Method and device for determining quality of welded part, and method for operating continuous steel sheet processing line

Abstract

In the present invention, the kurtosis in the temperature distribution in the longitudinal direction of a steel sheet is calculated for each prescribed steel sheet width region from a detected two-dimensional temperature distribution of a welded part (ST4), and the kurtosis in the temperature distribution in the longitudinal direction of the steel sheet in the prescribed steel sheet width region of the welded part to be determined is compared with a specified threshold value to determine the quality of the welded part (ST5).

Description

Method and device for determining the quality of welds, and method for operating a continuous steel plate processing line

[0001] The present invention relates to a method and apparatus for determining the quality of a weld, a method for operating a continuous steel plate processing line, and in particular to a method and apparatus for determining the quality of a weld between steel plates welded on a continuous steel plate processing line.

[0002] In production lines for manufacturing and processing steel sheets, when steel sheets are subjected to pretreatments such as pickling or the application of rust-preventive oil, performing each treatment on each steel sheet individually results in poor production efficiency and is impractical. For this reason, a method is used in which the ends of individual steel sheets are welded together using a welding machine installed on the production line (a continuous steel sheet processing line) to join the steel sheets, thereby performing these treatments continuously. As a method for welding steel sheets, seam welding, a type of lap resistance welding, is generally used. In seam welding, the ends of the steel sheets in the feed direction, generally the longitudinal ends, are overlapped, and a pair of electrode wheels pressed against each other from above and below are rotated and moved in the width direction of the steel sheets while passing current through them, thereby continuously welding the steel sheets in the width direction of the steel sheets.

[0003] Although it is rare, poor welding can occur in such seam welding, and this can cause the weld to break within the production line, resulting in a production line shutdown. If the production line is shut down due to a break in the weld of the joining steel plate, not only will the operating rate decrease, but it will also take a long time to restore the production line.

[0004] A method and apparatus for determining the quality of such welds in steel plates is described, for example, in Patent Document 1 below. This weld quality determination method and apparatus uses ultrasonic flaw detection, scanning the weld in the longitudinal and width directions of the steel plate while focusing an ultrasonic beam transmitted from a point-focus probe at the nugget position of the weld. Then, a scope image of the reflected echo from the weld in the longitudinal direction of the steel plate and a scope image of the steel plate in the width direction of the steel plate are combined to obtain a tomographic image of the weld, and the quality of the weld is determined from the proportion of the molten portion in this tomographic image.

[0005] Furthermore, the method and device for determining the quality of a weld described in Patent Document 2 detects an abnormality in an electrode wheel from a defective part in a weld, and calculates the temperature distribution in the width direction of the steel plate at the weld using the detected two-dimensional temperature distribution in the weld. If the maximum value of this temperature distribution in the width direction of the steel plate is not within a predetermined range, the weld in that region in the width direction of the steel plate is determined to be a defective part (or a candidate for a defective part).

[0006] In addition, a method and device for determining the quality of a welded portion described in Patent Document 3 detects the occurrence of spatter (dust) due to reactive current during seam welding as a weld defect, and determines the temperature distribution of the welded portion in the steel plate width direction using the detected two-dimensional temperature distribution of the welded portion.The method and device then determine the welded portion as defective if the average value of this temperature distribution in the steel plate width direction is equal to or less than a first threshold value and the temperature difference between the maximum and minimum values ​​of the temperature distribution in the steel plate width direction is equal to or greater than a second threshold value.

[0007] JP 2000-180421 A JP 2013-22598 A International Publication No. 2018 / 181398

[0008] In the weld quality determination method and device described in Patent Document 1, the weld is immersed in water to prevent attenuation of the ultrasonic amplitude. However, because the temperature of the weld exceeds 500°C immediately after welding, it is practically impossible to determine the quality of the weld using the weld quality determination method and device described in Patent Document 1 while immersing the weld in water on a production line. Furthermore, the weld quality determination methods and devices described in Patent Documents 2 and 3 both use the temperature distribution in the steel plate width direction at the weld to determine the quality of the weld. However, the temperature distribution in the steel plate width direction alone cannot evaluate the heat input state within the weld bead width at the weld, in other words, the heat input state in the steel plate longitudinal direction. In other words, even if the maximum or average value of the steel plate width direction temperature distribution in the weld exceeds (or falls below) a threshold value, if the heat input state in the steel plate longitudinal direction in a certain steel plate width direction region is not equivalent to the heat input state when the weld is good, the weld may be defective in that steel plate width direction region.

