Page:Encyclopædia Britannica, Ninth Edition, v. 13.djvu/363

IRON 347 The phosphoric anhydride in the basic process slag appears to exist as calcium phosphate, and not as iron phosphate ; for after roasting to pcroxidize iron, no soluble phosphate is dissolved out on digestion with ammonium sulphide, nor is any formed by fusion with sodium chloride, whilst sulphurous acid solution readily dis solves out phosphate (Pattinson and Stead). Basic Lining Material. Some of the earliest of Bessemer s experiments (made at Dowlais) on his air-blowing process were made with a converter lined with Stourbridge firebrick, and in this vessel a Bessemer metal was made which contained only minute quantities of carbon and silicon, and much less phosphorus than the batches subsequently prepared from the same phosphorized Welsh pig in other converters lined with ganister, the non-success of which sub stances as commercial products (owing to their brittleness due to the phosphorus present) ultimately led to the use of hrematite and other phosphorus-free pig only for Bessemerizing. Without doubt the superiority of the earliest samples was due to the less silicious character of the brick lining. The lining materials used by Snelus in his experiments on the subject were lime and limestone, especially magnesian limestone ; those first employed by Thomas and Gilchrist were crushed limestone and sodium silicate solution added so as to moisten the limestone, which was then rammed into the converter like ganister. Bricks made of a limestone containing some aluminous silicate and fired at a very high temperature were then employed, but were found to be subject to disintegration by moisture when kept in stock ; magnesian limestone bricks containing a littje silica and alumina similarly prepared answered much better. Kiley has found that freshly burnt pretty pure magnesian limestone mixed with about 10 or 15 per cent, of crude petroleum can be rammed into converters or moulded by hydraulic pressure into bricks, the substance in either case becoming compact and hard upon firing, so as to present a very durable lining material. Instead of petroleum, crude shale oil, resin oil, or tar may be used to moisten the lime. The bricks thus prepared do not slake or dis integrate on keeping, or even if immersed in water, provided they have been fired at a high temperature ; in this case they contract slightly, whereas if only comparatively slightly heated they do not materially diminish in volume on firing. 1 38. The Uchatius Process. In the process of puddling ( 23) the oxidation of the carbon and other impurities of the pig iron is essentially effected by oxide of iron incorporated mechanically with the fluxed mass, and derived either from the oxidation of part of the iron of the pig, or from the fettling, or both. By fusing down in crucibles a mixture of small fragments of pig iron and ferric oxide of tolerable purity in suitable proportions it might therefore be expected that the percentage of carbon of the iron would be reduced so that a steel would result, a portion of the iron oxide added becoming simultaneously reduced to the metallic state; this experiment was actually made by Reaumur upwards of a century ago ; the reaction forms the foundation of the Uchatius process, patented in 1855. In order to obtain a usable steel, the iron oxide employed should also contain manganese oxide ; the pro duct of the continued roasting of a manganiferous spathic ore answers well. Independently of the costliness of crucible operations, however, as compared with other modes of production, the method is open to objection on the score of the practical difficulty in exactly regulating the degree of carbonization of the resulting steel, and also in its requiring a tolerably pure pig iron in the first place, so that, like the Bessemer process. proper, it is unsuited for the production of steel from many classes of iron. The method has, however, been employed on a manufacturing scale in Sweden, the non-phosphorized charcoal smelted from Swedish magnetite being employed along with some of the crushed ore ; whilst a modification of the process, in which an open hearth heated by a regenerative furnace is employed instead of crucibles, has been employed of late years by Siemens (see 39), and is usually known as the " ore process " for open hearth steel making. At Wikmans- hytta in Sweden a few years ago various qualities of steel were prepared from the richest Bispberg mine ores stamped fine and intermixed with pig iron granulated by running 1 For further details respecting the working of the Snelus-Thomas- Gilchrist process, see various papers in the Journal I. and S. Inst., 