Extruded plastic film method and apparatus for the manufacture thereof

Claim 1

A die for melt-extruding tubular thermoplastic film comprising: a. a cylindrical base plate having a central opening therein; b. a hollow cylindrical core section concentrically removably mounted in the central opening of said base section, said core section having an annular outer wall including a lower cylindrical outer wall portion seated on and projecting above the upper surface of said base plate and an upper, outwardly inclined, outer wall portion attached to said lower cylindrical outer wall portion; c. a forming ring section removably mounted on the upper surface of said base section and surrounding said annular outer wall of said core section, said forming ring section having a bottom wall and an outwardly inclined, annular inner wall which is spaced from said upper, outwardly inclined, outer wall portion of said core section to define a conical passage terminating in a die orifice for extrusion of said tubular thermoplastic material; d. said base plate having a ring-shaped recess in its upper surface opposite and spaced from said bottom wall of said forming ring to provide a ring-shaped chamber which joins said conical passage at its lower end; e. a flow control ring Movably mounted in said ring-shaped chamber and adapted to be positioned to change the height of said ring-shaped chamber at its juncture with the lower end of said conical passage; and f. said base plate being provided with two inlet ports spaced about 180* apart, which ports communicate with said ring-shaped chamber whereby separate streams of molten thermoplastic material may be simultaneously fed to said die.