JPH0336252A - High speed hot dipping method - Google Patents

Abstract

PURPOSE:To obtain a uniform plating at high speed at the time of plating a traveling band steel while bringing the steel into contact with the meniscus of a molten metal extruded from a nozzle by sucking a gas entrained by the traveling steel. CONSTITUTION:The opening of a nozzle 4 directed toward the lower surface or vertical surface of a traveling band steel 2 is approached to the steel 2. A molten metal 9 is supplied to the nozzle 4 by static pressure to form a liq. reservoir in the opening and to form a meniscus between the molten metal 9 and the steel 2, and hot dipping is carried out. The gas entrained by the traveling steel 2 is sucked by an exhaust pump 6 from a nozzle 5 slit or perforated in the cross-direction arranged on the upstream side of the nozzle 4 in the traveling direction of the steel 2. Consequently, the gaseous atmosphere is moved in the opposite direction to the traveling of the steel 2. By this method, the deposition of dross is prevented, the plating amt. is uniformized, workability is improved, and the plating speed is increased.

Description

[Detailed description of the invention] (Industrial application field) The present invention relates to a high-speed hot-dip plating method.

(Prior art) Zn, /J, Sn, Pb, and alloy-based coated steel sheets of these metals are widely used as materials for automobiles, construction, electrical equipment, and cans, and are used to improve quality and productivity. is important.

In the conventional hot-dip plating method, the surface of the steel strip is cleaned by heating it in a reducing gas atmosphere, and then the steel strip is introduced into a molten bath of the metal to be coated for immersion plating. A method that controls the amount of adhered molten metal by removing excess molten metal with a gas jetted through a slit-shaped nozzle, or a method that controls the amount of adhered molten metal by removing excess molten metal with a jet of gas after contacting only one side with the molten metal. There is something to control. Such immersion plating is Zn plating, AI
As typified by plating and turn plating, it has been adopted as a manufacturing method for materials that are widely used today.

The disadvantage of this method is that when the steel strip passes through the plating bath, a part of the strip is eluted into the plating bath, and most of the eluted F
The e then forms an intermetallic compound with the bath components and floats in the bath, becoming so-called floating dross. This floating dross gets mixed into the plating layer during plating, degrading the appearance, corrosion resistance, workability, etc. of the product. Next, the capacity of the plating bath must be large enough to allow the steel strip to be introduced and immersed into the bath using a bot roll.

When changing the bath composition of a conventionally large capacity plating bath, especially when making a major change and changing the product type, it is necessary to pump out a portion of the plating bath and replenish or add plating metals and additive metals. . This requires a great deal of cost, time, and labor, and there is a limit to the types of products that can be manufactured on a single plating line. In addition, due to the long immersion time, the metal and steel plate react and form a thick brittle alloy layer that deteriorates workability, so measures have been taken to thin the alloy layer by adding additive elements to the plating bath. As the degree of processing becomes more severe, limits are being reached. Furthermore, oxygen in the air reacts with the molten metal to generate oxidized dross, which wastes the molten metal and adheres to the surface of the steel strip, impairing its appearance.

Next, the amount of plating deposited is generally controlled by the gas squeezing method as mentioned above, but the line speed is 160 m/min.
If the speed exceeds min, the metal that has been squeezed out will fly off violently and become a splash that will stick to the steel strip, and the amount of plated metal that will be lifted up by the steel strip will increase, resulting in a large amount of dross, and there is a limit to how high the speed can be increased. Ta.

The method disclosed in Japanese Patent Publication No. 57-24066, in which molten metal is coated using the roll-yaw 1 method, is advantageous in changing the bath composition, but it also causes problems such as contamination of the plating bath and
The problem of speeding up cannot be solved.

U.S. Patent No. 3,201,275 also discloses a method that solves the above problem when applied to hot-dip plating, but this method uses capillary action to generate resin from a resin solution whose liquid level is lower than that of the coating nozzle. Coating is performed by sucking up the solution, forming a meniscus of resin solution in the coating nozzle, and bringing it into contact with the tape. When this method is applied to hot-dip plating, the following problems arise.

