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9/8/98 AC 43.13-1B small parts such as rod end fittings in a con- tainer of suspension, which has just been stirred for about 30 seconds, is an excellent method. (5) Check for the presence of particle accumulation in the sharp radii. It is necessary that the level of magnetization and the particle application result in the formation of nonrele- vant indications. Lack of indications will re- quire remagnetization to a higher level, more care in applying the particles, or both. (6) Wash the parts in a clean suspension vehicle only enough to remove the weakly- held particle accumulations causing the non- relevant indications. Particles at true cracks will be more strongly held and will persist if the washing is gently done. This can be ac- complished by flowing or directing a stream of liquid vehicle over the part, or for a small component, by gently stirring in a container of the vehicle. Closely observe the removal of the nonrelevant particle accumulations in the region to be examined to avoid excessive washing. If washing is prolonged beyond the minimum needed to remove the nonrelevant indications, the small defect indications may also be washed away. A few trials will help to develop the best method and time required for washing. (7) Check for crack indications with optical magnification and ample lighting. The smaller indications that are attainable by this procedure cannot be reliably seen or evaluated with the unaided eye. 5-51. DEMAGNETIZATION AND POST- EXAMINATION CLEANING. Parts should be magnetized longitudinally last before de- magnetizing. NOTE: Circular magnetism cannot be read with a field meter since it is an internal magnetic field. However, if the last shot, was a coil shot the meter can read it if a magnetic field is pres- ent. a. Demagnetization. Demagnetize be- tween successive magnetization of the same part, to allow finding defects in all directions, and whenever the residual magnetism inter- feres with the interpretation of the indications. Also, demagnetize all parts and materials after completion of magnetic particle examination. Test all parts at several locations and parts for residual magnetism of complex configuration at all significant changes in geometry. Repeat demagnetization if there is any appreciable de- flection of the field indicator needle. (1) AC method. Hold the part in the AC demagnetizing coils and then move the part slowly and steadily through the coils and approximately 3 to 4 feet past the coils. Re- peat this process until the part loses its residual magnetism. Rotate and tumble parts of com- plex configuration as they are passed through the coils. (2) DC method. Place the part in the same relative position as when magnetized and apply reversing DC current. Gradually reduce the current to zero and repeat the process until the residual magnetic field is depleted. b. Post-Examination Cleaning. (1) When oil suspensions are used, sol- vent clean or remove the part until all magnetic particles and traces of oil are removed. Par 5-50 Page 5-27PDF Image | AFS-640
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