Flow analysis of screw extrusion in three-dimensional concrete printing

Recent advances in three-dimensional concrete printing necessitated the detailed understanding of the operation and performance of screw extruders. This paper shows that the volumetric output rate can be approximated using the rotating barrel and stationary screw assumption (drag flow equation), which is used routinely in polymer melt extrusion calculations. Verification is provided by comparisons to experimental results available in the literature and to computer flow simulations for fluids with yield stress. Significant insight is obtained using fully three-dimensional simulations. This includes particle pathlines, which form “a helix within a helix,” axial pressure profiles, and the effect of yield stress, which is relatively small on the output rate but large on torque and power. The computer simulation also predicts unyielded flow zones in the extruder channel at low screw rotation speeds.