Abstract:
A heat exchanger which employs porous tubes wherein tube melting at the time of attaching the porous tubes to the header tanks is prevented, the heat exchanger provided with an entry header tank which has an inflow port, an exit header tank which has an outflow port, and a plurality of tubes having passages for refrigerant flowing between the entry header tank and the exit header tank, the tubes being porous tubes which are formed by bending or rolling from flat sheets and being brazed at the two end parts to the entry header tank and exit header tank, wherein the outer surfaces of the tubes are provided with brazing materials which are used for brazing to the entry header tank and exit header tank and wherein the inner surface and outer surface of the entry header tank and exit header tank are made brazing material-free.

Description:
TECHNICAL FIELD 
       [0001]    The present invention relates to a parallel flow type of heat exchanger which is arranged at the front in an engine room of a vehicle and which is provided with porous tubes constituted by inner fin tubes. 
       BACKGROUND ART 
       [0002]    In a heat exchanger which is applied to a refrigerant condenser of an air-conditioning system for automobile use, a structure which is comprised of a plurality of porous tubes which are fabricated by extrusion and are inserted at their two sides into header plates of header tanks at predetermined intervals and which is provided with outer fins for heat dissipation use between the porous tubes and other porous tubes has been employed. However, in recent years, due to the demand for reducing costs of heat exchangers, the most costly parts, the porous tubes, are being fabricated by, instead of extrusion, sheet forming for bending belt-shaped sheet members to form tubes and providing inner fins at the insides so as to simplify the method of production, lighten the weight, and reduce the costs. 
         [0003]    Porous tubes which are obtained by sheet forming for bending belt-shaped sheet members to form tubes and providing inner fins at the insides are called “inner fin tubes”. A heat exchanger which employs such inner fin tubes is disclosed in PLT 1. The biggest advantages of production of inner fin tubes by sheet forming of belt-shaped sheet members are the ease of reducing weight by suitably setting the sheet thickness and the greater degree of freedom of shaping than the extrusion method and therefore the enlarged heat conduction area etc. and consequent ability to improve the heat exchange performance of the heat exchanger. 
         [0004]    A heat exchanger which uses the inner fin tubes which are shown in PLT 1 etc. is for use for air-conditioning systems for vehicular use. Its configuration is shown simplified in  FIG. 1 . The heat exchanger  1  is provided with a core part  2 , entry side header tank  3 , and exit side header tank  4  which are brazed together. The core part  2  is comprised of a plurality of inner fin tubes  10  and a plurality of outer fins  20  alternately stacked and reinforcing members constituted by side plates  25  at the end parts at the two sides in the stacking direction (up-down direction in figure). In the heat exchanger  1 , the air which is blown through the core part  2  is used to cool the refrigerant which flows through the insides of the inner fin tubes  10 . 
         [0005]    At the insides of the entry side header tank  3  and exit side header tank  4 , in this example, separators  26  are provided. At the two end parts, caps  23  and  24  which close the opening parts of the header tanks are brazed. The insides of the entry side header tank  3  and exit side header tank  4  are separated by the separators  26  into a plurality of spaces. Further, the entry side header tank  3  has an inflow port  21  for the refrigerant, while the exit side header tank  4  has an outflow port  22  for the refrigerant. Further, the refrigerant which flows from the inflow port  21  to the inside of the heat exchanger  1  flows through the insides of the entry side header tank  3  and exit side header tank  4  which are separated by the separators  26  and the insides of the inner fin tubes  10  as shown by the broken lines and discharged from the outflow part  22 . Note that, the number of the inner fin tubes  10  and the number of the separators  26  which are shown in  FIG. 1  are examples and do not show the numbers and flow paths of refrigerant in an actual heat exchanger  1 . 
         [0006]      FIG. 2  explains the configuration of the inside of an inner fin tube  10  of the heat exchanger  1  which is shown in  FIG. 1  and the flow path of refrigerant which flows through the inside of it. The inner fin tube  10  is comprised of a tube  11  formed with a cross-section wave-shaped inner fin  12  inserted in it. The tube  11  is a tube member with a horizontal cross-section of a flat shape (shape close to oval shape) perpendicular to the longitudinal direction (flow path direction of refrigerant) obtained by bending a thin (for example thickness 0.2 mm) aluminum belt-shaped sheet member. 
