JP7209487B2 - ALUMINUM FIN AND HEAT EXCHANGER EXCELLENT IN HYDROPHILIC AFTER BRAZING PROCESS AND METHOD FOR MANUFACTURING THE SAME - Google Patents

Description

TECHNICAL FIELD The present invention relates to aluminum fins and heat exchangers which are excellent in hydrophilicity after brazing, and to a method for manufacturing the same.

Heat exchangers in which copper tubes and aluminum fins are mechanically joined are widely used as heat exchangers for air conditioning such as air conditioners.
However, due to the recent rise in the price of copper metal, there is an increasing demand to replace all the members including the tube with inexpensive aluminum. Aluminum is lightweight, has excellent workability and thermal conductivity, can be recycled, and is inexpensive.

As an example of this type of air-conditioning heat exchanger, as described in Patent Document 1 below, a first header collection pipe and a second header collection pipe are arranged on the left and right with a certain space therebetween. A heat exchanger is known in which a plurality of flat tubes made of an aluminum alloy are arranged vertically, and vertically meandering corrugated fins are provided between the upper and lower flat tubes.
In the heat exchanger described in Patent Document 1, fin heat transfer parts are arranged between vertically arranged flat tubes, ventilation paths are defined between the flat tubes, and air flowing through the ventilation paths and the flat tubes heat is exchanged with the fluid flowing inside the

In order to suppress the retention of condensed water in extruded perforated flat tubes made of aluminum alloy, a flux composition consisting of a synthetic resin containing a methacrylic acid ester polymer or copolymer as a main component, a brazing flux, and an organic solvent is used. A flat tube for a heat exchanger, the surface of which is coated with an object, is described in Patent Document 2 below.

JP 2012-163317 A JP-A-11-239867

In order to improve the hydrophilicity of aluminum-made fins, pre-coated fins in which the fins are pre-coated with an organic paint are used in the above-described conventional heat exchangers that combine copper and aluminum. However, with aluminum heat exchangers, it is necessary to perform brazing heat treatment in a furnace at approximately 600°C in order to join the members. There was a problem that it was not possible to secure
Also, if a water glass-based inorganic paint is used for the precoated fins, the hydrophilicity after the brazing heat treatment can be ensured to some extent, but there is a problem that the surface of the fins is discolored, resulting in defects in appearance.

In view of these circumstances, the present invention provides a type of fin in which a hydrophilic film is formed in advance before brazing. This was made as a result of extensive studies to provide a fin that does not cause such problems.
In the present invention, it was found that by applying a boehmite film of a predetermined thickness to aluminum fins, it is possible to impart excellent hydrophilicity to the fins even after the brazing heat treatment, and that discoloration does not occur.
An object of the present invention is to provide aluminum fins and heat exchangers which are excellent in hydrophilicity after brazing, and a method of manufacturing the same.

The aluminum fin of the present invention is provided in a heat exchanger comprising a tube made of aluminum or an aluminum alloy having a refrigerant flow path therein and an aluminum fin made of aluminum or an aluminum alloy brazed to the tube. An aluminum fin, having a hydrophilic film made of boehmite film with a thickness of 100 to 7000 Å on at least one of the front surface and the back surface, and the color value of the surface provided with the hydrophilic film is L: 70 to 100, a : -3 to +5, b: -3 to +10.
Preferably, the aluminum fin of the present invention has a hydrophilic coating made of boehmite coating with a thickness of 1000 to 3500 Å.
In the aluminum fin of the present invention, it is preferable that the water contact angle after the brazing heat treatment is 10° to 30° on the surface provided with the hydrophilic film.

In the heat exchanger of the present invention, any one of the aluminum fins described above is brazed to an aluminum or aluminum alloy tube, and the surface provided with the hydrophilic film has a color value of L: 70 to 100, a : -3 to +5, b: -3 to +10 .
A heat exchanger of the present invention comprises a plurality of aluminum or aluminum alloy tubes in which a plurality of aluminum fins according to any one of the above are arranged at predetermined intervals, and the plurality of aluminum fins are inserted or penetrated. are brazed to the aluminum fins, and the plurality of tubes are individually brazed to header tubes.

In the heat exchanger of the present invention, a brazing coating film containing Si powder and Zn-containing flux is formed on the outer surface of the tubular body before brazing, and the brazing material layer is formed from the brazing coating film after brazing. Formed configurations can be employed.
In the heat exchanger of the present invention, a configuration in which a sacrificial anode layer is formed on the surface of the tube by diffusion of Zn contained in the brazing coating can be adopted.

A method for manufacturing a heat exchanger according to the present invention is a method for manufacturing a heat exchanger by brazing a tube having a refrigerant flow path thereinside to any of the aluminum fins described above, A brazing coating film containing Si powder and Zn-containing flux is formed on the outer surface of the tube, Si and Zn in the brazing coating film are diffused toward the tube side by heat treatment during brazing, and Zn is added to the outer surface side of the tube. is formed by diffusing a sacrificial anode layer.

In the case of the aluminum fin according to the present invention, excellent hydrophilicity can be imparted to the aluminum fin even after brazing by forming a boehmite film having a specified thickness as a hydrophilic film before brazing. At the same time, it is possible to provide an aluminum fin with a beautiful appearance without causing discoloration on the surface of the hydrophilic coating even after heating by brazing.
If it is a heat exchanger according to the present invention, it is a structure in which aluminum fins of the type that are provided with a hydrophilic film in advance corresponding to the precoat fins are joined to the tubes by brazing, so manufacturing using precoat fins It is possible to provide a heat exchanger that can be manufactured by a process equivalent to the process, has aluminum fins imparted with good hydrophilicity even after brazing, and has a good appearance of the fins.

