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Blast furnace


Blast furnace
For many centuries the iron was mined in syrodutnyh furnaces way open even in ancient times. While on the ground in abundant fusible ore, this method is quite satisfied the needs of production. But in the Middle Ages, when iron demand began to increase, in metallurgy it is increasingly had to use a refractory ore. For the extraction of iron was required a higher temperature, "melting". While only two ways know its improvement: 1) an increase in the furnace height; 2) strengthening the blast.
So gradually the XIII century of syrodutnoy kiln formed a higher and more advanced smelting furnace, dubbed shtukofena, meaning "furnace, fabricate Critz." Shtukofeny were first step on the way to the blast furnace. They first appeared in the iron-rich Styria, and then in the Czech Republic and other mining areas. These furnaces can be achieved and a higher process temperature refractory ore more. Mine shtukofena was shaped double truncated cone tapers towards the throat (the so-called upper, open part of the furnace, through which portions (Kolosha) loaded ore and coal) and to the bottom. The wall had one opening for the lance (pipe through which a furnace by bellows pumped air) and for pulling Kritsa. The process of alteration of the ore into iron occurred in shtukofenah exactly the same as in syrodutnyh kilns, but there has been progress: a closed mine well concentrating the heat, and thanks to its height (up to 3, 5 m) fusion was evenly slower and fuller, so that the ore provided more used. Regardless of the intentions of smelters in shtukofenah obtained once all three types of iron sources: cast iron, which flowed like garbage together with the slag, malleable iron and steel in Critz, a thin layer covered the Critz. (Recall that the iron, steel and iron metallurgy is called the proper alloy chemistry of iron and carbon difference between them is the amount of carbon: in soft bloomery (welded) iron it is not more than 0, 04% in steel - up 1. 7% of the iron - a 1, 7% Although the amount of carbon varies such minor extent on the properties of iron, steel and cast iron are very different from each other:. iron is a soft metal, is well amenable forged steel in contrast, very solid, perfectly preserves the cutting quality;... cast iron - hard and brittle metal, it is not amenable to forging carbon number significantly affects other properties of the metal in particular, the more it is in iron, the easier it melts Pure iron - sufficiently refractory metal and cast iron melts at much lower temperatures).

Benefits shtukofena, however, were not enough for all refractory ores. It took a strong blow. Human forces to maintain the temperature turned out to be no longer sufficient, and to drive the bellows began to be used a water wheel. waterwheel shaft supplied planted it in the breakdown of the cams, which delayed the cap canted leather bellows. two bottles there for each smelter, working alternately. The advent of hydraulic motors and bellows should be referred to the end of the XIV century, as already in the XV century, many foundry therefore shifted from the mountains and hills down - in the valleys and on river banks. This improvement was the starting point for a major shift in the technology industry, as led to the discovery of iron, its casting and peredelochnyh properties.

Indeed, the strengthening of the blast impact on the entire course of the process. Now furnace developed such high temperature that the reduction of the metal ores from happening before the formed slag. Iron alloyed with carbon begun and converted to the iron, which, as noted above, has a lower melting point, so that instead of a conventional furnace become viscous Kritsa appear completely molten mass (iron). First, this metamorphosis is very unpleasant impression of medieval metallurgists. Frozen pig iron was stripped of all the natural properties of iron, it is not forged, weld, from it was impossible to make durable tools, flexible and sharp weapons. Therefore iron long considered garbage production and smelters very hostile to him. However, what it was to do with it? When recovering iron from refractory ores a fair part of it went into the iron Do not throw out all that iron together with the slag! Gradually, the waste iron steel slag is cooled down to choose from and let the second melted, adding it to the first grade, and then on his own. This unexpectedly discovered that the iron quickly melted in the furnace and then reinforced blast easily converted into bloomery iron, which in terms of quality, not only is not inferior, but even in many respects better than that of iron, which is obtained from the ore. And as the cast iron melts at a lower temperature, redistribution of the required less fuel and less time. So during the XV century, first unconsciously and groping, and then fully realized, it was made the greatest discovery in metallurgy - peredelochny process. Widespread use he found already in the XVI century in connection with the spread of blast furnaces.

