Temperature control device for endless rolling line

In an endless rolling line, a speed of a material to be rolled changes with a flying thickness change. A temperature control device executes predictive calculation of a speed change amount of the material to be rolled associated with the flying thickness change and updates a speed pattern. The temperature control device executes feedforward control of an amount of a coolant to cool the material to be rolled based on a latest speed pattern and a measured temperature value of the material to be rolled in an entry side of the heat exchanger. In parallel with the feedforward control, the temperature control device executes feedback control of coolant volume based on an error between the measured temperature value of the material to be rolled in the delivery side of the heat exchanger and a target value.

FIELD

The present invention relates to a temperature control device for endless rolling line. More particularly, the present invention relates to the temperature control device which is configured to control temperature of a material to be rolled in an endless rolling line.

BACKGROUND

JPH8-300010A discloses a hot rolling device which performs a flying thickness change in which a target plate thickness of a material to be rolled in a delivery side of a mill is changed during rolling, i.e. during flying. The hot rolling device comprises a roughing mill and a finishing mill. A slab rolled by the roughing mill is called as a rough bar and it is rolled in the roughing mill down to a target thickness of the rough bar as an intermediate. The finishing mill continuously rolls the rough bar from the roughing mill and downs plate thickness of the rough bar to a target product thickness. The rough bar rolled by the finishing mill is called as a strip. Since name varies depending on its site, the material to be rolled that spans two or more of the roughing mill, the finishing mill and the delivery side of the finishing mill will be also referred to simply as a “rolling material” in this specification. The flying thickness change is performed by changing the target bar thickness in the roughing mill and/or changing the target (product) thickness in the delivery side of the finishing mill. According to the flying thickness change, a plurality of coils differing in thickness can be manufactured from a single slab.

In recent years, the endless rolling line for manufacturing coils by directly connecting a continuous caster with a hot rolling line has been constructed. In the endless rolling line, it is unnecessary to reheat the slab for rolling in the hot rolling line after the slab cast in the continuous caster is once cooled. Therefore, according to the endless rolling line, it is possible to reduce energy consumption amount involved in manufacturing the coils.

As a technique related to the flying thickness change in the endless rolling line, there is a temperature control device disclosed in JP5733230B. When the plate thicknesses of a preceding material and a succeeding material differ due to the flying thickness change, this temperature control device calculates speed change amount of the rolling material so that an end portion of the succeeding material is kept within a desired temperature range when a head end of the succeeding material is located in the delivery side of the finishing mill. The temperature control device also changes and makes constant speed of the rolling material, based on calculated speed change amount of the rolling material, before a tail end portion of the preceding material passes through the finishing mill. This temperature control device also changes roll gaps of stands of the finishing mill and tension between these stands so that the plate thickness of the rolling material (i.e., succeeding material) after the flying thickness change is of the desired thickness. According to such the temperature control, it become possible to control the temperature of the succeeding material within a permissible range.

However, in the temperature control, the roll gaps of the stands of the finishing mill and the tension between these stands are changed based on predictions executed before the flying thickness change. According to the temperature control, it become possible to keep the speed of the rolling material in the delivery side of the finishing mill constant when the tail end portion of the preceding material passes through the finishing mill. However, in the endless rolling line, casting speed of the continuous caster is dominant and it is difficult to change the speed of the rolling material to a desired rate. Therefore, when considering even such the constraint on speed change, the temperature control is insufficient and there is room for improvement.

Another technique related to the flying thickness change in the endless rolling line is the temperature control device disclosed in JP2010-529907A. The temperature control device detects or presets the casting speed or mass flow (multiplication of plate thickness and casting speed) of the slab and controls strip temperature in the delivery side of the finishing mill in view of change in the casting speed or the mass flow. However, this temperature control is not a control that incorporates speed change of the roughing mill and/or that of the delivery side of the finishing mill associated with the flying thickness change into speed pattern. For this reason, countermeasures against the speed change of the rolling material changes associated with the flying thickness change are inadequate and there is room for improvement.

CITATION LIST

Patent Literature

SUMMARY

Technical Problem

The present invention has been made to solve the problems mentioned above, and an object of the present invention is to provide the temperature control device in which controllability of temperature of the rolling material is enhanced when the flying thickness change of the rolling material is performed in the endless rolling line.

Solution to Problem

In order to achieve the object mentioned above, the present invention is a temperature control device for endless rolling line which is configured to control temperature of a material to be rolled to in an endless rolling line in which a continuous caster is directly connected with a hot rolling line.

The endless rolling line comprising:

a heating furnace which is configured to heat the material to be rolled extracted from the continuous caster;

a mill which is configured to roll the material to be rolled extracted from the heating furnace with a plurality of stands;

a heat exchanger which is disposed downstream of the mill and/or between the stands of the mill, and is configured to exchange heat with at least one of the material to be rolled after rolling by the mill and the material to be rolled during rolling by the mill;

a delivery-side thermometer which is disposed downstream of the heat exchanger; and

an entry-side thermometer which is disposed upstream of the heat exchanger.

The temperature control device is further configured to:

calculate a plate thickness schedule which defines stand delivery-side target plate thicknesses which are target values of the material to be rolled in each delivery side of the stands based on an operation instruction including a target plate length which is a target value of plate length of the material to be rolled, a mill delivery-side target plate thickness which is the target value of plate thickness of the material to be rolled in the delivery side of the mill, and a target temperature which is a target value of temperature of the material to be rolled when it passes through a position where the delivery-side thermometer is disposed;

execute predictive calculation of speed change amount of the material to be rolled in each delivery side of the stands that changes when the mill delivery-side target plate thickness is changed based on the plate thickness schedule and the speed of material to be rolled in each delivery side of the stands;

create a speed patter on the material to be rolled based on the speed change amount;

execute feedforward control of heat exchanging amount based on the latest speed pattern of the material to be rolled and a measured temperature value from the entry-side thermometer; and

execute feedback control of the heat exchanging amount based on an error between the measured temperature value from the delivery-side thermometer and the target temperature.

The temperature control device is further configured to:

create the speed pattern of a preceding material at which a head end portion of the preceding material is extracted from the heating furnace;

execute first update of the speed pattern of the preceding material at which the head end portion of the preceding material reaches the mill;

execute second update of the speed pattern of the preceding material and create the speed pattern of a succeeding material at which the head end portion of the succeeding material is extracted from the heating furnace; and

execute third update of the speed pattern of the preceding material and update of the speed pattern of the succeeding material at which the head end portion of the succeeding material reaches the mill.

