JP2011191324A - Flaw detection probe - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a flaw detection probe estimating easily the depth of a flaw based on an output, without worsening detection precision of the flaw. <P>SOLUTION: A conductor is wound in an angled barrel shape having a polygon of a cross section perpendicular to the center axis to form an excitation coil 11, and an annular detection coil 12 is arranged to surround one side face of the angled barrel shape of excitation coil 11 to constitute the flaw detection probe 1. The one side face of the excitation coil 11 surrounded by the detection coil 12 is made to serve as a flaw detection surface of the flaw detection probe 1. A part with a parallel component being maximum with respect to a surface of a flaw detection object in a magnetic field generated by the excitation coil 11 and a part with a perpendicular component being maximum therewith are positioned together inside the detection coil 12 to obtain a simple increase relation between the depth of the flaw and the output from the flaw detection probe 1. The depth of the flaw is easily estimated based on the output from the flaw detection probe 1, without worsening the detection precision of the flaw, since an S/N ratio is enhanced compared with the case of a small diameter of the detection coil 12. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to a flaw detection probe used when flaw detection is performed by an eddy current flaw detection method.

  Conventionally, as one of the non-destructive testing methods for inspecting the presence of scratches on metal materials, processed parts or products, eddy currents are induced on the surface of the test object, and changes in eddy currents due to the presence of scratches are detected. There are eddy current flaw detection methods that can detect flaws. In the eddy current flaw detection method, a penetrating coil method that performs flaw detection by inserting a long test object into a solenoid coil that induces eddy current, and a flaw detection probe including a coil that induces eddy current are used as test objects. There is a probe coil method in which flaw detection is performed by approaching the surface. In the penetration coil method, only a long material whose cross section is formed in a circle, hexagon or the like is a test object. On the other hand, the probe coil method performs a flaw detection by bringing a small-sized flaw detection probe close to the surface of the test object, and therefore has the merit that it can cope with any shape of the test object. .

  FIG. 11 is a schematic diagram showing a configuration example of a conventional flaw detection probe. The flaw detection probe includes an annular excitation coil 51 and an annular detection coil 52 having the same diameter arranged in parallel to each other, and a surface opposite to the surface of the detection coil 52 facing the excitation coil 51 is used as a flaw detection surface. Yes. When performing eddy current flaw detection using a flaw detection probe, the surface of the test object and the flaw detection surface are appropriately spaced apart from each other, and the flaw detection probe is arranged so that the central axis of the excitation coil 51 is substantially orthogonal to the surface of the test object. And an alternating current is passed through the exciting coil 51. An alternating current generates an alternating magnetic field that penetrates the exciting coil 51, and an eddy current is induced on the surface of the test object by the alternating magnetic field. A voltage is generated between both terminals of the detection coil 52 by an alternating magnetic field caused by an alternating current flowing through the exciting coil 51 and an alternating magnetic field caused by an eddy current.

  When there is a flaw on the surface of the test object, eddy current flows along the flaw, so the flow path of the eddy current changes from that when there is no flaw. Therefore, when the flaw detection probe moves from a portion where no flaw exists to a portion where a flaw exists, the strength and direction of the alternating magnetic field generated by the eddy current changes, and this alternating magnetic field induces between both terminals of the detection coil 52. The applied voltage changes. Therefore, the presence or absence of a flaw can be detected by measuring the voltage generated between both terminals of the detection coil 52.

  However, in the flaw detection probe shown in FIG. 11, the output of the voltage generated between both terminals of the detection coil 52 includes a component that depends on the distance between the excitation coil 51 and the surface of the test object, the so-called lift-off value. Therefore, noise resulting from the change in lift-off is mixed in the output result. Since it is difficult to extract only the component resulting from the presence of a flaw from the output result, there is a problem that it is difficult to analyze in detail the nature of the flaw such as the type and depth of the flaw.

  In order to solve this problem, a flaw detection probe that does not generate noise due to a change in lift-off has been developed. Non-Patent Document 1 discloses a flaw detection probe that does not generate noise due to a change in lift-off. FIG. 12 is a schematic perspective view showing the structure of the flaw detection probe disclosed in Non-Patent Document 1. A rectangular cylinder-shaped coil in which windings are wound around the other four surfaces including the bottom surface and the top surface is defined as the exciting coil 53, with the direction perpendicular to the two opposing surfaces of the rectangular parallelepiped as the center axis direction. In the center of the bottom surface of the excitation coil 53, an annular detection coil 54 whose central axis is orthogonal to the bottom surface of the excitation coil 53 is disposed. During flaw detection, the flaw detection probe is arranged so that the bottom surface of the excitation coil 53 is substantially parallel to the surface of the test object.

