JP2591025B2 - Electric Zn plating method for steel strip having excellent plating adhesion and / or chemical conversion treatment - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a method for sequentially arranging a plurality of plating cells and electroplating a steel strip on a steel strip.

[Prior art] In general, electric Zn plating of steel strip is performed by a continuous electroplating line in which a plurality of plating cells having a metal Zn or an insoluble electrode as an anode are arranged using an electrolytic solution containing Zn ²⁺ as a plating metal. The electrolytic treatment is performed by using a steel strip as a cathode. Usually, the structure of each plating cell and the structure of the anode are the same.

In this type of electro-Zn plating method, the amount of plating directly affects performance such as corrosion resistance, and therefore, it is necessary to control the amount of plating to a specified predetermined amount. Since the plating amount of the electro-Zn plating is proportional to (plating current) × (plating time), the plating amount control is performed by total current control which controls the total current flowing through all plating cells. The total current is evenly distributed to each plating cell. Since the structure of each plating cell and the structure of the anode are the same, the current density of each plating cell is the same. Further, when the current of the plating cell changes, the current density of the plating cell changes accordingly.

[Problems to be Solved by the Invention] However, in the above-described continuous electroplating line, welding or inspection of a steel strip using a looper on the line entrance side may be performed during operation. In some cases, the steel strip may be wound on a coil by splitting the steel strip using a looper. During this time, the line speed of the plating cell is adjusted to a low speed so that the steel strip does not stop at the plating cell. In this case, when the line speed changes, the plating time changes, so it is necessary to change the total current necessary to obtain a predetermined plating adhesion amount. Since the total current after the change is evenly distributed to each plating cell, the current density of each plating cell is the same after the current change. The formation of the plating layer on the surface of the steel strip in the initial stage is very important for the adhesion of the plating, which is one of the characteristics of the plating film. , It is difficult to obtain a stable plating adhesion film.

The formation of the plating layer on the surface of the steel strip in the final stage is very important for the chemical conversion property, which is one of the characteristics of the plating film. Therefore, it is difficult to obtain a stable chemical conversion treatment film.

In particular, when a Pb-based insoluble electrode is used as the anode, Pb ²⁺ eluted in the plating bath tends to enter the plating film at a low current density, and therefore, the chemical conversion property of the plating film is reduced. It is said.

An object of the present invention is to solve the problems of the prior art and to provide a method of electro-Zn plating a steel strip capable of forming a plating film having excellent plating adhesion and chemical conversion treatment even when the line speed changes. And

[Means and Actions for Solving the Problems] In order to achieve the above object, the present invention uses the following means.

(1) In a method of sequentially arranging a plurality of plating cells and performing electro-Zn plating on a steel strip, the plating cells are roughly classified into cells at an initial stage, an intermediate stage, and a final stage, and the current of the plating cells at the initial stage is the density was fixed at a constant current density in the range of 10~40A / dm ^2, performed when the line speed during the electroplating operation is changed, the adjustment of the required plating current in the plating cell, except for the plating cell of the initial phase This is an electrical Zn plating method for a steel strip having excellent plating adhesion (hereinafter, referred to as a first invention).

(2) In a method of sequentially arranging a plurality of plating cells and performing electro-Zn plating on a steel strip, the plating cells are roughly divided into an initial stage, an intermediate stage, and a final stage, and the current of the plating cell in the final stage is determined. the density was fixed at a constant current density in the range of 60~120A / dm ^2, performed when the line speed during the electroplating operation is changed, the adjustment of the required plating current in the plating cell, except for the plating cell of the final stage This is an electrical Zn plating method for steel strip with excellent chemical conversion treatment (hereinafter referred to as the second method).
Invented).

(3) In a method of sequentially arranging a plurality of plating cells and performing electro-Zn plating on a steel strip, the plating cells are roughly classified into cells at an initial stage, an intermediate stage, and a final stage, and the current of the plating cells at the initial stage is measured. is fixed a density constant current density in the range of 10~40A / dm ^2, the current density of the plating cell of the final stage is fixed at a constant current density in the range of 60~120A / dm ^2, during the electroplating operation If the line speed changes
This is an electric Zn plating method for a steel strip having excellent plating adhesion and chemical conversion treatment in which a necessary plating current change is adjusted in the plating cell at the intermediate stage (hereinafter, referred to as a third invention).

In the initial stage plating cell, the steel strip is directly zinc-plated, and then the Zn plating formed in the earlier stage plating cell is further plated with Zn. Therefore, the state of adhesion of the Zn plating formed in the plating cell in the initial stage will affect the state of adhesion of the plating film formed as it is, and in order to obtain a plating film having excellent plating adhesion. It is important that a Zn plating layer formed in the initial stage is used.

