Seam welding method and seam welding apparatus for thin steel plates

Abstract

To provide a seam welding method of a thin steel plate.SOLUTION: Continuous processing of a thin steel plate measures a plate temperature of a thin steel plate before seam welding, and seam welds the thin steel plate, using a weld current value obtained by correcting influence on the measured plate temperature of the thin steel plate. As a weld current value It obtained by correcting the influence of the plate temperature, a following expression: It=IT(1+αt(T-t)) (where IT: reference weld current value (weld current value in a case in which the plate temperature is a reference plate temperature of T°C) (unit: kA), T: reference plate temperature (°C), t: measured plate temperature (°C), and αt: coefficient) is used. Thereby, especially, quality of a seam weld part of a high tensile thin steel plate is made stable, the continuous processing of the thin steel plate exhibits effects to prevent troubles including breakage of the seam weld part at the time of passing through a steel plate, and to prevent lowering of productivity and occurrence of malfunction articles.SELECTED DRAWING: Figure 2

Description

[Technical Field]

[0001] The present invention relates to a seam welding method and apparatus for thin steel sheets in a continuous processing line, and more particularly to the optimization of the welding current. [Background technology]

[0002] In general, mash seam welding (hereinafter also called seam welding) is widely used in continuous processing lines for thin steel sheets (hereinafter also called thin steel sheets). In seam welding, the trailing end of the preceding steel sheet and the leading end of the following steel sheet are slightly overlapped, and a welding current is supplied to the overlapping area while applying pressure with a rotating electrode (electrode wheel) and rotating it, performing resistance welding.

[0003] In seam welding, welding conditions such as welding current and electrode pressure are generally known to be important from the standpoint of the joint strength of the weld. Moreover, welding conditions such as welding current and electrode pressure are greatly influenced by the composition and thickness of the thin steel plate. If the welding conditions are inappropriate, for example, if the welding current is too high, spatter will occur. On the other hand, if the welding current is too low, the strength of the weld will be insufficient, and the weld may fracture during continuous processing. If the weld fractures, the operation of the continuous processing line will stop, leading to a decrease in productivity and the generation of a large number of defective products.

[0004] Therefore, when performing seam welding, it was necessary to conduct numerous welding tests for each type of steel and plate thickness of the material to be welded, and to perform cross-sectional observations and tensile tests on the welded area in order to set the optimal welding conditions. However, conducting numerous welding tests for each target steel plate is time-consuming, laborious, and not economical. Given this situation, there was a demand for a simple method that could set the optimal welding conditions without conducting welding tests for each target steel plate.

[0005] In response to such demands, for example, Patent Document 1 proposes a mash seam welding method. In the mash seam welding method described in Patent Document 1, the optimal welding current density is determined based on the Mn content of the plate materials to be joined, and the welding current is set based on the obtained optimal welding current density. The optimal welding current value is greatly influenced by the Mn content in the steel plate, and the optimal welding current density i(kA / (mm) 2 ·min) is expressed as follows: i 2 = A × Mn(mass%) + B (where A and B are constants) It is stated that the optimal welding current density can be easily determined by the method described in Patent Document 1, enabling efficient joining.

[0006] Furthermore, Patent Document 2 describes a method for overlapping seam welding of thin sheet coils. In the overlapping seam welding method described in Patent Document 2, fluctuations in the applied pressure during welding are detected, and the appropriate welding current I is determined by the following formula I = I0(P / P0) 1 / 3 (Here, I0: initial welding current value, P: applied pressure after variation, P0: initial applied pressure) The welding current is controlled by calculating it using the method described in Patent Document 2. According to the lap seam welding method described in Patent Document 2, a stable and good nugget can be obtained even if the pressing force fluctuates, and a lap seam welded joint with sufficient strength can be formed. [Prior art documents] [Patent Documents]

[0007] [Patent Document 1] Japanese Patent Publication No. 2003-136252 [Patent Document 2] Japanese Patent Application Publication No. 4-228274 [Overview of the Initiative] [Problems that the invention aims to solve]

[0008] However, in recent years, in the continuous processing line of thin steel plates, the processing volume of high-tensile steel plates has been increasing. In high-tensile steel plates, in order to ensure high strength and good mechanical properties, the alloying elements added are also diversified, and the addition amount thereof also tends to increase. In such seam welding of high-tensile steel plates, the appropriate range of welding conditions is narrow, and it is difficult to maintain high quality of the seam welded portion. In particular, this tendency is strong in high-tensile steel plates with a tensile strength of 590 MPa or more.

