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- Iscritto il: 31/03/2010, 18:26
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Steel production in quantity 'low cost' attributed to Henry Bessemer (1813-98) and Robert Mushet (1811-91). Bessemer was a prolific inventor with a highly developed business sense.
Having had some success with inventions such as the manufacture of gold paint and the consolidation of graphite mines of pencils, Bessemer comincio'ad interested in steel production, led by well-known low resistance of iron cannons used in the Crimean War .
After several experiments, Bessemer had the revolutionary idea of blowing air through the liquid pig iron to remove excess carbon and other cosi'il impurezze.Egli got its main patent in 1855 but, in its original form, the Bessemer steel was of low quality 'because' and sulfur oxides contained in excess.
However, in 1856 Mushet received in turn a series of patents for a method very similar to that differed from Bessemer mainly for the fact that the impurities that were not burned by the air blowing, you could control with the addition of a substance called "spiegeleisen", a special cast iron produced in Germany which contained manganese.
It was the addition of propio Manganese, in the last phases of the blow, which happened assicuro'il the Bessemer process.
The Bessemer steel is produced in an apparatus called the Bessemer converter, which consists of a crucible or pear-shaped container mounted on pivots so that it can be reversed.
It has no external heat source and the bottom of the drive There is a public swerie holes or nozzles through which air puo'soffiare.
To run the converter, it is reversed so that the mouth is under gettodi dell'altoforno exit and you will pay a charge which is 5 to 30 tons of molten pig iron (ie 'iron at 1200 degrees which contains about 4.5% carbon and small amounts' of silicon and manganese).
Since the drive is reversed, the charge ends up on the bottom of the container without clogging the nozzle holes.
At this point it blows air through these holes and allow the converter back into an upright position so that 'the air is forced to bubble through the molten iron, the air oxidizes so' before manganese and silicon in the iron, forming a slag floating on the surface charge. It controls the process by observing the color and character of the flame produced at the mouth of the converter.
At this stage are short and reddish-brown.
After a few minutes manganese and silicon are completely oxidized and the air begins to remove the carbon at this stage the flames become whitish-yellow and lengthen disproportionately.
Finally, when the carbon was removed, the flames fade and close the puffs of air.
During blowing, the combustion of carbon, manganese and silicon which together amount to about 6% of the charge, produces a heat quantita'di remarkable that not only is sufficient to raise the temperature of the charge itself and then to offset the increase the melting temperature due to loss of carbon, but also enough to overheat the whole were it not for small quantita'di scrap iron are added to cool the environment, thus avoiding 'damaging the refractory lining of the converter.
At the end of blowing, you get the "blown metal, field pure iron that is added after the solid carbon, manganese, and sometimes silicon.
Manganese is used to adjust the level of sulfur that is removed in the process.
Sulphur 'a nuisance in steelmaking because' it does not oxidize, but instead form iron sulphide FeS, which has peculiarita'di be soluble in molten iron but not iron solidified.
Consequently, during cooling, the iron sulfide separates the edges of the crystals and weakens the steel.
The addition of manganese in MnS FeS transforms, and that 'none in the steel liquid and then ends up in slag, and also decreases the solubility' oxygen in the steel.