A mixing section for an extrusion screw has an inlet end and an outlet end as well as alternating wiping lands and barrier lands. The wiping lands have a greater helix angle than the barrier lands. The wiping lands and the barrier lands define inlet channels which narrow toward the outlet end and outlet channels which widen toward the outlet end. A helical pattern of mixing channels is cut into the wiping lands and the barrier lands. The mixing channels may be oriented generally at approximately right angles to the wiping lands and the barrier lands. A portion of the extrudate encounters the inside wall surfaces of the mixing channels and changes direction which improves the mixing of the extrudate.

In a multi-shaft extruder for the processing of free-flowing material having a barrel and a plurality of co-rotating, tightly intermeshing conveyor shafts (1 to 3) arranged in parallel which have at least two flights and are each guided in a bore (1 to 3) in the barrel, each conveyor shaft (1 to 3) is spaced with the ridge (O) of one of its flights from the bore wall (1, 2, 3) by a clearance over at least part of the processing length of the extruder, whereas a gap is formed between the ridge (a, b, c) of another of its flights and the bore wall (1, 2, 3). The conveyor shafts (1 to 3) are arranged in an offset manner relative to each other at an angle such that, at least in one rotational position, the conveyor shaft (2) arranged between two conveyor shafts (1 to 3) is coatable with the free-flowing material on its flanks (A, B) between its ridges (b, O) by means of the gap-forming ridges (a, c) of the two adjacent conveyor shafts (1 and 3), with the said flanks (A, B) being cleanable again from the free-flowing material by means of the ridges (O) of the two adjacent conveyor shafts (1 and 2) spaced from the bore wall (1, 2, 3) by a clearance in at least one further rotational position of the conveyor shaft.

In a multi-shaft extruder for the processing of free-flowing material having a barrel and a plurality of co-rotating, tightly intermeshing conveyor shafts (1 to 3) arranged in parallel which have at least two flights and are each guided in a bore (1 to 3) in the barrel, each conveyor shaft (1 to 3) is spaced with the ridge (O) of one of its flights from the bore wall (1, 2, 3) by a clearance over at least part of the processing length of the extruder, whereas a gap is formed between the ridge (a, b, c) of another of its flights and the bore wall (1, 2, 3). The conveyor shafts (1 to 3) are arranged in an offset manner relative to each other at an angle such that, at least in one rotational position, the conveyor shaft (2) arranged between two conveyor shafts (1 to 3) is coatable with the free-flowing material on its flanks (A, B) between its ridges (b, O) by means of the gap-forming ridges (a, c) of the two adjacent conveyor shafts (1 and 3), with the said flanks (A, B) being cleanable again from the free-flowing material by means of the ridges (O) of the two adjacent conveyor shafts (1 and 2) spaced from the bore wall (1, 2, 3) by a clearance in at least one further rotational position of the conveyor shaft.