KR20210053949A - Metal pipe manufacturing method and cleaning method - Google Patents

Abstract

In the cleaning of a metal tube having a chemical conversion film and a lubricating film formed on the surface thereof, both energy saving (low cost) and good cleaning properties are realized. The manufacturing method of the metal pipe P includes a preparation step (S1) for preparing a metal element pipe, a lubricating step (S2) in which a chemical conversion film is formed on the surface of the element pipe, and a lubricating film is formed on the chemical conversion film, and chemical conversion. A cold drawing step (S3) in which cold drawing is performed on an element tube on which a film and a lubricating film is formed to form a metal tube (P) of a predetermined dimension (S3), and a cleaning process in which a chemical film and a lubricating film are removed by cleaning the metal tube (P). (S4) is provided. The cleaning step (S4) is a step (S41) of immersing the metal pipe (P) in an alkali degreasing liquid that is not heated at a high temperature in the alkali cleaning tank (11), And a step (S42) of immersing the metal pipe P after being immersed in the alkaline degreasing liquid while generating fine bubbles in the cleaning liquid together.

Description

Metal pipe manufacturing method and cleaning method

The present disclosure relates to a method for manufacturing a metal tube and a cleaning method. In particular, the present disclosure relates to a method for cleaning a metal tube formed by performing a cold drawing process on an element tube having a chemical conversion coating and a lubricating coating formed on the surface thereof.

When cold drawing is performed in the manufacturing process of a metal pipe, a large frictional force is generated between the element pipe of the metal and the drawing tool. In order to reduce this frictional force, prior to the cold drawing, the material pipe is subjected to a lubricating treatment.

In the lubricating treatment before cold drawing, for example, a chemical conversion film such as a phosphate film, an oxalate film, or a chromate film is formed on the surface of the element pipe. On the chemical conversion film, a lubricating film is formed from a higher fatty acid salt (soap) or the like. The chemical conversion film prevents direct contact between the element pipe and the drawing tool to improve seizure resistance, and improves the lubricity by increasing the adhesion between the element pipe and the lubricating film.

After finishing the element pipe into a metal pipe having a predetermined size by cold drawing, the metal pipe is washed to remove the chemical conversion film and the lubricating film. These coatings are firmly bonded to the material of the metal tube. For this reason, it is difficult to remove each film from the metal tube.

As one of the methods for cleaning metallic materials and the like, a cleaning method using ultrasonic waves is known. For example, Patent Document 1 discloses a method of pickling a metal tube by irradiating ultrasonic waves to an end portion of a tube while rubbing a plurality of metal tubes with each other in an acid solution. According to Patent Document 1, in a portion of the metal tube that rubs against each other, scale is removed by a gamma action due to friction and a dissolution action by an acid solution. At the end of the tube where friction does not occur, the scale is removed by ultrasonic waves promoting the dissolution action by the acid solution.

Patent Document 2 discloses a method for descaling a hot-rolled steel sheet using a combination of ultrasonic waves and microbubbles. According to Patent Document 2, by supplying microbubbles to the ultrasonically applied portion of the hot-rolled steel sheet, cavitation is reliably generated and a descaling effect can be reliably obtained.

Patent document 3 discloses a cleaning device in which ultrasonic waves and microbubbles are used in combination. In the cleaning apparatus, the cleaning liquid in the cleaning tank is irradiated with ultrasonic waves from an ultrasonic generator. A circulation path is connected to the washing tank. The cleaning liquid in the cleaning tank is introduced into the degassing device through a circulation path. The degassing device separates dissolved air from the cleaning liquid to generate microbubbles. The microbubbles are supplied to the cleaning tank through the circulation path to reduce the dissolved air concentration in the cleaning liquid. According to Patent Document 3, when the dissolved air concentration in the cleaning liquid is less than or equal to the specified value, the sound pressure of ultrasonic waves is not lowered, and good cleaning can be efficiently performed.

Japanese Patent Application Laid-Open No. Hei 3-177590 Japanese Patent Laid-Open No. 2000-256886 Japanese Patent Laid-Open No. 2007-29944

As described above, after cold drawing, it is necessary to wash the metal tube to remove the chemical conversion film and the lubricating film. The adhesion between the chemical conversion film and the lubricating film and the metal pipe is very high. For this reason, in cleaning the metal tube after cold drawing, even if the method or apparatus of each patent document is simply used, it is difficult to reliably remove each film from the metal tube.

Conventionally, degreasing treatment and pickling treatment are performed on metal pipes after cold drawing. That is, first, the lubricating film is removed from the metal tube by the degreasing treatment, and then the chemical conversion film is removed from the metal tube by the pickling treatment. Specifically, for example, a metal tube is subjected to a degreasing treatment with an alkaline degreasing liquid at a high temperature of 70°C or higher, and then, a pickling treatment is performed. In the degreasing treatment, the metal soap component in the lubricating film forms a complex, and other soap components are dissolved. In order to ensure sufficient complex formation and dissolution, it is necessary to use a high temperature alkaline degreasing liquid. However, in order to heat the alkaline degreasing liquid to a high temperature, there is a problem that a large amount of energy is required, the amount of energy used (consumption amount) increases, and the cost increases accordingly. On the other hand, if the alkaline degreasing liquid is not heated to a high temperature (70°C or higher), complex formation and dissolution of the soap component does not proceed, and the lubricating film remains in the metal tube.

The present disclosure makes it a subject to realize both energy saving (low cost) and good cleaning properties in cleaning a metal tube in which a chemical conversion film and a lubricating film are formed on the surface.

The method of manufacturing a metal pipe according to the present disclosure includes a preparation step of preparing a metal element pipe, a lubricating step of forming a chemical conversion film on the surface of the element pipe, and forming a lubricating film on the chemical conversion film, and a chemical conversion film and a lubricating film. A cold drawing step of performing a cold drawing process on an element pipe to form a metal tube having a predetermined size, and a washing step of washing the metal tube to remove a chemical conversion film and a lubricating film are provided. The cleaning process is a process of immersing a metal tube in an alkali degreasing liquid that is not heated at a high temperature in an alkaline cleaning tank, and by irradiating ultrasonic waves into the cleaning liquid in the ultrasonic cleaning tank and generating fine bubbles in the cleaning liquid while immersing in the alkaline degreasing liquid. It includes a step of immersing the subsequent metal pipe in a cleaning solution.

According to the present disclosure, both energy saving (low cost) and good cleaning properties can be realized in cleaning a metal tube in which a chemical conversion film and a lubricating film are formed on the surface.

1 is a flowchart of a method for manufacturing a metal tube according to an embodiment.
2 is a side view of an alkali cleaning device used in an alkali cleaning step in the manufacturing method according to the embodiment.
3 is a III-III cross-sectional view of the alkali cleaning device shown in FIG. 2.
4 is a plan view of an ultrasonic cleaning device used in an ultrasonic cleaning process in a manufacturing method according to an embodiment.
5 is a VV cross-sectional view of the ultrasonic cleaning device shown in FIG. 4.
6 is a diagram illustrating a discharge mechanism that can be employed in the ultrasonic cleaning device shown in FIG. 4.
7 is a diagram illustrating another discharge mechanism that can be employed in the ultrasonic cleaning device shown in FIG. 4.
8A is a diagram schematically showing the surface of a metal tube after cold drawing.
8B is a diagram schematically showing the surface of a metal tube after an alkali washing step.
8C is a diagram schematically showing the surface of a metal tube during an ultrasonic cleaning step.
9 is a graph showing a change in the amount of carbon adhering to the inner surface of a metal tube for Examples, Comparative Example 1, and Comparative Example 2. FIG.
10 is a scanning electron microscope image of the inner surface of each metal tube cleaned by the cleaning method of Example and Comparative Example 1. FIG.

The method of manufacturing a metal pipe according to the embodiment includes a preparation step of preparing a metal element pipe, a lubricating step of forming a chemical conversion film on the surface of the element pipe, and forming a lubricating film on the chemical conversion film, and a chemical conversion film and a lubricating film formed thereon. A cold drawing step of performing a cold drawing process on an element pipe to form a metal tube having a predetermined size, and a washing step of washing the metal tube to remove a chemical conversion film and a lubricating film are provided. The cleaning process is a process of immersing a metal tube in an alkali degreasing liquid that is not heated at a high temperature in an alkaline cleaning tank, and by irradiating ultrasonic waves into the cleaning liquid in the ultrasonic cleaning tank and generating fine bubbles in the cleaning liquid while immersing in the alkaline degreasing liquid. It includes a step of immersing the subsequent metal pipe in a cleaning solution.

