Open hearth furnace 1

Open hearth furnace

Tapping open-hearth furnace, VEBEdelstahlwerk, Germany, 1982

Open hearth furnaces are one of a number of kinds of furnace whereexcess carbon and other impurities are burnt out of pig iron to producesteel. Since steel is difficult to manufacture owing to its high meltingpoint, normal fuels and furnaces were insufficient and the open hearthfurnace was developed to overcome this difficulty.

In 1865, the French engineer Pierre-Émile Martin took out a licensefrom Siemens and first applied his regenerative furnace for makingsteel. Their process was known as the Siemens-Martin process, andthe furnace as an "open-hearth" furnace. Most open hearth furnaceswere closed by the early 1990s, not least because of their slowoperation, being replaced by the basic oxygen furnace or electric arcfurnace.

While arguably the first primitive open hearth furnace was the Catalanforge, invented in Spain in the eighth century, but it is usual to confinethe term to certain nineteenth century and later steelmaking processes, thus excluding bloomeries (including theCatalan forge), finery forges, and puddling furnaces from its application.

Open hearth process

A. gas and air enterB. pre-heated chamber

C. molten pig ironD. hearth

E. heating chamber (cold)F. gas and air exit.

The open hearth process is a batch process and a batch is called a"heat". The furnace is first inspected of possible damages. Once it isready or repaired, it is charged with light scrap, such as sheet metal,shredded vehicles or waste metal. Once it has melted, heavy scrap,such as building, construction or steel milling scrap is added, togetherwith pig iron from blast furnaces. Once all steel has melted, slagforming agents, such as limestone, are added. The oxygen in iron oxideand other impurities decarburize the pig iron by burning the carbonaway, forming steel. To increase the oxygen contents of the heat, ironore can be added to the heat.

The process is far slower than that of Bessemer converter and thuseasier to control and take samples for quality control. Preparing a heatusually takes 8 h to 8 h 30 min to complete into steel. As the process isslow, it is not necessary to burn all the carbon away as in Bessemerprocess, but the process can be terminated at given point when desiredcarbon contents has been achieved.

The furnace is tapped the same way a blast furnace is tapped; a hole is drilled on the side of the hearth and the rawsteel is let to flow out. Once all the steel has been tapped, the slag is skimmed away. The raw steel may be cast intoingots; this process is called teeming, or it may be used on continuous casting for the rolling mill.The regenerators are the distinctive feature of the furnace and consist of fire-brick flues filled with bricks set on edgeand arranged in such a way as to have a great number of small passages between them. The bricks absorb most of theheat from the outgoing waste gases and return it later to the incoming cold gases for combustion.

Open hearth furnace 2

History

Siemens furnace from 1895

Sir Carl Wilhelm Siemens developed the Siemens regenerativefurnace in the 1850s, and claimed in 1857 to be recovering enoughheat to save 70–80% of the fuel. This furnace operates at a hightemperature by using regenerative preheating of fuel and air forcombustion. In regenerative preheating, the exhaust gases from thefurnace are pumped into a chamber containing bricks, where heat istransferred from the gases to the bricks. The flow of the furnace is thenreversed so that fuel and air pass through the chamber and are heatedby the bricks.Through this method, an open-hearth furnace can reachtemperatures high enough to melt steel, but Siemens did not initiallyuse it for that.

In 1865, the French engineer Pierre-Émile Martin took out a license from Siemens and first applied his regenerativefurnace for making steel. The most appealing characteristic of the Siemens regenerative furnace is the rapidproduction of large quantities of basic steel, used for example to construct high-rise buildings. The usual size offurnaces is 50 to 100 tons, but for some special processes they may have a capacity of 250 or even 500 tons.

The Siemens-Martin process complemented rather than replaced the Bessemer process. It is slower and thus easier tocontrol. It also permits the melting and refining of large amounts of scrap steel, further lowering steel productioncosts and recycling an otherwise troublesome waste material. Its worst drawback is the fact that melting and refininga charge takes several hours. This was an advantage in the early 20th C.,as it gave plant chemists time to analyze thesteel and decide how much longer to refine it. But by about 1975, electronic instruments such as atomic absorptionspectrophotometers had made analysis of the steel much easier and faster. The work environment around an openhearth furnace is said to be extremely dangerous, although that may be even more true of the environment around abasic oxygen or electric arc furnace.Basic oxygen steelmaking eventually replaced the open hearth furnace. It rapidly superseded both the Bessemerprocess and Siemens-Martin process in Western Europe by the 1950s and in Eastern Europe by the 1980s. The openhearth steelmaking had superseded Bessemer process in UK by 1900, but elsewhere in Europe, especially inGermany, the Bessemer and Thomas processes were used until the late 1960s when they were superseded by basicoxygen steelmaking. The last European open hearth furnace in the former East Germany was stopped in 1993. In theUS, steel production using the Bessemer process ended in 1968 and the open hearth furnaces had stopped by 1992.The last open hearth shop in China was shut down in 2001. The nation with the highest share of steel produced withopen hearth furnaces (almost 50%) is Ukraine.[1] The process is still in use in both India and Russia.

References[1] http:/ / www. energystar. gov/ ia/ business/ industry/ 41724. pdf

Further reading• K. Barraclough, Steelmaking 1850–1900 (Institute of Metals, London 1990), 137–203.• W. K. V. Gale, Iron and Steel (Longmans, London 1969), 74–77.

External links• Precursors to the Blast Furnace (http:/ / www. davistownmuseum. org/ toolPreBlastFurnace. html)• "Administering Doses of Liquid Iron to Steel Furnaces" (http:/ / books. google. com/

books?id=7igDAAAAMBAJ& pg=PA64), Popular Science, February 1919, page 64, scanned by Google Books.

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Article Sources and ContributorsOpen hearth furnace  Source: http://en.wikipedia.org/w/index.php?oldid=506552931  Contributors: Andrewa, Bwwm, CavalloRazzo, Cheaposgrungy, DMahalko, DocKrin, DocWatson42,Dorieo, Eman2129, Erik9, Gaius Cornelius, Glenn, GorgeCustersSabre, Heron, InformationalAnarchist, Jonked, Kjkolb, Mandarax, MarkBolton, Mmarre, Morgan Riley, Northfox, Pathh,Peterkingiron, Petri Krohn, Pol098, Redrose64, Rosa Lux, Sam Hocevar, Shrike001, Shrout1, Sitush, Stevenwmccrary58, SultanOfVelocicaptorXVI, Suviljan, Tom harrison, Unara, Vrenator,WOSlinker, Wizard191, Wtshymanski, Yvwv, Zigger, 37 anonymous edits

Image Sources, Licenses and ContributorsFile:Fotothek df n-34 0000203 Metallurge für Hüttentechnik.jpg  Source: http://en.wikipedia.org/w/index.php?title=File:Fotothek_df_n-34_0000203_Metallurge_für_Hüttentechnik.jpg License: Creative Commons Attribution-Share Alike 3.0 Germany  Contributors: Karsten11, Morgan Riley, SlickImage:open-hearth.jpg  Source: http://en.wikipedia.org/w/index.php?title=File:Open-hearth.jpg  License: Public Domain  Contributors: CheaposgrungyImage:Siemensmartin12nb.jpg  Source: http://en.wikipedia.org/w/index.php?title=File:Siemensmartin12nb.jpg  License: Public Domain  Contributors: Cirt, Ies, Mddkpp, Morgan Riley,Romary, 6 anonymous edits

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