JP2017110246A - Copper pipe - Google Patents

Abstract

PROBLEM TO BE SOLVED: To surely obtain effect for suppressing generation of ant-lair-like corrosion while enhancing productivity with securing thermal conductivity which is a characteristic of a copper tube.SOLUTION: In a copper tube having a zinc coating 12 on an outer peripheral surface, thickness of the zinc coating 12 is set at 10 μm or less to secure thermal conductivity and time for forming the zinc coating 12 is shortened to enhance productivity. On the other hand, thickness of the zinc coating 12 is set at 1 μm to obtain a full effect for preventing generation of ant-lair-like corrosion and anticorrosive effect is maintained.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a copper tube used as a heat transfer tube for air conditioning equipment, refrigeration equipment and the like, and more particularly to a copper pipe capable of suppressing the occurrence of ant nest corrosion.

The copper tube is made of copper or a copper alloy, and is excellent in corrosion resistance, thermal conductivity, workability, etc., and thus is suitably used for a heat transfer tube and the like as described above.
However, a rare form of corrosion called ant nest corrosion is rarely generated in copper pipes. The ant nest-like corrosion is a fine local corrosion, and the corrosion cross section has a complicated shape like an ant nest. That is, the corrosion hole is a minute pinhole, and the inside is a minute cavity that branches in a complicated manner. The inside of the cavity is mainly filled with cuprous oxide as a corrosion product.

The main cause of ant nest-like corrosion is a corrosion medium such as an organic acid present in the environment of use, which can occur in the presence of water and oxygen.
In order to suppress this corrosion, for example, the inventions of Patent Documents 1 and 2 below are disclosed. The invention of Patent Document 1 is to perform a surface treatment for keeping the pH of the copper tube surface at 4 to 8.6. As the surface treatment, hot dip galvanizing and zinc-containing paints are mentioned.

  The invention of the following Patent Document 2 has a configuration in which a metal zinc layer having a thickness of 0.1 μm to 50 μm is formed on the surface of a copper tube. The metal zinc layer is formed by electroplating or the like. According to this structure, zinc elutes in the adhering water in which the corrosion medium is dissolved, and the zinc moves the adhering water to the alkali side by the cathode reaction accompanying the elution, thereby suppressing the occurrence of corrosion.

  In both inventions of Patent Documents 1 and 2, a layer containing zinc is formed on the entire surface where corrosion is to be suppressed.

  However, uniformly forming the zinc-containing layer evenly over the entire surface is burdensome from the technical and cost viewpoints. If the zinc-containing layer is formed by electroplating, the film thickness is more uniform than hot-dipping due to the characteristics of electroplating, but the plating thickness depends on the current distribution. There are variations between parts and variations between objects to be plated, and a uniform plating thickness is not always obtained. For this reason, when the thickness is 0.1 μm as in Patent Document 1, sufficient effects may not be obtained, and the sustainability tends to be insufficient.

  On the contrary, when the zinc-containing layer is thickened, the anticorrosion effect is easily obtained, but when the film thickness is 50 μm, the good thermal conductivity as a characteristic of the copper tube is impaired. In addition, when the zinc-containing layer is formed by electroplating, the plating process takes time and the productivity is not good.

JP 2000-313968 A JP 2000-304491 A

  Therefore, the main object of the present invention is to ensure that the effect of suppressing the occurrence of ant nest corrosion is ensured while ensuring thermal conductivity and productivity.

  The present invention is a copper tube having a zinc coating on at least one of an outer peripheral surface and an inner peripheral surface, and the zinc coating has a thickness of 10 μm or less and a copper tube of 1 μm or more.

  In this configuration, zinc is eluted from the zinc film having a thickness of 10 μm or less, and the occurrence of corrosion is suppressed. In addition, since the zinc coating covers the substrate without being thickened, the thermal conductivity is prevented from being lowered. In addition, when the zinc coating is formed by electroplating, the plating processing time can be shortened. On the other hand, since the zinc film has a thickness of 1 μm or more, the zinc elution amount is secured and the anticorrosion action is sufficiently maintained.

