JP2008150642A - Method and device for producing hot dip plated steel sheet - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a hot dip plating method by which the occurrence of edge overcoat and whiskers can be suppressed even when causing warpage in a steel sheet. <P>SOLUTION: In the production of a hot dip plated steel sheet, when gas is blown to the surface of a steel sheet from a wiping nozzle, and the coating weight of plating is controlled, auxiliary nozzles are installed in the upper and lower parts of the edge parts of the wiping nozzle, respectively. The gas flows blown from the upper and lower auxiliary nozzles are allowed to collide with the gas flow blown from the wiping nozzle, and further, the flow rate of the gas blown from the upper and lower auxiliary nozzles is controlled to 1.5 to 10 times the flow rate of the gas from the wiping nozzle. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to the manufacture of hot dip galvanized steel sheets, and more particularly to a method and apparatus for hot dip plating that suppresses the generation of defects such as edge overcoats and whiskers on the plating surface.

When manufacturing a hot-dip plated steel sheet, as shown in FIG. 1 (a), gas is blown from the wiping nozzle onto the surface of the steel sheet pulled up from the hot-dip plating bath, and excess plating metal is wiped off to adjust the amount of adhesion. At that time, it is known that defects such as edge overcoat and whiskers occur.
Edge overcoat is a phenomenon in which the gas spray pressure at the end of the steel sheet decreases due to the interference of the gas flow from the wiping nozzles on the front and back of the steel sheet, and the amount of plating attached to the end of the steel sheet becomes larger than the center of the width. There has been proposed a technique for preventing an edge overcoat by installing an auxiliary nozzle on the end side of the nozzle.

For example, Patent Document 1 discloses that the gas from the auxiliary nozzle is sprayed from the upper part to the collision position of both ends of the steel strip of the blowing gas from the wiping nozzle. Is shown to be at a higher pressure than the wiping nozzle.
Patent Document 2 discloses that heated gas is blown from an auxiliary nozzle installed at an upper end of the wiping nozzle at a pressure 9 to 11 times that of the wiping nozzle.
In Patent Document 3, in the region of 30 to 170 mm from the edge of the metal strip to the center in the width direction, the auxiliary nozzle disposed above the wiping nozzle is directed toward the tip of the wiping nozzle and exceeds the injection pressure of the wiping nozzle. It has been shown to blow gas with pressure.

By the way, in recent years, as a plated steel sheet having better corrosion resistance, a Zn—Al—Mg-based hot-dipped steel sheet has been developed and used in building materials and the like.
In such a plating composition containing Al and Mg, the steel sheet is immersed in a hot dipping bath, and after being pulled out of the plating bath, oxides are likely to be generated on the surface of the plating layer. Since the thickness of the oxide film generated before wiping increases, unless the wiping pressure is increased, beard is likely to occur due to the separated oxide film remaining.
However, the steel plate for building materials has a plate thickness of about 1.0 mm to 9.0 mm. When a thick steel plate is passed through, the plate passing speed is about 50 mpm due to the capability of the annealing furnace. Moreover, since the plating thickness is about 15 μm to 45 μm, the pressure of the wiping nozzle must be suppressed to about 30 kPa.

  For this reason, an oxide film is more likely to be generated in a bath in which Mg or AL is added at a high concentration, compared with a bath of 99% by mass or more of Zn such as general hot dip galvanizing. Since the flow pressure is also low, it is difficult to remove the generated oxide film, and thus there is a problem that the above-mentioned beard is likely to occur.

As an example of preventing such generation of whiskers, for example, in Patent Document 4, gas is blown to the plating surface near the edge until the solidification of the plating metal above the wiping nozzle is completed. It is shown that slanting downward tension due to the plated metal at the edge of the steel plate, which causes generation of whiskers and the like, is alleviated.
Further, in Patent Document 3, when the gas is blown from the auxiliary nozzle disposed above the wiping nozzle, if the blowing position is closer to the edge side than 30 mm, the edge overcoat is eliminated, but the beard-like appearance defect at the end portion Is described as occurring.

