Method for preventing mill slip, method for rolling a metal sheet, method for manufacturing a metal sheet, apparatus for preventing mill slip, and metal sheet rolling apparatus

Abstract

To provide a mill slip prevention method, a metal plate rolling method, a metal plate manufacturing method, a mill slip prevention device and a metal plate rolling device, each enabling a plate speed to be measured without being affected by a rolling oil coolant and fumes and enabling mill slip to be prevented especially in a rolling mill intermediate stand by calculating an advance rate from the obtained plate speed.SOLUTION: A mill slip prevention method comprises: a measurement step of measuring a rotational speed of a small diameter roll which is provided on the exit side of a rolling stand and is brought into contact with a rolled material when rolling a metal plate in a rolling line in which the plurality of rolling stands are provided; a plate speed calculation step of calculating a plate speed being the speed of the rolled material on the exit side of the rolling stand from the rotational speed; an advance rate calculation step of calculating an advance rate of the rolled material from the plate speed and a peripheral speed of a pressure roll of the rolling stand; and an adjustment step of changing a rolling condition of at least one of the rolling stand and the small diameter roll when the advance rate becomes equal to or less than a preset threshold.SELECTED DRAWING: Figure 3

Description

Technical Field

[0001] The present invention relates to a method for preventing mill slip, a method for rolling a metal sheet, a method for manufacturing a metal sheet, a mill slip prevention device, and a metal sheet rolling device.

Background Art

[0002] In cold rolling of steel sheets, when the concentration of lubricating oil is too high, the number of rolling passes increases, and the roughness of the work roll (WR) decreases, the steel sheet being rolled slips on the rolling mill, and the occurrence of mill slip increases. When mill slip occurs, thickness fluctuations occur, resulting in defective quality parts and a decrease in yield. In the worst case, sheet breakage occurs, leading to a decrease in productivity due to a long line stop. As an evaluation of mill slip, the advancement rate obtained from the speed difference between the WR speed and the sheet speed on the mill exit side is used. Since the work roll is a driving roll, it is easy to obtain the circumferential speed from the motor rotation speed. Therefore, the important thing is the measurement of the sheet speed, and generally, a laser Doppler type sheet speed meter is used. However, between the stands of the rolling mill, due to the poor environment where rolling oil coolant and fumes can accumulate, the laser Doppler sheet speed meter, which is an optical device, is affected by the measurement and is difficult to maintain and manage.

[0003] In Patent Document 1, a slip prevention technique is proposed in which the advancement rate is measured, and when the advancement rate becomes equal to or less than a threshold value, tension control is performed so that the advancement rate becomes equal to or greater than the threshold value, and the tension setting table is updated. However, there is no mention of the method of the sheet speed meter, and it is difficult to measure at the intermediate stand due to the above-mentioned problems. Also, the rolling conditions are controlled only by tension. Generally, when the rolling speed is low, it is advantageous for slip, so the control of the rolling speed is on the deceleration side, leading to a decrease in production efficiency. However, for some materials, when the rolling speed is equal to or higher than a certain value, the advancement rate tends to increase. Therefore, for such materials, the control of the rolling speed is also useful for slip prevention.

Prior Art Documents

Patent Documents

[0004] Patent Document 1 Japanese Patent Application Laid-Open No. 2017-70953 Summary of the Invention Problems to be Solved by the Invention

[0005] As described above, a laser Doppler plate speed meter may be used to measure the speed of a steel plate in cold rolling. However, between the stands of a rolling mill, due to the poor environment where rolling oil coolant and fumes accumulate, the laser Doppler plate speed meter, which is an optical instrument, is affected by the measurement and is difficult to maintain and manage, which poses a problem. Therefore, the present invention has been made paying attention to the above problems, and it is possible to measure the plate speed without being affected by rolling oil coolant and fumes, and by calculating the lead ratio from the obtained plate speed, it is possible to prevent mill slip, especially in the intermediate stand of a rolling mill. An object of the present invention is to provide a mill slip prevention method, a metal plate rolling method, a metal plate manufacturing method, a mill slip prevention device, and a metal plate rolling device. Means for Solving the Problems

[0006] (1) According to one aspect of the present invention, when rolling a metal plate in a rolling line provided with a plurality of rolling mill stands, it is provided on the outlet side of at least any one of the plurality of rolling mill stands, and measures the rotational speed of a small-diameter roll in contact with the material to be rolled. A measurement step, a plate speed calculation step of calculating the plate speed, which is the speed of the material to be rolled on the outlet side of any one of the rolling mill stands, from the rotational speed, and the plate speed and the circumferential speed of the rolling roll of any one of the rolling mill stands. An advancement rate calculation step of calculating the advancement rate of the material to be rolled, and an adjustment step of changing at least one of the rolling conditions of any one of the rolling mill stands and the small-diameter roll when the advancement rate becomes equal to or less than a preset threshold value. A mill slip prevention method is provided.

