Single-screw extruder with hollow rotor member

A single-screw extruder, comprising:

• a cylindrical rotor member having a diameter and a length L;
• a feeding zone;
• and
• a feed opening,
• the rotor member being arranged in a barrel,
• a cylindrical surface of the rotor member carrying cavities and/or projections arranged in helically extending rows,
• the helically extending rows of the rotor member having a pitch and depth in the feeding zone of the rotor member, wherein the pitch of a screw is a distance between two consecutive flights, and wherein the feeding zone is that part of the rotor member that is directly under the feed opening and five laps of screw flight following the feed opening,
• the extruder further comprising a drive system configured to rotate the rotor member in the barrel, the drive system being located on a drive system side of the single-screw extruder and comprising an electric motor;
• wherein a relation of the depth to the diameter of the rotor member, d:D, is not more than 1:20, and
• wherein a relation of the pitch of the rotor member to the diameter of the rotor member, P:D, is not more than 1:4.