Twin-screw extruder having respective conical nose screw sections

Claim 1

An extruder, comprising: an elongated barrel presenting an inlet end and an outlet end, a material inlet adjacent said inlet end thereof and a pair of separate, generally tubular, juxtaposed head sections proximal to said outlet end of the barrel and defining respective chambers separated by a central wall, each of said outlet end head sections being of decreasing cross-sectional area along the length thereof, said outlet end head sections serving to divide and receive material passing through said barrel, said elongated barrel having an outer surface that is imperforate between the outlet end head section and the outlet end of the barrel; a pair of elongated, juxtaposed, axially rotatable flighted screws positioned within said barrel for moving material therethrough, each of said screws including an elongated, flighted, generally frustoconical outlet end screw section of decreasing cross-sectional area along the length of the outlet end screw section which is substantially complemental with a corresponding one of said outlet end sections, each of said outlet end screw sections having a rearward margin and a forward margin, the length of each of said outlet end screw sections being greater than he greatest diameter of the outlet end screw section, each of said outlet end screw sections having a peripheral helical flighting portion extending forwardly from said rearward margin of the outlet end screw section, each of said flighting portions intermeshing with the flighting portion of the other outlet end screw section by a predetermined depth of intermesh which progressively decreases the flighting portions extending forwardly from the rearward margins of said end screw sections until the flighting portions completely separate from each other at a point spaced rearwardly from said outlet end of said barrel, each of said outlet end screw sections extending into and being substantially complementally received by a corresponding outlet end head section for providing a bearing-type support for each of said flighted screws by virtue of passage of material into and through said head sections, and into surrounding relationship to the outlet end screw sections, during operation of said extruder; restricted orifice die structure; and means mounting said die structure adjacent the outlet end of said barrel and in a spaced apart relationship to the forward margins of said outlet end section, the spacing between said outlet end section forward margins and said die structure being less than the length of one of said generally frustoconical outlet end sections.