Patent Publication Number: US-2022234127-A1

Title: Welding device for non-circular plate and producing method for non-circular plate structure

Description:
TECHNICAL FIELD 
     The present disclosure relates to a welding device for a non-circular plate and a producing method for a non-circular plate structure. 
     BACKGROUND 
     Patent Document 1 discloses the configuration of a plate structure used as a heat exchanging part provided for a shell-and-plate type heat exchanger. The plate structure is formed by laminating a number of plates each having the same outer shape and two refrigerant flow holes. As shown in FIG. 13 of Patent Document 1, a producing method for the plate structure first includes joining a pair of plates at peripheral edge portions of the refrigerant flow holes to form a pair plate. Next, the method includes laminating and arranging a plurality of pair plates, and joining outer peripheral edges of the plates arranged to face each other between the pair plates, thereby producing a plate structure constituted by at least two sets of pair plates. When the produced plate structure is used as the above-described heat exchanging part, flow paths for a first refrigerant flowing on a front-surface side of each plate and a second refrigerant flowing on a back-surface side are formed such that these refrigerants exchange heat. 
     Patent Document 2 discloses a welding device for producing a plate structure by using a non-circular plate whose curvature of an outer peripheral edge is different in the circumferential direction. The welding device welds with torch the outer peripheral edges of a plurality of laminated non-circular plates while rotating the respective plates in the circumferential direction. In the case of the non-circular plate, since the curvature of the outer peripheral edge is different in the circumferential direction, outside air is likely to enter a welded part, making it difficult to always hold a gas shielding effect by a shielding gas. The welding device disclosed in Patent Document 2 obtains the gas shielding effect by a shield nozzle including a stationary nozzle and a movable nozzle capable changing orientation. 
     CITATION LIST 
     Patent Literature 
     
         
         Patent Document 1: JP5690532B (FIG. 13) 
         Patent Document 2: WO2018-066137A1 
       
    
     SUMMARY 
     Technical Problem 
     In the welding device disclosed in Patent Document 2, the shield nozzle is disposed only downstream of the welded part in a rotation direction of the plurality of laminated plates, and thus the gas shielding effect may be decreased upstream of the welded part. Further, outside air may enter the welded part from between the stationary nozzle and the movable nozzle even downstream in the rotation direction of a plate laminated body, and the gas shielding effect may be decreased by the incoming air. 
     An object of an embodiment according to the present disclosure is to improve the gas shielding effect on the welded part by the shielding gas, when a plurality of non-circular plates whose outer shape is not a perfect circle are laminated and the outer peripheral edges of the adjacent non-circular plates are welded. 
     Solution to Problem 
     (1) A welding device for a non-circular plate according to an embodiment of the present disclosure includes a chuck for gripping and rotatably supporting a plurality of laminated non-circular plates, a welding torch for welding outer peripheral edges of adjacent non-circular plates among the plurality of laminated non-circular plates, a stationary shield box, and a movable shield box which is position-adjustable with respect to the welding torch so as to form a shield space surrounding the welding torch with the stationary shield box. 
     In the present specification, a “non-circular plate” refers to not a plate whose outer peripheral edge is composed by an arc having the same curvature in the circumferential direction like a perfect circle, but refers to a plate of a shape having a curvature which is different in the circumferential direction. For example, the non-circular plate refers to a plate of a shape whose distance from a rotation center to the outer peripheral edge is different in the circumferential direction when rotated by the chuck, like an ellipsoidal plate. For instance, the plate shape is not limited to a shape whose outer peripheral edge is composed of only arc, such as an ellipse, but may include a shape other than arc in a part of the outer peripheral edge. Further, “outer peripheral edges of adjacent non-circular plates” may simply be referred to as “adjacent plate outer peripheral edges”, and an “outer peripheral edge of a non-circular plate” may simply be referred to as a “plate outer peripheral edge”. 
     In welding, the plurality of laminated non-circular plates are gripped from both sides by the chuck and rotated. The plurality of gripped non-circular plates are welded at the adjacent plate outer peripheral edges by the welding torch while being rotated, thereby producing a plate laminated body. The plate laminated body can increase the number of plates by sequentially welding new plates. With the above configuration (1), it is possible to form a wide shield space surrounding the welding torch, by the above-described stationary shield box and the above-described movable shield box. Thus, for the welded part, it is possible to improve a gas shielding effect in an entire region in the periphery of the welded part including an upstream region in the rotation direction of the plurality of laminated non-circular plates. Further, since the movable shield box is position-adjustable with respect to the welding torch, even if a curvature of the plate outer peripheral edge greatly changes from an outer peripheral edge of the welded part in a region surrounded by the movable shield box, it is possible to dispose the movable shield box in proximity to the outer peripheral edge. Therefore, since it is possible to improve the gas shielding effect by the movable shield box, it is possible to prevent a welding defect due to occurrence of blowhole, welding scale, or the like. 
