JPH02179858A - Method for adjusting composition in molten metal plating bath - Google Patents

Abstract

PURPOSE:To rapidly and precisely adjust the composition in a plating bath by previously storing a molten metal free of a concn. adjusting component and a molten metal having a high content of the component, and replacing the molten metal plating bath through a molten metal charging and discharging pot. CONSTITUTION:A band steel 6 is supplied from a snout 7, dipped in the plating molten metal 2 such as molten zinc in the plating bath 1 through a sink roll 3, and continuously plated with the molten metal. In this plating method, the plating bath 1 is constituted of plural components such as Zn, Al, and Pb. In addition, a molten metal 9 of Zn, etc., free of the concn. adjusting component such as Al and Pb is charged into a first premelt pot 8, and a molten metal 11 having a high content of the concn. adjusting component into a second premelt pot 10. The molten metals 9 and 11 are appropriately replenished from the ports 8, 10 in conformity to the concn. necessary for plating and a decrease in the amt. of plating bath 1. When the kinds of plating are changed, a specified amt. of the plating bath 1 is bailed out into a third premelt pot 16 for charging and discharging molten metal, and then the plating bath 1 is replenished and adjusted to obtain desired concn. and amt.

Description

DETAILED DESCRIPTION OF THE INVENTION <Industrial Application Field> The present invention relates to a method for adjusting the concentration of components outside a plating bath in molten metal plating.

<Prior art> Continuous hot-dip plating involves immersing a continuously running steel strip in a bath of molten plating metal for a predetermined period of time, and then applying gas wiping to the surface of the steel strip removed from the plating bath to achieve a predetermined plating. It is a wiping method in which a desired plating is applied to the surface of a copper strip by adjusting the basis weight, and hot-dip galvanizing is a typical example.

Originally, galvanized steel sheets were used as building materials due to their excellent corrosion resistance.
Widely used as steel sheets for home appliances and automobiles, hot-dip galvanizing currently has inferior surface quality compared to electrogalvanizing, but it consumes less energy, the cost of molten metal for plating is lower, and it is easier to use. It is attracting attention in the mass production of galvanized steel sheets because it can be made thicker.

By the way, in continuous hot-dip galvanizing, in addition to using a pure zinc bath, hard and brittle Fe-
AJ2 may be added to the zinc bath in order to suppress the growth of the Zn alloy layer (r phase: Fe5Znzt) and improve plating adhesion. That is, by forming an AfL-enriched layer (such as Fe3 AJ25) at the interface between the plating layer and the base steel, the Fe-Zn alloy layer at the interface between the zinc and the base steel is moderately suppressed, and the plating layer This prevents the peeling off (bacterial).

In addition to the addition of AJ2 mentioned above, a small amount of Pb may also be added to form spangles (flower patterns) on the plating surface, and the addition rate of AJ2 and Pb varies depending on the purpose of the galvanized steel sheet. ing.

In such continuous hot-dip galvanizing, the components (Zn, Afl, Pb) in the plating bath are i)! Since it is reduced by carry-out due to the plating layer adhering to the strip surface, i) generation of floating dross and its removal from the plating bath, it is necessary to replenish the reduced components to the plating bath.

A conventional method of replenishing ingredients to a hair bath will be explained below.

First, the composition and supplementary components (ingot) of the hot-dip galvanizing bath are shown in Table 1 below. Note that hot-dip galvanized steel sheets generally include not only pure zinc plating baths but also steel sheets having bath compositions as shown in Table 1.

Table 1 To give a representative explanation of the types Gl and GA in Table 1 above, when the liquid level of the plating bath decreases, approximately 1 ton of 0.3
~0.5 wt% A It -Z n alloy ingot was put into a plating bath and the bath components were analyzed at intervals of several hours.As a result, as the AjZ concentration decreased, one
Ingredients were replenished by placing an appropriate number of ingots of 10 wt% Afl-Zn alloy weighing approximately 1 kg into a plating bath (for example, see Japanese Patent Laid-Open No. 274750/1983).

Note that AJ with a higher An concentration than the target An concentration of the bath component
! -The reason for introducing Zn alloy ingot is the above-mentioned A.
The A
This is because the rate of decrease of 1 is greater.

