JPH04232236A - Method for controlling component of plating bath at the time of changing composition - Google Patents

Abstract

PURPOSE:To rapidly change a plating bath to other plating bath in spite of the considerably different compsns. CONSTITUTION:Plural sub-pots 22, 32 separately contg. plating baths having different compsns. are used. At the time of plating, the plating bath in one of the sub-pots 22, 32 is injected into a main pot 20. At the time of changing the compsn., the plating bath in the main pot 20 is drawn out and returned to one of the sub-pots 22, 32 and then the plating bath in the other is injected into the main pot 20.

Description

[Detailed description of the invention]

0001

[Field of Industrial Application] The present invention relates to a method for controlling the composition of a plating bath when changing the composition when performing hot-dip plating with plating baths having different compositions, and in particular, a method for controlling the composition of a plating bath suitable for use in continuous hot-dip metal plating. The present invention relates to a plating bath component control method that allows rapid switching of plating bath components.

0002

[Prior Art] Continuous hot-dip plating involves immersing a continuously running steel strip in a bath of molten plated metal for a predetermined period of time, and then gas-wiping the surface of the steel strip removed from the bath to achieve a predetermined plating. It is a plating method that applies desired plating to the surface of a steel strip by adjusting the amount of plating applied, and hot-dip galvanizing is a typical example.

[0003] Galvanized steel sheets originally have excellent corrosion resistance, so they are widely used as building materials, home appliances, and steel sheets for automobiles. However, hot-dip galvanizing currently has inferior surface quality compared to electrogalvanizing. However, because it consumes less energy, the cost of molten metal for plating is low, and it can be easily coated thickly, it is attracting attention for the mass production of galvanized steel sheets.

By the way, in continuous hot-dip galvanizing, in addition to using a pure zinc bath, a hard and brittle Fe-Zn alloy layer (Γ layer: Fe 3 Zn
In order to suppress the growth of 11) and improve plating adhesion, Al 2 may be added to the zinc bath. That is, an Al enriched layer (Fe 3 A) is formed at the interface between the plating layer and the base steel.
By forming a Fe-Zn alloy layer at the interface between zinc and base steel, the formation of a Fe-Zn alloy layer at the interface between zinc and base steel is appropriately suppressed, and peeling (powdering) of the plating layer is prevented.

In addition to the above addition of Al, a small amount of Pb is also added to form spangles (flower pattern) on the plating surface.
The addition rate of these Al and Pb varies depending on the use of the galvanized steel sheet.

[0006] The target concentration for each typical product type is approximately as shown in FIG.

[0007] Here, the units of concentration are all % by weight, and the remainder of the components shown in FIG. 1 is Zn. Further, the effective Al concentration is defined as the Al concentration minus the Fe concentration. This is Fe melted from the slip.
This is because they create impurities and interfere with Al.

Among the component types shown in FIG. 1, the GI duct is a so-called high Pb material, and the GI, 1&1/2, and GA are
This is a so-called low Pb material.

In continuous zinc hot-dip plating using plating solutions having various compositions, it is necessary to change the concentration of the plating solution and adjust it within the range shown in FIG. 1 when changing the product type. Also, line conditions (coating amount, line speed,
The reduction amount of plating solution changes depending on the plate width, etc.), the change in Al concentration, and the change in Pb concentration.
It is necessary to replenish supplies. The reasons why the plating solution decreases include removal by the plating layer adhering to the surface of the steel strip, the formation of floating dross, and its removal from the plating bath.

As a method for replenishing components to a plating bath, the applicant has already disclosed in Japanese Patent Application Laid-Open No. 1-165753 a method of using a plurality of pre-melt pots in which replenishing components are melted in advance, or at least one pre-melt pot and replenishing components. using at least one hopper containing metal ingots or metal powder particles, and replenishing the components from the pre-melt pot, or the pre-melt pot and hopper, to correspond to the required replenishment concentration and the reduction in the plating bath. We are proposing a unique method of replenishing ingredients to plating baths.

[0011] Furthermore, in JP-A-63-169369, a part of the hot-dip galvanizing bath is taken out and introduced into a separate bath to remove A.
Al in a hot-dip galvanizing bath characterized by adding a l agent to adjust the amount of Al, then introducing a galvanizing bath, and continuing until the amount of Al in the galvanizing bath reaches a predetermined amount. A method of adjustment is disclosed.

