JP7276263B2 - Surface inspection device - Google Patents

Description

TECHNICAL FIELD The present invention relates to an apparatus for detecting surface defects in a hot-rolled steel sheet, and more particularly to a surface inspection apparatus for detecting convex defects in a steel sheet caused by flaws in rolling rolls.

Roll flaws exist in the rolling process of hot-rolled steel sheets, and the recognition rate of the flaws changes depending on the type and size of the unevenness. Among them, convex defects with a light degree have the lowest detection rate. For example, in Patent Document 1, it is reported that the defect detection rate increases by irradiating obliquely in the plate width direction with two or more lights as shown in FIG. 9 in the equipment arrangement shown in FIG. .

This roll flaw is a product defect in which a pitch-like flaw is transferred to the steel sheet being rolled due to a defect on the surface of the rolling roll. If a flaw occurs, it is necessary to prevent transfer to the next material by replacing the rolling roll. .

Therefore, it is very important to improve the defect recognition rate so that the roll can be replaced immediately, and the occurrence of product defects can be minimized, and at the same time, the yield can be improved.

In the apparatus disclosed in Patent Document 2, as shown in FIG. 10, an optical system is proposed in which the steel plate 1 of the object to be inspected, the strobe illumination 2 of the light-projecting part, and the area camera sensor 3 of the light-receiving part are arranged at the positions of specular reflection. It is

JP 2006-177789 A Japanese Patent Application Laid-Open No. 2001-111759

However, in the case of an inspection apparatus in which the light projecting part has diffuse irradiation, the detection rate for each light receiving part corresponding to the plate width direction of the object to be inspected is not uniform as shown in FIG. The convex defect detection rate may decrease at positions where the light-receiving part and the light-receiving part are aligned, that is, positions of specular reflection (for example, 6a and 8b, 6b and 8d, and 6c and 8f in FIG. 1(a)). It turns out.

Moreover, although Patent Document 1 states that the optimum light projection angle of the optical system is 20°, this evaluation is based on the assumption that the optical system is installed downstream of the pinch roll 4 shown in FIG. 8 . Furthermore, the light projection pattern in the width direction in the evaluation of the pinch roll upstream side is limited to only two types, 0° and 20°, and the signal intensity in each width direction is not mentioned.

When the distance between the light projecting part and the object to be inspected is 2000 mm and the diffusivity of the light from the light projecting part is defined as 1/2 of the peak value, the light projecting part is positioned at an angle of 25° to the width direction of the inspection band. It has more diffusibility. Therefore, for equipment having a plurality of light projection units, not only the angle evaluation by one light projection unit, but also the oblique light angle in the width direction of the light projection unit and the ratio of the signal S and the noise N (hereinafter referred to as S /N ratio) must be clarified for each width position.

Patent document 2 aims to improve the defect detectability by detecting the specular reflection component of the light from the light emitting unit and the light receiving unit, based on the relationship between the specular reflection positions of the light emitting unit and the light receiving unit. The detection rate was not sufficient for this purpose.

SUMMARY OF THE INVENTION The present invention has been made in view of the above circumstances, and provides an apparatus for uniformly detecting surface defects of hot-rolled steel sheets, particularly convex defects of steel sheets caused by scratches on rolling rolls. The purpose is to

The inventors searched for the optimum light projection angle from the surface properties of convex defects, and since the specular reflection component from the light projection part reduces the detection rate of the light reception part, by installing a light shielding plate, it is possible to improve the rolling process. It has been found that convex defects on an object to be inspected can be uniformly detected in the plate width direction regardless of the position of the light-receiving part.

In order to solve the above-described problems and achieve the object, a first surface inspection apparatus according to the present invention includes a light projecting unit that irradiates light onto an inspection target surface of an object to be inspected and a light receiving unit that receives reflected light. , wherein the light emitting unit and the light receiving unit are installed behind the rolling rolls and before the rolls that compress or sandwich the object to be inspected, wherein the optical axis of the light receiving unit is the object parallel to the rolling direction of the object to be inspected and perpendicular to the surface to be inspected; It is characterized by installing a light shielding plate for blocking component light in a vertical plane.

