Abstract:
A heat exchanger assembly that includes a tube having an internal surface and an external surface. An aluminum-based component is disposed adjacent to the tube, the aluminum-based component has an aluminum-based material that has a magnesium content that is above 0.3%, wherein the aluminum-based component is joined to the tube using a brazing flux applied during a controlled atmosphere brazing process.

Description:
BACKGROUND OF THE INVENTION  
       [0001]     1. Field of the Invention  
         [0002]     The present invention relates to a heat exchanger for automotive vehicles manufactured by controlled atmosphere brazing (“CAB”). In particular, the present invention regards the use of fin materials containing a higher than normal amount of magnesium (“Mg”) to add strength to the heat exchanger while maintaining an adequate fin-to-tube brazing bond or fillet that is required for excellent heat transfer.  
         [0003]     2. Discussion of Related Art  
         [0004]     It is known to provide automotive vehicles with heat exchangers such as condensers, evaporators, heater cores and coolers generally made of aluminum or aluminum alloys. These heat exchangers are alternating rows of tubes or plates to facilitate fluid transfer through the heat exchanger. The heat exchangers often include convoluted fins brazed to the external surfaces of the tubes to provide increased surface area to enhance heat transfer with the air passing over the heat exchanger. Additionally, tanks, headers and side supports are used to construct the heat exchanger.  
         [0005]     As described in U.S. Pat. No. 5,771,962, the entire contents of which are incorporated herein by reference, one known process for brazing the fins to the tubes and turbulators is a process known as “controlled atmosphere brazing” (CAB). When the CAB process is employed with heat exchangers made of aluminum or aluminum alloys, the fins typically are made of 3xxx series aluminum that contains a very low level of magnesium, such as 0.3 percent. It is generally understood that when levels of magnesium higher than 0.3% are contained in aluminum heat exchanger components the interaction between the magnesium and the KALF flux known as NOCOLOK prevents the bond or fillet between the heat exchanger components from occurring and thereby foiling the CAB process. Thus, when the magnesium level in the fin material exceeds 0.3 percent, the CAB process will not bond the fins to the tubes, which reduces heat transfer performance and heat exchanger structural integrity.  
         [0006]     Faced with the above competing interests—improving brazing attachment versus improving fin strength, several solutions have been proposed. One proposed solution is to use a triple clad material to provide a boundary between a high magnesium bearing base material and the outer clad layer. Such a structure is known to be sold by Finspong Heat Transfer AB of Sweden. This structure limits the amount of high strength material contained in the tube alloy due to the minimal thicknesses being used in tube production. This leads to a tube alloy with minimal increases in strength.  
         [0007]     A second proposed structure is to limit the amount of magnesium allowed in the aluminum used to form the heat exchanger that lies below 0.3%. This trace amount of magnesium does not interfere with the flux and allows it to break down the aluminum oxide layer on the surface of the components, which enables the bond or fillets to form between the components that make up the heat exchanger. While the bond or fillets are formed with this magnesium content, the strength characteristics of the fin are limited. To overcome this limitation, the fin is made thicker by increasing the material&#39;s gage to provide the required strength. One disadvantage of such a proposal is that increasing the gage thickness results in increasing weight and cost for the heat exchanger.  
         [0008]     In view of the above-described disadvantages, it is an object of the present invention to provide a heat exchanger that uses a fin material that is higher in strength than fin materials that are used with known CAB processes.  
         [0009]     Another object of the present invention is to maintain the strength of a heat exchanger while also reducing in weight and cost the heat exchanger.  
       SUMMARY OF THE INVENTION  
       [0010]     One aspect of the present invention regards a heat exchanger assembly that includes a tube having an internal surface and an external surface. An aluminum-based component is disposed adjacent to the tube, the aluminum-based component has an aluminum-based material that has a magnesium content that is above 0.3%, wherein the aluminum-based component is joined to the tube using a brazing flux applied during a controlled atmosphere brazing process.  
         [0011]     A second aspect of the present invention regards a method for manufacturing a heat exchanger assembly that includes providing a tube having an internal surface and an external surface. Disposing an aluminum-based component adjacent to the tube, the aluminum-based component having an aluminum-based material that has a magnesium content that is above 0.3%. Applying a brazing flux during a controlled atmosphere brazing process so as to join the aluminum-based component to the tube.  
         [0012]     Each of the above aspects of the present invention provides the advantage of providing a heat exchanger that uses a fin material that is higher in strength than fin materials that are used with known CAB processes.  
         [0013]     Each of the above aspects of the present invention provides the advantage of maintaining the strength of a heat exchanger while also reducing in weight and cost the heat exchanger.  
         [0014]     The present invention, together with attendant objects and advantages, will be best understood with reference to the detailed description below in connection with the attached drawings. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0015]      FIG. 1  is a partial perspective view of an embodiment of a heat exchanger assembly according to the present invention;  
         [0016]      FIG. 2  is a sectional view taken along line  2 - 2  of  FIG. 1 ;  
         [0017]      FIG. 3  is an enlarged view of circle  3  of  FIG. 2 ; and  
         [0018]      FIG. 4  is a sectional view of a second embodiment of a heat exchanger assembly according to the present invention. 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0019]     An embodiment of a heat exchanger assembly  10 , according to the present invention, is shown in  FIG. 1 . The heat exchanger assembly  10  is a condenser for an air conditioning system (not shown) of a vehicle such as an automotive vehicle (not shown). The heat exchanger assembly  10  may be a condenser, evaporator, heater core, radiator or transmission oil cooler.  
