Method for setting an operating point of a film stretching machine and film stretching system for producing a plastics film

A method for setting an operating point for a film stretching system for producing a plastics film, wherein the film stretching system comprises:

• a chill roll;
• an extruder arrangement and a die, wherein the extruder arrangement is designed to supply a plastics melt to the die and wherein the plastics melt can be discharged from the die onto the chill roll;
• a stretching arrangement which has at least one longitudinal stretching system which comprises at least one stretching stage in the longitudinal direction and is arranged after the chill roll;
• a motor arrangement for driving the chill roll and the stretching arrangement;
• an operating terminal;
• a memory device;
• a control device which is designed to control the motor arrangement, the extruder arrangement and the operating terminal;
• wherein the operating point is defined by linked production variables of the film stretching system, wherein:
• a first production variable is a thickness of the fully stretched plastics film, and wherein the first production variable is adjustable in a range between a minimum permissible thickness of the fully stretched plastics film and a maximum permissible thickness of the fully stretched plastics film;
• and
• a second production variable is a plastics material output quantity of the extruder arrangement, and wherein the second production variable is adjustable in a range between a minimum permissible plastics material output quantity of the extruder arrangement and a maximum permissible plastics material output quantity of the extruder arrangement;
• and
• a third production variable is a line speed of the film stretching system, and wherein the third production variable is adjustable in a range between a minimum permissible line speed of the film stretching system and a maximum permissible line speed of the film stretching system;
• wherein the method comprises:
• acquiring an input by the operator terminal, wherein the input contains:
• a) one target value for the first production variable;
• or
• b) one target value for the second production variable;
• or
• c) one target value for the third production variable;
• specifying:
• a) a setting value for the second production variable and a setting value for the third production variable in order to achieve the target value for the first production variable);
• or
• b) a setting value for the first production variable and a setting value for the third production variable in order to achieve the target value for the second production variable);
• or
• c) a setting value for the first production variable and a setting value for the second production variable in order to achieve the target value for the third production variable, wherein specifying the two setting values for the production variables for which no target value has been acquired is done in such a way that the two setting values are specified automatically to achieve the acquired target value;
• and
• in such a way that initially a reserve remains for the minimum and/or maximum possible setting values wherein this reserve is changed during operation;
• controlling the motor arrangement and the extruder arrangement by the control device in such a way that the operating point consisting of or comprising the target value and two setting values is reached.