JP6172129B2 - Hot rolling strip finishing method - Google Patents

Description

  The present invention relates to a finish rolling method capable of efficiently producing a high-quality hot-rolled steel strip.

  The rolling mills installed in the hot rolling line for producing the hot-rolled steel strip are roughly classified into a rough rolling mill and a finishing rolling mill. In recent years, as the properties required for hot-rolled steel sheets have become more stringent, the temperature of the hot-rolled steel strip discharged to the exit side of the finishing mill (hereinafter referred to as finishing) A technology has been developed in which a suitable range of the delivery side temperature) is set according to the composition and application of the hot-rolled steel strip, and finish rolling is performed while the finish delivery temperature is maintained within the range.

Control for maintaining the finishing delivery temperature within a predetermined range can be easily performed if the speed of the hot-rolled steel strip passing through the finishing rolling mill (hereinafter referred to as the sheet passing speed) is reduced. However, a decrease in the plate passing speed causes a decrease in the productivity of the hot rolled steel strip. for that reason,
(a) Improvement in accuracy of finishing side temperature control, that is, improvement in quality of hot-rolled steel strip,
(b) Productivity improvement of hot-rolled steel strip,
Technology to achieve both is being studied.

  For example, in Patent Document 1, the temperature of the hot-rolled steel strip is measured on the exit side of the rough rolling mill and the entrance side of the finish rolling mill, and based on the measured value of the temperature and the position information of the hot-rolled steel strip by tracking. A technique for performing feedforward control for adjusting the amount of water sprayed between the stands is disclosed. However, since this technique does not adjust the sheet passing speed according to the measured value of the finishing side temperature, it is difficult to achieve both the increase in the passing speed and the stable maintenance of the finishing side temperature.

  Patent Document 2 discloses a technique for measuring the temperature of a hot-rolled steel strip on the entry side of a finish rolling mill and adjusting the sheet feeding speed according to the difference between the measured value and a target value. Although this technology can be expected to improve productivity by properly adjusting the plate feed speed, the measured value of the finish side temperature is not reflected in the adjustment of the plate speed, so the finish side temperature is within the target range. It is difficult to maintain.

Patent Document 3 discloses a technique for measuring the finishing side temperature of a hot-rolled steel strip and accelerating the sheet feeding speed stepwise based on the measured value and the predicted value of the finishing side temperature. Since this technology changes the sheet feeding speed from the start of hot rolling line operation, before the tension acting on the hot-rolled steel strip stabilizes (ie, the tip of the hot-rolled steel strip is discharged from the finishing mill. It is permissible to change the plate feed speed before), and in this case, there arises a problem that it becomes difficult to maintain the finishing side temperature within the target range. In addition, according to the transition of the plate passing speed disclosed in FIG. 3 of the cited document 3, the plate passing speed is changed four times (that is, the acceleration rate is added) between the times t ₃ and t _4. The added acceleration rate is different. In order to change the acceleration rate itself many times, not only a complicated configuration of equipment is required, but also operation management is complicated.

  That is, a technique for making the above (a) and (b) compatible with simple means has not been established yet.

JP 2012-40593 Japanese Patent Laid-Open No. 10-277627 JP 2012-223813 A

  The present invention eliminates the problems of the prior art, improves the accuracy of finish-side temperature control with simple means, can stably produce a hot-rolled steel strip of good quality, It aims at providing the finish rolling method which can aim at the improvement of productivity of a hot-rolled steel strip.

This inventor examined the technique which changes a sheet-feeding speed, performing finish rolling. As a result, it was found that the operation of the finishing mill could be continued without problems if the sheet feeding speed was changed (that is, the acceleration rate was added to the sheet feeding speed) in a state where a stable tension was applied to the hot-rolled steel strip. Therefore, the tension acting on the hot-rolled steel strip was studied in detail. as a result,
(A) The tension of the hot-rolled steel strip is not necessarily constant until the end of the hot-rolled steel strip is discharged from the final stand of the finish rolling mill toward the winder,
(B) After the tip of the hot-rolled steel strip is discharged from the final stand of the finish rolling mill toward the winder, stable tension acts on the hot-rolled steel strip.
(C) When the tip of the hot-rolled steel strip bites into the winder, a more stable tension acts on the hot-rolled steel strip.
(D) It was found that the tension does not change during the winding of the hot-rolled steel strip. Therefore, productivity can be improved by adding an acceleration rate to the sheet feeding speed when the tip of the hot-rolled steel strip is discharged from the final stand of the finish rolling mill toward the winder. And when the front-end | tip of a hot-rolled steel strip bites into the winder, productivity can be further improved by further increasing the sheet passing speed.

