KR19990084931A - Manufacturing method of electro galvanized steel sheet with excellent black pattern resistance - Google Patents

Abstract

The present invention relates to a method for manufacturing an electrogalvanized steel sheet having a beautiful surface appearance by suppressing the occurrence of black fringes of an electroplated steel sheet, and manufacturing an electroplated steel sheet using a horizontal type electroplating equipment using an insoluble anode of a zinc sulfate bath. In this method, arsenic is added to the plating bath in an amount of 0.05 g / l or more and less than 3 g / l, thereby preventing the vacancy of iron ions through elution of iron ions from the steel sheet, thereby suppressing the occurrence of black pattern during phosphate treatment after plating. SUMMARY OF THE INVENTION The present invention provides a method of manufacturing an electrogalvanized steel sheet having excellent black pattern resistance.

Description

Manufacturing method of electro galvanized steel sheet with excellent black pattern resistance

The present invention relates to a method for producing an electro-zinc plated steel sheet having a beautiful surface appearance by suppressing occurrence of black pattern of an electroplated steel sheet, and more particularly, plating in an insoluble zinc sulfate plating bath used in a horizontal electroplating bath. In order to prevent the elution of iron by the strong acid of the bath, and to prevent the black pattern generated after the phosphate treatment due to the vacancy of iron and zinc on the plated steel sheet, arsenic is added to the plating bath to suppress the iron dissolution of the steel sheet. It relates to a method for producing an electrogalvanized steel sheet excellent in black pattern resistance, characterized in that to prevent the vacancy of iron.

Sulfuric acid bath plating using horizontal cells has many different aspects from the existing radial hydrochloric acid plating baths. In other words, unlike the conventional hydrochloric acid bath, zinc ions are not supplied by melting of the anode and are supplied by melting metal zinc into the plating solution. Therefore, the working pH of the plating solution is controlled to be low in the range of 0.8 to 1.2, so that zinc ions are deposited as much as the amount of zinc deposited on the steel sheet. It should be possible to replenish quickly. Therefore, due to the low pH of the plating solution, iron ions are eluted from the steel sheet, and the eluted iron ions are vaccinated in the plating layer during electro zinc plating. At this time, the difference in plating voltage occurs due to the local flow rate difference over the full width of the steel sheet, and the amount of vacancy in the plating layer is different during electro zinc plating. If the phosphate is treated later, there is a problem in that the black pattern outline becomes more pronounced due to the severe difference in whiteness, thereby harming the surface appearance.

In order to solve this problem, plating at low current density (60 ~ 70A / dm ² ) can suppress black pattern generation, but it is impossible due to productivity problem, and also chelate to selectively remove only Fe ions among ions in the plating solution. There is a method of removing iron ions by the reagent, but it was difficult to apply due to problems such as high cost and low efficiency.

The present invention has been made to solve the above problems, in the sulfuric acid bath using an insoluble anode using a horizontal cell, due to the low pH of the iron is eluted from the steel sheet to prevent the iron vacancy in the plating layer during electro zinc plating Its purpose is to provide a method.

In order to achieve the above object, the present invention adds arsenic to the plating bath to prevent the elution of iron from the steel sheet, the iron is vaccinated during electro zinc plating to suppress the occurrence of black pattern after phosphate treatment electroplated steel sheet with a beautiful surface appearance It provides a method of manufacturing.

1 is a graph showing the inhibition of iron dissolution of a steel sheet according to the amount of arsenic added in the zinc sulfate plating solution.

Hereinafter, the present invention will be described in more detail.

The present invention is to increase the hydrogen polarization of the steel sheet used as a cathode in the sulfuric acid bath of the electro-zinc plating using an inorganic inhibitor such as arsenic to suppress hydrogen-generating corrosion to suppress the leaching of iron ions of the steel sheet.

In general, zinc has been used for a long time in automotive steel plates or home appliances because it is plated on the surface of the steel sheet to protect the base iron and is easy to plate. Electrozinc plating baths have been used for a long time especially in steel sheets for home appliances. Electro-zinc plating baths can be divided into horizontal, vertical and radial types, and they can be divided into hydrochloric acid and sulfuric acid baths depending on the plating solution and soluble and insoluble anodes depending on the dissolution of the anode. Among them, the insoluble anode, which has excellent plating structure and surface appearance and has the advantage of high current density work by reducing the distance between poles, is used in sulfuric acid baths to supply zinc ions by dissolving metal zinc in plating solution. The system is adopted. Therefore, when the pH of the plating bath is in the range of 0.8 to 1.2, it is possible to supply zinc ions more than the amount of zinc deposited on the steel sheet by increasing the dissolution rate of the metal zinc. However, since the pH of the plating solution is low, the dissolution rate of the plated steel sheet increases in the plating solution, and iron ions are eluted from the steel sheet and present as impurities in the solution.

This iron ion is a precious metal of about 0.32 V compared to the precipitation potential of zinc, so it is easy to precipitate, and thus vacancy is formed on the steel plate simultaneously with zinc in a plating bath in which zinc and iron ions are present.

