JP2006337039A - Defect-detecting method of metal body, and scanning type magnetic detector - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To sufficiently detect a defect of a magnetic metal body, using a magnetic impedance effect type sensor by a magnetic leakage flux testing method. <P>SOLUTION: Demagnetization or magnetization processing is applied so that the magnetization state of the metal body is made uniform. Then, a magnetic detector, having a coil for applying a magnetic field to the metal body and the magnetic impedance effect type sensor for detecting magnetic leakage flux at the defect part of the metal body, scans the surface of the metal body, while applying the magnetic field to it by the coil. Even if the metal body is distorted locally and magnetically, it will locally become magnetized by remanence, and the magnetic leakage flux noise occurs, the demagnetization or magnetic processing is applied to make the magnetization state uniform so that the magnetic impedance effect type sensor does not react to this, and the defect is detected using the magnetic impedance effect type sensor by the magnetic leakage flux testing method. Thus, the influence of magnetic leakage flux noise by the remanence is eliminated, and the defect parts of the metal body can be detected at original high sensitivity, based on the magnetic impedance effect. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a defect detection method for a metal body and a scanning magnetic detector used in the method.

When defects such as scratches are present in the magnetic metal body, the reluctance of the defect portion increases, and when the magnetic flux is passed through the metal body, the magnetic flux leaks at the defect portion.
Therefore, in order to detect a defect in a magnetic metal body, magnetizing the metal body, scanning the surface of the metal body with a magnetic sensor, detecting a magnetic flux leakage location, and detecting the defect location, so-called leakage magnetic flux flaw detection Known as a test method.
In this test method, the magnetization method is varied according to the shape, dimensions, etc. of the test product, and the shaft energization method, the right angle energization method, the probe method, the current penetration method, the coil method, the interpole method, and the magnetic flux penetration according to the test product. One of the laws is selected.
In the conventional magnetic flux leakage test method, a Hall sensor, a magnetoresistive element, a fluxgate sensor, or the like is used as a magnetic sensor. Even if the magnetization method described above is selected, it is light in terms of sensitivity and spatial resolution. It is difficult to detect a defect or a defect that exists deep from the surface.

Recently, a sensor using the magneto-impedance effect has been developed as a magnetic sensor with higher sensitivity, higher spatial resolution, and faster response than Hall sensors, magnetoresistive elements, fluxgate sensors, etc., and a magnetic detection method using the sensor has also been proposed. Has been. (Patent Document 1).
JP 7-181239 A

As is well known, magnetization is a phenomenon in which magnetic dipoles (micromagnets) are aligned in one direction. Thus, even before the metal body is magnetized, it is often the case that a magnetic flux is locally deformed and a leakage magnetic flux is locally generated with residual magnetism.
According to the results of earnest studies by the present inventors, when the above-described magneto-impedance effect type sensor is used as a magnetic sensor for a leakage magnetic flux flaw detection test method, the magneto-impedance effect type sensor generates a small leakage magnetic flux already generated before magnetization. It also turned out to be a detection error.

  Conventionally, when flaws in a plate-shaped metal body are detected by the leakage magnetic flux flaw detection test method, the magnetization is probed (using an electrode that can be moved freely by hand, and a current is applied to each region of the test product to be flawed to detect local defects. A magnetic circuit is formed by two electrodes in a horseshoe type electromagnet and a test product, a magnetic field is passed from one electrode to the other, and the surface of the magnetic field is measured with a magnetic sensor. However, there is a problem that it is difficult to determine the lightness of a flaw of a defect because the magnetic field strength varies depending on the location, and even if the defect has the same size, the magnitude of the leakage magnetic flux varies depending on the location.

  An object of the present invention is to make it possible to satisfactorily detect a defect in a magnetic metal body using a magneto-impedance effect type sensor by a leakage magnetic flux test method.

