Extrusion die for multi-channelled profiles - with pneumatic jets for balancing partition wall stresses

摘要

Extrusion die for making profiles or board with several internal longitudinal channels, has the die mandrel also drilled, to provide an air jet for each profile channel to maintain a shape stabilising internal pressure until the extrudate firms up. Pref. the incoming air is preheated (to 60-80 degrees C) during its passage into the die or by an ancillary heat exchanger. The jets provide internal pressurisation which is readily adjusted to counteract contraction stresses induced by variable haul off conditions, (in preference to quench treatments which may render the extrudate too cold and stiff to accept subsequent ancillary shaping operations, e.g. corrugation).