JPH07113788A - Eddy current flaw detection probe coil - Google Patents

Abstract

(57) [Summary] [Object] The present invention generates an eddy current only in a very limited local area of a material to be inspected by an eddy current flaw detection method using a probe coil, and thereby, a high S / Improve N and detection sensitivity. [Structure] A primary coil is arranged in the center pole of a triangular ferromagnetic core, and a probe coil in which a pair of secondary coils is arranged on each pole on both sides is installed close to the material to be inspected. An alternating current is supplied to the primary coil of the probe coil so that a strong beam-like magnetic flux crosses the material to be inspected, and an eddy current is generated in a very limited area of the material to be inspected. Is extracted as a difference between the induced voltages generated in the pair of secondary coils, and a minute defect is detected from the change in the difference voltage.

Description

Detailed Description of the Invention

[0001]

[Industrial field] Non-magnetic aluminum plate, copper plate and S
It is possible to detect minute defects online in real time in each manufacturing mill by targeting a US plate or a ferromagnetic steel plate, which is useful for quality control in the manufacturing process as well as shipping inspection.

[0002]

2. Description of the Related Art Known techniques for inspecting a wide material having a plate-like conductor inspection material include an ultrasonic flaw detection method in which an ultrasonic probe is arranged in an array, and a conductor inspection material being a ferromagnetic material. Magnetization of the material to be inspected for conductor, leakage magnetic flux flaw detection method for measuring leakage flux from the defect part, and crossing of alternating magnetic flux to the material to be inspected for conductor,
This AC magnetic flux generates an eddy current in the conductor inspection material,
There are eddy current flaw detection methods and the like that detect defects from changes in this eddy current.

In the known art, the eddy current flaw detection method is a flaw detection method suitable for high-speed flaw detection online, since it does not require a contact material at the time of flaw detection and can perform flaw detection unlike the ultrasonic flaw detection method. .

FIG. 6 shows a schematic structure of an eddy current flaw detection method using a probe coil according to a known technique. In the figure, 1 is a plate-shaped conductor inspection material, 2 is an E-type ferromagnetic core, P is a primary coil wound around a central pole of the E-type ferromagnetic material, and S ₁ and S ₂ are outside the central pole. A pair of secondary coils wound on a pole, Φ
Is a magnetic flux distribution of alternating current generated from the central pole of the primary coil P, OSC is an oscillator, 5 is a phase shifter, 3 is a signal amplifier, 4
Is a synchronous detector

The operation of the eddy current flaw detection method, which is a known technique, is shown in FIG.
Will be briefly explained.

When an alternating current is supplied from the oscillator OSC to the primary coil P wound around the center pole of the E-type ferromagnetic material, a magnetic field is generated from the center pole, and as shown in FIG. A local eddy current is generated in the conductor inspection material.

Now, as shown in FIG. 6, when the material to be inspected is a healthy part, the magnetic flux generated from the central pole has a symmetrical magnetic flux distribution characteristic with respect to the pair of poles (for the secondary coil). The distribution of the eddy current generated in the inspection material is also symmetrical with respect to the center of the central pole.

Therefore, the magnetic flux generated by the eddy current is also symmetrical, and the values of the voltages e ₁ and e ₂ induced in the pair of secondary coils S ₁ and S ₂ are equal.

Under this condition, when the conductor inspection material moves in the direction of the arrow and the defect I passes under the probe coil, the electric resistance of the defective portion is infinite with respect to the sound portion of the base material and the magnetic permeability is high. Since the value of 1 is 1, the generation of eddy currents in the defective portion is reduced.

As a reaction to this, a difference occurs in the values of the induced voltages generated in the pair of secondary coils S ₁ and S ₂ with a time lag. Therefore, in order to extract this difference, it is possible to obtain an output of the difference voltage e _Z = 1e ₁ -e ₂ 1 by connecting a pair of secondary coils in opposite phases as shown in the figure.