As an aspect of this invention, it is good also as a copper pipe which has the said zinc membrane | film | coat only on an outer peripheral surface.
In this configuration, complete thermal conductivity is maintained on the inner peripheral surface without the zinc film. On the other hand, the anticorrosive action as described above is performed by the zinc film on the outer peripheral surface which is easily exposed to the corrosion medium.

  Another means for solving the problem is a method of manufacturing a copper pipe having a zinc film on at least one of an outer peripheral surface and an inner peripheral surface, and the zinc film is formed by subjecting the material copper pipe to an electrogalvanizing treatment. It is the manufacturing method of the copper tube which forms and performs the said electrogalvanization process so that the thickness of the said zinc membrane | film | coat is 10 micrometers or less, and it becomes 1 micrometer or more.

  In this configuration, the electrogalvanizing treatment is performed for a certain period of time under predetermined conditions to form a zinc film having a thickness in the above range. The zinc film has a thickness of 10 μm or less and covers the substrate without being thick, thereby suppressing a decrease in thermal conductivity. Since it is not thick, a certain time for performing the electroplating process is shortened. On the other hand, since the zinc film has a thickness of 1 μm or more, the zinc elution amount is secured and the anticorrosion action is sufficiently maintained.

As an aspect of this invention, after the electrogalvanizing treatment, chromate treatment may be performed to form a chromate coating on the surface of the zinc coating.
In this configuration, the chromate film improves the durability of the zinc film and maintains a sufficient anticorrosive action even with a relatively thin zinc film. Moreover, since the application is a heat transfer tube such as an air conditioner or refrigeration equipment, the chromate film may be a trivalent chromate film in consideration of the environment.

As an aspect of the present invention, the electrogalvanizing treatment may be performed after bending the material copper tube to form a hairpin processed portion.
In this configuration, since the electro-galvanizing process is performed on the material copper tube in which the hairpin processed part is formed in advance, the zinc film can be completely prevented from being damaged when the hairpin processed part is formed, and the above-described anticorrosion Get the action reliably. In addition, since batch processing is possible, processing in a small amount is possible, and the plating processing facility can be made compact, which leads to reduction in processing cost.

  According to the present invention, it is possible to suppress the occurrence of ant nest corrosion while ensuring thermal conductivity and productivity.

The cross-sectional view of a copper tube. Sectional drawing of the principal part of a copper pipe. The graph which shows the relationship between the plating time and plating thickness in a straight pipe. The perspective view of the copper tube which has a hairpin processed part. The flowchart which shows the manufacturing process of the copper pipe which has a hairpin process part. Explanatory drawing which shows the plating thickness measurement position of a hairpin process part. The graph which shows the relationship between the plating time and plating thickness in the copper pipe which has a hairpin processed part. The photograph which shows the external appearance of the test body before and after the test. A cross-sectional photograph of the maximum corroded portion of a copper pipe where corrosion has occurred.

An embodiment for carrying out the present invention will be described below with reference to the drawings.
FIG. 1 is a cross-sectional view of a copper tube 11 used as a heat transfer tube or the like, or a copper tube 11 as an intermediate body before becoming a heat transfer tube or the like. The copper tube 11 has a zinc coating 12 on at least one of the outer peripheral surface and the inner peripheral surface. That is, the zinc coating 12 is formed on either the outer peripheral surface or the inner peripheral surface, or both. In this example, the example which has the zinc membrane | film | coat 12 only in an outer peripheral surface is shown. The zinc film 12 is formed on the entire surface of the outer peripheral surface by electrogalvanizing.

  The thickness t of the zinc coating 12 is 10 μm or less and 1 μm or more. This suppresses the decrease in the thermal conductivity of the copper tube 11 due to the thickening of the zinc coating 12, and shortens the formation time of the zinc coating 12, while obtaining a sufficient anticorrosion effect, and the zinc coating over a predetermined period. This is to enable sufficient elution.

  Preferably, the thickness of the zinc film is 3 μm or more and 7 μm or less. If it is 3 μm or more, pinholes generated during the growth of the zinc film by electroplating can be reduced, and the effect of suppressing the occurrence of white rust accompanying the elution of the zinc film becomes remarkable. Moreover, if it is 7 micrometers or less, it is because the anticorrosion effect is implement | achieved by suppressing the zinc film processing cost, suppressing the said white rust generation | occurrence | production.

