Page:Encyclopædia Britannica, Ninth Edition, v. 13.djvu/336

320 IRON from Bolley s Technology], on which the fuel (coke or char coal) is piled, the combustion being urged by a blast of air, which also par- it tially oxidizes the iron, both as it melts and sub sequently ; the molten mass when the opera tion is complete is either run out into moulds, chilled by throw ing water on to FIG. 31. Plan of fig. 30. it (the solidified upper surface being removed as a rough cake), or tapped into a separate similar open furnace or into a puddling furnace, in which the conversion into malleable inm is finished. The effect of this first treatment is materially to reduce the percentage of total carbon, and almost entirely to remove the silicon present, the latter forming a slag with the oxidized iron together with more or less of the ash of the fuel ; when the metal from the refinery is cast, it soli difies as "white iron" destitute or nearly so of graph i- toidal carbon. Sometimes the removal of carbon and silicon is accelerated by adding to the fluxing pig mill scales or other tolerably pure readily fusible iron oxide; lime is also sometimes added, with the intention of either parti ally removing sulphur present in the pig or preventing its further absorption from the fuel. A modification of the refinery has been introduced by Parry specially applicable to the direct treatment of the molten metal from the blast furnace ; the molten pig being tapped straight into the refinery hearth, a jet of superheated steam is made to play upon its surface (the temperature being maintained by an air blast in addi tion) ; the oxidation of the iron is then rapidly effected, with evolu tion of hydrogen from the decomposition of the steam ; in tins way a notable saving in fuel is said to be effected. In South Wales a coke refinery has been largely employed to partially purify the iron subsequently finished in an ordinary puddling furnace ; this refinery or running-out fire is a rectangular hearth with two or more tuyeres delivering blast slanting-wise downwards upon the surface of the fused metal, which is simply introduced as pig piled up on the hearth alternately with layers of coke, melted down, and kept fused with the blast playing on its surface for some time. Owing to the partial removal of silicon, &c., in this previous treatment, the subsequent puddling develops less cinder, and accordingly is sometimes distin guished as dry puddling ; whilst puddling proper (consisting of the fusion in a more or less modified Cort s furnace of the pig, and its complete treatment therein at one operation) is spoken of as jrig- boiling, the term "boiling" being derived from the rapid effer vescent evolution of carbon oxide from the fused mass at a certain stage, when the iron oxide reacts vigorously on the dissolved carbon. The following analyses by Rocholl illustrate the changes pro duced during the refining of Bowling cold blast pig : Pig- Just Melted. 10 Minutes after Fusion. 20 Minutes after Fusion. 28 Minutes after Fusion. Refined Metal. 94-4(11 95-324 95-240 95-521 95-708 96-013 Carbon (total) .... Silicon 3-68G 1-255 3-510 0-575 3-707 0-478 3-G44 0273 3-544 0-154 3-342 0-130 Sulphur 0-033 0-034 0-038 0-032 0-025 0-025 Phosphorus 0565 0-557 0537 . 0-530 0-509 0-490 100-000 100-000 100-000 100-000 100-000 100-000 Puddling. In the "dry puddling " process (which, as compared with the " pigboiling " process, is so little used that the generic term " puddling " is much more frequently employed to indicate the latter operation than the former), the iron which has passed through the refinery is placed on the bed of a reverberatory furnace together with a certain amount of mill cinder or other fettling, and melted down in a somewhat oxidizing atmosphere, the result of which is the formation of a fluxed mixture of pig iron and iron oxide ; this is well stirred, whilst the flame keeps it fluid, so that the iron oxide gradually reacts on the carbon, silicon, phosphorus, and sulphur present, oxidizing them and converting them either into gases which escape, or oxides which by uniting with ferrous oxide form a readily fusible slag. As this process goes on, just as in the charcoal finery, the consistency of the mass alters, the whole thicken ing firstly to a porridge-like substance and finally to a mixture of pasty solid lumps partly of coherent spongy malleable iron and partly of fluxed slag, mechanically adherent thereto, and dripping from the spongy mass when this is lifted. When the proper consistency is reached the iron is said to " come to nature " ; the spongy mass is then raked together with the iron rabble or stirring rod employed, and formed into a rough loosely coherent "ball," which is worked as described in 25. The use of the refinery conjoined with the dry puddling process has almost ceased in England ; certain brands of Yorkshire iron, however, of high reputation, are still prepared in this vay. The superiority of the metal is largely due to tho carefulness with which the plates and bars finally prepared are made ; the puddled bars are broken into fragments, and each piece carefully examined as to its fracture, the crystalline portions being worked up separately from the fibroid portions which yield the better plates ; by piling, reheating, and rolling, &c., the fragments are worked into bars, which are again piled and rolled into plates. Cold blast pig is preferred for certain of these brands. In the " pigboiling " process, or puddling par excellence as now understood, the main differences as compared with the preceding are that raw pig iron is used in the first instance instead of refined pig, so that the purification takes longer owing to the greater amount of impurity to be removed, and, in consequence of this and of the larger amount of fettling used, a much larger amount of slag or " tap cinder " is formed ; in other respects the operation is much the same. The furnace is usually lined in the first instance by melting down and partially oxidizing scrap iron on the bed so as to make a firm foundation ; " bull dog" or roasted tap cinder, mainly consisting of ferric oxide and silica, also forms a material largely used, the upper surface being finished off with a layer of a smooth unctuous variety of haematite or with "blue billy" ( 5) or some other variety of ferric oxide. In order to facilitate the removal of phosphorus and sulphur in the puddling forge, numerous chemical reagents have been employed incorporated with the mass by stirring . Thus common salt and manganese dioxide have been recommended by Schafhiiutl, chlorides of phosphorus, arsenic, and sulphur being said to be formed and volatilized, whilst manganese is communicated to the iron, and by its oxidizing action whilst becoming oxidized itself promotes the purification ; moreover it renders the slag more fusible. Henderson employs a mixture of titaniferous iron ore and fluor spar, whereby fluorides of phosphorus, silicon, &c., are said to be evolved. Good results are said to be produced by the employment of fluorides (cryolite or fluor spar) as a flux in puddling. Sherman recommends iodide of potassium ; according to Siemens, who carefully tried the Sherman process at the Landore works, no appreciable diminution is produced in the amount of sulphur and phosphorus by the addition of the iodide even in some considerable quantity both during the ordinary process of puddling and in a steel converting furnace, and the same kind of negative result has also been testified to by others, notably Snclus (Journal I. and S. Inst., 1871, ii. 181), and also by Euverte after full trial at Terre Noire. On the other hand, trials of the Henderson process appear to indicate that it causes a more rapid purification than ordinary puddling ; thus in experiments made at Blochairn Works, Glasgow, the following percentages of phosphorus were obtained : Original pig iron 1 14 per cent. Partly refined iron 30 minutes after fusion 23 ,, 40 ,, 0-15 50 ,, 0-12 Final wrought iron 07 , , The resulting cinder contained considerably less phosphorus than that in the pig employed, so that apparently some notable amount was volatilized.