Patent ID: 7097442

Claim:
An extruder comprising: at least three screw shafts having the same outer diameter and the same root diameter and each having a waveform-shaped screw thread, said at least three screw shafts being engaged with each other and being arranged in parallel and substantially horizontally and so that a distance between longitudinal center axes of adjacent screw shafts is equal; a drive unit operable to rotate all of said screw shafts at the same velocity and in the same direction; and a barrel having a screw fitting part, all of said screw shafts being rotatably inserted in said screw fitting part, said screw fitting part being configured to knead and move an extrusion material in a thread groove of a first one of said screw shafts to a thread groove of an adjacent second one of said screw shafts via rotation of said screw shafts by said drive unit, all of said screw shafts being arranged in said screw fitting part so that a clearance between a thread groove of each of said screw shafts and a crest of an adjacent engaged screw shaft is constant, said thread grooves of all of said screw shafts being shaped and arranged to move the extrusion material along an inner surface of said barrel via the rotation of said screw shafts.