Bloomery 1473011 223635525 2008-07-05T00:26:56Z Zorrobot 7218328 robot Adding: [[nn:Jernvinne i Noreg]], [[no:Jernvinne i Norge]] {{otheruses}} A '''bloomery''' is a type of [[furnace]] once widely used for [[smelting]] [[iron]] from its [[iron oxides|oxides]]. The bloomery was the earliest form of smelter capable of smelting iron. A bloomery's product is a porous mass of iron and [[slag]] called a '''''bloom'''''. This mix of slag and iron in the bloom is termed ''[[sponge iron]]'', which is usually consolidated ([[Shingling (metallurgy)|shingled]]) and further [[forge]]d into [[wrought iron]]. The bloomery has now largely been superseded by the [[blast furnace]], which produces [[pig iron]]. ==Structure and process== [[Image:Bas fourneau.png|right|200px]] A bloomery consists of a pit or [[chimney]] with heat-resistant walls made of earth, clay, or stone. Near the bottom, one or more clay pipes enter through the side walls. These pipes, called [[tuyère]]s, allow air to enter the furnace, either by natural draft, or forced with a [[bellows]]. An opening at the bottom of the bloomery may be used to remove the bloom, or the bloomery can be tipped over and the bloom removed from the top. The first step taken before the bloomery can be used is the preparation of the [[charcoal]] and the [[iron ore]]. The charcoal is produced by heating wood to produce the nearly pure carbon fuel needed for the refining process. The ore is broken into small pieces and ''roasted'' in a fire to remove any moisture in the ore. Any large impurities in the ore can be crushed and removed. Since slag from previous blooms may have a high iron content, slag from previous blooms can be broken up and recycled into the bloomery with the new ore. In operation, the bloomery is preheated by burning charcoal, and once hot, [[iron ore]] and additional charcoal are introduced through the top, in a roughly one to one ratio. Inside the furnace, [[carbon monoxide]] from the incomplete combustion of the charcoal [[redox|reduces]] the iron oxides in the ore to metallic iron, without melting the ore; this allows the bloomery to operate at lower temperatures than the melting temperature of the ore. As the desired product of a bloomery is iron which is easily forgeable, nearly pure, and with a low [[carbon]] content, the temperature and ratio of charcoal to iron ore must be carefully controlled to keep the iron from absorbing too much carbon and thus become unforgeable. [[Limestone]] can also be added to the charge (about 10% of the ore weight) as a [[Flux (metallurgy)|flux]], to remove impurities. The small particles of iron produced in this way fall to the bottom of the furnace and become welded together to form a spongy mass of the bloom. The bottom of the furnace also fills with molten slag, often consisting of [[fayalite]], a compound of [[silicon]], oxygen and iron mixed with other impurities from the ore. Because the bloom is highly porous, and its open spaces are full of slag, the bloom must later be reheated and beaten with a hammer to drive the molten slag out of it. Iron treated this way is said to be ''wrought'', and the resulting nearly pure iron ''[[wrought iron]]''. ==History== {{see also|Smelting#Early iron smelting|l1=Early iron smelting}} Iron appears to have been smelted in the west as early as 3000 BC, but bronze smiths, not being familiar with iron, did not put it to use until much later. In the west, iron began to be used around 1200 BC, presumably as a replacement for bronze, which was becoming harder to come by due to shortages in [[copper]] and [[tin]]. The onset of the [[Iron Age]] in most parts of the world coincides with the first widespread use of the bloomery. While earlier examples of iron are found, their high [[nickel]] content indicates that this is [[meteor]]ic iron. Other early samples of iron may have been produced by accidental introduction of iron ore in [[bronze]] smelting operations. [[China]] has long been considered the exception: by 5th century BC, metalworkers in the southern [[state of Wu]] had invented the [[blast furnace]], and the means to both cast iron and to decarburize the carbon-rich [[pig iron]] produced in a blast furnace to a low-carbon, wrought iron-like material. It was thought that the Chinese skipped the bloomery process completely, starting with the blast furnace and the [[finery forge]] to get wrought iron. Recent evidence, however, shows that bloomeries were used earlier in China, migrating in from the west as early as 800 BC, before being supplanted by the locally developed blast furnace. Early bloomeries were relatively small, smelting less than 1 kg of iron with each firing. Medieval Europe saw the construction of progressively larger bloomeries, leveling off at around 15 kg on average, though exceptions did exist. The use of [[waterwheel]]s to power the bellows allowed the bloomery to become larger and hotter; European average bloom sizes quickly rose to 300 kg, where they leveled off through the demise of the bloomery. Water powered bellows and larger bloomeries also increased the heat to the point where the iron could melt; this was not considered desirable because it allowed carbon to diffuse into the molten iron, producing unworkable pig iron. Molten iron was not desirable until the advent of the blast furnace. In [[England]] and [[Wales]], despite the arrival of the blast furnace in the [[Weald]] in about 1491, bloomery forges (probably using water-power for a hammer as well as the bellows) were operating in the west Midland region beyond 1580. In [[Furness]] and [[Cumberland]], they operated into the early 17th century and the last one in England (near [[Garstang]]) did not close until about 1770.<ref name="English books">H. R. Schubert, <I>History of the British Iron and Steel Industry<I> (1957). R. F. Tylecote, <I>History of Metallurgy<I> (1991).</ref> It survived in [[Spain]] and southern [[France]] as [[Catalan]] Forges to the mid 19th century, in [[Austria]] as the ''stuckofen'' to 1775. In [[Adirondacks]], [[New York]], new bloomeries using the [[hot blast]] technique were built in the 19th century.<ref name="Adirondacks">Gordon C. Pollard, 'Experimentation in 19th century bloomery production: evidence from the Adirondacks of New York' <I>Historical Metallurgy<I> 32(1) (1998), 33-40.</ref> ==References== {{reflist}} == External links == * [http://www.ironsmelting.net/ Technology and archaeology of the earliest iron smelting and smithing] * [http://iron.wlu.edu/Bloomery_Iron.htm Rockbridge bloomery] * [http://www.wealdeniron.org.uk/Expt/index.htm WIRG experimental bloomery] * [http://www.davistownmuseum.org/toolPreBlastFurnace.html Precursors of the blast furnace] * [http://www.unc.edu/courses/rometech/public/content/mines_and_iron/Roger_Smith/roger/BLOOM4.htm Roger Smith's article on bloomery construction] * [http://science.howstuffworks.com/iron3.htm How Stuff Works] * [http://iron.wlu.edu/ The Smelter's Art Experimental Iron Production at The Rockbridge Bloomery] * [http://www.staff.hum.ku.dk/dbwagner/EARFE/EARFE.html Early use of iron in China] [[Category:Industrial furnaces]] [[Category:Steelmaking]] [[Category:Iron]] [[Category:Metallurgy]] [[de:Rennofen]] [[fr:Bas fourneau]] [[is:Rauðablástur]] [[nl:Laagoven]] [[no:Jernvinne i Norge]] [[nn:Jernvinne i Noreg]] [[pl:Dymarka]] [[ru:Горн (печь)]] [[fi:Pätsi]]