According to a first aspect of the present invention, there is provided a method for detecting a defect in a metal body, wherein a demagnetization or magnetization process is performed so that the magnetization state of the metal body is uniform, and then a magnetic field is applied to the metal body and a defect portion of the metal body. A magnetic detector having a magneto-impedance effect type sensor for detecting a leakage magnetic flux of the metal is scanned while applying a magnetic field by the coil. Here, defects include not only scratches but also thinning, rust, cracks, deterioration, etc. (hereinafter the same).
According to a second aspect of the present invention, there is provided a method for detecting a defect in a metal body, wherein a demagnetization or magnetization process is performed so that the magnetization state of the metal body is uniform, and then a magnetic field is applied to the metal body and a defect portion of the metal body. A magnetic detector having a magneto-impedance effect type sensor for detecting a normal component of the leakage magnetic flux of the magnetic field is scanned while applying a magnetic field by the coil.
According to a third aspect of the present invention, there is provided a metal body defect detection method comprising: a magnetic detector including a coil that applies a magnetic field to a metal body and a magneto-impedance effect type sensor that detects a leakage magnetic flux at a defect portion of the metal body; Scanning is performed by applying an alternating magnetic field of a predetermined frequency by a coil, and during this scanning, the sensor output is detected through a filter that includes the predetermined frequency in the passband and blocks the passage of direct current.
A defect detection method for a metal body according to claim 4 is a magnetic detector comprising a coil for applying a magnetic field to the metal body and a magneto-impedance effect type sensor for detecting a normal component of leakage magnetic flux at the defect portion of the metal body. The surface of the sensor is scanned while applying an alternating magnetic field of a predetermined frequency by the coil, and during this scanning, a sensor output is detected through a filter that includes the predetermined frequency in a pass band and blocks the passage of direct current.
The defect detection method for a metal body according to claim 5 is the defect detection method for a metal body according to any one of claims 1 to 4, wherein a magnetic field is applied in a crossing direction, preferably in a direction orthogonal to the direction of the defect in the metal body. It is characterized by.
The defect detection method for a metal body according to a sixth aspect is the method for detecting a defect of a metal body according to any one of the first to fourth aspects, wherein the scanning is performed in two directions intersecting each other, preferably in two directions orthogonal to each other.
A defect detection method for a metal body according to a seventh aspect is the defect detection method for a metal body according to any one of the first to fourth aspects, wherein scanning is performed in two directions intersecting each other, preferably in two directions orthogonal to each other and an intermediate direction between these two directions. It is characterized by that.
A scanning magnetic detector according to an eighth aspect is a magnetic detector used in the defect detection method for a metal body according to any one of the first to seventh aspects, wherein a coil that applies a magnetic field to the metal body and a leakage magnetic flux at the defect location are detected. A magneto-impedance effect type sensor for detecting; and two magneto-impedance effect elements of the sensor separated by a predetermined distance with respect to the scanning direction; and a detection unit that detects a differential output of both elements; It is characterized by that.
The scanning magnetic detector according to claim 9 is a magnetic detector used in the defect detection method for a metal body according to any one of claims 1 to 7, and a magnetic impedance effect for detecting leakage magnetic flux at a defect portion of the metal body. A U-shaped coil in which a coil-shaped sensor is housed in a frame and a coil for applying a magnetic field to a metal body is wound around a U-shaped iron core so that the U-shaped open side can be brought close to the surface of the metal body. It is characterized by wearing.

(1) Even if a metal body is locally magnetically distorted and locally has residual magnetism and leakage magnetic flux noise is generated, demagnetization or magnetization so that the magneto-impedance effect sensor does not react to this. After processing to make the magnetized state uniform, a defect is detected using a magneto-impedance effect type sensor by the leakage flux test method, so that the influence of leakage magnetic flux noise due to the residual magnetism is eliminated and the magnetic impedance is eliminated. It is possible to detect a defective portion of a metal body with high sensitivity based on the effect.
Alternatively, an AC magnetic field having a predetermined frequency is used for magnetization, and this predetermined frequency component is passed and detected by a filter that blocks the passage of direct current. Defects can be detected with the original high sensitivity based on.
(2) Since the relative positional relationship between the magneto-impedance effect type sensor and the magnetizing coil is fixed, the magnetic field strength and direction directly below the magneto-impedance effect element are constant regardless of the moving position of the magneto-impedance effect type sensor. Therefore, magnetic flux leakage at a defect location through which the magneto-impedance effect element passes is generated under a constant magnetic field, and the severity of the defect can be appropriately evaluated based on the same standard.
(3) Since the detection is performed in consideration of the fact that the magnitude of the leakage magnetic flux at the defect location is affected by the relative relationship between the magnetic field direction and the defect direction, the degree of serious damage of the defect is accurately evaluated from this aspect. it can.

