JPH08150407A - Continuous hot rolling method - Google Patents

Abstract

(57) [Abstract] [Purpose] To provide a continuous hot rolling method, and in particular, to provide a method of finish rolling a joint portion of a sheet bar. [Structure] A sheet bar after rough rolling is continuously joined by joining it to a preceding sheet bar having different steel types, sheet thickness, sheet width, and material temperature during rolling by a finishing rolling mill at the first stand entry side of the finishing rolling mill. In the continuous hot rolling method of rolling in the same manner, the setting value of the finishing mill is changed to the setting value of the succeeding material before the joining point of the preceding material and the following material enters the first stand or after passing through the final stand. By doing so, it is possible to suppress breakage near the joint point in the finish rolling mill.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a continuous hot rolling method, and more particularly to a method for finish rolling a joint portion of a sheet bar.

[0002]

2. Description of the Related Art Conventionally, a thin sheet hot rolling mill is usually composed of, for example, a 3-stand rough rolling mill and a 7-stand finishing rolling mill, and a sheet bar sent from the rough rolling mill is used as a finishing rolling mill. Continuous rolling is performed so that the plate thickness of each stand becomes the set plate thickness, and the exit side plate temperature of the final stand becomes the set temperature.

By the way, in recent years, prior to finish rolling, there has been proposed a method of joining sheet bars to each other and continuously performing hot rolling using a technique disclosed in, for example, Japanese Patent Application Laid-Open No. 62-234679. (See, for example, JP-A-6-39404). This continuous hot rolling method has begun to be adopted for the purpose of preventing the trouble of passing through when the sheet bar is bitten and the trouble of narrowing when slipping out, which occurs during normal rolling in finish rolling.

The continuous hot rolling method will be described in detail. As shown in FIG. 2, the sheet bar rolled to a predetermined size by the rough rolling machine 1 is cut by the shear 2 at the front and rear ends. , For example, finish rolling is performed by the finish rolling mill 3 including seven stands of F _{1 to} F ₇ .
At that time, by the movable welding machine 4 provided on the entrance side of the finish rolling mill 3, the trailing end portion of the preceding sheet bar (hereinafter referred to as the preceding material) A and the following sheet bar (hereinafter referred to as the following material). That is, the tip of B is butt-joined and continuously fed into the finish rolling mill 3, and finish rolling is performed so that desired strip thickness, strip width and material temperature can be obtained.

[0005]

However, in the above continuous hot rolling method, the technique of joining the sheet bars has a certain time limit of the rolling process, so that it is possible to obtain a reliable joining strength. At present, it cannot be said that the joining technology has been established. Therefore, when continuously finishing rolling a preceding material A and a succeeding material B having different sizes (plate thickness, plate width, etc.), steel types, material temperatures, etc., a travel time changing technology (rolling machine roll during rolling) However, there is a problem in that a fracture occurs at the joining point when a technique of changing the set values such as the gap and the roll peripheral speed from the set values of the preceding material to the set values of the following material is applied.

An object of the present invention is to provide a continuous hot rolling method which solves the problems of the prior art as described above.

[0007]

According to the present invention, a sheet bar after rough rolling is rolled by a finishing rolling machine to a preceding sheet bar having a different steel grade, sheet thickness, sheet width and material temperature. In a continuous hot rolling method of joining at one stand entry side and continuously rolling, the finish rolling machine before the joining point of the preceding material and the following material is caught in the first stand or after passing through the final stand. In the continuous hot rolling method, the set value of is changed to the set value of the following material.

Before or after the joining point of the preceding material and the following material is bitten into each stand of the finish rolling mill or after passing through each stand, the setting of the next stand or the immediately preceding stand is sequentially changed. You may do it.

[0009]

[Operation] The present inventors have obtained the following findings as a result of intensive experiments and research to solve the above-mentioned problems. In the joined sheet bar, when a tension (bending force of the plate) of 5 kgf / mm ² or more is applied to the joining point, the sheet breaks due to the tensile stress acting on the plate end portion of the joining point.