Japanese Patent Laid-Open No. 48-42931 Japanese Patent Publication No.55-41295 Japanese Patent Laid-Open No. 10-265930 JP 2000-96201 A

In the steel sheet for building materials as described above, since the plate thickness is large and the plating weight is large, the plate passing speed is reduced accordingly, and warpage tends to occur in the width direction of the steel plate when it comes out of the plating bath. Moreover, since the steel plate is thick, it is difficult to correct the generated warp before wiping.
According to the studies by the present inventors, it has been found that when the steel sheet is warped, the following problems occur even if the auxiliary nozzle as described above is used. That is,

(A) Normally, assuming that there is no warp, the gas flow from the auxiliary nozzle is adjusted to collide with the gas flow from the wiping nozzle on the steel plate surface. There may be a shift between the steel plate and the nozzle.
(B) At this time, when the gas from the auxiliary nozzle is blown stronger than the gas from the wiping nozzle, such as when the plating thickness is thick, as shown in FIG. 1B, the gas is blown out from the wiping nozzle and the auxiliary nozzle. The collision position of the gas on the steel plate is shifted downward.
(C) Then, a portion where the pressure is reduced occurs at the boundary in the width direction between the auxiliary nozzle and the wiping nozzle, and thereby, a pressure distribution is generated at the boundary position in the threading direction, and as a result, the amount of plating attached to this portion is large. Become.

(D) Moreover, since the collision position on the steel plate of the gas flow ejected from the wiping nozzle is lowered, the relationship with the collision position on the opposite surface becomes asymmetric, and the plating solution wraps around the end of the steel plate. In particular, in the case of Zn-Al-Mg-based hot dipping, when the phenomenon of (c) above occurs, a split oxide film called whiskers is generated along with the overcoat at the end, and this is also the case of plating. It becomes a defect.
(E) Further, when the gas amount of the auxiliary nozzle is increased and the collision position further shifts downward, a line is formed between the auxiliary nozzle discharge part and the main nozzle discharge part (about 1 to 3 mm, see the upper left figure in FIG. 6). -Like overcoat occurs. This linear overcoat causes a winding shape defect when wound on a coil. In particular, in the case of Zn—Al—Mg-based hot dipping, this linear overcoat is likely to occur. This is thought to be due to differences such as higher viscosity than Al plating and a different surface oxide film from Al plating when the plating layer is semi-solidified.

  Particularly recently, as a paint base treatment, instead of chromate treatment, it has become possible to apply a treatment liquid with a roll coater.In this case, if there is an edge overcoat, the above-described linear overcoat, Since the contact pressure to the roll coater in that portion becomes high, the wear of the coater surface becomes a problem. Compared to hot dip galvanized steel sheets, the amount of the overcoat in the case of Zn-Al-Mg hot dip galvanized steel sheets, which have a large amount of plating, is more demanding to prevent their occurrence. .

However, the conventional technique does not consider the above-described problems when warping occurs in the steel sheet, and particularly, edge overcoat, linear overcoat, whiskers, etc. in hot-dip plating of thick steel sheets. Occurrence could not be prevented.
Accordingly, an object of the present invention is to provide a method and an apparatus capable of performing hot dipping while suppressing the generation of edge overcoats, linear overcoats, and whiskers.

In order to solve the above-mentioned problems, the present invention is characterized in that it is as follows in the production of a hot-dip galvanized steel sheet.
(1) In a method for manufacturing a hot-dip galvanized steel sheet in which gas is blown from the wiping nozzle onto the steel sheet surface to control the amount of plating, the auxiliary nozzles are installed above and below the end of the wiping nozzle, and the gas discharged from the upper and lower auxiliary nozzles. The flow collides with the gas flow discharged from the wiping nozzle at a position between the surface of the steel plate and the tip of the nozzle, and the gas flow rate of the gas discharged from the upper and lower auxiliary nozzles is equal to the gas flow rate from the wiping nozzle. It is characterized by being 1.5 to 10 times.
(2) In the method for producing a hot-dip galvanized steel sheet, the distance between the position where the gas flow of the upper and lower auxiliary nozzles collides with the gas flow of the wiping nozzle and the tip of the wiping nozzle is the distance between the tip of the wiping nozzle and the steel plate. It is characterized by being 10% or more.
(3) In the method for manufacturing a hot-dip galvanized steel sheet, the position where the gas flow of the lower auxiliary nozzle and the gas flow of the wiping nozzle collide is more than the position where the gas flow of the upper auxiliary nozzle and the gas flow of the wiping nozzle collide. It is characterized by being shifted by 2 mm or less to the steel plate side.
(4) In the manufacturing method of the hot-dip galvanized steel sheet, the value of (discharge flow rate of the upper auxiliary nozzle / discharge flow rate of the lower auxiliary nozzle) is further set in the range of 0.9 to 1.2.

