JP2542467B2 - Method for producing hot dip galvanized steel sheet - 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 producing a hot-dip galvanized steel sheet, and more particularly to a method for controlling a skin-pass rolling machine for skin-pass rolling of an alloyed hot-dip galvanized steel sheet.

[0002]

2. Description of the Related Art Cold-rolled steel sheets have been conventionally used for thin steel sheets such as automobile body outer panels and exterior panels for household electrical appliances or sheet metal furniture where the finished appearance after painting is important. Regarding the image clarity after coating and the formability such as press working, it is usual to achieve both of these by adjusting the surface roughness in skin pass rolling (also referred to as temper rolling). Among them, in applications such as steel sheets for automobiles where rust prevention is strongly required, surface-treated steel sheets such as galvanized steel sheets are in widespread use, and when strong rust prevention is required. Is being subjected to so-called alloying treatment after plating to increase the basis weight, but the surface roughness of the galvannealed steel sheet has a fine unevenness peculiar to the galvanizing step and the alloying step. It is known that, when it is generated, the surface is roughened, and both the sharpness after painting and the press formability are significantly deteriorated.

Therefore, according to Japanese Patent Laid-Open No. 2-274858, a plurality of surface roughness adjusting means are provided in series, and for example, the first skin pass rolling machine smoothes the surface of the steel sheet to some extent to generate a flat portion. Then, it has been proposed to obtain a hot-dip galvanized steel sheet having a desired flat portion and recessed surface roughness with a second skin pass rolling mill. Further, according to Japanese Patent Laid-Open No. 59-1636, the surface roughness (R
z, JIS ten-point average roughness) is 10 to 20 μm, and after skin pass rolling with a rolling reduction of 1.0% or less, the rolling reduction is further performed using a roll with a surface roughness (Rz) of 5 μm or less
A method for producing a clear-painted coated steel sheet is proposed, in which skin rolling is performed at 1.0% or less to bring the total reduction rate to 2.0% or less and then coating is performed.

[0004]

By the way, generally, in a skin pass rolling mill, constant load control or constant elongation control is performed by operating the rolling force and tension. However, even if the load constant control or the elongation constant control is performed in the skin pass rolling in the hot dip galvanized steel sheet production line, the surface roughness cannot be controlled by these controls. Surface roughness (Ra, center line average roughness) of galvannealed steel sheet that has undergone alloying treatment in particular
Is as large as 1.5 to 2.5 μm, and there is a problem with pressability and paintability, so it is necessary to reduce the surface roughness by skin pass treatment, but even if skin pass is performed under the same conditions, depending on the degree of alloying, use The surface roughness of the product also greatly changes with the aging of the work rolls, and it is difficult to control the surface roughness within a certain range.

The point ◯ in FIG. 3 shows how the surface roughness of the product after the skin pass varies according to the alloying degree of the material in the conventional control method. The surface roughness of the roll used is
Ra = 1.0 μm, Elongation rate 1.0% Constant thickness control 0.4 ~
3.2 mm, basis weight 30-90 gr / m ² , line speed 60-
It is 140m / min. In addition, the point ◯ in FIG. 4 shows the change in the product surface roughness depending on the number of coils rolled by the same work roll (corresponding to almost the elapsed time). The initial surface roughness of the roll used was Ra = 1.0 μm, the elongation was controlled to be 1.0%, and the degree of alloying was set to 0.9%. It can be seen that the surface roughness of the roll is transferred to the product surface as it is, and the product surface roughness decreases uniformly as the number of coils increases.

The present invention solves these problems and provides a method for controlling a skin pass rolling machine which controls the surface roughness of an alloyed hot-dip galvanized steel sheet within a certain range. With the goal.

[0007]

The present invention provides a skin pass rolling machine for skin pass rolling a galvannealed steel sheet which has been subjected to an alloying treatment, based on the results of measurement of the surface roughness and elongation of the steel sheet after plating. It is characterized by correcting the rolling down force or rolling down force and tension of the machine.

[0008]

[Operation] According to the present invention, a surface roughness measuring device for measuring the surface roughness of the steel strip to be treated is installed immediately after the skin pass mill, and the rolling force or the rolling force and tension of the skin pass mill is corrected according to the measurement result. Then, the surface roughness of the product can be kept constant by performing feedback control.