[0009] The present invention has been made in view of the above-mentioned problems, and an object of the present invention is to provide a method for determining the quality of a weld, an apparatus for performing the same, and a method for operating a continuous steel plate processing line, which enable evaluation of the heat input state in the longitudinal direction of the steel plate at the weld, thereby enabling reliable determination of the quality of the weld.

[0010] In order to achieve the above-mentioned object, one embodiment of the present invention provides a method for determining the quality of a welded portion, which determines the quality of the welded portion of both materials after welding the tail end of a leading metal strip and the front end of a trailing metal strip using a welding machine, and which comprises: a temperature distribution acquisition step for acquiring the temperature distribution in the longitudinal direction of the metal strip of the welded portion to be determined; a temperature distribution kurtosis calculation step for calculating the kurtosis of the temperature distribution in the longitudinal direction of the metal strip of the welded portion to be determined for each specified width region of the metal strip; and a welded portion quality determination step for determining the quality of the welded portion to be determined based on the calculated kurtosis of the temperature distribution in the longitudinal direction of the metal strip.

[0011] In a further aspect of the present invention, the quality of the weld is determined to be good when the kurtosis of the temperature distribution in the longitudinal direction of the metal strip calculated for each predetermined width region of the metal strip is equal to or less than a specified threshold. In a further aspect of the present invention, the metal strip is a steel strip. A method for operating a continuous steel sheet processing line according to one aspect of the present invention is summarized as including a step of determining the quality of a weld using the above-mentioned method for determining the quality of a weld.

[0012] In addition, one embodiment of the present invention provides a weld quality determination device that uses a welding machine to weld the tail end of a leading metal strip to the front end of a trailing metal strip and then determines the quality of the weld between the two materials, and is summarized as comprising: a temperature distribution acquisition unit that acquires the temperature distribution in the longitudinal direction of the metal strip of the weld to be determined; a temperature distribution kurtosis calculation unit that calculates the kurtosis of the temperature distribution in the longitudinal direction of the metal strip of the weld to be determined for each specified width region of the metal strip; and a weld quality determination unit that determines the quality of the weld to be determined based on the calculated kurtosis of the temperature distribution in the longitudinal direction of the metal strip.

[0013] According to the present invention, by calculating the kurtosis of the temperature distribution in the longitudinal direction of the metal strip from the temperature distribution in the weld for each predetermined width region of the metal strip, it is possible to evaluate the heat input state in the longitudinal direction of the metal strip at the weld for each width region. Therefore, by comparing this heat input state with the heat input state in a good state during normal welding, it is possible to reliably determine the quality of the weld.

[0014] Fig. 1 is a schematic configuration diagram of a weld quality determination system which is one embodiment of a weld quality determination method and device thereof of the present invention. Fig. 2 is a block diagram of a weld quality determination device constructed in the computing machine of Fig. 1. Fig. 3 is an explanatory diagram of a two-dimensional temperature distribution, peak temperature, and kurtosis in a good weld. Fig. 4 is an explanatory diagram of a two-dimensional temperature distribution, peak temperature, and kurtosis in a poor weld. Fig. 5 is an explanatory diagram of a steel plate longitudinal direction temperature distribution in the two-dimensional temperature distribution of Fig. 3. Fig. 6 is an explanatory diagram of a steel plate longitudinal direction temperature distribution in the two-dimensional temperature distribution of Fig. 4.

[0015] An embodiment of a method for determining the quality of a weld, an apparatus therefor, and a method for operating a continuous steel plate processing line according to the present invention will be described in detail below with reference to the drawings. The embodiment shown below exemplifies an apparatus and method for embodying the technical concept of the present invention, and the technical concept of the present invention does not limit the quality determination logic, apparatus configuration, etc. to the embodiment described below. Also, the drawings are schematic.

