T.O. 33B-1-13-183.1.9.12.4Hand-HeldCoil.For longitudinal magnetization of shafts, spindles, rear axles, and similar small parts, the hand-held AC coil offers asimple and convenient method of inspecting for transverse cracks. Parts are magnetized and demagnetized with thesame coil.3.1.9.12.5DemagnetizingEquipment.The most common type of demagnetizing equipment consists of an open, tunnel-like coil through which AC is passedat the line frequency, usually 60-Hertz. The larger type equipment is frequently placed on its own stand, incorporatinga track or carriage to facilitate moving large and heavy parts through the demagnetizing equipment. Thedemagnetizing equipment can also include tabletop units, yokes, or plug-in coils that are more suited for thedemagnetization of small parts. However, the large stationary type equipment is preferable when geometricallycomplex parts are involved. The use of demagnetization and demagnetization equipment s discussed in detail inSection 6.SECTION IIPRE- AND POST-MPI CLEANING & PRE-MPI DISASSEMBLY3.2 PRE-ANDP0ST-MPICLEANING&PRE-MPIDISASSEMBLY.3.2.1 Pre-InspectionCleaning.3.2.1.1 Definition.Pre-cleaning is the removal of all foreign material (paint, grease, oil, corrosion, layout dye, wax crayon markings, etc.)which may interfere with magnetic particle testing that has accumulated since the general cleaning operation but priorto inspection.3.2.1.2 NecessityforPre-InspectionCleaning.Parts or surfaces should be clean and dry before they are subjected to any magnetic particle inspection process. Thecleaning process used must not reduce the effectiveness of the inspection process that follows. The cleaning process isrequired to remove all contaminants, foreign matter, and debris that might interfere with the application of current orthe movement of the magnetic particles on the test surface. Note, however, that thin coatings such as cadmium,chromium or paint, if in good condition, will not interfere with the inspection process and do not necessarily have to beremoved.3.2.2 ConsiderationswhenselectingACleaningProcess.No single cleaning method can assure removal of all types of contaminants. Most methods are limited to the removalof only a few types of contaminants. Further, some cleaning methods require equipment that may not be adaptable tothe specific job conditions, i.e., such as cleaning large parts or cleaning in place on an aircraft. Finally, some processesmay cause corrosion of the part to be inspected. The cleaning process must then be chosen with knowledge of thecontaminant, the alloy and the accessibility of the part to be inspected.3.2.3 TypicalCleaningMethods.CAUTIONImproper cleaning procedures/materials can cause severe damage. Cleaning shouldbe accomplished by trained and qualified personnel. For Air Force personnel, T.O.1-1-691 applies. For Navy personnel, use NA 0l-lA-509. For Army personnel, useTM1-1500-344-23.
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