EP3862466A1 - Verfahren zur herstellung eines metallrohres und verfahren zum waschen eines metallrohres - Google Patents

Verfahren zur herstellung eines metallrohres und verfahren zum waschen eines metallrohres Download PDF

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Publication number
EP3862466A1
EP3862466A1 EP19868663.6A EP19868663A EP3862466A1 EP 3862466 A1 EP3862466 A1 EP 3862466A1 EP 19868663 A EP19868663 A EP 19868663A EP 3862466 A1 EP3862466 A1 EP 3862466A1
Authority
EP
European Patent Office
Prior art keywords
metal tube
ultrasonic
washing liquid
washing
cleaning
Prior art date
Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
Pending
Application number
EP19868663.6A
Other languages
English (en)
French (fr)
Other versions
EP3862466A4 (de
Inventor
Takamitsu Takagi
Hiromitsu Date
Eri HOSHIBA
Current Assignee (The listed assignees may be inaccurate. Google has not performed a legal analysis and makes no representation or warranty as to the accuracy of the list.)
Nippon Steel Corp
Original Assignee
Nippon Steel Corp
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by Nippon Steel Corp filed Critical Nippon Steel Corp
Publication of EP3862466A1 publication Critical patent/EP3862466A1/de
Publication of EP3862466A4 publication Critical patent/EP3862466A4/de
Pending legal-status Critical Current

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Classifications

    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B21—MECHANICAL METAL-WORKING WITHOUT ESSENTIALLY REMOVING MATERIAL; PUNCHING METAL
    • B21C—MANUFACTURE OF METAL SHEETS, WIRE, RODS, TUBES OR PROFILES, OTHERWISE THAN BY ROLLING; AUXILIARY OPERATIONS USED IN CONNECTION WITH METAL-WORKING WITHOUT ESSENTIALLY REMOVING MATERIAL
    • B21C43/00—Devices for cleaning metal products combined with or specially adapted for use with machines or apparatus provided for in this subclass
    • B21C43/02—Devices for cleaning metal products combined with or specially adapted for use with machines or apparatus provided for in this subclass combined with or specially adapted for use in connection with drawing or winding machines or apparatus
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B08—CLEANING
    • B08B—CLEANING IN GENERAL; PREVENTION OF FOULING IN GENERAL
    • B08B3/00—Cleaning by methods involving the use or presence of liquid or steam
    • B08B3/04—Cleaning involving contact with liquid
    • B08B3/10—Cleaning involving contact with liquid with additional treatment of the liquid or of the object being cleaned, e.g. by heat, by electricity or by vibration
    • B08B3/12—Cleaning involving contact with liquid with additional treatment of the liquid or of the object being cleaned, e.g. by heat, by electricity or by vibration by sonic or ultrasonic vibrations
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B08—CLEANING
    • B08B—CLEANING IN GENERAL; PREVENTION OF FOULING IN GENERAL
    • B08B9/00—Cleaning hollow articles by methods or apparatus specially adapted thereto 
    • B08B9/02—Cleaning pipes or tubes or systems of pipes or tubes
    • B08B9/023—Cleaning the external surface
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B08—CLEANING
    • B08B—CLEANING IN GENERAL; PREVENTION OF FOULING IN GENERAL
    • B08B9/00—Cleaning hollow articles by methods or apparatus specially adapted thereto 
    • B08B9/02—Cleaning pipes or tubes or systems of pipes or tubes
    • B08B9/027—Cleaning the internal surfaces; Removal of blockages
    • C—CHEMISTRY; METALLURGY
    • C23—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; CHEMICAL SURFACE TREATMENT; DIFFUSION TREATMENT OF METALLIC MATERIAL; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL; INHIBITING CORROSION OF METALLIC MATERIAL OR INCRUSTATION IN GENERAL
    • C23C—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; SURFACE TREATMENT OF METALLIC MATERIAL BY DIFFUSION INTO THE SURFACE, BY CHEMICAL CONVERSION OR SUBSTITUTION; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL
    • C23C22/00—Chemical surface treatment of metallic material by reaction of the surface with a reactive liquid, leaving reaction products of surface material in the coating, e.g. conversion coatings, passivation of metals
    • C23C22/82—After-treatment
    • C23C22/83—Chemical after-treatment
    • C—CHEMISTRY; METALLURGY
    • C23—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; CHEMICAL SURFACE TREATMENT; DIFFUSION TREATMENT OF METALLIC MATERIAL; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL; INHIBITING CORROSION OF METALLIC MATERIAL OR INCRUSTATION IN GENERAL
    • C23G—CLEANING OR DE-GREASING OF METALLIC MATERIAL BY CHEMICAL METHODS OTHER THAN ELECTROLYSIS
    • C23G1/00—Cleaning or pickling metallic material with solutions or molten salts
    • C—CHEMISTRY; METALLURGY
    • C23—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; CHEMICAL SURFACE TREATMENT; DIFFUSION TREATMENT OF METALLIC MATERIAL; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL; INHIBITING CORROSION OF METALLIC MATERIAL OR INCRUSTATION IN GENERAL
    • C23G—CLEANING OR DE-GREASING OF METALLIC MATERIAL BY CHEMICAL METHODS OTHER THAN ELECTROLYSIS
    • C23G1/00—Cleaning or pickling metallic material with solutions or molten salts
    • C23G1/14—Cleaning or pickling metallic material with solutions or molten salts with alkaline solutions
    • C—CHEMISTRY; METALLURGY
    • C23—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; CHEMICAL SURFACE TREATMENT; DIFFUSION TREATMENT OF METALLIC MATERIAL; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL; INHIBITING CORROSION OF METALLIC MATERIAL OR INCRUSTATION IN GENERAL
    • C23G—CLEANING OR DE-GREASING OF METALLIC MATERIAL BY CHEMICAL METHODS OTHER THAN ELECTROLYSIS
    • C23G3/00—Apparatus for cleaning or pickling metallic material
    • C23G3/04—Apparatus for cleaning or pickling metallic material for cleaning pipes
    • C—CHEMISTRY; METALLURGY
    • C23—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; CHEMICAL SURFACE TREATMENT; DIFFUSION TREATMENT OF METALLIC MATERIAL; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL; INHIBITING CORROSION OF METALLIC MATERIAL OR INCRUSTATION IN GENERAL
    • C23G—CLEANING OR DE-GREASING OF METALLIC MATERIAL BY CHEMICAL METHODS OTHER THAN ELECTROLYSIS
    • C23G5/00—Cleaning or de-greasing metallic material by other methods; Apparatus for cleaning or de-greasing metallic material with organic solvents
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B08—CLEANING
    • B08B—CLEANING IN GENERAL; PREVENTION OF FOULING IN GENERAL
    • B08B2209/00—Details of machines or methods for cleaning hollow articles
    • B08B2209/005—Use of ultrasonics or cavitation, e.g. as primary or secondary action

Definitions

  • the present disclosure relates to a manufacturing method and a cleaning method of a metal tube.
  • the present disclosure particularly relates to a cleaning method of a metal tube formed by applying cold drawing to a material tube with a chemical conversion coating film or a lubricating film on its surface.
  • a chemical conversion coating film such as a phosphate film, an oxalate film, a chromate film, or the like is formed on the surface of the material tube.
  • a lubricating film is formed of a high fatty acid salt (soap) or the like.
  • the chemical conversion coating film reduces frictional resistance by preventing a direct contact between the material tube and the drawing tool, and improves lubricity by enhancing adhesion between the material tube and the lubricating film.
