EXTRUSION OF PASTES CONTAINING PLATE-LIKE PARTICLES

The addition of platelike particles into ileal. spherical powder syste ms causes changes in the packing behaviour of the system and alters th e flow behaviour of pastes formed from such mixtures. It is shown that , as coarse platelets are added to fine powders, the packing density i ncreases brit riot to the degree predicted by simple packing models in which the diameter ratio of the two components is used. The behaviour is only slightly better predicted by the use of platelet thickness to determine the ratio between particle geometries, and an alternative a pproach to estimating a ratio is suggested. Simple tests such as tap d ensity or water absorption were not found to accurately predict the pa cking, arcing to flocculating and mixing difficulties, but hy measurin g the rheological properties of pastes in which high shear is applied in the mixing of the pastes, a more consistent approximation to the pa cking behaviour call be established. The addition of platelike particl es to pastes is shown to affect the mechanical properties of the mater ial. The greater. the addition of platelets, the greater the reduction in strength in green bodies and the greater the propensity for the ma terial to produce weld lines ol lamination defects.