Tab for corner portion and welding method of four-face box

Abstract

To provide a tab for a corner portion and a welding method of a four-face box that enable welding of a corner portion to be efficiently performed when four-face boxes are welded to each other.SOLUTION: A tab 1 for a corner portion includes: a first plate part 6 that is installed in a side of an X-direction (first direction) of a first inclination end surface 211 to contact a second inclination end surface 212 and is provided so as to be flush with the first inclination end surface 211; and a second plate part 7 that is connected to the first plate part 6, is installed in a side of the X-direction of the first connection surface 411 to contact with a second connection surface 412 and a second end surface 312, and is provided so as to be flush with the first connection surface 411.SELECTED DRAWING: Figure 5

Description

[Technical Field]

[0001] The present invention relates to a corner tab and a method for welding a four-sided box. [Background technology]

[0002] When welding four-sided boxes together, welding the corners where the straight portions of the grooves that extend in a straight line along each of the orthogonal faces of the four-sided boxes are connected will cause molten metal to leak into the other straight portion when one straight portion is welded, so a member may be provided at the corner to prevent molten metal from leaking into the straight portions that extend in different directions (see, for example, Patent Documents 1 and 2). [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Publication No. 2020-082081 [Patent Document 2] Japanese Patent Publication No. 2020-199530 Summary of the Invention [Problem to be solved by the invention]

[0004] In recent years, efforts have been made to improve welding efficiency by using welding robots and automatic welding equipment. However, when welding four-sided boxes together using welding robots or automatic welding equipment, only the straight lines are welded, and the corners are not welded at present. Therefore, in order to improve welding efficiency using welding robots or automatic welding equipment, it is necessary to weld the corners more efficiently.

[0005] SUMMARY OF THE INVENTION It is therefore an object of the present invention to provide a corner tab and a welding method for four-sided boxes that can more efficiently weld corners when welding four-sided boxes together. [Means for solving the problem]

[0006] In order to achieve the above object, a corner tab according to the present invention is a corner tab that is installed at a corner of a groove when a groove is formed between end faces of a first four-sided box and a second four-sided box that are arranged in an axial direction and welding is performed, the end face of the first four-sided box having: a first inclined end face that extends in a first direction perpendicular to the axial direction and gradually inclined in a direction from one side that is the outer periphery of the first four-sided box to the other side that is the inner periphery of the first four-sided box in a second direction perpendicular to both the axial direction and the first direction, toward the second four-sided box; and a second inclined end face that extends in the second direction and gradually inclined in a direction from one side that is the outer periphery of the first four-sided box to the other side that is the inner periphery of the first four-sided box in the first direction, the first inclined end face and the second inclined end face being connected at a corner of the first four-sided box, the end face of the second four-sided box having a first end face that extends in the first direction and is perpendicular to the axial direction and a second end face that extends in the second direction and is perpendicular to the axial direction, The first end surface and the second end surface are connected at corners of the second four-sided box, the first inclined end surface and the first end surface are arranged at an interval in the axial direction, a first connection surface connecting the first inclined end surface and the first end surface is provided between an edge portion of the first inclined end surface on the other side in the second direction and an edge portion of the first end surface on the other side in the second direction, and the second inclined end surface and the second end surface are arranged at an interval in the axial direction, A second connection surface connecting the second inclined end surface and the second end surface is provided between the edge portions of the two end surfaces on the other side in the first direction, and the corner tab has a first plate portion that is installed on the side of the first inclined end surface in the first direction, contacts the second inclined end surface, and is arranged to be flush with the first inclined end surface, and a second plate portion that is connected to the first plate portion, installed on the side of the first connection surface in the first direction, contacts the second connection surface and the second end surface, and is arranged to be flush with the first connection surface.

