Hall, Joseph

SUBJECT AREA: Metallurgy

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b. 1789

d. 1862

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English ironmaker who invented the wet puddling process.

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Hall was a practical man with no theoretical background: his active years were spent at Bloomfield Ironworks, Tipton, Staffordshire. Around 1816 he began experimenting in the production of wrought iron. At that time, blast-furnace or cast iron was converted to wrought iron by the dry puddling process invented by Henry Cort in 1784. In this process, the iron was decarburized (i.e. had its carbon removed) by heating it in a current of air in a furnace with a sand bed. Some of the iron combined with the silica in the sand to form a slag, however, so that no less than 2 tons of cast iron were needed to produce 1 ton of wrought. Hall found that if bosh cinder was charged into the furnace, a vigorous reaction occurred in which the cast iron was converted much more quickly than before, to produce better quality wrought iron, a ton of which could be formed by no more than 21 cwt (1,067 kg) of cast iron. Because of the boiling action, the process came to be known as pig boiling. Bosh cinder, essentially iron oxide, was formed in the water troughs or boshes in which workers cooled their tools used in puddling and reacted with the carbon in the cast iron. The advantages of pig boiling over dry puddling were striking enough for the process to be widely used by the late 1820s. By mid-century it was virtually the only process used for producing wrought iron, an essential material for mechanical and civil engineering during the Industrial Revolution. Hall reckoned that if he had patented his invention he would have "made a million". As luck would have it, the process that he did patent in 1838 left his finances unchanged: this was for the roasting of cinder for use as the base of the puddling furnace, providing better protection than the bosh cinder for the iron plates that formed the base.

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Bibliography

1857, The Iron Question Considered in Connection with Theory, Practice and Experience with Special Reference to the Bessemer Process, London.

Further Reading

J.Percy, 1864, Metallurgy. Iron and Steel, London, pp. 670 ff. W.K.V.Gale, Iron and Steel, London: Longmans, pp. 46–50.

LRD