JP2982620B2 - Iron material for replenishing iron ions in iron-zinc alloy electroplating solution and method for replenishing iron ions and zinc ions - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION The present invention relates to an iron-zinc alloy electroplating solution, an insoluble electrode, and a method for replenishing iron- and zinc ions in the iron-zinc alloy electroplating solution. The present invention relates to an iron material for replenishing iron-zinc alloy plating solution and a method for replenishing iron ions and zinc ions in an iron-zinc alloy plating solution when forming an iron-zinc alloy electroplating layer on the surface of a steel strip.

[0002]

2. Description of the Related Art As a method for continuously forming an iron-zinc alloy electroplating layer on the surface of a cold-rolled steel sheet or a galvannealed steel sheet, an iron-zinc alloy electroplating solution is used; While supplying iron ions and zinc ions in the iron-zinc alloy electroplating solution, a direct current is passed between the insoluble anode and the steel sheet, thus continuously iron-zinc alloy electroplating on the surface of the steel sheet. Methods for forming layers are known.

[0003] As a method of replenishing iron ions and zinc ions into an electroplating solution, for example, Japanese Patent Publication No.
The following method is generally performed as disclosed in Japanese Patent Application Laid-Open No. -23200 and Japanese Utility Model Application Laid-Open No. 58-148068 (hereinafter referred to as Prior Art 1).

[0004] That is, as shown in the schematic system diagram of FIG. 2, a metal iron melting device 2 ′ and a metal zinc melting device 3 ′ are respectively arranged in parallel with a plating solution circulation tank 1 ′. 'Fill metal iron inside and metal zinc melting equipment
Fill metallic zinc in 3 '.

[0005] Plating solution circulation tank 1 'and metallic iron melting device 2'
And a conduit 4 'through which the plating solution circulates. A pump 5 'is provided in the middle of the conduit 4', and a filter 6 'is provided on the outlet side of the metallic iron melting device 2' of the conduit 4 ', and a branch pipe 7' reaching the inlet side of the metallic iron melting device 2 'is provided. Connecting. Similarly, a conduit 4 'through which the plating solution circulates is connected between the plating solution circulation tank 1' and the metal zinc dissolving device 3 '. conduit
A pump 5 'is provided in the middle of 4', and a filter 6 'is provided on the outlet side of the metallic zinc dissolving device 3' of the conduit 4 ', and a branch pipe 7' connected to the inlet side of the metallic zinc dissolving device 3 'is connected. I do.

[0006] The electroplating solution guided from the electroplating tank (not shown) into the plating solution circulation tank 1 'by the conduit 8' is:
Guided through conduits 4 'to each of the metal iron melting device 2' and the metal zinc melting device 3 'connected in parallel to the circulation tank 1',
In the metal iron melting device 2 ′ and the metal zinc melting device 3 ′,
Metallic iron and metallic zinc are dissolved in the electroplating solution.
The plating solution in which the metallic iron was dissolved and the plating solution in which the metallic zinc was dissolved were returned to the circulation tank 1 'through the conduit 4', respectively, mixed in the circulation tank 1 ', and then passed through the conduit 9'. It is sent to the electroplating tank.

[0007] Thus, the plating solution from the electroplating tank is circulated through the circulation tank 1 ', the metal iron melting device 2' and the metal zinc melting device 3 ', and the flow rate and the melting device 2',
By controlling the amounts of metallic iron and metallic zinc in 3 ', predetermined amounts of iron ions and zinc ions are replenished in the plating solution.

In dissolving metallic iron and metallic zinc in an electroplating solution by the above-described method, metallic zinc having an extremely high purity (99.99% or more) can be obtained on an industrial scale. As for iron, it is extremely difficult to obtain a high-purity iron such as metallic zinc, and even if it is available, it is expensive, so that metallic iron containing some impurities must be used.

Accordingly, the electroplating solution in which the metallic iron is dissolved in the metallic iron dissolving apparatus 2 'contains a relatively high concentration of impurities. The electroplating solution in which zinc metal is dissolved in the zinc dissolving apparatus 3 'is mixed in the circulation tank 1' and fed to the electroplating tank.

