Extrusion of a paste material has a significant position in the processing of powder materials. The reduction between the barrel and die, often with a complicated cross-section, is a necessary detail of each extruder. If a deformation element of special design is situated in this zone, it has a positive influence on the process of extrusion. Its shape can be varied. In this case, it is a rotor with blades that move on the surface of the matrix, which has influence on the rate of shear strain. The effects decrease the apparent viscosity and extrusion pressure. (C) 2004 Elsevier B.V. All rights reserved.