JPH1072653A - Dross removing device for galvanizing equipment and method therefor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a dross removing device for galvanizing equipment which is simple in construction, has high durability, a high removing efficiency of dross and facilitates the discharge of the dross to the outside of the equipment and a dross removing method. SOLUTION: The dross removing device of the galvanizing equipment has a dross settling vessel 3 disposed adjacently to a plating cell 1 and transfer pipings 4, 5 for transferring molten zinc between the plating cell 1 and the dross settling vessel 3. These transfer pipes 4, 5 have straight pipe parts 4a, 5a and bent pipe parts 4b, 5b. These straight pipe parts 4a, 5a have a taper of 1/200 to 1/25 and the bent pipe parts 4b, 5b have curvature of >=2 times the diameter of the pipings and have the taper above the taper of the straight pipe parts 4a, 5a.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a dross removing apparatus and method in a hot dip galvanizing facility.

[0002]

2. Description of the Related Art Dross surface defects are the most serious of the surface defects of galvanized steel sheets. Dross is a foreign substance (FeZn ₇ or the like) generated by a reaction between iron and zinc eluted from a steel sheet to be plated, and has a diameter of 5 to 300 μm in terms of a spherical shape. This dross will accumulate at the bottom of the plating tank if it is stationary without the flow of molten zinc. However, since the molten zinc is agitated by the running of the steel sheet, the rotation of the roll in the bath in the plating tank, or the natural convection of the molten zinc generated by the zinc ingot, the dross with a very small difference in specific gravity from the zinc melt is at the bottom. The steel sheet cannot be deposited on the steel sheet, or even if it is deposited, it is rolled up and adheres to the plated steel sheet, which becomes a surface defect of the hot-dip galvanized steel sheet by dross.

[0003] Conventionally, in order to remove dross, a very large number <
The proposal has been made. These proposals include a method in which a zinc melt is pumped out of a plating tank to precipitate dross, a method in which filtration is performed, a method in which Al is added and flotation is performed, and the like.

[0004] However, despite many proposals, none of the conventional proposals have been put to practical use. The reason is that even though these proposed technologies can be realized on a desk, there are many problems in the complexity, durability and operability of the mechanism in actual equipment, and it is impossible to actually adopt them. is there.

A typical precipitation method is described in JP-A-53-88.
No. 633, JP-A-56-170260, JP-A-3-2
67357 and JP-A-4-154948.

Japanese Patent Application Laid-Open No. 53-88633 discloses that a zinc melt in a sedimentation tank is cooled to form dross in the sedimentation tank.
It is disclosed to remove the precipitate. Further, in the embodiment, the size of the sedimentation tank is set to about １ ／ of the size of the plating tank.
Is shown. However, dross cannot be sufficiently removed by this method.

[0007] Japanese Utility Model Application Publication No. Sho 56-170260 discloses that dross is pumped together with a zinc melt from the bottom of a plating tank and introduced into a sedimentation box, and after the dross is settled and removed, the zinc melt is returned to the plating tank. It has been disclosed. However, this publication does not describe means for precipitating dross.

Japanese Patent Application Laid-Open No. 3-267357 discloses providing a baffle plate in a settling tank. But,
The effect of promoting dross sedimentation described in this publication is small. That is, this gazette does not propose any fundamental measures for sedimentation removal of dross.

Japanese Patent Application Laid-Open No. 4-154948 discloses that in order to prevent dross from settling in a plating tank, the plating tank is made to have a specific size and shape, and dross is easily deposited and deposited on the bottom of the settling tank. Thus, it has been shown that the sedimentation tank has sufficient plane area and depth.

By the way, regarding the sedimentation tank, in the dross treatment, unlike the field of water treatment, the technology is not accumulated and systematized at all, and the dross generation and growth mechanism is different from the foreign matter in the water as shown below. Because they are completely different, the techniques described in these prior art documents cannot be said to show a specific means for making dross easily sedimented.

[0011] dross iron zinc compound iron generated in zinc and the chemical reaction is a solvent which is a solute (FeZn _13, F
eZn _7, an Fe etc. ₅ Zn _21). And the solubility of iron in the zinc melt is greatly affected by temperature, for example,
It is 0.04% at 460 ° C and 0.01% at 430 ° C. The change in the temperature of the solubility and the change in the concentration of the solute have a great influence on the formation and growth of dross. In addition, dross is thought to undergo a phase transformation as it grows. Different phases have different physical properties such as density. That is, the sedimentation behavior is different. The above does not occur in water treatment for exogenous foreign substances having no reactivity with water.

