KR100312407B1 - Method of coloring hot dip galvanized steel sheet in cgl(continuous galvanizing line) - Google Patents

Abstract

PURPOSE: A method of coloring hot dip galvanized steel sheets in CGL(continuous galvanizing line) by adjusting the thickness of TiO2 coating after galvanizing operation. CONSTITUTION: In one embodiment, the method of coloring hot dip galvanized steel sheets in CGL(continuous galvanizing line) includes: (i) dipping a steel sheet to be galvanized in a plating bath containing 0.1-0.5wt.% of Ti, 0.004wt.% or less of Al, a balance Zn and other unavoidable impurities at a temperature range of 475 to 570deg.C for 1-3 seconds, wherein the steel sheet to be galvanized is in advance heated to the same temperature as the plating bath; (ii) heating the surface of a galvanized steel sheet at 500deg.C for 1-2 seconds. In the other embodiment, the method of coloring hot dip galvanized steel sheets in CGL(Continuous Galvanizing Line) includes: (i) dipping a steel sheet to be galvanized in a plating bath containing 0.1-0.5wt.% of Ti, 0.004wt.% or less of Al, a balance Zn and other unavoidable impurities at a temperature range of 475 to 570deg.C for 1-3 seconds, wherein the steel sheet to be galvanized is in advance heated to the same temperature as the plating bath; (ii) quenching the surface of a galvanized steel sheet by spraying coolant under the conditions of a liquid pressure of 1 to 2kg/cm¬2 and an air pressure of 3kg/cm¬2.

Description

Coloring method of hot dip galvanized steel sheet in continuous plating process

The present invention relates to a color adjustment method of a colored hot dip galvanized steel sheet, and more particularly, a method of coloring a colored hot dip galvanized steel sheet in a continuous plating process by adjusting the thickness of an oxide film by post-treatment adjustment such as heating or cooling after plating. It is about.

Hot-dip galvanized steel sheet is widely used as a steel sheet for electronic materials, home appliances and automobiles because of its excellent corrosion resistance. Recent trends in such hot dip galvanized steel sheets require colorization in harmony with the appearance of attention. In other words, in steel towers, street lamps, guardrails, soundproof walls and other appearances where hot-dip galvanized steel is mainly used, it is required to have an aesthetic color that harmonizes with the surroundings rather than having a simple metallic color as before.

Conventionally, this request has been met by color coating of the hot dip galvanized steel sheet by applying solvent coating or powder coating after hot dip galvanizing. However, in the conventional method, zinc in the plated film of the hot-dip galvanized steel sheet is decomposed into fatty acids and alkylli, which are constituents of the paint fraction, to form zinc stone, and the film of the paint used for coloring does not adhere to the plated layer surface. Has the drawback. In addition, the conventional coloring method is applied to the hot-dip galvanized steel sheet additionally, resulting in an increase in the process and an increase in cost, and causes a problem of environmental pollution by paints and solvents.

With respect to such a conventional coating method after hot dip galvanizing, a colored hot dip galvanized steel sheet production method is known in which a coloring element having a color unique to a plating bath is added to color the hot dip galvanized layer itself.

For example, Japanese Patent Publication No. 63-247331 discloses a method of coloring zinc using a plating bath in which at least one of Ti, Pb, Cd, Cu, Sn, Bi, Sb, and In is added to a zinc plating bath. Is starting. Here, the hot dip galvanized steel sheet of various colors is obtained by adjusting the degree of oxidation by depositing 60 seconds or more in a plating bath having the above-described component system and maintaining it for 5-30 seconds in a temperature atmosphere of 450-550 ° C. In addition, Japanese Patent Publication No. 63-241132 uses a zinc alloy of 0.2-0.1 wt% of Ti-0.05-1 wt% of Cu-Zn, and performs plating at a bath temperature of 490-530 ° C. -The plated layer is colored by heating for 50-150 seconds in the temperature range of 520 ℃ and by hot water cooling or after forced air cooling in the air.

However, the conventional coloring method of zinc by the addition of a coloring element is a discontinuous zinc plating process, the deposition time is long and needs to be maintained for a long time at high temperature after plating.

However, the continuous plating process has a short deposition time of 3 seconds or less, and cannot be maintained for a long time in a high temperature atmosphere after plating, and a method of coloring a hot-dip galvanized steel sheet by adding a coloring element in the continuous plating process is required. .

