Page:Encyclopædia Britannica, Ninth Edition, v. 13.djvu/361

IRON 345 large portion of the circle covered by it cannot be used for running ingots into moulds, being occupied by the converters ; in most American works the two converters are placed side by side, so as to leave a larger space for the casting bed when the metal is not used direct from the blast furnace. A range of cupolas is fitted up at a convenient distance, some larger for melting the pig, some smaller for the spiegeleisen ; the molten metal is either run out from these direct into one or other of the converters through a shoot or gutter of iron lined with fireclay and sand, or is tapped into an intermedi ate collecting ladle, and when the requisite quantity is collected run rapidly into the converter either by "tipping" the ladle over so that the metal runs out together with some little amount of slag floating on its surface, or by means of a tapping hole at the bottom. This latter arrangement allows the charging of the converter to be more quickly effected ; when the iron is tapped directly from the blast furnace into the converter by means of an intermediate ladle, the cupolas are of course unnecessary, save those for molting the spiegeleisen. The blast is generated by an ordinary blowing engine, but at a considerably greater pressure than that used for blast fur naces, 20, 25, and even 30 Ib per square inch pressure being employed. The casting ladle into which the contents of the con verters are emptied by tilting them up sufficiently when the opera tion is finished is a large iron bucket lined with clay with a hole at the bottom filled up with a perforated firebrick, into which fits a stopper consisting of a stout iron rod covered with a thick fireclay tube to protect the rod from the fused steel ; when the ladle is full of molten metal, and the hole is closed by the stopper, the ladle is swung round by means of a crane over the ingot moulds (of cast iron) ; the stopper is then lifted, when the fused steel runs out, the scoria; floating on the top of the metal being thus retained and pure steel only poured. Sounder ingots are obtained by running the metal into a cavity communicating by firebrick tubes with the bottoms of the moulds, so as to fill them from below, than by filling them from above directly. Detailed descriptions of the plant employed in various first-class American Bessemer works are given by Holley and Lenox Smith in a series of articles in Engineering, 1877 and following years. The mode of carrying out the operation is briefly as follows : the charge of pig iron being run into the converter, this is swung back into the vertical position, the blast being automatically turned on in so doing ; when the blowing is at an end, the converter is turned into a nearly horizontal position, the blast being thereby shut off ; a weighed quantity of fused spiegeleisen is then run in, and the total contents of the converter forthwith poured into the cast ing ladle ; formerly the converter was erected for a few seconds and the blast blown through to mix the spiegeleisen and blown metal, but that is now found to be unnecessary. The ingots are finally reheated and passed through the rolling mills after forging so as to reduce them to rails, bars, plates, &c., as required, the machinery for this purpose being identical in character with that employed for malleable iron ( 25). The following analyses illustrate the general composition of " Bessemer steel " as made in different European countries, the first two specimens being prepared by Bessemer s original process (with out addition of spiegeleisen, 27), and the others by the Bessemer- Mushet combination process (from report of E. Brusewitz to the Swedish iron office, Jcrn-Kontords Annaler, 1871, 199). Westanfors (Sweden). Barrow-in- Furness. Germany. Xeu- berg. ( Particulars Without addition of Spiegeleisen. For Coarse Wire. Rails from Pig pool- in Man- guneau. Rails from Working- ton Hfenia- tite and German Mangani- ferous Pigs. Bo ler Plates : Pig used direct from Blast Fur nace. Very soft. Hard. Carbon 0-085 0-008 trace 0-025 trace 99-882 0-950 0-047 0-463 0-032 trace 99-508 0-200 0-179 0-214 0-026 0-030 98-351 0-150 0-091 0-264 0-132 0-025 99-338 0-046 0-634 0-638 0-093 0-045 98-544 0-250 0-016 0-136 d-oio 99-588 Manganese Phosphorus Sulphur Iron by difference. 