     (2) In an embodiment, in the above configuration (1), the stationary shield box is disposed so as to surround the welding torch, and the movable shield box is disposed on an outer side of the stationary shield box relative to the welding torch. 
     With the above configuration (2), it is possible to form the wide shield space in the periphery of the welding torch by the stationary shield box and the movable shield box, as well as it is possible to suppress that outside air enters the shield space by the movable shield box disposed on the outer side of the stationary shield box. Thus, it is possible to improve the gas shielding effect on the welded part. 
     (3) In an embodiment, in the above configuration (2), a pair of movable shield boxes are, respectively, disposed upstream and downstream of the stationary shield box in a rotation direction of the plurality of laminated non-circular plates. 
     With the above configuration (3), it is possible to block the outside air that enters the welded part accompanied by the rotation of the plurality of laminated non-circular plates with the movable shield box disposed upstream in the rotation direction of the non-circular plates, as well as it is possible to ensure the wide shield space downstream of the welded part with the movable shield box disposed downstream in the rotation direction. 
     Note that “the rotation direction of the plurality of laminated non-circular plates” may simply be referred to as “the rotation direction”. 
     (4) In an embodiment, in the above configuration (3), each of the pair of movable shield boxes is configured to independently be position-adjustable with respect to the welding torch. 
     With the above configuration (4), even if the curvature of the plate outer peripheral edge is different between upstream and downstream of the welded part in the rotation direction, the pair of movable shield boxes are independently position-adjustable, and thus can be disposed close to the outer peripheral edge upstream and downstream. Thus, it is possible to improve the gas shielding effect by the respective movable shield boxes. 
     (5) In an embodiment, in any one of the above configurations (1) to (4), the movable shield box is mounted on the stationary shield box to be rotatable around a support shaft disposed along a direction orthogonal to a rotation direction of the plurality of laminated non-circular plates. 
     With the above configuration (5), since the movable shield box is mounted rotatably around the above-described support shaft, the movable shield box is position-adjustable in a direction getting close to or away from the plate outer peripheral edge. Thus, the movable shield box can always be disposed in proximity to the plate outer peripheral edge in the entire circumferential region, making it possible to improve the gas shielding effect by the movable shield box. 
     (6) In an embodiment, in any one of the above configurations (1) to (5), an interior space of the stationary shield box and an interior space of the movable shield box form a continuous space. 
     With the above configuration (6), it is possible to form the wide shield space combining the interior spaces of the stationary shield box and the movable shield box in the periphery of the welding torch. Thus, it is possible to improve the gas shielding effect in the periphery of the welded part. 
     (7) In an embodiment, in the above configuration (6), the movable shield box opens to the stationary shield box and is closed on an opposite side to the stationary shield box. 
     With the above configuration (7), since the stationary shield box and the movable shield box internally form the continuous space, it is possible to form the wide shield space separated from the outside in the periphery of the welding torch. Thus, it is possible to improve the gas shielding effect in the periphery of the welded part. 
     (8) In an embodiment, in any one of the above configurations (1) to (7), the welding device for the non-circular plate is configured such that an inner surface of the movable shield box facing the plurality of laminated non-circular plates is formed into an arc shape, and a curvature radius of the inner surface is substantially the same as a curvature radius of a portion having a maximum curvature radius of the outer peripheral edges of the plurality of laminated non-circular plates. 
     With the above configuration (8), since the curvature radius of the inner surface of the movable shield box coincides with the maximum curvature radius of the plate outer peripheral edge, it is possible to minimize a gap between the plate outer peripheral edge and the inner surface of the movable shield box in the entire circumferential region of the outer peripheral edge. Thus, it is possible to improve the gas shielding effect by the movable shield box. 
     (9) In an embodiment, in any one of the above configurations (1) to (8), the welding device for the non-circular plate includes an actuator for enabling position adjustment of the movable shield box with respect to the welding torch. 
     With the above configuration (9), by the above-described actuator, the movable shield box can always be disposed proximately over the entire circumference of the plate outer peripheral edge. Thus, it is possible to improve the gas shielding effect by the movable shield box. 
     (10) In an embodiment, in the above configuration (9), the welding device for the non-circular plate includes a control part for controlling an operation of the actuator based on a rotation angle of the chuck. 
     With the above configuration (10), since the operation of the actuator is controlled by the above-described control part based on the rotation angle of the chuck, the movable shield box can always be disposed proximately over the entire circumference of the plate outer peripheral edge. Thus, it is possible to improve the gas shielding effect by the movable shield box. 
     (11) In an embodiment, in any one of the above configurations (1) to (10), one of the stationary shield box and the movable shield box is configured to be insertable into the other. 
     With the above configuration (11), the movable shield box can undergo position adjustment without interfering with the stationary shield box, and even if the movable shield box moves relatively to the stationary shield box, the gap where outside air enters is not formed between the stationary shield box and the movable shield box. 
