JPH1147812A - Method for preventing sheet camber in hot rolling - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a preventing method of sheet camber by which the sheet camber generated in the hot rolling of a thick plate and hot strip is effectively prevented. SOLUTION: This method is a method for preventing the generation of the sheet camber in rolling of the next pass by calculating the position of the pass line and the circumferential speed difference between upper and lower work rolls which are necessary to prevent the generation of the sheet camber having the measured amount of the sheet camber and controlling either or both of the position of the pass line and the circumferential speed difference between the upper and lower rolls based on the calculated position of the pass line and the circumferential speed difference between the upper and lower work rolls. The shape ratio in rolling of the next pass is calculated and, in the case that shape ratio is 0.8-1.2, the sheet camber is prevented by applying the position control of the pass line and, in the case that shape ratio is over 1.2, by applying either or combination of both of the position control of the pass line and control of the circumferential speed difference between the upper and lower work rolls.

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 warpage of a steel sheet from being generated at a tip end of a steel sheet in a thick plate rolling or a hot strip rough rolling in a reverse rolling.

[0002]

2. Description of the Related Art The vertical warpage (hereinafter referred to as "sheet warpage") of a steel plate tip caused by reverse rolling in thick plate rolling or hot strip rough rolling is caused by equipment trouble such as breakage of a stripper guide and waist bending caused by downward warpage. Etc., and various adverse effects such as quality deterioration due to generation of uneven cooling in a controlled rolled material or the like.

[0003] Sheet warpage that causes such extremely large operational problems is caused by a temperature difference between the upper and lower surfaces of the steel sheet, a difference in friction coefficient,
Because many factors such as the difference in peripheral speed between the upper and lower work rolls and the amount of pickup of the lower work roll are complicatedly overlapped, the prevention method is extremely difficult, and even though more research has been conducted than before. Nevertheless, it has not been completely prevented.

[0004] Japanese Patent Publication No. 02-30761 discloses that after setting a pass line at an optimum position, a sheet warpage amount expected to be generated based on a measured difference between upper and lower surface temperatures of a material to be rolled is predicted. There is disclosed a method for preventing sheet warpage by imparting a difference in peripheral speed between upper and lower work rolls necessary for preventing sheet warpage to a work roll and rolling the work roll. However, when the relationship between the peripheral speed difference and the sheet warpage amount is obtained, the shape ratio is not taken into consideration, so that the sheet warpage may be promoted depending on conditions.

[0005] The shape ratio refers to the ratio of the contact arc length (the roll circumference of the portion in contact with the material to be rolled during rolling) and the average sheet thickness, ie, contact arc length / average sheet thickness.

[0006] The average thickness (h _m ) is given by h _m = (H + h) / H, where H is the thickness at the entrance to the rolling mill and h is the thickness at the exit side of the rolling mill.
2. On the other hand, in Japanese Patent Publication No. 04-62806, the relationship between the shape ratio, the peripheral speed ratio of the upper and lower work rolls and the amount of sheet warpage is obtained in advance, and when the shape ratio is 1.0 or more and less than 2.0, The work roll on the side where warpage occurs is made faster than the other work roll, and when the shape ratio is 2.0 or more, the work roll on the side where warpage occurs is made slower than the other work roll to perform rolling. A method for preventing the occurrence of warpage is disclosed.

However, this method is a method for preventing the occurrence of sheet warpage only by controlling the upper and lower work roll peripheral speed differences, and it has been difficult to sufficiently prevent the sheet warpage only by controlling the work roll peripheral speed difference.

[0008]

SUMMARY OF THE INVENTION The present invention has been made in view of the above problems, and has been made in consideration of the above-described problems. Accordingly, the present invention has been made in view of the above circumstances. It is an object to provide a method.