Hereinafter, embodiments of the present invention will be described with reference to the drawings.
FIG. 1 shows an example of a circuit configuration of a magnetic sensor using a magneto-impedance effect element.
In FIG. 1, reference numeral 1 denotes a magneto-impedance effect element, which has a zero magnetostriction or a negative magnetostriction having an outer shell portion in which magnetic domains whose spontaneous magnetization directions are opposite to each other in the circumferential direction of the wire are alternately separated by domain walls. Amorphous alloy wire is used. The inductance voltage component in the output voltage between both ends of the wire generated when a high-frequency excitation current is passed through an amorphous magnetic wire having zero magnetostriction or negative magnetostriction is generated by the circumferential magnetic flux generated in the cross section of the wire. This occurs due to the magnetization of the easily magnetizable outer shell in the circumferential direction. Therefore, the circumferential magnetic permeability mu _theta depends on the circumferential direction of magnetization of Dosotokara portion. Therefore, when a detected magnetic field is applied in the axial direction of the amorphous wire being energized, the circumferential magnetic flux and the detected magnetic field magnetic flux generated by the energization are combined to generate an externally magnetizable external material. shift direction of the magnetic flux acting on the shell from the circumferential direction, correspondingly hardly occur magnetization in the circumferential direction, the circumferential permeability mu _theta changes, the inductance voltage content will vary. This fluctuation phenomenon is called a magnetic inductance effect, which can be said to be a phenomenon in which the high-frequency excitation current (carrier wave) is modulated by a detected wave (signal wave). Further, when the frequency of the energization current is in the order of MHz, a high-frequency skin effect appears greatly, and the skin depth δ = (2ρ / wμ _θ ) ^1/2 (μ _θ is the circumferential permeability, ρ as described above. electrical resistivity, w is shows the angular frequency, respectively) is changed by mu _theta, as the mu _theta is the so changed by the detected magnetic field, the resistance voltage division also be detected magnetic field in the wire between both ends output voltage It will fluctuate with. This fluctuation phenomenon is called a magneto-impedance effect, which can be said to be a phenomenon in which the high-frequency excitation current (carrier wave) is modulated by a detected wave (signal wave).

In FIG. 1, 2 is a high-frequency power supply circuit for applying a high-frequency excitation current to the magneto-impedance effect element, 3 is a detected magnetic field (signal wave) acting in the axial direction of the magneto-impedance effect element, and the high-frequency excitation current (carrier wave). A detector circuit that demodulates the modulated modulated wave, 4 an amplifier circuit that amplifies the demodulated wave, 5 an output terminal, 6 a negative feedback coil, and 7 a bias magnetic field coil.
For the magneto-impedance effect element 1, an amorphous ribbon, an amorphous sputtered film, or the like can be used in addition to an amorphous wire having zero magnetostriction or negative magnetostriction.

