JP5773704B2 - Continuous hot dipping equipment - Google Patents

Description

  The present invention relates to a continuous hot dipping apparatus for continuously dipping and pulling up a steel strip in a hot dipping bath.

  Conventionally, in the production of Zn-plated steel sheet, Zn-Al-Mg alloy-plated steel sheet, Zn-Al-based alloy-plated steel sheet, Al-plated steel sheet, etc., the steel strip is continuously conveyed into the hot dipping bath, and the sink roll It is the mainstream to use a continuous hot dipping apparatus that changes the traveling direction of the steel strip to the pulling direction and pulls it vertically. In such a continuous hot dipping apparatus, foreign matter adheres to the surface of the sink roll as the operation time elapses, which may deteriorate the surface properties of the plated steel sheet. In particular, when manufacturing hot-dip Zn-Al alloy-plated steel sheets (so-called galvalume steel sheets, etc.), foreign substances mainly composed of hard Al-Si-Fe intermetallic compounds tend to wrap around the sink roll surface, resulting in frequent surface defects called ablation. It was often a problem. In order to alleviate this kind of trouble, it is effective to replace the sink roll at an early stage, but this greatly reduces the productivity.

  Therefore, as a technique for preventing the adhesion of foreign matter on the surface of the sink roll, a method of mechanically removing foreign matter attached to the surface of the sink roll with a scraper during operation has been proposed (Patent Document 1). According to this method, the wrapping of the foreign matter can be suppressed by always cleaning the entire width of the sink roll with the scraper.

  However, in the actual operation, when a wide scraper for applying a mechanical external force to the entire width of the sink roll surface is used, it is not always easy to achieve stable cleaning of the roll. Since the sink roll oscillates to some extent, it is difficult to stably apply a uniform load to the entire width of the sink roll, and a portion where the effect of removing foreign matters is insufficient in the width direction of the sink roll tends to occur. In addition, since a resistance against rotation of the sink roll increases when a very large load is applied, there is a drawback that it is difficult to sufficiently secure a mechanical external force applied per unit length in the width direction with a wide scraper.

  In view of this, it was considered promising to apply a scraper having a short length in the width direction and adjust the contact force between the scraper and the roll surface so as to be as uniform as possible. In this case, the operation of partially cleaning the surface of the sink roll is repeated over the entire width while moving the scraper periodically or continuously in the width direction of the sink roll. As a result, a larger mechanical external force can be applied per unit length in the width direction than when a wide scraper is used, so that the performance of scavenging foreign matter is improved and the mechanical external force in the width direction of the scraper is reduced. Since the uniformity is reduced, the ability to scrape foreign matter can be evenly exhibited over the entire width of the sink roll.

JP 2004-218057 A Japanese Patent No. 3993715 Japanese Patent No. 4042912

  Using a scraper with a short width in the width direction as described above, the method of partially cleaning the surface of the sink roll over the entire width is extremely advantageous in that uniform foreign matter removal can be performed in the width direction of the roll. is there. However, since foreign matter is wound little by little on the roll surface not in contact with the scraper during operation, when cleaning the new part by moving the scraper in the width direction, the foreign matter is already wound to some extent. As a result, the amount of foreign matter to be scraped off tends to increase. The foreign matter scraped off becomes dross and rides on the flow of molten metal around the sink roll, and may be caught between the steel strip and the sink roll. Since dross resulting from the scraped foreign matter is often composed of relatively coarse particles, the biting of the dross causes a large defect on the surface of the hot dip plated steel sheet, which is often a problem.

  On the other hand, an apparatus for removing dross in the plating bath and a dross removing method using the apparatus have already been developed (Patent Documents 2 and 3). The technology has been utilized in actual operations and has achieved certain effects. However, even if such a dross removal technique is used in combination, the current situation is that the trouble caused by the foreign matter scraped off by a short scraper has not been drastically solved.

