A blast furnace is a type of metallurgical furnace used for smelting to produce industrial metals pig iron, but others such as lead or copper. Blast refers to the combustion air being "forced" or supplied above atmospheric pressure. In a blast furnace, fuel and flux are continuously supplied through the top of the furnace, while a hot blast of air is blown into the lower section of the furnace through a series of pipes called tuyeres, so that the chemical reactions take place throughout the furnace as the material falls downward; the end products are molten metal and slag phases tapped from the bottom, waste gases exiting from the top of the furnace. The downward flow of the ore and flux in contact with an upflow of hot, carbon monoxide-rich combustion gases is a countercurrent exchange and chemical reaction process. In contrast, air furnaces are aspirated by the convection of hot gases in a chimney flue. According to this broad definition, bloomeries for iron, blowing houses for tin, smelt mills for lead would be classified as blast furnaces.
However, the term has been limited to those used for smelting iron ore to produce pig iron, an intermediate material used in the production of commercial iron and steel, the shaft furnaces used in combination with sinter plants in base metals smelting. Cast iron has been found in China dating to the 5th century BC, but the earliest extant blast furnaces in China date to the 1st century AD and in the West from the High Middle Ages, they spread from the region around Namur in Wallonia in the late 15th century, being introduced to England in 1491. The fuel used in these was invariably charcoal; the successful substitution of coke for charcoal is attributed to English inventor Abraham Darby in 1709. The efficiency of the process was further enhanced by the practice of preheating the combustion air, patented by Scottish inventor James Beaumont Neilson in 1828. Archaeological evidence shows that bloomeries appeared in China around 800 BC, it was thought that the Chinese started casting iron right from the beginning, but this theory has since been debunked by the discovery of'more than ten' iron digging implements found in the tomb of Duke Jing of Qin, whose tomb is located in Fengxiang County, Shaanxi.
There is however no evidence of the bloomery in China after the appearance of the blast furnace and cast iron. In China blast furnaces produced cast iron, either converted into finished implements in a cupola furnace, or turned into wrought iron in a fining hearth. Although cast iron farm tools and weapons were widespread in China by the 5th century BC, employing workforces of over 200 men in iron smelters from the 3rd century onward, the earliest extant blast furnaces were built date to the Han Dynasty in the 1st century AD; these early furnaces used phosphorus-containing minerals as a flux. Chinese blast furnaces ranged from around two to ten meters depending on the region; the largest ones were found in modern Sichuan and Guangdong, while the'dwarf" blast furnaces were found in Dabieshan. In construction, they are both around the same level of technological sophistication The effectiveness of the Chinese blast furnace was enhanced during this period by the engineer Du Shi, who applied the power of waterwheels to piston-bellows in forging cast iron.
Donald Wagner suggests that early blast furnace and cast iron production evolved from furnaces used to melt bronze. Though, iron was essential to military success by the time the State of Qin had unified China. Usage of the blast and cupola furnace remained widespread during Tang Dynasties. By the 11th century, the Song Dynasty Chinese iron industry made a switch of resources from charcoal to coke in casting iron and steel, sparing thousands of acres of woodland from felling; this may have happened as early as the 4th century AD. The primary advantage of the early blast furnace was in large scale production and making iron implements more available to peasants. Cast iron is more brittle than wrought iron or steel, which required additional fining and cementation or co-fusion to produce, but for menial activities such as farming it sufficed. By using the blast furnace, it was possible to produce larger quantities of tools such as ploughshares more efficiently than the bloomery. In areas where quality was important, such as warfare, wrought iron and steel were preferred.
Nearly all Han period weapons are made of wrought iron or steel, with the exception of axe-heads, of which many are made of cast iron. Blast furnaces were later used to produce gunpowder weapons such as cast iron bomb shells and cast iron cannons during the Song dynasty; the simplest forge, known as the Corsican, was used prior to the advent of Christianity. Examples of improved bloomeries are the Stückofen or the Catalan forge, which remained until the beginning of the 19th century; the Catalan forge was invented in Catalonia, during the 8th century. Instead of using natural draught, air was pumped in by a trompe, resulting in better quality iron and an increased capacity; this pumping of airstream in with bellows is known as cold blast, it increases the fuel efficiency of the bloomery and improves yield. The Catalan forges can be built bigger than natural draught bloomeries; the oldest known blast furnaces in the West were built in Dürstel in Switzerland, the Märkische Sauerland in Germany, at Lapphyttan in Sweden, where the complex was active between 1205 and 1300.
