JP3370531B2 - Corrosion protection method for inner surface of aluminum alloy heat transfer tube - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The method of anticorrosion treatment of the inner surface of a heat transfer tube made of an aluminum alloy according to the present invention is a heat transfer tube made by extruding an aluminum alloy to heat-exchange a corrosive fluid such as a heater core or a radiator. It is used to prevent corrosion from progressing from the inside of this heat transfer tube when it is installed in a vessel.

[0002]

2. Description of the Related Art As disclosed in, for example, Japanese Patent Publication No. 4-59077, a heat transfer tube 1 as shown in FIG. 3 made by extrusion molding an aluminum alloy has been widely known. . The heat transfer tube 1 is provided with a plurality of flow paths 4 and 4 inside by providing a plurality of partition walls 3 and 3 inside an oval outer peripheral wall 2. As a heat exchanger using the heat transfer tube 1 as described above, there is a conventional Japanese Patent Publication No. 4-5.
As described in Japanese Patent No. 9077, a heat exchanger 5 as shown in FIG. 4 is widely known.

The heat exchanger 5 has curved portions 6 and 6 and straight portions 7 and 7 formed by bending the heat transfer tube 1 in a zigzag manner.
And are alternately continued, and corrugated heat transfer fins 8 and 8 are provided between the adjacent linear portions 7 and 7. Further, an inlet connector 9 is connected to one end opening of the heat transfer tube 1 and an outlet connector 10 is connected to the other end opening of the heat transfer tube 1, so that the fluid to be heat-exchanged in the heat transfer tube 1 is connected to the one end opening. From the other end to the opening. Then, heat is exchanged between the fluid flowing inside the heat transfer tube 1 and the air flowing outside the heat transfer tube 1.

Conventionally, the heat exchanger 5 as described above has been used as a condenser or an evaporator for constituting an automobile air conditioner. Therefore, only the refrigerant which is a non-corrosive fluid flows in each heat transfer tube 1, and it is not necessary to consider the corrosion from the inside. For this reason, conventionally, an anticorrosive film is formed only on the outer surface where corrosion may occur due to the attachment of rainwater, snow melting salt, or the like. As this anticorrosion coating, as described in, for example, Japanese Patent Publication No. 3-46547, there is widely known one in which the surface of the heat transfer tube 1 is galvanized or a sprayed coating of zinc is formed. Has been.

[0005]

When the heat transfer tube 1 as shown in FIG. 3 is used for a heat exchanger 5 in which a non-corrosive fluid is flown inside the heat transfer tube, such as a condenser or an evaporator,
No particular problem occurs. On the other hand, the heat transfer tube 1 is
When installed in a heat exchanger such as a heater core or a radiator that flows a corrosive fluid (cooling water) inside the heat transfer tube,
It is necessary to consider the corrosion from the inside.

In order to prevent the heat transfer tube 1 from corroding from the inside without deteriorating the heat exchange performance of the heat transfer tube 1, sacrificial corrosion is applied to the inner surfaces of the flow paths 4, 4 of the heat transfer tube 1. It is effective to form a zinc diffusion layer that functions as a layer.
Then, in order to form such a zinc diffusion layer on the inner surface of each of the flow paths 4 and 4, after forming a zinc plating layer on the inner surface, heating is performed at the time of brazing (at about 600 ° C.). It is conceivable that zinc forming the plating layer is diffused to a portion near the inner surface of each of the flow paths 4 and 4 with a part of the aluminum alloy forming the heat transfer tube 1.

Further, in order to form a galvanized layer on the inner surface of each of the flow paths 4 and 4, for example, a zincate bath is considered, as described in Japanese Patent Publication No. 4-59077. However, even if a zinc plating layer is formed on the inner surface of each of the flow paths 4 and 4 by the zincate bath, the zinc plating layer becomes uneven in thickness due to abnormal deposition of zinc or the like. Therefore, it is difficult to form a zinc diffusion layer that exhibits good anticorrosion performance over the entire inner surface of each of the flow paths 4 and 4. Moreover, since the zincate bath is an alkaline bath, from the viewpoint of preventing corrosion of the heat transfer tube 1 made of aluminum alloy, it is necessary to perform sufficient post-treatment such as internal cleaning after the plating treatment, which inevitably results in increased cost. The anticorrosion treatment method for the inner surface of the aluminum alloy heat transfer tube of the present invention was invented in view of such circumstances.

