Nippon Kokan Kabushiki Kaisha

Hideya Tanabe

Isamu Komine

Katsuhiko Shimada

Tsuguo Takahashi

Shuichi Tsunozaki

Masayoshi Yamada

The surface defect detecting apparatus for rotating cylindrical metal pieces which move in a lengthwise direction relative to a sensor block, has a plurality of eddy-current flaw detecting coils facing the test piece. The sensor block rotates about a horizontal axis extending vertically with respect to the axis of the test piece to follow up deflections of the test piece in the direction of the axis of rotation. Front and rear ends of the sensor block, have a pair of guide wheels that engage the piece; also present are color marking nozzles for marking defective areas in response to detector signals. Relative movement in the longitudinal direction of the test piece is carried out by means of a carriage carrying the sensor block. Each guide wheel is spaced from another in a plane transverse to the longitudinal direction of the test piece. A number of coils with designated impedances are connected to a generator and are disposed in longitudinal direction of the test piece in a single sensor holder within the sensor block. The holder has turning wheels at front and rear ends thereof in a longitudinal direction of the test piece, and are each positioned between the guide wheels in a direction for spiral scanning, and in rotatable contact with the outer surface of the test piece. Impedances of the coils are selected to allow feedback amplifiers to form a feedback circuit with two of the coils and are linear for eddy-current signals corresponding to different flaw depth ranges. Signals of a detector unit associated with different flaw depth range are amplified within the linear characteristic range and supplied to nozzles which spray different colors depending on flaw depth.

Surface defect detecting apparatus for use with rotating circularly

A surface defect detecting apparatus having at least one sensor block for movement in respect of rotating cylindrically shaped electrically conductive metallic material to be inspected by scanning an outer portion of the surface of the material. The sensor block has spaced guide wheels at front and rear parts thereof in the spiral scanning direction which rotate in response to the rotation of the material; and a coil holder for supporting a plurality of eddy-current flaw detecting coils arranged longitudinally in a row in the direction of movement, intermediate between pairs of guide wheels at the front and rear parts opposite to the outer surface of said material with a predetermined gap therebetween. A turning wheel at each of the front and rear parts of the coil holder is rotatable with respect to the outer surface of the material so as to maintain the predetermined gap. An AC signal of a predetermined frequency applied from an oscillator to the coils produces corresponding eddy currents in material to be inspected. The coils are divided into a first group and a second group with one group of coils being defined by coils other than those coils in an adjoining row to that group, phase shifters feed the AC signal to coils of the first group resulting in a shift in phase by a predetermined amount, as reference signal to detectors formed as phase detectors. The phase detectors are associated with coils of the latter group, with a phase different from that of the AC reference signal respectively applied to a second group of coils and to the phase detectors of the first group of coils.

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Yokohama, Japan

Hideya Tanabe