Abstract:
An object of the present invention is to provide a heat exchanging fin capable of preventing cracks from forming in the flares of the collared tube holes, even if the metallic plate section is made of the thin and tough material. In the heat exchanging fin, a metallic plate section has a plurality of tube holes. A plurality of collars are respectively extended from edges of the tube holes. A plurality of flares are respectively formed at front ends of the collars. Each flare includes a plurality of radially extended sections, which are radially outwardly extended from the front end of each collar, and separation between the metallic plate section and each radially extended section is fixed.

Description:
BACKGROUND OF THE INVENTION  
         [0001]    The present invention relates to a heat exchanging fin and a method of manufacturing the heat exchanging fin, more precisely relates to a heat exchanging fin, in which collars are formed to respectively enclose tube holes, through which heat exchanging tubes will be inserted, and the collars respectively have flares at their front ends, and a method of manufacturing the heat exchanging fin.  
           [0002]    The heat exchanging fin, which is employed in room air conditioners, car air conditioners, etc., has: a rectangular metallic plate section, which is made of a metal, e.g., aluminum; and a plurality of collared tube holes being provided in the metallic plate section with separations and having a prescribed height.  
           [0003]    A heat exchanger is assembled by the steps of: piling the heat exchanging fins, in which the collared tube holes are coaxially arranged; inserting heat exchanging tubes, which are made of a metallic material having high heat conductivity, e.g., copper, through the coaxial tube holes; and expanding the heat exchanging tubes, which have been inserted through the tube holes, so as to integrate the heat exchanging tubes with the heat exchanging fins.  
           [0004]    The conventional heat exchanging fin is manufactured by the steps by a drawing manner, which is shown in FIGS.  14 I- 14 VI, or a drawless manner, which is shown in FIGS.  15 A- 15 D.  
           [0005]    In the drawing manner, shown in FIGS.  14 I- 14 VI, a shallow projected section  106 , which has a columnar shape or a truncated cone shape, is formed in a thin aluminium plate section  100  (see FIG. 14I). Diameter of the shallow projected section  106  is greater than that of the collared tube holes to be formed. Next, the diameter of the shallow projected section  106  is reduced and height thereof is gradually higher by drawing the shallow projected section  106  (see FIGS.  14 II- 14 IV).  
           [0006]    A top face of the projected section  109 , which is formed by drawing the shallow projected section  106  until reaching a prescribed height, is opened and burred to make a cylindrical section  104  (see FIG. 14V). Further, a flare  105  is formed by bending a top end of the cylindrical section  104  (see FIG. 14V).  
           [0007]    In the drawless manner, shown in FIGS.  15 A- 15 D, a base hole  101 , which is enclosed by a projected part  102 , is formed by boring and burring the metallic plate section  100  (see FIG. 15A). Then, diameter of the base hole  101  is made greater and the projected part  102  is squeezed until a cylindrical section  104  which has a prescribed height is formed (see FIGS. 15B and 15C).  
           [0008]    Next, the flare  105  is formed by bending the top end of the cylindrical section  104  (see FIG. 15D).  
           [0009]    The heat exchanging fins having the collared tube holes, which include the cylindrical sections  104  and the flares  105 , are formed by the manner shown in FIGS.  14 I- 14 VI or FIGS.  15 A- 15 D. When the heat exchanging fins are piled, the flares  105  of one heat exchanging fin contact a bottom face of the adjacent heat exchanging fin, so that the separation between the heat exchanging fins can be defined.  
           [0010]    In the manner shown in FIGS.  14 I- 14 VI or FIGS.  15 A- 15 D, the base hole, which is bored in the top face of the projected section  109  or in the metallic plate section  100 , is a circular hole. And, in the manner shown in FIGS.  14 I- 14 VI or FIGS.  15 A- 15 D, the width of the flare  105 , which is formed to enclose an circular edge of the top end of the cylindrical section  104 , is fixed.  
           [0011]    These days, light heat exchanging fins are required, so thickness of the metallic plate section  100  must be thinner.  
           [0012]    On the other hand, tough heat exchanging fins are also required. Namely, the heat exchanging fins, which are not only thin but also tough, are required, so the metallic plate section  100  is made of a thin and tough metallic material.  
