Brass
Brass is an alloy of copper and zinc, in proportions which can be varied to achieve different colours and mechanical, electrical, acoustic, and chemical properties, but copper typically has the larger proportion, generally copper and zinc. In use since prehistoric times, it is a substitutional alloy; atoms of the two constituents may replace each other within the same crystal structure.
Brass is similar to bronze, a copper alloy that contains tin instead of zinc. Both bronze and brass may include small amounts of a range of other elements, including arsenic, lead, phosphorus, aluminium, manganese, and silicon. Historically, the distinction between the two alloys has been inconsistent, and increasingly museums use the more general term "copper alloy".
Brass has long been popular for its bright, golden appearance and is used for drawer pulls and doorknobs. It has also been widely used for sculpture and utensils because of its low melting point, high workability, durability, and electrical and thermal conductivity. Brasses with higher copper content are softer and more golden coloured; conversely, those with less copper and more zinc are harder and more silvery.
Brass is commonly used in applications where corrosion resistance and low friction are required, such as locks, hinges, gears, bearings, ammunition casings, zippers, plumbing, hose couplings, valves, SCUBA regulators, and electrical plugs and sockets. It is used extensively for musical instruments such as horns and bells. The composition of brass makes it a favorable substitute for copper in costume jewelry and fashion jewelry, as it exhibits greater resistance to corrosion. Brass is not as hard as bronze, so is not suitable for most weapons and tools. It is also not suitable for marine usage as the zinc reacts with minerals in salt water, which leaves the porous copper behind. Marine brass, with added tin, avoids this, as does bronze.
Brass is often used in equipment that must be nonsparking, such as fittings and tools used near flammable or explosive materials.
Properties
Brass is more malleable than bronze or zinc. The relatively low melting point of brass 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.Today, almost 90% of all brass alloys are recycled. Because brass is not ferromagnetic, ferrous scrap can be separated from it by passing the scrap near a powerful magnet. Brass scrap is melted and recast into billets that are extruded into the desired form and size. The general softness of brass means that it can often be machined without the use of cutting fluid, but with exceptions.
Aluminium makes brass stronger and more corrosion-resistant. It also causes a highly beneficial hard layer of aluminium oxide to be formed on the surface that is thin, transparent, and self-healing. Tin has a similar effect and finds its use especially in seawater applications. Combinations of iron, aluminium, silicon, and manganese make brass wear- and tear-resistant. The addition of as little as 1% iron to a brass alloy results in an alloy with a noticeable magnetic attraction.
Brass corrodes in the presence of moisture, chlorides, acetates, ammonia, and certain acids. This often happens when the copper reacts with sulfur to form a brown and eventually black surface layer of copper sulfide, which if regularly exposed to slightly acidic water such as urban rainwater, can then oxidize in air to form a patina of green-blue copper carbonate. Depending on how the patina layer was formed, it may protect the underlying brass from further damage.
Although copper and zinc have a large difference in electrical potential, the resulting brass alloy does not experience internalized galvanic corrosion because of the absence of a corrosive environment within the mixture. However, if brass is placed in contact with a "more" noble metal such as silver or gold in such an environment, the brass will corrode galvanically; conversely, if brass is in contact with a "less" noble metal such as zinc or iron, the less noble metal will corrode and the brass will be protected.
Lead content
To enhance the machinability of brass, lead is often added in concentrations of about 2%. Since lead has a lower melting point than the other constituents of the brass, it tends to migrate towards the grain boundaries in the form of globules as it cools from casting. The pattern the globules form on the surface of the brass increases the available lead surface area, which in turn, affects the degree of leaching. In addition, cutting operations can smear the lead globules over the surface. These effects can lead to significant lead leaching from brasses of comparatively low lead content.Regulations, California, USA
In October 1999, the California attorney general sued 13 key manufacturers and distributors over lead content. In laboratory tests, state researchers found the average brass key, new or old, exceeded the California Proposition 65 limits by an average factor of 19, assuming handling twice a day. In April 2001, manufacturers agreed to reduce lead content to 1.5%, or face a requirement to warn consumers about lead content. Keys plated with other metals are not affected by the settlement, and may continue to use brass alloys with a higher percentage of lead content.Also in California, lead-free materials must be used for "each component that comes into contact with the wetted surface of pipes and pipe fittings, plumbing fittings and fixtures". On 1 January 2010, the maximum amount of lead in "lead-free brass" in California was reduced from 4.0 to 0.25% lead.
