JPH0627314B2 - Manufacturing method of zero spangle steel sheet - Google Patents

Description

The present invention relates to a method for producing a beautiful zero spangle hot-dip galvanized steel sheet (zero spangle steel sheet) having a uniform appearance.

<Prior Art and Its Problems> Zero spangle steel sheets, which are counted as high-grade hot-dip galvanized steel sheets, have a steel sheet to be plated 1 immersed in a hot-dip zinc bath 3 in a zinc pot 2 as shown in FIG. After changing the direction with the sink roll 4 and pulling it up from the molten zinc bath 3, and then adjusting the basis weight with the pressurized gas from the wiping nozzle 6 directly above the guide roll 5, the zinc adhered to the surface layer has not been solidified. Among them, a step of spraying "a chemical solution mainly composed of ammonium phosphate" together with pressurized air from the chemical solution nozzle 7 to suppress the average dendrite particle diameter (spangle diameter) when the surface zinc is cooled and solidified to the extent that it cannot be visually recognized. It has been manufactured through.

By the way, in such a continuous hot dip galvanizing process, since an "edge overcoat" in which the end portion in the plate width direction of the steel sheet is thicker than the center portion is more likely to occur, as a countermeasure against that, it is usually shown in FIG. Such a "slit nozzle having wide slit portions 8 ', 8'at the position of the slit 8 facing the steel plate edge" is used.

However, increasing the amount of gas blown to the steel plate edge portion using the slit nozzle shown in FIG. 4 leads to promotion of cooling and solidification of adhered zinc at the end portion of the steel sheet in the plate width direction. If an attempt is made to perform an appropriate chemical treatment based on the central portion, the treatment of the end portions will not be in time and the untreated state will not be obtained, and there is a problem that a zero spangle steel sheet having a uniform appearance cannot be obtained.

<Means for Solving the Problems> Therefore, the present inventors have conducted various experiments to provide a method for stably producing a beautiful and beautiful zero spangle steel sheet in the sheet width direction without causing an edge overcoat. As a result of repeated research, the following (a) to (b)
We have come to the knowledge as shown in. That is, (a) The heat transfer coefficient (heat removal rate) from directly under the wiping nozzle to the chemical liquid nozzle by the "pressurized gas sprayed from the wiping nozzle and flowing along the surface of the plated steel sheet".
In the center portion in the plate width direction, as shown in FIG. 5, it is very large immediately below the nozzle, but it attenuates sharply as it goes in the running direction of the plated steel plate. This is because the flow velocity is reduced due to the entrained flow (entrained air flow) from the surroundings, and the heat transfer coefficient is reduced.

(b) On the other hand, at the edge in the plate width direction, the slit spacing of the wiping nozzle is larger than that in the central part, and the flow rate of boosted gas is large. Since the gas tends to be discharged toward the side, the momentum of the gas flow in this part is strong, and the gas flow velocity hardly decreases. Therefore, the heat transfer coefficient (heat removal coefficient) Attenuation is small (see Fig. 5).

(c) For this reason, the dendrites of the plated steel plate end portions are undercooled compared to the plate width direction central part (for example, the temperature distribution is 420 ° C at the plate width central part and 410 ° C at the end parts). Growth begins to occur, and when the aim is set at the center of the plated steel sheet in the plate width direction and the timing of spraying the chemical liquid is determined, the chemical liquid treatment effect cannot be obtained.

(d) However, in front of the chemical liquid nozzle position downstream of the wiping nozzle, a suction device for the gas flow propagating along the surface of the plated steel sheet is arranged, and immediately after that, an airflow cooling device for forcibly cooling the steel sheet surface is provided. When the pressurized gas flow is forcibly discharged from the steel plate surface by the gas flow suction device, and then a cooling gas is blown to the steel plate surface by the blast cooling device, the gas flows from the wiping nozzle along the plated steel plate surface. An extremely smooth flow of the pressurized gas toward the flow suction device is generated, the influence of the flow velocity decrease due to the entrained flow in the central portion in the plate width direction is suppressed as much as possible, and the pressure is discharged from the central portion in the plate width direction toward the end. The gas flow is also reduced as much as possible, and the heat transfer coefficient (heat removal rate: cooling capacity) due to the boosted gas becomes equal in the plate width direction, so that uniform temperature distribution can be achieved. Moreover, in addition to this, the temperature control of the steel plate surface during the chemical solution treatment is facilitated by adjusting the air flow rate of the blast cooling device, so that a uniform chemical solution treatment effect can be secured in the plate width direction.

