Seam welding method and seam welding device of thin steel plate

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 method and apparatus for seam welding thin steel plates in a continuous processing line, and in particular to optimizing a welding current. [Background technology]

[0002] Generally, mash seam welding (hereinafter also referred to as seam welding) is widely used in continuous processing lines for thin steel sheets (hereinafter also referred to as thin steel sheets). In seam welding, the rear end of the preceding steel sheet and the front end of the following steel sheet are slightly overlapped, and the overlapped area is pressurized with a rotating electrode (electrode wheel) and rotated while supplying a welding current to perform resistance welding.

[0003] In seam welding, it is generally known that welding conditions such as welding current value and electrode pressure are important from the viewpoint of the joint strength of the weld. Moreover, welding conditions such as welding current value and electrode pressure are greatly affected by the composition, plate thickness, etc. 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 break during continuous processing. If the weld breaks, the operation of the continuous processing line will be stopped, leading to a decrease in productivity and the generation of a large number of defective products.

[0004] For this reason, when performing seam welding, it is necessary to perform a large number of welding tests for each steel type and plate thickness of the material to be welded, and to perform cross-sectional observation of the welded part and tensile tests, etc., to set the optimal welding conditions. However, performing a large number of welding tests for each target steel plate, etc. requires a lot of time and effort, and is not economical. Under these circumstances, a simple method for setting the optimal welding conditions without performing a welding test for each target steel plate, etc. has been desired.

[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, an optimum 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 optimum welding current density obtained. The optimum welding current value is greatly influenced by the Mn content in the steel plate, and the optimum welding current density i (kA / (mm 2 ·min) is expressed by the following formula i 2 =A×Mn(mass%)+B (where A and B are constants) According to the mash seam welding method described in Patent Document 1, it is possible to easily find the optimum welding current density, and it is possible to achieve efficient joining.

[0006] Patent Document 2 describes a lap seam welding method for thin plate coils. In the lap seam welding method described in Patent Document 2, a change in welding pressure during welding is detected, and an appropriate welding current I is calculated according to the following formula: I = I0(P / P0) 1 / 3 (where I0 is the initial welding current value, P is the applied pressure after the change, and P0 is the initial applied pressure). According to the lap seam welding method described in Patent Document 2, a stable and good nugget can be obtained even if the welding pressure varies, and a lap seam welded joint having sufficient strength can be formed. [Prior art documents] [Patent documents]

[0007] [Patent Document 1] JP 2003-136252 A [Patent Document 2] Japanese Patent Application Publication No. 4-228274 Summary of the Invention [Problem to be solved by the invention]

[0008] However, in recent years, there has been a trend toward increasing the amount of high-tensile steel plates processed in continuous thin steel plate processing lines. In order to ensure high strength and good mechanical properties in high-tensile steel plates, the alloy elements added are becoming more diverse and the amounts of these elements added are also increasing. In seam welding of such high-tensile steel plates, the appropriate range of welding conditions is narrow, making it difficult to maintain high quality in the seam welds. This trend is particularly 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 seam welding apparatus for thin steel plates that can maintain high quality of seam welds 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 problem]

[0010] In order to achieve the above object, the present inventors have intensively studied the cause of the deterioration of the quality of seam welds of high tensile steel plates. As a result, they have come to the conclusion that the quality of seam welds of high tensile steel plates, in particular, tends to deteriorate in winter when the temperature is low, and that the sheet temperature of the steel plate has a large effect on the quality of the seam welds. They thought that in winter when the temperature is low, the sheet temperature of the steel plate to be welded also decreases, and the quality of the welds deteriorates.

[0011] Therefore, two high-tensile steel plates (thickness: 1.20 mm) with a tensile strength of 590 MPa or more were prepared as a pair, one for the leading material and one for the trailing material. Then, as shown in Figure 3, the trailing end of the leading steel plate was overlapped with the leading end of the trailing steel plate, and seam welding was performed by supplying a welding current while applying pressure and rolling the overlapping portion with a pair of upper and lower electrode wheels. The steel plate temperature was measured before seam welding. Then, the weld temperature was measured after seam welding. The welding conditions for seam welding were the same except for the plate temperature.