[0009] Therefore, an object of the present invention is to provide a seam welding method and a seam welding apparatus for thin steel plates that can maintain high quality of a seam welded portion even when the steel plate to be processed is a high-tensile steel plate with a tensile strength of 590 MPa or more.

Means for Solving the Problems

[0010] In order to achieve the above object, the present inventors earnestly studied the cause of the deterioration of the quality of the seam welded portion of high-tensile steel plates. As a result, particularly, since the quality of the seam welded portion of high-tensile steel plates tends to deteriorate in winter when the temperature is low, it was thought that the temperature of the steel plate has a great influence on the quality of the seam welded portion. In winter when the temperature is low, it was considered that the temperature of the steel plate, which is the material to be welded, also decreases, and the quality of the welded portion deteriorates.

[0011] Therefore, high-tensile steel plates (plate thickness: 1.20 mm) of 590 MPa grade or more in tensile strength were prepared as a set of two sheets, a leading material and a trailing material. Then, as shown in FIG. 3, the rear end portion of the leading steel plate and the front end portion of the trailing steel plate were overlapped, and seam welding was performed by supplying a welding current while pressing and rolling the overlapping portion with a pair of upper and lower electrode wheels for joining. Before the seam welding, the temperature of the steel plate was actually measured. And after the seam welding, the temperature of the welded portion was measured. In addition, the welding conditions of the seam welding other than the plate temperature were the same.

[0012] The obtained results are shown in FIG. 2 in relation to the temperature of the seam welded portion and the plate temperature t of the steel plate. It can be seen from FIG. 2 that the temperature of the seam weld portion shows a relationship proportional to the plate temperature t of the steel sheet. From this, it was found that it is necessary to adjust the welding current value according to the plate temperature t of the steel sheet so that the temperature of the seam weld portion is within a predetermined range, considering the temperature of the seam weld portion as an index of the quality of the seam weld portion. That is, it was found that it is necessary to perform seam welding with a welding current value obtained by actually measuring the plate temperature of the workpiece to be welded and correcting the influence of the plate temperature of the workpiece to be welded.

[0013] Based on such findings, the present invention was further studied and completed. That is, the gist of the present invention is as follows. [1] A method for seam welding thin steel sheets in a continuous production line of thin steel sheets, wherein the rear end portion of a preceding thin steel sheet and the front end portion of a succeeding thin steel sheet are overlapped and seam welded, a plate temperature measuring step of actually measuring the plate temperature of the thin steel sheet, a welding current value setting step of setting a welding current value for the seam welding, and a welding step of performing seam welding with the set welding current value, in this order, wherein the welding current value setting step includes a step of setting a welding current value for the seam welding based on the actually measured plate temperature of the thin steel sheet obtained in the plate temperature measuring step. A method for seam welding thin steel sheets, characterized by the above. [2] In the above step, the welding current value for the seam welding to be set is the following formula (1) I t =I T (1 + α t (T - t)) ··· (1) Here, I T : reference welding current value (welding current value when the plate temperature is the reference plate temperature T °C) (unit: kA), T: reference plate temperature (°C), t: actually measured plate temperature (°C), α t : coefficient The welding current value I t defined by is used. The method for seam welding thin steel sheets according to [1], characterized by the above. [3] The method for seam welding thin steel sheets according to [2], wherein the actually measured plate temperature t of the thin steel sheet is the actually measured plate temperature of the succeeding thin steel sheet. [4] The seam welding method for thin steel plates according to [2], characterized in that the reference plate temperature T is 20°C. [5] The seam welding method for thin steel plates according to [2], wherein the reference plate temperature T and the measured plate temperature t satisfy Tt > 0. [6] The seam welding method for thin steel plates according to any one of [1] to [5], characterized in that the thin steel plate is a high-tensile steel plate with a tensile strength of 590 MPa or more. [7] A seam welding apparatus for thin steel sheets in a continuous manufacturing line for thin steel sheets, comprising an upper and lower pair of electrode rings, a clamping device, and a welding current supply means, which overlaps the rear end of a preceding thin steel sheet and the front end of a following thin steel sheet and seam welds them, further A seam welding apparatus for thin steel plates, comprising: a plate temperature measuring means for measuring the plate temperature of the thin steel plate; and a welding current control means for setting a welding current value based on the measured plate temperature. [Effects of the Invention]

