EP4474531A1

EP4474531A1 - Method for circulating iron-based electroplating solution, method for manufacturing iron-based electroplating solution, and method for manufacturing alloyed hot-dip galvanized steel sheet

Info

Publication number: EP4474531A1
Application number: EP22932353.0A
Authority: EP
Inventors: Gentaro Takeda; Hideyuki Takahashi; Maiko Watanabe; Yoichi Makimizu
Original assignee: JFE Steel Corp
Current assignee: JFE Steel Corp
Priority date: 2022-03-18
Filing date: 2022-12-27
Publication date: 2024-12-11
Also published as: US20250198043A1; MX2024011397A; EP4729668A2; JPWO2023176096A1; WO2023176096A1; EP4729667A2; KR20240151189A; EP4474531A4; CN119013441A; JP7586310B2

Abstract

Provided are a method for circulating an iron-based electroplating solution, a method for manufacturing an iron-based electroplating solution, and a method for manufacturing an alloyed hot-dip galvanized steel sheet, which can be used to obtain an iron-based electroplating solution that is stably capable of being operated with high electrolytic efficiency without sludge contamination and is capable of being power-saved without requiring large-scale equipment. In the method for circulating the iron-based electroplating solution, an iron-based electroplating solution (P) used in an electroplating cell (10) for iron-based electroplating is circulated and adjusted. The iron-based electroplating solution (P) used in the electroplating cell (10) is caused to pass through at least a reduction tank (30), a vertical centrifugal solid-liquid separation device (40), and a final adjustment tank (50) in this order, and then is put into the electroplating cell (10). In the reduction tank (30), an iron source for reduction according to a concentration of Fe³⁺ (Fe trivalent ion) in the iron-based electroplating (P) solution transferred to the reduction tank (30) is put.

Description

Technical Field

The present invention relates to a method for circulating an iron-based electroplating solution for circulating and adjusting an iron-based electroplating solution used in an electroplating cell, a method for manufacturing an iron-based electroplating solution, and a method for manufacturing an alloyed hot-dip galvanized steel sheet including performing an iron-based electroplating process.

Background Art

In recent years, in the field of automobiles, home electric appliances, building materials, and the like, there has been an increasing demand for high-tensile steel sheets (high-tensile steel materials) that can be used for reducing the weight of structures and the like. It has been found that, for example, a steel sheet having an excellent hole expansion property by containing Si in a steel, or a steel sheet having excellent ductility, and in which residual γ formability is likely to be formed by containing Si, or Al and Mn can be obtained as the high-tensile steel material.
However, in a case of manufacturing an alloyed hot-dip galvanized steel sheet using a high-tensile steel sheet containing a large amount of Si or Mn (in particular, 0.2% by mass or more) as a base material, the following problems occur. The alloyed hot-dip galvanized steel sheet is manufactured by heating and annealing a steel sheet of a base material at a temperature of about 600°C to 900°C in a reducing atmosphere or a non-oxidizing atmosphere, performing a hot dip galvanizing process on the steel sheet, and further heating and alloying the galvanized steel sheet. Here, Si and Mn in the steel are easily oxidizable elements, and are selectively oxidized even in a reducing atmosphere or a non-oxidizing atmosphere that is generally used, and are concentrated on a surface of the steel sheet to form an oxide. This oxide causes a decrease in wettability with molten zinc during the plating process, thereby causing unplating. Therefore, as Si and Mn concentrations in the steel increase, the wettability rapidly deteriorates, and thus unplating occurs frequently. In addition, even in a case where the unplating does not occur, there is a problem that the plating adhesiveness is deteriorated. Further, in a case where Si and Mn in the steel are selectively oxidized and concentrated on the surface of the steel sheet, there is a problem that significant alloying delay occurs in an alloying process after hot dip galvanizing, which also significantly inhibits productivity.
For such a problem, for example, PTL 1 discloses a method for manufacturing a high-tensile hot-dip galvanized steel sheet of performing plating Fe of 0.2 to 2 g/m² on a base steel sheet, and then adjusting a direct flame type heating furnace (DFF) and a radiation heating furnace (RTF) under predetermined conditions, to suppress Si, Mn, or Al, which is a difficult-plating element contained in steel, from being surface-diffused and forming an oxide. By suppressing Si, Mn, or Al from being surface-diffused and forming an oxide, an unplating phenomenon can be prevented, excellent plated surface quality and excellent adhesiveness of plating can be secured, high strength can be secured, and manufacturing cost can be further reduced. However, in an iron-based plating solution, Fe²⁺ that is consumed in plating film electrodialysis and Fe³⁺ that does not undergo the electrodialysis reaction are present. In a plating solution with large amount of Fe³⁺, it has been found that there are problems of a decrease in plating electrolytic efficiency, occurrence of a pipe clogging trouble due to generation of sludge (a fine solid), adhesion of sludge to a steel sheet, and occurrence of a restriction on continuous operation due to sludge removal maintenance.
With regard to this problem, PTL 2 discloses a method of efficiently reducing Fe³⁺ by an in-tank stirring mechanism in a case of supplying an iron powder for Fe³⁺ reduction, ion replenishment to a plating solution, and dissolution.
PTL 3 discloses an iron ion supply method in an iron-based alloy electroplating, of efficiently reducing Fe³⁺ by defining a relationship between a diameter and a height of a cylindrical iron chip-filled layer in an iron chip dissolution tank, or setting a concentration of Fe³⁺ in a plating solution on the side of the iron chip dissolution tank to 5 g/L or more, and a relative flow rate between an iron chip during the iron chip dissolution and the plating solution to be pressed to 3 m/min or more.
PTL 4 discloses a high-efficiency reduction method for trivalent Fe ions in an iron-based electroplating solution, of performing Fe³⁺ reduction with high efficiency by setting a ratio H (= S/Q) of a surface area Sm² of an iron powder filled in a stirring tank to a plating solution circulation rate Qm³/hr in the stirring tank to 1 ≤ H ≤ 5.
PTL 5 discloses a sludge separation processing device of a continuous electroplating device that adds an aggregation precipitant to a plating solution containing sludge partially extracted and transferred from a plating solution circulation tank, and stirs and mixes the plating solution to precipitate the sludge to separate and collect the sludge, in a sludge precipitate tank, to efficiently remove sludge generated in an electroplating solution.
Although not specified as being for electroplating, PTL 6 discloses a horizontal centrifugal separation device that is a general-purpose centrifugal separation device having improved seal performance and capable of continuous operation in a compact manner.

