FOUNDING, OF IRON. The opera tions of an iron foundry consist in re melting the pig-iron of the blast furnaces, and giving it an endless variety of forms, by casting it in moulds of different kinds, prepared in appropriate manners. Coke is the only kind of fuel employed to effect the fusion of the cast-iron.
The essential parts of a well-mounted iron foundry are, Magazines for pig-irons of different qualities, which are to be mixed in cer tain proportions, for producing castings of peculiar qualities ; as also for coal, coke, sands, clay, powdered charcoal, and cow-hair for giving tenacity to the loam mouldings.
One or more coke ovens.
A workshop for preparing the pattern and materials of the moulds. It should contain small edge millstones for grind ing and mixing the loam, and another mill for grinding coal and charcoal.
A vast area, called properly the foun dry, in which the moulds are made and filled with the melted metal. These moulds are in general very heavy, con sisting . f two parts at least, which must be separated, turned upside down seve• ral times, and replaced very exactly upon one another. The casting is generally effected by means of large ladlekor pots, in which the melted iron is trOsported from the cupola, where it is fused. Hence, the foundry ought to be provided with cranes, having jibs movable in every direction.
A stove in which such moulds may be readily introduced as require to be en tirely deprived of humidity, and where a strong heat may be uniformly main tained.
Both blast and air furnaces, capable of melting speedily the quantity of cast iron to be employed each day.
A blowing machine to urge the fusion in the furnaces.
The mode of casting metal pipes will serve to illustrate many different varie ties of iron-founding. There is formed, in the first place, a core or central pat tern of cast-iron, with alternate grooves and ridges extending from end to end. Round this is wrapped a covering of hay or straw rope, and this rope is plastered with a layer of wet loam or clay, worked until the exterior surface becomes cylin drical, and corresponding in diameter with the internal dimensions of the pipe to be made. From this mode of forma tion it follows that there are hollow chan nels or gutters beneath the straw-rope, and these serve for the exit of heated air in the subsequent processes. The core, when formed, is sprinkled with powder ed charcoal, and placed in a heated oven to harden. Meanwhile, the mould for giving the external form of the pipe is being prepared. A model, or pattern, is
made, corresponding exactly with the exterior of the pipe to be made, and with this pattern a mould, or cavity, is form actin a smooth oed of sand, in two halves. Then, when the core is placed and sup ported concentrically in this mould, there is a cylindrical space between the two, equal to the thickness of the intended pipe. Holes for the admission of the melted metal, and others for the exit of the heated air, are provided, and the metal is poured in from the ladles or vessels before alluded to. It will be plain, on a little consideration, that the exterior of the core must give the in terior form to the pipe, while the interior of the mould must give the exterior form to the pipe.
In casting pipes of large diameter, the core and mould are built up vertically in a pit as deep as the pipes are long ; and matters are so arranged that the liquid metal is poured in at one end. In cast ing large cylinders for steam-engines and other purposes, the formation of the mould and core is a matter of much im portance ; each being formed of brick work built up cylindrically, and of such dimensions that the larger may inclose the former, leaving a space between them equal to the intended thickness of the metal cylinder. The outer surface of the inner cylinder, or core, and the inner surface of the outer cylinder, or mould, are wrought very smooth and regular ; and both cylinders being adjusted in a pit, melted metal is poured into the va cuity between them. Thus is the cylin der formed. The process of boring, to which such cylinders, as well as cannon and other articles requiring a smooth in terior, are afterwards subjected, is not, as the name seems to imply, the boring or making a hole, but a planing, scrap ing, or cutting away of the inner surface, till it becomes regular and smooth from end to end.
In all large specimens of casting, such as bed-plates for marine engines, arches for bridges, beams for roofs, plates for large cisterns and tanks, turn-tables for railways, framework for engines and ma chines of. various kinds, and such like, the mould is made in sand on the floor of the casting-house, from Moulds or patterns previously constructed in ac cordance with the working drawings, and the liquid metal is poured into these moulds at once from the blast-furnace, or from the ponderous vessels, or from a cupola-furnace, according to the cir cumstances of the case.