KR20150022406A - Method for controlling dip coating weight in hot dip coating process - Google Patents

Abstract

The present invention relates to a method for controlling plating weight according to a change in line speed in a hot dipping process. The method for controlling plating weight according to a change in line speed in a hot dipping process includes: a first step for determining whether a speed set value of a line transferring plated steel sheets is changed from a current speed (V1) to a target speed (V2); a second step for calculating the time (tr) the line speed to reach from the current speed (V1) to the target speed (V2) based on a speed difference (ΔV) between the current speed (V1) and the target speed (V2) and the line speed change rate (Vr) inputted by a placing line operator if determined that the set value of line speed is changed to the target speed (V2); a third step for comparing the target speed reaching time (tr) with the pressure response time (tp) of a predetermined air knife; a fourth step for calculating a target pressure (P2) based on the current speed (V1), the target speed (V2), and the current pressure (P1) of air knife and changing the injection pressure of air knife from the current pressure (P1) to the target pressure (P2) at once if determined that the target speed set value reaching time (Tr) is similar to the pressure response time (tp) of air knife; a fifth step for measuring a line speed (V) at a predetermined cycle until the current speed (V1) reaches the target speed (V2) and changing the air knife target pressure (P2) based on the measured line speed (V) if determined that the target speed set value reaching time (Tr) is greater than the pressure response time (tp); and a sixth step for changing a distance (S) to a surface of steel sheet and the air knife pressure (P) at the same time if determined that the target speed set value reaching time (Tr) is less than the pressure response time (tp).

Description

TECHNICAL FIELD [0001] The present invention relates to a method of controlling a plating amount according to a line speed change in a hot-

The present invention relates to a method for controlling the amount of zinc plating adhered to the surface of a steel sheet passed through a zinc bath in a steel plate hot dip galvanizing process. More specifically, The present invention relates to a method of controlling a plating amount in accordance with a change in line speed in a hot plate hot dip galvanizing process in which a variation in plating amount can be minimized by setting an injection pressure of an air knife in consideration of a pressure response time of an air knife.

In the case of a steel sheet produced in a steel mill, it is common to perform plating on the surface in order to improve physico-chemical properties such as corrosion resistance and to improve the appearance. In recent years, the plating process has been classified as a very important work process in the process of producing electric steel sheets and automobile steel sheets used for special purposes.

As a typical plating process, a hot dip coating method in which a steel sheet is passed through a bath containing a hot dip coating solution and an electroplating method using an electrolytic solution are exemplified. As a typical plating work of electrons, a hot dip galvanizing step of a galvanized steel sheet can be mentioned.

Since the plating operation is performed in such a manner that the molten plating solution is adhered to the surface of the steel sheet while the steel sheet passes through the bath containing the molten plating solution such as molten zinc in the molten plating step, Equipment is needed.

Normally, the amount of plating adhered to the surface of the steel sheet is adjusted according to the demand of the customer by spraying air of appropriate pressure using the air knife on the surface of the steel sheet passed through the bath, The method of controlling the amount of plating using a knife is called an air wiping method.

In the air-wiping system, as shown in FIG. 1, the steel sheet S is moved vertically upward after passing through the zinc bath 8. In this way, on both sides of the coated steel sheet SS, A method of cutting molten zinc adhering to the surface of a steel sheet SS by spraying the air on both sides of a coated steel sheet SS which is vertically upwardly moved by a pressure set according to the amount of custom plating of the demand value by installing knives 6 and 7 To control the amount of plating.

As a main parameter influencing the plating amount in the hot-dip coating process of the air-wiping method, a transfer rate (hereinafter also referred to as a line speed) of a steel plate plated, an air jet pressure of the air knife, . Accordingly, in order to optimally adjust the target plating amount, it is necessary to appropriately set the line speed, the jetting pressure of the air knife, and the distance between the air knife and the surface of the steel sheet.

However, the line speed is frequently changed in various process parameters in the hot-dip coating process. In order to compensate for the variation of the plating amount due to the change of the line speed, the spraying pressure of the air knife and the distance between the air knife and the surface of the steel sheet must be changed.

For example, the applicant Korea Patent Application No. 10-2010-082222 call according to the present invention, the line speed for the air knife pressure set point P _k V _k in the case that varies in V _{k + 1} in V _k a V the pressure set in the _{k + 1} P _{k + 1,} equation _{ln (P k + 1) =} ln (P k) + α [ln (V k + 1) - ln (V k)] output by the And the setting value of the jetting pressure of the air knife is changed according to the line speed.