Citation List

Patent Literatures

PTL 1: WO 2013/100615
PTL 2: JP H3-2399 A
PTL 3: JP H3-243798 A
PTL 4: JP H6-306697 A
PTL 5: JP 2012-188715 A
PTL 6: WO 2009/072209

Summary of Invention

Technical problem

However, the following problems are found in an iron ion supply method in iron-based alloy electroplating disclosed in PTL 2 and PTL 3, a high-efficiency reduction method for trivalent Fe ions in an iron-based electroplating solution disclosed in PTL 4, a sludge separation processing device of a continuous electroplating device disclosed in PTL 5, and a horizontal centrifugal separation device disclosed in PTL 6 of the related art.
That is, in the iron ion supply method in the iron-based alloy electroplating disclosed in PTL 2 and PTL 3, and the high-efficiency reduction method for trivalent Fe ions in the iron-based electroplating solution disclosed in PTL 4, a reduction method of high efficient Fe³⁺ is disclosed, however, the amount of an iron powder or iron chips to be added is not known in these methods. Therefore, even in a case where the reduction efficiency of Fe³⁺ is excellent, Fe³⁺ remains when an amount of iron source is small with respect to Fe³⁺ present in the plating solution. Accordingly, plating electrolytic efficiency is reduced, or Fe³⁺ is changed to sludge, which adversely affects the operation. On the other hand, in a case where the amount of iron source is excessive with respect to Fe³⁺ present in the plating solution, there is a problem that damage to a pipe is increased due to the excess iron source, or an increase in sludge due to an increase in PH of the plating solution caused by the reduction reaction is promoted, which also adversely affects the operation.
In addition, a sludge separation processing device of a continuous electroplating device disclosed in PTL 5 is a so-called precipitation method in which an aggregation precipitant is added to a plating solution containing sludge, and stirred and mixed to precipitate the sludge to separate and collect the sludge, in a sludge precipitate tank. However, in the sludge separation processing device of the continuous electroplating device disclosed in PTL 5, large-scale equipment is required to correspond to the continuous production of the iron-based electroplating solution due to a small processing flow rate, which is a problem in terms of cost or installation space.
In addition, in a case of a horizontal centrifugal separation device disclosed in PTL 6, although the continuous operation is possible, there is a problem in that it is not possible to completely remove fine sludge contained in the iron-based electroplating solution, and a separation rate of the sludge can be realized to be only about up to 70%.
Accordingly, the present invention has been made to solve the above-described problems of the related art, and an object of the present invention is to provide a method for circulating an iron-based electroplating solution, a method for manufacturing an iron-based electroplating solution, and a method for manufacturing an alloyed hot-dip galvanized steel sheet, which can be used to obtain an iron-based electroplating solution that is stably capable of being operated with high electrolytic efficiency without sludge contamination and is capable of being power-saved without requiring large-scale equipment.

Solution to Problem

In order to achieve the above object, a method for circulating an iron-based electroplating solution according to an aspect of the present invention, in which an iron-based electroplating solution used in an electroplating cell for iron-based electroplating is circulated and adjusted, includes causing the iron-based electroplating solution used in the electroplating cell to pass through at least a reduction tank and a vertical centrifugal solid-liquid separation device in this order to perform a process, then putting it into the electroplating cell, and in which, in the reduction tank, an iron source for reduction according to a concentration of Fe³⁺ (Fe trivalent ion) in the iron-based electroplating solution transferred to the reduction tank is put.
In addition, a method for manufacturing an iron-based electroplating solution according to another aspect of the present invention includes manufacturing an iron-based electroplating solution by performing circulation and adjustment by the method for circulating an iron-based electroplating solution described above.
Further, a method for manufacturing an alloyed hot-dip galvanized steel sheet according to still another aspect of the present invention includes performing an iron-based electroplating process on a steel sheet using the iron-based electroplating solution manufactured by the method for manufacturing the iron-based electroplating solution described above.

Advantageous Effects of Invention

According to the method for circulating the iron-based electroplating solution, the method for manufacturing the iron-based electroplating solution, and the method for manufacturing the alloyed hot-dip galvanized steel sheet according to the present invention, it is possible to provide the method for circulating the iron-based electroplating solution, the method for manufacturing the iron-based electroplating solution, and the method for manufacturing the steel sheet, which can be used to obtain an iron-based electroplating solution that is stably capable of being operated with high electrolytic efficiency without sludge contamination and is capable of being power-saved without requiring large-scale equipment.

Brief Description of Drawings

FIG. 1 is a schematic configuration diagram of electroplating equipment to which a method for circulating the iron-based electroplating solution according to an embodiment of the present invention is applied.

