JP2002210583A - Method and facility for continuous welding of steel strip in longitudinal direction - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method and a facility for continuous welding of a steel strip in the longitudinal direction in which the welding is performed ensuring the pass restriction, thermal deformation of a welded part and an area in the vicinity thereof is suppressed, and a wide welded steel strip of excellent shape characteristics can be manufactured at a low cost with high productivity when the steel strips are butted to each other in the width direction and the butted part is continuously welded in the longitudinal direction. SOLUTION: Carrying surfaces of two steel strips adjacent to each other in the width direction are converged in the same plane on the carrying line and butted to each other, and immediately after the steel strips are continuously welded in the longitudinal direction with the pass restricted, the steel strips are supported by a pair of support rolls and pressed by a pair of press rolls arranged facing each other above and below the pair of support rolls with the pass restricted. Thermal strain of the welded part is eliminated by heating the butt-welded part.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for abutting welding edges of strip-shaped steel sheets adjacent in the width direction which are conveyed in parallel.
The present invention relates to a method for continuous welding in the longitudinal direction by, for example, laser beam welding and a continuous welding facility.
For example, when steel sheets of different types (plate thickness or material, etc.) are used for adjacent parts such as an automobile body, a joining blank material capable of integrally forming these parts is required. The present invention is to carry out parallel welding of two or more strip-shaped steel sheets in the width direction and continuous welding in the longitudinal direction to secure welding quality and to reduce the cost of the joining blank material and the wide welding strip-shaped steel sheet having good shape characteristics. In addition, the present invention relates to a continuous welding method and a continuous welding equipment in the longitudinal direction of a strip-shaped steel sheet that can be manufactured with high productivity.

[0002]

2. Description of the Related Art Conventionally, as a method of manufacturing a joining blank material as described above, there has been known a method in which strip-shaped sheets are butted together without a gap, and welding is performed while moving a welding machine along the butted portion. I have. in this way,
There is a problem that handling for welding is complicated, cost is increased, and sufficient productivity cannot be secured. It is also known to perform welding by moving both the steel strip and the welding machine.However, since the steel strip cannot be continuously conveyed in the welding equipment, the length of the welding length is reduced by the welding machine and the steel strip. There is a problem in that the welding is limited by the moving stroke, continuous welding cannot be performed over the entire length of the coil, and sufficient productivity cannot be secured.

[0003] Recently, various improvements have been made to solve the above-mentioned problems of the conventional method.
As disclosed in the gazette, by fixing the welding machine, and by conveying the strip-shaped steel sheet to the welding position by the welding machine in a state where the side ends of the strip-shaped steel sheet are abutted with each other, the butt portion of the strip-shaped steel sheet is continuously irradiated by a laser beam. There has been proposed a method of conveying and guiding a strip-shaped steel sheet on the assumption that it is welded in a specific manner. That is, as shown in FIGS. 6 and 7, the welding side edges of the strip-shaped steel plates a and b are adjacent to each other, and one of the side edges is guided by the guiding members c and b in the same vertical plane. There is disclosed a method of conveying and guiding a strip-shaped steel sheet to be brought into contact with a surface, and to be fed to a welding machine e by being brought into contact with each other without any gap in the same horizontal plane on separate conveying planes arranged side by side and inclined at an acute angle α.

In this method, the strip-shaped steel plates a and b, which are conveyed vertically apart, are pushed in by a conveying roller r and a vertical roller g which are arranged obliquely, and the side ends on the welding side are placed in the same vertical plane. Guide surfaces c and da of guide members c and b
The belt-shaped steel plates a and b are converged on the same plane by the grip roller f to abut the side ends of the strip-shaped steel plates a and b. This is configured to be welded by e.

[0005] As described above, when the side edges of the two strip-shaped steel plates are butt-welded continuously in the longitudinal direction, heat distortion is generated in the butt-welded portion and a region near the welded portion due to welding heat, and stable welding accuracy can be ensured. In addition, there is a problem that the quality of the welded portion is reduced, and that the obtained welded strip-shaped steel plate undergoes thermal deformation as shown in FIG.
This phenomenon occurs remarkably, particularly when a thin strip-shaped steel sheet is to be welded, and when strip-shaped steel sheets having different thicknesses are to be welded. Also, when the strip-shaped steel plates are butted from the inclination direction, the tendency is more prominent as the inclination angle is larger.

