JP2014010004A - Slab surface flaw inspection method and facility - Google Patents

Abstract

PROBLEM TO BE SOLVED: To inspect the full surface of a hot slab in a high temperature state.SOLUTION: During continuous steel casting, each of a top surface 1a, a ground surface 1b, and both side faces 1c and 1d of a hot slab 1 moved in a hot temperature state is irradiated with light from a one-dimensional line light source 3. The reflected lights of the lights applied to the top surface 1a, the ground surface 1b, and both the side faces 1c and 1d of the hot slab 1 from the one-dimensional line light source 3 are continuously picked up by a one-dimensional imaging device 4. An image processing device 5 generates a two-dimensional image from the reflected lights continuously imaged by the one-dimensional imaging device 4. A detection/determination device 6 detects, based on the two-dimensional image generated by the image processing device 5, a slab surface flaw, and determines to feed only a surface flaw detected slab to a precision processing step. Thus, only flaw detected slabs are selected to be fed to an offline slab precision processing step.

Description

  The present invention relates to a method for inspecting the surface quality of a slab in a high temperature state in a steel manufacturing process, and equipment for performing the method.

Surface flaws such as vertical cracks may occur on the surface of a continuously cast slab.
Therefore, in the conventional continuous casting process, as shown in FIG. 7, the hot visual inspection is carried out by extracting the continuously cast slab. The hot visual inspection refers to a visual inspection performed at a high temperature without lowering the slab to room temperature.

  The inspection by sampling is because it is not possible to secure the time and man-hours to inspect the entire surface of all slabs online, but the slab in which wrinkles occurred as a negative effect is not subject to hot visual inspection, There is a case where it is sent out to the next process without being maintained. In this case, defects such as sliver and scab occur in the rolling coil.

  On the other hand, all steel grades with strict product quality requirements (hereinafter referred to as strict grades) are extracted, and general steel grades (hereinafter referred to as generic grades) are extracted, and offline visual inspection is performed in the slab finishing process. It is carried out. The cold visual inspection refers to a visual inspection performed after the slab is once cooled to room temperature.

  And the generation | occurrence | production of surface wrinkles was detected by this cold visual inspection, the hot gas is sprayed from the nozzle to the surface, and it is cut and the scarf process which removes wrinkles, or the surface grinding by a grinder is implemented. .

  These slabs subjected to the cold visual inspection not only require a long cooling process but also require reheating of the slab before the next rolling process, resulting in cost and process losses. On the other hand, if there is a flaw in the slab that was not subject to the sampling inspection in general materials, this defective slab will flow out to the next process.

  Therefore, it is desirable to inspect all the slabs continuously cast hot, but when imaging the surface of a hot slab with an imaging device, the light emitted by the slab itself may be ignored for reasons described later. Can not. Hereinafter, the light emitted by the slab itself is referred to as “self-luminous”.

  As a countermeasure, for example, in Patent Document 1, two-dimensionally obtained from reflected light from a light source having an intensity distribution having a peak wavelength in a shorter wavelength region with respect to the wavelength of self-emission of a high-temperature slab in a hot state. A method for detecting surface defects by analyzing an image is disclosed.

  In the case of the method disclosed in Patent Document 1, in order to detect all wrinkles of any shape generated on the surface of the slab moving on the transport roll, the slab surface is detected by two light sources, a one-dimensional light source and a two-dimensional light source. It is necessary to irradiate the same position simultaneously.

  When inspecting the top surface of the slab moving on the transport roll, for example, as shown in FIG. 4 of Patent Document 2, the one-dimensional light source and the two-dimensional light source disclosed in Patent Document 1 are arranged above the transport roll. Just do it.

  However, when inspecting the ground-side surface of a slab that moves on a transport roll, the area that can be imaged at one time is obstructed by the transport roll, so a two-dimensional light source that irradiates a predetermined area range may be used. Can not. In other words, the ground side surface of the slab cannot be inspected by the method disclosed in Patent Document 1.

  Since the occurrence of wrinkles may be independent between the top surface and the ground surface of the slab, even if only the top surface is inspected by the method disclosed in Patent Document 1 and the slab is free of wrinkles, the ground side It cannot be judged that the surface is healthy. That is, in the case of the inspection method disclosed in Patent Document 1, an offline cold visual inspection and care are necessary to inspect the ground surface.

