JPH08300008A - Device for welding sheet bar in fully continuous hot rolling - Google Patents

Abstract

PURPOSE: To control positions of sheet bars and to obtain the optimum conditions of mating surfaces of the welding at the time of clamping the sheet bars by controlling the movement of welding equipment to a welding position and controlling welding in the width direction along the welding position. CONSTITUTION: After measuring difference in level between the upper edges of the mating faces 10 of the sheet bars with level sensors, a vertically adjusting device 5 for the position of the sheet bar and clamping device 4-2 are synchronously operated while holding the sheet bar 3-2 and, after judging that the difference in level between the upper edges of the mating faces 10 is zero with the level sensors, the devices are stopped. After judging that the welder 2 reaches just above the mating faces 10 with the sensors while moving the welder in this state with a welder position controller 9, welding is started while moving the welder 2 in the width direction along the mating faces 10 at a prescribed speed with the welder position controller 9. And, after judging that welding is executed to a prescribed position with the sensors, welding is completed.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a device for joining sheet bars by welding at the entrance side of a finish rolling mill when performing full continuous hot rolling.

[0002]

2. Description of the Related Art Conventionally, in hot tandem rolling of thin sheets, a slab of a finite length sent from the steelmaking process is roughly rolled into a sheet bar, which is rolled by a multi-stand hot finishing rolling machine. Then, the coil is wound into a coil to form a thin coil having a predetermined size. However, in finish rolling, unsteady rolling is inevitable when the tip of the sheet bar is pinched and the trailing edge of the sheet bar slips out due to the finite length of the sheet bar. From the viewpoint of prevention, it is necessary to slow down the sheet passing speed when passing the leading and trailing ends of the sheet bar, which is a factor that hinders productivity. As a countermeasure, it is considered to join a sheet bar having a finite length between a rough rolling mill and a finish rolling mill to perform endless finish rolling.

As shown in FIG. 6 of Japanese Patent Laid-Open No. 4-89110, a coil box 15, a leveler 12, a shear 13, a movable induction heating joining device 18, and a finishing rolling mill 14 are shown.
A process consisting of is disclosed. That is, the rear end portion of the sheet bar 3-2 during finish rolling and the front end portion of the sheet bar 3-1 after rough rolling unwound from the coil box 15 are each cut by the shear 13 to form a smooth mating surface. Then, these mating surfaces are butted, and the sheet bar is joined by the joining device 18 in synchronism with the movement of the sheet bar, whereby the finish rolling machine 14 performs full continuous rolling.

The feature of this method is that a movable induction heating welding device 18 is used as a welding machine. That is, after heating the material temperature in the vicinity of the mating surface of the sheet bar to the vicinity of the melting point by the movable induction heating bonding device 18, the mating surface is pressed to perform upset bonding, and burrs due to plastic deformation of the mating surface are removed. After preventing the occurrence of defects during finish rolling, finish rolling is performed. Since the burr rises to the thickness of the upper and lower plates of the joint portion to a thickness of about the plate thickness, it takes a long time to completely remove the burr and it is difficult to incorporate it into the existing line. Therefore, various applications of welding methods with less burr have been studied.

In Japanese Unexamined Patent Publication (Kokai) No. 61-52904, the trailing end of the preceding rolled material and the leading end of the trailing rolled material are butt welded by arc welding, in which case the melting depth of the weld and the plate thickness of the rolled material. A method for joining sheet bars to prevent plate breakage from a weld in the subsequent finish rolling is disclosed by specifying the ratio of 2/3 or more. Since the sheet thickness of the sheet bar immediately before finishing is usually about 30 to 45 mm, according to this method, the melting depth of arc welding is at least 20 to 3 mm.
Must secure 0 mm. In order to achieve such a melting depth, it is usual to perform groove processing on the mating surfaces in advance and perform build-up welding. Judging from the cross-section of the welded portion shown in FIG. 7 disclosed in Japanese Patent Laid-Open No. 61-52904, it is considered that the present invention is premised on the groove processing and the overlay welding. Generally, since the groove processing requires a great amount of processing time, this method cannot be directly applied to the existing line. That is, it is necessary to develop welding technology that can secure the necessary penetration depth without groove processing.

