JP3127815B2 - Method for controlling coating weight in hot metal plating - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to continuous hot-dip galvanizing such as continuous hot-dip galvanizing of a steel strip, and to wiping a strip passing continuously through a plating bath above the bath at a position above the plating bath. The present invention relates to a plating adhesion amount control method for adjusting a plating adhesion amount by injecting gas from a nozzle.

[0002]

2. Description of the Related Art Conventionally, the amount of plating in continuous hot metal plating of a strip is adjusted by a pair of wiping nozzles 3, 4 above a hot metal plating bath 2 as shown in FIG.
Gas is sprayed from the wiping nozzles 3 and 4 onto the strip 1 that passes through the plating bath and travels continuously above the bath, thereby scraping off excess hot-dip plating metal adhering to the strip surface. Have been

As a method for controlling the amount of coating in such continuous hot metal plating, for example, Japanese Patent Application Laid-Open No.
No. 696 discloses a method of controlling the amount of plating W based on a relational expression using a line speed V of a strip, a gas injection pressure P of a wiping nozzle, and a distance B between a nozzle and a strip as factors. Conventionally, many relational expressions using such factors have been published, and for example, the following relational expression is known as one of them.

(Equation 3) Here, the values of the respective coefficients h ₀ , h ₁ , h ₂ , and h ₃ in the above relational expression are determined by the multiple regression calculation from the actual plating adhesion amount.

Japanese Patent Application Laid-Open No. Hei 5-171395 discloses the above three control factors (line speed V, gas injection pressure P of wiping nozzle, nozzle-strip) in consideration of the influence of the strip thickness on the amount of plating. There is disclosed a plating adhesion amount control method in which the thickness t is combined with the distance B) and the plating adhesion amount is controlled by the following relational expression.

(Equation 4)

Further, Japanese Patent Application Laid-Open No. Hei 6-296923 discloses that a gas jet from a wiping nozzle is divided into a developed area and a fully developed area by a distance between a nozzle and a strip. A method of controlling the amount of plating by using the following different relational expressions in the developed region and the fully developed region in consideration of the different effects on the amount of coating is disclosed.

(Equation 5)

In each of the above-described methods for controlling the amount of coating, feedforward control or feedback control is performed using the respective relational expressions to control the amount of plating. Therefore, in order to accurately control the coating weight, the accuracy of the plating weight relation formula itself is an important factor.

[0007]

However, according to the study by the present inventors, it has been found that in order to control the coating weight in continuous hot-dip metal plating with high accuracy, factors other than the factors used in the above-described prior art are required. It is also necessary to consider various factors and factors. That is, as these factors and factors, for example, when the region of the gas jet from the wiping nozzle is strictly distinguished, the existence of a region called a transition region between the developed region and the fully developed region, the plating bath temperature, Factors such as the plating bath component, the temperature of the plate entering the plating bath, and the steel type of the strip can be mentioned.

[0008] On the other hand, in order to obtain a coating weight in a range from about 30 g / m ² thin per side to about 120 g / m ² thick per side, the gas injection pressure of a wiping nozzle to be used and Operating conditions, such as nozzle-strip distance, are also quite extensive. Therefore,
In order to always control the coating weight with high precision under such a wide range of operating conditions, the above-mentioned plating weight relation formula needs to be considerably high precision, but in the conventional method described above, It has been found that it is difficult to always control the coating weight with high precision under such a wide range of operating conditions. Therefore, an object of the present invention is to provide a plating adhesion amount control method capable of always controlling a plating adhesion amount from thin plating to thick plating with high accuracy.

[0009]

Means for Solving the Problems In order to solve such problems, the method for controlling the amount of applied coating of the present invention has the following features. [1] A method for controlling the amount of coating by injecting a gas from a wiping nozzle at a position above the plating bath onto a strip continuously traveling above the bath after passing through the molten metal plating bath, comprising the following (1) A method for controlling the amount of plating in hot-dip metal plating, which comprises injecting a gas from a wiping nozzle under conditions satisfying the expression to control the amount of plating.

(Equation 6)

[2] A method for controlling the amount of plating by injecting a gas from a wiping nozzle at a position above the plating bath onto a strip continuously traveling above the bath after passing through the molten metal plating bath. A plating amount control method in molten metal plating, wherein a gas is injected from a wiping nozzle under a condition satisfying the expression (2) to control the plating amount.

