JPH09104957A - Dross removing method and device for galvanizing equipment - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a dross removing device and dross removing method for galvanizing equipment characterized by a simple construction, high durability, high efficiency of removing dross and ease of discharge of the dross to the outside of the equipment. SOLUTION: This dross removing device of the galvanizing equipment has a dross settling vessel 3 which is installed adjacently to a plating cell 1 and transporting means 4, 5, 6 which transfer a zinc melt L between the plating cell 1 and the dross settling vessel 3 at a transfer rate of >=2 to <=20m<3> /hour. The capacity of the part to be stored with the zinc melt of the plating cell 1 is >=3m<3> and the transfer rate of the zinc melt is within 10 hours and is <=40m<3> . The capacity of the part to be stored with the zinc melt of the settling vessel 3 is >=20m<3> .

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. The dross is a foreign substance (FeZn ₇ or the like) generated by the reaction of iron and zinc eluted from the steel plate to be plated, and its size is 5 to 300 μm in terms of spherical equivalent diameter. If the dross is in a quiet state with no flow of molten zinc, it remains deposited on the bottom of the plating tank. However, when the zinc melt is vigorously agitated by running of the steel plate to be plated or rotational movement of the roll in the bath, the difference in specific gravity between the zinc melt and the zinc melt is very small, so the dross is rolled up from the bottom part and becomes a steel plate to be plated. It adheres and becomes a dross surface defect.

[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 if these proposed techniques are established on a desk, in actual equipment, the mechanism is too complicated, the removal is incomplete, the durability is insufficient, and the separated dross is generated. This is because the discharge to the outside of the facility may be complicated.

A typical precipitation method is described in JP-A-53-88.
No. 633, JP-A-56-170260, JP-A-3-2
67357, JP-A-3-271353, and JP-A-4-
No. 154948 and Japanese Patent Application Laid-Open No. 5-98405.

Japanese Unexamined Patent Publication (Kokai) No. 53-88633 discloses that the zinc melt in the settling tank is cooled and dross is generated and removed in the settling tank. Further, the example shows that the size of the precipitation tank is set to about 1/4 of the size of the plating tank. However, dross is not sufficiently removed by this method.

In Japanese Utility Model Laid-Open No. 56-170260, a dross is pumped together with a zinc melt from the bottom of a plating tank, introduced into a settling box, the dross is settled and removed, and then the zinc melt can be returned to the plating tank. It is disclosed. However, this publication does not disclose means for precipitating dross, which is the most important in the present invention.

Japanese Patent Application Laid-Open No. 3-267357 discloses providing a baffle plate in a settling tank. However, the effect of promoting dross sedimentation described in this publication is weak.
That is, this gazette does not propose any fundamental measures for sedimentation removal of dross. Further, in a settling tank having a baffle plate as shown in this publication, even if dross is settled, the removal work is obstructed by the baffle plate, which is very complicated.

Japanese Unexamined Patent Publication No. 3-271353 discloses that a plurality of precipitation tanks are provided. This is functionally the same as the above-mentioned Japanese Patent Laid-Open No. 3-267357. Each of the tanks disclosed in JP-A-3-271353 corresponds to the space between the lower baffles of JP-A-3-267357.
Therefore, even in the technique disclosed in this publication, Japanese Unexamined Patent Publication No.
As with 267357, it cannot solve the dross problem.

In Japanese Patent Laid-Open No. 4-154948, in order to prevent dross from settling in the plating tank, the plating tank has a specific size and shape, and dross easily deposits and accumulates on the bottom surface of the settling tank. Thus, it has been shown that the settling tank has a sufficient flat area and depth.

However, regarding the settling tank, unlike the field of water treatment, the dross treatment does not accumulate and systematize the technology at all, and as shown below, the dross generation / growth mechanism is different from the foreign matter in the water. Since it is completely different, it cannot be said that the technique disclosed in this publication shows a concrete means for facilitating precipitation and deposition of dross.