FIG. 8 shows an example of the cross-sectional shape of the abutting surface of the sheet bar which is not groove-processed when the sheet thicknesses of the preceding and following sheet bars are the same (t _B = t _T ). Its features are that it is close to the I groove because there are few parts corresponding to the groove, the mating surface is inclined by an angle θ from the vertical surface, and the level of the upper surface to be welded differs between the leading and trailing seat bars. That is, a step f is generated due to sagging during shearing of the shear. Further, FIG. 9 shows an example of the cross-sectional shape of the abutting surface of the sheet bar which is not groove-processed when the sheet thicknesses of the leading and trailing sheet bars are different (t _B <t _T ).
In this case, the level difference f of the upper surface to be welded is considerably large. That is, it can be understood that the geometrical condition of the mating surface greatly changes depending on the thickness of the sheet bar and the characteristics of the shear used.

On the other hand, in order to secure the required melting depth, it is necessary to understand the influence of the step f of the welding surface and the gap g of the mating surface on the melting depth. Almost nothing. Therefore, the inventors conducted a hot welding test in various states of the mating surfaces by the laser welding method and the arc welding method, and investigated the cross section of the joint. 2 shows the case where the step f of the surface to be welded is relaxed (f = 0) using the seat bar of FIG. 9, and FIG. 3 shows the welded portion when the step f of FIG. A cross section is shown. In the former case, the welding state was stable and the melting depth became deep as the capacity of the welding machine was fully utilized as shown in FIG. Let δ be the melting depth effective for joining in this case. On the other hand, in the latter case, as shown in FIG. 3, the upper end portion of the high-level sheet bar is also melted, so that the melting depth effective for joining is reduced by that amount and becomes approximately δ-f. That is, the larger the step f, the lower the bonding strength. In the case of arc welding,
Due to the step, the welding becomes unstable and a welding defect may occur, or in the worst case, the welding wire may pierce the seat bar and interrupt the welding.

Further, when the inclination of the mating surfaces is large, the welding direction of the welding machine deviates from the inside of the mating surfaces, so that in the case of the laser welding method with a narrow melting width, the substantial amount of joining the mating surfaces is reduced. However, it was found that a sufficient melting depth can be obtained when the welding method of the welding machine is matched to the in-plane.

Further, in the case of arc welding, even when there is no large step on the mating surface of the sheet bar, when the gap between the mating surfaces is 0 mm, the state is close to that of bead-on-plate welding, and the ideal groove is provided. To move away from the conditions,
There were cases where the melting depth became shallow and welding defects occurred frequently. However, even in this case, it was found that a sufficient melting depth can be secured by providing an appropriate gap on the mating surfaces.

From the above results, when the welding method is applied to the joining, the positions of the sheet bar and the welding machine are controlled in a butt state suitable for the welding condition when the leading and trailing sheet bars are clamped. We found that is essential.

Japanese Unexamined Patent Publication No. 60-244401 discloses a sheet bar joining apparatus which uses a high-frequency heating method to raise the temperature,
A method and apparatus for upsetting and joining mating surfaces is disclosed. However, with this method, since the welding machine is not applied, it is not necessary to control the level of the sheet bar in units of mm, and since the mating surface is constantly pressed, it is not necessary to adjust the gap between the mating surfaces. Therefore, there is no disclosure regarding the attitude control of the welding machine and the seat bar position adjusting device. Therefore, it is difficult to directly apply this device to the joining of the sheet bars by welding.

[0012]

[Problems to be Solved by the Invention] As described above,
When performing butt welding of the sheet bar on the entry side of the hot finish rolling mill, the conventional method cannot control the position of the mating surface of the sheet bar to a state suitable for welding.
There is a problem in that the welding strength decreases due to a decrease in the melt depth when the plate thickness is different or when there is a step on the welding surface due to a chaff, which causes welding defects. Therefore, there has been a restriction on the rolling schedule for changing the plate thickness.
Further, since the welding direction of the welding machine cannot be controlled, there is a disadvantage that the welding strength is lowered when the inclination of the mating surface is large. Further, in arc welding, it is necessary to provide an appropriate gap on the mating surface to maximize the melting depth, but it was difficult to control the gap on the mating surface with high precision by the conventional method. .

Therefore, the present inventors have made the present invention by clarifying a control range required under actual machine conditions by a hot welding test and examining an apparatus that realizes such a control function. is there. That is, an object of the present invention is to control the position of the seat bar when the seat bar is clamped, and to realize the optimum condition of the mating surface for welding.

