Continuous Casting of Metals and Alloys

a process for producing castings and stock, based on a uniform displacement of metal with respect to the zones of casting and crystallization. In this case, the casting mold may be stationary or may move regularly (reciprocating motion of small amplitude or rotational motion along a closed curve of limited length).

Continuous casting of metals in the USSR and abroad was first used in industry in the 1930’s, and the method became widespread in the mid-1940’s. Continuous casting theoretically makes possible the production of castings of virtually any length; however, in practical terms, the length of castings is determined by the capacity of the foundry, by the requirements of the processing plants, and by organizational and economic considerations. Production of castings of limited length by the continuous method is sometimes incorrectly called semicontinuous casting.

In continuous casting, the uniform rates of supply of molten metal, the crystallization of the metal, and removal of the finished casting provide constancy of the composition, structure, and properties of the metal over the entire length of the casting. Enhanced heat removal through direct cooling of the metal with water makes possible an increase in the crystallization rate and, by correct selection of the rate of casting, the creation of directed crystallization, mainly along the axis of the casting; this leads to the production of dense castings or stock with a fine internal grain structure and uniform chemical composition. In comparison with batch casting, continuous casting also reduces waste and loss of metal, labor expenditures, and use of foundry equipment and tools.

A distinction is made among continuous casting (1) in crystallizers (ingot molds) and rolls, (2) in a trough (groove), and (3) between moving belts, depending on the equipment used to form the castings. The most common continuous casting method uses a metal sliding crystallizer and has come to be called continuous steel casting. A fundamentally new method for continuous casting of aluminum alloys, with formation of castings in an electromagnetic field (electromagnetic crystallizer casting), has been developed and put into practice. The process is distinguished by (1) the absence of contact between the crystallizing casting and the walls of the metal mold, which prevents the formation of gross surface defects; (2) a very small distance between the meniscus of the metal and the zone of direct water cooling, which increases the rate of crystallization; and (3) crystallization of the metal in an electromagnetic field, with forced movement within the crater, which produces the fine-grained structure of the metal.

Continuous casting is used in modern metallurgy for the production of all castings of aluminum and magnesium alloys, as well as of most heavy nonferrous metals. In the production of castings of refractory metals and titanium, continuous casting in an inert medium or under vacuum is usually combined with the continuous melting process. In this case, the filling of the mold is determined by the rate of melting of the consumable electrode or of the charge that is fed into the melting zone, rather than by the rate of pouring of the melt. In the case of aluminum and copper and their alloys, integrated processes for the casting and subsequent rolling of stock are becoming more widespread. Such processes include the production of rod wire (when the stock is formed in a groove in the rim of a rotating wheel) and sheet stock (by crystallization of metal between rolls or between two water-cooled belts). Casting between belts ensures maximum productivity of the integrated process as a result of the increased duration of contact between the solidifying metal and the belt. This principle has been used in continuous casting machines designed by the American engineer S. Hazlitt and by the All-Union Research and Design Institute of Metallurgical Machine Building, as well as in other machines.

Integrated processes are sometimes classified with ingotless metal rolling; however, in this case, the hardened metal is deformed, whereas the term originally implied the deformation of metal during hardening.