JP2797910B2 - Continuous hot-dip plating method and dross removing apparatus used in the method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a continuous hot-dip galvanizing method in which a strip-shaped metal member such as a strip (hereinafter abbreviated as "strip") is continuously immersed in a hot-dip zinc bath and hot-dip galvanized. The present invention relates to a method and an apparatus for preventing dross in a bath from adhering to the surface of a steel strip.

[0002]

2. Description of the Related Art In a continuous hot-dip galvanizing equipment for strip, in order to perform hot-dip galvanizing, as shown in FIG. 6, an annealed strip 1 is sucked into a plating bath 3 through a snout 2 and rolled in a bath. 4, the strip 1 is inverted and pulled up vertically, and immediately after the strip comes out of the plating bath 3, the molten zinc adhering to the strip surface is wiped off with an air knife 5 to adjust the thickness of the hot-dip plating layer. ing.

The plating bath 3 is generally box-shaped and has a horizontal bottom. Further, in the plating bath, a wake is caused quasi-steadily by the passage of the strip 1 and the rotation of the roll in the bath. Further, in the plating bath, an induction heating device 6 is used to adjust the bath temperature, whereby a circulating flow is generated quasi-steadily. When the passing speed (line speed), size, and the like of the strip 1 are changed, the strip 1 is constantly flowing while the strength and direction of the circulating flow and the circulating flow slightly change.

[0004] Further, in the plating bath, Fe is leached from the strip 1, the metal roll 4 and a frame supporting the same, and this is combined with zinc to form FeZn.
A dross whose main component is ₇ is generated. This dross
In the initial stage of its formation, the particle size is as small as several μm, and it floats or migrates in the tank together with the bath flow, etc., but gradually grows and grows to several tens to several hundred μm, and deposits on the bottom of the bath (hereinafter, referred to as This dross is called a bottom dross). When the accumulation amount of the bottom dross increases, the number of cases where the bottom dross is again wound up by the accompanying flow such as the running of the strip 1 and the rotation of the roll, adheres to the strip surface, and significantly deteriorates the surface quality (this is called a dross defect) ). For this reason, since the dross particle size that appears as a dross defect of the strip 1 is several tens of μm or more, removal of this bottom dross and prevention of winding-up are major issues in the quality of the hot-dip galvanized steel sheet.

[0005] In recent years, the need for corrosion resistance especially for automobile bodies has increased, and the ratio of surface-treated steel sheets used for automobile bodies has been increasing. In particular, hot-dip galvanized steel sheets can be supplied at low cost and have excellent rust prevention properties, and therefore, their application sites have been extended to exterior parts (so-called bodies). However, since the surface of the steel sheet for exterior is required to be beautiful, the problem of the dross defect described above becomes more and more evident, and it is required to solve it immediately.

Conventionally, in order to prevent this dross defect from occurring, two or more plating baths are installed and replaced periodically (for example, every 10 to 20 days), and the dross deposited on the bottom of the used plating bath is used. The scooping method is repeated. In a facility having only one plating bath, the line is suspended for several days, and cleaning and removal are performed once every two to three months.
There are places that go around. In any case, in order to perform the botrodros removal operation, naturally, it is necessary to suspend for several to several tens of hours or more, and therefore, in reality, continuous and stable production cannot be continued. Also, even during use between 10 and 20 mouths, the amount of deposited dross gradually increases, so in the middle to late use period, the line speed may be lowered to suppress the dross from being wound up, Various operational restrictions must be imposed, such as reducing the operation of the induction heating device for controlling the bath temperature.

[0007] In view of the above, various measures have recently been considered to reduce the number of pauses and continue continuous and stable production. For example, if the plating bath used is Al
To add 2FeZn ₇ + 5Al → Fe ₂ Al ₅ +14
There is a method of causing the reaction of Zn to cause Fe ₂ Al ₅ to float to collect bottom dross, and a method of collecting and depositing dross by pumping it with a pump or N ₂ bubble. 170260 No. 2, Kaikai
146153). However, the former has a problem in that a part of Al remains in the plating bath and Al% increases, so that a product defect such as poor alloying is likely to occur. In the latter method, the molten zinc bath containing the bottom dross is drawn out of the system to remove the dross, and then returned to the plating bath. For this reason, problems have arisen in the measures for solidifying molten zinc, the continuous removal method and capacity of the recovery and removal device, the efficiency of dross collection from the plating tank, the installation space, and the like.

