JPH01177346A - Method for supplying component to plating bath - Google Patents

Abstract

PURPOSE:To inhibit fluctuations in the concentration of the component in a plating bath and to stably obtain superior plating quality by supplying required components from plural hoppers filled with the metal grains of supplementary components, respectively, to a plating bath containing plural components. CONSTITUTION:A steel strip 6 fed through a snout 7 is dipped into a molten metal 2 for plating containing Zn and Al in a plating bath tank 1 and is allowed to travel through the above molten metal 2 via a sink roll 3, a correcting roll 4, a stabilizing roll 5, etc., to undergo hot dipping. At this time, required amounts of Zn grains 10 and Al-Zn grains 13 as supplementary components are discharged respectively from hoppers 8, 11 via rotary feeders 9, 12 according to required supplementary concentrations and the amount of the plating bath 1 reduced, and then, they are supplied by means of a conveyor 14. It is preferable that the above required supplementary concentrations and the amount of the plating bath reduced are determined according to plating conditions.

Description

DETAILED DESCRIPTION OF THE INVENTION <Industrial Application Field> The present invention relates to a method for replenishing components to a plating bath in hot-dip metal plating.

Prior art and its problems 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 copper strip removed from the plating bath. It is a plating method in which desired plating is applied to the surface of a copper strip by adjusting the coating weight to a predetermined coating 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 the plating solution is lower, and it can be easily coated with thick coatings. Because it is possible, it is attracting attention for mass production of galvanized steel sheets.

By the way, in continuous hot-dip galvanizing, in addition to using a pure zinc bath, hard and brittle Fe-
Afl was added to the zinc bath to suppress the growth of the Zn alloy layer (r layer: Fes Zn2□) and improve plating adhesion.
may be added. That is, by forming an A°C enriched layer (Fe2Aus) 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 peeling of the plating layer is prevented. It is intended to prevent

In addition to the addition of An mentioned above, a small amount of PB may be added to form a spangle (flower pattern) on the plating surface, and the addition rate of A1 and PB varies depending on the purpose of the galvanized steel sheet. ing.

In such continuous hot-dip galvanizing, the components (Zn, An, Pb) in the plating bath are 1) carried out by the plating layer adhering to the surface of the copper strip, and 2) generated floating dross and removed to the outside of the plating bath. Therefore, it is necessary to replenish the plating bath with the reduced components.

A conventional method of replenishing components to a plating 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 explain representatively the types Gl and GA in Table 1 above, when the liquid level of the plating bath decreases, about 1 ton of 0.
As a result of immersing an ingot of 3~0.5wt% Aj2-Zn alloy in a plating bath and analyzing the bath components over several hours, it was found that as the An concentration decreased, one
Ingredients were replenished by placing an appropriate number of 10 wt % An-Zn alloy ingots weighing approximately 1 kg into the plating bath.

In addition, the number of bath ingredients * A 11? The reason for introducing an AjZ-Zn alloy ingot with a higher AJ2 concentration than the R degree is that the AJ2 This is because the rate of decrease 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 takes 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 U concentration continues to decrease, the He1 concentration in the plating bath fluctuates greatly depending on the pitch at which 10 wt% AfL-Zn alloy ingots are introduced (at intervals of several hours), as shown in the comparative example in FIG.

If the AIL concentration in the plating bath fluctuates in this way, the uniformity of the AIL-enriched layer described above will be impaired, making it impossible to obtain stable plating quality, and in continuous hot-dip galvanizing, the Au concentration in the plating bath will change. The number of plated areas that deviate from the target value 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 taken into account, and moreover, the A℃ content is constant.
- Since the Zn alloy ingot is charged, it is impossible to replenish the components at an arbitrary A°C concentration, and it is not possible to finely adjust the A1 concentration in the plating bath.

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 is necessary to have excellent plating adhesion even during deep drawing processing by press forming. The formation of an enriched layer has become essential. Therefore, it is necessary to manage the A° C. concentration during plating in a more i-class manner.

