JP4677846B2 - Manufacturing method of molten metal plated steel strip - Google Patents

Description

  The present invention relates to a method for manufacturing a molten metal-plated steel strip in which a gas wiping nozzle is blown onto a surface of a steel strip that is continuously pulled up from a molten metal plating bath to control the thickness of the deposited metal.

  In the continuous hot dipping process, as shown in FIG. 1, after immersing the steel strip 10 in a plating bath 23 generally filled with a molten metal, the step of pulling the steel strip 10 vertically upward, Gas wiping extending in the width direction of the steel strip provided facing the steel strip 10 so that the molten metal adhering to the surface of the steel strip is uniform in the width direction and the longitudinal direction of the plate and has a predetermined adhesion amount. A gas wiping method is performed in which gas is ejected from the nozzle 22 onto the steel strip 10 to scrape excess molten metal and control the amount of molten metal deposited. The gas wiping nozzle 22 is usually longer than the width of the steel strip and extends to the outside of the width end of the steel strip in order to cope with various steel strip widths and at the same time, the positional deviation in the width direction when the steel strip is pulled up. ing. In such a gas wiping method, the molten metal falling below the steel strip scatters to the surroundings due to the turbulence of the jet colliding with the steel strip 10, so-called splash occurs, and the steel strip surface quality is deteriorated.

  In order to increase the production amount in the continuous process, the steel strip passing speed (line speed) may be increased. However, when controlling the coating amount by gas wiping method in the continuous hot dipping process, the initial adhesion amount immediately after passing through the plating bath of the steel strip increases as the line speed increases due to the viscosity of the molten metal. In order to control the amount within a certain range, the wiping gas pressure has to be set to a higher pressure, thereby greatly increasing the splash and maintaining good surface quality. As shown in FIG. 2, the splashes generated at both ends of the steel strip collide with each other in the longitudinal direction of the steel strip between the gas injected from the wiping nozzles arranged on the front and back surfaces of the steel strip ((a) , (C)) and separation ((b), (d)) occur, and the turbulence of the jet increases and splash is generated. Therefore, this is particularly called edge splash.

  A method of reducing the occurrence of the splash as described above is disclosed as follows.

  Patent Document 1 discloses a method of injecting gas by offsetting the wiping nozzles on the front and back surfaces of the steel strip for the purpose of preventing C warpage of the steel strip. Since it can be avoided, it has the effect of suppressing edge splash.

  Patent Document 2 discloses a method in which a suction chamber is provided in the vicinity of the outlet of the wiping nozzle and the generated splash is appropriately sucked to prevent deterioration of the quality of the plated steel strip.

In Patent Document 3, an edge plate is provided on the outer side of both ends of the steel strip, and an inclined guide for changing the flow of the injected gas inward is provided at the lower portion of the steel plate side corner of the edge plate body to reduce splash as well as noise. It is disclosed.
JP-A-4-116148 JP-A-6-41710 JP 2003-321756 A

However, in the method disclosed in Patent Document 1, the gas pressure must be 1.0 to 2.0 kg / cm ² to correct the C warpage. Even if there is no interference, splash splashing is significantly worsened. By making the nozzle position and angle movable in order to offset the wiping nozzle, the rigidity of the apparatus itself is reduced, and defects such as a pattern with a specific frequency on the surface of the plated steel strip are likely to occur. In addition, since the optimum offset amount changes slightly depending on the operating conditions, even if it is set in advance, the offset amount must be finely adjusted in response to changes in the operating conditions, and the adjustment of the nozzle position and angle is severe. Therefore, defects such as splash increase in an unsteady state until the adjustment to the predetermined setting is completed.

  In the method disclosed in Patent Document 2, splash defects can be temporarily avoided by sucking the generated splash in the vicinity of the wiping nozzle. However, since the occurrence of splash itself is not reduced, maintenance of the chamber when used regularly. There is a problem that it is necessary to frequently perform maintenance and the load of maintenance increases. The maintenance frequency can be lowered by taking measures such as lowering the suction force of the suction chamber, but in this case, the splash suction effect is insufficient. Further, Patent Document 2 does not have a specific description of the required suction flow rate, but it is considered that a considerable flow rate must be sucked in order to collect splashes scattered over a wide range, resulting in a large equipment cost. .

