JP7157168B2 - METHOD OF MANUFACTURING AND CLEANING METAL PIPE - Google Patents

Description

TECHNICAL FIELD The present disclosure relates to a method for manufacturing and cleaning a metal tube. The present disclosure particularly relates to a method for cleaning a metal pipe formed by cold drawing a blank pipe 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 tube, a large frictional force is generated between the metal tube and the drawing tool. In order to reduce this frictional force, lubricating treatment is applied to the mother tube prior to cold drawing.

In the lubrication treatment before cold drawing, a chemical conversion coating such as a phosphate coating, an oxalate coating, or a chromate coating is formed on the surface of the blank pipe. A lubricating film is formed on the chemical conversion film with a higher fatty acid salt (soap) or the like. The chemical conversion coating prevents direct contact between the blank tube and the drawing tool to improve seizure resistance, and also enhances the adhesion between the blank tube and the lubricating coating to improve lubricity.

After the blank pipe is finished 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 strongly associated with the material of the metal tube. Therefore, it is difficult to remove each coating from the metal tube.

A cleaning method using ultrasonic waves is known as one of the methods for cleaning metal materials and the like. For example, Patent Literature 1 discloses a method of pickling a plurality of metal tubes by rubbing them together in an acid solution and irradiating ultrasonic waves to the ends of the tubes. According to Patent Literature 1, scales are removed from portions of the metal pipes that are rubbed against each other by the friction-reducing effect of the rubbing and the dissolution effect of the acid solution. At the tube ends where rubbing does not occur, the ultrasonic waves accelerate the dissolving action of the acid solution, thereby removing the scale.

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

Patent Literature 3 discloses a cleaning device that uses both ultrasonic waves and microbubbles. In the cleaning apparatus, the cleaning liquid in the cleaning tank is irradiated with ultrasonic waves from the ultrasonic generator. A circulation path is connected to the cleaning tank. The cleaning liquid in the cleaning tank is introduced into the degassing device through the circulation path. The deaerator separates dissolved air from the cleaning liquid to generate microbubbles. The microbubbles are supplied to the cleaning tank through the circulation path and reduce the dissolved air concentration of the cleaning liquid. According to Patent Document 3, by setting the dissolved air concentration of the cleaning liquid to a specified value or less, the sound pressure of ultrasonic waves does not decrease, and efficient and good cleaning can be performed.

JP-A-3-177590 JP-A-2000-256886 JP 2007-29944 A

As described above, after cold drawing, it is necessary to clean the metal tube to remove the chemical conversion coating and the lubricating coating. Adhesion between the chemical conversion coating and the lubricating coating and the metal pipe is very high. For this reason, it is difficult to reliably remove each film from the metal pipe by simply using the method or apparatus of each patent document in cleaning the metal pipe after cold drawing.

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

An object of the present disclosure is to realize both energy saving (low cost) and good detergency in cleaning metal pipes having chemical conversion coatings and lubricating coatings formed on their surfaces.

A method for manufacturing a metal pipe according to the present disclosure includes a preparation step of preparing a metal base pipe, a lubrication step of forming a chemical conversion film on the surface of the base pipe, forming a lubricating film on the chemical conversion film, A cold drawing step of cold drawing the blank pipe on which the lubricating film is formed and forming it into a metal pipe of a predetermined size, a washing step of washing the metal pipe to remove the chemical conversion film and the lubricating film, Prepare. The cleaning process includes a step of immersing the metal pipe in an alkaline degreasing solution that is not heated to a high temperature in an alkaline cleaning tank, and a step of irradiating ultrasonic waves into the cleaning solution in an ultrasonic cleaning tank while generating fine bubbles in the cleaning solution. and a step of immersing the metal tube in the cleaning liquid after being immersed in the alkaline degreasing liquid.

According to the present disclosure, both energy saving (low cost) and good detergency can be achieved in cleaning a metal pipe having a chemical conversion film and a lubricating film formed on the surface.

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

A method for manufacturing a metal pipe according to an embodiment includes a preparation step of preparing a metal pipe, a lubrication step of forming a chemical conversion film on the surface of the metal pipe, forming a lubricating film on the chemical conversion film, a chemical conversion film and A cold drawing step of cold drawing the blank pipe on which the lubricating film is formed and forming it into a metal pipe of a predetermined size, a washing step of washing the metal pipe to remove the chemical conversion film and the lubricating film, Prepare. The cleaning process includes a step of immersing the metal pipe in an alkaline degreasing solution that is not heated to a high temperature in an alkaline cleaning tank, and a step of irradiating ultrasonic waves into the cleaning solution in an ultrasonic cleaning tank while generating fine bubbles in the cleaning solution. and a step of immersing the metal tube in the cleaning liquid after being immersed in the alkaline degreasing liquid.

In the method for manufacturing a metal pipe according to the above embodiment, after the lubricating film and the chemical conversion film as the base film for the lubricating film are formed on the blank pipe, the blank pipe is formed into a metal pipe of a predetermined size by cold drawing. do. A metal tube obtained by cold drawing is cleaned (alkaline degreasing) by the following method. That is, the metal pipe is first immersed in an alkaline degreasing liquid that has not been heated to a high temperature. The alkaline degreasing liquid that is not heated to a high temperature in the present disclosure is typically an alkaline degreasing liquid that does not undergo active heat treatment using a heater (for example, a steam heater or an electric heater) for the alkaline degreasing liquid. Alkaline degreasing liquid with a natural liquid temperature corresponding to the ambient temperature around the equipment (air temperature and temperature inside the factory building). In this case, the energy used (consumed) for heating the alkaline degreasing liquid becomes unnecessary. However, when the temperature of the alkaline degreasing liquid is lower than 20.degree. C., the alkaline degreasing liquid is heated to a temperature of about 20.degree. For example, in winter when the air temperature is low, the temperature of the alkaline degreasing liquid may drop below 20°C. In such a case, a positive heat treatment is performed so that the liquid temperature is about 20 to 40.degree. In this case, energy is used for heating the alkaline degreasing liquid, but since there is no need to heat to a high temperature (70° C. or higher) as in the conventional case, the amount of energy used can be reduced.