As a result, when performing electroplating on a steel sheet in an electroplating tank, depending on the type and concentration of the above-described impurities contained in the electroplating solution, iron-zinc having a desired component composition may be present on the steel sheet. It becomes difficult to form an alloy electroplating film, and further, poor adhesion of the plating film, deterioration of corrosion resistance, poor plating appearance, and the like may occur.

As a means for solving the above-mentioned problem, for example, Japanese Patent Application Laid-Open No. 63-282297 discloses an iron material for replenishing iron ions in which the content of a specific impurity component is limited.
t.% or less, Si: 0.1 wt.% or less, Cu: 0.1 wt.% or less, Sb:
There is disclosed an iron material for replenishing iron ions in an iron-based plating solution (hereinafter referred to as Prior Art 2), comprising 0.01 wt.% Or less, Sn: 0.01 wt.% Or less, the remaining Fe and impurities.

On the other hand, Japanese Patent Application Laid-Open No. 3-150400 discloses that a metal iron melting device and a metal zinc melting device are arranged in series, and the electroplating solution is led to the metal iron melting device to dissolve the metal iron in the plating solution. Then, the plating solution in which the metallic iron is dissolved is led to a metallic zinc dissolving apparatus to dissolve the metallic zinc in the plating solution, and when the metallic zinc is dissolved, the impurities in the plating solution are deposited on the surface of the metallic zinc. A method (hereinafter referred to as Prior Art 3) is disclosed.

That is, as shown in the schematic system diagram of FIG. 3, a metal iron melting device 2 ′ and a metal zinc melting device 3 ′ are respectively arranged in series with a plating solution circulation tank 1 ′, and the plating solution is Connect the circulating conduit 4 '. A pump 5 'is provided in the middle of the conduit 4', and a filter is provided in the conduit 4 'on the outlet side of each of the metal iron melting device 2' and the metal zinc melting device 3 'of the conduit 4'.
6 'is provided and connected to a conduit 4' on the outlet side of each of the filters 6 'is a branch pipe 7' leading to the respective inlet side of the metal iron melting device 2 'and the metal zinc melting device 3'.

The electroplating solution guided from the electroplating tank (not shown) into the plating solution circulation tank 1 'by the conduit 8'
First, the metallic iron is dissolved in the plating solution in the metallic iron dissolving device 2 ′ filled with metallic iron, and then the metallic zinc is dissolved in the plating solution in the metallic zinc dissolving device 3 ′. When dissolving the metallic zinc, impurity ions in the plating solution precipitate on the surface of the metallic zinc. As a result, the content of impurities in the plating solution is reduced, and predetermined amounts of iron ions and zinc ions are replenished in the plating solution.

[0015]

Prior art 2 has the following problems. That is, there are many types of impurities contained in metallic iron. Therefore, it is difficult to form an iron-zinc alloy electroplated film having a desired component composition on a steel sheet due to impurities not specified by Prior Art 2 or a combined effect of a plurality of types of impurities. Poor adhesion of the plating film, deterioration of corrosion resistance, poor plating appearance, and the like cannot be sufficiently prevented.

Prior art 3 has the following problem.
That is, in the actual operation, due to the difference in dissolution rate between metallic iron and metallic zinc, and the fluctuation of the iron content in the plating film, etc., in the plating bath, only iron ions or zinc ions are independently supplied. It may be necessary. However, in the method of Prior Art 3, since the metal iron melting device and the metal zinc melting device are arranged in series, it is not possible to supply only the iron ions or zinc ions alone. Therefore, the method of Prior Art 3 is difficult to apply to actual operation.

Accordingly, an object of the present invention is to solve the above-mentioned problems and to form a metal-iron melting device and a metal-zinc melting device in order to form an iron-zinc alloy electroplating layer continuously on the surface of a steel sheet. By circulating the solution and dissolving metal iron and metal zinc in the plating solution, when replenishing iron ions and zinc ions in the plating solution, a high-quality iron-zinc alloy electroplating solution can be obtained, Moreover,
When a difference in the dissolution rate between metallic iron and metallic zinc, or a change in the iron content in the plating film, etc., occurs, it is possible to replenish iron ions or zinc ions alone in the plating bath. Another object of the present invention is to provide an iron material for replenishing iron ions and a method for replenishing iron ions and zinc ions in an iron-zinc alloy electroplating solution suitable for actual operation.