[0006]

SUMMARY OF THE INVENTION According to the present invention, when the strip steel plates are butted in the width direction and the butted portions are continuously welded in the longitudinal direction, the above-mentioned problem is advantageously solved and the strip steel plate is welded. The welding side edges are butt-butted and welding is performed in a state where the path constraint is ensured, and the thermal deformation of the welded area and the area near the welded area is suppressed to produce a wide welded steel strip with good shape characteristics at low cost. It is an object of the present invention to provide a continuous welding method and a continuous welding equipment in the longitudinal direction of a strip-shaped steel sheet that can be manufactured with high productivity.

[0007]

The gist of the present invention to achieve the above object is as follows (1) to (3). (1) The strip-shaped steel sheets adjacent to each other in the width direction that are conveyed in parallel are converged on the same plane on the transfer line and abutting path restraint (meaning that the strip-shaped steel sheet is transferred while being lightly restrained,
Hereinafter, this is referred to as “path constraint”. Immediately after continuous welding in the longitudinal direction, while being supported by a pair of support rolls, the pair of support rolls are pressed by a pair of press rolls arranged so as to face each other up and down to constrain the path and butt. A method for continuously welding a strip-shaped steel sheet in a longitudinal direction, wherein a weld portion and a region near the weld portion are heated to remove thermal distortion of the weld portion.

(2) The strip-shaped steel sheet according to (1), wherein when the butt-welded portion has a temperature range of 300 to 500 ° C., the butt-welded portion and the region near the weld portion are heated to 400 to 700 ° C. Continuous welding method in the longitudinal direction.

(3) A path restraining device for converging and confining the strip-shaped steel plates adjacent to each other in the width direction conveyed in parallel in the same plane on the conveying line and constraining the path, and a continuous welding of the butt portion in the longitudinal direction. A welding machine, a pair of support rolls arranged on the right and left by forming a heating space with the butt portion sandwiched in the transfer line immediately after the welder, and sandwiching the butt portion by vertically opposing the pair of support rolls, respectively; A pair of pressing rolls arranged on the left and right so as to form a heating space, a pressing mechanism for pressing this pressing roll to apply a path restraining force to the strip-shaped steel plate, and between a pair of supporting rolls and a pair of pressing rollers. A continuous welding equipment in the longitudinal direction of a strip-shaped steel sheet, comprising a heating device arranged to remove thermal distortion of a welded portion.

[0010]

BEST MODE FOR CARRYING OUT THE INVENTION The present invention relates to, for example, a method of unwinding a strip steel sheet from two strip steel coils and conveying the strip steel sheet in parallel to one side of a strip steel sheet and the other strip steel sheet. Alternatively, the lower surface and the upper surface are butted in the same plane and introduced into the continuous welding equipment, and the butted portion of the welding side of one strip steel plate and the other strip steel plate is continuously welded in the longitudinal direction by, for example, a laser beam. Then, the continuous welding method and this continuous welding method, which are applied in a line for continuously manufacturing wide-width welded strips of the same kind and different thicknesses of strip or different kinds of strips of the same thickness or different thickness, are applied. The present invention is a continuous welding facility, and is particularly characterized by having a configuration for suppressing deformation of a welded portion and a region in the vicinity of the welded portion due to thermal distortion due to welding heat.

In the present invention, immediately after the conveying surfaces of the two strip-shaped steel strips adjacent in the width direction are converged on the same plane on the conveying line and continuously welded in the longitudinal direction, they are supported by a pair of support rolls, By heating the butt weld in a state where it is pressed by a pair of pressing rolls disposed so as to face each other on the pair of support rolls and constrains the path, the heat distortion is suppressed while suppressing the deformation due to the thermal distortion of the weld. This effectively suppresses thermal deformation of the welded portion of the welded strip-shaped steel sheet that can be effectively removed.

In the present invention, the path restraining force between the pair of supporting rolls and the pair of pressing rolls is determined by the thickness difference of the strip-shaped steel sheet, It can be adjusted arbitrarily according to the etc., when thin strip steel sheet is to be welded, even when strip steel sheet of different thickness is to be welded, while suppressing deformation by suppressing the butt weld part with path Heating can be performed, the heating accuracy can be ensured stably, the thermal distortion of the welded portion can be effectively removed, and the quality of the welded portion and the shape characteristics of the obtained welded strip steel plate can be improved.

