JP2021154358A - Design method of mash seam welding machine, mash seam welding machine, mash seam welding method, and method for manufacturing hot-rolled steel sheet - Google Patents

Abstract

To provide a design method of a mash seam welding machine which makes a combination of a preceding steel sheet and a subsequent steel sheet to be welded suitable, and can avoid damage of an electrode ring or its peripheral components due to an axial load acting on the electrode ring; a mash seam welding machine; a mash seam welding method; and a method for manufacturing a hot-rolled steel sheet.SOLUTION: A design method of a mash seam welding machine designs each of a pair of electrode rings 11a and 11b and those peripheral components 12a, 13a, 14a, 12b, 13b and 14b so that when an axial load acting in an axial direction of the electrode ring to each of the pair of electrode rings is represented by F and a rigidity value of each of the pair of electrode rings and those peripheral components is represented by F0, which are calculated by the following expression (A): F=k×(t1×TS1+a×t2×TS2), plate thicknesses and tensile strengths of a preceding steel sheet 21 and a subsequent steel sheet 22 and rigidities of each of the pair of electrode rings and those components satisfy F≤F0.SELECTED DRAWING: Figure 1

Description

The present invention relates to a method for designing a mash seam welder, a mash seam welder, a mash seam welding method, and a method for manufacturing a hot-rolled steel sheet.

The mash seam welder superimposes the tail end of the leading steel plate and the tip of the trailing steel plate, pressurizes the superposed portion with a pair of upper and lower electrode rings, and at the same time continuously welds while passing a welding current. The thickness of the joint is reduced by rolling the joint portion heated to a high temperature and softened with a pair of upper and lower electrode rings.
Conventionally, as a mash seam welding method using this type of mash seam welding machine, for example, those shown in Patent Documents 1 and 2 and Non-Patent Document 1 are known.

In the mash seam welding method shown in Patent Document 1, the ends of two metal plates are overlapped, the overlapped portion is pressurized by a pair of upper and lower electrode rings, and the two pieces are continuously welded while passing a welding current. This is a mash seam welding method for joining metal plates of. Then, the axis cores of the pair of upper and lower electrode rings are inclined in the horizontal plane in opposite directions with respect to the axis orthogonal to the welding line formed in the overlapping portion of the two metal plates, and the pair of upper and lower electrode rings are tilted. Two metal plates are joined while actively driving.

Further, the metal plate joining method shown in Patent Document 2 is a metal plate joining method in which two metal plates are joined and then the joint portion of the metal plates is rolled by a pair of upper and lower pressure rollers. Then, the shaft cores of the pair of pressure rollers are inclined in a horizontal plane with respect to a straight line orthogonal to the joint line of the joint portion, and the step of the joint portion is raised while actively driving the pair of pressure rollers. Roll in the direction of travel.
Further, the new mash seam welder shown in Non-Patent Document 1 has determined welding conditions and welding methods by experiments and analysis in order to enable welding having rolling resistance up to a maximum plate thickness of 6 mm.

International Publication No. 2010/004656 International Publication No. 2010/004657

"Development of a new mash seam welder that realizes continuous rolling up to a steel plate thickness of 6 mm", Mitsubishi Heavy Industries Technical Report, Vol. 49, No. 4, (2012)

By the way, in the welding of steel plates with a mash seam welder, the axial direction of the electrode rings is obtained by pressurizing the portion where the tail end of the leading steel plate and the tip of the trailing steel plate are overlapped with a pair of upper and lower electrode rings. Material flow occurs in. Due to this material flow, a load in the axial direction (hereinafter referred to as an axial load) acts on the electrode ring, and a phenomenon occurs in which the electrode ring is displaced in the axial direction. Conventionally, mash seam welders have been mainly applied to welding relatively thin steel sheets of less than 2 mm, but in recent years, they have also been applied to welding relatively thick steel sheets such as hot-rolled steel sheets with a thickness of about 6 mm. It has come to be. For this reason, the amount of material flow generated in the axial direction of the electrode ring increases during pressurization, the amount of displacement of the electrode ring in the axial direction increases, and the electrode ring and the superposed portion of the steel plate are displaced, which is normal. Welding could not be performed, and problems such as a decrease in the strength of the welded portion began to occur.

Here, in any of the above-mentioned conventional mash seam weldings shown in Patent Documents 1 to 3, the phenomenon that an axial load acts on the electrode ring and the overlapping portion of the electrode ring and the steel plate is displaced is considered. Therefore, there is a problem that normal welding cannot be performed and problems such as a decrease in the strength of the welded portion occur.
On the other hand, in the conventional mash seam welding as shown in Patent Documents 1 to 3, there is no clear standard for the combination of the leading steel plate and the trailing steel plate to be welded. Therefore, it is necessary to perform a welding test in advance for each new combination of the leading steel plate and the trailing steel plate to determine whether or not normal welding can be performed. Depending on the combination of the leading steel plate and the trailing steel plate to be welded, Due to the occurrence of the material flow described above, an excessive axial load acts on the electrode ring, which may damage the electrode ring or peripheral parts of the electrode ring.

Therefore, the present invention has been made to solve these conventional problems, and an object thereof is caused by an axial load acting on an electrode ring, in which a combination of a leading steel plate and a trailing steel plate to be welded is suitable. It is an object of the present invention to provide a method for designing a mash seam welder capable of avoiding damage to the electrode ring or its peripheral parts, a mash seam welder, a mash seam welding method, and a method for manufacturing a hot-rolled steel sheet.

In order to achieve the above object, the design method of the mash seam welder according to one aspect of the present invention includes a pair of electrode rings that pressurize the overlapped portion of the leading steel plate and the trailing steel plate to be welded. A method for designing a mash seam welder that continuously welds the leading steel plate and the trailing steel plate by passing a welding current while running a pair of electrode rings in the overlapped portion, wherein the leading steel plate and the trailing steel plate are welded together. The thickness and tensile strength of each of the trailing steel plates and the rigidity of each of the pair of electrode rings and their peripheral parts are calculated by the following equation (A), and each electrode ring of the pair of electrode rings. On the other hand, when the axial load acting in the axial direction of the electrode rings is F and the rigidity values of each of the pair of electrode rings and their peripheral parts are F0, the pair of electrode rings are arranged so that F ≦ F0. The gist is to design each and its peripheral parts.
Here, F = k × (t1 × TS1 + a × t2 × TS2)… (A)
t1: Thickness (mm) of the steel plate on the upper side of the superposition
TS1: The tensile strength of the steel plate on the upper side of the superposition (kgf / mm ² )
t2: Plate thickness (mm) of the steel plate on the lower side of the superposition
TS2: tensile strength of the steel plate under the superposition (kgf / mm ² )
k: Constant determined by the mash seam welder a: Constant indicating the contribution of the lower steel plate to the upper steel plate

Further, the mash seam welder according to another aspect of the present invention includes a pair of electrode rings that pressurize the overlapped portion of the leading steel plate and the trailing steel plate to be welded, and the pair of electrode rings are overlapped with each other. A mash seam welder that continuously welds the leading steel plate and the trailing steel plate by passing a welding current while running on the portion, and the thickness and tensile strength of the leading steel plate and the trailing steel plate, respectively. The gist is that the rigidity of each of the pair of electrode rings and their peripheral parts has a relationship of F ≦ F0 described above.

