Patent ID: 8721940

Claim:
Method for producing a vessel ( 2 ) by stretch blow-moulding in a mould ( 11 ) from a preform ( 3 ) made of plastic material, comprising the operations consisting in: heating the preform ( 3 ) to a predetermined heating temperature (T); introducing the preform ( 3 ) in the mould ( 11 ); stretching the preform ( 3 ) by means of a rod ( 16 ) displaced at a predetermined stretching speed (V E ); at a predetermined moment, called pre-blowing cue (t P ), controlling the opening of an electrovalve ( 22 ) for establishing a communication between the inside of the preform ( 3 ) and a source ( 20 ) of gas at a predetermined medium pre-blowing pressure (P P ) and a pre-blowing flow rate (D P ); at a predetermined moment, called blowing cue (t s ), controlling the opening of an electrovalve ( 26 ) for establishing a communication between the inside of the preform ( 3 ) a source ( 24 ) of gas at a predetermined high blowing pressure; measuring the pressure (P) inside the preform ( 3 ); detecting a pressure peak between the pre-blowing cue (t p ) and the blowing cue (t s ); memorising the moment (t B ) at which this pressure peak occurs as well as the corresponding pressure (P B ) inside the preform ( 3 ); comparing the moment (t B ) and the pressure (P B ) of the peak detected with, respectively, a predetermined moment and pressure for a theoretical pressure peak; if the measured peak and the theoretical peak are not confounded, modify at least one of the following parameters: pre-blowing pressure (P P ), pre-blowing flow rate (D P ), the pre-blowing cue (t P ), stretching speed (V E ), heating temperature (T).