Back shield fixture and welding method of metal pipe using the same

Abstract

To provide a back shield fixture capable of stably retaining such a state as to cover a tube with a peripheral portion of sheet material, and to provide a method of welding a metal pipe using the back shield fixture.SOLUTION: A back shield fixture has a ring-shaped tube 11 and a sheet material 12 which is arranged within a metal pipe P in such a state that a peripheral part 16 with which the tube 11 is covered is interposed by the tube 11 and the inside of the metal pipe P to clog the inside of the metal pipe P. The sheet material 12 includes N pieces of split pieces 17 of which a peripheral part 16 is formed in the circumferential direction, the peripheral part 16 is folded to the center part side of the tube 11 in which fluid is filled over the whole circumference and covers the tube 11, actuates a force toward the center part of the tube 11 with respect to M pieces of split pieces 17 containing two sets of opposing split pieces 17, of N pieces of split pieces 17, and such a sheet temporarily retaining means 22 that a peripheral part 16 maintains covers the tube 11 is attached to the peripheral part 16. Therein, N is an integer of 4 or more, and M is an integer of 4 or more and N or less.SELECTED DRAWING: Figure 5

Description

Technical Field

[0001] The present invention relates to a backshield jig for shielding the back surface of a welded portion of a metal pipe from the atmosphere with a backshield gas, and a method for welding a metal pipe using the same.

Background Art

[0002] When connecting two metal pipes made of a metal such as stainless steel that is easily oxidized by welding in the atmosphere by welding, in order to prevent oxidation on the back side of the welded portion (usually near the portion where the openings of the respective metal pipes come into contact), that is, on the inner surface side of the metal pipe, an area including a portion corresponding to the back side of the welded portion in the metal pipe is made into an inert gas atmosphere. As a method of making a predetermined area in a metal pipe into an inert gas atmosphere, there is a method of installing a backshield jig that closes a predetermined location in the metal pipe inside the metal pipe, and a specific example thereof is disclosed in Patent Document 1.

[0003] The backshield jig disclosed in Patent Document 1 has a circular sheet material and a ring-shaped tube having a diameter shorter than that of the sheet material. The operator overlaps the sheet material and the tube filled with air and inflated so that their centers coincide on a flat workbench installed outside the metal pipe, and then folds the peripheral portion of the sheet material toward the center over the entire circumference so that the tube is covered by the peripheral portion of the sheet material.

[0004] The operator inserts the sheet material and the tube covered by the peripheral portion of the sheet material into the metal pipe through the opening of the metal pipe, and after the entire peripheral portion of the sheet material is sandwiched between the tube and the inner surface of the metal pipe and the sheet material is in an extended state, the sheet material and the tube are pushed into a predetermined position inside the metal pipe, and a predetermined position inside the metal pipe is closed off by the sheet material. Next, air is filled into the tube via an air supply hose having one end connected to the tube, and the pressure inside the tube is increased to a value necessary for sealing by the backshield jig and for fixing the tube and the sheet material, and the sheet material and the tube are installed inside the metal pipe. Thereby, a predetermined space inside the metal pipe including the welded portion becomes a closed space.

[0005] Thereafter, an inert gas is injected into the closed space to replace the atmosphere in the closed space with the inert gas, and the metal pipe is welded. Here, if there is a twist in the peripheral edge of the sheet material installed inside the metal pipe, the sealing performance between the back shield jig and the inner surface of the metal pipe will deteriorate. Therefore, at the peripheral edge of the sheet material, divided pieces are formed by radial cuts at a plurality of locations to prevent the peripheral edge of the sheet material from being twisted.

[0006] After the welding of the metal pipe is completed, the operator evacuates the air from the tube to shrink the tube, pulls the other end of the air supply hose that was led out of the metal pipe through the outlet formed in the metal pipe, and takes out the tube from the metal pipe via the outlet. One end of a string is fixed to the sheet material, and the other end of the string is arranged outside the metal pipe via the outlet. The operator pulls the string and takes out the sheet material from the metal pipe via the outlet.

Prior Art Documents

Patent Documents

[0007]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0008] However, in Patent Document 1, since the sheet material and the tube are pushed into the metal pipe in a state where the tube is covered with the divided pieces of the sheet material, depending on the orientation of the sheet material and the tube, the divided pieces of the sheet material may come off the tube due to gravity or the like. Furthermore, due to the friction between the sheet material and the metal pipe that occurs when the sheet material and the tube are pushed into the metal pipe, the divided pieces of the sheet material may shift with respect to the tube, and the divided pieces may come off the tube. As a result, there is a problem that it takes time to install the sheet material and the tube on the metal pipe.

