JP2010117281A - Method and device for detecting surface defect of slab - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method of detecting a surface defect of a slab for precisely detecting the surface defect such as slag biting produced in the slab. <P>SOLUTION: In the method for detecting the surface defect produced in the slab from the surface unevenness state and surface brightness distribution of the slab by irradiating the surface of the slab with a laser beam 8 to measure the surface unevenness state of the slab and imaging the surface of the slab to obtain the surface brightness distribution of the slab, the unevenness change ratio in the longitudinal direction of the surface of the slab is calculated by an unevenness change ratio calculating circuit 11, the position and size of the low brightness surface part of the slab determined to be the defect in the surface brightness distribution are calculated and, when the calculated position of the low brightness surface part of the slab coincides with the position of a part where the absolute value of the unevenness change ratio becomes a predetermined threshold value or above, the calculated position of the low brightness surface of the slab is determined to be the defect position of the slab and the size of the low brightness surface part of the slab determined as the defect position is determined as the size of the surface defect produced at the defect position. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a method and an apparatus for detecting a surface defect of a slab, and particularly suitable for inspecting whether or not a surface defect requiring maintenance has occurred in a slab obtained by continuously casting molten steel. The present invention relates to a surface defect detection method and a slab surface defect detection apparatus.

  Generally, molten steel refined in a converter or the like is cast from a dundish 2 into a mold (mold) 3 through a ladle 1 as shown in FIG. The molten steel cast into the mold 3 becomes a continuous cast material in which only the surface layer portion is solidified while passing between a large number of pinch rollers 4 arranged below the mold 3, and a cooling water sprinkler (not shown) After being cooled by cooling water sprinkled from and solidified to the inside, it is cut into a predetermined length by a cutting device 5 to form a slab 6.

  Various surface defects occur in the slab obtained as described above. For example, when bubbles are involved during casting of molten steel, surface defects called blowholes having a diameter of about 0.3 to 4 mm are generated on the slab surface. Further, when a large bending stress is applied during solidification of the molten steel, surface defects called cracks are generated on the slab surface. Furthermore, when the powder for continuous casting is rolled up as a lump at the time of casting molten steel, a surface defect called no-biting having a larger area than blow holes and cracks occurs on the slab surface. Since these surface defects all cause a reduction in the surface quality of the slab, it is necessary to inspect whether or not a surface defect requiring maintenance has occurred in the slab obtained by continuously casting molten steel.

As a method for inspecting whether or not a surface defect has occurred in a slab obtained by continuously casting molten steel, a pair of illuminating devices that irradiate a predetermined area on the slab surface from both directions are mutually connected along the slab moving direction. An imaging device is arranged between the pair of illumination devices so as to face each other and receive the illumination light reflected on the slab surface by incidence from the illumination device in a direction substantially perpendicular to the slab surface. A method for detecting the presence or absence of surface defects (see Patent Document 1), and manufacturing a slab by removing heat through a cooling drum from molten steel supplied to a hot water pool formed between a pair of cooling drums. At the time, a method of detecting the presence or absence of cracks by detecting the depth of the slab surface immediately after passing through the cooling drum with a laser distance meter is known (see Patent Document 2).
JP 2004-219358 A JP-A-2-224851 (page 2, lower left column, line 2 to page 2, lower right column, line 13)

However, since the method disclosed in Patent Document 1 detects a surface defect generated in the slab from the density of the slab surface image obtained by the imaging apparatus, whether the detected surface defect is a bite or noro. There is a problem that it is impossible to determine whether the surface defect is other than biting (for example, blowhole, crack, etc.).
On the other hand, since the method disclosed in Patent Document 2 inspects the presence or absence of surface defects from the depth of the surface dent measured by the laser distance meter, as in the method disclosed in Patent Document 1, There is a problem in that it is impossible to determine whether the generated surface defect is a blowhole or a crack or a bite.
The present invention has been made in view of the above-described problems, and an object of the present invention is to provide a slab surface defect detection method and a slab surface defect detection apparatus capable of accurately detecting surface defects such as slotting generated in a slab. And