[0018]

Means for Solving the Problems Claim 1 of the present invention provides:
The invention in which the component composition of the iron material for replenishing iron ions is specified, wherein C, Si, Mn, P,
When the content of S, Cu, Cr and Al is C: 0.003 wt.% Or less,
Si: 0.005 wt.% Or less, Mn: 0.05 wt.% Or less, P: 0.002
wt.% or less, S: 0.003 wt.% or less, Cu: 0.003 wt.% or less,
It is characterized by being limited to Cr: 0.01 wt.% Or less and Al: 0.003 wt.% Or less.

A second aspect of the present invention relates to a method for replenishing iron ions and zinc ions into an iron-zinc alloy electroplating solution, wherein the iron-zinc alloy electroplating solution from an electroplating tank is plated with a plating solution. It is led to a circulation tank, and the plating solution is filled with a metal iron dissolving device filled with metallic iron and metallic zinc, which are connected in series with the plating solution circulation tank by a circulation conduit. Circulating between the metal zinc dissolving device, the metal iron dissolving device to dissolve the metal iron in the plating solution, and then, in the plating solution in which the metal iron is dissolved, the metal zinc dissolving in the metal zinc dissolving device. The method for dissolving and thus replenishing iron and zinc ions in an iron-zinc alloy electroplating solution, wherein the metallic iron to be charged into the metallic iron dissolving apparatus is as described above. Using an iron material having a component composition of, and connecting the electroplating solution circulation tank and each of the metal iron melting device and the metal zinc melting device in parallel by another conduit, In addition, by operating an on-off valve provided in the another conduit, only the iron ions or only the zinc ions can be independently supplied into the electroplating solution.

[0020]

The reason for limiting the component composition of the iron material for replenishing iron ions to the above-mentioned range in the first aspect of the present invention will be described below. When C exceeds 0.003 wt.% And / or Si exceeds 0.005 wt.%, C and / or Si dissolves at the time of dissolution, and this remains as a floating substance in the plating solution to contaminate the plating solution. Therefore, the C content in the iron material for replenishing iron ions should be limited to 0.003 wt.% Or less, and the Si content should be limited to 0.005 wt.% Or less.

At least one of Mn, P, S, Cu, Cr and Al has a content described below, that is, Mn: 0.05 wt.%,
P: 0.002 wt.%, S: 0.003 wt.%, Cu: 0.003 wt.%, C
If r: 0.01 wt.% and Al: 0.003 wt.%, the deposition behavior and the crystals deposited become abnormal, resulting in poor plating quality. Therefore, the Mn content is 0.05 wt.% Or less, and the P content is
002 wt.% Or less, S content is 0.003 wt.% Or less, Cu content is
0.003 wt.% Or less, Cr content should be limited to 0.01 wt.% Or less, and Al content should be limited to 0.003 wt.% Or less.

Next, the method according to claim 2 of the present invention will be described.
Description will be made based on the schematic process diagram shown in FIG. As shown in FIG. 1, a plating solution circulation tank 1, a metal iron melting device 2, and a metal zinc melting device 3 are connected in series by a circulation conduit 4. In the middle of the first conduit 4a connecting the plating solution circulation tank 1 and the metallic iron melting device 2, a pump 5a is provided.
Are provided, and in the middle of a second conduit 4b connecting the metal iron melting device 2 and the metal zinc melting device 3 and a third conduit 4c connecting the metal zinc melting device 3 and the plating solution circulation tank 1, Each is provided with a filter 6.

In the metallic iron melting device 2, the content of C, Si, Mn, P, S, Cu, Cr and Al as metallic iron for replenishing iron ions is C: 0.003 wt.%. Below, Si: 0.005 w
t.% or less, Mn: 0.05 wt.% or less, P: 0.002 wt.% or less,
S: 0.003 wt.% Or less, Cu: 0.003 wt.% Or less, Cr: 0.01 w
An iron material having a component composition limited to t.% or less and Al: 0.003 wt.% or less is filled. In addition, metal zinc melting device 3
The inside is filled with zinc metal for supplementing zinc ions.

