Method for blow-molding containers, and machine for said method

A method for producing thermoplastic containers by stretch-blow molding including a series of production cycles during each of which a new container is produced, each production cycle comprising a pre-blow-molding phase where a preform is connected through a nozzle to a pre-blow-molding air system so that the preform becomes a container ready to be blow molded during an overall blow-molding phase, the method comprising successively at least the following sub-phases:

• conducting blow molding or a series of blow moldings by connecting the container successively to increasingly higher-pressure air systems;
• then performing a recovery or a series of recoveries by connecting the container successively to increasingly lower-pressure recovery air systems, until a final recovery where the container is connected to a final air system;
• then performing a degassing by connecting the container to atmospheric pressure;
• and
• finally opening the mold by disconnecting the nozzle,
• wherein at least one characteristic point of the pressure in the container is selected that is taken from selectable points that are:
• when there are several blow moldings, the transition between two successive blow moldings, and
• when there are several recoveries, the transition between two successive recoveries, and
• the transition between the final recovery and the degassing,
• wherein, for each selected characteristic point,
• a scanning time zone is determined where the selected characteristic point is found,
• a triggering criterion is determined, the triggering criterion representing a progress status of an air pressure stabilization between two receptacles during at least the scanning time zone, the two receptacles being defined by the container and one of the air systems to which the container is connected before the selected characteristic point, and
• a predetermined value of the criterion is determined,
• wherein, during a data acquisition phase that extends over at least one production cycle, the pressure is measured in the container to register a pressure curve along at least the scanning time zone of each selected characteristic point,
• wherein, for each selected characteristic point, the following are determined from the pressure curve measured:
• an actual instant corresponding to said selected characteristic point,
• an actual value of the criterion at the selected characteristic point, and
• a target instant to trigger, in a subsequent production cycle, the passage to the sub-phase that is subsequent to the selected characteristic point, such that:
• when the actual value of the criterion is less than or equal to the predetermined value, the target instant is the instant for which the criterion has assumed a value equal to the predetermined value, and
• when the actual value of the criterion is strictly greater than the predetermined value, the target instant is subsequent to the actual instant and is determined to ensure that at the target instant, the criterion assumes a value approaching or coinciding with the predetermined value.