It is very advantageous if the temperature of the plating bath can be lowered and the amount of addition of the coloring element can be increased in the production of colored hot dip galvanized steel sheet by the addition of the coloring element. By reducing the occurrence of dross and adhesion, it is possible to prevent the color difference in the width direction and the length direction and the inhibition of the surface appearance, and also to shorten the heating time because the color change at the same temperature is accelerated by increasing the amount of the coloring elements added. This is because a colored hot dip galvanized steel sheet excellent in plating layer surface smoothness and surface quality can be obtained.

It is therefore an object of the present invention to provide a method for coloring hot-dip galvanized steel sheet in a continuous plating process that can reduce the temperature of the plating bath and increase the amount of coloring elements to obtain colored hot-dip galvanized steel sheet with excellent color. .

The object of the present invention is a method of coloring a hot-dip galvanized steel sheet by adding a coloring element in a continuous plating process, by hot-dip galvanizing by adjusting the thickness of the oxide film on the surface of the plating layer by heating the surface of the plating layer after plating. It is achieved by providing a coloring method for coloring the steel sheet. Here, for example, a zinc alloy system composed of 0.1 to 0.5 wt% of Ti, 0.004 wt% or less of Al and the balance Zn, and unavoidable impurities is used as the plating bath component system, and the plating system is maintained at 475 to 570 ° C. After plating the plated material heated to the same temperature as the plating bath for 1 to 3 seconds to deposit and plated, the surface of the plated layer can be heated to 500 ℃ temperature for 1 to 2 seconds to color the hot dip galvanized steel sheet.

In addition, an object of the present invention is a method of coloring a hot-dip galvanized steel sheet by the addition of a coloring element in a continuous plating process, by adjusting the thickness of the oxide film on the surface of the plating layer by quenching the surface of the plating layer after plating. It is achieved by providing a coloring method for coloring a plated steel sheet. Here, for example, a zinc alloy system composed of 0.1-0.5 wt% Ti, 0.004 wt% or less of Al, the balance Zn, and unavoidable impurities is used as the plating bath component system, and this plating system is maintained at 475-570 ° C. After depositing and plating the plated material heated to the same temperature as the plating bath for 1-3 seconds, the surface of the coating layer was sprayed for 1 second under the spraying conditions of 1-2 Kg / cm ² and 3Kg / cm ² air pressure. The galvanized steel sheet may be colored by quenching during spraying.

1 is a view showing a change in the thickness of the oxide film (TiO ₂ ) of the plating layer surface according to the plating bath temperature and the post-treatment method.

Hereinafter, the present invention will be described with reference to the accompanying drawings.

As the steel sheet introduction temperature and the plating bath temperature increase, the surface of the plating layer shows the color change in the order of gold, purple, and blue. That is Ti added colored hot-dip galvanized steel sheet is plated to bring about the color change of the coating layer depending on the bath temperature, which colors by the interference degree of light according to the thickness difference of TiO ₂ of the surface of the plating layer, not according to the composition change of the oxide film It's about making a difference. In order to confirm this fact, the chemical composition of the plating layer color, the chemical composition of the surface of the plating layer, and the thickness of the oxide, and the thickness of the oxide of the naturally cooled colored hot-dip galvanized steel plate after plating using a Ti-containing plating bath containing 0.1-0.5wt% were measured. Analysis was carried out using (X-ray photoelectron spectroscopy). As a result, the colored hot-dip galvanizing chemical bonding of the plating layer oxide film of the steel sheet state coating, regardless of the bath temperature, in other words, but is configured in the same manner as TiO ₂ + ZnO, regardless of the plating layer color, TiO ₂ oxide film depending on the coating bath temperature The thickness of was found to change. That is, as the plating bath temperature increases, as shown in FIG. 1, the thickness of the Ti oxide film TiO ₂ increases. Therefore, it can be seen that the color change of the plating layer due to the change in the plating bath temperature of the Ti-added hot-dip galvanized steel sheet is not caused by the change in the composition of the oxide film but by the degree of interference of light due to the difference in the thickness of TiO _{2 on} the surface of the plating layer.

Therefore, in order to change the color of the Ti-added hot-dip galvanized steel sheet, the thickness of the oxide film is adjusted by adjusting the post-treatment conditions such as heating or cooling after plating according to the present invention without forming plating conditions such as the temperature of the plating material and the plating bath. The adjustment allows the production of colored hot dip galvanized steel sheets of various colors.

The growth of the thickness of the oxide film in the plating layer by directly heating the plating layer at a temperature of 500 ° C. for 1 second immediately after plating under the same plating conditions as in FIG. 1 is accelerated than the case of natural cooling after plating at the same temperature, resulting in a thick oxide film. do. Therefore, heating in the oxidizing atmosphere immediately after plating corresponds to the case of plating in a plating bath one step or more higher than the formation of the plating layer in the case of natural cooling. Here, the plating layer heating is sufficient to directly heat only the surface of the plating layer with the flame of the burner, rather than maintaining it for a long time in a high temperature furnace as in the discontinuous plating process. Therefore, there is no problem that color is removed by alloying by high temperature and long time heating as in the prior art, and it does not cause a problem of productivity degradation because it does not cause a decrease in line speed in the continuous plating process.

