JP2001254162A - Method of supplying molten metal into continuous hot dipping coating metal bath and its supplying device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a supplying method and a supplying device for molten coating metal into a hot dipping coating metal bath, by which the variation of temperature in a coating metal bath is reduced to the level lower than that by the conventional method, when a metal ingot is supplemented into the coating metal bath, and the sticking of dross onto a material to be coated can be restrained. SOLUTION: When the hot dip metal coating is applied to the surface of a metal hoop by continuously dipping and drawing up the metal hoop into a bath vessel holding the molten coating metal, the metal ingot for supplementing the molten coating metal is disposed on the bath surface at the upper part of the bath vessel. Further, this metal ingot is heated and melted by an amount corresponding to the amount carried out in the drawing-up of the metal hoop from the molten coating metal in the bath vessel and the dross removal, so as to drop this molten coating metal into the bath.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method and an apparatus for supplying a molten metal to a continuous molten metal plating bath. The present invention relates to a technique for supplying a plating bath.

[0002]

2. Description of the Related Art Hot-dip galvanized steel sheets are relatively inexpensive and have excellent rust-preventing ability, and are therefore widely used as steel sheets for automobiles and steel sheets for home appliances.

[0003] This hot-dip galvanized steel sheet is generally manufactured continuously through the following steps. That is, FIG.
As shown in FIG. 1, after a rolled steel sheet 15 (hereinafter, referred to as a steel strip 15 for continuous operation) is run at a constant speed and passed through an annealing furnace (not shown), a cover for preventing oxidation (referred to as a snout 1) is provided. The steel sheet is obliquely penetrated into the plating bath 2 held in the bathtub 16, and is turned vertically by a roll 3 (sink roll 3) provided in the plating bath 2 and pulled out of the bathtub 16. The pulled-up steel strip 15 is subsequently wiped of the molten zinc adhered to the surface with a gas jetted from a nozzle called a gas wiping nozzle 5, and adjusted to a predetermined plating adhesion amount. If necessary, heat treatment may be performed through the alloying furnace 7 to diffuse iron into the galvanized layer to form a galvannealed steel strip. The components of the plating bath 2 held in the bath 16 include:
In addition to zinc, 0.1-0.2 mass% of aluminum (A) previously contained to improve the adhesion of the plating layer adhered to the steel strip 15 and the powdering resistance (powdering resistance).
l) and the amount of iron (F
e). Since these components adhere to the surface of the steel strip 15 and are taken out of the bathtub 16 during operation, they gradually decrease. Therefore, during operation, in order to keep the bath surface level (height) constant, the Al-containing zinc ingot 8 (hereinafter, simply referred to as ingot) is gripped by the supporting means 9 and immersed in the bath to be dissolved. I have. In the plating bath 2, intermetallic compounds such as bottom dross (FeZn ₇ ) in which Fe and Zn eluted from a steel strip or the like and floating dross (Fe _{2 A 15} ) in which Fe and Al are associated are precipitated or deposited. Floating.

By the way, if these dross is adhered to the surface of the material to be plated 15 (in this case, a steel strip) by the flow of the plating bath 2 to form a product steel sheet, then, when the steel sheet is press-formed, the steel sheet is subjected to press damage. Or the mold may be damaged. Therefore, it is necessary to minimize dross in the plating bath 2 during operation. The generation of dross is considered to be a phenomenon in which Fe and Al are precipitated when the concentration thereof becomes higher than the solubility in a plating bath (hot-dip zinc). Since the solubility decreases when the temperature of the plating bath is low, the temperature of the plating bath 2 at the supply position of the ingot 8 is greatly reduced during the supply of the ingot described above, and the dross cannot be avoided. There is also.

Therefore, in order to prevent the temperature fluctuation of the plating bath 2 at the time of supplying the ingot, research and development have been conventionally performed, and there are many disclosed techniques.

For example, there is a technique in which a subpot for dissolving an ingot is separately provided adjacent to a bathtub, and the plating tank and the subpot are connected by a communication pipe provided with a solidification preventing means. Japanese Patent Application Laid-Open No. 63-238252 discloses a technique in which a removable cover is provided on a sub-pot to prevent oxidation during melting. Further, Japanese Patent Application Laid-Open No. 5-186857 discloses a technique in which an ingot supply unit having a heating device is provided in a bathtub, the vicinity of the ingot supply unit and the heating device are surrounded by a weir, and the temperature inside and outside the weir is independently controlled. are doing.

