JP2023123908A - Defect measuring device, defect measuring method, manufacturing facility for galvanized steel plate, manufacturing method for galvanized steel plate, and quality control method for galvanized steel plate - Google Patents

Abstract

To provide a defect measuring device and a defect measuring method capable of directly and quickly measuring the appearance characteristics of the surface of a galvanized steel sheet caused by a stripe defect in a simple optical system.SOLUTION: Disclosed is a defect measurement device according to the present invention which measures a stripe defect on the surface of a galvanized steel sheet. This measurement device includes: irradiation means for irradiating the surface of the galvanized steel sheet with line illumination light; and imaging means for photographing a surface image of the galvanized steel sheet by receiving the line illumination light reflected on the surface of the galvanized steel sheet. The irradiation means and the imaging means are arranged so that the difference between an irradiation angle and a light receiving angle of the line illumination light falls within a range of 20° or more and 40° or less.SELECTED DRAWING: Figure 1

Description

TECHNICAL FIELD The present invention relates to a defect measuring device, a defect measuring method, a zinc-based plated steel sheet manufacturing facility, a zinc-based plated steel sheet manufacturing method, and a zinc-based plated steel sheet quality control method.

The surface texture of steel products is an important factor in the appearance of steel products, and surface textures that impair the appearance of steel products significantly reduce the value of steel products. Changes in appearance characteristics due to surface properties are often caused by minute shapes such as surface roughness of the surface of steel products, chemical composition, bias in film thickness, and the like. For example, in a zinc-based plated steel sheet, fine (several 100 nm to several μm) irregularities such as streaky defects are generated on the surface, and the irregularities become conspicuous by the coating treatment in the post-process, which may impair the appearance. The unevenness is caused by slight segregation of the surface components in the manufacturing process of the zinc-based plated steel sheet, which causes uneven progress in the degree of alloying of iron and zinc. In addition, since the uneven progress of the degree of alloying is extended in the rolling direction of the steel sheet by the rolling process, the unevenness often occurs as streaks with a width of several hundred μm to several tens of mm in the rolling direction of the steel sheet.

However, the change in the appearance characteristics of the zinc-based plated steel sheet due to the fine unevenness of the streak-like defect (hereinafter referred to as a streak-like defect) is such that a faint streak-like pattern can be confirmed by visual observation. . In addition, since the amount of unevenness is small and the ratio of fine unevenness to the generated surface is small, it is difficult to directly measure and quantify the unevenness. Against this background, past research and development focused on how to improve the appearance, and evaluation of the appearance relied solely on visual inspection. Specifically, Patent Literatures 1 and 2 describe a method of visually judging the appearance of a hot-dip galvanized steel sheet. On the other hand, for quantification of such appearance characteristics, a method of irradiating a plated surface with a pulsed laser beam and spectroscopically analyzing the emission spectrum for each pulse for each analysis point (see Patent Document 3), A method of inspecting a pattern called spangle from the areas of bright and dark portions of an image obtained by irradiating light has been proposed (see Patent Document 4).

Japanese Patent Application Laid-Open No. 2020-153004 JP 2018-44190 A JP 2006-317379 A JP-A-11-72317

However, the methods described in Patent Documents 1 and 2 not only cause variations in judgment of the appearance characteristics of the zinc-based plated steel sheet depending on the individual, but also vague criteria for appearance characteristics, so whether the appearance is truly improved. I can't seem to get it to be persuasive. On the other hand, the method described in Patent Document 3 is a method of analyzing the plating structure rather than a method of quantifying the appearance characteristics of a zinc-based plated steel sheet, and the influence of the analysis results on the appearance must be further evaluated. It is indirect from the point of view of character judgment. In addition, since only the point irradiated with the pulsed laser beam is evaluated, the pulsed laser beam must be scanned in order to evaluate the appearance of the entire surface, which results in a large-scale apparatus. Moreover, it is difficult to measure a streak defect having a width smaller than the spot diameter of the pulsed laser beam. Moreover, since the method described in Patent Document 4 uses an area sensor, the optical system may vary within the field of view. In addition, only spangles are evaluated, and it is not clear whether even minute unevenness of streak defects can be evaluated.

