JP3373109B2 - Tin-free steel appearance defect remedies - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for removing and repairing appearance defects of tin-free steel which have appearance defects during or after electrochromic plating of steel sheets.

[0002]

2. Description of the Related Art In the production process of tin-free steel, in which cold-rolled steel sheet is subjected to electrochromic plating, oil is removed by electrolysis of the steel sheet in an alkaline aqueous solution, immersion in an acid aqueous solution or acid treatment before electrochromic plating. Dissolution, removal, and activation of oxides and the like are performed by electrolysis in an aqueous solution.

However, if the necessary processing conditions at this time are not sufficiently satisfied, it is known that color tone defects and color unevenness occur due to uneven adhesion of chromium or chromium oxide during or after electrochromic plating. As an example of this, Japanese Patent Publication No. 53-15685 is disclosed. In other words, in order to prevent the appearance defects of tin-free steel, pretreatment before electrochromic plating is important, but in the case of the conventional tin-free steel manufacturing method, the prevention of appearance defects that occur during or after electrochromic plating. However, since the appearance defects are found only after the plating is actually performed, defective materials are inevitably generated, which leads to a decrease in productivity and equipment operation rate, and product yield. There was a problem that caused a decrease and an increase in manufacturing costs.

The main causes of the appearance defect during or after the plating described above are foreign matter adhesion due to partial loss of equipment members, oil leakage at the roll bearing portion, damage to rolls in the plating equipment, and transfer marks due to wear. However, it is difficult to predict the occurrence of defects due to streaky stains, etc., and no matter how accurate the operation management of equipment is,
The occurrence was unavoidable with a certain probability.

[0005]

DISCLOSURE OF THE INVENTION The present invention provides a first-class product by removing the defects of the appearance defect-generating material, which are inevitably generated during or after plating in the production of tin-free steel as described above. The purpose is to provide the technology for relief.

[0006]

The present invention relates to a tin-free steel appearance defect relief method in which a steel sheet is electrochromed, wherein the sulfuric acid concentration is reduced after degreasing the electrochromed steel sheet in an alkaline aqueous solution. After electrolysis with an electric charge of 3 C / dm ² or more in an aqueous solution of 10 g / l or more, again,
This is a tin-free steel appearance defect relief method characterized by performing electrochromic plating.

In the present invention, it is preferable that after the electrolysis in the sulfuric acid aqueous solution, a rinsing treatment is performed, and the rinsing-treated steel sheet is subjected to the above-mentioned electrochromic plating again.

[0008]

BEST MODE FOR CARRYING OUT THE INVENTION The present invention will be described in more detail below. INDUSTRIAL APPLICABILITY The present invention is preferably applied as a method for relieving the appearance defects of tin-free steel, which is a steel sheet obtained by subjecting a cold-rolled steel sheet to electrochromic plating, and more preferably, metal chromium is provided on the surface of the cold-rolled steel sheet, and chromium hydrate oxide is provided thereon. It is preferably used as a method for repairing appearance defects of tin-free steel, which is an electrochrome plated steel sheet on which a thin film made of is formed.

The inventors of the present invention conducted an experiment using tin-free steel, which had become defective due to an appearance defect, and as a result, electroplated in an alkaline aqueous solution, immersed in an aqueous sulfuric acid solution or electrolyzed in an aqueous sulfuric acid solution, and then plated with chromium. When metal chromium or chromium oxide remains on the steel plate before chrome plating, uneven chromium adhesion occurs during chrome plating, resulting in a steel plate with poor color tone or uneven color in the width direction of the steel plate. It turned out to be done.

Further, as a method of removing the appearance defect of the tin-free steel, it is necessary to completely remove the metallic chromium and the chromium oxide on the steel plate before electrochromic plating the steel plate having the appearance defect again. ,for that purpose,
The electrolysis condition in the acid solution is that the amount of electricity is 3 C / dm ² or more,
It was also found that the sulfuric acid concentration in this case was 10 g / l or more.

