Bending metal of a square section at right angles with the sides is not very difficult, but bending such a section in line with the diagonal is quite difficult, because the edges are liable to be marred where they rest on the anvil and where the blows are delivered. The best method of making bends of this kind is to heat the metal only where the bend is to be, and then to bend it by pressure or pulling, while the work is held securely in the vise, hardy hole, or swage block. If the heating cannot be confined to the desired space, all excessively heated parts should be cooled.
Oval sections are easily bent through their short diameters, but in bending through the long diameters, the same method should be pursued as described above for bending the square section in the plane of its diagonal. Further explanations for bending are given on pages [118]-121.
55. Upsetting is the operation of enlarging metal at some desired point or place. It is done by hammering, ramming, or jarring. When a piece of metal is too long it can be shortened by upsetting, or when it is too thin at a certain place it can be thickened by the same method. This is done by having the metal hot only at the point or place where the upsetting is required. It is frequently necessary to cool the metal where the heat is not needed in order to confine the upsetting to the desired place.
Upsetting is not a very difficult operation as long as the metal is kept perfectly straight; otherwise the task will prove tedious and the metal may break from the constant bending back and forth. Bending will always take place, but breaking generally can be prevented by having the metal hot when it is straightened. The greatest difficulty in this respect will be experienced when operating on common wrought iron.
Upsetting by hammering is done by holding the metal perpendicularly on the anvil or something solid enough to withstand the blows which will be delivered upon it. Figure [36] shows this method.
Fig. 36.—Upsetting by Hammering.
If the end of a bar is being upset, and the upsetting is supposed to extend up through the bar for some distance, the heated end should be placed on the anvil as shown in the figure, because the anvil will slightly chill the end of the bar, and the upsetting will continue much farther than if the blows were delivered on the hot end. Striking the hot end with the hammer increases the diameter of the end excessively, because the contact of the hammer does not have a tendency to cool the metal.
Fig. 37.—“Backing up” Metal.