[0016] FIG. 1 is a schematic diagram of a seam welding machine 1 equipped with a weld quality determination system, illustrating one embodiment of a weld quality determination method and device therefor. The weld quality determination system of this embodiment determines the quality of welds between a preceding steel sheet 2 and a following steel sheet 3 processed in a continuous steel sheet processing line (production line). The seam welding machine 1 is installed in this continuous steel sheet processing line and seam welds the tail end of the preceding steel sheet 2 to the leading end of the following steel sheet 3. In a continuous steel sheet processing line, for example, a steel sheet unwound from a coil is generally fed longitudinally, so this feed direction is defined as the longitudinal direction of the steel sheet, and the sheet surface (horizontal) direction perpendicular to this is defined as the width direction of the steel sheet. In FIG. 1, the direction seen as the length of the steel sheets 2 and 3 corresponds to the width direction of the steel sheets, and the direction perpendicular to the plane of the drawing is the longitudinal direction of the steel sheets. 1 shows a state in which the tail end of the preceding steel plate 2 and the front end of the following steel plate 3 are overlapped one above the other, and seam welding is performed in the width direction of the steel plates at this overlapping position. The tail end is the rear end in the steel plate feed direction, and the front end is the front end in the steel plate feed direction.

[0017] The seam welding machine 1 is mounted on a frame 11 having a U-shaped cross section and an opening on one side in the width direction of the steel plates, and the steel plates 2, 3 are fed longitudinally into the opening of the frame 11. A plurality of wheels 12 that can rotate left and right in the drawing are attached to the underside (bottom) of the frame 11, and are configured to move back and forth left and right in the drawing by the rotational driving force of a drive motor (not shown). The frame 11 is provided with a pair of electrode wheels 7 facing each other above and below, i.e., in the direction in which the overlapping steel plates 2, 3 are sandwiched, and a pair of swaging rolls 8 at the same height as the pair of electrode wheels 7 also facing each other in the direction in which the overlapping steel plates 2, 3 are sandwiched.

[0018] Of these, each of the pair of electrode wheels 7 is a roll-shaped electrode, connected to a drive motor (not shown), and rotated in the circumferential direction of the roll by the rotational driving force of this drive motor. Each electrode wheel 7 is connected to a power supply device (not shown) with different polarities. Each electrode wheel 7 is attached to the frame 11 via a pressure cylinder 13 that applies pressure in the vertical direction in the figure, i.e., in the direction in which the overlapping steel sheets 2 and 3 are sandwiched. In some cases, the pressure cylinder 13 is provided on only one of the electrode wheels 7 (usually the upper electrode wheel).

[0019] The pair of swaging rolls 8 are reduction rolls, and as will be described later, are positioned to pressurize the welded joint after the overlapping steel sheets 2 and 3 have been welded by the pair of electrode wheels 7. Although the pair of swaging rolls 8 are shown facing each other in the figure, their rotation axes are inclined in opposite directions to each other in the horizontal plane, so that they are twisted relative to each other. Each of the pair of swaging rolls 8 is connected to a drive motor (not shown) and rotated in the circumferential direction of the roll shape by the rotational driving force of the drive motor. Each swaging roll 8 is attached to the frame 11 via a pressure cylinder 14 that presses the overlapping steel sheets 2 and 3 in the vertical direction in the figure, i.e., in the direction sandwiching the overlapping steel sheets 2 and 3. The pressure cylinder 14 may be provided on only one of the swaging rolls 8 (usually the upper swaging roll) 8.

[0020] This seam welding machine 1 performs seam welding as follows. First, prior to seam welding, the positions of the trailing end of the preceding steel plate 2 and the leading end of the trailing steel plate 3 are adjusted so that they overlap with a predetermined overlap using side guides that adjust the widthwise positions of the steel plates 2, 3 and clamping devices that hold the steel plates 2, 3. Once the trailing end of the preceding steel plate 2 and the leading end of the trailing steel plate 3 are overlapped with the predetermined overlap in this manner, a pair of electrode wheels 7 presses the overlapping portion while current is passed between the electrode wheels 7, causing the contact portions of the two steel plates 2, 3 to melt with each other due to Joule heat. Therefore, by rotating the wheels 12 to move the frame 11 from left to right in the figure, and rotating and moving each electrode wheel 7 in the widthwise direction of the steel plates while current is passed between the pair of electrode wheels 7, the overlapping portions of the trailing end of the preceding steel plate 2 and the leading end of the trailing steel plate 3 are welded sequentially and continuously in the widthwise direction of the steel plates.

