Thursday, February 23, 2012

The Bessemer Process

The Bessemer process was the first inexpensive industrial process for the mass-production of steel from molten pig iron. The process is named after its inventor, Henry Bessemer, who took out a patent on the process in 1855. The process was independently discovered in 1851 by William Kelly. The process had also been used outside of Europe for hundreds of years, but not on an industrial scale. The key principle is removal of impurities from the iron by oxidation with air being blown through the molten iron. The oxidation also raises the temperature of the iron mass and keeps it molten.
Bessemer converter, schematic diagram

The process using a basic refractory lining is known as the basic Bessemer process or Gilchrist-Thomas process after the discoverer Sidney Gilchrist Thomas.

The Bessemer process revolutionized steel manufacture by decreasing its cost, from £40 per long ton to £6–7 per long ton during its introduction, along with greatly increasing the scale and speed of production of this vital raw material. The process also decreased the labor requirements for steel-making. Prior to its introduction, steel was far too expensive to make bridges or the framework for buildings and thus wrought iron had been used throughout the Industrial Revolution. After the introduction of the Bessemer process, steel and wrought iron became similarly priced, and most manufacturers turned to steel. Some claim the availability of cheap steel allowed large bridges to be built and enabled the construction of railroads, skyscrapers, and large ships; however, the largest ship of the 19th century was the iron SS Great Eastern launched in 1858, high pressure steam-powered locomotive railways appeared in 1825 with the opening of the Stockton and Darlington railway (the first passenger railway opened in 1830 between Liverpool and Manchester), and the first modern large suspension bridge was the Menai Suspension Bridge completed in 1826: the latter both decades before mass produced steel. Other important steel products—also made using the open hearth process—were steel cable, steel rod and sheet steel which enabled large, high-pressure boilers and high-tensile strength steel for machinery which enabled much more powerful engines, gears and axles than were possible previously. With large amounts of steel it became possible to build much more powerful guns and carriages, tanks, armored fighting vehicles and naval ships. Industrial steel also made possible the building of giant turbines and generators thus making the harnessing of water and steam power possible. The introduction of the large scale steel production process paved the way to mass industrialisation as observed in the 19th–20th centuries

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