  On the bottom surface of the exciting coil 53, the windings are arranged in parallel at substantially equal intervals. By passing an alternating current through the exciting coil 53, an eddy current parallel to the winding is generated on the surface of the test object immediately below the bottom surface of the exciting coil 53. This eddy current is an eddy current in which the flowing direction is substantially parallel and the current density is uniform. Since the AC magnetic field due to the AC current flowing through the exciting coil 53 and the AC magnetic field due to the eddy current are hardly linked to the annular detection coil 54, when there is no flaw on the surface of the test object, between the two terminals of the detection coil 54 Is substantially zero. Therefore, even when the lift-off changes, the output between both terminals of the detection coil 54 hardly includes noise. If there is a scratch on the surface of the test object, the flow path of the eddy current changes due to the eddy current flowing along the scratch, so that an alternating magnetic field linked to the detection coil 54 due to the eddy current that has changed the flow path is generated. And a voltage is generated between both terminals of the detection coil 54. As described above, by using the flaw detection probe disclosed in Non-Patent Document 1 as shown in FIG. 12, a flaw detection test can be performed without being affected by noise caused by a change in lift-off. Therefore, by using the flaw detection probe shown in FIG. 12, the flaw detection sensitivity in the flaw detection test is improved, so that the flaw detection test using this flaw detection probe has been put to practical use.

Koyama Kiyoshi and Hoshikawa Hiroshi “Study on Fundamental Characteristics of Uniform Eddy Current Probes in Eddy Current Testing”, Nondestructive Inspection, Japan Nondestructive Inspection Association, November 2000, Vol. 49, No. 11, p. 775-781

  The present inventor conducted a flaw detection experiment in order to confirm the practicality of the flaw detection probe configured as shown in FIG. Artificial flaws were generated on a metal test piece, and a flaw detection test was performed on the test piece using a flaw detection probe having the structure shown in FIG. FIG. 13 is a characteristic diagram showing the output of the flaw detection probe with respect to the depth of the artificial flaw on the surface of the test piece. The horizontal axis indicates the distance from a predetermined position on the test piece to the scratch. The vertical axis represents the output voltage of the detection coil 54 that has undergone phase detection in response to the alternating current flowing in the excitation coil 53, and this is the output of the flaw detection probe. The excitation coil 53 of the flaw detection probe had a 12 mm square cube shape, and the detection coil 54 had a diameter of 5 mm. Carbon steel SS400 was used for the test piece. The frequency of the alternating current flowing through the exciting coil 53 was 50 kHz, and the lift-off was 1 mm. In FIG. 13, the test result which performed the flaw detection test with respect to the artificial wound whose depth of a wound is 0.6 mm-8.0 mm is shown.

  As shown in FIG. 13, as the depth of the artificial wound increases to 0.6 mm, 1.2 mm, 1.8 mm, and 2.0 mm, the amplitude of the output of the flaw detection probe obtained for the artificial wound becomes smaller. To go. For an artificial flaw having a flaw depth of 2.0 mm or more, the amplitude of the output of the flaw detection probe increases as the flaw depth increases. Further, although not shown in the drawing, it has been observed that in the case of an artificial flaw having a flaw depth of less than 0.6 mm, the output amplitude of the flaw detection probe increases as the flaw depth increases. That is, it has been found that depending on the depth of the flaw, the output of the flaw detection probe may increase as the flaw depth increases, and conversely, the output of the flaw detection probe may decrease. In this state, since the change in the flaw depth does not simply correspond to the change in the flaw detection probe output, it is difficult to estimate the flaw depth when the flaw detection probe output is obtained. This phenomenon is also observed in a flaw detection experiment using a nonmagnetic aluminum test piece, and it has been confirmed that this phenomenon occurs regardless of the material. Further, among the output waveforms of the flaw detection probe output for each artificial flaw shown in FIG. 13, the output obtained for the artificial flaw having a flaw depth of 1.2 mm, 1.8 mm, 2.0 mm, and 2.4 mm. The waveform is a waveform in which two signal waveforms are superimposed, and it is estimated that two types of phenomena occur.

  Next, the inventor measured the perpendicular component of the magnetic field generated on the surface of the test piece by the exciting coil 53 with respect to the test piece surface. FIG. 14 is a characteristic diagram showing the measurement result of the vertical component of the magnetic field generated by the excitation coil 53 with respect to the test piece surface. Using a planar coil having a diameter of 5 mm, the perpendicular component of the magnetic field generated around a 12 mm square cubic excitation coil 53 with respect to the test piece surface was measured on the test piece surface. The frequency of the alternating current flowing through the exciting coil 53 was 50 kHz, and the lift-off was 1 mm. The horizontal axis indicates the relative distance from the position directly below the center of the exciting coil 53 along the direction parallel to the central axis of the exciting coil 53, the vertical axis indicates the output voltage of the planar coil, and the strength of the magnetic field. Corresponding to The sign indicated by the vertical axis corresponds to the direction of the vertical component of the magnetic field. The vertical component of the magnetic field shown in the figure is distributed so that the magnetic field strength is maximized at the end of the exciting coil 53 and the magnetic field strength is minimized at the central portion of the exciting coil 53. Correspondingly, the component of the magnetic field parallel to the surface of the test piece is distributed so that the magnetic field strength is minimized at the end of the exciting coil 53 and the magnetic field strength is maximized at the central portion of the exciting coil 53. Since eddy currents are generated by the vertical and parallel components of these magnetic fields, two types of eddy currents are generated on the surface of the test piece. Therefore, as shown in FIG. 13, the output of the flaw detection probe has a waveform in which two signal waveforms are superimposed. Further, since the eddy current generated on the surface of the test piece is generated according to the vertical component and the parallel component of the magnetic field having different strengths depending on the position, the direction and the strength change depending on the position. In the flaw detection probe shown in FIG. It has been found that it is difficult to actually obtain a substantially parallel and uniform eddy current as disclosed in Patent Document 1. This is the reason why the change in the flaw depth does not simply correspond to the change in the output of the flaw detection probe.