  • the metal tube is cleaned for removal of the chemical conversion coating film and the lubricating film. These films are strongly coupled with the material of the metal tube. Therefore, it is difficult to remove these films from the metal tube.
  • Patent Literature 1 discloses an acid pickling method wherein a plurality of metal tubes are rubbed with one another in an acid liquid while the tube end portions are irradiated with ultrasonic waves.
  • a cleaning method using ultrasonic waves is known.
  • Patent Literature 1 discloses an acid pickling method wherein a plurality of metal tubes are rubbed with one another in an acid liquid while the tube end portions are irradiated with ultrasonic waves.
  • scale is removed by an abrasion effect brought by the rubbing and by a dissolution effect brought by the acid liquid.
  • the dissolution effect brought by the acid liquid is strengthened by the ultrasonic waves, and thereby, scale is removed therefrom.
  • Patent Literature 2 discloses a method for removing scale from a hot-rolled steel plate by using ultrasonic waves and microbubbles. According to Patent Literature 2, microbubbles are supplied to an ultrasonic wave exposed portion of the hot-rolled steel plate, and cavitation is certainly caused. This certainly provides a scale removal effect.
  • Patent Literature 3 discloses a washing apparatus that uses ultrasonic waves and microbubbles.
  • ultrasonic waves are radiated into a washing liquid in a washing tank from an ultrasonic generator.
  • a circulation route is connected to the washing tank.
  • the washing liquid in the washing tank is introduced into a deaerator through the circulation route.
  • the deaerator separates dissolved air from the washing liquid and generates microbubbles.
  • the microbubbles are supplied to the washing tank through the circulation route, and thus, the concentration of air dissolved in the washing liquid is decreased.
  • maintaining the concentration of air dissolved in the washing liquid at a level equal to or lower than a predetermined value makes it possible to carry out efficient and good washing without causing a decrease in the sound pressure of the ultrasonic waves.
  • a degreasing treatment and an acid pickling treatment are applied to a metal tube formed by cold drawing. Accordingly, first, the lubricating film is removed by the degreasing treatment, and thereafter, the chemical conversion coating film is removed by the acid pickling treatment. More specifically, the degreasing treatment is applied to the metal tube, for example, by using an alkaline degreasing fluid at a high temperature of 70 °C or higher, and thereafter, the acid pickling treatment is applied.
  • the degreasing treatment a complex is produced from metallic soap components in the lubricating film, and other soap components are dissolved. In order to attain sufficient complex production and sufficient dissolution, it is necessary to use a high-temperature alkaline fluid.
  • An object of the present disclosure is to achieve both energy conservation (low cost) and good cleaning performance in cleaning a metal tube with a chemical conversion coating film and a lubricating film on its surface.
  • a metal tube manufacturing method includes: a preparing step of preparing a metallic material tube; a lubricating step of forming a chemical conversion coating film on the surface of the material tube and forming a lubricating film on the chemical conversion coating film; a cold drawing step of applying cold drawing to the material tube with the chemical conversion coating film and the lubricating film thereon to form the material tube into a metal tube with specified dimensions; and a cleaning step of cleaning the metal tube to remove the chemical conversion coating film and the lubricating film.
  • the cleaning step includes: a step of soaking the metal tube in a non-highly-heated alkaline degreasing fluid in an alkaline cleaning tank; and a step of soaking the metal tube after soaked in the alkaline degreasing fluid in a washing liquid in an ultrasonic washing tank while radiating ultrasonic waves into the washing liquid and generating fine bubbles in the washing liquid.
  • the present disclosure makes it possible to achieve both energy conservation (low cost) and good cleaning performance in cleaning a metal tube with a chemical conversion coating film and a lubricating film on its surface.
  • a metal tube manufacturing method includes: a preparing step of preparing a metallic material tube; a lubricating step of forming a chemical conversion coating film on the surface of the material tube and forming a lubricating film on the chemical conversion coating film; a cold drawing step of applying cold drawing to the material tube with the chemical conversion coating film and the lubricating film thereon to form the material tube into a metal tube with specified dimensions; and a cleaning step of cleaning the metal tube to remove the chemical conversion coating film and the lubricating film.
  • the cleaning step includes: a step of soaking the metal tube in a non-highly-heated alkaline degreasing fluid in an alkaline cleaning tank; and a step of soaking the metal tube after soaked in the alkaline degreasing fluid in a washing liquid in an ultrasonic washing tank while radiating ultrasonic waves into the washing liquid and generating fine bubbles in the washing liquid.
  • the material tube is cold-drawn and thereby formed into a metal tube with specified dimensions.
  • the metal tube obtained by cold drawing is cleaned (subjected to alkaline degreasing) in the following way.
  • the metal tube is first soaked in a non-highly-heated alkaline degreasing fluid.
  • a non-highly-heated alkaline degreasing fluid typically means an alkaline degreasing fluid that is not positively heated by a heater or the like (for example, a steam heater or an electric heater)and is at natural temperature according to the atmospheric temperature around the alkaline degreasing facilities (air temperature or temperature in the factory building). In this case, there is no need to use (consume) energy to heat the alkaline degreasing fluid. However, when the temperature of the alkaline degreasing fluid is below 20 °C, the alkaline degreasing fluid is heated to about 20 to 40 °C.
  • a heater or the like for example, a steam heater or an electric heater
  • the temperature of the alkaline degreasing fluid may drop below 20 °C.
  • the alkaline degreasing fluid is positively heated so that the temperature of the fluid becomes about 20 to 40 °C.
  • energy is used to heat the alkaline degreasing fluid; however, it is not necessary to heat the alkaline degreasing fluid to so high a temperature (70 °C or higher) as conventionally needed, and the usage of energy can be reduced.
  • the metal tube By soaking the metal tube in a non-highly-heated alkaline degreasing fluid, production of a complex and dissolution are caused on some part of the lubricating film, and the lubricating film is partly removed from the surface of the metal tube.
  • the metal tube is soaked in a washing liquid provided with ultrasonic waves and fine bubbles.
  • the lubricating film on the surface of the metal tube was partly removed by the alkaline degreasing treatment, and therefore, it is possible to peel off the remaining lubricating film from the metal tube by a physical action such as ultrasonic cavitation or the like.
  • the temperature of the alkaline degreasing fluid may be affected by reaction heat or circulation of the alkaline degreasing fluid in the cleaning apparatus during the cleaning process, but the warming of the alkaline degreasing fluid due to these effects is not considered as a positive heating treatment.
  • the ductility of the chemical conversion coating film is extremely low. Therefore, when the metal tube is cold-drawn, the chemical conversion coating film on the metal tube possibly cracks. Accordingly, by soaking the metal tube in the washing liquid supplied with ultrasonic waves and fine bubbles and by applying a physical action such as ultrasonic cavitation or the like to the metal tube, it is possible to peel off the chemical conversion coating film from the metal tube.
  • the concentration of oxygen dissolved in the washing liquid is preferably 5.2 mg/L or lower.
  • the metal tube cleaning method is a method for cleaning a metal tube obtained by applying cold drawing to a material tube with a chemical conversion coating film and a lubricating film formed thereon.
  • the cleaning method includes: a step of soaking the metal tube in a non-highly-heated alkaline degreasing fluid in an alkaline cleaning tank; and a step of soaking the metal tube after soaked in the alkaline degreasing fluid in a washing liquid in an ultrasonic washing tank while radiating ultrasonic waves into the washing liquid and generating fine bubbles in the washing liquid.
