Standard Practice for Electromagnetic (Eddy Current) Examination of Copper and Aluminum Redraw Rod for Electrical Purposes

Abstract

5.1 Eddy current instrumentation provides timely and useful information regarding the acceptability of copper and aluminum rod for quality control purposes, as well as providing for early warning that unacceptable rod is being produced. Eddy current testing is a nondestructive method of locating surface discontinuities in a product. Signals can be produced by discontinuities located on the surface of the rod. Since the density of eddy currents decreases nearly exponentially as the distance from the surface increases, deep-seated defects may be undetected. 5.1.1 An exception is the detection of subsurface ferromagnetic inclusions with an additional, or shared, winding enveloped in a DC magnetic field and the addition of appropriate instrumentation. The coil winding, acting as a transducer, generates a voltage as the magnetized inclusion passes through, providing an electrical signal separate from the eddy current response to surface imperfections. The rod is transparent to the DC effect allowing high sensitivity to ferromagnetic inclusions, in the absence of eddy current noise. The method is inherently speed sensitive but is enhanced by high throughput speeds enabling the detection of small subsurface ferromagnetic inclusions which are particularly detrimental to rod quality. 5.2 Some indications obtained by this practice may not be relevant to product quality. For example, a signal may be caused by minute flaws or irregularities, by anomalies in the material, or a combination thereof, that are not detrimental to the end use of the product. Nonrelevant indications, referred to as “noise,” can mask unacceptable discontinuities. On the other hand, relevant indications are those that may result from unacceptable discontinuities and should be determined by agreement between the user and the supplier. Any indication that is believed to be irrelevant shall be regarded as unacceptable until it is demonstrated by reexamination or other means to be nonrelevant.