JPH0980028A - Method and apparatus for multiple frequency eddy current flaw detection by single exciting coil system - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a method and an apparatus whose flaw detection accuracy is enhanced and whose detection accuracy of the kind of a flaw is enhanced. SOLUTION: In the eddy current flaw detection of a steel material by using a flaw detection coil, a current at a high frequency f1 and a current at a low frequency f2 sre superposed so as to be supplied to a single exciting coil 16 through which the steel material 17 is passed. A first component having a first phase shift with reference to an f1 component voltage for the exciting coil 16 in a voltage at the high frequency f1 induced in a detection coil 18 is extracted, two orthogonal components and a length which express the first component as a vector are computed on the basis of the first component, and a flaw is detected when they are at a set value of higher. In addition, a second component having a second phase shift with reference to an f2 component voltage for the exciting coil 16 in a voltage at the low frequency f2 induced in the detection coil 18 is extracted, two orthogonal components and a length which express the second component as a vector are computed on the basis of the second component, and a flaw is detected when they are at a set value or higher.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to surface flaw detection of steel material, and particularly, although not intending to be limited to this, eddy current flaw detection of a steel bar and wire rod manufactured by hot rolling using an exciting coil and a detection coil. More specifically, the present invention relates to a method and apparatus for detecting flaws by a method, in which a high frequency and a low frequency are applied to a single through-type excitation coil, and a change in eddy current due to a flaw is detected as a change in voltage induced in the detection coil. The present invention relates to a multi-frequency eddy current flaw detection method and apparatus for discriminating a plurality of flaws.

[0002]

2. Description of the Related Art Eddy-current flaw detection is a method for generating a magnetic field in an exciting coil to nondestructively detect a flaw in a material to be inspected of a magnetic metal body, generating an eddy current in the material to be inspected, and causing The change in current is detected as the change in voltage induced in the detection coil. Conventionally, when detecting flaws by eddy current flaw detection at a single frequency, it is easy to detect bald defects, but for other flaws, the product edge is sampled and guaranteed by flaw inspection and visual inspection of the entire product. It was However, this method has a problem that the entire length cannot be guaranteed except for the bald defects.

Japanese Examined Patent Publication No. 58-11571 discloses that two types of frequencies, in which the high frequency is 4 to 16 times the low frequency, are applied to the flaw detector from each oscillator, and the flaw signal of the steel pipe is determined from the ratio of flaw signals of each frequency. An eddy current flaw detection method for estimating the defect depth is disclosed.

Japanese Examined Patent Publication No. 63-14905 discloses that the exciting coil is simultaneously energized with currents of different test frequencies, each test frequency component of the induced voltage of the detection coil is picked up by a filter, and flaw detection information of each test frequency is detected. It is explained that there is a conventional mixing method for generating a flaw and a switching method for performing flaw detection at different test frequencies in time division by using a pair of flaw detection coils. We propose a method to detect flaws at each test frequency by using a coil, find the difference in flaw detection output, and remove the noise factor between the test frequencies.

Japanese Utility Model Publication No. 62-5652 discloses an eddy current flaw detector of the mixing type. In this case, a plurality of high-frequency oscillators are used to generate and mix a plurality of frequencies, which are applied to the exciting coil, and the induced voltages of the respective high-frequency oscillators are canceled out by using voltage generators and buffer resistors. An eddy current flaw detection device is described that includes a plurality of variable phase shifters that receive an output signal and outputs a reference signal for phase detection, and a phase detector that outputs a plurality of flaw signals corresponding to respective frequencies.

[0006]

Conventionally, when a flaw is detected by eddy current flaw detection at a single frequency, it is easy to detect a bald-like flaw, but for other flaws, the edge of the product is sampled and the flaw inspection and the product are performed. It was guaranteed by a visual inspection of the whole. But,
This method has a problem in that the entire length cannot be guaranteed except for the bald defects.

Further, even when a plurality of frequencies are used, conventionally, if the emphasis is placed on the detection of a bald defect, for example, the detection omission of foreign matter trapping is large, or if the emphasis is placed on the detection of foreign body trapping, then the hair loss occurs. It is difficult to discriminate between flaw types, such as deterioration in flaw detection accuracy, and improvement of flaw detection accuracy that is not related to flaw types is desired.

The first object of the present invention is to improve the defect detection accuracy, and the second object is to improve the detection accuracy of each defect type.

