JPH08178900A - Leakage flux type flaw detector - Google Patents

Abstract

PURPOSE: To provide a leakage flux type flaw detector which detects defects in the end part of a plate. CONSTITUTION: When a leakage magnetic flux from a plate material S magnetized by an excitation yoke 2 is detected by a probe 5 scanning in parallel to the surface of the plate, one magnetic pole 3b of the excitation yoke 2 is arranged adjacently to the end face of the plate material S via a predetermined gap (h), and the other magnetic pole 3a is disposed adjacently to the surface of the plate material S via a predetermined gap (g). The probe 5 is turned within a plane parallel to the surface of the plate to scan up to the side face of the magnetic pole 3b on the end face of the plate material. Accordingly, defects can be detected irrespective of the direction of the defective part up to a position very close to the end part of the plate.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a leakage magnetic flux flaw detector, and more particularly to a leakage flux flaw detector suitable for detecting edge seams and dents generated at the end of a plate surface.

[0002]

2. Description of the Related Art Conventionally, ultrasonic flaw detection, eddy current flaw detection, optical flaw detection and the like have been used as highly efficient surface flaw detection methods for plate materials. A comparison of these performances is as follows. Ultrasonic flaw detection method: It is based on surface waves using a tire probe, but the SN ratio is low, defects only up to a depth of about 0.3 mm can be detected, and a dead zone of about 20 mm remains at the plate edge. Eddy current flaw detection method: Defects up to a depth of 0.2 mm can be detected,
There is almost no edge dead zone, but the influence of the material is large,
The scale peeling part becomes noise. Optical flaw detection method: Cracks under the black skin cannot be detected in principle.

As described above, each method has advantages and disadvantages. Therefore, as an alternative method, the magnetic flux leakage flaw detection method can detect defects with a depth of about 0.2 mm, has high detection sensitivity, is not easily affected by the material and surface condition, and can also obtain defect depth information. Therefore, it is considered to be suitable for surface flaw detection of plate materials. Here, the leakage magnetic flux flaw detection method will be described with reference to, for example, a magnetic flaw detection device proposed in Japanese Patent Laid-Open No. 5-312786, as shown in FIG. 8, the flaw detection unit 21 has a gap K at the bottom. A magnetic field generating section (hereinafter, simply referred to as an excitation yoke) 24 of an electromagnet including a U-shaped core 22 and a coil 23, and a leakage magnetic detection section (hereinafter, simply referred to as a probe) that incorporates a magnetic flux density sensor such as a Hall element. ) 25 and.

By bringing the magnetic poles 22a and 22b of the core 22 close to the plate material S by the gap g, the magnetic flux starting from the magnetic pole 22a forms a magnetic circuit which reaches the other magnetic pole 22b via the plate material S, If S has surface scratches such as pinholes, gouges, and oblique holes, and internal scratches such as non-metallic inclusions and blowholes, the magnetic flux leaks out of the plate S from these defective portions, and the leaked magnetic flux is detected by the probe 24. Detect with.
As a result, it is possible to detect a defective portion such as a surface scratch or an internal scratch on the plate material S.

[0005]

As described above, the leakage magnetic flux flaw detection method has features not found in the ultrasonic flaw detection method, the eddy current flaw detection method, and the optical flaw detection method. If we try to apply it, in a conventional device for a flat surface,
Due to the structural restrictions of the excitation yoke 24, the dead zone at the plate edge is 50 mm.
Since it becomes the above, it is insufficient for the inspection of the plate edge.

[0006] It is an object of the present invention to provide a defect detecting device at the edge of a plate which solves the problems of the prior art as described above.

[0007]

According to a first aspect of the present invention, there is provided an apparatus for detecting a leakage magnetic flux of a material to be inspected magnetized by an exciting yoke by a probe which scans in parallel with a flaw detection surface.
A leakage magnetic flux flaw detector according to claim 1, wherein one magnetic pole of the exciting yoke is arranged close to an end surface of a material to be inspected with a predetermined gap, and the other magnetic pole is arranged close to a flaw detection surface with a predetermined gap. .

Further, the invention of claim 2 is provided with a swivel mechanism for swiveling the probe in a plane parallel to the flaw detection surface and scanning up to the side surface of one of the magnetic poles of the exciting yoke disposed on the end surface of the material to be inspected. It is characterized by that.

[0009]

According to the invention of claim 1, one magnetic pole of the excitation yoke is abutted against the end surface of the plate material, and the other magnetic pole is aligned with the surface of the plate material. Can be formed, and by this, it is possible to detect flaws up to the vicinity of the plate edge.

According to the second aspect of the invention, the swivel mechanism swivels the probe in a plane parallel to the plate surface,
Since scanning is performed up to the side surface of one of the magnetic poles of the excitation yoke arranged on the end surface of the plate material, flaw detection can be performed up to the vicinity of the plate end regardless of the orientation of the defective portion.

