Steel mill
From Biocrawler, the free encyclopedia.
Steel mills are the industrial plants where pig iron is converted into steel. Steel is an alloy of iron produced through iron ore, coke, limestone being smelted in a blast furnace. Steel mills also remove impurities such as excess carbon to produce a strong steel. Steel mills also turn molten steel into blooms, ingots, or slabs through hot rolling and continuous casting.
Integrated plants
An integrated steel plant has all the functions for primary steel production:
- ore reduction,
- ironmaking,
- steelmaking,
- bloom casting
- roughing rolling/billet rolling
- product rolling.
The principle raw materials for an integrated plant are iron ore, limestone, coal (or coke).
Integrated plants are large facilities typically only economical to build in 2,000,000 ton per year annual capacity and up. Final products made by an integrated plant are usually large structural sections, heavy plate, strip, wire rod, railway rails, and occasionally long pruducts such as bars and pipe.
A major environmental hazard associated with integrated steel mills is the pollution produced in the manufacture of coke, which is an essential intermediate product in the reduction of iron ore in a blast furnace.
Integrated plants may also adopt some of the processes used in mini-mills, such as arc furnaces and direct casting, to reduce production costs.
World integrated steel production capacity is at or close to world demand, so competition between suppliers results in only the most efficient producers remaining viable. However, due to the large employment of integrated plants, often governments will financially assist an obsolescent facility rather than take the risk of having thousands of workers thrown out of jobs. Such measures in products then sold in international trade lead to allegations of dumping.
Mini mills
A mini-mill is a secondary steel producer. Usually it obtains most of its iron from scrap steel, recycled from used automobiles and equipment or byproducts of manufacturing. 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.
Capacities of mini-mills vary; some plants may make as much as 1,000,000 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. Originally the mini-mill concept was adapted to production of bar products only, such as concrete reinforcing bar, flats, angles, channels, pipe, and light rails. Since the late 1980's, successful introduction of the direct strip casting process has made mini-mill production of strip feasible. Often a mini-mill will be constructed in an area with no other steel production, to take advantage of local resources and lower-cost labour. Mini-mill plants may specialize, for example, making coils of rod for wire-drawing use, or pipe, or in special sections for transportation and agriculture.
See also
