JPH0953164A - Hot dip metal plating method and device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent the leakage of molten metal and the gushing of gas into metal bath and to produce a hot dip metal plated steel sheet having excellent quality by adjusting the gaseous pressures of the upper and lower surfaces of the molten metal bath with an inert gas at the time of rising the steel sheet in the molten metal and subjecting the steel sheet to hot dip metal plating. SOLUTION: The oxygen free steel sheet 1 from an annealing furnace 16 is perpendicular directionally changed by a deflector roll 7 and is passed into an upper pressure chamber 13 while the leakage of the gaseous pressure is prevented by a sealing device 8. This steel sheet is passed through a sealed aperture 11 in the bottom of a plating bath vessel 12 contg. the molten metal 2 of Zn, etc., to be plated and in risen in the molten Zn 2, by which the surfaces are plated with the molten Zn; thereafter, the Zn coating weights on the surfaces are adequately adjusted by a plating amt. adjusting device 6. A nonoxidizing gas, such as H2 or N2 , is forcibly fed from a supplying port 14 into a pressure chamber 13 disposed in the lower part of the plating bath vessel 12 in this stage to regulate the pressure of the molten Zn in the sealed aperture 11, by which the leakage of the molten Zn 2 from the sealed aperture 11 and conversely the rise of the nonoxidizing gas in the pressure chamber 13 in the sealed aperture 11 and the consequent occurrence of plating defect are prevented.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a molten metal plating method and apparatus used in the production of hot dip galvanized steel sheets, and more particularly, to dipping the steel sheet continuously through the molten metal bath from the opening at the bottom of the container. The present invention relates to a plating method and apparatus using a so-called aerial pot which is pulled up to perform plating.

[0002]

2. Description of the Related Art Molten metals (eg Zn, Al, Mg, M)
(n, Pb and its alloys) A general manufacturing method of a plated steel sheet is as follows. That is, after the cold-rolled steel sheet surface is cleaned and annealed, the steel sheet temperature is adjusted to a temperature suitable for plating, and the steel sheet is immersed in a plating bath without being oxidized. Excess molten metal adhering to the steel plate surface in the bath is removed by an adhering amount adjusting device such as gas wiping to adjust the adhering amount, and then cooled as it is.

FIG. 13 shows a conventional hot-dip galvanized steel sheet manufacturing apparatus. The steel sheet 1 is drawn into the molten metal bath 2 through a tubular portion called a snout 4, is pulled up in the vertical direction by a sink roll 3, and is plated through a support roll 5 and an adhesion amount adjusting device 6. In such a conventional apparatus, when deposits such as dross are formed on the surface of the sink roll 3, a flaw is created on the surface of the steel plate 1 or the deposit migrates to the surface of the steel plate 1 and becomes a surface defect. There is. In many cases, since the sink roll 3 does not have a drive system, when the steel plate 1 slips and the rotation of the sink roll 3 becomes discontinuous, a scratch is formed on the surface of the steel plate 1. When the plating operation is continued for a further long time, the surface of the sink roll 3 becomes uneven, and therefore it is necessary to take it out of the molten metal bath for maintenance.

As described above, the conventional hot-dip galvanized steel sheet manufacturing apparatus has a drawback that the operability is deteriorated due to the presence of equipment in the bath such as a sink roll. Also, the presence of bath equipment such as sink rolls makes the molten metal bath extremely large. Therefore, when several types of hot-dip galvanized steel sheets are manufactured on the same plating line, the hot-dip bath may be completely replaced or the part of the bath may be assembled and another plating solution may be added depending on the switching of operations. There is a need. The former requires a long time to replace due to structural problems of the device, while the latter requires a relatively slow pumping speed of the device, such as a pump, and a long time to adjust the components of the molten metal bath due to the replacement. It requires a great deal of expense, time and labor. Therefore, there are limits to the types of products that can be manufactured on the same plating line. Further, since the bath capacity is large, there is a problem that a large amount of dross is generated and a steel sheet surface defect is easily generated.