In the method for manufacturing a metal tube according to the above embodiment, after forming a lubricating film and a chemical conversion film as a base film of the lubricating film on an element pipe, the element pipe is formed into a metal pipe having a predetermined size by cold drawing. The metal tube obtained by cold drawing is cleaned (alkali degreasing) by the following method. That is, the metal tube is first immersed in an alkali degreasing liquid that has not been heated at a high temperature. The alkaline degreasing liquid that is not heated at high temperature in the present disclosure is typically around an alkaline degreasing facility in which an active heat treatment using a heater (for example, a steam heater or an electric heater) is not performed on the alkaline degreasing liquid. It refers to an alkaline degreasing liquid with a natural liquid temperature according to the ambient temperature of (temperature or the temperature inside the factory building). In this case, energy used (consumed) for heating the alkaline degreasing liquid becomes unnecessary. However, when the temperature of the alkali degreasing liquid is less than 20°C, the alkali degreasing liquid is heated so that the temperature is about 20 to 40°C. For example, in winter seasons where the temperature is low, the temperature of the alkali degreasing liquid may decrease to less than 20°C. In such a case, an active heat treatment is performed so that the liquid temperature is about 20 to 40°C. In this case, energy for heating the alkaline degreasing liquid is used, but since it is not necessary to heat it to a high temperature (70°C or higher) as in the prior art, the amount of energy used can be reduced.

Complex formation and dissolution occur in a part of the lubricating film by immersion in such an alkali degreasing liquid which is not heated at a high temperature, and the lubricating film is partially removed from the surface of the metal tube. Next, the metal tube is immersed in a cleaning liquid to which ultrasonic waves and fine bubbles have been applied. Since a part of the lubricating film on the surface of the metal tube is in a state of being damaged by the alkaline degreasing treatment, it can be peeled off from the metal tube by a physical action such as ultrasonic cavitation.

In addition, the temperature of the alkaline degreasing liquid may be affected by the reaction heat during the washing treatment or by circulating the alkaline degreasing liquid in the cleaning device. It shall not be included in the active heat treatment.

The ductility of the Martian coating is very small. For this reason, when cold drawing is performed on a metal tube, it is thought that a crack occurs in the chemical conversion film on a metal tube. Accordingly, by immersing the metal tube in a cleaning solution to which ultrasonic waves and fine bubbles have been applied, a physical action such as ultrasonic cavitation is applied to the metal tube, so that the chemical conversion film can also be peeled off from the metal tube.

As described above, according to the manufacturing method according to the embodiment, when removing each film from the metal tube, it is not necessary to heat the alkali degreasing liquid to a high temperature of 70°C or higher as in the prior art. Therefore, it is possible to realize both energy saving (low cost) and good cleaning properties.

In the above manufacturing method, while the metal tube is immersed in the cleaning liquid in the ultrasonic cleaning tank, it is preferable that the dissolved oxygen concentration of the cleaning liquid is 5.2 mg/L or less.

By setting the dissolved oxygen concentration of the cleaning liquid to be irradiated with ultrasonic waves to 5.2 mg/L or less, good ultrasonic cleaning properties can be ensured.

The cleaning method of a metal tube according to an embodiment is a method for cleaning a formed metal tube by performing cold drawing on an element tube having a chemical conversion coating and a lubricating coating formed thereon. The cleaning method includes a step of immersing a metal tube in an alkaline degreasing liquid that is not heated at a high temperature in an alkaline cleaning tank, and immersing in an alkaline degreasing liquid while irradiating ultrasonic waves into the cleaning liquid in the ultrasonic cleaning tank and generating fine bubbles in the cleaning liquid. A step of immersing the metal pipe after the cleaning in a cleaning solution is provided.

In the above cleaning method, while the metal tube is immersed in the cleaning liquid in the ultrasonic cleaning tank, it is preferable that the dissolved oxygen concentration of the cleaning liquid is 5.2 mg/L or less.

Hereinafter, embodiments of the present disclosure will be described with reference to the drawings. In each figure, the same reference numerals are attached to the same or corresponding configurations, and the same description is not repeated.

1 is a flowchart of a method for manufacturing a metal tube according to the present embodiment. As shown in FIG. 1, the manufacturing method of a metal tube includes a preparation process (S1), a lubrication process (S2), a cold drawing process (S3), and a washing process (S4). The lubricating step S2 includes a chemical conversion film forming step S21 and a lubricating film forming step S22. The cleaning process (S4) is an alkali degreasing process of a metal tube on which a chemical conversion film and a lubricating film are formed, and includes an alkali cleaning process (S41) and an ultrasonic cleaning process (S42). First, the alkaline cleaning device used in the alkaline cleaning step S41 and the ultrasonic cleaning device used in the ultrasonic cleaning step S42 will be described, respectively.

[Alkaline cleaning device]

2 is a side view schematically showing the alkali cleaning device 10 used in the alkali cleaning step S41. 3 is a III-III cross-sectional view of the alkali cleaning device 10 shown in FIG. 2.

2 and 3, the alkali cleaning device 10 includes an alkali cleaning tank 11, a storage tank 12, and a circulation pipe 13.

(Alkaline washing tank)

The alkali washing tank 11 has a tank main body 111 and a lid 112. The jaw main body 111 has an opening in its upper surface. The lid 112 is configured to cover the opening of the tank main body 111.

The tank main body 111 is comprised so that the metal tube P can be accommodated. During alkaline cleaning, in the bath main body 111, a plurality of metal pipes P are usually accommodated at the same time. An alkali degreasing liquid is supplied to the tank main body 111. Alkaline degreasing liquid is a known alkaline solution used in general alkaline degreasing treatment, for example, sodium hydroxide (NaOH) aqueous solution, sodium silicate (Na ₂ SiO ₃ ) aqueous solution, sodium carbonate (Na ₂ CO ₃ ) aqueous solution, etc. . Additives, such as a surfactant and a chelating agent, can be added suitably to an alkali degreasing liquid.

The jaw body 111 has a rectangular shape when viewed from a plan view, for example. The jaw main body 111 has a bottom surface 111a and a circumferential wall 111b extending upward from the periphery of the bottom surface 111a. The bottom surface 111a is an inclined surface that descends from one end 111c side in the longitudinal direction of the jaw main body 111 toward the other end 111d side. The depth of the jaw body 111 increases from the end portion 111c toward the end portion 111d.

A plurality of support members 113 may be provided in the tank body 111. The plurality of support members 113 are arranged at intervals along the longitudinal direction of the jaw main body 111. The support member 113 supports the metal tube P so that the metal tube P does not directly contact the bottom surface 111a. Each support member 113 is formed in a U-shape, for example.

(Reservoir tank)

The storage tank 12 is disposed below the alkali washing tank 11. The storage tank 12 is formed in a hollow rectangular parallelepiped shape, for example. An alkali degreasing liquid is stored in the storage tank 12. In the vicinity of the end portion 111c of the tank body 111, the storage tank 12 communicates with the tank body 111 via a circulation pipe 13. In the vicinity of the end portion 111d of the tank body 111, the storage tank 12 communicates with the tank body 111 via a communication port 14. The communication port 14 is configured to be able to open and close.

(Circulation piping)

The circulation pipe 13 connects the tank main body 111 and the storage tank 12 in the vicinity of the end 111c of the tank main body 111 of the alkaline cleaning tank 11. The circulation pipe 13 is configured so that the alkaline degreasing liquid in the storage tank 12 can be supplied to the tank body 111. For example, the circulation pipe 13 is provided with a pump 131 (FIG. 3) for sending the alkaline degreasing liquid from the storage tank 12 to the tank body 111.

[Ultrasonic cleaning device]

4 is a plan view of the ultrasonic cleaning device 20 used in the ultrasonic cleaning step S42. 5 is a V-V cross-sectional view of the ultrasonic cleaning device 20 shown in FIG. 4.

