JP2003075381A - Defect detector and method for detecting defect of metal band, computer program therefor, and computer- readable storage medium - Google Patents

Abstract

PROBLEM TO BE SOLVED: To allow automation and to surely detect a defect such as a surface flaw. SOLUTION: This detector is provided with a laser irradiation device 1 for emitting a laser 103 band-likely to provide a uniform energy distribution along a sheet-width direction of a surface of a steel sheet 101, and an infrared detector 2 for measuring a sheet-width-directional surface temperature distribution of the steel sheet 101 heated by the laser irradiation device 1, in a conveying- directional downstream of the laser irradiation device 1. Since the surface of the steel sheet 101 is heated uniformly along the sheet-width direction by the bandlike laser 103, a temperature gets substantially uniform in a portion where no defect such as the surface flaw 102 exists, and a temperature change is generated in a portion where the defect exists, because of an influence thereof. The presence of the defect such as the surface flaw 102 is determined by an information processing part 3, based on the surface temperature distribution detected by the infrared detector 2.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a defect detection device, method, computer program, and computer-readable storage medium for detecting defects such as surface flaws in metal strips such as steel plates.

[0002]

2. Description of the Related Art In a steel plate production line in the steel industry, in order to ensure the quality of the steel plate, defect inspection is performed to inspect defects such as surface defects of the steel plate. As such a defect inspection, a visual inspection by an inspection engineer on site is adopted as the most reliable method. Further, many methods have been proposed in which the presence or absence of a surface flaw is determined by irradiating the surface of a steel sheet with light and detecting the change in the characteristic amount of the reflected and scattered light.

[0003]

However, the above-described method of being visually inspected by an inspection engineer imposes a human burden, and the detection accuracy is changed due to the depth of experience of the inspection engineer, fatigue of long-time work, and the like. As a result, it becomes difficult to ensure reliable quality assurance.

Further, in the method of irradiating light and detecting the change in the characteristic amount of the reflected and scattered light, the accuracy of detecting a relatively large flaw is high, but for example, a minute flaw having a flaw width of several mm or less should be detected. Is very difficult, especially on high speed transport lines. Also, if the surface of the steel sheet is oxidized and covered with an oxide film, most of the irradiated light will be absorbed,
The detection accuracy becomes worse.

The present invention has been made in view of the above points, and it is an object of the present invention to enable automation and to reliably detect defects such as surface defects.

[0006]

SUMMARY OF THE INVENTION A metal band defect detecting device of the present invention is a metal band defect detecting device for detecting a defect in a metal band, which comprises irradiating a laser on the surface of the metal band. A laser irradiation means for heating, a temperature distribution detecting means for detecting a surface temperature distribution in a range heated by the laser, and a judging means for making a defect judgment based on the surface temperature distribution detected by the temperature distribution detecting means. It has a feature in that it is equipped.

The metal band defect detection method of the present invention is
A method for detecting defects in a metal band for detecting defects in the metal band, comprising: a laser irradiation procedure for irradiating a surface of the metal band with a laser for heating; and detecting a surface temperature distribution in a range heated by the laser. It is characterized in that it has a temperature distribution detecting procedure and a judging procedure for making a defect judgment based on the surface temperature distribution detected by the temperature distribution detecting procedure.

Further, the computer program of the present invention uses laser irradiation means for irradiating the surface of the metal strip with a laser to heat it, and temperature distribution detection means for detecting the surface temperature distribution in the range heated by the laser. And a computer program for executing a process for detecting a defect in the metal strip, characterized by causing a computer to execute a determination process for performing a defect determination based on a surface temperature distribution detected by the infrared detecting means. Have.

[0009]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of a metal band defect detection apparatus, method, computer program, and computer-readable storage medium according to the present invention will be described below with reference to the drawings.

(First Embodiment) FIG. 1 shows an outline of a metal band defect detecting apparatus according to the first embodiment.
4B is a view of the side surface of the conveyed steel plate 101, and FIG. In addition, in FIG.
7 shows a flow of defect detection processing in the embodiment. Note that FIG. 1 shows a state in which a surface flaw 102 having a certain width extends long parallel to the transport direction on the surface of the transport steel plate 101 (metal strip). Defects such as surface flaws formed after rolling are often caused by long stretching of pinholes and inclusions inside the steel sheet, and are generally extended in the rolling direction (conveying direction).

