JPH05271888A - Hot-dip metal coating device - Google Patents

Abstract

PURPOSE:To reduce the deposition of impurities on a plated steel strip and to improve the quality and yield of the product in the hot-dip metal coating of the strip. CONSTITUTION:This device is provided with a hot-dip metal coating bath 2 for a steel strip 5, a centrifugal separator 8 for separating a solid inclusion in a molten metal 3, a flotation device 9 for separating the solid inclusion in the molten metal 3 and steel strip passage slits 19a and 19b with the upper and lower parts hot-dip metal coated. The lower slit 19b is dipped in a plating bath, a wiping nozzle 6 is provided inside, and a seal box 19 filled with a nonoxidizing or reducing atmosphere is furnished. The molten metal 3 in the bath 2 is passed through the separator 8 and flotation device 9 and returned to the molten metal in the box 19.

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 apparatus.

[0002]

2. Description of the Related Art In a hot-dip galvanizing bath such as a hot-dip galvanizing bath, when Fe dissolved from a steel strip or equipment in the bath exceeds a solid solution limit, it reacts with Al or Zn and precipitates, which is generally called dross. It becomes a solid inclusion. This inclusion is deposited on the bottom of the bath as FeZn ₇ due to Al concentration in the bath,
Although Fe ₂ Al ₅ floats on the bath surface, most of Fe ₂ Al ₅ floats in the bath in the process. In addition, Zn reacts with oxygen in the atmosphere on the bath surface to form ZnO, which also forms solid inclusions called dross and accumulates on the bath surface. Both of them adhere to the plated steel strip and deteriorate the plating quality.

As a method for removing the inclusions, a method of filtering using a ceramic filter (Japanese Patent Laid-Open No. 62-202070) has been disclosed. It is not practical because there is a problem that it is clogged, the removal performance is lowered and it cannot be used stably for a long time, and it is not possible to reduce the deterioration of the plating quality due to the adhesion of dross.

As a method of preventing the dross on the bath surface from adhering to the steel sheet, a seal box having a steel sheet passage slit at the top and an open bottom surface is formed so that the steel sheet and the wiping nozzle are simultaneously covered near the plating bath surface. A method of providing the inside to maintain non-oxidizing property or reducing property (JP-A-51-114334)
However, this method is effective only for reducing the amount of ZnO generated and the amount of deposition on the steel plate, and it was not possible to reduce the deterioration of plating quality due to the deposition of Fe ₂ Al ₅ dross.

[0005]

According to the present invention, it is possible to stably remove inclusions for a long period of time without the trouble of managing and maintaining the equipment, thereby significantly reducing quality deterioration due to dross adhesion. It is an object of the present invention to provide a molten metal plating device.

[0006]

The present invention is directed to a molten metal plating bath for steel strip, a centrifugal separator having a function of centrifuging solid inclusions in the molten metal, and floating solid inclusions in the molten metal. A flotation device having a separating function, and a steel strip passage slit having a molten metal plating on the upper and lower portions are provided, and the steel strip passage slit at the lower portion is immersed in a plating bath and has a wiping nozzle inside. Is arranged,
Further, the seal box whose inside is maintained in a non-oxidizing or reducing atmosphere and the molten metal in the molten metal plating bath are allowed to pass through the centrifugal separation and levitation separation device and refluxed into the molten metal in the seal box. The molten metal plating apparatus is provided with a device for

[0007]

In order to solve the above-mentioned problems, the present invention has a function of separating molten metal in a molten metal plating bath into a container having a function of centrifuging solid inclusions in the molten metal bath and a function of floatingly separating it. By passing through the inside, the solid inclusions are separated and cleaned, and the steel strip passage slits having the molten metal plating are provided on the upper and lower parts of the solid inclusions. It is soaked, a wiping nozzle is arranged inside, and the inside is refluxed into the molten metal in the seal box maintained in a non-oxidizing or reducing atmosphere.

FIG. 8 shows an example of centrifugal separation ability of Fe--Al type inclusions in molten zinc in one embodiment of the present invention shown in FIGS. When the diameter of the centrifuge layer 8a is 600 mm, the state in which the dross introduced at the end of the centrifuge tank moves to the center with the passage of time is 60 rpm (Fig. 8 (a)), 120
The rpm (FIG. 8B) is shown for each particle size of inclusions. Separation capacity changes depending on the particle size of dross, the number of rotations of the magnetic field in the centrifugal separation tank, and the processing time. If the rotation speed is less than 20 rpm, there is almost no separation effect even if the particle size is large, and if it exceeds 200 rpm, there is a problem of zinc scattering due to rotation.
A treatment within the range of 200 rpm is suitable.

