Ultrasonic Method

TM 1-1520-265-23 2-40 Change 4 b. Refer to Ultrasonic Method, paragraph 1.4.12. Set up on free edge of weight as follows: (1) SETUP - Attach the transducer and cable to the ultrasonic unit. Couple the transducer to the upper surface of the bifilar weight leg with the sound beam directed towards the free edge. The transducer’s forward edge will be over the edge of the bifilar weight, slide the transducer back and forth in this position to produce a signal from the lower free edge of the weight. This signal is generated by the first leg of the sound beam path (1/2 skip distance). Verify the signal by “damping” the lower edge with a finger moistened with couplant. See Fig. 2-18, view A. Maximize this signal and adjust the gain to obtain 100% Full Screen Height (FSH). Mark the location of this signal along the time base line of the CRT with an aircraft marking pencil and write down the gain setting as “Gain #1 bD”. Slide the transducer away from the free edge, the lower edge signal will decrease in amplitude and be replaced with another signal approximately twice the distance from the IP. This signal is from the upper free edge generated from the second leg of the sound path (full skip distance). See Fig. 2-18, view B. Verify this signal by “damping” the upper edge and adjust the amplitude of this signal to 100% FSH. Mark the location of this signal along the time base line and write down the gain setting as “Gain #2 dB”. (2) INSPECTION (a) Couple the transducer to the upper inboard surface of the bifilar weight leg so that the sound beam is directed towards the sintered bond line. Inspect the entire length of both the upper and lower bond lines. See Fig. 2-18, view C. (b) Ultrasonic inspection of the full thickness is required for Zones A and C. (c) Inspection of the full thickness may not be possible in Zone B. (3) ACCEPTANCE/REJECTION CRITERIA - A signal detected at or between the locations marked along the time base line is considered an unbond. Indications detected near the location of the signal from the upper free edge will be evaluated at the “Gain #2 dB” setting. A signal of 80% FSH or greater is rejectable. A signal that appears near the location of the signal from the lower free edge will be evaluated at the “Gain #1 dB” setting. A signal of 80% or greater is rejectable. 2.18.3.6 Inspection Procedure. Couple the transducer to the upper surface of the bifilar weight. Direct the sound beam towards the sintered bond line. Slide the transducer back and forth to interrogate the sintered bond line with both legs of the sound beam. Any signals appearing on the CRT at or between the markings along the time base line greater than 20% FSH will be evaluated at their appropriate gain settings in accordance with the established acceptance/rejection criteria. Repeat the inspection procedure for both the upper and lower bond lines on all the bifilar weights. 2.18.3.7 Marking and Recording of Inspection Results. Mark and record inspection results as required by paragraph 1.3. 2.18.4 Backup Method. None required. 2.18.5 System Securing. The bifilar weight requires cleaning to remove inspection media. Refer to Post Cleaning and Restoration of Part or Area After NDI, paragraph 1.4.16.