The sheet brass is procured from the mills where it is rolled, and the brass wire is also supplied from the special manufactories where it is drawn ready for use.
Making Moulds.
The method of making moulds for casting iron has already been mentioned, and those employed by the Brassfounder are quite similar, the tools used by the mould maker being the trowel, mallet, rule, and sand hook, the shovel for removing the sand, the brush for sweeping the surface, the bellows for blowing off the dust, and the compasses for measuring accurately.
Brush. Sand Hook. Compasses. Bellows. Shovel. Rule. Trowel. Mallet.
The principal materials for making foundry moulds for brass castings are fine sand and loam mixed in various proportions, according to the nature of the work. New sand is used for fine castings, old sand for ordinary work. The requisite external support is given by a couple of shallow rectangular iron frames without tops or bottoms, called flasks or casting boxes.
The two halves constituting a casting box carry ears corresponding exactly with one another, one set pierced with holes, the other furnished with points entering truly into these holes, and which may be made fast in them by cross-pins or wedges. One of the flasks is laid face downward on a board longer and wider than it, and is then rammed full of moulding sand; the surface is struck off level with a straight metal bar or scraper, a little loose sand is sprinkled upon it, and another board of proper size placed over it and rubbed down close. The two boards and the flask contained between them are turned over and the top board is taken off; the clean surface of moist sand now exposed is dusted over with perfectly dry fine parting sand, or very fine red brickdust. The patterns or models are now properly arranged on the surface of the same, the cylindrical or thick parts being partly sunk in the latter, and care being also taken to leave sufficient space between the several patterns to prevent one part breaking into the other, and also passages or ingates, by which to pour in the metal and allow the air to escape. The patterns are arranged on both sides a central passage or runner, technically called a ridge, from which again small lateral passages are made, leading into every section of the mould. The general surface is then properly arranged with the aid of small trowels, and a little fine parting sand or brickdust is shaken over it. When this has been accomplished, the upper part of the flask is fitted to the lower by the pins, and then also rammed full of mould sand. The fine dry parting sand or brickdust serves to prevent the two halves from sticking together. A board is now placed on the top of the upper half, and struck smartly in different places with a mallet, after which the upper half and its board are lifted up very gently and quite level, and then turned over, so that the upper half rests inverted on its board. The models are next removed, and channels scooped out from the cavities left by them to the hollows or pouring holes (ingates) at the end of the flask. Solid cores of sand or metal are adjusted in the proper places when the article is required to be cast hollow (brass cocks, for instance), and also iron rails intended to have brass heads cast on them, or such other articles of iron as are required to be solidly united with the brass. The faces of both halves are now finally dusted with waste flour or meal dust; the two halves are then replaced upon each other, and the box is fixed together by screw clamps. The moulds for fine castings (articles with ornamental surfaces, as screens, sconces, bell-levers, &c.) are faced with various fine substances, such as charcoal, loamstone, rottenstone, &c. that they may retain a sharp impression; after which they are most carefully dried. For ordinary work it is generally considered better that the sand should retain a little moisture, though great care must be taken in this respect, to guard against the danger of explosion.
Braces. Set Moulds. Cores.