JPH10180330A - Plate thickness control method in hot strip mill - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent defective plate thickness in the chip end part and the tail end part of a strip by setting the objective plate thickness smaller than a reference value in the part wherein hardness rapidly becomes large and setting the objective plate thickness larger than the reference value in the part wherein hardness rapidly becomes small in accordance with the variation of hardness in the longitudinal direction of the strip. SOLUTION: The difference Δh between the plate thickness result value (h) and the objective plate thickness ho is calculated with an adder-substracter 33 and the value is outputted to a compensating circuit 34. A reduction position varying quantity ΔS capable of achieving the plate thickness deviation Δh is calculated with the compensating circuit 34 and the value is outputted to a screw down device 2. Therefore, since the reduction position is set so as to rise from a little larger position than the conventional one in the chip end part of the strip 5, the actual plate thickness becomes larger than the reference value in the beginning of the chip end part, but does not exceed the allowable upper limit. Also, since the objective plate thickness is larger than the reference value in this part, the controlled variable becomes smaller and the response delay of control is more reduced than the case when the reference value is objective plate thickness.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a method for controlling the thickness of a hot strip mill.

[0002]

2. Description of the Related Art Conventionally, in hot rolling of strip, automatic thickness control called AGC (Automatic Gauge Control) has been performed in order to reduce thickness variation in the longitudinal direction of a material to be rolled. .

In a general gauge meter system as the AGC, for example, a rolling position (roll opening degree by a rolling device) and a rolling load are measured to calculate the thickness of the delivery side. Feedback control for changing the rolling position by the deviation from the thickness is performed. In this method, if it is assumed that the calculated thickness is equal to the actual thickness and that there is no response delay of the actuator (such as the hydraulic servo of the rolling-down device), the thickness variation in the longitudinal direction of the material to be rolled is limited. It can be reduced without. For this reason, the accuracy of the thickness calculation value is dealt with by increasing the response of the actuator to the response delay by installing a correction circuit or the like. However, setting the response delay to "0" is a physical matter. Impossible.

[0004] Further, the strip introduced into the hot strip mill has a large temperature change in the longitudinal direction at the tip portion, the tail end portion, and the skid portion (the portion in contact with the skid pipe in the heating furnace). The portion has a sharp change in hardness in the longitudinal direction of the strip.

Therefore, for example, in a continuous rolling mill having a plurality of roll stands, the rolling load of the latter stand is changed in the longitudinal direction of the strip based on the results of the former stand, so that the strip at the latter stand is changed. Feed-forward control is performed to compensate for the elastic deformation of. Similarly, a method of estimating the height fluctuation of the hydraulic cylinder of the screw-down device and the amount of AGC response delay at the time of biting of the leading end of the strip from the results of the previous stage stand and correcting them by feedforward control. There is also.

[0006]

However, in the conventional method, since the target value of the thickness is the same in the longitudinal direction of the strip, the hardness in the longitudinal direction such as the leading end portion and the tail end portion of the strip is reduced. In a portion that fluctuates rapidly, the amount of change in the rolling position becomes extremely large, and the thickness of the strip at the leading end or the trailing end may be out of an allowable range, resulting in a defective product due to a response delay of the feedback control.

FIG. 3 is a graph showing an example of the result of controlling the thickness of a conventional gauge meter AGC. These graphs respectively show (a) hardness distribution, (b) fluctuation of the rolling position, and (c) fluctuation of the actual thickness of the strip in the longitudinal direction of the strip.

[0008] The tip of the strip is very hard, and the hardness is rapidly reduced from this point. During this time, the roll-down position is controlled to be rapidly raised (roll opening is increased). However permissible, the actuator response is too late with the control amount is too large, which is set around the reference value T ₀ as, which is the sheet thickness tolerance (target thickness of the portion A shown in FIG. 3 (c) (Between the upper limit _Tu and the allowable lower limit _Td ). Further, since the hardness rapidly increases near the tail end of the strip, the roll-down position is controlled to be rapidly lowered (roll opening is closed). In this case, too, the control amount is too large, and the response of the actuator cannot be made in time. As shown in a portion B in FIG.

The present invention focuses on such a problem of the prior art, and in a method of controlling a thickness of a hot strip mill, a plate at a leading end portion or a trailing end portion of a strip is considered in consideration of a response delay of feedback control. It is an object to prevent a thickness defect.

