|Properties of brass|
|Micrograph of rolled and annealed brass|
Cu Zn x
Technically: CuZnX, where
X = zinc content in percent
|colour||Golden yellow; lighter with increasing zinc content|
decreases with increasing zinc content
|density||8.41 g / cm³ (CuZn40) to
8.86 g / cm³ (CuZn5)
|electric conductivity||19 M S / m (CuZn20) to 33 MS / m (CuZn5) (decreasing with increasing zinc content)|
|Specific heat capacity||approx. 377 J / (kg K) (depending on alloy)|
|Linear coefficient of thermal expansion||18.5 10 −6 / K at 20 ° C (CuZn30)|
|tensile strenght||310 to 460 MPa (N / mm²)|
|Yield point||120 to 420 MPa (N / mm²)|
|modulus of elasticity||78 to 123 GPa (kN / mm²)|
|Torsional modulus||37 GPa (kN / mm²)|
|Speed of sound||4430 m / s|
Brass (from Middle High German messinc ) is a copper alloy with up to 40% zinc . Other metals can be added in smaller proportions in order to give the cast or wrought alloys certain properties. Objects made of brass have a brass (e) ne (from Middle High German messīn , "made of brass, brass") color.
The color of brass is primarily determined by the zinc content: with up to 20% zinc, brass is brownish to brownish-reddish, with over 36% light yellow to almost white-yellow. The processing properties of brass are significantly influenced by proportions of lead or tin , the corrosion properties by nickel . Typical cast alloys are brass and gunmetal with an additional alloy metal, lead.
If the zinc content is low and another metal is the second main component of the copper alloy, the alloy is not called brass, but bronze (tin), nickel silver ( nickel ), white tombac ( arsenic ) or silicon tombac ( silicon ).
Brass is a little harder than pure copper, but not as hard as bronze . The melting point is lower than that of bronze and decreases with increasing zinc content. In contrast to copper or aluminum, there is no gas content in the melt that reduces the quality of the castings. The zinc vapor pressure at temperatures around 900 ° C acts like flushing degassing. The escaping zinc immediately turns into fine flaky zinc oxide in the air, which as zinc smoke interferes with casting and is also harmful if inhaled ( metal fume fever ). A protective cover using suitable mixtures counteracts this.
Brass is non- magnetic , so it is generally unaffected by magnetic fields and does not produce sparks. Therefore, it is used for special tools.
In contrast to steel and aluminum alloys, brass cannot be hardened through heat treatment . The achievable strength values are determined by the alloy composition.
With zinc contents up to max. 37% of the alloys can be cold formed, as only the alpha phase is present (wrought alloys). The beta phase occurs with an increasing zinc content and only hot forming at> 600 ° C is possible.
Etymology and history
The origin of the word brass is not entirely clear, whereas the alloy was already known to Aristotle (384–322 BC) because of its gold-like appearance . Some explanations lead the name back to a people in the Colchis who were called "Mossynoics" ("wooden tower residents"), others see the relationship to the Latin massa and mean a lump of metal on the open hearth. What is certain is that brass was first specifically melted from copper and calamine around 1550 AD (see below), but it was not understood until the middle of the 17th century how to melt brass from copper and zinc. “Brass” quickly spread as a collective term for alloys based on copper / zinc. The tombaks , copper-zinc alloys with a copper content of> 80%, became more popular. The name is said to go back to the Malaysian tambaga .
Written evidence of the use of brass is provided by Cicero , among others , who complained in his De officiis that the immorality of many traders made them sell brass instead of gold . Among other things through the writings of Pliny the Elder , the use of the word Oreichalkos ( Aurichalkum ) for brass is common. The production of brass from the components copper and the zinc-containing mineral calamine ( Smithsonite , also noble calamine Zn [CO 3 ]) as well as the moistened coal dust added to reduce calamine is also handed down by Pliny the Elder . These ingredients were mixed together and the mixture was placed in several crucibles - usually seven to nine per kiln. The mixture was then heated up to the melting temperature (> 900 ° C). This process, which takes around 12 hours and is known today as " cementation ", resulted in raw brass , also known as Arco , which was poured together for a second melting process in order to increase quantity and quality. At that time, this was true of both ancient Greece and the Roman Empire - without any precise knowledge of the gold-like alloy composition. Between the 1st and 4th centuries AD, the Romans also practiced the brass-making process described by Pliny in the areas of Germania they occupied .