Description of Embodiments

Hereinafter, an embodiment of the present invention will be described with reference to drawings. The embodiment to be described below exemplifies devices or methods for embodying a technical idea of the present invention, and the technical idea of the present invention does not specify the material, shape, structure, arrangement, and the like of a configuration component to the following embodiment.
In addition, the drawings are schematic. Therefore, it should be noted that a relationship, ratio, and the like between the thickness and a plane dimension are different from the actual ones, and there are parts where the relationship or ratio of the dimensions are different between the drawings.
FIG. 1 illustrates a schematic configuration of electroplating equipment to which a method for circulating an iron-based electroplating solution according to an embodiment of the present invention is applied.
Electroplating equipment 1 illustrated in FIG. 1 includes an electroplating cell 10 for iron-based electroplating, which performs an iron-based electroplating process on a steel sheet S to be a material to be plated. The electroplating cell 10 is a horizontal plating cell, allows the steel sheet S to travel in a horizontal direction by a conducting roll 14, supplies an iron-based electroplating solution P in a process tank 11 to a gap between the steel sheet S and a pair of anode electrodes 12, and performs an iron-based electroplating process on both surfaces of the steel sheet S by applying electricity to a plated surface of the steel sheet S, which is a cathode, and the pair of anode electrodes 12. In FIG. 1, reference numeral 13 is a plating solution nozzle header. In the present embodiment, the electroplating cell 10 is a horizontal plating cell, but may be any type of cell such as a vertical plating cell or a radial cell. In addition, in the electroplating cell 10, a plurality of the process equipment may be connected to each other, or an intermediate tank may be provided between the process equipment.
Here, the "iron-based electroplating solution" is defined as an electroplating solution in which a concentration of Fe ions in plating solution-containing metal ions is 60% or more.
In addition, the electroplating equipment 1 includes a plating solution circulation tank 20 that supplies the iron-based electroplating solution P to the electroplating cell 10. The process tank 11 of the electroplating cell 10 and the plating solution circulation tank 20 are connected by a pipe 15 for transferring the iron-based electroplating solution P from the process tank 11 to the plating solution circulation tank 20 to circulate the iron-based electroplating solution P. In addition, one plating solution nozzle header 13 of the electroplating cell 10 and the plating solution circulation tank 20 are connected by a pipe 24 and a pipe 26 branched from the pipe 24 through which the iron-based electroplating solution P is supplied from the plating solution circulation tank 20 to the one plating solution nozzle header 13 by a pump 25. In addition, the other plating solution nozzle header 13 of the electroplating cell 10 and the plating solution circulation tank 20 are connected by the pipe 24 and a pipe 27 branched from the pipe 24 through which the iron-based electroplating solution P is supplied from the plating solution circulation tank 20 to the other plating solution nozzle header 13 by the pump 25. It is desirable that the plating solution circulation tank 20 is sealed with a nitrogen gas (N₂ gas) to make the iron-based electroplating solution P to not come into contact with air and be in a non-oxidized state.
In addition, the electroplating equipment 1 includes a reduction tank 30 that reduces Fe³⁺ (Fe trivalent ion) in the iron-based electroplating solution P from the plating solution circulation tank 20. The plating solution circulation tank 20 and the reduction tank 30 are connected by a pipe 21 through which the iron-based electroplating solution P transferred from the process tank 11 to the plating solution circulation tank 20 is supplied to the reduction tank 30 by a pump 22. On this pipe 21, an Fe³⁺ meter 23 that measures a concentration of Fe³⁺ (Fe trivalent ion) contained in the iron-based electroplating solution P before the iron-based electroplating solution P is supplied to the reduction tank 30 is installed. The Fe³⁺ meter may use any method capable of measuring the concentration of Fe³⁺ (Fe trivalent ion), and for example, a spectrophotometer may be used.
Then, an iron source (an iron powder or an iron chip) for reduction corresponding to the concentration of Fe³⁺ (Fe trivalent ion) in the iron-based electroplating solution P measured by the Fe³⁺ meter is put in the reduction tank 30. The iron source to be put may be appropriately adjusted according to the reduction efficiency, but it is desirable to set the iron source to be put to be generally 1.1 to 1.3 times the concentration of Fe³⁺ (Fe trivalent ion). In addition, a stirrer 31 that stirs the iron-based electroplating solution P in the reduction tank 30 is installed in the reduction tank 30. In addition, a PH meter 32 that measures the PH of the iron-based electroplating solution P in the reduction tank 30 is installed in the reduction tank 30. Since the PH of the iron-based electroplating solution P being reduced increases due to the addition of the iron source and there is a possibility that sludge is increased, sulfuric acid is put so that the PH is constantly maintained to be 2.3 or less. A lower limit of the PH of the iron-based electroplating solution P being reduced is not limited; however, the PH is preferably 1.0 or more, and more preferably 2.0 or more, from a viewpoint of reducing a PH readjustment step in a final adjustment tank 50 and reducing a chemical liquid adjustment amount, which will be described later. In addition, the reduction tank 30 is sealed with a nitrogen gas (N₂ gas) to make the iron-based electroplating solution P to not come into contact with air and be in a non-oxidized state.
In addition, the electroplating equipment 1 includes a vertical centrifugal solid-liquid separation device 40 that separates the sludge in the iron-based electroplating solution P from the iron-based electroplating solution P. The reduction tank 30 and the solid-liquid separation device 40 are connected by a pipe 33 through which the iron-based electroplating solution P reduced in the reduction tank 30 is supplied to the solid-liquid separation device 40 by a pump 34. The solid-liquid separation device 40 is a vertical centrifugal separation type in which a screw 43 is disposed to extend in a vertical direction (a vertical direction of FIG. 1), and includes a screw outer tube 42 that differentially rotates a solid (sludge) and a liquid in the iron-based electroplating solution P as a raw solution such that the solid and the liquid are centrifugally separated by a difference in specific gravity, and a screw 43 provided in the screw outer tube 42, in a centrifugal separation tube 41. Then, a rotary shaft 44 of the screw 43 is formed in a tubular shape such that the iron-based electroplating solution P as a raw solution is derived from the screw 43 into the screw outer tube 42, and a diffusion opening portion 48 is formed on a side surface of the rotary shaft 44. The screw outer tube 42 and the screw 43 are provided in the centrifugal separation tube 41. A raw solution supply port 45 that supplies the iron-based electroplating solution P as a raw solution from the pipe 33 to the diffusion opening portion 48 is formed in the rotary shaft 44 of the screw 43 in the centrifugal separation tube 41. In addition, a separated water discharge port 46 is provided on a side surface of the centrifugal separation tube 41, and a solid discharge port 47 for discharging a solid (sludge) is provided on a bottom surface of the centrifugal separation tube 41. As the vertical centrifugal solid-liquid separation device 40, for example, a solid-liquid separation device disclosed in JP 2007-38068 A can be used.
