What is Thin Slab? Steel Foundations
A thin slab is a semi-finished flat product produced by the continuous casting process, also known as thin slab casting. Thin slabs have a rectangular cross-section with a thickness typically ranging from 2.2” to 4.3” inches (55 mm to 110 mm).
The casting process is similar to the thick slab casting process, but due to the smaller cross-section the overall height of the caster is smaller, and the strand can be cut with a shear instead of a torch. Thin slab casters are typically constructed in-line with hot rolling equipment, which eliminates the need for a separate hot roll process.
The thin slab casting process begins with a ladle full of liquid steel suspended 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 nozzle suspended over the continuous casting mold.
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. When compared to the thick slab casting process, the thin slab process cools much faster, so its metallurgical length is shorter. This allows the overall height of the caster to be smaller.
Eventually, the solidified strand is bent from vertical to horizontal and then cut by a shear system into individual slabs. Most thin slab casters are constructed in-line with a reheat furnace to homogenize the slab temperature, a descaler to remove any oxide surface scale, and rolling stands to hot roll the slab into a hot rolled coil (HRC). The hot rolled coil is cooled by water sprays, then coiled by the coiling stand at the end of the line. When compared to thick slab casting, this process conserves energy by eliminating the need to completely reheat a cold thick slab prior to the hot rolling process.
The smaller size of the thin slab caster along with being constructed in line with the hot rolling equipment gives this process a much smaller overall footprint and allows it to be built almost anywhere.