It is a perspective view showing a heat exchanger of a 1st embodiment. FIG. 2 is a cross-sectional view of the heat exchanger shown in FIG. 1 taken along a plane perpendicular to the length direction of the tube; FIG. 2 is a cross-sectional view of the heat exchanger shown in FIG. 1 taken along the longitudinal direction of the tube, showing the state before the brazing process. FIG. 2 is a cross-sectional view of the heat exchanger shown in FIG. 1 taken along the longitudinal direction of the tube, showing a state after a brazing process; It is a front view which shows the heat exchanger of 2nd Embodiment. It is a partial expanded sectional view of the heat exchanger of 2nd Embodiment. FIG. 5 is a partial cross-sectional view showing the heat exchanger assembly before brazing the heat exchanger of the second embodiment;

An example of an embodiment of the present invention will be described in detail below with reference to the accompanying drawings. In the drawings used in the following explanation, in order to make the features easier to understand, the characteristic parts may be shown enlarged for convenience. Not necessarily.

FIG. 1 is a perspective view showing the heat exchanger 11 of the first embodiment.
The heat exchanger 11 of the first embodiment is used for applications such as heat exchangers for indoor/outdoor units of room air conditioners, outdoor units for HVAC (Heating Ventilating Air Conditioning), and heat exchangers for automobiles. It is an all-aluminum heat exchanger with

As shown in FIG. 1, the heat exchanger 11 is arranged in parallel with a pair of header pipes 14 spaced apart from each other in the left and right direction, and between the pair of header pipes 14 in parallel with each other with a space between them. A plurality of flat tubes 22 joined substantially perpendicularly to the header tube 14 and brazed to the outer surface (upper or lower surface) 12b of the tubular bodies 12 constituting these tubes 22 dissipate heat to the outside air. A plurality of fins (aluminum fins) 13 are provided. A supply pipe 15 for supplying refrigerant to the tubes 22 via the header pipes 14 is connected to one upper end portion of the pair of left and right header pipes 14 . A recovery pipe 16 for recovering the refrigerant that has passed through the tube 22 is connected to the lower end of the other header pipe 14 . The tubes 22, fins 13, header pipe 14, supply pipe 15, and recovery pipe 16 are all made of aluminum or aluminum alloy.

FIG. 2 is a partial cross-sectional view of heat exchanger 11 taken along a plane orthogonal to the length direction of tube 22 . As shown in FIG. 2, a plurality of (six in this embodiment) refrigerant flow paths 12a are formed inside the tubular body 12 that constitutes the tube 22 and are aligned along the width direction. Further, as shown in FIG. 2, the fin 13 has a plurality of notch portions 19 having a shape corresponding to the cross-sectional shape of the tube 22 and vertically spaced apart from each other by a predetermined distance. Tubes 22 are fitted into the cutouts 19 and fixed by brazing.

3 and 4 are partial cross-sectional views of the heat exchanger 11 taken along the longitudinal direction of the tubes 22. FIG. 3 shows the state before the brazing process, and FIG. 4 shows the brazing process. Indicates the state after. A plurality of fins 13 are arranged in parallel along the length direction of the tube 22 , and the tube 22 is inserted through the notch 19 . The plurality of fins 13 are arranged parallel to each other at regular intervals. The fin 13 has a bent portion 20 bent to one side in the thickness direction of the fin 13 along the outer surface 12b of the tube 22 on the periphery of the notch portion 19 . The bent portion 20 can be formed by, for example, burring.

The tube 22 and the fins 13 are arranged so that the tube 22 skewers the plurality of fins 13 arranged at regular intervals, and the tube 22 is fitted into the notch 19 of the fin 13 and fixed by brazing. .
In the state before brazing shown in FIG. 3, the gap between the bent portion 20 formed in the notch portion 19 of the fin 13 and the upper or lower surface of the tube 22 is preferably 10 μm or less.
In the fins 13 of the present embodiment, the tube 22 is inserted through the notch 19, but instead of the notch 19, a slit-shaped through hole is provided in the fin 13, and the tube 22 is inserted through the through hole. It may be configured.

The main components of the heat exchanger 11 are described in more detail below.
<<Fin>>
The fin 13 has a plate-like substrate 3 made of aluminum or an aluminum alloy, and hydrophilic coatings 1 provided on the first surface 3 a and the second surface 3 b of the substrate 3 .
<Base material>
The base material 3 is made of an alloy mainly composed of pure aluminum such as JIS 1050 series or JIS 3003 series aluminum alloy. Further, the base material 3 may be made of an aluminum alloy obtained by adding about 2% by mass of Zn to a JIS3003 series aluminum alloy.

It is preferable that the base material 3 is made of a material having a pitting potential lower than that of the tubular body 12 constituting the tube 22 . Corrosion of the tubular body 12 may lead to refrigerant leakage. By making the pitting potential of the substrate 3 more base than the pitting potential of the tubular body 12 , it is possible to delay the occurrence of pitting corrosion in the tubular body 12 due to preferential corrosion of the fins 13 .
The base material 3 is produced by melting an aluminum alloy having the above composition by a conventional method, and processed through a hot rolling process, a cold rolling process, a pressing process, and the like. In addition, the manufacturing method of the base material 3 is not particularly limited in the present invention, and a known manufacturing method can be appropriately adopted.