The present invention has been made in view of the above problems, and the object thereof is to improve zinc-based plated steel sheets caused by fine unevenness in the form of streak defects (hereinafter referred to as streak defects) with a simple optical system. An object of the present invention is to provide a defect measuring apparatus and a defect measuring method capable of directly measuring surface appearance characteristics in a short time. Another object of the present invention is to provide a production facility and a production method for a zinc-based plated steel sheet that can produce the zinc-based plated steel sheet with a high yield. Another object of the present invention is to provide a quality control method for zinc-based plated steel sheets capable of providing high-quality zinc-based plated steel sheets.

A defect measuring apparatus according to the present invention is a defect measuring apparatus for measuring streak defects on the surface of a zinc-based plated steel sheet, comprising irradiation means for irradiating the surface of the zinc-based plated steel sheet with line illumination light, and the zinc-based imaging means for capturing a surface image of the zinc-based plated steel sheet by receiving the line illumination light reflected on the surface of the plated steel sheet, wherein the irradiation means and the imaging means are configured to receive the line illumination light. They are arranged so that the difference between the irradiation angle and the light receiving angle is within the range of 20 degrees or more and 40 degrees or less.

computing means for calculating, from a surface image of the zinc-based plated steel sheet, a feature quantity of the streak-like defect in a direction parallel to the rolling direction of the zinc-based plated steel sheet as an index of the streak-like defect; is preferably arranged such that the extending direction of the line illumination light is perpendicular to the rolling direction of the galvanized steel sheet.

The computing means generates a corrected image in which the luminance unevenness in the vertical direction is corrected from the surface image of the zinc-based plated steel sheet, selects an image of an area including the streak defect from the corrected image, and selects the selected image. It is preferable to calculate the index from the image of the streak defect.

A defect measurement method according to the present invention is a defect measurement method for measuring streak-like defects on the surface of a zinc-based plated steel sheet, comprising an irradiation step in which an irradiation means irradiates the surface of the zinc-based plated steel sheet with line illumination light; an imaging step of capturing a surface image of the zinc-based plated steel sheet by receiving the line illumination light reflected by the surface of the zinc-based plated steel sheet, wherein the irradiating means and the imaging means are , so that the difference between the irradiation angle and the reception angle of the line illumination light is in the range of 20 degrees or more and 40 degrees or less.

A manufacturing facility for a zinc-based plated steel sheet according to the present invention comprises manufacturing equipment for manufacturing a zinc-based plated steel sheet, and a defect measuring device according to the present invention for measuring the surface of the zinc-based plated steel sheet manufactured by the manufacturing facility. Prepare.

A method for manufacturing a zinc-based plated steel sheet according to the present invention comprises a manufacturing step of manufacturing a zinc-based plated steel sheet, and measuring the surface of the zinc-based steel sheet manufactured in the manufacturing step using a defect measurement method according to the present invention. and a measuring step.

A method for quality control of a zinc-based plated steel sheet according to the present invention includes a measurement step of measuring the surface of a zinc-based plated steel sheet using the defect measurement method according to the present invention; and a quality control step for quality control of the plated steel sheet.

According to the defect measuring apparatus and the defect measuring method of the present invention, it is possible to directly measure the appearance characteristics of the surface of a zinc-based plated steel sheet caused by streak defects in a short time with a simple optical system. Moreover, according to the manufacturing equipment and manufacturing method of the zinc-based plated steel sheet according to the present invention, the zinc-based plated steel sheet can be manufactured with a high yield. Moreover, according to the method for quality control of a zinc-based plated steel sheet according to the present invention, it is possible to provide a high-quality zinc-based plated steel sheet.

