Abstract:
An improved bending apparatus for bending a radiused corner at a window in a brazed heat exchanger core where no tubes and fins are located. A cylindrical mandrel and sliding pressure die are designed to completely surround the manifold in the areas of the window and provide a continuous, rolling contact area or profile support around the manifold as the bending moment is applied.

Description:
[0001]    The invention relates to a method and apparatus for bending a brazed aluminum heater exchanger. Priority is claimed to provisional application 61/188,440, filed Aug. 8, 2008. 
     
    
     TECHNICAL FIELD OF INVENTION 
     Background of Invention 
       [0002]    Brazed aluminum heat exchangers of the type having spaced header tanks (or manifolds), flat elongated tubes corrugated air fins or centers have been a commonplace in automotive applications, where they are of a relatively small face area and installed flat, such as air conditioning condensers. It is known to bend such automotive heat exchangers into a V or U shape, as shown in U.S. Pat. No. 4,876,778, but this is a relatively simple and straightforward bend in which the tubes and fins (core face) themselves are bent, perpendicular to the tubes, not the heavier manifolds themselves, which remain straight 
         [0003]    That same U or V shaped bend of the core face can be applied to stationary air conditioning applications as well (residential heat pump, for example), but such applications often require a more difficult bending operation in which the tubes are left unbent, straight, and vertical, while the manifolds are bent into a rectangular perimeter. The vertical tubes drain condensation better, but the manifolds are heavier and more difficult to bend. Several different bending apparatuses and methods are known. A typical apparatus consists of a cylindrical solid mandrel that engages the tube the core face, between the manifolds, and opposed flat clamps engaging the outer core face and/or manifolds, one of which is held stationary and the other of which is swung in to bend the core around the cylindrical mandrel. The core is bent into a 90 degree, radiused corner or corners. Another issue is the behavior of the tubes and fins at the “corners” where the manifolds are bent. These can buckle and deform, presenting at least an aesthetic objection, if not a diminution in performance. Fins may also pull away from the tubes in the bend area, decreasing performance. This limits how tight or small a bend radius can be achieved. 
         [0004]    Published Japanese application JP-2005090806 shows the basic bend configuration described above, and discloses some prior approaches to the bending problem. The most basic approach is to simply remove (leave out) the tubes and fins at the corners, and to cover the resulting open windows with a screen of some sort in the final installation. This has the obvious drawback of removing a considerable amount of heat exchange area out of the core face, besides necessitating the addition of some sort of screen at the corners to “fill in” the missing area and avoid disturbance of the forced air flow at the paths of least resistance. This is especially a problem if the bending apparatus and technique do no allow for a tight, sharp bend, because more tubes and fins have to be left out. What the art fails to disclose is a bending method and apparatus designed to bend the manifolds, even free of tubes and fins, into such a tight and well controlled radiused corner. A typical bender will clamp the core on one side of the bend area, and apply a bending force to the other, either across the core area or the manifolds or both, but no measures are taken to actively control the profile and shape of the bent sections of the manifold. 
     
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         [0005]    This invention will be further described with reference to the accompanying drawings in which: 
           [0006]      FIG. 1  is a front and top view of a heat exchanger having a core window prior to bending. 
           [0007]      FIG. 1  is a face on view of a heat exchanger core having a core window prior to bending. 
           [0008]      FIG. 2  is a cross section of  FIG. 1 , 
           [0009]      FIG. 3  shows the cross section of  FIG. 2  post bending. 
           [0010]      FIG. 4  shows a perspective view of the bending apparatus. 
           [0011]      FIG. 5  shows the same perspective apparatus view with the bent heat exchanger in place. 
           [0012]      FIG. 6  shows a cross section through  FIG. 5 . 
           [0013]      FIGS. 7A-D  show progressive sequences of the bending process. 
       
    
    
