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This work deals with the melting of polymeric bulk materials and the melt penetration into the solid bed utilizing a model experiment that simulates the melting process in single screw plasticating units. The polymer granules are pressed onto a heated rotating shaft. The thickness distribution of the resulting melt film is measured according to the principle of optical triangulation (light intersection). This new method and the measurement of the bulk density using a piston position measurement were presented earlier by the authors. The combination of these different principles allows the determination of the melt penetration into the solid bulk as it takes place in the delay zone of single screw plasticating units.The melting behavior of spheroidal and cylindrical shaped polypropylene-homopolymer (PP-H) bulk solids is analyzed at different applied pressure. Spheroidal bulk solids show significant advantages compared to cylindrical shaped granules which melt much slower, particularly at higher pressures. ...

The influence of the pellet shape on the external coefficient of friction of polypropylene and on the mass flow rate of a single screw extruder is presented in this conference paper. The external coefficient of friction describes the friction between the polymeric bulk material and the screw or the barrel surface. In general, the external coefficient of friction should be rather low at the screw surface and high at the barrel surface in order to achieve a high mass flow rate and sufficient pressure build-up in the conveying zone of a single screw extruder. The measurements of the external coefficient of friction of polypropylene pellets, which are dependent on the shape and the dimensions of the pellets at processing conditions (pressure and velocity), are carried out using a previously developed tribometer. The tests were performed at room temperature on a polished hardened shaft made of screw steel. The effect of the shape of the polypropylene pellets on the mass flow rate is studied using a single screw extruder (Measuring extruder type Dr. Collin E20M). Two different temperature profiles were used for the extrusion experiments. When using the long cylindrical polypropylene pellets a higher extruder output can be achieved compared to the virgin material.