An open-hearth furnace or open hearth furnace is any of several kinds of industrial
furnace
A furnace is a structure in which heat is produced with the help of combustion.
Furnace may also refer to:
Appliances Buildings
* Furnace (central heating): a furnace , or a heater or boiler , used to generate heat for buildings
* Boiler, used t ...
in which excess
carbon
Carbon () is a chemical element with the symbol C and atomic number 6. It is nonmetallic and tetravalent
In chemistry, the valence (US spelling) or valency (British spelling) of an element is the measure of its combining capacity with o ...
and other impurities are burnt out of
pig iron
Pig iron, also known as crude iron, is an intermediate product of the iron industry in the production of steel which is obtained by smelting iron ore in a blast furnace. Pig iron has a high carbon content, typically 3.8–4.7%, along with silic ...
to
produce steel. Because
steel
Steel is an alloy made up of iron with added carbon to improve its strength and fracture resistance compared to other forms of iron. Many other elements may be present or added. Stainless steels that are corrosion- and oxidation-resistant ty ...
is difficult to manufacture owing to its high
melting point
The melting point (or, rarely, liquefaction point) of a substance is the temperature at which it changes state from solid to liquid. At the melting point the solid and liquid phase exist in equilibrium. The melting point of a substance depends ...
, normal fuels and furnaces were insufficient for
mass production
Mass production, also known as flow production or continuous production, is the production of substantial amounts of standardized products in a constant flow, including and especially on assembly lines. Together with job production and batch ...
of steel, and the open-hearth type of furnace was one of several technologies developed in the nineteenth century to overcome this difficulty. Compared with the
Bessemer process
The Bessemer process was the first inexpensive industrial process for the mass production of steel from molten pig iron before the development of the open hearth furnace. The key principle is steelmaking, removal of impurities from the iron by ox ...
, which it displaced, its main advantages were that it did not expose the steel to excessive
nitrogen
Nitrogen is the chemical element with the symbol N and atomic number 7. Nitrogen is a nonmetal and the lightest member of group 15 of the periodic table, often called the pnictogens. It is a common element in the universe, estimated at se ...
(which would cause the steel to become
brittle
A material is brittle if, when subjected to stress, it fractures with little elastic deformation and without significant plastic deformation. Brittle materials absorb relatively little energy prior to fracture, even those of high strength. Bre ...
), was easier to control, and permitted the melting and refining of large amounts of
scrap iron and steel.
[
The open-hearth furnace was first developed by ]German
German(s) may refer to:
* Germany (of or related to)
**Germania (historical use)
* Germans, citizens of Germany, people of German ancestry, or native speakers of the German language
** For citizens of Germany, see also German nationality law
**Ger ...
-born engineer Carl Wilhelm Siemens
Sir Carl Wilhelm Siemens (4 April 1823 – 19 November 1883), anglicised to Charles William Siemens, was a German-British electrical engineer and businessman.
Biography
Siemens was born in the village of Lenthe, today part of Gehrden, near Han ...
. In 1865, the French engineer Pierre-Émile Martin
Pierre-Émile Martin (; 18 August 1824, Bourges, Cher – 23 May 1915, Fourchambault) was a French industrial engineer. He applied the principle of recovery of the hot gas in an open hearth furnace, a process invented by Carl Wilhelm Siemens.
I ...
took out a license from Siemens and first applied his regenerative furnace for making steel
Steel is an alloy made up of iron with added carbon to improve its strength and fracture resistance compared to other forms of iron. Many other elements may be present or added. Stainless steels that are corrosion- and oxidation-resistant ty ...
. Their process was known as the Siemens–Martin process or Martin–Siemens process, and the furnace as an "open-hearth" furnace. Most open hearth furnaces were closed by the early 1990s, not least because of their slow operation, being replaced by the basic oxygen furnace
Basic oxygen steelmaking (BOS, BOP, BOF, or OSM), also known as Linz-Donawitz steelmaking or the oxygen converter processBrock and Elzinga, p. 50. is a method of primary steelmaking in which carbon-rich molten pig iron is made into steel. Blowing ...
or electric arc furnace
An electric arc furnace (EAF) is a furnace that heats material by means of an electric arc.
Industrial arc furnaces range in size from small units of approximately one-tonne capacity (used in foundries for producing cast iron products) up to ab ...
.[Philippe Mioche, « Et l'acier créa l'Europe », Matériaux pour l'histoire de notre temps, vol. 47, 1997, p. 29-36]
Whereas the earliest example of open-hearth steelmaking is found about 2000 years ago in the culture of the Haya people
The Haya (or Bahaya) are a Bantu ethnic group based in Kagera Region, northwestern Tanzania, on the western side of Lake Victoria. With over one million people, it is estimated the Haya make up approximately 2% of the population of Tanzania. His ...
, in present day Tanzania
Tanzania (; ), officially the United Republic of Tanzania ( sw, Jamhuri ya Muungano wa Tanzania), is a country in East Africa within the African Great Lakes region. It borders Uganda to the north; Kenya to the northeast; Comoro Islands and ...