Dross is an iron-zinc compound (FeZn ₁₃ (ζ which is produced by a chemical reaction of solute iron with zinc which is a solvent).
Phase), FeZn ₇ (δ phase), Fe ₅ Zn ₂₁ (Γ phase), etc.). Then, the solubility of iron in the zinc melt is strongly influenced by temperature, for example, 0.04% at 460 ° C., 43
It is 0.01% at 0 ° C. This change in solubility with temperature has a great influence on the generation and growth of dross in combination with the temperature itself. Furthermore, it is considered that dross undergoes phase transformation from ζ phase and δ phase to Γ phase 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 the water treatment intended for foreign foreign substances which are not reactive with water. In JP-A-5-98405, the sphere equivalent diameter is 50 μm.
It is disclosed to install a small-capacity sedimentation tank capable of removing the dross by sedimentation. However, this publication does not show any specific means for precipitating dross, and the settling tank introduced in this invention has a very low dross precipitation efficiency.

[0014]

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 removal efficiency of dross, and discharge of dross out of equipment. It is an object of the present invention to provide a dross removing device and a dross removing method in a hot dip galvanizing facility that are easy to perform.

[0015]

SUMMARY OF THE INVENTION The present invention provides a method for generating dross.
It was completed as a result of detailed studies on the growth behavior, the sedimentation behavior of dross, the size of dross, which is a practical problem as surface defects, and the structures and materials suitable for actual equipment.

[0016] First, in the present invention, in the plating part of the hot dip galvanizing equipment, a zinc melt is provided between the dross precipitation tank provided adjacent to the plating tank and between the plating tank and the dross precipitation tank. And a transfer means for transferring at a transfer rate of 2 m ³ / hour or more and 20 m ³ / hour or less, wherein the capacity of the portion of the plating tank in which the zinc melt is to be stored is 3 m ³ or more and the transfer amount of the zinc melt is 10 Provided is a dross removing apparatus in a hot dip galvanizing facility, which is within a time period and 40 m ³ or less, and a capacity of a portion of the settling tank for storing a zinc melt is 20 m ³ or more.

Secondly, according to the present invention, a dross precipitation tank is provided adjacent to the plating tank in the plating section of the zinc plating facility, and 2 m ³ / m from the plating tank to the dross precipitation tank is provided.
Transfer the zinc melt at a transfer rate of not less than 20 m ³ / hour and not less than
The volume of the zinc melt in the plating tank is 3 m ³ or more and the transfer amount of the zinc melt is within 10 hours and 40 m ³ or less, the zinc melt in the precipitation tank is 20 m ³ or more, and the zinc melt in the precipitation tank is Provided is a method for removing dross in a hot dip galvanizing facility, characterized in that the temperature of the liquid is 430 ° C. or higher and the temperature of the zinc melt in the plating tank is lower than that, and dross is precipitated and removed in the precipitation tank.

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. This is the reason why the capacity of the plating tank and the circulation amount of the melt are limited. The size of the dross, which is a practical problem as a surface defect, is about 100 in diameter.
μm or more. The larger the particle size of the dross, the more likely it is to settle. According to the actual measurement, the sedimentation velocity of dross is about 1.2 m / hour at a diameter of 100 μm and about 5 at 200 μm.
m / hour. In the settling tank, it is important to grow the dross as much as possible by lowering the melt temperature and slowing the flow rate, and to take sufficient residence time, that is, settling time. This is the reason why the capacity of the precipitation tank and the melt temperature are limited. In this way, the harmful dross is settled and removed, and further the iron content is also reduced, and then the zinc melt is returned to the plating tank.