Further, Japanese Patent Application Laid-Open Nos. 4-220149 and 4-221050 disclose a constitution in which a settling tank is incorporated in a circulation system for pumping dross with a pump. And a method for efficiently separating the dross by increasing the diameter of the dross. However, even in this method, heating and heating for adjusting the bath temperature are performed.
Since a cooling function is required, inconveniences such as an increase in production cost, an increase in the scale of the apparatus, and measures against evaporated zinc at a high temperature are considered.

In any case, fine particles sensitive to a flow change having a specific gravity of about 3 to 6% are recovered from opaque high-temperature liquid metal, and molten zinc is safely and stably pumped up and circulated to easily dross. The reality was that there was no definitive method, and there was no decisive factor. In addition, in the case of a system that has multiple plating tanks and is used for replacement, the fixing device of the pumping and removing device is restricted, and the pumping piping and return piping are attached and detached, the method of treating molten zinc remaining in the piping, etc. The problem remains.

As described above, several techniques relating to pumping dross → separation / removal → return of the cleaning bath have been proposed, but many of them are only proposed and actually used. There are few examples.

The following three problems can be considered as the background. i) The hot-dip galvanizing bath has a roll in the bath, frames supporting the bath, a steel strip passing through the bath forms a blind spot, and the like.
For this reason, the installation position and movable range of the pumping pipe, return pipe, nozzle and the like are extremely restricted. This makes it difficult to efficiently collect dross deposited on the entire bottom surface of the plating tank.

Ii) The scale of the pumping and circulating system is relatively large due to the settling tank, the number of pumps, the heat compensation function, and the like, and it is difficult to additionally install the existing equipment. Moreover, in recent years, there are many facilities that install a plurality of plating tanks.
Attachment and removal of pumping pipes and return pipes, and treatment of molten zinc remaining in the pipes have not been established, including work safety aspects.

Iii) In any of the dross separation methods such as sedimentation separation and separation using a filter, an apparatus or an operation procedure for recovering only the separated dross from the apparatus has not been established. For example, in the case of the sedimentation method, the bread plate or the bucket is taken out and sealed with the main unit at the time of attachment and removal (penetration of molten zinc into the bread plate and the back surface of the bucket). Lacks realism.

[0014]

DISCLOSURE OF THE INVENTION The inventors of the present invention, in Japanese Patent Application No. 5-20950, aim at preventing the bottom dross from being deposited immediately under a roll in a bath by controlling the flow in a hot-dip coating tank. We proposed a hot-dip plating method equipped with a guide plate. This method guides the accompanying flow of the steel strip and the accompanying flow of the rolling roll in the direction from the position where the steel strip enters the plating tank to the roll in the bath in a direction away from the steel strip, and thus sinks. Dross is characterized in that it concentrates intensively on the bottom of the plating tank on the entry side of the steel strip and does not roll up again.

According to this method, the guide plate completely prevents re-winding and floating of dross during use of the plating tank,
As long as the sign is not buried, the effect is exhibited.
By reducing the number of times of replacing the plating bath to the limit, it is possible to produce a plated steel sheet having a beautiful surface property without dross defects.

Further, in this method, if the dross accumulated during the operation can be continuously separated and removed, the plating bath does not need to be replaced, and the dross removing work that has been performed off-line after the replacement is eliminated. be able to. In addition, there is no need to install two or more plating baths, so that facility construction costs and operation costs can be significantly reduced.

The present inventors have thoroughly pursued a continuous hot-dip galvanizing method and apparatus free from dross defects, developed the guide plate system shown in Japanese Patent Application No. 5-20950, and developed a complete system. I thought it needed to be established.

The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a continuous hot-dip plating method for efficiently collecting dross deposited on the bottom of a plating bath and a dross recovery apparatus used in the method. Is what you do.

Another object of the present invention is to provide a continuous hot-dip galvanizing method and a simple hot-dip galvanizing method in which the additional equipment is simple, the separated dross is easily collected, and the work safety is taken into consideration. A dross recovery device to be used is provided.