  In the method disclosed in Patent Document 3, although collision between most wiping gases can be avoided by the edge plate, the edge plate and the end portion of the steel band are sure to be near the steel band, which is particularly important in preventing the occurrence of splash. There is a problem that a gap must be formed, and the behavior of the gas entering the gap causes the splash to adhere to the edge plate, resulting in a lump of grains and a defect such as a so-called liquid pool that adheres to the steel plate. In addition, the squeezing force itself cannot be improved.

  The object of the present invention is to solve the above-mentioned problems, increase the wiping force of the wiping gas, efficiently control the amount of hot-dip plating even at low pressure, and prevent collision between wiping gases facing each other on the front and back surfaces of the steel strip. An object of the present invention is to provide a method for manufacturing a hot-dip metal-plated steel strip that can avoid and reduce the occurrence of splash.

  Means of the present invention for solving the above problems are as follows.

  (1) A plurality of nozzles whose gas injection directions are inclined with respect to the steel strip surface continuously pulled up from the molten metal plating tank are provided, and a synthetic jet of gas injected from the plurality of nozzles is used as a molten metal bath A method of manufacturing a molten metal-plated steel strip that is sprayed onto the surface of a steel strip that has been pulled up to control the thickness of the adhered metal, and adjusts the gas pressure of gas injected from at least one of the plurality of nozzles And the collision position with the steel strip of the said synthetic jet is changed, The manufacturing method of the hot-dip metal plating steel strip characterized by the above-mentioned.

  (2) A plurality of nozzles whose gas injection directions are inclined with respect to each of the front and back surfaces of the steel strip continuously pulled up from the molten metal plating tank are provided, and the gas injected from the plurality of nozzles is synthesized. A method of manufacturing a molten metal-plated steel strip in which a jet is blown onto the surface of the steel strip pulled up from the molten metal bath to control the thickness of the deposited metal. A method of manufacturing a hot-dip metal-plated steel strip, characterized by being displaced in the direction.

  (3) Manufacture of hot-dip metal-plated steel strip according to (2), characterized in that the longitudinal collision position of the steel strip front and back composite jets is shifted by changing the jet angle of the steel strip front and back composite jets Method.

  (4) Among the plurality of nozzles, when the nozzle having the fastest flow rate of the gas injected separately from the front and back of the steel strip is the main nozzle and the nozzle other than the main nozzle is the sub nozzle, the gas of the main nozzle on the front and back of the steel strip By making the injection direction symmetrical with respect to the steel strip surface (the steel strip center plane in the plate thickness direction) and making the gas injection direction of the sub nozzle on the front and back of the steel strip asymmetric with respect to the steel strip surface, The method for producing a hot-dip metal-plated steel strip according to (3), wherein the steel jet longitudinal collision position of the synthetic jet is shifted.

  (5) The gas injection direction of the main nozzle on the front and back of the steel strip and the gas injection direction of the sub nozzle on the front and back of the steel strip are made symmetrical with respect to the steel strip surface (the steel strip center plane in the plate thickness direction), respectively. By changing the gas pressure of the gas jetted from the front and back sub-nozzles (at least one sub-nozzle when there are multiple sub-nozzles), the steel strip longitudinal collision position of the steel strip front and back is shifted. The manufacturing method of the hot-dip metal-plated steel strip according to (3), which is characterized.

  (6) The ratio S / b of the collision amount S in the longitudinal direction of the steel strip in the synthetic jet on the front and back of the steel strip and the slit gap b of the main nozzle is in the range of 0.1 ≦ S / b ≦ 5. (4) Or the manufacturing method of the hot-dip galvanized steel strip as described in (5) characterized by the above-mentioned.

  (7) Relationship between the pressure of the main nozzle, the pressure of the sub nozzle, the angle formed by the gas injection direction of the main nozzle and the gas injection direction of the sub nozzle, and the steel strip surface collision position of the synthetic jet of the gas injected from each nozzle (4) to (6), characterized in that the deviation amount of the collision position in the longitudinal direction of the steel strip in the synthetic jet on the front and back of the steel strip is adjusted within a predetermined range using the relationship obtained above. The manufacturing method of the hot-dip metal plating steel strip in any one of them.