As shown in FIG. 4, the ultrasonic cleaning device 20 includes an ultrasonic cleaning tank 21, a supply mechanism 22, a plurality of discharge mechanisms 23, a plurality of ultrasonic irradiation mechanisms 24, and a plurality of It is provided with a fine bubble generating mechanism (25). The ultrasonic cleaning device 20 further includes a plurality of buffer members 26.

(Ultrasonic cleaning tank)

The ultrasonic cleaning tank 21 is comprised so that the metal tube P can be accommodated. In the case of ultrasonic cleaning, in the ultrasonic cleaning tank 21, a plurality of metal pipes P are usually accommodated at the same time. In the ultrasonic cleaning tank 21, a cleaning liquid for cleaning the metal pipe P is stored. The type of cleaning liquid is not particularly limited, and can be appropriately selected and employed from known cleaning liquids. The washing liquid is water (tap water, industrial water), for example.

The ultrasonic cleaning tank 21 has, for example, a rectangular shape when viewed in a plan view. The ultrasonic cleaning tank 21 has its upper surface open. The bottom surface of the ultrasonic cleaning tank 21 is an inclined surface that descends from one end in the longitudinal direction toward the other end. The depth of the ultrasonic cleaning tank 21 increases from one end in the longitudinal direction toward the other end.

The material of the ultrasonic cleaning tank 21 is not particularly limited. Examples of the material of the ultrasonic cleaning tank 21 include metal materials such as stainless steel, plastic resins such as fiber-reinforced plastic (FRP) or polypropylene (PP), or acid-resistant bricks. The alkali cleaning tank 11 and the storage tank 12 (FIG. 2) described above can also be formed of the same material as the ultrasonic cleaning tank 21.

(Supply mechanism)

The supply mechanism 22 supplies a cleaning liquid to the ultrasonic cleaning tank 21. The supply mechanism 22 has at least one supply pipe 221. In this embodiment, the supply mechanism 22 has a plurality of supply pipes 221. The cleaning liquid is supplied to the ultrasonic cleaning tank 21 through each supply pipe 221. The plurality of supply pipes 221 are arranged at intervals. For this reason, the cleaning liquid is dispersed and supplied to the ultrasonic cleaning tank 21. When three or more supply pipes 221 are present, from the viewpoint of uniform supply of a new cleaning liquid, it is preferable that the intervals of the supply pipes 221 are substantially equal.

In this embodiment, the plurality of supply pipes 221 are provided along one side wall of the pair of side walls in the longitudinal direction of the ultrasonic cleaning tank 21. However, the position and number of the supply pipes 221 are not particularly limited. One or more supply pipes 221 may be provided on both side walls of the ultrasonic cleaning tank 21 in the longitudinal direction. Further, in addition to or instead of the sidewall in the longitudinal direction of the ultrasonic cleaning tank 21, one or more supply pipes 221 may be provided on the sidewall in the width direction of the ultrasonic cleaning tank 21.

(Discharge mechanism)

Each discharge mechanism 23 discharges the cleaning liquid from the ultrasonic cleaning tank 21 when the amount of the cleaning liquid in the ultrasonic cleaning tank 21 exceeds a predetermined amount. The plurality of discharge mechanisms 23 are arranged at intervals. For this reason, the cleaning liquid is dispersed and discharged from the ultrasonic cleaning tank 21. When three or more discharging mechanisms 23 are present, it is preferable that the spacing between the discharging mechanisms 23 is substantially equal. Further, the number of discharge mechanisms 23 may be one.

In the present embodiment, the plurality of discharging mechanisms 23 are provided along side walls opposite to the supply pipe 221 among a pair of side walls in the longitudinal direction of the ultrasonic cleaning tank 21. However, the position and number of the discharge mechanism 23 are not particularly limited. Of the pair of side walls in the longitudinal direction of the ultrasonic cleaning tank 21, the discharge mechanism 23 may be provided on the side wall on the side of the supply pipe 221. Further, in addition to or instead of the side wall in the longitudinal direction of the ultrasonic cleaning tank 21, one or more discharge mechanisms 23 may be provided on the side wall in the width direction of the ultrasonic cleaning tank 21.

In FIG. 6, the discharge mechanism 23A which can be adopted for the ultrasonic cleaning device 20 is illustrated. The discharge mechanism 23A includes a discharge port 231 and a discharge pipe 232.

The discharge port 231 is an opening formed in the side wall of the ultrasonic cleaning tank 21. The discharge pipe 232 is provided outside the ultrasonic cleaning tank 21 and is connected to the discharge port 231. The cleaning liquid is discharged from the ultrasonic cleaning tank 21 through the discharge port 231 and the discharge pipe 232.

In the ultrasonic cleaning device 20, the reference liquid level S of the cleaning liquid in the ultrasonic cleaning tank 21 is set. When cleaning the metal pipe P, the cleaning liquid is supplied to the ultrasonic cleaning tank 21 until the liquid level reaches the reference liquid level S. In the depth direction of the ultrasonic cleaning tank 21, the position of the lower end of the discharge port 231 substantially coincides with the position of the reference liquid level S.

6, when the level of the cleaning liquid in the ultrasonic cleaning tank 21 exceeds the level of the reference liquid level S, the amount of the cleaning liquid exceeding the reference level S is discharged from the outlet ( 231). For example, when the supply mechanism 22 supplies a new cleaning liquid to the ultrasonic cleaning tank 21 in a state where the cleaning liquid level in the ultrasonic cleaning tank 21 coincides with the reference liquid level S, the supply amount is substantially The same amount of cleaning liquid overflows from the discharge port 231.

In this way, the discharge mechanism 23A discharges the cleaning liquid from the ultrasonic cleaning tank 21 when the amount of the cleaning liquid in the ultrasonic cleaning tank 21 exceeds the liquid amount (a predetermined amount) corresponding to the reference liquid level S. do.

In FIG. 7, another discharge mechanism 23B that can be employed in the ultrasonic cleaning device 20 is illustrated. The discharge mechanism 23B includes a discharge port 233, a discharge pipe 234, a discharge pump 235, and a liquid level detection means (not shown). Further, as the liquid level detection means, a commercially available liquid level sensor or the like can be used.

The discharge port 233 is an opening formed in the side wall of the ultrasonic cleaning tank 21. The discharge port 233 is provided at an arbitrary height lower than the reference liquid level S in the side wall of the ultrasonic cleaning tank 21. The discharge pipe 234 is provided outside the ultrasonic cleaning tank 21 and is connected to the discharge port 233. The cleaning liquid is discharged from the ultrasonic cleaning tank 21 through the discharge port 233 and the discharge pipe 234.

The discharge pump 235 is installed in the middle of the discharge pipe 234. When the level of the cleaning liquid in the ultrasonic cleaning tank 21 exceeds the level of the reference liquid level S, the discharge pump 235 transfers the cleaning liquid to the amount exceeding the reference liquid level S from the ultrasonic cleaning tank 21 It is controlled to suck. For example, in response to a signal from the liquid level detecting means disposed in the ultrasonic cleaning tank 21, when the liquid level of the cleaning liquid exceeds the reference liquid level S, the discharge pump 235 is driven, and the level of the liquid level of the cleaning liquid is increased. When the height of the reference liquid level S is lowered, the discharge pump 235 is controlled to stop driving.

In this way, similar to the discharge mechanism 23B and the discharge mechanism 23A (FIG. 6), when the amount of the cleaning liquid in the ultrasonic cleaning tank 21 exceeds a predetermined amount, the cleaning liquid is discharged from the ultrasonic cleaning tank 21 do.

(Ultrasonic irradiation mechanism)

Returning to FIG. 4, the ultrasonic irradiation mechanism 24 irradiates ultrasonic waves into the cleaning liquid in the ultrasonic cleaning tank 21. As the ultrasonic irradiation mechanism 24, a known ultrasonic vibrator, which is generally employed in ultrasonic cleaning, can be used.

The frequency of the ultrasonic waves irradiated by the ultrasonic irradiation mechanism 24 is preferably 20 kHz to 200 kHz. By setting the frequency of the ultrasonic wave to 20 kHz or more, it is possible to prevent large-sized bubbles generated from the surface of the metal tube P from inhibiting the propagation of ultrasonic waves in the cleaning liquid, resulting in deterioration of cleaning properties. By setting the frequency of the ultrasonic wave to 200 kHz or less, the straightness of the ultrasonic wave becomes strong and the uniformity of cleaning can be prevented from deteriorating. The frequency of the ultrasonic wave is more preferably 20 kHz to 150 kHz, and still more preferably 25 kHz to 100 kHz.

