The extrusion of alumina composite billets

To prepare an extruded body with uniform wax distribution, the extrusion of a laminated billet that consists of plates of discs with a low aspect ratio is attempted. Surface micro-cracks arising from the lack of formability of a low wax content billet can be overcome by placing a higher wax content disc at the bottom of the composite billet. By extrusion of these billets, the lower part of the billet coats the upper part, and as a result, a flow-free extruded body can be obtained. Further, by the vacuum-sealing of the composite billet, a specimen free from air or water inclusions derived from penetration between the constituent disc can be prepared. The specimen obtained from this procedure shows higher flexural strength than those from non-sealed billet.