A second conduit 4b connecting the metallic iron dissolving device 2 and the metallic zinc dissolving device 3 is connected to another conduit 10 which branches off from the second conduit 4b and reaches the plating solution circulation tank 1. And the metal iron melting device 2 are connected to the first conduit 4a,
It is also connected by a second conduit 4b and another conduit 10. On the other hand, the plating solution circulation tank 1 and the metal zinc dissolving device 3
Is connected between the plating solution circulation tank 1 and the metal zinc dissolving apparatus 3 by a third conduit 4c and another conduit 11.

A first on-off valve 12 is provided in the middle of another conduit 10 branching from the second conduit 4b, and a second conduit between the branch point with the other conduit 10 and the metal zinc dissolving device 3 is provided. 4b is provided with a second on-off valve 13. A plating solution supply conduit 8 and a plating solution discharge conduit 9 are connected to the plating solution circulation tank 1.

During normal operation, the iron-zinc alloy electroplating solution guided from the electroplating tank (not shown) into the plating solution circulation tank 1 by the plating solution supply conduit 8 is supplied to the pump 5a.
Is fed to the metallic iron melting device 2 through the first conduit 4a, then to the metallic zinc melting device 3 through the second conduit 4b, and then plated through the third conduit 4c. Return to the liquid circulation tank 1. As described above, when the plating solution is circulating in the plating solution circulation tank 1, the metal iron dissolving device 2, and the metal zinc dissolving device 3, the first on-off valve 12 provided in the middle of another conduit 10 is closed. , The second conduit provided in the second conduit 4b
The on-off valve 13 is open. At this time, the pump 5b provided in the middle of another conduit 11 connecting the plating solution circulation tank 1 and the metal zinc dissolving device 3 does not operate.

As a result, first, the metallic iron is dissolved in the plating solution in the metallic iron dissolving device 2, and then, the metallic zinc is dissolved in the plating solution in which the metallic iron is dissolved in the metallic zinc dissolving device 3. Thus, the plating solution sequentially circulates between the plating solution circulation tank 1, the metal iron dissolving device 2, and the metal zinc dissolving device 3, so that iron ions and zinc ions are supplied to the iron-zinc alloy electroplating solution.

When it is necessary to supply only iron ions to the plating solution alone due to a difference in dissolution rate between metallic iron and metallic zinc, a change in the iron content in the plating film, and the like,
Open the first on-off valve 12 provided in the middle of another conduit 10,
The second on-off valve 13 provided in the second conduit 4b is closed. As a result, the plating solution in the plating solution circulation tank 1
Is fed to the metallic iron melting device 2 through the first conduit 4a, and then returned to the plating solution circulation tank 1 through the second conduit 4b and another conduit 10. Thus, the plating solution circulates between the plating solution circulating tank 1 and the metal iron dissolving device 2, and only iron ions are supplied to the iron-zinc alloy electroplating solution.

If it is necessary to supply only zinc ions to the plating solution by itself, the plating solution is provided in the middle of another conduit 11 connecting between the plating solution circulation tank 1 and the metal zinc dissolving device 3. The operated pump 5b is operated. As a result, the plating solution in the plating solution circulation tank 1 is sent to the metal zinc dissolving apparatus 3 through another conduit 11 and then the third conduit 4c
To the plating solution circulation tank 1. Thus,
The plating solution circulates between the plating solution circulation tank 1 and the metal zinc dissolving device, and only zinc ions are supplied to the iron-zinc alloy electroplating solution.

The iron material for replenishing iron ions filled in the metallic iron dissolving apparatus 2 has the above-described component composition, and its impurities are limited to a very small amount over a wide range. Therefore, as before, impurities remain in the plating solution, contaminating the plating solution, electrodeposition behavior due to the impurities,
The problem of impairing the plating quality does not occur due to abnormalities of the electrodeposited crystal.

During normal operation, the metallic iron melting device 2
In the above, the metallic iron is dissolved in the plating solution, and then, in the metallic zinc dissolving device 3, the metallic zinc is dissolved in the plating solution in which the metallic iron has been dissolved. As a result, the content of impurities in the plating solution can be reduced as a result of substitution and precipitation on the surface of metallic zinc.

