JP6555282B2 - Lap welding equipment and lap welding method for hot rolled steel sheet - Google Patents

Description

  The present invention relates to a hot-rolled steel sheet (hereinafter referred to as “hot-rolled steel sheet”) that is transported in advance before supplying the hot-rolled steel sheet for each single coil wound up with the hot-rolled steel sheet and supplying it to a process for continuous processing (for example, pickling). The present invention relates to a lap welding equipment and a lap welding method in which a hot-rolled steel sheet (hereinafter referred to as a subsequent hot-rolled steel sheet) and a subsequent hot-rolled steel sheet (hereinafter referred to as a subsequent hot-rolled steel sheet) are overlapped and joined by electric resistance welding.

  The hot-rolled steel sheet obtained by hot rolling is subjected to various treatments (for example, pickling) as necessary in order to improve its quality characteristics. From the viewpoint of improving productivity by continuously processing hot-rolled steel sheets in these processes, the rear end of the preceding hot-rolled steel sheet and the front-end part of the subsequent hot-rolled steel sheet are joined before being supplied to the process. This technology has been put into practical use. As a means for joining the preceding hot-rolled steel sheet and the subsequent hot-rolled steel sheet, electric resistance welding is widely adopted.

On the other hand, the surface of a hot-rolled steel sheet is covered with an oxide inevitably generated by hot rolling. The oxide is an oxide generated when a material (slab) is heated in a furnace prior to hot rolling.
Since such an oxide has extremely low conductivity, it is difficult to superimpose hot-rolled steel sheets whose surfaces are covered with an oxide film (hereinafter referred to as an oxide film) and join them by electric resistance welding.

  In view of this, a technique has been developed to remove the oxide film at the site where the hot-rolled steel plates are in contact with each other and the site where the electrodes are in contact with the hot-rolled steel plate before performing electrical resistance welding. For example, Patent Document 1 discloses a technique for removing an oxide film at an end of a hot-rolled steel sheet with a rotating brush. An example of the arrangement of the hot-rolled steel sheet and the rotating brush is schematically shown in FIG. In FIG. 4, arrow A is the traveling direction of the hot-rolled steel sheet. Therefore, FIG. 4 is an example in which the oxide film at the rear end of the preceding hot-rolled steel sheet is removed in detail.

When the end of the hot-rolled steel plate is flat, the pair of rotating brushes 3 are brought into contact with the upper and lower surfaces when the end of the hot-rolled steel plate 2 reaches a predetermined position (see FIG. 4 (a)). And the oxide film of both upper and lower sides is removed to a rear end with the progress (the direction of arrow A) of the hot-rolled steel plate 2.
In addition, although illustration is abbreviate | omitted, the oxide film of upper and lower surfaces is similarly removed from the front-end | tip part of a subsequent hot-rolled steel plate.

  Next, by overlapping the rear end portion of the preceding hot-rolled steel plate and the front end portion of the subsequent hot-rolled steel plate, the base irons having no oxide film are brought into contact with each other. Since the ground iron is also exposed on the outer surface of the overlapped portion (that is, the upper surface of the one hot-rolled steel plate and the lower surface of the other hot-rolled steel plate), the electrode is brought into contact with the ground iron. . In this way, electric resistance welding can be performed stably.

  However, the end of the hot-rolled steel sheet 2 has a problem that warpage is likely to occur. Conventionally, the end of the hot-rolled steel sheet 2 is straightened by a straightening machine (so-called leveler), but it is possible to completely eliminate the warp of the end of the hot-rolled steel sheet 2 and obtain a flat hot-rolled steel sheet up to the end. Have difficulty. When the pair of rotating brushes 3 are brought into contact with the end portions of the hot-rolled steel plate 2 where the warpage has occurred, a deviation M in the longitudinal direction of the steel plate occurs at a position where the pair of rotating brushes 3 comes into contact (see FIG. 4B). . As a result, the region from which the oxide film on the upper surface of the hot-rolled steel sheet has been removed and the region from which the oxide film on the lower surface has been removed do not coincide with the positions set in advance as the positions where the electrodes contact in the operating conditions of electric resistance welding.

