A composite model has been developed to simulate a starve fed single screw extrusion of thermoplastics. The model is based on combining melt conveying models with new melting models. Illustrative computations are made for low-density polyethylene and polypropylene at various operating conditions. Simulations are made for axial fill factor, pressure, temperature, and melting profiles. The results are validated experimentally. POLYM. ENG. SCI., 54:2362-2374, 2014

A review paper is presented on modeling for polymer extrusion for both single screw and twin-screw extrusion. An issue of global modeling is discussed, which includes modeling for solid conveying, melting, melt flow, and co-operation of the screw/die system. The classical approach to global modeling of the extrusion process, which is based on separate models for each section of the screw, i.e., solid transport section, melting and pre-melting sections, and the melt flow section is presented. In this case, the global model consists of the elementary models. A novel continuous concept of global modeling based on CFD (Computational Fluids Dynamics) computations is also presented, and a concept of using the DEM (Discrete Element Method) computation coupled with CFD computations is discussed.

Previous experimental studies of the polymer behavior in a starve fed single screw extrusion process have shown that contiguous solids melting mechanism which is observed for flood fed extrusion was not observed for starve fed extrusion. A new two-stage physical model of polymer melting in a starve fed single screw extrusion has been proposed with conductive mechanism for melting in the partially filled region and dispersed melting mechanism in the fully filled region. Mathematical models have been proposed for melting in both those regions. The models have been validated experimentally.

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ABSTRACT:A global computer model has been developed for starve-fed nonconventional single-screw extrusion. The model has been built by combining a new melt conveying model with recently developed melting models. Mixing screw equipped with dispersive mixing element of Maddock has been considered as an example for modeling. Extensive fully three-dimensional non-Newtonian Finite Element Method (FEM) computations have been performed to model the melt flow in mixing elements. Screw pumping characteristics have been computed and modeled for these elements at various power law indices. These characteristics have been implemented into the global model of the process. Computations were made for low-density polyethylene at various operating conditions. Fill factor, pressure, temperature, and melting profiles were simulated and validated experimentally. It has been confirmed by computation and experimentation that melting in starve-fed single-screw extruders is totally different compared with melting in flood-fed extruders. It is faster, and the screw length needed for melting extends with an increase of the flow rate. The screw is fully filled for some distance from the die only and starved beyond it. This distance is dependent on the flow rate and screw speed. C