That is, in general, in the hot rolling of ordinary steel, the steel is heated and rolled to a low level of deformation resistance of 10 to 30 kgf / mm ² , and therefore the tension applied to the sheet bar is roughly the same.
Maintained and controlled below 10 kgf / mm ² . The reason is that when a tension of 10 kgf / mm ² or more is applied to a hot-rolled steel sheet, the tensile resistance acts on the plate edge due to the low deformation resistance of the steel sheet, and the width increases from the plate edge toward the center in the plate width direction. This is because there is a problem that shrinkage and plate breakage (yield point) occur. (In cold rolling, since the rolling material is rolled without applying heat, the deformation resistance is high and the level of tension applied to the plate is
It is known that it can withstand yielding up to about 40 kgf / mm ² . ) However, at the joining point, the deformation resistance is reduced by 20 to 30% due to further heating and joining of the sheet bar, and it is difficult to join over the entire width due to the time constraint of the rolling process. from problems such that the remaining is 30% of the unbonded portion, to ensure that the large tension does not act directly junction to prevent the plate breaking, i.e. the tension level suppressed to approximately 5 kgf / mm ² or less It was discovered through experiments and research that this is necessary. If the running time is changed after the joining point passes through the final stand of the finishing mill, the tension acting on the joining point can be suppressed to 5 kgf / mm ² or less, so that the plate breakage can be prevented.

FIG. 3 exemplifies the change of running time at the final stand F ₇ of the finish rolling mill. The roll gap setting value during rolling of the preceding material A is 2.2 mm, and the joining point is at time X (F At the time of Y after passing through ( ₇ stands) and a distance of ΔL, the roll reduction position is corrected at a speed of, for example, 2 mm / sec, and the roll gap set value for the trailing material B is set.
As a result of changing the setting to 1.0 mm, the tension acting on the joint is 5 kgf /
It was able to be suppressed to less than mm ² .

It should be noted that the distance ΔL may be any timing as long as it is after the time when the joining point has passed the roll bite, but in the case of the final stand F ₇ , if there is a tracking error or the like if it is about 5 m, Since the tension between the final stand F ₇ and the coiler becomes a value considerably smaller than 5 kgf / mm ² , there is no influence on the joint point. If the trailing material B is thicker than the preceding material A when the incoming plate thickness is greater than that of the trailing material B, or before the joining part enters the first stand of the finishing mill. When the preceding material A is thick, it is possible to prevent the plate from breaking by setting the joining portion after passing through the final stand of the finish rolling mill.

In the joined sheet bars, the thicker the outgoing side plate thickness of each stand and the final stand, the more difficult the tensile or compressive stress generated during rolling is to propagate and accumulate inside the plates. That is, in plate rolling, rectangular slab, when rolling from a sheet bar to a rectangular plate of a predetermined thickness and width,
Since the front and rear ends of the plate are unsteady deformation, it is difficult to form a clean rectangle, and the flare shape tends to be formed as shown in FIG. This non-uniform deformation causes a secondary tensile stress inside the material, and particularly for the joint portion, the joint plate is torn and broken from the plate end portion due to the tensile stress. In other words, the tensile stress caused by the unsteady deformation in the plate joint portion is less likely to propagate and accumulate inside the plate as the plate thickness is larger, and thus plate breakage can be prevented.

From the above, the reason why the running distance is changed before the joining portion enters the first stand of the finishing rolling mill or after passing through the final stand is that the joining portion is either the preceding material A or the following material B. This is because the plate breakage can be prevented by rolling with the plate thickness on the thicker side. Therefore, the preceding material A and the succeeding material B, which are continuously finish-rolled, are now.
Regarding the conditions, the material temperature, the plate width, and the steel type, which are the respective conditions, are the same, and the delivery side plate thickness h _A ≠ h _B is explained. First, the delivery side plate thicknesses h _A and h _B are compared, and h _A
When ≦ h _B , the roll gap setting value is changed to S _A → S _B before the joining point of both materials enters the finish rolling mill. On the other hand, when h _A > h _B , the roll gap value of the finish rolling mill is changed to S _A → S _B when the joining point of both materials passes through the final stand of the finish rolling mill.

In addition, when the predecessor material A enters the finishing rolling mill,
Side plate thickness H_AAnd incoming plate thickness H of trailing material B _BTo compare with
You may That is, H_A≤H_BIn case of, contact of both materials
Roll at the point before the point when the finish rolling mill enters
Gap setting value is S_A→ S_BChange the setting to H_A> H_B
In the case of, the joining point of both materials is the final stand of the finishing mill.
When it comes out, the roll gap value of the finish rolling mill is set to S_A→ S
_BChange the setting to.

Further, the hardness of the preceding material A and the hardness of the following material B are compared.
Then, you may shift the change timing of the set value.
Yes. That is, the hardness of the seat bar depends on its material and pressure.
It is determined by the rolling temperature, which is generally low.
The throat hardness tends to increase. Therefore, the preceding material A and the following material B
Material temperature T_A, T_BAnd compare T_A≤T_BWhen
Since the preceding material A is harder than the following material B,
Set the roll gap setting value before the joining point enters the finishing mill.
S_A→ S_BChange the setting to T_A> T_BIn case of, contact of both materials
Roll when the point passes through the final stand of the finishing mill
Gap value is S _A→ S_BChange the setting to.

