JP2003194728A - Flaw inspection method for steel plate - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a flaw inspection method for a steel plate in which an excess inspection caused by the zigzag running of a shape defect on the steel plate can be prevented, in which an undetected range can be reduced as far as possible, and in which a flaw can be detected with satisfactory accuracy. <P>SOLUTION: In the flaw inspection method for the steel plate, a surface flaw on the steel plate 1 which is connected in a welding point 2 so as to be conveyed continuously is inspected by setting a dead zone region in an edge part of the steel plate 1, a dead zone region 4 in an inspection machine is set largely in its widthwise direction at a definite distance from the welding point 2 at the steel plate 1, and a dead zone region 5 in the inspection machine 3 after that is narrowed so as to be inspected. <P>COPYRIGHT: (C)2003,JPO

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention can prevent overdetection caused by meandering running of a defective shape portion of a steel sheet, and further reduce the undetected range as much as possible. The present invention relates to a method for inspecting flaws on a steel sheet, which can detect flaws with high accuracy. 2. Description of the Related Art Conventionally, a steel plate has been inspected for flaws in order to guarantee a product of constant quality without flaws in coil production. As this flaw inspection method, it is common to perform a surface flaw of a steel sheet connected at a welding point and continuously conveyed by an image processing means by setting a dead zone at an edge portion of the steel sheet. Here, the dead zone is set at the edge for the following reason. In other words, the shape of the steel plate is not strictly a fixed plate, but has a slight variation in width, thickness, and the like. May meander inside. When such meandering occurs, when the edge portion is image-processed, a sharp shift in the horizontal direction of the steel sheet is recognized as an image similar to a vertically long flaw called a heddle (hereinafter, referred to as overdetection). Therefore, it is treated as a defective product. Therefore,
As a kind of masking action on the edge of the steel plate,
This is to prevent the occurrence of overdetection as described above by setting a dead zone region having a fixed width. The dead zone is usually set to have a sufficient width so as to cover a welding point of a steel plate having a particularly large meandering width. [0003] However, although the setting of the dead zone can prevent the occurrence of over-detection, defects such as flaws existing in the dead zone cannot be detected at all, so that the defect at the edge portion of the steel plate can be prevented. There is a problem of shipping without detection. As described above, it is necessary to increase the width of the dead zone in order to reliably prevent the occurrence of overdetection, while it is necessary to reduce the width of the dead zone in order to detect a defect at the edge of the steel sheet. At the present time, a method of setting a dead zone that can satisfy both of these conflicting conditions has not been solved. SUMMARY OF THE INVENTION The present invention solves the above-mentioned conventional problems and can reliably prevent overdetection caused by meandering running of a defective shape portion of a steel plate. An object of the present invention is to provide a steel sheet flaw inspection method capable of detecting a defect of an edge part as much as possible by minimizing a non-detection range of an edge part of a steel sheet as much as possible and significantly improving detection accuracy as a whole. It is completed. [0005] A method for inspecting the flaws of a steel sheet according to the present invention, which has been made to solve the above-mentioned problems, comprises the steps of: In the method for inspecting flaws of a steel sheet, in which a dead zone is set at an edge portion of the steel sheet for inspection, a certain distance from a welding point of the steel sheet is set such that the dead zone of the inspection machine is made large in the width direction, and thereafter, The inspection is performed by narrowing the dead zone of the inspection machine. Preferred embodiments of the present invention will be described below with reference to the accompanying drawings. The drawings are plan views for conceptually explaining the process of inspecting the flaws of a continuously conveyed steel sheet, where 1 is a continuously conveyed steel sheet, and 2 is an end face of a pair of steel sheets. The welding point 3 is an inspection machine for detecting the presence or absence of a defect by performing image processing on the central part and both ends of the steel sheet. A dead zone is set at the edge of the steel plate 1, and the surface flaws of the continuously conveyed steel plate 1 are inspected by the image processing means while masking by the dead zone at the edge of the steel plate. The configuration is basically the same as the conventional method for inspecting flaws on a steel sheet. In the present invention, as the dead zone of the inspection machine 3, the dead zone is made larger in the width direction for a certain distance from the welding point 2 of the steel sheet 1, and after that, the dead zone is made narrower in the width direction. The