Linking particle properties to paste extrusion flow characteristics using discrete element simulations

Extrusion is a widely used process for forming pastes into designed shapes, and is central to the manufacture of many industrial products. The extrusion through a square-entry die of a model paste of non-Brownian spheres suspended in a Newtonian fluid is investigated using discrete element simulations, capturing individual particle contacts and hydrodynamic interactions. The simulations reveal inhomogeneous velocity and stress distributions, originating in the inherent microstructure formed by the constituent particles. Such features are shown to be relevant to generic paste extrusion behaviour, such as die swell. The pressure drop across the extruder is correlated with the extrudate velocity using the Benbow-Bridgwater equation, with the empirical parameters being linked directly to particle properties such as surface friction, and processing conditions such as extruder wall roughness. Our model and results bring recent advances in suspension rheology into an industrial setting, laying foundations for future model development, paste formulation and extrusion design.