Accumulation extruder head with mechanical coupling between an output of a mechatronic assembly and a pusher element

A method for extrusion with accumulation of a load of thermoplastic resin in the form of a tubular parison, comprising:

• feeding an extruded thermoplastic resin to a head body (10) of an accumulation extruder head, the load being fed to an accumulation chamber (13a) with a central vertical axis (z) defined inside an internal cavity (13) of the head body, until the accumulation chamber is filled with a predefined load of thermoplastic resin;
• expelling the accumulated load of thermoplastic resin in the form of a tubular parison through a bottom outlet mouth (11) communicating with the accumulation chamber (13a);
• wherein a piston (18) is coaxially inserted inside the accumulation chamber (13a) and moves in a reciprocating manner inside the accumulation chamber along the central vertical axis (z);
• in an upward direction during the filling step, from a lowered expulsion position into a raised position;
• in an expulsion direction during the expulsion step, from a raised position into the lowered expulsion position;
• wherein the head comprises a mechatronic assembly (30) comprising an output element (31), linearly displaceable along the central vertical axis (z) between a raised position and a lowered position, and a plurality of electric actuators, each of which rotationally drives a respective rotating element which is coupled to the output element (31) by means of a coupling such that rotation of the rotating element displaceably drives the output element in the vertical direction,
• wherein the electric actuators are controlled and configured to drive in a coordinated manner said rotating elements so as to jointly displace said output element (31);
• wherein, during the expulsion step, the output element is driven in the expulsion direction from the raised position into the lowered position and cooperates with an input element (41) of a pusher assembly (40) which is rigidly coupled to the piston (18) for displacement therewith, so as to push the piston (18) in the expulsion direction towards the lowered position;
• wherein, in the filling step for filling the accumulation chamber, the output element (31) of the mechatronic assembly (30) is detached from the input element (41) of the pusher assembly so as to allow movement of the piston in the upward direction;
• characterized in that the input element (41) of the pusher assembly (40) is mechanically coupled with the output element (31) via coupling means (31c) configured to keep the input element (41) engaged with the output element (31), leaving a degree of play for relative movement in the vertical direction greater than or equal to a predefined minimum distance.