The next article of importance in the lead manufacture is pipe or tubing. There have been various modes of producing it: the original mode, from some specimens of very old pipe that we have seen, appears to have been the wrapping of a strip of sheet lead, with parallel sides, round a cylinder, so as to make their edges meet, and then unite them with solder. The specimens alluded to present phenomena worthy of notice in this place: the lead was full of holes, and was corroded more or less in every part, except at the seam, which the solder had entirely protected; and the solder itself was as sound and perfect as when it first left the plumber's hands.
Another mode of making lead-pipe, which probably succeeded the foregoing, and is still practised by some plumbers, is the following: - An iron mould is provided, which is divided into halves, and forms, when put together, a hollow cylinder of the external diameter of the extended pipe; in this cylinder is put an iron rod or cord, extending from the top to the bottom, and leaving all round a space between it and the cylinder of the intended thickness of the pipe. The lead is poured in at a spout, formed by two corresponding notches cut in each half of the mould, and a similar hole is made at another place for the escape of air. The mould is fastened down upon a bench, upon which, at one end, and in a line with its centre, is a rack moved with toothed wheels and pinions. When the pipe is cast, a hook at the end of the rack is put into an eye at the end of the iron core, which, by the action of cog-wheels and pinions, is drawn so far out that about two inches of it only remain in the end of the pipe; the two halves of the mould, which fasten together by wedges or screws, are now separated from the pipes, and are fastened upon the iron core, and the two inches of lead-pipe attached to it.
Melted lead is now again poured into the mould, when the fluid lead unites with the end of the first piece of pipe; and this process being continued, pipe of any required length may be made.
A third method, which was patented in 1790 by the great iron master, John Wilkinson, consists in casting a very thick pipe in a mould, having a cylindrical core of the same diameter as the intended pipe, and then inserting a polished iron mandril up the bore of the pipe, in which it is to be successively passed through a series of roundgrooves, precisely in the same manner as has been described under our article Iron, for making round bars. Every time that the pipe is passed through, the lead is compressed upon the mandril, consequently reduced in its thickness, but extended in length, while the internal bore remains unaltered, except the improvement it derives from condensation of the metal against the polished mandril.
A fourth method is mentioned in Mr.Wilkinson's specification, which, since the expiration of the patent, has been, and is still practised with unimportant variations by all the considerable manufacturers of lead pipe: it consists as follows:- Very thick short pieces of pipe are cast, similar to those described in the preceding method; the external diameter may be two or three times that of the intended pipes, but the internal the same. The central hole for the mandril of triblet does not extend the entire length of the pipe, but terminates with a much smaller hole at the extremity; a stop to the triblet is thus formed, which is employed in the succeeding operation, which is that of drawing the lead pipe through a hole precisely in the same manner as wire is drawn. The triblet or polished mandril is of somewhat greater length than the pipe intended to be manufactured by it, which is commonly from nine to twelve feet Through the small hole of the cast-lead pipe is then passed a screw, which is screwed into the end of the triblet, that abuts against the shoulder; and it is by this connexion with the triblet that the lead pipe is drawn successively through a series of separate steel plates, each having a different sized hole, and which are successively deposited in solid recesses made in very firm bearings, and are exchanged for smaller after the pipe has passed through the larger one.
The table or draw bench on which the operation is conducted is usually about 30 feet in length; it is provided with a strong endless hitch-chain passing around chain wheels at the ends of the bench, to one of which the power is communicated. The screw fastened to the end of the triblet passes through the draw-hole, and is then secured by a hook and eye, or other fastening, to the endless chain; the machinery being then thrown into gear by the ordinary means, the chain drags the lead through the steel hole, by which its dimensions are reduced, and its length increased. The motion of the chain is now reversed, either by machinery connected with the power, or .the chain is thrown out of gear with the power, when the chain can usually be drawn back by hand, and the draw plate changed; when, by throwing into gear again, the work is renewed, and so continued until reduced to the required dimensions; a small piece of each end of the pipe being cut off it is finished.
A very ingenious mode of casting lead pipe of any length by a continuous process, was invented by Mr. John Hague, and patented by him in 1822, which we ought not to omit noticing in this place. A rectangular cast-iron vessel, containing the lead, was placed over a suitable furnace, to melt and preserve it in a fluid state; through this vessel, in a horizontal direction, was passed a very stout cast-iron cylinder, each end of which came to the outside of the vessel, at a short distance from which they were each connected to a small reservoir of water to keep them cool. A hole ahout half an inch in diameter was made in the upper side of the cylinder through which the latter was charged with the fluid metal, and the hole was then stopped by a plug screwed down from above. The internal diameter of this cylinder was about six inches, and throughout its length of two feet its surface was cut into a screw thread; and into this a solid screw plunger worked from one extremity, which by itis revolution gradually forced the metallic fluid through a mould and core fixed at the end, where the pipe was constantly drawn off as it solidified (by the cooling influence of one of the before-mentioned reservoirs of water) on to a drum, loaded with a weight upon its axis, which caused the drum to turn round with just sufficient force to wind the pipe upon it as it was formed.