(5) In a hot-dip plated steel sheet manufacturing apparatus that controls the amount of plating applied by blowing gas from the wiping nozzle onto the steel sheet surface, auxiliary nozzles are installed above and below the end of the wiping nozzle and discharged from the upper and lower auxiliary nozzles. The direction of the upper and lower auxiliary nozzles is set so that the gas flow to collide with the gas flow discharged from the wiping nozzle at a position between the surface of the steel plate and the tip of the wiping nozzle.
(6) In the hot-dip plated steel plate manufacturing apparatus, the distance between the gas flow of the upper and lower auxiliary nozzles and the gas flow of the wiping nozzle and the tip of the wiping nozzle is between the tip of the wiping nozzle and the steel plate. The direction of the upper and lower auxiliary nozzles is set so as to be 10% or more of the distance.
(7) In the hot-dip plated steel plate manufacturing apparatus, the position where the gas flow of the lower auxiliary nozzle and the gas flow of the wiping nozzle collide with each other than the position where the gas flow of the upper auxiliary nozzle and the gas flow of the wiping nozzle collide with each other. The direction of each of the upper and lower auxiliary nozzles is set so as to be shifted by 2 mm or less.

  According to the present invention, even when hot-plating is performed on a thick steel plate under conditions where the amount of plating is large and the plate passing speed is low, warping occurs in the width direction at the stage of removal from the plating bath. Even when the plated steel sheet is hot-dip plated, hot-dip plating can be performed while suppressing the generation of defects such as edge overcoats, linear overcoats and whiskers on the plating surface.

Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings.
In the continuous hot dipping line, after the steel sheet is immersed in the plating bath, in the process of pulling upward, the gas discharged from a pair of wiping nozzles arranged on the steel sheet outlet side of the plating bath is blown onto the steel sheet, thereby The excess plating metal adhering to the back surface is wiped off to control the amount of plating.

  At that time, only the wiping nozzle causes overcoating of the end as described above. Therefore, an auxiliary nozzle is installed at the end to suppress edge overcoat. However, in order to further prevent the occurrence of overcoat, when the gas of the auxiliary nozzle is increased, the collision point of the gas flow on the steel plate is bent downward. This phenomenon is particularly noticeable when the steel plate is warped and the steel plate and the nozzle are separated.

  And if the collision point of a gas flow is bent below, generation | occurrence | production of overcoat cannot be prevented as mentioned above. Furthermore, for highly oxidizing plating baths containing Al and Mg, it is necessary to discharge the gas from the auxiliary nozzle stronger than usual to scrape off the oxide film, but the gas discharge pressure from the auxiliary nozzle must be increased. Then, the collision part of the gas flow of the auxiliary nozzle and the wiping nozzle is further disturbed, and the generation of the pressure drop part at the boundary part is promoted. Therefore, as described above, a linear overcoat is generated between the auxiliary nozzle discharge part and the main nozzle discharge part.

Therefore, the present inventors have installed an auxiliary nozzle below the wiping nozzle (hereinafter referred to as the main nozzle) to prevent the gas collision point on the steel plate from being bent downward. Considering the cases 1 to 3 below, the flow rate of the discharge gas flow from the auxiliary nozzle (hereinafter sometimes referred to as the auxiliary gas flow), and the discharge gas flow from the auxiliary gas flow and the main nozzle (hereinafter, The position where the main gas flow collides was variously changed, and an experiment was conducted to investigate the degree of the downward bending of the main gas flow and the edge overcoat amount.
Case 1: Only the upper auxiliary nozzle is installed Case 2: Upper and lower auxiliary nozzles are installed (upper auxiliary nozzle / lower auxiliary nozzle flow rate ratio = 1.2)
Case 3: Vertical auxiliary nozzle installation (upper auxiliary nozzle / lower auxiliary nozzle flow rate ratio = 0.9 to 1.0)