The pair of pressing rollers can be independently adjusted vertically by a vertical position adjusting mechanism. When a belt-shaped steel sheet having a different thickness is to be welded, the position of the pressing surface can be provided with a thickness difference step. It is more effective to easily make a difference in the pressing force. The pair of pressing rollers may be freely rotatable. When the length of the heating zone is set to several tens cm or more,
It is also effective to use a plurality of strip-shaped steel plates arranged in the length direction.

When the length of the heating zone is set to several tens cm or more, it is effective to use a plurality of support rolls arranged in the longitudinal direction of the strip-shaped steel sheet. In the case of a light-weight structure, it may be freely rotatable. However, in the case of a heavy-weight structure, if there is a possibility of occurrence of slip between the belt-shaped steel plate to be supported, a drive roll may be used to synchronize the transfer line speed. May be rotated.

The supporting surfaces of the pair of supporting rolls and the pressing surface of the pair of pressing rollers are for holding the band-shaped steel plate in a pressed state and restricting the path, so that the supporting surface has sufficient rigidity and the supporting surface has a band-like shape. It is made of a material that satisfies the conditions that do not scratch the surface of the steel sheet and that does not cause erosion etc. even if the heated high-temperature part of the strip-shaped steel sheet is sandwiched, such as chromium plating, ceramic spraying, or heat-resistant rubber lining on steel. Those that have been used are preferred.

As the heating device, it is preferable to use an electric heating device such as an induction heating device or a high-frequency heating device, which can easily control the heating region and control rapid heating, a laser beam heating device, a plasma heating device, or the like. When the heating device is capable of heating only one side of the welded portion (for example, a laser beam heating device), the heating device is disposed on each of the support roll side and the pressing roll side, or the temperature generated on the front and back of the welded portion. It is disposed only on the support roller side provided on the surface opposite to the welding heat input surface which has the effect of eliminating the difference and uniformly heating the entire thickness region. In the case where the heating device is disposed on each of the support roll side and the pressing roll side, changing the heating conditions is considered.

In order to sufficiently secure the effect of removing the thermal distortion by welding, depending on the material and size, the thermal distortion is likely to appear as deformation of the welded strip steel plate.
When the temperature is in the temperature range of 00 to 500 ° C., it is effective to heat to a temperature range slightly higher than this temperature range. 300
When the temperature is lowered to a temperature lower than ° C., the deformation is progressing at that point, and even if heating is performed from this state, the deformation suppressing effect is insufficient. If the temperature is higher than 500 ° C., the heating does not contribute much to the deformation suppressing effect.

It is preferable that the heating temperature is set in a temperature range that does not adversely affect the properties of the base metal, as a welded portion and a region near the welded portion of 2 to 3 mm from the welding line.
As for the heating, it is preferable to perform heating at a heating rate of 50 ° C./sec to 200 ° C./sec to a temperature range of 400 to 700 ° C. If the temperature is lower than 400 ° C., the effect of removing the strain is not sufficient, and if the temperature is higher than 700 ° C., the properties of the base material are adversely affected (a decrease in strength and a decrease in hardness). If the heating rate is less than 50 ° C./sec, the heating time is prolonged, so that the temperature rises to the peripheral portion.
When the temperature exceeds ℃ / sec, the temperature gradient between the welded portion, the region near the weld and the peripheral portion becomes large, and a sufficient strain removing effect cannot be obtained.

In order to secure the preferable heating conditions as described above, the heating by the heating device is performed when the temperature of the welded portion is 30 degrees.
Immediately after the welding position in the temperature range of 0 to 500 ° C 100 to 4
It is effective to start from the position of 00 mm and reach the maximum temperature within the path constraint region where the flatness of the welded strip-shaped steel sheet can be maintained. For this purpose, it is effective to set a heating zone and a heating pattern so that heating can be started just before the pass constraint start position. The length of the heating zone is
Although it depends on the material, size, type of heating device, thickness of the welded portion, line speed, etc., it is sufficient that the heating temperature and the heating speed are 100 to 400 mm in order to secure the above-mentioned heating temperature and heating speed.

As a welding machine, a laser welding machine using a YAG, CO ₂ laser, a semiconductor laser, or the like, which can perform welding at a higher speed than other welding means and has a wide application range even in welding between dissimilar materials. Is preferred, a welding machine capable of non-contact type heat source input, for example, a plasma welding machine,
A plasma-assisted laser welding machine or the like can be used.

