Copper rod requirements for magnet wire

Because of stringent demands imposed upon rod producers by manufacturers of magnet wire, the highest quality copper being produced today is usually channelled towards this very important segment of the wire industry. Unfortunately, there are no existing specifications presently in use that can predict quantitively such factors as drawability, annealing behaviour, surface quality, and conformability. Inasmuch as ASTM specification B49 (Hot-rolled copper redraw rod for electrical purposes) describes only very general requirements such as 99.90% copper, tensile elongation exceeding 30%, conductivity greater than 100% IACS and surface quality “free of all imperfections not consistent with good commercial practice”, a wide spectrum of rod grades having considerable variation in quality frequently finds its way into the magnet wire marketplace. Consequently, a need exists to replace subjective opinions concerning copper rod quality with meaningful parameters that not only can be accurately measured, but, equally important, can give some estimate of processing capability and final (bare) wire quality. The purpose of this paper is to help fill this void and remove some of the guesswork and inconsistencies frequently employed to assess rod performance. No attempt will be made to develop a working set of specifications.