  • the concentration of oxygen dissolved in the washing liquid is preferably 5.2 mg/L or lower.
  • FIG. 1 is a flowchart showing a metal tube manufacturing method according to an embodiment.
  • the metal tube manufacturing method includes a preparing step S1, a lubricating step S2, a cold drawing step S3, and a cleaning step S4.
  • the lubricating step S2 includes a chemical conversion coating film forming step S21 and a lubricating film forming step S22.
  • the cleaning step S4 is a step of applying alkaline degreasing to the metal tube with a chemical conversion coating film and a lubricating film formed thereon, and the cleaning step S4 includes an alkaline cleaning step S41 and an ultrasonic washing step S42.
  • an alkaline cleaning apparatus to be used at the alkaline cleaning step S41 and an ultrasonic washing apparatus to be used at the ultrasonic washing step S42 are described.
  • FIG. 2 is a schematic side view of an alkaline cleaning apparatus 10 to be used at the alkaline cleaning step S41.
  • FIG. 3 is a sectional view of the alkaline cleaning apparatus 10 shown in FIG. 2 along line III-III.
  • the alkaline cleaning apparatus 10 includes an alkaline cleaning tank 11, a storage tank 12, and circulation piping 13.
  • the alkaline cleaning tank 11 includes a tank body 111 and a lid 112.
  • the tank body 111 has an open upper side.
  • the lid 112 is configured to cover the open side of the tank body 111.
  • the tank body 111 is configured to accommodate metal tubes P.
  • a plurality of metal tubes P are accommodated at the same time to be subjected to alkaline cleaning.
  • An alkaline degreasing fluid is supplied to the tank body 111.
  • the alkaline degreasing fluid is a known alkaline solution for use in common alkaline degreasing, such as sodium hydroxide (NaOH) aqueous solution, sodium silicate (Na 2 SiO 3 ) aqueous solution, sodium carbonate (Na 2 CO 3 ) aqueous solution, or the like.
  • An interfacial active agent, a chelate agent and some other additives may be added to the alkaline degreasing fluid, as appropriate.
  • the tank body 111 is, for example, rectangular in a planar view.
  • the tank body 111 includes a bottom 111a, and a peripheral wall 111b extending upward from the periphery of the bottom 111a.
  • the bottom 111a has an inclined surface downwardly inclined from one end 111c to the other end 111d along the length direction of the tank body 111.
  • the depth of the tank body 111 becomes greater with increasing distance from the end 111c and with decreasing distance from the end 111d.
  • a plurality of supports 113 may be provided in the tank body 111.
  • the plurality of supports 113 are arranged in the length direction of the tank body 111 at intervals.
  • the supports 113 are to support the metal tubes P such that the metal tubes P will not come into direct contact with the bottom 111a.
  • each of the supports 113 substantially has a U-shape.
  • the storage tank 12 is located under the alkaline cleaning tank 11.
  • the storage tank 12 is, for example, shaped like a hollow rectangular parallelopiped.
  • the alkaline degreasing fluid is stored.
  • the storage tank 12 communicates with the tank body 111 through the circulation piping 13.
  • the storage tank 12 communicates with the tank body 111 through a communication hole 14.
  • the communication hole 14 is openable and closable.
  • the circulation piping 13 connects the tank body 111 and the storage tank 12 near the end 111c of the tank body 111 of the alkaline cleaning tank 11.
  • the circulation piping 13 is configured to supply the alkaline degreasing fluid in the storage tank 12 to the tank body 111.
  • the circulation piping 13 includes a pump 131 (see FIG. 3 ) to send the alkaline degreasing fluid from the storage tank 12 into the tank body 111.
  • FIG. 4 is a plan view of an ultrasonic washing apparatus 20 to be used at the ultrasonic washing step S42.
  • FIG. 5 is a sectional view of the ultrasonic washing apparatus 20 shown in FIG. 4 along line V-V.
  • the ultrasonic washing apparatus 20 includes an ultrasonic washing tank 21, a supply mechanism 22, a plurality of discharge mechanisms 23, a plurality of ultrasonic radiation mechanisms 24, and a plurality of fine bubble generation mechanisms 25.
  • the ultrasonic washing apparatus 20 further includes a plurality of cushions 26.
  • the ultrasonic washing tank 21 is configured to accommodate the metal tubes P.
  • the ultrasonic washing tank 21 usually, a plurality of metal tubes P are accommodated at the same time to be subjected to ultrasonic washing.
  • a washing liquid for washing of the metal tubes P is stored in the ultrasonic washing tank 21.
  • the kind of the washing liquid is not particularly limited, and it is possible to arbitrarily select and adopt one of well-known washing liquids.
  • the washing liquid is, for example, water (tap water or industrial water).
  • the ultrasonic washing tank 21 is rectangular in a plan view.
  • the ultrasonic washing tank 21 has an open upper side.
  • the bottom surface of the ultrasonic washing tank 21 is an inclined surface downwardly inclined from one end to the other end along the length direction.
  • the depth of the ultrasonic washing tank 21 becomes greater with increasing distance from the one end and with decreasing distance from the other end in the length direction.
  • the material of the ultrasonic washing tank 21 is not particularly limited.
  • metallic materials such as stainless steel, etc.
  • plastic resin such as fiber-reinforced plastic (FRP), polypropylene (PP), etc., acid-proof brick, and the like are usable as the material of the ultrasonic washing tank 21.
  • FRP fiber-reinforced plastic
  • PP polypropylene
  • acid-proof brick and the like are usable as the material of the ultrasonic washing tank 21.
  • the above-described alkaline cleaning tank 11 and the storage tank 12 can be formed of the same material as the material of the ultrasonic washing tank 21.
  • the supply mechanism 22 supplies the washing liquid to the ultrasonic washing tank 21.
  • the supply mechanism 22 includes at least one supply pipe 221.
  • the supply mechanism 22 includes a plurality of supply pipes 221.
  • the washing liquid is supplied to the ultrasonic washing tank 21 through the supply pipes 221.
  • the plurality of supply pipes 221 are arranged at intervals. Therefore, the washing liquid is decentrally supplied to the ultrasonic washing tank 21.
  • the plurality of supply pipes 221 are arranged along one of two lengthwise extending side walls of the ultrasonic washing tank 21.
  • the number and arrangement of the supply pipes 221 are not particularly limited.
  • one or more supply pipes 221 may be arranged.
  • one or more supply pipes 221 may be arranged along at least one of two widthwise extending side walls of the ultrasonic washing tank 21.
  • Each of the discharge mechanisms 23 discharges the washing liquid from the ultrasonic washing tank 21 when the amount of washing liquid in the ultrasonic washing tank 21 exceeds a predetermined amount.
  • the plurality of discharge mechanisms 23 are arranged at intervals. Accordingly, the washing liquid is decentrally discharged from the ultrasonic washing tank 21.
  • the plurality of discharge mechanisms 23 are arranged along the lengthwise extending side wall of the ultrasonic washing tank 21 on the opposite side of the side wall where the supply pipes 221 are arranged.
  • the number and arrangement of the discharge mechanisms 23 are not particularly limited.
  • the discharge mechanisms 23 may be arranged along the lengthwise extending side wall of the ultrasonic washing tank 21 where the supply pipes 221 are arranged.
  • one or more discharge mechanisms may be arranged along at least one of two widthwise extending side walls of the ultrasonic washing tank 21.
