JP7673676B2 - Zn-Ni alloy plated steel sheet manufacturing method and manufacturing equipment - Google Patents

Description

The present invention relates to a manufacturing method for efficiently producing Zn-Ni alloy plated steel sheets with excellent corrosion resistance, and manufacturing equipment used in this manufacturing method.

Zn-Ni plated steel sheets are used as surface-treated steel sheets for automobiles. Zn-Ni plating is generally produced by electroplating. Compared to pure Zn plating, Zn-Ni plating is known to have superior corrosion resistance, and is used as steel sheet for hot pressing. In Zn-Ni plating, the Ni content in the film affects the corrosion resistance, so it is necessary to control the Ni content within an appropriate range. On the other hand, it is known that the electrodeposition of Zn-iron alloys, including Zn-Ni alloys, is an irregular codeposition in which Zn, a less noble metal, deposits preferentially over iron group metals.

Moreover, electroplated steel sheets are annealed in a continuous annealing line, and then manufactured in an electrogalvanizing line separate from the continuous annealing line. The coiled cold-rolled steel sheets are transported to the electrogalvanizing line, where they are subjected to a degreasing process to remove rust-preventive oil, a pickling process to remove the surface oxide film and activate the surface, an electroplating process to deposit 5 to 80 g/ ^m2 of zinc or zinc alloy on one side, and a chemical conversion treatment process to apply various chemical conversion films to improve corrosion resistance and paintability, before being shipped as electrogalvanized steel sheets.

A horizontal flow cell system as shown in Fig. 1 is known as a general method for electroplating steel sheets. In this horizontal flow cell system electroplating apparatus, a passage 43 partitioned by electrode plates 42a and 42b is formed between two pairs of rolls, a conductor roll 40 and a backup roll 41, and when a steel sheet P is passed through this passage 43, a plating solution 30 is supplied from a nozzle header 44 to a gap between the steel sheet P and the electrode plates 42a and 42b, and an electric current is applied between the front surface of the steel sheet P and the electrode plates 42a and 42b, with the electrode plates 42a and 42b as anodes and the steel sheet P as a cathode, thereby subjecting the steel sheet P to electric Fe plating. This system has the advantage that the front and back surfaces of the steel sheet can be plated simultaneously. The above electroplating apparatus usually has about 5 to 15 cells connected together, and performs continuous plating while passing the steel sheet through the passage. The plating weight per cell is thin, at 1-5 g/ ^m2 , and this plating method involves laminating these layers, and since the current can be controlled according to the line speed and sheet width, the distribution of the coating weight in the width and length directions can be made uniform within 0.5-1 g/ ^m2 , and a beautiful appearance can be obtained, which is another major feature. Because it is a laminated plating method, for example, in the case of zinc-plated steel sheets for electrical use, ^which have a final coating weight of about 20 g/ ^{m2, the plating section does not become a bottleneck in production efficiency, but in the case of Zn-Ni-plated steel sheets for automobiles, which require higher corrosion resistance and have a final coating weight of over 60 g/m2} , the plating section becomes a bottleneck in production efficiency because the sheet running speed must be reduced in order to achieve the desired coating weight.

Furthermore, if the shape of the steel sheet is warped in the width direction during passing, the distance between the steel sheet and the electrode will differ in the width direction, changing the current distribution (more current flows in parts where the steel sheet-electrode distance is short than in parts where the steel sheet-electrode distance is long), resulting in uneven coating weight. In the case of Zn-Ni plated steel sheets for automobiles with a final coating weight of more than 60 g/ ^m2 , excessive coating weight will be applied in some parts in order to guarantee the in-plane lower limit coating weight, which will cause problems during press working, so it is necessary to control the coating weight to be uniform in the width direction.

The following technique is disclosed here as a high speed electroplating method.
FIG. 3 of Patent Document 1 discloses a method for producing an electroplated steel sheet at a high current density, in which a nozzle header provided with a plurality of plating solution jetting ports is disposed on the back surface of an electrode at a distance from the electrode, and through holes are provided through the electrode at positions of the electrode corresponding to each plating solution jetting port of the nozzle header for guiding the plating solution from the nozzle header to between the steel sheet and the electrode, and plating solution is jetted from the plurality of plating solution jetting ports of the nozzle header to impinge on the steel sheet in a direction substantially perpendicular to the steel sheet for plating.