The temperature control device may be further configured to:

calculate, based on the operation instruction, a plate thickness changing time as time required to change the plate thickness of the material to be rolled in the delivery side of the mill when the mill delivery-side target plate thickness is changed;

calculate speed change rate of the material to be rolled in each delivery side of the stands in case of changing the mill delivery-side target plate thickness by dividing the speed change amount by the plate thickness changing time; and

if the speed change rate of the stand is outside a permissible range, change the stand delivery-side target plate thickness of the same stand.

The temperature control device may be further configured to:

calculate rolling reduction rate of each stand in case of changing the mill delivery-side target plate thickness; and

if the rolling reduction rate of the stand is outside the permissible range, change the stand delivery-side target plate thickness of the same stand.

Advantageous Effects of Invention

According to the present invention, it is possible to execute predictive calculation of the speed change amount of the material to be rolled accompanied by the flying thickness change, to create or update the speed pattern based on this speed change amount, and to execute feedforward control and feedback control of the heat exchanging amount in the heat exchanger. Therefore, it is possible to control with a high degree of accuracy the temperatures of the preceding material and the succeeding material in the delivery side of the mill within the permissible range.

DESCRIPTION OF EMBODIMENTS

Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. Note that, even when the embodiments below mention about a value such as number, quantity, amount and range, the present invention is not limited by the referred values unless the value is explicitly referred in the present invention or clearly specified to the value in principle. In addition, the configuration and the steps of the embodiments below are not essential to the present invention unless explicitly referred in the embodiments or clearly specified to the configuration in principle.

First Embodiment

FIG. 1is a diagram for illustrating an exemplary configuration of an endless rolling line to which a temperature control device according to an embodiment of a first embodiment of the present invention is applied.

The endless rolling line shown inFIG. 1comprises a continuous caster10, a heating furnace12, a roughing mill14, a finishing mill16, a coiler entry-side shear18and a coiler20as main facilities.

The continuous caster10continuously casts slabs. The heating furnace12heats the slab extracted from the continuous caster10and sends it to the roughing mill14. The roughing mill14usually includes two to four stands (a first stand R1to a third stand R3inFIG. 1). The roughing mill14rolls the slab from the heating furnace12by its stands. In a delivery side of the roughing mill14, the rolled slab is referred to as a rough bar and is rolled down with the roughing mill until a rough bar thickness to a target.

The rough bar rolled by the roughing mill14is sent to the finishing mill16. The finishing mill16usually includes five to seven stands (a first stand F1to fifth stand F5inFIG. 1). The finishing mill16further rolls the rough bar from the roughing mill14by its stands. In the delivery side of the finishing mill16, the rolled rough bar is called a strip and is reduced by the finishing mill to a target plate thickness (a product thickness) of the strip.

The strip rolled by the finishing mill16is sent to the coiler20. The coiler20winds the strip from the finishing mill16into a coil. In the endless rolling, the coiler entry-side shear18cuts the strip around a plate thickness change to produce a plurality of coils from a successively cast slab. As shown inFIG. 1, the coiler20includes at least two. For example, when the strip located downstream of a cut point (coiler side) (hereinafter also referred to as a “preceding material”) is wound by the coiler20on a frontward-side (i.e., a side remote from the finishing mill16), the strip located upstream of the cut point (mill side) (hereinafter also referred to as a “succeeding material”) will be wound by the coiler20on a rearward-side (i.e., a side close to the finishing mill16). During the strip is wound by the coiler20on the rearward-side, the coil wound by the coiler20on the frontward-side is dispensed and the coiler20on the frontward-side prepares for winding after a subsequent cut.

The endless rolling line shown inFIG. 1measures temperature of the rolling material at various points for stable rolling and material management of products. A roughing mill delivery-side thermometer22measures temperature of the rough bar in the delivery side of the roughing mill14. A finishing mill entry-side thermometer24measures the temperature of the rough bar in the entry side of the finishing mill16. A finishing mill delivery-side thermometer26measures the temperature of the strip in the delivery side of the finishing mill16. A coiler entry-side thermometer28measures the temperature of the strip upstream of the coiler20. The temperatures of the rolling material measured at various points are used as inputs of temperature control executed by a temperature control device.

The endless rolling line comprises a heat exchanger30and coolers32and34as actuators operated in accordance with the temperature control. The heat exchanger30heats or cools the rough bar. The heat exchanger30heats the rough bar, for example by induction heating, but may also heat the rough bar by combustion heat of fuels. The heat exchanger30cools the rolling material, for example, with coolant from spray nozzles. Upon cooling, a heat insulating cover for controlling falling amount of the temperature of the rough bar may be used as appropriate. The cooler32is provided between two adjacent stands in the finishing mill16. The cooler32cools the strip, for example, with the coolant from the spray nozzles. The cooler34cools the strip, for example, with the coolant from laminar nozzles.

<Explanation of Operation in Endless Rolling Line>

A basic operation in the endless rolling line will be explained. In a successive rolling, a plurality of coils which differ in plate thickness are produced from a single slab. Specifically, roll gaps of the stands of the roughing mill14and the finishing mill16are changed during the rolling of the rolling material. At the same time, tensions between these stands are changed. In this way, the bar thickness in the delivery side of the roughing mill14and the plate thickness in the delivery side of the finishing mill16are changed. A cutting position is determined in advance from a target plate length or the like prior to the rolling, and when the cutting position arrives at the coiler entry-side shear18, the strip is cut. The cutting of the strip is performed around a plate thickness change part in order to reduce a yield as much as possible. In this way, the coil from the preceding material and the coil from the succeeding material that differs from the preceding material in the plate thickness are manufactured.

In the endless rolling line, the single slab extracted from the continuous caster10is sent to the rolling line. Therefore, speed of the slab in the entry side of the roughing mill14is governed by manufacturing speed (i.e., casting speed) of the slab in the continuous caster10. If the casting speed is constant, the speed of the rolling material in the stand delivery side changes in accompany with the flying thickness change. This change in speed of the rolling material results in temperature control disturbances.

FIG. 2is a block diagram for illustrating the exemplary configuration of the temperature control device according to the first embodiment of the present invention. The temperature control device shown inFIG. 2includes a setting calculation function40, a temperature control function42, a gap change function44, a speed control function46and a tracking function48as main functions.

The setting calculation function40is a function to determine a plate thickness changing point based on a plate thickness of the preceding material and a target plate length of the preceding material. The setting calculation function40includes as low-order functions a flying thickness change amount determination function40a, a speed change amount calculation function40band a speed pattern create function40c.