It is preferable that the ultrasonic irradiation mechanism 24 has a frequency sweep function. The frequency sweep function is a function of irradiating ultrasonic waves to the cleaning liquid while sweeping a frequency in the range of ±0.1 kHz to ±10 kHz centering on a selected specific frequency. By changing the frequency of the ultrasonic wave by the frequency sweep function, the frequency resonance diameter to be described later fluctuates, and microbubbles contributing to cavitation cleaning can be increased.

When the wavelength of the ultrasonic wave becomes 1/4 of the wavelength corresponding to the thickness of the irradiated object, the ultrasonic wave passes through the irradiated object. By changing the frequency of the ultrasonic wave by the frequency sweep function, it is possible to satisfy the condition that the wavelength of the ultrasonic wave at various positions of the metal pipe P is 1/4 of the wavelength corresponding to the thickness of the metal pipe P. For this reason, it is possible to transmit ultrasonic waves from the outside to the inside of the metal tube P at various positions of the metal tube P.

In this embodiment, on the inner surface of each side wall of the ultrasonic cleaning tank 21, at least one ultrasonic irradiation mechanism 24 is provided. However, the position and number of the ultrasonic irradiation mechanism 24 are not specifically limited. One or more ultrasonic irradiation mechanisms 24 may be provided on the bottom of the ultrasonic cleaning tank 21. When a plurality of ultrasonic irradiation devices 24 are installed in the ultrasonic cleaning tank 21, it is preferable to arrange the ultrasonic irradiation devices 24 so that ultrasonic waves are uniformly propagated throughout the ultrasonic cleaning tank 21. As a result, since the oscillation load of the individual ultrasonic irradiation mechanisms 24 becomes uniform, interference between the generated ultrasonic waves can be prevented.

(Fine bubble generation mechanism)

The fine bubble generation mechanism 25 bubbles the dissolved gas in the cleaning liquid in the ultrasonic cleaning tank 21 to generate fine bubbles. The fine bubble generating mechanism 25 is disposed outside the ultrasonic cleaning tank 21. A plurality of fine bubble generating mechanisms 25 are disposed along one side wall of the ultrasonic cleaning tank 21 in the longitudinal direction. However, the position and number of the fine bubble generating mechanism 25 are not particularly limited.

Each fine bubble generating mechanism 25 includes pipes 251 and 252 and a fine bubble generating device 253. The pipes 251 and 252 connect the ultrasonic cleaning tank 21 and the fine bubble generator 253. The cleaning liquid from the ultrasonic cleaning tank 21 is introduced into the fine bubble generator 253 through a pipe 251. The fine bubble generator 253 generates fine bubbles by using the dissolved gas in the cleaning liquid. The fine bubbles are returned to the ultrasonic cleaning tank 21 through the pipe 252 together with the cleaning liquid.

The fine bubble generating device 253 can be appropriately selected from known fine bubble generating devices. As a known fine bubble generator, for example, by shearing of bubbles, passing through micropores of bubbles, depressurizing (pressure change) of liquid, pressure dissolution of gas, ultrasonic waves, electrolysis, or chemical reaction, It is known to generate fine bubbles. It is preferable that the fine bubble generating device 253 facilitates control of the cell diameter and concentration of the fine bubbles. As the fine bubble generating device 253, for example, a known fine bubble generating device that generates fine bubbles by causing a pressure change of the liquid in the circulation path of the liquid can be employed.

Here, fine bubbles refer to fine bubbles having an average cell diameter of 100 μm or less. In particular, fine bubbles having an average cell diameter of μm size are referred to as microbubbles, and fine bubbles having an average cell diameter of nm size may be referred to as nanobubbles. The average cell diameter is a diameter at which the number of samples becomes the largest in the number distribution with respect to the diameter of fine bubbles.

The average bubble diameter of the fine bubbles in the cleaning liquid is preferably 0.01 μm or more from the viewpoint of preventing the enlargement of the fine bubble generating mechanism 25 and facilitating control of the bubble diameter. Further, the average cell diameter of the fine bubbles is preferably 100 μm or less from the viewpoint of preventing an increase in the floating speed of the fine bubbles and inhibition of propagation of ultrasonic waves to the metal tube P. More preferably, the fine bubbles are microbubbles having an average cell diameter of 1 μm to 50 μm.

It is preferable that at least some of the fine bubbles in the cleaning liquid have a cell diameter equal to or less than the frequency resonance diameter. The frequency resonance diameter refers to a diameter that resonates with the frequency of ultrasonic waves in the cleaning liquid. It is preferable that the fine bubble generating mechanism 25 generates fine bubbles in the cleaning liquid so that the ratio of the number of fine bubbles having a bubble diameter less than or equal to the frequency resonance diameter to the total number of fine bubbles is 70% or more. Considering the existence of bubbles that expand immediately after the fine bubbles are generated, the ratio is more preferably 80% or more and 98% or less. Thereby, the propagation efficiency of ultrasonic waves in the cleaning liquid can be improved.

^{The concentration (density) of fine bubbles in the cleaning liquid is preferably 10 3} particles/mL or more from the viewpoint of improving the propagation property of ultrasonic waves and securing the number of nuclei of ultrasonic cavitation. ^{In addition, the concentration of fine bubbles generated in the cleaning liquid is preferably 10 6} particles/mL or less in order to prevent the fine bubble generating mechanism 25 from being enlarged and increased in number.

The average cell diameter and concentration of fine bubbles can be measured by a known device such as a particle counter in the liquid or a cell diameter distribution measuring device.

(Absence of buffer)

The buffer member 26 is disposed in the ultrasonic cleaning tank 21. The plurality of buffer members 26 are arranged in the longitudinal direction of the ultrasonic cleaning tank 21.

As shown in FIG. 5, the buffer member 26 has a substantially U-shape. The metal pipe P in the ultrasonic cleaning tank 21 is placed on the buffer member 26. The inner surface of the buffer member 26 is located inside the ultrasonic cleaning tank 21 from the ultrasonic irradiation device 24. For this reason, the metal tube P does not come into contact with the ultrasonic irradiation mechanism 24, and the ultrasonic irradiation mechanism 24 is protected from the metal tube P.

[Method of manufacturing metal pipe]

The alkali cleaning device 10 (FIG. 2) and the ultrasonic cleaning device 20 (FIG. 4) are used when cleaning the metal tube P in the manufacture of the metal tube P. Hereinafter, the manufacturing method of the metal tube P is demonstrated. Referring again to FIG. 1, the manufacturing method of the metal tube P includes a preparation step (S1), a lubrication step (S2), a cold drawing step (S3), and a washing step (S4).

(Preparation process)

In the preparation step (S1), an element pipe manufactured by hot working is prepared. At one end of the material pipe, necking is performed for a cold drawing step (S3) to be described later. That is, processing, such as tapping or contraction, is applied to one end of the element pipe so that it becomes thinner compared to other portions.

The element pipe prepared in the preparation step (S1) is, for example, an element pipe made of stainless steel or an element pipe made of Ni-based alloy. The element pipe made of stainless steel is a steel pipe containing 10.5% or more of Cr. When the material pipe is a stainless steel pipe, it is preferable that it is a chemical composition shown below. In terms of mass%, C: 0.01 to 0.13%, Si: 0.75% or less, Mn: 2% or less, P: 0.045% or less, S: 0.030% or less, Ni: 7 to 14%, and Cr: 16 to 20%. And the main balance is Fe (typically, the balance is Fe and impurities). The chemical composition is, instead of a part of Fe in the balance, in mass%, Nb: 0.2 to 1.1%, Ti: 0.1 to 0.6%, Mo: 0.1 to 3%, Cu: 2.5 to 3.5%, any one or 2 It may contain more than a species. Further, instead of a part of Fe in the balance, 0.001 to 0.1% of B and 0.02 to 0.12% of N may be contained in mass%.

