Effect of Flux Direction To locate a defect in a part, it is essential that the magnetic lines of force pass approximately perpendicular to the defect. It is therefore necessary to induce magnetic flux in more than one direction since defects are likely to exist at any angle to the major axis of the part. This requires two separate magnetizing operations, referred to as circular magnetization and longitudinal magnetization. The effect of flux direction is illustrated in Figure 8-15. Circular magnetization is the induction of a magnetic field consisting of concentric circles of force about and within the part which is achieved by passing electric current through the part. This type of magnetization will locate defects running approximately parallel to the axis of the part. Figure 8-16 illustrates circular magnetization of a camshaft. In longitudinal magnetization, the magnetic field is produced in a direction parallel to the long axis of the part. This is accomplished by placing the part in a solenoid excited by electric current. The metal part then becomes the core of an electromagnet and is magnetized by induction from the magnetic field created in the solenoid. In longitudinal magnetization, the magnetic field is produced in a direction parallel to the long axis of the part. This is accomplished by placing the part in a solenoid excited by electric current. The metal part then becomes the core of an electromagnet and is magnetized by induction from the magnetic field created in the solenoid. In longitudinal magnetization of long parts, the solenoid must be moved along the part in order to magnetize it. [Figure 8-17] This is necessary to ensure adequate field strength throughout the entire length of the part. Solenoids produce effective magnetization for approximately 12 inches from each end of the coil, thus accommodating parts or sections approximately 30 inches in length. Longitudinal magnetization equivalent to that obtained by a solenoid may be accomplished by wrapping a flexible electrical conductor around the part. Although this method is not as convenient, it has an advantage in that the coils conform more closely to the shape of the part, producing a somewhat more uniform magnetization. The flexible coil method is also useful for large or irregularly shaped parts for which standard solenoids are not available.

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