     (12) In an embodiment, in the above configuration (11), the movable shield box is mounted on the stationary shield box to be rotatable around a support shaft disposed along a direction orthogonal to a rotation direction of the plurality of laminated non-circular plates, and at least a part of the movable shield box is configured to be insertable into the stationary shield box, and at least a part of the movable shield box is formed into an arc shape centered on the support shaft. 
     With the above configuration (12), since the section of the movable shield box inserted into the stationary shield box is formed into the arc shape centered on the above-described support shaft, the movable shield box inserted into the stationary shield box is always maintained at a certain distance from the above-described support shaft. Therefore, it is possible to minimize the gap between the stationary shield box and the movable shield box, making it possible to suppress that outside air enters from between the stationary shield box and the movable shield box. 
     (13) In an embodiment, in any one of the above configurations (1) to (12), the stationary shield box and the movable shield box are each provided with a shielding gas supply nozzle. 
     With the above configuration (13), it is possible to uniquely adjust and supply shielding gas amounts needed for the stationary shield box and the movable shield box, respectively. Thus, it is possible to improve the gas shielding effect by the stationary shield box and the movable shield box. 
     (14) In an embodiment, in any one of the above configurations (1) to (13), the chuck supports the plurality of laminated non-circular plates in a horizontal position, and the welding torch is disposed above the plurality of laminated non-circular plates and configured to be able to perform downward welding. 
     When the welding torch is in a horizontal position and performs welding in the horizontal position, a subtle disturbance such as sag is likely to occur in a welding bead under the influence of gravity, which is likely to cause poor welding. To cope therewith, with the above configuration (14), since the welding torch can perform downward welding on the plurality of laminated non-circular plates, it is possible to resolve disturbance in the welding bead under the influence of gravity. 
     (15) A producing method for a non-circular plate structure according to an embodiment includes a positioning step of performing positioning by laminating at least two sets of pair plates, each of which is constituted by a pair of non-circular plates joined such that outer peripheral edges thereof are superimposed in a front view, such that the outer peripheral edges of the non-circular plates are butted between the two sets of pair plates, a welding step of welding, with a welding torch, the outer peripheral edges butted to each other, while rotating the at least two sets of pair plates in a circumferential direction of the pair plates, and a shield step of shielding a periphery of the welding torch by a stationary shield box for the welding torch and a movable shield box which is position-adjustable with respect to the welding torch, in the welding step. 
     With the above method (15), during welding, it is possible to form a wide shield space surrounding the welding torch, by the stationary shield box and the movable shield box. Thus, it is possible to improve the gas shielding effect in the entire region in the periphery of the welded part including the upstream region of the welded part in the rotation direction. Further, since the movable shield box is position-adjustable with respect to the welding torch, performing position adjustment on the movable shield box in accordance with the curvature of the plate outer peripheral edge, it is possible to dispose the movable shield box in proximity to the plate outer peripheral edge over the entire circumference of the plate outer peripheral edge. Thus, it is possible to improve the gas shielding effect. 
     Advantageous Effects 
     According to some embodiments, it is possible to improve a gas shielding effect by a shielding gas in a wide region in the periphery of a welded part, when outer peripheral edges of adjacent plates among a plurality of laminated non-circular plates are welded. Therefore, it is possible to suppress a welding defect due to occurrence of blowhole or the like. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         FIG. 1  is an explanatory diagram showing an operation procedure of a welding device according to an embodiment. 
         FIG. 2  is a side view of the welding device according to an embodiment. 
         FIG. 3  is a front view of a welding torch composing the above-described welding device. 
         FIG. 4  is an enlarged front view showing a part of the above-described welding torch by a cross-section. 
         FIG. 5  is a perspective view of the above-described welding torch. 
         FIG. 6  is a process drawing showing a producing process for a non-circular plate structure according to an embodiment. 
         FIG. 7  is a flowchart showing a welding method for the non-circular plate structure according to an embodiment. 
         FIG. 8  is a front view showing an operating state of the above-described welding torch. 
         FIG. 9  is a cross-sectional view of the center of the welding torch according to an embodiment. 
         FIG. 10  is a process drawing showing the operation of the above-described welding torch in sequence. 
     
    
    
     DETAILED DESCRIPTION 
     Some embodiments of the present invention will be described below with reference to the accompanying drawings. It is intended, however, that unless particularly identified, dimensions, materials, shapes, relative positions and the like of components described or shown in the drawings as the embodiments shall be interpreted as illustrative only and not intended to limit the scope of the present invention. 
     For instance, an expression of relative or absolute arrangement such as “in a direction”, “along a direction”, “parallel”, “orthogonal”, “centered”, “concentric” and “coaxial” shall not be construed as indicating only the arrangement in a strict literal sense, but also includes a state where the arrangement is relatively displaced by a tolerance, or by an angle or a distance whereby it is possible to achieve the same function. 
