Of the refinery of cast iron, or its conversion into bar-iron, in England

—This operation is naturally divisible into three distinct parts. The first, or the finery properly speaking, is executed in peculiar furnaces called running out fires ; the second operation completes the first, and is called puddling ; and the third consists in welding several iron bars together, and working them under forge hammers, and between rolls. 1. The finery furnaces are composed of a body of brickwork, about 9 feet square; rising but little above the surface of the ground. The hearth, placed in the middle, is two feet and a half deep; it is rectangular, being in general, 3 feet by 2, with its greatest side parallel to the face of the tuyères; and it is made of cast iron in four plates. On the side of the tuyères there is a single brick wall. On the three other sides, sheet iron doors are placed, to prevent the external air from cooling the metal, which is almost always worked under an open shed, or in the open air, but never in a space surrounded by walls. The chimney, from 15 to 18 feet high, is supported upon four columns of cast iron; its lintel is four feet above the level of the hearth, in order that the labourers may work without restraint. The number of tuyères is from two to three; they are placed at the height of the lip of the crucible or hearth, and distributed so as to divide its length into equal parts; their axes being inclined towards the bottom, at an angle of from 25° to 30°, so as to point upon the bath of melted metal as it flows. The cast-iron nose-pipe is encased, and water is made to circulate in the hollow space by means of cylindrical tubes; being introduced by one tube, and let off by another, so as to prevent the tuyères from getting burned in the proce . Two nozzles are usually placed in each tuyère, to render the blast constant and uniform; and for the same end, the air impelled by the bellows, is sometimes received at first in a regulator. The quantity of air blown into the fineries is considerable; being nearly 400 cubic feet per minute for each finery; or about the eighth part of the consumption of a blast furnace. IMG:4147767755307473660_illo0700.png:Finery furnace The finery furnace, or running out fire, is represented in figs. 590. and 591. It is a smelting hearth, in which by first fusing and then cooling gray cast iron in a peculiar way, it is converted into white cast iron, called fine iron, or fine metal, of the quality of forge pig, for making malleable iron by the puddling proce . The furnace resembles the forge hearth employed in Germany and France for converting forge pig into wrought iron; but it differs, particularly in this, that the fused iron is run out into an oblong iron trough, for sudden congelation. a is the air-chest, in communication with the blowing cylinder, or bellows; the air being conducted through at least two blast pipes to the fire, and sometimes through even 4 or 6 pipes. b is the side of the furnace, corresponding to the tuyère plates, in which are the openings for the blast pipes. All the sides of the furnace are hollow, and are kept cool by the circulation of water through the cavity between them. c is the front wall of the furnace, having a strong cast-iron plate containing the tap holes for running off the melted metal. d d is the exterior wall of the furnace, which corresponds to the contre-vent and ash-hearth of the French refining forge. e , is the top plate upon which the coke is piled up in store. f f , f f , iron props of the chimney, (not shown in this view). g , cast-iron trough into which the fine iron is run off in fusion; which is sometimes made in one piece, but more usually in separate plates joined together. Beneath this mould a stream of water is made to flow. h is the bottom of the hearth, covered with sand. In the finery proce , the hearth or crucible of the furnace is filled with coke; then six pigs of cast iron are laid horizontally on the hearth, namely, four of them parallel to the four sides, and two in the middle above; and the whole is covered up in a dome-form, with a heap of coke. The fire is now lighted, and in a quarter of an hour the blast is applied. The cast iron flows down gradually, and collects in the crucible; more coke being added as the first quantity burns away. This operation proceeds by itself; the melted metal is not stirred about, as in some modes of refinery, and the temperature is always kept high enough to preserve the metal liquid. During this stage the coals are observed continually heaving up, a movement due in part to the action of the blast, and in part to an expansion caused in the metal by