When the plating layer is directly heated by the burner after plating, two colors may be mixed as in the case of natural cooling. In such a case, a solid plating layer may be obtained by increasing the heating temperature or lengthening the heating time. . As described above, the present invention can easily adjust the thickness of the surface oxide film of the plating layer by directly heating only the surface of the plating layer immediately after plating. Thus, a uniform and vivid purple light blue colored hot dip galvanized steel sheet is obtained without increasing the temperature of the plating material and the plating bath. To manufacture. Therefore, the present invention, which directly heats the surface of the plating layer by post-plating treatment method, is used because the plating layer surface color corresponds to the color produced at the plating bath temperature higher than the color adjustment of the plating layer oxide due to the change in plating bath temperature and thus the color. It is possible to reduce the bath temperature, and furthermore, even when the amount of the coloring element added to the plating bath is lowered together with the lowering of the plating bath temperature, dross generation is reduced, so that the amount of the coloring element added to the plating bath can be increased. Accordingly, since the color change at the same temperature is faster, it is possible to shorten the heating time. Therefore, the present invention which directly heats only the surface of the plated layer in the continuous plating process is superior to the surface layer smoothness and surface quality compared to the conventional natural cooling.

In the embodiment of the present invention, the amount of Ti added to the coloring element is increased from 0.1-0.3 wt% Ti to 0.1-0.5 wt% Ti of natural cooling. In the case where the Al content of the plating bath is 0.004 wt% or more, an oxide film of Al is formed. Therefore, the zinc bath is made to be 0.004 wt Al% or less and the zinc alloy having the balance of zinc is used as the plating bath. Plating bath temperature is 570 ℃ or less to obtain a variety of colors by adjusting the heating temperature and time. In this case, the length of the heating time in the continuous plating process should be attached to many devices, and when the heating temperature is increased, the plating layer is alloyed, so the plating bath temperature is limited to 475-570 ° C. In addition, when the adjustment range of the heating temperature and time is increased, the above problems are caused, so the heating temperature is limited to 500 ° C., and the heating time is adjusted in conjunction with the line speed and the color change. Maintaining -2 seconds to produce a colored plate of uniform and vivid color.

In addition to the post-treatment method of heating the surface of the plating layer as described above, the color of the colored hot-dip galvanized steel sheet may be variously adjusted by adjusting the thickness of the oxide film on the surface of the plating layer by quenching immediately after plating.

In the case of solution spraying under the condition of solution pressure 1kg / cm ² and air pressure 3kg / cm ² after plating, as in the case of FIG. 1, since the oxide film formation on the surface of the plating layer is suppressed by the rapid cooling, the formation of the oxide film on the surface of the plating layer is suppressed. Compared with the natural cooling and heat treatment, the thickness of the oxide film can be seen to be greatly reduced. In other words, the quenching treatment of the surface of the plating layer immediately after plating shows a color of one step lower or lower than that of the case of natural cooling after plating at the same plating bath temperature or heating after plating. .

In addition, when quenching is performed immediately after plating, two colors may be mixed when the spraying conditions are not appropriate as in the case of post-treatment heat treatment.However, by adjusting the spraying conditions appropriately, the cooling rate may be increased or decreased to uniformly color. Hot-dip galvanized steel sheet can be produced. In another embodiment of the present invention, the ammonium hydrogen phosphate-based solution having excellent cooling ability is used as the injection solution, but water or other refrigerants may be used depending on the cooling rate. In addition, the spray nozzle eliminates irregularities on the surface of the plating layer by spray particles by using a two-fluid nozzle in which a solution and air are mixed in the nozzle and sprayed in a spray state, thereby increasing the cooling capacity. In particular, there is injected particles and spray amount is influenced by the solution pressure and the air pressure, in other embodiments of the present invention, maximize the cooling capacity in the solution pressure 1kg / cm ^2, air pressure 3kg / cm ² of the conditions. As described above, when the oxide film thickness and color of the surface of the plating layer are adjusted by quenching after plating, the amount of the coloring element added to the plating bath is slow because the formation rate of the oxide layer after plating is slow and the color change of the coloring oxide film is slow. It is possible to increase it compared to natural cooling. For example, in another embodiment of the present invention, it is possible to extend the amount of Ti content, which is a coloring element, from 0.1-0.3 wt% to 0.1-0.5 wt% in general. In addition, when quenching under the same spray conditions immediately after plating, it can be seen that it is preferable to manage the plating bath temperature at 570 ° C. or less in gold and purple colors. Therefore, since the plating bath does not need to be heated to a high temperature, it is possible to prevent dross formation and adhesion by the high temperature plating bath, thereby greatly improving the plating layer surface smoothness and plating surface quality. In particular, the color adjustment of the surface of the plating layer by quenching immediately after plating can remove the latent heat of the plating material as well as the surface of the plating layer, thereby preventing the formation of an alloy layer at the interface between the plating material and the plating layer due to the latent heat of the thick material and the after-plating material. Machinability was greatly improved during processing.

