G.
Eddy Current Inspection of the Fan Rotor Blades
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BOEING PROPRIETARY - Copyright (C) - Unpublished Work - See title page for details.
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WARNING:_______ TO PREVENT INJURY TO YOUR HANDS, GLOVES SHOULD BE WORN WHEN YOU
HANDLE THE BLADES.
CAUTION:_______ NICKS IN THE LEADING AND TRAILING EDGE BECOME MORE IMPORTANT
THE CLOSER THEY ARE TO THE ROOT OF THE BLADE. THEREFORE, MAKE
SURE THAT THE PART OF THE BLADE FROM THE PART SPAN SHROUD TO
THE PLATFORM IS TOUCHED VERY CAREFULLY TO PREVENT DAMAGE TO
THAT AREA.
(1) Prepare the blade for the inspection.
WARNING: DO NOT GET METHYL ETHYL KETONE (MEK) IN YOUR MOUTH OR
_______ EYES, OR ON YOUR SKIN. DO NOT BREATHE THE FUMES FROM MEK. PUT ON A PROTECTIVE SPLASH GOGGLE AND GLOVES WHEN YOU USE MEK. KEEP MEK AWAY FROM SPARKS, FLAME AND HEAT. MEK IS A POISONOUS AND FLAMMABLE SOLVENT WHICH CAN CAUSE INJURY TO PERSONS OR DAMAGE TO EQUIPMENT.
(a)
Wipe the edges of the blades with a lint-free cloth which has been made moist with Methyl Ethyl Ketone (MEK).
(b)
Use a No. 240 grit emery cloth to remove any irregular areas on the surface before you do the inspection.
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(2) Calibrate and set the equipment.
NOTE: Instrumentation should be calibrated before and after
____ each set of blades is inspected. Also calibrate the equipment if the instrumentation has been turned off. Teflon tape on the tip of probe tip must be changed regularly to prevent wear on the probe tip.
(a) Connect any of these probes: PWA75909, PWA28404 or PWA28443 to the eddy current instrument. If a recorder is used, connect the recorder to the eddy instrument. Then turn on the instrument and the recorder, if applicable, and allow both to warm up as specified by the manufacturers.
NOTE: If the Model 680 chart recorder is used, a fine
____ control potentiometer must also be used to change the resistance in the circuit. This is used to adjust the eddy current trace to the correct amplitude.
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////////////////////////A / PW4000 SERIES /747-400 / ENGINES/MAINTENANCE MANUAL ////////////////////////
(b)
Cover the rub surface of the probe tip with teflon tape which has a thichness of six mil. This allows the probe to follow the surface more easily and also decreases the wear on the probe tip.
(c)
Set the instrument to the Fe position.
(d)
Tune the probe with a PWA28403 Crack Standard to set the lift-off compensation. Use the edge of the tool which has the sharp radius and is away from the crack standard slot. Move the probe across the slot moderately fast and with a constant velocity. Adjust the probe so that the meter deflection is five units when the probe is moved across the standard slot. If an optional recorder is used, set the sensitivity on the recorder so that the eddy current trace makes a 2.5-3.0 inch (63.5-76.2 mm) spike when the probe is moved across the standard slot.
NOTE: Moderately fast is specified as approximately 0.5 in
____
per second (12.700 mm per second).
A spike is a fast movement of the meter which is over the base meter level.
(e) If a recorder is used, adjust the speed of the chart to get a four to six inch trace as the probe is moved along the edge of the blade.
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(3) Do the inspection of the blade edge.
NOTE: As the probe moves closer to the platform, the edge of
____ the blade may become too thick to fit into the probe. Therefore, it is permitted to slowly lift the probe off the blade edge if the usual eddy current signal for lift-off appears.
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