JPH09143654A - Method for removing dross for galvanizing and device therefor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To efficiently remove dross and to recover zinc by blowing a high- temp. gas from the rear surface of a filter to remove the dross deposited on this filter at the time of separating zinc and the dross by using the filter from a dross-contg. hot dip coating liquid. SOLUTION: The plating liquid contg. the dross 19 is continuously sucked via a piping 9 from the bottom in a plating cell and is introduced into a dross removing device 10 where the zinc and the dross 19 are separated by the obliquely arranged filter 13. The molten zinc subjected to the filtration is returned to the plating cell via a piping 11. This filter 13 is provided with nozzles 15 for blowing the high-temp. gas and a variable type flow regulating plate 16 for changing the blow distribution of the high-temp. gas. When the dross 19 deposits on and in the filter 13, the introduction of the plating liquid contg. the dross 19 is stopped and the high-temp. gas of >=800 deg.C is blown through the nozzles 15 to the filter 13 to remove the dross 19 by the wind pressure. The removed dross is discharged via a withdrawal door 17 to a dross receiver 18.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method and an apparatus for efficiently and continuously removing dross generated in a galvanizing bath in a galvanized bath for producing a galvanized steel sheet.

[0002]

2. Description of the Related Art As steel sheets for automobiles, especially for North American export vehicles, rock salt is sprayed to prevent freezing in winter, so that plated steel sheets for vehicle bodies are required to have higher corrosion resistance. It suffices that zinc is coated to a set thickness, but in the plating process, dross mainly occurs due to the following causes, and if a plating thickness of more than the set plating thickness (for example, 30μ) is mixed, plating scratches will occur. And the product value is reduced in appearance. Also, the dross taken in electrochemically becomes a binary compound of Fe.Al.Zn or a ternary compound to generate a secondary current and cause corrosion.

Dross includes top dross floating on the surface of the zinc bath, floating dross floating in the liquid, and bottom dross settling on the bottom. Of these, the top dross is Fe ₂ Al that reacts with solid fine particles formed by the reaction of the steel plate and zinc, or with Al and the like contained in the liquid.
What floats on the liquid surface as a ternary compound of ₅ or Fe / Al / Zn, or finely divided zinc separated from the gas squeezing device, reacts with oxygen in the air to become zinc oxide, which also floats. I will indicate what I did. Also, bottom dross means Fe
Fine particles composed of Zn _{7 and the} like gradually grow and have a specific gravity slightly higher than that of molten zinc, so that they are deposited on the bottom of the apparatus.

At present, when a certain amount of dross is removed, the dross is usually pumped up by a long ladle made of stainless steel wire mesh according to the experience of a worker on site, drained, transferred to a container called dross pack and discarded. This stainless steel wire mesh has a very low filtration efficiency (efficiency of not discarding pure zinc as much as possible). That is, if the mesh of the wire mesh is made coarse in order to shorten the draining time, large dross will be collected in the zinc tank, and if it is made small, the filtration time will be too long. Moreover, there is a drawback that a large amount of pure zinc has to be discarded together with the dross due to clogging.

In order to improve the present situation, as a filtering method, a ceramic material is used as a filtering material (for example, JP-A-63-50454, JP-A-4-16014).
1) and as a chemical reaction method, a method of reacting an iron wire mesh with an aluminum alloy and removing it (Japanese Patent Laid-Open No. 5-17
1383) or using a recovery agent (see, for example, Japanese Patent Laid-Open No.
3-58224) and the like have been proposed.

[0006]

However, in any of the methods, the dross accumulates on the filter and is gradually clogged, which deteriorates the filtration performance and requires the recovery device to be stopped and the filter to be replaced. Frequent stoppage of this recovery device leads to an increase in manufacturing costs. Also, the filter to be replaced and discarded contains a large amount of zinc inside, which also increases the cost.

[0007] Therefore, in the industry, it has been desired to extend the life of the filter as much as possible, that is, to reduce the frequency of replacement and to reduce the cost increase.

[0008]

In view of the above circumstances, the present inventor has completed the method and apparatus of the present invention as a result of earnest research, and the feature is that the method is Hot dip galvanizing solution containing dross is pumped out from the hot dip galvanizing tank, zinc and dross are separated by a filter outside the system, and when recovering zinc, hot gas is blown from the back of the filter to deposit on the inside and inside of the filter. The dross is removed, and in the device, it is placed close to the hot dip galvanizing tank, and the filter that separates zinc and dross can be opened and closed on one side of the filter upper surface. Door, a nozzle that blows high-temperature gas toward the filter on the side surface of the lower surface of the filter that faces the openable door, and sends high-temperature gas that is blown through the nozzle. In that it has a writing hot gas generator and the pipe.