A path restraining device for welding is a structure capable of converging a band-shaped steel plate butted on the same plane, for example, by sandwiching it between a support (including a roll) and a pressing body (including a roll). It is desirable to use a structure that can adjust the rolling force between the (roll-containing) and the pressing body (roll-containing) to adjust the path restraining force. This path restraining device may be arranged so that it can be independently restrained for each strip-shaped steel sheet, or may be arranged so as to be able to restrain the butted strip-shaped steel sheets at the same time. You may.

[0022]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described with reference to FIGS. This embodiment, the steel strip 1 _1, 1 ₂ of the two rows of the welding object, and of different thicknesses, is shown in the case of using a laser beam welding machine 5 as the continuous welder.

FIG. 1 shows that the welding edges of _two strip-shaped steel plates 1 ₁ and 12 adjacent in the width direction are butted, and the butted portion is continuously welded in the longitudinal direction by a laser beam emitted from a laser beam welding machine 5. 1 shows an example of equipment arrangement of a line for continuously producing a wide welded strip steel plate 1a.

In this example of the equipment arrangement, the decoiler 2₁,
2_TwoStrip steel sheet 1 unwound from₁, 1_TwoIs different
Strip-shaped steel sheet 1 while parallel transport at an angle₁And strip steel plate 1_Two
Guide device 3 in the process of converging the lower surface of
a, 3b, welding edge on the welding side without gap
Then, the path is restrained by the path restraining device 4 and
Guide to the integrated laser beam welding machine 5, where the belt
Steel plate 1₁And strip steel plate 1 _TwoWith the path restrained
The joint radiated from the laser beam welding machine 5
Strip steel plate 1 welded in the longitudinal direction with a laser beam₁,
1_TwoAnd a welded strip steel plate 1a made of

In a state where the welded strip-shaped steel plate 1a immediately after welding is path-constrained by the support roll 6 and the pressing roll 7, the welded portion is heated by a heating device (not shown in FIG. 1) to suppress deformation due to thermal distortion, and After securing the stable characteristics, it is cut into a predetermined size by the output side shear 9 to be made into a wide welding steel plate 1b and stored in the pallet 10.

In the present invention, immediately after the butted portions of the _two strip-shaped steel plates 11 and ₁₂ are welded in the longitudinal direction by the laser beam irradiated from the laser beam welding machine 5, the support roll 6 and the support roll 6 The main feature of the present invention is that the welding portion is heated in a state where the path is constrained by the pressing roll 7 to suppress deformation of the welding portion due to thermal distortion.

FIG. 2 shows an example of a path restricting structure for restricting the path of the welded strip steel plate 1a immediately after welding and an example of a heating device for heating the welded portion.
This will be described more specifically with reference to FIGS. First, the path restraining structure includes a pair of support rolls 6a and 6b in which a welding strip-shaped steel plate 1a on a transfer line immediately after welding a butt portion is disposed on the left and right sides by forming a heating space 11u with a welding portion w interposed therebetween.
A pair of pressing rolls 7a, 7b, which are vertically opposed to the pair of supporting rolls on the upper side of the transport line, and which are arranged on the left and right so as to form a heating space 11o with the welding portion interposed therebetween.
When being installed to the frame 12 a pair of press rolls 7a via the elevating body 13, the whole was liftably supported 7b, welded steel strip 1a (the steel strip 1 ₁ and 1 ₂₎ in the pressing mechanism for imparting path binding 14 and a vertical position adjusting mechanism 15 for independently adjusting the vertical positions of the pair of pressing rolls 7a and 7b.

Here, a vertical position adjusting mechanism 1 for independently adjusting the vertical position of the pair of pressing rolls 7a, 7b.
Was is given provided 5, according to the deformation condition of the steel strip 1 ₁ and the steel strip 1 _2, the pressing force against the steel strip 1 ₁ and the steel strip 1
_{In order} to make a difference in the pressing force with respect to ₂ or to constrain the band-shaped steel plates having different thicknesses, a pair of pressing rolls 7a and 7b
This is convenient when a thickness difference step is provided between the pressing surfaces.
However, it is not indispensable to provide the pressing mechanism 14 and the vertical position adjusting mechanism 15 together. For example, when only a strip-shaped steel plate having the same thickness is to be welded, the vertical position adjusting mechanism 15 may be omitted.

