JPH02217453A - Method for post-processing plated steel strip in hot-dip metal parting - Google Patents

Abstract

PURPOSE:To obtain the hot-dip metal plated steel strip of high quality with high productivity by surrounding molten metalspraying nozzles and a nonoxidizing gas- wiping nozzle together with a metallic face in a plating tank by a seal box. CONSTITUTION:A steel strip 3 discharged from an in-line continuous annealing furnace 2 is passed via a sink roll 4 into a plating tank 1. The plated steel strip 3 is sprayed with molten metal having the same or equal compsn. to that of the plating metal from a pair of slit-shaped nozzles 5 and is sprayed with a gas from a wiping nozzle 9 to regulate the coating weight. In the method for post-processing the above plated steel strip 3, a seal box 11 surrounding the above nozzles 5, wiping nozzle 9 and the surface of molten metal in the plating tank 1 is provided. As the above spraying gas, a nonoxidizing gas is furthermore used. The opening degree of a cap 13 at the outlet 12 for steel strips in the seal box 11 is moreover regulated to hold the inside to positive pressure, preferably to >= +5mm H2O. In this way, the high productivity of the hot-dip metal plating and the beauty of the plated face are maintained and the new generation of dross and its sticking to the steel strip 3 can be prevented.

Description

DETAILED DESCRIPTION OF THE INVENTION <Industrial Application Field> The present invention relates to a method for post-treatment of plating cavities in hot-dip metal plating.

<Prior art> Most molten metal plated steel strips are produced by a method such as continuously introducing a pre-cleaned copper strip into a tank filled with molten metal, plating in the tank, and then gas wiping or roll squeezing. For example, t
When producing Pi-dip galvanized steel, 41F, the surface of the steel strip is generally cleaned in a heating furnace in a reducing atmosphere, brought to a steel strip temperature suitable for plating, and then heated to about 450 to 490°C. The galvanized steel was guided into a hot-dip galvanizing tank and plated in the tank, and then as a post-treatment, the coating weight was adjusted by so-called gas wiping, which sprayed air, nitrogen, or steam onto the surface of the plated steel (11). 55-
48102, JP-A-54-8125)
.

The conceptual principle of adjusting the amount of plating deposited using the gas wiping method is to install a slit-shaped nozzle that sandwiches the line at both ends on a belt conveyor line that rises almost vertically from the hot-dip galvanizing tank. By continuously spraying wiping gas onto the passing plated steel strip, the upward flow of molten zinc that adheres to the surface of the steel strip and tries to rise is blocked by the collision energy of the gas, and as a result, the amount of coating deposited is adjusted. This is what I am trying to do.

However, the gas wiping method has the following problems.

In other words, the amount of molten zinc that adheres to the copper strip and rises increases as the speed of the copper strip, that is, the line speed increases, and under the same gas wiping conditions, the higher the line speed, the higher the amount of molten zinc that adheres to the copper strip and rises. The amount of plating deposited increases.

Therefore, in order to reduce the amount of plating deposited under such high speed conditions, it is necessary to increase the Ui thrust energy of the wiping gas, that is, to increase the speed of the gas blown out from the slit-shaped nozzle, or to increase the amount of gas, or to divert the gas downward. Efforts were needed to make the bones faster.

However, this causes problems such as splashing on the surface of the copper strip after plating, so there is a limit to reducing the amount of plating adhesion M while increasing the line speed of the copper strip, so it is difficult to improve productivity. It was difficult to do so.

In addition, in the gas wiping method, the steel after plating treatment (1
Solid matter such as brick debris and dross floating in the plating bath adheres to the F surface, causing problems such as deterioration of surface appearance or quality characteristics as so-called foreign matter adhesion defects. This is due to the solid matter such as brick debris and dross being caught up in the rising flow of the molten metal that adheres to the steel () that has passed through the plating tank and remains on the plated steel strip after adjustment. It is something. In particular, the roll drawing method has the disadvantage of frequently causing poor appearance due to defects on the drawing roll surface or foreign matter deposited on the roll surface.

In order to solve this problem, molten metal having the same or equivalent composition as the plating metal is applied to the plated steel 4iF that has passed through the plating bath through a pair of slit-shaped nozzles installed in the steel strip conveyance line on the plating transport side. A post-treatment method for galvanized steel 4 (F) in hot-dip metal plating characterized by spraying is disclosed in JP-A-63-109150. Effective, Fe-At type.

In addition, this technology can achieve the target level in suppressing the adhesion of dross and brick debris, which are mainly composed of Pe-Zn alloys, to the plating surface61! W was given.

However, after experiencing continuous long-term operation using the same technology, a new type of dross was observed that had never been experienced before. When we investigated this dross in detail, we found that
It has been found that the characteristics of dross are that fine ZnO-based and At-O-based oxides are aggregated and metallic zinc surrounds them. Furthermore, a detailed study of the dross generation mechanism revealed that this type of dross is produced when molten zinc is sprayed through a slit-shaped nozzle in the molten metal plating tank located below. When falling onto a molten metal surface, the metal surface is moved violently, causing oxidation of the falling molten zinc or the molten zinc in the plating tank.