However, if the sheet feeding speed of the hot-rolled steel strip is increased (that is, an acceleration rate is added), the finish side temperature of the hot-rolled steel strip is likely to rise. Therefore, the technology for controlling the finishing side temperature within the target range was studied. as a result,
(E) After increasing the sheet feeding speed, when the temperature of the hot-rolled steel strip rises too much, the sheet feeding speed is kept constant (that is, the addition of acceleration rate is stopped) and installed between each stand of the finishing mill. By adjusting the spray water amount of the cooling water spray (hereinafter referred to as inter-stand spray), the cooling capacity can be effectively utilized.
(F) After the hot-rolled steel strip has been sufficiently cooled, productivity can be improved by starting to add an acceleration rate again and increasing the sheeting speed.
(G) It has been found that by repeating the addition start and stop without changing the acceleration rate as a constant value, complicated equipment configuration and operation management become unnecessary.

  The present invention has been made based on such knowledge.

That is, the present invention makes constant the sheet feeding speed before the tip of the hot-rolled steel strip is discharged from the final stand of the finish rolling mill installed in the hot rolling line in the direction of the winder, Until the tip is discharged from the final stand, it is finished rolling with an acceleration rate of the sheet feeding speed being α (m / min / second) until it is caught in the winder, and the winder winds the hot-rolled steel strip. After the start of cutting, the finishing rate is continued with β (m / min / sec) as the rate of plate speed and α <β, and the temperature of the hot-rolled steel strip on the exit side of the final stand is preset. When the threshold M is exceeded, the addition of the acceleration rate β is stopped and finish rolling is continued, and when the temperature of the hot-rolled steel strip on the exit side of the final stand is equal to or lower than the threshold M, the finish rolling is continued with the acceleration rate β added. It is a finish rolling method for hot-rolled steel strip .

In other words, if the constant sheet feeding speed before the end of the hot-rolled steel strip is discharged from the final stand is V ₁ (m / min), the winding is performed after the end of the hot-rolled steel strip is discharged from the final stand. The plate passing speed until biting into the machine is relative to the elapsed time t ₁ (seconds) after the start of addition of the acceleration rate α.
Plate speed = V ₁ + αt ₁
It becomes. Further, the sheet feeding speed after the winder starts winding the hot-rolled steel strip is V ₂ (m / min) when the tip of the hot-rolled steel strip is caught in the winder. Then, with respect to the elapsed time t ₂ (seconds) after the start of the addition of the acceleration rate β,
Plate speed = V ₂ + βt ₂
It becomes. Here, the sheet passing speed means a value obtained by converting the rotation speed of the work roll of the final stand into the traveling speed of the hot-rolled steel strip.

  In the finish rolling method of the present invention, while the addition of the acceleration rate β is stopped and the finish rolling is performed at a constant sheet feed speed, the inter-stand spray is performed based on the temperature of the hot-rolled steel strip on the exit side of the final stand. It is preferable to perform feedback control for adjusting the amount of jet water. In addition, while finishing rolling while increasing the sheet feeding speed by adding the acceleration rate β, the spray water amount of the inter-stand spray is adjusted based on the temperature of the hot-rolled steel strip on the first stand entrance side of the finishing mill. It is preferable to perform feedforward control. Furthermore, after the addition of the acceleration rate β is stopped, it is preferable to perform finish rolling with the addition of the acceleration rate β when the temperature of the hot-rolled steel strip on the exit side of the final stand falls below a preset threshold value N. Here, N <M.

  According to the present invention, it is possible to stably produce a hot-rolled steel strip having a good quality by improving the accuracy of finish-side temperature control by simple means, and the productivity of the hot-rolled steel strip. Therefore, there is a remarkable effect in the industry.

