For such iron, a cherry-red heat will suffice. This heat is produced by ovens or stoves. In these ovens, all sheet iron, and rods which require an extra polish, or tempering, are heated. Charcoal billets, from the forge, are also heated in them, to be rolled into rod iron of small size.

a. These ovens may be heated by a variety of methods, and with almost any kind of fuel; still, every caution is requisite to prevent, as far as possible, the access of free oxygen and steam, for both steam and oxygen occasion waste of iron. For these reasons, our statement must be received with some qualification. Wood, turf, and brown coal are, so far as their capacity for generating heat is concerned, an excellent fuel; but, unless they are very dry, the steam generated from their. hygroscopic water will oxidize, and thus destroy an amount of iron whose expense will not be counterbalanced by the entire profits derived from the fuel employed. Therefore, instead of using the raw material, it will be found advantageous to use only the charcoal derived from charring it.

The same objections which apply against any fuel containing water-which of course excludes the use of all kinds of heating, reheating, and puddling furnaces-apply against waste flame, for this contains a large amount of steam, or free oxygen.

b. The ancient form of a heating oven was that of a common bake oven, with this difference, that the bottom was formed of iron bars. Upon these bars, placed in the form of a grate, coal from ten to fifteen inches in depth was laid. The iron was placed upon the coal, after the oven was heated. In some establishments, such ovens are still employed. It is evident that a portion of the iron in contact with the fuel-particularly raw fuel, such as turf, brown coal, and bituminous and anthracite coal-must be wasted. The only instance in which such an arrangement may be considered profitable is where wood charcoal is employed. Even the best coke or turf coal is not sufficiently pure to guarantee success. Stone coal, coke, and turf are never free from sulphur, and this sulphur will of course combine with the iron. A waste of iron is thus occasioned exactly proportionate to the amount of sulphur the fuel contains. In addition to this, sulphur blackens the metal, which, in the case of sheet iron and nail plates, gives rise to very disagreeable consequences. Fuel burned in this way, even though spread in a high column upon the grate, never combines with all the oxygen which passes through the coal; the result is a waste of iron. Therefore, there is every reason why such ovens are not serviceable.

c. Heating ovens of a superior kind are at present constructed on the principle of the reverberatory furnace. In these, the fuel and iron are properly separated, and all contact between them obviated. Fig. 123 represents a vertical section of a heating oven for sheet

Fig. 123.

Heating oven for sheet iron.

iron; a is the hearth, b the fire grate, and c the chimney. The height of the furnace is often thirty inches. The object of this is partly to prevent the contact of the flame and iron, but principally to gain room for setting the sheet edgewise; they are thus set on both sides of the furnace; besides, in the middle of the hearth, sufficient room is left for laying a sheet or two flatwise. d is a cast iron plate, forming a sliding door. The chimney has two flues, the one inside, the other outside of the oven. Its draft is weak, and the smoke or flame frequently issues from the mouth, in which case it is carried off by the second or outside flue. Fig. 124 represents a vertical section across the furnace and the flues; and Fig. 125 a ground-plan of the furnace, hearth, and fireplace. The cast iron plate e is here shown more distinctly. Its object is to protect the bricks or stones from the destructive agency of the tongs and iron. Like puddling and reheating furnaces, these ovens are built of fire bricks, inclosed with cast iron plates, and preserved from the effects of expansion and contraction by wrought iron cross binders. A slight variation from the form of the oven we have described, occasioned as well by individual taste as by locality, is sometimes.

observed; still, the one we have presented is the one generally

Fig. 124.

Front elevation of a heating oven.

employed for the manufacture of sheet iron. If it is desirable that the surface of the iron should be kept very clean, the fire bridge

Fig. 125.

Ground-plan of a heating oven.

and the inside flue may be raised; but, in all such cases, pure fuel is our safest reliance.

IX. Shears, and Turning Machines.

These are of much importance in a rolling mill. The first we shall describe somewhat minutely; but a brief description of the latter must suffice.

a. When rollers are cast, and ready for turning, they are placed upon a strong and heavy turning lathe, and the gudgeons and couplings turned between points. They are then put into cast iron standards, into which brass pans are inserted. In the latter, the gudgeons revolve. At first, the rollers are turned into smooth cylinders. After a set is thus far completed, the grooves are cut in, according to a design previously drawn on a board. Sheet iron or sheet brass patterns are made for each groove in every every roller. These should be preserved, in case a roller is injured, or fails to answer its purpose. Rollers for sheet iron are of course smooth cylinders, but it is not necessary that the bottom and top of the roller should be of the same diameter. Those for thin sheet iron should be turned one upon the other, that their surfaces may be perfectly parallel. Unless there is too great a variation in the surfaces, this may be done in the housings. After using the rollers for a time, their surface is apt to become rough. Its smoothness may be restored by cutting it with one edge of a square piece of cast steel, from three to four inches in length. This operation is generally performed in the housings, for the moving of the rollers to the turning lathe is attended with great expense. Good hard rollers are turned with difficulty by common methods. A steady turning machine, of slow motion, excellent cast steel chisels, and patience, are the conditions of success. Hard rollers are required for making thin and polished sheet iron. They are polished by means of emery and leaden pans, which extend almost quite around the roller.

b. The shears required in a mill are the movable hand-shears, for cutting small rod and hoop iron, and force-shears connected with a waterwheel or steam-engine, for cutting common bar, rough bar, and sheet iron. The first are small lever shears, fastened upon a two inch plank, as represented in Fig. 126. The length of the whole is about two feet or thirty inches. The shears are placed at each end of a pile where small bar or hoops are deposited. The boys, who catch behind the rollers, cut off the bad ends, before a rod or hoop is laid down.

c. Fig. 127 represents the common force-shear. It is a powerful cast iron lever, varying, according to locality and purpose, from

seven to twelve feet in length. The excentric a is generally fastened upon the main shaft, or, if such is not accessible, upon any

Fig. 126.

Portable hand-shear.

other strong and well-supported shaft. The foundation must be very firm, and not inferior in solidity to the roller trains. The steel

Fig. 127.

Shear moved by an excentric.

blades are made of good shear or cast steel, tightly fitted into the cast iron lever and standard, and screwed on with screw bolts. For the cutting of heavy bar and rough bar, the standard block is generally placed very low, about a foot above ground; but for cutting common bar and sheet iron, it is raised from two feet to thirty inches above ground. If sheet iron is principally brought to the shears, an iron frame b, b, as high as the lower cutter, is to be fastened to the standard. Upon this frame, the sheet is moved. In working sheet iron, shears of this construction are attended with some disadvantage. The acute angle at the points, and the obtuse angle close to the fulcrum which they form, in addition to the difficulty of adjusting them accurately, make them somewhat objectionable.