<Hydrophilic film>
The fins 13 have the hydrophilic films 1 on the first surface 3a and the second surface 3b of the base material 3 and the other peripheral surfaces. The hydrophilic film 1 is a boehmite film with a thickness of about 100 Å to 10000 Å.
A boehmite film is a film formed by immersing aluminum or an aluminum alloy in high-temperature water of 90 to 100° C. or holding it in pressurized steam.
Pure water can be used as high-temperature water, but water obtained by adding a small amount of aqueous ammonia to pure water may also be used. Alternatively, deionized water may be used and an additive such as triethanolamine may be added to adjust the pH to be slightly alkaline to promote the growth of the boehmite film.
The boehmite film can also be obtained by applying an alkaline or neutral paint to the aluminum fin substrate 3, drying it, and then washing it with hot water or water.

The hydrophilic film 1 made of boehmite film is a film that can be called a precoat film formed on the base material 3 of the fins 13 before brazing.
The boehmite film preferably has a thickness of 100 Å to 10,000 Å as described above so that it exhibits the desired hydrophilicity after brazing, does not adversely affect brazeability, and does not discolor after brazing.
If the thickness of the boehmite film is less than 100 Å, the water contact angle after the repeated dry-wet test described later after brazing becomes poor. There is a problem that the brazeability of the case is lowered. The thickness of the boehmite film is preferably in the range of 1000 to 7000 Å, more preferably in the range of 2000 to 3500 Å, in order to achieve both the best water contact angle and excellent brazeability.

<<Tube>>
As shown in FIG. 3 , the tube 22 has a tubular body 12 and a brazing material layer 5 formed on an outer surface (upper or lower surface) 12 b of the tubular body 12 . As shown in FIG. 2, the tubular body 12 is a multi-hole flat tube in which a plurality of coolant channels 12a are formed. As the tube, a tube made by bending and forming an aluminum alloy brazing sheet can also be used.
The tubular body 12 is made of, for example, a pure aluminum system such as JIS 1050 series or an alloy mainly composed of a JIS 3003 series aluminum alloy. As an example, Si: 0.10 to 0.60%, Fe: 0.1 to 0.6% by mass, Mn: 0.1 to 0.6% by mass, Ti: 0.005 to 0.2% by mass, It is produced by extruding an aluminum alloy containing Cu: less than 0.1% by mass and the balance being aluminum and unavoidable impurities.
The tubular body 12 is preferably made of a material having a pitting potential higher than that of the fillet 5A formed through the brazing process and the pitting potential of the base material 3 of the fins 13 . Thereby, corrosion of the base material 3 of the fillet 5A and the fins 13 is started before corrosion of the tubular body 12 is started, and corrosion of the tubular body 12 can be delayed.

The tubular body 12 of the tube 22 before brazing shown in ^FIG . A brazing material layer 5 having a compounding composition of flux (KZnF ₃ ): 3.0 to 20.0 g/m ² and binder (for example, acrylic resin): 0.5 to 8.5 g/m ² is formed. there is
In the heat exchanger 11 before brazing shown in FIG. . The brazing material layer 5 is cooled after being heated to around 600° C. (brazing step), thereby solidifying in a state filled between the opposing surface 20a and the tube 22, and forming a fillet 5A ( brazing material layer), and joins the fins 13 and the tube 22 by brazing.

As shown in FIG. 2, the outer surface 12b of the tube 12 includes a flat surface (upper surface) 6A and a back surface (lower surface) 6B, and adjacent first and second sides 6C and 6D. Consists of The first side surface 6C is located on the opening side of the notch 19 of the fin 13 and is open to the outside. The second side surface 6D is located on the opposite side of the first side surface 6C and is surrounded by the notch 19. As shown in FIG.
The brazing material layer 5 is formed, for example, on a region of the outer surface 12b of the tubular body 12 in contact with the fins 13, that is, on the front surface 6A and the rear surface 6B of the tubular body 12. As shown in FIG. In addition, on the surface 6A and the back surface 6B of the tubular body 12 after brazing, Si and Zn contained in the brazing material layer 5 are diffused toward the tubular body 12 at the brazing temperature to form the surface layer of the tubular body 12. A sacrificial anode layer comprising Si and Zn is formed.

The composition forming the brazing material layer 5 will be described below.
<Si powder>
The Si powder reacts with Al constituting the tubular body 12 of the tube 22 to form a braze that joins the fins 13 and the tube 22. During brazing, the Zn-containing flux and the Si powder melt to form a brazing liquid.
Zn in the flux uniformly diffuses into this brazing liquid and spreads uniformly over the surface of the tubular body 12 . Since the diffusion rate of Zn in the brazing liquid, which is a liquid phase, is significantly higher than that in the solid phase, uniform Zn diffusion is achieved, and the Zn concentration in the planar direction of the surface of the tubular body 12 becomes substantially uniform. As for the diffusion in the depth direction from the surface of the tubular body 12, since Si becomes a eutectic with Al to lower the melting point, Zn diffuses in a state of eutectic composition on the surface of the tubular body 12. A sacrificial anode layer having a predetermined thickness is formed on the surface of the tubular body 12 . The formation of this sacrificial anode layer can improve the corrosion resistance of the tube 22 .