[0007] In order to achieve the above object, the present invention provides a welding method for a four-sided box, in which a corner tab as claimed in claim 1 is installed at a corner of a groove when a groove is provided between an end face of a first four-sided box and an end face of a second four-sided box arranged in an axial direction and welding is performed, the method comprising: a corner tab installation step of installing a corner tab at the corner of the groove; an end face welding step of welding the end face of the first four-sided box and the end face of the second four-sided box; and a step of removing the corner tab after the end face welding step to remove the corner tab. and a corner tab installation portion welding process for welding the area where the end face welding process is performed, the end face welding process comprising a first welding process for welding the portion of the groove formed by the first inclined end face, the first connecting surface, and the first end face and extending in the first direction, a second welding process for welding the corner portion of the groove, and a third welding process for welding the portion of the groove formed by the second inclined end face, the second connecting surface, and the second end face and extending in the second direction, the first welding process, the second welding process, and the third welding process being performed consecutively.

[0008] In the present invention, by installing corner tabs at the corners of the grooves of the four-sided boxes to be joined, recesses are formed at the corners of the grooves with a cross-sectional shape similar to that of the linear portion formed by the first inclined end face, the first connecting face, and the first end face and extending in the first direction. This allows the corners to be welded efficiently in succession to the welding of the linear portion. After welding the corners, the linear portion formed by the second inclined end face, the second connecting face, and the second end face in the groove and extending in the second direction can be welded immediately. Furthermore, when welding is performed using a welding robot or automatic welding equipment, welding of corners and straight sections can be performed consecutively, making the welding work more efficient. Furthermore, since the corner tab has a shape in which the first plate portion and the second plate portion are joined together, it is easy to manufacture and manage, and also easy to install and remove. [Effects of the Invention]

[0009] According to the present invention, when welding four-sided boxes together, corners can be welded more efficiently. [Brief explanation of the drawings]

[0010] [Figure 1] FIG. 10 is a view of the first and second four-sided boxes and corner tabs to be joined, viewed from the Y direction. [Figure 2] FIG. 10 is a view of the first and second four-sided boxes and corner tabs to be joined, viewed from the X direction. [Figure 3] FIG. 2 is a cross-sectional view taken along line AA in FIG. [Figure 4] FIG. 2 is a cross-sectional view taken along line BB in FIG. [Figure 5] 10 is a view of the welded portion between the first four-sided box and the second four-sided box as viewed from the X direction. [Figure 6] This is a view of the welded portion between the first four-sided box and the second four-sided box as seen from the Y direction. [Figure 7] FIG. 6 is a cross-sectional view taken along line CC in FIG. 5. [Figure 8] FIG. 10 is a perspective view of a corner tab. [Figure 9] 9 is a view of the corner tab as seen from direction D in FIG. 8. [Figure 10] 10 is a view of the corner tab as seen from the direction E in FIG. 9. [Figure 11] FIG. 9 is a perspective view of a corner tab having a symmetrical shape to the corner tab shown in FIG. 8. [Figure 12] 12 is a view of the corner tab as seen from the direction F in FIG. 11. FIG. [Figure 13] 13 is a view of the corner tab as seen from the direction G in FIG. 12. DETAILED DESCRIPTION OF THE INVENTION

[0011] Hereinafter, a corner tab and a welding method for a four-sided box according to an embodiment of the present invention will be described with reference to FIGS. As shown in Figures 1 and 2, the corner tab 1 according to this embodiment is used to weld a first four-sided box 2 and a second four-sided box 3, which are arranged next to each other on a box column 11. As shown in Figures 1 to 4, the first four-sided box 2 and the second four-sided box 3 are each rectangular tubular. The cross-sectional shapes of the first four-sided box 2 and the second four-sided box 3 are substantially the same. The first four-sided box 2 and the second four-sided box 3 are installed coaxially, with their axes extending vertically and their openings facing vertically. The first four-sided box 2 is located on the upper side, and the second four-sided box 3 is located on the lower side.