Soon discovered iron and other positive properties. The solid Critz was not easy to get it out of the oven. This usually takes a few hours. Meanwhile, the oven cool down, warm-up it went extra fuel, spent extra time. Release of furnace molten iron was much easier. The oven did not have time to cool down, and it can be immediately load new batch of ore and coal. The process can take place without interruption. In addition, cast iron has excellent castability. (Recall that for many centuries the only way of processing iron was forged.) By the middle of the XIV century, is the first rough castings from it. With the development of the use of iron artillery expanded. First, it began to be used on the casting cores, and then casting parts guns themselves. However, until the end of the XV century iron it was still poor quality - heterogeneous, insufficiently liquid, with traces of ash. From it came out rough and unpretentious gravestone products, hammers, furnace boilers and other uncomplicated products.

Casting of iron required some changes in the furnace device; there were the so-called blauofeny (ancillary furnace), represents the next step in the blast furnace. They differed greater height (6.5 meters) than shtukofeny and allow continuity at very high melting temperatures. However, the idea that the process of manufacture of iron can be divided into two stages (ie in a furnace to smelt iron continuously, and the other - to adapt the pig iron), did not come immediately. In blauofenah received both iron and cast iron. When melting ended, slag discharged through the hole located below the lance. After cooling, it was crushed and separated blood oranges iron. Critz get more ticks and scrap, and then treated with a hammer. Kritsa The largest weighed 40 pounds. In addition, it pulled out of the furnace up to 20 tons of pig iron. A melting lasted 15 hours. On the recovery of Kritsa needed 3 hours to prepare a furnace for smelting - 4-5 hours.

Finally we came to the idea of ​​a two-stage smelting process. Advanced blauofeny turned into a new kind of oven - the blast, which was intended solely to produce pig iron. Along with them was finally recognized peredelochny process. Syrodutny process became widely displaced two-step processing of iron. First of iron ore were prepared, then the secondary smelting iron - iron. The first stage is called the blast furnace process, the second - bloomery redistribution. The oldest blast furnaces appeared in Siegerland (Westphalia) in the second half of the XV century. Constructions differ from their blauofenov three features: the shaft height greater, more powerful blower unit and the increased volume of the upper part of the shaft. These furnaces achieved a significant rise in temperature and has a longer smooth smelting ore. First, we build a blast furnace with a closed chest, but soon discovered the front wall and expanded the horn blast furnace received with open chest. Such a blast furnace at the height of 4 to 5 m per day gave 1600 kg cast iron.

Recycles pig iron in the finery of a similar device with syrodutnoy oven. The operation began with a load of charcoal and feed blast. After charcoal flared up near the nozzle, put iron ingots. Under the influence of high temperature iron melt, drop by drop trickled down, passed through the area against the lances and lost here of the carbon. As a result, the metal to thicken and from the molten state into a dough-like mass of low-carbon iron. This mass is lifted crowbars to a nozzle. Under the impact of the blast there was a further carbon burnout, and again settled to the bottom of the hearth metal quickly makes a soft, easily weldable. Gradually formed at the bottom of com - bloom weighing 50-100 kg and more, which are extracted from the crucible for forging under the hammer in order to compact it and extruding the molten slag. The whole process takes from 1 to 2 hours. The day finery could receive about 1 ton of metal, and the output of the finished ball iron amounted to 90-92% of the weight of iron. Quality ball iron was higher syrodutnogo, as it contained less slag.

The transition from the single-stage (syrodutnogo) to the two-step process (domain and bloomery) allowed several times to raise the productivity of labor. The increased demand for the metal was satisfied. But soon Metallurgy met with difficulties of a different kind. iron smelting demanded a huge amount of fuel. For centuries, Europe was cut down many trees and destroyed thousands of hectares of forest. In some states, laws prohibiting uncontrolled felling were adopted. Especially sharply this question was in England. Due to the lack of charcoal the British were forced most of the iron they need to import from abroad. In 1619 Dodley first used in the smelting of coal. However, the widespread use of coal hampered the presence of sulfur, which prevents a good dressing of iron. Clean coal sulfur learned only in 1735, when Derby found a way to absorb the sulfur by means of quicklime in the thermal coal treatment in closed crucibles. Thus it was obtained a new reducing agent - coke.

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