[0014] According to the present invention, the quality of seam welds in high-tensile thin steel sheets is stabilized, and problems such as seam weld breakage during continuous processing of thin steel sheets can be prevented, thereby reducing productivity and preventing the occurrence of defective products, resulting in significant industrial benefits. [Brief explanation of the drawing]

[0015] [Figure 1] This is a schematic diagram illustrating an example of a seam welding apparatus used in the present invention. [Figure 2] This graph shows the effect of the measured temperature of the steel plate on the seam weld temperature. [Figure 3] This is a schematic diagram illustrating the general outline of the seam welding method. [Modes for carrying out the invention]

[0016] In the seam welding method for thin steel sheets, the rear end of a preceding steel sheet (leading material) and the leading end of a following steel sheet (following material) are overlapped, and welding current is supplied (energized) to the overlapped portion while applying pressure and rolling a pair of upper and lower electrode rings to join the overlapping portion (seam welding). Here, "thin steel sheet" refers to a steel sheet with a thickness in the range of 0.3 to 2.5 mm.

[0017] In seam welding, the electrical resistance of the metal (steel plate) is used to generate heat and join the materials. Therefore, when the electrical resistance decreases and the amount of heat generated decreases, the temperature of the seam weld decreases. Generally, it is known that the electrical resistivity of metal decreases as the temperature decreases, so when the temperature of the steel plate (plate temperature) decreases due to a decrease in ambient temperature, the electrical resistance decreases and the amount of heat generated decreases, resulting in a decrease in the temperature of the seam weld as shown in Figure 2.

[0018] A decrease in seam weld temperature does not significantly affect the quality of the weld in relatively easy-to-weld materials such as mild steel. However, in high-tensile steel plates, which are difficult to weld, the difference between the weld temperature at which the nugget is formed and the weld temperature at which dust is generated is small, so the impact on the quality of the weld cannot be ignored. Examples of such high-tensile steel plates include those with a tensile strength of 590 MPa or higher.

[0019] [Plate temperature measurement process] In this invention, the temperature of the thin steel sheet to be welded is measured before seam welding. For steel sheets with high thermal conductivity, the temperature of the sheet and the ambient temperature are approximately the same, so it can be assumed that the temperature of the later sheet and the earlier sheet are approximately the same. From the viewpoint of ease of work, it is preferable to measure the temperature of the later sheet when measuring the thin steel sheet. In this invention, the plate temperature of the steel plate to be welded is preferably measured by the plate temperature measuring means 4 shown in Figure 1. The obtained measured plate temperature is then transmitted to the welding current control means 5.

[0020] [Welding current value setting process] In the welding current value setting step, the welding current value for seam welding is set. In this invention, the welding current value for seam welding is set based on the measured plate temperature of the thin steel plate obtained in the plate temperature measurement step.

[0021] The welding current value set in this step is a welding current value I corrected for the influence of the measured plate temperature t of the thin steel plate, based on the measured plate temperature (measured plate temperature) of the thin steel plate. t Let's assume that.

[0022] In this invention, the welding current value corrected for the effect of the measured plate temperature t is given by the following equation (1): I t =I T (1+α t (Tt)) ... (1) Here, I T : Reference welding current value (welding current value when the plate temperature is the reference plate temperature T℃) (Unit: kA), T: Reference plate temperature (℃), t: Actual plate temperature (℃), α t :coefficient The welding current value I defined by t It is preferable to do so.

