JP5440014B2 - ERW Weld Monitoring Method - Google Patents

Description

  The present invention relates to a method for monitoring an electric seam welded portion that monitors a welded portion in an electric resistance welded pipe production line.

An electric sewing tube is manufactured by forming a strip (tube material) into a cylindrical shape with a molding machine, heating and melting both edges of the V-shaped gap by high-frequency current conduction, and pressurizing and joining with a squeeze roll. Is done.
Welding conditions are reflected in a moderate temperature, a suitable forming condition, a suitable material and an operating level. Here, by capturing changes in measurable elements, it is possible to determine whether welding is appropriate, to determine the cause of improperness, and to control input power in a feed-forward manner. The basic idea of welding monitoring and heat input control is to capture and set feedback.

FIG. 7 shows induction type high frequency electric resistance welding pipe welding, and FIG. 8 shows contact type high frequency electric resistance welding pipe welding. In the figure, 3a is a work coil for electromagnetic induction, 3b and 3c are tips (contactors) for contact energization, 2a and 2b are squeeze rolls, 1 is a pipe material to be welded, and 1b and 1c are V-shaped. An edge portion forming a gap, 1a is a welding point, and 3d is a high-frequency oscillation device.
The work coil 3a or the chips 3b and 3c are arranged at the front stage of the squeeze rolls 2a and 2b, and thereby the opposite edges of the V-shaped gap formed in the tube material 1 by a multistage forming roll (not shown). When a high-frequency current i is passed through 1b and 1c, the opposing edges 1b and 1c are heated by the high-frequency current to reach the maximum temperature at the welding point 1a and are pressure-bonded by the squeeze rolls 2a and 2b.

  In the high-frequency welding, a high-frequency current is concentratedly applied to the edge to heat the edge to the welding temperature and press-contact. Since the high-frequency current reciprocates along the two edges, the current concentrates at the edge due to the proximity effect, and at the same time, the current concentrates at the corner at the edge due to the skin effect. When heating to the center of the edge at the welding temperature, the corner is overheated and melted, repelling electromagnetic force, the speed of the material approaching the collision point, movement of the collision point, fluctuation of the heating current, and accompanying heat input fluctuation And a complex mode in which the restoring action by the surface tension of the molten metal interacts, and defects are likely to occur.

  In such electric welded pipe welding, a phenomenon that is characteristic of the welding state appears depending on the magnitude of heat input, pipe diameter, and plate thickness. When not much heat input is applied, welding is performed at the welding point 1a, and the position of the welding point is almost unchanged. When the heat input is increased, as shown in FIG. 6, it is eliminated by the electromagnetic force due to the current flowing through the molten metal and is not welded at the V convergence point 1a, but at the edges 1b and 1c, the molten part 4a is located behind the convergence point 1a. , 4b are formed. The pipe material 1 is moving, and the melting parts 4a and 4b are welded.

In the above-described electric resistance welded pipe welding, the following method has been known as a conventional method for monitoring the welding heat input state among the welding states.
(1) A judgment method with the naked eye of the operator. (2) A method of measuring the temperature of a weld using a radiation thermometer, which is a method of converting total radiant energy into temperature, and using a ratio of energy levels of two specific wavelengths among the total radiant energy. How to convert to (3) A method of electrically detecting a change in resonance frequency and determining an excessive amount of heat input. (4) A method of grasping the shape of the protrusion of the beat after welding.

  Furthermore, even if the heat input is appropriate, if the edge is twisted, the edge shakes, or the squeeze roll pressure (upset) changes, welding failure may occur. As a monitoring method that can be grasped including condition changes, the welded part and the heat generating metal part on the welding entrance side are scanned by the imaging means and divided into a plurality of images, and the feature amount of these images is obtained by the image processing part. There is a method for obtaining appropriate analysis of the welding state and heat input control by obtaining an analysis signal and determining whether the welding state is appropriate based on the analysis signal (Patent Document 1: [0002] to [0013]).