         [0007]    Specifically, the tube  11  is comprised of a belt-shaped sheet member with a center part which is bent into an arc to form a curved end part  11   a  and with parallel parts  11   p  which extend from this curved end part  11   a  to form a swaged part  11   b  at the end part at the opposite side from the curved end part  11   a  of the parallel parts  11   p.  At this time, the two end parts of the belt-shaped sheet member are made different in lengths from the curved end part  11   a  for swaging at the swaged part  11   b.  The inner fin  12 , like the tube  11 , is formed in a wave shape by rolling a thin (for example thickness 0.1 mm) aluminum belt-shaped sheet and providing flat plate parts  15  and  16  at the two end parts. The bent parts  14  of the wave parts of the inner fin  12  are brazed at the inside wall surface  13  of the tube  11 , while the end part of the flat plate part  16  is brazed to the inside wall surface  14  of the curved end part  11   a.  On the other hand, the end part of the flat plate part  15  of the inner fin  12  is joined with the tube  11  by swaging at the swaged part  11   b.    
         [0008]      FIG. 3  shows the state of a header tank of the heat exchanger  1  which is shown in  FIG. 1 , for example, the exit side header tank  4 , to which the inner fin tubes  10  which are shown in  FIG. 2  are connected. The exit side header tank  4  is formed by a header plate  41  through which the inner fin tubes  10  are inserted and a tank plate  42  which are joined together. The front end parts of the inner fin tubes  10  are inserted through the header plate  41  and stick out into the space inside the exit side header tank  4 .  FIG. 4  is a view of the exit side header tank  4  which is shown in  FIG. 3  as seen from the arrow L direction. The header plate  41  and the tank plate  42  are provided with a brazing material between them. The front end parts of the inner fin tubes  10  which are inserted into the header plate  41  are brazed to the header plate  41  by the brazing material which is arranged between the header plate  41  and the tank plate  42 . 
       CITATIONS LIST 
     Patent Literature 
       [0009]    PLT 1: Japanese Patent Publication No. 2007-125590A 
       SUMMARY OF INVENTION 
     Technical Problem 
       [0010]    However, if brazing the front end parts of the inner fin tubes  10  to the header plates  41  by brazing material which is arranged between the header plates  41  and the tank plates  42 , there was the problem that the brazing material of the header plates  41  flows into the inner fin tubes  10  and melts the tubes. Further, as shown in  FIG. 5 , there was the problem that at the portions of the header tanks (here, the entry side header tank  3 ) provided with the separators  26 , the brazing material flows into the header plates  31  through the separators  26  and flows into 
         [0011]    the inner fin tubes  10  to melt the tubes. Here, tube melting will be explained in detail.  FIG. 6  shows the vicinity of a swaged part  11   b  of an inner fin tube  10  which is normally brazed. The tube  11  has parallel parts  11   p.  The belt-shaped sheet member is bent at points at the same lengths from the not shown curved end part whereby slanted parts  11   c  are formed. The slanted parts  11   c  are bent at the parts of the belt-shaped sheet member which abut against each other. Between the long end part  11   e  and the short end part  11   f  of the belt-shaped sheet member, a flat plate part  15  of an inner fin  12  is sandwiched. In that state, the end part  11   e  of the belt-shaped sheet member is folded back to the end part  11   f  side to form the swaged part  11   b.  In this example, the end part  15   a  of the flat plate part  15  sticks out from the short end part  11   f  of the belt-shaped sheet member and is bent around the short end part  11   f  side of the belt-shaped sheet member by the long end part  11   e  of the folded back belt-shaped sheet member. 