Immersion in such an alkaline degreasing solution that has not been heated to a high temperature causes complex formation and dissolution in a part of the lubricating film, thereby partially removing the lubricating film from the surface of the metal pipe. Next, the metal pipe is immersed in a cleaning liquid to which ultrasonic waves and fine bubbles are applied. Since the lubricating film on the surface of the metal pipe is partially deficient due to the alkaline degreasing treatment, it can be peeled off from the metal pipe by physical action such as ultrasonic cavitation.

The temperature of the alkaline degreasing solution may be affected by the heat of reaction during the cleaning process or by circulating the alkaline degreasing solution in the cleaning apparatus. This is not included in the active heat treatment described above.

The ductility of the conversion coating is very small. For this reason, it is thought that cracks occur in the chemical conversion film on the metal pipe when cold drawing is applied to the metal pipe. Therefore, by immersing a metal pipe in a cleaning solution to which ultrasonic waves and fine bubbles are imparted and applying a physical action such as ultrasonic cavitation to the metal pipe, the chemical conversion film can also be peeled off from the metal pipe.

As described above, according to the manufacturing method according to the embodiment, when removing each film from the metal pipe, it is not necessary to heat the alkaline degreasing liquid to a high temperature of 70° C. or higher as in the conventional art. Therefore, both energy saving (low cost) and good washability can be realized.

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

By setting the dissolved oxygen concentration of the cleaning liquid irradiated with ultrasonic waves to 5.2 mg/L or less, it is possible to ensure good ultrasonic cleaning performance.

A method for cleaning a metal pipe according to an embodiment is a method for cleaning a metal pipe formed by cold drawing a blank pipe having a chemical conversion film and a lubricating film formed on the surface thereof. The cleaning method includes a step of immersing the metal pipe in an alkaline degreasing solution that is not heated to a high temperature in an alkaline cleaning tank, and a step of irradiating the cleaning solution in the ultrasonic cleaning tank with ultrasonic waves and generating fine bubbles in the cleaning solution. and a step of immersing the metal pipe in the cleaning liquid after being immersed in the alkaline degreasing liquid.

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

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

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

[Alkaline cleaning equipment]
FIG. 2 is a side view schematically showing the alkaline cleaning device 10 used in the alkaline cleaning step S41. FIG. 3 is a III-III cross-sectional view of the alkaline cleaning apparatus 10 shown in FIG.

Referring to FIGS. 2 and 3, alkaline cleaning apparatus 10 includes alkaline cleaning tank 11 , storage tank 12 , and circulation pipe 13 .

(Alkaline cleaning tank)
The alkaline cleaning tank 11 has a tank main body 111 and a lid 112 . The tank main body 111 has an opening on its upper surface. The lid 112 is configured to cover the opening of the tank body 111 .

The tank main body 111 is configured so that the metal pipe P can be accommodated therein. During alkali cleaning, a plurality of metal pipes P are normally housed in the tank main body 111 at the same time. An alkaline degreasing liquid is supplied to the tank main body 111 . The alkaline degreasing solution 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 and the like. Additives such as a surfactant and a chelating agent can be appropriately added to the alkaline degreasing solution.

The tank main body 111 has, for example, a rectangular shape in plan view. The tank main body 111 has a bottom surface 111a and a peripheral wall 111b extending upward from the peripheral edge of the bottom surface 111a. The bottom surface 111a is an inclined surface that descends from one longitudinal end 111c of the tank body 111 toward the other longitudinal end 111d. The depth of the tank body 111 increases from the end 111c toward the end 111d.

A plurality of support members 113 may be provided inside the tank body 111 . The plurality of support members 113 are arranged at intervals along the longitudinal direction of the tank body 111 . The support member 113 supports the metal pipe P so that the metal pipe P does not come into direct contact with the bottom surface 111a. Each support member 113 is formed in a substantially U shape, for example.

(storage tank)
The storage tank 12 is arranged below the alkaline cleaning tank 11 . The storage tank 12 is formed, for example, in the shape of a hollow rectangular parallelepiped. The storage tank 12 stores an alkaline degreasing liquid. The storage tank 12 communicates with the tank body 111 via the circulation pipe 13 in the vicinity of the end portion 111 c of the tank body 111 . The storage tank 12 communicates with the tank body 111 through the communication port 14 in the vicinity of the end portion 111 d of the tank body 111 . The communication port 14 is configured to be openable and closable.

(Circulation piping)
The circulation pipe 13 connects the tank main body 111 and the storage tank 12 in the vicinity of the end portion 111 c of the tank main body 111 of the alkali cleaning tank 11 . The circulation pipe 13 is configured to be able to supply the alkaline degreasing liquid in the storage tank 12 to the tank main 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 main body 111 .

[Ultrasonic cleaning equipment]
FIG. 4 is a plan view of the ultrasonic cleaning device 20 used in the ultrasonic cleaning step S42. FIG. 5 is a VV cross-sectional view of the ultrasonic cleaning apparatus 20 shown in FIG.

As shown in FIG. 4, the ultrasonic cleaning apparatus 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 fine bubble generation mechanisms 25. , provided. The ultrasonic cleaning device 20 further includes a plurality of cushioning members 26 .

(Ultrasonic cleaning tank)
The ultrasonic cleaning tank 21 is configured to accommodate the metal pipe P. As shown in FIG. During ultrasonic cleaning, a plurality of metal pipes P are normally housed in the ultrasonic cleaning tank 21 at the same time. A cleaning liquid for cleaning the metal pipe P is stored in the ultrasonic cleaning tank 21 . The type of cleaning liquid is not particularly limited, and can be appropriately selected from known cleaning liquids. The cleaning liquid is, for example, water (tap water, industrial water).

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

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

(supply mechanism)
The supply mechanism 22 supplies cleaning liquid to the ultrasonic cleaning bath 21 . The supply mechanism 22 has at least one supply pipe 221 . In this embodiment, the supply mechanism 22 has multiple 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. Therefore, the cleaning liquid is dispersedly supplied to the ultrasonic cleaning tank 21 . When there are three or more supply pipes 221, it is preferable that the intervals between the supply pipes 221 are substantially equal from the viewpoint of uniform supply of new cleaning liquid.