JP-A-5-318142

Any of the above-described conventional techniques is a method devised so as to optimize the welding state.
However, even with the best welding conditions within the scope of the prior art, very fine weld defects may still occur. This is a case where fine foreign matter is mixed in the electric-welded welded portion and a case where a paddle or the like is present at the end portion (edge portion) of the band material (tube material). In other words, iron oxide or iron on the surface of the tube material is peeled off during the electric seam forming welding process and exists as a small amount of dust in the atmosphere. In the electric seam welding process, the molten steel generated during welding is sputtered. Although present, when these dusts and spatter particles rarely jump into the weld, welding defects may occur. Furthermore, even when a portion where a slight wrinkle is generated at the end portion of the strip is electro-welded, the wrinkle may cause a welding defect. All of these welding defects are as small as several mm or less, and even with the above-described conventional technology, it was extremely difficult to detect welding defects caused by such minute disturbance factors. .

  As described above, in the conventional technology, it is extremely difficult to detect minute welding defects of several mm or less that are generated due to dipping of dust or spatter particles in the ERW weld line or wrinkles at the end of the strip in the ERW pipe production line. There was a problem of being.

The present invention has been made to solve the above problems, and the gist thereof is as follows.
(Claim 1)
During operation of the ERW pipe manufacturing line that continuously welds the edges of the V-shaped gap formed by forming the strip into a tubular shape, as a monitoring region at a position spaced 20 to 500 mm downstream from the welding point The predetermined luminance distribution in the line length direction of the linear region substantially orthogonal to the welding line is captured as an image signal obtained by photographing at a photographing speed of 1 ms or less and a photographing number of 1000 times / s or more with a luminance sensor composed of a line scan camera. While monitoring this, calculate the sum and / or half-value width of the instantaneous luminance, which is the luminance distribution information for each frame, and use the time-dependent data of this calculation result to determine whether dust or spatter rarely enters or the edge of the band. A method of monitoring an electro- welded welded portion, characterized by detecting a DS, that is, a dark spot, corresponding to the occurrence of a welding defect caused by a small wrinkle .
(Claim 2)
The detection time information of the DS is converted into corresponding pipe forming length position information by the tracking function, the pipe forming length position where the welding defect has occurred is specified, and the position information is used for the refining process downstream of the pipe forming process. 2. The method for monitoring an electro-welded weld according to claim 1, wherein the pipe length portion including the weld defect is excluded from the product pipe.

  According to the present invention, in the ERW pipe production line, a minute of about several mm or less generated by rare jumps of dust or spatter particles into the ERW welded part, or minute wrinkles attached to the end of the band material. As a result, it is possible to easily detect even a welding defect, and to provide a remarkably high quality ERW pipe, thereby improving the reliability of the quality.

The schematic perspective view which shows one example of the form for implementing this invention FIG. 1 is a schematic plan view according to the example of FIG. Schematic diagram showing the transition of luminance distribution monitoring data Diagram showing an example of the transition curve of the sum of instantaneous luminance with respect to pipe length Diagram showing one example of transition curve of half-value width of instantaneous luminance with respect to pipe length Explanatory drawing showing welding mode as background technology Perspective view showing induction type high frequency electric resistance welded pipe welding as background art Perspective view showing fusion type high frequency electric resistance welded welding as background technology

Inventors repeated experiment and examination in order to solve the said subject, and acquired the following knowledge.
(1) When dust or spatter rarely jumps into the welded part to cause a welding defect, or when a flaw is formed at the end of the band material and is welded to cause a welding defect. The luminance distribution state on the outgoing side instantaneously changes to the dark side.
(2) However, in the downstream region of less than 20 mm from the welding point, the change in the luminance of the weld defect portion is disturbed by the luminance of the surrounding molten portion, so that it cannot be sufficiently observed.
(3) Further, in the downstream region of more than 500 mm from the welding point, the change in the luminance of the weld defect portion is reduced, and the discrimination becomes difficult.