<Problems to be Solved by the Invention> Based on the recognition that new dross generation and adhesion to the copper strip as described above occur due to violent agitation of the molten metal surface in the molten metal tank, the object of the present invention has been achieved. is JP-A-63-109
This paper proposes a technology that suppresses the generation of new dross and adhesion to the copper strip without sacrificing the high productivity and beauty of the plated surface, which are the goals of the technology disclosed in Publication No. 150. .

<Means for Solving the Problems> In other words, the present invention provides a method in which molten metal having the same or equivalent composition as the plating metal is applied to the plated steel 11) that has passed through the plating bath, and the steel on the plating transport side (jF conveyance line is installed). When gas is sprayed through a pair of slit-shaped nozzles and then through a wiping nozzle provided above the nozzles, a seal box is provided that surrounds the nozzles, the wiping nozzles, and the molten metal surface of the plating tank. , a non-oxidizing gas is supplied to the wiping nozzle to adjust the amount of adhesion, and the inside of the seal box is preferably kept at a positive pressure of +51111
This is a method for post-treatment of a plated steel strip in hot-dip metal plating, whose main purpose is to control the temperature to +XO or higher.

<Function> The technique disclosed in the above-mentioned Japanese Patent Application Laid-Open No. 63-109150 greatly contributes to the effect of reducing the amount of plating deposited, that is, to increasing the productivity of hot-dip metal plating. It is incomplete in terms of suppressing the generation of dross from objects, etc. Therefore, Zn-0 series, A! We aimed to develop a technology to suppress the production of -0-based oxides.

As a result, by surrounding the wiping nozzle and slit-shaped nozzle for adjusting the amount of adhesion with a seal box, and supplying non-oxidizing gas from the wiping nozzle to maintain a positive pressure inside, it is possible to adjust the amount of adhesion and create a non-oxidizing atmosphere. We obtained the knowledge that it is possible to simultaneously achieve the creation and creation of new products, and that there is also a secondary effect that makes the effect of reducing the amount of adhesion even more pronounced.

Also, when obtaining a suitable non-oxidizing level inside the seal box, check the opening degree of the steel strip outlet provided in the seal box! P
It has been found that the object of the present invention can be achieved more effectively by setting the internal pressure to +5 11 □0 or more.

In addition, the internal pressure of the seal box is preferably positive pressure→-5
The purpose of the invention, that is, the effect of suppressing the generation of dross such as Zn-0-based oxides and reducing the amount of adhesion, can be achieved by setting the value of va lll0 or more. This seems to be because by increasing the internal pressure of the seal box, the infiltration of air from the opening is suppressed, and the oxygen content m inside the seal box is reduced.

According to the inventor's research, the amount of gas such as nitrogen or argon supplied from the wiping nozzle to adjust adhesion ffl is usually increased or decreased depending on the target adhesion amount, so even if the opening degree of the seal box is constant, For example, when the amount of wiping gas is small, the internal pressure decreases and air inevitably enters the seal box from the opening (steel strip outlet), making it impossible to obtain a suitable non-oxidizing level (oxygen concentration). ,Also,
When the amount of wiping gas is large, the internal pressure becomes abnormally high and air infiltration is relatively reduced, but a wind pattern appears on the plating surface, which is thought to be caused by the gas flow flowing out from the opening, and the aesthetic appearance looks like a river. I can sleep.

Therefore, the opening of the seal box needs to have an opening degree that corresponds to the wiping gas supply m.

A suitable opening degree is an internal pressure of 5 m11. O~100rmI
It should be set within the range of t t O.

The present invention will be described in detail below with reference to the drawings.

First, Figure 1 schematically shows the main parts of a production line for galvanized steel strips. In the figure, 1 is a plating tank filled with molten metal, 2 is an in-line continuous annealing furnace, 3 is a copper strip, and 4 5 is a pair of slit-shaped nozzles installed in the steel strip conveyance line on the exit side of the plating tank 1, and this nozzle 5 is connected to a pressure pump 6 for supplying molten metal to the plating tank 1.
, a header 7, and a discharge speed regulator 8, and is configured to spray molten metal onto the surface of the steel 4iF 3 that has passed through the plating bath 1. Further, 9 is a wiping nozzle for spraying a non-oxidizing gas such as nitrogen and argon onto the surface of the steel strip 3, and 10 is a ladder for the wiping nozzle 9. 11 is a seal box that surrounds the slit-shaped nozzle 5, the wiping nozzle 9, and the molten metal surface of the plating tank.

