The basic oxygen furnace is used to purify pig iron into molten steel by oxidizing impurities and adding oxygen. The furnace is lined with alkaline refractory materials and loaded with scrap steel and pig iron. Oxygen is blown through the mixture, creating a chemical reaction that raises the temperature and creates slag. The purified steel is tapped into a ladle and the slag is poured into a separate container. The slag can be crushed for further use.
A basic oxygen furnace (BOF) is the machinery used to purify pig iron by oxidizing impurities into slag and converting the remainder into molten steel with an injection of oxygen. It is the primary method used for steel production worldwide. The steel produced is chemically tested and can be further modified by adding alloys. The process is called basic oxygen furnace due to the alkalinity of the refractory and the addition of alkali materials during production.
A heat, or batch, begins with the same structure as the oven, i.e. an elongated vessel. The container is lined with alkaline refractory materials such as magnesite and burnt lime. The refractory is necessary for the vessel to withstand the extreme temperatures and high level of oxidation that occurs in the basic oxygen furnace.
The furnace is tilted at an angle and loaded, or filled, with about one-third scrap steel and two-thirds molten pig iron that has been liquefied in a blast furnace. Streams of lime or dolomite are added. A computer program uses the chemical analysis of cast iron to determine the optimal proportions of iron, scrap steel and fluxes and to program the oxygen blow-in time.
The mixture is exposed to a stream of pure oxygen blown through a water-cooled tube for about 20 minutes. The tip height of the oxygen flow into the vessel can be adjusted during blowing. The process is controlled and monitored by a computer.
The carbon and silicon in the mix oxidize and create a huge volume of heat which melts the scrap. This chemical reaction rapidly raises the temperature in the basic oxygen furnace to approximately 3,000° Fahrenheit (1,649° Celsius). Oxidized silicon becomes silica and combines with fluxes to form slag. The sulfur and phosphorus content of iron is absorbed by the slag. The carbon monoxide and carbon dioxide created by the process are vented through pollution control equipment.
After oxygen blowing, the furnace contains layers of molten steel and slag. The vessel is tilted to allow sampling and analysis of the purified material. A preheated container called a ladle is moved into position under the base oxygen furnace. The molten steel is tapped, or poured, into the ladle. The detectors have the function of preventing the slag from mixing with the steel. The steel can be altered with iron, silicon or manganese alloys for specific uses or sent for casting without further modifications.
After touching all the steel, the slag is poured into a separate container. The slag is cooled and allowed to stabilize over a period of months. After this time, the slag can be crushed for further use, often as aggregate for construction projects.
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