[0012]

SUMMARY OF THE INVENTION The present invention has been made in view of the above circumstances, and has a simple structure and high durability, high dross removal efficiency, and is unlikely to cause operational trouble. An object of the present invention is to provide a dross removing apparatus and a dross removing method in a hot dip galvanizing facility.

[0013]

SUMMARY OF THE INVENTION The present invention provides a method for generating dross.
It was completed as a result of detailed studies on growth behavior, dross sedimentation behavior, and structures and materials suitable for practical equipment. That is, the present invention provides a dross sedimentation tank provided adjacent to a plating tank, and transfers and circulates a zinc melt between the plating tank and the dross sedimentation tank in the plating section of the hot-dip galvanizing equipment. Transfer means, the transfer means comprising a pipe for transferring the zinc melt, having a straight pipe portion and a curved pipe portion, wherein the straight pipe portion has a taper of 1/200 to 1/25. A dross removing apparatus in a hot-dip galvanizing facility, wherein the curved pipe portion has a curvature not less than twice the pipe diameter and has a taper greater than the taper of the straight pipe portion.

Further, in the above dross removing apparatus, there is provided a dross removing apparatus in a hot dip galvanizing facility, wherein the cross-sectional shape of the pipe in the transfer means is circular or vertically long elliptical.

Further, in any one of the above dross removing apparatuses, there is provided a dross removing apparatus in a hot-dip galvanizing facility, wherein the pipe in the transfer means is made of ceramics.

Further, in any one of the above-mentioned dross removing apparatuses, there is further provided a dross removing apparatus in a hot-dip galvanizing facility, further comprising a temperature control means for controlling a temperature of the pipe in the transfer means. I do.

Further, in the plating section of the hot-dip galvanizing equipment, a dross sedimentation tank provided adjacent to the plating tank, and the zinc melt is transferred and circulated between the plating tank and the dross sedimentation tank. Transport means,
The transfer means includes a pipe for circulating the zinc melt, the pipe having a straight pipe portion and a curved pipe portion, wherein the straight pipe portion is 1 /
A dross removing apparatus in a hot-dip galvanizing facility, having a taper of 200 to 1/25, the curved pipe portion having a curvature of twice or more the pipe diameter, and having a taper greater than the taper of the straight pipe portion. The dross removing method used, wherein an amount of the molten zinc to be transferred is set to 50% or less of a cross-sectional area of the pipe, and a portion other than the molten zinc of the pipe is filled with an inert gas to transfer the molten zinc. The present invention provides a dross removing method for a hot dip galvanizing facility.

Further, in the dross removing method using the dross removing apparatus, the temperature of the molten zinc transferred from the plating tank to the settling tank by the transferring means may be 5 or more during the transfer.
Provided is a method for removing dross in a hot-dip galvanizing facility, wherein the temperature is controlled so as to decrease by at least ℃.

The operation of the present invention configured as described above is as follows. Dross is generated in the plating tank according to the throughput of the steel sheet, and is sent to the settling tank before the dross grows and becomes harmful. The important thing is to circulate the molten zinc for a long time. Although this seems easy at first glance, it is difficult to actually circulate the molten zinc for a long time without clogging the piping.

In order to prevent clogging of the piping, it is generally considered to heat the piping itself. However,
When the molten zinc is heated by heating the pipe itself, the iron solubility is increased as described above, and dross may be lost during transfer. Further, since the steam pressure of molten zinc rapidly rises as the temperature rises, a large amount of fumes becomes a problem. This is also considered to be one of the reasons that the conventional proposal has not been put to practical use. Furthermore, since the pipe is heated unevenly in a normal heating state, the pipe is thermally deformed and the flow of the molten zinc cannot always be kept good.