In the magneto-impedance effect element 1, as described above, the direction of the magnetic flux acting on the outer shell portion that is easily magnetized in the circumferential direction by combining the circumferential magnetic flux based on the excitation current and the axial magnetic flux due to the detected magnetic field. Is shifted from the circumferential direction, the circumferential permeability μ _θ is changed, the inductance is changed, and the impedance is changed by the change of the skin depth of the high frequency skin effect of the circumferential permeability μ _θ . Accordingly, although even the circumferential direction positional shift phi by the synthesized magnetic field by ± of the detected magnetic field becomes ± phi, the circumferential direction of the magnetic field reduction ratio cos (± phi) is unchanged, the degree of reduction in thus mu _theta is of the detected magnetic field It does not change depending on the direction. Accordingly, the detected magnetic field-output characteristics are substantially bilaterally symmetrical with respect to the y axis when the detected magnetic field is taken on the x axis and the output is taken on the y axis as shown in FIG. This detected magnetic field-output characteristic is non-linear. With non-linear characteristics, it is difficult to measure with high sensitivity. Therefore, negative feedback is applied by a negative feedback coil to linearize the output characteristics as shown in FIG. In FIG. 2B, Δw is a linear range in which the gain A without negative feedback is very large and the gain is determined only by the feedback rate β. However, since the polarity of the detected magnetic field cannot be determined with this output characteristic, the bias magnetic field is applied by the bias coil 7 so that the polarity can be determined as shown in FIG. That is, the characteristic of (b) in FIG. 2 is moved in the negative direction of the x-axis by the bias magnetic field, and the maximum range of the detected magnetic field is kept within the range of the single oblique line region to −Hmax to + Hmax. Further, as shown in FIG. 2D, a linear characteristic passing through the origin by zero point adjustment (the gradient coefficient k does not change). Therefore, in FIG. 2D, when the detected magnetic field is + He, the output is + Eo, and when the detected magnetic field is -He, the output is -Eo, and the detected magnetic field can be accurately measured based on polarity discrimination. .

FIG. 3 shows a circuit configuration of a magnetic sensor different from the above using a magneto-impedance effect element.
In FIG. 3, reference numerals 1a and 1b denote magneto-impedance effect elements having substantially the same characteristics, reference numeral 2 denotes a high-frequency power supply circuit for supplying an exciting current to both magneto-impedance effect elements 1a and 1b, and reference numerals 3a and 3b denote magnetic impedance effect elements 1a and 1b. A detector circuit that demodulates a modulated wave obtained by modulating a high-frequency excitation current (carrier wave) with a detected magnetic field (signal wave) that acts in the axial direction of the detector, and 40 is a differential amplifier that differentially amplifies the demodulated wave output of both detector circuits Circuit 5 is an output terminal, 6a and 6b are negative feedback coils for negatively feeding back the output of the differential amplifier circuit 40 to the magneto-impedance effect elements 1a and 1b, and 7a and 7b are biases for the magneto-impedance effect elements 1a and 1b. This is a magnetic field coil.
In FIG. 3, if the magnetic field acting in the axial direction of each magneto-impedance effect element is Hexa and Hexb, the differential output Eout is given by Eout = k (Hexa−Hexb).

The magneto-impedance effect element 1, 1a, 1b is an alloy of transition metal and non-metal having a non-metal composition of 10 to 30 atomic%, particularly an alloy of transition metal and non-metal having a non-metal content of 10 to 30. accounting for atomic%, can or transition metal non-transition metals of Fe and Co is B and Si to use a non-metallic composition is B and Si in Fe, for example, the composition Co _{70 .5} B ₁₅ Si ₁₀ Fe _4.5, length 2000Myuemu～6000myuemu, those outside diameter 30μm~50μmφ be used.

  The magnetic field detection limit -Hmax to + Hmax in (d) of FIG. 2 is normally +2.5 Gauss to -2.5 Gauss.

  In the above, a normal high frequency such as a continuous sine wave, a pulse wave, or a triangular wave can be used as the high frequency excitation current, and examples of the high frequency excitation current source include a Hartley oscillation circuit, a Colpitts oscillation circuit, a collector tuning oscillation circuit, and a base tuning oscillation. In addition to a normal oscillation circuit such as an oscillation circuit, a square wave generator that integrates the square wave output of a crystal oscillator through an integration circuit via a DC cut capacitor and amplifies the triangular wave of the integration output by an amplification circuit, and oscillates a COMS-IC The triangular wave generator etc. which were used as a part can be used.