0012

[Problem to be solved by the invention] According to the former method,
Although it is possible to cope well with concentration adjustment and reduction of the plating bath when plating the same product, it may not necessarily be suitable if the Al concentration or Pb concentration of the plating bath needs to be significantly changed due to the change of product. The problem was that there was.

On the other hand, in the latter case, there is only one separate bath that receives the removed plating solution, and the Al concentration is adjusted in the separate bath using a de-aluminum agent, etc., so the concentration of the plating bath can be significantly increased. When a change is desired, it still takes time and is not efficient.

The present invention has been made to solve the above-mentioned conventional problems, and it is an object of the present invention to provide a method for controlling the components of a plating bath that can quickly control the components of the plating bath when changing the composition.

[0015]

[Means for Solving the Problems] The present invention provides a method for controlling the composition of a plating bath when switching the composition when performing hot-dip plating using plating baths with different compositions. At least two sub-pots containing plating solutions of different compositions are used, and during plating, the plating solution is poured into the main pot from one of the sub-pots, and when the composition is switched, the plating solution is pumped out from the main pot. The above objective is achieved by pouring the plating solution from the other subpots into the main pot after returning the plating solution to the subpot.

[0016] Furthermore, a pre-melt pot in which adjusting or replenishing components are melted in advance is also used, and the components are supplied from the pre-melt pot to the main pot in order to correspond to the required concentration and reduction amount of the plating solution. It is something.

[0017] Furthermore, an adjustment or replenishment component ingot charging means is also used to charge ingots into the main pot or pre-melt pot in order to correspond to the required concentration and reduction amount of the plating solution.

[0018]

[Operation] In the present invention, at least two sub-pots are used in addition to the main pot. These sub-pots contain plating solutions having different compositions. For plating, plating solution is poured into the main pot from one of the sub-pots. On the other hand, when switching the composition, the plating solution is pumped out from the main pot and returned to the subpot, and then the plating solution is poured into the main pot from another subpot to perform plating. Therefore, since the plating solution in the main pot can be replaced quickly, the composition can be changed quickly.

[0019] Furthermore, a pre-melt pot in which adjusting or replenishing components are melted in advance is used, and the components are supplied from the pre-melt pot to the main pot in order to correspond to the required concentration and the amount of decrease in the plating solution. In this case, the patent application
Similar to -165753, it can accurately respond to decreases in plating solution and component variations during plating of the same product. Furthermore, even when switching products, if the change in the composition of the plating solution is small, it may be possible to quickly respond by supplying components from a pre-melt pot.

[0020]Furthermore, when an adjustment or replenishment component ingot input means is used in combination, and ingots are loaded into the main pot or pre-melt pot in order to correspond to the required concentration and reduction amount of the plating solution, It can accommodate large fluctuations in the plating solution components in the main pot or pre-melt pot. Incidentally, fluctuations in the components caused by charging the ingot can be adjusted by, for example, supplying the components from a pre-melt pot.

[0021]

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

FIG. 2 is a diagram schematically showing an example of the configuration of equipment for carrying out the present invention.

In FIG. 2, the annealed strip (for example, steel strip) 10 coming out of the snout 12 is transferred to the sink roll 1.
The molten metal for plating is immersed in the molten metal for plating (for example, molten zinc) 21 of the main pot 20 by 4, then forced to curve by the collecting roll 16, and stabilized by stopping rocking by the stabilizing roll 18. After being pulled up from 21, it is adjusted to a predetermined plating area weight by gas wiping (not shown).

In this manner, strip 10 is continuously coated with hot-dip metal.

When performing hot-dip galvanizing, as mentioned above, Al is added to the plating bath to improve plating adhesion, or a small amount of Pb is added to form spangles on the plating surface. will be held. Therefore, the composition of the molten metal 21 for plating is Al-Zn
system or Al-Pb-Zn system, etc., and Al or P
The addition rate of b is also appropriately determined depending on the use and type (see FIG. 1) of the galvanized steel sheet to be manufactured.

In such continuous hot-dip galvanizing, the decrease in plating solution, Al concentration fluctuation, and Pb concentration fluctuation, which vary depending on line conditions such as coating amount, line speed, and sheet width, are estimated, and Zn, Al, Pb It is necessary to replenish supplies. In addition, the Al concentration and Pb of the plating solution due to product switching
It is necessary to switch the concentration.

