JP3068379B2 - Surface transfer treatment method for heat transfer tubes - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for improving the surface hydrophilicity of copper and copper alloy heat transfer tubes for heat exchangers processed into a predetermined tube shape, and more particularly to a metal tube by generating plasma discharge or corona discharge. The present invention relates to a method for hydrophilically treating a heat transfer tube for imparting hydrophilicity to the surface of the heat transfer tube.

[0002]

2. Description of the Related Art Conventionally, the following methods are known as methods for improving the surface hydrophilicity of a metal heat transfer tube for a heat exchanger.

(1) Mechanical polishing method Copper and copper alloy heat transfer tubes are degreased and washed with a solvent or the like, and then the surface of the tubes is polished with a wire brush or a sandpaper to obtain drawn oil, rolled oil, This is a method of improving surface hydrophilicity by removing organic substances such as cutting oil with a wire brush or sandpaper.

(2) Surface chemical treatment method This is a method for improving the surface hydrophilicity by cleaning and activating the surface of the heat transfer tube with sulfuric acid and an activator.

(3) Heat treatment method Heat treatment is applied to copper and copper alloy heat transfer tubes to evaporate and separate organic substances such as drawing oil, rolling oil, cutting oil and the like adhering to the tube surface, thereby improving hydrophilicity. It is.

[0006]

However, in the above-mentioned conventional methods for treating the surface of a heat transfer tube with hydrophilicity, any of them can obtain a certain degree of hydrophilicity, but is not sufficient, and has the following problems. is there.

[0007] In the mechanical polishing method, good hydrophilicity can be obtained immediately after the treatment, but the copper and copper alloy heat transfer surface exposed by the polishing is active and is easily affected by the surrounding atmosphere. As a result, dirt or the like adheres and the hydrophilicity deteriorates with time. Further, cleaning with a solvent has a problem in terms of environmental hygiene such as an adverse effect on the human body.

In the surface chemical treatment method, facilities such as pickling and water treatment are required, and the maintenance cost for these facilities is high. In addition, since the processing generally takes a long time, productivity is poor. Furthermore, like the mechanical polishing method,
Immediately after the treatment, good surface hydrophilicity can be obtained, but there is a disadvantage that the hydrophilicity deteriorates with time.

In the heat treatment method, it is necessary to raise the temperature of the copper and copper alloy surface to the decomposition temperature of processing oil (normally 300 ° C. or higher) and hold the pipe surface until it is clean. If the time is prolonged, in the case of a copper tube generally used as a heat transfer tube, the mechanical strength decreases because the temperature exceeds the softening temperature. There is also a flame treatment method in which only the copper and copper alloy surfaces are locally heated to a flame in order to avoid softening due to temperature rise.However, the flame is uniformly applied to the entire circumference of the pipe, and the pipe is not softened. Processing is difficult, and processing unevenness is likely to occur.

[0010] In addition, since the flame treatment is usually performed in the atmosphere, discoloration is caused not only on the outer surface of the tube but also on the inner surface of the tube by heating. In the case of water heat exchange in which heat is exchanged by passing water through the pipe, if there is discoloration in the pipe, corrosion will occur at that part,
Problems such as leaks may occur.

SUMMARY OF THE INVENTION In view of the above problems, an object of the present invention is to provide a method for treating a surface of a heat transfer tube which is excellent in surface hydrophilicity, has little deterioration over time, and has good productivity.

[0012]

As a means for solving the above-mentioned problems, the present invention provides a method in which a copper or copper alloy heat transfer tube is heated to 250 to 350 ° C. in an atmosphere containing an inert gas as a main gas.
The method is characterized in that a corona discharge or a plasma discharge is performed after heating and holding for 5 to 10 minutes at a temperature of 5 hours, and a method for treating the surface of copper and copper alloy heat transfer tubes for hydrophilicity.

[0013]

The present invention will be described below in more detail.

In the present invention, first, a copper and copper alloy heat transfer tube is heated at a temperature of 2 in an atmosphere containing an inert gas as a main gas.
Heat and hold at 50-350 ° C for 5-10 minutes. By this heating and holding, oil and the like on the tube surface are evaporated and separated to some extent.

The heating atmosphere is mainly composed of an inert gas such as N ₂ in order to prevent discoloration when evaporating and separating oil and the like on the tube surface. desirable.

That is, it is desirable that the atmosphere contains an O ₂ concentration of 3% or less, a CO concentration of 1 to 5%, and the remainder made of an inert gas such as N ₂ . When the O ₂ concentration exceeds 3%,
Discoloration easily occurs on the inner and outer surfaces of the pipe, and in the case of water heat exchange in which water is passed through the pipe to exchange heat, corrosion due to the discoloration may occur. When the CO concentration exceeds 5%, the surface of the heat transfer tube is activated by a reducing action, and discoloration occurs due to adsorption of moisture. On the other hand, when the CO concentration is less than 1%, oxygen in the atmosphere cannot be reduced completely, so oxidation and discoloration occur. It is easy to occur.