[0021] The welded portion formed by the pair of electrode wheels 7 is then pressed by a pair of swaging rolls 8 that pass by. Because the portion pressed by the swaging rolls 8 is immediately after welding, the fusion zones of the two steel sheets 2, 3 are pressed together by the pressure. At this time, the rotation axes of the pair of swaging rolls 8 are twisted relative to each other, so the pressed weld zone is in a substantially flat state. Therefore, in seam welding using this seam welding machine 1, the overlapping portion of the two steel sheets 2, 3 is pressed and welded by the pair of electrode wheels 7, reducing the level difference in the weld zone compared to before welding. Furthermore, the shape of the weld zone is flattened by the pressure applied by the pair of swaging rolls 8. Although the bead portion formed by the weld is substantially flat in seam welding, the term "weld bead" is used conventionally in this specification.

[0022] A radiation thermometer is attached to the frame 11 as the thermometer 6, which detects the temperature of the welded portion of the steel plates 2 and 3 immediately after welding with a pair of electrode wheels 7. The thermometer 6 is configured to detect the radiation temperature (surface temperature) of the welded portion at a predetermined number of measurement points (e.g., at predetermined distances) along the longitudinal direction of the steel plates, repeating this process each time the frame 11, i.e., the thermometer 6, moves a predetermined distance along the width of the steel plates. Therefore, after one seam welding, a two-dimensional temperature distribution (matrix) consisting of temperature distributions in the width and longitudinal directions of the steel plates can be obtained (using a method similar to that described in Patent Document 3). The temperature detected by the thermometer 6 is input to a computing device, specifically, a personal computer (hereinafter, referred to as PC) 4. The PC 4 is connected to a welding machine control device 5 that controls the seam welding machine 1.

[0023] Needless to say, PC 4 is a processing unit with advanced arithmetic processing capabilities, and is also equipped with input / output devices for inputting signals from sensors and outputting signals to displays and printers, and a storage device for storing programs, data, etc. New application software can also be stored in the storage device. The input / output devices of PC 4 can also exchange information with other processing units, such as the welding machine control device 5. The welding machine control device 5 is also constructed with a computer system, such as a programmable logic controller.

[0024] The PC 4 uses stored statistical analysis application software to construct a weld quality determination device, as shown in Figure 2. Figure 2 is a block diagram of this weld quality determination device and also shows a flowchart of a weld quality determination method performed by this weld quality determination device. In this weld quality determination device (weld quality determination method), the two-dimensional temperature distribution processing unit (two-dimensional temperature distribution processing step) ST1 first reads the temperature (distribution) in the longitudinal direction of the steel plate in the weld, detected by the thermometer 6. The read temperature (distribution) in the longitudinal direction of the steel plate is aligned and accumulated in the steel plate width direction, forming a two-dimensional temperature distribution in the weld. Specifically, for example, each detected temperature is assigned to a coordinate point in the steel plate width direction and the steel plate longitudinal direction, creating a two-dimensional temperature distribution map (matrix). The position in the steel plate width direction is obtained, for example, by converting the rotation information of the corresponding electrode wheel 7. Therefore, the thermometer 6 and this step ST1 constitute a two-dimensional temperature distribution detection unit. It is also possible to directly obtain the two-dimensional temperature distribution using a device capable of detecting the temperature of a two-dimensional region, such as a thermal imaging camera (thermoviewer).

[0025] Next, in the data preprocessing unit (data preprocessing step) ST2, the read two-dimensional temperature distribution data of the weld (which will be the subject of judgment later) is preprocessed. Specifically, the read temperature distribution in the longitudinal direction of the steel plate is normalized. Data normalization of the temperature distribution in the longitudinal direction of the steel plate is performed by excluding temperature data other than that of a predetermined weld from the read two-dimensional temperature distribution data, and the remaining region is used as a judgment region for whether the weld is good or bad. Specifically, regions that are not actually welded at both ends of the steel plate in the width direction and both ends of the steel plate in the longitudinal direction are excluded by judging whether the temperature is within a predetermined range.