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

(Ejection mechanism)
Each discharge mechanism 23 discharges the cleaning liquid from the ultrasonic cleaning tank 21 when the amount of cleaning liquid in the ultrasonic cleaning tank 21 exceeds a predetermined amount. A plurality of ejection mechanisms 23 are arranged at intervals. Therefore, the cleaning liquid is dispersed and discharged from the ultrasonic cleaning tank 21 . When there are three or more ejection mechanisms 23, it is preferable that the intervals between the ejection mechanisms 23 are approximately equal. In addition, the number of ejection mechanisms 23 may be one.

In this embodiment, the plurality of discharge mechanisms 23 are provided along the side wall opposite to the supply pipe 221 of the pair of longitudinal side walls of the ultrasonic cleaning tank 21 . However, the position and number of the ejection mechanisms 23 are not particularly limited. A discharge mechanism 23 may be provided on the side wall on the supply pipe 221 side of the pair of longitudinal side walls of the ultrasonic cleaning bath 21 . In addition to or instead of the longitudinal side wall of the ultrasonic cleaning tank 21 , one or more discharge mechanisms 23 may be provided on the lateral side wall of the ultrasonic cleaning tank 21 .

FIG. 6 illustrates a discharge mechanism 23A that can be employed in the ultrasonic cleaning device 20. As shown in FIG. The ejection mechanism 23A includes an ejection port 231 and an ejection pipe 232 .

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

In the ultrasonic cleaning apparatus 20, a 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. The position of the lower end of the discharge port 231 substantially coincides with the position of the reference liquid surface S in the depth direction of the ultrasonic cleaning bath 21 .

As indicated by the two-dot chain line in FIG. 6, when the liquid level of the cleaning liquid in the ultrasonic cleaning tank 21 exceeds the height of the reference liquid level S, the cleaning liquid exceeding the reference liquid level S is drained. Overflow from outlet 231 . For example, when the supply mechanism 22 supplies new cleaning liquid to the ultrasonic cleaning tank 21 in a state where the liquid level of the cleaning liquid in the ultrasonic cleaning tank 21 matches the reference liquid level S, the supply amount is substantially the same as the supply amount. A quantity of cleaning liquid overflows from outlet 231 .

Thus, 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 (predetermined amount) corresponding to the reference liquid level S. .

7 illustrates another discharge mechanism 23B that can be employed in the ultrasonic cleaning apparatus 20. As shown in FIG. 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). A commercially available liquid level sensor or the like can be used as the liquid level detection means.

The outlet 233 is an opening formed in the side wall of the ultrasonic cleaning bath 21 . The outlet 233 is provided at an arbitrary height lower than the reference liquid level S on the side wall of the ultrasonic cleaning bath 21 . The discharge pipe 234 is provided outside the ultrasonic cleaning tank 21 and 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 provided in the middle of the discharge pipe 234 . When the liquid level of the cleaning liquid in the ultrasonic cleaning tank 21 exceeds the height of the reference liquid level S, the discharge pump 235 sucks out the cleaning liquid exceeding the reference liquid level S from the ultrasonic cleaning tank 21 . controlled as For example, when the liquid level of the cleaning liquid exceeds the reference liquid level S according to the signal from the liquid level detection means arranged in the ultrasonic cleaning bath 21, the discharge pump 235 is driven to increase the liquid level of the cleaning liquid. When the liquid level falls below the reference liquid level S, the drive of the discharge pump 235 is stopped.

Thus, the discharge mechanism 23B also 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, similarly to the discharge mechanism 23A (FIG. 6).

(Ultrasonic irradiation mechanism)
Returning to FIG. 4, the ultrasonic irradiation mechanism 24 irradiates the cleaning liquid in the ultrasonic cleaning tank 21 with ultrasonic waves. As the ultrasonic irradiation mechanism 24, a known ultrasonic oscillator generally used in ultrasonic cleaning can be used.

The frequency of the ultrasonic waves emitted by the ultrasonic wave emitting mechanism 24 is preferably 20 kHz to 200 kHz. By setting the frequency of the ultrasonic wave to 20 kHz or higher, it is possible to prevent large-sized bubbles generated from the surface of the metal pipe P from hindering the propagation of the ultrasonic wave in the cleaning liquid and deteriorating the cleaning performance. . By setting the frequency of the ultrasonic wave to 200 kHz or less, it is possible to prevent deterioration of the cleaning uniformity due to the strong straightness of the ultrasonic wave. The frequency of ultrasonic waves is more preferably 20 kHz to 150 kHz, still more preferably 25 kHz to 100 kHz.

The ultrasonic irradiation mechanism 24 preferably has a frequency sweep function. The frequency sweep function is a function of irradiating the cleaning liquid with ultrasonic waves while sweeping the frequency in a range of ±0.1 kHz to ±10 kHz centering on a specific selected frequency. By changing the frequency of the ultrasonic wave using the frequency sweep function, the frequency resonance diameter, which will be described later, is changed, 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 object to be irradiated, the ultrasonic wave passes through the object to be irradiated. By changing the frequency of the ultrasonic wave with the frequency sweep function, it is possible to satisfy the condition that the wavelength of the ultrasonic wave is 1/4 of the wavelength corresponding to the thickness of the metal pipe P at various positions of the metal pipe P. can. Therefore, ultrasonic waves can be transmitted from the outside to the inside of the metal pipe P at various positions of the metal pipe P.

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

(Fine bubble generation mechanism)
The fine bubble generating mechanism 25 generates fine bubbles by bubble-forming gas dissolved in the cleaning liquid in the ultrasonic cleaning tank 21 . The fine bubble generating mechanism 25 is arranged outside the ultrasonic cleaning bath 21 . A plurality of fine bubble generating mechanisms 25 are arranged along one longitudinal side wall of the ultrasonic cleaning bath 21 . However, the position and number of fine bubble generating mechanisms 25 are not particularly limited.

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

The fine bubble generator 253 can be appropriately selected from known fine bubble generators. As a known fine bubble generator, for example, fine bubbles are generated by shearing bubbles, passing bubbles through fine pores, decompressing liquid (pressure change), dissolving gas under pressure, ultrasonic waves, electrolysis, chemical reaction, etc. known to cause It is preferable that the fine bubble generator 253 can easily control the diameter and concentration of the fine bubbles. As the fine bubble generator 253, for example, a known fine bubble generator that generates fine bubbles by causing a pressure change in the liquid in the liquid circulation path can be employed.