On the other hand, a technique has been developed in which molten metal is held in a container having an opening at the bottom, a steel plate is dipped from below the opening and then pulled up and plated.
In this case, preventing leakage of molten metal from the bottom opening of the container has been an important issue. For example, in Japanese Patent Laid-Open No. 4-356, the opening at the bottom of the container is made extremely narrow, and the distance between the side wall of the opening (sealing plate) and the steel plate is 0.0.
The thickness of 5 to 1 mm prevents the molten metal from flowing down and leaking from the container, and it is simply stated that a static pressure is applied downward. In Japanese Patent Laid-Open No. 4-36446, in the case of molten metal, especially molten zinc, the technique of Japanese Patent Laid-Open No. 4-356 is further provided with a plunger and a bath gauge to improve the bath surface level from the viewpoint of plating quality. Is controlling. Japanese Unexamined Patent Publication (Kokai) No. 63-109148 proposes an aerial pot by circulation, but here, it is briefly described that static pressure is applied to a steel strip introducing portion as an assisting force. Further, Japanese Patent Laid-Open No. 63-109149 proposes an aerial pot using an electromagnetic pump, but here, it is briefly described that static pressure is applied to a steel strip introduction portion as an assisting force. Further, JP-A-63-
Japanese Patent No. 303045 proposes an aerial pot by electromagnetic force, but here it is stated that gas is injected to a steel strip passage position.

[0006]

The problem with the plating method using the air pot is, firstly, how to hold the metal bath, and how to prevent the molten metal from flowing downward from the bottom opening. is there. Also, when applying gas pressure to the lower surface of the metal bath, it is very important to prevent the lower gas from entering the bath and to prevent the gas from being caught in the steel strip. When gas invasion occurs, the interface becomes unstable and often causes leakage of molten metal. In addition, gas is often entrained in the steel strip to cause non-plating.

Further, particularly in hot dip galvanizing, from the viewpoint of plating quality, the time during which the steel sheet is immersed in the molten metal bath is important, and the bath surface height of the molten metal bath is adjusted to an arbitrary value. It is also important to be able to manage it strictly. The inventors of the present invention have obtained the following findings from an experiment of holding a molten metal bath without using a seal due to electromagnetic force in a plating technique using an air pot.

A) If the head pressure determined by the height of the molten metal bath surface and the pressure of the gas below the opening of the bottom of the molten metal container are equal, the lower interface of the molten metal is stable and the molten metal bath is optional. B) can be maintained at the bath surface height of b) The difference between the head pressure of the molten metal and the pressure of the gas below the bottom opening of the molten metal container is the surface tension of the molten metal and the difference between the molten metal and the steel plate or container. If it exceeds a certain value determined by the contact angle and the distance between the molten metal container and the steel sheet, the lower interface of the molten metal bath becomes unstable, causing leakage of molten metal and ejection of gas.

When the prior art is reexamined based on the above findings, the prior art is completely insufficient for stable holding of a molten metal bath having an appropriate bath surface height. For example, in the technique disclosed in Japanese Patent Laid-Open No. 4-356, static pressure is simply applied, but there is no indication of the value to be taken, allowable error, means for measuring and adjusting, and the molten metal bath surface height. Regarding this, it is difficult to maintain the height of the molten metal bath by balancing the head pressure of the molten metal and the differential pressure between the upper and lower interfaces because there is no method for controlling this. Further, since the height of the bath surface cannot be freely changed, it is difficult to secure the plating quality. Further, it is practically difficult to maintain the gap between the steel plate and the seal plate at 0.05 to 1 mm for a long time, and there is a problem that the steel plate locally contacts the seal plate and scratches the steel plate surface.

Further, Japanese Patent Laid-Open No. 63-109148,
The same is true of the technique disclosed in Japanese Patent Laid-Open No. 63-109149. Especially in these technologies, circulation of molten metal,
Due to the combined use of electromagnetic force, the phenomenon near the interface is more complicated,
Despite the need for advanced gas pressure management that takes into account all the forces generated, there is no indication of its value and its permissible error, means of measuring or adjusting, and molten metal. There was no means for measuring and adjusting the height of the bath surface.

