|Brass from Wikipedia
Brass is an alloy of copper and
zinc; the proportions of zinc and copper can be varied to create a range
of brasses with varying properties.
By comparison, bronze is principally
an alloy of copper and tin. Bronze does not necessarily contain tin, and
a variety of alloys of copper, including alloys with arsenic, phosphorus,
aluminium, manganese, and silicon, are commonly termed "bronze". The term
is applied to a variety of brasses and the distinction is largely historical,
both terms having a common antecedent in the term latten.dia
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. Because it is softer than most other metals
in general use, brass is often used in situations where it is important
that sparks not be struck, as in fittings and tools around explosive gases.
The malleability and acoustic properties
of brass have made it the metal of choice for musical instruments such
as the trombone, tuba, trumpet, cornet, euphonium, tenor horn, and French
horn which are collectively known as the brass within an orchestra. 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 of the reed family, brass strips (called tongues) are used as the
reeds, which beat against the shallot (or beat "through" the shallot in
the case of a "free" reed).
Brass has higher malleability than
bronze or zinc. The relatively low melting point of brass (900 to 940 °C,
1652 to 1724 °F, 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 .303 lb/cubic
inch, 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
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.
To enhance the machinability of
brass, lead is often added in concentrations of around 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.
Silicon is an alternative to lead;
however, when silicon is used in a brass alloy, the scrap must never be
mixed with leaded brass scrap because of contamination and safety problems.
In October 1999 the California State
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 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
January 1, 2010, the maximum amount of lead in "lead-free brass" in California
was reduced from 4% to 0.25% lead. The common practice of using pipes for
electrical grounding is discouraged, as it accelerates lead corrosion.
Corrosion-resistant brass for
The so-called dezincification resistant
(DZR or DR) brasses 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.
Germicidal and antimicrobial
The copper in brass makes brass
germicidal. Depending upon the type and concentration of pathogens and
the medium they are in, brass kills these microorganisms within a few minutes
to eight hours of contact.
The bactericidal properties of brass
have been observed for centuries and were confirmed in the laboratory in
1983. Subsequent experiments by research groups around the world reconfirmed
the antimicrobial efficacy of brass, as well as copper and other copper
alloys (see Antimicrobial copper-alloy touch surfaces). Extensive structural
membrane damage to bacteria was noted after being exposed to copper.
In 2007, U.S. Department of Defense’s
Telemedicine and Advanced Technologies Research Center (TATRC) began to
study the antimicrobial properties of copper alloys, including four brasses
(C87610, C69300, C26000, C46400) in a multi-site clinical hospital trial
conducted at the Memorial Sloan-Kettering Cancer Center (New York City),
the Medical University of South Carolina, and the Ralph H. Johnson VA Medical
Center (South Carolina). Commonly touched items, such as bed rails, over-the-bed
tray tables, chair arms, nurse's call buttons, IV poles, etc. were retrofitted
with antimicrobial copper alloys in certain patient rooms (i.e., the “coppered”
rooms) in the Intensive Care Unit (ICU). Early results disclosed in 2011
indicate that the coppered rooms demonstrated a 97% reduction in surface
pathogens versus the non-coppered rooms. This reduction is the same level
achieved by “terminal” cleaning regimens conducted after patients vacate
their rooms. Furthermore, of critical importance to health care professionals,
the preliminary results indicated that patients in the coppered ICU rooms
had a 40.4% lower risk of contracting a hospital acquired infection versus
patients in non-coppered ICU rooms. The U.S. Department of Defense investigation
contract, which is ongoing, will also evaluate the effectiveness of copper
alloy touch surfaces to prevent the transfer of microbes to patients and
the transfer of microbes from patients to touch surfaces, as well as the
potential efficacy of copper-alloy based components to improve indoor air
In the U.S., the Environmental Protection
Agency regulates the registration of antimicrobial products. After extensive
antimicrobial testing according to the Agency’s stringent test protocols,
355 copper alloys, including many brasses, were found to kill more than
99.9% of methicillin-resistant Staphylococcus aureus (MRSA), E. coli O157:H7,
Pseudomonas aeruginosa, Staphylococcus aureus, Enterobacter aerogenes,
and vancomycin-resistant Enterococci (VRE) within two hours of contact.