Here, fine bubbles refer to fine bubbles having an average bubble diameter of 100 μm or less. In particular, fine bubbles having an average bubble diameter of μm are sometimes referred to as microbubbles, and fine bubbles having an average bubble diameter of nm are sometimes referred to as nanobubbles. The average bubble diameter is the diameter at which the number of samples is the maximum in the number distribution of the diameters 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 fine bubble generating mechanism 25 from becoming large and facilitating the control of the bubble diameter. Further, the average bubble diameter of the fine bubbles is preferably 100 μm or less from the viewpoint of increasing the floating speed of the fine bubbles and preventing the propagation of ultrasonic waves to the metal pipe P from being hindered. More preferably, fine bubbles are microbubbles having an average bubble diameter of 1 μm to 50 μm.

At least part of the fine bubbles in the cleaning liquid preferably have a bubble diameter equal to or smaller than the frequency resonance diameter. The frequency resonance diameter is the diameter that resonates with the frequency of ultrasonic waves in the cleaning liquid. The fine bubble generating mechanism 25 preferably generates fine bubbles in the cleaning liquid such that the number of fine bubbles having a bubble diameter equal to or smaller than the frequency resonance diameter accounts for 70% or more of the total number of fine bubbles. Considering the presence of bubbles that expand immediately after the generation of fine bubbles, 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 the fine bubbles in the cleaning liquid is preferably 10 ³ /mL or more from the viewpoint of improving the propagation of ultrasonic waves and securing the number of nuclei for ultrasonic cavitation. Further, the concentration of the fine bubbles generated in the cleaning liquid is preferably 10 ⁶ /mL or less in order to prevent the size and number of the fine bubble generating mechanisms 25 from increasing.

The average bubble diameter and concentration of fine bubbles can be measured with a known device such as a liquid particle counter or a bubble diameter distribution measuring device.

(buffer member)
The buffer member 26 is arranged inside the ultrasonic cleaning bath 21 . A plurality of buffer members 26 are arranged in the longitudinal direction of the ultrasonic cleaning bath 21 .

As shown in FIG. 5, the cushioning member 26 is generally U-shaped. The metal pipe P in the ultrasonic cleaning bath 21 is placed on the buffer member 26 . The inner surface of the buffer member 26 is positioned inside the ultrasonic irradiation mechanism 24 in the ultrasonic cleaning bath 21 . Therefore, the ultrasonic wave irradiation mechanism 24 is protected from the metal pipe P without the metal pipe P coming into contact with the ultrasonic wave irradiation mechanism 24 .

[Manufacturing method of metal pipe]
The alkali cleaning device 10 (FIG. 2) and the ultrasonic cleaning device 20 (FIG. 4) are used when cleaning the metal pipe P in manufacturing the metal pipe P. As shown in FIG. A method for manufacturing the metal pipe P will be described below. Referring again to FIG. 1, the method for manufacturing the metal pipe P includes a preparation step S1, a lubrication step S2, a cold drawing step S3, and a cleaning step S4.

(Preparation process)
In the preparation step S1, a blank pipe manufactured by hot working is prepared. One end of the blank tube is subjected to a drawing process for a cold drawing step S3, which will be described later. That is, one end portion of the blank tube is subjected to processing such as hammering or drawing so as to be thinner than the other portion.

The base pipe prepared in the preparation step S1 is, for example, a base pipe made of stainless steel or a base pipe made of a Ni-based alloy. A blank tube made of stainless steel is a steel tube containing 10.5% or more of Cr. When the base pipe is a stainless steel pipe, it preferably has the chemical composition shown below. % by 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: 16-20%, with the main balance being Fe (typically, the balance being Fe and impurities). The chemical composition is, in mass%, replacing part of the remaining Fe, Nb: 0.2 to 1.1%, Ti: 0.1 to 0.6%, Mo: 0.1 to 3%, Cu: Any one or more of 2.5 to 3.5% may be contained. Further, in place of part of the remaining Fe, 0.001 to 0.1% by mass of B and 0.02 to 0.12% of N may be contained.

Further, a blank tube made of a Ni-based alloy is a tube made of an alloy having the highest Ni content in each component of the alloy. When the base pipe is a Ni-based alloy pipe, for example, it has the 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: 19.5-24. 0%, Mo: 2.5 to 4.0%, Ti: 1.2% or less, and Fe: 22% or more, and the main balance is Ni (typically, the balance is Ni and impurities is). The chemical composition contains at least one of Cu: 0.5% or less, Nb: 4.5% or less, and Al: 2.0% or less, in mass%, in place of part of the remaining Ni. good too.

(Lubrication process)
Austenitic stainless steel pipes and Ni-based alloy pipes have excellent strength, but have a large working load (frictional force) during cold drawing. Therefore, the lubrication step S2 is performed after the preparation step S1 and before the cold drawing step S3. This lubrication step S2 includes a chemical conversion film forming step S21 and a lubricating film forming step S22.

(Chemical film forming process)
In the chemical conversion coating forming step S21, a chemical conversion coating is formed on the surface of the blank pipe. In the chemical conversion film forming step S21, scales generated during hot working or the like are removed from the blank pipe by a known pickling treatment, and then the blank pipe is immersed in a chemical conversion treatment solution for a predetermined period of time. Thereby, a chemical conversion film is formed on the surface of the blank tube.

Although the chemical conversion treatment liquid used in the chemical conversion film forming step S21 is not particularly limited, it is, for example, an oxalate treatment liquid. In this case, an oxalate film consisting mainly of iron (II) oxalate is formed on the surface of the blank tube.

(Lubricating film forming process)
After the chemical conversion coating forming step S21, the blank tube is subjected to water washing and neutralization treatment, and the lubricating coating forming step S22 is performed. In the lubricating film forming step S22, a lubricating film is formed on the chemical conversion film formed on the blank tube in the chemical conversion film forming step S21. In the lubricating film forming step S22, the blank tube on which the chemical conversion film is formed is immersed in the lubricating treatment liquid for a predetermined period of time. After that, the blank pipe is taken out from the lubricating treatment liquid and dried sufficiently. Thereby, a lubricating film is formed on the chemical conversion film.

