JP4779529B2 - Method for manufacturing molten metal-plated steel strip and gas wiping nozzle - Google Patents

Description

  The present invention relates to a manufacturing method of a molten metal plated steel strip and a gas wiping nozzle capable of improving plating scraping power of a gas wiping nozzle, reducing splash scattering and preventing edge overcoat in a hot dip plating process. It is.

  In a continuous hot dipping process or the like, as shown in FIG. 3, the steel strip 10 is immersed in a plating bath 25 generally filled with a molten metal and the direction is changed by a sink roll 24, and then the steel strip 10 is moved vertically. After the step of pulling upward, the steel strip width direction provided opposite to the steel strip so that the molten metal adhering to the steel strip surface has a predetermined plating thickness uniformly in the plate width direction and the plate longitudinal direction. There is provided a gas wiping device for jetting gas from a gas wiping nozzle 22 extending to the steel strip to squeeze out excess molten metal and control the amount of adhesion of the molten metal. The gas wiping nozzle is usually longer than the width of the steel strip, that is, extending beyond the end of the width of the steel strip, in order to cope with various widths of the steel strip and at the same time to shift in the width direction when the steel strip is pulled up. ing. In such a gas wiping device, since the jet that collides with the steel strip edge portion faces slightly outside and the impact force decreases, the edge overcoat in which the plating thickness of the steel strip edge portion becomes thicker than the central portion The surface of the steel strip is deteriorated by the occurrence of so-called splash, in which molten metal falling below the steel strip is scattered by the disturbance of the jet that collides with the steel strip.

  In order to solve the above problem, an auxiliary nozzle (sub nozzle) is arranged around the wiping nozzle (main nozzle) that mainly controls the amount of molten metal adhering to the steel strip. A method for improving the performance of the nozzle, a method for improving the uniformity of the collision force in the width direction, or a method for recovering the generated splash is disclosed as follows.

  In the method disclosed in Patent Document 1, the main nozzle is formed by providing auxiliary nozzles (sub-nozzles) that are independently controllable and sprayed on the upper and lower portions of the main nozzle and divided into three or more in the width direction. It is said that the main jet flow from the air is suppressed and the gas flowing along the steel plate after the collision is stabilized.

  The method disclosed in Patent Document 2 is a result of making the front end of the jet nozzle of the partition plate of the main nozzle and the sub nozzle an acute angle, tilting the sub nozzle 5 to 20 ° with respect to the main nozzle, and lengthening the potential core. The adhesion amount controllability is increased and the jet flow is stabilized, so that the noise is also reduced.

The method disclosed in Patent Document 3 is a method in which a suction chamber is provided in the immediate vicinity of the wiping nozzle outlet, and the generated splash is sucked to reduce splash defects.
JP-A-1-230758 JP-A-10-204599 JP-A-6-41710

  However, in the method disclosed in Patent Document 1, an unstable vortex is generated in the vicinity of the partition plate of the main nozzle and the sub nozzle, and the shearing vortex is increased by the mixing action of the vortex, and the collision gas causes the vortex on the steel plate. It was found that the static pressure distribution formed was gentle, the plating scraping amount was reduced, and the splash was liable to deteriorate. Moreover, since a considerable amount of gas is injected from the sub nozzle, it is disadvantageous in terms of piping and energy costs.

  The method disclosed in Patent Document 2 has been implemented to solve the problems of Patent Document 1. However, when the sub-jet is given from the vicinity thereof at the same speed as the main jet, the three jets are immediately combined into one jet, so that apparently from the nozzle having a slit gap three times that of the main nozzle. Equivalent to injecting. It is generally known that the potential core of a two-dimensional free jet is about 6 to 10 times the injection width. Therefore, it is natural that the potential core length of such a jet becomes long, and it is not different from a jet from a nozzle having one wide jet port, and the amount of scraping of the plating is in spite of the increase in the amount of gas to be input. There are few, and it is unsuitable for the thinning control of a molten metal. In addition, it is necessary to make the tip angle of the partition plate of the injection port to be 5 ° or less, and operational risks such as a decrease in nozzle rigidity and inconvenience of nozzle cleaning become a problem. Since the supply gas to the sub-flow nozzle requires the same pressure as that of the main nozzle, the equipment becomes complicated and the energy cost is high.