This differential output voltage is applied to the signal amplifier 3 and amplified to a desired value, and then added to the synchronous detector 4 and the output voltage of the oscillator OSC is added to the phase shifter 5 to shift only the desired value. The synchronized reference voltages e _R are simultaneously applied to the synchronous detector 4 for detection.

At the output terminal of the detector 4, an output voltage proportional to the amplitude value of the output voltage of the signal amplifier 3 and corresponding to the phase difference Q from the reference voltage is obtained.

By measuring this output voltage, it is possible to indirectly non-destructively detect the defects present in the conductor inspection material.

[0014]

However, the conventional known techniques have the following problems, and it is strongly desired to improve the detection performance.

(1) Although it is possible to detect flaws by contact, and is suitable for online and real-time flaw detection, the detection performance for minute defects is inferior to that of ultrasonic flaw detection or X-ray method.
There is a difficulty in lacking high reliability.

(2) The detection limit of minute defects in the known technique of eddy current flaw detection is generally a drill through hole with a hole diameter of 0,1.
mm.

(3) The reason why the detection sensitivity to this minute defect is small is that most of the magnetic flux generated from the primary coil pole of the E-shaped core does not intersect the conductor inspection material, and the secondary coil poles on both sides are directly present. This is because a strong magnetic flux cannot locally cross the conductor inspection material.

(4) Therefore, the practical detection limit in the prior art is an artificial defect (drill hole) with a hole diameter of 0.3.
mm.

[0019]

Means for Solving the Problems In the eddy current flaw detection method, E
Using the mold core, for the primary coil and the central pole,
In a known technique in which a secondary coil is arranged on a pair of poles,
An AC magnetic flux is generated from the pole for the primary coil in the conductor inspection material to generate a local eddy current, and a change in the eddy current generated in the sound portion and the defective portion of the conductor inspection material is changed by the voltage induced in the secondary coil. It is extracted as a difference.

Therefore, in order to improve the detection sensitivity for minute defects, it is determined depending on whether the beam-shaped AC magnetic flux can strongly cross the conductor inspection material.

Therefore, as shown in FIG. 1, of the three poles of the ferromagnetic core constituting the probe coil, the two outer poles are inclined toward the center pole.

With this structure, when an alternating current is supplied to the primary coil, most of the magnetic flux generated from the central pole intersects the material to be inspected in the form of a beam, so that a stronger eddy current is locally generated. Is possible.

As a result, the voltage induced in the secondary coil wound around the pole outside the central pole becomes a value in which the local information of the material to be inspected is extracted more efficiently, and the detection sensitivity for minute defects is improved. Can be planned.

[0024]

In the structure shown in FIG. 1, a conductor inspection material is installed below the probe coil in which the primary coil is arranged in the central pole and the secondary coils are arranged in a pair of poles on both sides, and an alternating current is applied to the primary coil. Is supplied, a magnetic circuit is formed by the central pole for the primary coil, the conductor inspection material, and the pair of cores for the secondary coil.

The permeability μ of the ferromagnetic core is 10 as described above.
^Since the values of ³ to 10 ⁴ are retained, the magnetic flux generated from the primary coil core crosses the material to be inspected, and then the tips of the pair of secondary coil cores arranged outside the central pole. A magnetic flux distribution characteristic passing through the portion is obtained.

That is, since the distance W between the pair of secondary coil poles on both sides from the tip of the central pole of the ferromagnetic core is the smallest at the tip of each pole interval between the central poles, the magnetic resistance of the magnetic circuit is the highest. It becomes a small value, and the magnetic flux generated from the central pole has a magnetic flux distribution passing through the tip portions of a pair of poles arranged on both sides after intersecting with the conductor inspection material.

Therefore, the magnetic flux (N pieces) generated from the central pole is divided into about two at the center of the central pole, and it becomes possible to locally intersect the material to be inspected with a beam in a beam-like distribution, and micro defects. The detection sensitivity and S / N can be improved.