[0008]

The method of anticorrosion treatment of the inner surface of the aluminum alloy heat transfer tube of the present invention prevents corrosion from progressing from the inner surface of the heat transfer tube formed by extrusion molding the aluminum alloy. It forms an anticorrosion film for the purpose. Such an anticorrosion treatment method for the inner surface of the aluminum alloy heat transfer tube of the present invention, the inner surface of the heat transfer tube, the viscosity obtained by dispersing and mixing zinc powder and fluoride powder in a highly viscous binder that decomposes without carbonization at high temperature. the mixture,
The amount of zinc powder adhered to the inner surface of the heat transfer tube is 0.5 to
After coating with regulations so as to fit in the range of 30g / m ^2, this
By raising the temperature of the heat transfer tube, to form a zinc diffusion layer on the inner surface of the heat transfer tube. In addition, according to claim 2,
The anticorrosion treatment method for the inner surface of the heat transfer tube made of aluminum alloy is
The particle size of the zinc powder to be dispersed and mixed in the viscous binder,
It is set to 10 to 30 μm.

[0009]

According to the method of anticorrosion treatment of the inner surface of the aluminum alloy heat transfer tube of the present invention as described above, the zinc powder and the fluoride powder dispersed and mixed in the binder are adhered to the heat transfer tube due to the adhesive force of the high viscosity binder. Can be evenly attached to the inner surface. After the zinc powder and the fluoride powder are adhered to the inner surface of the heat transfer tube in this way and the temperature of the heat transfer tube is raised to the brazing temperature (about 600 ° C.), the binder is decomposed and sublimated. Fluorine generated from the fluoride powder removes the oxide film existing on the inner surface of the heat transfer tube. As a result, the zinc powder comes into direct contact with the aluminum alloy forming the heat transfer tube at the inner surface portion of the heat transfer tube and diffuses into the aluminum alloy to form a zinc diffusion layer on the inner surface portion. The zinc diffusion layer thus formed acts as a sacrificial corrosion layer to prevent corrosion of the heat transfer tube from progressing from the inner surface in the thickness direction of the heat transfer tube. Moreover, in the case of the present invention, a viscous mixture
Inner surface of this heat transfer tube when applying to the inner surface of this heat transfer tube
The amount of zinc powder adhered to is in the range of 0.5 to 30 g / m ² .
Since it is regulated so that it will fit, from the inner surface part of this heat transfer tube
Effectively prevent corrosion from progressing in the thickness direction of this heat transfer tube
it can.

[0010]

1 shows a heat transfer tube 1 whose inner surface is anticorrosion-treated by the method of the present invention, and FIG. 2 shows heat transfer tubes 1 and 1 arranged parallel to each other in the flow direction of a fluid (cooling water). It is sectional drawing which each shows a part of heat exchanger comprised with the heat transfer fin 8. The heat transfer tube 1 is, for example, JIS A
Like 3003 material, it is made by extrusion-molding an aluminum alloy having the required strength. By providing a plurality of partition walls 3 inside the oblong outer peripheral wall 2, a plurality of flow paths can be provided inside. It is provided with paths 4 and 4.

In order to form the zinc diffusion layers 11, 11 for corrosion protection on the inner peripheral surface of each of the flow paths 4, 4 which is the inner surface of the heat transfer tube 1 as described above, decomposition occurs without carbonization at high temperature. After applying a viscous mixture in which zinc powder and fluoride powder are dispersed and mixed in the highly viscous binder, the temperature of the heat transfer tube 1 is raised. As the high-viscosity binder satisfying the above conditions, acrylic resin, polybutene, etc. can be used. The zinc powder used has a particle size of 5 to 50 μm, and more preferably 10 to 30 μm. Further, as the above-mentioned fluoride powder, a fluoride-based flux is used. For example, KAl described in JP-B-58-27037 and marketed under the trademark "NOCOLOK"
Mixtures of F ₄ and K ₃ AlF ₆ are the most preferred of the currently readily available fluxes. In addition to this, as described in JP-B-4-48556, the flux of K ₂ AlF ₅ compound or KF and Al is also used.
A flux of a mixture with F ₃ can also be used.
Furthermore, the fluoride-based flux described in JP-A-63-177998-9 and JP-A-1-104494-7 can be used.

