Apparatus for friction stir applications and method for manufacturing such an apparatus

A friction stir extrusion apparatus for extruding material, comprising a housing, a transport screw and a feeder, the housing comprising a body with a round cavity and extending along a rotational axis and having an input opening for a material feed and an output opening for extruded 5 material, the transport screw having helical ridges along its length is arranged within the cavity and adapted for rotating inside the cavity, the feeder adapted for feeding the material feed to the input opening, wherein a first portion of the cavity is tapered towards the output opening and the transport screw is 10 tapered along the first portion of the cavity, and a first gap perpendicular to the rotational axis and a second gap parallel to the rotational axis between the helical ridge of the transport screw and the inner wall of the cavity are each constant and non-zero along the first portion. 15 [fig lA]