     Further, for instance, an expression of a shape such as a rectangular shape or a cylindrical shape shall not be construed as only the geometrically strict shape, but also includes a shape with unevenness or chamfered corners within the range in which the same effect can be achieved. 
     On the other hand, an expression such as “comprise”, “include”, “have”, “contain” and “constitute” are not intended to be exclusive of other components. 
       FIG. 1  is an explanatory diagram showing an operation procedure of a welding device  10  for a non-circular plate according to an embodiment.  FIG. 2  is a side view of the welding device  10 .  FIG. 3  is a front view of a welding torch for the welding device  10 ,  FIG. 4  is an enlarged front view showing a part of the same by a cross-section, and  FIG. 5  is a perspective view of the same. As shown in  FIGS. 1 and 2 , the welding device  10  includes a chuck  12  for gripping a plurality of laminated non-circular plates  100  from both sides in a lamination direction and for rotatably supporting the plurality of non-circular plates, and a welding torch  16  for welding adjacent plate outer peripheral edges of the plurality of non-circular plates  100  gripped by the chuck  12 . The chuck  12  rotates about the axis of a rotational shaft  18  (a rotation center O in  FIG. 2 ) along the lamination direction of the non-circular plates  100  and rotates the plurality of laminated non-circular plates  100 . 
     As shown in  FIGS. 3 and 4 , the welding device  10  includes a stationary shield box  28  and a movable shield box  30 . The movable shield box  30  is configured to be position-adjustable with respect to the welding torch  16  so as to form a shield space s surrounding the welding torch  16  with the stationary shield box  28 . 
     In welding, the plurality of laminated non-circular plates  100  are gripped from both sides by the chuck  12  and rotated, and the adjacent plate outer peripheral edges are welded by the welding torch  16  while being rotated. Thus, the new non-circular plates  100  are sequentially welded with respect to a non-circular plate laminated body  102  (may simply be referred to as the “laminated body  102 ”, hereinafter) including the at least two non-circular plates  100  by using the welding device  10 , making it possible to increase the number of non-circular plates of the laminated body  102 . Further, by the stationary shield box  28  and the movable shield box  30 , it is possible to form the wide shield space s (a shield space combining an interior space s (s 1 ) of the stationary shield box  28  and an interior space s (s 2 ) of the movable shield box  30 ) surrounding the welding torch  16 , during welding. Thus, for the welded part, it is possible to improve a gas shielding effect in an entire region in the periphery of the welded part including an upstream region in the rotation direction. Further, since the movable shield box  30  is position-adjustable with respect to the welding torch  16 , even if a curvature of the plate outer peripheral edge greatly changes from an outer peripheral edge of the welded part in a region surrounded by the movable shield box  30 , it is possible to dispose the movable shield box  30  in proximity to the plate outer peripheral edge. Therefore, since it is possible to improve the gas shielding effect by the movable shield box  30 , it is possible to prevent a welding defect due to occurrence of blowhole or the like. 
     The laminated body  102  produced through the above-described welding process is used as, for example, a heat exchanging part of a shell-and-plate type heat exchanger.  FIG. 1  also shows a producing process for a non-circular plate structure  102  ( 102   a ) (may simply be referred to as the “structure  102  ( 102   a )”. hereinafter) produced by welding the outer peripheral edges of the adjacent non-circular plates  100  among the plurality of pair plates, as an embodiment of the laminated body  102 . 
       FIG. 6  shows a producing process for the structure  102  ( 102   a ). In each of the plurality of non-circular plates  100  constituting the structure  102 ( 102   a ), protrusions and recesses  104  having a waveform cross-section are formed. In the non-circular plate  100 , two refrigerant flow holes  108  whose phases are different by 180 degrees with reference to the center of a plate surface are formed in the vicinity of an outer peripheral edge  106 . The outer peripheral edge  106  and inner peripheral edges  110  forming the refrigerant flow holes  108  are formed in a narrow annular flat surface connected to the protrusions and recesses  104 . A plate-like body forming a flat surface of the outer peripheral edge  106  and plate-like bodies forming flat surfaces of the inner peripheral edges  110  have a height difference by a step between the protrusion and the recess of the protrusions and recesses  104 . 
     First, the two non-circular plates  100  are superimposed with back surfaces thereof being opposite to each other (with the protrusions or the recesses of the protrusions and recesses  104  being arranged back-to back), and the inner peripheral edges  110  of the two refrigerant flow holes  108  arranged to face each other are circumferentially welded as indicated by an arrow u, thereby producing a pair plate  112 . At this time, between the outer peripheral edges  106  of the adjacent non-circular plates  100 , a clearance c is formed which is twice the size of the step between the protrusion and the recess of the protrusions and recesses  104  formed in the non-circular plates  100 . In the next step, a number of pair plates  112  are superimposed, the outer peripheral edges  106  of the adjacent pair plates  112  are brought into contact with each other, and a contact surface is circumferentially welded as indicated by an arrow v. The structure  102  ( 102   b ) is thus produced. The structure  102  ( 102   b ) is housed in a hollow container of the shell-and-plate type heat exchanger, and is immersed in a refrigerant stored in the hollow container. 