[0011]

Embodiments of the present invention will be described in detail below with reference to the drawings. FIG. 1 is a schematic diagram showing the configuration of an embodiment of the present invention. In the figure, reference numeral 1 is a flaw detection head for detecting a plate end portion of the present invention, and 2 is an exciting yoke in which coils 4a and 4b are wound around magnetic poles 3a and 3b of a core 3. A probe 5 is attached to the rotating disk 6. 7 is a rotary shaft that rotates the rotary disk 6 parallel to the surface of the plate S, 8 is a pulley attached to the other end of the rotary shaft 7, 9 is a drive motor,
10 is a pulley attached to the rotating shaft 9a of the drive motor 9,
Reference numeral 11 is a V-belt wound around the pulley 8 and the pulley 10.
12 is a slip ring attached to the end of the rotary shaft 7,
The signal detected by the probe 5 is output to an external flaw detector (not shown). The thickness of the magnetic pole 3b in the height direction is substantially the same as the plate thickness of the plate S, and the side surface on the probe side is located at the same height as the flaw detection surface of the plate S or is slightly sunk. It

In the flaw detection head 1 constructed as described above, one magnetic pole 3a of the core 3 faces the surface of the plate S with a gap g, and the other magnetic pole 3b has a gap h on the side end surface of the plate S. It is arranged so as to face each other. When an exciting signal having a predetermined frequency is applied to the coils 4a and 4b to excite the core 3, a uniform magnetic field is applied to the plate material S sandwiched between the magnetic pole 3a which is the N pole and the magnetic pole 3b which is the S pole. appear.

When this is shown in a plan view, as shown in FIG. 2, the angle θ formed by the two points a and b where the locus R of the probe 5 crosses the edge ridge M of the plate S and the center position O is defined. 90 °
The center position O of the excitation yoke 2 is positioned so that As a result, in the plate end region, the probe 5 can perform two scans in a direction substantially orthogonal to each other.

That is, the probe 5 scans while drawing a spiral locus R as shown in FIG. 3. If, for example, there is a defective portion at the point P, the probe 5 is 1 for this defective portion. In the second time, scanning is performed from the arrow c side, and in the second time, scanning is performed from the arrow d side. by this,
Even if a probe having a strong directivity is used, it is possible to detect the defect portion in any direction.

The angle θ related to the locus of the probe 5
Is practically no problem even if it deviates a little from 90 °.
There is no significant difference in detectability within the range of 60 to 120 °. In this way, the plate material S is held while maintaining the posture of the flaw detection head 1.
Scanning while traveling along the edge of the plate S, or by traveling the plate S while the flaw detection head 1 is stationary, it is possible to perform flaw detection of defects on the surface or the inner surface of the plate S over the entire length. You can

Now, the examination result of the magnetic flux density distribution of the exciting yoke 2 will be described. The width W shown in FIG. 4; 300 mm × length L; 500 mm × plate thickness t; a plate material S having a thickness of 18 mm, a gap g between the plate surface and the magnetic pole 3a and a gap h between the plate end face and the magnetic pole 3b are set to 3 mm, and the opening is formed. Dimension T × U is 210 × 30
The flaw detection head 1 of 0 (mm ² ) was set at a position where the distance Y was 50 mm from the end in the width direction.

The excitation conditions for the flaw detection head 1 used in this experiment were as follows: test frequency: 8 kHz, excitation voltage: 300 V, excitation current: 6.2 A, resonance current: 17.5 A (maximum value), number of coil windings: 40 T , Magnetic field strength; 248 AT. FIG. 5 shows the result of measuring the magnetic flux densities in the gaps g and h from the point C to the point D over the entire width of the exciting yoke 2 at this time.
In this figure, ● indicates the magnetic pole 3a side (g), and ◆ indicates the magnetic pole 3b side (h). In addition, when the plate S is not provided, the side of the magnetic pole 3a is indicated by a circle, and the side of the magnetic pole 3b is indicated by a diamond.

From this figure, when there is a plate material S, the magnetic pole 3
It can be seen that a sufficiently high magnetic flux density can be obtained although the magnetic flux density changes depending on the measurement position because the gap between a and 3b and the plate material S slightly changes. Further, it can be seen that when the plate material S is not present, uniform magnetic flux densities are formed on the magnetic pole 3a side and the magnetic pole 3b side, and the magnetic field of the excitation yoke 2 itself is uniform.

As a result, since the inside of the plate material S located at the gaps g and h between the magnetic poles 3a and 3b is a ferromagnetic material, the magnetic flux density is equal to or higher than that measured at the gaps g and h. It is clear that the magnetic field is sufficient and uniform for flaw detection. In addition, practically, the width 210 of the excitation yoke 2 in which a particularly uniform magnetic flux density is formed.
It is advisable to set the width within 110 mm within 110 mm as the evaluation area.

