Method to determine hot permeability and strength of ceramic shell moulds

This paper reports on an improved method to evaluate both the strength and the permeability of ceramic shell specimens under high temperature conditions. In order to maintain safe testing conditions and use lower testing pressure, a spherical wax model, larger than the standard ping-pong ball, was used to prepare ceramic shells. Compressed air was introduced into ceramic shell specimen held at 900 °C. Air flow and pressure drop across the shell wall were measured and hot permeability was calculated according to Darcy's law. Air pressure was subsequently increased and recorded up to bursting point. A hoop stress formula was used to calculate the hot strength from the bursting pressure. This very simple method is easy to implement in foundries.