BRASS. The quality of brass depends upon the proportions of its two constituents, copper and zinc. The greater the quantity of zinc the lighter the color and the more brittle and springy the alloy, while, on the other hand, the greater the quantity of copper, the redder the color and the tougher but softer the alloy. Technically, the term brass is extended to in clude compounds of copper and tin, as in.brass ordnance, the brasses or bearings of machinery, etc.; but such alloys of copper and tin,. though styled hard brass, are more strictly varieties of bronze. Brass foil, frequently nbt more than 1-50,000 of an inch in thickness and known as Dutch leaf, is made beating out sheets of very thin brass containing a large proportion of copper. Copper and zinc alloys resembling brass are well known in the trade as gilding metal, Mannheim gold, pinchbeck, bath metal, Bristol brass, Muntz sheathing metal, spelter solder and mosaic gold.
In the manufacture of brass, either of two processes may be followed. The direct method is to fuse the zinc in a crucible and gradually add the copper in pieces. But this process is attended witli disadvantage, owing to the vola tile and oxidizable nature of zinc. The indirect method of forming brass is generally followed; it consists in beating in crucibles or pots a mixture'of calamine (carbonate of zinc), char coal and thin pieces of scrap or grain copper. For ordinery purposes brass is first cast into plates of about 100 pounds weight (//i to I/2 inch thick) which can be readily broken up, remelted and cast in a mold of any desirable shape or size.
The following are the usual proportions in the several varieties of brass: Red brass-4 parts copper to 1 part zinc; yellow brass-2 parts copper to I part zinc; Muntz metal-3 parts copper to 2 parts zinc; Spelter solder —1 part copper to 1 part zinc. For brass wire the mixture generally used is five parts copper to three parts zinc, but the proportions vary greatly according to the purpose for which the wire is to be used, For some purposes, such as the manufacture of pins, where rigidity is of more importance than toughness, and cheapness is essential, it is possible to use Muntz metal, while for drawing into very fine gauges and weaving into the gauze that is used largely in paper-making machinery, much richer grades are employed.
The alloying of copper and spelter is per formed in crucibles, generally made 16 inches in depth and 10 inches in diameter at the top, tapering to about 9 inches in diameter at the bottom, the thickness of the walls being about one inch. These crucibles are heated in furnaces." This furnace is fired with solid fuel and has a natural draft, the height of the chim ney stacks varying from 40 where each furnace has its separate stack, to 150 feet where a number of furnaces are connected to one stack. Gas furnaces are also used in combina tion with generators, in which case producer gas, or sometimes water gas, is burned in place of the solid fuel; in these it is usual to heat 10 or 12 crucibles in one furnace or chamber. Re verberatory • and tilting furnaces are employed for large castings in sand molds, but for cast ing ingots in metal molds it is usual to employ a crucible furnace of the ((wind furnace" type, the fuel' commonly used being coke. Tilting furnaces are largely used in America. The oldest method of making brass, still largely used, is as follows: The metal is cast into long harrow ingots of about 1 cwt. each and from 3 to 4 inches wide. molds are generally made of cast-iron, cast in halves, which are clamped together with wrought-iron rings. The molds are placed below the surface of the floor of the casting shop and are supported against the side of the pit at an angle of about 60 degrees. Boards are placed across for the caster to stand upon while pouring the metal from the crucible into the mold. The metal, after careful skimming, is poured into the mold at the top and when it has set the rings are slipped off the mold and the upper half removed, leaving the casting or ingot exposed. Before the metal is poured into the mold the inside of the mold is well brushed and dressed with resin and cotton-seed oil to prevent adhesion, or carbon in a fine state and whale oil arc used, which give the mold an even surface. The ingots are next rolled when cold between ordinary flat rolls until the desired thickness is obtained.