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Diagram of electric arc furnace

An electric arc furnace (EAF) is a furnace that heats charged material by means of an electric arc. A furnace is a device used for Heating The name derives from Latin fornax, Oven. An electric arc is an Electrical breakdown of a gas which produces an ongoing plasma discharge, resulting from a current flowing through normally nonconductive

Arc furnaces range in size from small units of approximately one ton capacity (used in foundries for producing cast iron products) up to about 400 ton units used for secondary steelmaking. Units of mass There are three similar units of Mass called the ton: Long ton (simply ton in countries such as the United A foundry is a Factory which produces Metal Castings from either Ferrous or non-ferrous alloys Cast iron usually refers to grey cast iron, but identifies a large group of Ferrous Alloys which solidify with a Eutectic. Steelmaking is the second step in producing Steel from Iron ore. Arc furnaces used in research laboratories and by dentists may have a capacity of only a few dozen grams. Dentistry' is the "evaluation diagnosis prevention and/or treatment (nonsurgical surgical or related procedures of diseases disorders and/or conditions of the oral cavity Temperatures inside an electric arc furnace can rise to 1,800 degrees Celsius. The Celsius Temperature scale was previously known as the centigrade scale.

Contents

History

Steel mill with two arc furnaces
Steel mill with two arc furnaces

The first electric arc furnaces were developed by Paul Héroult, of France, with a commercial plant established in the United States in 1907. The French scientist Paul ( Louis-Toussaint) Héroult ( April 10 1863 – May 9 1914) was the inventor of the Aluminium This article is about the country For a topic outline on this subject see List of basic France topics. The United States of America —commonly referred to as the Year 1907 ( MCMVII) was a Common year starting on Tuesday (link will display the full calendar of the Gregorian calendar (or a Common year Initially "electric steel" was a specialty product for such uses as machine tools and spring steel. A machine tool is a powered mechanical device typically used to fabricate metal components of machines by Machining, which is the selective removal of metal Spring steel is a low alloy Medium carbon steel with a very high Yield strength. Arc furnaces were also used to prepare calcium carbide for use in carbide lamps. Calcium carbide is a Chemical compound with the Chemical formula of Ca[[Carbide C2]] Carbide lamps, also known as acetylene gas lamps, are simple lamps that produce and burn Acetylene (C2H2 which is created by the reaction

In the 19th century, a number of men had employed an electric arc to melt iron. The 19th century of the Common Era began on January 1, 1801 and ended on December 31, 1900, according to the Gregorian calendar Iron (ˈаɪɚn is a Chemical element with the symbol Fe (ferrum and Atomic number 26 Sir Humphry Davy conducted an experimental demonstration in 1810; welding was investigated by Pepys in 1815; Pinchon attempted to create an electrothermic furnace in 1853; and, in 1878 - 79, Sir William Siemens took out patents for electric furnaces of the arc type. Sir Humphry Davy 1st Baronet FRS MRIA (17 December 1778 &ndash 29 May 1829 was a British Chemist and inventor Year 1810 ( MDCCCX) was a Common year starting on Monday (link will display the full calendar of the Gregorian calendar (or a Common year Year 1815 ( MDCCCXV) was a Common year starting on Sunday (link will display the full calendar of the Gregorian calendar (or a Common year Year 1853 ( MDCCCLIII) was a Common year starting on Saturday (link will display the full calendar of the Gregorian Calendar (or a Common Year 1878 ( MDCCCLXXVIII) was a Common year starting on Tuesday (link will display the full calendar of the Gregorian calendar (or a Common Year 1879 ( MDCCCLXXIX) was a Common year starting on Wednesday (link will display the full calendar of the Gregorian calendar (or a Common Carl Wilhelm Siemens (en Charles William Siemens, known as Sir William Siemens) ( 4 April, 1823 &ndash 19 November, 1883 A patent is a set of Exclusive rights granted by a State to an inventor or his assignee for a fixed period of time in exchange for a disclosure of an The Stessano electric furnace is an arc type furnace that usually rotates to mix the bath. The Girod furnace is similar to the Héroult furnace.

