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HISTORY OF TECHNOLOGY, TECHNOLOGY, OBJECTS AROUND US
Blast furnace. History of invention and production
Directory / The history of technology, technology, objects around us Blast furnace, blast furnace - a large metallurgical, vertically located shaft-type smelting furnace for smelting iron and ferroalloys from iron ore. The most important feature of the blast-furnace process is its continuity throughout the entire furnace campaign (from the construction of the furnace to its "major" repair) and the counterflow of rising tuyere gases with a column of materials continuously descending and growing from above with new portions of the charge.
For many centuries, iron was mined in cheese-blowing furnaces using a method discovered in ancient times. As long as low-melting ores were found in abundance on the surface of the earth, this method fully satisfied the needs of production. But in the Middle Ages, when the demand for iron began to increase, metallurgy increasingly had to use refractory ores. To extract iron from them, a higher “melting” temperature was required. At that time, only two methods were known to increase it: 1) increasing the height of the furnace; 2) increased blast. So gradually, by the XNUMXth century, a higher and more advanced melting furnace was formed from the cheese-making furnace, which received the name shtukofen, that is, "a furnace that makes crackers." Shtukofen were the first step on the way to the blast furnace. They first appeared in iron-rich Styria, then in the Czech Republic and other mining regions. In these furnaces, higher temperatures could be reached and more refractory ores could be processed. The shukofen shaft had the shape of a double truncated cone, tapering towards the top (the so-called upper, open part of the furnace, through which ore and coal were loaded in portions (heads)) and towards the bottom. There was one hole in the wall for a tuyere (a pipe through which air was blown into the furnace with the help of bellows) and for pulling out the chicken. The process of converting ore into iron took place in shtukofen in exactly the same way as in raw-blast furnaces, but there was progress: the closed mine concentrated heat well, and due to its height (up to 3 m), the smelting proceeded more evenly, more slowly and more fully, so that the ore was more used. Regardless of the intentions of the smelters, all three types of iron raw materials were obtained at once in shtukofen: cast iron, which flowed like garbage along with slag, malleable iron in the molds, and steel, which covered the mold with a thin layer. (Recall that iron, steel and cast iron in metallurgy are called the actual alloy of chemical iron with carbon. The difference between them lies in the amount of carbon: for example, in soft bloomery (welded) iron it is no more than 5%, in steel - up to 0, 04%, in cast iron - more than 1%. Despite the fact that the amount of carbon varies within such small limits, iron, steel and cast iron are very different from each other in their properties: iron is a soft metal that lends itself well to forging, steel, on the contrary, is a very hard material that retains excellent cutting qualities; cast iron is a hard and brittle metal that cannot be forged at all. The amount of carbon significantly affects other properties of the metal. In particular, the more it is in the iron, the easier it melts. Pure iron is a fairly refractory metal, while cast iron melts at much lower temperatures.) The advantages of the shukofen were, however, insufficient for all refractory ores. A stronger blow was required. Human forces were no longer enough to maintain the temperature, and a water wheel was used to power the furs. The shaft of the water wheel was equipped with cams planted on it in a breakdown, which pulled back the covers of wedge-shaped leather bellows. For each melting furnace there were two bellows, which worked alternately. The appearance of hydraulic engines and bellows must be attributed to the end of the XNUMXth century, since already in the XNUMXth century many smelters moved down from the mountains and hills to the valleys and river banks. This improvement was the starting point for the largest shift in the technology of metallurgy, as it led to the discovery of cast iron, its foundry and reworking properties. Indeed, the increase in blast affected the entire course of the process. Now such a high temperature has developed in the furnace that the reduction of metal from the ore occurs before slag is formed. Iron began to alloy with carbon and turn into cast iron, which, as noted above, has a lower melting point, so that a completely molten mass (cast iron) began to appear in the furnace instead of the usual viscous flash. At first, this metamorphosis struck the medieval metallurgists very unpleasantly. Frozen cast iron was deprived of all the natural properties of iron, it was not forged, not welded, it was impossible to make durable tools, flexible and sharp weapons from it. Therefore, cast iron was considered a waste of production for a long time and smelters were very hostile to it. However, what was to be done with it? During the recovery of iron from refractory ores, a fair part of it went into cast iron. Do not throw away all this iron along with slag! Gradually, unusable pig iron began to be selected from the cooled slag and allowed into the second remelting, first adding it to the ore, and then on its own. At the same time, it was unexpectedly discovered that cast iron quickly melts in a furnace and, after increased blasting, easily turns into bloomery iron, which in its quality is not only not inferior, but even in many respects better than the iron that was obtained from ore. And since cast iron melts at a lower temperature, this redistribution required less fuel and took less time. Thus, during the XNUMXth