Screw-type extrusion granulating apparatus, especially for producing very fine granules

A screw-type extrusion granulating apparatus for extruding a moistened powder material into granules, said apparatus comprising a housing defining a screw chamber for receiving said moistened material, a rotatably driven conveying screw disposed in said screw chamber for pressurizing conveyance of said moistened powder material through said screw chamber, and a die supported in axial alignment with said conveying screw and extending axially from one end of said screw chamber, said die being of a generally uniform thickness in the shape of a dome and having a plurality of extrusion openings of substantially uniform size and shape formed therethrough in a generally uniform array over substantially the entire surface area thereof, said extrusion openings being oriented radially with respect to the dome shape of said die and being of a cross-sectional dimension approximately the same as the thickness of said die, said conveying screw having a terminal end extending axially interiorly of said die in the shape of a dome spaced from said die and an extrusion blade having a blade edge, said extrusion blade projecting from said dome-shaped terminal end toward said die to terminate at said blade edge and said blade edge being curved in general correspondence to said die and being at a substantially uniform radial spacing from said dome-shaped terminal end, said extrusion blade applying a nipping action to said moistened powder material between said dome-shaped terminal end and said die to thereby facilitate movement of said moistened powder material generally uniformly into and through said extrusion openings to emerge therefrom as granules.