Different from the arc type of electrothermic furnace is the induction type furnace. An induction furnace is an electrical Furnace in which the heat is applied by Induction heating of a conductive medium (usually a Metal) in a Crucible The Kjellin furnace and the Röchling-Rodenhauser furnace are two. The Grönwall furnace produced steel at Trollhattan, in Scandinavia. Trollhättan ( is a city (pop 53952 (2007 in Västergötland, Sweden, and the seat of Trollhättan Municipality, Västra Götaland Terminology and usage As a cultural term "Scandinavia" has no official definition and is subject to usage by those who identify with the culture in question as well

While EAFs were widely used in World War II for production of alloy steels, it was only afterwards that electric steelmaking began to expand. The low capital cost for a mini-mill - around US$140-200 per ton of annual installed capacity, compared with US$1,000 per ton of annual installed capacity for an integrated steel mill - allowed mills to be quickly set up in war-ravaged Europe, and also allowed them to successfully compete with the big United States steelmakers, such as Bethlehem Steel and U.S. Steel, for low-cost, carbon steel 'long products' (structural steel, rod and bar, wire and fasteners) in the U. Steel Mill was one of Bruce Springsteen 's early bands and performed regularly on the Jersey Shore, in Virginia, and also in California from 1969 Units of mass There are three similar units of Mass called the ton: Long ton (simply ton in countries such as the United Steel Mill was one of Bruce Springsteen 's early bands and performed regularly on the Jersey Shore, in Virginia, and also in California from 1969 The United States of America —commonly referred to as the The Bethlehem Steel Corporation (1857–2003 based in Bethlehem Pennsylvania, was once the second-largest Steel producer in the United States, after The United States Steel Corporation ( is an integrated Steel producer with major production operations in the United States, Canada, and Central Europe Carbon steel, also called plain carbon steel, is Steel where the main alloying constituent is Carbon. Structural steel is Steel construction Material, a profile, formed with a specific Shape or cross section and certain standards of A wire is a single usually cylindrical, elongated string of drawn Metal. A fastener is a Hardware device that mechanically joins or affixes two or more objects together S. market. When Nucor - now one of the largest steel producers in the U. Nucor Corporation ( is one of the largest steel producers in the United States and the largest of the "mini-mill" operators (those using Electric arc furnaces S. [1] - decided to enter the long products market in 1969, they chose to start up a mini-mill, with an EAF as its steelmaking furnace, soon followed by other manufacturers. Whilst Nucor expanded rapidly up and down the Eastern U. S. , the companies that followed them into mini-mill operations concentrated on local markets for long products, where the use of an EAF allowed the plants to be flexible with production, according to local demand. This pattern was also followed in countries around the world, with EAF steel production primarily used for long products, while integrated mills, using blast furnaces and basic oxygen furnaces, cornered the markets for 'flat products' - sheet steel and heavier steel plate. A blast furnace is a type of metallurgical Furnace used for Smelting to produce metals generally Iron. A basic oxygen furnace, also known as an LD converter, is the place within an integrated steel mill where molten iron from the blast furnace is changed into liquid Sheet metal is simply Metal formed into thin and flat pieces It is one of the fundamental forms used in Metalworking, and can be cut and bent into a variety In 1987, Nucor made the decision to expand into the flat products market, still using the EAF production route[2]. The fact that an EAF uses scrap steel as feedstock, instead of raw iron, has impacted on the quality of the flat product made from EAF steel, because of the limited amount of control over the impurities that are contained within the scrap.

Construction

An electric arc furnace used for steelmaking consists of a refractory-lined vessel, usually water-cooled in larger sizes, covered with a retractable roof, and through which one or more graphite electrodes enter the furnace. A refractory is a material that retains its strength at high Temperatures ASTM C71 defines refractories as "non-metallic materials having those chemical and physical The Mineral graphite, as with Diamond and Fullerene, is one of the Allotropes of carbon. An electrode is an Electrical conductor used to make contact with a nonmetallic part of a circuit (e The furnace is primarily split into three sections:

The hearth may be hemispherical in shape, or in an eccentric bottom tapping furnace (see below), the hearth has the shape of a halved egg. In modern meltshops, the furnace is often raised off the ground floor, so that ladles and slag pots can easily be maneuvered under either end of the furnace. In Foundry work a ladle is a container used to transport and pour out molten metals Separate from the furnace structure is the electrode support and electrical system, and the tilting platform on which the furnace rests. Two configurations are possible: the electrode supports and the roof tilt with the furnace, or are fixed to the raised platform.

