JP3268219B2 - Eddy current detector - Google Patents

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 for detecting an abnormality such as a defect by exciting an eddy current in an object to check the soundness of the object such as a metal plate.

[0002]

2. Description of the Related Art Generally, an eddy current flaw detector is used to determine the presence or absence of a defect in a metal body such as a metal flat plate and to confirm its soundness. As shown in FIG. 4, a conventional eddy current flaw detector includes an excitation coil 101, a detection coil 102,
Flaw detector 100 composed of magnetic core 103 and display screen 1
The flaw detector 120 includes the flaw detector 100 and the flaw detector 120 connected by a connection cable 130. Note that the magnetic core 103 is used to increase the detection sensitivity.
It is formed of a ferromagnetic material that easily passes a magnetic field.

Reference numeral 110 denotes an object made of a metal body such as a metal plate; 111, a surface defect in the object 110; 131, a magnetic field generated by the exciting coil 101;
An eddy current 133 excited in the subject 110 by the magnetic field 131 generated by the reference numeral 1 is a magnetic field generated by the eddy current 132.

Referring to FIG. 5, which shows an electrical connection state of the eddy current flaw detector, an exciting coil 101 is
An alternating current having a constant magnitude (amplitude) and a constant frequency is supplied from the oscillator 141 to generate a magnetic field 131, and the magnetic field 131 links with the subject 110, thereby causing an eddy current 132 in the subject 110. Induced. The eddy current 132 is generated concentrically with the exciting coil 101 when the subject 110 is healthy (when there is no defect). The eddy current 132 also induces a magnetic field 133, which affects the magnetic field 131 generated by the exciting coil 101.

The detection coil 102 includes an excitation coil 131
Generated by an eddy current 132
Are affected, and an AC voltage is induced. Since the magnetic field 131 generated by the excitation coil 101 is always kept constant, it is possible to detect an abnormality (existence of a defect or the like) of the subject 110 by focusing on a change in the voltage induced in the detection coil 102. Can be.

Various signal processing circuits are present inside the flaw detector 120. The signal processing circuit extracts only a change in voltage induced in the detection coil 102 and displays the change on the display screen 121 as a waveform.

When a defect exists in the object 110, the flow of the eddy current 132 changes with respect to the case where there is no defect.
At this time, since the magnetic field 133 due to the eddy current 132 also changes with respect to the case where there is no defect, the voltage induced in the detection coil 102 also changes. This change in voltage can be observed on the display screen 121 of the flaw detector 120 to determine the presence or absence of a defect.

In practice, the waveform of the display screen 121 of the flaw detector 120 at this time is observed while moving the flaw detector 100 along the subject 110. As described above, in the eddy current detection, the presence or absence of a defect can be determined by observing the waveform that appears on the display screen 121 of the flaw detector 120 at that time while moving the flaw detector 100 on the surface of the subject 110, The health of the subject 110 can be known.

[0009]

When the above-described conventional flaw detector is used, as shown in FIG.
Of the magnetic field generated by the magnetic field (the magnetic field 135 passing through the front surface of the subject 110 and the magnetic field 136 passing through the back surface of the subject 110) and the influence of the magnetic field due to all eddy currents induced by these magnetic fields. The detection coil 102 receives it.

Here, since the magnetic fluxes (magnetic fields) having the same direction have a repulsive action, the magnetic fields 135 and 136 generated by the exciting coil 101 spread relatively widely.
Eddy currents induced at zero are also widely distributed. The voltage amplitude generated in the detection coil 102 due to an abnormality such as a defect existing in the object 110 is determined by the amount and the amount of the eddy current flowing in the object 110 at the abnormal portion. When the eddy current flowing through the subject 110 is widely distributed as in the related art, the density of the eddy current is low, and the amount of the eddy current acting on the small defect 112 existing in the subject 110 becomes small.
This phenomenon is particularly noticeable when a small defect 112 exists on the back side of the probe.

Therefore, when a large defect is scanned, the display screen 121 of the flaw detector 120 is scanned as shown in FIG.
Shows a large waveform 122, but when a small defect is scanned, as shown in FIG.
, Only a small waveform 124 appears. That is, the conventional eddy current flaw detector has a problem that the detection performance for a small defect is low. An object of the present invention is to provide an eddy current flaw detector with improved detection performance for small defects.

[0012]

SUMMARY OF THE INVENTION In order to solve the above-mentioned problems, the present invention reduces the dispersion of a magnetic field acting on a subject by improving the shape of a magnetic core around which an exciting coil and a detecting coil are wound. In addition, a magnetic field due to an eddy current generated by the magnetic field acts on the detection coil intensively.

