GB908415A - Improvements in or relating to extrusion nozzles - Google Patents

Abstract

<PICT:0908415/IV(a)/1> An elongated slot extrusion nozzle for laminar products includes at its output end a discharge passage defined by limiting walls curved in the form of circular arcs arranged in such a manner as to cause material being extruded to be deflected, after introduction into the discharge passage, out through an outlet aperture therein in a direction substantially normal to that followed by the material upon its introduction into the passage, p the dispositions of the centres of curvature of the limiting walls and the arrangement of the outlet aperture being such, that on the exertion by the material being extruded of a pressure on one of the limiting walls sufficient to cause yielding thereof relative to the other limiting wall, no appreciable increase of the width of the outlet aperture takes place. The nozzle channel may be so curved that the flow of substance is deflected through approximately 90 degrees. As shown, nozzle lips 12 and 14 are carried by upper and lower nozzle parts 1 and 2, 12 being supported on batten 13 and 14 on head batten 15. Material is supplied from screw press 5 via the insert 6 of oval cross-section, to extrusion channel 7, from which it passes through distribution chamber 8 and constriction 9 controlled by gate 11 to the outlet gap 10. The lower part 2 is reduced in cross-section along line GH by the depression 16 on the lower side and chamber 8 on the upper side. The distance of the plane of reduced cross-section from the curved pair of lips corresponds roughly to the radius of curvature R of the lower lip, so that the centre of curvature of the lips lies on the line GH at the point J which is in the bending stress neutral zone.