JP2007114137A - Method and apparatus for detecting crack of slab - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a crack detecting method capable of detecting the crack of a black skin slab inexpensively and precisely; and also to provide a crack detector of the slab. <P>SOLUTION: In the crack detecting method of the slab for detecting the lateral crack present in the corner part of a material to be inspected made of a magnetic metal material such as the slab or the like by an E-type eddy current sensor, the distances between the E-type eddy current sensor and the front or back and side surface of the material to be inspected are respectively kept constant and a scanning plate insulated from the uneven shape or properties of the front or back of the material to be inspected is arranged. The E-type eddy current sensor is scanned in the longitudinal direction of the material to be inspected on the scanning plate. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a slab crack detection method and apparatus for detecting lateral cracks present in a corner portion of a slab.

  There are various methods using the eddy current flaw detection method for detecting transverse cracks generated at the corner of the slab. Among them, for example, there is a method using a two-frequency method disclosed in Patent Document 1 in order to discriminate between noise caused by an oscillation mark and a crack signal.

In this method, the probe coil is excited by passing currents of two different frequencies, and the noise signal component of one frequency component of the detection signal and the flaw signal component of the other frequency component are vectorized for each frequency component. One or both of the frequency components of the detection signal are phase-rotated so that they coincide with one orthogonal axis in the plane, so that the component orthogonal to the noise signal of the one frequency component and the flaw signal component of the other frequency component Extracting orthogonal components, making both extracted components orthogonal on a new vector plane, and discriminating crack signals from noise signals based on the ratio of the difference between the maximum and minimum values of each orthogonal component in the signal trajectory It is an eddy current flaw detection method characterized by
JP 60-161556 A

  However, since the method of Patent Document 1 performs complex signal processing, there is a problem that if this is to be put into practical use, improvements including the probe and the substrate are required, and the cost increases. In the method of Patent Document 1, the noise component is specified only for the oscillation mark. However, in the flaw detection with the black skin slab, in addition to the oscillation mark, the scale of the slab surface and vibration / slab during the sensor scan There are various noises having a phase angle different from that of the oscillation mark, such as vibration during conveyance. In that case, there is a problem that discrimination by a plurality of noises becomes insufficient in the discrimination by the two-frequency method.

  The present invention has been made in view of the above circumstances, and it is an object of the present invention to provide a slab crack detection method and apparatus capable of detecting cracks in a black skin slab at low cost and with high accuracy.

  The invention according to claim 1 of the present invention is a slab crack detection method in which a lateral crack existing in a corner portion of a slab is detected by an E-type eddy current sensor, between the E-type eddy current sensor and the front or back surface of the test material. And a distance between the side surfaces is kept constant, and a scanning plate that is insulated from the uneven shape and properties of the front or back surface of the test material is disposed, and the test material on the scanning plate is arranged in the longitudinal direction. The slab crack detection method is characterized by scanning the E-type eddy current sensor.

  The invention according to claim 2 of the present invention is the slab crack detection method according to claim 1, wherein the excitation frequency of the E-type eddy current sensor is set to a low frequency of about several kHz, such as the surface of an oscillation mark or a scale. A slab crack detection method characterized by separating a property noise signal and a crack signal and increasing an eddy current penetration depth.

  The invention according to claim 3 of the present invention is the slab crack detection method according to claim 2, wherein the phase angle is set to maximize the crack signal or minimize the surface texture noise. It is.

  Furthermore, the invention according to claim 4 of the present invention is the slab crack detection device for detecting a lateral crack existing in the corner portion of the slab with an E-type eddy current sensor, wherein the E-type eddy current has an excitation frequency as low as several kHz. The sensor, the E-type eddy current sensor, and the distance between the front and back surfaces of the test material and between the side surfaces thereof were kept constant, and the uneven shape and properties of the front and back surfaces of the test material were insulated. A slab crack detection device comprising a scanning plate.

According to the present invention, a scanning plate made of a non-magnetic material is installed in a slab corner, and the eddy current sensor is scanned on the scanning plate, and a slab surface property noise signal such as an oscillation mark or a scale slab surface property noise signal and a crack signal Since we set the excitation frequency as low as several kHz, where the phase angle difference spreads, and the phase angle setting that maximizes the crack signal or minimizes the surface texture noise,
Black skin slab whose vibration noise signal during sensor scanning is reduced, slab surface property noise signal and crack signal can be clearly distinguished, S / N improvement can be realized, and the scale is finally covered on the crack The detection accuracy improvement of crack detection can be achieved.

