METALS METALLURGY. 



sometimes larger. About an hour and a half is 

 required to work off a charge. 

 The puddled ball so formed is a spongy lump 



Fig. 5. Puddling Furnace : 



A, fireplace ; B, hearth on which the iron is puddled ; C, chimney ; 

 D, fire-bridge. 



of malleable iron, mixed with liquid cinder, and 

 requires to be welded into a coherent mass, an 

 operation which at the same time squeezes out the 

 cinder. This is called shingling, and is usually 

 done either by a tilt or lever hammer, or by 

 a direct -acting steam-hammer. After being 

 thoroughly hammered into a solid oblong mass, 

 the iron is formed into bars by means of grooved 

 .rollers at the rolling-mill. This product is called 

 puddled bar, and in order to produce finished 

 iron, these bars are next cut into short lengths, 

 and formed into a pile of convenient size, which 

 is then raised to the welding heat, hammered and 

 rolled into any required form of bar, sheet, or plate. 

 Sometimes this 'piling' operation is done twice. 



Malleable iron differs greatly in its properties 

 from cast-iron. The latter is practically incom- 

 pressible, but it can be comparatively easily torn 

 asunder. Malleable iron, on the contrary, pos- 

 sesses great tenacity, and is, moreover, very malle- 

 able and ductile, so that, when heated, it can be 

 rolled into sheets as thin as paper, or drawn into 

 the finest wire. Unlike cast-iron, it is very diffi- 

 cult to fuse, but it possesses the valuable property 

 of welding that is, two pieces can be completely 

 united together by hammering at a white-heat. 

 Malleable iron is employed for an endless variety 

 of articles requiring strength and lightness com- 

 bined. Most of the lighter portions of machinery 

 are constructed of it. Much is consumed in the 

 manufacture of locks, hinges, nails, wire-work, and 

 small sheet-iron vessels, included under the gene- 

 ral term 'hardware.' In constructive architecture 

 and engineering, its use is greatly extending for 

 roofs, floors, bridges, and the like ; while for ship- 

 building it is now almost the only material em- 

 ployed, so far as the frame-work and sides of 

 vessels are concerned. Armour-plates and guns 

 for heavy shot have of late years been made of 

 wrought-iron, of extraordinary size, and especially 

 thickness, for a material so difficult to manipulate 

 in large masses. 



Steel differs from malleable iron in containing 

 a varying proportion of carbon, usually from A to 

 2 per cent. When rich in carbon it closely 

 resembles cast-iron in composition, except that 

 it is more free from impurities. Steel can be 

 made by adding carbon during the direct reduc- 

 tion of a pure iron ore in a furnace or crucible, 

 but the results of this method are scarcely ever 

 uniform. The finer kinds of steel are still made 



by the old cementation process that is, by the 

 roundabout plan of first converting cast into 

 malleable iron, by depriving the former of its 

 carbon, and then adding carbon again by heating 

 the iron with charcoal. The bars of malleable 

 iron are put lengthwise in layers into fire-clay 

 chests or troughs, with ground charcoal between 

 each layer. A suitable fireplace heats the troughs, 

 which are in pairs, and the whole is kept at a glow- 

 ing red-heat from seven to fourteen days, accord- 

 ing to the kind of steel required. When sufficiently 

 cool the bars are removed, and are found to have 

 undergone a remarkable change. They have lost 

 their toughness, and are now quite brittle and 

 fusible, besides being covered all over with blisters ; 

 hence the name ' blister-steel.' These are sup- 

 posed to be formed by the evolution of carbonic 

 oxide gas. Blister-steel is not homogeneous, and 

 requires to be melted in crucibles and cast into 

 ingots before it is fit to be made into cutting 

 instruments and other objects where soundness 

 and uniformity of texture are required. Hammered 

 or tilted steel has a remarkably fine grain, and 

 is of great tenacity if the operation be carefully 

 performed. Shear-steel is made by welding to- 

 gether a number of pieces of blister-steel under 

 the hammer, so as to form a single bar with a 

 section of about two inches square. If this is 

 broken in two, welded together, and drawn out 

 again, it forms double shear-steel. 



The boldest and most noted attempt which has 

 yet been made to improve on the older methods 

 of making both malleable iron and steel, is that of 

 Mr Henry Bessemer, whose process was patented 

 in 1856. Bessemer's first idea was to blow air 

 through molten cast-iron till either malleable iron 

 or steel was produced ; but his process is only 

 suitable for making steel, for which it required to 

 be modified. 



The various steps in the Bessemer process, as 

 at present conducted, are as follow : Pig-iron is 

 melted either in a cupola or reverberatory fur- 

 nace, and run in the liquid state into a con- 

 verting vessel, such as is shewn in section in 

 fig. 6. This converter, or ' kettle,' as it is called 

 in Sheffield, is of wrought-iron, lined either with 

 fire-brick or with a siliceous material called 

 'ganister,' and is suspended on trunnions, so as 

 to admit of its being turned from an upright to a 

 horizontal position by means of hydraulic appar- 

 atus. The capacity of a converter varies from 

 three to seven tons. In the bottom there are 

 seven tuyeres, each with seven holes of one half- 

 inch in diameter, through which atmospheric air 

 is blown with a pressure of from 15 to 20 Ibs. per 

 square inch by a blowing-engine. The molten 

 iron in the converter is therefore resting, from 

 the first, on a bed of air, the strength of the blast 

 being sufficient to keep it from falling through 

 the tuyeres into the blast-way. During the blow- 

 ing off of the carbon at this stage a striking and 

 magnificent effect is produced by the roar of the 

 blast, and the volcano-like shower of sparks and 

 red-hot fragments from the mouth of the con- 

 verter, as well as by the dazzling splendour of 

 the flame. In about fifteen or twenty minutes, 

 the whole of the carbon is dissipated, the tem- 

 perature of the metal having meanwhile risen 

 higher than that produced by any other metal- 

 lurgical operation. This first ' blow being over, 

 the converter is lowered to a horizontal position, 



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