KR100449576B1 - Method of brazing aluminum and aluminum brazing material - Google Patents

Abstract

The present invention relates to an aluminum brazing method and an aluminum brazing material, wherein an aluminum brazing material consisting of a mixture of aluminum brazing metal powder, a flux, a binder and a diluent alcohol is coated on the surface of an aluminum-based extruded flat tube strip. The strip and the aluminum pin is characterized in that the brazing together.

Description

Aluminum brazing method and aluminum brazing material {METHOD OF BRAZING ALUMINUM AND ALUMINUM BRAZING MATERIAL}

TECHNICAL FIELD The present invention relates to an aluminum brazing method and an aluminum brazing material, and more particularly, to an aluminum brazing method and an aluminum brazing material for brazing a heat exchanger made of aluminum or an aluminum alloy, which will be described later as a heat exchange tube of an aluminum material and an aluminum material. .

In general, aluminum heat exchangers having aluminum fins brazed on aluminum heat exchange tubes are widely used. Also, to increase the heat exchange rate, the heat exchange tubes are made of extruded flat tube strips of aluminum-based materials.

One method of brazing the fin and the extruded flat tube strip together to produce a heat exchanger configured as described above is to use flux to coat and braze the brazing metal powder on an aluminum surface; As an example of this brazing method, first, a method of separating and coating a brazing metal powder and a flux powder and a second method of mixing the brazing metal powder and a flux powder and coating the mixture are known.

However, the first method of separating and coating the brazing metal powder and the flux powder is accompanied by a problem that the process is very complicated. In addition, the second method of coating the mixture by mixing the braze metal powder and the flux powder is smaller than the first method, but has a potential problem of not having a homogeneous mixture of powders. If the mixture is heterogeneous, in some where the flux is present in greater amounts, improper brazing material leads to excess flux remaining after brazing; In other words, there is a known local melt due to the excess of brazing material and simultaneously reduces the active brazing due to the lack of flux at the position exceeding the brazing metal powder.

In addition, if the particle diameter of the brazing metal powder is too large, there is a known local melting due to the excessive brazing material in some parts. In other words, if the particle size of either or both of the brazing metal powder or the flux powder is too fine, the particles will easily aggregate and contain heterogeneity which causes the same type of problem as the problem according to the second method.

In addition, when the binder is not used, there is a problem that the coating material is peeled off after drying. Moreover, when a low volatility liquid such as water is used as the solvent for the mixture, the drying time is increased and problems such as heterogeneity and concentration difference occur.

The present invention is to solve the above problems. It is an object of the present invention to provide an aluminum brazing method and an aluminum brazing material which can make the brazing uniformly easy and reliable.

To accomplish the above object, one method of aluminum brazing is characterized by coating an aluminum brazing material consisting of a mixture of aluminum metal powder, flux, binder and alcohol for diluting the binder on the brazing surface.

The binder, thermoplastic acrylic copolymer, which melts into an aliphatic alcohol having 1 to 8 carbon atoms, is evaporated without decomposition during the process of raising the temperature for brazing. In addition, the brazing metal powder is a metal used alone for brazing or a metal which reacts with an aluminum surface and is a brazing material produced by a low melting point metal layer.

In addition, the average particle diameter of the brazing metal powder is preferably 2 to 60 µm. Furthermore, the ratio of the specific gravity of the brazing metal powder and the specific gravity of the flux (specific gravity of the brazing metal powder / specific gravity of the flux) is preferably 0.7 to 1.3.

In addition, the ratio of the particle size of the braze metal powder to the particle size of the flux powder (particle size of the brazing metal powder / flux of the flux) is preferably 0.7 to 1.3.

In the present invention, the flux coating process and the brazing metal powder coating process can be carried out together by coating a mixture of aluminum metal powder, flux, binder, and binder dilution alcohol on the surface to be brazed. This can prevent the problem that the coating is peeled off after drying the coating film of the mixture of the brazing metal powder and the flux.

1 is a schematic perspective view showing one embodiment of a brazing heat exchanger according to the brazing method of the present invention;

Figure 2 is a schematic perspective view showing an extruded flat tube strip and fins brazed together by the brazing method of the present invention.

Explanation of symbols on the main parts of the drawings

1: inlet port 2: outlet port

3: header pipe 4: flat tube strip

5: corrugated pin 6: brazing material

In the following, the invention is described with reference to the accompanying drawings. The case where this invention is used as an aluminum type heat exchanger is demonstrated.

As shown in FIG. 1, the heat exchanger is parallel to a pair of header pipes 3, header pipe 3 having either inlet 1 or inlet 2 for the heating medium. It consists of corrugated fins 5 arranged between an extruded flat tube strip 4 and an extruded flat tube strip 4 as well connected heat exchange tubes. The header pipe 3 and the extruded flat tube strip 4 are formed of an extruded material of aluminum alloy, and the corrugated fins 5 are formed by bending an aluminum alloy sheet material. The header pipe 3, the extruded flat tube strip 4 and the corrugated fins 5 are brazed together using the brazing material of the present invention to constitute a heat exchanger.

For example, to braze the extruded flat tube strip 4 and the corrugated fins 5 as shown in FIG. 2, the brazing material 6 of the present invention is an extruded flat tube strip 4. It can be coated on the surface of and the corrugated pins 5 can be coated on the surface.