In a case where such a vertical centrifugal solid-liquid separation device 40 is used, even in a case of sludge containing a wide range of particle diameters of 0.5 to 100 um, which is contained in the iron-based electroplating solution P, the sludge can be separated and collected with a collection rate of 90% or more. However, even in this solid-liquid separation device 40, in a case where a centrifugal force is increased, fine sludge having a particle diameter of 5 um or less is not separated and is carried to a cleaning liquid side, and thus the separation efficiency is reduced. Therefore, it is desirable that the centrifugal force is set to 1000 to 1800 G and a difference in speed between the screw 43 and the screw outer tube 42 is set to 1.0 to 2.0 rpm. In a case where the centrifugal force is 1000 G or less, the centrifugal force is insufficient, and the separation effect is small, and thus, separation performance is deteriorated. In a case where the difference in speed between the screw 43 and the screw outer tube 42 is 1.0 rpm or less, a scraping time by the screw 43 is short, and the separation efficiency is reduced. In a case where the difference in speed is more than 2.0 rpm, the scraping time by the screw 43 is increased, but mixing of fine particles into the cleaning liquid is increased, and thus, the separation efficiency is reduced as a result, which is not desirable.
A solid receiving tank 49 that receives a solid (sludge) discharged from the solid discharge port 47 is provided on a lower portion of the solid-liquid separation device 40.
In addition, it is preferable that the electroplating equipment 1 includes a final adjustment tank 50 that adjusts the iron-based electroplating solution P from which the solid (sludge) is separated by the solid-liquid separation device 40 to a plating solution state suitable for efficient iron-based electroplating. It is preferable that the separated water discharge port 46 of the solid-liquid separation device 40 and the final adjustment tank 50 are connected by a pipe 55 through which the iron-based electroplating solution P from which the solid (sludge) is separated by the solid-liquid separation device 40 is supplied to the final adjustment tank 50. On the final adjustment tank 50, an Fe³⁺ meter 52 that measures a concentration of Fe³⁺ (Fe trivalent ion) contained in the iron-based electroplating solution P is installed. In addition, a PH meter 51 that measures the PH of the iron-based electroplating solution P in the final adjustment tank 50 is installed in the final adjustment tank 50.
In the final adjustment tank 50, the iron-based electroplating solution P from which the solid (sludge) is separated by the solid-liquid separation device 40 is adjusted to a plating solution state suitable for efficient iron-based electroplating. Specifically, pure water, dilute sulfuric acid, and a heater are used to adjust the concentration of Fe³⁺ (Fe trivalent ion) in the iron-based electroplating solution P to be 4.0 g/L or less, the PH of the iron-based electroplating solution P in the final adjustment tank 50 to be 2.0 to 2.3, and a solution temperature of the iron-based electroplating solution P to be 40°C to 55°C. By bringing the iron-based electroplating solution P into this liquid state, the electroplating efficiency of 70% or more is achieved, and it is possible to achieve power-saving production. It is still more desirable that the concentration of Fe³⁺ (Fe trivalent ion) in the iron-based electroplating solution P is adjusted to 2.0 g/L or less, the PH of the iron-based electroplating solution P in the final adjustment tank 50 is adjusted to 2.2 to 2.3, and the solution temperature of the iron-based electroplating solution P is adjusted to 40°C to 45°C, in which case, it is possible to achieve the electroplating efficiency of 80% or more.
It is preferable that the final adjustment tank 50 and the plating solution circulation tank 20 are connected by a pipe 53 through which the iron-based electroplating solution P finally adjusted in the final adjustment tank 50 is supplied to the plating solution circulation tank 20 by a pump 54.
Next, a liquid circulation method for the iron-based electroplating solution of the electroplating equipment 1 will be described.
As the iron-based electroplating solution P, a mixed solution of ferrous sulfate and sodium sulfate is mainly used. Although Fe²⁺ (Fe divalent ion) is present in most parts in an initial stage, an anodic oxidation phenomenon: Fe²⁺ → Fe³⁺ + e^- is inevitably generated on an insoluble anode surface in the electroplating cell 10. In addition, an air oxidation phenomenon: 2Fe²⁺ + 1/2O₂ + H₂O → 2Fe³⁺ + 2OH^- is also generated by stirring the iron-based electroplating solution P with air, and the concentration of Fe³⁺ (Fe trivalent ion) in the iron-based electroplating solution P is increased. In a case where this iron-based electroplating solution P is used without being reformed, the amount of Fe³⁺ (Fe trivalent ion) is excessive, and thus the plating electrolytic efficiency is reduced. In addition, in a case where Fe³⁺ (Fe trivalent ion) increases and the PH of the iron-based electroplating solution P is 2.4 or more, a reaction of 3Fe³⁺ + 7/2SO₄ ^2- + 2OH^- + 1/2Na₂SO₄ + 4H₂O → NaFe₃(SO₄)₂(OH)₆(natrojarosite) + 2H₂SO₄ is promoted, and fine sludge called natrojarosite is generated. In a case where this sludge is left as it is, it coarsens and causes clogging of a pipe or adhesion to a steel sheet, which is a cause of poor appearance. Therefore, it is required to remove the sludge while it is fine. Thus, the reason why the iron-based electroplating solution P has to be reduced before such a reaction progresses is as described in the related art.
Therefore, in the method for circulating the iron-based electroplating solution according to the present embodiment, first, the iron-based electroplating solution P used in the electroplating cell 10 and discharged from the electroplating cell 10 is transferred to the plating solution circulation tank 20 through the pipe 15.
Next, the iron-based electroplating solution P is sucked from the pipe 21 installed at a position close to the iron-based electroplating solution P discharged from the electroplating cell 10 in the plating solution circulation tank 20 by the pump 22, and is transferred to the reduction tank 30.