[0009] The present invention has been made in view of such circumstances, and an object thereof is to provide a backshield jig in which a state where a tube is covered at a peripheral edge portion of a sheet material is stably maintained, and a welding method for a metal tube using the same.

Means for Solving the Problems

[0010] The backshield jig according to the first invention that meets the above object is a backshield jig having a ring-shaped tube and a sheet material disposed in the metal tube so as to close the inside of the metal tube with a peripheral edge portion covering the tube being sandwiched between the tube and the inside of the metal tube. The sheet material includes a peripheral edge portion in which N divided pieces are formed in the circumferential direction, and the peripheral edge portion is folded toward the center portion of the tube filled with fluid over the entire circumference to cover the tube. For M of the N divided pieces including two sets of opposing divided pieces among the N divided pieces, sheet temporary fixing means for applying a force toward the center portion of the tube to maintain the state where the peripheral edge portion covers the tube is attached to the peripheral edge portion. However, N is an integer of 4 or more, and M is an integer of 4 or more and N or less.

[0011] The welding method according to the second invention that meets the above object is a welding method for welding a metal object to an opening in a metal tube with a sheet material whose peripheral edge covering a ring-shaped tube is sandwiched between the inside of the tube and the metal tube, and the method includes: a first step of overlapping the tube filled with fluid inside the inner side of the peripheral edge of the sheet material in which N divided pieces are formed in the circumferential direction, folding the peripheral edge over the entire circumference toward the center of the tube, and covering the tube with the peripheral edge; a second step of attaching the sheet material to the tube by using a sheet temporary fixing means that applies a force toward the center of the tube to M divided pieces including two sets of opposing divided pieces among the N divided pieces to maintain the state where the peripheral edge covers the tube; a third step of pushing the sheet material together with the tube into the metal tube from the opening while applying a force toward the center of the tube to the M divided pieces; a fourth step of bringing a metal object close to the opening and restricting the inflow of air into the vicinity of the opening in the metal tube; and a fifth step of supplying an inert gas to the vicinity of the opening in the metal tube to replace the air with the inert gas, and then welding the metal tube and the metal object from the outside of the metal tube. However, N is an integer of 4 or more, and M is an integer of 4 or more and N or less.

Effect of the Invention

[0012] The back shield jig according to the first invention has a sheet material provided with a peripheral edge in which N divided pieces are formed in the circumferential direction. The peripheral edge is folded toward the center of the tube filled with fluid over the entire circumference to cover the tube. A sheet temporary fixing means that applies a force toward the center of the tube to M divided pieces including two sets of opposing divided pieces among the N divided pieces to maintain the state where the peripheral edge covers the tube is attached to the peripheral edge. Therefore, it is possible to stably maintain the state where the peripheral edge of the sheet material covers the tube.

[0013] Further, in the welding method according to the second invention, a tube filled with fluid is overlapped inside the peripheral edge of a sheet material having N divided pieces formed in the circumferential direction at the peripheral edge, and the peripheral edge is folded toward the center side of the tube over the entire circumference. A first step of covering the tube at the peripheral edge, and for M divided pieces including two sets of opposing divided pieces out of the N divided pieces, a sheet temporary fixing means for applying a force toward the center of the tube to maintain the state where the peripheral edge covers the tube, and a second step of attaching the sheet material to the tube, a third step of pushing the sheet material together with the tube into the metal tube from the opening while applying a force toward the center of the tube to the M divided pieces, a fourth step of bringing a metal object close to the opening to restrict the inflow of air into the vicinity of the opening inside the metal tube, and after supplying an inert gas to the vicinity of the opening inside the metal tube to replace the air with the inert gas, a fifth step of welding the metal tube and the metal object from the outside of the metal tube. Therefore, when pushing the sheet material together with the tube into the metal tube, it is possible to stably maintain the state where the peripheral edge of the sheet material covers the tube.

Brief Description of the Drawings

[0014]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Figure 6

Figure 7

Figure 8

Embodiments for Carrying Out the Invention

[0015] Subsequently, while referring to the attached drawings, embodiments embodying the present invention will be described to facilitate understanding of the present invention. As shown in FIGS. 1 to 5, a backshield jig 10 according to a first embodiment of the present invention includes a ring-shaped tube 11 and a sheet material 12 disposed in a metal tube P in a state where a peripheral edge portion 16 covering the tube 11 is sandwiched between the inside of the tube 11 and the metal tube P to close the inside of the metal tube P. Details will be described below.

