JPH01147047A - Controlling method for galvanizing bath - Google Patents

Abstract

PURPOSE:To maintain good plating workability for a long period and to improve quality of a plated product and productivity by raising Al concn. in a galvanizing bath contained in a subpot and also blowing bubbles to float and separate dross in the bath and returning this bath to a main pot. CONSTITUTION:The bath 2 in a main pot 1 is introduced into a subpot 8 from the main pot 1 with a circulation pump 4 and a Zn ingot 9 contg. Al is introduced and dissolved by heat of a heater and dross in the bath is allowed to react with Al and its specific gravity is made light and dross is made easy to float on the bath 2 level. At this time, dross is rapidly floated on the bath 2 level by blowing plenty of fine bubbles from a bubble blowing device 7 provided to the lower part of the subpot 8 and the floated dross is removed to the outside of the system. Thereby the clean and proper-temp. bath 2 in the subpot 8 in which Al concn. has been regulated to proper value by reduction of Al concn. due to reaction with dross is returned to the main pot 1 with a pump 5. Consequently, the bath 2 in the main spot 1 is always proper in composition and temp. and cleanly kept and thereby quality of a plated product and productivity can be improved.

Description

[Detailed Description of the Invention] <Industrial Application Field> The present invention provides a plating bath that can efficiently remove dross from a hot-dip galvanizing bath and constantly maintain a state in which dross does not adhere to plated products. This relates to management methods.

<Background technology> For example, the "dross" that tends to be generated in the plating bath during continuous hot-dip galvanizing of steel sheets not only adheres to the steel sheets and causes a significant deterioration of quality, but also works on the line to suppress the adhesion as much as possible. It is also a major factor in hindering productivity as it requires work to be done at a reduced speed.

However, as a countermeasure against this dross, Af,
Ill! A proposal has been made to increase the Al concentration ratio in the dross by adding salt or high M-containing Zn ingots, float the dross on the bath surface due to the resulting decrease in specific gravity, and remove the floating dross artificially or mechanically (e.g., Kaisho 50-5921
8), but the bath composition in the main pot in which the steel plate is immersed (
In particular, the A1 concentration) has an appropriate value depending on the type of plating product (normal spangle product, alloy product, etc.), and the above-mentioned measure of varying the Al1f71 degree of the plating bath in the main pot was not preferable in terms of product quality. Furthermore, if this measure is taken, the bottom dross in the main pot will become floating dross during the transition period when it floats to the bath surface due to the decrease in specific gravity due to the increase in Al concentration, and the floating dross will adhere to the steel plate and temporarily damage the plated steel plate. There was also the problem that it was difficult to do anything to prevent the quality from deteriorating.

<Means for Solving the Problems> Therefore, the present inventors have devised a method to solve the above-mentioned problems seen in hot-dip galvanizing operations and to constantly and stably obtain clean plated products free of dross adhesion. As a result of conducting research from various viewpoints in order to provide a means for managing plating baths, the following findings (al to (C)) were obtained.

That is, (a) When considering only the separation of dross generated in the hot-dip galvanizing bath, the above-mentioned proposed method of adding M to the plating bath and flotation-separating the dross is extremely effective. However, as mentioned above, if this method is carried out in the main pot in which the material to be plated is immersed, it may cause a sudden change in the composition of the plating bath, or the adhesion of dross to the plated product during the transition period when the dross floats to the bath surface. It is impossible to prevent this from occurring and adversely affecting the performance of the plated product. However, if a sub-pot is provided separately from the main pot, the hot-dip galvanizing bath introduced into the sub-pot is subjected to the above method to separate the dross, and then the dross is circulated back to the main port. , a sudden change in the composition of the plating bath in the main pot does not occur, and furthermore, it is possible to suppress a sudden increase in floating dross in the plating bath in the main pot, even if only temporarily.

(b) However, simply adding 82 to the hot-dip galvanizing bath does not cause the floating separation of dross to proceed so quickly.
As a result, the circulation of the plating bath to the main pot is delayed, which tends to cause a decrease in work efficiency. However, if non-reactive gas is blown into the bottom of the sub pot as fine bubbles to bubble the hot dip galvanizing bath containing M, This accelerates the reaction in the subpot (M-enrichment reaction to the bottom dross), and the fine dross that takes time to float adheres around the blown air bubbles and quickly rises to the bath surface together with the air bubbles. The bath can be managed without adversely affecting work efficiency.

(C) In addition, a sub-pot equipped with a heating device for melting the ingot and maintaining the bath temperature is used, and A1 added for dross separation is included in the zinc ingot for replenishing the hot-dip galvanizing bath. By dissolving the dross in the sub pot, the floating separation of the dross is carried out more smoothly, and temperature changes in the plating bath in the main pot are also prevented, making it possible to permanently continue good plating work.

This invention was made based on the above knowledge, and [
A sub-pot equipped with a heating device and a bubble blowing device is attached to the main pot of the hot-dip galvanizing equipment via a plating bath circulation device, and an Al-containing zinc ingon for replenishment is dissolved in the plating bath in the sub-pot. Therefore, A in the plating bath in the sub-pot
It is characterized by raising the temperature by 74 degrees, blowing air bubbles from the bottom of the sub-pot to float and separate the dross in the bath, and returning the hot-dip galvanizing bath to the main pot.

Hereinafter, the method of the present invention will be explained in detail with reference to the drawings.

