The influence of the viscous and elastic components of a visco-elastic binder phase on the extrusion behaviour of a tungsten carbide-cobalt hardmetal paste was investigated by studying the paste over a range of temperatures, 30-42°C, where the binder changed from a semi-solid gel to a viscous liquid. The extrusion behaviour of the paste was studied by ram extrusion and quantified by the Benbow-Bridgwater (BB) method. The elastic and viscous components of the binder were studied separately by means of oscillatory and steady shear techniques in a controlled stress rheometer using rough parallel plates. The paste behaviour fitted the four parameter BB model well: the initial bulk yield stress parameter, r 0 , increased linearly with the binder elastic modulus, G 0 , while both the velocity dependence parameters a and b were linearly related to the binder steady shear viscosity. Analysis of paste-wall slip parameters gave estimated slip layer thicknesses of 2-5 particle diameters. List of symbols Roman APre-exponential factor in Eq. (6) (Pa s) C Carreau relaxation time constant (s) d 10 10 % of the population are smaller than this diameter (m) d 50 50 % of the population are smaller than this diameter (m) d 90 90 % of the population are smaller than this diameter (m) d [4,3] Volume moment (De Brouckere) mean diameter (m) D Die land diameter (m) D 0 Barrel diameter (m) E Activation energy in Eq. (6) (J mol -1 ) G 0 Elastic shear modulus (Pa) G 0 B Elastic shear modulus of unloaded binder (Pa) G 00 Viscous shear modulus (Pa) [k] Intrinsic viscosity (-) K Herschel-Bulkley consistency (Pa s k ) L Die land length (m) m Benbow-Bridgwater die entry velocity index (-) n Benbow-Bridgwater wall slip velocity index (-) pCarreau power law index (-) P ex Extrusion pressure (Pa) P 1 Component of extrusion pressure associated with die entry flow (Pa) P 2 Component of extrusion pressure associated with die land flow (Pa) R Universal gas constant (J mol -1 K -1 )Mean extrudate velocity (m s -1 )Greek a Benbow-Bridgwater extensional deformation velocity coefficient (Pa s m m -m ) bBenbow-Bridgwater wall slip velocity coefficient (Pa s n m -n ) _ cShear rate (s -1 ) _ c app Apparent shear rate (s -1 )

Drying of cemented carbide paste extrudates is studied experimentally.  Discs, cylindrical rods and tubes are tested: end effects are important.  A shrinking core model could be fitted to the data yet failed to describe all geometries.  A pseudo-Fickian model was found to represent all geometries adequately.

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