KR100815683B1 - Iron elution and dross reduction method in zinc plating bath - Google Patents

Abstract

The present invention relates to a galvanizing operation of a steel sheet, and more particularly, a method of reducing the amount of iron eluted from the steel sheet and reducing the amount of dross generated by iron when the steel sheet for the plating operation passes through the galvanizing bath. It is about.

In the present invention, in the process of producing a hot-dip galvanized steel sheet by passing the steel sheet into the galvanizing bath, the aluminum-containing previa plating solution is introduced through a snout (2) installed in the galvanizing bath (3), In the method of reducing iron dissolution and dross in a galvanizing bath, it is possible to minimize the dissolution of iron by promoting reaction of iron and aluminum and to minimize the occurrence of dross by maintaining the solid solution of iron according to continuous aluminum input. It is about.

Zinc, Plating, Iron Elution, Dross, Snout

Description

METHOD FOR REDUCING Fe DISSOLUTION AND DROSS AMOUNT IN A ZINC PLATING TANK}

1 is a side view of a galvanizing operation of a steel sheet in a conventional galvanizing bath;

2 is a graph of solid solution curves of aluminum and iron with temperature; And

3 is a side view of the galvanizing operation of the steel plate in the galvanizing bath by the iron elution and dross reduction method in the galvanizing bath according to the present invention.

Explanation of symbols on the main parts of the drawings

 1 .... steel plate 2 .... snout

 3 .... galvanized bath 4 .... sink roll

 5 .... Air Knife 6 .... Top Roll

 7 .... pre-plating bath 8 .... passage

The present invention relates to a galvanizing operation of a steel sheet, and more particularly, a method of reducing the amount of iron eluted from the steel sheet and reducing the amount of dross generated by iron when the steel sheet for the plating operation passes through the galvanizing bath. It is about.

A general hot dip galvanized steel sheet is a plated product made by plating zinc on an iron plate (1), and has excellent corrosion resistance due to sacrificial rust prevention by zinc. In addition, there is an alloyed hot-dip galvanized steel sheet which improves workability, weldability and paintability by reheating the already formed plating layer to make a pure zinc layer into an intermetallic compound of iron and zinc.

Due to their low price, these products are replacing electric galvanized steel sheet which is recently used for automotive exterior. However, strict surface quality is required for use in automotive exteriors.

1 is a side view of a galvanizing operation of a steel sheet in a conventional galvanizing bath.

Referring to FIG. 1, a conventional galvanizing operation is performed while the steel sheet 1 is wound around the sink roll 4 in the galvanizing bath 3, and discharged to the upper side of the galvanizing bath 3. Afterwards, the plating thickness is controlled by the air knife 5 disposed on both sides, and the post-process is performed through the top roll 6 installed outside the galvanizing bath 3.

By the way, while the steel sheet 1 passes through the galvanizing bath 3 during the galvanizing operation, aluminum (Al) is added when the amount of zinc in the galvanizing bath 3 decreases due to the passage of the steel sheet 1. Ingot will be used. At this time, when an ingot enters the galvanizing bath 3, a temperature difference around the ingot is generated, and the solid solution of iron instantly drops in the vicinity, and the crystallized iron reacts with aluminum or zinc to generate dross. Let's go.

2 is a graph of the solubility curve of aluminum and iron with temperature.                         

Referring to FIG. 2, it can be seen that the solid solution limit of iron increases when the temperature increases or the aluminum concentration decreases. It can be seen that the aluminum concentration, which is a condition for producing a normal alloyed hot-dip galvanized steel sheet, is 0.135 wt%, and the solid solution of iron at a plating bath temperature of 460 ° C. is 0.025 wt%.

However, this relationship is calculated in the state of thermodynamic equilibrium, so when the actual steel sheet passes through the plating bath, a partial non-equilibrium state occurs according to the flow phenomenon of the steel sheet 1, and the solid solution around the steel sheet is aluminum. Since it is exhausted by the reaction with iron, the solubility of iron increases with decreasing aluminum.

The amount of iron eluted by the increased solubility limit is increased and when the increased iron is separated from the steel sheet by the galvanizing bath (3) flow, it becomes supersaturated due to the solubility corresponding to the concentration of the existing aluminum. The supersaturated iron reacts with aluminum or zinc to form dross.

