JP3261677B2 - Manufacturing method of flux for brazing aluminum - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing a flux for brazing aluminum.

[0002]

2. Description of the Related Art In recent years, aluminum is often used for heat exchangers such as radiators of automobiles, and accordingly, attention has been paid to aluminum brazing technology.

[0003] For example, Japanese Patent Publication No. 58-27037 discloses that solid aluminum fluoride and potassium fluoride are pulverized, and the ratio of aluminum fluoride is 50 to 60% and potassium fluoride is 50 to 40%. The mixture was intimately mixed, and the resulting mixture was melted and stirred in a graphite crucible at 625 to 650 ° C., and potassium tetrafluoroaluminate (KAlF ₄ ): 65.
6-99.9%, potassium hexafluoroaluminate (K ₃ AlF ₆ ): 34.4-0.1% as a molten mixture,
A method is described in which this is rapidly solidified and then pulverized into fine powder and used as a flux for brazing aluminum.

[0004] The flux used in this method is non-hygroscopic and does not impair the corrosion resistance of aluminum unlike conventional fluxes based on chlorides. However, a large amount of energy is required to melt the solid mixture at 625 to 650 ° C. during production. In addition, manufacturing processes such as pulverization of raw materials, intimate mixing, melting, quenching, and pulverization of a solidified product are complicated, and it takes time to produce a final product.
In particular, meticulous management is necessary to obtain a uniform product,
The complexity of the process imposes a heavy burden on product costs.

On the other hand, Japanese Patent Application Laid-Open No. 57-205317 describes a method in which a small amount of a potassium compound such as potassium hydroxide or potassium chloride is added to a fluoroaluminic acid solution to precipitate and produce potassium tetrafluoroaluminate. I have. (However, here, "potassium tetrafluoroaluminate" includes a mixture with potassium hexafluoroaluminate). Japanese Patent Publication No. 1-60360 discloses that Al: F is added to hydrofluoric acid.
Is within a range from 1: 4 to 4.5, and a potassium compound is added thereto under acidic conditions of pH 4 or less, and potassium pentafluoroaluminate hydrate (K ₂
A method for producing a brazing flux consisting of AlF ₅ .H ₂ O) and potassium tetrafluoroaluminate is described.

In the former invention (JP-A-57-205317) , a potassium compound is used in an excessively small amount (K: Al molar ratio of 0.60 to 0.6).
95: 1) must be used. Therefore, not only when potassium chloride is used as the potassium compound, but also when caustic potassium is used, the liquidity of the reaction solution becomes acidic. Similarly, in the latter invention (Japanese Patent Publication No. 1-60360) , it is essential that the pH of the reaction solution is 4 or less at the end of the reaction with the potassium compound. The reason is described as being to avoid hydrolysis of the fluoroaluminum ion. As described above, in any of the conventional methods, the yield of potassium fluoroaluminate is low because the potassium salt is precipitated under acidic conditions. The former (JP-A-57-205317
No.) , the yield is 70 to 70% based on fluorine.
It does not exceed 80% (almost the same on Al basis). The latter (Tokuhei 1-
No. 60360) does not provide data on the yield,
It is considered to be about the same as the former (JP-A-57-205317) .

Further, since each reaction is a method for producing potassium fluoroaluminate by neutralizing fluoroaluminic acid (Al: F in hydrofluoric acid is 1: 1).
It is fluoroaluminic acid that is produced by dissolving aluminum hydroxide within the range of 4 to 4.5), the change in pH during neutralization, and the change in temperature inevitably change the composition of the precipitated salt. It is extremely difficult to obtain a uniform product in which the ratio between the tetrafluoro and pentafluoro forms is strictly controlled. Thus the melting point is not stabilized, when used as full <br/> Lux for brazing, there is a possibility that trouble occurs in a uniform brazing.

[0008] In the production of a flux, the incorporation of K ₂ AlF ₅ .H ₂ O into the flux should be avoided as much as possible. Because K ₂ AlF ₅ .H ₂ O is 490-550 ° C
Endothermically decomposes into KAlF ₄ and K ₃ AlF ₆ . Inventors have actually changed the content of K ₂ AlF ₅ · H ₂ O fluxes where (the balance being KAlF ₄ and K ₃ AlF ₆₎ was subjected to brazing test aluminum using, K ₂
It has been found that when the content of AlF ₅ .H ₂ O is 5% or more, the bonding strength tends to be weak. On the other hand, when the content was 5% or less, almost no effect was observed. Although the cause is not known, it is thought that the structural change of the flux particles occurs due to the endothermic phenomenon during the dehydration or thermal decomposition of the applied flux, which has an effect such as impairing the adhesion between the flux and aluminum. Guessed.