           [0013]    Extensibility of the thin and tough metallic material is less than that of a thick and soft metallic material, so it is improper for the thin and tough metallic material to press and form the heat exchanging fins. When the flare  105  is formed by bending the top end of the cylindrical section  104 , the flare  105  is outwardly pulled. In the case of using the thin and tough material which has the small extensibility, a crack  106  is apt to be formed in the flare  105  (see FIG. 16) because the end of the flare  105  is extremely extended.  
         SUMMARY OF THE INVENTION  
         [0014]    An object of the present invention is to provide a heat exchanging fin capable of preventing cracks from forming in the flares of the collared tube holes, even if the metallic plate section is made of the thin and tough material.  
           [0015]    Another object of the present invention is to provide a method of manufacturing said heat exchanging fin.  
           [0016]    To achieve the objects, the inventor of the present invention has studied. Then, he found that forming cracks in the flares of the collared tube holes could be prevented by forming three radially extended sections as the flare.  
           [0017]    The basic structure of the heat exchanging fin of the present invention comprises:  
           [0018]    a metallic plate section having a plurality of tube holes;  
           [0019]    a plurality of collars each of which is extended from an edge of each tube hole; and  
           [0020]    a plurality of flares each of which is formed at a front end of each collar,  
           [0021]    wherein each flare includes a plurality of radially extended sections, which are radially outwardly extended from the front end of each collar, and separation between the metallic plate section and each radially extended section is fixed.  
           [0022]    In the heat exchanging fin, a shape of an outer edge of each flare may be formed into a polygonal shape. The polygonal shape may be a triangle, a tetragon, etc.  
           [0023]    In the heat exchanging fin, the radially extended sections of each flare may be provided to locate their apexes with regular separations in the circumferential direction.  
           [0024]    In the heat exchanging fin, a shape of an outer edge of each flare may be formed into a regular polygonal shape. The regular polygonal shape may be a regular triangle, a regular tetragon, etc.  
           [0025]    In the heat exchanging fin, each flare may include a plurality of narrow sections, which are radially outwardly extended from the front end of each collar and their width is narrower than that of the radially extended sections.  
           [0026]    In the heat exchanging fin, the radially extended sections of each flare may be provided with regular separations in the circumferential direction.  
           [0027]    The basic structure of the method of manufacturing the heat exchanging fin including: a metallic plate section having a plurality of tube holes; a plurality of collars each of which is extended from an edge of each tube hole; a plurality of flares having prescribed height, each flare being formed at a front end of each collar,  
           [0028]    comprises the steps of:  
           [0029]    forming a cylindrical section, in which higher sections and lower sections are alternately formed at a front end, along the edge of each tube hole; and  
           [0030]    forming the flare of each collar by radially outwardly bending the higher sections of the cylindrical section.  
           [0031]    In the method, the cylindrical section having the higher sections and the lower sections may be formed by the steps of:  
           [0032]    forming a projected section, which is formed into a columnar or a truncated cone shape, in the metallic plate section by drawing the metallic plate section;  
           [0033]    boring a base hole, which is formed into an elliptic or a polygonal shape, in the projected section; and  
           [0034]    burring the base hole so as to form the cylindrical section, in which at least two higher sections are formed at the front end, along the edge of the tube hole.  
           [0035]    In the method, the base hole may be formed into a triangle or a tetragon.  
           [0036]    In the method, the higher sections may be provided at the front end of the cylindrical section with regular separations in the circumferential direction.  
           [0037]    In the method, the base hole is formed into a regular triangle or a regular tetragon.  
           [0038]    In the method, the cylindrical section having the higher sections and the lower sections may be formed by the steps of:  
           [0039]    boring a base hole, which is formed into an elliptic or a polygonal shape, in the metallic plate section;  
           [0040]    burring the base hole; and  
           [0041]    drawing a projected part, which is projected from an edge of the burred base hole, so as to form the cylindrical section, in which at least two higher sections are formed at the front end, along the edge of the tube hole.  
           [0042]    In the method, the base hole may be formed into a triangle or a tetragon.  
           [0043]    In the method, the higher sections may be provided at the front end of the cylindrical section with regular separations in the circumferential direction.  
           [0044]    In the method, the flare may include a plurality of radially extended sections, which are radially outwardly extended from the front end of the collar, and a plurality of narrow sections, which are radially outwardly extended from the front end thereof and whose width is narrower than that of the radially extended sections, wherein the flare is formed by radially outwardly bending the higher sections of the cylindrical section.  
           [0045]    As described above, a force pulling an outer edge of the flare is greater than a force pulling an inner edge thereof when the flare, which encloses the top end of the collar with fixed width, is formed by bending the top end of the cylindrical section.  
