Residual stresses and cracking in large ceramic injection mouldings subjected to different solidification schedules

In ceramic injection moulding, the moulding dimensions and the residual stresses are related to the hold pressure history during solidification in the cavity. In conventional moulding, the residual stresses are generally compressive at the surface. In this work, an insulated sprue device was made. It allows prolonged pressure transmission to the moulding and this can result in residual tensile stresses at the surface of thick section mouldings. At very low holding pressures (<9 MPa) or under conditions of premature gate solidification, a reversal of the sign of surface stresses occurs with compressive stresses near the surface. The appearance of cracks during binder removal was related to these residual stresses. For 25 mm thick mouldings which were subjected to a low but persistent hold pressure of 5 MPa no defects developed during the binder removal stage.