In FIG. 1, reference numeral 1 denotes a laser irradiation device, and as shown in FIG. 1B, the laser 103 is band-shaped in the plate width direction of the surface of the steel plate 101, that is, a uniform energy distribution is obtained in the plate width direction. The rectangular laser 103 is irradiated so as to be obtained (step S1 in the flowchart of FIG. 2). A CO ₂ laser, a YAG laser, a semiconductor laser, or the like may be used as the laser.

Reference numeral 2 denotes an infrared detector, which measures the surface temperature distribution in the plate width direction of the steel plate 101 heated by the laser irradiation device 1 on the downstream side of the laser irradiation device 1 in the conveying direction (in the flowchart of FIG. 2). Step S2).

An information processing unit 3 includes an input unit 3a and a determination unit 3b. Surface temperature distribution information in the width direction of the steel plate 101 measured by the infrared detection device 2 is input to the input unit 3a. Then, in the determination unit 3b, the steel plate 1
01 Surface flaw 1 based on the surface temperature distribution information in the plate width direction
Whether there is a defect such as 02 is determined (step S3 in the flowchart of FIG. 2).

FIG. 3 shows an example of the surface temperature distribution in the plate width direction in the case where the defect (surface flaw 102) shown in FIG. 1 exists. The surface of the steel plate 101 is a band-shaped laser 10.
Since it is heated uniformly in the plate width direction by 3 as shown in the figure, the temperature becomes almost uniform at the location where the surface flaw 102 does not exist, whereas at the location where the surface flaw 102 exists, as shown in FIG. A temperature change occurs due to the influence (see arrow a). Therefore, the determination unit 3b of the information processing unit 3
In, for example, if there is a temperature change that exceeds a certain threshold value, it can be determined that a defect exists in the changed portion.

As described above, in the defect detecting apparatus of this embodiment, the surface of the steel plate 101 is heated by the laser,
Defects such as surface defects can be detected by capturing the surface temperature change in the plate width direction. Therefore, it becomes possible to automate the defect detection without imposing a human burden, and the temperature change will surely appear even in the case of a defect such as a minute surface flaw. The accuracy can be increased. Further, even if the surface of the steel sheet 101 is oxidized and covered with an oxide film, there is no problem due to absorption as in the detection method using reflected light, so that defects can be detected reliably. Becomes Rather,
Since the absorption rate of laser is improved in the case of oxide steel sheet,
The detection accuracy can be increased even with a laser having a relatively low output.

Moreover, since the laser is used, the steel plate 101
The surface can be heated uniformly. As a heating method, for example, induction heating may be considered, but in the case of induction heating, it is difficult to uniformly heat the surface of the steel sheet, and the inside of the steel sheet is also heated depending on the frequency. The heat inside the steel plate has a considerable effect on the temperature of the steel plate surface, and as a result, the surface temperature distribution is promptly homogenized and the effects of defects such as surface flaws are negated. May be low. In order to prevent this, it is necessary to perform induction heating at an extremely high frequency, but an apparatus therefor becomes expensive, and the influence of material change due to surface overheating cannot be ignored. On the other hand, in the laser heating, the surface of the steel plate 101 can be uniformly heated in the plate width direction in a line shape, and the influence of defects such as surface defects can be clearly detected, and the risk of overheating is small. In particular, when a semiconductor laser is used, it is possible to significantly reduce the cost as compared with the conventional CO ₂ laser or YAG laser due to the progress of the semiconductor laser technology in recent years.

(Second Embodiment) In the first embodiment, the infrared detector 2 is arranged on the downstream side of the laser irradiation device 1 in the conveying direction.
There is temperature unevenness on the surface, and the temperature distribution is not uniform. Therefore, especially when the original temperature unevenness is large, it becomes difficult to capture the singular temperature due to the above-described defects such as surface defects.

Therefore, in the second embodiment, as shown in FIG. 4, the infrared detector 4 is arranged not only on the downstream side of the laser irradiation device 1 in the conveying direction but also on the upstream side thereof. That is, the infrared detection devices 2 and 4 are arranged on the upstream and downstream sides of the laser irradiation device 1 and the measurement positions measured by the infrared detection devices 2 and 4 are synchronized.

