Iron furnace

“ The iron is remelted in a puddling furnace, as it is called, which is heated with raw coal, and there, by a series of operations, the object of which is to give the iron malleability and toughness by expelling the carbon, it is manipulated until it acquires the consistency of a solid white-hot ball. ”

“ The charge may be melted down on the “open hearth” itself, or, as in the more advanced practice, the pig iron may be brought in the molten state from the blast furnace in which it is made. Then the furnaceman, controlling the decarburization and purification of the molten charge by his examination of test ingots taken from time to time, gradually oxidizes and so removes the foreign elements, and thus brings the metal simultaneously to approximately the composition needed and to a temperature far enough above its present melting-point to permit of its being cast into ingots or other castings. ”

“ He proposed to accomplish this by using a reverbatory gas furnace, into which the crude iron from the blast furnace is poured, and in which it may be mixed with other irons, and so treated as to insure uniformity. Pig iron of different qualities, or any metals or metalloids or fluxes, can be added and mixed with the metal as may be necessary to bring it to the required character. The process is so manifestly different from that described by Jones that it demands no further attention. ”

“ In the acid-lined furnace no attempt is made to reduce the phosphorus. It would be futile. Therefore the materials charged must be very low in phosphorus and sulphur. No lime additions are made, the flame simply melts down the pig iron and scrap, the iron oxide later is added from time to time to keep up the boil until the test bars show that the carbon as well as the silicon and manganese have been eliminated as fully as is desired. ”

“ When the furnace was charged, the doors were closed until the metal was sufficiently fused, when the workman opened an aperture and worked or stirred about the metal with iron bars, when an ebullition took place, during the continuance of which a bluish flame was emitted, the carbon of the cast-iron was burned off, the metal separated from the slag, and the iron, becoming reduced to nature, was then collected into lumps or loops of sizes suited to their intended uses, when they were drawn out of the doors of the furnace. ”

“ When the metal is melted in the great furnace it is run out into a huge clay crucible, practically a colander, by reason of several openings in the bottom, through which the metal would run were it not impeded by a strong blast of air under great pressure, which is forced through all the interstices of the iron, and instead of cooling it, raises the heat to a greatly increased intensity. This burns away the carbon, which constitutes the chief difference between cast iron and malleable iron, and also some other matters ”

“ When iron ores are to be roasted, which require but a simple calcination to disengage the combined water and carbonic acid, egg-shaped furnaces, similar to those in which limestone is burned in contact with fuel, may be conveniently employed; and they present the advantage of an operation which is continuous with a never-cooling apparatus. The analogy in the effects to be produced is so perfect, that the same furnace may be used for either object. Greater dimensions may, however, be given to those destined for the calcination of iron ores. ”

“ It is merely a place of many ditches, or run-ways, that lead the molten iron from the furnace to the ladle. Very little iron is ever "cast," since the blast-furnaces here make iron only for the sake of swiftly transporting it, while still hot, to the Bessemer and open-hearth, for further metamorphosis into steel. ”

“ On its way from the blast furnace to the converter or open hearth furnace the pig iron is often passed through a great reservoir called a “mixer,” which acts also as an equalizer, to lessen the variation in composition of the cast iron, and as a purifier, removing part of the sulphur and silicon. ”

“ Various forms of furnaces are used, such as stationary and rolling furnaces; but whatever the style of furnace, the process is based on the decarbonization of the metal, and the charge of pig iron does not come in direct contact with the fuel, as in the open-hearth process. An advantage gained in using the puddling furnace is that various kinds of fuel can be employed without injury to the product of iron, also various labor-saving devices, which have recently been invented, can be better used. ”

“ It is well known that the blast furnace is the first into which the ore is introduced, for the purpose of converting it into malleable iron, and much, therefore, depends upon the state in which the pig metal passes from this furnace, whether subsequent operations will furnish an iron of the first quality or not. ”

“ By thus finishing the operation with steam a more uniform color is obtained, due probably to the oxidation of any protoxide of iron that might possibly have been produced during the last reduction, thus insuring a coating consisting only of magnetic oxide. Wrought-iron or steel, of course, requires no "pickling," as there is no sand to be removed. The furnace is heated to the same temperature as for cast-iron, and then the charge is run in and heated up with a strongly reducing flame until it reaches a bright red. ”

“ Thus a furnace in which a fire of carbonaceous matter is kept up and urged to the highest possible degree of intensity by blowing machines, is necessary. When the earths are pure, even the highest heat of furnaces is incapable of fusing them, and although the oxides of the ancient metals, and among the rest, the oxide of iron, increase the fusibility of one of the earths; still, if but one earth be present, it is only in a few cases that the simple ore will furnish the means of its own fusion. ”

“ To begin the process, they are piled in a furnace between alternate layers of charcoal, the surfaces kept carefully from contact, and are there subjected to fire for eight or nine days. To enable the workmen to watch the process, small trial pieces are so placed that they can be drawn out for examination through a small hole in the front of the furnace. In large furnaces, twelve tons of iron are converted at once. The long-continued heat, which is kept below the melting-point, drives off the impurities; the bars, from contact with the charcoal, become carbonized and hardened ”