  Patent Document 3 discloses a technique for detecting a rolled steel plate camber using laser light, and Patent Document 4 discloses a technique for measuring a three-dimensional shape of a high-temperature object. It is possible to detect abnormal slab shapes such as bulging that occur during casting. However, with the techniques disclosed in Patent Documents 3 and 4, it is difficult to obtain an accuracy enough to detect wrinkles generated on the slab surface.

JP-A-9-152322 Special table 2010-524695 gazette JP-A-5-118840 Japanese Patent Laid-Open No. 2001-99615

  The problem to be solved by the present invention is that there was no method for inspecting the entire surface of a slab in a high temperature state hot.

The slab surface wrinkle inspection method of the present invention is
In order to be able to inspect the entire surface of the slab at a high temperature hot,
In continuous casting of steel, each of the top surface, ground side surface, and both side surfaces of a hot slab moving in a high temperature state is irradiated with light from a one-dimensional line light source, and these irradiation lights are respectively transmitted to the ceiling. A two-dimensional image is generated by continuously capturing the reflected light reflected from the side surface, the ground surface, and both side surfaces using a one-dimensional imaging device, and the surface of the slab is based on these two-dimensional images. The main feature is to detect wrinkles and determine that only slabs with slab surface wrinkles are sent to the refining process.

  The slab surface flaw inspection method of the present invention irradiates light on the entire surface of the hot slab from a one-dimensional line light source, and continuously captures an image of the entire surface of the hot slab with uniform luminance with a one-dimensional imaging device. Since the surface defect is detected based on the two-dimensional image generated in this manner, the entire surface of the slab in a high temperature state can be inspected hot without using a two-dimensional surface light source or an imaging device.

The method of the present invention described above
A one-dimensional line light source that irradiates light on each of the top surface, ground surface, and both side surfaces of a hot slab that moves in a high temperature state during continuous casting of steel;
A one-dimensional imaging device that continuously images reflected light of the light irradiated from the one-dimensional line light source to the top surface, the ground surface, and both side surfaces of the hot slab;
An image processing device that generates a two-dimensional image from reflected light continuously captured by the one-dimensional imaging device;
A detection / determination device that detects a surface slab surface of a slab based on a two-dimensional image generated by the image processing apparatus and determines that only a slab in which the slab surface surface defect is recognized is sent to a refining process;
It can implement using the slab surface flaw inspection equipment of this invention provided with.

  In the present invention, it is possible to carry out surface quality inspection on the entire surface of the slab in the hot state, so it is possible to select only slabs in which surface defects have been found and send them to an offline slab refining process Become. In addition, hot materials can be sent directly to strict materials. Therefore, it is possible to shorten the lead time and the long cooling process caused by the cold inspection and the reheating cost generated in the next process.

It is the figure which showed the relationship between the self-light-emitting wavelength of a hot slab, and a radiant energy density. It is the figure which showed the irradiance distribution of the horizontal direction in the position 2100mm away from the light source. It is a block diagram of the surface quality inspection method using the imaging device which performed the preliminary experiment. It is the figure which showed the relationship between the inclination angle of the imaging device with respect to a slab, and the irradiance in a measurement position. In order to capture the surface image of the entire surface of the slab online, the schematic configuration of the slab surface defect inspection equipment of the present invention in which the imaging device described in FIG. 3 is installed on the top surface, the ground surface, and the left and right sides of the slab It is the schematic diagram which showed. It is the figure which showed the slab adjustment process after the slab surface quality inspection introduction by this invention. It is a figure explaining the conventional slab surface inspection process.

  The object of the present invention is to make it possible to inspect the entire surface of a slab in a high temperature state in a hot manner. The reflected light reflected by the respective surfaces of the one-dimensional irradiation light irradiated on the entire surface of the hot slab is reflected in a one-dimensional manner. This was realized by detecting based on a two-dimensional image generated by continuously capturing images with an imaging device.

Hereinafter, the present invention will be described along with the progress up to the solution of the problems of the present invention.
In order to inspect the ground side surface of the slab hot online, use a light source and an imaging device that have mechanical durability to falling objects and high-temperature atmospheres, with a limited field of view between the transport rolls. You have to image.

  For that purpose, it is necessary to determine the necessary range of the light source, the inclination angle of the imaging device with respect to the slab to be measured, the distance between the slab and the imaging device, etc. within the optimum range, but so far as explained in the prior art However, there is no description or suggestion about the above point.

