JP2012073055A - Steel plate surface inspection method and apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a steel plate surface inspection apparatus and device each of which is capable of surely detecting a minute defect occurring on a steel plate immediately after casting.SOLUTION: The steel plate surface inspection apparatus includes: a mist spray nozzle for spraying a fine mist to the steel plate immediately after casting to cool a surface of the steel plate; an imaging device for imaging radiation light from a cooled part during cooling or immediately after cooling; and a signal processor for detecting a defect occurring on the steel plate by image processing of a picked-up image.

Description

  TECHNICAL FIELD The present invention relates to a steel sheet surface inspection method and apparatus, and more particularly to a high temperature steel piece such as a slab immediately after casting, and an apparatus suitable for inspection of surface defects such as edge (end) cracks in a steel sheet.

  As a major factor of defects generated on the surface of a thick plate or thin plate after rolling, there is a surface defect of a cast slab (steel piece). If surface defects in the slab (steel piece) stage before rolling can be detected in advance, it is possible to suppress the occurrence of defective products on thick and thin plates by performing treatment such as care.

  For this reason, the surface of the slab (steel piece) after casting is monitored visually or by a surface inspection device, and the presence or absence of surface defects is detected and inspected. In addition, the surface temperature is monitored by a thermo viewer or the like. In the inspection by the surface inspection device, a light source and a CCD camera are arranged, the surface is imaged, and the surface of the steel sheet is based on the information on the surface image (shading of the image due to shape factors such as irregularities, material, surface properties, etc.) There is a technique for detecting abnormalities and defective portions (for example, Patent Document 1).

JP 2002-303582 A

  However, since the slab (steel piece) immediately after casting is high temperature, it is difficult for the operator to visually inspect at a close distance directly from the environment. In addition, although remote monitoring using an ITV camera or the like and temperature monitoring using a thermoviewer are performed, it is difficult to monitor the fine state of the surface with a normal ITV camera because the slab (steel slab) is hot. In the temperature monitoring by the viewer, there is a problem that even if the temperature distribution and fluctuation of the entire slab (steel slab) can be detected, it is difficult to detect fine defects.

  In addition, slabs (steel pieces) after casting are usually cooled once and reheated as necessary in the lower process, and may undergo a processing process called rolling, and surface inspection is performed after this cooling process or cooling. It is possible to do it. However, in the cooling process or after cooling, oxidation of the slab (steel piece) surface proceeds and scale is generated on the surface, so that direct confirmation of the steel sheet surface is difficult and satisfactory steel sheet surface inspection cannot be performed.

  Furthermore, even if it is considered to perform inspection after cleaning the surface of the slab (steel piece), the surface property changes (unevenness) due to the cleaning, and it is difficult to completely remove the scale, etc. Inspection has become difficult. In addition, among surface defects such as slabs (steel pieces), irregularities such as blow holes can be detected without the influence of scales, but fine defects such as cracks (adhesion) can be detected. It is difficult.

  In view of these problems of the prior art, an object of the present invention is to provide a steel sheet surface inspection method and apparatus capable of reliably detecting fine defects occurring in a steel sheet immediately after casting.

  The above problems can be solved by the following invention.

[1]
The steel sheet immediately after casting is cooled by mist spraying, the cooled portion is imaged during or immediately after cooling, and the imaged image is processed to detect defects generated in the steel sheet. Surface inspection method.

[2] In the steel sheet surface inspection method according to [1] above,
A method for inspecting a steel sheet surface, wherein a defect generated in the steel sheet is detected by performing a difference process between an image immediately before cooling in the cooling portion and an image during or immediately after cooling.

[3]
A mist spray nozzle for spraying fine mist on the steel plate immediately after casting and cooling the surface,
An imaging device for imaging radiation from a cooling part during or immediately after cooling;
A steel plate surface inspection device, comprising: a signal processing device that detects defects generated in the steel plate by performing image processing on a captured image.

