JPH0356655A - Hot dip metal plating method - Google Patents

Abstract

PURPOSE:To form a plating layer of a uniform thickness on the surface of a steel sheet by passing the steel sheet pulled up from a hot dip plating bath through an inert atmosphere contg. hydrogen halide and controlling the coating weight with wiping nozzles. CONSTITUTION:A steel sheet 1 subjected to degreasing, pickling and coating with a flux is dipped in a hot dip plating bath 3 to coat the surface of the steel sheet 1 with a molten metal. When the steel sheet 1 rises from the bath 3, it is passed through an inert gas box 5 contg. hydrogen halide to dissolve oxide on the plated surface and iron oxide in pinholes. An inert gas is then blown on the steel sheet 1 from wiping nozzles 4a, 4b to regulate the coating weight. A plating layer of a uniform thickness is efficiently formed on the surface of the steel sheet 1.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to a molten metal plating method, and more particularly to a molten metal plating method that is optimal for forming a uniformly thick plating coating on the surface of a steel plate.

Conventional technology Hot-dip metal plating of steel sheets is currently widely used, and its applications are increasing year by year. Among them, fj galvanized steel sheets have recently come into widespread use as rust-preventing steel sheets for automobile bodies, and the number of galvanized steel sheets produced has also increased significantly. Conventionally, a common method for increasing the corrosion resistance of steel sheets is to coat them with a metal different from iron. For example, when the metal different from iron is Zn, the presence of Zn electrochemically protects the iron. For this purpose, many plated steel sheets are generally coated with ZN, A/, etc.

In addition, thick plating with a large amount of different metals such as Zn is theoretically better in corrosion resistance, which is why galvanized iron sheets used as roofing materials are required to have thick plating.

In addition, efforts are being made to bring the potential as close as possible to iron as a way to improve corrosion resistance. For example, Zn-5
Products such as %AI plating and Zn-54%/l-1.6% S1 plating have come into production in recent years. In this type of molten metal plating method, the amount of plating was adjusted using two rolls as shown in Figure 3 between 1955 and 1955, but later it became possible to withstand high-speed plating and to make fine adjustments. Moreover, in order to control the plating uniformly, a gas wiping method (hereinafter referred to as the gas method) as shown in FIG. 4 has been generally adopted.

In this gas method, after the steel plate is immersed in the plating bath, in the process of lifting it up, an inert gas such as nitrogen gas is ejected from the gas wiping nozzle 4 to the upstream and downstream sides of the steel plate to adjust the plating appearance. It is something to do. The problem with this gas plating method is that the amount of plating is limited.
! II, it is difficult to deposit a certain amount of basis weight or more. For example, as shown in JIS G 3302, galvanized iron plates have a maximum Z of 275 g/m2 (38 μm Min).
27 is the maximum coating weight, and when plating aluminum steel plates, the coating weight is 300Q with the coating height symbol 200 as shown in JIS G 3314.
/m' (110 μm) is the maximum date amount. Thick plating is not specified because uniform plating is impossible for a thickness greater than 1 mm. In the case of hot-dip metal plating of objects such as structures whose appearance is not particularly required, for example, there are cases in which a layer of 50 μm of zinc is deposited, but this does not result in a plated product with a uniform appearance.

The problems with conventional hot-dip metal plating are as follows:
The issue is how to even out the plating coating at the time of coating amount control using the roll method or gas method. In plating lines that require particularly high speed, the roll method has been changed to a gas method, but this gas method provides uniform plating.
As a result of research on the type of gas used in this gas method, it has become possible to achieve a uniform appearance by using water vapor, combustion exhaust gas, nitrogen gas, etc. However, when it comes to thick plating, the plating film is not uniform due to oxidation of the coating metal, changes in viscosity, etc., and the plated product becomes extremely uneven.
0 g/ra2, 450 for aluminum plating
CJ /'m2, 200 (] / for lead plating
The current situation is that it is extremely difficult to obtain a product with a plating adhesion of m2 or more (all amounts on both sides).