[0016] In the present embodiment, as shown in FIGS. 1, 4, and 5(B), the backshield jig 10 is used when butt-welding an opening T of a cap-shaped metal tube (an example of a metal object) Q to an opening S at one end of the metal tube P from the outside of the metal tube P and the metal tube Q. Both the metal tube P and the metal tube Q are made of a metal (such as stainless steel) that easily oxidizes in the atmosphere when heated to a high temperature by welding or the like. Therefore, after the space including the vicinity of the opening S inside the metal tube P and inside the metal tube Q (hereinafter, also referred to as the "welding vicinity space") is made in a state where the inflow of the atmosphere is restricted using the backshield jig 10, welding is performed by supplying an inert gas to make the space an inert gas atmosphere. This prevents the inside of the metal tube P and the metal tube Q from oxidizing during welding. Note that the metal object fixed to the metal tube P by welding is not limited to a cap-shaped metal tube.

[0017] The tube 11 is formed of an elastic material (rubber in this embodiment). As shown in FIG. 1, the other end of a gas hose 14 provided with an injection port 13 at one end is connected to the tube 11. The injection port 13 is exposed when a cap 15 attached to one end of the gas hose 14 is removed, and air is supplied to the tube 11 via the gas hose 14 by an air supply device (not shown) connected to the exposed injection port 13. Note that in FIGS. 2 to 4, the description of the gas hose 14 is omitted.

[0018] A sheet material 12 separate from the tube 11 is generally circular as shown in FIGS. 1 and 2, and N divided pieces 17 arranged in the circumferential direction are formed over the entire circumference at the peripheral edge (outer peripheral portion) 16 of the sheet material 12. The N divided pieces 17 are formed by making N cuts in the peripheral edge 16 at equal intervals in the radial direction (substantially the radial direction) of the sheet material 12 (that is, each divided piece 17 has the same circumferential length). Therefore, the sheet material 12 has a peripheral edge 16 in which N divided pieces 17 are formed in the circumferential direction. N is an integer of 4 or more, and in this embodiment, N = 12. Note that the circumferential lengths of the respective divided pieces 17 may be different.

[0019] A single long member 18 is attached to each divided piece 17. The long member 18 has a rubber string (an example of a string-like elastic body) 19 with one side (base side) fixed to the divided piece 17, and a ring portion 20 provided on the other side (tip side) of the rubber string 19. The ring portion 20 may be formed of a rubber string piece continuous with the other end of the rubber string 19 (that is, a single rubber string is constituted by the rubber string 19 and the rubber string piece) (for example, the rubber string piece is formed into a ring shape and fastened with a metal fitting), or may be a ring-shaped member (for example, a metal ring) attached to the rubber string 19. In this embodiment, on each divided piece 17, one side of the rubber string 19 is fixed to the circumferential center on the outer side in the radial direction of the sheet material 12.

[0020] Next, the sheet material 12 is attached to the tube 11, and the sheet material 12 is used to block a predetermined position inside the metal tube P. Each step from the butting of the opening S of the metal tube P and the opening T of the metal tube Q to the welding will be described. In the present embodiment, the metal tube P and the metal tube Q are arranged with their axes vertical, and are welded with the metal tube Q placed on the metal tube P.

[0021] <Step 1> As shown in FIG. 2, the tube 11 arranged horizontally is overlapped on the sheet material 12 placed in a spread state on the horizontal table so that the center of the sheet material 12 and the center of the tube 11 coincide in plan view. In the present embodiment, the tube 11 is pre-filled with air, but the tube 11 may be filled with air after the tube 11 is placed on the sheet material 12.

[0022] In the present embodiment, with the tube 11 overlapped on the spread sheet material 12, in the sheet material 12, the outer region of the tube 11 in plan view corresponds to the peripheral edge portion 16, and the peripheral edge portion 16 is composed of N divided pieces 17 and the annular region inside thereof. Therefore, in Step 1, the air-filled tube 11 is overlapped inside the peripheral edge portion 16 of the sheet material 12. Note that the sizes of the divided pieces of the sheet material and the size of the tube may be adjusted so that the peripheral edge is composed only of N divided pieces.

[0023] <Step 2> Next, as shown in FIGS. 3 and 4, the peripheral edge portion 16 of the sheet material 12 is folded toward the center portion side of the tube 11 over the entire circumference to cover the tube 11 with the peripheral edge portion 16. In the present embodiment, all of the N divided pieces 17 are in a state of covering the tube 11. Therefore, the sheet material 12 is folded so that the peripheral edge portion 16 wraps around the center portion side of the air-filled tube 11 over the entire circumference to cover the tube 11. When the peripheral edge portion 16 is folded toward the center portion side of the tube 11, all of the N long members 18 are arranged in the radial direction of the sheet 12, and the N ring portions 20 are arranged annularly at intervals around the center portion of the tube 11.

