KR102237181B1 - coating method of tube for aluminum heat exchanger - Google Patents

Abstract

The present invention relates to a method for coating a tube for an aluminum heat exchanger, and to a method for coating a tube for an aluminum heat exchanger capable of increasing durability of a heat exchanger by uniformly applying a brazing composition capable of improving corrosion resistance to a tube. The coating method of the tube for an aluminum heat exchanger of the present invention includes a composition step of mixing 20 to 50% by weight of a flux powder, 40 to 70% by weight of a binder, 5 to 30% by weight of zinc powder, and 1 to 20% by weight of lithium powder to obtain a composition for brazing in the form of a paste; and a coating step of applying the brazing composition to the tube.

Description

Coating method of tube for aluminum heat exchanger

The present invention relates to a coating method for an aluminum heat exchanger tube, and relates to a coating method for an aluminum heat exchanger tube capable of increasing durability of a heat exchanger by uniformly applying a brazing composition capable of improving corrosion resistance to the tube.

In general, a heat exchanger refers to a device that performs heat exchange between two fluids separated by a solid wall, and a heat exchanger in a narrow sense refers to a device that exchanges heat between two process streams without a phase change. , In a broad sense, it includes a cooler, a condenser, and the like.

Such heat exchangers are widely used for heating, air conditioning, power generation, cooling, and waste heat recovery. Heat exchangers commonly used in air conditioners or vehicle cooling systems consist of a header and a tank, and are installed opposite to each other up and down or left and right to guide the entry and exit of the refrigerant, and are arranged at regular intervals between both header tanks to heat the refrigerant The tube and the heat dissipation fin are arranged between each of the tubes to dissipate heat transferred from the tube into the atmosphere, and the pipes may be further coupled to the header tank so that the heat exchange medium can flow in and out.

In the conventional heat exchanger configured as described above, both ends of the tubes are inserted into the tube insertion holes of the header tank installed in parallel with each other, and the radiating fins are arranged between the tubes, supported by a fixing jig, and put into the brazing furnace. .

In the heat exchanger supported by the fixing jig and put into the brazing furnace, the flux applied to the tube is melted so that the tube and the header tank are joined, and the tube and the radiating fin are joined.

Conventionally, the coating is performed by spraying the flux on the tube, but in this case, there is a problem that the amount of flux is increased and it is difficult to control the thickness of the coating film.

Korean Patent Application Publication No. 10-2009-0133005 discloses a flux coating method and apparatus for a heat exchanger tube, and a coating composition.

The coating method has an advantage of solving the problem of the spraying method since the flux is applied to the tube by a roll coating method using a roller. However, this roll coating method has a problem that only one surface of the tube can be applied.

In addition, the flux used in the coating method uses a flux powder of an alloy containing a zinc-based or silicon-based metal, but such a flux powder has low corrosion resistance, and particularly, when exposed to moisture, there is a problem that corrosion proceeds rapidly. .

Republic of Korea Patent Laid-Open Patent No. 10-2009-0133005: Flux coating method and apparatus for heat exchanger tubes, and coating composition

The present invention was created to improve the above problems, and provides a coating method for an aluminum heat exchanger tube that can increase the durability of the heat exchanger by uniformly applying a brazing composition that can improve corrosion resistance to the tube. have.

The coating method of the tube for an aluminum heat exchanger of the present invention for achieving the above object includes 20 to 50% by weight of flux powder, 40 to 70% by weight of a binder, 5 to 30% by weight of zinc powder, and 1 to 20% by weight of lithium powder. A composition step of mixing% to obtain a composition for brazing in a paste form; It includes; a coating step of applying the brazing composition to the tube.

The coating step is coated while passing the tube between the upper coating roller and the lower coating roller, and the upper coating roller is in contact with a pair of upper supply rollers and rotates while receiving the brazing composition through the upper supply rollers, The lower coating roller is in contact with a pair of lower supply rollers and rotates to receive the brazing composition through the lower supply rollers, and the brazing composition is injected between the upper supply rollers and the lower supply rollers. .