FIG. 1 is a conceptual diagram showing an example of an implementation situation of the present invention.
Code (1) houses the hot-dip galvanizing bath (2),
3) is the main pot for continuously dipping and depositing the zinc layer. In the plating equipment used in the present invention, the main pot (1) is equipped with, for example, a circulation pump +41.
(A sub-pot (8) equipped with a heating device (6) and a bubble blowing device (7) is installed via a plating bath circulation device composed of 51, etc.). is also equipped with an ingot charging machine α for charging the zinc ingot (9).In the drawing, the symbol aυ is a zinc roll, and α2 is a machine for keeping the plating bath in the main pot at a predetermined temperature. It is a heating device.

Now, for controlling the plating bath, the hot-dip galvanizing bath pumped out from the main pot (1) by the circulation pump (4) is led to the sub-pot (8). Next, this secondary pot (8
) A zinc ingot (9) is charged from an ingot feeder 0ω into a hot-dip galvanizing bath housed in the hot-dip galvanizing bath, and is melted by thermal energy from a heating device (6).

The zinc ingot (9) to be charged is for replenishing the molten zinc consumed by the plating work, but as described above, it contains A1 for floating dross. Therefore, as the ingot melts, Al also smoothly dissolves and diffuses into the plating bath, making the plating bath composition higher in Al fM than that in the main pot (1). For this reason,
The bottom dross and floating dross contained in the hot-dip galvanizing bath react with the AE, and their specific gravity becomes lighter, making them easier to float to the bath surface.

At this time, a large number of fine bubbles are blown into the bath from the bubble blowing device (7) installed at the bottom of the sub pot (8), so that the reaction of converting the bottom dross in the bath to floating dross progresses, and at the same time The dross adheres around the air bubbles and quickly floats to the bath surface. The floating dross is then manually or mechanically removed from the system.

Subsequently, either the dross is removed and cleaned and the A1 concentration is reduced due to reaction with the dross, or a zinc ingot containing substantially no Al is further added to the M
The molten zinc in the sub-pot at the appropriate temperature, when the concentration has reached the appropriate value,
It is returned to the main pot (11) by a circulation pump (5) or the like.

Therefore, the hot-dip galvanizing bath (2) in the main pot (1) is always kept in an appropriate composition and temperature and in a clean state, and there is no risk of deterioration of product quality or work problems due to dross adhesion.

Here, it is preferable that the bubbles blown in from the bottom of the sub-pot do not react with the plating bath, such as N2 gas, Ar gas, Co! Fine bubbles made of inert gas such as gas are preferred. Further, the amount of M contained in the zinc ingot is not particularly limited, and may be determined in light of the operational results while also taking into account the amount of supplementary zinc.

Next, the present invention will be explained in more detail with reference to Examples.

<Example> First, Al concentration: 0.12% by weight, PB concentration: 0.1
100 kg of a hot-dip galvanizing bath containing 0% by weight and 0.05% by weight of Fe was pumped out from an actual steel strip continuous hot-dip galvanizing pot and placed in a separate pot equipped with a heating device.

Next, the plating bath was heated, and then a zinc ingot containing 10% by weight of AN, 0.10% by weight of Pb, and 0.05% by weight of Fe was added to the plating bath.
After adjusting the concentration to 3.0% by weight, using a stainless steel pipe (inner diameter: 10φ) with many small holes of 0.1φ, bubbles of N2 gas heated to about 450℃ were introduced from the bottom of the pot. I blew it. Note that the flow rate of N2 gas from the pipe was 100/min, and the blowing time was about 10 minutes.

After the bubble injection is finished, this time A is 〇Shigekage, Pb
A zinc ingot having a composition of: 0.10%, Fe: 0.05% or less was introduced into the plating bath.
Component adjustments were made until the density became 0.12-fold.

This series of steps is shown in Figure 2.
The state of dross in the plating bath was investigated at each time point shown in (b), (c), and (ii). In addition, to investigate the dross in the bath, the hot-dip galvanizing bath was pumped out at each of the above points, solidified into a 15 cal ingot, and then each sample was cut in half to determine the number of dross per cut surface l ctl. Adopted.

The results are shown in Fig. 3.As shown in Fig. 3, when adding E-containing zinc ingot to the bath according to the method of the present invention and bubbling the bath by blowing fine bubbles, dross is produced each time. In the end, the amount of dross in the plating bath was reduced by 9
It can be confirmed that as much as 8% can be removed.

In addition, when we prepared an actual hot-dip galvanizing equipment as shown in Figure 1 and continued continuous hot-dip galvanizing work on steel strips according to the procedure explained earlier, there were no particular work problems (,
It was also confirmed that plated steel sheets of good quality could be manufactured over a long period of time.

<Summary of Effects> As explained above, according to the present invention, it is possible to maintain good plating workability over a long period of time while constantly keeping the dross in the main pot low. It brings about industrially useful effects, such as greatly contributing to improvements in quality and productivity.

[Brief explanation of the drawing]

FIG. 1 is a conceptual diagram illustrating an example of the method of the present invention. FIG. 2 is a process diagram showing the steps adopted in the example and the timing of collecting dross investigation samples. FIG. 3 is a graph showing the results obtained in Examples. In the drawing, ■...Main bot 2...Hot-dip galvanizing bath. 3... Steel strip, 4,5... Circulation pump. 6.12...Heating device, 7...Bubble blowing device. 8... Sub-pot, 9... Zinc ingot. 10...Ingot feeder, 11...Zin roll.

Claims (1)

[Claims] A sub-pot equipped with a heating device and a bubble blowing device is attached to the main pot of the hot-dip galvanizing equipment via a plating bath circulation device, and an Al-containing zinc ingon for bath replenishment is dissolved in the plating bath in the sub-pot. This method is characterized by increasing the Al concentration in the plating bath in the sub-pot, and floating and separating the dross in the bath by blowing air bubbles from the bottom of the sub-pot, and returning the hot-dip galvanizing bath to the main pot. How to manage a galvanizing bath.