           [0046]    The top end of the cylindrical section has rough and hard faces, which are formed when the metallic plate section is bored and broken by a die-punch set. Thus, if the greater pulling force, which pulls the outer edge of the flare in the circumferential direction, is applied to the flare, which is formed by bending the top end of the cylindrical section, the cracks are apt to be formed in the vicinity of the outer edges of the flares.  
           [0047]    On the other hand, in the present invention, the flare of the collar is constituted by a plurality of the radially extended sections, which are arranged at the front end of the collar with separations. With this structure, the pulling force applied to one of the radially extended sections does not influence other radially extended sections. The greater pulling force capable of pulling the outer edge of the flare can be prevented when the flare is formed at the front end of the cylindrical section by bending, so that forming the cracks in the flare can be prevented.  
           [0048]    To manufacture the heat exchanging fins having the collared tube holes, the height of the cylindrical sections must be a prescribed height. Especially, in the conventional heat exchanging fins, the whole edge of the top end of the cylindrical section must have a prescribed height, so the cylindrical section is drawn or squeezed until the whole edge of the top end reaches the prescribed height.  
           [0049]    On the other hand, in the present invention, the front end of the cylindrical section is uneven, namely the front end has the higher sections and the lower sections. And, the top ends of the higher sections must have a prescribed height. The whole edge of the front end of the cylindrical section need not have the prescribed height, so the heat exchanging fins can be easily manufactured. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0050]    Embodiments of the present invention will now be described by way of examples and with reference to the accompanying drawings, in which:  
         [0051]    [0051]FIG. 1 is a perspective view of the heat exchanging fin of an embodiment of the present invention;  
         [0052]    [0052]FIG. 2 is a plan view of a collared tube hole  14  of the heat exchanging fin shown in FIG. 1;  
         [0053]    [0053]FIG. 3 is a sectional view of the collared tube hole  14  taken along a line A-A shown in FIG. 2;  
         [0054]    FIGS.  4 A- 4 D are sectional views showing the steps of manufacturing the heat exchanging fin shown in FIG. 1;  
         [0055]    [0055]FIG. 5 is a plan view of a base hole  26  bored in the step shown in FIG. 4B;  
         [0056]    [0056]FIG. 6A- 6 D are sectional views showing the steps of manufacturing the heat exchanging fin shown in FIG. 1;  
         [0057]    [0057]FIG. 7 is a plan view of a base hole  30  bored in the step shown in FIG. 6A;  
         [0058]    [0058]FIG. 8 is a perspective view of the heat exchanging fin of another embodiment;  
         [0059]    [0059]FIG. 9 is a plan view of a collared tube hole  41  of the heat exchanging fin shown in FIG. 8;  
         [0060]    [0060]FIG. 10A is a plan view of the base hole  26  bored in the step shown in FIG. 4B;  
         [0061]    [0061]FIG. 10B is a plan view of the base hole  30  bored in the step shown in FIG. 6A;  
         [0062]    [0062]FIG. 11 is a perspective view of the heat exchanging fin of another embodiment;  
         [0063]    [0063]FIG. 12 is a plan view of a collared tube hole  52  of the heat exchanging fin shown in FIG. 11;  
         [0064]    [0064]FIG. 13A is a plan view of the base hole  26  bored in the step shown in FIG. 4B;  
         [0065]    [0065]FIG. 13B is a plan view of the base hole  30  bored in the step shown in FIG. 6A;  
         [0066]    FIGS.  14 I- 14 VI are sectional views showing the steps of manufacturing the conventional heat exchanging fin;  
         [0067]    FIGS.  15 A- 15 D are sectional views showing the steps of manufacturing the conventional heat exchanging fin; and  
         [0068]    [0068]FIG. 16 is a perspective view of the collared tube hole, in which the crack is formed in the flare. 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0069]    Preferred embodiments of the present invention will now be described in detail with reference to the accompanying drawings.  
         [0070]    [0070]FIG. 1 is the perspective view of the heat exchanging fin of the embodiment. The heat exchanging fin  10  shown in FIG. 1 includes: a rectangular metallic plate section  12 , which is made of aluminum; and a plurality of collared tube holes  14 , which are linearly arranged in the longitudinal direction of the plate section  12 . Each collared tube hole  14  has a collar  20 , in which an edge of a tube hole  16  is enclosed by a flare  18 .  
