Plasticating control apparatus for injection machine

A plasticating control apparatus for an in-line screw type injection machine, comprising:

• a resin pressure sensor for detecting as an electrical signal a pressure of a molten material at a distal end of a heating cylinder during plastication;
• an electric motor whose rotational speed is controlled in response to a control signal;
• means for directly converting the rotational speed of said electric motor to reciprocal movement of a hydraulic piston for driving a screw;
• and a control circuit for receiving the electrical signal from said resin pressure sensor and supplying the control signal to said electric motor in accordance with the electrical signal, the control signal supplied from said control circuit to said electric motor being adapted to control the rotational speed of said electric motor and hence a backward speed of the screw such that the pressure of the molten material at the distal end of said heating cylinder is not a negative pressure but substantially zero kg/cm.sup.2.