JP2862155B2 - How to adjust the amount of 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 a method for adjusting the amount of deposited metal on a molten metal, and more particularly to a method for injecting gas by a wiping nozzle to determine the amount of deposited metal on the surface of a strip pulled up by passing through a molten metal plating bath such as molten zinc. The present invention relates to a method for adjusting the amount of deposited molten metal plating adjusted by the method.

[0002]

2. Description of the Related Art Generally, in hot-dip galvanizing such as continuous hot-dip galvanizing, a strip is immersed and passed through a plating bath and then pulled up. This is done by removing the metal.

[0003] In the above continuous molten metal plating, it is extremely important to accurately adjust the amount of molten metal adhered to the strip so as to have a target value.

[0004] Such adjustment of the amount of coating on a continuous molten metal plating line is subdivided into many types in view of the variety of uses of the product after plating, corrosion resistance, cost, and the like. Therefore, not only when changing the type, but also when changing the target adhesion amount, the nozzle injection pressure P, the nozzle-strip interval D, the wiping nozzle height H, the wiping nozzle slit thickness B, and the strip moving speed V Needs to be changed and set appropriately and quickly.

[0005] As a method of adjusting the amount of adhesion when performing hot-dip metal plating, for example, the methods disclosed in JP-A-54-149331, JP-B-56-12316 and JP-A-1-92324 are known.

In Japanese Patent Application Laid-Open No. 54-149331, the gas pressure at the strip surface is taken as a function of the distance from the plating bath surface, and the nozzle height, the nozzle-strip interval, the gas injection pressure are set so as to satisfy the function. In Japanese Patent Publication No. 56-12316, the gas deposition pressure is expressed as a function of the nozzle spacing, height, angle, line speed, and the plating weight. In addition, JP-A-1-92324 uses a relational expression between the wiping pressure and the adhesion amount and a relational expression between the nozzle interval and the adhesion amount when performing feedback control of the plating adhesion amount immediately above the nozzle. To adjust the amount of plating.

Conventionally, as disclosed in the above publication, a feedback control method based on the wiping nozzle injection pressure P, nozzle-strip interval D, strip speed V, molten metal adhesion amount W, etc. Adhesion amount W
In general, a method of performing feedforward control based on a relational expression between a factor and an operation factor has been practiced.

In general, when the feedforward control or the feedback control is performed, the injection pressure P of the wiping nozzle or the nozzle pressure in accordance with the target adhesion amount is adjusted in order to adjust the adhesion amount of the molten metal to the continuously moving strip.
The strip interval D is determined based on the relational expression between the molten metal adhesion amount W and the operation factor. Therefore, in order to accurately adjust the amount of deposited molten metal, it is important that the above relational expression used for control can accurately and accurately represent the wiping phenomenon of the molten metal over the entire operation range.

[0009]

However, the relational expression used in the conventional method for adjusting the coating weight of hot-dip metal plating disclosed in the above-mentioned publications is an empirical expression in which the correlation between the respective factors is experimentally obtained. And the same relational expression is applied uniformly without considering the operation range.

Therefore, there is an error between the calculated value of the adhesion amount obtained from the relational expression and the actual value, and the error increases as the operation range (range in which the operation factor is changed) increases, and the actual molten metal becomes larger. The amount of products whose adhesion amount deviates from the target value (in the case of a steel sheet for an automobile, within the specified value ± 2 g / m ² ) increases.

The fact that the amount of deposited molten metal deviates from the target value due to the accuracy of the relational expression appears as a steady deviation not only in the feedforward control but also in the feedback control. However, there is a problem that it is not possible to adjust the amount of the adhered molten metal having a high density.

SUMMARY OF THE INVENTION The present invention has been made to solve the above-mentioned conventional problems. When the operating factor is changed due to factors such as product type change or strip shape, the plating adhesion amount is set to a target value according to the change condition. It is an object of the present invention to provide a molten metal plating adhesion amount adjusting method capable of setting an appropriate relational expression between an adhesion amount and an operation factor, which can be controlled, and accurately adjusting the plating adhesion amount based on the relational expression. I do.