However, in the above replenishment method using ingots,
It takes time for the ingot put into the plating bath to melt and spread in the bath to form a uniform plating bath (the heavier the ingot, the longer it takes), and it may take some time for the ingot to melt and spread in the bath to form a uniform plating bath. A in the bath until the next injection.
Since the °C concentration continues to decrease, the He1 concentration in the plating bath fluctuates greatly depending on the pitch at which 10 wt% Ait-Zn alloy ingots are introduced (at intervals of several hours), as shown in the comparative example in FIG.

In this way, A ILI in the plating bath! If the temperature varies by 1 degree, the uniformity of the AJ2-enriched layer described above will be impaired, making it impossible to obtain stable plating quality, and in continuous hot-dip galvanizing, the An concentration in the plating bath will deviate from the target value. The number of plated parts increases, leading to a decrease in plating quality.

In addition, in the conventional component replenishment method described above, the relationship with plating conditions is not considered, and moreover, Aj2 content is constant.
In order to input the fl-Zn alloy ingot, any AJ
It is impossible to replenish components at two concentrations, and AJ in the plating bath
2. It is not possible to finely adjust the density.

In recent years, hot-dip galvanized steel sheets have become popular due to their low manufacturing costs.
It is expected that it will be applied to mass-produced automobile exterior panels, but for this purpose it must have excellent adhesion to deep drawing by press forming. The formation of a °C-enriched layer is essential. Therefore, it is necessary to more strictly control the Aa concentration in the plating bath.

Taking these points into consideration, the conventional component replenishment method by charging ingots has a limit in reducing fluctuations in Af concentration, and has not been able to stably obtain satisfactory plating quality.

The above is a method for adjusting the component concentration in the plating bath in hot-dip galvanizing of the same product type, but on the other hand, it is necessary to adjust the AJ2 concentration in the plating bath to 0.1 to 0.2% depending on the product type. For example, in hot-dip galvanizing, in non-alloy plating (GI), in order to ensure plating adhesion,
In iron-zinc alloy plating (GA), which is heat-treated after plating, the Aj2 concentration is adjusted to 0 to facilitate the alloying process. It is often adjusted to .1 to 0.15% (using a low A°C bath).

At this time, when adjusting from a low A℃ bath to a high AJZ bath,
Although it can be easily adjusted by adding AfL to the bath, there has been no effective means for adjusting from a high A1 bath to a low AIL bath, and for example, the following method has been used.

1) Since A2 in the plating bath is preferentially consumed by plating, we manufacture products that do not require strict control of An concentration (such as building materials), and during this period, the concentration is naturally reduced by stopping supply of An. . Here, AJZ in the plating bath
The reason why is preferentially consumed is that A in the plating layer on the steel plate
This is because the IZ concentration and the AJ2 concentration in the dross are higher than the AJZ concentration in the plating bath. The problem with this method is that whenever the AJZ concentration is lowered, it is necessary to manufacture products such as building materials for a long time without strict AJZ concentration control, and chance-free production cannot be achieved.

++) After lowering the A1 concentration by pumping out a part of the plating bath into another bath and adding an Aλ removing agent, return it to the original plating bath and repeat this operation until the predetermined concentration is reached (for example, (see Japanese Patent Application Laid-Open No. 169369/1983),
The problem with this method is that large-scale equipment is required, such as an addition device for the A1-removal agent and a collection device for fumes, dust, etc. generated during the A1-removal reaction.

111) Install two sub-pots with the same capacity as the plating bathtub,
In the case of this method, in which the entire volume of the plating bath is replaced by a pump (see, for example, Japanese Utility Model Application Publication No. 162254/1983), there is a problem in that the line must be stopped, which reduces productivity.

<Problems to be Solved by the Invention> The present invention solves the above-mentioned drawbacks of the prior art, suppresses concentration fluctuations of components in the plating bath when manufacturing the same product, and suppresses fluctuations in the concentration of components in the plating bath when changing products. It is an object of the present invention to provide a method for adjusting the concentration of components in a molten metal plating bath, which allows the concentration to be changed quickly and to stably obtain good plating quality.

