JP4487603B2 - Continuous molten metal plating method and apparatus - Google Patents

Description

  The present invention relates to a method and apparatus for continuous hot metal plating, such as continuous hot dip galvanizing, and more particularly to a method and apparatus for improving plating thickness uniformity.

  3 and 4 show an example of a conventional continuous hot dip galvanizing apparatus.

  The steel strip 1 is continuously supplied into the molten zinc bath 2 (plating tank), and the steel strip 1 is pulled upward via the sink roll 22. Next, by blowing gas from the gas wiping nozzle 23 onto the surface of the steel strip 1 above the molten zinc bath 2, the molten zinc adhering to the surface of the steel sheet is squeezed out, and the amount of adhesion (ie plating thickness) To control.

However, in the gas wiping method, the following problems may occur, and particularly defects at the edge of the steel strip become a problem. That is:
(A) When reducing the plating thickness without reducing the productivity, the collision pressure of gas wiping, that is, the gas pressure must be increased. However, increasing the gas pressure induces molten metal splash and causes surface defects. In particular, this splash is often generated and manifested at the edge of the steel strip where the air currents on the front and back of the steel strip collide.

  (B) Since the collision pressure of the wiping gas against the steel strip surface decreases in principle at the edge portion, the amount of adhesion at the edge portion called an edge overcoat is abnormally increased. This is not only a waste of plating material, but also causes a defective shape when wound into a coil shape, and an appearance defect called uneven baking when alloying is performed in a subsequent process.

  These problems are rooted in the use of gas for wiping. As a method for solving this problem, for example, Japanese Patent Application Laid-Open No. 2000-212714 discloses a method for controlling the amount of adhesion using electromagnetic force. However, this method has a problem that, in principle, an induced current flows through the steel strip, so that there is a problem that the steel strip is heated, and there is a problem that the adhesion amount is strongly influenced by warpage and vibration of the steel plate. It is not easy.

  Japanese Patent Application Laid-Open No. 09-209101 discloses a method of sandwiching a steel strip with a blade and controlling the amount of adhesion. However, this method is not practical because the amount of adhesion is uneven when the steel sheet is warped or vibrated.

Japanese Laid-Open Patent Publication No. 01-147049 discloses a continuous hot dipping apparatus in which electromagnets are arranged in front (FIG. 2), after (FIG. 1), or before and after (FIG. 3) a gas wiping nozzle. According to these apparatuses, vibration is applied to the steel strip pulled up from the hot dipping bath using an electromagnet, and the amount of plating is adjusted by blowing gas from a gas wiping nozzle onto the surface. However, in this method, since the effect of shaking off the molten metal by vibration is insufficient, it is not possible to expect an excessively large reduction in the flow rate of airflow, and the effect is limited.
JP 2000-212714 A JP 09-209101 A Japanese Patent Laid-Open No. 01-147049

  The present invention has been made in view of the problems with the plating thickness control method in the conventional continuous molten metal plating as described above, and the object of the present invention is to provide a plating layer in the vicinity of the edge of the metal strip. An object of the present invention is to provide a continuous molten metal plating method and apparatus capable of suppressing the occurrence of defects and improving the uniformity of the plating thickness in the width direction of the steel strip.

The continuous molten metal plating method of the present invention comprises:
In a continuous molten metal plating method in which a metal band is passed through a molten metal bath and a plating layer is adhered to the surface of the metal band,
In the vicinity of the edge of the metal strip pulled up from the molten metal bath, the vibrating body is brought close to the surface of the metal strip, and a part of the molten metal adhering to the surface is scraped off.
Next, gas is blown from the gas wiping nozzle to the surface of the metal strip over the entire width of the metal strip to squeeze out the molten metal adhering to the surface.

  The technical points of the method of the present invention will be described below. When plating thickness control is performed using only a gas wiping nozzle as in the prior art, most defects occur near the edge of the steel strip. This is because at the time of gas wiping, a considerable amount of molten metal adheres in the vicinity of the edge portion, and the amount is sufficient to be blown away by the wiping gas. Therefore, if the molten metal is squeezed in advance in the portion, the occurrence of defects near the edge portion can be suppressed. According to the method of the present invention, a vibrating body is installed in the vicinity of the edge portion of the metal strip before the gas wiping nozzle, and the molten metal attached to the surface of the metal strip is scraped off using the vibrating body. As a result, the occurrence of defects in the plating layer in the vicinity of the edge portion of the metal strip can be suppressed.

