Twin screw extruder with conical non-parallel converging screws

Abstract

An improved twin screw extruder device ( 14 ) is provided which is capable of producing a wide variety of high quality extrudates having greatly varying final properties, without the need for extensive machine modifications. The extruder ( 14 ) includes a barrel ( 16 ) together with a co-rotating twin screw assembly ( 22 ). The assembly ( 22 ) is made up of a pair of screws ( 50, 52 ) having central, tapered shafts ( 54, 56 ) equipped with outwardly extending helical flighting ( 58, 60 ); the screws ( 50, 52 ) are non-parallel and are positioned so that the flighting ( 58, 60 ) thereof is intercalated along the length of the screws ( 50, 52 ). The flighting is of specialized configuration and tapers along the length of the screws ( 50, 52 ) preferably at an angle of taper different than that of the shafts ( 54, 56 ); moreover, the width of the outer flighting surfaces ( 70, 72 ) increases along the length of the shafts ( 54, 56 ). This screw geometry defines a series of alternating upper and lower close-clearance high-pressure nip areas ( 78 ) defined by the flighting ( 58, 60 ) which serves to propel an extrudable mixture forwardly towards the outlet end ( 20 ) of the barrel ( 16 ). However, passageways ( 80 ) and kneading zones ( 82 ) are also defined between the screws ( 50, 52 ), which assures full mixing, shearing and cooking of the material. The extruder device ( 14 ) is capable of producing high density sinking aquatic feeds as well as expanded, low density products merely by changing the rotational speed of the screws ( 50, 52 ) together with appropriate temperature control. In another embodiment, a fluid extraction extruder ( 138 ) is provided having a specialized extruder head ( 140 ) including an outer shell ( 144 ) and an inner, elongated, slotted sleeve ( 152 ).

We claim:  
     
         1 . An extruder head comprising an elongated body having an outer shell and an inner extraction sleeve disposed within said shell, said sleeve having an inner surface defining an internal, elongated passageway adapted to receive at least one extrusion screw component and an outer surface, with a plurality of slots formed in the sleeve and extending from said inner surface to said outer surface, said slots configured to permit an extracted fluid to pass therethrough for collection in said shell.  
     
     
         2 . The extruder head of  claim 1 , wherein said shell includes an extracted fluid outlet.  
     
     
         3 . The extruder head of  claim 1 , at least certain of said slots being tapered and having a width adjacent said inner surface which is less than the width thereof adjacent said outer surface.  
     
     
         4 . The extruder head of  claim 1 , said passageway being tapered along the length thereof.  
     
     
         5 . The extruder head of  claim 1 , said passageway being of generally FIG. 8 configuration to accommodate side-by-side extrusion screws.  
     
     
         6 . The extruder head of  claim 1 , said sleeve formed of a plurality of interconnected, elongated bars.  
     
     
         7 . An extruder comprising 
 an elongated barrel presenting a material inlet and a material outlet; and    at least one elongated axially rotatable, helically flighted screw located within said barrel and operable for moving material from said inlet to said outlet,    said barrel including a section having an outer shell and an inner extraction sleeve disposed within said shell, said sleeve having an inner surface defining an internal, elongated passageway receiving a portion of said screw and an outer surface, with a plurality of slots formed in the sleeve and extending from said inner surface to said outer surface, said slots configured to permit an extracted fluid to pass there-through for collection in said shell,    said at least one screw and said sleeve cooperatively configured for extraction of fluid from said material during passage through said barrel section, and collection of said fluid within said shell    
     
     
         8 . The extruder of  claim 7 , wherein said shell includes an extracted fluid outlet.  
     
     
         9 . The extruder of  claim 7 , at least certain of said slots being tapered and having a width adjacent said inner surface which is less than the width thereof adjacent said outer surface.  
     
     
         10 . The extruder of  claim 7 , said passageway being tapered along the length thereof.  
     
     
         11 . The extruder of  claim 7 , said passageway being of generally FIG. 8 configuration to accommodate side-by-side extrusion screws.  
     
     
         12 . The extruder of  claim 7 , said sleeve formed of a plurality of interconnected, elongated bars.  
     
     
         13 . The extruder of  claim 7 , said section being located adjacent said outlet.