<Si powder coating amount: 1.0 to 5.0 g/m ² >
If the coating amount of the Si powder is less ^than 1.0 g/m ² , brazing formation may be insufficient. It is not preferable because the thickness of the Therefore, the Si powder content in the brazing material layer 5 is preferably 1.0 to 5.0 g/m ² .
<Si powder particle size: maximum particle size: D (99): 30 μm or less>
If the particle size of the Si powder is 30 μm or less in D(99), it is possible to form a uniform sacrificial anode layer. may not be able to form Therefore, the particle size of the Si powder is preferably 30 μm or less at the maximum particle size D(99). Note that D(99) is the particle diameter of particles that accumulate from particles having a small volume ratio and form 99% of the total. All of these values can be measured by a laser light scattering method.

<Zn-containing flux, Zn-free flux>
The Zn-containing flux has the effect of forming a sacrificial anode layer consisting of a Zn diffusion layer on the surface of the tubular body 12 during brazing and improving pitting resistance. It also has the effect of destroying the oxide film on the outer surface of the tubular body 12 during brazing, promoting the spread and wetting of the braze, and improving the brazeability. Since this Zn-containing flux has higher activity than a Zn-free flux, good brazeability can be obtained even with relatively fine Si powder. One or more of KZnF ₃ , ZnF ₃ and ZnCl ₂ can be used as the Zn-containing flux. A non-Zn containing flux may be added to the Zn containing flux.
Fluoride-based fluxes and potassium fluoroaluminate-based fluxes as Zn-free fluxes are fluxes containing KAlF ₄ as the main component, and various compositions with additives are known. Examples include a composition of K ₃ AlF ₆ +KAlF ₄ and Cs _(x) K _(y) F _(z) . In addition, a fluoride-based flux (for example, a potassium fluoroaluminate-based flux) to which a fluoride such as LiF, KF, CaF ₂ , AlF ₃ , or K ₂ SiF ₆ is added can also be used. Addition of fluoride-based flux (for example, potassium fluoroaluminate-based flux) in addition to Zn flux contributes to improvement in brazeability.
<Amount of flux applied: 3.0 to 20.0 g/m ² >
If the coating amount of the Zn-containing fluoride-based flux is less than 3.0 g/m ² , the potential difference in the heat exchanger 11 will be low, and the sacrificial effect may not be exhibited. In addition, insufficient removal of the oxide film on the surface of the material to be brazed (tubular body 12) may lead to defective brazing. On the other hand, if the coating amount exceeds 20.0 g/m ² , the potential difference becomes excessive, the corrosion rate increases, and the anticorrosion effect due to the existence of the sacrificial anode layer may be shortened. For this reason, it is preferable to set the coating amount of the Zn-containing fluoride-based flux to 3.0 to 20.0 g/m ² . As the Zn-containing fluoride-based flux, _KZnF3 can be used as an example. The non-Zn containing fluxes described above can be added in addition to the Zn containing fluxes.

<Binder>
The brazing material layer 5 can contain a binder in addition to Si powder and Zn-containing fluoride flux. Examples of the binder are preferably acrylic resins. The binder has the effect of fixing the Si powder and Zn ^- containing flux necessary for forming the sacrificial anode layer to the surface 6A and the back surface 6B of the tubular body 12. Si powder and Zn flux may come off from the tube 12 during brazing, and a uniform sacrificial anode layer may not be formed. On the other hand, if the coating amount of the binder exceeds 8.5 g/m ² , the binder residue may deteriorate the brazeability, and a uniform sacrificial anode layer may not be formed. Therefore, it is preferable that the coating amount of the binder is 0.5 to 8.5 g/m ² . Note that the binder usually evaporates due to heating during brazing.

The method of forming the brazing material layer 5 composed of Si powder, flux and binder is not particularly limited in the present invention, and may be a spray method, a shower method, a flow coater method, a roll coater method, a brush coating method, an immersion method, or a static method. It can be carried out by an appropriate method such as an electrocoating method.
Further, the formation area of the brazing material layer 5 may be the whole surface 6A, the rear surface 6B, and the second side surface 6D of the tubular body 12, or may be a part thereof. Furthermore, although the brazing material layer 5 is not formed on the first side surface 6C of the tubular body 12 of the present embodiment, it may be partially formed on the first side surface 6C depending on the application method. The present invention does not exclude such.

<<Manufacturing method>>
An example of a method of manufacturing the heat exchanger 11 having the fins 13 and the tubes 22 described above will be described below.
First, the tube 22 and the fins 13 are prepared. The fins 13 are formed with the hydrophilic film 1 over the entire surface including the first surface 3a and the second surface 3b of the base material 3 . A boehmite film having a thickness of 100 to 4000 Å is formed on the entire surface of the fin 13 by, for example, holding the fin 13 in the above-described high-temperature water.
The fin 13 is formed with a notch portion 19 and a bent portion 20 on the periphery thereof. Further, as the tube 22, a tube having the brazing material layer 5 formed in advance on a part of the outer surface 12b of the tubular body 12 is prepared.
Next, as shown in FIG. 3 , a plurality of fins 13 are arranged in parallel, and the tube 22 is inserted through the notch 19 .

Next, a brazing step is performed in which the temperature is higher than the melting point of the brazing material layer 5, for example, 580 to 620.degree. The heating melts the brazing material layer 5 formed on the outer surface 12b of the tubular body 12 to form a brazing liquid. This brazing liquid flows into the gap between the facing surface 20a of the bent portion 20 of the fin 13 and the outer surface 12b of the tubular body 12 by capillary force, and fills the gap. Further cooling causes the brazing liquid to solidify to form a fillet 5A (brazing material layer) as shown in FIG. The fillet 5A joins the tube 22 and the fins 13 together.