  Based on the above findings, in the present invention, as shown in FIGS. 1 and 2, for example, the edges 1b and 1c of the V-shaped gap formed by forming the tube material 1 whose initial form is a strip into a tubular shape are formed. During the operation of the ERW pipe manufacturing line that continuously welds, a line substantially orthogonal to the welding line 1w, which is predetermined as the monitoring region 11 at a position separated by a distance L = 20 to 500 mm downstream from the welding point 1a. The luminance distribution of the region is captured as an image signal obtained by photographing with the luminance sensor 10 and monitored. Here, “substantially orthogonal” means that the crossing angle is within a range of 90 ° ± 10 °. If the length direction of the linear region defined as the monitoring region 11 is not substantially orthogonal to the weld line 1w, it is difficult to capture the change in instantaneous luminance.

  The luminance sensor 10 is also called a luminance camera and has a function of photographing the monitoring area 11 and deriving a luminance distribution in the photographed screen. An example of such a brightness sensor is a commercially available line scan camera. The luminance information (instantaneous luminance) for each photographing frame of the luminance sensor 10 is captured in a PC (personal computer) or the like as shown in FIG. 1 and image-processed, so that a distribution curve of instantaneous luminance as schematically shown in FIG. Can be monitored as time-varying data of the image signal corresponding to. The DS (dark spot) corresponding to the occurrence of welding defects due to rare jumps in dust or spatter or minute flaws at the end of the strip can be detected from the time-dependent data monitored. The information can be converted into the corresponding pipe length position information by the normally used tracking function, and the pipe length position where the welding defect has occurred can be specified, and the position information is notified to the refining process downstream of the pipe forming process. Thus, the pipe length portion including the weld defect can be surely excluded from the product pipe.

  By the way, the speed of electric resistance welding (weld line generation speed or pipe forming speed) is classified as a high-speed welding method among various welding methods, and may be welded at a speed exceeding 100 m / min. At these welding speeds, in order to discriminate a welding defect of several mm or less, the photographing speed (exposure time of one photographing frame) must be 1 ms (= 1/1000 second) or less. When the imaging speed exceeds 1 ms, portions other than the luminance change portion of the weld defect portion enter the same imaging frame to a considerable extent, and DS detection becomes difficult. Furthermore, in order not to miss a minute welding defect, the number of times of photographing (number of photographing frames) must be 1000 times per second (1000 frames per second) or more. If the number of times of photographing is less than 1000 times per second, the weld defect part may be removed from the photographing frame, resulting in oversight.

Therefore, in the present invention, even when the speed of ERW welding exceeds 100 m / min, the luminance distribution monitored by the luminance sensor so that the welding defect portion can be reliably identified and the welding defect portion is not overlooked. Is preferably captured as an image signal by shooting at a shooting speed of 1 ms or less and a shooting count of 1000 times / s or more.
In addition, the luminance distribution captured as an image signal obtained by photographing with the luminance sensor does not necessarily indicate a simple and smooth mountain-shaped curve shape as shown in the schematic diagram of FIG. In many cases, a complicated curve shape is shown, and it is difficult to immediately perform DS detection (that is, instantaneous determination of suitability of the welding state) from instantaneous luminance data of such a complicated distribution curve shape. Therefore, the inventors examined a method for overcoming this difficulty, and as a result, DS detection was reliably and reliably performed by processing the image signal and using the result of calculating the sum of instantaneous luminance and / or the half-value width. I found it easier. FIG. 4 shows an example of a transition curve of the sum of instantaneous luminance obtained by processing and calculating the image signal with respect to the tube forming length, and FIG. 5 shows processing and calculation of the same image signal as in FIG. An example of the transition curve with respect to the tube forming length of the half-value width of the instantaneous luminance is shown. These transition curves in FIGS. 4 and 5 show a shape having a clear recess in a substantially flat shape, and it can be understood that the tube-forming length portion where DS is generated can be detected reliably and easily. Further, it has been found that the calculation of the sum of the instantaneous luminance and / or the half-value width is preferably performed in real time from the viewpoint of saving the capacity of the data storage means.

  Therefore, in the present invention, even when the image signal shows a complicated curve shape, the image can be detected reliably and easily with less storage means (that is, whether the welding state is instantaneously determined). It is preferable to process the signal in real time to calculate the sum and / or the half value width of the instantaneous luminance, and to determine the suitability of the instantaneous welding state based on the calculation result.

