In such fabricating processes as extrusion and injection molding it is frequently necessary to force a granular polymer through a channel. Frictional forces between polymer and channel walls lead to a drop in pressure through the granular material. Simultaneously, the applied pressure causes a compaction of the granules.
Assuming that the granular mass has certain fluid‐like properties, a simple theoretical expression for pressure transmission is derived. Comparison with data on saran powders and granular polystyrenes shows good agreement between theory and experiment. The effect of lubrication is shown also.
The compaction of granular polystyrene follows the same pattern as that observed in the earth's crust. The porosity decreases exponentially with increasing pressure. The ``compressibility coefficient'' for the porosity of granular polystyrene is comparable with that given for clays and shales.