<:Means for solving aa> In order to achieve the above object, according to the present invention, in a method for adjusting the concentration of components in a plating bath when performing hot dip plating in a plating bath containing a plurality of components, the concentration At least one first pre-melt pot pre-melted with metal that does not contain a concentration adjusting component, at least one second pre-melt pot pre-melted with metal containing a high concentration of concentration adjusting component, and at least one for receiving and discharging molten metal. When plating the same product using three third pre-melt pots, components are replenished from the first and/or second pre-melt pots to correspond to the required replenishment concentration and the amount of decrease in the plating bath. After switching the type and adjusting the concentration adjustment component from high concentration to low concentration, the trunk pumps a predetermined amount of the plating bath into the third pre-melt pot for receiving and discharging the molten metal, and then removes the metal that does not contain the concentration adjustment component. A method for adjusting the concentration of components in a molten metal plating bath is provided, which comprises replenishing the same amount from a first pre-melt pot that has been melted in advance.

Further, according to the present invention, the metal containing a high concentration of the concentration adjusting component pumped into the third pre-melt pot for receiving and discharging molten metal is used as a replenishing component to the plating bath when plating the same type of product next time. A method for adjusting the concentration of components in a hot-dip metal plating bath is provided.

Further, according to the present invention, a spacer is used to adjust the level of the plating bath when the plating bath is pumped into a third pre-melt pot for receiving and discharging molten metal. A method of adjusting component concentration is provided.

The present invention will be described below based on preferred embodiments shown in the accompanying drawings.
This will be explained in more detail.

FIG. 1 is a side view schematically showing an example of the configuration of equipment for carrying out the method of adjusting component concentration in a molten metal plating bath according to the present invention.

In the plating bath 1, the annealed steel strip 6 coming out of the snout 7 is immersed in the molten metal for plating (for example, molten zinc) 2 by the zinc roll 3, and then straightened by the collecting roll 4 and stabilized. After being stabilized by stopping the rocking by the rising roll 5 and being pulled up from the molten metal for plating 2, it is adjusted to a predetermined plating area weight by gas wiping (not shown).

In this way, the steel strip 6 is continuously coated with hot-dip metal.

When performing hot-dip galvanizing, as mentioned above, it is possible to add AJ2 to the plating bath to improve plating adhesion, or to add a small amount of PB to form spangles on the plating surface. be exposed. Therefore, the composition of the molten metal 2 for plating is A11-Zn type or AJ2 type.
-Pb-Zn system, etc., and the addition rate of AJ:L and pb is appropriately determined depending on the use, type, etc. of the galvanized steel sheet to be manufactured.

For example, i) the composition of the molten metal 2 for plating is 0, 01~
0. 2wt%Pb-0,1~0.2wt%AJZ-Z
a galvanized steel sheet or an alloyed galvanized steel sheet (G1.GA) which is an alloy of n alloy, ii) a zinc-aluminum alloy plated steel sheet (GALFAN) whose molten metal 2 for plating has a composition of 5 wt% Au-Zn alloy, or 1ii) The composition of the molten metal 2 for plating is 1.4wt%Si
-55 wt% AJZ-43, 6 wt% Zn zinc-aluminum alloy plated steel sheet (GALVALUME), etc.

The uses of i) are mainly for building materials, home appliances, and automobile interior panels, and the uses of if) and 1ii) are mainly for building materials.

In such continuous hot-dip galvanizing, the plating layer adhering to the surface of the steel strip 6 generates carryover and floating dross, and by removing this from the plating bath, the liquid level of the molten metal 2 for plating is lowered. descend. Therefore, it is necessary to replenish so as to keep the liquid level constant and to keep the composition of the molten metal 2 for plating constant at the target value.

In addition, the floating dross combines with A1 in the molten metal 2 for plating with Fe eluted from the steel strip 6 to become Fe, An,
This is what has floated to the surface of the plating bath (its specific gravity is smaller than the molten metal 2 for plating), or what has been oxidized by zinc on the bath surface.

Further, the reduction in the molten metal for plating 2 does not occur in proportion to the content (concentration) of each component (Zn, AJZ, Pb) in the molten metal for plating 2. That is, regarding the reduction of A2, since an AJZ enriched layer (FezAJ2. etc.) is formed at the interface between the base steel and the plating layer, the A1 concentration in the take-out is higher than the AJ2 concentration in the molten metal 2 for plating, In addition, the composition of the floating dross removed to the outside of the plating bath is that in the molten metal 2 for plating with an A1 concentration of 0.1 to 0.2 wt%, AfL = Fe = 2 to 4 wt%, and the balance is Zn.
Therefore, the decrease in the Ai concentration in the molten metal for plating is
Significant compared to other ingredients.

Therefore, replenishment of components to the plating bath is necessary for molten metal for plating.
As a result of replenishing the amount so that the liquid level reaches the target value, rather than at a concentration equal to the composition of molten metal 2 for plating,
It is also necessary to adjust the composition to the target value.

In the present invention, when plating the same product type, components are replenished into the plating bath as follows. 1st
As shown in the figure, pre-melt bots 8, 10 and 16 are installed on the sides of the plating bath 1, and the first pre-melt bot 8 contains a molten Z obtained by melting an ingot.
n9, a molten A1-Zn alloy 11 obtained by melting an ingot is stored in the second pre-melt pot 10.

The third pre-melt pot 16 is used for receiving and discharging molten metal, and is normally empty.

When replenishing the components, pumps 12 and 14 are operated to charge molten Zn 9 and molten An-Zn alloy 11 into plating bath 1 via conduits 13 and 15, respectively.

Replenishment of such components is carried out by adjusting the input amounts from the first and second pre-melt pots 8.10 so as to correspond to the necessary replenishment concentration and the amount of decrease in the plating bath as described above. In addition, when plating the same type of metal and when the molten metal 2 for plating is a binary alloy, at least two Brimelts must be used to replenish the components to correspond to the required replenishment concentration and the decrease in the amount of plating bath. All you need is a bot.
The amount of molten Zn9 and molten Au-Zn alloy 11 introduced from the first and second Brimelt bottles 8.10 can be adjusted by using a pump that can control the flow rate as the pump 12.14, or by controlling the flow rate in the middle of the conduit 13.15. This may be done by means such as providing a control valve (not shown).

In addition, the form of replenishment may be either continuous replenishment in which replenishment is performed at intervals during plating, or intermittent replenishment in which replenishment is performed at predetermined intervals. The forms may be different. In addition, when performing intermittent replenishment, it is preferable that the replenishment pitch be as short as possible, since concentration fluctuations in the molten metal 2 for plating will be reduced.

When the liquid level of the first and second Brimelt bottles 8.10 decreases, the first and second Brimelt bottles 8.10
A Zn ingot and an A11-Zn alloy ingot were added to each to compensate for the reduced amount.

The conduits 13.15 are preferably heated and maintained at a temperature above the melting point of the metal passing through them so that molten metal does not solidify within them and cause blockages. Also, conduit 13.1
The input port 131.151 at the tip of 5 is the first in plating bath 1.
The inside of the steel strip 6,
It may be located on the outside or near the side, and the conduit 13
．． 15 may be branched and a plurality of inlets 131 and 151 may be arranged at various locations in the plating bath 1. By doing so, the uniformity of the concentration of the molten metal 2 for plating in the plating bath 1 is promoted. preferable.

In this way, when replenishing the components to the plating bath 1 by charging molten metal, there is an advantage that fluctuations in the bath temperature of the plating bath can be suppressed compared to the conventional method of charging ingots.

As a means for replenishing the plating bath 1 with the molten Zn 9 and the molten Aλ-Zn alloy 11 from the first and second Brimelt bottles 8.10, the pump described above is used! The method is not limited to the method using 2.14, but for example, a spacer (not shown) may be inserted into the molten metal 9.11 of the first and second Brimelt bottles 8.10 to raise the liquid level and cause overflow. It is also possible to introduce the molten metal 9.11 into the plating bath 1 by using the method shown in FIG. In this case, the amount of molten metal 9.11 introduced is adjusted by the amount of spacer insertion.

In addition, the first and second pre-melt pots 8.10 are sealed, and high-pressure gas is fed into the first and second pre-melt pots 8.10 by a compressor (not shown), and the pressure is used to fill the first and second pre-melt pots. It is also possible to push out the molten metal 9.11 inside and throw it into the plating bath 1.