[0012] The results are shown in Figure 2 as a relationship between the seam weld temperature and the steel plate temperature t. From Fig. 2, it can be seen that the seam weld temperature is proportional to the sheet temperature t of the steel sheet. From this, it was found that the seam weld temperature should be considered as an index of the quality of the seam weld, and that seam welding should be performed by adjusting the welding current value according to the sheet temperature t of the steel sheet so that the seam weld temperature falls within a specified range. In other words, it was found that it is necessary to actually measure the sheet temperature of the material to be welded and perform seam welding with a welding current value corrected for the effect of the sheet temperature of the material to be welded.

[0013] The present invention has been completed based on these findings and further studies. [1] A method for seam welding thin steel plates in a continuous thin steel plate production line, in which the rear end of a preceding thin steel plate and the front end of a following thin steel plate are overlapped and seam welded, A sheet temperature measuring step of actually measuring the sheet temperature of the thin steel sheet; a welding current value setting step of setting a welding current value for the seam welding; a welding step of performing seam welding at the set welding current value, A method for seam welding thin steel plates, characterized in that the welding current value setting process includes a step of setting a welding current value for the seam welding based on the actual sheet temperature of the thin steel plate obtained in the sheet temperature measuring process. [2] In the above step, the welding current value of the seam welding to be set is expressed by the following formula (1). I t =I T (1+α t (Tt)) ...(1) Here, I T : Reference welding current value (welding current value when the sheet temperature is the reference sheet temperature T°C) (unit: kA), T: Reference plate temperature (℃), t: Actual plate temperature (℃), α t :coefficient The welding current value I is defined as t The method for seam welding of thin steel plates described in [1] is characterized by the above. [3] The method for seam welding of thin steel plates described in [2], characterized in that the measured sheet temperature t of the thin steel plate is the measured sheet temperature of the succeeding thin steel plate. [4] The method for seam welding thin steel plates according to [2], characterized in that the reference plate temperature T is 20°C. [5] A method for seam welding of thin steel plates as described in [2], in which the reference plate temperature T and the measured plate temperature t satisfy Tt>0. [6] A method for seam welding thin steel plates according to any one of [1] to [5], characterized in that the thin steel plates are high-tensile steel plates with a tensile strength of 590 MPa or more. [7] A seam welding device for thin steel plates in a continuous manufacturing line for thin steel plates, comprising a pair of upper and lower electrode wheels, a clamping device, and a welding current supplying means, and for overlapping and seam-welding a rear end portion of a preceding thin steel plate and a front end portion of a following thin steel plate, further comprising: A seam welding device for thin steel plates, comprising: a sheet temperature measuring means for measuring a sheet temperature of the thin steel plate; and a welding current control means for setting a welding current value based on the measured sheet temperature. Effect of the Invention

[0014] According to the present invention, the quality of the seam welds of high tensile steel sheet is stabilized, and problems such as breakage of the seam welds during sheet passing can be prevented in the continuous processing of thin steel sheet, and a decrease in productivity and the occurrence of defective products can be prevented, thereby providing significant industrial benefits. [Brief description of the drawings]

[0015] [Figure 1] FIG. 1 is an explanatory diagram illustrating a schematic diagram of an example of a seam welding device used in the present invention. [Diagram 2] 1 is a graph showing the effect of the measured temperature of a steel plate on the temperature of a seam weld. [Diagram 3] FIG. 1 is an explanatory diagram illustrating an outline of a seam welding method. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0016] In the seam welding method for thin steel plates, the rear end of a preceding steel plate (leading material) is overlapped with the front end of a following steel plate (following material), and the overlapped portion is joined (seam welded) by supplying (energizing) a welding current while pressing and rolling the overlapped portion with a pair of upper and lower electrode wheels. Note that the "thin steel plate" referred to here is a steel plate 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 parts. Therefore, when the electrical resistance decreases and the amount of heat generated decreases, the temperature of the seam weld drops. It is generally known that the electrical resistivity of metals decreases as their temperature drops, and when the temperature of the steel plate (plate temperature) drops due to a drop in air temperature, the electrical resistance decreases and the amount of heat generated decreases, resulting in a drop in the temperature of the seam weld as shown in Figure 2.

[0018] A decrease in seam weld temperature does not have a significant effect on the quality of the weld in materials that are relatively easy to weld, such as mild steel. However, in the case of 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 spatter occurs is small, so the effect on the quality of the weld cannot be ignored. An example of such a high-tensile steel plate is a high-tensile steel plate having a tensile strength of 590 MPa or more.