  When a shift occurs in the area where the oxide film is removed, the oxide film remains at the position where the electrode is brought into contact, or the oxide film remains between the preceding hot rolled steel sheet and the subsequent hot rolled steel sheet. Problems arise. The oxide film remaining in this manner hinders current supply in electric resistance welding, and as a result, deteriorates the work efficiency of electric resistance welding and decreases the bonding strength.

Japanese Patent Laid-Open No. 2001-150145

  The present invention eliminates the problems of the prior art, and in performing lap welding of hot-rolled steel sheets, not only hot-rolled steel sheets with flat ends but also oxide films of hot-rolled steel sheets with warped ends. It is an object of the present invention to provide a hot-rolled steel lap welding equipment and a lap welding method that can efficiently remove electric power from a predetermined position, perform electric resistance welding efficiently and stably, and obtain sufficient joint strength. .

  The inventor is a simple and effective means for removing the oxide film on the hot-rolled steel sheet, so even if the hot-rolled steel sheet is warped at the end, the rotary brush is in a position where it contacts. A technique that can reliably remove the oxide film at a predetermined position without causing a shift was studied, and the following knowledge was obtained.

  When removing the oxide film on the end of a flat hot-rolled steel sheet, the contact area between the hot-rolled steel sheet and the rotating brush produced by bringing a pair of rotating brushes into contact with the upper and lower surfaces of the end is the upper surface side and the lower surface. The sides are equal. Therefore, the frictional force between the rotating brush and the hot-rolled steel sheet is also equal on the upper surface side and the lower surface side. As a result, the vibration of the hot-rolled steel sheet can be suppressed and the position of the rotating brush can be stabilized.

  On the other hand, when removing the oxide film from the hot-rolled steel sheet with warping at the end, the rotating brush comes into contact with the arcuate curve formed at the end by warping. The contact area between the rotating brush and the rotating brush is not equal on the upper surface side and the lower surface side, and the frictional force between the rotating brush and the hot-rolled steel sheet also differs between the upper surface side and the lower surface side. As a result, in addition to the problem that displacement (that is, separation from the pass line) and vibration of the hot-rolled steel sheet cannot be suppressed, a problem that the position of the rotating brush fluctuates also occurs. As a result, in the state where the oxide film remains in the range set as the region to remove the oxide film, the end of the hot-rolled steel sheet is overlapped and electric resistance welding is performed, so current supply is hindered, As a result, the work efficiency of electric resistance welding deteriorates and the joint strength decreases.

  That is, it has been found that the problems of the prior art occur due to the above-described causes. Therefore, if the edge in the longitudinal direction of the steel sheet (hereinafter referred to as the edge) is restrained from the periphery of the edge of the hot-rolled steel sheet to prevent displacement or vibration, the hot-rolled steel sheet has warped at the edge. However, it is possible to reliably remove the oxide film at a predetermined position without causing a shift at the position where the rotating brush contacts, and as a result, the electric resistance welding is performed stably and efficiently in the overlap welding. A predetermined bonding strength can be obtained.

The present invention has been made based on such knowledge.
That is, the present invention is a lap welding equipment for removing the oxide film from the rear end portion of the preceding hot-rolled steel plate and the front end portion of the subsequent hot-rolled steel plate, and further superposing and joining them by electric resistance welding. A shearing machine (so-called shear) that cuts the trailing edge of the rolled steel sheet and the leading edge of the subsequent hot-rolled steel sheet, and the trailing edge of the preceding hot-rolled steel sheet and the leading edge of the subsequent hot-rolled steel sheet on the exit side of the shearing machine Clamp to be gripped, rotating brush for removing the oxide film from the upper and lower surfaces of the leading edge of the preceding hot rolled steel sheet and the leading edge of the following hot rolled steel sheet, and the trailing edge of the preceding hot rolled steel sheet from which the oxide film has been removed by the rotating brush And a welding machine for performing electrical resistance welding by superimposing a front portion and a tip portion of a subsequent hot-rolled steel sheet.

