An extrusion machine, comprising: a screw element defining longitudinal, circumferential, and radial directions, the screw element comprising a first section and a second section positioned sequentially along the longitudinal direction; the first section comprising a first core including a plurality of facets positioned adjacent to each other in the circumferential direction, each facet extending in the longitudinal direction over the first section, each facet joined to an adjacent facet along splines extending longitudinally over the first section, wherein the first core has a diameter that increases in a continuous manner along the longitudinal direction towards the second section; a first helically-shaped screw flight wrapped around the first core of the screw element, the first helically-shaped flight extending longitudinally over the first section and projecting radially outward of the plurality of facets; the second section comprising a second core extending along the longitudinal direction and having a cylindrically-shaped surface; and a second helically-shaped screw flight wrapped around the second core of the screw element, the second helically-shaped flight extending longitudinally over the second section and projecting radially outward from the second core; characterized in that the first section further comprises a spacer core positioned between the first core and the second core, the spacer core extending along the longitudinal direction and forming a frustoconical surface that decreases in diameter towards the second core. a screw element defining longitudinal, circumferential, and radial directions, the screw element comprising a first section and a second section positioned sequentially along the longitudinal direction; the first section comprising a first core including a plurality of facets positioned adjacent to each other in the circumferential direction, each facet extending in the longitudinal direction over the first section, each facet joined to an adjacent facet along splines extending longitudinally over the first section, wherein the first core has a diameter that increases in a continuous manner along the longitudinal direction towards the second section; a first helically-shaped screw flight wrapped around the first core of the screw element, the first helically-shaped flight extending longitudinally over the first section and projecting radially outward of the plurality of facets; a first core including a plurality of facets positioned adjacent to each other in the circumferential direction, each facet extending in the longitudinal direction over the first section, each facet joined to an adjacent facet along splines extending longitudinally over the first section, wherein the first core has a diameter that increases in a continuous manner along the longitudinal direction towards the second section; a first helically-shaped screw flight wrapped around the first core of the screw element, the first helically-shaped flight extending longitudinally over the first section and projecting radially outward of the plurality of facets; the second section comprising a second core extending along the longitudinal direction and having a cylindrically-shaped surface; and a second helically-shaped screw flight wrapped around the second core of the screw element, the second helically-shaped flight extending longitudinally over the second section and projecting radially outward from the second core; characterized in that the first section further comprises a spacer core positioned between the first core and the second core, the spacer core extending along the longitudinal direction and forming a frustoconical surface that decreases in diameter towards the second core. <EOS>