the discharge of gaseous oxide of carbon. When all the pig iron is collected at the bottom of the hearth, which happens commonly at the end of two hours, or two and a half, the tap hole is opened, and the fine metal flows out with the slag, into the loam-coated pit, on a plate 10 feet long, 3 broad, and from 2 inches to 2 1 ⁄ 2 thick. A portion of the slag forms a small crust on the surface of the metal; but most part of it collects in a basin scooped out at the bottom of the pit, into which the fine metal is run. A large quantity of water is thrown on the fine metal, with the view of rendering it brittle, and perhaps of partially oxidizing it. This metal suddenly cooled, is very white, and po e es in general a fibrous radiated texture; or sometimes a cellular, including a considerable number of small spherical cavities, like a decomposed amygdaloid rock. If the cast iron be of bad quality, a little limestone is occasionally used in the above operation. Three samples of cinder, analyzed by Berthier, gave, | Silica | 0·276; | protox. of iron, | 0·612; | alumina, | 0·040; | phosp. acid, 0·072, Dudley. | | — | 0·368 | — | 0·610 | — | 0·015; | puddling of Dowlais. | | — | 0·424 | — | 0·520 | — | 0·033; | ditto. | The remarkable fact of the presence of phosphoric acid, shows how important this operation is to the purification of the iron. The charge varies from a ton and a quarter to a ton and a half of pigs; and the lo by the proce varies from 12 to 17 per cent. The fine metal is broken into fragments, and sent to the puddling furnace after the product of each operation has been weighed. The coal consumed in the fine metal proce is from 4 to 5 hundred weight for the ton of cast iron. About 10 tons may be refined per diem , a quantity somewhat greater than the supply from a blast furnace; but the fineries are not worked on the Sun days; and therefore a smelting furnace just keeps one of them in play. Whatever care be taken in this proce , the bar iron finally resulting is never so good as if wood charcoal had been used in the refinery; and hence in making sheet iron for the tin plate manufacture, wood charcoal is substituted for coke in one Welsh establishment. The cast iron treated with charcoal, gets into clots or lumps in the finery furnace, which are lifted out, set under the hammer, and flattened into thin cakes. The main effect of the finery proce , is probably the separation of the plumbaginous part of the charcoal, which is di eminated through the gray cast iron in a state of imperfect chemical combination. When that is removed the metal becomes more homogeneous, having no crystalline carbon present to counteract its transition into pure iron; much of the silica and manganese are also vitrified together, and run off in the finery cinder. IMG:4147767755307473660_illo0701a.png:Puddling furnace 2. The puddling furnace , is of the reverberatory form. It is bound generally with iron, as represented in the side view, fig. 592. , by means of horizontal and vertical bars, which are joined together and fixed by wedges, to prevent them from starting asunder. Very frequently, indeed, the reverberatory furnaces are armed with cast-iron plates over their whole surface. These are retained by upright bars of cast iron applied to the side walls, and by horizontal bars of iron, placed acro the arch or roof. The furnace itself is divided interiorly into three parts; the fire-place , the hearth , and flue . The fire-place varies from 3 1 ⁄ 2 to 4 1 ⁄ 2 feet long, by from 2 feet 8 inches to 3 feet 4 inches wide. The door way by which the coke is charged, is 8 inches square, and is bevelled off towards the outside of the furnace. This opening consists entirely of cast iron, and has a quantity of coal gathered round it. The bars of the fire grate are movable, to admit of more readily clearing them from ashes. IMG:4147767755307473660_illo0701b.png:Puddling furnace Fig. 593. is a longitudinal section referring to the elevation, fig. 592. , and fig. 594. is a ground plan. When the furnace is a single one, a square hole is left in the side of the fire-place opposite to the door, through which the rakes are introduced, in order to be heated. IMG:4147767755307473660_illo0702.png:Damper a is the fire door; b , the grate; c , the fire bridge; d d , cast-iron hearth plates, resting upon cast-iron beams e e , which are bolted upon both sides to the cast-iron binding plates of the furnace. f is the hearth covered with cinders or sand; g , is the main working door, which may be opened and shut by means of a lever g′ , and chain to move it up and down. In this large door there is a hole 5 inches square, through which the