Cast Iron
Cast iron is the product of the iron smelting-furnace. Iron occurs in nature, almost universally, in a state of combination. The mineral masses which it forms with oxygen, carbon, sulphur, and the metals, and from which it is extracted, are called its ores. It is strongly magnetic, and rubs into a black powder. Magnetic iron ore (loadstone) is one of the richest ores of the iron, containing 72 per cent of iron and 28 of oxygen. Specular or red iron ore is very hard, and sometimes presents a polished appearance, brown in color; but its powder is always red--by which means it may be distinguished from the magnetic oxide. This ore contains 63 per cent of iron and 36 of oxygen. Red hematite is much used, being very plentiful, as also is brown hematite, which is found in almost all parts of the world; it contains about 86 per cent of peroxide of iron to about 14 of water. Clay ironstone occurs amongst the coal measures, and contains only about 37 per cent of iron. Bisulphide of iron, or pyrites, occurs in large quantities under different forms. Pyrites is prized chiefly as a source of other substances; it is never worked for its iron.
The richer iron ores yield a good iron by simply heating the broken ore with charcoal in an open fire with blast. The ore is deoxidized, or, in other words, deprived of its oxygen by the carbon of the fuel, and the reduced iron is gathered into a pasty mass called a "bloom," while the earthy impurities contained in the ore combine with a portion of the oxide of iron to form a slag. Very much of the iron is, by this method, lost in the slag, and there is also a great waste of fuel; but the method is so simple that it may be practised by people possessing little knowledge of chemistry, and for this reason it is no doubt the oldest method of extracting iron from its ores. The metal is not usually obtained pure in the extraction or iron from its common ores, as it contains more or less carbon, which imparts to it a fusible nature; for which reason iron in this state is designated "pig iron," or cast iron. The processes connected with the reduction of the ores consist of, first, calcining or roasting (this is done to expel carbonic acid, water, sulphur, and other volatile ingredients of the ore); secondly, the reduction of the oxide of iron to the metallic state by ignition with carbon; thirdly, the separation of the earthy impurities of the ore by fusion with other matters into a slag; and, fourthly, the carbonizing and melting of the reduced iron. The purest kind of iron ores do not require to be previously calcined, but with most of them it is essential.
Some of the larger examples of blast-furnaces have a width at the boshes of 25 feet, and are over 100 feet in height. These are commonly called smelting-furnaces, because the process of separating the iron from its ore, called reducing, is conducted in them. The top or mouth of the furnace serves for charging as well as for the escape of smoke, etc., and is therefore both door and chimney. The tuyeres at the bottom, like the ordinary cupola, serve to supply the air, which is forced in by means of immense blowing-engines. To economize fuel, the blast is sometimes heated to over 1000 degrees before it is delivered into the furnace. The furnace is sometimes charged with alternate layers of fuel (coal or coke and sometimes charcoal), ore, and limestone. When the heat has become sufficiently intense the carbon of the fuel deoxidizes the iron, and carbonic acid is also expelled from the lime, leaving it caustic. Sand and clay, in greater or less quantities, now remain combined with the iron; the lime, acting as a flux, unites with these and forms a slag. The iron as it melts falls to the bottom of the furnace, from whence it is allowed to flow at intervals through a tapping-hole, which when not in use is kept stopped with sand. The slag flows out over a dam, arranged in such a manner as to retain the molten iron, but to permit the escape of the slag, which floats on the iron as fast as it accumulates in sufficient quantity. As fresh supplies of fuel, ore, and flux are charged at the top, the melted iron is tapped at the bottom; where channels from the tap-hole lead the metal into sows, and from thence into the pigs; the process goes on without stoppage, sometimes for years.
The product of the smelting-furnace is, as has been previously stated, "cast iron," containing from 2 to 6 per cent of carbon, which in the white irons is chemically combined with the iron; while in the gray it is principally graphitic, mechanically distributed through the iron. There are also other impurities contained in cast iron, including silicon, sulphur, and phosphorus, and sometimes manganese. Cast iron is easily distinguished from malleable by its granular texture and brittleness, which precludes all possibility of forging; but it is this very quality that gives it its value as a foundry iron, because it can be so readily remelted and cast into moulds. It is presumed that cast iron expands at the moment of assuming the solid from the liquid state; this expansion being caused by the particles assuming a crystalline arrangement as the mass solidifies, but that a subsequent contraction takes place gradually as it becomes cold. See WATER-TUYERE; CALCINATION; ORES; SOW; PIG IRON.
Cast-iron pipes are tubes of cast iron for conveying water or other fluids. Elbows, bends, curve, branch, tee, flange, hawse, as well as odd shapes of water and other pipes, etc., all come under the general name of jobbing pipes, and are made in almost every foundry. But the straight-length socket pipe, of which so many thousand tons, of every dimension almost, are made each year for the water-works systems, are now all made by firms devoted exclusively to the manufacture of that class of castings. The defects formerly existing by reason of the employment of unskilled labor at nearly all the pipe foundries have long since ceased to exist, as the work now emanating from these concerns incontestably proves.