At Noraskog in the Swedish parish of Järnboås, there have been fou
A cupola or cupola furnace is a melting device used in foundries that can be used to melt cast iron, Ni-resist iron and some bronzes. The cupola can be made any practical size; the size of a cupola can range from 1.5 to 13 feet. The overall shape is cylindrical and the equipment is arranged vertically supported by four legs; the overall look is similar to a large smokestack. The bottom of the cylinder is fitted with doors which swing down and out to'drop bottom'; the top where gases escape can be open or fitted with a cap to prevent rain from entering the cupola. To control emissions a cupola may be fitted with a cap, designed to pull the gases into a device to cool the gases and remove particulate matter; the shell of the cupola, being made of steel, has refractory brick and plastic refractory patching material lining it. The bottom is lined in a similar manner but a clay and sand mixture may be used, as this lining is temporary. Finely divided coal can be mixed with the clay lining so when heated the coal decomposes and the bod becomes friable, easing the opening up of the tap holes.
The bottom lining is ` rammed' against the bottom doors. Some cupolas are fitted with cooling jackets to keep the sides cool and with oxygen injection to make the coke fire burn hotter. Cupola furnaces were built in China as early as the Warring States period, although Donald Wagner writes that some iron ore melted in the blast furnace may have been cast directly into molds. During the Han Dynasty, most, if not all, iron smelted in the blast furnace was remelted in a cupola furnace. A modern cupola furnace was made by French scientist and entomologist René-Antoine Ferchault de Réaumur around 1720. To begin a production run, called a'cupola campaign', the furnace is filled with layers of coke and ignited with torches; some smaller cupolas may be ignited with wood to start the coke burning. When the coke is ignited, air is introduced to the coke bed through ports in the sides called tuyeres. Wood, charcoal, or biomass may be used as fuel for the cupola’s fire. Flammable gases can be added to air and blown through the tuyere section of the furnace to add fuel to the fire.
When the coke is hot, solid pieces of metal are charged into the furnace through an opening in the top. The metal is alternated with additional layers of fresh coke. Limestone is added to act as a flux; as the heat rises within the stack the metal is melted. It drips down through the coke bed to collect in a pool at the bottom, just above the bottom doors. During the melting process a thermodynamic reaction takes place between the blast air; the carbon in the coke combines with the oxygen in the air to form carbon monoxide. The carbon monoxide further burns to form carbon dioxide; some of the carbon is picked up by the falling droplets of molten metal which raises the carbon content of the iron. Silicon carbide and ferromanganese briquettes may be added to the charge materials; the silicon carbide dissociates and carbon and silicon enters into the molten metal. The ferromanganese melts and is combined into the pool of liquid iron in the'well' at the bottom of the cupola. Additions to the molten iron such as ferromanganese, Silicon carbide and other alloying agents are used to alter the molten iron to conform to the needs of the castings at hand.
Pea-sized raw ore of metals such as iron, copper and those containing precious metals can be melted in the cupola or blast furnace furnace. Vannoccio Biringuccio describes how to separate metals and slag by pouring the melted ore contents from the furnace into a small pool peeling off layers of slag or metal from the top as they cool into a solid; the operator of the cupola is known as the "cupola tender" or "furnace master". During the operation of a tapped cupola the tender observes the amount of iron rising in the well of the cupola; when the metal level is sufficiently high, the cupola tender opens the "tap hole" to let the metal flow into a ladle or other container to hold the molten metal. When enough metal is drawn off the "tap hole" is plugged with a refractory plug made of clay; the cupola tender observes the furnace through the sight peep sight in the tuyeres. Slag will rise to the top of the pool of iron being formed. A slag hole, located higher up on the cylinder of the furnace, to the rear or side of the tap hole, is opened to let the slag flow out.