  Preferably, a flat blade is used as the vibrating body, and the blade is vibrated to bring the tip thereof into contact with the molten metal on the surface of the metal strip. At this time, the adhesion amount of the molten metal can be controlled by adjusting the relative position of the vibration center of the blade with respect to the travel path of the metal strip.

  Preferably, the frequency of vibration applied to the blade in the direction perpendicular to the traveling path of the metal band is 1 kHz or more.

  Preferably, the amplitude of vibration applied to the blade in the direction perpendicular to the traveling path of the metal strip is set to 1 μm or more and 100 μm or less.

  Preferably, the blade is disposed at a height of 50 mm or more and 200 mm or less below the gas wiping nozzle. This is because when the distance to the gas wiping nozzle is 50 mm or less, the blade may disturb the air flow of wiping. On the other hand, when the distance is 200 mm or more, the scraped molten metal is removed from the inside to the edge portion. This is because the effect of providing the blade is halved.

Preferably, the blade is disposed so as to scrape off a part of the molten metal in a region having a width of 50 mm or more and 300 mm or less in the vicinity of the edge portion of the metal strip. This is because, in a width of 50mm or less, is insufficient as a countermeasure against the edge overcoat, whereas, even in the above 300 mm, because not always superior effect is obtained as a measure of edge overcoat.

The continuous molten metal plating apparatus of the present invention is
In a continuous molten metal plating apparatus in which a metal strip is passed through a molten metal bath and a plating layer is attached to the surface of the metal strip,
A vibrating body disposed near the edge of the metal strip pulled up from the molten metal bath, and scraping off a portion of the molten metal on the surface of the metal strip;
An oscillating device for vibrating the vibrating body to contact the molten metal on the surface of the metal band;
A gas wiping nozzle disposed above the vibrating body and close to the travel path of the metal strip, for blowing the gas onto the surface of the metal strip over the entire width of the metal strip to squeeze the molten metal;
It is provided with.

  Preferably, a flat blade is used as the vibrator. An oscillating device is attached to this blade, and the blade is vibrated to bring its tip into contact with the molten metal on the surface of the metal strip. Furthermore, a push-in device for adjusting the relative position of the vibration center of the blade with respect to the travel path of the metal strip is provided, and the amount of molten metal attached can be controlled by adjusting the position of the blade using this push-in device. it can.

  According to the continuous molten metal plating method and apparatus of the present invention, the molten metal in the vicinity of the edge is scraped off by bringing the vibrating body into contact with the surface of the metal band before the gas wiping nozzle, so that the molten metal can be splashed. It is possible to suppress the occurrence of defects in the vicinity of the edge portion of the resulting metal band and improve the uniformity of the plating thickness.

  1 and 2 show an example of the arrangement of blades for scraping off molten metal near the edge of a steel strip in a continuous molten metal plating apparatus according to the present invention. Note that the overall configuration of the continuous molten metal plating apparatus is the same as that of FIG.

  In the figure, 1 is a steel strip (metal strip), 2 is a molten zinc bath (molten metal bath), 3a, 3b, 4a, 4b are blades (vibrating bodies), 5a, 5b, 6a, 6b are vibrators (oscillators). ), 7a, 7b, 8a and 8b represent oscillators (oscillators), and 9a, 9b, 10a and 10b represent pushing devices.

  In this example, as shown in FIGS. 1 and 2, a gas wiping nozzle 23 is disposed above the molten zinc bath 2, and the left and right edges of the steel strip 1 are located below the gas wiping nozzle 23 (that is, the front side). A total of four flat blades 3a, 3b, 4a, 4b are arranged so as to be in contact with the surface (front side and back side) of the steel strip 1 in the vicinity. Vibrators 5a, 5b, 6a, and 6b are attached to the blades 3a, 3b, 4a, and 4b, respectively, and the vibrators 5a, 5b, 6a, and 6b are respectively connected to the oscillators 7a, 7b, 8a, and 8b. It is connected to the. Furthermore, each vibrator 7a, 7b, 8a, 8b is connected to pushing devices 9a, 9b, 10a, 10b.

