Abstract:
A brazing method for brazing components is provided. The method includes the steps of: coating a bonding portion between the components with a brazing material made of Cu—Sn—Ni—P alloy; introducing reducing gas into a brazing furnace; mounting the components in the brazing furnace; and increasing temperature in the brazing furnace so that the components are brazed. The brazing method provides excellent bonding condition. Specifically, the brazing material steadily penetrates into the bonding portion between the components so that the components are brazed steadily.

Description:
CROSS REFERENCE TO RELATED APPLICATION  
       [0001]     This application is based on Japanese Patent Application No. 2003-271462 filed on Jul. 7, 2003, the disclosure of which is incorporated herein by reference.  
       FIELD OF THE INVENTION  
       [0002]     The present invention relates to a brazing method for providing excellent bonding condition.  
       BACKGROUND OF THE INVENTION  
       [0003]     A conventional brazing method for a heat exchanger is disclosed in Japanese Patent Application Publication No. H10-286666. In the method, a surface of a fin, a tube or a plate is clad (i.e., coated) with a brazing material, and then, both of them are assembled. After that, a heat treatment is performed so that they are brazed.  
         [0004]     Specifically, the brazing material is composed of Cu, 6 to 15 wt. % of Sn, 5 to 7 wt. % of Ni, and 5 to 8 wt. % of P so that the melting point of the brazing material is lowered. Further, the heat treatment is performed in inert gas atmosphere such as nitrogen gas or argon gas at a temperature between 680° C. and 700° C. during three minutes. Thus, the method provides excellent operating efficiency, safety, and low cost.  
         [0005]     However, it is required that the brazing material steadily penetrates between components so that the components are steadily bonded. Specifically, a portion (e.g., a bonding portion between a tube and a tank) necessitates water-tightness or air-tightness of inner fluid in the heat exchanger. In some cases where the surface of the component is covered with an oxide film having a certain production state, the oxide film is not removed by a reducing function of phosphorous in the brazing material. Thus, the penetration (i.e., fluidity) of the brazing material is deteriorated by the oxide film. Therefore, to improve the penetration (i.e., fluidity) of the brazing material, a flux is necessitated. However, when the flux is used in the brazing method, a cost of the flux is added. Further, additional processes for applying the flux and for removing the flux after brazing are necessitated so that a manufacturing cost is increased.  
       SUMMARY OF THE INVENTION  
       [0006]     In view of the above problem, it is an object of the present invention to provide a brazing method for providing excellent bonding state. Specifically, in the method, a brazing material of Cu—Sn—Ni—P alloy is used without any flux.  
         [0007]     A brazing method for brazing components is provided. The method includes the steps of: coating a bonding portion between the components with a brazing material made of Cu—Sn—Ni—P alloy; introducing reducing gas into a brazing furnace; mounting the components in the brazing furnace; and increasing temperature in the brazing furnace so that the components are brazed.  
         [0008]     In the above method, the reducing gas can remove an oxide film disposed on the surfaces of the components without using a flux. Thus, the brazing material steadily penetrates into the bonding portion between the components so that the components are brazed steadily.  
         [0009]     Preferably, the components are a part of a heat exchanger, in which inner fluid flows.  
         [0010]     In this case, the brazing method is suitably used for the heat exchanger, which necessitates water-tightness or air-tightness by the brazing method.  
         [0011]     Preferably, the brazing material is made of Cu, 6 to 15 wt. % of Sn, 5 to 7 wt. % of Ni, and 5 to 8 wt. % of P.  
         [0012]     Preferably, the temperature in the brazing furnace after the step of increasing the temperature is in a range between 600° C. and 800° C. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0013]     The above and other objects, features and advantages of the present invention will become more apparent from the following detailed description made with reference to the accompanying drawings. In the drawings:  
         [0014]      FIG. 1A  is a front view showing a radiator, and  
         [0015]      FIG. 1B  is a side view showing the radiator according to a preferred embodiment of the present invention;  
         [0016]      FIG. 2A  is a cross sectional view showing the radiator taken along line IIA-IIA in  FIG. 1B , and  
         [0017]      FIG. 2B  is a view on arrow IIB in  FIG. 2A ;  
         [0018]      FIG. 3  is a front view showing test pieces for testing penetration of a brazing material; and  
         [0019]      FIG. 4  is a graph explaining a test result.  
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT  
       [0020]     A brazing method according to a preferred embodiment is provided. The method is suitably used for a heat exchanger made of copper or copper alloy. In the preferred embodiment, the brazing method is applied to a radiator  100  for cooling an engine (not shown) of a construction machine, as shown in  FIGS. 1A  to  2 B.  
         [0021]     Here, in components (which is described in detail as follows) of the radiator  100 , a fin  111  is made of copper based material, and other components are made of brass based material. The fin  111  and other components are bonded together by the brazing method with a copper based brazing material (described in detail later).  
         [0022]     The radiator  100  is composed of a core  110 , an upper tank  120 , and a lower tank  130 . The core  110  is a heat exchanger for cooling coolant water (i.e., the inner fluid flowing through the radiator  100 ) discharged from the engine. The core  110  is composed of a fin  111 , a tube  112 , a side plate  113  and a core plate  114 .  
