JP2000218319A - Hot rolled steel plate buckling prevention method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent generation of a hot rolled steel plate buckling when a hot rolled coil is rewound as it just being hot rolled. SOLUTION: When a hot rolled coil is rewound by a coil rewinder equipped with a pressure roll, a pressure roll having a diameter sufficient for making a steel plate surface layer bending distortion εp being caused by a forced entry of the roll at 1.4% or more is used. The coil is rewound when the steel plate to be rewound is going to be separated or its vicinity, while pressing the steel plate with a pressure roll. In this case, εp= 1/(D/t+1)} ×100%, D is a diameter (mmϕ) of the pressure roll, and t is a steel plate thickness (mm).

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for preventing a hot-rolled steel sheet from being bent at the time of rewinding a hot-rolled coil by a coil rewinding apparatus provided with a pressure roll.

[0002]

2. Description of the Related Art FIG. 4 is a diagram showing a main part of a coil rewinding device on the picking line entrance side. Steel sheet S during coil rewind
In order to prevent meandering, a pressure roll 2 is attached to the payoff reel 1, and the pressure roll 2
Rewind the coil while pressing against the coil. At this time, if the coil that has been hot-rolled is unwound, the steel plate S is bent as shown in FIG. This buckling causes deterioration in the yield of a product such as a so-called pickling external sales coil that sells a steel sheet that has been descaled as a product because the appearance of the steel sheet is impaired.

[0003] It is known that buckling is caused by a Luders band due to the yield point elongation of a hot-rolled steel sheet. Therefore, conventionally, for steel sheets where the occurrence of buckling is a problem, such as pickling externally sold coils, a light cold working is performed in advance with a skin pass line,
After eliminating the yield point elongation of the steel sheet, it is inserted into the pickling line and descaled.

[0004]

However, installing the hot-rolled coil in a skin pass line separate from the pickling line leads to an increase in manufacturing cost.

[0005] The present invention has been made in view of the above circumstances, and has as its object to provide a method of preventing a hot rolled steel sheet from breaking at the time of unwinding a hot rolled coil that has been hot rolled.

[0006]

Means of the present invention for solving the above problems are as follows.

(1) When unwinding a hot-rolled coil with a coil unwinding device equipped with a pressure roll, a pressure roll having a diameter capable of increasing the bending strain ε _{P of the} surface layer of the steel sheet caused by the pressing of the pressure roll to 1.4% or more. A method of preventing the breakage of a hot-rolled steel sheet, wherein the coil is rewound while the steel sheet is pushed by the pressure roll at or near the separation of the steel sheet to be rewound. Here, ε _P = {1 / (D / t + 1)} × 100 (%) D: diameter of pressure roll (mmφ), t: thickness of steel plate (mm)

(2) The method for preventing breakage of a hot-rolled steel sheet according to (1), wherein the amount of pressing of the pressure roll is adjusted according to the thickness of the steel sheet.

(3) The method for preventing breakage of a hot-rolled steel sheet according to (1) or (2), wherein the steel sheet is pushed in by a pressure roll while cooling the steel sheet at the rewinding portion.

[0010]

BEST MODE FOR CARRYING OUT THE INVENTION The present invention will be described below together with the background to the invention.

As shown in FIG. 1, the hot-rolled hot-rolled steel sheet has a yield point elongation (YPEL) of about 2%. When the coil is rewound while pressing the pressure roll with the coil rewinding device on the pickling line entrance side, the thinner the steel plate, the more the occurrence of breakage of the waist which causes downgrade. The reason for this is that the yield point elongation of the steel sheet is reduced by bending with a pressure roll, but the thin steel sheet has a smaller amount of bending deformation due to the pressure roll than the thick steel sheet, It was thought that the decrease in yield point elongation was small, and the occurrence of hip breaks increased.

If the amount of bending deformation caused by the pressure roll is increased for a thin steel plate, occurrence of buckling may be reduced. The present inventors consider that reducing the diameter of the pressure roll is an inexpensive and effective means for increasing the amount of bending deformation imparted to the steel sheet, and using a small-diameter pressure roll, hot rolling is performed. The hot rolled coils of various thicknesses were unwound while pushing the steel sheet in with a coil rewinding device on the side of the pickling line, descaled by hydrochloric acid pickling, and the degree of bending of the steel sheet after descaling was investigated. FIG. 2 shows the results of the investigation. In FIG. 2,
The roll of 210 mmφ is a conventional roll, and the roll of 140 mmφ is a roll with a reduced diameter. The bending deformation of the steel sheet was evaluated by the bending strain ε _P of the surface layer of the steel sheet defined by the following equation. ε _P = {1 / (D / t + 1)} × 100 (%) D: diameter of pressure roll (mmφ), t: steel plate thickness (mm)

The degree of buckling was evaluated by visually observing the surface of the steel sheet according to the following criteria. ◎: No waist break occurs. ○: Waist break within the acceptable range occurs as a normal pickling external sales coil. ×: Fail break occurs as a normal pickling external sales coil.

