An automatic ultrasonic-testing apparatus has been developed for integral-type crankshafts used in four-stroke engines for marine and power-plant industries. The apparatus adopts a unique phased-array technique applicable to fillets and comprises a scanning mechanism that enables its probe to rotatably follow the surfaces of eccentric shafts, while maintaining stable scanning pitch and coupling. The defect detectability has turned out to be φ0.5 mm flat-bottom hole (FBH) at depths down to 50 mm.
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