In this way, the iron-zinc alloy electroplating solution supplied with iron ions and zinc ions and having a low impurity content at the time of iron ion replenishment is supplied to the circulation tank 1
Is supplied to an electroplating tank (not shown) through a conduit 9.

The above-described precipitation of impurity ions during the dissolution of zinc metal also occurs in the prior art 1 shown in FIG. 2, in which a metal iron dissolving device and a metal zinc dissolving device are connected in parallel to a plating solution circulation tank. Has been done to some extent.
However, in the case of Prior Art 1, the impurities in the metallic iron are not limited to a sufficiently low amount.

Further, in the case of the prior art 1, the plating solution in which the metallic iron is dissolved in the metallic iron dissolving apparatus 2 'and the content of impurities is increased is used for dissolving the metallic zinc in the metallic zinc dissolving apparatus 3'. The plating solution mixed with the plating solution in the plating solution circulation tank 1 ′ and having the content of impurities reduced to some extent by such mixing circulates between the metal zinc dissolution apparatus 3 ′. Therefore, the effect of removing impurities by precipitation of impurity ions is extremely low.

On the other hand, according to the method of the present invention, the impurities in the iron material for replenishing iron ions filled in the metal iron melting apparatus 2 are limited to a very small amount over a wide range. In addition, since the plating solution containing a very small amount of impurities circulates between the metal zinc dissolving apparatus, the efficiency of impurity removal by precipitation of impurity ions is extremely high.

The iron content and the zinc content in the plating solution can be determined by the filling amount of metallic iron in the metallic iron dissolving device 2, the filling amount of metallic zinc in the metallic zinc dissolving device 3, the metallic iron dissolving device and the metallic iron dissolving device. Each of the zinc dissolving devices has a structure in which a plurality of small devices are connected in parallel, and can be controlled by changing the ratio of both by changing the number of operating devices.

[0037]

Next, the present invention will be described with reference to Examples and Comparative Examples. A cold-rolled steel strip having a thickness of 0.8 mm is subjected to an iron-zinc alloy electroplating process while replenishing iron ions and zinc ions under the following conditions according to the process of the present invention shown in FIG. An iron-zinc alloy electroplated film was formed on the surface of
Nos. 1-3 were prepared.

[0038] (1) plating solution component composition _{FeS0 4 · 7H 2 O: 300} g / l ZnS0 4 · 7H 2 O: 150 g / l Na 2 S0 4: 50 g / l

(2) Plating solution temperature: 50 ° C. (3) Plating solution flow rate: 2 m / sec (4) Plating current density: 100 A / dm ² (5) Insoluble anode: Pt-Ir coated Ti electrode

(6) Supplementary metal zinc: High-purity granular zinc of 99.99% or more (particle diameter: 2 to 3 mm) (7) Supplementary metal iron: C, Si, Mn,
P, S, Cu, Cr and Al content columnar iron material having a component composition limited within the scope of the present invention (3mmφ × 3mm)

(8) Metal iron dissolving apparatus: 80 mm diameter, 4 liter capacity packed tower type, plating solution is supplied from the bottom and discharged from the top (9) Metal zinc dissolving apparatus: the same packed tower type as above,
80mm diameter, 2 liter capacity (10) Target plating amount: 40 g / m ² (11) Target iron content: 13-17 wt.%

When it is necessary to supply iron ions alone to the plating solution due to a difference in dissolution rate between metallic iron and metallic zinc and a change in the iron content in the plating film, etc.
By switching the first on-off valve 12 and the second on-off valve 13, the plating solution sent to the metal iron dissolving device is returned to the plating solution circulation tank, and circulated between the plating solution circulation tank and the metal iron dissolution device. Thus, only iron ions were supplied to the plating solution.

Comparative Example 1 Prior art 1 shown in FIG. 2 in which a metal iron melting device and a metal zinc melting device were connected in parallel to a plating solution circulation tank for a 0.8 mm thick cold rolled steel strip. In the other steps, iron- and zinc ions are replenished under the same conditions as in the above-mentioned embodiment, while iron-
A zinc alloy electroplating treatment was performed to form an iron-zinc alloy electroplating film on the surface of the cold-rolled steel strip, and Comparative Sample Nos. 1 to 3 were prepared.

