JPH11325793A - Member for heat exchanger - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a member for heat exchanger excellent in resistance against honey comb corrosion and in which cracking due to stress corrosion does not take place. SOLUTION: An underlying layer 1a of at least one kind selected from nickel, cobalt, chromium, silver or a group of alloys thereof having average thickness of 0.1-2 μm is formed on the surface of a member for heat exchanger composed of copper or copper alloy and a coating containing metal zinc powder or a zinc plating layer 1b having average thickness of 0.1-50 μm is formed on the underlying layer 1a.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a heat exchanger member.

[0002]

2. Description of the Related Art Heat exchangers are used for air conditioner indoor and outdoor units.
A heat transfer tube made of copper or copper alloy with excellent corrosion resistance, heat conductivity, workability, etc. is expanded and joined to fins usually made of aluminum or aluminum alloy, used for indoor units of air conditioning equipment using cold and hot water, etc. The cross fin type is the mainstream. Focusing on such copper properties, copper fins may be used in some cases.

In such a heat exchanger, for example, a fin is formed by pressing an aluminum plate to form a collar portion (hereinafter referred to as a “fin collar”) through which a heat transfer tube passes.
After laminating a plurality of the fins so that the positions of the fin collars are aligned with each other, the heat transfer tubes are inserted into the fin collars, and the heat transfer tubes are further expanded to join them.

[0004] When the heat exchanger acts as an evaporator, such as an indoor unit during a cooling operation or an outdoor unit during a heating operation, the fin surface temperature of the heat exchanger is lower than the surrounding air. As a result, the dew point on the fin surface decreases, and the water vapor in the atmosphere becomes dew water and adheres to the fin. Also, water droplets may adhere for some reason.

[0005] However, dew condensation and water droplets (hereinafter referred to as "adhered water") block the gaps between the fins to form bridges, increase ventilation resistance and noise, and cause a decrease in cooling and heating capacity.

[0006] In order to solve the above problem, the fin surface is coated with a hydrophilic film so that the adhered water flows down along the hydrophilic film of the fin so that the gap between the fins is not closed. Is adopted. Conventionally, various materials having a water glass, a polar group or the like have been used as a material of the hydrophilic film having such a function. These films are composed of hydrophilic groups (-OH groups,> C
= O group, -NH ₂ group, -COOH group, etc.) are exposed, the contact angle between the adhered water and the film surface becomes smaller, and the adhered water flows down the surface as described above. It is easier to go.

[0007]

However, when the fin surface is coated with the hydrophilic film as described above, the following problems are likely to occur. In other words, the fin collar and the heat transfer tube do not completely adhere to each other even by the expansion joint, and a gap is formed between the two. When the fin and the heat transfer tube surface are coated with the hydrophilic film, the attached water can easily enter the gap. . If the adhering water contains a corrosive medium, local ant-nest corrosion occurs on the surface of the heat transfer tube in the gap.

In particular, recently, there has been a tendency to reduce the distance between the fins in order to reduce the size of the heat exchanger, and the heat transfer tubes may be completely covered by the laminated fin collars and may not be exposed to the outside. On the other hand, the surface of the heat transfer tube is exposed to the adhering water staying in the gap between the fin collar and the heat transfer tube for a long time.

By the way, ant-nest-like corrosion is caused by the dissolution of copper as a component of a heat transfer tube in an organic acid (a carboxylic acid such as formic acid or acetic acid). Since formaldehyde and alcohol generated from the adhesive for plywood and cloth are generated even when oxidized, the indoor unit of the air conditioner is often used when exposed to an environment containing a corrosive medium.

As a technique for preventing such corrosion of the copper tube, a technique of forming a copper-zinc alloy on the surface of the copper tube has been proposed (see JP-A-62-1856).

[0011] However, the copper-zinc alloy causes stress corrosion cracking (SCC) and causes an embrittlement layer, which causes a problem that the pipe is easily broken at the time of pipe expansion joining, and is inevitable when brazing copper pipes to each other. There is a problem that it is formed in a uniform manner.