[Examples of the present technology]

An embodiment of the technique of the present application will be described in detail with reference to FIG. In FIG. 1, 1 is a material to be inspected, 2 is a ferromagnetic core for probe coil, P is a primary coil, S ₁ and S ₂ are a pair of secondary coils, and W is a central pole and an outer side 1
The interval between the pair of secondary coil poles (hereinafter referred to as the pole interval), Q is the inclination angle of the pair of secondary coil cores, and L is the relative distance between the lower end of the pole and the inspected material 1 (hereinafter lift-off). ,) Is the distribution of the AC magnetic flux generated from the center pole of the primary coil.

The operation of the present technique will be described below with reference to FIG. 1 and the prior art FIG. An aluminum material was used as the conductor inspection material 1.

An alternating current is supplied from the known oscillator 0sc shown in FIG. 6 to the primary coil wound on the central pole shown in FIG. 1, and as shown in FIG. It becomes possible to cross the beam-shaped AC magnetic flux, and most of the magnetic flux generated from the central pole crosses the conductor inspection material.

Therefore, a strong eddy current can be locally generated in the conductor inspection material, the conductor inspection material moves in the direction of the arrow in FIG.
When passing under the pole of the book, even if the magnetic flux intersects the defect I in the form of a beam, the defect portion has an extremely large electric resistance as compared with the conductor inspection portion, so that no eddy current is generated.

Therefore, in order to extract the difference between the voltages e ₁ and e ₂ induced in the pair of secondary coils, the pair of secondary coils S
₁ , ₁ and S ₂ are connected in reverse connection with each other, and applied to the signal amplifier 3 in the same manner as in the prior art to amplify the desired value, and then the signal is added to the synchronous detector 4 for detection.

By measuring the output of the synchronous detector 4, very small defects can be detected with high sensitivity.

FIG. 2 shows the pole spacing W of the ferromagnetic core as 2
mm, tilt angle of the pair of poles for the secondary coil
The relative detection sensitivity characteristics for a through-hole having a hole diameter of 0.1 mm when changed to four levels of Q = 0, 15, 30, 45 degrees are shown.

As shown in FIG. 2, when the ratio of the lift-off L and the pole interval W is changed from 0.5 to 4 the hole diameter becomes 0,
The detection sensitivity characteristic for an artificial defect of 1 mm improves as the angle Q of the pair of secondary coil poles increases.

In particular, when W / L = 0,5 is set for flaw detection, and in the case where the inclination angle is 30 ° to 45 ° in comparison with the inclination angle Q = 0 °, the detection sensitivity for artificial defects is improved five times or more. .

In FIG. 2, the relative detection sensitivity of 1,0
Is the inclination angle Q = 0 ° of the pair of secondary coil poles, and is a characteristic normalized by the detection sensitivity when W / L = 4 is set.

FIG. 3 shows that in the technique of the present application, the interval W between the primary coil pole and the pair of secondary coil poles is 2, 4, and 6.
When the W / L ratio is 1.0 at mm and 3 levels, d = 0, when the hole diameter processed in the aluminum plate is W = 2, as in FIG.
1 mm, d = 0,2 mm when W = 4, d when W = 6
The artificial defect of = 0,3 mm is detected and the test result of the S / N characteristic with respect to the inclination angle of the pair of secondary coil poles is shown.

As shown in FIG. 3, as the value of the inclination angle Q of the pair of secondary coil poles increases, the S /
It was confirmed that the N characteristic was improved, and it was found that when the value of the tilt angle Q was 30 °, it could be improved about 2,25 times.

In the S / N characteristic curve of FIG. 3, the relative S / N value of 1 and 0 is the inclination angle Q = 0 ° and W =
S / N for artificial defects at 2, 4, 6 mm is 1,
It was normalized to 0 and displayed.

