JP3266899B2 - Method and apparatus for flaw detection of magnetic metal body - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method and an apparatus for detecting minute defects such as inclusions present inside or on a surface of a magnetic metal body by a magnetic flux leakage inspection method.

[0002]

2. Description of the Related Art In the case of a metal material or the like, if there is a defect inside or on the surface, a problem such as strength or the like may occur. Therefore, for quality control or quality assurance, an X-ray transmission method, an ultrasonic inspection method, or the like. Various non-destructive tests have been performed. For example, an X-ray transmission method and an ultrasonic flaw detection method are used to detect a crack in a welded portion of a steel pipe. On the other hand, near-surface defects and thin strips, especially online,
An electromagnetic method, that is, a leakage magnetic flux method or an eddy current flaw detection method is often used.

[0003] In ultra-thin steel sheets for can-making materials, if there are defects such as inclusions, problems such as the generation of flange cracks during can-making may occur. Detectors have been developed. For example, Japanese Patent Application Laid-Open No. Hei 3-175352 discloses that a magnetizer 22 for magnetizing a steel sheet is provided on one side of a steel sheet 21 and leakage caused by a defect is provided on the other side, as shown in FIG. A method has been proposed in which a magnetic sensor array 23 for detecting magnetic flux is arranged in the width direction, and each of the magnetic sensor arrays 23 is inserted into non-magnetic rolls 24 and 25 to perform flaw detection. According to such a method, the distance between the sensor 23 and the test object 21 can be kept small and stable, and a minute defect in the steel plate can be detected at high speed without contact.

[0004]

However, in the prior art including the method described in Japanese Patent Application Laid-Open No. 3-175352, when the internal or surface defect to be detected is small, or when the internal defect of a thick metal band is detected. Is detected, the defect signal is weakened, the S / N ratio is relatively deteriorated, and it becomes difficult to detect the defect. In particular, formation noise caused by the test object often becomes a problem. The formation noise can be reduced by optimizing the measurement conditions, but as the defect signal becomes smaller, it becomes more difficult to distinguish between the formation noise and the defect signal, and the defect detection becomes more difficult. . For example, in the case of detecting a foreign substance such as an inclusion, which is a problem in an ultra-thin steel plate for can making, there is a problem that a sufficient detection capability cannot be obtained with the conventional technology.

The present invention has been made to solve such a problem, and an object of the present invention is to make it possible to detect a minute defect that cannot be sufficiently detected by the conventional magnetic flux leakage inspection method.

[0006] The problem is that a magnetic field is applied to the magnetic metal body to be inspected to magnetize the inspection part, and that the leakage magnetic flux generated from the defect of the magnetic metal body must be at least one of the measurement conditions different from each other.
To make the formation noise appear differently.
Under the conditions, a plurality of leakage magnetic flux detection signals are detected by a plurality of magnetic sensors to obtain a plurality of leakage magnetic flux detection signals, and signals obtained from substantially the same inspection site of the plurality of leakage magnetic flux detection signals are compared with each other. Using a composite flaw detection signal obtained by performing a signal processing including an operation of relatively emphasizing a defect signal that is present in at least two signals relative to a noise signal, a defect of the magnetic metal body is determined. The problem is solved by a flaw detection method for a magnetic metal body characterized by detecting.