  Therefore, the inventors conducted the following studies in order to establish a hot online surface quality inspection method for the entire surface of the slab in order to simplify the process and prevent the outflow of the defective slab to the next process.

  When imaging the surface of a hot slab in a hot state, the self-emission emitted from the slab cannot be ignored. The self-emission emitted from this slab is red light or infrared light having a wavelength of 0.6 μm or more, and its emission intensity (meaning black body radiation intensity) is uniquely determined from the surface temperature and wavelength of the slab. Follow the plank distribution.

  According to the Planck distribution, the black body radiation intensity B (λ, T) and radiant energy density u ′ (λ, T) of an electromagnetic wave including light is expressed by the following formula 1 as a temperature T and a wavelength λ.

  When the plank distribution is integrated over the entire wavelength region, the total energy E of the blackbody radiation is obtained, and its value is proportional to the fourth power of the temperature T (absolute temperature (K)) as shown in the following equation 2.

  That is, the radiant energy density of the self-light emission proportional to the fourth power of the surface temperature of the slab varies greatly depending on the wavelength. Since the hot slab has a temperature difference in the width direction, as shown in FIG. 1, the emission intensity is higher at the center of the width where the surface temperature is higher.

  Therefore, in order to simultaneously detect wrinkles generated at the center in the width direction of the slab and wrinkles generated at the corners in the width direction, the difference in light emission intensity generated in the width direction of the slab is suppressed, and uniform brightness in the width direction. Therefore, it is necessary to take an image of the slab surface.

  Therefore, using an optical filter that cuts off the wavelength range of the slab's self-emission and an imaging device that irradiates the surface of the slab with a light source that has a different wavelength range from the slab's self-emission, uniform brightness over the entire width of the slab An image of the slab surface was generated from the reflected light and used for wrinkle inspection.

  Also, in order to inspect the ground side surface of the slab on the transport roll, in order to image the ground side surface of the slab, an imaging device installed below the transport roll unless the slab is lifted from the transport roll by a crane or the like Therefore, it is difficult to capture a two-dimensional image with a narrow field of view.

  Furthermore, a cutting burr, a scale, etc. fall under the conveyance roll, and it is a severe environment where a high temperature slab passes through the upper part.

  Therefore, the ground side surface of the slab must be imaged within a limited field of view between the transport rolls using a light source and an imaging device having mechanical durability to falling objects and high-temperature atmospheres. And the necessary width, the inclination angle of the imaging device with respect to the slab to be measured, and the distance between the slab and the imaging device are important.

  Therefore, in order to solve the above-mentioned problems, the inventors of the present invention have both a light source and an imaging device that continuously capture a two-dimensional image of the slab surface over the entire length by imaging the slab surface with one-dimensional line rays. It was decided to collect.

  Furthermore, for the above examination, the inventors assumed a continuous casting machine as a preliminary experiment as a preliminary experiment, and a long side from a line light source (blue light emitting diode having a width of 400 mm) placed 2100 mm away from the surface of the slab. A slab having a side width of 1200 mm was projected, and an investigation was made as to whether or not surface defects could be discriminated from the captured image.

First, as a precondition, in the case of the imaging apparatus used in the preliminary experiment, it was necessary to secure an irradiance of 55 mW / m ² or more at the imaging position in order to determine wrinkles generated on the slab surface. However, it goes without saying that the irradiance value changes depending on the imaging device used (for example, the aperture value).

FIG. 2 shows an irradiance distribution at a position 2100 mm away from a light beam projected from a line light source having a width of 400 mm. From FIG. 2, it can be seen that in the preliminary experiment, a stable irradiance distribution of 55 mW / m ² or more was obtained over the entire area of the long side width of 1200 mm of the slab. Thus, by using a line light source having an effective width of at least 1/3 of the long side width of the slab to be measured, it is possible to image not only the long side width but also the short side width of the slab. I found out.

  FIG. 3 shows a block diagram of the surface quality inspection method using the imaging apparatus for which the preliminary experiment was performed. Reference numeral 1 denotes a slab to be inspected on the transport roll 2, and a slit is formed on the ground-side surface 1 b of the slab 1 from a line light source 3 using a blue light emitting diode having an effective width of 1/3 of the long side width of the slab 1. Irradiate light.

  The irradiated slit light is reflected by the ground-side surface 1b of the slab 1, and is selectively separated by blocking red light and infrared light due to self-emission emitted from the slab 1 when passing through the optical filter 4b through the lens 4a. Light is imaged as a one-dimensional image by the image sensor 4c. Reference numeral 4 denotes an image pickup apparatus in which a lens 4a, an optical filter 4b, and an image pickup element 4c are arranged in association with each other.

