JP5638544B2 - Eddy current testing probe - Google Patents

Description

  The present invention relates to an eddy current flaw detection probe.

  The principle of eddy current flaw detection is that an eddy current is induced in a test object by an AC magnetic field generated by a coil for a conductive test object, and the defect impedance is changed from the change in the impedance of the coil due to the eddy current disturbance due to the defect. This is a method for evaluating the presence or absence.

  Generally, an upper eddy current flaw detection probe can be efficiently penetrated into the surface of an object to be inspected by arranging the coil (excitation coil) for generating an alternating magnetic field so that the axial direction thereof is orthogonal to the surface of the object to be inspected. . A current (eddy current) is generated on the surface of the inspection object so as to cancel the alternating magnetic field generated from the exciting coil in accordance with the law of electromagnetic induction. If there is a defect, the flow path of this eddy current changes, and the eddy current changes the magnetic field distribution on the subject surface. A defect is detected by capturing this change with a detection coil.

  When eddy current testing is intended to detect minute defects, if a magnetic material is simply excited by a single coil, the magnetic field shows a distribution that spreads widely in space, and eddy currents are also widely generated. For this reason, it becomes a subject that spatial resolution becomes low. In order to overcome this problem, the probe shown in Patent Document 1 has an excitation coil having an excitation coil and an excitation coil that generates an alternating magnetic field along the object to be inspected by a magnetic material core that forms a loop-shaped magnetic circuit. It is. By reducing the gap of the magnetic material core, the eddy current generation region can be narrowed.

Republished patent (WO2003 / 091655)

  In the case of detecting minute defects by eddy current flaw detection, it is important to suppress noise factors in addition to spatial resolution. As a signal factor other than the defect, there is a signal that depends on a distance (lift-off) between the magnetic body and the inspection object. In order to suppress the lift-off signal, the probe of the cited document 1 uses a method of canceling by connecting two detection coils in a differential manner. In this case, although it is possible to reduce the lift-off signal, in reality, an unbalance due to an error in the dimensions and electrical characteristics (resistance, inductance, capacitance) of each detection coil cannot be offset and is generated as a signal. In addition, if the gap of the magnetic material core in the excitation part is reduced to narrow the eddy current generation region, the excitation magnetic field flows directly into the core without entering the specimen, resulting in a decrease in the amount of eddy current generation. In particular, the detection sensitivity of defects is reduced.

  An object of the present invention is to provide a probe having excellent detectability of micro defects by suppressing generation of a lift-off signal and narrowing an eddy current generation region.

The exciter in the eddy current flaw detection probe according to the present invention includes a magnetic material plate arranged so as to sandwich one gap arranged on the inspection surface of the object to be inspected, one detection coil arranged in the gap portion, and the above-mentioned It is composed of a conductive plate arranged immediately above the detection coil , and the exciter is an arrangement in which a certain gap is provided in parallel with the surface of the magnetic material plate facing the object to be inspected. The widest flat portion is disposed in a direction orthogonal to the inspection surface of the object to be inspected and orthogonal to the width direction of the gap, and is disposed adjacent to the detection coil. And

  According to the present invention, it is possible to provide a probe having excellent detectability of a micro defect by suppressing the generation of a lift-off signal and narrowing the eddy current generation region.

It is explanatory drawing of the eddy current test probe structure which shows Example 1. FIG. It is explanatory drawing which shows magnetic field distribution when there is no board | plate which has the electroconductivity with the nonmagnetic material of Example 1. FIG. FIG. 4 is an explanatory diagram showing a magnetic field distribution of Example 1. It is explanatory drawing which shows the detection coil arrangement | positioning of Example 1. FIG. It is explanatory drawing which shows the detection coil arrangement | positioning of Example 1. FIG. It is explanatory drawing of the eddy current test probe structure which shows Example 2. FIG. 6 is an explanatory diagram illustrating a magnetic field distribution of Example 2. FIG. It is explanatory drawing of the eddy current test probe structure which shows Example 3. FIG.

  Examples of the present invention will be described below.

  Example 1 is shown in FIG. The exciter of this probe is obtained by winding an exciting coil around a magnetic material having a gap at one location. Specifically, a member in which an exciting coil 1 is wound around a U-shaped magnetic material 2, and a magnetic material plate 3 arranged with a certain gap at a leg portion of the U-shaped magnetic material 2, 4. The magnetic material plates 3 and 4 are arranged in parallel to the surface facing the device under test 10. The magnetic material 2 and the magnetic material plates 3 and 4 may be an integral structure magnetic material having a gap in part.

  One detection coil 5 is arranged in the gap portion. The axial direction of the detection coil is arranged in a direction orthogonal to the magnetic field across the gap. Specifically, the axial direction of the detection coil shown in FIG. 5 is a direction orthogonal to the surface of the device under test 10, and the axial direction of the detection coil shown in FIG. 4 is parallel to the surface of the device under test 10. There are two types of directions perpendicular to the width direction of the gap.

