Forge-Practice - Elementary

FORGE-PRACTICE.

CHAPTER I.

GENERAL DESCRIPTION OF FORGE AND TOOLS.

Forge.—The principal part of the forge as generally made now is simply a cast-iron hearth with a bowl, or depression, in the center for the fire. In the bottom of this bowl is an opening through which the blast is forced. This blast-opening is known as the tuyere. Tuyeres are made in various shapes; but the object is the same in all, that is, to provide an opening, or a number of openings, of such a shape as to easily allow the blast to pass through, and at the same time, as much as possible, to prevent the cinders from dropping into the blast-pipe.

There should be some means of opening the blast-pipe beneath the tuyere and cleaning out the cinders which work through the tuyere-openings, as some cinders are bound to do this no matter how carefully the tuyere is designed.

When a long fire is wanted, sometimes several tuyeres are placed in a line; and for some special work the tuyeres take the form of nozzles projecting inwardly from the side of the forge.

Coal.—The coal used for forge-work should be of the best quality bituminous, or soft, coal. It should coke easily; that is, when dampened and put on the fire it should cake up, form coke, and not break into small pieces. It should be as free from sulphur as possible, and make very little clinker when burned.

Good forge-coal should be of even structure through the lumps, and the lumps should crumble easily in the hand. The lumps should crumble rather than split up into layers, and the broken pieces should look bright and glossy on all faces, almost like black glass, and show no dull-looking streaks.

Ordinary soft coal, such as is used for steaming-coal, makes a dirty fire with much clinker. Steaming-coal when broken is liable to split into layers, some of which are bright and glossy, while others are dull and slaty-looking.

Fire.—On the fire, to a very great extent, depends the success or failure of all forging operations, particularly work with tool-steel and welding.

In building a new fire the ashes, cinders, etc., should be cleaned away from the center of the forge down to the tuyere. Do not clean out the whole top of the forge, but only the part where the new fire is wanted, leaving, after the old material has been taken out, a clean hole in which to start the fresh fire.

The hearth of the forge is generally kept filled with cinders, etc., even with the top of the rim.

Shavings, oily waste, or some other easily lighted material should be placed on top of the tuyere and set on fire.

As soon as the shavings are well lighted, the blast should be turned on and coke (more or less of which is always left over from the last fire) put on top and outside of the burning shavings. Over this the green coal should be spread.

Green coal is fresh coal dampened with water. Before using the forge-coal it should be broken into small pieces and thoroughly wet with water. This is necessary, as it holds together better when coking, making better coke and keeping in the heat of the fire better. It is also easier to prevent the fire from spreading out too much, as this dampened coal can be packed down hard around the edges, keeping the blast from blowing through.

The fire should not be used until all the coal on top has been coked. As the fire burns out in the center, the coke, which has been forming around the edge, is pushed into the middle, and more green coal added around the outside.

We might say the fire is made up of three parts: the center where the coke is forming and the iron heating; a ring around and next to this center where coke is forming; and, outside of this, a ring of green coal.

This is the ordinary method of making a small fire.

This sort of fire is suitable for smaller kinds of work. It can be used for about an hour or two, at the end of which time it should be cleaned. When welding, the cleaning should be done much oftener.

Large Fires.—Larger fires are sometimes made as follows: Enough coke is first made to last for several hours by mounding up green coal over the newly started fire and letting it burn slowly to coke thoroughly. This coke is then shoveled to one side and the fire again started in the following way: A large block, the size of the intended fire, is placed on top of the tuyere and green coal is packed down hard on each side, forming two mounds of closely packed coal. The block is taken out and the fire started in the hole between the two mounds, coke being added as necessary. This sort of a fire is sometimes called a stock fire, and will last for some time. The mounds keep the fire together and help to hold in the heat.

For larger work, or where a great many pieces are to be heated at once, or when a very even or long-continued heat is wanted, a furnace is used. For furnace use, and often for large forge-fires, the coke is bought ready-made.

