JPH0560730A - Method and apparatus for magnetic flaw detection of metal strip - Google Patents

Abstract

(57) [Abstract] [Purpose] To obtain a magnetic flaw detection method and apparatus for a metal strip capable of detecting a wide range of flaws from a main flaw inside or on the surface of the metal strip to a minute flaw and a welded portion with high sensitivity. [Structure] One row or two in the direction perpendicular to the running direction of the metal strip
Selection means for selecting each pair of magnetic sensors 1-1 and 1-2 from the magnetic sensor group arranged in a row, and peak hold circuits 3-1 and 3-for obtaining the maximum peak value of the output of each pair of magnetic sensors. 1, a difference calculation circuit 4 for calculating the difference between the maximum peak values of each pair, a second threshold calculation circuit 5 for calculating a second threshold from the difference calculation value, a preset first threshold and the second It is provided with first and second comparing means 6-1 and 6-2 for respectively comparing the threshold value and the flaw signal.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method and apparatus for magnetic flaw detection of defects or welds on the surface and inside of non-magnetic metal strips such as continuously running steel and alloys.

[0002]

2. Description of the Related Art As a publicly known document for detecting flaws on the surface and inside of a steel sheet such as a thin steel strip in a running state, for example, Japanese Patent Application No. 1-272183 discloses "a flaw detection method for a steel sheet". (Hereinafter referred to as Document 1). 10 to 12 are drawings according to Document 1 above, FIG. 10 is a block diagram of a magnetic flaw detector for a steel plate, FIG. 11 is a schematic sectional view of a flaw detection unit, and FIG. 12 is a detection signal and a first threshold value and It is explanatory drawing with two threshold values. In FIGS. 10 and 11, 51 is a steel plate, 52 is a hollow roll, 53 is a coil, 54 is a magnetic core, 55 is a sensor, 56 and 59 are comparison circuits, 57 is a peak value detection circuit, and 58 is an average value detection circuit. Is.

In the magnetic flaw detector having the structure shown in FIG. 10, a flaw detecting section housed in the hollow coil 52 shown in FIG. 11 is installed on the lower side in contact with a continuously running steel plate. The traveling steel plate 51 is magnetized by exciting the magnetic core 54 with the coil 53 in the hollow coil 52, and if a flaw is present on the surface or inside of the magnetized steel plate, a leakage magnetic flux is generated at this flaw portion. This leakage magnetic flux is the magnetized core 5
It is detected by a sensor 55 provided between the four. The detection signal obtained from the sensor 55 is compared with a preset first threshold value (shown in FIG. 12) in the comparator 56, and the main flaw of the steel sheet is detected by the detection signal exceeding the first threshold value. To do.

Further, the detection signal obtained from the sensor 55 is input to the peak value detection circuit 57, and the peak value of the detection signal which does not reach the first threshold value among the detection signals from the sensor 55 is determined as the moving direction of the steel sheet. Then, a desired peak value is selected as a representative of the plurality of peak values among the plurality of peak values thus detected, and such a representative value is selected. Repeated several times along the moving direction of the steel sheet. Next, the average value of the representative values thus selected a plurality of times is calculated by the average value calculation circuit 58, and the discrimination signal level of the microscopic flaw having the average value thus calculated as the second threshold is shown in FIG. Shown in. Then, the second threshold value is supplied to the comparison circuit 59,
The detection signal that exceeds the second threshold value is detected as a minute flaw signal as compared with the detection signal that does not reach the first threshold value. Naturally, the detection signal below the second threshold value is processed as a noise signal.

Further, as a known document of a noise eliminator for a magnetic flaw detector for a steel sheet, for example, "Noise eliminator for a thin steel strip magnetic flaw detector" disclosed in Japanese Utility Model Laid-Open No. 3-33362 (hereinafter referred to as Document 2). There is. 13 to 17
13A and 13B are drawings relating to the above-mentioned document 2, FIG. 13 is a partially cutaway sectional view of a magnetic flaw detection portion, FIG. 14 is an electric circuit diagram of FIG. 13, FIG. 15 is an output waveform diagram of FIG. 14, and FIG. FIG. 17 is a waveform diagram for explaining the detection signal of Document 2 and FIG. 17 is a characteristic diagram of element spacing and output. In FIGS. 13 and 14, 61 is an exciting coil, 62 is an electromagnet, X is a thin steel strip, and Y is Y.
Is a flaw, and A and B are magnetic sensitive elements.

In the device shown in FIGS. 13 to 14,
In a flaw detection device that generates a magnetic field in the traveling direction of a traveling thin steel strip and detects a leakage magnetic flux generated by an internal or surface flaw by a magnetic sensitive element group to give a flaw signal, between the magnetic poles of the electromagnet 62 shown in FIG. In addition, the magnetic sensitive element groups are arranged in two rows A and B with respect to the traveling direction, and the interval is 0.5 to
When it is arranged so as to be 2.0 mm, and the electric circuit of FIG. 14 is used to detect the added value obtained by adding the detected values (instantaneous detected values shown in FIG. 15) obtained from the two magnetic sensitive elements, As compared with the conventional detection signal shown in FIG. 17A, the flaw signal is doubled and the noise signal is reduced as compared with the conventional detection signal shown in FIG. 17B. Be done. In this case, as shown in FIG. 16, the distance between the element groups A and B is 0.5 to 2.0 mm (the peak is about 1.0 m).
It is disclosed that, if m), internal or surface defects can be detected with high sensitivity.

[0007]

However, the flaw detection method of the steel sheet according to the above document 1 has a problem that the second threshold cannot be flexibly changed according to the type of flaw of the steel sheet. That is, as the flaws of the steel sheet, dot flaws (there are different sizes of hole diameters), linear flaws (there are a running direction and a direction at right angles to this, etc.), surface flaws and welds (welding before cold rolling) And both of the post-cold rolling welding), and it is not easy to set the second threshold value to an appropriate value corresponding to each of these flaws.