  And the board 6 which adjoins a detection coil and has electroconductivity with a nonmagnetic material is arrange | positioned. The conductive plate made of the non-magnetic material is disposed so as to stand on the detection coil. The plate 6 is arranged in parallel with the leg portions of the U-shaped magnetic material 2. (The widest plane portion of the plate 6 is arranged in a direction orthogonal to the inspection surface of the object to be inspected 10 and orthogonal to the width direction of the gap.) As the plate 6 having conductivity with a nonmagnetic material, Copper and aluminum are desirable.

  With this configuration, when the exciter is excited with an alternating current, in other words, when an alternating current is passed through the exciting coil 1, a magnetic field is generated. Most of the magnetic field across the gap portion is generated in parallel with the inspection object 10. FIG. 2 shows the XZ plane of FIG. 1 with respect to the gap portion. (FIG. 2 does not show a detection coil.) The magnetic field generated by the exciting coil 1 flows through a gap formed by the magnetic material plates 3 and 4. Here, when there is no electrically conductive plate 6 made of a non-magnetic material, the magnetic material plates 3 and 4 are arranged in parallel with the inspection surface of the object to be inspected 10, so that the magnetic field 11 across the gap. Most of this occurs in parallel with the surface of the device under test 10. An eddy current circulates in the inspection object 10 due to some bulge of the magnetic field 11. This eddy current is indicated by 12, 13, and 14 in the figure.

  On the other hand, the conductive plate 6 made of a non-magnetic material is adjacent to the detection coil, and the widest flat portion of the plate is orthogonal to the inspection surface of the object to be inspected and orthogonal to the width direction of the gap. FIG. 3 shows a schematic diagram of the magnetic field when arranged. The magnetic field 15 across the gap acts on the non-magnetic material and the conductive plate 6, and an eddy current flows through the plate 6. By this action, the magnetic field 15 is distributed so as to be pushed toward the object 10 to be inspected, which is the opposite side to the conductive plate 6 made of a nonmagnetic material. As a result, the magnetic field acting on the object to be inspected 10 increases as compared with the case where there is no conductive plate 6 made of a nonmagnetic material, and the eddy current generated in the object to be inspected 10 also increases. This eddy current is indicated by 16, 17 and 18 in the figure. Since the value of the eddy current generated corresponding to the gap width increases, a large eddy current can be generated in a narrow region, and the detection sensitivity is improved even for a minute defect.

  Next, the principle of suppressing the lift-off signal with one detection coil will be described with reference to FIGS. FIG. 4 shows the case where the axis of the detection coil is parallel to the inspection surface of the device under test 10 and coincides with the direction perpendicular to the width direction of the gap. (The non-magnetic material and the conductive plate 6 are not shown in the figure) The detection coil 20 is voltage-induced by a magnetic field component in the axial direction and measured by a measuring instrument. (A measuring instrument is not shown) The detection coil 20 arranged as described above detects a magnetic field in the Y-axis direction in the figure. In other words, a magnetic field component that is parallel to the inspection surface of the object to be inspected 10 and orthogonal to the gap direction between the magnetic material plates 3 and 4 is detected. The magnetic field around the detection coil 20 has no magnetic field component in the Z-axis direction of the magnetic field 15 as in the XY plane shown in the lower diagram of FIG. When the distance between the probe and the object to be inspected 10 (lift-off) changes, only the magnitude of the magnetic field 15 changes, and no magnetic field component is generated in the Z-axis direction. For this reason, no induced voltage is generated in the detection coil 20 even if the lift-off changes.

  FIG. 5 shows a case where the axis of the detection coil is orthogonal to the inspection surface of the inspection object 10. A voltage is induced in the detection coil 21 by the magnetic field component in the axial direction and is measured by a measuring instrument. (A measuring instrument is not shown) The detection coil 21 arranged as described above detects a magnetic field in the Z-axis direction in the figure. In other words, a magnetic field component orthogonal to the inspection surface of the inspection object 10 is detected. As in the XZ plane shown in the lower diagram of FIG. 5, the magnetic field component in the Z-axis direction of the magnetic field 15 is the center of the gap width formed by the magnetic material plates 3 and 4 (YZ plane passing through half the gap width). Is symmetric. Thus, by arranging the detection coil 21 at the center of the gap width formed by the magnetic material plates 3 and 4, the total sum of the Z-axis components of the magnetic field 15 interlinking with the detection coil 21 becomes zero. That is, the induced voltage of the detection coil 21 is not generated. When the distance (lift-off) between the probe and the object to be inspected 10 changes, only the magnitude of the magnetic field 15 changes. Similarly, the detection coil 21 and the chain arranged at the center of the gap width formed by the magnetic material plates 3 and 4 are connected. The sum of the Z-axis components of the magnetic field 15 that intersects is zero. That is, no induced voltage is generated in the detection coil 20 even if the lift-off changes. As a result, it is possible to suppress the lift-off signal with one detection coil, and the dimensions and electrical characteristics (resistance, inductance, capacitance) of each detection coil, which are problems when differentially connecting two detection coils, are used. ), The lift-off signal generated by the error can be suppressed.