It is better not to include H ₂ , but up to 4% is acceptable. This is because if it exceeds 4%, there is a risk of explosion due to heating.

When the heating temperature is lower than 250 ° C., the efficiency of removing oil from the tube surface is low. When the heating temperature is higher than 350 ° C., for example, in the case of copper generally used as a heat transfer tube material,
Causes softening. When the holding time is less than 5 minutes, the efficiency of removing organic substances and the like is low, and when the holding time is more than 10 minutes, the strength of the tube is reduced and the productivity is deteriorated. Therefore, it is necessary to set the heating temperature to 250 to 350 ° C. and the heating holding time to 5 to 10 minutes.

The remaining organic substances such as oils on the tube surface can be separated and removed to some extent by heating and holding in the above atmosphere, but the hydrophilicity is not sufficient at this stage.

Then, a corona discharge or a plasma discharge is applied to the heat-treated copper and copper alloy heat transfer tubes to obtain good hydrophilicity with little deterioration over time. The case of corona discharge will be described below, but the same effect can be obtained in the case of plasma discharge.

In the case of the corona discharge treatment, a voltage is applied between the heat-transfer tube subjected to the above-mentioned heat treatment and an electrode separated from the tube surface by a predetermined distance to generate a corona discharge. Electrons collide with the surface of the heat transfer tube due to corona discharge, and the remaining organic substances that could not be completely removed by the heat treatment alone are separated and reduced by the collision of the electrons by the discharge. ] To a hydrophilic group [-C = O]. Further, a film of metal oxide is formed on the surface of the heat transfer tube by the oxidizing action of ozone generated by a by-product of the discharge, but this metal oxide has no activity like a simple metal, and exists in a stable and porous state. Therefore, it is hardly affected by the surrounding atmosphere. Therefore, good hydrophilicity can be obtained, and the hydrophilicity can be maintained for a long time.

By the way, a heat transfer surface having good hydrophilicity can be obtained only by corona discharge. However, in a mass production process, a thick oil film remains on the surface of the heat transfer tube or the residual oil state varies, so that the processing time is long. Or the processing effect becomes uneven. Therefore, by performing the above-described heat treatment before performing the corona discharge treatment, a heat transfer tube having stable hydrophilicity can be efficiently obtained.

The processing conditions for corona discharge and plasma discharge are not particularly limited, and it goes without saying that they can be determined as appropriate.

Next, an embodiment of the present invention will be described.

[0025]

【Example】

As a test material (heat transfer tube), a phosphorus deoxidized copper smooth tube having an outer diameter of 16 mm and a wall thickness of 0.6 mm was used, and a heating device shown in FIG. 1 was used. The heat treatment was performed at various heating temperatures and times while sending the atmosphere gas of the above. In addition, the copper tube used as a test material was manufactured in a process of melting → extrusion → drawing → annealing → drawing as a process. FIG.
Among them, 1 is a heat transfer tube, 10 is a heater, 11 is an atmosphere gas supply port, and 12 is a conveyor for conveying the heat transfer tube.

First, the atmosphere gas contained O ₂ and CO, and a trace amount of H ₂ , and the balance consisted of N _{2. The} O ₂ concentration and the CO concentration were changed as shown in FIGS. As shown in FIG.
_{(2) No} discoloration is observed in the heat transfer tube up to a concentration of 3%, 3 to 3.3.
%, Local discoloration was observed, and when it exceeded 3.5%, discoloration occurred in the entire tube. It was also confirmed that discoloration occurred when the CO concentration was 0.9% or less and 5.2% or more.

Next, the results of an investigation on the effects of temperature and heating time in the heat treatment will be described. Atmosphere gas composition O ₂ concentration of 1.5%, CO concentration 2.6%, H ₂ concentration of 1.5
%, The balance was N ₂ gas, and the temperature and the heating time were varied to investigate the change in tensile strength and the amount of residual oil on the surface.

As shown in FIG. 6 and FIG.
If it is lower than 50 ° C., the effect of removing residual oil is low, and if it is higher than 350 ° C., softening occurs. The heating temperature is 250-350 ° C
If the heating time is 5 minutes or less, the residual oil removing effect is low, and if the heating time exceeds 15 minutes, softening occurs. Therefore, the heating temperature is 250-350 ° C., and the heating time is 5
It was confirmed that -10 minutes was preferable.

Next, after the heat treatment in the heating device of FIG.
The result of the treatment with the corona discharge device shown in FIGS. 2 and 3 will be described.

2 and 3, 2a and 2b are grounding rolls,
3a and 3b are guide rolls, 4 is an electrode, 4a is an insulator adhered inside the electrode, 5 is an air cooling pipe, 6 is a transformer, 7
Is an oscillator, 8 is an air cooling pipe, and 9 is a power supply.