The viscosity is low and the red hot molten slag will flow easily. Sometimes the slag which runs out the slag hole is collected in a small cup shaped tool, allowed to cool and harden, it is visually examined. With acid refractory lined cupolas a greenish colored slag means the fluxing is adequate. In basic refractory lined cupolas the slag is brown. After the cupola has produced enough metal to supply the foundry with its needs, the bottom is opened, or'dropped' and the remaining materials fall to the floor between the legs; this material is subsequently removed. The cupola can be used over. A'campaign' may last a few hours, a day, weeks or months; when the operation is over, the blast is shut off and the prop under the bottom door is knocked down so that the bottom plates swing open. This enables the cupola remains to drop into a bucket. T
Ferrous metallurgy is the metallurgy of iron and its alloys. It began far back in prehistory; the earliest surviving iron artifacts, from the 4th millennium BC in Egypt, were made from meteoritic iron-nickel. It is not known when or where the smelting of iron from ores began, but by the end of the 2nd millennium BC iron was being produced from iron ores from Sub-Saharan Africa to China; the use of wrought iron was known by the 1st millennium BC, its spread marked the Iron Age. During the medieval period, means were found in Europe of producing wrought iron from cast iron using finery forges. For all these processes, charcoal was required as fuel. Steel was first produced in antiquity as an alloy, its process of production, Wootz steel, was exported before the 4th century BC from India to ancient China, the Middle East and Europe. Archaeological evidence of cast iron appears in 5th-century BC China. New methods of producing it by carburizing bars of iron in the cementation process were devised in the 17th century.
During the Industrial Revolution, new methods of producing bar iron by substituting coke for charcoal were devised and these were applied to produce steel, creating a new era of increased use of iron and steel that some contemporaries described as a new Iron Age. In the late 1850s, Henry Bessemer invented a new steelmaking process, that involved blowing air through molten pig iron to burn off carbon, so to produce mild steel; this and other 19th-century and steel making processes have displaced wrought iron. Today, wrought iron is no longer produced on a commercial scale, having been displaced by the functionally equivalent mild or low carbon steel; the largest and most modern underground iron ore mine in the world is located in Kiruna, Norrbotten County, Lapland. The mine, owned by Luossavaara-Kiirunavaara AB, a large Swedish mining company, has an annual production capacity of over 26 million tonnes of iron ore. Iron was extracted from iron–nickel alloys, which comprise about 6% of all meteorites that fall on the Earth.
That source can be identified with certainty because of the unique crystalline features of that material, which are preserved when the metal is worked cold or at low temperature. Those artifacts include, for example, a bead from the 5th millennium BC found in Iran and spear tips and ornaments from Ancient Egypt and Sumer around 4000 BC; these early uses appear to have been ceremonial or ornamental. Meteoritic iron is rare, the metal was very expensive more expensive than gold; the early Hittites are known to have bartered iron for silver, at a rate of 40 times the iron's weight, with the Old Assyrian Empire in the first centuries of the second millennium BC. Meteoric iron was fashioned into tools in the Arctic, about the year 1000, when the Thule people of Greenland began making harpoons, knives and other edged tools from pieces of the Cape York meteorite. Pea-size bits of metal were cold-hammered into disks and fitted to a bone handle; these artifacts were used as trade goods with other Arctic peoples: tools made from the Cape York meteorite have been found in archaeological sites more than 1,000 miles distant.
When the American polar explorer Robert Peary shipped the largest piece of the meteorite to the American Museum of Natural History in New York City in 1897, it still weighed over 33 tons. Another example of a late use of meteoritic iron is an adze from around 1000 AD found in Sweden. Native iron in the metallic state occurs as small inclusions in certain basalt rocks. Besides meteoritic iron, Thule people of Greenland have used native iron from the Disko region. Iron smelting—the extraction of usable metal from oxidized iron ores—is more difficult than tin and copper smelting. While these metals and their alloys can be cold-worked or melted in simple furnaces and cast into molds, smelted iron requires hot-working and can be melted only in specially designed furnaces. Iron is a common impurity in copper ores and iron ore was sometimes used as a flux, thus it is not surprising that humans mastered the technology of smelted iron only after several millennia of bronze metallurgy; the place and time for the discovery of iron smelting is not known because of the difficulty of distinguishing metal extracted from nickel-containing ores from hot-worked meteoritic iron.