[0024] <Step 3> Thereafter, as shown in FIG. 4, fasteners 21 are attached to the respective ring portions 20 arranged around the central portion of the tube 11, and a force directed toward the central portion of the tube 11 is applied to each of the long members 18, so that the peripheral edge portion 16 maintains a state of covering the tube 11 (that is, even if a force in a direction in which the sheet material 12 shifts relative to the tube 11 acts on the sheet material 12 or the tube 11, the state in which the peripheral edge portion 16 covers the tube 11 is stably maintained). Thereby, the attachment of the sheet material 12 to the tube 11 is completed.

[0025] The fastener 21 can be manually changed in shape from linear to annular or from annular to linear, and the portions corresponding to both side ends are connectable to each other in the linear state. The operator inserts the linear fastener 21 through all N ring portions 20 and connects both side ends of the fastener 21 so that the N ring portions 20 do not fall out of the fastener 21. In the present embodiment, the fastener 21 is a non-elastic body (in the sense of being substantially non-elastic), and a sheet temporary fixing means 22 for maintaining the state in which the peripheral edge portion 16 covers the tube 11 is mainly constituted by N long members 18 and the fastener 21.

[0026] Here, in the present embodiment, the sheet temporary fixing means 22 applies a force directed toward the central portion of the tube 11 to all N divided pieces 17. However, letting M be an integer of 4 or more and N or less, a force directed toward the central portion of the tube 11 may be applied only to M divided pieces 17 including two sets of opposing divided pieces 17 among the N divided pieces 17 so as to maintain the state in which the peripheral edge portion 16 covers the tube 11.

[0027] In this case, the sheet temporary fixing means 22 includes M long members 18 respectively attached to the M divided pieces 17, and a fastener 21 attached to the M long members 18 and applying a tension force (a pulling force directed toward the central portion of the tube 11) toward the central portion of the tube 11 to the M long members 18. Further, the fastener 21 is linear, passes through the ring portions 20 of each of the M long members 18, and both side ends are connected to form an annular shape, and the inserted M ring portions 20 are in a state where they are prevented from falling out.

[0028] For example, a long member 18 may be attached to each of two sets of opposing divided pieces 17 (a total of four divided pieces 17) out of the twelve divided pieces 17, and a fastener 21 may be attached to the four long members 18, so that a force directed toward the center of the tube 11 is applied only to the four divided pieces 17. In this case, the first set of opposing divided pieces 17 and the second set of opposing divided pieces 17 preferably have a cross-shaped positional relationship. For example, the divided pieces 17 forming the first pair may be the divided pieces 17 arranged at the 12 o'clock position and the 6 o'clock position respectively, and the divided pieces 17 forming the second pair may be the divided pieces 17 arranged at the 3 o'clock position and the 9 o'clock position respectively.

[0029] <Step 4> After the attachment of the sheet material 12 to the tube 11 is completed, the operator fits the sheet material 12 together with the tube 11 into the opening S of the metal tube P as shown in FIG. 5(A). The sheet material 12 attached to the tube 11 has the entire peripheral edge portion 16 sandwiched between the tube 11 and the inside of the metal tube P, and the region inside the peripheral edge portion 16 is in an extended state. One end of a string-like member 23 is fixed to the center of the sheet material 12. In FIGS. 2 to 4, the description of the string-like member 23 is omitted.

[0030] <Step 5> Next, while maintaining the state in which a force directed toward the center of the tube 11 is applied to the N divided pieces 17, the operator pushes the sheet material 12 together with the tube 11 from the opening S of the metal tube P to a predetermined position inside the metal tube P, adds air into the tube 11 via the gas hose 14 to expand the tube 11, and securely fixes the sheet material 12 and the tube 11 inside the metal tube P. Thereby, the process of closing the predetermined position inside the metal tube P with the sheet material 12 is completed.

[0031] <Step 6> After removing the fastener 21 linearly from the N ring portions 20 and removing the fastener 21 from inside the metal tube P, as shown in FIG. 5(B), the metal tube P and the metal tube Q are butted against each other so that the opening S of the metal tube P and the opening T of the metal tube Q are in a facing state and close to each other. A welding vicinity space is formed by the region from the position blocked by the sheet material 12 inside the metal tube P to the opening S and the region inside the metal tube Q. A cylinder J communicating with the welding vicinity space is fixed to the side opposite to the side where the opening T of the metal tube Q is formed (the closed side). When butting the metal tube P and the metal tube Q, one end portion provided with the injection port 13 of the gas hose 14 and the other end portion of the string-like member 23 (the side opposite to the side connected to the sheet material 12) are arranged outside the metal tube P and the metal tube Q via the cylinder J of the metal tube Q.