This method involves the following steps: (1) A magnetic field is applied to a magnetic metal body to be inspected.
A magnetizer that magnetizes the inspection part by applying a magnetic field, and (2) a magnetic metal body
Leakage flux generated from the defect of at least
Formation noise is different because one item is different from each other
Flux leakage detection by detecting under multiple conditions
Multiple magnetic sensors to obtain signals and (3)
Leakage magnetic flux inspection signal obtained from substantially the same inspection site
For signals, at least two of the plurality of signals
Defect signals that are commonly present in the signal
Signal processing that includes calculations that emphasize
And a magnetic metal inspection device having a
Can be applied. In addition, this method comprises the steps of (1) a magnetizer for magnetizing a magnetic metal body, and (2) a row of three magnetic poles made of an E-shaped ferromagnetic body so as to be along the running direction of the magnetic metal body. An E-shaped magnetic sensor comprising an E-shaped core and a coil wound around the central magnetic pole of the E-shaped core, and arranged in pairs on both sides so as to sandwich the same portion of the magnetic metal body to be inspected; ) A signal processing including an operation of emphasizing a defect signal which is present in the two leaked magnetic flux detection signals detected by the paired E-type magnetic sensors relatively to a noise signal. A magnetic metal object flaw detector comprising: an arithmetic unit for obtaining a composite flaw detection signal obtained by performing the test; and (4) a determination circuit for determining the presence or absence or the class of the defect of the magnetic metal body from the composite flaw detection signal. Can be implemented.

[0008] Since signal processing including an operation of emphasizing a defect signal that is present in at least two of a plurality of signals in common with a noise signal is performed, the S / N ratio is reduced. It is possible to detect minute defects with high accuracy.

[0009]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The measurement conditions refer to conditions generally considered in the detection of magnetic flux leakage, and include items such as a filter, a measurement surface of a metal strip, a distance between a sensor and an object to be inspected, and a magnetization. The force, magnetization direction, type of sensor, and the like can be considered. In the present invention, a plurality of leakage magnetic flux detection signals are obtained by a plurality of magnetic sensors at least different from each other.

As a signal to be calculated, a pair of signals obtained from the front and back surfaces of the non-test magnetic metal body at substantially the same location can be used. While the defect signal is obtained in the same way on the front and back surfaces of the magnetic metal body to be inspected, the noise component is affected by the surface properties and the like of the magnetic metal body to be inspected. Therefore, by calculating the signals on the front and back surfaces, the defect signal component can be increased relative to the noise component.

As a signal to be operated, a signal processed by a plurality of filters having mutually different filter constants can be used. That is, for example, FIG.
As shown in the following, if the first band-pass filter is a lower frequency band including the defective frequency, and the second band-pass filter is a higher frequency band including the defective frequency,
Although the defect signal is common to both, the noise component does not always appear at the same position because the frequency bands of both are different. Therefore, by calculating the signals that have passed through these band-pass filters, the defect signal component can be increased relative to the noise component.

In this case, using a plurality of sensors,
Each output may be passed through a filter having a different frequency band, or only one sensor may be used, and the output from the sensor may be branched and passed through a filter having a different frequency band.

As signals to be calculated, signals obtained from a plurality of magnetic sensors having different distances (lift-offs) between the sensor and the metal body flaw detection surface can be used.
When the lift-off changes, as shown in FIG. 4, the cover range on the metal body detected by the sensor changes, so that the noise source to be detected changes, and as a result, the noise detected by the sensor differs. Becomes Therefore, when the lift-off is changed, the defect signal is detected in the same manner, but the noise is different. Therefore, the defect signal component can be increased relative to the noise component by calculating the signals obtained from the sensors having different lift-offs.

Signals obtained from a plurality of different types of magnetic sensors can be used as signals to be calculated. Depending on the type of the sensor, the coverage range differs, or the sensor has a difference function such as a sensor using an E-type core and the sensor does not have a difference function like a general sensor. Both sensors are designed to detect defective signals, but the noise signals are different due to these types of differences. Therefore, by calculating signals obtained from a plurality of sensors of different types, it is possible to increase the defect signal component relative to the noise component.

In addition, other than the items shown here, a signal from a defect can be obtained, and noise is used as a signal to be calculated if the output is different under each measurement condition. be able to.

As described above, for a plurality of signals obtained from substantially the same inspection site among a plurality of leakage magnetic flux detection signals obtained under a plurality of different measurement conditions, at least two of the plurality of signals are used. A defect is detected using a composite flaw detection signal obtained by performing signal processing including an operation of emphasizing a defect signal commonly present in a signal relative to a noise signal.

The operation in the case of using two types of leakage magnetic flux detection signals is generally expressed by the following equation (1).