The centers of the medieval processing of brass (brass or gunmetal ) were the Meuse Valley , Flanders , Brabant and Aachen. In the Meuse valley there were deposits of Galmei, which were processed into brass with imported copper, so that all products from this area have been referred to as Dinanderie after the main town of Dinant since the 14th century . Famous, often figuratively decorated casts from the Romanesque period are sometimes made of brass (even if the material is often referred to as bronze , from which it is not always easy to distinguish externally): The baptismal font of Reiner von Huy in Liège (1107–1118), The Cappenberg Barbarossa head or the candlestick in the Milan Cathedral (around 1200) are part of it, as well as numerous ecclesiastical furnishings: lavabo kettles and basins, jugs and aquamaniles , holy water buckets and incense kettles, lecterns , engraved grave slabs (Netherlands, England), chandeliers, later also in the secular area Jugs, bowls and other household utensils.
Since the late Middle Ages also made of sheet metal are driven vessels are more common, first the Beckenschläger bowls of the 15th and especially the 16th century, and later all kinds of household appliances such as jugs, kettle , chafing dishes , snuff boxes , bed pans , scales, candlesticks , trays , Frames, fittings and much more. In pre-industrial times, however, cast brass was used in addition to all kinds of fittings, for example table lamps, weights, table bells, mortars , taps , door knockers and scientific instruments.
Copper crystallizes in the cubic crystal system with a face-centered cubic structure (crystal class: hexakisoctahedral ). Its melting point is 1083.62 ° C ( boiling point : 2927 ° C) and its density is 8.96 g / cm³.
Zinc, on the other hand, crystallizes in the hexagonal crystal system with hexagonal close packing (crystal class: dihexagonal dipyramidal ) and melts at 419.53 ° C. Even its boiling point of 907 ° C is still well below the melting point of copper. The density of zinc is, however, 7.14 g / cm³, relatively similar to that of copper.
Despite the large differences in terms of melting behavior and crystal structure, copper and zinc are able to form mixed crystals , more precisely substitution mixed crystals . But since zinc has a slightly larger atomic diameter, the unit cell of copper is distorted and strained by the built-in zinc atoms, which is the cause of the greater hardness of brass compared to pure copper.
Even the molten alloying of the two metals does not cause any great difficulties despite the widely spaced melting points. It is only necessary to ensure that the melt does not overheat and that it is processed as quickly as possible after reaching the casting temperature in order to avoid uncontrolled zinc burn-off.
In addition, the enamel surface must be covered in order to prevent excessive oxidation due to the absorption of atmospheric oxygen. Suitable covering agents include dry quartz sand , charcoal, and crushed glass . When dry and well coked, charcoal also has the advantage of being able to effectively prevent zinc burn-off.
Phases and Structures
Due to the different crystal systems, zinc has only limited solubility in copper . Technically usable brasses contain between 5 and a maximum of 45 percent zinc.
Zinc dissolves in solid copper up to a maximum proportion of 32.5% without changing the structure and forms with this a face-centered cubic (kfz) substitution solid solution, which is referred to as α-phase or α-brass. The solidus line sinks in the area of the pure α-phase from 1083.62 ° C (0% Zn) to 902 ° C (32.5% Zn).
In the range between 32.5% and 36.8% zinc, in addition to the α phase, there is also a β phase that solidifies in the body-centered cubic (krz) lattice. Up to about 37% zinc, however, the β-phase converts back into the α-phase at lower temperatures.
Alloys with about 50% copper and 50% zinc crystallize either in the β-phase or the β'-phase: At temperatures below 468 ° C the β'-phase is stable, with eight copper atoms surrounding eight zinc atoms and the cesium chloride - Take structure. Above 468 ° C, in the β phase, the atoms are statistically distributed over the lattice sites of a body-centered cubic lattice.
Above 50% zinc, further intermetallic Hume-Rothery phases occur, the γ, δ and ε phases. The hexagonal structure of the zinc is possible from a zinc content of 97.25%. However, since the γ phase is characterized by its extreme brittleness, such alloys are technically useless.
Types of brass
The common types of brass differ in their zinc content, which is given in percent in the name. In practice, however, all brass alloys contain at least 58 percent copper, since below this level they become brittle and difficult to process.
The collective term "cast brass" applies to cast parts. The alloy CuZn37, which contains 37 percent zinc, is most commonly used. The earlier nomenclature provided for the designation Ms followed by the copper content, here Ms 63.
Brass can contain up to three percent lead. With a significantly higher lead content, the alloy then belongs to the category of special brass, which can also contain other elements.
The alloy CuZn30 has the best plastic deformability of all types of brass. As cartridges for artillery projectiles were often made from it in the past due to its high elongation at break , this alloy is also known colloquially as cartridge brass .