A higher fatty acid salt (soap) can be used as the lubricating treatment liquid. In this case, the lubricating treatment liquid reacts with the chemical conversion film to form a metal soap. That is, the lubricating coating includes a metal soap layer on the chemical conversion coating and a soap layer on the metal soap layer. For example, when the chemical conversion film is an oxalate film and the lubricating treatment 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 the chemical conversion film and the lubricating film are formed on the blank pipe by the lubrication step S2, the cold drawing step S3 is performed. In the cold drawing step S3, the blank tube is formed into a metal tube having a predetermined size by subjecting the blank tube to a known cold drawing process. For example, the end portion of the raw pipe subjected to the drawing process is passed through a die (not shown) and gripped by a gripper (not shown), and the gripper is moved to pull out the raw pipe from the die. As a result, the outer diameter of the blank tube is finished to a predetermined outer diameter. When adjusting the wall thickness of the blank pipe, the blank pipe is drawn with the mandrel inserted.

(Washing process)
A metal pipe having a predetermined size obtained through the cold drawing step S3 is washed in a washing step S4 to remove the chemical conversion film and the lubricating film. The cleaning step S4 includes an alkali cleaning step S41 and an ultrasonic cleaning step S42.

(Alkaline cleaning process)
Referring to FIGS. 2 and 3 again, 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 apparatus 10 . In the alkali cleaning step S<b>41 , first, the metal pipe P is placed inside the tank body 111 . A plurality of metal pipes P are normally arranged in the tank main body 111 , but one metal pipe P may be arranged in the tank main body 111 . The metal pipe P is placed in the alkali cleaning bath 11 by a crane or the like. Specifically, the metal pipe P is placed on the support member 113 . Thereby, a gap is generated between the metal pipe P and the bottom surface 111 a of the tank main body 111 .

The alkaline degreasing liquid is not supplied to the tank main body 111 at the time when the metal pipe P is arranged in the tank main body 111 . After accommodating the metal pipe P in the empty tank main body 111 , the upper surface of the tank main body 111 is covered with the lid 112 .

Subsequently, the alkaline degreasing liquid in 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 alkaline cleaning tank 11 above by driving the pump 131 . The alkaline degreasing liquid flows into the tank main body 111 from the end portion 111c side and flows to the end portion 111d side. The alkaline degreasing liquid passes through the inside of the metal pipe P, between the metal pipe P and the bottom surface 111a, between the metal pipe P and the peripheral wall 111b, and the like.

While the alkaline degreasing liquid is being supplied to the bath body 111, the communication port 14 near the downstream end 111d is closed. Therefore, the alkaline degreasing liquid is stored in the tank main body 111 .

An alkaline degreasing liquid that has not been heated to a high temperature is stored in the storage tank 12 . Therefore, the tank body 111 is supplied with an alkaline degreasing liquid that has not been heated to a high temperature. Here, the alkaline degreasing liquid that has not been heated to a high temperature is, as described above, the alkaline degreasing liquid that is typically subjected to active heat treatment using a heater (for example, a steam heater or an electric heater). It is an alkaline degreasing liquid with a liquid temperature corresponding to the ambient temperature of the alkaline cleaning device 10 . However, for example, in winter when the air temperature is low, when the ambient temperature of the alkaline cleaning device 10 drops and the temperature of the alkaline degreasing liquid drops below 20°C, the liquid temperature should be adjusted to about 20°C to 40°C. , the alkaline degreasing liquid can be heated. However, even in winter when the air temperature is low, the temperature of the alkaline 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, the temperature of the alkaline degreasing liquid may exceed 40° C. in summer when the temperature is high. In such a case, it is not necessary to cool the alkaline degreasing liquid to 40° C. or lower. Even if the temperature of the alkaline degreasing liquid naturally rises to a high temperature (higher than 40°C) without active heat treatment (without consuming energy for heating the alkaline degreasing liquid), This is because both energy saving (low cost) and good cleanability can be achieved. There is no particular upper limit to the temperature of the alkaline degreasing solution when the alkaline degreasing solution is not subjected to active heat treatment. It is considered to be about 60°C. In this manner, the tank main body 111 (alkaline cleaning tank 11) is typically supplied with an alkaline degreasing liquid having a temperature corresponding to the ambient temperature of the alkaline cleaning apparatus 10 (that is, an unheated alkaline degreasing liquid). and stored. However, when the temperature of the alkaline degreasing liquid drops below 20° C., the alkaline degreasing liquid heated to 40° C. or less is supplied to the tank main body 111 (the alkaline cleaning tank 11) and stored therein.

When the alkaline cleaning tank 11 is filled with the alkaline degreasing liquid that has not been heated to a high temperature, the supply of the alkaline degreasing liquid to the tank body 111 is stopped. The metal pipe P is held for a predetermined period of time in the high-temperature unheated alkaline degreasing liquid filled in the alkaline cleaning bath 11 . The time for holding the metal pipe P may be determined as appropriate, and is, for example, 1 to 5 minutes.

Next, the communication port 14 is opened to discharge the alkaline degreasing liquid from the tank main body 111 to the storage tank 12 . As a result, in the tank main body 111, the alkaline degreasing liquid flows from the end portion 111c side toward the end portion 111d side. The alkaline degreasing liquid passes through and around the metal pipe P. All the alkaline degreasing liquid in the tank main body 111 is collected in the storage tank 12 .

Supplying the alkaline degreasing solution from the storage tank 12 to the alkaline cleaning tank 11, holding the metal pipe P in the alkaline degreasing solution, and discharging the alkaline degreasing solution from the alkaline cleaning tank 11 to the storage tank 12 are regarded as one cycle. A predetermined number of cycles are performed. As the number of times the cycle is performed increases, the washability also improves. The number of times the cycle is performed can be, for example, 2 to 5 times. The time required for one cycle depends on the capacity of the alkaline cleaning tank 11 and the like, but can be, for example, about 5 to 15 minutes.

After performing the above 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. This completes the alkali cleaning step S41.

In the alkaline cleaning step S41, it is preferable to generate a flow of the alkaline degreasing liquid in the alkaline cleaning tank 11. As shown in FIG. As a result, in addition to the chemical action of the alkaline degreasing liquid itself, the metal pipe P can be alkaline cleaned by the physical action of the flow of the alkaline degreasing liquid. In this embodiment, a flow of the alkaline degreasing liquid is generated in the alkaline cleaning tank 11 during the process of supplying and discharging the alkaline degreasing liquid. In this embodiment, when the alkaline cleaning tank 11 is filled with the alkaline degreasing liquid, the flow of the alkaline degreasing liquid is temporarily stopped, but the alkaline degreasing liquid may continue to flow within the alkaline cleaning tank 11 . However, the alkaline cleaning step S41 can also be carried out in a state where the alkaline degreasing liquid is always stationary without generating a flow of the alkaline degreasing liquid in the alkaline cleaning bath 11 .