  The present invention remarkably suppresses dross caused by the scraped foreign matter from being caught between the steel strip and the sink roll in the production of a continuous hot-dip galvanized steel sheet in which the foreign matter adhering to the sink roll surface is scraped off with a scraper. To provide practical technology for

The purpose of the above is a position (steel strip) where the steel strip is detached from the sink roll in the hot dipping apparatus in which the sink roll is installed in the hot dipping bath to change the traveling direction of the steel strip continuously conveyed to the pulling direction. A scraper that mechanically removes foreign matter adhering to the surface of the sink roll at the outer periphery of the sink roll between the band stripping position) and the position at which the steel strip starts to contact the sink roll (steel strip contact start position) In addition, a continuous melting provided with a shielding plate for changing the flow direction of the molten metal around the sink roll between the scraper installation position and the steel strip contact start position so as to satisfy the following installation conditions (a) to (c) Achieved by plating equipment.
[Shielding conditions]
(A) The gap d between the sink roll surface and the lower end of the shielding plate is 8 mm or less over the entire width of the sink roll.
(B) The distance R _TOP from the rotation axis of the sink roll to the upper end of the shielding plate over the entire width of the sink roll is not less than 1.5 times the sink roll radius R (however, there is a portion where the upper end of the shielding plate protrudes on the bath surface). In some cases, this restriction does not apply to that part).
Of the horizontal section cut (c) shielding蔽板, in all of the horizontal cross-section cut front surface of the shielding plate width central portion exclusion area (limited to horizontal section below the bath surface), the normal of the front surface of the shield Is in the width center excluded area and is directed away from the width center line, and the angle between the normal and the width center line is 5 to 45 ° throughout the width center excluded area.
Here, “width direction” means a direction parallel to the rotation axis of the sink roll, and “width center plane” means a plane passing through the center of the sink roll in the width direction and perpendicular to the rotation axis. The “part excluded region” means a region where the distance in the width direction from the width center plane is 5% or more of the sink roll width W _R , and the “width center line” means an intersection line of the width center plane and the horizontal plane in the horizontal plane The “front surface” means the surface of the shielding plate on the scraper side.

This apparatus is particularly effective when applied to a molten Zn-Al alloy plating bath composed of Al: 50-60%, Si: 0.1-3%, the balance Zn and inevitable impurities, for example. .
Further, in mass%, Al: 2 to 20%, Mg: 0.5 to 5%, Si: 0 to 3%, Ti: 0 to 0.1%, B: 0 to 0.05%, the balance Zn and Even when applied to a molten Zn—Al—Mg alloy plating bath made of inevitable impurities, a great effect of improving the surface properties can be obtained depending on the plating conditions.

The scraper is 0.1 to 0.5 times the sink roll surface width direction length W _S sink roll width W of the portion in contact with the _R, plating bath outside via a movable mechanism in the widthwise direction It is particularly preferred that it is attached to the member.

  According to the present invention, in a continuous hot dipping apparatus generally used for the production of Zn plated steel sheets, Zn—Al—Mg alloy plated steel sheets, Zn—Al alloy plated steel sheets, Al plated steel sheets, It became possible to simultaneously realize the cleaning of the surface of the inner sink roll and the suppression of dross biting, which was likely to occur at the same time, by a simple method. As a result, particularly in the production of a hot-dip Zn-Al alloy-plated steel sheet, which has conventionally been susceptible to foreign matter wrapping around the sink roll surface, the surface quality is greatly improved and the productivity is improved by extending the sink roll replacement period. . Further, even in a plating type (Zn plating, Al plating, etc.) in which dross entrainment has not been a problem, a further improvement in surface quality can be expected.

The figure which illustrated typically the cross section perpendicular | vertical to the sink roll rotating shaft in the hot dipping bath in the hot dipping apparatus according to this invention. The figure which illustrated typically the horizontal cross section which cuts the shielding board in the hot dipping bath in the hot dipping apparatus according to this invention.

  FIG. 1 schematically illustrates a cross section perpendicular to a sink roll rotation axis in a hot dipping bath in a hot dipping apparatus according to the present invention. The portion visible behind the cross section is omitted. There is a sink roll 2 in the hot dipping bath 1. The steel strip 3 is continuously conveyed in the direction of the arrow, the traveling direction is changed along the surface of the sink roll 2 in the hot dipping bath 1, and the steel strip 3 is pulled up in the vertical direction. The position at which the steel strip 3 starts to contact the surface of the sink roll 2 (reference numeral 12) is referred to as a “steel strip contact start position”, and the position at which the steel strip 3 is separated from the surface of the sink roll 2 (reference numeral 11) This is referred to as the “leave position”. As the surface member of the sink roll 2, stainless steel (for example, SUS316) or the like is employed. A direction parallel to the rotation axis 10 of the sink roll 2 is referred to as a “width direction” in the present specification.

