JP3116786B2 - Finishing Temperature Control Method in Finish Rolling of Hot Rolled Steel Strip - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to the final rolling of a finish rolling mill in the finish rolling of a hot-rolled steel strip, and more particularly to a continuous finishing rolling in which a rough rolled material is joined on the entry side of the finishing rolling mill and the finish rolling is continuously performed. The present invention relates to a method for controlling a finishing temperature of a steel strip at a stand exit (hereinafter, referred to as a finish rolling mill exit side).

More specifically, a change in the finishing temperature caused by a change in the product thickness in the continuous finishing rolling (hereinafter referred to as a change in the finishing thickness during running) is prevented, and even if the thickness changes, a predetermined finishing temperature is maintained. To appropriate rolling speed change and steel strip cooling method for obtaining steel.

[0003]

2. Description of the Related Art A conventional method for manufacturing a hot-rolled steel strip has a thickness of 20 mm.
0 to 300mm, weight of 10 to 40ton slab 11
After reheating to 00 to 1250 ° C., a rough rolling step of rolling into a rough rolled material having a thickness of 25 to 50 mm with several rolling mills,
This rough rolled material is thickness 1.2 to 1.2 with a 6 to 7 stand rolling mill.
And a finish rolling step of rolling to a product thickness of 12.5 mm.

Conventionally, in finish rolling, the roll opening and speed of each stand of a finishing mill are set in accordance with the target product dimensions and mechanical characteristics for each rough rolled material. In particular, in order to secure the mechanical properties of the product, it is important to make the temperature of the rolled material (finish temperature) on the exit side of the finish rolling mill appropriate, and the rolled material in the finish rolling mill depends on the product thickness. The rolling speed is determined in consideration of the temperature drop.

[0005] The rolling speed, that is, the peripheral speed of the rolls of each stand of the finishing mill, is associated with the thickness (roll-down schedule) of the entrance and exit of each stand. In addition, as speed parameters that influence the finishing temperature, there are a rolled material speed (finishing speed) on the exit side of the finishing mill and a rolling material speed on the entrance side of the finishing mill.

Normally, given the target thickness and mechanical characteristics of a product, the entrance and exit plate thicknesses of each stand (in consideration of the motor power, load resistance, plate crown and shape characteristics of each stand of the finishing mill). The rolling pass speed) and the finishing rolling speed for securing the finishing temperature are determined, and the roll peripheral speed of each stand is determined from the rolling pass schedule and the finishing speed.

FIG. 4 is a diagram showing an example of a finishing speed and a finishing temperature in a conventional method of finish rolling a rough rolled material one by one.

As shown in FIG. 4, in the conventional method of finish-rolling rough-rolled materials one by one, in order to pass the leading end of the rolled material through a row of finishing mill stands without rolling trouble, it is necessary to secure a finishing temperature. It is necessary to reduce the speed to a required speed or less, and it is inevitable to take a method of accelerating the end of the rolled material to a speed at which the finishing temperature can be secured after passing through the finishing mill. Therefore, especially in a thin hot-rolled steel strip as in the example of FIG.
There was a problem that several hundred meters from the leading end of the rolled material would be lower than the target finishing temperature.

In recent years, a continuous finish rolling method in which a rough rolled material is joined before a finish rolling mill and the rough rolled material is continuously supplied to the finish rolling mill has begun to be adopted.

In this continuous finish rolling method, the first rough rolled material is the same as the conventional rolling method, but after the second roll, there is no restriction on the passing speed of the finishing mill at the leading end of the rolled material,
Finish rolling can be performed at a high rolling speed high enough to secure the finishing temperature, and it is easy to secure the finishing temperature of thin hot rolled steel strip, which was difficult with the above-mentioned conventional method of finishing rolling one rough-rolled material one by one. There is an advantage that you can.

However, this continuous finish rolling method has an advantage in the case where the rolled material having the same product thickness (finish thickness) is continuously rolled as described above, but it is difficult to cope with the case where the product dimensions are different. Met. In the production of hot-rolled steel strip, there is a limit to the number of continuous rolling of the same product dimensions, and in order to maximize the benefits of continuous finishing rolling, finishing continuous rolling is required even when the product dimensions are different. The development of technologies that can be performed is an important issue.

