JP2009255132A - Electric welding system - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To solve the problem that it is difficult to decrease welding defects by a traditional technology to a level which sufficiently satisfies quality requirements of electric weld steel pipe used in a severe environment. <P>SOLUTION: The welding system for electric welded pipe comprises a work coil 2 to perform high frequency heating on a work 10 (which is a metal strip in a raw material stage but becomes a pipe after electric welding), a squeeze rolls 5, 5 to perform pressure welding, a high speed camera 6 which can perform a consecutive photographing for more than 10 ms at a shutter speed of shorter than 1/200 second in the proximity of a welding point 3 of the work. Based on the images taken by the high-speed camera, an image processing apparatus 100 to judge deviation between a narrow aperture zone length L, which is obtained by measuring a length of a narrow aperture zone 4 from a weld point 3 to V convergence point 7, and a designated range (F+A1, F+A2), which is based on a function F(t, d, v), wherein t is thickness of metal strip, d is outside diameter of pipe, and v is welding speed, and a control unit 110 to adjust power supply amount to the work coil depending on these judgments, are also included. <P>COPYRIGHT: (C)2010,JPO&amp;INPIT

Description

  The present invention relates to an electric resistance welding system, and in particular, manufactures an electric resistance welded pipe excellent in welding quality by controlling the amount of heat input during electric resistance welding to reduce minute oxides generated in a welded portion. The present invention relates to an electric resistance welding system.

  In recent years, along with the development of molding and welding technology, various ERW welded pipes such as carbon steel pipes, stainless steel pipes, Ti pipes, superalloy pipes, etc. have been manufactured. And so on. The use conditions of ERW welded pipes in these applications are becoming increasingly severe year by year, and the quality requirements for welded parts tend to become stricter, and prevention of welding defects is an important issue.

  In general, in the manufacture of ERW welded pipes, a workpiece made of a metal strip is rounded continuously by roll forming into an open pipe shape having seam portions facing both ends of the width. A method is employed in which a pipe is welded (electro-sewing welding) by high-frequency heating and squeeze pressure welding. In such a manufacturing method, if the heat input amount (Joule heat generation amount) at the time of ERW welding is too low, the weld defect in which the seam part is not welded mainly or the cold welding defect caused by insufficient melting of the seam part It is known that a weld defect referred to as occurs. On the other hand, it is known that if the heat input is too high, a weld defect called a penetrator is likely to occur in the seam portion.

  It is known that the position of the welding point changes as the heat input changes. That is, the seam portion of the workpiece has a V shape with a narrow interval in the direction of threading, and the geometric V convergence point is a welding point, but the position of this welding point is not necessarily constant, and welding is performed. Varies depending on conditions. Therefore, in order to stabilize the welding point at the reference position, the area is photographed online with a camera installed in the vicinity of the welding point, and the brightness level of the obtained image is binarized to detect the welding point position. It is known that the heat input voltage of the welding machine is controlled so that the deviation between the current welding point position and a predetermined reference welding point position becomes zero (Patent Document 1).

Moreover, the phenomenon in which a welding point separates from a V convergence position with a change in the amount of heat input is known (Non-Patent Document 1). In this phenomenon, the welding point moves forward (downstream in the material passing direction) from the V convergence position, and a narrow gap portion in which the seam portion is not welded is developed between the V convergence position and the welding point. Appear. As a method of optimally controlling the welding heat input in order to prevent welding defects by capturing the shape change information in the vicinity of the welding point, a method of monitoring the frequency fluctuation of the welding power source and controlling the heat input so as to optimize it ( Patent Document 2) is known.
JP-A-8-71638 JP 61-135490 JP Steelmaking Research No.297, p.84-93

  However, according to the prior art, it is difficult to reduce welding defects to the extent that the quality requirements of the ERW welded pipe used in a harsh environment are sufficiently satisfied, and this is a problem.

  The inventors diligently studied to solve the above problems, and as a result, obtained the following knowledge. That is, as shown in FIG. 2, if the heat input condition is appropriate (FIG. 2 (b)), the position of the welding point 3 changes to the middle, and the rear side from the welding point 3 (upstream in the material passing direction). The variation in the length L of the narrow gap portion 4 formed in the range from the V convergence position (position where the end faces 1 and 1 change from the diagonally opposed state to the frontally opposed state) 7 is also middle. On the other hand, when the welding heat input is low (FIG. 2 (a)), the position variation of the welding point 3 is small and almost no narrow gap is formed, and when the welding heat input is high (FIG. 2 (c)) The rear narrow gap 4 becomes larger, and its length L varies greatly within a short time of 0.1 second or less. There may be some places as if the seam portions are joined within the length range of the narrow gap portion 4, but such places are ignored. That is, when the narrow gap portion 4 looks like a broken line, the foremost end of the extended range of the broken line is used as the welding point 3 and the length from there to the V convergence position 7 is adopted as the length of the narrow gap portion 4. .