[0009]

[Means for Solving the Problems]

(1) In the method of the first aspect of the present invention, in the eddy current flaw detection of a steel material using a flaw detection coil including an excitation coil and a detection coil, a high-frequency f1 current is applied to a single excitation coil (16) which the steel material (17) penetrates. And a low frequency f2 current are superposed and energized,
A first component of the voltage of the high frequency f1 induced in the detection coil (18) having a first phase shift (θ ₁ ) with respect to the current of the high frequency f1 of the exciting coil (16) is extracted, and the first component is extracted. From the components, at least one of the two orthogonal components (x, y) and the length (v) in the case of representing it by a vector is calculated, and when it is equal to or more than a set value, it is detected as a flaw, and the detection coil A second component of the voltage of the low frequency f2 induced in (18) having a second phase shift (θ ₂ ) with respect to the current of the low frequency f2 of the exciting coil (16) is extracted, and the second component is extracted. At least one of the two orthogonal components (x, y) and the length (v) in the case of expressing it as a vector is calculated from the component, and when it is equal to or larger than the set value, it is detected as a flaw.
In addition, in order to facilitate understanding, symbols of corresponding elements or corresponding items in the embodiments shown in the drawings and described later are added for reference in parentheses.

The operation and effect will be described below. First, the principle of eddy current flaw detection will be described. When the exciting coil (16) and the detecting coil (18) in which an alternating current is applied are brought close to the conductor (17), an eddy current is generated in the conductor by electromagnetic induction. The magnetic flux generated by this eddy current is generated in the direction of canceling the magnetic flux of the exciting coil (16). The induced voltage V generated in the detection coil (18) by this is expressed by the following equation, where S is the area affected by the magnetic flux density B and φ is the magnetic flux interlinking with the detection coil (18).

[0011]

[Equation 1]

This voltage V induced in the detection coil (18)
Represents changes in eddy currents generated in the conductor (17) and changes in magnetic flux between the coils (16, 18) and the conductor (17). The measurement principle is to analyze the coil impedance based on this voltage V to detect the change in eddy current due to a flaw and the change in magnetic flux between the coil (16, 18) and the conductor (17). FIG. 3 shows changes in impedance of the detection coil (18) due to changes in the crack C, magnetic permeability μ, lift-off LO and conductivity σ. What is important in this figure is that the change in impedance with respect to crack C, that is, the flaw, is large when the conductor (17) is a cold magnetic material. On the contrary, when the conductor (17) is a non-magnetic substance that is hot (at the Curie point or higher), the change in impedance due to a flaw is small.

That is, when detecting a flaw in a steel bar and a wire rod manufactured by hot rolling by eddy current flaw detection, it is easy to detect a whisker-like thing in which the surface of the flaw is cooled and becomes a magnetic substance. In FIG. 3, the non-magnetic material has a Curie temperature of about 790 ° C. or higher. The Curie temperature is the place where the steel transforms and the magnetism changes, and noise will occur frequently when eddy current flaw detection occurs near this, so it must be avoided.

Another important thing as an eddy current flaw detection is
It means that there is a penetration depth of eddy current. Penetration depth δ
Is expressed by the following formula: δ = √ (ρ / πfμ) ρ: Electric resistivity μ: Permeability f: Frequency That is, the penetration depth δ becomes smaller at high frequencies and the penetration depth at low frequencies. δ becomes large.

The main defects to be detected in the present invention are shallow and long bald defects and foreign matter biting deeply into the test material. According to the above-mentioned principle, the flaw-like flaws are good for flaw detection at high frequency, and the foreign matter biting is good at flaw detection at low frequency. In order to realize this, a multi-frequency eddy current flaw detection method capable of flaw detection at high frequency and low frequency at the same time is required. On the other hand, even at the same frequency, the detection coil (1
The phase shift (θ ₁ , θ ₂ ) of the flaw-corresponding component of the voltage V induced in 8) with respect to the excitation AC is different between the bald-shaped flaw and the foreign matter biting, and the flaw-corresponding component is separated (extracted) from the voltage V. If you do
It is preferable to set the flaw component extraction phase to the flaw type target in order to detect various flaws with high accuracy.

According to the present invention, the high-frequency f1 current and the low-frequency f2 current are superposed on the single exciting coil (16) through which the steel material (17) penetrates, and the high-frequency f1 induced in the detection coil (18) is induced.
Since the component and the low-frequency f2 component are extracted and the flaw detection is performed based on each of them, for example, f1 is set to a value suitable for detecting a bald defect, and f2 is set to a value suitable for detecting foreign matter trapping. Thus, both types of flaws can be detected with high accuracy. In addition, the first component of the voltage of high frequency f1 induced in the detection coil (18) having the first phase shift (θ ₁ ) is extracted, and similarly the second component of the voltage of low frequency f2 (second phase shift ( Since the second component with θ ₂ ) is extracted and flaw detection is performed based on each,
For example, by setting the first phase shift (θ ₁ ) to a value suitable for detecting a bald defect, and the second phase shift (θ ₂ ) to a value suitable for detecting foreign matter trapping, both types of Both defects can be detected with higher accuracy.

