JPH1112711A - Continuous hot dip metal coating method and continuous hot-dipping device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To effectively execute the prevention of floating material on bath surface without damaging the workability and the productivity by plating while shifting the dipping position of a steel band into the base surface in a snout to the position near the outlet side of the steel band from the center position of the snout at the time of regular plating. SOLUTION: At the time of regular plating, the dipping position of the steel band 1 into the plating bath is shifted to the outlet side of the steel band 1 regarding the inner wall of the snout 4 from the center position 10 of the snout and it is plated. By this method, the sticking of dross to the steel band 1 in the snout 4 can be prevented by reducing the dross invaded in the snout 4 along a sink roll 6. The larger the shifting quantity of the dipping position of the steel band 1 is, the less the dross invaded in the snout 4 is. Therefore, this position is desirable to shift by the bath surface width (the inlet and outlet side direction distance) from the center on the plating bath surface in the snout, i.e., by >=1/4 of the snout thickness, but in the case the steel band 1 approaches too near the inner wall of the snout, since it is fear to develop scratched flaw with the piled dross on the bath surface, the interval with the inner wall of the snout is desirable to be >=30 mm.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a hot-dip galvanizing method such as hot-dip galvanizing, and more particularly to a hot-dip metal plating method for improving the appearance of the surface of a steel strip and a hot-dip metal plating apparatus suitable for this method. About.

[0002]

2. Description of the Related Art Various types of continuous hot-dip metal plating lines are conventionally known as a method for continuously applying a hot-dip metal plating to a steel strip. Things are used. FIG. 1 shows a continuous hot-dip galvanizing line, in which a cold-rolled steel strip 1 is directly heated in a non-oxidizing furnace 2 and annealed and reduced in an annealing furnace 3 in a reducing atmosphere with H ₂ gas, followed by a snout. 4, is guided to a Zn bath 5, rises vertically upward by a sink roll 6, is drawn out of the bath, and has a gas wiper 7 on the Zn bath 5.
Is adjusted to a predetermined plating adhesion amount, and then wound around a coil by the take-up reel 8 to form a product. In such a plating method, when the steel strip is continuously subjected to hot-dip Zn plating, the bath surface 5a inside the snout 4 and the bath surface 5b outside the snout 4 are provided with Zn oxide (ash), Fe-Al based It was inevitable that many compounds and Fe-Zn-based compounds (these Fe-Al-based compounds and Fe-Zn-based compounds were collectively referred to as "dross") would float or accumulate on the bottom. .
If these oxides and dross penetrate into the snout and adhere to the steel strip, surface defects on the plated surface and non-plating may be caused, and the product quality of the plated steel strip may be significantly reduced. Are known.

By the way, in order to prevent the deterioration of product quality caused by such oxides and dross adhering to the steel strip, conventionally, the line is stopped and the H ₂ gas in the annealing furnace 3 is removed. Measures have been taken such as purging with N ₂ gas and releasing the snout 4 to remove suspended matter on the bath surface 5a, and periodically scraping dross of the bath surface 5b where the steel strip 1 rises. However, these methods, stop lines, N ₂ gas purge of the annealing furnace requires a long time to process, such as suspended solids removal was achieved, thereby forcing a drop in productivity and workability.

[0004] Therefore, in order to prevent deterioration of product quality such as surface irregularity defects and non-plating of the plated steel strip caused by these oxides and dross, there has been a need for prevention and removal of suspended matter. Much research has been done and suggestions have been made. For example, JP-A-56-146869 discloses a method of physically swinging a snout bath surface to prevent dross from adhering to the surface of a steel strip, and JP-A-60-230969 discloses an electromagnetic pump in a snout. Japanese Patent Laid-Open Publication No. 3-197657 proposes a method of sucking impurities on a metal bath surface together with a molten metal, in which floating dross is collected at a corner of a bath tub and Zn attached to the dross is stirred and separated. . In addition, JP-A-3-27
Japanese Patent Application Laid-Open No. 7-184715 discloses a method of controlling the temperature of the inner wall of a snout to prevent ash or the like from adhering.
In the official gazette, a shield plate is installed above the sink roll body,
A method has been proposed in which another shielding plate whose upper end is higher than the snout tip is provided between the shielding plate and the snout to block dross moving in the snout direction along the flow of the sink roll. Further, Japanese Patent Application Laid-Open No. Hei 6-306556 discloses a method in which a flow straightening plate is installed in a plating bath, and an accompanying flow containing dross generated by a sink roll and a steel plate is guided to a container installed in the bathtub and accumulated. Japanese Patent Application Laid-Open No. 7-102352 proposes a method in which the center of the metal band in the width direction of the metal band to be plated is shifted to one side with respect to the center of the plating bath, and a dross removing device is arranged over the wide width.

