CHAPTER XVI.

FORGING PROCESSES.

"FORGING" is the shaping of wrought iron or steel whilst it is hot by hammering, or by squeezing (see Chap. III., on Manufacture of Iron and Steel). Besides iron and steel there are a few copper alloys which can be forged, but these are special mixtures for specific work. Forging, like other branches of engineering workshop practice, has undergone considerable change, and can now be divided into several distinct departments.

Heavy Forging Shop.-The heavier class of work is wrought under powerful steam hammers, hydraulic forming presses, bending rolls, cogging mills, and tilt hammers (which are not so much in use as formerly). In the same shop fixed

and portable riveting machines and multiple drilling machines are also generally found.

H

Angle-iron Smithy. Another special shop is devoted to the treatment of angle-iron bars of the various sections LUH (Fig. 369). Here the fires are open all round, so as to allow the smith facility when heating up the bars for bending, forming, or welding, as the case may be. Angle smiths are very skilful, but are restricted to this work alone, and are not accustomed to general forging.

FIG. 369. Sections of angle iron.

Forming" Shop.—The “forming" shop is a modern development, and is unique, inasmuch as the workmen are generally unskilled, the work being done by special machines. The forgings produced are of the highest class, and are made as follows: The bars to be bent are uniformly heated in a furnace, from whence they are removed separately to the table of a forming machine (" Bulldozer"), which in its motion and appearance somewhat resembles an ordinary planing machine (see Figs. 370, 371). A pair of dies having the exact form the bar is intended to assume are cast in iron. One of the dies is rigidly secured to the machine table, and another fixed in perfect alignment to a vertical column located at the end of the machine bed. The heated bar is then squeezed between the dies, and thus receives an impression

of their particular shape. Dies of other forms are sometimes used at the opposite end of the machine table, enabling a forging to be produced by both the forward and backward stroke of the table. The dies are frequently changed and others substituted for different work.

The under framework for tramcars is an example illustrating this method of working. The peculiar bends given to some of these bars

necessitated the use of gauges and templates, and the skill of a firstclass workman to direct the hammermen where to strike when the work was entirely done by hand at the anvil. In addition to this, the forgings had to be overhauled and twisted to suit (which is obviously necessary in all forged work which has not to be machined, i.e. planed or shaped).

Compared with this, each forging made in the above machine is exactly true to pattern, and is much more quickly produced since it is formed in one operation only. These machines are used "gang" punching plates, also for straightening purposes.

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Fig. 370 represents a single-geared "Bulldozer" for light running where speed is more important than power. These machines make from 35 to 50 strokes per minute.

Two examples of bent work are given in Fig. 372. These are too well known to need description. The Smith's Hearth.-A smith's hearth was formerly a brick struc

ture; it is now generally constructed of iron, in two principal forms, those of a stationary character (Figs. 374, 374A), and those made to run on wheels, called portable forges (Fig. 375).

Tuyere. In the smithy the hearth is usually fitted with a tuyere,

through which the air passes direct to the fire from the fan or blower. The tuyere B is made of wrought iron or mild steel, shown in Fig. 373; the air pipe and the nozzle are surrounded with water supplied from a

tank, A, at the back of the hearth. This water is to keep the tuyere from being injured by the heat of the fire. Waterless tuyeres of cast iron are sometimes used, but these are not so good or reliable as the above.

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Bent crank and dies.

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Eye bolt and dies.

FIG. 372.-Bent work by above.

The Air Blast.-The air to blow up a means of revolving vanes, as contained in a very small hearths, by means of a bellows.

smithy fire is obtained by "fan" or "blower," or, for Whichever form is used, the

air is drawn into a receiver and forced through a pipe leading directly to the heart of the fire.

Of the former class, Fig. 376 is an illustration of a "blower." This is considered one of the most economical, as the power required

to run this machine is very little, while the speed of revolution is about 300 per minute. In this machine there are two " revolvers," which are connected in such a manner as to permit of no backward escapement of air. B shows a "blower" of a large size, with engine attached, suitable for a large number of forge fires invented by " Root."

Fire. On the bed of the hearth a layer of spent or burnt fuel is laid, to prevent the fire from spreading. Immediately below the air nozzle a hollow is made, into which the fire is placed. In ordinary working a small, nut-sized coke, called "breeze," is preferred, which is obtained by passing coke in its usual form through a crushing mill. For welding purposes this breeze is "floated," i.e. only that portion which will float is used.