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Brass the Yellow Metal.....
The generic term
"brass" covers a wide range of copper-zinc alloys with differing
combinations of properties, including: |
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Machinability
of Brass:
Machined
components can be cheaper in brass than in mild steel.
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All
brasses are intrinsically easy to machine
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The
addition of small amounts of lead to brasses further improves this property
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'Free
machining brass' sets the standard by which other materials are judged when
machinability is being assessed
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Higher
machining speeds and lower rates of tool wear mean the overall production
costs are minimised
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Tolerances
are held during long production runs and surface finish is excellent.
Conductivity
of Brass:
Brasses
have good electrical and thermal conductivities and are markedly superior in
this respect to ferrous alloys, nickel-based alloys and titanium.Their
relatively high conductivity, combined with corrosion resistance, makes them an
ideal choice for the manufacture of electrical equipment, both domestic and
industrial. Condenser and heat
exchanger tubing also require the good thermal conductivity of copper and its
alloys.
Cost
Effective and Recycling of Brass:
Introduction
Most people recognise the high price
commanded by brass scrap. Indeed many of us, after a DIY project
such as installing a new kitchen or bathroom, collect together the old brass
taps and fittings and sell them to our local scrap merchant in an attempt to
recoup some of our expenditure. The reason such a premium price is paid for
brass scrap is because it is essential to the economics of the brass industry.
Brass for extrusion and hot stamping is
normally made from a basic melt of scrap of similar composition – adjusted by
the addition of small amounts of virgin copper or zinc as required to meet the
specification before pouring. The use of brass scrap bought at a significantly
lower price than the metal mixture price means that the cost of the fabricated
brass is considerably less than it might otherwise be. How many designers
consider this when designing new products or seeking cost savings in existing
products.
Brass machined parts and stampings
Free machining 60/40 brass with small
additions of lead is particularly cost-effective and environmentally friendly
when used for the manufacture of machined parts and stampings. Firstly, the
swarf produced as a result of high speed machining (typically metal removal
rates are two to three times those of mild steel) can be sold as scrap.
Secondly, when brass components reach the end of their long and useful life they
too can be readily recycled. The stamping temperatures for brasses are lower
than those required for ferrous alloys making it an energy efficient process;
the low stamping temperature also gives an increased die life. Stamping is a
near-net-shape process but the small amount of swarf produced by machining is
again recyclable. Brass is also cost-effective and kind to the environment
because it does not normally need plating or painting to prevent corrosion.
Special purpose alloys
Brass swarf arising from machining
operations can be economically remelted but it should be substantially free from
excess lubricant, especially those including organic compounds that cause
unacceptable fumes during remelting. The presence in brass of some other
elements such as lead is often required to improve machinability so such scrap
is frequently acceptable. Besides the common free-machining brasses, there are
many others made for special purposes with properties modified to give extra
strength, hardness, corrosion resistance or other attributes, so strict
segregation of scrap is essential.
When brass is remelted, there is
usually some evolution of the more volatile zinc. This is made up in the melt to
bring it back within specification. The zinc is evolved as oxide that is drawn
off and trapped in a baghouse and recycled for the manufacture of other
products.
Brass sheet, strip and wire
The 70/30 brass to be made into sheet,
strip or wire form must be significantly free of harmful impurities in order to
retain ductility when cold. It can then be rolled, drawn, deep drawn, swaged,
riveted, spun or cold formed. It is normal therefore to make it substantially
from virgin copper and zinc, together with process scrap arising from processing
that has been kept clean, carefully segregated and identified.
Conclusion
Brass is a cost-effective engineering
material ideally suited for the manufacture of machined and stamped items. The
need for plating or painting to prevent corrosion in normal circumstances is
eliminated, but when required for cosmetic purposes or to give additional
protection against corrosion it is easily plated. Brass is readily recycled
without loss of properties and the infrastructure to do so has been proven over
many years.
Brass
is readily joined:
Brasses may readily be joined to other
copper alloys or to other metals by most of the commercial joining processes
such as:
- Riveting
- Soft soldering
- Brazing
- Friction welding
- Modern adhesive joining practice
Maleable
and Ductile:
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Brasses
with a copper content greater than 63% can be extensively deformed at room
temperature, and are widely used for the manufacture of complex components
by pressing, deep drawing, spinning and other cold forming processes.
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If
the copper content is below 63% and no other alloying elements are present,
the room temperature ductility is reduced, but such alloys can be
extensively hot worked by rolling, extrusion, forging and stamping.
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Strength,
ductility and formability are retained at low temperatures, making the
alloys ideal for cryogenic applications.