[0026] Next, in a two-dimensional temperature distribution storage unit (two-dimensional temperature distribution storage step) ST3, the two-dimensional temperature distribution that has been mapped and preprocessed is stored in a storage device. Here, data on the temperature distribution in the longitudinal direction of the steel plate is also stored (memorized) at the same time.

[0027] Next, in the temperature distribution kurtosis calculation unit (temperature distribution kurtosis calculation step) ST4, after one welding run is completed, the kurtosis of the steel plate longitudinal temperature distribution data is calculated for each predetermined distance in the steel plate width direction (hereinafter referred to as a predetermined steel plate width region) for the two-dimensional temperature distribution that has been subjected to the above preprocessing. Kurtosis is an index that represents the sharpness of the distribution, and here, the definition that the kurtosis of a normal distribution is 0 is used as the basis. If the temperature distribution data has a sharper (peaked) shape than the normal distribution, the kurtosis will be greater than 0, and conversely, if the shape is gentler than the normal distribution, the kurtosis will be less than 0. Kurtosis will be described in detail later, but in this embodiment, it is calculated according to the following formula 1.

[0028]

[0029] Here, n is the number of samples (=temperature distribution data in the longitudinal direction of the steel plate) in a predetermined steel plate width region, and x ｉ is the sample value at point i (i = 1 to n), x ａ is the average value of the samples, and s is the standard deviation of the samples. Furthermore, i is set to 1 at the rear side in the steel sheet feed direction and increases (increments) toward the front side in the steel sheet feed direction. When the number of scans of the thermometer 6 included in the predetermined steel sheet width region is m, m is preferably 1. However, taking into account the case of multiple scans, the kurtosis calculation method may include any of the following (1) to (3): (1) Calculate the average value of m waveforms (temperature distributions), and calculate the kurtosis of this average value. (2) Calculate the kurtosis of a waveform that represents the m waveforms (for example, the waveform of the first scan). (3) Use the average value of all kurtosis of the m waveforms as a representative. (URL: https: / / ja.wikipedia.org / wiki / %E5%B0%96%E5%BA%A6#:~:text=%E5%B0%96%E5%BA%A6%EF%BC%88%E3%81%9B%E3%82%93% E3%81%A9%E3%80%81%E8%8B%B1,%E3%82%92%E3%82%82%E3%81%A4%E5%88%86%E5%B8%83%E3%81%A7%E3%81%82%E3%82%8B%E3%80%82 reference)

[0030] Next, in the weld quality determination unit (weld quality determination step) ST5, the kurtosis of the calculated steel plate longitudinal temperature distribution data for each steel plate width region is compared with a preset threshold value. If the kurtosis of the steel plate longitudinal temperature distribution data for all steel plate width regions is equal to or less than the threshold value, the weld to be determined is determined to be well welded. The threshold value is set, for example, based on the past two-dimensional temperature distribution stored in step ST3. Setting a kurtosis threshold value for each steel plate parameter further improves the determination accuracy. The kurtosis may be calculated and used as a threshold value for each temperature distribution acquisition scan performed by the thermometer 6. Furthermore, the thermometer 6 may perform a temperature distribution acquisition scan (once) at predetermined distances in the steel plate width direction, and the kurtosis of the temperature distribution may be calculated and used as a threshold value for determination. In this embodiment, if the weld to be determined is not well welded, the determination result is output to the welding machine control device 5. When a poor weld determination result is input to the welding machine control device 5, the line control device controlling the continuous steel plate processing line stops the continuous steel plate processing line.