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

Referring to FIG. 4 again, prior to the ultrasonic cleaning of the metal pipe P, the cleaning liquid is stored in the ultrasonic cleaning bath 21 . A cleaning liquid is supplied to the ultrasonic cleaning bath 21 by a supply mechanism 22 . However, at the stage 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 . The cleaning liquid supplied to the ultrasonic cleaning bath 21 preferably has a dissolved oxygen concentration of about 7 mg/L to 11 mg/L. The cleaning liquid is typically water (tap water or industrial water). When the cleaning liquid is water (tap water or industrial water) with a water temperature of 10 to 35° C., the dissolved oxygen concentration of the cleaning liquid is 7 mg/L to 11 mg/L. More preferably, the cleaning liquid supplied to the ultrasonic cleaning bath 21 has a dissolved oxygen concentration of about 8 mg/L to 10 mg/L. When the cleaning liquid is water (tap water or industrial water) with a water temperature of 15 to 25° C., the dissolved oxygen concentration of the cleaning liquid is 8 mg/L to 10 mg/L. The dissolved oxygen concentration serves as an indicator of the amount of dissolved gas in the cleaning 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 mechanism 23 starts discharging the cleaning liquid. The supply mechanism 22 continues to supply the cleaning liquid to the ultrasonic cleaning tank 21 even after the liquid level of the cleaning liquid reaches the reference liquid level S. As a result, in the ultrasonic cleaning tank 21, the cleaning liquid is discharged simultaneously with the supply of the cleaning liquid. The amount of cleaning liquid discharged at this time is substantially equal to the amount of cleaning liquid supplied.

The metal pipe P transported from the alkali 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 bath 21 using a crane or the like. Normally, 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, new cleaning liquid is continuously supplied to the ultrasonic cleaning tank 21 by the supply mechanism 22 . This cleaning liquid is typically water (tap water or industrial water). On the other hand, the discharge mechanism 23 continuously discharges the cleaning liquid exceeding the reference liquid level S from the ultrasonic cleaning tank 21 . As a result, it is possible to suppress deterioration of the cleaning power due to excessive contamination of the cleaning liquid in the ultrasonic cleaning tank 21 . The amount of cleaning liquid (per unit time) that the supply mechanism 22 supplies to the ultrasonic cleaning tank 21 can be determined in consideration of the amount of cleaning liquid stored in the ultrasonic cleaning tank 21 and the degree of contamination of the cleaning liquid. The cleaning liquid discharged from the ultrasonic cleaning bath 21 by the discharge mechanism 23 is discarded after a predetermined wastewater treatment.

Further, while the metal pipe P is immersed in the cleaning liquid, the cleaning liquid is irradiated with ultrasonic waves 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 dissolved gas in the cleaning liquid, thereby reducing the dissolved oxygen concentration of the cleaning liquid. 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 bath 21 to preferably 4.5 mg/L or less, more preferably 4.2 mg/L or less.

Specifically, the supply mechanism 22 supplies a cleaning liquid having a dissolved oxygen concentration of approximately 7 mg/L to 11 mg/L, preferably approximately 8 mg/L to 10 mg/L, to the ultrasonic cleaning tank 21 . When this cleaning liquid passes through the fine bubble generator 253 of the fine bubble generating mechanism 25, the gas dissolved in the cleaning liquid is converted into fine bubbles, and the dissolved oxygen concentration of the cleaning liquid decreases. 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. L or less, more preferably 4.2 mg/L or less. This makes it possible to ensure good detergency in a wide range of ultrasonic sound pressure. Under such a dissolved oxygen concentration, the sound pressure of ultrasonic waves is preferably 120 mV or more in order to ensure good detergency.

The dissolved oxygen concentration of the cleaning liquid in the ultrasonic cleaning bath 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 may not be particularly managed or controlled.

The dissolved oxygen concentration [mg/L] is a value measured with a commercially available dissolved oxygen concentration meter (LAQUA OM-71, manufactured by Horiba, Ltd.). The sound pressure [mV] was measured using a commercially available ultrasonic sound pressure meter (sound pressure level monitor 19001D manufactured by Kaijo Co., Ltd.) in a measurement mode in which the average measured value for 5 seconds was measured. This is the value when the vibration transmission rod (vibration transmission rod) is immersed in water 100 mm from the liquid surface of the cleaning liquid and measured. These measured values are respectively defined as the dissolved oxygen concentration and the sound pressure in the present disclosure.

After holding the metal pipe P in the cleaning liquid in the ultrasonic cleaning bath 21 for a while, the metal pipe P is pulled up from the ultrasonic cleaning bath 21 . In the ultrasonic cleaning step S42, the arrangement of the metal pipe P in the ultrasonic cleaning tank 21, the holding of the metal pipe P in the cleaning liquid, and the pulling up of the metal pipe P from the ultrasonic cleaning tank 21 are regarded as one cycle. A predetermined number of cycles are performed. The retention time of the metal pipe P in the cycle and the number of times the cycle is performed can be determined so that the total immersion time of the metal pipe P in the cleaning liquid is equal to or longer than a predetermined time. The total immersion time of the metal pipe P may be appropriately set according to the amount of the film adhering to the metal pipe P and the like. The total immersion time of the metal pipe P is, for example, 30 seconds or longer, and more preferably 1 minute or longer.

When pulling up the metal pipe P from the ultrasonic cleaning tank 21, it is preferable to incline the metal pipe P with respect to the horizontal plane. As a result, the liquid inside the metal pipe P can be drained. When performing the above cycle a plurality of times, it is preferable to change the tilting direction for each cycle.

After the metal pipe P is immersed in the cleaning liquid for a preset total immersion time or more, the metal pipe P is recovered from the ultrasonic cleaning bath 21 using a crane or the like. Also at this time, it is preferable to pull up the metal pipe P while tilting it. Thereby, it is possible to prevent the cleaning liquid from remaining inside the metal pipe P.

