JPS62205256A - Method for controlling extent of sticking by hot dipping - Google Patents

Abstract

PURPOSE:To enable high-speed thin sticking by combining wringing with wringer rolls with the blowing of a nonoxizing gas. CONSTITUTION:A steel sheet 2 is fed to a hot dipping bath 6 through a snout 4 kept in a nonoxidizing atmosphere and it is pulled up from the bath 6 through a sink roll 8. Wringer rolls 14 placed between the surface 10 of the bath 6 and wiping nozzles 12 are heated from the insides to a temp. above the m.p. of a metal for not dipping. The hot dipped steel sheet 2 is passed through the wringer rolls 14 to wring out a molten metal sticking in excess. A heated nonoxidizing gas is then blown on both sides of the steel sheet 2 from the wiping nozzles 12 to further control the extent of sticking weight.

Description

Detailed Description of the Invention (Industrial Field of Application) The present invention provides a method for controlling the coating weight of hot-dip plating, in particular, a combination of squeezing with a squeezing roll and spraying of heated non-oxidizing gas to achieve high-speed thin coating. This invention relates to a method for controlling the amount of molten metal.

(Prior art) In recent years, hot-dip galvanizing, especially molten galvanizing, has seen a remarkable spread and expansion of its uses. Aimed at light weight. Today's objective is line speed of 150m/+iin or more, with eyes and marks! [t70mg/
Although it is a high-speed thinner basis weight of less than m'', to date there has been no product that has achieved such a target value in an actual operating line.

Incidentally, as a method for scraping off excess molten metal adhering to a steel plate pulled up from a plating bath in a continuous melt plating line, trW& control using a gas wiping nozzle has conventionally been performed.

In this method, the adhesion amount W (I+/n?) is determined by the nozzle-metal strip distance D (non-), the nozzle slit gap B (mm), and the gas pressure P (kg/cal). That is, in order to decrease W, it is necessary to decrease D, increase B, and increase P. As the line speed (mpm) of the metal strip increases, these changes are necessary to increase the drawing force of the molten metal. parameters must be manipulated as described above. however,
There is a limit to the reproduction of D, B, and I'; for example, with D, vibration and warping of the metal strip are unavoidable, so
At present, it is difficult to reduce the thickness to 15 or less, and
Increasing the amount of water causes an increase in the gas flow rate, which leads to an increase in bath surface splash and further increases in cost.

It is desired to establish a method for producing light weight while ensuring line productivity (production 1, line speed, gas cost, etc.).

JP-A-55-50457 discloses a method in which excess molten metal is removed by a squeezing roll provided above the plating bath and then gas wiping is performed. In this case, as a modification example, a heating means is provided between the plating bath and the drawing roll to heat the molten metal and the drawing roll, but what is specifically shown is burner heating. Since air is also used as a wiping gas, surface oxidation of the molten metal is inevitable, and the viscosity increases rapidly with the formation of such oxides, even if the wiping gas pressure is increased. High-speed thinning is no longer possible.

(Problems to be Solved by the Invention) An object of the present invention is to provide a hot-dip plating density control method that enables high-speed thinning.

A more specific object of the present invention is to achieve a line speed of 150
mpm or more, the basis weight on both sides is 70 g/m or less, preferably at a line speed of 150 mpm or more, the basis weight on both sides is 40 g/m.
An object of the present invention is to provide a hot-dip plating coating weight control method that enables high-speed thinning of the coating weight as follows.

(Means for Solving the Problems) As a result of various studies to achieve the above-mentioned object, the present inventors found that a combination of a squeezing roll and gas wiping is effective for high-speed thinning. It has been found that it is effective to make the temperature of the molten metal at the gas wiping position higher than the melting point of the metal and to prevent its oxidation as much as possible. 1 Specifically, when a metal strip pulled up from a plating bath is removed with a squeeze roll to remove the excess, and then further thinned with a gas wiping nozzle installed above the squeeze roll, I) Non-oxidizing gas is used for gas wiping. and ii) the surface temperature of the squeeze roll is above the melting point of the molten metal in the plating bath, and equal to or above the temperature of the metal strip or the molten metal on the metal strip, to achieve the aforementioned objective. We found that this is important.

