The Behavior of Bulk Solids in the Solids Conveying Zone of Smooth Barrel Single Screw Extruders: Friction, Bulk Density and Pressure Anisotropy

This work deals with the material parameters of bulk solids in the solid conveying zone. New measurements show that the coefficient of friction of polypropylene-Homopolymer (PP-H) bulk material is clearly dependent on the frictional distance. Furthermore, a new mathematical model for the bulk density regarding the pressure and the temperature is presented. This model considers the melting point and the pvT-data and needs only three parameters to approximate the bulk density depending on pressure and temperature. The model fits experimental data from room temperature up to the melting point. There is a smooth crossover to the pvT-data at the melting point. These are clear advantages compared to existing models. The same approach approximates the pressure anisotropy sufficiently as well.