KR100570309B1 - Manufacturing process and apparatus for electrically galvanized steel sheet having smooth surface - Google Patents

Abstract

The present invention suppresses the generation of surface defects caused by the material steel sheet and the plating solution when performing zinc plating on a cold rolled steel sheet in a continuous electroplating process having two or more plating cells. The present invention relates to a device capable of producing a long time and a method of manufacturing a galvanized steel sheet produced by the device.

The device features: Separating a plurality of plating cells into the front end and the rear end, and having at least one flushing system between them to prevent the plating liquid attached to the steel plate from the plating cell of the front end to be mixed into the plating liquid at the rear end by the action of this flushing system. To help.

The plating method in this apparatus is as follows. In the front plated cell, a plating solution containing 0.5 to 2 kg / m3 of aluminum ions in the plating solution and 0.05 to 0.3 kg / m3 of cobalt or nickel ions or a sum thereof is added to a fine (001) plane. Zinc crystals with a low ratio of preferred orientations are plated, and in the back-end plating cell, zinc crystals with high preferred orientation and high whiteness of (001) planes are prepared using a plating solution containing cobalt and nickel ions totaling 0.1 kg / m3 or less. Plate. By doing so, the streaks generated due to the nonuniformity of the crystal structure of the cold rolled steel sheet and the iron ions present in the zinc plating solution reduce the surface defects of the black pattern generated by the plating layer uneven vacancies and plate the light colored zinc layer.

Flushing system, back end plating cell

Description

Manufacturing process and apparatus for electrically galvanized steel sheet having smooth surface

Figure 1 is a schematic diagram showing a cleaning system for removing the electrolyte on the steel sheet after the shear plate plating in the present invention

2 is a schematic diagram of a continuous electroplating process to which the washing system according to the present invention is added.

♠ Explanation of symbols on the main parts of the drawing ♠

S: steel sheet 1: pure water supply tank

2: washing liquid circulation tank 3: washing liquid conductivity control system

4, 5: Ringer's Roll 6: flushing liquid injector

7: washing liquid discharge pipe 8: washing liquid collection device

9, 10 and 11: automatic control valve 12: conductivity measuring cell

The present invention suppresses the generation of surface defects caused by the material steel sheet and the plating solution when performing zinc plating on a cold rolled steel sheet in a continuous electroplating process having two or more plating cells. The present invention relates to a device capable of producing a long time and a method of manufacturing a galvanized steel sheet produced by the device.

The device features: By separating a plurality of plating cells into a front end and a rear end, and having one or more flushing systems therebetween, the plating liquid attached to the steel plate in the plating cell of the front end can be prevented from being mixed in the plating solution of the rear end by the action of this flushing system. Make sure

The plating method in this apparatus is as follows. In the front plated cell, a plating solution containing 0.5 to 2 kg / m3 of aluminum ions in the plating solution and 0.05 to 0.3 kg / m3 of cobalt or nickel ions or a sum thereof is added to a fine (001) plane. Zinc crystals with a low ratio of preferred orientations are plated, and in the back-end plating cell, zinc crystals with high preferred orientation and high whiteness of (001) planes are prepared using a plating solution containing cobalt and nickel ions totaling 0.1 kg / m3 or less. Plate. By doing so, the streaks generated due to the nonuniformity of the crystal structure of the cold rolled steel sheet and the iron ions present in the zinc plating solution reduce the surface defects of the black pattern generated by the plating layer uneven vacancies and plate the light colored zinc layer.

In general, galvanized galvanized steel sheet is used as a material of home appliances, building materials and automobiles. In the continuous electroplating process, after zinc plating, post-treatment such as chromium treatment, phosphate treatment, and anti-fingerprint treatment is mainly performed. The galvanized steel sheet thus treated is often used for unpainting, but may also be used without coating. If there is dark or dark streaks on the surface of the plating layer, the shape or color may partially appear even after the above-described post-treatment.