[0017]

BEST MODE FOR CARRYING OUT THE INVENTION

(2) According to the method of the second aspect of the present invention, in eddy current flaw detection of a steel material using a flaw detection coil including an excitation coil and a detection coil, a high-frequency f1 current is applied to a single excitation coil (16) through which the steel material (17) penetrates. And a low frequency f2 current are superposed and energized,
A first component of the voltage of the high frequency f1 induced in the detection coil (18) having a first phase shift (θ ₁ ) with respect to the current of the high frequency f1 of the exciting coil (16) is extracted, and the first component is extracted. The component is represented by a vector, and when the vector direction (x ₁ , y ₁ ) is within the set range and the vector length (v ₁ ) is greater than or equal to the set value, it is detected as a flaw and induced in the detection coil (18). The low frequency f
A second component of the voltage of 2 having a second phase shift (θ ₂ ) with respect to the low frequency f2 current of the exciting coil (16) is extracted,
This second component is represented by a vector, and the vector direction (x ₂ ,
If y ₂ ) is within the setting range and the vector length (v ₂ ) is greater than or equal to the setting value, a defect is detected.

That is, the first component and the second component are represented by vectors, and when the vector direction (x, y) is within the set range and the vector length (v) is equal to or larger than the set value, a flaw is detected. The vector is, for example, an arrow shown in FIG. 3, and in the case of a flaw (for example, a crack), the direction of the vector is within a specific range, and by setting the set range to the range of the flaw, the flaw is substantially damaged. Only detected. Vector length (v)
In the case of a flaw, since it corresponds to the size (spreading and depth) of the flaw, the set value may be set to the minimum flaw size corresponding value to be detected.

(3) The multi-frequency eddy current flaw detector using the single excitation coil system of the present invention corresponds to a single excitation coil (16) through which a steel material (17) penetrates; and a change in magnetic flux generated in the steel material (17). Detecting coil (18) for inducing a voltage; Energizing means (1 to 5, 14, 15) for simultaneously and continuously applying a high frequency f1 current and a low frequency f2 current to the exciting coil (16); 18) The first to extract the voltage of the high frequency f1 induced in
Filter (10 ₁ ); of the voltage extracted by the first filter (10 ₁ ),
A first component having a _first phase shift (θ ₁ ) with respect to the high frequency f1 current of the exciting coil (16) is extracted, and from this first component, two orthogonal components (x , y)
And first component detecting means (9 ₁ , 11 ₁ , 12 ₁ ) for calculating first vector information including at least one of the length (v); first evaluating means (13) for quantizing the first vector information. ₁ ); a second for extracting the voltage of the low frequency f2 induced in the detection coil (18)
Filter (10 ₂ ); of the voltage extracted by the second filter (10 ₂ ),
A second component having a _second phase shift (θ ₂ ) with respect to the low frequency f2 current of the exciting coil (16) is extracted, and from this second component, two orthogonal components (in the case of being represented by a vector) x, y)
And second component detecting means (9 ₂ , 11 ₂ , 12 ₂ ) for calculating second vector information including at least one of the length (v); and second evaluating means for quantizing the second vector information. (13 ₂ );

(4) The multi-frequency eddy current flaw detector using the single excitation coil method of the present invention corresponds to a single excitation coil (16) through which the steel material (17) penetrates; the magnetic flux change generated in the steel material (17). Detecting coil (18) for inducing a voltage; Energizing means (1 to 5, 14, 15) for simultaneously and continuously applying a high frequency f1 current and a low frequency f2 current to the exciting coil (16); 18) The first to extract the voltage of the high frequency f1 induced in
Filter (10 ₁ ); of the voltage extracted by the first filter (10 ₁ ),
The first vector information having a _first phase shift (θ ₁ ) with respect to the high frequency f1 current of the exciting coil (16) is extracted, and the first component is expressed by the direction and length of the vector.
First component detecting means (9 ₁ , 11 ₁ , 12 ₁ ), which is converted into (x, y, v);
When the first vector information (x, y, v) is in the direction within the first set range, the length (v) represented by it is quantized (S, L, M).
First evaluation means (13 ₁ ); second filter (1) for extracting the voltage of the low frequency f2 induced in the detection coil (18)
0 ₂ ); The second phase shift of the voltage extracted by the second filter (10 ₂ ) with respect to the low frequency f2 current of the exciting coil (16)
Second component detecting means (9 ₂ ) for extracting a second component having (θ ₂ ) and converting the second component into second vector information (x, y, v) represented by the direction and length of the vector. , 11 ₂ , 12 ₂ ); and when the second vector information (x, y, v) is in the direction within the second set range, the second length (v) represented by the second vector information (x, y, v) is quantized.
Evaluating means (13 ₂ );

(5) In addition to the above (3) or (4), the multi-frequency eddy current flaw detector by the single excitation coil system of the present invention has a quantization data ( ₁ ) generated by the first evaluation means (13 ₁ ). (S, M, L)
First frequency detection means (1
9, 21); and, quantized de second evaluation means (13 ₂₎ is generated - data (S, M, second frequency detecting means for detecting the frequency of occurrence of the same ones L) (19, 21); Is further provided.