[0009]

Means for Solving the Problems The inventors of the present invention have conducted rigorous numerical analysis such as the finite element method, which has been conventionally attempted, since the plate warpage is an unsteady phenomenon that occurs when a material is engaged with a work roll. Then, we thought that it was extremely difficult to accurately grasp the actual phenomena, and investigated and examined the warpage generation behavior in actual rolling in detail. As a result, the following findings were obtained.

1) In order to prevent the occurrence of sheet warpage, it is preferable to perform rolling by controlling the peripheral speed difference between the upper and lower work rolls and controlling the pass line position alone or in combination. Cannot be prevented effectively.

2) Even if the peripheral speed difference control rolling of the upper and lower work rolls is applied to rolling having a shape ratio of 0.8 to 1.2, occurrence of sheet warpage cannot often be prevented.

3) Pass line position control is effective in preventing board warpage regardless of the shape ratio.

4) In rolling after descaling using high-pressure water, there is an effect on the sheet warpage due to the descaling, and the sheet warpage is more reliably controlled by controlling the pass line position and roll peripheral speed in consideration of the influence. Can be prevented.

The present invention has been made based on such findings, and the gist thereof is as follows.

(1) After a steel sheet is rolled by a reverse hot rolling mill, the amount of warpage generated at the front end of the steel sheet is actually measured by a sheet warpage detector, and the path line position and the sheet warpage amount determined in advance are determined. From the relationship or the relationship between the peripheral speed difference between the upper and lower work rolls and the amount of sheet warpage, the path line position required to prevent the occurrence of the plate warpage of the measured plate warpage amount, and the peripheral speed difference between the upper and lower work rolls, A method of controlling one or both of the pass line position and the peripheral speed of the upper and lower work rolls based on the calculated pass line position and the peripheral speed difference between the upper and lower work rolls to prevent the occurrence of sheet reversal in rolling in the next pass. The shape ratio in the rolling of the next pass is calculated, and the shape ratio is 0.8 or more and 1.2
In the following cases, pass line position control rolling is applied, and if the shape ratio is less than 0.8 or exceeds 1.2, either one of pass line position control rolling and upper and lower work roll peripheral speed difference rolling, or A method for preventing sheet warpage in hot rolling, comprising applying a combination of the two to prevent sheet warpage.

(2) After rolling a steel sheet with a reverse hot rolling mill, the amount of warpage generated at the front end of the steel sheet is measured by a sheet warpage detector, and if descaling is not performed before rolling in the next pass, The measured plate warpage amount is assumed to be the warpage amount generated in the next pass rolling, and when descaling is performed before rolling in the next pass, the actual measured plate warpage amount is changed by descaling obtained in advance. The amount of warpage corrected by the amount of warpage is assumed to be the amount of warpage generated in the rolling of the next pass, and the relationship between the pass line position and the amount of warpage determined in advance or the peripheral speed difference between the upper and lower work rolls and the amount of warpage is determined. From the relationship, the path line position required to prevent the occurrence of the plate warpage of the assumed plate warpage amount, the peripheral speed difference between the upper and lower work rolls are calculated, and the calculated pass line position, the peripheral speed difference between the upper and lower work rolls are calculated. Pass line rank based on A method of controlling one or both of the peripheral speeds of the upper and lower work rolls to prevent the occurrence of sheet warpage in the rolling of the next pass. When the ratio is 0.8 or more and 1.2 or less, pass line position control rolling is applied, and the shape ratio is set to 0.
If less than 8 or more than 1.2, either pass line position control rolling or upper and lower work roll peripheral speed difference rolling,
Alternatively, a method for preventing sheet warpage in hot rolling, comprising applying a combination of the two to prevent sheet warpage.

The shape ratio refers to the ratio of the contact arc length to the average plate thickness, that is, the contact arc length / average plate thickness. Here, Sawakocho is circumferential length of the work roll in the portion provided in contact with the material to be rolled during rolling, the average thickness (h _m) is the rolling mill entry side thickness of the H, the side plates out rolling mill Assuming that the thickness is h, h _m = (H +
h) / 2.