         [0012]    Further, the long end part  11   e  and one slanted part  11   c  of the belt-shaped sheet member are brazed together by a brazing material  51 , while the flat plate part  15  of the inner fin  12  and the inside surfaces of the slanted parts  11   c  are brazed together by the brazing material  52 . Further, the bent parts  14  of the inner fin  12  and the inner wall surface  13  of the tube  11  are brazed by the brazing material  53 .  FIG. 7  shows the swaged part  11   b  of the inner fin tube  10  which is shown in  FIG. 6  and shows the state where tube melting  5  occurs. If tube melting  5  occurs, the tube  11  is reduced in thickness, a hole is formed in the tube  11  at the part of the tube melting  5 , and refrigerant leaks out. 
         [0013]      FIG. 8  shows another example of an inner fin tube  10 . The inner fin tube  10  has an inner fin  12  inside of it. The tube  11  is swaged and closed by the swaged part  11   b.    FIG. 9  shows the state where tube melting  6  and  7  occurs at the swaged part  11   b  of the inner fin tube  10  which is shown in  FIG. 8 . In this way, even if the shape of the inner fin tube differs, there was the problem that if brazing material is arranged at the header tank side, at the time of brazing of the inner fin tube, the brazing material passes through the header plate to flow into the inner fin tube causing tube melting. 
         [0014]    Inflow of brazing material to the inner fin tube occurs due to the step difference at the swaged part of the tube which is formed by the bent sheet, so up to now measures have been taken such as welding together the swaged part or reducing the step difference at the swaged part. However, each of these measures leads to increased cost. Further, special steps are required where the brazing temperature has to be strictly managed. Insufficient measures have been taken against the flow of brazing material to the inside of the inner fin tube. 
         [0015]    The present invention, in consideration of the above problem, provides a heat exchanger which is brazed after tubes are assembled into the header tanks wherein tube melting at the time of attachment of the tubes to the header tanks can be prevented and productivity can be improved. 
       Solution to Problem 
       [0016]    To solve the above problem, the present invention provides a heat exchanger ( 1 ) which has a plurality of tubes ( 11 ) which are provided with refrigerant passages inside them and a pair of header tanks ( 3 ,  4 ) to which end parts of the tubes ( 11 ) are brazed, wherein brazing materials ( 8 ) which are used for brazing to the header tanks ( 3 ,  4 ) are arranged at the outer circumferential surfaces of the tubes ( 11 ), and the base materials of the metal sheet members which form the header tanks ( 3 ,  4 ) are exposed at the inner circumferential surfaces and outer circumferential surfaces of the header tanks ( 3 ,  4 ). 
         [0017]    According to the heat exchanger of the present invention, the brazing material which is necessary for brazing a tube and a header tank is supplied from the outer circumferential surface of the tube, so tube melting at the time of brazing is prevented, and the heat exchanger is improved in productivity. 
         [0018]    Further, reference notations attached above are examples which show the correspondence with specific examples of the later explained embodiments. 
     
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         [0019]      FIG. 1  is a front view which shows the streamlined configuration of a heat exchanger of the comparative art. 
           [0020]      FIG. 2  is a perspective view which shows an inner fin tube which is used at the heat exchanger which is shown in  FIG. 1 . 
           [0021]      FIG. 3  is a partial perspective view of a heat exchanger which shows the state where inner fin tubes which are shown in  FIG. 2  are connected to a header plate of a header tank of the heat exchanger which is shown in  FIG. 1 . 
           [0022]      FIG. 4  is a cross-sectional view of the header tank which is shown in  FIG. 3  as seen from an arrow L direction. 
           [0023]      FIG. 5  is a partial perspective view which shows the state where the brazing material of the tank plate flows into the header plate through a separator and the brazing material flows into an inner fin tube. 
           [0024]      FIG. 6  is a partial enlarged cross-sectional view which shows a swaged part of an inner fin tube which is normally brazed. 
           [0025]      FIG. 7  is a partial enlarged cross-sectional view which shows the state where tube melting occurs at the swaged part of the inner fin tube which is shown in  FIG. 6 . 
           [0026]      FIG. 8  is a cross-sectional view which shows another example of an inner fin tube. 