Then, in the calculation unit 3c of the information processing unit 3, the surface temperature distribution (before heating) measured by the infrared detection device 4 on the upstream side (before heating) and the infrared ray on the downstream side at the same measurement position of the conveyed steel plate 101. The difference from the surface temperature distribution (after heating) measured by the detection device 2 is obtained. And
The determination unit 3b determines the presence or absence of a defect such as the surface flaw 102 based on the difference information of the surface temperature distribution. Thereby, the temperature deviation after the laser heating with respect to the original temperature unevenness of the steel plate 101 can be captured, the influence due to the temperature unevenness can be removed, and the temperature change due to the influence of defects such as surface defects can be emphasized.

In the first and second embodiments described above, the detection of the presence / absence of a defect has been mainly described, but it is also possible to perform more specific detection as described below.

For example, by continuously detecting defects at regular time intervals Δt and capturing the surface temperature distribution in the plate width direction at regular intervals in the longitudinal direction of the steel plate, the length of defects such as surface defects in the conveying direction can be determined. It is also possible to estimate. Figure 5
As shown in (A), the surface temperature distribution in the plate width direction at a certain time t (in the case of the second embodiment, the surface temperature deviation distribution) is detected, and defects such as surface defects are detected. And After that, as shown in FIG. 5B, Δt, 2Δ
If the same surface temperature distribution in the plate width direction (surface temperature deviation distribution in the case of the second embodiment) is continuously detected while t, ... LP
Then, the length of defects such as surface defects in the transport direction is (nΔt ×
LP).

Further, it is possible to estimate not only the presence or absence of a defect but also the type of the defect. FIGS. 6, 8 and 10 show isothermal deviation distribution diagrams when a defect exists. The horizontal axis represents the plate width [m], and here, the plate width is 0.03 m to 0.
The part of 07m is extracted. Further, the vertical axis represents the distance [m] from the laser irradiation end point, and here, the portion of the distance 0.2 m to 0.4 m from the end point is extracted. The numbers displayed in the figure show the temperature difference between before laser irradiation (before heating) and after laser irradiation (after heating). Further, the transport speed of the steel sheet is 360 mpm.

FIG. 6 shows the results when there is a defect in which alumina-based inclusions having a depth of about 0.8 mm are caught in the surface of the steel sheet. (A) shows laser irradiation of 2 × 10 ⁶ W / m ² . 2B shows the case where laser irradiation of 2 × 10 ⁷ W / m ² (slit width of about 20 mm) was performed. As shown in FIG. 7, alumina-based inclusions 104 are present on the surface of the steel plate 101 at a position near 0.05 m in the plate width direction.

In this case, since the thermal conductivity of the alumina-based inclusions 104 is smaller than that of the steel sheet 101, the heat is localized near the surface when laser heating. Further, since the heat capacity of the alumina-based inclusions 104 is smaller than that of the steel sheet 101, the temperature drop due to the rapid heat removal from the surface after passing through the laser heating region causes a decrease in the temperature of the steel sheet 1.
01 is larger than the surface. For this purpose, the steel plate 101
In the plate width direction of the surface, the temperature rise is lower in the range where the alumina-based inclusions 104 are present (range x) than in the range where the alumina-based inclusions 104 are not present (range y). Therefore, as shown in FIG. 6, the result is that the surface temperature deviation is low at a position near the plate width of 0.05 m.

FIG. 8 shows the result when there is a defect in which alumina inclusions are buried at a depth of about 0.8 mm from the surface of the steel sheet. (A) shows laser irradiation of 2 × 10 ⁶ W / m ^2. In this case, (B) shows the case of laser irradiation of 2 × 10 ⁷ W / m ² . As shown in FIG. 9, the alumina-based inclusions 104 are present inside the surface of the steel plate 101 at a position near 0.5 m in the plate width direction of the steel plate 101.

In this case, the steel plate 1 is heated by laser heating.
01 in the width direction of the surface plate
In comparison with the rate at which heat is transferred from the surface of the steel sheet 101 to the inside in the range (range y) where no
In the range (range x) in which is present, the rate of heat transfer from the surface of the steel plate 101 to the inside is small. That is, the alumina-based inclusions 104 function as a heat insulating material, and the surface temperature of the upper part thereof is in the range y where the alumina-based inclusions 104 do not exist.
Since it is less likely to decrease than the surface temperature of, the surface temperature deviation becomes high at a position near the plate width of 0.05 m, as shown in FIG.

