Abstract:
The present invention relates to a flux cored wire and the method and apparatus for manufacturing the same. The flux cored wire in accordance with the present invention can prevent the flux filled inside strip from leaking out and the moisture in the atmosphere from penetrating into the flux. The method of the present invention also does not require longer processing time. For this, the flux cored wire in accordance with the present invention is comprised of: an inner tubular body formed with flat strip by curling up the side edges of the strip into a tubular body having a seam and filed with flux inside; and an outer tubular body formed with flat strip by curling up the side edges of the strip into a tubular body having a seam and wrapping around the inner tubular body in tight contact.

Description:
FIELD OF THE INVENTION 
       [0001]    The present invention relates to a flux cored welding wire (FCW), more particularly, the flux cored welding wire with improved hydrogen crack property at low temperature and less porosity in the weldment and the method for preparing the same. 
       DESCRIPTION OF THE RELATED ART 
       [0002]    In general, flux cored wire (hereinafter, “FCW”) is a steel wire filled with flux comprising slag forming agent, arc stabilizer, deoxidizer, denitrifier, alloy substances and iron content inside the hollow part of wire for arc welding. 
         [0003]    When compared with solid wire, the FCW provides more stable arc, finer and smaller spatter particles, cleaner beads with better spreadability, and the slag is spread thoroughly, and anti-exfoliation and anti-cracking property is excellent. Due to these benefits, FCW is widely used for the butt welding and fillet welding in the ships, vehicles, bridges, architectures and other steel structures. 
         [0004]    As shown in  FIG. 1 , to manufacture the FCW described above, a steel strip  10  wound on a strip feeder is fed and progressively formed into a tubular body by passing through a plurality of primary forming rollers  21  during when the side edges of the strip are bent upwards progressively. The tubular steel strip  10  is filled with flux  30  through the flux hopper  22 , and further passed through a multiple number of secondary forming rollers  23 , wound into a round, tubular shape, passed through the drawing dies  24  and drawing drums  25 , and the finished FCW is wound on the wire reel  26 . 
         [0005]    However, the FCW produced by the conventional arts described above, as shown in  FIG. 2(   a ) or  2 ( b ), has seam  11  between the bent ends of the strip  10 , through which the atmosphere containing hydrogen may enter to be combined with the flux  30  inside, raising the hydrogen content in the welding material which can result in weld defects. In addition, the flux  30  inside the wire may leak out through the seam  11  during welding and deteriorate arc stability. 
         [0006]    Conclusively, the conventional FCW is not suitable as a low hydrogen welding material. Here, low hydrogen welding material contains  5  ml or less of hydrogen per  100  g of weldment. 
         [0007]    To this end, flux cored wires which have removed the seam  11  by welding are provided. As shown in  FIG. 3 , such seamless flux cored wires remove the seam  11 , as shown in  FIG. 3(   b ) by high frequency resistance welding or laser welding the seam  11  of the strip  10  having passed the secondary forming rollers  23  shown in  FIG. 3(   a ). Here, the device  91  of  FIG. 1  is a welder installed to remove the seam  11 . 
         [0008]    However, in the course of welding the seamless type flux cored wires with high frequency resistance welding method, the flux  30  adheres to the seam  11  due to the strong magnetic field and the vibration generated by the high speed forming work, and welded. Consequently, non-metallic flux frequently causes weld defects, leading to cut off of the wire in the wire drawing process and lower operation efficiency. 
         [0009]    The European Patent No. EP 0489167B1 discloses a method which can prevent the productivity degradation due to the weld defect, however, the method requires complicated manufacturing process and high heat treatment cost. Laser welders can be used to dissolve the complicated process where heat treatment processes are performed twice. However, this method also cannot avoid the defect caused by the flux adhering to the seam by the vibration of the process equipment. To solve this problem, Korean Patent Reg. No. 10-0821365 discloses a method where the cross section is formed by overlapping and laser welded. 
         [0010]    The Korean Patent Reg. No. 10-987346 discloses a method which the problems of the seamless flux cored wires described above by coating the entire outer surface of the flux cored wires, whose seam is not welded but the strip is bent by overlapping, with liquid resin. 
         [0011]    However, this method requires an extra process of curing the liquid resin coating. Because the curing process cannot be performed continuously with the manufacturing process of the flux cored wires, the entire processing time becomes longer. Furthermore, considering that most resins are weak to high temperature, the application of the flux cored wires at high temperature working environment is difficult. 
