Co-extrusion apparatus and method for producing multiple-layered thermoplastic pipe

A balanced flow die apparatus for manufacturing multiple-layered thermoplastic pipe, comprising:

• a. a main extrusion passageway leading to a die outlet and and having an annular cross-section for transporting a first annular stream of thermoplastic;
• b. an inner laydown means circumscribed by said main extrusion passageway for applying a layer of thermoplastic to the inner surface of said first annular stream of thermoplastic;
• c. an outer laydown means disposed circumferentially about said main extrusion passageway for applying a layer of thermoplastic to the outer surface of said first annular stream of thermoplastic;
• each of said inner and outer laydown means including an annular radial orifice communicating with said main extrusion passageway, an annular feed ring supplying thermoplastic to said orifice, and a pressure balanced annular reservoir chamber connected to said annular feed ring for balancing the flow of thermoplastic through said orifice;
• and
• d. a sleeve and a spindle secured to said die apparatus adjacent said die outlet in end-to-end relation with said annular extrusion passageway;
• said sleeve and spindle forming an extended extrusion passage wherein the layers of thermoplastic are stabilized before exiting the die.

A balanced flow die apparatus for manufacturing multiple-layered thermoplastic pipe, comprising:

• a. a die body having a central longitudinal passage, one end of said die body defining a die inlet and the opposite end defining a die outlet;
• b. a cylindrical mandrel disposed within the longitudinal passage of said die body in spaced relationship therewith, said mandrel and said die body defining thereby a main extrusion passageway, and said mandrel having a tapered head facing said die inlet for converting a cylindrical solid stream of thermoplastic into an annular stream;
• c. an inner laydown means disposed within said mandrel for applying a layer of thermoplastic to the inner surface of said annular stream of thermoplastic;
• d. an outer laydown means disposed in said die body circumferentially about said main extrusion passageway for applying a layer of thermoplastic to the outer surface of said annular stream of thermoplastic, each of said inner and outer laydown means comprising an annular radial orifice communicating with said main extrusion passageway, an annular feed ring supplying thermoplastic to said orifice, and a pressurebalanced annular reservoir chamber connected to said annular feed ring for balancing the flow of thermoplastic through said orifice;
• e. means for feeding thermoplastic to each of said inner and outer laydown means;
• and
• f. a sleeve secured within said die body outlet and a spindle secured to said mandrel in end-to-end relation therewith;
• said sleeve and spindle forming an extended extrusion passageway wherein the layers of thermoplastic are stabilized before exiting the die.