[0012] The directions in which the sides of the rectangular cross-sectional shapes of the first four-sided box 2 and the second four-sided box 3 extend are referred to as the X direction and the Y direction. Of the outer peripheral surface 22 of the first four-sided box 2 and the outer peripheral surface 32 of the second four-sided box 3, the surfaces along the X direction are referred to as first outer peripheral surfaces 221, 321, and the surfaces along the Y direction are referred to as second outer peripheral surfaces 222, 322. The X direction corresponds to the first direction in the claims. The Y direction corresponds to the second direction in the claims. In this embodiment, the X direction and the Y direction are horizontal.

[0013] A gap is provided between the bottom end surface 21 of the first four-sided box 2 and the top end surface 31 of the second four-sided box 3. A backing metal 4 is provided along the inner peripheral surfaces of the first four-sided box 2 and the second four-sided box 3. The backing metal 4 fills the gap between the bottom end surface 21 of the first four-sided box 2 and the top end surface 31 of the second four-sided box 3. The backing metal 4 is provided in a rectangular cylindrical shape. The groove formed by the bottom end surface 21 of the first four-sided box 2, the top end surface 31 of the second four-sided box 3, and the outer surface 41 of the backing metal 4 is the groove 5. The groove 5 is in the shape of a rectangular frame along the outer peripheral surface 22 of the first four-sided box 2 and the outer peripheral surface 32 of the second four-sided box 3. The portion of the groove 5 extending in the X direction or the Y direction is referred to as a straight portion, and the portion where the straight portion extending in the X direction and the straight portion extending in the Y direction connect is referred to as a corner.

[0014] The bottom end surface 21 of the first four-sided box 2 is a surface that gradually slopes downward from the outside toward the inside of the first four-sided box 2. The portion of the bottom end surface 21 of the first four-sided box 2 that is continuous with the first outer peripheral surface 221 of the first four-sided box 2 is referred to as the first inclined end surface 211, and the portion that is continuous with the second outer peripheral surface 222 is referred to as the second inclined end surface 212. The first inclined end surface 211 and the second inclined end surface 212 are connected at a corner of the first four-sided box 2. A boundary line 213 between the first inclined end surface 211 and the second inclined end surface 212 extends gradually upward from the inside toward the outside of the first four-sided box 2, and extends in a direction that is inclined at 45° with respect to each of the X direction, Y direction, and Z direction.

[0015] The upper end surface 31 of the second four-sided box 3 is a surface perpendicular to the axial direction. The portion of the upper end surface 31 of the second four-sided box 3 that is continuous with the first outer peripheral surface 321 of the second four-sided box 3 is referred to as the first end surface 311, and the portion that is continuous with the second outer peripheral surface 322 of the second four-sided box 3 is referred to as the second end surface 312. The first end surface 311 and the second end surface 312 are connected at a corner of the second four-sided box 3. The first end surface 311 of the second four-sided box 3 is located below the first inclined end surface 211 of the first four-sided box 2. The second end surface 312 of the second four-sided box 3 is located below the second inclined end surface 212 of the first four-sided box 2.

[0016] The backing metal 4 is provided so as to span the inner peripheral surfaces of the first four-sided box 2 and the second four-sided box 3. The backing metal 4 is welded to the first four-sided box 2 and the second four-sided box 3. Of the outer surfaces of the backing metal 4, the surface facing the Y direction and between the first inclined end surface 211 and the first end surface 311 is referred to as the first connecting surface 411, and the surface facing the X direction and between the second inclined end surface 212 and the second end surface 312 is referred to as the second connecting surface 412.

[0017] As shown in FIGS. 5 to 7 , corner tabs 1 are provided at the corners of the groove 5 on both sides in the X direction of the first inclined end face 211 of the first four-sided box 2 and the second connection surface 41 of the backing plate 4. The shapes of the corner tabs 1 provided at the corners of grooves 5 adjacent in the X direction are symmetrical in the X direction. One of the corner tabs 1 symmetrical in the X direction is shown in FIGS. 8 to 10 , and the other is shown in FIGS. 11 to 13 . Below, the corner tabs 1 shown in FIGS. 8 to 10 will be described, and a description of the corner tabs 1 shown in FIGS. 11 to 13 will be omitted. In the corner tabs 1 shown in FIGS. 11 to 13 , the same reference numerals as in FIGS. 8 to 10 are used for parts corresponding to the corner tabs 1 shown in FIGS. 8 to 10 .