Here, before the iron-based electroplating solution P is supplied to the reduction tank 30, the concentration of Fe³⁺ (Fe trivalent ion) contained in the iron-based electroplating solution P is measured by the Fe³⁺ meter 23 installed in the pipe 21.
Next, after the iron-based electroplating solution P is put into the reduction tank 30, an iron source for reduction (an iron powder or an iron chip) is put according to the concentration of Fe³⁺ (Fe trivalent ion) measured in advance. The iron source to be put may be appropriately adjusted according to the reduction efficiency, but as described above, it is desirable to set the iron source to be put to be generally 1.1 to 1.3 times the concentration of Fe³⁺ (Fe trivalent ion). For example, in a case where the concentration of Fe³⁺ (Fe trivalent ion) is 4.0 g/L, it is desirable to put the iron source at a concentration of 4.4 to 5.2 g/L. The iron-based electroplating solution P in the reduction tank 30 is constantly stirred by the stirrer 31, and at the same time, the PH of the iron-based electroplating solution P is constantly measured by the PH meter 32 and monitored. Since the PH of the iron-based electroplating solution P being reduced may increase by putting the iron source and the sludge may increase as described above, sulfuric acid is put into the reduction tank 30 such that the PH is constantly maintained to be 2.3 or less. Here, a lower limit of the PH of the iron-based electroplating solution P being reduced is not limited; however, as described above, the PH is preferably 1.0 or more, and more preferably 2.0 or more, from a viewpoint of reducing a PH readjustment step in a final adjustment tank 50 and reducing a chemical liquid adjustment amount, which will be described later. In addition, the reduction tank 30 is sealed with a nitrogen gas (N₂ gas) to make the iron-based electroplating solution P to not come into contact with air and be in a non-oxidized state.
Next, the iron-based electroplating solution P reduced in the reduction tank 30 is transferred to the solid-liquid separation device 40 by the pump 34 through the pipe 33. The solid-liquid separation device 40 used in the present embodiment is a vertical centrifugal solid-liquid separation device having the above-described configuration. The iron-based electroplating solution P is put into the raw solution supply port 45 formed in the rotary shaft 44 of the screw 43 from the pipe 33 and is supplied to the diffusion opening portion 48. The iron-based electroplating solution P is introduced into the screw outer tube 42 from the diffusion opening portion 48 and is centrifugally separated into a solid (sludge) and a liquid due to a difference in specific gravity. Thereafter, the liquid is transferred to the final adjustment tank 50 through the pipe 55 from the separated water discharge port 46. On the other hand, the solid (sludge) is discharged from the solid discharge port 47 to the solid receiving tank 49.
Here, since the solid-liquid separation device 40 is a vertical centrifugal solid-liquid separation device, the sludge can be separated and collected with a collection rate of 90% or more even in a case of the sludge having a wide range of particle diameters of 0.5 to 100 um, which is contained in the iron-based electroplating solution P, as described above. However, even in this solid-liquid separation device 40, in a case where a centrifugal force is increased, fine sludge having a particle diameter of 5 um or less is not separated and is carried to a cleaning liquid side, and thus the separation efficiency is reduced. Therefore, as described above, it is desirable that the centrifugal force is set to 1000 to 1800 G and a difference in speed between the screw 43 and the screw outer tube 42 is set to 1.0 to 2.0 rpm. In a case where the centrifugal force is 1000 G or less, the centrifugal force is insufficient, and the separation effect is small, and thus, separation performance is deteriorated. In a case where the difference in speed between the screw 43 and the screw outer tube 42 is 1.0 rpm or less, a scraping time by the screw 43 is short, and the separation efficiency is reduced. In a case where the difference in speed is more than 2.0 rpm, the scraping time by the screw 43 is increased, but mixing of fine particles into the cleaning liquid is increased, and thus, the separation efficiency is reduced as a result, which is not desirable. The solid-liquid separation device 40 can also cope with continuous operation for 24 hours since periodic internal washing of the device is not required, and production adjustment or interruption due to sludge is not required.
Next, in the final adjustment tank 50 to which the iron-based electroplating solution P is transferred, the iron-based electroplating solution P from which the solid (sludge) is separated by the solid-liquid separation device 40 is adjusted to a plating solution state suitable for efficient iron-based electroplating. Specifically, as described above, it is preferable that pure water, dilute sulfuric acid, and a heater are used to adjust the concentration of Fe³⁺ (Fe trivalent ion) in the iron-based electroplating solution P to be 4.0 g/L or less, the PH of the iron-based electroplating solution P in the final adjustment tank 50 to be 2.0 to 2.3, and a solution temperature of the iron-based electroplating solution P to be 40°C to 55°C. By bringing the iron-based electroplating solution P into this liquid state, the electroplating efficiency of 70% or more is achieved, and it is possible to achieve power-saving production. It is still more desirable that the concentration of Fe³⁺ (Fe trivalent ion) in the iron-based electroplating solution P is adjusted to 2.0 g/L or less, the PH of the iron-based electroplating solution P in the final adjustment tank 50 is adjusted to 2.2 to 2.3, and the solution temperature of the iron-based electroplating solution P is adjusted to 40°C to 45°C, in which case, it is possible to achieve the electroplating efficiency of 80% or more.
Then, the iron-based electroplating solution P finally adjusted in the final adjustment tank 50 is transferred to the plating solution circulation tank 20 by the pump 54 through the pipe 53.
Finally, the iron-based electroplating solution P transferred to the plating solution circulation tank 20 is supplied to one plating solution nozzle header 13 of the electroplating cell 10 by the pump 25 through the pipe 24 and the pipe 26, the iron-based electroplating solution P is supplied to the other plating solution nozzle header 13 of the electroplating cell 10 by the pump 25 through the pipe 24 and the pipe 27, and the circulation of the iron-based electroplating solution P is finished.
In the method for manufacturing the iron-based electroplating solution, the iron-based electroplating solution P is manufactured by performing circulation adjustment by the method for circulating the iron-based electroplating solution.