Therefore, in this equipment, in addition to the main pot 20, there is also a high Pb sub-pot 22 in which, for example, a high Pb plating solution for GI duct is stored, and the high Pb
A pump 24 and a conduit 26 for pouring the high Pb plating solution from the sub pot 22 to the main pot 20, and a pump 28 and a conduit 30 for pumping the high Pb plating solution from the main pot 20 and returning it to the high Pb sub pot 22. and low Pb for GI, 1&1/2, GA, etc.
A low Pb sub-pot 32 in which a plating solution is stored, and a low Pb sub-pot 32 that contains a plating solution, and a low Pb sub-pot 32 that contains a plating solution.
a pump 34 and a conduit 36 for pouring plating solution;
A pump 38 and a conduit 40 are provided for pumping out the low Pb plating solution from the main pot 20 and returning it to the low Pb subpot 32.

Therefore, for example, when performing plating with a low Pb plating solution, the low Pb plating solution is poured from the low Pb sub-pot 32 into the main pot 20, and plating is performed. At this time, the low Pb sub-pot 32 becomes empty.

On the other hand, change the plating solution from low Pb to high Pb.
If you want to switch to the low Pb plating solution, pump out the low Pb plating solution from the main pot 20 and replace it with the empty low Pb plating solution.
After returning to the sub-pot 32, a high-Pb plating solution is poured from the high-Pb sub-pot 22 into the main pot 20 to perform plating.

The same applies to switching from a high Pb plating solution to a low Pb plating solution.

In this way, the sub-pot containing the plating solution poured into the main pot 20 is always kept empty, and when changing the plating solution, the plating solution is returned to the sub-pot, thereby making it possible to change the composition of the plating solution when changing the product. It can be done quickly.

On the other hand, in such continuous hot-dip galvanizing, the plating layer adhering to the surface of the strip 10 generates carry-over and floating dross, and by removing this from the plating bath, the molten metal 21 for plating is removed. Fluid level drops. Therefore, it is necessary to replenish so as to keep the liquid level constant and to keep the composition of the molten metal 21 for plating constant at the target value.

Here, the floating dross is caused by Fe eluted from the strip 10 and Al in the molten metal 21 for plating.
Combines with Fe 2 Al 5, which floats to the surface of the plating bath (its specific gravity is smaller than the molten metal 21 for plating)
or the zinc on the bath surface is oxidized.

Note that the decrease in the molten metal 21 for plating is due to the amount of each component (Zn, Al, Pb, etc.) of the molten metal 21 for plating.
) does not decrease in proportion to its content (concentration). That is, regarding the reduction of Al, since an Al enriched layer (Fe 2 Al 3 etc.) is formed at the interface between the base steel and the plating layer, the Al concentration in the take-out is lower than the Al concentration in the molten metal 21 for plating. Also, the composition of the floating dross removed from the plating bath is Al concentration 0.
．． In 1-0.2% molten metal for plating, Al =
Since Fe is 2 to 4% and the balance is Zn, the Al concentration in the molten metal for plating decreases more significantly than other components.

Therefore, the components are not replenished into the plating bath at a concentration equal to the composition of the molten metal 21 for plating, but by replenishing the components in such an amount that the liquid level reaches the target value.
The composition of the molten metal 21 for plating must also be set to a target value.

Therefore, in this equipment, Al-Z containing, for example, 1.8% Al, which is a replenishing component of the plating solution, is added.
A high Al pre-melt pot 42 in which an ingot of n alloy is melted in advance, a pump 44 for pouring, for example, 1.8% molten Al from the high Al pre-melt pot 42 into the main pot 20, a conduit 46, and Ladle (
ladle) 48 and the high Al pre-melt pot 42,
For example, an Al ingot feeder 50 for feeding an ingot of 1.8% Al-Zn alloy, a Zn pre-melt pot 52 in which a pure Zn ingot, which is a replenishing component of the plating solution, is melted in advance, and A pump 54, a conduit 56, and a ladle 58 for pouring, for example, pure Zn from the melt pot 52 to the main pot 20;
Zn ingot feeder 60 for feeding ingots, a pre-melt pot 62 for pumping out a part of the plating solution in the main pot 20 during component adjustment and pouring it as necessary, and a main pot. A pump 64 and a conduit 66 for pumping out a portion of the plating solution from the pumping pre-melt pot 62 to the main pot 20, and a ladle 68 for returning the plating solution from the pumping pre-melt pot 62 to the main pot 20. We are prepared.