1A and 1B are a side view and a front view showing the configuration of a defect measuring apparatus according to one embodiment of the present invention. FIG. 2 is a diagram showing definitions of the irradiation angle of the line light source and the light receiving angle of the line sensor. FIG. 3 is a flow chart showing the flow of quantification processing, which is an embodiment of the present invention. FIG. 4 is a diagram showing an example of a surface image of a hot-dip galvanized steel sheet. FIG. 5 is a diagram showing a corrected image of the surface image shown in FIG. FIG. 6 is a diagram showing an example of a streak defect image and profile. FIG. 7 is a diagram showing an example of a streak defect image and a profile when there is a streak defect and when there is no streak defect. FIG. 8 is a diagram showing an example of transition of indices when there is a streak defect and when there is no streak defect. 9A and 9B are a side view and a front view showing the configuration of a modification of the defect measuring apparatus according to one embodiment of the present invention.

Hereinafter, with reference to the drawings, a defect measuring apparatus, a defect measuring method, a zinc-based plated steel sheet manufacturing facility, a zinc-based plated steel sheet manufacturing method, and a zinc-based steel sheet quality control method according to an embodiment of the present invention will be described. explain.

In this specification, the term "zinc-based plated steel sheet" means a plated steel sheet containing zinc in the coating layer. Specifically, the galvanized steel sheet includes a hot-dip galvanized steel sheet (GI), an alloyed hot-dip galvanized steel sheet (GA) obtained by alloying a hot-dip galvanized steel sheet, an electrogalvanized steel sheet (EG), and Zn-Ni plating. Steel plate, Zn-Mg plated steel plate, Zn-Al-Mg plated steel plate (e.g. Zn-6 mass% Al-3 mass% Mg alloy plated steel plate, Zn-11 mass% Al-3 mass% Mg alloy plated steel plate, etc.), Zn -Al plated steel plate (eg, Zn-5 mass% Al alloy plated steel plate, Zn-55 mass% Al alloy plated steel plate, etc.) and the like can be exemplified. In addition, one or two of nickel, cobalt, manganese, iron, molybdenum, tungsten, titanium, chromium, aluminum, magnesium, lead, antimony, tin, copper, and silicon may be added as a small amount of dissimilar metal elements or impurities in the plating layer. It may contain more than one seed. Moreover, the plated layer may be formed by forming two or more layers of the same type or different types of plated layers.

In addition, as the steel type of the steel sheet that is the base of the zinc-based plated steel sheet, the steel composition is, in mass%, C: 0.0001% or more and 0.25% or less, Si: 0.001% or more and 2.0% or less, Mn : 0.01% to 3.0%, P: 0.001 to 0.02%, S: 0.0001 to 0.02%, Al: 0.001% to 0.10%, N : containing 0.0001% or more and 0.007% or less, and the balance being Fe and unavoidable impurities. In addition to the above essential elements, as optional elements, Cr: more than 0% and 2.0% or less, Nb: 0.001% or more and 1.0% or less, V: 0.001% or more and 1.0% or less, W: More than 0% and 0.3% or less, Ni: more than 0% and 2.0% or less, Cu: more than 0% and 2.0% or less, Mo: more than 0% and 1.0% or less, B: more than 0% and 0.01 % or less Ti: 0.001% or more and 0.1% or less, Ca: more than 0% and 0.03% or less, Mg: more than 0% and 0.03% or less may be included as appropriate. Furthermore, in addition to the above steel types, the present invention works more effectively if it is a cold-rolled steel sheet.

[Configuration of Defect Measuring Device]
First, referring to FIGS. 1 and 2, the configuration of a defect measuring apparatus according to an embodiment of the present invention will be described.

1(a) and 1(b) are a side view and a front view showing the configuration of a defect measuring apparatus according to an embodiment of the present invention. As shown in FIGS. 1A and 1B, a defect measuring apparatus 1 according to one embodiment of the present invention is a cut plate sample S partially cut from a zinc-based plated steel plate (hereinafter abbreviated as steel plate). This is an off-line defect measuring apparatus that quantifies the appearance characteristics as an index of streak-like defects on the surface of the cut plate sample S. A defect measuring apparatus 1 includes a linear stage 2 , a line light source 3 , a line sensor 4 and an arithmetic device 5 . It is desirable that the cut plate sample S be as flat as possible.