In brazing, the brazing material layer 5 is melted by heating to an appropriate temperature in an appropriate atmosphere such as an inert atmosphere. In this case, the activity of the flux increases, and Zn in the flux diffuses to the thick side of the brazing material (the base material 3 of the fins 13). promotes wetting between the brazing material and the material to be brazed by destroying the oxide film of
During brazing, part of the aluminum alloy matrix forming the tubular body 12 of the tube 22 reacts with the composition of the brazing material layer 5 to become wax, and the tubular body 12 and the fins 13 of the tube 22 are brazed. . Zn in the flux is diffused in the upper and lower surface layers of the tubular body 12 by brazing to form a sacrificial anode layer that is more base than the inside of the tubular body 12 .

<< effect >>
According to the structure of the present embodiment, good brazing is achieved, and fillet 5A (brazing material layer) of sufficient size is formed between tubular body 12 and fins 13 .
The fillet 5A has a more base pitting potential than the tubular body 12 and the fins 13 . Therefore, it is possible to preferentially corrode the tubular body 12 and the fins 13 and delay the pitting corrosion of the tubular body 12 and the fins 13 .
Further, even after the step of melting and solidifying the brazing material layer 5, the hydrophilic film 1 made of the boehmite film remains and can impart hydrophilicity to the fins 13. FIG.

In the step of melting and solidifying the brazing material layer 5 of the tube 22 to join the fins 13 and the tube 22 together, it is preferable to braze the header tube 14 to the tube 22 at the same time.

Since the fins 13 after brazing shown in FIG. 4 are formed with the hydrophilic film 1 made of a boehmite film that has undergone a heat treatment process during brazing, the hydrophilicity of the fins 13 can be increased.
Hydrophilic film 1 made of boehmite film can maintain hydrophilicity even after a heating process at a temperature of around 600° C. during brazing. Therefore, the hydrophilic film 1 can be formed by a pre-coating process in which the base material 3 of the fins 13 is previously formed before the heat exchanger 11 is assembled. Since the process of forming a hydrophilic film by post-coating after brazing becomes unnecessary, the heat exchanger 11 can be provided with a simplified manufacturing process.

In the above-described embodiment, a structure in which the brazing material layer 5 for brazing is provided on the outer surface such as the front surface or the back surface of the tube 22 is adopted. It is also possible to employ a structure in which a brazing filler metal is arranged around the portion to be joined and brazed using the brazing filler metal.
The tubes 22 and the fins 13 may be joined by brazing by melting the brazing filler metal by heating during brazing and spreading the melted brazing filler metal over the boundaries between the tubes 22 and the fins 13 .

Alternatively, the fins 13 may be composed of a two-layered brazing sheet consisting of a core material layer and a brazing material layer, and the tube 22 may have no brazing material layer.
In this case, the boehmite layer can be provided on one side or both sides of the core layer. Alternatively, the fins 13 are formed from a brazing sheet having a three-layer structure in which brazing material layers with boehmite layers provided on both sides of a core material layer are laminated (three-layer structure with a core material and brazing material layers on both sides with boehmite layers). can also

When using a brazing sheet, as an example, the core material is, in mass%, Mn: 0.5 to 2.0%, Si: 1.3% or less, Fe: 0.25% or less, Cu: 0.5% Below, Zn: 4.0% or less, made of an aluminum alloy having a composition of the balance Al and unavoidable impurities, the brazing material layer contains Si: 5.0 to 13.0% by mass, and the balance A combination consisting of an aluminum alloy having a composition of Al and unavoidable impurities can be exemplified.

In the above-described embodiment, an example in which the present invention is applied to the heat exchanger having the plate fin structure shown in FIGS. 1 and 2 has been described. You may apply to the heat exchanger using.
FIG. 5 is a front view showing a second embodiment of a heat exchanger to which corrugated fins are applied.
The heat exchanger 30 of this second embodiment includes header pipes 31 and 32 which are arranged in parallel with a space between them in the left and right direction, and the header pipes 31 and 32 are arranged in parallel with a space between them, and It is mainly composed of a plurality of flat tubes 33 joined perpendicularly to header pipes 31 and 32 and corrugated fins 34 attached to each tube 33 . The header pipes 31, 32, tubes 33 and fins 34 are made of aluminum alloy. As the aluminum alloy forming the tubes 33, an aluminum alloy equivalent to the aluminum alloy forming the tubes 22 of the heat exchanger 11 of the first embodiment can be applied. The aluminum alloy forming the fins 34 can be the same aluminum alloy as the aluminum alloy forming the fins 13 of the heat exchanger 11 of the first embodiment.

A plurality of slits 36 are formed in the opposing sides of the header pipes 31 and 32 at regular intervals in the longitudinal direction of each pipe, and the ends of the tubes 33 are inserted through the opposing slits 36 of the header pipes 31 and 32. A tube 33 is installed between the header pipes 31 and 32 . Further, fins 34 are arranged between a plurality of tubes 33, 33 that are laid between the header pipes 31, 32 at predetermined intervals, and these fins 34 are brazed to the front side or rear side of the tubes 33. As shown in FIG.
As shown in FIG. 6, a first fillet portion 38 is formed by the brazing material at the portion where the end portion of the tube 33 is inserted into the slit 36 of the header pipes 31 and 32, and the tube 33 is connected to the header pipes 31 and 32. brazed. A second fillet portion 39 is formed by the brazing material generated in the portion between the corrugated fins 34 with the corrugated fins 34 facing the top surface or the back surface of the adjacent tube 33 . Corrugated fins 34 are brazed to the side and back sides.
Like the fins 13 of the previous embodiment, the fins 34 each have a plate-like substrate made of aluminum or an aluminum alloy and hydrophilic coatings provided on the first and second surfaces of the substrate. are doing. The hydrophilic coating in this example consists of a hydrophilic coating equivalent to the hydrophilic coating 1 applied in the previous embodiment.

