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in focus
Strength
Brasses are versatile Brass is an alloy of copper and zinc, the
amount of zinc varying from five to 45 Brasses are medium strength
and cost-effective per cent to create a range of brasses, engineering materials. In the softened
or annealed condition they are ductile
each with unique properties. There are
materials, ideal for two distinct types of brass. Those with and strong but, when hardened by cold
less than 35 per cent zinc are known as working, their strength increases. The
designing complex alpha brasses because only one solid addition of small quantities of
solution (alpha) is present. These alloys manganese, aluminium, tin, silicon, iron
and long lasting are ductile at room temperature and and nickel in brass produces a family of
components. Ken ideal for cold working. Brasses with
more than 35 per cent are called alpha-
high tensile brasses that can have
tensile strengths in excess of
Kempson explains. beta or duplex alloys and are ideal for 500MN/m2. 750MN/m2 can be obtained
hot working (see Figure 1). in some alloys by extreme cold working.
Brasses have good impact resistance
The properties of brass and do not shatter or crack when
Small amounts of other elements can subject to a high impact load.
be added to brass to improve its primary
properties. See the table right. Corrosion resistance
For general purposes the corrosion
Machinability resistance of standard free machining
Brass has excellent machinability, alloys is excellent. The addition of tin in
however, this can be improved by naval and admiralty brasses (originally
adding three per cent lead to give free- developed for seawater service) further
cutting high-speed machining brasses. improves corrosion resistance. The
addition of a small amount of arsenic to
alpha brass alloys produces a
dezincification resistant brass,
frequently used for water fittings.
Conductivity
Brasses have good electrical and
thermal conductivity. Combined with
good corrosion resistance, this makes
them ideal for the manufacture of
electrical equipment. Condenser and
heat exchanger tubing also makes use
of the good thermal conductivity of
copper alloys. Brasses do not spark
when struck by other materials and are
approved for use in hazardous
environments. They are also suitable for
use at cryogenic temperatures since
their properties are retained or slightly
improved (mechanical values are
available at -197ºC). Strength is
maintained up to 200°C.
The presence of lead in brass has a
lubricating effect providing good low
friction and wear properties that are
utilised in pinions, instrumentation and
Figure 1: Copper-zinc phase diagram. clock gears. The addition of silicon in
engineering designer May/June 2004 1
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Duplex materials that have good
Element Quantity Property enhanced
ductility at hot working temperatures
Lead 1 to 3 per cent Machinability are usually used for extrusion. The
resulting structure of the material is
Manganese uniform with a fine grain structure.
Aluminium Yield strength
Silicon 0.75 to 2.5 per cent Up to 500MN/m2 Hot stamping
Nickel
Iron
Aluminium Corrosion resistance
Arsenic 0.4 to 1.5 per cent especially in sea water
Tin
Elements can be added to brass to improve its primary properties.
special brasses makes them ideal for brass scrap, bought at a much lower
use in heavy duty bearings. price than the metal mixture price,
Hot stamping.
means that fabricated brass is cheaper
Hygiene than it might otherwise be. Scrap is Hot stampings are made by forming hot
Copper is bacteriostatic and its content obtained from offcuts from within the slugs of brass between shaped dies
in brasses has the effect of restricting mill, swarf from machine shops, that are designed and made to give
the growth of micro-organisms on brass clippings from hot stampings and components that require minimum
surfaces. Tests on door knobs and presswork and from brass components finishing.
finger plates have shown that those being recycled. It is easily remelted Hot stampings have high strength,
made of clean brass are far less likely back to its original state without loss of are free from porosity, are near-net-
than other materials to encourage the properties and the high value of any shape, give close consistent
growth of the organisms causing swarf or scrap produced during component tolerances, have a superior
nosocomal infections. manufacture should be taken into surface finish and give optimum metal
account when costing. Likewise, when usage. They are easy to jig for accurate
calculating the lifetime cost of a finish machining of faces, holes and
product, the ease with which a brass threads.
component is recycled at the end of its
life needs to be taken into account. Hot rolling
Brass scrap typically has a value of 40 Continuously cast metal slabs are
per cent of the new material. reduced to the required thickness by
hot rolling.
Manufacturing processes
Brass can be turned into components Cold working
by most common manufacturing Cold working leads to improved surface
processes. finish and dimensional accuracy. By
Tests on door knobs and finger plates
have shown that those made of clean applying progressive amounts of cold
brass are more hygienic. Hot working working the tensile strength, proof
Casting strength and hardness of the alloy
The fluidity of brass when molten increases, with a consequent reduction
Aesthetics permits it to be cast to shape by all in ductility, as measured by elongation.