The linear stage 2 is a conveying device on which the cut plate sample S is placed and which conveys the cut plate sample S along the rolling direction of the steel plate.

The line light source 3 irradiates the surface of the cut plate sample S with line illumination light extending in a direction perpendicular to the rolling direction of the steel plate. The irradiation direction of the line illumination light and the conveying direction of the cut plate sample S are preferably parallel to the rolling direction of the steel plate. Light may be applied. Further, in this embodiment, the line illumination light was applied in a direction parallel to the rolling direction of the steel sheet, because the direction of stretching of the streak-like defects often coincides with the rolling direction of the steel sheet. On the other hand, when the stretching direction of the streak defects does not coincide with the rolling direction of the steel sheet, it is preferable to irradiate the line illumination light in a direction parallel to the stretching direction of the streak defects. The line light source 3 functions as irradiation means according to the present invention.

The line sensor 4 is composed of an imaging device having one or more lines of imaging elements arranged in a direction perpendicular to the rolling direction of the steel plate. The line sensor 4 continuously captures images of the cut-plate sample S transported by the linear stage 2 by receiving line illumination light reflected from the surface of the cut-plate sample S, and stores data of the captured images. is output to the arithmetic unit 5 . When an image of the cut plate sample S is captured using a general digital camera and a spot light source, the appearance of the streak defect changes because the irradiation angle and the light receiving angle of the illumination light differ depending on the imaging position. Therefore, in the defect measuring apparatus 1 of the present embodiment, the cut plate sample S is scanned using the linear stage 2 while limiting the illumination light irradiation direction and the imaging direction to a direction parallel to the rolling direction of the steel plate. In such a mode, the entire cut plate sample S can be imaged under uniform optical conditions, which is very preferable. The line sensor 4 functions as imaging means according to the present invention.

When the irradiation angle of the line light source 3 and the light receiving angle of the line sensor 4 with respect to the direction perpendicular to the surface of the cut plate sample S shown in FIG. image can be obtained. The specular reflection component decreases as the difference between the irradiation angle of the line light source 3 and the light receiving angle of the line sensor 4 increases, while the diffuse reflection component increases. As a result of detailed observation of the surface of the cut plate sample S, the inventors of the present invention found that when the optical condition approaches the regular reflection condition, the specular reflection component becomes noise. It was found that the surface roughness of the texture itself of the cut plate sample S was emphasized, and the signal of the streak defect was buried. Therefore, the difference between the irradiation angle of the line light source 3 and the light receiving angle of the line sensor 4 is set within a range of 20 degrees or more and 40 degrees or less. This angle range can be obtained by learning, for example, a machine learning method for the angle range in which the difference in the indices of the streak-like defect described later becomes the largest depending on the presence or absence of the streak-like defect.

Moreover, it is preferable that the light-receiving luminance of the line sensor 4 is not too dark and not saturated. Further, it is preferable that the resolution of the image of the cut plate sample S in the width direction (the direction perpendicular to the rolling direction of the steel plate) is sufficiently smaller than the width direction pitch of the streak defects to be evaluated. For example, when evaluating a streak defect with a minimum width of 0.5 mm, the resolution in the width direction is preferably 0.25 mm or less. On the other hand, the resolution of the image of the cut plate sample S in the longitudinal direction (rolling direction of the steel plate) is not particularly limited, but preferably does not change when the cut plate sample S is conveyed. For this purpose, the linear stage 2 may be used to transport the cut sample S at a constant speed, or an image of the cut sample S may be captured using a pulse signal corresponding to the transport amount of the cut sample S as a trigger signal. .

As for the wavelength of the line illumination light and the wavelength of the light received by the line sensor 4, the purpose of the present embodiment is to quantify the appearance characteristics of the zinc-based plated steel sheet by visual inspection as an index of streak defects. Therefore, it is preferable to use a wavelength in the visible light region. In addition, since the sensitivity characteristics of Si elements used in cameras for visible light generally include near-infrared light, it is preferable to remove wavelengths in the infrared region by inserting an infrared light cut filter. Furthermore, it is preferable that the wavelength of the line illumination light is broad enough for visual observation.

The computing device 5 is configured by an information processing device. The computing device 5 generates a surface image of the cut plate sample S by connecting the data of the images in the width direction continuously photographed by the line sensor 4 in the longitudinal direction. Then, the arithmetic device 5 quantifies the index of the streak defect by executing a quantification process, which will be described later, on the surface image of the cut plate sample S that has been generated. The computing device 5 functions as computing means according to the present invention.

[Quantification processing]
Next, a quantification process that is an embodiment of the present invention will be described with reference to FIG.

FIG. 3 is a flow chart showing the flow of quantification processing, which is an embodiment of the present invention. The flowchart shown in FIG. 3 starts at the timing when the calculation device 5 generates the surface image of the cut plate sample S, and the quantification process proceeds to the process of step S1.

In the process of step S1, the arithmetic device 5 corrects (removes) the luminance unevenness in the width direction (the direction perpendicular to the rolling direction of the steel plate) of the surface image of the cut plate sample S, thereby removing the streak defects from the surface. To obtain the same measurement value regardless of the position in the image. Specifically, the optical system is designed to obtain uniform brightness in the width direction, but even so, uneven brightness occurs in the width direction due to the influence of the smooth changes in reflection characteristics of the steel plate itself. do. Therefore, the arithmetic unit 5 first removes the low-frequency components contained in the surface image of the cut plate sample S. FIG. Then, the arithmetic unit 5 generates, as a corrected image, an image obtained by taking the ratio of the luminance of the surface image from which only the low-frequency components are extracted and the luminance of the image from which the low-frequency components are removed.

If the low-frequency component is simply removed, the same streak defect will have a stronger contrast if the peripheral brightness value is high, and will become weaker if it is low. It depends on the position in the image. On the other hand, by generating, as a corrected image, an image obtained by taking the luminance ratio of the surface image from which only the low-frequency components are extracted and the image from which the low-frequency components are removed, the high-luminance and low-luminance portions of the peripheral portion can be obtained. It is possible to average the difference in the contrast of the streak defects that occurred in the The irradiation angle of the line light source 3 is 10 degrees, the light receiving angle of the line sensor 4 is 40 degrees, the resolution in the width direction is 0.11 mm, and the resolution in the longitudinal direction is 0.08 mm. FIG. 4 shows the resulting image. FIG. 5 shows a corrected image of the surface image shown in FIG. Thereby, the process of step S1 is completed, and the quantification process proceeds to the process of step S2.

In the process of step S2, the arithmetic unit 5 selects an image of a certain range of areas including the streak defect from the corrected image generated by the process of step S1, and selects an image of the area including the selected streak defect. A streak defect image is generated by setting the image as a streak defect image. FIG. 6A shows an example of selecting a region containing streak defects. After selecting the area, the image is color-corrected to make it easier to understand. In this example, the longitudinal length is chosen to be sufficient to include stable regions of white and black streaks that are unsightly vertical streaks. In addition, since the streak-like defect in the streak-like defect image may be thin depending on the location, it is preferable to select an area where the streak-like defect is stably generated as much as possible. Also, if there is foreign matter other than the linear defect such as dirt or defects around the linear defect, the image of the foreign matter becomes a noise factor in the linear defect image, so the image of the foreign matter is excluded from the image selection range. is preferred. Thereby, the process of step S2 is completed, and the quantification process proceeds to the process of step S3.