Banking Fires.—When a forge-fire is left it should always be banked. The coke should be well raked up together into a mound and then covered with green coal. This will keep the fire alive for some time and insure plenty of good coke for starting anew when it does die out. A still better method to follow, when it is desired to keep the fire for some time, is to bury a block of wood in the center of the fire when banking it.

Oxidizing Fire.—When the blast is supplied from a power fan, or blower, the beginner generally tries to use too much air and blow the fire too hard.

Coal requires a certain amount of air to burn properly, and as it burns it consumes the oxygen from the air. When too much blast is used the oxygen is not all burned out of the air and will affect the heated iron in the fire. Whenever a piece of hot iron comes in contact with the air the oxygen of the air attacks the iron and forms oxide. This oxide is the scale which is seen on the outside of iron. The higher the temperature to which the iron is heated, the more easily the oxide is formed. When welding, particularly, there should be as little scale, or oxide, as possible, and to prevent its formation the iron should not be heated in contact with any more air than necessary. Even on an ordinary forging this scale is a disadvantage, to say the least, as it must be cleaned off, and even then is liable to leave the surface of the work pitted and rough. If it were possible to keep air away from the iron entirely, no trace of scale would be formed, even at a high heat.

If just enough air is blown into the fire to make it burn properly, all the oxygen will be burned out, and very little, if any, scale will be formed while heating. On the other hand, if too much air is used, the oxygen will not all be consumed and this unburned oxygen will attack the iron and form scale. This is known as oxidizing; that is, when too much air is admitted to the fire the surplus oxygen will attack the iron, forming oxide, or scale. This sort of a fire is known as an oxidizing fire and has a tendency to oxidize anything heated in it.

Anvil.—The ordinary anvil, Fig. 1, has a body of cast iron, wrought iron, or soft steel, with a tool-steel face welded on and hardened. The hardened steel covers just the top face, leaving the horn and the small block next the horn of the softer material.

FIG. 1.

The anvil should be so placed that as the workman faces it the horn will point toward his left.

The square hardie-hole in the right-hand end of the face is to receive and hold the stems of hardies, swages, etc.

For small work the anvil should weigh about 150 lbs.

Hot and Cold Chisels.—Two kinds of chisels are commonly used in the forge-shop: one for cutting cold stock, and the other for cutting red-hot metal. These are called cold and hot chisels.

The cold chisel is generally made a little thicker in the blade than the hot chisel, which is forged down to a thin edge.

Fig. 2 shows common shapes for cold and hot chisels, as well as a hardie, another tool used for cutting.

FIG. 2.

Both chisels should be tempered alike when made.

The cold chisel holds its temper; but, from contact with hot metal, the hot chisel soon has its edge softened. For these reasons the two chisels should never be used in place of each other, for by using the cold chisel on hot work the temper is drawn and the edge left too soft for cutting cold metal, while the hot chisel soon becomes so soft that if used in place of the cold it will have its edge turned and ruined.

It would seem that it is useless to temper a hot chisel, as the heated work, with which the chisel comes in contact, so soon draws the temper. When the chisel is tempered, however, the steel is left in a much better condition even after being affected by hot metal on which it is used than it would be if the chisel were made untempered.

Grinding Chisels.—It is very important to have the chisels, particularly cold chisels, ground correctly, and the following directions should be carefully followed.

The sides of a cold chisel should be ground to form an angle of about 6o° with each other, as shown in Fig. 3. This makes an angle blunt enough to wear well, and also sharp enough to cut well.

FIG. 3.

The cutting edge should be ground convex, or curving outward, as at B. This prevents the corners from breaking off. When the edge of the chisel is in this shape, the strain of cutting tends to force the corners back against the solid metal in the central part of the tool. If the edge were made concave, like C, the strain would tend to force the corners outward and snap them off. The arrows on B and C indicate the direction of these forces.

Hot chisels should be ground sharper. The sides should be ground at an angle of about 30° instead of 60°.