That is, all of the above technical means are insufficient in terms of preventing molten metal from leaking, preventing gas from being ejected, and ensuring plating quality. In addition, JP-A-4-3
The technique disclosed in Japanese Patent No. 6446 has a means for measuring the height of the molten metal bath surface and adjusting it, but does not have a means for controlling the pressure of the lower gas. As a result,
The range of bath surface height is limited to an extremely limited range in order to operate while avoiding leakage of molten metal or ejection of gas,
It was difficult to secure the plating quality.

Further, in Japanese Patent Laid-Open No. 63-303045, the molten metal is prevented from flowing out at the bottom of the bath by the electromagnetic force and the gas injection device. It induces and damages stable threading,
Since the pressure fluctuation at the bottom surface of the bath is large, there is a problem that the atmosphere is entrained by the steel sheet from the opening at the bottom of the bath, and that portion becomes unplated.

Therefore, in any of the methods, it was difficult to simultaneously achieve the problems of preventing molten metal from leaking, preventing gas from being blown out, and ensuring the plating quality. The present invention provides a hot-dip metal plating method and an apparatus therefor that can simultaneously solve these problems. Further, it is an object of the present invention to provide an apparatus for obtaining a hot-dip galvanized steel sheet which enables stable passing of the steel sheet and has no surface defects.

[0014]

The present invention is a method for plating a molten metal in which a steel sheet is immersed in a molten metal bath so as to penetrate from the bottom to the top and then pulled up to perform plating. The molten metal bath surface height or the differential pressure, or both the molten metal bath surface height and the differential pressure are controlled so that the differential pressure of the gas pressure matches the head pressure of the molten metal. A method for plating a molten metal is provided.

The bath surface height referred to here is the distance from the lower interface of the molten metal container to the upper bath surface of the molten metal, but it is substantially from the molten metal bottom opening to the molten metal upper bath. It may be a surface. The gas pressure applied to the upper surface of the metal bath may be negative pressure. The apparatus of the present invention which can suitably carry out the above method is provided with an opening at the bottom of a container holding a molten metal bath, the steel sheet is continuously immersed in the bath through the opening, and the container is pulled upward. In a molten metal plating apparatus for plating, a lower pressure chamber through which a steel sheet passes is provided immediately below the opening, which is a molten metal plating apparatus. Furthermore, it is preferable to provide a sealing device at the part where the steel plate enters the lower pressure chamber, and
It is more preferable to attach a gas supply chamber communicating with the lower pressure chamber.

In the apparatus of the present invention, the lower pressure chamber covering the lower space of the bottom opening of the molten metal container, means for adjusting the gas pressure of the lower pressure chamber, and the molten metal bath surface inside the molten metal container. A molten metal plating apparatus comprising: a means for adjusting the height; and a calculation control means for calculating and controlling the mutual relationship between the gas pressure of the lower pressure chamber and the height of the bath surface. In this apparatus, further, the upper pressure chamber covering the upper surface of the molten metal, a means for adjusting the gas pressure of the upper pressure chamber, the gas pressure of the upper pressure chamber and the lower pressure chamber, and the interrelationship of the bath surface height are calculated. It is preferable to include an arithmetic control unit for controlling the operation.

[0017]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments and operations of the present invention will be described. In the present invention, as an example, a bath 12 as shown in FIG. 1 is used as a bath of molten metal. After annealing in the annealing furnace 16 in a non-oxidizing or reducing atmosphere, the steel sheet is passed through the lower pressure chamber 13 and the bath 12 and drawn upward. Seal opening 1 at the bottom of the bath holding molten metal 2
From 1, the steel plate 1 which is conveyed vertically by the deflector roll 7 and whose warp is corrected by the support roll 5 is continuously introduced to perform plating. A lower pressure chamber 13 is provided immediately below the seal opening 11 and immediately above the annealing furnace 16 so as to be disconnected from the annealing furnace and to be able to independently control the atmosphere. By applying a constant static pressure to the seal opening 11 while passing through the seal opening 11 as an additional bath holding force, the molten metal is prevented from flowing out from the opening at the bottom of the bath,
It is possible to perform stable plating for a long time.