Further, in the mash seam welding method according to another aspect of the present invention, the overlapped portion of the leading steel plate and the trailing steel plate to be welded is pressed by a pair of electrode rings by using the mash seam welding machine described above. The gist is that the leading steel plate and the trailing steel plate are continuously welded by passing a welding current while running each of the pair of electrode rings in the overlapped portion.
The gist of the method for producing a hot-rolled steel sheet according to another aspect of the present invention is that the hot-rolled steel sheet is manufactured by the above-mentioned mash seam welding method.

Further, in the method for manufacturing a hot-rolled steel sheet according to another aspect of the present invention, a pair of electrode rings that pressurize a superposed portion of a leading steel plate and a trailing steel sheet to be welded are run on the superposed portion. A method for manufacturing a hot-rolled steel sheet having a mash seam welding step of continuously welding the leading steel sheet and the trailing steel sheet by passing a welding current, and each of the leading steel sheet and the trailing steel sheet. The gist is that it is determined that welding is possible only when the thickness and tensile strength and the rigidity of each of the pair of electrode rings and their peripheral parts satisfy the above-mentioned relationship of F ≦ F0.

According to the design method of the mash seam welder, the mash seam welder, the mash seam welding method, and the method for manufacturing a hot-rolled steel plate according to the present invention, the combination of the leading steel plate and the trailing steel plate to be welded is suitable for the electrode. Provided are a method for designing a mash seam welder, a mash seam welder, a mash seam welder, and a method for manufacturing a hot-rolled steel plate, which can avoid damage to the electrode ring or its peripheral parts due to an axial load acting on the ring. can. Further, according to the mash seam welding method according to the present invention, normal welding can be performed without causing problems such as a decrease in the strength of the welded portion.

It is a schematic block diagram of the mash seam welder designed by the design method of the mash seam welder which concerns on one Embodiment of this invention. It is the figure which looked at the state which the superposition part of the tail end part of the leading steel plate and the tip part of a trailing steel sheet was welded by a pair of upper and lower electrode rings from the direction orthogonal to the axial direction of the electrode rings. It is the figure which looked at the state in which the superposition part of the tail end part of the leading steel plate and the tip part of a trailing steel sheet was welded by a pair of upper and lower electrode rings from the axial direction of the electrode rings. It is a functional block diagram of the evaluation apparatus of mash seam welding applied to the design method of the mash seam welding machine which concerns on one Embodiment of this invention. It is a flowchart which shows the flow of processing in the evaluation apparatus of mash seam welding shown in FIG. It is a graph which shows the relationship between the constant a and the correlation coefficient of the approximate expression. It is a graph which shows the relationship between the measured axial load and the displacement amount of an electrode ring. It is a graph which shows the relationship between the axial load F calculated by the formula (A), and the number of weldings.

The inventors have studied various phenomena in which the electrode ring is displaced in the axial direction and normal welding cannot be performed. There are cases where stable and normal welding can be performed and cases where normal welding cannot be performed. However, thin steel plates can be stably welded, and thick steel plates tend to have poor welding. Therefore, we thought that the reason why the amount of displacement of the electrode ring in the axial direction (perpendicular to the welding direction) increased was that the equipment rigidity against the tensile strength generated from the plate was insufficient, and reinforced the electrode ring and its peripheral members. However, it was found that normal welding was possible. However, the strength cannot be increased infinitely due to the relationship with the equipment cost. It is necessary to design appropriate equipment in consideration of the specifications of the steel sheet processed on the production line where the welding machine is installed.

The inventors examined in detail the relationship between various specifications of the plate to be welded on the line and the equipment conditions, and found that there is a correlation between the thickness and strength of the plate and the equipment rigidity regarding the quality of welding. I found it. Then, they have found that stable welding can be performed by keeping the plate thickness and tensile strength of each welding target and the rigidity of the welding equipment, particularly the electrode ring and its peripheral members, in a predetermined relationship, and have reached the present invention.
The present invention is based on this study, and "designing""to have a predetermined relationship" means that the rigidity of the equipment corresponds to the thickness and tensile strength of the plate to be welded in the steel sheet production line. Means to set as appropriate.

Hereinafter, embodiments of the present invention will be described with reference to the drawings. The embodiments shown below exemplify devices and methods for embodying the technical idea of the present invention, and the technical idea of the present invention describes the material, shape, structure, arrangement, etc. of the components. It is not specified in the following embodiments. The drawings are schematic. Therefore, it should be noted that the relationship, ratio, etc. between the thickness and the plane dimension are different from the actual ones, and there are parts where the relationship and ratio of the dimensions are different between the drawings.

FIG. 1 shows a schematic configuration of a mash seam welder designed by a method for designing a mash seam welder according to an embodiment of the present invention. The mash seam welder 1 has a pair of upper and lower electrode rings 11a. , 11b, and a front side clamping device 23 and a rear side clamping device 24.
The upper electrode ring 11a is fixed to the upper rotating shaft 12a, and both ends of the upper rotating shaft 12a are rotatably supported by the upper electrode ring supporting member 14a via a pair of bearings 13a. The upper electrode ring support member 14a is fixed to the lower end of the pressing member 18 provided on the upper carriage 15a via the linear guide 19 so as to be able to move up and down. The pressing member 18 is moved up and down by a pressing cylinder 20 fixed to the upper carriage 15a. The upper carriage 15a is movably provided on the upper frame 17a via the linear guide 16a in a direction orthogonal to the plate-passing direction (direction orthogonal to the paper surface in FIG. 1).

On the other hand, the lower electrode ring 11b is arranged at a position vertically opposed to the upper electrode ring 11a and is fixed to the lower rotating shaft 12b. Both ends of the lower rotary shaft 12b are rotatably supported by the lower electrode ring support member 14b via a pair of bearings 13b. The lower electrode ring support member 14b is fixed to the lower carriage 15b. The lower carriage 15b is provided on the lower frame 17b via a linear guide 16b so as to be movable in a direction orthogonal to the plate passing direction. The lower carriage 15b moves in synchronization with the upper carriage 15a.

