Method and apparatus for pinning the edges of an extruded mass

A method for pinning edges of an extruded polymeric mass (10), comprising the following steps:

• extruding a polymeric mass (10) from an extrusion die (12);
• pre-cooling in at least two pre-cooling steps,
• wherein:
• two areas are defined in the extruded polymeric mass (10) along each of external edges of the polymeric mass, having a width respectively equal to (a) and (b) (15′ and 15) and a length equal to the length of the extruded mass (10), wherein the area having the width (a) (15′), which is a variable width, is arranged flush with an edge of the extruded mass (10), and wherein the area having the width (b) (15) is adjacent to the area having the width (a) (15′), internally with respect to the edge of the extruded mass (10), and
• a third area is defined having a width equal to (c), (16), and a length equal to the length of the extruded mass (10), adjacent to the area having the width (b) (15), internally with respect to the edge of the extruded mass (10);
• wherein in a first pre-cooling step of the at least two pre-cooling steps, the area (16) having a width (c) of the polymeric mass (10) is pre-cooled by action of an air flow, before the extruded mass (10) is cast and comes into contact with a surface of a rotating cylinder (11) positioned at a distance (d) from the extrusion die (12);
• wherein in a second subsequent pre-cooling step of the at least two pre-cooling steps, the area (15) having a width (b) is pre-cooled by action of a second air flow, before the extruded mass (10) is cast and comes into contact with the surface of the rotating cylinder (11) positioned at the distance d from the extrusion die (12);
• and
• electrostatically charging, in at least two electrostatic charging steps, the extruded polymeric mass (10), wherein:
• in a first electrostatic charging step of the at least two electrostatic charging steps, the area having the width (b) (15), after the pre-cooling, is electrostatically charged to favor its adhesion to the surface of the rotating cylinder (11) and ensure a desired heat exchange between the area having the width (b) and the rotating cylinder;
• and
• in a second electrostatic charging step of the at least two electrostatic charging steps, the area having a width (a) (15′), arranged flush with the edges of the extruded mass (10), externally with respect to the area having a width (b) (15), treated in the first electrostatic charging step, is electrostatically charged.