[0012] As a technique for changing the product dimensions, particularly the finish thickness in the continuous finish rolling, there is a document "Development of a running thickness changing system in a hot rolling finish rolling mill" (CAMP-ISIJ, V
ol. 7 (1994), p. As described in 1389), there is a so-called running thickness changing method in which the roll opening of each stand is changed at the timing when the position where the product thickness is to be changed passes through each finishing stand.

[0013]

However, when the above-mentioned method for changing the strip thickness during running is carried out, there is a problem that the temperature drop of the rolled material in the finishing mill changes and the finishing temperature changes. In particular, when the thickness of the product is small, a large change in the finishing temperature occurs even with a slight change in the thickness, making it difficult to secure the mechanical properties of the product.

SUMMARY OF THE INVENTION The present invention has been made in view of the above-mentioned problems of the prior art, and has a small change in the finishing temperature even when the strip thickness is changed during running, and furthermore, a hot-rolling method capable of accurately obtaining a target finishing temperature. An object of the present invention is to provide a method for controlling a finishing temperature in finish rolling of a steel strip.

[0015]

SUMMARY OF THE INVENTION The present invention provides a method of controlling a finishing temperature in a running thickness change in which a finished thickness is changed during finish rolling of a hot-rolled steel strip by a multi-stand finishing mill. The method is characterized in that it is performed in the following procedure.

(1) When the Finished Sheet Thickness is Reduced by Changing the Running Strip Thickness Before the sheet thickness change, the finishing speed is increased to a rolling speed for rolling the rolled material after the sheet thickness change to the target finishing temperature.

At the same time as the speed increase, cooling between stands is started so that the finishing temperature of the rolled material before the change of the sheet thickness does not increase.

After the completion of the speed increase, the thickness change is started.

The cooling between stands on the exit side of the stand where the plate thickness change is started is stopped.

(2) When the Finished Thickness is Increased by Changing the Running Thickness The thickness change is started.

At the same time as the above-mentioned thickness change, the inter-stand cooling on the exit side of the stand from which the thickness change was started is started in order to roll to the target finishing temperature after the thickness change at the finishing speed before the thickness change.

After the thickness change is completed, the speed is reduced to the finishing speed at which the target finishing temperature is reached without cooling between stands.

At the same time as the above-described deceleration, cooling between the stands is stopped.

[0024]

FIG. 3 is a structural diagram showing an example of a 7-stand continuous finishing rolling line.

The continuous finish rolling method will be described with reference to FIG.

The rough rolled material 15 rolled by the rough rolling mill (not shown) is wound up by a coil box (not shown), and then transferred to a rewinding machine 1 installed in a stage preceding the finishing mill 5. While being conveyed and rewound, it is conveyed to the rough rolled material joining machine 2. Here, the rear end of the preceding rough rolled material 15 and the trailing rough rolled material 15
Are supplied to the finishing mill 5 through the edge heater 3 and the cropper 4. The finish-rolled material 16 that has been finish-rolled is cut by a high-speed cutting machine (high-speed shearing machine) 8 and then wound on a down coiler 10. Here, reference numeral 6 indicates a finishing thermometer, 7 and 9 indicate pinch rolls, and F1 to F7 indicate respective stands of the finishing mill 5.

The difference between the continuous finish rolling line and the conventional finish rolling line is that the unwinding machine 1 for joining the rough rolled material.
And the rough rolled material joining machine 2, and the pinch roll 7 and the high-speed cutting machine 8 for cutting the rolled material after finish rolling, the installation position of the coil box is farther from the finish rolling machine 5 than before. It is installed at the position.

The difference between the conventional finish rolling conditions and the continuous finish rolling conditions is the passing speed of the finishing mill at the leading end of the rolled material. In the conventional rolling, the conveying speed from the rough rolling mill to the finishing rolling mill is fast, but the passing speed is regardless of the finishing temperature condition,
At first 700m at the exit speed (finish speed) of finishing mill
pm, and especially in the rolling of thin steel strips, after the completion of threading, it is necessary to secure the finishing temperature and then perform rolling to accelerate the finishing speed to 1000 mpm or more. For this reason, as shown in FIG. 4, the finishing temperature is low at the leading end of the rolled material, and has a temperature pattern that rises with acceleration.