In addition, the element tube made of a Ni-based alloy is a tube made of an alloy having the highest Ni content in each component in the alloy. When the material tube is a Ni-based alloy tube, it is, for example, a chemical composition shown below. By mass%, C: 0.05% or less, Si: 0.5% or less, Mn: 1% or less, P: 0.030% or less, S: 0.030% or less, Cr: 19.5 to 24.0%, Mo: 2.5 to 4.0%, Ti: It contains 1.2% or less, and Fe: 22% or more, and the main balance is Ni (typically, the balance is Ni and impurities). The said chemical composition may contain 1 or more types of Cu: 0.5% or less, Nb: 4.5% or less, and Al: 2.0% or less in mass% instead of a part of Ni in the remainder.

(Lubrication process)

An austenitic stainless steel pipe or a material pipe of an Ni-based alloy pipe has excellent strength, while a working load (friction force) during cold drawing is also large. Therefore, after the preparation process (S1), before the cold drawing process (S3), the lubrication process (S2) is performed. This lubricating step S2 includes a chemical conversion film forming step S21 and a lubricating film forming step S22.

(Formation process of chemical conversion film)

In the chemical conversion film forming step S21, a chemical conversion film is formed on the surface of the element pipe. In the chemical conversion film formation step S21, after the scale generated during hot working or the like is removed from the element pipe by a known pickling treatment, the element pipe is immersed in the chemical conversion treatment liquid for a predetermined time. Thereby, a chemical conversion film is formed on the surface of the element pipe.

The chemical conversion treatment liquid used in the chemical conversion film formation step S21 is not particularly limited, but is, for example, an oxalate treatment liquid. In this case, an oxalate film mainly composed of iron (II) oxalate is formed on the surface of the element pipe.

(Lubrication film formation process)

After the chemical conversion film formation step (S21), water washing and neutralization treatment are performed on the element pipe, and the lubricating film formation step (S22) is performed. In the lubricating film forming step S22, a lubricating film is formed on the chemical conversion film formed in the element pipe in the chemical conversion film forming step S21. In the lubricating film forming step S22, the element pipe on which the chemical conversion film was formed is immersed in the lubricating liquid for a predetermined time. After that, the material pipe is taken out from the lubricating liquid and dried sufficiently. Thereby, a lubricating film is formed on the chemical conversion film.

As the lubricating liquid, a higher fatty acid salt (soap) can be used. In this case, the lubricating liquid reacts with the chemical conversion film to form a metallic soap. That is, the lubricating film includes a metal soap layer on the chemical conversion film and a soap layer on the metal soap layer. For example, when the chemical conversion film is an oxalate film and the lubricating liquid is sodium stearate, the main component of the metal soap layer is iron stearate, and the main component of the soap layer is sodium stearate.

(Cold drawing process)

After forming the chemical conversion film and the lubricating film on the material pipe by the lubricating step S2, a cold drawing step S3 is performed. In the cold drawing step (S3), the element pipe is formed into a metal pipe having a predetermined size by performing a known cold drawing process on the element pipe. For example, the end of the material pipe on which the necking process has been performed is passed through a die (approximately shown) and held by a gripper (approximately shown), and the material tube is drawn out from the die by moving the gripper. Thereby, the outer diameter of the material pipe is finished to a predetermined outer diameter. In the case of adjusting the thickness of the element pipe, drawing is performed while the mandrel is inserted into the element pipe.

(Washing process)

The metal tube of a predetermined size obtained through the cold drawing step (S3) is cleaned in the cleaning step (S4) in order to remove the chemical conversion film and the lubricating film. The cleaning process S4 includes an alkali cleaning process S41 and an ultrasonic cleaning process S42.

(Alkaline cleaning process)

Referring again to FIGS. 2 and 3, the alkali cleaning step S41 is a step of immersing the metal pipe P in the alkali degreasing liquid in the alkali cleaning tank 11 in the alkali cleaning device 10. In the alkali cleaning process S41, first, the metal pipe P is arrange|positioned in the tank main body 111. Usually, a plurality of metal pipes P are arranged in the bath main body 111, but one metal pipe P may be arranged in the bath main body 111. The metal pipe P is disposed in the alkali washing tank 11 by a crane or the like. Specifically, the metal tube P is mounted on the support member 113. Thereby, a gap is created between the metal tube P and the bottom surface 111a of the tank main body 111.

The alkali degreasing liquid is not supplied to the tank body 111 at the time when the metal pipe P is arranged in the tank body 111. After the metal tube P is accommodated in the empty bath main body 111, the upper surface of the bath main body 111 is covered with a cover 112.

Subsequently, the alkaline degreasing liquid from the storage tank 12 is supplied to the alkaline cleaning tank 11 through the circulation pipe 13. The alkaline degreasing liquid in the storage tank 12 is sent to the upper alkaline cleaning tank 11 by driving the pump 131. The alkaline degreasing liquid flows into the tank main body 111 from the end 111c side, and flows to the end 111d side. The alkali degreasing liquid passes through the inside of the metal tube P, between the metal tube P and the bottom surface 111a, between the metal tube P and the peripheral wall 111b, and the like.

While supplying the alkali degreasing liquid to the tank main body 111, the communication port 14 near the end portion 111d on the downstream side is in a closed state. Therefore, the alkali degreasing liquid is stored in the tank main body 111.

In the storage tank 12, an alkali degreasing liquid that has not been heated at a high temperature is stored. For this reason, the alkali degreasing liquid which has not been heated at high temperature is supplied to the bath main body 111. Here, the alkaline degreasing liquid that is not heated at a high temperature means, as described above, typically, an alkaline cleaning device that does not actively heat the alkaline degreasing liquid using a heater (for example, a steam heater or an electric heater) or the like. It refers to the alkaline degreasing liquid at the liquid temperature according to the ambient temperature in (10). However, for example, in the winter season where the temperature is low, when the ambient temperature of the alkali cleaning device 10 is lowered and the temperature of the alkali degreasing liquid is lowered to less than 20°C, the liquid temperature may be about 20°C to 40°C. , Alkaline degreasing liquid can be heated. However, even in the winter season where the temperature is low, the temperature of the alkali degreasing liquid is usually 20°C or higher due to the heat generated by the pump 131 that sends the alkaline degreasing liquid from the storage tank 12 to the alkaline cleaning tank 11. . On the other hand, in summer when the temperature is high, the temperature of the alkaline degreasing liquid may exceed 40°C. In such a case, it is not necessary to cool the alkaline degreasing liquid to 40°C or less. Energy saving (low cost) and good cleaning performance, even if the temperature of the alkali degreasing solution naturally becomes high (temperature higher than 40°C) without active heat treatment (without consuming energy for heating with respect to the alkaline degreasing solution). This is because both sides can be realized. In addition, when the alkali degreasing liquid is not subjected to an aggressive heat treatment, there is no particular upper limit on the temperature of the alkaline degreasing liquid, but it is generally considered that the temperature at which the alkali degreasing liquid is not actively heated is only about 60°C. As described above, in the tank main body 111 (alkali cleaning tank 11), typically, an alkali degreasing liquid having a temperature corresponding to the ambient temperature of the alkali cleaning device 10 (that is, an alkali degreasing liquid not subjected to heat treatment) Is supplied and stored. However, when the temperature of the alkali degreasing liquid is lowered to less than 20°C, the alkaline degreasing liquid heated to 40°C or less is supplied to the tank body 111 (alkali washing tank 11) and stored.

When the alkali cleaning tank 11 is filled with an alkali degreasing liquid that has not been heated at a high temperature, the supply of the alkali degreasing liquid to the tank main body 111 is stopped. The metal pipe P is held for a predetermined time in an alkali degreasing liquid that has not been heated at a high temperature filled in the alkali cleaning tank 11. The time to hold the metal tube P may be appropriately determined, but is, for example, 1 to 5 minutes.

Next, the communication port 14 is opened, and the alkali degreasing liquid is discharged from the tank main body 111 to the storage tank 12. Thereby, in the tank main body 111, the alkali degreasing liquid flows from the end 111c side toward the end 111d side. The alkali degreasing liquid passes inside and around the metal pipe P. All of the alkaline degreasing liquid in the tank main body 111 is recovered in the storage tank 12.