  A scraper 4 that mechanically removes foreign matter adhering to the surface of the sink roll 2 is provided between the steel strip separation position 11 and the steel strip contact start position 12 on the outer periphery of the sink roll 2. The tip of the scraper 4 is made of a heat-resistant and wear-resistant special alloy (for example, Stellite (registered trademark)). Although the scraper 4 is attached to the support member 41, it is desirable that the scraper 4 can follow the swing of the sink roll 2 using a spring mechanism or the like.

The scraper 4 may have a wide width that covers the entire width W _R of the sink roll 2, but by applying a scraper 4 having a length in the width direction that is considerably shorter than W _R , The contact force per unit length can be further increased, and the variation of the contact force in the width direction can be made more uniform. The scraper 4 whose width direction length is shorter than W _R is attached to a member outside the plating bath via a mechanism movable in the width direction. During operation, the roll surface of the part is cleaned for a certain period with the position in the width direction fixed, then shifted in the width direction, and the roll surface of the part is similarly cleaned for a certain period. By repeating this operation over the entire width of the roll, the clean state of the entire roll surface is maintained. However, foreign matter gradually adheres to the surface portion of the sink roll 2 to which the scraper 4 is not applied, during operation. Therefore, it is important to manage the shift time of the scraper 4 so that the entire roll surface is cycled before the surface quality of the plated steel sheet is adversely affected. A drive device in the width direction may be provided so that the scraper 4 can be operated while reciprocating in the width direction.

As a result of various investigations, the width direction length W _S of the scraper 4 is the relation between the sink roll width W _R, it is more effective to limit the length of the W _S ≦ 0.5W _R. It may be W _S ≦ 0.4W _R. However, because it leads to a decrease of productivity increase in the number of shifts to too short a width direction, it is desirable that the W _S ≧ 0.1W _R.

In the hot dipping apparatus according to the present invention, in addition to the scraper 4, a shielding plate 5 for changing the flow direction of the molten metal is further provided between the installation position of the scraper 4 and the steel strip contact start position 12. As installation conditions for the shielding plate 5, the following points must first be satisfied.
(A) The gap d between the surface of the sink roll 2 and the lower end of the shielding plate 5 is 8 mm or less over the entire width of the sink roll 2.

  According to many experiments by the inventors, when the gap d exceeds 8 mm, the flow of the molten metal passing through the gap increases as the sink roll 2 rotates, and the scraper 4 scrapes off the roll surface. The dross caused by the foreign matter is easily carried on the flow of the molten metal and passes through the gap. The dross that has passed through the gap is caught between the steel strip 3 and the sink roll 2 at the steel strip contact start position 12 to form a surface defect of the plated steel plate. Therefore, the gap d needs to be adjusted to 8 mm or less, and more preferably 5 mm or less.

The smaller the gap d, the better for preventing dross biting. However, if the gap d is too close, the sink roll 2 gradually rises due to wear of the rotating shaft mechanism during operation. There is a risk of surface contact. On the other hand, the surface of the sink roll 2 is worn by mechanical contact with the scraper 4. Under operating conditions with a high wear rate, the gap d may gradually widen. Therefore, in consideration of these conditions, it is necessary to manage such that the gap d is maintained at 8 mm or less, preferably 5 mm or less. For example, under operating conditions where the gap d gradually decreases, the gap d is set to 8 mm at the largest portion in the initial state, the operation is started, and the lower end of the shielding plate 5 comes into contact with the sink roll 2. A gap management method can be applied in which the gap d is readjusted in the same manner as in the initial state before (for example, when d becomes 1 mm at the minimum portion).
It is desirable that the shielding plate 5 is directly attached to the frame housing the sink roll 2 in order to control the gap d with high accuracy.