(6) In addition to the above (5), the multi-frequency eddy current flaw detector according to the present invention, which uses the single excitation coil system, has the first
Alternatively, an alarm means (21, 24) for issuing an alarm when the frequency detected by the second frequency detection means (19, 21) is equal to or higher than a set value; and a means for marking a steel material position corresponding to the frequency equal to or higher than the set value. (21,800); is further provided.

(7) In addition to the above (3) or (4), in the multi-frequency eddy current flaw detector using the single excitation coil method of the present invention, the induced voltage of the detection coil (18) is the steel material (17) is the detection coil. Level detection means (21) for detecting whether the level is high due to being at the position (18); Synchronous pulse generation means (2) for generating an electric pulse having a frequency proportional to the moving speed of the steel material (17)
9); and, when the level detecting means (21) detects a low level and when the synchronizing pulse generating means (29) does not generate an electric pulse, a warning means (21, 24); is further provided.

(8) In addition to the above (5), the multi-frequency eddy current flaw detector using the single excitation coil system of the present invention is a steel material.
Means (900) for measuring the surface temperature of (17); Means (21, 24) for generating an alarm when the surface temperature is above the Curie temperature; Surface temperature of the steel material (17) and first and second frequency detecting means (19,2
It further comprises a flaw recognition means (21) for determining the presence / absence of a flaw based on the frequency detected by 1); and a means (21, 26) for outputting the surface temperature and the flaw presence of the steel material (17).

(9) In addition to the above (3) or (4), the multi-frequency eddy current flaw detector using the single excitation coil system of the present invention has, in addition to the above (3) or (4), orthogonal two components (x, y) first and second sensitivity adjusting means (11 ₁ , 11 ₂ ) for adjusting respective levels; corresponding to cross-sectional size information (diameter) of the steel material (17), energization frequencies f1, f of the exciting coil (16)
2, the pass bands of the first and second filters (10 ₁ , 10 ₂ ), the first and second phase shifts (θ ₁ , θ ₂ ), and the first and second evaluation means (13 ₁ , 13). The quantization threshold value of ₂ ) is held in the memory, these pieces of information corresponding to given cross-section size information (diameter) are read from the memory, and the value indicated by the read information is set to the energizing means (1 to 5). , 14, 15), first and second filter (10 _{1.10 2),} first and second component detecting means (9 _1, 11 _1, 12 _{1/9 2,} 11 _2, 12 _2), and, Parameter setting means (22) set in the first and second evaluation means (13 ₁ , 13 ₂ ); and an input means (33) for giving sectional size information (diameter) to the parameter setting means (22). / 23); is further provided.

Other objects and features of the present invention will become apparent from the following description of embodiments with reference to the drawings.

[0027]

FIG. 2 shows an outline of one embodiment of the present invention, and FIG. 1 shows the configurations of the eddy current flaw detector 700 and flaw detection processing circuits 100 and 200 shown in FIG. The oscillation circuit 1 is 12 MH
A pulse having a frequency of Z is generated and applied to the first set of frequency dividing circuits 2 ₁ and 2 ₂ whose frequency dividing ratio is variable. The frequency dividing circuit 2 ₁ is 12 MH at the first frequency dividing ratio given by the microcomputer MPU21.
A first pulse obtained by dividing Z is generated. The first frequency division ratio has a small value, and the first pulse is a phase synchronization pulse of a high frequency f1 signal described later. Frequency dividing circuit 2 _2, microcomputer - generating a second pulse derived by dividing the 12MHZ in second division ratio data MPU21 gave. The second frequency division ratio has a large value, and the second pulse is a phase synchronization pulse of the low frequency f2 signal described later.

The second set of frequency dividing circuits 3 ₁ and 3 ₂ generate pulses that define one period of the high frequency f1 and f2 signals (sine waves), and the shaping circuits 4 ₁ and 4 ₂ shape the signals into sine waves. , The buffer amplifiers 5 ₁ and 5 ₂ adjust the level of the sine wave.
In this way, the AC sine wave signals f1 and f2 of the high frequency f1 and the low frequency f2 are generated and given to the mixer 14. The mixer 14 synthesizes the AC sine wave signals f1 and f2. The composite wave is applied to the power amplifier 15, and a voltage of a level proportional to the composite wave is applied to the feedthrough excitation coil 16. A test material (a steel bar or a wire manufactured by hot rolling) passes through the coil winding center position of the exciting coil 16.

The detection coil 18 induces a voltage having substantially the same frequency as the frequency of the AC voltage applied to the exciting coil 16. The voltage generated by the detection coil 18 is the amplifier 7
It is amplified by ₁ , 7 ₂ . The filters 8 ₁ and 8 ₂ respectively extract the high frequency f1 component and the low frequency f2 component, and the phase detection circuits 9 ₁ and 9 ₂ further add each component by the phase synchronous detection to the orthogonal two component Xo (for example sin) of the vector representation. Value) and Yo (cos value). Phase synchronization signal is 0 °
The / 90 ° sample pulse generation circuits 6 ₁ and 6 ₂ provide the phase detection circuits 9 ₁ and 9 ₂ .

