On‐Line measurement of parison geometry during blow molding: Parison swelling for three high‐density polyethylenes with different molecular weights and molecular weight distributions

Abstract

AbstractAn image analysis technique has been developed to measure diameter and thickness distribution of a parison during the extrusion stage in blow molding. The system operates on‐line during extrusion on any commercial blow‐molding machine. The system has been developed to help development of new blow‐molding resins by increasing our understanding of the connection between polymer structure and parison shape. The system can also be used for die design during optimization of a production process. The combined use of experimental design and multivariate projection techniques makes this an efficient tool for the practical processing engineer. Experiments done on three high‐density polyethylene blow‐molding resins show the importance of measuring the time dependence of the diameter and thickness distribution under different extrusion conditions for a given polymer. Our results show that many of the swell and sag related properties we see cannot be directly inferred from standard laboratory swell‐experiments.