Abstract:
A method of brazing a temporarily assembled heat exchanger includes the steps of spraying an ionized fluid such as water on one surface. A powdered electrostatically charged flux is blown onto the opposite surface of the heat exchanger. A portion of the powdered flux is attracted to the one surface by the ionized fluid. Therefore, the flux material is uniformly spread across the heat exchanger. Finally, the heat exchanger is heated and brazed.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     Applicants have filed this same day, a commonly assigned application, Ser. No. 07/736,629 entitled &#34;Brazing Method.&#34; The disclosure of this application is hereby incorporated by reference in its entirety. 
     TECHNICAL FIELD 
     The present invention relates to a brazing method, and more particularly, to a method of coating an object with a flux. 
     BACKGROUND OF THE INVENTION 
     Heat exchangers including a serpentine flat tube and corrugated fins disposed between parallel sections of the tube used in an air conditioning system are well known. In brazing the serpentine tube and corrugated fins, various methods for coating flux have been employed. For example, a slurry of flux may be sprayed onto the heat exchanger, or the heat exchanger can be dipped into a flux bath, or electrostatic powdered flux may be blown onto the heat exchanger. The electrostatic powder is a dry powder, thus water is not used in blowing or coating the heat exchanger. It is not necessary to use a drying process when blowing an electrostatic powdered flux. On the other hand, it is necessary to use a drying process when spraying a slurried flux or when the heat exchanger is dipped in a flux bath. The coat of flux is relatively even, but despite cost savings over manually applying the flux, these methods suffer from disadvantages. 
     The brazing method using the above method of blowing a powdered electrostatic flux is explained as follows. A heat exchanger is temporarily assembled by disposing corrugated fins between the parallel flat outer surfaces of a serpentine flat tube which is fixed in position by a jig. The temporarily assembled heat exchanger is charged with electricity in reverse polarity to the flux. The powdered electrostatic flux is then blown onto one side surface of the heat exchanger. The powdered electrostatic flux attaches to the sides of the heat exchanger by an attractive electrical force. Thereafter, the heat exchanger is heated in a furnace, which completes the brazing process. 
     However, since the flux coats or attaches to the surface of the heat exchanger by only an attractive electrical force, this gives rise to a poorly coated heat exchanger. In addition, since the flux is blown onto only one side of the heat exchanger, the amount of flux which attaches to the other side of the heat exchanger is considerably less. Thus, a lack of uniformity in attaching the flux exists. 
     Alternatively, and as a means for solving the above problems, it has been suggested that two machines be employed for blowing the flux on both sides of the heat exchanger. If two machines are used in this way, then the cost of the fluxing method significantly increases. Also, the amount of flux that attaches to the heat exchanger does not increase as the amount of flux being blown onto the heat exchanger increases. However, some of the excess flux will be carried into the furnace. The excess flux is waste which causes the interior of the furnace to be fouled. 
     SUMMARY OF THE INVENTION 
     It is a primary object of the present invention to provide a brazing method which may improve the efficiency of attaching flux to an article. 
     It is another object of the present invention to provide a brazing method which may produce an article at low cost. 
     A brazing method according to the present invention comprises the steps of spraying water onto a surface of a temporarily assembled article, blowing a powdered electrostatic flux toward one surface of the article and heating the article in a furnace for brazing thereof. 
     Further objects, features and other aspects of the present invention will be understood from the following detailed description of the preferred embodiment of the present invention with reference to the annexed drawings. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a schematic perspective view illustrating the steps of spraying water and blowing powdered electrostatic flux. 
     FIG. 2 is a perspective view of a temporarily assembled heat exchanger. 
     FIG. 3 is a schematic view illustrating machines for spraying water and blowing a powdered electrostatic flux. 
     FIG. 4 is a schematic perspective view illustrating a heating process. 
     FIG. 5(a) is a cross-sectional view of a part of a heat exchanger illustrating the condition of flux that is attached in accordance with a conventional brazing method. 
     FIG. 5(b) is a cross-sectional view of a part of a heat exchanger illustrating the condition of flux that is attached in accordance with one embodiment of the present invention. 
     FIG. 6 is a flow diagram showing the steps in the brazing process. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     Referring to FIGS. 1-4 and 5(b), a brazing method according to one embodiment of the invention is shown. With reference to FIG. 1, a process of spreading or spraying water or some other ionized fluid and blowing, or expelling, a powdered electrostatic flux onto a heat exchanger is shown schematically. 
     Flux chamber 1 includes inlet opening 1a and outlet opening 1b. Overhead conveyor 2 extends through both openings 1a and 1b. Heat exchanger 3 is hung on overhead conveyor 2 by wires 2a. Water spraying machine 4 is disposed adjacent inlet opening 1a on one side of flux chamber 1. Electrostatic coating machine 5 is disposed adjacent outlet opening 1b on the other side of flux chamber 1. Thus, water spraying machine 4 will face one side surface of heat exchanger 3, while electrostatic coating machine 5 faces the other side surface. 
