STUDY OF THE METHOD BY CADINHES.
The province of Minas Geraes ocupies a vast extent in the empire of Brazil, its superficies being about 900,000 square kilometers, representing nearly a third of the total surface.
The population is relatively small and is disseminated throughout a much broken country, where the means of communication are very few. So it is necessary to succeed in producing what iron is needed by means that are simple and that require but quickly erected works built of such material as may be at hand. The iron ore is found in very great abundance in this region and is very easily mined.
In the center of a mass of quartzites that seem lo constitute the upper level of the eruptive grounds of the province, there are found strata of an ore of iron designated as itabirite--a mixture of oxide of iron and quartz. These strata are of great thickness, and have numerous outcrops that permit of their being worked by quarrying.
These itabirites present themselves under two very distinct aspects and offer a certain difference in their composition. Some are essentially friable, and are called by the vulgar name of jacutingaes. It is this variety (which is the one most easily mined) that is principally consumed in the forges. The others, on the contrary, are compact. Their exploitation is more difficult, and before putting them into the furnaces it is necessary to submit them to breakage and screening; so the use of them is more limited.
The first variety contains less iron and more gangue, but, per contra, possesses much oxide of manganese. The second, on the contrary, is formed almost wholly of oxide of iron with but little gangue and only traces of oxide of manganese. The following are analyses of these two varieties of ore:
| Friable Ore | |
|---|---|
| Fe2O2 | 84.9 |
| Oxide of manganese | 9.2 |
| Water | 1.9 |
| Quartz | 4.1 |
| ------ | |
| 100.1 | |
| Compact Ore | |
|---|---|
| Fe2O3 and traces ofmanganese | 99.6 |
| Quartz | 1.1 |
| ------ | |
| 100.7 | |
Situation of the Forges.--A forge is usually placed on the bank of a brook, or rather of a torrent, which supplies the fall of water necessary for the motive power by means of a flume about a hundred meters in length. In most cases the forge is surrounded on all sides with a forest which yields the wood necessary for the manufacture of the charcoal, and is in the vicinity of the iron quarry, so as to reduce the expense of hauling the ore as much as possible. The neighboring rocks furnish the foundation stones and stones for the furnaces; the decomposed schist gives the cement and refractory coating, and the forest provides the wood necessary for the construction of the road, sheds, etc. The head of the trip hammer, the anvils, and the tools are the only objects that it is necessary to procure, and even these the master of the forge often manufactures in part, after beginning production with an incomplete set.
[Illustration: 7a FIG 1.--FOUR-CRUCIBLE FURNACE AND FORGE; (PLAN).]
General Arrangement of a Forge.--A forge usually consists of one or two furnaces of three or four crucibles (the one shown in plan in Fig. 1 has only one four crucible furnace, A); 1 or 2 two fire reheating furnaces, B; 1 trip hammer, C, actuated by a hydraulic wheel, D; 2 tromps which drive the wind, one of them, E, into the cadinhes (crucibles), and the other, F, into the reheating furnace; 2 anvils, G and H, placed near the furnace, for working delicate pieces; and finally, the different tools that serve for maneuvering the bloom and finishing the bars. The charcoal is preserved from rain under a shed, l. The ore, which is brought in as needed, is dumped in a pile at M, in the vicinity of the crucibles. The buildings are set back against the mountain, and the water is led in by a double flume, L and N, made of planks, and empties on one side into the wheel and into the tromp, F, and on the other into the tromp, E, and then runs into a double waste channel, P and Q, which carries it to the stream.
FIG 2.--FOUR-CRUCIBLE FURNACE; (PLAN).
Four Crucible Furnace (Fig. 2).--The arrangement of a furnace is very simple. It consists of a cube of masonry containing several cylindrical apertures with elliptic bases, whose large axis is paralleled with the smaller side of the masonry. This form recalls that of a crucible; and these cavities are, moreover, so named. In the front part of each cadinhe there is a rectangular aperture that gives access to the bottom of the crucible and facilitates the removal of the bloom therefrom. At the back part there is a small aperture for the introduction of the tuyere, and which permits, besides, of the nozzle of the latter being easily got at so as to see whether the blast is working properly.
The sides of the crucibles are covered with a thin layer of refractory clay, and their bottoms have a spherical concavity to hold the bloom. The tuyere, which is fitted to a wooden conduit of square section that runs along the back of the masonry, is placed in the axis of the cadinhes and enters the masonry at a few centimeters from the bottom in such away that its nozzle comes just flush with the surface of the refractory lining. This arrangement prevents the tuyere from getting befouled by scoriæ during the operation of the furnace and thus interfering with the wind.
Tromp.--The tromp which furnishes the necessary wind to the cadinhes consists of a hollow wooden conduit, a (Fig. 3), of square section, which enters a chamber, b, along a length of 0.1 m. This conduit, which is about 7 meters in height, receives the water from the flume through the intermedium of an ajutage of pyramidal form, which serves to choke the vein of liquid, and the extremity of which is at a few centimeters from the conduit in order to facilitate the entrance of the air; the latter being attracted by an ill defined action that is supposed to be due to its being carried along by the water, and to a depression produced by choking the flow of the liquid.
FIG. 3.--THE TROMP.
Since the air that is sucked in during the operation has constantly same pressure, there is no valve for regulating the entrance of the water into the vertical conduit. Upon issuing from the latter, the mixture of air and water strikes the surface of the water in the chamber, b, and the violence of the shock upon the bottom is deadened by the interposition of a stone. While the water is escaping through a lateral aperture in the chamber, b, the air is reaching the tuyeres through a wooden conduit of square section which is fitted to an aperture in the upper part of the chamber. This sorry arrangement, which obliges the mixture of air and water to penetrate the water at the bottom of the upright conduit, a, retards the separation of the two fluids, and results in damp air being forced into the crucibles.
The Trip Hammer.--Fig. 4 shows the general arrangement of the apparatus that go to make up the forging mill. The hammer and cam shaft have their axes parallel, and the latter is placed in the prolongation of the axis of the wheel. The hammer consists of a roughly squared beam, 4 meters in length, and of 0.25 m. section. The head, A, consists of a mass of iron weighing 150 kilos, including the weight of the straps that surround the beam on every side of the piece of iron. The axis of rotation is situated at the other extremity of the beam, B. The cam shaft which serves to maneuver the trip hammer is provided with four cams which lift the beam at a point near the hammer. The length of this shaft (to the extremity of which is adapted the water wheel) is 4.75 m., and its diameter is 0.50 m. The wheel is an overshot one, 3.25 m. in diameter by 1 m. in width. The water, which is led to it by a flume, acts upon it by its weight and impact, and is retained in the buckets and kept from overshooting the mark by a jacket made of planks.
FIG. 4.--THE TRIP HAMMER.
The anvil upon which the hammer strikes is surrounded by a bed of stones (quartzites) derived from the neighboring rocks. It is a mass of iron, 75 kilogrammes in weight. In order to prevent vibrations in the trip hammer when it is lifted, and increase the number of blows, there is established a spring beam, which is formed of unsquared timber, which is firmly fastened at one of its extremities, and which receives at the other end the shock of the hammer head when the latter reaches the end of its upward travel.
Reheating Furnace.--This is a double fire furnace, like those used in our smithies, except that the wind, instead of being forced into it by means of a bellows, is supplied by a tromp which receives water from the same channel as the wheel. The two furnace tuyeres are arranged exactly like those of the cadinhes, upon a wooden conduit which starts from the wind chamber (Fig. 5). This furnace serves to prevent the cooling of such blooms as are awaiting their turn to be shingled, and of such bars of finished iron as are being made into tools.