The invention relates to an extruder intended for shaping a viscous material such as a rubber mixture, including a screw which is rotated about an axis (XX') inside a hollow shaft (100) and having one or more helical threads (501) extending radially outwards from a central shaft (500) of the screw, the extruder including a homogenisation area (H) of the material through which a screw portion including interrupted thread elements (505) forming free annular spaces (506) extends axially, and a hollow shaft portion defining said homogenisation area having thread elements (210) extending radially inwards into said free annular spaces (506). According to the invention, the hollow shaft portion defining the homogenisation area is, in turn, rotated about the axis XX' to form a rotary hollow shaft.