JPH0358827B2 - - Google Patents

Description

[Detailed description of the invention]

[Field of Application of the Invention] The present invention relates to a method for manufacturing a heat exchanger, and in particular, a method suitable for manufacturing a heat exchanger composed of metal members such as fins and tubes, such as in room air conditioners, car air conditioners, etc. Regarding. [Background of the Invention] Generally, in the above-mentioned type of heat exchanger, a fluid flows as a cooling medium or a heating medium through a metallic channel having a large contact area with the fluid. In order to increase the contact area of fluid, the shape of the metal forming the flow path becomes complex. For example, in a heat exchanger consisting of fins and tubes to increase the contact area, the tubes are arranged in holes or grooves provided in the fins, and the fins and tubes are connected by brazing. In this case, the flux used for brazing was chloride-based. Since chloride-based flux is highly corrosive, the method of manufacturing heat exchangers using this flux requires complete removal of the flux after brazing. This method has disadvantages in that it requires a large number of steps such as washing, and the cost of the equipment is also high. In order to eliminate these drawbacks, Al-Si system
Mg-added brazing filler metal or Al-Si system with Bi,
Attempts have been made to use a brazing filler metal containing a small amount of Sr, Sb, etc., and to perform brazing in a vacuum or inert gas without using flux. (Tokuko Showa 48-
(No. 31821, Japanese Patent Publication No. 50-4466) However, the Al material normally used for the fins and tubes of heat exchangers is susceptible to corrosion, and is particularly susceptible to electrolytic corrosion that forms local batteries. For this reason, in heat exchangers such as automobile radiators and condensers for car air conditioners, which are installed in high temperatures and in an atmosphere where dust is present, which promotes corrosion, pitting corrosion occurs frequently within a short period of time. This had the problem of degrading the function of the device and even causing it to stop functioning. In order to deal with the above problem, there is a method of containing a predetermined amount of Zn in the core material of the cooling fin, thereby lowering the potential and actively corroding the cooling fin to prevent pitting corrosion from occurring in the tube. is being attempted. However, with this method, it is difficult to form a surface layer uniformly containing cooling fins Zn, and there is still a problem in preventing pitting corrosion. Recently, a method has been proposed in which a tube is pre-plated with Zn and a Zn diffusion layer is formed in the brazed portion when such a tube and fin are brazed with a fluoride-based non-corrosive flux. (Unexamined Japanese Patent Publication 1987)
−198257) However, with this method, tube
Zn plating requires a large number of pre-treatment and post-treatment steps, and since Zn is easily oxidized, it is necessary to store the tube after plating and use expensive fluoride-based non-corrosive flux. [Object of the invention] The object of the present invention is to solve the problems of the prior art,
It is an object of the present invention to provide a method for manufacturing a heat exchanger that can easily manufacture a heat exchanger with excellent pitting corrosion resistance without using flux. [Summary of the Invention] The method for manufacturing a heat exchanger of the present invention is such that at least one of the metal members to be joined to each other by brazing is formed of a brazing sheet clad with a brazing material, and Brazing is carried out without flux in an atmosphere above the melting point of the brazing filler metal constituting the brazing sheet and below the melting point of the metal member, and then brazing is carried out at a temperature below the melting point of the brazing filler metal of the brazing sheet and without flux. The method is characterized in that a vapor of a metal less noble than the metal member or an alloy thereof is deposited on the surface of the metal member including at least the brazed portion in an oxidizing atmosphere to form a diffusion layer or an alloy layer of the metal. . In the present invention, the metal members that are joined to each other by brazing are composed of cooling fins, liquid passage tubes, etc., and these metal members are made of aluminum.
However, one side to be bonded can be made of Al, and the other side can be made of a material selected from Cu, Ti, and Fe bases. At least one of the metal members is made of a brazing sheet whose surface is clad with a brazing material. After such metal members, at least one of which is made of a brazing sheet, are assembled according to the structure of each heat exchanger, they are heated in a vacuum or in a non-oxidizing atmosphere and brazed without flux. At this time, the heating temperature needs to be higher than the melting point of the brazing material from the viewpoint of brazing processing, but it needs to be lower than the melting point of the metal member from the viewpoint of preventing deformation of the metal member. The non-oxidizing atmosphere may be an atmosphere using H ₂ gas in addition to Ar gas and N ₂ gas. Since it can be brazed without flux, it is extremely advantageous for brazing heat exchangers with a complex structure in which the gaps between the fins are small and a large number of fins and tubes are joined. Next, the diffusion layer or alloy layer formed on the surface of the metal member including the brazed portion is made of a metal less noble than the metal member. By using a base metal, metal members such as fins and tubes can be protected from being sacrificially corroded by the surrounding corrosive environment. The formation of the diffusion layer or alloy layer is carried out at a temperature below the melting point of the brazing material in order to secure the brazed portion. The base metal must have a melting point below the melting point of brazing and must be able to generate steam. Therefore, the base metal should be arbitrarily selected depending on the material of the metal members such as fins and tubes and the material of the brazing filler metal, but when the metal member is Al or its alloy, Zn and Zn alloy are preferable. Zn