It is an arrangement figure showing typically an example of a finishing mill to which the present invention is applied. It is a graph which shows the example of transition of the sheeting speed in finish rolling of the present invention. It is a graph which shows the example of transition of the sheeting speed in finish rolling of the present invention. It is a graph which shows transition of the sheeting speed in the finish rolling performed for the comparison.

  FIG. 1 is a layout diagram schematically showing an example of a finishing mill to which the present invention is applied. Moreover, FIG. 2 is a graph which shows the example of transition of the sheeting speed in the finish rolling of this invention. Hereinafter, an example in which the finishing rolling method of the present invention is applied to a seven-stand finishing mill will be described with reference to FIGS. However, the finishing mill to which the present invention is applied is not limited to seven stands.

  The hot-rolled steel strip 2 advances in the direction of arrow S in FIG. 1 and is subjected to finish rolling while sequentially passing through the roll stand from the first roll stand 3 (hereinafter referred to as the first stand) of the finish rolling mill 1. Then, it is discharged from the final stand 4 (that is, the seventh stand) and further wound by a winder (not shown).

  An entrance thermometer 5 is disposed on the entry side of the first stand 3, and an exit side thermometer 6 is disposed on the exit side of the final stand 4. Further, an inter-stand spray 7 is disposed between the first stand 3 to the final stand 4 to inject cooling water onto the hot-rolled steel strip 2.

When finishing rolling of the hot-rolled steel strip 2 is started, the tip of the hot-rolled steel strip 2 sequentially passes through the roll stand from the first stand 3. At this time, since the restraint state of the hot-rolled steel strip 2 by each roll stand changes every moment, the tension acting on the hot-rolled steel strip 2 is not necessarily constant. And when the front-end | tip of the hot-rolled steel strip 2 is discharged | emitted to the exit side of the last stand 4, the tension | tensile_strength which acts on the hot-rolled steel strip 2 is stabilized. In this way, the plate passing speed is kept constant until the end of the hot-rolled steel strip 2 is discharged from the final stand 4, and the value is set to V ₁ (m / min) (see FIG. 2). The sheet passing speed means a value obtained by converting the rotation speed of the work roll of the final stand 4 into the traveling speed of the hot-rolled steel strip.

Subsequently, the tip of the hot-rolled steel strip 2 proceeds from the final stand 4 and bites into the winder. However, when the tip of the hot-rolled steel strip 2 is discharged to the exit side of the final stand 4, the plate feed speed is increased. By adding the acceleration rate α (m / min / sec), the hot-rolled steel strip 2 advances while increasing the sheet passing speed. That sheet passing speed of the tip of the hot rolled strip 2 until bite free the winding machine, V ₁ increases with time, the elapsed time after starting the addition of the acceleration rate α as t ₁ (seconds) + Αt ₁ (see FIG. 2). Here, since the tension acting on the hot-rolled steel strip 2 is stable, there is no problem in the operation of the finishing mill 1 even if the sheet feeding speed is increased.

Furthermore, the hot-rolled steel strip 2 is wound around a coil by a winder. When the tip of the hot-rolled steel strip 2 is caught in the winder, the plate feed speed is accelerated by an acceleration rate β (m / min / second). Is added, the finish rolling is continued while further increasing the sheet passing speed (that is, α <β), and the hot-rolled steel strip 2 is wound up. The sheet passing speed after starting the winding of the hot rolled steel strip 2 is V ₂ (m / min) when the sheet passing speed when the tip of the hot rolled steel strip 2 is caught in the winder is V ₂ + βt ₂ with respect to the elapsed time t ₂ (seconds) after the start of the addition of the acceleration rate β.

If the sheet passing speed is continuously increased in this way, the cooling capacity by the inter-stand spray 7 becomes insufficient, and as a result, the finish side temperature of the hot rolled steel strip 2 rises. Therefore, the finish delivery temperature is measured by the delivery thermometer 6 on the delivery side of the final stand 4, and the measured value is compared with a preset threshold value M. Then, when the measured value of the finishing delivery temperature exceeds the threshold value M, the addition of the acceleration rate β is stopped, and finishing rolling is continued at a constant sheet feeding speed. The plate passing speed at this time is V ₃ (see FIG. 2).