In the case of a conventional roll having a diameter of 210 mm, the plate thickness is 3.
When the roll diameter is less than 0 mm, the rejected waist break occurs as a pickling external sales coil. However, when the roll diameter is 140 mm, the rejected waist break does not occur as the pickling external sales coil. Further, from FIG. 2, in any of the rolls, when the bending strain ε _{P of the} surface layer of the steel sheet is 1.4% or more, there is no occurrence of rejected bending, and the bending strain ε _{P of the} surface layer of the steel sheet is 2.2% or more. In the case of, it was found that breakage of the waist did not occur.

In the present invention, based on the above findings, a pressure roll having a diameter capable of increasing the bending strain ε _{P of the} surface layer of the steel sheet due to the indentation of the pressure roll to 1.4% or more is used. It is more preferable to use a roll having a diameter capable of increasing the bending strain ε _P to 2.2% or more, since the occurrence of hip break can be reliably prevented.

When the diameter of the pressure roll is reduced, when the thickness of the steel sheet is increased, the bending strain ε _{P of the} surface layer of the steel sheet becomes unnecessarily large, and the workability of the steel sheet is deteriorated, for example, the total elongation is reduced. Therefore, to ensure good workability while preventing buckling, depending on the thickness of the steel sheet,
It is preferable to adjust the pressing force of the pressure roll and the amount of pushing to adjust the curvature of the steel sheet, and secure a necessary bending strain ε _{P of the} surface layer of the steel sheet. In order to prevent buckling while preventing the workability of the steel sheet from deteriorating, it is preferable to adjust the bending strain ε _{P of the} surface layer of the steel sheet to fall within a range of 1.4 to 4.0%.

Further, by pressing the steel plate with a pressure roll while cooling the steel plate at the coil rewinding portion, the effect of preventing breakage of the hip can be further improved. In a normal soft hot-rolled steel sheet, the temperature of the steel sheet subjected to bending by a pressure roll is preferably set to 40 ° C. or lower.
It is already known that lowering the temperature of the steel sheet can prevent the occurrence of buckling, and for example, it is possible to cool the hot-rolled coil in advance and reduce the temperature before charging the pickling line. This is a simple method. According to the method of the present invention, the following effects are further obtained as compared with the case where the coil is cooled in advance.

When a bending process is performed by the pressure roll, a temperature gradient is formed in the thickness direction, and the temperature of the surface layer having a large amount of bending strain is lowered, so that the effect of preventing the Luders band is more excellent.

The steel sheet discharged from the rewinding device is descaled using an acid solution. Since the temperature of the acid solution in the pickling line is as high as 70 to 90 ° C., the steel sheet once cooled is heated again. According to the method of the present invention, since the temperature at the central portion of the sheet thickness is higher than the surface layer, the steel sheet discharged from the rewinding device has reheating from the central portion, so that the cost for reheating the steel sheet can be reduced.

Since the time required for cooling can be reduced, the in-process period between the hot rolling line and the pickling line can be shortened, or the amount of in-process coils can be reduced.

Next, an embodiment of the present invention will be described with reference to the drawings. FIG. 3 is a diagram showing a main part of the coil rewinding device on the pickling line entry side. In FIG. 3, 1 is a payoff reel, 2 is a pressure roll, 3 is a backup roll, 6 is a spray device for cooling the steel sheet S,
Cooling water is injected onto both sides of the steel sheet immediately after being rewound from the payoff reel 1.

As the pressure roll 2, a roll having a diameter capable of increasing the bending strain ε _{P of the} surface layer of the steel sheet to 1.4% or more, more preferably 2.2% or more is used.

The pushing amount adjusting device 5 has a position adjusting mechanism for moving the position of the pressure roll 2 to the running position of the steel plate via the spray device 6 and the backup roll 3 in accordance with the coil diameter, and furthermore, to reduce the thickness of the steel plate. Accordingly, the position of the pressure roll 2 is adjusted to adjust the pushing amount of the steel sheet S.

Using the present apparatus, the hot-rolled coil is rewound from the pay-off reel 1, and if necessary, both surfaces of the steel sheet S immediately after unwinding are water-cooled using the spray device 6,
The pressure roll 2 is pushed into the steel sheet S to make the bending strain ε _{P of the} surface layer of the steel sheet equal to or more than 1.4%, the steel sheet S is transferred, descaled by a pickling device (not shown) through the pinch roll 4, and discharged. It is wound by a winding device (not shown). After descaling, a steel sheet with a surface appearance suitable for pickling external sales coils is obtained. In the case of water cooling, the temperature of the steel sheet subjected to bending by the pressure roll is preferably set to a temperature of 40 ° C. or less.