  In the lap welding equipment of the present invention, the first clamp that grips the trailing edge of the preceding hot-rolled steel sheet on the outlet side of the shearing machine, and the first clamp that grips the leading edge of the subsequent hot-rolled steel sheet on the outlet side of the shearing machine. 2 clamps. Furthermore, a CCD camera that images the rear end of the preceding hot-rolled steel sheet from which the oxide film has been removed by a rotating brush and the front end of the subsequent hot-rolled steel sheet, and a portion where the oxide film has been removed by analyzing the image captured by the CCD camera It is preferable to include an arithmetic device that determines whether or not there is a positional shift, and a display device that displays the determination result determined by the arithmetic device.

  Further, the present invention relates to a lap welding method in which an oxide film is removed from a rear end portion of a preceding hot rolled steel plate and a front end portion of a subsequent hot rolled steel plate and further overlapped and joined by electric resistance welding. The rear end crop of the rear hot-rolled steel sheet and the front end of the subsequent hot-rolled steel sheet are cut with a shearing machine, and the rear end edge of the preceding hot-rolled steel sheet and the front end edge of the subsequent hot-rolling steel sheet are gripped with a clamp on the outlet side of the shearing machine. After removing the oxide film from the upper and lower surfaces of the leading edge of the preceding hot rolled steel sheet and the leading edge of the subsequent hot rolled steel sheet using a brush, the trailing edge of the preceding hot rolled steel sheet and the leading edge of the subsequent hot rolled steel sheet Is a lap welding method for hot-rolled steel sheets in which electric resistance welding is performed by superimposing steel sheets.

  In the lap welding method of the present invention, the oxide film is removed from the upper and lower surfaces of the rear end part using a rotating brush while holding the rear end edge of the preceding hot rolled steel sheet with the first clamp on the exit side of the shearing machine, Next, it is preferable to perform electric resistance welding after removing the oxide film from the upper and lower surfaces of the tip portion using a rotating brush while holding the tip edge of the subsequent hot-rolled steel plate with the second clamp. Furthermore, the rear end of the preceding hot-rolled steel sheet from which the oxide film has been removed by the rotating brush and the front end of the subsequent hot-rolled steel sheet are photographed with a CCD camera, and the image photographed with the CCD camera is transmitted to the arithmetic device, It is preferable to analyze the image and determine whether or not the position where the oxide film has been removed is misaligned, and display the determination result determined by the arithmetic device on the display device.

  According to the present invention, when performing lap welding of hot-rolled steel sheets, not only the hot-rolled steel sheets with flat ends, but also the oxide film of the hot-rolled steel sheets with warping at the ends are removed from predetermined positions, Since electrical resistance welding can be performed efficiently and stably, and a predetermined joint strength can be obtained, an industrially significant effect is achieved.

It is a schematic diagram which shows the example which performs the lap welding of a hot-rolled steel plate using the lap welding equipment which concerns on this invention. It is a schematic diagram which shows the example of the apparatus accompanying the rotating brush in FIG. It is a schematic diagram which shows the other example of the apparatus accompanying the rotating brush in FIG. It is a schematic diagram which shows the prior art which removes an oxide film. It is a top view which shows typically the example of the crack generate | occur | produced by the Eriksen test.

  FIG. 1 is a schematic diagram showing an example in which lap welding of a hot-rolled steel sheet 2 is performed using the lap welding equipment according to the present invention, and an arrow A in FIG. That is, FIG. 1 is an example in which the rear end portion of the preceding hot-rolled steel plate 2a and the front end portion of the subsequent hot-rolled steel plate 2b are overlapped and joined by electric resistance welding. In addition, in FIG. 1, conveyance apparatus (for example, pinch roll etc.) for supplying the hot-rolled steel plate 2 from the hot-rolling coil 1 to the rotating brush 3 is abbreviate | omitted illustration. Also, the devices associated with the rotating brush 3 are shown in FIGS.