In the present invention, in order to prevent pressure fluctuation at the seal opening 11 at the bottom of the bath and to exert a constant pressure during the passage, the gas supply chamber 1 is provided on both sides of the lower pressure chamber 13.
7 is provided, and the two chambers are partitioned by a shielding plate 18 or the like. By providing the gas supply chamber 17 partitioned by the shielding plate 18 or the like, the vibration of the steel sheet 1 due to the gas injection is not induced, and the pressure fluctuation in the seal opening 11 is reduced to improve the bath holding property and the inclusion of the atmosphere. Prevent and steel plate 1
It enables stable stripping and plating. The shield plate 18 here is for partitioning the lower pressure chamber 13 and the gas supply chamber 17, and the shape thereof is not particularly limited.

Further, as shown in FIG. 2, if the shielding plates 18 are installed in multiple stages, the pressure fluctuation in the lower pressure chamber 13 is further reduced, which is preferable. Further, the atmosphere in the lower pressure chamber 13 needs to be non-oxidizing with respect to the steel sheet 1. When the atmosphere in the lower pressure chamber 13 is oxidizable with respect to the steel plate 1 to be plated, an oxide film is formed on the surface of the steel plate 1 and local non-plating occurs even if the steel plate 1 is immersed in the molten metal. So prevent this. For example, by using a mixed gas composed of hydrogen and nitrogen, it is possible to prevent the surface of the steel sheet 1 from being oxidized and obtain good plating properties.

Further, by installing at least one pair of sealing devices 8 in the steel plate intrusion part at the lower end of the lower pressure chamber 13,
Airtightness in the lower pressure chamber 13 is enhanced, and a constant pressure can be constantly applied to the opening 11 at the bottom of the bath. When a roll-shaped seal device 8 is used, the pair of seal rolls has a structure in which a steel plate is sandwiched, and also has a function of suppressing the vibration of the steel plate, which enables stable threading. It is suitable. Further, if the sealing devices are installed in multiple stages in the plate passing direction, the airtightness of the lower pressure chamber is further improved. Further, the gas exhaust port 15 is provided in the gas supply chamber 17.
By providing the above, it is preferable since the atmosphere in the lower pressure chamber 13 can be controlled independently.

In the present invention, as an example, the sealing material installed at the bottom of the bath is used to hold the molten metal, but since the surface of the steel sheet is not flawed, the sealing material and the steel sheet are not in contact with each other, and the molten metal does not flow out. It is necessary to have a gap. The pressure in the lower pressure chamber 13 is controlled according to the bath height. When the sealed lower pressure chamber 13 which is separated from the annealing furnace is not provided directly below the seal opening 11 of the bath 12 and the gas supplied from the gas supply port is directly injected to the steel plate and the bath is held by the pressure. The atmosphere of the steel sheet was frequently entrained from the seal opening 11 and non-plating occurred. Therefore, when the gas supply pressure is lowered to such an extent that the entrainment of the atmosphere is suppressed, the pressure fluctuation acting on the seal opening 11 is large, frequent flow of molten metal is observed, and stable plating is performed for a long time. Was impossible.

If a sealing device is not used at the lower end of the lower pressure chamber 13, the airtightness of the lower pressure chamber 13 will decrease,
When the lower pressure chamber 13 is maintained at a high pressure, the gas supply amount has to be increased, and the controllability of the pressure inside the lower pressure chamber 13 is lowered. Further, as the material of the sealing material 10 used as an example of the present invention, it is preferable to use silicon nitride-based, silicon carbide, or ceramics such as graphite powder. Since ceramics are expensive, a thermal spray material may be used instead. The selection of these materials is based on the experimental results of examination of corrosion resistance, thermal shock resistance, and wettability with molten metal.

In order to prevent the temperature of the steel plate to be plated in the lower pressure chamber 13, that is, the plate temperature immediately before plating from decreasing, a preheated atmosphere is supplied to the gas supply chamber 17,
A device for heating the lower pressure chamber 13 with a heater may be installed. When performing plating, determine the distance that the steel sheet should be immersed in the molten metal from the immersion time required for plating quality and the steel plate passing speed, and based on this, determine the height of the molten metal bath surface. Determine the target value to be used.

