**6.3 Mould and sprue pre-heat temperature**

It is essential for the mould and the sprue to be adequately heated prior to carrying out countergravity casting. The pre-heat prevents chilling of the melt as it flows up from the crucible. Improperly pre-heated sprue and mould will cause increased melt viscosity and a tendency for the melt to get stuck in the sprue or incomplete mould filling. Figure 12 shows premature solidification of melt inside the sprue due to inadequate pre-heat of the mould and sprue assembly.