Therefore, the present inventors have conducted many experiments in order to prevent such clogging of the pipe. As a result, it has been found that it is important to appropriately adjust the taper of the pipe and the radius of curvature of the curved portion of the pipe in order to prevent clogging of the pipe. Regarding the taper of the straight part of the pipe,
If the taper is smaller than 1/200, there is a risk that a horizontal portion may be generated due to thermal deformation of the pipe. If a horizontal portion is formed, molten zinc may solidify in that portion when an emergency stop is performed. In addition, when the taper exceeds 1/25, the flow of the molten zinc becomes faster, so that the molten zinc splashes in the pipe, and when the molten zinc flows into the plating tank or the sedimentation tank, the surrounding gas is entrained to generate new impurities. There is a risk. Therefore, in the present invention, it is necessary to set the taper of the straight pipe portion of the pipe to 1/200 to 1/25. Since the clogging is more likely to occur in the curved pipe portion, the taper is set to be equal to or larger than that of the straight pipe portion, and the curvature is set to be twice or more the pipe diameter.

Further, when the inside of the pipe used for the transfer means is filled with molten zinc, the flow resistance increases, and in the case of an emergency, there is a possibility of solidification. Therefore, it is desirable to flow the molten zinc into the pipe in an unfilled state. . At this time, a smooth flow can be formed by setting the filling rate to 50% or less of the sectional area of the pipe. In order to maintain such a filling rate, the portion of the pipe other than the molten zinc may be filled with an inert gas to transfer the molten zinc. In this case, the flow rate of the molten zinc in the pipe fluctuates, but by setting the cross-sectional shape of the pipe to a circular or vertically elliptical shape, a constant flow rate of the molten zinc can be ensured even at a low flow rate or a high flow rate. Therefore, the possibility that the molten zinc stagnates or solidifies in the pipe is extremely reduced.

Further, by providing the temperature control means for controlling the temperature of the pipe, the dross removal efficiency can be improved by utilizing the above-mentioned change in the solubility of iron. In this case, it is necessary to use 5 pipes from the plating tank to the sedimentation tank.
It is desirable that there be a temperature drop of not less than 0 ° C and a temperature rise of not less than 5 ° C in the piping from the precipitation tank to the plating tank.

Further, by using ceramics for the piping material, there is no problem of zinc erosion, and thermal deformation due to heating of the piping is reduced as compared with the case where metal is used, so that the above-mentioned effect can be effectively achieved.

[0025]

DESCRIPTION OF THE PREFERRED EMBODIMENTS A specific example of the present invention will be described with reference to FIGS. FIG. 1 is a sectional view showing a dross removing apparatus according to an embodiment of the present invention, and FIG. 2 is a plan view thereof. The hot dip galvanizing equipment has a plating tank 1 in which a zinc melt L is stored, and a dross removing device. The dross removing device includes a sedimentation tank 3 provided adjacent to the plating tank 1.
A first transfer pipe 4 for transferring the zinc melt from the plating tank 1 to the precipitation tank 3, a second transfer pipe 5 for transferring the zinc melt from the precipitation tank 3 to the plating tank 1, Transfer piping 5
And a pump 6 provided at Further, a temperature control device 9 for controlling the temperature of the pipe is provided so as to surround the first transfer pipe 4. An induction heating device 10 is provided near the second transfer pipe 5 outside the precipitation tank 3.

The steel sheet S to be plated out of the heating furnace is conveyed to the plating tank 1 via the snout 11,
Is immersed in the zinc melt L stored in the tank. Then, after the steel sheet S is turned by the sink roll 2 provided in the plating tank 1, the steel sheet S passes in the direction indicated by the missing mark.

During this time, iron atoms elute from the steel sheet S to be plated. As the form of elution of iron atoms at this time, there is a case where the powdery substance attached to the steel sheet and the minute iron-zinc alloy layer formed on the steel sheet surface are separated and dissolved, or when there is a case where it is directly eluted from the steel sheet. Conceivable.

In this way, the dissolved iron content reprecipitates and grows into dross. The amount of dross generated is proportional to the throughput of the steel sheet (total surface area of the passing steel sheet). The amount generated when a 1 mm steel plate is passed at a speed of 120 m / min is:
Approximately 50 kg / hour. The dross immediately after generation is extremely small, having a diameter of 5 to 10 μm. At this size, the sedimentation velocity is slow. The molten zinc temperature during the operation in the plating tank 1 is 455 to 465 ° C., and this temperature is determined by the temperature and heat capacity of the steel sheet to be passed, the amount of heat radiated from the plating tank, and the amount of heating to the plating tank.

