Casting Powder contains low melting constituents that instantly generate liquid slag, which penetrates into the gap between the mould and the solidifying shell of the billet. Casting Powder is added in small amounts and continuously over the casting duration. The melting of the Casting Powder occurs slowly in layers. Hence, the top surface of the liquid metal in the billet / slab / bloom always remains protected from the atmosphere.
Traditionally Casting Powder is used for bloom and slab casting. Now, it is used for billet (open) casting also as an alternative to mould oil for some plants.