JPH0615486A - Production of flux for brazing - Google Patents

Abstract

PURPOSE:To reduce the cost of production of the flux for brazing by using inexpensive alpha-AlF3 as a raw material in the production of the fluoride flux. CONSTITUTION:This flux for brazing is basically constituted by mixing alpha-AlF3 powder having 5 to 100m<2>/g specific surface area into an aq. KF soln. to cause an exothermic reaction and evaporating away moisture by the reaction heat thereof. Mixing of the alpha-AlF3 powder while stirring the aq. KF soln. or drying of the residues at 100 to 200 deg.C in the atm. after evaporating the moisture may be added.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION The present invention relates to an automotive capacitor,
The present invention relates to a method of manufacturing a flux used for brazing aluminum heat exchangers such as radiators and car heaters.

In this specification, the term aluminum is used to include its alloy.

[0003]

2. Description of the Related Art For example, when the aluminum heat exchanger is manufactured by brazing, a flux is used in order to remove an oxide film formed on the material surface and achieve good brazing joining. Non-corrosive fluoride fluxes are widely used because of the advantage that they do not produce corrosive residues after brazing.

A typical example of the above-mentioned fluoride-based flux is potassium aluminum fluoride salt produced by the reaction of KF and AlF _3, and an example of the method for producing such a flux is disclosed in JP-A-62-40998. It is disclosed in the publication. In this manufacturing method, γ-AlF ₃ and KF each having a particle size of 74 μm or less are mixed in a predetermined ratio, and the mixture is fired to form potassium aluminum fluoride salt to obtain a powdery flux. .

However, the method disclosed in Japanese Unexamined Patent Publication No. 62-40998 requires adjustment of the particle size of γ-AlF ₃ and KF which are raw materials, and since KF has high hygroscopicity, Since the particle size adjustment must be performed in a dry atmosphere, it was a very laborious manufacturing method. Therefore, the present applicant has proposed a method disclosed in Japanese Patent Laid-Open No. 63-309395 as a method that does not require such a trouble. In this method, first, a predetermined amount of KF is dissolved in water, and a predetermined amount of γ-AlF ₃ and / or β-AlF ₃ is mixed with this KF aqueous solution to form a potassium aluminum fluoride salt, and a reaction is generated. Moisture is evaporated and removed by heat to obtain flux.

[0006]

However, AlF ₃ used in the above-mentioned two methods for producing a fluoride-based flux is limited to γ type or β type, and α-AlF ₃ is excluded. ing.

That is, JP-A-62-40998 describes that "α-AlF ₃ is industrially disadvantageous because it is difficult to complete the reaction with KF in a short time". It has been clarified that the amount of potassium aluminum fluoride salt produced is extremely small when α-AlF ₃ is used. The applicant of the present invention also discloses Japanese Patent Laid-Open No. 63-3093.
In 95 JP, described as "alpha-AlF ₃ can not obtain the desired flux in order not occur exothermic reaction be mixed aqueous KF", when using the alpha-AlF ₃ are, KF Unreacted KF and KF-2H ₂ based on the compositional analysis results of the solution obtained by adding α-AlF ₃ to the aqueous solution.
It was revealed that a large amount of O remained.

However, γ-AlF ₃ and β-AlF
₃ is more expensive than α-AlF ₃ and γ-AlF ₃ or β-for producing the fluoride-based flux as described above.
The fact that only AlF ₃ can be used increases the manufacturing cost of the fluoride flux, which is a problem in the conventional manufacturing method.

In order to solve the above problems, the present invention uses inexpensive α-AlF ₃ as a raw material in the production of a fluoride-based flux, and can reduce the production cost. The present invention is intended to provide a method for manufacturing a flux for use.

[0010]

[Means for Solving the Problems] In order to achieve the above-mentioned object, the inventors have conducted various experiments and researches, and as a result, α-Al
It was found that the reactivity between F ₃ and KF is related to the specific surface area of α-AlF ₃ , and α-AlF ₃ was excluded as a raw material for production because potassium aluminum fluoride salt was not produced in the conventional production method. What was done was the α-AlF used in the comparative experiment with γ-AlF ₃ and β-AlF _3.
It was found that this was because the specific surface area of ₃ was very small.

