Open-sand Moulding
The process of moulding castings that have one plain side, in the sand floor of the foundry. Even for such castings it is usual to cover them with a cope, which, when secured, permits of pressure being applied to force the metal close to the upper surface, so that the casting has nearly the same appearance all over; but when the metal is poured into an open mould it must assume a horizontal position of its own accord. If, when the open mould has been cast, fine dry sand is scattered evenly over the surface of molten iron to the depth of one-fourth of an inch, it will shield the metal from the action of the atmosphere and thus prevent the formation of blisters, which almost always rise when the surface is left unprotected. When the mass has solidified more sand may be added with the shovel, in such quantity and location as will favor equal cooling of the whole. See BED. Ordnance signifies, in its most comprehensive sense, every kind of artillery, including guns, mortars, howitzers, etc. Many of the early pieces of ordnance were made of hooped bars. The mortar, which was introduced about the commencement of the fourteenth century, was the first European firearm. About the beginning of the fifteenth century bronze cannon were cast, and it is probable that cast-iron cannon of small calibre were made during the sixteenth century. However, there is positive evidence of iron cannon being cast about 1740 by English workmen, who were afterwards taken across the Channel to teach French-men the art.
Cannon-founding has therefore been practised nearly five hundred years; but it would appear, from the wonderful specimens in steel and wrought iron lately produced by Armstrong, Whitworth, Krupp, and some others, that the art of casting ordnance was doomed to decay, as even the monster 300-pounder rifled Parrott and the 15-inch 450-pounder Rodman appear almost insignificant when compared with the more modern steel monsters constructed by the above-named inventors.
Bronze and cast-iron cannon are cast in loam or sand in moulds prepared in the customary manner. They are cast vertically, with an addition to the length to make up for shrinkage, and also to carry off the sullage. It was formerly the practice to cast them hollow; since then, however, solid ones have occasionally been preferred. But the results were not satisfactory, and the Rodman principle has been extensively adopted, the idea being to cool the metal in layers from the inside outwards, thus modifying the initial strain upon the gun, and producing the best results that may be expected from cast iron for ordnance purposes. The method is to flow cold water through the core-barrel during the process of casting and for a stated time afterwards, according to the thickness of the casting. The manner of constructing the mould is as follows: The mould is a dry-sand one, contained in circular sectional casings of length sufficient for the casting with its sinking head. The chief feature is the core-barrel, which consists of a sound, watertight cast pipe or barrel, with flutes on its exterior surface along its whole length, to permit the gas to escape upwards from behind the hemp and loam with which the barrel is coated. After the mould has been closed together the barrel is attached to a spider or tripod, the legs of which rest upon the top flange of the casing; adjustable screws at the ends of each leg admit of a ready adjustment of the core after it has been suspended and lowered into its place in the mould. The water for cooling is led to the bottom of the core-barrel by a pipe which stands central in the space; it then ascends through the annular space between the pipe and the barrel, and flows off by a suitable arrangement at the top. For a 15-inch gun treated this way the barrel may be withdrawn in about twenty hours, after which a continuous flow of cold air is forced through the bore until the casting is cool enough to be removed, which in this case is about nine or ten days. See SPIDER; COREBARREL; DRY-SAND MOULDING.