         [0023]     The fin  111  is a heat radiator for radiating heat of the coolant water to a cooling wind side effectively. The fin  111  is formed from a thin band plate into a corrugated plate. The tube  112  is a member for passing the coolant water inside thereof. The tube  112  is formed such that the thin band plate is folded to be a flat oval in a cross section thereof, and then, both edges of the thin band plate are welded. The fin  111  and the tube  112  are alternately laminated so that they are aligned in a left-right direction in  FIG. 1A . A side plate  113  as a reinforcing member is disposed outside of the outermost laminated fin  111  in the laminated fins  111 , which is disposed outermost in the laminated direction. Here, multiple allays (e.g., three allays) of the tube  112  are formed in a flowing direction of the cooling wind in  FIG. 1B .  
         [0024]     The core plate  114  is a shallow box shaped component having a standing periphery for engaging with the opening of each of the upper and lower tanks  120 ,  130 . The core plate  114  is formed from a flat plate by a folding method or a drawing method. Multiple burring holes  114   a  are formed in a part of the core plate  114 , which corresponds to an edge of the tube  112  (i.e., a tube edge  112   a ) in a longitudinal direction. The burring hole  114   a  has a flange protruding to the inside of the tank. The tube edge  112   a  is inserted into the burring hole  114   a . The fin  111 , the tube  112 , the side plate  113  and the core plate  114  are brazed at each connecting portion.  
         [0025]     The upper and lower tanks  120 ,  130  are box shaped vessels having the opening disposed on a core plate  114  side. The opening of the tank  120 ,  130  is brazed with the core plate  114  so that they are brazed. An inlet pipe  121  and an outlet pipe  131  are brazed on each surface of the tanks  120 ,  130  disposed on an opposite tube side (i.e., a top or bottom surface of the tank  120 ,  130 ), respectively. The inlet pipe  121  and the outlet pipe  131  connect to the inside of the tanks  120 ,  130 , respectively. Thus, the radiator  100  is completed.  
         [0026]     The coolant water discharged from the engine is introduced into the radiator through the inlet pipe  121 , and then, the coolant water flows through the upper tank  120 , the core  110  (i.e., the tube  112 ), and the lower tank  130 . Then, the coolant water flows out of the radiator  100  through the outlet pipe  131 . The coolant water is cooled while flowing through the radiator  100 .  
         [0027]     The brazing method of the radiator  100  according to the preferred embodiment is described as follows.  
         [0028]     The brazing material is made of alloy composing copper (i.e., Cu), tin (i.e., Sn), nickel (i.e., Ni), and phosphorous (i.e., P). Each weight percentage is, for example, 75% of copper, 15% of tin, 5% of nickel and 5% of phosphorous, respectively. The melting point of the brazing material is about 600° C.  
         [0029]     The brazing material is preliminarily applied on each surface of the components ( 112 - 114 ,  120 ,  121 ,  130 ,  131 ) except for the fin  111 . Then, the components ( 111 - 114 ,  120 ,  121 ,  130 ,  131 ) are engaged together and they are fixed by a jig so that the radiator  100  is temporarily assembled.  
         [0030]     Then, the temporary assembly of the radiator  100  is disposed in a brazing furnace so that the components ( 111 - 114 ,  120 ,  121 ,  130 ,  131 ) are integrally brazed. Here, hydrogen gas (i.e., H 2 ) as reducing gas is introduced into the brazing furnace. Brazing temperature condition is in a range between 600° C. and 800° C.  
         [0031]     Thus, an oxide film disposed on the surfaces of the components ( 111 - 114 ,  120 ,  121 ,  130 ,  131 ) is removed by the reducing gas (i.e., the hydrogen gas) without using a flux. Thus, the brazing material steadily penetrates into each bonding portion between the components ( 111 - 114 ,  120 ,  121 ,  130 ,  131 ) so that the excellent brazing condition is obtained. Specifically, the brazing method is suitably used for the radiator (i.e., the heat exchanger)  100 , which necessitates the water-tightness or air-tightness between the tube  112  and the core plate  114  by the brazing method.  
         [0032]      FIGS. 3 and 4  explain a testing method for confirming the effect of the brazing method and a test result.  FIG. 3  explains the testing method for confirming the effect. A clearance having a predetermined slant angle is provided between an upper test piece  140  and a lower test piece  141 . Then, the brazing material  1  is sandwiched by the upper and lower test pieces  140 ,  141 . A fillet length L of the brazing material  1 , which is formed in the clearance, is measured. The fillet length L is defined as shown in  FIG. 3 .  
         [0033]      FIG. 4  shows the result of the test. In the present method with using the hydrogen reducing furnace and without using flux, the fillet length L is obtained to be the same length as the conventional method with using the nitrogen furnace and with using flux. The actual brazing condition (i.e., the fixation) between the tube  112  and the core plate  114  is such that, in the conventional method, defective penetration of the brazing material is occurred in about one-third of the total number of joint of tube  112  and core plate  114 . The defect is mainly occurred at a rounding portion (i.e., R portion) of the tube  112 . However, in the present method, all fixations provide excellent penetration of the brazing material.  
         [0034]     Further, since the brazing material is made of the Cu—Sn—Ni—P alloy, the melting point is lowered in the brazing process so that the reduction of strength of the components is prevented.  
         [0035]     Although the reducing gas in the brazing process is the hydrogen gas, the reducing gas can be a carbon monoxide gas (CO) or the like.  
         [0036]     Further, although the brazing method is used for the radiator  100  of the construction machine, the method can be used for another radiator of another four-wheel vehicle. Furthermore, the method can be used for another heat exchanger instead of the radiator  100 , for example, an intercooler, a condenser, a heater core, an evaporator or the like.  
         [0037]     Such changes and modifications are to be understood as being within the scope of the present invention as defined by the appended claims.