Method for nondestructive magnetic inspection and rubber-like magnetic

Abstract

Magnetizable recording medium for nondestructive magnetic particle inspection of an object or part, for detection of defects and metallurgical conditions therein, in the form of a rubber-like resilient pad, e.g. a cast silicone rubber pad, having dispersed therein magnetic oxides, e.g. ferromagnetic particles, of high magnetic retentivity, and having high magnetic remanent flux density, e.g. of the order of about 1,850 gauss, or higher, and a magnetic coercive force of the order of about 280 oersteds, or higher. There can be embedded or sandwiched into the magnetizable rubber-like pad an open-mesh fabric, e.g. a silk layer, to provide magnetic recordable pads of improved dimensional stability and reuseability. Such magnetic recording medium or pad is placed on the surface of the object, the object and pad are magnetized to record on such pad, magnetic indications of such defects and metallurgical conditions, the pad is removed from the object, and a viewing device is placed on the area of the magnetized rubber-like pad previously in contact with the object, such device preferably being one containing a suspension of weakly magnetic crystals in a transparent liquid vehicle, and viewing through such device the outlines and indications of the defects and metallurgical conditions in the object, produced by the re-orientation of the magnetic particles of the suspension, and corresponding to the magnetic indications recorded on the magnetized rubber-like recording medium or pad. The magnetically recordable rubber-like pad can be used to record multiple recordings of a plurality of cracks at any angles to each other, or to make multiple recordings of parallel cracks or duplicate recordings of the same crack, without erasing the initial crack recording, or can be used to determine the depth of a crack. The magnetized recording pad can be demagnetized and erased by application of a high coercive demagnetizing flux, and reused.