JPH11279736A - Gas wiping method suitable for thick plating - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a thick hot dip metal plating steel sheet having uniform plating thickness by stabilizing blasting pressure distribution in the width direction of wiping gas flow even in the case of lowering the static pressure peak. SOLUTION: The nozzles for wiping having a lower side front end inclining surface 13 at 10-200 mm length L and 65-90 deg. inclining angle θ are disposed in both sides of the steel sheet 1 pulled up from the surface 8 of a hot-dipping bath 4 at 10-100 mm height H from the surface 8 of the hot-dipping bath 4 and 5-50 mm depth D from a nozzle hole 11 to the surface of the steel sheet 1, and the pressurized gas is blown into both surfaces of the front and the back sides of the steel sheet 1 from the nozzle 10 for wiping. Since the descending flow (a2 ) is pulled with eddy (a4 ) generated between the bath surface 8 and the nozzle bottom surface 12, dynamic pressure of the descending flow (a2 ) is raised and the static pressure peak is lowered at the neutral point (b), and the blasting pressure distribution suitable to the thick plating is obtd.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a gas wiping method for removing excess hot-dip galvanized metal adhering to a steel strip pulled up from a hot-dip galvanizing bath, and particularly suitable for adjusting the basis weight of a thick hot-dip galvanized steel sheet. .

[0002]

2. Description of the Related Art In a hot-dip galvanizing line, as shown in FIG. 1, a steel strip 1, which is a raw plate for plating, is conveyed to a reduction annealing furnace 2 maintained in a reducing atmosphere to activate the surface of the steel strip 1. Hot-dip plating bath 4 from reduction annealing furnace 2 through snout 3
Has been sent to. The steel strip 1 goes around the sink roll 5 immersed in the hot-dip plating bath 4, and its traveling direction is changed upward. Next, the steel strip 1 is sent out of the hot-dip plating bath 4 via the support roll 6, and the amount of hot-dip metal deposited is adjusted by the wiping action of the gas injected from the wiping device 7. The hot-dip coated steel strip 1 is subjected to an alloying heat treatment as necessary, and is conveyed to the next step. By wiping excess hot-dip coated metal with the wiping device 7, the basis weight is adjusted and the surface properties of the hot-dip coated steel strip are stabilized. When manufacturing a hot-dip galvanized steel strip that requires thickening, a large amount of hot-dip metal is accompanied by the steel strip 1 pulled up from the hot-dip bath 4 to reduce the squeezing of the hot-dip metal by the wiping device 7. ing.

[0003]

By reducing the pressure of the gas injected from the wiping device 7, the amount of hot-dip metal removed can be reduced. However, if the header pressure of the wiping device 7 is simply reduced, the nozzle pressure becomes unstable, and a predetermined wiping action cannot be obtained. For example, the wind pressure distribution of the wiping gas in the width direction of the steel strip 1 fluctuates, and the wiping action at the edge portion is reduced. As a result, a larger amount of hot-dip plating metal is more likely to adhere to the edge portion than at the center portion in the width direction. . The reduction in gas pressure also reduces the action of removing dross accompanying the ascending steel strip 1 from the hot-dip plating bath 4. The dross adhering and remaining on the surface of the steel strip 1 is taken as it is as a foreign substance into the hot-dip coating layer, and significantly deteriorates the quality of the hot-dip steel sheet obtained. The present invention has been devised to solve such a problem, and by increasing the gas flow descending along the steel strip surface and reducing the static pressure on the steel strip surface facing the nozzle port. The purpose of the present invention is to obtain a thick-coated hot-dip coated steel sheet which maintains a good wiping action even when wiping at a reduced gas pressure, does not involve foreign matter caused by dross, and has an effectively adjusted basis weight. I do.

[0004]

According to the gas wiping method of the present invention, in order to achieve the object, a length L = 10-20.
0 mm, a wiping nozzle having a lower front inclined surface at an inclination angle θ of 65 to 90 degrees, a height H from the molten metal bath surface to the nozzle bottom surface of H = 10 to 100 mm, and a height H from 10 to 100 mm from the nozzle opening to the steel strip surface. It is arranged on both sides of a steel strip pulled up from a hot-dip plating bath at a position of a distance D = 5 to 50 mm, and a pressurized gas is blown from a wiping nozzle toward both the front and back surfaces of the steel strip.