[0032] <Step 7> Insert the other end of the gas hose 25, one end of which is connected to a supply device of an inert gas (such as argon gas), into the welding vicinity space via the cylinder J, supply the inert gas into the welding vicinity space via the gas hose 25 to replace the air in the welding vicinity space with the inert gas (after making the welding vicinity space an inert gas atmosphere), and then weld the metal tube P and the metal tube Q from the outside of the metal tube P and the metal tube Q to fix the metal tube Q to the metal tube P. In FIG. 5(B), the description of the long member 18 is omitted.

[0033] <Step 8> After completion of welding, discharge the air in the tube 11 via the gas hose 14, pull out the gas hose 14 and take out the tube 11 from the welding vicinity space to the outside via the cylinder J, and then pull the string-like member 23 and take out the sheet material 12 together with the N long members 18 from the welding vicinity space to the outside via the cylinder J.

[0034] Therefore, in a state where the peripheral portion 16 covering the ring-shaped tube 11 is blocked near the opening S in the metal tube P by the sheet material 12 sandwiched between the inside of the tube 11 and the metal tube P, the welding method of welding the metal tube Q (metal object) to the opening S includes, inside the peripheral portion 16 of the sheet material 12, overlapping the tube 11 filled with fluid, folding the peripheral portion 16 toward the central portion side of the tube 11 over the entire circumference, and covering the tube 11 with the peripheral portion 16 in a first step; for M of the N split pieces 17 including two sets of opposing split pieces 17, a second step of attaching the sheet material 12 to the tube 11 while maintaining the state where the peripheral portion 16 covers the tube 11 by the sheet temporary fixing means 22 that applies a force toward the central portion of the tube 11; a third step of pushing the sheet material 12 together with the tube 11 into the metal tube P from the opening S in a state where a force toward the central portion of the tube 11 is applied to the M split pieces 17; a fourth step of bringing the metal tube Q into contact with the opening S and restricting the inflow of air into the vicinity of the opening S in the metal tube P by the sheet material 12 and the metal tube Q; and a fifth step of supplying an inert gas to the vicinity of the opening S in the metal tube P to replace the air with the inert gas, and then welding the metal tube P and the metal tube Q from the outside of the metal tube P. The fastener 21 is removed from the M long members 18 and taken out into the outer space of the metal tube P after the third step and before the fourth step.

[0035] In the present embodiment, the rubber string 19, that is, the long member 18 having a string-shaped elastic body and the non-elastic fastener 21 are used in combination, but it is not limited to this. A long member having a string-shaped non-elastic body (in the sense of substantially non-elastic body) and an elastic member fastener may be combined, a long member having a string-shaped elastic body and an elastic member fastener may be combined, or a long member having a string-shaped non-elastic body and a non-elastic member fastener may be combined. Furthermore, the fastener does not necessarily have to be changed in shape from linear to annular or from annular to linear. For example, a fastener having an annular shape (not becoming linear) and a long member having one side attached to a split piece and a hook on the other side may be adopted, and the hook may be hung on the fastener to apply a tension toward the central portion of the tube to the long member.

[0036] Also, the sheet temporary fixing member does not necessarily have to have a long member and a fastener. With the peripheral edge portion of the sheet material folded toward the central portion side of the tube over the entire circumference, a string attached by a running stitch to the front side near the central portion of the tube of each divided piece, or a string passed through a hole formed in the front side of each divided piece and attached thereto may be used as the sheet temporary fixing member. The string attached by a running stitch to the front side of each divided piece also acts with a force toward the central portion of the tube to maintain the state where the peripheral edge portion covers the tube.

[0037] Here, the main role of the sheet temporary fixing means 22 is to prevent the sheet material 12 from shifting from the tube 11 when the tube 11 and the sheet material 12 are pushed into the metal tube P. In addition to this role, a sheet temporary fixing means may be adopted that also plays a role of preventing the tube 11 and the sheet material 12, which are pushed into the metal tube P and positioned at a predetermined position, from moving or tilting due to the pressure or the like inside the metal tube P.

[0038] Referring to FIGS. 6 to 8, a back shield jig 50 having a sheet temporary fixing means 51 that not only plays a role of preventing the sheet material 12 from shifting from the tube 11 when the tube 11 and the sheet material 12 are pushed into the metal tube P, but also plays a role of preventing the tube 11 and the sheet material 12 positioned in the metal tube P from moving or tilting will be described. Note that the same reference numerals are given to the same configurations as those of the back shield jig 10 in the back shield jig 50, and detailed descriptions thereof are omitted.

