The Modelling of Extrusion Processes for Polymers—A Review

Abstract

Extrusion processes are widely used in industries that aim to produce advanced solutions for increasingly sophisticated demands in the plastic, food, and pharmaceutical sectors. Though the process has been in use since the 1930s, limited information is available on the analytical computation of extrusion. Generally, production has been carried out based on empirical experience and trial-and-error approaches. The development of industrial operations is, however, best addressed by modelling the processes involved, and the flow of polymer melts and fibers in extruders has been subjected to some previous studies. Also included an overview of design of a die as well as challenges in sheet/film production. This article systematically and critically reviews the literature related to the process design, machine design, process parameters, flow models, and flow analysis of extrusion with a focus on modelling the extrusion of composite materials.

Theoretical Evaluation of the Melting Efficiency for the Single-Screw Micro-Extrusion Process: The Case of 3D Printing of ABS

“…In addition, the critical switch point defined at Br equal to 1 is pushed further away. Notably, the observed values of the conventional Br number, at the beginning of the compression section, are consistent with the reported balance between shear heat and conduction heat in previous work [35].…”

“…For AM melting, some substantial differences can be noted compared to conventional larger extruders, as already highlighted in the Introduction. The rotational speeds in micro-extrusion can be substantially lower and less heat is generated due to shear rate differences, while better heat transfer characteristics are established due to the higher heat transfer area-to-volume ratio [35,36]. This leads to lower values for the so-called Brinkman number (Br), which is a dimensionless number commonly used in polymer processing, indicating the ratio between the viscous heating to the (molecular) conduction heating [49][50][51][52][53].…”

“…Upon reducing the SSE size, a higher heat transfer area-to-volume ratio is manifested compared to larger machines. Better heat transfer characteristics are thus reported for micro-extruders [35,36], further highlighting the differences in optimal processing conditions. A deep understanding of the effect of the machine size on the melt performance specifically in the range of the smaller sizes-as relevant for SSE-based EAM-is however still lacking.…”

“…80% of the total heat required for polymer melting is generated by this mechanism. The remaining heat is externally supplied through thermal resistances installed around the extruder barrel, thus conduction [35]. Upon reducing the SSE size, a higher heat transfer area-to-volume ratio is manifested compared to larger machines.…”

“…In the present work, a numerical model based on previous studies regarding the melting mechanism in SSEs [24,[33][34][35][36][37][38][39][40][41][42][43][44][45] is therefore presented to evaluate the melt evolution of a reference polymer ABS along the screw length for an AM pellet-based micro-extruder, also comparing the results with conventional extrusion. The developed model can be easily integrated into a real-time controller to actively tune the positions where the complete melting of the pellets should happen during a micro-extrusion AM process, as algebraically based mathematical relations are established between processing/material parameters and the melting efficiency.…”