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Investment casting, which is also called precision casting or
the lost wax process, has been known since ancient times. There
was a notable period in China, during the Shang Dynasty (1766
to 1122 B.C.), when exquisite artifacts were cast in bronze by
the lost wax process, some of which are on display in museums
today.
This method of casting allows considerable freedom of design and
permits intricate and precise reproduction of large and small
objects. Centuries ago it started out being used for artifacts
and sculptures, and today it is also still used for sculptures,
because in the hands of a skilled art foundry, fine details and
features may be faithfully reproduced.
Investment casting for industrial or artistic applications involves
the use of an expendable wax or plastic pattern of the part to
be cast. In industrial applications duplicate patterns are usually
attached to a central sprue in clusters suitable for their size.
In both cases a ceramic shell is built up around the pattern or
cluster of patterns by alternately dipping it in liquid slurry
and dry stucco refractories. Autoclaving and high-temperature
firing of the shell removes the wax or plastic from the interior.
Molten copper or bronze is then poured into the hot molds by gravity,
or with pressure, vacuum or centrifugal assists. After solidification
the mold material is removed from the castings.
The main applications for investment castings are those involving
intricate, complex and sometimes delicate parts with close tolerances.
Such applications may call for high heat transfer or heat resistance,
good mechanical properties, and corrosion resistance, all with
castings that have soundness, reliability, and integrity.
Many metals may be investment cast, but in the copper field those
that are in most common use are beryllium copper, silicon bronze,
manganese bronze, aluminum bronze and leaded red brass (commonly
known as 85-5-5-5), depending on the requirements of the particular
application. Investment casting is frequently chosen for production
aircraft parts, such as pitot heads and other components. It is
used for delicate aerospace hardware, high-tech, military and
medical equipment, keys and locks, and machine parts of many types.
Jewelers and dentists use the process to produce small intricate
castings.
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