  In the method disclosed in Patent Document 3, the sucked air is simply discharged, and the energy loss is very large. Further, since splash is often generated at both ends of the steel plate, it is not an efficient method to suck with a uniform suction force in the width direction. On the other hand, if the suction force is too large, the spraying gas for controlling the basis weight is diffused in the central portion in the width direction, and the wiping force is reduced.

  The present invention solves the above problems, improves the plating scraping force (wiping force) by suppressing the spread of the main jet of the gas wiping nozzle, further reduces energy loss, reduces splash scattering, It is another object of the present invention to provide a method for producing a molten metal-plated steel strip and a gas wiping nozzle that can prevent edge overcoat.

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

  (1) In a manufacturing method of a molten metal plated steel strip in which the thickness of the deposited metal is controlled by blowing a gas from a gas wiping nozzle onto the surface of the steel strip that is continuously pulled up from the molten metal plating bath, A main nozzle that injects a gas for controlling the thickness, and at least one of the upper and lower portions of the main nozzle, which is inclined with respect to the injection direction of the gas injected from the main nozzle, and slower than the gas injected from the main nozzle One sub-nozzle for injecting the gas is provided, a suction port near the gas wiping nozzle is provided to suck the gas in the vicinity of the gas wiping nozzle, the foreign matter is removed from the sucked gas, and the gas from which the foreign matter has been removed is jetted from the sub-nozzle. A method for producing a hot-dip metal-plated steel strip.

  (2) While sucking a larger amount of atmosphere near the ends of the steel strip width direction than the central portion of the steel strip width direction, the gas jetting speed of the gas from the sub nozzle is set at both ends of the steel strip width direction of the steel strip width direction. The method for producing a molten metal-plated steel strip according to (1), wherein the part side is made faster.

  In a gas wiping nozzle that controls the thickness of the deposited metal by blowing gas onto the surface of the steel strip that is continuously pulled up from the molten metal plating bath, a main nozzle that mainly injects a gas that controls the thickness of the deposited metal; In the vicinity of the gas wiping nozzle, a sub nozzle that injects gas at a lower speed than the gas injected from the main nozzle, which is inclined with respect to the injection direction of the gas injected from the main nozzle, on at least one of the upper and lower portions of the main nozzle A gas supply system that sucks the gas near the gas wiping nozzle through a fan from a suction port provided in the gas supply system and sends the sucked gas to the sub nozzle, and removes foreign matters in the gas sucked in the middle of the gas supply system A gas wiping nozzle comprising a foreign matter removing means.

  (4) The gas according to (3), wherein three or more fans are installed in the nozzle width direction, and the amount of gas suction is larger in the fan near the both ends than in the center in the width direction. Wiping nozzle.

  According to the present invention, the jet flow ejected from the main nozzle is prevented from diffusing by the low-speed jet flow from the sub nozzle, thereby improving the wiping force. Further, after the gas around the nozzle is suctioned and cleaned, this gas is supplied to the sub nozzle, thereby reducing energy loss and preventing splash and edge overcoat.

  The details of the embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a cross-sectional view of a gas wiping nozzle according to an embodiment of the present invention. A gas such as air or nitrogen gas is supplied to the main nozzle 1 which mainly controls the plating thickness by a blower or the like (not shown). The gas may be a heated gas. Sub nozzles 2, 2 ′ are installed above and below the main nozzle 1. From the sub nozzles 2, 2 ', a gas inclined with respect to the injection direction of the gas injected from the main nozzle is injected. The gas wiping nozzle of FIG. 1 sucks gas around the nozzle from a suction port provided in the vicinity of the sub nozzles 2 and 2 ′, and supplies gas to the sub nozzles 2 and 2 ′. Is provided. The gas supply systems 3, 3 ′ incorporate fans 5, 5 ′. The fans 5 and 5 'suck the gas around the nozzle and supply the sucked gas to the sub nozzles 2 and 2'. Three or more fans 5, 5 'are installed in the wiping nozzle width direction with respect to one gas suction / exhaust system. The sucked air mainly contains foreign matters such as molten metal droplets, and these foreign matters are removed by the filters 4, 4 ′. The air supplied by the fans 5, 5 ′ undergoes pressure fluctuations due to the rotation of the fans 5, 5 ′, but this can be eliminated by the rectifying plates 6, 6 ′. The filters 4 and 4 ′ may be any one having heat resistance against the sucked gas temperature. For example, a SUS304 mesh filter or the like can be used.