A (x) = M1 (x) * M2 (x) (1) where x is a position on the inspection object, and M1 (x) is obtained under a certain measurement condition (measurement condition 1). M2 (x) indicates the leakage magnetic flux detection signal value at the position x obtained under another measurement condition (measurement condition 2).
Are operators (eg, multiplication, sum of squares, M1 (x), M2
(x) Addition after taking absolute values of both, M1 (x), M2
(x) operator that takes the smaller value after taking the absolute value of both). A (x) is the result of the operation at position x.

At this time, a change in the signal due to the defect can be detected under all of a plurality of different measurement conditions, even if the magnitude is different, so that the change appears at the same position, and the noise is locally detected. If the measurement conditions are selected so as to be different, it is possible to improve the S / N ratio using the difference between the defect signal and the noise. At a position where formation noise is large in one of the leakage magnetic flux detection signals, formation noise is small in the other leakage magnetic flux detection signal. The noise part is relatively weakened as compared with the defective signal appearing in (1). Similar effects can be expected for the sum after the sum of the squares, M1 (x), and M2 (x) after taking the absolute values of both. In the calculation that takes the smaller of the absolute values of both, the leakage flux detection signal takes a large value in the defective part, so the result of the calculation that takes the smaller one does not become so small, but the noise part is one of the two. May be small, and by taking the smaller one, the calculation result may be considerably smaller. Therefore, relatively defective parts are compared to noise parts.
Be emphasized.

The type of operation is such that a defect signal similar between the two leakage magnetic flux signals is strengthened, while both are not necessarily at the same position,
Alternatively, any calculation may be used as long as noise that does not appear as the same waveform is relatively weakened. This can be selected according to the nature of the noise or the defect signal, or according to restrictions in realizing the device.

In the above example, the calculation between the two kinds of leakage magnetic flux detection signals has been described as an example, but it is not necessary to limit to two kinds. By using signals having many different measurement conditions, it is expected that the effect of enhancing a defective signal and relatively reducing the degree of enhancement of noise will be increased. For example,
Assuming that M1 (x), M2 (x), M3 (x), and M4 (x) are leakage magnetic flux detection signal data taken under different conditions,
B (x) shown in the following equation (2) can be used for determining the presence or absence of a defect. B (x) = abs [M1 (x) × M2 (x) × M3 (x)] + abs [M4 (x)] (2) where abs [Y] is a function that takes the absolute value of Y is there.

In this case, a case is described in which one type of calculation result is used to determine the presence or absence of a defect.
This is not limited to one, and it is also possible to use two or more. For example, a final determination can be made by combining the determination results of A (x) and B (x). In addition, it is possible to add a judgment using only the conventional leakage magnetic flux detection signal. In such a case, the determination circuit checks whether or not each of the thresholds has been exceeded for not only one signal but also a plurality of signals, and further combines the results to determine whether or not there is a defect, a class. The final decision regarding

As a result, it is possible to detect a minute defect that cannot be detected by a simple conventional magnetic flux leakage method due to poor S / N.

[0024]

DESCRIPTION OF THE PREFERRED EMBODIMENTS One embodiment of the present invention will be described below with reference to the drawings. FIG. 1 is a diagram showing an example of an apparatus according to the present invention.
In FIG. 1, 11 is a steel plate, 12 and 13 are E-type magnetic sensors, 14 is a coil, 15 is a DC magnetizing device, 16 and 17 are band pass filters, 18 is a multiplier, and 19 is a judgment circuit.

On one side of the steel plate 11, an E-type sensor 12 is arranged, and on the other side, a DC magnetizing device 15 and another E-type sensor 13 are arranged. The DC magnetizing device 15 magnetizes the inspected portion of the steel plate 11 to the saturation region. The steel plate 11 includes an E-type sensor 12, a magnetizer 15, and an E-type sensor 1.
3, the three legs (magnetic poles) 12a, 12b, and 12c of the sensor core are arranged along the moving direction. Among these three coils, the coil 14 wound around the foot 12b at the center of the E-type sensor is used as a magnetic detection unit, and the time differential value of the magnetic flux linked to the coil is measured.