[4] In the steel sheet surface inspection apparatus according to [3] above,
The imaging device captures an image immediately before cooling in the cooling portion,
The said signal processing apparatus detects the defect which arose in the said steel plate by performing the difference process of the image just before the said cooling, and the image during the said cooling or immediately after cooling, The steel plate surface inspection apparatus characterized by the above-mentioned.

  According to the present invention, the surface of the steel plate immediately after casting is cooled by mist spraying, and the cooled portion is imaged during or immediately after cooling. Therefore, when there is a defect, the surface temperature including the defective portion is reduced. Since an equilibrium (temperature distribution) occurs and the emitted light from the surface changes, defects can be detected on the captured image. Further, since the inspection is performed immediately after casting, the surface inspection can be performed stably without being affected by the surface properties such as oxidation of the steel sheet surface and generation of scale.

It is a figure which shows the structural example and application example of a steel plate surface inspection apparatus. It is a figure which shows typically the mode of cooling by mist spray. It is a figure explaining the defect part emphasis by edge part mist cooling.

  If there are surface defects such as cracks on the edge surface by cooling the edge part of slab (steel piece) etc. immediately after casting, the heat removal (heat dissipation) from the surface due to cooling will change and the defect The present inventors have conceived the present invention from the knowledge obtained by the present inventors that a surface temperature imbalance (temperature distribution) including a portion occurs and a change occurs in emitted light (thermal radiation) from the surface.

  However, in the present invention, the surface or edge of the slab (steel piece) is not intended to cool the material itself, but heat is removed from the surface to generate temperature imbalance and distribution between the defective and normal parts. The purpose is to make it cool, and rapid and steep cooling is unnecessary.

  Including this point, the direct spraying and spraying of cooling water has a large temperature drop, and there is a possibility that cracks and cracks may occur due to the temperature drop, and it is difficult to perform appropriate cooling. Further, cooling with gas such as air blow is not effective because it cannot be effectively cooled and it is difficult to control the cooling range. Cooling (heat removal) of the surface by mist spray is effective.

  FIG. 1 is a diagram illustrating a configuration example and an application example of a steel sheet surface inspection apparatus. In the figure, 1 is an imaging device, 2 is a signal processing device, 3 is an image display device, 4 is a transport line, 5 is a transport roll, 6 is PLG, 7 is a steel plate, 8 is an image recording device, and 9 is a mist spray nozzle. Respectively.

  The conveyance line 4 is composed of a plurality of conveyance rolls 5 (for example, a diameter of 400 mm and a length of 5000 mm) arranged at regular intervals, and conveys the steel plate 7 on the conveyance line by rotating the roll. Further, a PLG (PuLse Generator) 6 for measuring the rotation speed of the roll is installed in the transport line 4 in order to track the transport of the steel plate 7.

  In the present embodiment, the steel plate 7 is a slab (steel piece) immediately after casting, and the edge portion is imaged. Therefore, the imaging device 1 (a specific device is a CCD camera or a thermo viewer) is provided on the side of the line. Is arranged.

  The temperature of the slab (steel piece) immediately after casting is high (800 ° C or higher), and imaging can be performed by detecting infrared or near infrared radiation (thermal radiation) from the slab (steel piece). In particular, no light source is provided.

  In this embodiment, a 1000 × 1000 pixel CCD camera is used, the lens and the installation position are adjusted so that one side of the field of view is 300 mm at the slab (steel piece) edge position, and the resolution per pixel is It is set to 0.3 mm or less.

  The image captured by the CCD camera is output according to the steel plate conveyance speed (that is, in synchronization with the output of the PLG 6). Is captured without gaps. Although an example of application to the edge is shown here, application to the upper and lower surfaces is also possible. In that case, in order to ensure resolution, it is necessary to arrange a plurality of cameras.

  A mist spray nozzle 9 is installed immediately before the image pickup position by the CCD camera, and mist (water in a fine mist state) is sprayed from the mist spray nozzle 9 to the slab (steel piece) edge portion to be conveyed. Then, cooling is performed by utilizing absorption of heat of vaporization when evaporating (herein, also referred to as mist spray cooling or mist cooling).