The archaeological evidence seems to point to the Middle East area, during the Bronze Age in the 3rd millennium BC. However, wrought iron artifacts remained a rarity until the 12th century BC; the Iron Age is conventionally defined by the widespread replacement of bronze weapons and tools with those of iron and steel. That transition happened at different times as the technology spread. Mesopotamia was into the Iron Age by 900 BC. Although Egypt produced iron artifacts, bronze remained dominant until its conquest by Assyria in 663 BC; the Iron Age began in India about 1200 BC, in Central Europe about 600 BC, in China about 300 BC. Around 500 BC, the Nubians who had learned from the Assyrians the use of iron and were expelled from Egypt, became major manufacturers and exporters of iron. One of the earliest smelted iron artifacts, a dagger with an iron blade found in a Hattic tomb in Anatolia, dated from 2500 BC. About 1500 BC, increasing numbers of non-meteoritic, smelted iron objects appeared in Mesopotamia and Egypt.
Nineteen meteoric iron objects were found in the tomb of Egyptian ruler Tutankhamun, who died in 1323 BC, including an iron dagger with a golden hilt, an Eye of Horus, the mummy's head-stand and sixteen
Smelting is a process of applying heat to ore in order to extract out a base metal. It is a form of extractive metallurgy, it is used to extract many metals from their ores, including silver, iron and other base metals. Smelting uses heat and a chemical reducing agent to decompose the ore, driving off other elements as gases or slag and leaving the metal base behind; the reducing agent is a source of carbon, such as coke—or, in earlier times, charcoal. The carbon removes oxygen from the ore; the carbon thus oxidizes in two stages, producing first carbon monoxide and carbon dioxide. As most ores are impure, it is necessary to use flux, such as limestone, to remove the accompanying rock gangue as slag. Plants for the electrolytic reduction of aluminium are generally referred to as aluminium smelters. Labourers working in the smelting industry have reported respiratory illnesses inhibiting their ability to perform the physical tasks demanded by their jobs. Smelting involves more than just melting the metal out of its ore.
Most ores are the chemical compound of the metal and other elements, such as oxygen, sulfur, or carbon and oxygen together. To extract the metal, workers must make these compounds undergo a chemical reaction. Smelting therefore consists of using suitable reducing substances that combine with those oxidizing elements to free the metal. In the case of carbonates and sulfides, a process called "roasting" drives out the unwanted carbon or sulfur, leaving an oxide, which can be directly reduced. Roasting is carried out in an oxidizing environment. A few practical examples: Malachite, a common ore of copper, is copper carbonate hydroxide Cu22; this mineral undergoes thermal decomposition to 2CuO, CO2, H2O in several stages between 250 °C and 350 °C. The carbon dioxide and water are expelled into the atmosphere, leaving copper oxide, which can be directly reduced to copper as described in the following section titled Reduction. Galena, the most common mineral of lead, is lead sulfide; the sulfide is oxidized to a sulfite, which thermally decomposes into lead oxide and sulfur dioxide gas.
The sulfur dioxide is expelled, the lead oxide is reduced as below. Reduction is the final, high-temperature step in smelting, in which the oxide becomes the elemental metal. A reducing environment pulls the final oxygen atoms from the raw metal; the required temperature varies over a large range, both in absolute terms and in terms of the melting point of the base metal. Examples: Iron oxide becomes metallic iron at 1250 °C 300 degrees below iron's melting point of 1538 °C. Mercuric oxide becomes vaporous mercury near 550 °C 600 degrees above mercury's melting point of -38 °C. Flux and slag can provide a secondary service after the reduction step is complete: they provide a molten cover on the purified metal, preventing contact with oxygen while still hot enough to oxidize; this prevents impurities from forming in the metal. Metal workers use fluxes in smelting for several purposes, chief among them catalyzing the desired reactions and chemically binding to unwanted impurities or reaction products.
Calcium oxide, in the form of lime, was used for this purpose, since it could react with the carbon dioxide and sulfur dioxide produced during roasting and smelting to keep them out of the working environment. Of the seven metals known in antiquity, only gold occurred in native form in the natural environment; the others – copper, silver, tin and mercury – occur as minerals, though copper is found in its native state in commercially significant quantities. These minerals are carbonates, sulfides, or oxides of the metal, mixed with other components such as silica and alumina. Roasting the carbonate and sulfide minerals in air converts them to oxides; the oxides, in turn, are smelted into the metal. Carbon monoxide was the reducing agent of choice for smelting, it is produced during the heating process, as a gas comes into intimate contact with the ore. In the Old World, humans learned to smelt metals in prehistoric times, more than 8000 years ago; the discovery and use of the "useful" metals — copper and bronze at first iron a few millennia — had an enormous impact on human society.