Normal tarnishing was found to not impair antimicrobial effectiveness.
Antimicrobial tests have also revealed
significant reductions of MRSA as well as two strains of epidemic MRSA
(EMRSA-1 and EMRSA-16) on brass (C24000 with 80% Cu) at room temperature
(22 °C) within three hours. Complete kills of the pathogens were observed
within 4 1?2 hours. These tests were performed under wet exposure conditions.
The kill timeframes, while impressive, are nevertheless longer than for
pure copper, where kill timeframes ranged between 45 to 90 minutes.
A novel assay that mimics dry bacterial
exposure to touch surfaces was developed because this test method is thought
to more closely replicate real world touch surface exposure conditions.
In these conditions, copper alloy surfaces were found to kill several million
Colony Forming Units of Escherichia coli within minutes. This observation,
and the fact that kill timeframes shorten as the percentage of copper in
an alloy increases, is proof that copper is the ingredient in brass and
other copper alloys that kills the microbes.
The mechanisms of antimicrobial
action by copper and its alloys, including brass, is a subject of intense
and ongoing investigation. It is believed that the mechanisms are multifaceted
and include the following: 1) Potassium or glutamate leakage through the
outer membrane of bacteria; 2) Osmotic balance disturbances; 3) Binding
to proteins that do not require or utilize copper; 4) Oxidative stress
by hydrogen peroxide generation.
Research is being conducted at this
time to determine whether brass, copper, and other copper alloys can help
to reduce cross contamination in public facilities and reduce the incidence
of nosocomial infections (hospital acquired infections) in healthcare facilities.
Also, owing to its antimicrobial/algaecidal
properties that prevent biofouling, in conjunction with its strong structural
and corrosion-resistant benefits for marine environments, brass alloy netting
cages are currently being deployed in commercial-scale aquaculture operations
in Asia, South America, and the USA.
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. The problem was caused by high residual stresses
from cold forming of the cases during manufacture, together with chemical
attack from traces of ammonia in the atmosphere. The cartridges were stored
in stables and the ammonia concentration rose during the hot summer months,
so initiating brittle cracks. The problem was resolved by annealing the
cases, and storing the cartridges elsewhere.
|Admiralty brass contains 30% zinc, and 1% tin which inhibits
dezincification in many environments.
Aich's alloy typically contains 60.66% copper, 36.58%
zinc, 1.02% tin, and 1.74% iron. Designed for use in marine service owing
to its corrosion resistance, hardness and toughness. A characteristic application
is to the protection of ships' bottoms, but more modern methods of cathodic
protection have rendered its use less common. Its appearance resembles
that of gold.
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 ? and ?'
phase; the ?'-phase is body-centered cubic and is harder and stronger than
?. Alpha-beta brasses are usually worked hot.
Aluminium brass contains aluminium, which improves its
corrosion resistance. It is used for seawater service and also in Euro
coins#Small-denomination 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. Used for ammunition cases.
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 bullet "jackets", e.g. full metal jacket bullets.
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.
Lead-free brass as defined by California Assembly Bill
AB 1953 contains "not more than 0.25 percent lead content".
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.
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.
Muntz metal is about 60% copper, 40% zinc and a trace
of iron, used as a lining on boats.
Naval brass, similar to admiralty brass, is 40% zinc and
Nickel brass is composed of 70% copper, 24.5% zinc and
5.5% nickel used to make pound coins in the pound sterling currency.
Nordic gold, used in 10, 20 and 50 cts euro coins, contains
89% copper, 5% aluminium, 5% zinc, and 1% tin.
