JPH10282065A - Eddy current flaw detector - Google Patents

Abstract

PROBLEM TO BE SOLVED: To detect a linear flaw occurring on the surface of an object, e.g. a steel plate, with high sensitivity by arranging a plurality of rows of detection coils while shifting in the direction orthogonal to the relative moving direction of the object. SOLUTION: Detection coils 3A-3C are formed of a printed wiring on an insulating film substrate 33. Each detection coil comprises a pair of spiral coil parts 31, 32 of identical shape and the detection coils are arranged in three rows in the moving direction of a steel plate. Detection coils in each row are arranged while being shifted by one third of the width of coil part 31 or 32 in the breadthwise direction of the steel plate. Consequently, the combined detection sensitivity of these detection coils 3A-3C is represented by the uppermost line of the sensitivity curves of respective detection coils and it is sustained at a sufficiently high level in the breadthwise direction of the steel plate without dropping significantly. Consequently, a linear flaw extending in the longitudinal direction of the steel plate can be detected accurately regardless of the passing direction thereof through an eddy current flaw detector in the breadthwise direction of the steel plate.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an eddy current flaw detector, and more particularly to an improvement in the arrangement of detection coils in a multi-channel flaw detector.

[0002]

2. Description of the Related Art An eddy current flaw detector uses an exciting coil to generate an eddy current on a surface layer of a steel plate or the like, which is a member to be inspected. It detects the presence of a linear scratch or the like. Among such eddy current flaw detectors, a so-called multi-channel type flaw detector in which a plurality of detection coils are arranged in the width direction of a steel plate or the like in order to simultaneously and efficiently perform flaw detection in the width direction of a conveyed steel plate or the like is known. FIG. 6 shows an example.

In FIG. 1, a rectangular parallelepiped ferrite core 1 having substantially the same width as the steel sheet P is disposed immediately above a steel sheet P moving in a direction perpendicular to the paper surface.
Is wound. On the lower surface of the ferrite core 1 facing the surface of the steel sheet P, a number of detection coils 3 are provided in a row in the width direction (W direction) of the steel sheet P. Each detection coil 3
Is formed on the insulating film substrate 33 by known printed wiring, and details of the shape of the detection coil 3 are shown in FIG.
It is shown in (B). The detection coil 3 is formed in a rectangular spiral shape in plan view as shown in the figure, and each detection coil 3 is constituted by a pair of coil portions 31 and 32 having opposite spiral directions in order to obtain a differential output. ing.

[0004]

In such a conventional eddy current flaw detection apparatus, the detection sensitivity of the detection coil 3 for flaws along the moving direction (longitudinal direction) of the steel sheet P is as shown in FIG. Becomes As is clear from the figure, since the detection sensitivity is 0 at the boundary between each detection coil 3 or each of the coil portions 31 and 32, a flaw passing near this boundary may not be detected. In addition to the scratches extending in the longitudinal direction of the surface of the steel sheet P, there are also scratches extending at an angle to the longitudinal direction of the steel sheet or extending in a direction perpendicular to the longitudinal direction. Therefore, the detection sensitivity of the conventional detection coil is not sufficient.

Accordingly, the present invention is to solve such a problem, and to provide an eddy current flaw detection apparatus capable of detecting a linear flaw or the like generated on the surface of a flaw detection target such as a steel plate with high sensitivity. With the goal.

[0006]

In order to achieve the above object, in the first invention, an eddy current is generated in the surface layer of the test object (P) by the exciting coil (2), and the surface of the test object (P) has an eddy current. Detection coils (3A to 3A) corresponding to changes in eddy current
In the eddy current flaw detector which detects the presence of the flaw from the voltage change of C), the detection coils (3A to 3C) are arranged in a plurality of rows in the relative movement direction of the flaw-detected body (P), and the detection coils (3A to 3C) are arranged. To 3C) are shifted from each other in a direction orthogonal to the relative movement direction of the test object (P). In this case, the shift amount for each column is preferably a distance obtained by dividing the width of the detection coil by the number of columns. In addition, the width dimension of the detection coil is the width dimension of each coil section when the detection coil is configured by a pair of coil sections to obtain a differential output.

