In welding this structure, the heat is equally diffused all through the mass; and thus the great evil of unequal expansion and contraction is avoided. When the steam hammer is brought into play, its face is a “swage” of circular form, calculated to clasp a large portion of the upper part, whilst a corresponding space is formed in the anvil; and by gradually turning the shaft, the whole is forged into a perfect round. The peculiar advantage gained by this mode of proceeding, is not only the facility with which heat is diffused through the mass, but that each segment is made to act like a wedge on its neighbour; thus producing the most solid forging that has yet been attained. This is rendered still more perfect, both as regards strength and durability, from the fact that a hollow axle has been produced; the great advantages of which it would be out of place to dilate upon in this work.
We trust that these anticipated misfortunes may be avoided by the construction of a more perfect shaft; and that, not only for the sake of the shareholders, but for the credit of the engineer who devised this great vessel—deservedly one of the wonders of the world. A spare shaft would be profitable ballast, if of no more value to the Leviathan.
Rolled railway-carriage axles were constructed for me with perfect success on this principle nearly twenty years ago, at the Walker Iron Works, near Newcastle-on-Tyne. The idea has, however, been in a measure “shelved;” but necessity will bring it into use again.
The only engineer who has, by practical experience, satisfied himself that large masses of wrought iron are totally useless for making heavy ordnance is Mr. Nasmyth; whose monster cannon, which was to astonish the whole world, proved, when heated, to have so little cohesion that it would scarcely hold together whilst being lifted from the furnace to the anvil. And, to his credit be it said, Mr. Nasmyth, seeing that wrought iron would not answer the purpose, manfully gave up his hopeless task. Similar experience would probably make some of our present engineers wiser men.
My experience in manufacturing the largest wrought iron guns which it is prudent to construct, sufficiently proves the truth of these assertions.
Harpoon gun-barrels, one inch and a half in the bore, having the metal at the breech end an inch and a quarter thick, will stand a proof which invariably bursts a thicker barrel; in fact, all experience tends to show that light wrought iron or steel barrels are stronger than unusually heavy ones. As all depends on the principle of condensing the fibres of the iron, ceteris paribus, the greater the condensation the greater the strength, and the less the condensation the greater the weakness.