Nonaqueous Aluminum Nitride Extrusion: II, Die-Land Flow and Tribology

Die‐land flow on extruding a nonaqueous aluminum nitride plastic body was analyzed using simultaneous orifice and capillary rheometry. Extrudate slip on the wall of the die‐land was observed and concluded to involve frictional slip of extrudate particles against the die‐wall and the viscous flow of an annular liquid. Results supported a model of a hydroplaning mechanism for the radial consolidation of the particle and binder network with complementary syneresis of liquid. The thickness of the apparent annular slip film was calculated to be submicrometer and to increase with an increase in the extrudate velocity and a decrease in the bulk yield stress and diameter of the die‐land. The flow stress on approaching the critical volume concentration of particles terminating plastic flow increased abruptly for shear of the body in the die‐entry but more gradually for slip in the die‐land. Shear resistance in the die‐land was significantly decreased on adding a lubricant and was very dependent on the contact stress between the particle network and the die‐wall, controlled by the degree of pore saturation for an unsaturated body and the volume of particles and binder for the saturated extrudate.