Red brass is both an American term for the copper-zinc-tin
alloy known as gunmetal, and an alloy which is considered both a brass
and a bronze. It typically contains 85% copper, 5% tin, 5% lead, and 5%
zinc. Red brass is also an alternative name for copper alloy C23000, which
is composed of 14–16% zinc, 0.05% iron and lead, and the remainder copper.
It may also refer to ounce metal, another copper-zinc-tin alloy.
Rich low brass (Tombac) is 15% zinc. It is often used
in jewelry applications.
Tonval brass (also called CW617N or CZ122 or OT58) is
a copper-lead-zinc alloy.
White brass contains more than 50% zinc and is too brittle
for general use. The term may also refer to certain types of nickel silver
alloys as well as Cu-Zn-Sn alloys with high proportions (typically 40%+)
of tin and/or zinc, as well as predominantly zinc casting alloys with copper
Yellow brass is an American term for 33% zinc brass.
Although forms of brass have been in use since prehistory,
its true nature as a copper-zinc alloy was not understood until the post
medieval period because the zinc vapor which reacted with copper to make
brass was not recognised as a metal. The King James Bible makes many references
to "brass". The Shakespearean English form of the word 'brass' can mean
any bronze alloy, or copper, rather than the strict modern definition of
brass. The earliest brasses may have been natural alloys made by smelting
zinc-rich copper ores. By the Roman period brass was being deliberately
produced from metallic copper and zinc minerals using the cementation process
and variations on this method continued until the mid 19th century. It
was eventually replaced by speltering, the direct alloying of copper and
zinc metal which was introduced to Europe in the 16th century.
Early copper zinc alloys
In West Asia and the Eastern Mediterranean early copper
zinc alloys are now known in small numbers from a number of third Millennium
BC sites in the Aegean, Iraq, the United Arab Emirates, Kalmykia, Turkmenistan
and Georgia and from 2nd Millennium BC sites in West India, Uzbekistan,
Iran, Syria, Iraq and Israel. However, isolated examples of copper-zinc
alloys are known in China from as early as the 5th Millennium BC.
The compositions of these early "brass" objects are very
variable and most have zinc contents of between 5% and 15% wt which is
lower than in brass produced by cementation. These may be "natural alloys"
manufactured by smelting zinc rich copper ores in reducing conditions.
Many have similar tin contents to contemporary bronze artefacts and it
is possible that some copper-zinc alloys were accidental and perhaps not
even distinguished from copper. However the large number of copper-zinc
alloys now known suggests that at least some were deliberately manufactured
and many have zinc contents of more than 12% wt which would have resulted
in a distinctive golden color.
By the 8th–7th century BC Assyrian cuneiform tablets mention
the exploitation of the "copper of the mountains" and this may refer to
"natural" brass. Oreichalkos, the Ancient Greek translation of this term,
was later adapted to the Latin aurichalcum meaning "golden copper" which
became the standard term for brass. In the 4th century BC Plato knew oreichalkos
as rare and nearly as valuable as gold and Pliny describes how aurichalcum
had come from Cypriot ore deposits which had been exhausted by the 1st
Brass making in the Roman World
During the later part of first millennium BC the use of
brass spread across a wide geographical area from Britain and Spain in
the west to Iran, and India in the east. This seems to have been encouraged
by exports and influence from the Middle-East and eastern Mediterranean
where deliberate production of brass from metallic copper and zinc ores
had been introduced. The 4th century BC writer Theopompus, quoted by Strabo,
describes how heating earth from Andeira in Turkey produced "droplets of
false silver", probably metallic zinc, which could be used to turn copper
into oreichalkos. In the 1st century BC the Greek Dioscorides seems to
have recognised a link between zinc minerals and brass describing how Cadmia
(zinc oxide) was found on the walls of furnaces used to heat either zinc
ore or copper and explaining that it can then be used to make brass.