That is, the eddy current flaw detector of the present invention is formed of a ferromagnetic material, and is provided with a central magnetic core, an inner cylindrical magnetic core, and an outer cylindrical magnetic pole coaxially on a disk-shaped magnetic core. A magnetic core material, provided on the outer periphery of the inner cylindrical magnetic core portion, an excitation coil for inducing an eddy current in the subject, and provided on the outer periphery of the center magnetic core portion, of the eddy current induced in the subject. And a detection coil for detecting a change. The center core may be rod-shaped or cylindrical.

In the thus constructed eddy current flaw detector of the present invention, the magnetic field generated by the excitation coil acts on the subject via the central magnetic core and the inner cylindrical magnetic core to generate an eddy current. Let it. On the other hand, only a magnetic field that passes through the center core acts on the detection coil, and a voltage is induced by a change when the magnetic field is affected by the magnetic field due to the eddy current generated in the subject.

The magnetic field passing through the inner cylindrical magnetic core portion and the magnetic field passing through the central magnetic core portion are substantially in the same direction in the region acting on the subject, and the magnetic fields generated in the same direction repel each other. The magnetic field passing through is repelled by the magnetic field passing through the inner cylindrical magnetic core, and is concentrated at a more central portion of the central magnetic core. For this reason, the eddy current induced in the subject by the magnetic field passing through the central magnetic core portion is concentrated in the central portion, and if there is a defect in this portion, the ratio of the eddy current acting on the defect increases. Further, the change in the magnetic field due to the eddy current is efficiently detected by the detection coil provided on the outer periphery of the central magnetic core. Therefore, even a small defect can be detected well.

[0016]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a diagram showing a configuration of an eddy current flaw detector according to one embodiment of the present invention. 1A is a cross-sectional view of the eddy current flaw detector, FIG. 1B is a plan view of FIG. 1A from the A side, and FIG. 1C is a plan view of FIG. 1A from the B side. FIG.

The center magnetic core 1 is placed on the circular disc-shaped magnetic core 11.
2, the inner cylindrical magnetic core 13 and the outer cylindrical magnetic pole 14 are coaxially arranged to form the magnetic core material 10. The disk-shaped magnetic core 11, the central magnetic core 12, the inner cylindrical magnetic core 13, and the outer cylindrical magnetic pole 14 are made of a ferromagnetic material that passes a magnetic field well.

A wire is wound around the outer periphery of the inner cylindrical magnetic core 13 to form the exciting coil 20. The detection coil 21 is formed by winding a wire around the outer periphery of the center magnetic core portion 12. The ends of the wires constituting the excitation coil 20 and the detection coil 21 are taken out of the magnetic core material 10 from the holes 15 provided in the disc-shaped magnetic core portion 11 and are connected to the flaw detector through a cable in the same manner as a conventional flaw detector. (Not shown).

Next, the operation of this embodiment will be described with reference to FIG. An alternating magnetic field is generated by supplying an alternating current of a constant magnitude (amplitude) and a constant frequency to the exciting coil 20 from an oscillator in the flaw detector. In this case, a magnetic field (hereinafter, referred to as a central magnetic field) 40 due to a magnetic flux passing through the central magnetic core portion 12-the outer space (air, the subject)-the external cylindrical magnetic pole portion 14-the disk-shaped magnetic core portion 11-the central magnetic core portion 12. ,
A magnetic field (hereinafter, referred to as a peripheral magnetic field) 41 due to magnetic flux passing through the inner cylindrical magnetic core 13-the outer space (air, the subject)-the outer cylindrical magnetic pole 14-the disk-shaped magnetic core 11-the inner cylindrical magnetic core 13. Is formed. Here, the magnetic field generated inside the central magnetic core 12 is substantially the same as the central magnetic field 40.

As shown in FIG. 2, a central magnetic field 4 between the central magnetic core 12 and the subject 30 (hereinafter, referred to as a central space).
The peripheral magnetic field 41 in the space between the zero, the inner cylindrical magnetic core portion 13 and the subject 30 (hereinafter referred to as the peripheral space) is oriented in substantially the same direction. Since the magnetic fields in the same direction always repel each other, the central magnetic field 40 in the central space and the peripheral magnetic field 41 in the peripheral space repel each other. Therefore, the central magnetic field 40 in the central space is more concentrated on the central portion, and the peripheral magnetic field 41 in the peripheral space is more diffused on the outer peripheral portion.

On the other hand, an eddy current is induced in the subject 30 by the central magnetic field 40. The eddy current is concentrated below the central magnetic core portion 12 and its density increases, so that the magnitude of the magnetic field induced by the eddy current also increases. When the eddy current induced by the central magnetic field 40 changes due to the presence of a defect, the change in the eddy current affects the central magnetic field 40.