As described above, iron eluted from the steel sheet 1 in the galvanizing bath 3 reacts with zinc or aluminum to form Fe-Al and Fe-Zn-based dross to form dross defects on the surface of the plated steel sheet. To cause a big problem in the plating properties of the steel sheet.

Usually Fe-Al-based dross has a lower specific gravity than zinc, so it is mainly present in the upper side of the plating bath, Fe-Zn-based dross is mainly present in the lower portion of the plating bath because the specific gravity is higher than zinc. These dross sizes range from a few um to tens of um.

In order to prevent such dross defects, by transferring molten zinc to an auxiliary plating bath installed separately from the hot dip galvanizing bath and lowering the temperature, the dross present in the plating bath is removed, removed and then supplied to the hot dip galvanizing bath. Is proposed in Japanese Patent Application Laid-Open No. 53-88633. In addition, Japanese Patent Application Laid-Open No. 4-99258 removes the dross by changing the Fe-Zn-based dross present in the lower part of the plating bath to Fe-Al-based dross by transferring the zinc plating bath to the auxiliary plating bath and then adding Al. A method was proposed.

However, in the conventional method as described above, in the case of Japanese Patent Application Laid-Open No. 53-88633, the amount of supersaturation of iron generated by the temperature difference becomes small since the temperature difference is not severe as the auxiliary plating bath is 430 ° C. compared with the plating bath of 460 ° C. Due to this, the size of the drought crystallized is very small, less than 10um and there is a problem in that it takes a lot of time to settle and reuse it in the lower part of the auxiliary plating bath.

In addition, in the case of Japanese Patent Application Laid-Open No. 4-99258, since pure Al is added in the auxiliary plating bath to increase the Al concentration, there is a problem in that the main plating bath and the components must be adjusted in the same manner in order to reuse the zinc.

The present invention has been proposed in order to solve the conventional problems as described above, when the steel sheet for the plating operation passes through the galvanizing bath, injecting a preliminary flue solution to activate the reaction of iron and aluminum to suppress the elution of iron. The zinc concentration is controlled to be higher than the aluminum concentration in the entire plating bath so that the solubility of iron in the entire plating bath is the same as that of the non-equilibrium solid solubility caused by the movement of the steel sheet inside the snout. The purpose is to provide a method for reducing the iron dissolution and dross in the plating bath.

The present invention as a technical configuration for achieving the above object, in the process of producing a hot-dip galvanized steel sheet by passing the steel plate into the galvanizing bath, the preliminary containing aluminum through the snout installed in the galvanizing bath By injecting a zinc plating solution, the iron in the galvanizing bath minimizes the occurrence of dross by suppressing the dissolution of iron due to the reaction of iron and aluminum and maintaining the solid solution of iron due to the continuous addition of aluminum. By elution and dross reduction methods.

3 is a side view of the galvanizing operation of the steel plate in the galvanizing bath by the iron elution and dross reduction method in the galvanizing bath according to the present invention.

Referring to FIG. 3, the method for reducing iron and dross in a zinc plating bath according to the present invention is to pass the steel plate 1 into a zinc plating bath to produce a hot dip galvanized steel sheet. 3) Through the snout (2) installed into the injecting the aluminum-containing Yevia flue solution, it is possible to maintain the uniformity of the iron dissolution inhibited by the promotion of the reaction of iron and aluminum and iron solidity according to the continuous aluminum input This is the way to minimize the occurrence of dross.

In addition, in the method for reducing iron and dross in the zinc plating bath according to the present invention, the snout 2 is extended to the front end of the sink roll 4 in which the steel sheet 1 is wound in the zinc plating bath 3. After the addition, the Yevia lead solution is added to manage the aluminum concentration in the snout 2 to be higher than the aluminum concentration in the whole galvanizing bath 3 to maintain the solid solubility of iron and the solubility of aluminum.

The reason for using the pre-melted zinc in the iron elution and dross reduction method in the zinc plating bath (3) according to the present invention is a zinc plating bath (3), and a pre-plating bath (7) connected to the passage (8) and This is to minimize the change in the solubility of iron that can be caused by the temperature difference.

