CEMENTING FURNACES.
We do not propose to elaborate the method of producing steel by the old processes, but simply to give the chief points, in order to trace the modes and means of the manu facture, and to illustrate the new developments or inventions which arrive at the desired object directly, instead of indirectly, as by the old and roundabout process of decar bonization and recarbonization.
The furnace of cementation, in which bar iron is converted into bar or blister steel, is represented in the foregoing figures. It is generally rectangular, and covered in by a groined or cloister arch; it contains two cementing-chests, c, c, made either of fire stone or fire-brick; each chest, or cementing-trough, is about feet wide, 3 feet deep, and 12 feet long, and capable of cementing about six tons of bar iron at each heat. One of these chests is placed on each side of the fire-grate A B, which occupies the whole length of the furnace, and is from 13 to 14 feet long. The grate is 14 inches broad, and rests from 10 to 12 inches below the inferior plane or bottom-level of the chests; the height of the top of the arch above the chests is 5i feet; the bottom of the chests is nearly on a level with the ground, so that the bars do not need to be lifted high in charging the furnace.
The flame rises between the two chests, passes also below and around them through the horizontal and vertical flues d, and issues from the furnace by an opening, H, in the top of the vault, and by orifices, t, which communicate with the chimneys placed in the angles. The whole is placed within a large cone of bricks 25 or 30 feet high, and open
at top; this cone increases the draft, makes it more regular, and carries off the smoke from the establishment.
The furnace has three doors: two, T, above the chests serve to admit and remove the bars; they are about 7 or 8 inches square; in each of them a piece of sheet iron is put, folded back on its edges, so as to save the wall in sliding the bars in and out of the chests.
A workman en,ters by the middle door P to arrange the bars; the trial bars are taken out from time to time through the apertures s, which are prepared for the purpose. The bars are laid in strata in the chests along with powdered charcoal made from young timber; these bars are three inches broad, and one-third of an inch thick; they must not be allowed to touch each other, but are separately imbedded in the charcoal; the uppermost layer is covered with a stratum of loamy matter from 4 to 5 inches thick.
The furnace must be heated gradually, not reaching its maximum temperature before 8 or 9 days, while the cooling lasts 5 or 6 days, and the whole operation 18 or 20 days. About 13 tons of coal are consumed in this period.
Many of our old steel-manufacturers make a great mystery about the secret in gredients—ashes, salt, &c.—which it was insisted must be used; but the best steel can be made without them as well as with them.