Method for forming containers with multiple walls

Method for forming a container (2) comprising an open neck (8) by blow molding or stretch blow molding of a preform (3) with multiple walls made of plastic material, with said method comprising:

• An operation for installing the preform (3) in a mold (14) bearing the impression of the container (2), with this mold (14) comprising at least two half-molds (14A, 14B) that can occupy a closed position in which the half-molds (14A, 14B) are assembled;
• An operation for locking half-molds (14A, 14B) in the closed position;
• A blow-molding phase that consists in linking the interior of the preform (3) to a pressurized gas source (20, 21) by means of the opening that is made in its neck (8), for a predetermined length of time, for forming the container (2), by applying at least a blow-molding pressure (PS);
• A degassing phase beginning at a degassing start time (Tdeg) and consisting in the linking of the container (2) thus formed to the environment at ambient pressure (PA) so as to bring the pressure in the container back to the ambient pressure;
• the method further comprising:
• A continuous measurement (300) of the pressure prevailing in the area of the neck (8) during the degassing phase;
• The determination (400) of the length of time that has elapsed (Dec) between the beginning of the degassing and attaining a reference pressure (Pref;
• PA) in the area of the neck (8);
• The comparison (500) of the length of time that has elapsed with a theoretical length of time (Dth) starting from which the pressure in the area of the neck (8) in theory attains the reference pressure (Pref;
• PA);
• Maintaining (700) the locking of the mold if the length of time that has elapsed (Dec) is less than the theoretical length of time (Dth).