       SUMMARY 
       [0012]    The purpose of the present invention which is devised to solve the problems of the conventional methods described above is to provide FCW and the method and apparatus for manufacturing the same, stably preventing the leakage of the flux in the wire and infiltration of external humidity and shortening the process time. 
         [0013]    In addition, the present invention provides a low hydrogen-content welding material of 5 ml or less of hydrogen per 100 g of weldment, by preventing the source of hydrogen, that is, moisture in the atmosphere from infiltrating into the flux. The present invention also provides the manufacturing process and productivity the same as the conventional methods by enabling seam welding on the outer surface which is required to produce perfect seamless FCW necessary for surface copper coating to obtain stable arc. 
         [0014]    The FCW of the present invention devised to achieve the above objects, is characterized by being comprised of: the steel strip formed into a tubular body having a seam and filled with flux inside; and the outer tubular body formed with steel strip and having a seam, wrapping around the inner tubular body. 
         [0015]    Here, the seams of the inner tubular body and outer tubular body are arranged at different positions to prevent overlapping. 
         [0016]    In addition, the seams of the inner tubular body and outer tubular body are arranged at different positions away from each other by at least 60 degrees from the center of the tubular bodies. 
         [0017]    In addition, the FCW of the present invention is further characterized by the outer tubular body being formed in a seamless structure by removing the seam of the outer tubular body by welding. 
         [0018]    The manufacturing apparatus for the FCW in accordance with the present invention is characterized by being comprised of: A first strip feeder which feeds the steel strip from a strip roll for forming an inner tubular body; a second strip feeder which feeds the steel strip from a strip roll for forming an outer tubular body; a first forming portion of the first forming station which progressively bends upward the right and left side edges of the strip fed from the first strip feeder to form an inner tubular body having a part of the outer surface is open; a flux filling portion which fills flux into the inner tubular body formed in the first forming portion and a part of which is open; a first closing portion where the open part of the inner tubular body filled with the flux is contacted with each other; a second forming station which progressively bends upward the right and left sides of the strip fed from the second strip feeder to form an outer tubular body which wraps around the outer surface of the inner tubular body formed in the first closing portion; and a drawing portion which draws the outer tubular body formed in the second forming portion into FCW. 
         [0019]    Here, the first and the second forming stations comprise a plurality of forming rollers which process the strips into tubular bodies, respectively, and the forming rollers consisting the closing portion of the first forming station and the forming rollers consisting the second forming station form the inner tubular body and the outer tubular body in an arrangement where their seams formed by the side edges of the strips are not at the same position. 
         [0020]    In addition, the forming system further comprises a welder which welds the seam of the outer tubular body formed by the second forming station, between the second forming station and the drawing portion. 
         [0021]    The manufacturing method of the FCW in accordance with the present invention is characterized by being comprised of the steps of: the first step which forms a steel strip into an inner tubular body having hollow space inside and an open seam in the circumference, by bending the side edges progressively upwards; the second step which fills flux into the inner tubular body formed in the first forming step through the open seam; the third step which presses the open seam of the inner tubular body filled with flux in the second step, so that the side edges adhere close together; the fourth step which forms an outer tubular body by progressively bending upwards the side edges of a strip, wrapping around the inner tubular body formed in the previous step; and the fifth step which forms FCW by drawing the outer tubular body to reduce the diameter progressively. 
         [0022]    Here, the positions of the seams of the inner and outer tubular body formed by the side edges of the strips in the fourth step are characterized by being apart from each other. 
         [0023]    In addition, the method further comprises a welding step which welds the seam of the outer tubular body formed in the fourth step to form seamless structure, before the fifth step. 
         [0024]    The FCW in accordance with the present invention can stabilize the weld arc and wire feedability by preventing the moisture, which is the cause of high hydrogen content, in the atmosphere from entering the flux and the flux from leaking out during welding, because the FCW has a double tubular body structure and the seams of the tubular body are at different positions. 
         [0025]    In addition, since the seam of the outer tubular body can be removed by welding, seamless type flux cored wires can be manufactured. 