Note that the AfL component of plating bath 1 is replenished by melting Aj! −Z
The reason for using n alloy 11 is as follows. The bath temperature of the plating bath 1 is such that the composition of the molten metal 2 for plating is 0.1~
For 5wt% AIL-Zn alloy, approximately 450-480°C
However, since the melting point of AIL alone is 660° C., when the molten AIL is poured into the cleaning bath 1, it solidifies. On the other hand, if Aft, -Zn alloy is used, its melting point will be lower (the melting point of 10 wt% AJZ-Zn alloy is 43
0°C), there is no inconvenience of coagulation occurring when it is put into a plating bath. Therefore, in the present invention, when replenishing a metal component having a melting point higher than the bath temperature, an alloy of the metal and another metal, especially the main component metal (in this example, zinc), is used. It is preferable to lower the melting point, preferably below the bath temperature, before adding it to the plating bath. However, the present invention does not preclude the provision of a molten AJZ Brimeltbot and replenishment by AIL alone. Further, as described below, the molten Au brimelt pot can also be used as a molten Aλ-Zn premelt bot for replenishment.

In addition, as shown in FIG. 2, there are a pre-melt bot A containing molten Zn, a pre-melt bot B containing molten AJl,
and pre-melt pots C, D, and E% F containing molten AJZ-Zn alloys with different AIL concentrations, respectively, and one or more of pre-melt pots A, C, D, and E% F can be optionally used. It is also possible to select a suitable amount of molten metal from each of these and charge it into the plating bath 1.

When the liquid level of any of the pre-melt bots C, D, and E% F decreases, predetermined amounts of molten Zn and molten A1 from the pre-melt bots A and B are respectively introduced into that pre-melt bot. For example, when replenishing Primelt Bot C, the amount of each input from Primelt Bots A and B is adjusted so that it is equal to the A1 concentration of Primelt Bot C.

When the composition of the molten metal in each pre-melt bot is as shown in Table 2 below, Table 3 below shows an example of replenishment from each pre-melt bot to the plating bath with respect to the composition of the plating bath.

FIG. 3 is a side view schematically showing another configuration example of equipment for carrying out a method of replenishing components to a plating bath when plating the same product type.

In the equipment shown in the figure, first and second pre-melt bottles 8 and 10 similar to those described above and a hopper 18 containing metal powder grains 20 as a supplementary component are installed,
Molten Zn 9 and molten AX-Zn alloy 11 are charged into the plating bath 1 from the second pre-melt bottles 8 and 10, respectively, and a predetermined amount of metal powder particles 20 are charged into the plating bath from the hopper 18.

A blade (rotary feeder) 19 is installed at the opening at the lower end of the hopper 18, and as the blade 19 rotates, a fixed amount of metal powder particles in the hopper are cut out and thrown into the plating bath 1. Note that, unlike the illustration, the hopper 18 is installed at a position a considerable distance away from the plating bath, and the metal powder particles 2 cut out from the hopper 18 are
0 may be conveyed by a conveyor and thrown into the plating bath 1.

In hot-dip galvanizing, a small amount of PB may be added to the molten metal 2 for plating in order to form spangles on the plating surface, as described above. That is, the composition of the molten metal 2 for plating is Pb-Aj! -Zn alloy, and this pb acid component can be replenished by introducing metal powder particles 20 using pb grains. Note that, since the melting point of PB is 327°C, which is lower than the bath temperature (450 to 480°C) of plating bath 1, the PB particles introduced into plating bath 1 quickly melt and diffuse.

The particle size of the metal powder particles 20 is not particularly limited, but is preferably about 1 to 10 mm. If it is less than 1 mm, minute particles will float in the bath and easily adhere to the copper strip, and 10
This is because if the value exceeds ++un, the accuracy of density adjustment becomes rough. Note that the metal powder particles 20 are not limited to PB particles, but may also be Pb-Z particles.
It may be grains of n-alloy, or powder grains of other metals or alloys.

In such equipment, when plating the same type of metal and the molten metal 2 for plating is a binary alloy,
At least one pre-melt pot and one hopper are required to replenish the necessary replenishment concentration and components corresponding to the reduced amount of the rinsing bath.

In the present invention, the amount of component replenishment may be determined by, for example, a method in which bath components are analyzed in a timely manner and based on the analyzed values, or a method is determined based on estimated values determined empirically. Although it is possible, it is preferable to determine the necessary replenishment concentration and the amount of decrease in the plating bath based on the plating conditions, and replenish the components based on this, as described below.

The present inventors have determined that the plating bath composition is 0.05 to 0.20 wt%.
As a result of conducting experiments and discussions to investigate the relationship between the amount of decrease in the An component and the wiping conditions in hot-dip galvanizing using An-Zn, the following knowledge was obtained.

