Back‐calculation of the die swell phenomenon of rubber compounds by means of torsional rheometry

Abstract

AbstractThe die swell phenomenon of capillary experiments with various ratios of length to diameter of capillary dies is investigated. This knowledge is important for the design of injection heads for the extrusion of rubber profiles. To predict the die swell of capillary experiments, additional tests with a torsional rheometer has been performed. For polymers, the combination of such rheological data is possible under usage of the empirical relationship by Cox and Merz. With the introduction of a scaling factor this rule is also applicable for rubber compounds. With the relationship of Laun and the new scaling factor a back‐calculation of the first normal stress difference is done. Finally, the die swell of arbitrary capillary experiments for industry‐used rubber compounds can be computed without introduction of new material parameters. For this task a relationship of Tanner is used, which connects the die swell and the first normal stress difference. An adaptation of the capillary viscometer allows the experimental investigation of the die swell and, thus, a validation of the presented approach. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008