As a plating method for making the plating amount uniform, Figure 1 of Patent Document 2 discloses a method for correcting C-warp by providing ribs on both ends of the width of a cushion-shaped nozzle electrode to increase static pressure.

JP 2005-272999 A Japanese Unexamined Patent Publication No. 60-86296

According to the method described in Patent Document 1, high current density plating is possible with pure Zn plating. On the other hand, Zn-Ni alloy plating requires different appropriate electrode shapes, plating solution spray conditions, and current density conditions from those of pure Zn plating, making it difficult to supply fresh plating solution to the steel sheet surface. Therefore, when carrying out Zn-Ni alloy plating, it is desirable to avoid unevenness in the deposition amount in the width direction, Ni content in the plating film falling outside the desired range, and large warping of the steel sheet in the plating cell that causes in-plane changes in the electrode-steel sheet distance.

The method of Patent Document 2 has the effect of flattening the shape of the steel sheet, but due to the structure in which the plating solution is likely to stagnate, when Zn-Ni alloy plating is performed at a high current density of 60 A/dm2 or ^more , the Ni content in the plating film falls outside the desired range, and therefore it is not possible to increase the sheet passing speed to produce a Zn-Ni alloy plated steel sheet.

The present invention has been made in consideration of the above problems, and aims to propose a method that enables the production of steel sheets with a uniform plating layer without reducing the sheet passing speed when applying Zn-Ni alloy plating, especially when forming a Zn-Ni plating layer with a high adhesion amount.

The gist of the present invention for solving the above problems is as follows.
1. A method for producing a Zn-Ni alloy plated steel sheet, comprising the steps of: supplying a plating solution toward a steel sheet in a gap between a continuously traveling steel sheet and an electrode plate disposed opposite the steel sheet and applying an electric current to the electrode plate as an anode and the steel sheet as a cathode, thereby electroplating the steel sheet with a Zn-Ni alloy,
The method for producing a Zn-Ni alloy plated steel sheet has a plating solution discharge rate, which is a ratio of a flow rate of the plating solution flowing out to a back side of the electrode plate not facing the steel sheet to a flow rate of the plating solution supplied to the steel sheet, of 10% or less.

2. The method for producing a Zn-Ni alloy-plated steel sheet described in 1 above, wherein the steel sheet has a composition containing, by mass%, 0.3% or less of C, and 1.0 to 6.0% in total of at least one of Si and Mn.

3. A manufacturing facility for Zn-Ni alloy plated steel sheet, comprising electrode plates arranged facing each other along the running line of the steel sheet, and a spray nozzle for supplying plating solution from the electrode plate side toward the running line, the electrode plate being the anode and the steel sheet being the cathode, and the plating solution discharge rate, which is the ratio of the flow rate of plating solution flowing out to the back side of the electrode plate not facing the steel sheet to the flow rate of plating solution supplied from the spray nozzle, is 10% or less.

4. The manufacturing equipment for Zn-Ni alloy plated steel sheet described in 3, wherein the electrode plate has at least one through hole extending in a direction intersecting with the running line and penetrating the electrode plate, and the injection nozzle is disposed in at least one of the through holes.

5. The manufacturing equipment for Zn-Ni alloy plated steel sheet described in 3 or 4 above, which has, in order from the traveling line side, a back plate and a jet header on the back side of the electrode plate, the jet header is connected to a plurality of the jet nozzles extending through the back plate and the electrode plate, the back plate is connected to the back side of the electrode plate via an electrode connection part, and an insulator is placed in the space between the back plate and the electrode plate by the electrode connection part.

6. The manufacturing equipment for the Zn-Ni alloy plated steel sheet described in 5 above, which comprises one or more plating cells in which the electrode plates are assembled together as a group of multiple sheets and tightly combined with one of the back plates.

7. The manufacturing equipment for Zn-Ni alloy plated steel sheet described in 6, in which the jet header is divided into multiple parts in each of the plating cells at a position that does not interfere with the electrode connection part.