, and in Europe in the Catalan forge
A bloomery is a type of metallurgical furnace once used widely for smelting iron from its oxides. The bloomery was the earliest form of smelter capable of smelting iron. Bloomeries produce a porous mass of iron and slag called a ''bloom''. ...
, invented in Spain in the 8th century, it is usual to confine the term to certain 19th-century and later steelmaking processes, thus excluding bloomeries (including the Catalan forge), finery forge
A finery forge is a forge used to produce wrought iron from pig iron by decarburization in a process called "fining" which involved liquifying cast iron in a fining hearth and removing carbon from the molten cast iron through oxidation. Finery ...
s, and puddling furnace
Puddling is the process of converting pig iron to bar (wrought) iron in a coal fired reverberatory furnace. It was developed in England during the 1780s. The molten pig iron was stirred in a reverberatory furnace, in an oxidizing environment, ...
s from its application.
Open-hearth process
The open-hearth process is a batch process and a batch is called a "heat". The furnace is first inspected for possible damage. Once it is ready or repaired, it is charged with light scrap, such as sheet metal, shredded vehicles or waste metal. The furnace is heated using burning gas. Once the charge has melted, heavy scrap, such as building, construction or steel milling scrap is added, together with pig iron from blast furnaces. Once all the steel has melted, slag-forming agents such as limestone are added. The oxygen in iron oxide and other impurities decarburizes the pig iron by burning excess carbon away, forming steel. To increase the oxygen content of the heat, iron ore can be added.[A Study of the Open Hearth: A Treatise on the Open Hearth Furnace and the Manufacture of Open Hearth Steel. Harbison-Walker Refractories Company. (2015), 102 pag, , ]
The process is far slower than that of the Bessemer converter
The Bessemer process was the first inexpensive industrial process for the mass production of steel from molten pig iron before the development of the open hearth furnace. The key principle is removal of impurities from the iron by oxidation with ...
and thus easier to control and sample for quality assessment. Preparing a heat usually takes eight to eight and a half hours, and longer to finish the conversion into steel. As the process is slow, it is not necessary to burn all the carbon away as in the Bessemer process, but the process can be terminated at any given point when the desired carbon content has been achieved.[
The furnace is tapped in the same way a ]blast furnace
A blast furnace is a type of metallurgical furnace used for smelting to produce industrial metals, generally pig iron, but also others such as lead or copper. ''Blast'' refers to the combustion air being "forced" or supplied above atmospheric ...
is tapped; a hole is drilled in the side of the hearth and the raw steel flows out. Once all the steel has been tapped, the slag is skimmed away. The raw steel may be cast into ingots, a process called ''teeming'', or it may be used in continuous casting in the rolling mill.[
The regenerators are the distinctive feature of the furnace and consist of fire-brick flues filled with bricks set on edge and arranged in such a way as to have a great number of small passages between them.][ The bricks absorb most of the heat from the outgoing waste gases and return it later to the incoming cold gases for combustion.
]
History
Carl Wilhelm Siemens
Sir Carl Wilhelm Siemens (4 April 1823 – 19 November 1883), anglicised to Charles William Siemens, was a German-British electrical engineer and businessman.
Biography
Siemens was born in the village of Lenthe, today part of Gehrden, near Han ...
developed the Siemens regenerative furnace in the 1850s, and claimed in 1857 to be recovering enough heat to save 70–80% of the fuel. This furnace operates at a high temperature by using regenerative preheating of fuel and air for combustion
Combustion, or burning, is a high-temperature exothermic redox chemical reaction between a fuel (the reductant) and an oxidant, usually atmospheric oxygen, that produces oxidized, often gaseous products, in a mixture termed as smoke. Combusti ...
. In regenerative preheating, the exhaust gases from the furnace are pumped into a chamber containing bricks, where heat is transferred from the gases to the bricks. The flow of the furnace is then reversed so that fuel and air pass through the chamber and are heated by the bricks. Through this method, an open-hearth furnace can reach temperatures high enough to melt steel, but Siemens did not initially use it for that.[Basic Open Hearth Steelmaking, with Supplement on Oxygen in Steelmaking, third edition (The Seely W. Mudd Series) The American Institute of Mining, Metallurgical, and Petroleum Engineers (1964). Gerhard, Derge. ASIN B00IJLRL40.]
In 1865, the French engineer Pierre-Émile Martin
Pierre-Émile Martin (; 18 August 1824, Bourges, Cher – 23 May 1915, Fourchambault) was a French industrial engineer. He applied the principle of recovery of the hot gas in an open hearth furnace, a process invented by Carl Wilhelm Siemens.
I ...
took out a license from Siemens and first applied his regenerative furnace for making steel. The most appealing characteristic of the Siemens regenerative furnace is the rapid production of large quantities of basic steel, used for example to construct high-rise buildings.[ The usual size of furnaces is 50 to 100 tons, but for some special processes they may have a capacity of 250 or even 500 tons.
Siemensmartin12nb.jpg, Siemens furnace from 1895.
Forno Martin Siemens, 1917 - san dl SAN IMG-00001419.jpg, 30-ton Siemens–Martin furnace, section, 1917.