According to the present invention, a steel sheet having an appearance defect after electrochromic plating is electrolyzed in an aqueous solution containing 10 g / l or more of sulfuric acid so as to have an electric quantity of 3 C / dm ² or more. Tin-free steel, which has once become defective in appearance, can be saved as a first-class product by completely removing metallic chromium, chromium oxide, and other substances that cause defects in appearance, and then performing electrochromic plating again. It became so.

As described above, in the present invention,
The sulfuric acid concentration of the aqueous sulfuric acid solution is preferably 10 g / l or more, more preferably 10 to 100 g / l. If the amount is less than 10 g / l, defective defects are not completely removed, resulting in poor color tone of the steel sheet. It is not preferable in terms of cost and drug cost.
In addition, there is almost no effect of electrolytic cleaning that matches the increase in concentration.

Furthermore, the quantity of electricity during the electrolytic pickling in an aqueous sulfuric acid solution, is preferably 3C / dm ² or more, further preferably in the range of 3~20C / dm ^2. 3C
When it is less than / dm ² , defective defects are not completely removed, and the color tone of the obtained steel sheet is bad. On the contrary, when it exceeds 20 C / dm ² ,
The adhered chromium is completely removed, and further, the iron of the original plate dissolves and dissolves into the solution, which is liable to cause contamination. Further, there are many problems such as significant consumption of electrodes, saturation of the effect of electrolytic pickling, and increase in power consumption.

Further, in the present invention, more preferably, after electrolysis in a sulfuric acid aqueous solution, a treatment with a rinse solution is performed, and immediately after that, the above-mentioned electrochromic plating is again applied to the rinse-treated steel sheet. preferable. The purpose of rinsing is to prevent the introduction of sulfuric acid into the plating solution in the subsequent step, and the purpose of immediate plating is to prevent the generation of rust on the acid-activated steel sheet. A warm pure water spray or the like is preferably used as the rinse liquid.

[0015]

EXAMPLES The present invention will be specifically described below with reference to examples. FIG. 1 is a side view showing a pretreatment apparatus and an electrochromic plating apparatus used in this example. In FIG. 1, 1 is a tin-free steel having an appearance defect, 2 is an alkaline solution, 3 is a rinse solution, 4 is a sulfuric acid solution, 5,
7 is an electrode (cathode), 6 and 8 are electrodes (anode), 10 is a degreasing tank using an alkaline aqueous solution (hereinafter referred to as an alkali degreasing tank),
11 and 13 are rinse tanks, 12 is an electrolytic tank using a sulfuric acid aqueous solution (hereinafter referred to as sulfuric acid electrolytic pickling tank), 14 is a deflector roll, 15,
24 is a sink roll, 20 is an electric chrome plating tank, 21a, 21
b is an electrode, 22 is a plating solution, 23a and 23b are energizing rolls, 25
Indicates the traveling direction of the steel strip.

In this embodiment, a NaOH aqueous solution was used as the alkaline aqueous solution 2, and warm pure water was used as the rinsing liquid 3. Tin-free steel (hereinafter referred to as steel strip) 1 that has an appearance defect is alkali-degreased or alkali-electrolytically degreased in an alkaline aqueous solution in an alkali degreasing tank 10, and the alkali adhering to the steel strip surface is removed in a rinse tank 11. .

The steel strip 1 treated in the alkaline degreasing bath 10 and the rinse bath 11 is subjected to electrolytic pickling in a sulfuric acid electrolytic pickling bath 12, and then the acid adhering to the steel strip surface is removed in a rinse bath 13. It The steel strip 1 treated in the rinse tank 13 is again subjected to electric chromium plating in the electric chromium plating tank 20.

The appearance defect of the defective tin-free steel used in this example is due to the damage of the roll after the plating section in the electrochromic plating equipment, and the rubber powder from the damaged roll is formed on the surface of the steel strip after plating. (Φ 0.1 to 1 mm
(Large) were randomly attached. Using this tin-free steel with poor appearance, alkali degreasing and sulfuric acid electrolytic pickling were performed under the conditions shown in Table 1, and then electrochromic plating was performed again under the following conditions.