[0010]

According to a first aspect of the present invention, there is provided a method for controlling a thickness of a hot strip mill, wherein the hardness is rapidly increased in accordance with a change in hardness in a longitudinal direction of the strip. It is characterized in that the target plate thickness is set to be smaller than the reference value in a portion where the target plate thickness is set, and the target plate thickness is set to be larger than the reference value in a portion where the hardness sharply decreases.

According to a second aspect of the present invention, there is provided a method for controlling a thickness of a hot strip mill, wherein the target thickness is set to be larger than a reference value at the leading end of the strip and the target thickness is set to be smaller than the reference value at the tail end of the strip. It is characterized by.

[0012]

Embodiments of the present invention will be described below. FIG. 1 is a schematic configuration diagram showing an apparatus configuration capable of performing a thickness control method corresponding to an embodiment of the present invention.

Here, a hot strip mill 1 for finish rolling is shown, and a pressing-down position detection value S is output from a pressing-down device 2 of the hot strip mill 1 to a sheet thickness actual calculation circuit 31 of a control device 3. It has become so. Also, the work roll 11 of the hot strip mill 1
Is detected by the speed detector 4, and the detected value (rolled roll speed detected value) V is output to the sheet thickness actual calculation circuit 31. Further, the rolling load applied to the strip 5 in the hot strip mill 1 is detected by the load detector 6, and the detected value (rolling load detection value) is detected.
P is output to the board thickness calculation circuit 31.

The rolling position (longitudinal position) of the strip 5 by the hot strip mill 1 is detected by a rolling position detector 7 and the detected value (rolled position detected value) L is calculated by a target thickness calculating circuit of the controller 3. 32.

The sheet thickness actual calculation circuit 31 of the control device 3 calculates the input roll-down position detection value S, rolling roll speed detection value V,
Using the rolling load detection value P and the roll thickness detection value P, the actual thickness value h at the exit side of the hot strip mill 1 is calculated according to a predetermined calculation formula, and the calculated value is output to the adder / subtractor 33. Control device 3
The target thickness calculating circuit 32 calculates the target thickness h ₀ according to the input rolling position detection value L based on the target thickness-rolling position characteristic curve shown in FIG. Is output to the adder / subtractor 33.

Here, the target thickness-rolling position characteristic curve of FIG. 2 (b) is obtained from the tip at which the hardness sharply decreases in accordance with the hardness distribution in the longitudinal direction of the strip shown in FIG. 2 (a). In the part, the target plate thickness is set to be slightly larger than the reference value T ₀ from the beginning, gradually increased from there, and set to return to the reference value T ₀ near the middle point of the hardness decrease. Further, at the tail end portion where the hardness sharply increases, the target plate thickness is set gradually smaller than the reference value T ₀ from near the start point of the hardness increase,
It is set so as to return to the reference value T ₀ near the middle point of the hardness rise.

The adder / subtractor 33 calculates a difference Δh (= h−h ₀ ) between the actual thickness h and the target thickness h _0, and outputs the value to the compensation circuit 34. The compensation circuit 34 calculates the thickness deviation Δh
Is calculated, and the value is output to the screw-down device 2.

Therefore, at the leading end of the strip,
As shown in FIG. 2 (c), the roll-down position (roll opening) is set so as to rise from a position slightly larger than in the past, and as shown in FIG. Is larger than the reference value T ₀ , but the allowable upper limit _Tu
Can not be exceeded. Also, in this section, since the target thickness is greater than the reference value T _0, the reference value T ₀
Is smaller than the target thickness, and the control response delay is also smaller.

Thereafter, from the point where the target sheet thickness returns to the reference value T ₀ , the actual rise in the sheet thickness becomes smaller than the reference value T ₀ due to a delay in control response and the rapid rise of the rolling position cannot be made in time. Since the plate thickness is set to be large, it is possible to prevent the rapidly reduced plate thickness from falling below the allowable lower limit _Td .

Further, at the tail end of the strip, the target thickness is set to be small from the position where the hardness before the strip starts to increase, and as shown in FIG. The beginning of the minute is smaller than the reference value T _0, but can be set not to fall below the allowable lower limit T _d . Also, in this section, since the target thickness is smaller than the reference value T _0, the control amount than the reference value T ₀ is a target thickness is reduced, the response delay of the control is also reduced.

