STEEL 809 



bricks : each ' pot' is 3 feet wide, 3 feet deep, and 12 feet long. One is placed on 

 one side, and the other, on the contrary side of the fire-grate, A B, which occupies the 

 whole length of the furnace, and is 13 to 14 feet long ; the grate is 15 to 16 inches 

 broad, and the bars rest from 10 to 12 inches below the inferior plane or bottom level 

 of the 'pots;' the height of the arch at the centre is 5- feet above the top of the 

 'pots,' the bottoms of which are nearly level with the ground, so that the bars of iron 

 do not need lifting so high when charging them into the furnace. The flame rises 

 between the two 'pots ; ' it passes also below and around them, through the horizontal 

 and vertical flues, d, and issues from the furnace through the six small chimneys, H, into 

 a large conical space which is built around the whole furnace, 30 to 40 feet high, open 

 at the top. This cone increases the draft of the furnace, and carries away the smoke. 

 There are three openings in the front of the arch: two, T,fy. 1905, above the pots 

 serve to admit and remove the bars ; they are about 8 inches square ; in each a piece 

 of iron is placed upon which the bars slide in and out of the furnace. The workman 

 enters by the middle opening, p, to arrange the bars, which he lays flat in the pots and 

 spreads a layer of charcoal, ground small, between each layer ; the bars are laid near 

 each other, excepting those next to the side of the pot. which are placed an inch 

 from it ; the last stratum of iron is covered with a thick layer of charcoal, and the 

 whole is carefully covered witli loamy earth, 4 to 5 inches thick. The iron is gra- 

 dually heated ; in about four days it has become fully heated through, and the furnace 

 has then attained its maximum heat, which is maintained for 2 or 3 days, until the 

 first test bar is drawn out ; the heat is afterwards regulated, according to the degree 

 of hardness which may be required. The iron is converted in 8 days if for soft steel, 

 and in 9 to 1 1 days if for harder purposes. 



Conversion usually commences in 60 to 70 hours after the furnace is lighted. The 

 pores of the iron being opened by heat, the carbon is gradually absorbed by the mass 

 of the bar, but the carbonisation or conversion is effected, as it were, in layers. To 

 explain the theory in the clearest manner, suppose a bar to be composed of a number 

 of laminae ; the combination of the carbon with the iron is first effected on the sur- 

 face, and gradually extends from one lamina to another, until the whole is carbonised. 

 To effect this complete carbonisation, the iron requires to be kept at a considerable 

 uniform heat for a length of time. Thin bars of iron are much sponer converted 

 than thick ones. Re'aumur states, in his experiments, that if a bar of iron -^ths 

 of an inch thick is converted in 9 hours, a bar T 3 s ths of an inch would require 

 36 hours to attain the same degree of hardness. The carbon introduces itself suc- 

 cessively, the first lamina or surface of a bar combining with a portion of the carbon 

 with which it is in contact, gives a portion of the carbon to the second lamina, at the 

 same time taking up a fresh quantity of carbon from the charcoal ; these successive 

 combinations are continued until the whole thickness is converted : from which theory 

 it is evident that from the exterior to the centre the dose of carbon becomes propor- 

 tionately less. Steel so produced cannot be said to be perfect ; it possesses in some 

 degree the defect of natural steel, being more carbonised on the surface than at the 

 centre of the bar. From this theory we perceive that steel made by cementation is 

 different in its character from that produced directly from crude metal. In conversion 

 the carbon is made successively to penetrate to the centre of the bar, whilst in the 

 production of natural steel, the molecules of metal which compose the mass are per se 

 charged with a certain percentage of carbon necessary for their steelification ; not 

 imbibed, but obtained by the decarbonisation of the crude iron down to a point requi- 

 site to produce steel. 



Bar steel is also used for manufacturing shear steel. It is heated, drawn to lengths 

 3 feet long, then subjected to a welding heat, and some six or eight bars are welded 

 together, precisely as described in the refinement of natural steel; this is called single 

 shear. It is further refined by doubling the bar, and submitting it to a second welding 

 and hammering ; the result is a clearer and more homogeneous steel. During the 

 last few years the manufacture of this steel has been limited, mechanics preferring 

 a soft cast steel, which is much superior, when properly manufactured, and which can 

 be very easily welded to iron. 



The process of melting bar steel, and thus producing cast steel, was first practically 

 carried on by Mr. Huntsman of Attercliffe: the process itself is very simple. Fig. 1906 

 shows a cross section of the furnace commonly used. 



The furnace A, is square, lined with fire-stone 12 inches by 22 wide, and 36 inches 

 deep from the grate-bar to the under side of the cover B. c is a crucible, of which 

 two are placed in one 'melting-hole.' D is the flue into the chimney, K, which is about 

 40 feet high, lined with fire-brick. There is an air-flue, which is used to regulate the 

 draught at F. G is the ashpit, and H the cellar which is arched over. 



The steel is broken in pieces and charged into the crucible, which is placed on a 

 stand and provided with a cover ; coke is used as a fuel, and an intense heat is 



3 Ji2 