  Here, FIG. 1 exemplifies one cross section perpendicular to the rotating shaft 10, but “over the entire width of the sink roll 2” means all cross sections that cut the surface of the sink roll 2 among such vertical cross sections. Means that it is necessary to satisfy the above-mentioned predetermined condition (the same applies to (b) described later).

As installation conditions for the shielding plate 5, the following points must be satisfied.
(B) The distance R _TOP from the rotating shaft 10 of the sink roll 2 to the upper end of the shielding plate 5 over the entire width of the sink roll 2 is not less than 1.5 times the sink roll radius R (however, the upper end of the shielding plate 5 is the bath). If there is a part on the surface, do not apply this restriction to that part).

  The shielding plate 5 applied in the present invention plays an important role of forming a flow of molten metal in the width direction in the hot dipping bath 1 as described later. For this purpose, it is necessary that the upper end of the shielding plate 5 be at a sufficiently high position over the entire width of the sink roll 2. If the upper end position of the shielding plate 5 is too low, the molten metal near the outer periphery of the sink roll 2 flowing along with the rotation of the sink roll 2 gets over the shielding plate 5 and easily flows into the steel strip contact start position 12 side. For this reason, it becomes difficult to prevail the flow in the width direction, and the problem of dross biting is not sufficiently improved.

According to the inventors' detailed examination, the distance R _TOP from the rotating shaft 10 of the sink roll 2 to the upper end of the shielding plate 5 is set to 1.5 times or more of the sink roll radius R over the entire width of the sink roll 2. Thus, the flow in the width direction can be made dominant. It is more effective to set it to 1.8 times or more. As the distance from the surface of the sink roll 2 increases, the flow of the molten metal that occurs with the rotation of the sink roll 2 becomes smaller. The upper limit of the upper end position is not limited, but considering the installation space, R _TOP may be set in a range that is usually 2.5 times or less of the sink roll radius R at the lowest position in the width direction.

FIG. 2 schematically illustrates a horizontal cross section (as viewed from above vertically) of the shielding plate 5 in the hot dipping bath in the hot dipping apparatus according to the present invention. In the drawing, the projected shape of the sink roll 2 is shown for convenience. The description of the portion of the shielding plate 5 visible behind this cross section is omitted to avoid complication. The projection position of the contact portion of the scraper 2 on the surface of the sink roll 2 is also illustrated (reference numeral 42). And it is movable over the entire width of the roll width W _R on the scraper contact portion 42 in the width direction (direction parallel to the rotation axis projection line 13).

Here, a plane that passes through the center of the sink roll 2 in the width direction and is perpendicular to the rotation axis is referred to as a “width center plane”. A line of intersection between the width center plane and the horizontal cross section is referred to as a “width center line” (reference numeral 14). An area where the distance in the width direction from the width center plane is less than 5% of the sink roll width W _R is referred to as a “width center area” (reference numeral 7). A region in which the distance in the width direction from the width center plane is 5% or more of the sink roll width W _R , that is, a region excluding the width center region 7 is referred to as a “width center excluded region” (reference numerals 8A and 8B). The surface of the shielding plate 5 on the scraper side (steel strip separating position 11 side) is referred to as “front surface” (reference numeral 51).

In addition to the above (a) and (b), it is important to satisfy the following points as installation conditions for the shielding plate 5.
(C) Of all the horizontal cross sections that cut through the shielding plate 5, the shielding plate 5 in all horizontal cross sections that cut the front surface 51 of the shielding plate 5 in the width center excluded regions 8A and 8B (limited to the horizontal cross section below the bath surface). The normals 52A and 52B of the front surface 51 of the front surface 51 face away from the width center line 14 in the width center excluded areas 8A and 8B, and the normal lines 52A and 52B extend over the entire width center excluded areas 8A and 8B. And the angles θ _A and θ _B formed by the width center line 14 are 5 to 45 °.

In the present invention, the shielding plate 5 performs an important function of guiding the flow of the molten metal generated at the outer peripheral portion of the sink roll 2 to both sides in the width direction. It was found that when a flow in the width direction is formed in the hot dipping bath 1, the flow over the shielding plate 5 is remarkably suppressed, and dross biting is greatly reduced. Using this flow behavior, it is possible to effectively suppress the biting of dross containing prone coarse particles in the width direction length W _S was used considerably shorter scraper 4 than the roll width W _R, short Combined with the uniform cleaning effect of the surface of the sink roll 2 obtained by using the scraper 4, it becomes possible to produce a plated steel sheet having a more excellent surface quality.