Due to the structural feature of the core being E-shaped, the magnetic flux linked to the coil is not affected by the foot 12 at one end.
a and the magnetic flux passing through a magnetic loop including the middle foot 12b and the other end of the magnetic loop including the foot 12c and the middle foot 12b. for that reason,
Noise components common to both loops are canceled, and defective signal components not common to both loops are selectively detected. The operation of the E-type sensor 13 is also
The operation is the same as that of the second operation.

By passing the sensor output through appropriate band-pass filters 16 and 17, a leakage magnetic flux detection signal (differential value) is obtained.
Can be obtained.

Here, an example will be described in which multiplication of signals from the same inspection position of two leakage magnetic flux detection signals obtained by two sensors arranged on both sides of the steel plate so as to sandwich the position of the steel plate is used as the calculation. The sensitivity in the depth direction in the steel sheet is relatively high near the front side with the sensor, and relatively low near the back side without the sensor. Therefore, the sensor 12 and the sensor 13 generate signals differently depending on the position of the signal or noise source in the depth direction.

FIG. 2A shows the position x on the test object as the horizontal axis, and the vertical axis as the sensor 12 after processing such as a band-pass filter.
6 shows a leakage magnetic flux detection signal Ma (x) by a.
The S / N ratio is about 1.8 because not only the signal is large at the defective part but also the formation noise caused by the inspection object is large. FIG. 2B shows a leakage magnetic flux detection signal M by the sensor 13 similarly processed by a band-pass filter or the like.
b (x). In this case as well, a defect signal is output at the same position as Ma (x). However, since there is formation noise due to the inspection object, the S / N ratio is also about 1.9. Here, multiplication is performed for each signal value from the same position. When the operation result A (x) is expressed by an equation, the following operation is performed: A (x) = Ma (x) × Mb (x) (3)

In this case, since the size of the defect is to some extent, the defect signal appears in both signals and their positions are almost the same. Therefore, by multiplication, the defect corresponding portion of the signal A (x) after the calculation is obtained. Becomes larger. On the other hand, the formation noise is not always the same at the same position due to the difference in the sensitivity distribution in the depth direction between the two sensors. For example, noise from a noise source near the surface may be detected by one sensor, but less detected by the other sensor. In that case, when both are multiplied, the noise-corresponding portion of the signal A (x) after the operation is generally not larger than that of the defective signal portions. In other words, the defect signal portion is emphasized as compared with the formation noise portion, so that it is easy to determine the presence or absence of a defect by using the operation result A (x), and the defect detection ability is improved. In this example, the S / N ratio has increased to 5.2.

The judgment circuit 19 compares the defect signal value with a predetermined threshold value by using the signal having a good S / N ratio obtained in this way, thereby judging the presence or absence of a defect and judging the defect class. I do.

[0032]

According to the present invention, the defect detection is performed by using a composite flaw detection signal obtained by calculating signal waveforms of a plurality of eddy current flaw detection signals having different measurement conditions obtained from substantially the same inspection site. By judging the presence or absence and the degree of harm, it is possible to detect a defect that cannot be sufficiently obtained with the conventional method and is difficult to detect.

[Brief description of the drawings]

FIG. 1 is a diagram showing one embodiment of an apparatus according to the present invention.

FIG. 2 is a diagram showing a leakage magnetic flux detection signal and a signal of a calculation result thereof.

FIG. 3 is a diagram illustrating a relationship between a frequency of a defect and a noise and a band of a band-pass filter.

FIG. 4 is a diagram showing a lift-off of a sensor, a detection range, and a range of a noise source.