As the alloy, Zn-Al, Zn-Sn, etc. are suitable. Such Zn and Zn alloys generate steam at 500-600°C, which is sufficient to alloy with Al. In addition, a non-oxidizing atmosphere such as Ar, N ₂ , H ₂ or the like is preferable to a vacuum, since a uniform corrosion-inhibiting metal film can be formed on the surface of the metal member by convection of the metal vapor. A corrosion-inhibiting metal film can be formed by steam convection, so the gaps between the fins are small.
A corrosion-inhibiting metal film can be formed efficiently and easily even on heat exchangers with complex shapes. Furthermore, when the heat of the metal member heated during brazing has not completely decreased, that is, within a temperature range where a diffusion layer or an alloy layer of the metal can be formed by adhesion of metal vapor, the metal member is moved to a separate room. , the metal vapor deposition process can be performed continuously and efficiently with the brazing process. [Embodiments of the Invention] An embodiment of a heat exchanger composed of fins and tubes will be described with reference to FIG. Similar to the conventional heat exchanger 1, a large number of liquid passage tubes 2 and cooling fins 3 are stacked alternately, and liquid passage and seat plates 4, 4' are installed at both ends. These members are integrally joined together by brazing. As shown in FIG. 1B, the cooling fins 3 are formed of a brazing sheet in which a core material 5 mainly made of Al is clad with an Al--Si--P brazing material 6. To explain the materials of each member in detail, the liquid passage tube 2 is
The core material of the cooling fin 3 is A3003, the brazing material is Al-10%Si-0.05%P-0.8%Cu, and the liquid passage and seat plates 4 and 4' are each made of A1050. Before assembly, each metal member of the heat exchanger constructed as described above is degreased with trichloride, and
% aqueous solution was used for alkaline cleaning. These metal members were combined and brazed by heating at 615° C. for 30 seconds in N ₂ gas with a gas dew point of −30° C. Next, open the shutter of the evaporation chamber and let the temperature rise to approx.
The metal member was inserted in a heated state into an evaporation chamber maintained at .degree. The brazed heat exchanger 1 is slowly cooled from 615°C to 550°C, and Zn vapor is immediately deposited thereon. The Zn lump used at this time had a purity of 99% and was placed on the heater in the evaporation chamber. _N2 gas has a dew point of −30
It was warm at ℃. Place the metal part in the evaporation chamber for about 7 minutes,
After that, the shutters that had been lowered were opened and sent into the cooling room. Example 2 Another shape of the heat exchanger is shown in FIG. A heat exchanger with such a shape is called a corrugated heat exchanger. That is, the fins 8 are arranged between the flat tubes 7 and each contact point is brazed. and,
As shown in FIG. 2b, the fins 8 are formed of a brazing sheet in which a core material 9 mainly made of Al is clad with an Al--Si--P brazing material 10. To describe the material and shape of each member in detail, the fin 8 is A3003, the brazing material is Al-9%Si-
0.05%P-0.2%Mg, dimensions 50 x 0.17 (cross section,
Fin length: 20mm), and flat tube 7 is
It is made of A1050 and has dimensions of 50 x 4 holes x 1.5 (cross section). Then, Zn vapor was applied to a three-stage combination of these metal members in the same manner as in Example 1. As a comparative example, a heat exchanger having the same shape as that used in Example 1 was used, except that a brazing sheet clad with Al8%Si-0.5%Mg was used to braze the fin material, and the heat exchanger was 2×10 ^{- 5} torr vacuum, 610
℃ and a heat exchanger brazed for 60 seconds (Comparative Example 1), and a heat exchanger with the same shape as that used in Example 2, except that Al
A brazing sheet clad with -9%Si-0.3%i was applied, and _N2 gas with a gas dew point of -65℃ was used.
A heat exchanger brazed under conditions of heating at 615°C for 60 seconds (Comparative Example 2) was also subjected to a comparative test. In addition, the heat exchanger had the same shape as that used in Example 2, except that a brazing sheet made of A4343 brazing filler metal was applied, and the non-corrosive flux was 46% KF and 54% AlF ₃ by weight. Approximately 10% of Zn powder is added to the composition.
After applying an aqueous solution to the entire surface of the heat exchanger and subsequently drying the water, apply _N2 gas with a gas dew point of -30°C to 610°C.
A heat exchanger (Comparative Example 3) brazed under the conditions of 60 seconds at ℃ was also subjected to a comparative test. Polarization curves were measured in a 3% NaCl aqueous solution using sample pieces obtained by cutting out a portion of the tubes of these heat exchangers, and the presence or absence of a corrosion-inhibited region was adjusted. In addition, corrosion tests were conducted to investigate pitting corrosion resistance.
It was conducted for 150 hours using the JISH8601 Cass test. Table 1 shows the presence or absence of corrosion suppression zones and pitting depth of various heat exchangers. The corrosion suppression region in the polarization curve roughly corresponds to the passive region found in stainless steel, for example, and means that a resistive film is formed in which the progress of corrosion is significantly attenuated.