inspection apparatus has a characteristic configuration in that the inspection is performed. In other words, in the past, a dead band region having a fixed width was set, but in the present invention, the width of the dead band region is changed in accordance with the movement amount (walk amount) of the steel plate to be inspected, and the occurrence of overdetection is determined. It is intended to satisfy both conflicting objectives of prevention and maximum detection of a steel plate edge defect. According to the analysis of the present inventor, it has been found that the meandering phenomenon of the steel sheet appears only during a certain distance from the welding point, and has a habit of converging to stable running after that, and the dead zone area only for the certain distance. Is made large in the width direction, it is based on the finding that overdetection can be sufficiently prevented from occurring.
The concept of variably controlling the width of the dead zone in accordance with the amount of walk of the steel sheet as described above is a completely novel thing which has not been heretofore, and is a feature of the present invention. The fixed distance from the welding point 2 of the steel sheet 1 means the amount of movement of the steel sheet 1 until the meandering phenomenon of the steel sheet 1 converges to stable running, and is individually set based on the type and shape of the steel sheet. You. In addition, the wide dead zone region 4 secures a sufficient masking action so that the edge portion of the steel plate 1 does not affect the image processing screen of the inspection device 3 even if the steel plate 1 meanders. Means the width that can be prevented. On the other hand, the narrow dead zone 5 means the minimum width for ensuring the masking action so that the edge of the steel sheet 1 does not affect the stable running of the steel sheet 1, and the undetected range is reduced as much as possible. Is what you do. The dead zone can be set to an arbitrary width and length by inputting an electric signal into the image processing screen of the inspection machine 3. As an example, a chrome-plated steel sheet having a width of 1000 mm and a thickness of 0.24 mm is produced at a line speed of 15 mm.
The results of investigating the relationship between the threading length from the welding point, the amount of the edge dead zone, and the presence or absence of overdetection when traveling at 0 mpm were as shown in Table 1. The evaluation was evaluated as x when there was continuous overdetection, Δ when there was occasional overdetection, and ○ when there was no overdetection. The fact that the dead zone is 35 mm is a value that has been empirically determined from the past, and a dead zone of 35 mm was conventionally set over the entire length of the steel sheet. However, it has been confirmed that overdetection does not occur even if the dead zone is narrowed as the passing length from the welding point increases, and in the case of this steel plate, the dead zone becomes 25 mm after moving over 401 m. It has been found that no over-detection occurs even if the value is set to. As a result, for a steel plate of 401 m or more, the inspection of the edge portion can be performed in a region 10 mm larger in the width direction, and a defect in a region that has not been conventionally inspected can be checked, so that the inspection accuracy can be greatly improved. Was. [Table 1] As described above, according to the present invention, the welding point 2
For a certain distance from, the dead zone region 4 of the inspection device 3 is made large in the width direction, and after that, the dead zone region 5 of the inspection device 3 is narrowed to perform inspection, thereby preventing overdetection and preventing steel sheet edge portions. The conflicting task of maximizing defect detection was solved together. By increasing the inspection accuracy in this way, it is possible to avoid shipping a defective product, and further to eliminate the work of re-inspecting the steel sheet, thereby significantly improving the productivity. As is apparent from the above description, the present invention can reliably prevent overdetection caused by meandering of a defective shape portion of a steel sheet, and can detect undetected edges of a steel sheet. The range can be made as small as possible, and the edge defect can be detected as much as possible, so that the detection accuracy as a whole can be significantly improved. Therefore, the present invention is extremely significant as a method for inspecting flaws on a steel sheet that has eliminated the conventional problems and contributes to industrial development.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a plan view for conceptually explaining a process of inspecting a steel plate for flaws. [Explanation of Signs] 1 Steel plate 2 Welding point 3 Inspection machine 4 Wide dead zone 5 Wide dead zone

Claims (1)

Claims 1. A flaw inspection of a steel sheet in which a surface flaw of a steel sheet connected and continuously conveyed at a welding point is inspected by setting a dead zone region at an edge of the steel sheet. A method for inspecting a flaw of a steel sheet, wherein a dead zone area of the inspection machine is increased in a width direction at a certain distance from a welding point of the steel sheet, and thereafter, the inspection area is narrowed and inspected.