[0009]

The present inventors have conducted various studies on various fluorides in order to supply a useful brazing agent having a uniform composition at a low cost. For example, it has been found that a uniform brazing agent can be produced very easily. That is, in the presence of water, aluminum fluoride has low solubility (0.
Β-aluminum fluoride trihydrate (about 4%) is a stable phase, and usually precipitates in this form from an aqueous solution. However, when prepared and stored under certain conditions, it is possible to make metastable α-aluminum fluoride having high solubility particularly exist as a supersaturated solution, and it is preferable to add a potassium fluoride solution thereto. Have found that a uniform mixture of fluoroaluminum salts having a constant composition can be produced by simultaneously charging and reacting both solutions under certain conditions.

[0010]

SUMMARY OF THE INVENTION The present invention provides: (1) fluorinated Al
Reacting the aqueous solution of minium with the aqueous solution of potassium fluoride
Aluminum brazing made of fluoroaluminum salt
A method for producing a flux for use, comprising a F / Al molar ratio
Using an aqueous solution of α-aluminum fluoride adjusted to
Adjust K / Al molar ratio when mixing potassium iodide aqueous solution
And K ₂ to AlF ₅ · H ₂ O content of 4.9 or less of aluminum
The present invention relates to a method for producing a brazing flux.

The production method of the present invention is characterized in that (2) F / Al mole
Use the α- aluminum fluoride aqueous solution the ratio 3.2 to 3.6
Then, an aqueous solution of potassium fluoride was added with a K / Al molar ratio of 1.0.
By mixing and reacting in the range of 0 to 1.20, 0.1 to 20% of K ₃ AlF ₆ , 4.9% or less of K ₂ Al
A method for producing an aluminum brazing flux consisting of F ₅ .H ₂ O and the balance KAlF ₄ , (3) concentration 3
Α-aluminum fluoride solution of 0% by weight or less and a concentration of 30
The two solutions were simultaneously charged into the reaction vessel at a constant rate so that the rate of the potassium fluoride solution of at least
Includes a production method in which the reaction is performed in a temperature range of 0 to 90 ° C.

The aqueous solution of aluminum fluoride used in the present invention must be an aqueous solution of α-aluminum fluoride. This is generally obtained by reacting dilute hydrofluoric acid with aluminum hydroxide or by reacting silicic hydrofluoric acid with aluminum hydroxide and separating the resulting silica. The latter case is particularly economically advantageous because the recovered silicic acid from the phosphoric acid production plant is available. In order to keep this solution in a metastable state, it is preferable to keep the concentration of the solution at 30% or less, the solution temperature at 80 ° C or less, and the molar ratio of F / Al at 3.2 to 3.6.

The potassium fluoride solution can be used at any concentration below the saturation concentration. A preferred solution concentration is 30% by weight or more. When the potassium fluoride concentration is less than 30%, the product concentration is low, and the yield is significantly reduced.

An aluminum fluoride solution and a potassium fluoride solution are reacted in a molar ratio of K / Al in the range of 1.0 to 1.20. When the molar ratio exceeds 1.20, the content of K ₃ AlF ₆ in the product exceeds 20%, and the melting point of the flux increases to 580 ° C. or more, which is not preferable. Also,
When the molar ratio is less than 1.00, the yield of the product fluoroaluminum salt decreases. Particularly preferred molar ratios are in the range of 1.05-1.15.

The reaction between the aluminum fluoride solution and the potassium fluoride solution is preferably performed at a temperature in the range of 10 to 90 ° C. When the liquid temperature exceeds 90 ° C., β-aluminum fluoride salt precipitates, and the concentration of aluminum fluoride in the solution decreases, so that the yield decreases. On the other hand, if the liquid temperature is lower than 10 ° C., the filterability of the product precipitate deteriorates. A particularly preferred temperature range is 60 to 80C. Since the reaction is hardly exothermic, it is heated if necessary. Also, the mixture is appropriately stirred so that the two liquids are sufficiently mixed. In order to keep the K / Al ratio constant during the reaction, the two components were charged into the reaction vessel.
At the same time, it is preferable to carry out a small amount at a constant rate. Further, it is preferable that the charging port to the reaction vessel is also the same or is provided at a position close to the charging port.