(Equation 7)

[0011]

BEST MODE FOR CARRYING OUT THE INVENTION When a gas is injected from a wiping nozzle to a strip surface on which a molten metal is plated to scrape off excess molten metal adhered to the strip surface, the force for scraping the molten metal is determined by the force from the wiping nozzle. The collision pressure of the gas jet is dominant. Here, there is a relationship of the following equation (3) between the collision pressure Ps of the gas jet, the flow velocity u of the gas jet, and the density ρ of the jet gas, and therefore, the velocity u of the gas jet is
Has a great influence on the scraping power.

(Equation 8)

[0012] maximum flow velocity u _m of gas jets, which can be expressed by a function of the distance y from the wiping nozzle outlet,
The maximum flow rate u _m is 3 by the distance y as shown in FIG. 2
Can be divided into two areas. First, y ≦ shown in FIG.
In l ₁ region (developing area), there is a potential core of a gas flow rate does not decline, the maximum flow velocity u _m can be expressed by the following equation (4).

(Equation 9) Here, u ₀ is the gas flow velocity immediately after the exit of the wiping nozzle.

[0013] Next, in the region of y ≧ l ₂ (fully developed region), the potential core because the influence of the gas jet outside reaches the jet center disappeared completely, the maximum flow velocity u _m is below
As shown in equation (5), the distance y decreases in proportion to a certain multiplier.

(Equation 10) On the other hand, l ₁ <between these unfolded areas and fully developed areas
In y <l ₂ range (transition region), the potential core as the distance y becomes larger gradually disappeared, concerns the maximum flow velocity u _m and the distance y can be expressed by the following equation (6).

[Equation 11]

From the above points, it is strictly speaking that the coating weight needs to be controlled in each of the above three areas by a different coating weighting relational expression. Since the distance from the wiping nozzle is used in the transition region, and when the operation is performed outside the transition region, the distance does not greatly deviate from the transition region. Was. Then, the above equation (6), which expresses more strictly the effect of the nozzle-strip distance on the gas flow rate that is deeply related to the plating adhesion amount, is incorporated into the adhesion amount-related expression, that is, the nozzle-strip distance. It has been found that by setting the term of the distance in the form of the above equation (6), it is possible to control the amount of applied plating with higher precision than before.
That is, it was found that by injecting gas from the wiping nozzle under the condition satisfying the following equation (1), the amount of plating applied can be controlled with high accuracy.

(Equation 12)

Further, in addition to the factors of the line speed V, the gas injection pressure P of the wiping nozzle, and the distance B between the nozzle and the strip used in the above equation (1), the strip plate thickness t and the plate temperature T entering the plating bath T Has a great influence on the viscosity of the molten metal adhering to the strip, which has an effect on the amount of plating applied. Therefore, by injecting gas from the wiping nozzle under the conditions satisfying the following equation (2) incorporating these factors into the adhesion amount relational equation,
It was found that the amount of plating could be controlled with higher precision.

(Equation 13) Here, k _{1 to} k ₆ in the above formulas (1) and (2) are constants obtained by performing multiple regression calculations from the actual values of the amount of applied plating, and m ₁ and m ₂ are wiping nozzles. It is based on the shape (slit gap, slit length, outer shape of the nozzle tip, etc.), and is a constant experimentally obtained from the measurement of the flow velocity of the gas jet.

As described above, the plating bath temperature also affects the viscosity of the molten metal. However, the plating bath temperature is a factor that does not change in a steady operation, and therefore, is not included in the relation formula for the coating amount in the present invention. Absent. As a specific control method for controlling the amount of plating by using the above equations (1) and (2),
The amount of plating applied after wiping was measured, and the gas injection pressure P or the nozzle was adjusted so that a predetermined amount of plating was obtained.
The distance B between strips is controlled based on the above equation (1) or (2). For example, when the gas injection pressure P is selected as a control factor, the gas injection pressure P is calculated by substituting the value other than this factor and the value of the predetermined plating adhesion amount into the above equation (1) or (2). However, by controlling to that value, it becomes possible to obtain a predetermined plating adhesion amount.

