JPH1114600A - Eddy current flaw-detecting device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To reduce the scattering in flaw detection sensitivity by arranging a plurality of pairs of an excitation coil and a detection coil on the end face of a core body that opposes a body whose flaw is to be detected and making different the polarities of adjacent excitation coils each other. SOLUTION: Three excitation coils 2 are provided in three rows while shifting each position in the longitudinal direction on a lower surface that opposes the steel plate of a ferrite core body 1 in a rectangular block shape. Detection coils 3A-3C consisting of a pair of coil parts 31 and 32 are provided directly below the excitation coils 2. The excitation coils 2 and the detection coils 3A-3C are formed and laminated spirally on an insulation film substrate by printed wiring and the polarities of the adjacent excitation coils 2 differ. As a result, an eddy current being generated in a steel plate due to the excitation coils 2 draws eddies in opposite directions directly below each excitation coil 2. Therefore, a flaw detection sensitivity becomes nearly equal in any of the detection coils 3A-3C, thus eliminating the scattering in the flaw detection sensitivity.

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 a multi-channel flaw detector for preventing variations in flaw detection sensitivity.

[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 detection devices, a so-called multi-channel flaw detection device in which a plurality of detection coils are arranged in the width direction of a steel plate or the like in order to efficiently perform flaw detection in a width direction of a conveyed steel plate or the like is known. . An example is shown in FIG. 6. An exciting coil 4 is wound around the outer periphery of a ferrite core body 1 having a rectangular block shape, and a plurality of (in FIG. 3) detection coils 3
Are provided in a line. Each detection coil 3 is formed on an insulating film substrate (not shown) by known printed wiring.

[0003]

According to an experiment conducted by the inventor, in the above-described conventional eddy current flaw detection apparatus, the eddy current E generated in the steel plate P is, as shown in FIG. It flows strongly in the opposed steel plate region, and hardly flows in the steel plate region facing the inner peripheral portion of the lower surface of the core body 1. Therefore, in the case of FIG. 6, the detection coils 3 provided at the left and right ends of the lower surface of the core body 1 can obtain sufficient flaw detection sensitivity, but the detection coil 3 provided at the center does not have sufficient flaw detection sensitivity. This is clear from the magnetic flux distribution just below the core body 1 shown in FIG. 7, and the magnetic flux density is small at a lower position corresponding to the inner peripheral portion of the lower surface of the core body 1. Note that the magnetic flux density in FIG. 7 is shown as a relative value with its maximum value being 1.00.

Therefore, as shown in FIG. 8, for example, a plurality of core members 1 are provided in the width direction of the steel plate, and an excitation coil 5 and a detection coil 6 are formed on the lower surface of each core member 1 by printed wiring, respectively. By sequentially switching the energization to each excitation coil 5 to avoid interference with each other, each core 1
It is conceivable that an independent eddy current is generated in the steel plate immediately below the steel sheet. According to this, the variation in the flaw detection sensitivity between the detection coils 6 can be suppressed to some extent. However, since the switching circuit needs to be provided, the energization system becomes complicated, and if the installation position of each core body 1 is shifted up and down, Again, there is a possibility that a large variation occurs in the flaw detection sensitivity.

The present invention solves such a problem, and an eddy current flaw detection apparatus capable of effectively suppressing a variation in flaw detection sensitivity among a plurality of detection coils without complicating a current supply system to an excitation coil. The purpose is to provide.

[0006]

In order to achieve the above object, according to the first aspect of the present 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) is generated. Detection coil (3) according to the change of the eddy current (E)
A to 3C) In an eddy current flaw detection device for detecting the presence of a flaw based on a voltage change, a core body (1) facing a body to be flawed (P)
Excitation coil (2) and detection coil (3A to 3A)
A plurality of pairs C) are arranged, and the polarities of the adjacent exciting coils (2) are alternately changed. The pair of the excitation coil and the detection coil may be laminated by printed wiring or the like, or may be formed by forming a plurality of protrusions on the end surface of the core body and winding the coil wires of both coils in a superposed manner.