[0007] (2) In the method for preventing mill slip according to (1) above, as the small-diameter roll, a roll having a slit at its end is used, and in the measurement step, an eddy current sensor is used to measure the rotational speed of the small-diameter roll. (3) The method for preventing mill slip according to claim 2, wherein in the measurement step, the rotational speed is measured by counting the number of passes of the slit using the eddy current sensor, and a variable threshold value is used as the threshold value of the downstream sensor when detecting the passage of the slit.

[0008] (4) In any one of the methods for preventing mill slip according to (1) to (3) above, in the strip speed calculation step, the strip speed at the center position of the thickness of the material to be rolled is calculated by adding the thickness of the material to be rolled to the diameter of the small-diameter roll to calculate the peripheral speed of the small-diameter roll. (5) In any one of the methods for preventing mill slip according to (1) to (4) above, in the strip speed calculation step, a smoothed strip speed is calculated by performing a moving average on the calculated strip speed.

[0009] (6) In any one of the methods for preventing mill slip according to (1) to (5) above, in the strip speed calculation step, the sampling period for obtaining the measurement result of the rotational speed in the measurement step is calculated from the sampling theorem at the maximum strip speed of the target line. (7) According to one aspect of the present invention, there is provided a method for rolling a metal sheet using any one of the methods for preventing mill slip according to (1) to (6) above. (8) According to one aspect of the present invention, there is provided a method for manufacturing a metal sheet using any one of the methods for preventing mill slip according to (1) to (6) above.

[0010] (9) According to one aspect of the present invention, it is provided on a rolling line provided with a plurality of rolling mill stands, provided on the outlet side of at least any one of the plurality of rolling mill stands, a small-diameter roll in contact with the material to be rolled, a speedometer for measuring the rotational speed of the small-diameter roll, calculating the sheet speed, which is the speed of the material to be rolled on the outlet side of any one of the rolling mill stands, from the rotational speed, and further calculating the advancement rate of the material to be rolled from the peripheral speed of the rolling roll of any one of the rolling mill stands, and a control device for changing at least one of the rolling conditions of any one of the rolling mill stands and the small-diameter roll when the advancement rate becomes equal to or less than a preset threshold value, a mill slip prevention device is provided.

[0011] (10) In the mill slip prevention device of (9) above, the small-diameter roll has a slit at the end, and the speedometer is an eddy current sensor. (11) According to one aspect of the present invention, a metal sheet rolling device provided with the mill slip prevention device of (9) or (10) above is provided.

Effects of the Invention

[0012] According to one aspect of the present invention, it is possible to measure the sheet speed without being affected by rolling oil coolant or fumes, and by calculating the advancement rate from the obtained sheet speed, it is possible to prevent mill slip particularly at the intermediate stand of the rolling mill, a mill slip prevention method, a metal sheet rolling method, a metal sheet manufacturing method, a mill slip prevention device, and a metal sheet rolling device are provided.

Brief Description of the Drawings

[0013]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Figure 6

Mode for Carrying Out the Invention

[0014] In the following detailed description, embodiments of the present invention will be described with reference to the drawings. In the description of the drawings, the same or similar parts are denoted by the same or similar reference numerals, and duplicate descriptions are omitted. Each drawing is schematic and may differ from the actual one. Further, the embodiments shown below are examples of devices and methods for embodying the technical idea of the present invention, and the technical idea of the present invention does not specify the materials, structures, arrangements, etc. of the components as the following. The technical idea of the present invention can be variously modified within the technical scope defined by the claims described in the claims.

[0015] <Mill Slip Prevention Device> A mill slip prevention device 1 according to an embodiment of the present invention is provided in a cold rolling line where cold rolling of a steel sheet 3 is performed, as shown in FIG. 1. In the cold rolling line, a plurality of rolling mill stands 2 having work rolls 20, which are a pair of rolling rolls, are arranged side by side in the rolling direction of the steel sheet 3. Further, in the cold rolling line, a plurality of small-diameter rolls 10 that are in contact with the steel sheet 3 and adjust the tension of the steel sheet 3 to be rolled are provided between adjacent rolling mill stands 2. Furthermore, in the cold rolling line, the rolling speed and reduction ratio at the rolling mill stand 2 and the tension at the plurality of small-diameter rolls 10 are adjusted by a control device 13 described later. In the example shown in FIG. 1, only one rolling mill stand 2 is illustrated, and as the cold rolling line, at least one rolling mill stand 2 is provided on the downstream side in the conveyance direction (the right side in FIG. 1) of the illustrated rolling mill stand 2. Further, when the illustrated rolling mill stand 2 is an intermediate rolling mill stand, at least one more rolling mill stand 2 is further provided on the upstream side in the conveyance direction (the left side in FIG. 1).

[0016] The mill slip prevention device 1 includes a small-diameter roll 10a, a speedometer 11, an arithmetic unit 12, and a control unit 13. The small-diameter roll 10a is one of a plurality of small-diameter rolls 10 provided between the rolling mill stands 2, that is, on the outlet side of the rolling mill stand 2 shown in FIG. 1. As shown in FIG. 2, the small-diameter roll 10a is provided with at least one slit 100 on the circumferential side surface of the end portion in the longitudinal direction parallel to the rotation axis. When a plurality of slits 100 are provided, the slits 100 are provided at equal intervals in the circumferential direction of the small-diameter roll 10a. In order to improve the measurement accuracy, it is preferable to provide four or more slits 100 and shorten the distance between the slits 100. Further, the slit 100 is a groove having a depth detectable by the speedometer 11. In the example shown in FIG. 2, the shape of the slit 100 is rectangular, but other shapes may be used as long as they are detectable by the speedometer 11. Furthermore, the slit 100 is preferably provided at a location that does not contact the steel plate 3 at the end of the small-diameter roll 10a.

[0017] The speedometer 11 is an eddy current sensor and is provided so as to be able to measure the end portion of the small-diameter roll 10a provided with the slit 100. In such a speedometer 11, by measuring the end portion of the small-diameter roll 10a, a change in voltage generated when the small-diameter roll 10a rotates and the slit 100 reaches the measurement position is detected. Thereby, the passage of the slit 100 can be detected from this change in voltage. Then, from the time from when the slit 100 passes until the next slit 100 passes and the distance between the slits 100, the rotational speed N [revolutions / min (rpm)] of the small-diameter roll 10a can be calculated.

[0018] As will be described later, the arithmetic unit 12 calculates the sheet speed v [m / min (mpm)] and the forward slip rate f of the steel plate 3 on the outlet side of the rolling mill stand 2 using the rotational speed N of the small-diameter roll 10a measured by the speedometer 11. As will be described later, the control unit 13 determines the possibility of mill slip occurring using the forward slip rate f calculated by the arithmetic unit 12, and adjusts rolling conditions such as the tension of the steel plate 3 and the rolling speed as necessary.

[0019] <Method for Preventing Mill Slip> In the method for preventing mill slip according to this embodiment, first, as shown in FIG. 3, a measurement step (S100) of measuring the rotational speed N of the small-diameter roll 10a by the speedometer 11 is performed. The rotational speed N measured in step S100 is transmitted to the arithmetic unit 12.

[0020] In the measurement step, an overcurrent sensor is used as the speedometer 11 to detect a change in voltage that occurs when the slit 100 of the small-diameter roll 10a reaches the measurement position, and the rotational speed N is measured by counting the number of passages of the slit 100. The determination that the slit 100 has passed is based on the criterion that the detected voltage exceeds a certain threshold value. As the threshold value, a constant voltage value may be used. However, there is a possibility that the detection output may change due to disturbances or the like. At this time, if the threshold value is determined to be a constant value, it may not be possible to accurately determine the passage of the slit 100. For example, FIG. 4 shows a state in which the detection output (voltage) has changed due to disturbances or the like in the determination with a constant threshold value. In FIG. 4, the timing at which the detection output indicated by the dotted line exceeds the threshold value is detected as the timing of the passage of the slit 100. As shown in FIG. 4, when the detection output (voltage in FIG. 4) changes due to factors such as disturbances, the passage of the slit 100 may not be detected if the threshold value is constant.

[0021] In order to cope with such changes in detection output, it is preferable to use a variable threshold as the threshold value. By using a variable threshold value, it is possible to accurately determine passage even in the presence of disturbances. As a method of using a variable threshold value, for example, as shown in FIG. 5, the most recent output record of the speedometer 11 may be subjected to a moving average, and the obtained value may be used as the threshold value for passing through the slit 100. Alternatively, a value obtained by adding +α to the most recent detection record at a location other than the slit 100 may be used as the threshold value. In this case, for example, when there are a plurality of slits 100, the location other than the slit 100 may be between adjacent slits 100. FIG. 6 shows a case where a value obtained by adding +α to the detection record between the slits 100 is used as the threshold value when there are a plurality of slits 100. In FIG. 6, the section where the voltage value is constant is the location between the slits 100, and when the voltage value in this section is exceeded, passage through the slit 100 is detected.

[0022] Next, a plate speed calculation step of calculating the plate speed v of the steel plate 3 by the arithmetic unit 12 is performed (S102). In the plate speed calculation step, the arithmetic unit 12 uses the following formula (1) to calculate the plate speed v, which is the speed of the steel plate 3 on the outlet side of the rolling mill stand 2, from the rotational speed N of the small-diameter roll 10a measured in step S100, the diameter D [mm] of the small-diameter roll 10a, and the plate thickness t [mm] of the steel plate 3. In the calculation of the plate speed v using formula (1), the circumferential speed at the center position of the plate thickness of the steel plate 3 is calculated as the plate speed v by adding the plate thickness t of the steel plate 3 to the diameter D of the small-diameter roll 10a. v = N × π × (D + t) / 1000 ···(1)

[0023] In the plate speed calculation step, when calculating the plate speed v from the results obtained from the speedometer 11, the arithmetic unit 12 acquires the measurement result of the circumferential speed at the speedometer 11 at a sampling period β [msec]. And the sampling period required to accurately detect the slit 100 is set as follows. The ON time interval T [msec] of the detection voltage is related to the detection range d [mm] of the speedometer 11, the length h [mm] of the slit 100, and the maximum plate speed V of the target line MAXIt is represented by the formula (2) using [m / min]. And the sampling period required to accurately detect the slit 100 is obtained from the sampling theorem by the formula (3). Note that the sampling period in the formula (3) is the minimum required value, and the set sampling period β is preferably shorter than this. T = (d + h) / V MAX ×60 ···(2) β = T / 2 ···(3)

[0024] Furthermore, an advancement rate calculation step for calculating the advancement rate f of the steel plate 3 by the arithmetic unit 12 is performed (S104). In the advancement rate calculation step, the plate speed v calculated in step S102 and the WR speed v which is the peripheral speed of the work roll 20 R are used to calculate the advancement rate f using the following formula (4). The work roll 20 for which the WR speed V R is used is the work roll closest to the upstream side in the conveyance direction of the small-diameter roll 10a as shown in FIG. 1. The arithmetic unit 12 obtains the WR speed V of the work roll 20 R either via the control device 13 or directly from the work roll 20. Note that the WR speed V R is the same as the rolling speed in the rolling mill stand 2. f = (v - v R ) / v R ···(4)

[0025] Thereafter, the control device 13 determines whether or not the advancement rate f is equal to or less than a preset threshold value (S106). The threshold value is set as a value that can prevent the occurrence of mill slip, and can be, for example, 0.0048 (0.48%). When it is determined in step S106 that the lead ratio f is less than or equal to the threshold value, the control device 13 determines that there is a possibility of mill slip occurring, and performs an adjustment process of adjusting the rolling conditions of the steel sheet 3 (S108). The rolling conditions include the inter-stand tension which is the tension of the steel sheet 3 between the rolling mill stands 2, the rolling speed, and the reduction ratio conditions. The control device 13 adjusts at least one of the inter-stand tension, the rolling speed, and the reduction ratio conditions by controlling at least one of the small-diameter rolls 10 and the rolling mill stands 2. Note that how much the control device 13 adjusts each condition is appropriately set according to various conditions such as the specifications of the cold rolling line, the installation position of the rolling mill stands, the rolling conditions before adjustment, the size and steel type of the steel sheet 3, etc. Also, the adjustment cost of the rolling conditions may be determined from past rolling results.

[0026] When it is determined in step S106 that the lead ratio f exceeds the threshold value, or after step S108, the mill slip prevention process shown in FIG. 3 ends. Note that the process shown in FIG. 3 is preferably repeated while the steel sheet 3 is being rolled in the cold rolling line. According to the mill slip prevention device 1 and the mill slip prevention method having the above configuration, by using the eddy current sensor in the speedometer 11, the speed of the steel sheet 3 can be accurately measured without being affected by the rolling oil coolant or fumes. Therefore, even in a poor environment between the rolling mill stands 2, the lead ratio f can be accurately calculated, and by adjusting the rolling conditions using the calculated lead ratio f, the occurrence of mill slip can be prevented. As a result, a decrease in production efficiency can be suppressed, and the yield of the product can also be improved. Also, compared with the case of using optical equipment, maintenance and management are easier. Note that the mill slip prevention device 1 according to the present embodiment is particularly effective when the rolling mill stand 2 is an intermediate stand in the cold rolling line.

[0027] In the method for manufacturing a metal plate according to the present embodiment, a steel plate 3 which is a metal plate is manufactured using the method for preventing mill slip according to the present embodiment. Further, in the method for rolling a metal plate according to the present embodiment, the steel plate 3 which is a metal plate is rolled using the method for preventing mill slip according to the present embodiment. Furthermore, the metal plate rolling apparatus according to the present embodiment is a cold rolling line which is a metal plate rolling apparatus, and includes the mill slip preventing apparatus according to the present embodiment.

[0028] <Modification example> As described above, the present invention has been described with reference to specific embodiments, but these descriptions are not intended to limit the invention. By referring to the description of the present invention, those skilled in the art will also be clear about other embodiments of the present invention including various modification examples together with the disclosed embodiments. Therefore, it should be understood that the embodiments of the invention described in the claims also cover embodiments including these modification examples described herein alone or in combination.

[0029] For example, in the above embodiment, the case of rolling a steel plate on a cold rolling line has been described, but the present invention is not limited to such an example. For example, not limited to a cold rolling line, other rolling lines may be used as long as they are facilities for continuous rolling with a plurality of rolling mill stands. Further, the material to be rolled may be a metal plate other than the steel plate 3, such as an aluminum plate. Also, in the above embodiment, it is assumed that the change of the rolling conditions is automatically performed by the control device 13, but the present invention is not limited to such an example. For example, when it is determined in step S106 that the draft f is equal to or less than the threshold value, a configuration may be adopted in which the operator is notified by voice or display that the draft f is decreasing. In this case, when the decrease of the draft f is notified, the operator appropriately adjusts the rolling conditions manually.

[0030] Furthermore, in the above embodiment, an eddy current sensor is used for the speedometer 11, but the present invention is not limited to such an example. Furthermore, the mill slip prevention device 1 may be provided on at least one of the plurality of rolling mill stands 2 provided on the cold rolling line. That is, a plurality of mill slip prevention devices 1 may be provided on the plurality of rolling mill stands 2 respectively.

[0031] Furthermore, in the above embodiment, the plate speed v is calculated using the formula (1), but the present invention is not limited to such an example. For example, when the steel plate 3 is sufficiently small with respect to the diameter of the small-diameter roll 10a, etc., when the lead ratio f can be calculated with sufficient accuracy without considering the plate thickness t, the plate speed v may be calculated by the following formula (5) without considering the plate thickness t. As described above, by considering the plate thickness t, the lead ratio f can be calculated with higher accuracy. v = N×π×D / 1000 ···(5)

[0032] Furthermore, in the above embodiment, it is preferable to provide four or more slits 100 in order to improve the measurement accuracy. However, the number of slits 100 that can be created depends on mechanical constraints and system constraints. As a mechanical constraint, the maximum number of slits is determined so as not to detect two slits simultaneously from the size of the sensor head of the speedometer 11. As shown in the formula (6), using the width h [mm] of the slit 100, the diameter D [mm] of the small-diameter roll 10a, and the distance H [mm] between the slits 100, the maximum number of grooves n is calculated by dividing the circumference of the small-diameter roll by the sum of the width h and the distance H. And the number of slits to be created is required to be n or less. In addition, in order to prevent the speedometer 11 from detecting two slits 100 simultaneously, h ≤ H. As a system constraint, since the operation cycle α of the arithmetic unit 13 needs to be less than or equal to half of the time for passing through the speedometer 11 of the slit 100, from the operation cycle α [msec] of the arithmetic unit 13 and the maximum plate speed V MAX [m / min] of the target line, the maximum number of grooves m is calculated using the formula (7). The smaller of the calculated maximum number of grooves n due to mechanical constraints and the maximum number of grooves m due to system constraints becomes the finally determined maximum number of grooves, leading to the maximum accuracy limit. n = D×π / (H + h) ···(6) m = D×π×30 / (VMAX ×α) ···(7)

[0033] As an example, the concept when it is assumed that the width h of the slit 100 is 10 mm, the diameter D of the small-diameter roll 10a is 240 mm, the calculation cycle of the arithmetic unit is 1 msec, and the maximum sheet speed of the line is 1320 m / min will be described. First, since the width h of the slit 100 is 10 mm, from h ≦ H, the distance H between the slits 100 must be at least 10 mm. Including this, it can be seen from equation (6) that the maximum number of grooves n for mechanical constraints is 37. Next, it can be seen from equation (7) that the maximum number of grooves m for system constraints is 17. Comparing the maximum number of grooves n for mechanical constraints and the maximum number of grooves m for system constraints, the final maximum number of grooves is 17. Dividing the circumference of the small-diameter roll by this number of grooves gives approximately 44 mm. That is, H + h is 44 mm. Here, consider the influence on the speed for one slit. Assume the cases where the slit passes 22 times and 23 times in 100 msec, and calculate the distance the sheet advances in 100 msec for each number of passing slits and the speed at this time. As a result, as shown in Table 1, the influence on the speed of one slit is approximately ±13 m / min when considered proportionally. The percentage of the degree of influence of this speed difference on the peripheral speed of the WR is defined as the advancement rate accuracy [%], and the results calculated using equation (4) are shown in Table 2.

[0034]

Table 1

[0035]

Table 2

[0036] If the necessary number of slits 100 cannot be obtained and the target measurement accuracy cannot be sufficiently achieved, smoothing processing such as moving average may be performed on the calculated plate speed. When the influence on the speed caused by the number of slits is added to the actual speed, the detection speed is dispersed into two values. This degree of dispersion leads to poor accuracy. In this method, by utilizing the correlation between the ratio of the appearance frequencies of these two dispersed values and the actual speed, and performing smoothing to estimate the actual speed based on the bias of these two values, the advancement rate accuracy [%] can be improved. Furthermore, since the influence of a difference in the number of passing slits due to the reading start timing on the total number of passing slits in the moving average section decreases in inverse proportion to the moving average number, it is possible to improve the advancement rate accuracy [%] by increasing the moving average number. Table 3 shows the advancement rate accuracy [%] for each moving average number when the number of slits is 4, the slit width h is 10 mm, the small-diameter roll diameter D is 240 mm, the WR speed is 991.5 m / min, the maximum plate speed of the line is 1320 m / min, and the calculation period of the arithmetic unit is 1 msec. However, due to the delay in the calculation result compared with the actual speed accompanying the smoothing process, appropriate adjustment is necessary.

[0037]

Table 3

Example

[0038] Examples conducted by the present inventors will be described. In the examples, steel plates 3 with different strength standards were cold-rolled while changing the rolling speed, and the change in the advancement rate f was investigated. Specifically, for materials with a strength standard of 270 MPa to 590 MPa, rolling was performed at a maximum of 6 levels of rolling speed from 300 m / min to 1200 m / min, and the advancement rate f was measured. Table 1 shows the measurement results of the advancement rate f under each condition. In Table 1, the unit of the advancement rate f is %, and it is the value obtained by multiplying the value calculated by equation (4) by 100.

[0039]

Table 4

[0040] In the example, the occurrence of mill slip was confirmed under the conditions where the strength standard was 590 MPa and the rolling speed was 600 m / min (draft rate f: -0.58%). Also, the occurrence of mill slip was not confirmed under other conditions. Therefore, it was confirmed that it is possible to prevent mill slip by maintaining a draft rate f of -0.48% or more, which is the minimum among the conditions where mill slip was not confirmed. Also, when the rolling speed is high, the draft rate f decreases. Therefore, it is useful to control the rolling speed so that the draft rate f does not become lower than the above-mentioned slip limit value (-0.48%) in order to prevent slip. However, for the case where the strength standard is 340 MPa, a tendency was confirmed that the draft rate f increases with an increase in speed with a rolling speed of 800 m / min as the boundary. In this case, it is possible to achieve both prevention of mill slip and improvement of production efficiency by avoiding the speed range where the draft rate f is the lowest and increasing the rolling speed.