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Brasses do not
spark when struck and are approved for use in hazardous environments
Finishing
and Plating of Brass:
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Brasses
may be polished to a high surface finish which can then be either easily
repolished when required or lacquered to preserve the natural colour,
enamelled or plated with chromium, nickel, tin, silver, gold, etc. as
required. Alternatively, the surface can be toned to a range of colours,
from "bronze" through various shades of brown, to blue-black and
black, using commercially available toning chemicals. These coloured
finishes are frequently used for decorative and architectural metalwork.
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All
types of common plating processes may be used. For many other metals it is
usual to use a copper plate underlayer. This is not required on brass
because it is easily polished and does not need the expense of an initial
copper strike. To give extra corrosion protection to steel when used against
brass, cadmium plating of the brass was traditional but this has now been
generally replaced by zinc.
Corrosion
Resistance of Brass:
Brasses have excellent resistance to
corrosion that makes them a natural, economic first choice for many
applications.
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Atmospheric
exposure of the brasses results in the formation of a thin protective green
"patina", a visually attractive feature in buildings.
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Brass
will remain essentially unaffected for an unlimited period of time, i.e. it
will not rust away like iron and steel.
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Seawater
can be handled successfully providing the correct alloy is chosen, and there
is a long history of the use of brass tube and tube fittings, valves, etc.
in domestic plumbing, central heating, seawater lines, steam condensers and
desalination plant.
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High
tensile brasses containing manganese have particularly excellent resistance
to atmospheric corrosion, continual exposure resulting in a gradual
darkening of the bronze colour.
When exposed to the atmosphere, brass tends to form a protective tarnish film
that impedes corrosion beyond a few micrometers into the metal surface. The
tarnish will deepen in color from bronze to dark brown, and may eventually take
on the green color of a patina in some environments. The important point is that
brass's corrosion rate in normal atmospheric conditions is low and
self-limiting, and the corrosion products that do form are not objectionable.
In addition to atmospheric corrosion resistance, brass also withstands exposure
to a wide range of water compositions, including automotive coolant solutions.
Brass is generally inert to organic liquids and gases, although it should not be
used in mineral acids or acid salts. Alkaline salts are less objectionable.
Brass is susceptible to three types of corrosion. These include stress-corrosion
cracking, which can arise in ammoniacal environments, amines, mercury compounds
and nitrite solutions. Sulfides will promote pitting attack of copper and copper
alloys, especially under alternating aerobic and anaerobic (sulfiding)
conditions such as might be caused by episodic exposure to polluted seawater.
Brasses are perhaps the least susceptible copper alloys to sulfide pitting.
Also, road salt solutions contaminated with sulfide-laden exhaust emissions do
not appear to affect brass. Brass can, immersed in acidic and mildly basic
waters, corrode by dezincification, but this also has not been a problem in
automotive applications. (For service in such environments brass compositions
are modified by small additives of alloying elements that inhibit
dezincification.)
Good
Strength of Brass:
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In
the softened or annealed condition, the brasses are ductile and strong but
when hardened by cold working techniques such as rolling or drawing, their
strength increases markedly. Strong, stiff structures can be assembled from
extruded-and-drawn sections. Bars and rolled sheet and plate can be
fabricated into containers and other items of plant which work under
pressure.
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The
strength of brasses is substantially retained at temperatures up to around
200oC and reduces by only about 30% at 300oC which
compares favourably with many alternative materials.
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The
brasses are very suitable for use at cryogenic temperatures since the
properties are retained or slightly improved under these operating
conditions.
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For
applications demanding higher strengths the "high tensile brasses"
are available. These contain additional alloying elements which further
improve the properties.
Color
of Brass:
Brasses
are extensively used for durable decorative applications and for the manufacture
of functional items where aesthetic appeal is a requirement in addition to a
long service life.
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In
brasses, the red of copper is toned to a range of attractive yellow hues by
the addition of varying amounts of zinc ranging from the gold-like colours
of the 95/5, 90/10, 85/15 and 80/20 alloys (appropriately called
"gilding metals") through the more subtle variations in the 70/30,
2/1 and 64/36 series of brasses to the stronger yellow colour of the 60/40
alloy, formerly known as "yellow metal".
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Aluminium
brasses have a distinctive silvery sheen.
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The
addition of manganese to certain brasses gives them an attractive bronze
colour when extruded.
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High
tensile brasses, some of which are otherwise known as "manganese
brasses" or previously "manganese bronzes" are particularly
suitable for architectural applications since they can also be patinated to
a range of durable brown and bronze finishes.