  Next, the inventor measured the parallel component of the magnetic field generated by the exciting coil 53 on the surface of the test piece while changing the length of the exciting coil 53. FIG. 15 is a characteristic diagram showing the measurement result of the parallel component of the magnetic field generated by the exciting coil 53 with respect to the test piece surface. The horizontal axis indicates the relative distance from the position directly below the center of the exciting coil 53 along the direction parallel to the central axis of the exciting coil 53, and the vertical axis indicates the output voltage of the planar coil, and the magnetic field strength. Correspond. The excitation coil 53 had a width and height of 12 mm, and the magnetic field was measured for the excitation coil 53 whose length in the central axis direction was 12 mm, 24 mm, and 36 mm, respectively. In the figure, when the length of the exciting coil 53 is 12 mm, 24 mm, and 36 mm, the measurement results are shown by a solid line, a broken line, and a one-dot chain line, respectively. It can be seen that the longer the length of the exciting coil 53, the wider the region where the intensity of the parallel component of the magnetic field is maximum and becomes uniform regardless of the position. In this region, since the strength of the parallel component of the magnetic field is uniform and the strength of the vertical component of the magnetic field is minimal, the magnetic field is substantially parallel to the test piece surface and is substantially parallel to the test piece surface. Various eddy currents are generated.

  Based on the above results, a substantially parallel and uniform eddy current is generated on the surface of the test object, and there is a simple increase between the change in the depth of the flaw and the change in the amplitude of the output of the detection coil 54 that detects the flaw. It can be seen that it is necessary to make the length about three times longer than the width of the exciting coil 53 in order to obtain the above. However, in a normal flaw detection test, a worker performs a flaw detection operation in which a flaw detection probe is held by hand, so that a flaw detection probe held by a worker by hand has an outer diameter of 18 mm in diameter so that it can be easily held by hand. Desirably less than or equal to. In order to reduce the outer dimension of the flaw detection probe to a diameter of about 18 mm or less, the length of the exciting coil 53 needs to be 12 mm or less at most. Therefore, the region where the eddy current becomes substantially uniform on the test object is narrow. Thus, it is difficult to obtain a simple increase relationship between the change in the flaw depth and the change in the output of the flaw detection probe. Therefore, a flaw detection probe capable of manual flaw detection has a problem that it is difficult to estimate the flaw depth from the output of the flaw detection probe.

  As a method for obtaining a simple increase relationship between the change in the depth of the flaw and the change in the output of the flaw detection probe using the excitation coil 53 having a dimension of 12 mm or less, the diameter of the detection coil 54 is reduced and the vertical direction of the magnetic field is reduced. A method is conceivable in which the output signal of the detection coil 54 is measured at a very small portion at the center of the exciting coil 53 where the component is the smallest and the parallel component is the largest. However, when the area of the detection coil 54 is reduced by reducing the diameter of the detection coil 54, the output voltage of the detection coil 54 is lowered, and the signal-to-noise (S / N) ratio of the output signal is deteriorated. There is a problem that decreases.

  The present invention has been made in view of such circumstances, and an object of the present invention is to easily estimate the depth of the scratch from the output without deteriorating the detection accuracy of the scratch. It is to provide a flaw detection probe.

  The flaw detection probe according to the present invention is a flaw detection probe comprising: an excitation coil that induces eddy current in a flaw detection target; and a detection coil that outputs a signal corresponding to the state of the eddy current induced in the excitation coil. Is formed by winding a conductor in a rectangular tube having a polygonal cross section perpendicular to the central axis, and the detection coil is arranged so that the central axis intersects one side surface of the rectangular cylindrical excitation coil. A conductor is wound around one side surface.

  In the present invention, a flaw detection probe is configured by arranging a detection coil so as to surround one side surface of an excitation coil in which a conductor is wound in a rectangular tube shape, and one side surface of the excitation coil surrounded by the detection coil is connected to the flaw detection probe. The flaw detection surface. As a result, the portion where the parallel component of the magnetic field generated by the exciting coil is maximum and the portion where the vertical component is maximum are both located inside the detection coil, and the scratch on the surface of the flaw detection target is detected. Changes in eddy current due to the presence occur inside the detection coil.

