Metallurgical furnace

<h2 id="air-blast-furnaces">Air blast furnaces</h2>

<p>Many furnace designs for smelting combine ore, fuel, and other <a href="/facts/Reagent/c3GLInCu">reagents</a> like <a href="/facts/Flux/Aw3P5Bvb">flux</a> in a single chamber. Mechanisms, such as <a href="/facts/Bellows/pNg84XnM">bellows</a> or motorized fans, then drive pressurized blasts of air into the chamber. These blasts make the fuel burn hotter and drive chemical reactions.
</p><p>Furnaces of this type include:
</p>
<ul><li>The <a href="/facts/Blast_furnace/DJzUB2EG">blast furnace</a>, used to produce <a href="/facts/Pig_iron/bxLL2NaR">pig iron</a> from <a href="/facts/Iron_ore/rQMEvgMh">iron ore</a>. These can be subdivided into:
<ul><li><a href="/facts/Cold_blast/D9XBsArm">Cold blast</a> furnaces</li>
<li><a href="/facts/Hot_blast/fCP4RelL">Hot blast</a> furnaces</li></ul></li>
<li>The <a href="/facts/Bloomery/E2NDd6EF">bloomery</a>, a precursor to the blast furnace that produces <a href="/facts/Sponge_iron/lEnkCk7M">sponge iron</a> from ore</li>
<li>The <a href="/facts/Blowing_house/gtpbaDaf">blowing house</a>, a traditional furnace for smelting <a href="/facts/Tin/obW9mqc3">tin</a></li>
<li>The <a href="/facts/Smeltmill/JfKeISQT">smeltmill</a>, a traditional furnace for smelting <a href="/facts/Lead/EYljasJN">lead</a></li></ul>
<h3>Blowing in</h3>
<p>Even smaller, pre-industrial bloomeries possess significant <a href="/facts/Thermal_mass/r63KHQ7y">thermal mass</a>. Raising a cold furnace to the necessary temperature for smelting iron requires a significant amount of energy, regardless of modern technology. For this reason, metallurgists will try their best to keep blast furnaces running continuously, and shutting down a furnace is seen as an unfortunate event.
</p><p>Conversely, starting up a new furnace, or one that had been temporarily shut down, is often a special occasion. In traditional bloomeries, several rounds of fuel would need to be burnt away before the furnace was ready to accept a charge of ore. In English, this process became known as "blowing in" the furnace, while a furnace that had to be shut down and went cold had been "blown out", terms that are still applied to contemporary blast furnaces.<a class="footnote-ref" id="fnref:2" href="#fn:2"><sup>2</sup></a><a class="footnote-ref" id="fnref:3" href="#fn:3"><sup>3</sup></a>
</p>
<h2 id="reverberatory-furnaces">Reverberatory furnaces</h2>
<p>A <a href="/facts/Reverberatory_furnace/fuILeeWX">reverberatory furnace</a> still exposes the reaction chamber, where metal or ore is combined with reagents, to a stream of exhaust gases. However, no fuel is directly added to the chamber, and combustion occurs in a separate chamber. Furnaces of this type include:
</p>
<ul><li>The <a href="/facts/Open_hearth_furnace/4157lRCs">open hearth furnace</a>, a 19th-20th century <a href="/facts/Steelmaking/95arHmry">steelmaking</a> method for refining pig iron into <a href="/facts/Steel/aN6qWo4H">steel</a></li>
<li>The <a href="/facts/Puddling_furnace/5RmNM4GT">puddling furnace</a>, a 18th-19th century method for refining pig iron into <a href="/facts/Wrought_iron/zynpjrIv">wrought iron</a></li></ul>
<h2 id="refining-converters">Refining converters</h2>
<p>In metallurgy, furnaces used to <a href="/facts/Refining_(metallurgy)/QCXENs8m">refine</a> metals further, particularly iron into steel, are also often called <a href="/facts/Converting_(metallurgy)/193o52gc">converters</a>:
</p>
<ul><li>Steelmaking converters
<ul><li>The <a href="/facts/Basic_oxygen_furnace/yg5Ht8fC">basic oxygen furnace</a></li>
<li>The <a href="/facts/Bessemer_converter/Al0kr3a3">Bessemer converter</a></li></ul></li>
<li>The <a href="/facts/Manh%25C3%25A8s%25E2%2580%2593David_converter/7Bsb3n2x">Manhès–David converter</a> for refining copper <a href="/facts/Matte_(metallurgy)/5VGGcCLS">matte</a> into pure "blister" copper</li></ul>
<h2 id="electric-furnaces">Electric furnaces</h2>

