MANUFACTURE AND PROPERTIES OF WROUGHT IRON :

Suitable Pig Iron is melted in the hearth of a Puddling furnace (a furnace having an open hearth to which air can be admitted) and after the charge is melted,, additions of millscales (iron oxides) are made to further the oxidation. Silicon and manganese oxidise first since they have the greatest affinities for oxygen,and form an iron-manganese silicate slag on the surface of molten iron. The carbon is then begin to oxidise as the puddler stirs the mill-scale into the charge,, and causes violent agitation as the bubbles of carbon monoxide burst through the slag with spurts of blue flame called "Puddlers Caudles". Finally,, when all the silicon, manganese, carbon and phosphorus have been oxidised, almost pure iron remains in the furnace. The melting point of pure iron is 1537°C whereas that of pig iron charged was only about 1150°C. Since the furnace temperature is only bewteen 1300-1400°C it follows that as pure iron is formed it must solidify.

When this happens the puddler collects the pasty iron together into balls weighing about 80 lb each and withdraws then from the furnace. They are transferred together with much entangled slag to the forming hammer, where much of the entrapped slag is expelled. After rolling, the crude bars are cut and piled together in a reheating furnace and again forged to make the slag distribution more even. The remaining slag is thus elongated into fibres along the direction of rolling.

Typical composition of wroughtiron is carbon : 0.02-0.03%, Silicon : 0.02-0.10%, Sulphur : 0.008-0.02%, Manganese : Nil-0.02%, Phosphorus : 0.05-0-25% Slag : 0.05-1.50% Iron - Balance.

Wrought iron is a highly refitted iron with a small amount of slag forged out into fibres. The iron content is 99%. The slag-characteristic of wrought iron is useful in black smithing operations and gives the material its peculiar fibrous structure, which diminishes the effect of fatigue caused by shock and vibration.

It is tough, malleable and ductile and has an ultimate strength, of 150N/Sq.mm. It cannot be melted but at a white heat, it becomes soft enough to take any shape under the hammer, i.e., it can be forged. It can also be welded readily. It can withstand sudden and excessive shock without permanent injury. It can neither be hardened nor tempered like steel. It rusts more quickly than cast iron but stands salt water better.

Bolts and nuts, Anchor chains, Crane hooks, Couplings, pipe and pipe fittings, plates, sheets, bars and boiler tubes are the principal forms in which wrought iron is used.

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