Brass is a metal composed primarily of copper and zinc. Copper is the main component, and brass is usually classified as a copper alloy. The color of brass varies from a dark reddish brown to a light silvery yellow depending on the amount of zinc present; the more zinc, the lighter the color. Brass is stronger and harder than copper, but not as strong or hard as steel. It is easy to form into various shapes, a good conductor of heat, and generally resistant to corrosion from salt water. Because of these properties, brass is used to make pipes and tubes, weather-stripping and other architectural trim pieces, screws, radiators, musical instruments, and cartridge casings for firearms.
Ancient metalworkers in the area now known as Syria or eastern Turkey knew how to melt copper with tin to make a metal called bronze as early as 3000 B.C. Sometimes they also made brass without knowing it, because tin and zinc ore deposits are sometimes found together, and the two materials have similar colors and properties.
By about 20 B.C.-A.D. 20, metalworkers around the Mediterranean Sea were able to distinguish zinc ores from those containing tin and began blending zinc with copper to make brass coins and other items. Most of the zinc was derived by heating a mineral known as calamine, which contains various zinc compounds. Starting in about 300 A.D., the brass metalworking industry flourished in what is now Germany and The Netherlands.
Although these early metalworkers could recognize the difference between zinc ore and tin ore, they still didn't understand that zinc was a metal. It wasn't until 1746 that a German scientist named Andreas Sigismund Marggraf (1709-1782) identified zinc and determined its properties. The process for combining metallic copper and zinc to make brass was patented in England in 1781.
The first metal cartridge casings for firearms were introduced in 1852. Although several different metals were tried, brass was the most successful because of it's ability to expand and seal the breech under pressure when the cartridge was first fired, then contract immediately to allow the empty cartridge casing to be extracted from the firearm. This property led to the development of rapid-fire automatic weapons.
The main component of brass is copper. The amount of copper varies between 55% and 95% by weight depending on the type of brass and its intended use. Brasses containing a high percentage of copper are made from electrically refined copper that is at least 99.3% pure to minimize the amount of other materials. Brasses containing a lower percentage of copper can also be made from electrically refined copper, but are more commonly made from less-expensive recycled copper alloy scrap. When recycled scrap is used, the percentages of copper and other materials in the scrap must be known so that the manufacturer can adjust the amounts of materials to be added in order to achieve the desired brass composition.
The second component of brass is zinc. The amount of zinc varies between 5% and 40% by weight depending on the type of brass.
Some brasses also contain small percentages of other materials to improve certain characteristics. Up to 3.8% by weight of lead may be added to improve machinability. The addition of tin improves corrosion resistance. Iron makes the brass harder and makes the internal grain structure smaller so that the metal can be shaped by repeated impacts in a process called forging. Arsenic and antimony are sometimes added to brasses that contain more than 20% zinc in order to inhibit corrosion. Other materials that may be used in very small amounts are manganese, silicon, and phosphorus.
The traditional names for various types of brass usually reflected either the color of the material or the intended use. For example, red brass contained 15% zinc and had a reddish color, while yellow brass contained 35% zinc and had a yellowish color. Cartridge brass contained 30% zinc and was used to make cartridges for firearms. Naval brasses had up to 39.7% zinc and were used in various applications on ships.
Unfortunately, scattered among the traditional brass names were a number of misnomers. Brass with 10% zinc was called commercial bronze, even though it did not contain any tin and was not a bronze. Brass with 40% zinc and 3.8% lead was called architectural bronze, even though it was actually a leaded brass.
As a result of these sometimes confusing names, brasses in the United States are now designated by the Unified Numbering System for metals and alloys. This system uses a letter—in this case the letter "C" for copper, because brass is a copper alloy—followed by five digits. Brasses whose chemical composition makes them suitable for being formed into the final product by mechanical methods, such as rolling or forging, are called wrought brasses, and the first digit of their designation is I through 7. Brasses whose chemical composition makes them suitable for being formed into the final product by pouring molten metal into a mold are called cast brasses, and the first digit of their designation is 8 or 9.
The manufacturing process used to produce brass involves combining the appropriate raw materials into a molten metal, which is allowed to solidify. The shape and properties of the solidified metal are then altered through a series of carefully controlled operations to produce the desired brass stock.
Brass stock is available in a variety of forms including plate, sheet, strip, foil, rod, bar, wire, and billet depending on the final application. For example, brass screws are cut from lengths of rod. The zigzag fins used in some vehicle radiators are bent from strip. Pipes and tubes are formed by extruding, or squeezing rectangular billets of hot brass through a shaped opening, called a die, to form long, hollow cylinders.
The differences between plate, sheet, strip, and foil are the overall size and thickness of the materials. Plate is a large, flat, rectangular piece of brass with a thickness greater than about 0.2 in. (5 mm)—like a piece of plywood used in building construction. Sheet usually has the same overall size as plate, but is thinner. Strip is made from sheet that has been cut into long, narrow pieces. Foil is like strip, only much thinner. Some brass foil can be as thin as 0.0005 in (0.013 mm).
The actual manufacturing process depends on the desired shape and properties of the brass stock, as well as the particular machinery and practices used in different brass plants. Here is a typical manufacturing process used to produce brass sheet and strip.
During production, brass is subject to constant evaluation and control of the materials and processes used to form specific brass stock. The chemical compositions of the raw materials are checked and adjusted before melting. The heating and cooling times and temperatures are specified and monitored. The thickness of the sheet and strip are measured at each step. Finally, samples of the finished product are tested for hardness, strength, dimensions, and other factors to ensure they meet the required specifications.
Brass has a combination of strength, corrosion resistance, and formability that will continue to make it a useful material for many applications in the foreseeable future. Brass also has an advantage over other materials in that most products made from brass are recycled or reused, rather than being discarded in a landfill, which will help ensure a continued supply for many years.
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Hombostel, Caleb. "Brass." In Construction Materials: Types, Uses, and Applications. New York: John Wiley and Sons, 1991.
Kroschwitz, Jacqueline I., and Mary Howe-Grant, eds. "Copper Alloys." In Encyclopedia of Chemical Technology, 4th ed. New York: John Wiley and Sons, Inc., 1993.
Metalworld. http://www.metalworld.com (June 19, 2000).
— Chris Cavette