As another skeleton of the present invention, in the above apparatus, the transfer means includes a first transfer pipe for transferring a zinc melt from the plating tank to the precipitation tank, and from the precipitation tank to the plating tank. A second transfer pipe for transferring the zinc melt and a pump provided on at least one of the first and second transfer pipes are provided, and the pump is a pump that utilizes the levitation force of bubbles. And the second transfer tube and pump are made of a ceramic material. Further, the above apparatus may further include a cooling means for cooling the zinc melt in the first transfer pipe. Furthermore, in the above apparatus, the first transfer pipe of the transfer means may have a zinc melt suction port located at the bottom of the plating tank. Furthermore, in the above method, the temperature of the zinc melt in the precipitation tank is 5 ° C. or more lower than the temperature of the zinc melt in the plating tank. Furthermore, in the above method, the liquid level of the zinc melt in the plating tank and the liquid level of the zinc melt in the precipitation tank may be substantially equal.

The adoption of a pump (hereinafter abbreviated as gas lift pump) utilizing the levitation force of bubbles and ceramics contributes to stable operation and a great improvement in durability. The reason why the plating tank and the precipitation tank have substantially the same liquid level is to facilitate the use of the gas lift pump. Further, by providing a cooling means for cooling the zinc melt in the first transfer pipe, the melt can be cooled to a temperature suitable for dross growth / sedimentation. When the melt temperature is lower than the temperature in the plating bath by 5 ° C. or more, the dross growth promoting effect becomes remarkable. Furthermore, by providing a suction port at the bottom of the plating tank, the collection and transfer efficiency of dross can be improved.

[0021]

DETAILED 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, and a second transfer pipe 5 for transferring the zinc melt from the precipitation tank 3 to the plating tank 1. And a pump 6 provided on the transfer pipe 5. In addition, the first transfer pipe 4
The cooling means 9 is provided so as to surround the induction heating device 10, and the induction heating device 10 is provided near the second transfer pipe 5 outside the precipitation tank 3.

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

During this period, iron atoms are eluted from the steel strip S to be plated. At this time, it is considered that there are two modes of elution of iron atoms: a case where the iron atoms are directly eluted from the steel strip and a case where the fine iron-zinc alloy layer formed on the surface of the steel sheet is separated and then dissolved.

In this way, the dissolved iron content reprecipitates and grows into dross. The amount of dross generated is proportional to the amount of processed steel sheet (surface area). When a 1 mm steel strip is run at a speed of 150 m / min, the generated amount is about 60 kg /
It is time. Immediately after the generation, the dross has a very small diameter of 5 to 10 μm and is in the ζ phase. This ζ phase is small and has a small difference in specific gravity from the zinc melt, so that it is difficult to settle. The melt temperature in the plating tank 1 is about 460 ° C., but this temperature is determined from the viewpoint of plating workability.

The zinc melt L is sent from the plating tank 1 to the precipitation tank 3 by a transfer pipe 4 as a transfer means. The transfer amount of the zinc melt L at this time must be an amount that can sufficiently remove dross from the plating tank 1. From this viewpoint, the lower limit of the transfer amount is specified to be 2 m ³ / hour.

On the other hand, considering only the elimination of dross, the greater the transfer amount of the zinc melt L, the better. However, as will be described later, if the transfer amount is increased, the capacity of the precipitation tank 3 must be increased correspondingly, and the hot dip galvanizing equipment itself becomes large, which is uneconomical. Therefore, from such a viewpoint, the upper limit of the transfer amount of the zinc melt is specified to be 20 m ³ / hour.

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

The time required for the generated dross to grow to a diameter of 100 μm, which is a harmful size in the stirring environment in the actual operation of the plating tank 1, is about 10 hours according to the analysis of the growth behavior of the dross in the actual operation. Is estimated to be Therefore, in the present invention, from this point of view, the capacity of the portion of the plating tank 1 in which the zinc melt is to be stored is 10 times the zinc melt transfer amount.
It is specified that the time is less than or equal to minutes. Further, when the amount of zinc melt in the plating tank 1 exceeds 40 m ³ , a stagnation region of the melt flow appears at the bottom corner of the plating tank 1, and dross will stay there for a long time. Plating tank 1 to avoid
The volume of the portion where the zinc melt of (1) is to be stored is defined as 40 m ³ or less. On the other hand, in order to avoid the growth of the pores, it is desirable that the capacity of the plating tank 1 be small, but the lower limit is 3 m ³ due to restrictions in manufacturing the device.

