THE CEMENT Consists principally of charcoal; and there is sufficient evidence that pure charcoal will make the best steel. All descriptions of iron, however, are not similarly composed; and as carbon alone does not make the very best steel, there is a necessity for a compound cement. The charcoal is used in the form of a coarse powder, the grains of the size of blasting powder; it is sifted, and the fine dust, a great deal of which is made in pounding the coal, is thrown away. Sometimes the charcoal is cut by a sharp knife, set in a machine similar to a straw-cutter. Charcoal made from the harder woods, such as whiteoak and black-jack, hickory, dogwood, sugar maple, &c., give us the greatest quantity of cement, and of the best kind. The addition of refuse tobacco, such as is thrown away by segar manufacturers, may prove of advantage to the cement. An addition of ten or fifteen per cent. of pure lampblack is also an improvement, but rather expensive. In the Western States, or the bituminous coal region, lampblack may be made cheaply; but if not of the purest kind of coal, it will injure the steel. Sulphurous coal, therefore, should not be used. Anthracite powder, coke powder, and black lead or plumbago, are inadmissible, either pure or in admixture with charcoal. The cement generally in use is composed of charcoal mixed with one-tenth part of good wood-ashes, and about one-thirtieth of common salt. The whole of it is then moistened and well mixed. Some establishments vary the cement slightly, but the majority use the proportions above given. For some descriptions of iron, charcoal alone makes the best cement. In such cases, the wood of the gum, poplar, sassafras, &c., which make but little ashes, should be charred. Charcoal made from pine is to be rejected, as it is too soon exhausted. Some metallurgists have tried and recommended the addition of borax, prussiate of potash, horn, bones, vinegar, manganese, sal-ammonia, and a variety of other things; but none of these admixtures have any beneficial effect upon the steel. Experiments have been tried with a view of making steel by conducting carburetted hydrogen gas between bars of hot iron; or leading carbonic oxide gas to it; or cementing with diamond powder, and similar projects. These experiments, however, have all proved abortive; bad iron cannot be converted into good steel, under any circumstances; and it is certain that charcoal powder is at least equal to dia mond powder, or anything else that has been tried up to the present time. The size, form and material of the convertingchest has some influence on the quality of the steel made. For spring-steel, the boxes may be three feet high and three feet wide; such a box will take a charge thirty inches high. The chest, however, had better be not more than thirty inches each way; this size will consume a little more fuel than the other, but that loss is richly made up in the superior quality of the product. In wide and high chests, particularly the latter, the central bars are never so well cemented as they should be, while the extreme bars absorb too much carbon. As a general rule, American converting-chests are not wider than thirty inches; while in Europe we frequently find them of the larger size mentioned. The length of the boxes is unlimited, except by the strength of the furnaces. Long boxes require to be well secured by iron binders; of course, with shorter boxes, this is not so important. In this country we find no boxes less than twelve feet long, and they do not often extend beyond twenty. The grate is somewhat troublesome to manage in long furnaces; but this is not of much consequence. size of the grate is of some importance in the result; The it is better in all instances to have it too large than too small. A grate two feet wide by thirty inches deep is a good size for bituminous coal, with thirty inch boxes. For wood or anthracite coal, the grate should be four feet wide. In this case the boxes will be rather far apart, because the bottom of each box is to rest on solid masonry, and there will consequently be a considerable loss of heat. To avoid this loss, we put another box in the open space, thus making three boxes in the furnace. The middle box is to rest upon a series of fire-brick arches, which are sprung upon the tongues; and as these arches are higher than those tongues, the middle box will be higher than the other two, and the whole will assume the arrangement represented in fig. 28. narrower. The flues around the boxes are to be of uniform size, and so arranged as to make an equal heat all over the furnace. If, after the first trial, it is found that the boxes work hotter in one place than in another, the flues in the hottest parts are to be made The arch is to be as flat as possible, and at least nine inches thick. The spring or height of the arch will depend upon the resistance of the rough walls of the furnace; if these are secure, and the furnace well provided with iron binders, the arch may be very flat. The flues are generally in the centre of the arch; but should the furnace work hotter in the centre than on the sides, some flues may be opened at the sides, where it is found to work too cold. In some instances the boxes have no flues at the ends; this is allowable where spring-steel only is made; but for shear or cast steel it is an ill-advised economy, as the ends of the bars are always better cemented when the fire plays freely at the ends of the chests. |