  (8) The method for producing a molten metal-plated steel strip according to (5) or (6), wherein the pressure of the sub nozzle is adjusted so as to reduce the amount of splash generated.

  (9) The method for producing a molten metal-plated steel strip according to any one of (4) to (8), wherein at least one sub nozzle is provided in each of an upper part and a lower part of the main nozzle.

  According to the present invention, by jetting a jet inclined at a predetermined angle with respect to the jet of the main nozzle from the sub nozzle at a speed slower than that of the main jet, the collision pressure of the jet rises on the surface of the steel strip, and the steel The pressure gradient of the collision pressure distribution in the banding plate direction becomes steep. This jet improves the scraping power of the plating, and when the required plating thickness is achieved, it is possible to lower the jet pressure of the main jet and increase the distance between the nozzle and the steel strip compared to the conventional technology. In addition to the fact that the nozzles are less likely to be clogged and the nozzles are less likely to be clogged, splashing is further less likely to occur by avoiding collisions between the wiping gases on the front and back of the steel strip. It is possible to control the thickness of the molten metal plating efficiently and with little splash, and thinning is possible even during high-speed feeding.

  In the present invention, the collision between the wiping gases on the front and back of the steel strip can be avoided without making the gas wiping nozzle itself a movable structure, so that a decrease in the rigidity of the wiping device can be prevented, and the rigidity of the wiping device can be reduced. The problem that a pattern-like defect having a specific frequency occurs on the surface of the belt can also be solved.

  Hereinafter, embodiments of the present invention will be described in detail.

  FIG. 3 shows a schematic configuration example of a gas wiping nozzle used in the practice of the present invention. FIG. 4 is an enlarged view of the tip portion of the gas injection port of the gas wiping nozzle 1 of FIG. FIG. 5 is a schematic view showing a state in which the gas wiping nozzle of FIG. 3 is disposed opposite to both sides of the steel strip.

  The conventional gas wiping nozzle has one gas injection nozzle (simple slit), whereas the gas wiping nozzle 1 of FIG. 3 is injected between the nozzle body upper member 12 and the lower member 13 of the nozzle body. The main nozzle 7 that injects a main jet that mainly controls the amount of plating deposition, and the main nozzle 7 is partitioned by partition plates 14 and 15 adjacent to the upper and lower sides of the main nozzle 7. Each of the sub nozzles 8 and 9 is provided. In the gas wiping nozzle arranged opposite to both sides of the steel strip, there is one main nozzle for each of the front and back of the steel strip.

  The lower surface of the gas jet side end of the partition plate 14 and the upper surface of the gas jet side end of the partition plate 15 are flat and spaced in parallel to form the gas jet (slit) of the main nozzle 7. In the apparatus of this figure, the gas injection port of the main nozzle 7 is configured to inject gas in a direction substantially perpendicular to the steel strip surface.

  The upper surface of the gas jet outlet side end portion of the partition plate 14 is inclined with respect to the lower surface of the gas jet outlet end portion of the partition plate 14 (inclination angle θ), and the upper surface of the gas jet outlet end portion of the partition plate 14. And the lower surface of the gas jet outlet side end portion of the nozzle body upper member 12 are flat and arranged in parallel with a gap therebetween to form a gas jet outlet (slit) of the sub nozzle 8.

  Similarly, the lower surface of the gas outlet side end portion of the partition plate 15 is formed to be inclined with respect to the upper surface of the end portion of the gas outlet side of the partition plate 15 (inclination angle θ), and the gas outlet side of the partition plate 15 The bottom surface of the end portion and the top surface of the end portion on the gas outlet side of the lower member 13 of the nozzle body are flat and spaced in parallel to form the gas outlet (slit) of the sub nozzle 9.

