Page:Encyclopædia Britannica, Ninth Edition, v. 9.djvu/513

F U F U 481 Usually four patterns are fixed upon one table, so that four chairs are moulded at one operation, the withdrawal of the pattern being effected by lowering the table by a FIG. 2. Finished Castings, hydraulic press or other mechanical arrangement. The lower mould forming the base of the chair is a nearly flat plate moulded in another machine. In loam moulding, as used for large pipes or cylinders, a hollow core of iron or brick is placed in the centre of the foundry, and around it a layer of loam, that is, a mix ture of sand and clay rendered plastic by mixture with water, is laid on "by trowels and finished up by a revolving tem plate working round a central vertical spindle to the dimen sion of the interior, forming the "nowel" or core, which when dried is washed with finely ground charcoal and water. Upon this a loam pattern is made up by another template representing the outer surface of the cylinder to the thick ness of the finished work. This in like manner is dried and black-washed, and finally a shell of brickwork is built outside, leaving a few inches space between it and the second moulded surface, which is carefully filled up with loam, and forms the "cope" or mould proper. This when dried is lifted by a crane, and either separates from the pattern or " thickness " or drags it away with it, but in either case the latter is broken away, and when the cope is replaced the mould is ready for use as soon as the necessary air-vents, ingates, runner passages, <fec., have been provided. In many large foundries, however, gas and water pipes of large size are now produced from permanent moulds of cast iron faced with a thin layer of sand or loam ; the outer moulds, being divided into two parts, are brought up to the work and removed by trucks running upon railways. The method of moulding for bell-founding and statuary is generally similar in principle to that of a loam moulding, with this difference, that the thickness representing the finished object is made up not of loam but of wax, and in the case of statuary, where the object is to use as little metal as possible, it is usually very thin. A plaster cast divided into sections, taken from the original work, forms the matrix within which the wax is moulded of the proper thickness, the inside core being formed of clay with some metal bars to give support, when the work is large. When the plaster mould is removed, the waxen surface is finished up by the sculptor, and the outer mantle or mould proper is formed by coating it with a porous clay mixture. This when dried is carefully baked or burned in a furnace, and the wax melting at the same time leaves the hollow to receive the metal. It is sometimes necessary to leave holes in the casting to allow of the withdrawal of the surface ; these are afterwards stopped with plugs of the same metal. Great care is required in the placing of the ingates and runners so as to allow the mould to be regularly and rapidly filled, and prevent any part of the metal setting or chilling before the proper moment. Melting. This may be effected either with or without contact with the fuel. In the former case the metal is charged alternately with coke, and occasionally a little flux, into a cylindrical or slightly conical blast furnace known as a cupola, and accumulates in a hollow or sump at the bottom below the tuyeres or blast pipes, whence it is tapped out from time to time, either directly into the mould or more generally into a ladle, for conveyance to the moulds arranged upon the foundry floor. In the second case the fusion takes place either upon the bed of a reverberatory furnace or in crucibles in air furnaces heated by coke or by gaseous fuel. Of these methods the first or cupola is only fitted for iron founding, the reverberatory furnace is used for bronze and iron, and in special forms for steel ; while crucible melting is most general for brass and bronze small castings, as well as for the finer kinds of steel, or generally for any metal that is likely to be altered by direct contact with the fuel. The description of these appliances belongs more properly to the article FURNACE. The founder s ladle or " shank " is a bucket or cup-shaped vessel of wrought iron lined with a shell of fire-clay, with a lip for pouring, having two projecting handles. One of these is straight and serves as a pivot; the other with a cross bar called a crutch is used as a tipping handle when pouring. When of small size the filled ladle can be carried from the cupola to the work and poured by two men, but when of large size containing several tons of metal they are slung from a crane and tipped by a tangent screw and worm wheel, manipulated by a man standing at a distance. The perfection of ladle arrangement is to be seen in Bes- semer s process of steel making, where several tons of melted steel are distributed into a ring of ingot moulds in a circular pit by two or three men in a very few minutes. In Krupp s arrangements for making large steel castings from crucibles an intermediate or equalizing ladle is used. The crucibles, which contain about 70 ft) each, are drawn from the furnaces in regular order, and poured in such a manner that an uninterrupted stream of metal is kept up from the ladle to the mould. Large castings when filled from above are liable to be spongy or unsound in the upper part of the mould, or that last filled. In such cases an extra length is given at the top of the mould, as the unsound portion or dead-head is afterwards removed. This plan is usually followed in casting bronze guns. Sound and dense castings can be obtained by filling with a vertical side runner, so that the metal enters the mould from below and solidifies under the hydrostatic head represented by the vertical height of the runner. A method employed by Sir Joseph Whitworth, of applying hydraulic pressure to the metal in the mould until it solidifies, has been adopted with great success by the inventor in the prevention of blow holes and similar imperfections in steel ingots. In "chill casting" a portion of the surface of the whole or a part of the mould is made of cast iron, so that the metal brought in contact with it is rapidly cooled. It is adopted in the production of Palliser s cast iron projectiles for penetrating armour plates, rolls for boiler and other iron plates, and paper glazing, and in America for hardening the treads of railway wheels. The iron where in contact with the chill surface becomes white, of a platy crystalline structure, and intensely hard, while such portions as are cooled in contact with the sand remain finely granular, dark grey, and comparatively soft. (H. B.) FOUNDLING HOSPITALS are intended to save children from death by exposure, and it is therefore difficult to describe them properly apart from the general subject of infanticide. This practice was extremely common among nearly all ancient nations. It may still be studied in such horrible institutions of savage life as the Areoi of the Society Islands, or the Meebra of New South Wales ; and it may be found in the greatest variety of form among the tribes of Hindustan. 1 The motives which suggested the 1 Compare Moore on Hindu Infanticide, 1811, with Brown on In fanticide in India, 1868. In Baluchistan, where children are often drowned in milk, there is a euphemistic proverb, "The lady s daughter died drinking milk." IX. 61