Bloomary, a name sometimes given to a kind of furnace for the production of malleable iron from cast or pig iron, and sometimes to a similar furnace for the direct extraction of malleable iron from its ores. In both cases the lump of iron obtained, when finished under the hammer, is called a bloom, from the German Blume, a flower, because, it is said, the product is as it were the flower of the ore. The direct fabrication of malleable iron from the ore appears to have been practised from remote antiquity. The natives of India, Burmah, Borneo, Madagascar, and some parts of Africa practise the direct conversion of iron ores into metallic iron in furnaces which are rude bloomaries. In certain districts of India the amount of metallic iron thus produced is very considerable, and much of it is manufactured into steel; but the furnaces used are small in size and do not yield more than 30 or 40 lbs. of iron daily, with the labor of three or four men, and a great waste of ore and charcoal. The massive rich ore coarsely pulverized, or the grains of iron ore obtained by washing the sands in some places, are heated with charcoal in shallow open furnaces until reduced to the metallic state; but as the metal thus produced is infusible at the heat of these furnaces, it agglutinates into an irregular mass, known as a loup, which is afterward hammered and converted into a bloom.
Somewhat similar methods of making malleable iron have long been known in various countries of Europe, where under improved forms they are still followed, and have thence been brought to North America. Of these furnaces for the direct production of blooms from the ore five forms are known in Europe, viz.: the Corsican and Catalan forges, the German bloomary forge, the Osmund furnace, and the German Stuckofen or high bloomary furnace, which had high walls and approached in form the modern blast furnace, of which it seems to have been the immediate precursor. All of these employ a blast to increase the heat, but the name of blast furnace is technically given only to those furnaces in which by increasing the heat the reduced iron is subsequently carburetted and fused, being thus separated in the form of cast or pig metal from the melted impurities or slag, both of which are drawn off by tapping the furnace from time to time. The production of iron in this way is a continuous process, while in the various bloomary furnaces the operation is interrupted from time to time in order to remove from the hearth the accumulated mass of reduced but unmelted malleable iron, which is then freed from the slag or cinder by hammering.
Of these furnaces the Corsican is the most primitive form, and is now nearly if not quite disused. It was said to consume more than 800 lbs. of charcoal in making 100 lbs. of iron. - The Catalan forge or bloomary is so called from the province of Catalonia in Spain, Where it was formerly much used, as well as in the neighboring parts of France, especially in the department of Ariege. The Catalan forge as used in France consists of a rectangular hearth constructed chiefly of heavy iron plates, and in the largest size measures 40 by 32 inches, and is from 20 to 24 inches deep, or from 12 to 15 inches below the tuyere or pipe through which the blast enters. In some cases, however, furnaces of not more than one half these dimensions are built. The pressure of the blast does not exceed 1 1/2 or 1 3/4 inch of mercury, and the tuyere is directed downward at an angle of 30° or 40°. The wall facing the tuyere slopes outward toward the top, and in working the greater part of the charge of ore is heaped against it, and occupies from one third to one half of the cavity of the furnace, the remaining space being filled with ignited charcoal.
The ore is previously broken so that the largest lumps are not more than two inches in diameter, while from one third to one half of the material will pass through a screen the bars of which are four tenths of an inch apart. This finer ore is thrown on the surface of the fire from time to time during the operation, which is conducted with many precautions as to regulating the blast, stirring, and supplying the fine ore and coal. At the end of six hours, in the ordinary routine, there is withdrawn from the bottom of the furnace an agglomerated mass of reduced but unmelted iron, which is then forged into blooms or bars. The operation consumes, in one of the larger-sized forges, about 9 1/2 cwt. of iron ore (a limonite holding 40 or 50 per cent, of iron is treated in the Ariege) and 10 1/2 cwt. of charcoal, and yields 3 cwt. of bar iron. According to another calculation, there are required in this process, for the production of 100 lbs. of iron, 340 lbs. of charcoal and 312 lbs. of an ore containing from 45 to 48 per cent, of iron. Of this about seven tenths are obtained in the metallic state, the remainder passing into the slag; 100 lbs. of the ore yield 31 lbs. of bar iron and 41 lbs. of slag, which is a dark-colored basic silicate, very rich in oxide of iron.