The molten zinc L is sent from the plating tank 1 to the precipitation tank 3 by a transfer pipe 4 as a transfer means. At this time, the amount of the molten zinc L to be transferred must be sufficient to remove dross from the plating tank 1. Assuming that the dross sedimentation speed is the terminal speed, it is about 6 hours, though it depends on the depth of the plating tank used. From this viewpoint, it is preferable that the transfer amount is specified to be equal to or larger than the flow rate obtained by dividing the capacity of the plating tank 1 by 6.

On the other hand, considering only the elimination of dross, the greater the transfer amount of the molten zinc L, the better. However, as will be described later, when the transfer amount increases, it is required to increase the capacity of the settling tank 3 accordingly, and the hot-dip galvanizing equipment itself becomes large, which is uneconomical. On the other hand, a large dross sedimentation speed that causes a quality defect is approximately one hour. Therefore, from such a viewpoint, it is preferable that the upper limit of the transfer amount of the zinc melt is a flow rate obtained by dividing the capacity of the precipitation tank 3 by one hour.

The inlet of the melt in the transfer tank 4 in the plating tank 1 is desirably at the bottom of the plating tank 1. This is because the dross concentration at the bottom is higher than that at the top, and the dross collection and transfer efficiency is higher.

The dross 8 in the molten zinc transferred to the precipitation tank 3 is grown and precipitated here. The basic idea for increasing the sediment removal rate is to reduce the sedimentation time and iron solubility so that the dross itself can be as large as possible. For that purpose, the temperature of the molten zinc in the settling tank 3
By making the temperature lower than the temperature of the molten zinc in the plating tank 1, the iron solubility of the molten zinc decreases, and dross grows easily.
In this case, 5 mm is set in the pipe from the plating tank 1 to the settling tank 3.
It is desirable that there be a temperature drop of not less than 5 ° C. and a temperature rise of not less than 5 ° C. in the piping from the precipitation tank 3 to the plating tank 1.
Thereby, the dross removal efficiency can be improved.

In the present invention, the straight pipe portions 4a and 5a of the transfer pipes 4 and 5 are formed with a taper of 1/200 to 1/25. The curved pipe portions 4b and 5b have a diameter of 2 mm.
It has twice or more the curvature and has a taper equal to or greater than the straight pipe portions 4a and 4b. Thereby, pipe clogging can be effectively prevented. When flowing molten zinc through the transfer pipes 4 and 5, the amount of the molten zinc to be transferred is set to 50% or less of the cross-sectional area of the transfer pipes 4 and 5, and portions other than the molten zinc of the pipes are inert gas. It is preferred to fill and transfer the molten zinc. This ensures a smooth flow,
The clogging of the pipe can be more effectively prevented. Further, it is preferable that the cross-sectional shape of the transfer pipes 4 and 5 be circular or vertically long elliptical. As a result, a constant flow rate of the molten zinc can be ensured at both a low flow rate and a high flow rate, and the possibility that the molten zinc stagnates or solidifies in the transfer pipes 4 and 5 is extremely reduced. The transfer pipes 4 and 5 are preferably made of ceramics. As ceramics used for this, SiO ₂ , SiC, Al ₂ O ₃ , Si ₃
N ₄ and BN are exemplified.

Next, the actual operation results will be described.
Here, the transfer pipes 4 and 5 were made of ceramics (made of BN) having a circular cross section with an inner diameter of 100 mm, and the taper of the straight pipe portion was set to 1/100. The curved pipe portion was bent vertically with a curvature twice the pipe diameter. The transfer rate of molten zinc is 10 m ³ / h, and the transfer rate of molten zinc is 2
5%. The heating of the transfer pipe 4 was controlled such that the temperature of the molten zinc was reduced by 5 ° C. or more from the entrance of the plating tank 1 to the exit of the precipitation tank 3.

However, if the temperature of the molten zinc is 430 ° C. or lower, local solidification may occur. Therefore, the minimum temperature of the molten zinc was 430 ° C. Further, in the transfer pipe 5 returning from the precipitation tank 3 to the plating tank, heating was performed by the heating device 10 and the pipe heating device in the precipitation tank 3 so that the molten zinc at 460 ° C. could return to the plating tank 3.

