Page:The American Cyclopædia (1879) Volume IV.djvu/92

 CASTING porous sections over the whole surface, of such forms and dimensions as will be most convenient for drawing from the model, and also for sup- porting each other after the model is removed. (See fig. 22.) Iron rods and stays are placed in the section while they are being hammered together, and channels leading from the top to the bottom must be formed in them through which to pour the metal. They are represent- ed in the sectional cut, fig. 24. After this loam piece mould is completed, a number of the sections are laid in a bed of loam in a flask, and the forming of the core is commenced with- in the cavity. It is made of the same material, a very fine loam, which was used for the outer mould, except that sometimes it has mixed with it a small portion of molasses or paste. It is hammered together in the same way, and when completed is a facsimile of the original model. It must contain an iron frame, or a number of iron rods, to strengthen it, and also some pierced tubing for carrying off the expand- ed gases which are generated in pouring. Iron rods must also be passed in two or more pla- ces through it, their ends entering and rest- ing in the outer mould. When the latter has been carried up piece by piece and the hollow completely filled with the hammered loam, it is to be removed and the loam statue placed in the proper position, and its surface carefully pared down to a uniform depth. This forms the core, which is represented in fig. 23 by the of the core and the inner surface of the outer mould. It will be observed that in this case the holes for pouring and for the escape of air are made at the base of the statue, which for nil FIG. 28. Statue and Core of Mould. smaller statue. When placed within the outer mould and properly adjusted, there will be a space, equal in depth to the thickness of the paring, between every part of the surface FIG. 24. Perpendicular Section of Mould, a, a, a. Hollow mould, b, b. Channel in the cope for pouring the metal. c, c. Channel for discharging gases. a,d,d.d. Iron sup- ports for holding core in place. 6, e. Air tube in core. casting is to be turned upside down. In cast- ing statues in one piece, they are usually plac- ed in this position. A perpendicular section through both outer and inner parts of the mould and the containing flask has the appearance represented in fig. 24, with the exception that the iron framework for strengthening the parts has been omitted. Both core and outer piece mould are now placed in the oven and baked, having previously been carefully dressed and cleaned, and then washed with a mixture of water and plumbago or charcoal, or both com- bined. After the proper amount of baking, which should leave them dry and porous, the parts are taken and placed together in a flask, each part of which contains a bed perfectly ad- justed to the surface of the mould. The flask is then carefully secured with bolts to prevent any expansion or opening of the mould during the casting. Bronze containing 10 per cent, of tin requires a heat of about 2,000 F. to