Apparatus for magnetic inspection using magnetic shield

Electricity: measuring and testing – Magnetic – With means to create magnetic field to test material

Patent

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Details

324225, 324262, G01N 2783, G01R 3312

Patent

active

053571983

DESCRIPTION:

BRIEF SUMMARY
Technical Field

The present invention relates to a magnetic inspection method and a magnetic inspection apparatus wherein a magnetic field is generated by a magnetizer in a to-be-inspected object formed of a magnetic material such as steel plate and a leakage magnetic flux due to a defect on the object is detected by a magnetic sensor.


BACKGROUND ART

A magnetic inspection apparatus detects, by utilizing magnetism, defects such as internal and surface flaws and inclusion in a thin steel strip or a to-be-inspected object. It was reported that a magnetic inspection apparatus, in which a magnetic sensor array comprising linearly arranged magnetic sensors for detecting magnetic fluxes is built, is capable of successively detecting defects on a running thin steel strip over the entire width thereof (Published Unexamined Japanese Utility Model Application (PUJUMA No. 63-107849).
FIGS. 39 and 40 are schematic cross-sectional views showing, in different directions, the above-mentioned magnetic inspection apparatus for successively detecting the defects on the running thin steel strip. FIG. 41 is a side view showing the state in which the magnetic inspection apparatus is built in a support apparatus.
Referring to FIG. 41, a horizontal arm 12 is supported by a pair of spring members 13a and 13b within a frame 11 set on the floor of a room. Accordingly, the arm 12 is vertically movable. A stationary shaft 2 of the magnetic inspection apparatus is fixed at the center of the arm 12. A pair of guide rolls 14a and 14b for guiding a thin steel strip 10 on the outer peripheral surface of a hollow roll 1 are arranged on both sides of the frame 11.
In FIGS. 39 and 40, one end portion of the stationary shaft 2 penetrates the hollow roll 1 of a non-magnetic material along the center axis of the roll 1. The other end portion of the shaft 2 is fixed on the horizontal arm 12. The stationary shaft 2 is supported on the inner peripheral surfaces of both end portions of the hollow roll 1 by a pair of rolling bearings 3a and 3b such that the shaft 2 is situated along the center axis of the hollow roll 1. Accordingly, the hollow roll 1 is freely rotatable about the stationary shaft 2.
A magnetizing core 4c having a substantially U-cross section is fixed to the stationary shaft 2 by means of a support member 5 within the hollow roll 1, such that magnetic poles 4a and 4b of the core 4c are situated close to the inner peripheral surface of the hollow roll 1. A magnetizing coil 6 is wound around the magnetizing core 4c. Thus, the magnetizing core 4c and magnetizing coil 6 constitute a magnetizer 4. A magnetic sensor array 7 consisting of magnetic sensors 7a arranged linearly along the axis of the hollow roll 1 is fixed to the stationary shaft 2 between the magnetic poles 4a and 4b of the magnetizing core 4c.
A power cable 8 for supplying an excitation current to the magnetizing coil 6 and a signal cable 9 for taking out output signals from the magnetic sensors 7a of the magnetic sensor array 7 are led to the outside through the inside passage of the stationary shaft 2. Accordingly, the positions of the magnetizer 4 and magnetic sensor array 7 are fixed, and the hollow roll 1 rotates around the magnetizer 4 and magnetic sensor array 7 with a small gap.
when the outer peripheral surface of the hollow roll 1 of the magnetic inspection apparatus with the above structure is pressed on one side surface of the thin steel strip 10 under a predetermined pressure which runs, for example, in a direction a, the hollow roll 1 rotates in a direction b since the stationary shaft 2 is fixed on the horizontal arm 12.
In the above magnetic inspection apparatus, when an excitation current is supplied to the magnetizing coil 6, a closed magnetic path is formed by the magnetic poles 4a and 4b of the magnetizing core 4c and the running thin steel strip 10. If there is an internal or surface defect of the thin steel strip, the magnetic path in the thin steel strip is disturbed and a leakage magnetic flux occurs. The leakage magnetic flux is detected by the m

REFERENCES:
patent: 5021738 (1991-06-01), Vernon et al.
patent: 5089776 (1992-02-01), Furukawa et al.

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