In another embodiment of the present invention, 0.1-0.5 wt% Ti, 0.003 wt% Al-Zn zinc alloy is used as the plating bath, and the plating bath temperature is 570 ° C. or lower immediately after plating to adjust the solution pressure and air pressure to spray Various colors can be obtained by spraying with a spray, and in the continuous plating process, the spraying time is very short as 1-2 seconds, so it is limited to the conditions of solution pressure 1-2kg / cm ² and air pressure 3kg / cm ² .

Hereinafter, embodiments of the present invention will be described.

Cold rolled steel sheet of general low carbon steel having a thickness of 0.8 mm was cut into a width of 100 mm and a length of 200 mm to obtain a test piece. The specimen was degreased by dipping in an alkaline solution, and then heat-treated at annealing reduction temperature of 750 ° C. The pre-plated plating material was deposited in the plating bath of 0.1-0.5wt% Ti-0.003 wt% Al-Zn for 3 seconds at the plating bath temperature (same as the steel sheet insertion temperature) at 475-580 ℃ for 3 seconds. After plating to 150 g / m ² , a colored oxide film was formed by natural cooling (air cooling), heat treatment, and quenching (solution injection) in air as shown in Table 1.

The manufactured hot-dip galvanized steel sheet is an ESCA (X-ray Photoelectron Spectrometer) depth direction analyzer, which measures the thickness of TiO ₂ , the surface oxide film of the surface layer, and mixes the color and color in the width and length directions of the specimen. Table 1 shows the results of visual evaluation of the plating quality.

N0 Zinc alloy system (Ti content) Plating bath temperature (℃) Post Processing Condition Plating Quality Characteristics Evaluation Remarks Natural cooling (air cooling) * Heat treatment (temperature × time) ** Quick Cooling Treatment (Solution Pressure × Air Pressure) TiO ₂ thickness color Color mixing One 0.1-0.3 500 ○ - - 420 gold ○ Conventional example 2 0.1-0.3 525 ○ - - 450 Gold + purple × Conventional example 3 0.1-0.3 550 ○ - - 480 purple ○ Conventional example 4 0.1-0.3 570 ○ - - 570 Purple + blue × Conventional example 5 0.1-0.3 580 ○ - - 630 blue ○ Conventional example 6 0.1 to 0.5 500 - 500 × 1 470 purple ○ Inventive Example 7 0.1 to 0.5 500 - 500 × 1 470 purple ○ Inventive Example 8 0.1 to 0.5 550 - 500 × 1 550 Purple + blue × Comparative example 9 0.1 to 0.5 550 - 500 × 2 600 blue ○ Inventive Example 10 0.1 to 0.5 570 - 500 × 1 650 blue ○ Inventive Example 11 0.1 to 0.5 580 - 500 × 1 720 blue ○ Inventive Example 12 0.1 to 0.5 500 - - 1 × 3 380 gold ○ Inventive Example 13 0.1 to 0.5 525 - - 1 × 3 400 gold ○ Inventive Example 14 0.1 to 0.5 550 - - 1 × 3 440 Gold + purple × Comparative example 15 0.1 to 0.5 550 - - 1 × 2 410 gold ○ Inventive Example 16 0.1 to 0.5 570 - - 1 × 3 470 purple ○ Inventive Example 17 0.1 to 0.5 580 - - 1 × 3 480 purple ○ Inventive Example

* Heating temperature (℃) × time (sec)

** Solution Pressure (kg / cm ² ) × Air Pressure (kg / cm ² )

○: good, x: poor

As shown in Table 1, in order to manufacture a blue colored coating film (No5) in a conventional zinc alloy system of 0.1-0.3wt% Ti-0.003wt% Al-Zn, a high temperature plating bath temperature of 580 ° C or higher is required. In order to prevent dross from adhering to the surface of the plating layer, the range of addition of the coloring element should be limited.

