Cast Iron
Pig iron along with scrap iron, coke and limestone is melted in a vertical furnace called cupola. Here also the carbon and other impurities present oxidise in presence of a little amount of air, to form slag. The molten iron obtained from cupola furnace can be cast into moulds. It is, therefore, known as cast iron. It consists of 93-94% Fe, 2-4% carbon and a little of S, P, Si and Mn impurities. It is vary hard and brittle. It is cast into covers of manholes, drain-pipes, frames of machines etc.'
Wrought Iron
Wrought iron is the purest form of iron containing not more than 0 • 2 peri jnt carbon and 0-3 percent of other impurities, i.e., sulphur, phosphorus, silicon and manganese.
Manufacture
It is obtained from cast iron by removing the major portion of its impurities by the well known puddling process. The cast iron along with some scrap iron is heated on the hearth of a reverberatory furnace lined with haematite. Fe203. The hot gases and flames reflected from the roof of the furnace falls upon the charge placed on the hearth. The cast iron melts down and the molten mass is stirred or puddled at intervals by means of a long pole introduced through an inlet in the wall of the furnace. The haematite supplies the oxygen required to oxidise the carbon, sulphur, silicon, manganese and phosphorus present in the cast iron.
Carbon and sulphur are oxidised to carbon dioxide and sulphur dioxide, respectively. Silicon and manganese are oxidised to silica and manganous oxide, which combine to form manganous silicate.
3Si + 2Fe203 —* 3Si02 + 4Fe 3Mn + Fe203 —» 3MnO + 2Fe MnO + Si02 —» MnSi03
Slag
Phosphorus is oxidised to phosphorus pentoxide which forms ferric phosphate slag with haematite.
P205 + Fe203 —* 2FeP04
Slag
As the impurities are eliminated, the melting point of the metal rises and iron becomes pasty. The pasty mass is stirred which forms "balls" or "blooms" which are spongy in texture due to large amounts of slag. The balls are taken out from the furnace and the slag is squeezed out by hammering. Finally, iron is rolled into sheets or forged into bars.
Wrought iron is soft, grey, tough and can be welded. It is malleable and has a fibrous structure due to the presence of thin films of slag between layers of pure iron. The presence of slag makes it extremely tough and resistant towards rusting
and corrosion. It softens at 1000°C and melts at 1530°C. It is used to make articles which are subjected to sudden and repeated stresses such as chains, anchors, wires, bolt, agricultural implements and cores of electromagnets. It has now been largely replaced by mild steel owing to its high cost.
Pig iron along with scrap iron, coke and limestone is melted in a vertical furnace called cupola. Here also the carbon and other impurities present oxidise in presence of a little amount of air, to form slag. The molten iron obtained from cupola furnace can be cast into moulds. It is, therefore, known as cast iron. It consists of 93-94% Fe, 2-4% carbon and a little of S, P, Si and Mn impurities. It is vary hard and brittle. It is cast into covers of manholes, drain-pipes, frames of machines etc.'
Wrought Iron
Wrought iron is the purest form of iron containing not more than 0 • 2 peri jnt carbon and 0-3 percent of other impurities, i.e., sulphur, phosphorus, silicon and manganese.
Manufacture
It is obtained from cast iron by removing the major portion of its impurities by the well known puddling process. The cast iron along with some scrap iron is heated on the hearth of a reverberatory furnace lined with haematite. Fe203. The hot gases and flames reflected from the roof of the furnace falls upon the charge placed on the hearth. The cast iron melts down and the molten mass is stirred or puddled at intervals by means of a long pole introduced through an inlet in the wall of the furnace. The haematite supplies the oxygen required to oxidise the carbon, sulphur, silicon, manganese and phosphorus present in the cast iron.
Carbon and sulphur are oxidised to carbon dioxide and sulphur dioxide, respectively. Silicon and manganese are oxidised to silica and manganous oxide, which combine to form manganous silicate.
3Si + 2Fe203 —* 3Si02 + 4Fe 3Mn + Fe203 —» 3MnO + 2Fe MnO + Si02 —» MnSi03
Slag
Phosphorus is oxidised to phosphorus pentoxide which forms ferric phosphate slag with haematite.
P205 + Fe203 —* 2FeP04
Slag
As the impurities are eliminated, the melting point of the metal rises and iron becomes pasty. The pasty mass is stirred which forms "balls" or "blooms" which are spongy in texture due to large amounts of slag. The balls are taken out from the furnace and the slag is squeezed out by hammering. Finally, iron is rolled into sheets or forged into bars.
Wrought iron is soft, grey, tough and can be welded. It is malleable and has a fibrous structure due to the presence of thin films of slag between layers of pure iron. The presence of slag makes it extremely tough and resistant towards rusting
and corrosion. It softens at 1000°C and melts at 1530°C. It is used to make articles which are subjected to sudden and repeated stresses such as chains, anchors, wires, bolt, agricultural implements and cores of electromagnets. It has now been largely replaced by mild steel owing to its high cost.
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