screw for injecting plasticized material from said chamber through said nozzle, said unit comprising a cylinder affixed to said housing and a piston connected to said screw, said piston defining with said cylinder a piston extension chamber and a piston retraction chamber, hydraulic means for operating said piston and cylinder unit, said means comprising hydraulic feed lines connecting said chambers and a first multi-directional control valve in said lines, a linear amplifier having hydraulically fixed feedback and comprising said valve which is mounted for shifting movement to control the flow of hydraulic fluid through said lines for axially shifting said screw, an elongated threaded rotatable spindle threadedly connected with said piston, said first valve being mounted on said spindle such that the shifting movement thereof is effected upon spindle rotation, a first stepping motor coupled to said spindle for rotation of said spindle in accordance with the injection pressure and/or the rate of injection, whereby rotation of said spindle effects the movement of said first valve to control the flow of hydraulic fluid, the movement of said piston effecting an oppositely directed movement of said first valve via said spindle which is counteracted by said first motor.