In order to suck up molten metal by capillary action, the wall of the tube needs to have good wettability with the molten metal, and if the tube is made of such a material, it will react with the molten metal at the same time, contaminating the molten metal while sucking it up. It blocks the capillaries. Furthermore, since molten metal has a higher specific gravity than a resin solution, it is difficult to suck it up smoothly, and if the traveling speed of the metal strip increases, the supply of molten metal becomes insufficient and coating becomes impossible.

By the way, during high-speed sheet passing, the gas in the atmosphere accompanying the traveling metal band collides with the meniscus portion at high speed and the gas is drawn into the meniscus, so that the formed coating layer is not continuous and cannot be used.

JP-A-61-207555 discloses the following method as a means for smoothly supplying the molten metal. If a meniscus of molten metal is formed at the opening of the nozzle and the metal strip is run while the metal strip is in contact with the meniscus, the amount of molten metal flowing out from the opening will be greater than that in the case of free flow, which will increase the plating adhesion during continuous operation. The amount can be easily controlled. This outflow amount is caused by the wetting and adhesion of the molten metal, and the amount of adhesion is controlled to be constant depending on the speed of the traveling steel strip.

Although we have found a tentative solution to the problem of smooth supply of molten metal, on the other hand, the issue of atmospheric gas carried along with the metal strip colliding with the meniscus during high-speed threading remains unresolved, making it a limit for high-speed plating. There is.

JP-A-59-67357 focuses on a method of manufacturing an amorphous ribbon, in which molten metal is sprayed onto a steel plate running instead of a rotating disk through a slit I-shaped nozzle or a multi-hole nozzle, and the molten metal sprayed onto the steel plate. A method is disclosed in which the metal is directly cooled to form a coated metal. Specifically, a container containing molten metal is placed above a steel plate running on a drum, a slit-shaped nozzle or a multi-hole nozzle is attached to the container containing molten metal, and the distance between the nozzle tip and the plate is adjusted. close together, usually 11IIl
Must be 11 or less. Control of the flow rate of the molten metal depends on the height of the head or the pressurization method using static or other inert gas. Even in this method, atmospheric gas carried along with the steel strip running at high speed collides with the contact point between the molten metal and the steel strip and gets caught up in the molten metal, resulting in partial non-plating. There is a limit.

A similar problem is also experienced when extruding molten resin using the T-die method. In other words, when the extruded molten resin film is brought into contact with a cooling roll to cool it down, when the transport speed of the film becomes high, the atmospheric gas transported along with the film gets caught up in the film, causing partial film breakage. arise.

It is easy to imagine that in order to solve the above problems, the atmospheric gas can be removed, that is, create a vacuum, but in order to implement it in an actual continuous line, it is necessary to It is necessary to provide a decompression chamber, which increases the construction cost, but if the aim is to increase the speed, the amount of gas that must be removed increases, which makes it even more expensive, making it impossible to create an economically viable line.

(Problems to be Solved by the Invention) An object of the present invention is to provide a high-speed hot-dip plating method that can eliminate the drawbacks of the conventional hot-dip plating methods as described above.

(Means for Solving the Problems) The present inventors have completed the present invention as a result of various studies on methods for preventing atmospheric gas from being entrained in high-speed hot-dip plating.

In other words, the gist of the present invention is to arrange a nozzle on the lower surface or vertical surface of a running metal strip, bring the opening of the nozzle very close to the metal strip, and apply molten metal to the nozzle under static pressure. In this method, a pool of molten metal is formed at the opening by supplying molten metal, and a meniscus is formed between the molten metal and the metal strip to perform hot-dip plating. The present invention is a high-speed hot-dip plating method characterized by sucking gas that moves along with the running of the steel strip through slits or porous holes arranged in the width direction.

Embodiments of the present invention will be described below based on the drawings.

