This process involves the oxidation of impurities of pig iron by oxygen of the air into volatile gases of slag formation. It is followed by the addition of required amount of carbon and other alloying elements. The process is carried out in steal shaped furnace called Bessemer converter.The furnace is made of steel plates and is internally lined with silica (SiO2) /or Magnesia (MgO) bricks depending upon the nature of impurities present in pig iron.
When the impurities present are Si, P or S. a ,basic lining of magnesia (MgO), used the process is called basic Bessemer process. On the other hand. if the impurities present are Si or Mn, a lining of silica (SiO3) bricks is used, the process is called acid Bessemer process. The Bessemer converter can be tilted in any position and has a number of holes at the bottom to admit the blast of hot air. The molten pig iron is added into the Bessemer converter. A blast of hot air is allowed to enter through the holes. As the air passes through the molten metal, it oxidizes the impurities.
After the removal of the impurities, carbon present in the pig iron is oxidized to carbon monoxide which bums with a blue flame at the mouth of the converter. When carbon monoxide flame subsides, a calculated amount of spiegeleisn (an alloy of iron, manganese and carbon) is added. The blast of air is turned on again for a few minutes to homogenize the mass. At the end, the converter is tilted to pour out the molten mass.