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Vforge Upgrades Die-Casting System, Improves Rotor Properties
Electrical Conductivity Raised Above 100% IACS, Soundness Remains High in Two Motor Series (continued) The intent of the shot-by-shot melting system was to limit exposure of molten oxygen-free copper to the atmosphere and thus preserve its purity. This is important because the high conductivity of oxygen-free C10100 copper, 101% IACS min., depends on its low level of dissolved impurities, including oxygen, as shown in Figure 3. The melting system worked well enough when using only nitrogen as a cover gas; however, oxygen content of the charge rose from 60 ppm to 675 ppm, and conductivity fell to 95% IACS. Microstructural examination revealed a characteristic copper-copper oxide eutectic (Figure 4). Vforge engineers have improved the system’s effectiveness dramatically by shielding the melt with a mixture of 95% nitrogen/5% hydrogen. With the added protection provided by the nitrogen/hydrogen shielding gas, dissolved oxygen content appears to have remained at acceptable levels, since the microstructure shows no evidence of oxide eutectic (Figures 5a and 5b). Conductivity of the as-cast copper is between 100% and 101% IACS – nearly identical to that of the original melt stock and truly an astounding improvement, Cowie says. 
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