  The surface quality inspection image of the slab 1 obtained in this way is input to the image processing device 5, and a continuous surface quality inspection image over the entire width and length of the slab 1 is created to inspect the surface defects. .

  The linear light source 3 and the imaging device 4 installed below the transport roll 2 are housed in a steel protective jacket as a countermeasure against burrs and falling objects on the surface scale at the time of cutting, and pass above the high-temperature slab 1. In preparation for this, a water cooling device was provided. In addition, when detecting wrinkles on the top surface 1a and the ground surface 1b of the slab 1, the surface 1a, 1b is installed with an inclination θ from the vertical direction to the moving direction of the slab 1. .

  FIG. 4 shows the relationship between the inclination θ of the imaging device relative to the slab and the irradiance at the measurement position. From FIG. 4, it is understood that the surface defect can be detected without being affected by falling objects, a decrease in irradiance, and interference with the transport roll when the inclination θ of the imaging device is in the range of 10 to 45 °. It was.

The present invention has been made based on the above findings,
In continuous casting of steel, each of the top surface, ground side surface, and both side surfaces of a hot slab moving in a high temperature state is irradiated with light from a one-dimensional line light source, and these irradiation lights are respectively transmitted to the ceiling. A two-dimensional image is generated by continuously capturing the reflected light reflected from the side surface, the ground surface, and both side surfaces using a one-dimensional imaging device, and the surface of the slab is based on these two-dimensional images. It is a slab surface wrinkle inspection method characterized by detecting wrinkles and determining that only slabs with slab surface wrinkles are sent to a refining process.

And, the slab surface wrinkle inspection method of the present invention,
A one-dimensional line light source that irradiates light on each of the top surface, ground surface, and both side surfaces of a hot slab that moves in a high temperature state during continuous casting of steel;
A one-dimensional imaging device that continuously images reflected light of the light emitted from these line light sources to the top surface, the ground surface, and both sides of the hot slab;
An image processing device that generates a two-dimensional image from reflected light continuously captured by the one-dimensional imaging device;
A detection / determination device that detects a surface slab surface of a slab based on a two-dimensional image generated by the image processing apparatus and determines that only a slab in which the slab surface surface defect is recognized is sent to a refining process;
It can implement using the slab surface flaw inspection equipment of this invention provided with.

  The one-dimensional linear light source used in the implementation of the present invention preferably has a wavelength of not less than the lower limit of the visible light region and not more than 0.6 μm. According to JIS Z 8120, the wavelength range of the visible light region is defined such that the lower limit of the wavelength of the electromagnetic wave corresponding to visible light is approximately 360 to 400 nm, and the upper limit is approximately 760 to 830 nm. As shown in FIG. The reason why the lower limit is set to the lower limit of the visible light range is that it is difficult to visually match the field of view of the one-dimensional imaging device and the one-dimensional line light source when it is not visible light. It is.

  Specifically, the one-dimensional line light source used in the implementation of the present invention is a blue light-emitting diode having a large difference in wavelength range from the self-light-emitting diode among the light-emitting diodes having a long lifetime, low power and high brightness. It is desirable to use it.

  This is because when the wavelength is less than 0.45 μm, the sensitivity of the imaging device is lowered. On the other hand, when the wavelength is more than 0.5 μm, it becomes close to the peak wavelength of self-emission of the hot slab. It is.

  Also, the width of the one-dimensional line light source is preferably at least 1/3 of the long side width of the slab, based on the result of the preliminary experiment, in order to ensure stable brightness over the entire width of the slab.

  Moreover, it is desirable that the inclination angle of the imaging device installed on the ground surface side of the slab in the moving direction of the slab with respect to the vertical is within a range of 10 to 45 ° in order to ensure a success rate of wrinkle detection. The reason why the upper limit is 45 ° is to avoid a decrease in irradiance and interference with the transport roll, and the reason why the lower limit is 10 ° is to avoid the effects of falling objects such as cutting burrs and scales. is there.

Next, examples of the present invention will be described.
FIG. 5 is a slab surface flaw inspection apparatus according to the present invention in which the imaging device described in FIG. 3 is installed on the top surface, the ground surface, and the left and right sides of the slab in order to capture a surface image of the entire surface of the slab online. It is the schematic diagram which showed schematic structure.