  Each nozzle 7-9 has the separate pressure chambers 2-4 so that each injection gas pressure can be adjusted arbitrarily. The pressure chambers (headers) 2 to 4 are each supplied with wiping gas whose pressure is individually controlled from a gas supply system (not shown), and the wiping gas supplied to the pressure chambers 2 to 4 passes through the rectifying plate 5. It is supplied to the nozzle chambers 2a to 4a, and gas is injected from each of the nozzles 7 to 9. In the present specification, a jet of gas injected from the main nozzle is also referred to as a main jet, and a jet of gas injected from the sub nozzle is also referred to as a sub jet.

  The main jet from the main nozzle 7 is injected with a gas at a substantially right angle to the surface of the steel strip, and the sub jet from the sub nozzle 8 and the sub nozzle 9 is injected with a gas (inclination angle θ) inclined with respect to the main jet.

  FIG. 6 shows a collision pressure distribution curve of a two-dimensional jet when this gas wiping nozzle is used. In FIG. 6, (a) is a collision pressure distribution curve of a two-dimensional jet when only the main nozzle is used, and corresponds to a normal two-dimensional jet (two-dimensional jet of a conventional simple slit). (B) and (c) are when the main nozzle and the sub nozzle are used, (b) is when the pressure of the upper sub nozzle and the pressure of the lower sub nozzle are the same, and (c) is when the pressure of the upper sub nozzle is lower. This is a case where the pressure is higher than that of the sub nozzle.

  In FIG. 6, b is a slit gap, and y is a distance from the jet center (y = 0). Further, the horizontal axis is y / b, and the vertical axis is the pressure ratio with respect to the maximum pressure with the maximum pressure of the collision pressure distribution curve of (a) using only the main nozzle as a reference (1.0). y <0 is below the jet center (on the side of the hot-dip plating tank), and y> 0 is above the center of the jet (on the side of the anti-hot-dip plating tank).

  In the conventional simple slit nozzle, as shown in FIG. 6A, the collision pressure has a distribution symmetrical with respect to the jet center (symmetric with respect to the axis of y / b = 0), and the collision pressure distribution is It has a property that is almost determined by the nozzle outlet speed. Even if the wiping gas injection direction is inclined within a range of about ± 30 degrees from the direction perpendicular to the steel strip surface, the steepness of the pressure gradient of the collision pressure distribution curve (gradient of the collision pressure distribution curve in FIG. 6) changes almost. do not do. The steepness of the pressure gradient of the collision pressure distribution curve can be evaluated by the maximum value of the pressure gradient in the range of y / b from −1.5 to 0.

  When controlling the coating amount of molten metal, not only to increase the maximum impingement pressure of the wiping gas jet on the steel strip surface, but also to increase the scraping power of the plating and improve the control of the amount of coating, It is effective to make the pressure gradient of the collision pressure distribution curve in the banding plate direction steep.

  It can be seen from FIG. 6 that the peak of the collision pressure (maximum collision pressure) can be increased when the sub-jet is applied from both the upper part and the lower part of the main nozzle, compared to the case where the sub-jet is not applied. In addition, when the sub-jet is applied from both the upper and lower parts, if the injection speed of the sub-jet from the upper part is made faster than the injection speed of the sub-jet from the lower part, the peak of the collision pressure will not decrease and the negative side (Fig. It can be seen that the pressure gradient of the collision pressure becomes steeper in a range of y / b that is equal to or less than the value of y / b corresponding to the peak of the collision pressure. Therefore, when a wiping nozzle is installed in the upper part of the plating tank as shown in FIG. 5, a sub-jet that is slower than the main jet is injected from both the upper and lower parts of the main jet, and the pressure ratio of the upper and lower sub-jets As a result, the effect of steepening the lower pressure gradient by developing the upper part is expressed, and the lower sub-jet should prevent the main jet from diffusing and should not be injected so strongly that the injection direction is changed. .

