Page:The American Cyclopædia (1879) Volume IV.djvu/82

 CASTING moulds, which are usually of granite. Easily fusible metals are sometimes cast in moulds of plaster of Paris, which possesses some advan- tages as a mould material in consequence of the ease with which it may be given various forms, and their great permanency under favorable circumstances. Those metals, however, which have high melting points cannot conveniently be cast in plaster moulds, because this substance readily crumbles when subjected to a heat above 400 F. Before describing the casting of metals in sand and* loam moulds, a brief de- scription of the establishment where the work is performed is desirable. A well appointed foundery, in addition to the room required for the actual work of moulding and casting, should have rooms for storing and preparing the materials of the moulds, such as grinding and sifting the sand, loam, sea coal, coke, plumbago, or charcoal. There should also be a workshop for making the patterns which are to be used in the formation of the moulds. The moulding room embraces an area of great- er or less extent, but even in moderate estab- lishments it is necessarily of considerable size. Where heavy articles are founded there are huge cranes for lifting and moving moulds and castings from one place to another. The floors of such founderies are also covered or rather filled with moulding sand to a considerable depth, varying from 5 to 10 ft. Fig. 3 repre- sents the interior of a foundery for heavy cast- ings. In one part of the room, usually at one side, and sometimes adjoining another room FIG. 8. Interior of Iron Foundery. a, a. Cupola furnaces. 6, 6. Tuyeres, c. Crane, d. Ovens for baking moulds. . Cope of a greensand mould, made in the floor bed. /./. Temporary furnaces for forcing heat through the pipes g, g into a large mould, A. Mould of a steam cylinder, placed In a pit and in process of completion. for making light castings, stands the furnace for melting the metal. This may be an air furnace, or that form of a blast furnace known as the cupola, which is most in use at the pres- ent time. Anthracite coal is used for fuel to a great extent in this country, but coke is better, and wood charcoal the best, on account of con- taining no sulphur. Unlike the air furnace, which depends upon the ascending column of air in the chimney for its draught, it is fed by a current of air forced in at the bottom through tubes called tuyeres by^a blowing machine. The cupola is usually made of boiler iron in the form of a cylinder or cylindroid, lined with fire brick. It is from 10 to 16 ft. in height and from 3 to 6 ft. in diameter inside, and capable of melting from 5 to 15 tons of metal per hour. The chimney may be of brick, or of boiler iron lined with fire brick, which is more common. A cupola is often spoken of as holding a charge of so many tons of metal ; but as only a limited quantity of molten metal can be contained in it at one time, because it must be confined to the space below the tuyeres, its capacity is more correctly measured by the amount of metal it will melt in a given time. For a fuller description of its construction, see FURNACE. A sufficient explanation will be found in fig. 4 to enable the reader to understand the ma- nipulations connected with the process of cast- ing. The tuyeres, a, a, are seen to enter the cupola from 10 to 16 inches above its floor. The space just above the tuyeres has the shape of an inverted cone, which has the effect to hold the contents in such a relation to the blast as is best calculated to make it the most effectual. The floor of the cupola, ft, when in use is composed of sand 6 or 8 inches in depth, lying upon the bottom plate c, which rests upon supports, and may be dumped by their removal. Some cupolas are chambered at the lower section, the blast entering through a row