However, although the production of suspended matter on the bath surface is suppressed or removed to some extent by any of these methods, it has the following problems. That is, in the techniques disclosed in JP-A-56-146869, JP-A-60-230969, and JP-A-3-197657, vibrations are applied to the bath surface. There is a disadvantage that the dross floats in the bath and easily adheres to the steel strip surface. Further, the technique disclosed in Japanese Patent Application Laid-Open No. 3-277756 is effective in preventing surface defects, but has a problem that the plating adhesion tends to vary.
Further, in the technology disclosed in Japanese Patent Application Laid-Open No. 6-184715, the dross that intrudes into the snout along the sink roll is shielded by the shield plate, so that the closer the shield plate is to the sink roll, the higher the effect of preventing dross adhesion is. When the plate comes in contact with the sink roll, there is a drawback that the rotation of the sink roll is hindered and the steel strip is scratched. The technique disclosed in Japanese Patent Application Laid-Open No. 6-306556 requires costly maintenance of a pump used to guide an entrained flow containing dross into a container, and furthermore, dross (Fe- (Zn-based compounds). Also, JP-A-7-102
The technique disclosed in Japanese Patent Publication No. 352 can concentrate the dross flow at a specific place, but has a drawback that maintenance of the apparatus is costly because dross is removed by separation using a filter.

[0006]

As described above, ash generated due to the high vapor pressure of Zn and Zn oxidation oxidized by O _{2 in} the atmosphere are present on the Zn bath surface of the continuous hot metal plating line. A large number of dross and the like caused by Fe elution from the steel strip were suspended and adhered to the surface of the steel strip, which significantly deteriorated the product quality. However, for these issues,
With any of the conventional techniques, it has not been possible to stably obtain good quality, and it is disadvantageous in terms of cost. Accordingly, the present invention is to solve the above-mentioned problems of the prior art, and it is possible to prevent the adhesion of suspended matter on the bath surface without impairing workability and productivity, and to perform continuous molten metal effectively. An object of the present invention is to propose a plating method and a continuous hot-dip metal plating apparatus.

[0007]

Means for Solving the Problems In order to solve the above-mentioned problems, the inventors have conducted intensive investigations and studies focusing on the place and timing of occurrence of suspended matter in the bath, and studied the suppression of adhesion of suspended matter. investigated. In particular, in the vicinity of the steel strip rising portion, a large amount of Zn oxide oxidized by the wiping gas or O ₂ in the atmosphere, and near the place where the Zn or Al-Zn ingot is supplied, a local decrease in bath temperature, Al Based on the idea that dross precipitates a lot by increasing the concentration,
They have found a way to effectively control the adhesion of suspended matter.

That is, according to the present invention, a steel strip annealed in a high-temperature atmosphere is continuously guided into a hot-dip metal plating bath via a snout, turned vertically upward by a sink roll and drawn out of the plating bath. In the metal plating method,
This is a continuous hot-dip metal plating method characterized in that the steel strip intrudes into the inner bath surface of the snout so as to be deflected to a position closer to the steel strip exit side than the snout center position during steady plating. The present invention also provides the plating method, wherein
When replenishing the plating metal, the position where the steel strip enters the plating bath surface in the snout is shifted to a position closer to the steel strip entry side than the snout center position, and the plating metal is replenished from the steel strip entry side of the plating bath. This is a continuous hot-dip metal plating method.