[0023] Here, α in equation (1) t (Tt) is a term that corrects for the effect of the plate temperature of the thin steel sheet on the welding current value. In equation (1), a reference plate temperature T is selected, and the difference (Tt) between the reference plate temperature T and the measured plate temperature t is used, and the effect of plate temperature fluctuations is α t (Tt) Reference welding current value I T It was decided to correct α. t This is a coefficient used to correct the effect of plate temperature on the supplied welding current value, and it varies depending on the type of material being welded (steel plate), but for high-tensile steel plates with a typical tensile strength of 590 MPa or more, α t The range is 0.05 to 0.20. Furthermore, the reference plate temperature T is preferably a plate temperature that occurs frequently. For example, it is preferably 20 to 25°C, which is generally referred to as room temperature.

[0024] In other words, if the measured plate temperature t (°C) is the same as the reference plate temperature T (°C), then the welding current value I t The standard welding current value IT This is the case. When the plate temperature t is lower than the reference plate temperature T ((Tt)>0), the welding current value I t The standard welding current value I T If the plate temperature t is higher than the reference plate temperature T ((Tt) < 0), the welding current value I t The standard welding current value I T This will result in a further reduction. Especially in winter when the temperature is low, if the plate temperature t is lower than the reference plate temperature T (satisfying (Tt)>0), the welding current value will be the welding current value I defined by equation (1). t The standard welding current value I T The value is corrected to increase it further. This raises the temperature of the weld, increases the strength of the joint, and suppresses problems such as seam weld fracture. Note that the standard welding current value is I. T It is preferable to determine this in advance by conducting preliminary experiments for each steel plate in question. In the present invention, the welding current control means 5 shown in Figure 1 corrects the effect of the plate temperature on the actual plate temperature obtained in the plate temperature measurement process and the preset formula as described above to obtain a welding current value I t Perform the calculation.

[0025] [Welding Process] In the welding process, the welding current value I set in the welding current value setting process described above is used. t Seam welding is performed. In this invention, the welding current value I set in the welding current value setting step described above is used. t The welding current is supplied (energized) to the electrode rings 31 and 32 via the welding current supply means 51, and the overlapping portion is seam welded (joined).

[0026] [Seam welding equipment] The seam welding apparatus used in the seam welding method of the present invention comprises a pair of upper and lower electrode rings, a clamping device, and a welding current supply means, and further comprises a plate temperature measuring means 4 and a welding current control means 5, as shown in Figure 1.

[0027] As shown in Figure 3, the seam welding apparatus includes a pair of upper and lower electrode wheels 31 and 32. Each of the electrode wheels 31 and 32 is arranged to be rotationally driven (rolled) by a driving means (not shown). Furthermore, it is preferable that the seam welding apparatus includes a leading clamping device that clamps the leading steel plate 1 from above and below, and a trailing clamping device that clamps the trailing steel plate 2 from above and below. Each clamping device includes a pair of upper and lower clamping members 6 and 7, enabling them to grip and overlap the leading steel plate 1 and the trailing steel plate 2, respectively.

[0028] Furthermore, the plate temperature measuring means 4 includes a measuring terminal (plate thermometer) 41 and a calculation means 42. In the plate temperature measuring means 4, the measuring terminal (plate thermometer) 41 makes contact with the steel plate to be measured, the calculation means calculates the plate temperature (actual plate temperature), and transmits the obtained result (actual plate temperature) to the welding current control means 5. Examples of the measuring terminal 41 include thermocouples and infrared radiation thermometers.

[0029] Furthermore, the welding current control means 5 uses the transmitted measured plate temperature to correct the effect of the plate temperature on the welding current value I according to a preset formula. t The welding current value I is calculated. t The welding current is supplied to the electrode rings 31 and 32 via the welding current supply means 51, and the overlapping portion is joined by seam welding.

[0030] The present invention will be further described below based on the following examples. [Examples]

[0031] In a continuous processing line for thin steel sheets, a seam welding apparatus having a plate temperature measuring means 4 and a welding current control means 5 as shown in Figure 1 is used to overlap the rear end of a preceding thin steel sheet 1 (leading material) and the leading end of a following thin steel sheet 2 (following material). Then, while applying pressure and rolling the overlapping portion with a pair of upper and lower rotating electrodes (electrode wheels) 31 and 32, welding current is supplied via a welding current supply means 51 to perform seam welding and join the overlapping portion of the leading material 1 and the following material 2.