FIG. 10 shows a depth of about 0.8 mm from the surface of the steel plate.
2 shows the result when there is a defect in which a cavity exists at a position,
The case where laser irradiation of × 10 ⁶ W / m ² is performed is shown. Figure 11
As shown in FIG. 3, a cavity 105 exists inside the surface of the steel plate 101 at a position near 0.05 m in the plate width direction of the steel plate 101.

Also in this case, as in the case described with reference to FIGS. 8 and 9, the cavity 105 functions as a heat insulating material, and the surface temperature of the upper portion thereof is less likely to decrease than the surface temperature in the range y where the cavity 105 does not exist. Therefore, as shown in FIG. 11, a result that the surface temperature deviation becomes high at a position near the plate width of 0.5 m is obtained. In particular, since the cavity 105 has a higher heat insulating property than the alumina-based inclusion 104, the influence of the cavity 105 as a heat insulating material is more remarkable.

As described above, the surface temperature deviation distribution (first
In the case of the embodiment described above, it is possible to estimate the type of defect depending on whether the surface temperature distribution) is an upward convex or a downward convex, and further based on the degree of the convex.

In the embodiment described above, FIG.
As shown in FIG. 4, the laser beam 103 is irradiated in a strip shape over the entire width of the steel plate 101, but the width direction is divided into several portions, and a plurality of strip-shaped lasers 103 are emitted to each divided portion. You may do it.

Further, as shown in FIG. 12, the laser 103 focused at one point may be irradiated so as to scan in the plate width direction. The scanning direction of the laser beam uses a galvano mirror optical system or a polygon mirror optical system. The galvanometer mirror optical system is a method of reciprocating in the plate width direction, and the polygon mirror optical system is a method of scanning in one direction. FIG. 12 shows an example of the galvanometer mirror optical system. In this case, if the scan speed is set to be higher than the transport speed of the steel plate 101, the same effect as that obtained by irradiating the laser 103 in a strip shape can be obtained, and the laser irradiation device 1 can be downsized. Becomes

Further, as described above, by irradiating the laser 103 in the band shape or by irradiating the focused laser 103 so as to scan in the plate width direction, the plate width direction is heated in a line shape and the surface temperature distribution is obtained. I tried to capture, but steel plate 1
If a constant surface 01 is heated by a laser to capture the surface temperature change on the area, the defect can be detected more clearly.

Also, regarding the point of caution when irradiating a strip-shaped laser beam, the laser beam output at the plate width end is made smaller than that at the plate width center, and the plate width end and the plate width center are set. It is desirable to even out the temperature of the material in parts. This is because the heat mass of the material at the edge of the plate width is smaller than that at the center of the plate width, and therefore the temperature rises when the same amount of heat as at the center of the plate width is applied. For the same reason, when scanning and irradiating the focused laser beam in the plate width direction, the scanning speed of the laser beam at the end of the plate width is made higher than the scanning speed at the center of the plate width, It is desirable to equalize the temperature of the material at the width end and the plate width center.

(Other Embodiments) Each part of the information processing unit 3 described in the above embodiments is composed of a CPU of a computer or MPU, RAM, ROM, etc.,
The function is realized by the operation of a computer program stored in RAM, ROM or the like.

Therefore, the computer program itself is included in the scope of the present invention. As a transmission medium of the computer program, a communication medium (a wired line such as an optical fiber or a wireless line) in a computer network (LAN, WAN such as the Internet, a wireless communication network, etc.) system for propagating and supplying program information as a carrier wave Etc.) can be used.

Further, means for supplying the computer program to a computer, for example, a storage medium storing the computer program is included in the scope of the present invention. A CD-ROM, a flexible disk, a hard disk, a magnetic tape, a magneto-optical disk, a non-volatile memory card, or the like can be used as the storage medium.

[0037]

As described above, according to the present invention, the defect detection can be automated, and since the surface temperature distribution is captured, the detection accuracy can be improved and the metal strip surface is covered with the oxide film. It is possible to reliably detect even in cases such as those described above. Moreover, since the heating is performed by using the laser, it is possible to uniformly heat the irradiation range and to clearly detect the influence of defects such as surface defects.

