The breech ends of the musket-barrels were broached and tapped, and the muzzles were screwed externally, to connect the two without detached sockets. From the rapid increase of gas illumination, the old gun-barrels soon became scarce, and new tubes with detached sockets, made by the old barrel-forgers, were first resorted to. This led to a series of valuable contrivances for the manufacture of the wrought-iron tubes, commencing with Russell's patent, in 1824, under which the tubes were first bent up by hand hammers and swages, to bring the edges near together; and they were welded between semicircular swages, fixed respectively in the anvil, and the face of a small tilt-hammer worked by machinery, by a series of blows along the tube, either with or without a mandrel. The tube was completed on being passed between rollers with half-round grooves, which forced it over a conical or egg-shaped piece at the end of a long bar, to perfect the interior surface.
Various steps of improvement have been since made; for instance, the skelps were bent at two squeezes, first to the semi-cylindrical, and then to the tubular form, (preparatory to welding), between a swage-tool five feet long worked by machinery. The whole process was afterwards carried on by rollers, but abandoned on account of the unequal velocity at which the greatest and least diameters of the rollers travelled.
In the present method of manufacturing the patent welded tube, the end of the skelp is bent to the circular form, its entire length is raised to the welding heat in an appropriate furnace, and as it leaves the furnace almost at the point of fusion, it is dragged by the chain of a draw-bench, after the manner of wire, through a pair of tongs with two bell-mouthed jaws; these are opened at the moment of introducing the end of the skelp, which is welded without the agency of a mandrel.
By this ingenious arrangement, wrought-iron tubes may be made from the diameter of six inches internally and about one-eighth to three eighths of an inch thick, to as small as one-quarter inch diameter and one-tenth bore; and so admirably is the joining effected in those of the best description, that they will withstand the greatest pressures of gas, steam, or water, to which they have been subjected, and they admit of being bent both in the heated and cold state almost with impunity. Sometimes the tubes are made one upon the other when greater thickness is required; but these stout pipes, and those larger than three inches, are comparatively but little used.* See Note T, Appendix, Vol. II., pp. 963 - 969.
Various articles with large apertures are made, not by punching or cutting out the holes, but by folding the metal around the beak iron, and finishing them upon a triblet of the appropriate figure; thus the complete smithy is generally furnished with a series of cones turned in the lathe, for making rings the ends of which are folded together and welded, such as fig. 123, page 228. The same rings when made of such cast-steel as does not admit of being welded, are first punched with a small hole, and gradually thinned out by blows around the margin, until they reach the diameter sought; but this, like numerous other works, requires considerable forethought to proportion the quantity of the material to its ultimate form and bulk, so that the work may not in the end become either too slight or too heavy.
Chains may be taken as another familiar example of welding; in these the iron is cut off with a plain chamfer, as from the annular form of the links their extremities cannot slide asunder when struck; every succeeding link is bent, introduced, and finally welded. In some of these welded chains the links are no more than half an inch long, and the iron wire one-eighth of an inch diameter; several inches of such chain are required to weigh one pound: these are made with great dexterity by a man and a boy at a small fire. The curbed chains are welded in the ordinary form and twisted afterwards, a few links being made red-hot at a time for the purpose.
The massive cable-chains are made much in the same manner, although partly by aid of machinery: the bar of iron, now one, one and a half, or even two inches diameter, is heated, and thes-safe is made as a plain chamfer by a cutting machine; the link is then formed by inserting the end of the heated bar within a loop in the edge of an oval disk, which may be compared to a chuck fixed on the end of a lathe mandrel. The disk is put in gear with the steam-engine; it makes exactly one revolution, and throws itself out of motion; this bends the heated extremity of the iron into an oval figure, afterwards it is detached from the rod with a chamfered cut by the cutting machine, which at one stroke makes the second scarf of the detached link, and the first of that next to be curled up.
* A piece of tube of the smallest dimensions, and fourteen feet long, which has been bent cold almost into the form of the Gordian knot, may be seen at the Institution of Civil Engineers. The wrought-iron tubes of hydrostatic presses, which measure about half an inch internally, and one-fourth to three-eighths of an inch thick in the metal, are frequently subjected to a pressure equal to four tons on each square inch. Pipes proved to the same degree are also used in Mr. Perkins' patent apparatus for warming buildings, and in his patented steam-boiler. The safety of each of these is entirely secured by a fusible plug, which melts and allows the water to escape into the fire when its temperature exceeds any predetermined degree namely, from about 300° to 600° F., generally the former.
The link is now threaded to the extremity of the chain, closed together, and transferred to the fire, the loose end being carried by a traverse crane; when the link is at the proper heat, it is returned to the anvil, welded, and dressed off between top and bottom tools, after which the cast-iron transverse stay is inserted, and the link having been closed upon the stay, the routine is recommenced. The work commonly requires three men, and the scarf is placed at the side of the oval link, and flatway through the same. In similar chains made by hand it is perhaps more customary to weld the link at the crourn or small end.*