At this time, the amount of vacancies in the steel sheet is different according to the local plating overvoltage difference of the steel sheet. The difference in the amount of vacancies causes a black pattern defect in the plating liquid flow pattern due to the severe whiteness difference after the phosphate treatment of the electroplated steel sheet. Will be.

However, the steel sheet is a metal with high adsorption energy and has a high surface energy. When a small amount of arsenic is added to the electroplating sulfuric acid bath, the added arsenic significantly affects the steel sheet, resulting in an increase in hydrogen overvoltage, thereby inhibiting corrosion of the steel sheet. This suppresses the leaching of iron ions from the steel sheet. This arsenic only acts as a dissolution inhibitor for iron and has no problem in dissolving metal zinc balls.

Hereinafter, an Example is given and this invention is demonstrated in detail.

<Example>

In the experimental process of the present invention, in order to measure the rate at which the steel sheet elutes into the plating solution, the specimens having a thickness of 0.7 mm were uniformly cut to 33 Φ, and then washed and degreased three times with ultrasonic waves to form arsenic in the plating solution composition shown in Table 1. The amount of addition was varied from 0 to 5 g / l, placed in a 100 ml beaker, and then immersed for 30 minutes to determine the weight loss ratio before and after the test. Moreover, using weight loss, the dissolution inhibition rate was calculated | required by the following formula.

Melt inhibition rate (%) = (1- W / W °) × 100

Where W = specimen weight loss in a solution free of arsenic

W ° = specimen weight reduction in arsenic-containing solution

In addition, while varying the amount of arsenic added to the solution composition of Table 1, under the plating conditions of Table ² , the constant current density was measured by measuring the width of the burning occurring at the edge of the specimen while uniformly plating 120 A / dm ² using a large plating bath. saw. The size of the negative electrode specimen used for plating was 100 × 200 mm, the coating amount was 20 g / m ² , and the distance between the positive electrode and the negative electrode was 10 mm.

Zinc (g / l) pH Temperature (℃) 60 0.8 60

Temperature (℃) pH Current density (A / dm ² ) Coating Weight (g / dm ² ) Flow rate (m / sec) 60 0.8 120 20 1.5

FIG. 1 shows the elution inhibition rate of iron for the case where arsenic is not added to the existing plating solution and when the arsenic is not added. Even if only 1 g / l of arsenic is present in the solution, it can be seen that the rate of inhibition of iron dissolution is 99.5% compared to the conventional plating solution without arsenic. Table 3 shows the results of burning occurrence width of the cathode after plating according to the amount of arsenic added to the plating solution.

division Arsenic addition amount (g / l) Burning width of steel plate after plating (mm) Conventional example 0 0.15 Comparative example 0.05 0.16 3 2.1 Inventive Example 0.1 0.15 0.5 0.18 One 0.3 2 0.5 2.5 0.55

In the comparative example, when 0.05 g / l of arsenic was added, there was no problem in the burning occurrence width of the steel sheet after plating, but the dissolution inhibition rate was not so high, so iron ions were dissolved in the steel sheet and vaccinated together with zinc during plating, and after phosphate treatment, Black pattern appeared. However, in this case as well, the occurrence of black pattern was significantly reduced compared to the case where no arsenic was added. When 3 g / l of arsenic was added, the dissolution inhibition rate was excellent, but there was a problem in that the quality of the steel sheet had to be reduced by 2.1 mm burning at the edge of the steel sheet during the plating, and the edge of the steel sheet should be trimmed and used. Therefore, in the present invention, the content of arsenic is limited to 0.05g / l or more, less than 3g / l.

Therefore, by adding arsenic of 0.05g / l or more and less than 3g / l to the sulfuric acid bath to suppress the solubility of iron in the steel sheet, it also suppresses the partial vacancy of the iron in the plated steel plate during plating, resulting in phosphate treatment after plating. It is possible to suppress the occurrence of black pattern, and at the same time there is an effect that does not affect the plating quality.

According to the present invention as described above, in order to suppress the iron dissolution of the steel sheet generated in the low pH operating conditions of the plating bath in the electroplating equipment using the insoluble anode of zinc sulfate bath, 0.05 g / l or more, 3 g in the plating bath The addition of less than / l to suppress the dissolution of iron, and to prevent the vacancy of the iron of the plated steel sheet that may occur during plating has the effect of suppressing the black pattern generated after phosphate treatment.

Claims (1)

In the method for producing an electrogalvanized steel sheet using a horizontal electroplating apparatus using an insoluble anode of zinc sulfate bath, the leaching of iron ions from the steel sheet is performed by adding arsenic to the plating bath in an amount of 0.05 g / l or more and less than 3 g / l. The method of manufacturing an electro-zinc plated steel sheet having excellent black-pattern resistance, characterized in that it prevents the iron ions through vacancy and thereby suppresses the occurrence of black-patterns during phosphate treatment after plating.