Blog

Iron

History:

 

It’s unclear how and where primitive has found iron ore, smelted it and got the metal, iron. But the evidence suggests that the early men have known iron since 2400 or more years ago. It seems that at first, the early men have used the steady asteroids, which contain iron and nickel, and ascribing the heaven metal to iron by primitives emphasizes the matter. Later on, iron ore was known.

 

General View:

Iron is an element with the atomic letter of Fe, the atomic weight of 56, about 5% and the fourth available element of abundance rate in the earth crust. The stones, which have more than 20% iron, are known as iron ore. Extracting metallic iron from iron ore is done by a chemical action. It means iron oxide ores are released by carbon, oxidizing and iron element. For centuries, charcoal was used as an oxidizer, but since 1907 when a turning point appeared in iron steel affair, coke, which is also used as the most important fuel of blast furnace, replaced it.

 

To get one tone of pig iron, about 1.5 – 3 tons of iron ore, 900 – 1000 kg coke and 5 – 6 tons air is necessary. Limestone is employed as the fluxing agent in blast furnace. Steel and iron melting, firstly was done in primitive furnaces, which were made of stone or brick, blast was used for air and furnace height got up to 10 meters. Nevertheless, today by the invention of machines and entering under pressure air into the furnace, the height and diameter of the furnace is increased, new blast furnaces are made of iron plates stabling on some shafts with furnace body height of about 30 meters. Thus, industrial progress and increasing requirement of human beings to better kind of iron have made new blast furnaces.

 

Furnace Fuel:

Fuels in blast furnace do two actions: The action of making heating furnace and the action of oxidization.

They are divided into two major categories:  Natural and Synthetic.

Some natural fuels such as anthracite, bituminous and lynith coals have largely historical rather than economical aspects. Among synthetic fuels, which are coke and charcoal, coke is very important and is used in most of the plants.

The advantages of coke are porosity, solidity, abundance, its more combustibility and its inexpensiveness. To provide coke, several kinds of the coals, in which the available materials are different should be mixed and converted into coke in special furnaces. This action is called as carbonization. Coke chemical compound is 85 -94 percent of carbon and other materials includes volatile materials, ash, sulfur and moisture.

 

The required air for combustion and heating:

As mentioned before, about 5 – 6 tons of air is needed to get one ton of iron ore. Such air is composed of a mixture of two gases. Oxygen and Nitrogen with the ratio of 1 and 4 respectively. In new blast furnaces, air is blown into the furnace by turbine compressors. The turbines work with steam or electricity, and create more and steady swelter pressure. Gas compressors are also used to supply the swelter air of some blast furnaces. In such systems, blast furnaces gas with air got into the machines and is ignited after being compressed by the electric spark. The resulted pressure causes the compressor motor movement.

 

Fluxing Agents:

Fluxing agents are the most important fundamental materials of the blast furnace entrance after iron ore and fuel. Such agents do two actions: Melting the extant impurities in iron ore with a melting point higher than the furnace common temperature.

Some of the elements, which are oxidized with iron ore at the same time, or are dissolved in iron or combined with it, and it’s not possible to be separated, fluxing agents are combined with such impurities before being combined with iron. The sort of the fluxing agents depends on the fundamental materials of furnace entrance. If iron ore is alkali, the fluxing agent should be acidic (such as SiO2, silica). If iron ore is acidic, the fluxing agent should be alkali (such as limestone, dolomite and phosphate stones). When we don’t want the slag to be very fluid, neutral fluxing agents such as fluorspar with low melting point are used.

 

Blast furnace Slag:

Slag is a molten material, which is made through the interaction between fluxing agents, iron ore, fuel and the extant oxidizing impurities in metal, and by such interactions, the impurities that are not to be in cast iron are separated from iron ore.

The slag main fundamental materials are: Al203, MgO, CaO, SiO2 that consist 90% slag altogether. The remain 10% are FeO, MnO, MnS, CaS and …

 

The Slag Usages:

According to the chemical composition, physical properties and its cooling method, slag acquires different usages. Slag is cooled through three ways, and gets three forms depending on the cooling method:

Air-cooled slag is crushed and screened, and is used for the following purposes:

Hollow perpendicular blocks, road infrastructure, glassy sandstone to make ceramics, sewerage, Binder asphalt, etc.

The slag granulated with water is used for the following matters: cement, insulation, road infrastructure, constructional concrete materials, constructional blocks, railroad embankment, and other embankments and so on.

 

Light Slag:

The light slag usages are:

Constructional concrete materials, anti-fire materials, ground paving; constructional products as concrete prefabricate parts such as Tiwerestone and so on, bricks, soundproof tiles and partitions.