보빈형 근접장 와전류 검사 시스템의 개발에 관한 연구

Abstract

The bleed air duct (BAD), include some suspension structure and welding zones for efficient inner placement and separation considering fluid mechanics and air pressure. If the BAD is exposed to corrosive gas and humidity by long use, can get some cracks and might lead to destructions. Also, some BADs can be met with serious accident when there’s damage in the near of fuel pipe. Therefore, in appropriate manners, there should be regular check-ups that examining flaws and should take right actions on it. In the research, we suggested non-destructive examination system for checking a BAD’s cracks in non-continuous areas such as suspension and welding zones. In this study, we developed bobbin-type Hall sensors array (BIHaS) in near-field eddy current testing (NFECT) for inspection of the BAD. The BIHaS is placed beside an exciting bobbin-type coil in the NFECT to minimize the lift-off. We analyzed distortion of electromagnetic field distribution due to crack existence by finite element method (FEM). Using the result from the analysis, we designed and produced excite coil, sensor arrangement, and signal processing circuit. There are two types of sensor probe will be presented, which are used to inspect 38mm and 50mm inner diameter bleed air ducts. In the Ф38mm sensor probe, the exciting coil 80 turns of 0.2mm coated copper wire a on 34mm diameter and 5mm width in a plastic cylinder probe; the BIHaS has 45 hall sensors with interval of 8 degree (2.65mm) on 34mm diameter probe. And, in theФ50mm sensor probe, the exciting coil 80 turns of 0.2mm coated copper wire a on 48mm diameter and 5mm width in a plastic cylinder probe; the BIHaS has 63 hall sensors with interval of 5.7 degree (2.49mm) on 48mm diameter probe. Bobbin-type magnetic camera, which integrated exciting coil and BIHaS, is placed inside a fixed BAD, can move and measures signal at speed of 30mm/sec. The sensor output signal passed through filters, differential-type amplifiers, root-mean-square circuits, and transferred to a computer by AD converter (USB-6255, NI). Transferred signal displayed by 3D contour surface graph and 2D waterfall graph, and be used to evaluate the defect’s size. We verified effectiveness of the developed system by implementing 3mm ~ 30mm axial directional artificial cracks on several titanium BADs, which have thickness of 0.45mm and inner diameters of 38mm and 50mm.