Further, the present invention provides a plating bath in which a steel strip is introduced, a snout for introducing an annealed steel strip into the plating bath while shielding the atmosphere, and turning the steel strip upward in the plating bath. A continuous hot-dip metal plating apparatus, comprising: a sink roll for the steel strip; and an intruding position of the steel strip in the snout, the inner wall of the snout being relatively displaceable in the steel strip entry / exit direction. It is. And
In the above plating apparatus, it is preferable that the relative displacement between the entry position of the steel strip and the inner wall of the snout is performed by moving the snout. In these plating apparatuses, it is also preferable that the relative displacement between the intrusion position of the steel strip and the inner wall of the snout is performed by changing the position of the sink roll and / or the roll on the exit side of the annealing furnace.

[0010]

BEST MODE FOR CARRYING OUT THE INVENTION In the continuous hot-dip metal plating line shown in FIG. 1, the inventors plated a steel strip in a hot-dip zinc bath containing 0.1 to 0.2 mass% of Al, Investigating the adhesion behavior of dross to the steel strip,
The following findings were obtained. (1) Oxide dross and Fe-
Al-based dross has a higher specific gravity than molten zinc
-Fe dross is present in the lower part of the bath. (2) There is a lot of dross near the place where the Zn or Al-Zn ingot is replenished due to a local decrease in bath temperature and an increase in Al concentration. (3) There are relatively large oxide dross and Fe-Al dross at the top of the plating bath in the snout. (4) Most of the plating surface defects are oxide dross and Fe-
Caused by adhesion of Al dross. The basis is that the dross attached to the steel strip is converted to EPMA (X-ray microanalysis).
As a result, the Fe-Al-based substance was detected at the center thereof, and it was presumed that the Fe-Al-based dross was attached as coarse dross with the nucleus.

[0011] Further, the effects of the location of the steel strip intrusion in the snout on the flow behavior of the bath and the floating behavior of the dross were investigated by a water model experiment, and the following findings were obtained. (5) The plating bath flows along with the movement of the steel strip and the rotation of the sink roll. (6) The dross enters the snout from the exit side of the steel strip due to the accompanying flow of the sink roll. (7) More than 70% of the dross in the snout enters from the steel strip exit side, and the remaining 30% enters from the steel strip entrance side. (8) If the steel strip entry position in the snout shifts to the steel strip exit side,
The dross that enters the snout from the steel strip entry side increases, but the dross that enters the snout from the steel strip exit side decreases. Conversely, if the steel strip entry position in the snout shifts to the steel strip entry side, the dross that enters the snout from the steel strip entry side decreases, and the dross that enters the snout from the steel strip exit side increases.

Based on the above findings, the inventors deviate the steel strip entry position into the plating bath toward the steel strip outlet side or the inlet side relative to the inner wall of the snout according to the state of dross generation and flow. Accordingly, it was considered that oxide dross and Fe-Al dross penetrating into the snout could be reduced, and as a result, plating surface defects could be reduced.

Specifically, in the present invention, at the time of steady plating, the steel strip intrusion position into the plating bath is shifted from the snout center position 10 shown in FIG. 2 to the snout inner wall as shown in FIG. By plating so as to be deviated to the steel strip exit side, dross entering the snout along the sink roll can be reduced, and dross adhesion to the steel strip in the snout can be prevented. The greater the amount of deviation of the steel strip entry position into the plating bath, the more dross entering the snout can be reduced, and the bath surface width (distance in and out side) from the center of the plating bath surface in the snout, that is, the snout thickness It is preferable to shift by / 4 or more. However, if the steel strip is too close to the inner wall of the snout, abrasion may occur due to dross deposited on the bath surface. Therefore, it is preferable that the distance from the inner wall of the snout is not less than 30 mm.