[0018] The corner tab 1 has a first plate portion 6 and a second plate portion 7. The first plate portions 6 are provided on both sides in the X direction of the first inclined end face 211 of the first four-sided box 2 so as to be flush with the first inclined end face 211. The second plate portions 7 are provided on both sides in the X direction of the first connecting face 411 of the backing metal 4 so as to be flush with the first connecting face 411. The first plate portion 6 and the second plate portion 7 are joined by welding or the like, or are machined into one piece.

[0019] As shown in Figures 8 to 10, the first plate portion 6 is flat. The plate surface of the first plate portion 6 is triangular. One surface of the first plate portion 6 is referred to as the first surface 61, and the other surface is referred to as the second surface 62. The first surface 61 and the second surface 62 are parallel to each other. Of the end surfaces of the first plate portion 6, the end surfaces corresponding to the three sides of the triangle are referred to as the first to third tab end surfaces 63, 64, and 65. The second tab end surface 64 is a surface that is perpendicular to the plate surface of the first plate portion 6. The first tab end surface 63 and the third tab end surface 65 are surfaces that are not perpendicular to the plate surface of the first plate portion 6 but are oblique to the plate surface of the corner tab 1.

[0020] The shape of the first surface 61 and the shape of the second surface 62 are the same right triangle. Two edges corresponding to the two right-angled sides of the right triangle of the first surface 61 of the first plate portion 6 are referred to as a first edge 611 and a second edge 612, and the edge corresponding to the hypotenuse is referred to as a third edge 613. Two edges corresponding to the two right-angled sides of the right triangle of the second surface 62 of the first plate portion 6 are referred to as a fourth edge 621 and a fifth edge 622, and the edge corresponding to the hypotenuse is referred to as a sixth edge 623. The first tab end surface 63 is the surface between the first edge 611 of the first surface 61 and the fourth edge 621 of the second surface 62. The second tab end surface 64 is the surface between the second edge 612 of the first surface 61 and the fifth edge 622 of the second surface 62. The third tab end surface 65 is a surface between the third edge 613 of the first surface 61 and the sixth edge 623 of the second surface 62 .

[0021] The edge connecting the angle formed by the first edge 611 and the third edge 613 of the first surface 61 and the angle formed by the fourth edge 621 and the sixth edge 623 of the second surface 62 is referred to as the seventh edge 671. The edge connecting the angle formed by the first edge 611 and the second edge 612 of the first surface 61 and the angle formed by the fourth edge 621 and the fifth edge 622 of the second surface 62 is referred to as the eighth edge 672. The edge connecting the angle formed by the second edge 612 and the third edge 613 of the first surface 61 and the angle formed by the fifth edge 622 and the sixth edge 623 of the second surface 62 is referred to as the ninth edge 673. The seventh to ninth edges 671-673 are parallel to each other. The first surface 61 and the second surface 62 are positioned at positions offset in the longitudinal direction of the second edge portion 612 and the fifth edge portion 622 so that, when viewed from the thickness direction of the first plate portion 6, the first edge portion 611 of the first surface 61 is positioned closer to the corner between the fifth edge portion 622 and the sixth edge portion 623 than the fourth edge portion 621 of the second surface 62.

[0022] The second plate portion 7 is flat. The plate surface of the second plate portion 7 is rectangular. One surface of the second plate portion 7 is referred to as the third surface 71, and the other surface is referred to as the fourth surface 72. The third surface 71 and the fourth surface 72 are parallel to each other. The third surface 71 and the fourth surface 72 overlap when viewed from the thickness direction of the second plate portion 7. Of the end surfaces of the second plate portion 7, the end surfaces corresponding to each of the four sides of the rectangle are referred to as the fourth to seventh tab end surfaces 73-76. The fourth to seventh tab end surfaces 73-76 are surfaces perpendicular to the plate surface of the second plate portion 7.

