FOUNDERY of Small Works, or Casting in Sand. The sand commonly used for casting small works is at first of a pretty soft, yellowish, and clammy nature; but it being necessary to strew charcoal dust in the mould, it at length becomes of a quite black colour. The sand is worked over and over, on a board, with a roller and a sort of knife; and is placed over a trough to receive it, after it has by these means been sufficiently prepared.
This being done, the workmen take a wooden board of a length and breadth proportional to the things to be cast, and putting a ledge round it, they fill it with sand a little moistened, to make it duly cohere. They then take either wood or metal models of what they intend to cast, and apply them to the mould, and press them into the sand so as to leave their impression there. Along the middle of the mould is laid half a small brass cylinder, as the chief canal for the metal to run through, when melted, into the models or patterns; and from this chief canal are placed several others, which extend collaterally to each model or pattern placed in the frame. After this frame is finished, they take out the patterns, by first loosening them all round, that the sand may not give way; then they proceed to work the other half of the mould with the same patterns in just such another frame, only that it has pins, which, entering into holes corresponding to it in the other, make the two cavities of the pattern fall exactly on each other.
The frame, thus moulded, is carried to the melter, who, after extending the chief canal of the counterpart, and adding the cross canals to the several models in both, and strewing mill dust over them, dries them in a kind of oven prepared for the purpose. Both parts of the mould being dry, they are joined together by means of the pins; and to prevent them giving way, by reason of the melted metal passing through the chief cylindrical canal, they are screwed or wedged up like a kind of press.
Whilst the moulds are thus preparing, the metal is fusing in a crucible of a size proportional to the quantity of metal intended to be cast. When the moulds have cooled, the frames are unscrewed or unwedged, and the cast work taken out of the sand, which sand is worked over again for other casting.