Note that there are “collision” and “accompaniment” as a mode of combining two or more gas flows.
“Collision” is a merged form in which the flow direction of the main flow (here, the gas flow from the main nozzle) is bent by another gas flow (here, the gas flow from the auxiliary nozzle). "Is a merged form in which the flow velocity of the main flow is larger than the flow velocity of the other gas flow, and the other flow has the same direction as the flow of the main flow.

  In the present invention, the gas flow is combined in a “collision” form so that the gas flow from the main nozzle is kept straight by the upper and lower auxiliary nozzles. In the case of the “collision” mode, the gas flow rate of the gas discharged from the upper and lower auxiliary nozzles needs to be 1.1 times or more the gas flow rate from the main nozzle. If less than 1.1 times, two or more gas streams are “adjacent” streams.

  FIG. 2 shows a gas blowing state in each case, and FIG. 3 shows an example of a result obtained by an experiment. Note that the edge overcoat amount indicates the result of investigation on Case 2.

In FIG. 3, the main nozzle gas flow bending collision position is the downward bending of the main gas flow 3 when the collision position P of the auxiliary gas flow 4 and the main gas flow 3 is changed from the tip of the main nozzle 2 toward the steel plate 1. Shows the collision position of the auxiliary gas flow and the main gas flow when the predetermined value is exceeded, and the main nozzle tip when the maximum flow velocity when the main gas flow 3 collides with the steel sheet is bent downward by 3 mm or more The ratio of the distance D from the tip of the main nozzle 2 to the distance L between the steel plate and the steel plate, that is, the value of D / L.
The gas flow is a fluid having a spread and has a velocity distribution. For this reason, each collision position is defined as a position where the maximum flow velocity portion of each gas flow collides.

For example, for the case 1, when the ratio of the discharge flow rate of the nozzle is 0.5, the main gas flow at the position of 0.1 from the tip of the main nozzle toward the steel plate, that is, the position where D / L is 0.1. It shows that when the auxiliary gas flow collided, the main gas flow collided with the steel plate in a state of being bent downward by 3 mm or more.
Therefore, in each case, if the collision position of the main gas flow and the auxiliary gas flow is above the line in the figure, it indicates that the main gas flow is not substantially bent.

  From FIG. 2, in the case of cases 2 and 3 provided with auxiliary nozzles at the top and bottom, the main gas flow can be prevented from bending if the collision position of the main gas flow and the auxiliary gas flow is on the steel plate side from the position of 0 or 1. It has been found that edge overcoat can be prevented when the ratio of the discharge flow rates of the main nozzle and auxiliary nozzle is 1.5 or more. In contrast, in the case 1 in which only the upper auxiliary nozzle is provided, it has been found that when the discharge flow rate from the auxiliary nozzle is increased, the main gas flow is bent.

  The present invention has been made on the basis of the above-described results, and further examined the operating conditions of the auxiliary nozzle, and the present invention will be sequentially described below.

In the present invention, as shown in FIG. 4 (a), in the production of the hot dip galvanized steel sheet, when the amount of plating applied is controlled by spraying the gas discharged from the main nozzle 2 onto the surface of the steel sheet 1, Auxiliary nozzles are installed above and below the end.
At that time, the auxiliary gas flows 4, 5 discharged from the upper and lower auxiliary nozzles are set to the respective directions of the upper and lower auxiliary nozzles so as to collide with the main gas flow 3 at a position between the steel plate surface and the main nozzle tip, Even if the steel plate is warped, the auxiliary gas flow should not directly collide with the steel plate.

By doing so, even if the steel plate is warped and the steel plate position deviates from the middle of the front and back main nozzle positions, the auxiliary gas flows 4 and 5 do not directly collide with the steel plate as shown in FIG. The difference in collision pressure between the front and back surfaces of the steel sheet is small, and the collision position of the main gas flow at the outer part of the steel sheet is on the extension line of the steel sheet position, so that strong vortices can be formed near the edge of the steel sheet. There is no. For this reason, even if the steel plate is warped, generation of the edge overcoat is suppressed.
Also, even when the gas from the auxiliary nozzle is discharged more strongly than usual and the oxide film is scraped off, the collision part of the gas flow between the auxiliary nozzle and the main nozzle is not greatly disturbed, and a linear overcoat is also generated. Can be prevented.

