Twin screw extruder with conical non-parallel converging screws

Abstract

An improved twin screw extruder device ( ) 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 ( ) includes a barrel ( ) together with a co-rotating twin screw assembly ( ). The assembly ( ) is made up of a pair of screws ( ) having central, tapered shafts ( ) equipped with outwardly extending helical flighting ( ); the screws ( ) are non-parallel and are positioned so that the flighting ( ) thereof is intercalated along the length of the screws ( ). The flighting is of specialized configuration and tapers along the length of the screws ( ) preferably at an angle of taper different than that of the shafts ( ); moreover, the width of the outer flighting surfaces ( ) increases along the length of the shafts ( ). This screw geometry defines a series of alternating upper and lower close-clearance high-pressure nip areas ( ) defined by the flighting ( ) which serves to propel an extrudable mixture forwardly towards the outlet end ( ) of the barrel ( ). However, passageways ( ) and kneading zones ( ) are also defined between the screws ( ), which assures full mixing, shearing and cooking of the material. The extruder device ( ) 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 ( ) together with appropriate temperature control. In another embodiment, a fluid extraction extruder ( ) is provided having a specialized extruder head ( ) including an outer shell ( ) and an inner, elongated, slotted sleeve ( ).