Each of the upper electrode ring 11a and the lower electrode ring 11b is rotationally driven by a driving means (not shown).
Further, the front side clamping device 23 clamps the leading steel plate 21 to be welded from above and below, and includes a pair of upper and lower clamping members 23a and 23b. The upper clamp member 23a is moved up and down by the pressing cylinder 25. Further, the rear side clamping device 24 clamps the trailing steel plate 22 to be welded from above and below, and includes a pair of upper and lower clamping members 24a and 24b. The upper clamp member 24a is moved up and down by the pressing cylinder 26.

When welding the leading steel plate 21 and the trailing steel plate 22, first, as shown in FIG. 2, the tail end portion 21a of the leading steel plate 21 and the tip end portion 22a of the trailing steel plate 22 are joined to the leading steel plate 21. The tail end 21a is placed on the upper side and overlapped. Next, in that state, the leading steel plate 21 is gripped by the clamp members 23a and 23b of the front side clamping device 23 to fix the position of the leading steel plate 21, and the trailing steel plate 22 is held by the clamping members 24a and 24b of the rear side clamping device 24. To fix the position of the trailing steel plate 22. Next, the pressing member 18 is lowered by the pressing cylinder 20 to lower the upper electrode ring 11a, and the pair of upper and lower electrode rings 11a and 11b form a tail end portion 21a of the leading steel plate 21 and a tip portion 22a of the trailing steel plate 22. Pressurize the overlapped part of. Then, the pair of upper and lower electrode rings 11a and 11b are moved in a direction orthogonal to the plate direction (direction orthogonal to the paper surface in FIG. 1), and welding is continuously performed while a welding current is applied. As a result, the tail end portion 21a of the leading steel plate 21 and the tip end portion 22a of the trailing steel plate 22 are joined.

Here, when welding the tail end portion 21a of the leading steel plate 21 and the tip portion 22a of the trailing steel plate 22, as shown in FIG. 2, the tail end portion 21a of the leading steel plate 21 and the tip of the trailing steel plate 22 The thickness of the overlapped portion with the portion 22a is reduced by pressurizing the pair of upper and lower electrode rings 11a and 11b. At this time, each of the leading steel plate 21 and the trailing steel plate 22 is restrained by the front clamp device 23 and the rear clamp device 24 at a portion separated from the pair of upper and lower electrode rings 11a and 11b by a certain interval. It is in a state of being thrust at the boundary surface of the welded portion, and a part of the rolled portion is rolled so as to protrude from the boundary surface.

Assuming that the reaction force of the leading steel plate 21 at the boundary surface of the welded portion is F1, the reaction force of the trailing steel plate 22 is F2, and the pushing force of the protruding portion of the leading steel plate 21 on the upper side is F3, each of F1 to F3 is It can be expressed as the following equations (1) to (3). The pushing force of the protruding portion of the trailing steel plate 22 on the lower side is F4. The effects of reaction force and pushing force appear vertically symmetrically.
F1 = α × TS1 × t1 × W… (1)
F2 = β × TS2 × t2 × W… (2)
F3 = γ × TS1 × t1 × W… (3)
^{Here, α, β, and γ are proportional constants, TS1 is the tensile strength (kgf / mm 2} ) of the leading steel plate 21 (the leading steel plate 21 on the side in contact with the upper electrode ring 11a) on the upper side of the superposition, and t1 is. It is the plate thickness (mm) of the leading steel plate 21 on the upper side of the superposition. Further, W is the width (mm) of the welded portion 27 shown in FIG. 3, TS2 is the tensile strength (kgf / mm ² ) of the trailing steel plate 22 which is the lower side of the superposition, and t2 is the trailing side which is the lower side of the superposition. The thickness (mm) of the steel plate 22.

Further, the axial load F'of the portion in contact with the upper electrode ring 11a is given by the following equation (4).
F'= F1-F2 + F3 ... (4)
When this equation (4) is expanded by the above equations (1) to (3),
F'= (α x TS1 x t1 x W)-(β x TS2 x t2 x W) + (γ x TS1 x t1 x W) = (α + γ) x TS1 x t1 x W-β x TS2 x t2 x W ... (5).

Here, since the axial load F acting on the upper electrode ring 11a is proportional to the axial load F', assuming that the proportionality constant is μ,
F = μ × {(α + γ) × TS1 × t1 × W-β × TS2 × t2 × W} ... (6).
Summarizing the constants from the equation (6), the axial load F acting on the upper electrode ring 11a can be expressed as the following equation (A).
F = k × (TS1 × t1 + a × TS2 × t2)… (A)
Here, the constant k = μ × (α + γ) × W, and the constant a = −β / (α + γ). The constant k is a constant determined by the mash seam welder, and the constant a is a constant indicating the contribution of the lower trailing steel sheet to the upper leading steel sheet.

On the other hand, the axial load F'' at the portion in contact with the lower electrode ring 11b and the axial load F acting on the lower electrode ring 11b will also be calculated. Assuming that the reaction force of the leading steel plate 21 at the boundary surface of the welded portion is F1, the reaction force of the trailing steel plate 22 is F2, and the pushing force of the protruding portion of the trailing steel plate 22 on the lower side is F4, then F1, F2, Each of F4 can be expressed as the following equations (7) to (9).
F1 = α × TS1 × t1 × W… (7)
F2 = β × TS2 × t2 × W… (8)
F4 = θ × TS2 × t2 × W… (9)

^{Here, α, β, and θ are proportional constants, TS1 is the tensile strength (kgf / mm 2} ) of the leading steel plate 21 (the leading steel plate 21 on the side in contact with the upper electrode ring 11a) on the upper side of the superposition, and t1 is. It is the plate thickness (mm) of the leading steel plate 21 on the upper side of the superposition. Further, W is the width (mm) of the welded portion 27 shown in FIG. 3, TS2 is the tensile strength (kgf / mm ² ) of the trailing steel plate 22 which is the lower side of the superposition, and t2 is the trailing side which is the lower side of the superposition. The thickness (mm) of the steel plate 22.

Further, the axial load F ″ of the portion in contact with the lower electrode ring 11b is given by the following equation (11).
F''=-F1 + F2 + F4 ... (10)
When this equation (10) is expanded by the above equations (7) to (9),
F''=-(α x TS1 x t1 x W) + (β x TS2 x t2 x W) + θ x TS2 x t2 x W = -α x TS1 x t1 x W + (β + θ) x TS2 x t2 x W ... (11).