Comparative Example 2 C, Si, Mn, P, S, Cu, Cr
And using an iron material in which at least one content of Al is out of the range of the present invention, and performing an iron-zinc alloy electroplating treatment while replenishing iron ions and zinc ions under the same conditions as in the above-described embodiment. Then, an iron-zinc alloy electroplating film was formed on the surface of the cold-rolled steel strip, and comparative specimens Nos. 4 to 6 were prepared.

[Comparative Example 3] C, Si, Mn, P, S, Cu, Cr
And the same iron material as in Comparative Example 2 in which the content of at least one of Al and Al is out of the range of the present invention, and a metal-iron melting device and a metal-zinc melting device are provided in the plating solution circulation tank shown in FIG. An iron-zinc alloy electroplating process is performed while replenishing iron ions and zinc ions under the same conditions as in the above-mentioned embodiment by the steps of prior art 1 connected in parallel, and iron-zinc alloy is electroplated on the surface of the cold-rolled steel strip. A zinc alloy electroplated film was formed, and comparative specimens Nos. 7 to 9 were prepared.

Table 1 shows the composition of the replenishing metal iron used in the preparation of the test specimens Nos. 1 to 3 of the present invention and the test specimens Nos. 1 to 9, and the coating weight and plating film of each test specimen. 2 shows the Fe content in the steel.

[0047]

[Table 1]

Specimens Nos. 1-3 of the Present Invention and Specimens for Comparison
For each of Nos. 1 to 9, the plating appearance, corrosion resistance and adhesion of the plating film were examined and evaluated as described below.

(1) Plating appearance: The color tone and plating unevenness of the plating film were visually inspected and evaluated as follows. ：: good, △: slightly poor, ×: bad.

(2) Corrosion resistance: Each of the test sample of the present invention and the test sample for comparison was subjected to a full-dip type zinc phosphate treatment to form a zinc phosphate coating, and then subjected to cationic electrodeposition coating. To a thickness of 2 on the zinc phosphate coating.
A coating of 0 μm was formed and then the coating was cross cut. With respect to the specimen subjected to the cross cut in this way, the blister width of the coating film of the cross cut part of the specimen after 720 hours in the salt spray test specified in JIS Z2371 was measured, and the blister width was used. The evaluation was as follows. ○: blister width 2 mm or less, Δ: blister width more than 2 mm, 4 mm or less, ×: blister width more than 4 mm.

(3) Adhesion of plating film: Each of the test sample of the present invention and the test sample for comparison was bent by an OT bending machine with its plating surface inside, and then opened, and then an adhesive tape was stuck on the surface. Then, the adhesive tape was peeled off and evaluated according to the degree of blackening of the adhesive tape as follows. ：: good, △: slightly poor, ×: bad.

Table 1 also shows the evaluation results of the above-mentioned tests on the test samples Nos. 1 to 3 of the present invention and the test samples Nos. 1 to 9 for comparison.

As is clear from Table 1, the comparative specimen N
o.1 to 3 are specimens of the present invention No.1 to 3
As shown in FIG. 2, despite the use of an iron material having the same C, Si, Mn, P, S, Cu, Cr, and Al contents as defined in the present invention, Since the plating solution circulation tank was connected to the metal iron dissolving device and the metal zinc dissolving device in parallel according to the process of the prior art 1, the appearance of the plating film was poor in each case. The adhesion of the coating was also poor.

The test specimens Nos. 4 to 6 were supplied in spite of being subjected to the iron-zinc alloy electroplating process while replenishing iron ions and zinc ions in accordance with the process of the present invention shown in FIG. Specimen No.4 as metal iron for comparison
Since the steel used had a high content of Si, P and Cr outside the range of the present invention, the appearance of the plating film was poor. Further, Comparative Sample No. 5 was poor in appearance and adhesion of the plating film because an iron material having a large content of C, Si and Cr exceeding the range of the present invention was used. And, for the comparative sample No. 6, since the content of C, Si, P and Cr was all higher than the range of the present invention, the appearance of the plating film was extremely poor, and the corrosion resistance and Adhesion was also poor.