8. The facility for producing a Zn-Ni alloy-plated steel sheet according to 5 above, wherein the jet header has a plating solution piping for supplying a plating solution into the jet header, and a ratio Ak/An of a cross-sectional area Ak of the plating solution piping to a total cross-sectional area An of the injection ports of the injection nozzles connected to the jet header is 2.5 or more.
Here, the manufacturing facility of the above No. 8 is preferably the manufacturing facility of the Zn-Ni alloy plated steel sheet according to any one of the above Nos. 5 to 7.

The manufacturing method of electroplated steel sheet of the present invention makes it possible to efficiently manufacture Zn-Ni alloy plated steel sheet with a uniform plating layer.

FIG. 1 is a schematic diagram of a conventional horizontal flow cell setup. 1 is a schematic cross-sectional side view of an electroplating cell of the present invention. FIG. 2 is an enlarged view of the periphery of a circular tube nozzle of the electroplating cell of the present invention.

Hereinafter, the method for producing a Zn-Ni alloy plated steel sheet of the present invention will be specifically described with reference to the drawings.
The method for producing a Zn-Ni alloy plated steel sheet of the present invention is characterized in that, when a plating solution is supplied toward a steel sheet in a gap between a continuously running steel sheet and an electrode plate arranged opposite the steel sheet and an electric current is passed through the electrode plate as an anode and the steel sheet as a cathode to perform Zn-Ni alloy electroplating, the method has a plating solution discharge rate, which is the ratio of the flow rate of plating solution flowing out to the back side of the electrode plate not facing the steel sheet to the flow rate of plating solution supplied to the steel sheet, of 10% or less.

First, one embodiment of a hot-dip galvanizing manufacturing facility used in the manufacturing method of hot-dip galvanized steel sheet of the present invention will be described with reference to FIG. 2. In the embodiment shown in FIG. 2, a steel sheet P is made to travel horizontally on a traveling line, and a pair of electrode plates 10 are arranged opposite to the continuously traveling steel sheet P. The electrode plates 10 are preferably insoluble. Furthermore, a conductor roll 20 and a backup roll 21 for passing electricity through the steel sheet P are arranged upstream and downstream of the electrode plate 10 in the traveling direction of the steel sheet P, respectively.

The conductor roll 20 may be made of a hard chrome plating that uses highly conductive copper or nickel plating as the base. The material and thickness of the electrode plate 10 are not particularly limited, but a suitable material is titanium coated with iridium oxide, and the thickness is preferably 5 to 100 mm. The distance between the steel plate P and the electrode plate 10 is also not particularly limited, but is preferably in the range of 2 to 20 mm.

A back plate 12 is arranged on the back surface of each electrode plate 10 (the side opposite the steel plate P) via an electrode connection part 11, and the current output from a rectifier (not shown) is input to the back plate 12 through a current-carrying rod 16. A nozzle header 14 for supplying plating solution 30 is arranged on the back surface of the back plate 12. To ensure uniform current distribution, it is preferable that the back plate 12 is formed as a single unit within one cell. On the other hand, it is preferable that the electrode plate 10 facing the steel plate is appropriately divided in the width direction and length direction in consideration of replacement work, etc.

The nozzle header 14 has a plurality of circular tube nozzles 15 made of an insulating material that extend from the back plate 12 side to the electrode plate 10 side through a plurality of through holes 10a and 12a provided in the electrode plate 10 and the back plate 12, respectively, and remain within the through holes 10a of the electrode plate 10. Here, it is preferable to form the circular tube nozzles 15 from an insulating material because by making the entire plating solution supply system from an insulating material, unintended electrolytic deposition in the plating solution flow path can be avoided, and damage to components due to sparks between the circular tube nozzles 15 and the electrode plate 10 can be avoided.

The circular pipe nozzle 15 is preferably positioned so that its axis is perpendicular to the surface of the steel sheet P. The plating solution 30 is supplied to the circular pipe nozzle 15 from the nozzle header 14 and sprayed toward the steel sheet P from the nozzle at the tip of the circular pipe nozzle 15.

In this way, while the steel sheet P is traveling horizontally, plating solution 30 is supplied to the gap between the steel sheet P and the electrode plate 10, and with the electrode plate 10 serving as the anode and the steel sheet P serving as the cathode, electricity is passed between the plating surface of the steel sheet P and the electrode plate 10 to electroplate the steel sheet.