  A flaw detection probe according to the present invention is a flaw detection probe comprising an exciting coil that induces eddy current in a flaw detection target, and an annular detection coil that outputs a signal corresponding to the state of the eddy current induced in the exciting coil. The excitation coil is formed by winding a conductor in a rectangular tube shape having a polygonal cross section perpendicular to the central axis, and the detection coil has a length in at least one direction in the central axis direction of the excitation coil. The one side diameter of the detection coil is substantially parallel to the central axis of the excitation coil on the outside of one side surface of the exciting coil having a rectangular tube shape, and the detection coil The detection coil is arranged so that a central axis intersects the one side surface.

  In the present invention, the outer side of one side of the exciting coil in which a conductor is wound in a rectangular tube shape is formed such that the length of the diameter in at least one direction is equal to or longer than the length in the central axis direction of the exciting coil. The flaw detection probe is configured by arranging the annular detection coil so that the diameter direction equal to or longer than the length of the exciting coil is parallel to the central axis direction of the exciting coil. One side surface of the excitation coil in which the detection coil is arranged outside is defined as a flaw detection surface of the flaw detection probe.

  In the present invention, by arranging the detection coil so as to surround the flaw detection surface of the exciting coil in which a conductor is wound in a rectangular tube shape, a change in eddy current due to the presence of a flaw is generated inside the detection coil. A simple increasing relationship can be obtained between the change in the flaw depth and the change in the output of the flaw detection probe. Therefore, in the flaw detection test, the depth of the flaw can be easily estimated from the output of the flaw detection probe. In addition, since the detection coil diameter is large so as to surround the flaw detection surface of the excitation coil, the detection coil output is reduced at a minute portion where the vertical component of the magnetic field by the excitation coil is minimized by reducing the detection coil diameter. Compared with the method of obtaining the voltage, the output voltage of the detection coil is increased and the S / N ratio is improved. Therefore, the depth of the scratch can be easily estimated from the output without deteriorating the detection accuracy of the scratch.

  In the present invention, since the length of the diameter is equal to or greater than the length of the excitation coil in the central axis direction, it is caused by the presence of a flaw as in the case where the detection coil is arranged so as to surround the flaw detection surface of the excitation coil. A change in eddy current is generated inside the detection coil, and a simple increase relationship can be obtained between the change in the flaw depth and the change in the output of the flaw detection probe. Therefore, the depth of the scratch can be easily estimated from the output. In addition, since the outer diameter of the flaw detection probe can be made smaller than when the detection coil is arranged so as to surround the flaw detection surface of the excitation coil, it is possible to realize a flaw detection probe that is easier for an operator to use. .

It is a perspective view which shows the main structures of the flaw detection probe of this invention which concerns on Embodiment 1. FIG. It is a block diagram which shows the structure of the flaw detection apparatus using the flaw detection probe which concerns on Embodiment 1. FIG. It is a top view which shows typically the method of a flaw detection experiment. It is a characteristic view which shows the output of a flaw detection probe with respect to the depth of the artificial flaw produced | generated to the test piece of carbon steel. It is a characteristic view which shows the output of a flaw detection probe with respect to the depth of the artificial flaw produced | generated to the test piece of aluminum. It is a perspective view which shows the flaw detection probe which formed the exciting coil in the triangular cylinder shape. It is a perspective view which shows the flaw detection probe which has arrange | positioned the detection coil to the outer side of the flaw detection surface of an exciting coil. It is a perspective view which shows the flaw detection probe which has arrange | positioned the detection coil inside the flaw detection surface of an exciting coil. It is a perspective view which shows the main structures of the flaw detection probe of this invention which concerns on Embodiment 2. FIG. It is a block diagram which shows the structure of the flaw detection apparatus of this invention using the flaw detection probe which concerns on Embodiment 2. FIG. It is a schematic diagram which shows the structural example of the conventional flaw detection probe. It is a typical perspective view which shows the structure of the flaw detection probe disclosed by the nonpatent literature 1. It is a characteristic view which shows the output of a flaw detection probe with respect to the depth of the artificial flaw on the surface of a test piece. It is a characteristic view which shows the measurement result of the perpendicular | vertical component with respect to the test piece surface of the magnetic field produced | generated by an exciting coil. It is a characteristic view which shows the measurement result of the parallel component with respect to the test piece surface of the magnetic field produced | generated by an exciting coil.

(Embodiment 1)
Hereinafter, the present invention will be specifically described with reference to the drawings showing embodiments thereof.
FIG. 1 is a perspective view showing the main configuration of the flaw detection probe according to the first embodiment of the present invention. The flaw detection probe 1 includes an excitation coil 11 that induces an eddy current in a test target (flaw detection target) of a flaw detection test, and a detection coil 12 that outputs a signal corresponding to the state of the eddy current. The exciting coil 11 is formed by winding a conductor in a square tube with an air core having a rectangular cross section perpendicular to the central axis of the exciting coil 11. The detection coil 12 has an annular shape in plan view, and is formed by winding a conductor so as to surround one side surface of the rectangular cylindrical excitation coil 11. Note that the shape of the detection coil 12 in plan view is not limited to an annular shape, and may be other shapes such as a quadrangular ring or a hexagonal ring as long as it surrounds one side surface of the excitation coil 11. . The detection coil 12 is arranged so that the central axis intersects the one side surface of the exciting coil 11, and preferably the central axis is substantially orthogonal to the one side surface.

