JPS59143056A - Manufacture of continuously hot dipped steel sheet - Google Patents

Abstract

PURPOSE:To improve the adhesive strength of layers formed by hot dipping by directly blowing a reducing gas on a steel sheet in a reducing zone at a high temp. to accelerate the reducing reaction of the sheet. CONSTITUTION:A rolled steel sheet is heated in a nonoxidation heating zone to remove fats and oils sticking to the sheet. A reducing gas is directly blown on both sides of the sheet passing through a reducing zine to accelerate the reducing reaction of both sides of the sheet. The sheet is then sent to a hot dipping vessel through a cooling zone, and it is continuously hot dipped. Since both sides of the sheet are cleaned and activated, the adhesive strength of layers formed by hot dipping is improved.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for manufacturing a continuous hot-dip plated steel sheet, the purpose of which is to improve the adhesion of a plated layer.

The method for producing continuous hot-dip plated steel sheets involves heating a cold-rolled coil or a hot-rolled coil after pickling in a non-oxidizing furnace to remove oils and fats adhering to the surface of the steel sheet, and then reducing the surface of the steel sheet in a reducing furnace. A common method is to perform activation and annealing, cool the material in a cooling zone to a temperature suitable for plating, and then directly guide it through a snout into a hot-dip plating bath without exposing it to the atmosphere, and then plate it.

Figure 1 shows an example of a non-oxidizing furnace type continuous plating equipment, in which (1) is a non-oxidizing furnace, (2) is a reducing furnace, (3) is a cooling zone, (4) is a controlled cooling zone, (5) is snout, (6
) i-! It is a hot-dip plating bath, and the non-oxidation furnace (1) is used to heat C gas, LPG, natural gas, etc. at a high air-fuel ratio (0.85 to
0.90), and the inside of the furnace is Go-Go2-H,-I
(It is maintained at a high temperature of 1000 to 1300°C in an atmosphere of (hereinafter referred to as "AX gas" for convenience of explanation) is flowed countercurrently (hereinafter referred to as "AX gas") to the steel plate, so that annealing is performed at the same time as reduction in the furnace.
It's happening.

In other words, manufacturing continuous hot-dip galvanized steel sheets; this involves removing oil such as rolling oil in a non-oxidizing furnace, annealing in a reducing furnace, and improving the reducing power of the surface oxide film (measuring adhesion). There is an important point -C to ensure that reduction performance in particular greatly contributes to adhesion.Therefore, in the conventional hot-dip plating method, snout (5) part force〉AXX gas G,) is blown into the furnace to reduce the inside of the furnace. Since zinc is oxidized and reduced while maintaining its properties, there may be a difference in the adhesion of zinc on the front and back surfaces of the steel sheet, or a phenomenon may occur where adhesion is partially poor in the width direction. The cause of the former is that the reduction reaction force is weak, and the cause of the latter is that in the case of a horizontal furnace, as shown in Figure 2, the fuel is injected from the combustion burners (1-2) attached to the left and right furnace walls. This is because the combustion flame (1-3) tends upward and the combustion flame of the lower burner directly touches the lower surface of the steel plate 00, so that the lower surface side of the steel plate is strongly oxidized.

As a result of various studies to solve the above-mentioned conventional problems, the inventors discovered that reducing gas (
They discovered that by spraying AX gas directly onto the steel plate, poor adhesion caused by poor reduction can be improved.

That is, the present invention provides a method for cleaning and activating the surface of a steel plate and applying hot-dip plating using a continuous hot-dip plating furnace consisting of a non-oxidizing heating zone, a reduction zone, and a cooling zone. This method is characterized by promoting the reduction reaction by directly spraying a reducing gas onto the reactor.

In continuous hot-dip plating furnaces that manufacture hot-dip plated steel sheets, AX gas injected from the snout keeps the atmospheric gas in the furnace reducible, but poor adhesion of the plating occurs on the front and back surfaces of the plated steel sheets due to poor reduction. In such a case, a possible way to deal with this is to change the position of the AXX gas injection into the furnace or to prevent local heating caused by the combustion flame of the burner, but continuous hot-dip plating furnaces do not allow the AX gas to flow counter-currently to the steel sheet. Because it is a method that performs reduction and annealing at the same time in a sink furnace,
The AX gas injection position must be installed at the bottom of the snout (this is not a good idea as it requires improvements to the burner structure, heating method, furnace structure, etc. to prevent local heating due to the combustion flame of the burner). .Also, from the bottom of the snout,
In the conventional method of blowing X gas, the temperature of the steel plate to be plated drops considerably when it passes through the nout section (for example, 550°
C) Since the AX gas reacts with the steel plate at this lower temperature, it has a woody defect in that the reducing power of the surface oxide film is poor.