That is, the above-mentioned i) is to prevent oxidation as much as possible since the fluidity is inhibited by the oxidation and cooling of the molten metal by the wiping air in the commonly used air wiping, and the ii) is to prevent the oxidation as much as possible. This is to prevent fluidity from decreasing due to the viscosity upper limit due to solidification of the molten metal and temperature drop.

In this way, the present inventors recognized that securing the fluidity of molten metal is the most important point when performing high-speed thinning by roll drawing, and we I learned the effectiveness of trying to ensure sex.

For example, when the above wiping conditions (D, B, P) are constant, the basis weight of the molten metal is mainly determined by the fluidity (viscosity) of the molten metal. Further, viscosity is expressed as below and is a function of temperature and composition.

Viscosity -r (Temperature: 1 ML) That is, in the temperature region near the melting point, the viscosity greatly decreases even if the temperature increases slightly, so it is highly dependent on temperature. Further, regarding the composition, when an oxide is formed, since the melting point of the oxide is extremely high in -S, the influence on the decrease in viscosity due to oxidation is large.

Thus, the present invention was completed based on the finding that the molten metal temperature and the formation of oxides have a very large influence and are of critical significance on the above-mentioned high-speed thinning. .

Here, the gist of the present invention is that in a continuous hot-dip plating method in which a metal strip is continuously immersed in molten metal for plating, the metal strip pulled out of the plating bath is heated by an internal heating device. Excess basis weight molten metal is squeezed by passing it between rolls heated to a surface temperature higher than the melting point of the molten metal, and the area weight is further controlled by subsequently spraying heated non-oxidizing gas, This is a method for controlling the coating weight of hot-dip plating.

From another aspect, the gist of the present invention is that in a continuous hot-dip plating method in which a metal strip is continuously immersed in molten metal for plating, the metal strip pulled up from the plating bath is placed at the center of the roll axis. The wire is above the plating bath surface, and the plating bath surface is in contact with the roll body. This is a hot-dip plating area weight control method.

(Operation) Next, the present invention will be specifically explained with reference to FIG. In the following explanation, a steel plate is used as a metal strip and is galvanized. However, the present invention is not limited to this, and can be applied to continuous hot-dip plating of other metals. Of course, it is also applicable.

In FIG. 1, a steel plate 2 which has been appropriately cleaned or surface activated by conventional methods, such as continuous annealing in a reducing atmosphere, before being sent to a plating bath, is normally kept in a non-oxidizing atmosphere. 4 and is supplied to the plating bath 6.
It is pulled up from the plating bath via the zinc roll 8.

A squeezing roll 14 is provided on the plating bath surface lO between it and the wiping nozzle 12.

This squeeze roll 14 is heated from the inside to a temperature higher than the melting point of the plated metal using, for example, induction heating.
rTIc (Teexpera Lura Indic
Temperature control is carried out using the Ating Control)J. il! In the case of galvanizing, the surface temperature of this squeeze roll is usually controlled to be in the range of 430 to 480°C. Regarding the surface of the squeeze roll, it is important not to react with Zn to form an alloy layer, and Go-Cr-W thermal spraying, ceramics, Cr coating, etc. are effective.

The internal heating means of the squeezing roll may be of the induction heating type as described above, and its mechanism and temperature control system itself are already known and are considered not to require further explanation, so their explanation will be omitted.

An inert gas such as nitrogen gas is blown from the wiping nozzle 12 . The temperature of this gas is also controlled by rTICJ, and is usually controlled between 100 and 400°C.

Although not shown, the entire basis weight control device including the squeezing roll 14 and the wiping nozzle 12 may be surrounded by a hood to make the internal atmosphere non-oxidizing.

FIG. 2 shows another modified example, in which a part of the squeeze roll 14 is immersed in the plating bath 6. According to such a configuration, the above-mentioned internal heating is not required and the plating bath The heat from 6 can maintain the temperature hπ above the melting point of zinc, and the temperature of the squeeze roll can be easily controlled. in this way,
In order to keep the surface temperature of the squeezing roll above the melting point of the plating metal, when using a method in which the roll is brought into contact with the coating bath surface lO and rotated, in order to keep the roll in contact with the bath surface while squeezing the roll, as shown in Figure 3. As shown in a partially enlarged view, the center of the roll axis must be located above the bath surface 10. The immersion depth in the plating bath is 2-30% of the roll diameter.
, preferably 5 to 10%.

