|
Arabic
Bengali
Chinese
English
French
German
Hebrew
Hindi
Italian
Japanese
Korean
Malay
Polish
Portuguese
Spanish
Turkish
Ukrainian
Vietnamese|
HISTORY OF TECHNOLOGY, TECHNOLOGY, OBJECTS AROUND US
Cast steel. History of invention and production
Directory / The history of technology, technology, objects around us In the history of iron metallurgy, there were three revolutionary upheavals that had a profound impact on the entire course of human history: the first took place in ancient times, when raw-hearth furnaces appeared; the second occurred in the Middle Ages, after the discovery of the alteration process; the third occurred in the second half of the XNUMXth century and was associated with the start of the production of cast steel. Steel at all times remained the most necessary and desired product of iron metallurgy, because only it possessed the hardness and strength required for the manufacture of tools, weapons and machine parts. But before turning into a steel product, the metal had to undergo a number of labor-intensive operations. First, iron was smelted from ore. Then the cast iron was reduced to soft iron. Finally, by long-term forging of an iron ring, the necessary steel part was obtained from it (or only a blank for it, which was then subjected to final finishing on metal-cutting machines). The production of soft iron, and in particular forging, has long been the bottleneck in the iron processing process. They took the most effort and time, and the results were far from always satisfactory. This problem became especially acute in the XNUMXth century, when the demand for cheap steel increased sharply. Naturally, many scientists and inventors had an idea, which Bessemer later expressed: how to get a metal with the properties of iron and steel, but in liquid form, so that it can be used for casting? The solution of this problem required several decades of hard work of many metallurgists. Along the way, several important discoveries and inventions were made, each of which constituted an era in the history of iron processing. Until the end of the XNUMXth century, the conversion of cast iron into soft malleable iron took place only in bloomery furnaces. This method, however, was inconvenient in many respects. The metal obtained during it was heterogeneous - in places it approached in its qualities to malleable iron, in places - to steel. In addition, the work required a lot of time and physical effort. Since the fuel (coal) was in direct contact with iron, very high requirements were imposed on it, because any impurities affected the quality of the final product. The consumption of coal was very high (on average, it took up to 1 kg of coal to restore 4 kg of iron). In the largest forges, it was possible to get no more than 24 kg of iron in 400 hours. Meanwhile, the market demanded more and more iron and steel. To meet these requests, it was necessary to find a more perfect way to remake cast iron. A significant step forward on this path was the process of puddling proposed in 1784 by the Englishman Cort in a specially designed oven.
Puddling is the metallurgical process of converting cast iron into soft low-carbon iron (wrought iron). The essence of the process consists in melting cast iron in a special furnace without contact with fuel and stirring the molten metal with special rods, on which particles of molten iron stick, gradually forming a dough-like crust weighing up to 40-60 kg. At the exit from the puddling oven, the obtained kritsa is forged and sent for flattening. Pudding iron welds well, has high ductility, contains few impurities (phosphorus, sulfur, non-metallic inclusions). The principal device of the puddling oven was as follows. Fuel was burned in the furnace. The combustion products through the stone threshold fell into the working space of the furnace, where the loaded iron with ferruginous slags was located on the hearth. The slag under the action of the flame passed into a pasty state and partially melted. With an increase in temperature, the cast iron began to melt and its impurities burned out due to the oxygen contained in the slags. Thus, the cast iron was decarburized, that is, it turned into a spongy iron cry. An important difference between a puddling furnace and a bloomery furnace was that it allowed any fuel to be used as fuel, including cheap unrefined coal, and its volume was much larger.
Pudding ovens made iron cheaper. At the same time, unlike the screaming horns, Kort's oven did not require forced blowing. Air access and good draft were achieved thanks to a high pipe. This was one of the reasons why pudding ovens became widespread all over the world. However, a significant drawback of these furnaces was that the air blew only the upper part of the cast iron. In order for the reduction of iron to proceed evenly and throughout the volume, it was necessary to periodically open the furnace and stir the cast iron. It was hard manual labor. In addition, since the strength and capabilities of the worker were limited, the furnace could not be too large. (To allow stirring, Kort provided two pipes, one of which was under the furnace, and the second - at the end of the furnace. It was opened at the moment when it was required to reduce the temperature.) By the middle of the XNUMXth century, puddling ovens no longer met the new needs of industry. To keep up with demand, several furnaces had to be built for each large blast furnace (on average, ten puddling furnaces served one blast furnace). This increased the cost and made production more difficult. Many inventors have thought about how to replace puddling with a better way to recover iron. Before others, this problem was solved by the English engineer Bessemer. Bessemer came to metallurgy after many years of work on the improvement of artillery pieces and shells. He set himself the goal of finding a way to produce high quality cast steel from which cannons could be cast. Observing many times the melting of cast iron, he noticed that solid reduced iron is formed first of all near the blower pipes. This led him to the idea of obtaining steel by intensively blowing air through molten cast iron. Bessemer conducted his first experiments in a closed crucible, which he heated in a forge with coke. The result exceeded the wildest expectations. In less than an hour of blowing, he turned iron into first-class steel. In addition, further experiments have shown that there is no need to introduce heat into the metallurgical process from outside. The fact is that cast iron contains its own combustible material as impurities: silicon, manganese, carbon - in total about 45 kg of combustible materials for each ton of cast iron. By their combustion, they made it possible to significantly increase the melting temperature and obtain steel in a liquid state. In 1856, Bessemer publicly demonstrated the fixed converter he had invented. The converter had the form of a low vertical stove, closed on top with a vault with a hole for the exit of gases. On the side of the furnace there was a second hole for pouring cast iron. Finished steel was released through a hole in the lower part of the furnace (during the operation of the converter, it was clogged with clay). Blower tubes (tuyeres) were located near the hearth of the furnace. Since the converter was stationary, the purge was started before the iron was poured in. Otherwise, the metal would flood the tuyeres. For the same reason, it was necessary to blow through until all the metal was released. The whole process took no more than 20 minutes. The slightest delay in the release gave a marriage. This inconvenience, as well as a number of other shortcomings of the stationary converter, forced Bessemer to switch to a rotary kiln. In 1860, he took out a patent for a new converter design, which has survived in general terms to this day.
