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an apparatus for producing steel from molten pig iron by blasting with air or oxygen and also for making black copper or nickel matte by blowing air through mattes.
In ferrous metallurgy two types of converters are used: converters in which air is blown through the pig iron from below (the Bessemer and Thomas-Gilchrist processes) and converters that use an oxygen blast from above (the oxygen converter process). The barrel of a converter is a steel shell lined with refractory brick—acidic (Dinas) brick in the Bessemer converter and basic (dolomite) brick in the Thomas converter. The refractory-lined converter bottom is equipped with nozzles for supplying air. The nozzles are either run directly through the bottom or are set into separate refractory (chamotte) bricks (tuyeres). The air is fed through a hollow trunnion and a supply pipe into a windbox, from which it enters the pig iron from below and blows through it. The pressure of the blow is considerably greater than the ferrostatic pressure of the pig iron, which prevents it from entering the nozzle during the blow. The barrel is not symmetric in relation to the vertical axis; it has a curvature, called the back of the converter. This is done to increase the capacity of the converter when it is in the horizontal position. The top opening, or nose, is used for pouring in molten pig iron and pouring off steel and slag; converter gases are also discharged through the nose during the blow. The converter is tilted by a gear rack with a coupling rod driven by the piston of a hydraulic cylinder or by an electric motor through a reduction gear. During pouring in of the pig iron, the converter is in the horizontal position, and during the blow it is in the vertical position.
The small Bessemer converter has a closed bottom, and the nozzles are mounted horizontally in the rear wall so that the air or combined (air and oxygen) blast is directed toward the surface of the pig iron.
Unlike Bessemer and Thomas converters, converters for blasting pig iron with oxygen from above have a closed bottom without tuyeres or a windbox and are equipped with a belly; they sometimes have a drop bottom for easy maintenance. They have a capacity of 100–350 tons. The barrel is usually cylindrical, and the bottom is hemispherical and cup-shaped; the belly has the shape of a truncated cone that tapers upward. The upper opening (nose) of the belly is used for the pouring in of pig iron, the charging of scrap, and lime, and for discharging gases during the blow. The converter is equipped with a tap hole for separating the metal from the slag during pouring into the ladle. The shell of a converter is welded from thick steel plates and lined with resin-dolomite brick; the refractory lining is 700–900 mm thick. The lining is roasted before the converter is placed in operation. The refractory lining usually withstands 450–600 blows. The mechanism for tilting the converter consists of a transmission (reduction-gear) system connecting the trunnion to the drive. The speed of tilting can be varied from 0.01 to 2.0 rpm.
The water-cooled tuyere for supplying oxygen to the converter is usually made from three steel pipes mounted one within the other. The lower part of the tuyere ends in a tip (nozzle) made of red copper, through which oxygen enters the converter. A considerable quantity of waste gases is formed in the converter during the blow. Each converter is equipped with a waste-heat boiler and a gas-purifying unit to use the heat of the waste gases and to purify them. The converter process is controlled by computers, into which are fed data on the process (the composition and quantity of pig iron, scrap, lime, and waste gases; the flame temperature; and so on). The molten steel produced after the blow is emptied from the converter into a ladle mounted on a self-propelled, remote-control electrified cart and is transferred to the pouring section.
Cylindrical horizontal converters are mainly used in nonferrous metallurgy. They are 3–4 m in diameter and 6–9 m long and have a capacity of 40–100 tons. The steel converter barrel is lined with magnetite brick and covered with a layer of magnetite. The nose of the converter is used for pouring in the matte and charging fluxes, return materials, and concentrate, as well as for pouring off slag and molten metal. Fine material may be charged through the opening in the side wall by a pneumatic gun. The tuyeres for supplying air are located on one side of the converter. The converter has a tilting mechanism for discharging the molten products.
REFERENCESMartsinkovskii, D. B., and V. A. Pogrebinskii. Konverternye tsekhi bol’shoi proizvoditel’nosti. Moscow, 1961.
Afanas’ev, S. G. Kratkii spravochnik konvertershchika. Moscow, 1967.
Maiorov, A. I. Kislorodnye konvertery bol’shoi v SSSR iza rubezhom. Moscow, 1968.
S. G. AFANAS’EV
A device for processing alternating-current (ac) or direct-current (dc) power to provide a different electrical waveform. The term converter denotes a mechanism for either processing ac power into dc power (rectifier) or deriving power with an ac waveform from dc (inverter). Some converters serve both functions, others only one. See Alternating current, Direct current, Rectifier
Converters are used for such applications as (1) rectification from ac to supply electrochemical processes with large controlled levels of direct current; (2) rectification of ac to dc followed by inversion to a controlled frequency of ac to supply variable-speed ac motors; (3) interfacing dc power sources (such as fuel cells and photoelectric devices) to ac distribution systems; (4) production of dc from ac power for subway and streetcar systems, and for controlled dc voltage for speed-control of dc motors in numerous industrial applications; and (5) transmission of dc electric power between rectifier stations and inverter stations within ac generation and transmission networks. See Alternating-current motor, Direct-current transmission
The introduction of the thyristor (silicon-controlled rectifier) in the 1960s had an immediate effect on converter applications because of its ruggedness, reliability, and compactness. Power semiconductor devices for converter circuits include (1) thyristors, controlled unidirectional switches that, once conducting, have no capability to suppress current; (2) triacs, thyristor devices with bidirectional control of conduction; (3) gate turn-off devices with the properties of thyristors and the further capability of suppressing current; and (4) power transistors, high-power transistors operating in the switching mode, somewhat similar in properties to gate turn-off devices. Thyristors are available with ratings from a few watts up to the capability of withstanding several kilovolts and conducting several kiloamperes. See Semiconductor rectifier
converter(1) A device that changes one set of codes, modes, sequences or frequencies to a different set. See A/D converter.
(2) A device that changes current from 60Hz to 50Hz and vice versa.