Bessemer process



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The Bessemer process was the first inexpensive industrial process for the mass-production of oxidation through air being blown through the molten iron. The oxidation also raises the temperature of the iron mass and keeps it molten.  

Contents

The details of the process

Bessemer Converter

The process is carried on in a large ovoid steel container lined with clay or dolomite called the Bessemer converter. The capacity of a converter was from 8 to 30 tons of molten iron with a usual charge being around 15 tons. At the top of the converter is an opening, usually tilted to the side relative to the body of the vessel, through which the iron is introduced and the finished product removed. The bottom is perforated with a number of channels called tuyères through which air is forced into the converter. The converter is pivoted on trunnions so that it can be rotated to receive the charge, turned upright during conversion, and then rotated again for pouring out the molten steel at the end.

Oxidation

The oxidation process removes impurities such as magnesite linings are also sometimes used instead of dolomite) - this is also known as a Gilchrist-Thomas converter, named after its inventor, Sidney Gilchrist Thomas. In order to give the steel the desired properties, other substances could be added to the molten steel when conversion was complete, such as spiegeleisen (an iron-carbon-manganese alloy).

Managing the process

When the required steel had been formed, it was poured out into ladles and then transferred into moulds and the lighter slag is left behind. The conversion process called the "blow" was completed in around twenty minutes. During this period the progress of the oxidation of the impurities was judged by the appearance of the flame issuing from the mouth of the converter: the modern use of photoelectric methods of recording the characteristics of the flame has greatly aided the blower in controlling the final quality of the product. After the blow, the liquid metal was recarburized to the desired point and other alloying materials are added, depending on the desired product.

Predecessor processes

Before the Bessemer process Britain had no practical method of reducing the carbon content of finery forges in Sweden.

This process was refined in the 1700s with the introduction of Benjamin Huntsman's pig iron. The earliest Bessemer converters produced steel for £7 a long ton, although they priced it initially at around £40 a ton.  

History

Both Bessemer and Huntsman were based in the city of Sheffield, England. Sheffield has an international reputation for steel-making, which dates from 1740, when Benjamin Huntsman discovered the crucible technique for steel manufacture, at his workshop in the district of Handsworth. This process had an enormous impact on the quantity and quality of steel production and was only made obsolete, a century later, in 1856 by Henry Bessemer's invention of the Bessemer converter which allowed the true mass production of steel. Bessemer had moved his Bessemer Steel Company to Sheffield to be at the heart of the industry. The city's Kelham Island Museum still maintains one of the UK's last examples of a working Bessemer converter [from Workington, Cumbria] for public viewing.

Importance

The Bessemer process revolutionized steel manufacture by decreasing its cost, and greatly increasing the scale and speed, while also decreasing the labour requirements. Prior to its introduction, steel was far too expensive to make bridges or the framework for buildings and wrought iron had been used throughout the Industrial Revolution. After its introduction, steel and wrought iron became similarly priced, and most manufacturers turned to steel.

Obsolescence

In the U.S., commercial steel production using this method stopped in 1968. It was replaced by processes such as nitrogen which was part of the air blast passing through the steel.

See also

References

  • A retrospective of 20th century steel making technology

Notes

  1. ^ "Bessemer process". Britannica 2. (2005). Encyclopedia Britannica. 168. Retrieved on 2005-08-06. 
  2. ^ "Kelly, William". Britannica 6. (2005). Encyit was a good in ventionclopedia Britannica. 791. Retrieved on 2005-08-06. 
  3. ^ Ponting, Clive (2000), , Pimlico, ISBN 0-7126-6572-2
 
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