  As shown in FIG. 1, the subsequent hot-rolled steel sheet 2 b delivered from the hot-rolled coil 1 cuts the tip crop with a shearing machine 4 (so-called shear). Therefore, the edge in the steel plate longitudinal direction (hereinafter referred to as the front edge) of the tip of the subsequent hot-rolled steel plate 2b is formed in a straight line perpendicular to the steel plate longitudinal direction. Subsequently, the subsequent hot-rolled steel sheet 2b is conveyed to the rotating brush 3 and the oxide film at the tip is removed. Since the rotating brushes 3 are arranged as a pair of upper and lower parts, the oxide films on both the upper and lower surfaces of the front end portion of the subsequent hot-rolled steel sheet 2b are removed.

At this time, the preceding hot-rolled steel sheet 2a is in a state where the rear end crop has already been cut by the shearing machine 4 and the oxide films on both the upper and lower sides of the rear end portion have been removed. Therefore, the edge in the steel plate longitudinal direction (hereinafter referred to as the rear edge) at the rear end of the preceding hot-rolled steel plate 2a is formed in a straight line perpendicular to the steel plate longitudinal direction.
Then, the rear end portion of the preceding hot-rolled steel plate 2a and the front end portion of the subsequent hot-rolled steel plate 2b are overlapped in the welding machine 5 to perform electric resistance welding.

  Here, the removal of the oxide film will be described in detail with reference to FIG. FIG. 2 is a schematic diagram for explaining in detail the rotating brush and the equipment associated therewith in FIG. 1, and an arrow A in FIG. 2 indicates the traveling direction of the hot-rolled steel plates 2a and 2b.

  As shown in FIG. 2, in the present invention, when removing the oxide film on the rear end portion of the preceding hot-rolled steel plate 2a and the front end portion of the subsequent hot-rolled steel plate 2b, the clamp 6 is used for the rear of the preceding hot-rolled steel plate 2a. The end edge and the end edge of the subsequent hot-rolled steel sheet 2b are gripped. Not only when the leading end of the preceding hot-rolled steel sheet 2a and the leading end of the subsequent hot-rolling steel sheet 2b are flat, but also when warping occurs, the warping is caused by correcting with a straightening machine (not shown). It has been reduced. Moreover, since the leading edge of the preceding hot-rolled steel plate 2a and the leading edge of the subsequent hot-rolled steel plate 2b are both formed in a straight line perpendicular to the longitudinal direction of the steel plate, they can be easily gripped by the clamp 6. Can do.

  Then, while the preceding hot-rolled steel sheet 2a is advanced in the direction of arrow A, the pair of rotating brushes 3 are brought into contact with the upper and lower surfaces of the rear end portion to remove the oxide film. The clamp 6 and the succeeding hot-rolled steel plate 2b follow the progress of the preceding hot-rolled steel plate 2a, so that the oxide film on the rear end of the preceding hot-rolled steel plate 2a is removed, and then the clamp 6 is passed. Therefore, the pair of rotating brushes 3 are retracted. After the clamp 6 passes, the pair of rotating brushes 3 are brought into contact with the upper and lower surfaces of the subsequent hot-rolled steel sheet 2b to remove the oxide film. When the removal of the oxide film is completed, the preceding hot-rolled steel sheet 2a and the subsequent hot-rolled steel sheet 2b are released from the clamp 6 and fed to the welding machine 5. After the end portion where the rotating brush 3 does not contact and the oxide film remains (that is, the rear end portion of the preceding hot-rolled steel plate 2a and the front end portion of the subsequent hot-rolled steel plate 2b) is sheared by the shearing machine 4, welding is performed. It is.

As described above, the preceding hot-rolled steel sheet 2a, the clamp 6, and the subsequent hot-rolled steel sheet 2b may be advanced in the direction of arrow A with respect to the rotating brush 3, or the preceding hot-rolled steel sheet 2a, the clamp 6, and the subsequent hot-rolled steel sheet. The rotating brush 3 may be advanced in the direction opposite to the arrow A with respect to the steel plate 2b.
In addition, the operation | movement which makes the rotary brush 3 contact | abut and the operation | movement which retracts uses the power source 8 (for example, a cylinder etc.) conventionally known for reciprocation.