[0013]

According to the present invention, a wiping nozzle is disposed above a molten metal bath, and gas is blown from the wiping nozzle to a strip passed through the molten metal bath to adhere the molten metal to the strip. in adhesion amount adjustment method of molten metal plating to adjust the amount, and the slit thickness B of the word <br/> Ipingunozuru, the relation between the distance D from the nozzle up to the strip, expanded in the gas jet from the wiping nozzles Regarding the constant C defining the boundary between the region and the fully developed region, it differs between (i) the case of D / B ≦ C (expanded region) and (ii) the case of D / B> C (fully developed region). The adhesion amount of the molten metal to the strip is adjusted based on the adhesion amount relational expression. (I) When D / B ≦ C, the following adhesion amount relational expression (I) not including the slit thickness B _{More, W = h 1 × ρ M} × {(K-1) / (2 × η × K × P A)} a × D b × [μ × V / {(P / P A) (K-1) ^{/ K} -1}] ^c (I) (ii) In the case of D / B> C, W = h ₂ × ρ _M × ｛according to the following adhesion amount relational expression (II) including the slit thickness B. (K-1) / (2 × η × K × P A)} a × (D / B d) × [μ × V / {(P / P A) (K-1) / K -1}] c ... (II) (wherein, W; molten metal coating weight, h _1, h _2; constants, [rho
_M : Molten metal density, K: Gas specific heat ratio, η: Nozzle efficiency, P _A : Gas pressure at nozzle outlet, P: Gas pressure acting on molten metal surface, μ: Molten metal viscosity, V: Strip speed, a , B, c, d; constants (b, d ≒ 1/2)) The above object was achieved by adjusting the amount of molten metal deposited on the strip.

[0014]

[0015] The present invention also slit thickness B and the nozzle of the wiping nozzle - by controlling at least one of the strip spacing D, while maintaining the relationship of the (i) D / B ≦ C , the adhesion amount By adjusting the amount of molten metal adhered to the strip based on the relational expression (I) , the above-mentioned object has been achieved more reliably.

[0016]

The present invention has been made based on the following detailed findings obtained by various studies by the present inventors.

The first finding is that, as a result of theoretically analyzing the wiping phenomenon of the molten metal by gas, the slit thickness B of the wiping nozzle and the nozzle-strip distance were determined due to the characteristics of the gas jet from the wiping nozzle. It is important to divide the relative relationship with D into the following two cases, and to consider the relational expression between the plating adhesion amount and the operation factor in each case separately.

(I) D / B ≦ C (ii) D / B> C

Here, C corresponds to a constant that defines a boundary between a developed region and a fully developed region in a gas jet from a wiping nozzle described later. Actually, the type of the wiping gas, the temperature of the wiping gas, the nozzle shape Is a constant that is determined experimentally.
A value of about 9 is used.

Hereinafter, the theoretical analysis will be described in detail with reference to FIGS.

As shown in FIG. 2, the strip S which is immersed and passed through a plating bath 12 made of a molten metal accommodated in a plating bath 10 and then pulled up, has a height H from the plating bath 12. At the position of wiping nozzle 14
And wiping excess molten metal by spraying the molten metal adhering to the surface of the strip S with the injection pressure P. 3, the wiping state of the molten metal at the position of the wiping nozzle 14 is a representation schematically, gas pressure P from the wiping nozzle 14 against the strip S lifted from the plating bath 12 of molten metal The flow state of the molten metal adhering to the strip S when the jet F is sprayed is represented by the following equation (1) in the coordinate system shown in FIG. , (2).