         [0071]    As shown in FIG. 2, the flare  18  includes: radially extended sections  18   a , which are outwardly extended a front (upper) end of the collar  20 ; and narrow sections  18   b , whose width is narrower than that of the radially extended sections  18   a . The radially extended sections  18   a  are provided along an outer circumferential face of the collar  20  with regular separations.  
         [0072]    As shown in FIG. 1, the flare  18  is formed into a regular tetragon and its corners are rounded.  
         [0073]    Note that, the shape of the flare  18  is not limited to the regular tetragon, it may be a rectangle and may have angular corners, etc.  
         [0074]    A sectional view of the collared tube hole  14  taken along a line A-A of FIG. 2 is shown in FIG. 3. As shown in FIG. 3, The radially extended sections  18   a  have flat sections (upper faces, of the radially extended sections  18   a ). When the heat exchanging fins  10  are vertically piled, the flat sections of the radially extended sections  18   a  contact a bottom face of another heat exchanging fin  10 , which is located on the upper side so as to support said heat exchanging fin. The separation between the metallic plate section  12  and each flat section of the radially extended section  18   a  is fixed, so that the radially extended section  18   a  can stably support the upper heat exchanging fin  10 , and the adjacent heat exchanging fins  10  can be separated with fixed separations.  
         [0075]    The narrow sections  18   b  have no flat sections, so they do not support another heat exchanging fin  10 . Preferably, the height of the highest points of the narrow sections  18   b  is equal to that of the flat sections of the radially extended sections  18   a . If the height of the narrow sections  18   b  is lower than that of the radially extended sections  18   a , an outer circumferential face of the heat exchanging tubes, which are pierced through the tube holes  16  of the piled heat exchanging fins  10 , are exposed. If the tubes are seen between the heat exchanging fins  10 , the external appearance and hear exchangiblity are bad.  
         [0076]    As shown in FIG. 3, the narrow sections  18   b  are outwardly bent with respect to an inner circumferential face of the tube hole  16 , so that the heat exchanging tube can be smoothly inserted in the tube hole  15 .  
         [0077]    A method of manufacturing the heat exchanging fin  10 , which includes the collared tube holes  14  formed by the drawing manner shown in FIGS.  14 I- 14 VI, shown in FIGS.  1 - 3  will be explained with reference to FIGS.  4 A- 4 D.  
         [0078]    In FIGS.  4 A- 4 D, a projected section  22  shown in FIG. 4A can be formed by the steps of FIGS.  14 I- 14 IV, which have been explained in the drawing manner shown in FIGS.  14 I- 14 VI.  
         [0079]    A base hole  26  is bored in a flat face  24  of the projected section  22 , which has been formed in the step of FIG. 4A (see FIG. 4B). As shown in FIG. 5, area of the base hole  26  is smaller than that of the flat face  24  of the projected section  22 , and the base hole  26  is formed into a regular tetragon whose corners are rounded.  
         [0080]    Next, the base hole  26 , which has been bored in the flat face  24  of the projected section  22 , is burred so as to form a cylindrical section  28  whose front (upper) end is zigzag formed (see FIG. 4C). In the zigzag front end of the cylindrical section  28 , higher sections  28   a  and lower sections  28   b  are alternately formed, namely four higher sections  28   a  (or four lower sections  28   b ) are arranged in the circurmferential direction with regular separations.  
         [0081]    The higher sections  28   a  correspond to middle parts of linear edges  26   a  of the base hole  26  shown in FIG. 5, which has been bored in the flat face of the projected section  22 ; the lower sections  28   b  correspond to corners  26   b  of the base hole  26  shown in FIG. 5.  
         [0082]    Then, the zigzag front end of the cylindrical section  28  are pressed, namely four higher sections  28   a  are simultaneously pressed to bend outwardly, so that four radially extended sections  18   a , which are radially outwardly extended from the front end of the collar  20 , are formed (see FIG. 4D). The higher sections  28   a  are pressed until the flat sections are formed; parts of the lower sections  28   b  are pressed to form the narrow sections  18   b , whose width is narrower than that of the radially extended sections  18   a  as shown in FIGS. 2 and 3. Preferably, the separation between the plate section  12  and each narrow sections  18   b  is equal to that between the plate section  12  and each radially extended section  18   a.    
