There is a period of human history, called the Iron Age.In those days, replacing stone tools came to similar products made from iron.While this metal in small amounts and smelted much earlier.This was mainly the iron extracted from meteorites.For example, on the monuments of Iraq and Syria have been found iron objects.A "birth date" of these monuments - the 27th century BC.But the real technological revolution has occurred when people have learned to smelt iron from iron ore.At first it learned to do in West Asia, then this technology came to Greece, Italy and gradually spread throughout Europe.This process has evolved over many centuries, and gradually iron and steel became the basis for other sectors of the economy.
And the main process in the foundry industry is the blast furnace process.And it happens in the blast furnace.Modern blast furnace - is a powerful and high-performance unit and there a huge number of charge and pig iron blast occurs.Metallurgical charge is a mixture of raw materials, which is loaded into the furnace for further melting.This iron ore is combined with the fuel.A fuel without which the blast furnace iron becomes impossible, usually a coke, which is sometimes replaced with coal dust and natural gas.A coke - the same coal which is calcined without access of air.It has a high combustion temperature and a good fuel for blast process.
blast furnace is designed so that the production of iron in it is a continuous process.The iron oxide and carbon is continuously moving the shaft furnace from the top down, and it moves toward the air.The carbon contained in the coke, which in this process has a dual role.When burned it heats itself oven to the desired temperature and at the same time forms a gas CO.And via this gas iron oxide is converted to metal.In this reaction, carbon dioxide is obtained, which is given in the upper part of the furnace and molten metal which is produced in the bottom thereof.And this process is stopped only when needed to make repairs of blast furnace.Typically, such repairs are changing the internal brickwork (lining), which eventually burn out.
And the very production of pig iron in a furnace can be described by simple equations.Air that is blown into the furnace, come into contact with the coke and "forces" it burn.Last burning, forming carbon monoxide, which is in the gaseous state.This gas plays a major role in the reduction of iron oxide.A recovery that happens when the temperature of the mixture of ore and coke up to 600-700 degrees.This results in a firm but spongy and porous iron.Then it moves to the lower, hotter part of the stove (forge), where melted and discharged to the outside.
But these equations can be used only for an ideal system.That is an iron oxide should be clean, free of impurities, the same applies to the carbon.A purging air shall consist of one oxygen.Then iron production goes smoothly and according to the scheme described above.But actually contains much iron ore (50%) of waste material, which consists mainly of silicates.And the air, as everyone knows, consists essentially of nitrogen, which simply passes through the furnace, the unreacted.But the main problem lies precisely in silicates.And so they were separated from the iron and withdrawn from the furnace, these silicates should be brought to the liquid state.A melt silicates only after interaction with lime CaO.And for this purpose in the furnace together with ore is charged a certain amount of limestone (flux).It is placed in the top of the blast furnace, and he, after the respective reactions is converted into lime.And silicate impurities iron ore reacting with this lime melted to a liquid state and removed from the blast furnace slag.And slag that is slightly less than that of cast iron.
And after a solidifying slag turns to dark glassy material.And in the recent past, near metallurgical enterprises could see heaps of this stuff.But now the production of pig iron has become a kind of waste-free, because the slag is nowadays widely used.It is used as a filler for concrete and as rail ballast.From it produce slag wool, and with it is anti-skid coating roads.A pig iron derived from a blast furnace is already the basis for the production of steel, and the foundation of all ferrous metals.