[0023] The edges of the third surface 71 corresponding to each of the four sides of the rectangle are designated as the tenth to thirteenth edges 711-714. The edges of the fourth surface 72 corresponding to each of the four sides of the rectangle are designated as the fourteenth to seventeenth edges 721-724. The fourth tab end surface 73 is the surface between the tenth edge 711 of the third surface 71 and the fourteenth edge 721 of the fourth surface 72. The fifth tab end surface 74 is the surface between the eleventh edge 712 of the third surface 71 and the fifteenth edge 722 of the fourth surface 72. The sixth tab end surface 75 is the surface between the twelfth edge 713 of the third surface 71 and the sixteenth edge 723 of the fourth surface 72. The seventh tab end surface 76 is the surface between the thirteenth edge 714 of the third surface 71 and the seventeenth edge 724 of the fourth surface 72.

[0024] The edge connecting the angle formed by the tenth edge 711 and the thirteenth edge 714 of the third surface 71 and the angle formed by the fourteenth edge 721 and the seventeenth edge 724 of the fourth surface 72 is referred to as the eighteenth edge 771. The edge connecting the angle formed by the tenth edge 711 and the eleventh edge 712 of the third surface 71 and the angle formed by the fourteenth edge 721 and the fifteenth edge 722 of the fourth surface 72 is referred to as the nineteenth edge 772. The edge connecting the angle formed by the eleventh edge 712 and the twelfth edge 713 of the third surface 71 and the angle formed by the fifteenth edge 722 and the sixteenth edge 723 of the fourth surface 72 is referred to as the twentieth edge 773. The edge connecting the angle formed by the 12th edge 713 and the 13th edge 714 of the third surface 71 and the angle formed by the 16th edge 723 and the 17th edge 724 of the fourth surface 72 is referred to as the 21st edge 774.

[0025] The first plate portion 6 and the second plate portion 7 are integrally formed such that the first tab end surface 63 of the first plate portion 6 and the fourth tab end surface 73 of the second plate portion 7 overlap and are joined together, or such that the first tab end surface 63 of the first plate portion 6 and the fourth tab end surface 73 of the second plate portion 7 overlap. The shapes of the first tab end surface 63 of the first plate portion 6 and the fourth tab end surface 73 of the second plate portion 7 are substantially identical. The first surface 61 of the first plate portion 6 is not flush with the third surface 71 of the second plate portion 7 but is inclined relative to the third surface 71. The second surface 62 of the first plate portion 6 is not flush with the fourth surface 72 of the second plate portion 7 but is inclined relative to the fourth surface 72. As shown in FIG. 9 , the inclination angle of the first surface 61 of the first plate portion 6 relative to the first tab end surface 63 and the inclination angle of the second surface 62 relative to the first tab end surface 63 have the same value (indicated by θ in the drawing). This inclination angle is the same as the inclination angle of the first inclined end surface 211 of the first four-sided box 2 relative to the horizontal plane (see FIG. 4, indicated by θ in the drawing). The second tab end surface 64 of the first plate portion 6 and the fifth tab end surface 74 of the second plate portion 7 are arranged flush with each other.

[0026] The length dimensions of the first edge 611 of the first plate portion 6 and the tenth edge 711 of the second plate portion 7 are the same value, and are the same value as the thickness dimension (dimension d in Figures 3 and 4) of the plate material forming the first four-sided box 2 and the second four-sided box 3.