More specifically, the set pressure change value? P of the air knife is calculated using the following equation (1) with the line speed set value input by the operator as an input.

Where a is the coefficient of influence of the line speed on the amount of plating, c is the coefficient of influence of the pressure on the plating amount, V1 is the currently set line speed, i.e., the conveying speed of the steel sheet, and? V is the amount of change in the speed set value. Namely, V1 is the current line speed setting value, and V2 is the changed line speed setting value, where DELTA V = V2 - V1. P1 is the injection pressure of the currently set air knife.

When the line speed is V1 and the jetting pressure of the air knife is P1, when the line speed is changed to V2, the plating amount changes from Cw1 to Cw2 in a steady state, so that the plating amount deviation? Cw = Cw1-Cw2 is generated. Therefore, it is necessary to change the air knife injection pressure from P1 to P2 so as to prevent the plating amount deviation from occurring in the steady-state section by estimating the amount of plating amount deviation caused by the line speed change.

When the line speed set value change amount [Delta] V changed by the driver in the plating line is input to the air knife pressure set amount calculation computer, the pressure change amount [Delta] P is calculated using the equation (1), and the pressure set value P2 = P + ΔP is calculated and sent to PLC (Programmable Logic Controller). Then, the PLC sends the pressure set value (P2) to the air knife pressure controller to control the air knife pressure to the set value (P2).

When the pressure set value is calculated using the above formula (1), the rate of change of the line speed with time, that is, the line speed change rate Vr = line speed change amount? V / time (t) There is a problem that a variation in the plating amount occurs when the difference in the pressure control response speed is different, particularly when the rate of change of speed (Vr) is smaller than the response speed of the air knife. When the line speed changes very slowly, the time at which the pressure of the air knife reaches the steady state according to the pressure set value to be newly set is faster than the time at which the line speed reaches the changed speed set value V2, A plating amount deviation interval is generated as shown in Fig. For example, in Fig. 2, if the time required for the line speed to reach V2 from V1 is t2 and the time required for the pressure to reach the set value P2 is t1, the pressure of the air knife is set to The set amount of plating is reached. At the time point t2 when the line speed becomes V2 from this time point t1, an amount larger than the target amount of plating is plated on the steel sheet, causing a variation in the amount of plating.

On the contrary, when the speed change rate Vr is higher than the response speed of the air knife, the air knife pressure does not reach the set value P2 even when the line speed reaches V2. Therefore, In the section, less than the amount of mokpo plating is plated on the steel sheet.

The present invention can minimize the variation of the plating amount by adjusting the jetting pressure of the air knife and the interval of the air knife to the steel plate in accordance with the necessity in consideration of the relationship between the rate of change of the line speed and the pressure response time of the air knife, And an object of the present invention is to provide a plating amount control method according to a change in line speed in a steel plate hot-dip plating process.

According to another aspect of the present invention, there is provided a method of controlling a plating amount according to a line speed change in a hot-dip plating process, the method comprising the steps of changing a speed setting value of a line for feeding a plated steel sheet from a current speed V1 to a target speed V2 A first step of judging whether or not the image is formed; If it is determined that the set value of the line speed is changed to the target speed V2, the speed difference? V between the current speed V1 and the target speed V2 and the line speed change rate Vr input by the plating line driver, (Tr) required for the vehicle to reach the target speed V2 from the current speed V1; A third step of comparing a target speed arrival time (tr) with a predetermined pressure response time (tp) of the air knife; When it is determined that the target speed set value arrival time tr and the air knife pressure response time tp are similar, the target pressure P2 is calculated from the current speed V1, the target speed V2 and the current pressure P1 of the air knife A fourth step of changing the injection pressure of the air knife from the current pressure P1 to the target pressure P2 at one time; If it is determined that the target line speed arrival time time tr is larger than the air knife pressure response time tp, the line speed V is measured at a predetermined cycle until the current speed V1 reaches the target speed V2 A fifth step of repeating the process of changing the target pressure P of the air knife based on the measured line speed V; And the target speed arrival time tr is smaller than the air knife pressure response time tp, a sixth step of simultaneously changing the pressure P of the air knife and the gap S between the air knife and the steel sheet surface .

Preferably, in the third step, it is determined that tr and tp are similar when 0.8 x tp <tr <1.2 x tp, and when 1.2 x tp <tr, tr is determined to be faster than tp, 0.8 x tp, tr is judged to be slower than tp.

