Bessemer Converter (steel)

Invented by : Sir Henry Bessemer

Invented in year : 1856

Bessemer Converter is a large pear-shaped container in which molten iron is converted to steel by the Bessemer process. Bessemer process is a method for making steel by blasting compressed air through molten iron to burn out excess carbon and impurities. The process and the converter are both named after its inventor, Henry Bessemer, who took out a patent on the process in 1855. 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.

History

The story of Bessemer's Steel Process is a classic example of the military's impetus to technological development. During the Crimean War in 1854, Bessemer invented a new type of artillery shell. The Generals reported that the cast-iron cannon of the time were not strong enough to deal with the forces of the more powerful shell. Starting in January 1855 he began working on a way to produce steel in the massive quantities required for artillery  and by October he filed his first patent related to the Bessemer process. On 24 August 1856 Bessemer first described the process to a meeting of the British Association in Cheltenham which he titled "The Manufacture of Iron Without Fuel." It was published in full in The Times. The Bessemer process involved using oxygen in air blown through molten pig iron to burn off the impurities and thus create steel

According to his autobiography Bessemer first started working with an ordinary reverberatory furnace but during a test a couple of pig ingots got off to the side of ladle and were sitting above it in the hot air of the furnace. When Bessemer went to push them into the ladle he found that they were steel shells: the hot air alone had converted the outer parts of the ingots to steel. This crucial discovery led him to completely redesign his furnace so that it would force high-pressure air through the molten iron using special air pumps. Intuitively this would seem to be folly because it would cool the iron, but due to exothermic oxidation both the silicon and carbon react with the excess oxygen leaving the surrounding molten iron even hotter, facilitating the conversion to steel.

An American, William Kelly, had held a patent for "a system of air blowing the carbon out of pig iron" a method of steel production known as the pneumatic process of steel-making. Air is blown through molten pig iron to oxidise and remove unwanted impurities. Bankruptcy forced Kelly to sell his patent to Bessemer, who had been working on a similar process for making steel. Bessemer patented "a de-carbonization process, utilizing a blast of air" in 1855.

Development in the invention of Bessemer Converter

The Dowlais Iron Company  was the first licensee of the Bessemer process, constructing the world’s most powerful rolling mill in 1857, and producing its first Bessemer steel in 1865.

In 1868, a process named as Siemens-Martin process was developed. It used 'Open-Hearth' Furnace to produce Steel.  The Siemens-Martin process complemented rather than replaced the Bessemer process. It is slower and thus easier to control. It also permits the melting and refining of large amounts of scrap steel, further lowering steel production costs and recycling an otherwise trouble waste material. In the US, steel production using the inefficient open hearth furnaces had stopped by 1992.

The Basic Oxygen Steel-making replaced the open hearth furnace. The first Basic Oxygen Steel-making process was the LD (Linz-Donawitz) process developed in 1952 by voestalpine AG in Linz, Austria. The LD-converter is named after the Austrian place-names Linz and Donawitz (a district of Leoben). The LD converter is a refined version of the Bessemer converter where blowing of air is replaced with blowing oxygen.

Role of  Bessemer Converter in the improvement of human life

• The Bessemer process revolutionized the world. Prior to its widespread use steel was far too expensive to use in most applications, and wrought iron was used throughout the industrial revolution. After its introduction steel and wrought iron were similarly priced, and all manufacture turned to steel. Bessemer process was the first inexpensive industrial process for the mass-production of steel from molten pig iron.

• The availability of cheap steel allowed large bridges to be built and enabled the construction of rail-roads, skyscrapers, and large ships.

• Other important steel products were 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.

• The dominant steel manufacturing technology of today is an extension and refinement of the one developed by Bessemer.