Since the axial load F acting on the lower electrode ring 11b is proportional to the axial load F'', assuming that the proportionality constant is μ,
F = μ × {−α × TS1 × t1 × W + (β + θ) × TS2 × t2 × W} ... (12).
Summarizing the constants from the equation (12), the axial load F acting on the lower electrode ring 11b can be expressed as the equation (A) like the axial load F acting on the upper electrode ring 11a.
F = k × (TS1 × t1 + a × TS2 × t2)… (A)
Here, the constant k = −α × μ × W, the constant a = − (β + θ) / α. The constant k is a constant determined by the mash seam welder, and the constant a is a constant indicating the contribution of the lower leading steel plate to the upper trailing steel plate.

Here, in the mash seam welding evaluation device applied to the design method of the mash seam welding machine according to the embodiment of the present invention, an axial load acts on a pair of upper and lower electrode wheels 11a and 11b to act on the pair of upper and lower electrode wheels 11a and 11b. In order to quickly evaluate the weldable combination of the leading steel plate 21 and the trailing steel plate 22 to be welded so that the overlapped portion of the leading steel plate 21 and the trailing steel plate 22 does not shift, without performing a welding test in advance. , The configuration shown in the functional block diagram of FIG. 4 is adopted.

That is, the evaluation device 30 for mash seam welding includes an axial load calculation unit 31, an evaluation unit 32, and an output unit 33.
Here, the evaluation device 30 for mash seam welding is a computer system for realizing each function of the axial load calculation unit 31 and the evaluation unit 32 on computer software, that is, by executing a computer-readable program. Then, this computer system communicates with various dedicated computer programs stored in advance in the hardware, via a recording medium such as a CD-ROM, a DVD-ROM, or a flexible disk (FD), or via the Internet or the like. By executing a computer program installed in hardware via a network, each of the above-mentioned functions can be realized by software. Further, the output unit 33 is realized by an output device such as a printer.

The axial load calculation unit 31 calculates the axial load F represented by the above equation (A) acting on each of the upper electrode ring 11a and the lower electrode ring 11b.
Here, when calculating the axial load F, it is preferable that the value of the constant a in the equation (A) is in the range of -1 ≦ a ≦ 0. The reason will be explained.
The axial load F acting on the upper electrode ring 11a was actually measured with an actual welding machine and approximated to the above equation (A). Parameters that affect the displacement of the electrode ring 11a are extracted, and among the parameters, "tensile tension TS1 of the leading steel plate x plate thickness t1" and "tensile tension TS2 of the trailing steel plate x plate thickness t2" are between the axial load F. It was found that the correlation coefficient (dispersion ratio) was high. The correlation coefficient (correlation coefficient of the approximate expression) between "strength TS1 of the leading steel plate x plate thickness t1", "tensile tension TS2 of the trailing steel plate x plate thickness t2" and the axial load F changes depending on the constant a. The relationship between the correlation coefficient of the approximate expression and the constant a was as shown in FIG. Referring to FIG. 6, when the constant k = 10 and the constant a = −0.5 in the above equation (A), the correlation coefficient of the approximate equation was 0.8, and the correlation was the highest. As a result, the axial load F is calculated assuming that the value of the constant a in the above equation (A) is −0.5 and the value of the constant k is 10. As shown in FIG. 6, when the constant a is less than -01 or larger than 0, the correlation coefficient of the approximate expression is less than 0.4 and the correlation is considered to be small. Therefore, the equation (A) The value of the constant a in is not limited to 0.8, and is preferably in the range of -1 ≦ a ≦ 0. The value of the constant a is not limited to 0.8, but is set in the range of -1≤a≤0, and the value of the constant k is set to 10 when calculating the axial load F acting on the upper electrode ring 11a. The same applies not only when calculating the axial load F acting on the lower electrode ring 11b.

Further, the evaluation unit 32 evaluates whether or not the leading steel plate 21 and the trailing steel plate 22 can be welded based on the axial load F calculated by the axial load calculating unit 31.
Here, the evaluation unit 32 evaluates that the leading steel plate 21 and the trailing steel plate 22 can be welded when the axial load F calculated by the axial load calculating unit 31 satisfies the following equation (B), and (B). ) When the equation is not satisfied, welding of the leading steel plate 21 and the trailing steel plate 22 is evaluated as impossible.
F ≤ F0 ... (B)
F0: Rigidity value of each of the pair of electrode rings 11a and 11b and their peripheral parts

Here, the peripheral parts of the upper electrode ring 11a are an upper rotating shaft 12a for fixing the upper electrode ring 11a, a pair of bearings 13a provided at both ends of the upper rotating shaft 12a, and a bearing 13a for the upper rotating shaft 12a. It means the upper electrode ring support member 14a that is supported via the upper electrode ring. Further, the peripheral parts of the lower electrode ring 11b are a lower rotary shaft 12b for fixing the lower electrode ring 11b, a pair of bearings 13b provided at both ends of the lower rotary shaft 12b, and a lower rotary shaft 12b. Means the lower electrode ring support member 14b that supports the vehicle via the bearing 13b.

When the axial load F calculated by the axial load calculation unit 31 does not satisfy the equation (B), the axial load F is larger than F0, and the difference in the amount of displacement between the upper electrode ring 11a and the lower electrode ring 11b. Will increase and derailment will occur, resulting in poor welding. Further, in this case, the bearing units of the electrode rings 11a and 11b may be damaged. On the other hand, when the axial load F calculated by the axial load calculation unit 31 satisfies the equation (B), the axial load F becomes F0 or less, and the displacement amounts of the upper electrode ring 11a and the lower electrode ring 11b are so large. No welding defects occur. Further, in this case, the bearing units of the electrode rings 11a and 11b are not damaged.
Here, the rigidity values of F0: each of the pair of electrode rings 11a and 11b and their peripheral parts are determined according to the rigidity of the mash seam welder to be used, and are appropriately determined according to the mash seam welder to be used. Will be done.