  The tip of the blade 3a, 3b, 4a, 4b is brought into contact with the surface of the traveling steel strip 1 in a vibrating state, and the melt adheres to the surface of the steel strip 1 near the left and right edges. Scrap off some of the metal. At this time, by adjusting the relative positions of the blades 3a, 3b, 4a, and 4b with respect to the travel path of the steel strip 1, the thickness of the molten metal on the surface of the steel strip can be controlled near the left and right edges. The steel strip 1 that has passed between the blades 3a, 3b, 4a, 4b then passes between the gas wiping nozzles 23, where gas is sprayed onto the surface of the steel strip over the entire width of the steel strip 1. As a result, the molten metal is drawn down, and the final plating thickness is adjusted.

  In this way, by applying vibration to the blades a, 3b, 4a, and 4b and bringing them into contact with the surface of the steel strip 1, the amount of adhesion can be controlled stably without degrading the plating quality. When a vibration is applied to an object, a levitation force is generated. Therefore, when viewed microscopically, the vibrating blade and the steel strip (base material) are in a non-contact state, and thus surface defects such as scratches do not occur.

  Further, as a result of the tests by the inventors of the present application, it has been found that the vibration frequency needs to be 1 kHz or more, and more preferably 10 kHz or more. This is because a pattern corresponding to this vibration appears on the plating surface. When the frequency is low, the pattern due to vibration is recognized by the human eye as a defect, but when the frequency is high, the pattern pitch is high. This is because it becomes smaller and is not recognized by human eyes.

  The amplitude applied to the blade is preferably 1 μm or more and 100 μm or less. This is because the non-contact effect cannot be obtained when the thickness is 1 μm or less, and the difference in adhesion amount due to vibration becomes significant when the thickness is 100 μm or more.

  The width (effective wiping width: We) of the blade that contacts the edge of the steel strip is preferably 50 mm or more. This is because the edge overcoat and the edge splash cannot be sufficiently prevented at 50 mm or less. In addition, the blade position in the width direction of the steel strip may be in a form that follows the edge of the steel strip, or the blade width may be determined in consideration of meandering and width changes of the steel strip. good.

  Control of the molten metal adhesion amount at the edge portion is performed by adjusting the push-in amount. However, the relationship between the push-in amount and the adhesion amount varies depending on the frequency, amplitude and output of the vibration to be added. For example, when the amount of adhesion is desired to be smaller than the current value, the amount of pressing is increased. However, when the amount of pressing is simply increased, scratches may occur. Such a case can be solved by increasing the output of the vibration oscillator and increasing the vibration amplitude.

In order to investigate the performance of the plating thickness control by the method of the present invention, a test was conducted using the apparatus shown in FIGS. 1 and 2 under the following conditions. The size of the cold-rolled steel strip used for the test is 0.75 mm thick and 1000 mm wide. The blade was installed at the same height on both sides at a position 100 mm below the gas wiping nozzle (h = 100 in the figure). The size of the blade was 25 mm thick, 200 mm wide, and 400 mm deep. However, in consideration of meandering, the effective wiping width (We) was set to 150 mm. The line speed was 90 mpm and the tension was 2 kg / mm ² . The vibration applied to the blade was 19.5 kHz, and the amplitude of the blade tip was 30 μmp-p. The power required for vibration was 2.5 kW on one side and 5 kW on both sides in total. The pushing force for bringing the blade into contact with the surface of the steel strip was adjusted to 140 kg / m ² in consideration of the uniformity of the adhesion amount. This pushing force is appropriately adjusted so as to minimize the variation in the amount of adhesion.

A gas wiping nozzle having a nozzle gap of 0.9 mm was used, and the distance was 10 mm and the gas pressure was 0.55 kgf / cm ² so that the amount of plating adhered at the center was 50 g / m ² .

Table 1 shows the results. In this table, the average adhesion amount (g / m ² ) and the maximum adhesion amount difference in the width direction depending on the presence or absence of the vibrating blade (5 observation points, positions of 50, 250, 500 mm from the left and right edges) And the relationship between the edge splash amount. However, the amount of edge splash is the weight of the splash at the position A in FIGS. 1 and 2 (the size of the measurement area is 100 × 100 mm) per unit time (1 minute) and unit area (1 m ² ). It is a converted value.