Supply of an alkali degreasing liquid from the storage tank 12 to the alkali cleaning tank 11, maintenance of the metal pipe P in the alkali cleaning liquid, and discharge of the alkali degreasing liquid from the alkali cleaning tank 11 to the storage tank 12 With 1 cycle, this cycle is carried out a predetermined number of times. As the number of times the cycle is performed increases, the cleaning property is also improved, but it is preferable to determine the number of implementations in consideration of the balance of cleaning properties and operability. The number of times the cycle is performed can be, for example, 2 to 5 times. The time required per cycle varies depending on the capacity of the alkaline cleaning tank 11 and the like, but can be, for example, about 5 to 15 minutes.

After carrying out the said cycle a predetermined number of times, the lid 112 is removed from the tank body 111, and the metal pipe P is pulled up from the tank body 111 using a crane or the like. Thereby, the alkali cleaning process (S41) is ended.

In the alkali cleaning step (S41), it is preferable to generate a flow of the alkali degreasing liquid in the alkali cleaning tank (11). Thereby, in addition to the chemical action of the alkali degreasing liquid itself, alkali cleaning of the metal pipe P can be performed by a physical action by the flow of the alkaline degreasing liquid. In the present embodiment, in the process of supplying and discharging the alkaline degreasing liquid, a flow of the alkaline degreasing liquid occurs in the alkaline cleaning tank 11. In the present embodiment, when the alkaline degreasing liquid is filled in the alkaline cleaning tank 11, the flow of the alkaline degreasing liquid is temporarily stopped, but the alkaline degreasing liquid may continue to flow in the alkaline cleaning tank 11. However, it is also possible to perform the alkaline cleaning step (S41) in a state in which the alkaline degreasing liquid is always stopped without generating a flow of the alkali degreasing liquid in the alkaline cleaning tank 11.

(Ultrasonic cleaning process)

After the alkali cleaning process S41 is performed, the ultrasonic cleaning process S42 is performed. The ultrasonic cleaning step S42 is a step of immersing the metal pipe P after being immersed in an alkaline degreasing liquid in a cleaning liquid to which ultrasonic waves and fine bubbles have been applied. In the ultrasonic cleaning process S42, the ultrasonic cleaning apparatus 20 (FIG. 4) which is an apparatus different from the alkaline cleaning apparatus 10 (FIG. 2) used in the alkali cleaning process S41 is used. That is, after the alkali cleaning process S41 is finished, the metal pipe P is transferred from the alkali cleaning device 10 to the ultrasonic cleaning device 20. The metal pipe P after the alkali cleaning process S41 may be washed with water before the ultrasonic cleaning process S42. Thereby, the alkali degreasing liquid adhering to the metal pipe P can be washed off.

Referring again to FIG. 4, prior to the ultrasonic cleaning of the metal tube P, the cleaning liquid is stored in the ultrasonic cleaning tank 21. The cleaning liquid is supplied to the ultrasonic cleaning tank 21 by the supply mechanism 22. However, in the step of supplying the cleaning liquid to the empty ultrasonic cleaning tank 21, the cleaning liquid may be supplied to the ultrasonic cleaning tank 21 by means other than the supply mechanism 22. It is preferable that the cleaning liquid supplied to the ultrasonic cleaning tank 21 has a dissolved oxygen concentration of about 7 mg/L to 11 mg/L. The washing liquid is typically water (tap water or industrial water). When the washing solution is water (tap water or industrial water) with a water temperature of 10 to 35°C, the dissolved oxygen concentration of the washing solution is 7 mg/L to 11 mg/L. It is more preferable that the cleaning liquid supplied to the ultrasonic cleaning tank 21 has a dissolved oxygen concentration of about 8 mg/L to 10 mg/L. When the washing liquid is water (tap water or industrial water) having a water temperature of 15 to 25°C, the dissolved oxygen concentration of the washing liquid is 8 mg/L to 10 mg/L. The dissolved oxygen concentration becomes an index of the amount of dissolved gas in the washing liquid.

When the liquid level of the cleaning liquid in the ultrasonic cleaning tank 21 exceeds the reference liquid level S (FIG. 6 or 7), the discharging of the cleaning liquid by the discharging mechanism 23 is started. The supply mechanism 22 continuously supplies the cleaning liquid to the ultrasonic cleaning tank 21 even after the liquid level of the cleaning liquid reaches the reference liquid level S. Thereby, in the ultrasonic cleaning tank 21, the cleaning liquid is discharged simultaneously with the supply of the cleaning liquid. The discharge amount of the cleaning liquid at this time is substantially the same as the supply amount of the cleaning liquid.

The metal pipe P transferred from the alkaline cleaning device 10 (FIGS. 2 and 3) to the ultrasonic cleaning device 20 is immersed in the cleaning liquid stored in the ultrasonic cleaning tank 21 for a predetermined time. The metal pipe P can be immersed in the cleaning liquid in the ultrasonic cleaning tank 21 using a crane or the like. Usually, a plurality of metal pipes P are immersed in the cleaning liquid at the same time, but the metal pipes P may be immersed in the cleaning liquid one by one.

While the metal pipe P is immersed in the cleaning liquid, a new cleaning liquid is continuously supplied to the ultrasonic cleaning tank 21 by the supply mechanism 22. This washing liquid is typically water (tap water or industrial water). On the other hand, the cleaning liquid exceeding the reference liquid level S is continuously discharged from the ultrasonic cleaning tank 21 by the discharge mechanism 23. Thereby, a decrease in cleaning power due to excessive contamination of the cleaning liquid in the ultrasonic cleaning tank 21 can be suppressed. The amount (per unit time) of the cleaning liquid supplied by the supply mechanism 22 to the ultrasonic cleaning tank 21 can be determined in consideration of the storage amount of the cleaning liquid in the ultrasonic cleaning tank 21 and the degree of contamination of the cleaning liquid. The cleaning liquid discharged from the ultrasonic cleaning tank 21 by the discharge mechanism 23 is discarded through a predetermined drainage treatment.

Further, while the metal tube P is immersed in the cleaning liquid, ultrasonic waves are irradiated to the cleaning liquid by the ultrasonic irradiation mechanism 24, and fine bubbles are supplied by the fine bubble generation mechanism 25.

In the ultrasonic cleaning step S42, the fine bubble generating mechanism 25 bubbles the dissolved gas in the cleaning liquid, so that the dissolved oxygen concentration in the cleaning liquid is lowered. The fine bubble generating mechanism 25 reduces the dissolved oxygen concentration of the cleaning liquid in the ultrasonic cleaning tank 21 to 5.2 mg/L or less. The fine bubble generating mechanism 25 lowers the dissolved oxygen concentration of the cleaning liquid in the ultrasonic cleaning tank 21 to more preferably 4.5 mg/L or less, further preferably 4.2 mg/L or less.

Specifically, the supply mechanism 22 supplies a cleaning liquid having a dissolved oxygen concentration of about 7 mg/L to 11 mg/L, preferably about 8 mg/L to 10 mg/L to the ultrasonic cleaning tank 21. When this cleaning liquid passes through the fine bubble generation device 253 of the fine bubble generation mechanism 25, the dissolved gas in the cleaning liquid is finely bubbled, and the dissolved oxygen concentration of the cleaning liquid is lowered. By circulating the cleaning liquid between the ultrasonic cleaning tank 21 and the fine bubble generating mechanism 25, the dissolved oxygen concentration of the cleaning liquid in the ultrasonic cleaning tank 21 is 5.2 mg/L or less, more preferably 4.5 mg/L or less. , More preferably 4.2 mg/L or less. This makes it possible to ensure good cleaning properties in a wide range of ultrasonic sound pressures. Under such a dissolved oxygen concentration, in order to ensure good cleaning properties, the sound pressure of ultrasonic waves is preferably 120 mV or higher.

In addition, the dissolved oxygen concentration of the cleaning liquid in the ultrasonic cleaning tank 21 is usually 2.0 mg/L or more. However, the lower limit of the dissolved oxygen concentration of the cleaning liquid in the ultrasonic cleaning tank 21 does not need to be particularly managed or controlled.

The dissolved oxygen concentration [mg/L] is a value measured with a commercially available dissolved oxygen concentration meter (manufactured by Horiba Corporation, LAQUA OM-71). Sound pressure [mV] is a measurement mode in which an average measured value for 5 seconds is measured using a commercially available ultrasonic sound pressure meter (Kaijo-made sound pressure level monitor type 19001D). Probe (vibration transmission rod with piezoelectric element) Is the value when measured by placing it in water 100 mm from the liquid level of the cleaning solution. These measured values are taken as dissolved oxygen concentration and negative pressure in the present disclosure, respectively.

