JPH09178392A - Manufacture of heat exchanger made of aluminum and being excellent in corrosion resistance - Google Patents

Abstract

PROBLEM TO BE SOLVED: To manufacture a heat exchanger made of aluminum and being excellent in corrosion resistance without causing a problem of pollution due to release of sexivalent chromium and the like, by coating the surface with a metal oxide film by a sol-gel process. SOLUTION: A plurality of flat tube elements 1 each of which is formed by joining the peripheral end parts of paired core plates 3 by soldering and has a refrigerant passage inside and a plurality of corrugated fins 2 are stacked alternately and soldered, while side plates 4 are placed outside the outermost fins 2 and an inlet header 5 and an outlet header are provided. On the other hand, a sol solution of a metal oxide is prepared and made to stick on the stacked type heat exchanger by a dip coating method. Next, the heat exchanger whereon the sol solution sticks is subjected to a drying treatment by leaving it in the atmosphere at room temperature and then subjected to a heating treatment in the atmosphere of oxygen. These processes from sticking to heating are repeated. Herein the metal oxide is an oxide of Zr, Ti, Hf or Al.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for manufacturing an aluminum heat exchanger, which is used as an evaporator, a condenser, an industrial radiator, an oil cooler, etc. for a car air conditioner, and in particular, an aluminum heat exchanger excellent in corrosion resistance. The present invention relates to a method for manufacturing a heat exchanger.

In this specification, the term aluminum is used to mean aluminum and its alloys.

[0003]

2. Description of the Related Art Aluminum heat exchangers such as those described above are designed to withstand use in corrosive environments.
It may be configured to have corrosion resistance.

As one of the methods for imparting such corrosion resistance, there is a method in which a heat exchanger is surface-treated to form a film having corrosion resistance. Since such a surface treatment method can be applied to a thin aluminum material, by applying it to an aluminum material such as ultra-super duralumin which is excellent in strength but slightly inferior in corrosion resistance, it is thin and lightweight, and strength, There is an advantage that a heat exchanger having excellent corrosion resistance can be provided.

Conventionally, as a surface treatment method for forming a corrosion resistant film on a heat exchanger as described above, it has been generally practiced to subject the heat exchanger to chromate treatment and then, if necessary, further coat a resin. It was

[0006]

However, since the chromate treatment uses CrO ₃ and a mineral acid in the treatment liquid, the release of hexavalent chromium into the atmosphere has become a pollution problem, and its release regulations are becoming stricter year by year. Therefore, there is an urgent need to develop a surface treatment method to improve the corrosion resistance of a new aluminum heat exchanger that replaces the chromate treatment.

In view of the above problems, an object of the present invention is to provide a manufacturing method capable of manufacturing an aluminum heat exchanger having excellent corrosion resistance without causing pollution problems due to the release of hexavalent chromium. To do.

[0008]

In order to achieve the above object, a method of manufacturing an aluminum heat exchanger having excellent corrosion resistance according to the present invention comprises coating a surface with a metal oxide film by a sol-gel method. It is characterized by.

In the sol-gel method, a solution of a metal organic or inorganic compound is generally hydrolyzed and polycondensed to prepare a sol solution, which is further gelled by further reaction, and the gel is heated. This is a method of obtaining a solid of a metal oxide. Specifically, after the sol solution is attached to the object to be treated by some method, the sol on the surface of the object to be treated is gelated by drying, and the gel is further heated to form a metal oxide film. To form a coating on the object to be treated. In the present invention, such a sol-gel method is used because a uniform and dense metal oxide film can be reliably formed by a relatively simple process.

The metal constituting the metal oxide is
Although it is not particularly limited, Zr, Ti, Hf, Si and Al are required to form a hard and more excellent corrosion resistance film.
It is preferable to use one or more of the above. Further, a metal alkoxide is preferable as the metal compound which is the starting material of the sol-gel method. Specific examples thereof include zirconium tetranormal butoxide, titanium tetraisopropoxide, hafnium ethoxide, tetraethyl orthosilicate, aluminum secondary butoxide and the like.

The sol solution is prepared by dissolving one or more of the above metal compounds in a solvent such as alcohol and adding water, an acid and other additives. The concentration of the metal compound or the like in the sol solution is arbitrary, but a fine sol such as fins of a heat exchanger, which is an object to be processed, may be clogged with the sol solution, so that the sol having a relatively low viscosity is used. It is preferable to prepare a solution. Specifically, the viscosity is 1 to 10 mP
a · s is desirable.