According to the present invention, since there is a means for adjusting the height of the molten metal bath surface inside the container and a means for measuring the height of the molten metal bath surface, the molten metal bath surface The bath surface height can be controlled so that the height reaches this target value. Further, according to the present invention, a lower pressure chamber that covers the bottom opening of the container is provided, and means for adjusting the pressure of the gas supplied to the lower pressure chamber is provided, and means for measuring the pressure of the lower pressure chamber is provided. Have Further, a means for measuring the pressure on the upper side of the molten metal is provided, so that the pressure difference between the upper and lower interfaces of the molten metal becomes equal to the head pressure of the molten metal determined by the target value of the height of the molten metal bath surface. Control the pressure.
As a result, it is possible to simultaneously prevent leakage of molten metal, prevention of gas ejection, and ensuring of plating quality.

Any method may be used for controlling the head pressure of the molten metal and the pressure difference between the upper and lower interfaces of the molten metal to be the same. (A) The actual bath surface height of the molten metal is measured, Control the differential pressure so that the head pressure of the metal becomes (b) Measure the actual differential pressure at the upper and lower interfaces, and control the bath surface height of the molten metal so that the head pressure of the molten metal becomes this value. (C) Any of the above (a) and (b) may be used in combination for control.

In practice, the head pressure of the molten metal and the pressure difference between the upper and lower interfaces may not match due to the precision and responsiveness of the measuring equipment and adjusting means. When the difference exceeds a value determined by the surface tension of the molten metal, the contact angle between the molten metal and the steel plate, the container, and the distance between the molten metal container and the steel plate, the lower interface of the molten metal becomes unstable and the head pressure is reduced. When it is large, molten metal leaks, and when the head pressure is small, gas is ejected. Therefore, when controlling the height of the bath surface and the pressure of the pressure chamber, it is necessary to pay attention to the equipment selection and operation method, and to carry out within the allowable accuracy.

Although the bath surface height may be gradually changed at the start or end of the actual operation, the difference between the head pressure of the molten metal and the upper and lower interfaces of the molten metal is always maintained with the above accuracy even during the change. It is necessary that the pressures match.

[0028]

Next, the present invention will be described based on embodiments. Plating was performed using the apparatus of one embodiment of the present invention shown in FIG. After annealing the steel plate 1 (plate width: 500 mm, plate thickness: 0.7 mm), it is introduced from the seal opening 11 at 470 ° C. through the deflector roll 7. Zinc is used as the molten metal bath 2 held in the bathtub 12, and the sealing material 10 and the steel plate 1 are used.
2.5mm gap between the molten metal bath and 2
Height of 30mm (head pressure of molten metal 200mmA
q), the molten zinc bath temperature is 470 ° C., and the plate passing speed is 60 m.
/ Min plating was performed. On the other hand, a lower pressure chamber 13 was provided immediately below the seal opening 11, and a mixed gas of 95% nitrogen + 5% hydrogen was enclosed at 200 mmAq at a dew point of -20 ° C and continuous plating was performed. Zinc did not flow out from the opening 11, and stable plate passing could be maintained and continuous plating operation was possible.

Further, plating was performed under the same conditions as in the above example except that the pressure in the lower pressure chamber was set to 0 mmAq. As a result, zinc flowed out from the seal opening 11 at the bottom of the bath, and the plating operation could not be continued. Further, plating was performed under the same conditions as in the above-mentioned example except that a gas supply port was provided immediately below the seal opening, gas was injected at 200 mmAq toward the steel plate, and the zinc bath was held by the gas supply pressure. As a result, zinc did not flow out from the seal opening 11 at the bottom of the bath, but gas entrapped by the steel plate 1 occurred in the seal opening 11 and non-plating was observed, and the plating operation could be continued. There wasn't.