century, at first unconsciously and gropingly, and then quite consciously, the greatest discovery in metallurgy was made - the reworking process. It found wide application already in the XNUMXth century in connection with the spread of blast furnaces. Soon, other positive properties were discovered in cast iron. Hard kritz was not easy to get out of the oven. This usually took several hours. Meanwhile, the furnace cooled down, additional fuel was used to heat it up, and extra time was spent. It was much easier to release molten iron from the furnace. The furnace did not have time to cool down and it could be immediately loaded with a new portion of ore and coal. The process could go on continuously. In addition, cast iron had excellent casting qualities. (Recall that for many centuries the only way to process iron was forging.) By the middle of the XIV century, the first rough castings from it were attributed. With the development of artillery, the use of cast iron expanded. At first, it was used for casting cannonballs, and then for casting individual parts of the cannons themselves. However, until the end of the XNUMXth century, cast iron was still of poor quality - heterogeneous, insufficiently liquid, with traces of slag. Rough and unpretentious tombstones, hammers, furnace boilers and other uncomplicated products came out of it. Cast iron required some changes in the design of the furnace; the so-called blauofen (blowing furnaces) appeared, representing the next step towards the blast furnace. They were distinguished by a greater height (5-6 m) than shtukofen, and allowed the continuity of melting at a very high temperature. True, the idea that the iron-making process can be divided into two stages (that is, cast iron is continuously smelted in one furnace, and cast iron is converted into iron in the other) did not come immediately. Blauofen produced both iron and cast iron at the same time. When the melt was completed, the slag was released through an opening located below the tuyere. After cooling, it was crushed and cast iron pellets were separated. The kritsa was pulled out with large tongs and a crowbar, and then processed with a hammer. The largest kritsy weighed up to 40 pounds. In addition, up to 20 pounds of cast iron was pulled out of the furnace. One heat lasted 15 hours. It took 3 hours to extract the chicken, and 4-5 hours to prepare the furnace for melting. Finally came up with the idea of a two-stage smelting process. Improved blauofen turned into a new type of furnace - a blast furnace, which was intended exclusively for the production of pig iron. Together with them, the reworking process was finally recognized. The cheese-making process began to be replaced everywhere by the two-stage method of iron processing. First, cast iron was obtained from the ore, then, during the secondary remelting of cast iron, iron. The first stage was called the domain process, the second - the critical redistribution.
The oldest blast furnaces appeared in the Siegerland (Westphalia) in the second half of the 4th century. Their designs differed from the Blauofen in three ways: a higher shaft height, a stronger blower, and an increased volume of the upper part of the shaft. In these furnaces, a significant increase in temperature was achieved and an even longer even smelting of the ore was achieved. At first they built blast furnaces with a closed chest, but soon the front wall was opened and the hearth was expanded, obtaining a blast furnace with an open chest. Such a blast furnace at a height of 5 m produced up to 1600 kg of pig iron per day. Pig iron was processed into iron in a bloomery, similar in design to a cheese-blast furnace. The operation began with the loading of charcoal and the supply of blast. After the charcoal flared up near the nozzle, cast-iron ingots were placed. Under the action of high temperature, the cast iron melted, flowed down drop by drop, passed through the area opposite the tuyeres and lost part of the carbon here. As a result, the metal thickened and passed from the molten state into a pasty mass of low-carbon iron. This mass was lifted by crowbars to the nozzle. Under the influence of blast, carbon was further burned out, and the metal again settled on the bottom of the hearth quickly became soft, easily weldable. Gradually, a lump was formed at the bottom - a cry weighing 50-100 kg or more, which was removed from the hearth for forging under a hammer in order to compact it and squeeze out liquid slag. The whole process took 1 to 2 hours. About 1 ton of metal could be obtained per day in a bloomery furnace, and the yield of finished bloomery iron was 90-92% of the iron weight. The quality of bloomery iron was higher than raw iron, since it contained less slag. The transition from a single-stage (raw-dough) process to a two-stage (blast-furnace and blooming) process made it possible to increase labor productivity several times. The increased demand for the metal was met. But soon metallurgy met with difficulties of a different kind. The smelting of iron required a huge amount of fuel. Over several centuries, many trees have been cut down in Europe and thousands of hectares of forest have been destroyed. In some states, laws have been passed prohibiting uncontrolled logging. This issue was especially acute in England. Due to the lack of charcoal, the British were forced to import most of the iron they needed from abroad. In 1619, Dodley first used coal in smelting. However, the widespread use of coal was hindered by the presence of sulfur in it, which interferes with the good production of iron. It was not until 1735 that Derby found a way to remove sulfur from coal, when Derby found a way to absorb sulfur using quicklime during heat treatment of coal in closed crucibles. So a new reducing agent was obtained - coke.
Author: Ryzhov K.V.
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