JPH08100247A - Method for preventing infiltration of dross into snout of continuous hot dipping equipment for steel strip - Google Patents

Abstract

PURPOSE: To prevent the dross existing in a snout from circulating again in the snout by forming a hole, communicating with the inside and outside of the snout, in the sidewalls, on the upper side in the direction of the width of a steel strip, of the end of the snout immersed in a hot dipping bath. CONSTITUTION: An oblong through hole 15 of a snout 4 is formed in the upper side wall 14, on the side of a sink roll, of the end of the snout 4 immersed in a hot dipping bath, in the part through which a steel strip 1 is to be passed. A plating bath stream in the direction of the snout 4 is allowed to flow through the oblong hole 15 into the snout 4, by which the circulation of dross through the snout 4 can be sealed. If a spray nozzle 16 is disposed on the outside of the oblong hole 15 and the plating bath liquid outside the snout 4 is forcedly sprayed through the oblong hole 15 onto the surface of the steel strip 1, the sealing effect can be increased.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method of preventing dross from entering a snout of a continuous hot dip galvanizing apparatus for steel strips, which prevents the dross of snout from circulating and again entering the snout.

[0002]

2. Description of the Related Art Hot-dip galvanizing of steel strips such as zinc and aluminum is carried out by a continuous hot-dip galvanizing machine. As shown in FIG. In order to prevent 1 from being oxidized in the atmosphere when it comes out of the reducing furnace 2, the reducing furnace 2 and the plating bath 3 are connected by a duct-shaped snout 4, and a reducing gas is supplied to the inside. . The snout 4 has a base connected to the reduction furnace 2 and a tip end soaked in a lower plating bath to prevent the reducing gas from flowing out, but the snout 4 is arranged vertically with respect to the bath surface. Has been done. The plating bath 3 extending in the extension direction of the tip of the snout 4 is synchronized in the extension direction of the snout 4.
The steel strip 1 from the snout 4 is circulated on the lower side of the steel strip 5 and then vertically lifted from the plating bath 3 by the gas expansion device 6 placed opposite to both sides of the steel strip 1. Excessive plating metal attached to the strip 1 is removed.

However, in this apparatus, when the steel strip 1 is immersed in the plating bath 3, it is corroded by the plating metal and the iron is eluted, so that an intermetallic compound between the eluted iron and the plating metal is produced, and the plating bath is formed. Float in 3. Further, since the plating bath 3 is exposed to the atmosphere, the plating metal is oxidized by the atmosphere and the oxide thereof floats on the surface of the plating bath. Furthermore, since the reducing gas supplied to the snout 4 contains a small amount of oxygen and water, an intermetallic compound of iron and plating metal or plating metal oxide is generated. Although these are called dross, since the dross is plated on the steel strip together with the plating metal, if the plating bath 3 contains a large amount of dross, the appearance and quality of the product will be impaired. The most problematic part of the dross is in the snout 4. Since this dross is surrounded by the snout 4, it does not easily flow out due to the plating bath flow generated by the frictional resistance of the steel strip 1.
As the plating work continues, the concentration will increase, and the appearance and quality of the product will deteriorate.

Therefore, various methods for removing dross in the snout 4 have been conventionally proposed. For example, hot-dip galvanizing of strip that sucks molten zinc outside the snout with a pump and discharges it from one side of the snout in the width direction of the steel strip, and the discharged zinc causes the dross inside the snout to flow to the other side. Method (JP-A-61-186463), a method for producing a continuous hot-dip galvanized steel sheet in which a dross inside the snout is sucked with a pump or the like and discharged outside the snout (JP-A-3-150338), a bath A continuous hot dip galvanizing apparatus in which the hot dip zinc is sucked by a pump and cleaned by filtration or the like, and then sprayed with a nozzle at the tip of the snout so that the hot dip zinc comes into contact with the steel strip (Japanese Patent Laid-Open No. 5
No. 9955), a method for continuous hot dip coating of steel strip in which the molten metal in the central portion of the bath with a small amount of dross is sucked with a pump and sprayed on the bath surface steel strip in the snout from the bath to remove the dross in the snout. (JP-A-5-287482)
And so on. However, since all of these methods require pumping the molten metal, maintenance and inspection of the molten metal are difficult.