FIG. 3 is a schematic diagram showing another example of the rotating brush and the equipment associated therewith in FIG. 1, and shows an example in which the oxide film on the rear end portion of the preceding hot rolled steel sheet 2a is removed.
In the embodiment shown in FIG. 3, a pair of clamps 6 a and 6 b are disposed on the entry side and the exit side of the rotary brush 3 (two sets in total). When the rear end of the preceding hot-rolled steel sheet 2a passes through the rotating brush 3, a clamp 6a (hereinafter referred to as a first clamp) on the rotating brush 3 grips the rear end edge of the preceding hot-rolled steel sheet 2a. The clamp 6b on the outlet side of the rotating brush 3 (hereinafter referred to as the second clamp) is retracted. In this way, the pair of rotating brushes 3 are brought into contact with the upper and lower surfaces of the rear end portion while the preceding hot-rolled steel plate 2a is advanced in the direction of arrow A to remove the oxide film.

And although illustration is abbreviate | omitted, after the removal of the oxide film of a rear-end part is complete | finished, the 1st clamp 6a releases the preceding hot-rolled steel plate 2a, and moves to a retracted position.
Next, while gripping the leading edge of the subsequent hot-rolled steel plate 2b with the second clamp 6b, the subsequent hot-rolled steel plate 2b is advanced in the direction of arrow A, and the oxide films on both the upper and lower surfaces are removed with the rotating brush 3. When the removal of the oxide film at the tip end is completed, the second clamp 6b releases the subsequent hot-rolled steel sheet 2b and moves to the retracted position.
Also in the embodiment shown in FIG. 3, the end portion where the rotating brush 3 does not contact and the oxide film remains (that is, the rear end portion of the preceding hot-rolled steel plate 2a and the front end portion of the subsequent hot-rolled steel plate 2b) is used as the shearing machine 4. After shearing, welding is performed.

  2 and 3, since the oxide film is removed in a state where the trailing edge of the preceding hot rolled steel sheet 2a and the leading edge of the subsequent hot rolled steel sheet 2b are constrained, the preceding hot rolled steel sheet 2a and Displacement and vibration of the subsequent hot-rolled steel sheet 2b can be prevented, and as a result, displacement of the position where the rotating brush 3 contacts can be prevented.

2 and 3, two CCD cameras 7 are provided on the exit side of the rotating brush 3 to photograph both the upper and lower surfaces of the preceding hot-rolled steel plate 2a and the subsequent hot-rolled steel plate 2b. Is preferred. Conventionally known lighting equipment is used as a light source necessary for photographing. In the image obtained in this way, the part where the oxide film has been removed (namely, the part where the ground iron is exposed) is bright, the part covered with the oxide film is slightly dark, and the background is dark. The image is transmitted to the arithmetic unit and image analysis is performed. The arithmetic unit identifies the part from which the oxide film has been removed and the part covered with the oxide film, and oxidizes a position set in advance (hereinafter referred to as a predetermined position) so that overlay welding can be performed smoothly. It is determined whether or not the film has been removed reliably. Such image analysis can be performed using commercially available software.
The determination result determined by the arithmetic device is displayed on the display device. The display device uses conventionally known means such as displaying on a screen, printing on paper, notifying by voice, or blinking an electric light.

  When it is determined that the oxide film at a predetermined position has been removed on both the upper and lower surfaces (that is, a bright part in the image matches a predetermined position set in advance), the rotating brush 3 does not come into contact and is oxidized. After the end portion where the film remains (that is, the rear end portion of the preceding hot-rolled steel plate 2a and the front end portion of the subsequent hot-rolled steel plate 2b) is sheared by the shearing machine 4, it is fed to the welding machine 5 (see FIG. 1). .

  If it is determined that the oxide film remains at a predetermined position (that is, the bright portion in the image does not match the predetermined position set in advance and a deviation occurs), the hot-rolled steel sheet is removed from the shearing machine. 4 is cut back and the end portion is cut, and then the oxide film is removed again, and the image taken by the CCD camera 7 is analyzed by an arithmetic unit to confirm that the oxide film at a predetermined position has been reliably removed. Determine whether or not.

