Leonhard Perko

Flow behaviour of rubber in capillary and injection moulding dies

ABSTRACT This study is concerned with the flow behaviour of a rubber compound in capillary and injection moulding dies in the temperature range of 80–120°C. The injection moulding die designs had a tapered angle ranging from 40° up to 150°. The rheological characterisation of the rubber compound in the capillary dies showed that rubber slips at the wall, and this was modelled with an appropriate slip law. The pressure drops in the system were measured for all tapered dies. Numerical simulations were then carried out with a purely viscous (Carreau) model and a multimode viscoelastic (K-BKZ) model. The results showed a good agreement with the experiments for both the capillary and the injection moulding dies, provided that slip is included in the simulations as determined experimentally.

Flow Behavior of PP-Polymer Nanocomposites in Capillary and Injection Molding Dies

Abstract For simulation of thin-wall injection molding, accurate viscosity data measured at shear rates up to 800,000 s−1 and more are important, but not available in any commercial material database. Such data can be measured on conventional injection molding machines with the help of a rheological mold, which is constructed like a standard injection mold with interchangeable dies. It enables operators to measure viscosity in time on their own machines at practically relevant shear rates (from 102 s−1 to 2 × 106 s−1). A special feature allows measuring the pressure dependency of viscosity using closed-loop counter pressure control. Experimental data are evaluated taking into account the melt temperature rise due to dissipative heating. Using capillary dies having different diameters, D, and length-to-diameter L/D ratios, a full rheological characterization has been carried out for a polypropylene-filled nanocomposite, and the experimental data have been fitted both with a viscous model (Cross) and a viscoelastic one (the Kaye – Bernstein, Kearsley, Zapas/Papanastasiou, Scriven, Macosko or K-BKZ/PSM model). Four injection molding dies have been also used to reach apparent shear rates up to 800,000 s−1. Particular emphasis has been given on the pressure-dependence of viscosity. It was found that only the viscoelastic simulations were capable of reproducing the experimental data well, while any viscous modeling always underestimates the pressures, especially at the higher apparent shear rates and L/D ratios.