The heat exchanger 30 of this embodiment comprises header pipes 31, 32, a plurality of tubes 33 and a plurality of fins 34 installed between them to form a heat exchanger assembly 41 as shown in FIG. , which is manufactured by heating and brazing. Zn diffused layers 42 are formed on the front and back sides of the tube 33 by heating during brazing.

Before brazing, the tube 33 is coated with a brazing coating 37 having the same composition as the brazing material layer 5 described above on the front and back surfaces to which the fins 34 are to be joined. The tube 33 is made of a flat multi-hole tube equivalent to the tube 22 described above, and has a plurality of coolant passages 33C formed therein. 33A and a side surface adjacent to the back surface 33B.

The aluminum alloy forming the header pipes 31 and 32 is preferably an aluminum alloy based on an Al--Mn system.
For example, it is preferable to contain Mn: 0.05 to 1.50%, and as other elements, Cu: 0.05 to 0.8% and Zr: 0.05 to 0.15%. can.

FIG. 7 shows a heat exchanger assembly 41 in which the header pipes 31 and 32, the tubes 33 and the fins 34 are assembled using the tubes 33 to which the brazing coating film 37 is applied on the joint surface with the fins 34. , showing a state before heat brazing. In the heat exchanger assembly 41 shown in FIG. 7, the tube 33 is attached by inserting one end thereof into a slit 36 provided in the header pipe 31 . A brazing material layer 43 is provided on the surface side of the core material 31A of the header pipes 31 and 32 .

A heat exchanger assembly 41 composed of header pipes 31, 32, tubes 33 and fins 34 assembled as shown in FIG. The material layer 43 and the brazing coating film 37 are melted and then solidified to join the header pipe 31 and the tube 33, and the tube 33 and the fin 34, respectively, as shown in FIG. An exchanger 30 is obtained. At this time, the brazing filler metal layer 43 on the inner peripheral surfaces of the header pipes 31 and 32 melts and flows near the slit 36 to form the first fillet portion 38 to join the header pipes 31 and 32 and the tube 33 together. . Further, the brazing coating film 37 on the front and back surfaces of the tube 33 melts to become Al--Si braze or Al--Si--Zn braze, which flows near the fins 34 by capillary force to form a second fillet portion 39. The tube 33 and the fins 34 are joined together. Also, the brazing material layer 43 provided on the surfaces of the header pipes 31 and 32 remains slightly on the surface after brazing.

At the time of brazing, the coating film 37 for brazing and the brazing material layer 43 are melted by heating to an appropriate temperature in an appropriate atmosphere such as an inert atmosphere in a heating furnace or the like. As a result, the activity of the flux increases, and Zn in the flux precipitates on the surface side or bottom side of the brazing material (tube 33) and diffuses in the thickness direction thereof. promotes wetting between the brazing material and the material to be brazed by destroying the oxide film on both surfaces.
Brazing conditions are not particularly limited. As an example, the inside of the heating furnace is made into a nitrogen atmosphere, the heat exchanger assembly 41 is heated to a brazing temperature (substantial temperature reached) of 580 to 620° C. at a temperature increase rate of 5° C./min or more, and the brazing temperature is maintained for 30 seconds or more. It may be held and cooled at a cooling rate of 10°C/min or more from the brazing temperature to 400°C.

Zn in the flux is diffused on the upper and lower surfaces of the tube 33 by brazing to form a Zn diffused layer 42 on the surface side or the lower surface side of the tube 33, and a region receiving Zn diffusion on the tube surface side or the lower surface side. becomes more base than the inner side of the tube 33 in the wall thickness direction (the region where Zn is not diffused). Here, the inner side of the tube 33 in the thickness direction indicates a region deeper in the thickness direction of the tube 33 than the surface region or the back surface region of the tube 33 where the Zn diffusion layer 42 is formed.

In the heat exchanger 30 shown in FIGS. 5 and 6, both surfaces of the fins 34 are formed with hydrophilic films made of boehmite films having a thickness of about 100 Å to 4000 Å. Therefore, hydrophilicity equivalent to that of the heat exchanger 11 described above can be obtained. That is, since the fins 34 after brazing shown in FIGS. 5 and 6 are formed with a hydrophilic film made of a boehmite film that has undergone a heat treatment process during brazing, the hydrophilicity of the fins 34 can be increased. can.
The hydrophilic film made of the boehmite film described above can maintain its hydrophilicity even through a heating process at a temperature of around 600° C. during brazing. Therefore, the hydrophilic coating can be formed by a pre-coating process in which the base material of the fins 34 is pre-formed before the heat exchanger 30 is assembled. Since the step of forming a hydrophilic film by post-coating after brazing becomes unnecessary, the heat exchanger 30 can be provided with a simplified manufacturing process.
In addition, the heat exchanger 30 can obtain excellent corrosion resistance like the heat exchanger 11 of the previous embodiment.