As the binder, a solvent or 3-methoxy-3-methyl-1-butanol is mixed with an acrylic resin.

As described above, the present invention can improve corrosion resistance by reducing corrosion compared to a conventional flux by using a brazing composition in which zinc and lithium metal are added. In addition, it is possible to reduce the occurrence of white powder at the junction by improving the corrosion resistance and suppressing the occurrence of white rust.

In addition, in the present invention, since roll coating is possible on both sides of the tube at the same time, coating is quick and simple, so that the manufacturing time of the heat exchanger can be shortened and uniform coating is possible.

1 is a configuration diagram showing a state in which a composition for brazing is applied to a tube according to an example of the present invention,
2 is an exploded perspective view showing an aluminum heat exchanger assembly assembled using a tube to which a brazing composition is applied.

Hereinafter, a method of coating an aluminum heat exchanger tube according to a preferred embodiment of the present invention will be described in detail.

A method of coating a tube for an aluminum heat exchanger according to an embodiment of the present invention includes a composition step of obtaining a composition for brazing in the form of a paste, and a coating step of applying the composition for brazing to the tube. We look at each step in detail.

1. Creation stage

First, a composition for brazing is prepared by mixing a flux powder, a binder, a zinc powder, and a lithium powder. The brazing composition is made in the form of a sticky paste.

The brazing composition applied to the present invention is added with zinc and lithium metal to improve corrosion resistance. In addition, it is possible to effectively reduce the occurrence of white powder at the junction by greatly suppressing the occurrence of white rust while improving the corrosion resistance.

The composition for brazing applied to the present invention may be formulated by mixing 20 to 50% by weight of flux powder, 40 to 70% by weight of a binder, 5 to 30% by weight of zinc powder, and 1 to 20% by weight of lithium powder. .

The flux powder is melted during brazing to bond the aluminum base material and at the same time prevent the formation _{of an aluminum oxide (Al 2} O _{3) film on the surface of the aluminum base material.} Aluminum fluoride can be used as the flux powder. Preferably, aluminum potassium fluoride may be used as aluminum fluoride. As aluminum potassium fluoride, any one or two or more selected from _{KAlF, KAlF 4} and K ₃ AlF _{6 may be used in combination.} A commercial product, NOCOLOK flux, can be used as such a flux powder.

It is appropriate that the flux powder is contained in a proportion of 20 to 50% by weight in the total composition. When the content of the flux powder is less than 20% by weight, brazing performance is lowered, and when it exceeds 50% by weight, excessive residue is generated.

When the flux powder, zinc powder, and lithium powder are mixed, the binder provides adhesion and facilitates application to the surface of the base material.

The binder can be obtained by mixing a solvent or 3-methoxy-3-methyl-1-butanol with an acrylic resin. For example, it can be prepared by mixing an acrylic resin and a solvent as a binder in a weight ratio of 1:5 to 30. In addition, as a binder, acrylic resin and 3-methoxy-3-methyl-1-butanol may be mixed in a weight ratio of 1:5 to 30 to form a composition. And, if necessary, water may be further added to the binder.

Acrylic resin helps the diffusion of metal materials and does not have any adverse effect on the bonding surface of the base material as it evaporates and disappears during brazing. The kind of acrylic resin that can be used in the present invention is not greatly limited. For example, it may be formed by polymerizing at least one monomer selected from the group consisting of acrylic acid, methacrylic acid, ester of acrylic acid, ester of methacrylic acid, acrylonitrile, methacrylonitrile, acrylamide and methacrylamide. have. For example, polyacrylate or polymethyl methacrylate may be used as the acrylic resin.

Solvent or 3-methoxy-3-methyl-1-butanol is added as a solvent. As the solvent, any one selected from aminoethylethanolamine, triethanolamine, toluene, and methanol may be used.

It is appropriate that the binder is contained in a proportion of 40 to 70% by weight in the whole composition. When the content of the binder is less than 40% by weight, the adhesive strength is lowered, and when it exceeds 70% by weight, the fluidity is lowered.