By the reaction of the aluminum fluoride solution and the potassium fluoride solution, KAlF ₄ , K ₃ AlF ₆ and K ₂ A
1F ₅ .H ₂ O is produced. As described above, the composition of the potassium fluoroaluminum salt mixture is K / Al in the reaction.
It depends on the molar ratio.

[0017]

The method of the present invention is carried out by mixing a solution of a readily soluble salt, so that complicated and high energy cost steps such as pulverization and melting of the raw material as in the conventional method are not required, and the method is simple and low cost. And a uniform target product can be manufactured. In addition, the method of the present invention is based on a mild, non-pyrogenic reaction that occurs between salts, so that the composition is highly stable and the control of the reaction is extremely easy.
The reaction yield is also very high.

[0018]

DETAILED DESCRIPTION OF THE INVENTION Hereinafter, the present invention will be described in detail with reference to examples. Table 1 shows the results of Examples and Comparative Examples.
Are shown together. Analytical method is aluminum is oxine weight
Method, potassium for flame photometry, fluorine for thorium titration
According to

[0019]

Example 1 In a 5 liter polyethylene reaction vessel (A) equipped with a stirrer, 2340 g (23.4 g) of 20% dilute hydrofluoric acid was added.
Was heated to 40 ° C. in a water bath, and 553 g (7.09 mol) of aluminum hydroxide was added thereto little by little while cooling in a water bath so that the liquid temperature did not exceed 80 ° C., and reacted. Dissolved. The F / Al molar ratio of the aluminum fluoride solution after the reaction was 3.30, and the concentration was 20.6% by weight. Another 5 liter polyethylene reactor with stirrer
About 1 liter of warm water heated to 80 ° C. is charged into (B),
The aluminum fluoride solution and the 50% potassium fluoride solution were added thereto at a molar ratio of K / Al of 1.1,
Each was charged simultaneously with a metering pump. Specifically, the charging of the aluminum fluoride solution was set at 48.2 g / min, and the charging of the 50% potassium fluoride solution was set at 15.1 g / min, and the charging was completed in about 1 hour. The inlets for both solutions were at the same location in the reaction tank. The reaction tank (B) was kept at 80 ° C. by heating the external bath during the reaction.

After completion of the charging, stirring was continued at 80 ° C. for about 1 hour, and then the mixture was cooled to room temperature, and the formed precipitate was filtered by suction, washed with water, and dried at 100 ° C. The yield of the precipitate after drying was determined by calculating the amount of KAlF ₄ produced by total fluorine in the reaction mixture by 100%.
% And 98.7% when, was extremely high value.

The reaction solution was sampled and analyzed at 20 minutes after the start of the reaction and at the end of the reaction. Both samples showed almost the same results, and it was confirmed that a uniform composition was obtained. The original final product by analysis
Elementary charges Al: 18.02%, K: 29.42 %, F: 5
1.90%, for a total of 99.34% .

The product fluoroaluminum potassium salt mixture was analyzed by X-ray diffraction (K ₃ AlF ₆ has a diffraction angle (2θ) of 29.9, and K ₂ AlF ₅ .H ₂ O has a diffraction angle (2θ).
θ): 38.1, KAlF ₄ has a diffraction angle (2θ): 28.9). A calibration curve was prepared from the content of each standard sample and the peak height of the X-ray diffraction intensity, and the quantitative value of each component from the X-ray diffraction chart and the content value of each potassium salt from the elemental analysis results were calculated. Judging comprehensively, the component composition is
KAlF ₄ : 89%, K ₃ AlF ₆ : 8 to 10%, K ₂ AlF ₅
· H ₂ O: was 3-4%. The melting point of the product is 562.
° C (by DTA measurement).

[0023]