A second surface inspection apparatus according to the present invention comprises a light projecting section for irradiating light onto an inspection target surface of an object to be inspected and a light receiving section for receiving reflected light, the light projecting section and light receiving section comprising: A surface inspection apparatus installed downstream of rolling rolls and upstream of rolls for compressing or nipping an object to be inspected, wherein the optical axes of the light projecting part and the light receiving part are not in a regular reflection relationship with each other, and the light receiving part The optical axis of the part is parallel to the rolling direction of the object to be inspected and is inclined in a plane perpendicular to the surface to be inspected, and the light projecting part is arranged for rear irradiation.

Further, in the surface inspection apparatus according to the present invention, it is a more preferable solution that the light projecting unit irradiates light from a direction of 25 to 45 degrees with respect to a perpendicular line to the surface to be inspected in cross-sectional view in the width direction. considered to be obtained.

ADVANTAGE OF THE INVENTION According to this invention, even a slight convex defect of a hot-rolled steel plate can be uniformly and accurately detected in the width direction of the steel plate.

(a) It is a graph comparing the detection rate in the width direction when inspecting an object having a convex defect using a conventional surface inspection apparatus, and (b) the positional relationship between the light emitting unit and the light receiving unit. It is a conceptual diagram showing It is an enlarged micrograph showing an example of a convex defect. An example of observing a convex defect by changing the light projection direction, (a1) shows a conceptual diagram in which the light projection part is arranged along the rolling direction, (a2) is an observation photograph thereof, and (b1) shows a conceptual diagram in which a light projecting part is arranged in a direction orthogonal to the rolling direction, and (b2) is an observation photograph thereof. FIG. 2 is a conceptual diagram of an apparatus for confirming the influence of the tilt angle θ of the light source on the detection of convex defects, (a) showing a perspective view, and (b) a cross-sectional view in the width direction (AA view). shows a conceptual diagram of 4 is a graph showing the influence of the tilt angle θ of the light source on the detection of convex defects. FIG. 4 is a diagram showing a light projection pattern having a plurality of light projection parts; FIG. 7 is a graph showing results detected with each light projection pattern in FIG. 6. FIG. It is a side schematic diagram which shows the equipment arrangement which installed the conventional surface inspection apparatus. It is a schematic diagram which shows the projection angle of the conventional surface inspection apparatus. It is a schematic diagram which shows the positional relationship of the to-be-tested object of the conventional surface inspection apparatus, a light-projection part, and a light-receiving part.

The inventors observed the surface of the defect portion to detect the convex defect. Defective samples were selected that could not be detected by existing surface inspection equipment, and the samples were cut by passing them through in the skin-pass process in an unpressurized state.

As a result, as shown in FIG. 2, it was found that the convex defect portion was an aggregate of fine uneven defects along the rolling direction. FIG. 3 shows a conceptual diagram when the light projection direction is set along the rolling direction F (a1) and in a direction (b1) perpendicular to the rolling direction F, and camera imaging results (a2, b2) of the respective light receiving units. As is clear from FIG. 3, it was found that oblique light in the direction perpendicular to the rolling direction is effective. The above knowledge is also described in Patent Document 1, but this minute defect is obtained by locally pressing the convex defect portion with a pinch roll 4 in FIG. However, it was positioned as the occurrence of fine unevenness.

However, the hot-rolled steel sheet itself has a convex crown of 20 μm or more, and the roll center itself of the pinch roll also has a convex crown of 500 μm for a defect having a convex amount of about 10 μm. From the above facts, it is considered that the central portion of the width of the hot-rolled steel sheet is pressed by 520 μm or more compared to the edges. Therefore, the width center of the hot-rolled steel sheet does not show minute changes in the roughness of the surface layer as compared with the edges. In addition, the thickness of the hot-rolled steel sheet itself fluctuates, and even if the pinch roll load fluctuates by about 3 to 5 tf, the surface properties in the longitudinal direction do not change. In other words, since it is difficult to imagine that pinch rolls will cause fine irregularities, it is considered that the fine irregularities in the defective portion have already been produced by the work rolls of the finishing mill 1 in FIG.

