Solids Conveying in Injection Molding Machines—Analytical Model for Smooth and Grooved Feed Sections Derived From DEM Simulations

ABSTRACT

Solids conveying is a key aspect for the design of polymer processing machines, especially for processes with high screw speeds, grooved feed sections, and material with low bulk density. Insufficient solids conveying can limit the achievable throughput of the machine. In injection molding, such limitations are highly relevant in packaging applications and are a primary cause for air residue in the final product. As manufacturers adapt machines to the challenges posed by these materials by adding shallow grooves to the feed section, existing analytical models fail to replicate the physical solids conveying mechanism. In this paper, a thorough review and rework of analytical models for solids conveying is presented. Models for injection molding are benchmarked against the throughput achieved in experimental investigations for smooth and grooved feed sections in a special test rig. As significant deviations are observed, a new conveying case for shallow grooves is defined based on experimental investigations and numerical simulations. An analytical model describing the achievable throughput in feed sections is developed for the new conveying case, using coupled Discrete Element Method and Multibody Systems simulations in a Design of Experiments. The resulting model accurately predicts the throughput achievable for virgin material, regrind, and post‐consumer flakes.