[0020]

According to the continuous hot-dip plating method of the present invention, a strip-shaped metal member is introduced into a hot-dip plating solution in a hot-dip bath, and the strip-shaped metal member introduced into the hot-dip plating solution is rolled in a bath. The step of lifting from the hot-dip bath by the rotation of the bath, and the accompanying flow generated by the introduction of the strip-shaped metal member and the accompanying flow generated by the rotation of the roll in the bath, the guide member disposed in the hot-dip bath, from the strip-shaped metal member Guide the dross contained in the hot dip plating solution to the bottom of the hot dipping bath by introducing the dross contained in the hot dip plating bath, and immerse the lower suction port of the riser pipe into the hot dipping bath by introducing the hot dipped metal member Then, a step of sucking the molten plating solution from a lower suction port of the riser pipe by a vacuum pump and a gas lift pump, and filtering dross contained in the sucked molten plating solution. And separating removed using the steps of returning the molten plating solution dross was separated off, the hot dipping the bathtub through downcomer communicates with the riser,
It has.

[0021] In the hot-dip plating bath of the present invention,
The dross removing device that removes the deposited dross has a hot-dip plating solution suction port at the bottom and a gas lift pump inside, a riser pipe that can suck the hot-dip plating solution in the hot-dip bath, and a hot-dip plating at the bottom. A liquid discharge opening is opened, the upper part is connected to the upper part of the riser pipe, and a molten plating liquid descending pipe capable of discharging the molten plating liquid sucked from the riser pipe, and a molten plating liquid flowing from the riser pipe to the descending pipe. A dross removing filter removably attached to the passage, wherein when the hot-dip plating solution sucked from the rising pipe is discharged from the down pipe, the dross contained in the hot-dip plating solution is removed by the filter. I have to.

[0022]

According to the present invention, dross is intensively deposited on the bottom of the hot-dip bath by the guide member at the strip entry side, the riser is installed in the hot-dip bath, and the lower suction port of the riser is dross-deposited. Position. Then, the plating solution is sucked from the lower suction port of the ascending pipe by the action of the gas lift pump, and the dipped molten plating solution is separated and removed from the plating bath by a filter, and the molten plating solution from which the dross has been removed is subjected to hot-dip plating by the downcomer pipe. Return to bathtub. The filter is removably mounted and replaced when the dross accumulates.

[0023]

An embodiment of the present invention will be described. FIG. 1 shows a schematic configuration of a continuous hot-dip galvanizing apparatus applied to the method of the present invention, in which (a) is a transverse sectional view and (b) is a longitudinal sectional view. This apparatus arranges a roll 4 in a bath in a hot-dip plating bath 3,
The snout 2 is disposed above the hot-dip bath 3.
Then, the strip 1 that has been heat-treated in the annealing furnace 20 is guided into the hot-dip bath 3 by the snout 2, and then guided out of the hot-dip bath 3 by the rotating roll 4 in the bath. This causes the strip surface to be hot-dip plated. The thickness of the hot-dip zinc coated on the strip 1 is adjusted by the Sure knife 5. A guide member 21 is disposed in the hot-dip plating bath 3. This guide member 21
Is equivalent to the guide plate shown in Japanese Patent Application No. 5-20950,
At a position between the introduction position of the strip 1 and the roll 4 in the bath and below the strip 1, an extension surface of the guide member 21 is provided.
It is provided at an angle that intersects the traveling direction of the strip 1 between the introduction position of the strip 1 and the roll 4 in the bath. And introduction of strip 1 and roll 4 in bath
The guide member 21 guides these accompanying flows in a direction away from the strip and deposits dross contained in the molten plating solution at the bottom of the hot-dip bath 3 on the strip introduction side. Let it. This guide member 21 can be pulled up from the hot-dip plating bath along the direction of the arrow as shown in FIG.

Further, a dross removing device 22 is disposed in the hot-dip plating bath 3. The dross removing device 22 can be installed either vertically or inclinedly, and can be mechanically pulled up and stored by an automatic elevating device when the plating bath is replaced, as shown by a broken line in FIG. The filter 15 containing the dross D can be collected from the dross removing device 2 along the dross collection guide 26. Further, the dross removing device 22 can reciprocate by the rail 23 in the width direction of the hot-dip bath 3 as shown in FIG.
In the figure, 24 is a zinc ingot, and 27 is a vacuum pump.