Figure 3 shows an enlarged view of one nozzle header 14 and its surroundings in the electroplating device 56 described above. The tip of the circular tube nozzle 15 is long enough to remain inside the through hole 10a so as not to protrude beyond the surface of the steel sheet P side of the electrode plate 10 toward the steel sheet P side. Furthermore, to prevent the plating solution 30 from flowing out of the through hole 10a to the back side of the electrode plate 10, the space formed between the electrode plate 10 and the back plate 12 by the electrode connection part 11 (including any gap between the inner wall of the through hole 10a and the circular tube nozzle 15) must be blocked with an insulator 13 made of, for example, resin.

That is, at least the space formed between the electrode plate 10 and the back plate 12 must be filled with the insulator 13 so that the plating solution does not flow out from the steel sheet P side between the electrode plate 10 and the back plate 12. If there is a gap between the inner wall of the through hole 10a of the electrode plate 10 and the outer circumferential surface of the circular tube nozzle 15, it is preferable to fill it with the insulator 13. Here, if the above-mentioned gap in the through hole 10a can be completely filled so that there is no liquid leakage, there is no need to fill the gap between the electrode plate 10 and the back plate 12 with the insulator 13. However, considering that it is technically or cost-wise difficult to completely block the above-mentioned gaps in all of the many through holes of the electrode plate 10 with the insulator, it is more convenient to block the space formed between the electrode plate 10 and the back plate 12 with the insulator 13.

In order to pass current uniformly from the back plate 12 to the multiple electrode plates 10, it is preferable to machine the connection surface between the back plate 12 and the electrode connection part 11 smoothly and then fasten them with bolts (not shown). This structure is extremely effective in assembling this device. In other words, it is structurally possible to fasten the back plate 12 and the electrode plate 10 without providing the electrode connection part 11, but if the back plate 12 and the electrode plate 10 are in close contact only around the fastening bolt and a small gap occurs at a position slightly away from the fastening bolt, a spark will occur at the position of the gap when electricity is applied, damaging the back plate 12 and the electrode plate 10, so such a structure is undesirable.

Furthermore, as described above, by filling the gap between the back plate 12 and the electrode plate 10 with the insulator 13, uneven current flow between the back plate 12 and the electrode plate 10 can be avoided. If the material filling the gap between the back plate 12 and the electrode plate 10 is not an insulator, current will flow in places other than the electrode connection part 11, resulting in uneven current distribution when the electrode plate is viewed from the steel plate.

With the above structure, the plating solution does not flow out of the through holes onto the back side of the electrode plate 10, so the jet of plating solution from the circular tube nozzle 15 is concentrated in the gap between the electrode plates 10, and the plating solution jet pressure can be applied to the steel sheet P passing through the gap without any waste. As a result, a straightening force acts on both the top and bottom of the steel sheet P, making it possible to pass the poorly shaped steel sheet through and pass electricity through it while flattening it.

Here, in one section of electroplating shown in Fig. 2 (3 cells: electrode size of one cell: width 1.5 m × length in sheet passing direction 1 m), the pressing force on the steel sheet P by the jet of plating solution from the circular tube nozzle was investigated for the case of using the electrode plate provided with the discharge holes described in the above-mentioned Patent Document 1 and the case of using the electrode plate shown in Fig. 3 according to the present invention. That is, in one section of electroplating shown in Fig. 2, a total of 120 circular tube nozzles with an inner diameter of φ8 mm were arranged on one side of a pair of electrode plates, 10 in the electrode width direction × 12 rows in the sheet passing direction, and the pressing force applied to the steel sheet when a total flow rate of plating solution of 2.5 m ³ /min was sprayed toward the gap between the electrode and the steel sheet, which was 20 mm apart, was measured. As a result, in the electrode provided with the discharge holes described in Patent Document 1, the only point where the pressing force on the steel sheet acted was the collision position of the plating solution jet from the nozzle, and the pressing force acting on one side of the steel sheet was 290 N in total (1.53 N per nozzle). In contrast, in the electrode of the present invention shown in FIG. 3 , the plating solution is discharged only from the inlet and outlet sides of the steel sheet P of the electrode plate, and therefore the pressure corresponding to the pressure loss of the plating solution flowing between the nozzle and the steel sheet is applied to the entire electrode surface (the effective area on which the steel sheet pressing force actually acts is approximately 50% of the electrode plate area), resulting in a form in which the steel sheet is pressed, and it was found that the steel sheet pressing force reaches 3,500 N, more than 12 times as much.
In this way, according to the present invention, straightening forces act from above and below the steel sheet in the plating cell, making it possible to flatten a steel sheet with a poor shape while passing it through and passing a current through it.