           [0027]      FIG. 9  is a partial enlarged cross-sectional view which shows the state where tube melting occurs at the swaged part of the inner fin tube which is shown in  FIG. 8 . 
           [0028]      FIG. 10  is a cross-sectional view of an inner fin tube of a first embodiment of the present invention. 
           [0029]      FIG. 11  is a partial enlarged cross-sectional view which shows a part of a swaged part of the inner fin tube of  FIG. 10 . 
           [0030]      FIG. 12A  is a cross-sectional view of a brazing material-free header plate and tank plate which are used for an inner fin tube and heat exchanger of the first embodiment of the present invention,  FIG. 12B  is a cross-sectional view of a modification of the first embodiment where there is a sacrificial material at the outside of the header plate of the brazing material-free header plate and tank plate which are shown in  FIG. 12A ,  FIG. 12C  is a partial perspective view of a heat exchanger which shows an embodiment of providing a brazing material at one surface of a separator of an entry side and exit side header tank which is provided with a brazing material-free header plate and tank plate,  FIG. 12D  is a cross-sectional view of an embodiment where the entry side and exit side header tanks are one-piece bodies and have cross-sections of circular shapes,  FIG. 12E  is a cross-sectional view of an embodiment where the entry side and exit side header tanks are one-piece bodies and have cross-sections of oval shapes,  FIG. 12F  is a cross-sectional view of an embodiment where the entry side and exit side header tanks are one-piece bodies and have cross-sections of irregular shapes, and  FIG. 12G  is an enlarged view of a principal part X of  FIG. 12B . 
           [0031]      FIG. 13  is an assembled perspective view of a header plate and a brazing material-free separator which is used for the same which shows a second embodiment of the present invention. 
           [0032]      FIG. 14  is an assembled perspective view of a header plate and a brazing material-free separator which is used for the same which shows a modification of the second embodiment of the present invention. 
           [0033]      FIG. 15  is a side cross-sectional view and front view of a first specific example of a separator of a third embodiment of the present invention. 
           [0034]      FIG. 16  is a side cross-sectional view and front view of a second specific example of a separator of a third embodiment of the present invention. 
           [0035]      FIG. 17  is a front view of a third specific example of a separator of a third embodiment of the present invention. 
           [0036]      FIG. 18  is a front view of a fourth specific example of a separator of a third embodiment of the present invention. 
           [0037]      FIG. 19  is a front view of a fifth specific example of a separator of a third embodiment of the present invention. 
           [0038]      FIG. 20  is a front view of a sixth specific example of a separator of a third embodiment of the present invention. 
       
    
    
     DESCRIPTION OF EMBODIMENTS 
       [0039]    Below, referring to the drawings, embodiments of the present invention will be explained. In the embodiments, parts which are configured the same are assigned the same reference notations and explanations will be omitted. Parts of the embodiments of the present invention which are the same in configuration as the comparative art forming the basis of the present invention are assigned the same reference notations and explanations are omitted. 
         [0040]      FIG. 10  shows an inner fin tube  10  of a first embodiment of the present invention. Further,  FIG. 11  shows a part X of  FIG. 10  enlarged. An inner fin tube  10  is comprised of a belt-shaped sheet member which is folded back to hold an inner fin  12  inside of it. The belt-shaped sheet member is formed by thin (for example thickness 0.2 mm) aluminum. It is folded back into an arc shape at a portion at slightly different distances from the two end parts to form a curved end part  11   a.  The belt-shaped sheet member is folded back until becoming parallel to form parallel parts  11   p.  The two end parts of the belt-shaped sheet member are bent at portions of the same distance from the curved end part  11   a  to form predetermined lengths of slanted parts  11   c,  then are further bent so that the two end parts become parallel. 