It is to be remarked that in this direct method of treatment a portion of the oxide of iron is always consumed in fluxing the impurities of the ore, so that the purest ores are generally sought for the purpose. In the blast furnace, on the contrary, by the judicious use of lime or other basic fluxes, the slags are obtained almost free from iron, and the loss of the metal is thus avoided. - The German bloom-ary furnace was formerly used in Silesia and the Palatinate, and is described at some length by Karsten (1816), but is dismissed with a few words in Bruno Kerl's treatise (Huttenkunde, 1864 iii. 427), from which its use would seem to be nearly or quite abandoned in Germany. According to Karsten, the German bloomary consists of an iron pot, or a box of iron plates, in either case lined with refractory bricks, and having an internal diameter of from 14 to 21 inches, and the same depth, the dimensions varying with the fusibility of the ore, the force of the blast, and the quality of the coal. The tuyere is horizontal. The furnace having been filled and heaped up with burning charcoal, the ore is thrown upon the fire by shovelfuls at a time, until a loup of sufficient size has been formed at the bottom of the hearth, as already described in the Catalan method.
When the blast is too intense, or the coal very dense, it may happen that the reduced iron becomes carburetted by the excessive heat to such an extent as to produce a steel-like iron, or even molten cast iron, instead of a loup of soft malleable iron. A similar state of things sometimes occurs in the Catalan forge, and is occasionally taken advantage of to produce an imperfect kind of steel. From the above description it will be seen that the method by the German bloomary differs from that by the Catalan in the fact that in the latter the greater part of the charge of ore is placed at the commencement of the operation, in a coarsely broken state, on the sloping wall of the furnace, opposite the tuyere, while the remaining portion is subsequently projected in a more finely divided condition upon the surface of the fire. In the German method, on the contrary, the whole of the ore is reduced to this finer condition, and is added by small portions; a plan which dispenses with the charging of the furnace with ore after each operation, as in the Catalan method, and permits of a continuous working, interrupted only by the withdrawal of the loups from time to time. - The German bloomary in an improved form is extensively used for the reduction of iron ores in the United States, where it is known by the name of the bloomary fire, the Jersey forge, or the Cham-plain forge; it is also frequently called the Catalan forge, from which, as already shown, it is distinct in form and still more distinct in the manner in which it is worked.
This latter seems however to be unknown, at least in the northern and eastern portions of the United States. The German bloomary was probably introduced into North America early in the last century. Among the forges in operation in New Jersey and Pennsylvania in 1856, Lesley, in his "Iron Manufacturers' Guide," mentions one as having been established in 1733 and another in 1725. The magnetic iron sands of the seacoast early attracted the attention both of the American colonists and of metallurgists in England, as appears from the experiments of Dr. Mohlen as early as 1742 upon what was called the Virginian black sand (the name of Virginia being at a still earlier period given to the whole coast from Canada to Florida). These black sands from Killingworth, Connecticut, were there successfully treated in a bloomary furnace in 1762 by the Rev. Jared Elliot, who obtained blooms of 50 lbs. weight of iron, which was afterward made into steel of superior quality, and for his discovery received the following year a medal from the society of arts of London. Steel works had at that time been erected in Connecticut for the treatment of the metal thus produced, but were abandoned on account of an act of parliament forbidding the manufacture of steel in the British colonies.
In the districts where it was first worked, including northern New Jersey and the adjacent parts of New York and Pennsylvania, the bloomary process has fallen into disuse since wood has become scarce, and extensive workings of coal in the vicinity, with great facilities for transportation, have rendered it more profitable to treat the ores in the blast furnace than in the bloomary fire. In northern New York, on the contrary, the use of the bloomary process has continued to extend within the past few years, and in 1808 the production of iron by this method in that region was estimated at nearly 40,000 tons, a large portion of which is consumed at Pittsburgh for the manufacture of steel by cementation, for which it is much prized. Two establishments in the vicinity of Keeseville had in that year respectively 18 and 21 bloomary fires, and the whole number in activity in Essex and Clinton counties in 1867 was said to be 136. It is only in mountainous regions, abounding in rich iron ores and wood suitable for charcoal, and still inaccessible to railways, that this process can hold its ground. Its advantages are, that the outlay and floating capital required are inconsiderable, and the consumption of charcoal comparatively small.