     As described above, the structure  102  ( 102   a ) is produced by alternately welding the inner peripheral edges  110  of the refrigerant flow holes  108  and the outer peripheral edges  106  of the plurality of non-circular plates  100  in the lamination direction. Consequently, on one surface side of each non-circular plate  100 , a first flow path opened to an interior space of the above-described hollow container, and a second flow path closed with respect to the interior space of the hollow container and communicating with the refrigerant flow holes  108  are formed. Then, a first refrigerant flowing through the first flow path and a second refrigerant flowing through the second flow path can exchange heat via each non-circular plate  100 . 
     In the embodiment shown in  FIG. 2 , the chuck  12  grips the inner peripheral edge  110  of the non-circular plate  100  with clicks  13 . The laminated body  102  rotates about the rotation center O that coincides with the axis of the rotational shaft  18  along the lamination direction of the non-circular plates  100 . 
     In an embodiment, as shown in  FIG. 2 , a support  14  is constituted by a support roller. Thus, since the support  14  can rotatably supports the laminated body  102 , with the welding torch  16  fixed at a fixed position on the outer side of the laminated body  102 , it is possible to easily weld the adjacent plate outer peripheral edges while rotating the laminated body  102 . 
     In an embodiment, the above-described support roller is configured to be able to make a driven rotation in accordance with a rotation of the laminated body  102 . Thus, the rotating laminated body  102  is supported easily. 
     In an embodiment, the support  14  is constituted by the first support  14  ( 14   a ) and the second support  14  ( 14   b ) disposed on both sides of a vertical surface Sv across the vertical surface Sv passing through the rotation center O of the chuck  12 . The non-circular plate  100  is supported by the first support  14  ( 14   a ) and the second support  14  ( 14   b ), making it possible to stably support the laminated body  102 . 
     In the non-circular plate  100 , a distance from the rotation center O to the outer peripheral edge  106  is different in the circumferential direction. Thus, in an embodiment, the support  14  is configured to be able to adjust a support height in accordance with a rotation angle of the chuck  12 . Thus, the chuck  12  can support the laminated body  102  while holding the rotation center O at the fixed position. 
     In an embodiment, as shown in  FIG. 1 , the chuck  12  is constituted by a pair of chucks  12  ( 12   a,    12   b ) for gripping the laminated body  102  to be sandwiched from both sides in the axial direction. The pair of chucks  12  ( 12   a,    12   b ) are mounted on stands  20  ( 20   a,    20   b ), respectively. The stands  20  ( 20   a,    20   b ) are disposed on a base  22 , on an upper surface of the base  22 , a rail  24  is disposed along a direction of an arrow a, and the one stand  20  ( 20   a ) is slidable on the rail  24 . Further, the support  14  is supported by a common frame  26  with the stand  20  ( 20   a ), and is slidable on the rail  24  together with the stand  20  ( 20   a ). Thus, the pair of chucks  12  ( 12   a ) approaches the other chuck  12  ( 12   b ) to grip the laminated body  102  with the chuck  12  ( 12   b ), or separates from the other chuck  12  ( 12   b ), thereby being able to cancel gripping of the laminated body  102 . A drive part (not shown) for rotating the chuck  12  ( 12   a,    12   b ) is disposed in the stand  20  ( 20   a,    20   b ). 
     In an embodiment, as shown in  FIG. 5 , the stationary shield box  28  is disposed so as to surround the welding torch  16 . Further, the movable shield box  30  is disposed on the outer side of the stationary shield box  28  relative to the welding torch  16 . It is possible to form the wide shield space s (s 1 +s 2 ) in the periphery of the welding torch  16  by the stationary shield box  28  and the movable shield box  30 , as well as it is possible to suppress that outside air enters the shield space s by the movable shield box  30  disposed on the outer side of the stationary shield box  28 . Thus, it is possible to improve the gas shielding effect on the welded part. 
     In  FIGS. 3 and 4 , a direction of an arrow b indicates the rotation direction of the non-circular plate  100 . In an embodiment, as shown in  FIGS. 3 and 4 , a pair of movable shield boxes  30  ( 30   a,    30   b ) are, respectively, disposed upstream and downstream of the stationary shield box  28  in the rotation direction of the non-circular plate  100 . Thus, it is possible to block the outside air that enters the welded part accompanied by the rotation of the non-circular plate  100  with the movable shield box  30  ( 30   a ) disposed upstream in the rotation direction, as well as it is possible to ensure the wide shield space s downstream of the welded part with the movable shield box  30  ( 30   b ) disposed downstream in the rotation direction. 
