Numerical investigation of the temperature influence on the melt predistribution in a spiral mandrel die with different polyolefins

Abstract

Abstract The main goal in the design of spiral mandrel dies for blown film extrusion is to achieve a homogeneous velocity distribution of the plastics melt at the die outlet. However, thermal inhomogeneities in the die can lead to an uneven flow distribution despite a rheologically optimized design of the die. The thermal inhomogeneities are especially dominant in the predistributor of spiral mandrel dies. Against this background, the temperature influence on the melt distribution in the predistributor is investigated for different polyolefins with the help of flow simulations in Polyflow (Ansys). The simulation models the whole predistributor and takes both the heat transfer in the predistributor and the shear heating in the melt into account. Afterwards, simulations are conducted in which the thermal design measures for the homogenization of the flow in the die are applied. With the combination of heating cartridges, brass inserts, and isolating gaps in the die, a significant homogenization of the predistribution can be achieved. Finally, the simulation results are validated in practical tests, whereby a good agreement between simulation and measurement can be observed.