Therefore, Al and Zn can be replenished by a method similar to that disclosed in JP-A-1-165753, for example.

Here, the ladle is used for fine adjustment, and the pump is used for coarse adjustment.

[0039] If the amount of concentration fluctuation in the main pot 20 that needs to be adjusted is large, it may not be possible to fully adjust it by simply replenishing from the pre-melt pot 42 or 52. Therefore, in the present invention, the main pot 20 A Zn ingot charging machine 70 and a Pb charging hopper 72 are provided for automatically and directly charging Zn ingots and small Pb ingots into the pot 20, respectively.
l Small ingot 74 and Pb small ingot 76 can be directly fed manually.

[0040] The main pot 20 and pre-melt pots 42 and 52 are each equipped with a level meter and a thermometer.

The operation of the embodiment will be explained in detail below.

(1) Product type switching At the time of product type switching, normal replenishment when manufacturing the same type, which will be explained later, is stopped.

■When the Al concentration decreases: First, the liquid in the main pot 20 is pumped out from the pumping pre-load until the level of the bath surface in the main pot 20 decreases from the current bath level by a predetermined amount Δh determined according to the change in Al concentration. Pump into melt pot 62.

Next, the Zn pre-melt pot 52 is replenished into the main pot 20 until the bath surface level of the main pot 20 returns to the level before pumping out.

Next, density correction is performed by a method that will be explained in detail later in section (2).

■When the Al concentration increases, first the high Al pre-melt pot 42 to the main pot 2
0, the bath level of the main pot 20 is lower than the current bath level by a predetermined amount Δh determined according to the change in Al concentration.
Pour the water until it rises.

Next, density correction is performed by a method that will be explained in detail in section (2) later.

■When switching the Pb concentration, first transfer the entire amount of liquid from the main pot 20 to the sub pot (GI
High PBb for ducts, low Pb for other cases
(for use).

[0049] The entire amount of liquid is poured into the main pot 20 from the remaining sub-pots.

[0050] If the main pot level becomes lower than the reference level by replacing the entire amount of plating solution, raise the level by one of the following methods.

That is, if it is not necessary to change the type (aluminum concentration change) after replacing the entire volume (main pot type = next manufactured type), the decrease in the bath level can be compensated for by changing the bath level to the Zn ingot feeding machine 7.
Automatic feeding of pure Zn 1 ton ingot by 0, or 10% Al 20 kg small ingot 74, pure Pb
Replenishment is performed by manually introducing a 5 kg small ingot 76.

At this time, the number n1 of pure Zn 1 ton ingots to be introduced is determined from the following inequality.

[0053]

[Math 1]

[0054] Here, the code Bp is the main pot 20
The liquid level [mm] is the liquid level [mm], and A is the amount of rise in the bath level [mm] for 1 ton of Zn.

[0055] According to the input number n1 determined in this way, n1 pure Zn 1 ton ingots, 10
%Al 20kg small ingot (3/4) n1 piece (rounded down to the nearest whole number), pure Pb 5kg small ingot n1/5
pieces (rounded down to the nearest decimal place, not included if it is not a GI duct)
,throw into. Note that if n1 is less than or equal to zero, no replenishment is performed.

On the other hand, if it is necessary to change the type after refilling the entire volume (main pot type ≠ next production type), the Al
When the concentration decreases, perform the same operation as ①. Also, when the Al concentration increases, perform the same operation as ①. Note that if the main pot level becomes lower than the reference liquid level after the concentration switching is completed, the same operation as in the case where the type switching is unnecessary is performed to introduce the ingot.

Next, density correction is performed by the method described in detail in the next section (2).

(2) Concentration Correction The Al and Pb concentrations in the main pot 20 are measured, and if they deviate from the target concentration, the concentration is corrected.

Regarding the Al concentration correction, the effective Al concentration Peal of the main pot 20 measured by the operator
From [%], the number n2 of 10% Al 20 kg small ingots 74 is calculated. Note that when the measured concentration Peal is higher than the target effective Al concentration Poal [%],
No correction is made. When it is low, replenish the amount of Al that is insufficient. The number of supplies n2 is determined by the following formula. Note that numbers below the decimal point are rounded down.