  In the copper tube 11 having such a configuration, the material copper tube 11a is subjected to an electrogalvanization process to form a zinc film 12, and the electrogalvanization process is performed with a thickness of the zinc film 12 of 10 μm or less and 1 μm. It is manufactured by going as described above.

  After the electrogalvanization treatment, chromate treatment is performed to form a chromate film 13 on the surface of the zinc film 12 as shown in FIG. The chromate film 13 is preferably a trivalent chromate film.

  The electrogalvanization is performed by dipping in a plating solution after sufficiently performing the necessary pretreatment on the material copper tube 11a. When the material copper pipe 11a is a straight pipe, since the current at the time of electrogalvanization circulates to the pipe end portion, the inner peripheral surface of the end portion is also galvanized. In order to form them only, it is preferable to cut off the end after electrogalvanizing, plug the silicon so that the plating solution does not enter the end, or remove the end from the plating solution.

  When an oxide film is formed on the inner peripheral surface of the copper tube 11 during the electrogalvanizing process, the thickness is made as thin as possible. This is because the thermal conductivity is considered to decrease. Specifically, the thickness of the oxide film (copper oxide and cuprous oxide) is preferably 0.1 μm or less.

The conditions for electrogalvanizing are set such that the current density and time are such that a zinc film having a desired thickness is formed. For example, when electrogalvanizing a copper tube having an outer diameter of 9.0 mm, a wall thickness of 0.28 mm, and a length of 1000 mm, the zinc concentration is 10 g / L, the sodium hydroxide concentration is 110 g / L, and the plating solution temperature is about 25. ° C., a current density of 3A / dm ^2, when the plating time of 20 minutes, the thickness of the zinc coating of about 6μm will be obtained. In order to form a zinc film of 1 μm or more and 10 μm or less, electrogalvanizing treatment for 5 minutes or more and 33 minutes or less may be performed under the above-described conditions. In particular, in order to make the thickness of the zinc film 3 μm to 7 μm, electrogalvanizing treatment is performed for 12 minutes or more and within 24 minutes.

The chromate treatment is performed by a known appropriate method (standard method of catalog using commercially available trivalent chromate treatment agent). By this treatment, chromate ions are reduced by dissolution of zinc, the pH is increased, and a film mainly composed of trivalent chromium hydroxide (Cr (OH) ₃ ) is formed on the galvanized surface. . As schematically shown in FIG. 2, the chromate film 13 formed by the chromate treatment is extremely thin (thickness is less than 0.5 μm) but has excellent corrosion resistance. The treatment method (immersion for about 1 minute at a treatment solution temperature of 30 ° C.) is also simple and can be performed at low cost.

Here, the result of having investigated the relationship between the plating time and the plating thickness in the straight pipe which is the straight material copper pipe 11a is shown.
The experimental conditions are as follows.
Material: Copper tube with outer diameter of 7.94 mm, wall thickness of 0.31 mm, length of 900 mm Electrogalvanizing conditions: Current density 3 A / dm ² , plating time 1 min, 5 min, 20 min, 40 min Chromate after electrogalvanization When two types of materials that were not treated were manufactured and the thickness of the plating was measured by observing the cross section, the result as shown in FIG. 3 was obtained.

  FIG. 3 is a graph showing the relationship between the plating time and the plating thickness in a straight pipe, with the processing time (minutes) on the horizontal axis and the plating thickness (mm) on the vertical axis. The plating thickness was measured when the treatment time was “5 minutes”, “20 minutes”, and “40 minutes”.

  As can be seen from FIG. 3, it can be seen that a zinc film of at least 1 μm (0.001 mm) can be obtained in a plating time of 5 minutes, whether or not the chromate treatment. It can also be seen that a zinc film having a thickness of 10 μm (0.01 mm) or more can be obtained if the plating time is as long as 40 minutes. In addition, although the plating thickness was not measured, the zinc film disappeared by the glossing treatment (pickling) performed in the normal treatment for those with a plating time of 1 minute.