As described above, the rolling conditions such as steel type, strip width, rolling temperature and the like may be compared to change the setting of means such as the work roll bender and the rolling position. Table 1 shows an example in which the rolling conditions are compared and the setting change timing is described.
In this table, the rolling conditions to be compared are shown in the upper column with the rolling conditions of the preceding material and in the lower column with the rolling conditions of the subsequent material. Further, the steel type S ₁ has a higher deformation resistance level under the same rolling condition than the steel type S ₂ , and the symbol “−” indicates that the preceding and following materials have the same conditions.

[0018]

[Table 1]

In this table, it means that the rolling conditions for determining the setting change timing can be roughly compared with the strip thickness level and the load level. This is because the plate thickness of the joint becomes thicker, and the crown, width, longitudinal shape change during rolling on the joint is due to the set value of the shape control means at the time of a small load. It is possible to prevent the plate from breaking at the joint for two reasons of the stress.

Further, the timing of changing the setting may be performed before biting into each stand or after passing through each stand. This is because, for example, when the outlet plate thicknesses h _A and h _B are compared and h _A > h _B , the joining point is F ₂
When you reach between F ₂ stand and F ₃ stand after leaving the stand, change the roll gap of F ₁ stand to the setting of the trailing material B, and after leaving the F ₃ stand, set the roll gap of F ₂ stand. Is changed to that of the trailing material B, and conversely, for example, when the outgoing side plate thicknesses h _A and h _B are compared and h _A ≦ h _B , the joining point is F ₆ before being bited into the F ₅ stand. to change the roll gap of the stand and the F ₇ stand on the setting of the following material B.

That is, since the rolling mill sandwiching the joint is rolled without changing the setting, the tension fluctuation due to the change in running time is less likely to occur and the plate thickness of the joint becomes thicker.
Plate breakage is less likely to occur. In addition, such a rolling method of the traveling distance changing technique is preferable because the off-gauge length of the plate is shorter than that in the case of the traveling distance changing technique based on the above-mentioned findings. However, it is difficult to track the joint portion and control the rolling reduction accordingly, and therefore, a considerably higher technique is required for its implementation as compared with the above-mentioned traveling distance changing technique.

[0022]

Embodiments of the present invention will be described in detail below with reference to the drawings. FIG. 1 is a block diagram showing a configuration of a control device of a hot finish rolling mill to which the present invention is applied, and a finish rolling mill 3 includes seven stands F _{1 to} F ₇ . Each stand is composed of a pair of upper and lower work rolls 5 and 5 and backup rolls 6 and 6, and the work rolls 5 and 5 are driven by a roll drive motor 7.

A speed controller 8 and a roll gap controller 9 are attached to each stand, and are controlled by a roll peripheral speed command value V _i and a roll gap command value S _i output from the arithmetic and control unit 10, respectively. . A material thermometer 11 for measuring the material temperature and a first joining point tracking device 12 for tracking and detecting the joining point P between the preceding material A and the following material B are installed on the entrance side of the finish rolling mill 3. A second joint point tracking device 13 is installed on the exit side of the finish rolling mill 3, and these signals are input to the arithmetic and control unit 10. Further, in the arithmetic and control unit 10,
Prior to rolling, various information such as the steel types of the preceding material A and the following material B, rolling speed, strip thickness, strip width, etc. is given from the host computer 14.

Therefore, the arithmetic and control unit 10 uses the material thermometer 11
Using the information such as the measured temperature by the above, the roll peripheral speed setting value and the roll gap setting value for the leading material A and the trailing material B at each stand are calculated in advance, and the first joining point tracking device 12 Alternatively, depending on the tracking detection signal of the joining point P between the preceding material A and the following material B from the second joining point tracking device 13, it is determined whether the joining point P arrives at each stand or the joining point P has passed. Judgment is made and each command value of each stand is changed from the set value of the preceding material A to the set value of the following material B.

Next, an example to which the present invention is applied when performing continuous rolling using the finish rolling mill 3 of the 7 stands F _{1 to} F ₇ configured as described above will be described. Now, for example, the type of steel is general low carbon steel, the rough rolling mill outlet side plate thickness (= finishing rolling mill inlet side plate thickness) is 30 mm, and the preceding material A having a plate width of 1250 mm is finished by the finishing rolling mill 3 to have a finishing plate thickness of 3.0 mm and an outlet side temperature When rolling at 830 ° C, the leading end of the trailing material B at the trailing end is, for example, a general low carbon steel of the general rolling mill with a plate thickness of 30 mm and a plate width of 1250 mm. Finishing and rolling mill 3
Shall be rolled to a finish plate thickness of 2.0 mm and an outlet temperature of 830 ° C.

