Investigations to the influence of material and grain shape on the dissipation in the solids conveying of single-screw extruders

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While modeling the process conditions of single screw extruders the pellets size and shape is widely neglected. It is only considered for the design of grooved bushes. Nevertheless the pellets size and shape have a strong influence on the flow conditions in the screw channel. Internal and external friction affect the solid conveying as well as the melting process. While the solid conveying strongly depends on the friction coefficients ratio, the melting process is influenced by their absolute values. Sharp-edged pellets cause high internal friction and therefore dissipation in the solid plug. More spherical pellets with a smooth surface however produce less friction. Cylindrical pellets even could arrange in that way that they roll over on each other. This effect would induce much less dissipation. Common models describing the melting process in the screw channel neglect the dissipation in the solid bed yet. Therefore, in this research project the influence of the pellets material and shape on their dissipation is to be investigated using polyamide and polypropylene. These materials will be granulated using hot and cold-pelletizing. Then, the solid conveying and the melting process will experimentally investigated, simulated and mathematically modeled.