Roll peripheral speed control device, roll peripheral speed control method, and method for manufacturing hot-rolled steel strip

Abstract

To provide a roll peripheral speed control device, roll peripheral speed control method, and method for manufacturing a hot-rolled steel strip capable of suppressing warping from the time before a pre-finishing stage only with a change in operational conditions without additional equipment investment.SOLUTION: A roll peripheral speed control device 10, when rough rolling a slab S using a rough rolling mill 3 which consists of multiple rough rolling stands R1 to Rn including an upstream rough rolling stand Rn-1 and a downstream rough rolling stand Rn capable of performing tandem rolling, controls the peripheral speeds of work rolls 3a, 3b in the upstream rough rolling stand Rn-1 and the downstream rough rolling stand Rn such that the rolling speed of the slab S by the upstream rough rolling stand Rn-1 alone is slower than the rolling speed of the slab S by both of the upstream rough rolling stand Rn-1 and the downstream rough rolling stand Rn after the slab S is bitten by the downstream rough rolling stand Rn.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to a roll peripheral speed control device that controls the peripheral speeds of the work rolls of an upstream roughing mill and a downstream roughing mill when rough rolling a slab using a plurality of roughing mills including an upstream roughing mill and a downstream roughing mill capable of tandem rolling, a roll peripheral speed control method, and a method for manufacturing a hot-rolled steel strip. [Background technology]

[0002] In general, hot-rolled steel strips are produced by heating a slab to a predetermined temperature in a heating furnace, rolling this heated slab to a predetermined thickness in a roughing mill to form a rough bar, heating the rough bar with a heating device such as an edge heater or a bar heater, and then finish-rolling it in a finishing mill consisting of multiple stands to form a hot-rolled steel strip of a predetermined thickness, cooling this hot-rolled steel strip on a hot table with a cooling device, and then winding it up with a coiler.

[0003] In the continuous hot rolling for producing such hot rolled steel strips, shape defects such as "warping" at the tip of the rolled material may occur at each stand of the roughing mill and the finishing mill. If the tip of the rolled material is warped upward, it may come into contact with the equipment inside the rolling mill, causing damage to the equipment or leaving the hot rolled steel strip as a semi-finished product. In such a case, the rolling of the subsequent cycle must be stopped, resulting in a significant loss of operational productivity.

[0004] As conventional examples for reducing the upward camber at the leading end of a hot-rolled steel strip, those shown in Patent Documents 1 and 2, for example, are known. The method for manufacturing a hot-rolled steel strip shown in Patent Document 1 involves roughly rolling a slab into a rough bar using a rough rolling mill, roughly straightening the warp of the rough bar using a first warp straightening device, and then finish-straightening the warp of the rough bar using a second warp straightening device. Thereafter, the rough bar is heated using an induction heating device, and the heated rough bar is subsequently finish-rolled using a finish rolling mill to produce a hot-rolled steel strip.

[0005] This makes it possible to suppress warping that occurs at the tip of the rough bar due to rough rolling and to properly straighten the bar before sending it to the finish rolling process. In addition, the method of reducing the tip upward warpage of a hot-rolled steel sheet in hot finish rolling shown in Patent Document 2 is to perform hot finish rolling of a steel sheet using a finishing mill consisting of multiple horizontal rolling mills, in which at least one or more horizontal rolling mills are used preferentially from the front stage to perform horizontal rolling to the product thickness, and the remaining rear stage horizontal rolling mills are pass-through stands that do not perform horizontal rolling. Then, the roll gap of this pass-through stand is set to be 1 to 10 mm larger than the product thickness, and the roll peripheral speed is set to be faster than the roll peripheral speed of the final horizontal rolling mill among the front stage horizontal rolling mills that performed horizontal rolling to the product thickness, to perform hot finish rolling.

[0006] This makes it possible to reduce the amount of upward warping of the hot-rolled steel sheet at the exit of the finishing rolling mill, and to suppress the occurrence of problems with winding by the coiler and variations in the cooling rate within the steel sheet during water cooling performed after finishing rolling. [Prior art documents] [Patent documents]

[0007] [Patent Document 1] JP 2004-351484 A [Patent Document 2] JP 2015-42410 A Summary of the Invention [Problem to be solved by the invention]

[0008] However, the conventional method for producing a hot-rolled steel strip disclosed in Patent Document 1 and the method for reducing tip upward warping of a hot-rolled steel sheet in hot finish rolling disclosed in Patent Document 2 have the following problems. That is, in the case of the hot-rolled steel strip manufacturing method shown in Patent Document 1, in addition to the roughing mill, the induction heating device, and the finishing rolling mill, first and second warping straightening devices are required, which poses a problem of high capital investment costs.