[0014]

SUMMARY OF THE INVENTION The gist of the present invention is a joining device for joining the leading end portion of a sheet bar after rough rolling to the trailing end portion of a sheet bar during preceding finish rolling and performing complete continuous rolling. There, a traveling carriage that travels in synchronization with the preceding sheet bar during finish rolling, a preceding clamp device provided on the traveling carriage for gripping a rear end portion of the preceding seat bar, and a trailing seat bar A trailing clamp device that grips the leading end portion, a front-back adjusting device that adjusts the front-back distance between the joining surface of the trailing end portion of the leading sheet bar and the joining surface of the leading end portion of the trailing sheet bar, the leading clamping device and the rear A vertical adjustment device that adjusts the vertical position of the joint surface provided on either or both of the row clamp devices, a front-back distance measurement sensor that measures the front-rear distance of the joint surface, and a vertical position that measures the vertical position of the joint surface. Position measuring sensor And a joint position control device that controls the actuator of the front-back adjustment device based on the measurement result of the sensor that measures the front-back distance, and controls the actuator of the vertical position adjustment device of the joint surface based on the measurement result of the vertical position measurement sensor. And a welding position sensor that detects the upper surface position of the welding position, a welding device that can move the welding position of the seat bar from above in the width direction, a welding position sensor that detects the width direction position of the welding machine, and a position Based on the measurement result of the sensor, the welding device for the continuous bar, which is equipped with a welding control device that controls the welding device to move to the joining position and controls the welding in the width direction along the joining position. is there.

Preferably, in the seat bar joining apparatus, one or more welding machines are arranged in the width direction.
It is characterized by a laser welding machine with an output of 20 kW or more per unit. Further, in the above-mentioned sheet bar joining apparatus, one or more welding machines are arranged in the width direction, and the output is 20 kW or more per one arc welding machine.

Further, in the sheet bar joining apparatus, a welding wire is used as a sensor for detecting the upper edge of the mating surfaces. Further, in the above-mentioned sheet bar joining apparatus, the electrodes for arc welding are arranged substantially symmetrically with respect to the abutting surface.

[0017]

The present invention will be described in detail below with reference to the drawings showing the embodiments of the present invention. First, the operation of the present invention will be described. First, the operation of the welding device will be described. FIG. 1 is a side view of a welding apparatus of the present invention, in which 1 is a welding apparatus main body having a bogie structure, 2 is a welding machine main body such as a laser welding machine or an arc welding machine, and 3-1 is a trailing side after being unwound from a coil box Sheet bar, 3-2 is a preceding sheet bar during finish rolling, 4-1 is a clamping device for a succeeding sheet bar, 4-
Reference numeral 2 is a preceding seat bar clamping device, 5 is a seat bar position vertical adjusting device, 6 is a seat bar position longitudinal adjusting device, 6-1 is an actuator of the seat bar sub-clamping mechanism, and 6-2 is a seat bar position adjusting device. Sub-clamp mechanism, 6-3 actuator for forward / backward movement of seat bar, 7 welding machine running rail, 8 welding machine running wheel, 9 welding machine position control device, 9-1 welding direction control mechanism , 9-2 is a front-back adjustment mechanism for the position of the welder, 9-3 is a reference plane for adjusting the welder position, 9-4 is a vertical adjustment mechanism for the position of the welder,
Reference numeral 10 indicates a mating surface of the seat bar.

In synchronism with the preceding sheet bar 3-2 during finish rolling which runs at the rolling speed on the entry side of the finish rolling mill, the joining device 1 having a bogie structure runs while rotating the wheels 8 on the rail 7. After the sensor (not shown) determines that the end of the preceding seat bar 3-2 has reached just under the welding machine 2, it is clamped by the clamp device 4-2 to fix the preceding seat bar 3-2 to the joining device 1. To do. Next, a sensor (not shown) indicates that the end of the succeeding sheet bar 3-1 sent from the coil box or the rough rolling machine at a speed higher than that of the joining device 1 has reached almost directly below the welding machine 2. After the judgment, the actuator 6-1 of the sub-clamp mechanism and the sub-clamp mechanism 6-2 integrated therewith actuate to clamp the trailing seat bar 3-1 and to move the seat bar forward and backward 6-. 3 operates to bring the mating surfaces 10 of the seat bar 3-2 and the seat bar 3-1 into contact with each other. After the actuator 6-3 is activated again and the longitudinal position sensor (not shown) determines that the sheet bar 3-1 has been fed by a predetermined amount (optimum alignment surface gap), the clamp device 4-1 is activated and the seat bar 3- 1 is the main unit 1
Fixed to. Next, with a level sensor (not shown)
After measuring the step on the upper edge of the mating surface 10 of the seat bar,
Seat bar position vertical adjustment device 5 and clamp device 4-2
Operates in synchronization with gripping the seat bar 3-2, and stops after the level sensor determines that the step on the upper edge of the mating surface 10 of the seat bar is zero.

