**3.4 Pouring defects**

During pouring of the melt, there is considerable splashing and sloshing about of the melt. This entrains significant quantities of air and non-metallic inclusions in the mould. Such entrained material degrades casting quality. This problem is often mitigated by incorporation of complex gating systems designed using advanced Computational Fluid Dynamics (CFD) modules. Such casting simulation software is able to predict and avoid bubble streams in metals castings (Waterman, 2010).

Some of the problems outlined above have been resolved by advancements in pressure die casting, improved investment casting techniques and centrifugal casting. These techniques individually solve some, but often not all of the problems with gravity-assisted pour of an air-melt. For instance, in conventional die casting, melt is sprayed at high velocity into the die and cavity-atmosphere tends to be admixed and entrapped in castings during the turbulent cavity-fill (Jorstad, 2003). The process of air melting and pouring also inevitably introduces oxides, formed during melting, into the cast product. Significant inclusions segregation at grain boundaries are thus very common with gravity assisted sand casting.