The impact was so pervasive that scholars traditionally divide ancient history into Stone Age, Bronze Age, Iron Age. In the Americas, pre-Inca civilizations of the central Andes in Peru had mastered the smelting of copper and silver at least six centuries before the first Europeans arrived in the 16th century, while never mastering the smelting of metals such as iron for use with weapon-craft. In the Old World, the first metals smelted were lead; the earliest known cast lead beads were found in the Çatal Höyük site in Anatolia, dated from about 6500 BC, but the metal may have been known earlier. Since the discovery happened several millennia before the invention of writing, there is no written record about how it was made; however and lead can be smelted by placing the ores in a wood fire, leaving the possibility that the discovery may have occurred by accident. Lead is a common metal, but its discovery had little impact in the ancient world, it is too soft to use for structural elements or weapons, though its high density relative to other metals makes it ideal for sling projectiles.
However, since it was
Joule heating known as Ohmic heating and resistive heating, is the process by which the passage of an electric current through a conductor produces heat. Joule's first law known as the Joule–Lenz law, states that the power of heating generated by an electrical conductor is proportional to the product of its resistance and the square of the current: P ∝ I 2 R Joule heating affects the whole electric conductor, unlike the Peltier effect which transfers heat from one electrical junction to another. James Prescott Joule first published in December 1840, an abstract in the Proceedings of the Royal Society, suggesting that heat could be generated by an electrical current. Joule immersed a length of wire in a fixed mass of water and measured the temperature rise due to a known current flowing through the wire for a 30 minute period. By varying the current and the length of the wire he deduced that the heat produced was proportional to the square of the current multiplied by the electrical resistance of the immersed wire.
In 1841 and 1842, subsequent experiments showed that the amount of heat generated was proportional to the chemical energy used in the voltaic pile that generated the current. This led Joule to reject the caloric theory in favor of the mechanical theory of heat. Resistive heating was independently studied by Heinrich Lenz in 1842; the SI unit of energy was subsequently named the joule and given the symbol J. The known unit of power, the watt, is equivalent to one joule per second. Joule heating is caused by the body of the conductor. A voltage difference between two points of a conductor creates an electric field that accelerates charge carriers in the direction of the electric field, giving them kinetic energy; when the charged particles collide with ions in the conductor, the particles are scattered. Thus, energy from the electrical field is converted into thermal energy. Joule heating is referred to as ohmic heating or resistive heating because of its relationship to Ohm's Law, it forms the basis for the large number of practical applications involving electric heating.
However, in applications where heating is an unwanted by-product of current use the diversion of energy is referred to as resistive loss. The use of high voltages in electric power transmission systems is designed to reduce such losses in cabling by operating with commensurately lower currents; the ring circuits, or ring mains, used in UK homes are another example, where power is delivered to outlets at lower currents, thus reducing Joule heating in the wires. Joule heating does not occur in superconducting materials, as these materials have zero electrical resistance in the superconducting state. Resistors create electrical noise, called Johnson–Nyquist noise. There is an intimate relationship between Johnson–Nyquist noise and Joule heating, explained by the fluctuation-dissipation theorem; the most fundamental formula for Joule heating is the generalized power equation: P = I where P is the power converted from electrical energy to thermal energy, I is the current travelling through the resistor or other element, V A − V B is the voltage drop across the element.
The explanation of this formula is: = × Assuming the element behaves as a perfect resistor and that the power is converted into heat, the formula can be re-written by substituting Ohm's law, V = I ∗ R, into the generalized power equation: P = I V = I 2 R = V 2 / R where R is the resistance. When current varies, as it does in AC circuits, P = U I where t is time and P is the instantaneous power being converted from electrical energy to heat. Far more the average power is of more interest than the instantaneous power: P a v g = U rms I rms = I rms 2 R = U rms 2 / R where "avg" denotes average over one or more cycles, "rms" denotes root mean square; these formulas are valid for an ideal resistor, with zero reactance. If the reactance is nonzero, the formulas are modified: P a v g = U rms I rms cos ϕ = I rms 2 Re = U rms 2 Re