  From the above results, by using the wiping nozzle of FIG. 3 to appropriately control the sub-jets from the sub-nozzles 8 and 9 provided at the upper and lower parts of the main nozzle 7 with respect to the main jet from the main nozzle 7. The diffusion of the main jet from the nozzle 7 is suppressed, and the main jet and the sub jet are synthesized immediately after the injection, and the pressure distribution curve has one high peak as shown in FIG. By forming the steep synthetic jet and spraying the synthetic jet 6 onto the steel strip 10 that has passed through the hot dipping bath, the plating scraping power can be increased and the adhesion amount controllability can be improved. Further, since the plating scraping power can be improved, the adhesion amount controllability is excellent even during high-speed plate feeding.

  From the viewpoint of improving the plating scraping power, the following is preferable. The speed of the upper sub-jet is preferably in the range of 20 to 80% (4 to 65% in terms of pressure) of the main jet. If it is this range, an effect will become large, so that speed is quick. The lower sub-jet velocity is preferably 45 to 80% of the upper sub-jet velocity (20 to 65% in terms of pressure, but less than the main jet velocity).

  The inclination angle θ of the gas injected from the sub nozzle with respect to the gas injected from the main nozzle is preferably in the range of 5 ° ≦ θ ≦ 70 °. When the inclination angle θ is less than 5 °, the collision pressure increases as compared with the case of only the main jet, but the leading end of the partition plate is deformed and the nozzle opening is generated, and the uniformity in the nozzle width direction may not be ensured. There is. When the inclination angle θ exceeds 70 °, the collision pressure cannot be increased as compared with the case of the main jet alone. In consideration of nozzle performance, nozzle rigidity, ease of nozzle cleaning, nozzle weight, etc. in addition to nozzle performance, a range of 15 ° ≦ θ ≦ 45 ° is more desirable. When the sub nozzles are provided above and below the main nozzle, the present invention is implemented by adjusting the injection gas pressure, etc. even if the inclination angle θ of the gas injected from the sub nozzle with respect to the gas injected from the main nozzle is different between the top and bottom Is possible.

  The collision pressure ratio hardly affects the nozzle gap of the main nozzle 7, and the nozzle gap of the sub nozzles 8 and 9 is effective in the range of 0.1 mm to 2.5 mm. In addition to performance, considering the energy savings due to nozzle processability, uniformity in the width direction, and reduction of the supply air amount, it is desirable that the thickness is 0.3 mm to 1.5 mm, and more desirably 0.3 mm to 1.0 mm. .

The nozzle gap of the main nozzle is not particularly limited, and may be employed in normal gas wiping. For example, it is 0.5-2 mm. Moreover, the pressure of the main nozzle is applicable to the pressure range normally used, for example, 0.1-2.0 kgf / cm < ² >.

  In FIG. 6, when the injection speed of the sub jet from the upper part is made faster than the injection speed of the sub jet from the lower part, the peak of the collision pressure moves to the negative side, that is, moves to the hot dipping bath side. This means that even if the wiping nozzle body is fixed, the injection direction of the synthetic jet can be changed by changing the sub-jet conditions. For this reason, the lower sub-jet has been studied in more detail under the conditions that only prevent the main jet from diffusing and change the injection direction, and the main and sub-jets at the jet collision position when only the main jet is blown. It was found that the collision position change of the synthetic jet: y is expressed by the following formula (1).

Here, L: Nozzle-steel strip distance, θ: Upper sub-jet inclination angle, Pm: Main jet pressure, Ps: Upper sub-jet pressure. Note that y, L, θ, Pm, and Ps are parameters shown in FIG.

The occurrence of edge splash can be suppressed by offsetting the steel strip collision position of the jet from the wiping nozzle on the front and back surfaces of the steel strip. The wiping nozzle used in the practice of the present invention can change the injection direction of the synthetic jet by changing the sub-jet conditions even when the wiping nozzle body is fixed. Therefore, in the actual machine production line for hot dip galvanized steel sheet, the wiping nozzle having the structure shown in FIG. 3 is configured such that the gas injection direction of the main nozzle on the front and back of the steel strip is the steel strip surface (in the plate thickness direction). It is arranged opposite to both sides of the steel strip so as to be symmetrical with respect to the center plane of the steel strip, and by changing the pressure of the sub-jet of the wiping nozzle facing the front and back of the steel strip, The effect of reducing the splash by changing the offset amount and avoiding mutual interference was investigated.
The survey results are shown in FIG. From FIG. 8, the offset amount S that can be increased by reducing the splash is in a range where S / b satisfies 0.1 ≦ S / b ≦ 5 with respect to the nozzle gap b of the main nozzle. I understood it. S / b is more preferably in a range satisfying 0.3 ≦ S / b ≦ 4. However, the offset amount S (mm) is expressed by the following equation (2).
S = | y1-y2 | (2)
Here, y1: change amount (mm) of the steel strip surface collision position of the synthetic jet of the front side nozzle, y2: change amount (mm) of the steel strip surface collision position of the synthetic jet of the back side nozzle. In the present specification, the front nozzle is a nozzle disposed on the sink roll side, and the back nozzle is a nozzle disposed on the opposite side of the sink roll.

