JPH06294775A - Detector and detecting apparatus for nonoriented defect - Google Patents

Abstract

PURPOSE:To detect a defect highly precisely irrespective of the orientation thereof. CONSTITUTION:In regard to a detector being formed of a material of high permeability shaped in a cube of which the opposite faces are square and having a construction wherein an exciting coil is wound on one terminal of the cube and two sets of detecting coils intersecting the wound exciting coil perpendicularly are provided, the two sets of the detecting coils passing the central part of the material of high permeability are wound crosswise so that they intersect each other.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a defect detector for applying non-destructive non-destructive inspection of surface defects of steel by applying AC magnetism to the surface of the steel.

[0002]

2. Description of the Related Art Conventionally, an eddy current flaw detection method has been known as a method for detecting defects in a steel material. This is because the coil is placed close to the material to be inspected, and when a high-frequency current is passed through it, an eddy current flows on the surface of the non-inspection material. The change is used to detect the defect. This eddy current flaw detection method has a drawback that a change in the distance from the material to be inspected or a change in the magnetic permeability of the material directly changes the impedance greatly. To avoid this drawback, two detection coils are used. Method for canceling the influence of the variation of the distance and the variation of the magnetic permeability of the material to be inspected by differentially coupling, and the exciting coil is wound in parallel with the surface of the material to be inspected disclosed in Japanese Patent Publication No. 61-028938. A coil has been proposed and put into practical use, in which a coil for detecting a secondary magnetic flux is wound around an exciting coil at right angles to each other to detect only a change in magnetic flux due to a defect.

[0003]

However, in order to detect a directional defect such as a crack of a steel material, the prior art has the following problems. First, in the method of differentially coupling the first two coils, if the direction of the defect is a direction intersecting the arrangement direction of the two coils at a right angle as shown in FIG. It is possible to detect defects by sequentially passing the coils over the defects when moving the. However, as shown in FIG. 6B, when the defect and the coil are in the same direction, only one of the coils has a defect at the part where the coil starts to be applied to the defect and the part where the coil is removed from the defect. Although it appears, in the middle part, defects are detected at the same time in the two coils, so they cancel each other by differential and almost no defect can be detected. Further, most of the defects have shallow edges and gentle slopes and deep central portions, so that the detection signals at the edges are small and it is difficult to judge that they are defects. In the second method, in which the exciting coil is wound parallel to the surface of the material to be inspected and the detecting coil is wound orthogonally to the exciting coil, defects parallel to the detecting coil can be detected very accurately. There is a drawback that orthogonal defects cannot be detected.

Therefore, in the conventional method, a plurality of detectors are required to detect defects in all directions, and there are problems that the cost is high and the installation space is large and there are restrictions.

The present invention has been made in view of such circumstances, and an object thereof is to provide a defect detector capable of detecting a defect in any direction with high sensitivity.

[0006]

According to the present invention, an exciting coil is wound around one end of the cube on a cubic high magnetic permeability material whose opposing surfaces are square, and two sets of detections orthogonal to the wound exciting coil are provided. In a detector having a coil, two sets of detection coils passing through a central portion of a high-permeability material are wound in a cross shape so as to intersect with each other, thereby making it possible to simultaneously detect defects in the steel material in all directions. The amplitude ratios of the detection signals detected by the two sets of detection coils are compared, the direction of the defect is determined from the ratio of the compared signals, and the amplitude of the defect signal is corrected based on the determined direction of the defect.

[0007]

With the defect detecting device configured as described above,
A single detector enables highly accurate detection regardless of the defect direction. Therefore, it is not necessary to prepare a plurality of detectors because it is necessary to detect defects in various directions, and it is possible to detect defects with high accuracy at low cost.