Dross 8 in the melt transferred to the settling tank 3
Are grown and precipitated here. The basic idea for increasing the sedimentation removal rate is to make the dross itself as large as possible in size and specific gravity and to ensure a sufficient sedimentation time. The compound phase of the dross changes with the growth, the specific gravity gradually increases from the ζ phase to the δ phase, and further to the Γ phase, and the difference in specific gravity from zinc gradually increases and the sediment tends to settle.

The conditions for accelerating the growth of dross are that the temperature of the melt in the precipitation tank is lower than the temperature in the plating tank and that the flow of the melt is as gentle as possible. By lowering the melt temperature, the degree of supersaturation of iron as a solute is increased and the dross as a precipitated crystal is gently grown. The upper limit of the melt temperature is set to the melt temperature in the plating tank because if it exceeds this temperature, the dross growth promoting effect does not appear.

A lower melt temperature is desirable for promoting the growth of dross. The melt temperature is 5 ° C below the temperature in the plating tank
When it is lower than the above value, the growth promoting effect becomes remarkable. However, since the melting temperature of zinc is 420 ° C, there is a lower limit for stable operation, and from that viewpoint, 430 ° C is substantially the lower limit.

Needless to say, the basis for slowing the melt flow in the settling tank, that is, for decreasing the flow velocity is to increase the capacity of the settling tank. One of the reasons for setting the lower limit of the zinc melt volume in the settling tank to 20 m ³ is to obtain a slow flow velocity suitable for dross growth. Needless to say, the basis for ensuring the settling time is to increase the capacity of the settling tank. The larger the value, the higher the removal rate.

Another reason for setting the lower limit of the zinc melt capacity of the settling tank to 20 m ³ is below 100 μm in diameter.
This is because the harmful dross that has grown to the above can not be sufficiently precipitated. This is just for reference, but try estimating the required capacity of the settling tank for water treatment.

In the case of water treatment, the removal rate in the case of an ideal normal flow is given by the Kamp's equation, removal rate = sedimentation rate / (inflow of water / surface area of sedimentation tank). From this formula, the diameter of the dross is 100 μm
In this case, the depth of the sedimentation tank is 1 m, the inflow of zinc melt is 20 m ³ / hour, and the volume of the sedimentation tank at which complete removal is achieved is 16 m ³ .

As described above, the larger the capacity of the settling tank 3 is, the higher the settling efficiency is. However, considering the facility cost, the capacity is preferably 100 m ³ or less. The melt from which the dross has been removed is transferred by the second transfer pipe 5 to the plating tank 1
Is returned to. As the pump 6 for transfer, it is preferable to use a gas lift pump that utilizes the floating force of bubbles. Nitrogen gas is supplied to the pump via conduit 7. Since the lift of the gas lift pump is small, the smaller the liquid level difference between the plating tank 1 and the precipitation tank 3, the better. If possible, it is desirable that they are almost equal.

The gas lift pump has a tubular body as its main structural member and has a simple structure, so that it can be made into ceramics. Metals are unsuitable as a material for the transfer means because the molten zinc causes severe corrosion of molten metal. For stable operation, the material of the transfer tube is preferably ceramics.

The types of ceramics used for these are graphite, BN, AIN, SiN, Al ₂
Examples include O ₃ type, SiC type, SiO ₂ type, ZrO ₂ type, and MgO type.

The pump 6 includes first and second transfer pipes 4, 5
Either one-it should be incorporated. The transfer pipe, which is not equipped with a pump, transfers the melt by a siphon method. In order for this method to be easily realized, it is essential that the liquid levels of the melt in the plating tank 1 and the precipitation tank 3 are substantially equal.