[0005]

The present inventors have investigated and studied the effects of the wiping nozzle on the flow of gas blown onto the steel strip surface from various viewpoints. As a result, when disposing the wiping nozzle with the increased inclination angle of the lower front end inclined surface in a specified positional relationship with respect to the molten steel bath surface and the steel strip surface, the gas descending along the steel strip surface. It has been found that the flow increases and the static pressure decreases at the neutral point where the injected gas separates into an upward flow and a downward flow. The increase in the downward flow and the decrease in the static pressure are presumed to be caused by the following mechanism based on the result of investigation of the gas flow state by the simulation test.

The wiping gas injected from the nozzle port 11 of the nozzle 10 facing the steel strip 1 pulled up from the hot-dip plating bath 4 collides with the surface of the steel strip 1, as shown in FIG. As a result, ascending flow a ₁ and descending flow a ₂ flow along the surface of the steel strip 1. Downdraft a ₂ is a horizontal flow a ₃ is deflected in the molten metal surface 8 of the hot-dip plating bath 4. Further, since the nozzle 10 is usually arranged at a position of a height H = 10 to 100 mm from the molten metal surface 8, the pressure between the nozzle bottom surface 12 and the molten metal surface 8 is easily reduced. In the nozzle 10 in which the inclination angle θ of the lower front end inclined surface 13 is large, the descending flow a ₂ is narrowed by the surface of the steel strip 1 and the lower front end inclined surface 13, so that the straightness of the descending flow a ₂ is increased. Therefore, the pressure between the nozzle bottom surface 12 and the molten metal surface 8 tends to be reduced, and the horizontal flow a ₃
Some of deflected nozzle bottom 12 side, vortex a ₄ to rotate in the counterclockwise direction in FIG. 2 is generated. On the other hand, in the nozzle with a small inclination angle θ, the descending flow a ₂ passing between the surface of the steel strip 1 and the lower front end inclined surface 13 is more likely to diffuse along the nozzle bottom surface 12, and the vortex a ₄ Does not occur.

After the reversal, the vortex flow a ₄ is a flow that pulls down flow a ₂ from between the surface of the steel strip 1 and the lower front end inclined surface 13. Therefore, the flow rate of downflow a ₂ is increased, wiping gas from the nozzle 10 is lowered static pressure peak at the neutral point b to break up the upward flow a ₁ flows downward a _2, to remove excess molten coating metal The effect is weakened, and a pressure distribution suitable for thickening is obtained. An increase in the flow rate of the descending flow a ₂ means an increase in the dynamic pressure, and depresses foreign matter such as dross c remaining on the steel strip 1 pulled up from the hot-dip plating bath 4 and returns it to the hot-dip plating bath 4. Is also effective. Order to generate and flow increase in downflow a ₂ vortex a _4, was studying the shape and position of the nozzles. As a result, the length L of the lower front end inclined surface 13 is 10 to 200 mm,
When the inclination angle θ is set to 65 to 90 degrees, the height H from the molten metal surface 8 to the nozzle bottom 12 is set to 10 to 100 mm, and the distance D from the nozzle port 11 to one steel strip 1 is set to 5 to 50 mm, that optimal vortex a ₄ and downflow a ₂ are obtained found from many experimental results.

The length L and the inclination angle θ of the lower front end inclined surface 13 are important for forming a wind tunnel between the steel strip 1 and the lower front end inclined surface 13 to enhance the straightness of the descending flow a _2. Is a factor. When the length L and the inclination angle θ of the lower front end inclined surface 13 are maintained in the range of L = 10 to 200 mm and θ = 65 to 90 degrees, the straightness of the downflow a ₂ can be enhanced by the wind tunnel effect, and under reduced pressure is a part of the side front end inclined surface 13 beyond the nozzle bottom surface 12, the generation of vortex a ₄ by Kalman phenomenon is promoted. The flow rate of downflow a ₂ is increased by vortex a ₄ occurred. When the length L is less than 10 mm, the wind tunnel formed between the steel strip 1 and the lower front end inclined surface 13 is short,
It is not granted sufficient linearity in downflow a _2. Conversely 200
In a length L of greater than mm, the center of the vortex a ₄ becomes far from the wiping action point b on the steel strip 1, the static pressure reduction action in the b point on the steel strip 1 is weakened. The inclination angle θ is less than 65 degrees, the flow path cross-sectional area of the downward flow a ₂ is is for gas diffusion increase occurs, it is not applied sufficient linearity in downflow a _2.
Further, the gas stream flowing along the lower front end inclined surface 13 on the nozzle bottom surface 12 occurs, the generation of vortex a ₄ is suppressed. Conversely, if the inclination angle exceeds 90 degrees, the space for absorbing warpage, fluttering, and the like of the steel strip 1 pulled up from the hot-dip plating bath 4 is reduced.