Next, plating was performed using the apparatus of one embodiment of the present invention shown in FIG. A pressure chamber 25 (lower pressure chamber) is continuously provided on the outlet side of the continuous annealing furnace 35, and a molten metal container 23 is continuously provided thereto. This molten metal container 23
The steel sheet 1 penetrates through the molten metal 2 from the bottom opening 24 of the above, and is immersed so as to penetrate upward. The height of the bath surface of the molten metal 2 is measured by a displacement measuring device 26 including a laser displacement meter.
The height of the bath surface of the molten metal 2 is immersed in a metal bath, and a plunger 27 is provided as a vertically movable adjusting means. Pressure chamber 2
The pressure of 5 is measured by a diaphragm type pressure transmitter 28 as a gas pressure measuring means. The pressure on the upper surface of the molten metal 2 is also measured by the diaphragm type pressure transmitter 28a. These measured values are input to the arithmetic and control unit 21. As the pressure adjusting means of the pressure chamber 25, a flow rate adjusting valve 29 provided in the pressure fluid supply pipe 36 is controlled. A seal roll 32 is used in a portion of the pressure chamber 25 that penetrates the steel plate 1 as a mechanism for holding pressure. Further, the distance between the opening 24 at the bottom of the molten metal container and the surface of the steel sheet 1 passing therethrough is 2 mm.

Pressure in lower pressure chamber 25 660 mmAq
(Gauge), pressure in the upper pressure chamber is 0 mmAq (gauge), bath surface height of molten metal is 100 mm (molten metal head pressure of 660 mmAq), and stable bath holding is possible.
A high-quality hot dip galvanized steel sheet could be manufactured. Further, when the pressure in the lower pressure chamber 25 was lowered to 630 mmAq under the same conditions, leakage of molten metal occurred. Next, when the pressure in the lower pressure chamber 25 was raised to 690 mmAq, the lower gas was entrained in the molten metal and an unplated portion was formed on the surface of the plated steel sheet.

FIG. 4 is a flow chart of control of the apparatus of FIG. First, the target value Hs of the bath surface height of the molten metal 2 is set. When the measured value H of the bath surface height is input from the displacement measuring device 26, the arithmetic unit 21 sets the bath surface height H to the target value Hs.
Is compared with the target value Hs. That is, a command is issued to the control device 22 to adjust the bath surface height. Next, the pressure P ₁ of the pressure chamber 25 and the pressure P _{2 of the} upper surface of the metal bath are input to the arithmetic unit 21 from the pressure transmitters 28 and 28a. The arithmetic unit 21 matches the dimensions of the bath surface height and the pressure data, compares the pressure difference P ₁ -P ₂ between the upper and lower surfaces of the molten metal 2 with the bath surface height head H of the molten metal 2, and this becomes equal. Thus, the pressure P ₁ of the pressure chamber 25 and / or the pressure P ₂ of the upper surface of the metal bath are controlled. That is, the opening of the flow control valve 29 is adjusted so that the pressure in the pressure chamber 25 depends on the magnitude of the pressure.

FIG. 5 is a flowchart of another control of the apparatus shown in FIG. The pressure P ₁ of the pressure chamber 25 and the pressure P _{2 of the} upper surface of the metal bath are input to the arithmetic unit from the pressure transmitters 28 and 28a. On the other hand, the measured value H of the bath surface height of the molten metal 2 is input from the displacement measuring device 26. The arithmetic and control unit 21 compares the data of the bath surface height and the pressure with the dimensions and compares the pressure difference P ₁ -P ₂ between the upper and lower surfaces of the molten metal 2 with the bath surface height head H of the molten metal 2 so that they become equal. Control device 22
Command to adjust the bath height.

FIG. 6 is a flow chart of control for operating all of the variables of the apparatus of FIG. Pressure P of pressure chamber 25
_1, the pressure P _{2 on} the upper surface of the metal bath, the set value of the target value Hs of the bath surface height of the molten metal 2 and the measured value H of the bath surface height are input to the arithmetic and control unit 21. Matching dimensions of bath surface height and pressure data, molten metal 2 pressure difference between upper and lower surfaces P ₁ -P ₂
And the bath surface height head H of the molten metal 2 are compared, and the bath surface height H is controlled to be equal and the bath surface height H is set to the target value H.
It is compared with s and controlled to match the target value Hs.
That is, all elements are controlled according to the situation.