  As can be seen from Table 1, based on the method of the present invention, the molten metal is scraped off at the edge of the steel strip in front of the gas wiping nozzle, thereby improving the uniformity of the amount of plating and at the same time reducing the amount of splash generated. Can be greatly reduced.

  In the above example, the front and back blades are installed at the same height. However, the installation height can be changed so that an adjustment range of the pushing amount of the front and back blades can be secured.

The figure which shows an example of arrangement | positioning of the blade for scraping off a molten metal in the continuous molten metal plating apparatus based on this invention. The figure which shows an example of arrangement | positioning of the braid | blade about the width direction of a steel strip in the apparatus of FIG. The figure which shows an example of the conventional continuous hot dip galvanizing apparatus. The figure explaining the gas wiping nozzle for controlling the plating thickness in the conventional continuous zinc metal plating apparatus.

Explanation of symbols

1 ... steel strip (metal strip),
2 ... Molten zinc bath (molten metal bath),
3a, 3b, 4a, 4b ... blade (vibrating body),
5a, 5b, 6a, 6b ... vibrator (oscillator),
7a, 7b, 8a, 8b ... oscillator (oscillator),
9a, 9b, 10a, 10b ... pushing device,
22 ... Sink roll,
23: Gas wiping nozzle.

Claims (8)

In a continuous molten metal plating method in which a metal band is passed through a molten metal bath and a plating layer is attached to the surface of the metal band,
A part of the molten metal adhering to the surface of the edge of the metal band pulled up from the molten metal bath by bringing the vibrating body close to the surface of the metal band in the width direction of 50 mm to 300 mm in the width direction of the metal band Scrape
Next, a continuous molten metal plating method is characterized in that gas is blown from the gas wiping nozzle to the surface of the metal band over the entire width of the metal band to squeeze out the molten metal adhering to the surface.   The vibrating body is a flat blade, and the tip of the blade is brought into contact with the molten metal on the surface of the metal band, and the blade is melted by adjusting the relative position of the vibration center of the blade with respect to the travel path of the metal band. The continuous molten metal plating method according to claim 1, wherein the amount of metal adhesion is controlled. The continuous molten metal plating method according to claim 2, wherein a frequency of vibration in the thickness direction of the metal strip applied to the blade is set to 1 kHz or more. Continuous molten metal plating method according to claim 2, wherein the blade is applied to, or less thickness direction amplitude 1μm or 100μm vibration of the metal strip.   The continuous molten metal plating method according to claim 2, wherein the blade is disposed at a height of 50 mm or more and 200 mm or less below the gas wiping nozzle. In a continuous molten metal plating apparatus in which a metal strip is passed through a molten metal bath and a plating layer is attached to the surface of the metal strip,
A vibration body for scraping off a part of the molten metal on the surface of the metal band, disposed in a region of a width of 50 mm or more and 300 mm or less in the width direction of the metal band of the edge portion of the metal band pulled up from the molten metal bath;
An oscillating device for vibrating the vibrating body to contact the molten metal on the surface of the metal band;
A gas wiping nozzle disposed above the vibrating body and close to the travel path of the metal strip, for blowing the gas onto the surface of the metal strip over the entire width of the metal strip to squeeze the molten metal;
A continuous molten metal plating apparatus comprising: In a continuous molten metal plating apparatus in which a metal strip is passed through a molten metal bath and a plating layer is attached to the surface of the metal strip,
A flat blade for scraping off a part of the molten metal on the surface of the metal band, disposed in an area of a width of 50 mm or more and 300 mm or less in the width direction of the metal band at the edge of the metal band pulled up from the molten metal bath; ,
An oscillation device for vibrating the blade to bring the tip into contact with the molten metal on the surface of the metal strip,
A pushing device for adjusting the relative position of the vibration center of the blade with respect to the travel path of the metal strip;
A gas wiping nozzle disposed above the blade in the vicinity of the travel path of the metal strip, for blowing the gas to the surface of the metal strip over the entire width of the metal strip to squeeze the molten metal;
A continuous molten metal plating apparatus comprising: The continuous molten metal plating apparatus according to claim 7 , wherein the blade is disposed at a height of 50 mm or more and 200 mm or less below the gas wiping nozzle.

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