The part was cast in a pure copper alloy with 98% electrical conductivity. (The conductivity of copper is measured according to the International Annealed Copper Standard for conductivity.) Pure copper alloys have a minimum copper content of 99.3%; anything less causes a notable dip in electrical conductivity.

“Impurities in copper, such as traces of conventional metals that may get added, will ruin the conductivity,” said Dan Burnstein, president of Burnstein von Seelen, Abbeville, S.C., a permanent mold caster of copper parts. “It’s critical to keep the material clean.”

Converted from a 32-piece fabrication, this high conductivity pure copper casting is used in electrical and mechanical load carrying units for a 38 KV breaker. THe casting is able to carry electrical loads up to 95 KV.

But the exact amount needed to de-oxidize the material cannot be determined, so a surplus of those elements remains in the metal after solidification. The extra elements detract from the copper’s conductivity.
Rather than adding a deoxidizing agent to the melt, controlled amounts of gas to disperse shrinkage in melting operations maintain the integrity of the copper’s conductivity, which allows copper castings to compete with copper fabrications.

Hardened Heart

Copper in its pure form is a soft material, so for many copper applications, alloying elements, such as nickel and copper, are added to promote strength and hardness. But beware: “Copper is very soft, but as soon as you alloy, you give up its conductivity,” Burnstein said.

Alloys like nickel and chrome can drop the conductivity percentage of the material to the mid to low 80s. Similarly, aluminum can be used in some electrical applications, but with 34% conductivity, parts may be required to be three times the size of a pure copper design.

However,  achieving the highest level of conductivity may be optimal, but in many cases, the strength of the component is just as, if not more, important.  For many applications, 80% conductivity is enough to meet their needs. High copper alloys contain more than 95% copper along with a percentage of strengthening alloys, such as beryllium, chromium or cobalt, which can be taken into the melt at high temperatures and precipitate once the casting cools. This precipitation increases the strength of the alloy, and because the alloying elements are no longer in solution, the copper matrix maintains high conductivity. For instance, chromium-copper exhibits up to twice the strength of pure copper with 80% of its electrical conductivity 80%.

However, one property often must be sacrificed to reach higher limits for another property. For instance, beryllium copper alloys either exhibit high conductivity with moderate strength, or moderate conductivity at high strength. While pure copper exhibits ultimate tensile and yield strengths of 28 and 4 ksi, beryllium copper can exhibit strengths of 80 and 40 ksi, but electrical conductivity is reduced to 20%.

Applications for high copper alloys include heavy-duty pole line and other electrical hardware. MetalcastingDesign.com