  The flaw detection probe 1 configured as described above is appropriately separated from the test object with one side surface of the excitation coil 11 surrounded by the detection coil 12 as a flaw detection surface, with the flaw detection surface facing the surface of the test object. Used by manipulating the surface of the test object in the state.

  FIG. 2 is a block diagram illustrating a configuration of a flaw detection apparatus using the flaw detection probe 1 according to the first embodiment. The flaw detection apparatus includes a flaw detection probe 1, and an oscillator 21 is connected to the excitation coil 11. The oscillator 21 is configured to generate an alternating current having a predetermined frequency and supply the generated alternating current to the exciting coil 11. An amplifier 22 is connected to the detection coil 12. The amplifier 22 is configured to receive an output of a voltage generated at both ends of the detection coil 12, appropriately amplify the output from the received detection coil 12, and output an amplified signal. A phase detector 23 is connected to the oscillator 21 and the amplifier 22. The phase detector 23 receives a signal output from the amplifier 22 as an input signal, receives an alternating current generated by the oscillator 21 as a reference signal, detects a signal having the same frequency as the reference signal from the input signal, and detects the amplitude of the detected signal. And a signal proportional to the phase difference between the reference signal and the detected signal. The phase detector 23 is connected to a voltmeter 24 that measures the voltage indicated by the signal output from the phase detector 23. The voltmeter 24 is configured to output digital data indicating the measured voltage. The voltmeter 24 is connected to a recording unit 25 such as a personal computer (PC) that receives and records the digital data output from the voltmeter 23. The voltmeter 24 may be configured to output analog data indicating a voltage, and the recording unit 25 is a recording device such as a pen recorder that records the value of the data output from the voltmeter 24 on a recording sheet. There may be.

  In the flaw detection apparatus shown in FIG. 2, when the oscillator 21 generates an alternating current, the generated alternating current flows through the exciting coil 11, and an eddy current is generated on the surface of the test object. When there is a scratch on the surface of the test object, a voltage is generated at both ends of the detection coil 12 due to a change in the eddy current on the surface of the test object, and the amplifier 22 generates a voltage generated at both ends of the detection coil 12. And outputs a signal obtained by appropriately amplifying the received output to the phase detector 23. The phase detector 23 receives the signal from the amplifier 22 as an input signal, receives the alternating current from the oscillator 21 as a reference signal, and is a signal proportional to the amplitude of the signal having the same frequency as the reference signal and the phase difference from the reference signal. Is output. The voltmeter 24 receives the signal from the phase detector 23, measures the voltage indicated by the received signal, outputs digital data indicating the measured voltage, and the recording unit 25 records the digital data output by the voltmeter 24. To do.

  A flaw detection experiment was performed using the flaw detection apparatus having the above configuration. The exciting coil 11 was formed by winding a linear 0.2 mm polyimide wire 160 times, and made a cubic shape with a side of 12 mm as a whole. An annular bobbin having an inner diameter of 16 mm surrounding the flaw detection surface of the exciting coil 11 was arranged, and the detection coil 12 was formed by winding a linear 70 μm polyimide wire around the annular bobbin 120 times. Carbon steel SS400 and aluminum A1050 were used as test pieces. Each test piece had a width of 60 mm and a length of 550 mm. The artificial flaw was generated by machining with a width of 0.3 mm and a test piece width of 50 mm.

  FIG. 3 is a plan view schematically showing a flaw detection test method. In the flaw detection test, the flaw detection probe 1 is arranged so that the flaw detection surface of the flaw detection probe 1 faces the surface of the test piece and the winding direction of the excitation coil 11 is substantially parallel to the length direction of the artificial flaw. As indicated by the white arrow inside, the flaw detection probe 1 is moved in a direction perpendicular to the length direction of the artificial flaw, and the output signal of the detection coil 12 at each position on the test piece is measured by the voltmeter 24 and recorded. Recorded in.

  FIG. 4 is a characteristic diagram showing the output of the flaw detection probe 1 with respect to the depth of the artificial flaw generated on the test piece of carbon steel. The horizontal axis indicates the distance from a predetermined position on the test piece to the scratch. The vertical axis represents the voltage value obtained by measuring the voltage of the signal output from the phase detector 23 by the voltmeter 24, and this is the output of the flaw detection probe 1. The frequency of the alternating current flowing through the exciting coil 11 was 50 kHz, and the lift-off was 1 mm. In the figure, the flaw detection result for each artificial flaw having a flaw depth of 0.5 mm to 10 mm is shown. As shown in the figure, the amplitude of the output of the flaw detection probe 1 simply increases in proportion to the depth of the scratch. That is, unlike the conventional case shown in FIG. 13, a simple increase relationship can be obtained between the change in the flaw depth and the change in the output of the flaw detection probe 1 according to the present invention.