By recovering the metal pipe P, the ultrasonic cleaning step S42 is completed. In the ultrasonic cleaning tank 21, ultrasonic waves and fine bubbles are continuously applied to the cleaning liquid, and the cleaning liquid is supplied and discharged. Therefore, ultrasonic cleaning of another metal pipe P can be continuously performed.

When the ultrasonic cleaning of the metal pipe P is carried out continuously, the cleaning liquid in the ultrasonic cleaning tank 21 is removed by bringing the metal pipe P into the ultrasonic cleaning tank 21 with an alkaline degreasing liquid, water, or the like that does not contain fine bubbles. dissolved oxygen concentration in When the dissolved oxygen concentration of the cleaning liquid increases, it is preferable to stop the ultrasonic cleaning of the metal pipe P until the fine bubble generating mechanism 25 sufficiently reduces 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, the ultrasonic cleaning of the metal pipe P after the alkali cleaning step S41 is restarted. good.

In this embodiment, the metal pipe P is arranged in the ultrasonic cleaning tank 21 after the cleaning liquid is stored in the ultrasonic cleaning tank 21 . However, it is also possible to store the cleaning liquid in the ultrasonic cleaning tank 21 after placing the metal pipe P in the empty ultrasonic cleaning tank 21 .

[Effects of Embodiment]
In this embodiment, the metal pipe P after cold drawing is immersed in an alkaline degreasing liquid that has not been heated to a high temperature, and then immersed in a cleaning liquid to which ultrasonic waves and fine bubbles are applied. As a result, the chemical conversion film and lubricating film formed on the metal pipe P can be removed without using a high-temperature alkaline degreasing liquid.

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

As shown in FIG. 8A, a chemical conversion film 31 is formed on the surface of the metal pipe P after cold drawing. A lubricating film 32 is formed on the chemical conversion film 31 . Lubricating coating 32 includes metal soap layer 321 and soap layer 322 . For example, the chemical conversion film 31 has an iron (II) oxalate film of 1 to 100 μm, preferably 5 to 40 μm, and the lubricating film 32 has a metal soap (iron stearate) layer 321 and a soap (sodium stearate) layer 322. The total thickness is 10 to 1000 μm, preferably 50 to 200 μm.

Cracks occur in the chemical conversion film 31 in the metal pipe P after cold drawing. This is probably because the ductility of the chemical conversion coating 31 is very small, so that the chemical conversion coating 31 does not stretch during cold drawing and breaks. On the other hand, the lubricating coating 32 extends due to heat generated during cold drawing and covers the chemical conversion coating 31 that has cracked.

As shown in FIG. 8B, when the cold-drawn metal pipe P is immersed in an alkaline degreasing solution that has not been heated to a high temperature, the lubricating film 32 covering the chemical conversion film 31 is partially removed. Specifically, part of the metal soap layer 321 reacts with the alkaline degreasing liquid to form a complex, and part of the soap layer 322 dissolves in the alkaline degreasing liquid. As a result, after the alkali cleaning step S41, the lubricating film 32 of the metal pipe P is partially missing.

When the metal pipe P from which the lubricating film 32 has been partially removed is subjected to ultrasonic cleaning, the lubricating film 32 peels off from the metal pipe P starting from the chipped portion, as shown in FIG. 8C. When the lubricating film 32 covering the chemical conversion film 31 is peeled off, the chemical conversion film 31 is also peeled off from the metal pipe P starting from cracks generated during cold drawing. The chemical conversion film 31 and the lubricating film 32 are peeled off from the metal pipe P by physical action such as ultrasonic cavitation.

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

Since the chemical conversion film 31 is chemically bonded to the material of the metal pipe P, it has conventionally been necessary to remove it from the metal pipe P by pickling. 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, the chemical conversion coating 31 can be removed in addition to the lubricating coating 32 only by alkaline cleaning and ultrasonic cleaning. Therefore, the pickling process for removing the chemical conversion film 31 becomes unnecessary, and the cleaning process of the metal pipe P can be simplified.

In this embodiment, fine bubbles are generated in the cleaning liquid in the ultrasonic cleaning step S42. As a result, the ultrasonic waves in the cleaning liquid can be scattered and propagated three-dimensionally. Therefore, the cleanability of the metal pipe P is improved. Further, in the ultrasonic cleaning step S42, the dissolved gas in the cleaning liquid is fine-bubbled, so that the dissolved oxygen concentration of the cleaning liquid is 5.2 mg/L or less, more preferably 4.5 mg/L or less, and still more preferably 4.5 mg/L or less. .2 mg/L or less. Therefore, it is possible to ensure good ultrasonic cleaning performance in a wide sound pressure range.

Although the embodiments according to the present disclosure have been described above, the present disclosure is not limited to the above embodiments, and various modifications can be made without departing from the scope of the present disclosure.

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

The present disclosure will be described in more detail below by way of examples. However, the present disclosure is not limited to the following examples.

[Example]
In order to confirm the effect of cleaning a metal pipe according to the present disclosure, a cleaning test was conducted on a metal pipe P after cold drawing using an alkali cleaning device 10 shown in FIG. 2 and an ultrasonic cleaning device 20 shown in FIG. Carried out. That is, in the alkaline cleaning device 10, after performing the alkaline cleaning step with the alkaline degreasing liquid that is not heated to a high temperature, in the ultrasonic cleaning device 20, the ultrasonic cleaning step with the cleaning liquid imparted with ultrasonic waves and fine bubbles was performed. In this example, the temperature of the alkaline degreasing liquid used in the alkaline cleaning step was a temperature corresponding to the ambient temperature of the alkaline cleaning apparatus 10, specifically about 25.degree. In this example, the metal pipe P was washed with water after the alkali cleaning step and before the ultrasonic cleaning step.

[Comparative Example 1]
As Comparative Example 1, the metal pipe P after cold drawing was subjected to an alkali cleaning step using a high-temperature alkaline degreasing liquid. After the high-temperature alkali washing step, the metal pipe P was washed with water. Also in Comparative Example 1, an alkali cleaning device 10 similar to that of the example was used. In Comparative Example 1, the ultrasonic cleaning step after the alkaline cleaning treatment was not performed.