     A producing method for the structure  102  ( 102   a ) according to an embodiment performs steps S 10  to S 16  shown in  FIG. 7 . First, in the preparation step S 10 , at least two sets of pair plates  112  are prepared. That is, as shown in  FIG. 6 , the inner peripheral edges  110  are joined in a state where the two non-circular plates  100  are in a positional relationship where the outer peripheral edges  106  are superimposed in a front view, thereby forming one set of pair plates  112 . Next, the laminated body  102 , which is positioned by laminating the two sets of pair plates  112  such that the outer peripheral edges of the adjacent non-circular plates  100  among the pair plates  112  are butted to each other, is gripped from both sides in the lamination direction (positioning step S 12 ). The outer peripheral edges butted to each other are welded with the welding torch  16  while rotating the two sets of pair plates  112  gripped by the chuck  12  ( 12   a,    12   b ) around the axis of the rotational shaft  18  (rotation center O) (welding step S 14 ). In the welding step S 14 , the periphery of the welding torch  16  is shielded by the stationary shield box  28  surrounding the welding torch  16  and the movable shield box  30  which is position-adjustable with respect to the welding torch  16  (shield step S 16 ). 
     With the above method, during welding, it is possible to form the wide shield space s (the space combining the interior space s (s 1 ) of the stationary shield box  28  and the interior space s (s 2 ) of the movable shield box  30 ) surrounding the welding torch  16 . Thus, it is possible to improve the gas shielding effect in the entire region in the periphery of the welded part including the upstream region of the welded part in the rotation direction. Further, since the movable shield box  30  is position-adjustable with respect to the welding torch  16 , with position adjustment in accordance with the curvature of the plate outer peripheral edge  106 , it is possible to dispose the movable shield box  30  in proximity to the plate outer peripheral edge  106  over the entire circumference of the plate outer peripheral edge  106 . Thus, it is possible to improve the gas shielding effect. 
       FIG. 8  shows the operation of the welding torch  16  during welding. As shown in  FIG. 8 , even if the curvature of the plate outer peripheral edge  106  changes in the circumferential direction, the position of the movable shield box  30  is adjusted in accordance with the curvature of the plate outer peripheral edge  106 , making it possible to proximately dispose the movable shield box  30  in the entire circumferential region of the plate outer peripheral edge  106 . Therefore, it is possible to improve the gas shielding effect by the movable shield box  30 . 
     The producing direction for the structure  102  ( 102   a ) using the welding device  10  according to an embodiment will be described with reference to  FIG. 1 . In step (1), the structure  102  ( 102   a ) , which includes the at least two sets of pair plates  112  constituted by the plurality of pair plates  112  and welded at the plate outer peripheral edges, has already been produced and is supported by the support  14 . A new one set of pair plates  112  to be welded to the structure  102  ( 102   a ) is supplied thereto. At this time, the stand  20  ( 20   a ) is at a position retreated from the stand  20  ( 20   b ). In step (2), the stand  20  ( 20   a ) approaches the stand ( 20   b ) to position the pair plate  112  such that outer peripheral edges of the adjacent non-circular plates  100  among the pair plate  112  disposed in an end portion of the structure  102  ( 102   a ) are butted to each other. 
     In step (3), the welding torch  16  is disposed on the outer side of the plate outer peripheral edges butted to each other, and the welding torch  16  welds the entire circumference of the outer peripheral edges butted to each other while rotating the chuck  12  ( 12   a,    12   b ) about the rotational shaft  18 . After the end of welding, in step (4), gripping of the pair plate  112  by the chuck  12  ( 12   b ) is canceled, and the stand  20  ( 20   a ) is retreated from the stand  20  ( 20   b ). 
       FIG. 9  shows one configuration example of an internal structure of the center of the welding torch. The welding torch  16  includes a tungsten electrode  32  at the center, and performs arc welding in which a voltage is applied to the tungsten electrode  32  and a welded part W (the adjacent plate outer peripheral edges  106  butted to each other) to form an arc Ac between the tungsten electrode  32  and the welded part W. The welded part W is melted by heat of the arc Ac to form a weld pool Wp, thereby welding the plate outer peripheral edges. A center nozzle  34  is disposed around the tungsten electrode  32 , and a center gas g 1  for forming the arc Ac is supplied from the inner side of the center nozzle  34  toward the welded part W. Further, a shield nozzle  36  is concentrically disposed on the outer side of the center nozzle  34 , and a shielding gas g 2  is supplied from the inner side of the shield nozzle  36  toward the welded part W. 
     In an embodiment, as shown in  FIGS. 3 and 4 , the pair of movable shield boxes  30  ( 30   a,    30   b ) are each configured to independently be position-adjustable with respect to the welding torch  16 . As shown in  FIG. 8 , the curvature of the outer peripheral edge  106  is not always the same upstream and downstream of the welded part in the rotation direction. According to the present embodiment, even if the curvature of the outer peripheral edge  106  is different between upstream and downstream of the welded part in the rotation direction, the pair of movable shield boxes  30  ( 30   a,    30   b ) are independently position-adjustable, and thus can be disposed close to the plate outer peripheral edge  106  upstream and downstream of the welded part. Thus, it is possible to improve the gas shielding effect by the respective movable shield boxes  30  ( 30   a,    30   b ). 