On the other hand, in continuous finish rolling, the conveyance from the unwinding of the rough rolled material to the finish rolling mill depends on the finish rolling speed and is slower than in the conventional rolling. Since there is no such material, it is possible to perform rolling at a finishing speed at which a target finishing temperature is obtained.

By winding the rough rolled material using the coil box, the rough rolled material is uniformly heated, and the temperature non-uniformity due to the skid mark temperature drop shown in FIG. 4 is greatly reduced. Is obtained.

The present inventor has investigated the temperature drop characteristics of the rolled material based on the rolling conditions in these continuous finishing rolling lines, and clarified the finishing temperature change characteristics due to the change in the running thickness in the finish rolling. The knowledge leading to the invention method was obtained.

FIG. 5 is an explanatory diagram showing finishing temperature characteristics in continuous finishing rolling. The rough rolled material thickness is 30 mm, the unwinding temperature is 1100 ° C., and the rolled material from the unwinding to the exit of the finishing mill is not cooled. FIG. 6 is a diagram in which FIG. 5 is further arranged by the rolling material speed on the entrance side of the finishing mill.

As can be seen from FIGS. 5 and 6, continuous finish rolling is characterized in that the finish temperature is determined by the rolling material speed at the entrance to the finish rolling mill irrespective of the finished plate thickness.

The above-mentioned finishing temperature characteristics were analyzed, and the following finishing temperature characteristics in changing the running plate thickness were considered.

(1) When the running speed is changed while keeping the finishing speed the same, when the finished plate thickness is reduced, the speed at the entrance to the finishing mill decreases, and the finishing temperature also decreases.

When the finishing temperature is lower than the target value, the mechanical properties of the product deteriorate. Therefore, when the finishing temperature is lower than the target value, the finishing speed needs to be increased. In order to increase the finishing speed, it is necessary to increase the peripheral speed of the rolls of all stands of the finishing mill.However, since the amount of increase is inversely proportional to the change in sheet thickness, the amount of increase in thin rolling is large, and the mill motor is accelerated. It requires at least 5 to 10 seconds in terms of performance.

Therefore, if the speed is increased simultaneously with the change of the thickness,
The thickness change area becomes longer due to the influence of the speed-up time, and the yield decreases. In addition, the aforementioned document (CAMP-ISIJ,
Vol. 7 (1994), p. As described in 1389), speed control is necessary for mass flow control in changing the thickness, and simultaneous increase in speed leads to deterioration in the accuracy of the mass flow control, and is not a good measure.

(2) When the running speed is changed while keeping the finishing speed the same, when the finished plate thickness is increased, the speed at the entrance to the finishing mill increases, and the finishing temperature rises.

FIG. 7 is a flow diagram of the finishing temperature control device when the running thickness is changed according to the method of the present invention.

With reference to FIG. 7, the procedure of the method of controlling the finishing temperature when changing the sheet thickness during running according to the present invention will be described in detail.

(1) In the case where the sheet thickness is reduced by changing the sheet thickness during running (S-50, YES) The finishing speed at which the target finishing temperature can be secured with the changed finished sheet thickness is obtained in advance, and before the sheet thickness is changed. (S-51, a).

If the finishing speed is increased before the change of the sheet thickness, the finishing temperature of the rolled material before the change increases, so that it is necessary to cool the rolled material in the finishing mill in order to prevent this. In advance, determine the amount of increase in the finishing temperature at the time of speed increase and the rolled material cooling conditions between stands required to offset this, and if the rolled material cooling is started at the same time as the start of speed increase, the finishing temperature should be kept constant. (S-51, b).

If the thickness is changed after the speed increase is completed,
The finishing temperature can be set to the target value under the condition that there is no inter-stand cooling after the change (S-52, a).

However, in the preceding material, since the inter-stand cooling is performed, the timing of stopping the cooling becomes important.
Since the thickness change is performed at multiple stands while tracking the thickness change position from the upstream stand of the finishing mill, the cooling stop timing differs between each stand, and the stand at the stand exit side where the thickness change is completed Only the intercooling is stopped (S-52, b).