The thickness of the steel sheet and the pressure roll 2
Indentation amount and bending strain ε of steel sheet surface layer _PSeeking for a relationship
Using the pushing amount adjusting device 5 according to the thickness of the steel sheet.
Adjust the pressing force of pressure roll 2 and push in
To adjust the bending strain ε of the steel sheet surface layer._PIs within the specified range, eg
For example, if it is set within the range of 1.4 to 4.0%,
Steel plates with good workability can be manufactured while preventing breakage.
You.

The present invention is particularly suitable as a method for preventing a soft hot-rolled steel sheet having a tensile strength at which buckling is likely to occur, having a tensile strength of 40 kg / mm ² or less, from buckling.

[0027]

DESCRIPTION OF THE PREFERRED EMBODIMENTS In the apparatus shown in FIG. 3, a normal pressure roll having a diameter of 210 mm (conventional example) and a diameter of 140 mm were used.
Using a small-diameter pressure roll of φ, 90 mmφ (Invention Example 1 and Invention Example 2), unwind the coil of the hot-rolled soft-rolled steel sheet, descaling by pickling with hydrochloric acid, and descaling the steel sheet. The degree of surface buckling was investigated.
In Invention Example 1, the water cooling condition (whether or not water cooling is performed) in the rewinding section was changed. In addition, in Inventive Examples 1 and 2, the pressing amount of the pressure roll was adjusted so that the bending strain ε _{P of the} surface layer of the steel sheet did not exceed 4.0%. Table 1 shows the survey results.

The degree of buckling was evaluated by visually observing the surface of the steel sheet and according to the following criteria. ◎: No waist break occurs. ○: Waist break within the acceptable range occurs as a normal pickling external sales coil. ×: Fail break occurs as a normal pickling external sales coil.

[0029]

[Table 1]

In the case of the conventional example, if the sheet thickness t is less than 3.0 mm, the bending strain ε _{P of the} surface layer of the steel sheet is less than 1.4%, so that a waist break which is unacceptable as an pickling external sales coil occurs.

On the other hand, in the case of the example of the present invention, the evaluation level of the waist break is within the acceptable range as a normal pickling external sales col at all plate thicknesses. The effect of preventing hip breakage when water cooling is performed in the rewinding section is improved as compared with the case where water cooling is not performed (Invention Example 1). Further, in Invention Example 2, the bending strain ε of the steel sheet surface layer
_{Since P} is maintained at 2.2% or more, no break in the back is observed even under anhydrous cooling.

[0032]

According to the present invention, even if a hot-rolled coil that has been hot-rolled is inserted into a pickling line, no buckling occurs. For this reason, it is not necessary to previously load the skin pass line in order to eliminate the elongation at the yield point for a product such as an pickling external sale coil in which the occurrence of buckling is a problem, and the manufacturing cost can be reduced. Further, by adjusting the amount of pressing of the pressure roll in accordance with the thickness of the steel sheet, it is possible to prevent occurrence of hip break without impairing workability.

[Brief description of the drawings]

FIG. 1 is a stress-strain diagram of a hot-rolled steel sheet as hot-rolled.

FIG. 2 is a view showing a state of occurrence of buckling of a hot-rolled steel sheet as hot-rolled.

FIG. 3 is a view showing a main part of a coil rewinding device on the entrance side of the pickling line for explaining the embodiment of the present invention.

FIG. 4 is a view showing a main part of a conventional coil rewinding device on the entrance side of the pickling line.

FIG. 5 is a perspective view showing a state in which a steel plate breaks when a hot-rolled coil that has been hot-rolled is unwound in an pickling line.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Pay-off reel 2 Pressure roll 3 Backup roll 4 Pinch roll 5 Push amount adjustment device 6 Spray device S Steel plate (hot rolled steel plate)

Continuation of the front page (72) Inventor Hidenori Shimada 1-2-1 Marunouchi, Chiyoda-ku, Tokyo F-term (reference) 4E026 CB02 EA02

Claims (3)

[Claims] When a hot-rolled coil is unwound by a coil rewinding device equipped with a pressure roll, a pressure roll having a diameter capable of increasing a bending strain ε _{P of a} surface layer of a steel sheet by pressing of the pressure roll to 1.4% or more. A method for preventing buckling of a hot-rolled steel sheet, wherein the coil is rewound while the steel sheet is pushed by the pressure roll at or near the separated steel sheet to be rewound. Here, ε _P = {1 / (D / t + 1)} × 100 (%) D: diameter of pressure roll (mmφ), t: thickness of steel plate (mm) 2. The method for preventing buckling of a hot-rolled steel sheet according to claim 1, wherein the pressing amount of the pressure roll is adjusted according to the thickness of the steel sheet. 3. The method for preventing breakage of a hot-rolled steel sheet according to claim 1, wherein the steel sheet is pressed by a pressure roll while cooling the steel sheet at the rewinding section.