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

A twin-screw assembly (10,20) for elastomer mixture extruders, comprising two screws (21,22) with a threaded part having a single-start thread, which are arranged intermeshing and counter-rotating with parallel longitudinal axes of rotation (X-X) inside a cylinder (10), so as to form a throughflow channel for passage of the mixture flow consisting of the union of a plurality of C-chambers (Cx), each defined by the free volume inside the cylinder (10) and comprised in a single rotation of the thread for a single screw, the twin-screw assembly being provided with an upstream opening (13) for the intake of mixture into the throughflow channel,

• wherein the throughflow channel for passage of the flow comprises, from upstream to downstream in the longitudinal direction (X-X) of axial extension of the screws and advancing movement of the mixture, at least three different sectors (30,40,50), which include:
• an intake sector (30), which is adapted to capture the mixture fed from the outside and to push it downstream along the longitudinal direction (X-X) and which has a volume of the C-chambers forming the throughflow channel for passage of the flow which is constant over at least two pitches of the thread of each screw;
• a transition sector (40), downstream of the intake sector, which has a volume of the C-chambers forming the flow channel which is variable, decreases and is smaller than the volume of the C-chambers of the intake sector;
• a high-pressure sector (50), downstream of the transition sector, which has a volume of the C-chambers forming the flow channel which is constant over at least one pitch and smaller than the volume of the C-chambers of the intake and transition sectors, and is adapted to cause a compression of the mixture so as to obtain a maximum pressure of the mixture.

A method for extruding elastomer mixtures comprising the following steps:

• feeding an elastomer mixture to a twin-screw assembly of a mixture extruder comprising two screws (21,22) with a threaded part, which are arranged intermeshing and counter-rotating with parallel longitudinal axes of rotation (X-X) inside a cylinder (10), so as to form a throughflow channel for passage of the mixture flow from upstream to downstream, consisting of the union of a plurality of C-chambers, each defined by the free volume between respective screws inside the cylinder and comprised in a single rotation of the thread for a single screw;
• the elastomer mixture being fed inside the throughflow channel for passage of the mixture flow of the twin-screw assembly through a mixture intake opening (13);
• capturing the elastomer mixture and pushing the same downstream through the throughflow channel for the mixture flow, in an intake sector (30) of the twin-screw assembly, which has a volume of the C-chambers forming the flow channel which is constant over at least two pitches of the thread of each screw;
• advancing of the elastomer mixture through a transition sector (40) of the throughflow channel for passage of the mixture flow, the transition sector (40) being arranged downstream of the intake sector in the longitudinal direction (X-X) of axial extension of the screws and advancing movement of the mixture and having a volume of the C-chambers forming the flow channel which is variable, decreases and is smaller than the volume of the C-chambers of the intake sector;
• advancing and compression of the elastomer mixture in a high-pressure sector (50) which is arranged downstream of the transition sector and which has a volume of the C-chambers forming the flow channel which is constant over at least one pitch and smaller than the volume of the C-chambers of the intake and transition sectors so as to cause the compression of the mixture and obtain a maximum pressure of the mixture;
• passage of the elastomer mixture at a maximum pressure through an extrusion head (60) arranged downstream of the high-pressure sector (50).