  In the conventional case, the portion where the parallel component of the magnetic field generated by the exciting coil with respect to the surface of the test object is maximum is located inside the detection coil, and the portion of the magnetic field perpendicular to the surface of the test object is maximum. It was located outside the detection coil. On the other hand, in the present invention, the portion where the parallel component of the magnetic field generated by the exciting coil 11 is maximum and the portion where the vertical component is maximum are both located inside the detection coil 12. That is, in the conventional case, eddy currents caused by the parallel component and the perpendicular component of the magnetic field generated by the excitation coil with respect to the surface of the test object are located inside and outside the detection coil. In the present invention, both types of eddy currents are located inside the detection coil 11. Therefore, since all changes in eddy current due to the presence of flaws occur inside the detection coil 11, a simple increase relationship can be obtained between the flaw depth change and the flaw detection probe 1 output change. Presumed to be possible.

  FIG. 5 is a characteristic diagram showing the output of the flaw detection probe 1 with respect to the depth of the artificial flaw generated on the aluminum test piece. In this case, the frequency of the alternating current flowing through the exciting coil 11 was 25 kHz. In the figure, the flaw detection result for each artificial flaw having a flaw depth of 0.1 mm to 10 mm is shown. As shown in the figure, as in the case where the test piece is made of carbon steel, the amplitude of the output of the flaw detection probe 1 simply increases in proportion to the depth of the flaw. That is, in the present invention, it has been found that a simple increase relationship can be obtained between the change in the depth of the flaw and the change in the output of the flaw detection probe 1 regardless of the presence or absence of magnetism in the test object.

  As described above, in the present invention, by arranging the detection coil 12 so as to surround the flaw detection surface of the exciting coil 11 in which a conductor is wound in a rectangular tube shape, a change in eddy current due to the presence of a flaw is detected by the detection coil 12. And a simple increase relationship can be obtained between the change in the depth of the flaw and the change in the output of the flaw detection probe 1. Therefore, in the flaw detection test, the depth of the flaw can be easily estimated from the output of the flaw detection probe 1. Further, since the diameter of the detection coil 12 is formed so as to surround the flaw detection surface of the exciting coil 11, the diameter of the detecting coil is reduced to detect a minute portion where the vertical component of the magnetic field by the exciting coil 11 is minimum. Compared with the method of obtaining the output voltage of the coil, the output voltage of the detection coil 12 is increased and the S / N ratio is improved. Therefore, the depth of the scratch can be easily estimated from the output without deteriorating the detection accuracy of the scratch.

  In the configuration example of the flaw detection probe 1 shown above, the form in which the excitation coil 11 is formed in a rectangular tube shape is shown, but the shape of the excitation coil 11 is not limited to this, and is perpendicular to the central axis of the excitation coil 11. The cross section may be a polygon other than a square. FIG. 6 is a perspective view showing the flaw detection probe 1 in which the exciting coil 11 is formed in a triangular tube shape. The exciting coil 11 is formed by winding a conductor in a triangular cylindrical shape whose cross section perpendicular to the central axis of the exciting coil 11 is a triangle, and the detection coil 12 is arranged so as to surround one side of the exciting coil 11 having a triangular cylindrical shape. Has been. The flaw detection probe 1 uses one side surface of the excitation coil 11 surrounded by the detection coil 12 as a flaw detection surface. The cross section perpendicular to the central axis of the exciting coil 11 is preferably formed in an isosceles triangle shape with one side included in the flaw detection surface as the base. Since the current flowing through the surface other than the flaw detection surface of the exciting coil 11 is a useless current that does not contribute to the generation of eddy currents in the test object, forming the exciting coil 11 into a triangular cylindrical shape results in a rectangular cylindrical shape. As compared with the exciting coil, useless current is reduced, and electric power for performing a flaw detection test can be reduced. Further, the exciting coil 11 may have a cross section perpendicular to the central axis of the exciting coil 11 in other polygonal shapes such as a trapezoidal shape or a hexagonal shape.

  In the configuration example of the flaw detection probe 1 described above, the detection coil 12 is arranged so as to surround the flaw detection surface of the excitation coil 11. However, the arrangement of the detection coil 12 is not limited to this. The form which has arrange | positioned the detection coil 12 to the outer side of the flaw detection surface of the exciting coil 11 of a rectangular tube shape may be sufficient. FIG. 7 is a perspective view showing the flaw detection probe 1 in which the detection coil 12 is arranged outside the flaw detection surface of the excitation coil 11. In the flaw detection probe 1, a detection coil 12 is disposed outside one side surface of the exciting coil 11 having a rectangular tube shape so that the central axis is linked to the side surface, and the excitation coil 11 in which the detection coil 12 is disposed. One side is used as a flaw detection surface. The detection coil 12 preferably has a central axis substantially orthogonal to the one side surface of the excitation coil 11. The detection coil 12 is located between the flaw detection surface of the excitation coil 12 and the test object. The detection coil 12 is formed so that the length of the diameter in at least one direction is equal to or larger than the length of the central axis direction of the excitation coil 11, and the direction of the diameter larger than the length of the excitation coil 11 is the excitation coil 11. It is arrange | positioned so that it may become substantially parallel to the center axis direction.

