Wrought-iron pipes are made out of plates of the required thickness, length, and breadth; so that when coiled into a circular form, the edges may lap over each other. To make sound, good work of this kind requires great address and rapidity of execution in the welding operation; so that the ordinary smith rarely attempts it, preferring to purchase the article, or get it made by the regular tube-makers. The manufacture of wrought-iron tubes has lately, with considerable success, been effected by machinery, under a patent granted to Mr. Whitehouse (for Mr. Russel), of Wednesbury. The sides of the metal being bent up with swages, so as to bring the edges nearly together, he introduces the tubes so prepared into a furnace, and, when brought to a welding heat, to the operation of a small tilt-hammer: the face of the hammer, as well as that of the anvil, have semi-cylindrical grooves, corresponding with the size and shape of the tubes under manufacture; and between these the tube is gradually passed along, receiving in its progress a rapid succession of blows from the hammer.
When the welding is thus completed, the tubes are in a rough state; they are therefore again heated in the furnace, and passed between large round rollers, which give to the tubes a smooth exterior surface; as they emerge from the pressure thus given, they come in contact with a fixed round rod, of the proper size of the bore of the tubes or pipes, over which they are forced by the rollers; and thus the interior as well as the exterior are brought to a smooth and true cylindrical surface.
Cast-iron pipes, of which immense quantities are used for the conveyance of gas, water, and other fluids, are made in the following manner. The mould for casting is thus prepared: strong cast-iron flanged cylinders, about three feet long, and having an internal diameter greater than the outside of the intended pipe. These cylinders divide longitudinally into halves, which are secured together by iron cramps; in this state one of them is placed upright upon a firm foundation, underneath the jib of a crane, to which is suspended a smooth cylindrical mandril; this mandril is then lowered perpendicularly into the centre of the cylindrical mould until it rests in a hole in the stand at the bottom, and leaves around the mandril a void space of equal dimensions, in which position it is secured by wedging pieces at the top. Sand duly prepared and moistened is then put into the void space by degrees, until it is filled, ramming it down at intervals, to render it equally solid throughout. The smooth mandril is then carefully drawn out by the crane, and the sand-charged cylinder is removed to the drying stove. Other cylinders are similarly charged, and dried in the stove.
To make the core, the moulder takes a quadrangular bar of iron, about a foot longer than the intended pipe, wraps it along with a hay-band, and inserts it centrically into a pipe smooth in the inside, of the length, and of the same internal diameter as the required pipe; a mixture of sand loom, hair, etc. is now rammed between the cylinder, and is thus forced amongst the fibrous matter around the bar, to which it firmly adheres when drawn out of the smooth-sided cylinder; the core thus produced being dried in the stove, is ready for the casting. As the length of cast-iron pipes for water is usually nine feet, three of the before-mentioned cylindrical sand-boxes are put into requisition for the purpose; they are placed one upon the other upright in a pit, and connected together by cotters through their flanges. The sand and loam core before mentioned, is now carefully lowered from a jib into the centre of the combined sand-boxes, which is insured by a projecting piece of the iron bar entering a socket at the bottom, and the upper end is secured by a collar of clay.
The space now left between the core and the cylinder of sand is now filled with liquid metal through an orifice in the clay at top, by means of a ladle, charged from the tap hole of the furnace, which is carried and poured into the mould by the casters, if not too heavy; but if so, this carriage is assisted by a truck Or drag, and the ladle or pot discharged by the aid of pulley tackle. When the mould is cooled, it is hoisted by the crane altogether from the pit; the outer cases are taken off, the iron rod withdrawn, and the pipe being cleared from the sand inside and out, is ready for clearing, examination, and use. In the casting of very large cylinders, a similar process is adopted, except that the metal is allowed to flow directly from the furnace, along a trench into the mould.