Technology; Continuous Casting in Steel

ALTHOUGH the technology of continuous casting has been around for two decades, most domestic steel producers had found it uneconomical and impractical until recently.
But steelmaking energy costs have doubled since the 1973 oil embargo and pressure has intensified from such competitors as the Japanese, who in 1980 cast 58 percent of their steel through the new process. Some of the large domestic steelmakers are now making a major effort to build new continuous casters. The domestic industry now casts about 17 percent of its steel through the process.

The process was patented by Henry Bessemer in 1865 but was not developed on a large scale until after World War II. Its use in the 1980's is expected to be significant, however. ''The most important technological change for integrated steelmakers during the next 10 years will be greater adoption of continuous casting,'' according to a report by the Federal Office of Technology Assessment.

The United States Steel Corporation, for example, announced last year that it would install a continuous slab caster at its historic Edgar Thomson Works and at its Lorain Works in Ohio. David M. Roderick, chairman, said that the nation's largest steel company would then have eight such casters and would be able to cast about 29 percent of its raw steel through the process.
The National Steel Corporation, which installed the first large continuous caster in this country in 1968 at its Weirton Works in West Virginia, will be able to cast more than 50 percent of its steel continuously by 1982.

And such other large steelmakers as Armco are adding casters. In continuous casting, freshly refined molten steel is transformed directly into steel products such as slabs, billets and blooms, which can then be finished in mills into various steel products such as sheet, rods and beams.
In the process, molten steel is poured into a vessel called a tundish, which allows the steel to flow at a constant rate into a water-cooled mold. A solid skin is formed and the hardened steel is pulled continuously out of the bottom of the mold. It is then cut into various lengths.
In the traditional method, molten steel is poured into ingot molds. When it cools and hardens, the mold is stripped away. The ingot can then be stored. It must be reheated, however, before it can be formed into slabs, billets and blooms suitable for rolling.
During heating in the old process, the surface oxidizes and part of the steel must be removed through a process called scarfing. These various steps lead to the loss of some of the steel, which becomes scrap and is recycled.

The savings in energy, manpower and waste in continuous casting come mostly from the elimination of various steps needed under traditional methods.
The total energy saving is estimated to be about 10 percent in making semifinished steel products. The average saving on a ton of steel has been estimated to be about 3 million British thermal units, or about $12.

The other major advantage is that the process eliminates much of the scrap and increases the yield from the raw steel of semifinished steel products by about 10 to 15 percent. Continuous casters thus fit in with current industry strategy of seeking to raise capacity by making plants more efficient.

The manpower savings are estimated to be 10 to 15 percent by the Department of Labor. In older plants some workers are absorbed in running the caster and in the finishing mills.
There are a few potential disadvanages. If a continuous caster breaks down, the primary steelmaking process has to be held up also. There are also a small number of steels that have not yet been cast through the process - basically because the casting methods have not been perfected -though the list has been decreasing.

Milton Deaner, vice president of engineering for National Steel, which has had one the most extensive and longest experiences with continous casting, said that the company has been very satsified with the process. He said that executives of plants without casters were eager to have them installed. ''No one has reservations to build them, it's just to get the money to build one,'' he said. A caster can cost from $120 million to $150 million