         [0041]    The belt-shaped sheet member is folded back as explained above to form the flat tube  11 . At the inside, an inner fin  12  is housed whereby a flat shaped flow path of the medium is formed. The inner fin  12  is formed into a wave shape by rolling a thin (for example thickness 0.1 mm) aluminum belt-shaped sheet member in the same way as the tube  11 . At the two end parts, flat plate parts  15  and  16  are provided. The bent parts  14  of the wave shaped parts of the inner fin  12  are brazed to the inside wall surface  13  of the tube  11 . The end part of the flat plate part  16  is also brazed to the inside wall surface  13  of the curved end part  11   a.  On the other hand, the end part of the other flat plate part  15  of the inner fin  12  is sandwiched between the two end parts bent to become parallel. 
         [0042]    The two end parts  11   e  and  11   f  of the belt-shaped sheet member which sandwich the flat plate part  15  of the inner fin  12  in the first embodiment become longer at the end part  11   e  than the end part  11   f.  Accordingly, the end part  11   e  is folded back to the end part  11   f  side in a state sandwiching the flat plate part  15  and the end part  11   f  and is swaged to join them whereby the swaged part  11   b  is formed. In the first embodiment, a brazing material  8  is arranged (clad) at the outer surface as a whole at the thus formed inner fin tube  10 . The amount of this brazing material  8  becomes an amount which is required for brazing the inner fin tube  10  to the entry side and exit side header tanks  3  and  4  when inserting and brazing the two end parts of the inner fin tube  10 , as shown in  FIG. 3 , to the entry side and exit side header tanks  3  and  4 . 
         [0043]    In this case, the inner circumferential surfaces N and outer circumferential surfaces S of the header plates  31  and  41  which form the entry side header tank  3  and the exit side header tank  4 , as shown in  FIG. 12A , are made brazing material-free. That is, the metal sheet members which form the header plates  31  and  41  are made sheet members with the base material exposed (bare materials) and can be made single layer members with no brazing material. By this configuration, the brazing material which is used when joining the inner fin tube  10  to the entry side and exit side header tanks  3  and  4  is supplied from the sufficient amount of brazing material  8  which was clad at the outer surface of the inner fin tube  10  (see  FIG. 10  and  FIG. 11 ). The brazing material is not present at the tank plates  32  and  42 , so the brazing material no longer flows from the tank plates  32  and  42  to the inner fin tube  10  and the tube melting of the inner fin tube  10  no longer occurs. As a result, the stability at the time of brazing the inner fin tube  10  is improved and the scope of application of the brazing temperature can be broadened. 
         [0044]    As explained above, the brazing material which flows to the inside of the inner fin tube  10  is a sufficient amount of brazing material  8  which is clad over the entire outer surface of the inner fin tube  10 . For this reason, the amount of the brazing material which is supplied to the brazing part of the inner fin tube  10  becomes sufficient, and the brazing fillet of the inner fin tube  10  can be made larger. Further, a fillet commensurate with the amount of brazing material of the part itself is formed and the brazeability of parts other than the inner fin tube  10  is also improved. 
         [0045]    Here, consider the case of the comparative art where the brazing material which is at the entry side and exit side header tanks  3  and  4  flows into the inner fin tube  10  and where the brazing material which is at the entry side and exit side header tanks  3  and  4  and the brazing material of the inner fin tube  10  are connected. In this case, the size of the fillet radius of the fillet which is formed at the inner fin  12  and the size of the fillet radius which is formed at the tank plate  32  and header plate  31  become substantially equal. However, in this case, the amounts of brazing material at the entry side and exit side header tanks  3  and  4  are small, so the size of the fillet radius of the tank plate  32  and header plate  31  ends up becoming the same 0.1 mm or so as the fillet radius of the fillet which is formed at the inner fin  12 . That is, sometimes the size of the fillet radius which is formed at the tank plate  32  and the header plate  31  is extremely small and the gap at the part requiring brazing cannot be filled resulting in leakage. 