(2) In the case where the finished plate thickness is increased by changing the running plate thickness (S-50, NO) Deceleration is performed after the changed plate thickness. This is because if the speed is reduced before the change of the sheet thickness, the finishing temperature of the preceding rolled material decreases (S-53, a) → (S-54, a).

When the sheet thickness is changed without deceleration of the finishing speed, as described above, the finishing inlet speed increases and the finishing temperature also increases, so that the rolled material needs to be cooled. The cooling timing is opposite to the above-described change of the thickness reduction, and the inter-stand cooling at the stand exit side where the thickness change is started is simultaneously performed (S-5).
3, b), the cooling stop timing is performed simultaneously with the start of the finishing speed deceleration (S-54, b).

The cooling between stands is performed by installing a cooling device such as a cooling spray having a sufficient capacity between the stands. However, even if a cooling device is installed on the entrance side of the finishing mill to improve the cooling capacity. Good.

As the refrigerant, it is desirable to use water in consideration of safety, stability, cost, and the effect on the quality of the plate and equipment, but a cooling accelerator such as a surfactant is added to the oil or water. May be used.

As described above, when the running thickness is changed by continuous finishing rolling, the finishing temperature is changed by performing both the finishing speed change and the stand-to-stand rolled material cooling with good timing without using the conventional rolling method. It is possible to set an appropriate value. In particular, in thin rolling, the change amount of the finishing speed is large, and the effect of optimizing the finishing temperature by the method of the present invention is great.

It should be noted that the method of the present invention can be applied not only to continuous finish rolling, but also to changes in the running strip thickness in normal finish rolling, such as producing different product thicknesses within one coil (one rough rolled material). Needless to say.

[0051]

FIG. 1 is a block diagram of a 7-stand finishing mill in a continuous finishing rolling line in which the method of the present invention is carried out. This continuous finish rolling line is the same as that shown in FIG. 3 and the same reference numerals in the figure denote the same equipment.

In FIG. 1, reference numerals 11-i (i = 1 to 1)
7) is a roll gap control device for controlling the thickness of each stand, M is a roll drive motor (mill motor) for each stand, 12-i is a speed control device for the mill motor M, 13
-I is a control valve, and 14-i is a cooling spray between stands. Further, reference numeral 20 denotes a finishing temperature control device for changing the running strip thickness for carrying out the method of the present invention, wherein the logic and control commands shown in FIG.
Is a rolling control device of the finishing mill.

As the rough rolled material in the above-mentioned continuous finishing rolling line, the steel type is low carbon steel, the thickness is 30 mm, and the unwinding temperature is 11
The target finish temperature is 850 to 875 ° C.
The actual finishing rolling operation was carried out.

The cooling between stands is 3000
A cooling spray having a cooling capacity of kcal / m ² h ° C.
-2, F2-3, F3-4, F5-6, F6-
Water cooling was carried out by installing the apparatus in seven spaces.

FIG. 2 is a view showing the change of the plate thickness in the embodiment of the present invention.
It is a figure which shows a finishing speed, the cooling condition between stands, and a finishing temperature control result.

FIG. 2 (a) is a view showing the finish thickness condition which is the exit thickness of the finish rolling mill 5, and the thickness is changed from 2.3 mm to 1.6.
mm → 1.2 mm → 1.6 mm.

FIG. 2B shows that the finishing speed is increased after the thickness change when the running thickness is changed to reduce the thickness, and the finishing speed is changed before the thickness is changed when the running thickness is changed to increase the thickness. Shows the finishing temperature when deceleration is performed.

In this example, the timing of increasing the finishing speed is poor, the temperature of the rolled material before and after the change of the plate thickness is lowered by 40 to 60 ° C., and the mechanical characteristics of the product are deteriorated in the temperature lowered portion. In addition, due to the temperature fluctuation, the rolling load fluctuates, the thickness fluctuates, and the mass flow control by changing the running thickness becomes unstable. Was.

FIG. 2C shows the case where the finishing speed is increased / decreased in accordance with the method of the present invention (no cooling between stands), and there is no decrease in the finishing temperature before and after the change of the plate thickness.
There is a temperature rise of ° C. Although the change in the mechanical properties of the product in this temperature rise region is not so large, a change in sheet thickness due to a change in rolling load is observed, and although the degree of danger is smaller than the case shown in FIG. , May lead to rolling trouble.