From the above results and considerations, it was considered that the convex defect causes diffuse reflection due to oblique light in the width direction, and the S/N ratio improves toward the bright side (FIG. 3(b2)). Further, it can be seen that when the light-receiving portion receives specularly reflected light that is stronger than diffusely reflected light, the defective portion is mixed with the non-defective portion (FIG. 3(a2)). This is clear when comparing the actual defect detection rate from the positional relationship between the light receiving sections 8a to 8g and the light sources 6a to 6c as shown in FIG. The situation where the position, the light emitting part, and the light receiving part are aligned on a straight line is consistent. In other words, it indicates that part of the light-receiving units receive the specularly reflected light due to the diffusion component of the light possessed by the light-projecting unit, thereby lowering the defect detection rate.

Based on the above, confirmation experiments were conducted in order to clarify the optimum oblique light angle in the width direction.
First, assuming that the inspection device is installed upstream of the pinch roll 4, the flat portion in the minute irregularities generated downstream of the pinch roll 4 is not measured. FIG. 4(a) shows a schematic perspective view of the arrangement of the inspection device 3. As shown in FIG. FIG. 4(b) shows the arrangement of each device in cross-sectional view (A--A view) in the width direction (W). In this apparatus, the defect was irradiated with a single light projection, and the S/N ratio was evaluated when the optical axis 62 of the light projection unit 6 was tilted with respect to the normal to the surface to be inspected. FIG. 5 is a graph showing the results, showing the angle (light source angle) .theta. The N ratio relationship is shown graphically. The results of different samples under the same test conditions are shown as Sample A (○) and Sample B (Δ). As a result, it was confirmed that the S/N ratio of the convex defect was improved when the light source angle θ was in the range of 25 to 45°.

Next, as shown in FIG. 6, a plurality of inspection apparatus patterns having two or more light projection units 6 were prepared, and the S/N comparison of the convex defect portion with the optical system of the existing technology was performed as shown in FIG. Regarding the notation of FIG. 9, the number of each light projecting unit 6 is the number of numerical values in parentheses, and is separated by commas [,]. Hereinafter, the left side with respect to the strip traveling direction is defined as the operation side, and the right side as the drive side, and the leftmost number in parentheses is the operation side, and the rightmost number is the drive side. In addition, the angle θ [°] formed by the optical axis 62 of the light projecting part and the perpendicular to the surface to be inspected in the cross section in the width direction (W) is indicated numerically, and the irradiation toward the operation side is indicated as a negative [-]. , the irradiation toward the drive side is denoted as positive [+]. Next, as an example, the notation of (+25, , -25) indicates that there are two light projection units. The optical axis 62 of the light projecting unit 6 located on the operation side is tilted at 25° with respect to the perpendicular line to the surface to be inspected in the cross section in the width direction (W) and irradiates toward the drive side. On the other hand, the optical axis 62 of the light projecting unit 6 located on the drive side is tilted at 25° with respect to the perpendicular line to the surface to be inspected in the cross section in the width direction (W) and irradiates toward the operation side. The light receiving portions 8 are arranged as 8a, 8b, 8c, 8d, 8e, 8f, and 8g from the operation side. The optical axis 62 of the light projecting part 6 is inclined by 10° with respect to the axis perpendicular to the surface to be inspected in the cross section in the rolling direction (F), and the optical axis 81 of the light receiving part 8 is in the cross section in the rolling direction (F) to be inspected. It is tilted by 3° with respect to the axis perpendicular to the surface. The optical axes 62 and 81 of both the light projecting section 6 and the light receiving section 8 are inclined toward the finishing mill 1 side. Also, the distance from the light projecting unit 6 to the inspection object 9 was fixed at 3100 mm.

