JP3011395B2 - Method for producing thick galvanized steel sheet with excellent surface properties - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for manufacturing a hot-dip galvanized steel sheet for preventing hot water wrinkles, which is a bad appearance of a thick hot-dip galvanized steel sheet.

[0002]

2. Description of the Related Art In general, a method for producing a hot-dip galvanized steel sheet is to continuously anneate a galvanized sheet such as a cold-rolled steel strip in a non-oxidizing or slightly reducing atmosphere and then place it in a zinc bath or a zinc bath containing aluminum. A method of adjusting the thickness (basis weight) of a galvanized layer by injecting and immersion plating and injecting a gas for squeezing gas (wiping gas) onto a steel strip immediately after withdrawing from a bath is used.

[0003] In this case, in controlling the basis weight by the wiping gas, the steel strip vibrates and, due to the irregular flow of the molten metal in the plating layer, corrugated ripples (also referred to as dripping) on the plating surface. ) Often occurs, and when a galvanized surface is used as a coating base surface in the use of an exterior plate, the surface properties, particularly smoothness, of the coating film are impaired, and the appearance However, it cannot be used for an exterior plate that should be adapted to the excellent coating treatment, and greatly affected the yield of plated steel sheets.

[0004] Conventionally, as a method of preventing hot water wrinkles, which is a poor appearance of a hot-dip galvanized steel sheet, before introducing the steel sheet into a hot-dip galvanizing bath, the surface of the steel sheet is roughened using a skin pass mill, a tension leveler or the like. There is a method of adjusting the thickness according to the thickness of the plating layer (weight per unit area) to suppress the occurrence of hot water wrinkles (see JP-A-55-21564).

However, in the case of the above method, there is a problem in cost due to the necessity of installing a skin pass mill, a tension leveler and the like in a pre-process of the hot-dip galvanizing bath. Also, when these are installed, it is difficult to obtain the ideal surface roughness due to the chemical and physical changes accompanying the pickling and recrystallization in the pretreatment equipment and the annealing furnace, and the occurrence of hot lines is completely prevented. It was difficult to prevent, leaving room for improvement.

[0006]

SUMMARY OF THE INVENTION An object of the present invention is to solve the above-mentioned problems of the prior art and to provide a method for producing a hot-dip galvanized steel sheet which can effectively prevent the occurrence of hot water lines. And

[0007]

SUMMARY OF THE INVENTION The present invention, in order to solve the above problems, relates to a thick galvanized steel sheet.
This technology sets the line speed and the height of the gas wiping nozzle from the surface of the bath for each plate thickness region to prevent the occurrence of hot lines. That is, the present invention relates to a method for producing a thick galvanized steel sheet having a basis weight of at least one surface of a steel sheet of 100 [g / m ² ] or more, wherein a line speed and / or gas A method for producing a thick galvanized steel sheet having excellent surface properties, characterized by controlling the height of a wiping nozzle from a plating bath surface.

In the present invention, an appropriate lower limit of the line speed from the viewpoint of preventing occurrence of hot water wrinkles with respect to the thickness of the steel sheet is determined in advance, and based on the result, the line is adjusted in accordance with the change in the thickness of the steel sheet. It is preferable to control the speed to be equal to or higher than the lower limit. Further, in the present invention, the upper and lower limits of the height of the wiping nozzle are determined in advance from the aspect of preventing hot water wrinkles from being generated with respect to the thickness of the steel sheet. Preferably, the height of the wiping nozzle is controlled to be within the range of the upper and lower limits.

[0009]

The present invention will be described below in more detail. The inventors of the present invention have conducted intensive studies on the occurrence of hot water wrinkles in hot-dip galvanized steel sheets and measures to prevent the hot water wrinkles. The present invention was found out that the number of steel sheets was large, the line speed was low, the height of the gas wiping nozzle from the plating bath surface was high, and the flapping of the steel sheet at the wiping nozzle part was large.

According to the method of the present invention, the thickness of the steel sheet and the line speed, or the thickness of the steel sheet and the height of the gas wiping nozzle from the plating bath surface (hereinafter referred to as the height of the wiping nozzle) are determined in advance. By obtaining a range in which wrinkles do not occur, and controlling the line speed and the height of the wiping nozzle so as to be within the range when the plate thickness is changed, it is possible to effectively prevent occurrence of hot water wrinkles. .