The flying thickness change amount determination function40ais a function to calculate the plate thickness schedule and plate thickness changing time based on an operation instruction50. In the plate thickness schedule, target values of the plate thickness of the rolling material in the delivery side of the stands are set per stand. The plate thickness changing time is a period in which the plate thickness corresponding to the target plate thickness of the preceding material is changed to the plate thickness corresponding to the target plate thickness of the succeeding material. The plate thickness changing time is calculated based on at least one of the plate thickness target value of the succeeding material in the delivery side of the finishing mill and the plate thickness change amount of the strip in the finishing delivery side of the mill (i.e., a difference between the product plate thicknesses of the preceding material and the succeeding material). That is, the plate thickness changing time is calculated based on the plate thickness schedule.

The speed change amount calculation function40bis a function to execute predictive calculation of the speed change amount of the rolling material associated with the flying thickness change. The speed change amount is calculated based on the plate thickness schedule of the succeeding material, the plate thickness schedule of the preceding material, and the speed of the rolling material in each delivery side of the stands. The detail of the speed change amount calculation function40bwill be described later.

The speed pattern create function40cis a function to create or update the speed pattern of the rolling material based on the speed change amount. The detail of the speed pattern create function40cwill be described later.

The temperature control function42includes as the low-order function an initial output determination function42a, a feedforward control function42b, and a feedback control function42c.

The initial output determination function42ais a function to determine an initial flow amount of the coolant supplied from the coolers32and34based on latest speed pattern received from the setting calculation function40.

The feedforward control function42bis a function to determine a flow amount of the coolant from the cooler32based on a measured temperature value52received from the finishing mill entry-side thermometer24and the latest speed pattern. The feedforward control function42bis also a function to determine the flow amount of the coolant from the cooler34based on the measured temperature value52received from the finishing mill delivery-side thermometer26and the latest speed pattern.

The feedback control function42cis a function to change the flow amount of the coolant from the cooler32so as to correct an error between the measured temperature value52received from the finishing mill delivery-side temperature meter26and a target temperature. The feedback control function42cis also a function to change the flow amount of the coolant from the cooler34so as to correct the error between the measured temperature value52received from the coiler entry-side thermometer28and the target temperature.

The gap change function44is a function to change each roll gap of the stands at timings instructed by the tracking function48based on each plate thickness change amount at the stands (i.e., the difference between a present target value and a next target value of the plate thickness of the rolling material set per stand) that is received from the setting calculation function40.

The speed control function46is a function to adjust each rolling speed of the stands. When the roll gap of the stand is changed by the gap change function44, the speed control function46adjusts the rolling speed of the same stand to keep tensions between the stands approximately constant.

The tracking function48is a function to track the plate thickness changing point and to activate the setting calculation function40, temperature control function42and gap change function44at appropriate timings.

The operation instruction50includes at least a product dimension of the preceding material and the succeeding material (i.e., plate thickness, plate width and plate length). The operation instruction50includes target values of the temperature of the rolling material at various points in the hot rolling line (i.e., the target values of the finishing mill entry-side temperature, the finishing mill delivery-side temperature and the coiler approach temperature).

<Temperature Change of Rolling Material Associated with Flying Thickness Change>

As mentioned above, in the endless rolling line, the speed of the slab in the entry side of the roughing mill is governed by the casting speed. Thus, if the casting speed does not change, the speed of the slab in the entry side of the roughing mill is constant. If the casting speed is unchanged, the speed of the rolling material rolled in the mill is governed by the mass flow constant regulation established between the stands. That is, under a casting speed constant condition, when the plate thickness of the rolling material is reduced by a certain stand, the speed of the rolling material in the delivery side of the same stand becomes larger than the speed in the entry side of the same stand.

For example, consider a case where each rolling reduction rate of the stands of the finishing mill is changed in a sequential order to change the plate thickness of the strip (i.e., the product thickness) in the delivery side of the final stand of the finishing mill.

The rolling reduction rate is defined by the following equation (1).
r(i)=(H(i)−h(i))/H(i)  (1)
r(i): the rolling reduction rate of the stand i (1≤i≤n)
H(i): the plate thickness of the rolling material in the entry side of the stand i
h(i): the plate thickness of the rolling material in the delivery side of the stand i

According to the mass flow constant regulation, when the rolling reduction rate of the stand i changes, the speed of the rolling material in the delivery side of the stand i changes. Since the speed of the delivery side of the stand i and that of the entry side of an adjacent stand i+1 which is located in a downstream of the stand i need to be synchronized, the speed of the rolling material in the entry side of the adjacent stand i+1 changes as well as the speed of the rolling material in the delivery side of the stand i. Furthermore, the speed of the rolling material in the delivery side of adjacent stand i+1 will also change. As a result, the speed of the rolling material in the delivery side of the finishing mill changes gradually as the speed of the rolling material changes in the respective stand.

Referring toFIGS. 3 to 4, it will be specifically described that the speed of the strip in the delivery side of the finishing mill changes gradually with the change of the speed of the rough bar in the respective stand of the finishing mill.FIG. 3is a diagram for explaining movement condition of the plate thickness changing point during rolling. As shown inFIG. 3, at Timing1, the plate thickness changing point54locates at the first stand F1. At Timing2, the plate thickness changing point54has moved to the delivery side of the fifth stand F5. At Timing3, the plate thickness changing point54has moved to just under the toiler entry-side thermometer28.

At the Timing1, the roll gap is narrowed in order to reduce the plate thickness of the rough bar in the delivery side of the first stand F1. Similarly, in order to reduce the plate thickness of the rolling material in each delivery side of the second stand F2to the fifth stand F5, each roll gap of the stands is narrowed. Each roll gap of the stands is changed at each timing when the plate thickness changing point54is moved to each position of the second stand F2to the fifth stand F5.FIG. 4shows the speed of the rolling material in each delivery side of the stands when such the rolling is performed. The vertical axis ofFIG. 4represents the speed of the rolling material in each delivery side of the stands of the finishing mill.

As shown inFIG. 4, when the roll gap of the first stand F1is narrowed at the Timing1, each speed of the rolling material in the delivery side of the second stand F2to the fifth stand F5increases with mass flow constant regulation, and then becomes constant. Further, when each roll gap of the stands is narrowed at respective timings when the plate thickness changing point54has moved to each position of the stands, the speeds of the rolling material in the delivery sides of the stand which narrows its roll gap and the stand located downstream of the narrowing stand show the same behavior as the behavior after the Timing1. For example, if the roll gap of the stand is narrowed at Timing1.3when the plate thickness changing point54locates at the third stand F3, the speed of the rolling material in the delivery side of the third stand F3to the fifth stand F5becomes fast and thereafter, either speeds become constant.

