SCREW TYPE INJECTION MOLDING MACHINE

PROBLEM TO BE SOLVED: To prevent a trouble such as a disturbance of a forward or reverse operation of a torpedo due to a leakage of a molten resin to an infinitesimal gap between an outer wall of the torpedo and a cylindrical part of a cylinder head. SOLUTION: A torpedo 7 moving forward or reversely by a linearly driving means 16 for the torpedo in a cylinder head 4 has a reservoir 6 for storing a molten resin at a center. A plurality of inner channel holes 8a extended in an axial direction at an interval in a circumferential direction are provided in an outer wall 7d surrounding the reservoir 6. A molten resin supplied to the screw 2 in a plasticizing step flows through an inner channel hole 8a through a rear end groove 19a of the torpedo 7, and is stored in the reservoir 6. The outer wall 7d of the torpedo 7 and a cylindrical part 4b of the head 4 are sealed therebetween by a piston ring or the like to prevent an invasion of the resin.