         [0083]    In the method shown in FIGS.  4 A- 4 D, the step of boring the base hole  26 , which is formed into the regular tetragon, in the flat face  24  of the projected section  22  (see FIG. 4B) and the step of burring the base hole  26  (see FIG. 4C) may be executed separately. The boring step and the burring step may be executed simultaneously. In this case, the steps may be executed in a press machine, in which the steps are executed in a stroke of a movable die.  
         [0084]    In the boring step in which the base hole is bored in the flat face  24  of the projected section  22  (see FIG. 4B), the corners of the tetragonal base hole  26  may be angular, and the base hole  26  may be formed into a rectangular shape.  
         [0085]    A method of manufacturing the heat exchanging fin  10 , which includes the collared tube holes  14  formed by the drawless manner shown in FIGS.  15 A- 15 D, shown in FIGS.  1 - 3  will be explained with reference to FIGS.  6 A- 6 D.  
         [0086]    In the drawless manner, a base hole  30  is bored in the metallic plate section  12  (see FIG. 6A). As shown in FIG. 7, the base hole  30  is formed into the regular tetragon, and its corners are rounded.  
         [0087]    Next, the base hole  30  is burred to form a burred hole  34  whose edge is enclosed by a projected part  32  (see FIG. 6B). Then, diameter of the burred hole  34  is increased, and the projected part  32  is squeezed until an upper zigzag end of a cylindrical section  36  reaches a prescribed height (see FIG. 6C). In the upper zigzag end of the cylindrical section  36 , higher sections  36   a  and lower sections  36   b  are alternately formed. Four higher sections  36   a  (or four lower sections  36   b ) are arranged in the circumferential direction of the cylindrical section  36  with regular separations.  
         [0088]    The higher sections  36   a  correspond to middle parts of linear edges  30   a  of the base hole  30  shown in FIG. 7, which has been bored in the metallic plate section  12 ; the lower sections  36   b  correspond to corners  30   b  of the base hole  30  shown in FIG. 7.  
         [0089]    Then, the zigzag front end of the cylindrical section  36  are pressed, namely four higher sections  36   a  are simultaneously pressed to bend outwardly, so that four radially extended sections  18   a , which are radially outwardly extended from the front end of the collar  20 , are formed (see FIG. 6D). The higher sections  36   a  are pressed until the flat sections are formed; parts of the lower sections  36   b  are pressed to form the narrow sections  18   b , whose width is narrower than that of the radially extended sections  18   a  as shown in FIGS. 2 and 3. Preferably, the separation between the plate section  12  and each narrow sections  18   b  is equal to that between the plate section  12  and each radially extended section  18   a.    
         [0090]    In the step of boring the base hole  30  in the plate section  12  (see FIG. 6A), the tetragonal base hole  30  may have angular corners, and the base hole  30  may be formed into a rectangle.  
         [0091]    In the method shown in FIGS.  6 A- 6 D, the step of boring the base hole  30 , which is formed into the regular tetragon, in the plate section  12  (see FIG. 6A) and the step of burring the base hole  30  (see FIG. 6B) may be executed separately. The boring step and the burring step may be executed simultaneously. In this case, the steps may be executed in a press machine, in which the steps are executed in a stroke of a movable die.  
         [0092]    In the drawing manner shown in FIG. 4A- 4 D, the base hole  26 , which is formed into the regular tetragon, is bored in the flat face  24  of the projected section  22  (see FIGS.  6 A- 6 D), the height of the collared tube hole  14  is higher than that of a collared tube hole based on a circular base hole  27 , which is indicated by a one-dot chain line shown in FIG. 5. In FIG. 5, parts “a”, which are located between the tetragonal base hole  26  and the circular base hole  27  enclosing the base hole  26 , will constitute the higher sections  28   a  of the cylindrical section  28  shown in FIG. 4C, which is formed by burring the base hole  26 , so that the height of the collared tube hole  14  can be higher.  
         [0093]    To make the flare  18 , the higher sections  28   a  of the cylindrical section  28  are pressed and bent to form the radially extended sections  18   a . So the height of the top ends of the higher sections  28   a  of the cylindrical section  28 , from the metallic plate section  12 , must be a prescribed height; the whole edge of the top end of the cylindrical section  28  need not have the prescribed height.  
         [0094]    When four radially extended sections  18   a  are formed by simultaneously bending four higher sections  28   a , the radially extended sections  28   a are arranged along the edge of the collar  20  with separations, so the pulling force applied to one of the radially extended sections  18   a  does not influence other radially extended sections  18   a.    