To achieve the above effects, it is essential that the plating solution drainage rate during electroplating is 10% or less. In other words, if the plating solution drainage rate exceeds 10%, the flow rate of the plating solution flowing between the electrode plate and the steel sheet decreases, and the steel sheet pressing force decreases.

In addition, in a single divided jet header 14 as shown in FIG. 3, the ratio Ak/An of the cross-sectional area Ak of the plating solution pipe 14a that supplies the plating solution 30 to the jet header 14 and the total cross-sectional area An of the nozzles of the circular pipe nozzles 15 provided in the jet header 14 is preferably 2.5 or more. In other words, if Ak/An is less than 2.5, the pressure distribution in the jet header is likely to become non-uniform, and there is a risk that the variation in the injection speed from the circular pipe nozzle 15 will increase, and problems such as uneven adhesion may occur. In addition, if Ak/An exceeds 12, a sudden contraction pipe state will occur in which the flow path cross-sectional area from the jet header to the circular pipe nozzle changes significantly, resulting in large pressure loss and requiring excessive capacity for the plating solution delivery pump, so from an economical point of view, it is preferable to set it to 12 or less.

The above-mentioned cross-sectional areas are the minimum areas of the inner cross sections perpendicular to the axial direction of each tube. In addition, when there are multiple plating solution pipes and circular tube nozzles in each jet header 14, the total cross-sectional areas of each tube are Ak and An, respectively. Therefore, in the jet header 14 shown in FIG. 4, Ak is the cross-sectional area of the plating solution pipe 14a, and An is the total cross-sectional area of the three jet nozzles of the circular tube nozzle 15.

Incidentally, in a conventional electroplating apparatus, a current density of about 5 to 20 A/ ^dm2 is required to stably produce a Zn-Ni plating film with a Ni content of 10 to 15%, whereas the electroplating apparatus of the present invention enables production at 30 to 250 A/ ^dm2 . In the case of a horizontal electroplating apparatus, at a current density of 250 A/dm2 or ^more , power loss due to the electrical resistance of the plating solution and Joule heat in the steel sheet and electric circuit becomes large, and power consumption becomes too high relative to the productivity improvement achieved by increasing the sheet threading speed, making economical production impossible.

The above-mentioned plating target is not particularly limited, and may be any steel plate. Examples of plating targets include ordinary steel, stainless steel, and aluminum plates. The present invention is effective when applied to steel plates, and is particularly advantageous when applied to high-tensile steel plates. As high-tensile steel plates, steel plates having the composition shown below are suitable. Note that the "%" in the following composition means mass % unless otherwise specified.

C: 0.025-0.300%
C forms a retained austenite layer, a martensite phase, etc. in the steel structure, which facilitates improving workability, so it is preferable to contain 0.025% or more. On the other hand, if it exceeds 0.300%, weldability deteriorates, so the C content is preferably 0.300% or less.

Si: 0.2-2.5%
Since Si is an effective element for strengthening steel and obtaining good material properties, 0.2% or more is added to high-tensile steel sheets. If the Si content is less than 0.2%, expensive alloying elements are required to obtain high strength. On the other hand, if the Si content exceeds 2.5%, the formation of an oxide film during oxidation treatment is suppressed. In addition, the alloying temperature is also increased, making it difficult to obtain the desired mechanical properties. Therefore, the Si content is preferably 2.5% or less.

Mn: 1.5-3.5%
Mn is an element that is effective in increasing the strength of steel. In order to ensure a tensile strength of 590 MPa or more, it is preferable to include 0.5% or more. On the other hand, if it exceeds 3.0%, it may become difficult to ensure weldability, plating adhesion, and strength-ductility balance. Therefore, the Mn content is preferably 1.5 to 3.5%.

In addition to the above components, the following elements may also be contained.
Al: 0.001-1.000%
Al is added for the purpose of deoxidizing molten steel, but if its content is less than 0.001%, this purpose is not achieved. On the other hand, if its content exceeds 1.000%, Al forms oxides on the surface, which deteriorates the plating appearance (surface appearance). Therefore, the Al content may be 0.001% or more and 1.000% or less.