“ We know that if burned in a furnace this ton of high grade fuel would generate much heat. Burned inside of the mass of molten metal it generates exactly that same amount of heat and the heat is applied with such rapidity, directness and efficiency that the molten iron which had a temperature of 2300° F., say, when charged, in nine or ten minutes 131has become steel with a temperature of about 3000° F. simply through this rapid oxidation of its 4 to 6 per cent of metalloids. ”

“ This is what is called a "blast furnace," because the draught for the fires is made artificially by the forcing in of a strong current of air. Much iron is smelted in that region, the ore coming from the famous Cornwall ore hills near by. The Colebrook produces about 175 tons of iron daily.
It was on a hazy June morning that our party took a new trolley-car that had been running only a few days, and after riding a short distance into the country, alighted quite near the furnace, which seemed to be composed of a few gray stone buildings, and several high red stacks. ”

“ In the blast furnace more iron could be made in a day than could be made by the forge in a month. In some of the early blast furnaces a thousand pounds of iron could be made at one melting and we read of one early furnace that produced 150 tons of iron in a year. ”

“ The blast furnace was introduced in the iron industry. A blast of hot air was constantly forced from a stove into the lower part of the furnace which was heating at high temperature a mixture of the iron ore and a reducing agent that combined with the oxygen released. ”

“ Thus, iron-masters used to think that the best way of smelting iron in the blast-furnace was to blow the furnace with cold air; science, however, showed that, instead of being cold, the air sent into the furnace should be made as hot as possible. ”

“ Mushet says, "The greatest produce in iron per furnace with the Black Band and cold blast never exceeded 60 tons a-week. The produce per furnace now averages 90 tons a-week. Ten tons of this I attribute to the use of raw pit-coal, and the other twenty tons to the use of hot blast." [Papers on Iron and Steel, 127.] The produce per furnace is now 200 tons a-week and upwards. The hot blast process was afterwards applied to the making of iron with the anthracite or stone coal of Wales ”

“ More or less success has ensued, but without ever surmounting all the obstacles arising from the great fusibility of the sulphuret of iron. For sometimes it runs into one mass, or at least into lumps agglutinated together in certain parts of the furnace, and the operation is either stopped altogether, or becomes more or less languid; the air not being able to penetrate into all the parts, the roasting becomes consequently imperfect. ”

“ In starting the furnace, the bottom is prepared by ramming it with charcoal-powder that has been soaked in milk of lime and dried, so that each particle is coated with a film of lime, which serves to reduce the loss of current by conduction through the lining when the furnace becomes hot. A sheet iron case is then placed within the furnace, and the space between it and the walls rammed with limed charcoal; the interior is filled with fragments of the iron or copper to be alloyed, mixed with alumina and coarse charcoal, broken pieces of carbon being placed in position to connect the electrodes. ”

“ This carburizing is an indispensable part of the process, because through it alone can the iron be made fusible enough to melt at the temperature which can be generated in the furnace, and only when liquid can it be separated readily and completely from the slag. In fact, the molten iron is heated so far above its melting point that, instead of being run at once into pigs as is usual, it may, without solidifying, be carried even several miles in large clay-lined ladles to the mill where it is to be converted into steel. ”

“ The open-hearth process does this by two distinct steps: (1) by oxidizing and removing these elements by means of the flame of the furnace, usually aided by the oxygen of light charges of iron ore, and (2) by diluting them with scrap steel or its equivalent. The “pig and ore” or “Siemens” variety of the process works chiefly by oxidation, the “pig and scrap” or “Siemens-Martin” variety chiefly by dilution, sometimes indeed by extreme dilution, as when 10 parts of cast iron are diluted with 90 parts of scrap. ”

“ The retorts and flues are made entirely of fire-brick, from special patterns. The outside is protected by a wrought iron jacket made of No. 14 iron. The puddling furnace is of the ordinary construction, except in the working bottom, which is made longer to accommodate two charges of ore, and thus utilize more of the waste heat in reducing the ore to metallic iron. ”

“ So the ore is brought from the mines to the furnace, the coke and limestone arrive from another region, and batteries of huge blast furnaces through the country make from them the pig iron.
1. No advantage has been found in furnaces having a height of over 110 feet.
The chemical laboratory plays a very important rôle in iron making. ”

“ A blast furnace should go for four or five years without needing restoration. From 31⁄2 to 4 tons of coal, inclusive of the coal of calcination, are required in Staffordshire to obtain one ton of cast iron; and the expense in workmen’s wages is about 15 shillings on that quantity.
At the Cyfartha works of Messrs. Crawshay in South Wales, the average price of the lithoid carbonate of iron, ready for roasting, is only 7s. 6d. a ton, and its richness is about 33 per cent. The furnaces for roasting the ore in that country are made in the form of cylinders, placed above an inverted cone. ”