As made by the regular establishments, pipes are all cast vertically in cast-iron casings, having the core on a barrel. The flasks are rammed vertically on fixed foundations, with guide to receive the mandrel or pattern. The cores are accurately struck on barrels, in the customary way, the barrels being provided with ample means for handling and self-adjustment; which leaves little to be done except to elevate the dried core, and lower it into the prepared seat at the bottom of the mould. Moulds and cores are thoroughly dried before casting.
The following table gives the weight of one foot in length of pipes from 1 inch to 22 inches diameter:
Diam. Thickness. Weight. Diam. Thickness. Weight. Diam. Thickness. Weight. Ins. Ins. Lbs. Ins. Ins. Lbs. Ins. Ins. Lbs. 1 1/4 3.06 3 1/4 1/2 18.4 5 5/8 34.34 3/8 5.05 5/8 23.72 3/4 42.28 1 1/4 1/4 3.67 3/4 29.64 5 1/2 1/2 29.4 3/8 6. 3 1/2 1/2 19.66 5/8 37.44 1 1/2 3/8 6.89 5/8 25.27 3/4 45.94 1/2 9.8 3/4 31.2 6 1/2 31.82 1 3/4 3/8 7.8 3 3/4 1/2 20.9 5/8 40.56 1/2 11.04 5/8 26.83 3/4 49.6 2 3/8 8.74 3/4 33.07 7/8 58.96 1/2 12.23 4 1/2 22.05 6 1/2 1/2 34.32 2 1/4 3/8 9.65 5/8 28.28 5/8 43.68 1/2 13.48 3/4 34.94 3/4 53.3 2 1/2 3/8 10.57 4 1/4 1/2 23.35 7/8 63.18 1/2 14.66 5/8 29.85 7 1/2 36.66 5/8 19.05 3/4 36.73 5/8 46.8 2 3/4 3/8 11.54 4 1/2 1/2 24.49 3/4 56.96 1/2 15.91 5/8 31.4 7/8 67.6 5/8 20.59 3/4 38.58 1 78.39 3 3/8 12.28 4 3/4 1/2 25.7 7 1/2 1/2 39.22 1/2 17.15 5/8 32.91 5/8 49.92 5/8 22.15 3/4 40.43 3/4 60.48 3/4 27.56 5 1/2 26.94 7/8 71.76 7 1/2 1 83.28 1 122.62 1 161.82 8 1/2 41.64 12 1/2 61.26 16 1/2 80.87 5/8 52.68 5/8 77.36 5/8 101.82 3/4 64.27 3/4 93.7 3/4 123.14 7/8 76.12 7/8 110.48 7/8 144.76 1 88.2 1 127.42 1 166.6 8 1/2 1/2 44.11 12 1/2 1/2 63.7 16 1/2 1/2 83.3 5/8 56.16 5/8 80.4 5/8 104.82 3/4 68 3/4 97.4 3/4 126.79 7/8 80.5 7/8 114.72 7/8 149.02 1 93.28 1 132.35 1 171.6 9 1/2 46.5 13 1/2 66.14 17 1/2 85.73 5/8 59.92 5/8 83.46 5/8 107.96 3/4 71.7 3/4 101.08 3/4 130.48 7/8 84.7 7/8 118.97 7/8 153.3 1 97.98 1 137.28 1 176.58 9 1/2 1/2 48.98 13 1/2 1/2 68.64 17 1/2 1/2 88.23 5/8 62.02 5/8 86.55 5/8 111.06 3/4 75.32 3/4 104.76 3/4 134.16 7/8 88.98 7/8 123.3 7/8 157.50 1 102.09 1 142.16 1 181.33 10 1/2 51.46 14 1/2 71.07 18 5/8 114.1 5/8 65.08 5/8 89.61 3/4 137.84 3/4 78.99 3/4 108.46 7/8 161.9 7/8 93.24 7/8 127.6 1 186.24 1 108.84 1 147.03 19 5/8 120.24 10 1/2 1/2 53.88 14 1/2 1/2 73.72 3/4 145.2 5/8 68.14 5/8 92.66 7/8 170.47 3/4 82.68 3/4 112.1 1 195.92 7/8 97.44 7/8 131.8 20 5/8 126.33 1 112.68 1 151.92 3/4 152.53 11 1/2 56.34 15 1/2 75.96 7/8 179.02 5/8 71.19 5/8 95.72 1 205.8 3/4 86.4 3/4 115.78 21 5/8 132.5 7/8 101.83 7/8 136.15 3/4 159.84 1 117.6 1 156.82 7/8 187.6 11 1/2 1/2 58.82 15 1/2 1/2 78.4 1 215.52 5/8 74.28 5/8 98.78 22 5/8 138.6 3/4 90.06 3/4 119.49 3/4 167.24 7/8 106.14 7/8 140.4 7/8 196.46 To find the weight of a pipe, let the following rule be observed: To the inner diameter add the thickness of metal; multiply by 3.1416 for the circumference, and the product by the thickness. This gives the number of inches contained in the end section of the casting, which, when multiplied by the length, gives the total cubic inches, which, if multiplied by the weight of a cubic inch of the metal used, will give the total weight. See COLUMNS.