As described above, since the plate thickness and the speed of the rolling material are gradually changed, the temperature of the strip in the delivery side of the final stand is changed in a complicated manner. If the rolling reduction rate of the stand is changed to increase, as well as the change in the speed, processing heat associated with change in shape and frictional heat generated between the rolls and the rolling material are increased, thereby the temperature of the rolling material is increased. On the other hand, if the plate thickness of the rolling material decreases, surface area of the rolling material increases, so that the temperature of the rolling material tends to decrease. As just described, the temperatures of the rolling material changes in the complex manner.

<Problems Associated with Flying Thickness Change>

FIG. 5is a diagram for explaining problems when the plate thickness and the speed of the rolling material are gradually changed. The CT (Coiling Thermometer) measured value shown inFIG. 5represents a measured temperature value from the coiler entry-side thermometer28shown inFIG. 1. The CT measured value increases because cooldown time is mainly shortened due to the increase of the speed of the rolling material in the delivery side of the final stand F5. If the feedback control is executed to increase the flow amount of the coolant, the target temperature can be achieved. However, the temperature decreases at the timing when the coolant passes through the coiler entry-side thermometer28. This is because since the plate thickness becomes thin downstream of the plate thickness changing point, the temperature is easy to decreased whereas the flow amount of the coolant is increased to cool excessively due to a feedback control output.

The plate thickness just under CT shown inFIG. 5represents the plate thickness of the strip just under the coiler entry-side thermometer28. As described inFIGS. 3 to 4, at Timing1, the plate thickness changing point is at the first stand F1. Therefore, at the Timing1, the plate thickness just under CT is still in the same plate thickness as that before the change (the plate thickness of the preceding material). The plate thickness just under CT changes at the Timing3when the plate thickness changing point passes just under the coiler entry-side thermometer28.

The speed just under CT shown inFIG. 5represents the speed of the strip just under the coiler entry-side thermometer28. As described with reference toFIG. 4, the speed of the strip in the delivery side of the fifth stand F5increases gradually at the timing when each roll gap of the stands is narrowed. And, the coiler entry-side thermometer28locates downstream of the finishing mill16. Therefore, the speed just under CT increases gradually from the Timing1to the Timing2, as does the speed of the strip in the delivery side of the fifth stand F5.

The Total flow amount shown inFIG. 5represents a total flow amount of the coolant from the cooler34shown inFIG. 1. Total flow amount reflects a correcting flow amount, i.e., the FB flow amount, based on the feedback control based on the error between the target temperature of the strip just under the coiler entry-side thermometer28and the CT measured value. In the example shown inFIG. 5, the FB flow amount is increased as the CT measured value increases after the Timing1, thereby the Total flow amount is increased. However, there is a possibility that the increase in CT measured value is unable to suppress because the feedback control is delayed. Actually, in the case shown inFIG. 5, the CT measured value exceeds an upper limit immediately after the Timing1.

Further, in the example shown inFIG. 5, the feedforward control of the flow amount of the coolant from the cooler34is executed in parallel with the feedback control mentioned above. InFIG. 5, since the plate thickness is reduced by the flying thickness change, the Total flow amount is changed from the Timing2to the Timing3by the execution of the feedforward control.

The feedforward control is started at a timing when the plate thickness changing point is approaching the cooler34(more specifically, at a timing slightly later than the Timing2). Therefore, the Total flow amount decreases after this timing. Before this timing, however, the feedback control has been executed. Therefore, there is a possibility that the CT measured value is greatly lowered because it is strongly affected by the FB flow amount. Actually, in the case shown inFIG. 5, the CT measured value exceeds a lower limit before and after the Timing3.

<Features of Temperature Control in First Embodiment>

Therefore, in the temperature control device according to the first embodiment, the temperature control described below is executed by using the configuration shown inFIG. 2. This temperature control will be described with reference toFIGS. 6 to 8.FIG. 6is a flow chart for explaining exemplary processing when the temperature control device according to the first embodiment of the present invention executes an operation related to the flying thickness change.FIGS. 7 and 8are diagrams for showing the movement condition of the rolling material at respective timings explained inFIG. 6. InFIGS. 6 to 8, it is assumed that a preceding material60and a succeeding material62are present in a single rolling material, and the target plate thicknesses in the delivery side of the finishing mill16differ in each other.

As shown inFIG. 6, the temperature control device first executes setting calculation of the preceding material60at the timing when the preceding material60is extracted from the heating furnace12(see Timing6.1inFIG. 7) (step S10). Specifically, the temperature control device calculates the plate thickness schedule and the plate thickness changing time of the preceding material60by the flying thickness change amount determination function. The temperature control device also calculates, based on the plate thickness schedule, the speed change amount by the speed change amount calculation function. Then, the temperature control device creates, based on the speed change amount, the speed pattern of the preceding material60by the speed pattern create function.

Subsequent to the step S10, the temperature control device executes the setting calculation of the preceding material60at the timing when the head end portion60aof the preceding material60reaches the finishing mill entry-side thermometer24(see Timing6.2inFIG. 7) (step S12). Specifically, the temperature control device calculates the plate thickness schedule and the plate thickness changing time of the preceding material60by the flying thickness change amount determination function. The temperature control device also calculates, based on the plate thickness schedule, the speed change amount by speed change amount calculation function. Then, the temperature control device updates, based on the speed change amount, the speed pattern of the preceding material60by the speed pattern create function (a first update).

In addition, the temperature control device determines an initial flow amount by the initial output determination function based on the speed pattern of the first updating preceding material60. The initial flow amount is an initial value of the flow amount of the coolant supplied from the cooler32and34to cool the preceding material60. Then, the temperature control device starts to execute the feedforward control of the amount of the coolant supplied from the cooler32and34by the feedforward control function based on the initial flow amount.

Subsequent to the step S12, the temperature control device executes the setting calculation of the succeeding material62at the timing when the succeeding material62is extracted from the heating furnace12(see Timing6.3inFIG. 7) (step S14). If the target plate thicknesses in the delivery side of the roughing mill14differ between the preceding material60and the succeeding material62, the temperature control device calculates the plate thickness schedule and the plate thickness changing time of the succeeding material62by the flying thickness change amount determination function. The temperature control device also calculates the speed change amount by speed change amount calculation function based on the plate thickness schedule. Then, the temperature control device creates the speed pattern of the succeeding material62by the speed pattern create function based on the speed change amount and updates the speed pattern of the preceding material60(second update).