In the process of step S3, the arithmetic unit 5 performs luminance averaging process in the longitudinal direction on the linear defect image generated by the process of step S2. Specifically, if the luminance of the linear defect portion and the luminance of the peripheral portion in the linear defect image generated by the process of step S2 are simply compared as they are, the surface properties such as the surface roughness of the steel sheet itself increases the variability. Therefore, considering the feature that the streak defect extends in the longitudinal direction, the arithmetic device 5 performs luminance averaging processing in the longitudinal direction on the streak defect image. In other words, the arithmetic unit 5 generates a one-dimensional (linear) profile by compressing the two-dimensional streak defect image to 0-dimensional in the longitudinal direction while keeping the width in the one-dimensional direction. Specifically, the arithmetic unit 5 performs processing in the longitudinal direction so as to obtain a representative value that reflects the characteristics of the longitudinal direction in the two-dimensional streak defect image. For example, since the streak defect image is a two-dimensional matrix, the streak defect image can be expressed as I(p, q) (1≤p≤P, 1≤q≤Q, P×Q resolution) (FIG. 6). (a)). Therefore, in the case of the averaging process, the one-dimensional profile L(p) (1≤p≤P) can be calculated by Equation (1) shown below. A one-dimensional profile L(p) calculated from the linear defect image shown in FIG. 6(a) is shown in FIG. 6(b).

Processing other than averaging includes maximum value processing (processing using the maximum luminance value in the longitudinal direction as the representative value), minimum value processing (processing using the minimum luminance value in the longitudinal direction as the representative value), central Examples include value processing (processing using the median value of luminance in the longitudinal direction as a representative value) and percentile processing (processing in which luminance values are rearranged in descending order and the luminance values of a predetermined order are adopted). However, any processing may be used as long as the representative value of the streak-like defect portion can be stably obtained in the longitudinal direction. Also, the length of the streak defect image in the longitudinal direction is preferably long enough to reduce variations due to surface roughness. For example, when averaging processing is employed, noise due to surface roughness is generated randomly, and assuming that the noise has a normal distribution, the noise is multiplied by √Q by averaging the Q points. Therefore, let the length of the linear defect image in the longitudinal direction, that is, the number of points to be averaged in the longitudinal direction be Q, the signal of the representative point of the linear defect be S, the noise of the healthy portion be N, and the required SN ratio be ρ. , ρ preferably satisfies the following formula (2).

In the process of step S4, the arithmetic unit 5 extracts the numerical value of the position corresponding to the streak defect from the one-dimensional profile obtained by the process of step S3, and uses the numerical value as the index of the streak defect. When the streak defect is brighter than the surrounding area, the signal intensity appears on the positive side, and when it is dark, the signal strength appears on the negative side. The value may be used as an indicator of streak defects. Here, FIGS. 7A and 7B show a linear defect image and a one-dimensional profile when there is a linear defect and when there is no linear defect. The black and white arrows in FIG. 7(a) indicate the positions of visually confirmed streak defects, and the numerical values −6.8 and +3, 4 indicate the numerical values of the one-dimensional profile at the streak defect positions. It can be seen that the numerical values obtained are in good agreement with the intuitive visual judgment. FIG. 8 shows the transition of the index for a sample with a streak defect and a sample without a streak defect when the irradiation angle of the line light source 3 is fixed at 10 degrees and the light receiving angle of the line sensor 4 is changed. In the example shown in FIG. 8, the difference between the maximum value and the minimum value is used as the index in order to use the extracted numerical value as the index of the streak defect. This is because it is clear that the larger the difference between the maximum value and the minimum value of the extracted numerical values, the more serious the streak defects and the worse the appearance characteristics of the galvanized steel sheet. In addition, the "difference between the indicator with defect and the indicator without defect" in FIG. is the subtracted value. The index for the absence of streak defects (in the case of FIG. 8, the difference between the maximum value and the minimum value in the region without streak defects) is an index originally possessed by the galvanized steel sheet to be measured, such as background noise. considered to be equivalent. Therefore, by subtracting the index without the streak defect corresponding to the background noise from the index with the streak defect (in the case of FIG. 8, the difference between the maximum value and the minimum value in the region with the streak defect), It is possible to emphasize the change in the index when there is a streak defect.