Comparative Example 1 The same reaction vessel (A) as in Example was charged with 1500 g (22.5 mol) of 30% dilute hydrofluoric acid and placed in a water bath at 40 g.
And heated to 580 g of aluminum hydroxide (7.
Was added little by little so as not to exceed a liquid temperature of 80 ° C. to prepare an α-aluminum fluoride aqueous solution (the F / Al molar ratio of the aluminum fluoride aqueous solution after the reaction was 3.02,
The concentration is 30.0% by weight). Incidentally, the reaction apparatus, method after this are the same as in Example 1 instrumentation other than input speed different from the 34.7 g / min 15.8 g / min is aluminum fluoride aqueous solution and 50% aqueous potassium fluoride solution . Also, K / Al
Is 1.1 as in Example 1. in this case,
In the latter half, β-aluminum fluoride trihydrate was precipitated, and the solution became cloudy, and it often occurred that the aluminum fluoride aqueous solution could not be charged by the pump. The method of treating the product after the completion of the reaction is the same as in Example 1. The yield of the generated flux after drying was 97.3% on a fluorine basis, but as a result of X-ray diffraction, a crystal peak of AlF ₃ .3H ₂ O was recognized, and β-aluminum fluoride was mixed. It was confirmed that. In addition, KAlF ₄ > K ₂ AlF ₅ .H ₂ O> K ₃ Al
The peak of the F ₆ was observed in this order. Of generated flux
Element amount : Al: 17.73%, K: 28.51%, F: 5
1.64%, for a total of 97.88% . The component composition based on the X-ray diffraction peak and the elemental analysis result is AlF ₃ .3H _{2
O: 6~8%, KAlF 4:} 70%, K 2 AlF 5 · H 2 O:
11~15%, K ₃ AlF _6: was 8% to 10%.

[0024]

EXAMPLE 2 1900 g (2.37 mol) of recovered hydrofluoric acid from a phosphoric acid production plant having a concentration of 18.0% of hydrofluoric acid
Is placed in a 5 liter polyethylene reactor (A) equipped with a stirrer, which is heated to 70 ° C. After that, 345 g (4.42 mol) of aluminum hydroxide is almost uniformly charged in about 5 minutes and reacted. During this time, the liquid temperature was 98
ま で 100 ° C. Al (OH) ₃ / H ₂ Si during the reaction
The F ₆ molar ratio is 1.86. After charging the aluminum hydroxide, stirring was continued for about 10 minutes, and then precipitated silica was separated by a small vertical centrifuge. After shaking well, remove silica
Washing was performed twice with 60 ml of warm water at 90 ° C., and the washing was combined with the previous filtrate. This liquid is an aqueous solution of α-aluminum fluoride. The concentration of aluminum fluoride is 16.5%
(Conversion value by Al) 363 g (4.32 mol) was obtained with AlF ₃ . The subsequent apparatus and method are all the same as Example 1 except that the specific charging rates of the aluminum fluoride aqueous solution and the 50% potassium fluoride aqueous solution are 36.6 g / min and 9.2 g / min, respectively. . The yield of the final product flux was 92.7% based on fluorine. Elemental amount by elemental analysis is A
l: 17.29%, K: 30.25%, F: 51.61
% And a total of 99.15% . The composition of the component according to the X-ray diffraction peak and the result of elemental analysis is as follows : KAlF ₄ : 84%, K
₃ AlF ₆ : 13 to 15%, K ₂ AlF ₅ .H ₂ O: 2%
Was.

[0025]

Example 3 The reaction molar ratio when reacting with a 50% aqueous solution of potassium fluoride in the flux production process was K / Al = 1.
The same operation as in Example 1 was repeated except that the value was 20 (specifically, aluminum fluoride was 48.2 g / min, 50%
An aqueous solution of potassium fluoride was simultaneously charged at a rate of 16.4 g / min in about 1 hour). The yield of the produced flux after drying was 99.6% on a fluorine basis. Elemental amount based on analysis results
The Al: 17.20%, K: 31.05 %, F: 51.41
%, For a total of 99.66%. The composition of the component based on the X-ray diffraction results and the elemental analysis values was as follows : KAlF ₄ : 78%, K ₃ Al
_{F 6: 17~19%, K 2} AlF 5 · H 2 O: at 4 to 4.9%
there were.

[0026]

Embodiment 4 The reaction molar ratio when reacting with a 50% aqueous solution of potassium fluoride in the production process of the flux is K / Al = 1.
The same operation as in Example 1 was repeated except that the amount was set to 00 (specifically, 48.2 g / min of aluminum fluoride, 50%
An aqueous potassium fluoride solution was simultaneously charged at a rate of 13.7 g / min in about one hour.) The yield of the produced flux after drying was 96.4% on a fluorine basis. Elemental amount based on analysis results
Is Al: 18.36%, K: 28.65%, F: 52.73
%, For a total of 99.74%. The component composition based on the X-ray diffraction results and the elemental analysis values was as follows : KAlF ₄ : 91%, K ₃ Al
_{F 6: 4~6%, K 2} AlF 5 · H 2 O: was 3-4%.