Preferably, in the fourth step, the target pressure P2,

The pressure change value AP to be changed from the current pressure P 1,

[Equation 1]

Where? P is the pressure change value, a is the coefficient of influence of the line speed on the amount of plating, c is the coefficient of influence of the pressure on the plating amount, V1 is the current velocity,

, And then the target pressure P2 is obtained by

&Quot; (3) &quot;

.

Preferably, in the fifth step,

Measuring a current line speed (V) after a predetermined period of time;

The speed difference? V between the current line speed V and the reference speed Vrff,

&Quot; (4) &quot;

를 이용하여 구하는 단계;

;

A step 53 of comparing ΔV with a predetermined reference value X;

The target pressure P2 of the air knife,

&Quot; (5) &quot;

(Where a and c are parameters of the plating amount prediction equation and P is the pressure of the current air knife);

Setting a pressure of the air knife to a target pressure P2;

Setting a current line speed (V) to a reference speed (Vrff); And

And repeating the steps if the condition that? V> X is satisfied.

Preferably, in the sixth step,

(? S) of the gap of the air knife relative to the surface of the steel sheet,

&Quot; (6) &quot;

(Where? 1 is a constant and? V is a speed difference between the current speed V1 of the line and the target speed V2)

The target interval S2 to be changed,

&Quot; (7) &quot;

(Where S1 is the spacing of the current air knife relative to the surface of the steel sheet);

The target pressure P2 of the air knife,

&Quot; (8) &quot;

B is the coefficient of influence of the distance between the lip of the air knife nozzle and the surface of the steel plate on the plating amount, c is the coefficient of influence of the air knife injection pressure on the plating amount, , Cw is a target plating amount, V2 is a target line speed, and S2 is a gap between the lip of the air knife nozzle and the surface of the steel sheet); And

And controlling the jetting pressure of the air knife and the gap between the air knife nozzle lip and the surface of the steel sheet by setting the target pressure P2 and the gap S2, respectively.

Preferably, the step of obtaining the interval S2 with respect to the surface of the steel sheet of the air knife nozzle lip may include setting the interval S2 to the upper limit value or the lower limit value when the obtained interval S2 is larger than the predetermined upper limit value or lower than the predetermined upper limit value The method comprising the steps of:

According to the method of controlling the plating amount according to the line speed change in the hot dip galvanizing process according to an embodiment of the present invention as described above, The deviation of the plating amount can be minimized by setting the jetting pressure of the air knife in consideration of the rate of change of the line speed as well as the rate of change of the line speed and the pressure response time of the air knife. Further, the control of the deviation of the plating amount due to the change of the line speed can be further optimized by adjusting the distance between the lip of the air knife nozzle and the surface of the steel sheet, in addition to the jetting pressure of the air knife, if necessary.

1 is a view schematically showing a plating amount control apparatus in a general hot-dip plating process.
FIG. 2 is a graph for explaining a problem that a plating amount variation occurs in the conventional plating amount control method.
FIG. 3 is a view schematically showing a configuration of a plating amount control apparatus for performing a plating amount control method according to a line speed change in a hot-dip plating step according to an embodiment of the present invention.
4 is a flowchart illustrating a plating amount control method according to a line speed change in a hot dip coating process according to an embodiment of the present invention.
FIG. 5 is a flowchart illustrating a control method when the target speed arrival time tr is determined to be greater than the air knife pressure response time tp in the plating amount control method according to the embodiment of the present invention.
FIG. 6 is a flowchart illustrating a control method when the target speed arrival time tr is determined to be smaller than the air knife pressure response time tp in the plating amount control method according to the embodiment of the present invention.

Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings.

When the rate of change of the line speed and the pressure response time of the air knife are similar when the set value of the line speed is changed, the method of controlling the plating amount according to the line speed change in the hot- When the set value of the line speed is changed, the pressure set value change amount DELTA P with respect to the line speed is calculated using the formula (1) using the plating amount prediction model with the difference DELTA V of the line speed set value, And the pressure response time of the air knife is different, the pressure set value of the air knife may be changed by another method, the pressure set value of the air knife may be changed as occasion demands, and the gap between the air knife and the surface of the steel plate may be adjusted, Is compensated for.

FIG. 3 is a diagram schematically showing a system configuration for implementing a plating amount control method according to a line speed change according to an embodiment of the present invention. 4 is a flowchart illustrating a plating amount control method according to a line speed change according to the present invention.