[0009] The height H from the molten metal surface 8 to the bottom surface 12 can be adjusted by spraying a wiping gas while the fluidity of the hot-dip metal deposited on the steel strip 1 is high,
This is an important factor in creating a decompressed atmosphere between the air and the molten metal surface 8. When maintaining the height H in the range of 10 to 100 mm,
Since the wiping gas is blown onto the hot-dip galvanized metal having a high fluidity, surplus hot-dip galvanized metal is efficiently removed. Further, the ratio of opening between the nozzle bottom surface 12 and the molten metal surface 8 to the external space in the nozzle width direction is reduced, and the air flowing from the external space between the nozzle bottom surface 12 and the molten metal surface 8 is suppressed. Thus, the space between the nozzle bottom surface 12 and the molten metal surface 8 can be easily maintained in a reduced pressure atmosphere. When the height H exceeds 100 mm, a wiping gas is sprayed on the hot-dip galvanized metal with reduced fluidity, so that not only high pressure is required, but also excessive hot-dip galvanized metal cannot be efficiently removed. . The flow rate of such air is increased flowing between the nozzle bottom surface 12 and the molten metal surface 8 from the outside, the ambient pressure increases between the nozzle bottom surface 12 and the molten metal surface 8, generation of vortex a ₄ becomes difficult . Conversely the height H does not reach 10mm, the molten metal surface continuous wind tunnel occurs to between 8 and nozzle bottom 12 from between the steel strip 1 and a lower front inclined surface 13, rather the occurrence of vortex a ₄ weak Become.

The distance D from the nozzle port 11 to one surface of the steel strip
Is an important factor for obtaining an appropriate static pressure at the neutral point b of the steel strip 1 surface. When the distance D is maintained in the range of 5 to 50 mm, the static pressure required for wiping can be obtained even if the gas pressure is reduced. The static pressure increases as the distance D decreases, but at a distance D of less than 5 mm, the steel strip 1 pulled up from the hot-dip plating bath 4 absorbs warpage and fluttering so that the nozzle tip does not contact the steel strip 1. It becomes difficult to maintain the state. On the other hand, at a distance exceeding 50 mm, not only an excessive gas pressure is required to obtain an appropriate static pressure, but also a gap between the steel strip 1 and the lower front end inclined surface 13 is opened, and from both sides in the nozzle width direction. The flow rate of the gas flowing out increases, and the utilization efficiency of the gas that works to remove excess hot-dip galvanized metal decreases.

The length L of the lower front end inclined surface 13 is 10-20.
Nozzle 10 with 0 mm and inclination angle θ of 65 to 90 degrees
Can be obtained not only by designing the nozzle itself, but also by attaching an angle adjusting plate or an angle adjusting block to the front inclined surface of the nozzle 10. A nozzle using an angle adjusting plate or an angle adjusting block can be used for gas wiping under normal operating conditions by changing the inclination angle of the angle adjusting plate or removing the angle adjusting block. The length L of the lower front end inclined surface 13 is set to 1 by the design of the nozzle itself.
When the thickness is 0 to 200 mm and the inclination angle θ is 65 to 90 degrees, the wind pressure distribution is constant even when a hot-dip galvanized steel strip is manufactured with a normal weight per unit area. The amount can be adjusted.

[0012]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A lower front end inclined surface 13 is formed by using a nozzle 10 having a slit-shaped nozzle port 11 having a length L and an inclination angle .theta. The effects of the length L, the inclination angle θ, the height H from the molten metal surface 8 to the nozzle port 11 and the distance D from the nozzle port 11 to the steel strip 1 on the gas wiping action were investigated.