[0009] In addition, in the case of the method for reducing the tip upward warpage of a hot-rolled steel sheet in hot finish rolling shown in Patent Document 2, the warpage in the horizontal rolling mill on the rear stage of the finishing mill can be suppressed, but the warpage before the horizontal rolling mill on the rear stage of the finishing mill including the roughing mill cannot be dealt with. Therefore, the present invention has been made to solve these conventional problems, and an object of the present invention is to provide a roll peripheral speed control device, a roll peripheral speed control method, and a hot rolled steel strip manufacturing method that can suppress warping before the pre-finishing stage by simply changing the operating conditions without making additional capital investments. [Means for solving the problem]

[0010] In order to solve the above problems, one embodiment of the present invention provides a roll peripheral speed control device that controls the peripheral speeds of the work rolls of the upstream rough rolling stand and the downstream rough rolling stand when rough rolling a slab using a rough rolling mill consisting of multiple rough rolling stands, including an upstream rough rolling stand and a downstream rough rolling stand capable of tandem rolling, and controls the peripheral speeds of the work rolls of the upstream rough rolling stand and the downstream rough rolling stand so that the rolling speed of the slab by only the upstream rough rolling stand is slower than the rolling speed of the slab by both the upstream rough rolling stand and the downstream rough rolling stand after the slab is bitten into the downstream rough rolling stand.

[0011] In addition, a roll peripheral speed control method according to another aspect of the present invention is a roll peripheral speed control method for controlling the peripheral speeds of the work rolls of each of the upstream rough rolling stand and the downstream rough rolling stand when rough rolling a slab using a rough rolling mill consisting of multiple rough rolling stands, including an upstream rough rolling stand and a downstream rough rolling stand capable of tandem rolling, and the gist of the method is to control the peripheral speeds of the work rolls of each of the upstream rough rolling stand and the downstream rough rolling stand so that the rolling speed of the slab by only the upstream rough rolling stand is slower than the rolling speed of the slab by both the upstream rough rolling stand and the downstream rough rolling stand after the slab is bitten into the downstream rough rolling stand.

[0012] In addition, a manufacturing method of a hot-rolled steel strip according to another aspect of the present invention is characterized in that, when rough rolling a slab using a rough rolling mill consisting of multiple rough rolling stands, including an upstream rough rolling stand and a downstream rough rolling stand capable of tandem rolling, the rough rolling step includes controlling the peripheral speeds of the work rolls of the upstream rough rolling stand and the downstream rough rolling stand using the above-mentioned roll peripheral speed control method to rough roll the slab. Effect of the Invention

[0013] According to the roll peripheral speed control device, the roll peripheral speed control method, and the hot-rolled steel strip manufacturing method of the present invention, warping before the pre-finishing stage can be suppressed simply by changing the operating conditions without making any additional capital investment. [Brief description of the drawings]

[0014] [Figure 1] 1 is a schematic configuration diagram of a hot rolling line equipped with a roll peripheral speed control device according to an embodiment of the present invention. [Diagram 2] 2 is a flowchart for explaining a process flow in the roll peripheral speed control device shown in FIG. [Diagram 3] FIG. 2 is a schematic diagram showing the mechanism of bowing caused by the bite angle of a steel sheet on the entry side of a rolling mill. [Figure 4]FIG. 2 is a schematic diagram showing the mechanism of bowing caused by the bite angle of a steel sheet on the entry side of a rolling mill. [Diagram 5] This is a schematic diagram to explain the mechanism by which the rolling speed of the slab by only the upstream rough rolling stand is made slower than the rolling speed of the slab by both the upstream rough rolling stand and the downstream rough rolling stand, thereby applying tension to the slab at the moment of being bitten by the downstream rough rolling stand, thereby suppressing the occurrence of warping. [Figure 6] 1 is a graph showing the relationship between the thickness of a hot-rolled steel strip and the amount of upward camber at the delivery side of a finishing rolling stand F1, comparing a case where a hot-rolled steel strip is produced according to an example of the present invention with a case where a hot-rolled steel strip is produced according to a comparative example. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0015] Hereinafter, embodiments of the present invention will be described with reference to the drawings. The embodiments shown below are merely examples of devices and methods for embodying the technical concept of the present invention, and the technical concept of the present invention is not limited to the following embodiments in terms of the materials, shapes, structures, arrangements, etc. of the components. In addition, the drawings are schematic, and therefore, it should be noted that the relationship between thickness and planar dimensions, ratios, etc. may differ from the actual relationship between thickness and planar dimensions, and the drawings may include parts in which the relationship between dimensions and ratios differ from one another.