  From this result, it is considered that the zinc coating 12 having a thickness of 1 μm or more and 10 μm or less can be obtained on the outer peripheral surface of the straight pipe if the plating time is 5 minutes or more and 40 minutes under the above plating conditions. In this experiment, it was assumed that the treatment liquid naturally occurred with the gas generated during electroplating without forced stirring, but it became faster by supplying the treatment liquid (zinc) to the copper surface with forced stirring. Plating thickness increases. For this reason, when manufacturing the copper pipe 11, the time which electrogalvanization requires may be short, and the improvement of productivity can be aimed at.

  To manufacture the copper tube 11 having the hairpin processing portion 15 as shown in FIG. 4, as shown in the flowchart of FIG. 5, the material copper tube 11a is first bent n12 to form the hairpin processing portion 15. After that, pretreatment n12 such as alkaline degreasing and rinsing is performed, and electrozinc plating treatment n13 is performed to form a zinc film 12, followed by post-treatment n14 such as rinsing and activation treatment, chromate treatment n15, rinsing (and After the post-treatment n16 is performed in order, drying n17 is performed.

About the copper tube 11 which has the hairpin process part 15, the relationship between the plating time of the hairpin process part 15 and plating thickness was investigated.
The experimental conditions are as follows.
Material: Copper tube with an outer diameter of 7.94 mm, a wall thickness of 0.31 mm, an inner diameter of the hairpin processed portion of 14 mm, and a length from the hairpin processed portion to the tube end of 14.5 mm Electrogalvanizing conditions: Current density 3 A / dm ^2. Plating time 5 minutes, 20 minutes, 40 minutes. The hairpin processed part 15 was hung on a hanger in a posture facing sideways and immersed in a plating solution.

  In this case as well, as described above, a non-chromate treated product after electrogalvanizing was manufactured, and the cross-sectional observation was performed to measure the plating thickness. When measuring the plating thickness, an average value of the entire characteristic shape was obtained. A method for obtaining the average value will be described with reference to FIG. FIG. 6 is a front view (FIG. 6A) and a side view (FIG. 6B) of a copper tube having a hairpin processed portion 15. As shown in FIG. 6 (a), the mandrel-side curve starting point of the semicircular arc-shaped part that bends in a U-shape is defined as a 0 degree region, from which regions of 45 degrees, 90 degrees, 135 degrees, and 180 degrees are defined. The 180 degree region was identified as “A”, the 135 degree region as “B”, the 90 degree region as “C”, the 45 degree region as “D”, and the 0 degree region as “E”. Further, as shown in FIG. 6B, a point (circular or substantially circular cross-section) located on the innermost side on the curved inner peripheral side of the U-shaped curve at the outer peripheral surface position of the circular or substantially circular cross-section of the copper tube 11. The innermost point on the curved inner circumference on the line along the longitudinal direction of the copper tube passes through the center, and the outermost point on the outer circumferential side of the copper tube passes through the center of the circular or substantially circular cross section. The point on the curved outer peripheral side on the line along the longitudinal direction) was defined as “outside”, and the two left and right points on the line perpendicular to the line connecting “inside” and “outside” were defined as “left” and “right”.

  Then, the plating thicknesses of “outside”, “right”, “inside”, and “left” in the pipe circumferential direction in “A”, “B”, “C”, “D”, and “E” shown in FIG. The average value in each part of “right” “inside” and “left” was calculated, and the average value of the whole was obtained. As a result, a result as shown in FIG. 7 was obtained.