[Brief description of drawings]

FIG. 1 is a schematic diagram showing an outline of a metal band defect detection device according to a first embodiment.

FIG. 2 is a flowchart showing a flow of defect detection processing in the first embodiment.

FIG. 3 is a diagram showing an example of a surface temperature distribution in the plate width direction when surface defects are present.

FIG. 4 is a schematic diagram showing an outline of a metal band defect detection device according to a second embodiment.

FIG. 5 is a diagram for explaining a case where a similar surface temperature distribution in the plate width direction (surface temperature deviation distribution) is continuously captured from a certain time t until nΔt elapses.

FIG. 6 is a diagram showing an isothermal deviation distribution map in the case where there is a defect in which an alumina-based inclusion is caught on the surface of a steel sheet.

FIG. 7 is a schematic diagram showing a state in which alumina-based inclusions 104 are present on the surface of the steel plate 101.

FIG. 8 is a diagram showing an isothermal deviation distribution map in the case where there is a defect in which an alumina-based inclusion is embedded inside the steel sheet surface.

FIG. 9: Alumina-based inclusion 1 from the surface of the steel plate 101 to the inside
It is a schematic diagram which shows a mode that 04 exists.

FIG. 10 is a diagram showing an isothermal deviation distribution map in the case where there is a defect in which a cavity exists inside the steel sheet surface.

FIG. 11 is a schematic view showing a state in which a cavity 105 exists inside the surface of a steel plate 101.

FIG. 12 is a schematic diagram showing how a laser beam 103 focused on one point is irradiated so as to scan in the plate width direction.

[Explanation of symbols]

1 Laser irradiation device 2 Infrared detector 3 Information processing section 3a Input section 3b Judgment unit 3c arithmetic unit

Claims (11)

[Claims] 1. A metal band defect detection device for detecting defects in a metal band, comprising laser irradiating means for irradiating a surface of the metal band with a laser to heat the surface, and a range of a range heated by the laser. A defect detecting device for a metal band, comprising: a temperature distribution detecting means for detecting a surface temperature distribution; and a judging means for making a defect judgment based on the surface temperature distribution detected by the temperature distribution detecting means. 2. The defect detecting device for a metal band according to claim 1, wherein the laser irradiation means irradiates a laser beam in a band shape in a plate width direction of the metal band. 3. The defect detection device for a metal band according to claim 1, wherein the laser irradiation unit irradiates the laser so that the laser beam is scanned in the plate width direction of the metal band. 4. The heating in the plate width direction is performed at predetermined intervals in the longitudinal direction of the metal strip.
Alternatively, the defect detection device according to item 3. 5. Another temperature distribution detection means for detecting the surface temperature distribution of the metal strip before the laser irradiation by the laser irradiation means, and the other temperature distribution detection means for the same range on the metal strip. The surface temperature distribution before heating measured by the above, and the calculating means for calculating the difference between the surface temperature distribution after heating measured by the temperature distribution detecting means are provided, and the determining means is obtained by the calculating means. The defect detection apparatus for a metal strip according to claim 1, wherein defect determination is performed based on a difference in surface temperature distribution. 6. The laser is a Co ₂ laser, a YAG laser or a semiconductor laser.
5. The defect detection device for a metal band according to any one of items 1 to 5. 7. The defect detection device for a metal band according to claim 1, wherein the surface of the metal band is covered with an oxide film. 8. The defect detection device for a metal strip according to claim 1, wherein the metal strip is transported by a transport line. 9. A method for detecting defects in a metal band for detecting defects in the metal band, comprising: a laser irradiation procedure for irradiating a surface of the metal band with a laser to heat the surface; and a range of a range heated by the laser. A defect detection method for a metal band, comprising: a temperature distribution detection procedure for detecting a surface temperature distribution; and a determination procedure for performing a defect determination based on the surface temperature distribution detected by the temperature distribution detection procedure. 10. A defect of the metal strip using a laser irradiating means for irradiating the surface of the metal strip with a laser to heat it, and a temperature distribution detecting means for detecting a surface temperature distribution in a range heated by the laser. A computer program for executing a process for detecting a defect, the program causing a computer to execute a determination process for performing a defect determination based on the surface temperature distribution detected by the temperature distribution detecting means. 11. A computer-readable storage medium in which the computer program according to claim 10 is stored.