1018 



IRON 



iron bars, while still hot, are cut by the shears into a length proportional to the size of 

 the iron bar that is wanted, and four rows of these are usually laid over each other 

 into a heap or pile which is placed in the re-heating furnace, and exposed to a free 

 circulation of heat, one pile being set crosswise over another. In a half or three 

 quarters of an hour the iron is hot enough, and the pieces now sticking together are 

 carried in successive piles to the bar drawing cylinders to bo converted into strong 

 bars, which are reckoned of middle quality. When a very tough iron is wanted, as 

 for anchors, another welding and rolling must be given. In the re-heating ovens the 

 loss is from 8 to 10 per cent, on the large bar, and from 10 to 12 in smaller work. 

 The consumption of coals in heating the large piles averages 7 cwts. to the ton of iron 

 charged ; in the smaller sizes 10 cwts. ; and in heating the guide rolled iron 10 cwts. 

 The re-heating furnace is shown in section in Jig. 1282 : it differs but little from a 

 puddling furnace. The whole interior, with the exception of the hearth a, is made of 

 fire-brick ; the hearth is made of sand. For this purpose a pure siliceous sand is re- 

 quired ; the coarser the better. The hearth slopes considerably towards the flue, the 

 object of which is to keep the hearth dry and hard. The iron wasted in re-heating 

 combines with the silica of the sand, forming a very fusible cinder, which flows off 



through the opening at b, at 

 which there is a small fire to 

 keep the cinder liquid. The 

 thickness of the sand bottom is 

 from 6 to 12 inches, resting on 

 fire-brick ; it generally requires 

 re-making after two or three 

 heats. The height of the fire- 

 brick arch, or its distance from 

 the sand bottom, is from 8 to 

 12 inches. The area of the 

 fireplace averages 12 feet, and 

 the width of the furnace varies 

 from 5 to 8 feet. When the 

 piles are charged into the fur- 

 nace, the door is shut, and fine 

 coal is dusted around its edges to exclude the cold air; the temperature is raised to the 

 highest intensity as quickly as possible, and the workman turns the piles over from time 

 to time that they may be brought to an uniform welding heat in the shortest possible time. 

 It is thought by many that a purer iron is obtained by subjecting the balls as they 

 come out of the puddling furnace to the action of the hammer at first rather than to 

 the roughing rollers, as by the latter process vitrified specks remain in the metal, 

 which the hammer expels. Hence in some works the balls are first worked under 

 the forge-hammer, and these stampings being afterwards heated in the form of pies or 

 cakes, piled over each other, are passed through the roughing mills. 



Bars intended for boiler or tin plates are made from the best cold-blast mine iron. 

 The raw pig is refined in the usual manner with coke, the loss amounting to from 

 2 to 3 cwts. per ton. It is then refined a second time with charcoal, the loss 

 amounting again to from 2,\ to 3 cwts. per ton. After this second refining, it is beaten 

 into flat plates white hot by the tilt hammer and thrown into cold water ; the sudden 

 chilling makes it more easily broken into small slabs. The slabs are piled in heaps 

 and welded in the hollow fire, coke being the fuel ; the slabs are laid across the fire, 

 and do not come into contact with the fuel ; the blast is thrown under the fuel, and 

 the heat is immense ; when the piles are nearly at the fusing point, they are with- 

 drawn and passed under the rollers ; they are again heated in the hollow fire, then 

 again rolled and heated a third time in the ordinary reverberatory furnace, after 

 which they are drawn out into flat bars for boiler-plates, or for tin plate : the loss in 

 these operations amounts to from 3.1 to 4 cwts. per ton. About 9 heats are ac- 

 complished in 12 hours, each heat consisting of 2j cwts. of refined metal, and con- 

 suming 5 baskets of charcoal. 



The bars intended for tin plates are repeatedly heated and rolled until of the 

 requisite thinness, the plates are then cut into squares, and annealed by exposing 

 them for several hours to heat in covered iron boxes, being allowed to cool very slowly ; 

 this gives the plates the proper degree of pliancy. The next operation is that of 

 pickling; the plates are immersed in dilute sulphuric acid for the purpose of re- 

 moving from their surfaces all oxide and dirt ; after remaining in the acid for the 

 requisite time, they are thoroughly washed in successive troughs of water, and then 

 dried in sawdust; finally, the surfaces of the metal are prepared for the reception 

 of the tin, by rubbing them with leather upon cushions of sheepskin. The spent 

 sulphuric acid is run out into evaporating pans, and the sulphate of iron crystalJjsed 