100-000 100-000 100-000 100-000 100-000 100-000 Analyses illustrating the composition of the sla i 37. are given 37. The Basic Process. On attentively examining the history of the puddling process, especially the improve ment effected by Rogers in substituting bottoms of iron coated with fettling of iron oxide for the sand bottoms originally used by Cort, and also the various experi ments that have been made during the last dozen years or so both on puddling by machinery and refining and purifying iron, the general conclusion deducible seems to be that when phosphorized metal is in presence of iron oxide in a fused state, or of a melted mixture of iron oxide and ferrous silicate containing an amount of the latter not above a certain limit, the tendency of the phosphorus is to become oxidized and converted into phosphate, which separates in the cinder, leaving a purer iron ; whilst on the other hand if the cinder is mainly silicate, especially of the metasilicate or " acid " type (R,O, SiO 2 ), the tendency is rather the other way, part of the metallic iron becoming oxidized whilst the phosphate is reduced, thus communi cating phosphorus to the remaining iron. 1 Accordingly, in the modern ordinary puddling process, especially when machine puddling and regular mechanical agitation are substituted for hand labour, and when plenty of fettling of ferric oxide (not largely silicious) is employed, and in Bell s and Krupp s purification processes, phosphorus is largely removed from the pig ; whilst on the other hand in the older method of puddling on sand bottoms and in the ordinary Bessemer blowing process the first action of the oxygen of the blast is concentrated rather on the silicon than on the iron (at least so far as the ultimate chemical change is concerned), and in consequence a highly silicious cinder results, so that removal of phosphorus by oxidation becomes impracticable ; this result, moreover, is intensified by the nature of the lining material (ganister) used for the converters ; similarly, in the Heaton process phosphorus is sometimes removed to a considerable extent and sometimes not, according as the soda produced by the decomposition of the nitrate and the iron oxide formed modify the character of the slag produced by the oxidation of the silicon and formation of silicates, rendering it of an " acid " or " basic " silicious character. Again, according to Riley, when the whole of the iron is reduced in the blast furnace, so that the cinder contains none, or practically none, the pig contains all the phosphorus present ; but if the cinder contains unreduced iron to any extent, it also retains a proportionate amount of phosphorus, being then much more basic. The temperature also seems somewhat to influence the reaction of iron oxide on phosphorus and of iron on phosphate ; the higher the temperature the more pronounced apparently is the tendency of the metal to retain phosphorus, i.e., the less is the tendency of the phosphorus to oxidize and separate from the metal. Guided by these considerations, Snelus took out a patent in 1872 2 for the use of lime or limestone 1 An instructive experiment on this point has been made by Pourcel. A quantity of metal (3 tons) containing 2 5 per cent, of carbon and 5 of phosphorus was melted in a Siemens-Martin hearth, the scoria; removed, and the atmosphere made highly oxidizing (hot air alone passing); in fifteen minutes jets of carbon oxide were formed, and some of the silicon and iron was oxidized, forming a cinder containing no phosphorus. The bath was then heated up again and the cinder removed; and after some silico-manganeisen (10 per cent, silicon, 20 per cent, manganese) had been added, the oxidation by air alone was proceeded with ; at first no carbon oxide was liberated (indicating the preferential oxidation of silicon), but after fifteen minutes more the jets reappeared ; the cinder now was found to contain phosphates, the percentage of phosphorus in the metal having become reduced to 35, indicating that the iron and manganese oxides formed, whilst partly reacting on carbon and chiefly on silicon, nevertheless to some extent attacked the phosphorus. The atmosphere was now made much less powerfully oxidizing by turning on the gas supply as usual ; in fifteen minutes the phosphorus had disappeared from the cinder, and was wholly taken up again by the iron, which now contained 50 per cent, as at first, showing that prolonged contact with the silicious cinder enabled metallic iron (containing more or less carbon) to reduce the phosphate of this cinder, thus inverting the operation effected during the rapid oxidation of iron set up in the first part of the experiment. 2 The idea of employing calcareous and other basic linings to fur naces used for the purification of iron by methods other than the pneumatic process of Bessemer is of considerably older date than 1872; thus such substances were used years ago by Siemens and Chatelier in the earliest experiments on the open-hearth process ( 39), bauxite being extensively employed then, and also in Siemens s subsequent direct precipitation process. The use of lime in puddling has often been tried as an addition to the fettling, whilst in the Siemens ore process limestone is usually added as a flux. XIII. 44