Tubular extrusion die

Claim 1

A die for extruding a tubular sheet of thermoplastic film material comprising: (a) a housing having a longitudinal opening therethrough defining a first axis; (b) an elongated mandrel positioned within said housing opening and spaced therefrom to form an annular conduit extending in the direction of said axis; (c) a base plate connected to said housing at the upstream end thereof; (d) a plurality of means for spacing said mandrel from said base plate to provide a space therebetween, each of said spacing means having an axis parallel to said first axis whereby said mandrel and said base plate have spaced apart juxtaposition walls extending radially from said first axis and in communication with said annular conduit; (e) each of said spacing means having a first groove formed in one of said mandrel and said base plate walls extending substantially radially from said first axis to one side of said one of said spacing means and tangentially from said one of said spacing means, each of said spacing means having a second groove formed in one of said mandrel and said base plate walls extending substantially radially from said first axis to another side of said spacing means and tangentially from said spacing means, whereby the tangential extensions of each one of said grooves intersect; and (f) means for introducing molten thermoplastic material through said base plate into said space between said mandrel and said base plate whereby such thermoplastic material flows radially outwardly from said first axis to said annular conduit.