JPH07180016A - Device for controlling concentration of al in bath of continuous hot dip galvanizing line - Google Patents

Abstract

PURPOSE:To drastically reduce the time required for switching of production of a hot dip galvanized steel sheet and a hot dip galvannealed steel sheet in a hot dip galvanizing line and to drastically reduce initial and running costs. CONSTITUTION:A device 7 for supplying molten Zn or Zn ingot of a high Al concn. to the hot dip coating bath surface in a snout and sealing equipment 6 for preventing the intrusion of the molten Zn of the high Al concn. in the snout onto the inner side of the snout 4 immersed into the hot dip metal coating bath are installed to a device for immersing a steel strip 1 through the snout 4 into the hot dip metal coating bath 9 and galvanizing this steel strip. As a result, the Al concn. in the bath in the continuous hot dip galvanizing line is controlled and the time required for switching of the production of the galvanized steel sheet and the galvannealed steel sheet is remarkably shortened. In addition, the initial and running costs are remarkably reduced.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an apparatus for producing a rust-preventive Zn-plated steel sheet used for automobiles, home appliances, building materials and the like.

[0002]

2. Description of the Related Art At present, the Zenzimer method is the mainstream as a method for producing a hot-dip Zn-plated steel sheet. In this method, after reducing and activating the surface of the steel sheet with a hydrogen stream at a high temperature, several tens to hundreds of 1
A hot-dip Zn-plated steel sheet is manufactured by passing the steel sheet at a speed of 0 m / min, pulling up the steel sheet from the hot-dip Zn bath, and adjusting the coating amount by a gas flow or the like. At this time, Fe-
In order to prevent the Zn alloy layer from being thickly formed and deteriorating the adhesion of the plating layer, 0.15 to
It is usual to add 0.2% by weight of Al. The added Al reacts with the steel sheet preferentially over Zn in the Zn bath to form an Fe—Al or Fe—Zn—Al alloy layer (hereinafter abbreviated as “Fe—Al alloy layer”).
It is possible to suppress the alloying reaction of —Zn and thereby manufacture a hot-dip Zn-plated steel sheet having good adhesion.

An alloyed zinc-plated steel sheet used as an anticorrosion steel sheet for automobiles is a steel sheet coated with a Fe--Zn alloy by heating a hot-dipped steel sheet to react zinc with the steel sheet. . In this case, in order to improve the equipment productivity, the Al concentration in the molten Zn bath is set to about 0.10% by weight so that the alloying reaction can easily proceed.

As described above, in the production of hot-dip Zn-plated steel sheets and alloyed hot-dip Zn-plated steel sheets, it is necessary to change the Al concentration in the hot-dip Zn bath to 0.1% and 0.2%.
When increasing the Al concentration, pure Al or high concentration of A
The objective can be achieved relatively easily by dissolving the Zn lump containing l. However, in order to reduce the Al concentration, it is necessary to pump out a predetermined amount of molten Zn bath and add pure Zn. The temperature of the molten Zn bath is usually 450 ° C
It is needless to say that this work involves a great deal of labor, cost, and time, considering that the capacity of the molten Zn pot is 100 tons or more.

For this reason, when these two types of hot-dip Zn-plated steel sheets are produced separately by a single hot-dip Zn plating line (hereinafter referred to as “line”), two hot-dip Zn pots are prepared and the line is temporarily stopped. It is possible to move the pot to replace it, or change the pass line to immerse the steel plate in another pot. In addition to the above, various preparatory work is required for switching the two types of manufacturing products in the hot-dip Zn plating line, but the current situation is that the switching of the plating bath is the rate-limiting operation.

[0006]

However, even if the manufacturing type is changed by such a method, it takes several hours to change the type. Needless to say, it is wasteful to prepare two large pots with Zn dissolved therein.

[0007]

DISCLOSURE OF THE INVENTION The present invention provides a method for separately producing a hot-dip Zn-plated steel sheet and an alloyed hot-dip Zn-plated steel sheet without stopping the line as in the prior art. In the production of hot-dip galvanized steel sheet, the surface-activated steel sheet first reacts with hot-dip Zn in an annealing furnace in a relatively narrow space called snout. Therefore, by controlling the plating bath component in this snout, particularly the Al concentration, the alloying reaction is allowed to proceed or be suppressed, thereby enabling the two types of Zn-plated steel sheets to be manufactured separately. .

A first aspect of the present invention is an apparatus for immersing a steel strip in a molten Zn plating bath through a snout to perform molten Zn plating, wherein molten Zn containing Al at a concentration different from that of the plating bath is applied to the surface of the molten plating bath in the snout. Continuous hot dip galvanizing, characterized in that it has a multi-chamber structure inside the portion of the snout immersed in the hot dip bath as a sealing device for preventing the Zn bath inside and outside the snout from mixing with each other. This is a device for controlling the Al concentration in the bath in the line.

