Injecting apparatus with check valve

A screw injecting apparatus comprising:

• a heating cylinder for heating a molding material being transferred therethrough, the heating cylinder having a nozzle at one end thereof;
• a screw received in the heating cylinder rotatably and movably back and forth and having a tip end portion spaced backward from the nozzle, the screw, when rotating in one direction, feeding a melt of molding material toward the nozzle while the screw is pushed back by a reaction of the melt accumulated around the tip end portion of the screw head;
• a check valve for preventing the melt from flowing backward toward the screw, the check valve comprising
• a seat ring mounted on the tip end portion of the screw and movable in unison with the screw, the seat ring having an axial groove for the passage therethrough of the melt, and
• a check ring mounted on the tip end portion of the screw in tandem relation to the seat ring and rotatable relatively to the screw and the seat ring within a predetermined angular range, the check ring having an axial groove for the passage thererthrough of the melt, the axial groove of the check ring and the axial groove of the seat ring being phased such that rotation of the screw in said one direction causes the axial groove in the check to communicate with the axial groove in the seat ring, thereby permitting passage of the melt through the check valve, and rotation of the screw in the reverse direction causes the axial groove of the seat ring to be closed by a body of the check ring, thereby blocking passage of the melt through the check valve;
• and
• a control unit for controlling operation of the screw such that in a metering phase of molding process, the screw rotates in said one direction to feed a melt of molding material toward the nozzle, when a metered amount of melt is accumulated forward of the tip end portion of the screw, the screw moves backward by a predetermined distance to reduce the reaction from the metered melt and, thereafter, the screw rotates in the reverse direction to cause the screw to move forward until the amount of forward movement of the screw becomes substantially equal to said predetermined distance.