■ An A1-enriched layer (Fe2
As, etc.) are formed, the AlI concentration in the plating layer is higher than the AfL concentration in the plating bath. The AJZ concentration in the rough plating layer is not always constant with respect to the amount of deposited plating, but is a function of the amount of deposited plating as shown in FIG. Therefore, it is possible to know the amount of decrease due to A.degree. C. removal from the amount of plating deposited.

■ The main component of floating dross is Fe, which is formed by the combination of Fe eluted from the steel strip and AJ2 in the plating bath.

A (1,s) or zinc oxide, and as a result of analyzing the components of this dross AJ!=Fe=2~4wt
%, the balance was found to be Zn.

Therefore, the amount of decrease in the AJZ component due to the generation of floating dross is equal to the amount of Fe eluted from steel, etc., and by understanding this, it is possible to know the amount of decrease in AIL due to floating dross.

From the above (1) and (2), the total decrease in Zn and An in the plating bath is expressed by the following formula.

To 1 total decrease amount = f (V, B, C, θ, W) Zn total decrease amount - g (V, B, C, θ, W) V; line speed B: plate width C: Aj2 concentration θ in bath : Penetration plate temperature W: Decreased amount of Zn and AJ2 in the cleaning bath and Z
The reduction rate of n and AJ2 is determined by the plating conditions (plating amount,
It was found that it can be determined by the plate width, line speed, plate temperature, etc.).

Conventionally, only an A11-Zn alloy ingot with an A1 concentration (content rate) higher than the A1 concentration in the plating bath was put into the plating bath, and the replenishment concentration of AIL was not changed depending on the plating conditions. There wasn't. In contrast, with the present invention, which determines the necessary replenishment concentration of bath components and the amount of reduction in the plating bath based on the plating conditions, it is possible to replenish the components more appropriately, and the concentration of each component in the plating bath can be more narrowly controlled. Furthermore, even if the plating conditions (plating amount, plate width, line speed, plate temperature, etc.) change, it can be accommodated.

In general, there are n Primeltbots (n≧2), and C
n is the concentration of the specific component in the nth pre-melt bot, Q
If n is the supply amount from the nth Primeltbot,
The required replenishment amount Q1 and the required concentration C'' are expressed by the following equations.

Q" = Q+ +Q2+...Qn These Q' and C' are determined from the above plating conditions, and the Q
``Replenishment may be performed by adjusting Q1 to Qn so as to have the value of C5.

Above, the method of replenishing components to the plating bath when plating the same product according to the present invention has been representatively explained for hot-dip galvanizing containing Aλ acid components, but the present invention is not limited to hot-dip galvanizing. It can be applied to all types of molten metal plating, such as plating, tin-lead alloy plating, and molten aluminum plating.

Next, in the present invention, a method of adjusting the concentration adjusting component from high concentration to low concentration by switching the plating type will be explained using a case where hot-dip galvanizing is performed as a representative example.

In FIG. 1, the first pre-melt pot 8 contains molten Zn9 obtained by melting an ingot, and the second pre-melt pot 1o contains molten Zn9 obtained by melting an ingot.
The Zn alloy 11 is stored and the third pre-melt pot 16 is normally empty at first. The A It Q14 degree of the molten AjZ-Zn alloy 11 needs to be sufficiently higher in concentration than the high concentration Al1-Zn alloy in the plating bath 1 before switching. If this AIL concentration is not high enough, the next high concentration Aj! - This will hinder the adjustment of the Zn bath and the replenishment of the A1 component.

In this state, the high concentration AjZ-Zn in plating bath 1
To switch the alloy to a low concentration Afl-Zn alloy, first, the pump 17 is operated while the bath surface is detected by the bath level meter 21, and a predetermined amount of the molten metal 2 in the plating bath 1 is pumped through the conduit 22 into the third Pour into pre-melt pot 16. As the bath level meter 21, for example, a laser liquid level meter or the like is used. The pumping amount may be adjusted by using a pump capable of controlling the flow rate as the pump 17, or by providing a flow control valve (not shown) in the middle of the conduit 22.

