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Open hearth furnaces are one of a number of kinds of furnace where excess carbon and other impurities are burnt out of pig iron to produce steel. Since steel is difficult to manufacture due to its high melting point, normal fuels and furnaces were insufficient and the open hearth furnace was developed to overcome this difficulty.
Technically perhaps, the first primitive open hearth furnace was the Catalan forge, invented in Catalonia, Spain in the 8th century, but it is usual to confine the term to certain 19th century and later steelmaking processes, thus excluding bloomeries (including the Catalan forge), finery forges, and puddling furnaces from its application.
The Siemens regenerative furnace
Sir Carl Wilhelm Siemens developed the Siemens regenerative furnace in the 1850s, and claimed in 1857 to be recovering enough heat to save 70-80% of the fuel. This furnace operates at a high temperature by using regenerative preheating of fuel and air for combustion. In regenerative preheating, the exhaust gases from the furnace are pumped into a chamber containing bricks, where heat is transferred from the gases to the bricks. The flow of the furnace is reversed so that fuel and air pass through the chamber and are heated by the bricks. Through this method, an open-hearth furnace can reach temperatures high enough to melt steel, but Siemens did not initially use it for that.
The regenerators are the distinctive feature of the furnace and consist of fire-brick flues filled with bricks set on edge and arranged in such a way as to have a great number of small passages between them. The bricks absorb most of the heat from the outgoing waste gases and return it later to the incoming cold gases for combustion.
Open Hearth steelmaking
In 1865, Emile Martin and Pierre Martin took out a licence from Siemens and first applied his furnace for making steel. Their process was known as the Siemens-Martin process, and the furnace as an "open-hearth" furnace. The rapid production of large quantities of basic steel, such as that which is used to construct tall buildings, is the most appealing characteristic of the Siemens regenerative furnace. The usual size of furnaces is 50 to 100 tons, but for some special processes they may have a capacity of 250 tons or even 500 tons. The Siemens-Martin process complemented rather than replacing the Bessemer process. It was slower and thus easier to control.
Basic oxygen steelmaking or LD process replaced the open hearth furnace.
Further reading
- K. Barraclough, Steelmaking 1850-1900 (Institute of Metals, London 1990), 137-203.
- W. K. V. Gale, Iron and Steel (Longmans, London 1969), 74-77.
External links
"Open hearth furnace"