[0039] The back shield jig 50 according to the second embodiment of the present invention has a tube 11, a sheet material 12, and a sheet temporary fixing means 51, and is a jig that closes a predetermined position inside the metal tube P with the sheet material 12 fixed to the tube 11 by the sheet temporary fixing means 51. As shown in FIGS. 6 and 7, the sheet temporary fixing means 51 includes N long members 52 each having one end fixed to N divided pieces 17, a bundling portion 54 formed with through holes 53 through which the N long members 52 are inserted, and a support member 55 having one end connected to the bundling portion 54 and the other end disposed in the outer space of the metal tube P. In FIGS. 6 and 7, the description of the gas hose 14 connected to the tube 11 and the string-like member 23 connected to the sheet material 12 is omitted.

[0040] The back shield jig 50 is common to the back shield jig 10 in that the peripheral edge 16 of the sheet material 12 is folded so as to wrap around the central portion side of the tube 11 overlapped with the sheet material 12 to cover the tube 11, and a tension toward the central portion of the tube 11 is applied to each of the N long members 52 attached to the N divided pieces 17. On the other hand, the back shield jig 50 is different from the back shield jig 10 in the configuration for applying a force toward the central portion of the tube 11 to each divided piece 17.

[0041] In the back shield jig 50 as well, it is not necessary to apply a force toward the central portion of the tube 11 to all of the N divided pieces 17, and the force toward the central portion of the tube 11 may be applied only to 4 divided pieces 17 corresponding to 2 sets of opposing divided pieces 17 among the N divided pieces 17. That is, a force toward the central portion of the tube 11 may be applied to M divided pieces 17 including 2 sets of opposing divided pieces 17 among the N divided pieces 17.

[0042] Each long member 52 is longer than the long member 18, and in the present embodiment, a string-like inelastic body is adopted for the long member 52. In the present embodiment, as shown in FIG. 7, the bundling portion 54 is a cylindrical metal body. The support member 55 is composed of a metal rod having one end welded to the bundling portion 54, and the other end is bent so as to be lockable to the opening of the cylindrical body J.

[0043] Also, the state where the peripheral edge portion 16 of the sheet material 12 is folded toward the central portion side of the tube 11 and covers the tube 11 is maintained as follows. That is, the bundling portion 54 is arranged near the central portion of the tube 11, and a portion having a distance to one end portion of the long member 52 of each long member 52 is inserted into the through hole 53 of the bundling portion 54. The portion from the portion where each long member 52 is inserted through the through hole 53 to the other end portion is pulled toward the other end portion, and a force toward the central portion of the tube 11 is applied to each divided piece 17, whereby the above state is maintained.

[0044] Next, the steps from attaching the sheet material 12 to the tube 11, closing a predetermined position inside the metal tube P with the sheet material 12, butting the opening S of the metal tube P and the opening T of the metal tube Q, and welding them will be described. First, in the same procedure as Steps 1 and 2 when using the back shield jig 10, the peripheral edge portion 16 of the sheet material 12 covers the tube 11, and the following Steps 3a and subsequent steps are performed.

[0045] <Step 3a> As shown in FIG. 7, each long member 52 is passed through the through hole 53 of the bundling portion 54 arranged near the central portion of the tube 11, and each long member 52 is fixed to the support member 55 or another member in a state where each long member 52 is pulled toward the other end portion of the long member 52, and a force toward the central portion of the tube 11 is applied to the peripheral edge portion 16 (N divided pieces 17), so that the state where the peripheral edge portion 16 covers the tube 11 is stably maintained, and the attachment of the sheet material 12 to the tube 11 is completed.

[0046] <Step 4a> The operator fits the sheet material 12 together with the tube 11 into the opening S of the metal tube P as shown in FIG. 8(A).

[0047] <Step 5a> While maintaining the state where a force directed toward the center of the tube 11 is applied to the peripheral portion 16, the operator pushes the sheet material 12 together with the tube 11 from the opening S of the metal tube P to a predetermined position inside the metal tube P, adds air into the tube 11 to expand the tube 11, fixes the sheet material 12 and the tube 11 inside the metal tube P, and closes the predetermined position inside the metal tube P with the sheet material 12. When pushing the sheet material 12 and the tube 11 to a predetermined position inside the metal tube P, the bundling portion 54 and the support member 55 are moved in accordance with the movement (movement speed and movement direction) of the sheet material 12 and the tube 11.

