INFLUENCE OF THE FLOW CHANNEL GEOMETRY ON THE DEGASSING PRESSURE IN FOAM EXTRUSION

摘要

The onset of bubble formation or in other words the degassing pressure is an important value for the designing of a die for extrusion foaming. Therefore, the effect of flow channel geometry on the degassing pressure was examined with a newly developed slit die concept. The determination of the onset of bubble nucleation was carried out with an optical spectroscopy technique. In this study we used four different flow channel geometries to determine the degassing pressure for different flow conditions. Additionally simulation experiments were used to compare the different flow channel geometries in terms of shear rate, pressure drop rate and velocity changes to gain data for the scale-up. It was shown, that the degassing pressure is a function of the flow conditions. With increasing shear rate, elongation rate and pressure drop rate the degassing pressure increases.