Further, the noise removing device in the thin steel strip magnetic flaw detector according to the above-mentioned document 2 is not always effective for various flaws of the steel plate, and the added value obtained by adding the instantaneous detection values obtained from the two magnetic sensitive elements is used. If it is taken out, there is a problem that the flaw signal is rather reduced and the signal-to-noise ratio (hereinafter referred to as S / N) may be deteriorated. This is because this document 2 adds and outputs instantaneous detection values of the same polarity obtained from two magnetic sensitive elements at the same timing,
If the peak signals of the same polarity cannot be obtained from the two magneto-sensitive elements at the timing of addition, the S / N will be rather lowered.

The present invention has been made to solve the above problems, and a metal capable of obtaining a flaw detection signal with an improved S / N corresponding to various defects inside or on the surface of the metal strip. An object is to obtain a magnetic flaw detection method and device for a strip.

[0010]

A method and an apparatus for magnetic flaw detection of a metal strip according to the present invention generate a magnetic field in the traveling direction of a traveling metal strip to prevent leakage flux generated by a defect in the inside or the surface of the metal strip. A method and apparatus for magnetic flaw detection of a metal strip, wherein a plurality of magnetic sensitive elements arranged in a line at right angles to the running direction of the metal strip to detect and obtain a defect signal are provided. Selecting means for selecting two magnetic sensitive elements so as to form a pair, and two detection signals obtained for each pair of magnetic sensitive elements selected by the selecting means for each constant running section of the metal strip. A peak hold means for detecting a maximum peak value and a difference between two maximum peak values detected by the peak hold means for each pair of magnetic sensitive elements are calculated. Then, the difference calculation means for outputting this as a flaw signal value for each traveling section of the magnetic sensitive element of each pair, and the flaw signal value for each traveling section of the magnetic sensitive element of each pair output by the difference computing means. Compared to the preset first threshold,
When the first threshold value is exceeded, a first comparison means for detecting this as a main flaw of the metal strip and a flaw signal value for each traveling section of each pair of magnetically sensitive elements output by the difference calculation means are predetermined. After multiplying the coefficient of, a predetermined bias value is added to make it a calculated value of the corresponding section, and a moving average value of the calculated value and a plurality of section calculated values stored over the past plural sections is calculated, A second threshold value calculating means for outputting the moving average value as a second threshold value for each in the next running section, and a flaw signal for each running section of each pair of magnetic sensitive elements output by the difference calculating means. Second comparing means for comparing with a respective second threshold value calculated and output by the threshold value calculating means in the immediately preceding traveling section, and detecting this as a minute flaw in the metal strip when the second threshold value is exceeded. It is equipped with and.

Further, the magnetic flaw detection method and apparatus for a metal strip according to the present invention generate a magnetic field in the traveling direction of the traveling metal strip, and the leakage magnetic flux generated by the defect in the inside or the surface of the metal strip travels through the metal strip. In the method and apparatus for magnetic flaw detection of a metal band, a defect signal is detected by a plurality of magnetically sensitive elements arranged in two rows at right angles to the direction.
A plurality of magnetic sensitive elements arranged side by side in a row are selected so that each magnetic sensitive element in the front row and each magnetic sensitive element in the rear row immediately behind the magnetic sensitive element are paired, or each magnetic sensitive element in the front row is selected. Selection means for selecting a pair of the sensitive element and each of the back-side magnetic sensitive elements located at positions other than directly behind, and two detections obtained for each pair of magnetic sensitive elements selected by the selecting means. Peak hold means for detecting the maximum peak value of the signal for each constant traveling section of the metal strip, and 2 for each of the pair of magnetically sensitive elements detected by the peak hold means.
Difference calculation means for calculating a difference between two maximum peak values and outputting the difference as a flaw signal value for each traveling section of each pair of magnetic sensitive elements; and for each pair of magnetic sensitive elements output by the difference calculation means. First comparison means for comparing the flaw signal value for each traveling section with a preset first threshold value and detecting it as a major flaw of the metal strip when the first threshold value is exceeded, and the difference calculation. The flaw signal value of each pair of magnetic sensitive elements output by the means is multiplied by a predetermined coefficient, and then a predetermined bias value is added to obtain a calculated value of the corresponding section. Second threshold value calculation means for calculating a moving average value with a plurality of section calculation values stored over a section, and outputting the moving average value as a second threshold value for each in the next traveling section, and the difference calculation means. Of each pair of magnetic sensitive elements output by Is compared with the respective second threshold values calculated and output by the second threshold value calculation means in the immediately preceding traveling section, and when the second threshold value is exceeded, this is detected as a minute flaw in the metal strip. And two comparison means.

[0012]