FIG. 2 shows the structure of the dross removing device. This device is made of metal such as stainless steel, but may be of an internal refractory lining type. This device is
The downcomer 11 is arranged in parallel with the riser 10, and both are connected to the upper tank 1.
It is connected by two. The riser pipe 10 has an opening at the lower end, and a nozzle 13 is provided here, and dross D deposited in the hot-dip plating bath 3 is sucked from the nozzle 13 in a wide range.
A gas lift pipe 14 forming a gas lift pump is inserted into the riser pipe 10. Then, the molten plating solution is sucked into the riser pipe 5 by blowing an inert gas such as N ₂ or Ar from the gas lift pipe 14. The gas may be blown from the inner peripheral wall of the riser as shown in FIG. 3A, or may be a structure in which the gas lift pipe 14 'is arranged outside and the tip is inserted from the lower end of the riser as shown in FIG. 3B. Good. The downcomer 11 is freely changeable in length, direction and the like and can be replaced. Further, as the arrangement of the riser and the downcomer, as shown in FIG. 5, a structure in which the lower part of the downcomer 11 'is inserted into the riser 10 may be used.
At the downcomer inlet (A section) installed in the upper tank 12,
A bucket-shaped filter 15 is installed so as to be inserted into the downcomer 5. The filter 15 is formed of glass fiber, ceramic fiber, metal (such as stainless steel) mesh, or the like. As shown in FIG. 4A, the fixing structure of the filter 15 is such that a projection is provided on the mounting portion 12a of the upper tank 12, and the support portion 15a of the filter 15 is brought into point contact with
Alternatively, as shown in FIG.
This is a simple fixing structure in which a concave portion is provided in a, and a convex portion is provided in the supporting portion 15a, and the mounting portion 12a and the supporting portion 15a are fitted to each other. Further, the mounting portion 12 of the filter 15
a has a built-in heater 25, so that even after the plating solution reflux operation is stopped in the dross removing device, local heating and holding is performed so that the contact portion with the filter 15 becomes 450 ° C. or higher. I have. This makes it possible to always maintain the zinc that has entered the contact surface between the device and the filter in a molten state, and to easily remove and attach the filter 15 after the operation is stopped. This fixation method allows for a small amount of leakage (leak between the filter and the downcomer that is in point contact, etc.) and facilitates desorption rather than passing the entire volume of the circulating bath through the filter. It is important.

Next, the upper tank 12 has a closed structure, and has an exhaust port 16 for an inert gas charged for a gas lift pump and an opening door 17 for removing a filter. Exhaust can also be performed by a steam eject, a vacuum pump, or the like. In addition, the heater 25 is built in the inner peripheral wall of the tank,
It is possible to control in synchronization with the plating bath temperature (about 460 ° C.). Further, a bath surface sensor (not shown) is provided in the upper tank 7, and the gas lift amount can be controlled by the bath surface sensor. That is, by using the above-described apparatus, bath reflux can be easily started and stopped, and particularly when the operation is stopped, molten zinc does not remain in the apparatus due to gravity. Moreover, since the filter 15 can be easily attached and detached, and only the dross D can be collected, a compact apparatus can be designed if the frequency of attachment / detachment is ignored. In addition, by combining with the guide member, dross can be efficiently removed only by disposing the pumping nozzle only on the entrance side of the steel strip in the plating bath. This position has relatively little restriction on the installation space and movable range in the bathtub, and facilitates additional installation on existing equipment.

When the dross D accumulates in the filter 15, the opening door 17 is opened, and the filter 15 is opened.
1 and is collected outside as shown in FIG.

Next, a specific example of the dross removing apparatus of the present invention will be described. For example, the depth of the plating bath is 2000 mm, and the inner diameter of the riser is 200 A. The head is set to 1000 mm from the plating bath surface.

N ₂ gas is supplied at 4 Nm ³ / min (240 Nm
³ / h) When injected, the ring flow rate of molten zinc is about 2.5 m ³
/ Min (150 m ³ / h). This value is
Because it is difficult to measure the actual annular flow rate, wood metal and N ₂
It is estimated from simulation experiments with gas. Further, the amount of dross deposited is approximately 0.3 to 0.5 based on the service period of the plating bath and the actual dross removal performance off-line.
Calculated as 8T / D. That is, if it is considered that the amount to be removed by the present apparatus may be the same as the amount to be deposited, dross is 0.1 volume.
It is only necessary to be able to separate about 1 m ³ / D, and it is sufficient to prepare a 50 cm ³ bucket filter. Since the removal and attachment of the bucket filter of the present apparatus is easy, the collection operation is about once a day.

[0030]

According to the present invention, since the dross is removed by circulating the plating solution, the inside of the plating bath can always be kept clean with simple equipment, and the filter can be attached and detached. The replacement eliminates the need to replace the plating tank and remove dross off-line after the replacement. Further, it is not necessary to stop the line for replacing the plating tank, and it is possible to continuously and stably produce a beautiful galvanized steel sheet having a good surface texture. further,
Since the dross is deposited on the bottom of the plating bath at the entry side of the band-shaped metal member, the dross may be removed, thereby facilitating the design of the apparatus. In addition, when a new line is installed, it is not necessary to install two or more plating baths, and it is possible to greatly reduce equipment operation costs and energy costs for maintaining baths.

