KR100328930B1 - The hot rolling method for controlling the thickness and in the top end of strip - Google Patents

Abstract

PURPOSE: A rolling method for preventing thickness and width defects of strip at the front end part of hot rolled strip is provided to minimize strip thickness deviation and strip widthwise deviation at the front end part of the hot rolled strip by appropriately controlling driving of looper for tension control. CONSTITUTION: The rolling method for preventing generation of thickness and width defects of strip at the front end part of hot rolled strip comprises the processes of maintaining angular velocity of looper driving speed control patterns to a certain angle of Wh during the early stage of driving of looper; and decreasing driving speed of the looper when angle of the looper reaches θL so that excessive tension generated on rolled strip during threading is minimized by determining the decrease amount of the angular velocity of the looper by the following expression 1 using the minimum driving speed of the looper WL, reference value of looper angle θL, and marginal portion of the looper angle θmrg.

Description

Rolling method to prevent thickness and plate width defect of hot rolled plate tip part {THE HOT ROLLING METHOD FOR CONTROLLING THE THICKNESS AND IN THE TOP END OF STRIP}

According to the present invention, in a hot finishing mill in which rolling is continuously performed, plate thickness deviation and plate width deviation generated at the tip of the rolling plate are minimized by appropriately controlling the driving of the tension control looper provided between the rolling mills. The present invention relates to a rolling method for preventing thickness and plate width defects from the ends of hot rolled plates.

In general, the hot rolling process proceeds in the order of slab heating → rough rolling → finishing rolling → cooling → winding to produce hot rolled steel sheet.

As shown in FIG. 2A, finishing rolling consists of six to seven rolling mills, which are continuously rolled, and may be said to be the most important process among the hot rolling processes that influence the dimensional accuracy of the rolled sheet.

Typically, a process in which the leading end of the rough rolling is completed and rolled while passing through the first stand of the finishing mill to the final stand is called a mailing process.

Rolling in the mailing process causes a variety of abnormal phenomena compared to the center portion, and the occurrence rate of deviation of plate thickness and plate width is very high.

Therefore, many attempts have been made to increase the error rate of the product through more precise rolling equipment control in the tip portion, that is, the mailing process.

The physical phenomenon that occurs during the customs clearance during hot finishing rolling is described in more detail as follows.

First, the rolled plate is placed on the looper until the rolled plate passing through the stand 1 reaches the stand 2. At this time, the looper serves as a transfer guide of the rolled plate rather than the original purpose of tension control of the rolled plate.

Secondly, when the conveyed rolling plate reaches the second stand, the motor which rotates the rolling mill at the moment of entering the idle idle rolling mill 2 is subjected to a large load, which causes a rapid decrease in the rolling speed of the second stand. (See Figure 3b)

Third, unlike the reduction of the rolling speed of the second stand, the speed of the first stand is kept constant, so that the excess of the rolled plate occurs between the first and second stands, which is called a loop. The more the rolling speed of the second stand decreases, the greater the amount of loops (see Fig. 3a).

Fourth, when 0.1 second has elapsed since the rolled plate is inserted into the second stand, the looper starts to rise from the lowest angle of 6 °. Since the looper is not in contact with the strip at the beginning of the drive due to the excess length of the rolled plate generated by the speed difference between the first and second stands, the looper continues to rise until it comes into contact with the rolled plate. (See Figure 4A)

Fifth, when the rolled plate and the looper come into contact with each other by the rising of the looper, tension is generated in the strip (see FIG. 4B), and the control is performed so that the generated tension and the angle of the raised looper coincide with the reference values.

The tension applied to the rolled plate and the angle of the looper can be adjusted by adjusting the rolling speed of the first stand.

For example, if the angle of the looper is formed higher than the reference value, if the rolling speed of the first stand is reduced while the rolling speed of the second stand remains the same, the surplus rolling plates between the stands generated in the third term will be reduced. If the rolling speed is continuously reduced, the generated tension is increased and the looper is pushed down, thereby reducing the angle of the looper.

The physical phenomenon in the mailing process as described above does not occur only between the first and second stands, but is a rolling phenomenon that occurs equally among all the stands until the rolled plate exits the final stand.

By the way, if the looper is not appropriately raised when contacting the rolling plate in the fifth term, there is a problem that the looper is impacted on the hot plate, resulting in a bad dimension of the rolling plate.

Therefore, in the hot finishing mill, the plate generated at the tip of the rolled plate by minimizing excessive tension generated in the rolled plate by smoothly contacting the rolled plate by appropriately controlling the driving speed of the tension control looper provided between the rolling mills. The purpose is to produce high quality products by reducing thickness variation and plate width deviation.

According to the present invention having the above object, the drive speed control pattern of the looper is maintained at a constant angle at the initial angle of the looper after the angular velocity is ω _{H. When} the angle of the looper reaches θ _L , the driving speed is lowered, but the amount of decrease in the looper angular velocity is decreased. The minimum driving speed ω _L and the reference value of the looper angle θ _ref and the looper angle margin θ _mrg are determined from the following equations to minimize excessive tension generated in the rolled plate during the sheeting process.

1 is a tension change of the rolled plate in the plate shown in normal rolling.

2A is a schematic diagram of a finishing mill as a schematic diagram of a hot rolling facility.

2B is a state diagram showing a drive control system of a looper as a schematic diagram of a hot rolling facility.