In the galvanized layer, the main factors that can cause streaks or stains under normal working conditions are the case of arithmetic streaks or spot patterns on the surface of the steel sheet and high concentration of iron ions in the plating solution. If spots or streaks occur on the steel sheet, the spray of water is uneven or the temperature is uneven during hot rolling, resulting in non-uniform iron oxide.The traces can be confirmed because the surface roughness and crystal size are different after pickling. have. When the steel sheet is cold rolled and then annealed, there is a difference between the normal top and the surface roughness and crystal size. When zinc is electroplated on this site, a difference occurs between the orientation of the crystal and the size of the crystal, which is different from that of the plated surface.

Iron ions present in the plating liquid are generated by the electron exchange reaction between hydrogen ions and iron because the steel plate is immersed in the plating liquid before the pickling liquid is buried in the steel plate and mixed into the plating liquid or zinc is plated. It has been found in Korean Patent Publication No. KR2003-0042797 that in the plating process, these iron ions are vaccinated in the plating layer, thereby causing a decrease in the whiteness of the plating layer, for example, about 2 by 1000 ppm increase.

In addition, a high amount of iron and metal hydroxide is vaccinated at the site where the flow rate of the plating liquid is slow or at the periphery of the oxygen bubble due to the high negative electrode voltage. When the iron content in the plating layer is less than 0.4%, as the iron content increases, the crystal structure of the galvanized layer becomes fine and the color appears dark. In particular, because the interfacial heterogeneity is increased due to the refinement of crystal structure and the vacancy of hydroxide, it becomes darker than other parts because more phosphate is attached during phosphate treatment.

As described above, as a method of preventing both the pattern defect of the material steel sheet and the pattern defect caused by iron ions in the plating solution, there is a method disclosed in Korean Unexamined Patent Publication No. KR2000-0042195. In such a conventional method, an organic additive is added to the front end of the plating cell to refine the crystal grains of the galvanized layer, and the rear end of the plating cell uses a plating solution without the addition of the organic additive to brighten the color. This technique only applies to hydrochloric acid based plating solutions using soluble anodes and there are major problems when applied to practical processes. In the continuous plating process, the steel sheet continuously passes through the front end portion and the rear end plating cell, so that the front end plating liquid is buried in the steel plate and mixed with the subsequent plating liquid. Therefore, when the continuous plating time passes to some extent, it becomes impossible to manufacture a bright colored plated steel sheet.

In addition, when this technique is applied to a sulfuric acid plating solution using an insoluble anode, the organic additive is decomposed at the anode to be converted into a solid sludge to contaminate the plating surface. In addition, techniques similar to the present invention have been disclosed in Japanese Laid-Open Patent Publications JP8-193292 (1996) and JP4-110489 (1992). However, these methods do not suppress the generation of streaks because the plating liquids at the front end and the rear end are the same.

In the present invention, the plating liquid of the front end portion is prevented from being mixed into the rear end portion between the front end portion and the plating cell of the rear end portion by being buried in the steel plate. In addition, by adding a combination of inorganic aluminum ions and cobalt or nickel ions, which are not decomposed at the insoluble anode, zinc crystals can be effectively micronized even in a very small amount.

Accordingly, an object of the present invention is to provide a method and apparatus for manufacturing an electro-galvanized steel sheet having a bright color without surface defects and non-uniform streaks caused by the pattern of the material steel sheet and the iron ions in the plating solution. There is this.

Light color is a color that many people prefer and dark and uneven stripes do not appeal to many people, so the present invention is to produce a plated steel sheet having a light color without any uneven stripes.

In order to achieve the above purpose, the electroplating equipment is divided into three processes of shear plating, flushing system and back plating.

In the present invention, the manufacturing process of the galvanized steel sheet in which zinc is plated on the steel sheet includes a pretreatment step for degreasing and pickling the steel plate, and a post-treatment step such as washing, phosphate treatment, chrome treatment, and anti-fingerprint treatment after plating. There is this.

The electrogalvanization process is subdivided into front plating, water washing and post plating processes. The galvanizing solution is used separately at the front end and the rear end, and washing with water is carried out to reduce the amount of mixing of the front end plating solution into the rear end plating solution. Here, the plating cell of the front end part or the rear end part may use any of the known horizontal, vertical and radial types.
Process characteristics of the present invention will be described in more detail below.