<p>Just as other industries have trended towards <a href="/facts/Electrification/QbQynVHW">electrification</a>, electric furnaces have become prevalent in metallurgy. However, while any furnace can theoretically use an electrical <a href="/facts/Heating_element/q0GLQufX">heating element</a>, process specifics mostly limit this approach to furnaces with lower power demands. 
</p><p>Instead, electric metallurgical furnaces often apply an <a href="/facts/Electric_current/Dc1xdnUX">electric current</a> directly to batches of metal. This is particularly useful for <a href="/facts/Recycling/x9X7GAzz">recycling</a> (still relatively pure) <a href="/facts/Scrap/lPWqt9vd">scrap</a> metal, or remelting <a href="/facts/Ingot/j7kzdag2">ingots</a> for <a href="/facts/Casting/cFJ0hPuU">casting</a> in <a href="/facts/Foundries/Hww9Nrmr">foundries</a>. The absence of any fuel or exhaust gases also makes these designs versatile for heating all kinds of metals.<a class="footnote-ref" id="fnref:4" href="#fn:4"><sup>4</sup></a> Such designs include:
</p>
<ul><li><a href="/facts/Electric_arc_furnace/GgYK6Nz1">Electric arc furnaces</a> (EAFs), which apply current to the metal via <a href="/facts/Electrode/251PaKX8">electrodes</a> over an <a href="/facts/Electric_arc/1hUPPAG0">electric arc</a>
<ul><li>The <a href="/facts/Flodin_furnace/hhqoPNIg">Flodin furnace</a> is an early EAF, specially designed to smelt iron from ore through the direct addition of <a href="/facts/Carbon/ukrgQexo">carbon</a></li></ul></li>
<li><a href="/facts/Electric_induction_furnace/MI49lJYl">Electric induction furnaces</a>, which heat the metal through <a href="/facts/Eddy_currents/KvHNx1v7">eddy currents</a>, requiring metal mostly free of gangue and <a href="/facts/Corrosion/lIC7H4we">corrosion</a></li></ul>
<h2 id="other-furnaces">Other furnaces</h2>
<p>Other metallurgical furnaces have special design features or uses. One function is heating material short of melting, in order to perform <a href="/facts/Heat_treatment/xR2tVyTU">heat treatment</a> or <a href="/facts/Hot_working/oPVX3MQg">hot working</a>. Basic furnaces used this way include:
</p>
<ul><li>A <a href="/facts/Forge/B1JVtzy4">forge</a> is the traditional <a href="/facts/Metalsmith/HtUrxrpX">metalsmith</a>'s hearth for heating metal while <a href="/facts/Forging/SYFomJNp">forging</a></li>
<li>Soaking pits are large heated chambers, typically in-ground, where steel slabs are reheated before <a href="/facts/Rolling_(metalworking)/FQ6AQVld">rolling</a></li></ul>
<p>Another class of furnaces isolate the material from the surrounding atmosphere and contaminants, enabling advanced heat treatments and other techniques:
</p>
<ul><li><a href="/facts/Muffle_furnace/3mPWIy3f">Muffle furnaces</a> enclose the material to keep out contaminants and divert any exhaust away from the area</li>
<li><a href="/facts/Autoclave/bg1J3cXJ">Autoclaves</a> are reinforced, seal airtight, and can expose material to heat and elevated <a href="/facts/Pressure/eyc37GRG">pressure</a></li>
<li><a href="/facts/Vacuum_furnace/FDbFVWG9">Vacuum furnaces</a> are similar to autoclaves, but expose the material to a <a href="/facts/Vacuum/BTk3goyV">vacuum</a> instead</li></ul>
<h2 id="notes">Notes</h2>

<h2 id="references">References</h2>

<ol>
<li id="fn:1"><p>D, C. H. (1923-11-24). "Metallurgical Furnaces". Nature. 112 (2821): 755–756. doi:10.1038/112755a0. ISSN 1476-4687. S2CID 28751324. <a href="https://www.nature.com/articles/112755a0" target="_blank">https://www.nature.com/articles/112755a0</a> <a href="#fnref:1" class="footnote-back-ref">↩</a></p></li>
<li id="fn:2"><p>Eggert, Gerald (15 January 2008). "How to "Blow In" a Newly Built or a Cold Iron Furnace". Medieval Studies. Medieval Technology and American History. One-Minute Essays. Penn State University. Archived from the original on 26 September 2023. Retrieved 18 February 2024. <a href="https://web.archive.org/web/20230926220330/https://www.engr.psu.edu/mtah/essays/howto_blowin.htm" target="_blank">https://web.archive.org/web/20230926220330/https://www.engr.psu.edu/mtah/essays/howto_blowin.htm</a> <a href="#fnref:2" class="footnote-back-ref">↩</a></p></li>
<li id="fn:3"><p>City Gate Service <a href="https://www.citygatesusa.com/" target="_blank">https://www.citygatesusa.com/</a> <a href="#fnref:3" class="footnote-back-ref">↩</a></p></li>
<li id="fn:4"><p>The absence of any additional chemistry is not always an advantage though. For example, smelting iron is still mostly done with blast furnaces, partly because the carbon monoxide created by burning coke is also excellent for chemically reducing the iron. <a href="/wiki/Carbon_monoxide" target="_blank">/wiki/Carbon_monoxide</a> <a href="#fnref:4" class="footnote-back-ref">↩</a></p></li>
</ol>

Metallurgical furnace open-in-new

Metallurgical furnace