iron may be worked with the paddles or rakes; it may also be closed air-tight. There is a second working door h , near the flue, for introducing the cast iron, so that it may soften slowly, till it be ready for drawing towards the bridge. i , is the chimney, from 30 to 50 feet high, which receives commonly the flues of two furnaces, each provided with a damper plate or register . Fig. 595. , shows the main damper for the top of the common chimney, which may be opened or shut to any degree by means of the lever and chain. k , fig. 593. , is the tap or flo hole far running off the slag or cinder. The sole is sometimes made of bricks, sometimes of cast iron. In the first case it is composed of fire-bricks set on edge, forming a species of flat vault. It rests immediately on a body of brickwork either solid or arched below. When it is made of cast iron, which is now beginning to be the general practice, it may be made either of one piece or of several. It is commonly in a single piece, which, however, causes the inconvenience of reconstructing the furnace entirely when the sole is to be changed. In this case it is a little hollow, as is shown in the preceding vertical section; but if it consists of several pieces, it is usually made flat. The hearths of cast iron rest upon cast-iron pillars, to the number of four or five; which are supported on pedestals of cast iron placed on large blocks of stone. Such an arrangement is shown in the figure, where also the square hole a , fig. 592. , for heating the rake irons, may be observed. The length of the hearth is usually six feet; and its breadth varies from one part to another. Its greatest breadth, which is opposite the door, is four feet. In the furnace, whose horizontal plan is given above, and which produces good results, the sole exhibits, in this part, a species of ear, which enters into the mouth of the door. At its origin towards the fireplace, it is 2 feet 10 inches wide; from the fire it is separated, moreover, by a low wall of bricks (the fire-bridge) 10 inches thick, and from 3 inches to 5 high. At the other extremity its breadth is 2 feet. The curvature presented by the sides of the sole or hearth is not symmetrical; for sometimes it makes an advancement, as is observable in the plan. At the extremity of the sole furthest from the fire, there is a low rising in the bricks of 2 1 ⁄ 2 inches, called the altar, for preventing the metal from running out at the flo -hole when it begins to fuse. Beyond this shelf the sole terminates in an inclined plane, which leads to the flo , or outlet of the slag from the furnace. This flo is a little below the level of the sole, and is hollowed out of the basement of the chimney. The slag is prevented from concreting here, by the flame being made to pa over it, in its way to the sunk entry of the chimney; and there is also a plate of cast iron near this opening, on which a moderate fire is kept up to preserve the fluidity of the scoriæ, and to burn the gases that escape from the furnace, as also to quicken the draught, and to keep the remote end of the furnace warm. On the top of this iron plate, and at the bottom of the inclined plane, the cinder accumulates in a small cavity, whence it afterwards flows away; whenever it tends to congeal, the workman must clear it out with his rake. The door is a cast-iron frame filled up inside with fire-bricks; through a small hole in its bottom the workmen can observe the state of the furnace. This hole is at other times shut with a stopper. The chimney has an area of from 14 to 16 inches. The hearth stands 3 feet above the ground. Its arched roof, only one brick thick, is raised 2 feet above the fire-bridge, and above the level of the sole, taken at the middle of the furnace. At its extreme point near the chimney, its elevation is only 8 inches; and the same height is given to the opening of the chimney. In most iron-works the sole is covered with a layer of refractory sand, from 2 1 ⁄ 2 to 3 inches thick, which is lightly beat down with a shovel. At each operation a portion of the sand is carried away; and is replaced before another. Within these few years, there has been substituted for the sand a body of pounded slags; a substitution which has occasioned, it is said, a great economy of iron and fuel. The fine metal obtained by the coke is puddled by a continuous operation, which calls for much care and skill on the part of the workmen. To charge the puddling furnace, pieces of fine metal are succe ively introduced with a shovel, and laid one over another on the sides of the hearth, in the form of piles rising to the roof; the middle being left open for puddling the