In this way, the oxide film is removed from both the upper and lower surfaces of the rear end portion of the preceding hot-rolled steel plate 2a and the upper and lower surfaces of the leading end portion of the subsequent hot-rolled steel plate 2b, and the preceding hot-rolled steel plate 2a and the subsequent hot-rolled steel plate 2b. Is fed to the welding machine 5. And in the welding machine 5, the rear-end part of the preceding hot-rolled steel plate 2a and the front-end | tip part of the subsequent hot-rolled steel plate 2b are piled up. As a result, the base irons of the preceding hot-rolled steel plate 2a and the subsequent hot-rolled steel plate 2b come into contact with each other. Further, on the outer surface of the overlapped portion, the ground iron is exposed at a predetermined position, and the pair of upper and lower electrodes 9 can be brought into contact with the ground iron by a normal operation of the welding machine 5.
Therefore, a current necessary for electric resistance welding flows from one electrode 9 to the other electrode 9 without any trouble.

  As described above, by applying the present invention, in lap welding of hot-rolled steel sheets, electric resistance welding can be performed efficiently and stably, and sufficient joint strength can be obtained. By joining the rolled steel sheets, it can be continuously supplied to the next step (for example, pickling).

  Using the lap welding equipment shown in FIG. 1, lap welding of hot-rolled steel plates (plate width 600 to 1800 mm, plate thickness 1.2 to 6.0 mm) was performed, and the strength of the obtained joints was investigated. The procedure will be described.

  As a device attached to the rotating brush in FIG. 1, the clamp and CCD camera shown in FIG. 2 were adopted. Then, by superimposing the rear end portion of the preceding hot-rolled steel plate 2a and the front end portion of the subsequent hot-rolled steel plate 2b, which are determined by image analysis to remove the oxide film at predetermined positions on both the upper and lower surfaces, electric resistance welding Was done. This is referred to as Invention Example 1.

Next, as a device attached to the rotating brush in FIG. 1, the first clamp, the second clamp and the CCD camera shown in FIG. 3 were adopted. Then, by superimposing the rear end portion of the preceding hot-rolled steel plate 2a and the front end portion of the subsequent hot-rolled steel plate 2b, which are determined by image analysis to remove the oxide film at predetermined positions on both the upper and lower surfaces, electric resistance welding Was done. This is referred to as Invention Example 2.
Inventive Examples 1 and 2 were able to perform electric resistance welding without causing troubles of equipment or troubles related to operation.

  For further comparison, without using a clamp and a CCD camera, after simply removing the oxide film with a rotating brush, the rear end portion of the preceding hot rolled steel plate 2a and the front end portion of the subsequent hot rolled steel plate 2b are overlapped, Electrical resistance welding was performed. This is a comparative example.

  Test pieces (5 pieces each, 15 pieces in total) were cut out from the joint portions of the electric resistance welding obtained in Invention Examples 1 and 2 and Comparative Example. Then, a test piece was placed on a die (that is, a base with a hole), and the center of the test piece was pushed in with a punch and squeezed into the die to form a protrusion, thereby examining the occurrence of cracks in the joint (so-called Eriksen test). As a result, as shown in FIG. 5 (c), a weld having a crack 12 along the joint 10 is regarded as a poor weld, and the number of test pieces determined as the poor weld is shown in Table 1. The inner diameter of the die was 30 mm, and the pushing length of the punch was 10 mm.

  As shown in FIG. 5 (a), when the crack 12 is not generated in the joint portion 10 inside the substantially circular region which is the bottom 11 of the protrusion, and the crack 12 is formed in the joint portion 10 as shown in FIG. 5 (b). On the other hand, when it occurred perpendicularly (or when the direction of cracking was not parallel to the weld line), it was determined that welding was performed well and a predetermined strength was obtained.

  In each of the inventive examples, electric resistance welding could be performed efficiently and stably, and as can be seen from Table 1, sufficient joint strength could be obtained.