     In an embodiment, as shown in  FIGS. 3 and 4 , the movable shield box  30  is mounted on the stationary shield box  28  to be rotatable about a support shaft  40  disposed along a direction orthogonal to the rotation direction (the direction of the arrow b) of the non-circular plate  100 . Thus, the movable shield box  30  is position-adjustable in a direction getting close to or away from the plate outer peripheral edge  106 . Thus, the movable shield box  30  can always be disposed in proximity to the plate outer peripheral edge  106  in the entire circumferential region of the plate outer peripheral edge  106 , making it possible to improve the gas shielding effect by the movable shield box  30 . 
     In an embodiment, as shown in  FIGS. 3 and 4 , the interior space s (s 1 ) of the stationary shield box  28  and the interior space s (s 2 ) of the movable shield box  30  form a continuous space. Thus, it is possible to form the wide shield space s (s 1 +s 2 ) separated from the outside in the periphery of the welding torch  16 , making it possible to improve the gas shielding effect in the periphery of the welded part. 
     In an embodiment, as shown in  FIGS. 3 and 4 , the movable shield box  30  opens to the stationary shield box  28  and is closed on an opposite side to the stationary shield box  28 . Thus, the stationary shield box  28  and the movable shield box  30  internally form the continuous shield space s (s 1 +s 2 ), making it possible to form the wide shield space s separated from the outside in the periphery of the welding torch  16 . Thus, it is possible to improve the gas shielding effect in the periphery of the welded part. 
     In an embodiment, as shown in  FIGS. 3 and 4 , the welding device is configured such that an inner surface  42  of the movable shield box  30  facing the outer peripheral edge of the non-circular plate  100  is formed into an arc shape, and a curvature radius of the inner surface  42  is substantially the same as a curvature radius of a portion having a maximum curvature radius of the outer peripheral edge of the non-circular plate  100 . Thus, since the curvature radius of the inner surface  42  of the movable shield box  30  coincides with the maximum curvature radius of the plate outer peripheral edge  106 , it is possible to minimize a gap between the plate outer peripheral edge  106  and the inner surface  42  of the movable shield box  30  in the entire circumferential region of the plate outer peripheral edge  106 . Thus, it is possible to improve the gas shielding effect by the movable shield box  30 . 
     Note that “substantially the same” means that the ratio between the inner surface  42  of the movable shield box  30  ad the maximum curvature radius of the outer peripheral edge  106  falls within ±5%. However, the ratio preferably falls within ±3%. 
     In an embodiment, as shown in  FIG. 3 , the welding device  10  includes an actuator  44  for enabling position adjustment of the movable shield box  30  with respect to the welding torch  16 . Thus, the movable shield box  30  can always be disposed proximately over the entire circumference of the plate outer peripheral edge  106 . Thus, it is possible to improve the gas shielding effect by the movable shield box  30 . 
     In an embodiment, as shown in  FIG. 3 , the actuator  44  includes a servomotor  46 , and a ball screw  48  moving vertically in engagement with an output shaft of the servomotor  46 . The ball screw  48  has a lower end portion connected to the movable shield box  30  ( 30   a,    30   b ) via a link bar  50 . Since the ball screw  48  is moved vertically by the operation of the servomotor  46 , the movable shield box  30  ( 30   a,    30   b ) rotates in the direction getting close to or away from the plate outer peripheral edge  106  with the support shaft  40  serving as a fulcrum. 
     In an embodiment, as shown in  FIG. 3 , the welding device  10  includes a control part  52  for controlling the operation of the actuator  44  based on a rotation angle θ of the chuck  12 . The rotation angle θ refers to an angle at which the non-circular plate  100  rotates clockwise about the rotation center O from a state of the non-circular plate  100  shown in  FIG. 2  where θ=0°  FIG. 10  shows the welding torch  16  operating in accordance with transition of the rotation angle θ. As shown in  FIG. 10 , the control part  52  performs position adjustment such that the inner surface  42  of the movable shield box  30  ( 30   a,    30   b ) approaches the plate outer peripheral edge  106  in accordance with the rotation angle θ. Thus, the operation of the actuator  44  is controlled by the control part  52  based on the rotation angle θ of the chuck  12 , the movable shield box  30  can always be disposed in proximity to the plate outer peripheral edge  106 . Thus, it is possible to improve the gas shielding effect by the movable shield box  30 . 
     In an embodiment, as shown in  FIG. 3 , since the control part  52  controls the operation of the servomotor  46 , the movable shield box  30  can always be disposed in proximity to the plate outer peripheral edge  106 . 
