Embodiments of an extruder comprise an extruder housing having an internal wall and a single screw coaxially disposed within the extruder housing, the single screw comprising a shank, wherein the shank and/or a region of the internal wall proximate the shank comprises helical channels. The extruder further comprises a feed channel downstream of the shank, and a visco-seal comprising the helical channels and the annular gap between the shank and the internal wall, wherein the annular gap is variable across its length.

A material extrusion mechanism includes a cylinder including a supply port to which a material is supplied, a screw including a spiral flight section that rotates on a rotation axis extending in a vertical direction, a first cooling section surrounding a part of the screw, a heating section surrounding a part of the screw below the first cooling section, and at least one nozzle configured to discharge the plasticized material. At least a part of the supply port overlaps the first cooling section in a horizontal direction, the screw includes a first portion where an outer diameter of the flight section is a first diameter and a second portion wherein the outer diameter of the flight section is a smaller second diameter, the first portion overlaps the heating section in the horizontal direction, and the second portion overlaps the first cooling section in the horizontal direction.

A material extrusion mechanism includes a cylinder including a supply port to which a material is supplied, a screw including a spiral flight section that rotates on a rotation axis extending in a vertical direction, a first cooling section surrounding a part of the screw, a heating section surrounding a part of the screw below the first cooling section, and at least one nozzle configured to discharge the plasticized material. At least a part of the supply port overlaps the first cooling section in a horizontal direction, the screw includes a first portion where an outer diameter of the flight section is a first diameter and a second portion wherein the outer diameter of the flight section is a smaller second diameter, the first portion overlaps the heating section in the horizontal direction, and the second portion overlaps the first cooling section in the horizontal direction.