Puddling Process of Wrought Iron

Wrought iron is virtually pure iron, containing a large number of minute threads of slag lying parallel to each other, thereby giving the metal a fibrous appearance when broken. It contains negligible carbon percentage and therefore, does not harden when quenched in water. Wrought iron is produced by puddling process in reverberatory furnace.

Puddling Process             

Wrought iron is produced in reverberatory furnace by puddling process which is similar to open hearth furnace with combustion taking place at one end only. The furnace is lined with iron oxide. (in the form of mill scale or ore).  Pig iron is   charged   into the furnace. The carbon present in pig iron is melted and eliminated by the iron oxide lining. When practically all of the carbon and other impurities have been eliminated, the metal has a higher melting point and begins to form into a pasty mass. This pasty mass of metal and slag is well stirred (puddling) and formed into a bar, which is then removed from the furnace. The bulk of the slag is then squeezed from this mass by means of a mechanical squeezer and the iron is then rolled into bars. Now the material is a mixture of high purity iron and some slag (about 0.7%).

Composition of Different Types of Iron

Type of Iron Carbon% Sulphur% Silicon% Manganese% Phosphorus% Iron%
Pig Iron 1-4.5 <1 1-2 0.1-1.5 0.5-2 95-96
Grey Cast iron 2.5-3.8 0.1 1.1-2.8 0.4-1 0.15 95-96
White Cast Iron 4.5 0.1 0.5-1.5 0.2-0.8 0.18 94
Mottled Cast Iron. 3.50 0.75 0.75 0.75 0.75 93.5
Nodular cast iron 3.2-4.1 <0.03 1-2.78 0.3-0.8 <0.10 94.5
Malleable cast iron 2.2-2.8 0.03- 0.1 0.7- 1.1 0.3 – 0.4 0.10 97.5
Wrought Iron 0.02-0.03 0.08-0.02 0.02-0.01 0.02 0.05-0.25 98.5-99.5

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