The Bessemer method was a real revolution in the field of metallurgy. In 8-10 minutes, his converter turned 10-15 tons of cast iron into ductile iron or steel, which would previously have taken several days of operation of a puddling furnace or several months of operation of the former bloomery. However, after the Bessemer method began to be applied in industrial conditions, its results turned out to be worse than in the laboratory, and the steel came out of very poor quality. For two years Bessemer tried to solve this problem and finally found out that in his experiments cast iron contained little phosphorus, while in England cast iron smelted from iron ores with a high phosphorus content was widely used. Meanwhile, phosphorus and sulfur did not burn out along with other impurities; from cast iron, they fell into steel and significantly reduced its quality. This, and besides the high cost of the converter, led to the fact that the Bessemer method was very slowly introduced into production. And 15 years later in England, most of the cast iron was melted down in puddling furnaces. Converters are much more widely used in Germany and the USA.
Along with the Bessemer method of steel production, the open-hearth method soon acquired a huge role. Its essence was that cast iron was fused with scrap iron in a special regenerative furnace. This furnace was invented and built in 1861 by German engineers Friedrich and William Siemens for the needs of the glass industry, but it was most widely used in metallurgy. The composition of the furnace included gas producers (or gas generators), the furnace itself with heat regenerators (or regenerators) for heating gas and air, and a foundry compartment (yard).
Generators and regenerators were interconnected by a special system of channels for gas, air and combustion products. The latter were discharged into a chimney up to 40 m high, which provided the necessary draft. The generators were located under the hearth or on the sides of the furnace. The regenerators were special chambers for heating gas and air. Special variable valves directed gas and air into one chamber or another, and the combustion products were discharged into the pipe. The combustion took place in the following way. Gas and air were each heated in their own chamber, and then entered the melting space, where combustion took place. The combustion products, having passed over the bottom of the furnace, rushed into the regenerators and gave up most of their heat to the regenerator masonry, and then went into the chimney. In order for the process to proceed continuously, with the help of valves, air and gas were directed first to one pair of regenerators, then to another. As a result of such thoughtful heat exchange, the temperature in the furnace reached 1600 degrees, that is, it exceeded the melting temperature of pure carbon-free iron. The creation of high-temperature furnaces opened up new horizons for metallurgy. By the middle of the 1864th century, all industrial countries had huge stocks of scrap iron. Due to its high refractoriness, it could not be used in production. French engineers Émile and Pierre Martin (father and son) proposed to fuse this scrap iron with cast iron in a regenerative furnace and thus obtain steel. In XNUMX, at the Sireil plant, under the leadership of Siemens, they carried out the first successful smelting. Then this method began to be applied everywhere. Open-hearth furnaces were cheaper than converters and therefore were more widely used. However, neither the Bessemer nor the open-hearth method made it possible to obtain high-quality steel from ore containing sulfur and phosphorus. This problem remained unresolved for a decade and a half, until in 1878 the English metallurgist Sidney Thomas came up with the idea of adding up to 10-15% lime to the converter. In this case, slags were formed that could retain phosphorus in strong chemical compounds. As a result, phosphorus burned out along with other unnecessary impurities, and cast iron turned into high-quality steel. The significance of Thomas' invention was enormous. It made it possible to produce steel on a large scale from phosphorus-containing ores, which were mined in large quantities in Europe. In general, the introduction of the Bessemer and open-hearth processes made it possible to produce steel in unlimited quantities. Cast steel quickly won its place in industry, and since the 70s of the XIX century, wrought iron almost completely fell into disuse. Already in the first five years after the introduction of open-hearth and Bessemer production, world steel output increased by 60%. Author: Ryzhov K.V.
Artificial leather for touch emulation
15.04.2024 Petgugu Global cat litter
15.04.2024 The attractiveness of caring men
14.04.2024
▪ All HSPA multimedia features on a single chip ▪ The biological clock regulates the functioning of the immune system ▪ New multi-standard TV audio processors and audio demodulators ▪ Invented fabric that mosquitoes won't bite through
▪ section of the site RF power amplifiers. Article selection ▪ article And I did a good deed in the midst of reigning evil. Popular expression ▪ article Sharpening machine. home workshop ▪ Article Glass cups. Focus Secret
Home page | Library | Articles | Website map | Site Reviews
www.diagram.com.ua |
We recommend interesting articles Section 
See other articles Section 
Latest news of science and technology, new electronics:
All languages of this page