Minimill
A minimill is traditionally a secondary steel producer; however, Nucor (one of the world's largest steel producers), as well as one of its competitors, Commercial Metals Company (CMC) use minimills exclusively. Usually it obtains most of its iron from scrap steel, recycled from used automobiles and equipment or byproducts of manufacturing. Direct reduced iron (DRI) is sometimes used with scrap, to help maintain desired chemistry of the steel, though usually DRI is too expensive to use as the primary raw steelmaking material. A typical mini-mill will have an electric arc furnace for scrap melting, a ladle furnace or vacuum furnace for precision control of chemistry, a strip or billet continuous caster for converting molten steel to solid form, a reheat furnace and a rolling mill.
Originally the minimill concept was adapted to production of bar products only, such as concrete reinforcing bar, flats, angles, channels, pipe, and light rails. Since the late 1980s, successful introduction of the direct strip casting process has made minimill production of strip feasible. Often a minimill will be constructed in an area with no other steel production, to take advantage of local resources and lower-cost labour. Minimill plants may specialize, for example, making coils of rod for wire-drawing use, or pipe, or in special sections for transportation and agriculture.
Capacities of minimills vary; some plants may make as much as 3,000,000 tons per year, a typical size is in the range 200,000 to 400,000 tons per year, and some old or specialty plants may make as little as 50,000 tons per year of finished product. Nucor Corporation, for example, annually produces around 9,100,000 tons of sheet steel from its 4 sheet mills, 6,700,000 tons of bar steel from its 10 bar mills and 2,100,000 tons of plate steel from its 2 plate mills.
Since the electric arc furnace can be easily started and stopped on a regular basis, minimills can follow the market demand for their products easily, operating on 24 hour schedules when demand is high and cutting back production when sales are lower.
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