On the other hand, as a method of removing dross without using a pump, an inert gas is blown from one side of the snout to the other side so that the dross floating on the bath surface in the snout is turned to the other side. A device for removing oxides in snout in molten metal plating (Japanese Patent Application Laid-Open No. 4-276052) has been proposed in which dross accumulated in the weir is discharged to the outside and is discharged to the outside. In the case of continuous plating, when dross is attached during movement and the spraying strength of the inert gas is large, the dross on the bath surface vibrates and a wavy pattern is generated in the plating layer.

[0006]

SUMMARY OF THE INVENTION The present invention provides a snout for a continuous hot dip galvanizing apparatus for steel strips, which is provided with the dross removing means without the above problems.

[0007]

According to the present invention, holes for communicating the inside and outside of the snout are provided on both side walls in the width direction of the steel strip at the tip of the snout immersed in the hot dip plating bath.

[0008]

The present inventors think that the dross in the snout can be removed by using this because the steel strip that the plating bath passes through is constantly stirred and fluidized. The investigation was conducted using a liquid model device capable of simulation of 1/5 scale. FIG. 1 shows this liquid model device. An aqueous sodium chloride solution 8 and a tracer acrylic bead 9 dispersed in this aqueous solution are put in a water tank 7 having an open upper part, and a synchro 5 is placed therein. Dip the guide roll 10 corresponding to the
Two feed rolls 11 and 11a are horizontally arranged above and outside of the endless belt 1 corresponding to the steel strip 1.
2 was stretched to form an endless track. And snout 4
A flat rectangular duct 13 corresponding to
It was arranged in parallel with the endless belt 12 between the guide roller 10 and the guide roller 10, and the lower part was immersed in the sodium chloride aqueous solution 8. In this liquid model device, the endless belt 12 shown in FIG.
Was rotated counterclockwise, and when the endless belt 12 entered the sodium chloride aqueous solution 8, the upper side was the front side and the lower side was the back side.

In this liquid model device, the endless belt 12 is used.
When the endless belt 12 is rotated, the acrylic bead 9 on the back side moves from the entrance side of the endless belt 12 to the bottom side of the guide roller 10 as the endless belt 12 moves, as shown by the flow line A in FIG. It was observed that the belt went around and went up to the exit side of the endless belt 12. Endless belt 12 on the acrylic beads 9 on the front side
The flow between the duct 13 and the guide roll 10 collides with the guide roll 10 as shown by the flow line B, and as shown by the flow line C. It moved in the direction opposite to the endless belt 12 and went up into the duct 13.

The acrylic bead 9 between the guide roll 10 and the bath surface moves up to the bath surface and then moves toward the duct 13 along the bath surface, as shown by the flow line D in FIG. It was recognized that the duct 13 collided. The rise of the acrylic beads 9 into the duct 13 was also caused by the centrifugal force of the guide roll 10 as shown by the flow line E in FIG.

From the above examination, the acrylic beads 9 on the surface side of the endless belt 12 in the duct 13 are
As a result, it was found that although it moved to the vicinity of the guide roll 10, it rose again and circulated in the duct 13.
Therefore, the inventors of the present invention have made the acrylic resin shown by the flow line D
Focusing on the collision of the pipe 9 with the duct 13, a hole is made in the wall 13a on the guide roll 10 side of the duct 13, and the flow of the sodium chloride aqueous solution 8 flowing toward the duct 13 flows into the duct 13 through the hole. By doing so, the flow of the sodium chloride aqueous solution 8 existing in the duct 13 circulating from the opening of the duct 13 is sealed, and the dross in the snout 4 is circulated in the snout 4 by the continuous molten metal plating apparatus. The upper wall 13 of the duct 13
When a hole was formed in a, it was found that the acrylic beads 9 were flowing in at a considerable speed.