  As described above, according to the present embodiment, the magnetic field direction between the gaps can be changed by using a non-magnetic material that is conductive with respect to sensitivity reduction caused by reducing the gap of the magnetic material core of the excitation unit. The detection sensitivity is improved by directing it toward the object to be inspected. Also, due to errors in the dimensions and electrical characteristics (resistance, inductance, capacitance) of each coil when two detection coils are connected in operation. The generated lift-off signal can be suppressed by using one detection coil and appropriately arranging it between the gaps.

  Example 2 is shown in FIG. This is a structure in which the magnetic field generated in the portion other than the gap portion is shielded by the non-magnetic material and the conductive metals 22 and 23 in the first embodiment. The non-magnetic conductive materials 22 and 23 are arranged in parallel to the inspection surface of the inspection object 10 so as to cover the magnetic material plates 3 and 4 in which a certain gap is formed. It arrange | positions on the outer surface of the surface of 10 side, and the leg part of the magnetic material 2. FIG. Further, the same effect can be obtained when the non-magnetic materials 22 and 23 having conductivity are arranged only on the surface of the magnetic material plates 3 and 4 arranged with a certain gap on the object 10 side. .

  As shown in FIG. 7, the magnetic material plate 3 leaks to the device under test 10 from other than the gap between the magnetic material plates 3 and 4 in the magnetic field 23 due to the action of the non-magnetic material and the conductive metals 22 and 23. , 4 is contained. As a result, the magnetic field 23 shows a distribution that is narrower than that of the first embodiment and expands only in the gap portion. The eddy current generated in the test object 10 by the magnetic field 23 is circulated by the eddy current 25 that is generated in the gap portion from the back to the front in the vertical direction of the paper, and the eddy currents 24 and 26 that are directed from the front to the back in the vertical direction of the paper. To be generated.

  FIG. 8 shows a third embodiment. This is a modification of the structure of the exciter described in the first and second embodiments. By applying currents in opposite directions to the two exciting coils 32 and 33, a magnetic field is generated in the gap between the magnetic material plates 3 and 4 in the same direction as in FIG. Although not shown in the drawing, the same effect can be obtained when a nonmagnetic material and a conductive metal are disposed only on the surface of the magnetic material plates 3 and 4 disposed with a certain gap on the side of the object to be inspected 10. It is done.

  Here, as a specific material example of the magnetic material, it is desirable to use a ferrite core, which is a magnetic material, or a laminated material of a high permeability material such as a permalloy foil strip, an iron-based amorphous foil strip, or an electromagnetic steel plate. Further, it is desirable to select the thickness so that the skin depth δ of the eddy current expressed by the equation (1) is larger than the thickness of the magnetic material by the test frequency to be used. The thickness is the eddy current skin depth expressed by equation (1), and it is desirable that the skin depth at the test frequency to be used be smaller than the shield material thickness. In addition to the detection coil, the same effect can be obtained by using a Hall element or a GMR element as the magnetic field detection element disposed in the gap.

  As described above, according to the present invention, a magnetic material provided with a gap is arranged and a magnetic field is applied to generate an eddy current in the subject using a magnetic flux across the gap. As a result, an eddy current can be generated in a small area, and the defect detection area can be made a small area, so that the resolution can be increased.

DESCRIPTION OF SYMBOLS 1 Excitation coil 2 Magnetic material 3, 4 Magnetic material plate 5 Detection coil 10 Inspected object

Claims (3)

In an eddy current flaw detection probe that uses an excitation coil and magnetic material as an exciter,
The exciter is disposed on a magnetic material plate disposed so as to sandwich one gap disposed on the inspection surface of the object to be inspected, one detection coil disposed in the gap portion, and immediately above the detection coil. Consists of conductive plates ,
The exciter has an arrangement in which the magnetic material plate is provided with a certain gap in parallel to a surface facing the object to be inspected, and the conductive plate has the widest flat part on the inspection surface of the object to be inspected. The eddy current flaw detection probe is arranged in a direction perpendicular to the gap and perpendicular to the width direction of the gap and adjacent to the detection coil. In claim 1 ,
The detection coil arranged in the gap is perpendicular to the inspection surface of the inspection object or parallel to the inspection surface of the inspection object and orthogonal to the width direction of the gap. probe. In claim 1 or 2 ,
An eddy current flaw detection probe characterized in that a plate having conductivity different from the plate having conductivity is arranged on the surface on the inspected object side so as to cover the magnetic material plate provided with the gap.