[0009]

EXAMPLE FIG. 1 is a part of a hot dip galvanizing line showing the configuration of an example of the present invention. The cold-rolled steel sheet 1 as a raw material is subjected to a pretreatment process such as an annealing furnace, passed through a zinc bath in a zinc pot 2 and plated with molten zinc on its surface, while passing through an alloying furnace 3 while rising upward. After being alloyed, it is skin-passed by a skin-pass rolling machine 5 installed in the rear through a cooling device 4 and sent to an outlet-side winding facility or the like.

The surface roughness and elongation of the steel sheet after the skin pass are measured by a surface roughness measuring device 7 installed immediately after the skin pass rolling machine 5 and a well-known extensometer (not shown), and this is controlled by the skin pass rolling machine. The device 8 is fed back to correct the rolling force or the rolling force and tension. A contact type is also known as a surface roughness measuring device,
In the present invention, the alloyed steel strip surface is soft and may be flawed, so a non-contact type is preferable. As a non-contact type surface roughness measuring device, there is a device utilizing scattering of reflected light described in JP-A-2-32207. Even if it is a contact type, a rotating probe type eddy current type sensor or the like can be used if conditions such as making the probe surface material soft such as rubber are set.

It is known that there is a certain correlation between the degree of alloying and the surface roughness before skin pass,
By utilizing this relationship, a known alloying degree measuring device 6 can be used instead of the surface roughness measuring device. In this case, since the alloying degree does not change by skin pass rolling, the installation position of the alloying degree measuring device 6 does not need to be limited to immediately after the skin pass rolling machine 5 and may be located behind the alloying furnace 3.

Next, a specific control method of the skin pass rolling mill according to the present invention will be described. If the rolling force is increased in the skin pass rolling, the surface roughness after rolling becomes smaller.Therefore, the rolling force can be corrected by the detection signal of the surface roughness measuring device and controlled within the preset surface roughness range. . However, in skin pass rolling, it is also necessary that the elongation rate be within the set range, so if the elongation rate deviates from the set value in order to obtain the specified surface roughness, the rolling force should be corrected within the range that the elongation rate allows. Instead, the deficiency corrects the tension downwards to achieve the desired surface roughness. These procedures are shown in the flow diagram of FIG.

Although an example of an inline skin pass rolling machine installed in the hot dip galvanizing line has been described with reference to FIG. 1, the present invention is not limited to this, and a coil taken out from the hot dip galvanizing line can be used. It goes without saying that the present invention can be applied to the case of performing a skin pass rolling with a skin pass rolling machine outside the line.

[0014]

Effect of the Invention In FIGS. 3 and 4, a dot indicates data according to the present invention. The operating conditions are the same as those described for the points. As you can see from these figures,
According to the present invention, the surface roughness of the hot-dip galvanized steel sheet can be made substantially constant irrespective of the degree of alloying and the roll usage. In the example of the plating plant in which the present invention is carried out, customer troubles such as press cracking due to defective roughness, which has conventionally occurred 10 times or more per year, are almost eliminated, and the quality and the yield are greatly improved.

[Brief description of drawings]

FIG. 1 is a line layout diagram showing a configuration of the present invention.

FIG. 2 is a flow diagram showing an operation procedure of the present invention.

FIG. 3 is a graph showing changes in surface roughness according to the alloying degree according to the conventional method and the present invention.

FIG. 4 is a graph showing changes in surface roughness depending on the number of rolled coils according to a conventional method and the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Steel plate 2 Zinc pot 3 Alloying furnace 4 Cooling device 5 Skin pass rolling machine 6 Alloying degree measuring device 7 Surface roughness measuring device 8 Control device

 ─────────────────────────────────────────────────── ─── Continuation of the front page (56) Reference JP-A-4-91801 (JP, A) JP 54-40457 (JP, B2)

Claims (1)

(57) [Claims] 1. A skin-pass rolling machine for skin-pass rolling an alloyed hot-dip galvanized steel sheet, based on the measurement results of surface roughness and elongation of the steel sheet after plating, A method for manufacturing a hot-dip galvanized steel sheet, which comprises correcting tension.