  • FIG. 6 shows an exemplary discharge mechanism 23A that is employable in the ultrasonic washing apparatus 20.
  • the discharge mechanism 23A includes a discharge outlet 231 and a discharge pipe 232.
  • the discharge outlet 231 is a hole made in a side wall of the ultrasonic washing tank 21.
  • the discharge pipe 232 is located outside the ultrasonic washing tank 21 and connected to the discharge outlet 231.
  • the ultrasonic washing liquid is discharged from the ultrasonic washing tank 21 through the discharge outlet 231 and the discharge pipe 232.
  • a reference liquid surface level S is predetermined for the washing liquid in the ultrasonic washing tank 21.
  • the washing liquid is supplied to the ultrasonic washing tank 21 until the surface of the washing liquid reaches the reference liquid surface level S.
  • the position of the lower edge of the discharge outlet 231 is substantially same as the position of the reference liquid surface level S.
  • the washing liquid in the ultrasonic washing tank 21 becomes higher than the reference liquid surface level S
  • the washing liquid overflows through the discharge outlet 231 by an amount corresponding to the excess over the reference liquid surface level S.
  • the supply mechanism 22 newly supplies the washing liquid to the ultrasonic washing tank 21
  • the washing liquid overflows through the discharge outlet 231 by an amount substantially same as the amount of supply.
  • the discharge mechanism 23A discharges the washing liquid from the ultrasonic washing tank 21 when the amount of washing liquid in the ultrasonic washing tank 21 exceeds the amount defined by the reference liquid surface level S
  • FIG. 7 shows another exemplary discharge mechanism 23B that is employable in the ultrasonic washing apparatus 20.
  • the discharge mechanism 23B includes a discharge outlet 233, a discharge pipe 234, a discharge pump 235, and a liquid surface detector (not shown).
  • a liquid surface detector a commercially available liquid level sensor or the like may be used.
  • the discharge outlet 233 is a hole made in a side wall of the ultrasonic washing tank 21.
  • the discharge outlet 233 is located on the side wall of the ultrasonic washing tank 21, at a lower level than the reference liquid surface level S.
  • the discharge pipe 234 is located outside the ultrasonic washing tank 21 and connected to the discharge outlet 233. The washing liquid is discharged from the ultrasonic washing tank 21 through the discharge outlet 233 and the discharge pipe 234.
  • the discharge pump 235 is located in the middle of the discharge pipe 234.
  • the discharge pump 235 is controlled to suck the washing liquid from the ultrasonic washing tank 21 by an amount corresponding to the excess over the reference liquid surface level S.
  • the discharge pump 235 is controlled as follows based on signals sent from the liquid surface detector located in the ultrasonic washing tank 21.
  • the discharge pump 235 is driven, and when the surface of the washing liquid becomes lower than the reference liquid surface level S, the drive of the discharge pump 235 is stopped.
  • the discharge mechanism 23B discharges the washing liquid from the ultrasonic washing tank 21 when the amount of washing liquid in the ultrasonic washing tank 21 exceeds a predetermined amount.
  • the ultrasonic radiation mechanisms 24 radiate ultrasonic waves into the washing liquid in the ultrasonic washing tank 21.
  • the ultrasonic radiation mechanisms 24 well-known ultrasonic vibrators commonly used in ultrasonic washing may be used.
  • the frequency of ultrasonic waves radiated from the ultrasonic radiation mechanisms 24 is preferably 20 kHz to 200 kHz.
  • the frequency of ultrasonic waves is 20 kHz or more, there is no fear that ultrasonic wave propagation in the washing liquid is blocked by large bubbles emitted from the surfaces of the metal tubes P, and washing performance degradation can be prevented.
  • the frequency of ultrasonic waves is 200 kHz or less, a decrease in the uniformity of washing due to the strong straightness of the travel of ultrasonic waves can be prevented.
  • the frequency of ultrasonic waves is more desirably 20 kHz to 150 kHz, and still more desirably 25 kHz to 100 kHz.
  • the ultrasonic radiation mechanisms 24 preferably have a frequency sweeping function.
  • the ultrasonic radiation mechanisms 24 are capable of radiating ultrasonic waves into the washing liquid while sweeping the frequency within the range of ⁇ 0.1 kHz to ⁇ 10 kHz from a predetermined frequency.
  • the frequency-resonance diameter which will be described later, changes, and it becomes possible to increase the number of microbubbles that contribute to cavitation washing.
  • the ultrasonic waves pass through the object.
  • the frequency of ultrasonic waves By changing the frequency of ultrasonic waves by using the frequency sweeping function, it becomes possible, in various portions of the metal tubes P, to satisfy the condition that the wavelength of ultrasonic waves is a quarter of the wall thicknesses of the metal tubes P. Accordingly, in various portions of the metal tubes P, ultrasonic waves can penetrate the metal tubes P from outside to inside.
  • At least one ultrasonic radiation mechanism 24 is set on the inside surface of each side wall of the ultrasonic washing tank 21.
  • the number and arrangement of the ultrasonic radiation mechanisms 24 are not particularly limited.
  • One or more ultrasonic radiation mechanisms 24 may be set on the bottom surface of the ultrasonic washing tank 21.
  • the ultrasonic radiation mechanisms 24 are arranged in such a manner as to achieve uniform ultrasonic wave propagation in the entire ultrasonic washing tank 21. In this case, the ultrasonic radiation mechanisms 24 have the same load in oscillation, and interference between the ultrasonic waves radiated from the ultrasonic radiation mechanisms 24 can be prevented.
  • the fine bubble generation mechanisms 25 generate fine bubbles from gasses dissolved in the washing liquid in the ultrasonic washing tank 21.
  • the fine bubble generation mechanisms 25 are located outside the ultrasonic washing tank 21.
  • the plurality of fine bubble generation mechanisms 25 are arranged along a lengthwise extending side wall of the ultrasonic washing tank 21.
  • the number and arrangement of the fine bubble generation mechanisms 25 are not particularly limited.
  • Each of the fine bubble generation mechanisms 25 includes pipes 251 and 252, and a fine bubble generator 253.
  • the pipes 251 and 252 connect the ultrasonic washing tank 21 and the fine bubble generator 253.
  • the washing liquid is introduced from the ultrasonic washing tank 21 to the fine bubble generator 253 through the pipe 251.
  • the fine bubble generator 253 generates fine bubbles by using gasses dissolved in the washing liquid.
  • the fine bubbles are returned to the ultrasonic washing tank 21 together with the washing liquid through the pipe 252.
  • the fine bubble generator 253 can be arbitrarily selected from known fine bubble generators.
  • the known fine bubble generators are, for example, fine bubble generators that generate fine bubbles by shear of bubbles, passage of bubbles through fine holes, reduction in liquid pressure (change in pressure), dissolution of gasses under pressure, ultrasonic waves, electrolyzation, chemical reaction, etc.
  • the fine bubble generator 253 is preferably such a thing as the bubble diameter and the density of fine bubbles can be easily controlled.
  • the fine bubble generator 253 may be a known fine bubble generator that generates fine bubbles by causing a pressure change of a liquid in the middle of circulation of the liquid.
  • Fine bubbles mean minuscule bubbles with an average bubble diameter of 100 ⁇ m or less.
  • fine bubbles with an average bubble diameter on the order of micrometers are referred to as microbubbles
  • fine bubbles with an average bubble diameter on the order of nanometers are referred to as nanobubbles.