In the electroplating cell 10, the iron-based electroplating process is performed using the iron-based electroplating solution P that is circulated and adjusted as described above with respect to the steel sheet S. Thereafter, an alloyed hot-dip galvanized steel sheet is manufactured by heating and annealing the steel sheet S that is subjected to the iron-based electroplating process in a post-step, performing a hot dip galvanizing process on the heated and annealed steel sheet S, and further heating and alloying the galvanized steel sheet S.
That is, the method for manufacturing the alloyed hot-dip galvanized steel sheet includes performing an electroplating process on the steel sheet S using the iron-based electroplating solution manufactured by the method for manufacturing the iron-based electroplating solution described above. Thereafter, an alloyed hot-dip galvanized steel sheet is manufactured by heating and annealing the steel sheet S that is subjected to the iron-based electroplating process in a post-step, performing a hot dip galvanizing process on the heated and annealed steel sheet S, and further heating and alloying the galvanized steel sheet S.
In this way, according to the method for circulating the iron-based electroplating solution, the method for manufacturing the iron-based electroplating solution, and the method for manufacturing the alloyed hot-dip galvanized steel sheet according to the present embodiment, the iron-based electroplating solution P used in the electroplating cell 10 is caused to pass through at least the reduction tank 30, the vertical centrifugal solid-liquid separation device 40, and the final adjustment tank 50 in this order, and then is put into the electroplating solution. In the reduction tank 30, an iron source for reduction is put according to the concentration of Fe³⁺ (Fe trivalent ion) in the iron-based electroplating solution P transferred to the reduction tank 30.
As a result, it is possible to obtain an iron-based electroplating solution that is stably capable of being operated with high electrolytic efficiency without sludge contamination and is capable of being power-saved without requiring large-scale equipment.
In addition, according to the method for circulating the iron-based electroplating solution, the method for manufacturing the iron-based electroplating solution, and the method for manufacturing the alloyed hot-dip galvanized steel sheet according to the present embodiment, sulfuric acid is put into the reduction tank 30 such that the PH of the iron-based electroplating solution P in the reduction tank 30 is maintained at 2.3 or less. As a result, it is possible to avoid the possibility that the PH of the iron-based electroplating solution P increases due to the addition of the iron source and the sludge increases.
In addition, according to the method for circulating the iron-based electroplating solution, the method for manufacturing the iron-based electroplating solution, and the method for manufacturing the alloyed hot-dip galvanized steel sheet according to the present embodiment, the reduction tank 30 is sealed with a nitrogen gas. As a result, the iron-based electroplating solution P in the reduction tank 30 can be brought into a non-oxidized state without coming into contact with air.
In addition, according to the method for circulating the iron-based electroplating solution, the method for manufacturing the iron-based electroplating solution, and the method for manufacturing the alloyed hot-dip galvanized steel sheet according to the present embodiment, the vertical centrifugal solid-liquid separation device 40 includes the screw outer tube 42 that differentially rotates a solid and a liquid in a raw solution such that the solid and the liquid are centrifugally separated by a difference in specific gravity, and the screw 43 provided in the screw outer tube 42. Then, the rotary shaft 44 of the screw 43 is formed in a tubular shape such that the raw solution is derived from the screw 43 into the screw outer tube 42, and a diffusion opening portion 48 is formed on a side surface of the rotary shaft 44. Accordingly, the iron-based electroplating solution P transferred to the solid-liquid separation device 40 is supplied from the rotary shaft 44 of the screw 43 to the diffusion opening portion 48 and is introduced into the screw outer tube 42 from the diffusion opening portion 48. In the screw outer tube 42, the solid (sludge) and the liquid are centrifugally separated from each other due to the difference in specific gravity. Therefore, even in a case of sludge containing a wide range of particle diameters of 0.5 to 100 um, which is contained in the iron-based electroplating solution P, the sludge can be separated and collected with a collection rate of 90% or more.
In addition, according to the method for circulating the iron-based electroplating solution, the method for manufacturing the iron-based electroplating solution, and the method for manufacturing the alloyed hot-dip galvanized steel sheet according to the present embodiment, in the final adjustment tank 50, sulfuric acid and pure water are used to adjust the concentration of Fe³⁺ (Fe trivalent ion) in the iron-based electroplating solution P to be 2.0 g/L or less, the PH of the iron-based electroplating solution P to be 2.0 to 2.3, and a solution temperature of the iron-based electroplating solution P to be 40°C to 55°C. Accordingly, by bringing the iron-based electroplating solution P into this liquid state, the electroplating efficiency of 70% or more is achieved, and it is possible to achieve power-saving production.
In addition, the iron-based electroplating process is performed using the iron-based electroplating solution P circulated and adjusted by the method for circulating the iron-based electroplating solution according to the present embodiment, the plated appearance of the manufactured alloyed hot-dip galvanized steel sheet is free from sludge marks and is beautiful, and thus the above-described effect can be obtained.
Although the embodiments of the present invention have been described above, the present invention is not limited thereto and can be modified and improved in various ways.
For example, in the reduction tank 30, it is not necessarily need to put sulfuric acid such that the PH of the iron-based electroplating solution P in the reduction tank 30 is maintained at 2.0 to 2.3.
In addition, the reduction tank 30 does not necessarily need to be sealed with a nitrogen gas.
In addition, in the final adjustment tank 50, it is not necessarily need to adjust the concentration of Fe³⁺ (Fe trivalent ion) in the iron-based electroplating solution P to 2.0 g/L or less.
In addition, in the final adjustment tank 50, it is not necessarily need to adjust the PH of the iron-based electroplating solution P to 2.0 to 2.3.
Further, in the final adjustment tank 50, it is not necessarily need to adjust the solution temperature of the iron-based electroplating solution P to 40°C to 55°C.
In addition, the iron-based electroplating solution P used in the electroplating cell 10 is caused to pass through the plating solution circulation tank 20, the reduction tank 30, the vertical centrifugal solid-liquid separation device 40, and the final adjustment tank 50 in this order, and then is put into the electroplating cell 10, however, it is not necessary to pass through the plating solution circulation tank 20.

