Abstract: In a magnetic inspection apparatus for a thin steel strip of the invention, a pole-to-pole distance of a magnetizer, which is housed in a hollow roller contacting a traveling thin steel strip to oppose the thin steel strip, is set between twice and eight times a distance between magnetic poles and the thin steel strip. A position of a magnetic sensor in the travel direction of the thin steel strip is shifted from the central position of the magnetic poles to a travel direction side by a small distance. In this invention, a pair of hollow rollers are provided to sandwich upper and lower surfaces of a traveling thin steel strip, and magnetic sensors are respectively housed in the hollow rollers. As a result, a position of a defect in the direction of the thickness of the thin steel strip, and a defect size can be accurately detected.

Abstract: A magnetic defect detector having a pair of rotatable cylinders made of nonmagnetic material which pinch a running steel strip therebetween, two pairs of bearings being engaged with the end parts of the pair of cylinders. A pair of stationary shafts are respectively housed in the cylinders, the end parts of which are engaged with the bearings. A yoke is housed in one of the cylinders, the free ends of which are placed near to the pinched strip, and a magnetizing coil surrounds the yoke. At least one sensor is housed in the other of the cylinders, and it is placed near to the pinched strip.