In addition, during molten metal plating, if there is dirt or oxides on the surface of the steel during the process of pulling up the material to be plated from the molten metal, the plating may not be uniform, resulting in an uneven surface, or the surface may be uneven at the time of pulling up. If the oxides are not removed, a non-uniform coating layer formed by the oxides will result in a mesh product with a poor appearance. Various techniques have been tried to improve the appearance of molten metal plating, and uniformity using a gas method has generally been adopted. However, when it comes to thick plating, it is necessary to reduce the force of this wiping to achieve thick plating, but in this case, an oxide film generated in the plating bath or during the process of being pulled up has an adverse effect on the plating surface.

For example, in lead-8% tin alloy plating, the highest basis weight is 1 9 8 G/'l2 for this reason, and beyond this, only products with poor appearance can be obtained.

Problems to be Solved by the Invention The present invention aims to solve the above-mentioned problems. Specifically, the present invention provides a method for molten metal plating that lowers the surface tension of the oxide coating generated during molten metal plating and dissolves it to form a uniform plated coating. This paper proposes a method.

Means for solving the problem and its operation, that is, the present invention provides 78rI! After being immersed in a metal plating bath, the steel sheet is pulled out of the plating bath to form a plating coating on the steel sheet.The steel sheet is pulled out of the plating bath by passing through an inert gas atmosphere containing hydrogen halide formed on the surface of the plating bath. Then, the amount of plating is controlled by injecting inert gas from wiping nozzles arranged on both sides of the steel plate.

Hereinafter, the structure 1i12 which is a means of the present invention and its operation will be further explained as follows.

The present inventors investigated how to make the surface and pinholes uniform, which are uneven due to the oxide film and non-plating that occur in the plating bath or during the process of being pulled out of the plating bath, and found that the It has been found that by using an inert gas containing hydrogen halide, the metal oxide can be replaced with chloride to make the surface uniform, and it is also possible to dissolve the ingots in the unplated areas such as via holes and irregularities.

Further research and development were carried out, and the present invention was established based on this research.

Hereinafter, the method of the present invention will be explained in detail with reference to the drawings.

FIGS. 1 and 2 are longitudinal sectional views of an example of an apparatus used in carrying out the method of the present invention, and FIGS. 3 and 4 are longitudinal sectional views of an example of a conventional apparatus, respectively. be.

1 is a steel plate, 2 is a plating roll, 3 is a plating bath, 4a
, 4b is a nozzle, 5 is a hydrogen halide containing gas box, 6 is a hydrogen halide gas flow rate regulator, 7a and 7b are nozzles, 8 is hydrogen halide, 9 is nitrogen gas, 10I. t
A mixer is shown.

First, as shown in Fig. 1, the plating bath used to carry out the method of the present invention has a box containing hydrogen halide gas on the plating bath surface, and a steel plate on both sides above the box. Adhesion amount adjustment gas wiping nozzle 4
A% 4b has been taken advantage of. The present invention uses this gA@ to remove oxides on the plating surface with hydrogen halide. Here, the steel plate 1 entering the plating bath is a steel plate reduced by hydrogen gas in the Sendzimer method, or a steel plate 1 coated with flux after degreasing and pickling in the method using flux. The surface of these steel sheets is coated with molten metal, but when it rises from the plating bath, it is placed in a hydrogen halide containing gas box 5 in which hydrogen halide is mixed. The oxides, etc. of the base iron are dissolved, and the plated surface becomes a beautiful, uniform coating. This hydrogen halide rises upward, and while the atmosphere is maintained, excess plating is removed by the plated@quantity adjusting gas wiping nozzles 4a, 4b, and the desired plated@mounted product is produced. Also. The device shown in Figure WS2 is different from the one shown in Figure 1, in that it is a gas mixer 1 for gas wiping.
This method uses hydrogen octaride mixed with 0. Hydrogen halide 8 is mixed with a wiping gas such as nitrogen gas 9 in a mixer 10, and the nozzle 7a
, 7b, hydrogen halide-containing gas is blown onto the surface of the steel strip as it travels, and this gas flows upward and downward, removing and dissolving oxides on the surface of the plating bath and oxides present on the steel strip, and uniformly dissolving them. It can be plated surface.

