The production of iron

The iron ore is refined in the blast furnace to produce pig-iron (diagram to right). The charge is made up of three parts, iron ore, coke and limestone in variable proportions according to the grade of ore. It is taken to the top of the furnace by skips and emptied continuously into the double bell arrangement. This valve system prevents heat loss.

Heated air is blasted into the bottom of the furnace from the bustle pipes through the tuyeres, the oxygen making the coke burn fiercely.

The limestone starts to decompose and the iron and impurities begin to separate. This is called 'reduction'. The limestone absorbs the impurities into a molten waste called slag.

The heavy liquid falls to the bottom of the hearth, while the lighter slag floats on top. Periodically, the slag and iron are tapped off separately. The slag which is run off first is used for ballast and road making. The waste gases are collected and passed through a cleaning plant before being used to pre-heat the blast.

The process runs continuously for years, stopping only when the fire-brick lining needs replacing.

From the blast furnace, the molten iron is used in one of two ways. It is either fed into a casting machine, producing small bars of iron termed ‘pigs’, known collectively as 'pig-iron', for future resmelting in an electric arc furnace or refining into cast iron. The other method in the modern integrated steelworks, it is conveyed in molten state by brick lined steel ladles, straight to the steel making furnace.

The pig iron produced has a carbon content of about 3-4 together with small quantities of impurities.