As the above detection circuit, for example, a configuration in which a modulated wave is half-wave rectified by an operational amplifier circuit and this half-wave rectified wave is processed by a parallel RC circuit or an RC low-pass filter to obtain an envelope output of the half-wave rectified wave, A configuration in which the modulated wave is half-wave rectified by a diode and the half-wave rectified wave is processed by a parallel RC circuit or an RC low-pass filter to obtain an envelope output of the half-wave rectified wave can be used.
Further, it is possible to use tuning detection in which a signal wave is sampled by multiplying the modulated wave by a square wave having a frequency fs tuned to the modulated wave (frequency fs).
In the above-described embodiment, the detected magnetic field is extracted by demodulating the modulated wave. However, the present invention is not limited to this, and a high-frequency excitation current wave modulated by the detected magnetic field (signal wave) acting on the magneto-impedance effect element ( Any suitable detecting means can be used as long as it can detect the detected magnetic field from the carrier wave.

The negative feedback coil and the bias magnetic field coil can be wound around a magneto-impedance effect element. Further, as shown in FIG. 4, a negative feedback coil and a bias magnetic field coil can be wound around an iron core constituting a magneto-impedance effect element and a loop magnetic circuit. 4 (a) is a side view showing an example of a magneto-impedance effect unit with an iron core coil, FIG. 4 (b) is a bottom view, and FIG. 4 (c) is a cross-sectional view of FIG. It is sectional drawing.
In FIG. 4, reference numeral 100 denotes a substrate chip, and for example, a ceramic plate can be used. Reference numeral 101 denotes an electrode provided on one side of the substrate piece, and includes a magneto-impedance effect element connecting projection 102. This electrode can be provided by printing and baking a conductive paste, for example, a silver paste. 1x is a magneto-impedance effect element connected between the protrusions 102 and 102 of the electrodes 101 and 101 by soldering or welding. As described above, an amorphous wire, amorphous ribbon, sputtered film, or the like having zero or negative magnetostriction can be used. 103 is a C-type iron core made of iron or ferrite, 6x is a negative feedback coil wound around the C-type iron core, 7x is a bias magnetic field coil, and the magneto-impedance effect element 1x and the C-type iron core 103 The both ends of the C-type iron core 103 are fixed to the other surface of the substrate piece 100 with an adhesive or the like so as to constitute a loop magnetic circuit. The iron core material may be a magnetic material having a small residual magnetic flux density. Examples thereof include permalloy, ferrite, iron, amorphous magnetic alloy, magnetic powder mixed plastic, and the like.

FIG. 5 shows an example of the magnetic detector 8 used in the present invention. FIG. 5A is a front view, FIG. 5B is a side view, and FIG. The ha cross-sectional view in a) is shown respectively.
In FIG. 5, reference numeral 81 denotes a frame, and two plates 811 and 811 are fastened by a spacer 812. A is a magneto-impedance effect type sensor, which belongs to the differential type shown in FIG. 2, and has two magneto-impedance effect elements 1a and 1b arranged on the substrate piece 100 as shown in FIG. As shown in FIG. 4, each magneto-impedance effect element is provided with an iron core, and a magnetic feedback effect with an iron core coil is obtained by winding a negative feedback magnetic coil and a bias magnetic coil for each magneto-impedance effect element on each iron core. As shown in FIG. 5 (c), a drive circuit b, a differential amplifier circuit, and a high-frequency circuit including a detection circuit, a differential amplifier circuit, and a high-frequency excitation current generation circuit for the magneto-impedance effect elements 1a and 1b are provided. The magnetic impedance effect unit B with iron core coil is connected to a circuit board C on which a battery c as a power source of an exciting current generating circuit is mounted by a conductor bar e. Yes connected, it is fixed to the frame 81 with the holder 813 houses the circuit board C in the frame 81.
Reference numeral 82 denotes a U-shaped coil for magnetization, in which a coil is wound around a U-shaped iron core, and a magnetic field having the same direction and the same strength is applied to both magneto-impedance effect elements 1a and 1b as shown in FIG. As shown in FIG. As the U-shaped iron core, permalloy, ferrite, iron, amorphous magnetic alloy, magnetic powder mixed plastic, or the like can be used.

  In FIG. 5, E indicates the surface of a metal body as the object to be detected, and the magnetic detector 8 directs the magneto-impedance effect elements 1a and 1b in the normal direction on this surface, and the tips of the elements are close to the surface E. At the same time, the iron core end 820 of the U-shaped coil 82 is moved close to the surface E.