A second aspect of the present invention is an apparatus for immersing a steel strip in a molten Zn plating bath through a snout to perform molten Zn plating, and a Zn lump containing Al at a concentration different from that of the plating bath is formed on the surface of the molten plating bath in the snout. Equipment for supplying after preheating and a multi-chamber structure inside the portion of the snout immersed in the hot dip plating bath as a sealing device for preventing the Zn bath inside and outside the snout from being mixed, This is a device for controlling the Al concentration in the bath in the hot dip galvanizing line.

A third aspect of the present invention is characterized in that, in the first or second aspect of the invention, a metal flow generator is further provided as a sealing device for preventing the Zn baths inside and outside the snout from being mixed. A device for controlling Al concentration in a bath in a continuous hot-dip galvanizing line.

[0011]

When the hot dip galvanizing is performed using this equipment, 0.1% Al-
A Zn bath is used. Therefore, in the production of the galvannealed steel sheet, there is no difference from the conventional method. When a normal hot-dip galvanized steel sheet is manufactured, in order to suppress the alloying reaction, Zn containing a high concentration of Al is supplied to the surface portion of the snout where the steel sheet first contacts and reacts. , Fe-Z in the first stage of plating reaction
An Fe—Zn—Al alloy layer necessary for suppressing the n-alloying reaction can be generated to produce a hot-dip Zn-plated steel sheet having good adhesion. In this case, sealing equipment is required to prevent the mixing of molten zinc inside and outside the snout so that Al added in the snout does not spread throughout the pot, and as will be described later, the snout may be modified by various operational measures. It is possible to minimize the mixing of molten Zn inside and outside.

The present invention shortens the switching time of the plating bath as compared with the conventional one, and in order to switch the manufacturing type in a short time, the alloying furnace, the minimum spangler, etc. are replaced in a short time. Needless to say, various conditions other than the plating bath are required such as possible. When using this equipment, when changing the manufacturing type from alloyed hot-dip galvanized steel sheet to hot-dip galvanized steel sheet, (1) the sealing equipment in the snout is operated, and (2) it contains a high concentration of Al. An appropriate amount of molten Zn or Zn lumps may be supplied to the bath surface in the snout, and (3) the bath temperature in the snout may be kept high by an appropriate method. To change the product type in reverse, use (1)
The supply of the Zn bath containing a high concentration of Al may be stopped, and (2) the snout seal may be released. In this case, since the Al concentration of the entire Zn bath may be slightly increased by the operation of (2) (although it is very small in view of the ratio of the volume in the snout and the volume of the entire Zn bath), it is necessary. According to (1)
It suffices to give an appropriate time difference to the operations of (2) and (2). As a result, it is possible to switch the product type in the hot-dip galvanizing line in a time of several minutes to tens of minutes.

[0013]

EXAMPLE An example in which the present invention is applied to a continuous hot dip coating line will be described below with reference to FIGS. (In FIGS. 1 and 2, equipment not directly related to the present invention, such as a gas wiping nozzle for adjusting the amount of plating deposit, a bath support roll for straightening the strip shape at the gas wiping nozzle, etc. It is omitted.)

FIG. 1 shows a state in which the equipment of the present invention is applied to the snout 4 and the plating bath 9 of the continuous hot dip galvanizing line. The strip 1 surface-activated in the furnace 2 is fed to the plating bath 9 by the turndown roll 3 without contacting the atmosphere, and the tip passes through the snout 4 in which the tip is immersed in the plating bath 9. After being dipped in 9, it is pulled up from the plating bath through the sink roll 8. A premelt pot 10 containing Al at a concentration higher than that of Al in the plating bath is provided in the vicinity of the plating bath 9, and the molten Zn having a high Al concentration sucked up by the metal pump 11 is passed through the supply pipe 12 to the snout 4 It is added to the plating bath surface inside.

Generally, as can be seen from the figure, when the snout is installed for a long time (or when the expansion device 5 is installed in the snout), the steel sheet is snout for about 1/4 or more of the immersion time in the plating bath. The Fe—Zn alloying reaction proceeds by reacting with the molten Zn inside. However, by adding molten Zn having a high Al concentration as described above to the plating bath surface, the Al concentration on the bath surface can be locally increased and an Fe-Al alloy layer can be formed on the steel plate surface. This suppresses the Fe-Zn alloying reaction even when the Al concentration of the Snout outer plating bath is 0.1% Al or less, whereby a hot-dip Zn-plated steel sheet having good adhesion can be manufactured.