  The best mode for carrying out the present invention will be described below with reference to the drawings. FIG. 1 is a diagram for explaining an outline of a slab crack detection device according to the present invention. In the figure, 1 is an E-type eddy current sensor, 1a is an excitation coil, 1b and 1c are detection coils, 2 is cracked, 3 is a slab, 4 is a scanning plate, 5 is an AC power supply, 6 is a bridge circuit, and 7 is a differential amplifier. , 8 represents a phase detector, and 9 represents a data processor.

  The magnetic flux generated in the excitation coil 1a at the center leg of the E-type sensor 1 by energization of the AC power source 5 passes through the front or back surface of the slab 3 and passes through the detection coils 1b and 1c on both side legs, and the excitation coil 1a. A flow of magnetic flux returning to is formed. When there is no crack 2 as shown in the figure on the slab, the induced voltages generated in the detection coils 1b and 1c are the same, and therefore the difference between them is almost zero.

  However, if there is a defect such as a transverse crack on the front and back surfaces of the slab, the magnetoresistance on the 1b side and the magnetoresistance on the 1c side are different, so that there is a difference between the voltage induced in 1b and the voltage induced in 1c. The output of the phase detector 8 is obtained through the circuit 6 and the differential amplifier 7. When the E-type eddy current sensor 1 is scanned in the longitudinal direction, the output after phase detection draws a sine curve with the central axis of the E-type eddy current sensor 1 as the center, so that a defect can be detected.

  FIG. 3 is a diagram schematically showing a scanning portion of the E-type eddy current sensor. Fig.3 (a) is a perspective view from diagonally forward, and shows the slab to be detected in a transparent state. The crack 2 shown here is a crack called “key crack” that occurs in the corner portion of the slab. Moreover, FIG.3 (b) is sectional drawing from a right side surface.

  A scanning plate 4 made of a non-magnetic material (for example, non-magnetic SUS or vinyl chloride) is placed on the upper surface (front or back surface) of the slab 3 so as to follow the side surface of the slab 3. Further, the E-type eddy current sensor 1 is placed on the scanning plate 4 to scan the E-type eddy current sensor 1 in the longitudinal direction.

  As shown in FIG. 3B, the scanning plate 4 has the E-type eddy current sensor 1 mounted thereon, the distance in the width direction to the side surface of the slab 3 is constant, and the distance in the height direction to the upper surface of the slab 3 ( Make sure that lift-off is constant. The E-type eddy current sensor 1 may be scanned manually or automatically using a motor or the like. For example, the E-type eddy current sensor 1 may be a guide-like structure capable of scanning the sensor so that no rattling or vibration occurs during scanning. It is good to do. This is to prevent noise due to backlash and vibration and increase the S / N ratio to improve detection accuracy.

  Further, when the scanning plate 4 is modified so that another E-type eddy current sensor 1 is placed as shown by the broken line in FIG. 3B, the side surface of the slab 3 can be scanned from the side so as to scan from two directions. Lateral cracks occurring on the side surfaces can also be detected.

  FIG. 2 is a flowchart showing a crack detection processing procedure in the present invention. The processing procedure will be described below with reference to FIG.

(1) Excitation frequency setting (Step01)
Here, the excitation frequency applied to the excitation coil is set, and the excitation frequency is related to the penetration depth of the eddy current. In selecting the excitation frequency, a comprehensive judgment is made based on three indexes: a) depth of defect to be detected, b) surface properties, and c) phase separation from vibration. Table 1 below lists qualitative characteristics depending on the frequency band from the viewpoint of a) the defect depth to be detected and b) the surface properties.

An excitation frequency of 1 to 2 kHz is suitable for crack detection of about 0.1 to 0.2 mm in a black skin slab with many surface scales. FIG. 4 is a conceptual diagram of a vector diagram of the crack signal and surface texture noise from the viewpoint of phase separation from c) vibration. As an example, the outline of the vector diagram and the penetration depth are shown in comparison with those with excitation frequencies of 64 kHz and 2 kHz, and the concept of setting the excitation frequency is shown.