[0060]

[Math 2]

[0061] Here, Q is the capacity of the main pot 20 [
kg].

Regarding the Pb concentration correction, the number n3 of pure Pb 5 kg small ingots 76 to be introduced is calculated from the Pb concentration Ppb [%] of the main pot 20 measured by the operator. The measured concentration Ppb is the target Pb concentration Ppb*[
%], no correction is performed. When the amount is low, the following formula is used to replenish the amount of Pb that is insufficient, n3. Note that numbers below the decimal point are rounded down.

[0063]

[Math 3]

(2) During line operation during production of the same type of product, the plating solution is carried out due to various factors in addition to adhesion to the surface of the strip 10. Therefore, as shown in FIG. 3, the amount taken out and the resulting decrease in Al 2 and Pb are estimated, and the decreased amount is replenished.

Factors causing plating solution to be taken out other than adhesion to the strip surface are as follows.

・Discharged as zinc oxide after passing through a zinc recovery machine ・Discharged together with top dross ・Discharged as a sample for component measurement ・Discharged due to evaporation ・Discharged due to other reasons

■ Estimation of amount of decrease in Al and Pb in plating solution Amount of decrease in the entire plating solution attached to the strip and taken out ΔQ1 [kg], Similarly, amount of decrease in Al ΔAl1 [kg]
Similarly, the amount of decrease ΔPb1 [kg] in Pb is estimated using the following equations (step 100 in FIG. 3).

[0068]

[Math 4]

Here, Mp is the amount of adhesion on both sides of the strip (sum of the amount of adhesion on the front and back sides) [g/m 2 ], Mo
is the amount of plating on the front side [g/m 2 ], Mu is the amount of plating on the back side [g/m 2 ], W is the width of the strip [mm], and LSp is the line speed [mpm].
], Pgalo is the Al concentration [%] in the front plating layer,
Pgalu is the Al concentration [%] in the back side plating layer, Pp
b is the estimated Pb concentration [%] in the plating bath.

[0070] Furthermore, at the interface of the plating layer of the strip, A
Since the l enriched layer is formed, the Al concentration Pgal in the plating layer is higher than the Al concentration Pal of the plating solution. On the other hand, the Pb concentration in the plating layer is equal to the Pb concentration Ppb in the plating bath.

Mp in these estimation formulas is the actual value of the adhesion amount, but if the adhesion amount meter or alloying degree meter is out of order, the set value can be used.

[0072] Al in the plating bath combines with Fe eluted from the strip to form Fe called floating dross.
2 It becomes dross whose main component is Al 5 . F in the bath
e Assuming that the concentration is saturated and that all Fe dissolved from the strip becomes floating dross, Fe
The elution amount Ffe is expressed by the following formula.

[0073]

[Math 5]

[0074] Here, Ppfe is the F of the main pot.
e Concentration actual value [%], Tm is the plate temperature entering the main pot [°C], Tz is the main pot plating bath temperature [°C], and K is a constant.

By integrating the Fe elution amount ΔFfe calculated using this equation (7), the amount of A due to dross is
The amount of decrease ΔAl2 is estimated by the following equation (step 110 in FIG. 3).

[0076]

[Math 6]

Estimated Al concentration in the plating bath Pal [%
] and the estimated Pb concentration value Ppb [%] are estimated by the following equation.

[0078]

[Math 7]

Here, Ppal is the main pot A
l Concentration actual value [%], Phal is the Al concentration of the high-Al pre-melt pot [%], Pkal is the Al concentration of the pre-melt pot for pumping [%], ΔQal is the high-Al pre-melt pot after the previous sampling ΔQk is the amount of replenishment from the pot [kg], ΔQk is the amount of replenishment from the pre-melt pot for pumping out [kg], ΔAl is the total decrease in Al [kg], and Ial is the amount of 1 after the immediately preceding sampling.
The number of 0% Al 20 kg small ingots input, ΔQ is the amount of plating solution decrease [kg], ΔQzn is the amount of replenishment from the Zn pre-melt pot after the last sampling [kg],
Izn is the number of pure Zn 1 ton ingots added to the main pot after the last sampling, Pppb is
The actual Pb concentration value [%] in the main pot, Ipb is the number of pure Pb 5 kg ingots introduced after the previous sampling, and ΔPb is the Pb reduction amount [kg].

