Copper is a pure metal and can be found naturally in
the ground. Copper by itself is soft and ductile and reddish brown in
color. When 40% zinc is added to 60% copper, an alloy called brass is
made. Copper melts at 1981°F. When zinc is added the melting point is
lowered to 1650°F. This 60-40 brass is very common because it has the
highest strength of the copper zinc alloys. When copper is alloyed with
tin, the result is bronze. A common bronze is phosphor bronze which is
about 10% tin. Copper is noted for its ability to conduct electricity.
Based on a scale of 1 to 100, copper is rated at 100 for electrical
conductivity. Alloys of copper, such as brass and bronze, have much
lower conductivity values, being in the range of about 25. When repair
welding of electrical components, the filler alloy used must be
considered as to electrical conductivity.Copper is also noted for its
thermal conductivity or its ability to conduct heat. This is the reason
for using copper for heat exchanger applications such as radiation, air
conditioning condensers and evaporators, welding torch tips, etc. This
is also the reason large copper parts often seem difficult to weld
repair. Welders generally anticipate a certain amount of time when
preheating prior to welding and think of the part they are working on as
steel, which builds up heat in a local area relatively quickly. Because
copper transmits the heat away from the heating area, it takes much
longer to bring the weld area up to proper welding temperatures. The
welder, thinking steel, starts to weld on a part not sufficiently
preheated. The results are poor appearing weld deposits with little or
no penetration, weld spatter, and possible surface porosity in the
weld.The choice of welding method will usually depend on the type of
base metal, its configuration and ultimate use. Arc welding is most
popular for heavy sections, while torch is generally used for smaller
parts or on copper parts that contain zinc. Brazing can be done
successfully on all the copper-base metals. The most popular type of
brazing is done with a silver brazing alloy such as Slik-SilTM106.
Soldering can be done easily on most copper base alloys if suitable
fluxes are used on clean surfaces.
