Extrusion head for thermoplastic plastic hose and pipe production has extrusion gap with fixed wall section and segmented wall sections which overlap at their edges and swivel to vary gap diameter

摘要

A mandrel and die ring(2) form a gap(3) whose bordering surfaces comprise a fixed collar(4) and a segmented section(5) with variable diameter. Segments(6) have a wall section in contact with melt and a circular arc wall section(9) which swivels around an axis(7). When segments are swiveled the collar lies against the circular arc section of the segments. Side edges of the segments overlap and meet each other at contact faces. - Segments(6) overlap in the form of a fan. Inner and outer segments alternate with each other. Contact faces between segments are wedge shaped and extend either completely or partly over a part of the segment wall thickness. Side edges of each segment in the nozzle gap are formed as thin walled blade edges which deform under melt pressure and are pressed against the more stable overlapping area of an adjacent segment. Each metal segment is mounted on an axle which passes through bores in stiffening ribs(13) on the rear side of the circular arc section(9). An adjustment system comprising a lever(14) on the back of each segment acts in conjunction with an operating ring(15) of an axial control mechanism(16) in response to the pressure in the nozzle gap. The adjustment can be made according to a set program during extrusion. The segments and collar are mounted on the die ring(2) and the mandrel also has a mechanism for varying mandrel diameter.