While finishing rolling at a constant plate feed speed V ₃ , adjusting the cooling capacity by the spray 7 between the stands, and if the finish side temperature of the hot-rolled steel strip 2 is sufficiently lowered, the addition of the acceleration rate β is started again To do. The method of restarting the addition of the acceleration rate β can be performed by measuring the elapsed time after the addition of the acceleration rate β is stopped with a timer and performing a predetermined time. However, in the present invention, from the viewpoint of controlling the finishing delivery temperature with high precision, measurements of the finishing delivery temperature is that to resume additional acceleration rate β when below the threshold N set in advance. Here, N <M.

The sheet feeding speed after the addition of the acceleration rate β is resumed is V ₃ + βt ₃ with respect to the elapsed time t ₃ (seconds) after the addition is resumed.

In this way, finish rolling is continued, and when the measured value of the finish delivery temperature exceeds the threshold value M, the addition of the acceleration rate β is stopped and the finish rolling is continued at a constant sheet feeding speed. The plate passing speed at this time is V ₄ (see FIG. 2). Then, finish rolling is performed at a constant sheet feed speed V ₄ until the finish delivery temperature of the hot-rolled steel strip 2 is sufficiently lowered.

  In the present invention, the number of times of repeating the start and stop of adding the acceleration rate β to the plate passing speed is not particularly limited. While comparing the measured value of the finishing side temperature with the threshold values M and N, repeating the start and stop of the addition of the acceleration rate β and performing finish rolling to the rear end of the hot-rolled steel strip 2, the finishing side The accuracy of temperature control can be improved and the productivity of the hot-rolled steel strip 2 can be improved. In addition, these effects can be obtained by a simple means of repeatedly starting and stopping the addition of the acceleration rate β.

  While the addition of the acceleration rate β is stopped and finish rolling is performed at a constant sheet passing speed, based on the measured value of the finish side temperature measured by the exit side thermometer 6 installed on the exit side of the final stand 4. It is preferable to perform feedback control for adjusting the amount of cooling water sprayed from the inter-stand spray 7. The reason is that when the feedforward control based on the measured value of the entry-side thermometer 5 is performed at a constant sheet passing speed, the finish-side temperature of the hot-rolled steel strip 2 is likely to fluctuate.

  On the other hand, the temperature of the hot-rolled steel strip 2 is measured with the inlet side thermometer 5 installed on the inlet side of the first stand 3 while finishing rolling while adding the acceleration rate β and increasing the sheet passing speed. Then, it is preferable to perform feedforward control for adjusting the amount of cooling water sprayed from the inter-stand spray 7 based on the measured value. The reason is that if the feedback control based on the measured value of the delivery side thermometer 6 is performed while increasing the sheet passing speed, the finish delivery side temperature of the hot-rolled steel strip 2 is likely to fluctuate.

  The means for adjusting the amount of spray water of the inter-stand spray 7 is not particularly limited. For example, a method of adjusting the number of nozzles for injecting cooling water or adjusting the amount of cooling water supplied to the nozzles can be used.

  According to the research results of the present inventor, the acceleration rate α is in the range of 1 to 15 m / min / second and the acceleration rate β is 5 to 50 m / min for the hot rolled steel strip 2 having a thickness of 1.2 to 10 mm. / Second is preferable.

  Using the finish rolling mill 1 shown in FIG. 1, finish rolling of the hot-rolled steel strip 2 (sheet thickness 2 mm, width 1200 mm) was performed by the method of the present invention. The procedure will be described. FIG. 3 is a graph showing the transition of the sheet passing speed in the finish rolling.

  Finish rolling is performed at a constant sheet feed speed until the tip of the hot-rolled steel strip 2 is discharged to the exit side of the final stand 4, and acceleration is performed when the tip of the hot-rolled steel strip 2 is discharged to the exit side of the final stand 4 Finish rolling was performed while increasing the sheet feeding speed by adding a rate α (8 m / min / sec).

  And when the front-end | tip of the hot-rolled steel strip 2 was caught in the winder, the acceleration rate (beta) (20 m / min / sec) was added, and finish rolling was performed, further increasing the sheeting speed. During the period during which the acceleration rate β is added to the plate passing speed, feed forward control is performed to adjust the amount of cooling water sprayed from the inter-stand spray 7 based on the temperature of the hot-rolled steel strip 2 measured by the entry-side thermometer 5. Was done.

