The invention relates generally to continuous casting.
More particularly, the invention relates to a mold for the continuous casting of metals, e.g., steel, and to a continuous casting method.
Steel sheet made from continuously cast steel is currently produced from a continuously cast slab having a thickness in the range of about eight to twelve inches. The slab is cut into sections as it emerges from the continuous casting machine, and the sections are reheated and passed through a roughing train to produce sheet bar. The sheet bar is hot rolled and then processed further for direct use or cold rolling.
It has long been recognized that reheating of the slab sections for roughing consumes considerable amounts of energy while the roughing equipment constitutes a large capital expenditure as well as a source of substantial maintenance costs. Accordingly, many attempts have been made to continuously cast steel to a gage corresponding to that of sheet bar.
Continuous casting of steel to the gage of sheet bar poses many problems. To begin with, sheet bar generally has a thickness of one to two inches. If a continuous casting mold is designed so that the inlet opening of the casting passage has a thickness corresponding to the thickness of sheet bar, the opening is quite narrow and it is extremely difficult to aim the casting stream into the mold. Furthermore, sheet bar has a relatively great width of twenty to one hundred inches which means that the width of the casting passage must be of this order. When the thickness of the casting passage is small, there then arises the problem of distributing the molten steel entering the mold over the width of the casting passage. Thus, if the casting stream is directed into the center of the mold in accordance with current casting practice, the steel tends to solidify before reaching the edges of the casting passage. An additional difficulty arises when casting high grade steels. In order to protect such steels from atmospheric contamination, it is the practice to teem the steel into the mold via a ceramic shroud or tube which bridges the gap between the mold and the tundish. The shroud must have a certain diameter, and the portion of the shroud which is immersed in the mold must have a clearance of at least one-half inch on all sides. Therefore, if the inlet opening of the casting passage has a thickness corresponding to the gage of sheet bar, it is not possible to employ a shroud.
The preceding problems have been alleviated to a degree by designing the inlet opening of the casting passage with a central portion wide enough to receive a pouring shroud. On either side of the central portion is a lateral portion having a thickness equal to the desired final gage, and the central portion narrows in a direction towards each of the lateral portions. The central portion also narrows in a direction from the inlet end to the outlet end of the casting passage so that the outlet opening has a uniform thickness corresponding to the desired gage.
While the problems involved in introducing molten steel into the mold have been reduced by widening the central portion of the inlet opening, there are considerable problems in withdrawing the continuously cast strand from the mold. These withdrawal problems have prevented successful continuous casting of steel to the gage of sheet bar.