[0007]

However, in the technique of separately providing a sub-pot adjacently, the equipment becomes large due to the addition of the sub-pot, and the cost becomes enormous, which is not practical. In addition, the transfer of the molten zinc through the communication pipe has a drawback that the zinc erodes the pipe or that it is difficult to make the temperature of the subpot and the plating bath uniform. Further, in the sub pot, JP-A-63-23825
Even if the cover described in JP-A No. 2 is provided, it has not yet been possible to completely prevent temperature fluctuation and oxidation of the plating bath. In addition, even in the technique described in Japanese Patent Application Laid-Open No. 5-186857, the change in bath temperature near the ingot supply section surrounded by a weir is smaller than when no weir is provided, but the temperature difference still exists, Occurrence was inevitable. In addition, although the weir is made of a material that is resistant to the erosion of Zn, there is a problem that the temperature is likely to be high and the life is short because the material is close to the heating device.

In view of the foregoing, the present invention has been made in view of the above circumstances, and has made it possible to reduce the temperature fluctuation of the plating bath when replenishing the metal ingot to the plating bath and to suppress the adhesion of dross to the material to be plated. It is an object of the present invention to provide a method and an apparatus for supplying molten metal to a vessel.

[0009]

Means for Solving the Problems In order to achieve the above object, the inventor has conducted intensive studies focusing on minimizing a decrease in the temperature of a plating bath, and has embodied the results in the present invention.

That is, according to the present invention, when a metal strip is immersed and pulled up continuously in a bath holding a molten metal, and the surface of the metal strip is coated with a molten metal, the above-mentioned bath is placed on the bath surface above the bath. A metal ingot for replenishing the molten metal is arranged, and the metal ingot is heated and melted in an amount corresponding to the amount removed from the plating bath in the bathtub by pulling up the metal band and removing the dross, and the molten metal is poured into the bath. Is supplied to the continuous hot-dip metal plating bath.

The present invention also provides a method for supplying a molten metal to a continuous molten metal plating bath, wherein the metal strip is a steel strip and the molten metal is zinc containing aluminum.

Further, the present invention relates to a continuous molten metal plating apparatus provided with a bath for holding a molten metal, continuously dipping and lifting a metal band into the molten metal, and applying a molten metal plating to the surface of the metal band. A continuous hot-dip metal plating bath, comprising: means for supporting a metal ingot that can move up and down to hold the metal ingot on the bath surface above the bathtub; and heating means for heating and melting the metal ingot. Of molten metal supply device.

In the present invention, the heating means is preferably an induction heating coil, or the heating means may be provided with a sensor for detecting the amount of the metal ingot melted and dropped. In addition, in the present invention, the vicinity of the falling position of the molten metal in the bathtub is separated by a barrage plate having a length reaching a depth of 300 to 1000 mm below the bath surface, or plating is performed from a heated melting part of the metal ingot. It is preferable to provide a gas injection nozzle for blowing an inert gas into a space in a path where the molten metal falls into the bathtub.

According to the present invention, the metal ingot, which is a supply source of the molten metal, is heated above the plating bath, melted, and then dropped into the plating bath in a molten state at substantially the same temperature as the plating bath. The temperature of the bath does not fluctuate during operation. As a result, the generation of dross is suppressed, and the occurrence of defects in the product steel sheet due to the dross adhesion to the metal strip is greatly reduced.

[0015]

Embodiments of the present invention will be described below with reference to the drawings.

As shown in FIG. 1, the apparatus for supplying a molten metal to a continuous molten metal plating bath according to the present invention holds a molten metal 2 and continuously immerses and pulls up a metal band 15 therein. Bathtub 1 for hot-dip metal plating on the surface of metal strip 15
In the continuous hot-dip metal plating apparatus provided with
A vertically movable metal ingot supporting means 9 for holding the metal ingot 8 on the bath surface above the metal ingot 8;
And a heating means 10 for heating and dissolving.