FIG. 9 shows a locus 20 of the flow of solid inclusions with and without a weir. Figure 9
When there is a weir as in (a), the solid inclusions are effectively levitated as compared with FIG. 9 (b) where there is no weir. The floated inclusions are removed by trapping with a flux such as ammonium chloride. The number of weirs is not particularly limited. Further, in the present invention, as shown in FIGS. 1, 2, 5 and 6, a seal box 19 having a steel sheet passing slit in the upper and lower portions is provided in the vicinity of the plating bath to maintain the inside in a non-oxidizing or reducing property. This prevents the generation of ZnO on the inner bath surface. By using N ₂ gas for wiping and setting the upper slit to (plate width + 40 mm) x 40 mm, the internal O ₂
The concentration can be kept below 100ppm, and ZnO is hardly formed.

The seal box disclosed in Japanese Patent Laid-Open No. 51-114334 has a bottom open to the bath, whereas in the present invention, the bottom opening is made of a steel plate. It is only a slit for preventing the entry of dross from the bottom and refluxing the cleaned bath above to the bath surface inside the box, so that the bath near the steel plate inside the box can be always kept clean. ..

That is, according to the present invention, it is possible to greatly reduce the inclusion of inclusions generated in the plating bath and on the bath surface and deteriorating the quality of the steel sheet. As a metal used in the molten metal plating bath, aluminum, tin, etc. can be used in addition to zinc.

[0012]

Embodiments of the present invention will be described with reference to the drawings.
FIG. 1 is a block diagram of an apparatus used in one embodiment of the present invention.
The steel strip 5 passes through the molten metal 3 in the plating tank 2 by the snout 1 and the sink roll 4, and the basis weight is adjusted by the wiping nozzle 6 installed in the seal box.

In the present invention, the molten metal (for example, molten zinc) 3 in the plating tank 2 is pumped up by the pump 7 or the like, the container 8 having a centrifugal separation function for solid inclusions, and then another container having a floating separation function. The solid inclusions are removed by passing through the container 9, and the cleaned molten metal is refluxed into the molten metal in the seal box 19. The seal box 19 has a steel strip passage slit 19 with a molten metal plating on the upper and lower parts.
a and 19b are provided, the steel strip passage slit 19b therebelow is immersed in the plating bath 3, and a wiping nozzle 6 is provided inside, and the inside is maintained in a non-oxidizing or reducing atmosphere. ing.

Here, as shown in FIG. 3, the apparatus 8 having the function of centrifuging solid inclusions is equipped with a rotating magnetic field generator 8b on the outer circumference of the centrifuge tank 8a.
The molten metal in a is rotated in the horizontal direction.
For example, in the case of a hot dip galvanizing bath, the solid inclusions to be removed are Fe-Al alloys containing Fe ₂ Al ₅ as the main component, and their specific gravity
4.2 is smaller than the specific gravity of molten zinc, which is 6.7. Therefore, by giving rotation, the inclusions gather in the center.

Further, as shown in FIG. 4, the apparatus 9 having the floating separation function for solid inclusions has a primary weir 9b, a secondary weir 9c, a third weir 9d, and a fourth weir inside a floating separation tank 9a. 9e is provided, and an upward flow is created while the molten metal introduced from the inlet 9f flows out from the outlet 9g. For example, in the case of a hot dip galvanizing bath, an Fe-Al alloy having a large grain size easily floats in a short time, but as the grain size becomes smaller, it takes a longer time to make it difficult to float. It is floated in a short time by providing a weir. In the figure, 10 is a removing device inlet pipe, 11 is a removing device connecting pipe, and 12 is a removing device outlet pipe.

As described above, according to the present invention, the molten metal that has passed through the devices 8 and 9 and has been cleaned is refluxed to the plating bath through piping or the like, so that the adhesion of inclusions to the surface of the steel strip is greatly reduced. be able to. In addition, as shown in FIG.
Even if the order of and 9 is reversed, the same removal effect can be obtained.

FIGS. 5 and 6 show an embodiment in which one solid inclusion removing device 13, 14 having both centrifugal separation and floating separation functions is used, and in this case also, FIG. 1 and FIG. Moreover, the same effect as that of the embodiment can be obtained. As shown in FIG. 7, the device 13 of FIG. 5 comprises a device 15 having a centrifugal separation function and a device 16 having a floating separation function, and the devices 15 and 16 are connected at the bottom of an inner wall 17. 18a is the primary weir, 18b is the secondary weir, and 18c is 3
The next weir, 18d, is the fourth weir.

The solid inclusion removing device 14 of FIG. 6 is the device 15 and 16 of FIG. 7 in which the arrangement order is reversed, and has the same effect. In addition, as shown in FIGS. 1, 2, 5, and 6, near the plating bath, the steel sheet passage slits 19a are formed in the upper and lower portions,
By providing a seal box 19 having 19b and keeping the interior non-oxidizing or reducing, Z on the inner bath surface
Prevents the generation of nO.

According to the present invention, the inclusions in the plating bath can be prevented from adhering to the plated steel strip and impairing the quality, and the amount of inclusions and top dross floating on the plating bath surface can be greatly reduced. be able to. As the metal used in the molten metal plating bath, aluminum, tin or the like can be used in addition to zinc.

