JPH01147046A - 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 removing foreign matters in the galvanizing bath contained in a main pot by filtration and floatation separating operation and clarifying the bath. CONSTITUTION:The height of the galvanizing bath 2 level in a subpot 5 is regulated to same level as a main pot by a communication part 4 and when the bath 2 of the downstream side of a partition wall 6 is returned to the main pot 1 with a circulation pump 11, the bath 2 level of the downstream side part is lowered and difference is caused between this bath level and a bath 2 level of the upstream side of the partition wall 6. Therefore the bath 2 of the upstream side is transferred quietly and smoothly to the downstream side through an inflow port 9 and the foreign matters in the bath 2 are filtered with a ceramic filter 8 without uneven clogging. The foreign matters passed through the filter 8 are allowed to float on the bath 2 level by bubbling due to a bubble blowing device 7 and are removed and discharged to the outside of the system. Therefore, when returning the bath 2 free from the foreign matters by filtration and floatation separating operation to the main pot 1 with the pump 11, the bath 2 in the main pot 1 is always kept in a clean state and thereby quality of a plated product and productivity can be improved.

Description

[Detailed Description of the Invention] <Industrial Application Field> This invention is directed to the treatment of inclusions (dross, etc.) in hot-dip galvanizing baths.
The present invention relates to a method for managing a plating bath that can efficiently remove particles and constantly maintain a state in which no inclusions are attached to plated products.

<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, Al is placed inside the main pot.
A proposal was made to increase the He1 concentration ratio in the dross by adding Al salt or a high Al-containing Zn ingot to float the dross on the bath surface, and to remove the floating dross artificially or mechanically (for example, in Japanese Patent Application Laid-Open No. 1983-1993). -59218), but the bath composition (especially AI concentration) in the main pot in which the steel plate is immersed has an appropriate value depending on the plating product (type of normal spangle product, alloy product, etc.). The above measure of varying the A1:a degree of the bath was not desirable 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 AIl 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.

Separately, a proposal has recently been made to remove dross from the hot-dip plating bath by filtering it with a ceramic filter (Japanese Patent Laid-Open No. 62-202070
issue).

This method can remove dross from the bath without changing the plating bath composition, so it can be said to be a very advantageous means for maintaining the quality of the plating product. However, it is difficult to introduce the plating bath into the filtration container. Since a power device such as a pump must be used, the plating bath in the main pot becomes cloudy, increasing the risk of dross adhering to the product.Furthermore, the flow of the bath passing through the ceramic filter is circulated in the filtration container. Because it is created by suction by a pump, the bath flow tends to be partially non-uniform, which tends to cause filter clogging, and therefore, it is necessary to constantly impinge on a portion of the filter with blowing gas to prevent clogging. There were some inconveniences.

<Means for Solving the Problems> The present invention solves the above-mentioned problems encountered in hot-dip galvanizing operations, and provides a means for managing a plating bath that can always stably obtain clean plated products free of dross adhesion. It was developed to provide a hot-dip galvanizing bath, and its characteristics are as follows: ``A pot above a hot-dip galvanizing bath is equipped with a partition wall having a plating bath inlet with a ceramic filter below the bath surface, and an air bubble blowing device. A sub-pot is arranged through a communication part, and a plating bath is introduced into the sub-pot through the communication part, and the plating bath is transferred from the plating bath inlet to the ceramic filter due to the difference in bath surface height within the sub-pot. through the plating bath to the downstream part of the partition wall, and bubble the plating bath by blowing bubbles with the bubble blowing device to separate inclusions in the plating bath, and return this plating bath to the main bond. .

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), and the steel strip (
3) is the main pot for continuously dipping and depositing the zinc layer. In the plating equipment used in the present invention, a sub pot (5) is installed in the main pot (1) via a communication portion (4). Moreover, the sub-pot (5) has a part where the hot-dip galvanizing bath (2) flows from the main pot (1) through the communication part (4) and a part that accommodates the plating bath where dross separation is performed. A partition wall (6) for partitioning the plating bath and a bubble blowing device (7) for bubbling the plating bath are provided. 8) is connected to the plating bath inlet (9) which is opened in the partition wall (6). In the drawings, the symbol α0) is a zinc roll, αυ is a plating bath circulation pump, and (2) is a heating device for maintaining the plating bath at a predetermined temperature.

Now, in the above-mentioned plating equipment, the hot-dip galvanizing bath (2) housed in the main pot (1) can be smoothly and quietly transferred to the secondary pot without requiring any special power equipment etc. due to the presence of the communication part (4). It penetrates into the pot (5) and maintains the same level of bath surface height in the secondary pot (5) as in the main pot (1).