Here, the heating device is constituted by an induction heating device 8, and the heating area by the induction heating device 8 is between a pair of support rolls 6a and 6b and between a pair of pressing rollers 7a and 7b. The heat distortion can be removed by heating the welded portion w and the region near the welded portion. Here, the heating start point in the induction heating device 8 is, as shown in FIGS. 3 and 4, a pair of support rolls 6a and 6b.
And a path constraint line pa by a pair of pressing rolls 7a and 7b.
(Pb) is located xa away from the laser beam welding machine 5 side, and xb is located away from the welding point wp, and the heating end point is located xc away from the path constraint line pa (pb).
Therefore, the length of the heating zone here is xa + xc
It is.

[0030] In the present invention, in the produced continuous welding equipment as described above, the steel strip 1 ₁ and 1 ₂ 2 Article in parallel conveying, butt welding side edge converge the conveying surface in the same plane Immediately after the butt portion is irradiated with a laser beam from the laser beam welding machine 5 and the butt portion is continuously welded in the longitudinal direction, the welding strip-shaped steel plate 1a is paired on the transport line with the restraint device 4 to pass the butt portion. The path between the supporting rolls 6a, 6b and the pair of pressing rolls 7a, 7b is constrained, and the welding w portion and the area near the welding portion are heated by the induction heating device 8, so that the heating accuracy is stably ensured. In addition, the thermal distortion in the region near the welded portion is removed to suppress the thermal deformation, and the quality of the welded portion and the shape characteristics of the obtained welded strip steel plate can be improved.

In this case, since the path restraining mechanism capable of arbitrarily adjusting the path restraining force and the welding function are integrated into a simple structure and compact, it can be easily installed on a line. However, it is not essential to integrate the path restraining mechanism and the welding function.

The present invention is not limited to the above embodiment. For example, the band-shaped steel plate to be welded may be of a different steel type or of the same steel type, and the present invention is applicable to both cases of the same thickness and different thicknesses. Although the above-described embodiment shows the case where two strip steel plates are butt-welded, the present invention can be applied to, for example, the case where three strip steel plates are butt-welded. Even when the present invention is applied to the case where there is a time difference of 5 to 20 seconds or more between the welding portions, the deformation of the entire welded strip-shaped steel plate can be prevented.

The main surface of the belt-shaped steel plate to be welded is a horizontal surface in the width direction, but the present invention can be applied to a vertical or inclined conveying surface. Further, constituting the present invention, a support roll, a pressing roll, a pressing down mechanism, a vertical position adjusting mechanism, a transport device, a guide device, a path restraining device during welding,
Regarding the type structure, arrangement, number of arrangements of the welding machine, the structure and heating conditions of the heating device, etc., the above claims are satisfied according to the steel type, size, number of strips, welding conditions, equipment arrangement, etc. of the strip steel plate to be welded Changes within the scope of the change.

[0034]

Experiment thickness 1.4 mm, the steel strip of width 400 mm (steel type: high tensile strength) 1 _1, thickness 0.7 mm, width 400
mm of the steel strip (steel type: high tensile) as the 1 ₂ welded, using a continuous welding installation according to the invention as shown in FIGS. 1 to 4, carried out in the longitudinal direction of the continuous welding experiments according to the invention, obtained The shape of the welded strip steel plate and the quality of the welded area and the area near the welded area were investigated. The experimental conditions and experimental results will be described below in comparison with the case of the comparative example.

[0035]

[Experiment conditions] Welding machine Laser beam welding machine Model / output: YAG laser 4kw Weld bead width: 1.1mm Pass restraint Support roll diameter: 180mm Press roll diameter: 60mm Pass restraint force: 980N

Induction heating device Heating capacity: 1.5 kW Heating zone length: 100 to 400 mm (xa + xc) Heating temperature: 500 to 700 ° C (heating rate 30 to 250 ° C)
/ Sec) Heating width: 2 to 3 mm left and right from the butt line Heating start point position: 600 mm from welding point wp (x
b), a position 100 mm from the path constraint line pa (xa) Temperature of the weld immediately before the start of heating: 300 to 500 ° C. Heating end point position: a position 100 mm from the path constraint line pa (xc) Line speed: 5 m / min

(1) In the experimental example of the present invention, as shown in FIG. 5, no deformation was observed in the welded portion of the welded strip-shaped steel plate and in the region near the welded portion. (2) In contrast, in the conventional example in which heating was not performed immediately after welding, as shown in FIG. 8, significant deformation was observed in the welded portion of the welded strip-shaped steel plate and in the region near the welded portion. (3) Under the above experimental conditions, when the heating temperature was 350 ° C., the effect of suppressing the deformation by heating was not sufficient, and slight deformation was observed in the welded portion of the welded strip-shaped steel plate and in the region near the welded portion. . (4) Under the above experimental conditions, when the heating temperature was set to 750 ° C., a decrease in the base material properties (strength and hardness) was observed in the welded portion of the welded strip-shaped steel plate and in the region near the welded portion.

