continuous casting - octagonal caster

Continuous casting of steel is a process in which liquid steel is continuously solidified into a strand of metal. Depending on the dimensions of the strand, these semi-finished products are called slabs, blooms or billets. The process was invented in the 1950s in an attempt to increase the productivity of steel production. Previously only ingot casting was available which still has its benefits and advantages but does not always meet the productivity demands. Since then, continuous casting has been developed further to improve on yield, quality and cost efficiency.
Liquid steel is supplied to the continuous caster from the secondary steelmaking shop. The ladle is usually delivered by crane and positioned into a ladle turret, which subsequently rotates the ladle into the casting position. A slide gate in the bottom of the ladle is opened to allow the liquid steel to flow via a protective shroud into a tundish, a vessel that acts as a buffer between the ladle and the mold. As the tundish fills, stopper rods are raised in order to allow the casting of steel into a set of water-cooled copper molds below the tundish.
Solidification begins at the mold walls and the steel is withdrawn from the mold by a dummy bar. As it leaves the mold, the strand of steel requires a sufficiently thick solid shell to carry the weight of the liquid steel that it contains, i.e. the ferrostatic pressure.
Throughout the entire casting process, the mold oscillates vertically in order to separate the solidified steel from the copper mold. This separation is further enhanced by introducing a mold powder into the mold.
The strand is withdrawn from the mold by a set of rolls which guide the steel through an arc until the strand is horizontal. The rolls have to be positioned close enough together to avoid bulging or breaking of the thin shell.
As the steel leaves the mold, it has only a thin solidified shell which needs further cooling to complete the solidification process. This is achieved in the so-called secondary cooling zone, in which a system of water sprays situated between the rolls are used to deliver a fine water mist onto the steel surface. At this point, the steel, solidified shell and liquid center, is called the strand.
After the strand has been straightened and has fully solidified, it is torch-cut to pre-determined product lengths. These are either discharged to a storage area or to the hot rolling mill.
reference-from net and various articles