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

<Object of the Invention> The object of the present invention is to solve the above-mentioned drawbacks of the prior art, to suppress concentration fluctuations of the components in the plating bath, and to provide components for the plating bath that can stably obtain good plating quality. The purpose is to provide a replenishment method.

<Structure of the invention> Such objects are achieved by the present invention as described below.

That is, the present invention provides a method for replenishing components into a plating bath when performing hot-dip plating in a plating bath containing a plurality of components, using a plurality of hoppers containing metal grains as replenishment components, and adjusting the required replenishment concentration and The present invention provides a method for replenishing components to a plating bath, characterized in that components are replenished from the hopper so as to correspond to the amount of decrease in the plating bath.

Further, it is preferable that the necessary replenishment concentration and the amount of decrease in the plating bath are determined by the plating conditions.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The method of replenishing components to a plating bath according to the present invention will be described in detail below with reference to preferred embodiments shown in the accompanying drawings.

FIG. 1 is a side view schematically showing an example of the configuration of equipment for carrying out the method of replenishing components to a 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 a molten metal for metal plating (for example, molten zinc) 2 by a zinc roll 3, and then bent (C-warped) by a collecting roll 4. is corrected, the bath core is stabilized by stopping the swinging by the stabilizing roll 5, and after being lifted from the molten metal 2 for plating, it is adjusted to a predetermined plating area weight by gas wiping (not shown). In this way, the steel strip 6 is continuously plated with molten metal.

When performing hot-dip galvanizing, as mentioned above, it is possible to add A°C to the plating bath to improve plating adhesion, or to add a small amount of PB to form spangles on the plating surface. It will be done. Therefore, the composition of the molten metal 2 for plating is Al1-Zn-based or Al2-
It is a Pb-Zn type, etc., and the addition rate of Afl 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 for plating is 0.0f ~
0.2w% Pb-0.1~0. 2wt%Af
1. - Zn alloy galvanized steel sheet or alloyed galvanized steel sheet (Gl, GA), if) the composition of the molten metal for plating is 5 wt% A℃ - Zn alloy coated steel sheet (GALFAN), or 1ii) The composition of the molten metal for plating is 1.4wt%St-
Examples include 55 wt% AJZ-43.6 wt% Zn zinc-aluminum alloy plated steel sheet (GALVALUME).

The uses of i) are mainly for building materials, home appliances, and automobile interior panels, and the uses of it) and 1ff) 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 the composition of the molten metal for plating constant at the target value. The main component of the floating dross is Aj! in the Fe molten metal for plating 2 eluted from the steel strip 6! Combines with to become Fe2Au5,
This floats to the surface of the plating bath (its specific gravity is lower than that of the molten metal for plating).

Further, the reduction in the molten metal for plating 2 does not result from a decrease in each component (Zn, An, Pb) of the molten metal for plating in proportion to the content (concentration) thereof. That is, regarding the reduction of A1, an Al-enriched layer (Fe
2A15) is formed, so A in taking out
! The composition of the floating dross that is higher than the A°C concentration of the molten metal 2 for plating and is removed to the outside of the plating bath is Au=Fe= Since Zn accounts for 2 to 4 wt% and the remainder is Zn, the decrease in the A°C concentration in the molten metal for plating is more significant than for other components. Therefore, instead of replenishing the components to the plating bath at a concentration equal to the composition of the molten metal 2 for plating, the components are replenished in such an amount that the liquid level reaches the target value, and as a result, the composition of the molten metal 2 for plating also reaches the target value. (Note that supplementation of components may be performed at a concentration approximately equal to the target value).

In the present invention, components are replenished into the plating bath as follows. As shown in FIG. 1, hoppers 8 and 11 are installed on the side of the plating bath 1, and the hopper 8 stores Zn grains 9, and the hopper 11 stores AjZ-Zn alloy grains 13. .

Rotary feeders 9 and 12 are installed at the lower end openings of each hopper 8 and 11, respectively, and when replenishing ingredients, these are operated to feed a predetermined amount of Zn grains 9 and Al1-Zn alloy grains 13 from the hoppers 8 and 11, respectively. It is cut out, transported by a conveyor 14, and thrown into the plating bath 1.