  In order to achieve the above object, the invention according to claim 1 is directed to irradiating the surface of the slab with laser light to measure the surface irregularity of the slab and to image the surface of the slab to obtain the surface luminance distribution of the slab. And detecting a surface defect generated on the surface of the slab from the surface unevenness state and the surface luminance distribution, and calculating the unevenness change rate in the longitudinal direction of the slab surface from the surface unevenness state of the slab. And calculating the position and size of the low-luminance surface portion of the slab that is determined to be a defect in the surface luminance distribution, and the position of the portion where the absolute value of the unevenness change rate is equal to or greater than a predetermined threshold; When the position of the low-luminance surface portion matches, the position is determined as a defect position, and the size of the low-luminance surface portion determined as the defect position is the size of the surface defect generated at the defect position. It is characterized in that constant.

  The invention according to claim 2 irradiates the surface of the slab with laser light to measure the surface unevenness state of the slab, acquires the surface luminance distribution of the slab by imaging the surface of the slab, and the surface unevenness state. A surface defect detection device for detecting a surface defect generated on the surface of the slab from the surface luminance distribution, a laser beam receiving means for receiving the laser beam reflected by the surface of the slab, and the laser beam receiving unit Surface unevenness measuring means for measuring the surface unevenness state of the slab based on the laser beam received by the means, and unevenness in the longitudinal direction of the slab surface from the surface unevenness state of the slab measured by the surface unevenness state measuring means An unevenness change rate calculating means for calculating a change rate, an imaging means for imaging the surface of the slab to obtain surface luminance information of the slab, and output from the imaging means An image signal processing means for processing the image signal to obtain the surface luminance distribution of the slab, and a low luminance surface portion for detecting a low-luminance surface portion of the slab determined as a defect from the surface luminance distribution obtained by the image signal processing means. The position of the portion where the absolute value of the unevenness change rate calculated by the brightness surface portion detecting means and the unevenness change rate calculating means is equal to or greater than a predetermined threshold, and the low brightness detected by the low brightness surface portion detecting means When the position of the surface portion coincides with the surface defect, the position is determined as the defect position, and the size of the low-luminance surface portion determined as the defect position is determined as the size of the surface defect generated at the defect position. And a judging means.

  According to the first and second aspects of the present invention, when the presence / absence or type of surface defect is specified based only on the signal output from the laser light receiving means, or the surface is determined based only on the image signal output from the imaging device. As the presence / absence and type of defects are specified, there is less possibility of mistakenly determining that surface defects such as biting have occurred on the surface of the slab, and surface defect detection accuracy is improved. Thus, it is possible to accurately detect surface defects such as biting in the slab.

Hereinafter, a slab surface defect detection method and a slab surface defect detection apparatus according to the present invention will be described with reference to FIGS.
FIG. 1 is a diagram showing a schematic configuration of a slab surface defect detection apparatus according to an embodiment of the present invention. As shown in FIG. 1, the slab surface defect detection apparatus according to an embodiment of the present invention is a laser projector. 7a, 7b, a laser receiver 9 as a laser beam receiving means, a surface unevenness state measuring circuit 10 as a surface unevenness state measuring means, an unevenness change rate calculating circuit 11 as an unevenness change rate calculating means, and an illumination as a slab surface illumination means Devices 12a and 12b, CCD cameras 13a and 13b as imaging means, an image signal processing device 14 as image signal processing means, a low brightness surface portion detection circuit 15 as low brightness surface portion detection means, and a surface defect determination means A determination device 16 is provided.

  The laser projectors 7 a and 7 b project a slit-shaped laser beam 8 having a beam width of, for example, 0.1 to 0.2 mm onto the surface of the slab 6 that is an inspection object, and are constant in the width direction of the slab 6. Arranged at intervals. The laser projectors 7a and 7b are disposed at a position where the radiant heat from the slab 6 does not reach (for example, a position spaced 2500 mm or more upward from the surface of the slab). The laser beam 8 is projected from almost right above. The laser light projected on the surface of the slab 6 from the laser projectors 7 a and 7 b is reflected on the surface of the slab 6 and then enters the laser receiver 9.