[0022]

(Equation 1)

Where μ: molten metal viscosity
[rho _M; molten metal density u; velocity distribution of the molten metal g; gravity P; gas pressure acting on the molten metal surface t; final coating weight V; strip speed x, y; molten metal in x position; coordinate δ Thickness

In the above equation (1), when y = 0, u = V, y = δ
Is solved under the boundary condition that (d'u / d'y) = 0 (d 'represents partial differentiation), and by simultaneous with the equation (2), the maximum pressure gradient of gas pressure [dP / Dx]
_When the relation at _max is obtained, the following equation (3) is obtained. For convenience, [] of [dP / dx] in equation (3) represents an absolute value (the same applies to equations (4), (8), and (9) below).

T = {(4/9) × μ × V / [dP / dx] _max ｝ ^1/2 (3)

From the above equation (3), the plating adhesion amount W can be described by the following equation (4).

[0027] _{W = ρ M × t = ρ} M × {(4/9) × μ × V / [dP / dx] max} 1/2 ... (4)

On the other hand, according to the two-dimensional free jet theory, FIG.
As shown in the figure, a development region composed of a potential core having no attenuation of the central velocity of the gas jet F and mixing regions on both sides of the potential core,
And a fully developed region, which is a fully developed turbulence. The velocity distribution in each of the above areas is expressed by the following equations (5) and (6).

(I) Expansion area (D / B ≦ C)

[0030]

(Equation 2)

(Ii) Fully developed region (D / B> C)

V = C ₀ × v ₀ × (B / D) ^1/2 × sech ² (σ ₂ × x / D) (6) where v: jet velocity v ₀ ; uniform velocity D at the nozzle outlet A distance from the nozzle in the direction of the jet center line B; a nozzle slit thickness σ ₁ , σ ₂ , C ₀ ;

The dynamic pressure of the gas is expressed by the following equation (7). Here, ρ _A is the gas density at the nozzle outlet.

P = (1/2) ρ _A · v ² (7)

When the equation (5) or the equation (6) is applied to the equation (7), the maximum pressure gradient becomes the following equation (8) or (9)
It can be expressed by an equation.

(I) Expansion area

[0037]

(Equation 3)

(Ii) Fully developed area

[0039]

(Equation 4)

The gas jet velocity v ₀ included in the above equations (8) and (9) can be obtained assuming an isentropic flow.

From the law of conservation of energy, the following equation (10) is established. In addition, when the flow speed is high and a state change occurs within a short time, the change is an adiabatic change, that is, in the case of isentropic change, The following equation (11) holds.

[0042]

(Equation 5)

P / ρ ^k = const (11) k: Specific heat ratio of gas (k = 1.4 for diatomic molecules)

From the above equations (10) and (11), the energy conservation law of the isentropic flow can be described by the following equation (12).

[0045]

(Equation 6)

In this equation (12), assuming that the flow velocity v in the nozzle is equal to 0, and using the relationship of equation (11), the following equation (1) is obtained.
3) Equation is obtained.

[0047] _{v 0 = [{2K / (} K-1)} × (P A / ρ A) × {(P / P A) (K-1) / K -1}] 1/2 ... (13)

Actually, since there is an energy loss in the nozzle and the like, the following equation (14) is used in consideration of the nozzle efficiency η.

[0049]

(Equation 7)

Next, the above equation (14) is substituted into the equation (8) or (9), and these are further substituted into the equation (4) to express the relationship between the plating adhesion amount and each control factor. Equations (15) and (16) can be derived.

[0051]

(Equation 8)

In the above equations (15) and (16), the value of the boundary point C between the development area and the fully developed area (7.4)
83) is an example, where the nozzle characteristic constant C ₀ ,
Using document values as σ ₁ and σ ₂ , equation (15) = (16)
C was obtained as an equation . The value of this C is preferably determined by determining these nozzle characteristic constants actually measure the flow velocity distribution of the gas jet.

When comparing the above equations (15) and (16), among the factors, ρ _M , μ, V, and P show the same degree of influence, but D and B have different influences. , (I
) In the development region, the adhesion amount W is proportional to D ^1/2 , and (ii)
In the fully developed region, the amount of adhesion W is proportional to D / ^B1 / ² .

Thus, the following (A) to (C) are found.

(A) In the development area, the influence of the nozzle-strip distance D is small.