[0031] The upper part of Figure 3 shows the two-dimensional temperature distribution in the width direction and longitudinal direction of the steel plate in a weld with good weldability, with the gray areas indicating high-temperature areas above a certain temperature. As is clear from the figure, in a weld with good weldability, the high-temperature region in the longitudinal center of the steel plate, i.e., the center of the weld bead width, is maintained at a constant longitudinal width in the steel plate width direction. The upper part of Figure 4 shows the two-dimensional temperature distribution in the width direction and longitudinal direction of the steel plate in a weld with poor weldability, with the dark gray areas indicating high-temperature areas, as in Figure 3. As is clear from the figure, in a weld with poor weldability, the longitudinal width of the high-temperature region in the longitudinal center of the steel plate, i.e., the center of the weld bead width, fluctuates. The middle parts of Figures 3 and 4 show the maximum temperatures (peak temperatures) in the two-dimensional temperature distribution of each weld shown in the upper part of each figure. For example, if a good weld is determined based on the maximum temperature in this two-dimensional temperature distribution being equal to or greater than the threshold value indicated by the dashed line in the figure, then all welds would be determined to be good welds, but the actual welds in Figure 4 are poorly welded. Note that the dashed lines on both the left and right sides of each figure represent the positions of both ends of a given weld in the steel plate width direction, and the areas on either side of these lines are essentially not welded. That is, in the preprocessing of step ST2 of the calculation process in Figure 2, the gray areas in the upper part of each figure are extracted as the judgment areas for the weld.

[0032] Figure 5 shows the longitudinal temperature distributions of the steel plate in each width region of the two-dimensional temperature distribution in Figure 3 superimposed on each other. Although the actual longitudinal temperature distributions of the steel plate vary slightly from one width region to another, they are almost always superimposed on a single longitudinal temperature distribution waveform, and this state is symbolically represented. In contrast, Figure 6 shows the longitudinal temperature distributions of the steel plate in each width region of the two-dimensional temperature distribution in Figure 4 superimposed on each other. The actual longitudinal temperature distributions of the steel plate vary greatly from one width region to another, and there are many superimposed longitudinal temperature distribution waveforms of the steel plate. However, this figure symbolically represents a typical longitudinal temperature distribution waveform of the steel plate. Compared to the longitudinal temperature distribution of the steel plate during normal welding, i.e., a good weld condition, shown in Figure 5, the longitudinal temperature distribution of the steel plate with poor welding deviates from this distribution in various ways, and in many cases the deviation is significant.

[0033] The longitudinal temperature distributions of the steel plate shown in Figures 5 and 6 indicate the heat input state of the weld. The longitudinal temperature distribution of the steel plate during normal welding in a normal welding state shown in Figure 5 is almost consistent across the width of the steel plate, so the kurtosis, which represents the sharpness of the peak shape of the distribution, is also almost constant across the width of the steel plate. The peak shape of the longitudinal temperature distribution of the steel plate during normal welding is gentler than that of a normal distribution, so the kurtosis of the longitudinal temperature distribution of the steel plate during normal welding is less than 0. In contrast, the longitudinal temperature distribution of the steel plate during abnormal welding in an abnormal welding state shown in Figure 6 has a varied peak shape and the sharpness of the distribution varies. However, compared to Figure 5, the overall tendency is for the sharpness of the distribution to be greater, and therefore the kurtosis of the longitudinal temperature distribution of the steel plate during abnormal welding is greater than 0. The weld quality determination system of this embodiment was developed based on this knowledge and achieves higher welding abnormality detection accuracy than conventional methods. The lower part of Fig. 3 shows the kurtosis of the temperature distribution in the longitudinal direction of the steel plate at a weld in a good welded state, and the lower part of Fig. 4 shows the kurtosis of the temperature distribution in the longitudinal direction of the steel plate at a weld in a poorly welded state. The kurtosis of the temperature distribution in the longitudinal direction of the steel plate in Fig. 3 is stable and far below the threshold indicated by the dashed line in each figure. In contrast, the kurtosis of the temperature distribution in the longitudinal direction of the steel plate in Fig. 4 exceeds the threshold at multiple points in a given steel plate width region, and the kurtosis is extremely unstable.

[0034] The occurrence frequency of weld defects in seam welding is approximately 1 / 4000, and statistical methods using measured temperature data inevitably require thousands of analysis targets. However, because the occurrence frequency is low, it takes a very long time to collect training data that can be tagged as abnormal from analysis targets with the same material specifications and welding conditions. Therefore, with kurtosis, an unsupervised statistical method, as described above, the threshold value for kurtosis in the longitudinal temperature distribution during abnormal welding can be obtained relatively quickly by increasing the amount of applicable actual data accumulated. Furthermore, as is clear from Figures 5 and 6 , the kurtosis of the longitudinal temperature distribution of steel plates is intuitively easy to understand, does not require a model of temperature data during normal welding, and has the advantage of being easy to handle data, such as requiring a small computational load.