As a method for adhering the sol solution to the object to be treated, a conventionally known method such as a dip coating method, a spin coating method, a roll coating method may be appropriately adopted, but an object having a complicated shape can be easily treated. It is preferable to use the dip coating method because it can be processed.

Further, according to the present invention, it is sufficient that a metal oxide film is formed on the surface of the heat exchanger as a result, and it is not always necessary to perform the film forming treatment after the heat exchanger is completed. For example, it may be processed at the stage of component parts before being assembled in a heat exchanger, or, in the case of a product formed from a coil such as fins, a film is formed in the state of coil form before forming. You may. Of course, the heat exchanger may be treated after completion, and the timing of the treatment is not limited. In order to coat the metal oxide film with good adhesion, it is preferable to sufficiently degrease, wash, and dry the object to be treated before attaching the sol solution.

After the deposition of the sol solution, the drying and heating steps are sequentially carried out. By this drying and heating process, the sol solution attached to the surface of the object to be treated is gelled. The drying may be carried out, for example, by leaving it in the air at room temperature to 60 ° C. for 5 to 10 minutes. On the other hand, it is preferable that the heating after drying is performed in an oxygen-containing atmosphere from the viewpoint that a dense and high adhesive force can form a more excellent corrosion resistant film. Specifically, the temperature is 150 to 350 ° C. for 5 hours in the atmosphere or oxygen stream.
It is good to do in the range of ~ 60 minutes. The metal oxide film is formed by the heating process.

The film thickness of the metal oxide is 0.1 to 5.0.
It is better to set to μm. If it is less than 0.1 μm, the effect of preventing corrosion resistance is poor, and conversely if it exceeds 5.0 μm, the effect is saturated. It is desirable to form the film by repeating the above-mentioned steps of adhesion, drying and heating a plurality of times. By repeating the treatment, a film is formed over a plurality of layers, and more excellent adhesion, smoothness, denseness, and corrosion resistance are exhibited. The thickness of the film can be controlled by adjusting the number of times the adhesion, drying, and heating steps are repeated, the concentration of metal oxide components in the sol solution, the viscosity of the sol solution, and the pulling rate from the sol solution in the case of the dip coating method. You can do it by doing.

According to the above-mentioned sol-gel method, the aluminum heat exchanger can be coated with the metal oxide film which is a corrosion resistant film without releasing pollutant components such as hexavalent chromium into the atmosphere. Further, since the coated metal oxide film is dense in itself, the surface of the heat exchanger coated with the film is shielded from the atmosphere and the like, and water and the like do not permeate. Therefore, the heat exchanger subjected to chromate treatment. Excellent corrosion resistance equivalent to or higher than. Further, since the metal oxide film has water repellency, even if a corrosive liquid such as salt water adheres, the metal oxide film is repelled and long-term contact with the corrosive liquid is avoided, so that the corrosion resistance is further improved. Also, even if water droplets adhere to the fins due to the operation of the heat exchanger as in the case where the heat exchanger is used as an evaporator, the water droplets are repelled and roll off,
The pressure loss of the ventilation air due to the accumulation of water droplets is suppressed, and the heat exchange efficiency of the heat exchanger can be maintained high.

[0017]

EXAMPLE A specific example of a method for manufacturing an aluminum heat exchanger according to the present invention will be described below.

As the object to be treated, the laminated aluminum heat exchanger shown in FIGS. 1 and 2 was used. This laminated heat exchanger is used for an evaporator for car coolers, and is formed by brazing the peripheral ends of a pair of core plates (3) and (3) together with a refrigerant inside. Plural flat tube elements with passages (1)
And a plurality of corrugated fins (2) are alternately laminated and brazed. JIS3003 alloy was used as the aluminum forming the heat exchanger. Further, in FIGS. 1 and 2, (4) and (4) are side plates arranged outside the outermost fin, and (5)
(6) is an entrance header and an exit header.

On the other hand, various sol solutions shown in Table 1 were prepared. Each sol solution was prepared by mixing a plurality of components shown in Table 1 and thoroughly stirring them. Moreover, the viscosity of the sol solution is 1.3 to 1.6 m in all cases.
Pa · s.