Note that FIG. 7 shows the relationship between the measured axial load and the displacement amounts of the electrode rings 11a and 11b when welding is performed under the welding conditions of the examples described later. As shown in FIG. 7, when the measured axial load is 4000 kgf or less, the displacement amount of the electrode rings 11a and 11b in the axial direction is in the range of ± 4.0 mm, and the electrode rings 11a and 11b are not derailed. , Welding was good. The positive and negative signs of the displacement amount are positive when the electrode ring 11a in FIG. 2 is displaced to the right and the electrode ring 11b is displaced to the left. On the other hand, when the measured axial load was larger than 4000 kgf, the displacement amount of the electrode rings 11a and 11b in the axial direction exceeded 6.0 mm, and the electrode rings 11a and 11b were derailed, resulting in poor welding. The amount of displacement of the pair of electrode rings 11a and 11b in the axial direction is the axial direction of the center position of the pair of electrode rings 11a and 11b at the contact positions of the pair of electrode rings 11a and 11b with the steel plates 21 and 22. Indicates the distance at. Therefore, in the present embodiment, the possibility of welding the leading steel plate 21 and the trailing steel plate 22 is evaluated with the rigidity value of each of the pair of electrode rings 11a and 11b and their peripheral parts being 4000 kgf.
Further, the output unit 33 outputs whether or not the leading steel plate 21 and the trailing steel plate 22 evaluated by the evaluation unit 32 can be welded.

Next, the processing flow of the evaluation device 30 for mash seam welding will be described with reference to FIG.
The axial load calculation unit 31 of the evaluation device 30 executes steps S1 to S4 shown below, which are the axial load calculation steps. Further, the evaluation unit 32 executes the evaluation steps S5 to S7. Further, the output unit 33 executes step S8.
First, in step S1, when the axial load calculation unit 31 receives the evaluation start command from an input device (not shown), it acquires the plate thickness t1 and the tensile strength TS1 of the preceding steel plate 21 to be welded by the mash seam welder 1 shown in FIG. do. The axial load calculation unit 31 acquires the plate thickness t1 and the tensile strength TS1 of the preceding steel plate 21 to be welded, which is input by the operator to an input device (not shown).

Next, in step S2, the axial load calculation unit 31 acquires the plate thickness t2 and the tensile strength TS2 of the trailing steel plate 22 to be welded by the mash seam welder 1 shown in FIG. The axial load calculation unit 31 acquires the plate thickness t2 and the tensile strength TS2 of the trailing steel plate 22 to be welded, which is input by the operator to an input device (not shown).
Then, in step S3, the axial load calculation unit 31 inputs a constant determined by the k: mash seam welder in the equation (A) input to an input device (not shown) by an operator, and a: a steel plate on the lower side with respect to the steel plate on the upper side. Get a constant that indicates the contribution of. As described above, the constant k is 10. As described above, the constant a is set to −0.5 in the present embodiment.

Next, in step S4, the axial load calculation unit 31 calculates the axial load F acting in the axial direction on the respective electrode rings 11a and 11b of the pair of upper and lower electrode rings 11a and 11b by the above equation (A).
Then, in step S5, the evaluation unit 32 determines whether or not the axial load F calculated in step S4 satisfies the above equation (B). That is, it is determined whether or not F ≦ F0.
At this time, F0: the rigidity values of each of the pair of electrode rings 11a and 11b and their peripheral parts are determined as 4000 kgf as an example. F0 is stored in the storage unit in advance.

Then, when the determination result is YES, that is, when the calculated axial load F is the rigidity value F0 = 4000 kgf or less of each of the pair of electrode wheels 11a and 11b and their peripheral parts, the process proceeds to step S6, and the determination result is No. In the case of, that is, when the calculated axial load F is larger than the rigidity value F0 = 4000 kgf of the mash seam welder, the process proceeds to step S7.
Then, in step S6, the evaluation unit 32 evaluates that the leading steel plate 21 and the trailing steel plate 22 can be welded.
On the other hand, in step S7, the evaluation unit 32 evaluates that welding of the leading steel plate 21 and the trailing steel plate 22 is impossible.
Then, in step S8, the output unit 33 outputs the evaluation result.

As described above, according to the mash seam welding evaluation method and the evaluation device 30 applied to the design method of the mash seam welder according to the present embodiment, the electrode rings 11a and 11b of the pair of upper and lower electrode rings 11a and 11b are respectively. On the other hand, when the load acting on the electrode rings 11a and 11 in the axial direction is an axial load F, this axial load F is calculated by the above equation (A) (axial load calculation step: steps S1 to S4, axial load). Calculation unit 31). Then, based on the calculated axial load F, whether or not the leading steel plate 21 and the trailing steel plate 22 can be welded is evaluated (evaluation steps: steps S5 to S7, evaluation unit 32). As a result, the leading steel plate 21 and the trailing steel plate 22 are welded according to the above equation (A) using the plate thickness t1 and tensile strength TS1 of the leading steel plate 21 to be welded and the plate thickness t2 and tensile strength TS2 of the trailing steel plate 22. Can be evaluated. As a result, the axial load F acts on the electrode rings 11a and 11b to weld the leading steel plate 21 and the trailing steel plate so that the overlapped portions of the electrode rings 11a and 11b and the leading steel plate 21 and the trailing steel plate 22 do not deviate from each other. The weldable combination of the steel plates 22 can be quickly evaluated without performing a welding test in advance.

Further, in the evaluation steps (steps S5 to step S7, evaluation unit 32), the axial load F calculated in the axial load calculation steps (steps S1 to step S4, axial load calculation unit 31) is the same as the above equation (B). It is evaluated that welding of the leading steel plate 21 and the trailing steel plate 22 is possible when the preceding steel plate 21 and the trailing steel plate 22 are satisfied, and it is evaluated that welding of the leading steel plate 21 and the trailing steel plate 22 is impossible when the equation (B) is not satisfied. As a result, the axial load F acts on the electrode rings 11a and 11b to weld the leading steel plate 21 and the trailing steel plate so that the overlapping portions of the electrode rings 11a and 11b and the leading steel plate 21 and the trailing steel plate 22 do not deviate from each other. The weldable combination of the steel plates 22 can be evaluated with higher accuracy.

Further, in the axial load calculation step (steps S1 to S4, axial load calculation unit 31), the axial load F is calculated with the value of the constant a in the above equation (A) as the range of -1≤a≤0. As a result, the correlation coefficient between the parameters "strength TS1 of the leading steel plate x plate thickness t1" and "tensile tension TS2 of the trailing steel plate x plate thickness t2" and the axial load F is high, and the axial load in the equation (A) is high. F can be calculated, and the weldable combination of the leading steel plate 21 and the trailing steel plate 22 to be welded can be evaluated with higher accuracy.
Then, based on the evaluation result output by the output unit 33, the leading steel plate 21 and the trailing steel plate 22 evaluated to be weldable are welded by the mash seam welder 1 shown in FIG.