As Tombak brasses are designated by> 67% copper. Tombac is mainly used for handicraft purposes and, depending on the copper content, is sold under the trade name Rottombak (90% Cu), Gold or Middle Tombac ( 85% Cu) and Yellow Tombac (72% Cu). The 5 and 10 pfennig coins of the DM period , minted until 2001, were made of tombac-plated steel. Tombac is also used as a shell for pistol and rifle projectiles, where it envelops the inner, softer lead core.
Silicon tombac is not one of the tombacs, but one of the various special brasses . White copper , known as white tombac , is not a copper-zinc alloy, but a copper- arsenic alloy, i.e. not a type of brass.
A number of brass instruments are often made of "gold brass" (actually "gold tombac") and are sometimes electroplated with silver.
Table brass is used in watchmaking for gears and other parts stamped from sheet metal. Decorative elements, including those of the classic military type (helmets, breastplates), were also made from table brass. Before the advent of small-caliber high - speed ammunition, it was also used to clad steel-jacketed projectiles for rifles and pistols, as it gave the projectile better spin in rifled barrels . Table brass was used as a gold substitute in jewelry making.
The alloy used as tallow gold for cheap jewelry is not a "gold tombak", but a gunmetal alloy made of copper, zinc, tin and lead, which is plated with gold to make it look like.
Alloys with 56 to 80 percent copper that were previously used for cast iron were referred to as brass , thus clarifying the distinction between gunmetal and bronze. The "brass foundry" even had their own guild.
Copper contents of 58% to 60% differentiate the area of so-called wrought brass alloys from that of cast alloys. The wrought alloys include the industrially important lead-containing cutting brass (also known as "automatic brass"). They have a different crystal lattice structure ( krz and not more kfz ) than brass with a Zn content of up to 38.95% and can contain lead in fine droplets as a chip breaker. The lead does not dissolve in the crystal lattice, but is present as a finely dispersed phase. The lead content varies between 0.5% and max. 3.5%. The more lead it contains, the better the material can be machined and the finer the chips. More than 3.5% lead only slightly improves the machinability, but causes problems when melting the alloy.
Alloys based on copper-zinc, to which other alloying elements are added ( lead > 3%, silicon , iron , nickel , manganese or aluminum ), are called special brass . A well-known copper-zinc-nickel alloy is German silver . The special brass type with the greatest structural relevance is silicon tombac , high strength values and good castability in gravity die casting and die casting make the alloy suitable for series or mass production of structural parts.
Other types of brass
For other types of brass see: Chrysorin , Cuivrepoli , Deltametall , Duranametall , Nordic Gold , Prinzmetall (folk etymologically redesigned from " Bronze "), Rauschgold , Platine , Muntzmetall ("yellow metal"), "Potin jaune"
Brass as a mineral
The International Mineralogical Association (IMA) currently (as of 2011) recognizes Zhanghengite (β-brass) and Danbait (CuZn 2 ) as two copper-zinc alloys as independent minerals . In the 9th edition of the systematics of minerals according to Strunz used by the IMA, they are classified in the mineral class of "elements" and there in the department of "metals and intermetallic compounds". Together with the minerals (N) α-brass , β'-brass , γ-brass , ε-brass , η-brass , tongxinite and zinc copperite , published without testing by the IMA, they belong to the "brass group" with the system No. 1.AB.10 within the "zinc-brass family".
As long as you had to empirically melt copper together with zinc spar to produce brass, sophisticated uses were not possible. They limited themselves primarily to jewelry, cult and art objects. This area of application, along with others, remained for brass into the 21st century, primarily for gold-colored alloys, i.e. handles and fittings, also because of their oligodynamic - bactericidal properties.
The possible uses of brass are diverse, and this applies above all when considering the cast and wrought alloys , which differ from one another in terms of their zinc content and thus the phase formation , not to mention special brass here.
Brass is of technical importance where good electrical conductivity and mechanical stability are important at the same time . Antennas and waveguides are made of brass. Pins made of brass wire are used for connectors . Brass wires with a galvanized surface can also be used for this purpose. Common qualities in the wire sector are CuZn2 , CuZn15 , CuZn30 , CuZn37 .
From a cast alloy with 39% zinc, 3% lead, the remainder copper, the so-called armature brass, near-net-shape fittings and fittings are manufactured in sanitary installations; Because of its good machinability, it is assigned to automatic brass, which is otherwise made from wrought material. The lower corrosion resistance compared to pure alpha brass, even compared to chloride-free tap water, is accepted.