Zinc (Zn) powder is corroded before aluminum by the sacrificial anode effect, thereby preventing corrosion of the heat exchanger tube. In the present invention, the zinc powder is used in the form of a fine powder having a particle size of 200 to 400 mesh. Since zinc is used in powder form as described above, uniform dispersion is possible when the flux composition is applied to the base material.

It is appropriate that the zinc powder is contained in an amount of 5 to 30% by weight in the whole composition. When the content of zinc powder is less than 5% by weight, corrosion resistance is deteriorated, and when it exceeds 30% by weight, excessive corrosion may occur.

Lithium (Li) powder prevents corrosion by blocking the white rust phenomenon occurring at the bonding site after brazing and prevents cracking at the bonding site.

When exposed to moisture after brazing with a conventional flux, a white substance (percent) is formed on the surface of the joint. This white substance is a hydroxide produced by contact with moisture by some substances such as zinc contained in the flux. Zinc produces zinc hydroxide. The white powder generated by the white rust phenomenon is scattered in the air, causing a problem of polluting the surrounding environment.

The brazing composition applied to the present invention is added with lithium powder to suppress white rust caused by moisture to improve corrosion resistance. Lithium powder is used in the form of a fine powder having a particle size of 200 to 400 mesh. Since lithium is used in powder form, uniform dispersion is possible when the flux composition is applied to the base material.

It is appropriate that the lithium powder is contained in an amount of 1 to 20% by weight in the total composition. If the content of the lithium powder is less than 1% by weight, the rust inhibiting effect may decrease, and if it exceeds 20% by weight, the bonding property may decrease.

Zinc and lithium added to the brazing composition are used as metals composed of a single element, not in the form of compounds or alloys combined with other elements. Zinc and lithium applied to the present invention may have a purity of 99.99% or more. In the present invention, since zinc and lithium are used in powder form, dispersibility and uniformity can be improved.

2. Coating step

Next, the brazing composition is applied to the tube.

Typically, a tube for a heat exchanger is manufactured by extruding an aluminum wire into a hollow tube shape.

In the present invention, a composition for brazing is applied to a tube using a roll coating method. Fig. 1 shows a state in which the composition for brazing is applied to a tube by a roll coating method.

Referring to FIG. 1, the upper coating roller 21 and the lower coating roller 31 are arranged vertically spaced apart. The tube 10 passes between the upper coating roller 21 and the lower coating roller 31. The outer circumferential surface of the upper coating roller 21 is in contact with the upper surface of the tube 10, and the outer circumferential surface of the lower coating roller 31 is in contact with the lower surface of the tube 10.

A pair of upper supply rollers 22 are installed to deliver the brazing composition to the upper coating roller 21. The upper supply roller 22 can be divided into an upper main roller 23 rotating in contact with the upper coating roller 21 and an upper sub-roller 25 rotating in contact with the upper main roller 23.

The brazing composition (1) is supplied between the upper main roller 23 and the upper sub-roller 25. When a certain amount is continuously supplied between the upper sub-roller 25 and the upper main roller 23, the brazing composition is adhered to the outer circumferential surface of the upper main roller 23. Therefore, while the brazing composition is attached to the outer circumferential surface of the upper coating roller 21 that rotates in contact with the upper main roller 23, the brazing composition has a constant thickness on the upper surface of the tube 10 in contact with the upper main roller 21. Is applied.

A pair of lower supply rollers 32 are installed to deliver the brazing composition to the lower coating roller 31. The lower supply roller 32 may be divided into a lower main roller 33 that rotates in contact with the lower coating roller 31 and a lower sub-roller 35 that rotates in contact with the lower main roller 33.

The brazing composition (1) is supplied between the lower sub-roller 35 and the lower main roller (33). When a certain amount is continuously supplied between the lower sub-roller 35 and the lower main roller 33, the brazing composition is adhered to the outer circumferential surface of the lower main roller 33. Therefore, while the brazing composition is attached to the outer circumferential surface of the lower coating roller 31 that rotates in contact with the lower main roller 33, the brazing composition has a constant thickness on the lower surface of the tube 10 in contact with the lower main roller 31. Is applied.