On the basis of the above facts, the present invention uses the upper wall 14 on the side of the synchro 5 of the tip of the snout 4 dipped in the plating bath 3 to form the inner and outer parts of the snout 4 on the threaded portion of the steel strip 1. A hole for communicating with each other is provided, and a plating bath flow in the direction of the snout 4 is made to flow into the snout 4 so as to seal the dross circulating in the snout 4.

In order to enhance the sealing effect, a nozzle or the like may be arranged outside the hole so that the plating bath solution outside the snout 4 is forcibly ejected from the hole. This forced ejection has a large sealing effect when the plating bath solution is ejected obliquely toward the traveling direction of the steel strip 1. As shown in FIG. 3, the direction of the jet flow is S,
When the angle between the direction of the jet S and the steel strip 1 is θ,
When the velocity of the jet S was 3 to 18 m / min and the strip running speed of the steel strip 1 was 50 to 170 m / min, the result was 9
It has been found that it is preferable to set it to 0 ° or less. FIG.
Is the jet speed S of 6 m / min, the strip running speed of the steel strip 1 is 10
It shows the dross distribution rate when the direction of the jet flow S is variously changed at 0 m / min.

FIG. 5 shows that when the angle θ between the direction of the jet S of the plating bath liquid and the steel strip 1 is set to 60 ° and the velocity of the jet S is relative to the strip running speed of the steel strip, We have investigated whether or not there is a dross intrusion prevention effect, and the shaded area is the area where the dross distribution ratio has decreased compared to the past. Here, with the dross distribution rate, as described in the examples below, the dross in the snout 4 is observed with a probe, and the ratio of the area where the dross exists to the surface side area of the snout 4 is taken as the distribution rate. It is a representation. Further, the area having the effect of preventing dross intrusion in FIG. 5 is a state in which the area is reduced by 30% or more as compared with the conventional case. As a means for ejecting the plating bath solution, there is a method of supplying the plating bath solution to the nozzle by a gas pump using an inert gas that is less eroded by the plating bath solution or a pump that uses a method of sucking the liquid by vacuum suction in the container. Can be mentioned. Note that general propeller-type and screw-type pumps are difficult to maintain and inspect because the plating bath liquid is significantly corroded.

In the case of the present invention, the dross present on one side of the steel strip 1 cannot be removed. However, from the experimental results of the liquid model device, only the flow that flows out of the duct 13 is observed on the back surface side of the endless belt 12 in the duct 13, and it is considered that dross retention on the back surface side is small. Real Snout 4
Even if the inside is observed, the dross hardly stays on the back side, so there is no practical problem in removing the dross only on the front side.

[0016]

【Example】

Example 1 In the continuous hot-dip metal plating apparatus of FIG. 9, the snout 4 had a width of 2200 mm and a thickness of 200 mm, and the tip portion was immersed in the plating bath 3 for 390 mm as shown in FIG.
Four long holes 15 with a short diameter of 50 mm and a long diameter of 300 mm are formed in the upper side wall 14 on the side of the synchro 5 and the center thereof is 12 from the tip.
It is opened at equal intervals so that it is located at 5 mm, and the thickness is 1.0 m.
m, width 1200 mm, steel strip 1 passing speed 100 m / mi
n was continuously plated for 8 hours. 170 for plating bath 3
A ton zinc bath (460 ° C.) was used.

Embodiment 2 In Embodiment 1, the injection nozzle 16 is provided outside each elongated hole 15.
Is arranged at 60 ° to the steel strip 1 as shown in FIG. 7, and the plating bath liquid outside the snout 4 is jetted perpendicularly to the surface side of the steel strip 1 at a velocity of 6 m / min. The steel strip 1 was continuously plated at a strip speed of 120 m / min for 8 hours.

FIG. 8 shows the profile of the snout 4 on the surface side of the steel strip.
The distribution state of the dross is observed by inserting the plugs, and the ratio of the area where the dross exists to the surface side area of the snout 4 is expressed as a distribution rate. The dross distribution rate is similar to that of the snout 4 observed. Compared to the case where the hole 15 was not formed, the case where the elongated hole 15 was formed was reduced by 30%, and the case where the injection nozzle 16 was arranged outside the elongated hole 15 was decreased by 70%.

