Concentric sleeves for flow baffles in film extrusion die - to induce uniform axial flow without residual flow weld lines

摘要

A die head for extrusion of tubular thermoplastic film is fitted with two concentric sleeves with oblique ends of opposing sloped to define a distribution passage for material entering the die via a radial inlet. The inner sleeve baffles the flow to balance the pressure drop across the die and produce uniform annular flow co-axial with he die core mandrel. Part of the mandrel is fluted to impart a helical twist to the coaxial extrudate flow. The design suppresses introduction of weld lines by convergeant transverse or longitudinal flow (i.e. no mandrel bridges exist to split the flow and convergent circumferential flow is avoided.) The mandrel can readily incorporate coaxial pressure/coolant gas circulation passages of relatively large bore.