Effect of Wall Slip on the Extrusion Characteristics of 3D Printing of Cementitious Materials

This paper investigates the impact of wall slip on the screw extrusion of cementitious materials. A wall slip extrusion model is developed based on the theory of infinite parallel plates. Then, the extrusion characteristics under different slip conditions of the screw and the cylinder wall are discussed. Finally, the Finite Element Method is used to verify the conclusions drawn from theoretical model analysis. The results show that when −1≤a←1/3 (where a is the ratio of pressure flow to the sum of drag flow and slip flow), slippage on either the screw wall or the cylinder wall can reduce the extrusion flow rate, and the number of flow recirculation planes is one. When −1/3≤a≤1, the number of flow recirculation planes increases to two, and screw wall slip is conducive to expanding the extrusion flow rate. Conversely, cylinder wall slip may reduce the extrusion flow rate. Moreover, the simulation results are consistent with those of the theoretical model, further verifying the rationality of the model.