Solids Conveying in Lab Scale Smooth Barrel Single Screw Extruders Regarding the Material Parameters` Dependence on Pressure, Temperature and Velocity

This work deals with the modeling of the solids conveying zone of a smooth barrel single screw Extruder (SSE) regarding two different shaped polypropylene homopolymer bulk solids (spheroidal and cylindrical) and compares the results to experiments performed at a lab scale SSE. The bulk density and the pressure anisotropy coefficient were measured in dependence on pressure and temperature utilizing a special measuring device. The external coefficient of friction was measured in dependence on pressure, temperature and the sliding velocity using a unique tribometer. In this work a segmented model of the solids conveying zone of a smooth barrel SSE is utilized in combination with a damped Newtonian solver to calculate the pressure rise of the single elements at a given solids conveying rate which is known from practical extrusion experiments. Furthermore the interface- temperature between the polymeric bulk and the barrel of the extruder is calculated. The bulk density and the pressure anisotropy coefficient are applied as functions of temperature and pressure, the coefficient of friction additionally depends on the frictional velocity. Numerous iterations are needed to gain a convergent result for every single segment. The results obtained by the different approaches of Darnell and Mol, Schneider, Schöppner or Hyun et al. [1] are compared to values measured at a lab scale single screw extruder. In the extrusion experiments the cylindrical shaped bulk solids showed a higher throughput and a faster pressure build-up development than the spherical shaped bulk solids. The determination of the bulk solid properties showed rather low differences of the bulk density, the external coefficient of friction and the pressure anisotropy coefficient. This work shows the results of a segmented calculation of the solids conveying zone regarding the material parameters` dependence on pressure, temperature and velocity and the differences to a simplified calculation considering averaged values.