Patent ID: 7056456

Claim:
An extrusion method in which method an annular material flow is created by extruding material into an annular extrusion channel comprising a tubular filtering unit, whereby material is filtered by making it flow through a surface of the tubular filtering unit, the filtering unit having at least an outer layer, an inner layer and a filtering layer, the outer and inner layers of the filtering unit being substantially stationary and having between them the filtering layer that can be moved, the outer and inner layers having openings and the material is arranged to flow sideways in the filtering layer, whereby it is filtered and the filtered material remains in the filtering layer on the side of the openings of the layer first in the flow direction of the material, wherein the filtering unit is cleaned by moving the filtering layer in such a manner that the filtered material settles at the openings of the layer last in the flow direction of the material and due to the material flow, the filtered material particles flow out of the extruder.