Some sixty five chemical elements of commercial importance are customarily classified as metals. They are distinguished from other elements by characteristic physical properties, more commonly referred to as metallic properties, such as high melting temperature low specific heat, good electrical and thermal conductivity metallic luster, hardness and the ability to be deformed permanently without fracture. Examples of metals are iron.aluminium, magnesium, lead, tin, nickel, chromium etc.
Metals are found in nature either in the free state as metals, or in the combined state, in the form of their compounds, which are known as “Ores". From these the metals are extracted by various manufacturing processes. Ores are generally obtained in the form of oxides, sulfides, sulfate, carbonates, nitrates. phosphates and silicates.
Manufacture of Pig Iron
Pig iron is the crude impure iron extracted from iron ore and is the basic material from which cast iron, wrought iron ad steel are obtained. Pig iron contains on average about 94% iron, and 4% carbon, the remainder being sulfur, silicon, phosphorous and other impurities.
Pig iron is manufactured by smelting the iron ore in a blast furnace, (See Fig.) so named, as a very high temperature is obtained inside it, by forcing a blast of heated air. The common ores are haematite, magnetite and siderite.
A modern blast furnace is a vertical shaft, about 100 ft. high, having a maximum interior diameter of 30 ft; lined inside with fire bricks; and yields 700 to 1000 tons of pig iron in 24 hours.
Charges of ore, fuel (coke) and flux (lime-stone or dolomite) are intermittently fed into the furnace through a hopper, provided with a “double cup-and-cone” device at the top of the furnace. A high temperature (1300° C to 1650“ C) is obtained near the bottom of the furnace by forcing in a blast of hot air through the blast pipe surrounding the furnace and through tuyeres (“Tweers”). The flux helps the melting of the ore and the removal of the impurities in the form of slag. The slag floating on the surface of the molten mass is removed every two hours through the “draw hole in, the side of the furnace near the bottom. The molten metal is tapped periodically from the base of the furnace into channels and branches formed in the sand bed adjoining the furnace. ' The solidified iron when cooled is broken into short lengths of about,3 ft. and removed. This entails much exhausting manual labor and an alternative method of dealing with the metal is sometimes adopted. It consists of casting into a pig casting machine in which iron molds carried on an endless chain are used and into which the metal is poured whilst the conveyor" is moving.
Due to la great number of impurities present in pig iron, it is weak and brittle and hence it is not used in that condition. Pig iron is only used as the basic material for producing cast iron, wrought iron and steel by suitable processes.
Cast Iron normally contains 3 to 3'5% of Carbon, 0'6 to 25% of Silicon, 0'5 to 09% of Manganese, 0.3 to 1‘% of Phosphorus, 0.8 to 1% of sulfur and the remainder Iron. Cast iron is produced by smelting pig iron with coke and lime-stone» in a small furnace known as “Cupola”. The Cupola, like the blast furnace consists of a cylindrical steel shell, lined with refractory firebricks and is provided with tuyeres and notches from which metal and slag are tapped. Pig Iron is generally mixed with iron and steel scrap in a proportion depending upon the quality of the Cast Iron required. The iron melts land sinks to the bottom of the furnace, and is tapped into a ladle or into the molds. During the process manganese and silicon get oxidized.
Cast Iron is brittle and weak. It has crystalline Structure. It is very hard if chilled. It casts easily, wears to good surface and resists crushing. It is used for marking off and surface tables, vee blocks and frames for workshop machinery.
Manufacture of Wrought Iron
Wrought Iron is iron from which most of the impurities have been removed and is one of the purest forms of iron produced. It contains less than about 0.15% 'carbon. It is produced from pig iron by the Puddling; process which reduces the amount of impurities. Generally pig iron is charged directly to the puddling furnace. The puddling process is carried out in a small, reverberatory furnace, the hearth of which is lined with iron oxide in the form of scale from steel rolling mill or of high grade iron ore. Sometimes preliminary refining operation of pig iron is done by subjecting the molten pig iron to an air blast in order to remove.silicon and most of the phosphorous and to convert the free carbon into combined carbon. The pig iron is melted down and iron oxide is added and thoroughly mixed with the charge. The temperature is allowed to fall and most of the impurities are oxidized and removed in the form of slag. The purified iron has by this time become pasty (pure iron has a higher melting point than pig iron) and is worked up into balls on the bed of the furnace. The balls of iron are removed and the slag still adhering is expelled by hammering squeezing and the balls are then rolled into bars. They are improved in quality by subsequent process of piling, re-heating and re-rolling.
Wrought Iron is ductile, malleable, fairly strong and soft; easily magnetized and welded. It is used for cores of dynamos and lifting chains.
