Calculation of the pellet transportation in grooved feed zones, considering varying conveying mechanisms at high screw speeds

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Single-screw extrusion is an important production process for large-scale plastic product manufacturing at low cost. In recent year, so-called high-speed extruders have gained momentum. These systems operate at screw speeds a lot higher than for conventional processes and thus generate a higher output and productivity. Especially for mass-production industries like blow film or others, the combination of such high outputs at small extruder sizes is very promising. Therefore, many current research activities focus on the optimization and applicability of these systems. However, conventional approaches for screw and barrel design cannot longer be used, as the baseline assumptions for the throughput calculations are not valid for high screw speeds. Therefore, new or optimized methods are required.Especially the phenomenon of a decreasing specific throughput at higher screw speeds has to be considered. As this problem has been well known for decades, a variety of constructive counter measure were developed in the past. However, these solutions still have their limits at such high screw speeds, which is why the phenomen has to be integrated in the mathematical description of the conveying mechanisms. The throughput calculation for conventional extruders is usually based on the axial conveying speed, the free intersection of the screw channel and the bulk density of plastic pellets. This leads to a linear correlation between screw-speed and throughput, which cannot be held up for high-speed extruders. There are approaches to make corrections in order to consider the decreasing specific throughput, however, they all require a statistical calibration of heuristic correction factors, which different authors have obtained by performing experiments or simulations, which limits the applicability to the tested materials.Therefore, the objective of this project is to expand and enhance throughput calculation models based on actual and measureable values of the screw and barrel design and the pellet characteristics. Other than former approaches, no statistical or heuristic factors shall be used. Also, physically plausible effects like the occurring centrifugal forces will be considered.