In the second embodiment, as the heat exchanger 30 using corrugated fins, a structure in which the brazing material layer 37 for brazing is provided on the outer surface such as the upper surface or the lower surface of the tube 33 is adopted. A structure may be employed in which the material layer 37 is omitted and brazing is placed around the portions to be joined by brazing between the tube 33 and the fins 34 .
The tube 33 and the fins 34 may be joined by brazing by melting the brazing filler metal by heating during brazing and spreading the melted brazing filler metal over the boundary between the tube 33 and the fins 34 .

Alternatively, the fins 34 may be composed of a two-layered brazing sheet consisting of a core material layer and a brazing material layer, and a structure in which the brazing material layer 37 is not provided on the tube 33 may be employed.
In this case, the boehmite layer can be provided on both sides of the core layer. Alternatively, the fin 34 is composed of a brazing sheet having a three-layer structure (a three-layer structure consisting of a core layer and brazing material layers on both sides provided with a boehmite layer) in which brazing material layers with boehmite layers provided on both sides of a core material layer are laminated. You can also

When using a brazing sheet, as an example, the core material is, in mass%, Mn: 0.5 to 2.0%, Si: 1.3% or less, Fe: 0.25% or less, Cu: 1.3% Below, Zn: 4.0% or less, made of an aluminum alloy having a composition of the balance Al and unavoidable impurities, the brazing material layer contains 5.0 to 13.0% by mass, and the balance Al and A combination made of an aluminum alloy having a composition of unavoidable impurities can be exemplified.

EXAMPLES The present invention will be described in more detail below with reference to Examples, but the present invention is not limited to these Examples.
<<Preparation of sample>>
A plate-like substrate containing Si: 0.4 to 1.0% by mass, Mn: 1.0 to 2.0% by mass, Zn: 1.0 to 3.5% by mass, and the balance being inevitable impurities and Al A hydrophilic film made of a boehmite film having the type and thickness shown in Table 1 below was formed on the material by immersing it in high-temperature water at 90°C. The film thickness of the hydrophilic film was adjusted by adjusting the time of immersion in hot water for 5 to 30 minutes.
Some samples used a paint instead of a boehmite film to form a hydrophilic film. It was formed so as to have a film thickness shown in Table 1.
"Film thickness measurement"
The film thickness of the boehmite film and the precoat film was measured using a depth profile by an X-ray photoelectron spectrometer (XPS). The analysis was carried out using PHI5000VersaProbeIII manufactured by ULVAC-PHI, with X-ray source: 25 W, pass energy: 26 eV, and step: 0.05 eV. The sputtering conditions were acceleration voltage: 2 kV, raster range: 2 mm x 2 mm, _SiO2 sputtering rate: 4.7 nm/min. The film thickness was calculated in terms of _SiO2 .

Next, an aluminum alloy for tubes containing 0.3 to 0.5% by mass of Si, 0.2 to 0.4% by mass of Mn and the balance of unavoidable impurities and Al is melted, and the alloy is formed into a cross-sectional shape. (Thickness: 0.26 mm x Width: 17.0 mm x Total thickness: 1.5 mm) A flat aluminum alloy tube for a heat exchanger was used.
Further, brazing filler metal layers were formed on the surface (upper surface), back surface (lower surface), and second side surface of this tubular body. The brazing material layer consists of 3 g of Si powder (D(99) particle size 10 μm), 6 g of Zn-containing flux ( _KZnF3 powder: D(50) particle size 2.0 μm), 1 g of acrylic resin binder, and 3- It was formed by roll-coating a solution consisting of a mixture of methoxy-3-methyl-1-butanol and 16 g of isopropyl alcohol and drying.

Using the 11 tubes and the corrugated fins (10 pieces) formed into a corrugated shape, 10 tubes are assembled to the fins to construct a temporary mini-core test body, and these test bodies are placed in a nitrogen atmosphere furnace. Brazing was performed under the condition of holding at 600° C. for 3 minutes. By this brazing, a sacrificial anode layer was formed on the front and back surfaces of the tube on which the brazing film had been formed, and the fins provided with a hydrophilic film made of boehmite film were brazed. It was used as an exchanger test piece.

<<Test>>
Next, using these heat exchanger test pieces, a fin discoloration observation test, a hydrophilicity evaluation test, and a brazeability evaluation test, which will be described below, were carried out.

[Fin Discoloration Observation Test]
For fins after brazing at 600°C for 3 minutes, the color value measured with a color difference meter satisfies the ranges of L: 70 to 100, a: -3 to +5, and b: -3 to +10. It was determined that there was no discoloration. Color values not satisfying the ranges of L: 70 to 100, a: -3 to +5, and b: -3 to +10 were judged to be discolored.
[Hydrophilicity: Water contact angle after repeated dry-wet test]
A test piece after brazing at 600° C. for 3 minutes was immersed in running water for 8 hours and then dried for 16 hours. If the water contact angle at this time was 40° or less, it was judged to have good hydrophilicity.
[Brazability: Fin bonding rate evaluation test]
For each brazed-bonded fin, the fin was stripped from the tube and the fin-bond trace remaining on the tube surface was observed. Then, the number of unjoined portions (places where brazing was performed but no mark of the joint was left) was counted. Observations were made at 100 locations on one test piece, and those in which 80 or more locations (80% or more) were normally joined were judged to have good brazability.