[0016] FIG. 1 shows a schematic configuration of a hot rolling line equipped with a roll peripheral speed control device according to one embodiment of the present invention. The hot rolling line 1 shown in Fig. 1 includes a heating furnace 2 for heating a slab S to a predetermined temperature, a rough rolling mill 3 for rough rolling the heated slab S to a predetermined thickness to produce a rough bar B, and a finish rolling mill 4 for finish rolling the rough rolled rough bar B to produce a hot rolled steel strip SP of a predetermined plate thickness. The hot rolling line 1 also includes a cooling device 5 for cooling the finish rolled hot rolled steel strip SP, and a winding device 7 for winding the cooled hot rolled steel strip SP via pinch rolls 6.

[0017] In other words, the hot rolled steel strip SP is manufactured through a heating process in which the slab S is heated to a predetermined temperature in a heating furnace 2, a rough rolling process in which the heated slab S is roughly rolled to a predetermined thickness in a rough rolling mill 3 to form a rough bar B, a finish rolling process in which the rough rolled rough bar B is finish rolled in a finish rolling mill 4 to form a hot rolled steel strip SP of a predetermined plate thickness, a cooling process in which the hot rolled steel strip SP is cooled in a cooling device 5, and a winding process in which the cooled hot rolled steel strip SP is wound up by a winding device 7.

[0018] Here, the roughing mill 3 includes a plurality of (1 to n: n is an arbitrary integer of 2 or more) roughing rolling stands R1 to R n are provided in order from the upstream side to the downstream side in the conveying direction (rolling direction). n Of these, the two upstream rough rolling stands R n-1 and downstream roughing stand R n Both rough rolling stands R n-1 ,R n The distance between the roughing stands is short, making it possible to perform tandem rolling. In other words, the leading edge of the slab S is located downstream of the roughing stand R. n When the slab S is being inserted into the upstream rough rolling stand R n-1 The upstream roughing stand R n-1 and downstream roughing stand R n The slab S is rolled in both of the rough rolling stands R1 to R2. n Each of these rolling mills is equipped with an upper work roll 3a and a lower work roll 3b for rough rolling the slab S, and an upper backup roll 3c and a lower backup roll 3d for supporting the upper work roll 3a and the lower work roll 3b, respectively.

[0019] The finishing rolling mill 4 includes a plurality of (1 to N: N is an arbitrary integer of 2 or more) finishing rolling stands F1 to F N are provided in order from the upstream side to the downstream side in the conveying direction (rolling direction). NEach of these rolling mills is provided with an upper work roll 4a and a lower work roll 4b for finish rolling the rough bar B, and an upper backup roll 4c and a lower backup roll 4d for supporting the upper work roll 4a and the lower work roll 4b, respectively.

[0020] In addition, the hot rolling line 1 includes a plurality of rough rolling stands R1 to R n When the slab S is rough-rolled by the rough rolling mill 3 consisting of the rough rolling stand R n-1 and downstream roughing stand R n The rough rolling mill 3 has a plurality of rough rolling stands R1 to R2, each of which has a peripheral speed of an upper work roll 3a and a lower work roll 3b. n A roll peripheral speed control device 10 is provided to control the peripheral speeds of both the upper work roll 3a and the lower work roll 3b. The detailed processing of the roll peripheral speed control device 10 will be described later.

[0021] A host computer 11 is connected to the roll peripheral speed control device 10. The host computer 11 controls the size of the hot rolled steel strip SP, such as the thickness and width of the hot rolled steel strip SP to be produced, the steel type of the hot rolled steel strip SP, and each rough rolling stand R1 to R2 determined from the size and steel type of the hot rolled steel strip SP to be produced. n The roll peripheral speed setting values ​​of the upper work roll 3a and the lower work roll 3b in each rough rolling stand R1 to R n The information on the diameters of the upper work roll 3 a and the lower work roll 3 b and the like is sent to the roll peripheral speed control device 10 .

[0022] In the continuous hot rolling for producing such a hot-rolled steel strip SP, each of the rough rolling stands R1 to R2 of the rough rolling mill 3 is n , each finishing rolling stand F1 to F N In this case, "warping" may occur at the tip of the material being rolled (slab S, rough bar B). If the tip of the material being rolled is warped upward or downward, it may come into contact with the equipment inside the rolling mill, causing damage to the equipment or leaving the hot-rolled steel strip as a semi-finished product. In such a case, rolling for the following cycle must be stopped, resulting in a significant loss of operational productivity.