Influence of length L of lower front end inclined surface 13 The nozzle 1 in which the inclination angle θ of the lower front end inclined surface 13 is set to a constant value of 75 degrees and the length L of the lower front end inclined surface 13 is variously changed.
0, and the height H from the molten metal surface 8 to the nozzle bottom surface 12 is H =
50 mm, distance D from nozzle opening 11 to one surface of steel strip D = 2
The nozzle 10 was arranged at a position of 0 mm. Then, gas was blown onto the steel strip 1 at a header pressure of 0.20 kg / cm ² , and the wind pressure was measured at the neutral point b. As can be seen from the measurement results in Table 1, when the length L of the lower front end inclined surface 13 was less than 10 mm, the wind pressure hardly decreased, and a decrease in the wind pressure was detected in the range of L = 10 to 200 mm. However, when the length L exceeds 200 mm, the wind pressure starts to increase, and it is found that the wind pressure reducing effect disappears when L = 250 mm.

[0014]

Influence of inclination angle θ of lower front end inclined surface 13 The length L of the lower front end inclined surface 13 is a fixed value of 60 mm, and the nozzle 10 having variously changed inclination angles θ is formed from the molten metal surface 8 to the nozzle bottom surface 12. Height H = 50mm, 100mm and 150m
m, distance D from nozzle port 11 to one surface of steel strip D = 20 mm
, Gas was blown onto the steel strip 1 at a header pressure of 0.20 kg / cm ² , and the wind pressure was measured at the neutral point b. As shown in FIG. 3 showing the measurement results, when the nozzle 10 is arranged at a height H = 50 mm from the molten metal surface 8 to the nozzle bottom surface 12, when the angle is less than 60 degrees, almost no influence of the inclination angle θ on the wind pressure is detected. However, when it exceeded 60 degrees, the wind pressure decreased greatly according to the inclination angle θ. The effect of the inclination angle θ on the decrease in wind pressure was more remarkable when H = 50 mm than when the height H from the molten metal surface 8 to the nozzle bottom 12 was H = 100 mm.

Further, the inclination angles θ = 30 degrees and θ = 75 degrees
The width direction wind pressure distribution of the steel strip 1 for the nozzle 10
As a result, the nozzle 10 with the inclination angle θ = 75 degrees was obtained.
The wind pressure distribution shown in FIG.
As compared with the pressure distribution, the pressure was reduced uniformly in the entire plate width direction.
The static pressure at the neutral point b is that of the nozzle 10 with the inclination angle θ = 30 degrees.
0.057kg / cm in case^Two Was tilted
0.052k for nozzle 10 with oblique angle θ = 75 degrees
g / cm^Two And had been low. Below along the surface of steel strip 1
Downstream a_Two Dynamic pressure of the nozzle 10 with the inclination angle θ = 30 degrees
0.023kg / cm in case^Two Was tilted
0.028 k in the case of the nozzle 10 having the oblique angle θ = 75 degrees
g / cm ^Two And was higher.

Influence of Height H from Hot Surface 8 to Nozzle Bottom 12 The length L and the inclination angle θ of the lower front end inclined surface 13 are maintained at constant values of L = 60 mm and θ = 75 degrees, respectively. Face 8
The height H from the nozzle to the nozzle bottom 12 is variously changed and the height H
The effect of wind on wind pressure was investigated. The nozzle 10 was arranged at a position D = 20 mm from the nozzle port 11 to the steel strip 1, and gas was supplied at a header pressure of 0.20 kg / cm ² to the steel strip 1.
And the wind pressure was measured at the neutral point b. As can be seen from the measurement results in Table 2, when the height H from the molten metal surface 8 to the nozzle bottom 12 was in the range of 10 to 100 mm, the wind pressure at the neutral point b was reduced. Increased, and when H = 150 mm, no wind pressure reduction effect was observed. At a height H of less than 10 mm, the vertical movement of the molten metal surface became severe, and the wind pressure tended to increase.

[0018]

Influence of the distance D from the nozzle port 11 to the steel strip 1 surface The inclination angle θ and the length L of the lower front end inclined surface 13 are maintained at constant values of θ = 75 degrees and L = 60 mm, respectively. The height H from 8 to the nozzle bottom 12 is 50 mm and 150 m.
m, the nozzle 10 was arranged at a position where the distance D from the nozzle port 11 to the steel strip 1 was variously changed, and the header pressure was 0.20 k.
A gas was blown onto the steel strip 1 at g / cm ² , and the wind pressure was measured at the neutral point b. As shown in the measurement results in Table 3,
The height H from the nozzle to the nozzle bottom 12 is 50 mm and 150 mm.
Under the condition of mm, when the distance D from the nozzle port 11 to one surface of the steel strip became 50 mm or less, the wind pressure was reduced.
The wind pressure reduction effect increases as the distance D decreases, but
The distance D less than mm is not practical because the tip of the nozzle 10 may come into contact with the steel strip 1 due to the flapping of the steel strip 1.