Next, a method for designing a mash seam welder according to an embodiment of the present invention will be described.
In the design method of the mash seam welder 1, the thickness and tensile strength of the leading steel plate 21 and the trailing steel plate 22 and the rigidity of each of the pair of electrode rings 11a and 11b and their peripheral parts are as follows (A). Axial load acting on the electrode rings 11a and 11b of the pair of electrode rings 11a and 11b in the axial direction of the electrode rings 11a and 11b, which is calculated by the formula (same as the formula (A) in the evaluation method described above). , And when the rigidity value of each of the pair of electrode rings 11a and 11b and their peripheral parts is F0, each of the pair of electrode rings 11a and 11b and its peripheral parts are designed so that F ≦ F0.
Here, F = k × (t1 × TS1 + a × t2 × TS2)… (A)
t1: Thickness (mm) of the steel plate on the upper side of the superposition
TS1: The tensile strength of the steel plate on the upper side of the superposition (kgf / mm ² )
t2: Plate thickness (mm) of the steel plate on the lower side of the superposition
TS2: tensile strength of the steel plate under the superposition (kgf / mm ² )
k: Constant determined by the mash seam welder a: Constant indicating the contribution of the lower steel plate to the upper steel plate

The t1, TS1, t2, TS2, k, and a in the formula (A) are the same as the t1, TS1, t2, TS2, k, and a in the formula (A) in the above-mentioned evaluation method, and their preferred numerical values are also The same is true.
That is, in the design method of the mash seam welder 1, each of the pair of electrode rings 11a and 11b and its peripheral parts, that is, so as to satisfy the evaluation standard (B) F ≦ F0 in the evaluation unit 32 described above. The upper electrode ring 11a and its peripheral parts are designed, and the lower electrode ring 11b and its peripheral parts are designed. Here, the peripheral parts of the upper electrode ring 11a are an upper rotating shaft 12a for fixing the upper electrode ring 11a, a pair of bearings 13a provided at both ends of the upper rotating shaft 12a, and a bearing 13a for the upper rotating shaft 12a. It means the upper electrode ring support member 14a that is supported via the upper electrode ring. Further, the peripheral parts of the lower electrode ring 11b are a lower rotary shaft 12b for fixing the lower electrode ring 11b, a pair of bearings 13b provided at both ends of the lower rotary shaft 12b, and a lower rotary shaft 12b. Means the lower electrode ring support member 14b that supports the vehicle via the bearing 13b.

Therefore, when the evaluation result by the evaluation unit 32 described above is weldable, the upper electrode ring 11a and its peripheral parts and the lower electrode ring 11b and its peripheral parts are left as they are without any design change.
On the other hand, when the evaluation result by the evaluation unit 32 described above is not weldable, the upper electrode ring 11a and its peripheral parts or the lower electrode ring 11b and its peripheral parts are designed so that F ≦ F0, respectively. change. For example, the material of the upper electrode ring support member 14a or the lower electrode ring support member 14b is changed in order to increase the rigidity value of the upper electrode ring 11a and its peripheral parts or the rigidity value of the lower electrode ring 11b and its peripheral parts. Alternatively, the number of parts constituting the upper electrode ring support member 14a or the lower electrode ring support member 14b is reduced to reduce the number of joints.

As a result, the combination of the leading steel plate 21 and the trailing steel plate 22 to be welded is suitable, and damage to the electrode rings 11a, 11b or its peripheral parts due to the axial load F acting on the electrode rings 11a, 11b is avoided. It is possible to provide a design method for a mash seam welder 1 capable of forming a mash seam welder 1.
Further, by designing the upper electrode ring 11a and its peripheral parts, the lower electrode ring 11b and its peripheral parts so that F ≦ F0, respectively, the upper electrode ring 11a and the lower electrode ring 11b are designed. The amount of displacement in the axial direction can be set to a predetermined value or less (5.0 mm or less).

The mash seam welder 1 designed by the above-mentioned design method has the thickness and tensile strength of the leading steel plate 21 and the trailing steel plate 22, and the rigidity of each of the pair of electrode rings 11a and 11b and their peripheral parts. However, the electrode rings 11a and 11b are calculated with respect to the electrode rings 11a and 11b of the pair of electrode rings 11a and 11b, which are calculated by the above-mentioned equation (A) (the same as the equation (A) in the evaluation method described above). When the axial load acting in the axial direction is F and the rigidity values of each of the pair of electrode rings 11a and 11b and their peripheral parts are F0, F ≦ F.

As a result, the combination of the leading steel plate 21 and the trailing steel plate 22 to be welded is suitable, and damage to the electrode rings 11a, 11b or its peripheral parts due to the axial load F acting on the electrode rings 11a, 11b is avoided. It is possible to provide a mash seam welder 1 capable of providing a mash seam welder 1.
Further, in the mash seam welder 1, by setting F ≦ F0, the displacement amount of the upper electrode ring 11a and the lower electrode ring 11b in the axial direction can be set to a predetermined value or less (5.0 mm or less). ..

Further, in the mash seam welding method according to the present invention, using such a mash seam welder 1, the overlapping portion of the leading steel plate 21 and the trailing steel plate 22 to be welded is formed by a pair of electrode rings 11a and 11b. The leading steel plate 21 and the trailing steel plate 22 are continuously welded by applying pressure and applying a welding current while running each of the pair of electrode rings 11a and 11b in the above-mentioned overlapping portion.
Further, in the method for manufacturing a hot-rolled steel sheet according to the present invention, the hot-rolled steel sheet is manufactured by the above-mentioned mash seam welding method.

Further, in the method for manufacturing a hot-rolled steel sheet according to the present invention, while running a pair of electrode rings 11a and 11b that pressurize the overlapped portion of the leading steel sheet 21 and the trailing steel sheet 22 to be welded at the overlapped portion. This is a method for manufacturing a hot-rolled steel sheet having a mash seam welding step in which a leading steel sheet 21 and a trailing steel sheet 22 are continuously welded by passing a welding current. In this method of manufacturing the hot-rolled steel plate, the thickness and tensile strength of the leading steel plate 21 and the trailing steel plate 22 and the rigidity of each of the pair of electrode rings 11a and 11b and their peripheral parts are determined by the above-mentioned (A). ) (Same as equation (A) in the evaluation method described above), which acts on the electrode rings 11a and 11b of the pair of electrode rings 11a and 11b in the axial direction of the electrode rings 11a and 11b. When the load is F and the rigidity values of each of the pair of electrode rings 11a and 11b and their peripheral parts are F0, it is determined that welding is possible only when F ≦ F0 is satisfied.