Further, the conduit 22 is preferably heated and kept at a temperature equal to or higher than the melting point of the metal passing through so that the molten metal does not solidify inside the conduit and cause clogging. The tip entrance/exit 221 of the conduit 22 is not limited to the case where it is arranged at the location shown in FIG. 1 in the plating bath 1! -! It may be arranged inside, outside or near the side of the IF 6 , or the conduit 13 . 15 may be branched and a plurality of immersion openings 131 . This is preferable because it promotes uniformity of the concentration of the molten metal 2 for plating in the plating bath 1.

Next, the pump 12 is operated while detecting the bath surface of the plating bath 1 with the bath level meter 21, and the first pre-melt pot 8
The amount of molten Zn9 corresponding to the amount pumped out is transferred to the conduit 1.
After step 3, it is poured into plating bath 1.

In this way, the molten metal 2 in the rice plating bath 1 can be switched to a predetermined low concentration AJZ-Zn alloy.

The relationship between the An concentration of the molten metal 2 in the plating bath 1 before and after the above switching and the pumping amount are expressed by the following formula (%) where: C5; Au of the high concentration AJZ-Zn alloy plating bath
wt% C2: Af1 wt% of low concentration An-Zn alloy plating bath Ml: Weight of high concentration AjZ-Zn alloy plating bath before pumping (tons) M2: Pumping amount of high concentration Aλ-Zn alloy plating bath (tons) High concentration A pumped into the third pre-melt pot 16
The 11-Zn alloy can be used to replenish the components of a low concentration Al1-Zn alloy plating bath or for the next high concentration Aj2-Zn alloy plating bath.

In addition, when pumping a predetermined amount of the high concentration An-Zn alloy into the third pre-melt pot 16, if the bath level of the plating bath 1 decreases and it becomes impossible to seal the tip of the snout, Spacer 2 corresponding to the volume to be compensated as shown in Figure 5
It is effective if the molten metal 2 is pumped out while submerging Zn 3 in an appropriate place in the plating bath 1, and the molten Zn9 corresponding to the pumped amount is poured into the plating bath 1 while pulling up the spacer 23. It is true.

<Example> (Example 1 of the present invention) Hot-dip galvanizing was carried out under the following conditions using the equipment configured as shown in FIG.

Plating bath composition: 0.17±0.01wt% AjiL (target straight) -Z
n First pre-melt pot composition: Pure Zn Second pre-melt pot composition: 2wt% AJZ-Zn Plating conditions Plate thickness: 0.7 mm Plate width: 1200 m+n Line speed: 120 m/min Plating deposition amount (one side): 90 g/ rn” Calculated from these plating conditions, the AjZ concentration to be replenished is 0.5 wt%.
, the reduction amount of the plating bath is 35 kg/min.
Therefore, 26 kg of pure Zn was collected from the first pre-melt pot.
/ min 2wt% A1 from the second Brimelt bottle
1-Zn alloy was continuously supplied at a rate of 9 kg/win.

The conduit between each Brimelt pot and the plating bath is heated by a heater to prevent the molten metal from solidifying within the tube.
Heated to ~480°C.

Next, apply this high concentration AJ2-Zn plating bath to 0.14±0
．． 01wt%An (direct to target) - Switched to Zn plating bath.

The weight of the plating bath is 100 tons (2.8m x 3.2m)
x 1.7 m depth), and the discharge rate of the pump was 3 tons/min.

Therefore, after pumping 17.6 tons of high-concentration AjL-Zn plating bath to the third pre-melt pot for receiving and receiving,
Approximately 17.6 tons of Zn was supplied from the pre-melt pot. The fluctuation in the bath level at this time was detected by a laser bath level meter and was 289 mm.

Further, the time required for this concentration switch was 17.6 tons total 3 tons x 2 = 12 minutes, which was much shorter than the conventional method (about 8 hours).

(Comparative Example) The plating bath composition and plating conditions were the same as those in Inventive Example 1, and a 0.4 wt% AjZ-Zn alloy ingot weighing 1 ton was heated at a pitch of about 29 minutes, and a 10 wt% AI weighing 20 kg was heated at a pitch of about 29 minutes.
The L-Zn alloy ingot was intermittently introduced into the plating bath at intervals of about 8 hours to replenish the components.