(B) In the unfolded area, there is no relation to the slit thickness B of the nozzle.

(C) It is necessary to distinguish the relationship between the amount of adhesion and the control factor based on the magnitude relationship of the ratio D / B between D and B.

As described in detail above, it has been shown that the relationship between the plating adhesion amount and each of the influence factors differs depending on the relative relationship between the nozzle-strip distance D and the nozzle slit thickness B. Therefore, it is important to distinguish and consider the regions according to the value of D / B, and to apply the relational expression of the plating adhesion amount to the respective regions as in the above formula (15) or (16). .

The expressions (15) and (16) are merely examples, and the present invention is not limited to these two expressions. For example, constants and powers can be changed as appropriate.

The second finding is that, as is clear from the above equations (15) and (16), the plating adhesion amount is D / B ≦ C and D / B ≦ C.
/ B> C, the degree of influence of the operation factor differs,
When D is kept constant and D is changed, in the area of D / B> C, the wiping efficiency increases (wiping becomes easy) as D / B decreases, but in the area of D / B ≦ C, D / B ≦ C. Even if B changes, the wiping efficiency hardly changes. This state is shown in FIG. It is generally known that wiping efficiency increases as D decreases.

At the same time, it has been experimentally found that as the flow rate of the wiping gas is reduced, the splash (splash of molten metal) generated from the surface of the plating bath can be reduced. That is, when other conditions are the same, the occurrence of splash can be reduced by reducing the slit thickness B.

A third finding is that, in addition to the theoretical analysis described above, as a result of further experimental studies, the physical properties of the molten metal affecting the wiping characteristics are evaluated as a function of the temperature of the molten metal at the position of the nozzle to be wiped. Is important.

That is, FIG. 6 shows the relationship between the plating metal (molten metal) temperature at the position of the wiping nozzle and the plating adhesion error (actual adhesion-calculated adhesion when the dependence of the plating metal temperature is not taken into consideration). It shows the relationship,
As is apparent from FIG. 6, the wiping characteristics decrease with the decrease in the plating metal temperature. However, when considering the dependence of the plating temperature on the position of the wiping nozzle, the error was found to be very small.

Hereinafter, as an example, a method for calculating the plating metal temperature at the position of the wiping nozzle and a method for considering the physical properties of the plating metal will be described with reference to FIG.

[0065] As shown in FIG. 2, is immersed in a plating bath 12 of the temperature T _M strip S of the temperature T _z.0 is at line speed V, becomes the temperature T _Z.1 close to the plating bath temperature T _M It is pulled up from the plating bath 12. The strip temperature T _z.1 exiting the plating bath 12 is given by the following equation (17) based on the heat transfer to the flat plate in the molten metal.

T _Z.1 = T _M + (T _z.0 −T _M ) × exp {− (2 × α _M × l _M ) / (ρ _S × C _ps × t _S × V)} (17) Here, α _M ; Heat transfer coefficient between plating bath and strip l _M ; Immersion distance in plating bath ρ _S ; Strip density C _ps ; Strip specific heat t _S ; Strip thickness

The strip S _having the temperature T _z.1 is cooled by the wiping gas to _{reach the} temperature T _z.2 of the deposited metal at the position of the wiping nozzle 14. This temperature T _z.2 can be expressed by the following equation (18).

[0068] _{T z.2 = T g + (T} z.1 -T g) × exp {(- 2 × α × H) / (ρ s × C ps × t s' × V)} ... (18) here, T _g; terms of strip thickness and the strip heat capacity reference; distance t _s' from the plating bath surface to the nozzle; heat transfer coefficient by wiping gas (a function of nozzle pressure) H; wiping gas temperature α ejected from the nozzle Sum of the deposited metal thickness

Next, the temperature dependency of the viscosity μ of the deposited metal is set by, for example, the following equation (19) using the deposited metal temperature obtained by the above equation (18).

[0070]

(Equation 9)

By applying the viscosity μ of the deposited metal obtained from the above equation (19) to the above equation (15) or (16), it is possible to adjust the plating adhesion amount with higher accuracy.