Brasses are extensively used for durable casting processes. It is an ideal metal
decorative applications and for the for investment casting and its ability to Drawing
manufacture of functional items where be gravity or pressure cast enables near The cold work in the case of extruded
aesthetic appeal is required, as well as a net complex parts to be made in any products such as rods, bars, sections,
long service life. Aluminium brasses volume depending on the process tubes and wire, is applied by drawing
have a distinctive silvery sheen and the chosen. Brass can be centrifugally cast, through reducing dies. Drawing extruded
addition of manganese to certain ideal for the manufacture of tubular rod through a series of reducing dies
brasses gives them an attractive bronze shaped components. It can also be produces wire, which is used for the
colour when extruded. High tensile continuously cast. manufacture of circlips, zip fasteners,
brasses, some of which are known as rivets screws etc. Because of the
manganese brasses, are particularly Extrusion amount of cold work imparted it may be
suitable for architectural applications Billets, cut from continuously cast logs, necessary to anneal between draws.
because they can be patinated to a preheated to between 600°C and
range of durable brown and bronze 800°C, are forced through a die that is Riveting, cold heading, thread
finishes. shaped in the form of the finished rolling
product. This gives round rod, square, The single-phase alloys can be readily
Recyclability hexagonal or special profiles as riveted-over and are used to
Recycling brass scrap is essential to the required. The use of a mandrel allows manufacture cold-formed parts. Rivets,
economics of the industry. The use of hollow extrusions to be produced. pins, screws and similar items are
2 engineering designer May/June 2004
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mass-produced from wire by cold technique for making dished ends of Joining
heading. hollow vessels, flanges for water Brasses lend themselves to being
vessels, ball floats, electrical switchgear joined by most common processes. The
Seamless tube products and similar items. Diameters close tolerances to which brass
Tube is made from hollow extruded up to 4000mm and thicknesses up to components can be manufactured
tubeshells, which are cold drawn to 25mm can now be spun to close makes it ideal for joining by silver
size by a succession of passes drawing tolerances, maintained through short or brazing which produces leak tight joints
dies, with interstage anneals as long production runs. Tooling costs are without melting and distorting the
required and supplied either in straight much lower than press tools and brasses to be joined. Modern MIG and
lengths or coil. A selection of brasses is differing material thickness can be tried TIG welding processes can successfully
available with properties to suit on the same tool during product weld most brasses with the correct
applications from telescopic aerials to development. choice of filler alloy.
marine condensers. The CuproBraze process is a new
Brass tubes can be made to bespoke Machining joining method applied in the
shapes and sizes. The inside shapes During machining the cutting tool forms manufacture of high strength and
can be different from the outside and chips or shavings by producing a continual performance radiators and other
can have specified wall thickness, series of fractures of the metal being cut. automotive heat exchangers that are 10
uniform or uneven. Another frequent Whilst all brasses are intrinsically easy to per cent cheaper than aluminium
need is for an oblong tube with the machine, this can be improved with the equivalents and 35 per cent lighter than
corners either square or typically addition of small amounts of lead. Higher traditional copper brass radiators. This
radiused to half the wall thickness. machining speeds and lower rates of tool environmentally friendly process
Often, one side must be significantly wear mean that overall production costs produces strong and reliable brazed
thicker than the other. For tubular heat are minimised, tolerances are held during copper/brass joints using a specially
exchangers, such as oil coolers, there long production runs and surface finish is developed fluxless brazing process.
are concentric tubes, the flow of excellent.
coolant can be made turbulent by
helical grooves or raised ridges. The brasses are a versatile family
of copper alloys which can be
Cold rolling manufactured by the full range of
Slabs of continuously cast metal that metal forming processes from
have been reduced in thickness by hot cost-effective, durable, recyclable
rolling are passed through a series of components.
rolls. Each pass reduces the thickness For more information visit
of the material increasing its strength, Copper Development
but reducing its ductility. Hard rolled Association's website
brasses have better ductility www.brass.org.
longitudinally in line with the rolling Machining.
direction, rather than in the transverse
direction. This is ideal for springs or
other flexible parts.