  The surface texture noise such as oscillation mark & scale and the phase angle of each signal locus of the ellipse due to cracking are the same in the case of 64 kHz and cannot be separated, whereas in the case of 2 kHz, θ It can be seen that each can be separated.

  Therefore, in this example, judging from the above three indices a) to c), setting the excitation frequency from 2 kHz to 2 kHz is more suitable for crack detection of about 0.1 to 0.2 mm in the black skin slab. It can be said.

(2) Phase angle setting (Step02)
Since the excitation frequency is set in the previous step, the next step is to set the phase angle (rotate the coordinate axes) that maximizes the crack signal or minimizes surface texture noise.

(3) Installation of scanning plate (Step03)
The nonmagnetic magnetic scanning plate shown in FIG. 3 is set on the slab corner, and further a sensor head (E-type eddy current sensor) is set thereon. When a hot slab is targeted, it is preferable to apply water cooling or a heat insulating material to the sensor head and the scanning plate as a heat countermeasure. The scanning plate is made of a nonmagnetic and rigid material (such as nonmagnetic SUS). The target slab may be moved from the conveyance line to an off-line flaw detection location, or may be in a stationary state on the conveyance line if there is a scannable space.

(4) Collecting detection data (Step 04)
The sensor head is manually or automatically scanned in the operation direction of the scanning plate to collect detection data. If there is a lift-off fluctuation exceeding several mm, it is preferable to correct the sensor output value by measuring the fluctuation amount.

(5) Data processing (Step 05)
The phase-detected output signal is taken into a data processing device at a fixed time or a fixed length cycle, and after processing such as filtering, a signal waveform as shown in FIG. 5 is obtained.

(6) Crack detection (Step 06)
When the peak to peak signal level exceeds a preset threshold, it is judged that there is a crack (see Fig. 5), and the result is announced to the operator as an alarm and detected on a monitor or the like. The position of the broken crack is displayed and the operator is notified. By tracking the scanning position, the position where the crack is detected may be specified and marked with paint or the like. In addition, inspection results such as crack presence / absence, crack signal level, and crack position may be stored together with the scratch map.

  According to the present invention described above, it is possible to improve the detection accuracy of crack detection in a black skin slab whose scale is finally covered on the crack.

It is a figure explaining the outline | summary of the slab crack detection apparatus which concerns on this invention. It is a flowchart which shows the crack detection processing procedure in this invention. It is the figure which showed typically the scanning part of the E type eddy current sensor. The conceptual diagram of the vector diagram of a crack signal and surface property noise is shown. It is the figure which showed an example of the eddy current signal waveform and crack judgment.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 E type eddy current sensor 1a Excitation coil 1b, 1c Detection coil 2 Crack 3 Slab 4 Scan plate 5 AC power supply 6 Bridge circuit 7 Differential amplifier 8 Phase detector 9 Data processor

Claims (4)

In a slab crack detection method for detecting a lateral crack existing in a corner portion of a slab with an E-type eddy current sensor,
A scanning plate that maintains a constant distance between the E-type eddy current sensor and the front or back surface and side surfaces of the test material, and is insulated from the uneven shape and properties of the front or back surface of the test material. A slab crack detection method comprising: arranging and scanning the E-type eddy current sensor in a longitudinal direction of the test material on the scanning plate. In the slab crack detection method according to claim 1,
A slab characterized in that the excitation frequency for the E-type eddy current sensor is set to a low frequency of about several kHz, the surface property noise signal such as an oscillation mark and scale is separated from the crack signal, and the penetration depth of the eddy current is increased. Crack detection method. In the slab crack detection method according to claim 2,
A slab crack detection method characterized by setting a phase angle that maximizes a crack signal or minimizes surface texture noise. In a slab crack detection device for detecting a lateral crack existing in a corner portion of a slab with an E-type eddy current sensor,
The E-type eddy current sensor having an excitation frequency as low as several kHz;
The E-type eddy current sensor, a scanning plate that keeps the distance between the front and back surfaces and the side surfaces of the test material constant, and is insulated from the uneven shape and properties of the front or back surface of the test material; ,
A slab crack detection device comprising: