JP2021117011A - Surface defect inspection apparatus for metal plate - Google Patents

Abstract

To provide a surface defect inspection apparatus for a metal plate that can detect a clear distinction between the harmfulness and harmlessness of appearance abnormality on the rear surface of a running metal plate.SOLUTION: A surface defect inspection apparatus for a metal plate comprises: a front-side pinch roller (12); a rear-side pinch roller (16) for forming a pass line of a metal plate (14) in between with the front-side pinch roller (12); a rear surface inspection roller (18) for abutting from above against the metal plate (14) on the pass line; a lighting unit (22) for radiating light to an imaging target position (20) formed on the rear surface of the metal plate (14) by the abutment of the rear surface inspection roller (18); and a reflection light imaging unit (24) for imaging the reflection light at the imaging target position (20). A guide roller (30), which is in noncontact with the rear surface inspection roller (18), is arranged between the rear surface inspection roller (18) and the rear-side pinch roller (16). The guide roller (30) lifts the pass line of the metal plate (14) upwards in order to gain momentum.SELECTED DRAWING: Figure 1

Description

In the present invention, a metal plate, which is an object of surface inspection, is irradiated with illumination light from a light source, the reflected light is imaged by an imaging camera, and the signal of the obtained image is processed to inspect surface defects. The present invention relates to a surface defect inspection device for a metal plate.

A type of metal plate, which is a type of steel sheet produced through the annealing process and temper rolling process, has appearance abnormalities that appear on its surface, such as hesitation defects, winding defects, and lateral displacement defects. The steel sheet containing it is a defective product. In the final inspection process of special steel and ordinary steel, unlike plated products and stainless steel products, in order to suppress rust between processes and flaws due to misalignment of coils, cold rolling or temper rolling oil is attached. Need to be inspected. In addition, annealing fringes that are inevitably generated by annealing are also included. A steel sheet containing these abnormal appearances may not be a defective product depending on the product application. Therefore, at the steel sheet manufacturing site, it is required to accurately distinguish these appearance abnormalities.
It should be noted that what is harmful and what is harmless among the various appearance abnormalities described above differs depending on the user of the metal plate. Therefore, what is harmful and what is harmless among the appearance abnormalities is determined by the quality contract between the user and the manufacturer, and the manufacturer has the inspection items and inspection standards according to the contract. It is required to distinguish between harmful and harmless appearance abnormalities.

Conventionally, as a technique of this kind, for example, in the following Patent Document 1 (Japanese Patent No. 6117398), an illumination unit that illuminates an image pickup target portion supported from below by a roll on a traveling steel plate surface. The angle formed by the first diffused reflected light imaging unit that captures the diffusely reflected light in the direction in which the angle formed by the normal reflection direction is the first angle γ and the angle formed by the normal reflection direction is the second angle δ (however, δ). A second diffused reflected light imaging unit that images diffused reflected light in the direction of> γ), a first diffused reflected image signal obtained by imaging by the first diffused reflected light imaging unit, and a second diffused reflected light imaging. The image signal processing unit includes an image signal processing unit that processes a second diffused reflection image signal obtained by imaging the unit, and the image signal processing unit has a brightness lower than a predetermined first threshold value among the first diffused reflection image signals. A surface defect inspection apparatus is disclosed that detects a portion having a second diffused reflection image signal having a brightness higher than a predetermined second threshold value as a surface defect portion.
According to such a technique, it is possible to distinguish between harmful and harmless appearance abnormalities by inspecting a steel sheet whose surface has not been surface-treated such as plating.

Japanese Patent No. 6117398

However, the above-mentioned prior art has the following problems.
As described above, there is no problem when the surface defect of the metal plate is inspected at the part to be imaged formed on the surface (upper surface) of the metal plate by supporting the running metal plate from below with a roll. For example, in order to simultaneously inspect both the front and back surfaces (both upper and lower surfaces) of a traveling metal plate, the metal plate is supported from above with a roll to detect surface defects of the imaging target portion formed on the back surface (lower surface) of the metal plate. At the time of inspection, if the metal plate to be inspected is, for example, a thin material having a high spreadability, there is a problem that the inspection accuracy of the back surface of the metal plate is lowered. To elaborate on this point, the part to be imaged on the metal plate is provided at a position where the pass line supported by the roll is extremely stable, but the traveling metal plate is as in the case of inspecting the back surface of the metal plate. When the roll is pressed against the top to support it, there is nothing to support the metal plate, so the metal plate (supported by the roll from above) hangs down due to its own weight and the path line flutters. Will be. As a result, the reflection level of the signal at the part to be imaged cannot be stabilized, and it is difficult to distinguish between harmful and harmless appearance abnormalities. In order to solve this problem, the pass line may be stabilized by applying back tension to the traveling metal plate, but the metal plate to be inspected has, for example, a Vickers hardness of about 90 to 170 HV and a plate thickness. In the case of thin annealed material of 0.5 mm or less, if back tension is applied to the extent that the pass line is stable, slip flaws will occur due to the urethane pinch roll (with power), or the line will enter and exit. Problems such as difficulty in speed synchronization on the side and inability to operate at high speed occur.

Therefore, an object of the present invention is to provide a surface defect inspection device for a metal plate capable of clearly distinguishing and detecting harmful and harmless appearance abnormalities on the back surface side of the traveling metal plate.

In order to achieve the above object, the present invention comprises, for example, as shown in FIGS. 1 and 2, the surface defect inspection apparatus 10 for a metal plate is configured as follows.
That is, the upper and lower sets of the front pinch rolls 12 and the upper and lower sets of the rear pinch rolls 16 forming a pass line on which the metal plate 14 runs between the front pinch rolls 12 and the front pinch rolls 12 run on the pass lines. The back surface inspection roll 18 that comes into contact with the metal plate 14 from above and the back surface inspection roll 18 that is arranged below the traveling metal plate 14 and that comes into contact with the metal plate 14 are said to be concerned. An illumination unit 22 that irradiates light toward the imaging target portion 20 formed on the back surface of the metal plate 14, a reflected light imaging unit 24 that images the reflected light at the imaging target portion 20, and a reflected light imaging unit thereof. An image signal processing unit 26 for detecting a surface defect portion of the metal plate 14 based on an image signal obtained from the reflected light imaged in 24 is provided. A guide roll 30 that is not in contact with the back surface inspection roll 18 is disposed between the back surface inspection roll 18 and the rear pinch roll 16, and the guide roll 30 is used to cover the metal plate 14 of the metal plate 14. Lift the pass line upward and urge it.

The surface defect inspection device for a metal plate of the present invention has the following effects.
A guide roll is placed between the backside inspection roll and the rear pinch roll, and the guide roll lifts the path line of the metal plate upward to urge it, so the lowest point of the backside inspection roll. A metal plate is wrapped around the front and rear surfaces to form an imaging target portion. As a result, the fluttering of the metal plate is eliminated in the part to be imaged, the reflection level of the signal (reflected light) in the part to be imaged is stable, and the harmfulness and harmlessness of the appearance abnormality on the back surface side of the traveling metal plate are clearly distinguished. It is possible to provide a surface defect device for a metal plate that can be detected.
Further, since the guide roll is not in contact with the back surface inspection roll, the oil applied to the surface of the metal plate is squeezed and dropped to contaminate the reflected light imaging part, the lighting part, etc., or the light of light. It is possible to prevent interference with the shaft.

In the present invention, the diameter of the back surface inspection roll 18 is 100 mm or more, and the winding angle θ1 of the metal plate 14 around the back surface inspection roll 18 at the imaging target portion 20 is 10 ° or more. Is preferable.
Further, of the winding angle θ1 of the metal plate 14 around the back surface inspection roll 18 at the imaging target portion 20, the metal plate 14 travels from the lowest point P1 of the back surface inspection roll 18. It is preferable that the angle θ2 on the downstream side in the direction is 2 ° or more.
In these cases, in addition to the above-mentioned effects becoming more remarkable, the entire surface defect inspection device can be compactly integrated, and the metal plate can be prevented from being warped after passing through the guide roll. Will be able to.

Further, it is preferable that the present invention adds a unique configuration described in an embodiment described later.

It is a flow chart which shows the outline of the surface defect inspection apparatus of the metal plate of one Embodiment in this invention. It is a schematic flow chart which enlarged the main part in FIG. It is a defect information image output when the location where a minute lateral deviation occurs on the front and back of the metal plate is inspected by using the surface defect inspection apparatus of the metal plate of one embodiment of the present invention. This is a defect information image output when a minute lateral deviation occurrence location on the front and back of the metal plate is inspected using a conventional surface defect inspection device for the metal plate.

Hereinafter, the surface defect inspection apparatus for the metal plate of the present invention will be described with reference to the drawings.
FIG. 1 is a flow chart illustrating an outline of a surface defect inspection device 10 for a metal plate according to an embodiment of the present invention. The metal plate surface defect inspection device 10 of the present invention is installed on the pass line of the metal plate 14 in a continuous pickling line, a plating / color coating line, a slitter line, etc., and is harmful to the appearance abnormality appearing on the surface of the metal plate 14. As shown in this figure, front pinch roll 12, rear pinch roll 16, front surface inspection roll 17, back surface inspection roll 18, illumination units 21 and 22, reflected light imaging. It is roughly composed of units 23 and 24, an image signal processing unit 26, an inspection result output unit 28, and a guide roll 30.
The metal plate 14 in the present embodiment is a steel plate, the surface of which has not been plated, and in which oil is adhered.

The front pinch roll 12 is a roll (rotating body) that forms the starting point of the pass line of the metal plate 14 introduced into the surface defect inspection apparatus 10 of the present invention, and abuts on the back surface of the metal plate 14 to support it. The upper and lower rolls 12a on the front side and the upper roll 12b on the front side which is arranged directly above the lower roll 12a on the front side and sends the metal plate 14 sandwiched in cooperation with the lower roll 12a on the front side to the downstream side in the traveling direction. It consists of a set of rolls.

The rear pinch roll 16 is a roll (rotary body) that forms the end point of the pass line of the metal plate 14 introduced into the surface defect inspection device 10 of the present invention, and is in contact with the back surface of the metal plate 14 to support it. The rear lower roll 16a and the metal plate 14 arranged directly above the rear lower roll 16a and sandwiched in cooperation with the rear lower roll 16a are sent to the post-process of the surface defect inspection. It is composed of a pair of upper and lower rolls with a roll 16b.

The surface inspection roll 17 abuts on the back surface of the metal plate 14 running immediately after the front pinch roll 12 among the pass lines formed in the surface defect inspection device 10, supports the back surface, and runs the metal plate. It is a roll (rotating body) for forming an image pickup target portion 19 on the surface of the metal plate 14 so that the metal plate 14 does not shake in the plate thickness direction. The surface inspection roll 17 preferably has a diameter of 100 mm or more. This is because if the diameter of the surface inspection roll 17 is 100 mm or more, it is possible to form an image pickup target portion 19 suitable for inspection of surface defects. In the illustrated embodiment, a hard urethane rubber roll having a diameter of 200 mm is used as the surface inspection roll 17.

The back surface inspection roll 18 comes into contact with the surface of the metal plate 14 running between the surface inspection roll 17 and the rear pinch roll 16 of the pass lines formed in the surface defect inspection apparatus 10. This is a roll (rotating body) for supporting the metal plate 14 from above and forming an image pickup target portion 20 on the back surface of the metal plate 14 so that the metal plate 14 does not shake in the plate thickness direction. Like the front surface inspection roll 17 described above, the back surface inspection roll 18 preferably has a diameter of 100 mm or more. In the illustrated embodiment, the back surface inspection roll 18 also employs a hard urethane rubber roll having a diameter of 200 mm.

Here, the positional relationship between the front surface inspection roll 17 and the back surface inspection roll 18 described above will be described. In the side view, a pair of upper and lower front pinch rolls 12 contacts (front lower rolls that come into contact with each other via the metal plate 14). The contact point between the 12a and the front upper roll 12b) and the contact point of the upper and lower pair of rear pinch rolls 16 (the contact point between the rear lower roll 16a and the rear upper roll 16b that come into contact with each other via the metal plate 14) are connected. The highest point P0 of the front surface inspection roll 17 is arranged above the horizontal line L1 with respect to the horizontal line L1, and conversely, the lowest point P1 of the back surface inspection roll 18 is below the horizontal line L1. Is arranged in. With such a configuration, the metal plate 14 is wound around the surfaces of the front surface inspection roll 17 and the back surface inspection roll 18, and particularly in the surface inspection roll 17, the fluttering of the metal plate 14 is suppressed. The imaging target portion 19 can be formed.

The illumination unit 21 irradiates the image pickup target portion 19 on the surface (upper surface) of the metal plate 14 with illumination light, and as a light source thereof, LED-type line illumination that irradiates the illumination light in the plate width direction of the metal plate 14. Is used. The light source of the illumination unit 21 is not limited to this, and a halogen lamp, a HID lamp, a fluorescent lamp, or the like can be used instead of the LED.
In the metal plate surface defect inspection device 10 of the illustrated embodiment, the illumination unit 21 is a surface 31 (hereinafter, also referred to as “orthogonal surface 31”) orthogonal to the traveling direction of the metal plate 14 at the imaging target portion 19 on the surface of the metal plate 14. It is installed on the upstream side of the metal plate 14 in the traveling direction, and the incident angle α of the illumination light on the surface of the metal plate 14 is set to a predetermined sharp angle with respect to the orthogonal surface 31.

The illumination unit 22 irradiates the image pickup target portion 20 on the back surface (lower surface) of the metal plate 14 with illumination light, and as a light source thereof, illuminates the metal plate 14 in the plate width direction in the same manner as the above-mentioned illumination unit 21. LED type line lighting that irradiates light is used. The light source of the illumination unit 22 is not limited to this, and a halogen lamp, a HID lamp, a fluorescent lamp, or the like can be used instead of the LED.
In the metal plate surface defect inspection device 10 of the illustrated embodiment, the illumination unit 22 is a surface 32 (hereinafter, also referred to as “orthogonal surface 32”) orthogonal to the traveling direction of the metal plate 14 at the imaging target portion 20 on the surface of the metal plate 14. It is installed on the upstream side of the metal plate 14 in the traveling direction, and the incident angle β of the illumination light on the surface of the metal plate 14 is set to a predetermined sharp angle with respect to the orthogonal surface 32.

The reflected light imaging unit 23 captures diffusely reflected light that is not easily affected by oil coating unevenness on the surface of the metal plate 14 among the light reflected by the imaging target portion 19 on the surface of the metal plate 14 by the illumination light emitted from the illumination unit 21. A high resolution CMOS line sensor camera is used. The reflected light imaging unit 23 is not limited to this, and a CMOS area sensor camera, a CCD line sensor camera, or the like can be used instead of the CMOS line sensor camera. Further, the spatial resolution and the density resolution of the reflected light imaging unit 23 are appropriately selected according to the type of appearance abnormality to be detected.
In the present embodiment, the reflected light imaging unit 23 is installed on the downstream side of the metal plate 14 in the traveling direction from the above-mentioned orthogonal surface 31, and among the reflected light from the surface of the metal plate 14, the reflected light is more than the specular reflected light. The low-angle camera 23a that captures the first diffusely reflected light 34 that forms a large angle with the orthogonal surface 31, and the second diffusely reflected light that forms a larger angle between the orthogonal surface 31 than the first diffusely reflected light 34. It is composed of a high-angle camera 23b that captures images of 36. The reflected light imaging unit 23 is not limited to those composed of two types of cameras that capture diffusely reflected light, such as a low-angle camera 23a and a high-angle camera 23b, and for example, one type according to a purpose. It may be configured to capture the diffusely reflected light of the above.

The reflected light imaging unit 24 captures diffusely reflected light that is not easily affected by oil coating unevenness on the surface of the metal plate 14 among the light reflected by the imaging target portion 20 on the surface of the metal plate 14 by the illumination light emitted from the illumination unit 22. As in the case of the reflected light imaging unit 23 described above, a high-resolution CMOS line sensor camera is used. The reflected light imaging unit 24 is not limited to this, and a CMOS area sensor camera, a CCD line sensor camera, or the like can be used instead of the CMOS line sensor camera. Further, the spatial resolution and the density resolution of the reflected light imaging unit 24 are appropriately selected according to the type of appearance abnormality to be detected.
In the present embodiment, the reflected light imaging unit 24 is installed on the downstream side of the metal plate 14 in the traveling direction from the orthogonal surface 32, and among the reflected light from the surface of the metal plate 14, the reflected light is more than the specular reflected light. The low-angle camera 24a that captures the first diffusely reflected light 38 that forms a large angle with the orthogonal surface 32, and the second diffusely reflected light that forms a larger angle between the orthogonal surface 32 than the first diffusely reflected light 38. It is composed of a high-angle camera 24b that captures images of 40. The reflected light imaging unit 24 is not limited to those composed of two types of cameras that capture diffusely reflected light, such as a low-angle camera 24a and a high-angle camera 24b, and for example, one type according to a purpose. It may be configured to capture the diffusely reflected light of the above.

The image signal processing unit 26 processes the image signal obtained by imaging the diffusely reflected light by the reflected light imaging units 23 and 24 to extract the appearance abnormality of the metal plate 14, and further, harmful and harmless of the extracted appearance abnormality. Classification judgment. The image signal processing unit 26 is composed of, for example, an arithmetic processing unit such as a PC (personal computer) or a microcomputer in which various programs necessary for executing appearance abnormality determination logic such as surface defects are stored. As one of the necessary programs, there is a threshold selection program for selecting a threshold value when the image signals obtained by the reflected light imaging units 23 and 24 are binarized.