Specifically, a heating means 10 (see FIG. 2) in which an induction heating coil 13 is incorporated along the inner wall of the refractory material cylinder 14 and above the bathtub 16 is installed in a non-contact manner with the bath surface. is there. Support means 9 for gripping and moving (elevating) the ingot 8 in the axial direction so that the metal ingot 8 as a supply source of the plating bath 2 is inserted into the heating means 10 by a required length. It is provided. With such a configuration, the ingot 8 can be continuously heated and melted in a required amount, and the metal can be constantly dropped into the plating bath in a molten state. That is, the molten metal can be supplied to the plating bath 2 without direct contact between the ingot 8 and the plating bath 2 which are the cause of the temperature drop of the plating bath 2. In the above description, the induction heating coil 13 is used for the heating means 10, but the present invention is not limited to this. This is because a burner using gas, heavy oil, or the like as a fuel may be used.

Here, the reason why the ingot 8 is continuously heated and melted in a required amount is that the ingot 8 adheres to the metal strip (steel strip or the like) 15 during the plating operation and a part of the plating bath 2 becomes a bathtub 16.
This is because the plating bath is always replenished in an amount corresponding to the amount pulled out and the amount removed when the dross is scraped off from the plating bath. These amounts can be calculated in advance once the operating conditions are determined. Then, during operation, heating is performed by adjusting the amount of current and the amount of fuel supplied to the induction heating coil 13 so that the amount corresponding to the calculated value is melted. Therefore, a relationship between the amount of the current or the fuel and the amount of the ingot dissolved is necessary, and the relationship may be determined in advance by analyzing test operation or past operation data.

Next, the inventor has further improved the molten metal supply apparatus according to the present invention described above, and
In addition, the sensor 1 for detecting the amount of melting and dropping of the metal ingot 8
7 was provided. This aims at further improving the effect of the present invention if the amount of dissolution can be actually confirmed. In other words, even if there is no relationship between the amount of current or fuel and the amount of dissolution described above, the amount of dissolution can be adjusted,
It becomes possible to supply the molten metal to the plating bath with high accuracy. As the sensor 17, any load cell that detects a change in the weight of the ingot 8, a distance meter that detects a change in the length, or the like may be used.

Further, in the present invention, the vicinity of the falling position of the molten metal 2 in the bathtub 16 is set to be 300 to 1000 mm below the bath surface.
The partition plate 11 has a length that reaches the depth of the plate. This is to prevent unnecessary flow and waving from occurring in the plating bath 2 due to the fall of the molten metal. Thereby, stable adhesion of the molten metal to the plating target material 15 can be guaranteed. The length of the partition plate to reach a depth of 300 to 1000 mm below the bath surface is such that if it is less than 300 mm, the vibration of the liquid surface when the molten zinc falls has an adverse effect on the plating, and if it exceeds 1000 mm, the replenishment of the replenished components will occur. Is significantly slowed down, causing inconvenience. In addition, the area | region in planar view of the partitioned plating bath should just be a magnitude | size which does not interfere with dross scraping.

Further, in the present invention, a gas injection nozzle 18 for blowing an inert gas into a space in a path range where the molten metal falls from the heated and melted portion of the metal ingot 8 to the plating bath 2 is provided. This prevents oxidation of the molten metal falling from the ingot 8 to the plating bath,
This is because dross generation can be suppressed. Nitrogen gas and argon gas can be used as the inert gas.

The present inventor has also described the method of supplying a molten metal to a plating bath using such an apparatus. However, since all the requirements have been described above, description thereof will be omitted.

[0023]

EXAMPLE An ultra-low carbon steel strip was hot-dip galvanized using a continuous hot-dip galvanizing line installed downstream of an annealing furnace at a cold-rolled steel sheet manufacturing plant. At this time, the plating operation is performed separately when the hot-dip galvanizing apparatus according to the present invention shown in FIG. 1 and the conventional apparatus shown in FIG. 3 are respectively installed in a bath holding a continuous hot-dip galvanizing bath. Was. The steel strip 15 was 0.7 mm in thickness and 1200 mm in width, and was immersed in the plating bath 2 and pulled up at a running speed of 120 m / min. The temperature of the plating bath was 465 ° C., and the coating weight was 45 (g / m ² ) on one side of the steel strip 15. According to a preliminary study, the amount of reduction of the plating bath (hot-dip zinc) 2 during operation was about 850 kg / hr (attached to the plate as a plating layer: about 800 kg / hr, dross scraping:
About 50 kg / hr). Therefore, it is necessary to supply molten zinc in an amount corresponding to this amount, which was performed by dissolving an aluminum-containing zinc ingot (aluminum 0.3 mass%). The ingot 8 has a cross section of 350 mm.
It is a square column with a length of 1000 mm.