FIG. 4 is a block diagram showing another embodiment of the technique of the present application. In FIG. 4, 1 is a ferromagnetic material for the material to be inspected, M is an electromagnet for magnetizing the material to be inspected, Mc ₁ . Mc ₂
Is a magnetizing coil for the electromagnet M, Ms is a probe coil Pc
Magnetic shield core, Pc is a probe coil configured as shown in FIG.

In the eddy current flaw detection method, when the material to be inspected is a ferromagnetic material, noise due to a local change in magnetic characteristics of the ferromagnetic material is removed, so that the material to be inspected is magnetically saturated with a strong magnet. This is well known.

However, if the conductor core material is magnetized and the ferromagnetic core for the probe coil is magnetically saturated, it becomes impossible to utilize the features of the present technology. In order to prevent these adverse effects, a technique of applying a magnetic shield is also known.

However, as shown in FIG. 1 of the present technique, it was discovered that in the ferromagnetic core for the probe coil Pc, the magnetic shield effect is enhanced by tilting the secondary coil pole toward the primary coil pole side. .

FIG. 4 shows a configuration for testing the shield effect by placing the magnetic shield ferromagnetic core Ms outside the probe coil Pc when the disturbance magnetic field intersects the probe coil Pc.

In FIG. 4, a pair of magnetizing coils Mc ₁ . M
Each coil of c ₂ is fed in series, an alternating current of 50 Hz is supplied from a magnetizing power source (not shown) to this magnetizing coil, and a pair of secondary coils of the probe coil Pc are additively connected,
The voltages e _N1 and e _N2 induced in the pair of secondary coils were added, and the shield effect was evaluated from the amplitude value of the output voltage of the added voltage e _N = e _N1 + e _N2 .

FIG. 5 shows the test results obtained by the configuration shown in FIG.
The inclination angle Q of the pair of secondary coil poles is set to four levels (0
(°, 10 °, 30 °, 45 °). In FIG. 5, a Gauss meter was installed at a point A with an inclination angle Q of 0 degree, and the magnetic flux density of 0.035 Tesla was normalized to 1.0, and the shield effect characteristics were displayed.

As shown in FIG. 5, when the inclination angle of the pole for the secondary coil becomes large, the amplitude of the added output voltage e _N of the pair of secondary coils becomes small, and it is found that the shield effect is high.

The improvement of the shield effect is achieved by the relative distance M between the shield core Ms and the tips of the pair of secondary coil poles.
_{This is because the L} value is wide corresponding to the tilt angle.

Further, when the value of the inclination angle Q is 30 ° and 45 °, almost the same shield effect is obtained, and the relative output reaches 0.90 at 0.04 Tesla. This is because the shield core Ms approaches saturation due to the magnetic field strength of the electromagnet,
The shield effect seems to be decreasing.

When performing eddy current flaw detection online in the manufacturing process using the probe coil of the present technology, array probe probes arranged at regular intervals in the direction of the material to be inspected are placed close to the material to be inspected. It is possible to inspect the entire width and the entire length of the material to be inspected by running the material to be inspected.

However, when inspecting online, the lift-off fluctuation between the material to be inspected and the probe coil changes the defect detection sensitivity. Therefore, the probe coils arranged in an array are arranged at regular intervals before and after (line direction). Install a pair of anti-vibration rollers for conductor inspection material, or if there is a bridle roll on the production line,
By arranging probe coils arranged in an array close to the bridle roll, it is possible to prevent vibration of the conductor inspection material and perform inspection.

Further, when the conductor inspection material is inspected on-line with a ferromagnetic material, the conductor inspection material is magnetically saturated by a magnet in order to remove local magnetic noise (as is known) of the conductor inspection material. As a magnetizing method, a magnet is installed in a non-magnetic roll, and the non-magnetic roll is conveyed and magnetized by conducting a material to be inspected on the conductor, or a pair of rolls are arranged at regular intervals in the line running direction, A method of magnetizing by installing a magnet near the center is adopted, but the eddy current flaw detection method using the probe coil of the present technology does not limit the magnetizing conditions.