  FIG. 7 is a bar graph showing the outer part, the right part, the inner part, and the left part on the horizontal axis and the thickness of the galvanized film on the vertical axis. The plating time is “5 minutes” and “20 minutes”. "40 minutes" is the result of examining two types of chromate treated and not. Fig. 7 (a) shows chromate treatment "Yes", plating time "5 minutes", Fig. 7 (b) shows chromate treatment "Yes", plating time "20 minutes", Fig. 7 (c) shows chromate treatment "Yes". The plating time is “40 minutes”. FIG. 7 (d) shows the chromate treatment “no”, plating time “5 minutes”, FIG. 7 (e) shows the chromate treatment “no”, plating time “20 minutes”, and FIG. 7 (f) shows the chromate treatment “no”. The plating time is “40 minutes”. In each graph, the plating thickness of each part of “outside”, “right”, “inside”, and “left” is measured from “A” (180 degree part) to “E” (0 degree part). On the other hand, the average value obtained from the five points “A” to “E” is the average value of “outside”, and similarly “A” to “E” for “right”, “inside”, and “left” respectively. The average value obtained from the five points of the part is shown as a bar graph as the average value of “right”, “inside”, and “left”. In addition, the total average value of the hairpin portion under each processing condition obtained from the four average values of “outside”, “right”, “inside”, and “left” is entered in FIGS. 7 (a) to 7 (f). ing. 7 (a) is 0.6 μm, FIG. 7 (b) is 5.8 μm, FIG. 7 (c) is 11.8 μm, FIG. 7 (d) is 1.0 μm, FIG. 7 (e) is 6.3 μm, FIG. 7F shows 11.3 μm.

  As can be seen from these graphs, a zinc film having a thickness of 10 μm (0.01 mm) or more can be obtained with or without the chromate treatment if a plating time of 40 minutes is taken. When the plating time was 5 minutes, the zinc coating was less than 1 μm (0.001 mm) with the chromate treatment, but if the plating time was made slightly longer or forced stirring, the average was 1 μm (0.001 mm) It can be expected that the above zinc coating is obtained. Also, when the plating time is 20 minutes and 40 minutes, the plating thickness of “inner” seems to be thinner than other parts, but the plating thickness of the “inner” part is also 10 μm on average in the plating time of 40 minutes. You can see that

  From this result, it is considered that the zinc coating 12 having a thickness of 1 μm or more and 10 μm or less can be obtained on the outer peripheral surface when the plating time is longer than 5 minutes and up to 40 minutes in the hairpin processed part under the above plating conditions. In particular, if the plating time is 20 minutes, it is considered that the zinc coating 12 that fits in the range of 3 μm to 7 μm can be reliably obtained at all sites.

  For this reason, even when it has the hairpin process part 15, the time which electrogalvanization requires in the manufacture of the copper pipe 11 may be short, and improvement of productivity can be aimed at. In addition, since the hairpin processing portion 15 is formed in advance before the electrogalvanization treatment, it is not necessary to apply a load to the formed zinc coating 12 by bending, so that it is possible to avoid the disadvantage that the zinc coating 12 is damaged. .

  The following copper tubes were manufactured, and the occurrence of ant nest corrosion was observed.

  As shown in FIG. 1, the copper tube 11 is provided with a zinc coating 12 only on the entire outer peripheral surface. Specifically, a phosphorus-deoxidized copper (JIS H3300 C1220T OL material) tube was used as the material copper tube (material copper tube 11a). The copper tube 11a has an outer diameter of 7.94 mm, a wall thickness of 0.31 mm, and a length of 100 mm. The zinc coating 12 as described above is formed on the entire outer surface.

  The zinc coating 12 is formed by electrogalvanization, and the zinc coating 12 has a difference in thickness due to a difference in plating treatment time. The plating treatment time is 5 minutes, 20 minutes, and 40 minutes. See FIG. 3 for the difference in thickness of the zinc coating 12 due to the difference in plating time.

  For comparison, in addition to a copper tube having only the zinc coating 12, a copper tube having a chromate treatment to form a chromate coating 13 on the surface of the zinc coating and a copper tube having no zinc coating 12 and having a phosphorous deoxidized copper as it is ( PDC) and a copper tube (OFC) of oxygen-free copper as it is. The sizes of these copper pipes are as follows: PDC and copper pipe 11 have an outer diameter of 7.94 mm and a wall thickness of 0.31 mm, OFC has an outer diameter of 9.0 mm and a wall thickness of 0.26 mm, and the length is 100 mm. is there.

  The following experiments were conducted on these specimens to examine the occurrence of ant nest corrosion.

