Device for producing and smoothing plastic films or plastic plates

A device for producing and smoothing plastic films or plastic sheets, respectively, comprising

• plastic-melt-producing means for producing a plastic melt from a thermoplastic material,
• a slit die having two opposing die lips that are adjustable in the distance to each other, which form a die gap between each other, wherein the slit die may be supplied with plastic melt from the plastic-melt-producing means,
• a roller smoothing unit having two smoothing rollers, of which at least one is cooled, which form an adjustable smoothing gap between each other for receiving the flow of the plastic melt discharged by the slit die, wherein the smoothing rollers cool the flow of the plastic melt down to the solidification thereof as a plastic-film or plastic-sheet web, thereby smoothing the surfaces;
• at least one thickness gauge for measuring the thickness of the plastic-film or plastic-sheet web, which is arranged downstream of the smoothing rollers;
• and
• a controller for controlling the thickness of the plastic-film or plastic-sheet web, wherein the controller has setpoint value inputs:
• for setting the setpoint thickness of the plastic-film or plastic-sheet web;
• and
• for setting either the volumetric flow rate of the plastic melt discharged by the plastic-melt-producing means or for setting the line speed,
• wherein the controller has actual value inputs
• for capturing the current torque of at least one roller;
• for capturing the rotational speed or the circumferential speed of at least one roller;
• and
• capturing the current thickness of the plastic-film or plastic-sheet web measured by the thickness gauge,
• wherein the controller has control signal outputs, by way of which
• the controller sends setpoint rotational speed signals or setpoint circumferential speed signals calculated from the captured current torques of the rollers to the drives of the rollers;
• the controller outputs a smoothing-gap setpoint distance signal calculated from the setpoint thickness and the captured current torques of the rollers for adjusting the smoothing gap, and
• the controller sends either—in the case of a specified line speed—setpoint plastic-melt volumetric flow rate signals calculated from the setpoint thickness or the actual thickness of the plastic-film or plastic-sheet web to the plastic-melt-producing means,
• or—in the case of a specified plastic-melt volumetric flow rate—setpoint line speed signals calculated from the setpoint thickness and the actual thickness of the plastic-film or plastic-sheet web and/or setpoint circumferential speed signals derived therefrom to the drives of the rollers.