MANUFACTURE OF STEEL
Three basic raw materials are needed in large quantities for the production of steel
- Iron Ore
- Coal
- Lime stone
The first step in the steel manufacture begins at the blast furnace. To separate iron from iron ore► coke (substance when gas is taken out of coal), limestone and dolomite are charged into the blast furnace
Temperature raised to 1600oF. This high temp causes the coke to burn and melt the iron. This red hot iron drained at an opening at the base of the furnace. Natural gas is often injected to reduce the amount of coke consumed. The dolomite and limestone combine with the non-ferrous elements of the ore to form a slag, which floats on the top of the molten iron and is removed separately. The product of the blast furnace is known as “Pig Iron” the basic ingredient of steel
It takes 2 tons of iron ore, 2/3 ton of coke, ½ ton of limestone, 4 tons of air to make 1 ton of Pig iron. Some of the pig iron goes to the foundries to make iron castings, but the vast majority is re melted and used in the production of steel in steel furnace. Several types of furnaces are used for the production of steel including
- Open Hearth Furnace
- Bessemer Furnace
- Electric Furnace
- New Oxygen Furnace
OPEN-HEARTH FURNACE
The open hearth furnace is called “open” because the charge is exposed to the sweep of flames over the surface. Molten pig iron, scrap iron and steel, limestone and high grade iron ore are charged into an open-hearth furnace. Limestone is put in first to act as a flux, then the scrap and iron ore are introduced. When they have began to melt, molten pig iron is added. The ingredients are heated using natural gas a fuel. Refining takes from 3½ to 7 hours at a temperature up to 30000F. During this period samples are taken and checked. Impurities are removed by limestone. Burnt lime may be added to hasten(fasten) the absorption of sulfur and phosphorus. When the molten steel is ready, it is drawn from the furnace in giant ladles, from which it is poured into “ingot moulds”. The moulds containing the ingots are then transported for cooling. The moulds are then removed, and the ingots placed in pits, where they are reheated to a uniform temperature high enough for rolling. Hot ingots goes into a blooming mill, where variety of products are made from these ingots, including sheets, rods, plates, pipes, wires, nails etc.