Brass is an alloy made from copper and zinc. It was probably discovered sometime after 1000 B.C.E. by a people called the Mossynoeci, who lived near the Black Sea in northeast Turkey. They made brass, or what they thought was white bronze, by heating copper with charcoal and powdered zinc ore. The Persians used it from the fifth century B.C.E., and by the end of the first century B.C.E. the Romans were making brass coins. A flourishing brass industry had developed in northwest Europe by the middle of the fourth century C.E. The first use of brass casting in Britain was at the end of the 17th century, when a foundryman, John Lofting, began making casrass thimbles, which until then had been imported from Holland. The output from his factory exceeded 20,000 thimbles per week. The brass casting industry then spread to America, where it was centered in New England.
Brass manufacture
There is a wide range of brasses, all of them copper alloys containing up to 50 percent zinc and often smaller amounts of other elements such as tin, lead, nickel, manganese, aluminum, and iron. The action of seawater on brass tends to separate the zinc from the copper, and to prevent this from happening, small amounts (0.02 percent to 0.1 percent) of arsenic or antimony—and in the United States, phosphorus—are added to brasses used on ships.
Brasses are classified according to the amount of zinc that they contain. The proportion of zinc in a brass has an important effect on its physical properties. Loinc brass, containing between 5 percent and 20 percent zinc, has a reddish color and is known as red brass or low brass. This material is often used for making costume jewelry. When the brass contains about 30 percent zinc, it is called yellow brass or high brass. The uses of yellow brass include making musical instruments and parts for electrical appliances, plumbing equipment, and gun cartridge cases.
Brasses are made in foundries from precisely weighed amounts of pure copper, zinc, and the other constituent elements plus clean higrade copper scrap. One of the problems in making brass is the difference in melting points between the constituent metals: zinc melts at 786°F (419°C) but copper does not melt until 1981°F (1083°C). If the two metals are heated together, the zinc will boil away before the copper has melted, but if the copper is heated first and then solid zinc is added, most of the zinc will dissolve into the copper. An excess of zinc is added to make up for the small amount that inevitably boils away. The metal is heated in oil or gaired crucible furnaces, reverberatory furnaces (in which flames pass over the metals and heat is radiated from the roof of the furnace), and electric arc, or electric induction, furnaces.
The molten brass is poured from the furnace into molds. These molds produce either cylindrical billets, which are used to make tubes and rods, or ingots and slabs, which are used for brass sheets, plates, and strips. The metal is poured carefully to ensure that the molds are properly filled, with no air bubbles in the metal or in the spaces between the casting and the mold. To prevent the casting from sticking to the molds, a coating of a suitable lubricant such as graphite or an oiased compound is applied to the inside of the mold before the metal is poured in to it.