Corrosion-resistant brass for harsh environments
Dezincification-resistant brasses, sometimes referred to as CR brasses, are used where the risk of corrosion is large and where normal brasses do not meet the requirements. Applications with high water temperatures, chlorides present, or deviating water qualities play a role. For example, DZR-brass is used 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.An example of DZR brass is C352 brass, with about 30% zinc, 61–63% copper, 1.7–2.8% lead, and 0.02–0.15% arsenic. The lead and arsenic significantly suppress zinc loss.
"Red brasses", a family of alloys with high copper proportion and generally less than 15% zinc, are more resistant to zinc loss. One of the metals called red brass is 85% copper, 5% tin, 5% lead, and 5% zinc. Copper alloy C23000, which is also known as red brass, contains 84–86% copper and 0.05% each iron and lead, with the balance being zinc.
Another such material is gunmetal, from the family of red brasses. Gunmetal alloys contain roughly 88% copper, 8–10% tin, and 2–4% zinc. Lead can be added for ease of machining or for bearing alloys.
"Naval brass", for use in seawater, contains 40% zinc, but also 1% tin. The tin addition suppresses zinc leaching.
The NSF International requires brasses with more than 15% zinc, used in piping and plumbing fittings, to be dezincification-resistant.
Use in musical instruments
The high malleability and workability, relatively good resistance to corrosion, and traditionally attributed acoustic properties of brass, have made it the usual metal of choice for construction of musical instruments whose acoustic resonators consist of long, relatively narrow tubing, often folded or coiled for compactness; silver and its alloys, and even gold, have been used for the same reasons, but brass is the most economical choice. Collectively known as brass instruments, or simply "the brass", these include the trombone, tuba, trumpet, cornet, flugelhorn, baritone horn, euphonium, tenor horn, and French horn, and many other "horns", many in variously sized families, such as the saxhorns.Other wind instruments may be constructed of brass or other metals, and indeed most modern student-model flutes and piccolos are made of some variety of brass, usually a cupronickel alloy similar to nickel silver. Clarinets, especially low clarinets such as the contrabass and subcontrabass, are sometimes made of metal because of limited supplies of the dense, fine-grained tropical hardwoods traditionally preferred for smaller woodwinds. For the same reason, some low clarinets, bassoons, and contrabassoons feature a hybrid construction, with long, straight sections of wood, and curved joints, neck, and/or bell of metal. The use of metal also avoids the risks of exposing wooden instruments to changes in temperature or humidity, which can cause sudden cracking. Though the saxophones and sarrusophones are classified as woodwind instruments, they are normally made of brass for similar reasons, and because their wide, conical bores and thin-walled bodies are more easily and efficiently made by forming sheet metal than by machining wood.
The keywork of most modern woodwinds, including wooden-bodied instruments, is also usually made of an alloy such as nickel silver. Such alloys are stiffer and more durable than the brass used to construct the instrument bodies, but still workable with simple hand tools—a boon to quick repairs. The mouthpieces of both brass instruments and, less commonly, woodwind instruments are often made of brass among other metals as well.
Next to the brass instruments, the most notable use of brass in music is in various percussion instruments, most notably cymbals, gongs, and orchestral bells. Small handbells and "jingle bells" are also commonly made of brass.
The harmonica is a free reed aerophone, also often made from brass. In organ pipes of the reed family, brass strips are used as the reeds, which beat against the shallot. Although not part of the brass section, snare drums are also sometimes made of brass. Some parts on electric guitars are also made from brass, especially inertia blocks on tremolo systems for its tonal properties, and for string nuts and saddles for both tonal properties and its low friction.