  In the above description, the image is taken immediately after the mist cooling, but if it is cooled by a fine mist spray, the image can be taken in the cooling state. Furthermore, if a CCD camera is installed in front of the cooling unit, the state before and after cooling is imaged, and the comparison and difference before and after cooling are performed, the temperature change accompanying cooling can be detected more efficiently.

  FIG. 2 is a diagram schematically showing a state of cooling by mist spray. The cooling by mist spraying is performed on the defective portion (cracked portion) 10 generated at the edge portion of the steel plate 7 and the state of imaging is shown.

  Furthermore, FIG. 3 is a diagram for explaining emphasis on a defective portion by edge portion mist cooling. FIG. 3 (a) shows a case where edge imaging is performed without performing mist cooling. When there is a defect portion formed in a state of being in close contact with a normal portion, the surface temperature distribution of the edge portion is substantially uniform. It is difficult to distinguish the defective part from the normal part from the surface temperature distribution. However, when mist cooling is performed on the edge as shown in FIG. 3B, the heat removal (heat dissipation) from the surface changes (the heat removal between the defective part and the normal part is different), and the surface including the defective part. A temperature imbalance (temperature distribution) occurs, and the light emitted from the surface (thermal radiation) changes. Compared with the case where mist cooling is not performed, the defect portion becomes more obvious from the change in the captured image (surface temperature distribution), and the defect portion can be detected.

  In order to reliably emphasize the cracked portion by removing heat from the edge portion by mist spraying, it is necessary to appropriately carry out depending on the temperature and shape of the target slab (steel piece). For this reason, it is important to be able to control and change the cooling conditions including the spray amount of the mist spray, the shape of the spray nozzle, and the mist particle diameter.

  In this embodiment, an example of application to a conveyance line has been shown, but the present invention can be similarly applied to a slab during casting in a continuous casting line.

  An imaging signal from the CCD camera is input to the signal processing device 2 (see FIG. 1). The signal processing device 2 extracts a temperature fluctuation portion (a portion with high or low image luminance) in the image of the edge portion, and determines whether or not it is a defect from information including the shape and position of the extraction portion, Perform detection.

  The captured image is sent to the image display device 3, and the captured image is displayed in synchronization with the conveyance of the slab (steel piece). When a defect is detected by the signal processing unit 2, defect information is transmitted to the image display device 3, and the image display device 3 displays the presence / absence of defect detection when a captured image is displayed.

  Further, the captured image is transmitted to the image recording device 8, and the entire image of the inspection object material is recorded. It is also possible to read out a necessary image from the images recorded in the image recording device 8 and perform display, inspection, and confirmation again.

DESCRIPTION OF SYMBOLS 1 Imaging device 2 Signal processing device 3 Image display device 4 Conveyance line 5 Conveyance roll 6 PLG
7 Steel plate 8 Image recording device 9 Mist spray nozzle 10 Defect (crack)

Claims (4)

The steel sheet immediately after casting is cooled by mist spraying, the cooled portion is imaged during or immediately after cooling, and the imaged image is processed to detect defects generated in the steel sheet. Surface inspection method. In the steel sheet surface inspection method according to claim 1,
A method for inspecting a steel sheet surface, wherein a defect generated in the steel sheet is detected by performing a difference process between an image immediately before cooling in the cooling portion and an image during or immediately after cooling. A mist spray nozzle for spraying fine mist on the steel plate immediately after casting and cooling the surface,
An imaging device for imaging radiation from a cooling part during or immediately after cooling;
A steel plate surface inspection device, comprising: a signal processing device that detects defects generated in the steel plate by performing image processing on a captured image. In the steel sheet surface inspection apparatus according to claim 3,
The imaging device captures an image immediately before cooling in the cooling portion,
The said signal processing apparatus detects the defect which arose in the said steel plate by performing the difference process of the image just before the said cooling, and the image during the said cooling or immediately after cooling, The steel plate surface inspection apparatus characterized by the above-mentioned.