By the first century BC brass was available in sufficient
supply to use as coinage in Phrygia and Bithynia, and after the Augustan
currency reform of 23 BC it was also used to make Roman dupondii and sestertii.
The uniform use of brass for coinage and military equipment across the
Roman world may indicate a degree of state involvement in the industry,
and brass even seems to have been deliberately boycotted by Jewish communities
in Palestine because of its association with Roman authority.
Brass was produced by the cementation process where copper
and zinc ore are heated together until zinc vapor is produced which reacts
with the copper. There is good archaeological evidence for this process
and crucibles used to produce brass by cementation have been found on Roman
period sites including Xanten and Nidda in Germany, Lyon in France and
at a number of sites in Britain. They vary in size from tiny acorn sized
to large amphorae like vessels but all have elevated levels of zinc on
the interior and are lidded. They show no signs of slag or metal prills
suggesting that zinc minerals were heated to produce zinc vapor which reacted
with metallic copper in a solid state reaction. The fabric of these crucibles
is porous, probably designed to prevent a build up of pressure, and many
have small holes in the lids which may be designed to release pressure
or to add additional zinc minerals near the end of the process. Dioscorides
mentioned that zinc minerals were used for both the working and finishing
of brass, perhaps suggesting secondary additions.
Brass made during the early Roman period seems to have
varied between 20% to 28% wt zinc. The high content of zinc in coinage
and brass objects declined after the first century AD and it has been suggested
that this reflects zinc loss during recycling and thus an interruption
in the production of new brass. However it is now thought this was probably
a deliberate change in composition and overall the use of brass increases
over this period making up around 40% of all copper alloys used in the
Roman world by the 4th century AD.
Brass making in the medieval period
Little is known about the production of brass during the
centuries immediately after the collapse of the Roman Empire. Disruption
in the trade of tin for bronze from Western Europe may have contributed
to the increasing popularity of brass in the east and by the 6th–7th centuries
AD over 90% of copper alloy artefacts from Egypt were made of brass. However
other alloys such as low tin bronze were also used and they vary depending
on local cultural attitudes, the purpose of the metal and access to zinc,
especially between the Islamic and Byzantine world. Conversely the use
of true brass seems to have declined in Western Europe during this period
in favour of gunmetals and other mixed alloys but by the end of the first
Millennium AD brass artefacts are found in Scandinavian graves in Scotland,
brass was being used in the manufacture of coins in Northumbria and there
is archaeological and historical evidence for the production of brass in
Germany and The Low Countries areas rich in calamine ore which would remain
important centres of brass making throughout the medieval period, especially
Dinant – brass objects are still collectively known as dinanterie in French.
The baptismal font at St Bartholomew's Church, Liège in modern Belgium
(before 1117) is an outstanding masterpiece of Romanesque brass casting.
The cementation process continued to be used but literary
sources from both Europe and the Islamic world seem to describe variants
of a higher temperature liquid process which took places in open-topped
crucibles. Islamic cementation seems to have used zinc oxide known as tutiya
or tutty rather than zinc ores for brass making resulting in a metal with
lower iron impurities. A number of Islamic writers and the 13th century
Italian Marco Polo describe how this was obtained by sublimation from zinc
ores and condensed onto clay or iron bars, archaeological examples of which
have been identified at Kush in Iran. It could then be used for brass making
or medicinal purposes. In 10th century Yemen al-Hamdani described how spreading
al-iglimiya, probably zinc oxide, onto the surface of molten copper produced
tutiya vapor which then reacted with the metal. The 13th century Iranian
writer al-Kashani describes a more complex process whereby tutiya was mixed
with raisins and gently roasted before being added to the surface of the
molten metal. A temporary lid was added at this point presumably to minimise
the escape of zinc vapor.