  After suction, the gas purified by the filters 4, 4 ′ is supplied to the sub nozzles 2, 2 ′ and is injected from above and below the main nozzle 1. From the sub nozzles 2 and 2 ′, jets having a lower speed than the jets jetted from the main nozzle 1 are jetted. The speed of the jet flow ejected from the sub nozzles 2 and 2 'is controlled by controlling the rotational speed of the fans 5 and 5'. The jet flow injected from the main nozzle 1 is prevented from diffusing by the low-speed jet flow from the sub nozzles 2 and 2 ', and the wiping force is improved.

  In addition, as shown in Fig. 2, three or more fans are installed in the nozzle width direction so that the number of rotations of each fan can be controlled individually, and it is suitable for steel plate edges with high splashing and low plating scraping force. If the rotation speed of the fan is larger than the rotation speed of the fan corresponding to the central part of the steel sheet, the amount of gas suction at the part corresponding to the steel strip edge part will increase, and while collecting the splash, Since the impinging pressure of the jet can be increased, a more uniform basis weight distribution in the width direction is possible.

  In order to further control the suction force in the nozzle width direction and the injection amount in the width direction from the sub nozzle, it is preferable to provide a partition plate that divides the fan chambers 7 and 7 'into three or more divisions in the width direction. . In FIG. 2, five fans 5 and 5 ′ are installed in the width direction, and two partition plates 8 are divided so as to divide two fans corresponding to both ends of the steel strip and one fan corresponding to the central portion. A sheet is provided. The number of fans 5, 5 'may be three or more and the number of partition plates 8 may be two or more (three or more divisions), and is not limited to the arrangement shown in FIG.

The gas wiping nozzle of the present invention shown in FIG. 1 was installed in a gas wiping apparatus of a continuous hot dip galvanizing line, a manufacturing experiment of hot dip galvanized steel sheet was performed, and a comparison with a conventional nozzle was performed. The manufacturing conditions are the same for the slit gap of the main nozzle and the slit gap of the sub nozzle (both 0.8 mm), the nozzle height from the molten zinc bath 420 mm, the molten zinc bath temperature 460 ° C., etc. The thickness was 1.0 mm × 1.8 m. The sub nozzles were provided above and below the main nozzle, and five fans for supplying air to the sub nozzles were installed in the width direction as shown in FIG. 2 and divided into three by a partition plate. When all the five fans are rotated at an output of 100%, the sub-nozzle pressure reaches 0.2 kgf / cm ² uniformly in the width direction, and is 0.4 to 1.. It does not exceed ² kgf / cm ² . As the filter, SUS304 mesh filters were arranged in a plurality of stages, and the last one was 0.1 mm with the smallest mesh spacing.

  Table 1 shows the other manufacturing conditions, the amount of plating adhesion, the variation in the amount of plating adhesion (standard deviation of 10 points in the width direction), and the amount of splash generated. The splash generation amount is a ratio of the steel strip length determined to have a splash defect in the inspection process to the steel strip length passed under each manufacturing condition, and includes a slight splash defect that does not cause a problem in practice.

  In Example 1, all the fan rotation speeds were set to 100%, but the amount of adhesion decreased and the splash decreased to 1/10 compared to Comparative Example 1 with only the main nozzle. However, since the fan rotation speed is uniform in the width direction, the variation in the adhesion amount due to the edge overcoat was hardly reduced.