According to the present invention, a magnetic field is generated in the traveling direction of the traveling metal strip, and the leakage magnetic flux generated by a defect inside or on the surface of the metallic strip is arranged in a line at right angles to the traveling direction of the metal strip. In a method and an apparatus for magnetic flaw detection of a metal band for detecting a defect signal by detecting a plurality of magnetic sensitive elements provided, the selecting means comprises a pair of two magnetic sensitive elements at a predetermined interval from the plurality of magnetic sensitive elements. select. The predetermined interval means that when a defect having the maximum size determined as a detection target is provided in the metal band and one magnetic sensitive element for detecting the defect is moved in the width direction of the metal band, When the position where the maximum value of the flaw signal is obtained from the sensitive element is the first position and the position where the flaw signal is not obtained at all is the second position, the position is between the first position and the second position. Refers to the interval. Therefore, it is not the interval between the magnetically sensitive elements arranged in the one row. In the case of a steel strip, the predetermined interval is usually about 10 to 20 times the lateral width of the defect having the maximum size. The peak hold means is
The maximum peak value of each of the two detection signals obtained for each pair of magnetically sensitive elements selected by the selection means is detected for each constant traveling section of the metal strip. The difference calculation means calculates the difference between the two maximum peak values detected by the peak hold means for each magnetic sensitive element of each pair, and uses this as a flaw signal for each running section of the magnetic sensitive element of each pair. Output as a value. The first comparison means compares the flaw signal value for each traveling section of each pair of magnetic sensitive elements output from the difference calculation means with a preset first threshold value,
When the threshold value is exceeded, this is detected as a major flaw in the metal strip. The second threshold value calculation means multiplies a flaw signal value for each traveling section of each pair of magnetic sensitive elements output by the difference calculation means by a predetermined coefficient, then adds a predetermined bias value, and calculates this for the corresponding section. Value, a moving average value of the calculated value and a plurality of section calculated values stored over a plurality of past sections is calculated, and the moving average value is calculated for each second value in the next traveling section.
Output as a threshold. The second comparing means calculates the flaw signal for each traveling section of each pair of magnetic sensitive elements output by the difference calculating means by the second threshold calculating means in the immediately preceding traveling section, and outputs it. Compared with two thresholds, when exceeding the second threshold, this is detected as a minute flaw in the metal band.

Further, in the present invention, a magnetic field is generated in the traveling direction of the traveling metal strip, and the leakage magnetic flux generated by a defect inside or on the surface of the metal strip is arranged in two rows in a direction perpendicular to the traveling direction of the metal strip. In a method and an apparatus for magnetic flaw detection of a metal band for detecting a defect signal by detecting a plurality of magnetically sensitive elements arranged, a selecting means is provided in each of the plurality of magnetically sensitive elements arranged in two rows. Either the element and each of the back row magnetically sensitive elements located directly behind it should be selected as a pair, or each of the front row magnetically sensitive elements and each back row magnetically sensitive element other than directly behind should be paired. And choose to. The peak hold means detects the maximum peak value of each of the two detection signals obtained for each pair of magnetically sensitive elements selected by the selecting means for each constant traveling section of the metal strip. The difference calculation means calculates the difference between the two maximum peak values detected by the peak hold means for each magnetic sensitive element of each pair, and uses this as a flaw signal for each running section of the magnetic sensitive element of each pair. Output as a value. The first comparison means compares the flaw signal value for each traveling section of each pair of magnetically sensitive elements output by the difference calculation means with a preset first threshold value, and when it exceeds the first threshold value, Is detected as a major flaw in the metal strip. The second threshold value calculation means multiplies a flaw signal value for each traveling section of each pair of magnetic sensitive elements output by the difference calculation means by a predetermined coefficient, then adds a predetermined bias value, and calculates this for the corresponding section. As a value, a moving average value of the calculated value and a plurality of section calculated values stored over a plurality of past sections is calculated, and the moving average value is output as a second threshold value for each of the following traveling sections. The second comparing means calculates the flaw signal for each traveling section of each pair of magnetic sensitive elements output by the difference calculating means by the second threshold calculating means in the immediately preceding traveling section, and outputs it. Compared with two thresholds, when exceeding the second threshold, this is detected as a minute flaw in the metal band.

[0014]

DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 is a system diagram of a flaw detection signal processing unit for a metal strip according to the present invention. In the figure, 1-1 and 1-2 are a pair of magnetic sensitive elements (hereinafter referred to as magnetic sensors) located in a relatively close position selected from a magnetic sensitive element group (hereinafter referred to as magnetic sensor group) included in the magnetic flaw detector. ), Which are referred to as # 1 and # 2 magnetic sensors. How to select the pair of magnetic sensors will be described with reference to FIGS. The magnetic flaw detector will be described with reference to FIGS. 3 and 4. FIG. 2 is a waveform diagram for explaining the operation of FIG. 1. In FIG. 2, (a) is a section update signal, (b) is # 1 sensor output and its peak hold value, (c) is # 2 sensor output. And the peak hold value thereof, and (d) shows the difference calculation value of the peak hold values of # 1 and # 2.

Reference numeral 2 in FIG. 1 denotes a section signal generator, which receives a metal band carrier speed signal and generates and outputs a section update signal every time the metal band is carried for a certain section length. In the present invention, the # 1 and # 2 magnetic sensors 1-1 and 1-
Since the output signals of 2 are detected as the maximum peak value in the fixed section length instead of the respective instantaneous values, the length of the fixed section is set so as not to be too large (for example, about 10 cm in the case of a thin steel strip). To be done. Now, assuming that the transport speed in the case of a thin steel strip as a metal strip is 200 m / min and the section length is 10 cm, a section update signal may be generated at a cycle of about 33.3 msec (millisecond). The generated section update signal is used as two peak hold circuits 3-1 and 3
-2, and is supplied to the difference calculation circuit 4 and the second threshold calculation circuit 5. FIG. 2A shows the section update signal and sections a, b, c, d and e between the signals.

3-1 and 3-2 in FIG. 1 are # 1 respectively.
And the # 2 peak hold circuit, and the section signal generator 2
Every time a section update signal is supplied from the difference calculation circuit 4, the peak hold value which is the maximum peak value in the previous section is supplied.
To the # 1 and # 2 magnetic sensors 1-1 and 1 respectively during the current section.
After unifying the polarities of the sensor output signals sequentially input from -2, the maximum peak value is obtained and held. When the next section update signal is input, the peak hold value held until then is supplied to the difference calculation circuit 4, and the operation of the next peak hold is repeated again. Here, the unification of the polarities of the sensor output signals means that, since an output signal of both positive polarity and negative polarity is originally obtained from the magnetic sensor, for example, only the negative polarity signal is extracted and the amplification degree is 1 and only the polarity is inverted. Inverting into a positive polarity signal through an inverting amplifier to make all the sensor output signals a positive polarity signal (see FIG. 8). As a result, the peak hold circuit may find the maximum voltage value (here, the maximum peak value) of one polarity (for example, positive polarity).