In the first aspect of the present invention, the polarities of the adjacent exciting coils are alternately made different, so that the eddy currents generated on the surface of the inspection object by these exciting coils have opposite current eddy directions. . As a result, the current directions of the adjacent eddy currents coincide with each other in the boundary area, and independent eddy currents of sufficient strength are generated on the surface of the test object directly below each excitation coil without weakening. This allows
Each detection coil paired with the excitation coil can detect a flaw with substantially the same and sufficient sensitivity, and the variation in flaw detection sensitivity between the detection coils is eliminated. According to the first invention,
Since all the excitation coils can be energized simultaneously,
It is not necessary to sequentially switch and energize the exciting coil as in the conventional case, and the circuit configuration of the energizing system is simplified.

According to the second aspect of the present invention, the density of the coil wire (21) of each exciting coil (2) is made dense at the coil outer periphery and sparse at the coil inner periphery. According to the second aspect of the present invention, since the magnetic flux density becomes uniform in a wide range in each excitation coil, the variation in the flaw detection sensitivity due to the position of the flaw in each detection coil paired with the excitation coil is eliminated.

In the third aspect of the present invention, the coil wire (21) of the exciting coil (2) is provided only on the outer periphery of the coil. In the third invention, the uniformity of the magnetic flux density is slightly inferior to that of the second invention, but the formation of the coil wire of the exciting coil becomes easier.

[0010]

BEST MODE FOR CARRYING OUT THE INVENTION

(First Embodiment) FIG. 1 is a perspective view of an eddy current flaw detector according to the present invention. In the figure, on the lower surface of a rectangular block-shaped ferrite core body 1 opposed to a steel plate P, three exciting coils 2 are provided in three rows shifted from each other in the longitudinal direction. FIG. 2 is a view of the lower surface of the core body 1 viewed from below. The detection coils 3 </ b> A to 3 </ b> A each including a pair of coil portions 31 and 32 are provided immediately below each excitation coil 2 (on the front side in the drawing).
3C is provided. The excitation coil 2 and the detection coils 3A to 3C are spirally formed by printed wiring on an insulating film substrate (not shown) by a known structure (concentrically drawn in FIGS. 1 and 2) and laminated. ing. Then, as shown by N and S in FIG. 2, the polarity of the adjacent ones of the exciting coils 2 is alternately changed. In order to make the polarities different, the spiral direction of the exciting coil 2 is reversed or power is supplied in the opposite direction. In addition,
In the present embodiment, the coil portions 31 and 32 of the detection coils 3A and 3B in the first and second rows are formed obliquely in directions different from each other by 90 ° in order to enable detection of flaws in all directions.

As described above, since the polarities of the adjacent exciting coils 2 are alternately changed, the eddy current E generated on the steel sheet P by each exciting coil 2 is, as shown in FIG. Eddies are drawn in the opposite directions immediately below the right side of the drawing (the figure shows only the eddy currents generated by the three exciting coils 2 in the frontmost row). These eddy currents do not weaken each other because their current directions coincide with each other in the boundary area, and the eddy currents immediately below the respective exciting coils 2 independently draw eddies having almost the same strength. Therefore, any of the detection coils 3A
3C, the flaw detection sensitivities are substantially the same, and variations in the flaw detection sensitivities among the plurality of detection coils 3A to 3C are eliminated.

Further, in this embodiment, as shown in FIG. 3A, in each of the exciting coils 2, a coil wire 21 is formed only on the outer peripheral portion of the coil. FIG. 3B shows the magnetic flux density measured by the exciting coil 2 measured on the line XX ′ crossing the coil immediately below the exciting coil 2. As is clear from the figure, the magnetic flux density has a sufficiently large value of substantially the same level over a wide range of the inner peripheral portion of the coil. As a result,
Since a uniform eddy current having a large density is generated on the steel plate P facing a wide range of the coil inner peripheral portion of the exciting coil 2, any position on the steel plate P immediately below each of the detection coils 3A to 3C is damaged. Even if there is, this can be detected with sufficient sensitivity. Therefore, in each of the detection coils 3A to 3C,
Variations in flaw detection sensitivity depending on the position of the flaw are also eliminated.

