Every-day Science: Volume 6. The Conquest of Nature

by Henry Smith Williams; Edward Huntington Williams

In order to dump the wheelbarrow loads into the furnaces it was necessary to raise the bell. This was always dangerous, and frequently resulted in the suffocation or injury of the workmen on the staging. For when the bell was raised there was an escape of poisonous gases, which might flare out in a sheet of flame, with the possibility of burning or suffocating the workmen. The fumes from these gases, if inhaled in small quantities, might simply cause coughing, hiccoughing, or dizziness; but when inhaled in large quantities they struck down a man like the fumes of chloroform, suffocating him in a few seconds if he was not removed at once into a purer atmosphere. Indeed, the likelihood of this was so great that at many of these furnaces a special workman was detailed to take the position on the staging, well out of range of the gas, his sole duty being to rescue any of the men who might be overcome, and hurry them as quickly as possible down the elevator shaft into the pure atmosphere below. It was not an uncommon thing in the neighborhood of these older furnaces to see stretched about on the ground at the base several workmen in various stages of suffocation. Fortunately, by use of precautionary measures, fatal accidents were rather unusual, the men being overcome only temporarily, and usually recovering quickly and returning to work.

But the poisonous gas coming from the top of the furnace was not the only, nor the worst, danger constantly menacing the men on the staging. Their greatest dread was the possibility of explosions occurring in the furnace, which might hurl the bell into the air and deluge the upper structure with molten metal. Against this possibility there was no safeguard in the older furnaces, explosions occurring without warning and frequently with terrible effects. But fortunately these older types of furnaces are being rapidly replaced by the newer forms in which the danger to life, at least from gas and explosions, is minimized. And even in the older furnaces, improvements in the structure of the bell and in methods of filling have greatly lessened the dangers.

In the modern type of blast-furnace the work at the top formerly performed by men on the staging is accomplished entirely by machinery. The general appearance of these furnaces is that of huge iron pipes or kettles mounted on several iron legs. The outer structure, or shaft, is constructed of plate iron, but this is lined with fire brick of considerable thickness, and may have a water jacket interposed between these bricks and the shaft. About this large kettle are smaller kettles of somewhat similar shape having pipes leading from their tops to the larger structure. These smaller kettles are the "stoves" used in producing the hot air for the furnace.

The working capacity of some of these furnaces is in the neighborhood of a thousand tons of iron a day, although the average furnace produces only about half that quantity. The powerful machinery used for charging these monster caldrons hauls the ore and other charging materials to the top and dumps it in car-load lots.

In the older methods of manufacturing steel, the contents of the blast-furnaces were first drawn off into molds and allowed to cool into what is known as pig-iron. It was then necessary to re-heat this iron and treat it by the various methods for producing the kind of steel desired. By the newer methods, however, time and money are saved by converting the liquid iron from the blast-furnace directly into steel without going through the transitional stage of cooling it into pigs. Pigs of iron are still made in enormous quantities, to be sure, but mostly for shipment to distant places or for stores as stock material. For statistical purposes, however, the entire product of the blast-furnace, whether liquid or solid, is known as "pig iron."

The older method of removing the iron from the blast furnaces was by tapping at the opening near the bottom, the stream of liquid iron being allowed to flow into a connected series of sand molds, each mold being about three feet long by three or four inches wide. The bottom of these molds was flat but as the metal cooled in them the upper surface became round in shape, assuming a fanciful resemblance to a pig's back. In this molding a great amount of time was wasted in the slow process of cooling, and a large expenditure of energy wasted in this handling and re-handling of the metal.

In modern smelting works, however, pigs are no longer cast in sand molds, the molten metal from the furnace being discharged directly into iron molds attached to an endless chain. These molds are long, narrow, and shallow, having the general shape of sand molds. Each mold as it passes beneath the opening in the furnace remains just long enough to receive the requisite amount of metal to fill it, and then moves on to a point where it is either sprayed with water, or cooled by actually passing through a tank of water, emerging from this bath with the metal sufficiently solidified so that it may be dropped into a waiting car at the turning point of the endless chain. In this manner the charge from the blast-furnace may be drawn, cooled, and converted into pigs, loaded into cars, and hauled away without extra handlings or loss of time, the whole process occupying practically no more time than the initial step of tapping by the older method.

Where the contents of the blast-furnace are to be converted into steel at once, the molten metal is run off into movable tanks which carry it directly to the steel furnaces. These tanks, holding perhaps twenty tons of metal, are made of thick iron lined with fire brick, and arranged on low, flat cars designed specially for the purpose. These tanks are run under the spout of the furnace, filled with molten metal, and drawn to the steel works, possibly five miles away. As a rule, the distance is much less, but as far as the condition of the metal is concerned distance seems to make little difference, as even at the extreme distance there is no apparent cooling of the seething mass. The intense heat given off by these trains necessitates specially constructed cars, tracks, bridges, and crossings.

The destination of this train load of iron pots is the "mixer"—a great 200-ton kettle in which the products from the various furnaces are mixed and rendered uniform in quality. On the arrival of the train at the mixer, Titanic machinery seizes the twenty-ton pots and dumps their contents bodily into the glowing pool in the great crucible. Like the filling process, this operation occupies only a few minutes.

From the mixer the metal is poured out into ladles and transferred immediately to the "converter"—the important development of Sir Henry Bessemer's discovery that has made possible the modern steel industry. This converter resembles in shape some of the old mortars used in the American Civil War—barrel-shaped structures suspended vertically by trunnions at the middle and having an opening at the top. Into this opening at the top the metal from the mixer is poured and when the converter has been sufficiently charged a blast of cooled air is blown in at the bottom through the molten metal. This blast emerges at the top as a long roaring flame, of a red color at first but gradually changing into white, and then faint blue. These changes in color are indicative of the changes that are taking place in the metal, and the appearance of a certain shade of color indicates that the conversion into steel is complete, and that it is time for shutting off the blast of air. Any mistake in this matter—even the variation of thirty seconds' time—means a loss of thousands of dollars in the quality of steel produced. The man whose duty it is to determine this important point, therefore, holds an exceptionally delicate and responsible position, and receives pay accordingly.