The # 1 and # 2 peak hold circuits 3-
As the peak hold value obtained for each section by 1 and 3-2, the maximum value of only the noise signal generated if there is no flaw to be detected in the metal band in the section,
If the metal band has some kind of flaw, the maximum value of the superimposed signal of the noise signal and the flaw signal is output. 2B and 2C, the output value of the # 1 magnetic sensor and the peak hold value V1a for each section are determined for each section a, b, c, and d determined by the section update signal.
V1b, V1c and V1d, the output value of the magnetic sensor # 2 and the peak hold values V2a, V2b,
V2c and V2d are shown respectively. Further, the respective peak hold values in this example indicate the maximum values of only the noise signals generated, with no flaws to be detected in the metal band in the respective sections a to d.

Reference numeral 4 in FIG. 1 denotes a difference calculation circuit, which is # 1 and #.
2 is a circuit for calculating the difference between the peak hold values of the previous section output each time each section is updated from the two peak hold circuits 3-1 and 3-2. As described above, the peak hold value for each section may be a noise signal component only or a noise signal component and a flaw signal component may be superimposed. Therefore, in the case where the output signal of the difference calculation circuit 4 has no flaw in any of the corresponding sections of the area in which the two magnetic sensors are in charge, and the peak hold values of the two sensor outputs are only the maximum peak value of the noise signal. , The difference between the two noise signal maximum values (ie, the noise level difference signal) is obtained. Since the two peak hold values shown in the examples of (b) and (c) of FIG. 2 are only the maximum value of the noise signal, (d) of the same figure in this example shows the previous section. The difference between the maximum values of the two noise signals thus obtained (that is, the noise level difference signal) is calculated and shown as the difference calculation value in this section.

Further, there is a flaw in a certain section of the area covered by the magnetic sensor of either # 1 or # 2, and the peak hold value of the sensor output is the maximum value of the superimposed signal of the flaw signal and the noise signal. If only the maximum value of the noise signal is obtained for the peak hold value from the other sensor, the noise signal is almost canceled by calculating the difference between these two signals, and only the maximum value of the flaw signal is obtained. Will be Therefore, in this case, the difference calculation circuit 4 outputs the flaw signal maximum value of the immediately preceding section (this is the flaw signal of the present invention) every time the traveling section is updated. As described above, the difference calculation circuit 4 in the present invention sequentially outputs the noise level difference signal or the flaw signal in the immediately preceding section every time the traveling section of the metal strip is updated.

In order to obtain the flaw signal described above, in the present invention, one of the output signals of the two magnetic sensors includes a flaw signal component, but the other does not include a flaw signal component, and both of them. A pair of magnetic sensors are selected and used such that the output signals of the magnetic sensors include noise signal components of substantially the same level. A method of selecting the pair of magnetic sensors will be described in detail with reference to FIGS. 5 and 6.
The outline is that the mutual distance is not too close and too far from the magnetic sensor groups arranged in one or two rows in a direction perpendicular to the running direction according to the size and shape of the flaws of the metal strip. The two magnetic sensors that are not nearby are selected. The difference signal output from the difference calculation circuit 4 is the defect signal for each section when there is a defect and the noise level difference signal when there is no defect, and the noise level difference signal is the same as the # 1 and # 2 comparison circuits 6-1 and 6-2. It is supplied to the threshold value calculation circuit 5, respectively.

Reference numeral 5 in FIG. 1 denotes a second threshold value calculation circuit, which is a second threshold value detection circuit for detecting a minute flaw based on the noise level difference signal when the metal band having a high probability of occurrence and having no flaw is supplied from the difference calculation circuit 4. 2 is a circuit for calculating a threshold value. However, since the probability of occurrence is small, a flaw signal in the case of a flaw may be input, so that the influence of this flaw signal is removed as much as possible by the moving average processing described later. Now, from the difference calculation circuit 4 to the noise level difference signal ΔV as shown in FIG.
i (ΔVi = V1i to V2i, i = a, b, c, d,
...) is input, in order to calculate the second threshold value, first, a coefficient α having a value around 1 (for example, 0.7
<Α <1.5) is multiplied, and the fixed bias voltage β is added to this, and the calculated value Vi (Vi = α · ΔVi +) in the section.
β) is calculated. As a specific example, when the input signal is 0.5V, if α = 1 and β = 0.5V, the calculated value Vi in that section is 1V.

Next, in order to average the fluctuation of the calculated value Vi for each section, the calculated value Vi of the present section and a plurality of previously stored sections over a plurality of past sections (that is, a predetermined length of the metal strip) are stored. Of the section calculation values Vi-n, ... Vi-1 are calculated, and this moving average value is calculated as the second moving section of the next traveling section.
The threshold value is supplied to the # 2 comparison circuit 6-2. This moving average has a low probability of occurrence as an input signal, but when a flaw signal is input or when the noise level changes abruptly, these effects are removed as much as possible so that the second threshold does not fluctuate rapidly. This is done in order to In this embodiment, the coefficient α and the bias voltage β are set so that the second threshold has a value near 1 V, but the value always fluctuates in accordance with the noise level detected by the magnetic sensor. .. Then, a flaw signal that exceeds the second threshold value is detected as a minute flaw.

6-1 is a # 1 comparison circuit, which compares the flaw signal input from the difference calculation circuit 4 with a first threshold value (for example, 1.5 V) fixed to a level higher than the second threshold value. , Those exceeding the first threshold are detected as major flaws. Reference numeral 6-2 is a # 2 comparison circuit, which similarly compares the flaw signal input with the second threshold value supplied from the second threshold value calculation circuit 5 and detects those exceeding the second threshold value as a minute flaw. To do.