[0027] As shown in FIGS. 5 to 7 , the corner tab 1 is installed between the corner of the first four-sided box 2 and the corner of the second four-sided box 3, i.e., at the corner of the groove 5. The sixth tab end face 75 of the second plate portion 7 is in surface contact with the second end face 312 of the second four-sided box 3. The seventh tab end face 76 of the second plate portion 7 is in surface contact with the second connecting surface 412 of the backing plate 4. The third tab end face 65 of the first plate portion 6 is in surface contact with the second inclined end face 212 of the first four-sided box 2. The first surface 61 of the first plate portion 6 is positioned flush with the first inclined end face 211 of the first four-sided box 2. The third surface 71 of the second plate portion 7 is positioned flush with the first connecting surface 411 of the backing plate 4. The ninth edge portion 673 of the first plate portion 6, which is the upper edge of the third tab end face 65, overlaps with the outer edge of the second inclined end face 212. The fifth tab end surface 74 of the second plate portion 7 and the second tab end surface 64 of the first plate portion 6 are arranged flush with the second outer peripheral surface 222 of the first four-sided box 2 and the second outer peripheral surface 322 of the second four-sided box 3.

[0028] By providing the corner tab 1 at the corner of the groove 5 as described above, a recess is formed that is surrounded by the first surface 61 of the first plate portion 6 of the corner tab 1, the third surface 71 of the second plate portion 7, and the upper end surface 31 of the second four-sided box 3, as shown in Fig. 6. This recess separates a straight portion extending in the X direction from a straight portion extending in the Y direction in a cross section that has the same shape as the straight portion extending in the X direction of the groove 5.

[0029] A method for welding the first four-sided box 2 and the second four-sided box 3 using the corner tabs 1 (a method for welding four-sided boxes) will be described. The first four-sided box 2 and the second four-sided box 3 are joined together via a backing metal 4, and a groove 5 is formed. A corner tab setting step is carried out in which corner tabs 1 are set at each corner of the groove 5 as described above. An end face welding process is performed to weld the bottom end face 21 of the first four-sided box 2 to the top end face 31 of the second four-sided box 3. The end face welding process is performed using a welding robot or an automatic welding device. In the end face welding process, the following first to third welding processes are performed. In the first welding process, welding is performed on the linear portion of the groove 5 extending in the X direction, i.e., the portion surrounded by the first inclined end face 211 of the first four-sided box 2, the first connecting surface 411 of the backing plate 4, and the first end face 311 of the second four-sided box 3. In the second welding process, welding is performed on the corner of the groove 5, i.e., the portion surrounded by the first surface 61 of the first plate portion 6 of the corner tab 1, the third surface 71 of the second plate portion 7, and the top end face 31 of the second four-sided box 3. In the third welding step, welding is performed on the portion of the groove 5 extending in the Y direction, i.e., the portion surrounded by the second inclined end face 212 of the first four-sided box 2, the second connecting surface 412 of the backing plate 4, and the second end face 312 of the second four-sided box 3. The first welding step, the second welding step, and the third welding step are performed consecutively. After the end face welding process, the corner tabs 1 are removed by gouging, and a corner tab installation portion welding process is carried out in which the lower end surface 21 of the first four-sided box 2 and the upper end surface 31 of the second four-sided box 3 are welded together at the portion where the corner tabs 1 were removed. The corner tab installation portion welding process is carried out by a welding technician. In this manner, the first four-sided box 2 and the second four-sided box 3 are welded together.

[0030] In the method for welding four-sided boxes according to this embodiment, by installing corner tabs 1 at the corners of the first four-sided box 2 and the second four-sided box 3 to be joined, recesses are formed at the corners of the groove 5 that are shaped as extensions of the linear portions extending in the X direction, so that the corners can be efficiently welded continuously with the linear portions extending in the X direction. Furthermore, even when welding is performed using a welding robot or automatic welding equipment, the corners can be welded continuously with the linear portions extending in the X direction, making the welding work more efficient. The corner tab 1 has a shape in which the first plate portion 6 and the second plate portion 7, each of which is flat, are joined together, and therefore is easy to manufacture, install and remove.

