Packing and solidification in ceramic injection moulding

The occupation of volume in large ceramic injection mouldings solidified un der different pressures using two moulding techniques is considered. Large (60 x 45 x 25 mm) alumina injection mouldings were prepared in cavities fit ted with conventional (metallic) and insulated [poly(ether ether ketone)] s prues. These provide quite distinct solidification histories which, in turn , influence the physical properties of the moulding and the extent and type of defects it contains. In the former case, the gate solidified after 26 s whereas, in the latter, the hold pressure could be applied for over 240 s In insulated sprue moulding, the advance of the solid liquid boundary durin g packing and solidification was traced by fractography. Pressure was varie d from 5 to 120 MPa. The interdependencies of moulding mass, apparent densi ty, local density, polymer crystallinity, and microstructure were accounted for as a function of pressure and pressure transmission method. Changes in polymer crystallinity due to different cooling rates at different position s in the mouldings were insufficient to account for observed density differ ences. Systematic changes in the mass as a function of hold pressure were r elated to macroporosity in conventional mouldings and to microporosity in i nsulated sprue mouldings.