  • the average bubble diameter is a diameter at which the number of samples is the largest in a number distribution of fine bubble diameter.
  • the average bubble diameter of the fine bubbles in the washing liquid is preferably equal to or greater than 0.01 ⁇ m in order to eliminate the necessity of enlarging the fine bubble generation mechanisms 25 and to facilitate control of the bubble diameter.
  • the average bubble diameter of fine bubbles is preferably equal to or less than 100 ⁇ m in order to prevent the fine bubbles from increasing in drift-up rate and from blocking the propagation of ultrasonic waves to the metal tubes P. More desirably, the fine bubbles are microbubbles with an average bubble diameter of 1 ⁇ m to 50 ⁇ m.
  • the fine bubbles in the washing liquid have bubble diameters equal to or less than a frequency-resonance diameter.
  • the frequency-resonance diameter means a bubble diameter that resonates to the frequency of ultrasonic waves in the washing liquid.
  • the fine bubble generation mechanisms 25 preferably generate fine bubbles in the washing liquid such that the ratio of the number of fine bubbles with bubble diameters equal to or less than the frequency-resonance diameter to the total number of fine bubbles is 70% or more. Considering that some fine bubbles expand immediately after the outbreak thereof, it is more desirable that the above-described ratio is within the range of 80% to 98%. This arrangement makes it possible to improve the propagation efficiency of ultrasonic waves in the washing liquid.
  • the concentration (density) of fine bubbles in the washing liquid is preferably equal to or more than 10 3 bubbles per mL. Also, in order to avoid the necessity of increasing the size of each of the fine bubble generation mechanisms 25 and the necessity of increasing the number of fine bubble generation mechanisms 25, the concentration (density) of fine bubbles in the washing liquid is preferably equal to or less than 10 6 bubbles per mL.
  • the average bubble diameter and the concentration of fine bubbles can be measured by known devices, such as a particle counter for counting particles in liquid, a bubble diameter distribution measurement device, etc.
  • the cushions 26 are located in the ultrasonic washing tank 21.
  • the plurality of cushions 26 are arranged in the length direction of the ultrasonic washing tank 21.
  • each of the cushions 26 has substantially a U-shape.
  • the metal tubes P are placed on the cushions 26 in the ultrasonic washing tank 21.
  • the respective inside surfaces of the cushions 26 are positioned closer to the center of the ultrasonic washing tank 21 than the ultrasonic radiation mechanisms 24. Therefore, there is no fear that the metal tubes P may come into contact with the ultrasonic radiation mechanisms 24, and the ultrasonic radiation mechanisms 24 can be protected from the metal tubes P.
  • the alkaline cleaning apparatus 10 FIG. 2
  • the ultrasonic washing apparatus 20 FIG. 4
  • the method for manufacturing a metal tube P will hereinafter be described.
  • the method for manufacturing a metal tube P includes a preparing step S1, a lubricating step S2, a cold drawing step S3, and a cleaning step S4.
  • a material tube formed by hot working is prepared.
  • Necking is applied to one end portion of the material tube for the cold drawing step S3, which will be described later.
  • hammering, drawing or the like is applied to one end portion of the material tube so that the end portion will be narrower than any other portion.
  • the material tube set for the preparing step S1 is, for example, a material tube made of stainless steel or a material tube made of a Ni-based alloy.
  • the material tube made of stainless steel is a steel tube containing 10.5% or more Cr.
  • the chemical composition thereof preferably contains, in 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%, the balance being mainly Fe (typically the balance being Fe and impurities).
  • the chemical composition may contain at least one of, in mass %, Nb: 0.2 to 1.1%, Ti: 0.1 to 0.6%, Mo: 0.1 to 3%, and Cu: 2.5 to 3.5% as substitute for part of Fe in the balance. Also, the chemical composition may contain, in mass %, B: 0.001 to 0.1% and N: 0.02 to 0.12% as substitute for part of Fe in the balance.
  • a Ni-based alloy tube is a tube in which the content of Ni is the highest of all the components of the alloy.
  • the chemical composition thereof contains, for example, in 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: 1.2% or less, and Fe: 22% or more, the balance being mainly Ni (typically, the balance being Ni and impurities).
  • the chemical composition may contain, in mass%, at least one of Cu: 0.5% or less, Nb: 4.5% or less, Al: 2.0% or less as substitute for part of Ni in the balance.
  • the lubricating step S2 includes a chemical conversion coating film forming step S21 and a lubricating film forming step S22.
  • a chemical conversion coating film is formed on the surface of the material tube.
  • scale that was produced during hot working or the like is removed from the material tube in a known acid pickling process, and thereafter, the material is soaked in a chemical conversion treatment liquid for a predetermined time. Thereby, a chemical conversion coating film is formed on the surface of the material tube.
  • the chemical conversion treatment liquid used at the chemical conversion coating film forming step S21 is not particularly limited, but the chemical conversion treatment liquid is, for example, an oxalate solution.
  • the chemical conversion treatment liquid is, for example, an oxalate solution.
  • an oxalate film consisting mainly of iron oxalate (II) is formed on the surface of the material tube.
  • the material tube is washed with water and neutralized, and the lubricating film forming step S22 is carried out.
  • a lubricating film is formed on the chemical conversion coating film formed on the surface of the material tube at the chemical conversion coating film forming step S21.
  • the material tube with the chemical conversion coating film formed thereon is soaked in a lubricating treatment liquid for a predetermined time. Thereafter, the material tube is taken out from the lubricating treatment liquid, and is completely dried. In this way, a lubricating film is formed on the chemical conversion coating film.
  • the lubricating treatment liquid As the lubricating treatment liquid, a high fatty acid salt (soap) is usable. In this case, the lubricating treatment liquid reacts to the chemical conversion coating film, and as a result, a metallic soap is produced. Therefore, the lubricating film includes a metallic soap layer on the chemical conversion coating film, and a soap layer on the metallic soap layer.
  • the chemical conversion coating film is an oxalate film and when the lubricating treatment liquid is sodium stearate, the metallic soap layer consists mainly of iron stearate, and the soap layer consists mainly of sodium stearate.
  • the cold drawing step S3 is carried out.
  • known cold drawing is applied to the material tube to form the material tube into a metal tube with specified dimensions.
  • the necked end portion of the material tube is inserted in dies (not shown) and held by a gripper (not shown), and the gripper is moved to draw the material tube out from the dies.
  • the outside diameter of the material tube is finished to a predetermined outside diameter. If the wall thickness of the material tube needs to be adjusted, the drawing is performed with a mandrel inserted in the material tube.
  • the metal tube with specified dimensions obtained by the cold drawing step S3 is cleaned at the cleaning step S4 so that the chemical conversion coating film and the lubricating film are removed.
  • the cleaning step S4 includes an alkaline cleaning step S41 and an ultrasonic washing step S42.
  • the alkaline cleaning step S41 is a step of soaking a metal tube P in an alkaline degreasing fluid in the alkaline cleaning tank 11 of the alkaline cleaning apparatus 10.
  • the metal tube P is placed in the tank body 111.
  • a plurality of metal tubes P are placed in the tank body 111, but only one metal tube P may be placed in the tank body 111.
  • the metal tubes P are placed in the alkaline cleaning tank 11 by a crane or the like. Specifically, the metal tubes P are put on the supports 113. Accordingly, there is a space between the metal tubes P and the bottom 111a of the tank body 111.
  • the alkaline degreasing fluid has not been supplied to the tank body 111.
  • the lid 112 is put on the tank body 111 to cover the upper side thereof.