Although the embodiments of the present invention have been described above, the present invention is not limited to this, and various modifications and improvements can be made.
For example, although the example of welding with the leading steel plate 21 on the upper side and the trailing steel plate 22 on the lower side has been described, the leading steel plate 21 may be welded on the lower side and the trailing steel plate 22 may be welded on the lower side.
Further, the constant k in the equation (A) is not limited to 10 and can be appropriately set. Further, the constant a in the equation (A) is not limited to −0.5, and can be appropriately set within the range of -1 ≦ a ≦ 0.

Further, F0 in the equation (B) is not limited to 4000 kgf. That is, F0 is a rigidity value sufficient to reduce the displacement amount of the pair of electrode rings 11a and 11b in the traveling direction to 5.0 mm or less, and depends on the tensile strength and thickness of the leading steel plate 21 and the trailing steel plate 22 to be joined. Can change. The amount of displacement of the pair of electrode rings 11a and 11b in the axial direction is more preferably 4.0 mm or less, still more preferably 2.0 mm or less.
Further, regarding the evaluation method of mash seam welding, the axial load F or the load corresponding thereto is calculated by the equation (A) or the relational expression corresponding thereto using a computer system (evaluation device 30), and the calculated axial load is calculated. Weldability of the leading steel plate 21 and the trailing steel plate 22 is evaluated based on the load F, but it may be calculated and evaluated manually without using a computer system.

Further, when the design of the upper electrode ring 11a and its peripheral parts is changed so that F ≦ F0, the upper electrode ring 11a and its peripheral parts are not changed in design, and the upper electrode ring 11a and its peripheral parts are not changed. At least one of the peripheral parts may be redesigned to increase the rigidity value F0 of the upper electrode ring 11a and the peripheral parts thereof.
Further, when the design of the lower electrode ring 11b and its peripheral parts is changed so that F ≦ F0, the lower electrode is not changed in design of both the lower electrode ring 11b and its peripheral parts. At least one of the ring 11b and its peripheral parts may be redesigned to increase the rigidity value F0 of the lower electrode ring 11b and its peripheral parts.

Further, the design method of the mash seam welder includes a pair of electrode rings 11a and 11b that pressurize the overlapped portion of the leading steel plate 21 and the trailing steel plate 22 to be welded, and the pair of electrode rings 11a and 11b are overlapped. This is a design method for a mash seam welder that continuously welds the leading steel plate 21 and the trailing steel plate 22 by passing a welding current while running at the mating portion. In the design method of this mash seam welder, the axial load acting on each of the pair of electrode rings 11a and 11b in the axial direction and the rigidity of each of the pair of electrode rings 11a and 11b and their peripheral parts have a predetermined relationship. The pair of electrode rings 11a and 11b and their peripheral parts may be designed so as to be. Here, the axial load is determined from the respective plate thicknesses and tensile strengths of the leading steel plate 21 and the trailing steel plate 22. Further, the "predetermined relationship" may satisfy other than F≤F0, and "designing" "to have a predetermined relationship" means the thickness of the steel sheet to be welded in the steel sheet production line and the thickness of the steel sheet to be welded. This means that the rigidity of the equipment is appropriately determined according to the axial load of each of the pair of electrode rings 11a and 11b determined from the tensile strength.

In the design method of this mash seam welder, it is preferable that the displacement amount of the pair of electrode rings 11a and 11b in the axial direction is 5.0 mm or less.
Further, the mash seam welder includes a pair of electrode rings 11a and 11b that pressurize the overlapped portion of the leading steel plate 21 and the trailing steel plate 22 to be welded, and the pair of electrode rings 11a and 11b are overlapped at the overlapped portion. This is a mash seam welder that continuously welds the leading steel plate 21 and the trailing steel plate 22 by passing a welding current while running. Then, in this mash seam welder, the axial load acting on each of the pair of electrode rings 11a and 11b in the axial direction and the rigidity of each of the pair of electrode rings 11a and 11b and their peripheral parts have a predetermined relationship. You may try to meet. The meanings of "axial load" and "predetermined relationship" are the same as in the case of the above-mentioned mash seam welder design method.

In this mash seam welder, it is preferable that the displacement amount of the pair of electrode rings 11a and 11b in the axial direction is 5.0 mm or less.
Further, in the mash seam welding method, the overlapped portion of the leading steel plate 21 and the trailing steel plate 22 to be welded is pressed by a pair of electrode rings 11a and 11b by using the mash seam welding machine described above, and a pair of electrode rings 11a and 11b are used. The leading steel plate 21 and the trailing steel plate 22 may be continuously welded by passing a welding current while running each of the electrode rings 11a and 11b at the overlapped portion.

Further, in the method for manufacturing the hot-rolled steel sheet, the hot-rolled steel sheet may be manufactured by the above-mentioned mash seam welding method.
Further, in the method of manufacturing a hot-rolled steel sheet, a welding current is passed while running a pair of electrode rings 11a and 11b that pressurize the overlapped portion of the leading steel sheet 21 and the trailing steel sheet 22 to be welded at the overlapped portion. As a result, it has a mash seam welding step in which the leading steel plate 21 and the trailing steel plate 22 are continuously welded. In this method for manufacturing a hot-rolled steel sheet, the axial load acting on each of the pair of electrode rings 11a and 11b in the axial direction and the rigidity of each of the pair of electrode rings 11a and 11b and their peripheral parts have a predetermined relationship. It may be determined that welding is possible only when the condition is satisfied. The meanings of "axial load" and "predetermined relationship" are the same as in the case of the above-mentioned mash seam welder design method.

In setting the welding conditions, first, in the mash seam welder 1 shown in FIG. 1, welding is performed with a combination of various steel plates appropriately selected from the range of ^{plate thickness 1.5 to 6.0 mm and tensile strength 20 to 60 kgf / mm 2.} Was done. Then, the axial load acting on the electrode rings 11a and 11b was actually measured, an approximate expression was derived, and the evaluation was performed as shown in FIG. It was found that the highest correlation was found between "thickness t1", "strength TS2 of trailing steel plate x plate thickness t2" and the axial load F. Further, as shown in FIG. 7, when the relationship between the actually measured axial load and the displacement amount of the electrode rings 11a and 11b was evaluated, welding failure occurred when the axial load exceeded 4000 kgf under this condition.