However, as in this invention, a high temperature reduction zone (for example, a furnace temperature of 10
If AXX gas is sprayed directly onto the top and bottom surfaces of the steel plate at temperatures between 00 and 1300°C, the reducing power in this reduction zone will be further enhanced, thereby preventing poor adhesion on the front and back surfaces of the steel plate and in the direction of the inside of the steel plate. It becomes possible. Furthermore, this method has the advantage that it can be easily applied to existing equipment, since the purpose can be achieved by simply installing an AX gas injection pipe in the reduction furnace.

Figure 3 shows an embodiment of this invention, in which a reduction furnace (2
) is installed on the side wall of the steel plate q0 so as to be able to advance and retreat in the width direction of the steel plate q0, and AX gas (G2) is directly applied to the upper surface and F surface of the steel plate 0Q on the hearth roller (2-2). Allow it to be sprayed. The AX gas injection pipe (2-1) is
For example, two pieces of L-T' can be installed at the same height position at a desired interval. Further, the installation location thereof may be in each zone of the reduction furnace, or may be limited to a certain zone. Furthermore, the reason why this injection pipe is made movable is to be able to control the spraying position of the Ax gas in the width direction of the steel plate, and to accommodate changes in the width of the steel plate. (2-8) is a radiant tube.

As mentioned above, an AX gas injection pipe is installed in the reduction furnace of the continuous hot-dip plating equipment, and AXX gas G is blown in from the snout.
When the AX gas (G2) is further sprayed directly onto the hot steel plate C1O from the injection pipe (2-1) in the reducing atmosphere created by 1), the reduction reaction on the front and back surfaces of the steel plate is further promoted. . Similarly, when AX gas is sprayed intensively on both ends of the steel plate, which are likely to be locally heated by the burner flame, the reduction reaction in those parts is promoted, plating adhesion is improved, and plating peeling can be prevented.

Next, an example will be shown in which hot-dip plating was carried out by applying the method of the present invention to an actual continuous hot-dip plating equipment in the manner shown in FIG.

〔Example〕

(I) Operating conditions ■ Test material: plate thickness 0.4 mm, plate width 914 plates ■ Furnace atmosphere temperature Non-oxidizing furnace: 1000°C Reduction zone: 900°C Cooling zone: 650°C Adjusted cooling zone -550 °C Snout part -550°C ■ Reducing gas injection amount Snout part: N, gas 100 Nrrf/Hr 4-
AXX gas N275 pH H2 25%) 120 Nm'/Hr Reduction band: AX gas 2096 ON door, /H [(Jl
) Effect ■ Poor adhesion phenomenon Conventional 50Ton/month → 15Ton
Decreased in /'month■ Line speed Conventional 80n/m 1 [1→
As explained above, according to the method of this invention, since AX gas is sprayed directly onto the steel plate in the high-temperature reduction zone, it is possible to improve the adhesion of the hot-dip plated steel plate, and to increase the line speed. It is possible to improve the quality and productivity of hot-dip galvanized steel sheets, making it possible to improve industrial (
This is extremely beneficial.

[Brief explanation of the drawing]

Fig. 1 is a schematic diagram showing an example of a non-oxidizing furnace type continuous hot-dip plating equipment, Fig. 2 is a schematic diagram showing an example of a combustion situation in a non-oxidizing furnace, and Fig. 3 is an embodiment of the present invention. FIG. ■...Non-oxidation furnace, 2...Reduction furnace, 2-1...AX
X gas injection tube, 3... Cooling zone, 4... Adjustment cooling zone, 5
...Snout, G,, G2...AX gas. Applicant Sumitomo Metal Industries Co., Ltd. Agent 1) Yoshihisa Figure 1 Figure 3

Claims (1)

[Claims] In a method of cleaning and activating the surface of a steel plate and applying hot-dip plating through continuous hot-dip plating, which consists of a non-oxidizing heating zone, a reduction zone, and a cooling zone, reducing gas is directly sprayed onto the upper and lower surfaces of the steel plate as it passes through the reduction zone. A method for producing a continuous hot-dip plated steel sheet, characterized by promoting reduction reactions on the front and back surfaces of the steel sheet.