In the first aspect of the present invention, the detection coils are provided in a plurality of rows and are shifted from each other in a direction orthogonal to the relative movement direction of the flaw-detected body. Therefore, even if the flaw extending in the relative movement direction of the test object passes near the boundary where the detection sensitivity of one row of detection coils or coil portions is close to 0, the detection coil or coil portion of another row has
Since the light passes through a portion having sufficient detection sensitivity other than the vicinity of the boundary, the combined detection sensitivity of the entire eddy current flaw detection device is in a direction (width direction) orthogonal to the relative movement direction of the test object.
It becomes sufficiently high at any of the positions. Thereby, even if the above-mentioned flaw occurs at any position in the width direction of the flaw-detected body, this can be reliably detected. If the shift amount for each column is a distance obtained by dividing the width of the detection coil by the number of columns,
The difference between the maximum value and the minimum value of the combined detection sensitivity can be minimized.

In the second invention, the number of columns is three.
In this way, the combined detection sensitivity of the entire eddy current flaw detector can be maintained sufficiently high at any position in the width direction of the flaw-detected body while reducing the number of detection coils and reducing the cost. Is possible.

According to the third aspect of the present invention, the detection coils (3A to 3C) are arranged in a plurality of rows in the relative movement direction of the test object, and the detection object (P) of the detection coils (3A to 3C) is arranged.
The angle (θ) with respect to the relative movement direction is changed for each row.

In the third aspect of the present invention, the detection coils are provided in a plurality of rows, and the angle of the detection coils with respect to the direction of relative movement of the test object is changed for each row. Therefore,
Scratches extending at a certain angle with respect to the relative movement direction of the test object, even if the detection sensitivity is reduced in one row of detection coils in accordance with the installation angle, but in other rows of detection coils, Since the angle of the flaw of the flaw-detected body is different from the installation angle of the detection coil, sufficient detection sensitivity can be obtained. As a result, the combined detection sensitivity of the entire eddy current flaw detection device is sufficiently high even if the flaws on the flaw-detected object extend in any angle direction with respect to the relative movement direction of the flaw-detected body. It can be detected reliably.

In the fourth invention, the detection coils (3A to 3A)
3C) has three rows, and the detection coils (3A to 3
The angles of C) with respect to the direction of relative movement of the flaw-detected body (P) are set to three types: 45 °, 90 °, and 135 °. In this way, the combined detection sensitivity of the entire eddy current flaw detector can be reduced to a flaw extending at an angle with respect to the relative movement direction of the flaw-detected body, while reducing the number of detection coils and reducing the cost. On the other hand, it can be kept sufficiently high.

[0012]

BEST MODE FOR CARRYING OUT THE INVENTION

(First Embodiment) FIG. 1 shows an arrangement of detection coils of an eddy current flaw detector. The detection coils 3A to 3C are formed by printed wiring on an insulating film substrate 33 provided on the lower surface of the ferrite core 1 (FIG. 6), as already described in the conventional example. Each of the detection coils 3A to 3C has a pair of the same-shaped coil portions 31, which have a rectangular spiral shape and have the spiral direction opposite to each other.
32, and are arranged in three rows before and after the moving direction of the steel sheet P (FIG. 6) (the longitudinal direction of the steel sheet P, indicated by arrows in FIG. 1). The detection coils 3 </ b> A to 3 </ b> C in the front and rear rows are mutually connected to each other by the width of the coil part 31 (or the coil part 32).
The position is shifted by / 3 in the width direction of the steel sheet.