As is clear from the results shown in Table 1, a boehmite film is formed on a fin as a precoating film, and this fin is used to construct a mini-core test piece for a heat exchanger, which is then brazed using a brazing coating film. As a result, it was found that a heat exchanger having excellent hydrophilicity and excellent brazing properties without causing discoloration of the fin surface can be manufactured.
The contact angle value after the repeated dry-wet test was in the range of 10 to 30°. Even under the severe test environment of 14 cycles of immersion in running water for 8 hours followed by drying for 16 hours, the mini-core test specimen of the example exhibited excellent hydrophilicity that could maintain a low contact angle on the fin surface. I was able to get
On the other hand, in Comparative Example No. 12, the boehmite film was too thin, so the contact angle was large after the repeated dry-wet test. In Comparative Example No. 13, the boehmite film was too thick, resulting in poor brazeability.
Aluminum brazing is characterized by the fact that the oxide film that exists on the aluminum surface during the brazing heat treatment is weakened by the effect of the flux, and the melted brazing material flows on the surface, allowing multiple points to be joined together. On the other hand, if the hydrated aluminum oxide film layer, which is the boehmite film, is too thick, the flux contained in the brazing filler metal paint cannot sufficiently weaken the oxide film, hindering the flow of the molten brazing filler metal. It was found that the brazeability deteriorated by

Comparative example No. 14 is an example in which an acrylic resin precoat film is used instead of the boehmite film, Comparative example No. 15 is an example in which a polyvinyl alcohol precoat film is used instead of the boehmite film, and Comparative example No. 16 is a boehmite film. This is an example in which carboxymethyl cellulose is used as a precoat film in place of the film. When films of these organic materials were used as precoat films, the respective resins were damaged by being heated to 600° C. during brazing, and the hydrophilicity that these resins should have was greatly impaired.

Comparative Example No. 17 is an example in which the boehmite film is replaced with a sodium silicate precoat film, and Comparative Example No. 18 is an example in which the boehmite film is replaced with a lithium silicate precoat film. These silicate films are materials that are more resistant to heat than the above-mentioned resin films, so although they have excellent hydrophilicity after brazing, the film surface is discolored, so the color change is large, and the appearance of the fins after brazing is poor. As a result, the above defects were exhibited.
From these test results, it was found that a heat exchanger using a boehmite film with a film thickness within the desired range as a precoat film on the surface of the fins would be excellent in hydrophilicity, free from the problem of discoloration in appearance, and good in brazability. It has been found that the heat exchanger can also be provided by

DESCRIPTION OF SYMBOLS 1... Hydrophilic film 3... Base material 3a... First surface 3b... Second surface 5... Brazing material layer 5A... Fillet (brazing material layer) 6A... Front surface 6B... Back surface 6C... First side 6D Second side 11 Heat exchanger 12 Tubular body 12a Refrigerant channel 12b Outer surface 13 Fin 14 Header pipe 15 Supply pipe 16 Recovery Tube 19 Notch portion 20 Bent portion 20a Opposing surface 22 Tube.

Claims (9)

An aluminum fin provided in a heat exchanger comprising an aluminum or aluminum alloy tube having a refrigerant flow path inside and an aluminum fin made of aluminum or aluminum alloy brazed to the tube , the surface and at least one of the back surface is provided with a hydrophilic film made of a boehmite film with a thickness of 100 to 7000 Å, and the color value of the surface provided with the hydrophilic film is L: 70 to 100, a: -3 to +5, b : An aluminum fin having excellent hydrophilicity after brazing, characterized by -3 to +10. 2. An aluminum fin having excellent hydrophilicity after brazing according to claim 1, characterized by comprising a hydrophilic film made of a boehmite film having a thickness of 1000 to 3500 Å. Excellent hydrophilicity after brazing according to claim 1 or claim 2, characterized in that the water contact angle after brazing heat treatment on the surface provided with the hydrophilic film is 10° to 30° . aluminum fins. The aluminum fin according to any one of claims 1 to 3 is brazed to an aluminum or aluminum alloy tube, and the color value of the surface provided with the hydrophilic film is L: 70 to 100, a: - 3 to +5, b: -3 to +10. The aluminum fin according to any one of claims 1 to 3 is a corrugated fin, a plurality of tubes made of aluminum or aluminum alloy are arranged in parallel, the corrugated fins are brazed between these tubes, and the plurality of 5. A heat exchanger according to claim 4, wherein the tubes are individually brazed to the header pipe. A plurality of aluminum or aluminum alloy tubes in which a plurality of aluminum fins according to any one of claims 1 to 3 are arranged at predetermined intervals, and the plurality of aluminum fins are inserted or penetrated is said 5. The heat exchanger of claim 4, wherein the aluminum fins are brazed and said plurality of tubes are individually brazed to header tubes. A brazing coating film containing Si powder and Zn-containing flux is formed on the outer surface of the tubular body before brazing, and the brazing material layer is formed from the brazing coating film after brazing. A heat exchanger according to any one of claims 4-6. 8. The heat exchanger of claim 7, wherein a sacrificial anode layer is formed on the tube surface by diffusion of Zn contained in the brazing coating. A method for manufacturing a heat exchanger by brazing a tube having a coolant channel thereinside to the aluminum fin according to any one of claims 1 to 3, wherein Si powder is applied to the outer surface of the tube. and Zn-containing flux are formed, Si and Zn in the brazing coating film are diffused to the tube side by heat treatment at the time of brazing, and Zn is diffused to the outer surface side of the tube. A method for manufacturing a heat exchanger, characterized by forming a layer.

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