The present invention is preferably applied to a method for producing a thick galvanized steel sheet having a basis weight of at least one side of a steel sheet per one side of the steel sheet of 100 [g / m ² ] or more. This is, as described above, the required plating adhesion amount (plating basis weight).
This is because, when the content is large, hot wrinkles are liable to occur particularly in the production of a thick galvanized steel sheet having a basis weight of 100 [g / m ² ] or more, and therefore the present invention is preferably applied.

The basis weight to which the present invention is preferably applied is 230 [g / m ² ] or less. This is because the basis weight is
If it exceeds 230 [g / m ² ], the amount of adhesion increases, and it becomes difficult to make the amount of adhesion uniform on the surface of the plated steel sheet. FIG. 1 shows the relationship between the steel sheet thickness D and the line speed LS and the occurrence of hot water wrinkles obtained by the present invention.

As shown in FIG. 1, it has been found that there is an area of an appropriate line speed according to the thickness of the steel sheet. That is, an area of an appropriate line speed with respect to a steel sheet thickness is determined in advance, and based on the result, the line speed is controlled in accordance with a change in the steel sheet thickness, thereby preventing occurrence of hot lines. Becomes possible.

In the present invention, the line speed is adjusted according to the change in the thickness of the steel sheet so as to fall within the range of the following equations (1), (2) and (3) based on the hot water wrinkle limit area in FIG. It is preferable to control. LS (mpm) ≧ 110, [if D (mm) ≦ 0.50] ・ ・ ・ ・ (1) LS (mpm) ≧ −80D (mm) +150, [if 0.50 <D (mm) ≦ 1.00] ・・ ・ (2) LS (mpm) ≧ 70, [when D (mm)> 1.00] ・ ・ ・ ・ ・ ・ (3) In equations (1), (2) and (3), LS is the line speed ( mp
m .: m / min), and D indicates the thickness of the steel plate.

In the present invention, it is more preferable that the following formula (1 ') based on the acceptable region of hot water in FIG.
It is preferable to control the line speed so as to fall within the ranges of (2 ′) and (3 ′). LS (mpm) ≧ 120, [if D (mm) ≦ 0.50] ... (1 ′) LS (mpm) ≧ −80D (mm) +160, [if 0.50 <D (mm) ≦ 1.00]・ ・ ・ ・ (2 ′) LS (mpm) ≧ 80, [when D (mm)> 1.00] ・ ・ ・ ・ ・ ・ (3 ′) Equations (1 ′), (2 ′) and (3 ′) LS indicates the line speed, and D indicates the thickness of the steel plate.

Next, FIG. 2 shows a graph obtained by the present invention.
The relationship between the steel plate thickness D, the height H of the gas wiping nozzle from the molten metal surface, and the occurrence of hot lines is shown. As shown in FIG. 2, it was found that there was a region of an appropriate height H of the wiping nozzle according to the thickness of the steel plate. That is,
The area of the height H of the wiping nozzle appropriate for the steel sheet thickness is determined in advance, and based on the result, H is controlled in accordance with the steel sheet thickness to prevent the occurrence of hot lines. It becomes possible.

In the present invention, the range of the following formulas (4), (5) and (6) based on the hot water wrinkle limit region (including the hot water wrinkle acceptable region) indicated by the hatched portion in FIG. Preferably, the height of the wiping nozzle is controlled in accordance with the thickness of the steel plate. 260 ≧ H (mm) ≧ 240, [if D (mm) ≦ 0.50] ... (4) 255 ≧ H (mm) ≧ 235, [if 0.50 <D (mm) ≦ 1.00]・ ・ ・ ・ (5) 250 ≧ H (mm) ≧ 230, [if D (mm)> 1.00] ・ ・ ・ ・ ・ ・ ・ ・ ・ (6) In equations (4), (5) and (6), H indicates the height of the gas wiping nozzle from the plating bath surface, and D indicates the thickness of the steel plate.