Af in the plating bath for the above-mentioned invention example 1 and comparative example
Changes in L concentration over time were investigated. The results are shown in the graph of FIG. As is clear from this graph, in Invention Example 1, there was less variation in the AjZ concentration in the plating bath than in the comparative example, and there was almost no variation in the A°C concentration from the target value.
Therefore, it was found that the desired plating quality could be stably obtained.

Next is this high concentration AJ! -Zn plating bath 0.14±0
．． 01wt%AJ2 (eyes are straight) - Switched to Zn plating bath.

The switching was performed by pumping the high concentration Al1-Zn plating bath into a separate bath (capacity 5 tons), adding ZnCJ22 as an AIL removal agent, lowering the Al concentration to about 0.05 wt%, and returning it to the plating bath, which was repeated 5 times. Ta. The time required for switching was approximately 3 hours.

<Effects of the Invention> Since the present invention is configured as described above, when plating the same type of product, the concentration and amount of the components to be replenished can be arbitrarily selected. Fluctuations in the concentration of the components inside can be suppressed, and good plating quality can be stably obtained.

In particular, when determining the necessary replenishment concentration of components and the reduction amount of the plating bath from the plating conditions, it becomes possible to replenish the components more appropriately, and even if the plating conditions change, it is possible to respond to the changes. Therefore, it becomes possible to strictly control the concentration of components in the plating bath.

In addition, when changing the type of plating and adjusting the concentration adjustment component from a high concentration to a low concentration, the pre-melt pot for molten metal receiving and discharging can be used to quickly and accurately adjust with a single plating bath receiving and discharging operation. Therefore, productivity can be improved.

[Brief explanation of the drawing]

FIG. 1 is a diagrammatic side view schematically showing an example of the configuration of equipment for carrying out the method for adjusting the concentration of components in a molten metal plating bath according to the present invention. FIGS. 2 and 3 are diagrammatic side views schematically showing other configuration examples of equipment for carrying out a method of replenishing components to a plating bath. FIG. 4 is a graph showing the relationship between the amount of plating deposited and the Aλ concentration in the plating layer. FIG. 5 is a diagrammatic plan view of a hot dip metal plating bath with spacers. FIG. 6 is a graph showing changes over time in the AJ2 concentration in the plating bath. Explanation of symbols 1... Plating bath, 2... Molten metal for plating, 3... Zinc roll, 4... Correcting roll, 5... Stabilizing roll, 6... Steel strip, 7 ... Snout, 8... First pre-melt pot, 9... Molten Zn. 10... Second pre-melt pot, 11... Molten AIL-Zn alloy, 12.14.17... Pump, 13.15.22... Conduit, 131.151... Immersion port, 16 ...Third pre-melt pot, 18...Hopper 19...Blade, 20...Metal powder grain, 21...Bath level meter, 221...Inlet/outlet, 23...Spacer, A ,B,C,D,E. F...Primelt pot

Claims (3)

[Claims] (1) In a method for adjusting component concentration in a plating bath when performing hot-dip plating in a plating bath containing a plurality of components, at least one first pre-melt pot pre-melted with metal that does not contain concentration adjusting components; Necessary replenishment when plating the same product type using at least one second pre-melt pot pre-melted with metal containing a high concentration of adjustment components and at least one third pre-melt pot for receiving and discharging molten metal. Components are replenished from the first and/or second pre-melt pots to correspond to the concentration and amount of decrease in the plating bath, and when changing the plating type and adjusting the concentration adjustment component from a high concentration to a low concentration, the plating bath After pumping a predetermined amount of molten metal into the third pre-melt pot for receiving and discharging molten metal,
A method for adjusting the concentration of components in a molten metal plating bath, characterized in that the same amount of metal that does not contain the concentration adjusting component is replenished from a first pre-melt pot that has been melted in advance. (2) In the method for adjusting component concentration in a molten metal plating bath according to claim 1, plating when the molten metal pumped into the third pre-melt pot for receiving and discharging molten metal is used for plating the same type of metal next time. A method for adjusting the concentration of a component in a hot-dip metal plating bath, characterized in that the component is used as a replenishing component to the bath. (3) In the method for adjusting the concentration of components in a molten metal plating bath according to claim 1 or 2, when the plating bath is pumped into the third pre-melt pot for receiving and discharging molten metal, a spacer is used to control the plating bath. A method for adjusting the concentration of components in a hot-dip metal plating bath, characterized by adjusting the level of.