[0018]

Embodiments of the present invention will be described below in detail.

The reason for actually measuring the amount of sheet warpage at the front end of the steel sheet after rolling by the sheet warp detector is to assume that the actually measured sheet warpage is the amount of sheet warpage generated during rolling in the next pass.

In reverse rolling, since the amount of sheet warpage generated in the previous pass and the amount of sheet warpage generated in the next pass are substantially the same, the amount of sheet warpage in the previous pass is assumed to be the amount of warpage generated in the next pass rolling. I do.

Next, the relationship between the peripheral speed difference between the upper and lower work rolls and the amount of sheet warpage, the relationship between the pass line and the amount of sheet warpage, and the path required to prevent the occurrence of sheet warpage from this relationship. When the line position, the method of calculating the peripheral speed difference between the upper and lower work rolls and the shape ratio are 0.8 or more and 1.2 or less, pass line position control rolling is applied, and the shape ratio is 0.8
If less than or more than 1.2, application of either one of pass line position control rolling and upper and lower work roll peripheral speed difference rolling or a combination of both will be described below.

(1) Relationship between peripheral speed difference between upper and lower work rolls and sheet warpage In order to examine the relationship between peripheral speed difference between upper and lower work rolls and sheet warpage, the peripheral speed difference between upper and lower work rolls was variously changed as follows. Reverse rolling was performed under the conditions.

Work roll diameter: 200 mm Heating temperature: 1150 ° C. Reduction rate: 2.5 to 45% FIG. 1 is a diagram showing the relationship between the peripheral speed difference and the amount of warpage in rolling at a shape ratio of 0.72.

FIG. 2 is a diagram showing the relationship between the peripheral speed difference and the amount of warpage in rolling at a shape ratio of 1.63.

FIG. 3 is a diagram showing the relationship between the peripheral speed difference and the amount of warpage in rolling at a shape ratio of 0.93 and 1.07.

In each of these figures, the horizontal axis represents the difference between the peripheral speeds of the upper and lower work rolls replaced with a different velocity, and the amount of warpage is represented by the curvature [1 / radius of curvature ρ: (1 / mm)]. .

The differential speed ΔV represents the ratio between the upper roll speed _Vu and the lower roll speed _VL as described below. △ V = The _{(V L -V u) / V} u × 100 (%), the shape ratio, refers to the previously described contact arc length / average thickness, the contact arc length is in contact with the material to be rolled during rolling It is the circumferential length of the work roll in the part where it does.

The contact arc length ld can be obtained by the following equation.

[0029]

(Equation 1)

The average plate thickness h _m is obtained by h _m = (H + h) / 2. In addition, H is the thickness of the rolling mill entrance side, and h is the thickness of the rolling mill exit side.

The shape ratio X is obtained by the following equation (1).

[0032]

(Equation 2)

[0033] Here, R: the work roll radius △ h: reduction ratio = H-h h _m: average thickness = (H + h) / 2 H: thickness at entrance side h: apparent from out side thickness FIGS. 1 and 2 As described above, there is a certain relationship between the difference between the circumferential speeds of the upper and lower work rolls and the curvature, and the relationship also differs depending on the shape ratio. That is, when the shape ratio is as small as 0.72 as shown in FIG. 1, warpage occurs on the low-speed roll side, and when the shape ratio is as large as 1.63 as shown in FIG. Occurs.

However, as shown in FIG. 3, in the peripheral speed difference rolling with a shape ratio of about 1, an unstable phenomenon occurs in which warpage occurs in both the high-speed roll side and the low-speed roll side.

The reason for this is that, in the warpage in the peripheral speed difference rolling, a force for generating sheet warpage on the low-speed roll side and a force for generating warpage on the high-speed roll side are mixed. It is probable that because the two forces just balanced near 0, warpage occurred in both the high-speed roll side and the low-speed roll side with a slight change in conditions.

