Extruder

A single-screw extruder configured to extrude a solid raw material containing moisture, the extruder comprising:

• a barrel having a hollow tubular shape in a longitudinal direction, wherein a hopper into which a raw material is put is coupled to one side of the barrel, and a discharge port through which a dehydrated raw material is discharged is provided on the other side of the barrel;
• a rod-shaped screw provided with screw threads on an outer circumferential surface thereof so that the screw is mounted within the barrel to transfer a raw material put into the hopper to the discharge port while axially rotating in one direction;
• a vent part disposed at one point between the hopper and the discharge port to discharge vapor generated within the barrel to the outside;
• and
• a heater part mounted on the barrel to heat the raw material, wherein the raw material introduced into the barrel through the hopper is gradually heated by the heater part while being transferred within the barrel through the screw,
• a kneading zone, in which raw materials transferred by the screw threads are compressed, is formed on the screw, and
• since the raw material is melted within the barrel so that at least a portion of the raw material is phase-changed into a liquid state, a heating temperature of the heater part and an axial rotation speed of the screw are controlled so that a sealing membrane that shields an inner transverse section of the barrel is formed from the phase-changed raw material in the kneading zone,
• wherein the kneading zone is disposed between the vent part and the hopper, and
• wherein the screw comprises:
• a first forward zone in which the screw threads are provided to transfer the raw material, which is put from the hopper, toward the discharge port when rotating axially;
• the kneading zone in which the screw threads are provided to compress the raw material, which is transferred from the first forward zone, when rotating axially;
• a second forward zone in which the screw threads are provided to transfer the raw material, which passes through the kneading zone, toward the discharge port when rotating axially;
• and
• a sub-kneading zone in which the screw threads are provided to recompress the raw material, which is transferred from the second forward zone, when rotating axially, and
• wherein a distance between the sub-kneading zone and the vent part is greater than three times a diameter of the barrel.