In a magnetic metal body to detect a defect, it is often the case that a magnetic flux is locally deformed and has a residual magnetism to locally generate a leakage magnetic flux. The magnetic field strength of the locally leaked magnetic flux is within the detection magnetic field range ± 2.5 Gauss of the magneto-impedance effect type sensor.
This location of the residual magnetic band is not a flaw, and if a local leakage magnetic flux based on this residual magnetism is detected, an error occurs.
In order to detect a defect in a magnetic metal body according to the present invention, the magnetization state of the metal body is set to 0 or a uniform uniform value by a demagnetizer or a magnetizer. If the magnetized state of the metal body is made uniform, normally there will be no magnetic flux leakage from the surface, even if it exists, it can be detected by using the differential type as described above. Absent.

In the demagnetization process, for example, as shown in FIG. 7 (a), if the residual magnetic flux density is 0a, a positive magnetic field is applied by a demagnetizer and a point c of the saturation magnetic field passes through b along the broken line. After that, the demagnetizer is detected in the detection area by repeating the operations of reversing the magnetic field from the saturation magnetization state and gradually decreasing the magnetic field, and gradually reducing the hysteresis ring to eliminate the residual magnetization. You can use the method of going while moving.
In the magnetizing process, for example, as shown in FIG. 7B, if the residual magnetic flux density exists in 01 to 0n, a positive magnetic field is applied by the magnetizer and points 1 to The magnetizer detects that n reaches the point c of the saturation magnetic field, and then gradually decreases the magnetic field from the state of saturation magnetization and fixes the residual magnetic flux density at a point m higher than the points 1 to n. You can use the method of moving while moving to the area.

  After the pretreatment for demagnetization or magnetization in this way, the gas detector 8 is brought close to the surface E of the metal body and the magneto-impedance effect elements 1a and 1b are brought close to the surface E in the normal direction. The magnet 82 is energized with a direct current to magnetize the metal body with a DC magnetic field, and the surface of the metal body is detected by the magnetic field detector 8 in a predetermined direction X, as shown in (a) and (b) of FIG. Scan with Y. Scanning can be performed by a robot.

で与えられる。
図１０は図９の（ハ）に示す漏洩磁束の法線成分に対する前記差動式磁気インピーダンス効果の検出出力を示している。
而して、図９の（ハ）においてピークが傷の巾両端で生じ、図１０の（イ）におけるピーク間の間隔Δｔは、傷の巾をｗ、走査速度をｖとすれば、
Δｔ＝ｗ／ｖ
で与えられる。
磁気インピーダンス効果素子間の間隔をＤとすれば、前方の磁気インピーダンス効果素子の検出出力Ｅａと後方の磁気インピーダンス効果素子の検出出力Ｅｂとが時間Ｄ／ｖ＝ΔＴの間隔で離隔され、傷の巾ｗに較べて磁気インピーダンス効果素子間の間隔Ｄが充分に広いと、両出力は重ならない。磁気インピーダンス効果素子間の間隔Ｄに対し傷の巾ｗが広くなって両出力が重なっても、差動のために図１０の（ロ）に示すように重畳部分では検出波高値が加算により大きくされる。傷の巾ｗ（２ａ）が広くなると、前記の数式からも明らかなように、漏洩磁束密度が小さくなり検出値がそれだけ減少されるが、前記の重なりによる検出波高値の増加のために、巾の広い傷でも充分に検出可能である。 When a magnetic field is passed through a scratched metal body, the reluctance of the scratched part is high, and as shown in FIG. 9 (a) [sectional view] and FIG. 9 (b) [plan view] Leaks, and the normal component of the leakage magnetic flux is as shown in FIG.
According to the defect model by the magnetic dipole, when the magnetic intensity of the magnetic dipole is σ, the width of the scratch is 2a, and the depth of the scratch is d, the normal component ΔBz of the leakage flux is