Open hearth furnace size evolution sketch.svg, lang=en, Evolution of the size of open-hearth furnaces.
The Siemens–Martin process complemented rather than replaced the ]Bessemer process
The Bessemer process was the first inexpensive industrial process for the mass production of steel from molten pig iron before the development of the open hearth furnace. The key principle is steelmaking, removal of impurities from the iron by ox ...
. It is slower and thus easier to control, allowing production of better product. It also permits the melting and refining of large amounts of scrap steel, further lowering steel production costs and recycling an otherwise troublesome waste material. One of its important drawbacks is that melting and refining a charge takes several hours. This was an advantage in the early 20th century, as it gave plant chemists time to analyze the steel and decide how much longer to refine it. But by about 1975, electronic instruments such as atomic absorption spectrophotometers had made analysis of the steel much easier and faster. The work environment around an open-hearth furnace is said to be extremely dangerous, although that may be even more true of the environment around a basic oxygen or electric arc furnace.[
On the one hand, the process achieves lesser ]economies of scale
In microeconomics, economies of scale are the cost advantages that enterprises obtain due to their scale of operation, and are typically measured by the amount of output produced per unit of time. A decrease in cost per unit of output enables ...
than the Bessemer, so its steel was costlier in former's heyday, but on the other, it was more suitable for countries which couldn't produce lots of steel anyway due to limitations of natural resources.
Basic oxygen steelmaking
Basic oxygen steelmaking (BOS, BOP, BOF, or OSM), also known as Linz-Donawitz steelmaking or the oxygen converter processBrock and Elzinga, p. 50. is a method of primary steelmaking in which carbon-rich molten pig iron is made into steel. Blowing ...
eventually replaced the open-hearth furnace. It rapidly superseded both the Bessemer and Siemens–Martin processes in western Europe by the 1950s and in eastern Europe by the 1980s. Open-hearth steelmaking had superseded the Bessemer process in UK by 1900, but elsewhere in Europe, especially in Germany, the Bessemer and Thomas processes were used until the late 1960s when they were superseded by basic oxygen steelmaking
Basic oxygen steelmaking (BOS, BOP, BOF, or OSM), also known as Linz-Donawitz steelmaking or the oxygen converter processBrock and Elzinga, p. 50. is a method of primary steelmaking in which carbon-rich molten pig iron is made into steel. Blowing ...
. The last open-hearth furnace in the former East Germany
East Germany, officially the German Democratic Republic (GDR; german: Deutsche Demokratische Republik, , DDR, ), was a country that existed from its creation on 7 October 1949 until its dissolution on 3 October 1990. In these years the state ...
was stopped in 1993. In the US, steel production using the Bessemer process ended in 1968 and the open-hearth furnaces had stopped by 1992. In Hunedoara steel works
The Hunedoara steel works, formally ArcelorMittal Hunedoara and formerly the Hunedoara Ironworks ( ro, Uzinele de Fier Hunedoara), Hunedoara Steel Works (''Combinatul Siderurgic Hunedoara''), Siderurgica Hunedoara and Mittal Steel, is a steel mil ...
, Romania
Romania ( ; ro, România ) is a country located at the crossroads of Central Europe, Central, Eastern Europe, Eastern, and Southeast Europe, Southeastern Europe. It borders Bulgaria to the south, Ukraine to the north, Hungary to the west, S ...
the last 420-tonne capacity open-hearth furnace was shut down on 12 June 1999 and demolished and scrapped between 2001 and 2003, but the eight smokestacks of the furnaces remained until February 2011. The last open-hearth shop in China was shut down in 2001. The nation with the highest share of steel produced with open-hearth furnaces (almost 50%), as of 2010s, was Ukraine. The process is still in use in India and some parts of Ukraine. Russia retired its last hearth furnace in March 2018, and was considering preserving it as a museum artifact.
See also
* Bessemer process
The Bessemer process was the first inexpensive industrial process for the mass production of steel from molten pig iron before the development of the open hearth furnace. The key principle is steelmaking, removal of impurities from the iron by ox ...
* Cementation (metallurgy) process
* Methods of crucible steel production
*AJAX furnace
The AJAX furnace was a modification of the tilting open hearth furnace that used blown oxygen to improve productivity. The process was used in the UK during the 1960s at a time of transition from open hearth to oxygen based steel making.
History a ...
, oxygen based open hearth process
References
Further reading
*
*
*
External links
Precursors to the Blast Furnace
"Administering Doses of Liquid Iron to Steel Furnaces"
''Popular Science
''Popular Science'' (also known as ''PopSci'') is an American digital magazine carrying popular science content, which refers to articles for the general reader on science and technology subjects. ''Popular Science'' has won over 58 awards, incl ...
'', February 1919, page 64, scanned by Google Books
Google Books (previously known as Google Book Search, Google Print, and by its code-name Project Ocean) is a service from Google Inc. that searches the full text of books and magazines that Google has scanned, converted to text using optical c ...
.
{{Authority control
Steelmaking
Industrial furnaces