668

THEORY AND PRACTICE OF ENGINEERING.

Book II.

the edges met, they were soldered together: pipes so made are very liable to burst,from the soldered joint giving way. Some of the pipes found at Lyons, near the Romanaqueducts, were evidently made in this manner, and perfectly agree in form with thoseVitruvius describes.

Pipes are sometimes cast in an iron mould made in two halves, and afterwards united toform a hollow cylinder, into which a core or iron rod, the size of the intended bore, is intro-duced ; the two halves of the iron mould are secured in their position by screws or wedges,which make the core that occupies the centre fit in such a manner that there is an equaldistance all round to receive the melted metal, which enters it by means of a spout, carebeing taken to allow the air to escape. The mould is fixed to a long bench, and a rackmoved by toothed wheels and pinions is fitted to one end of it, in a line with the centreof the mould, which by means of a hook connected with an eye at the end of the coreenables it to be drawn out when the pipe is cast; when this is done, the iron halves whichform the mould are separated, and the pipe is moved onwards, an inch or two of its endalone occupying the mould; the halves are then again secured together with the corebetween them, and its end entered again, an inch or more into the first piece of pipe; themould is filled.with melted lead, the heat of which unites it with the end of the first piece*so as to double its length, and the core being again drawn out is ready to be used foranother piece. Any length of pipe may be thus cast, but the metal is very subject to airbubbles, and the joinings are far from sound. The usual method now is, to cast the leadin an iron mould upon a cylindrical rod of the size of the intended bore, leaving around thecore a space three or four times the thickness of the intended pipe; after they are cast inshort lengths, they are drawn through holes of steel plates, and reduced to the thicknessrequired. Another process is to reduce the pipe by passing it through two rollers of aflatting mill, in each of which semicircular grooves are formed all round, so that the two

MACHINE FOR FORMING LEAD PIPES.

rollers when united have circular cavities between them, which gradually diminish indiameter from one end of the rollers to the other. The pipe after passing through thelargest cavity, then the others to the smallest, is diminished in its thickness or substance;and by this process also hardened and rendered stronger.

The section shows the two half moulds screwed up in their place, with the core or trebletin its position; and great care is required that the interior surface of the former is trulycylindrical, and that the latter is accurately turned in a lathe, so that an equal spaceis left around or between the two, or the metal will be cast unequal in thickness. Theinclined plane on which the process is conducted is necessary, in order that when the metalis poured in at the cup at the lower extremity, the air may pass out at a hole or vent leftat the upper end, where the hook is connected with the rack. The core has a neck orsmaller part at the end, which prevents its being drawn through the pipe; and by meansof the rack and pinion, the pipe is drawn to its required length.

The other machine has a strong timber framework with a cog-wheel moved by asteam-engine or water-wheel, and which can be put in motion by the handles or leversshown above the stage. The drum of the cog-wheel has a pair of spiral grooves formedon its circumference, for the reception of two chains, the ends of which are hooked to alittle carriage on wheels, and which has at the back a double claw to engage in the notchesmade at the end of the core or treblet. In the middle of the bed is u cast-iron frame,