The zinc powder, the fluoride powder and the high-viscosity binder are kneaded by adding an organic solvent such as alcohol for adjusting the viscosity, and then the flow paths 4, 4 provided in the heat transfer tube 1 described above.
Pour inside. By this pouring operation, the zinc powder and the fluoride powder are evenly attached to the inner peripheral surfaces of the flow paths 4 and 4 by the adhesive force of the highly viscous binder. The amount of adhesion is regulated so that the amount of zinc powder adhered to the inner peripheral surface of each of the flow paths 4 and 4 falls within the range of 0.5 to 30 g / m ² . After the zinc powder and the fluoride powder are adhered to the inner surface of the heat transfer tube in this manner, the heat transfer tubes 1 and 1 and the heat transfer fins 8 are combined with other components such as a tank (not shown) to generate heat. Configure an exchange. This heat transfer fin 8 has a so-called double-sided clad material formed by laminating JIS A4343 material (aluminum alloy containing a large amount of Si and having a low melting point), which is a brazing material, on both sides of a JIS A 3003 material to be a core material in a corrugated shape. It is a corrugated fin that was formed.

When the heat transfer tubes 1 and 1 and the heat transfer fins 8 are combined as described above, the heat transfer tubes 1 and 1 and the heat transfer fins 8 are placed in a heating furnace while being held down by a jig. Put, JIS A 4343 material melts, but JIS 3003
The material is raised to the brazing temperature (about 600 ° C), which is the temperature at which it does not melt. Based on this temperature rise, the outer surfaces of the heat transfer tubes 1 and 1 are brazed to the heat transfer fins 8 and the zinc diffusion layers 11 and 11 are formed on the inner peripheral surfaces of the heat transfer tubes 4 and 4. Is formed.

That is, by heating for the brazing, the high-viscosity binder attached to the inner peripheral surfaces of the flow paths 4, 4 is decomposed and sublimated (the organic solvent is evaporated before the high-viscosity binder is decomposed and sublimated). At the same time, the fluorine generated from the fluoride powder removes the oxide film existing on the inner peripheral surfaces of the flow paths 4 and 4 of the heat transfer tube 1. As a result, the zinc powder comes into direct contact with the aluminum alloy (JIS A 3003 material) forming the heat transfer tube 1 at the inner peripheral surface portions of the flow paths 4 and 4, and diffuses into the aluminum alloy. The zinc diffusion layers 11, 11 are formed on the inner peripheral surface portions of the flow paths 4, 4. The zinc diffusion layers 11 and 11 thus formed act as sacrificial corrosion layers, so that corrosion (pitting corrosion) occurs from the inner peripheral surface of each of the flow paths 4 and 4 in the thickness direction of the heat transfer tube 1.
Prevent progress.

[0015]

EXAMPLES In order to confirm the effects of the present invention, experiments conducted by the present inventors will be described. JIA A 3003
By extruding the material, a heat transfer tube 1 having a sectional shape as shown in FIGS. 1 and 2 and a plate thickness of 0.4 mm was produced. Acrylic resin powder was added to the flow paths 4 and 4 of the heat transfer tube 1
Parts, 50 parts of zinc powder having a particle size of 10 to 30 μm, 40 parts of isopropyl alcohol, and 5 parts of “NOCOLOK” flux were kneaded, and the zinc powder was poured into each of the flow paths 4 and 4. After adhering to the peripheral surface, the alcohol was evaporated to dry the inner peripheral surface of each of the flow paths 4 and 4. In this way, the heat exchanger is constructed by combining the heat transfer tube 1 having zinc powder adhered to the inner peripheral surface of each of the flow paths 4 and 4 and the corrugated heat transfer fin 8 having a plate thickness of 0.13 mm. did. In addition, this heat transfer fin 8 is a JIS A
JIS A4343 material is laminated on both sides of 3003 material,
Made from double-sided clad material.

After the heat transfer tubes 1 and 1 and the heat transfer fins 8 are combined as shown in FIG. 2, "NOCOLOK" flux is applied to the surfaces of the heat transfer tubes 1 and 1 and the heat transfer fins 2 It was applied at a rate of ˜3 g / m ² and dried. afterwards,
It was heated to 600 ° C. in a nitrogen gas atmosphere, and the constituent members of the heat exchanger including the heat transfer tubes 1 and 1 and the heat transfer fins 8 were integrally brazed. With the heating for brazing, the zinc diffusion layer 1 is formed on the inner peripheral surface of each of the flow paths 4 and 4.
1 and 11 were formed.

