Brass

Brass, alloy composed of copper and zinc; probably the most widely used non-ferrous alloy. It has been known from very early times; it is mentioned in the Old Testament as being manufactured into instruments of music, ornaments and various other things. In all probability these were not made from brass, but from bronze, since we have no clue to the composition of the metal. The Romans used an alloy which they called aurichalcum, and this seems to have been brass. Monumental brasses are the earliest traces of the use of the metal in Great Britain. In the reign of Henry VIII, the export of brass was forbidden, a fact which indicates that the manufacture of brass was extensively carried on in England. The former method of production was that of mixing with powdered zinc ore small quantities of copper. The mixture was then heated in large pots over a furnace. The modern process is that of mixing metallic zinc with copper, in crucibles or in a reverberatory furnace, the copper being first reduced to a molten state, and then molten zinc added. When crucibles are used, there is less waste. The molten metal is then poured from the crucibles into moulds to form ingots for remelting.

There are many commercially important compositions of brass. Increase in the zinc concentration up to 30 per cent increases the strength and ductility of the alloys; further addition from 30 to 50 per cent zinc increases the strength but decreases the ductility, and zinc in excess of 50 per cent makes brass brittle. Brass with 10-15 per cent zinc has a golden colour and is known as gilding metal; it is used for architectural work and cheap jewellery. Brass with 30 per cent zinc (known as 70/30 brass) has the best combination of strength and ductility and is used for engineering ware requiring great ductility in manufacture, such as wire, sheet, and tubes. The commonest form of brass contains 40 per cent zinc and is known as 60/40 brass, yellow brass, or Muntz metal, after the name of its Birmingham inventor. It is much stronger than 70/30 brass and has the advantage of being amenable to hot working, which is not possible with lower zinc compositions. 60/40 brass is used for castings, extrusions, hot stampings, etc.

When brasses are used in sea-water, dezincification, a progressive leaching of the zinc, occurs. The remaining copper is much weaker than the original brass and eventually fractures. Dezincification in 70/30 brass is cured by a small addition of arsenic but there is no complete cure for the 60/40 type. The general corrosion resistance of brasses is improved by the addition of 1 per cent tin. These Improvements are combined in the alloys known as Admiralty brass and Naval brass.

The brass trade in England is carried on chiefly at Birmingham. The various processes are casting, rolling and drawing, stamping, tube-drawing and casing, and brass finishing. Brass finishing includes dipping, burnishing, lacquering, etc. When an article in brass is made, it goes through a cleansing process in acid, and then it is dipped into a solution of nitric acid. For the process of burnishing, polished steel tools are used, and the article is washed in a weak solution of acid, after which it is dried in sawdust. When lacquering is done the work is heated, and while in this state a coating of varnish, made of shellac dissolved in spirit, is spread over the surface of the article.

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