A typical alternating current furnace has three electrodes. An alternating current ( AC) is an Electric current whose direction reverses cyclically as opposed to Direct current, whose direction remains constant This article deals with where how and why "three phase" is used Electrodes are round in section, and typically in segments with threaded couplings, so that as the electrodes wear, new segments can be added. The arc forms between the charged material and the electrode, and the charge is heated both by current passing through the charge and by the radiant energy evolved by the arc. The electrodes are automatically raised and lowered by a positioning system, which may use either electric winch hoists or hydraulic cylinders. A winch is a mechanical device that is used to pull in (wind up or let out (wind out or otherwise adjust the " Tension " of a Rope or Wire rope A Hydraulic cylinder (also called a linear Hydraulic motor) is a mechanical Actuator that is used to give a linear Force through a linear stroke The regulating system maintains an approximately constant current and power input during the melting of the charge, even though scrap may move under the electrodes while it melts. The mast arms holding the electrodes carry heavy busbars, which may be hollow water-cooled copper pipes, used to convey current to the electrode holders. A busbar in Electrical power distribution refers to thick strips of Copper or Aluminium that conduct Electricity within a switchboard Copper (ˈkɒpɚ is a Chemical element with the symbol Cu (cuprum and Atomic number 29 Modern systems use 'hot arms', where the whole arm carries the current, increasing efficiency. These can be made from copper-clad steel or aluminium. WikipediaNaming Since the electrodes move up and down automatically for regulation of the arc, and are raised to allow removal of the furnace roof, heavy water-cooled cables connect the bus tubes/arms with the transformer located adjacent to the furnace. A cable is one or more Wires or Optical fibers bound together typically in a common protective jacket or sheath A transformer is a device that transfers Electrical energy from one circuit to another through inductively coupled Electrical conductors To protect the transformer from the heat of the furnace, it is installed in a vault.

The furnace is built on a tilting platform so that the liquid steel can be poured into another vessel for transport in the steel making process. The operation of tilting the furnace to pour off molten steel is called "tapping". Originally, all steelmaking furnaces had a tapping spout closed with refractory that washed out when the furnace was tilted, but often modern furnaces have an eccentric bottom tap-hole (EBT) to reduce inclusion of nitrogen and slag in the liquid steel. Nitrogen (ˈnaɪtɹəʤɪn is a Chemical element that has the symbol N and Atomic number 7 and Atomic weight 14 Slag is the By-product of Smelting Ore to purify Metals They can be considered to be a mixture of metal Oxides however These furnaces have a taphole that passes vertically through the hearth and shell, and is set off-centre in the narrow 'nose' of the egg-shaped hearth. It is filled with refractory sand, such as olivine, when it is closed off. The Mineral olivine (when gem-quality also called Peridot) is a Magnesium Iron silicate with the formula ( Mg Modern plants may have two shells with a single set of electrodes that can be transferred between the two; one shell preheats scrap while the other shell is utilised for meltdown. Other DC-based furnaces have a similar arrangement, but have electrodes for each shell and one set of electronics.

AC furnaces usually exhibit a pattern of hot- and cold-spots around the hearth perimeter, with the cold-spots located between the electrodes. Modern furnaces mount oxygen-fuel burners in the sidewall and use them to provide chemical energy to the cold-spots, making the heating rate of the steel more even. Additional chemical energy is provided by injecting oxygen and carbon into the furnace, historically through lances in the slag door, but more commonly today through multiple wall-mounted injection units.