  Put 100 mL of formic acid aqueous solution with a concentration of 100 ppm as a corrosive medium in a 1 L internal container, put the test specimen in a test tube and stand it in a state where it is not in direct contact with the formic acid aqueous solution, and change the atmosphere in the container to oxygen After the replacement, it was left in a room temperature room for 4 weeks (28 days). In order to replace the atmosphere in the container with oxygen after the start of the experiment, oxygen gas was changed to 1 L / min. At a flow rate of 5 minutes.

  The maximum corrosion depth was measured by observing a cross section of several places where corrosion was considered to occur in appearance observation and searching for the maximum corrosion depth portion on the outer peripheral surface. The corrosion depth was determined by measuring the depth from the outer surface of the copper tube cross section. The cross-sectional photographs were taken together.

  The appearance after the experiment, that is, before and after contact with the corrosive medium is shown in the photograph of FIG. From this photograph, it can be seen that the longer the plating time and the thicker the zinc film 12, the smaller the generation of white powder, and the lower the generation of white powder the chromate treatment.

  The test results are as shown in Table 1. Table 1 shows all the test specimens arranged vertically, with the sample name and the maximum corrosion depth (mm) arranged on the right side. For the copper tube having the zinc coating 12, two samples were evaluated. For comparison, two samples were also evaluated for phosphorus deoxidized copper (PDC) and oxygen-free copper (OFC). “No corrosion” means that no corrosion was found. Otherwise, the maximum corrosion depth was entered, and a cross-sectional photograph of that part was taken. A cross-sectional photograph is shown in FIG. In the photograph, only the sample in which the upper side is the outer peripheral surface side of the copper tube and corrosion is recognized is shown.

* Corrosion depth is measured from the outer surface of the copper tube cross section.

As can be seen in Table 1, in the case of the test body having the zinc coating 12, the occurrence of corrosion on the outer peripheral surface was recognized, with the plating time being 20 minutes and 40 minutes, without the chromate coating 13. I couldn't. On the other hand, in the phosphorus-deoxidized copper pipe (PDC) and the oxygen-free copper pipe (OFC), ant nest corrosion occurred. However, the corrosion depth of the oxygen-free copper tube (OFC) was generally shallower than that of the phosphorus-deoxidized copper tube (PDC). In the case of the specimen having the zinc coating 12, when the plating time is 5 minutes, there is a case where ant nest corrosion can be confirmed and a case where ant nest corrosion is confirmed, It was found that the film disappeared due to sacrificial protection.

  From this result, under the current corrosion test conditions, if the plating time is 5 minutes and the zinc coating 12 is less than 1 μm, there is a possibility that sufficient anticorrosion effect may not be obtained, and the sustainability is inferior compared to others. It is thought that. However, if the thickness of the zinc film 12 is 1 μm or more, particularly when the zinc film is formed with a plating time of 20 minutes which can be a thickness exceeding 3 μm, a sufficient anticorrosive effect can be obtained and durability can be improved. It can be considered sufficient.

DESCRIPTION OF SYMBOLS 11 ... Copper pipe 11a ... Material copper pipe 12 ... Zinc film 13 ... Chromate film 15 ... Hairpin processing part

Claims (6)

A copper tube having a zinc coating on at least one of the outer peripheral surface or the inner peripheral surface,
The copper pipe whose thickness of the said zinc membrane is 10 micrometers or less and is 1 micrometers or more. The copper pipe according to claim 1 which has said zinc coat only on an outer peripheral surface. A method for producing a copper tube having a zinc coating on at least one of an outer peripheral surface or an inner peripheral surface,
Electrolytic galvanizing treatment for copper pipe material to form a zinc film,
A method of manufacturing a copper tube, wherein the electrogalvanizing treatment is performed so that the thickness of the zinc coating is 10 μm or less and 1 μm or more. The method for producing a copper tube according to claim 3, wherein after the electrogalvanizing treatment, chromate treatment is performed to form a chromate coating on the surface of the zinc coating. The method for producing a copper tube according to claim 4, wherein the chromate film is a trivalent chromate film. After forming the hairpin processing part by bending the material copper tube,
The manufacturing method of the copper pipe as described in any one of Claims 3-5 which performs the said electrogalvanization process.