[Brief description of the drawings]

FIG. 1 is a schematic explanatory view showing one embodiment of the present invention,
(A) and (b) show different examples.

FIG. 2 is an enlarged sectional view of a main part of FIG.

FIG. 3 is an enlarged view of a lower end portion of the riser tube of FIG.
(B) shows different examples.

FIGS. 4A and 4B are enlarged views of a portion A of FIG. 1, and FIGS.

FIG. 5 is a diagram showing another embodiment of the arrangement of the riser and the downcomer.

FIG. 6 is a schematic explanatory view of a conventional device.

[Explanation of symbols]

1 ... strip, 2 ... snout, 3 ... plating bath, 4 ...
Roll in bath, 5 ... Air knife, 6 ... Induction heating device, 10
... up pipe, 11 down pipe, 12 upper tank, 13 nozzle, 14 gas lift pipe, 15 filter, 16 ...
Exhaust port, 17 ... Opening door, 18 ..., 19 ..., 20 ... Annealing furnace, 21 ... Guide member, 22 ... Dross removing device, 23 ... Rail, 24 ... Zinc ingot, 25 ... Heater, 26 ... Degree loss recovery guide, 27 ... Vacuum pump

──────────────────────────────────────────────────続 き Continued on the front page (72) Noboru Taguchi, 1-2-1, Marunouchi, Chiyoda-ku, Tokyo Nippon Kokan Co., Ltd. (72) Masahiro Iwabuchi 1-1-2, Marunouchi, Chiyoda-ku, Tokyo Nippon Kokan (56) References JP-A-4-323354 (JP, A) JP-A-4-232235 (JP, A) JP-A-3-31460 (JP, A) JP-A-4-649 (JP, A) U) Shokai Sho 61-191466 (JP, U) (58) Field surveyed (Int. Cl. ⁶ , DB name) C23C 2/00-2/40

Claims (3)

(57) [Claims] 1. A step of immersing a lower suction port of a riser pipe in a hot-dip plating bath of a hot-dip plating bath, and sucking the hot-dip plating solution from the lower suction port into the riser pipe by evacuation and a gas lift pump. Separating and removing dross contained in the hot-dip plating solution using a filter, and returning the hot-dip plating solution from which the dross has been separated and removed to the hot-dip bath through a downcomer communicating with the riser. A continuous hot-dip plating method comprising: 2. A step of introducing a strip-shaped metal member into a hot-dip plating solution in a hot-dip bath, and pulling up the strip-shaped metal member introduced into the hot-dip plating solution from the hot-dip bath by rotating a roll in the bath. The accompanying flow generated by the introduction of the band-shaped metal member and the accompanying flow generated by the rotation of the roll in the bath are guided by the guide member arranged in the hot-dip plating bath in a direction away from the band-shaped metal member, and are included in the molten plating solution. Depositing the dross to be deposited on the bottom of the hot-dip bath with the band-shaped metal member introduced, and immersing the lower suction port of the riser pipe on the hot-dip bath side of the hot-dip bath with the band-shaped metal member introduced, and raising the dross from the lower suction port by evacuation and a gas lift pump A step of sucking the hot-dip plating solution into the pipe, a step of separating and removing dross contained in the sucked hot-dip plating solution using a filter, and a step of separating the dross. METHOD continuous hot dipping with the removed melted plating solution, and a step of returning to the hot dipping the bathtub through downcomer communicates with the riser. 3. A dross removing apparatus for removing dross floating and deposited in a hot dip bath, wherein a hot dip plating solution suction port is opened at a lower portion and a vacuum pump and a gas lift pump are provided. A rising pipe capable of sucking the molten plating solution, and a molten plating solution discharge port opened at a lower portion, an upper portion connected to an upper portion of the rising tube, and a molten plating solution descending tube capable of discharging the molten plating solution sucked from the rising tube. A dross removing filter removably mounted in the path of the hot-dip plating solution from the riser to the downcomer, when the hot-dip plating solution sucked from the riser is discharged from the downcomer into the hot-dip bath. And a dross removing device for removing dross contained in the hot-dip plating solution with the filter.