Screw and twin-screw assembly for use in elastomer mixture extruders and associated method for extrusion of elastomer mixtures

A screw (21;22) adapted for use in a twin-screw assembly with intermeshing screws of an elastomer mixture extruder, comprising a threaded part with a thread and which defines at least three different sectors (30,40,50) of the screw along a longitudinal direction (X-X) of axial extension from upstream to downstream, wherein the at least three sectors comprise:

• an intake sector (30), which is adapted to capture and push a mixture downstream along the longitudinal direction (X-X) and which has a cross-section(S) of a throughflow channel comprised between adjacent flanks of the thread which is constant over at least two pitches or a rotation through 720 degrees of the thread;
• a transition sector (40), downstream of the intake sector, which has a cross-section(S) of the throughflow channel which is variable and smaller than the cross-section of the throughflow channel of the intake sector and is designed to cause an increase in thrusting pressure acting on the mixture in transit in the longitudinal direction (X-X);
• a high-pressure sector (50), downstream of the transition sector, which has a cross-section of the throughflow channel which is minimal and constant over at least one pitch and designed to cause compression of the mixture to obtain a maximum pressure of the mixture,
• wherein the thread of said threaded part along each sector of the at least three sectors is a single-start thread and a geometry of the screw in the high-pressure sector (50) has a crest width (W) of a thread crest where W=(0.3-0.4)D, and is constant over one or two pitches, where D is an external diameter of the screw.