1879 and 1880, and in Iron, &c. into a rapidly revolving wheel in a water tank. Only hard steel for miners picks, cutting tools, razors, dies, lie., were thus prepared, containing 7 to l - 3 per cent, of carbon, about 50 Ib being melted in each crucible at one operation ; the crucibles lasted longer than in ordinary cast steel making, usually for some half dozen heats. Eostaing effected the granulation of the iron by running the melted pig on to a rapidly revolving horizontal cast iron disk, so that the liquid was scattered around (by centrifugal action) in globules which solidified into a kind of iron shot ; these being sifted into tolerably uniform sizes admitted of the production of a more nearly homogeneous metal than would otherwise have been obtained. The principles of Uchatius and Eostaing s patents, however, were long previously known and even patented ; thus in 1761 J. Wood obtained a patent for reducing iron " into small grains (according to art) by pouring it into water upon a wheel or roller turned briskly round," and for decarbonizing the granulated metal by fusing with various fluxes, &c. , including iron cinder, scales, and scorise ; whilst Mushet has described, as being in use long ago at Cyfartha, a method of granulating iron by pouring on to a revolving horizontal stone in a water trough molten pig iron, stating that the granulated metal was fused with oxide of iron in the form of bloomery cinders, and thereby rendered less easily fusible and capable of welding, in short, that it was decarbonized to a greater or lesser extent. The method of purification or refining of pig iron proposed by Bell ( 24) is substantially the Uchatius process applied on a large scale and at a somewhat lower temperature, with mechanical agitation and interruption at a certain stage. By stopping the pro cess when the action has only gone on sufficiently long to oxidize the majority of the silicon and phosphorus without materially affecting the carbon, a refined cast iron is produced ; whilst, were somewhat more carbon removed by longer action, a kind of Uchatius steel would result EllershaiLsai s process consisted in running molten pig iron upon a bed of iron oxide, sprinkling ore on the surface, and running on another layer of pig iron, and so on until a mass of alternate layers of pig and oxide is formed ; on heating this the pig gradually becomes decarbonized, the reaction being in fact a kind of modifica tion of the "malleable cast iron " process described in 22. Finally the mass is forged and rolled. The results obtained were not uniformly satisfactory, whilst the fuel consumption was found to be large ; accordingly the method never became anything much more than an experimental process. 39. The Siemens-Martin Process. As already stated, this process in its original form is substantially the method patented by Heath in 1845, with the addition of the use of a regenerative furnace, and of certain improvements in the working details, &c., the effect of which jointly is just to convert a practically useless process into a most valuable working method. Fig. 5 represents the kind of furnace employed. Since the date of Heath s patent the fusion of steel by means of a fan blast in an open hearth (under a layer of molten glass to protect from the oxidizing action of the flame which was the main cause of failure in Heath s original process) was experimented upon by Sudre and a commission from the French emperor (consisting of Deville, Beaulieu, and Caron) at the Montataire iron works, with the result of showing that, whilst the operation could be readily effected and a good tool steel prepared, the practical difficulties in the way, especially the corrosion of the furnace and the great cost of the requisite fuel, rendered the process commercially of but little value. In 1863, however, Chatelier attempted to prepare cast steel by puddling a good pig iron so as to form a very mild puddled steel, and then fusing it, not in crucibles, but on the hearth of a furnace containing molten pig and fitted on the regenerative principle. To enable the hearth to resist the high temperature it was composed of a bed of bauxite, a material highly suitable, so far as in fusibility and the absence of injurious ingredients are concerned, but open to the objection of not indurating properly, and consequently becoming dislodged and floating up to the surface of the fused mass ; this inconvenience was subsequently remedied by mixing the bauxite with a 1 per cent, solution of calcium chloride, moulding the paste into bricks, and calcining them, whereby a highly refractory coherent bottom can be obtained. Siemens, however, prefers (Chem. Soc. Journal.