Slag

“ The slag-pot is a conical vessel, with a rounded apex, poised, base uppermost, on four little legs; when it is full, an iron frame work of a cart runs up, seizes it on opposite sides as though with two hands, and wheels it, glowing and fuming, out where a mole of slag is pushing itself over into the white gravel of the gulch, and where it is deposited red and crackling among heaps of like cones, some fading into the ashy hues of spent heat, some black and shining like inverted crucibles of polished iron. ”

“ This is cast iron; you see pigs of it piled up on the wharves in seaports, the outside incrusted with the sand in which it was run, and looking as rough, some of it, as the cinders of a smith's forge. It is highly charged with carbon, coarse, hard, and brittle; can neither be filed, welded, nor worked, under the hammer; is more or less filled with slag and other impurities, and fit only, when melted again and purified, to be cast into pots, pans, stoves, wheels, and various articles. It is now melted two or three times more, and slightly hammered, to beat off some of the slag. ”

“ In the furnaces the molten iron, because of its greater specific gravity, settles to the bottom, while the slag floats to the top. The slag, by the way, is not, as I had supposed, altogether worthless, but is used for railroad ballast and in the manufacture of cement.
The molten iron drawn from the blast furnaces runs in glittering rivulets (which, at a distance of twenty or thirty feet, burn the face and the eyes) , into ladle cars which are like a string of devils' soup bowls, mounted on railroad trucks ready to be hauled away by a locomotive and served at a banquet in hell. ”

“ The disorders to which blast furnaces are liable, have a tendency always to produce white cast iron. The colour of the slag or scoriæ is the surest test of these derangements, as it indicates the quality of the products. If the furnace is yielding an iron proper for casting into moulds, the slag has an uniform vitrification, and is slightly translucid. When the dose of ore is increased in order to obtain a gray pig iron, fit for fabrication into bars, the slag is opaque, dull, and of a greenish-yellow tint, with blue enamelled zones. ”

“ So it is now in this fierce blast from Hell’s furnace, the Great War, that the National fire is rekindled and each metal is slowly sinking its own individuality into the common form carefully stirred by the hand of the Almighty, and in the white heat, as the pure metal is tempered until it rings true and measures to the old standard, the slag is cast aside. ”

“ Smelting of the drawn slag, on the slag-mill hearth.—The black slag of the reverberatory [758] furnace is broken by hammers into small pieces, and mixed in proper proportions with the coal cinders that fall through the grate of the reverberatory fire. The leaden matts that float on the surface of the bath, and the dust deposited in the chimney, are added, along with some poor ore containing a gangue of fluor spar and limestone, which had been put aside during the mechanical preparation. With such a mixture, the slag-hearth, already described, figs. ”

“ Slag felt, a preparation of slag wool, which is a material produced by blowing off waste steam into the slag of iron furnaces, is also used for this purpose. In the case of the slag felt the process is as follows: On the under side of the joists, fillets are nailed to wooden blocks 1 in. thick, and to these fillets the lathing for the plaster ceiling is affixed. ”

“ The quality and proportion of flux should, if possible, be so chosen that the formation of the slag sets in only after the metal has been reduced and molten; or else part of the basic oxide of the metal to be extracted may be dissolved by the slag and its reduction thus be prevented or retarded. Slags are not a necessary evil; if an ore were free from gangue we should add gangue and flux from without to produce a. slag, because' one of its functions is to form a layer on the regulus which protects it against the further action of the blast or furnace gases. ”

“ The molten metal is not run off but remains with the slag in the pit until it is cool when the latter is chipped away and the shapeless mass of iron is ready to be worked into spears and lances by the blacksmiths. ”

“ Slag as a Building-Material.—"What shall be done with the slag?" is always a very urgent question for the proprietors of iron-works. Many are the plans which have been proposed for the utilization of this waste material, but, if we are to judge of their value by the amount of slag utilized, it must be confessed that they do not help to answer the iron-manufacturers' question. And yet many of the processes for the conversion of slag into a material for building would seem to promise very fair results. ”

“ While the worthless slag is doing so much sputtering and making so lively a show of itself, the silver and lead have quietly sunk to the bottom as fast as the heat liberated them from the mass of the boiling ore, and now come oozing up from a small exit far below the slag-spout, into a well at the side of the furnace. As fast as needful, this liquid ‘bullion’ is ladled out and poured into iron moulds, where it remains until it cools into solid ‘pigs’ or bars of lead weighing about fifty pounds each, and carrying about two per cent. ”

“ But it is to the earthy impurities here given off that we especially wish to direct attention. This slag, as it is termed, when drawn from the furnace, is run into oblong sand-moulds, from which, when cold, it is taken outside to the 'slag-bank,' as it is called—'slag-mountain,' we prefer saying; and an ugly mountain it is!—where it is broken into small pieces, examined to see whether it still contains metal, and if not, is left to accumulate. It consists essentially of silicon, oxygen, iron; or, to speak more correctly, it is a silicate of the protoxide of iron. ”

“ The effect of the introduction of slag would seem to be to retrace the steps usually taken in producing steel, viz., to separate the iron from its impurities, and then to add definite quantities of carbon and such other ingredients as are found to neutralize the effects of certain impurities not fully removed. ”

“ The slag is so much lighter than iron that when the ore is melted the slag floats on top just as oil floats on water, and can be drained out of the furnace through a higher opening than that through which the iron flows. The slag tap is open most of the time, but the iron tap is opened only once in about six hours. It is a magnificent sight when a furnace is "tapped" and the stream of iron drawn off. ”