In the derivation of the above equation (18), it is _assumed that the temperature of the deposited metal immediately after being _pulled up from the plating bath 12 is equal to the strip temperature T _z.1 . Under general operating conditions,
Since the two temperatures are substantially equal, there is no particular problem. However, the temperature may be formulated as being different from the strip temperature and the deposited metal temperature.

As described in detail above, based on the first finding, the relation between the nozzle-strip distance D and the slit thickness B of the nozzle can be used to distinguish and use the relation formula (control formula). It is possible to improve the prediction accuracy of the relational expression between the amount of plating and the operation factor.

Therefore, in the so-called development region, the above equation (15), which is not related to the nozzle thickness B, is used. In the so-called fully developed region, the nozzle-strip distance D is used.
And (16) including both the nozzle thickness and the nozzle slit thickness B.
By controlling at least one of the nozzle-strip interval D and the nozzle slit interval B, the nozzle pressure P, the nozzle height H, the strip speed V, and the like using the equations, the target plating can be performed over a wide operation range. It becomes possible to perform hot-dip metal plating with the attached amount.

According to the second finding, in order to increase the wiping efficiency, it is preferable to perform wiping in the region of D / B ≦ C, and the wiping gas flow rate is proportional to the slit thickness B of the nozzle. Therefore, as the slit thickness B decreases, the flow rate of the wiping gas can be reduced, and the economical advantage is high.

Furthermore, when the slit thickness B is reduced, splash generated from the plating bath surface can be reduced.

Accordingly, it is necessary to reduce the slit thickness B as much as possible while controlling at least one of D and B within a range satisfying D / B ≦ C, without reducing the wiping efficiency and without reducing the wiping gas flow rate. It is possible to reduce the number of splashes.

When the constant C was determined by experiment, a value having a range of 6.6 to 8.1 including the measurement accuracy was obtained. Therefore, in the case where the amount of plating is adjusted using the above equation (15) in the development area, the C value obtained from the experiment is determined.
Is preferably adjusted to the range of the following equation (20) with reference to the average value Ca.

Ca −1 ≦ D / B ≦ Ca +1 (20)

When controlling the slit thickness B to a desired value, a nozzle disclosed in, for example, JP-A-63-238254 can be used.

Incidentally, Japanese Patent Publication No. 49-37898 discloses a method of experimentally determining the correlation between the adhesion amount W and the slit thickness B and limiting the slit thickness B to a certain range. No adjustment of the amount of plating is performed based on the relative relationship between the slit interval D and the slit thickness B.

According to the third finding, when the plating amount is adjusted according to the above equation (15) or (16), the temperature dependence of the viscosity of the molten metal included in each equation is determined. Therefore, it is possible to adjust the plating amount with higher precision.

[0083]

Embodiments of the present invention will be described below in detail with reference to the drawings.

FIG. 7 is a block diagram schematically showing a molten metal plating control apparatus applied to the first embodiment according to the present invention.

After the strip S is immersed in and passed through the plating bath 12 accommodated in the plating bath 10, the controller S is pulled up and further moved. On both sides of the strip S pulled up from the plating bath 12, a gas having a predetermined pressure is blown from the wiping nozzle 14 to both sides thereof. The direction of the strip S immersed in the plating bath 12 can be changed by the sink roll 16.

The wiping nozzle 14 is provided with an adjuster 18
, The nozzle interval D and the nozzle slit thickness B can be adjusted, and the height H can be adjusted by the adjuster 20.

A width direction film thickness meter 22 is provided in front of the strip S in the traveling direction, and a detection signal from the film thickness meter 22 is supplied to a feedback characteristic compensator 24, a feedback controller 26, and an operation amount selector. The signal is input to the adjuster 18 via the control signal.