  In this way, finish rolling is performed while increasing the sheet feeding speed at the acceleration rate β, and when the finish delivery temperature measured by the delivery thermometer 6 exceeds the threshold M (875 ° C.), the addition of the acceleration rate β is stopped. Then, finish rolling was continued at a constant sheet passing speed. During the period in which the addition of the acceleration rate β is stopped, feedback control is performed to adjust the amount of cooling water sprayed from the inter-stand spray 7 based on the finish discharge temperature measured by the discharge thermometer 6. Then, when the finish delivery temperature measured by the delivery thermometer 6 fell below the threshold value N (870 ° C.), the acceleration rate β was added again, and finish rolling was performed while further increasing the sheet feeding speed. This is an invention example.

  Next, the finish rolling of the hot-rolled steel strip 2 (plate thickness 2 mm, width 1200 mm) of the same dimensions performed for comparison will be described. FIG. 4 is a graph showing the transition of the sheet passing speed in the finish rolling.

  Finish rolling is performed at a constant sheet feed speed until the tip of the hot-rolled steel strip 2 is discharged to the exit side of the final stand 4, and acceleration is performed when the tip of the hot-rolled steel strip 2 is discharged to the exit side of the final stand 4 Finish rolling was performed while increasing the sheet feeding speed by adding the rate α.

  And, when the tip of the hot-rolled steel strip 2 is caught in the winder, an acceleration rate β is added, and finish rolling is performed while further increasing the sheeting speed, and the sheeting speed reaches a preset target value. Then, finish rolling was performed at a constant sheet feeding speed. The period during which the plate feeding speed is increased by adding the acceleration rate β and the period during which the addition of the acceleration rate β is stopped and the plate passing speed is made constant are based on the finishing delivery side temperature measured by the delivery side thermometer 6. Then, feedback control for adjusting the amount of cooling water sprayed from the inter-stand spray 7 was performed. This is a comparative example.

  In the finish rolling of the inventive example and the comparative example, a time T (second) in which the measured value of the finish side temperature by the exit side thermometer 6 exceeds the upper limit (890 ° C.) of the allowable range was measured. The results are shown in Table 1. In Table 1, the ratio of T with respect to the time required until the rear end is discharged after the front end of the hot-rolled steel strip 2 is discharged from the final stand 4 is shown as a temperature deviation occurrence rate (%).

  As is apparent from Table 1, in the present invention, the accuracy of the finish side temperature control is greatly improved.

DESCRIPTION OF SYMBOLS 1 Finishing mill 2 Hot-rolled steel strip 3 First stand 4 Final stand 5 Incoming thermometer 6 Outlet thermometer 7 Spray between stands

Claims (3)

The plate feed speed before the tip of the hot-rolled steel strip is discharged from the final stand of the finish rolling mill installed in the hot rolling line to the winder is constant, and the tip of the hot-rolled steel strip is the final Finishing rolling is performed with an acceleration rate of the sheet feeding speed being α (m / min / sec) until it is caught in the winder after being discharged from the stand, and the winder winds the hot-rolled steel strip. Then, the finishing rolling is continued with β (m / min / sec) as the rate of acceleration of the sheet passing speed and α <β, and the temperature of the hot-rolled steel strip on the exit side of the final stand is set in advance. When the set threshold value M is exceeded, the addition of the acceleration rate β is stopped and the finish rolling is continued, so that the temperature of the hot-rolled steel strip on the exit side of the final stand satisfies the following formula (1) in advance: and a below the set threshold N is added to the acceleration rate β pull the finish rolling Finish rolling method of hot-rolled steel strip and performing come.
N <M (1) While the addition of the acceleration rate β is stopped and the finish rolling is performed at a constant sheet feeding speed, the spray water amount of the inter-stand spray is adjusted based on the temperature of the hot-rolled steel strip on the outlet side of the final stand. The method of finish rolling a hot-rolled steel strip according to claim 1, wherein feedback control is performed. While performing the finish rolling while increasing the sheet feeding speed by adding the acceleration rate β, the amount of spray water sprayed between the stands is based on the temperature of the hot-rolled steel strip on the first stand entrance side of the finishing mill. 3. The method of finish rolling a hot-rolled steel strip according to claim 1 or 2, wherein feedforward control for adjusting the feed rate is performed .

Images