After holding the metal pipe P in the cleaning liquid in the ultrasonic cleaning tank 21 for a while, the metal pipe P is pulled up from the ultrasonic cleaning tank 21. In the ultrasonic cleaning step S42, the arrangement of the metal pipe P into the ultrasonic cleaning tank 21, the holding of the metal pipe P in the cleaning liquid, and the lifting of the metal pipe P from the ultrasonic cleaning tank 21 are performed. As one cycle, this cycle is carried out a predetermined number of times. The holding time of the metal tube P in the said cycle and the number of times the cycle is performed can be determined so that the total immersion time of the metal tube P in the cleaning liquid becomes a predetermined time or longer. The total immersion time of the metal tube P may be appropriately set depending on the amount of the film attached to the metal tube P, and the like. The total immersion time of the metal tube P is, for example, 30 seconds or longer, and more preferably 1 minute or longer.

When the metal tube P is pulled up from the ultrasonic cleaning tank 21, it is preferable to incline the metal tube P with respect to the horizontal plane. Thereby, the liquid in the metal tube P can be removed. In the case of performing the cycle a plurality of times, it is preferable to change the tilting direction for each cycle.

When the metal pipe P is immersed in the cleaning liquid for more than a predetermined total immersion time, the metal pipe P is recovered from the ultrasonic cleaning tank 21 using a crane or the like. Also at this time, it is preferable to raise the metal tube P while tilting it. Thereby, it is possible to prevent the cleaning liquid from remaining inside the metal tube P.

By recovering the metal tube P, the ultrasonic cleaning process S42 is completed. Subsequently, in the ultrasonic cleaning tank 21, ultrasonic waves and fine bubbles are applied to the cleaning liquid, and the cleaning liquid is supplied and discharged. For this reason, it is possible to subsequently perform ultrasonic cleaning of the other metal tube P.

When the ultrasonic cleaning of the metal tube P is continuously performed, an alkali degreasing liquid or water that does not contain fine bubbles is introduced into the ultrasonic cleaning tank 21, so that the inside of the ultrasonic cleaning tank 21 There is a possibility that the dissolved oxygen concentration in the cleaning liquid will increase. When the dissolved oxygen concentration of the cleaning liquid increases, it is preferable to stop the ultrasonic cleaning of the metal tube P until the fine bubble generating mechanism 25 sufficiently lowers the dissolved oxygen concentration. When the dissolved oxygen concentration of the cleaning liquid becomes 5.2 mg/L or less, 4.5 mg/L or less, or 4.2 mg/L or less, ultrasonic cleaning of the metal tube P after the alkaline cleaning step S41 may be restarted.

In this embodiment, after storing the cleaning liquid in the ultrasonic cleaning tank 21, the metal pipe P is arrange|positioned in the ultrasonic cleaning tank 21. However, after arranging the metal tube P in the empty ultrasonic cleaning tank 21, the cleaning liquid may be stored in the ultrasonic cleaning tank 21.

[Effect of embodiment]

In the present embodiment, the metal pipe P after cold drawing is immersed in an alkali degreasing liquid that has not been heated at a high temperature, and then immersed in a cleaning liquid to which ultrasonic waves and fine bubbles have been applied. Thereby, the chemical conversion film and the lubricating film formed on the metal tube P can be removed without using a high-temperature alkaline degreasing liquid.

Hereinafter, the action of the cleaning step S4 in the method for manufacturing the metal tube P of the present embodiment will be described with reference to FIGS. 8A to 8C. 8A is a diagram schematically showing the surface of the metal tube P after cold drawing. 8B is a diagram schematically showing the surface of the metal tube P after the alkali washing step S41. 8C is a diagram schematically showing the surface of the metal tube P in the ultrasonic cleaning step S42.

As shown in FIG. 8A, on the surface of the metal tube P after cold drawing, a chemical conversion film 31 is formed. On the chemical conversion film 31, a lubricating film 32 is formed. The lubricating film 32 includes a metal soap layer 321 and a soap layer 322. For example, as the chemical conversion film 31, the iron (II) oxalate film is 1 to 100 μm, preferably 5 to 40 μm, and as the lubricating film 32, a metal soap (iron stearate) layer 321 and soap (sodium stearate) ) The layers 322 are combined to form 10 to 1000 μm, preferably 50 to 200 μm.

In the metal tube P after cold drawing, cracks are generated in the chemical conversion film 31. This is considered to be because the chemical conversion film 31 has a very small ductility, and thus the chemical conversion film 31 does not stretch and breaks during cold drawing. On the other hand, the lubricating film 32 increases due to heat generation during cold drawing, and covers the chemical conversion film 31 in which cracks have occurred.

As shown in FIG. 8B, when the metal tube P after cold drawing is immersed in an alkali degreasing liquid that has not been heated at a high temperature, the lubricating film 32 covering the chemical conversion film 31 is partially removed. Specifically, a part of the metal soap layer 321 reacts with the alkaline degreasing liquid to form a complex, and a part of the soap layer 322 is dissolved in the alkaline degreasing liquid. Thereby, after the alkali washing step S41, in the metal tube P, a part of the lubricating film 32 is in a state where it is missing.

When ultrasonic cleaning is performed on the metal pipe P from which the lubricating film 32 has been partially removed, as shown in Fig. 8C, the lubricating film 32 is peeled from the metal pipe P starting from the defective portion. When the lubricating film 32 covering the chemical conversion film 31 is peeled off, the chemical conversion film 31 is also peeled from the metal tube P based on a crack generated during cold drawing. The chemical conversion film 31 and the lubricating film 32 are peeled off from the metal tube P by a physical action such as ultrasonic cavitation.

As described above, according to the cleaning step (S4) in the method for manufacturing the metal tube P of the present embodiment, the chemical conversion film 31 and the chemical conversion film 31 from the metal tube P after cold drawing, without using a high-temperature alkaline degreasing liquid. The lubricating film 32 can be removed. Therefore, energy saving (low cost) and good cleaning properties can be realized.

Since the chemical conversion film 31 is bonded to the material of the metal tube P by chemical bonding, it has conventionally been required to be removed from the metal tube P by pickling treatment. That is, after removing the lubricating film 32 from the metal pipe P with a high-temperature alkaline degreasing liquid, it was necessary to pickle the metal pipe P in order to remove the chemical conversion film 31. However, according to the cleaning method according to the present embodiment, in addition to the lubricating film 32, the chemical conversion film 31 can also be removed by only alkaline cleaning and ultrasonic cleaning. Therefore, the pickling treatment for removing the chemical conversion film 31 becomes unnecessary, and the cleaning process of the metal tube P can be simplified.

In this embodiment, fine bubbles are generated in the cleaning liquid in the ultrasonic cleaning step (S42). Thereby, ultrasonic waves in the cleaning liquid can be scattered and propagated in three dimensions. For this reason, the cleaning property of the metal tube P is improved. In addition, in the ultrasonic cleaning step (S42), the dissolved oxygen concentration in the cleaning liquid is 5.2 mg/L or less, more preferably 4.5 mg/L or less, and still more preferably 4.2 mg/L, as the dissolved gas in the cleaning liquid is finely bubbled. It becomes L or less. Therefore, it is possible to ensure good ultrasonic cleaning properties in a wide range of negative pressures.

As mentioned above, although the embodiment according to the present disclosure has been described, the present disclosure is not limited to the above embodiment, and various modifications can be made without departing from the spirit thereof.

For example, according to the above embodiment, it is possible to omit the pickling treatment for removing the chemical conversion film 31, but the pickling treatment may not be excluded, and the pickling treatment may be performed after ultrasonic cleaning. When the metal pipe P after cleaning is pulled up from the ultrasonic cleaning tank 21, there is a possibility that dust floating in the ultrasonic cleaning tank 21 (a part of the film removed by cleaning, etc.) will adhere to the metal pipe P. have. In this way, in order to remove contamination that may be re-adhered to the surface of the metal tube, pickling may be performed. In addition, even in this case, it is possible to remove the contamination on the surface of the metal tube by a shorter time than the conventional pickling treatment.