Brass alloys are also among the materials suitable for bearings . The zinc-rich alloys CuZn37Al1 and CuZn40Al2 are used, i.e. with 1 or 2% aluminum content.
High-strength brass alloys with more than 32.5% zinc and the resulting formation of a beta phase can be used as cast propellers for pleasure craft in fresh water. This material is not suitable for seawater due to corrosion .
Wrought brass alloys solidifying in the pure alpha phase with a max. 58 parts copper, the remainder zinc including two percent lead. The possible uses for cast and wrought alloys are expanded considerably if other elements are alloyed in addition to 1–2% lead. In particular, aluminum (increased wear resistance) and, if necessary, an additional 5% nickel (ship propeller) considerably expand the range of applications for brass. This also includes silicon and manganese.
Zinc-containing welding consumables with additions of silicon, silver or tin are recommended ( except for MIG welding , which requires zinc-free alloys) (see DIN 1733). The lead content should not exceed one percent.
The addition of aluminum is problematic because it is easy to oxidize, which leads to oxide inclusions in the casting. Preventive melt treatment is therefore essential.
Brass with a zinc content of 30% and the resulting good cold formability is used to manufacture cartridge cases.
Brass releases small amounts of copper ions over the surface, which have a disinfecting effect. This is also known as self-disinfection or oligodynamy . Brass door handles, door plates and light switches are sometimes used in hospitals etc. to combat hospital germs. Viruses also become inactive within hours.
When melting brass, zinc vapor escapes as early as 900 ° C, i.e. close to the casting temperature, which immediately reacts in the air to form zinc oxide , which forms a white smoke. Inhaling leads to irritation, tiredness and fever - the “casting fever” or “zinc fever”, which is known and feared among foundries. See also metal fume fever . It is an acute toxic effect - no long-term damage is known.
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- Carl Johann Bernhard Karsten : System of metallurgy: historical, statistical, theoretical and technical . G. Reimer, Berlin 1831 (492 pages, limited preview in Google book search).
On historical technology and art history
- Jean Squilbeck: Dinanderie , in: Rhein und Maas - Art and Culture 800–1400 , exhibition catalog. Museum Schnütgen , Cologne 1972, pp. 67–72,
- Hermann P. Lockner: Brass - A manual about brass equipment of the 15th-17th centuries Century , Klinkhardt and Biermann, Munich 1982, ISBN 3-7814-0201-0 .
- Anna-Elisabeth Theuerkauff-Liederwald: Medieval bronze and brass vessels: buckets, jugs, lavabo vessels (= bronze devices of the Middle Ages , volume 4). Deutscher Verlag für Kunstwissenschaft , Berlin 1988, ISBN 3-87157-099-0 , pp. 11-25.
- Thomas Dexel: Types of Appliances . The metal device of Central Europe from the late Middle Ages to the 19th century. Klinkhardt and Biermann, Munich 1981, ISBN 3-7814-0157-X .
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- Kupferinstitut - data sheet CuZn5 (PDF 286 kB)
- Kupferinstitut data sheet CuZn37 (PDF 259 kB)
- Les Laitons ( Memento of the original from March 29, 2013 in the Internet Archive ) Info: The archive link was inserted automatically and has not yet been checked. Please check the original and archive link according to the instructions and then remove this notice. (French, p. 5; PDF; 1.4 MB)
- Friedrich table book - metal and machine technology . 168th edition. Bildungsverlag EINS, Troisdorf 2008, ISBN 978-3-427-51033-8 , p. 3 .
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- Duden .
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- stolberg-abc.de: Roman brass
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- German Copper Institute: Brass
- "Tombak", according to Giesserei-Lexikon, 17. Edition, Schiele and Schön, Berlin 1997, ISBN 3-7949-0606-3
- Beat Kneubuehl, Robin M. Coupland, Markus A. Rothschild: Wound ballistics: Basics and applications - page 104, 164, 2008, ISBN 978-3-540-79008-2 .
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- brass . In: Merck's Warenlexikon . 3rd ed. 1884 ff., P. 351 f.
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- For standardized brass cast and wrought alloys, see details in DIN EN 17660 and information sheet i5, copper-zinc alloys, brass and special brass. (DKI series of publications) Düsseldorf, without year, tab 14 and 15.
- Copper against germs: expectations were exceeded . baulinks.de. July 2, 2009. Retrieved March 28, 2020.
- Hospitals: doorknobs made of brass . aerzteblatt.de. Retrieved March 28, 2020.
- Gene Emery: Coronavirus can persist in air for hours and on surfaces for days: study ( English ) reuters.com. March 17, 2020. Accessed March 28, 2020.