Page:Encyclopædia Britannica, Ninth Edition, v. 13.djvu/337

IRON 321 Parry has proposed after puddling in the ordinary way to recar- bonize the iron by melting it along with coke and a little lime, &c. (to avoid sulphuration as much as possible), in a cupola furnace, and then to puddle a second time ; the phosphorus being considered by him to be reduced in each puddling operation to about one-fifth of the original amount, the double puddling would convert even a moderately phosphorized pig into a tolerably pure bar iron. Very good iron has thus been made from highly phosphorized pig on a moderately large scale (some 80 tons). Appliances for Puddling. The Puddling Forge. The puddling furnace introduced by Cort in 1784 differs from those in use at the present day only in one essential par ticular, viz., that whereas Cort used a bed of sand on which to run the metal fused previously in a running-out fireplace, the modern furnace as improved by Rogers some half century ago has a bed of iron plates cooled by air spaces underneath and covered with roasted scrap iron or with " bulldog," on to which the metal is heaped, having been previously refined or not according as the dry puddling or pig boiling process is used. The substitution of iron bottoms and a firm bed for the loose sand effects a great saving in iron through the formation of much less silicious cinder, and a great saving in time on account of repairs to the bed being much less frequently required ; moreover, a much greater degree of purification from phosphorus is at the same time brought about. Fig. 32 represents the general arrangement of a puddling furnace ; a is the charging door for the fuel, d the bridge with an air course to cool it, c the bed supported on iron plates with air courses under them, f the exit flue leading to the chimney stack, which is sur mounted with a damper k worked by a chain i from within the shed in which the forge is placed ; b is the ashpit, g the slag-hole, and e FIG. 32. Puddling Furnace. the working door suspended by a chain from a lever with a counter poise attached h, resting on the front side of the furnace roof. A large number of patterns of puddling furnaces differing one from the other in details have been constructed by various inventors ; the limits of the present article as to length forbid that these should be minutely discussed. Instead of using solid coal or coke as fuel for the puddling forge, gas is equally applicable, i.e., such as is described in 10. I:i order to apply at will an oxidizing or a reducing atmosphere, it is only requisite to regulate the supply of air (usually hot blast) to the reverbcratory furnace in which the gas is used. In Silesia gas puddling furnaces have been long in use, consisting of producers in which coal is burnt by means of a number of small jets of air forced in at the base of a square brick chamber some 5 feet in height, the top of the chamber being level with the bridge of an ordinary reverberatory furnace, the producer taking the place of the firegrate. In this way a mixture of nitrogen and carbon oxide with more or less hydrogen and carburetted hydrogens from the distilla tion of the coal results, the combustion of which in the reverberatory is effected by blowing a series of jets of heated air from a row of tuyeres arranged horizontally, or from a long narrow horizontal slit- shaped tuyere, across the issuing gases so as to form something like a gigantic blow-pipe, or series of parallel blow-pipe flames, which are somewhat inclined downwards so as to impinge on the substances in the bed of the furnace. Similar arrangements have been adopted elsewhere ; thus in Carinthia gas-fired puddling furnaces are in use where wood is the fuel, the producer and furnace proper adjoining one another, and the combustion of the gas being completed in the furnace by a jet of blast from a tuyere inclining somewhat downwards ; the blast is moderately heated by being made to circulate through flues under the furnace bed, thus also cooling the brickwork ; the pigs to be puddled are previously heated up to near their fusing point by the waste gases from a previous operation, being placed in a chamber just beyond the hearth. The waste gases have also been employed to heat the air blast by placing a pistol- pipo or other equivalent kind of stove between the furnace and the chimney. Several furnaces for thus utilizing the waste heat have been introduced, in England in particular ; J. Head describes under the name of the " Newport furnace " a somewhat analogous arrangement, a dry steam jet being used in connexion with the air blast ; a great diminution in consumption of fuel is thus said to be produced (Journal I. and S. Inst., 1872, p. 220). The Siemens regenerative furnace as applied to puddling consists essentially of a furnace fired by the gases from a Siemens gas producer heated (along with the air requisite to burn them) by means of Siemens regenerators ( 10). The chief difference between this form of furnace, represented by fig. 33, and the Carinthian FIG. 33. Siemens Ptegenerative Puddling Furnace. gas furnaces is that the flame does not enter at one end and issue at the other, but leaves the furnace at the same end as that at which it enters, circulating in the furnace, and thereby leaving the other end free for access by means of an ordinary door. Accord ing to Siemens the loss of weight between pig and puddled bar did not exceed 2 per cent, on an average of six months continuous working, whilst the consumption of coal (including the reheating furnace) was 30 cwts. 3 qrs. 8 It) per ton of finished wire roil (3 cwts. of ordinary fettling being used per ton of iron). Modifications of the Siemens furnace have been adopted in various iron-works differ ing more or less in detail, but not greatly in general principle ; thus the Ponsard furnace ( 40) and the Swindell furnace mainly differ in having the producer placed close to the furnace so that the gases are used directly without passing through the regenerators, which are only used to heat the air. The total fuel used in a Swindell puddling furnace in a large American works on a four months average was 2024J lt> of slack per ton of yield in iron (2240 Ib), or 904 per unit of iron ; the furnace, however, was not at work at night, so that a greater consumption of fuel was occasioned than would have been with double shifts of workmen. Kosmann has made a careful comparison (PrcussichcrZeitschr.f. JBerg-, llnttcn-, und Salinenwcscii, 1870, 145) between the effects and relative economy of puddling in the ordinary manner and in a Siemens regenerative gas puddling furnace, arriving at the conclusion that the latter is preferable in all cases where an extremely high heat is required, and where the fuel is of bad quality and unsuitcd for use in the ordinary way, or when a fixed temperature and particular constant quality of flame are required for any length of time. If, however, these conditions are not required, there is little ad vantage in the Siemens furnace over the ordinary one, whilst the latter admits of waste heat being utilized for heating boilers, &c. The waste of iron is nearly equal in the two cases, the _ordi- nary furnace being slightly at a disadvantage ; thus the cinder contained XIII. 41