         [0095]    By boring the regular tetragonal base hole  26  in the flat face  24  of the projected section  22 , the height of the collared tube hole  14  can be higher than that of the collared tube hole based on the circular base hole  27 . If the height of the collared tube hole  14  is equal to that of the collared tube hole based on the circular base hole  27 , the height of the projected section  22  can be lower. Thus, the thickness of the metallic plate section  12  may be thinner and harder than that of a metallic plate section in which the circular base holes  27  will be bored.  
         [0096]    In the case of the collared tube hole, which is manufactured by the drawing manner shown in FIGS.  14 I- 14 VI, if the thickness of the aluminum plate section  12  is 0.1 mm and the diameter of the tube hole  16  is 10 mm, the height of the collar can be 2 mm or less. On the other hand, in the case of the drawing manner shown in FIGS.  4 A- 4 D, the height of the collar  20 , which has the flare  18 , can be 2.3 mm.  
         [0097]    In the drawless manner shown in FIGS.  6 A- 6 D too, the parts “a”, which are located between the regular tetragonal base hole  30  and a circular base hole  31  (indicated by a one-dot chain line) enclosing the base hole  30 , are formed in the plate section  12 , so that the parts “a” make the cylindrical section  36  shown in FIG. 6C, which is formed by burring the base the base hole  30 , increasing the diameter of the burred base hole  34  and squeezing the projected part  32 , higher.  
         [0098]    To make the flare  18 , the higher sections  36   a  of the cylindrical section  36  are pressed and bent to form the radially extended sections  18   a . So the height of the top ends of the higher sections  36   a  of the cylindrical section  36  must be a prescribed height; the whole edge of the top end of the cylindrical section  36  need not have the prescribed height. When four radially extended sections  18   a  are formed by simultaneously bending four higher sections  36   a , the pulling force applied to one of the radially extended sections  18   a  does not influence other radially extended sections  18   a  as well as the drawing manner.  
         [0099]    If the height of the collared tube hole  14  is equal to that of the collared tube hole based on the circular base hole  31 , the height of the cylindrical section  36  can be lower. Thus, degree of increasing the diameter of the burred base hole  34  and squeezing the projected part  32  can be lower, so the collared tube hole  14  having the prescribed height can be formed even if the plate section  12  is made of a thin and hard material having lower extensibility.  
         [0100]    In the above described embodiments, the external shape of the flare  18  of the collared tube hole  14  is the regular tetragonal shape. But the external shape of the flare  18  is not limited, so the external shape of the flare  18  of the collared tube hole  14  may be a regular triangle as shown in FIG. 8.  
         [0101]    The heat exchanging fin shown in FIG. 8 includes: the rectangular metallic plate section  12 , which is made of aluminum; and a plurality of the collared tube holes  41 , which are linearly arranged in the longitudinal direction of the plate section  12 . Each collared tube hole  41  has the collar  20 , in which an edge of the tube hole  16  is enclosed by a flare  42 .  
         [0102]    As shown in FIG. 9, the flare  42  includes: radially extended sections  42   a , which are outwardly extended the front (upper) end of the collar  20 ; and narrow sections  42   b , whose width is narrower than that of the radially extended sections  42   a . The radially extended sections  42   a  are provided along the outer circumferential face of the collar  20  with regular separations.  
         [0103]    As shown in FIG. 8, the flare  42  is formed into a regular triangle and its corners are rounded.  
         [0104]    Note that, the shape of the flare  42  is not limited to the regular triangle having the rounded corners, it may have angular corners and it may be a equilateral triangle, etc.  
         [0105]    The heat exchanging fins shown in FIGS. 8 and 9, which have the collared tube holes  41 , can be manufactured by the method shown in FIGS.  4 A- 4 D or FIGS.  6 A- 6 D. The methods shown in FIGS.  4 A- 4 D and FIGS.  6 A- 6 D have been described, so detailed explanation will be omitted.  
         [0106]    Note that, in the boring step (see FIG. 4B or  6 A), the shape of the base hole  26  or  30  is formed into the regular triangle  43  or  44 , which has the rounded corners, as shown in FIG. 10A or  10 B, so that the heat exchanging fins having the collared tube holes  41 , whose shape is shown in FIG. 8 or  9 , can be manufactured.  
         [0107]    The step shown in FIG. 10A corresponds to the step shown in FIG. 4B; the step shown in FIG. 10B corresponds to the step shown in FIG. 6A.  
