NMWR-9-2815-220 Overhaul Manual for M60 M88 Engine AVDS-1790-2CA, AVDS-1790-2DA, AVDS-1790-2DR Download
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NMWR 9-2815-220 GENERAL MAINTENANCE, OVERHAUL, AND REPAIR PROCEDURES—Continued 0005 00 DIAGNOSTIC AND AUTOMATED TEST EQUIPMENT - Continued (2) Longitudinal magnetization is that in which the magnetic lines of force run the length of the part and is applicable for detection of traverse discontinuities. (a) Magnetization is accomplished by placing the part between the poles of electromagnets or in a coil carrying suitable current. (b) The effective field on either side of a coil is 6 to 9 inches. Long parts must be magnetized in sections. (c) Longitudinal magnetization can be accomplished by wrapping a cable in coil fashion around large parts. (d) The part to be magnetized must be at least twice the length of its short dimension. (e) The long axis should be parallel to the axis of the coil. (f) The part should be held against the inside wall of the coil and not be positioned in the center of the coil. (3) A complete magnetic particle test shall consist of both circular and longitudinal magnetization so conducted that the magnetic lines of force will be traverse to any discontinuity in the piece. h. Value of Flux Density. The strength of magnetic field is referred to as the flux density. Size, shape, and material affect the strength of the field. (1) Circular magnetization should be 800 to 1200 ampere-turns for each 1 inch of outside diameter. Longitudinal magnetization should be 3000 to 5000 ampere-turns for each 1 inch of outside diameter. NOTE An ampere-turn is the product of the number of turns in the coil times the number of amperes used. (2) Since the field that is either too weak or too strong will create too little or too much flux leakage at discontinuities, the above densities may be adjusted either up or down after observing the behavior of the magnetic particles. i. Processes. There are two wet processes, visible particle (nonfluorescent) and fluorescent particle, and a dry particle process. (1) Concentration of wet particles will be tested daily for proper bath strength. (2) Visible wet process particle and dry particle indications will be inspected using a minimum of 100 foot- candles of white light. (3) Wet fluorescent particle indications will be inspected in a darkened booth using a black light (ultra- violet) with an intensity of 800 microwatts per square centimeter. (4) Light intensities will be measured with approved light meters at the surface of the parts. 0005 00-15 Change 1