36 THE ARCHITECTURE REFERENCE + SPECIFICATION BOOK
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Chapter 3: Metals
Metals play an enormous role in almost every component of many projects and build-
ing types, from structural steel to sheet-metal ductwork, from drywall partition studs to
oxides used as paint pigments. Metals of most varieties occur in nature as oxide ores,
which can be mined and worked to extract and rene the metals, separating them
from other elements and impurities. Metals fall under two broad categories: ferrous
(containing iron) and nonferrous. Ferrous metals are generally stronger, more abun-
dant, and easier to rene, but they have a tendency to rust. Nonferrous metals tend
to be easier to work and most form their own thin oxide layers that protect them from
corrosion.
MODIFYING METAL
PROPERTIES
Most metals in their chemically pure and
natural form are not very strong. To be suit-
able for construction and other functions,
their properties must be altered, which can
be done in several ways, often dependent on
the proposed use of the metal.
Alloys
Metals are mixed with other elements,
usually other metals, to create an alloy.
For example, iron mixed with small
amounts of carbon produces steel.
Generally, the alloy is stronger than its
primary metal ingredient. In addition to
improved strength and workability, al-
loys provide self-protecting oxide layers.
Heat-Treated Metals
Tempering: Steel is heated at a moder-
ate rate and slowly cooled, producing a
harder and stronger metal.
Annealing: Steel and sometimes
aluminum alloys are heated to very
high temperatures and cooled slowly,
softening the metal so that it is easier
to work.
Cold-Worked Metals
At room temperature, metals are rolled
thin, beaten, or drawn, making them
stronger but more brittle by altering their
crystalline structures. Cold-worked met-
als may be reversed by annealing.
Cold rolling: Metal is squeezed between
rollers.
Drawing: Drawing metal through increas-
ingly smaller orices produces the wires
and cables used to prestress concrete,
which have ve times the structural
strength of steel.
Coated Metals
Anodizing: A thin oxide layer of controlled
color and consistency is electrolytically
added to aluminum to improve its sur-
face appearance.
Electroplating: Chromium and cadmium
are coated onto steel to protect it from
oxidation and improve its appearance.
Galvanizing: Steel is coated with zinc to
protect it against corrosion.
Other coatings: Coatings can include
paints, lacquers, powders, uoropoly-
mers, and porcelain enamel.
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Job: 03-30364 Title: Rp-Architecture Reference & Specification
#175 DTP: 216 Page: 36
Job: 03-30364 Title: Rp-Architecture Reference & Specification
#175 DTP: 216 Page: 37
(RAY) (Text)
(P 285U)
Metals 37
03
FABRICATION TECHNIQUES
Casting: Molten metal is poured into a shaped
mold. The metal produced is weak but can be
made into many shapes, such as faucets or
hardware.
Drawing: Wires are produced by pulling metal
through increasingly smaller holes.
Extrusion: Heated (but not molten) metal is
squeezed through a die, producing a long metal
piece with a shaped prole.
Forging: Metal is heated until exible and
then bent into a desired shape. This process
improves structural performance by imparting a
grain orientation onto the metal.
Grinding: Machines grind and polish metal to
create at, nished surfaces.
Machining: Material is cut away to achieve a
desired shape. Processes include drilling, milling
(with a rotating wheel), lathing (for cylindrical
shapes), sawing, shearing, and punching. Sheet
metal is cut with shears and folded on brakes.
Rolling: Metal is squeezed between rollers.
Hot rolling, unlike cold, does not increase the
strength of metal.
Stamping: Sheet metal is squeezed between
matching dies to give it shape and texture.
Joining Metals
Welding: In this high-temperature fusion, a gas
ame or electric arc melts two metals and allows
the point of connection to ow together with ad-
ditional molten metal from a welding rod. Welded
connections are as strong as the metals they
join and can be used for structural work.
Brazing and soldering: In these lower-
temperature processes, the two metals are
not themselves melted but joined with the solder
of a metal with a lower melting point: Brass or
bronze are used in brazing, lead-tin alloy is used
in soldering. Too weak for structural connections,
brazing and soldering are used for plumbing
pipes and roong.
Mechanical methods: Metals can also be drilled
or punched with holes, through which screws,
bolts, or rivets are inserted.
Interlocking and folding: Sheet metal can be
joined by such connections.
Casting
Drawing
Extrusion
Forging
Grinding
Machining
Rolling
Stamping
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