The laser receiver 9 receives laser light 8 reflected from the surface of the slab 6 to obtain surface unevenness information of the slab 6, and a signal output from the laser receiver 9 is a surface unevenness state measurement circuit 10. To be supplied.
The surface unevenness state measurement circuit 10 continuously measures the unevenness state of the slab surface in the width direction of the slab 6 in the longitudinal direction that is the traveling direction of the slab 6 based on the signal output from the laser receiver 9 to measure the entire surface of the slab. The data output from the surface unevenness state measurement circuit 10 is supplied to the unevenness change rate calculation circuit 11.

The unevenness change rate calculation circuit 11 processes the surface unevenness data of the slab 6 measured by the surface unevenness state measurement circuit 10 to calculate the unevenness change rate in the longitudinal direction of the slab surface. The signal output from 11 is supplied to the determination device 16 as surface defect information generated on the surface of the slab 6.
The illuminating devices 12a and 12b irradiate the surface of the slab 6 with illumination light over the entire width of the slab 6, and these illuminating devices 12a and 12b are, for example, a plurality arranged at regular intervals in the width direction of the slab 6. The halogen lamp is made up of. The illumination devices 12a and 12b are arranged at intervals in the longitudinal direction of the slab 6, and a space portion for arranging CCD cameras 13a and 13b described later between the illumination devices 12a and 12b. Is formed.

The CCD cameras 13a and 13b image the illumination area irradiated with the illumination light emitted from the illumination devices 12a and 12b on the surface of the slab 6 from a direction substantially perpendicular to the surface of the slab 6. By using, for example, a line CCD camera as these CCD cameras 13a and 13b, the resolution in the longitudinal direction is about 5 to 10 times smaller than when measuring the uneven state of the slab surface.
The image signal processing device 14 processes the image signals output from the CCD cameras 13a and 13b to obtain the surface luminance distribution of the slab 6, and the signal output from the image signal processing device 14 is a low luminance surface portion. It is supplied to the detection circuit 15.

The low-luminance surface portion detection circuit 15 detects a low-luminance surface portion (low-luminance surface portion determined to be a defect) of the slab 6 that is lower than a preset threshold among the surface luminance distribution obtained by the image signal processing device 14. The signal output from the low luminance surface portion detection circuit 15 is supplied to the determination device 16.
The determination device 16 determines the presence or absence of surface defects based on the unevenness change rate in the longitudinal direction of the slab surface calculated by the unevenness change rate calculation circuit 11 and the low brightness surface portion of the slab 6 detected by the low brightness surface portion detection circuit 15. The generation position, type, size, and the like are determined, and the position information acquisition unit 17, the comparison unit 18, and the determination unit 19 are included.

In the position information acquisition unit 17, the absolute value of the unevenness change rate in the direction of recessing inside the slab calculated by the unevenness change rate calculation circuit 11 (hereinafter simply referred to as “absolute value of unevenness change rate”) is determined in advance. The slab surface position information of a portion that is equal to or greater than the threshold value is acquired, and the slab surface position information acquired by the position information acquisition unit 17 is supplied to the comparison unit 18.
The comparison unit 18 detects the position of the low-luminance surface portion detected by the low-luminance surface portion detection circuit 15 and the slab surface position information acquired by the position information acquisition unit 17 (the absolute value of the unevenness change rate is equal to or greater than a predetermined threshold value. The comparison result of the comparison unit 18 is supplied to the determination unit 19.

  The determination unit 19 determines the presence / absence, occurrence position, type, size, etc. of the surface defect based on the comparison result of the comparison unit 18, and the position of the low luminance surface portion detected by the low luminance surface portion detection circuit 15. And the slab surface position acquired by the position information acquisition unit 17 is determined as a defect position, and the surface defect generated at the defect position is the size of the low brightness surface portion determined as the defect position. It is comprised so that it may determine with the magnitude | size of.