[0032] The thin steel sheet used was a high-tensile steel sheet with a tensile strength of 590 MPa or higher (thickness: 1.20 mm). Before performing seam welding, the temperature t (°C) of the trailing material 2 was measured using the temperature measuring terminal 41 (plate thermometer) of the plate temperature measuring means 4, and the obtained measured plate temperature was transmitted to the welding current control means 5. The welding current control means 5 used the measured plate temperature t of the transmitted steel sheet and the following equation (1) to determine the welding current value I to be supplied during seam welding. t The following equation was calculated. Equation (1) is the following equation I t =I T (1+α t (20-t)) ... (1) Here, I t is the welding current value supplied during seam welding, t is the measured plate temperature of the steel plate (°C), and 20 is the reference plate temperature T (°C). Also, α t α is a coefficient used to correct for the effect of plate temperature on the supplied welding current. t =0.1(kA / ℃) was used.

[0033] The welding current value I calculated using the above equation (1) t The present invention exemplifies a case where seam welding was performed using [the specified method]. On the other hand, without measuring the temperature of the steel plate, a constant welding current (reference welding current value I) is used. T A comparative example was used when seam welding was performed using the supplied material.

[0034] The aforementioned seam welding procedures were performed between December 2022 and April 2023 (a period of 5 months), and the occurrence of problems in the seam welds was investigated. As a result, problems such as plate fracture occurred in 1.2% of the total number of joints in the comparative example. On the other hand, no problems occurred in the present invention example. The total number of joints during the investigation period was 500 for the present invention example and 2000 for the comparative example example. [Explanation of Symbols]

[0035] 1. Preceding steel plate (preceding material) 2. Subsequent steel plates (subsequent material) 31 Upper electrode ring (upper electrode ring) 32 Lower electrode ring (lower electrode ring) 4 Plate temperature measurement means 41 Temperature measuring terminal (plate meter) 42 Calculation means 5. Welding current control means 51 Welding current supply means 6. Pre-clamping member 7 Rear clamping member

Claims

1. A seam welding method for thin steel sheets in a continuous manufacturing line for thin steel sheets, wherein the trailing end of a preceding thin steel sheet and the leading end of a following thin steel sheet are overlapped and seam-welded, The thin steel sheet is a high-tensile steel sheet with a tensile strength of 590 MPa or more. A plate temperature measurement step for actually measuring the plate temperature of the thin steel plate, A welding current value setting step for setting the welding current value for the aforementioned seam welding, The process comprises, in this order, a welding process in which seam welding is performed with the aforementioned set welding current value, The welding current value setting step includes setting the welding current value for the seam welding based on the measured plate temperature of the thin steel plate obtained in the plate temperature measurement step. In the above step, the welding current value for the seam welding to be set is given by the following equation (1): I t =IT (1+α t (T-t)) (1) Here, IT: Reference welding current value (welding current value when the plate temperature is the reference plate temperature T°C) (unit: kA), T: Reference plate temperature (°C), t: Measured plate temperature (°C), αt: Coefficient in the range of 0.05 to 0.20 A seam welding method for thin steel plates, characterized in that the welding current value I t is defined as follows.

2. The seam welding method for thin steel plates according to claim 1, characterized in that the measured plate temperature t of the thin steel plate is the measured plate temperature of the thin steel plate to be welded later.

3. The method for seam welding a thin steel plate according to claim 1, characterized in that the reference plate temperature T is 20°C.

4. The method for seam welding a thin steel plate according to claim 1, wherein the reference plate temperature T and the measured plate temperature t satisfy T - t > 0.

5. A seam welding apparatus for thin steel sheets in a continuous manufacturing line for thin steel sheets, comprising a pair of upper and lower electrode rings, a clamping device, and a welding current supply means, which performs seam welding by overlapping the rear end of a preceding thin steel sheet with the front end of a following thin steel sheet using the seam welding method for thin steel sheets described in claim 1, further comprising a plate temperature measuring means for measuring the plate temperature of the thin steel sheet, and a welding current control means for setting a welding current value based on the measured plate temperature.

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