  3 is a transport roll 2 for irradiating light on the entire surface of the slab 1 of 700 to 850 ° C. drawn from the mold, that is, the top surface 1a, the ground surface 1b, and the both side surfaces 1c and 1d. This is a one-dimensional line light source arranged above, below and on both sides of the slab 1 that moves at a speed of 20 m / min.

  The line light sources 3 arranged above and below the slab 1 are provided at positions 2100 mm apart from the top surface 1a and the ground surface 1b of the slab 1, respectively. Moreover, what was arrange | positioned on the both sides | surfaces 1c and 1d of the slab 1 is provided in the position 500 mm away from the side surfaces 1c and 1d of the slab 1, respectively.

  The light source of the line light source 3 employs, for example, a blue light emitting diode with a wavelength of 0.45 μm in order to suppress a difference in light emission intensity generated in the width direction of the slab 1 and to capture an image of the slab surface with uniform brightness. doing.

  The linear light source 3 for irradiating light on the top surface 1a and the ground surface 1b is 420 mm wide so that it is at least 1/3 of the width (1250 mm) of the slab 1. On the other hand, the linear light source 3 that irradiates the side surfaces 1c and 1d with light has a width of 100 mm because the thickness of the slab 1 is 227 mm.

  Reference numeral 4 denotes continuously reflected light of light irradiated from the one-dimensional light source 3 onto the top surface 1a, the ground surface 1b, and both side surfaces 1c and 1d of the slab 1 moving on the transport roll 2. It is a one-dimensional imaging device that images.

  Among the one-dimensional image pickup devices 4, one that picks up the reflected light from the top surface 1 a of the slab 1 is arranged so as to pick up the reflected light from the vertical line. Moreover, what image | photographs the reflected light from the ground side surface 1b of the slab 1 is arrange | positioned so that it may image from the position inclined 30 degrees in the moving direction of the slab 1 with respect to the perpendicular | vertical.

  On the other hand, what picks up the reflected light from the side surfaces 1c and 1d of the slab 1 is arranged so as to pick up an image from a position inclined by 30 ° so that the top surface 1a side of the slab 1 narrows with respect to the vertical.

  The line light source 3 emits light to each of the top surface 1a, the ground surface 1b, and the both side surfaces 1c and 1d of the slab 1 so that the reflected light can be imaged by the imaging device 4 arranged at the above position. Needless to say, it is arranged at a position to irradiate.

  Although the one-dimensional imaging device 4 is not shown in FIG. 5, as described in FIG. 3, the wavelengths of red light, infrared light, and the like due to self-emission emitted from the lens and the slab 1 exceed 0.6 μm. An optical filter for blocking light and an image sensor for imaging light selectively separated by the optical filter are provided.

  Then, the image processing device 5 generates a two-dimensional image from the reflected light continuously captured by the one-dimensional imaging device 4, and the detection / determination device 6 uses the generated two-dimensional image for the slab 1. A surface flaw is detected, and it is determined that only the slab 1 in which the slab surface flaw is recognized is sent to the refining process.

  The method of the present invention uses the slab surface flaw inspection facility of the present invention having the above-described configuration, and each surface of the top surface 1a, the ground surface 1b, and both side surfaces 1c and 1d of the hot slab 1 moving in a high temperature state. The surface wrinkles are detected, and only the slab 1 in which the surface wrinkles are recognized is determined to be sent to the refining process.

  FIG. 6 shows a slab refining process after the introduction of the slab surface quality inspection according to the present invention. According to the present invention, only the slab in which wrinkles are found can be sent offline to the slab refining process. In addition, since strict materials can be directly sent hot, not only the lead time is shortened, but also the cost required for slab refining and reheating in the next process can be reduced.

  Table 1 below shows a comparison between the invention example in which the surface slab inspection of the slab was performed hot under the above-described inspection conditions and the conventional example in which the visual inspection was performed in cold.

  In the conventional example of a general material, 285 sheets are extracted from 3383 cast slabs to form cold cast pieces, and 3098 cast slabs excluding the extracted 285 sheets are directly transferred hot. (The final acceptance rate of the casting slab) is 91.6%.

  However, the number of rejected judgment materials in the visual surface flaw inspection of the cold cast slab thus extracted was 8, and the pass rate of the actual surface flaw of the cast slab was 99.7%.

