Experimental investigation and improved modeling of the melting process in single-screw extruders with a grooved plasticizing barrel

Abstract

In the field of extrusion, nowadays, the main goals are reduction of the manufacturing costs as well as improvements in output and product quality. A very promising high performance extruder fulfills those requirements and is already used in the European industry. This new type of single-screw extruder was introduced to the European plastics industry in 1999 and consists of a combination of a grooved plasticizing barrel with a barrier screw. Although the exceptional performance of this extruder system has already been investigated comprehensively, the melting mechanisms are still not fully understood. Therefore, in the past both an analytical Newtonian model and a numerical non-Newtonian model using the finite difference method (FDM) had been developed at the IKT to predict the melting rate along the screw. In the present work, an enhanced analytical model is presented and compared to experimental investigations. The experimental study includes a qualitative method using optical analysis of the cross sections along the barrel. Hence, the melting process can be further characterized and assumptions of the previous analytical model are validated and partially extended. The enhanced mathematical model is based on the theory of melting in conventional single-screw extruders, the previous model and the experimental results. The model iteratively calculates the melt film thickness δ0 while considering the melt to be a shear thinning fluid with temperature-dependent viscosity. Finally, the mathematical model is compared with the experimental results, the previous analytical model and a numerical simulation using the finite difference method (FDM). It could be shown that the simulations are in good agreement with the experimental results.