     DETAILED DESCRIPTION OF INVENTION 
       [0014]    In accordance with a preferred embodiment of this invention, referring to  FIGS. 1 and 2 , a basic, pre bend core  10  is stacked and brazed as shown. In the figure, allowance is made for only one bend, but that could also include two or three bend areas, as well, all of which would be handled identically. Core  10  includes a series of what will ultimately be vertically oriented flat extruded aluminum tubes  12  running between parallel, upper and lower cylindrical aluminum manifolds  14 . Manifolds  14  need not absolutely have a cylindrical cross section, although that is preferred for pressure resistance. Brazed between adjacent tubes  12  are conventional corrugated air fins or centers  16 . Core  10  is conventional but for a deliberate removal of tubes  12 , about eight or nine in number, leaving an open window  18  and an unslotted length of manifolds  14  of approximately 4 inches. This would vary depending on the size of the core. The open area would necessitate some accommodation in a typical core stacker mechanism, such a spacer to fill in the window  18  temporarily. While the provision of the window  18  at the bend area or corner (what will ultimately be a corner) is not new per se, the subject invention provides a novel apparatus and method that takes better advantage of the window  18  to provide a tight, symmetrical and undeformed bend, with minimal stress to adjacent tubes  12 . 
         [0015]    As disclosed in  FIGS. 4 ,  5  and  6  the improved bending apparatus used in the method of the subject invention is designed to apply the bending force only to the manifolds  14 , and to provide additional, active support of the manifolds  14  in the bend area in particular. A central post  20  rotatable about its center axis carries identical upper and lower semi-cylindrical bending mandrels  22 , each of which has a semi cylindrical trough  24  bounded by semi cylindrical upper and lower trough edges  26  and  28 . Trough  24  is semi cylindrical both along its length, and in its cross section, matching in its cross section the profile of manifold  14 . Mandrel  22  also carries a straight back up clamp  30  which has a straight trough  32  of the same cross section as semicylindrical trough  24 , bounded by straight upper and lower edges  34  and  36 . The troughs  24  and  32  are sized to fit closely around the manifolds  14 , with the upper edges  26  and  34  aligned along the center line (12 o&#39;clock position) of manifold  14 , but with the lower edges  28  and  36  just clearing the inner of core  10 . The lower one of the mandrels  22  is an exact minor image of the upper one, so it is to be understood that the terms “upper edge” and “lower edge” would be reversed, even though the basic shape is the same. Extending radially inwardly from the semi cylindrical mandrel lower edge  28  is a semi cylindrical lobe  38 , which is concentric to upper edge  26 , and which subtends enough arc length to substantially equal the straight length of that portion of the manifold  14  located within the window  18 . A pair of pressure plate dies  40  located on the opposite side of core  10 , one opposed to each mandrel  22 , each has a semi cylindrical, straight trough  42  equal in cross section to mandrel straight trough  32 , bounded by upper and lower edges  44  and  46 . Upper edge  44  also is aligned with the center line of manifold  14 , while the lower edge  46  clears the outer face of core  10 . Extending inwardly form the lower edge  46  is a straight lobe  48 , beginning just in from the end of each die  40 , which is coplanar to upper edge  44  and which has a straight length substantially equal to the arc length of semi cylindrical lobe  38 . A pair of clamp plates  50 , each of which has a straight trough  52  of semi cylindrical cross section equal in size to the mandrel back up clamp straight trough  32 , is each located opposed to a respective mandrel back up clamp  30 . 
         [0016]    The operation of the apparatus described above to carry out the method of the invention is described by reference to  FIGS. 7A-7D . Core  10  is placed with upper and lower manifolds  14  located between opposed pairs of clamp plates  50  and mandrel back up clamps  30  on the leading side of the window  18 . The lead edge of the each semi cylindrical lobe  38  is aligned the front edge of a window  18 , as is the lead edge of a straight lobe  48  on a pressure plate die  40 . The location of these two lead edges of lobes  38  and  48  is shown by the dotted line, which intersects the turning axis of the post  20  and may be referred to as the line of tangency, and represents a rolling point or area through which the window sections of the manifolds  14  continuously move as they are bent. Next, the upper and lower manifolds  14  are tightly clamped between opposed pairs of mandrel back up clamps  30  and clamp plates  50 , while the pressure plates dies  40  are moved into alignment with the clamp plates  50 . This brings the lead edges of the lobes  38  and  48  into clamping engagement, inside the window  18 , so that the entire outer profile (both the inner and outer halves) of that part of the manifolds  14  within the windows  18  is contained closely within the surrounding troughs  24  and  42 . That is, the upper edges  26  and  44  are tightly clamped at the 12 o&#39;clock line of the manifolds  14 , and the lobes  38  and  48  are tightly clamped at the 6 0&#39;clock one of the manifolds, within the windows  18 . This provides the maximal possible support to the manifolds  14  in that area, more so than known bending apparatuses. 
         [0017]    Next, as seen in  FIGS. 7A-7D , post  20  is turned counter clockwise, thereby swinging the mandrels  22  in the same direction, and the clamp plates  50  engaged with the mandrel back up clamps  30  are swung in the same direction about the same pivot axis to maintain the tight grip on the manifolds  14 . This serves to pull that portion of the manifolds  14  to the right of the tangency line, that portion encompassed by the windows  18 , around and into the mandrel semicylindrical trough  24 . Concurrently, the pressure plate die  40  is slid straight to the left at a rate sufficient to maintain the straight lobe  48  in rolling, non-sliding contact with the semicylindrical lobes  38 , which move into the windows  18  as the manifolds  14  are bent into a matching radius and the straight lobes  48  concurrently move out of the bending windows  18 . Therefore, during the entire bending process, that part of the manifolds  14  moving into the bend is continuously supported by the troughs  26  and  42  between the upper trough edges  26  and  44 , which maintain rolling contact, and the lower lobe edges  38  and  48 , which also maintain rolling contact. A continuously rolling area of profile support located centered on the dotted line of tangency maintains the profile, supporting both the inner half of the profile in one trough and the outer half of the profile in another trough, throughout the bend. (Upper and lower, as designations, would be reversed for the lower mandrel  22 , of course) This serves both to maintain the circular profile of the manifolds as well as to protect the joints of the tubes  12  with the manifolds  14 , since all of the bending force is applied to the manifolds  14  only. This allows the radius of the bend to be tightened, as well. 
         [0018]    While this invention has been described in terms of the preferred embodiments thereof, it is not intended to be so limited, but rather only to the extent set forth in the claims that follow. Fundamentally and most simply, the basic invention entails supporting the entire profile of that portion of the manifolds located within the open area of the window during the bending process, between a rotatable cylindrical mandrel supporting the inner side of the mandrels, which has the desired radius and inner arc length of the bend to be created, and an opposed straight pressure die supporting the other side of that portion of the manifolds, and which slides along its length at a rate that maintains a continual rolling contact between it and the cylindrical mandrel as the bending force is applied, however it is applied, and until the bend is completed. It is an additional advantage to provide a pair of clamping elements in the lead of the bend area, by incorporating a straight back up clamp on the mandrel and an opposed clamp plate. It is also advantageous to support more of the manifold on the leading side of the bend and to also apply the bending force through that back up clamp, and to support more of the manifold on the trailing side of the bend with an additional length on the pressure die, more than is necessary just to support the profile of the bend. The additional manifold support provided on the leading and trailing sides of the bend cannot support the entire circumference of the manifold profile, because of the intervening tubes, but still provides an advantage. The manifold profile could be a shape other than round, meaning that the various supporting troughs would have a different matching cross sectional shape (square or elliptical), but the rolling contact lobes that provide all round support to the profile would have the same basic structure.