The term "pumping" as used herein includes manual pumping with a ladle or the like, suction with a pump, etc., and any method such as continuous type or batch type may be used. In short, a plating solution containing dross may be used. Say to move from inside to another place. In the present invention, zinc may be pumped from any of the upper layer portion, the middle portion and the bottom portion. That is, the dross can be top dross or bottom dross.

The filter may be a commonly used zinc filter, and may be any of stainless steel, graphite, ceramics and the like. The roughness of the eyes may be the same as the conventional one. In addition, this filter can be arranged in an inclined manner so that dross accumulated on the upper surface can easily flow during regeneration. By doing this, you will be more efficient,
Dross can be removed in a short time.

It is also preferable to use a filter made of glassy carbon as this filter. Glassy carbon has a turbostratic structure in which crystals of carbon are extremely small, and is characterized by high hardness and gas impermeability.It is composed of so-called glassy and non-oriented microstructure, The cross section is also black glass-like, which is different from a granular structure such as a general carbon material. Starting materials for carbon are phenol resin, furan resin, carbodiimide, cellulose, etc., which are gradually carbonized. The porous material used in the present invention uniformly disperses the above-mentioned starting materials and low-melting-point materials, for example, particles of acrylic, urethane, NBR, etc., and keeps them at a temperature between the melting points of both to melt the low-melting-point material. A porous body is formed by permeation and removal into a solid. It is obtained by firing and carbonizing this.

Glassy carbon has a melting point of about 3700 ° C. and is strong against heat, and has a poor affinity with dross as compared with a ceramic filter, so that dross does not enter the filter and clogging does not occur. In the experiment, the mesh is 3.5
About 5.0 mm was suitable.

[0013] To recover zinc generally means to return the molten zinc once pumped out from the plating layer to the plating layer again. However, it may be taken out as solid zinc.

The high temperature mentioned here means a temperature of 740 ° C. or higher which is the melting point of dross. However, 800 ° C. or higher is preferable for smooth operation. According to the experiment, as shown in FIG. 3, when the temperature is around 800 ° C. as a boundary, the dross removal time is drastically lengthened below that, and when the temperature is below a certain level, the dross removal cannot be completed completely. The type of gas may be any gas such as air or combustion exhaust gas. There is no need to use a special gas as the sprayed material is discarded.

The hot gas blowing step is performed after stopping the introduction of zinc containing dross into the filter. The introduction is stopped, the outlet of the dross is opened, hot gas is blown from the opposite side, and the dross is discharged from the outlet by the wind pressure. When the wind pressure of the hot gas alone does not fly, the scraping operation may be performed using a scraping tool. Since the temperature is high, it is automatically performed.

Further, this high-temperature gas is not only discharged from the outlet after the dross is blown off, but a part of the hot gas is passed through a molten plating solution containing dross and / or zinc separated and recovered is contained in the plating tank. It can also be passed through the return pipe. By doing so, since the insides of these pipes are kept at a high temperature, it becomes possible to prevent zinc containing dross from being fixed in the pipes during the regeneration process.

Next, the present explanation device will be explained. A door that can be opened and closed is a door provided at the dross outlet,
Dross is taken out from here. During normal operation, this is a part that is hermetically closed and serves as a wall surface or an inclined bottom surface of the molten zinc passage.

Further, the high temperature gas blowing nozzle is a high temperature gas injection port and may be one or plural. Further, this nozzle may be provided in a predetermined case. Further, the direction of this nozzle may be changed. Further, instead of the nozzle, a straightening plate (louver-shaped) that can adjust the blowing direction and the quantitative distribution of the high temperature gas may be provided in the case upstream of the nozzle. With this configuration, the high temperature gas can be appropriately sprayed according to the dross deposition distribution on the filter, the remaining amount, and the like. A normal method may be used to move the rectifying plate and the nozzle in the direction.

Further, a pipe for supplying a molten plating solution containing dross, which is connected to the dross separation case, and a gas discharge port provided in the vicinity of the plating tank of the pipe for returning the molten zinc after separating the dross to the plating tank are provided. By utilizing and guiding the high-temperature gas during regeneration to the pipe, it becomes possible to prevent zinc containing dross from being fixed in the pipe during the regeneration process.

[0020]

BEST MODE FOR CARRYING OUT THE INVENTION The present invention will now be described in more detail based on the embodiments of the invention shown in the drawings. FIG. 1 is a schematic view showing a use position of an apparatus for carrying out the method of the present invention. Steel plate 1 sent from the previous process is Snout 2
Is introduced into the zinc bath 6 of the plating tank 5 as a guide, pulled up through the sink roll 3 and the support roll 4, and plated in the zinc bath 6. In this example, the dross 7 is sucked from the bottom of the plating tank 5. Suction is continuously performed by the pump 8 and guided to the dross removing device 10 of the present invention through the dross pipe 9. The molten zinc separated and recovered here is returned to the plating tank by the zinc recovery pump 12 through the zinc recovery pipe 11. This is the separation step, and when the dross removal step (recovery step) is reached, the two pumps are stopped and hot gas is introduced.