FIG. 5 is a diagram showing an example of the related art.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 11 Steel plate 12, 13 E type sensor 12a, 12b, 12c Foot of E type sensor 14 Coil 15 DC magnetizing device 16, 17 Band pass filter 18 Multiplier 19 Judgment circuit

──────────────────────────────────────────────────続 き Continuation of the front page (56) References JP-A-57-108656 (JP, A) JP-A-63-133054 (JP, A) JP-A-58-83253 (JP, A) 119760 (JP, U) (58) Field surveyed (Int. Cl. ⁷ , DB name) G01N 27/72-27/90

Claims (10)

(57) [Claims] 1. A magnetic field is applied to a magnetic metal body to be inspected to magnetize an inspection part, and a leakage magnetic flux generated from a defect of the magnetic metal body is made different from at least one item of measurement conditions .
Under multiple conditions where formation noise appears differently,
Detected by a plurality of magnetic sensors to obtain a plurality of leakage magnetic flux detection signals, and at least two of the plurality of leakage magnetic flux detection signals are obtained from signals obtained from substantially the same inspection site. Detecting a defect in a magnetic metal body using a composite flaw detection signal obtained by performing signal processing including an operation that emphasizes a defect signal that is commonly present in two signals relative to a noise signal A flaw detection method for a magnetic metal body, characterized in that: 2. The magnetic metal body of claim 1, wherein the at least two signals include pairs of signals obtained from substantially the same front and back surfaces of the untested magnetic metal body. Flaw detection method. 3. The flaw detection method according to claim 1, wherein the at least two signals include signals processed by a plurality of filters having different filter constants. Method. 4. The apparatus according to claim 1, wherein the at least two signals include signals obtained from a plurality of magnetic sensors having different distances between the sensor and the inspection surface of the metal object to be inspected. The method for flaw detection of a magnetic metal body according to any one of the above items. 5. The magnetic metal body according to claim 1, wherein the at least two signals include signals obtained from a plurality of different types of magnetic sensors. Flaw detection method. 6. An arithmetic operation for emphasizing a defect signal commonly present in a signal relative to a noise signal is multiplied ,
Sum of squares or the smaller of the absolute values of each signal
Testing method of a magnetic metal body according to any one of claims 1 to 5, characterized in that either of the operation that. 7. A magnetizer for magnetizing a magnetic metal body, and (2) an array of three magnetic poles made of an E-shaped ferromagnetic material so that a row of three magnetic poles is along a running direction of the magnetic metal body. (3) an E-shaped magnetic sensor comprising an E-shaped core arranged and a coil wound around the central magnetic pole of the E-shaped core, and arranged in pairs on both sides so as to sandwich the same portion of the magnetic metal body to be inspected; A signal processing including an operation of emphasizing a defect signal which is present in the two leakage magnetic flux detection signals detected by the paired E-type magnetic sensors relatively to a noise signal is performed. (4) A magnetic metal object flaw detection device comprising: an arithmetic unit for obtaining a composite flaw detection signal obtained by the above; and (4) a judgment circuit for judging the presence or absence or the class of the defect of the magnetic metal body from the composite flaw detection signal. 8. An arithmetic unit for obtaining a composite flaw detection signal obtained by performing an operation for emphasizing a defect signal which is present in common between two leakage magnetic flux flaw detection signals relative to a noise signal is a multiplier. A magnetic metal body flaw detector according to claim 7. 9. Applying a magnetic field to a magnetic metal body to be inspected
A magnetizer for magnetizing the inspection unit; (2) Reduce leakage magnetic flux generated from defects in magnetic metal
And one of the measurement conditions differs from each other,
Detect under multiple conditions where noise comes out differently
A plurality of magnetic sensors for obtaining a leakage magnetic flux detection signal by (3) Substantially the same of these plurality of leakage magnetic flux detection signals
The signals obtained from the inspection site are compared with each other,
Defect signals common to at least two of the signals
Operation that emphasizes the signal relative to the noise signal
Including a signal processing device for performing signal processing
Genital flaw detector. 10. A defect signal which is commonly present in a signal is detected.
An operation that emphasizes the noise signal relatively
Arithmetic, sum of squares, or smaller value after taking the absolute value of each signal
10. An operation which takes any one of the following:
3. A magnetic metal body flaw detector according to claim 1.