The temperature control device also continues to execute the feedforward control of the amount of the coolant supplied from the cooler32by the feedforward control function based on the speed pattern of the second updating preceding material60and the measured temperature value from the finishing mill entry-side thermometer24. In addition, the temperature control device continues to execute the feedforward control of the amount of the coolant supplied from the cooler34by the feedforward control function based on the updated speed pattern of the preceding material60and the measured temperature value from the finishing mill delivery-side thermometer26.

Subsequent to the step S14, the temperature control device starts the flying thickness change in the roughing mill at the timing when the head end portion62aof the succeeding material62reaches the entry side of the first stand R1(see Timing6.4inFIG. 7) (step S16). Specifically, the temperature control device changes the roll gap of the first stand R1by the gap change function based on the plate thickness schedule of the succeeding material62. The same processing executed in the step S16is also executed at respective timings when the head end portion62areaches each entry side of the second stand R2and the third stand R3.

In addition, the temperature control device adjusts each rolling speed of stands by the speed control function at respective timing when the roll gaps of the first stand R1to the third stand R3are changed. However, the changes in the speed of the rolling material associated with the adjustments of this rolling speed have been considered in the updating of the speed pattern of the preceding material60by the speed pattern create function and in the feedforward control executed based on the same speed pattern. That is, the feedforward control is executed while anticipating the temperature change of the rolling material due to the adjustment of the rolling speed by the speed control function.

If the target plate thickness in the delivery side of the roughing mill14does not change between the preceding material60and the succeeding material62, the processing of the steps S14and S16are not executed.

Subsequent to the step S16, the temperature control device executes the setting calculation of the succeeding material62at the timing when the head end portion62areaches the finishing mill entry-side thermometer24(see Timing6.5inFIG. 8) (step S18). Specifically, the temperature control device calculates the plate thickness schedule and the plate thickness changing time of the succeeding material62by the flying thickness change amount determination function. The temperature control device also calculates the speed change amount by the speed change amount calculation function based on the plate thickness schedule. Then, the temperature control device updates the speed pattern of the preceding material60by the speed pattern create function based on the speed change amount (a third update), and updates the speed pattern of the succeeding material62.

In addition, the temperature control device continues to execute the feedforward control of the amount of the coolant supplied from the cooler34by the feedforward control function based on the speed pattern of the third updating preceding material60and the measured temperature value from the finishing mill delivery-side thermometer26. In addition, the temperature control device determines the initial flow amount by the initial output determination function based on the updated speed pattern of the succeeding material62. The initial flow amount is the initial value of the flow amount of the coolant supplied from the cooler32to cool the succeeding material62. Then, the temperature control device starts to execute the feedforward control of the amount of the coolant supplied from the cooler32by the feedforward control function based on the initial flow amount.

Subsequent to the step S18, the temperature control device starts the flying thickness change in the finishing mill at the timing when the head end portion62areaches the entry side of the first stand F1of the finishing mill16(see Timing6.6inFIG. 8) (step S20). Specifically, the temperature control device changes the roll gap of the first stand F1by the gap change function based on the plate thickness schedule of the succeeding material62in the finishing mill16. The same processing executed in the step S20is also executed at respective timings when the head end portion62areaches each entry side of the second stand F2to the fifth stand F5.

In addition, the temperature control device adjusts by the speed control function each rolling speed of the stands at each timing when the roll gaps of the first stand F1to the fifth stand F5are changed. However, the changes in the speed of the rolling material associated with the adjustment of the rolling speed have been considered in the updating of the speed patterns of the preceding material60and the succeeding material62by the speed pattern create function and in the feedforward control based on these speed patterns. That is, the feedforward control is executed while anticipating the temperature change of the rolling material due to the adjustment of the rolling speed by the speed control function.

Subsequent to the step S20, the temperature control device determines the initial flow amount by the initial output determination function based on the speed pattern of the latest succeeding material62at the timing to reach the finishing mill delivery-side thermometer26(see Timing6.7inFIG. 8) (step S22). The initial flow amount is the initial value of the flow amount of the coolant supplied from the cooler34to cool the succeeding material62. Then, the temperature control device starts to execute the feedforward control of the amount of the coolant supplied from the cooler34by the feedforward control function based on the initial flow amount.

Note that the temperature control device executes the feedback control by the feedback control function during the steps S10to S22. Specifically, the temperature control device executes the feedback control by the feedback control function based on the error between the measured temperature value from the finishing mill delivery-side temperature meter26and its target value. The temperature control device also executes the feedback control by the feedback control function based on the error between the measured temperature value from the coiler entry-side thermometer28and its target value. The measured temperature value from the finishing mill delivery-side thermometer26may be disturbed as the plate thickness changing point passes just under the finishing mill delivery-side thermometer26. The same applies to the measured temperature value from the coiler entry-side thermometer28. In such cases, the temperature control device temporarily holds the feedback output to keep the flow amount of the coolant from the cooler32or34constant.

<Speed Change Amount Calculation Function>

Next, a predictive calculation method of the speed change amount by the speed change amount calculation function will be described.

The mass flow constant regulation prior to the flying thickness change is expressed by the following equation (2).
v(E)h(E)=v(0)Ah(0)A= . . . =v(i)Ah(i)A=v(i+1)Ah(i+1)A= . . . =v(n)Ah(n)A(2)
v(E): the casting speed [m/s]
h(E): the plate thickness of the slab [m]
v(i)A: the speed of the rolling material in the delivery side of the stand i [m/s]
h(i)A: the plate thickness of the rolling material in the delivery side of the stand i [m]
v(n)A: the speed of the strip in the delivery side of the final stand n [m/s]
h(n)A: the plate thickness of the strip in the delivery side of the final stand n [m]

The mass flow constant regulation after the flying thickness change is completed in all of the stands is expressed by the following equation (3).
v(E)h(E)=v(0)Bh(0)B= . . . =v(i)Bh(i)B=v(i+1)Bh(i+1)B= . . . =v(n)Bh(n)B(3)
v(i)B: the speed of the rolling material in the delivery side of the stand i [m/s]
h(i)B: the plate thickness of the rolling material in the delivery side of the stand i [m]
v(n)B: the speed of the strip in the delivery side of the final stand n [m/s]
h(n)B: the plate thickness of the strip in the delivery side of the final stand n [m]

The casting speed remains unchanged before and after the flying thickness change. Therefore, the following relationships (4) and (5) are derived from the equations (2) and (3).
v(n)Ah(n)A=v(n)Bh(n)B=v(i)Bh(i)B(4)
⇔(v(i)B/h(n)A)=(v(n)A/h(i)B)  (5)

After the completion of the flying thickness change at a stand j (i≤j≤n), and in a situation where the plate thickness changing point locates between the stand j and a stand j+1, the speed of the rolling material in the entry side of the stand j+1 changes from v(j)Ato v(j)B in accompany with the change of the speed of the rolling material in the delivery side of the stand j. However, the plate thickness changing point does not reach the entry side of the stand j+1. Therefore, the plate thickness H(j+1)Aof the rolling material in the entry side of the stand j+1 is equal to the plate thickness h(j)Aprior to the flying thickness change. Focusing on this, the mass flow constant regulation which is established, at the timing when the plate thickness changing point locates between the stand j and the stand j+1, among the entry side of the stand j+1, the delivery side of stand j+1, and each delivery side of the stands located downstream of the stand j+1 is expressed by the following equation (6).
v(j)Bh(j)A=v(j+1)A(j)h(j+1)A= . . . =v(n)A(j)h(n)A(6)
v(j+1)A(j): the speed of the rolling material in the delivery side of the stand j+1 at the timing when the plate thickness changing point locates between the stand j and the stand j+1 [m/s]
v(n)A(j): the speed of the rolling material in the delivery side of the final stand n at the timing when the plate thickness changing point locates between the stand j and the stand j+1 [m/s]

FIG. 9is a diagram for explaining the equation (6). As explained above, in the situation where the plate thickness changing point locates between the stand j and the stand j+1, the speed of the rolling material in the entry side of the stand j+1 is equal to v(j)B, and the plate thickness H(j+1)A in the entry side of the stand j+1 is equal to the plate thickness H(j)A of the rolling material in the delivery side of the stand j. Therefore, the mass flow in the entry side of the stand j+1 is expressed by v(j)Bh(j)A. Then, the mass flow v(j)Bh(j)Ais equal to the mass flow (j+1)A(j)h(j+1)Ain the delivery side of stand j+1, and is also equal to the mass flow v(n)A(j)h(n)Ain the delivery side of the final stand n.

The relation of the equation (6) holds even when the plate thickness changing point is between the stand j−1 and the stand j. Specifically, the mass flow constant regulation which is established, at the timing when the plate thickness changing point locates between the stand j−1 and the stand j, among the entry side of the stand j, the delivery side of stand j, and each delivery side of the stands located downstream of the stand j is expressed by the following equation (7).
v(j−1)Bh(j−1)A=v(j)A(j-1)h(j)A= . . . =v(n)A(j-1)h(n)A(7)

From the equations (6) and (7), the speed change amount of the rolling material in the delivery side of a stand k (j≤k≤n) in a case where the plate thickness changing point moves from the entry side to the delivery side of the stand j is expressed as follows:

v⁡(k)A⁡(j)-v⁡(k)A⁡(j-1)=⁢(h⁡(j)A/h⁡(k)A)⁢v⁡(j)B-⁢(h⁡(j-1)A/h⁡(k)A)⁢v⁡(j-1)B=⁢h⁡(j)Λ⁢(v⁡(k)A⁢h⁡(j)B)-h⁡(j-1)A⁢(v⁡(k)A⁢h⁡(j-1)B)⁢(from⁢⁢the⁢⁢equation⁢⁢(5))=⁢v⁡(k)A⁢((h⁡(j)A/h⁡(j)B)-v⁡(k)A⁢(h⁡(j-1)A/h⁡(j-1)B))=⁢v⁡(k)A⁢{(h⁡(j)A/h⁡(j)B)-(h⁡(j-1)A/h⁡(j-1)B)}(8)
v(k)A(j): the speed of the rolling material in the delivery side of the stand k at the timing when the plate thickness changing point locates between the stand j and the stand j+1 [m/s]
v(k)A(j-1): the speed of the rolling material in the delivery side of the stand k at the timing when the plate thickness changing point locates between the stand j−1 and the stand j [m/s]
<Speed Pattern Create Function>

Next, the speed pattern which is created or updated by the speed pattern create function will be described.

FIG. 10is a diagram for showing an exemplary speed pattern created or updated by the speed pattern create function. The CT position shown inFIG. 10represents the position of the coiler entry-side thermometer28shown inFIG. 1. The FDT (Finishing mill Delivery Thermometer) position shown inFIG. 10represents the position of the finishing mill delivery-side thermometer26shown inFIG. 1. The site64shown on the horizontal axis ofFIG. 10is a site of the preceding material60located at the FDT position when the head end portion62areaches the finishing mill entry-side thermometer24(see Timing6.5shown inFIG. 8). The site64is also depicted in Timings6.6and6.7shown inFIG. 8.

The solid line shown inFIG. 10represents a speed history of the site64when the change in the speed of the rolling material due to the flying thickness is predicted and incorporated into the speed pattern. As shown by the solid line, the speed of the rolling material at the timing when the site64locates at the FDT position is constant. However, as described in the explanation of the step S18shown inFIG. 7, at the Timing6.5shown inFIG. 8, the setting calculation of the succeeding material62is executed and the speed pattern of the preceding material60is updated. Therefore, from the timing after the site64passes the FDT position, the speed of the site64starts to increase gradually. Further, as described in the explanation of the step S22shown inFIG. 7, the head end portion62areaches the delivery side of the finishing mill16at the Timing6.7shown inFIG. 8. That is, at the Timing6.7ofFIG. 8, the flying thickness change in all of the stands of the finishing mill16is completed. Therefore, the speed of the site64becomes constant again from the timing slightly before the site64reaches the CT position.

The broken line shown inFIG. 10represents the speed history of the site64when the change in the speed of the rolling material due to the flying thickness change is not incorporated into the speed pattern. As shown by the dashed line, the speed of the site64remains constant unless the change in the speed of the rolling material is incorporated into the speed pattern. Therefore, the temperature of the site64shifts to an unexpected temperature range.

<Advantageous Effects of Temperature Control According to First Embodiment>

FIG. 11is a diagram for illustrating advantageous effects of the temperature control according to the first embodiment of the present invention. The CT measured value, the plate thickness just under CT, the speed just under CT, the Total flow amount and the FB flow amount shown inFIG. 11are as described with reference toFIG. 5.

As can be seen by comparingFIG. 5withFIG. 11, in the temperature control of the first embodiment, the Total flow amount starts to increase before the Timing1, and the Total flow amount is greatly decreased after the Timing2. This is because the feedforward control in which the change in the speed of the rolling material is incorporated into the speed pattern has been executed before the Timing1. Therefore, inFIG. 11, the FB flow amount remains almost unchanged, and the Total flow amount is adjusted by the feedforward control while the plate thickness changing point passes through the finishing mill. By the adjustment of the Total flow amount, the CT measured value is controlled between the upper limit and the lower limit.