First, the line-speed setting value and the line-speed change rate Vr set by the operator of the plating line through the input panel 1 are read at every calculation cycle in the air knife setting value calculator 2 to determine whether there is a change in the line speed, It is determined whether the line speed set value is changed from the current speed V1 to the target speed V2 (step S101).

If there is a change in the line speed, from the speed difference? V between the current speed V1 and the newly set target speed V2 and the line speed change rate Vr until the line speed reaches the changed target speed V2 The time tr required is calculated using the following equation (step S102).

Here, tr is the time required for the line speed V to reach V2 at the speed change rate Vr when the line speed set value is changed from the current speed V1 to the target speed V2.

Next, the time tr calculated using the equation (2) is compared with the pressure response time tp of the air knives 6 and 7 (steps S103 and 104). The pressure response time tp of the air knives 6 and 7 is set such that the actual pressure of the air knives 6 and 7 changes from P1 to the target pressure P2 when the injection pressure setting value of the air knives 6 and 7 is changed from P1 to P2 And the response time required until the change is made.

In an embodiment of the present invention, tr and tp are compared to each other when tr and tp are similar, when tr is larger than tp, and when tr is smaller than tp. In this case, tr is determined to be greater than tp when 0.8 x tp <tr <1.2 x tp, and tr is determined to be equal to tp when 1.2 x tp <tr, . Of course, judging whether tr and tp are similar is not necessarily based on 20% (that is, 0.8 or 1.2) of tp, and it may be set appropriately according to need. In the plating line to which this embodiment is applied, when tr is within about 20% as compared with tp, the rate of change of the line and the rate of change of pressure of the air knives 6 and 7 are almost coincident with each other, .

1. If tr is similar to tp

When it is determined that tr and tp are similar to each other, the target pressure P2 is obtained from the current velocity V1, the target velocity V2 and the current pressure P1 of the air knife in the same manner as the conventional method, , 7) is changed from the current pressure P1 to the target pressure P2 at one time.

First, the pressure change value? P is calculated using Equation (1) (S105).

[Equation 1]

As described above,? P is the pressure change value, a is the influence coefficient of the line speed on the plating amount, c is the influence coefficient of the pressure on the plating amount, V1 is the current velocity,? V is the velocity difference, to be.

Then, the target pressure P2 is calculated from [Delta] P using [Equation 3] (S106).

When the target pressure P2 is calculated, the target pressure P2 is inputted to the air knife pressure regulator 4 through the PLC 3 to adjust the pressure of the air knives 6 and 7 (S107).

2. If tr is greater than tp

When tr is determined to be larger than tp, the line speed V is measured at a predetermined cycle until the current speed V1 reaches the target speed V2 and the measured line speed V The target pressure P of the air knives 6 and 7 is changed. By doing so, the pressure change of the air knives 6 and 7 can be followed in accordance with the speed change of the line, and the deviation between the target plating amount and the actual plating amount can be minimized.

The concrete contents will be described with reference to FIG.

First, after a predetermined time has elapsed, the current line speed V is measured (S201).

The speed difference? V between the measured current speed V and the reference speed Vrff is calculated using the following equation (S202).

Here, Vrff is a reference value used for calculating the speed difference DELTA V, and V is an actual line speed measured at the current calculation time point. At the beginning of the calculation, Vrff is an arbitrary value stored in advance in the air knife set point calculator 2, but later becomes the line speed at the immediately preceding calculation time as described later.

When the velocity change value? V calculated in the equation (4) is larger than the predetermined fixed value X (S203), the target pressure P2 of the air knives 6, 7 is calculated using the following equation (5) S204).

Here, a and c are parameters of the plating amount predicting formula, and P is a pressure value at the current calculation time point. exp represents an exponential function, and ln is a natural logarithm.

When the target pressure P2 is calculated through the equation (5), the target pressure P2 is inputted to the air knife pressure regulator 4 through the PLC 3 to adjust the pressure of the air knives 6 and 7 (S205) .

Then, the reference speed Vrff is replaced with the current actual line speed V (i.e., Vrff = V) (S206).

The target pressure P2 of the air knives 6 and 7 is continuously changed while repeating steps S201 to S206. Finally, when the actual line speed reaches the target speed V2, DELTA V becomes zero. In this case, since the calculation condition DELTA V > = X for performing step S204 and subsequent steps is not satisfied, the target pressure P2 is maintained unchanged do.