FIG. 3 is a schematic cross-sectional view of the magnetic flaw detection portion cut along a plane parallel to the running direction of the metal strip, and FIG. 4 is a schematic cross-sectional view of the magnetic flaw detection portion cut along a plane perpendicular to the running direction of the metal strip. Is. In the figure, 14a and 14b are metal bands 12.
Is a pair of hollow rolls provided on the upper side and the lower side of the hollow roll so as to hold it. Each hollow roll 14a, 14
b is made of a non-magnetic material. Although the outer diameters differ from each other, the thickness t1 of the upper hollow roll 14a is set to be smaller than the thickness t2 of the lower hollow roll 14b. This is because a force is applied downward to the lower hollow roll 14b due to the weight of the metal strip 12, so that the thickness t2 of the lower hollow roll 14b is increased to prevent the hollow roll from being deformed or damaged, and the upper hollow roll 14a is magnetically sensitive. This is because the element group is included so that the thickness t1 can be reduced to improve the magnetic detection sensitivity.

One end of each of the hollow fixed shafts 21a and 21b is passed through each central shaft of each hollow roll 14a and 14b. The other end of the fixed shaft 21b of the lower hollow roll 14b is fixed to a frame of a building (not shown). On the other hand, the other end of the fixed shaft 21a of the upper hollow roll 14a is biased by a very weak spring (not shown) against the fixed shaft 21b of the lower hollow roll 14b. The fixed shafts 21a, 21b are located at the central axes of the hollow rolls 14a, 14b, respectively, and the pair of rolling bearings 22a, 22b, 23a, 2 are provided.
The hollow rolls 14a, 14b are supported by the inner peripheral surfaces of both ends of the hollow rolls 14a, 14b via the 3b. Therefore, each hollow roll 14
The a and 14b freely rotate about the fixed shafts 21a and 21b as the rotation center axes. In the hollow roll 14a, a magnetic sensitive element group (magnetic sensor group) 24 formed by arranging a plurality of magnetic sensitive elements (magnetic sensors) in the axial direction is oriented downward via a support member 25 on a fixed shaft 21a. It is fixed. The tip of the magnetic sensitive element group 24 faces the inner peripheral surface of the upper hollow roll 14a with a minute gap. The detection signals output from the magnetic sensitive element group 24 for each element are the signal line cable 1 passing through the fixed shaft 21a.
It is guided to the signal processing unit of FIG. 1 via 8a.

On the other hand, in the lower hollow roll 14b,
A magnetized iron core 26 having a substantially U-shaped cross-section is formed at each free end 26.
It is fixed to the fixed shaft 21 via a support member 27 in a posture in which a faces upward. Then, each free end 26 of the magnetized iron core 26
a faces the inner peripheral surface of the hollow roll 14b with a minute gap. A magnetizing coil 28 is wound under the magnetized iron core 26. The magnetizing current of the magnetizing coil 28 is supplied from the magnetizing power supply device via the power cable 17a passing through the fixed shaft 21b. Therefore, the magnetic sensitive element 24 housed in the upper hollow roll 14a is
It faces the magnetizer composed of the magnetic iron core 26 and the magnetizing coil 28 housed in the lower hollow roll 14b via. In addition, the distance d1 between the magnetic sensitive element 24 and the metal strip 12,
And the distance between the magnetizer and the metal strip 12 is fixed.

In the magnetic flaw detector having such a structure,
When the metal strip 12 is run in the direction of the arrow shown in FIG. 3 at a constant speed, the downward force due to the tension of the metal strip 12 and the downward force due to gravity are applied to the lower hollow roll 14b. The side hollow roll 14b rotates in the arrow direction. Further, since the upper hollow roll 14a is also biased by the lower spring, it rotates in the arrow direction. Then, when the magnetizing power supply device is activated and an exciting current is supplied to the magnetizing coil 28, a closed magnetic path is formed by the magnetized iron core 26 and the running metal band. When defects such as flaws and bubbles are present inside or on the surface of the metal strip 12, the magnetic path inside the metal strip 12 is disturbed and leakage magnetic flux is generated. This magnetic flux is the magnetic sensitive element group 2
Each magnetic sensitive element (magnetic sensor) in 4 is detected as a defect signal.

FIG. 5 is a view for explaining a method of selecting a magnetic sensor group arranged in one row and magnetic sensors of each pair according to the present invention. FIG. 5A schematically shows n magnetic sensors S1 to Sn arranged in a row at equal intervals in a direction perpendicular to the traveling direction of the metal strip. Here, the distance between each magnetic sensor is 1
Once the area where the flaw can be detected is determined by the two magnetic sensors,
Adjacent magnetic sensors are set so that no gap is generated between the detection areas, that is, the sensor detection areas are slightly overlapped.

Next, a method of selecting each pair of magnetic sensors will be described. The magnetic sensor group arranged in one row in the direction perpendicular to the running direction of the metal strip is suitable for detecting dot-like flaws or linear flaws in the running direction. The selection criteria for the pair of magnetic sensors is
The output signal of one magnetic sensor contains a sufficient flaw signal, and the output signal of the other magnetic sensor contains no or almost no flaw signal. Moreover, the output signals of both magnetic sensors contain noise signals of substantially the same level. This is to calculate the difference between the peak hold values of the pair of magnetic sensor output signals to obtain the flaw signal of the present invention. Therefore, specifically, the distance between the two magnetic sensors should not be too close (because both magnetic sensors contain a defect signal if they are too close) and not too far (if they are too far, the two magnetic A pair of magnetic sensors with a predetermined interval described in the section of action is selected because the noise level difference signal of the sensor is large.

In FIGS. 5B and 5C, two magnetic sensors located at a distance twice the arrangement interval from the magnetic sensor group linearly arranged at equal intervals, that is, the odd number shown in FIG. 5B. Magnetic sensors S1 and S3, S5 and S7, ...
The even numbered magnetic sensors S2, S4 and S6 shown in (c).
, S8, ... Are selected as a pair of magnetic sensors. This is because the predetermined interval is approximately twice the array interval of the magnetic sensors.