     In an embodiment, control is performed such that the axis of the welding torch  16  coincides with a normal line L orthogonal to a tangent to the plate outer peripheral edge  106 . Thus, position adjustment of the pair of movable shield boxes  30  ( 30   a,    30   b ) becomes easy. 
     In an embodiment, as shown in  FIGS. 3 to 5 , one of the stationary shield box  28  and the movable shield box  30  is configured to be insertable into the other. Thus, the movable shield box  30  can undergo position adjustment without interfering with the stationary shield box  28 , and even if the movable shield box  30  moves relatively to the stationary shield box  28 , the gap where outside air enters is not formed between the stationary shield box  28  and the movable shield box  30 . 
     In an embodiment, as shown in  FIG. 4 , at least a part of the movable shield box  30  is configured to be insertable into the stationary shield box  28 , and at least a part of the movable shield box  30  is formed into an arc shape centered on the support shaft  40 . Thus, since the section of the movable shield box  30  inserted into the stationary shield box  28  is formed into the arc shape centered on the support shaft  40 , the movable shield box  30  inserted into the stationary shield box  28  is always maintained at a certain distance from the support shaft  40 . Therefore, it is possible to minimize the gap between the stationary shield box  28  and the movable shield box  30 , making it possible to suppress that outside air enters from between the stationary shield box  28  and the movable shield box  30 . 
     In an embodiment, as shown in  FIG. 4 , the stationary shield box  28  and the movable shield box  30  are provided with shielding gas supply nozzles  54  and  56 , respectively. Thus, it is possible to uniquely adjust and supply shielding gas amounts needed for the stationary shield box  28  and the movable shield box  30 , respectively. Thus, it is possible to improve the gas shielding effect by the stationary shield box  28  and the movable shield box  30 . 
     In an embodiment, the shielding gas supply nozzle  54  has an axis vertically disposed in the stationary shield box  28 , and shielding gas outlets are formed at intervals of 90° in the circumferential direction of a nozzle pipe, thereby configuring such that the shielding gas is injected in four directions from the nozzle pipe. Further, the shielding gas supply nozzle  56  is horizontally disposed in the movable shield box  30 , and shielding gas outlets are formed at intervals of 90° in top and sides, except for bottom, of a nozzle pipe, thereby configuring such that the shielding gas is injected in three directions of the top and sides of the nozzle pipe. Thus, direct spray to the welded part of the shielding gas injected from the shielding gas supply nozzle  56  is avoided, suppressing disturbance in a welding bead by the shielding gas. 
     In an embodiment, as shown in  FIG. 1 , the chuck  12  supports the non-circular plate  100  or the laminated body  102  in the horizontal position. Further, the welding torch  16  is disposed above the non-circular plate  100  or the laminated body  102 , and configured to be able to perform downward welding. When the welding torch  16  is disposed in the horizontal position and welds the plate outer peripheral edges  106  of the non-circular plates  100  or the laminated body  102 , a subtle disturbance such as sag is likely to occur in the welding bead under the influence of gravity, which is likely to cause poor welding. To cope therewith, in the present embodiment, since the welding torch  16  is disposed in a downward position and performs downward welding, it is possible to resolve disturbance in the welding bead under the influence of gravity. 
     INDUSTRIAL APPLICABILITY 
     According to some embodiments, when outer peripheral edges of non-circular plates are welded, it is possible to improve a shielding effect on a welded part by a shielding gas, and thus to prevent a welding defect due to occurrence of a blow hole, welding scale, or the like. 
     REFERENCE SIGNS LIST 
     
         
           10  Welding device 
           12  ( 12   a,    12   b ) Chuck 
           13  Click 
           14  ( 14   a,    14   b ) Support 
           14   a  First support 
           14   b  Second support 
           16  Welding torch 
           18  Rotational shaft 
           20  ( 20   a,    20   b ) Stand 
           22  Base 
           24  Rail 
           26  Frame 
           28  Stationary shield box 
           30  ( 30   a,    30   b ) Movable shield box 
           32  Tungsten electrode 
           34  Center nozzle 
           36  Shield nozzle 
           40  Support shaft 
           42  Inner surface 
           44  Actuator 
           46  Servomotor 
           48  Ball screw 
           50  Link bar 
           52  Control part 
           54 ,  56  Shielding gas supply nozzle 
           100 A Non-circular plate 
           102  Non-circular plate laminated body 
           102  ( 102   a ) Non-circular plate structure 
           104  Waveform protrusions and recesses 
           106  Outer peripheral edge 
           108  Refrigerant flow hole 
           110  Inner peripheral edge 
           112  Pair plate 
         Ac Arc 
         L Normal line 
         O Rotation center 
         W Welded part 
         Wp Weld pool 
         c Clearance 
         g 1  Center gas 
         g 2  Shielding gas 
         s Shield space 
         s (s 1 ), s (s 2 ) Interior space 
         θ Rotation angle