On the other hand, the ant-nest-like corrosion progresses at an extremely high speed, and corrodes inside the heat transfer tube in a short period of time, causing leakage of the refrigerant and losing the function of the air conditioner. I was For this reason, there has been a strong demand for the development of a heat exchanger having excellent corrosion resistance against ant-nest corrosion.

It is an object of the present invention to provide a heat exchanger member which can solve the above-mentioned problems in a heat exchanger, has excellent corrosion resistance against ant-nest corrosion, and does not cause stress corrosion cracking.

[0014]

In order to achieve the above object, according to the present invention, nickel, cobalt, chromium and silver, or those containing these as main components, are provided on the surface of a heat exchanger member made of copper or a copper alloy. An underlayer having an average thickness of 0.1 to 2 μm, which is made of at least one selected from the group of alloys to be used, is further formed on the underlayer. A heat exchanger member provided with a membrane or a galvanized layer is provided.

[0015]

FIG. 1 is a cross-sectional view showing a basic configuration example of a heat exchanger using a copper tube 1 which is a heat exchanger member of the present invention. In the figure, the heat exchanger is constituted by inserting the tube 1 through the fin collar 3 of the laminated fin 2 and fitting the tube 1 to the fin 2. On the surface of the tube 1, an underlayer 1a made of at least one selected from the group consisting of nickel, cobalt, chromium, and silver, or an alloy containing these as a main component, and a metal zinc powder-containing coating film 1b or Zinc plating layer 1b (hereinafter, referred to as
"The outermost layer" is formed. Note that the entire surface of the fin body 2 is previously coated with the hydrophilic film 4.

The heat exchange member made of copper or copper alloy according to the present invention may be used for either a heat transfer tube or a fin, but is particularly preferably used as a heat transfer tube.

When used for heat transfer tubes, it is desirable to use phosphorus deoxidized copper in order to prevent hydrogen embrittlement during brazing of the tubes.

Next, the outermost layer of the present invention will be described in detail.

Ant nest-like corrosion of a heat transfer tube proceeds as described above, as copper contained in components of the heat transfer tube and the like dissolves in attached water containing an organic acid.

Accordingly, the present invention provides a heat exchange member (heat transfer tube or the like) made of copper or a copper alloy, on the outermost surface, a film containing metal zinc itself or metal zinc powder which is a substance having a higher ionization tendency than copper. Is formed, zinc is preferentially dissolved in the acidic water adhering to the gap generated when the pipe body is joined to the fin collar, thereby changing the water adhering to the alkali side and rendering it harmless. It is a technical idea to suppress the elution of water and effectively prevent ant-nest corrosion of the heat transfer tube. Here, the change of the attached water to the alkaline side is due to the cathode reaction accompanying the dissolution of the metallic zinc in the attached water.

In the outermost layer 1b, zinc metal, particularly zinc metal powder, is not alloyed with the underlying copper, but remains in a highly reactive metal state, thereby dissolving zinc in adhering water, The formation reaction is promoted, and ant-nest corrosion, which is crevice corrosion, is effectively prevented.

The outermost layer may be formed by electrogalvanizing or hot-dip galvanizing the heat transfer tube, or may be formed by applying a resin or paint in which zinc metal powder is dispersed. In particular, it is preferable to perform the latter coating in terms of simplifying the equipment and preventing the plating solution or the like from entering the inside of the tube. In addition, when performing the coating, even if the hydrophilic film is coated on the object, it is not necessary to remove the hydrophilic film.Moreover, since the highly reactive zinc metal powder is appropriately dispersed in the coating film, It is also desirable in terms of accelerating the dissolution of zinc in the attached water. As such a resin or paint, for example, a paint using metal zinc powder as a pigment, so-called zinc-rich paint, can be used. In addition, a treatment agent in which metal zinc powder is dispersed in a colloidal silica-based hydrophilic treatment agent is also preferable. Can be used for

The average thickness of the outermost layer is set in the range of 0.1 to 50 μm. When the thickness is less than 0.1 μm, the above-described anticorrosion effect due to dissolution of zinc in the attached water comes to disappear in a short time. This is because, as a whole, it is wasteful and uneconomical, which leads to an increase in cost. The average thickness means the average value of the thickness of the coating film or the plating layer. The average thickness of the outermost layer can be adjusted by changing the number of coatings in the case of a coating film, adjusting the resin concentration by changing the mixing ratio of the resin or paint to the solvent, and adjusting the electric concentration in the case of the plating layer. The electrolysis time and current density may be changed for plating, and the immersion time and immersion frequency may be changed for hot-dip plating.

