Numerous types of furnaces utilizing electric current as the source of heat have been developed by a large number of investigators, but relatively few types have survived as practical tools for steelmaking.
Electric current can be used for heating in only two ways: (1) by utilizing the heat generated in electrical conductors by their inherent resistance to the flow of current, and (2) by utilizing the heat radiated by the electric arc.
Two general methods of heating by resistance are possible: (a) the indirect method in which the charge is heated by radiation and conduction from separate resistors through which the current is passed, and (b) the direct method in which the current is passed through the metal charge or bath itself.
Likewise, arc heating may be applied in two general ways: (a) the arcs may be made between electrodes, supported above the metal in the furnace, which thus is heated solely bу radiation from arc. This method is known as "indirect arc heating". (b) The arcs may be made between the electrodes and the metal. In this second method, known as "direct arc heating", the current must flow through the bath, so that the heat developed by the electrical resistance of the metal is added to that radiated from the arcs.
Arc furnaces are designed to melt steel electrically. The steel in the furnace forms the common conductor for the current flowing between the electrodes which enter the furnace through the roof. The mechanical details of this type of furnасе vary. For example, some furnaces tilt on rockers, others on trunnions; work material is charged into some furnaces through the doors, into others through the top by removing the roof. Figure showing a trunnion-type of furnace, will serve to illustrate the essential parts of a typical arc furnace.
Current is supplied from a suitable source, through the bus bar and electrode holders to the electrodes. Electrodes may be either graphite or amorphous carbon.
Arcs are sprung from the electrodes to the bath thus heating the metal both by direct conduction from the arc, and by radiation from the roof and walls. The height of the electrodes above the bath, and consequently the heat input, are controlled automatically by the winch motors, which raise and lower the electrodes.
The furnace proper consists of a cylindrical steel shell, lined with refractories. The inside diameter of the shell determines the capacity of the electric furnace. The detachable roof may be removed for top charging. The furnace is tilted about the stationary axis or trunnion, placed directly under the spout.
The refractories for the basic electric furnace should be carefully chosen. The hearth itself must be a basic material, such as magnesite or burned dolomite, to withstand the lime slags used in the basic process. Electric furnace refractories are subjected to severe service. They must be capable of with standing extremely high temperatures. Protection of refractories by water is possible, but it is an advantage of the larger furnaces.
In brief, the process consists of charging into the hearth of the furnace a known weight of scrap of suitable physical and chemical character, and melting down the material as quickly as possible. When the charge is melted, the usual practice is to add a quantity of burned lime with some fluorspar or sand to act as fluxes which together with the oxides resulting from the melting of the scrap, form a highly oxidized basic slag. This same end is sometimes accomplished by adding limestone or burned lime to the charge. Iron ore is added as required in order to oxidize carbon, phosphorus, chromium, and manganese from the bath.
Furnace sizes may range from 3 – ton to 200 – ton capacity.
Дополнительные слова и словосочетания:
1) indirect arc heating – косвенный нагрев
2) a bus bar – собирательная шина
3) lime slags – известковистые шлаки
4) burned lime – обожженная известь
5) a highly oxidized basic slag – высокожелезистый основной шлак
VII. Определите, соответствуют ли содержанию текста данные утверждения:
1. The refractories for the basic electric furnace should be carefully chosen.
2. White cast irons normally are not considered to be malleable.
3. Many different processes are used for production of cast parts.
4. Iron ore is added as required in order to oxidize carbon, phosphorus, chromium, and manganese from the bath.
5. The steel in the furnace forms the common conductor for the current flowing between the electrodes which enter the furnace through the roof.
VIII. Используя текст, переведите данные предложения на английский язык.
1. Существует два вида электродов.
2. Графитовые электроды требуются для больших электрических печей, в частности для производства высоколегированных сортов стали.
3. В расплавленную загрузку обычно добавляют известняк, плавиковый шпат или песок.
4. Электрический ток может быть использован для нагревания только в двух случаях.
5. Электрические печи сконструированы таким образом, чтобы плавить сталь при помощи электричества.
IX. Закончите предложения в соответствии с содержанием текста.
1. The furnace proper consists of a cylindrical steel shell, lined …
a) ferrous metal;
b) with refractories;
c) aluminium alloys.
2. Protection of refractories by water is possible, but it is an advantage of … .
a) the larger furnaces;
b) iron or steel plate;
c) opening at the lowest point.
3. Current is supplied from a suitable source, through the bus bar and electrode holders to … .
a) the large molds;
b) the ladle;
c) the electrodes.
4. The furnace is tilted about the stationary axis or trunnion, placed directly …
a) under regenerative chamber;
b) under the spout;
c) to the hearth.
5. This same end is sometimes accomplished by adding limestone or burned lime …
a) to the charge;
b) to the bottom;
c) to the pig iron and scrap.
X. Вставьте подходящие по смыслу слова:
(advantage; heating; generated; oxidize; detachable)
1. Iron ore is added as required in order to … carbon, phosphorus, chromium, and manganese from the bath.
2. Electric current can be used for heating by utilizing the heat … in electrical conductors by their inherent resistance to the flow of current.
3. The … roof may be removed for top charging.
4. Two general methods of … by resistance are possible.
5. Protection of refractories by water is possible, but it is an … of the larger furnaces.
XI. Пользуясь рис.3 (см. приложение), опишите электрическую печь.