Generally, the noise due to the surface properties of the material 17 to be inspected has a high frequency component, and the signal due to the dimension of the material to be inspected, the material change and the flaw detection speed has a low frequency component. Therefore, these quadrature two-component signals have high frequencies other than the target frequency,
Contains low frequency signals. The high pass / low pass filter circuits 10 ₁ and 10 ₂ remove such unnecessary noise signals.

Next, the quadrature two-component signal is supplied to the sensitivity adjusting circuit 11
After the amplitudes of the components are adjusted by ₁ and 11 ₂ , the quadrature two-component signal x, which expresses the voltage component having the phase shift due to the presence of a flaw by a vector expression, in the phase shifter vector generation circuits 12 ₁ and 12 ₂ according to the following equation. Phaser vector generation circuit 12 ₁ : x = X ₀ cos θ ₁ −Y ₀ sin θ ₁ y = X ₀ sin θ ₁ + Y ₀ cos θ ₁ X ₀ , Y ₀ : Phaser pre-signal x, y: phase Post-combination signal θ ₁ : Phase angle (phase shift of voltage component corresponding to a bald defect with respect to excitation voltage: set value obtained by experiment) Phaser vector generation circuit 12 ₂ : x = X ₀ cos θ ₂ -Y ₀ sin θ ₂ y = X ₀ sin θ ₂ + Y ₀ cos θ ₂ X ₀ , Y ₀ : signal before phase shifter x, y: signal after phase shifter θ ₁ : phase angle (phase of voltage component corresponding to foreign matter trapping flaw with respect to excitation voltage) Deviation: Setting value obtained by experiment) Vessel vector generating circuit 12 _1, 12 ₂ further, x signal, calculates the length v = √ vector a (x ² + y ²⁾ from the y signal. The x signal and the y signal generated by the phaser vector generation circuits 12 ₁ and 12 ₂ collectively mean the vector direction.

The above-mentioned two sets of x signal and y signal generated by the phase shifter vector generation circuits 12 ₁ and 12 ₂ are given to the oscilloscope OSP via the MPU 21 and the oscilloscope O.
SP is vector display according to x signal and y signal (2 sets)
I do.

The evaluation circuits 13 ₁ and 13 ₂ receive the x signal and the y signal.
Check if the direction represented by the signal (vector direction expressed by both) is the flaw existing range (set range),
If so, the v signal is changed to S (less than the first threshold value), M
(Equal to or more than the first threshold and less than the second threshold) and L (second
Quantize above threshold value). This is repeated in a predetermined short cycle.

Counter-circuit (six counters) 19
The evaluation circuit 13 _1, 13 S ₂ is generated, M, L (2
Each group of 6 pieces) is counted up. The pulse generator 28 is generated in the flaw detection result processing MPU 21 10
In response to a pulse of 0 msec period, each time it arrives,
The count data (six pieces) of the counter circuit 19 is read, and immediately thereafter, the counter circuit 19 is reset (count value is initialized to 0), and the data of the position register (one area of the internal memory) is read. The speed (output of F / V converter 27) x 100 msec equivalent value is incremented (counted up). When the rolled material sensor 36 detects the arrival of the tip of the material 17 to be tested, the timer board 25
The timer is triggered to give a time-over signal to the MPU 21 after the set time. Upon receiving this time-over signal, the MPU 21 instructs the eddy current flaw detector 700 and flaw detection processing circuits 100 and 200 to start flaw detection, monitors the voltage (average value or effective value) of the detection coil 18, and detects it. The position register is initialized when the material 17 reaches the existing level, and the pulse generated by the pulse oscillator 28 (100 ms
Since the reading of the count data (6 pieces) in response to ec) is started, the data of the position register represents the eddy current flaw detection position starting from the tip of the test material 17.

The flaw detection result processing MPU 21 uses a count data
Each time the data (count value of S, M, L for f1 & 6 count values of S, M, L for f2) is read, the count data (6) is checked and the count value is 1 or more. Data (f1 / f2 identification data + S / M /
L identification data + count data) and position register data at that time (a flaw detection position starting from the tip of the material 17 to be inspected) are given to the recorder 26 and the personal computer 22
Transfer to. The personal computer 22 gives the received data to the printer 35. The recorder 26 plots (dots) data on a coordinate system (6 sets) in which the horizontal axis represents the flaw detection position and the vertical axis represents the count value. The printer 35 sends S, M,
The flaw detection position and the count data are printed out for each of the six count values S, M, and L for the count value & f2 for each L.

The MPU 21 compares the threshold value assigned to each of the quantization (S, M, L) with the count value,
When the count value is equal to or larger than the threshold value, it is determined that there is a defect, and the alarm panel 24 is instructed to generate an alarm.
Is started, and when the count value matches the timing value at which the flawed position reaches the marking device 800, a marking instruction is given to the marking device 800. The alarm panel 24 responds to one instruction by sounding a buzzer and turning on an alarm lamp for a predetermined time. If there is a further alarm generation instruction within the predetermined time, the alarm is continued for a further predetermined time.