The shielding plate 5 is installed near the center in the width direction so that the normal direction of the front surface 51 is distributed to both sides. Although it is advantageous to equalize the flow state of the molten metal in the hot dipping bath 1 on both sides of the steel strip, the arrangement of the shielding plate 5 is symmetric on both sides. It was found that the same effect as in the case of perfect symmetry can be obtained. As a result of various studies, a point (reference numeral 53; “folding point”) closest to the steel strip separation position 11 in the front surface 51 is the width central portion region 7 (the distance in the width direction is the sink roll width W _R. If the turning point 53 is on the width center line 14, the effect is not much different. That is, in the width center region 7, the normal line of the front surface 51 may face either side in the width direction, and in this region, the front surface 51 facing the front (in the direction of the strip stripping position 11). There may be parts. The shape of the shielding plate 5 does not necessarily have to be completely symmetrical with respect to the turning point 53, and is adjusted within a range that satisfies the conditions according to the present invention according to the inner surface shape of the plating bath pot to be used. Can do.

On the other hand, the orientation of the front surface 51 in the width center excluded areas 8A and 8B is important. In this region, the normals 52A and 52B of the front surface 51 must both face away from the width center line 14 on both sides. Accordingly, it is possible to form a flow for escaping the molten metal that has traveled in the direction of the shielding plate 5 in the width direction. As a result of many experiments using a pilot line, the angles θ _A and θ _B formed between the normal lines 52A and 52B and the width center line 14 are set to 5 ° or more over the entire width center exclusion region 8A and 8B. The flow in the width direction can be dominant. The horizontal cross-sectional shape of the front surface 51 may be a straight shape or a curved shape, but in the case of a curved shape, θ _A and θ _B are 5 ° in any part of the width central portion exclusion regions 8A and 8B. Try to be above. The upper limits of θ _A and θ _B are limited by the installation space, but may be set within a range of 45 ° or less. It is good also as 30 degrees or less. In the case where the horizontal cross-sectional shape of the front surface 51 is a linear shape, it is desirable that θ _A and θ _B be 5 to 15 ° in consideration of application to many existing hot dipping apparatuses.

  FIG. 2 exemplifies a horizontal cross section at a certain height position. Depending on the height position, the front surface 51 of the shielding plate 5 has a width center exclusion region 8A, 8B in a horizontal section that cuts the shielding plate 5. There are cases where they appear inside and where they do not appear. For a horizontal cross section at a height position where the front surface 51 does not appear in the width center excluded areas 8A and 8B, there is no restriction on the direction of the normal line of the front surface 51. For the horizontal cross section at the height position where the front surface 51 appears in a part of the width center excluded area 8A, 8B, the above-mentioned provision for the normal direction is applied to the portion of the front surface 51 appearing in the cross section. To do. In addition, the shape of the lower end part of the shielding board 5 is set so that it may become a predetermined | prescribed curved shape according to the sink roll radius R so that the prescription | regulation of the above-mentioned clearance gap d can be satisfy | filled.

The hot dip plating apparatus having the above configuration is applicable to various hot dip platings. In particular, in mass%, Al: 50 to 60%, Si: 0.1 to 3%, the balance Zn and unavoidable impurities. When applied to a molten Zn—Al-based alloy plating bath, a very large merit can be obtained.
Further, in mass%, Al: 2 to 20%, Mg: 0.5 to 5%, Si: 0 to 3%, Ti: 0 to 0.1%, B: 0 to 0.05%, the balance Zn and Experiments using a pilot line that the degree of freedom in hot dipping conditions to achieve good surface properties is greatly improved even when applied to hot-dip Zn-Al-Mg alloy plating baths consisting of inevitable impurities Has been confirmed by.

The present invention can be applied to various scale hot dipping apparatuses. For example, the sink roll width W _R can be set in a wide range of 200 to 2000 mm. In the mass production site W _R there are many things about 1000~1750mm. The sink roll radius R is set in a range of, for example, 30 to 500 mm according to the width W _R.