As described above, according to the temperature control device of the first embodiment, the temperature of the strip at the coiler entry-side thermometer28, that is, the temperature of the strip immediately before winding by the coiler20can be controlled within the permissible range with high accuracy.

In the first embodiment mentioned above, the finishing mill16corresponds to the “mill” of the present invention. The coolers32and34correspond to the “heat exchanger” of the present invention. The finishing mill delivery-side temperature meter26and the coiler entry-side thermometer28correspond to the “delivery-side thermometer” of the present invention. The finishing mill entry-side thermometer24corresponds to the “entry-side thermometer” of the present invention if the finishing mill delivery-side temperature meter26corresponds to the “delivery-side thermometer”. The finishing mill delivery-side temperature meter26corresponds to the “entry-side thermometer” if the coiler entry-side thermometer28corresponds to the “delivery-side thermometer”.

Modification of First Embodiment

Incidentally, in the temperature control of the first embodiment mentioned above, the amount of the coolant from the cooler32and34shown inFIG. 1was controlled by setting these coolers as controlled objects of the feedforward control. However, number of the controlled objects of the feedforward control may be reduced to set only the cooler34as the controlled object. In this instance, the feedforward control may be executed in which the amount of the coolant from the cooler34is controlled based on the measured temperature value from the finishing mill delivery-side temperature meter26and the latest speed pattern. On the contrary, the number of the controlled objects of the feedforward control may be increased to add the heat exchanger30as the controlled object. In this instance, the feedforward control may be executed in which the amount of the coolant or the amount of heat from the heat exchanger30is controlled based on the measured temperature value from the roughing mill delivery-side thermometer22and the latest speed pattern.

The temperature control of the first embodiment mentioned above is executed to control the temperature of the strip in the permissible range immediately before the winding by the coiler20. Therefore, this object can be achieved if the amount of the coolant from the cooler34located immediately upstream of the coiler20is controlled at least by the feedforward control. Therefore, the temperature control of the first embodiment can be modified in various ways, as long as the amount of the coolant from the cooler34is controlled at least by the feedforward control.

Further, in the temperature control of the first embodiment mentioned above, the temperature of the strip immediately before the winding by the coiler20was controlled within the permissible range. However, the temperature of the rolling material controlled within the permissible range is not limited to the temperature immediately before the winding by the coiler20. That is, the temperature of the strip in the delivery side of the finishing mill16may be controlled within the permissible range. The temperature of the rough bar in the entry side of the finishing mill16may be controlled within the permissible range.

In the case where the temperature of the strip in the delivery side of the finishing mill16is controlled within the permissible range temperature, the amount of the coolant from the cooler32may be controlled at least by the feedforward control.FIG. 12is a diagram for explaining an exemplary temperature control in which the temperature of the strip in the delivery side of the finishing mill16is controlled within the permissible range temperature.FIG. 13is a diagram for explaining Timings1to3shown inFIG. 12.

The FDT measured value shown inFIG. 12represents the measured temperature value from the finishing mill delivery-side temperature meter26shown inFIG. 13. The plate thickness just under FDT represents the plate thickness of the strip just under the finishing mill delivery-side temperature meter26. The speed just under FDT represents the speed of the strip just under the finishing mill delivery-side temperature meter26. The Total flow amount represents the total flow amount of the coolant supplied from the cooler32shown inFIG. 13.

As shown inFIG. 13, at the Timing1, the plate thickness changing point54locates at the first stand F1. At the Timing2, the plate thickness changing point54has moved to the delivery side of the fifth stand F5. At the Timing3, the plate thickness changing point54has moved to just under the finishing mill delivery-side thermometer26.

In the temperature control of this modification, the Total flow amount starts to increase before the Timing1, and the Total flow amount decreases after the Timing2. This is because the feedforward control in which the change in the speed of the rolling material is incorporated into the speed pattern has been executed before the Timing1. Therefore, inFIG. 12the FB flow amount (i.e. the correcting flow amount based on the feedback control based on the error between the measured temperature value of the finishing mill delivery-side temperature meter26and its target value) remains almost unchanged and the FB flow amount is adjusted by the feedforward control while the plate thickness changing point passes through the finishing mill. By the adjustment of the Total flow amount, the FDT measured value is controlled between the upper limit and the lower limit.

In the case where the temperature of the rough bar in the entry side of the finishing mill16is controlled within the permissible range, the amount of the coolant or the amount of heat from the heat exchanger30may be controlled by the feedforward control.FIG. 14is a diagram for explaining an exemplary temperature control in which the temperature of the rough bar in the entry side of the finishing mill16is controlled within the permissible range temperature.FIG. 15is a diagram for explaining the Timings1to3shown inFIG. 14.

The FET (Finishing mill Entry Thermometer) measured value shown inFIG. 14represents the measured temperature value from the finishing mill entry-side thermometer24shown inFIG. 15. The plate thickness just under the FET represents the plate thickness of the rough bar just under the finishing mill entry-side thermometer24. The FET-down speed represents the speed of the rough bar just under the finishing mill entry-side thermometer24. The Total heating amount represents the amount of heat supplied from the heat exchanger30shown inFIG. 15.

As shown inFIG. 15, at the Timing1, the plate thickness changing point54locates at the first stand R1. At the Timing2, the plate thickness changing point54has moved to the delivery side of the third stand R3. At the Timing3, the plate thickness changing point54has moved to just under the finishing mill entry-side thermometer24.

In the temperature control of this modification, the Total heating amount starts to decrease before the Timing1and the Total heating amount is kept constant before the Timing2. This is because the feedforward control in which the change in the speed of the rough bar is incorporated into the speed pattern has been executed before the Timing1. Therefore, inFIG. 14, the FB heating amount (i.e., the correction heating amount based on the feedback control based on the error between the measured temperature value of the finishing mill entry-side thermometer24and its target value) remains almost unchanged, and the Total heating amount is adjusted by the feedforward control while the plate thickness changing point passes through the roughing mill. By the adjustment of the Total heating amount, the FET measured value is controlled between the upper limit and the lower limit.

Second Embodiment

Next, a second embodiment of the present invention will be described with reference toFIGS. 16 to 17. Note that descriptions overlapping with the first embodiment are omitted as appropriate.

FIG. 16is a block diagram for explaining an exemplary configuration of the temperature control device according to a second embodiment of the present invention. The temperature control device shown inFIG. 16has a setting calculation function40, temperature control function42, gap change function44, speed control function46and a tracking function48as main functions. These functions are as described with reference toFIG. 2.

The temperature control device according to the second embodiment differs from the temperature control device according to the first embodiment in that the setting calculation function40comprises a schedule control function40d.