On the other hand, in the case where the coil wire 21 is formed over the entire area of the coil as in the conventional excitation coil 2 'shown in FIG. The magnetic flux density measured on the −Z ′ line is shown in FIG.
As shown in (B), the maximum value is shown at the center of the coil, and the value rapidly decreases toward the outer periphery. Therefore, the density of the eddy current generated on the steel plate P facing the inner peripheral portion of the exciting coil 2 'is not uniform,
If the scratches deviate from the center of each of the detection coils 3A to 3C, a sufficiently high detection sensitivity cannot be obtained.

As described above, in the present embodiment, it is possible to eliminate not only the variation in the flaw detection sensitivity between the detection coils but also the variation in the flaw detection sensitivity in each detection coil.

(Second Embodiment) Instead of forming the coil wire 21 of the exciting coil 2 only on the outer peripheral portion of the coil as in the first embodiment, as shown in FIG. Is formed sparsely in the inner peripheral portion and dense in the outer peripheral portion, the magnetic flux density measured on the YY ′ line crossing the coil immediately below the exciting coil 2 is shown in FIG. like,
It becomes even more uniform on the steel plate P facing a wide range of the inner peripheral portion of the exciting coil 2. As a result, a more uniform eddy current can be obtained.
The variation in the flaw detection sensitivity depending on the position of the flaw in C can be further reduced.

In the first embodiment, a description has been given of a case in which pairs of excitation coils and detection coils are provided in three rows with their positions shifted in the width direction. However, the arrangement is not particularly limited as long as the number of pairs is plural.

In each of the above embodiments, the configuration in which the coil wire of the exciting coil is formed only on the outer peripheral portion of the coil, or the configuration in which the coil wire is formed sparsely in the inner peripheral portion and dense in the outer peripheral portion, are as follows. Even when employed alone, a special effect is achieved.

[0018]

As described above, according to the eddy current flaw detection apparatus of the present invention, it is possible to effectively suppress the variation in the flaw detection sensitivity among a plurality of detection coils without having to switch the power supply to the excitation coil.

[Brief description of the drawings]

FIG. 1 is a perspective view of a core body of an eddy current testing device according to a first embodiment of the present invention.

FIG. 2 is a plan view of a lower surface of a core body.

FIG. 3 is a plan view of an exciting coil and a graph of its magnetic flux density distribution.

FIG. 4 is a plan view of an exciting coil and a graph of its magnetic flux density distribution in a second embodiment of the present invention.

FIG. 5 is a plan view of a conventional excitation coil and a graph of its magnetic flux density distribution.

FIG. 6 is a perspective view of a core body of a conventional eddy current testing device.

FIG. 7 is a three-dimensional graph showing a magnetic flux density distribution immediately below a core body of a conventional eddy current flaw detector.

FIG. 8 is an exploded perspective view of a core body of the conventional eddy current testing device.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Core body, 2 ... Exciting coil, 21 ... Coil wire, 3A,
3B, 3C: detection coil, E: eddy current, P: steel plate (object to be inspected).

Claims (3)

[Claims] An eddy current flaw detection device that generates an eddy current in a surface layer of a flaw-detected object by an excitation coil and detects the presence of the flaw based on a voltage change of a detection coil according to a change in the eddy current caused by a flaw on the surface of the flaw-detected body. An eddy current flaw detection device, wherein a plurality of pairs of excitation coils and detection coils are arranged on an end face of a core body facing a flaw detection target, and the polarities of adjacent excitation coils are alternately changed. 2. The eddy current flaw detection device according to claim 1, wherein the density of the coil wire of each excitation coil is made dense at the coil outer periphery and sparse at the coil inner periphery. 3. The eddy current flaw detector according to claim 1, wherein the coil wire of the exciting coil is provided only on the outer peripheral portion of the coil.