As described above, according to the present invention, an upper coating roller 21 and a lower coating roller 31 are disposed on the upper and lower portions of the tube 10 so that the upper and lower surfaces of the tube can be simultaneously coated with a uniform thickness. Since roll coating is possible on both sides of the tube at the same time, the coating is quick and simple, and the manufacturing time of the heat exchanger can be shortened.

After coating, the tube is dried at an appropriate temperature (100~300℃). Through the drying process, the acrylic resin in the binder is cured and the solvent is removed by evaporation.

The coated tube 10 is assembled with the header tank 5 and the pin 7 as shown in FIG. 2 to make an assembly. In addition to the tube, it is of course possible to apply the flux composition to the header tank 5 and the fin 7 if necessary.

The header tank 5 has a hollow tubular structure, and a plurality of insertion holes 6 into which the tube 10 is inserted are formed at regular intervals. Both ends of the tube 10 are inserted into the insertion holes 6 of the header tank 5 on the left and right sides. The pin 7 is made to be corrugated using an aluminum sheet, and is inserted between the tube and the tube.

When the assembly is ready, the assembly is mounted on a jig and then put into a brazing furnace and heated. As the flux coated with the tube is melted, the tube and the header, the tube and the fin are joined.

When heating in a brazing furnace, brazing can be performed by increasing the temperature for each section from 300°C under an inert atmosphere, for example, a nitrogen atmosphere, and heating in a temperature range of 600°C or less.

The aluminum heat exchanger manufactured in this way can improve the corrosion resistance of the joint, and can reduce the occurrence of white powder by suppressing the occurrence of white rust.

Hereinafter, in order to check the corrosion resistance effect of the brazing composition applied to the present invention, an experiment was conducted as follows.

(Example)

For brazing in paste form by mixing 30% by weight of aluminum potassium fluoride flux powder (NOCOLOK, CAS No. 60304-36-1), 50% by weight of binder, 15% by weight of zinc powder, and 5% by weight of lithium powder The composition was prepared. As a binder, a mixture of acrylic resin and 3-methoxy-3-methyl-1-butanol in a weight ratio of 1:10 was used.

(Comparative Example 1)

A composition for brazing in the form of a paste was prepared by mixing 35% by weight of aluminum potassium fluoride flux powder (NOCOLOK, CAS No. 60304-36-1), 50% by weight of a binder, and 15% by weight of zinc powder. As a binder, a mixture of acrylic resin and 3-methoxy-3-methyl-1-butanol in a weight ratio of 1:10 was used.

(Comparative Example 2)

A composition for brazing in the form of a paste was prepared by mixing 40% by weight of aluminum potassium fluoride flux powder (NOCOLOK, CAS No. 60304-36-1) and 60% by weight of a binder. As a binder, a mixture of acrylic resin and 3-methoxy-3-methyl-1-butanol in a weight ratio of 1:10 was used.

<corrosion experiment>

After preparing a plate-shaped aluminum base material having a thickness of 2 mm, the brazing compositions of Examples and Comparative Examples 1 and 2 were applied to the surface of the base material, respectively, and then brazed, followed by a corrosion test through a salt spray test.

After the brazed aluminum base material was put into a chamber maintained at 47° C., an aqueous sodium chloride solution having a concentration of 5 wt% was sprayed for 168 hours, washed with flowing water for 1 minute, and then dried. The aluminum base material brazed with the brazing composition of Example was used as a test specimen, the aluminum base material brazed with the brazing composition of Comparative Example 1 was used as Comparative Sample 1, and the aluminum base material brazed with the brazing composition of Comparative Example 2 was used as a comparative sample. It was divided into 2.

^{The degree of corrosion was measured as the weight reduction per unit area (mg/cm 2} ) before and after the test of the specimen as shown in the following calculation formula, and the results are shown in Table 1 below. Five test specimens and comparative specimens 1 and 2 were each prepared and tested, and the weight loss per unit area was expressed as an average value.