  Since the flaw detection probe 1 shown in FIG. 7 has a diameter greater than or equal to the length of the exciting coil 11 in the central axis direction, the parallel component of the magnetic field generated by the exciting coil 11 with respect to the surface of the test object is maximized. Both the part and the part where the vertical component is maximum are located inside the detection coil 12. Therefore, as in the case where the detection coil 12 is arranged so as to surround the flaw detection surface of the excitation coil 11, a simple increase relationship can be obtained between the change in the flaw depth and the change in the output of the flaw detection probe 1. it can. Further, the configuration in which the detection coil 12 is disposed outside the flaw detection surface of the excitation coil 11 has a smaller outer diameter of the flaw detection probe 1 than the configuration in which the detection coil 12 is disposed so as to surround the flaw detection surface of the excitation coil 11. Therefore, it is possible to realize the flaw detection probe 1 that is easier for an operator to use when performing a manual flaw detection operation.

  Further, the flaw detection probe 1 may have a configuration in which the detection coil 12 is arranged inside the flaw detection surface of the rectangular tube-shaped excitation coil 11. FIG. 8 is a perspective view showing the flaw detection probe 1 in which the detection coil 12 is arranged inside the flaw detection surface of the excitation coil 11. A detection coil 12 is arranged inside one side surface of the exciting coil 11 having a rectangular tube shape so that the central axis is linked to the one side surface. The detection coil 12 preferably has a central axis substantially orthogonal to the one side surface. The flaw detection probe 1 uses one side surface of the excitation coil 11 on which the detection coil 12 is disposed as a flaw detection surface. The flaw detection surface of the excitation coil 11 is located between the detection coil 12 and the test object. By arranging the detection coil 12 inside the flaw detection surface of the excitation coil 11, the flaw detection surface of the excitation coil 11 can be brought closer to the surface of the test object. Therefore, the density of eddy current is made denser and a sensitive flaw detection test is possible.

(Embodiment 2)
FIG. 9 is a perspective view showing a main configuration of the flaw detection probe according to the second embodiment of the present invention. The flaw detection probe 3 includes an excitation coil 31, a first detection coil 32, and a second detection coil 33. The exciting coil 31 is formed by winding a conductor in an air-core square cylinder whose cross section perpendicular to the central axis is rectangular. The first detection coil 32 is formed in an annular shape having a diameter smaller than the length of the excitation coil 31 in the central axis direction, and is disposed outside one side surface of the excitation coil 31. The second detection coil 33 has an annular shape in plan view, and is formed by winding a conductor so as to surround one side surface of the excitation coil 31 in which the first detection coil 32 is disposed on the outside. The first detection coil 32 and the second detection coil 33 are arranged so that each central axis intersects the one side surface of the exciting coil 31, and preferably, each central axis is substantially orthogonal to the one side surface. The flaw detection probe 3 uses one side surface of the excitation coil 31 on which the first detection coil 32 is disposed as a flaw detection surface.

  FIG. 10 is a block diagram showing a configuration of a flaw detection apparatus of the present invention using the flaw detection probe 3 according to the second embodiment. The flaw detection apparatus includes a flaw detection probe 3, and an oscillator 41 is connected to the excitation coil 31. The oscillator 41 is configured to generate an alternating current having a predetermined frequency and supply the generated alternating current to the exciting coil 31. The first detection coil 32 is connected to the first amplifier 42, and the second detection coil 33 is connected to the second amplifier 43. The first amplifier 42 and the second amplifier 43 receive outputs of voltages generated at both ends of the first detection coil 32 and the second detection coil 33, respectively, and outputs from the received first detection coil 32 and second detection coil 33. Is appropriately amplified, and an amplified signal is output. The first amplifier 42 and the second amplifier 43 are connected to a first phase detector 44 and a second phase detector 45, respectively, and an oscillator 41 is connected to the first phase detector 44 and the second phase detector 45. Has been. The first phase detector 44 and the second phase detector 45 accept the signals output from the first amplifier 42 and the second amplifier 43 as input signals, respectively, and accept the alternating current generated by the oscillator 41 as a reference signal. A signal having the same frequency as the reference signal is detected from the signal, and a signal proportional to the detected signal amplitude and the phase difference between the reference signal and the detected signal is output.

  A first voltmeter 46 and a second voltmeter 47 that measure the voltage indicated by the output signal are connected to the first phase detector 44 and the second phase detector 45, respectively. The first voltmeter 46 outputs digital data (first signal) indicating the measured voltage, and the second voltmeter 47 is configured to output digital data (second signal) indicating the measured voltage. . The first voltmeter 46 and the second voltmeter 47 are connected to a calculation unit 48 that receives the digital data output from the first voltmeter 46 and the second voltmeter 47 and performs a calculation based on the received digital data. Yes.