As described above, the collision position P of both gas flows has a D / L of 0.1 or more, that is, 10% or more of the distance between the main nozzle tip and the steel plate toward the steel plate from the main nozzle tip to the steel plate side. To do.
When the collision position of both gas flows is close to the steel plate and the auxiliary gas flow also collides with the steel plate, if the warpage occurs in the steel plate, one auxiliary gas flow will not collide with the steel plate. The impact pressure on the front and back will be different. Since the distance between the steel plate and the nozzle is 10 mm and the warpage amount is usually 2 mm or less, when the warpage occurs in the steel plate, the collision position is a value of D / L in order to prevent one auxiliary gas flow from colliding with the steel plate. Is preferably 0.8 or less.

  In addition, as for the space | interval (LD) of a collision position and a normal (when there is no curvature) steel plate position, 5-15 mm is preferable. If this distance is 5 mm or less, the steel plate may come into contact with the nozzle when the steel plate vibration occurs. Further, when the thickness is 15 mm or more, the plating sagging is greatly generated. In addition, the amount of gas for controlling the basis weight increases.

The flow rate of the discharge gas flow of each auxiliary nozzle is 1.5 times or more the discharge flow rate of the main nozzle. From the point of bending of the main gas flow, it may be 0.5 times or more as shown in FIG. 3, but in order to prevent edge overcoat, it is necessary to make it 1.5 times or more as described above.
When the discharge flow rate from the auxiliary nozzle exceeds 10 times the discharge flow rate of the main nozzle, molten zinc accumulates at the boundary between the auxiliary nozzle and the main nozzle, and the plating adhesion amount is not uniform (linear or linear with continuous dots) Therefore, the flow rate ratio is preferably 10 times or less, more preferably 6 times or less.

  The gas discharge flow rate of the upper auxiliary nozzle / the gas discharge flow rate of the lower auxiliary nozzle is set to a range of 0.9 to 1.2. When the gas discharge flow rate of the upper auxiliary nozzle is in the range of 0.9 to 1.2 times the gas discharge flow rate of the lower auxiliary nozzle, as shown in the result of FIG. 3, the main gas flow is prevented from being bent. can do.

  The installation position of the auxiliary nozzle may be a vertically symmetrical position as shown in FIGS. 2 and 4, but may be asymmetrical as shown in FIG. 5. In that case, the upper and lower auxiliary gas flows 4 and 5 collide with the main gas flow 3 at positions shifted in front of the steel plate. In this way, when the collision points of the upper and lower auxiliary gas flows are slightly shifted, the gas flow from the main nozzle is more stable and more linear.

  At that time, it is preferable that the gas flow 5 of the lower auxiliary nozzle comes to the steel plate side as shown in FIG. This is because the steel strip moves upward, so that there is an upward flow in the vicinity of the position where the gas flow of the main nozzle collides with the steel plate, and when the gas flow 5 of the lower auxiliary nozzle comes to the steel plate side, Then, the flow of the lower nozzle becomes more dominant than the upper auxiliary nozzle flow, and the flow is in the same direction as the upward flow accompanying the movement of the steel strip. As a result, the turbulence of the flow in the vicinity of the steel plate is reduced, and the adhesion uniformity of the plating is also improved. The difference S between the collision positions of the gas flow 4 of the upper auxiliary nozzle and the gas flow 5 of the lower auxiliary nozzle is preferably 2 mm or less, and the collision positions of the upper and lower auxiliary nozzles preferably do not overlap. If the difference exceeds 2 mm, the main gas flow will shift downward, which is not appropriate. Although it depends on the setting accuracy of the equipment, the collision position difference is preferably in the range of 0.5 mm to 2 mm.

  Hereinafter, although the Example of this invention is described, the conditions employ | adopted in the Example are one example of conditions for confirming the feasibility and effect of this invention, and this invention is not limited to this example. Absent.