[0031] The above describes an embodiment of the corner tab and four-sided box welding method according to the present invention, but the present invention is not limited to the above embodiment and can be modified as appropriate within the scope of the spirit thereof. For example, in the above embodiment, welding is assumed to be performed using a welding robot or an automatic welding device, but corner tabs 1 may be installed and used for welding by a welding engineer.

[0032] The Sustainable Development Goals (SDGs) are 17 international goals adopted at the United Nations Summit in September 2015. The corner tab and four-sided box welding method according to this embodiment can contribute to achieving one of the 17 SDGs, for example, goal 11, "Sustainable cities and communities." [Explanation of symbols]

[0033] 1 Corner tab 2. First Four-Sided Box 3. Second Four-Sided Box 5 Bevel 6 1st plate part 7 Second plate part 21 Lower end surface 31 Upper end surface 61 Page 1 62 2nd page 63 First tab end face 64 Second tab end face 65 Third tab end face 71 Page 3 72 Page 4 73 End face of fourth tab 74 5th tab end face 75 End face of 6th tab 76 7th tab end face 211 1st inclined end face 212 2nd inclined end face 311 1st end face 312 Second end face 411 First connection surface 412 Second connecting surface

Claims

1. A corner tab is provided at a corner of a groove when welding is performed between an end face of a first four-sided box and an end face of a second four-sided box arranged in the axial direction, The end face of the first four-sided box is a first inclined end surface extending in a first direction perpendicular to the axial direction and gradually inclining in a direction toward the second four-sided box from one side that is an outer periphery of the first four-sided box toward the other side that is an inner periphery of the first four-sided box in a second direction perpendicular to both the axial direction and the first direction; a second inclined end surface extending in the second direction and gradually inclining in a direction toward the second four-sided box from one side that is the outer periphery of the first four-sided box in the first direction toward the other side that is the inner periphery of the first four-sided box, the first inclined end surface and the second inclined end surface are connected at corner portions of the first four-sided box, The end face of the second four-sided box is a first end surface extending in the first direction and perpendicular to the axial direction; a second end surface extending in the second direction and perpendicular to the axial direction, the first end surface and the second end surface are connected at a corner portion of the second four-sided box, The first inclined end surface and the first end surface are disposed with a gap in the axial direction, a first connection surface that connects the first inclined end surface and the first end surface is provided between an edge portion of the first inclined end surface on the other side in the second direction and an edge portion of the first end surface on the other side in the second direction; The second inclined end surface and the second end surface are disposed at an interval in the axial direction, a second connection surface that connects the second inclined end surface and the second end surface is provided between an edge portion of the second inclined end surface on the other side in the first direction and an edge portion of the second end surface on the other side in the first direction, The corner tab is a first plate portion disposed on a side of the first inclined end surface in the first direction, in contact with the second inclined end surface, and flush with the first inclined end surface; a second plate portion connected to the first plate portion, installed to the side of the first connection surface in the first direction, in contact with the second connection surface and the second end surface, and arranged flush with the first connection surface.

2. A method for welding four-sided boxes, comprising the steps of: forming a groove between an end face of a first four-sided box and an end face of a second four-sided box arranged in an axial direction and welding the groove; and installing the corner tabs according to claim 1 at the corners of the groove. a corner tab installation process in which a corner tab is installed at a corner portion of the groove; an end face welding process for welding an end face of the first four-sided box to an end face of the second four-sided box; a corner tab installation portion welding step in which the corner tab is removed after the end face welding step, and an area where the corner tab was previously provided is welded, The end face welding step includes: a first welding process for welding a portion of the groove formed by the first inclined end surface, the first connection surface, and the first end surface and extending in the first direction; A second welding process of welding the corner portion of the groove; a third welding step of welding a portion formed by the second inclined end surface, the second connection surface, and the second end surface in the groove and extending in the second direction, A welding method for a four-sided box, comprising successively performing the first welding step, the second welding step, and the third welding step.

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