The present invention has been made on the basis of such findings, and α- which is used as a raw material for manufacturing flux
The specific surface area of AlF ₃ is set within a predetermined range in which it can react with KF, and potassium fluoride aluminum salt is produced. More specifically, the basic configuration of the method for producing a brazing flux of the present invention has a specific surface area of 5 to 10 in a KF aqueous solution.
It is characterized in that 0 m ² / g of α-AlF ₃ powder is mixed to generate an exothermic reaction, and the heat of reaction is used to evaporate and remove water.

The reason why the specific surface area of α-AlF ₃ is deeply related to the reactivity with KF is presumed to be that the specific surface area is related to the reaction area and the reaction rate. Therefore,
If the specific surface area of α-AlF ₃ is less than 5 m ² / g, the potassium aluminum fluoride salt cannot be produced because the reactivity with KF is poor. Further, when the specific surface area of α-AlF ₃ exceeds 100 m ² / g, the water content of the KF aqueous solution evaporates before the reaction is completed, and the remaining reaction is delayed so that the reaction is not completed. Is not preferable for the production of A particularly preferable range of the specific surface area is 30 to 6
It is 0 m ² / g. The specific surface area of such alpha-AlF ₃ is known to be adjustable by controlling the firing process and the firing temperature is a method for producing normal alpha-AlF _3, is in the range of the present invention 5~100m ² /
g can be easily achieved by manufacturing at 300-600 ° C. Note that commercially available α-AlF ₃ is 600 ° C.
Often manufactured at high temperatures exceeding 5 m ^{2 with a} specific surface area of 5 m ^2.
Since it was less than 1 / g, inexpensive α-AlF ₃ was used in the above-mentioned method for producing a fluoride-based flux (methods described in JP-A-62-40998 and JP-A-63-309395). It is thought to be the cause of the failure.

The specific surface area of α-AlF ₃ is measured by
For example, the BET method can be used.

In the method for producing a brazing flux of the present invention, since KF has a very high solubility in water, it is not particularly necessary to adjust the particle size of KF, and even if it is a lump, it can be used as it is. Good. The concentration of the KF aqueous solution is not particularly limited as long as KF is completely dissolved. Further, it is not necessary to adjust the particle size of α-AlF ₃ either.
Most of AlF _{3 has} a particle size of 300 μm or less. The mixing ratio of these KF and α-AlF ₃ is KF; 55 to 30 wt%, α-AlF ₃ ; from the viewpoint that unreacted KF does not remain in the produced flux.
45-70 wt% is preferred.

When the α-AlF ₃ is mixed with the KF aqueous solution, the α-AlF ₃ powder may be uniformly dispersed, and at the same time, the mixture of these may be stirred in order to promote the reaction between them. preferable. The reaction proceeds by mixing and stirring, and most of the water is evaporated and removed by the heat of reaction, and KAlF ₄ , K ₂ AlF ₅ · H ₂ O and K ₃ Al are left as residues.
A potassium aluminum fluoride salt such as F ₆ is obtained as a simple substance and / or a complex thereof, and a flux is produced. When water remains in this residue, it is preferable to dry the residue in the atmosphere at a temperature of 100 to 200 ° C.

[0016]

Function: The specific surface area of α-AlF ₃ is 5 to 100 m ² / g.
By this, the reactivity with KF is enhanced. Then, various aluminum potassium fluoride salts are produced by mixing α-AlF ₃ in the KF aqueous solution, and the heat of reaction generated at this time evaporates and removes water to obtain a fluoride-based flux. Such a reaction is promoted by stirring both after mixing, and the production rate of the fluoride flux is increased. In addition, when water remains in the residue after evaporation, it is 100 to 200 in the atmosphere.
It may be dried at a temperature of ° C to be in the form of powder, which can improve the storage stability of the produced flux, the ease of measurement during use, and the like.

[0017]

EXAMPLES Next, specific examples of the method for producing the brazing flux of the present invention will be described. In this example,
A fluoride-based flux was prepared and its composition was analyzed, and aluminum brazed products were manufactured using these fluxes, and the brazed products were also evaluated.