Further, the reason why the pre-via fuel is added directly after extending the snout 2 to the front end of the sink roll 4 reduces the amount of aluminum dispersed throughout the zinc plating bath 3, and This is to increase the concentration of aluminum in the snout 2 to increase the rate of reaction with aluminum when the initial steel sheet 1 passes through the snout 2.

On the other hand, the aluminum concentration of the entire galvanizing bath (3) is maintained at 0.135wt%, but the aluminum concentration is reduced to 0.120wt% around the steel sheet 1, the resulting solid solution limit of iron to 0.035wt% Will increase. Therefore, a difference occurs with 0.025 wt% of the solubility of iron in the total galvanizing bath (3), and iron is supersaturated by this difference to form dross by reacting with aluminum or zinc.

Therefore, in order to maintain the solid solubility of the inside of the snout (2) and the iron solubility of the entire galvanizing bath (3), after extending the snout (2) to the sink roll (4) directly Yebiyeon lead By injecting the molten plating solution, the aluminum concentration inside the snout 2 is increased to 0.15 wt% to maintain the solid solution of iron at the same as the solid solution limit in the entire plating bath.

At this time, the concentration of aluminum directly added to the snout (2) is 1 ~ 3wt% is suitable when producing an alloyed hot-dip galvanized steel (GA), the aluminum concentration is 5 when producing a general hot-dip galvanized steel (GI) ˜7 wt% is suitable.

That is, in the case of an alloyed hot-dip galvanized steel sheet, the reason for limiting it to 1 to 3 wt% is difficult to maintain the aluminum concentration of the snout 2 at 0.15 wt% when it is 1 wt% or less, and when it is 3 wt% or more, the snout (2) This is because the concentration of aluminum becomes 0.15 wt% or more therein, and an intermetallic compound layer of iron and aluminum grows on the surface of the steel sheet 1 to suppress the alloying reaction of iron and zinc.

On the other hand, in the case of the general hot-dip galvanized steel sheet is limited to 5 ~ 7wt%, when the 5wt% or less, the aluminum concentration in the snout (2) is lowered, and the intermetallic compound of iron and zinc is formed on the surface of the steel sheet to form a workability This is because there is a problem of deterioration, and if it is 7wt% or more, the solubility of iron in the snout 2 is lower than the solubility limit of the entire galvanizing bath 3 so that supersaturated iron forms dross.

Hereinafter, the present invention will be described in detail through examples.

<Example>

The galvanizing bath (3) while changing the concentration of aluminum in the galvanizing bath (3) while varying the way ingots are introduced in the process of producing alloyed hot dip galvanized steel (GA) and general galvanized steel (GI). The amount of dross generated in the sample was measured and shown in Table 1 and Table 2, respectively.

Unit: wt% Alloy Steel Plate (GA) Plating bath Al concentration Premelt Al concentration Snout Al Concentration Dross generation (g / m2) Remarks Existing example One 0.125 - 0.118 72 2 0.130 - 0.121 68 3 0.135 - 0.125 65 4 0.140 - 0.128 60 Inventive Example 5 0.130 0.5 0.131 65 6 1.0 0.140 12 7 2.0 0.144 11 8 3.0 0.147 11 9 4.0 0.152 10 Alloying delay 10 0.135 0.5 0.136 50 11 1.0 0.148 10 12 2.0 0.150 9 13 3.0 0.151 9 14 4.0 0.159 8 Alloying delay 15 0.140 0.5 0.142 15 16 1.0 0.155 8 17 2.0 0.157 6 18 3.0 0.159 6 Alloying delay 19 4.0 0.167 5

As shown in Table 1, in the case of alloyed hot-dip galvanized steel (GA), the aluminum concentration of the total plating solution is appropriately 0.130 to 0.140 wt%, and the aluminum concentration of the preplating bath is 1 to 3 wt% (Invention Examples 6, 7, 8 , 11, 12, 13, 16, 17, 18) The amount of dross generated is about 10g, which is much lower than the existing 60g or more. However, when exceeding the 1 ~ 3wt% range dross increased (Invention Examples 5, 10, 15) or alloying delay phenomenon (Invention Examples 9, 14, 19) occurred.