Further, for example, the following cascade control is also possible. H> Hs and H> P ₁ -P ₂ ...... H decrease H <Hs and H> P ₁ -P ₂ ...... P ₁ increase H> Hs and H <P ₁ -P ₂ ...... lower the P ₁ H <Hs and,, H <lower the _{P 1 -P 2 ...... P 1 H} ><Hs and, changing _{H = P 1 -P 2 ...... H} , the P ₁ little by little H = Hs, and, H><shows an embodiment in the case of adopting the overflow system as adjusting means P ₁ -P ₂ ...... changing the P ₁ 7 in a molten metal bath surface level. Reference numerals other than the overflow opening 30 are the same as those in FIG. In the case of this example, the control device 22 adjusts the height of the overflow weir. With this method, the response of the height adjustment of the bath surface is slightly inferior, but the control accuracy of the bath surface is improved. The main control element depends on the pressure in the pressure chamber.

FIG. 8 shows an embodiment in which the amount of molten metal supplied to the molten metal container is controlled as means for adjusting the height of the molten metal bath surface. A molten metal tube 31 is provided. The other symbols are the same as those in FIG. In this case, it is easy to control the height of the bath surface in the direction of increasing the molten metal. The pressure chamber 25 is shown in FIG.
An example in which a labyrinth seal 34 is used in the portion where the steel plate 1 penetrates the pressure chamber is shown as the pressure holding mechanism. In this case, although the structure is simple, it is difficult to keep the pressure in the pressure chamber high, and the maximum pressure is about 120 mmAq. Further, FIG. 10 shows an embodiment in which seal rolls 32, 32a, ... Are provided in multiple stages as a pressure holding mechanism for the pressure chambers. In this case, the pressure holding effect is extremely high, but there is a drawback that the overall height becomes high and it is difficult to attach it to the existing continuous plating equipment.

FIG. 11 illustrates the principle of the present invention and is a cross-sectional view of the container 23 holding the molten metal 2. The molten metal 2 tends to leak downward from the bottom opening 24 due to the head pressure due to its height. On the other hand, the pressure acting on the upper and lower surfaces of the molten metal 2 tends to stop the leakage due to the pressure difference between the upper and lower sides. Further, the surface tension of the metal bath acts between the edge of the bottom opening 24 of the container 23 and the steel plate 1, and this surface tension also acts in the direction of stopping the leakage.
These working relationships are determined in relation to the size of the gap of the bottom opening 24.

As shown in FIG. 12, these relationships are linear relationships having a width. Therefore, by controlling within the range where the relationship shown in FIG. 12 is maintained, leakage of the metal bath can be prevented, and stable operation can be performed without causing ejection or entry of gas into the metal bath. The bath surface height measurement and adjustment means described above, and the pressure holding mechanism and adjustment means for the pressure chamber,
The pressure chamber and the means for measuring the pressure on the upper surface of the molten metal may be combined in any manner without limitation.

Although other equipment may be continuously installed before and after the apparatus according to the present invention, the present invention is not concerned with this. That is, the presence or absence of the adhesion amount control means such as the adhesion amount adjusting device 6, the continuous annealing furnace, and the alloying furnace is arbitrary.

[0040]

According to the present invention, in a molten metal plating method in which an opening is provided at the bottom of a molten metal container and a steel sheet is continuously immersed to perform plating, molten metal leakage prevention, gas ejection prevention, plating quality It became possible to reliably secure In addition, maintenance costs can be reduced because double-sided plating can be performed without the use of sink equipment such as sink rolls that easily cause surface defects.
By reducing the size of the pot, it is possible to suppress the amount of dross generated and change the plating type in a short time. In addition, it suppresses the vibration of the steel sheet and is excellent in bath holding property, and can be stably operated for a long time.

As a result, it becomes possible to enjoy the advantages of the molten metal plating method in which an opening is provided at the bottom of the molten metal container and the steel sheet is continuously dipped to perform plating, and the molten metal plating is economically performed. It became possible to do.

[Brief description of drawings]

FIG. 1 is a longitudinal sectional view of an embodiment of the present invention.