Since the high Al concentration molten Zn added in the snout has a lower density than the 0.1% Al-Zn bath outside the snout, the minimum amount necessary for the formation of the Fe-Al alloy is added. As long as you are doing it, it is basically hard to get out of the snout. However, it is necessary to devise a device to prevent the mixing of molten Zn inside and outside the snout, and as a countermeasure for this, the sink roll 7 is installed deeply, the expansion device 5 is installed in the snout 4, and the snout is immersed as deeply as possible. A seal facility 6 for preventing the mixture of molten zinc inside and outside is installed.

Further, the metal flow generator 7 may be installed in order to cancel the accompanying flow of the threaded plate depending on the conditions such as high speed production and deep infiltration of the snout. In addition, this sealing device, as described above,
A structure that can be quickly released when changing the manufacturing type from hot-dip galvanized steel sheet to alloyed hot-dip galvanized steel sheet.

Further, as described above, (1) the bath temperature inside the snout is kept high by setting the penetration plate temperature of the steel sheet higher than the bath temperature outside the snout, and the density of the molten Zn bath inside the snout is kept high. To reduce. (2) High A added to the snout
The 1-concentration molten Zn is set higher than the bath temperature in the snout. (3) When adding Zn taken out by plating, it is necessary to devise an operation such as charging a pure Zn lump containing no Al outside the snout, if necessary.
Even when the plating bath inside and outside the snout is not directly mixed, a part of the Fe-Al alloy layer formed on the steel sheet surface is dissolved in the plating bath outside the snout, so that Al leaks from the inside of the snout to the outside of the snout. . for that reason,
Implementation of (3) is particularly important. In FIG. 1, the molten Zn having a high Al concentration is supplied by the premelt pot and the pump, but the same effect can be obtained by supplying only a necessary amount of the Zn lump having a high Al concentration while melting.

The embodiment shown in FIG. 2 is an example in which a snout 13 having a double structure is provided and a device 14 for supplying a Zn lump having a high Al concentration into the snout is provided in the double structure of the snout. In this way, when supplying Zn lumps with high Al concentration,
Since the Al concentration in the snout and the bath temperature may become non-uniform, the metal flow generator 15 is installed in the double snout here. In addition, due to the reasons described above, Z
The n-lump feeder 14 must be provided with a preheating device or the like so that the bath temperature in the snout does not decrease. In this method, as compared with the method shown in FIG. 1, facilities such as a premelt pot and a molten Zn supply pipe are unnecessary, but the structure of the snout becomes complicated.

[0020]

According to the present invention, in the hot dip galvanizing line, the time required for switching between the production of the hot dip galvanized steel sheet and the alloyed hot dip galvanized steel sheet can be significantly shortened, and the equipment cost and running cost can be greatly reduced. Is.

[Brief description of drawings]

FIG. 1 is a schematic view of an apparatus of the present invention having equipment for supplying molten Zn having a high Al concentration to a plating bath surface.

FIG. 2 is a schematic view of an apparatus of the present invention having equipment for supplying Zn lumps having a high Al concentration to the plating bath surface.

[Explanation of symbols]

 1 strip 2 furnace 3 turndown roll 4 snout 5 snout expansion device 6 sealing device 7 metal flow generator 8 sink cool 9 plating bath 10 premelt pot for high Al concentration Zn 11 metal pump 12 pipe for supplying high Al concentration Zn 13 2 Heavy snout 14 Zn ingot supply / preheater 15 Metal flow generator

Claims (3)

[Claims] 1. An apparatus for immersing a steel strip through a snout into a hot dip Zn plating bath to perform hot dip Zn plating, wherein the surface of the hot dip plating bath in the snout has an Al concentration different from that of the plating bath.
For supplying molten Zn containing Zn and Zn inside and outside the snout
A device for controlling Al concentration in a bath in a continuous hot dip galvanizing line, comprising a multi-chamber structure inside a portion of the snout immersed in the hot dip bath as a sealing device for preventing the bath from mixing. 2. In an apparatus for immersing a steel strip through a snout into a hot dip Zn plating bath to perform hot dip Zn plating, the surface of the hot dip plating bath in the snout has an Al concentration different from that of the plating bath.
It is equipped with a multi-chamber structure inside the part of the snout immersed in the hot dip plating bath as a sealing device for preventing the Zn bath inside and outside the snout from mixing after being preheated. A device for controlling Al concentration in a bath in a continuous hot-dip galvanizing line, which is characterized. 3. The multi-chamber structure metal flow generator as claimed in claim 1, as a sealing device for preventing the Zn bath inside and outside the snout from being mixed with each other, inside the portion of the snout immersed in the hot dip plating bath. Characterized by having,
Device for controlling Al concentration in bath in continuous hot dip galvanizing line.