As shown in Table 1, both alkaline degreasing and sulfuric acid electrolytic pickling were tested under electrolytic conditions and electroless conditions. Plating bath composition: CrO ₃ 200 g / l, H ₂ SO ₄ 2.2 g / l Plating bath temperature: 50 ° C. Current density: 80 A / dm ^{2 The} obtained steel strip was evaluated based on the following criteria.

[Completeness of Removal of Defective Defects:] The obtained tin-free steel coil (coil after electrochromic plating again) was rewound at a low speed and a full length inspection was performed. ◯: There is no rubber powder defect. Δ: Dirt that is considered to be a mark of rubber powder defect remains (1 piece / 10
Less than 0 m).

X: Dirt that is considered to be a mark of rubber powder defect remains (1 piece / 100 m or more). [Presence or absence of stains and color tone:] The obtained tin-free steel coil (coil after electrochromic plating again) was rewound at low speed and full length inspection was performed. ◯: There is no stain, the color tone is uniform, and there is no difference from normal tin-free steel.

Δ: Light streak-like dirt was mixed. X: There is clear color unevenness in the width direction, and many stains are mixed. Table 1 shows the obtained evaluation results. As shown in Table 1, in the steel sheets of Examples according to the method of the present invention, defective defects were completely removed and the color tone was also good.

[0023]

[Table 1]

As described above, according to the present invention, when appearance defect defects occur in tin-free steel,
After degreasing the steel sheet with an alkali, the quantity of electricity in the sulfuric acid aqueous solution is 3
By electrolyzing at C / dm ² or more and removing all the metallic chromium and chromium oxide together with the appearance defect itself, it is possible to prevent defective color tone and uneven color when the above steel sheet is chromium-plated again, and It became possible to make a first-class product.

[0025]

According to the present invention, when an appearance defect defect occurs in tin-free steel, color tone defects and color unevenness are prevented from occurring when the steel plate is chromium-plated again, and a defective material is made into a first-class product. It has become possible.

[Brief description of drawings]

FIG. 1 is a side view showing a pretreatment device and an electrochromic plating device used in Examples.

[Explanation of symbols]

1 Tin-free steel with appearance defects 2 Alkaline aqueous solution 3 rinse liquid 4 Sulfuric acid aqueous solution 5, 7 electrodes (cathode) 6, 8 electrodes (anode) 10 Alkaline degreasing tank 11, 13 rinse tank 12 Sulfuric acid electrolytic pickling tank 20 Electric chrome plating bath 21a and 21b electrodes 22 Plating solution 23a, 23b energizing roll

─────────────────────────────────────────────────── --- Continuation of the front page (56) References JP-A-57-177998 (JP, A) JP-A-2-159396 (JP, A) JP-A-1-96397 (JP, A) JP-A-3- 180486 (JP, A) JP 58-210197 (JP, A) JP 61-281899 (JP, A) JP 3-82796 (JP, A) JP 53-15685 (JP, B2) Japanese Patent Publication No. 39-15404 (JP, B1) (58) Fields investigated (Int.Cl. ⁷ , DB name) C25D 5/14 C25D 5/26 C25D 5/34 C25D 5/48

Claims (2)

(57) [Claims] 1. A method for repairing appearance defects of tin-free steel obtained by electroplating a steel plate, comprising degreasing an electrochromic steel plate in an alkaline aqueous solution, and then in an aqueous solution having a sulfuric acid concentration of 10 g / l or more, A tin-free steel appearance defect repairing method, characterized in that electrochromic plating is performed again after electrolysis with an electric quantity of 3 C / dm ² or more. 2. The tin-free steel appearance defect repairing method according to claim 1, wherein after the electrolysis in the sulfuric acid aqueous solution, a rinsing treatment is performed, and the rinsing-treated steel sheet is subjected to the above-mentioned re-electrochromic plating.