The present invention has been made on the basis of the above findings and the like. “The pressure of the pressurizing gas is continuously sprayed onto the surface of the steel sheet that has passed through the molten zinc bath to adjust the basis weight, and then the spangle adjusting chemical liquid is sprayed. In the method of manufacturing a zero spangle steel sheet by attaching, as illustrated in FIG. 1 and FIG.
A gas flow suction device 9 and a blast cooling device 10 are arranged between the boosting gas jet nozzle portion (wiping nozzle 6) and the chemical liquid jet nozzle portion (chemical liquid nozzle 7) in this order and close to the chemical liquid jet nozzle portion. By this, the pressurized gas flow after being injected from the nozzle and colliding with the surface of the steel sheet is guided along the surface of the steel sheet in the running direction thereof, and positively while suppressing the occurrence of the temperature difference in the width direction of the steel sheet after the molten zinc is weighted. The effective cooling enables uniform temperature distribution in the plate width direction at the chemical solution nozzle part to stably manufacture a beautiful zero spangle steel plate with no unevenness. "

Here, as the blast cooling device, a device that blows out a cooling gas such as air from a plurality of slits defined in the steel sheet width direction as shown in FIG. 2 or a device that blows out a cooling gas from a large number of circular nozzle holes Etc., general ones are sufficient.

<Operation> In FIG. 1, the plated steel sheet 1 is the molten zinc bath 3 in the same manner as in the production of a normal zero spangle steel sheet.
After being dipped in and changed direction with sink roll 4,
Wiping nozzle 6 while being corrected by guide rolls 5 and 5
It is adjusted to a predetermined basis weight with pressurized gas from.

Then, the pressurizing gas after colliding with the steel plate surface rides on the suction flow of the gas flow suction device 9 after colliding with the steel plate surface, and
A "smooth boosted gas flow along the steel plate surface" is formed as shown by the arrows in the drawings and in Fig. 2 (a schematic view of the main part of Fig. 1 viewed from the direction perpendicular to the steel plate surface). Since the airflow cooling gas jet from the airflow cooling device 10 arranged close to the rear of the airflow suction device 9 blocks the gas at the gasflow suction device 9 and sucks it together with the gasflow suction device 9, The pressurized gas flow in the central portion is discharged from the gas flow suction device 9 to the outside of the system without causing the supercooling of the steel sheet end portion due to the transverse crossing in the end direction. Further, at this time, it is possible to surely prevent the possibility that a part of the boosted gas flow passes under the gas flow suction device 9 and adversely affects the cooling of the steel sheet.

On the other hand, the portion of the plated steel sheet that has passed through the gas flow suction device 9 while being uniformly cooled by the pressurized gas flow from the wiping nozzle 6 has a predetermined temperature due to the blast cooling gas injected from the blast cooling device 10. (When the operating conditions are changed, the injection amount of the blast cooling gas is adjusted to adjust the temperature), and the chemical solution is sprayed from the chemical solution nozzle 7.

At this time, a plurality of thermometers 11 are arranged in the plate width direction, and a damper of the blast cooling device 10 corresponding to the temperature distribution information in the plate width direction sent from the thermometers 11 via the signal converter 12. If the opening degree is determined by the controller 13 and the blast cooling gas amount is distributed in the plate width direction and is injected, the uniformity of the plate width direction temperature distribution at the position of the chemical injection nozzle 7 is further ensured. It can be anything.