“ The gases alone escaped, and the quantity of slag was so small that a daily cleaning sufficed to get rid of it. There was no longer any need of a barbarous colossus whose digestion caused disquietude, nor of any of the numerous and cumbersome appendages, the purifiers, the heaters, the blast machinery, and the constant current of water, with which it had been necessary to surround it. There was no longer any fear of stoppages or cooling down, nor any talk of demolishing or emptying the monster whilst still ablaze, because a twyer simply went wrong. ”

“ His process, which is applicable to almost any quality of slag, has the advantage over previous methods of making cement, that while in them the materials, lime, silica, and alumina, had to be brought together and carefully combined, in blast-furnace slag the combination has already been completely effected before the slag has left the furnaces, and generally with the proportions of silica and alumina that are required. By mixing the slag with an additional quantity of lime and calcining the mass, a strong and reliable cement of an agreeable color is produced. ”

“ The next step is to tap the furnace and draw off, first the molten slag, and then the molten metal. Generally the slag is run to waste, but sometimes it is preserved and submitted to treatment which permits its utilization. Some of these uses are road metal, railway ballast, slag bricks, slag wool, and hydraulic cement. Bricks are made by casting the molten slag in molds. To produce slag wool the molten slag is blown by a jet of steam, which produces small globules, to each of which is attached a long thin filament. ”

“ The charge which I have been kneading in my furnace has now “come to nature,” the stringy sponge of pure iron is separating from the slag. The “balling” of this sponge into three loaves is a task that occupies from ten to fifteen minutes. The particles of iron glowing in this spongy mass are partly welded together; they are sticky and stringy and as the cooling continues they are rolled up into wads like popcorn balls. The charge, which lost part of its original weight by the draining off of slag, now weighs five hundred fifty to six hundred pounds. ”

“ The thick fluid glass, called black slag, after reaching the cast-iron bottom of the furnace, having cooled and thickened a little, does not sink further, but is made to issue through a small taphole, and flow over the cinders placed in the pan, running into the pit filled with water in a continued stream. By falling while hot into cold water, the black slag is granulated, and, as small particles of lead may be carried over with it, through inattention on the part of the workman, or otherwise, the granulated slags are carefully washed at most smelting mills before being thrown away. ”

“ In building modern reverberatories, the foundation for the hearth is constructed of solid masonry or brickwork, or as at Anaconda, of a solid bed of slag, some 24 inches in depth, run in from an adjacent furnace. The I-beams used for carrying the bracing are erected in a surrounding trench, and a further quantity of slag (4 feet thick by 2 feet deep) is run in, thus yielding a perfectly rigid and impervious foundation (Fig. 26) . On the top of this slag-foundation is built a layer, 12 inches thick, of silica bricks, and upon this, the actual working bottom of the furnace is constructed. ”

“ As the flow from the iron notch decreases, the iron, and a small quantity of cinder or slag, which has been chilled by coming in contact with the cold surface of the trough, adhere to its sides and bottom. When the molten iron on the hearth is about exhausted, the blast is increased, and the material left on the hearth is blown out through the iron notch into the sand-trough. This also cools in the trough, and thus is formed what are known as trog h runners, consisting of iron and slag, which have been forced through the iron notch by letting on the blast as just mentioned. ”

“ Indeed, this local cooling aggravates the frothing. A cold lump of ore chills the slag immediately around it, just where its oxygen, reacting on the carbon of the metal, generates carbonic oxide; the slag becomes cool, viscous, and hence easily made to froth, just where the froth-causing gas is evolved. ”

“ The stones are completely glazed, and according to the different kinds of slag used are tinted of different colours. This operation is also employed advantageously with tiles, pipes, and earthenware.
If, in the preparation of fire-proof bricks, a certain proportion of mixture of clay and granulated slag be added to the mixture, very hard and durable fire bricks are obtained. These have been tested in a brass furnace, and experiments are being tried as to their applicability to building puddling furnaces. This granulated slag may also be advantageously used for manure. ”

“ Their composition must, however, be various, depending upon the nature of the ore from which they are produced; in all cases they are formed from the earthy matter contained in the ore and coal, which the metallic oxides convert into a glass.
In working a slag hearth, the workman's attention is principally required to supply grey slag and fuel as it is melted down and consumed, to keep the nozzle of the bellows clear, and to guard against the metallic lead running along with the slag, into the pit of water. ”

“ A vitreous material resembling wool, made by subjecting slag, when in a molten condition, to a strong blast. It was originally made in Wales in 1840, but the process was found injurious to the workmen, and so the manufacture was abandoned until about thirty years later, when it was taken up in Germany. As now made, a jet of steam is made to strike upon a flowing mass of molten slag as it falls from the spout into the slag-carriers. The steam scatters the slag into globules, and as each globule leaves the molten stream it turns into a fine thread. ”

“ The reason why the slag is not heated effectively is that the heat is developed only in the layer of metal itself, by its resistance to the induced current, and hence the only heat which the slag receives is that supplied to its lower surface by the metal, while its upper side is constantly radiating heat away towards the relatively cool roof above. ”

“ The furnace continued in full blast till that was melted. The liquid metal in the hearth is called slag. The iron oxide is put in it to make it more basic for the chemical reaction that is to take place. Adding the roll scale had cooled the charge, and it was thick like hoecake batter. I now thoroughly mixed it with a rabble which is like a long iron hoe. ”

“ And now another suggestion, based on the fact that slag is vitreous, is put forth, namely to convert it into glass. A mixture of sand, soda, and slag melted in a furnace will come out as glass. The experiment would not be expensive, for slag in any quantity may be had for nothing. ”