[0017]

【Example】

[Embodiment 1] Regarding the equation (a) used in the conventional method described above, the range of 5 ≦ B / D ≦ 16 (B: distance between nozzle and strip [mm], D: slit gap of wiping nozzle [Mm]), each coefficient was obtained from the actual operation data and the actual value of the coating weight by multiple regression calculation.
The calculated value based on the formula and the measured value of the coating weight were compared. The result is shown in FIG. According to this, in the conventional method, the correlation coefficient r was 0.921, and there was a variation within ± 10 g / m ² .

On the other hand, as an embodiment of the present invention, based on the same actual operation data as described above and the actual value of the coating weight,
The values of k ₁ to k ₄ in the equation (1) were obtained by multiple regression calculation, and the values of m ₁ and m ₂ were obtained based on the results of the gas jet flow velocity measurement. The values of k _{1 to} k ₄ , m ₁ , and m ₂ are as follows. _{k 1 = 3.89 k 2 = -0.447} k 3 = 0.187 k 4 = 0.375 m 1 = 0.272 m 2 = 3.65 Using these constants, calculated according to the above (1) The measured coating weight and the actual value of the coating weight were compared. FIG. 4 shows the results. According to the method of the present invention using the equation (1), the correlation coefficient r is 0.967, which can be kept within the range of ± 4 g / m ² , thereby greatly improving the accuracy of controlling the amount of plating applied. be able to.

Next, the values of k ₁ to k _{6 in} the above equation (2) are obtained by the multiple regression calculation from the actual operation data similar to the above and the actual value of the coating weight, and the values of m ₁ and m ₂ are obtained. The values were determined based on the results of gas jet velocity measurements. The values of k _{1 to} k ₆ , m ₁ , and m ₂ are as follows. _{k 1 = 26.9 k 2 = -0.443} k 3 = 0.196 k 4 = 0.326 k 5 = -0.0507 k 6 = -0.277 m 1 = 0.272 m 2 = 3. 65 Using these constants, the plating weight calculated according to the above equation (2) was compared with the actual value of the plating weight. The result is shown in FIG. According to this, since the above equation (2) also takes into account the viscosity of the molten metal, the accuracy is further improved as compared with the case where the above equation (1) is used, and the correlation coefficient r = 0.97
4 and can be suppressed to within ± 3 g / m ² .

[0020]

As described above, according to the method of the present invention, it is possible to always control the coating amount with high precision under a wide range of operating conditions. According to the invention of claim 2 of the present application, since control is performed using a relational expression that also takes into account the viscosity of molten metal, it is possible to perform particularly high-precision plating amount control.

[Brief description of the drawings]

FIG. 1 is a conceptual diagram showing a coating weight control unit in a continuous molten metal plating line.

FIG. 2 is a graph showing a relationship between a maximum flow velocity of a gas jet from a wiping nozzle and a distance from an exit of the wiping nozzle.

FIG. 3 is a graph showing a relationship between a calculated value of a coating weight and a measured value of the coating weight based on a plating weight relation formula employed in a conventional method.

FIG. 4 is a graph showing a relationship between a calculated value of a coating weight and a measured value of a coating weight based on the formula (1) defined by the present invention.

FIG. 5 is a graph showing a relationship between a calculated value of a coating weight and a measured value of a coating weight based on the formula (2) defined by the present invention.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Strip, 2 ... Hot-dip plating bath, 3, 4 ... Wiping nozzle, 5 ... Sink roll

──────────────────────────────────────────────────続 き Continuation of the front page (56) References JP-A-7-96771 (JP, A) JP-A-6-322504 (JP, A) JP-A-6-33212 (JP, A) 171395 (JP, A) JP-A-5-33110 (JP, A) (58) Field investigated (Int. Cl. ⁷ , DB name) C23C 2/00-2/40

Claims (2)

(57) [Claims] 1. A method for controlling the amount of plating by injecting gas from a wiping nozzle at a position above a plating bath onto a strip continuously traveling above the bath through a molten metal plating bath, comprising the following steps: A method for controlling the amount of plating in molten metal plating, which comprises injecting gas from a wiping nozzle under conditions satisfying the expression (1) to control the amount of plating. (Equation 1) 2. A method for controlling the amount of coating by injecting gas from a wiping nozzle at a position above the plating bath onto a strip continuously traveling above the bath through a molten metal plating bath, comprising: A method for controlling the amount of plating in molten metal plating, which comprises injecting gas from a wiping nozzle under conditions satisfying the expression (2) to control the amount of plating. (Equation 2)