Production of cast iron - the basis of ferrous metallurgy

There is a period in the history of mankind called the Iron Age. In those days, analogous products made of iron replaced the stone tools of labor. Although this metal in small quantities smelted and much earlier. Basically it was iron, mined from meteorites. For example, iron objects were found on the monuments of Iraq and Syria. And the "date of birth" of these monuments is the 27th century BC. But a real technological revolution happened already when people learned how to smelt iron from iron ore. First, it learned to do in Western Asia, then this technology got to Greece, Italy and gradually spread throughout Europe. This process was perfected over many centuries, and gradually the production of cast iron and steel became the basis for other branches of the national economy.

And the main process in the foundry industry is the blast furnace process. And he happens in a blast furnace. The modern blast furnace is a powerful and high-performance unit and in it from the huge amount of charge and blast is the smelting of cast iron. A smelting metallurgy is called a mixture of raw materials, which is fed into the furnace for further melting. This is iron ore in combination with fuel. And fuel, without which the blast furnace production of iron becomes impossible, is usually coke, which is sometimes replaced by coal dust or natural gas. A coke - this is the same coal, which was calcined without air access. It has a high combustion temperature and is a good fuel for blast furnace processes.

The blast furnace is designed so that the production of pig iron in it is an ongoing process. Iron oxide and carbon continuously move down the shaft of the furnace, and air moves towards them. Carbon is contained in coke, which in this process plays a dual role. When burned, it heats the furnace itself to the desired temperature and at the same time forms a CO gas. And with the help of this gas, the iron oxide is converted into a metal. As a result of this reaction, carbon dioxide is produced, which is discharged at the top of the furnace and a liquid metal that is released at the bottom of it. And this process is stopped only when it is required to repair the blast furnace. Usually at such repair change internal brickwork (lining) which eventually burns out.

And the production of cast iron in such a furnace can be described with the help of simple equations. The air that is blown into the furnace comes into contact with the coke and "makes" it burn. The last burned, forms carbon monoxide, which is in the gaseous state. This gas plays a major role in the reduction of iron oxide. And this recovery occurs when the temperature of a mixture of ore and coke reaches 600-700 degrees. As a result, solid, but spongy and porous iron is formed. Then it descends into the lower, hotter part of the furnace (bugle), where it melts and is released outside.

But these equations can only be used for an ideal system. That is, iron oxide should be pure, without impurities, the same applies to carbon. And the air for blowing must consist of one oxygen. Then the production of cast iron will go smoothly and according to the scheme described above. But in fact, iron ore contains a lot (more than 50%) of an empty rock, which mainly consists of silicates. And the air, as everyone knows, basically consists of nitrogen, which simply passes through the furnace without reacting. But the main problem is precisely in silicates. And that they are separated from the iron and removed from the furnace, these silicates must be brought to a liquid state. And silicates are melted only after interaction with lime CaO. And for this, a quantity of limestone (flux) is loaded into the furnace together with the ore. It is located in the upper part of the blast furnace, and after a corresponding reaction it turns into lime. And the silicate impurities of iron ore, reacting with this lime, are melted to the liquid state and are discharged from the blast furnace in the form of slag. And the slag of this is slightly less than the cast iron itself.

And after solidification, such a slag turns into a glassy material of a dark color. And in the recent past, near the metallurgical enterprises, you could see whole mountains of this material. But now the production of pig iron became in some way wasteless, because slag in our time has found wide application. It is used as a filler for concrete and as a railway ballast. From it, the slag is manufactured, and with its help an anti-skid coating of the roads is made. A pig iron produced from a blast furnace is already the basis for the production of steel, and the basis for all of the iron and steel industry.