         [0046]    As opposed to this, if making the inner circumferential surfaces N and outer circumferential surfaces S of the header plates  31  and  41  brazing material-free, the connection of the brazing material of the fillet which is formed between the tank plate  32  and header plate  31  and the brazing material of the fillet  52  or  53  which is formed at the inner fin  12  can be broken. As a result, it is possible to form a large fillet at the joint of the tank plate  32  and header plate  31  or the joint of the tank plate  32  and a cap  24 . That is, it is possible to form a large fillet of the fillet radius 0.3 mm to 0.6 mm or so which can inherently be obtained at the joint of the tank plate  32  and header plate  31  or the joint of the tank plate  32  and a cap  24 , the gap can be easily filled, and the brazeability can be improved. Note that, the “size of the fillet radius” which is referred to here envisions the case of using the generally widely used brazing material with 10 wt % of amount of Si. 
         [0047]    Further, the surface of the inner fin tube  10  sometimes has an anticorrosion layer or sacrificial brazing material on which the brazing material layer is superposed arranged on it, but by making the header plates  31  and  41  brazing material-free, it is possible to prevent the inflow of brazing material from the entry side and the exit side header tanks  3  and  4 , so the flow of brazing material to the surface of the inner fin tube  10  is also prevented. The brazing material ends up obstructing the action of the anticorrosion layer, so by preventing the flow of brazing material to the surface of the inner fin tube  10 , it is possible to improve the corrosion resistance of the inner fin tube  10 . 
         [0048]    Further, it is possible to use as the material of the header plates  31  and  41  a metal material which does not contain a brazing material and provide the inner circumferential surfaces N or outer circumferential surfaces S of the header plates  31  and  41  with a low potential anticorrosion layer constituted by a sacrificial material.  FIG. 12B  shows an embodiment which provides the outer circumferential surfaces S of the header plates  31  and  41  with a sacrificial material (anticorrosion layer)  9 . In this case, as shown in  FIG. 12G , as the header plates  31  and  41 , the surfaces of the metal sheet members (for example, comprised of aluminum alloy etc.) at the inner circumferential surface N sides may be made states with the base materials  311  and  411  exposed and the surfaces of the metal sheet members at the outer circumferential surface S sides of the header plates  31  and  41  may be made states with the surfaces of the base materials  311  and  411  clad by the sacrificial material  9 . Furthermore, as shown in  FIG. 12C , the header plates  31  and  41  are made brazing material-free, but one or both surfaces of the separators  26  may be provided with the brazing material  8 . In  FIG. 12C , the brazing material  8  are shown shaded. 
         [0049]    Still further, the inner circumferential surfaces N and outer circumferential surfaces S of the entry side and exit side header tanks  3  and  4  may be made brazing material-free even in the case where the entry side and exit side header tanks  3  and  4  are single-piece pipes  30  not split into header plates  31  and  41  and tank plates  32  and  42 . Further, the single-piece pipes  30  which are used for the entry side and exit side header tanks  3  and  4  are effective regardless of their cross-sectional shapes such as the circular shape which is shown in  FIG. 12D , the oval shape which is shown in  FIG. 12E , and the irregular shape which is shown in  FIG. 12F . Further, even when the entry side and exit side header tanks  3  and  4  are formed by single-piece pipes  30 , the materials which form the tanks may be exposed single layer types and may be provided at least at one of the inner circumferential surfaces N and outer circumferential surfaces S of the pipes  30  with a low potential sacrificial material (anticorrosion layer)  9 . In the entry side and exit side header tanks  3  and  4  which are shown from  FIG. 12D  to  FIG. 12F , the inner circumferential surface N of the pipe  30  which is shown in  FIG. 12E  is provided with the sacrificial material  9 , while the outer circumferential surface S of the pipe  30  which is shown in  FIG. 12F  is provided with the sacrificial material  9 . 
         [0050]    Note that, in the entry side and exit side header tanks  3  and  4  which are shown from  FIG. 12D  to  FIG. 12F  as well, the outer circumferential surface S of the pipe  30  which is shown in  FIG. 12E  may be provided with the sacrificial material and the inner circumferential surface N of the pipe  30  which is shown in  FIG. 12F  may be provided with the sacrificial material  9  needless to say. Whether the sacrificial material  9  is provided at the inner circumferential surface N of the pipe  30  or is provided at the outer circumferential surface S does not depend on the shape and structure of the pipe  30 . Further, both of the inner circumferential surface N and the outer circumferential surface S of the pipe  30  may be provided with the sacrificial material  9 . 
