Detecting Extended Complex-Shaped Defects in Electroconductive Plates Using a Magnetic Carrier

Abstract

We studied oscilloscope waveforms picked up from a magnetic head scanning a magnetic carrier with the recordings of the spatial distributions of magnetic fields due to artificial complex-shaped defects in the form of cuts in plates made of aluminum, lead, and copper. The defect opening was 10–100 μm, and the plate thickness was 60 μm or more. The defects were exposed to magnetic field pulses with a rise time in the range of 1.5–50 μs, while recording fields due to defects on a magnetic carrier. The strength of a primary magnetic field, created by a flat inductor, varied in the range of 5–30 kA/m. We provide photographs of plates with defects and dependences of the electric voltage U (y) on y-coordinate, read from an induction magnetic head scanning the magnetic carrier with the records of fields due to defects in plates of different thickness and at different heights above the plates. Based on the conducted research, conditions have been established for identifying screened-from-view extended complex-shaped defects in objects in the form of aluminum, lead, and copper plates. A method of pulsed magnetic testing of extended complex-shaped defects in these objects has been developed. The method allows recording instantaneous distributions of magnetic field across an area of 10 cm² or more with a resolution in the measurement plane of 0.01 mm², with pulsed magnetic fields due to defects displayed on monitor screen by constructing the records of U (y) in a plane that corresponds to the test-object surface. These results can be used for express detection of continuity defects in electrically conductive objects, as well as when studying various magnetic and electromagnetic methods of testing.