The upper and lower limits of the length L of the narrow gap portion 4 corresponding to appropriate welding conditions have a very good correlation with a function (for example, a linear function) using the workpiece thickness, pipe outer diameter, and welding speed as parameters. Have a relationship.
That is, instead of capturing the shape change information in the vicinity of the welding point, the length of the narrow gap is observed, and the welding heat input is optimized so that it falls within the appropriate range based on the above function. As a result, the present invention has the following gist configuration.
(Claim 1)
An electro-welding welding system that forms a workpiece made of a metal strip into a tube by electro-frequency welding with high-frequency heating and pressure welding of seam portions formed at both ends in the circumferential direction of an open tube formed by continuously roll-forming the material. A work coil that performs the high-frequency heating, a squeeze roll that performs the pressure welding, and a high-speed camera that can continuously shoot a portion near the welding point of the work at a shooting speed of 1/200 second or less for a time of 10 ms or longer. The length of the narrow gap from the welding point to the V convergence position is measured based on the image taken by the high-speed camera, the measured narrow gap length L, the thickness t of the metal strip, the outside of the tube An image processing apparatus that determines a deviation from the following predetermined range (F + A1, F + A2) based on the function F (t, d, v) of the diameter d and the welding speed v, and according to the determination result of the image processing apparatus And a control device that adjusts the amount of power supplied to the work coil. ERW welding system.

Specified range (F + A1, F + A2): “Value F + constant A1 of function F (t, d, v)” and “Value F + constant A2 of function F (t, d, v)” The range that is smaller. However, A1 <A2.
(Claim 2)
An electric resistance welded pipe manufactured using the electric resistance welding system according to claim 1.

  According to the electric seam welding system of the present invention, the length of the narrow gap portion from the welding point to the V convergence position can be measured with high accuracy, and the length of the narrow gap portion is optimized using this measurement length. In addition, by adjusting the amount of electric power supplied to the work coil, it is possible to manufacture an electric resistance welded pipe with extremely excellent welding quality. The ERW welded pipe manufactured using the ERW welding system of the present invention is highly reliable with reduced welding defects to the extent that it sufficiently satisfies the quality requirements when used in harsh environments. .

  Hereinafter, an embodiment of the present invention will be described in detail using an example shown in FIG. The workpiece 10 whose material is a metal strip is continuously rounded by roll forming to be an open pipe, and both end faces (seam portions) 1, 1 in the circumferential direction of the open pipe converge in a V shape, The squeeze rolls 5, 5 are heated and melted by a high-frequency current induced and supplied from the work coil 2, and appear as if they are joined at a V convergence position 7 and / or somewhere in the narrow gap 4. And the welding is completed at the position of the welding point 3 (see FIG. 2 for the welding point 3, the narrow gap portion 4, and the V convergence position 7). In addition, the bead 11 on the pipe outer surface side formed in the seam weld portion 9 on the downstream side of the welding point 3 is cut with a cutting tool 13 to bead scraps 12. Further, in order to increase the end surface heating efficiency by the work coil 2, the impeder 14 is supported by the rod 15 and arranged on the inner surface side of the open pipe.

  The high-speed camera 6 used in the present invention is digital. Of course, the recorded image is recorded. Moreover, what has an optical lens system is preferable. The high-speed camera 6 is preferably disposed at a position on the outer surface side of the workpiece 10 such that the entire length of the narrow gap portion 4 is within the same field of view. When the entire length of the narrow gap portion 4 does not fit in the visual field, the high-speed camera 6 may be moved in the tube axis direction and tilted to cover the entire length with a plurality of visual fields. In that case, the captured image is corrected. In this example, the light from the object to be photographed is directly incident on the field of view of the high-speed camera 6. However, the present invention is not limited to this, and the light from the object to be imaged is transmitted by a fiberscope or a reflecting mirror. The incident light may be incident on the field of view of the high-speed camera 6.

  The high-speed camera 6 must be capable of continuous shooting for 10 ms or longer at a shooting speed of 1/200 sec or less. When the shooting speed is slower than 1/200 second, it is difficult to capture the phenomenon that the length of the narrow gap changes in a short time, and the shot image of the seam weld is unclear. Therefore, it is necessary to use a high-speed camera capable of shooting at a fast speed of 1/200 second or less in order to capture the changing phenomenon as a clear captured image. In addition, under optimal heat input conditions, the length of the narrow gap changes with a certain degree of periodicity, and the change in length cannot be captured sufficiently with an observation time of less than 10 ms (continuous shooting time). It is necessary to use a high-speed camera capable of continuous shooting for 10 ms or longer.

An image including the four narrow gap images captured and recorded by the high-speed camera 6 is input from the image input board of the personal computer to the image processing apparatus 100 incorporated in the personal computer. An image input from the image input board is displayed on the monitor screen of the personal computer as necessary.
The image processing apparatus 100 functions as follows.
(1) Based on the input image including the narrow gap 4 image, the length L of the narrow gap 4 from the welding point to the V convergence position is measured.
(2) Predetermined function F (t, d, v) using data of material (metal strip) thickness t, pipe outer diameter d, welding speed (penetration speed) v related to workpiece 10 currently being passed And a predetermined range (F + A1, F + A2) is calculated using the calculation result F and predetermined constants A1, A2 (A1 <A2). When the unit of L is [mm], the units of t, d, and v are preferably [mm], [mm], and [mm / s], respectively.
(3) A deviation between the measured L and the calculated predetermined range (F + A1, F + A2) is determined, and the determination result is used as an output signal to the control device 110 via the D / O board. The determination of the deviation is performed as follows, for example.
When L ≦ F + A1, the deviation amount δ = L− (F + A1) (δ ≦ 0 at this time) is calculated and used as the determination result.
When L ≧ F + A2, the deviation amount δ = L− (F + A2) (δ ≧ 0 at this time) is calculated and used as the determination result.
When F + A1 ≦ L ≦ F + A2, the deviation amount δ = 0 is set as the determination result.

