Kneading screw and extruder

摘要

A kneading screw (1) is disclosed which comprises a screw body (11), the screw body (11) comprising a feed section (9) and a kneading section (10), the feed section (9) comprising screw segments (13) for feeding a to-be-kneaded material to a downstream side and the kneading section (10) comprising kneading segments (19) for kneading the material. The screw body is provided within the kneading section (10) with a multi-stage portion which gradually changes axially in rotating outside diameter. It is preferable that the multi-stage portion be constituted by kneading segments (19) of plural kneading discs different in rotating outside diameter. With such a construction, it is possible to avoid stress concentration on an axial part of the kneading screw (1) and thereby prevent breaking of a spline shaft and abnormal wear of kneading flights.