The extrusion mechanics of pastes—the influence of paste formulation on extrusion parameters

Abstract Paste rheology has been studied with a ram extruder in which there is convergent flow followed by extrusion through a tube of constant diameter, the die-land. Pastes have been made from particles of known size distribution and liquids of known rheology. The flow has been described successfully by regarding the convergent flow to be governed by a yield mechanism and the plug flow in the die-land by wall resistance. This gives rise to two important extrusion parameters, namely the yield value and wall stress. The seven different α-alumina pastes which have been studied all comply with this pattern. Both the yield value and wall stress are dependent on velocity. In each instance, the velocity effect is proportional to the effective viscosity of the liquid phase. Particle size distribution and liquid phase content each have a substantial effect on the extrusion parameters.