Page:Encyclopædia Britannica, Ninth Edition, v. 13.djvu/365

IRON 341) gas and blast and exit gases passing to the regenerators ; as the furnace revolves the liquid metal always forms a pool at the lowest portion, but any solid matter is carried round, alternately rising above the pool and being plunged beneath it ; the effect of this is greatly to facilitate melting down and also considerably to shorten the time requisite Fig. 62. Pernot Furnace. for oxidizing out the carbon. At the required stage of decarbonization the blast and gas supply are shut off, the spiegeleisen or ferro-manganese added, and the bogie with drawn carrying with it the hearth and metal ; or it may be tapped in situ, and removed only for repairs (relining, fettling, &c.). Comparing the working of a furnace of this kind with one of similar dimensions but fixed bed, Hackney found that the output of steel was about double in a given time, and the coal used per unit weight of steel was less than one half, viz., 40 to 43 instead of 0-90 (8 to 8J cwts. per ton instead of 18 cwts. ). At St Chamond an improved Pernot 7-ton furnace gave during three months working the following results per unit of ingot steel : Coal used for smelting 318 ,, lighting, repairing, &c 0156 Total 0-474 The metal used per unit of ingot steel was 1 -06, the output being about 21 tons per day of twenty-four hours, the conversion taking about seven hours per charge. In English works where the Siemens process ("ore process ") is used with fixed hearths the yield of steel is somewhat in excess of the metal used originally, but the time of working is inferior to that just mentioned, the yield with 5-ton furnaces being only some 14 tons per twenty-four hours. Holley states that the removable Pernot furnaces set up in America (especially at Springfield, where 20-ton hearths have been recently erected) are highly satisfactory, especially as regards the ease with which repairs can be made ; the hearth can be run out on Saturday night, and is cool enough to repair on Sunday ; firing up being commenced on Sunday night, the furnace is ready for the usual charge on Monday forenoon. Krupp s dephosphorizing pro cess is adopted to purify the pig before finishing in the Pernot hearth, the metal being run from the melting cupolas into the Krupp washing furnace, and thence into the steel furnace by means of a ladle. Essentially the Pernot furnace is an ingenious combination of various previously well-known principles, the rotat ing circular bed having been previously used not only for puddling iron, but also for roasting ores, and the withdrawing carriage having also been employed previously in the manufacture of armour plates, whilst the inclined axis had also been previously used. The Berard Process. This method is essentially a sort of combination of the Bessemer converter principle and of the open-hearth method. A double furnace is employed, heated by gas, and provided with movable tubes dipping into the melted metal, or with a tuyere at the base in the case of the first hearth, in which the metal is blown, and the carbon, &c., oxidized by means of an air-blast; in the fellow hearth the metal is partially recarbonized by the gases from coal similarly blown into it, the object being to facilitate the removal of sulphur and phosphorus. " Finally the purified metal is treated with spiegeleisen or ferro- manganese in the usual way. PonsardFiirnaceorForno-Convertisseur. This apparatus is essentially a combination of the Pernot furnace with the Bessemer converter, consisting of a hearth movable about an obliquely vertical axis (figs. 63, 64). Instead of rotating round and round on this axis, the hearth D only moves through half a revolution ; when in one position (as in- Fio. 63. Ponsard Forno-Convertisseur Transverse section. dicated in fig. 63) the surface of the molten metal is above the level of a series of tuyeres O fed by a blast pipe LMN ; under these circumstances the apparatus performs the functions of a Bessemer converter, the blast passing through the molten metal ; when it is half turned round, the tuyeres are raised above the surface of the metal and the blast is shut off, so that it then becomes an ordinary Siemens open hearth. The air blast is introduced, as in the Bessemer converter, through a hollow axis of rotation ; the hearth is fixed, as in the Pernot furnace, upon a carriage or bogie K, so that it can be withdrawn and the metal tapped out at the tapping hole P. A gas producer A is attached, the gases from which are burnt as they are formed without cooling by passing through a long pipe, &c., or heating by a regenerator ; the air used to burn them, how ever, is heated by a regenerative arrangement consisting of a pair of chambers H filled with brick stacked in a peculiar way ; through one chamber the waste flame passes by the flue EFG, heating it up ; through the other one used alter nately the air passes reaching the furnace by the flue CC. F is a chamber in the waste gas flue for the deposition of solid suspended matters, dust, &c., from the blowing opera-