Of the plurality of plating cells, one or more cells may be used as the front end and the remaining end as the plating cells, but it is most ideal that the number of the rear end plating cells is in the range of 20 to 30% of the entire plating cells. This is based on the following factors. Most galvanized steel sheets that require bright white are used for home appliances. In this case, the plating deposition amount is usually 20 g / m ² for one side.

Since the galvanized layer is low in hardness, scratches are easily generated by external contact. Therefore, it is necessary to increase the hardness of the plating layer by the microstructure of the plating layer and the addition of alloy. When the zinc plated in the post-plating cell is 3 g / m 2, about 85% of the surface area of the plated layer formed in the previous plating, 95% when 4 g / m 2 and 99% when 5 g / m 2 is formed in the post-plating cell. Will be covered. When the adhesion amount of zinc plated in the rear plating cell is 4 to 6 g / m 2, the color of the surface is almost dependent on the plating layer formed in the rear plating cell. This is about 20-30% of the total 20 g / m 2 deposition. Therefore, in the shear plating cell, it is preferable to set the ratio of the plating cell to 70-80% in order for the tissue to plate the fine plating layer thickly.

The following describes the flushing system of FIG. 1 between the front and back plating cells. The characteristic of this system is to wash the shear plating liquid on the steel plate with water to give the property to freely control the amount mixed in the rear plating liquid and to circulate the washing liquid so that the amount of water required can be extremely saved. .

Figure 1 shows a schematic view of the washing, that is, the cleaning system for removing the electrolyte on the steel plate after the shear plate plating in the present invention. In the figures, S is a steel plate, 1 is a pure water supply tank, 2 is a washing liquid circulation tank, 3 is a washing liquid conductivity control system, 4 and 5 is a Ringer roll, and 6 is a water A tax injector, 7 is a flushing discharge pipe, 8 is a flushing fluid collection device, 9, 10 and 11 are automatic valves for control, and 12 is a conductivity measuring cell.

The pure water supply tank (1) is intended to supply pure water to the flushing water circulation tank (2), if there is a water pipe that can supply a separate pure water only need to connect the automatic valve (10). The flushing liquid injector 6 is composed of a pump, a pipe, and a spray nozzle. What is necessary is just to spray 40-400m <1> / m <2> with respect to the unit area of a steel plate.

Although the ringer roll 4 may be omitted, it is more effective when the shear plating cell has a ringer roll. The electrolytic solution extruded by the ringer roll 4 is discharged to the shear cell plating solution, and the aqueous solution extruded by the ringer roll 5 and the aqueous solution extruded by the flushing liquid spraying device 6 are washed with water. ) And flows into the wash circulating tank (2) or the wash liquid discharge pipe (7). The flushing liquid conductivity control system 3 measures the conductivity of the flushing liquid from the conductivity measuring cell, and when it is equal to or lower than the set target value, the automatic control valve 10 is opened and the automatic control valves 9 and 11 are closed. In the case where the conductivity is high, the automatic control valve 10 is closed and the automatic control valves 9 and 11 are opened to control the inflow of the shear plating liquid into the subsequent plating liquid by the wash liquid conductivity control. It is characteristic.

The target value of conductivity set in the conductivity control system 3 is preferably 0.1 times the conductivity of the plating liquid of the shear plating cell. If it is lower than this, the consumption of pure water increases, and at high diameters, the incorporation of the shear plating solution in the rear plating solution increases, thereby reducing the whiteness of the plated product.

In the plating cell of the front end, the plating solution is made of hydrochloric acid or zinc sulfate so that Zn ²⁺ is 40 to 150 kg / m 3 and Al ³⁺ is 0.5 to 2 kg / m 3, and either Co ²⁺ or Ni ²⁺ is used. Make sure the sum of the two contains 0.05 ~ 0.3 kg / ㎥. The reason is that when these occur if the ion alone was added into each of which does not significantly reduce streaks occur, the Al ³⁺ to Co ²⁺ or Ni ² which contains one or two sum is 0.05 ~ 0.3 kg / ㎥ of stripes This is because the reduction effect increases.