Here, the partition wall (
6) When the plating bath on the downstream side is returned to the main pot (1), the bath level on the downstream side is lowered and the partition wall (6)
There is a difference between the bath surface and the upstream bath surface. For this reason, the partition wall (
6) The plating bath on the upstream side moves quietly and smoothly from the plating bath inlet (9) to the downstream side of the partition wall (6), but because the moving flow is uniform, the ceramic filter ( In step 8), the dross in the bath will be filtered out.

Furthermore, fine dross that has passed through the ceramic filter (8) can be deposited around the blown air bubbles by bubbling the plating bath by finely blowing inert gas from the bottom of the sub pot (5) using the air bubble blowing device (7). Since the plating bath easily floats to the bath surface, it can be easily removed from the system either manually or mechanically, and a clean plating bath is accommodated on the downstream side of the partition wall (6).

Therefore, if the above-mentioned plating bath, which has been freed of dross through filtration and flotation, is returned to the main pot (1) using the circulation pump 0υ, the hot-dip galvanizing bath (2) in the main pot (1) will always be in a clean state. There is no risk of deterioration of product quality or work problems due to dross adhesion.

In addition, FIG. 2 is a conceptual diagram showing another example of the present invention. The hot-dip galvanizing bath, which has become completely clean, is filtered through a ceramic filter (8).

That is, in the example shown in FIG. 2, the bubble blowing device (7) is placed on the upstream side of the partition wall (6), and fine dross is first floated and separated at this location in the sub pot (5). The plating bath, whose cleanliness has been increased in this way, passes through the ceramic filter (8) and flows into the downstream side of the partition wall (6) due to the difference in bath surface height as described above. 6) A clean plating bath will be accommodated on the downstream side.

Here, the ceramic ivy filter to be applied is made of materials such as An 203 type, Zr0z type, CaO type, etc., and has a porosity of 35 to 80% by volume and a pore diameter of 0.3 to 2.2.
A well-known number of about 11 is sufficient. Further, as the gas blown into the plating bath for bubbling, it is preferable to use nitrogen gas or other inert gas.

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

<Example> First, hot-dip galvanizing equipment as shown in FIG. 1 was prepared, and continuous hot-dip galvanizing of a copper strip was performed according to the procedure described above.

The ceramic filter used here was an A1□O3 type ceramic filter with a mesh roughness of 100, and the nozzle of the bubble blowing device was attached to a stainless steel pipe with an inner diameter of 10 wmφ.
A material with a large number of microholes of 1 mφ was used. Also,
The blown gas is heated (approximately 450°C) N2 gas, which passes through a ceramic filter and enters the plating bath heated and maintained at 470°C by a bath heating device from the bottom of the sub pot.
Blowing was carried out for about 10 minutes at a flow rate of 0 aL/min.

At this time, the hot-dip galvanizing bath (raw bath) from the main pot and the plating bath immediately after passing through the ceramic filter.

After pumping out each molten zinc bath from the plating bath after N2 gas bubbling and solidifying it into each 100 cJ ingot,
Cut chips from these ingots and use atomic absorption spectroscopy to
The degree of dross was investigated.

This method was applied to the investigation of dross by
As a result of component analysis of top dross and bottom dross, it became clear that both contained Fe.
Degree of dross (i.e. dross removal ability) by minute analysis
This is because we found out that it is possible to determine.

The results are shown in FIG. 3. As shown in FIG. 3, when ceramic filter filtration and gas bubbling were carried out according to the method of the present invention, the Fe concentration in the bath ranged from 0.053% by weight to 0.5% by weight. It was confirmed that the amount of dross in the bath was significantly reduced to 0.003% by weight, indicating that the dross in the bath was effectively removed.

Of course, when hot dip galvanizing of the copper strip was continued while returning the purified plating bath to the main pot, there was no unexpected clogging of the ceramic filter or other work troubles, and good quality was maintained for a long time. It was also confirmed that galvanized steel sheets can be produced.

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 conceptual diagram illustrating another example of the method of the present invention. FIG. 3 is a graph showing the results obtained in Examples. In the drawings: 1... Main pot, 2... Hot-dip galvanizing bath. 3... Steel strip, 4... Communication portion. 5... Sub-pot, 6... Partition wall. 7...Bubble blowing device. 8...Ceramic filter. 9... Plating bath inlet, 10... Zinc roll. 11... Circulation pump, 12... Heating device.

Claims (1)

[Claims] A sub-pot equipped with a partition wall having a plating bath inlet with a ceramic filter below the bath surface and an air bubble blowing device is disposed in the hot-dip galvanizing bath main pot via a communication part, and a sub-pot is provided through the communication part. Introducing a plating bath into the pot,
In this sub-pot, the plating bath is caused to flow from the plating bath inlet through the ceramic filter to the downstream part of the partition wall due to the difference in bath surface height, and the plating bath is bubbled by blowing bubbles with the bubble blowing device. A method for managing a hot-dip galvanizing bath, which is characterized by separating inclusions in the galvanizing bath and returning the galvanizing bath to the main pot.