As already explained, Al in the plating layer
The concentration Pgal is higher than the Al concentration Pal in the plating bath. FIG. 4 shows an example of the relationship between the amount of plating deposited and the Al concentration Pgal in the plating layer. A in the plating layer
l concentration Pgal is the Al concentration Pal in the plating solution
However, the Al concentration in the plating bath is fixed for each type of plating. As shown in Figure 4,
The relationship between the amount of plating deposited and the Al concentration Pgal in the plating layer is stored in a control device (not shown) as a polygonal line table, for example, and taken out and used at any time.

[0081] In addition, when the adhesion meter is out of order or the adhesion amount set value is 0g/m2, a table is created and stored in, for example, five levels according to the line speed based on the actual operating values. be able to.

The reduction amount ΔQ [kg] of the plating solution is estimated using the following equation (step 120 in FIG. 3).

[0083]

[Math. 8]

[0084] Here, L is a learning parameter, which can be updated based on actual values such as the main pot level, adhesion amount, replenishment amount, etc. In other words, in addition to adhesion to the strip, factors such as those already mentioned may be responsible for the decrease in plating solution, but since it is difficult to quantitatively calculate these factors, it is expressed as a ratio to the amount of plating deposited. and absorb it.

On the other hand, the total decrease in Al ΔAl [kg]
is estimated by the following equation (step 130 in FIG. 3).

[0086]

[Math. 9]

[0087] Here, Lal is a learning parameter,
Calculate and update based on actual values such as Al concentration, replenishment amount, adhesion amount, etc. l1 and l2 are coefficients that can be updated manually and can initially be set to l1=l2=1.0.

The decrease in Al may be caused by other factors besides adhesion to the strip and discharge as dross, but since it is difficult to quantitatively calculate these factors, the amount of Al adhering to the strip and the dross Estimate using quantity.

From the plating solution decrease amount ΔQ and the total Al decrease amount ΔAl determined by the above equations (11) and (12), the Al concentration to be replenished P*[%] and the replenishment amount Q*[k
g/sec] is expressed as in the following equation.

[0090]

[Math. 10]

[0091] Furthermore, the amount of decrease in Pb ΔPbn [kg] is
It is estimated as shown in the following equation (step 140 in FIG. 3).

[0092]

[Math. 11]

Here, the learning parameter L is the same as L in equation (11). That is, since the amount of decrease in Pb is approximately proportional to the amount of decrease in plating solution, the same learning parameter L for the amount of decrease in plating solution can be used.

■Replenishment method during GI duct manufacturing (step 150 in FIG. 3) For replenishment during GI duct manufacturing, ingots are directly put into the main pot 20. The types of ingots are as follows.

Zn...Pure Zn 1 ton (automatically introduced by the ingot feeder 70) Al...10% Al 20 kg (manually fed by the operator) Pb...Pure Pb 5 kg (manually fed by the operator or automatically fed by the hopper 72)

Zn ingots are introduced when the main pot level Bp is lower than the reference level by one ingot or more as determined by the main pot level meter. Also, if the level meter of the main pot is malfunctioning, please refer to (11)
) It is possible to make it possible to input the plating solution even when the plating solution decrease amount ΔQ calculated by the formula exceeds 1 ton.

[0097] Furthermore, when the total Al reduction amount ΔAl calculated by equation (12) exceeds a predetermined value (for example, 18 kg),
A predetermined amount corresponding to this, for example, nine small Al ingots 74 are thrown in.

Pb decrease amount ΔPb calculated by formula (15)
When the weight exceeds a predetermined value, for example 10 kg, a corresponding predetermined amount, for example two small Pb ingots 76, are introduced.

[0099] The amount of adhesion during GA production is measured using an alloying degree meter, but since alloyed parts are included, the measured value Mo
, Mu cannot be used as is to calculate the amount of reduction in plating solution, etc. Therefore, the following equation is used for correction.

[0100]

[Math. 12]

Here, Gofe is the iron content [%] of the front side alloy layer, and Gufe is the iron content [%] of the back side alloy layer.
].

[0102] In this example, since the concentration of the plating solution is adjusted based on the predicted value, there is a possibility that an error may occur in the concentration over a long period of time. Therefore, each concentration is periodically measured and corrected.

To measure the concentration, the operator samples the plating solution at several locations at predetermined intervals, and measures the Al concentration, Pb concentration, and
Measure the concentration and Fe concentration. Note that each concentration uses the average of several measured values. Furthermore, if there is liquid in the pre-melt pot 62 for pumping out, its Al 2 concentration, Pb 2 concentration, and Fe 2 concentration are also measured in the same manner.

As a result of the measurement, if the Al concentration and Pb concentration of the main pot 20 deviate from the upper and lower limit set values for each concentration, the Al concentration is corrected. Note that the Pb concentration is not corrected and the learning parameters are not updated at the next sampling.

Specifically, when the Al concentration is high,
Stop supplying from the pre-melt pot and supply pure Zn ingots to the main pot. The replenishment timing is when the main pot level Bp has decreased by one ingot or more from the reference level. The estimated Al concentration is calculated using equation (9) each time an ingot is introduced, and when the Al concentration reaches the target concentration, the supply is switched to the pre-melt pot.

On the other hand, when the Al concentration is low, the Al concentration is corrected by the method explained in the above section (2) concentration correction.

■Replenishment mode There are two plating solution replenishment modes: an ingot mode in which ingots are directly introduced, and a ladle mode in which ingots are replenished from a pre-melt pot.

In this embodiment, the ingot mode is used only in the following cases, and the ladle mode is used in other cases.

・GI duct manufacturing Return to ladle mode is at the start of product type switching.

- Ladle failure Return to ladle mode is when the ladle becomes usable.

- The Al concentration upper limit setting value returns to the overlaid mode when the Al concentration falls below the target value.

- If the calculated replenishment pitch is less than the shortest replenishment pitch, the mode returns to the ladle mode when the virtual stepped point passes the main pot.

[0113] The first replenishment when the ladle returns is performed using a temporary replenishment pitch.

[0114] In the above embodiment, the number of sub-pots was two, but it is clear that the number of sub-pots is not limited to this and may be three or more.

[0115]

As explained above, according to the present invention, by using at least two sub-pots containing plating solutions of different compositions, the plating solution in the main pot can be quickly switched.

[0116] Furthermore, when a pre-melt pot in which adjustment or replenishment components are melted in advance is used, concentration adjustment and supply of the plating solution can be carried out smoothly.

[0117] Furthermore, when an adjustment or replenishment component ingot feeding means is used in combination, it is possible to quickly respond even when there are large concentration fluctuations or level fluctuations.

[Brief explanation of the drawing]

FIG. 1 is a table showing continuous hot-dip galvanizing products and their target concentrations.

FIG. 2 is a diagram schematically showing a configuration example of equipment for implementing plating bath component control according to the present invention.

FIG. 3 is a flowchart showing a control procedure in an embodiment of the present invention.

FIG. 4 is a diagram showing an example of the relationship between the amount of plating deposited and the Al concentration in the plating layer.

[Explanation of symbols]

10... Strip, 20... Main pot, 21... Molten metal for plating, 22... High Pb sub-pot, 32... Low Pb sub-pot, 42... High Al pre-melt pot, 50... Al ingot feeder, 52... Zn pre-melt pot, 60, 70...Zn ingot feeding machine, 62...Pre-melt pot for pumping out, 72...Pb feeding hopper, 74...Al small ingot, 76...Pb small ingot.

Claims (3)

[Claims] Claim 1: A method for controlling the composition of a plating bath when switching the composition when performing hot-dip plating using plating baths with different compositions, comprising a main pot through which a material to be plated passes, and a plating solution containing a different composition. At the time of plating, the plating solution is poured into the main pot from one of the subpots, and when the composition is changed, the plating solution is pumped out from the main pot and returned to the subpot, and then A method for controlling plating bath components at the time of composition switching, characterized by pouring a plating solution from another sub-pot into a main pot. [Claim 2] In Claim 1, a pre-melt pot in which adjusting or replenishing ingredients are melted in advance is used, and the ingredients are supplied from the pre-melt pot to the main pot in accordance with the required concentration and reduction amount of the plating solution. A method for controlling plating bath components at the time of composition switching, characterized by: 3. According to claim 1 or 2, ingots are charged into the main pot or pre-melt pot so as to correspond to the required concentration and reduction amount of the plating solution by using an ingot charging means for adjustment or supplementary components. A method for controlling plating bath components at the time of composition switching, characterized by: