The encyclopedia · Engineering & Operations · Technical decision · 1856–1865
Bessemer blew air through molten iron and let the carbon fuel the process
Henry Bessemer blew air through molten iron so the carbon burned itself out and generated the heat, making steel cheap in bulk.
Barrow Haematite Steel Company
the move
Before the Bessemer process, making steel in bulk meant puddling: workers stirred a pool of molten wrought iron by hand, burning out the carbon slowly and at great expense. The result was strong but slow, so steel was a premium material and most everyday metalwork was weaker iron.
Henry Bessemer realized that the carbon in pig iron is itself a fuel. If you force air through the molten metal, the carbon combines with the oxygen and burns, and that combustion generates enough heat to keep the charge molten while the carbon drops to the level that makes steel.
The converter he devised let a large batch be blown in one vessel; the 1865 pilot at Barrow-in-Furness poured the first cast of steel with the process. Because the carbon did the heating, no expensive external fuel was added.
What had taken skilled men a long time now took minutes, and steel became cheap enough to replace wrought iron across the economy.
why it works
- The impurity that makes iron brittle is exactly the fuel that can burn it out, so the process pays for itself.
- Blowing air through a large converter scales far beyond a worker stirring a single pool by hand.
- No external heat means lower cost and no dependence on extra coal at the moment of conversion.
- It turned steel from a specialty into a commodity, the raw material for rails, bridges, ships and machines.
what transfers
The waste you are trying to remove is often the fuel you need — use an exothermic impurity to pay for its own removal.
what came after
Basic Oxygen Steelmaking, still the dominant way steel is made, is a descendant of Bessemer's idea of blowing oxygen through molten iron. Bessemer's process (with the later Gilchrist-Thomas modification to handle phosphoric ores) collapsed steel prices and let steel replace wrought iron in nearly every load-bearing use.
references
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