         [0051]      FIG. 13  shows a second embodiment of the heat exchanger of the present invention. In the second embodiment, the entry side header plate  31  and the exit side header plate  41  are made brazing material-free, and the separator  26  which is attached as a partition wall at the inside of the entry side header tank  3  and the exit side header tank  4  is made brazing material-free. The separator  26  of the second embodiment is used in the case of a structure where the header plates  31  and  41  have holes  33  and  43  (hole  33  at entry side header tank  3  and hole  43  at exit side header tank  4 ). That is, the metal sheet member which forms the separator  26  is made the exposed sheet member (bare material) where no brazing material is provided. 
         [0052]    In the case of this arrangement, the header plates  31  and  41  and the separator  26  are brazing material-free, but brazing material which is arranged at the tank plates  32  and  42  is supplied, whereby the header plates  31  and  41  and the separator  26  can be brazed. Tank brazing material flows through the fine clearances between the separator  26  and header plates  31  and  41  whereby these are brazed together. In this case, as the brazing material of the tank plates  32  and  42 , a brazing material with an amount of Si of 6 wt % or more is suitable. 
         [0053]      FIG. 14  shows a modification of the separator  26  of the second embodiment of the present invention which is shown in  FIG. 13 . The separator  26  of the modification is used in the case of a structure with grooves  34  and  44  at the two sides of the header plates  31  and  41  (groove  34  at entry side header tank  3  and groove  44  at exit side header tank  4 ). In the modification of the second embodiment as well, the metal sheet member which forms the separator  26  is made the exposed sheet member (bare material) where no brazing material is provided. Further, in the modification of the second embodiment, the holes at the header plates  31  and  41  at the joining sides with the inner fin tubes are eliminated, and grooves  34  and  44  are provided for attachment of the separator  26  at the two sides of the header plates  31  and  41 . For this reason, the flow paths of inflow of the brazing material from the outsides of the header plates  31  and  41  are cut. 
         [0054]    If, in this way, making the metal sheet member which forms the separator  26  a sheet member with the base material exposed and not providing a brazing material, that is, making it brazing material-free, it is possible to cut the flow paths of brazing material to the header plates  31  and  41  resulting in a further reduction in the occurrence of tube melting. 
         [0055]      FIG. 15  to  FIG. 17  show the configurations of separators  26  of a third embodiment of the heat exchanger of the present invention. The figures give cross-sectional views and front views of separator  26 . The third embodiment provides the two surfaces of the separator  26  with structures for holding the brazing material in the case where the two surfaces of the entry side header tank  3  or exit side header tank  4  are provided with brazing material and thereby prevents the inflow of the brazing material to the inner fin tubes  10 . 
         [0056]      FIG. 15  shows a first specific example of the separator  26 . A separator  26  of the same type as the separator  26  which was explained in  FIG. 13  is shown. In the first specific example of the separator  26 , the two surfaces of the separator  26  are provided with a plurality of parallel grooves  27 .  FIG. 16  shows a second specific example of the separator  26 . A separator  26  of the same type as the separator  26  which was explained in  FIG. 13  is shown. In the second specific example of the separator  26 , the two surfaces of the separator  26  are provided with a plurality of circular depressions  28  which are regularly arranged to the top and bottom and the left and right. These depressions  28  serve as brazing reservoirs in which melted brazing material is held. The depressions  28  may also be provided irregularly arranged.  FIG. 17  shows a third specific example of the separator  26 . A separator  26  of the same type as the separator  26  which was explained in  FIG. 13  is shown. In the third specific example of the separator  26 , the two surfaces of the separator  26  are provided with a plurality of oval depressions  29  which are regularly arranged to the top and bottom and the left and right. Oval depressions  29  may also be provided irregularly arranged. 
