Ringförmige, konzentrische Extruderdüse

摘要

An annular co-extrusion die for extruding multi-layer tubular plastic film has inner die members stacked one upon another. The inner die members have radially outwardly extending surfaces forming radially outwardly extending helical passages between respective pairs of die members. An annular outer die member surrounds the stacked inner die members and forms a longitudinally extending annular passage therebetween for conveying plastic material from the radially outwardly extending helical passages to an annular extrusion orifice. Each inner die member forms with an adjacent die member a first feed passage extending at least partly around the inner die member radially inwardly of the helical passages, the inner die member and the adjacent die member having a circumferentially extending clearance therebetween to enable plastic material fed into the first feed passage to pass through the clearance into the helical passages. Each inner die member also has at least one further feed passage extending substantially parallel to the longitudinal axis of the die from the lower end of the inner die member to an upper end thereof for communication with a feed passage or passages of the inner die member immediately above. The die also having passages in a lower end portion thereof for feeding different plastic materials from extruders to respective passages in the inner die members.