Metals are found in nature either in the free state as metals, or in the combined state, in the form of their compounds, which are known as “Ores". From these the metals are extracted by various manufacturing processes. Ores are generally obtained in the form of oxides, sulfides, sulfate, carbonates, nitrates. phosphates and silicates.
Classification
Metals used in engineering are mainly divided into two classes, ferrous and non-ferrous; A ferrous metal consists mainly of iron, whilst a non-ferrous metal has some other element as its base. Ferrous metals commonly used in engineering are wrought iron,cast iron and steel and non-ferrous metals are aluminium, magnesium, tin, copper etc.Manufacture of Pig Iron
Pig iron is the crude impure iron extracted from iron ore and is the basic material from which cast iron, wrought iron ad steel are obtained. Pig iron contains on average about 94% iron, and 4% carbon, the remainder being sulfur, silicon, phosphorous and other impurities.
Pig iron is manufactured by smelting the iron ore in a blast furnace, (See Fig.) so named, as a very high temperature is obtained inside it, by forcing a blast of heated air. The common ores are haematite, magnetite and siderite.
A modern blast furnace is a vertical shaft, about 100 ft. high, having a maximum interior diameter of 30 ft; lined inside with fire bricks; and yields 700 to 1000 tons of pig iron in 24 hours.
Charges of ore, fuel (coke) and flux (lime-stone or dolomite) are intermittently fed into the furnace through a hopper, provided with a “double cup-and-cone” device at the top of the furnace. A high temperature (1300° C to 1650“ C) is obtained near the bottom of the furnace by forcing in a blast of hot air through the blast pipe surrounding the furnace and through tuyeres (“Tweers”). The flux helps the melting of the ore and the removal of the impurities in the form of slag. The slag floating on the surface of the molten mass is removed every two hours through the “draw hole in, the side of the furnace near the bottom. The molten metal is tapped periodically from the base of the furnace into channels and branches formed in the sand bed adjoining the furnace. ' The solidified iron when cooled is broken into short lengths of about,3 ft. and removed. This entails much exhausting manual labor and an alternative method of dealing with the metal is sometimes adopted. It consists of casting into a pig casting machine in which iron molds carried on an endless chain are used and into which the metal is poured whilst the conveyor" is moving.
Properties and Uses of Pig Iron
Due to la great number of impurities present in pig iron, it is weak and brittle and hence it is not used in that condition. Pig iron is only used as the basic material for producing cast iron, wrought iron and steel by suitable processes.
Manufacture of Cast Iron
Cast Iron normally contains 3 to 3'5% of Carbon, 0'6 to 25% of Silicon, 0'5 to 09% of Manganese, 0.3 to 1‘% of Phosphorus, 0.8 to 1% of sulfur and the remainder Iron. Cast iron is produced by smelting pig iron with coke and lime-stone» in a small furnace known as “Cupola”. The Cupola, like the blast furnace consists of a cylindrical steel shell, lined with refractory firebricks and is provided with tuyeres and notches from which metal and slag are tapped. Pig Iron is generally mixed with iron and steel scrap in a proportion depending upon the quality of the Cast Iron required. The iron melts land sinks to the bottom of the furnace, and is tapped into a ladle or into the molds. During the process manganese and silicon get oxidized.
Properties and Uses of Cast Iron
Cast Iron is brittle and weak. It has crystalline Structure. It is very hard if chilled. It casts easily, wears to good surface and resists crushing. It is used for marking off and surface tables, vee blocks and frames for workshop machinery.
Manufacture of Wrought Iron
Wrought Iron is iron from which most of the impurities have been removed and is one of the purest forms of iron produced. It contains less than about 0.15% 'carbon. It is produced from pig iron by the Puddling; process which reduces the amount of impurities. Generally pig iron is charged directly to the puddling furnace. The puddling process is carried out in a small, reverberatory furnace, the hearth of which is lined with iron oxide in the form of scale from steel rolling mill or of high grade iron ore. Sometimes preliminary refining operation of pig iron is done by subjecting the molten pig iron to an air blast in order to remove.silicon and most of the phosphorous and to convert the free carbon into combined carbon. The pig iron is melted down and iron oxide is added and thoroughly mixed with the charge. The temperature is allowed to fall and most of the impurities are oxidized and removed in the form of slag. The purified iron has by this time become pasty (pure iron has a higher melting point than pig iron) and is worked up into balls on the bed of the furnace. The balls of iron are removed and the slag still adhering is expelled by hammering squeezing and the balls are then rolled into bars. They are improved in quality by subsequent process of piling, re-heating and re-rolling.
Properties and Uses of Wrought Iron
Wrought Iron is ductile, malleable, fairly strong and soft; easily magnetized and welded. It is used for cores of dynamos and lifting chains.
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