332 IRON results are obtained when lignite, wood, peat, or other fuel is employed, due allowance being made for its different calorific power. For reheating furnaces in which coal is burnt, the consumption of fuel is usually in excess of 50 per cent, of the metal ultimately rolled for each time it is reheated. The yield of puddle bars from a given quantity - of pig varies somewhat with the quality : in spite of some of the iron oxide of the fettling being reduced, the weight of malleable iron (cinder being deducted) finally obtained in hand furnaces is always somewhat less than that con tained in the pig iron used; the latter averaging say 94 or 95 per cent, of iron, the yield of puddle bar may be said to run from 88 to 92, averaging about 90 per cent. Before an ordinary class of iron ore is converted into gocd bar iron there is in practice requisite a consumption of coal (or of its equivalent in coke, taking say 3 parts of coke to represent 5 of coal) to about the following extent per 100 parts of malleable iron finally obtained, that is, when each operation is conducted about as economically as is practicable on the large scale : Smelting to pig iron (140 parts of pig) 250 Puddling to puddle bar (140 pig becoming 125 puddle bar) ... 140 Reheating for final rolling, &c. (125 puddle liar used) 60 Total 450 In reference to this last item the consumption of puddle bar varies much with circumstances ; a considerable fraction of the final iron is obtained in the form of mill scale, which is not lost, being utilized in the puddling forge, or for smelting, &c.; the rest is obtained in the form of cuttings, " crop ends," and "scrap " of various kinds, often not very largely inferior in value to the bar iron. 26. Puddled Steel and Natural Steel. If in the opera tion of converting pig iron into malleable iron by puddling in a reverberatory furnace the process be stopped before the decarbonization is complete (the temperature of the furnace being a little lower, so that the partial solidification of the mass on decarbonization " coming to nature " takes place more easily), the resulting metal is a more or less carbonized iron, which, when prepared from pig free from any large quantity of sulphur and phosphorus, is susceptible of many of the applications to which steel is put. Considerable skill in manipulation is necessary in order to obtain anything at all approaching to a uniform product, the tendency being towards the production of a mass with lumps of soft wholly decarbonized iron, and sometimes of but little decarbonized pig irregularly distri buted through it. This is best overcome by conducting the decarbonization more slowly and at a somewhat lower temperature than is usually done in ordinary puddling, and using less fettling and a less oxidizing atmosphere. A manganiferous pig is almost essential to the obtaining of a good product, first because the oxidation of the manganese gives a more fluid slag, and secondly because the small quantity retained by the product decreases the injurious effects of sulphur, phosphorus, &c., on the physical proper ties of the metal. The manufacture of puddled steel in England is now but small, the Bessemer and Siemens-Martin processes having largely super seded it. Occasionally, however, substances apparently consisting of badly puddled iron, and possessing some degree of hardening power, are sold under the name of steel ; but, not having been fused so as to give uniformity of composition, these products are incapable of being used advantageously for purposes for which the elasticity and capability of resisting wear and tear possessed by good steels are essential. The want of a definite understanding as to whether the term "steel" is nowadays to be understood as implying that the product has been completely fused (as maintained by some, see 3) or not leads occasionally to disputes and lawsuits, when inferior kinds of "puddled steel," or badly decarbonized puddled iron, are supplied under the terms of a contract which simply mentions "steel" as the character of the metal to be supplied, without pre cisely stating its nature, quality, or properties, or the mode of its production. On the Continent, puddled steels made from pig of pure qualities so far as sulphur and phosphorus are concerned are more extensively employed. Schilling has examined the relative rates at which carbon, silicon, phosphorus, and sulphur are eliminated from the pig irons of Gittelde and Zorge in a charcoal steel-puddling forge at Zorge (Hanover), obtaining the results given in the following table: Average Com position of Pig Iron used. At 47 mins. Charge Melted. CG mins. Com mence ment of Boil. 80 mins. During Boil. Ill mins. Beginning to come to Nature. 120 mins/ Final Steel. So-called com- bincd carbon j 1-81 I ll 2-49 2-360 2-2CO 1-330 Average. 1-01 0-47 0-24 0-170 o -fio 0-071 0-075 Sulphur o-io 0-03 0-027 0-012 trace trace 1-24 0-34 0-160 0-110 0-110 0-11 1-66 0-47 0-470 0-470 0-310 0-27 Iron (by differ- {_ enco) j 03-61 94-43 96-613 97-038 98-179 98-535 Total 100-00 100-00 100-000 100-000 100-000 100-000 Character of ) w product j Tough cast iron. White iron Slightly malleable white pig, cellular. Malleable very hard steel. Steel. Steel. Similar results have been obtained by other observers ; thus Parry gives the following analyses of British puddled steel (Ebbw Vale) and of the original pig employed : Tig Iron used. Puddled Steel. Carbon (total) 2-680 0-501 Silicon 2-212 0-106 Sulphur 0-426 0-002 Phosphorus 0-125 0-096 Manganese. 1 -230 0-144 Iron (by difference) 93-327 99-151 100-000 100-000 Natural steel is to refined pig iron ( 23) in the inverse relation that puddled iron is to puddled steel : the last is derived from pig iron by stopping the decarbonization at a. stage before it is complete ; the first is obtained by carry ing the refining process somewhat further than the stage usually attained in the refinery. The forge or hearth used for natural steel making is substantially like that employed for refining, a brasqued bottom of charcoal dust being put on, and the pig iron melted down and gradually decar bonized by the conjoined action of an inclined blast blowing downwards upon it and of the cinder floating above it ; if the decarbonization is carried too far a little fresh pig is added to recarbonize the whole. The details of the mani pulation (upon the mode of performance of which the character of the resulting product depends) vary in different localities ; thus Tiinner describes five distinct modifications practised in Siegen, Tyrol, Carinthia, and Styria ; save in these districts the manufacture of this class of steel is but small. The bars ultimately formed from the blooms are usually hammered out by hand entirely, and not machine rolled at all. For further details see Percy s Metallurgy. 27. Bessemer s (Oriyfiial] Process. The method usually known in this country as " Bessemer s process " of steel making does not, strictly speaking, belong to the class of methods now under discussion, being a combination-process consisting of two parts : one the Bessemer process proper, of which the essential feature is the conversion of cast iron into wrought iron by the method (due to Bessemer) of forcing air through the molten mass so as to burn out the carbon ; the other (due to Mushet) consisting of the con version of the molten wrought iron thus obtained into steel by mixing with it a suitable proportion of fused carbonized iron containing manganese, in the form of spiegeleisen or ferro-manganese ; this combination process is discussed more fully in 36.
Page:Encyclopædia Britannica, Ninth Edition, v. 13.djvu/348
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