A steel plate having a plate width of 1000 mm and a thickness of 1.6 mm was passed through a hot dipping line at a speed of 50 mpm. The composition of the plating solution used was mass%, and consisted of Mg: 3.0%, Al: 11.0%, and the balance Zn.
When adjusting the plating adhesion amount of the steel plate pulled up from the hot dipping bath, it was assumed that the steel plate was warped, and the steel plate was passed 3 mm away from the middle position of the main nozzles on the front and back. In addition, when gas was blown from the main nozzle over the entire width of the steel strip, an auxiliary nozzle was installed above or below the end of the main nozzle, and gas was blown from the auxiliary nozzle so as to collide with the gas flow of the main nozzle. .

  Table 1 shows the flow rate of gas discharged from each nozzle, the discharge height of the gas from the nozzle, the distance from the nozzle tip to the steel plate, the slit width of the nozzle in the main nozzle, and the auxiliary nozzle, Installation angle, discharge port shape (a slit taper in which the discharge port thickness of the nozzle changes in a taper shape in the nozzle width direction, the discharge port thickness closer to the inner side of the steel plate is 0 mm, and the thickness closer to the outer side of the steel plate is 0.8 mm The nozzle width and the position where the gas flow from the auxiliary nozzle collides with the gas flow from the main nozzle are shown.

FIG. 6 is a schematic diagram showing the distribution state of the collision pressure of the gas flow in the width direction of the steel sheet and the amount of plating adhesion in the case of the present invention example in which the upper and lower auxiliary nozzles are installed and the comparative example in which only the upper auxiliary nozzle is installed. It shows with. As for the collision pressure, the distribution is shown at the center position of the main nozzle and at positions 5 mm and 10 mm below the position.
In the case of the comparative example, the collision position of the gas blown out from the main nozzle and the auxiliary nozzle on the steel plate is shifted downward, and in particular, the pressure at the boundary in the width direction between the auxiliary nozzle and the main nozzle is 5 mm below the center of the main nozzle. As a result, a lowered portion was produced, and as a result, the plated metal came closer to the portion, and the amount of plating attached to the portion was large.
On the other hand, in the case of the invention example, there was no significant change in the collision pressure distribution at each position, and the occurrence of overcoat was almost suppressed.

FIG. 7 shows an example of the distribution of the collision pressure in the gas blowing region from the nozzle.
(A) When there is no gas blowing from the upper and lower auxiliary nozzles, (b) when there is only gas blowing from the upper auxiliary nozzles, (c) there is gas blowing from the upper and lower auxiliary nozzles Is the case.
The gas is blown from both sides (from the front side of the paper side and both sides of the back side) across the steel plate in a direction substantially perpendicular to the paper surface. The collision position of the blowing gas is set in the middle between the nozzle tip and the steel plate. A portion where the gas blowing pressure is high is white in the figure, and a portion where the pressure is higher is black in the white region.

In FIG. 7A, since no gas is blown from the auxiliary nozzle, the white region is bent due to the influence of the front and back gas, and disturbance is observed in the vicinity of the edge. For this reason, edge overcoat over the end portion occurs.
In FIG. 7 (b), it can be seen that the portion with high spraying pressure shown in white is bent to the upper right side in the vicinity of the right end of the auxiliary nozzle due to the blowing of gas from the upper auxiliary nozzle. In this case, since the pressure in the vicinity of the right end of the edge auxiliary nozzle is high, the pressure gradient in this portion becomes large as shown in the left diagram of FIG. A linear overcoat occurs. In addition, the edge overcoat over the end is not completely eliminated.

  In FIG. 7 (c), it can be seen that the portion where the spraying pressure shown in white is high is almost straight due to the spraying of the gas from the upper auxiliary nozzle. The phenomenon of bending to the upper right side as in the case of FIG. 7B is not seen. Further, the black portion having a higher pressure seen in the white region portion exists uniformly over almost the entire area of the edge auxiliary nozzle spraying portion as compared with the case of FIG. 7B. The linear overcoat generated in FIG. 7B and the edge overcoat over the end portions generated in FIGS. 7A and 7B can be eliminated simultaneously.