  The control device 110 commands the welding machine to change the welding power, for example, as follows, in accordance with the determination result (signal corresponding to the δ) sent from the image processing device 100. That is, when the current welding power is P, the welding power is commanded to be changed to P ′ = P + kδ (k is a predetermined positive coefficient) according to δ sent. The welding machine adjusts the amount of power supplied to the work coil 2 in accordance with this command. In addition, the adjustment method of supply electric energy (welding electric power) is a method of adjusting current under constant voltage (this method is adopted in the example of FIG. 1), a method of adjusting voltage under constant current, voltage, Any of the methods of adjusting the current together may be used. << Is this OK? >>

  As a result, the welding heat input can be accurately controlled within an appropriate range, and welding defects can be significantly reduced.

As an embodiment of the present invention, using the electric seam welding system of the present invention illustrated and illustrated in FIG. 1 (the present invention system for short), the material is 0.05% (mass%, the same applies hereinafter) C-0.2% Si-1.4% A work that is a hot-rolled steel strip of Mn steel (Ac ₃ transformation point: about 860 ° C) is electro-welded and welded while operating the system of the present invention under various conditions of t, d, and v. Got.
The high-speed camera uses a camera that can continuously shoot a part near the welding point of the workpiece at a shooting speed of 1/200 second or less for a time of 10 ms or longer. In this embodiment, the shooting speed is set to 1/500 seconds and the continuous shooting time is set to 100 ms.

The function F (t, d, v) and constants A1 and A2 for determining the predetermined range (F + A1, F + A2) were determined from the analysis of ERW steel pipe manufacturing experiment data.
F (t, d, v) = 0.259t + 0.013d-0.00548v, A1 = -6.16, A2 = 23.84
Was used. In the analysis of the ERW steel pipe manufacturing experiment data, the range of the parameters t [mm], d [mm], v [mm / s] of the function F (t, d, v) is t = 0.8 to 25.4 mm, d = 25.4 to 660 mm, v = 200 to 1500 mm / s. In this embodiment, t, d, and v are variously varied within the range.

  Five Charpy specimens with seam welds of 2mmV notch are obtained for each of the obtained ERW steel pipes under each condition, and Charpy impact tests are performed using these specimens. And the area ratio of the weld defects was measured. The weld defect area ratio data measured in this manner showed an average value = 0.06% and a standard deviation = 0.04% through all the conditions of this example.

  The welding defect area ratio data for the above-mentioned embodiment is the conventional one in which the electric power welding to the work coil is set by relying on experience without performing the photographing of the narrow gap portion with the high-speed camera and performing the electric resistance welding. Compared with the welding defect area ratio data (average value = 0.4%, standard deviation = 1.3%) obtained in the same way for the examples, both the average value and standard deviation are much smaller, and the present invention prevents welding defects. It is clear that the effect is extremely large.

It is explanatory drawing which shows one example of embodiment of this invention. It is explanatory drawing which shows the narrow gap part which concerns on this invention.

Explanation of symbols

1 End face (Seam part)
2 Work coil 3 Welding point 4 Narrow gap 5 Squeeze roll 6 High-speed camera 7 V convergence position 9 Seam weld
10 Workpiece (workpiece)
11 beads
12 Bead cutting waste
13 bytes
14 Impeda
15 rod
100 Image processing device
110 Controller

Claims (2)

An electro-welding welding system that forms a workpiece made of a metal strip into a tube by electro-frequency welding with high-frequency heating and pressure welding of seam portions formed at both ends in the circumferential direction of an open tube formed by continuously roll-forming the material. A work coil that performs the high-frequency heating, a squeeze roll that performs the pressure welding, and a high-speed camera that can continuously shoot a portion near the welding point of the work at a shooting speed of 1/200 second or less for a time of 10 ms or longer. The length of the narrow gap from the welding point to the V convergence position is measured based on the image taken by the high-speed camera, the measured narrow gap length L, the thickness t of the metal strip, the outside of the tube An image processing apparatus that determines a deviation from the following predetermined range (F + A1, F + A2) based on the function F (t, d, v) of the diameter d and the welding speed v, and according to the determination result of the image processing apparatus And a control device that adjusts the amount of power supplied to the work coil. ERW welding system.
Specified range (F + A1, F + A2): “Value F + constant A1 of function F (t, d, v)” and “Value F + constant A2 of function F (t, d, v)” The range that is smaller. However, A1 <A2.   An electric resistance welded pipe manufactured using the electric resistance welding system according to claim 1.

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