When plating is performed with the current density of the plating cell in the initial stage fixed at a constant current density of 40 A / dm ² or less, the plating adhesion of a subsequently formed plating film can be improved. However, if the current adhesion is less than 10 A / dm ² , the electrolysis efficiency is poor, which is not preferable in actual operation. Therefore, in order to obtain excellent plating adhesion, the current density of the plating cell in the initial stage is 10 to
It is necessary to fix to a constant current density in the range of 40 A / dm ² . In the plating cell in the final stage, since the surface layer of the plating film of the steel strip is formed, the state of adhesion directly affects the chemical conversion property of the subsequent chemical conversion treatment. In order to obtain a plating film having excellent chemical conversion properties, it is necessary to fix the current density of the plating cell in the final stage to a constant current density within the range of 60 to 120 A / dm ² . If the current density is less than 60 A / dm ² , the chemical conversion property deteriorates, and if the current density exceeds 120 A / dm ² , the effect of improving the chemical conversion property is leveled off, and no further effect can be expected.

[Embodiment of the Invention] Hereinafter, the present invention will be described with reference to the drawings. FIG. 1 is a schematic view showing a method of sequentially arranging a plurality of plating cells and performing electro-Zn plating on a steel strip 1. FIG. Plating cell A ₁
Each of the to A ₁₀ two sets of the pair of the anode 3 are disposed at regular intervals with respect to the steel strip 1. Conductor rolls 2 are provided on the entrance and exit sides of the plating cell, respectively.
Is arranged. Then, the steel strip is plated with Zn by an electrolytic reaction between the steel strip 1 of the cathode and the anode 3 via the plating solution. Rectifier 4 for each plating cell
, So that the current can be adjusted. 5 shows the circuit. These circuits are connected to a total current control circuit (not shown). Here, in the first invention, in order to obtain excellent plating adhesion,
The current density of the plating cell in the initial stage is fixed at a constant current density in the range of 10 to 40 A / dm ² . If the line speed changes during the electroplating operation, the plating current needs to be changed. Since the plating current of the plating cell in the initial stage is constant, the plating current is controlled such that the current of the difference between the required plating current and the plating current of the plating cell in the initial stage is distributed to the plating cells excluding the plating cell in the initial stage. .

For example, it arranged ten plating cell, a constant current density D in the range of current density of the first plating cell A ₁ of 10~40A / dm ²
When performing Zn plating while fixing to K ₁ (A / dm ² ), the required total current after changing the line speed during the electroplating operation
I _T (A), the electrode table of plating cell L (dm), when the steel strip width B (dm), plating current I ₁ of the plating cell A ₁
Is constant even after the line speed is changed, and I ₁ = DK ₁ × L × B (A)
Therefore, the plating current of the difference between the total current I _T (A) and the plating current I ₁ flowing through the plating cell A ₁ is calculated as
Sort to nine plating cells A _{2 to} A ₁₀ excluding A ₁ . Plating current I _2-10 flowing in each plating cell of plating cells A _{2 to} A _{10
Is, I 2-10 (I T -I 1} ) / 9 = (I 1 -DK 1 × L × B) / 9 (A)
Becomes Therefore, the current control of each plating cell may be controlled so as to be the current value obtained above.

In the second invention, the current density of the plating cell in the final stage is fixed to a constant current density in the range of 60 to 120 A / dm ² in order to obtain excellent chemical conversion treatment properties. If there is a change in the line speed during the electroplating operation, the plating current of the plating cell in the final stage is constant, so the current of the difference between the required total current and the plating current of the plating cell in the final stage is calculated as the current in the final stage. The plating current is controlled such that the plating current is distributed to the plating cells excluding the plating cells. It is possible to determine the plating current of each plating cell in the same manner as in the case of the first invention,
What is necessary is just to control the current value of each plating cell so that the current value is obtained.

In the third invention, the current density of the plating cell in the initial stage is increased by 10 to 40 in order to obtain excellent plating adhesion and chemical conversion treatment.
It is fixed to a constant current density in the range of A / dm ^2, to secure the current density of the plating cell of the final stage at a constant current density in the range of 60~120A / dm ^2. If the line speed changes during the electroplating operation, the plating current of the plating cell in the initial stage and the plating current of the plating cell in the final stage are constant. The plating current is controlled such that a current having a difference from the plating current of the plating cell of the first step is distributed to the plating cell at the intermediate stage. The plating current of each plating cell can be determined in the same manner as in the first and second inventions, and the current control of each plating cell may be controlled so as to be the determined current value.

Chemical conversion treatment is performed by subjecting Zn-plated steel sheet to phosphate treatment,
The evaluation was made based on the amount of the phosphate film formed. FIG. 2 shows the relationship between the plating current density of the final plating cell and the amount of the phosphate film formed by the phosphate treatment. 60 ~
At a high current density of 120 A / dm ^2, a phosphate film of 2.0 g / m ² or more can be obtained without being affected by Pb ²⁺ in the plating bath, so that the chemical conversion treatment is excellent.

Next, experimental results obtained by the method of the present invention will be described.

(Experimental Example 1) According to the plating conditions shown in Table 1, the initial plating stage was set as one tank of the first plating cell, and the line speed was 60 m / min to 20 m / min.
At 0 m / min, the plating adhesion of each formed plating film was tested. In addition, the case according to the method of the prior art was set as a comparative example. Table 2 shows the results.