[0019]

As described above, according to the present invention, the flow of the plating bath is used to prevent the dross existing in the snout from circulating again in the snout.
No need to use a pump. Further, when the plating bath liquid outside the snout is jetted into the snout, it is jetted inside the bath, so that the bath surface inside the snout is smooth and no wavy pattern is generated in the plating layer.

[Brief description of drawings]

FIG. 1 is a cross-sectional view of a liquid model device for simulating the flow distribution of plating metal in a plating bath.

FIG. 2 is a diagram showing movement of an acrylic bead in a water tank cross-sectional direction when an endless belt is rotated in the liquid model device of FIG.

FIG. 3 shows the angle between the direction of the jet flow of the plating bath liquid jetted into the snout and the steel strip.

FIG. 4 shows dross distribution ratios when the direction of the jetting flow of the plating bath liquid jetted into the snout is variously changed with respect to the strip steel strip.

FIG. 5 shows a region having an effect of preventing dross intrusion when the velocity of the jet flow of the plating bath solution is variously changed with respect to the velocity of the steel strip.

FIG. 6 is a front view of the snout in which a hole is formed in the first embodiment.

FIG. 7 is a side view of a snout in Example 2 in which a hole is formed and an injection nozzle is arranged in the hole.

FIG. 8 is a graph showing dross distribution ratios of Examples and Comparative Examples (conventional method).

FIG. 9 is a cross-sectional view of the vicinity of a plating bath in a continuous molten metal plating apparatus.

[Explanation of symbols]

1 ... Steel strip, 2 ... Reduction furnace, 3 ... Plating bath, 4 ... Snout,
5 ... synchro, 6 ... gas restrictor, 7 ... water tank, 8 ...
Aqueous sodium chloride solution, 9 ... Acrylic beads, 10 ... Guide roll, 11, 11a ... Feed roll, 12 ... Endless belt, 13 ... Duct, 13a ... Wall, 14 ... Upper side wall, 15
... slot, 16 ... injection nozzle,

Claims (4)

[Claims] 1. A steel strip, the surface of which has been cleaned by a pretreatment zone, is arranged vertically with respect to the bath surface, and a tip-shaped portion is passed through a duct-shaped snout whose tip is immersed in a plating bath. After soaking in the plating bath, orbiting the lower side of the synchronizer arranged in the extension direction of the snout to raise it from the plating bath. -Continuous hot-dip galvanizing of steel strip, characterized in that a hole for communicating the inside and outside of the snout is provided in the side wall of the steel strip, and the plating bath flow in the snout direction caused by the frictional resistance of the strip steel strip enters the snout through the hole. A method to prevent dross from entering the snout of the device. 2. A steel strip, the surface of which has been cleaned by a pretreatment zone, is arranged vertically with respect to the bath surface, and the tip of the steel strip is passed through a duct-shaped snout whose tip is immersed in a plating bath. After soaking in the plating bath, orbiting the lower side of the synchronizer arranged in the extension direction of the snout to raise it from the plating bath. -Dross intrusion into the snout of the continuous hot-dip galvanizing equipment for steel strips, which is characterized in that a hole for communicating the inside and outside of the snout is provided on the side wall of the steel strip, and the external plating bath solution is forcibly ejected into the snout through the hole. Prevention method. 3. The continuous hot-dip galvanizing apparatus for a steel strip according to claim 2, wherein the plating bath solution is jetted obliquely in the same direction as the traveling direction of the steel strip at an angle of 90 ° or less with respect to the steel strip. How to prevent dross from entering the snout. 4. The snout of the continuous hot-dip galvanizing apparatus for steel strip according to claim 2, wherein the jetting speed of the plating bath solution is set in a shaded region of FIG. 5 with respect to the strip running speed of the steel strip. How to prevent dross from entering inside.