We pass mow to the consideration of malleable or wrought iron. It differs from cast iron in being almost free of carbon. The great object in the processes adopted for the conversion of cast into malleable iron, accordingly-, is to deprive the former of its carbon. But it is also very do- , 4 --, --%,,,, l sirable to rid of deleterious in gredients, such as silicon, sulphur. I and phosphorus, which latter are I ..'' ei I generally present in minute quantities <. -''' t HIV; in the cast-iron. The ordinary pre, 1 r cesses for the manufacture of . -. _,„.
iron are refining, puddling, shingling o _,' h i I - t.
,,I , ii$ . ;k , ) Hammering, and rolling. The refinery .."-- g 104, _ is shown in section in fig. 2. It con- c , •-• , jt ,, C , sists of a flat hearth, A, covered with 1 ._,Rii-..t; sand or loam, and surrounded with ,. . — - -7 t' metal' troughs, 13, through which a < : ',„.,. ... , . ,,. , .,.
stream of water is constantly flowing, , , ' i '; to lice p the sides from melting. C are :,I the tuyeres in connection with the i , „,...•x : , .. ..., „..,. _., , \, .
blowing - engine. The cast - iron is . ..• melted with coke ou the hearth, and I * FIG. a blast of air kept blowing over it, which causes its carbon to unite with the oxygen of the air, and pass off as carbonic oxide gas. Oxygen also unites with silicon to form silica, and with iron to form the oxide. The silica of the sand uniting with oxide of iron, produces a slag of silicate of iron. The relined metal is finally run out in cakes on a bed of cast-iron, kept cool by a stream of water. Being only partially decarbonized by this process, it is next broken up for the puddling furnace. About 10 per cent of iron is lost in the refinery.
Fig. 3 shows a puddling furnace in longitudinal section. B represents the hearth; li, the grate or fire-place; and C, the chimney, which has a damper at the summit to regulate the draught. The grate is separated from the hearth by means , .i.. of a bridge, D, which prevents the77:v ..
, , direct contact of the with the.74 ---=_:_.. % '''$ 1.° -____, xv.. .k; ;.s. iron. White pig-iron, or at least 7,--,-----=; ;:,;--31,444. vi ' .,,,,,,, „ ij .t 1 such kinds as contain carbon in the / ' '' combined state only are best suited q‘ w.. :. ---&-- -1 ------------,.,
, o ./..ip.L. ju.c.n_li for puddling, because they become rigi ‘, pasty, and so more easily worked ----.. than gray iron containing graphitic ctlalirsb°coundwitlijoicn"pid.eoveisoullsotto i n is only in some districts that the Fin.S.--Puddlingl-mmace. "refining" process is much used, in .
others a portion only of the puddling furnace charge is refined; and in making inferior kinds of malleable iron, the is not previously refined at all. There are two ways of puddling now practiced: the first or older way, best applicable to refined iron, is called dry puddling, and in it the decarburization is produced chiefly by a strong current of air passing through the furnace: the second, or newer process, is called wet puddling or boiling, in which case the oxidizing of the carbon is effected chiefly by hematite, magnetic ore, basic slags, and other easily reduced materials, but to some extent also by the air.
The operation of puddling, thon,„..h differing in its detail's according to circumstances, is in a general way conducted as follows: A charge of from 4.1- to 5 cwts. of metal, including some hammer slag and iron scale, is placed on the bed of the furnace while' still hot from previous working. In about half an hour, when the furnace is in working order, the charge is melted, and is then stirred or "rabbled " for a considerable time„ when it begins to " boil " by the formation and escape of carbonic oxide, which forms jets of blue flame all over the surface. Gradually, as the carbon of the pig-iron is more and more oxidized, pasty masses of malleable iron separate, and these arc removed in halls commonly weighing about 80 lbs., but sometimes larger. About an hour and a half is required to work off a charge, and it takes from 22 to 26 cwts. of pig-iron to produce a ton of malleable iron. Siemens's regenerative gas-furnace, in which inferior fuels can be utilized, is applied to puddling as well as to other metallurgical processes; hut our space is too limited to give any of its details, or to describe the more recent revolving puddling furnace of Mr. Dunks, which is the most promising of any of the attempts yet made to puddle iron by mechanical means.