FIG. 2A shows the detection sensitivity when linear scratches extending in the longitudinal direction of the steel sheet P are detected by the detection coils 3A to 3C in each row. Also, in FIG. 2 (B),
The plane arrangement of the detection coils 3A to 3C in the region surrounded by the chain line in FIG. 1 is shown again in correspondence with the above detection sensitivity. Note that FIG.
The shapes of the detection coils 3A to 3C in (B) are horizontally long for easy understanding. In FIG. 2, the detection sensitivity curves of the detection coils 3A to 3C in each row are indicated by broken lines in FIG.
As indicated by the alternate long and short dash lines, each of the coil portions 31 and 3
2 is a repetitive waveform which becomes minimum at the left and right end positions and becomes maximum at an intermediate position between them. Here, in the present embodiment, as described above, the detection coils 3A to 3A
C and the steel sheet P each having a width of 1/3 of the width of the coil portion 31.
In the width direction W. Accordingly, the combined detection sensitivities of these detection coils 3A to 3C are obtained by connecting the top lines of the sensitivity curves of the detection coils 3A to 3C,
The steel sheet P is maintained at a sufficient height in the width direction W, and does not significantly decrease. Accordingly, even if a linear scratch extending in the longitudinal direction of the steel sheet P passes through the eddy current flaw detector at any position in the width direction W of the steel sheet P, it can be reliably detected.

(Second Embodiment) FIG. 3 shows another example of the arrangement of the detection coils of the eddy current flaw detector. As shown in the figure, the three rows of detection coils 3A to 3C in the present embodiment
In the row position (uppermost position in the figure), a pair of coil portions 31 and 3
2 is provided at an angle of 45 ° to the left with respect to the moving direction (arrow in FIG. 3) of the steel plate P (FIG. 6). Also, the second
At the row position, the pair of coil portions 31 and 32 are provided at an angle of 45 ° to the right with respect to the moving direction of the steel sheet P,
At the third row position, the pair of coil portions 31 and 32 are provided in the direction orthogonal to the moving direction (longitudinal direction L) of the steel sheet, that is, in the width direction W of the steel sheet, as in the first embodiment. Each of the three rows of detection coils 3A to 3C is further shifted in position in the width direction W of the steel plate P by １ ／ of the width of the coil portion 31.

A detection coil 3A for detecting a linear flaw extending in the longitudinal direction L of the steel sheet P with such an eddy current flaw detector.
3C are the same as those in the first embodiment because the three rows of detection coils 3A to 3C are provided at different positions in the width direction W of the steel sheet P as described above. Next, each detection coil 3A shown in FIG.
The top line of the sensitivity curve of ~ 3C is connected. In addition,
FIG. 4B shows the detection coil 3A in a region surrounded by a chain line in FIG.
3C is again shown in correspondence with the above-described detection sensitivity, and the shapes of the detection coils 3A to 3C are horizontally long for easy understanding. As described above, since the detection sensitivity of the eddy current flaw detector is maintained at a sufficient height in the width direction W of the steel sheet P, a linear flaw extending in the longitudinal direction L of the steel sheet P is detected at any position in the width direction W of the steel sheet P. Even if it passes through the eddy current flaw detector with
This can be reliably detected.

In this embodiment, linear scratches extending in a direction other than the longitudinal direction L of the steel sheet P can be detected with good sensitivity. For example, the width direction W of the steel sheet P, that is,
For a linear scratch extending in the direction in which the angle θ with respect to the steel plate longitudinal direction L is 90 ° in FIG.
In this case, no differential output is produced, so that the detection sensitivity becomes 0 as shown by the two-dot chain line in FIG. On the other hand, the longitudinal direction L of the steel sheet P
In contrast, the detection coils 3A and 3B in the first and second rows, which are provided at angles of 135 ° and 45 °, respectively, extend in the width direction W of the steel plate P and have linear scratches at an angle θ of 90 °. On the other hand, it has sufficient detection sensitivity as shown by a broken line or a dashed line in FIG. Then, the angle θ is changed from 0 ° to 180 °.
5, the detection coils 3 </ b> A to 3 </ b> C in the first to third rows have detection sensitivities indicated by broken lines, dashed lines, and dashed lines in FIG. 5, respectively. The sensitivity is obtained by connecting the top lines of the respective detection sensitivity curves. Therefore, it has sufficient detection sensitivity even for a linear flaw extending at an angle other than 0 °, that is, at an angle to the longitudinal direction L of the steel sheet P. In this manner, the eddy current flaw detection device of the present embodiment can reliably detect the presence of a linear flaw on the steel plate P regardless of the direction in which it extends.