In the present invention, it is more preferable to control both the line speed and the height of the wiping nozzle in accordance with the thickness of the steel sheet. Further, in the present invention, the height H of the wiping nozzle is used as a parameter, and an appropriate line speed L for the steel plate thickness D is determined in advance.
More preferably, the area of S is determined, and based on the result, the line speed is controlled in accordance with the thickness of the steel sheet and the height of the wiping nozzle, thereby preventing the occurrence of hot lines.

[0019]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be specifically described below based on embodiments. (Example 1) A cold-rolled steel sheet was annealed in a continuous hot-dip galvanizing equipment shown in FIG. 3 and then immersed in a hot-dip galvanizing bath to perform plating, and a gas wiping nozzle installed at a height of 245 mm above the molten metal surface was used. The amount of plating (weight per unit area) was adjusted to 175/175 [g / m ² ] to produce a galvanized steel sheet.

In FIG. 3, reference numeral 1 denotes a steel strip (steel plate);
2 is a gas wiping nozzle, 3 is a hot dip galvanizing bath,
Reference numeral 4 denotes an annealing furnace, and reference numeral 5 denotes a plating bath surface. In this embodiment, the steel plate thickness is 0.30 to 1.60 mm and the line speed is 50
It was changed to ~ 130m.pm, and the relationship with the occurrence of hot water wrinkles of the obtained plated steel sheet was examined. The experimental results are shown in FIG.

In FIG. 1, the criterion for the occurrence of hot water lines was determined as follows. ●: Fail = Galvanized steel sheet with visible hot water wrinkle As shown in FIG. 1, it was found that there was an appropriate range of line speed depending on the thickness of the steel sheet.

That is, by controlling the line speed to an appropriate range in accordance with the thickness of the steel sheet, it is possible to effectively prevent the occurrence of hot lines. (Example 2) The height of the gas wiping nozzle from the molten metal surface was changed to 200 to 350 mm, and the line speed was set to 120 m.p.
A hot-dip galvanized steel sheet was manufactured in the same manner as in Example 1 except that the value was changed to m.

FIG. 2 shows the experimental results. In FIG. 2, a hatched portion is a region satisfying the criteria for determining hot water wrinkles 〇 and に お け る in the first embodiment, and a portion other than the hatched portion is a region corresponding to the criteria for determining hot water wrinkles of the galvanized steel sheet. Is shown. As shown in FIG. 2, it was found that there was an appropriate range in the height of the wiping nozzle depending on the thickness of the steel sheet.

That is, by controlling the height of the wiping nozzle within an appropriate range in accordance with the thickness of the steel sheet, it is possible to effectively prevent the occurrence of hot lines.

[0025]

According to the method of the present invention, in the production of a hot-dip galvanized steel sheet, it is possible to effectively prevent the occurrence of hot lines, which is a fatal defect in appearance. Furthermore, according to the method of the present invention, for example, when connecting a coil or replacing a coil, the occurrence of hot water wrinkles is prevented by maintaining the line speed at the lower limit of the appropriate range, so that the line speed tends to increase. Therefore, the effect that a hot-dip galvanized steel sheet excellent in both product yield and production efficiency can be produced can be achieved, and its industrial value is great.

[Brief description of the drawings]

FIG. 1 is a graph showing the relationship between the thickness and line speed of a steel sheet and the occurrence of hot water wrinkles.

FIG. 2 is a graph showing the relationship between the thickness of a steel sheet, the height of a gas wiping nozzle from the surface of the nozzle, and the occurrence of hot lines.

FIG. 3 is a schematic explanatory view of a continuous galvanizing equipment.

[Explanation of symbols]

 Reference Signs List 1 steel strip (steel plate) 2 gas wiping nozzle 3 hot-dip galvanizing bath 4 annealing furnace 5 hot surface of plating bath

──────────────────────────────────────────────────続 き Continued on front page (58) Field surveyed (Int.Cl. ⁷ , DB name) C23C 2/00-2/40

Claims (1)

(57) [Claims] (1) the basis weight of at least one surface of the steel plate is 1
In the method for producing a hot-dip galvanized steel sheet having a thickness of not less than 00 [g / m ² ], controlling the line speed and / or the height of the gas wiping nozzle from the plating bath surface in accordance with the steel sheet thickness. A method for producing a thick galvanized steel sheet having excellent surface properties, characterized by the following features.