Given in.
FIG. 10 shows the detection output of the differential magnetic impedance effect with respect to the normal component of the leakage magnetic flux shown in FIG.
Thus, in FIG. 9C, peaks occur at both ends of the scratch width, and the interval Δt between the peaks in FIG. 10A is given by assuming that the width of the scratch is w and the scanning speed is v.
Δt = w / v
Given in.
If the distance between the magneto-impedance effect elements is D, the detection output Ea of the front magneto-impedance effect element and the detection output Eb of the rear magneto-impedance effect element are separated by an interval of time D / v = ΔT. If the distance D between the magneto-impedance effect elements is sufficiently wide compared to the width w, both outputs do not overlap. Even if the width w of the flaw becomes wide with respect to the distance D between the magneto-impedance effect elements and both outputs overlap, the detected peak value is increased by the addition in the overlapped portion as shown in FIG. Is done. As the flaw width w (2a) becomes wider, as apparent from the above formula, the leakage magnetic flux density is reduced and the detected value is reduced accordingly. Even wide scratches can be detected sufficiently.

Further, external noise such as geomagnetism for differential detection or internal noise in a detection circuit or the like caused by a temperature change of a circuit element or the like is not detected for differential detection.
Therefore, it is possible to sufficiently detect even wide scratches where the leakage magnetic flux density is small and defects existing deep from the surface of the metal body.

The intensity of the leakage magnetic flux varies depending on the direction of the flaws with respect to the magnetic field, and is maximized when it is orthogonal, decreases as the relative angle is narrowed, and is minimized when both directions coincide.
In FIG. 11, S is the distribution of the normal component of the leakage flux when the flaw direction and the magnetization direction are orthogonal, and W is the distribution of the normal component of the leakage flux when the flaw direction and the magnetization direction match. As the angle between the flaw direction and the magnetization direction approaches 90 ° → 0 °, the interval between peaks increases and the peak value decreases and the leakage flux distribution becomes flat as shown by the dotted line M, and the detection sensitivity increases. It goes down.
Therefore, when the direction of a defect such as a flaw is known as in a transport tube, it is desirable to set the direction of the U-shaped coil so that the direction of the magnetic field is perpendicular to the direction of the defect.
When the direction of a defect such as a flaw is unknown, the two directions orthogonal to each other, and further, in addition to these two directions, are detected as the scanning direction, and these detection results are comprehensively evaluated or scanned. It is preferable that the direction is the same and the detection is performed a plurality of times by changing the direction of the U-shaped coil, and these detection results are comprehensively evaluated.

In the above embodiment, the normal component (vertical component) of the leakage magnetic flux is detected, but the tangential component (parallel component) may be detected.
FIG. 12 shows a magnetic sensor in the magnetic detector used in this case. The magneto-impedance effect elements 1a and 1b are arranged on a common axis at intervals in the longitudinal direction and the U-shaped coil 82 As shown in FIG. 12B, except that the line connecting the iron core ends 820 and 820 is set to coincide with the symmetrical center line between the magneto-impedance effect elements 1a and 1b. For example, it is substantially the same as that shown in FIG.
In FIG. 12, E indicates the surface of the metal body to be detected, and the magnetic detector has the magneto-impedance effect elements 1a and 1b parallel to the surface E, and the side surfaces of the elements 1a and 1b are close to the surface E. At the same time, the iron core ends 820 and 820 of the U-shaped coil 82 are moved close to the surface E.

In the above embodiment, the metal body is magnetized by a DC magnetic field, but can be magnetized by an AC magnetic field. Even before the metal body is magnetized, even if the magnetic flux is locally distorted to have residual magnetism and leakage magnetic flux noise is generated locally, this leakage magnetic flux noise does not contain an AC component. . Therefore, an AC magnetic field is generated by the coil, a leakage magnetic field is generated at a defective portion of the metal body by this AC magnetic field, and a high-pass filter or a band-pass filter that includes the AC frequency in the pass band and blocks the passage of DC. If it detects through a filter, leakage magnetic flux noise can be prevented, and the above-mentioned pre-processing of demagnetization and magnetization can be omitted.
Further, by applying an external magnetic field in a wide frequency band, it is possible to detect information on the flaw depth according to the applied magnetic field frequency.

  In addition, if the detection is made through a high-pass filter or a band-pass filter that can block the external noise and internal noise frequency bands, the magneto-impedance effect sensor using the single magneto-impedance effect element shown in FIG. It can also be used.