[Comparative Example 2]
As Comparative Example 2, a cleaning process (ultrasonic cleaning process) using a cleaning liquid imparted with ultrasonic waves and fine bubbles was performed on the metal pipe P after cold drawing. In Comparative Example 2, the alkali cleaning step before the ultrasonic cleaning step was not performed.

[Test conditions]
In Example, Comparative Example 1, and Comparative Example 2, 20 metal pipes P were used, respectively. The chemical composition of the metal tube P is C: 0.08%, Si: 0.2%, Mn: 0.8%, Cu: 3.0%, Ni: 8.8%, Cr: 18% by mass. .5%, Nb: 0.5%, 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 pipe P, an iron (II) oxalate film of 10 μm is formed as a chemical conversion film 31, and a metallic soap (iron stearate) layer 321 and a soap (sodium stearate) layer 321 are formed as a lubricating film 32 on the iron (II) oxalate film. ) layer 322 was formed to a thickness of 100 μm. Other test conditions are shown in Table 1.

In Table 1, the 10-minute flow cycle consists of supplying the alkaline degreasing liquid to the alkaline cleaning tank 11, holding the metal pipe P in the alkaline degreasing liquid, and discharging the alkaline degreasing liquid from the alkaline cleaning tank 11. Means that the cycle was performed for 10 minutes. In Example and Comparative Example 1, a flow cycle of 10 minutes was repeated three times in the alkali cleaning step.

[evaluation]
The washability of the metal pipe P was evaluated for each of Example, Comparative Example 1, and Comparative Example 2. FIG. 9 is a graph showing changes in carbon (C) amount [mg/m ² ] adhering to the inner surface of the metal pipe P in Example, Comparative Example 1, and Comparative Example 2. As shown in FIG. The amount of carbon was measured using a commercially available measurement device (manufactured by LECO Japan LLC, type carbon/hydrogen/moisture analyzer 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 can be seen that the chemical conversion film and the lubricating film cannot be removed from the metal pipe P only by ultrasonic cleaning.

In the case of Comparative Example 1, the carbon content is 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 solution. However, the chemical conversion coating is not removed, and it is considered that part of the lubricating coating remains as described later. Therefore, it is necessary to pickle the metal pipe P after high-temperature alkali cleaning to remove the residual soap component and the chemical conversion film.

In the examples, the amount of carbon slightly decreases from before cleaning by performing alkaline cleaning with an alkaline degreasing liquid at about 25°C. This is because the lubricating film covering the chemical conversion film was partially removed, as described with reference to FIG. 8B. The amount of carbon in the example at the stage where alkaline cleaning with an alkaline degreasing liquid at about 25° C. is completed is greater than the amount of carbon after high-temperature alkaline cleaning in Comparative Example 1. It is believed that this is because the lubricating film can only be partially removed by alkaline cleaning with an alkaline degreasing solution at about 25°C. However, by performing ultrasonic cleaning thereafter, the amount of carbon is significantly reduced (to about several tens of mg/m ² ) as compared with the case of Comparative Example 1. In the case of Comparative Example 1, it is considered that most of the lubricating film has been removed. It can be seen from P that not only the lubricating film but also the chemical conversion film can be removed. In the case of the example, unlike the comparative example 1, it is possible to omit the subsequent pickling treatment. In addition, in order to more reliably remove the chemical conversion film, a pickling treatment may be performed.

FIG. 10 is a scanning electron microscope (SEM) image of the inner surface of each metal tube P cleaned by the cleaning methods 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 remaining soap component is confirmed. That is, in Comparative Example 1, it can be seen that the lubricating film was mostly removed from the cleaned metal pipe P, but partly remained. On the other hand, no residual soap component was observed in the metal pipe P washed by the washing method of the embodiment. Therefore, in the embodiment, the lubricating film is removed from the metal pipe P after cleaning. In addition, as shown in FIG. 9, in the case of the example, the amount of carbon after washing is significantly reduced compared to the comparative example 1, so not only the lubricating film but also the chemical conversion film is removed from the metal pipe P. It can be said that there is

From the above, it was confirmed that good detergency can be obtained by performing cleaning using both ultrasonic waves and fine bubbles after performing alkaline cleaning with an alkaline degreasing solution that has not been heated to a high temperature.

10: Alkali cleaning device 11: Alkali cleaning tank 20: Ultrasonic cleaning device 21: Ultrasonic cleaning tank P: Metal pipe

Claims (4)

A method for manufacturing a metal tube,
A preparatory step of preparing a metal tube;
a lubrication step of forming a chemical conversion film on the surface of the base pipe and forming a lubricating film on the chemical conversion film;
a cold drawing step of cold drawing the blank tube on which the chemical conversion coating and the lubricating coating are formed to form a metal tube having a predetermined size;
a cleaning step of cleaning the metal pipe to remove the chemical conversion coating and the lubricating coating;
with
The washing step includes
Alkaline degreasing solution that is not actively heat-treated in the alkaline cleaning tank (However, if the temperature of the alkaline degreasing solution is less than 20°C, a step of immersing the metal pipe in an alkaline degreasing solution that has been actively heat-treated in the
a step of immersing the metal pipe after being immersed in the alkaline degreasing solution in the cleaning solution while irradiating the cleaning solution in the ultrasonic cleaning tank with ultrasonic waves and generating fine bubbles in the cleaning solution;
A manufacturing method, including: The manufacturing method according to claim 1,
The manufacturing method, wherein the dissolved oxygen concentration of the cleaning liquid is 5.2 mg/L or less while the metal pipe is immersed in the cleaning liquid. A method for cleaning a metal pipe formed by cold drawing a blank pipe having a chemical conversion film and a lubricating film formed on the surface thereof, the method comprising the steps of:
Alkaline degreasing solution that is not actively heat-treated in the alkaline cleaning tank (However, if the temperature of the alkaline degreasing solution is less than 20°C, a step of immersing the metal pipe in an alkaline degreasing solution that has been actively heat-treated in the
a step of immersing the metal pipe after being immersed in the alkaline degreasing solution in the cleaning solution while irradiating the cleaning solution in the ultrasonic cleaning tank with ultrasonic waves and generating fine bubbles in the cleaning solution;
A cleaning method comprising: The cleaning method according to claim 3,
The cleaning method, wherein the dissolved oxygen concentration of the cleaning liquid is 5.2 mg/L or less while the metal pipe is immersed in the cleaning liquid.

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