When the magnetic flux passing through the coil changes with time, a voltage is induced in the coil. However, since the detection coil 21 of the flaw detector of this embodiment is wound around the central magnetic core 12, the detection coil 21 Detects a change in the magnetic field inside the central magnetic core 12, that is, a change in the central magnetic field 40.

When the object 30 has no defect, the eddy current is in a steady state and the magnetic field due to the eddy current does not change, so that the central magnetic field 40 is not affected. When the eddy current changes due to the presence of a defect, the magnetic field due to the eddy current affects the central magnetic field 40, and the change in the central magnetic field 40, that is, the magnetic field change in the central magnetic core 12, induces the detection coil 21. The voltage changes. Then, the induced voltage of the detection coil 21 is signal-processed by the flaw detector, a signal waveform due to the defect is displayed on the screen of the flaw detector, and flaw detection becomes possible.

As described above, according to the eddy current flaw detector of the present embodiment, the eddy current generated in the subject 30 is concentrated in the central portion below the central magnetic core portion 12, so that the magnetic field generated by the eddy current is large. In addition, since the magnetic field due to the eddy current intensively affects only the central magnetic field 40, that is, the internal magnetic field of the center core portion 12 around which the detection coil 21 is wound, not only large defects but also small defects can be detected with high sensitivity. can do.

Therefore, necessary repairs and the like can be accurately performed in the next step, so that the repair period is shortened, and the service life of various devices is increased. FIG. 3 shows a signal waveform when a defect exists in the subject. FIG. 3A shows a signal waveform when the defect is large, and FIG. 3B shows a signal waveform when the defect is small. As can be seen from the figure, the waveform 52 of the small defect has the same amplitude waveform as the waveform 51 of the large defect.

The present invention is not limited to the above embodiment. For example, in the above-described embodiment, a flat-shaped object has been described. However, the shape of the object is not limited to a flat plate, and the present invention can be applied to various objects such as a pipe, a tube, and a rod.

The magnetic core material may be formed by integrally molding a disc-shaped magnetic core, a central magnetic core, an inner cylindrical magnetic core, and an outer cylindrical magnetic pole, or these members may be formed separately and joined. May be done.

The center magnetic core is not limited to the rod shape, but may be a thin cylindrical shape. In addition, the present invention can be variously modified and implemented without departing from the gist thereof.

[0029]

As described above, according to the eddy current flaw detector of the present invention, the center magnetic core, the inner cylindrical magnetic core, and the outer cylindrical magnetic pole are coaxially provided on the disk-shaped magnetic core. By forming a magnetic core material made of a magnetic material and providing an excitation coil on the outer periphery of the inner cylindrical magnetic core and a detection coil on the outer periphery of the center core, eddy currents generated in the subject are concentrated at the center and It is possible to efficiently detect the change in the magnetic field due to the current, and it is possible to detect not only a large defect but also a small defect with high sensitivity.

[Brief description of the drawings]

FIG. 1 is a diagram showing a configuration of an eddy current flaw detector according to one embodiment of the present invention.

FIG. 2 is a diagram showing a state of a magnetic field generated by the eddy current flaw detector of FIG. 1;

FIG. 3 is a view showing a display waveform when the eddy current flaw detector of FIG. 1 is used.

FIG. 4 is a diagram showing a configuration of a conventional eddy current flaw detector.

FIG. 5 is a diagram showing an electromagnetic action of the flaw detector.

FIG. 6 is a diagram illustrating a state of a magnetic field of a conventional flaw detector.

FIG. 7 is a diagram showing an example of a display waveform by a conventional flaw detector.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 10 Magnetic core material 11 Disc-shaped magnetic core part 12 Center magnetic core part 13 Inner cylindrical magnetic core part 14 External cylindrical magnetic pole part 15 Hole through which a coil winding 20 Excitation coil 21 Detector coil 30 Subject 40 Central magnetic field 41 Peripheral magnetic field

──────────────────────────────────────────────────続 き Continuation of the front page (56) References JP-A-61-137057 (JP, A) JP-A-5-10924 (JP, A) JP-A-8-211025 (JP, A) JP-A-7-107 286992 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) G01N 27/72-27/90 G01R 33/00-33/18

Claims (1)

(57) [Claims] 1. A core material formed of a ferromagnetic material and having a center core, an inner cylindrical core, and an outer cylindrical magnetic pole coaxially provided on a disk-shaped core, and the inner cylindrical core. An excitation coil provided on the outer periphery of the portion for inducing an eddy current in the subject; and a detection coil provided on the outer periphery of the center core portion and detecting a change in the eddy current induced in the subject. An eddy current flaw detector characterized by the following.