While the preceding material A is being rolled by the finish rolling mill 3, the temperature of the tip of the following material B is measured, and the arithmetic and control unit 10
When the roll gap setting value and the roll peripheral speed setting value at each stand for the trailing material B were calculated in advance, the results shown in Table 2 were obtained.

[0027]

[Table 2]

Then, when a comparison calculation is performed in the arithmetic and control unit 10, the delivery side plate thickness is h _7A > h _7B , and therefore the roll gap set value of the final stand F ₇ is S _7A >.
Since it was S _7B , it was decided to change the roll gap setting value from S _{7A of the} preceding material A to the setting value S _7B of the following material B when the joining point P passed through the finish rolling mill 3. And
By the tracking function of the second joint point tracking device 13, the joint point P at the time of passing 5 m after passing the finish rolling mill 3 is detected, and the roll gap and roll peripheral speed of each stand are corrected to 2.5 mm / sec. When the running distance was changed at a speed, the tension applied to the joining point P could be suppressed to 5 kgf / mm ² or less.

Here, the tension load applied to the joining point P can be reduced by making the roll gap correction speed of each stand slower than 2.5 mm / sec. However, the important point of the present invention is that the tension acting on the seat bar with respect to the joining point P is 5 kgf / mm.
^Since the setting value of the finishing rolling mill 3 is changed during running so as to keep it to ² or less, the timing for changing the setting and the setting change speed (roll gap correction speed, roll peripheral speed correction speed, etc.) are not specified. Good.

In the above embodiment, the final stand F ₇
The case of comparing the roll gap setting values of the preceding material A and the following material B in the above was described, but the present invention is not limited to this, and the actual measured roll gap for the trailing end portion of the preceding material A is You may make it compare with the roll gap setting value of B. This is a more desirable method since the temperature drop at the rear end portion is generally larger than that at the front end portion, and the roll gap for obtaining the desired plate thickness is narrower than the set calculated value.

Further, in the above embodiment, the roll gap value in the finish setting calculation result is compared and the running distance change point is explained as being delayed (shifted) from the joint point P.
For example, other setting calculation result values generated from the load level such as the roll bender force and the set value of the tension may be compared as an index to be executed. Further, in the above-described embodiment, after passing through the final stand F ₇ , rolling was performed while changing the running distance to the set value of the trailing material B, but the first stand F due to the difference in rolling conditions between the leading material A and the trailing material B. It may be carried out in _one entry side, or specific stand F _i (however, i =. 2 to
The running distance may be changed before or after passing through 6).

[0032]

As described above in detail, according to the present invention, when continuously rolling the sheet bar joined at the entrance side of the finish rolling mill, the finish rolling set value or actual value of the preceding material and the following material Compared with the finish rolling set value of, the running point setting is changed before or after the joining point of both materials enters the finishing rolling mill, so that the tension applied to the joining point can be reduced, This makes it possible to suppress breakage near the joining point in the finish rolling mill.

[Brief description of drawings]

FIG. 1 is a block diagram showing a configuration of a control device of a hot finish rolling mill to which the present invention is applied.

FIG. 2 is a schematic diagram showing a conventional example.

FIG. 3 is a characteristic diagram illustrating a change in running distance according to the present invention.

FIG. 4 is a side view showing a joining point between a preceding material and a following material.

[Explanation of symbols]

1 rough rolling mill 3 finishing rolling mill 4 mobile welding machine 8 speed control device 9 roll gap control device 10 arithmetic control device 11 material thermometer 12 first joining point tracking device 13 second joining point tracking device 14 host computer F _1- F ₇ 1st-7th stand A Leading material B Trailing material

Claims (2)

[Claims] 1. A sheet bar after rough rolling is joined to a preceding sheet bar having different steel grade, sheet thickness, sheet width and material temperature being rolled by a finishing rolling mill at the first stand entry side of the finishing rolling mill. In the continuous hot rolling method of continuously rolling, before the joining point of the preceding material and the following material is caught in the first stand,
Alternatively, the continuous hot rolling method is characterized in that the set value of the finish rolling mill is changed to the set value of the following material after passing through the final stand. 2. The setting change of the next stand or the immediately preceding stand of the stand is sequentially performed before the joining point of the preceding material and the following material is caught in each stand of the finish rolling mill or after passing through each stand. The continuous hot rolling method according to claim 1, which is performed.