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Brass
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Brass is any alloy of copper and zinc; the proportions of zinc and copper can be varied to create a range of brasses with varying properties. In comparison, bronze is principally an alloy of copper and tin. Despite this distinction, some types of brasses are called bronzes.
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Brass is any alloy of copper and zinc; the proportions of zinc and copper can be varied to create a range of brasses with varying properties. In comparison, bronze is principally an alloy of copper and tin. Despite this distinction, some types of brasses are called bronzes. Brass is a substitutional alloy. It is used for decoration for its bright gold-like appearance; for applications where low friction is required such as locks, gears, bearings,doorknobs, ammunition, and valves; for plumbing and electrical applications; and extensively in musical instruments such as horns and bells for its acoustic properties. It is also used in zippers.
Brass has a muted yellow color, somewhat similar to gold. It is relatively resistant to tarnishing, and is often used as decoration and for coins. In antiquity, polished brass was often used as a mirror.
Brass has likely been known to humans since prehistoric times, even before zinc itself was discovered. It was produced by melting copper together with calamine, a zinc ore. In the German village of Breinigerberg, an ancient Roman settlement was discovered where a calamine ore mine existed. During the melting process, the zinc is extracted from the calamine and mixes with the copper. Pure zinc, on the other hand, has too low a boiling point to have been produced by ancient metalworking techniques. The many references to 'brass' appearing throughout the King James Bible are thought to signify another bronze alloy, or copper, rather than the strict modern definition of 'brass'.
Properties
The malleability and acoustic properties of brass have made it the metal of choice for brass musical instruments such as the trombone, tuba, trumpet, euphonium, and the French horn. Even though the saxophone is classified as a woodwind instrument and the harmonica is a free reed aerophone, both are also often made from brass. In organ pipes designed as "reed" pipes, brass strips are used as the "reeds".
Brass has higher malleability than copper or zinc. The relatively low melting point of brass (900 to 940°C, depending on composition) and its flow characteristics make it a relatively easy material to cast. By varying the proportions of copper and zinc, the properties of the brass can be changed, allowing hard and soft brasses. The density of brass is approximately 8400 to 8730 kilograms per cubic metre (equivalent to 8.4 to 8.73 grams per cubic centimetre).
Today almost 90% of all brass alloys are recycled. Because brass is not ferromagnetic, it can be separated from ferrous scrap by passing the scrap near a powerful magnet. Brass scrap is collected and transported to the foundry where it is melted and recast into billets. Billets are heated and extruded into the desired form and size.
Aluminium makes brass stronger and more corrosion resistant. Aluminium also causes a highly beneficial hard layer of aluminium oxide (Al2O3) to be formed on the surface that is thin, transparent and self healing. Tin has a similar effect and finds its use especially in sea water applications (naval brasses). Combinations of iron, aluminium, silicon and manganese make brass wear and tear resistant. A well known alloy used in the automotive industry is 'LDM C673', where the combination of manganese and silicon leads to a strong and resistant brass.
Applications
The so called dezincification resistant (DZR) brasses, like alloy 'LDM G563' (known for its brand name 'Enkotal'), are used where there is a large corrosion risk and where normal brasses do not meet the standards. Applications with high water temperatures, chlorides present or deviating water qualities (soft water) play a role. DZR-brass is excellent in water boiler systems. This brass alloy must be produced with great care, with special attention placed on a balanced composition and proper production temperatures and parameters to avoid long-term failures.
The copper in brass makes brass germicidal, via the oligodynamic effect. For example, brass doorknobs disinfect themselves of many bacteria within eight hours. This effect is important in hospitals, but useful in many contexts.
Brass door hardware is generally lacquered when new, which prevents tarnishing of the metal for a few years when located outside (and indefinitely when located indoors). After this most manufacturers recommend that the lacquer is removed (e.g. with paint stripper) and the items regularly polished to maintain a bright finish. Unlacquered brass weathers more attractively than brass with deteriorated lacquer, even if polishing is not carried out. Freshly polished brass is similar to gold in appearance, but becomes more reddish within days of exposure to the elements. A traditional polish is Brasso.
Brass was used to make fan blades, fan cages and motor bearings in many antique fans that date before the 1930s. Brass can be used for fixings for use in cryogenic systems, however its use is not limited to this.
Due to its natural heat conducting properties and its availability, brass was used to create the infamous Brazen Bull, a torture and execution device in ancient Greece.
Season cracking
Brass is susceptible to stress corrosion cracking, especially from ammonia or substances containing or releasing ammonia. The problem is sometimes known as season cracking after it was first discovered in brass cartridge cases used for rifle ammunition during the 1920s in the Indian Army. Brittle cracks could cause serious accidents if the case was too weak to resist the charge when the rifle was fired. The problem was caused by high residual stresses from cold forming of the cases during manufacture, and was cured by annealing the cases.
Brass types
- Admiralty brass contains 30% zinc and 1% tin which inhibits dezincification in most environments.
- Alpha brasses with less than 35% zinc, are malleable, can be worked cold, and are used in pressing, forging, or similar applications. They contain only one phase, with face-centered cubic crystal structure. Prince's metal or Prince Rupert's metal is a type of alpha brass containing 75% copper and 25% zinc. Due to its beautiful yellow color, it is used as an imitation of gold. The alloy was named after Prince Rupert of the Rhine.
- Alpha-beta brass (Muntz metal), also called duplex brass, is 35-45% zinc and is suited for hot working. It contains both a and ß' phase; the ß'-phase is body-centered cubic and is harder and stronger than a. Alpha-beta brasses are usually worked hot.
- Aluminium brass contains aluminium, which improves its corrosion resistance. It is used in Euro coins (Nordic gold).
- Arsenical brass contains an addition of arsenic and frequently aluminium and is used for boiler fireboxes.
- Beta brasses, with 45-50% zinc content, can only be worked hot, and are harder, stronger, and suitable for casting.
- Cartridge brass is a 30% zinc brass with good cold working properties.
- Common brass, or rivet brass, is a 37% zinc brass, cheap and standard for cold working.
- DZR brass is dezincification resistant brass with a small percentage of arsenic.
- Gilding metal is the softest type of brass commonly available. An alloy of 95% copper and 5% zinc, gilding metal is typically used for ammunition components.
- High brass contains 65% copper and 35% zinc, has a high tensile strength and is used for springs, screws, and rivets.
- Leaded brass is an alpha-beta brass with an addition of lead. It has excellent machinability.
- Low brass is a copper-zinc alloy containing 20% zinc with a light golden color and excellent ductility; it is used for flexible metal hoses and metal bellows.
- Naval brass, similar to admiralty brass, is 40% zinc and 1% tin.
- Red brass is an American term for the copper-zinc-tin alloy known as gunmetal, which is technically not brass,.
- Rich low brass (Tombac) is 15% zinc. It is often used in jewelry applications.
- White brass contains more than 50% zinc and is too brittle for general use.
- Yellow brass is an American term for 33% zinc brass.
- Manganese brass is a brass most notably used in making Golden Dollar coins in the United States. It contains roughly 70% copper, 29% zinc, and 1.3% manganese
See also
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