Another tool used for cutting is the hardie. This takes the place of the cold or hot chisel. It has a stem fitted to the square hole in the right-hand end of the anvil face, this stem holding the hardie in place when in use.

Cutting Stock.—When soft steel and wrought-iron bars are cut with a cold chisel the method should be about as follows: First cut about one-fourth of the way through the bar on one side; then make a cut across each edge at the ends of the first cut; turn the bar over and cut across the. second side about one-fourth the way through; tilt the bar slightly, with the cut resting on the outside corner of the anvil, and by striking a sharp blow with the sledge on the projecting end, the piece can generally be easily broken off.

Chisels should always be kept carefully ground and sharp.

A much easier way of cutting stock is to use bar shears, but these are not always at hand.

The edge of a chisel should never under any circumstances be driven clear through the stock and allowed to come in contact with the hard face of the anvil.

Sometimes when trimming thin stock it is convenient to cut clear through the piece; in this case the cutting should be done either on the horn, the soft block next the horn, or the stock to be cut should be backed up with some soft metal. An easy way to do this is to cut a wide strip of stock about two inches longer than the width of the face of the anvil, and bend the ends down to fit over the sides of the anvil. The cutting may be done on this without injury to the edge of the chisel. It is very convenient to have one of these strips always at hand for use when trimming thin work with a hot chisel.

The author has seen a copper block used for this same purpose. The block was formed like Fig. 4, the stem being shaped to fit into the hardie-hole of the anvil. This block was designed for use principally when trimming thin parts of heated work with a hot chisel.

FIG. 4.

Care should always be taken to see that the work rests flat on the anvil or block when cutting. The work should be supported directly underneath the point where the cutting is to be done; and the solider the support, the easier the cutting.

Hammers.—Various shapes and sizes of hammers are used, but the commonest, and most convenient for ordinary use, is the ball pene-hammer shown in Fig. 5.

The large end is used for ordinary work, and the small ball end, or pene, for riveting, scarfing, etc. These hammers vary in weight from a few ounces up to several pounds. For ordinary use about a 1 1/2- or 2-pound hammer is used.

Several other types in ordinary use are illustrated in Fig. 6. A is a straight-pene; B, a cross-pene; and C, a riveting-hammer.

FIG. 5.

FIG. 6.

Sledges.—Very light sledges are sometimes made the same shape as ball-pene hammers. They are used for light tool-work and boiler-work.

Fig. 7 illustrates a common shape for sledges. This is a double-faced sledge.

FIG. 7.

FIG. 8.

Sledges are also made with a cross-pene or straightpene, as shown in Fig. 8.

For ordinary work a sledge should weigh about 10 or 12 lbs.; for heavy work, from 16 to 20.

Sledges for light work weigh about 5 or 6 lbs.

Tongs.—Tongs are made in a wide variety of shapes and sizes, depending upon the work they are intended to hold. Three of the more ordinary shapes are illustrated.

The ordinary straight-jawed tongs are shown in Fig. 9. They are used for holding flat iron. For holding round iron the jaws are grooved or bent to the shape of the piece to be held.

Fig. 10 shows a pair of bolt-tongs. These tongs are used for holding bolts or pieces which are larger on the end than through the body, and are so shaped that the tongs do not touch the enlarged end when the jaws grip the body of the work.

FIG. 9.

FIG. 10.

FIG. 11.

Pick-up tongs, Fig. 11, are used for handling small pieces, tempering, etc., but are very seldom used for holding work while forging.

Fitting Tongs to Work.—Tongs should always be carefully fitted to the work they are intended to hold.

Tongs which fit the work in the manner shown in Fig. 12 should not be used until more carefully fitted. In the first case shown, the jaws are too close together; and in the second case, too far apart.

FIG. 12.

FIG. 13.

When properly fitted, the jaws should touch the work the entire length, as illustrated in Fig. 13. With properly fitted tongs the work may be held firmly, but if fitted as shown in Fig. 12 there is always a very wobbly action between the jaws and the work.

To fit a pair of tongs to a