Steel Slab Casting Steel Foundations
A slab is a semi-finished flat product produced by the continuous casting process, also known as slab casting or strand casting. It will be further processed by a hot strip mill into plate and/or strip.
The slab casting process begins with a ladle full of liquid steel hanging over a tundish. The tundish provides a buffer during ladle changes, which enables the casting process to be continuous. The tundish also provides the last opportunity for any inclusions and impurities to float out of the steel into the slag prior to entering the solidification mold. The molten steel in the tundish flows to the nozzles suspended over the continuous casting mold. A thick slab has a rectangular cross-section typically ranging from 9 to 12 inches (229 to 305 mm) thick and 40 to 100 inches (1,000 to 2,540 mm) wide.
As the steel flows from the tundish into the caster mold, the mold oscillates up and down to push the liquid steel deeper into the mold. The copper-lined caster mold is water-cooled so it doesn’t melt from the heat of the molten steel. Mold powder is applied at the top of the caster mold and melts, which lubricates the interface between the molten steel and the copper mold. While traveling through the oscillating mold, enough heat is removed to form a thin solidified shell on the surface of the strand, which allows it to stay intact as it exits the mold.
As the strand exits the mold and enters the spray chambers, most of the steel inside the strand is still molten. As it travels down through the caster, the spray chamber provides cooling from water sprays to further solidify the steel within the strand. The point in the process where the strand is completely solidified is called the metallurgical length of the caster, which can be almost to the end of the caster.
Eventually, the solidified strand is bent from vertical to horizontal and cut by gas torches into individual slabs that can be handled by an overhead crane, rail car, or a rubber-tired carrier to transport the slabs to the hot rolling process.