The direct mode of reduction can only be applied to rich ores, which to yield good results in the German or Catalan bloomary should contain not much less than 50 per cent, of iron, while much richer ores are to be preferred. Two tons, and of the richest and purest ores 1 1/2 ton, will under careful management yield one ton of blooms. The bloomary hearths used in northern New York vary in area from 27 x 30 to 28 x 32 inches, and in depth from 20 to 25 inches above the tuyere, and from 8 to 14 inches below. The sides are of heavy cast-iron plates, and the bottom, though often of beaten earth or cinders, is in the best constructed hearths also of iron, made hollow and kept cool by a current of water circulating through it. The side plates slope gently inward in descending, and rest on ledges in the bottom plate. A water box is let into the tuyere plate. The tuyere, which is inclined downward, has its opening in the form of a segment of a circle. In some localities these dimensions differ from those given; and the bloomaries lately erected at Moisie in the lower St. Lawrence, for the treatment of the magnetic iron sands, measure 32 x 30 inches, and have the tuyere nearly horizontal.
The blast employed in the American bloomaries has a pressure of 1 1/2 to 1 3/4 lb., and is heated to 550° or 600° F., by passing through inverted siphon tubes of cast iron placed in a chamber above the furnace. By the use of the hot blast the production of the furnaces is much increased, and a considerable saving of charcoal is effected without any deterioration in the quality of the metal. The working of these furnaces is conducted as follows: The fire being kept active and the furnace heaped with coal, the coarsely pulverized ore is scattered at short intervals upon the top of the burning fuel, and in its passage downward is reduced to the metallic state, but reaches the bottom without being melted and there accumulates, the grains agglomerating into an irregular mass or loup, while the earthy matters form a liquid slag or cinder which lies around and above it, and is drawn off from time to time through an opening in the front plate. At the end of two or three hours, or when a sufficiently large loup is formed, this is lifted by means of a bar from the bottom, brought before the tuyere for a few minutes to give it a greater heat, and then carried to the hammer, where it is wrought into a bloom; the bloomary fire itself being generally used for reheating.
This operation being concluded, the addition of ore to the fire is resumed, and the production of iron is kept up with but little interruption. A skilled workman will with a large-sized bloomary furnace bring out a loup of 300 lbs. every three hours, thus making the produce of a day of 24 hours 2,400 lbs. of rough blooms. The consumption of charcoal is from 250 to 300 bushels, (weighing 16 or 18 lbs. to the bushel) for each ton of 2,000 lbs. of blooms produced. In addition to the cost of the ore and coal, which varies somewhat with the locality, the estimate of a competent iron master in northern New York in 1868 gave for wages $9, and for general expenses $3 50, for each ton of blooms produced. - Several plans have been introduced having for their object the reduction of rich iron ores at low temperatures in close chambers by carbonic oxide, and the spongy metallic iron thus obtained was in many cases transferred at once to a hearth and converted into blooms. Such was the case in the methods of Clay, of Chenot, and of Renton. In the manufacture of blooms from cast iron by the Walloon method, now to a great extent superseded by puddling, the iron, generally purified by a first fusion in what is called a running-out fire, is brought in small portions at a time before the tuyere on a charcoal fire similar to the German bloomary fire just described, and known as a sinking fire.
It there melts down and is at the same time decarbonized, the product accumulating in the bottom of the furnace in a loup, which is treated in the manner already described and yields a bloom of malleable iron. The iron thus obtained is superior in quality to that produced by puddling, and for the finer kinds of metal the process is still practised in some parts of the United States, and to a considerable extent in Sweden, where a modification of the bloomary known as the Lancashire hearth is employed. The loss in this process of conversion is considerable, and the consumption of charcoal in the production of the pig iron and its subsequent conversion in the bloomary fire is about equal to that required in the direct process.