A mid-sized modern steelmaking furnace would have a transformer rated about 60,000,000 volt-amperes (60 MVA), with a secondary voltage between 400 and 900 volts and a secondary current in excess of 44,000 amperes. A transformer is a device that transfers Electrical energy from one circuit to another through inductively coupled Electrical conductors In a modern shop such a furnace would be expected to produce a quantity of 80 metric tonnes of liquid steel in approximately 60 minutes from charging with cold scrap to tapping the furnace. In comparison, basic oxygen furnaces can have a capacity of 150-300 tonnes per batch, or 'heat', and can produce a heat in 30-40 minutes. A basic oxygen furnace, also known as an LD converter, is the place within an integrated steel mill where molten iron from the blast furnace is changed into liquid Enormous variations exist in furnace design details and operations, depending on the end product and local conditions, as well as ongoing research to improve furnace efficiency - the largest scrap-only furnace (in terms of tapping weight and transformer rating) is in Turkey, with a tap weight of 320 metric tonnes and a transformer of 240 MVA.

To produce a ton of steel in an electric arc furnace requires on the close order of 400 kilowatt-hours per short ton of electrical energy, or about 440kWh per metric tonne; the theoretical minimum amount of energy required to melt a tonne of scrap steel is 300kWh (melting point 1520°C/2768°F). The short ton ( S/T) is a unit of mass equal to 2000 lb (around 907 This article is about the tonne or metric ton For other tons see Ton. Electric arc steelmaking is only economical where there is a plentiful supply of electric power, with a well-developed electrical grid.

Operation

Advantages of electric arc furnace for steelmaking

The use of EAFs allows steel to be made from a 100% scrap metal feedstock, commonly known as 'cold ferrous feed' to emphasise the fact that for an EAF, scrap is a regulated feed material. The primary benefit of this is the large reduction in specific energy (energy per unit weight) required to produce the steel. Another benefit is flexibility: while blast furnaces cannot vary their production by much and are never stopped, EAFs can be rapidly started and stopped, allowing the steel mill to vary production according to demand. A blast furnace is a type of metallurgical Furnace used for Smelting to produce metals generally Iron. Although steelmaking arc furnaces generally use scrap steel as their primary feedstock, if hot metal from a blast furnace or direct-reduced iron is available economically, these can also be used as furnace feed.

A typical steelmaking arc furnace is the source of steel for a mini-mill, which may make bars or strip product. Steel Mill was one of Bruce Springsteen 's early bands and performed regularly on the Jersey Shore, in Virginia, and also in California from 1969 Mini-mills can be sited relatively near to the markets for steel products, and the transport requirements are less than for an integrated mill, which would commonly be sited near a harbour for access to shipping.

Environmental issues

Although the modern electric arc furnace is a highly efficient recycler of steel scrap, operation of an arc furnace shop can have adverse environmental effects. Scrap is a term used to describe Recyclable materials left over from every manner of product consumption such as parts of vehicles building supplies and surplus materials Much of the capital cost of a new installation will be devoted to systems intended to reduce these effects, which include:

Because of the very dynamic quality of the arc furnace load, power systems may require technical measures to maintain the quality of power for other customers; flicker and harmonic distortion are common side-effects of arc furnace operation on a power system. Slag is the By-product of Smelting Ore to purify Metals They can be considered to be a mixture of metal Oxides however

Other electric arc furnaces

For steelmaking, direct current (DC) arc furnaces are used, with a single electrode in the roof and the current return through a conductive bottom lining or conductive pins in the base. Direct current ( DC) is the unidirectional flow of Electric charge. The advantage of DC is lower electrode consumption per ton of steel produced, since only one electrode is used, as well as less electrical harmonics and other similar problems. However, the size of DC arc furnaces is limited by the available electrodes and maximum allowable voltage. Maintenance of the conductive furnace hearth is a bottleneck in extended operation of a DC arc furnace. However, Danieli - makers of steel plant equipment - are preparing to install a 420-tonne DC furnace, powered by two 160 MVA transformers, in a Japanese steel mill. Instead of an upper graphite electrode and a lower conductive hearth, this EAF would have two upper graphite electrodes.

In a steel plant, a ladle furnace can be used to maintain the temperature of liquid steel during processing after tapping from the scrap-melting furnace. This also allows the molten steel to be kept ready for use in the event of a delay later in the steelmaking process. The ladle furnace consists of only the refractory roof and electrode system of a scrap-melting furnace, but it has no need for a tilting mechanism or scrap charging.

