JPS6339250Y2 - - Google Patents

Description

[Detailed explanation of the idea]

The present invention relates to an improvement of a blowing nozzle for controlling the amount of plating metal deposited on the surface of a steel strip during continuous hot-dip galvanizing of the steel strip. In continuous hot-dip plating, the steel strip is passed through a hot-dip metal bath, pulled out above the bath, and then the excessive amount of hot-dipped metal adhering to the surface is removed to control the amount of adhesion to a predetermined level. In recent years, instead of roll wiping, a gas wiping method using a blow-wiping nozzle has been used. As shown in Fig. 3, blowing nozzles 2 and 3 are directed at both the front and back sides of the steel strip s above the plating bath 1, and the excess plating metal is blown off with the jet gas from the nozzles. Due to this gas wiping, the line speed for galvanized steel sheets has increased year by year. However, as the line speed increases, the amount of plating metal lifted up by the steel strip increases, so the amount of plating metal deposited on the product tends to increase. On the other hand, the use of galvanized steel sheets continues to diversify.
For example, due to problems such as weldability, steel sheets with a smaller amount of plated metal are required. If the amount of plating metal deposited is simply reduced, the goal can be achieved by lowering the line speed, but this will result in a decrease in manufacturing efficiency and an increase in manufacturing costs. Other possible methods include increasing the pressure of the gas injected from the wiping nozzle, increasing the air volume by widening the width of the nozzle injection port (slit), or moving the wiping nozzle closer to the surface of the steel strip. However, increasing the pressure and air volume of the injected gas requires high-pressure, large-capacity equipment, which not only increases equipment costs but also causes severe nozzle noise and deteriorates the working environment. Installing the blowing nozzle close to the steel strip is a simple measure, but since the steel strip passing through the nozzle vibrates in the thickness direction (arrow x), the distance between the nozzle and the steel strip should not be too narrow. Contact between the two may occur, causing product defects due to damage to the plating layer on the surface of the steel strip or clogging of the nozzle slit. As the line speed increases, the vibration amplitude of the steel strip increases, so the distance between the nozzle and the steel strip must be increased accordingly. The wider the interval, the weaker the wiping force of the injected gas becomes, making it more difficult to reduce the amount of adhesion. For this reason, it is not possible to produce a plated steel sheet with a small amount of metal deposited under high-speed production, and the actual situation is that the line speed must be sacrificed in order to reduce the amount of metal deposited. The present invention solves the above problems, and by improving the nozzle shape, the wiping force is significantly increased, making it possible to obtain plated steel sheets with a small amount of adhesion even during high-speed production. FIG. 1 shows an embodiment of the present invention. The nozzle 3 of the present invention is characterized by having a thin wall thickness a at its tip and a small angle α between a side surface b that continuously slopes toward the rear of the nozzle from the tip and the gas injection direction C from the nozzle slit. It is preferable that the wall thickness a of the tip part is 2 mm or less, and the inclination angle α is 30 to 60 degrees.
Comparing this with a conventional blow-wiping nozzle, the conventional nozzle has a shape as shown in FIG. 4, with a front wall thickness a of about 5 mm and an inclination angle α of about 65 to 80 degrees. In such a conventional blowing nozzle, after the gas G injected from the nozzle slits 2 and 1 collides with the steel strip surface, it stagnates near the nozzle and obstructs the subsequent jetted gas flow, so the blowing force is weakened. It is being In contrast, the tip of the nozzle of the present invention is formed with an acute angle, so the gas flow dissipates smoothly after colliding with the steel strip, effectively preventing stagnation near the nozzle and interference with the jet gas flow. As a result of being resolved,
Even if the injection gas pressure and the distance from the steel strip are the same,
It applies a stronger wiping force to the steel strip surface than conventional nozzles, making it possible to further reduce the amount of plated metal deposited. This effect becomes stronger as the inclination angle α becomes smaller. From this point of view, it is more preferable that α is 45° or less. However, if α is made too small, the thickness of the tip becomes too thin due to the structure of the nozzle, causing problems such as insufficient strength and deformation due to heat effects, so the lower limit of α is set at 30°. FIG. 2 compares the blowing effect of the present invention and the conventional blowing nozzle in continuous hot-dip galvanizing. In the figure, the curve ~ indicates the nozzle of the present invention (however,
Tip wall thickness a: 2mm, inclination angle α: 60°,
45°, 30°) are conventional nozzles (tip wall thickness a: 5 mm, inclination angle α: 60°), gas injection pressure 0.6 Kgf/cm ² G, nozzle tip and steel strip surface. The spacing is 15mm. As is clear from the figure, the nozzle of the present invention has excellent wiping power and can reduce the amount of plated metal deposited compared to conventional nozzles, and the wiping power can be strengthened by making the tip shape more acute. Recognize. Gas injection port (slit) of the invented blowing nozzle
3. The shape and dimensions of 1 do not need to be special, but the width of the slit is of course wider than the width of the steel strip, and the wiping force of the injected gas can be applied over the entire width. It takes. Further, the tip of the nozzle can be given wear resistance by surface nitriding, chrome plating, hardening, overlay welding of hard material, etc. to increase durability. To blow away plated metal with the blowing nozzle of the present invention, it can be directed perpendicularly to the surface of the steel strip in the conventional manner, or in the direction opposite to the direction of movement of the steel strip.
It may be oriented at an appropriate angle with respect to the steel strip, and room temperature or heated air, inert gas, etc. may be injected at an appropriate pressure, for example, 0.05 to 2.0 Kgf/cm ² ·G. It should be noted that when a steel strip is pulled up from a plating bath, the amount of plating metal deposited on both side edges (edge parts) is greater than the center part, and overcoat tends to occur on the edge parts. For example, its strong wiping action can alleviate non-uniformity in the amount of adhesion in the board width direction and further improve plating quality. Examples 1 to 3 In continuous hot-dip galvanizing of steel strips (plate thickness: 0.5 mm, plate width: 914 mm), a galvanized steel plate was produced by controlling the amount of plated metal deposited using the blowing nozzle of the present invention. For comparison, we also used a conventional nozzle and conducted continuous hot-dip galvanizing under the same conditions. In either case, the injection gas pressure was 0.6 kgf/cm ² ·G, and the distance between the steel strip surface and the blowing nozzle tip was 15 mm. Test conditions and results are shown in Table 1.

[Table] As is clear from the above test results, by using the nozzle of the present invention, it is possible to obtain a plated steel plate at a high speed and with a low coating weight that cannot be obtained with conventional nozzles.

[Brief explanation of the drawing]

FIG. 1 is a vertical sectional view of the main part showing an embodiment of the present invention.
Figure 2 is a graph illustrating the blowing force of the blowing nozzle.
Figure 3 is a schematic diagram of the arrangement of the continuous melting and gluing equipment;
The figure is a longitudinal cross-sectional view of the main part of a conventional blow-wiping nozzle. 1...Plating bath, 2, 3...Blowing nozzle, S...
...Steel strip.

Claims (1)

[Scope of utility model registration request] A blowing nozzle for controlling the amount of molten galvanized metal adhering to the surface of a steel strip pulled up from a plating bath by removing with a jet gas,
The wall thickness a of the nozzle tip is 3 mm or less, and the angle α between the side wall surface b that slopes continuously from the tip toward the rear of the nozzle and the gas injection direction from the nozzle is 30 to
A blowing nozzle characterized by a 60° angle.