Eddy current testing
The eddy current method has been used for quite a long time to effectively control electrically conductive materials. In general, this method looks like this. Under the influence of an alternating electromagnetic field, the so-called eddy currents appear in the metal of the investigated part. They create their own electromagnetic field, which counteracts the external field. The appearance of the field of eddy currents is fixed by a measuring coil. All violations of the uniformity of the controlled product instantly increase the electrical resistance of the surface layer of the metal, which leads to a weakening of the eddy currents. When voltage and resistance are recorded on the coils, the necessary information about the properties of the object appears, as well as its position relative to the converter.
An important feature of the eddy current method of non-destructive testing is that it can be carried out without contact between the object and the transducer - their interaction occurs at those distances that are necessary for free movement of the transducer relative to the object (from fractions of a millimeter). This makes it possible to obtain quality control results even at very high speeds of the objects under study. This method is suitable for detection of such defects as corrosion, wear, erosion, pitting, cracks, damage and thinning of the walls. First of all, it is used to control the quality of various electrically conductive objects (metals, graphite, alloys, semiconductors). Devices implementing the eddy current method are used for the rapid detection of material shortcomings (defectometry and flaw detection), vibration control (vibrometry and thickness measurement) and determination of the structural state (structuroscopy). The main objects of eddy current monitoring are electrically conductive bars, pipes, wire, sheets, rails, plates, atomic reactor cases, rollers and bearing balls, fastening parts and many other industrial products.