The conduction aid is a compound having a solubility of not more than two or more of any one of KCl, NaCl, Na ₂ SO ₄ and K ₂ SO ₄ that are commonly used, but is usually 1.2 kmol / m 3 or less, and the temperature of the plating solution is 40 ~ 80 ℃, and the pH of the plating liquid is limited to 0.8 ~ 3.0 range. The pH of the plating liquid is limited to 0.8 to 3.0 because the current efficiency is too low when the pH is 0.8 or less, and aluminum ions are precipitated as sludge above 3.0. The temperature and current density of the plating solution are controlled in the range of 40 to 80 ° C. and 20 to 180 A / dm 2, respectively.

In the back plating cell, the plating solution is 40 ~ 150 kg / ㎥ of Zn ²⁺ using hydrochloric acid or zinc sulfate, and the conduction aid is a compound of any one or two of KCl, NaCl, Na ₂ SO ₄ and K ₂ SO ₄ It should be 0.6 mol / l or less and the temperature of the plating liquid is 40 ~ 80 ℃, and the pH of the plating solution is limited to 0.8 ~ 3.0 range. The reason for the PH limitation is as described above. Temperature and current density of the plating solution are also controlled in the range of 40 ~ 80 ℃, 20 ~ 180 A / dm 2 respectively. In other words, the concentration of the conductive assistant is lowered without adding an inorganic additive that causes crystal refinement to the front end plating liquid, because the whiteness of the plating layer is reduced by these.

 EXAMPLE

Example 1

In order to measure the process capacity of the washing process, the following experiment was conducted. In order to determine the degree to which the front plating solution is incorporated into the post plating solution, the concentration of Al ³⁺ mixed in the after plating solution was measured in the vertical plating process for 100 and 200 hours, and the results are shown in Table 1. In this case, the plating liquid circulating tanks at the front and rear stages are 50 m 3, the washing liquid circulation tank 2 is 5 m 3, and the amount of flushing liquid is 3 m 3 / h, the steel plate traveling speed and the strip width are 3 m / s and 1.2, respectively. m and the washing | cleaning liquid conductivity setting value were 20 mS. The conditions of the shear plating bath were as follows.

1) ZnSO ₄ : 1 kmol / ㎥

2) Na ₂ SO ₄ : 0.8 kmol / ㎥

3) Al ³⁺ and Co ²⁺ of the plating solution: 1.0 and 0.1 kg / ㎥, respectively

4) Plating solution pH 1.2

5) The temperature of the plating liquid: 60 ℃

The initial concentration and plating conditions of the subsequent plating solution were as follows.

1) ZnSO ₄ : 1 k mol / ㎥

2) Plating solution pH 1.2

3) the temperature of the plating liquid: 60 ℃

According to Example 1 above, the results of the comparison test with the conventional ones are shown in Table 1.

Table 1 (Unit: kg / ㎥)

As a result, during the continuous operation, the amount of aluminum ions in the shear plating liquid is mixed in the subsequent plating liquid and accumulated in the subsequent plating liquid increases with time. In addition, it can be seen that the amount of Al ³⁺ is very large when the Ringer roll and the water washing are not carried out or when the Ringer roll 4 is carried out, and the Al ³⁺ is further introduced and increased with time. However, in the case of the present invention subjected to the ringer roll and the water washing operation, it can be seen that even after a long time, the shear plating liquid did not flow into the rear plating liquid so as to darken the color of the surface.

Example 2

The extent to which the streaks of the raw material steel sheet and the iron ions in the plating liquid caused surface defects and the performance of the inorganic additive in the shear plating liquid of the present invention were measured. As a raw material steel plate, hot rolled steel was pickled, and a 2.5 mm thick steel plate having a pattern of arithmetic scale on the surface was rolled to a thickness of 1 mm, and then continuously annealed. Plating weight is 100 A / dm2 15 g / m2 in shear plating each at a rate of 5 g / m2 in back plating Was carried out. The composition of the rear plating solution is as described in Example 1, and the composition and plating conditions of the front plating solution are as follows. The surface state is shown in Table 2 as "bad" when it can be judged visually as stripes and "excellent" when there is no.

1) ZnSO ₄ : 1 kmol / ㎥

2) Na ₂ SO ₄ : 0.8 kmol / ㎥

3) Al ³⁺ and Co ²⁺ of the plating solution: as indicated in Table 2.