[0035] In this way, the weld quality determination system of this embodiment calculates the kurtosis of the temperature distribution in the longitudinal direction of the steel plate in a specified steel plate width region of the weld to be determined from the two-dimensional temperature distribution of the weld, and determines the quality of the weld based on the kurtosis of this temperature distribution in the longitudinal direction of the steel plate. This makes it possible to evaluate the heat input state of the weld in the longitudinal direction of the steel plate, i.e., the heat input state within the weld bead width, and by comparing this heat input state with the heat input state in a good state during normal welding, it is possible to reliably determine the quality of the weld.

[0036] Furthermore, by determining that the weld is good when the kurtosis of the temperature distribution in the longitudinal direction of the steel plate calculated for each predetermined steel plate width region is equal to or less than a specified threshold, the weld is determined to be defective if the kurtosis in any predetermined steel plate width region exceeds the threshold. This makes it possible to strictly evaluate the heat input state of the weld in the longitudinal direction of the steel plate in the steel plate width direction, thereby more precisely determining the quality of the weld.

[0037] The above describes the weld quality determination system according to the embodiment, but the present invention is not limited to the configuration described in the above embodiment, and various modifications are possible within the scope of the gist of the present invention. For example, in the above embodiment, a case where the quality of the weld between the tail end of the preceding steel plate and the front end of the following steel plate is determined is described, but the present invention can be similarly applied to metal strips other than steel plates.

[0038] REFERENCE SIGNS LIST 1 Seam welding machine (welding machine) 2 Leading steel sheet 3 Trailing steel sheet 4 PC (personal computer, computing machine) 5 Welding machine control device 6 Thermometer 7 Electrode wheel ST1 Two-dimensional temperature distribution processing unit (two-dimensional temperature distribution processing step) ST2 Data pre-processing unit (data pre-processing step) ST3 Two-dimensional temperature distribution storage unit (two-dimensional temperature distribution storage step) ST4 Temperature distribution kurtosis calculation unit (temperature distribution kurtosis calculation step) ST5 Weld pass / fail judgment unit (weld pass / fail judgment step)

Claims

1. A method for determining the quality of a welded portion, which uses a welding machine to weld the tail end of a leading metal strip and the front end of a trailing metal strip and then determines the quality of the welded portion of both materials, comprising: a temperature distribution acquisition step for acquiring the temperature distribution in the longitudinal direction of the metal strip of the welded portion to be determined; a temperature distribution kurtosis calculation step for calculating the kurtosis of the temperature distribution in the longitudinal direction of the metal strip of the welded portion to be determined for each specified width region of the metal strip; and a welded portion quality determination step for determining the quality of the welded portion to be determined based on the calculated kurtosis of the temperature distribution in the longitudinal direction of the metal strip.

2. The method for determining the quality of a weld as described in claim 1, characterized in that the weld is determined to be good when the kurtosis of the temperature distribution in the longitudinal direction of the metal strip calculated for each specified width region of the metal strip is below a specified threshold value.

3. A method for determining the quality of a weld as claimed in claim 1 or 2, wherein the metal strip is a steel strip.

4. A method for operating a continuous steel plate processing line, comprising a step of determining the quality of welds using the method for determining the quality of welds according to claim 3.

5. A weld quality determination device that uses a welding machine to weld the tail end of a leading metal strip and the front end of a trailing metal strip and then determines the quality of the weld between the two materials, comprising: a temperature distribution acquisition unit that acquires the temperature distribution in the longitudinal direction of the metal strip of the weld to be determined; a temperature distribution kurtosis calculation unit that calculates the kurtosis of the temperature distribution in the longitudinal direction of the metal strip of the weld to be determined for each specified width region of the metal strip; and a weld quality determination unit that determines the quality of the weld to be determined based on the calculated kurtosis of the temperature distribution in the longitudinal direction of the metal strip.

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