Continuous casting is an industrial production process in which a liquid material (metal) is pulled by gravitational force through a permanent build with high thermic conductivity and open bottom, called ingot mould, made by copper and externally cooled down by water.
During starting phase a false billet is put at the bottom in order to stop the liquid which begins to solidify as in contact with the walls. The false billet will go down as solidification proceeds.

Thanks to forced cooling inside the ingot mould metal solidifies on its surface while remaining liquid in a great internal portion of its section. Though this solid and scorching hot surface gives sufficient stability to the whole casted piece, letting it move forward along a straight course where it keeps forcedly cooling by certain direct water squirts. At this point the greater part of the casted piece is solidified.

 Solidified metal has smaller volume than the liquid metal, so it moves away from the ingot mould walls. During this phase thermic relationship changes: from metal-ingot mould to metal-air-ingot mould.
As the casted piece is theoretically with no end and is actually hundreds meter long, it gets sawed to size by a sawing machine and let cooling by air while laying on a roll path or preferably it directly gets put into a hot rolling mill in order to be worked further.