JPS59145774A - Continuous hot dipping method - Google Patents

Abstract

PURPOSE:To enable inexpensive control of the amt. to be plated under high- speed operation in the stage of subjecting a reduction-annealed metallic strip to continuous hot dipping without oxidizing the same by using a molten salt in wiping and adjusting the molten metal sticking on the metallic strip. CONSTITUTION:A reduction-annealed metallic strip 3 is conducted continuously into a plating bath 2 without oxidizing and is pulled perpendicularly from the bath surface via a sink roll 7. The molten plating metal 4 sticking on the strip 3 is wiped and adjusted by the resistance and surface tension at the boundary of the molten salt 5 in a salt bath furnace 9 in this state to adjust the same to a prescribed plating thickness. The furnace 9 encloses the rising part of the strip 3 and has a passing port 8 for the strip 3 in the upper part. The base of the furnace is opened and the bottom part thereof is dipped at all times in the bath 2. The salt 5 heated and adjusted to an adequate temp. is put afloat in the furnace 9 and the thickness T thereof is adjusted by supplying the salt 5 heated and adjusted to an adequate temp. in a salt bath furnace 10 by means of a pump P1 and a pipe 11 to said furnace.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a continuous hot-dip plating method that can improve the effect of wiping away hot-dip plated metal adhering to the surface of a metal strip.

In general, methods using roll squeezing and gas wiping are known as methods for controlling the amount of hot-dip plated metal deposited on a metal strip in continuous hot-dip plating. The roll squeezing method is a method in which the molten metal adhering to the metal strip is squeezed out using two grooved rolls placed opposite to each other on both surfaces of the metal strip, but it has the following problems. In other words, ■ There are many and complex control factors, and it is difficult to understand the factors.
Automatic control is not possible, ■ The uniformity of the plating coating distribution is poor, and it is necessary to apply more molten metal than necessary in order to pass the standards. ■ The life of the coding roll is short, requiring frequent roll changes. , ■ The upper limit of Finnupede is 60 to 80 m/min, and high-speed operation is not possible. ■ Is it possible to reduce the weight of molten metal to 50 to 80 m/min? /rr
The gas wiping method was developed as a means to solve all of these problems. Ta. The gas wiping method involves blowing high-pressure gas onto the surface of the steel plate from two nozzles placed opposite each other on both surfaces of the metal strip at a predetermined height from the surface of the plating bath, and using a gas jet knife to wipe away the molten metal that has adhered to the surface of the metal strip. This is a method of narrowing it down. However, this method also had the following problems. Namely, (1) As the passing speed of the metal strip increases, the amount of molten metal that adheres to the metal strip and lifts up from the plating bath increases significantly.

■ In response to an increase in the amount of molten metal lifted, the wiping gas pressure increases and a violent splash of molten metal occurs. This adheres to the surface of the metal strip, causing quality deterioration and locally blocking the nozzle, making plating operations impossible. In addition, these atomized molten metals do not dissolve in the plating bath again and accumulate around the plating machine, which not only impairs work efficiency, but also
This results in a significant deterioration of the molten metal consumption rate.

■ As the wiping gas pressure increases, the noise generated from the nozzle becomes louder and the working environment worsens.

■ When manufacturing thick sheets (when manufacturing products with a large amount of molten plated metal deposited on the surface of the metal strip), edge overcoat becomes noticeable at the edge of the m plate, resulting in a decrease in the yield of molten metal and poor flatness (occurrence of selvage). bring about.

For this reason, in continuous hot-dip plating using the gas wiping method, the metal strip passing speed (line speed) is 150 to 200 m/min, and the weight of the molten metal deposited is 80 to 40 m/min. /rd (single-sided) is considered to be almost the limit.

This invention proposes a method for controlling the amount of molten metal deposited to solve the above-mentioned drawbacks of the roll drawing method and the gas wiping method. In continuous hot-dip plating, which is performed by introducing the metal into the plating bath and then continuously pulling it out from the plating bath, the rising part of the metal band on the surface of the plating bath is surrounded by molten salt, and the molten salt wipes and adjusts the amount of hot-dip plated metal on the surface of the metal band. This is a continuous hot-dip plating method for controlling the amount of zinc deposited on hot-dip galvanized steel sheets at low cost and economically.

Next, details of the invention will be explained based on the drawings.

Figure 1 shows the metal strip (3) drawn out from the plating bath (2).
). Figure 2 shows the relationship between the fin speed and the amount of hot-dip plated metal lifted up. The faster the speed of the metal strip (3), the more This shows that the adhesion thickness χ of the hot-dip plated metal increases, and the amount of lift of the hot-dip plated metal (4) on the metal band (3) increases.

FIG. 8 shows a device according to the present invention in which the rising part of the metal band on the surface of the plating bath is surrounded by molten salt (5), and the resistance and interfacial tension at the interface between the molten salt (5) and the molten plated metal (4) are wiping, reducing the adhesion thickness χb, and suppressing the amount of lifting of the hot-dip plated metal (4). Incidentally, the hot-dip plating metal adhesion thickness χb can be adjusted by appropriately changing the thickness of the molten salt and the type of molten salt.
Figure (B) shows experimental results showing changes in the amount of lifting of the hot-dip plated metal when the thickness T of the molten salt is changed.