[0054]

As is apparent from the description of the technique of the present application, the effects shown in the following items can be obtained, and the problems of the prior art can be solved.

(1) The structure in which the pair of secondary coil poles is inclined toward the primary coil pole side allows the ratio W / L of the pole interval W and the lift-off L between the pole tip and the material to be inspected. Is 1 or less, which is about 1,5 times that of the prior art.
It was possible to achieve a sensitivity as high as 6 times.

(2) This makes it possible to set the value of the pole spacing W to a small value, and it is possible to cross the beam-shaped AC magnetic flux at a locally limited location with respect to the material to be inspected, and to detect minute defects. It is possible to improve the detection sensitivity to.

(3) By giving the tilt angle Q,
It is possible to improve the S / N for the same artificial defect by about 1,3 to 2,4 times as compared with the conventionally known technique.

(4) Further, it is possible to obtain an extremely high shield effect against disturbance noise (magnetic noise) at the time of eddy current flaw detection and a static magnetic field at the time of magnetic saturation when targeting a ferromagnetic material as a material to be inspected. it can.

(5) For a magnetic flux density of 0.02 Tesla, if the tilt angle of the pole is set to 30 degrees, a shield effect of about 7 times that of the tilt angle Q = 0 ° can be obtained. it can.

(6) By using the technique of the present application, the flaw detection result for the non-magnetic material and the ferromagnetic material as the material to be inspected for conductors,
It became possible to detect artificial defects with a pore size of 0.1 mm at S / N> 3 or more.

[Brief description of drawings]

FIG. 1 is a probe coil showing the basic configuration of the present application.

FIG. 2 Detection sensitivity characteristics for artificial defects according to the present technology

FIG. 3 S / N characteristics for artificial defects according to the present technology

FIG. 4 is a configuration diagram of another embodiment of the present technology.

FIG. 5 is a characteristic diagram showing a shield effect with respect to the external magnetic flux shown in FIG.

FIG. 6 Known technique of eddy current flaw detection method

[Explanation of symbols]

1 ... Conductor inspection material 2 ... Ferromagnetic material core 3 ... Signal amplifier 4 ... Synchronous detector 5 ... Phase shifter OSC ... Oscillator P ... Primary coil S ₁ S ₂ ...
One pair of secondary coils Q ... Inclination angle of one pair of secondary coil poles W ... Distance between center pole and one pair of secondary coil poles L ... Lift-off Φ ... Primary Distribution of magnetic flux generated from the coil pole M ... Electromagnet Mc ₁ Mc ₂
.. One pair of magnetizing coils Hs ... Shield core A ... Magnetic flux density measurement position Pc ... Probe coil M _L ... Relative distance between secondary coil pole and shield core

Claims (3)

[Claims] 1. A probe coil is installed close to and facing a material to be inspected, and a mutual induction method is used for the probe coil to generate an AC magnetic flux from the primary coil to locally apply the magnetic field to the material to be inspected. Eddy current flaw detection probe coil for detecting a defect existing in a material to be inspected by applying a large eddy current. A triangular coil 3 pole is used for the probe coil core, a primary coil is arranged in the central pole, and another 2 poles are used. A pair of secondary coils are installed in the primary coil, the primary coil poles are installed perpendicular to the material to be inspected, and the other pair of poles are tilted toward the center pole to supply an alternating current to the primary coil. A probe coil for eddy current flaw detection, wherein a difference in voltage induced in a pair of secondary coils is extracted. 2. The eddy current flaw detection probe coil according to claim 1, wherein a pair of outer secondary coil poles are tilted toward the central pole side with respect to the central pole of the triangular ferromagnetic core. A probe coil for eddy current flaw detection, wherein the inclination angle is set to 10 to 45 degrees. 3. The eddy current flaw detection probe coil according to (2), wherein a magnetic shield ferromagnetic core is arranged outside the triangular 3-pole ferromagnetic core to remove a disturbance magnetic field. A probe coil for eddy current flaw detection characterized by: