JP2008188604A - Temperature control method in cooling of steel sheet - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a temperature control method by which the temperature of object to be controlled such as winding temperature is controlled highly precisely even when abnormal temperature parts are generated on the surface of a steel sheet caused by defective flatness of the steel sheet and the scale generating state of the surface of the steel sheet on the outlet side of a finishing mill. <P>SOLUTION: The portion of sound parts in the width direction where the abnormal temperature cased by scale and the defective flatness are not generated is determined and its average temperature Tp(Fair) by using the maximum value Tp(Max) of the temperature in the width direction of the steel sheet which is measured after cooling and the allowable error ΔTp of the temperature Tp of the steel sheet from this maximum temperature Tp(Max). The average temperature Tp(Fair) of these sound parts is used as the temperature of the steel sheet in the temperature control in a process where the steel sheet after finish rolling is cooled and wound. The measured temperature of the steel sheet is stabilized in this way, the generation of temperature hunting after detecting the abnormal temperature part during feedback control of the winding temperature T2 is prevented, for example, and stable winding temperature control is made possible. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a temperature control method in a controlled cooling process after finish rolling of a hot rolled steel sheet.

  In the hot rolling of a thin steel plate, as shown in an example of the layout in FIG. 4, the slab 2 heated to a temperature range of about 1000 to 1300 ° C. in the heating furnace 1 is usually 1 to 4 rolling mills 3. Is rolled to a predetermined plate thickness by a rough rolling mill row 3a in which is disposed and a finishing rolling mill row 4a in which several rolling mills 4 are disposed, and then a hot run in which a water cooling zone 5 (cooling zone) is disposed. Water is cooled to a required temperature at the table 6, and the coil 7 is wound around a coil. The steel plate 8 having a temperature of about 900 ° C. at the end of finish rolling is cooled in the water cooling zone 5 so as to realize a winding temperature set to obtain a desired material. At that time, in addition to the thermometer 9 installed on the exit side of the final rolling mill 4f of the finishing rolling mill row 4a and the thermometer 9a installed in front of the coiler 7, it was installed in the middle of the water cooling zone 5 as necessary. The intermediate thermometer 9b is used to determine an ON / OFF pattern of a water cooling valve (not shown) in the water cooling zone 5 that can achieve a target winding temperature.

  FIG. 5 shows the flow of temperature control with respect to the coiling temperature. First, before the front end of the steel plate (rolled material) 8 passes through the final stand 4f of the finishing mill row 4a, the final stand 4f Based on the respective set values of the thickness (sheet thickness), the sheet passing speed (finish rolling speed) and the steel sheet temperature T1 of the outgoing steel sheet 8, and the target winding temperature T2a at the position of the thermometer 9a before the coiler 7. Then, using the temperature model for predicting the temperature history of the steel plate 8 in the water cooling zone 5, the valve position for turning on the water cooling valve and the valve position for turning off the water cooling valve are respectively determined by temperature calculation (S100 to S120). control). Then, the coiling temperature T2 is calculated based on each determined valve position to be turned ON / OFF (S130), and the difference (abs (T2a-T2c) between the target value T2a and the calculated value T2c of the coiling temperature T2 is calculated. )) Falls within the allowable range ΔT2a (S140). If it does not fall within the allowable range ΔT2a, the valve position (number of valves) to be turned ON / OFF is corrected (S150), and the correction of the valve position is repeated until abs (T2a-T2c) enters the allowable range ΔT2a. In this way, the optimum ON / OFF position of the water cooling valve is determined (setup control).

  Next, at the stage where the tip of the steel plate 8 has passed through the thermometer 9 on the outlet side of the final stand 4f of the finishing rolling mill row 4a, as shown in FIG. 6, the set value T1a of the steel plate temperature at the position of the thermometer 9 Using the difference ΔT1 with the actual measurement value T1m, the respective valve positions at which the water cooling valves are turned ON / OFF are recalculated (S200 to S230), feedforward control). Then, based on the position of the water cooling valve to be turned ON / OFF determined by recalculation, the coiling temperature T2 is calculated (S240), and the difference between the target value T2a of the coiling temperature T2 and the calculated value T2c (abs ( It is determined whether or not T2a-T2c) is within the allowable range ΔT2a (S250). If it does not fall within the allowable range ΔT2a, the water cooling valve position (valve number) to be turned ON / OFF is corrected (S260), and the correction of the valve position is repeated until abs (T2a-T2c) falls within the allowable range. In this way, the optimum ON / OFF position of the water cooling valve is corrected (feed forward control).

  Further, as shown in FIG. 7, when the steel plate 8 passes through the thermometer 9a before the coiler 7, the difference (abs (T2a-T2m)) between the target value T2a of the coiling temperature T2 and the measured value T2m is allowable. If not within the range ΔT2a (S300 to S330), the water cooling valve position to be turned ON / OFF is corrected so as to be within the allowable range (S340), and the winding temperature T2 is calculated (S350). It is determined whether or not the difference (abs (T2a−T2c)) between the target winding temperature T2a and the calculated winding temperature T2c falls within the allowable range ΔT2a (S360). If not within the allowable range, the valve position (number of valves) to be turned ON / OFF is corrected again (S340), and the correction of the valve position is repeated until abs (T2a-T2c) falls within the allowable range. In this way, the optimal water cooling valve position is corrected (feedback control).

  When the flatness of the steel plate 8 that has passed through the finish rolling mill row 4a is good, the coiling temperature T2 is relatively high, and the boiling mode is cooling in the film boiling temperature region (usually T2> 600 ° C.). Can control the coiling temperature with the desired accuracy (usually the target coiling temperature T2a ± 20 ° C.) by a general temperature control method whose temperature control flow is shown in FIGS. It is. However, when the flatness of the steel plate 8 is poor, a pool of water may be locally formed on the steel plate 8 during the cooling process, and cooling may proceed excessively, resulting in uneven temperature. Further, even when the flatness of the steel plate 8 is good, when the coiling temperature T2 is low and the boiling mode is cooled in the temperature range of nucleate boiling (usually T2 <500 ° C.), usually from film boiling to nucleate boiling. The transition to the boiling state does not occur on the steel sheet surface at the same time, but the transition timing in the boiling state is shifted, and the temperature distribution in the steel sheet surface is not a little. Furthermore, for example, in steel types where scales are likely to grow on the steel sheet surface, such as high-Si steel, the heat transfer coefficient in the steel sheet surface varies depending on the difference in the scale formation state on the steel sheet surface, thereby causing film boiling to nucleate boiling. Since the transition temperature to is different, a large temperature distribution is likely to be formed in the steel plate surface. Such temperature distribution due to the scale generation state occurs more significantly in the nucleate boiling region where the coiling temperature is low.

  In the conventional winding temperature control, as the winding temperature T2 to be controlled, a measured value at one location in the width direction of the steel sheet (usually the central portion in the width direction) is often used. When feedback measurement is applied to the fact that the measured value T2m of the coiling temperature is different from the target value T2a when the temperature measurement does not have a temperature distribution due to the generation of scales or poor flatness as described above on the steel sheet surface. The ON / OFF number of the water cooling valve in the water cooling zone 5 is changed based on the difference between the actual measurement value T2m of the winding temperature and the target value T2a. The target of this feedback control includes a time delay in which the change in the number of ON / OFF of the water cooling valve is reflected in the winding temperature T2 through a time difference generated by the distance between the water cooling valve and the coiling temperature measuring thermometer 9a. Since it is a control system, as shown in FIGS. 8B and 8C, when the control gain is increased, the cooling water flow rate hunts, and accordingly, hunting also occurs at the coiling temperature T2. As shown in (b) and (c), it is possible to control to a target temperature range (± 20 ° C.) of the coiling temperature by selecting an appropriate control gain. 8 (a) and 9 (a) increase for each control cycle because the rolling material (sheet material) tail has a long waiting time until rolling on the finishing rolling mill entrance side. The temperature drop due to air cooling increases toward the end side, and in order to compensate for this temperature drop, the plate feed speed is gradually increased from the front end to the rear end of the rolled material, and the amount of heat removed from the rolling roll is reduced to keep the finish rolling temperature constant. It is for controlling to keep.

  However, as described above, when the scale is generated on the surface of the steel plate, as schematically shown in FIG. 10, the temperature of the scale generation portion is lower than the other portions and is locally low in the plate width direction. Part is formed. In addition, when the flatness is poor, water that accumulates in the recesses on the surface is generated, so that the plate width as shown in FIGS. 11A and 11B is similar to the case shown in FIG. A temperature distribution is formed in which local low temperature portions exist in the direction. When such a local low temperature part due to scale generation or poor flatness, that is, an abnormal temperature part is included (FIGS. 10 and 11 (a), (b)), the plate length in the central part in the plate width direction The temperature transition in the direction is as shown in FIGS. 12 (a) and 12 (b). Thus, when the temperature generation part due to scale generation, flatness failure, and the boiling form is formed in the steel plate surface, the temperature in one place in the plate width direction, for example, the central part as in the past When the feedback control is performed based on the above, since the temperature being measured is not stable, the winding of the temperature abnormality portion after passing the winding thermometer 9a as shown in FIGS. 12 (a) and 12 (b) A hunting phenomenon at temperature T2 occurs.

For example, in Patent Document 1, the shape (for example, flatness such as steepness) of the material to be rolled on the exit side of the finish rolling mill is measured and the winding is performed with respect to such a problem in winding temperature control. A cooling control method that feeds forward after temperature control is disclosed. In this cooling control method, the shape (for example, steepness) of the tip of the rolled material measured by a flatness meter installed on the exit side of the final stand (rolling mill) of the finish rolling mill is determined between the rolled material and the cooling water. This is a method for controlling the cooling of the material to be rolled by reflecting the heat transfer coefficient and determining the water injection bank pattern of the cooling zone. And by this cooling control method, it is possible to improve the prediction accuracy of the winding temperature of the rolled material tip portion where the flatness is disturbed, and to make the winding temperature uniform in the longitudinal direction and the width direction of the rolled material, In addition, it is described that cracks due to overcooling in a portion where the shape of the tip of the material to be rolled immediately after finish rolling is not flat can be suppressed. Further, for example, in Patent Document 2, the position of occurrence of local supercooling in the steel sheet width direction after controlled cooling of a hot-rolled steel sheet is measured, and the surface of the rolling roll corresponding to the measured supercooling occurrence position is measured. Disclosed is a method of cooling a hot-rolled steel sheet that prevents local overcooling in the width direction of the steel sheet by adjusting the roughness by a method such as online roll grinding and controlling and cooling the steel sheet hot-rolled by this rolling roll. Has been.
JP 2005-270982 A JP 2001-129608 A

  However, in the cooling control method disclosed in Patent Document 1, for example, when the coiling temperature (T2) is measured at a site where the flatness of the steel plate is disturbed and a puddle is formed, the control accuracy is improved. When the feedback control for adjusting the number of water injection banks (the number of water cooling valves) is performed using the measured value (T2m) of the winding temperature, this feedback control becomes unstable, and the target winding temperature (T2a) is It can no longer be obtained. Further, in the cooling method disclosed in Patent Document 2, in general, in hot rolling of a thin steel plate, a winding thermometer 9a and a finish at a position where the influence of the steel plate surface roughness on temperature unevenness such as generation of scale is noticeable. The final rolling mill 4f of the rolling mill row 4a (see FIG. 4) is often 100 m or more away, and the scale adhesion on the steel sheet surface after finish rolling is a short pitch of about several meters. In many cases, the steel sheet width is adjusted by online adjustment of the surface roughness of the rolling roll at the part corresponding to the position of occurrence of local supercooling in the steel sheet width direction measured after controlled cooling. It is difficult to suppress local supercooling (cooling unevenness) in the direction.

  Then, the subject of this invention is the rapid process of the boiling form in the steel plate surface (heat-transfer surface) in the scale production | generation state and flatness defect of the steel plate surface in a finishing rolling mill delivery side in the cooling process after hot rolling. To provide a temperature control method capable of controlling the coiling temperature with high accuracy even when a temperature abnormal portion occurs on the surface of the steel sheet due to a change or the like.

  In order to solve the above problems, the present invention employs the following configuration.

That is, the temperature control method in steel plate cooling according to claim 1 is a temperature control method in steel plate cooling in the process of cooling and winding the steel plate after hot rolling in a cooling zone, and the temperature control method is: Step 1 of measuring the temperature distribution Tp (Y) in the width direction of the steel plate after cooling (Y is a coordinate in the width direction of the plate), the maximum value Tp (Max) of the measured temperature in the width direction of the steel plate, and the steel plate after cooling Using the tolerance ΔTp from the maximum value Tp (Max) of the temperature Tp, a site in the plate width direction of the healthy part where no temperature abnormality has occurred due to scale generation or flatness failure,
Tp (Max)> Tp (Y)> Tp (Max) -ΔTp ----------------------- (1)
Step 2 where the temperature range is such that the average temperature Tp (Fair) in the plate width direction of the healthy portion is Tp (Fair) = ΣTp (Y) ΔY (Fair) / ΣΔY (Fair) ----- --------- (2)
Step 3 in which the average temperature Tp (Fair) in the plate width direction of the healthy part is used as the steel plate temperature in the cooling temperature control.
Here, Σ on the right side of the above equation (2) represents the sum of only the healthy portions, ΔY (Fair) represents the plate width of each healthy portion, and ΣΔY (Fair) represents the sum of the plate widths of each healthy portion.

  By defining a healthy part having no temperature abnormality as described above and obtaining an average temperature Tp (Fair) of the healthy part in the plate width direction, for example, scale formation on the steel sheet surface during temperature control such as feedback control The steel plate temperature at which the temperature being measured is stable can be obtained without being affected by temperature abnormalities due to poor flatness.

  In the cooling control method for a hot-rolled steel sheet according to claim 2, the steel sheet temperature is a coiling temperature, and an allowable error ΔTp of the steel sheet temperature Tp is set smaller than a target allowable temperature range ΔT2a of the coiling temperature T2. It is characterized by.

  When the steel sheet temperature is the coiling temperature, the temperature due to the scale formation or poor flatness of the steel sheet surface is set by setting the tolerance ΔTp of the steel sheet temperature Tp to be smaller than the target allowable temperature range ΔT2a of the coiling temperature T2. Temperature hunting after the detection of an abnormal part is prevented and stable control is possible.

  In this invention, in the process of cooling and winding the steel sheet after hot rolling, the average temperature of the plate width direction healthy part after cooling that is not affected by the temperature abnormal part due to scale generation or flatness failure of the steel sheet surface is obtained. Since it used as steel plate temperature, the steel plate temperature measured at the time of temperature control is stabilized. In particular, when the steel sheet temperature is the coiling temperature, the allowable temperature ΔTp of the steel sheet temperature Tp is set to be smaller than the target allowable temperature range ΔT2a of the coiling temperature T2, and the average temperature Tp (Fair) of the healthy part is set. By calculating, it is possible to prevent the occurrence of temperature hunting after the detection of the temperature abnormal portion, to enable stable control, and to realize a controlled cooling process for obtaining a desired material.

  Embodiments of the present invention will be described below with reference to the accompanying FIGS.

  FIG. 1 shows a flow of temperature control in the case of performing feedback control of the winding temperature, which is an example of the temperature control method of the embodiment of the present invention. First, the target winding temperature T2a of the steel plate 8 is set, and an allowable error ΔT2 from the maximum value T2 (Max) in the plate width direction of the winding temperature distribution T2 (Y) is set (S10). Next, the sheet thickness, the sheet passing speed (finish rolling speed), and the steel sheet temperature (finish rolling temperature) T1 of the steel plate 8 that has passed through the finish rolling mill row 4a are set to the exit side of the final rolling mill 4f in the finish rolling mill row 4a. Measured by the installed thickness gauge 10 and the thermometer 9, respectively, and further by a thermometer 9a installed in front of the coiler 7, the winding temperature distribution T2 (Y) in the sheet width direction of the steel sheet (Y is a coordinate in the sheet width direction) ) Are measured (S20, S30, step 1), and these actual values are taken into the storage unit (not shown) of the computer. As for the sheet feeding speed, a value calculated based on the number of roll rotations of the final rolling mill 4f of the finish rolling mill row 4a is taken into the calculator as an actual value.

  Next, based on the actual value T2m (Y) of the winding temperature distribution T2 (Y) in the sheet width direction and the allowable error ΔT2 of the winding temperature T2, the above formula (1) is used to generate scale and flatness. A part in the plate width direction of the healthy part in which the temperature abnormality due to the defect does not occur is extracted (S40, step 2). And the average temperature T2 (Fair) of the board | plate width direction of a healthy part is calculated using said (2) Formula (S50, step 3). Next, it is determined whether the difference between the target winding temperature T2a and the average temperature T2 (Fair) of the healthy part is within the allowable temperature range ΔT2a of the target winding temperature T2a (S60). If not within the range ΔT2a, control is performed to correct the ON / OFF number of the water cooling valve of the water cooling zone 5 set by the setup control (see FIG. 5) (S70). Then, based on the actual value (T1 = T1m) (S20) of the plate thickness, plate passing speed and steel plate temperature (T1) and the ON / OFF number (S70) of the water cooling valve of the corrected water injection bank, the steel plate temperature model (water cooling Using the temperature model that predicts the temperature history of the steel plate 8 in the band 5, the winding temperature T2 is calculated again (S80). It is determined again whether the difference (abs (T2a−T2c)) between the calculated value T2c of the winding temperature T2 and the target winding temperature T2a is within the allowable temperature range ΔT2a (S90). If not within the allowable temperature range ΔT2a, the number of ON / OFF of the water cooling valve in the water cooling zone 5 is corrected again, and S70 to S90 are repeated. When it falls within the allowable temperature range ΔT2a, the feedback control at the control timing is terminated.

  The allowable error (allowable temperature error) ΔT2 from the maximum value T2 (Max) in the sheet width direction of the winding temperature T2 needs to be set smaller than the allowable temperature range ΔT2a of the target winding temperature T2a. As an example, when the allowable temperature range ΔT2a of the target winding temperature T2a is ± 20 ° C., that is, 40 ° C., the allowable error ΔT2 from the maximum value T2 (Max) of the temperature in the plate width direction is set to 2 of the allowable temperature range ΔT2a. FIGS. 2A and 2B show the results of applying the feedback control shown in FIG. 1 to the winding temperature control when the temperature is set to double the 80 ° C. FIG. When detecting an abnormal part of the temperature generated by scale generation (FIG. 10) or poor flatness (FIGS. 11 (a) and 11 (b)) and performing feedback control, the conventional central part in the plate width direction, etc. Control accuracy is improved by reaching the target temperature range ΔT2a earlier than when feedback control is performed based on temperature (see FIGS. 12A and 12B), but after detecting the temperature abnormal portion, Mild temperature hunting is observed. The control cycle on the horizontal axis is about 1 to 10 Hz.

  On the other hand, the allowable error ΔT2 is set to ΔT2 = 30 ° C. smaller than the allowable temperature range ΔT2a of the winding temperature, and the feedback control shown in FIG. 1 is applied to the winding temperature control of the embodiment. The results are shown in FIGS. 3 (a) and (b). 3 (a) and 3 (b), after detecting the temperature abnormal portion in both cases of scale generation and poor flatness, the measured value T2 (Fair) of the coiling temperature is quickly determined to be within the allowable temperature range ΔT2a (± 20 The calculated value T2c of the coiling temperature T2 and the measured value T2 (Fair) are in good agreement, and the water cooling valve is appropriately ON / OFF controlled by the feedback control shown in FIG. The effectiveness of the present invention was confirmed.

  The average temperature Tp (Fair) in the plate width direction of the healthy part calculated using the above equations (1) and (2) is not limited to the coiling temperature. It is possible to apply to the steel plate temperature at the position of the intermediate thermometer 9b of the band 5. Further, this average temperature Tp (Fair) can be applied not only to the hot-rolled steel sheet but also to the steel sheet temperature in the controlled cooling process of the thick steel sheet.

It is explanatory drawing which shows the flow of the temperature control of embodiment. (A) It is explanatory drawing which shows the temperature transition of the steel plate at the time of coiling temperature control in case an abnormal temperature part (scale production | generation part) is included (when allowable error (DELTA) T2 = 80 degreeC). (B) It is explanatory drawing which shows the temperature transition of the steel plate at the time of coiling temperature control in case an abnormal temperature part (flatness defect part) is included (when allowable error (DELTA) T2 = 80 degreeC). (A) It is explanatory drawing which shows the temperature transition of the steel plate at the time of coiling temperature control in case an abnormal temperature part (scale production | generation part) is included (when allowable error (DELTA) T2 = 30 degreeC). (B) It is explanatory drawing which shows the temperature transition of the steel plate at the time of coiling temperature control in case an abnormal temperature part (flatness defect part) is included (in the case of allowable error (DELTA) T2 = 30 degreeC). It is explanatory drawing which shows typically the cooling and winding equipment after the finishing rolling mill of a hot rolling mill. It is explanatory drawing which shows the setup control method of a general winding temperature. It is explanatory drawing which shows the feedforward control method of a general coiling temperature. It is explanatory drawing which shows the general feedback control method of coiling temperature. It is explanatory drawing which shows typically an example of transition of coiling temperature (T2) which performed feedback control (when control gain is large). It is explanatory drawing which shows typically an example of transition of winding temperature (T2) which performed feedback control (in the case of an appropriate gain). It is explanatory drawing which shows typically the temperature distribution of the board width direction of the steel plate which the low temperature part generate | occur | produced by the production | generation of the scale. (A), (b) It is explanatory drawing which shows typically the temperature distribution of the sheet width direction of the steel plate when a water pool generate | occur | produces by the flatness defect. It is explanatory drawing which shows typically the temperature transition of the steel plate at the time of coiling temperature control of a prior art in case an abnormal temperature part is included.

Explanation of symbols

1: Heating furnace 2: Slab 3: Rough rolling mill 3a: Rough rolling mill row 4, 4f: Finish rolling mill 4a: Finish rolling mill row 5: Water cooling zone 6: Hot run table 7: Coiler 8: Steel plates 9, 9a, 9b : Thermometer 10: Thickness gauge

Claims (2)

A temperature control method in steel plate cooling in the process of cooling and winding the steel plate after hot rolling in a cooling zone, wherein the temperature control method is a temperature distribution Tp (Y) in the steel plate width direction after cooling ( Y is a plate width direction coordinate), and a tolerance ΔTp from the measured maximum value Tp (Max) of the temperature in the steel plate width direction and the maximum value Tp (Max) of the steel plate temperature Tp after cooling. Using, the site in the plate width direction of the healthy part where temperature abnormality due to scale generation and flatness failure has not occurred,
Tp (Max)> Tp (Y)> Tp (Max) -ΔTp ----------------------- (1)
Step 2 where the temperature range is such that the average temperature Tp (Fair) in the plate width direction of the healthy portion is Tp (Fair) = ΣTp (Y) ΔY (Fair) / ΣΔY (Fair) ----- --------- (2)
The temperature control method in the steel plate cooling comprising the step 3 in which the average temperature Tp (Fair) in the plate width direction of the healthy part is used as the steel plate temperature in the temperature control.
Here, Σ on the right side of the above equation (2) represents the sum of only the healthy portions, ΔY (Fair) represents the plate width of each healthy portion, and ΣΔY (Fair) represents the sum of the plate widths of each healthy portion.   2. The temperature control in steel plate cooling according to claim 1, wherein the steel plate temperature is a coiling temperature, and an allowable error ΔTp of the steel plate temperature Tp is set to be smaller than an allowable temperature range ΔT2a of the coiling temperature T2. Method.

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