(Preparation of Flux) Industrial KF having a purity of 96% or more and α-AlF ₃ having various specific surface areas were used at a predetermined ratio, and the fluxes of Examples 1 to 3 and Comparative Example were prepared by the following procedure. It was created. The specific surface area of the alpha-AlF ₃ was used and shows a mixing ratio of KF and alpha-AlF ₃ in Table 1. The total amount of KF and α-AlF ₃ was 10 kg.

First, each predetermined amount of KF was completely dissolved in water corresponding to the weight of KF at 60 ° C. Then, each predetermined amount of α-AlF3 was added and mixed while stirring this KF aqueous solution. α
When the stirring was continued for another 10 minutes after the total amount of —AlF ₃ was added, the exothermic reaction started in Examples 1 to 3, and the stirring was stopped at this point. About 30 minutes after the stirring was stopped, most of the water was evaporated and a residue was obtained. Further, these residues were dried in the atmosphere at 200 ° C. for 300 minutes to obtain powdery fluxes of various potassium aluminum fluoride salts. Also,
In the comparative example, the exothermic reaction did not occur even if the stirring was continued for 10 minutes after the total amount of α-AlF ₃ was added to the KF aqueous solution. Moisture was evaporated and removed by heating for 500 minutes to obtain a powdery flux.

The composition of each flux thus obtained was analyzed, and the analysis results are also shown in Table 1.

[0021]

[Table 1] As is clear from Table 1, in Examples 1 to 3, KF and α-
It reacted with AlF ₃ to produce various potassium aluminum fluoride salts, and no unreacted KF or KF-2H 2 O was observed. For each such example, α-Al
In the comparative example using F _{3 having} a specific surface area smaller than the range of the present invention, almost no potassium aluminum fluoride salt was formed, and a large amount of KF and KF-2H ₂ O remained unreacted.

(Production of brazed product) A 0.75 mm thick extruded tube material made of A1100 alloy, a core material of A3003 alloy and an Al-9 wt% Si alloy as a clad material with a clad ratio of 10% and a thickness of 0. A corrugated heat exchanger was assembled using a fin material composed of a 15 mm double-sided brazing sheet. Then, a 5% suspension of each of the fluxes was applied to the surface of the assembly, and 605 ° C. × 5 in an N ₂ atmosphere.
Brazing was performed by heating for one minute.

With respect to each brazing product obtained as described above, the brazing property and the appearance state were visually observed, and the coating adhesion was evaluated. The adhesion of the coating film is determined by treating each brazing product with phosphoric acid chromate and spray-coating with an acrylic resin, and then scoring a 1 mm square square on the surface of the coating film and performing a tape peeling test. It was evaluated by the number of eyes (cross-cut test). The evaluation results are shown in Table 2.

[0024]

[Table 2] From the results in Table 2, by using the flux of each example of the present invention, good brazing can be performed, and the surface of the aluminum material after brazing is also clean and the coating adhesion is excellent. confirmed. On the other hand, in Comparative Example, the effect of promoting brazing was poor because no potassium aluminum fluoride salt was produced, the surface of the brazed product after brazing was browned and stained, and the adhesion of the coating film was poor.

[0025]

According to the present invention, it is possible to use α-AlF3, which has been considered to be inexpensive but unusable, as a raw material for producing a fluoride-based flux. Moreover, the produced flux has an excellent flux effect, and high-quality flux can be produced at low cost.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Shoichi Furuta, 6-224, Kaiyamacho, Sakai City, Osaka Prefecture Showa Aluminium Co., Ltd. (72) Inventor, Yukio Oshima 6-224, Kaiyamacho, Sakai City, Osaka Showa Al Minium Corporation

Claims (3)

[Claims] 1. A KF aqueous solution having a specific surface area of 5 to 100 m ^2.
/ G of α-AlF ₃ powder is mixed to generate an exothermic reaction, and water is evaporated and removed by the heat of reaction to produce a brazing flux. 2. The α− while stirring the KF aqueous solution.
The method for producing a brazing flux according to claim 1, wherein AlF ₃ powder is used. 3. The method for producing a brazing flux according to claim 1, wherein the residue is dried in the atmosphere at a temperature of 100 to 200 ° C. after the water content is evaporated and removed. .