Iron forgings from puddled bars are generally formed from piles 15 inches wide, 18 inches long, and about 10 to 12 inches high, heated, re-heated and worked until all cinder and slag are removed, and the required section attained. In piling, bars of different dimensions are used for each row, so that all the joints get fairly crossed, and the whole shingled down to either a slab, the average size of which is about 36 by 24 by 3 inches, or into billets. In ranking a. forging of large dimensions a number of slabs are piled together, with a small piece of iron between each, in order to equalise the heat of the whole, so that the centre may be of the same temperature as the outsides. The centre slabs have V pieces cut out in which to insert the staff end, which is driven in with a tup and securely welded. If a very large forging is required, and it is not thought advisable or is inconvenient to make large piles, double faggoting is reported to. Wrought iron scrap that has been well rattled, carefully piled and well shingled, makes better forgings than puddled bars. Another method is by "laying" or "weighing up" the staff, by which means it is gradually built up at one end to form the forging.

Where there is a great repetition of the same article, stamping by dies or moulds is the most economical and perfect way of forging. For large work the dies are made of mild steel, which gradually acquire a hard skin, but for small forgings they are made of the best steel eastings, in such a manner as to release the work in each case with the utmost facility, and generally, forgings are now designed with this point in view. In the case of hydraulic forging, swages or dies may be used of cast iron, which would very soon be broken up by the percussive blows of a hammer. Sometimes two or three dies are required, each bringing the metal nearer the desired shape, the number of dies and the proportion of work they have to perform being a matter of practical judgment. There should be considerable accommodation for the metal to flow equally, the mechanical work performed should be uniform throughout the whole mass, and all fins and surplus metal should be removed before each succeeding die is brought, into operation. A knowledge of M, Tresca's investigations on the flow of solids will materially assist in the design and judgment upon stamping dies and forgings, and M. Arbel's performances deserve citing, He forged wrought iron wheels to 8 feet in diameter by a pair of dies, forming the whole wheel complete. It was constructed by building up in the lower die the whole wheel, sections having already been stamped to the required shape. The upper die was fixed in the hammer tup, and after repeated blows, made a well-finished forging. This became a common process in the manufacture of waggon wheels, hut has now been superseded by steel eastings.

Hydraulic forging gives a maximum strength by forcing the fibre to flow into the required shape, and considerable economy is also entailed by the tool work saved in the machine shop. Soft steel will work more easily than iron, because it is comparatively without grain, and in the case of massive steel forgings the press, with its slow and powerful compression, will supersede the steam hammer.

With the abrupt blows of the latter, a large proportion of the sudden impact is absorbed upon the exterior of the forging, and, comparatively speaking, very little effect is produced upon the interior of the metal, owing to the resistance offered by the vis inertia of the mass to the sudden impact of the blow; and should a hammer be used that is really too light for the work it is performing, this surface absorption is so great that the forging or ingot has considerable tendency to pipe, or become hollow and unsound in the centre. In producing large forgings from ingots of mild steel, it is essential that they should receive throughout their whole mass as nearly as possible an equal distribution of the force required to shape them; and with forgings having sharp corners a pressure of 10 tons per square inch is required, and owing to the difficulty in obtaining duplicate work - certainly without repetition it will not pay - and by the rivalry of sound trustworthy castings, considerable impediments are brought to bear against the ardour that might be displayed in developing this class of work.

Crank axles are chiefly manufactured from Siemens-Martin steel, which, after forging and annealing, shall give results upon test bars machined from the blocks removed from between the sweeps, without any further hammering or annealing, of 28 to 32 tons per square inch tenacity, the elongation being not less than 20 per cent, on 3 inches, Whitworth or Woolwich bars; and a 1¬ inch bending test, placed upon 6 inch supports, to obtain a right angle without any signs of failure. The first results upon opening the test records of cranks made to the above specification for the Lancashire and Yorkshire Railway are 29 to 31 tons per square inch tenacity, 27 to 34 per cent, elongation, 39 to 50 per cent, contraction of area, and the bends doubling flat upon themselves.

An ingot should be cast considerably heavier than the finished forging, in order to get sufficient material to form a sound crank, the bottom portion of the ingot of course being used, and generally, when roughed down under a vertical hammer, this extra weight forms the bottle-neck in that class of ingot, and thi3 in its turn forms an attachment for clamping the heavy porter bar.

It is contended by most crank makers that the ingot should be about 24 inches square, and weigh not less than 70 cwt.; at least, it should be heavy enough to allow one-third of the upper portion to be removed, owing to the tendency of very mild steel to pipe. After casting the ingot, this pipe .should bo allowed sullicient time to definitely form itself, otherwise if the ingot is turned over or upon its side, part of the pipe will be parallel to the axis and part at right angles, or in some other objectionable place, and consequently it will be found later on somewhere in the forging. It is advisable to charge them into the re-heaters, or better, into the soaking pits before cooling; because in cooling sometimes a clink occurs, which is not always external, and consequently invisible even after machining; that is, an internal rupture takes place which will eventually become the starting place of a growing flaw. It has been found that steels high in manganese and silicon are especially prone to this evil. The hammer used for cogging the ingot down into a slab, Figs. 219 and 220, should not be less than 15 tons, but a smaller, about eight tons, may be used for finishing. Care should be exercised in heating, as a repetition without mechanical work will change the nature of the fracture of any forging.