It is a figure for demonstrating the method to adjust the plating adhesion amount by the conventional gas flow. It is a figure explaining how to arrange an auxiliary nozzle. It is a figure which shows the change of the overcoat amount and the main nozzle gas flow bending | flexion collision position at the time of changing arrangement | positioning of an auxiliary nozzle or a discharge flow velocity. It is a figure explaining the influence of the curvature of the steel plate in this invention. It is a figure which shows the other example of this invention. It is a figure for demonstrating the Example of this invention. It is a figure for showing the pressure distribution of the collision part of the present invention and a comparative example.

Explanation of symbols

1 Steel plate 2 Wiping nozzle (main nozzle)
3 Gas flow discharged from the wiping nozzle (main gas flow)
4 Gas flow discharged from the upper auxiliary nozzle 5 Gas flow discharged from the lower auxiliary nozzle P Collision position of the gas flow discharged from the wiping nozzle and the gas flow discharged from the auxiliary nozzle L Between the tip of the wiping nozzle and the steel plate Distance D Distance between the tip of the wiping nozzle and P S Shift amount of the position where the gas flow from the upper and lower auxiliary nozzles collides with the gas flow from the wiping nozzle

Claims (7)

  In a method for manufacturing a hot-dip plated steel sheet, in which gas is blown from the wiping nozzle onto the steel sheet surface to control the amount of plating, auxiliary nozzles are installed above and below the end of the wiping nozzle, and the gas flow discharged from the upper and lower auxiliary nozzles is respectively In addition to colliding with the gas flow discharged from the wiping nozzle at a position between the surface of the steel plate and the tip of the wiping nozzle, the average discharge velocity of the gas discharged from the upper and lower auxiliary nozzles is discharged from the wiping nozzle, respectively. A method for producing a hot-dip galvanized steel sheet, characterized in that it is 1.5 to 10 times the average discharge flow rate of the gas to be discharged.   The distance between the position where the gas flow of the upper and lower auxiliary nozzles collides with the gas flow of the wiping nozzle and the tip of the wiping nozzle is 10% or more of the distance between the tip of the wiping nozzle and the steel plate. The manufacturing method of the hot dip galvanized steel sheet as described in 2.   The position where the gas flow of the lower auxiliary nozzle and the gas flow of the wiping nozzle collide is shifted by 2 mm or less to the steel plate side from the position of collision of the gas flow of the upper auxiliary nozzle and the gas flow of the wiping nozzle. Item 3. A method for producing a hot dipped steel sheet according to Item 1 or 2.   The hot-dip galvanized steel sheet according to any one of claims 1 to 3, wherein a value of (discharge flow rate of upper auxiliary nozzle / discharge flow rate of lower auxiliary nozzle) is in a range of 0.9 to 1.2. Manufacturing method.   In a hot-dip plated steel plate manufacturing device that controls the amount of plating by blowing gas from the wiping nozzle onto the surface of the steel plate, auxiliary nozzles are installed above and below the end of the wiping nozzle, and the gas discharged from the upper and lower auxiliary nozzles, respectively. An apparatus for producing a hot-dip galvanized steel sheet, characterized in that the direction of each of the upper and lower auxiliary nozzles is set so that the flow collides with the gas flow discharged from the wiping nozzle at a position between the surface of the steel sheet and the tip of the wiping nozzle .   The upper / lower auxiliary is set so that the distance between the position where the gas flow of the upper / lower auxiliary nozzle and the gas flow of the wiping nozzle collide with the tip of the wiping nozzle is 10% or more of the distance between the tip of the wiping nozzle and the steel plate. 6. The apparatus for producing a hot-dip galvanized steel sheet according to claim 5, wherein each direction of the nozzle is set.   Each of the upper and lower auxiliary nozzles is positioned so that the position where the gas flow of the lower auxiliary nozzle and the gas flow of the wiping nozzle collide is shifted by 2 mm or less to the steel plate side from the position of collision of the gas flow of the upper auxiliary nozzle and the gas flow of the wiping nozzle. The apparatus for manufacturing a hot-dip galvanized steel sheet according to claim 5 or 6, characterized in that the direction of the is set.