As a result, after one month of continuous use, the dross amount in the plating tank was 10% or less of the conventional amount, and it was confirmed that there was no dross that would cause a problem in quality. On the other hand, it was confirmed that 90% of the amount of dross that had conventionally settled in the plating tank was deposited in the settling tank. During the use of this apparatus, the hot-dip galvanized steel sheet had no significant surface defects.

[0037]

As described above, according to the present invention,
A dross removing device in hot-dip galvanizing equipment, which has a simple structure and high durability, has high dross removal efficiency, and easily discharges dross to the outside of the facility. A dross removing method in a galvanizing facility can be realized.

[Brief description of the drawings]

FIG. 1 is a sectional view showing a dross removing device according to an embodiment of the present invention.

FIG. 2 is a plan view showing a dross removing device according to one embodiment of the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 ... Plating tank 2 ... Sink roll 3 ... Settling tank 4 ... First transfer pipe 4a, 5a ... Straight pipe part 4b, 5b ... Bent pipe part 5 ... Second transfer pipe 6 ... Pump 8 Dross 9 Temperature control device 10 Induction heating device L Molten zinc S Steel plate

Continuing on the front page (72) Inventor Keishi Yamashita 1-2-1, Marunouchi, Chiyoda-ku, Tokyo Nihon Kokan Co., Ltd. (72) Inventor Masahiro Iwabuchi 1-2-1, Marunouchi, Chiyoda-ku, Tokyo Nihon Kokan Stock In company

Claims (6)

[Claims] 1. A dross sedimentation tank provided adjacent to a plating tank in a plating part of a hot-dip galvanizing facility, and a transfer for transferring and circulating a zinc melt between the plating tank and the dross sedimentation tank. Means, comprising: a pipe for transferring a zinc melt, the pipe having a straight pipe portion and a curved pipe portion, wherein the straight pipe portion is 1 /
A hot-dip galvanizing facility, characterized in that it has a taper of 200 to 1/25, the curved pipe portion has a curvature of at least twice the pipe diameter, and has a taper greater than the taper of the straight pipe portion. Dross removing device. 2. A dross removing apparatus in a hot-dip galvanizing facility according to claim 1, wherein the cross-sectional shape of the pipe in the transfer means is circular or vertically elliptical. 3. The dross removing apparatus in a hot-dip galvanizing facility according to claim 1, wherein the pipe in the transfer means is made of ceramics. 4. The dross in a hot-dip galvanizing facility according to claim 1, further comprising a temperature control means for controlling a temperature of the pipe in the transfer means. Removal device. 5. A dross sedimentation tank provided adjacent to a plating tank in a plating section of a hot-dip galvanizing facility, and a transfer for transferring and circulating a zinc melt between the plating tank and the dross sedimentation tank. Means, wherein the transfer means comprises a pipe for circulating the zinc melt, the pipe having a straight pipe portion and a curved pipe portion, wherein the straight pipe portion is 1/200 to
It has a taper of 1/25, and the curved pipe portion has a diameter of 2
A dross removing method using a dross removing device in a hot-dip galvanizing facility, having a curvature of twice or more, and having a taper equal to or greater than the taper of the straight pipe portion, wherein the amount of the molten zinc to be transferred is reduced by the amount of the pipe. A dross removing method in a hot-dip galvanizing facility, wherein the cross-sectional area is set to 50% or less, and a portion other than the molten zinc of the pipe is filled with an inert gas to transfer the molten zinc. 6. A dross sedimentation tank provided adjacent to a plating tank in a plating section of a hot-dip galvanizing facility, and a transfer for transferring and circulating a zinc melt between the plating tank and the dross sedimentation tank. Means, wherein the transfer means comprises a pipe for circulating the zinc melt, the pipe having a straight pipe portion and a curved pipe portion, wherein the straight pipe portion is 1/200 to
It has a taper of 1/25, and the curved pipe portion has a diameter of 2
A dross removing method using a dross removing device in a hot-dip galvanizing facility, having a curvature of twice or more and having a taper equal to or greater than the taper of the straight pipe portion, wherein the dross is transferred from a plating tank to a sedimentation tank by the transfer means. A dross removing method in a hot-dip galvanizing facility, wherein the temperature is controlled so that the temperature of the hot-dip zinc is lowered by 5 ° C. or more during transfer.