[0008]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 shows the structure of the detector of the present invention, in which 1 is a main core, 2 is a high-frequency exciting coil for flowing an eddy current on the surface of the material to be inspected, which is a horizontal outer circumference of the core 1. Is wrapped around. 3-1 and 3-2 are detection coils for detecting a horizontal magnetic field component generated by the defect disturbing the eddy current on the surface of the material to be inspected. This is wound around the respective central portions of the combination of the two opposing sides of the horizontal plane of the main core 1 so as to be orthogonal to each other and orthogonal to the high frequency exciting coil 2. The detector includes the main core 1, the high frequency excitation coil 2, the detection coils 3-1, 3-2.
Composed of. FIG. 2 shows the detection principle, and 4-1 and 4-2 indicate the path of the eddy current. 5 is eddy current 4
2 shows the secondary magnetic flux generated by -1. Detection coil 3
-1 indicates the detection coil 3 on the plane perpendicular to the position indicated by the dotted line 6.
-2 is on a plane perpendicular to the position shown by the solid line 7, and the distributions of the vortex flow 4-1 are exactly the same on the left and right sides of the dotted line 6 and the solid line 7, and therefore the detection coils 3-1 and 3-2 have secondary shapes. Magnetic flux 5
However, there is no detection output. This relationship remains the same even if the gap between the inspected material and the detector changes. Next, reference numeral 8 indicates a crack-like defect having a length in the same direction as the dotted line 6 and a minute width in the orthogonal direction. In this case, an imbalance occurs in the distribution of the eddy currents 4-2 on the left and right of the dotted line 6 and a horizontal magnetic field component is generated to induce a voltage in the detection coil 3-1. Since no imbalance occurs, no horizontal magnetic field component is generated, and almost no voltage is induced in the detection coil 3-2. However, the crack-like defects are shown by the solid line 7.
When facing in the same direction as, the detection coil that generates the induced voltage is 3-2, and almost no voltage is induced in the detection coil 3-1.

FIG. 3 is a schematic representation of how an output is generated at the detector in the presence of defects.
Indicates the eddy current loop when there is no defect, and 10 indicates the eddy current loop when there is a rectangular defect in the same direction as the dotted line 6.
The latter swirl loop 10 can be replaced by a small current loop 12 and a swirl loop 11 in the absence of defects. That is, the difference from the eddy current loop 11 when there is no defect is only the small current loop 12. Therefore, this small current loop 12
It suffices to detect the influence of the occurrence of the above on the detection coils 3-1 and 3-2. However, in the rectangular defect in the same direction as the dotted line 6, the small current loop 12 forms a long loop in the same direction as the dotted line 6 and a large change is detected 3-1.
However, since only a very short loop is formed in the direction of the solid line 7, only a slight change affects the detection coil 3-2. That is, the defect in the dotted line 6 direction can be detected by the influence on the detection coil 3-1 on the dotted line 6. In the case of a rectangular defect in the same direction as the solid line 7, the small current loop 14 makes a long loop in the same direction as the solid line 7 and therefore a large change is exerted on the detection coil 3-2. Since only a short loop is created, only a minute change affects the detection coil 3-1. That is, the defect in the solid line 7 direction can be detected by the influence on the detection coil 3-2 on the solid line 7. Although not shown in the figure, the defect is the dotted line 6 and the angle α.
In the case of the direction with, the detection coil 3-depending on the angle α
The influences on 1 and 3-2 change, and as the angle α increases, the influence on the detection coil 3-1 decreases and the influence on the detection coil 3-2 increases. Angle α is 45
In the case of degrees, the influence on the detection coils 3-1 and 3-2 becomes equal.

FIG. 4 shows the relationship between the detector output and the defect.
At the position of the dotted line 15, for example, there is the detection coil 3-1
When the defect 8 of the material to be inspected moves in the direction of the arrow 16, the detection value of the output of the detector becomes as shown by 17. That is, when the defect 8 comes directly under the detection coil 3-1, the detection coil 3 is detected.
The left and right of -1 are balanced and the output becomes zero, and the maximum and minimum are shown before and after that. That is, the defect is detected by changing the detection value from the maximum value to the minimum value.