The moving length and moving speed of the strip S are respectively determined by the pulse oscillator 30 and the speed converter 3 provided on the major roll rotating in contact with the strip S.
2, the feedback characteristic compensator 2
4 and the feedforward control device 34.
The feedforward control device 34 receives signals from the manufacturing condition setting device 36 and the preset control device 38, respectively, and adjusts the pressure control valve 42 to a predetermined opening degree via the pressure regulator 40. It has become. The pressure of the gas ejected from the wiping nozzle can be adjusted by the pressure adjusting valve 42.

A signal from the manufacturing condition setting device 36 is input to the adjuster 18 via a preset control device 38. Further, the manipulated variable selector 2
8 is input to the height adjuster 20.

Next, a typical control example according to this embodiment will be briefly described.

In the case of feedforward control, when operating conditions such as the coating weight W, line speed V, and steel type change, the above equation (15) or (16) is used in accordance with the coating weight W and line speed V. A nozzle-strip interval D, a slit thickness B, and a nozzle injection pressure P as set values are determined using the equations. At that time, the nozzle-strip interval D is
In order to prevent the strip from coming into contact with the nozzles, the injection pressure P is set not to be lower than the upper limit, and the nozzle height H is normally set to the reference value.

When the set values are determined, the nozzle-strip interval D, the slit thickness B, and the injection pressure P are adjusted by the controller 1
8. The pressure is adjusted by the pressure adjuster 40 so that the set value is obtained. When it is necessary to adjust the nozzle height H, the nozzle height H is adjusted by the adjuster 20.

In the case of feedback control, the film thickness meter 22
In the case where there is a difference between the indicated value of the adhesion amount and the target value in the measurement result obtained by the above or when the line speed changes in the middle, the deviation amount of the adhesion amount or the line speed change amount is calculated based on the expression (15) or (16). Accordingly, at least one change amount of the nozzle-strip interval D, the slit thickness B, and the injection pressure P is calculated, and adjustment corresponding to the change amount is performed by the adjuster 18 and the pressure adjuster 40. Also in this case, the nozzle height H is basically set to a reference value.

Using the above controller, the amount of zinc (Zn) plating was controlled by applying the above equations (15) and (16), and the results shown in FIG. 1 were obtained.

FIG. 1A shows the above equation (15) and (16)
The equation shows the result of controlling the amount of plating applied in consideration of the temperature of the deposited metal at the wiping position. The operating conditions at this time are shown in Table 1 below.

FIG. 1B shows the result of the conventional method in which the same control unit is used to control the amount of plating by using the relational expression of the amount of deposition prepared as a regression equation of the operating factor.

FIG. 1 shows that in the conventional method, the amount of adhesion fluctuates depending on the strip speed, the target amount of adhesion, and the timing of the change in the strip shape, and that the deviation varies even in a steady state where the conditions do not change depending on the operating conditions. Can be seen. On the other hand, according to the method of the present invention, it is possible to control the amount to substantially the target amount without changing various conditions.

[0098]

[Table 1]

Next, a second embodiment will be described.

In this embodiment, the amount of plating is adjusted by controlling at least one of D and B within a development area, that is, a range satisfying D / B ≦ C.

Table 3 shows the results of hot-dip galvanizing using the same control device as in the first embodiment under the operating conditions shown in Table 2 below.

[0102]

[Table 2]

[0103]

[Table 3]

Table 3 shows the average value, but the wiping gas flow rate (consumption amount) is different from the conventional case.
The nozzle pressure could be increased within a range that did not hinder the operation (in the table, the wiping gas flow rate 1.0 was 5,500 N).
m ³ / hr, and the limiting nozzle pressure 1.0 corresponds to 0.65 Kg G, and the amount of generated splash is visually observed).

As described above, since the nozzle pressure can be increased, the control range of the amount of adhesion can be expanded, and plating with a small thickness can be performed even at a high line speed.

Although the present invention has been specifically described above, the present invention is not limited to the above-described embodiment, and can be variously modified without departing from the gist thereof.

[0107] For example, the relational expression for controlling the coating weight (controlled) (I) and (II), wherein (15) and (16) instead shall be limited respectively to formulas, the formula ( The values of the exponents a, b, c, d of I) and (II) may be values other than 1/2 according to the actual phenomenon.