Next, specific examples of the present invention will be described.
Using the apparatus having the structure shown in FIG. 5, an inclusion removing device 13 having the functions of centrifugal separation and floating separation having the structure shown in FIG. 7 is provided near the outside of the plating tank 2, and the zinc plating bath 3 is pumped by the pump 7. Inclusion removal device that pumps up and passes through the inlet side pipe 10.
It was introduced into 13 at a speed of 400 kg / min, and after centrifugal separation and floating separation in this, the steel strip was subjected to hot dip galvanizing while flowing back into the plating tank through the outlet pipe 12.

Centrifugation was performed under the following conditions. Centrifuge tank inner diameter: 600mm Magnetic field rotation speed: 120rpm Retention time in tank: 3min In the floating separation tank, as shown in Fig. 7, primary weir 18a, secondary weir 18b, tertiary weir 18c, and fourth weir 18d. Was established.

A seal box 19 is provided at the rising portion of the bath surface of the steel sheet so as to cover the steel strip 5 and the wiping nozzle 6, and the upper and lower slits have a box width of 40 mm.
Further, the upper slit is provided with a mechanism capable of closing a portion having no steel strip in the width direction. While the inclusions were removed and the molten zinc was refluxed to the bath surface in the seal box 19, continuous hot dip galvanizing of the steel strip was performed by N ₂ gas wiping.

As a comparative example, continuous hot dip galvanizing of a steel strip was performed in the same manner as above except that the inclusion removing device and the seal box were not used. According to the above method, the strip thickness of the steel strip is 0.9 mm, the strip width is 1200 mm, the line speed is 120 m / min, the basis weight is 45 g / m ² , and the molten zinc circulation speed between the plating tank and the inclusion removing device is 100 kg / min. When the alloyed hot-dip galvanized steel sheet 10000t was produced, Fe-Al-based floating dross was efficiently removed, ZnO-based top dross was hardly generated, and the number of inclusions adhered to the steel sheet was 5 / compared to the comparative example. m
^{It was} 0.001 pieces / m ² with respect to ² .

[0024]

As described above, according to the present invention, in hot metal plating of steel strip, it is possible to reduce the adherence of impurities to the plated steel strip and improve the product quality and yield. The effect of reducing impurities floating on the bath surface of the tank is obtained.

[Brief description of drawings]

FIG. 1 is an illustration of an embodiment of the device of the present invention.

FIG. 2 is an explanatory diagram of an embodiment of the device of the present invention.

FIG. 3 shows an embodiment of an apparatus having a centrifugal separation function of the present invention, (a) is a plan view and (b) is a longitudinal sectional view.

FIG. 4 is a cross-sectional view of an embodiment of an apparatus having a floating separation function according to the present invention.

FIG. 5 is an explanatory view of an embodiment of the device of the present invention.

FIG. 6 is an explanatory diagram of an embodiment of the device of the present invention.

7A and 7B show an embodiment of a container having a centrifugal separation function and a floating separation function according to the present invention, wherein FIG. 7A is a sectional view and FIG. 7B is a plan view.

FIG. 8 is a graph showing a centrifugal separation function in the present invention.

9] The present invention (FIG. 9A) and the conventional device (FIG. 9).
It is a figure which shows the example of the flow trace of the solid inclusion in (b)).

[Explanation of symbols]

 1 Snout 2 Plating tank 3 Molten metal 4 Sink roll 5 Steel strip 6 Wiping nozzle 7 Pump 8 Centrifugal separator with centrifugal separation function for solid inclusions 8a Centrifugal separation tank 8b Rotating magnetic field generator 9 Floating separation function for solid inclusions Flotation separation device 9a Flotation separation tank 9b Primary weir 9c Secondary weir 9d Third weir 9e Fourth weir 9f Flotation separation tank inlet 9g Flotation separation tank outlet 10 Removal device inlet side pipe 11 Removal device communication pipe 12 Removal device outlet side Piping 13 Solid inclusion removing device 14 Solid inclusion removing device 15 Device having a centrifugal separation function for solid inclusions 16 Device having a floating separation function for solid inclusions 17 Inner wall 18a Primary weir 18b Secondary weir 18c Tertiary weir 18d Quaternary weir 19 Seal box 19a Steel strip passage slit 19b Steel strip passage slit 20 Flow path of solid inclusions

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Katsunori Akiyoshi 1 Kawasaki-cho, Chiba-shi, Chiba Kawasaki Steel Co., Ltd. Chiba Works

Claims (1)

[Claims] 1. A molten metal plating bath for a steel strip, a centrifugal separator having a function of centrifuging solid inclusions in the molten metal, and a flotation separator having a function of floating and separating solid inclusions in the molten metal. And a steel strip passage slit having a molten metal plating on the upper and lower parts, the lower steel strip passage slit is immersed in the plating bath, and a wiping nozzle is arranged inside, A seal box maintained in a non-oxidizing or reducing atmosphere, and a device for allowing the molten metal in the molten metal plating bath to pass through the centrifugal separation and levitation separation device, and refluxing it into the molten metal in the seal box. A molten metal plating apparatus characterized by being provided.