         [0026]    In addition, according to the method and apparatus for manufacturing the FCW in accordance with the present invention, the FCW having double tubular body structure can be manufactured and all of the equipments can be arranged in a continuous process system, providing the benefits of simplified line structure and improved productivity. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0027]      FIG. 1  is a structural view showing the manufacturing system of the flux cored wires in accordance with the conventional arts, 
           [0028]      FIG. 2  is a cross sectional view showing the internal structure of the flux cored wires having seams manufactured in accordance with the conventional arts, 
           [0029]      FIG. 3  is a cross sectional view showing the internal structure of the seamless type flux cored wires without seams manufactured in accordance with the conventional arts, 
           [0030]      FIG. 4  is a cross sectional view showing the internal structure of the flux cored wires having seams manufactured in accordance with a preferable embodiment of the present invention, 
           [0031]      FIG. 5  is a cross sectional view showing the internal structure of the seamless type flux cored wires without seams manufactured in accordance with a preferable embodiment of the present invention, 
           [0032]      FIG. 6  is a structural view showing the manufacturing system of the flux cored wires in accordance with a preferable embodiment of the present invention, 
           [0033]      FIG. 7  is a progressive view showing the manufacturing process of the flux cored wires in accordance with a preferable embodiment of the present invention, and 
           [0034]      FIG. 8  is a structural view showing the manufacturing system of the flux cored wires in accordance with another preferable embodiment of the present invention. 
       
    
    
     DETAILED DESCRIPTION 
       [0035]    The apparatus and method for flux cored wires in accordance with the present invention are described in further details below by referring to the accompanying drawings of  FIG. 4  to  FIG. 8 . 
         [0036]      FIG. 4  shows the cross sectional view of the FCW in accordance with a preferable embodiment of the present invention. 
         [0037]    As shown in the figure, the FCW in accordance with an embodiment of the present invention is substantially characterized by being structured with an inner tubular body  50  and an outer tubular body  60 . 
         [0038]    The structure is described in further details by the structural components. 
         [0039]    Firstly, the inner tubular body  50  is forming the inner portion of the wire and filled with flux  30  inside. 
         [0040]    The inner tubular body  50  is formed by bending the side edges  52  of strip  51  and adhering them together to have a circular cross section, and the both ends  52  of the inner tubular body  50  form a seam  53  having very narrow gap. Here, both ends  52  of the inner tubular body  50  may be formed with overlapping portion a shown in  FIG. 5 . In this case, the position of the seam  53  is the tip of the end placed on the outer surface. 
         [0041]    In addition, the quantity of the flux  30  filled in the inner tubular body  50  is preferably 30 40 wt % of the total weight including the inner tubular body  50 . 
         [0042]    This is to prevent the weld defects which may be caused in the welding works carried out using the FCW by short filling ratio (less than 30%) and the trouble in the FCW manufacturing process due to excessive filling ratio (more than 40%) and secure the ratio of the flux  30  to the entire weight of the FCW including the outer tubular body  50  within the preferable range between 12˜15%. 
         [0043]    Here, the weld defect due to excessive ratio of flux  30  refers to the degradation of productivity caused by cut off of the wire in the drawing process due to excessive flux  30  ratio. 
         [0044]    The outer tubular body  60  which is the outer circumference of the wire, wraps the inner tubular body  50  to prevent flux  30  from leaking out through the seam  53  of the inner tubular body  50  and the moisture in the atmosphere from entering the flux. 
         [0045]    The outer tubular body  60  is formed by bending the side edges  62  of strip  61  and adhering them together to have a circular cross section, and wraps over the outer circumference of the inner tubular body  50 . 
         [0046]    Here, the ends  61  of the outer tubular body  60  forms a seam  63  having very fine gap. 
         [0047]    In the embodiments of the present invention, the seam  53  of the inner tubular body  50  and the seam  63  of the outer tubular body  60  are substantially arranged at different positions. 
         [0048]    By arranging the two seams  53  and  63  at different positions, the flux  30  cannot leak out through the seam  53  of the inner tubular body  50  and the atmosphere containing moisture cannot penetrate into the flux  30  through the seam  63  of the outer tubular body  60 . 
         [0049]    For the FCW products whose seam  63  of the outer tubular body is not welded, the seam  53  of the inner tubular body  50  and the seam  63  of the outer tubular body  60  are preferably separated by at least  60  degrees with reference to the centers of the tubular bodies  50  and  60 . If the clearance angle between the two seams  53  and  63  is 60 degrees or less, the sealing effect of the outer tubular body may be insufficient due to the short distance between the seam  53  of the inner tubular body  50  and the seam  63  of the outer tubular body  60 . 
