Factors influencing paste extrusion pressure and liquid content of extrudate in freeze-form extrusion fabrication

Freeze-form extrusion fabrication process extrudes an aqueous ceramic paste of high solids loading by ram extruder to fabricate 3-D ceramic green parts. An appropriate extrusion pressure is necessary to get the desired extrusion velocity, and the extrudate should be keep in the same composition during the extrusion process for fabricating uniform green parts. The ram velocity, die land geometry, and paste property are three main factors influencing paste extrusion process. In this paper, the experiments were carried out to determine the effect of the three factors on the extrusion pressure and liquid content of extrudate. The experimental results show that the ram velocity is a strong factor governing the extrusion pressure profiles and too low ram velocity can result in liquid phase migration. The die land diameter and paste viscosity have obvious impact on paste extrusion process, which is largely consistent to the Benbow–Bridgwater model but sometimes is influenced by liquid phase migration. A further analysis of paste extrusion process indicates that the varying of paste structure in different extrusion stage leads to the experimental phenomenon. The research can help to get better understanding of influence factors in paste extrusion and to give reference of controlling the process in freeze-form extrusion fabrication process.