improved twin screw extruder

improved twin screw extruder

improved twin screw extruder

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 surface 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 .

The present invention is broadly concerned with improved twin screw extrusion devices of a highly versatile nature which can be used for the production of a wide variety of end products of varying densities, cook values and expansion ratios, without the need for extensive machine modifications. The extruders of the invention include a twin screw assembly having non-parallel, tapered conical screws with the flighting of the screws intercalated along the length of the extruder barrel to define close-clearance, preferably constant dimension, alternating upper and lower nip areas and trailing kneading zones and reverse flow passageways; the nip areas create high pressure zones within the barrel which propel material forwardly, while the material is kneaded and allowed to reverse flow in the zones and passageways. In other embodiments, an infinitely variable die assembly including a shiftable stem movable between a waste disposal position and a variety of extrusion positions. A specialized fluid extraction final extruder head is also provided, which allows oils or other fluids to be efficiently extracted, particularly with the aid of a supercritical extractant such as carbon dioxide.

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