  The offset by optimizing the pressure Ps of the main nozzle of the wiping nozzle facing the front and back surfaces of the steel strip, the pressure Pm of the sub nozzle, and the inclination angle θ of the sub nozzle with respect to the main nozzle from the expressions (1) and (2). The quantity S can be adjusted to the required value, so that S / b can be within the required range.

  For example, by adjusting the pressure of the sub-nozzle of at least one of the gas wiping nozzles arranged opposite to the front and back of the steel strip, the change amount y of the collision position of the wiping gas on the steel strip surface is adjusted. Alternatively, the gas injection direction of the sub nozzle may be adjusted. As described above, according to the present invention, the injection direction of the injected gas can be arbitrarily changed while the wiping nozzle main body is fixed, and the collision position of the opposed jet can be offset to a required position. The gas turbulence due to the opposed jet can be reduced, and the occurrence of edge splash can be suppressed. If the nozzle height position or angle is made movable to adjust the offset amount of the collision position of the opposing jet of the wiping nozzle, the rigidity of the wiping device decreases, and pattern defects with a specific frequency on the surface of the plated steel strip However, since the movable mechanism of the wiping nozzle body for adjusting the offset amount becomes unnecessary, the rigidity of the entire wiping nozzle device can be increased, and the occurrence of such defects can be suppressed. It is easy to realize improvement and stable operation.

  According to the method of the present invention, there is no problem of occurrence of defects such as liquid pool due to gas flowing into the gap between the edge plate and the end of the steel strip, which occurs when the edge plate is used.

  Furthermore, in actual operation, as a pressure optimization method to reduce the amount of splash that is actually occurring, the operator may adjust the pressure of the sub nozzle while observing the splash splash condition visually, or wiping A weigh scale may be provided around the nozzle to quantify the amount of splash generated per unit time while adjusting the sub-nozzle pressure in a direction to reduce the amount of splash by feedback control. While monitoring and quantifying the splash amount by image processing, the sub nozzle pressure may be adjusted in a direction to reduce the splash amount by feedback control, or from the graph of offset amount optimization as shown in FIG. 8, 1 ≦ S / B (offset amount / nozzle gap) ≦ 2 It may be.

  The gas wiping device with the wiping nozzle shown in FIG. 3 installed in the production line of the hot dip galvanized steel sheet, the offset amount of the collision position of the wiping gas on the front and back of the steel sheet was changed, and the thickness 0.8 mm × width 2000 mm A hot dip galvanizing production experiment was conducted, and the amount of deposit controllability and the degree of splash occurrence were investigated. For comparison, a gas wiping device equipped with a conventional nozzle was installed and the same investigation was performed. The manufacturing conditions were the same, such as a nozzle height of 420 mm from the molten zinc bath and a molten zinc bath temperature of 460 ° C. The gas injection direction of the main nozzle was perpendicular to the steel plate surface, and the slit gap of the sub nozzle was 0.8 mm both in the top and bottom. Table 1 shows other manufacturing conditions, the amount of adhesion, and the results of the splash investigation. In Table 1, Production Examples 1 to 5 are examples using the gas wiping nozzle shown in FIG. 3, Production Examples 6 to 9 are examples using conventional nozzles, and Production Examples 10 and 11 are edge plates attached to the conventional nozzles. It is an example. The degree of occurrence of splash was monitored by a video camera installed on the side of the nozzle, quantified by the area of splash occupying the screen, and evaluated based on 1.0 as the management standard for the current operation (Production Example 6).