Electric arc furnaces are also used for production of ferroalloys and other non-ferrous alloys, and for production of phosphorus. Ferroalloy refers to various Alloys of Iron with a high proportion of one or more other element, Manganese or Silicon for example An alloy is a Solid solution or Homogeneous mixture of two or more elements, at least one of which is a Metal, which itself has Phosphorus, (ˈfɒsfərəs is the Chemical element that has the symbol P and Atomic number 15 Furnaces for these services are physically different from steel-making furnaces and may operate on a continuous, rather than batch, basis. Continuous process furnaces may also use paste-type (Soderberg) electrodes to prevent interruptions due to electrode changes. Such furnaces are usually known as submerged arc furnaces, because the electrode tips are buried in the slag/charge, and arcing occurs through the slag, between the matte and the electrode. Matte is a term used in the field of Pyrometallurgy given to the molten metal Sulfide phases typically formed during Smelting of Copper, A steelmaking arc furnace, by comparison, arcs in the open. The key is the electrical resistance, which is what generates the heat required: the resistance in a steelmaking furnace is the atmosphere, while in a submerged arc furnace, the slag or charge forms the resistance. Electrical resistance is a ratio of the degree to which an object opposes an Electric current through it measured in Ohms Its reciprocal quantity is The liquid metal formed in either furnace is too conductive to form an effective heat-generating resistance.

Amateurs have constructed a variety of arc furnaces, often based on electric arc welding kits contained by silical blocks or flower pots. Though crude, these simple furnaces are capable of melting a wide range of materials and creating calcium carbide etc. Calcium carbide is a Chemical compound with the Chemical formula of Ca[[Carbide C2]]

Vacuum arc remelting

In critical military and commercial aerospace applications, material engineers commonly specify VIM-VAR steels. VIM means Vacuum Induction Melted and VAR means Vacuum Arc Remelted. VIM-VAR steels become bearings for jet engines, rotor shafts for military helicopters, flap actuators for fighter jets, gears in jet or helicopter transmissions, mounts or fasteners for jet engines, jet tail hooks and other demanding applications.

Most grades of steel are melted once and are then cast or teemed into a solid form prior to extensive forging or rolling to a metallurgically sound form. In contrast, VIM-VAR steels go through two more highly purifying melts under vacuum. After melting in an electric arc furnace and alloying in an argon oxygen decarburization vessel, steels destined for vacuum remelting are cast into ingot molds. The solidified ingots then head for a vacuum induction melting furnace. This vacuum remelting process rids the steel of inclusions and unwanted gases while optimizing the chemical composition. The VIM operation returns these solid ingots to the molten state in the contaminant-free void of a vacuum. This tightly controlled melt often requires up to 24 hours. Still enveloped by the vacuum, the hot metal flows from the VIM furnace crucible into giant electrode molds. A typical electrode stands about 15 feet (5 meters) tall and will be in various diameters. The electrodes solidify under vacuum.

For VIM-VAR steels, the surface of the cooled electrodes must be ground to remove surface irregularities and impurities before the next vacuum remelt. Then the ground electrode is placed in a VAR furnace. In a VAR furnace the steel gradually melts drop-by-drop in the vacuum-sealed chamber. Vacuum arc remelting further removes lingering inclusions to provide superior steel cleanliness and further remove gases such as oxygen, nitrogen and hydrogen. Controlling the rate at which these droplets form and solidify ensures a consistency of chemistry and microstructure throughout the entire VIM-VAR ingot. This in turn makes the steel more resistant to fracture and/or fatigue. This refinement process is essential to meet the performance characteristics of parts like a helicopter rotor shaft, a flap actuator on a military jet or a bearing in a jet engine.

For some commercial or military applications, iron-based steel alloys may go through only one vacuum remelt, namely the VAR. For example, steels for solid rocket cases, landing gears or torsion bars for fighting vehicles typically involve the one vacuum remelt.

Vacuum arc remelting is also used in production of titanium and other metals which are reactive or in which high purity is required. Titanium (taɪˈteɪniəm is a Chemical element with the symbol Ti and Atomic number 22

References

  1. ^ www. worldsteel. org
  2. ^ Preston, R. , American Steel. Avon Books, New York, 1991


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