In the present invention, when the plating metal is replenished, the plating metal is replenished on the steel strip entrance side of the plating bath as shown in FIG. It is possible to reduce the amount of the bath having a large amount of precipitation reaching the steel strip exit side where the bath has a large penetration into the snout. Further, in accordance with this, as shown in the figure, the position of the steel strip entering the plating bath in the snout while replenishing the plating metal on the steel strip entry side is changed to the snout central position 10.
By plating more deviated to the steel strip entry side, it is possible to reduce the amount of baths with a lot of dross precipitation due to replenishment of plating metal from entering the snout from the steel strip entry side, and to reduce Dross adhesion can be prevented. The greater the amount by which the steel strip intrusion position into the plating bath is deviated, the more dross entering the snout can be reduced, and the bath surface width (distance in the entrance / exit direction) from the center of the plating bath surface in the snout,
That is, it is good to shift by 1/4 or more of the snout thickness, but if the steel strip is too close to the snout inner wall, dross deposited on the bath surface may cause abrasion, so the distance from the snout inner wall does not become 30 mm or less. It is preferable to do so.

In the method of the present invention, in order to replenish the plating metal, the plating metal ingot is immersed in a bath and then directly melted, or the plating metal is supplied as a pre-heated molten metal by a pump or the like. The method can be suitably applied to the case where the operation is performed. That is, when the metal ingot is immersed and inserted into the bath and directly melted, as described above, near the ingot immersion location, a local decrease in bath temperature,
Since dross increases due to the increase in Al concentration, melting is performed on the steel strip entry side, and the position where the steel strip enters the plating bath is shifted toward the steel strip entry side to prevent dross entering the snout. I do. Also, when the plating metal is supplied as a pre-heated molten metal as a plating metal by a pump or the like, a bath flow occurs due to the replenishment of the molten plating metal. In addition, the position where the steel strip enters the plating bath is shifted toward the steel strip entry side, thereby preventing dross entering the snout.

In order to carry out the method of the present invention described above, a continuous hot-dip metal plating apparatus provided with means capable of displacing the steel strip entry position into the plating bath toward the steel strip inner and outer sides with respect to the inner wall of the snout is provided. In normal plating, the steel strip entry position into the plating bath in the snout is shifted to a position closer to the steel strip exit side than the snout center position, and when replenishing plating metal on the steel strip entry side, the plating in the snout is The steel strip entry position into the bath is shifted to a position closer to the steel strip entry side than the snout center position. In this way, dross that intrudes into the snout can be suppressed, and dross adhesion to the steel strip in the snout can be suppressed.

Means for displacing the steel strip entry position into the plating bath in the snout toward the steel strip exit side or the entrance side with respect to the snout inner wall is that the steel strip does not meander or change the plating adhesion amount. A continuous hot-dip metal plating apparatus by moving the snout 4 can be suitably used, and dross adhesion to the steel strip in the snout can be suppressed. The movement of the snout can be dealt with by a simple and convenient method such as an air cylinder. In addition, as means for shifting the steel strip entry position into the plating bath inside the snout toward the exit side or the entrance side of the steel strip relative to the inner wall of the snout, the movement of the snout is difficult due to the space between the equipment and the equipment above the bath. In such a case, a device for changing the position of the sink roll 6 and / or the roll 12 on the exit side of the annealing furnace without changing the position of the snout can be suitably used. Similarly, it is possible to prevent the dross from adhering to the steel strip in the snout. Can be suppressed. Further, as a means for biasing the steel strip intrusion position into the snout inner plating bath toward the steel strip outlet side or the inlet side relative to the snout inner wall, for the purpose of securing space with equipment in or on the bath, If the movement of the snout alone or the change of the position of the sink roll and the exit roll of the annealing furnace cannot be achieved, an apparatus that uses both the movement of the snout and the change of the position of the sink roll and / or the exit roll of the annealing furnace is required. It can be suitably used and dross adhesion to the steel strip in the snout can be prevented. The above-mentioned effect can be similarly applied to the case where the sink roll for changing the direction in the plating bath is a floter roll.