Further, the content of metallic zinc powder in the coating film is as follows:
It is preferably at least 60% by weight in a dried state of the coating film.
This is because the higher the content of the metal zinc powder, the greater the amount of zinc dissolved in the attached water, and the greater the anticorrosion effect due to the alkalinization of the attached water. Therefore, it is preferable to increase the content of the metallic zinc powder within a range that does not affect the film forming property. It should be noted that the size of the metallic zinc powder should not be too large in consideration of solubility and uniform dispersibility, and it is usually preferable to set the particle size to 10 μm or less.

Next, the underlayer of the present invention will be described.

When zinc is present on the surface of the heat transfer tube, the heat at the time of brazing and joining the heat transfer tubes diffuses the zinc on the surface to form copper and a copper-zinc alloy, which are components of the heat transfer tube, resulting in stress. May cause corrosion cracking and tube embrittlement.

The underlayer according to the present invention exerts the effect of suppressing the diffusion of zinc in the outermost layer 1b to the heat transfer tube base, thereby preventing the above problem from occurring. The underlayer is made of any one of nickel, cobalt, chromium, and silver, or an alloy thereof. The reason for using these metals is that these metals have relatively high melting points and are less likely to diffuse into copper than zinc.

The average thickness of the underlayer is set in the range of 0.1 to 2 μm. If the thickness is less than 0.1 μm, the effect of suppressing the diffusion of zinc into the copper base is insufficient, and if it exceeds 2 μm, the effect of preventing the diffusion of zinc is no longer saturated, and this is economically disadvantageous. The average thickness may be adjusted by changing the electrolysis time, the current density, or the immersion time.

[0029]

EXAMPLES Examples 1 to 6 and Comparative Examples 1 to 4 Formation of base layer and outermost layer The outer surface of a phosphorous deoxidized copper tube (JIS standard H3300C1220, outer diameter 9.5 × wall thickness 0.3 mm × length 100, temper OL) is subjected to electroless Ni plating, A Zn film was formed on the upper layer by electroplating, and samples shown in Table 1 were prepared. As a comparative material, an untreated phosphor-deoxidized copper tube having the same dimensions was prepared. The average thickness of each layer was changed by adjusting the electrolysis time. The average thickness of the underlayer and the outermost layer was measured using a fluorescent X-ray test method and an electrolytic test method.

2. Assembly of heat exchanger Aluminum strip coated with a silica-based hydrophilic coating (JIS-A1200, 500 × 25 × 0.1 mm)
Is pressed to form 2 rows × 12 fin collars to form an aluminum fin body. The required number of the fin collars are made to coincide with each other and the fin collars are made to coincide with each other. Through the tube that formed the
The pipes were expanded with a mandrel and joined together to assemble a heat exchanger (external dimensions 500 × 25 × 250 mm).

3. Evaluation of heat exchanger samples The characteristics of each heat exchanger sample were evaluated according to the following specifications.

(1) Evaluation of Corrosion Resistance A 100% aqueous solution of 1% by volume formic acid was placed in a closed container having a capacity of 1 L.
into a 100 mL beaker so as not to come into direct contact with the liquid.
0 × 25 mm), and then placed in the closed container. Next, the atmosphere in the container was replaced with oxygen and kept at room temperature for 40 days. After the test, the heat transfer tube was separated from the heat exchanger sample and cut, and the maximum corrosion depth of the heat transfer tube at the cut surface near the fitting portion with the fin was measured by microscopic observation of the cross section. The smaller this value is, the more excellent the corrosion resistance is.