(Conventional example)
Conventionally, the edge of the V-shaped gap formed by roll forming into a tubular shape while continuously expanding a tube material, which is a steel strip wound in a coil shape in an initial form, into a linear shape, Heated by high frequency induction welding and welded by pressure welding with a squeeze roll, forming a welded pipe, cutting the bead of the weld with a bead cutting machine, heat treating the weld with a seam annealer, and adjusting the outer diameter with a sizer Then, using an electric resistance welded pipe production line (tube forming line) configured to cut to a predetermined length with a pipe cutting machine, the operating conditions of electric resistance welding speed (tube forming speed) = 20 to 120 m / min Below, an electric resistance welded tube having an outer diameter of 25.4 to 180 mm and a wall thickness of 1.2 mm to 9.0 mm was manufactured.

According to the results of quality feedback information after shipment of product pipes, there is generally a small welding defect of about several millimeters or less that could not be detected in the downstream finishing line at a rate of 1 place per 50 km of pipe length. There was room for improvement in reliability.
(Example of the present invention)
For the same pipe making line as in the conventional example, L = 200 mm (within the interval range between the squeeze roll and the bead cutting machine) in the form of FIG. 2 and a linear monitoring region (intersection angle with the weld line = 90 °) ) Is determined in advance, and the luminance distribution of the monitoring area is captured as an image signal obtained by photographing with a luminance sensor (using the Spider 2) during operation under the same operating conditions as the conventional example of the pipe forming line. . The shooting speed was 0.05 to 5 ms, and the number of shots was 200 to 20000 times / s, and the setting was changed within this range according to the pipe making speed. When the tube forming speed exceeded 100 m / min, the shooting speed was set to 1 ms or less and the number of shootings was set to 1000 times / s or more.

The image signal thus captured is processed in real time to calculate the sum of instantaneous luminances, a transition curve as shown in FIG. 4 is obtained from the calculation result, and this is compared with a predetermined luminance threshold value, thereby producing a tube length in which DS is generated. The position was specified and notified to the downstream finishing line.
As a result, it is possible to detect a minute weld defect of about several millimeters or less, which could not be detected in the past, and it is possible to eliminate the pipe-forming length portion including such a minute weld defect, so that a product pipe of extremely high quality can be obtained. The reliability of the quality has been significantly improved.
(Comparative example)
In the example of the present invention, L = 10 mm or 600 mm was changed, and other than that, monitoring of the luminance distribution was tried in the same manner as in the example of the present invention. However, in either case, DS could not be detected.

1 Tube material (initial form is strip)
1a Welding point (V convergence point, convergence point)
1b, 1c Edge 1w Welding wire 2a, 2b Squeeze roll 3a Work coil 3b, 3c Chip 3d High frequency oscillation device 4a, 4b Heating metal part including melting part 10 Luminance sensor 11 Monitoring area (Linear area substantially orthogonal to welding line )

Claims (2)

During operation of the ERW pipe manufacturing line that continuously welds the edges of the V-shaped gap formed by forming the strip into a tubular shape, as a monitoring region at a position spaced 20 to 500 mm downstream from the welding point The predetermined luminance distribution in the line length direction of the linear region substantially orthogonal to the welding line is captured as an image signal obtained by photographing at a photographing speed of 1 ms or less and a photographing number of 1000 times / s or more with a luminance sensor composed of a line scan camera. While monitoring this, calculate the sum and / or half-value width of the instantaneous luminance, which is the luminance distribution information for each frame, and use the time-dependent data of this calculation result to determine whether dust or spatter rarely enters or the edge of the band. A method of monitoring an electro- welded welded portion, characterized by detecting a DS, that is, a dark spot, corresponding to the occurrence of a welding defect caused by a small wrinkle . The detection time information of the DS is converted into corresponding pipe forming length position information by the tracking function, the pipe forming length position where the welding defect has occurred is specified, and the position information is used for the refining process downstream of the pipe forming process. 2. The method for monitoring an electro-welded weld according to claim 1, wherein the pipe length portion including the weld defect is excluded from the product pipe.

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