The process includes a non-crosslinked self-sealing composition which is introduced into an extrusion means, the geometric and thermodynamic characteristics of which have been specially adapted. The speed and temperature conditions of the extrusion means are adjusted so that, at an application nozzle forming the outlet die of the extrusion means, the self-sealing composition is crosslinked. The application nozzle is brought close to the internal surface of the casing previously set in relative motion with respect to the application nozzle, and an extruded and crosslinked bead that has a given width and profile is deposited directly on the internal surface of the casing.