         [0057]    If in this way providing the two surfaces of the separator  26  with grooves or holes, even if the two surfaces of the entry side header tank  3  and the exit side header tank  4  are provided with brazing material, the excess brazing material can be held at the grooves or holes and flow of excess brazing material to the header plate side can be prevented. As a result, excess brazing material no longer flows into the inner fin tubes and tube melting can be prevented. 
         [0058]      FIG. 18  to  FIG. 20  show fourth to sixth specific examples of the separator  26  of the third embodiment of the heat exchanger of the present invention. In the fourth specific example which is shown in  FIG. 18 , the two surfaces of the separator  26  are provided at a slant with grooves  35  which cut the brazing material flow paths. The grooves  35  are provided at the separator  26  asymmetrically. The grooves  35  may also be ribs. In the fifth specific example which is shown in  FIG. 19 , the two surfaces of the separator  26  are provided with grooves  36  which cut the brazing material flow path at an angle symmetrically with respect to the centerline of the separator  26 . The grooves  36  may also be ribs. In the sixth specific example which is shown in  FIG. 20 , the two surfaces of the separator  26  are provided with not only the grooves  36  which were explained in the fifth example, but also ribs  37  which cut the brazing material flow paths at an angle symmetrically with respect to the centerline of the separator  26 . The ribs  37  may also be grooves. 
         [0059]    The brazing material which causes tube melting flows to an inner fin tube through a brazing part of a separator  26  and an inside of a tank. Therefore, as shown in the first to the sixth specific examples, by providing the two surfaces of the separator  26  with grooves  36  or ribs  37 , it is possible to reduce or delay the amount of brazing material which flows from the inside of the tank through the separator  26  to the inner fin tube. That is, the grooves  36  or ribs  37  which are provided at the two surfaces of the separator  26  can extend the flow paths from the inside of the tank to the inner fin tube and can increase the time it takes for the brazing material to reach the inner fin tube due to the large flow resistance of the brazing material. As a result, it is possible to reduce the temperature difference from the core part before the brazing material reaches the inner fin tube, so tube melting is reduced. 
         [0060]    In the embodiments which were explained above, the type and thickness of the brazing material which was actually used was a brazing material with a 4 wt % to 5 wt % amount of Si and with a clad rate of 20% (since the sheet thickness t was 0.2 mm, the film thickness was 40 μm). However, in the present invention, as the brazing material which is clad at the tube surface, a usually used 10 wt % brazing material is also possible. The invention is effective even for a tube provided with a clad rate 10% (film thickness 20 μm) or so brazing material. That is, the invention is effective even for a tube with an amount of Si of the brazing material  8  at the tube surface of 3.5 wt % to 10 wt %. However, the amount of the brazing material at the tube surface is preferably 3.5 wt % to 7.5 wt %. 
         [0061]    As explained above, in the present invention, there is provided a heat exchanger which employs tubes which were produced by sheet bending wherein the brazing materials which are required at the time of brazing the tubes are supplied from the outer circumferential surfaces of the tubes, so tube melting at the time of brazing the tubes to the header tanks is prevented and the productivity of the heat exchanger is improved. Further, by making the separators which are provided at the inside of the header tanks brazing material-free or by providing the separators with structures for holding the brazing materials, tube melting at the time of brazing the tubes to the header tanks is prevented. Further, by combining the above-mentioned first to third embodiments, it is possible to further reduce the tube melting at the time of brazing the tubes to the header tanks. 
         [0062]    Note that, in the above-mentioned embodiments, examples of using tubes with inner fins at their insides as the tubes which were brazed to the header plates were explained, but it is also possible to use tubes in which no inner fins are arranged. In particular, if the tubes which are brazed to the header plates are tubes of structures comprised of sheet members which are folded back and are superposed at their two end parts, the brazing materials are sucked in at the superposed parts due to the capillary phenomenon, so the brazing materials easily pool near the superposed parts, but it is possible to prevent tube melting by application of the present invention. 
         [0063]    Further, in the above-mentioned embodiments, the example of use of aluminum as the material of the inner fin tubes and inner fins was explained, but in all of the above embodiments, it is possible to use aluminum alloy as the material of the inner fin tubes and inner fins.