[0048] <Step 6a> Thereafter, as shown in FIGS. 7 and 8(B), the metal tube P and the metal tube Q are butted against each other so that the opening S of the metal tube P and the opening T of the metal tube Q face each other and come into contact. When butting the metal tube P and the metal tube Q against each other, the other end of the long member 52, the other end of the support member 55, the one end provided with the injection port 13 of the gas hose 14, and the other end of the string-like member 23 (the side opposite to the side connected to the sheet material 12) are arranged outside the metal tube P and the metal tube Q via the cylindrical body J fixed to the metal tube Q.

[0049] The other end of the support member 55 is hung on the opening of the cylindrical body J to prevent the support member 55 and the bundling portion 54 from falling. When the butting of the metal tube P and the metal tube Q is completed, each long member 52 is inserted through the through hole 53 in which the portion having a distance to one end is arranged near the center of the tube 11, and the other end is arranged in the outer space of the metal tube P, and a tension is applied to apply a force directed toward the center of the tube 11 to the N (or M) divided pieces 17.

[0050] <Step 7a> One end of the gas hose 25 is put into the vicinity of the welding portion via the cylindrical body J as shown in FIG. 8(B). After making the vicinity of the welding portion into an inert gas atmosphere by supplying an inert gas via the gas hose 25, the gas hose 25 is taken out from the vicinity of the welding portion, and the metal tube P and the metal tube Q are welded from the outside of the metal tube P and the metal tube Q to fix the metal tube Q to the metal tube P.

[0051] <Step 8a> After welding is completed, release the state in which the N long members 52 are fixed, insert (drop) the N long members 52 into the vicinity of the welding area (the space inside the metal pipes P and Q) via the cylindrical body J, pull up the support member 55 together with the bundling portion 54, and take it out from the vicinity of the welding area via the cylindrical body J. Then, discharge the air in the tube 11 via the gas hose 14, pull the gas hose 14, take out the tube 11 from the vicinity of the welding area to the outside via the cylindrical body J, and then pull the string-like object 23 to take out the sheet material 12 from the vicinity of the welding area to the outside via the cylindrical body J together with the N long members 52.

[0052] Therefore, the welding method for welding a metal object (metal pipe Q) to the opening S of the metal pipe P using the back shield jig 50 is different from the welding method using the back shield jig 10 in at least the following three points.

[0053] (1) In the third step, insert each long member 52 into the through hole 53 arranged near the center of the tube 11, apply tension to each long member 52, and make the force in the direction of the center of the tube 11 act on the N (or M, the same applies hereinafter) split pieces 17.

[0054] (2) In the fourth step, the other end portions of each long member 52 and the other end portion of the support member 55 are in a state of protruding outside from the outlet (the through hole of the cylindrical body J) provided in the metal object (metal pipe Q) in contact with the opening S, and until the fifth step, a force is applied to the region of each long member 52 protruding outside to apply tension to each long member 52.

[0055] (3) After the fifth step, insert the region that has protruded outside from the outlet of each long member 52 into the metal pipe P through the outlet, and release the force in the direction of the center of the tube 11 acting on the N split pieces 17.

[0056] As described above, the embodiments of the present invention have been described. However, the present invention is not limited to the above-described forms, and all changes and the like that do not deviate from the gist are within the scope of application of the present invention. For example, the tube may be filled with a fluid other than air (such as water). Furthermore, it is not necessary to attach the long members to all the divided pieces, and the number of long members included in the sheet temporary fixing means may be less than the number of divided pieces. A plurality of long members may be attached to one divided piece, and the number of long members included in the sheet temporary fixing means may be more than the number of divided pieces.

[0057] The metal object welded to the opening of the metal tube does not have to be a cap-shaped metal tube. For example, the metal object welded to the opening of a metal tube (hereinafter referred to as "metal tube α") may be a cylindrical metal tube (hereinafter referred to as "metal tube β"). In that case, not only inside metal tube α but also inside metal tube β, the tube and the sheet material are installed. Then, by bringing the openings of metal tube α and metal tube β where the tube and the sheet material are both installed close to each other, the space near the weld of metal tube α is restricted from the inflow of the atmosphere by the sheet material fixed inside metal tube α, metal tube β, and the sheet material fixed inside metal tube β. Also, an insertion port for taking out the tube and the sheet material or the like is provided in metal tube β (which may be metal tube α).