When a slit nozzle type is used as the airflow cooling device 10, the slit gap B shown in FIG.
Is about 7 mm, and the nozzle height is about 30 mm from the steel plate surface. As a result, even if "plate warp" or "plate runout" occurs in the traveling plated steel plate, it is much easier and more stable to secure a uniform temperature distribution in the plate width direction and in the front and back surfaces.

As a result, the plated steel sheet, which is normally prone to overcooling at both ends in the plate width direction, has a uniform temperature distribution in the plate width direction immediately before the chemical liquid nozzle 7, so that a uniform chemical liquid treatment effect can be secured. Therefore, a very beautiful zero spangle steel plate can be obtained extremely stably.

Next, the effects of the present invention will be specifically described with reference to examples.

<Example> A zero spangle steel sheet was manufactured under the conditions shown in Table 1 using the zero spangle steel sheet manufacturing equipment as shown in FIGS. 1 and 2.

The wiping nozzle used as an example of the present invention is the fourth wiping nozzle.
In the type shown in the figure, the central slit spacing was 1.0 mm, the end slit spacing was 1.5 mm, which was very general,
Further, the slit nozzle type airflow cooling device has a slit gap B: 7 mm, a slit pitch: 100 mm, a distance between the steel plate surface and the nozzle: 30 mm, a cooling surface length: 500 mm, and an outlet flow velocity of 20 to 70 m /. We tried to achieve a uniform temperature distribution with a predetermined value in the width direction of the plated steel sheet and on the front and back surfaces by changing the interval between sec.

Table 1 also shows the temperature difference between the plate width direction and the front and back surfaces (difference from the target temperature) immediately before the chemical liquid nozzle at this time. Of course, it goes without saying that the result of the conventional example was obtained by the equipment in which the gas suction device and the airflow cooling device are not installed.

As is clear from the results shown in Table 1, according to the method of the present invention, even in the case where the operating conditions are different, even in the plate width direction and the front and back surfaces immediately before the chemical liquid nozzle. It can be seen that a wide temperature distribution can be achieved. Then, it was confirmed that a very beautiful zero spangle steel sheet having a uniform appearance can be stably obtained by the chemical treatment in this state.

<Summary of Effects> As described above, according to the present invention, it is possible to achieve uniform chemical treatment in the plate width direction while maintaining the effect of suppressing the edge overcoat without changing the normal wiping nozzle. Therefore, it is possible to stably produce a beautiful zero spangled steel sheet having a very high quality, which brings about an extremely useful effect in industry.

[Brief description of drawings]

FIG. 1 is a schematic explanatory view showing an embodiment of the present invention. FIG. 2 is an explanatory view of a main part of FIG. FIG. 3 is a schematic explanatory view of the conventional method. FIG. 4 is a perspective view of a conventional wiping nozzle. FIG. 5 is a graph showing the heat transfer coefficient (heat removal coefficient) of the boosted gas flow in the running direction of the steel sheet in the conventional method. In the drawings, 1 ... Plated steel plate, 2 ... Zinc pot, 3 ... Molten zinc bath, 4 ... Sink roll, 5 ... Guide roll, 6 ... Wiping nozzle, 7 ... Chemical solution nozzle, 8 ... Slit, 8 '... Wide slit part, 9 ... Gas flow suction device, 10 ... Impulse cooling device, 11 ... Thermometer, 12 ... Signal converter, 13 ... Controller.

Claims (1)

[Claims] 1. A method for producing a zero spangle steel sheet by spraying a pressurizing gas onto a steel sheet surface that has been continuously passed through a molten zinc bath to adjust the basis weight, and subsequently spraying a spangle adjusting chemical liquid, A gas flow suction device and a blast cooling device are arranged in this order between the boosting gas injection nozzle part and the chemical liquid injection nozzle part, and are arranged in close proximity to the chemical liquid injection nozzle part, whereby the steel plate surface injected from the nozzle is It is characterized in that the pressurized gas flow after the collision is guided along the surface of the steel sheet in the traveling direction thereof, and active cooling is performed while suppressing the occurrence of a temperature difference in the width direction of the steel sheet after the molten zinc is weighted. Of manufacturing a new zero spangle steel sheet.