According to Table 2, the current density of the first plating cell was 30 A /
plating adhesion even higher average current density is the line speed in the present invention method with a low current density is varied in dm ² whereas all was good, and plating all the plating cell at the same current density In the conventional method, plating adhesion at a current density of 50 A / dm ² is slightly poor, and plating adhesion at a current density of 100 A / dm ² is poor.

(Experimental example 2) Under the conditions shown in Table 3, plating was performed in a plating bath containing 2 to 2.5 ppm of Pb2 ⁺ . The final stage of plating was one tank of the final plating cell, and the current density was 100 A / dm ² . The line speed at this time was changed from 60 m / min to 200 m / min, and each formed plating film was subjected to a phosphate treatment to test the chemical conversion treatment. In addition, the case according to the method of the prior art was set as a comparative example. Table 4 shows the results.

As is clear from Table 4, in the method of the present invention, even in the case of the plating bath containing Pb ^{2+, the} amount of the phosphate film deposited was 2.0 g.
/ m ² or more, and the chemical conversion property is good. On the other hand, according to the conventional method, the average current density is 50 A / dm ²
In the following cases, the current density of the final plating cell is equal to the second density of the present invention.
Since the current density is lower than the lower limit of 60 A / dm ² of the present invention, the amount of the phosphate film adhered is small, and the chemical conversion treatment is slightly poor or poor.

(Experimental example 3) The initial stage of plating was one tank of the first plating cell, and the current density was 30 A / dm ^{2. The} last stage of plating was one tank of the final plating cell, and the current density was 100 A / dm ² . At this time, the line speed was changed from 60 m / min to 200 m / min, and the plating adhesion of each formed plating film and the phosphate conversion treatment of the plating film were tested. In addition,
The case according to the method of the prior art was used as a comparative example. The results are shown in Table 6.

According to Table 6, the current density of the first plating cell was 30 A /
Low current density dm ^2, the current density of the final plating cell 100A / dm
^{In the} method of the present invention having a high current density of ² , both the phosphate film adhesion amount and the plating adhesion are good. Also from this result, it can be seen that when the current density of the final plating cell is 60 A / dm ² or more, the influence of Pb ²⁺ is avoided, and a plating film having excellent chemical conversion property is formed.

On the other hand, according to the conventional method, the average current density is 30 A / dm ²
If, the current density of the final plating cell is below 60A / dm ^2, less phosphate film coating weight, chemical conversion treatability is bad and if the average current density is 50A / dm ^2, the first plating cell Since the current density exceeds 40 A / dm ² , the plating adhesion is slightly poor, and the current density of the final plating cell is 60 A / dm ^2.
Since less than dm ^2, less phosphate film coating weight, chemical conversion treatability is somewhat poor, The average current density is 100A / d
In the case of m ² , the current density of the first plating cell exceeds 40 A / dm ² , so that the plating adhesion is poor.

In the embodiment, the description has been given of the electric Zn plating. However, the method of the present invention can be applied to the case of Zn—Ni alloy plating and the like.

[Effects of the Invention] The present invention relates to a method for obtaining a predetermined amount of coating by electroplating by arranging a plurality of plating cells, and even if the line speed changes during the plating operation, the current density in the plating cells in the initial stage of plating is changed. Or, since the current density in the plating cell at the final stage of plating, or both are fixed, it is possible to obtain excellent chemical conversion treatment properties and / or adhesion of the plating film, so that the invention is industrially excellent. is there.

[Brief description of the drawings]

FIG. 1 is a schematic diagram for explaining the method of the present invention, and FIG. 2 is a diagram showing the relationship between the amount of phosphoric acid film deposited and the current density according to the method of the present invention. 1 ...... steel strip, 2 ...... conductor roll, 3 ...... anode, 4 ...... rectifier, A ₁ to A ₁₀ ...... plating cell.

Claims (3)

(57) [Claims] 1. A method for electroplating a steel strip by arranging a plurality of plating cells in sequence, wherein said plating cells are roughly divided into an initial stage, an intermediate stage, and a final stage. constant current density is fixed, when the line speed during the electroplating operation is changed, the plating cell, except for the adjustment of the required plating current plating cell of the early steps within the range of current density 10~40A / dm ² of An electrical Zn plating method for a steel strip having excellent plating adhesion, wherein the method is performed by: 2. A method of electroplating a steel strip by arranging a plurality of plating cells in sequence, wherein the plating cells are roughly divided into an initial stage, an intermediate stage, and a final stage cell, and the final stage plating cell is provided. constant current density is fixed, when the line speed during the electroplating operation is changed, the plating cell, except for the adjustment of the required plating current plating cell of the final stage in a range of current density 60~120A / dm ² of An electrical Zn plating method for a steel strip having excellent chemical conversion property, wherein 3. A method of electroplating a steel strip by sequentially arranging a plurality of plating cells, wherein the plating cells are roughly divided into an initial stage, an intermediate stage, and a final stage. with fixing the current density constant current density in the range of 10~40A / dm ² of current density of the plating cell of the final stage is fixed at a constant current density in the range of 60~120A / dm ^2, electroplating When the line speed changes during the operation, a necessary plating current is adjusted in the plating cell in the intermediate stage.