The steel strip 3 that has been cleaned in advance in the in-line continuous annealing furnace 2 becomes a plated steel strip by passing through the plating tank 1. In the present invention, the steel strip 3 that has passed through the plating tank 1 is treated at the exit side of the acid tank 1. The nozzle 5 sprays molten metal to perform post-treatment of the plated steel strip.

By providing the wiping nozzle 9 and the slit-shaped nozzle 5 in the seal box 11 and supplying non-oxidizing gas from the wiping nozzle 9, adhesion ffi can be adjusted and oxides such as Zn-0 can be suppressed.

In addition, although FIG. 1 shows an example in which molten metal is supplied from the plating tank 1 to be sprayed onto the plated steel 41)3, the plating tank 1
It can also be supplied from another system. Further, by heating such molten metal and adjusting the temperature to at least higher than the temperature of the molten metal filled in the plating tank 1, the viscosity is reduced, and as a result, the effect of gas wiping can be further enhanced.

Furthermore, by spraying a metal with a composition slightly different from that of the molten metal in the plating tank 1, a plated steel strip having a plating layer having a composition different from that of the plated steel strip passed through the plating tank 1 can be obtained.

In addition, although the seal box 11 does not cover the entire surface of the molten metal in the plating tank in FIG. 1, it may cover the entire surface. In this case, the amount of oxides generated is further reduced, and wasteful consumption of molten metal is suppressed. .

Further, the continuous annealing furnace 2 and the seal box 11 may be connected, and in this case, it is desirable to provide a partition wall between the two in consideration of repair of each part of the annealing furnace 2 and the seal box 11 during operation.

In addition, the lower the oxygen concentration in the seal box, the better, but if it is about 1000 u or less, there will be almost no difference in the effect of reducing oxide dross and adhesion due to the concentration difference.
Furthermore, if the value is set to less than about 100, the amount of zinc vaporized from the molten metal surface in the plating tank will increase, and the seal box
I have also experienced phenomena that are aesthetically undesirable, such as adhesion to the plated surfaces.

Furthermore, the steel strip outlet 12 provided in the seal box 11 is
As shown in Fig. 1, the structure is such that it surrounds the steel () from all directions, and L [13 is provided to sandwich the gil'tiF (thickness direction), so that the opening degree of this lid can be controlled. l! By adjusting the pressure, the internal pressure of the seal box can be controlled.

<Example> The method of the present invention shown in FIG. 1 and the conventional method shown in FIG. Zn-0 series,
The amount of dross deposited on AI-○ series oxide was compared. however,
In the example of the present invention, the oxygen concentration in the seal box was set to 400
-, but no significant difference was observed in the effect of suppressing oxide formation in the range of 100 to 1000%.

Table 1 shows the plating conditions and post-treatment conditions of the present invention example and the conventional example.

FIG. 3 is a graph showing the relationship between the line speed and the lower limit of the amount of plating deposited as an index of productivity in plating processing. The lower limit of the plating amount is the minimum amount of plating that does not cause splash adhesion. As is clear from Figure 3, for example, if the coating weight is 60 g/
rr (in the case of conventional line speed of 180 m/
However, in the case of the treatment according to the present invention, it is necessary to
Since it can be done at a high speed of 00 m/min, productivity increases.

Furthermore, as shown in Table 2, it can be seen that oxide-based dross is also significantly reduced.

Table 1 <Effects of the Invention> As detailed above, the present invention not only makes it possible to increase the productivity of hot-dip metal plating, but also improves the quality of the plating.

[Brief explanation of the drawing]

Fig. 1 is a schematic diagram of the main parts of a galvanized steel strip production line applied to the present invention, Fig. 2 is a schematic diagram of the main parts of a conventional galvanized steel strip production line, and Fig. 3 is a diagram showing line speed and coating weight. This is a graph showing the limits. ... In-line continuous annealing furnace, 4... Zinc roll, 7... Header, 9... Wiving nozzle, 11... Seal box, 13... Lid. DESCRIPTION OF SYMBOLS 1... Plating tank, 2 3... Copper strip, 5... Slit-shaped nozzle, 8... Discharge speed regulator, 10... Header, 12... Steel strip outlet,

Claims (1)

[Claims] 1. Spraying molten metal having the same or equivalent composition as the plating metal onto the plated steel strip that has passed through the plating tank through a pair of slit-shaped nozzles provided on the steel strip conveyance line on the exit side of the plating tank. ,
Next, when blowing gas through a wiping nozzle provided above the nozzle, a seal box is provided to surround the nozzle, the wiping nozzle, and the molten metal surface of the plating tank, and a non-oxidizing gas is supplied to the wiping nozzle,
A method for post-processing a plated steel strip in hot-dip metal plating, which comprises adjusting the amount of coating and maintaining a positive pressure inside the seal box. 2. The method for post-processing a plated steel strip in hot-dip metal plating according to claim 1, characterized in that the internal pressure of the seal box is controlled to +5 mmH_2O or higher.