Therefore, when evaluating the combination of the leading steel plate 21 and the trailing steel plate 22 that can be welded by the evaluation method applied to the design method of the mash seam welder according to the present embodiment, the constant k in the equation (A) is set to 10. The axial load F was calculated for each combination of the leading steel plate 21 and the trailing steel plate 22 with the constant a set to −0.5, and the evaluation was performed with F0 in the equation (B) set to 4000 kgf.
Various combinations of the leading steel plate 21 and the trailing steel plate 22 are appropriately selected from the range of the plate thickness of 1.5 to 6.0 mm and the tensile strength of 20 to 60 kgf / mm ^{2, and each combination is subjected to the formula (A) by the evaluation device 30.} The axial load F was calculated with the constant k set to 10 and the constant a set to −0.5. Then, welding was performed 450 times for each combination, and whether or not welding was possible was evaluated for each combination of the leading steel plate 21 and the trailing steel plate 22. The result is shown in FIG.

The horizontal axis of FIG. 8 is the axial load F calculated by the evaluation method (A) according to the evaluation method applied to the design method of the mash seam welder according to the present embodiment, and the vertical axis is the number of weldings (times). I took.
As shown in FIG. 8, when the axial load F calculated by the formula (A) is 4000 kgf or less, welding is good (successful) in any combination of the leading steel plate 21 and the trailing steel plate 22. On the other hand, when the axial load F calculated by the formula (A) is larger than 4000 kgf, 16 out of 20 welds were poor welding (welding failure).
Therefore, it was confirmed that the evaluation method applied to the design method of the mash seam welder according to the present invention and the weldable combination of the leading steel plate 21 and the trailing steel plate 22 to be welded by the evaluation device 30 can be evaluated with high accuracy.

1 Mash seam welder 11a Upper electrode ring (electrode ring)
11b Lower electrode ring (electrode ring)
12a Upper rotary shaft 12b Lower rotary shaft 13a Bearing 13b Bearing 14a Upper electrode ring support member 14b Lower electrode wheel support member 15a Upper carriage 15b Lower carriage 16a Linear guide 16b Linear guide 17a Upper frame 17b Lower frame 18 Pressing member 19 Linear Guide 20 Pressing Cylinder 21 Leading Steel Plate 21a Tail End 22a Trailing Steel Plate 22a Tip 23 Front Clamping Device 23a Upper Clamping Member 23b Lower Clamping Member 24 Rear Clamping Device 24a Upper Clamping Member 24b Lower Clamping Member 25 Pressing cylinder 26 Pressing cylinder 27 Welding part 30 Evaluation device 31 Axial load calculation part 32 Evaluation part 33 Output part

Claims (7)

A pair of electrode rings that pressurize the overlapped portion of the leading steel plate and the trailing steel plate to be welded are provided, and the welding current is passed while running the pair of electrode rings in the superposed portion to obtain the leading steel plate. It is a design method of a mash seam welder that continuously welds the trailing steel sheet.
The thickness and tensile strength of the leading steel plate and the trailing steel plate, and the rigidity of each of the pair of electrode rings and their peripheral parts are calculated by the following equation (A). When the axial load acting on each electrode ring in the axial direction of the electrode ring is F and the rigidity value of each of the pair of electrode rings and its peripheral parts is F0, the pair is set to F≤F0. A method for designing a mash seam welder, which comprises designing each of the electrode rings and their peripheral parts.
Here, F = k × (t1 × TS1 + a × t2 × TS2)… (A)
t1: Thickness (mm) of the steel plate on the upper side of the superposition
TS1: The tensile strength of the steel plate on the upper side of the superposition (kgf / mm ² )
t2: Plate thickness (mm) of the steel plate on the lower side of the superposition
TS2: tensile strength of the steel plate under the superposition (kgf / mm ² )
k: Constant determined by the mash seam welder a: Constant indicating the contribution of the lower steel plate to the upper steel plate The method for designing a mash seam welder according to claim 1, wherein the displacement amount of the pair of electrode rings in the axial direction is 5.0 mm or less. A pair of electrode rings that pressurize the overlapped portion of the leading steel plate and the trailing steel plate to be welded are provided, and the welding current is passed while running the pair of electrode rings in the superposed portion to obtain the leading steel plate. A mash seam welder that continuously welds the trailing steel sheet.
The thickness and tensile strength of the leading steel plate and the trailing steel plate, and the rigidity of each of the pair of electrode rings and their peripheral parts are calculated by the following equation (A). When the axial load acting on each electrode ring in the axial direction of the electrode ring is F and the rigidity value of each of the pair of electrode rings and its peripheral parts is F0, the relationship is that F ≦ F0. A featured mash seam welder.
Here, F = k × (t1 × TS1 + a × t2 × TS2)… (A)
t1: Thickness (mm) of the steel plate on the upper side of the superposition
TS1: The tensile strength of the steel plate on the upper side of the superposition (kgf / mm ² )
t2: Plate thickness (mm) of the steel plate on the lower side of the superposition
TS2: tensile strength of the steel plate under the superposition (kgf / mm ² )
k: Constant determined by the mash seam welder a: Constant indicating the contribution of the lower steel plate to the upper steel plate The mash seam welder according to claim 3, wherein the displacement amount of the pair of electrode rings in the axial direction is 5.0 mm or less. Using the mash seam welder according to claim 3 or 4, the overlapped portion of the leading steel plate and the trailing steel plate to be welded is pressed by a pair of electrode rings, and each of the pair of electrode rings is pressed. A mash seam welding method characterized in that the leading steel plate and the trailing steel plate are continuously welded by passing a welding current while traveling in the overlapped portion. A method for manufacturing a hot-rolled steel sheet, which comprises manufacturing a hot-rolled steel sheet by the mash seam welding method according to claim 5. By passing a welding current while running a pair of electrode rings that pressurize the overlapped portion of the leading steel plate and the trailing steel plate to be welded at the superposed portion, the leading steel plate and the trailing steel plate are continuously connected. A method for manufacturing a hot-rolled steel sheet having a mash seam welding process for welding.
The thickness and tensile strength of the leading steel plate and the trailing steel plate, and the rigidity of each of the pair of electrode rings and their peripheral parts are calculated by the following equation (A). When the axial load acting on each electrode ring in the axial direction of the electrode ring is F, and the rigidity value of each of the pair of electrode rings and its peripheral parts is F0, the relationship of F ≦ F0 is satisfied. A method for manufacturing a hot-rolled steel sheet, which is characterized in that only welding is possible.
Here, F = k × (t1 × TS1 + a × t2 × TS2)… (A)
t1: Thickness (mm) of the steel plate on the upper side of the superposition
TS1: The tensile strength of the steel plate on the upper side of the superposition (kgf / mm ² )
t2: Plate thickness (mm) of the steel plate on the lower side of the superposition
TS2: tensile strength of the steel plate under the superposition (kgf / mm ² )
k: Constant determined by the mash seam welder a: Constant indicating the contribution of the lower steel plate to the upper steel plate

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