In order to know the anticorrosion performance of the zinc diffusion layer formed on the inner peripheral surface of each of the flow paths 4 and 4 as described above, Cl ^-1 is ^added to 200
ppm, SO ₄ ^2- to 60 ppm, 30 ppm and Fe ^3+, the Cu ²⁺ 1pp
A corrosion test was performed using a corrosive liquid containing m. In this corrosion test, a corrosive liquid having the above composition and heated to 88 ° C. was circulated at a rate of 10 liter / min for 8 hours, then the circulation was stopped, and the process was left for 16 hours at room temperature for one cycle. As a result, 90 cycles (for 3 months) were performed. The results of this experiment are shown in Table 1 below.

[0018]

[Table 1]

As is clear from the description in Table 1, zinc powder having 0.5 g / m ² or more of zinc powder adhered to the inner peripheral surface of each of the flow paths 4 and 4 functions as a sacrificial corrosion layer on each inner peripheral surface. By forming the diffusion layers 11, 11, it is possible to effectively prevent the corrosion (pitting corrosion) from proceeding from the inner peripheral surface portions of the flow paths 4, 4 in the thickness direction of the heat transfer tube 1. When the amount of zinc powder attached to the inner peripheral surface of each of the flow paths 4 and 4 becomes excessive, the corrosion of the sacrificial corrosion layer portion proceeds too fast, and the corrosion products mixed in the cooling water become too large. . Therefore, it is preferable that the upper limit of the adhesion amount is about 30 g / m ² .

[0020]

EFFECTS OF THE INVENTION The method of anticorrosion treatment of the inner surface of the heat transfer tube made of aluminum alloy of the present invention is constructed and operates as described above, so that it has been difficult to obtain a uniform heat transfer tube on the inner surface of the heat transfer tube produced by extrusion molding. A zinc diffusion layer can be formed.
Further, it is possible to effectively prevent the corrosion from advancing from the inside of the heat transfer tube, which can contribute to the expansion of applications of such a heat transfer tube.

[Brief description of drawings]

FIG. 1 is a cross-sectional view of a heat transfer tube having a sacrificial corrosion layer formed by the method of the present invention.

FIG. 2 is a partial cross-sectional view showing an example of a heat exchanger configured by this heat transfer tube.

FIG. 3 is an end perspective view of a heat transfer tube which is a target of the present invention.

FIG. 4 is a perspective view showing an example of a conventionally known heat exchanger configured by this heat transfer tube.

[Explanation of symbols]

1 heat transfer tube 2 outer wall 3 partitions 4 channels 5 heat exchanger 6 curved part 7 Straight section 8 heat transfer fins 9 inlet connector 10 Outlet connector 11 Zinc diffusion layer

─────────────────────────────────────────────────── ─── Continuation of the front page (58) Fields surveyed (Int.Cl. ⁷ , DB name) C23C 10 / 28,10 / 30 F28F 19/06

Claims (2)

(57) [Claims] 1. A method for anticorrosion treatment of an inner surface of a heat transfer tube made of an aluminum alloy, which comprises forming an anticorrosion film for preventing corrosion from advancing from the inner surface of a heat transfer tube produced by extrusion-molding an aluminum alloy. In the inner surface of the heat transfer tube, a viscous mixture obtained by dispersing and mixing zinc powder and fluoride powder in a high-viscosity binder that decomposes without being carbonized at high temperature, the amount of zinc powder deposited on the inner surface of the heat transfer tube.
There was coated with regulations as to fit in the range of 0.5 to 30 g / m ^2, by raising the temperature of the heat transfer tube, to form a zinc diffusion layer on the inner surface of the <br/> heat transfer tube, Method of anticorrosion treatment on inner surface of aluminum alloy heat transfer tube. 2. The method for anticorrosion treatment of the inner surface of a heat transfer tube made of an aluminum alloy according to claim 1, wherein the zinc powder dispersed and mixed in the high-viscosity binder has a particle size of 10 to 30 μm.