  In the flaw detector of the present invention according to the present embodiment, when the oscillator 41 generates an alternating current, the generated alternating current flows through the exciting coil 31, and an eddy current is generated on the surface of the test object. When a flaw exists on the surface of the test object, a voltage is generated at both ends of the first detection coil 32 and the second detection coil 33 due to a change in eddy current on the surface of the test object, and the first amplifier 42, The second amplifier 43 receives the output of the voltage generated at both ends of the first detection coil 32 and the second detection coil 33, respectively, and the first phase detector 44 and the second signal respectively obtained by appropriately amplifying the received output. Output to the phase detector 45. The first phase detector 44 and the second phase detector 45 accept the signals from the first amplifier 42 and the second amplifier 43 as input signals, respectively, accept the alternating current from the oscillator 41 as a reference signal, A signal proportional to the amplitude of the signal of the same frequency and the phase difference from the reference signal is output. The first voltmeter 46 and the second voltmeter 47 receive signals from the first phase detector 44 and the second phase detector 45, respectively, measure the voltage indicated by the received signals, and indicate the measured voltage. The data is output to the calculation unit 48.

  The computing unit 48 performs four arithmetic operations on the digital data output from each of the first voltmeter 46 and the second voltmeter 47, and detects flaws due to the parallel component of the magnetic field generated by the exciting coil with respect to the surface of the test object. A process for separating the signal and the detection signal of the flaw due to the vertical component of the magnetic field on the surface of the test object is performed. In the first detection coil 32, the portion where the parallel component of the magnetic field is maximum is located on the inner side, and the portion where the vertical component of the magnetic field is maximum is located on the outer side. The detection signal of the scratch caused by the vertical component of the magnetic field is output in the opposite phase. On the other hand, in the second detection coil 33, the part where the parallel component of the magnetic field is maximum and the part where the vertical component is maximum are both located on the inner side. The detection signal of the flaw caused by the vertical component of is overlapped in the same phase and output. Therefore, the digital data output from each of the first voltmeter 46 and the second voltmeter 47 is appropriately amplified and then added to or subtracted from each other, thereby detecting flaws caused by the parallel component of the magnetic field. It is possible to separate the signal and the detection signal of the scratch caused by the vertical component of the magnetic field.

  As described above in detail, in the present embodiment, the first detection coil 32 having a diameter smaller than the length of the excitation coil 31 in the central axis direction is disposed outside one side surface of the excitation coil 31 and surrounds this side surface. By further disposing the second detection coil 33, the detection signal of the scratch caused by the parallel component of the magnetic field generated by the excitation coil with respect to the surface of the test object is separated from the detection signal of the scratch caused by the vertical component of the magnetic field. Is possible. Therefore, in the flaw detection test, it is possible to examine in detail whether or not there is a scratch on the surface of the test object.

  In the present embodiment, the second detection coil 33 is disposed so as to surround the flaw detection surface of the excitation coil 31. However, the present invention is not limited to this, and the length of the diameter in at least one direction is not limited to this. The second detection coil 33 formed to have a length equal to or greater than the length of the excitation coil 31 in the central axis direction has a diameter direction equal to or greater than the length of the excitation coil 31 parallel to the central axis direction of the excitation coil 31. 2 The form arrange | positioned on the outer side of the flaw detection surface of the excitation coil 31 so that the center axis | shaft of the detection coil 33 may cross | intersect the flaw detection surface of the excitation coil 31 may be sufficient.

DESCRIPTION OF SYMBOLS 1, 3 Flaw detection probe 11, 31 Excitation coil 12 Detection coil 32 1st detection coil 33 2nd detection coil 21, 41 Oscillator 23 Phase detector 44 1st phase detector 45 2nd phase detector

Claims (2)

In a flaw detection probe comprising an exciting coil that induces eddy current in a flaw detection target, and a detection coil that outputs a signal according to the state of the eddy current induced in the exciting coil.
The exciting coil is formed by winding a conductor in a rectangular tube shape having a polygonal cross section perpendicular to the central axis,
The flaw detection probe according to claim 1, wherein the detection coil is formed by winding a conductor so as to surround the one side surface so that a central axis intersects one side surface of the exciting coil having a rectangular tube shape. In a flaw detection probe comprising an exciting coil that induces eddy current in a flaw detection target and an annular detection coil that outputs a signal corresponding to the state of the eddy current induced in the exciting coil,
The exciting coil is formed by winding a conductor in a rectangular tube shape having a polygonal cross section perpendicular to the central axis,
The detection coil has a length of a diameter in at least one direction equal to or greater than a length in a central axis direction of the excitation coil,
Outside the one side surface of the exciting coil having a rectangular tube shape, the one-way diameter of the detection coil is substantially parallel to the central axis of the excitation coil, and the central axis of the detection coil is the one side surface. The flaw detection probe is characterized in that the detection coil is arranged so as to intersect.

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