In this state, the welding machine 2 is moved by the welding machine position control device 9 and, after it is judged by the sensor (not shown) that the welding machine 2 has just reached above the mating surface 10, the welding machine 2 controls the welding machine position. The welding is started while moving along the mating surface in the plate width direction by the device 9 at a predetermined speed. Then, after the sensor determines that the welding is performed up to a predetermined position, the welding is finished. After that, the seat bar is fixed until the joining portion is solidified by cooling to generate sufficient joining strength, and then the clamp devices 4-1 and 4-2 are opened to attach the joined sheet bars 3-1 and 3-2. At the same time opening
The welding apparatus main body stops moving, moves in the direction opposite to the feed direction, and waits for the next welding.

Next, the reason for limiting the specifications of the welding machine 2 will be described. The actual machine line length that can be used for joining is 5
When the rolling speed is 0 m or less and the rolling speed is 90 mpm, the time available for joining is about 30 sec, and the time available for welding / cooling is 20 sec or less. From the experimental results, it was found that welding is not completed within 20 seconds unless the melting width w is within 10 mm. Further, in order to prevent the plate from breaking in the rolling process, the effective melting depth of the welded portion must be at least 30% or more, preferably 40% or more of the plate thickness, and if the sheet bar plate thickness is about 40 mm, it is effective. Melting depth is 16
About mm is required. That is, it is necessary to perform welding with a melting depth / melting width ratio δ / w of 1.6 or more.

In FIGS. 4 and 5, the vertical axis represents the melting depth η and the horizontal axis represents the melting width w, and the output 20 is indicated by diagonal lines from the upper right to the lower left.
Welding conditions such as welding speed are changed with welding power of kW or more, and the range in which the sheet bar can be welded is shown, and the diagonal line from the upper left to the lower right indicates the welding conditions necessary for joining the sheet bars. That is, the range in which both diagonal lines overlap is a condition applicable in each welding method.

FIG. 4 shows the result of the laser welding method. The welding depth can be increased to about 40 mm and the welding width is 3 mm.
The following welding is possible. FIG. 5 shows the results of the arc welding method. The melting depth can be deepened up to about 30 mm and the welding width can be wide range from 4 mm to 10 mm.

In any of the laser welding method and the arc welding method, if the welding power is 20 kW or more per unit, the necessary welding conditions are satisfied. Therefore, in the present invention, the output per welding machine is 20 kW or more. Either the laser welding method or the arc welding method is used.

Next, the operation of the invention when an arc welder is used will be described. For strong welding,
It is essential to detect the position of the mating surfaces with high accuracy and perform welding accurately along the upper edge of the mating surfaces. In the case of arc welding, the welding speed is usually about 3 mpm, so multiple welding machines are used to shorten the welding time. Therefore, since the space around the welding machine is limited, the placement of the sensor becomes an issue. Therefore, a method is conceivable in which the welding wire used in the welding machine is also used as the sensor. In arc welding, since welding is performed while an arc is blown between the welding wire and the sheet bar, the welding voltage changes when the state of the welded portion changes. Therefore, by monitoring the welding voltage that changes regularly at the position of the mating surface due to the geometrical difference between the upper edge of the mating surface to be welded and the surface of the sheet bar, the tip of the welding wire is always positioned on the mating surface. Control welder position. This eliminates the need for a separate sensor for detecting the mating surface, which simplifies the structure of the welding device and is advantageous in terms of cost.