metal, as it is succe ively fused. Indeed, the whole are kept as far separate as po ible, to give free circulation to the air round the piles. The working door of the furnace is now closed, fuel is laid on the grate, and the mouth of the fire-place as well as the side opening of the grate, are both filled up with coal, at the same time that the damper is entirely opened. The fine metal in about twenty minutes comes to a white-red heat, and its thin-edged fragments begin to melt and fall in drops on the sole of the furnace. At this period the workman opens the small hole of the furnace door, detaches with a rake the pieces of fine metal that begin to melt, tries to expose new surfaces to the action of the heat, and in order to prevent the metal from running together as it softens, he removes it from the vicinity of the fire-bridge. When the whole of the fine metal has thus got reduced to a pasty condition, he must lower the temperature of the furnace, to prevent it from becoming more fluid. He closes the damper, takes out a portion of the fire, and the ribs of the grate, and also throws a little water sometimes on the semi-fused ma . He then works about with his paddle the clotty metal, which swells up, with the discharge of gaseous oxide of carbon, burning with a blue flame, as if the bath were on fire. The metal becomes finer by degrees, and le fusible; or in the language of the workmen, it begins to get dry . The disengagement of the oxide of carbon diminishes, and soon stops. The workmen continue meanwhile to puddle the metal till the whole charge be reduced to the state of incoherent sand; and at that time, the ribs of the grate are replaced, the fire is restored, and the register is progre ively opened up. With the return of the heat, the particles of metal begin to agglutinate, the charge becomes more difficult to raise, or in the labourers’ language, it works heavy . The refining is now finished, and nothing remains but to gather the iron into balls. The founder with his paddle takes now a little lump of metal, as a nucleus, and makes it roll about on the surface of the furnace, so as to collect more metal, and form a ball of about 60 or 70 pounds weight. With a kind of rake, called in England a dolly , and which he heats beforehand, the workman sets this ball on that side of the furnace most exposed to the action of the heat, in order to unite its different particles; which he then squeezes together to force out the scoriæ. When all the balls are fashioned, (they take about 20 minutes work,) the small opening of the working door is closed with a brick, to cause the heat to rise, and to facilitate the welding. Each ball is then lifted out, either with tongs, if roughing rollers are to be used as in Wales, or with an iron rod welded to the lump as a handle, if the hammer is to be employed, as in Staff ords hire. Thus we see that the operation lasts in whole from 2 hours to 2 1 ⁄ 2 ; in a quarter of an hour, the fine metal melts at its edges, when the puddling begins, in order to effect its division; at the end of an hour or an hour and a half, the metal is entirely reduced to a sand; a state that is kept up for half an hour by continual stirring; and finally, the balling operation takes nearly the same time. The charge for each operation is from 3 1 ⁄ 2 to 4 hundred weight; and sometimes the cuttings of bar-ends are introduced, which are puddled apart. The lo of iron is here very variable, according to the degree of skill in the workman, who by negligence may suffer a considerable body of iron to scorify or to flow into the hearth and raise the bottom. In good working, the lo is from 8 to 10 per cent. In Wales, the consumption of coal is estimated at one ton for every ton of fine metal. About five puddling furnaces are required for the service of one smelting furnace and one finery. The hearth of the puddling furnace should be exposed to heat for 12 hours before the work begins on the Mondays; and on the Saturdays, the old sole must be cleared out, by melting it off; and running it out by the flo -hole. Mr. Schafthault obtained, in May, 1835, a patent for the conversion of cast into wrought iron, by adding a mixture of black oxide of manganese, common salt and potter’s clay, in certain small portions, succe ively to the melting iron in the puddling furnace. The reheating furnaces , balling furnaces , or mill furnaces, are analogous to the puddling furnaces, but only of larger dimensions. The wood charcoal forge hearth is employed for working up scrap iron into boiler plate, . Here 22 bushels of charcoal are consumed in making one ton of iron of that description, from boiler plate parings.