FIG. 4 is a view showing the warpage generation behavior when rolling is performed while changing the shape ratio over a wide range while fixing the peripheral speed difference between the upper and lower work rolls.

FIG. 4 shows that the warpage in the peripheral speed difference rolling is such that when the shape ratio is <0.8, sheet warpage occurs on the low-speed roll side, and when the shape ratio is> 1.2, warpage occurs on the high-speed roll side. , 0.8 <shape ratio <1.2, an unstable phenomenon occurs in which warpage occurs in both the low-speed roll side and the high-speed roll side.

As described above, it can be seen that in rolling at a shape ratio other than 0.8 to 1.2, it is possible to prevent the occurrence of sheet warpage by controlling the peripheral speed of the work roll. The following expressions (2) and (3) are used to calculate the difference between the sheet warpage amount (warp curvature κ) and the upper and lower work roll peripheral speed difference for calculating the difference between the upper and lower work roll peripheral speeds required to prevent the occurrence of sheet warpage. Relational equation, determined by extensive testing.

When 0 <X <0.8:

[0040]

(Equation 3)

If 1.2 <X:

[0042]

(Equation 4)

Here, X: shape ratio ΔV: difference in peripheral speed between upper and lower work rolls a _{1 to} a ₅ : constant Further, sign (ΔV) is a function for changing the sign, and when ΔV <0: sign (△ V) = − 1 When ΔV ≧ 0: sign (△ V) = + 1.

(2) Relationship between pass line position and amount of warpage FIG. 5 is a diagram showing the relationship between the pass line position and warpage curvature. This figure is a diagram showing the result of measuring the generated curvature by performing reverse rolling while changing the pass line variously in the range of 10 mm up and down.

As apparent from FIG. 5, the warpage generation behavior when the pass line is variously changed is such that when the material to be rolled is inserted obliquely from below, downward warpage occurs, and when it is inserted obliquely from above, upward warpage occurs. Occur. In addition, the unstable phenomenon near the shape ratio of 1.0 caused by the different peripheral speed rolling does not occur in the pass line controlled rolling. Furthermore, even if the shape ratio is largely changed, the amount of occurrence of sheet warpage is almost the same value, and as a control factor for controlling sheet warpage, it can be said that pass line controlled rolling is more suitable than rolling at different peripheral speeds. .

However, the pass line has a limited range of change due to mechanical problems of the rolling mill. When correcting a large sheet warpage, the pass line position cannot be largely changed, and the sheet warpage control ability is not available. May be insufficient. Therefore, in order to sufficiently control the sheet warpage, it is desirable to apply both the pass line control rolling and the different peripheral speed rolling in combination.

The relationship between the plate warpage (warp curvature κ) and the pass line position can be expressed by the following equation (4).

Κ = b (X−Δh / 2) (4) where Δh: amount of reduction (inlet-side sheet thickness−outlet-side sheet thickness) b: constant X: shape ratio Pass-line controlled rolling , Controllable upper limit of plate warpage κ
_p can be obtained by the following equation (5).

Κ _p = g (△ h, h) (5) where Δh: reduction amount = H−h h: outlet side plate thickness H: inlet side plate thickness g: constant where κ _p is Since it differs depending on the rolling mill, it must be determined in advance for each rolling mill to be used.

The curves shown by the dotted lines in FIGS. 1, 2, 4 and 5 are the lines obtained by the above-mentioned equations (2), (3) and (4), and represent the actual hot rolling. It can be understood that the amount of warpage generated by the above can be expressed with high accuracy.

Next, a description will be given of sheet warpage when descaling is performed with high-pressure water before rolling.

The present inventors have conducted detailed investigations and studies on the behavior of sheet warpage occurring in the actual operation of hot rolling. As a result, even when rolling was performed under the same rolling conditions, It was found that the amount of sheet warpage was different between the case where the steel sheet was rolled without being subjected to the heat treatment. FIG. 6 shows an example of this. In this example, the amount of warpage generated is increased by about 50% by performing descaling.