P: 0.10% or less P is one of the elements that is inevitably contained, and since there is a concern that costs will increase if the content is less than 0.005%, it is desirable to have a content of 0.005% or more. On the other hand, as the content of P increases, the manufacturability of slabs deteriorates. Furthermore, the inclusion of P suppresses the alloying reaction and causes uneven plating. In order to suppress these, it is necessary to keep the content at 0.10% or less. Therefore, the amount of P may be 0.10% or less. It is preferably 0.05% or less.

S: 0.01% or less S is an element that is inevitably contained in the steelmaking process. However, if it is contained in a large amount, it deteriorates weldability. Therefore, S may be set to 0.01% or less.
When the above components are contained, the balance is Fe and unavoidable impurities.

Furthermore, one or more elements selected from B: 0.001 to 0.005%, Nb: 0.005 to 0.050%, Ti: 0.005 to 0.080%, Cr: 0.001 to 1.000%, Mo: 0.05 to 1.00%, Cu: 0.05 to 1.00%, Ni: 0.05 to 1.00%, and Sb: 0.001 to 0.200% may be contained as necessary.
When these elements are added, the appropriate contents and the reasons for limiting the contents are as follows:

B: 0.001-0.005%
At 0.001% or more, B has a quench-hardening promoting effect. On the other hand, at more than 0.005%, the chemical conversion treatability deteriorates. Therefore, when B is contained, the B content may be 0.001% or more and 0.005% or less.

Nb: 0.005-0.050%
Nb has the effect of adjusting strength (strength improvement) when it is 0.005% or more. On the other hand, if it exceeds 0.05%, it will lead to an increase in costs. Therefore, when Nb is contained, the Nb content may be 0.005% or more and 0.05% or less.

Ti: 0.005-0.080%
At 0.005% or more, Ti has the effect of adjusting strength (strength improvement). On the other hand, at more than 0.080%, it causes deterioration of chemical conversion treatability. Therefore, when Ti is contained, the Ti content may be 0.005% or more and 0.080% or less.

Cr:0.001~1.000%
At 0.001% or more, Cr has a hardenability effect. On the other hand, at more than 1.000%, Cr is concentrated on the surface, which deteriorates weldability. Therefore, when Cr is contained, the Cr content may be set to 0.001% or more and 1.000% or less.

Mo: 0.05-1.00%
Mo has the effect of adjusting strength (improving strength) when it is 0.05% or more, but when it exceeds 1.00%, it leads to an increase in costs. Therefore, when Mo is contained, the Mo content may be 0.05% or more and 1.00% or less.

Cu: 0.05-1.00%
Cu has an effect of promoting the formation of the residual γ phase when it is 0.05% or more, while Cu exceeding 1.00% leads to an increase in cost. Therefore, when Cu is contained, the Cu content may be 0.05% or more and 1.00% or less.

Ni: 0.05-1.00%
Ni has an effect of promoting the formation of the residual γ phase when it is 0.05% or more. On the other hand, if it exceeds 1.00%, it will lead to an increase in costs. Therefore, when Ni is contained, the Ni content may be 0.05% or more and 1.00% or less.

Sb: 0.001-0.200%
Sb can be contained from the viewpoint of suppressing nitridation and oxidation of the steel sheet surface, or decarburization of the steel sheet surface in a region of several tens of microns caused by oxidation. By suppressing nitridation and oxidation, the amount of martensite generated on the steel sheet surface is prevented from decreasing, and fatigue properties and surface quality are improved. Such effects can be obtained at 0.001% or more. On the other hand, if it exceeds 0.200%, toughness deteriorates. Therefore, when Sb is contained, the amount of Sb may be 0.001% or more and 0.200% or less.

Trace elements permitted in plating solutions include Pb (1.0 ppm or less), Cr (200 ppm or less), Hg (200 ppm or less), Cu (2.0 ppm or less), Cd (6.0 ppm or less), Sr (30 ppm or less), and sludge (solids content 100 ppm or less).