The inspection result output unit 28 is installed as necessary, and when a harmful appearance abnormality is extracted by the image signal processing unit 26, the fact that the harmful appearance abnormality is detected and the type of the detected harmful appearance abnormality are detected. Is notified to the user of this manufacturing process, the next manufacturing process, and if necessary by means such as display and printing. The inspection result output unit 28 is composed of, for example, a monitor device, a printer device, or the like.

The guide roll 30 is arranged between the back surface inspection roll 18 and the rear pinch roll 16 in a non-contact state with the back surface inspection roll 18, and the metal plate 14 is attached to the back surface inspection roll 18. It is a roll (rotating body) for lifting and urging the pass line upward so that the metal plate 14 does not hang down when the metal plate 14 is supported and formed on the back surface thereof.
In the present embodiment, a hard urethane rubber roll having a diameter of less than 100 mm (more specifically, a diameter of 90 mm) is used as the guide roll 30. By using a roll having a diameter smaller than that of the back surface inspection roll 18 in this way, it is possible to prevent the guide roll 30 from obstructing the path of the second diffusely reflected light 40 toward the reflected light imaging unit 24.

The winding angle θ1 of the metal plate 14 around the back surface inspection roll 18 at the imaging target portion 20 caused by lifting the pass line of the metal plate 14 due to the arrangement of the guide roll 30 is preferably 10 ° or more. .. Here, the winding angle θ1 is from the point P2 where the metal plate 14 and the back surface inspection roll 18 come into contact with each other on the upstream side of the pass line when the guide roll 30 is viewed from the side as shown in FIG. It is a central angle formed at the center C of the back surface inspection roll 18 corresponding to the arc up to the point P3 where the metal plate 14 and the back surface inspection roll 18 are separated on the downstream side thereof.
Further, of the winding angle θ1 of the metal plate 14 around the back surface inspection roll 18 in the imaging target portion 20, the angle θ2 on the downstream side of the metal plate 14 in the traveling direction from the lowest point P1 of the back surface inspection roll 18. Is more preferably 2 ° or more.
By giving the winding angle θ1 as described above, the metal plate 14 is completely free from fluttering at the imaging target portion 20, and the reflection level of the signal (diffuse reflected light 38 and 40 in the case of the present embodiment) at the imaging target portion 20. Is even more stable, and it is possible to more clearly distinguish and detect harmful and harmless appearance abnormalities on the back surface side of the traveling metal plate 14. In addition, the entire surface defect inspection apparatus can be compactly assembled, and it is possible to prevent the metal plate 14 from being warped after passing through the guide roll 30.

In this embodiment, the guide roll 30 is installed at the following position in order to realize the winding angle θ1 as described above. That is, the uppermost point P4 of the guide roll 30 is located above the lowest point P1 of the back surface inspection roll 18, and the pass line L2 from the back surface inspection roll 18 to the rear pinch roll 16 is tangent to the guide roll 30. The guide roll 30 was placed at a height at which it could be lifted by 7 mm at the position (h). Further, the point P5 on the most upstream side of the pass line on the guide roll 30 is arranged so as to be located slightly upstream of the point P6 on the most downstream side of the pass line on the back surface inspection roll 18.

Of the elements (members) constituting the surface defect inspection device 10 for the metal plate of the present invention as described above, all the other components except the image signal processing unit 26 and the inspection result output unit 28 are frames (not shown). It is attached to such as, and is configured as one unit.

Next, except that the surface defect inspection device 10 of the present embodiment provided with the guide roll 30 as described above (hereinafter referred to as “the device of the present embodiment”) and the guide roll 30 are not provided. The difference in the surface defect detection ability between the surface defect inspection apparatus having the same configuration as that of the embodiment (hereinafter referred to as “conventional apparatus”) will be described.
FIG. 3 is a defect information image output by inspecting a portion where a minute lateral displacement occurs on the metal plate 14 using the apparatus of this embodiment, and FIG. 4 is a defect information image output using the conventional apparatus. This is a defect information image output by inspecting a portion where a minute lateral displacement defect has occurred.
Here, the minute lateral displacement defect is a minute defect that occurs when the layers are rubbed against each other in a state where the metal plate 14 is wound up in a coil shape, and occurs on both the front and back surfaces of the metal plate 14. Further, the minute lateral displacement flaws are mainly localized in the form of expanding in the width direction of the metal plate 14 (the portion surrounded by the oblong ellipse in FIGS. 3 and 4 is the minute lateral displacement flaw). As shown in the upper right frame of FIG. 3, the silhouette of the minute lateral deviation imaged by the reflected light imaging units 23 and 24 of the present embodiment device and the conventional device is clear in the low angle cameras 23a and 24a. The silhouette is imaged in an unclear shape (below the trace level) with the high-angle cameras 23b and 24b.