1 Hot-rolled coil 2 Hot-rolled steel sheet
2a Pre-heated steel sheet
2b Subsequent hot-rolled steel sheet 3 Rotating brush 4 Shearing machine 5 Welding machine 6 Clamp
6a 1st clamp
6b Second clamp 7 CCD camera 8 Power source for reciprocating movement 9 Electrode
10 joints
11 Bottom of protrusion
12 crack

Claims (6)

An overlap welding facility that removes an oxide film from the rear end of the preceding hot-rolled steel sheet and the front end of the subsequent hot-rolled steel sheet, and further superimposes and joins by electrical resistance welding. A shearing machine that cuts the end crop and the front end crop of the subsequent hot-rolled steel sheet, and a rotation that removes the oxide film from the upper and lower surfaces of the rear end part of the preceding hot-rolled steel sheet and the front end part of the subsequent hot-rolled steel sheet The trailing edge which is the edge where the oxide film remains without contacting the brush and the rotating brush, and is the edge in the longitudinal direction of the steel sheet at the trailing edge of the preceding hot-rolled steel sheet on the exit side of the shearing machine and a clamp for gripping the steel plate longitudinal edge at which the tip edge of the distal end portion of the trailing hot-rolled steel sheet, the said rear end of said preceding hot-rolled steel sheet obtained by removing the oxide film by the rotary brush Overlapping the tip of the subsequent hot-rolled steel sheet Welding equipment superposition of hot rolled steel sheet characterized by having a a welding machine for electrical resistance welding.   A first clamp that grips the trailing edge of the preceding hot-rolled steel sheet on the outlet side of the shear, and a second clamp that grips the leading edge of the subsequent hot-rolled steel sheet on the outlet side of the shearer; The lap welding equipment for hot-rolled steel sheets according to claim 1, wherein   A CCD camera for photographing the rear end portion of the preceding hot-rolled steel sheet from which the oxide film has been removed by the rotating brush and the front-end portion of the subsequent hot-rolled steel sheet, and an image photographed by the CCD camera to analyze the image 3. The heat according to claim 1, further comprising: an arithmetic device that determines whether or not the position of the oxide film is removed, and a display device that displays a determination result determined by the arithmetic device. Lap welding equipment for rolled steel sheets. In the overlap welding method in which the oxide film on the rear end portion of the preceding hot-rolled steel plate and the front end portion of the subsequent hot-rolled steel plate is removed and further overlapped and joined by electrical resistance welding, the rear end crop of the preceding hot-rolled steel plate Cutting the tip crop of the subsequent hot-rolled steel sheet with a shearing machine, and using a rotating brush, the oxide film is formed from both the upper and lower surfaces of the rear end part of the preceding hot-rolled steel sheet and the front end part of the subsequent hot-rolled steel sheet. After removing, the rotating brush does not come into contact with the exit side of the shearing machine and the oxide film remains, and the rear end of the preceding hot-rolled steel sheet is the edge in the longitudinal direction of the steel sheet. edge and after removing the oxide film while the steel plate longitudinal edge at which the tip edge of the distal end portion of the trailing hot-rolled steel sheet is gripped by the clamp, the said rear end of said preceding hot-rolled steel sheet Overlap the tip of the subsequent hot-rolled steel sheet to Welding method superposition hot rolled steel sheet characterized by performing resistance welding.   An oxide film is removed from both upper and lower surfaces of the rear end portion using a rotating brush while holding the rear end edge of the preceding hot-rolled steel sheet with a first clamp on the exit side of the shearing machine, and then the subsequent hot rolling 5. The heat according to claim 4, wherein the electric resistance welding is performed after removing the oxide film from the upper and lower surfaces of the tip portion using a rotating brush while holding the tip edge of the steel plate with a second clamp. Overlap welding method for rolled steel sheets. The rear end portion of the preceding hot-rolled steel sheet from which the oxide film has been removed by the rotating brush and the front end portion of the subsequent hot-rolled steel sheet are photographed with a CCD camera, and the image photographed with the CCD camera is transmitted to an arithmetic unit. Then, the arithmetic device analyzes the image to determine the presence / absence of a position shift of the portion from which the oxide film is removed, and displays the determination result determined by the arithmetic device on a display device. Item 6. The method of lap welding of hot rolled steel sheets according to Item 4 or 5.

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