[0018]

EXAMPLE In the continuous hot-dip galvanizing line shown in FIG. 1, the Al concentration in the plating bath was 0.16 mass% and the plating bath temperature was 4%.
70 ° C., the line speed as 1.7 m / s, galvanized a coating weight 60g / m ³ Nb-Ti-based extreme low carbon steel strip, about the occurrence of surface defects due to dross resulting plated steel strip surface Was visually inspected. At this time, the position where the steel strip enters the plating bath in the snout and the position where the plated metal dissolves were variously changed. When the steel strip enters the plating bath at the center of the snout when the steel strip enters the plating bath (Fig. 2), the penetration point of the steel bath is 1 / of the plating bath surface in the snout from the snout center. 8, 1/4, 3/8 When the steel strip is set so as to be deviated to the outlet side (Fig. 3), the steel strip entry position into the plating bath is 1/8, 1/4, of the plating bath surface in the snout from the snout center position. It was assumed that it was installed so as to be deflected to the 3/8 entry side (Fig. 5). Also, when the steel strip entry position into the plating bath is shifted in the steel strip width direction
(Fig. 8) was also investigated. Table 1 shows the results of a steady-state investigation in which the plating metal was not melted. From Table 1, the invention example in which the steel strip intrusion position into the plating bath is closer to the steel strip exit side than the snout center position has a smaller number of surface defects than the case where it is on the entrance side than the snout center or the center position. It can be seen that the larger the amount of deviation to the steel strip exit side, the smaller the number of surface defects. Furthermore, the effect of shifting the steel strip entry position into the plating bath toward the operation side of the line was not confirmed.

Table 2 shows that, in each case where the position where the steel strip enters the plating bath was similarly changed, the replenishment of the plating metal was performed on the steel strip entry side of the plating bath (FIG. 4). FIG. 6 shows the results of investigation during replenishment of the plating metal when performed on the side surface (FIG. 6) and when performed on the steel strip exit side of the plating bath (FIG. 7). As shown in Table 2, the plating metal replenishment according to the present invention was performed on the steel strip entry side of the plating bath regardless of the plating metal replenishment method, and the steel strip entry position into the plating bath was shifted from the snout center position to the steel strip entry side. It can be seen that when deviated, plated steel strips with the least surface defects and excellent quality can be obtained. Furthermore, the effect of shifting the steel strip entry position into the plating bath toward the line operation side in the plate width direction was not confirmed.

[0020]

[Table 1]

[0021]

[Table 2]

[0022]

As described above, according to the present invention, the position where the steel strip enters the plating bath is deviated to the steel strip exit side from the center position of the snout to perform plating so that the steel strip enters the snout along the sink roll. This makes it possible to reduce the dross that occurs, and it is possible to significantly suppress dross adhesion to the steel strip in the snout in a steady state. Further, in the present invention, by supplying the plating metal on the steel strip entrance side of the plating bath, the bath having a high dross precipitation due to the temperature drop, the increase of the Al concentration, and the turbulent flow due to the supply of the plating metal causes the bath to enter the snout. It is possible to reduce the amount of steel that reaches the steel strip exit side, and by plating the steel strip entering the plating bath so that it deviates from the snout center position toward the steel strip entry side, dross precipitation due to replenishment of the plating metal is achieved. It is possible to reduce the amount of a large amount of bath entering into the snout from the steel strip entry side, and it is possible to effectively suppress dross adhesion to the steel strip in the snout when replenishing the plating metal. Further, according to the present invention, the change of the steel strip intrusion position into the plating bath inside the snout is performed by changing the position of the snout, the position of the sink roll and / or the position of the roll on the exit side of the annealing furnace, and the combination thereof. On the other hand, it can be effectively implemented by means for displacing relatively in the direction of the steel strip entrance and exit. Therefore, according to the present invention, it is possible to prevent surface irregularities and non-plating without lowering productivity, workability, etc., and to stably produce a plated steel strip having excellent quality at low cost. .

[Brief description of the drawings]

FIG. 1 is an explanatory view of a continuous molten metal plating line.

FIG. 2 is a view showing a conventional steel strip entry position into a plating bath in a snout.

FIG. 3 is a diagram showing a position where a steel strip enters a plating bath in a snout at a steady state.