Next, at a position 5 mm from the edge of the plate, a depth of 0.3
mm × width 0.2 mm × length 10 mm is provided with an artificial defect having a direction orthogonal to the ridgeline of the plate end, and the gap g between the magnetic pole 3a and the plate S is changed to reduce the SN ratio of background noise and defect signal. It was measured. The results are shown in Fig. 6. In this exciting yoke 2, it can be seen that even if the gap g is increased to about 10 mm, there is almost no effect on the detection sensitivity to defects. The fact that the gap g can be widened in this way can be said to be advantageous from the viewpoint of preventing collision with a material to be measured such as steel material.

An artificial defect having a depth of 0.3 mm, a width of 0.2 mm, and a length of 10 mm and having a direction orthogonal to the ridgeline of the plate end portion is removed from the plate end portion.
The test materials provided at the positions of 10 mm and 5 mm were manufactured, and the flaw detection was performed using the flaw detection head 1 of the present invention. The excitation condition of the flaw detection head 1 is the same as that in the case of FIG. 4 described above, and a low-pass filter of 1 kHz and a high-pass filter of 40 kHz are used. The result of the leakage magnetic flux density is shown in FIG.
They are shown in (a) and (b) respectively. As can be seen from the figure, the defect portion of 5 to 10 mm from the plate edge can be detected when the SN ratio is 2 or more. Therefore, according to the device of the present invention, the dead zone can be reduced to 5 to 10 mm from the edge of the plate.

Regarding the relationship between the directionality of the defect and the probe 5 in the above embodiment, the directional characteristics depending on the type, shape and size of the probe 5 to be used and the characteristics and detection limit of the target defect are combined. The use of the probe 5 and the scanning method may be appropriately determined. Further, although the probe 5 is swung in the above embodiment, the present invention is not limited to this, and instead of the swivel probe, a wide brush type probe in which a plurality of sensors are arrayed is used. Alternatively, even if the one equipped with the same one probe as in the prior art is configured to reciprocally scan at the end, it is possible to provide the detectability close to that of the turning method.

Further, in this embodiment, the flaw detection of the end portion of the plate material is described, but the present apparatus can be applied to the test material of other shapes as long as it is the side edge of the flat flaw detection surface such as a strip material. It is possible.

[0024]

As described above, according to the present invention,
By arranging one of the magnetic poles of the excitation yoke along the end surface of the plate material to be inspected with a predetermined gap, the undetected area at the plate end can be minimized, so that, for example, cracks under the black skin that are difficult to visually inspect. It is possible to detect defective parts such as, and improve the quality assurance of the product, and it is possible to perform the optimum cutting, which contributes to the improvement of the yield. In addition, the inspection cost can be reduced because manual inspection is not required.

[Brief description of drawings]

FIG. 1 is a schematic diagram showing the configuration of an embodiment of the present invention.

FIG. 2 is a sectional view taken along the line AA of FIG.

FIG. 3 is an explanatory diagram of a scanning locus of a probe.

FIG. 4 is a perspective view of an experimental device for measuring a magnetic flux density distribution of an exciting yoke.

FIG. 5 is a graph showing a measurement example of the magnetic flux density in the width direction of the exciting yoke.

FIG. 6 is a characteristic diagram showing the relationship between the gap of the magnetic pole 3a and the detection sensitivity.

7 (a) and 7 (b) are characteristic diagrams showing a measurement state of a leakage magnetic flux density at the time of detecting an artificial defect at a plate end portion.

FIG. 8 is a schematic diagram showing a conventional example of a leakage magnetic flux flaw detector.

[Explanation of symbols]

 1 flaw detection head 2 excitation yoke 3 cores 3a, 3b magnetic poles 4a, 4b coil 5 probe 6 rotating disk (swing mechanism) 7 rotating shaft (swing mechanism) 8, 10 pulley (swing mechanism) 9 drive motor (swing mechanism) 11 V-belt (Swivel mechanism) 12 Slip ring S Plate material (test material) g, h Gap

Claims (2)

[Claims] 1. A device for detecting a leakage magnetic flux of a material to be inspected magnetized by an excitation yoke by a probe scanning in parallel to a flaw detection surface, wherein one magnetic pole of the excitation yoke is provided at a predetermined gap on an end surface of the material to be inspected. And the other magnetic pole is disposed close to the flaw detection surface with a predetermined gap. 2. A swirl mechanism for swiveling the probe in a plane parallel to the flaw detection surface and scanning up to the side surface of one of the magnetic poles of the exciting yoke disposed on the end surface of the material to be inspected. Item 3. The leakage magnetic flux flaw detector according to Item 1.