  Production Example 1 is an example of gas wiping using the gas wiping nozzle shown in FIG. 3 under symmetrical conditions. Production Example 6 where the collision position of the wiping gas on the front and back of the steel plate is not offset only by the main nozzle, the main nozzle Compared to Production Example 7 in which the collision position of the wiping gas on the front and back surfaces of the steel plate is offset only and Production Example 10 in which this main nozzle is equipped with an edge plate, the amount of adhesion decreases due to the steep pressure gradient of the jet, and at the same time the splash The scattering of has also decreased.

  In the manufacturing example 2, the gas wiping nozzle shown in FIG. 3 is used, the S / b (offset amount / nozzle gap) is set to 0 by changing the inclination angle of the upper side flow nozzle without changing the pressure condition of each nozzle. .7. Production Example 3 Example 3 is an example in which the S / b is set to 0.3 by changing the pressure condition of the upper and lower side flow nozzles without changing the angle condition of each nozzle of the gas wiping nozzle shown in FIG. is there. In Production Example 2 and Production Example 3, compared to Production Example 6, Production Example 7 and Production Example 10, the amount of adhesion is reduced due to the steep pressure gradient of the jet, and at the same time, splash splash is greatly reduced. Moreover, compared with the manufacture example 1, although the adhesion amount is equivalent, the splash prevention effect is more excellent. In Production Example 2 in which S / b is within the preferred range of the present invention, the occurrence of splash is less than that in Production Example 3.

  In Production Example 4, the gas wiping nozzle shown in FIG. 3 is used, the pressure condition of each nozzle is not changed, the inclination angle of the upper side flow nozzle is changed, S / b is set to 0.4, and the plate passing speed is set. Is increased to 240 m / min. Compared with Production Example 9 and Production Example 11 with the same plate passing speed, the amount of adhesion and the occurrence of splash are small.

  In Production Example 5, the gas wiping nozzle shown in FIG. 3 was used, the pressure condition of the upper and lower side flow nozzles was changed without changing the angle condition of each nozzle, and S / b was set to 0.3. In the example in which the speed was increased to 240 m / min, compared to Production Example 9 and Production Example 11 with the same plate passing speed, both the amount of adhesion and the occurrence of splash were small, and the amount of splash generated was 140 m / min. This was equivalent to Production Example 6. When Manufacturing Examples 4 and 5 are compared, Manufacturing Example 4 having a larger S / b has less splash.

  In Production Example 8, the S / b is too large, and the splash generated by the upper nozzle of the two opposing nozzles falls on the lower nozzle, and the splash is more than in Production Example 6 and Production Example 7. Increased.

  INDUSTRIAL APPLICABILITY The present invention can be used as a method for producing a molten metal plated steel strip in which a gas wiping nozzle is sprayed on the surface of a steel strip that is continuously pulled up from a molten metal plating bath to control the thickness of the deposited metal. .

It is a longitudinal cross-sectional view which shows the manufacturing apparatus of a general continuous molten metal plating steel plate. It is a figure which shows the generation | occurrence | production mechanism of edge splash. It is a figure which shows the schematic structural example of the gas wiping nozzle used for implementation of this invention. FIG. 4 is an enlarged view of a spray nozzle tip of the gas wiping nozzle of FIG. 3. It is a figure which shows the form of the gas wiping nozzle of this invention. It is the figure which compared the pressure gradient when applying the subjet of the gas wiping nozzle of this invention. It is a schematic diagram explaining the collision position change y of the synthetic jet injected from the wiping nozzle used for implementation of this invention. It is a figure which shows the line acceleration effect with respect to S / b (offset amount / nozzle gap) of the nozzle of a steel plate front and back.