Thereafter, from the point where the target sheet thickness returns to the reference value T ₀ , the result of the sheet thickness sharply increases due to the response delay of the control and the rapid decrease of the rolling-down position cannot be made in time. since that was set small, the thickness results became rapidly increased, it can not exceed the allowable upper limit T _u.

That is, by setting the target plate thickness of the strip at the leading end portion to be larger than the reference value and at the tail end portion to be smaller than the reference value, the control amount becomes smaller than in the conventional case where the target plate thickness is constant. Since the response delay of control in that part is reduced, and the rapid fluctuation of the sheet thickness actual due to the subsequent response delay starts from a larger value at the tip and a smaller value at the tail end, Achievements can be kept within an acceptable range.

In the above-described embodiment, at the leading end of the strip, the target plate thickness is set slightly larger from the beginning, gradually increased from there, and returned to the reference value T ₀ near the middle point of the sharp decrease in hardness. but the timing of returning the target thickness to the reference value T ₀ is not limited to this, it may be within a range of hardness of the tip portion is rapidly decreased. Further, the first may be increased therefrom target thickness as a reference value T _0. Similarly, also at the tail end of the strip, the target thickness is set to the reference value T _0.
The timing of returning to is not limited to the vicinity of the intermediate point of the rapid increase in hardness, but may be within a range where the hardness of the tail end portion is rapidly increasing.

In the above-described embodiment, the target plate thickness is set so as to deviate from the reference value only at the leading end portion and the tail end portion of the strip. Obtain information about the distribution, and based on this, set the target plate thickness to a value smaller than the reference value at the part where the hardness suddenly increases, even in the part other than the leading end and tail end of the strip, The target plate thickness may be set to be larger than the reference value in a portion where the plate thickness becomes smaller. By doing so, it is possible to effectively prevent the thickness defect from occurring over the entire length of the strip.

[0025]

As described above, according to the method of the first aspect, in the portion where the hardness of the strip changes abruptly in the longitudinal direction, the control amount of the thickness control becomes smaller than the conventional one, so that the feedback control is performed. Even if there is a response delay, the plate thickness can be kept within an allowable range, and defective plate thickness can be prevented.

According to the method of the second aspect, the control amount of the thickness control becomes smaller than before at the leading end portion and the tail end portion of the strip where the hardness changes abruptly in the longitudinal direction. Even if there is, the thickness of the strip can be kept within an allowable range, and the thickness of the strip at the leading end and the tail end can be prevented.

[Brief description of the drawings]

FIG. 1 is a schematic configuration diagram showing an apparatus configuration capable of implementing a thickness control method corresponding to an embodiment of the present invention.

FIG. 2 is a graph showing an example of a result of thickness control by a method according to an embodiment, wherein (a) shows a distribution of hardness in a longitudinal direction of a strip, and (b) shows a target plate in a longitudinal direction of the strip. (C) shows the change of the rolling position in the longitudinal direction of the strip, and (d) shows the actual value of the plate thickness in the longitudinal direction of the strip.

3A and 3B are graphs showing an example of a result of thickness control by a conventional gauge meter AGC, wherein FIG. 3A shows a distribution of hardness in a longitudinal direction of a strip, and FIG. (C) shows the actual value of the plate thickness in the longitudinal direction of the strip, respectively.

[Explanation of symbols]

 REFERENCE SIGNS LIST 1 hot strip mill 2 reduction device 3 control device 4 speed detector 5 strip 6 load detector 7 rolling position detector 31 actual thickness calculation circuit 32 target thickness calculation circuit 33 adder / subtractor 34 compensation circuit

Claims (2)

[Claims] 1. According to a change in hardness in the longitudinal direction of a strip, a target thickness is set to be smaller than a reference value in a portion where hardness is sharply increased, and a target thickness is set in a portion where hardness is sharply reduced. Is set to be larger than a reference value. 2. A method for controlling a thickness of a hot strip mill, wherein a target thickness is set to be larger than a reference value at a leading end portion of a strip and a target thickness is set to be smaller than a reference value at a tail end portion of the strip. .