         [0050]    Considering the productivity of the manufacturing process and the guarantee for low hydrogen weld wire system, the clearance angle between the seams  53  and  63  is most preferably about 90 degrees. If the clearance angle between the seams  53  and  63  is greater than 90 degrees, the arrangement and operation of the forming rollers for forming the outer tubular body  60  become complicated and difficult. As such, the clearance angle between the seams  53  and  63  is most preferably about 90 degrees. 
         [0051]    In addition, in the preferable embodiment of the present invention, the thickness of the outer tubular body  60  is the same or greater than that of the inner tubular body  50 . 
         [0052]    This is because, while the outer tubular body  60  is exposed to the environmental impacts, such as wear or external load, the inner tubular body  50  is protected from the environmental impact by the outer tubular body  60  and the only requirement for the inner tubular body is the capability to prevent the flux from leaking out. Consequently, it is desirable that the thickness of the outer tubular body  60  is the same or greater than that of the inner tubular body  50 . 
         [0053]    Of course, the thicknesses of the inner tubular body  50  and the outer tubular body  60  should be determined appropriately taking the diameter of the whole wire into consideration. For example, in the embodiments of the present invention, the thickness of the strip  61  for the outer tubular body  60  and that of the strip  51  for the inner tubular body  50  are 0.6˜1.2 millimeters (mm) and 0.4˜0.8 mm, respectively. 
         [0054]    The wire in accordance with the embodiment of the present invention described earlier can be considered as a flux cored wire having a seam  63  because the outer tubular body  60  has a seam  63 . 
         [0055]    However, as shown in  FIG. 5 , the FCW in accordance with the embodiment of the present invention can be produced as s seamless type FCW by removing the seam  63  of the outer tubular body  60  by welding or other appropriate method. 
         [0056]    While the wire in accordance with the embodiment of the present invention described earlier can be considered as being consisted with two separate members of the inner tubular body  50  and the outer tubular body  60  which are produced with separate strips  51  and  61 , the inner tubular body  50  and the outer tubular body  60  forms substantially an integrated body in the drawing process. 
         [0057]    The manufacturing apparatus (hereinafter, “wire processing system”) for flux cored wires in accordance with the embodiment of the present invention is described below in detail. 
         [0058]    As shown in  FIG. 6 , the wire processing system in accordance with the embodiment of the present invention is substantially comprised of a first strip feeder  100 , a second strip feeder  200 , a first forming station  300 , flux filler  400 , a second forming station  500  and a drawing portion  700 . 
         [0059]    The components are described in further details below. 
         [0060]    The first strip feeder  100  feeds the steel strip  51  for forming the inner tubular body  50 . 
         [0061]    The first strip feeder  100  comprises a reel wound with the strip  51  and the thickness of the strip  51  is in the range between from 0.4 to 0.8 mm. 
         [0062]    The second strip feeder  200  feeds the steel strip  61  for forming the outer tubular body  60 . 
         [0063]    The second strip feeder  200  also comprises a reel just like the first strip feeder  100  and the thickness of the strip  61  is in the range between from 0.6 to 1.2 mm. 
         [0064]    The first forming station  300  forms the inner tubular body  50  with the strip  51  fed from the first strip feeder  100 , wherein the inner tubular body has a partially open slit. The first forming station comprises a first forming portion  310  in the strip feeder side and a first closing portion  320  in the downstream of the flux filler  400  which will be described later. 
         [0065]    The first forming portion  310  comprises a plurality of the forming rollers which form the cross section of the strip  51  into a “U” shape. For this purpose, the forming rollers are arranged on the right and left (or up and down) sides of the strip  51  along the feed direction of the strip  51  by pair-structure so that the sides of the strip  51  are bent upwards progressively towards each other. 
         [0066]    The flux filler  400  fills the inner tubular body  50  with flux  30  via the open slit formed in the first forming portion  310  and is positioned at the outlet of the first forming portion  310 . 
         [0067]    The flux filler  400  comprises a flux container (not shown) containing flux  30  and a feed belt feeding the flux  30  to the open slit of the inner tubular body  50 . 
         [0068]    The first closing portion  320  presses the open slit of the inner tubular body  50  filled with flux  30  towards each other so that the side edges of the strip adheres together tightly, and is positioned at the outlet side of the flux filler. 
