The first step in the manufacturing process is pig iron. The blast furnace is a simple furnace constructed for the manufacture of pig iron. Why is it called “pig iron”? Simply because in the early days of iron and steelmaking, when the blast furnace was tapped, the molten iron ran out of the tap hole and into small interconnected molds. The molds looked like a family of little pigs, hence the term (that has remained) pig iron.
Once the ore has been crushed into small, fine pellet-like pieces, washed and separated by in-line magnets, the crushed powder is then moved into what is known as separation cells. The purpose of the separation cells is to further remove impurities that are still contaminating the crushed ore.
The crushed, washed and powdered ore is brought to the blast furnace in small steel charging cars. It then rides up the side of the furnace on a specially constructed inclined track to the top of the blast furnace and is dumped into the furnace. At the same time, coke and limestone (fluxing agent) is added to the crushed and cleaned ore and dropped into the top of the blast furnace.
Gas-fired burners located near the base of the furnace are ignited and the combusted gases go directly into the blast furnace. As a result of the generated heat from the burners, the iron ore begins to melt and trickle down into the collection area of the blast furnace. Now the iron is in its molten state at a process temperature of approximately 3200°F in the lower reaches of the blast furnace.
Iron is the heaviest thing in the blast furnace, so its natural tendency is to melt and trickle to the bottom. In addition, preheated air is fed to the blast furnace burners to assist in generating the melting conditions within the blast furnace.
Once the base of the blast furnace has collected its charge of molten metal, it is “tapped”. This simply means that the molten iron is poured into the casting area of pigs, or it can be deposited (in the molten condition) into specially constructed rail cars for transportation in the molten state to the next stage of manufacture.
Pig iron is almost a useless commodity on its own. However, it is the first step in steelmaking. It can be a good foundational material for the manufacture of cast iron. Once it is transported to the mill in the molten condition, it is then used as the base material (iron) to make many different types of steel and cast irons.