In Europe a similar liquid process in open-topped crucibles
took place which was probably less efficient than the Roman process and
the use of the term tutty by Albertus Magnus in the 13th century suggests
influence from Islamic technology. The 12th century German monk Theophilus
described how preheated crucibles were one sixth filled with powdered calamine
and charcoal then topped up with copper and charcoal before being melted,
stirred then filled again. The final product was cast, then again melted
with calamine. It has been suggested that this second melting may have
taken place at a lower temperature to allow more zinc to be absorbed. Albertus
Magnus noted that the "power" of both calamine and tutty could evaporate
and described how the addition of powdered glass could create a film to
bind it to the metal. German brass making crucibles are known from Dortmund
dating to the 10th century AD and from Soest and Schwerte in Westphalia
dating to around the 13th century confirm Theophilus' account, as they
are open-topped, although ceramic discs from Soest may have served as loose
lids which may have been used to reduce zinc evaporation, and have slag
on the interior resulting from a liquid process.
Brass making in Renaissance and post medieval Europe
The Renaissance saw important changes to both the theory
and practice of brassmaking in Europe. By the 15th century there is evidence
for the renewed use of lidded cementation crucibles at Zwickau in Germany.
These large crucibles were capable of producing c.20 kg of brass. There
are traces of slag and pieces of metal on the interior. Their irregular
composition suggesting that this was a lower temperature not entirely liquid
process. The crucible lids had small holes which were blocked with clay
plugs near the end of the process presumably to maximise zinc absorption
in the final stages. Triangular crucibles were then used to melt the brass
16th century technical writers such as Biringuccio, Ercker
and Agricola described a variety of cementation brass making techniques
and came closer to understanding the true nature of the process noting
that copper became heavier as it changed to brass and that it became more
golden as additional calamine was added. Zinc metal was also becoming more
commonplace By 1513 metallic zinc ingots from India and China were arriving
in London and pellets of zinc condensed in furnace flues at the Rammelsberg
in Germany were exploited for cementation brass making from around 1550.
Eventually it was discovered that metallic zinc could
be alloyed with copper to make brass; a process known as speltering and
by 1657 the German chemist Johann Glauber had recognised that calamine
was "nothing else but unmeltable zinc" and that zinc was a "half ripe metal."
However some earlier high zinc, low iron brasses such as the 1530 Wightman
brass memorial plaque from England may have been made by alloying copper
with zinc and include traces of cadmium similar those found in some zinc
ingots from China.
However the cementation process was not abandoned and
as late as the early 19th century there are descriptions of solid state
cementation in a domed furnace at around 900–950 °C and lasting up
to 10 hours. The European brass industry continued to flourish into the
post medieval period buoyed by innovations such as the 16th century introduction
of water powered hammers for the production of battery wares. By 1559 the
Germany city of Aachen alone was capable of producing 300,000 cwt of brass
per year. After several false starts during the 16th and 17th centuries
the brass industry was also established in England taking advantage of
abundant supplies of cheap copper smelted in the new coal fired reverberatory
furnace. In 1723 Bristol brass maker Nehemiah Champion patented the use
of granulated copper, produced by pouring molten metal into cold water.
This increased the surface area of the copper helping it react and zinc
contents of up to 33% wt were reported using this new technique.
In 1738 Nehemiah's son William Champion patented a technique
for the first industrial scale distillation of metallic zinc known as distillation
per descencum or "the English process." This local zinc was used in speltering
and allowed greater control over the zinc content of brass and the production
of high zinc copper alloys which would have been difficult or impossible
to produce using cementation, for use in expensive objects such as scientific
instruments, clocks, brass buttons and costume jewellery. However Champion
continued to use the cheaper calamine cementation method to produce lower
zinc brass and the archaeological remains of bee-hive shaped cementation
furnaces have been identified at his works at Warmley. By the mid late
18th century developments in cheaper zinc distillation such as John-Jaques
Dony's horizontal furnaces in Belgium and the reduction of tariffs on zinc
as well as demand for corrosion resistant high zinc alloys increased the
popularity of speltering and as a result cementation was largely abandoned
by the mid 19th century.