As described above, the detector of the present invention does not have the defect that the defect cannot be detected depending on the direction of the defect by detecting with the detection coils 3-1 and 3-2 which are orthogonal to each other. It has overwhelmingly superior characteristics.

FIG. 5 shows an example of a detection signal processing device incorporating the above-mentioned detector. In FIG. 5, 2 is a high frequency excitation coil wound around the main core, and 3-1, 3-2 are detection coils. Reference numeral 22 is an oscillator for supplying a high frequency current to the high frequency coil 2, 23-1 and 23-2 are amplifiers of the detected voltage, and 24-1 and 24-2 are synchronous detectors. Two
Reference numeral 1 is a phase shifter, which sends a signal delayed by an arbitrary phase from the voltage phase of the oscillator 22, and outputs the signals by the synchronous detectors 24-1, 24-.
2 synchronous detection signals are generated. Synchronous detector 24-1, 2
The signals synchronously detected in 4-2 are further sent to the bandpass filters 25-1 and 25-2, and the defective signal components are extracted. The ratio ratio of the two signals is taken by the ratio device 26, and the defect direction judging device 27 judges the defect direction from this ratio. The defect signal corrector 28 corrects the defect signal amplitude from each defect signal component and defect direction. Reference numeral 29 is a comparator, which operates the alarm 30 by determining the amplitude of the defect signal. A recorder 31 records an analog signal and the presence / absence of a defect.

[0013]

As described above, according to the present invention, it is possible to detect a defect with high accuracy irrespective of the defect direction with a single detector.

[Brief description of drawings]

FIG. 1 is a perspective view showing a main part of an embodiment of the present invention.

FIG. 2 is a perspective view showing an eddy current of a material to be inspected.

FIG. 3 is a plan view showing an eddy current distribution.

FIG. 4 is a graph showing a voltage induced in a detection coil by a defect and relative movement of the detection coil.

5 is a block diagram showing a configuration of a processing device that processes a defect signal using the defect detector shown in FIG.

FIG. 6 is a graph showing a voltage induced in a detection coil by a relative movement of a defect and the detection coil in a conventional difference method.

[Explanation of symbols]

1: Main core 2: High frequency excitation coil 3-1 and 3-2: Detection coil 4-1 and 4-
2: Eddy current path 5: Secondary magnetic flux 6, 7: Position 8: Crack-like defect 9: Eddy current route without defect 10, 13: Eddy current route with rectangular defect 12, 14: Small current loop 15: Defect position 16: Moving direction 17: Detection value of detector output 21: Phase shifter 22: Oscillator 23-1, 23-2: Amplifier 24-1, 2
4-2: Synchronous detector 25-1, 25-2: Bandpass filter 26: Ratio device 27: Defect direction discriminator 28: Defect signal corrector 29: Comparator 30: Alarm device 31: Recorder 41: Difference coil 42: Defect 43: Differential coil moving direction 44, 45: Detection value of detector output

Front Page Continuation (72) Inventor Mitsuo Harada 20-1 Shintomi, Futtsu City Nippon Steel Corporation Technology Development Division

Claims (2)

[Claims] 1. A defect detector for applying non-contact non-destructive inspection of surface defects of a steel product by applying AC magnetism to the surface of the steel product,
A detector having a structure in which an exciting coil is wound around one end of the cube on a cubic high magnetic permeability material whose opposing surfaces are square, and two sets of detection coils orthogonal to the wound exciting coil are provided. An omnidirectional defect detector characterized in that two sets of detection coils passing through the central part of the are wound in a cross shape so as to cross each other. 2. A detector according to claim 1, a device for comparing amplitude ratios of detection signals detected by two sets of detector coils of the detector, and a device for determining a defect direction from the ratio of the compared signals. And a device for correcting the amplitude of a defect signal based on the determined defect direction, the non-directional defect detection device.