Explanation of Reference Numerals

[0058] 10: Back shield jig, 11: Tube, 12: Sheet material, 13: Injection port, 14: Gas hose, 15: Cap, 16: Peripheral edge, 17: Divided piece, 18: Long member, 19: Rubber string, 20: Ring portion, 21: Fastener, 22: Sheet temporary fixing means, 23: String-like object, 25: Gas hose, 50: Back shield jig, 51: Sheet temporary fixing means, 52: Long member, 53: Through hole, 54: Binding portion, 55: Support member, J: Cylindrical body, P, Q: Metal tubes, S, T: Openings

Claims

1. A back shield jig having a ring-shaped tube and a sheet material disposed in the metal tube to block the inside of the metal tube with a peripheral portion covering the tube being sandwiched between the inside of the tube and the metal tube, wherein the sheet material includes N divided pieces formed in the circumferential direction at the peripheral portion, and the peripheral portion is folded toward the center side of the tube filled with fluid over the entire circumference to cover the tube, and seat temporary fixing means for applying a force toward the center of the tube to maintain the state in which the peripheral portion covers the tube is attached to the peripheral portion with respect to M of the N divided pieces including two sets of opposing divided pieces. A back shield jig characterized by that. However, N is an integer of 4 or more, and M is an integer of 4 or more and N or less.

2. The back shield jig according to claim 1, wherein the seat temporary fixing means includes M long members respectively attached to the M divided pieces, and a fastener attached to the M long members to apply a tension toward the center of the tube to the M long members. A back shield jig characterized by that.

3. The back shield jig according to claim 2, wherein the long member has a string-shaped elastic body fixed to the divided piece on one side and a ring portion provided on the other side of the elastic body, and the fastener is linear and passes through the ring portions of the M long members respectively. A back shield jig characterized in that both side ends are connected to form an annular shape, and the M inserted ring portions are prevented from falling off.

4. The back shield jig according to claim 2, wherein the long member is a string-shaped inelastic body having one side fixed to the divided piece and a ring portion provided on the other side, and the fastener is an annular elastic member passing through the ring portion of each long member. A back shield jig characterized by that.

5. In the back shield jig according to claim 1, the sheet temporary fixing means includes M long members each having one end fixed to each of the M divided pieces, a bundling portion in which through holes are formed, and a support member having one end connected to the bundling portion and the other end disposed in the outer space of the metal tube. Each of the long members is inserted through the through hole in which a portion having a distance to the one end is disposed near the central portion of the tube, and is tensioned in a state where the other end is disposed in the outer space of the metal tube, and a force toward the central portion of the tube is applied to the M divided pieces. A back shield jig characterized by that.

6. A welding method for welding a metal object to an opening in a metal tube in a state where an opening near the opening in the metal tube is closed by a sheet material in which a peripheral portion covering a ring-shaped tube is sandwiched between the inside of the tube and the metal tube, A first step of overlapping the tube filled with fluid inside the peripheral portion of the sheet material in which N divided pieces are formed in the circumferential direction on the inner side of the peripheral portion, and folding the peripheral portion toward the central portion of the tube over the entire circumference to cover the tube with the peripheral portion; A second step of attaching the sheet material to the tube while maintaining the state where the peripheral portion covers the tube, using a sheet temporary fixing means for applying a force toward the central portion of the tube to M divided pieces including two sets of opposed divided pieces among the N divided pieces; A third step of pushing the sheet material together with the tube into the metal tube from the opening in a state where a force toward the central portion of the tube is applied to the M divided pieces; A fourth step of bringing a metal object close to the opening and restricting the inflow of air into the vicinity of the opening in the metal tube; A fifth step of supplying an inert gas to the vicinity of the opening in the metal tube to replace the air with the inert gas, and then welding the metal tube and the metal object from the outside of the metal tube. A welding method for a metal tube characterized by having. However, N is an integer of 4 or more, and M is an integer of 4 or more and N or less.

7. In the method for welding a metal tube according to claim 6, the sheet temporary fixing means includes M long members respectively attached to the M divided pieces, and a fixture attached to the M long members and applying a force toward the center of the tube to the M long members. After the third step and before the fourth step, the fixture is removed from the M long members and taken out into the outer space of the metal tube. A method for welding a metal tube, characterized by this.

8. In the method for welding a metal tube according to claim 6, each of the long members is a string member, and the sheet temporary fixing means includes M long members each having one end fixed to the M divided pieces, a bundling portion in which through holes are formed, and a support member connected to the bundling portion. In the third step, each of the long members is inserted through the through hole disposed near the center of the tube, and tension is applied to each of the long members to make the M divided pieces in a state where a force toward the center of the tube acts thereon. In the fourth step, the other ends of each of the long members and the other end of the support member are in a state of protruding outward from an outlet provided in the metal object that has come into contact with the opening, and until the fifth step, a force is applied to the region outside each of the long members to apply tension to each of the long members. After the fifth step, the region of each of the long members that has protruded outward from the outlet is inserted into the metal tube through the outlet, and the force toward the center of the tube acting on the M divided pieces is released. A method for welding a metal tube, characterized by this.

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