         [0108]    The higher sections  28   a  or  36   a , which are shown in FIG. 4C or  6 C, correspond to middle parts of linear edges  43   a  or  44   a  of the triangular base hole  43  or  44  shown in FIG. 10A or  10 B.  
         [0109]    Corners  43   b  or  44   b  of the triangular base hole  43  or  44 , which is included in the circular base hole  27  or  31 , will constitute the lower sections  28   b  or  36   b  of the cylindrical section  28  or  36  shown in FIG. 4C or  6 C.  
         [0110]    In FIGS.  1 - 10 B, the flares of the collared tube holes are formed into polygons, but the external shape of the flares may be ellipse as shown in FIG. 11.  
         [0111]    The heat exchanging fin shown in FIG. 11 includes: the rectangular metallic plate section  12 , which is made of aluminum; and a plurality of the collared tube holes  51 , which are linearly arranged in the longitudinal direction of the plate section  12 . Each collared tube hole  51  has the collar  20 , in which an edge of the tube hole  16  is enclosed by a flare  52 .  
         [0112]    As shown in FIG. 12, the flare  52  includes: radially extended sections  52   a , which are outwardly extended the front end of the collar  20 ; and narrow sections  52 b, whose width is narrower than that of the radially extended sections  52   a . The radially extended sections  52   a  are symmetrically provided with respect to the tube hole  16 .  
         [0113]    As shown in FIG. 12, the flare  52  shown in FIG. 11 is formed into an ellepse, and the radially expanded sections  52   a  are expanded in the longitudinal direction of the plate section  12 .  
         [0114]    The heat exchanging fins shown in FIGS. 11 and 12, which have the collared tube holes  51 , can be manufactured by the method shown in FIGS.  4 A- 4 D or FIGS.  6 A- 6 D. The methods shown in FIGS.  4 A- 4 D and FIGS.  6 A- 6 D have been described, so detailed explanation will be omitted.  
         [0115]    Note that, in the boring step (see FIG. 4B or  6 A), the shape of the base hole  26  or  30  is formed into the ellipse  53  or  54  as shown in FIG. 13A or  13 B, so that the heat exchanging fins having the collared tube holes  51 , whose shape is shown in FIG. 11 or  12 , can be manufactured.  
         [0116]    The step shown in FIG. 13A corresponds to the step shown in FIG. 4B; the step shown in FIG. 13B corresponds to the step shown in FIG. 6A.  
         [0117]    The higher sections  28   a  or  36   a , which are shown in FIG. 4C or  6 C, correspond to middle parts of edges  53   a  or  54   a , which is arranged in the direction of the line of upside, of the elliptical base hole  53  or  54  shown in FIG. 13A or  13 B.  
         [0118]    The edges  53   a  shown in FIG. 13A are curved edges, and the edges  54   a  shown in FIG. 13B are linear edges, but both edges  53   a  and  54   a  can be formed into the flares  52 .  
         [0119]    The edges  53   b  or  54   b  of the elliptical base hole  53  or  54 , which is included in the circular base hole  27  or  31 , will constitute the lower sections  28   b  or  36   b  of the cylindrical section  28  or  36  shown in FIG. 4C or  6 C.  
         [0120]    In the above described embodiments shown in FIGS. 1, 8 and  11 , the collared tube holes  14 ,  41  and  51  are linearly arranged in the longitudinal direction of the plate section  12 , but the collared tube holes  14 ,  41  and  51  may be arranged in two lines or in a zigzag form.  
         [0121]    Edges of the radially extended sections  18   a ,  42   a  and  52   a , which are radially outwardly extended from the upper ends of the collars  20 , may be curled toward the metallic plate sections  12 . In this case, the curled parts are formed in the radially extended sections  18   a ,  42   a  and  52   a ; no curled parts are formed in the narrow sections  18   b ,  42   b  and  52   b . With this structure, machining oil, which invades in the curled parts while press machining, can be easily removed. is described above, in the present invention, the collared tube holes having the prescribed height can be formed in the thin and hard plate section, so that the heat exchanging fins can be lighter.  
         [0122]    The invention may be embodied in other specific forms without departing from the spirit or essential characteristics thereof. The present embodiments are therefore to be considered in all respects as illustrative and not restrictive, the scope of the invention being indicated by the appended claims rather than by the foregoing description and all changes which come within the meaning and range of equivalency of the claims are therefore intended to be embraced therein.