(5) Under the above experimental conditions, when the temperature immediately before the start of heating is 250 ° C., deformation due to thermal strain is progressing at that time, and the deformation suppressing effect by heating is not sufficient, and Slight deformation was observed in the strip steel plate. (6) In the above experimental conditions, the temperature immediately before the start of heating is 6
In the case of 00 ° C., the effect of suppressing deformation by heating was not sufficient, and slight deformation was observed in the welded strip-shaped steel sheet. (7) Under the above experimental conditions, when the heating rate is 30 ° C./sec, the steel strip is heated to a range beyond the vicinity of the welded portion of the welded strip, and a middle-elongated shape collapse remains. Was. (8) Under the above experimental conditions, when the heating rate is 250 ° C./sec, the temperature difference between the region near the weld and the peripheral region increases, causing bending in the advancing direction, and the shape of the streaks is broken. Was observed.

[0039]

According to the present invention, when welding two or more strip steel plates by butt welding to produce a welded steel strip, the weld and the vicinity of the weld are heated immediately after welding to remove thermal distortion. Therefore, even when a thin strip-shaped steel sheet is to be welded, deformation due to welding can be suppressed more reliably, and its shape characteristics can be improved. It can be obtained with high productivity.

[Brief description of the drawings]

FIG. 1 is an explanatory side view conceptually showing an overall arrangement example of a continuous welding facility for a strip-shaped steel plate in a longitudinal direction of the present invention.

FIG. 2 is an explanatory front view showing a path restraining structure and a structural example of a heating device of the continuous welding equipment of the present invention in FIG. 1;

FIG. 3 is an explanatory side view taken along arrows Aa-Ab in FIG. 2;

FIG. 4 is an explanatory plan view taken on line Ba-Bb of FIG. 3;

FIG. 5 is an explanatory front view showing the shape of a welded strip steel sheet obtained in an experimental example of the present invention.

FIG. 6 is an explanatory plan view showing an example of a conventional continuous welding equipment arrangement in the longitudinal direction of a strip-shaped steel plate.

FIG. 7 is an explanatory side view of FIG. 6;

FIG. 8 is an explanatory front view showing an example of the shape of a welded strip steel sheet obtained by a conventional example.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ₁ , 1 ₂ Strip steel plate 2 ₁ , 2 ₂ Uncoiler 3a, 3b Guide device 4 Restraining device 5 Continuous welding machine 6, 6a, 6b Support roll 7, 7a, 7b Press roll 8 Heating device 9 Shear 10 Pallet 11o, 11u Heating Space 12 Stand 13 Elevating body 14 Depressing mechanism 15 Vertical position adjusting mechanism 16 Guide w Welding point wp Welding point pa, pb Path constraint line

Claims (3)

[Claims] 1. Immediately after a belt-shaped steel sheet adjacent in the width direction conveyed in parallel is converged in the same plane on a conveyance line and butt-pass-constrained and continuously welded in the longitudinal direction, it is supported by a pair of support rolls. In this state, the path is restrained by pressing with a pair of pressing rolls arranged so as to face each other on the pair of support rolls vertically, and the butt weld and the area near the weld are heated to remove the thermal distortion of the weld. A continuous welding method in the longitudinal direction of a strip-shaped steel plate. 2. The strip-shaped steel sheet according to claim 1, wherein when the butt weld reaches a temperature range of 300 to 500 ° C., the butt weld and the region near the weld are heated to 400 to 700 ° C. Longitudinal continuous welding method. 3. A path constraining device that converges and constrains the strip-shaped steel plates adjacent in the width direction conveyed in parallel in the same plane on a conveying line, and continuously welds the butted portions in the longitudinal direction. And a pair of support rolls arranged on the right and left by forming a heating space with the butting portion sandwiched in the transfer line immediately after the welding machine, and heating the pair of supporting rolls by vertically opposing the pair of support rolls. A pair of pressing rolls arranged on the left and right so as to form a space, a pressing mechanism that presses this pressing roll to apply a path restraining force to the strip-shaped steel plate, and is disposed between the pair of supporting rolls and between the pair of pressing rollers. And a heating device for removing a heat distortion of the welded portion, the continuous welding equipment in the longitudinal direction of the strip-shaped steel plate.