[0027]

Example 5 In the flux production process, the same operation as in Example 1 was repeated except that an aqueous solution of α-aluminum fluoride was charged into a reaction vessel in advance, and a 50% aqueous solution of potassium fluoride was added dropwise thereto little by little. (Same for final molar ratio of K / Al and total reaction time). At 20 minutes and 1 hour after the start of the dropping, the product was sampled and subjected to elemental analysis. The elemental amount according to the analysis result is: Al: 18.76% after 20 minutes,
K: 27.42%, F: 53.11%, total, 99.29
% , Al: 17.12% and K: 31.% after 1 hour.
24%, F: 50.90%, a total of 99.26% .
As a result of X-ray diffraction, the sample after 20 minutes had a KAl
F ₄ was the main component, and peaks of K ₂ AlF ₅ .H ₂ O and AlF ₃ .3H ₂ O were slightly observed. After 1 hour, the final product is composed mainly of KAlF ₄ , K ₂ AlF ₅ .H ₂ O, K ₃ A
Although a peak of IF ₆ was also observed, the peak of AlF ₃ .3H ₂ O disappeared. The flux yield after drying was 99.0% on a fluorine basis. The component composition based on the X-ray diffraction results and the elemental analysis values was as follows: KAlF ₄ : 76%, K ₃ AlF ₆ :
_{19~20%, K 2 AlF 5 ·} H 2 O: 4~4.9% met
Was.

[0028]

Comparative Example 2 Using the same apparatus, scale and method as in Example 1, α
-The same operation as in Example 1 was repeated except that an aqueous solution of aluminum fluoride was prepared, and in the subsequent flux production step , the reaction molar ratio when reacting with a 50% aqueous solution of potassium fluoride was changed to K / Al = 0.9. Was. Specifically, 48.2 g / minute of aluminum fluoride and 12.3 g / minute of a 50% aqueous solution of potassium fluoride were simultaneously charged in about 1 hour. The yield of the final product flux was 84.2 based on fluorine.
%Met. The elemental amount according to the analysis result is Al: 18.89
%, K: 28.02%, F: 52.90%, total 99.8
1%. The X-ray diffraction result showed that KAlF ₄ was the main component, and a peak of K ₂ AlF ₅ .H ₂ O was also recognized, but a peak of K ₃ AlF ₆ was not recognized.

[0029]

Comparative Example 3 Using the same apparatus, scale and method as in Example 1, α
-The same operation as in Example 1 was repeated except that an aqueous solution of aluminum fluoride was prepared, and in the subsequent flux production process , the reaction molar ratio when reacting with a 50% aqueous solution of potassium fluoride was changed to K / Al = 1.30. Was. Specifically, 48.2 g / minute of aluminum fluoride and 17.8 g / minute of a 50% aqueous solution of potassium fluoride were simultaneously charged in about 1 hour. The yield of the final product flux is 103.
9%. The elemental amount according to the analysis result is Al: 16.24
%, K: 50.04%, F: 32.66%, total 98.9
4%. The component composition based on the results of X-ray diffraction and elemental analysis was as follows: KAlF ₄ : 65%, K ₃ AlF ₆ : 27 to 29
%, K ₂ AlF ₅ .H ₂ O: 6 to 8%.

Table 1

──────────────────────────────────────────────────続 き Continued on front page (58) Field surveyed (Int.Cl. ⁷ , DB name) B23K 35/363 C01F 7/54

Claims (3)

(57) [Claims] An aqueous solution of aluminum fluoride and potassium fluoride
Reaction with an aqueous solution of
For producing aluminum brazing flux
An α-aluminum fluoride having an adjusted F / Al molar ratio
Mix aqueous potassium fluoride solution using aqueous sodium solution
By adjusting the molar ratio of _{K / Al K 2 AlF 5 ·} H 2 O content in
Manufacture flux of 4.9 or less for brazing aluminum
how to. 2. An aqueous solution of α-aluminum fluoride having a molar ratio of F / Al of 3.2 to 3.6 is used, and an aqueous solution of potassium fluoride is added thereto within a molar ratio of K / Al of 1.0 to 1.20. By mixing and reacting, 0.1 to 20% of K ₃ Al
F ₆ , 4.9% or less of K ₂ AlF ₅ .H ₂ O, with the balance being K
2. The production method according to claim 1, wherein an aluminum brazing flux comprising AlF ₄ is produced. 3. A mixture of α-aluminum fluoride having a concentration of 30% by weight or less and a potassium fluoride solution having a concentration of 30% by weight or more is simultaneously charged into the reaction vessel at a constant rate so that the proportions thereof are constant. And react in the temperature range of 10-90 ° C
The method according to claim 1 or 2, wherein