JPH0280545A - Method for preventing splash of hot dipping bath - Google Patents

Abstract

PURPOSE:To prevent the development of splash from hot dipping bath by vertically applying magnetic field to surface of the hot dipping both at the same time at the time of executing gas wiping on front and back surfaces of a steel plate drawing up from the hot dipping bath. CONSTITUTION:The steel plate 1 dipped into the plating bath 2 is vertically drawn up and the front and back surfaces of the steel plate 1 are gas-wiped with a wiping nozzle 4 to make the uniform prescribed thickness of the plating thickness on the products. Then, the magnetic pole 9 in the plating bath 2 and the magnetic pole 10 between the nozzle 4 and the hot dipping bath 2 are arranged and the magnet is constituted by connecting both poles as U-shape, and the magnetic field is vertically applied to the surface of the plating bath 2 together with the gas wiping. By this method, ripple of the hot dipping bath 2 caused by influence of the wiping gas flow is restrained and the development of splash is reduced.

Description

DETAILED DESCRIPTION OF THE INVENTION (Industrial Application Field) The present invention relates to a method for preventing splash that occurs during the production of hot-dip galvanized steel sheets.

(Conventional technology) A continuous hot-dip plating line processes thin steel sheets (hereinafter simply referred to as "steel sheets").
A plated steel sheet is manufactured using equipment that continuously unwinds the coil (called "Plating") and performs pre-treatment, plating, and post-treatment.

Figure 5 is a schematic front view, partially in section, showing the part of these facilities that applies plating to steel plates whose surfaces have been cleaned and activated, that is, the plating equipment. After being immersed in the plating bath 2, the direction is changed by the zinc roll 3 and pulled up, and the plating solution is applied to the front and back surfaces.

By the way, the steel plate 1 to which the plating solution was applied in the plating bath 2
Since the plating solution is pulled up from the plating bath 2 along with the excess plating solution, a wiping nozzle 4 is disposed above the exit side of the plating bath 2 of the steel plate 1 to which the plating solution is attached. By spraying wiping gas from the spout onto the front and back surfaces of the steel plate, this excess plating solution is squeezed out, and the plating thickness of the product is uniformly thinned to the required thickness, thereby improving quality. I was trying to improve. Note that 5 in FIG. 5 indicates an atmosphere box for setting the atmosphere around the wiping nozzle 4 to N2 atmosphere in order to maintain the gloss of the plating surface.

(Problems to be Solved by the Invention) However, when producing hot-dip plated steel sheets by such a method, there are drawbacks as described below.

As mentioned above, the amount of excess plating solution that accompanies the steel plate being pulled up from the plating bath increases in proportion to the conveying speed when the jetting force of the wiping gas is the same. Therefore, in order to improve production efficiency, the conveying speed is In order to increase the speed, the force of the wiping gas injected from the wiping nozzle must be increased.

However, as shown in the partially sectional enlarged schematic front view of the main part in FIG. Since the cycle of rippling and then rising again is repeated, ripples 7 are generated by the wiping gas flow 6 on the surface of the plating bath 2. When the jetting force of the wiping gas is increased, the speed of the wiping gas flow 6 increases, and the wiping gas flow 6 collides with the wave crest of the ripple 7, causing the plating solution at the wave crest to become droplets and scatter. , so-called splash 8 occurs.

The generated splash 8 is transferred to the wiping gas flow 6
It circulates in the atmosphere box 5 together with the atmosphere box 5.
Since it adheres and solidifies in a laminated manner on the inner circumferential wall of the atmosphere box 5 and the wiping nozzle 4, the adhered solidified layer grows in the atmosphere box 5 (imaginary line in Fig. 6) and hits the steel plate 1, causing nozzle clogging, etc. There was also a risk that this would require frequent removal work.

Furthermore, since the splash 8 is an active metal, it reacts with the atmosphere box 5 and the wiping nozzle 4 to form an alloy layer that is extremely difficult to remove. As a result, there is a problem in that it takes a lot of time to remove this alloy layer.
The period during which the equipment is stopped due to this frequent removal work causes a decline in product production efficiency.

Note that if the jetting force of the wiping gas is set to a level that does not cause splash, the excess plating solution adhering to the steel plate must be squeezed out within the capacity of this jetting force, so the conveyance speed of the steel plate must be reduced. This results in a decrease in product production efficiency.

Therefore, countermeasures such as enlarging the atmosphere box or coating the outer circumferential surface of the wiping nozzle with ceramic material have been taken, but these not only lead to an increase in equipment costs, but also make it difficult to suppress the occurrence of splash itself. Because it was impossible to do so, it was not possible to find a fundamental solution.

An object of the present invention is to provide a method for preventing splashing of a hot-dip plating bath, which can solve the above-mentioned problems.

(Means for Solving the Problem) As a result of closely observing the splash generated by gas wiping, the inventor found that the splash is generated from the crest of a ripple as shown in FIG. If we can attenuate the ripples,
It was thought that the occurrence of splashes could also be suppressed. By applying a magnetic field to conventionally flowing molten metal,
Since it is well known that flow can be suppressed, we considered using a magnetic field as a method for suppressing the above-mentioned waves.

The present invention has been made based on the above findings, and is a method for preventing splash that occurs during the production of hot-dip galvanized steel sheets. The gist of this method is to apply a magnetic field perpendicularly to the surface of the plating bath along with this gas wiping.

