Magnetic inspection apparatus for thin steel strip having magnetizer and detection coil within a hollow roller rotated by the steel strip

摘要

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. In a magnetic inspection apparatus for a thin steel strip of the invention, a magnetic detection circuit for detecting magnetic flux leakage caused by a defect in the interior or on the surface of a thin steel strip uses an over-saturation type magnetic sensor constituted by applying a detection coil around a ferromagnetic core. As a result, a defect detection sensibility and a defect detection precision are greatly improved.