Extrusion head with channels for producing inserts in a profiled band for manufacturing a pneumatic tire and corresponding extrusion method

A coextrusion method for the coextrusion of a complex profiled element made up of an assembly of profiled elements formed from distinct rubber compounds, in which, using a coextrusion machine comprising an upstream extruder and a downstream extruder delivering into an extrusion cavity formed by the space comprised between a lower wail of an extrusion head and a profiling wall positioned opposite the lower wall, steps are implemented during which:

• using the upstream extruder, a first rubber compound which emerges from an upstream extrusion canal in the lower wall of the extrusion head is delivered upstream of a first profiling blade referred to as the “upstream profiling blade”,
• a first profiled element, formed of the first rubber compound, is created in an upstream gap which is defined by the upstream profiling blade and the profiling wall, the first profiled element comprising at least a first profiled-element portion which is intended to form a sublayer and at least a second profiled-element portion which is intended to form a longitudinal insert, a base of which is in continuity of material with the sublayer, and which on the sublayer forms protrusion lateral walls which extend outwards with respect to an external surface of the first profiled element,
• using the downstream extruder, a second rubber compound is delivered via a downstream extrusion canal which opens into the lower wall of the extrusion head downstream of the upstream profiling blade, and the second rubber compound is brought together with a radially external surface of the first profiled element at the region where the stream of second rubber compound meets the stream of first rubber compound,
• the first profiled element and the second rubber compound are passed through a downstream gap which is positioned downstream of the downstream extrusion canal and which is defined by a second profiling blade, referred to as the “downstream profiling blade”, and the profiling wall, so as to create a complex profiled element formed of the first and of the second rubber compounds,
• wherein a portion of the first rubber compound, intended to form the insert, is circulated between walls of a channel which extend in a longitudinal direction between the upstream profiling blade and the downstream profiling blade, from an upstream end of the channel which is situated upstream of the meeting of the streams of the first and second rubber compounds, as far as a downstream end of the channel which is situated downstream of the meeting of the streams and upstream of the downstream profiling blade, the walls of the channel together forming a concave surface open towards the inside of the extrusion cavity and being positioned in such a way that the portion of the first rubber compound that enters the channel and that is intended to form the insert, as it progresses longitudinally along the channel, remains in continuity of material with the sublayer without being brought into contact with the second rubber compound, and so that the bringing-together of one or more lateral walls of the insert with the second rubber compound then takes place in the downstream gap defined by the downstream profiling blade and the profiling wall.