Positive displacement extrusion of viscous material

A method for extruding a viscous material with a positive displacement extruder which comprises (i) a main body having a chamber therein and an inlet and an outlet for the viscous material, said inlet and outlet being in communication with the chamber, (ii) a feed member rotatably arranged in the chamber of the main body and adapted to be driven for rotation so that the viscous material charged into the chamber through the inlet is extruded from the outlet, (iii) a mouthpiece having an inlet that is spaced in a circumferential direction from the outlet of the main body, and an extrusion nozzle in communication with the inlet of the mouthpiece, (iv) at least one cylinder device comprising a cylinder having an opening and a piston that can be reciprocated in the cylinder, said cylinder device being rotatable about a center axis of the extruder so that the cylinder opening is alternately brought into communication with the outlet of the main body and the inlet of the mouthpiece, (v) a cylinder device holder carrying the at least one cylinder, (vi) a drive mechanism connecting the feed member to the cylinder device holder, wherein said drive mechanism provides a common drive for the feed member and the cylinder device holder, and (vii) a stationary cam device for causing a reciprocating movement of the piston in the cylinder, wherein the method comprises the steps of:

• causing said at least one cylinder device to rotate about the center axis of the extruder;
• and
• charging the viscous material from the outlet of the main body into the cylinder, and subsequently discharging the viscous material from the cylinder into the inlet of the mouthpiece, during one turn of rotation of the cylinder device about the center axis of the extruder.