Explanation of symbols

1 Gas wiping nozzle 2 Main nozzle pressure chamber (main nozzle header)
3 Upper secondary nozzle pressure chamber (upper secondary nozzle header)
4 Lower secondary nozzle pressure chamber (lower secondary nozzle header)
5 Rectifying plate 6 Injection gas (synthetic jet)
7 Main nozzle 8 Upper sub nozzle 9 Lower sub nozzle 10 Steel strip (steel plate)
11 Molten metal 12 Nozzle body upper member 13 Nozzle body lower member 14, 15 Partition plate 21 Sink roll 22 Gas wiping nozzle 23 Molten metal (plating bath)
θ Inclination angle S with respect to the injection direction of the gas injected from the main nozzle in the injection direction of the gas injected from the sub nozzle S Offset amount b Slit gap

Claims (7)

A plurality of nozzles with gas injection directions inclined to each other are provided opposite to the front and back surfaces of the steel strip that is continuously pulled up from the molten metal plating tank, and the synthetic jet of the gas injected from the plurality of nozzles is melted. A method of manufacturing a molten metal-plated steel strip that sprays onto the surface of a steel strip pulled up from a metal bath to control the thickness of the adhered metal, and includes a plurality of nozzles, each having a gas jet injected separately from the front and back of the steel strip. When the nozzle with the fastest flow velocity is the main nozzle and the nozzle other than the main nozzle is the sub nozzle, the gas injection direction of the main nozzle on the front and back of the steel strip is relative to the steel strip surface (the steel strip center plane in the plate thickness direction). The gas jet direction of the sub nozzle on the front and back of the steel strip is asymmetric with respect to the steel strip surface, thereby changing the jet angle of the composite jet on the front and back of the steel strip, and the length of the steel strip on the front and back of the steel strip. and wherein shifting the direction collision position Method of manufacturing a molten metal plated steel strip that. A plurality of nozzles with gas injection directions inclined to each other are provided opposite to the front and back surfaces of the steel strip that is continuously pulled up from the molten metal plating tank, and the synthetic jet of the gas injected from the plurality of nozzles is melted. A method of manufacturing a molten metal-plated steel strip that sprays onto the surface of a steel strip pulled up from a metal bath to control the thickness of the adhered metal, and includes a plurality of nozzles, each having a gas jet injected separately from the front and back of the steel strip. When the nozzle with the fastest flow velocity is the main nozzle and the nozzles other than the main nozzle are sub nozzles, the gas injection direction of the main nozzle on the front and back of the steel strip and the gas injection direction of the sub nozzle on the front and back of the steel strip are respectively The gas pressure of the gas injected from the sub-nozzles on the front and back of the steel strip (when there are multiple sub-nozzles, at least one sub-nozzle) is made symmetrical with respect to the strip surface (the steel strip center plane in the plate thickness direction). By Changing the injection angle of the synthetic jet of the strip sides, the manufacturing method of the molten metal plated steel strip, characterized in that shifting the strip longitudinal collision position of the synthetic jet of the front and back steel strip. The ratio S / b of the collision amount S in the longitudinal direction of the steel strip in the synthetic jet on the front and back of the steel strip and the slit gap b of the main nozzle is in the range of 0.3 ≦ S / b ≦ 4 A method for producing a molten metal-plated steel strip according to claim 1 or 2 . The relationship between the pressure of the main nozzle , the pressure of the sub nozzle, the inclination angle of the sub nozzle with respect to the main nozzle, and the steel plate surface collision position of the synthetic jet of the gas injected from each nozzle is obtained, and the relationship obtained above is used. The deviation amount S of the collision position in the longitudinal direction of the steel strip in the synthetic jet on the front and back of the steel strip is adjusted so that S / b is within the range described in claim 3 . The manufacturing method of the hot-dip metal-plated steel strip as described in any one of the items. The method for producing a molten metal-plated steel strip according to any one of claims 2 to 4, wherein the pressure of the sub-nozzle is adjusted so as to reduce the amount of generated splash. The method for producing a molten metal-plated steel strip according to any one of claims 1 to 5 , wherein at least one sub nozzle is provided in each of an upper part and a lower part of the main nozzle. The method for producing a molten metal-plated steel strip according to claim 6, wherein an injection speed of the sub nozzle at the upper part of the main nozzle is made faster than an injection speed of the sub nozzle at the lower part of the main nozzle.

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