Extrusion die and method for forming dual wall corrugated plastic pipe and dual wall plastic pipe having a foam annular core

摘要

Extrusion dies for forming dual wall corrugated plastic pipe and dual wall plastic pipe having a foam annular core that provides homogenous melt flow to each axially displaced orifice by means of an individual concentric spiral mandrel are disclosed. Spiral mandrels transport the melt from the extruders initially in spiral paths and then to spiral paths having diminishing depths so that the melt from adjacent spiral paths mix axially resulting in an annular path of homogenous melt. Extrusion dies for real time, continuous and remote control of the openings of the axially displaced orifices by moving the die lip closest and furthest from the extruder in a precise manner are also disclosed. A means for controlling separation of the die lips for both the inner and outer wall walls of the pipe gives the pipe manufacturer the benefit of better controlling quality in real time and changing grades on the fly by controlling wall thickness.