Further, the molten metal plating control device actually used is not limited to the one shown in the above embodiment, and the type of plating is not limited to zinc plating.

[0109]

As described above, according to the present invention,
Nozzle - the relationship to determine the coating weight based on the relative relationship between the strip distance D and the slit thickness of the nozzle B (I), setting the (II), by using the relational expression, strike
Adjusted the amount of molten metal attached to the lip
Therefore , even when the operation factor is changed due to the change of the product type, the shape of the strip, or the like, the plating adhesion amount can be controlled to the target value.

Further, by applying the above-mentioned relational expression for determining the amount of deposition while maintaining the value of D / B in the development region, it becomes possible to adjust the amount of plating under high wiping efficiency conditions. In addition, the wiping gas flow rate and splash generation amount can be reduced over a wide operation range, and the limit nozzle pressure can be increased, so that the production can be increased.

[Brief description of the drawings]

FIG. 1 is a diagram showing the effect of one embodiment according to the present invention.

FIG. 2 is a schematic explanatory view showing a hot metal plating method.

FIG. 3 is a schematic diagram showing a state of wiping of a molten metal adhered to a strip.

FIG. 4 is a schematic explanatory view showing a state of a gas jet injected from a wiping nozzle.

FIG. 5 is a diagram showing a relationship between a wiping efficiency (ratio of an attached amount) in a development area and a slit thickness of a nozzle.

FIG. 6 is a diagram illustrating a relationship between a plating metal temperature and a plating adhesion amount error at a wiping nozzle position.

FIG. 7 is a block diagram showing a molten metal plating control device applicable to the embodiment according to the present invention.

[Explanation of symbols]

 10: plating bath, 12: plating bath, 14: wiping nozzle, B: slit thickness, D: nozzle-strip interval, S: strip.

 ──────────────────────────────────────────────────続 き Continuation of the front page (56) References JP-A-3-173757 (JP, A) JP-A-54-149331 (JP, A) Fully open 63-149957 (JP, U) Really open 1960- 25745 (JP, U)

Claims (2)

(57) [Claims] A wiping nozzle is disposed above a molten metal bath, and gas is blown from the wiping nozzle to a strip passed through the molten metal bath to adjust the amount of molten metal deposited on the strip. in adhesion amount adjustment method, a slit thickness B of the wiping nozzle, the relationship between the distance D from the nozzle until strip, with respect to a constant C that defines the boundary between the deployment region and the full development region in the gas jet from the wiping nozzles , (I) when D / B ≦ C (development area) and (ii) when D / B> C (fully developed area), the adhesion of the molten metal to the strip based on different adhesion relations. thereby adjusting the amount, (i) in the case of D / B ≦ C, the slit does not include the thickness B following deposition amount relational expression _{(I), W = h 1} × ρ M × {(K 1) / (2 × η × K × P A)} a × D b × [μ × V / {(P / P A) (K-1) / K -1}] c ... (I) (ii) When D / B> C, W = h ₂ × ρ _M × (K-1) / (2 × η × K × P ^{_{A)} a × (D /}} B d) × [μ × V / {(P / P A) (K-1) / K -1}] c ... (II) ( wherein, W; molten metal coating weight , H ₁ , h ₂ ; constant, ρ
_M : Molten metal density, K: Gas specific heat ratio, η: Nozzle efficiency, P _A : Gas pressure at nozzle outlet, P: Gas pressure acting on molten metal surface, μ: Molten metal viscosity, V: Strip speed, a , B, c, d; constants (b, d ≒ 1/2)) each of which adjusts the amount of molten metal deposited on the strip. 2. The method of claim 1, slit thickness B and the nozzle of the wiping nozzle - by controlling at least one of the strip interval D, the
(I) A method for adjusting the adhesion amount of molten metal plating, wherein the adhesion amount of molten metal to a strip is adjusted based on the adhesion amount relational expression (I) while maintaining the relationship of D / B ≦ C.