Brass

Brass bolt.

Brass tap.

Brass or azófar is an alloy of copper and zinc. The proportions of copper and zinc can be varied to create a variety of brasses with diverse properties. In industrial brasses the percentage of zinc is always kept below 50%. Its composition influences the mechanical characteristics, the fusibility and the ability to be formed by casting, forging, stamping and machining. When cold, the ingots obtained can be transformed into sheets of different thicknesses, rods or cut into strips that can be stretched to make wires. Its density also depends on its composition. In general, the density of brass is between 8.4 g/cm³ and 8.7 g/cm³ . Its melting point is between 900 and 940 °C, depending on the composition.

While bronze is instead primarily an alloy of copper with tin, some types of brasses are called 'bronzes'. Brass is a substitutional alloy used for decoration because its luster gives it a gold-like appearance, for applications where low friction is required such as locks and valves, for plumbing and electrical applications, and extensively in musical instruments such as trumpets and bells, as well as inexpensive cymbals (Power Beat, Paiste 101, 201 and in some quantities from the Pst series, Planet Z) for their acoustic properties.

Brass has been known to humans since prehistoric times, even before zinc itself was discovered. Then it was produced by mixing copper with calamine, a natural source of zinc. In the German villas of Breinigerberg, an ancient Roman site was discovered where a calamine mine existed. During the mixing process, the zinc is extracted from the calamine and mixed with the copper. Pure zinc, on the other hand, has a very low melting point to have been produced by ancient metalworking techniques.

History

Persian jar of brass of the centuryVII

Although brass has been used in various forms since prehistoric times, its true nature as an alloy of copper and zinc was not understood until the period after the Middle Ages, since zinc vapor reacting with copper to form brass was not recognized as a metal. The King James Bible makes many references to "brass" (brass in English), to translate the word "nechosheth" (bronze or copper) from Hebrew to Archaic English. The use in Early Modern English of the word "brass" it can mean any alloy of bronze or copper, an even less precise definition than the modern one.

The earliest brasses may have been natural alloys made by smelting zinc-rich copper ores. In ancient Rome, brass was deliberately produced from metallic copper and zinc ores using the cementation process, whose product was calamine brass. Variants of this method continued to be used until the mid-19th century. It would eventually be superseded by the speltering process, a system introduced in Europe in the 16th century consisting of the direct alloy of copper and metallic zinc.

Historically, brass has sometimes been referred to as "yellow copper".

Types of brass

Based on their Zn percentage, three main groups of brasses are recognized. ^{[citation required]}

• First-title batons, with a percentage of Zn less than 35 %
• Second-title batons, with Zn percentage of 33 to 44 %
• Third-title batons with Zn percentages greater than 44% without just industrial applications.

Some common alloys received special names; thus, the alloy of copper and zinc in a proportion of 80 to 20 was called “similor”; "Prince Albert metal" to the same alloy in the ratio 84 to 16; and "chrysocolla" to that of 82 parts of copper, 6 of zinc and 6 of tin.

Brass, according to the minority elements involved in the alloy, are malleable only when cold, and not when hot, and some are not malleable at any temperature. All types of this alloy become brittle when heated to near the melting point.

Brass is less hard than copper, but easy to machine, stamp and cast, it is resistant to oxidation, saline conditions and it is malleable, so it can be rolled into thin plates. Its malleability varies according to composition and temperature, and is different if it is mixed with other metals, even in minute amounts.

In lead brass, lead is practically insoluble in brass, and it separates in the form of fine globules, which favors the fragmentation of chips in machining. Lead also has a lubricating effect due to its low melting point, which reduces wear on the cutting tool. Brass admits few heat treatments and only recrystallization and homogenization annealing is performed.

Applications

Brass has a golden color, which is why it is used in costume jewelery and decorative elements. Other applications of brass cover the most diverse fields, from boilermaking to weapons, welding, the manufacture of wires, condenser tubes, electrical terminals and coinage. It is not attacked by salt water, which is why it is used in the construction of boats, in fishing equipment. It is also present in the manufacture of many wind musical instruments (such as trumpets, tubas, saxophones, some clarinets and flutes...), sound reeds for harmoniums, accordions and reed registers for musical organs. In addition, due to its antimicrobial action, it is used in hospital doorknobs, which disinfect themselves, unlike non-metallic ones.

Within decorative applications, it is used above all for making lamps, curtain rods and for some pieces worked in goldsmithing. The countries that show the highest consumption of this type of appliance are the countries of Eastern Europe, the Baltics or the former Soviet Union.^{[citation required]} Also the Arab countries, mainly the largest oil producers, and even some Asian countries.

Brass does not spark on mechanical impact, an atypical property for alloys. This characteristic makes brass an important material in the manufacture of containers for handling flammable compounds, and tools for use in the vicinity of flammable gases. Due to its easy machining and good price for recycled shavings, it is widely used for the manufacture of industrial valves. It is also used in the manufacture of ship propellers for its resistance to cavitation, and even in some computer cases where the motherboard is located.