And the corrosion inhibition rate of the test specimen and the comparative specimen 1 was calculated based on the weight loss of the comparative specimen 2. That is, the corrosion inhibition rate (%) of the test specimen was calculated as {(weight loss per unit area of comparative specimen 2-weight reduction per unit area of test specimen)/weight reduction per unit area of comparative specimen 2} × 100, and corrosion of comparative specimen 1 The inhibition rate (%) was calculated as {(weight loss per unit area of comparative specimen 2-weight loss per unit area of comparative specimen 1)/weight loss per unit area of comparative specimen 2}×100.

division Weight reduction per unit area (mg/cm ² ) Corrosion inhibition rate (%) Test specimen 1.27 48.8% Comparative Psalm 1 1.65 33.5% Comparative Psalm 2 2.48 -

Referring to the results of Table 1, the weight loss of the test specimen was 1.27 mg/cm ^2, which was found to be superior to the comparative specimen 1 and the comparative specimen 2 in corrosion resistance. In particular, the weight reduction due to corrosion was greatly reduced when compared to Comparative Sample 2 in which zinc powder and lithium powder were not added. The corrosion inhibition rate compared with the comparative specimen 2 was 33.5% for the comparative specimen 1 and 48.8% for the test specimen. Through this, it can be seen that the corrosion resistance can be greatly improved through the addition of zinc powder and lithium powder.

In addition, when comparing the test specimen and the comparative specimen 1, it was found that the corrosion inhibition rate could be improved by about 15% or more by adding lithium powder. Therefore, even if only zinc powder is added, it has the effect of improving the corrosion resistance, but it was confirmed that the addition of lithium powder can further improve the corrosion resistance.

<Percentage measurement experiment>

In the above corrosion test, the amount of percent formed in the test specimen obtained by corrosion through salt spray and the comparative specimen 1 was measured.

Each specimen was freely dropped from a height of 1 m three times, and then the weight of the percentage separated from the specimen was measured, and the average value is shown in Table 2 below.

division Percentage (mg) Test specimen 1,955 Comparative Psalm 1 8,037

Referring to the results of Table 2, in the case of comparative specimen 1, the amount of generation of hundred minutes was 8,037 mg, whereas in the case of the test specimen, it was found to be 1,955 mg. It was confirmed that the amount of percent produced in the test specimen was reduced by about 76% compared to the comparative specimen 1. Therefore, the present invention is expected to be able to effectively reduce the occurrence of white powder at the joint site by significantly suppressing the occurrence of white rust while improving corrosion resistance due to the addition of lithium powder.

In the above, the present invention has been described with reference to an embodiment, but this is only exemplary, and those of ordinary skill in the art will understand that various modifications and equivalent embodiments are possible therefrom. Therefore, the true scope of protection of the present invention should be determined only by the appended claims.

5: header tank 7: pin
10: tube 21: upper coating roller
31: lower coating roller

Claims (3)

20 to 50% by weight of flux powder, 40 to 70% by weight of binder, 5 to 30% by weight of zinc powder, and 1 to 20% by weight of lithium powder for suppressing the generation of white powder, which is a white hydroxide, on the surface of the bonding site A composition step of mixing the mixture to obtain a composition for brazing in the form of a paste;
Including; a coating step of applying the brazing composition to the tube,
The method of coating an aluminum heat exchanger tube, wherein the zinc powder and the lithium powder are each composed of a single element rather than a compound combined with other elements. The method of claim 1, wherein the coating step is coated while passing the tube through an upper coating roller and a lower coating roller,
The upper coating roller is in contact with a pair of upper supply rollers and rotates while receiving the brazing composition through the upper supply rollers, and the lower coating roller is rotated while being in contact with a pair of lower supply rollers. Through the brazing composition is delivered,
Coating method for an aluminum heat exchanger tube, characterized in that the brazing composition is injected between the upper supply rollers and the lower supply rollers. The aluminum heat exchanger tube according to claim 1, wherein the binder is an acrylic resin mixed with solvent or 3-methoxy-3-methyl-1-butanol. Coating method.

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