     With reference to FIG. 2, a temporarily assembled heat exchanger held together by a jig is shown. Heat exchanger 3 is made of aluminum and includes serpentine tube 3a and corrugated fins 3b disposed between the flat parallel surface portions or tube sections of serpentine tube 3a. Heat exchanger 3 is sandwiched between upper the jig members 6a and 6b and tightly secured by long nut and bolt mechanisms 7. Other means for securing the jig members will be readily recognized by those skilled in the art. 
     With reference to FIG. 3, the schematic construction of a water spraying machine 4 and an electrostatic coating machine 5 are illustrated. Water spraying machine 4 includes reservoir tank 4a, pump 4b and nozzle 4c. Water A contained in reservoir tank 4a is sprayed on one side surface 3c of heat exchanger 3 through nozzle 4c by pump 4b. Electrostatic coating machine 5 includes a supply of powdered flux within container 5a, high voltage generating device 5b, compressor 5c and gun 5d for blowing powdered electrostatic flux B. Powdered flux B is supplied to gun 5d from flux container 5a and is positive or negative charged with electricity by high voltage generating device 5b. Powdered and electrically charged flux B is blown toward the other side 3d of heat exchanger 3 by compressed air from compressor 5. 
     With reference to FIG. 4, a drying process and a brazing process are shown. Furnace 8 includes a preheat portion and a brazing portion. The preheat portion is adjacent inlet opening 8a and the brazing portion is adjacent outlet opening 8b. Heat exchanger 3 is dried in the preheat portion of furnace 8. After passing through the preheat portion of the furnace, heat exchanger 3 is conveyed into the brazing furnace. In the brazing portion, the assembly of the heat exchanger is completed. 
     The method of coating heat exchanger 3 with a flux and brazing heat exchanger 3 is described as follows and with reference to FIG. 6. Flat tube 3a and corrugated fins 3b which form heat exchanger 3 are temporarily assembled with jig 6 and nut and bolt mechanisms 7. Once temporarily assembled, heat exchanger 3 is hung on overhead conveyor 2 by wires 2a. Heat exchanger 3 is then charged with electricity such that the polarity is reversed to the polarity of flux B. Heat exchanger 3 is the conveyed into flux chamber 1 through inlet opening 1a. 
     Water is sprayed on one side surface. 3c of heat exchanger 3 by water spraying machine 4 in chamber The water clings to the surface of heat exchanger 3. Thereafter, heat exchanger 3 is moved in front of electrostatic coating machine 5 and flux B charged with electricity is blown toward the other side surface 3d of heat exchanger 3 by electrostatic coating machine 5. Since the water is attached or clings to side surface 3c, a portion of flux B blown toward surface 3d side is attracted to side surface 3c by the attractive electrostatic force as well as the attractive force of the water. 
     With reference to FIG. 5(a), the condition of attaching flux B to a heat exchanger using a conventional method is shown. The width of the layer of flux B attached to surface 3c of heat exchanger 3 is D1. The width of the layer of flux B attached to surface 3d of heat exchanger 3 is d&#39;1. The width of the layer of flux B attached to the central surface of heat exchanger 3 is d&#39;1. Flux B attached to a heat exchanger using one embodiment of the method of the present invention is illustrated in FIG. 5(b). The width of the layer of flux B attached to surface 3c of heat exchanger 3 is D2. The width of the layer of flux B attached to surface 3d of heat exchanger 3 is d&#39;2. The width of the layer of flux B attached to central surface 3e of heat exchanger 3 is d2. The width D2 is greater than the width D1. Furthermore, since the water is sprayed in the same chamber as the flux is blown in, the air in flux chamber 1 will have a high humidity. Therefore, water will attach to surface 3d and central surface 3e as well as surface 3c. Thus, the widths d&#39;2 and d2 are greater than the widths d&#39;1 and d1, respectively. 
     Heat exchanger 3 is disposed on conveyor 9 so that surface 3d of heat exchanger 3 faces upward. Thus, as shown in FIG. 5(b), the amount of the flux attached to side surface 3d of heat exchanger 3 is greater than that of the flux attached to surface 3c side thereof. When heat exchanger 3 is dried in the preheat portion of furnace 8, the flux on the side surface of heat exchanger 3d is melted and flows downwardly under the force of gravity. Thus, the amount of the flux on the surface of heat exchanger 3 becomes uniform. Heat exchanger 3 then enters the brazing portion of furnace 8 where the assembly is completed. 
     The invention has been described in detail in connection with a preferred embodiment. The preferred embodiment is illustrative only and thus, the invention is not restricted thereto. It will be easily understood by those skilled in the art that other variations and modifications can be made within the scope of this invention.