The replenishment of such components is carried out by adjusting the amount charged into the plating bath from each hopper 8.11 so as to correspond to the necessary replenishment concentration and the amount of reduction in the plating bath as described above.

In addition, when the molten metal 2 for plating is a binary alloy, at least two hoppers are sufficient in order to replenish the components to correspond to the required replenishment concentration and the amount of decrease in the plating bath. Zn grains 9 and A from each hopper 8.11
The input amount of the l1-Zn alloy grains 13 may be adjusted by adjusting the cutout amount of each rotary feeder 9.12.

In addition, in the present invention, the metal particles may be cut out from the hopper by other methods that do not use a rotary feeder, and the metal particles cut out from the hopper may be directly thrown into the plating bath without being conveyed by a conveyor. You can.

Furthermore, the form of replenishment may be either continuous replenishment, in which replenishment is performed at any time during plating, or intermittent replenishment, in which replenishment is performed at predetermined intervals. 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.

If the number of metal grains 10.13 in the hopper 8.11 decreases, the respective metal grains 10.13 are transferred to that hopper 8.11.
13 to make up for the decrease.

Note that the feeding section 141 of the belt conveyor 14 is
The steel strip 6 is not limited to the location shown in Figure 1 in the
Alternatively, a plurality of input portions 141 may be placed at various locations in the plating bath 1. This is preferable because it promotes uniformity of the concentration of the molten metal 2 for plating in the plating bath 1.

In this way, when replenishing the components to the plating bath 1 by adding metal particles, the melting after the addition to the plating bath takes place more quickly than in the conventional method of adding ingots. It has the advantage that it takes a short time for the concentration of molten metal for plating to reach the target key value.

The reason why the An component of the plating bath 1 is replenished as A1-Zn alloy grains 13 is as follows. Plating bath 1
The bath temperature is such that the composition of the molten metal for plating is 0.1 to 5 wt%.
AJ! - In the case of Zn alloy, the temperature is about 450 to 480°C, but since the melting point of A141 body is 880°C, even if one grain is put into the plating bath 1, it will not melt in the plating bath 1.

On the other hand, if A11-Zn alloy particles are used, the melting point will be lower (fowt%A11-Zn alloy melting point 430.
°C), it melts immediately after being put into the plating bath, and the above-mentioned disadvantages do not occur. 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 (zinc in this example), 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 hopper containing molten AA grains and replenishing AIt alone.

FIG. 2 is a side view schematically showing another example of the configuration of equipment for carrying out the method of replenishing components to a plating bath according to the present invention. In the equipment shown in the figure, hoppers 8 and 11 similar to those described above are used.
and other supplementary component metal particles (e.g. PB particles, Pb-Z
A hopper 15 containing Z alloy grains, etc.) 17 is installed, and in the same manner as above, Z
The n grains 9 and AIL-Zn alloy grains 13 are charged into the plating bath 1, and a predetermined amount of metal grains 1 are also removed from the hopper 15.
7 is put into the plating bath 1. A rotary feeder 16 is installed at the opening at the lower end of the hopper 15, and the operation of the rotary feeder 16 cuts out a fixed amount of metal grains in the hopper and feeds them into the plating bath 1. In addition, similar to hopper 8.11, the hopper 15 is installed at a position separated from the plating bath by a considerable distance, and the metal particles 17 cut out from the hopper 15 are conveyed by a conveyor and thrown into the plating bath 1. Good too.

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 for plating is a Pb-A11-Zn alloy,
PB acid component may be replenished by introducing metal particles 17 using PB particles.

The melting point of pb is 327°C, and the bath temperature of plating bath 1 (
(450 to 480°C), the PB particles introduced into the plating bath 1 quickly melt and diffuse.

In the present invention, the particle size of the metal particles 10, 13.17 is not particularly limited, but is preferably about 1 to 50 mm.

If it is less than 1 mm, minute particles will float in the bath and will tend to adhere to the steel strip 6, and if it exceeds 50 mm, the accuracy of concentration adjustment will become rough. Therefore, it is appropriate that the lower limit of the particle size is 1 mm and the upper limit is about 50 mm.