The reasons are as follows: 1) When descaling is performed, the state of water flowing to the plate surface is different between the upper surface side and the lower surface side, and the temperature is lower on the upper surface side than on the lower surface side.
2) The surface condition of the upper and lower surfaces may be different due to descaling.

Although it is difficult to theoretically elucidate and quantify the change in the state of the warpage due to the descaling, the present inventor has determined that, in the path where the descaling is performed, the sheet warpage amount obtained in the previous pass is used. Can be predicted with high accuracy by adding the correction term α to.

The correction term α varies depending on the sheet thickness, the rolling reduction, and the like, but can be expressed by the following functional equation (6).

Α = f (H, h, T, R) (6) where, H: incoming plate thickness h: outgoing plate thickness T: rolling temperature R: work roll diameter

However, since the function f shown in this equation is a function specific to the rolling mill and fluctuates due to descaling conditions and the like, it is necessary to calibrate whenever such a situation occurs.

Hereinafter, a method for preventing sheet warpage in actual rolling will be described.

FIG. 7 is a flowchart showing a method for controlling the peripheral speeds of the pass line and the upper and lower work rolls when the descaling is corrected.

First, the sheet warpage at the tip of the steel sheet after rolling is detected by a sheet warp detector installed on at least one of the front and rear surfaces of the hot rolling mill, and the warpage curvature κ is quantified. Next, it is determined whether or not to perform the descaling in the rolling of the next pass.
When descaling is performed, a correction term α is calculated based on the equation (5), and this correction term is added to the quantified warpage curvature κ to actually generate a warpage curvature κ ′ generated in the next pass.
Is estimated. When the descaling is not performed, it is assumed that the quantified warpage curvature κ is generated by the same amount in the next pass.

Next, the shape ratio X in the rolling of the next pass is calculated based on the above equation (1). The obtained curvature κ ′
It is determined whether (the curvature to which the correction term α is added when the descaling is performed) is a curvature that can be corrected by the pass line control. The upper limit of curvature κ _p that can be corrected is given by the above equation (4).
Can be obtained from

[0062] When the obtained warpage curvature κ'is kappa _p less than applies the pass line controlled rolling, achieving a correction plate warpage.

On the other hand, when the warpage curvature κ ′ is larger than κ _p , the calculated shape ratio X continues to be 0.8 <X <
It is determined whether or not it is included in the range of 1.2. If it is included, pass line controlled rolling is applied. If it is not included, pass line controlled rolling and different peripheral speed rolling are applied in combination.

By performing the sheet warpage control repeatedly until the rolling is completed according to the procedure described above, the sheet warpage can be prevented.

[0065]

EXAMPLE A low-carbon thick steel plate having a thickness of 140 mm and a width of 200 mm was reverse-rolled by using the following four-stage hot rolling mill according to a 10-pass schedule shown in Table 1.

Work roll diameter: 1010 mm Backup roll diameter: 2020 mm Descaling was performed on each entry side of 1, 3, 4, and 10 passes under the following conditions.

Descaling pressure: 130 kg / cm ² Descaler installation position: 500 from table roller top surface
mm Even when descaling is performed as an example of the present invention, the peripheral speed of the pass line or the work roll is controlled without correcting the influence on the sheet warpage, and the correction is performed in two cases.
Rolling was carried out. As a comparative example, rolling without any control was performed. The control means and control conditions applied in each pass are as shown in Table 1.

[0068]

[Table 1]

Table 1 also shows the curvature of the sheet measured after rolling in each pass.

As is apparent from Table 1, even in the case of the present invention in which the presence or absence of descaling is not considered, the effect of reducing the amount of sheet warpage is obtained as compared with the case where the warpage control is not performed. . In the example of the present invention in which the influence of the descaling is corrected in consideration of the presence or absence of the descaling, the warpage control effect is well exhibited in all the passes, and the sheet warpage amount of the final product is also 0.2 × 10 ⁻⁴ (1 / mm). ) And greatly reduced.