On the contrary, by directly heating to 500 ° C. for 1-2 seconds immediately after plating, uniformly colored purple zinc (No. 6, 7) and blue (No. 9, 10, 11) colored hot dip galvanized steel sheets are stably manufactured. Could. In addition, the color of the heat treatment by the post-treatment method immediately after plating (No. 6-11) is higher in one or two steps than in the case of natural cooling after plating at the same plating bath temperature (No. 1-5). Since it is possible to lower the plating bath temperature compared to natural cooling, it was possible to increase the Ti addition amount of the plating bath up to 0.5wt%.

Even after quenching, it is possible to produce gold (No. 12, 13, 15) and purple (No. 16, 17) colored plated steel sheets with excellent uniformity and clarity even by the quenching treatment of spraying the spraying solution for 1-2 seconds. Could. In the case of quenching by post-treatment method immediately after plating (No. 12-17), the color corresponded to the plating layer color plated at the plating bath temperature lowered by one or two steps compared to natural cooling. Since the formation rate of the oxide layer of the coloring element after plating is slow and the color change of the coloring oxide film is slow, the addition amount of the coloring element of the plating bath can be increased as compared with the conventional natural cooling method. Therefore, the Ti content of the plating bath can be added up to 0.5wt%. It was possible to raise.

Therefore, in the zinc alloy system of 0.1-0.5wt% Ti-0.003wt% Al-Zn, heat treatment and quenching are appropriately performed by the post-treatment method. Therefore, gold, purple and purple have excellent surface quality characteristics at the plating bath temperature lower than natural cooling. A blue colored hot dip galvanized steel sheet could be produced.

That is, when the plating bath temperature is sprayed for 1-2 seconds under the spraying condition of solution pressure 1-2kg / cm ² and air pressure 3kg / cm ² at 475-580 ° C (No. 12, 13), the gold color is the same. 1 second heat treatment at the plating bath temperature at 550 ° C. (No. 6,7) to purple color, 1-2 second heat treatment at the plating bath temperature of 540-570 ° C. to 500 ° C. (No. 9, 10) was able to produce a uniform and vivid colored molten zinc plated steel sheet of blue color.

Until now, the coloring element was limited to Ti. However, various coloring elements can be stably and easily colored on the surface of the plating layer by the above heat treatment and quenching treatment.

Thus, according to the present invention, after plating in a plating bath containing a coloring element having a color unique to the plating bath, the color change of the plating layer is made possible by adjusting post-treatment conditions such as heat treatment and quenching treatment. As described above, since the temperature of the plating bath is higher than 600 ° C., there is no need for coloring, a uniform and clear colored plated steel sheet can be manufactured by preventing the occurrence of dross on the surface of the plating bath and preventing the adhesion of the plating layer. In addition, even if the amount of Ti is increased due to a decrease in the plating bath temperature, it is possible to prevent dross generation and color difference, thereby enabling stable operation by expanding the amount of the coloring element added to the plating bath.

Claims (4)

In the method of coloring a hot-dip galvanized steel sheet by adding a coloring element in a continuous plating process, hot-dip galvanizing to color the hot-dip galvanized steel sheet by adjusting the thickness of the oxide film on the surface of the plating layer by heating the surface of the plating layer after plating. Method of coloring steel sheet. The method of claim 1, Zinc alloy system composed of 0.1-0.5 wt% Ti, 0.004 wt% or less of Al and the balance Zn and unavoidable impurities is used as the plating bath component system, and the same temperature as the plating bath in the plating bath in which this component system is maintained at 475-570 ° C. A method of coloring a hot-dip galvanized steel sheet which colors the hot-dip galvanized steel sheet by depositing and plating the plated material heated by heating for 1 to 3 seconds and then heating the surface of the plating layer at 500 ° C. for 1 to 2 seconds. In the coloring method of a hot-dip galvanized steel plate by addition of a coloring element in a continuous plating process, the hot-dip zinc which colors a hot-dip galvanized steel sheet by adjusting the thickness of the oxide film on the surface of a plating layer by quenching of the surface of a plating layer after plating. Method of coloring of plated steel sheet. The method of claim 3, wherein Zinc alloy system composed of 0.1-0.5 wt% Ti, 0.004 wt% or less of Al and the balance Zn and unavoidable impurities is used as the plating bath component system, and the same temperature as the plating bath in the plating bath in which this component system is maintained at 475-570 ° C. The plated material heated by heating was deposited by plating for 1-3 seconds, and then quenched by spraying for 1 second in the spray state under the spraying conditions of solution pressure 1-2 Kg / cm ² and air pressure 3Kg / cm ² . Coloring method of hot dip galvanized steel sheet for coloring galvanized steel sheet.

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