Note that the metal grains 17 are not limited to PB grains, but may also be grains of Pb-Zn alloy, or grains of other metals or alloys.

Next, an example of replenishment according to the present invention according to the composition of the scrubbing bath will be explained.

For example, when six hoppers A to F are provided and the composition of metal particles in each hopper is shown in Table 2 below, the table below shows an example of replenishment from each hopper to the plating bath according to the composition of the plating bath. Shown in 3.

Table 2 Table 3 In the present invention, the amount of component replenishment can be determined by, for example, a method of timely analyzing bath components and based on the analyzed value, or a method of determining based on an estimated value determined empirically. However, as described below, it is preferable to determine the necessary replenishment concentration and the amount of decrease in the plating bath from the plating conditions, and replenish the components based on this.

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 Al component and plating conditions regarding hot-dip galvanizing using An-Zn, the following findings were obtained.

■ An A1-enriched layer (Fe2
AJZ) in the plating layer is formed.
The a degree is higher than the Al concentration in the plating bath.
Furthermore, the A1 concentration in the plating layer is not always constant with respect to the amount of plating deposited, but is a function of the amount of plating deposited, as shown in FIG. Therefore, the amount of reduction in /lIL due to carry-over can be known from the amount of plating deposited.

■ The main component of the floating dross is Fe2A 11 s, which is formed by the combination of Fe eluted from the copper strip and 82 in the plating bath.As a result of analyzing the components of this dross, AjZ
It was found that Fe=2 to 4 wt%, and the balance was Zn. Therefore, the amount of decrease in the An component due to the generation of floating dross is equal to the amount of Fe eluted from the copper strip, and by understanding this, it is possible to know the amount of decrease in A1 due to the floating dross.

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

AJ2 total decrease amount = f (V, B, C, θ, w) Zn total decrease amount = g (V, B, C, θ, w) V Ni line speed B: Plate Width C: Al concentration in bath θ: Penetration Board temperature W: From the amount of plating deposited or above, the amount of decrease in Zn and Al2 in the plating bath and Z
It has been found that the respective reduction ratios of n and AJ:t can be determined by the plating conditions (plating amount, plate width, line speed, plate temperature, etc.).

Conventionally, the Aλ concentration (
In this method, an AIL-Zn alloy ingot with an AJZ content (concentration) was simply put into a plating bath, and the replenishment concentration of AJZ was not changed depending on the plating conditions. 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 controlled within a narrower range. 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 Brimeltbots (n≧2), and C
n is the concentration of the specific component in the nth Brimeltbot, Q
If n is the supply amount from the nth Brimeltbot, then
The required replenishment amount Q'' and the required concentration C8 are expressed by the following equation.

Q′″ = Q + + Q 2 + ” ”Q
n These Q'' and C'' are determined from the above-mentioned plating conditions, and replenishment may be performed by adjusting Ql to Qn so that the values of Q'' and CM become the same.

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

<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: 0.15±0.01 t% Aλ (target straight) remaining Zn 1st hopper storage: Pure Zn grains (average particle size 5 mm) 2nd hopper storage: 2wt% An-Zn alloy grains (Average particle size 5mm) Plating conditions Plate thickness: 0.7mm Plate width: 1200mm Line speed: 120 m/min Plating deposition amount (one side): 90g/rrf' Calculating from this plating condition, the A concentration to be replenished is 0.6wt%
, replenishment amount (decreased amount of plating bath) is 30 kg/min
It is. Therefore, 21 pure Zn grains are collected from the first hopper.
kg/min.

9kg/2wt% An-Zn alloy grains from the second hopper
I resupplied win. The form of replenishment was as follows: Pure Zn grains: 630 kg, 2 wt% A
11-Zn alloy grains: 270 kg were tested intermittently at a pitch of 30 minutes.

(Example 2 of the present invention) Hot-dip galvanizing was performed under the same conditions as Example 1 of the present invention using equipment configured as shown in FIG.