In FIGS. 5B and 5C, an example in which a pair of magnetic sensors is selected from the magnetic sensor groups arranged linearly at equal intervals instead of adjacent magnetic sensors. However, the present invention is not limited to this, and depending on the size of the flaw in the metal strip and the arrangement interval of the magnetic sensors, two magnetic sensors located at a distance three times the arrangement interval, that is, S1 and S4. , S2 and S5, S3 and S6, ... May be selected as a pair of magnetic sensors, respectively.

FIG. 6 is a diagram for explaining a method of selecting a magnetic sensor group arranged in two rows and a pair of magnetic sensors according to the present invention. In FIG. 6 (a), the direction 2 is perpendicular to the running direction of the metal strip.
S11 to Sn in the front row and S2 in the back row arranged side by side
1 to S2n, a total of 2 × n magnetic sensors are schematically shown. Here, the distance between the magnetic sensors in the front row and the rear row (that is, the sensor distance in the traveling direction) is restricted so that the upper limit thereof falls within the distance between the two free ends 26a of the magnetized iron core 26 shown in FIG. The sensor interval in the traveling direction is set so as to suit the type of flaw to be detected within the upper limit range, the details of which will be described with reference to FIGS. 7 and 8. The distance between the magnetic sensors adjacent in the horizontal direction in each row is the same as in FIG.

Next, a method of selecting each pair of magnetic sensors from the magnetic sensor group arranged in two rows in FIG. 6 will be described. FIG. 6 (b) shows S11 and S21, S12 and S22, ... S1n of the magnetic sensors arranged before and after in the traveling direction of the metal strip.
And S2n are selected as a pair of magnetic sensors. In this case, the selection method is suitable for detecting minute spot-like flaws or welds. 6C and 6D show magnetic sensors S11 and S22, and S13 and S diagonally rearward except for the magnetic sensors in the front row and in the rear row.
24, ..., S12 and S21, S14 and S23, ... are selected as a pair of magnetic sensors. In this case, the selection method is suitable for the detection of surface defects.

FIG. 7 is a diagram for explaining the sensor sensitive width in the traveling direction depending on the type of flaw in the thin steel strip according to the present invention.
FIG. 8 is a waveform diagram of the sensor response width of FIG. When the sensors in FIG. 6 are arranged in two rows, the distance between the sensors in the traveling direction is such that when the target flaw passes directly under the sensor, the sensor is responsive to the flaw signal to obtain a detection signal (hereinafter referred to as a sensing width. , The detection sensitivity (that is, S / N) in the difference calculation circuit 4 in FIG. 1 can be almost doubled. Further, in general, a large flaw produces a large sensor output, but a small flaw produces a small sensor output. Therefore, it is extremely effective to double the detection sensitivity by the difference calculation of the present invention.

FIG. 7 shows the result of an experiment in which the sensor sensitivity width in the running direction was obtained for various types of flaws starting from a minute flaw of 0.2 mmφ. FIG. 8A shows a drill hole (φ = 0.
2 mm), (b) of the figure shows the waveforms after the magnetic sensor output and the polarity were unified for the welds before cold rolling. From the magnetic sensor, negative polarity and positive polarity output signals corresponding to one AC cycle with respect to the traveling direction of the horizontal axis are obtained, respectively. The traveling distance corresponding to this one cycle is shown as the sensitive width. The waveform after the polarities are unified is shown as a waveform obtained by inverting the negative polarity signal of the magnetic sensor output to the positive polarity signal and performing full-wave rectification on the alternating current. From the experimental result of FIG. 7, the sensor interval in the running direction in FIG. 6 is 3 to 15 mm for the micro flaws of the thin steel strip, 20 to 30 mm for the weld before cold rolling of the thin steel strip, and It can be seen that it is appropriate to set 50 to 200 mm for the welded portion after cold rolling. In this way, the sensor interval in the traveling direction is set according to the type of flaw to be detected.

FIG. 9 is a diagram showing an embodiment of a selecting means for selecting each pair of magnetic sensors according to the present invention. In the figure, 24 is a magnetic sensor group arranged in two rows, 30 is a wiring change board, 40 is a measuring device, and the measuring device 40 includes only the # 1 to # 4 pair peak hold circuits 41 to 44 on the input side. It is shown. Each pair peak hold circuit has
The same two peak hold circuits as the # 1 peak hold circuit and the # 2 peak hold circuit shown in FIG. The wiring changing board 30 shown in FIG. 9 can arbitrarily change the wiring between the input end and the output end manually.
For example, the magnetic sensor paired with the magnetic sensor S11 is S2.
The wiring can be changed to 1 or S22 and connected to the input side of the # 1 pair peak hold circuit 41. Further, it is also possible to input the output signals of the respective magnetic sensors to the multiplexers and use the selection control signal to take out the desired output signals of the two magnetic sensors as a pair. The present invention thus doubles the S / N of the flaw signal obtained by the difference calculation of the peak hold value of the magnetic sensor output of each pair which is manually or automatically selected corresponding to the type of flaw of the metal strip. Therefore, not only the main flaw can be detected using the first threshold value, but also various flaws in a wide range from a minute flaw to a welded portion can be detected with high sensitivity by using the second threshold value calculated from the difference calculation result. it can.