  In Example 2, when the fan rotation speed was all 20%, the adhesion amount and the splash were slightly worse than in Example 1, but they were halved compared to Comparative Example 1.

  Example 3 is a case where the fan rotation speed is changed to 60 to 100% at both ends of the steel strip and 20% at the center. The plating adhesion amount and the splash were the same as those in Example 1, and the variation in the adhesion amount was reduced as compared with Example 1. The result was the best among all the conditions.

  In the fourth embodiment, the fan rotation speed is the same as that in the third embodiment, and the sheet passing speed is increased to 250 mpm. In Comparative Example 2, which is a case of a normal nozzle, the splash defects were so severe that it was almost impossible to operate, whereas in Example 4, the amount of plating adhesion and the amount of adhesion were reduced, and the amount of splash was compared. A state equivalent to that in Example 1 could be achieved.

  The comparative example 3 is a case where the gas sucked by blocking the injection port of the sub-flow nozzle is discharged to the outside (only suction is performed). Although the amount of splash generation decreased as compared with Comparative Example 1, the amount of plating adhesion slightly increased and the variation in adhesion amount also increased.

  The method for producing a steel strip of the present invention is a method for producing a molten metal-plated steel strip that improves the plating scraping power of the gas wiping nozzle, reduces splash scattering, and prevents edge overcoat in the hot dipping process. Can be used as

  The gas wiping nozzle of the present invention can be used as a gas wiping nozzle for producing the steel strip described above.

It is sectional drawing which shows one Embodiment of the gas wiping nozzle of this invention. It is a figure which shows the internal structure of the fan chamber of the gas wiping nozzle of this invention. It is sectional drawing which shows the manufacturing apparatus of a continuous molten metal plating steel plate.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Main nozzle 2, 2 'Sub nozzle 3, 3' Gas supply system 4, 4 'Filter 5, 5' Fan 6, 6 'Current plate 7, 7' Fan chamber 8 Partition plate 10 Steel strip (steel plate)
21 Support roll 22 Gas wiping nozzle 23 Support roll 24 Sink roll 25 Molten metal (plating bath)

Claims (4)

In the manufacturing method of the molten metal plating steel strip, which controls the thickness of the adhered metal by blowing gas from the gas wiping nozzle onto the surface of the steel strip that is continuously pulled up from the molten metal plating bath, the thickness of the adhered metal is mainly controlled. A main nozzle that injects a gas to be controlled, and a gas that is inclined with respect to the injection direction of the gas injected from the main nozzle and that is slower than the gas injected from the main nozzle, at least one of the upper and lower portions of the main nozzle Provide one sub-nozzle to inject, provide a suction port near the gas wiping nozzle to suck the gas near the gas wiping nozzle, remove foreign matter from the sucked gas, and inject the gas from which foreign matter has been removed from the sub-nozzle A method for producing a hot-dip metal-plated steel strip. While sucking more atmosphere in the vicinity of both ends in the steel strip width direction than in the central portion in the steel strip width direction, the gas jet velocity from the sub nozzle is set at the both ends in the steel strip width direction from the central portion in the steel strip width direction. The manufacturing method of the hot-dip metal-plated steel strip according to claim 1, wherein the speed is increased. In a gas wiping nozzle that controls the thickness of the deposited metal by blowing gas onto the surface of the steel strip that is continuously pulled up from the molten metal plating bath, a main nozzle that mainly injects a gas that controls the thickness of the deposited metal; In the vicinity of the gas wiping nozzle, a sub nozzle that injects gas at a lower speed than the gas injected from the main nozzle, which is inclined with respect to the injection direction of the gas injected from the main nozzle, on at least one of the upper and lower portions of the main nozzle A gas supply system that sucks the gas near the gas wiping nozzle through a fan from a suction port provided in the gas supply system and sends the sucked gas to the sub nozzle, and removes foreign matters in the gas sucked in the middle of the gas supply system A gas wiping nozzle comprising a foreign matter removing means. 4. The gas wiping nozzle according to claim 3, wherein three or more fans are installed in the nozzle width direction, and the amount of gas suction is larger in the fan near the both ends than in the center in the width direction.

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