FIG. 2 shows a cross section of the surface portion of the slab when a surface defect called no-biting occurs on the surface of the slab 6. As shown in FIG. 2, it can be seen that when a surface defect called no-biting occurs in the slab 6, the surface unevenness of the slab 6 changes sharply at the tip of the no-biting 20.
FIG. 3 shows an example of an output signal waveform of the unevenness change rate calculation circuit 11 when the bite is generated on the surface of the slab 6. As shown in FIG. 3, it can be seen that when the biting occurs on the surface of the slab 6, the unevenness change rate in the longitudinal direction of the slab surface calculated by the unevenness change rate calculation circuit 11 changes greatly.

Therefore, as described above, the absolute value of the unevenness change rate in the longitudinal direction of the slab surface calculated by the unevenness change rate calculation circuit 11 is compared with a predetermined threshold value, so that the slab 6 is bitten. In this case, since the absolute value of the unevenness change rate is equal to or greater than the threshold value, it is possible to accurately detect whether or not the surface defect generated in the slab 6 is biting.
Further, as described above, the unevenness change rate in the longitudinal direction of the slab surface is calculated from the surface unevenness state of the slab 6 measured by the surface unevenness state measuring circuit 10, and the slab 6 obtained by the image signal processing device 14 is calculated. Calculate the position and size of the low-luminance surface portion that is determined to be a defect in the surface luminance distribution, the position of the portion where the absolute value of the unevenness change rate is equal to or greater than a predetermined threshold, and the position of the low-luminance surface portion Is determined as the defect position, and the size of the low-luminance surface portion determined as the defect position is determined as the size of the surface defect generated at the defect position. Biting can be detected with high accuracy.

  Therefore, when the presence / absence, type, size, etc. of surface defects are specified based only on the signal output from the laser beam receiver 9, or surface defects are determined based only on the image signals output from the CCD cameras 13a, 13b. Like when the presence / absence, type, size, etc. are specified, it is less likely that the surface of the slab will have a surface defect such as a bite, which improves the detection accuracy of the surface defect. Therefore, it is possible to accurately detect a surface defect such as a bite generated in the slab 6.

Further, as described above, the illumination light irradiated onto the slab surface from the illumination devices 12a and 12b is imaged from the direction substantially perpendicular to the surface of the slab 6 by the CCD cameras 13a and 13b. It is possible to accurately detect the size of surface defects (for example, the size of the bite) generated on the surface.
In the above-described embodiment of the present invention, the laser light from the laser projector is projected onto the surface of the slab from directly above, but the present invention is not limited to this, and the laser light from the laser projector is transmitted to the slab. You may make it light-project on the surface from diagonally upward. However, in order to detect a surface defect with higher accuracy, it is preferable to project the laser beam from the laser projector onto the surface of the slab from directly above.

Further, in the above-described embodiment of the present invention, the laser light is projected onto the surface of the slab from the two laser projectors arranged in the width direction of the slab. However, the present invention is not limited to this. What is necessary is just to set the number of laser projectors suitably according to a width dimension.
In the above-described embodiment of the present invention, the laser beam reflected by the surface of the slab is received by one laser receiver. However, the present invention is not limited to this. A plurality of light receivers may be provided.

  Further, as a method of obtaining the unevenness change rate in the longitudinal direction of the slab surface, as in the embodiment of the present invention described above, the slab is irradiated while irradiating the surface of the slab with a slit-like laser beam long in the width direction of the slab. The slab surface may be moved in the longitudinal direction to determine the unevenness change rate in the longitudinal direction of the slab, or a slit-like or spot-like laser beam irradiated on the slab surface may be scanned in the width or longitudinal direction of the slab. The unevenness change rate in the longitudinal direction of the slab surface may be obtained.

Further, in the above-described embodiment of the present invention, the signal output from the laser receiver is differentiated to acquire the unevenness change rate in the longitudinal direction of the slab surface. For example, the unevenness change rate in the longitudinal direction of the slab surface may be acquired from the inclination between two measurement points measured by the surface unevenness state measurement circuit.
Moreover, in one Embodiment of this invention mentioned above, although the illumination light was irradiated to the surface of the slab from two illuminating devices, the number of illuminating devices is not specifically limited, For example, from one illuminating device. Illumination light may be applied to the surface of the slab, or illumination light may be applied to the surface of the slab from three or more illumination devices. The light source of the lighting device is not limited to the halogen lamp, and any light source that is normally used can be used in the present invention.