[0037]

As described above, according to the present invention, a magnetic field is generated in the traveling direction of a traveling metal strip, and a leakage magnetic flux generated by a defect inside or on the surface of the metallic strip is perpendicular to the traveling direction of the metal strip. In a method and apparatus for magnetic flaw detection of a metal strip for detecting a defect signal by detecting a plurality of magnetic sensitive elements arranged side by side in one or two rows in the same direction, the metal strip is provided in the one row depending on the type of flaw in the metal strip. From the plurality of magnetic sensitive elements arranged side by side, two magnetic sensitive elements at a predetermined interval are selected as a pair, and from the plurality of magnetic sensitive elements arranged side by side in the two rows, the one in the front row is selected. Select each magnetic sensitive element and each magnetic sensitive element in the rear row directly behind it so as to make a pair, or each magnetic sensitive element in the front row and each magnetic sensitive element in the rear row in a position other than directly behind That Selected to pair. For each pair of magnetically sensitive elements selected in this way, the difference between the peak hold values of the two detection signals obtained for each constant traveling section is calculated, and the detection sensitivity of the flaw signal obtained can be doubled. Therefore, not only the primary flaw can be detected using the first threshold value, but also the second flaw calculated from the difference calculation value.
It is possible to obtain an effect that various flaws in a wide range from a minute flaw to a welded portion can be detected with high sensitivity by using a threshold value.

[Brief description of drawings]

FIG. 1 is a system diagram of a flaw detection signal processing unit of a metal strip according to the present invention.

FIG. 2 is a waveform diagram for explaining the operation of FIG.

FIG. 3 is a schematic cross-sectional view of a magnetic flaw detection portion cut along a plane parallel to the traveling direction of a metal strip.

FIG. 4 is a schematic cross-sectional view of a magnetic flaw detection portion cut along a plane orthogonal to the traveling direction of a metal strip.

FIG. 5 is a diagram illustrating a method of selecting a magnetic sensor group arranged in a row and a pair of magnetic sensors according to the present invention.

FIG. 6 is a diagram illustrating a method of selecting a magnetic sensor group arranged in two rows and a pair of magnetic sensors according to the present invention.

FIG. 7 is a diagram illustrating a sensor sensitivity width in a traveling direction according to a type of a flaw of a thin steel strip according to the present invention.

FIG. 8 is a waveform diagram of the sensor sensitivity width of FIG.

FIG. 9 is a diagram showing an embodiment of selection means for selecting each pair of magnetic sensors according to the present invention.

FIG. 10 is a block diagram of a conventional magnetic flaw detector for a steel plate.

FIG. 11 is a schematic sectional view of a conventional flaw detection unit.

FIG. 12 is an explanatory diagram of a conventional detection signal and a first threshold value and a second threshold value.

FIG. 13 is a partially cutaway sectional view of a conventional magnetic flaw detection unit.

14 is an electric circuit diagram of FIG. 13. FIG.

FIG. 15 is an output waveform diagram of FIG.

FIG. 16 is a characteristic diagram of a conventional magneto-sensitive element interval and output.

FIG. 17 is a waveform diagram illustrating a detection signal of Document 2.

[Explanation of symbols]

 1-1 # 1 magnetic sensor 1-2 # 2 magnetic sensor 2 section signal generator 3-1 # 1 peak hold circuit 3-2 # 2 peak hold circuit 4 difference calculation circuit 5 second threshold value calculation circuit 6-1 # 1 Comparison circuit 6-2 # 2 comparison circuit

Continued Front Page (72) Inventor Hiroshi Maki 1-2-1, Marunouchi, Chiyoda-ku, Tokyo Nihon Steel Pipe Co., Ltd.

Claims (5)