FIG. 4 is a view showing a position where a steel strip enters a plating bath in a snout when a plating metal is supplied.

FIG. 5 is a view showing a position where a steel strip enters a plating bath in a snout in a comparative example.

FIG. 6 is a diagram showing a plating metal replenishing location in a comparative example.

FIG. 7 is a diagram showing a plating metal replenishing location in a comparative example.

FIG. 8 is a view showing a case where a position where a steel strip enters a plating bath is deviated in a width direction of the steel strip.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Steel strip 2 Non-oxidizing furnace 3 Annealing furnace 4 Snout 5 Zn bath 5a Bath surface in a snout 5b Bath surface of a steel strip rising part 6 Sink roll 7 Gas wiper 8 Winding roll 9 Plating metal replenishing device 10 Snout center position 11 Plating Metal ingot 12 Annealing furnace outlet roll

[Procedure amendment]

[Submission date] June 24, 1997

[Procedure amendment 1]

[Document name to be amended] Statement

[Correction target item name] 0018

[Correction method] Change

[Correction contents]

[0018]

EXAMPLE In the continuous hot-dip galvanizing line shown in FIG. 1, the Al concentration in the plating bath was 0.16 mass% and the plating bath temperature was 4%.
70 ° C., the line speed as 1.7 m / s, subjected to the molten zinc coating weight 60g / m ² Nb-Ti-based extreme low carbon steel strip, about the occurrence of surface defects due to dross resulting plated steel strip surface Was visually inspected. At this time, the position where the steel strip enters the plating bath in the snout and the position where the plated metal dissolves were variously changed. When the steel strip enters the plating bath at the center of the snout when the steel strip enters the plating bath (Fig. 2), the penetration of the steel strip into the plating bath is 1 / of the plating bath surface in the snout from the snout center. 8, 1/4, 3/8 When the steel strip is installed so as to be deviated to the outlet side (Fig. 3), the steel strip intrusion position into the plating bath should be 1/8, 1/4, It was assumed that it was installed so as to be deflected to the 3/8 entry side (Fig. 5). Also, when the steel strip entry position into the plating bath is shifted in the steel strip width direction
(Fig. 8) was also investigated. Table 1 shows the results of a steady-state investigation in which the plating metal was not melted. From Table 1, the invention example in which the steel strip entry position into the plating bath is closer to the steel strip exit side than the snout center position has a smaller number of surface defects than when the snout center or the entrance position is closer to the center position, It can be seen that the larger the amount of deviation to the steel strip exit side, the smaller the number of surface defects. Furthermore, the effect of shifting the steel strip entry position into the plating bath toward the operation side of the line was not confirmed.

Claims (5)

[Claims] 1. A molten metal plating method in which a steel strip annealed in a high-temperature atmosphere is continuously guided into a molten metal plating bath through a snout, turned vertically upward by a sink roll, and drawn out of the plating bath. A continuous hot-dip metal plating method characterized in that a steel strip intruding position into a bath surface of a snout is shifted to a position closer to a steel strip exit side than a central position of a snout during steady plating to perform plating. 2. The plating method according to claim 1, wherein
When replenishing the plating metal, the position where the steel strip enters the plating bath surface in the snout is shifted to a position closer to the steel strip entry side than the snout center position, and the plating metal is replenished from the steel strip entry side of the plating bath. A continuous hot-dip metal plating method. 3. A plating bath in which a steel strip is introduced, a snout for introducing an annealed steel strip into the plating bath while shielding the atmosphere, and a sink for turning the steel strip upward in the plating bath. A continuous hot-dip metal plating apparatus comprising: a roll; and a displaceable position of the steel strip in the snout that can be displaced relative to an inner wall of the snout in a direction toward and away from the steel strip. 4. The plating apparatus according to claim 3, wherein the relative displacement between the entry position of the steel strip and the inner wall of the snout is performed by moving the snout. 5. The plating apparatus according to claim 3, wherein the relative displacement between the entry position of the steel strip and the inner wall of the snout is performed by changing the position of the sink roll and / or the roll on the exit side of the annealing furnace.