Further, in the above-described embodiment of the present invention, the illumination area irradiated on the surface of the slab is imaged by two CCD cameras, but the number of CCD cameras as imaging means is not particularly limited. For example, the illumination light irradiation area may be imaged by one CCD camera, or the illumination light irradiation area may be imaged by three or more CCD cameras. Further, the image pickup means is not limited to the CCD camera, and any device that can acquire the luminance distribution on the slab surface can be used in the present invention.
In the above-described embodiment of the present invention, detection of surface defects on the upper surface side of the slab has been described, but the present invention can be similarly applied to detection of surface defects on the lower surface side of the slab. Furthermore, by providing the configuration of the present invention on the upper surface side and the lower surface side of the slab, it becomes possible to simultaneously detect defects on the upper and lower surfaces of the slab.

It is a figure which shows schematic structure of the slab surface defect detection apparatus which concerns on one Embodiment of this invention. It is a figure which shows the cross section of the surface layer part of a slab when the surface defect called the biting has occurred on the surface of the slab. It is a figure which shows an example of the output signal waveform of the uneven | corrugated change rate calculation circuit when the biting has occurred on the surface of the slab. It is a figure which shows typically an example of the continuous casting equipment of molten steel.

Explanation of symbols

1 Ladle 2 Dundish 3 Mold
4 Pinch roller 5 Cutting device 6 Slab 7a, 7b Laser projector 8 Laser light 10 Surface unevenness measuring circuit (surface unevenness measuring means)
11 Unevenness change rate calculation circuit (unevenness change rate calculation means)
12a, 12b Illumination device 13a, 13b CCD camera (imaging means)
14 Image signal processing device (image signal processing means)
15 Low brightness surface detection circuit (low brightness surface detection means)
16 determination device (surface defect determination means)
17 position information acquisition unit 18 comparison unit 19 determination unit

Claims (2)

The surface unevenness state of the slab is measured by irradiating the surface of the slab with a laser beam, and the surface luminance distribution of the slab is obtained by imaging the surface of the slab. From the surface unevenness state and the surface luminance distribution, A method of detecting surface defects generated on the surface of the slab,
The unevenness change rate in the longitudinal direction of the slab surface is calculated from the surface unevenness state of the slab, and the position and size of the low-luminance surface portion of the slab determined as a defect in the surface luminance distribution is calculated, When the position of the portion where the absolute value of the change rate is equal to or greater than a predetermined threshold matches the position of the low-luminance surface portion, the position is determined to be a defect position, and the low-luminance determined to be the defect position A slab surface defect detection method characterized in that the size of a surface portion is determined as the size of a surface defect generated at the defect position. The surface unevenness state of the slab is measured by irradiating the surface of the slab with a laser beam, and the surface luminance distribution of the slab is obtained by imaging the surface of the slab. From the surface unevenness state and the surface luminance distribution, A slab surface defect detection device for detecting surface defects generated on the surface of the slab,
Laser light receiving means for receiving laser light reflected by the surface of the slab;
Surface unevenness state measuring means for measuring the surface unevenness state of the slab based on the laser light received by the laser light receiving means;
An unevenness change rate calculating means for calculating an unevenness change rate in the longitudinal direction of the slab surface from the surface unevenness state of the slab measured by the surface unevenness state measuring means;
Imaging means for imaging the surface of the slab to obtain surface luminance information of the slab;
Image signal processing means for processing the image signal output from the imaging means to obtain the surface luminance distribution of the slab;
A low-luminance surface portion detecting means for detecting a low-luminance surface portion of a slab determined as a defect in the surface luminance distribution obtained by the image signal processing means;
The position of the portion where the absolute value of the unevenness change rate calculated by the unevenness change rate calculating means is equal to or greater than a predetermined threshold matches the position of the low brightness surface portion detected by the low brightness surface portion detecting means. And a surface defect determination means for determining the position as a defect position and determining the size of the low-luminance surface portion determined as the defect position as the size of the surface defect generated at the defect position. A slab surface defect detection device characterized by the above.

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