In the memory of the personal computer, the flaw detection frequencies f1 and f2 (division ratios to the frequency dividing circuits 2 ₁ and 2 ₂ ) which are flaw detection conditions for each wire diameter, the sensitivity (to the adjusting circuits 11 ₁ and 11 ₂ ), Filter pass band (to 10 ₁ and 10 ₂ ), phase θ ₁ and θ
₂ (to the phase shifter vector generation circuits 12 ₁ and 12 ₂ ) and the threshold value for flaw determination (to the MPU 21) are stored. This information group is called a table. The contents are illustrated in Table 1 and Table 2.

[0038]

[Table 1]

[0039]

[Table 2]

Before the flaw detection, the host computer 23 gives the wire diameter data of the material 17 to be inspected to the personal computer 22, or the operator inputs it to the personal computer 22 from the operation board 33. When the personal computer 22 transfers or inputs the wire diameter data, the flaw detection frequencies f1 and f2, the sensitivity, the pass band of the filter, and the phase θ ₁ are associated with the wire diameter represented by the wire diameter data. , Θ ₂ , the threshold value for defect determination are read from the table and transferred to the MPU 21. The MPU 21 sets the values indicated by these data in the flaw detection processing devices 100, 200 and itself (with respect to the threshold value).

A pulse generator 29 connected to the final roll of the finish rolling mill generates finger speed pulses having a frequency proportional to the rolling speed, which are supplied to the interface 20 and the F / V converter 27. The F / V converter 27 is
A rolling speed signal (analog voltage) having a level proportional to the frequency of the finger speed pulse is generated, and the interface 20
Give to. The MPU 21 digitally converts the rolling speed signal and reads it.

A marking device 800 is provided downstream of the eddy current flaw detector 700, and in response to a marking instruction given by the MPU 21, a solenoid valve between the paint spraying nozzle and the pressurized paint liquid tank is shortened. The coating is sprayed on the material 17 to be inspected for a period of time.

Detecting coil 18 and flaw detectors 100, 2
In order to prevent connection failure due to connection failure with 00, disconnection, etc., the MPU 21 controls the voltage of the detection coil 18 (an average value or an effective value of the voltage of the detection coil 18 while the pulse generator 29 generates pulses at a predetermined period or less). (Value) is monitored, and when it falls to a level without the test material 17, an alarm is output to the alarm board 24.

As described in the above-mentioned principle, the eddy-current flaw detection is easily detected when the surface of the flaw is cooled and becomes a magnetic substance. Conversely, this means that if there is no temperature difference between the test material 17 and the flaw, it is difficult to detect the flaw. Further, near the Curie temperature, the steel transforms, the magnetism changes, and noise frequently occurs. Therefore, many flaw signals are generated even though the material 17 to be inspected has no flaws.

For the above reasons, it is necessary to measure the surface temperature and the distribution of the test material 17. MPU21 is the test material 1
The temperature detected by the thermometer 900 for measuring the surface temperature and the internal temperature of 7 is digitally converted and read, and the surface / internal temperature difference of the test material 17 is calculated. When the detected temperature is near the Curie temperature, an alarm is output to the alarm board 24. The recorder 26 outputs the flaw detection data, the surface temperature, and the surface / internal temperature difference described above. This can also be monitored at the operator of the line inspecting the product. As a result, if there are many flawed signals and the surface temperature of the material to be inspected is near the Curie temperature, it can be judged to be the effect of the Curie temperature, and if there is a flawed signal and the surface / internal temperature difference is large, the material to be inspected 17 It is judged that there is a high possibility that there is a flaw, and it can be used for visual inspection of products.

Next, as an example of setting numerical values, flaw detection was carried out by setting the following conditions as flaw detection flaws by the multi-frequency eddy current flaw detection method and foreign matter entrapment.

-First Example- Wire diameter: 5.5φ Detection frequency: f ₁ 10KHZ For foreign object trapping detection f ₂ 30KHZ For bald spot detection Evaluation mode: f ₁ y signal f ₂ v signal Detection temperature: 1000 ° C. 5 shows the flaw detection results. Under the above conditions, the magnitude of the flaw signal at 10 KHZ was foreign matter trapping a ₁ > health flaw b ₁ , and it was found that foreign matter trapping was easier to detect. 3
On the contrary, the magnitude of the flaw signal at 0 KHZ is that the foreign matter is caught a ₂
<It was found to be bald defects b ₂ . Further, looking at the vector display of the oscilloscope OSP of FIG. 6, a foreign substance trapping tends to stably output a high signal along the y-axis, and a bald defect tends to vary in the direction and size of the vector. Therefore, the evaluation mode is 10K for detecting foreign matter trapping.
HZ determines the flaw level with the y signal, and 30KHZ for detecting bald flaws determines the flaw level with the v signal.