A pump may be incorporated into both the first and second transfer pipes 4 and 5. However, in this case, the first
And a means for controlling both pumps so that the transfer amounts in the second transfer pipes 4 and 5 become equal is indispensable.

The transfer means 4 to the settling tank has a structure provided with a cooling means 9 for cooling the melt. The cooling means 9 cools the melt to a temperature suitable for dross growth / sedimentation, for example, by air cooling.

It is desirable that the temperature of the melt returned to the plating tank 1 be substantially equal to the temperature of the melt in the plating tank in order to stabilize the plating operation. Induction heating device 10
Is a heating device for this purpose and heats the melt sucked by the pump 6.

According to such a dross removing apparatus, the dross contained in the zinc melt L transferred to the settling tank 3 can be effectively settled and removed despite the simple structure, and plating can be performed. The zinc melt containing almost no dross can be returned to the tank 1. Therefore, the dross-like surface defect of the galvanized steel sheet can be effectively prevented. Further, since the zinc settling tank 3 is not provided with a member such as a baffle plate which hinders the dross removal, the dross can be easily discharged. Further, since the structure is simple, the durability of the device is high.

[0043]

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 cross-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]

1 ... plating tank, 2 ... sink roll, 3 ... precipitation tank,
4 ... First transfer pipe, 5 ... Second transfer pipe, 6 ... Pump, 7 ... Conduit, 8 ... Dross, 9 ... Cooling means, 10
...... Induction heating device.

Claims (7)

[Claims] 1. A dross settling tank provided adjacent to a plating tank in a galvanizing section of a hot dip galvanizing facility, and a zinc melt 2 between the plating tank and the dross settling tank.
a transfer means for transferring at a transfer rate of not less than m ³ / hour and not more than 20 m ³ / hour, and the capacity of the portion of the plating bath where the zinc melt is to be stored is 3 m.
³ or more and within 10 hours of transfer of zinc melt and 4
0 m ³ or less, and the capacity of the portion of the settling tank for storing the zinc melt is 20 m 3.
A dross removing device in a hot dip galvanizing facility, characterized in that the number is ³ or more. 2. The first transfer pipe for transferring the zinc melt from the plating tank to the precipitation tank, and the second transfer pipe for transferring the zinc melt from the precipitation tank to the plating tank. And a pump provided on at least one of the first and second transfer pipes, the pump is a pump that utilizes the levitation force of bubbles, and the first and second transfer pipes and the pump are ceramic materials. The dross removing device in the hot dip galvanizing facility according to claim 1, wherein the dross removing device is formed of 3. The dross removing device in a hot dip galvanizing facility according to claim 1, further comprising cooling means for cooling the zinc melt in the first transfer pipe. 4. The melting apparatus according to claim 1, wherein the first transfer pipe of the transfer means has a zinc melt suction port located at the bottom of the plating tank. Dross removing device in galvanizing equipment. 5. A dross settling tank is provided adjacent to the plating tank in the galvanizing section of the galvanizing facility, and 2 m ³ / hour or more from the plating tank to the dross settling tank 2
The zinc melt is transferred at a transfer rate of 0 m ³ / hour or less, the volume of the zinc melt in the plating tank is set to 3 m ³ or more, and the transfer rate of the zinc melt is set within 10 hours and 40 m ³ or less. The zinc melt is set to 20 m ³ or more, the temperature of the zinc melt in the settling tank is set to 430 ° C. or higher and the temperature of the zinc melt in the plating tank is set to be lower than or equal to, and dross is precipitated and removed in the settling tank. Method for removing dross in hot dip galvanizing equipment. 6. The method for removing dross in a hot dip galvanizing facility according to claim 5, wherein the temperature of the zinc melt in the precipitation tank is 5 ° C. or more lower than the temperature of the zinc melt in the plating tank. . 7. The hot dip galvanizing facility according to claim 5, wherein the liquid level of the zinc melt in the plating tank and the liquid level of the zinc melt in the precipitation tank are substantially equal to each other. Method for removing dross.