Example Hereinafter, a more specific explanation will be given with reference to Examples.

Example 1. ? ]ll0.5a thick and width 500m,/m was degreased, pickled (salt aff1000.・l) for 11 hours, then coated with a ZnCl2 aqueous solution, and then washed with Pb-8% in the apparatus shown in Figure 1. Sn bath ('/rA degree 350-360℃)
The plating was carried out in an atmosphere adjusted so that the concentration of Cl gas in the air was 100 ppm, and plating was carried out using nitrogen gas. I outside these! The results of the evaluation test M are shown in Table 1. For comparison, the results of a similar test except that the ¥A setting shown in FIG. 4 was used are also shown in Table 1.

Table 1 Outside of Table 1 I! Evaluation test! A results were determined based on the following criteria.

◎・・・Excellent appearance ○・・・Good appearance Δ・・・Irregularities with slight horizontal stripes ×・・・Pothole-like defects Example 2 of a product with defective appearance. 0.4m. Plating was carried out using the apparatus shown in FIG. 2 using a steel strip having a thickness of 500 m/'m and a width of 500 m/'m. The plating bath is a galvanizing bath with znO. A 10% AI bath was used, and the plating bath temperature was 1460°C. A steel strip is immersed in this plating bath, and as it is pulled up, it is exposed to N 2 100 p.
I) m H C l jJ was injected from a nozzle to the upstream and downstream sides of the steel strip to control its area weight. 1 galvanized product with good appearance even at 40μm
I was pissed.

Effects of the Invention> As explained above, the present invention provides a method for removing halogenated metals formed on the surface of the plating bath when the steel plate is immersed in a molten metal plating bath and then pulled out of the plating bath to form a plating coating on the steel plate. The steel plate is pulled up from the plating bath by passing through an inert gas atmosphere containing hydrogen, and then an inert gas is applied from wiping nozzles arranged on both sides of the steel plate to control the amount of plating deposited. .

Therefore, according to the present invention, after passing through the atmosphere containing hydrogen halide gas, inert gas is injected from the wiping nozzle or inert gas containing hydrogen halide gas is injected from the gas wiping nozzle.
A uniform thickness plating of molten metal can be obtained efficiently.

[Brief explanation of drawings]

FIGS. 1 and 2 are longitudinal cross-sectional views of an example of an apparatus used in carrying out the method of the present invention, and FIGS. 3 and 4 are views of a conventional example, respectively. It is a longitudinal cross-sectional view which shows an example of f. Code 1...Steel plate 2...Plating roll 3...Plating bath 4a, 4b...Nozzle 5...Hydrogen halide containing gas box 6...
...Hydrogen halide gas flow rate regulators 7a, 7b...
... Nozzle 8 ... Hydrogen halide 9 ... Nitrogen gas 10 ... Mixer Fig. 1

Claims (1)

[Claims] 1) When a steel plate is immersed in a molten metal plating bath and then pulled out of the plating bath to form a plating coating, the steel plate is exposed to an inert gas containing hydrogen halide formed on the surface of the plating bath. A molten metal plating method comprising: passing through an atmosphere to pull the steel plate out of the plating bath; and then injecting inert gas from wiping nozzles arranged on both sides of the steel plate to control the amount of plating deposited. 2) When a steel plate is immersed in a molten metal plating bath and then pulled out of the plating bath to form a plating coating, an inert gas containing hydrogen halide is passed through wiping nozzles installed on both sides of the steel plate pulled out of the plating bath. A molten metal plating method characterized by controlling the amount of deposition by injecting gas. 3) The molten metal plating method according to claim 1 or 2, wherein the molten metal is a lead alloy. 4) The molten metal plating method according to claim 1, 2 or 3, wherein the molten metal is an alloy whose main components are aluminum, zinc, lead, and tin. 5) Claims 1 and 2, wherein the hydrogen halide is hydrogen chloride.
The molten metal plating method according to , 3 or 4. 6) The concentration of the hydrogen halide atmosphere is 1 ppm to 5 ppm.
The molten metal plating method according to claim 1, 2, 3, 4 or 5, wherein the molten metal plating method is 0%.