         [0020]     As shown in  FIG. 2 , the heat exchanger assembly  10  includes at least one, preferably a plurality, of tubes  12  or plates made of an aluminum-based material. By “aluminum-based” with respect to the tube  12  and components like the fins  22  mentioned below, is meant that the aluminum-based composition includes mostly aluminum, but may be alloyed with other metals like silicon, copper, magnesium, zinc and so forth. Each tube  12  extends longitudinally and is generally oval in shape. The aluminum based core material of tube  12  is preferably selected from the Aluminum Association 1XXX, 3XXX, 5XXX and 6XXX series aluminum alloys. The core aluminum material may and desirably does include magnesium. Preferably, the core material includes magnesium in an amount less than 3% by weight.  
         [0021]     Each tube  12  has an internal surface  14  and an external surface  16 . In those situations when the heat exchanger assembly  10  is a condenser, the tubes  12  are not clad as shown in  FIG. 3 . In those situation when the heat exchanger assembly is not a condenser, such as an evaporator, heater core, radiator or transmission oil cooler, the internal tube surface  14  and/or external tube surface  16  each have a silicon-aluminum composition cladding thereon, such as the cladding known as Aluminum Association 4343 or 4045, as shown in  FIG. 4 . It should be appreciated that the composition cladding  18  is made by rolling aluminum sheets of different alloys which is clad to the surfaces  14  and  16  as desired of the tube  12  by methods well known in the art.  
         [0022]     As shown in  FIGS. 1-3 , the heat exchanger assembly  10  includes at least one aluminum based fin component disposed adjacent the tube  12 , which is to be joined by brazing to the tube  12 . For example, the heat exchanger assembly  10  may include a turbulator  20  disposed within the tube  12  adjacent the internal surface  14 . The turbulator  20  extends longitudinally and laterally in a series of undulations. The turbulator  20  breaks up the flow of fluid passing through the tube  12  in use to effect heat transfer. In another example, the heat exchanger assembly  10  includes a fin  22  disposed adjacent the external surface  16  of tube  12 . The fin  22  extends longitudinally and laterally in a series of undulations. The turbulator  20  and fin  22  are each made of an aluminum-based material such as the Aluminum Association 5XXX or 6XXX series aluminum alloys. In the case of using the 5XXX series of aluminum alloys, the alloy has a magnesium content of 1.2 to 2%. In the case of using the 6XXX series of aluminum alloys, the alloy has a magnesium content of 0.2 to 1.2%. It is contemplated that the fin  22  can be an aluminum alloy that has a magnesium content ranging from 0.4 to 3%. The turbulator  20  and the fin  22  may be clad with a silicon-aluminum composition cladding, such as the cladding known as Aluminum Association 4343 or 4045. Generally, however, such cladding is not used for turbulator  20  and fin  22 .  
         [0023]     For manufacture of the heat exchanger assembly  10 , the turbulator  20  and fin  22  are joined to the tube  12  using a CAB furnace brazing process. A brazing flux is applied to a joint between the tube  12  and any component to be joined to the tube  12  by brazing, i.e., the turbulator  20  or fin  22 . An example of a suitable brazing flux is disclosed in U.S. Pat. No. 5,806,752, the entire contents of which are incorporated herein by reference. The brazing flux can be applied onto the joint area by such ways as brushing, dipping, and spraying, the latter being preferred because it provides more uniform application.  
         [0024]     For manufacture of the heat exchanger assembly  10 , the turbulator  20  and fin  22  are joined to the tube  12  using a CAB furnace brazing process. In the CAB process, the heat exchanger assembly  10 , with flux applied in at least the areas of the to be formed braze joints, is placed on a braze holding furnace fixture and preheated, for example, to a temperature in a range from about 425° F. to about 474° F. The heat exchanger assembly  10  and braze holding furnace fixture are transferred to a prebraze chamber where it is soaked for about 3-15 minutes at about 750° F. Subsequently, the hot heat exchanger assembly  10  and braze holding furnace fixture are transferred to a conveyor and moved through a CAB furnace which is purged by applying a nitrogen gas at inside the CAB furnace. It should be noted that a conveyor system may be used to convey the heat exchanger assembly  10  to one or more stations to perform all or substantially all of the described processes.  
         [0025]     In the CAB furnace, the heat exchanger assembly  10  is kept for 2-3 minutes at about 1095° F.-1130° F. The brazed heat exchanger assembly  10  is then cooled, removed and applied for its intended use. The end result of the process is that a strong bond between the fins  22  and the tubes  12  is formed without requiring the thickness of the fins  22  to be increased. In particular, the fins preferably have a thickness of approximately 0.002″ which is less than the fin thicknesses ranging from 0.003″ to 0.004″ used in previous processes.  
         [0026]     The foregoing description is provided to illustrate the invention, and is not to be construed as a limitation. Numerous additions, substitutions and other changes can be made to the invention without departing from its scope as set forth in the appended claims.