AMP - Advanced Manufacturing Park

Induction Skull melting

Titanium alloys are so reactive that they must be melted in a vacuum. Because they would react with linings normally used in melting systems, they are produced in a copper crucible that is water cooled to prevent it melting at the temperature of molten titanium – around 1700ºC. If the crucible failed to contain the titanium, and contact was made between the cooling water and the molten metal, a serious explosion would occur.

Consequently, melting systems for titanium alloys are complex engineering solutions to a considerable technical challenge that must also address serious safety issues. Induction skull melting (ISM) technology uses a water-cooled copper crucible but in this case it is segmented in such a way that an induction field can be established in the alloy placed inside the crucible, without the copper itself being heated by the induction field.

As the titanium alloy melts, it solidifies against the walls of the segmented crucible, forming a thin skin or ‘skull’ on the surface. Titanium has a low thermal conductivity, so the skull insulates the molten metal from the cooling effect of the crucible. Moreover, the effective power input is so high that the molten metal is partially levitated, which further reduces heat exchange between the liquid metal and the skull. This results in a much higher superheat being achieved and the stirring effect created by the induction field achieves a uniform temperature distribution throughout the melt.

High Performance Machining is performed at the CTi.