         [0069]    The first closing portion  320  comprises a plurality of forming rollers (not shown) which form the inner tubular body  50  filled with the flux  30  into a circular tube shape, and the forming rollers are arranged on the right and left (or up and down) sides of the inner tubular body  50  along the feed direction of the inner tubular body  50  by paired-structure. 
         [0070]    In the embodiment, the first closing portion  320  presses the side edges  52  of the inner tubular body  50  towards each other. However, a portion of the side edges  52  of the inner tubular body  50  can be formed in an overlapping configuration, as appropriate. 
         [0071]    The second forming station  500  forms the outer tubular body  60  with the strip  61  fed from the second strip feeder  200  around the outer surface of the inner tubular body  50  filled with the flux  30  by the flux filler  400 . The second forming station is positioned in the outlet side of the first closing portion  320  of the first forming station  300 . 
         [0072]    The second forming station  500  comprises the second forming portion  510  which forms the cross section of the strip  61  into a ‘U’ shape and the second closing portion  520  which presses the ends  62  of the strip  61  formed in the second forming portion  510 . 
         [0073]    The second forming portion  510  and the second closing portion  520  of the second forming station  500  comprise a plurality of the forming rollers which form the strip  61  fed from the second strip feeder  200  into a tubular shape, and the forming rollers are arranged on the right and left (or up and down) sides of the inner tubular body  50  by paired-structure along the feed direction of the inner tubular body  50 , discharged from the first closing portion  320 . 
         [0074]    Especially, the forming rollers comprising the second closing portion  520  are so arranged that the position of the seam  63  formed between the side edges  62  of the outer tubular body  60  is different from the seal  53  formed between the side edges  52  of the inner tubular body  50  which is formed by the first closing portion  320  of the first forming station  300 . 
         [0075]    Here, the member  620  in  FIG. 6  is a guide roll which guides the inner tubular body  50  from the first closing portion  320  of the first forming station  300  into the forming rollers of the second closing portion  520  of the second forming station  500  accurately. 
         [0076]    The drawing portion  700  draws the outer tubular body  60  formed in the second forming station  500  to reduce the diameter progressively, into flux cored wire, and positioned in the outlet side of the second forming station  500 . 
         [0077]    The drawing portion  700  comprises a plurality of dies  710  and drawing drums  720 , not shown bur generally used for wire drawing. 
         [0078]    In addition, the wire processing system in accordance with the embodiment of the present invention further comprises a wire reel  800  which winds the wire from the drawing portion  700 , and the wire reel  800  is positioned in the downstream of the drawing portion  700 . 
         [0079]    The manufacturing process of the flux cored wires using the wire processing system in accordance with the embodiment of the present invention is described in further details below by referring to the accompanying drawing  FIG. 7 . 
         [0080]    In the wire processing system, the thin strip  51  for forming inner tubular body  50  is fed from the first strip feeder  100 , and the strip  51  is fed into the first forming station  300  to pass through the forming rollers of the first forming portion  310  of the first forming station  300 . 
         [0081]    In the course of the strip  51  passing through the forming rollers of the first forming portion  310 , the side edges  52  of the strip  51  are bent upwards by the forming rollers progressively, so that the cross section of the strip profile becomes a “U” shape. In this process, the strip  51  forms the inner tubular body  50  having the hollow space for filling flux  30  and a part of the circumference is open. 
         [0082]    As described earlier, the inner tubular body  50  formed in the first forming portion  310  and a part of the circumference is open then passes through the flux filler  400  where the flux  30  is filled by the flux filler  400 . The process is illustrated in  FIG. 7(   a ). 
         [0083]    In addition, the quantity of the flux filled in the inner tubular body  50  is 30˜40 wt % of the total weight including the inner tubular body  50 . 
         [0084]    This can prevent the weld defects and process reject ratio caused by insufficient flux filling ratio (less than 30%) and satisfy the ratio of the flux  30  of 12˜15% to the entire weight including the outer tubular body  50  to be formed later. 
         [0085]    The inner tubular body  50  filled with the flux  30  in the above step is fed into the first closing portion  320  of the first forming station  300  and passed through the forming rollers of the first closing portion  320  described earlier. 
