CASTING 79 material is laid upon the surface until it has sufficient thickness to be scraped off by the templet, as shown in fig. 14. The top of the core may be swept and levelled by the arm, the templet being removed. If the cylinder is to be cast with a bottom, an iron plate is fitted to the upper end of the core, and a proper FIG. 15. Drying Ovens. thickness of loam laid upon it. This may be built upon the core,. or it may be done sepa- rately, and the parts put together after they are dried. When the core is finished it is lifted, by a crane by means of chains or rods at- tached to the circular plate upon which it rests, upon a car which passes on a track to one of the drying ovens represented in fig. 15. The templet is then placed at that distance from the spindle by which it will describe the inner cylindrical surface of the cope, which is built up with brickwork and loam in a similar man- Fio. 16. Sweeping the Cope. ner with that used for the core, except that for convenience it is usually built in two sections (see fig. 16). Iron rods are laid in the brick- work, passing from top to bottom, and securely 160 VOL. iv. 6 fastened to the bottom plate. A cap is then made by fitting an iron plate to the top, adding brick and loam, and securing it by the rods which pass through the walls from the bottom plate. When finished, all these parts are washed with a mixture of charcoal or plumbago dust and water, the mixture being sometimes applied two or three times. A strong cross piece of iron is then fastened to the top of the cope, hoisted by means of a crane upon the carriage, and taken to the oven. After both core and cope have been thoroughly dried, they are low- ered into a pit formed in the floor of the fur- nace. (See fig. 3, h.) Upon the bottom of this pit there is an iron foundation upon which the cope and the core both rest, and to which they are properly adjusted and secured. Care has been taken to provide the cope with the necessa- ry holes for pouring and for the discharge of air. Sand is then thrown into the pit about the sides of the mould, and well tamped down to prevent any spreading during the casting. The relation of the parts is represented in fig. 13. A powerful expansive force is applied to the interior of the mould when the hot metal is poured in, and the greatest precautions must be taken to have all the iron fastenings as well as the sand tampings strong enough to with- stand the pressure. Into the holes intended for the escape of air iron tubes are placed, of suffi- cient length to reach above a layer of loam which is now laid over the cope. Into the holes for pouring plugs are placed and the loam formed around them in cups, which are connected with channels through which the metal runs in pour- ing. In the figure a tube is seen leading a few inches downward from the lower part of the hollow of the core, then horizontally beyond the edge of the mould, and thence up to the surface of the foundery floor. This is for the purpose of carrying otf gaseous products from the core. In casting a cylinder without a bot- tom, it will only be necessary to have a tube extend directly upward to the surface. It will be noticed that the holes for pouring are placed immediately over the hollow mould, and not, as in casting statuary, connected with channels in the cope entering at the bottom of the mould. The securing of the mould for the cylinder of a large steamer is a matter which requires the greatest vigilance. The pit into which it is lowered must be dry, and is gen- erally built like a cistern and bricked and cemented on the sides and bottom ; and care must be taken to keep the mould dry till the casting is done. The cope must be well bolted to the bars that come through the sides from the bottom. A rim of iron plating may be placed around the part that projects above the ground, reaching high enough above the top of the cope to hold a layer of sand. A heavy iron cross is then raised over the mould and fastened with bolts, by which and also by its weight it aids in sustaining the strain at the time of casting. This is called packing. Fig. 17 represents the- packing of a mould for a large cylinder. To