The schedule control function40dis a function to determine for each stand whether or not change rate of the rolling material which is calculated based on the speed change amount by the speed change amount calculation function40bexceeds a threshold value. The schedule control function40dis also a function to reduce a change amount of the plate thickness of the rolling material in the stand to be determined when it is determined in the same stand that the speed change rate exceeds the threshold.

The schedule control function40dis also a function to determine for each stand whether or not the rolling reduction rate is within the permissible range. The schedule control function40dis also a function to changing the rolling reduction rate of the stand to an upper limit value or a lower limit value when it is determined in the same stand that the rolling reduction rate is outside the permissible range.

The schedule control function40dis also a function to reset the plate thickness schedule, change the plate thickness changing time and execute again the determination relating the speed change rate and the rolling reduction rate when it is determined that the plate thickness of the strip in the delivery side of the final stand cannot achieve the target value as a result of the adjustment of the change amount of the plate thickness of the rolling material in each stand and the adjustment of the rolling reduction rate in each stand.

<Feature of Temperature Control in Second Embodiment>

FIG. 17is a flow chart for explaining exemplary processing when the temperature control device according to the second embodiment of the present invention executes the operation related to scheduling. In the routines shown inFIG. 17, a default value of a counter is set to zero.

In the routine shown inFIG. 17, the temperature control device first inputs an initial value i=1 of the stand i (step S30), and calculates the speed change rate Δα(i) of the rolling material in the stand i (1≤i≤n) (step S32). The speed change rate Δα(i) is expressed by the following equation (9) using an equation obtained by replacing the variable of the equation (8) with i from k and the plate thickness changing time tFGC.
Δα(i)=Δv(i)/tFGC(9)
Δv(i)=v(i)A(j)−v(i)A(j-1)
v(i)A(j): the speed of the rolling material in the delivery side of the stand i at the timing when the plate thickness changing point is between the stand j (i≤j≤n) and the stand j+1 [m/s]
v(i)A(j-1): the speed of the rolling material in the delivery side of the stand k at the timing when the plate thickness changing point is between the stand j−1 and the stand j [m/s]

Subsequent to the step S32, the temperature control device determines whether or not an absolute value abs(Δα(i)) of the speed change rate of the rolling material (i.e., acceleration rate or deceleration rate of the rolling material) Δα(i) exceeds a threshold value Δαthre(step S34).

If it is determined in the step S34that abs(Δα(i))>Δαthreis satisfied, the temperature control device corrects the target value h(i)Bof the plate thickness in the delivery side of the stand i using the equation (10) or the equation (11) according to the value of Δα(i) (step S36). The temperature control device calculates the optimal tFGCoptof the plate thickness changing time tFGCusing the following equation (12).
h(i)B=h(i)A/{(h(i−1)Ah(i−1)B)+(tFGC*Δαthrev(n)A(j))} (if Δα(i)>0)   (10)
h(i)B=h(i)A/{(h(i−1)Ah(i−1)B)−(tFGC*Δαthrev(n)A(j))} (if Δα(i)<0)   (11)
tFGCopt(i)=Δv(i)/Δαthr(12)

Subsequent to the step S36, the temperature control device determines whether or not the rolling reduction rate γ(i) of the stand i is within the permissible range (step S38). In the step S38, the rolling reduction rate γ(i) is calculated as follows:
γ(i)=(h(i−1)B−h(i)B)/h(i−1)B(13)

The permissible range is defined by an upper limit γ(i)highand a lower limit γ(i)lowof the rolling reduction rate of the predetermined stand i. When it is determined that the rolling reduction rate γ(i) calculated by using the equation (13) is within the permissible range, the temperature control device proceeds to the processing of step S40.

On the other hand, if it is determined in the step S38that the rolling reduction rate γ(i) calculated by using the equation (13) is outside the permissible range, the temperature control device corrects the target value h(i)Bof the plate thickness in the delivery side of the stand i using the following equation (14) or equation (15) (step S42).
h(i)B=h(i)B*(1−γ(i)high) (if γ(i)>γ(i)high)  (14)
h(i)B=h(i)B*(1−γ(i)low) (if γ(i)<γ(i)low)  (15)

In the step S40, the temperature control device updates the valued of the stand i to i+1. Subsequently, the temperature control device determines whether or not i=n is satisfied for the present value of the stand i (step S44). When it is determined that i=n is not satisfied, the temperature control device returns to the processing of the step S32.

If it is determined in the step S44that i=n is established, the temperature control device determines whether or not the plate thickness h(n)Bof the strip in the delivery side of the final stand n achieves the target value (step S46). The temperature control device determines whether or not a difference between the plate thickness h(n)Band the target value is less than the threshold value, and determines whether or not the target value is achieved. If it is determined that the difference is equal to or greater than the threshold value, the temperature control device resets the plate thickness schedule once in operation S48. If it is determined that the difference is less than the threshold, the temperature control device exits the routine.

Subsequent to the step S48, the temperature control device determines whether or not the value of the counter is zero (step S50). If it is determined that the value of the counter is zero, the temperature control device changes the value of the counter from zero to one, and changes the plate thickness changing time tFGCusing the following equation (16) (step S52).
tFGC=max(tFGCopt(1),tFGCopt(2), . . . ,tFGCopt(n),tFGCmaxlmt)  (16)

After the change of the plate thickness changing time tFGC, the temperature control device returns to the processing of the step S30. On the other hand, if it is determined in the step S50that the value of the counter is not zero, the temperature control device exits the routine.

As described above, according to the routines shown inFIG. 17, the change amount of the plate thickness of the rolling material in the stand i can be adjusted based on the comparison between the speed change rate Δα(i) of the stand i and the threshold value. The rolling reduction rate γ(i) can also be adjusted based on the comparison of the rolling reduction rate γ(i) of the stand i with the permissible value. Furthermore, it is also possible to make the determination again on the speed change rate Δα(i) and the rolling reduction rate γ(i) based on the comparison of the plate thickness h(n)Bof the strip in the delivery side of the final stand n with the thresholds. Therefore, it is possible to suppress in each stand a sharp change in the speed of the rolling material due to the flying thickness change by keeping the speed change rate and the rolling reduction rate within appropriate ranges. Therefore, it is possible to further improve the accuracy of the temperature control by the temperature control device.

REFERENCE SIGNS LIST

40Setting calculation function

40aFlying thickness change amount determination function

40bSpeed change amount calculation function

40cSpeed pattern create function

40dSchedule control function

42Temperature control function

42aInitial output determination function

42bFeedforward control function

42cFeedback control function

44Gap change function

46Speed control function

52Measured temperature value

54Plate thickness changing point

60a,62aHead end portion