(Function) The method for preventing splash of a hot-dip plating bath according to the present invention is as follows:
When gas wiping the front and back surfaces of a steel plate that has been immersed in a plating bath and then pulled up, a magnetic field is applied perpendicular to the surface of the plating bath along with this gas wiping, so the ripples that move across the magnetic field carry a current. As a result, a force that suppresses the wave motion of the ripples comes into play.

(Example) Hereinafter, the method of the present invention will be explained based on the example shown in FIGS. 1 to 3.

FIG. 1 is an explanatory diagram showing the main parts of a hot-dip galvanized steel plate manufacturing apparatus for carrying out the method of the present invention. That is, in FIG. 1, 9 is one magnetic pole immersed in the plating bath 3, 10 is the other magnetic pole 10 disposed between the wiping nozzle 4 and the plating bath 2, and both 9 and 10 are U-shaped. They are connected in a shape to form a magnet. Note that this magnet may be a permanent magnet or a direct current electromagnet.

By the way, since zinc vapor tends to adhere to the magnetic pole 10 provided on the plating bath 2, a ceramic coating may be applied to the surface to make it slippery to prevent zinc vapor from adhering, or a surface heater may be attached to the magnetic pole 10. It is preferable to prevent the deposited zinc vapor from solidifying.

On the other hand, the metal forming the magnetic pole 9 provided in the plating bath 2 is
Since there is a risk of reacting with the activated hot-dip plating solution to form an alloy and eroding the magnetic pole 9, and since the temperature of the plating bath 2 is generally high, the magnetic pole 9 is coated with a refractory material. It is better to have heat resistance and corrosion resistance.

When a hot-dip plated steel sheet is manufactured using the hot-dip plated steel sheet manufacturing apparatus having the above-described configuration, a magnetic field is generated by the magnetic poles 9 and 1O provided in and above the plating bath 2 in the direction connecting the magnetic poles 9 and 10, Ripples 7 will pass through the magnetic field.

As is clear from magnetohydrodynamics, when a fluid passes through a magnetic field in this manner, an electric current flows within the fluid. When a current flows through the magnetic field, a force acts on the ripples 7, which are fluid, to suppress the wave motion as shown in FIG. 2, thereby suppressing the occurrence of splash.

Note that the greater the propagation speed of the ripples, the greater the current newly generated within the fluid, and the greater the suppressing force acting on the waves.

In addition, the magnetic field can be applied not only in the upper and lower positions sandwiching the surface of the plating bath 2 as in the above embodiments, but also in the upper and lower positions sandwiching the surface of the plating bath 3 from outside the container of the plating bath 2. You may do so. In this way, compared to immersing the magnetic pole in a plating bath, there is no need to consider the heat resistance and corrosion resistance of the magnetic pole (although it is necessary to choose a stronger magnetic pole). .

In this case, the container for the plating bath 2 is preferably made of a conductive material.

In this way, the current generated within the magnetic field between the plating bath 2 and the container will form a closed loop, and the current will only flow in one direction from the side of the container in the plating bath 2, and the current and magnetic field will be The wave suppression force works effectively without the interactions of the two canceling each other out.

By the way, based on the method of the present invention as described above, by applying a magnetic field perpendicularly to the surface of the plating bath, the generation of splash caused by wiping gas has been reduced, so that conventionally, the adhered splash had to be cleaned only once on the blade. As a result, it was decided that cleaning should be carried out once every three months.

Furthermore, as shown in Figure 3, even if the amount of wiping gas is increased, if a magnetic field is applied, the amount of splash does not significantly increase, so the amount of wiping gas can be increased, and the conveyance speed of the steel plate is faster than before. This made it possible to increase productivity.

(Effects of the Invention) As explained above, the method of the present invention, when gas wiping the front and back surfaces of a steel plate that has been immersed in a plating bath and then pulled up, performs gas wiping that is perpendicular to the surface of the plating bath. Since a magnetic field is applied to the wiping gas, the generation of ripples due to the influence of the wiping gas flow is suppressed, and the generation of splash from the crest of the ripples is reduced.

As a result, the number of times the adhering splash is cleaned is reduced.
This resulted in a reduction in the downtime of the hot-dip plating equipment due to cleaning.

Furthermore, even if the amount of wiping gas is increased, the amount of splash does not increase, making it possible to manufacture thinner steel sheets with higher efficiency than before, leading to improved productivity.

[Brief explanation of the drawing]

Fig. 1 is a schematic front view with a partial cross section of the main part for carrying out the method of the present invention, Fig. 2 is a diagram of the relationship between magnetic field and wave attenuation, and Fig. 3 is the wiping gas amount and the magnetic field conditions of the brush foot. Figure 4 is a diagram showing the occurrence of splash, Figure 5 is a diagram showing the occurrence of splash.
The figure is a schematic front view of a conventional hot-dip plating apparatus, and FIG. 6 is a diagram showing the state of adhesion of splash inside the atmosphere box. ■ is steel wire, 2 is plating bath, 4 is wiping nozzle, 9
．． 10 is the magnetic pole. Fig. 1 7ization@wrinklekasu 4 Fig. 4 Fig. 6

Claims (1)

[Claims] (1) A method for preventing splash that occurs during the production of hot-dip galvanized steel sheets, in which gas wiping is applied to the front and back surfaces of a steel sheet that is immersed in a plating bath and then pulled up. A splash prevention method for hot-dip plating characterized by applying a magnetic field perpendicular to the surface.