A steel strip 2 running through a container 1 containing molten metal 9 of Zn Aj Sn Pb and alloy metals of each of these metals.
A support roll 3 is installed on the opposite side of the steel strip (Fig. 1 (a)). A slit-shaped nozzle or a multi-hole nozzle 4 is attached to the container 1 containing the molten metal. , the distance between the nozzle tip and the steel strip is usually kept close to each other.
I or less. The outflow rate of the molten metal is controlled by the height of the head or static pressure, such as pressurization 8 with a non-oxidizing gas such as nitrogen.

In addition to the slit or hole 4 for extruding the molten metal, the nozzle is provided with a slit or hole 5 on the upper side in the direction of movement of the m band for sucking the atmospheric gas 10 conveyed on the surface of the 'tllI band. The purpose of this suction nozzle is not to reduce the pressure near the surface of the steel strip, but to move the atmospheric gas between the molten metal extrusion nozzle and the suction nozzle in the opposite direction to the running direction of the steel strip. The feature is that it does not require a differential pressure reduction mechanism or pump capacity. Atmospheric gas moving in the opposite direction to the steel strip running direction is no longer caught up in the meniscus. Wettability between the molten metal and the steel strip is necessary to ensure plating adhesion, and the cleanliness of the steel strip surface is important. For this purpose, known methods such as heating in a reducing atmosphere, degreasing, pre-damage treatment such as pickling, flux coating, etc. can be used. Further, the temperature of the steel strip is reduced to below the melting point of the molten metal.
It also requires heating, which is also the usual method for hot-dip plating.

Next, the present invention will be explained with reference to examples.

(Example) Figures 1(a) and 1(b) show an example of the method of implementing the present invention, in which the steel strip 2 was heated in a reducing gas atmosphere to make the surface clean. Examples of nozzle arrangement when traveling in the horizontal direction and when traveling in the vertical direction are also shown.

The running of the steel strip 2 is stabilized by a support roll 3, and a nozzle 4 for extruding molten metal is installed on the opposing surface. On the upper side in the running direction of the steel strip 2 on the same surface, a nozzle 5 for sucking atmospheric gas 10 conveyed by the steel strip is installed continuously or divided in the width direction of the steel strip. These nozzles 4 and 5 are placed close to the steel strip 2, and a molten metal container 1 is connected to the base of the molten metal extrusion nozzle 4, so that molten metal is supplied from the molten metal container 1 to the nozzle 4. A pipe from the exhaust pump 6 is connected to the suction nozzle.

Next, the rope belt 2 is plated with molten aluminum and molten aluminum is plated. The case where lead plating is applied will be explained.

In the case of hot-dip aluminum plating, the steel strip 2 has a thickness of 0.
The molten metal extrusion nozzle 4 had a gap of 0.7 mm at the opening and had a width of 490 mm. Similarly, the atmospheric gas suction nozzle 5 used had an opening gap of 0.8 mm and a width of 490 mm. For plating, the distance between the rope belt 2 and the tip of the molten metal extrusion nozzle 4 is 0.9 mm, and the distance between the tip of the atmospheric gas suction nozzle 5 is 1.
l 1.5111m. For extrusion of the molten metal, a pressure of 220 mmAq was applied using nitrogen gas, and as the height of the molten metal bath surface in the molten metal container decreased, the pressure was increased to 80 mm to control the extrusion outflow rate to be constant. . Figure 2 shows the relationship between bath surface height and extrusion pressure. FIG. 3 shows the relationship between the atmospheric gas suction speed and the unplated area ratio due to gas entrainment after plating. From these relationships, normal plating without gas entrainment could be obtained uniformly. In addition, the temperature of the molten aluminum is 670° C., the temperature of the steel strip 2 on the support roll 3 is 600° C., and the running speed of the steel strip 2 is 300° C.
Plating was performed under conditions of ~600 m/min1.

As a result, uniform plating without gas entrainment was obtained. In addition, a plated layer without any dross of intermetallic compounds was obtained, and the surface had a beautiful appearance without oxidized dross. The alloy layer was reduced to 0.2 μm or less, and a hot-dip plated steel plate with excellent workability and sufficient resistance to ironing could be obtained.

Furthermore, the following switching to hot-dip galvanizing could be easily performed by switching to a separately prepared nozzle.