The plating bath was supplied from the hopper with pure Zn grains at a rate of 21 kg/min from the first hopper, and with 2 wt% AjZ-Zn alloy grains from the second hopper at a rate of 9 kg/min.

(Example 3 of the present invention) Hot-dip galvanizing was carried out under the following conditions using equipment having the configuration shown in FIG.

Plating bath composition: 0.15±0.01wt%A10101
~0.02wt%pb Balance Zn First hopper storage: Pure Zn grains (average particle size 5mm) Second hopper storage: 2wt% AJ2-Zn alloy grains (average grain size 5mm) Third hopper storage: Pb grains (Average particle size 5 mm) Plating conditions Plate thickness: 0.7 mm Plate width +1200 mm Line speed: 120 m/min Plating deposition amount (one side): 90 g/rn' Calculating from these plating conditions, the Aj2 concentration to be replenished is 0. 8wt%
, the replenishment amount (decrease in plating bath ff1) is 30 kg/m
It is in. The replenishment form from the hopper to the plating bath is as follows:
21 kg/ll1n of pure Zn grains from the first hopper
, 9 2wt% AIL-Zn alloy grains from the second hopper
It was continuously replenished at a rate of kg/min. In addition, the amount of decrease in PB was 0.2 kg/hr, and the form of replenishment was such that PB grains were intermittently supplied from the third hopper at a rate of 1 kg at a pitch of 5 hours.

(Comparative Example) The plating bath composition and plating conditions were the same as those in Inventive Example 1, and a 0.4 wt% A℃-Zn ingot weighing 1 ton was heated at a pitch of about 33 minutes, and a 10 wt% Aj2 ingot weighing 20 kg was heated.
- Zn ingots were intermittently introduced into the plating bath for about 8 hours to replenish the components.

Changes in A1 concentration in the plating bath over time were investigated for the above-mentioned Inventive Examples 1.2.3 and Comparative Examples. The result is the fourth
Shown in the graph of figure. As is clear from this graph,
Examples 1, 2 and 3 of the present invention have less variation in the AJZ concentration during plating compared to the comparative example, and especially in Examples 2 and 3 of the present invention in which continuous replenishment was performed, there was almost no variation in the A1 concentration from the target value. Therefore, it was found that the desired plating quality could be stably obtained.

The same holds true for the PB concentration in the bath, and it was found that the PB replenishment method of Example 3 of the present invention almost eliminates concentration fluctuations and stabilizes the plating quality.

<Effects of the Invention> According to the method for replenishing components to a plating bath of the present invention, by replenishing components from a plurality of hoppers, the concentration and amount of replenishing components can be arbitrarily selected. Fluctuations in the concentration of components in the cleaning bath 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. This makes it possible to strictly control the concentration of components in the plating bath.

[Brief explanation of the drawing]

1 and 2 are diagrammatic side views each schematically showing a configuration example of equipment for carrying out the method of replenishing components to a plating bath according to the present invention. FIG. 3 is a graph showing the relationship between the amount of plating deposited and the AIL concentration in the plating layer. FIG. 4 is a graph showing the change in Afl concentration in the plating bath over time. Explanation of symbols 1... Plating bath, 2... Molten metal for plating, 3... Zinc roll, 4... Correcting roll, 5... Stabilizing gingerol, 6... Copper strip, 7 ...Snout, 8.11...Hopper, 9.12...Rotary feeder, 10...Zn
grain, 13-A A-Zn alloy grain, 14... conveyor, 15... hopper, 16... rotary feeder, 17... metal grain (pb grain) -m FIG, 3 second, 5 ( Storage capacity (g/m”)

Claims (2)

[Claims] (1) In a method of replenishing components to a plating bath when performing hot-dip plating in a plating bath containing multiple components, multiple hoppers containing metal grains of replenishment components are used to determine the required replenishment concentration and plating bath. A method for replenishing components into a plating bath, comprising replenishing components from the hopper to correspond to a decrease in the amount of components. (2) The method for replenishing components to a plating bath according to claim 1, wherein the necessary replenishment concentration and the amount of reduction in the plating bath are determined by plating conditions.