Wear
Resistance of Brass:
The presence of lead in brass has a
lubricating effect that gives good low friction and low wear properties utilised
in the plates, pinions and gears used in instruments and clocks. Special brasses
are available with additions of silicon that make the material ideal for use in
heavy duty bearings.
Brass
is Cost Effective:
There
are many factors, sometimes overlooked, that contribute to low costs of brass
components.
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Close
tolerance manufacturing techniques can be employed so that finishing costs
are minimal.
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Tooling
costs may be significantly lower than for other materials or processes.
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Ease
of machining means that production costs can be minimised.
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The
good corrosion resistance of the brasses means that the cost of protective
finishing is lower than for many other materials.
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In
addition to these benefits the high value of any process scrap can be used to
reduce production costs significantly.
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The
long service life normally expected of well-designed brass components means
that the costs of service failures are minimal.
![](images/Compare_brass_nuts.jpg)
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In today's cost conscious component parts industry, the difference
between a "good buy" and a "good bye" is often bottom
line cost. In this case, free-cutting brass is 17% less expensive than
its 12L14 steel counterpart!
It's simple math.
While up-front costs for brass may be higher,
once you factor in machining costs (brass is up to five time more
machinable), turnings value (steel scrap is worthless), and the need to
plate steel (brass naturally resists corrosion) - the bottom-line cost for
free-cutting brass is significantly lower per finished part.
And is doesn't stop there.
As automakers extend warranty warranty
periods and cover additional systems, down-the-road costs to remove
rusted, corroded steel parts can be significant. As the photo shows, brass
stands the test of time far better than zinc-coated steel.
For information on vendor sourcing and what makes free-cutting brass
the "good buy," call the Copper Development Association at 800
CDA-DATA; fax: 212-251-7234 |
Automotive
Hydraulic Tube Fitting/1,000 parts* |
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C36000 |
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12L14 Steel |
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$92.46 |
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Raw Material Cost |
$35.92 |
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-44.84 |
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Scrap/Turnings Value |
+0.00 |
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$47.62 |
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Net Raw Material Cost |
$35.92 |
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+28.44 |
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Cost of Machining |
+47.78 |
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+0.00 |
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Zinc Electrocoating |
+6.09 |
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$76.06 |
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Total Finished Parts Cost |
$91.79 |
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* Based on June 1994 costs. |
After only 314 hours exposure
to salt-spray (fog) corrosion testing (ASTM B 117), the zinc-coated steel
fitting (right) failed to meet customer specification. |
C36000 12L14 Steel
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The numbers say it all. In terms of finished part cost, brass is
a whopping 19.9% less expensive than 12L14 leaded steel.
Surprised? Don't be.
Brass may cost more up front, but brass turnings can
be reclaimed for 75-85% of the original brass value (steel scrap is worthless).
And while brass easily meets the yield strength requirements for small auto
component parts, it's five times more machinable than steel. That means higher
productivity and lower per-part cost. What's more, brass naturally resists
corrosion, eliminating the need for costly protective plating.
Transmission
Cooling Fitting/1,000 parts* |
12L14 |
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C36000 |
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$121.80 |
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Raw Material Cost |
$339.12 |
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-0.00 |
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Scrap/Turnings Value |
-196.24 |
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$121.80 |
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Net Raw Material Cost |
$142.88 |
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+126.39 |
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Cost of Machining |
+68.06 |
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+15.12 |
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Zinc Electrocoating |
+0.00 |
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$263.31 |
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Total Cost |
$210.94 |
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* Based on mid-1991 costs. |
Summary:
Here are the important points to bear in mind when considering
Brass for machine products:
- Brass is widely available and in plentiful supply.
- Brass' quality is assured by adherence to numerous standards;
- Brass's mechanical properties in service are adequate for the majority of
parts produced on automatic machines;
- Brass's extremely high machinability translates into lower product costs,
compared with leaded steel;
- Brass's close dimensional control and high surface finishes will be
reflected in higher product quality;
- Brass's natural corrosion resistance eliminates the need for expensive
electroplating. Customers perceive and appreciate the quality inherent in
solid brass components.
- Brass gives the designer freedom to conceive parts that would not be
economical in steel.
Finally, it is important that the designer takes into account the added
design freedom Brass makes possible. Brass lets the designer specify deep blind holes without concern for tool
breakage and high rejection rates. Brass also accepts fine detail and excellent surface finishes without
extracting a cost penalty for slow cutting speeds and expensive tooling.
Brass can simplify designs, and simpler designs can lower costs while improving
product quality.
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