The following describes examples of the present invention, but the technical scope of the present invention is not limited to the following examples.
An example of the present invention uses an electroplating apparatus (one cell) having the configuration shown in Figures 2 and 3. That is, the plating cell constituting the electroplating apparatus has an electrode length in the longitudinal direction of 2 m in each cell, and 15 cells are connected. The electrode plate is made of titanium, the current-carrying surface is coated with an iridium oxide film, and has a width that almost covers the strip.
As comparative examples, a general horizontal flow cell (FIG. 1) and a horizontal multi-hole plating cell having plating solution discharge holes (based on the description in FIG. 1 of Patent Document 1) were used.

Using each of the above plating manufacturing equipment examples, a Zn-Ni alloy plating process was performed by running a steel sheet 0.7 mm thick and 1200 mm wide at a sheet running speed of 0.7 to 3.5 m/s and setting the current density so ^that the plating coating weight would be 65 g/m2 per side with a plating efficiency of 70%. Specific sheet running speed and current density conditions are as shown in Table 1. The plating bath was a sulfuric acid bath, the components of which were zinc 24 to 40 g/L and nickel 45 to 70 g/L, and the pH was adjusted to 1.5 to 1.7.

The electroplated steel sheets thus obtained were subjected to measurement of the coating weight and Ni content in the coating. The coating weight and Ni content were calculated as the average value of 10 measurements taken in the longitudinal direction at 16 points in the width direction. The coating weight distribution in the width direction was calculated as the coating weight change rate (%) at both ends in the width direction (positions 30 mm from the steel sheet edge) relative to the coating weight at three points in the width direction center, and a good condition was 5% or less.
The results of the above measurements and evaluations are shown in Table 1 together with the electroplating conditions.

P steel plate 10 electrode plate 11 electrode connection part 12 back plate 13 insulator 14 jet header 15 cylindrical nozzle 16 current-carrying rod 20 conductor roll 21 backup roll

Claims (7)

A method for producing a Zn-Ni alloy-plated steel sheet, comprising the steps of: supplying a plating solution from a spray nozzle on the electrode plate in a direction perpendicular to a surface of the steel sheet in a gap between the continuously traveling steel sheet and an electrode plate disposed opposite the steel sheet along the steel sheet; and applying an electric current to the electrode plate as an anode and the steel sheet as a cathode, thereby electroplating the steel sheet with a Zn-Ni alloy,
A method for producing a Zn-Ni alloy-plated steel sheet, in which a plating solution discharge rate, which is a ratio of a flow rate of the plating solution flowing out to a back side of the electrode plate not facing the steel sheet to a flow rate of the plating solution supplied from the spray nozzle to the steel sheet, is set to 10% or less. The method for producing Zn-Ni alloy-plated steel sheet according to claim 1, wherein the steel sheet has a composition containing, by mass%, 0.3% or less of C, and 1.0 to 6.0% in total of at least one of Si and Mn. a back plate and a jet header on a back side of the electrode plate, in that order from the traveling line side, and a plurality of the jet nozzles extending through the back plate and the electrode plate are connected to the jet header, the back plate is connected to a back side of the electrode plate via an electrode connection part, and an insulator is disposed in a space between the back plate and the electrode plate, the space being defined by the electrode connection part; and a plating solution discharge rate, which is a ratio of a flow rate of plating solution flowing out to a back side of the electrode plate not facing the steel sheet to a flow rate of plating solution supplied from the jet nozzle, is 10% or less. The manufacturing equipment for Zn-Ni alloy plated steel sheet according to claim 3, wherein the electrode plate has at least one through hole extending in a direction intersecting with the running line and penetrating the electrode plate, and the injection nozzle is disposed in at least one of the through holes. The manufacturing equipment for Zn-Ni alloy plated steel sheet according to claim 3 or 4, which comprises one or more plating cells in which the electrode plates are assembled together as a group of multiple sheets and tightly combined with one of the back plates. The manufacturing equipment for Zn-Ni alloy plated steel sheets according to claim 5, wherein the jet header is divided into multiple parts in each of the plating cells at positions that do not interfere with the electrode connection parts. 5. The production facility for Zn-Ni alloy plated steel sheet according to claim 3 or 4, wherein the jet header has a plating solution piping for supplying a plating solution into the jet header, and a ratio Ak/An of a cross-sectional area Ak of the plating solution piping to a total cross-sectional area An of the injection ports of the injection nozzles connected to the jet header is 2.5 or more.

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