Then, the sol solution was attached to the laminated heat exchanger by a dip coating method. More specifically, the sol solution is placed in a nitrogen atmosphere having a relative humidity of 50 to 60%, the heat exchanger is dipped in the sol solution, shaken in the solution for several times, and then at 3 mm / sec. Pulled up at speed. The adhesion step was performed in a nitrogen atmosphere in order to avoid the influence of atmospheric humidity on the viscosity change of the sol, but it is not particularly limited to the nitrogen atmosphere.

Next, the heat exchanger having the sol solution adhered thereto was left to stand in the air at room temperature for 5 minutes to be dried, and then heat-treated in a pure oxygen atmosphere at 300 ° C. for 30 minutes.

The above-described adhesion process to heating process were repeated 2 to 6 times as shown in Table 2 to prepare various samples for the corrosion resistance test. Further, as comparative examples, two types of samples were prepared, one using the same heat exchanger as in the above-mentioned example, which was not subjected to any surface treatment, and the other which was chromate treated.

For each of the above samples, JIS Z237
The salt spray test according to 1 was performed, and the surface of the heat exchanger was visually observed at 144 hours, 500 hours, and 900 hours after the start of the test to evaluate the rusting condition. For evaluation of corrosion resistance, a rating number (hereinafter, RN) of 1 is used when the area where white rust is generated is 50% or more of the entire area, and then 25% or more and less than 50% is R.N. N. 2, 10%
R.I. N. If less than 3, 10% is R. N.
4. If no white rust occurred, R. N. It was evaluated as 5. Table 2 shows the above results.

[0024]

[Table 1]

[Table 2]

As is clear from Table 2 above, it has been confirmed that according to the present invention, corrosion resistance equivalent to that of the conventional chromate-treated heat exchanger can be obtained.

Further, the wettability of the film with water was measured by the contact angle measuring method, and the surface of the sample of the present invention of sample No. 1 was 102 °, which was 70 to 80 of the surface of the comparative sample of chromate-treated sample No9. The water repellency was higher than that of β.

[0027]

As described above, the present invention is a sol-
Since the surface treatment of the aluminum heat exchanger is performed by the gel method, it does not release pollutants such as hexavalent chromium into the atmosphere, and it is coated with a metal oxide film that exhibits corrosion resistance equivalent to or higher than that of chromate treatment. can do. Therefore, it is possible to provide a heat exchanger having excellent corrosion resistance without causing pollution problems and the like.

Moreover, since the coated metal oxide film has higher water repellency than the chromate-treated surface, even if a corrosive liquid containing salt etc. adheres, the metal oxide film rolls off immediately, so that long-term contact with the corrosive liquid is caused. Can be prevented, and the corrosion resistance of the heat exchanger can be improved more and more. In addition, even if water drops adhere to the fins or the like, they roll down on the fin surface, so that it is possible to suppress wind pressure loss that occurs when the water drops adhere to the fins, and it is possible to improve heat exchange efficiency.

The metal oxide is Zr, Ti, Hf, S.
When it is made of any one of i and Al, or an oxide of two or more kinds of metals, it is possible to provide a heat exchanging film having a more excellent corrosion resistance.

Further, in the sol-gel method, when the heating step is carried out in an oxygen-containing atmosphere, it is possible to form a dense, high-adhesion and excellent corrosion-resistant film, and a heat exchanger having even more excellent corrosion resistance. Can be provided.

[Brief description of the drawings]

FIG. 1 is a perspective view showing a disassembled part of an aluminum laminated heat exchanger used as a sample in an embodiment of the present invention.

FIG. 2 is a front view of the laminated heat exchanger.

[Explanation of symbols] 1 ... Tube element 2 ... Fin 3 ... Side plate

Front page continuation (72) Inventor Isao Makita 6224, Kaiyamacho, Sakai City, Showa Aluminum Co., Ltd. (72) Inventor, Mikio Kondo, 6224, Kaiyamacho, Sakai City, Showa Aluminum Co., Ltd.

Claims (3)

[Claims] 1. A method of manufacturing an aluminum heat exchanger having excellent corrosion resistance, which comprises coating a surface with a metal oxide film by a sol-gel method. 2. The metal oxide is Zr, Ti, Hf, Si,
The method for manufacturing an aluminum heat exchanger having excellent corrosion resistance according to claim 1, wherein the method comprises an oxide of at least one metal selected from any of Al. 3. The method for producing an aluminum heat exchanger having excellent corrosion resistance according to claim 1, wherein the heating step in the sol-gel method is performed in an oxygen-containing atmosphere.