4) Fe ²⁺ : 2,000 ppm

5) The temperature of the plating liquid: 60 ℃, pH 1.2 of the plating liquid

Table 2 (Unit: kg / ㎥)

The plating solution in the plating in the front end result Al ^3+, Co ²⁺ and Ni ²⁺ ions, if added alone to each, but not reduce the occurrence of stripes significantly Co ²⁺ or Ni ²⁺ to Al ^{3 +} one Or it is judged that the effect is great when adding both in combination. In particular, if the streaks are generated in the front plating, it can be seen that the defects still occur even after performing the back plating. In particular, it was found that by adding a combination of inorganic aluminum ions and cobalt or nickel ions, which are not decomposed at an insoluble anode, zinc crystals can be effectively micronized even in a very small amount. It can be understood that the cause of the streaks is due to the difference in crystal size and preferential orientation of the zinc crystal.

Example 3

In Example 2, the whiteness of the surface of the plated steel sheet subjected to the shear plating and the flushing process by the treatment process of the present invention and the addition amount of the conductive auxiliary material in the after plating solution were measured. Shown in

Table 3

As a result, the whiteness increases when the post plating is performed. In addition, since the whiteness decreases as the amount of the conductive assistant is increased in the subsequent plating solution, in order to manufacture a bright plated steel sheet, it is necessary to manage the amount of the conductive assistant in the subsequent plating solution to be 0.6 kmol / m 3 or less.

According to the present invention, it is possible to prevent the plating solution from the front end from being buried in the steel plate and mixed with the rear end, and the zinc crystal can be effectively removed even in a very small amount by adding a combination of inorganic aluminum ion and cobalt or nickel ion which are not decomposed at the insoluble anode. It could be made finer. Accordingly, there is no surface bonding of the plating layer caused by the pattern of the material steel sheet and the iron ions in the plating solution, and it is possible to manufacture an electrogalvanized steel sheet with bright colors.

Claims (3)

In the manufacturing process of the galvanized steel sheet for manufacturing a continuous galvanized steel sheet by treating the steel strip in a plating bath having two or more plating cells to plate the zinc on the steel sheet, A plurality of plating cells are separated into a front end and a rear end from the end of the traveling direction of the strip, and at least one flushing system is provided therebetween, so that the plating liquid attached to the steel plate in the front plating cell is the action of this flushing system. Addition of one or more Al ³⁺ ions and one or more Co ²⁺ or Ni ²⁺ ions to the front end plating solution so as not to be mixed in the plating solution, and the addition of one or more conduction aids such as chloride or sulfur oxide Method of producing a bright, stripe-free galvanized steel sheet, characterized in that to produce a galvanized steel sheet without streaks by inhibiting the mixing in the rear end plating solution According to claim 1, synthesis was carried out by separating the electro-plating process for producing a zinc-plated steel sheet does not have the bright stripes with a shear plating step, water washing step and the third step of the subsequent stage plating process, the plating solution Al ³⁺ to the front end 0.5 to 2 kg / ㎥ and the sum of either Co ²⁺ or Ni ²⁺ is contained 0.05 ~ 0.3 kg / ㎥, the conduction aid is KCl, NaCl, Na ₂ SO ₄ and K ₂ SO Combine any one or two of _four or more so as to have a solubility of not more than 1.2 kmol / ㎥ or less, the temperature of the plating solution is 40 ~ 80 ℃, the pH of the plating solution is 0.8 ~ 3.0, the current density of 20 ~ 180 A / dm 3 plating method of manufacturing a bright, stripe-free galvanized steel sheet, characterized in that the plating In order to manufacture a bright, stripe-free galvanized steel sheet, the water washing system apparatus of claim 1 includes a pure water supply tank (1), a wash liquid circulation tank (2), a wash liquid conductivity control system (3), and a pair of ringer rolls (4). 5) consists of a washing liquid injector (6), washing liquid discharge pipe (7), washing liquid collection device (8), automatic valves for control (9, 10, 11), conductivity measuring cell (12) or using some of them It is used to spray water between a pair of ringer rolls and to recycle the sprayed water, but to control the inflow of the shear plating liquid into the rear plating liquid by controlling the conductivity of the washing liquid. Manufacturing equipment

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