  • the alkaline degreasing fluid in the storage tank 12 is supplied to the alkaline cleaning tank 11 through the circulation piping 13.
  • the pump 131 is driven, the alkaline degreasing fluid in the storage tank 12 is sent upward to the alkaline cleaning tank 11.
  • the alkaline degreasing fluid flows into the tank body 111 from the end 111c side and flows toward the end 111d side.
  • the alkaline degreasing fluid flows through the respective inside of the metal tubes P, through the space between the metal tubes P and the bottom 111a, and the space between the metal tubes P and the peripheral wall 111b.
  • the communication hole 14 near the downstream end 111d is kept closed. Accordingly, the alkaline degreasing fluid is stored in the tank body 111.
  • the non-highly-heated alkaline degreasing fluid typically means an alkaline degreasing fluid that has not been positively heated by a heater or the like (for example, a steam heater or an electric heater) and is at a temperature corresponding to the atmospheric temperature around the alkaline cleaning apparatus 10.
  • the alkaline degreasing fluid may be heated to a temperature of about 20 °C to 40 °C.
  • the temperature of the alkaline degreasing fluid is usually maintained at 20 °C or higher because the pump 131 for sending the alkaline degreasing fluid from the storage tank 12 to the alkaline cleaning tank 11 generates heat.
  • the temperature of the alkaline degreasing fluid sometimes rises above 40 °C. In this case, it is not necessary to cool down the alkaline degreasing fluid to 40 °C or lower.
  • an alkaline degreasing fluid at a temperature corresponding to the atmospheric temperature around the alkaline cleaning apparatus 10 i.e., a non-heat-treated alkaline degreasing fluid
  • a non-heat-treated alkaline degreasing fluid is supplied to the tank body 111 (the alkaline cleaning tank 11) and stored therein.
  • the alkaline degreasing fluid is heated to a temperature not more than 40 °C is supplied to the tank body 111 (the alkaline cleaning tank 11) and stored therein.
  • the supply of the alkaline degreasing fluid to the tank body 111 is stopped.
  • the metal tubes P are held in the non-highly-heated alkaline degreasing fluid in the alkaline cleaning tank 11 for a predetermined time.
  • the holding time of the metal tubes P may be arbitrarily set as appropriate, and the holding time is, for example, 1 to 5 minutes.
  • the communication hole 14 is opened so that the alkaline degreasing fluid is discharged from the tank body 111 to the storage tank 12.
  • the alkaline degreasing fluid flows from the end 111c side toward the end 111d side.
  • the alkaline degreasing fluid flows through the respective inside and circumference of the metal tubes P. All the alkaline degreasing fluid in the tank body 111 is retrieved in the storage tank 12.
  • the supply of the alkaline degreasing fluid from the storage tank 12 to the alkaline cleaning tank 11, the holding of the metal tubes P in the alkaline degreasing fluid, and the discharge of the alkaline decreasing fluid from the alkaline cleaning tank 11 to the storage tank 12 are defined as one cycle, and this cycle is repeated a predetermined number of times. It is possible to achieve higher cleaning performance by repeating the cycle more. However, it is preferred to determine the number of cycles to be carried out in consideration of the balance between cleaning performance and operation efficiency. The number of cycles to be carried out may be, for example, 2 to 5.
  • the time for one cycle depends on the capacity of the alkaline cleaning tank 11, etc., and may be, for example, about 5 to 15 minutes.
  • the lid 112 is put off from the tank body 111, and the metal tubes P are pulled up from the tank body 111 by a crane or the like. Then, the alkaline cleaning step S41 is completed.
  • alkaline cleaning step S41 it is preferred to cause a flow of the alkaline degreasing fluid in the alkaline cleaning tank 11. Then, alkaline cleaning of the metal tubes P is carried out by the physical action of the flow of the alkaline degreasing fluid in addition to the chemical action of the alkaline degreasing fluid itself. In the present embodiment, in the process of supplying and discharging the alkaline degreasing fluid, a flow of the alkaline degreasing fluid in the alkaline cleaning tank 11 is caused.
  • the alkaline cleaning tank 11 when the alkaline cleaning tank 11 is filled with the alkaline degreasing fluid, the flow of the alkaline degreasing fluid is once stopped, but the alkaline degreasing fluid may be kept flowing in the alkaline cleaning tank 11.
  • the alkaline cleaning step S41 may be carried out without causing a flow of the alkaline degreasing fluid, that is, with the alkaline degreasing fluid kept stationary.
  • the ultrasonic washing step S42 is a step of soaking a metal tube P after soaked in the alkaline degreasing fluid in a washing liquid supplied with ultrasonic waves and fine bubbles.
  • the ultrasonic washing apparatus 20 FIG. 4
  • the metal tube P is conveyed from the alkaline cleaning apparatus 10 to the ultrasonic washing apparatus 20.
  • the metal tube P may be washed with water. This washes off the alkaline degreasing fluid from the metal tube P.
  • the washing liquid is stored in the ultrasonic washing tank 21.
  • the washing liquid is supplied to the ultrasonic washing tank 21 by the supply mechanism 22.
  • any other means than the supply mechanism 22 may be used to supply the washing liquid to the empty ultrasonic washing tank 21.
  • the washing liquid to be supplied to the ultrasonic washing tank 21 preferably has an 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 liquid is water (tap water or industrial water) at a temperature of 10 to 35 °C, the concentration of oxygen dissolved in the washing liquid is within the range of 7 mg/L to 11 mg/L.
  • the washing liquid to be supplied to the ultrasonic washing tank 21 more desirably has an oxygen concentration of about 8 mg/L to 10 mg/L.
  • the concentration of oxygen dissolved in the washing liquid is within the range of 8 mg/L to 10 mg/L.
  • the oxygen concentration serves as an index of the amount of gasses dissolved in the washing liquid.
  • the discharge mechanisms 23 start discharging the washing liquid.
  • the supply mechanism 22 continues supplying the washing liquid to the ultrasonic washing tank 21 even after the liquid surface of the washing liquid reaches the reference liquid surface level S. Therefore, discharge of the washing liquid from the ultrasonic washing tank 21 is carried out in parallel with supply of the washing liquid to the ultrasonic washing tank 21.
  • the amount of discharge of the washing liquid is substantially equal to the amount of supply of the washing liquid.
  • the metal tubes P that was conveyed from the alkaline cleaning apparatus 10 ( FIGS. 2 and 3 ) to the ultrasonic washing apparatus 20 is soaked in the washing liquid stored in the ultrasonic washing tank 21 for a predetermined time.
  • the metal tubes P can be placed in the ultrasonic washing tank 21 by a crane or the like to be soaked in the washing liquid.
  • a plurality of metal tubes P are soaked in the washing liquid at the same time; however, only one metal tube P may be soaked in the washing liquid at a time.
  • the washing liquid is newly supplied to the ultrasonic washing tank 21 continuously by the supply mechanism 22.
  • the washing liquid is typically water (tap water or industrial water).
  • the washing liquid is continuously discharged from the ultrasonic washing tank 21 by the discharge mechanisms 23 by an amount corresponding to the excess over the reference liquid surface level S. This makes it possible to prevent the washing performance from degrading due to excessive contamination of the washing liquid in the ultrasonic washing tank 21.
  • the amount (per unit time) of washing liquid supplied to the ultrasonic washing tank 21 by the supply mechanism 22 may be determined in consideration of the amount of washing liquid stored in the ultrasonic washing tank 21 and the degree of contamination of the washing liquid.