〔Effect of the invention〕

As described above, according to the present invention, the entire heat exchanger can be brazed in one piece, and the convection of metal vapor can efficiently corrode the surface of metal members even in heat exchangers with complex structures. Since it is possible to form a film having a suppression zone, a heat exchanger with excellent pore corrosion resistance can be manufactured. Furthermore, since flux is not used during brazing, steps such as cleaning after brazing are not required.

[Brief explanation of drawings]

FIG. 1a is an overall perspective view of a heat exchanger according to a first embodiment of the present invention, FIG. 1b is an enlarged view of a main part of FIG. 1a, and FIG. A perspective view of such a heat exchanger, FIG. 2b is an enlarged view of the main part of FIG. 2a,
FIG. 3 is an overall perspective view of a heat exchanger according to another embodiment of the present invention. 1...Heat exchanger, 2...Tube, 3...Fin, 4, 4'...Liquid passage and seat plate, 5...Heartwood, 6
...brazing metal, 7...flat tube, 8...fin, 9...heartwood, 10...brazing metal, 11...fin, 12...tube.

Claims (1)

[Claims] 1. At least one of the metal members to be joined to each other by brazing is formed by a brazing sheet clad with a brazing material, and the brazing sheet is formed in a vacuum or in a non-oxidizing atmosphere. brazing without flux at a temperature above the melting point of the brazing sheet and below the melting point of the metal member, and then at least brazing at a temperature below the melting point of the brazing material of the brazing sheet in a non-oxidizing atmosphere. A method for manufacturing a heat exchanger, characterized in that a vapor of a metal less noble than the metal member or an alloy thereof is deposited on the surface of the metal member including the metal member to form a diffusion layer or an alloy layer of the metal. 2. The method of manufacturing a heat exchanger according to claim 1, wherein the metal member is made of Al or an Al alloy, and the base metal is Zn. 3. The method of manufacturing a heat exchanger according to claim 1, wherein the metals formed by brazing each other are fins and tubes. 4. The fins and tubes are made of at least one material selected from Al and the other material selected from Al, Cu, Ti, and Fe bases.
4. A heat exchanger according to claim 3, comprising two materials.