Abstract
Many theoretical analyses of extrusion ignore the effect of the flight clearance when predicting the pumping capability of a screw. This might be reasonable for conventional extruder screws with “normal” clearances but leads to errors when more advanced screw designs are considered. We present new leakage-flow models that allow the effect of the flight clearance to be included in the analysis of melt-conveying zones. Rather than directly correcting the drag and pressure flows, we derived regression models to predict locally the shear-thinning flow through the flight clearance. Using a hybrid modeling approach that includes analytical, numerical, and data-based modeling techniques enabled us to construct fast and accurate regressions for calculating flow rate and dissipation rate in the leakage gap. Using the novel regression models in combination with network theory, the new approximations consider the effect of the flight clearance in the predictions of pumping capability, power consumption and temperature development without modifying the equations for the down-channel flow. Unlike other approaches, our method is not limited to any specific screw designs or processing conditions.
Highlights
Plasticating extruders abound in the polymer industry
Our parametric design study encompassing 9,231 independent setups provided numerical solutions for the dimensionless volume flow rate ΠVδ and the dissipation ΠQδ in the flight clearance as functions of the dimensionless input parameters t/Db, n, and Πpδ,x
We have proposed novel analytical regression models for predicting the volume flow rate and the viscous dissipation rate in the flight clearance of single-screw extruders
Summary
Plasticating extruders abound in the polymer industry. Due to their great versatility, they are used in many polymer-shaping operations, producing semi-finished plastic products such as films, pipes, profiles, sheets, and fibers. They are frequently found in compounding and recycling operations. Plasticating extruders come in various designs, the elementary processing steps are generally the same: (i) transport and (ii) melting of particulate solids, followed by (iii) mixing and (iv) pumping of the polymer melt. Numerous theoretical studies have modeled the extrusion process to increase the understanding of the transport mechanisms governing physical operation. Many analyses have modeled polymer-melt flows in single-screw extruders.
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