In this corona discharge device, a cylindrical tube provided at a fixed distance from the outer peripheral surface of the heat transfer tube is guided by the guide roll while passing through the device while being in contact with the ground roll. By applying a high-frequency high voltage from a transformer to the electrodes to generate corona discharge, many high-energy electrons can collide with the surface of the heat transfer tube. Oxygen in the air reacts with the discharge to generate ozone. The electrodes may be cooled by air from the air cooling pipe, and the processing section of the heat transfer pipe may be cooled.

The test material has an outer diameter of 16 mm and a wall thickness of 0.6 m.
m phosphorous deoxidized copper tubing was used. This copper tube was placed in an atmosphere consisting of nitrogen gas, with an O ₂ concentration of 1.5% and a CO concentration of 2.6.
%, An H ₂ concentration of 1.5%, and the balance N ₂ gas in an atmosphere having a composition of 300 ° C. for 8 minutes.

Next, using a corona discharge device shown in FIG. 2, a corona discharge treatment was continuously performed at a power of 1000 W while passing the copper tube through the electrode at a constant speed of 10 m / min. Thereafter, the amount of residual oil on the tube surface was measured by a solvent extraction method, and the water wettability was examined using a reagent mainly composed of water and ethylene glycol. Table 1 shows the results.

In the table, Example 1 of the present invention is an example in which a corona discharge treatment is performed after heat treatment in an N ₂ gas atmosphere, and Example 2 of the present invention is 1.5% in O ₂ concentration, 2.6% in CO concentration, H ₂ concentration 1.
This is an example in which a corona discharge treatment is performed after a heat treatment in an atmosphere having a composition of 5% and the balance of N ₂ gas. In Comparative Example 1, those of untreated Comparative Example 2 O ₂ concentration 1.5%, C
Heat treatment was carried out at a temperature of 300 ° C. for 8 minutes in an atmosphere having an O concentration of 2.6%, an H ₂ concentration of 1.5%, and a balance of N ₂ gas. In Comparative Example 3, a copper tube was treated with an organic solvent. After the cleaning, the brush is polished. In the table, the upper part of the wetting index is an example in which the hydrophilicity was examined by the above-described method after one day of the treatment, and the lower part was 30 days after the treatment.

As is clear from Table 1, the tube subjected to the heat treatment and corona discharge (hydrophilic treatment) by the method according to the present invention has a small surface residual oil and a large wettability index. Furthermore, it can be seen that there is no deterioration with time of the hydrophilic property as in the case of a tube treated by the conventional method, and that the good hydrophilic property is maintained.

With only corona discharge treatment without heat treatment,
In order to obtain the processing effects of Examples 1 and 2 of the present invention, processing at a line speed of 5 m / min at a discharge output of 1000 W is necessary. However, according to the present invention, the line speed can be doubled to 10 m / min, and the productivity is increased. Significantly improved.

[0038]

[Table 1]

The present invention can be applied not only to the outer surface but also to the inner surface of the pipe. In addition, the present invention can be applied not only to a smooth surface but also to a shape such as a corrugated surface having irregularities.

[0040]

As described above, according to the present invention,
Copper and copper alloy heat transfer tubes with reduced residual organic matter, good hydrophilicity and little change over time can be obtained, and are more productive than when only corona discharge or plasma discharge is used for treatment. Further, since cleaning with an organic solvent as in the conventional method can be omitted, there is no problem of environmental hygiene.

[Brief description of the drawings]

FIG. 1 is a diagram illustrating a heat treatment apparatus.

FIG. 2 is an overall view illustrating a corona discharge device.

FIG. 3 is a sectional view taken along line AA of FIG. 2;

FIG. 4 is a diagram showing the relationship between the concentration of O ₂ in a heating atmosphere gas and the occurrence of discoloration of a heat transfer tube.

FIG. 5 is a diagram showing the relationship between the CO concentration in a heating atmosphere gas and the occurrence of discoloration in a heat transfer tube.

FIG. 6 is a diagram showing a relationship between a heating temperature and a holding time and a tensile strength of a heat transfer tube.

FIG. 7 is a diagram showing a relationship between a heating temperature and a holding time and a residual oil amount on a heat transfer tube surface.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Heat transfer tube 2a, 2b Ground roll 3a, 3b Guide 4 Electrode 4a Insulator 5 Air cooling tube 6 Transformer 7 Oscillator 8 Air cooling tube 9 Power supply 10 Heater 11 Gas supply port 12 Conveyor

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Claims (2)

(57) [Claims] 1. A copper and copper alloy heat transfer tube in an atmosphere containing an inert gas as a main gas at a temperature of 250 to 350.degree.
A method for hydrophilically treating the surface of copper and copper alloy heat transfer tubes, wherein a corona discharge or a plasma discharge is performed after heating and holding for a minute. 2. An atmosphere containing an inert gas as a main gas is O.
_2. The method according to claim 1, comprising a concentration of 3% or less, a CO concentration of 1 to 5%, and the balance being an inert gas.