Examples

In order to verify the effects of the present invention, in Comparative Examples 1 to 3 and Examples 1 to 5, a power raw unit (kWh/T), electrolytic efficiency (%), and an appearance of an alloyed hot-dip galvanized steel sheet of a product were investigated. The alloyed hot-dip galvanized steel sheet is manufactured by performing the iron-based electroplating process on the steel sheet, then, heating and annealing the steel sheet that is subjected to the iron-based electroplating process in a post-step, performing the hot dip galvanizing process on the heated and annealed steel sheet, and further heating and alloying the galvanized steel sheet.
In Examples 1 to 5, the same electroplating equipment as the electroplating equipment 1 having the configuration illustrated in FIG. 1 was used.
In Comparative Examples 1 to 3, an electroplating cell, a plating solution circulation tank, and a final adjustment tank were the same as those in Examples 1 to 5, and a reduction tank used in PTL 4 (a ratio H (= S/Q) of a surface area Sm² of an iron powder filled in the reduction tank to a plating solution circulation rate Qm³/hr in the reduction tank to 1 ≤ H ≤ 5.) was set for the reduction tank. In addition, in Comparative Example 1, the same precipitation-type sludge precipitate tank as that used in PTL 5 was used as the solid-liquid separation device. Further, in Comparative Examples 2 and 3, the same horizontal centrifugal separation device as that used in PTL 6 was used as the solid-liquid separation device.
In the electroplating cells in Examples 1 to 5 and Comparative Examples 1 to 3, a length of an electrode in a longitudinal direction in one cell was 2 m, a distance between the steel sheet and the electrode was 30 mm on one surface, and two cells were connected to each other. An iron-based electroplating solution (plating bath) was used as a sulfuric acid bath, and components thereof were set to 55 to 65 g/L of an iron component and 5 to 7 g/L of a sodium component.

Investigation results of the power raw unit (kWh/T), the electrolytic efficiency (%), and the appearance of the alloyed hot-dip galvanized steel sheet of a product were shown in Table 1. "Appearance after plating" in Table 1 refers to the appearance of the alloyed hot-dip galvanized steel sheet of a product.

[Table 1]

	Electroplating cell						Reduction tank				Solid-liquid separation device			Final adjustment tank
	Steel sheet size	Sheet passing speed	Fe plating attachment amount	Power raw unit	Electrolytic efficiency	Appearance after plating	Fe³⁺ concentration before putting	Amount of iron put	pH	N2 purging	Type	Centrifugal force	Difference in speed of inner tube-outer tube	Fe³⁺ concentration	pH	Liquid temperature
	Thickness × width mm	m/min	g/m²	kWh/T	%		g/L	g/L	-	-	-	G	rpm	g/L	-	°C
Comp. Ex. 1	1.2 × 1200	90	6.0	160	45	Many sludge marks	10.3	Filling amount of 450 kg	3.2	No	Precipitation type	-	-	7.2	22	45
Comp. Ex. 2				223	38	Many sludge marks	12.3	Filling amount of 450 kg	3.5	Yes	Horizontal centrifugal	1500	-	8.5	22	45
Comp. Ex. 3				112	54	Few sludge marks	8.3	10.8	2.3	Yes	Horizontal centrifugal	1500	-	5.5	22	45
Ex. 1				54	79	Beautiful	3.5	4.6	2.3	Yes	Vertical centrifugal	1500	1.5	2.4	22	45
Ex. 2				66	71	Beautiful	5.5	7.7	2.5	Yes	Vertical centrifugal	1500	1.5	3.8	22	48
Ex. 3				47	85	Beautiful	3.7	4.4	2.1	Yes	Vertical centrifugal	1500	1.5	1.5	22	45
Ex. 4				66	71	Beautiful	3.5	4.9	1.8	Yes	Vertical centrifugal	1500	1.5	1.8	1.9	52
Ex. 5				61	74	Beautiful	3.2	4.5	2.3	No	Vertical centrifugal	1500	1.5	2.5	22	39