FIG. 2D is a diagram showing a change in the finishing speed and a change in the finishing temperature by the inter-stand cooling method in the method of the present invention. The finishing speed change timing is the same as in FIG. 2C, and is a case where inter-stand cooling is performed.

When the rolled material is water-cooled at the cooling timing of the method of the present invention using the above-described cooling device, the temperature rise (fall) before and after the change of the sheet thickness is prevented, and the roll can be rolled to the target finishing temperature. Further, there is an advantage that the thickness variation is small because the temperature variation is small, and the running thickness can be stably changed.

[0062]

According to the method of the present invention, it is possible to prevent a variation in the finishing temperature at the time of changing the strip thickness during running, which occurs when the rolled products having different product thicknesses are continuously finish-rolled. As a result, the mechanical properties of the product before and after the change of the thickness can be secured, and the yield loss can be greatly reduced. Furthermore, a stable change in the running thickness can be achieved by reducing the temperature fluctuation, thereby reducing the rolling trouble and relaxing the schedule restriction of the continuous rolling.

Further, since the degree of freedom in forming the product sheet thickness is increased and the continuous rolling amount is increased, the effect of improving the yield and productivity of the continuous finishing rolling is increased, and the hot-rolled steel strip is significantly reduced. Cost can be reduced.

[Brief description of the drawings]

FIG. 1 shows a continuous finishing rolling line 7 in which the method of the present invention was performed.
It is a block lineblock diagram of a stand finish rolling mill.

FIG. 2 is a diagram showing a change in sheet thickness, a finishing speed, a stand-to-stand cooling condition, and a finishing temperature control result in the example of the present invention.

FIG. 3 is a configuration diagram showing an example of a 7-stand continuous finishing rolling line.

FIG. 4 is a diagram showing an example of a finishing speed and a finishing temperature in a conventional method of finish rolling a rough rolled material one by one.

FIG. 5 is an explanatory diagram showing finishing temperature characteristics in continuous finish rolling.

FIG. 6 is a graph obtained by further arranging FIG. 5 by the rolling material speed on the entrance side of the finishing mill.

FIG. 7 is a flow diagram of a finishing temperature control device at the time of changing a running strip thickness in which the method of the present invention is performed.

[Description of Signs] 1 Rewinding machine (for rough rolled material) 2 Coarse rolled material joining machine 3 Edge heater 4 Cropshah 5 Finishing mill (finishing mill) -F1 to F7 Each stand of finishing mill 5 6 Finishing thermometer 7 Pinch roll 8 High-speed cutting machine during running (High speed shear) 9 Pinch roll (before down-coiler) 10 Down-coiler 11 Roll gap control device 12 Mill motor speed control device 13 Control valve 14 Stand-to-stand cooling spray 15 Coarse rolled material 16 Finish rolled material M roll Drive motor (mill motor) 20 Finishing temperature control device 21 Rolling control device of finishing mill

──────────────────────────────────────────────────続 き Continued on the front page (58) Field surveyed (Int. Cl. ⁷ , DB name) B21B 1/26 B21B 37/00-37/78 B21B 45/02

Claims (1)

(57) [Claims] 1. A method for controlling a finishing temperature at the time of changing a running strip thickness in which a finishing strip thickness is changed during finish rolling of a hot-rolled steel strip by a multi-stand finishing rolling mill, wherein the finishing strip thickness is changed by changing the running strip thickness. When reducing the speed, increase the finishing speed for rolling the rolled material after the thickness change to the target finishing temperature before changing the thickness, start cooling between stands simultaneously with the speed increase, and after completing the speed increase When the thickness change is started, cooling between stands on the exit side of the stand where the thickness change was started is stopped, and when the finished thickness is increased by changing the running thickness, start the thickness change and change the thickness. At the same time, cooling between stands on the exit side of the stand where the plate thickness change was started is started, and after completion of the plate thickness change, the cooling speed between the stands is reduced to the target finishing temperature without cooling between stands, and cooling between stands is stopped at the same time as the deceleration. Finishing temperature in finish rolling of hot rolled steel strip Control method.