As shown in FIG. 8, when the light-receiving angle of the line sensor 4 is around 10 degrees, which is close to the specular reflection area, microscopic specular reflections are sparsely present, and the index value is large regardless of the presence or absence of streak defects. . On the other hand, when the light-receiving angle of the line sensor 4 was increased, the signal value of the streak defect itself weakened, and the index value decreased regardless of the presence or absence of the streak defect. Then, when the light-receiving angle of the line sensor 4 is 40 degrees and is 30 degrees away from the regular reflection direction (when the difference from the irradiation angle of the line light source 3 is 30 degrees), the index difference due to the presence or absence of the streak defect became the largest. Specifically, when the light-receiving angle of the line sensor 4 was increased from 10 degrees, which is the regular reflection direction, the index began to rise at 30 degrees, reaching a peak at 40 degrees, and then decreased to 50 degrees. As a result, it was confirmed that when the irradiation angle of the line light source 3 is 10 degrees, the difference in the index can be increased when the light receiving angle of the line sensor 4 is within the range of 30 degrees to 50 degrees. Therefore, in this example, since the irradiation angle of the line light source 3 is fixed at 10 degrees, the line sensor 4 is arranged so that the light receiving angle of the line sensor 4 differs from the regular reflection direction within a range of 20 degrees or more and 40 degrees or less. Then, it can often be said that the conditions differing by 30 degrees are the best. For this reason, the difference between the irradiation angle of the line light source 3 and the light receiving angle of the line sensor 4 should be set within the range of 20 degrees or more and 40 degrees or less. As a result, the processing of step S4 is completed, and the series of quantification processing ends.

As is clear from the above description, the defect measuring apparatus 1 according to one embodiment of the present invention includes the line light source 3 that irradiates the surface of the zinc-based plated steel sheet with line illumination light, and the line light that is reflected from the surface of the zinc-based plated steel sheet. and a line sensor 4 for capturing a surface image of the zinc-based plated steel sheet by receiving the line illumination light. It is arranged so as to be within the range of 40 degrees or more. Thereby, it is possible to directly measure a streak-like defect in a short time with a simple optical system.

In addition, various effects can be obtained by using this index to grade the occurrence of streak defects (for example, the degree of appearance, frequency and size of streak defects, etc.) for each product. For example, indicators can be used for pass/fail judgment of products, indicators can be fed back to the operation of the manufacturing process to suppress the occurrence of streak defects, indicators can be combined with various other operational data and handled as large-scale data, Identifying the causes and conditions of occurrence of streak defects by variable analysis, predicting the risk of streak defect occurrence from other operation data, presenting the prediction results to the operation site, and automatically operating using the prediction results. be done.

In addition, the present invention is applied to a defect measuring device that constitutes a manufacturing facility for a zinc-based plated steel sheet, and the zinc-based steel sheet manufactured by a known or existing manufacturing facility is measured by the defect measuring device according to the present invention, and the zinc It is also possible to measure streak-like defects in the system-plated steel sheet. In addition, by applying the present invention to a defect measurement method included in a method for manufacturing a zinc-based steel sheet and providing a measurement step for measuring a zinc-based steel sheet manufactured by a known or existing manufacturing step, the zinc-based coating You may make it measure a line-like defect in a steel plate. According to such a zinc-based plated steel sheet manufacturing facility and metal strip manufacturing method, a zinc-based plated steel sheet can be manufactured with a high yield. Furthermore, by applying the present invention to a quality control method for a zinc-based plated steel sheet and providing a measurement step for measuring the zinc-based steel sheet, the quality of the zinc-based steel sheet can be determined from the measurement result of the streak defect of the zinc-based steel sheet. You may make it manage. According to such a quality control method for a zinc-based plated steel sheet, it is possible to provide a high-quality zinc-based plated steel sheet.

Although the embodiments to which the inventions made by the present inventors are applied have been described above, the present invention is not limited by the descriptions and drawings forming part of the disclosure of the present invention according to the embodiments.