(Other Embodiments) In the above-described first embodiment, the steel plate as the flaw-detected body is moved with respect to the detection coil. However, the detection coil may be moved with the steel plate fixed. In the second embodiment, the detection coils in the front and rear rows are provided to be shifted from each other in the width direction of the steel sheet as in the first embodiment. In the case where it is inclined, it is not always necessary to displace it in the width direction. Further, the arrangement angle of the detection coils in each row can be appropriately changed depending on the tendency of a scratch actually generated on the steel plate, and the number of rows is not limited to three. It is needless to say that the number of detection coils in each row can be appropriately increased or decreased according to the flaw detection range such as the width of the steel plate. In each of the above embodiments, the shape of the coil portion of the detection coil is a rectangular spiral, but may be a circular spiral or the like.

[0018]

As described above, according to the eddy current flaw detector of the present invention, linear flaws extending in any direction at any position on the surface of a flaw-detected body such as a steel plate can be reliably detected with high sensitivity. be able to.

[Brief description of the drawings]

FIG. 1 is a plan view showing an arrangement of detection coils according to a first embodiment of the present invention.

FIG. 2 is a diagram showing the correspondence between the arrangement of detection coils and detection sensitivity.

FIG. 3 is a plan view showing an arrangement of detection coils according to a second embodiment of the present invention.

FIG. 4 is a diagram showing a correspondence between arrangement of detection coils and detection sensitivity.

FIG. 5 is a detection sensitivity graph of a detection coil.

FIG. 6 is a side view showing an example of the eddy current flaw detector.

FIG. 7 is a plan view showing an arrangement of a conventional detection coil.

[Explanation of symbols]

1: Ferrite core, 2: Excitation coil, 3, 3A, 3
B, 3C: detection coil; 31, 32: coil part; P: steel plate (object to be inspected).

────────────────────────────────────────────────── ───

[Procedure amendment]

[Submission date] June 19, 1997

[Procedure amendment 1]

[Document name to be amended] Statement

[Correction target item name] Claim 3

[Correction method] Change

[Correction contents]

Claims (4)

[Claims] 1. An eddy current flaw detection device for generating an eddy current in a surface layer of a test object by an excitation coil, and detecting the presence of the flaw based on a voltage change of a detection coil according to a change in the eddy current due to a flaw on the surface of the test object. The detection coils are arranged in a plurality of rows in the relative movement direction of the test piece, and the detection coils are arranged so as to be shifted for each row in a direction orthogonal to the relative movement direction of the test piece. Eddy current flaw detector. 2. The eddy current flaw detector according to claim 1, wherein the number of rows is three. 3. An eddy current flaw detection device for generating an eddy current on a surface layer of a test object by an excitation coil and detecting the presence of a flaw based on a voltage change of a detection coil corresponding to a change of the eddy current due to a flaw on the surface of the test object. 2. The apparatus according to claim 1, wherein the detection coils are arranged in a plurality of rows in a relative movement direction of the test object, and an angle of the detection coil with respect to a relative movement direction of the test object is changed for each row. An eddy current flaw detector as described. 4. The method according to claim 1, wherein the number of rows of the detection coils is three, and the angles of the detection coils in each row with respect to the relative movement direction of the object to be detected are set to three types of 45 °, 90 °, and 135 °. The eddy current flaw detector according to claim 3, wherein