In Comparative Examples 1 to 3, the iron source was not put into the reduction tank according to the concentration of Fe³⁺ (Fe trivalent ion) before being put into the reduction tank. Therefore, the concentration of Fe³⁺ (Fe trivalent ion) could not be sufficiently reduced (in the final adjustment tank of Comparative Examples 1 to 3, the concentration of Fe³⁺ (Fe trivalent ion) in the reduction tank could not be sufficiently reduced, and thus the concentration of Fe³⁺ (Fe trivalent ion) was 5.5 g/L or more), and the electrolytic efficiency (%) was low as 54% or less. In addition, the power raw unit (kWh/T) was also high as 112 kWh/T or more. In addition, since the precipitation-type or horizontal centrifugal separation device was used as the solid-liquid separation device, the sludge could not be completely removed, and thus the sludge marks remained on the appearance of the alloyed hot-dip galvanized steel sheet of a product.
Meanwhile, in Examples 1 to 5, the iron source was put to the reduction tank according to the concentration of Fe³⁺ (Fe trivalent ion) before being put into the reduction tank. Therefore, the concentration of Fe³⁺ (Fe trivalent ion) could be sufficiently reduced (in the final adjustment tank of Examples 1 to 5, the concentration of Fe³⁺ (Fe trivalent ion) in the reduction tank could be sufficiently reduced, and thus the concentration of Fe³⁺ (Fe trivalent ion) was 3.8 g/L or less), and the electrolytic efficiency (%) was high as 71% or more. In addition, the power raw unit (kWh/T) was also low as 66 kWh/T or less. In addition, since the vertical centrifugal separation type was used as the solid-liquid separation device, the sludge was sufficiently removed, and the appearance of the alloyed hot-dip galvanized steel sheet of a product was beautiful.
Regarding the appearance of the product after plating in Table 1, a surface of a product (surface area of 10 m²) was observed, and in a case where 50 or more sludge marks were found, it was defined as "many sludge marks", in a case where 10 or more and less than 50 sludge marks were found, it was defined as "few sludge marks", and in a case where less than 10 sludge marks were found, it was defined as "beautiful".

Reference Signs List

1: electroplating equipment
10: electroplating cell
11: process tank
12: anode electrode
13: plating solution nozzle header
14: conducting roll
15: pipe
20: plating solution circulation tank
21: pipe
22: pump
23: Fe³⁺ meter
24: pipe
25: pump
26: pipe
27: pipe
30: reduction tank
31: stirrer
32: PH meter
33: pipe
34: pump
40: solid-liquid separation device
41: centrifugal separation tube
42: screw outer tube
43: screw
44: rotary shaft
45: raw solution supply port
46: separated water discharge port
47: solid discharge port
48: diffusion opening portion
49: solid receiving tank
50: final adjustment tank
51: PH meter
52: Fe³⁺ meter
53: pipe
54: pump
55: pipe
P: iron-based electroplating solution

Claims

A method for circulating an iron-based electroplating solution, in which an iron-based electroplating solution used in an electroplating cell for iron-based electroplating is circulated and adjusted, the method comprising causing the iron-based electroplating solution used in the electroplating cell to pass through at least a reduction tank and a vertical centrifugal solid-liquid separation device in this order to perform a process, then putting the iron-based electroplating solution into the electroplating cell; and
wherein, in the reduction tank, an iron source for reduction according to a concentration of Fe³⁺ (Fe trivalent ion) in the iron-based electroplating solution transferred to the reduction tank is put.
The method for circulating an iron-based electroplating solution according to claim 1, wherein, in the reduction tank, sulfuric acid is put such that a PH of the iron-based electroplating solution in the reduction tank is maintained at 2.3 or less.
The method for circulating an iron-based electroplating solution according to claim 1 or 2, wherein a nitrogen gas is sealed in the reduction tank.
The method for circulating an iron-based electroplating solution according to any one of claims 1 to 3, wherein the vertical centrifugal solid-liquid separation device includes a screw outer tube that differentially rotates a solid and a liquid in a raw solution such that the solid and the liquid are centrifugally separated by a difference in specific gravity, and a screw provided in the screw outer tube, a rotary shaft of the screw is formed in a tubular shape such that the raw solution is derived from the screw into the screw outer tube, and a diffusion opening portion is formed on a side surface of the rotary shaft.
The method for circulating an iron-based electroplating solution according to any one of claims 1 to 4, wherein the iron-based electroplating solution is processed by the vertical centrifugal solid-liquid separation device, and then caused to pass through a final adjustment tank, and in the final adjustment tank, the concentration of Fe³⁺ (Fe trivalent ion) in the iron-based electroplating solution is adjusted to be 4.0 g/L or less.
The method for circulating an iron-based electroplating solution according to claim 5, wherein, in the final adjustment tank, a PH of the iron-based electroplating solution is adjusted to 2.0 to 2.3.
The method for circulating an iron-based electroplating solution according to claim 5 or 6, wherein, in the final adjustment tank, a solution temperature of the iron-based electroplating solution is adjusted to 40°C to 55°C.
The method for circulating an iron-based electroplating solution according to any one of claims 1 to 4, wherein the iron-based electroplating solution is processed by the vertical centrifugal solid-liquid separation device, and then caused to pass through a final adjustment tank, and in the final adjustment tank, a concentration of Fe³⁺ (Fe trivalent ion) in the iron-based electroplating solution is adjusted to 2.0 g/L or less, a PH of the iron-based electroplating solution is adjusted to 2.0 to 2.3, and a solution temperature of the iron-based electroplating solution is adjusted to 40°C to 55°C with sulfuric acid and pure water.
A method for manufacturing an iron-based electroplating solution, the method comprising:
manufacturing an iron-based electroplating solution by performing circulation and adjustment by the method for circulating an iron-based electroplating solution according to any one of claims 1 to 8.
A method for manufacturing an alloyed hot-dip galvanized steel sheet, the method comprising:
performing an iron-based electroplating process on a steel sheet using the iron-based electroplating solution manufactured by the method for manufacturing an iron-based electroplating solution according to claim 9.