TM 1-1520-265-231-28 Change 21.4.8.1 Magnetic Particle Inspection Equipment. Considerations involved in the selection ofmagnetic particle inspection equipment include the type of magnetizing current and the location andnature of the inspection. The purpose of this manual is to support the accomplishment of NDI at theAVUM and AVIM levels. This dictates equipment that can be used on or off the helicopter at remotesites. Therefore, magnetic particle procedures in this manual use the electromagnetic yokes orprobes and hand-held coils as shown in Figure 1-6. This equipment is common and readily availableto AVUM and AVIM levels. Stationary magnetic particle equipment can be used if facilities, requiredshop equipment, and qualified NDI technicians are available. Refer to TM 1-1500-335-23(Nondestructive Inspection Methods manual) for stationary magnetic particle inspectiontechniques.1.4.8.1.1 Magnetic Yokes and Probes.. Portable induced field inspection equipment is generallyreferred to as either a probe or a yoke. These terms are synonymous and differ due tomanufacturer’s nomenclature. They are small, portable, easy to use, and can be used on or off thehelicopter. They induce a strong magnetic field into that portion of a part that lies between the polesor legs. This limits the magnetization to longitudinal; however, by turning the probe 90_ on the partfor the second position, cracks, either perpendicular or parallel to the axis of the part, can bedetected. Some yokes and probes have both AC and DC capabilities while others have AC only. Allprocedures in this manual use AC. AC provides a very desirable and useful field. The vibratory actionof AC adds significantly to the magnetic particle mobility enhancing the formation and build-up oflarger and sharper indications at discontinuities. An AC magnetic field is also used when it isnecessary to reveal only surface cracks, common to in-service parts due to fatigue and stresscracking. Yokes and probes utilizing AC for magnetization also have the additional advantage thatthey can be used for demagnetization.1.4.8.1.2 Hand-held Coil. For longitudinal magnetization of bolts, shafts, spindles, axles, andsimilar small parts, the hand-held coil offers a simple, convenient method of inspecting fortransverse cracks. It allows for equipment maintenance inspections wherever a coil can be appliedaround the part. Parts are magnetized and demagnetized with the same coil.1.4.8.2 Safety Precautions During Magnetic Particle Inspections. Follow safety precautions andinstructions contained in this manual and the Nondestructive Inspection Methods manual listed inTable 1-1.WARNINGBlack lights generate considerable heat during use. Extreme care must beexercised to prevent contacting the housing with any part of the body.To prevent injury to eyes, do not look directly into black light.Prolonged direct exposure of hands to the filtered black light’s main beam may beharmful. Suitable gloves shall be worn when exposing hands to the main beam.a. Follow manufacturer’s instructions when using black lights and filter.b. Do not wear sunglasses or glasses with light-sensitive lenses during fluorescent magneticparticle inspections. They can contribute to improper interpretation of defects.
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