  On the other hand, in the case of a general material in which the hot inspection of the present invention was performed with 2540 cast slabs, the number of rejected judgment materials was 5, and the hot direct feed rate was 99.8%. This is a value substantially equal to the acceptance rate of 99.7% of the actual cast slab of the conventional example, and it can be seen that the pass judgment of the surface defect of the cast slab can be performed only by the hot inspection of the present invention.

  On the other hand, in the conventional example of strict materials, 706 cast slabs were all made into cold slabs, and visual surface flaw inspection was conducted. The number of rejected judgment materials was 66, and the final surface flaw of the cast slab was accepted. The rate was 90.7%. In this case, the hot direct feed rate is of course 0%.

  On the other hand, in the case of the strict material in which the hot inspection of the present invention was performed with 503 cast slabs, the number of determination materials that were rejected was 48, and the hot direct feed rate was 90.5%. This is a value almost equivalent to the acceptance rate of 90.7% of the casting slab of the conventional example, and it can be seen that the acceptance judgment of the surface defect of the casting slab can be performed only by the hot inspection of the present invention.

  Therefore, according to the present invention, as before, it is not necessary to inspect the surface flaws in the cold, it is possible to omit the cold slab refining process, the lead time is shortened, It has been found that sufficient surface quality inspection accuracy can be obtained only by hot inspection.

  In addition, especially for strict materials, it is possible to realize hot direct feeding, which was impossible before, and it is possible to control the quality of surface flaws so that only slabs with slab surface flaws are sent to the refining process. As a result, even strict materials can be produced stably with an acceptance rate of 90% or more.

  Needless to say, the present invention is not limited to the above-described examples, and the embodiments may be appropriately changed within the scope of the technical idea described in the claims.

DESCRIPTION OF SYMBOLS 1 Slab 1a Top surface 1b Ground side surface 1c, 1d Side surface 3 Line light source 4 Imaging device 5 Image processing device 6 Detection / determination device

Claims (9)

  In continuous casting of steel, each of the top surface, ground side surface, and both side surfaces of a hot slab moving in a high temperature state is irradiated with light from a one-dimensional line light source, and these irradiation lights are respectively transmitted to the ceiling. A two-dimensional image is generated by continuously capturing the reflected light reflected from the side surface, the ground surface, and both side surfaces using a one-dimensional imaging device, and the surface of the slab is based on these two-dimensional images. A slab surface wrinkle inspection method characterized by detecting wrinkles and determining that only slabs with slab surface wrinkles are sent to a refining process.   2. The slab surface inspection method according to claim 1, wherein the one-dimensional line light source that irradiates the slab has a wavelength that is not less than a lower limit value of a visible light region and not more than 0.6 μm.   2. The slab surface inspection method according to claim 1, wherein the one-dimensional line light source that irradiates the slab has a wavelength of 0.45 or more and 0.5 μm or less.   In the case of the ground side surface of a slab, the imaging is performed by giving an angle of 10 ° or more and 45 ° or less with respect to the moving direction of the slab from the vertical direction to the ground side surface. The slab surface inspection method in any one of 1-3. A one-dimensional line light source that irradiates light on each of the top surface, ground surface, and both side surfaces of a hot slab that moves in a high temperature state during continuous casting of steel;
A one-dimensional imaging device that continuously images reflected light of the light irradiated from the one-dimensional line light source to the top surface, the ground surface, and both side surfaces of the hot slab;
An image processing device that generates a two-dimensional image from reflected light continuously captured by the one-dimensional imaging device;
A detection / determination device that detects a surface slab surface of a slab based on a two-dimensional image generated by the image processing apparatus and determines that only a slab in which the slab surface surface defect is recognized is sent to a refining process;
Slab surface flaw inspection facility characterized by comprising   6. The slab surface inspection facility according to claim 5, wherein a light source width of the one-dimensional line light source applied to the slab is at least 1/3 of a long side width of the slab.   7. The slab surface inspection facility according to claim 5, wherein the one-dimensional line light source that irradiates the slab has a wavelength that is not less than a lower limit value of a visible light region and not more than 0.6 μm.   The slab surface inspection facility according to claim 5 or 6, wherein the one-dimensional line light source irradiated to the slab has a wavelength of 0.45 or more and 0.5 µm or less.   In the case of the ground side surface of the slab, the imaging device is installed with an angle of 10 ° or more and 45 ° or less from the vertical direction to the moving direction of the slab with respect to the ground side surface. The slab surface inspection equipment according to any one of claims 5 to 8.

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