[0020]

Based on the above results, the lower front end inclined surface 13
10 having a length L = 60 mm and an inclination angle θ = 75 degrees
(Example of the present invention) and length L = 60 m of lower front end inclined surface 13
m, nozzle 10 (comparative example) with inclination angle θ = 30 degrees
Hot-dip plating with a height of 100 mm from the surface 8 of the plating bath 4
20 mm from both sides of steel strip 1 pulled out of bath 4
Inventive Example) and 30 mm (Comparative Example)
Using a wiping device, remove the line from the hot-dip plating bath 4.
Header on steel strip 1 being raised at a speed of 50 m / min
Pressure 0.20kg / cm^Two Wiping gas with width 15
It was sprayed on a steel strip 1 of 00 mm. Obtained hot-dip coated steel
When the band was examined, the basis weight in the comparative example was
300-320 g / m^Two And in the width direction
Is 320g / m in the center ^Two 360g /
m^Two And it was a thick distribution.

[0022] In contrast, the variation range of the basis weight in the present invention embodiment is a steel strip longitudinal 300~310g / m ^2, lateral shift in the central portion 310 g / m ^2, the edge portion 300
g / m ² . This means that the lower front end inclined surface 13 has a length L, an inclination angle θ,
When the height H and the distance D from the nozzle port 11 to the steel strip 1 are regulated in accordance with the present invention, the static pressure at the neutral point b is reduced, and a wiping action suitable for thickening is obtained, and the wind pressure of the wiping gas is obtained. It shows that the basis weight is stabilized by stabilizing the distribution. Further, the hot-dip plating layer formed in the example of the present invention did not contain any foreign matter due to residual dross.

[0023]

As described above, in the present invention, the length L of the lower front end inclined surface 13 is 10 to 200 mm,
A nozzle having an inclination angle θ of 65 to 90 degrees is set at a height H from the molten metal surface 8 to the nozzle bottom surface 12 of H = 5 to 100 mm, and the nozzle opening 11
Wiping using a wiping device arranged at a distance D of 5 to 50 mm from the steel strip to one surface of the steel strip lowers the static pressure at the neutral point and stabilizes the wind pressure distribution in the width direction of the steel strip. A flow can be formed. For this reason, it is possible to manufacture a thick-coated hot-dip coated steel sheet while suppressing a change in the basis weight.

[Brief description of the drawings]

[Fig. 1] Main parts of hot-dip plating equipment

FIG. 2 is a diagram illustrating a flow state of gas injected from a gas wiping nozzle.

FIG. 3 is a graph showing the effect of the inclination angle of the lower die front end inclined surface on the wind pressure on the steel strip surface.

FIG. 4 is a graph showing the wind pressure distribution in the steel strip width direction of gas blown onto the steel strip from nozzles having different inclination angles of the lower die front end inclined surface.

[Explanation of symbols]

1: Steel strip 2: Reduction annealing furnace 3: Snout 4:
Hot-dip plating bath 5: Sink roll 6: Support roll 7: Wiping device 8: Hot water surface 10: Nozzle 11: Nozzle port 12: Nozzle bottom surface 13: Lower front end inclined surface θ: Lower front end inclined surface L: Lower angle length of the side front end inclined surface H: height D from the melt surface to the nozzle opening a distance from the nozzle port to the steel strip surface a _1: upward flow a _2: downflow a _3: horizontal flow a
₄ : eddy current b: neutral point where it separates into upward flow and downward flow c: Foreign matter such as dross

Claims (1)

[Claims] 1. Length L = 10 to 200 mm, inclination angle θ
= 65 to 90 degrees, the height of the wiping nozzle having the lower front end inclined surface from the molten metal bath surface to the nozzle bottom surface is H = 10 to 100 mm, and the distance from the nozzle port to the steel strip surface is D = 5 to 5 mm. A gas wiping method suitable for thickening, wherein the gas wiping method is arranged on both sides of a steel strip pulled up from a hot-dip plating bath at a position of 50 mm and sprays a pressurized gas from a wiping nozzle toward both the front and back surfaces of the steel strip.