The brazing material 6 is formed from a mixture of aluminum brazing metal powder, flux, binder and alcohol for diluting the binder. In this case, the binder must meet the following requirements. In other words, the binder must be a thermoplastic acrylic copolymer such as PARALOID B-67 manufactured by Rohm and Haas Co., Ltd., capable of being mixed in aliphatic alcohols having 1 to 8 carbon atoms, and having an aluminum brazing temperature of, for example, 600 ° C. When raised to temperature it must evaporate without decomposition.

Binder dilution alcohols include methanol (methyl alcohol), ethanol (ethyl alcohol), propanol (isopropyl alcohol), butanol (butyl alcohol) and pentanol (amyl alcohol).

In addition, the aluminum brazing metal powder should be a metal that can be used alone for brazing or a metal that can be configured to braze by reacting with the aluminum surface to produce a low melting point metal layer. Metals that can be used for brazing alone include Al-Si, Al-Cu, Al-Zn, Al-Si-Cu, Al-Cu-Zn, Al-Si-Zn and Zn. Metals that can be constructed by reacting with an aluminum surface to produce a low melting metal layer are Si, Cu, and Ge and the like.

Flux can be either fluoride flux or sodium flux, but the corrosion resistant fluoride flux is selected from two. Fluoride fluxes include aluminum fluorides, fluorides of alkaline metals, fluorides of alkaline earth metals and the following fluoride compounds: KAlF ₄ , K ₂ AlF ₅ · H ₂ O, K ₃ AlF ₆ , AlF ₃ , LiF, CaF ₂ , NaF, Li ₃ AlF ₆ , RbF, CsF, BaF ₂ , KF, BaF ₂ or a flux having one or more of these components as main component is used.

In addition, the average particle diameter and specific gravity of the brazing metal powder and flux should be within the range of the table below.

TABLE 1

In addition, the ratio of the specific gravity of the brazed metal powder and the specific gravity of the flux should satisfy the following Equation (1), and the ratio of the metal powder particle size and the flux particle diameter should satisfy the following Equation (2).

In the foregoing, a parallel flow type heat exchanger having a plurality of extruded flat tube strips 4 arranged in parallel between a pair of header pipes 3 and a corrugated fin 5 between the extruded flat tube strips 4 Although described above, the apparatus is serpentine having heat exchange tubes, fins arranged in a manner similar to corrugated fins 5 between the extruded flat tube strips connected to the header pipe and the gaps of the extruded flat tube strips connected to the header pipes. It may be a type of heat exchanger.

Next, an experiment for coating and brazing the aluminum surface under the changing conditions described below for the brazing material of the present invention will be described.

Condition:

The results shown in Table 2 were obtained from experimental values constructed under the brazing material conditions below and the conditions specified above.

Brazing Experiment: Braze the corrugated fins (5) onto the tube strip by coating the brazing material on the aluminum extruded flat tube strip (4).

TABLE 2

0: Satisfactory result after brazing experiment.

Δ: slightly satisfactory result after heating and brazing.

X1: Unsatisfactory brazing at various positions (excess flux due to inhomogeneous mixture, brazing defect).

X2: local melting (more than brazing material in part due to inhomogeneous mixture, more than brazing material in part due to aggregation of fine brazing material, more than brazing material in part due to large particle diameter of brazing material).

X12: X1 + X2

-: No brazing experiment conducted

The results of the experiment were satisfied when the average particle diameter of the brazed metal powder was 2 µm to 60 µm, the ratio of the specific gravity of the metal powder to the specific gravity of the flux, and the ratio between the particle diameter of the metal powder and the particle diameter of the flux was between 0.7 and 1.3. Indicates that a brazing is obtained.

Similar results were also obtained when the dilutions of the binder for the brazing material described above were converted from isopropyl alcohol to aliphatic alcohols having 1 to 8 carbon atoms. The reason for using aliphatic alcohols having 1 to 8 carbon atoms is that when the number of carbon atoms is 9 or more, the solvent tends to decrease and solidify in water. A similar good result is the formation and brazing of low melting metal layers when metals such as Al-Cu or Al-Zn other than Al-12% Si are used alone as the brazing material or after metals such as Si or Cu react with the aluminum surface. It is obtained when contributing to and when fluxes such as KF-AlF ₃ other than KAlF ₄ -K ₃ AlF ₆ are used.

As described above, the flux coating process and the brazing metal powder coating process according to the present invention can be carried out at the same time, and brazing because the mixture of aluminum brazing metal powder, flux, binder and alcohol for diluting the binder is coated on the brazing surface. Reduce the effort of the process. In addition, since the binder is used, it is possible to prevent peeling after coating, and at the same time obtain a homogeneous and strong coating film.

Claims (5)

In the aluminum brazing method, Coating the aluminum-based surface with a brazing material comprising a metal powder, a flux, a binder and a mixture of the diluent alcohol for the binder, selected from the group consisting of Si powder, Zn powder, Cu powder and Ge powder; Brazing on said surface. The method of claim 1, Wherein said binder is a thermoplastic acrylic copolymer, soluble in aliphatic alcohols having from 1 to 8 carbon atoms, and evaporating without decomposition when elevated to the brazing temperature. The method of claim 1, The average particle diameter of the said brazing metal powder is in the range of 2-60 micrometers, The aluminum brazing method characterized by the above-mentioned. The method of claim 1, A ratio between the specific gravity of the brazing metal powder and the specific gravity of the flux is in the range of 0.7 to 1.3. The method of claim 1, The ratio of the particle diameter of the said brazing metal powder and the particle diameter of the said flux is the range of 0.7-1.3, The aluminum brazing method characterized by the above-mentioned.