Thus, according to the present invention, in any embodiment, the line speed is 150 III pm and the basis weight is 70 g/
This makes it possible to achieve a high-speed thin basis weight of less than rd, especially less than 40 g/nl.

Next, the present invention will be explained in more detail with reference to Examples. In the examples, "%" means "% by weight" unless otherwise specified.

Next, using the apparatus schematically shown in Figure 1, a continuous molten zinc coating test was conducted by actually threading the sheet at high speed.

The fused genus is 8l-0.16%, r'b=0.03%
, Fe=0°03%, and the balance was Zn, and the bath temperature was controlled at 460°C. The steel plate entered the plating bath from the snout at a material temperature of 460°C, and the material temperature when exiting the plating bath was the same 460°C.

The squeezing roll has an internal induction heating device, and the surface temperature is raised to 400°C in advance without the roll touching the steel plate.
The roll was brought into contact with the steel plate while maintaining this heated state. The roll surface temperature reached a constant temperature of 450° C. approximately 10 minutes after contacting the steel plate, ensuring a temperature above the melting point. Nitrogen gas heated to 400° C. was used as the wiping gas. Since the nitrogen gas was heated to 400°C, the material temperature could be maintained at 440°C even after passing through the wiping nozzle.

The relationship between the line speed and the basis weight obtained as a result of such a hot-dip galvanizing test is shown in FIG. 4 together with the results when the basis weight was controlled only by sopping with nitrogen gas at 400°C. As you can see from the graph in Figure 4, it's quite impressive! Sweat can be reduced to about 40% compared to wiping only, especially at high speeds (line speed 160 m).
The effect is significant below pm. Also, at a line speed of 120111pII+ or less, both sides have a fabric weight of ff1.
It is constant at 30 g/m, and 30 g/n on both sides seems to be the limit of this method.

For comparison, tests were conducted under the same conditions with 4 blows of room-temperature N2 gas, no squeezing roll, and using only a heated squeezing roll heated to 400°C.The line speed was 1611/sin, and the fabric weight was The amount is 110g
/s+” gave the best results.

Next, the results when the basis weight was adjusted by varying the heating temperature of the wiping gas are shown in a graph in FIG. 5 along with those of a comparative example in which no roll squeezing was performed.

Ring number 1! In this example, Example 1 was repeated using the apparatus shown in FIG. However, in the case of this example, the surface temperature of the squeezing roll is set to the melting point of zinc in advance without contacting the steel plate.
The roll was rotated off-line while in contact with the plating bath until the temperature reached 419°C or higher, and when the temperature reached the melting point or higher, the roll was brought into contact with the steel plate. Almost the same results as in Example 1 were obtained, and high-speed thinning was possible.

[Brief explanation of drawings]

FIG. 1 is a schematic explanatory diagram showing one example of a molten metal plating apparatus used to carry out the method of the present invention, and FIG. A schematic explanatory diagram showing an example, FIG. 3 is a partially enlarged view of the squeezing roll in FIG. 2, and FIG. 4 is a line when only heated gas wiping is used and when heated gas wiping and roll squeezing are used together according to the present invention. FIG. 5 is a graph showing the relationship between the speed and the Zn basis weight, and FIG. 5 is a graph showing the relationship between the Zn basis weight and the wiping gas temperature in the present invention. 2: Steel plate, 4: Snout, 6: Plating bath, 8 herring roll, 1O: Plating bath surface, 12: Wiping nozzle, 14: Squeezing roll

Claims (2)

[Claims] (1) In the continuous hot-dip plating method, in which a metal strip is continuously immersed in molten metal for plating, the metal strip is pulled out of the plating bath and has an internal heating device whose surface temperature is higher than the melting point of the molten metal. A method for controlling the basis weight of molten plating, the method comprising squeezing excess molten metal by passing it between rolls heated to a temperature of 100 mm, and further controlling the basis weight by subsequently spraying heated non-oxidizing gas. (2) In the continuous hot-dip plating method, in which a metal strip is continuously immersed in molten metal for plating, the metal strip that is pulled up from the plating bath is A method for controlling the basis weight of molten plating, which comprises squeezing excess molten metal through between rolls whose surfaces are in contact with the roll body, and then further controlling the basis weight by subsequently spraying heated non-oxidizing gas.