Cold stamping and pressing
Find out more about brass
Alpha brasses in sheet and strip have
good cold deformation properties and Copper Development Association presentations on particular
are therefore readily formed and (CDA) gives free brass lectures to manufacturing techniques are
shaped by cold stamping or pressing. universities offering design available on request. A CDA
Cold stamping and pressing is typically engineering degrees. The lecture representative visits the company
used to produce connectors, precision clarifies what brass is, the different premises eliminating the need to
mechanics, key blanks, contact types of brass and the effect of travel and saving time.
elements, decorative ware, jewellery alloying elements on the base alloy. In addition, CDA are running full
and clock making items. Properties of brass and the day CPD ‘Brass in focus’ seminars
manufacturing processes, as for designers and engineers. See
Deep drawing discussed in this feature, are www.brass.org/news/training/seminars.htm
Cold rolled brass strip is ideal for deep explained in more detail and for more details.
drawing. The starting sheet of flat illustrated with numerous samples.
brass is larger than the area of the The lecture concludes with a series For more information about the
punch and the outer parts of the sheet of case studies illustrating the university lectures, in-house
are drawn in towards the die as the benefits of designing in brass. presentations, or to register for a
operation proceeds. Cartridge cases A CPD approved presentation that seminar, contact Copper
made from 70/30 (cartridge) brass are a covers similar material to the Development Association,
typical example of a deep drawn university lecture, but which is 5 Grovelands Business Centre,
product. tailored more specifically to meet the Boundary Way, Hemel Hempstead,
needs of practising designers, is Herts, HP2 7TE. Telephone 01442
Spinning available to design teams and 275700, Fax 01442 275716 or Email
This can be a useful production consultancies. More in depth helpline@copperdev.co.uk
engineering designer May/June 2004 3
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Case study
Brass goes nuclear one of the worst materials for nuclear
applications and produces fluorine
finish using both traditional and modern
CNC techniques. Brass also has good
Raditec, A/V systems, environment when irradiated. Brass, by contrast, bearing properties, particularly when
monitoring specialists, supplies nuclear produces no harmful or hazardous
radiation tolerant image acquisition used in contact with other materials,
chemical by-products. In the case of
systems including television cameras, also a requirement of the system.
this nuclear tolerant zoom lens, (tolerant
endoscopes, borescopes and is used here as the preferred term Readily available from stock in a variety
accessories for use in nuclear facilities. rather than nuclear resistant, since the of sizes, brass meets all of these
Raditec also provides systems for construction and functional materials criteria, yielding a life of many years.
hostile and high temperature cannot avoid exposure, but must exhibit Dr Kath Langley, Manufacturing
environments, for example chemical the optimum tolerance), the application Director, Abakus, comments: “We are
plant monitoring. could be typically a camera system for aware of the full spectrum of materials
The company approached Abakus the inspection of fuel rods in nuclear
Scientific to design and build a unique available to us in lens body
reprocessing. In this environment any
and versatile zoom lens that could construction and we regularly subject
component failure is potentially
withstand a nuclear exposure level of hazardous and very expensive so it is alternative materials to life trials. In the
Cobalt 60 (1xMGray). Specifications for essential that the materials used give case of the ‘discrete’ lens, the tiny
instruments exposed to gamma the product compatibility with the brass gear wheels and the toothed ring
irradiation in nuclear environments environment and a long and trouble free are critical to the zoom function. We
incorporate a figure for the summation life. first tried using plastic for the ring and
of the total dose that the device must Brass is used extensively in these in tests it exhibited severe distortion in
survive whilst retaining an acceptable nuclear tolerant units. The specification
a short time, becoming almost a soft
degree of functionality. for the lens mounting and carrier
cornered, triangular shape. The second
system for such a high accuracy
So why brass? product requires it to be made from a trial used steel and rapidly displayed
Brass, unlike plastic, is unaffected for stable, corrosion resistant material that tiny traces of corrosion impeding its
all practical purposes by extended can be machined to extremely close function.
exposure to a nuclear environment. The tolerances with a high degree of We returned to the free-machining CZ
plastic material Teflon, for example, is repeatability, giving a very fine surface 121 brass that we use as standard in
most other lenses and the product now
functions perfectly and experiences no
long-term deterioration. We would have
liked the small weight-saving
potentially available with plastics, also
the marginal economy of steel, but at
the end of the day they were not up to
meeting the specification.
“One novel feature of this product is
the lens iris. After a serious number-
crunching exercise we developed a
uniquely profiled, machined miniature
brass plate which revolves and controls
iris aperture in a ‘diameter-linear’,
rather than f-stop linear, manner from
full aperture through to the total
blackout condition required for TV
camera calibration. The smoothness of
operation could not be obtained with
any other material than brass, its
inherent lubricity, surface to surface,
eliminates the need for organic or
fluorocarbon lubrication.”
4 engineering designer May/June 2004