Figure 3a is a graph showing a change in the speed of the motor during the plate state diagram showing the speed change of the stand motor No. 1.

Figure 3b is a state diagram showing the change in the speed of the motor during the plate showing the speed change of the second stand motor.

4A is a state diagram showing a change in tension in a rolled plate as a graph showing a change in driving and tension of a looper in a plate.

4B is a state diagram showing a change in tension in a rolled plate as a graph showing a change in driving and tension of a looper in a sheet;

5 is a block diagram implementing looper soft touch control of the present invention.

6 is a conceptual view of a looper angle control of the present invention.

7 is a tension change of the rolled plate of the plate when applying the present invention.

Fig. 8A is a state diagram showing the plate thickness deviation generation amount generated at the time of normal rolling as a tip plate thickness deviation generation chart showing the effect of the present invention.

8B is a state diagram showing the plate thickness deviation occurrence amount of the rolled plate tip portion when the present invention is applied as a tip plate thickness deviation generation chart showing the effect of the present invention.

<Description of the symbols for the main parts of the drawings>

1-7: Stand 1 of Hot Finish Rolling-Stand 7

8-13: Looper No. 1-Looper 6 for hot finishing rolling

14 hot rolled sheet

Fig. 5 shows a block diagram of the looper drive gear system. The portion indicated by the dotted line in FIG. 5 is a soft touch control system proposed in the present invention.

Soft touch system is a system that controls the looper to make smooth contact with the rolling plate by varying the driving speed of the looper according to the driving angle of the looper.

6 illustrates a looper driving speed control pattern input to the soft touch control system of the present invention. The horizontal and vertical axes in FIG. 6 will be described in more detail with reference to the looper driving speed control pattern.

First, in the initial stage of driving the looper, the angular velocity is maintained at a predetermined angle at the looper's driving speed (angular velocity) ω _H shown in Fig. 6, and then the driving speed is lowered when the angle of the looper reaches θ _L.

The reduction amount of the looper angular velocity at this time is determined from the following equation (1) using the minimum drive speed ω _L of the looper, the reference value θ _ref of the looper angle, and the looper angle margin θ _mrg .

The above specification of the looper driving speed control pattern used in the present invention is as follows.

The following is an example of simulation results using actual rolling conditions, that is, an example of the present invention.

1 is a view showing the tension change in the rolled plate generated during the plate when using a conventional looper driving method. At the tip of the rolled plate, that is, when the contact with the looper occurs, the tension is rapidly increased, and after some time, the tension is converged to the reference value.

However, the maximum tension generated is so high that the tension between the 6th and 7th stand is about 42N / mm2 which is about 3 times the reference value 13N / mm2.

On the other hand, the results of applying the looper drive speed control logic of the present invention is shown in FIG. As shown in FIG. 1, after the tension rises sharply at the tip of the rolled plate, it can be seen that the reference tension is controlled after a certain time.

However, as compared with FIG. 1, which is a result of using a conventional method, it can be easily seen that the magnitude of the sudden tension generated at the tip portion is greatly reduced when the looper driving pattern of the present invention is used.

In the case of the present invention, the maximum tension is generated between the 5th and 6th stand, and the magnitude thereof is about 22N / mm2 which is about 1.8 times the reference tension of 12N / mm2.

In general, the rolled plate causes plastic deformation when subjected to excessive force, so plastic deformation may occur in the rolled plate due to instantaneous excessive tension, and thus it may be easily guessed that the plate thickness will be reduced compared to the reference value.

8 is a view showing a change in the longitudinal plate thickness of the plate after rolling through the seven rolling mills, showing the effect of the present invention in comparison with the conventional method.

Fig. 8A shows the change in the plate thickness at the time of using the conventional method, and it can be seen that the thickness of 2.89 mm was reduced by about 40 um compared to the reference thickness of 2.93 mm at about 12.7 seconds due to excessive tension.

On the other hand, looking at Figure 8b as a result of using the present invention it can be seen that the plate thickness at the same position is only reduced to about 15um to the reference thickness of 2.915mm.

In both methods, the tip is thinner than the reference thickness due to excessive tension. However, when using the present invention compared to the conventional method it can be seen that the plate thickness variation is greatly reduced by greatly reducing the maximum generating tension.

In general, since the metal material is isotropic, when excessive tension is applied, not only the plate thickness but also the deformation in the plate width direction will occur at the same time. Therefore, the use of the looper speed control pattern algorithm of the present invention, which can reduce the plate thickness variation, greatly reduces the plate thickness variation and greatly reduces the plate width, thereby greatly improving the error rate of the rolled plate.

In the present invention as described above, in the hot finishing mill in which rolling is continuously performed, by controlling the driving of the tension control looper provided between the rolling mills properly, the tension generated in the rolled plate is minimized, and the plate thickness deviation generated at the leading end of the rolled plate. And plate width variation can be minimized.

Claims (1)

After a driving speed control pattern of the looper maintain a constant angle for the angular velocity is driven beginning of the looper to ω _H, when the angle of the looper reaches θ _L decrease in back looper angular velocity lower the driving speed is the minimum operating speed ω _L of the looper and Prevention of defects in the thickness and plate width of the hot rolled plate tip by minimizing excessive tension generated in the rolled plate during the sheeting process by determining from the following equation (1) using the reference value θ _ref and looper angle margin θ _mrg of the looper angle. Rolling method for.

(However, the specifications of the looper drive speed control pattern used in the present invention in the above formula is as follows.

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