.The different manufacturing processes of steel
. manufacturing process of steel by the bessemer process
. distinguish between acid process and basic process
Manufacturing processes
The different manufacturing processes of steel
-Bessemer process
-L. D process
-Electric process
-Open hearth process
Bessemer process
Sir Henry Bessemer, a British engineer invented this process of converting molten pig-iron to steel using a large pear shaped container. This is called the Bessemer converter.
It is a method of producing steel by blasting compressed air through molten iron and burning out the excess carbon and other impurities. This does not use any source of heat other than obtained from the oxidising process used to remove carbon and other impurities.
The three stages of this process are
-the preliminary stage
(The slag formation )
-the boil stage
(The brilliant flame blowing period)
-the finishing stage
(The reddish smoke period )
The molten pig iare from the blast furnace is poured into the converter. Then the blast of air at 150 to 250 KN/m2(killo Newton /m2) is directed into the molten metal, and the converter is rotated into an upright position. The conversion stage commence now.
At the preliminary stage, the oxygen of the blast oxidises the iron to ferrous oxide. As a slag, the ferrous oxide mixes with the metal. The silicon and manganese, due to their affinity for oxygen, are seperated as oxides and go into the slag. During this reaction, a large amount of heat is generated which increases the temparature from 1250°c to 1525°c. This stage lasts for 3 to 4 minutes.
The 2nd stage helps the burning of carbon from the molten bath. The dissolved carbon is oxidised by the ferrous oxide of the slag. At the same time, carbon monoxide will be burning at the nose of the converter with a dazzling white flame. This elimination of carbon takes place for about 8 to 12 minutes. The 3rd stage starts with the subsiding of the flame. It means that the carbon has been practically removed from the charge. This stage lasts for one or two minutes. Then the converter is brought to a horizontal position. To eliminate oxygen and to bring silicon, manganese and carbon content of the steel to a specific limit, de oxiders like ferro manganese, ferro silicon or aluminum are added to the metal bath.
The Bessemer process has the following disadvantages.
The steel produced by the Bessemer process will have an increased oxygen content which will impair its mechanical properties. Due to this reason, it cannot be used for producing cutting tools, spring and parts subject to impact, load etc..
When the Bessemer converter is line with silicous refractory material,this process is called acid process.
When the converter is lined with a basic refractory, it is called a basic process or thomas process.
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