JPH04356A - Device for producing hot dip metal coated steel sheet - Google Patents

Abstract

PURPOSE:To stably produce a hot dip galvanized steel sheet by providing a seal plate to the opening at the bottom of a vessel with a gap between the plate and a steel sheet to be plated and furnishing a gas wiper above a bath. CONSTITUTION:A steel sheet 2 is continuously introduced into the molten plating metal (zinc) bath 6 from an opening 4 at the bottom 9 of a vessel 8 (hollow pot) contg. the bath 6. A plating metal layer is deposited on the sheet 2 which is then pulled up. The seal plate 5 is provided to the opening 4 furnished at the bottom 9 of the vessel with a gap between the plate and sheet 2. The gas wiper 7 to wipe off the excess plating metal on the sheet 2 is provided above the bath 6. The gap between the plate 5 and sheet 2 is controlled to 0.05-1mm. The seal plate is made of ceramics of silicon nitride-boron nitride, etc. Consequently, a sink roll, etc., tending to cause a surface flaw need not be used in the bath.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention relates to an apparatus for continuously manufacturing hot-dip galvanized steel sheets and alloyed hot-dip galvanized steel sheets, and particularly relates to This invention relates to a production device around a plating bath with excellent operability for continuously and stably plating molten zinc (including molten zinc alloy; hereinafter referred to as "interval") onto the surface of a thin steel plate.

[Prior Art] Hot-dip galvanized steel sheets have excellent corrosion resistance and are relatively inexpensive, so they are widely used in the fields of building materials and home appliances. In addition, alloyed hot-dip galvanized steel sheets have excellent corrosion resistance and can withstand heavy press working, so their demand as steel sheets for automobiles has increased rapidly in recent years.

A general method for manufacturing hot-dip galvanized steel sheets and alloyed hot-dip galvanized steel sheets is as follows. In other words, after cleaning the surface of the thin steel plate after cold rolling in a pretreatment process,
The surface oxide film is removed by annealing in a non-oxidizing or reducing atmosphere, and then the steel sheet is cooled without oxidizing to lower the sheet temperature to the temperature of the zinc bath before entering the zinc bath. let Hot-dip galvanized steel sheets are produced by removing excess molten zinc that adhered to the surface of the steel sheet with a gas wiper using a gas wiper to adjust the zinc coating weight, and then cooling the sheet as it is. Alloyed hot-dip galvanized steel sheets are heat-treated to alloy the plating layer.

A hot-dip galvanizing apparatus with zinc roll is shown in FIG. The steel plate 2 is drawn into the zinc bath 6 through the snout 11, wrapped around a zinc roll 10, and pulled up in the vertical direction. The zinc roll 10 in the zinc bath conveys the steel plate 2 without contacting the rolls until the molten zinc on the surface of the steel plate solidifies by changing the direction of the steel plate 2 to which molten zinc has adhered in the vertical direction. This is an important device for preventing the occurrence of surface defects such as scratches. Since the zinc roll 10 is constantly kept in the molten zinc bath 6 at about 460° C., it is natural that it needs to have excellent erosion resistance. When deposits are formed on the surface of the zinc roll 10, they may cause scratches on the surface of the steel plate, or the deposits may migrate to the surface of the steel plate, resulting in surface defects.

Further, in many cases, the zinc roll does not have a drive system, so if the steel plate slips and the rotation of the zinc roll becomes discontinuous, scratches will be formed on the surface of the steel plate. Furthermore, if plating operations are continued for a long period of time, the surface of the zinc roll becomes uneven, so it is necessary to take it out of the zinc bath and clean it, and the presence of equipment in the bath reduces operability. .

In addition, due to the presence of in-bath equipment such as zinc rolls, the container for molten zinc is extremely thick (and the amount of molten zinc increases, so there is a problem that the degree of freedom when changing the type of plating is reduced. In order to solve problems like
Until now, methods that do not use zinc rolls have been proposed.

The roll coater method, the meniscus method, the curtain flow method, and the like are typical zinc roll-less hot-dip plating methods. Although these methods are suitable for single-sided plating, they are not appropriate plating methods when hot-dip plating is applied to both sides of a steel sheet because the heat treatment before plating is redundant and the mechanical properties of the steel sheet cannot be ensured.

Aerial potting has been proposed as a method that can be applied to double-sided plating without using zinc rolls. In other words, it is a manufacturing device in which molten zinc is held in a relatively small container, a steel plate is introduced from the bottom of the container, and the molten zinc is adhered to the surface of the steel plate. The main features of this manufacturing apparatus are a means for preventing leakage of molten zinc from the bottom of the container into which the steel plate enters, and a means for removing excess molten zinc adhering to the steel plate.

JP-A-63-109149 and JP-A-633109
No. 49 uses electromagnetic force to hold the zinc bath at the bottom of the container, and JP-A-63-109148 and JP-A-63-303045 use electromagnetic force to hold the zinc bath at the bottom of the container. and static pressure seals are used together. If electromagnetic force can be used effectively, there will be no mechanical contact with the surface of the steel plate, so it will not create defects on the surface of the steel plate, making it an ideal device.However, if you try to completely suppress the outflow of molten zinc,
Not only does the capacity of the excitation power source become extremely large, but also the magnetic force exerts an attractive force or a repulsive force on the steel sheet, which poses a problem in that the stable threading of the steel sheet is impaired. Also, JP-A-63-1
62847 and JP-A-1-139744 propose a method of suppressing the outflow of molten metal by sandwiching a steel plate between seal rolls, but deposits accumulate on the seal roll surface and cause scratches on the steel plate surface. There was a problem with attaching the .

[Problem to be Solved by the Invention 1] As a result of studying the problems in the conventional technology around the zinc bath when manufacturing hot-dip galvanized steel sheets and alloyed hot-dip galvanized steel sheets, the present invention has developed a method for double-sided plating while omitting the zinc roll. With this goal in mind, we decided to adopt an aerial pot as our manufacturing equipment. In order to maintain the zinc bath at the bottom of the container, which is important in an aerial pot, the present invention proposes the following device.

[Means for Solving the Problems] The present invention involves continuously introducing a steel plate to be plated into the bath through an opening provided at the bottom of a container holding hot-dip plated metal, and removing the steel plate with the coated metal layer from the bath. This is applied to a hot-dip metal-plated steel sheet manufacturing apparatus that manufactures hot-dip metal-plated steel sheets by lifting the container upward, and the opening provided at the bottom of the container has a gap between it and the steel sheet to be plated. A sealing plate is provided in the open space, and a gas wiper is provided above the pre-distribution bath for wiping away excess plating metal on the steel plate.

In this case, it is preferable to maintain the gap between the seal plate fixed to the bottom of the container and the continuously moving steel plate at 0.05 to 1 mm. Ceramics such as boron nitride, silicon carbide-boron nitride, graphite, and alumina-graphite are suitable.

[Effect] The specific structure and operation of the present invention will be explained next.

In the present invention, as a container for molten zinc, an aerial pot 8 as shown in FIG. Passing the steel plate 2 through between the seal plates 5 fixed to the container bottom 9 when the steel plate 2 supported by the trawl 3 is continuously introduced, molten zinc is attached to the surface of the steel plate, and then the steel plate 2 is passed in a substantially vertical direction. This prevents leakage of molten zinc from the opening 4 at the bottom of the container, and
This is a hot-dip galvanized steel sheet manufacturing apparatus that controls the amount of zinc coating by removing excess molten zinc adhering to the surface of the steel sheet using a gas wiper 7 provided above the zinc bath 6. In the present invention, the opening at the bottom of the container and In order to prevent zinc from flowing out through the gap between the steel plate and the vertically moving steel plate, a fixed seal plate with a small gap between the steel plate and the steel plate is used, which prevents surface scratches from occurring on the steel plate surface. do not have. Furthermore, by statically sealing the opening 4 at the bottom of the container with an inert gas such as N2, it is possible to further suppress the outflow of molten zinc. By using an inert gas such as N2 gas in the gas wiper 7, it is possible to suppress oxidation of molten zinc and prevent generation of oxide-based dross. Since the aerial pot of the present invention has a low head height and a small capacity, a zinc melting furnace is installed near the aerial pot to replenish the amount consumed by the steel plate and maintain the head height constant during operation. is necessary.

An important point in the aerial pot is the gap between the seal plate 5 fixed to the bottom 9 of the container and the continuously moving steel plate 2, and the seal plate 5 and steel plate 2 are in a non-contact state and molten zinc leaks. It is necessary to have a gap that does not
In the present invention, this gap is limited to 0.05 to 1 mm. Within this range, the support by the surface tension of the molten zinc and the action of the steel plate moving vertically upward will allow
Molten zinc will not flow downward from the gap between the seal plate 5 fixed to the steel plate 2 and the continuously moving steel plate 2. If this gap is less than 0.05 mm, contact between the steel plate and the seal plate will occur frequently, causing scratches and surface defects on the steel plate surface. On the other hand, if this gap becomes 1mm or more,
Even if the steel plate moves in the vertical direction, it is not preferable because molten zinc flows out from the gap between the seal plate 5 fixed to the container bottom 9 and the continuously moving steel plate 2.

In addition, as the material of the seal plate in the aerial pot of the present invention, boron nitride, graphite, and silicon nitride are used in the present invention.
Sintered bodies and composite sintered bodies whose main bodies are ceramics such as boron nitride, silicon carbide-boron nitride, and alumina-graphite can be used. These materials not only have excellent erosion resistance against molten zinc, but also excellent thermal shock resistance. These have been selected based on specific experimental results, and we have confirmed that they are all practical. By using relatively soft ceramics as the material for the seal plate, it is possible to prevent scratches on the surface of the steel plate as much as possible. Container bottom 9 at the beginning of production
Even if the gap between the seal plate 5 fixed to the steel plate 2 and the continuously moving steel plate 2 is too narrow, by making the seal plate a soft material as described above, the seal plate 5 can be moved until an appropriate gap is obtained. It will be scraped off by the continuously moving steel plate 2.