Unit: wt% General Purpose Steel Sheets (GI) Plating bath Al concentration Premelt Al concentration Snout Al Concentration Dross generation (g / m2) Remarks Existing example One 0.170 - 0.155 102 2 0.180 - 0.165 95 3 0.190 - 0.173 91 4 0.200 - 0.180 85 Inventive Example 5 0.170 4.0 0.168 85 Processing bond occurrence 6 5.0 0.175 32 7 6.0 0.180 30 8 7.0 0.182 29 9 8.0 0.189 45 10 0.180 4.0 0.175 70 11 5.0 0.184 30 12 6.0 0.187 28 13 7.0 0.192 25 14 8.0 0.210 42 15 0.190 4.0 0.184 35 16 5.0 0.184 28 17 6.0 0.186 25 18 7.0 0.190 22 19 8.0 0.221 47

In contrast, referring to Table 2, in the case of the general plated steel sheet (GI), since the solid solution of iron decreases as aluminum increases, the amount of dross generated is relatively high.

However, when the pre-plating bath is in the range of 5 to 7wt% in the invention example of the general plated steel sheet (Inventive Example 6, 7, 8, 11, 12, 13, 16, 17, 18), the dross generation amount is 30g and 90g of the existing example. It can be seen that much less than the above. However, if it is out of this range, the amount of dross is increased (inventive examples 5, 9, 10, 14, 15, 19) and deterioration occurs in workability.

In contrast, referring to Table 2, in the case of the general plated steel sheet (GI), since the solid solution of iron decreases as aluminum increases, the amount of dross generated is relatively high.

However, when the pre-plating bath is in the range of 5 to 7wt% in the invention example of the general plated steel sheet (Inventive Example 6, 7, 8, 11, 12, 13, 16, 17, 18), the dross generation amount is 30g and 90g of the existing example. It can be seen that much less than the above. However, if it is out of this range, the amount of dross is increased (inventive examples 5, 9, 10, 14, 15, 19) and deterioration occurs in workability.

As described above, when manufacturing the hot-dip galvanized steel sheet using the method proposed in the present invention, it is possible to reduce the elution of iron, thereby greatly reducing the amount of dross.

As described above, according to the method of iron elution and dross reduction in the galvanizing bath according to the present invention, when the steel sheet for the plating operation passes through the galvanizing bath, an injection of a previa fluid is activated to activate the reaction between iron and aluminum. By suppressing the elution of iron and managing the aluminum concentration inside the snout higher than the aluminum concentration in the whole plating bath, the solid solubility of the iron in the whole plating bath and the non-equilibrium solubility caused by the movement of the steel plate inside the snout By the same, there is a useful effect of greatly reducing the dross generation amount to improve the plating efficiency of the steel sheet.

While the invention has been shown and described with respect to specific embodiments thereof, it will be apparent to those skilled in the art that various changes and modifications can be made without departing from the spirit or scope of the invention as set forth in the claims below. I would like to clarify that knowledge is easy to know.

Claims (4)

In the process of producing a hot-dip galvanized steel sheet by passing the steel sheet into the galvanizing bath, Through the Snauut (2) installed in the galvanizing bath (3) by the addition of the aluminum-containing Yevia flue, the iron dissolution inhibited by the reaction of iron and aluminum and the iron solubility due to continuous aluminum input A method for reducing iron elution and dross in a galvanized bath characterized by minimizing the occurrence of dross by maintaining a uniform. The method of claim 1, The snout (2) is a method for reducing the iron dissolution and dross in the galvanizing bath, characterized in that the steel sheet (1) is extended to the front end of the sink roll (4) wound in the galvanizing bath (3). The method of claim 1, In the production of alloyed hot-dip galvanized steel sheet in the zinc plating bath (3), the weight of aluminum in the Yevia lead solution (7) to be 1 ~ 3wt%, the iron elution and de Loss Reduction Method. The method of claim 1, In the production of the hot-dip galvanized steel sheet, the iron elution and dehydration in the galvanized bath, characterized in that the weight percent of aluminum in the Yevia lead solution (7) introduced into the zinc plating bath (3) to be 5 ~ 7wt%. Loss Reduction Method.

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