FIG. 2 is a schematic view showing the inside of the dross removing device of the present invention. In the dross removing device 10, in order to remove the dross 19 accumulated on the upper surface of the filter 13, the nozzles 15 for spraying high temperature gas to the filter, the variable straightening plate 16 for changing the spray distribution of the high temperature gas, and the dross 19 accumulated on the upper surface of the filter. The high temperature gas is blown through the high temperature gas pipe 14 through the high temperature gas pipe 14. or,
The dross accumulated on the upper surface of the filter is discharged to the outside of the system and processed by the dross receiver 18. The dross pipe 9 and the zinc recovery pipe 11 are connected to the gas discharge port 2 near the plating tank.
0 is provided. This outlet 20 allows the hot gas to flow in these directions and keeps the piping between them at a high temperature.

Table 1 and FIG. 4 show various data when the production is carried out on a galvanized steel sheet production line of about 20,000 tons per month. The amount of dross deposited on the upper surface of the filter was about 20 kg on average in one step of filtration for 5 hours and 30 minutes, and could be completely removed in a regeneration time of 30 minutes. As a result, although the carbon filter was conventionally limited to three uses, no deterioration in separation performance was observed even after 100 uses. In addition, the dross piping and zinc recovery piping were heated and maintained by passing high temperature gas during regeneration, and the dross was prevented from sticking and maintenance-free was realized.

[Table 1]

[0023]

The present invention described in detail above has the following significant effects. Dross can be removed efficiently and zinc can be recovered, and the filter can be used repeatedly for a long period of time. There is almost no stoppage of the device due to replacement of the filter, which improves the efficiency of the device.

[Brief description of the drawings]

FIG. 1 is an overall schematic view showing an example of an apparatus for carrying out the method of the present invention.

FIG. 2 is an overall schematic view showing an example of the device of the present invention.

FIG. 3 is a graph showing the relationship between high temperature gas temperature and dross removal time.

FIG. 4 is a graph showing an implementation cycle when the method of the present invention is implemented.

[Explanation of symbols]

 1 strip 2 snout 3 sink roll 4 support roll 5 plating tank 6 zinc bath 7 dross 8 dross pumping pump 9 dross piping 10 dross removing device 11 zinc recovery piping 12 zinc recovery pump 13 filter 14 high temperature gas piping 15 nozzle 16 variable flow plate 17 Dross removal door 18 Dross receiver 19 Dross 20 Gas outlet

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Tetsuya Soda 3 Hikari, Kashima City, Ibaraki Prefecture Sumitomo Metal Industries, Ltd. Kashima Steel Works (72) Inventor Kenji Imae 1-12 Tomita-cho, Takatsuki-shi, Osaka No. Imae Kogyo Co., Ltd. (72) Inventor Yu Saito 1-7-12 Tomita-cho, Takatsuki City, Osaka Pref. Imae Kogyo Co., Ltd.

Claims (6)

[Claims] 1. A hot dip bath containing dross is pumped out from a hot dip galvanizing tank to separate zinc and dross by a filter outside the system, and when recovering zinc, a hot gas is blown from the back surface of the filter to obtain the filter. A method for removing dross in hot dip galvanizing, which comprises removing dross deposited on the surface and inside. 2. The method for removing dross in hot dip galvanizing according to claim 1, wherein the temperature of the high temperature gas is 800 ° C. or higher. 3. The hot dip galvanizing according to claim 1, wherein the hot gas is also passed through a pipe for passing a hot dip plating solution containing dross and / or a pipe for returning the separated and recovered zinc into a plating tank. Method for removing dross. 4. A filter which is arranged in the vicinity of a hot dip galvanizing bath and which separates zinc and dross,
A door that can be opened and closed on one side of the filter upper surface, a nozzle that blows high temperature gas toward the filter on the side of the filter lower surface that faces the openable door, and a high temperature gas that sends hot gas that is blown through the nozzle. An apparatus for removing dross in hot dip galvanizing, comprising a generator and piping. 5. A variable gas straightening plate capable of adjusting the blowing direction and distribution of high-temperature gas according to the distribution of dross deposited on the upper surface of the filter or the distribution of dross during regeneration and removal of the nozzle. The dross removing device for hot dip galvanizing according to claim 4, wherein the dross removing device is arranged on the upstream side. 6. A pipe for pumping a molten plating solution containing dross from the hot dip galvanizing tank and a pipe for returning zinc after dross separation to the hot dip galvanizing tank are connected to the upper and lower sides, respectively, and The dross removing device in hot dip galvanizing according to claim 4, wherein the pipe is provided with a gas discharge port that can be opened and closed near the inside of the hot dip galvanizing tank.