[0019] [Plate temperature measurement process] In the present invention, the sheet temperature of the thin steel sheet to be welded is measured before seam welding. In the case of a steel sheet with high thermal conductivity, the sheet temperature is almost the same as the air temperature, so the following steel sheet and the preceding steel sheet can be considered to have almost the same sheet temperature. From the viewpoint of ease of work, it is preferable to measure the sheet temperature of the following steel sheet. In the present invention, the sheet temperature of the following steel sheet is preferably measured by the sheet temperature measuring means 4 shown in Fig. 1. The obtained measured sheet temperature is then transmitted to the welding current control means 5.

[0020] [Welding current setting process] The welding current value setting step sets a welding current value for seam welding. In the present invention, the welding current value for seam welding is set based on the measured sheet temperature of the thin steel sheet obtained in the sheet temperature measuring step.

[0021] The welding current value set in this step is the welding current value I t Let us assume that.

[0022] In the present invention, the welding current value corrected for the effect of the measured plate temperature t is expressed by the following formula (1): I t =I T (1+α t (Tt)) ...(1) Here, I T : Reference welding current value (welding current value when the sheet temperature is the reference sheet temperature T°C) (unit: kA), T: Reference plate temperature (℃), t: Actual plate temperature (℃), α t :coefficient The welding current value I is defined as t It is preferable to set the above.

[0023] Here, α in Eq. (1) t (Tt) is a term that corrects the effect of the sheet temperature of the thin steel sheet on the welding current value. In formula (1), a reference sheet temperature T is selected, and the difference (Tt) between the reference sheet temperature T and the measured sheet temperature t is used to correct the effect of sheet temperature fluctuations, α t (Tt) is the reference welding current value I T In addition, α t is a coefficient for correcting the effect of plate temperature on the welding current value supplied. It differs depending on the type of material (steel plate) to be welded. For high-tensile steel plates with normal tensile strength of 590 MPa or more, α t The reference sheet temperature T is preferably set to a sheet temperature that occurs frequently, for example, 20 to 25° C., which is generally called room temperature.

[0024] That is, when the measured sheet temperature t (℃) is the reference sheet temperature T (℃), the welding current value I t is the reference welding current value IT When the sheet temperature t is lower than the reference sheet temperature T ((Tt)>0), the welding current I t is the reference welding current value I T If the sheet temperature t is higher than the reference sheet temperature T ((Tt) < 0), the welding current I t is the reference welding current value I T In particular, in the winter when the air temperature is low, when the sheet temperature t is lower than the reference sheet temperature T (satisfying (Tt)>0), the welding current is reduced to the welding current I defined by equation (1). t The reference welding current value I T This increases the temperature of the weld, increases the strength of the joint, and suppresses problems such as breakage of the seam weld. T It is preferable to determine in advance by conducting a preliminary experiment or the like for each steel plate to be treated. In the present invention, the welding current control means 5 shown in FIG. 1 calculates a welding current value I 1 corrected for the influence of the sheet temperature by using the measured sheet temperature obtained in the sheet temperature measurement process and the formula set in advance as described above. t Calculate the following.

[0025] [Welding process] In the welding process, the welding current value I set in the above-mentioned welding current value setting process is t In the present invention, the welding current value I set in the above-mentioned welding current value setting step is used for seam welding. t is supplied (energized) to the electrode wheels 31, 32 via the welding current supply means 51, and the overlapping portions are seam welded (joined).

[0026] [Seam welding equipment] The seam welding apparatus used in the seam welding method of the present invention includes a pair of upper and lower electrode wheels, a clamping device, and a welding current supplying means, and further includes a sheet temperature measuring means 4 and a welding current control means 5 as shown in FIG. 1.

[0027] As shown in Fig. 3, the seam welding apparatus is equipped with a pair of upper and lower electrode wheels 31, 32. Each of the electrode wheels 31, 32 is arranged so as to be rotationally driven (rolled) by a driving means (not shown). Furthermore, the seam welding apparatus preferably 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 of the clamping devices includes a pair of upper and lower clamp members 6, 7, enabling the leading steel plate 1 and the trailing steel plate 2 to be gripped and overlapped, respectively.

[0028] Moreover, the strip temperature measuring means 4 has a measuring terminal (strip thermometer) 41 and a calculation means 42. In the strip temperature measuring means 4, the measuring terminal (strip thermometer) 41 comes into contact with the steel strip to be measured, the calculation means calculates the strip temperature (actually measured strip temperature), and transmits the obtained result (actually measured strip temperature) to the welding current control means 5. Examples of the measuring terminal 41 include a thermocouple, an infrared radiation thermometer, etc.

