All crank-shafts are best when made of a hard metal that will admit beautifully polished surfaces for the crank-pins and axle-bearings. For this reason, a hard, highly tenacious steel, which will resist strains of vibration without being very liable to break, is pre-eminently the very best material of which crank-shafts can be made. And the reason why large crank-axles are not made of it is because it is an exceedingly rare product; and, when it is comatable, great difficulty is encountered in forging it into a large crank-shaft without spoiling it, or placing the lengths of the fibres into the wrong positions. But the great advance lately made in steel making by the Bessemer process enables us to hope that a steel which will be tough, hard, and also easily forged, may be produced at a not very distant time.

Summary

From the foregoing remarks and details of processes given in the previous sections of this chapter, an attentive student will learn that, however good the iron or steel may be which is used for forging, it is always desirable to devote some attention to the relative positions in which the several forging components are to be welded to each other, and the positions of the fibres in the work after being forged. From the details of processes already given, these six general rules may be deduced :

1. That all piston-rods should be so made, as to place the longitudinal axes of the constituent fibres parallel to the lengths of the piston-rods.

2. That the straight portions of all levers should be so forged, as to arrange the longitudinal axes of the fibres into a position of parallelism with the lengths of the levers.

3. That the lengths of the fibres in any curved junction of a fork-end or T-head with its respective rod should be parallel to or concentric with the curve itself.

4. Also that the lengths of the fibres in all lever bosses and fork-end bosses should constitute portions of rings whose centres are the centres of the holes in the bosses.

5. Also that the fibres in the arms of all crossheads should be disposed into a position of parallelism with the lengths of the crossheads.

6. And that all axles should be so made, as to put the lengths of the fibres into a position of parallelism with the lengths of the axles.

These general deductions relate to the principal portions of engine work, and may be reduced to this comprehensive general statement:

That the lengths of the fibres in all piston-rods, connecting-rods, and other rods generally, should be parallel to the line or direction of the motive force applied while in use; and that the lengths of the fibres in all levers, crank-pins, and axles generally should be at right angles to the direction of the force applied while in use.

To enable a beginner to appreciate these deductions and statements, it will be necessary for him to refer to the opening sections of this chapter, and to devote some attention to the sketches in Plates 1, 2, 3, and 4, that he may obtain a general idea of the shapes of the forgings he is considering.

The character, formation, and uniting together of forging components having been thus for the first time generally described, a description of the appliances and implements for facilitating the various processes is now added.

Shaping Implements. During the making or using of these implements, the fundamental principles of forging stated in the first sections of this chapter should be remembered in all cases that require good work; by no other means can good forgings be produced when ordinary bars or rods are used, whether they be Lowmoor, Bessemer, or any other product; therefore every tool, shaper, mould, or other implement that can be used or made to facilitate the forging by the first principles should be eagerly employed ; but all those implements or machines that put the metal into the outside shape without properly arranging the fibres should be avoided when circumstances permit.

Shaping moulds for forging purposes are more applicable to Bessemer ingots than to laminous bars, and especially when a Bessemer product nearly free from phosphorus and sulphur is accessible.

The principle involved in forging with moulds consists in shaping the metal to the required form by adopting the shortest method, entirely disregarding the internal arrangement of fibres; for this reason, tenacious Bessemer metal is very suitable for forging in moulds of all classes, small and large. Such metal can be upset without splitting; and, when newly cast, Bessemer product is devoid of an orderly side-by-side arrangement of fibres. While in this condition, it may be shaped, pressed, bent, or upset in any direction, if the metal itself is good.

It may be stated generally, that bending and pressing are the two principal operations in these shaping processes, and that the tools and shapers employed are of cast iron or of Bessemer metal; also that the great economy of time resulting from the use of shaping moulds requires that they should be employed by every manufacturer who has regularly to perform or conduct any kind of smiths' work, whether it be very small or, on the contrary, very large. Such shaping tools are equally applicable to work of all dimensions, whenever many articles are required to be of the same or similar shape.

The bending and shaping tools, and appliances for small work, shall be first described.