[Example 1 Next, the present invention will be explained based on examples.

Example 1 In the aerial pot 8 shown in FIG. 1, the steel plate side of the seal plate 5 is made of boron nitride, the gap between the seal plate 5 and the steel plate 2 is 0.5 mm, and the tip of the seal plate 5 is made of zinc. After annealing in a reducing atmosphere with the head height of bath 6 set to 50 mm and the molten zinc bath temperature set to 465°C,
A steel plate 2 with a width of 300 mm cooled to 65°C is heated for 50 m/
The sheet was threaded at a line speed of 10 minutes. When the amount of molten zinc deposited was controlled to 50 g/m2 using a N2 gas wiper, no molten zinc leaked from the opening 4 at the bottom of the container, and stable plating operations could be maintained.

Example 2 Same as Example 1 except that the steel plate side of the seal plate 5 is made of graphite, the gap between the seal plate 5 and the steel plate 2 is 0.1 mm, and the head height of the zinc bath at the tip of the seal plate is 100 mm. When the operating conditions were set, the opening 4 at the bottom of the container
There was no leakage of molten zinc from the tank (and stable plating operations could be maintained).

Example 3 The gap between the seal plate 5 and the steel plate 2 is O-8 mm, and the seal plate 5
The operating conditions were the same as in Example 1, except that the head height of the zinc bath 6 at the tip of the container was 30 mm, and the line speed of the thin steel plate with a plate width of 300 mm was 80 m/min. There was no leakage of molten zinc from No. 4, and stable plating operations could be maintained.

Comparative Example 1 The gap between the seal plate 5 and the steel plate 2 was 2.0 mm, and the head height of the zinc bath 6 at the tip of the seal plate 5 was 100 mm.
When the operating conditions were otherwise the same as in Example 1, molten zinc leaked from the opening 4 at the bottom of the container, making it impossible to maintain stable plating operation.

Comparative Example 2 In the aerial pot 8 shown in FIG. Head height 50mm, molten zinc bath temperature 465℃
In this state, after annealing in a reducing atmosphere,
50m of thin steel plate with a width of 300mm cooled to 465℃
The sheet was threaded at a line speed of /min. When the amount of molten zinc deposited was controlled to 50 g/m2 using an N2 gas wiper, no molten zinc leaked from the opening 4 at the bottom of the container, but scratches appeared on the steel plate surface and the product value decreased. It decreased significantly.

In the above explanation, only the example of hot-dip galvanizing on thin steel sheets has been described, but this does not mean that the present invention can be applied to molten Aβ and molten A! This does not preclude application to other hot-dip plating such as gold alloy plating, or heating and alloying the steel sheet and the plated metal layer after wiping.

[Effect of the invention 1] As described above, according to the hot-dip galvanized steel sheet manufacturing apparatus of the present invention, hot-dip galvanized steel sheets can be stably produced without using bath equipment such as zinc rolls that tend to cause surface defects. Since it can be manufactured, it has extremely great industrial significance.

[Brief explanation of the drawing]

FIG. 1 is a longitudinal cross-sectional view of a manufacturing apparatus for hot-dip metal-plated steel sheets according to an embodiment of the present invention, and FIG. 2 is a vertical cross-sectional view of a conventional manufacturing apparatus for hot-dip metal-plated steel sheets. l--Deflector roll 2--Steel plate 3--Support roll 4--Opening 5--Seal plate
6.-.Zinc bath 7..Gas wiper 8-.
・Aerial pot 9--Bottom lO...-Zin crawl 11...Snout diagram Diagram

Claims (1)

[Claims] 1. A steel plate to be plated is continuously introduced into the bath through an opening provided at the bottom of a container holding a hot-dip metal bath,
In a hot-dip metal-plated steel sheet manufacturing apparatus that manufactures a hot-dip metal-plated steel sheet by lifting a steel sheet with a plated metal layer above the bath, an opening provided at the bottom of the container has a gap between the plated steel sheet and the plated steel sheet. 1. An apparatus for manufacturing a hot-dip metal-plated steel sheet, characterized in that a seal plate is arranged with a gap between the bath and a gas wiper is provided above the bath for wiping off excess plating metal on the steel sheet. 2. Set the gap between the seal plate fixed to the bottom of the container and the steel plate to 0.
2. The apparatus for manufacturing a hot-dip metal plated steel sheet according to claim 1, wherein the thickness is 0.05 to 1 mm. 3. The apparatus for producing a hot-dip metal-plated steel sheet according to claim 1 or 2, wherein the seal plate is made of ceramics such as boron nitride, silicon nitride-boron nitride, silicon carbide-boron nitride, graphite, or alumina-graphite.