In FIG. 7, 0 (○) is the result for the prior art, which is the pattern (−25, 0, +25) of the light projecting unit 6 shown in FIG. It has been found that the S/N ratio decreases when 9 is on a straight line (specular reflection position). This agrees with the microscopic observation result (FIG. 3(a2)) in which the convex defect part is mixed with the texture of the hot-rolled steel sheet when the specular reflection component is strong. It was confirmed that the actual detection rate and the trend in FIG. 1(a) coincided.

7 <0-a> to <0-e> show a comparison of the projection patterns of FIGS. 6(a) to (e) with the projection pattern of 0. FIG. By changing the light projection pattern of FIG. 6(a) from three light projection parts to two light projection parts, the regular reflection component at the center part is reduced and the detection capability of the light receiving part 8d is improved. The detection capability of the receivers 8b and 8f receiving the components remained degraded. In the projection pattern of FIG. 6(b), by tilting the light projecting portion 6 further in the width direction, the intensity of the regular reflection component of each light receiving portion 8 is reduced, and the S/N ratio is uniformly improved. However, it was confirmed that some regular reflection components were included in the measurement range of the light receiving units 8b to 8f. In the light projection pattern of FIG. 6(c), by installing the light shielding plate 10 in the light projection part 6, the specular reflection component could be removed without lowering the S/N ratio. The light projection pattern of FIG. 6D is an inspection pattern having four light projection parts 6 to ensure the amount of light. It was not realistic because the cost of system modification when changing from three light projection units to four light projection units was high. FIG. 6(e) shows an inspection pattern in which the light-projecting part is largely moved by one in the width direction. Since the cost of indoor foundation work would increase, we abandoned the consideration of FIGS. 6(d) and 6(e).

From the principle, the surface inspection apparatus in the present embodiment reduces the inspection object (for example, hot-rolled steel strip) in which the roll flaws are generated in the rear stage of the rolling rolls that cause the roll flaws to be detected. Alternatively, it is preferably installed in the preceding stage of the sandwiching rolls.

1 Finishing rolling mill 2 Cooling band 3 Detecting device 4 Pinch roll 5 Down coiler 6 Light projection parts 6a, 6b, 6c Light projection part 61 Light flux 62 Optical axis of light projection part (light projection direction)
7 Metal band (object to be inspected)
8 light-receiving parts 8a, 8b, 8c, 8d, 8e, 8f, 8g light-receiving part 81 optical axis of light-receiving part 9 sample piece (object to be inspected)
10 Light shielding plate D Convex defect part DD Defect part S caused by rubbing between plates Non-defect part F Rolling direction W Width direction

Claims (3)

A light projecting part for irradiating light onto an inspection object surface of an object to be inspected and a light receiving part for receiving reflected light are provided, and the light projecting part and the light receiving part are arranged behind the rolling rolls and the object to be inspected is rolled down or sandwiched. A surface inspection device installed in the front stage of the roll to
The optical axis of the light-receiving part is parallel to the rolling direction of the object to be inspected and is inclined in a plane perpendicular to the surface to be inspected, and is inclined toward the rolling roll with respect to the axis perpendicular to the surface to be inspected. configured as
The light projecting part irradiates diffused light from a direction of 25 to 45° with respect to a perpendicular line to the inspection target surface in a cross-sectional view in the width direction, and the optical axis of the light projecting part is directed to the inspection target surface in the rolling direction cross section. configured to tilt toward the rolling roll with respect to the vertical axis,
A surface inspection apparatus according to claim 1, wherein said light projecting portion is provided with a light blocking plate for blocking component light in a plane parallel to the rolling direction of said object to be inspected and perpendicular to said surface to be inspected. the optical axis of the light-receiving unit is inclined by 3° toward the rolling roll with respect to the axis perpendicular to the surface to be inspected;
2. The surface inspection apparatus according to claim 1, wherein the optical axis of said light projecting section is inclined by 10 degrees toward said rolling roll with respect to an axis perpendicular to said surface to be inspected in a cross section in the rolling direction. 3. The surface inspection apparatus according to claim 1, wherein said light projecting part is not arranged in the center of the inspection target surface of said object to be inspected, but is arranged on both end sides thereof.

Images