Patent ID: 8167478

Claim:
A kneading screw comprising: a screw body comprising a feed section and a kneading section, said feed section comprising a screw segment for feeding a to-be-kneaded material to a downstream side, said kneading section comprising a kneading segment for kneading the material, said screw body further comprising a multi-stage portion having rotating outside diameters changing gradually axially, said multi-stage portion being formed in at least one of a connection between said kneading section and another section adjacent to said kneading section, and the interior of said kneading section, wherein when a stepped portion is formed between any of said segments constituting said multi-stage portion and a segment adjacent thereto, if the outside diameter of a spline shaft as a steel shaft extending axially through said multi-stage portion is assumed to be D, each difference δ in height in the radial direction of said multi-stage portion satisfies the relation of the following expression (1): δ/D 3 ≦4.0 E− 06, where δ: difference in height of each stepped portion constituting said multi-stage portion, (mm), D: outside diameter of said spline shaft, (mm).