If tr is less than tp

Finally, if tr is in the range of less than 0.8 times tp, this is the case where the rate of change Vr of the line speed is faster than the pressure response rate of the air knives 6, 7. In this case, even if the pressures of the air knives 6 and 7 are adjusted arbitrarily, there is a high probability that the coating amount deviation will occur in accordance with the time difference.

As a method of controlling the plating amount in accordance with the change of the line speed during the hot-dip plating process, there are a method of controlling the jetting pressure of the air knives 6 and 7 and a method of controlling the jetting speed of the nozzles of the air knives 6 and 7 There is a method of controlling the distance between the rip and the surface of the steel sheet SS. Since there is an optimum range of the pressures of the air knives 6 and 7 and there is an optimum range of the distance between the nozzle lip of the air knives 6 and 7 and the surface of the steel sheet SS, The control efficiency can be increased.

 Controlling the gap between the nozzle lip of the air knives 6 and 7 and the surface of the steel sheet SS is more effective than controlling the pressure of the air knives 6 and 7 when controlling the amount of plating by the same amount. This is because the time required for the air knives 6 and 7 to move so that the interval becomes S2 at S1 is much longer than the time (pressure response time tp) required for the pressure of the air knives 6 and 7 to change from P1 to P2 It is because it is short. However, in the case of the gap control, in the case where the C plate is formed in the steel sheet SS, the steel sheet SS is vibrated or the pass line is changed, the air knife 6 on the front side and the air knife 7 on the rear side There is a fear that the steel plate SS comes into contact with the lip of the nozzle of the air knife 7 when the gap becomes too narrow. Accordingly, in general, a method of controlling the pressure of the air knife 7 is used.

However, when the line speed arrival time tr is larger than the pressure response time tp of the air knife when the line speed is changed, the pressure response of the air knife 7 can not follow the line speed variation. Therefore, when tr is greater than tp, controlling only the pressure of the air knife 7 can not prevent a deviation from occurring between the target amount of plating and the actual amount of plating.

In view of this, in the embodiment of the present invention, when tr is larger than tp, the gap S between the nozzle lip of the air knife 7 and the steel plate surface and the jetting pressure P of the air knife 7 are simultaneously changed Corresponding to the rapid change in the speed of the line, the deviation of the plating amount is corrected.

This will be described in detail with reference to FIG.

First, a variation amount? S of the distance between the nozzle lip of the air knife 7 and the surface of the steel sheet SS is calculated using the following formula (6) (S301).

Here,? 1 is a constant, and? S is calculated in proportion to the magnitude of? V.

The interval S2 between the air knife 7 and the steel plate SS is expressed by the following equation (7) when the interval between the current steel plate SS surface and the lips of the nozzle of the air knife 7 is S1 (S302).

Here, S1 is a current interval, and? S is an interval variation amount? S calculated in proportion to the magnitude of? V using Equation (6).

If it is determined in step S303 that the calculated interval S2 is out of the predetermined lower limit value or the upper limit value, the interval S2 is set to the lower limit value or the upper limit value in step S304.

Next, the pressure set value is calculated using the following equation (8) (S305).

Where a is the coefficient of influence of the change in line speed on the plating amount, b is the coefficient of influence on the plating amount by the distance between the air knife nozzle and the steel plate surface, and c is the coefficient of influence . Cw is the target plating amount, V2 is the target line speed, and S2 is the distance between the lip of the air knife nozzle and the surface of the steel sheet calculated using the above formula (8).

When the distance S2 between the nozzle lip of the air knife 7 and the surface of the steel sheet SS and the target pressure P2 of the air knife 7 are determined through the above process, To the air knife pressure controller 4 and the air knife position controller 5 so that the air jet pressure of the air knife 7 and the distance between the nozzle lip of the air knife 7 and the surface of the steel plate SS are set (S306).

According to the plating amount control method according to the line speed change in the hot dip coating process according to the embodiment of the present invention, the rate of change of the line speed as well as the pressure response time of the air knife 7 are considered So that the deviation of the plating amount can be minimized by setting the jetting pressure of the air knife 7. The control of the variation of the plating amount due to the change of the line speed can be further optimized by adjusting the distance between the nozzle lip of the air knife 7 and the surface of the steel sheet SS in addition to the injection pressure of the air knife 7 have.

In the foregoing, the present invention has been shown and described with reference to certain preferred embodiments. It will be apparent to those skilled in the art that various modifications and variations can be made in the present invention without departing from the spirit or scope of the inventive concept as defined by the appended claims. You can do it.