  • the washing liquid discharged by the discharge mechanisms 23 from the ultrasonic washing tank 21 is subjected to a specified wastewater treatment and discarded.
  • the fine bubble generation mechanisms 25 uses gasses dissolved in the washing liquid to generate bubbles, and accordingly, the concentration of oxygen dissolved in the washing liquid becomes lower.
  • the fine bubble generation mechanisms 25 decrease the concentration of oxygen dissolved in the washing liquid in the ultrasonic washing tank 21 to 5.2 mg/L or lower.
  • the fine bubble generation mechanisms 25 decrease the concentration of oxygen dissolved in the washing liquid in the ultrasonic washing tank 21 desirably to 4.5 mg/L or lower, and more desirably to 4.2 mg/L or lower.
  • the supply mechanism 22 supplies the washing liquid with an oxygen concentration of about 7 mg/L to 11 mg/L, and preferably about 8 mg/L to 10 mg/L, to the ultrasonic washing tank 21.
  • the concentration of oxygen dissolved in the washing liquid in the ultrasonic washing tank 21 becomes 5.2 mg/L or lower, desirably 4.5 mg/L or lower, and more desirably 4.2 mg/L or lower. This makes it possible to achieve good ultrasonic washing performance in a wide sound pressure region. In order to certainly achieve good washing performance under such a dissolved oxygen concentration, it is preferred that the ultrasonic waves have a sound pressure of 120 mV or higher.
  • the concentration of oxygen dissolved in the washing liquid in the ultrasonic washing tank 21 is usually equal to or higher than 2.0 mg/L. However, it is not necessary to adjust or control the lower limit of the concentration of oxygen dissolved in the washing liquid in the ultrasonic washing tank 21.
  • the dissolved oxygen concentration [mg/L] is a value measured by a commercially available dissolved oxygen meter (LAQUA OM-71 made by Horiba, Ltd.).
  • the sound pressure [mV] is a value measured by a commercially available ultrasonic sound pressure meter (sound pressure level monitor 19001D made by KAIJO Corporation) in a measurement mode to calculate an average value for 5 seconds with a probe (vibration transmission bar with a piezoelectric element) inserted 100 mm deep in the liquid from the liquid surface.
  • measured values obtained in this way are considered as the dissolved oxygen concentration and the sound pressure, respectively.
  • the metal tubes P are pulled up from the ultrasonic washing tank 21.
  • placing the metal tubes P in the ultrasonic washing tank 21, holding the metal tubes P in the washing liquid, and pulling up the metal tubes P from the ultrasonic washing tank 21 are defined as one cycle, and the cycle is repeated a predetermined number of times.
  • the holding time of the metal tubes P in the cycle and the number of cycles to be carried out can be determined such that the total time of soaking the metal tube P in the washing liquid will be a specified time or longer.
  • the total soaking time of the metal tubes P may be arbitrarily determined according to the amount of films on the metal tubes P, and the like.
  • the total soaking time of the metal tubes P is, for example, 30 seconds or longer, and preferably, 1 minute or longer.
  • the metal tubes P are pulled up from the ultrasonic washing tank 21
  • the metal tubes P are preferably inclined from the horizontal surface. Thereby, the washing liquid is drained from the inside of the metal tubes P.
  • the direction of inclination of the metal tubes P is changed for each cycle.
  • the metal tubes P are soaked in the washing liquid for the predetermined total soaking time or longer, the metal tubes P are retrieved from the ultrasonic washing tank 21 by a crane or the like. At the moment, it is preferred to pull up the metal tubes P while inclining the metal tubes P. This prevents the washing liquid from remaining in the metal tubes P.
  • the ultrasonic washing step S42 is completed. Meanwhile, in the ultrasonic washing tank 21, ultrasonic waves and fine bubbles are provided to the washing liquid, and supply and discharge of the washing liquid are continued. Therefore, it is possible to successively carry out ultrasonic washing of other metal tubes P.
  • the metal tubes P are placed therein.
  • the metal tubes P may be placed in the ultrasonic washing tank 21 in an empty sate, and thereafter, the washing liquid may be stored in the ultrasonic washing tank 21.
  • a metal tube P after subjected to cold drawing is soaked in a non-highly-heated alkaline degreasing fluid, and thereafter, the metal tube P is soaked in a washing liquid provided with ultrasonic waves and fine bubbles.
  • the chemical conversion coating film and the lubricating film formed on the metal tube P can be removed with no use of a highly-heated alkaline degreasing fluid.
  • FIG. 8A is a schematic view of the surface of the metal tube P after subjected to cold drawing.
  • FIG. 8B is a schematic view of the surface of the metal tube P after the alkaline cleaning step S41.
  • FIG. 8C is a schematic view of the surface of the metal tube P during the ultrasonic washing step S42.
  • the metal tube P after cold drawing has a chemical conversion coating film 31 on its surface. Further, the metal tube P has a lubricating film 32 on the chemical conversion coating film 31.
  • the lubricating film 32 includes a metallic soap layer 321 and a soap layer 322.
  • an iron oxalate (II) film with a thickness of 1 to 100 ⁇ m, and preferably 5 to 40 ⁇ m, is formed.
  • a metallic soap (iron stearate) layer 321 and a soap (sodium stearate) layer 322 are formed to have a total thickness of 10 to 1000 ⁇ m, and preferably 50 to 200 ⁇ m.
  • the metal tube P after cold drawing has cracks in the chemical conversion coating film 31. This is considered to occur for the following reason.
  • the ductility of the chemical conversion coating film 31 is extremely low, and during the cold drawing, therefore, the chemical conversion coating film 31 does not expand and cracks. Meanwhile, the lubricating film 32 expands by heat generated by the cold drawing and covers the cracked chemical conversion coating film 31.
  • the lubricating film 32 which covers the chemical conversion coating film 31, is partly removed.
  • the metallic soap layer 321 partly reacts to the alkaline degreasing fluid and forms a complex, and the soap layer 322 is partly dissolved in the alkaline degreasing fluid. Accordingly, after the alkaline cleaning step S41, the lubricating film 32 on the metal tube P has been partly removed.
  • the lubricating film 32 When ultrasonic washing is applied to the metal tube P from which the lubricating film 32 has been partly removed, as shown in FIG. 8C , the lubricating film 32 is peeled off from the metal tube P with the part where the lubricating film 32 has been partly removed serving as points of origin.
  • the chemical conversion coating film 31 is peeled off from the metal tube P with the cracks caused during the cold drawing serving as points of origin.
  • the chemical conversion coating film 31 and the lubricating film 32 are peeled off from the metal tube P by the physical action such as ultrasonic cavitation, etc.
  • the cleaning step S4 of the manufacturing method of the metal tube P according to the present embodiment makes it possible to remove the chemical conversion coating film 31 and the lubricating film 32 from the metal tube P after cold drawing without using a highly-heated alkaline degreasing fluid. Accordingly, energy conservation (low cost) and good cleaning performance can be achieved.
  • the chemical conversion coating film 31 is chemically bound with materials of the metal tube P, it is conventionally necessary to carry out acid pickling to remove the chemical conversion coating film 31 from the metal tube P. Specifically, it is conventionally necessary to remove the lubricating film 32 from the metal tube P by using a highly-heated alkaline degreasing fluid and thereafter to carry out acid pickling of the metal tube P to remove the chemical conversion coating film 31. In the cleaning method according to the embodiment, however, not only the lubricating film 32 but also the chemical conversion coating film 31 can be removed by only alkaline cleaning and ultrasonic washing. Thus, it is no longer necessary to carry out acid pickling to remove the chemical conversion coating film 31, and the cleaning process of the metal tube P can be simplified.
