In the die entry region the material is forced into the nozzle with
smaller diameter than the cylindrical one. It causes an alteration of the
velocity profiles because the material flow conditions are in transition
state from the flow regime in the cylinder (low speed) to the flow regime
in the nozzle (high speed). This transition involves a high pressure
drop,which is recorded in the die entry. The capillary tube however, has
the main function of regulating the flow, preventing the formation of
surface defects that affect the extrusion quality. The compacted powder
reacts to the pressure induced in the capillary as a viscous solid, the viscosity
of which increases with decreasing porosity [17]. It is important
to note that the total pressure drop in the extruder rheometer, nΔPtot,
is given by the sum of two terms: the pressure drop in the die entry,
ΔPe, and the pressure drop in the capillary tube, ΔP:
In the die entry region the material is forced into the nozzle withsmaller diameter than the cylindrical one. It causes an alteration of thevelocity profiles because the material flow conditions are in transitionstate from the flow regime in the cylinder (low speed) to the flow regimein the nozzle (high speed). This transition involves a high pressuredrop,which is recorded in the die entry. The capillary tube however, hasthe main function of regulating the flow, preventing the formation ofsurface defects that affect the extrusion quality. The compacted powderreacts to the pressure induced in the capillary as a viscous solid, the viscosityof which increases with decreasing porosity [17]. It is importantto note that the total pressure drop in the extruder rheometer, nΔPtot,is given by the sum of two terms: the pressure drop in the die entry,ΔPe, and the pressure drop in the capillary tube, ΔP:
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