  In the magnetic field shown in FIG. 6, it is preferable that the two locations where the magnetic impedance effects 1a and 1b are located are two locations where the difference in magnetic field strength between the two locations is within ± 10%.

It is drawing which shows the circuit of an example of the magneto-impedance effect type sensor used by this invention. It is drawing which shows the output characteristic of the magneto-impedance effect type sensor used by this invention. It is drawing which shows the circuit of another example of the magneto-impedance effect type sensor used by this invention. It is drawing which shows the magneto-impedance effect element with an iron core coil in the magneto-impedance effect type sensor used by this invention. It is drawing which shows the magnetic detector used by this invention. 6 is a diagram showing a positional relationship between an applied magnetic field and a magneto-impedance effect element in the magnetic detector of FIG. It is drawing which shows the demagnetization or magnetization process in this invention. It is drawing which shows the scanning locus | trajectory of the magnetic detector in this invention. It is drawing which shows the leakage magnetic flux of a wound location. 3 is a diagram illustrating a detection waveform for a flaw according to the present invention. It is drawing which shows the change state by the magnetic field of the leakage magnetic flux distribution of a wound location. It is drawing which shows another example of the magnetic detector used by this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Magnetoimpedance effect element 1a Magnetoimpedance effect element 1b Magnetoimpedance effect element 8 Magnetic detector 81 Frame 82 U-shaped coil

Claims (9)

A coil that applies demagnetization or magnetization processing so that the magnetized state of the metal body is uniform, and then applies a magnetic field to the metal body, and a magnetic impedance effect type sensor that detects leakage magnetic flux at the defective portion of the metal body A method for detecting a defect in a metal body, comprising: scanning the surface of the metal body with a magnetic detector while applying a magnetic field by the coil. Magneto-impedance effect that detects the normal component of the magnetic flux leaking at the defect part of the coil and the coil that applies a magnetic field to the metal body after demagnetizing or magnetizing so that the magnetized state of the metal body is uniform A defect detection method for a metal body, characterized in that the surface of the metal body is scanned while applying a magnetic field by the coil with a magnetic detector having a mold sensor. A magnetic detector having a coil for applying a magnetic field to a metal body and a magneto-impedance effect type sensor for detecting leakage magnetic flux at a defective portion of the metal body, scanning the surface of the metal body while applying an alternating magnetic field of a predetermined frequency by the coil, During the scanning, the sensor output is detected through a filter that includes the predetermined frequency in the pass band and blocks the passage of direct current. A magnetic detector having a coil for applying a magnetic field to a metal body and a magneto-impedance effect type sensor for detecting a normal component of leakage magnetic flux at a defective portion of the metal body. An AC magnetic field having a predetermined frequency is applied to the surface of the metal body by the coil. And detecting a sensor output through a filter that includes the predetermined frequency in a pass band and blocks direct current passage during the scanning. 5. The defect detection method for a metal body according to claim 1, wherein a magnetic field is applied in a crossing direction with respect to the direction of the defect of the metal body. The metal body defect detection method according to claim 1, wherein scanning is performed in two directions intersecting each other. 5. The method for detecting a defect in a metal body according to claim 1, wherein scanning is performed in two directions intersecting each other and an intermediate direction between the two directions. A magnetic detector for use in the defect detection method for a metal body according to any one of claims 1 to 7, comprising a coil for applying a magnetic field to the metal body and a magneto-impedance effect type sensor for detecting leakage magnetic flux at the defect location, A scanning magnetic detector characterized in that two magneto-impedance effect elements of the sensor are separated from each other by a predetermined distance in the scanning direction, and the detection unit is a differential type detecting a differential output of both elements. It is a magnetic detector used for the defect detection method of the metal body in any one of Claims 1-7, The magneto-impedance effect type sensor which detects the leakage magnetic flux in the defect location of a metal body is accommodated in a flame | frame, A scanning magnetic detector comprising: a U-shaped coil in which a coil for applying a magnetic field is wound around a U-shaped iron core; and a U-shaped open side close to a metal surface. .

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