Explanation of Signs

[0041] 1 Mill slip prevention device 10, 10a Small-diameter roll 100 Slit 11 Speedometer 12 Arithmetic unit 13 Control device 2 Rolling mill stand 20 Work roll 3 Steel plate

Claims

1. When rolling a metal sheet on a rolling line provided with a plurality of rolling mill stands, a measuring step of measuring the rotational speed of a small-diameter roll provided on the outlet side of at least one of the plurality of rolling mill stands and adjusting the tension in contact with the material to be rolled; a sheet speed calculating step of calculating the sheet speed, which is the speed of the material to be rolled on the outlet side of any one of the rolling mill stands, from the rotational speed; an advancement rate calculating step of calculating the advancement rate of the material to be rolled from the sheet speed and the peripheral speed of the rolling roll of any one of the rolling mill stands; an adjustment step of changing at least one of the rolling conditions of any one of the rolling mill stands and the small-diameter roll when the advancement rate becomes equal to or less than a preset threshold value; comprising In the sheet speed calculating step, the sheet speed at the center position of the sheet thickness of the material to be rolled is calculated by calculating the peripheral speed of the small-diameter roll by adding the sheet thickness of the material to be rolled to the diameter of the small-diameter roll. A method for preventing mill slip.

2. As the small-diameter roll, one having a slit at the end is used, In the measuring step, the rotational speed of the small-diameter roll is measured using an eddy current sensor. The method for preventing mill slip according to claim 1.

3. In the measuring step, the rotational speed is measured by counting the number of passages of the slit using the eddy current sensor, and a variable threshold value is used as the threshold value of the eddy current sensor when detecting the passage of the slit. The method for preventing mill slip according to claim 2.

4. In the sheet speed calculating step, a smoothed sheet speed is calculated by moving-averaging the calculated sheet speed. The method for preventing mill slip according to any one of claims 1 to 3.

5. In the sheet speed calculating step, the sampling period for obtaining the measurement result of the rotational speed in the measuring step is calculated from the sampling theorem at the maximum sheet speed of the target line. The method for preventing mill slip according to any one of claims 1 to 3.

6. A method for rolling a metal sheet, using the method for preventing mill slip according to any one of claims 1 to 3.

7. A method for rolling a metal sheet, using the method for preventing mill slip according to claim 4.

8. A method for rolling a metal sheet, using the method for preventing mill slip according to claim 5.

9. A method for manufacturing a metal sheet, using the method for preventing mill slip according to any one of claims 1 to 3.

10. A method for manufacturing a metal sheet, using the method for preventing mill slip according to claim 4.

11. A method for manufacturing a metal sheet, using the method for preventing mill slip according to claim 5.

12. It is provided on a rolling line provided with a plurality of rolling mill stands, A small-diameter roll provided on the outlet side of at least any one of the plurality of rolling mill stands, which adjusts the tension in contact with the material to be rolled, A speedometer for measuring the rotational speed of the small-diameter roll, From the rotational speed, a plate speed, which is the speed of the material to be rolled on the outlet side of any one of the rolling mill stands, is calculated. Further, from the peripheral speed of the rolling roll of any one of the rolling mill stands, an arithmetic unit for calculating the lead ratio of the material to be rolled, A control device that changes at least one of the rolling conditions of any one of the rolling mill stands and the small-diameter roll when the lead ratio becomes equal to or less than a preset threshold value, Comprising, The arithmetic unit calculates the plate speed at the center position of the plate thickness of the material to be rolled by calculating the peripheral speed of the small-diameter roll by adding the plate thickness of the material to be rolled to the diameter of the small-diameter roll, a mill slip prevention device.

13. The small-diameter roll has a slit at its end, The speedometer is an eddy current sensor, the mill slip prevention device according to claim 12.

14. A metal sheet rolling device comprising the mill slip prevention device according to claim 12 or 13.

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