1: Input panel 2: Air knife setting value calculator
3: PLC 4: Air knife pressure regulator
5: Air knife position controller
6, 7: Air knife 8: Zinc plated bath
9: sink roll SS: steel plate

Claims (6)

A plating amount control method according to a line speed change in a hot-dip plating process,
A first step of determining whether a speed set value of a line to which a plated steel sheet is fed is changed from a current speed (V1) to a target speed (V2);
If it is determined that the set value of the line speed is changed to the target speed V2, the speed difference? V between the current speed V1 and the target speed V2 and the line speed change rate Vr input by the plating line driver, (Tr) required for the vehicle to reach the target speed V2 from the current speed V1;
A third step of comparing a target speed arrival time (tr) with a predetermined pressure response time (tp) of the air knife;
When it is determined that the target speed set value arrival time tr and the air knife pressure response time tp are similar, the target pressure P2 is calculated from the current speed V1, the target speed V2 and the current pressure P1 of the air knife A fourth step of changing the injection pressure of the air knife from the current pressure P1 to the target pressure P2 at one time;
If it is determined that the target speed arrival time tr is larger than the air knife pressure response time tp, the line speed V is measured at a predetermined cycle until the current speed V1 reaches the target speed V2, A fifth step of repeating the process of changing the target pressure P of the air knife based on the line speed V; And
If it is determined that the target speed arrival time tr is smaller than the air knife pressure response time tp, a sixth step of simultaneously changing the pressure P of the air knife and the gap S between the air knife and the steel sheet surface And the plating amount is controlled by changing the line speed in the hot-dip plating step. The method according to claim 1,
In the third step,
0.8 x tp <tr <1.2 x tp, it is determined that tr and tp are similar,
1.2 x tp < tr, tr is determined to be faster than tp, and
and when tr <0.8 x tp, tr is determined to be slower than tp. 3. The method according to claim 1 or 2,
In the fourth step, the target pressure P2,
The pressure change value AP to be changed from the current pressure P 1,
[Equation 1]

Where? P is the pressure change value, a is the coefficient of influence of the line speed on the plating amount, c is the coefficient of influence of the pressure on the plating amount, V1 is the current velocity,
, And then the target pressure P2 is obtained by
&Quot; (3) &quot;

Wherein the plating amount is determined by using a line speed change in the hot-dip plating process. 3. The method according to claim 1 or 2,
In the fifth step,
Measuring a current line speed (V) after a predetermined period of time;
The speed difference? V between the current line speed V and the reference speed Vrff,
&Quot; (4) &quot;

;
A step 53 of comparing ΔV with a predetermined reference value X;
The target pressure P2 of the air knife,
&Quot; (5) &quot;

(Where a and c are parameters of the plating amount prediction equation and P is the pressure of the current air knife);
Setting a pressure of the air knife to a target pressure P2;
Setting a current line speed (V) to a reference speed (Vrff); And
And repeating the steps when a condition of DELTA V &gt; X is satisfied. &Lt; Desc / Clms Page number 20 &gt; 3. The method according to claim 1 or 2,
In the sixth step,
(? S) of the distance between the air knife and the steel sheet surface,
&Quot; (6) &quot;

(Where? 1 is a constant and? V is a speed difference between the current speed V1 of the line and the target speed V2)
The interval (S2)
&Quot; (7) &quot;

(Where S1 is the spacing of the current air knife relative to the surface of the steel sheet);
The target pressure P2 of the air knife,
&Quot; (8) &quot;

B is the coefficient of influence of the distance between the lip of the air knife nozzle and the surface of the steel plate on the plating amount, c is the coefficient of influence of the air knife injection pressure on the plating amount, , Cw is a target plating amount, V2 is a target line speed, and S2 is a gap between the lip of the air knife nozzle and the surface of the steel sheet); And
And controlling the jetting pressure of the air knife and the distance between the lip of the air knife nozzle and the surface of the steel sheet by setting the target pressure (P2) and the gap (S2), respectively, To control the amount of plating. 6. The method of claim 5,
The step of obtaining the gap S2 with respect to the surface of the steel plate of the air knife nozzle may include setting the gap S2 to the upper limit value or the lower limit value when the obtained interval S2 is larger than the predetermined upper limit value or smaller than the lower limit value And controlling the plating amount according to the line speed change in the hot-dip plating step.

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