This is supported by the supporting means 9 and inserted into the heating means 10 at a constant speed of 960 mm / hr by the movement thereof, and is continuously heated and melted according to the supply method according to the present invention. It was dropped into the plating bath as zinc. As a result, no change in the temperature of the plating bath due to the supply of the molten metal was observed over the entire operation period. On the other hand, when the ingot 8 was directly inserted into the plating bath 2 and melted using the conventional apparatus, the temperature of the plating bath 2 dropped by about 20 ° C. in the vicinity of the insertion region of the ingot 8.

[0025] The product steel strip thus plated was cut into a steel sheet of a predetermined size, and then subjected to press working. As a result, in the hot-dip galvanized steel sheet manufactured by applying the method and apparatus for supplying a molten metal according to the present invention, the average rate of occurrence of defects due to dross adhesion (= defective tonnage due to defects / total production tonnage) is 0.1. It was reduced to 02%, and the quality of dross was dramatically improved. On the other hand, in the case of a steel plate manufactured by applying the conventional apparatus, the ratio was 0.1%.

In the above embodiment, a steel strip is used as the metal strip of the material to be plated, and zinc containing aluminum is used as the molten metal. However, the present invention is not limited to this. In other words, it does not matter if other non-ferrous metal bands or molten metals are used for each.

[0027]

As described above, according to the present invention, the fluctuation of the bath temperature which has conventionally occurred when the plating component is supplied to the bath by using the metal ingot is almost eliminated. As a result, the defects of the metal band caused by the attachment of dross are greatly reduced, and a metal-plated metal band having better plating quality than the conventional one can be manufactured.

[Brief description of the drawings]

FIG. 1 is a diagram schematically showing a longitudinal section of a molten metal supply device according to the present invention.

FIG. 2 is a diagram illustrating an example of a heating unit according to the present invention.

FIG. 3 is a diagram schematically showing a longitudinal section of a conventional molten metal supply device.

[Description of Signs] 1 Snout 2 Molten metal (plating bath) 3 Roll (sink roll) 4a Support roll in upper bath 4b Support roll in lower bath 5 Gas wiping nozzle 6 Support roll on bath 7 Alloying furnace 8 Metal ingot (Aluminum) 9 containing zinc ingot) 9 support means 10 heating means 11 partition plate 12 N ₂ purge pipe 13 induction heating coil 14 tubular refractory material 15 material to be plated (metal strip, steel strip) 16 bathtub (plating bathtub) 17 sensor 18 gas injection nozzle

Claims (7)

[Claims] 1. A method for continuously immersing and lifting a metal strip in a bath holding a molten metal and applying a molten metal plating to the surface of the metal strip. Disposing the metal ingot and heating and melting the metal ingot by an amount corresponding to the amount removed from the plating bath in the bathtub by pulling up the metal band and removing the dross, and dropping the molten metal into the bath. A method for supplying a molten metal to a continuous molten metal plating bath, characterized in that: 2. The method according to claim 1, wherein the metal strip is a steel strip and the molten metal is aluminum-containing zinc. 3. A continuous molten metal plating apparatus provided with a bath for holding a molten metal, continuously dipping and lifting a metal band therein, and applying a molten metal plating to a surface of the metal band, A means for supporting a metal ingot which can move up and down to hold the metal ingot on the bath surface above, and a heating means for heating and melting the metal ingot; Feeding device. 4. The apparatus for supplying molten metal to a continuous molten metal plating bath according to claim 3, wherein said heating means is an induction heating coil. 5. The apparatus for supplying molten metal to a continuous molten metal plating bath according to claim 3, wherein the heating means is provided with a sensor for detecting an amount of the metal ingot melted and dropped. 6. The method according to claim 3, wherein the vicinity of the falling position of the molten metal in the bathtub is partitioned by a shield plate having a length reaching a depth of 300 to 1000 mm below the bath surface. An apparatus for supplying molten metal to the continuous molten metal plating bath as described above. 7. The gas injection nozzle according to claim 3, further comprising a gas injection nozzle for blowing an inert gas into a space of a path where the molten metal falls from a heated and melted portion of the metal ingot to a plating bath. An apparatus for supplying molten metal to the continuous molten metal plating bath as described above.