<Example>

Hereinafter, the present disclosure will be described in more detail by examples. However, the present disclosure is not limited to the following examples.

[Example]

In order to confirm the cleaning effect of the metal tube according to the present disclosure, a cleaning test of the metal tube P after cold drawing using the alkali cleaning device 10 shown in FIG. 2 and the ultrasonic cleaning device 20 shown in FIG. 4 Carried out. That is, in the alkaline cleaning device 10, after performing an alkali cleaning process with an alkali degreasing liquid that has not been heated at a high temperature, in the ultrasonic cleaning device 20, an ultrasonic cleaning process using a cleaning liquid provided with ultrasonic waves and fine bubbles is performed. Carried out. In this embodiment, the temperature of the alkaline degreasing liquid used in the alkaline cleaning process is a temperature according to the ambient temperature of the alkali cleaning device 10, and specifically, about 25°C. In this example, after performing the alkali cleaning process, before performing the ultrasonic cleaning process, the metal tube P was washed with water.

[Comparative Example 1]

As Comparative Example 1, an alkali washing step with a high temperature alkaline degreasing liquid was performed on the metal pipe P after cold drawing. After the high-temperature alkali washing step, the metal pipe P was washed with water. Also in Comparative Example 1, the same alkaline cleaning apparatus 10 as in the Example was used. In Comparative Example 1, the ultrasonic cleaning process after the alkali cleaning treatment was not performed.

[Comparative Example 2]

As Comparative Example 2, a cleaning process (ultrasonic cleaning process) with a cleaning liquid to which ultrasonic waves and fine bubbles were applied was performed on the metal tube P after cold drawing. In Comparative Example 2, the alkaline cleaning step before the ultrasonic cleaning step was not performed.

[Exam conditions]

In Examples, Comparative Example 1, and Comparative Example 2, 20 metal tubes P were used, respectively. The chemical composition of the metal tube (P) is mass%, C: 0.08%, Si: 0.2%, Mn: 0.8%, Cu: 3.0%, Ni: 8.8%, Cr: 18.5%, Nb: 0.5%, the balance: Fe and impurities. The dimensions of the metal tube P are: outer diameter: 50.8 mm, thickness: 7.2 mm, and length: 8000 mm. On the surface of the metal tube P, an iron (II) oxalate film is 10 μm as a chemical conversion film 31, and a metal soap (iron stearate) layer 321 and a soap (iron stearate) layer 321 and soap ( Sodium stearate) layers 322 were combined to form 100 μm. Other test conditions are shown in Table 1.

In Table 1, the flow cycle for 10 minutes refers to the supply of the alkali degreasing liquid to the alkaline cleaning tank 11, the maintenance of the metal pipe P in the alkali cleaning liquid, and the alkali cleaning liquid from the alkali cleaning tank 11. It means that the cycle consisting of discharge was carried out over 10 minutes. In Examples and Comparative Example 1, in the alkaline washing step, the flow cycle for 10 minutes was repeated three times.

[evaluation]

About each of Examples, Comparative Example 1, and Comparative Example 2, the cleaning property of the metal tube P was evaluated. 9 is a graph showing changes in the amount of carbon (C) adhering to the inner surface of the metal tube P [mg/m ^{2] with respect to Examples, Comparative Example 1, and Comparative Example 2. FIG.} The amount of carbon was measured using a commercially available measuring device (manufactured by LECO Japan Co., Ltd., type-specific carbon/hydrogen/moisture analyzer model RC612).

As shown in Fig. 9, in the case of Comparative Example 2 in which only ultrasonic cleaning was performed, the amount of carbon hardly decreased from before cleaning. Therefore, it is understood that the chemical conversion film and the lubricating film cannot be removed from the metal tube P only by ultrasonic cleaning.

In the case of Comparative Example 1, the amount of carbon was reduced by performing alkaline cleaning with a high-temperature alkaline degreasing liquid. This indicates that most of the lubricating film could be removed by alkaline cleaning with a high-temperature alkaline degreasing liquid. However, it is considered that the chemical conversion coating has not been removed, and a part of the lubricating coating remains as described later. For this reason, it is necessary to pickle the metal pipe P after high-temperature alkali washing to remove residual soap component and chemical conversion film.

In Examples, by performing alkaline cleaning with an alkaline degreasing liquid at about 25° C., the amount of carbon is slightly reduced from before cleaning. This is because, as described with reference to Fig. 8B, the lubricating film covering the chemical conversion film has been partially removed. The carbon amount of the example at the stage in which the alkali cleaning with the alkali degreasing liquid at about 25°C was completed was greater than the carbon amount after the high-temperature alkali cleaning in Comparative Example 1. This is considered to be because the lubricating film can only be partially removed in the alkaline cleaning with an alkaline degreasing liquid at about 25°C. However, after that, by performing ultrasonic cleaning, the amount of carbon decreases to a greater extent than in the case of Comparative Example 1 (up to several tens of mg/m ^{2 ).} In the case of Comparative Example 1, since most of the lubricating film is considered to have been removed, even if it is alkaline cleaning with an alkaline degreasing liquid at a low temperature such as about 25°C, ultrasonic cleaning is performed after that, so that only the lubricating film from the metal pipe P is removed. In addition, it can be seen that the chemical conversion film can also be removed. In the case of the Example, unlike Comparative Example 1, it is possible to omit the subsequent pickling treatment. Further, in order to more reliably remove the chemical conversion film, a pickling treatment may be performed.

10 is a scanning electron microscope (SEM) image of the inner surface of each metal tube P cleaned by the cleaning method of Example and Comparative Example 1. FIG. As shown in FIG. 10, in the metal pipe P cleaned by the cleaning method of Comparative Example 1, a white residual soap component was confirmed. That is, in Comparative Example 1, the lubricating film has been substantially removed from the metal pipe P after washing, but it is understood that some remain. On the other hand, in the metal pipe P cleaned by the cleaning method of the embodiment, no residual soap component was observed. Therefore, in the embodiment, the lubricating film is removed from the metal pipe P after washing. In addition, as shown in Fig. 9, in the case of the example, since the amount of carbon after washing is significantly reduced compared to Comparative Example 1, it can be said that not only the lubricating film but also the chemical conversion film is removed from the metal tube P.

From the above, it was confirmed that, after performing alkaline cleaning with an alkaline degreasing liquid that has not been heated at a high temperature, good cleaning properties can be obtained by performing cleaning using a combination of ultrasonic waves and fine bubbles.

10: alkaline cleaning device 11: alkaline cleaning tank
20: ultrasonic cleaning device 21: ultrasonic cleaning tank
P: metal tube

Claims (4)

As a method of manufacturing a metal tube,
A preparation process for preparing a metal tube,
A lubricating step of forming a chemical conversion film on the surface of the material pipe and forming a lubricating film on the chemical conversion film,
A cold drawing step of performing a cold drawing process on the element pipe on which the chemical conversion film and the lubricating film are formed to form a metal tube having a predetermined size; and
Cleaning process of removing the chemical conversion film and the lubricating film by cleaning the metal pipe
And,
The cleaning process,
A step of immersing the metal pipe in an alkaline degreasing liquid that has not been heated at a high temperature in an alkaline cleaning tank, and
A step of immersing the metal pipe after immersion in the alkaline degreasing liquid while irradiating ultrasonic waves into the cleaning liquid in the ultrasonic cleaning tank and generating fine bubbles in the cleaning liquid.
Containing, the manufacturing method. The method according to claim 1,
While the metal tube is immersed in the cleaning liquid, the dissolved oxygen concentration of the cleaning liquid is 5.2 mg/L or less. A method for cleaning metal pipes formed by performing cold drawing processing on an element pipe having a chemical conversion film and a lubricating film formed on the surface thereof,
A step of immersing the metal pipe in an alkaline degreasing liquid that has not been heated at a high temperature in an alkaline cleaning tank, and
A step of immersing the metal pipe after immersion in the alkaline degreasing liquid while irradiating ultrasonic waves into the cleaning liquid in the ultrasonic cleaning tank and generating fine bubbles in the cleaning liquid.
A cleaning method comprising a. The method of claim 3,
While the metal tube is immersed in the cleaning liquid, the dissolved oxygen concentration of the cleaning liquid is 5.2 mg/L or less.

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