In Comparative Sample Nos. 7 to 9, the same iron material as Comparative Sample Nos. 4 to 6 having a component composition outside the scope of the present invention was used as replenishing metallic iron. Since the process was performed according to the prior art 1 in which the metal iron melting device and the metal zinc melting device were connected in parallel to the liquid circulation tank, the appearance, corrosion resistance and adhesion of the plating film were all poor.

On the other hand, the test specimens Nos. 1 to 3 of the present invention had the contents of C, Si, Mn, P, S, Cu, Cr and Al as supplementary metal iron limited to the scope of the present invention. Since the iron-zinc alloy electroplating treatment was performed while using iron material having the above-mentioned composition and replenishing iron ions and zinc ions according to the process of the present invention shown in FIG. 1, the plating appearance, corrosion resistance and plating All of the adhesion of the coating was excellent.

Furthermore, in the above embodiment, the Ni content of the replenishing metal iron is 0.01 wt.% Or less, and each of the contents of Pb, Sn, Cd, As and Sb is 0 or 0.0001 wt.%. As a result, the effect of improving the plating appearance, corrosion resistance, and plating film adhesion was further improved.

As described above, according to the present invention,
Circulating a plating solution through a metal iron melting device and a metal zinc melting device to dissolve metallic iron and metal zinc in the plating solution in order to continuously form an iron-zinc alloy electroplating layer on the surface of a steel sheet. Therefore, when replenishing the plating solution with iron ions and zinc ions, a high-quality iron-zinc alloy electroplating solution can be obtained, and the dissolution rate difference between metallic iron and metallic zinc, When fluctuations in iron content etc. occur, it is possible to replenish only iron ions or zinc ions alone in the plating bath,
Industrially useful effects such as extremely excellent results when applied to actual operations are brought about.

[Brief description of the drawings]

FIG. 1 is a schematic process chart showing a method of the present invention.

FIG. 2 is a schematic process diagram showing a method of Prior Art 1.

FIG. 3 is a schematic process chart showing a method of Prior Art 3;

[Explanation of symbols]

 1,1 'plating solution circulation tank, 2,2' metal iron melting device, 3,3 'metal zinc melting device, 4,4' circulation conduit, 4a first conduit, 4b second conduit, 4c third conduit, 5a, 5b, 5 'pump, 6, 6' filter, 7 'branch pipe, 8, 8' supply pipe, 9, 9 'discharge pipe, 10, 11 separate conduit, 12 first open / close valve, 13 second open / close valve.

Claims (2)

(57) [Claims] Claims: 1. C, Si, Mn, in iron material for replenishing iron ions.
The contents of P, S, Cu, Cr and Al are as follows: C: 0.003 wt.% Or less, Si: 0.005 wt.% Or less, Mn: 0.05 wt.% Or less, P: 0.
Iron-zinc alloy characterized by being limited to 002 wt.% Or less, S: 0.003 wt.% Or less, Cu: 0.003 wt.% Or less, Cr: 0.01 wt.% Or less, and Al: 0.003 wt.% Or less. Iron material for replenishing iron ions in electroplating solution. 2. The iron-zinc alloy electroplating solution from the electroplating tank is led to a plating solution circulation tank, and the plating solution is connected in series with the plating solution circulation tank by a circulation conduit. Circulating between a metal iron melting device filled with metal iron and a metal zinc melting device filled with metal zinc, dissolving the metal iron in the plating solution with the metal iron melting device, In the method of dissolving metal zinc in the metal zinc dissolving apparatus in the plating solution in which the metal iron is dissolved, and thus replenishing iron ions and zinc ions in the iron-zinc alloy electroplating solution,
As the metallic iron to be charged into the metallic iron melting device, an iron material having the component composition according to claim 1 is used, and the electroplating solution circulation tank, the metallic iron melting device and the metal zinc melting device are used. Each of them is connected in parallel by another conduit, and by operating the on-off valve provided on the circulation conduit and the another conduit, only iron ions or only zinc ions are separately contained in the electroplating solution. A method for replenishing iron- and zinc-ions in an iron-zinc alloy electroplating solution, characterized in that the replenishment can be carried out by the following method.