[Conventional example]
In a conventional general continuous hot dipping line, a hot-dip Zn-Al alloy-plated steel sheet was manufactured under the following conditions while cleaning the surface of the sink roll with a scraper.
-Plating bath composition: In mass%, Al: 55%, Si: 1.5%, the balance Zn and inevitable impurities.
Sink roll; radius R: 350 mm, surface width W _R : 1500 mm, surface material: SUS316.
-Scraper: Length in the width direction W _S : 500 mm, tip material: Stellite (registered trademark), the position was periodically shifted in the width direction, and the entire surface of the sink roll was repeatedly cleaned.
-Shield plate; not installed.
・ Plating bath temperature: 600 ℃ ± 10 ℃
Plated original sheet; Steel strip of a cold rolled annealed steel sheet having a thickness of 0.20 to 2.30 mm and a width of 610 to 1320 mm.
-Line speed: The range of 58-185 m / min.

The operation was continued for 14 days under the above conditions, and the surface properties of the obtained hot-dip galvanized steel sheet were investigated in-line by an inspection method in ordinary quality control. At that time, according to a certain standard, count the number of disqualified coils that cannot be shipped as `` skin strict standard material '' due to biting of dross, and divide that number by the total number of plate coils, and the defect rate Was calculated. In addition, in this disqualified coil, many what can be used as a general standard material which does not attach importance to skin are contained.
In this conventional example, many downgrade coils were generated. The occurrence rate is set to K ₀ (%), and this is used as a reference for evaluating the effect in each example described later.

[Invention Example]
Hot-dip Zn-Al alloy plating under the same hot-plating conditions as in the above-mentioned conventional example, except that a shielding plate was placed between the scraper placement position and the steel strip contact start position (reference numeral 12 in FIG. 1) according to the following conditions. A steel plate was produced.
-Shielding plate; By shielding two SUS316 flat plates, a shielding plate (with a total width of about 1700 mm) having a symmetrical shape at the turning point 53 (FIG. 2) was produced. The lower ends of the two flat plates are each formed in an arc shape along the surface of the sink roll. This shielding plate was attached to a frame that accommodated the sink roll, and a hot dipping apparatus having a configuration as shown in FIGS. 1 and 2 was constructed. The gap d between the sink roll surface and the lower end of the shielding plate was 8 mm (initial state). The distance R _TOP from the rotation axis of the sink roll to the upper end of the shielding plate was set to 680 mm (initial state) at the lowest position among the entire width of the sink roll. In this case, R _TOP is 1.94 times the initial value of the sink roll radius R (350 mm). The installation position of the shielding plate was made symmetrical on both sides with respect to the width center plane. That is, the turning point 53 in FIG. 2 is on the width center line 14. The normals 52A and 52B of the front surface 51 of the shielding plate face away from the width center line 14, and the angles θ _A and θ _B formed by the normals 52A and 52B and the width center line 14 are both 10 °. is there.

The operation was continued for 14 days in the same manner as in the above-described conventional example, and the surface properties of the obtained hot-dip galvanized steel sheet were evaluated according to the same criteria as in the above-described conventional example, to determine the rate of occurrence of broken coils K ₁ (%). As a result, in comparison with the conventional example, K ₁ / K ₀ = 0.21, and a significant quality improvement effect was recognized.

  The wear on the surface of the sink roll due to the mechanical contact of the scraper contributes to the direction of widening the gap d, and the rise of the sink roll due to wear of the rotating shaft mechanism contributes to the direction of narrowing the gap d. In the case of this example, it is known that the gap d tends to decrease slightly in consideration of the offset due to both of the above contributions. Therefore, in this example, the gap d is maintained at 8 mm or less during operation.

[Comparative Example]
Except that the shield plate is a single flat plate, and the angles θ _A and θ _B formed by the normal lines 52A and 52B and the width center line 14 are both 0 °, A hot-dip Zn—Al-based alloy-plated steel sheet was produced under the same hot-dip conditions as in the above-described example of the present invention.
Here, the distance R _TOP from the rotation axis of the sink roll to the upper end of the shielding plate is set to 700 mm (initial state) over the entire width of the sink roll. In this case, R _TOP is twice the initial value of the sink roll radius R (350 mm). The gap d between the sink roll surface and the lower end of the shielding plate was 8 mm (initial state) as in the above-described example of the present invention.