         [0086]    While the inner tubular body  50  passes through the forming rollers of the first closing portion  320 , as shown in  FIG. 7(   b ), the side edges  52  of the inner tubular body  50  is bent progressively upwards by the forming rollers and closed together. As a result, the inner tubular body  50  is formed into a tube having a very small slit (seam) at the closing part, and then fed into the second forming station  500 . 
         [0087]    While the inner tubular body  50  is being formed in the above described process, the thin strip  61  for forming the outer tubular body  60  is fed by the second strip feeder  200 , and the strip  61  is passed through the second forming portion  510  and the second closing portion  520  which comprise the second forming station  500 , sequentially. 
         [0088]    While the strip  61  to be formed into the outer tubular body  60  is passed through the forming rollers of the second forming portion  510  and the second closing portion  520 , the side edges  62  of the strip are bent progressively upwards to be formed into the outer tubular body  60  which wraps around the inner tubular body  50  which is passed through the flux filler  400  and the second forming station  500 . The process is illustrated in  FIG. 7(   c ) and  FIG. 7(   d ). 
         [0089]    As a result, the outer tubular body  60  having passed through the second forming station  500  wraps around the inner tubular body  50 , as shown in  FIG. 7(   e ), and the inside of the inner tubular body  50  is filled with the flux  30 . 
         [0090]    it should be noted that, in the above described process, the seam  63  formed by the side edges  62  of the outer tubular body  60  is positioned apart from the seam  53  of the inner tubular body  50  in order to prevent the moisture in the atmosphere from penetrating into the flux  30  in the hollow of the inner tubular body  50 . 
         [0091]    The outer tubular body  60  containing the inner tubular body  50  and having passed the second forming station  500 , is fed into the drawing portion  700 . While passing through the drawing portion  700 , the diameter of the outer tubular body is reduced into the flux cored wire, as shown in  FIG. 7(   f ), which is wound on the wire reel  800  and brought out. 
         [0092]    During the drawing process conducted in the drawing portion  700 , the outer tubular body  60  and the inner tubular body  50  are reduced in diameters and become practically an integrated body without boundary interface. 
         [0093]    Though the flux cored wires produced in accordance with the method of the present invention comprises an outer tubular body  60  formed with seam  63 , the outer tubular body  60  forms practically an integrated body with the inner tubular body  50 . As such, there is no gap between the inner and outer tubular bodies through which flux  30  or air can pass. In addition, since the position of the seam  63  of the outer tubular body  60  is apart from that of the seam  53  of the inner tubular body  50 , the leak of flux  30  and infiltration of the moisture in the atmosphere can be further prevented. 
         [0094]    In addition, the method and apparatus for processing flux cored wires in accordance with the embodiment of the present invention are not limited to processing the flux cored wires with seams. 
         [0095]    They are also applicable to the production process of seamless type flux cored wires. 
         [0096]    Seamless type flux cored wires can be processed by introducing a welding portion  910  which welds the seam  63  of the outer tubular body  60  formed in the second forming station  500 , between the second forming station  500  and the drawing portion  700 , and adding the process of seam welding. 
         [0097]    The welding portion  910  can be a laser welder, high frequency resistance welder, TIG or other types of welder, as appropriate. Seamless type flux cored wires processed with the welder  910  can prevent the flux  30  from leaking out and the moisture in the atmosphere from infiltrating into he flux. In addition, the electrical conductivity between the wire and welding tip is higher resulting in more stable arc and improved wire feedability. 
         [0098]    The flux cored wires in accordance with the present invention, even not applied with the welding for seamless wire structure, can provide a welding material with low hydrogen content, and if applied with the seam welding process, ultra-low hydrogen content welding wire added with stable arc and enhanced feedability can be produced. 
       NUMBERING SCHEME OF THE MAJOR PARTS OF THE DRAWINGS 
       [0000]    
       
           30 —Flux 
           50 —Inner tubular body 
           60 —Outer tubular body 
           51 ,  61 —Strip 
           52 ,  62 —Strip sides 
           53 ,  63 —Seam 
           100 —First strip feeder 
           200 —Second strip feeder 
           300 —First forming station 
           310 —First forming portion 
           320 —First closing portion 
           400 —Flux filler 
           500 —Second forming station 
           510 —Second forming portion 
           520 —Second closing portion 
           620 —Guided roll 
           700 —Drawing portion 
           710 —Dies 
           720 —Drawing drum 
           800 —Wire reel 
           910 —Welding portion