[Claims] 1. A plurality of magnetic fluxes are generated by generating a magnetic field in a traveling direction of a traveling metal strip and arranging leakage magnetic fluxes generated by defects inside or on the surface of the metal strip in a line at right angles to the traveling direction of the metal strip. In the magnetic flaw detection method for a metal band for detecting a defect signal by detecting the magnetic sensitive element according to, the two magnetic sensitive elements at a predetermined interval are selected from the plurality of magnetic sensitive elements to form a pair, and each of the selected Two maximum peak values of the two detection signals obtained for each pair of magnetic sensitive elements are detected for each constant traveling section of the metal strip, and two maximum peak values are detected for each pair of magnetic sensitive elements. Is calculated as a flaw signal value for each traveling section of the pair of magnetic sensitive elements, and the flaw signal value for each traveling section of the pair of magnetic sensitive elements is set to a first threshold value set in advance. Compared to When it exceeds the first threshold value, it is detected as a main flaw of the metal strip, and a flaw signal value for each traveling section of the pair of magnetic sensitive elements is multiplied by a predetermined coefficient and then a predetermined bias value is added. Then, using this as the calculated value of the corresponding section, a moving average value of the calculated value and a plurality of section calculated values stored over the past plural sections is calculated, and the moving average value is calculated for each of the next running sections. A second threshold value is set, and a flaw signal for each traveling section of the pair of magnetic sensitive elements is compared with a respective second threshold value calculated in the immediately preceding traveling section, and when the second threshold value is exceeded, A magnetic flaw detection method for a metal band, which comprises detecting this as a minute flaw in the metal band. 2. A plurality of magnetic fluxes generated by generating a magnetic field in the running direction of a running metal strip and arranging leakage fluxes generated by defects in the inside or the surface of the metal strip in two rows perpendicular to the running direction of the metal strip. In the magnetic flaw detection method for a metal band for detecting a defect signal by detecting the magnetic sensitive element, the magnetic sensitive element in the front row of the plurality of magnetic sensitive elements arranged side by side in the two rows and the rear row immediately behind the magnetic sensitive element And each of the magnetically sensitive elements of No. 2 are selected as a pair, and the maximum peak value for each constant traveling section of the metal strip of the two detection signals obtained for each of the selected magnetically sensitive elements of each pair is respectively set. The difference between the two maximum peak values detected for each pair of the magnetically sensitive elements is calculated and used as a flaw signal value for each running section of the pair of magnetically sensitive elements, Magnetic sensitive element Comparing the flaw signal value for each traveling section of 1 with a preset first threshold value, if it exceeds the first threshold value, this is detected as the main flaw of the metal strip, and the magnetic sensitive element of each pair is detected. The flaw signal value for each traveling section is multiplied by a predetermined coefficient, and then a predetermined bias value is added to obtain a calculated value for the corresponding section, and the calculated value and a plurality of section calculations stored over the past plural sections Value and a moving average value is calculated, and the moving average value is used as a respective second threshold value in the next traveling section, and a defect signal for each traveling section of the pair of magnetic sensitive elements is used as the preceding traveling section. The magnetic flaw detection method for a metal band, comprising: comparing with the respective second threshold value calculated in step 3, and detecting as a minute flaw in the metal band when the second threshold value is exceeded. 3. A plurality of magnetic fluxes are generated by generating a magnetic field in the running direction of a running metal strip and arranging leakage fluxes generated by defects inside or on the surface of the metal strip in two rows perpendicular to the running direction of the metal strip. In the magnetic flaw detection method for a metal strip for detecting a defect signal by detecting the magnetic sensitive element of the above, the magnetic sensitive elements in the front row of the plurality of magnetic sensitive elements arranged side by side in the two rows and the rear row at positions other than directly behind And each of the magnetically sensitive elements of No. 2 are selected as a pair, and the maximum peak value for each constant traveling section of the metal strip of the two detection signals obtained for each of the selected magnetically sensitive elements of each pair is respectively set. The difference between the two maximum peak values detected for each pair of the magnetically sensitive elements is calculated and used as a flaw signal value for each running section of the pair of magnetically sensitive elements, Magnetic sensitive element Comparing the flaw signal value for each traveling section of 1 with a preset first threshold value, if it exceeds the first threshold value, this is detected as the main flaw of the metal strip, and the magnetic sensitive element of each pair is detected. The flaw signal value for each traveling section is multiplied by a predetermined coefficient, and then a predetermined bias value is added to obtain a calculated value for the corresponding section, and the calculated value and a plurality of section calculations stored over the past plural sections Value and a moving average value is calculated, and the moving average value is used as a respective second threshold value in the next traveling section, and a defect signal for each traveling section of the pair of magnetic sensitive elements is used as the preceding traveling section. The magnetic flaw detection method for a metal band, comprising: comparing with the respective second threshold value calculated in step 3, and detecting as a minute flaw in the metal band when the second threshold value is exceeded. 4. A plurality of magnetic fluxes are generated by generating a magnetic field in the running direction of a running metal strip and arranging leakage fluxes generated by defects inside or on the surface of the metal strip in a line at right angles to the running direction of the metal strip. In the metal band magnetic flaw detector for detecting a defect signal by detecting the magnetic sensitive element, the selecting means for selecting two magnetic sensitive elements at a predetermined interval from the plurality of magnetic sensitive elements to form a pair, respectively. Peak holding means for detecting the maximum peak value of each of the two detection signals obtained for each pair of magnetically sensitive elements selected by the means for each constant running section of the metal strip, and each pair by the peak holding means. The difference between the two maximum peak values detected for each magnetic sensitive element is calculated, and this is output as a flaw signal value for each running section of the magnetic sensitive element of each pair. Difference calculation means and the pair of magnetic sensitive elements output from the difference calculation means, and compares the flaw signal value for each traveling section with a first threshold value set in advance. Is detected as the main flaw of the metal strip, and the flaw signal value for each traveling section of each pair of magnetic sensitive elements output by the difference computing means is multiplied by a predetermined coefficient and then a predetermined bias is applied. The values are added to make the calculated value of the corresponding section, a moving average value of the calculated value and a plurality of section calculation values stored in the past plural sections is calculated, and the moving average value is calculated as the next running section. 2nd threshold value calculating means for outputting as the respective second threshold value thereof, and the defect signal for each running section of each pair of magnetic sensitive elements output by the difference calculating means, the second threshold value calculating means immediately before running. Comparing with the second threshold of each one calculated and output in the interval It said second comparison means and the magnetic flaw detection method for a metal strip, characterized in that it comprises a detect this as a very small flaw of the metal strip when exceeding the second threshold value. 5. A plurality of magnetic fluxes are generated by generating a magnetic field in the traveling direction of a traveling metal strip and arranging leakage fluxes generated by defects inside or on the surface of the metal strip in two rows perpendicular to the traveling direction of the metal strip. In a magnetic flaw detector of a metal band for detecting a defect signal by detecting the magnetic sensitive element of the above, each magnetic sensitive element in the front row of the plurality of magnetic sensitive elements arranged side by side in the two rows and a rear row immediately behind the magnetic sensitive element And a selection means for selecting each pair of magnetic sensitive elements in the front row, or each pair of the magnetic sensitive elements in the front row and the magnetic sensitive elements in the rear row located at positions other than directly behind the front row. Peak holding means for detecting the maximum peak value of each of the two detection signals obtained for each pair of magnetically sensitive elements selected by the selecting means for each constant traveling section of the metal strip The difference between the two maximum peak values detected by the peak hold means for each magnetic sensitive element of each pair is calculated, and the difference is output as a flaw signal value of each traveling section of the magnetic sensitive element of each pair. Difference calculation means and the defect signal value for each traveling section of each pair of magnetic sensitive elements output by the difference calculation means are compared with a preset first threshold value. Is detected as the main flaw of the metal strip, and the flaw signal value for each traveling section of each pair of magnetic sensitive elements output by the difference computing means is multiplied by a predetermined coefficient and then a predetermined bias is applied. The values are added to make the calculated value of the corresponding section, a moving average value of the calculated value and a plurality of section calculation values stored in the past plural sections is calculated, and the moving average value is calculated as the next running section. Output as the second threshold value of each The second threshold calculating means calculates and outputs a flaw signal for each running section of each pair of magnetic sensitive elements output by the threshold calculating means and the second threshold calculating means for outputting the flaw signal in the immediately preceding running section. A magnetic flaw detector for a metal band, comprising: a second comparing unit that compares the threshold value with a second threshold value and detects the second threshold value as a minute flaw in the metal band.