Next, in the case of hot-dip galvanizing, the steel strip 2 has a thickness of 0, 5
mm, width 500+nm, the opening gap of the nozzle 4 for extruding molten metal was 0.6 mm, and the width was 490 mm. Similarly, the atmospheric gas suction nozzle 5 used had an opening gap of 0.8 mm and a width of 490 m. For plating, the distance between the rope strip 2 and the tip of the nozzle 4 for extruding molten metal was 0.8 mm, and the distance from the tip of the atmospheric gas suction nozzle 5 was 1.5 mm. The molten metal was extruded by applying a pressure of 600 mmAq with nitrogen gas, and as the height of the molten metal bath surface in the molten metal container decreased, the pressure was increased to 20402O40 to control the extrusion outflow rate to be constant. Figure 4 shows the relationship between bath surface height and extrusion pressure. FIG. 5 shows the relationship between the atmospheric gas suction speed and the unplated area ratio due to gas entrainment after plating. From these relationships, it was possible to obtain uniform plating without gas entrainment. In addition, the temperature of molten zinc is 460°C1
Plating was carried out under the following conditions: the temperature of the steel strip 2 on the support roll 3 was 400° C., and the running speed of the steel strip 2 was 300 to 600 m/min.

As a result, it was possible to obtain uniform plating without entrainment of atmospheric gas. In addition, a plated layer without any dross of intermetallic compounds was obtained, and the surface had a beautiful appearance without oxidized dross. It was possible to obtain a hot-dip plated steel sheet with an alloy layer of 0.1 μm or less and excellent workability that could sufficiently withstand press working.

(Effect of the invention) The production volume of recent hot-dip aluminum plating lines and hot-dip galvanizing lines is increasing, mainly for automobiles and building materials, and accordingly, line speeds are becoming faster and at the same time, the rise height after plating is becoming higher and higher. This tends to increase construction costs. On the other hand, with the diversification of product types, the number of product changeover losses on the same line is increasing. Furthermore, quality requirements are becoming increasingly high, and there is a strong demand for not only prevention of dross adhesion, but also uniformity of the amount of adhesion and improvement of workability. The method of the present invention can solve the above problems at once, and has the advantage of being applicable to other fields, such as high-speed coating of organic resin solutions, and is an innovative and valuable method that will lead to future surface treatment methods. It is.

[Brief explanation of drawings]

111(a) and 111(b) are diagrams showing an example of the plating method according to the present invention. FIG. 2 is a diagram showing the relationship between the extrusion pressure during molten argonium plating, the height of the bath surface in the container, and the extrusion outflow rate. FIG. 3 is a diagram showing the relationship between the atmospheric gas suction speed during molten aluminum plating and the unplated area ratio due to gas entrainment after plating. FIG. 4 is a diagram showing the relationship between the extrusion pressure during hot-dip galvanizing, the height of the bath surface in the container, and the extrusion outflow rate. FIG. 5 is a diagram showing the relationship between the atmospheric gas suction speed during hot-dip galvanizing and the unplated area ratio due to gas entrainment after plating. 1... Molten metal 〇-container, 2... Steel strip, 3... Support roll, 4... Molten metal extrusion nozzle, 5...
・Atmospheric gas suction nozzle, 6... Exhaust pump, 7.
... Exhaust piping, 8... Non-oxidizing pressurized gas for pushing up molten metal, 9... Molten metal, lO... Flow of atmospheric gas. ■ Mouth + ◇ ■ Mouth + ◇ 4 (U≦hon l arrogant~l・Doshi (Or〃approve) ′Ti″×1. /ψ

Claims (1)

[Claims] A nozzle is arranged on the underside or vertical surface of the traveling metal strip, the opening of the nozzle is brought very close to the metal strip, and molten metal is supplied to the nozzle using static pressure to form a pool of molten metal in the opening. In the method of performing hot-dip plating by forming a meniscus between the molten metal and the metal strip, the nozzle has a widthwise slit or a porous hole lined up in the width direction arranged in the direction in which the steel strip runs. A high-speed hot-dip plating method characterized by suctioning the accompanying moving gas.