In FIG. 4(A), molten salts a, b, and c are a: nitrate, b: halide salt, C: carbonate, and the velocity is V,
The relationship is <V2<V. From this experimental result, it is clear that when molten salt C is used, the fin speed can be increased to ①→■2 in order to obtain the same deposition amount as that during gas wiping plating. Also, Figure 4 (
It can be seen from B) that even if the molten salt thickness T is changed, the amount of lifting of the molten plated metal can be controlled.

FIG. 5 shows one embodiment of the invention.

In this invention, the reduction annealed metal band (3) is passed through the plating bath (6) continuously without being oxidized.
2), and when pulled vertically from the bath surface via the zinc roll (7), the resistance and interfacial tension at the interface of the molten salt (5) in the salt bath furnace (9) causes the metal strip (3) to be pulled up vertically from the bath surface. Adjust the amount of hot-dip plated metal adhesion (4) to reach the predetermined adhesion thickness χ
b.

The equipment configuration shown in FIG. 5 is as follows.

(1) is a plating tank, (2) is a plating bath, and (9) is a salt bath furnace provided so as to surround the rising portion of the metal band (3) on the surface of the plating bath.

The upper part of this salt bath furnace has an opening (8) for passing the metal band,
The bottom surface is open and the lower part is always shallowly immersed in the plating bath (2). Also, molten salt (5) is placed in a floating state inside this salt bath furnace, and is heated by heating devices such as an electric heater, an induction heating device, and a combustion burner (not shown), and is constantly controlled at an appropriate temperature. . 01 is the plating tank (1
) is another salt bath furnace installed outside the plating bath, which stores the molten salt (5) to be supplied to the salt bath furnace (9) on the surface of the plating bath, and is equipped with a suitable heating device (not shown). The internal molten salt (5) is controlled at an appropriate temperature. 0]) is a pipe that communicates with the salt bath furnace (9) and the molten salt (5) in the QO (5), and P is a pump installed in the pipe, which connects the salt bath furnace 00 to the salt bath. The molten salt (5) is supplied to and discharged from the furnace (9), and the thickness T of the molten salt layer in the salt bath furnace (9) is adjusted.

Next, the results of a comparative test of the wiping effect between the molten salt wiping method of the present invention and the conventional gas wiping method are shown in FIG.
Figure 7 shows the results of an investigation on the uniformity of the distribution of plating deposits in the width direction.

Test C: A cold-rolled foil coil with a thickness of 0.8 mm and a width of 914 ffllll was passed through a continuous hot-dip galvanized test fin using a non-oxidizing furnace at a line speed of 50 to 400 m/min, and was conducted under the conditions shown in Table 1. Ta.

Table 1 From the results shown in Table 1, it can be seen that the present invention is an inexpensive hot-dip plating method that makes it possible to control the amount of zinc deposited under high-speed operation.

The effects of this invention can be summarized as follows.

■ The cost and operating expenses of the equipment for controlling the amount of hot-dip plated metal are lower than those of the conventional gas wiping method.

■ Even when the metal strip passes at a speed of 200 m/min or more, the wiping force is extremely strong, making it suitable for high-speed plating.

■ Controlling the adhesion amount of hot-dip plated metal requires only controlling the thickness of the molten salt, making it easy to understand the control factors and suitable for automatic control.

■ Since the plating bath surface is covered with molten salt, the occurrence of top dross is reduced. In addition, because the wiping force acts uniformly over the entire width of the metal strip due to the action of the molten salt, the distribution of the amount of molten metal deposited in the middle direction is more uniform, and there is no need to apply extra molten metal. Usage intensity improves.

[Brief explanation of drawings]

Figure 1 is an explanatory diagram showing the state of adhesion of hot-dip plated metal, Figure 2
The figure is a diagram showing the speed of the metal strip and the lifting characteristics of hot-dip plated metal, Figure 8 is an explanatory diagram showing the wiping status of hot-dip plated metal by molten salt, and Figure 4 (A) is a diagram showing the type of molten salt and the molten metal. A diagram showing the lifting characteristics of plated metal, FIG. 4(B) is a diagram showing the thickness of molten salt and lifting characteristics of molten plated metal, and FIG. 5 is an explanatory diagram of an apparatus showing an embodiment of the present invention. , 6th
The figure is a diagram showing comparative test data on the wiping effects of the molten salt wiping method and the gas wiping method.
5... Molten salt, 9. lO...Salt bath furnace, 11...Pipe, P,...Pump. Applicant Sumitomo Metal Industries Co., Ltd. Agent Press 1) Yoshihisa Figure 1 T Figure 2 Raishin group → Figure 3 ↑ Figure 4 (A) (B) ノ] C
Noso 71cm Noah Figure 5 370 Figure 6 Raishin Shiichido (w/wiw) Standing in the direction of the city

Claims (1)

[Claims] In continuous hot-dip plating, in which a reduction-annealed metal strip is continuously introduced into a plating bath without being oxidized and then continuously pulled out of the plating bath, the rising part of the metal strip on the surface of the plating bath is surrounded by molten salt. A continuous hot-dip plating method, characterized in that the amount of hot-dip plating metal deposited on the surface of a metal strip is adjusted by wiping with the molten salt.