(2) Evaluation of stress corrosion cracking
After performing a heat treatment at 0 ° C. for 1 hour and expanding the mandrel at an inner diameter expansion rate of 10%, a time crack test (JISH330005.12A) specified in JIS was performed. Furthermore, the presence or absence of cracks when crushed to 50% of the pipe outer diameter before pipe expansion was visually determined.

Table 1 shows the results.

[0035]

[Table 1] The following is clear from Table 1.

(1) The heat exchanger tube for a heat exchanger of the present invention in which the underlayer and the outermost layer are formed does not generate stress corrosion cracking and has good corrosion resistance.

(2) As is clear from the comparison between each embodiment and Comparative Examples 1 and 2, in Comparative Example 1 where the underlayer was thin, stress corrosion cracking occurred, and in Comparative Example 2 where the outermost layer was thin. In the case, the corrosion resistance is significantly deteriorated as compared with the embodiment. From this, it is understood that the average thickness of the underlayer should be set to 0.1 to 2 μm and the average thickness of the outermost layer should be set to 0.1 to 50 μm.

(3) As is clear from the comparison between each example and Comparative Example 3, in the case of Comparative Example 3 in which no underlayer was formed, stress corrosion cracking occurred.

(4) Further, as is clear from comparison between each example and comparative example 4, in the case of comparative example 4 in which the underlayer and the outermost layer were not formed at all, the corrosion resistance was significantly higher than in the examples. And a through-hole was formed due to ant-nest corrosion.

Examples 7 to 11 Formation of underlayer and outermost layer The outer surface of a phosphor deoxidized copper tube (JIS standard H3300C1220, outer diameter 9.5 × wall thickness 0.3 mm × length 100, temper OL) is coated with Ag plating to an average thickness of 0.3 μm. After applying it,
A mixture of a colloidal silica-based hydrophilic treatment agent and a metal zinc powder having an average particle diameter of 10 μm was applied as a metal zinc powder-containing paint to prepare samples shown in Table 2. The average thickness of the underlayer was adjusted by adjusting the electrolysis time, and the average thickness of the coating film was changed by adjusting the mixing ratio of the resin and the solvent. The average thickness of the underlayer was measured using a fluorescent X-ray test method, and the average thickness of the coating film was measured using an eddy current test method.

2. Assembling of the heat exchanger and evaluation of the heat exchanger sample It was performed in the same manner as in Examples 1 to 6.

The results are shown in Table 2.

[0043]

[Table 2] The following is clear from Table 2.

(1) The heat exchanger tube for a heat exchanger of the present invention in which the outermost layer composed of the base layer and the metallic zinc-containing coating film is formed does not cause stress corrosion cracking and has good corrosion resistance.

(2) Further, as is apparent from a comparison between Example 7 and Examples 8 to 11, in Example 7, although very slight, rough skin corrosion occurred. For this reason, the zinc content in the dried film is preferably set to 60% by weight or more.

[0046]

As is apparent from the above description, according to the present invention, nickel, cobalt, chromium and silver, or alloys containing these as a main component, are formed on the surface of the heat exchanger member made of copper or copper alloy. An underlayer having an average thickness of 0.1 to 2 μm, which is made of at least one selected from the group consisting of
Furthermore, on the underlayer, an average thickness of 0.1 to 50 μm
Since the metal zinc powder-containing coating film or the galvanized layer is formed, it is possible to provide a heat exchanger member that has excellent corrosion resistance against ant-nest corrosion and does not cause stress corrosion cracking.

[Brief description of the drawings]

FIG. 1 is a cross-sectional view showing an example of a heat exchanger in which a tube as a heat exchanger member of the present invention is fitted to a fin.

[Explanation of symbols]

 1 tube 1a underlayer 1b outermost layer 2 fin body 1 fin color 2 hydrophilic film

Claims (1)

[Claims] An average thickness of at least one selected from the group consisting of nickel, cobalt, chromium, and silver or an alloy containing these as a main component is formed on a surface of a heat exchanger member made of copper or a copper alloy. And a base layer having an average thickness of 0.1 to 50 μm.
A member for a heat exchanger, wherein a coating film containing zinc metal having a thickness of μm or a zinc plating layer is formed.