As shown in the figure, the continuous caster is composed of a tundish, a mold, a mold oscillator, a group of cast-strand supporting rolls, rolls for bending and straightening the cast strand, rolls to pinch and withdraw the cast strands, a group of spray nozzles, a torch cutter for cutting the cast strand, a dummy bar for extracting the cast strand at the start of casting, and other components. The continuous billet caster casts round or square strands of small cross-section, and the continuous bloom caster casts strands of large cross-section. Both are used to produce materials for wire rod, bars, shapes, and pipe. The continuous slab caster produces wide rectangular strands of large cross-section, which are cut off as slabs for use as material for sheet and plate. Slabs for flat-rolled products are usually cast with a thickness of 100 to 250mm. In recent years, however, continuous casters which produce thinner slabs 30-80mm in thickness have been introduced. The thin slab caster eliminates the need for a roughing mill in the hot-rolling process. However, the steel throughput is limited to 1 million ton/year per strand in this process by the thin slab thickness even at higher casting speed, which is currently limited to about 7m/min. Consequently, the thin slab caster is usually combined with an electric furnace of matching output. This combination has been favorably adopted by minimills. The types of continuous casters include: (i) the vertical type, in which the mold and support rolls are arranged vertically; (ii) the vertical-and-bending type, in which the solid shell of the cast strand is bent in the horizontal direction at the position where solidification is sufficiently complete; (iii) the curved type, in which a curved mold and support rolls are arranged on an arc of the same radius, and the cast strand is straightened horizontally at the end of solidification; (iv) the vertical-and-progressive-bending type, in which the mold and a group of upper support rolls are arranged vertically and the cast strand still with a liquid core is progressively bent, and then progressively straightened to the horizontal position at the end of solidification; and (v) the horizontal type, in which the mold and support rolls are arranged horizontally. The vertical type is used to cast high-grade steels because it promotes the separation (by flotation) of nonmetallic inclusions poured into the mold, although the construction of the caster building becomes tall and hence expensive. The curved type is mainly applied for mass production of conventional products, because building costs can be reduced by the lower height. The vertical-and-progressive-bending type, which combines the advantages of the vertical and curved types, is being used increasingly for large sized slab casters which require improved quality and productivity. The horizontal type is used to produce billets on a small scale because the equipment and the building costs are comparatively low. Refractory nozzles are used to transfer the molten steel from the ladle to the tundish and then to the mold and prevent any reoxidation through contact with air. To avoid the entrainment of top slag, the bath depth of the tundish is increased, and dams and weirs are installed in the tundish to promote the separation of nonmetallic inclusions by flotation. The nozzle between the tundish and the mold, called the submerged entry nozzle, is designed in such a way that nonmetallic inclusions are not carried deep into the strand together with the molten steel flow, and therefore are not captured in the solidifying shell of the cast strand. A device for controlling the molten steel flow exiting from the nozzles by applying a magnetic field to the flow in the mold is also used for the same purpose and for improving the surface of the shell by suppressing turbulence of the melt meniscus. The mold is equipped with an oscillator (60-240cpm, 4-10mm amplitude) to prevent sticking of the cast strand to the mold. The support rolls are of high rigidity and the roll interval is short to minimize bulging due to ferrostatic pressure, preventing subsequent cracking and segregation due to such bulging. Water or water-mist spray nozzles for cooling are provided across the full width of the cast strand, from immediately below the mold to the crater bottom. Electromagnetic stirrers are sometimes installed below the mold and between the support rolls to stir the molten steel in the solidifying shell by electromagnetic induction and thus to increase the equiaxed dendrites, and to disperse the segregation of solute elements at the crater bottom position between many equiaxed dendrites. A device for applying a thicknesswise reduction to the cast strand is often provided at the crater bottom position to squeeze the solute enriched molten steel to the upper unsolidified molten steel. These two devices are often used in combination because neither by itself is fully adequate for preventing the segregation of solute elements.