Sensor -Based Process Monitoring by Inline Bubble Detection in Blown Film Extrusion

One key requirement for highly efficient production processes are steady and robust process conditions because they are most likely to ensure a constant product quality at the desired level. In blown film extrusion, film properties are predominantly influenced within the bubble formation zone, where the molten polymer expands from a thick-walled tube to a solid thin-walled sensitive film bubble. The characteristic bubble shape or contour, respectively, represents the state of balance resulting from all underlying process conditions and therefore its inline detection offers potential for an advanced process monitoring. Against this backdrop, the use of different measuring techniques, such as pyrometry, imaging or distance measurement, aims at an extensive and accurate description of the expanding film bubble. As a first step, a measurement setup for such an inline detection is presented in this paper. Initial measurement results from experimental tests on a small-scale blown film line confirmed the general applicability of the three techniques. Moreover, some key requirements and limitations regarding inline bubble detection have been identified. Future work in this current research project involves the development of a simulation model for the expanding film bubble that is based on the given sensor signals and allows process monitoring with focus on the film's quality.