[0029] In addition, the welding current control means 5 uses the transmitted measured sheet temperature to calculate a welding current value I t The obtained welding current value I t is supplied to the electrode wheels 31 and 32 via a welding current supply means 51, and the overlapping portions are seam-welded to join them.

[0030] The present invention will be further described below with reference to examples. EXAMPLES

[0031] In a continuous processing line for thin steel sheets, the rear end of a preceding thin steel sheet 1 (preceding material) and the front end of a following thin steel sheet 2 (following material) are overlapped using a seam welding device having a sheet temperature measuring means 4 and a welding current control means 5 shown in Fig. 1. Then, while the overlapped portion is pressed and rolled with a pair of upper and lower rotating electrodes (electrode wheels) 31, 32, a welding current is supplied via a welding current supply means 51 to perform seam welding and join the overlapped portion of the preceding material 1 and the following material 2.

[0032] The thin steel plate used was a high-tensile steel plate (plate thickness: 1.20 mm) with a tensile strength of 590 MPa or more. Before performing seam welding, the plate temperature t (°C) of the succeeding material 2 was measured by a temperature measuring terminal 41 (plate temperature gauge) of the plate temperature measuring means 4, and the obtained measured plate temperature was sent to the welding current control means 5. The welding current control means 5 determines the welding current value I to be supplied during seam welding using the measured plate temperature t of the sent steel plate and the following formula (1): t The formula (1) is as follows: 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 sheet temperature (℃), and 20 is the reference sheet temperature T (℃). t is a coefficient for correcting the effect of the sheet temperature on the supplied welding current, and α t = 0.1 (kA / ℃) was used.

[0033] The welding current value I calculated using the above formula (1) t The case where seam welding was performed using the above was taken as an example of the present invention. On the other hand, the plate temperature is not measured and a constant welding current (reference welding current value I T ) was supplied to perform seam welding as a comparative example.

[0034] The above seam welding was carried out between December 2022 and April 2023 (5 months) and the occurrence of problems in the seam welds was investigated. As a result, in the comparative example, problems such as plate breakage occurred in 1.2% of the total number of joints. On the other hand, no problems occurred in the examples of the present invention. The number of joints (total number) during the survey period was 500 for the examples of the present invention and 2000 for the comparative example. [Explanation of symbols]

[0035] 1. Leading steel plate (leading material) 2 Trailing steel plate (trailing material) 31 Upper electrode wheel (upper electrode wheel) 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 clamp member

Claims

1. A method for seam welding thin steel plates in a continuous thin steel plate production line, in which a rear end portion of a preceding thin steel plate and a front end portion of a following thin steel plate are overlapped and seam welded, A sheet temperature measuring step of actually measuring the sheet temperature of the thin steel sheet; a welding current value setting step of setting a welding current value for the seam welding; a welding step of performing seam welding at the set welding current value, A method for seam welding thin steel plates, characterized in that the welding current value setting process includes a step of setting a welding current value for the seam welding based on the actual sheet temperature of the thin steel plate obtained in the sheet temperature measuring process.

2. In the step, the welding current value of the seam welding to be set is expressed by 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 sheet temperature is the reference sheet temperature T℃) (unit: kA), T: reference board temperature (℃), t: measured board temperature (℃), α t :Coefficient The welding current I is defined as t 2. The method for seam welding of thin steel plates according to claim 1,

3. 3. The method for seam welding thin steel plates according to claim 2, wherein the measured sheet temperature t of the thin steel plate is the measured sheet temperature of the succeeding thin steel plate.

4. 3. The method for seam welding thin steel plates according to claim 2, wherein the reference plate temperature T is 20°C.

5. The method for seam welding thin steel plates according to claim 2, wherein the reference plate temperature T and the measured plate temperature t satisfy T-t>0.

6. 6. The method for seam welding thin steel plates according to claim 1, wherein the thin steel plates are high-tensile steel plates having a tensile strength of 590 MPa or more.

7. A seam welding device for thin steel plates in a continuous manufacturing line for thin steel plates, the device comprising a pair of upper and lower electrode wheels, a clamping device, and a welding current supplying means, and which overlaps a rear end portion of a preceding thin steel plate and a front end portion of a following thin steel plate to perform seam welding, further comprising: A seam welding device for thin steel plates, comprising: a sheet temperature measuring means for measuring a sheet temperature of the thin steel plate; and a welding current control means for setting a welding current value based on the measured sheet temperature.

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