In the case of the arc welding method, in order to supply the arc current flowing between the welding wire and the sheet bar to the sheet bar, the electrode must be brought into contact with the sheet bar.
Normally, the electrode is brought into contact with either the preceding seat bar or the following seat bar, but this method causes current to flow only in one seat bar, so the shape of the weld is asymmetric with respect to the mating surface. Therefore, the welding strength is reduced because it deviates from the ideal condition of symmetry. Therefore,
The electrodes will be arranged symmetrically with respect to the mating surface. Since a voltage drop occurs due to Joule heat generation between the mating surface and the electrode, the electrode position is preferably as close to the mating surface as possible. However, since there is not enough space near the mating surface,
It is preferable to incorporate the electrodes into the clamping device of the seat bar. That is, it is advantageous to embed electrodes in the sheet bar pressing dies of the succeeding sheet bar clamp device 4-1 and the preceding sheet bar clamp device 4-2, respectively. When it is difficult to embed the electrode in the clamp device, the electrode may be pressed against and brought into contact with the sheet bar at a position opposite to the mating surface with respect to the clamp device. Further, as the electrode material, a material having a small contact resistance such as copper or carbon is preferable.

As described above, the method of the present invention improves the drawbacks of the conventional method, and enables strong joining without cutting even by the tension acting on the finish rolling mill.

[0027]

EXAMPLE An example of the present invention will be described with reference to FIG. 1 and Tables 1 and 2. Width 110 rolled to 40 mm with a rough rolling mill
After winding a sheet bar with a length of 0 mm and a length of 80 m on a coil box, it is rewound and sent to a finishing rolling mill.
It welded to the sheet bar of the same dimension during finish rolling using the joining device of the mechanism shown in FIG.

At this time, the mating surfaces were brought into close contact with each other under the conditions shown in Table 1, and two carbon dioxide gas laser welders with an output of 45 kW were used to weld the mating surfaces over the entire width with a melting depth of 16 mm. The welding speed was 10 mpm, welding took 4 seconds, and cooling took about 2 seconds. Also, 10 seconds for fixing the seat bar before welding, 1se for removing the seat bar after welding
Since it took c, it took about 20 seconds in total for joining. The speed at the entrance of the finishing rolling mill was 60 mpm, and the running distance of the joining device was 20 m. 6 in Table 1 after welding
Although it was rolled to a plate thickness of 2 mm by a stand finish rolling mill, plate rolling did not occur and continuous rolling was possible.

Under the conditions shown in Table 2, a gap between the mating surfaces was opened by 1 mm, and six carbon dioxide shield arc welders having a secondary power source of 4000 A capacity were used to weld the mating surfaces with a melting depth of 16 mm over the entire width. did. The welding speed was 3 mpm, welding took 4 seconds, and cooling took 6 seconds. Also, it took 10 seconds to fix the seat bar before welding and 1 second to remove the seat bar after welding.
It took c time. Finishing mill entry speed is 60 mpm
The running distance of the joining device was 24 m. After welding, it was rolled to 2 mm by a 6-stand finishing rolling mill in Table 1, but plate rolling did not occur and continuous rolling was possible. The shielding gas was changed to the gas shown in Table 2, but both were capable of welding and continuous rolling in the same manner as carbon dioxide.

Next, the width 11 rolled by the rough rolling mill to 45 mm
After winding a sheet bar with a length of 00 mm and a length of 80 m into a coil box, it is rewound and sent out to a finish rolling mill. Using a joining device having a mechanism shown in FIG. 1, a thickness of 40 mm and a width of 1100 mm during finish rolling are used. Welded to the seat bar. At that time, as a result of welding under the conditions shown in Tables 1 and 2 without making the step on the upper surface of the mating surface about 0 mm, there were cases where the plate broke during the finish rolling. Then, as a result of welding under the conditions of Table 1 and Table 2 with the step of the upper surface of the mating surface set to about 0 mm by the seat bar position adjusting device, continuous rolling was possible without plate breakage during finish rolling. .

In the case of arc welding, a method using a camera and image processing and a method of monitoring the welding voltage were used to detect the position of the mating surfaces, both of which are capable of continuous rolling without breaking the plate during finish rolling. Met. However, the latter had lower initial costs and maintenance costs were lower.

When the welding electrodes are used by embedding them in the clamping devices of the leading and trailing sheet bars, respectively, compared with the case where the welding electrodes are embedded in one of the clamping devices,
Even if the welding speed was increased by about 10%, sufficient joint strength could be secured.

As described above, the trailing end portion of the preceding sheet bar and the leading end portion of the following sheet bar are firmly joined, and the plate of the sheet bar does not break during finish rolling, and the present invention is effective. found.