In the same manner as in the above-described conventional example and the present invention example, continuous operation was performed for 14 days, and the surface properties of the obtained hot-dip galvanized steel sheet were evaluated according to the same criteria as in the above-described conventional example, and the rate of occurrence of broken coils K ₂ (%) was obtained. It was. As a result, in comparison with the conventional example, K ₂ / K ₀ = 0.82, and although some improvement was observed, the improvement effect was inferior compared with the above-described example of the present invention. The reason for this is that the flow of the molten metal in the width direction cannot be prevailed by using a single flat plate as the shield plate, and is caused by foreign matter scraped off by the scraper by the flow over the upper end of the shield plate. It is thought that dross was carried to the steel plate contact start position and biting occurred frequently.

DESCRIPTION OF SYMBOLS 1 Hot dip plating bath 2 Sink roll 3 Steel strip 4 Scraper 5 Shield plate 7 Width center part region 8A, 8B Width center part exclusion region 10 Rotating shaft 11 Strip strip position 12 Strip strip start position 13 Rotating axis projection line 14 Width center Line 41 Support member 42 Scraper contact part 51 Front surface 52A, 52B Normal surface of front surface 53 Turning point

Claims (4)

The position where the steel strip separates from the sink roll in the hot dipping apparatus where the sink roll is installed in the hot dipping bath to change the moving direction of the steel strip that is continuously conveyed to the pulling direction (steel strip separation position) And a scraper that mechanically removes foreign matter adhering to the surface of the sink roll at the outer periphery of the sink roll between the position where the steel strip comes into contact with the sink roll (steel strip contact start position), and the scraper is installed. A continuous hot dipping apparatus provided with a shielding plate for changing the flow direction of the molten metal around the sink roll between the position and the steel strip contact start position so as to satisfy the following installation conditions (a) to (c).
[Shielding conditions]
(A) The gap d between the sink roll surface and the lower end of the shielding plate is 8 mm or less over the entire width of the sink roll.
(B) The distance R _TOP from the rotation axis of the sink roll to the upper end of the shielding plate over the entire width of the sink roll is not less than 1.5 times the sink roll radius R (however, there is a portion where the upper end of the shielding plate protrudes on the bath surface). In some cases, this restriction does not apply to that part).
Of the horizontal section cut (c) shielding蔽板, in all of the horizontal cross-section cut front surface of the shielding plate width central portion exclusion area (limited to horizontal section below the bath surface), the normal of the front surface of the shield Is in the width center excluded area and is directed away from the width center line, and the angle between the normal and the width center line is 5 to 45 ° throughout the width center excluded area.
Here, “width direction” means a direction parallel to the rotation axis of the sink roll, and “width center plane” means a plane passing through the center of the sink roll in the width direction and perpendicular to the rotation axis. The “part excluded region” means a region where the distance in the width direction from the width center plane is 5% or more of the sink roll width W _R , and the “width center line” means an intersection line of the width center plane and the horizontal plane in the horizontal plane The “front surface” means the surface of the shielding plate on the scraper side.   The continuous hot-dip plating bath according to claim 1, wherein the hot-dip plating bath is a hot-dip Zn-Al alloy plating bath composed of Al: 50-60%, Si: 0.1-3%, the balance Zn and inevitable impurities. Hot dipping equipment.   The hot dipping bath is in mass%, Al: 2 to 20%, Mg: 0.5 to 5%, Si: 0 to 3%, Ti: 0 to 0.1%, B: 0 to 0.05%, The continuous hot dipping apparatus according to claim 1, which is a hot-dip Zn-Al-Mg alloy plating bath comprising the remaining Zn and inevitable impurities. The scraper is 0.1 to 0.5 times the sink roll surface width direction length W _S sink roll width W of the portion in contact with the _R, plating bath outside via a movable mechanism in the widthwise direction The continuous hot dipping apparatus according to any one of claims 1 to 3, which is attached to a member.

Images