Reciprocating screw injection molding machine with hydraulic actuating mechanism with prefill valve

An injection molding machine having relatively movable mold carrying platens to define a mold cavity into which plasticized material is adapted to be injected when said platens are moved toward each other to close said mold and from which a molded part is adapted to be removed when said platens are moved apart to open said mold;

• one of said platens being movable and having a first piston thereon reciprocable in a first cylinder which has fluid communication with a prefill tank via a passage;
• a second relatively smaller cylinder secured to the head of said first cylinder and having a piston reciprocable therein with its piston rod slidably sealed in said head and connected to said first piston thus to move said one platen toward and away from the other platen to close or open said mold responsive to actuation of said second cylinder;
• a third cylinder secured to said head having a piston reciprocable therein with its piston rod extending into said passage to constitute a valve member movable in one direction in said passage responsive to fluid under pressure in one end of said third cylinder to open communication between said prefill tank and said first cylinder during movement of said first piston in opposite directions by said second piston and movable in the opposite direction in said passage responsive to fluid under pressure in the other end of said third cylinder to close said passage and open communication of said first cylinder with a fluid pressure source at the end of the mold closing movement of said one platen relative to the other platen via an orifice in the piston rod of said third piston which opens into said other end of said third cylinder thus to lock said mold in closed position for injection of plastic material into the mold cavity thereof.