The authors found that test results could be misleading, and that a key factor was the difference in the levels of impurities in the wire rod that was tested. High-purity copper (grades 6N and 8N) is most commonly produced by vacuum casting and applied for niche technology areas, whereas copper produced on an industrial scale usually has purity grades of 3N, 4N or 5N1. Both for economic and technical reasons, production of higher purity copper with current industrial plants for continuous melting, casting and rolling methods (Contirod, Southwire and Properzi) is not possible. The quality of cathode and copper wire rod is defined in ASTM B49 - 92 and BS - 10.36 as well as Polish PN - 77/H - 82120, PN - 76/H - 93672 PN - 83/M - 80003 standards. Despite the chemical composition, manufacturers of cathodes and wire rod apply electrical conductivity and annealing susceptibility of material as a basic factor indicating product quality. Whereas the first property directly results from the basic application of copper wire rod for electrical purposes, requirements for annealing susceptibility are dictated by the technological rigor during the wiredrawing process on multi-speed machines. The ability to properly perform wire annealing during the multiphase drawing process is a basic requirement that must be met by manufacturers of copper wire rod. Fig. 1 presents examples of scanning photos of copper wire scrap obtained from wire rod of various levels of impurities.
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