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Concept
Puddling (metallurgy)
Summary
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 to burn the carbon, resulting in wrought iron. It was one of the most important processes for making the first appreciable volumes of valuable and useful bar iron (malleable wrought iron) without the use of charcoal. Eventually, the furnace would be used to make small quantities of specialty steels.
Though it was not the first process to produce bar iron without charcoal, puddling was by far the most successful, and replaced the earlier potting and stamping processes, as well as the much older charcoal finery and bloomery processes. This enabled a great expansion of iron production to take place in Great Britain, and shortly afterwards, in North America. That expansion constitutes the beginnings of the Industrial Revolution so far as the iron industry is concerned. Most 19th century applications of wrought iron, including the Eiffel Tower, bridges, and the original framework of the Statue of Liberty, used puddled iron.
Modern puddling was one of several processes developed in the second half of the 18th century in Great Britain for producing bar iron from pig iron without the use of charcoal. It gradually replaced the earlier charcoal-fueled process, conducted in a finery forge.
Pig iron contains much free carbon and is brittle. Before it can be used, and before it can be worked by a blacksmith, it must be converted to a more malleable form as bar iron, the early stage of wrought iron.
Abraham Darby's successful use of coke for his blast furnace at Coalbrookdale in 1709 reduced the price of iron, but this coke-fuelled pig iron was not initially accepted as it could not be converted to bar iron by the existing methods. Sulfur impurities from the coke made it 'red short', or brittle when heated, and so the finery process was unworkable for it.
Official source
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