In the apparatus of this embodiment, as shown in FIG. 3, minute lateral deviation defects can be detected on both the front and back surfaces of the metal plate 14. On the other hand, in the conventional apparatus, as shown in FIG. 4, a minute lateral deviation can be detected on the front side of the metal plate 14, but a minute lateral deviation cannot be detected on the back side. Looking at the low-angle camera image and the high-angle camera image shown in the upper right frame of FIG. 4, the image of the portion detected as a defect is different from that of the minute lateral deviation shown in the upper right frame of FIG. Is. As described above, the reason why the conventional device could not detect the minute lateral deviation of the back surface of the metal plate 14 is that the running of the metal plate 14 flutters during the back surface inspection of the metal plate 14 and the path line is not stable, and the image signal. It can be mentioned that the processing unit 26 could not set a strict threshold value. Therefore, by using the present embodiment, it is possible to set a strict threshold value on the back surface as well as on the front surface, so that high inspection accuracy can be realized.

In the above-described embodiment, the front surface inspection roll 17 and the back surface inspection roll 18 are arranged in this order from the upstream side to the downstream side of the pass line of the metal plate 14, but it is necessary. If not, the surface inspection roll 17 and the illumination unit 21 and the reflected light imaging unit 23 incidental thereto may be omitted.
Further, the back surface inspection roll 18 and the front surface inspection roll 17 may be arranged in this order from the upstream side to the downstream side of the pass line of the metal plate 14. In this case, instead of providing a separate guide roll 30, the surface inspection roll 17 may be adjusted so that it can also be used as the guide roll 30.

In addition, it goes without saying that the present invention can make other changes within the range that can be assumed by those skilled in the art.

10: Metal plate surface defect detection device, 12: Front pinch roll, 14: Metal plate, 16: Rear pinch roll, 18: Back surface inspection roll, 20: Image target part, 22: Illumination part, 24: Reflected light Imaging unit, 26: image signal processing unit, 28: inspection result output unit, 30: guide roll, P1: lowest point of back surface inspection roll.

Claims (3)

A pair of upper and lower front pinch rolls (12) and a pair of upper and lower rear pinch rolls (16) forming a path line on which a metal plate (14) runs between the upper and lower set of front pinch rolls (12) and the above. A back surface inspection roll (18) that comes into contact with the metal plate (14) running on the pass line from above, and a back surface inspection roll (18) that is arranged below the metal plate (14) that runs. An illumination unit (22) that irradiates light toward an image pickup target portion (20) formed on the back surface of the metal plate (14) when the metal plate (14) comes into contact with the metal plate (14), and the above image pickup. The metal plate (14) described above is based on an image signal obtained from a reflected light imaging unit (24) that captures the reflected light at the target portion (20) and the reflected light imaged by the reflected light imaging unit (24). In a surface defect inspection device for a metal plate provided with an image signal processing unit (26) for detecting a surface defect portion,
A guide roll (30) that is in non-contact with the back surface inspection roll (18) is arranged between the back surface inspection roll (18) and the rear pinch roll (16), and the guide roll (30) is arranged. At 30), the pass line of the metal plate (14) is lifted upward and urged.
A surface defect inspection device for metal plates. In the surface defect inspection apparatus for the metal plate of claim 1,
The diameter of the back surface inspection roll (18) is 100 mm or more, and the diameter is 100 mm or more.
The surface of the metal plate, characterized in that the winding angle (θ1) of the metal plate (14) around the back surface inspection roll (18) at the imaging target portion (20) is 10 ° or more. Defect inspection equipment. In the surface defect inspection apparatus for the metal plate of claim 2,
Of the winding angle (θ1) of the metal plate (14) around the back surface inspection roll (18) at the imaging target portion (20), the lowest point of the back surface inspection roll (18). A surface defect inspection device for a metal plate, characterized in that the angle (θ2) on the downstream side in the traveling direction of the metal plate (14) from (P1) is 2 ° or more.

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