[0034]

[Table 1]

[0035]

[Table 2]

[0036]

EFFECTS OF THE INVENTION The present invention is constructed and operated as described above, and has a remarkable effect in joining the sheet bar on the entry side of the finish rolling mill during the total continuous hot rolling. There is.

[Brief description of drawings]

FIG. 1 is a side view of a welding apparatus showing an embodiment of the present invention.

FIG. 2 is a sectional view of a welded portion showing the operation of the present invention.

FIG. 3 is a cross-sectional view of a welded portion when welding is performed with a large step when the sheet bars have different plate thicknesses.

FIG. 4 is an explanatory view for the shape of a fusion zone of the present invention in laser welding.

FIG. 5 is an explanatory diagram related to the shape of a fusion zone of the present invention in arc welding.

FIG. 6 is a diagram showing an example of a sheet bar joining line according to a conventional technique.

FIG. 7 is a diagram showing an example of a conventional arc welding method.

FIG. 8 is a diagram showing an example of a matching method according to a conventional technique.

FIG. 9 is a diagram showing another example of a matching method.

[Explanation of Codes] 1 Joining device having a trolley structure 2 Welding machine 3 Seat bar 3-1 Rear seat bar 3-2 Preceding seat bar 4 Seat bar clamp device 4-1 Rear seat bar clamp device 4-2 Preceding Seat bar clamp device 5 Seat bar position vertical adjustment device 6 Seat bar position longitudinal adjustment device 7 Traveling rail 8 Traveling wheel 9 Welder position control device 9-1 Welding direction control mechanism 9-2 Welding position front and rear left and right devices Adjustment mechanism 9-3 Welder position adjustment reference plane 9-4 Welder position vertical adjustment mechanism 10 Mating surface 11 Pinch roll 12 Leveler 13 Shear 14 Finishing rolling machine 15 Coil box 16 Looper 17 Desuke 18 Mobile induction heating Joining device 19 Welding wire 20 Welding arc 21 Shielding gas t _T Thickness of leading sheet bar t _B Trailing seat bar Plate thickness f Step difference on the upper surface of mating surface θ Angle of inclination of mating surface g Gap between mating surfaces

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor, Kouhei Nakajima 20-1 Shintomi, Futtsu City, Chiba Shin Nippon Steel Co., Ltd.

Claims (5)

[Claims] 1. A joining device for joining a front end portion of a sheet bar after rough rolling to a rear end portion of a sheet bar during preceding finish rolling and performing complete continuous rolling, wherein: A traveling carriage that travels in synchronization with the seat bar,
A leading clamp device that is provided on the traveling carriage and that grips the rear end portion of the preceding seat bar, a trailing clamp device that grips the leading end portion of the trailing seat bar, and a joining surface of the trailing end portion of the leading seat bar. A front-rear adjustment device that adjusts the front-rear distance between the front end portion of the trailing seat bar and the joint surface, and a vertical position that adjusts the vertical position of the joint surface provided on either or both of the leading clamp device and the trailing clamp device. Actuator of front-rear adjustment device based on the measurement results of the adjusting device, the front-back distance measuring sensor that measures the front-back distance of the joint surface, the vertical position measurement sensor that measures the vertical position of the joint surface, and the sensor that measures the front-back distance The joint position control device that controls the actuator of the joint position vertical position adjustment device based on the measurement result of the vertical position measurement sensor, and the upper surface position of the joint position. A welding position sensor that comes out, a welding device that can move the welding position of the seat bar in the width direction from above, a welding position sensor that detects the width direction position of the welding machine, and based on the measurement result of the position sensor, A welding device for a sheet bar for continuous rolling, comprising: a welding control device that controls movement of the welding device to a joining position and controls welding in a width direction along the joining position. 2. The full continuous hot work according to claim 1, wherein a single or a plurality of the welding apparatuses arranged in the width direction of the welding machine is a laser welding machine having an output of 20 kW or more. Welding equipment for rolling sheet bars. 3. The welding of a seat bar according to claim 1, wherein the welding machine is a single or plural welding machines arranged in the width direction and has an output of 20 kW or more per one welding machine. apparatus. 4. The welding apparatus for a sheet bar for total continuous hot rolling according to claim 1, wherein a welding wire is used as a sensor for detecting the upper edge of the mating surfaces. 5. The welding apparatus for a fully continuous hot-rolled sheet bar according to claim 1, 3, or 4, wherein the electrodes for arc welding are arranged substantially symmetrically with respect to the abutting surface.