[0071]

According to the method for preventing sheet warpage of the present invention, it is possible to select an optimum warpage control means based on the warpage generation behavior obtained from actual rolling and to determine an accurate warpage control amount, thereby effectively reducing sheet warpage. Prevention and reduction.

[Brief description of the drawings]

FIG. 1 is a relationship between a different speed ratio and a curvature (shape ratio: 0.72)
FIG.

FIG. 2 shows a relationship between an abnormal speed ratio and a warpage curvature (shape ratio: 1.63).
FIG.

FIG. 3 shows the relationship between the differential velocity and the curvature (shape ratio: 1.07,
0.93).

FIG. 4 is a diagram showing a relationship between a shape ratio and a warpage curvature.

FIG. 5 is a diagram showing a relationship between a pass line position and a warpage curvature.

FIG. 6 is a diagram showing a warpage occurrence state depending on whether or not de-scaling is performed;

FIG. 7 is a flowchart showing a control method.

──────────────────────────────────────────────────の Continued on the front page (51) Int.Cl. ⁶ Identification code FI B21B 37/00 116M

Claims (2)

[Claims] 1. After rolling a steel sheet with a reverse hot rolling mill,
By measuring the amount of sheet warpage generated at the tip of the steel sheet with the sheet warp detector, from the relationship between the pass line position and the sheet warpage amount obtained in advance or the relationship between the peripheral speed difference between the upper and lower work rolls and the sheet warpage amount, The path line position required to prevent the occurrence of the plate warpage of the measured plate warpage amount, the peripheral speed difference between the upper and lower work rolls are calculated, and the calculated pass line position, the pass line position based on the peripheral speed difference between the upper and lower work rolls. And controlling one or both of the peripheral speeds of the upper and lower work rolls to prevent the occurrence of sheet warpage in the rolling of the next pass, and calculating the shape ratio in the rolling of the next pass, When the ratio is 0.8 or more and 1.2 or less, pass line position control is applied. When the shape ratio is less than 0.8 or exceeds 1.2, the difference between the pass line position control and the upper and lower work roll peripheral speed difference is applied. One of the controls,
Alternatively, a method for preventing sheet warpage in hot rolling, comprising applying a combination of the two to prevent sheet warpage. 2. After rolling a steel sheet with a reverse hot rolling mill,
Measure the amount of sheet warpage generated at the tip of the steel sheet with the sheet warpage detector, and if the descaling is not performed before rolling in the next pass, the measured sheet warpage amount is assumed to be the estimated sheet warpage generated in the rolling in the next pass. In the case where descaling is performed before rolling in the next pass, an estimated plate to be generated in the rolling in the next pass, the measured amount of sheet warpage corrected by the amount of sheet warpage that changes by descaling obtained in advance from the measured plate warpage is assumed. The amount of warpage, and the relationship between the previously determined pass line position and the amount of sheet warpage or the relationship between the peripheral speed difference between the upper and lower work rolls and the amount of sheet warpage prevent the occurrence of the sheet warpage of the assumed sheet warpage amount. Calculate the pass line position and the peripheral speed difference between the upper and lower work rolls, and calculate one or both of the pass line position and the peripheral speed between the upper and lower work rolls based on the calculated pass line position and the peripheral speed difference between the upper and lower work rolls. control A method of preventing the occurrence of sheet warpage in the rolling of the next pass, and calculating a shape ratio in the rolling of the next pass, and when the shape ratio is 0.8 or more and 1.2 or less, the pass line If position control is applied and the shape ratio is less than 0.8 or exceeds 1.2, either one of pass line position control and upper / lower work roll peripheral speed difference control or a combination of both is applied to reduce sheet warpage. A method for preventing sheet warpage in hot rolling, characterized by preventing the sheet warpage.