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Identification of defects in wires and bars by means of ultrasound
The BFI has developed an inspection system which uses two-dimensionally guided ultrasonic waves for the automatic detection of internal and surface defects (cracks, indentations, core defects such as shrinkage cavities, central porosity and inclusions) in wires and bars up to around 20 mm in diameter. The probes that it uses are electrodynamic ultrasonic transducers in the form of cylindrical feed-through coils, with which it is possible to generate and receive the bar waves contactlessly and without any coupling medium by the pulse-echo method. The propagation direction of these ultrasonic waves is axial, meaning that testing can, in principle, take place at sound velocity. The static testing of bars is equally as possible with the feed-through coils as inspecting endless products in drawing and rolling lines.
The size of the smallest detectable defect depends on the diameter and cross-sectional shape of the test object. Defects amounting to 0.4 % of a shape's cross-sectional area can be reliably detected.
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