For example, the above embodiment is an example using a cut plate sample, but by applying the present invention to a zinc-based plated steel sheet being transported online, an index of streak defects occurring over the entire length and width of the product, that is, zinc Quantification of the appearance properties of the system plated steel sheet can also be performed online. An application example of the present invention on-line is shown in FIG. In the example shown in FIG. 9, a line light source 3 and a line sensor 4 are installed for the zinc-based plated steel sheet ST being conveyed in the same manner as for the cut plate sample S, and pulse signals are generated by the encoder 6 in accordance with the rotation of the roll R. A surface image of the galvanized steel sheet ST is photographed using the pulse signal as a trigger. At this time, it is preferable to count the pulse values of the encoder 6 so as to be able to compare the occurrence positions of the streak defects. Then, the arithmetic unit 5 calculates the index of the streak defect in real time from the photographed surface image. Further, the arithmetic device 5 obtains information on the zinc-based plated steel sheet ST from the host PC 7 to determine the degree of harm of the index, and transmits the index to the host PC 7 to manage the index of the streak defect. Further, the arithmetic unit 5 calculates the index of the streak defects in the entire length and width of the zinc-based plated steel sheet ST to create an index map. At this time, by setting a threshold, only the image of the part where the streak defect actually occurred is saved. It may be useful for guarantee and factor analysis. Thus, other embodiments, examples, operation techniques, etc. made by those skilled in the art based on this embodiment are all included in the scope of the present invention.

REFERENCE SIGNS LIST 1 defect measuring device 2 linear stage 3 line light source 4 line sensor 5 computing device S cutting plate sample ST galvanized steel sheet

Claims (7)

A defect measuring device for measuring streak defects on the surface of a zinc-based plated steel sheet,
irradiating means for irradiating the surface of the zinc-based plated steel sheet with line illumination light;
an imaging means for capturing a surface image of the zinc-based plated steel sheet by receiving the line illumination light reflected on the surface of the zinc-based plated steel sheet,
The irradiation means and the imaging means are arranged so that the difference between the irradiation angle and the light reception angle of the line illumination light is within a range of 20 degrees or more and 40 degrees or less.
Defect measuring device. computing means for calculating, as an index of the line defect, a feature quantity of the line defect in a direction parallel to the rolling direction of the zinc-base plated steel sheet from the surface image of the zinc-base plated steel sheet;
2. The defect measuring apparatus according to claim 1, wherein said irradiation means is arranged such that the extending direction of said line illumination light is perpendicular to the rolling direction of said galvanized steel sheet. The computing means generates a corrected image in which the luminance unevenness in the vertical direction is corrected from the surface image of the zinc-based plated steel sheet, selects an image of an area including the streak defect from the corrected image, and selects the selected image. 3. The defect measuring apparatus according to claim 2, wherein said index is calculated from an image of a streak defect. A defect measurement method for measuring streak defects on the surface of a zinc-based plated steel sheet,
an irradiation step in which irradiation means irradiates the surface of the zinc-based plated steel sheet with line illumination light;
an imaging step of capturing an image of the surface of the zinc-based plated steel sheet by receiving the line illumination light reflected by the surface of the zinc-based plated steel sheet by an imaging means;
The irradiation means and the imaging means are arranged so that the difference between the irradiation angle and the light reception angle of the line illumination light is within a range of 20 degrees or more and 40 degrees or less.
Defect measurement method. Manufacturing facilities for manufacturing zinc-based plated steel sheets,
The defect measuring device according to any one of claims 1 to 3, which measures the surface of the zinc-based plated steel sheet manufactured by the manufacturing equipment;
A manufacturing facility for zinc-based plated steel sheets. A manufacturing step for manufacturing a zinc-based plated steel sheet;
A measuring step of measuring the surface of the zinc-based plated steel sheet manufactured in the manufacturing step using the defect measuring method according to claim 4;
A method for producing a zinc-based plated steel sheet, comprising: A measurement step of measuring the surface of a zinc-based plated steel sheet using the defect measurement method according to claim 4;
a quality control step of performing quality control of the zinc-based plated steel sheet from the measurement results of the streak-like defects in the measurement step;
A quality control method for a zinc-based plated steel sheet, comprising:

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