An example of the flaw detection chart at this time is shown in FIG.
When the flaw signal is output, the surface / internal temperature difference of the test material 17 may be large, and it has been confirmed that there is a bald flaw or foreign matter trapped at that position.

[0049] - a second example - wire diameter: 5.5Fai testing frequency: f ₁ 120 kHz foreign object biting detection f ₂ 30 kHz scab defect detection Evaluation Mode: f ₁ v signal angular range 35 ° ~90 ° f ₂ v Signal flaw detection temperature: 1000 ° C. FIG. 8 shows the flaw detection results. Although the tendency of the flaw signal to appear is the same as that in the first example, when viewing the vector display, the range of flaw occurrence due to foreign matter biting is from 35 ° to 90 ° in angle (direction of vector).
By masking the other range, the discrimination of foreign matter biting and bald spots was improved by about 20%.

-Third example-Wire diameter: 5.5φ Detection frequency: f ₁ 10KHZ For foreign object trapping detection f ₂ 20KHZ For bald spot detection Evaluation mode: f ₁ y signal f ₂ v signal Detection temperature: 790 ° C 9 shows the flaw detection results. It can be seen that the flaw detection temperature is around 790 ° C. Since 790 ° C is the Curie temperature, it can be seen that many flaw signals are generated. However, it can be seen that there is no large difference in the surface / internal temperature difference of the test material 17. Since the entire material 17 to be tested is the Curie temperature,
An alarm was output on the alarm panel.

[0051]

According to the multi-frequency eddy current flaw detection method using the single coil method of the present invention, it is possible to identify two or more types of flaws. Since it is a single excitation coil system, it is not necessary to install a plurality of eddy current flaw detection coils side by side or replace the flaw detection equipment at each frequency, so the equipment does not become large and the operation is simple.

Further, since the flaw detection temperature is also measured, it is checked whether there is a temperature change due to a flaw or whether the flaw is not detected at the Curie temperature. By using the flaw detection result of the eddy current flaw detection in combination, the quality is further improved. The accuracy of the guarantee can be expected to improve.

[Brief description of drawings]

FIG. 1 is a block diagram showing the configurations of an eddy current flaw detector 700 and eddy current flaw detection processing circuits 100 and 200 shown in FIG.

FIG. 2 is a block diagram showing a schematic configuration of an embodiment of the present invention.

FIG. 3 is a graph showing the impedance of the detection coil of the eddy current flaw detection coil with respect to cracks, magnetic permeability, lift-off and conductivity of a steel bar manufactured by hot rolling.

FIG. 4 is a flaw form diagram showing a plan view and a cross section of a barge flaw and a foreign matter biting of a steel bar manufactured by hot rolling.

5 is a graph showing an example of a flaw detection result by the flaw detection device shown in FIG.

6 is a graph showing the tip position of a vector appearing on the display surface of the oscilloscope OSP shown in FIG.

7 is a graph showing calculated values and measured values obtained by the flaw detection apparatus shown in FIG.

8 is a graph showing the position of the tip of a vector appearing on the display surface of the oscilloscope OSP shown in FIG.

9 is a graph showing calculated values and measured values obtained by the flaw detection apparatus shown in FIG.

[Explanation of symbols]

 OSP: Oscilloscope

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Hiromi Aramaki Hiromi 23-15 Suzuko-machi, Kamaishi-shi Nippon Steel Corporation Kamaishi Works (72) Inventor Takeshi Kumagaya 23-15 Suzuko, Kamaishi Steel Works Co., Ltd.Kamaishi Works (72) Inventor Yoichi Senda 23-15 Suzuko-cho, Kamaishi City Shin Nippon Steel Co., Ltd. 10-1 Nittetsu Technos Co., Ltd. (72) Inventor Kaneo Tsutsui 5-25-10 Himonya, Himonya, Meguro-ku, Tokyo Noahvil 22 Nippon Forster Co., Ltd.

Claims (9)

