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Gary Coffman
 
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Default Copper Casting In America (Trevelyan)

On Tue, 15 Jun 2004 16:53:26 -0400, Yuri Kuchinsky wrote:
Gary Coffman wrote:

[snip]

Casting dumb, smithing smart.


But casting and/or smithing (depending on the materials at
hand) is more smart than just smithing.


True, when the material isn't pure copper. Bronze casts very
nicely, for example, as do gold, silver, iron, etc. But pure copper
doesn't. As Key to Metals says, "Pure copper is extremely difficult
to cast as well as being prone to surface cracking, porosity problems,
and to the formation of internal cavities."

Commercially, pure copper is melted and cast using a furnace
that is inert gas purged, a crushed graphite cover is floated over
the melt, and when the melt reaches 1250 C, a small amount of
calcium boride or lithium metal is injected into the melt to act
as a deoxidizer.

While silcon bronze can be successfully gravity cast in a sand
mold, pure copper cannot. Pure copper needs to be pressure
molded, either via injection or centrifugal casting methods. The
molten metal should not be exposed to air during the casting
process.

Casting pure copper is a highly sophisticated process of the
modern industrial age. The techniques to do it successfully
were only developed near the end of the 19th century when
the demand for high purity copper castings for the electrical
industry drove research and development. It is still difficult
and expensive enough to do that aluminum, brass, or bronze
is substituted for pure copper wherever it is practical to do so
in electrical equipment.

Gary