FIG. 2 is a vertical sectional view of an embodiment of the present invention.

FIG. 3 is a longitudinal sectional view of an embodiment of the present invention.

FIG. 4 is a flowchart of an example.

FIG. 5 is a flowchart of an example.

FIG. 6 is a flowchart of an example.

FIG. 7 is a vertical sectional view of an embodiment of the present invention.

FIG. 8 is a vertical sectional view of an example of the present invention.

FIG. 9 is a vertical sectional view of an embodiment of the present invention.

FIG. 10 is a vertical sectional view of an example of the present invention.

FIG. 11 is an explanatory diagram showing a balance of forces due to pressure in a pressure chamber, upper gas pressure, a molten metal head, and surface tension.

FIG. 12 is a graph showing a balance between a pressure difference between a pressure chamber pressure and an upper gas pressure, a force due to a molten metal head and surface tension.

FIG. 13 is a vertical sectional view of a conventional plating apparatus.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 Steel plate 2 Molten metal 3 Sink roll 4 Snout 5 Support roll 6 Adhesion amount adjusting device 7 Deflector roll 8 Sealing device (seal roll) 9 Guide roll 10 Seal material 11 Seal opening 12 Bath tub 13 Lower pressure chamber 14 Gas supply port 15 Gas Exhaust port 16 Annealing path 17 Gas supply chamber 18 Shielding plate 21 Calculation control device 22 Control device 23 Container 24 Bottom opening 25 Pressure chamber 26 Displacement measuring device 27 Plunger 28, 28a Pressure transmitter 29 Flow control valve 30 Overflow opening 31 Melting Metal tube 32 Seal roll 33 Multi-stage sealing chamber 34 Labyrinth seal 35 Continuous annealing furnace 36 Fluid supply pipe

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Shigeru Unno 1 Kawasaki-cho, Chuo-ku, Chiba-shi, Chiba Kawasaki Steel Corporation Technical Research Institute (72) Chiaki Kato 1 Kawasaki-cho, Chuo-ku, Chiba Chiba (72) Inventor Teruo Hiramatsu, Kawasaki-cho, Chuo-ku, Chiba, Chiba Prefecture Kawasaki Steel Co., Ltd. Chiba Works

Claims (6)

[Claims] 1. A method for plating a molten metal in which a steel sheet is immersed in a bath of molten metal so as to penetrate from the bottom to the top and pulled up to perform plating, wherein the differential pressure of gas pressure applied to the upper and lower surfaces of the metal bath is A molten metal plating method, characterized in that the height of the molten metal bath surface and / or the differential pressure is controlled so as to match the head pressure of the molten metal. 2. A molten metal plating apparatus for performing plating by providing an opening at the bottom of a container holding a molten metal bath, continuously immersing a steel plate in the bath through the opening, and pulling it upward to perform plating. A molten metal plating apparatus characterized in that a lower pressure chamber through which a steel plate passes is provided immediately below the opening. 3. The apparatus for plating molten metal according to claim 2, wherein a sealing device is provided at a portion where the steel plate enters the lower pressure chamber. 4. The molten metal plating apparatus according to claim 2, further comprising a gas supply chamber communicating with the lower pressure chamber. 5. A molten metal plating apparatus for performing plating by forming an opening at the bottom of a container holding a molten metal bath, continuously immersing a steel plate in the bath through the opening, and pulling it upward to perform plating. A lower pressure chamber that covers the lower space of the bottom opening of the metal container, a means for adjusting the gas pressure in the lower pressure chamber, a means for adjusting the height of the bath surface of the molten metal inside the molten metal container, A molten metal plating apparatus, comprising: an arithmetic control unit that calculates and controls the mutual relationship between the gas pressure in the lower pressure chamber and the bath surface height. 6. An upper pressure chamber that covers the upper surface of the molten metal, a means for adjusting the gas pressure of the upper pressure chamber, the gas pressure of the upper pressure chamber and the lower pressure chamber, and the bath surface height. 6. The apparatus for plating a molten metal according to claim 5, further comprising: a control unit that arithmetically controls