[Claims] 1. In eddy current flaw detection of steel using a flaw detection coil including an excitation coil and a detection coil, a single excitation coil penetrated by the steel is superposed with a high-frequency f1 current and a low-frequency f2 current, and detected. A first component of the voltage of the high frequency f1 induced in the coil having a first phase shift with respect to the current of the high frequency f1 of the exciting coil is extracted, and the first component is extracted.
From the component, two orthogonal components in the case of expressing it by a vector and at least one of the lengths are calculated, and when it is equal to or more than a set value, a flaw is detected, and the low frequency f2 of the low frequency f2 induced in the detection coil is detected. A quadrature 2 when a second component of the voltage having a second phase shift with respect to the low frequency f2 current of the exciting coil is extracted and expressed as a vector from the second component
A multi-frequency eddy current flaw detection method using a single excitation coil method that calculates at least one of the component and length and detects a flaw when it is above a set value. 2. In eddy current flaw detection of steel using a flaw detection coil including an excitation coil and a detection coil, a high frequency f1 current and a low frequency f2 current are applied to a single excitation coil through which the steel material penetrates for detection. A first component of the voltage of the high frequency f1 induced in the coil having a first phase shift with respect to the current of the high frequency f1 of the exciting coil is extracted, and the first component is extracted.
The component is represented by a vector, and when the vector direction is within a set range and the length of the vector is a set value or more, it is detected as a flaw, and the low frequency f2 of the voltage of the low frequency f2 induced in the detection coil is detected. A second component having a second phase shift with respect to the current of the frequency f2 is extracted, and the second component is represented by a vector. When the vector direction is within the set range and the vector length is equal to or larger than the set value, there is a defect. Multi-frequency eddy current flaw detection method using single excitation coil method. 3. A single excitation coil through which a steel material penetrates; a detection coil which induces a voltage corresponding to a change in magnetic flux generated in the steel material; a high frequency f1 current and a low frequency f2 in the excitation coil.
Means for energizing the above currents simultaneously and continuously; a first filter for extracting the voltage of the high frequency f1 induced in the detection coil; with respect to the current of the high frequency f1 of the exciting coil of the voltage extracted by the first filter A first component that extracts a first component having a first phase shift and calculates first vector information including two orthogonal components and at least one of the lengths when the first component is expressed by a vector from the first component Detection means; first
First evaluation means for quantizing vector information; second filter for extracting the voltage of the low frequency f2 induced in the detection coil; for the current of the low frequency f2 of the exciting coil of the voltage extracted by the second filter The second with a second phase shift
Second component detecting means for extracting a component, and calculating from this second component second vector information including two orthogonal components and a length of at least one when representing it by a vector; and second vector information A multi-frequency eddy current flaw detector by a single excitation coil system, which comprises: 4. A single excitation coil through which a steel material penetrates; a detection coil for inducing a voltage corresponding to a change in magnetic flux generated in the steel material; a high frequency f1 current and a low frequency f2 in the excitation coil.
Means for energizing the above currents simultaneously and continuously; a first filter for extracting the voltage of the high frequency f1 induced in the detection coil; with respect to the current of the high frequency f1 of the exciting coil of the voltage extracted by the first filter First component detecting means for extracting a first component having a first phase shift and converting the first component into first vector information represented by the direction and length of the vector; First evaluation means for quantizing the length represented by the direction within the set range; second filter for extracting the low frequency f2 voltage induced in the detection coil; second filter for extracting A second component of the voltage having a second phase shift with respect to the low frequency f2 current of the exciting coil is extracted, and this second component is converted into second vector information represented by the direction and length of the vector. , Second component detection Stage; and, second vector information, when those directions within the second set range, second evaluation means for quantizing a length that it represents;
A multi-frequency eddy current flaw detector with a single excitation coil system. 5. A first frequency detecting means for detecting the occurrence frequency of the same quantized data generated by the first evaluation means; and a first frequency detecting means for detecting the same quantized data generated by the second evaluation means. The multi-frequency eddy current flaw detector according to claim 3 or 4, further comprising: a second frequency detecting means for detecting the occurrence frequency. 6. An alarm means for issuing an alarm when the frequency detected by the first or second frequency detecting means is equal to or higher than a set value; and a means for marking a steel material position corresponding to the frequency equal to or higher than the set value. The multi-frequency eddy current flaw detector according to claim 5, which comprises a single excitation coil system. 7. A level detecting means for detecting whether the induced voltage of the detection coil is at a high level due to the steel material being at the position of the detection coil; a synchronous pulse for generating an electric pulse having a frequency proportional to the moving speed of the steel material. 4. The method according to claim 3, further comprising: a generating unit; and a warning unit that generates information indicating that the flaw detection is impossible when the level detecting unit detects a low level and when the synchronous pulse generating unit does not generate an electric pulse. Item 4. A multi-frequency eddy current flaw detector using a single excitation coil system according to Item 4. 8. A means for measuring the surface temperature of a steel material; a means for issuing an alarm when the surface temperature is equal to or higher than the Curie temperature; a flaw based on the surface temperature of the steel material and the frequency detected by the first and second frequency detecting means. The multi-frequency eddy current flaw detector according to claim 5, further comprising: a flaw recognizing means for determining presence / absence; and a means for outputting the surface temperature of the steel material and the flaw presence. 9. First and second sensitivity adjusting means for adjusting the levels of the two orthogonal components of the vectors of the first component and the second component respectively; corresponding to the sectional size information of the steel material, the energizing frequency f1, of the exciting coil. f2, the passbands of the first and second filters, the first and second phases, and the quantization thresholds of the first and second evaluation means are held in a memory and correspond to given section size information. This information is read from the memory, and the value indicated by the read information is set in the energizing means, the first and second filters, the first and second component detecting means, and the first and second evaluating means. 5. A single-excitation coil system multiple perimeter according to claim 3 or 4, further comprising: parameter setting means; and input means for giving sectional size information to the parameter setting means. Number eddy current device.