  • the ultrasonic washing step S42 fine bubbles are generated in the washing liquid. Thereby, ultrasonic waves in the washing liquid are dispersed and propagated three-dimensionally. Then, the performance in washing the metal tube P is improved.
  • the fine bubbles are generated from gasses dissolved in the washing liquid, and the concentration of oxygen dissolved in the washing liquid is decreased to 5.2 mg/L or lower, desirably to 4.5 mg/L or lower, and more desirably to 4.2 mg/L or lower. Therefore, excellent ultrasonic washing performance can be achieved in a wide sound pressure region.
  • acid pickling to remove the chemical conversion coating film 31 can be omitted.
  • the embodiment is not to exclude acid pickling, and acid pickling may be carried out after the ultrasonic washing.
  • acid pickling may be carried out after the washing.
  • dirt some part of the films removed from the metal tube during the washing, etc. floating in the ultrasonic washing tank 21 may adhere to the metal tube P.
  • acid pickling may be carried out. Even in this case, as compared with a conventional method, it takes only a short time to remove the dirt from the metal tube surface by acid pickling.
  • a cleaning test of metal tubes P after subjected to cold drawing was conducted by using the alkaline cleaning apparatus 10 shown in FIG. 2 and the ultrasonic washing apparatus 20 shown in FIG. 4 .
  • the alkaline cleaning step by use of a non-highly-heated alkaline degreasing fluid was carried out, and thereafter, in the ultrasonic washing apparatus 20, the ultrasonic cleaning step by use of a washing liquid was carried out with ultrasonic waves and fine bubbles provided to the washing liquid.
  • the temperature of the alkaline degreasing fluid used at the alkaline cleaning step was a temperature corresponding to the atmospheric temperature around the alkaline cleaning apparatus 10, and specifically about 25 °C.
  • the metal tubes P were washed with water.
  • Comparative Example 1 alkaline cleaning by use of a highly-heated alkaline degreasing fluid was applied to metal tubes P after subjected to cold drawing. After the high-temperature alkaline cleaning, the metal tubes P were washed with water. In Comparative Example 1, the alkaline cleaning apparatus 10, which was also used in Example, was used. In Comparative Example 1, ultrasonic washing was not carried out after the alkaline cleaning.
  • Comparative Example 2 washing (ultrasonic washing) by use of a washing liquid was carried out with ultrasonic waves and fine bubbles provided to the washing liquid. In Comparative Example 2, alkaline cleaning was not carried out before the ultrasonic washing.
  • each of Example Comparative Example 1 and Comparative Example 2
  • 20 metal pipes P were used.
  • Each of the metal tubes P had a chemical composition containing, in mass%, C: 0.08%, Si: 0.2%, Mn: 0.8%, Cu: 3.0%, Ni: 8.8%, Cr: 18.5%, and Nb: 0.5%, the balance being Fe and impurities.
  • Each of the metal tubes P had the following dimensions: an outside diameter of 50.8 mm, a thickness of 7.2 mm, and a length of 8000 mm.
  • an iron oxalate (II) film with a thickness of 10 ⁇ m was formed, and as the lubricating film 32, a metallic soap (iron stearate) layer 321 and a soap (sodium stearate) layer 322 with a total thickness of 100 ⁇ m were formed on the iron oxalate (II) film.
  • Other test conditions are shown in TABLE 1. TABLE 1 Conditions and Method Step Example Comparative Example 1 Comparative Example 2 1.
  • Alkaline Cleaning Performed Performed Not Performed (1) Alkaline degreasing fluid (1) Alkaline degreasing fluid - liquid temperature: ordinary temperature - liquid temperature: 80°C or higher - NaOH: about 4% - interfacial active - NaOH: 3.2% or more agent: 0.03% (2) 10-minute flow cycle ⁇ 3 times - interfacial active agent: 0.2% or more (2) 10-minute flow cycle ⁇ 3 times 2.
  • Water Washing (Neutralization) Performed Performed Not Performed (1) liquid temperature: ordinary temperature (1) liquid temperature: 50°C (2) hanging soaking for 2 to 3 minutes (2) hanging soaking for 2 to 3 minutes 3. Ultrasonic Washing Performed Not Performed Performed
  • the 10-minute flow cycle in TABLE 1 means that it took 10 minutes to carry out one cycle of supplying an alkaline degreasing fluid to the alkaline cleaning tank 11, holding the metal tubes P in the alkaline degreasing fluid, and discharging the alkaline degreasing fluid from the alkaline cleaning tank 11.
  • the 10-minute flow cycle was repeated three times.
  • FIG. 9 is a graph showing changes in the amount of carbon (C) [mg/m 2 ] adhering to the inside surfaces of the metal tubes P in Example, Comparative Example 1, and Comparative Example 2.
  • the amount of carbon was measured by a commercially available measuring instrument (multiphase carbon-hydrogen/moisture analyzer RC612 made by LECO Japan Corporation).
  • Comparative Example 1 the amount of carbon was decreased by alkaline cleaning using a highly-heated alkaline degreasing fluid. This shows that the lubricating film was mostly removed by the highly-heated alkaline degreasing fluid. However, it is considered that the chemical conversion coating film was not removed and that the lubricating film partly remained as described below. Therefore, the metal tubes P must be subjected to acid pickling after the high-temperature alkaline cleaning so that the remaining soap constituent and the chemical conversion coating film can be removed.
  • Example 2 the amount of carbon was slightly decreased by alkaline cleaning using an alkaline degreasing fluid at about 25 °C. As described with reference to FIG. 8B , this is because the lubricating film covering the chemical conversion coating film was partly removed. The amount of carbon at the completion of the alkaline cleaning using the alkaline degreasing fluid at about 25 °C was greater than the amount of carbon at the completion of the high-temperature alkaline cleaning in Comparative Example 1. The reason is possibly that the lubricating film could be removed only partly by the alkaline cleaning using the alkaline degreasing fluid at about 25 °C.
  • Example 1 the amount of carbon was greatly decreased (decreased to several tens of milligrams per square meter) by the ultrasonic washing carried out thereafter, and the amount of carbon decreased in Example was much greater than the amount of carbon decreased in Comparative Example 1.
  • Comparative Example 1 the lubricating film was mostly removed.
  • Example by carrying out ultrasonic washing after the alkaline cleaning using a low-temperature (about 25 °C) alkaline degreasing fluid, it becomes possible to remove not only the lubricating film but also the chemical conversion coating film from each metal tube P. Unlike Comparative Example 1, in Example, it is not necessary to carry out acid pickling thereafter. However, in order to remove the chemical conversion coating film more certainly, acid pickling may be carried out.
  • FIG. 10 shows scanning electron microscopical (SEM) images of the inside surfaces of the metal tubes P subjected to the cleaning of Example and the cleaning of Comparative Example 1, respectively.
  • SEM scanning electron microscopical

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CN104032322B (zh) 2014-06-24 2016-03-23 浙江久立特材科技股份有限公司 一种用于钢管的脱脂清洗工艺
CN204325509U (zh) * 2014-12-18 2015-05-13 李东 一种覆膜铁皮的脱脂装置
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KR20210053949A (ko) 2021-05-12
CN112805409A (zh) 2021-05-14

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