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AC 43.13-1B CHG 1 5-45. PREPARATION OF SURFACE. a. Remove protective coatings according to the manufacturer’s instructions if necessary. Unless otherwise specified, magnetic particle examination should not be performed with coatings in place that could prevent the detec- tion of surface defects in the ferro-magnetic substrate. Such coatings include paint or chromeplatethickerthan0.003inch,orferro- magnetic coatings such as electroplated nickel thicker than 0.001 inch. b. Parts should be free of grease, oil, rust, scale, or other substances which will in- terfere with the examination process. If re- quired, clean by vapor degrease, solvent, or abrasive means per the manufacturer’s in- structions. Use abrasive cleaning only as nec- essary to completely remove scale or rust. Ex- cessive blasting of parts can affect examination results. c. Exercise extreme care to prevent any cleaning material or magnetic particles from becoming entrapped where they cannot be re- moved. This may require extracting compo- nents such as bushings, bearings, or inserts from assemblies before cleaning and magnetic particle examination. d. A water-break-free surface is re- quired for parts to be examined by water sus- pension methods. If the suspension com- pletely wets the surface, this requirement is met. e. Magnetic particle examination of as- sembled bearings is not recommended because the bearings are difficult to demagnetize. If a bearing cannot be removed, it should be pro- tected from the magnetic particle examination materials and locally magnetized with a mag- netic yoke to limit the magnetic field across the bearing. 9/27/01 5-46. METHODS OF EXAMINATION. Magnetic particle examination generally con- sists of: the application of magnetic particles; magnetization; determination of field strength; special examination techniques; and demag- netization and post-examination cleaning. Each of these steps will be described in the following paragraphs. 5-47. APPLICATION OF MAGNETIC PARTICLES. The magnetic particles used can be nonfluorescent or fluorescent (depend- ent on the examination required) and are ap- plied suspended in a suitable substance. Fluo- rescent particles are preferred due to their higher sensitivity. a. Wet Continuous Method. Unless oth- erwise specified, use only the wet continuous method. In the wet continuous method, the particle suspension is liberally applied to wet all surfaces of the part. The magnetizing cur- rent is applied at the instant the suspension is diverted from the part. Apply two shots of magnetizing current, each at least 1/2 second long. (1) Wet suspensions of fluorescent par- ticles, either in water or oil, should be used for most overhaul and in-service examinations ex- cept where the material, size, or shape of the part prohibits its use. (2) Water, with a suitable rust inhibitor and wetting agent, may be used as a liquid ve- hicle, provided that magnetic examination equipment is designed for use or is satisfacto- rily converted for use with water. b. Dry Continuous Method. This method is not recommended for use on aero- space components because of its lower sensi- tivity level. Page 5-22 Par 5-45PDF Image | AFS-640
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