Injection unit for an injection molding machine

An injection unit for an injection molding machine, comprising:

• a) a barrel for receiving a plasticizing screw, the barrel extending horizontally along an axis between a barrel front end and a barrel back end;
• b) a housing adjacent the barrel back end;
• c) a first cylinder within a cylindrical body rotatably supported in the housing for rotation about the axis;
• d) a shaft coaxial with the axis and axially fixed relative to the housing, the shaft having a shaft back end proximate a housing back end of the housing and a shaft front end spaced axially forward of the shaft back end;
• e) a piston slidably received in a first annular space radially intermediate a first inner surface of the first cylinder and an outer surface of the shaft, the piston including a second cylinder coaxial with the axis and having a second cylinder front end for connection to the plasticizing screw and a second cylinder back end spaced axially rearward of the second cylinder front end, the piston further including a first piston head received in sealed sliding fit in the first annular space and affixed to the second cylinder back end, and the piston fixed to rotate with the first cylinder and translatable relative to the first cylinder along the axis between advanced and retracted positions;
• f) a first pressure chamber in the first annular space axially rearward of the first piston head for urging the piston toward the advanced position when pressurized;
• g) a second piston head received in sealed sliding fit in an interior of the second cylinder and affixed to the shaft front end;
• and
• h) a second pressure chamber axially forward of the first piston head and in a second annular space radially intermediate the shaft and the second cylinder, the second pressure chamber bounded axially by the first and second piston heads for urging the piston toward the retracted position when pressurized.

An injection unit for an injection molding machine, comprising:

• a) a barrel for receiving a plasticizing screw, the barrel extending horizontally along an axis between a barrel front end and a barrel back end;
• b) a housing adjacent the barrel back end;
• c) a first cylinder within a cylindrical body rotatably supported in the housing for rotation about the axis;
• d) a piston slidably received in the first cylinder, the piston including a second cylinder having a second cylinder front end for connection to the plasticizing screw and a second cylinder back end spaced axially rearward of the second cylinder front end, the piston further including a first piston head in the first cylinder and affixed to the second cylinder back end, and the piston fixed to rotate with the first cylinder and translatable relative to the first cylinder along the axis between advanced and retracted positions;
• e) a first pressure chamber in the first cylinder axially rearward of the first piston head for urging the piston toward the advanced position when pressurized;
• and
• f) a second pressure chamber in the second cylinder axially forward of the first piston head for urging the piston toward the retracted position when pressurized.