[0023] The mechanism by which this "warping" occurs at the tip of the rolled material will be described with reference to Figures 3 and 4. Figure 3 shows the mechanism by which upward warping occurs due to the bite angle of the steel plate on the entry side of the rolling mill, and Figure 4 shows the mechanism by which downward warping occurs due to the bite angle of the steel plate on the entry side of the rolling mill. As shown in Fig. 3, when a steel sheet SS, which is a material to be rolled, bites into the roll bite of an upper work roll 21a and a lower work roll 21b in a rolling mill (regardless of whether it is a roughing mill or a finishing mill) from below (when the steel sheet SS bites diagonally upward at an angle of θ1 with respect to the rolling direction), the steel sheet SS bends downward near the roll bite. Since the steel sheet SS bends downward, a tensile stress 22 acts on the upper surface side of the steel sheet SS in the longitudinal direction, and a compressive stress 23 acts on the lower surface side of the steel sheet SS in the longitudinal direction. Due to the stress distribution in the thickness direction in the steel sheet SS near the roll bite entry side, the forward forward ratio during rolling decreases and the forward forward speed decreases on the upper surface side of the steel sheet SS where the tensile stress 22 acts. Conversely, the forward forward ratio during rolling increases and the forward forward speed increases on the lower surface side of the steel sheet SS where the compressive stress 23 acts. Since the forward speed of the upper surface of the steel plate SS is slow and the forward speed of the lower surface of the steel plate SS is fast, the steel plate SS after rolling has an upward camber.

[0024] On the other hand, as shown in FIG. 4, when the steel sheet SS, which is the material to be rolled, bites into the roll bite of the upper work roll 21a and the lower work roll 21b of the rolling mill from above (when the steel sheet SS bites diagonally downward at an angle of θ2 with respect to the rolling direction), the steel sheet SS bends upward near the roll bite. Since the steel sheet SS bends upward, a tensile stress 22 acts on the lower surface side of the steel sheet SS in the longitudinal direction, and a compressive stress 23 acts on the upper surface side of the steel sheet SS in the longitudinal direction. Due to the stress distribution in the thickness direction in the steel sheet SS near the roll bite entry side, the forward forward ratio during rolling decreases on the lower surface side of the steel sheet SS on which the tensile stress 22 acts, and the forward forward speed decreases. Conversely, the forward forward ratio during rolling increases on the upper surface side of the steel sheet SS on which the compressive stress 23 acts, and the forward forward speed increases. Since the forward forward speed on the lower surface side of the steel sheet SS is slow and the forward forward speed on the upper surface side of the steel sheet SS is fast, the steel sheet SS after rolling is warped downward.

[0025] Here, in order to stabilize the bite of the roll bite, it is necessary to apply an appropriate tension to the steel sheet SS at the moment it bites in. If tension is applied to the steel sheet SS, buckling does not occur when the steel sheet SS is bitten by the upper work roll 21a and the lower work roll 21b, the bite of the roll bite becomes stable, and it is considered that the occurrence of upward or downward warping of the steel sheet SS after rolling can be suppressed.

[0026] As a method for applying tension to the slab S as the material to be rolled, as shown in Fig. 5, the upstream roughing stand R n-1 and downstream roughing stand R n In the upstream rough rolling stand R n-1 The rolling speed of the slab S by the rolling chisel is n-1 and downstream roughing stand R n The rolling speed of the slab S is slower than that of the rough rolling stand R n The purpose of this is to apply tension to the slab S at the moment of biting by the rolling mill. n-1 The rolling speed of the slab S by the rolling chisel is n-1 and downstream roughing stand R n When the rolling speed of the slab S by both the rough rolling stand R and the rolling stand R is the same, n As a result, as shown on the left side of Figure 5, buckling occurs when the slab S is bitten by the upper work roll 3a and the lower work roll 3b, the biting of the roll bite becomes unstable, and the slab S (rough bar B) after rolling develops upward or downward bowing.

[0027] For this reason, in this embodiment, the roll peripheral speed control device 10 controls the upstream rough rolling stand R n-1 The rolling speed of the slab S by the rolling stand R is the same as that of the rough rolling stand R downstream of the slab S. n The upstream rough rolling stand R n-1 and downstream roughing stand R nThe rolling speed of the slab S by the upstream roughing stand R is slower than that of the upstream roughing stand R. n-1 and downstream roughing stand R n The peripheral speeds of the upper work roll 3a and the lower work roll 3b are controlled by the roll peripheral speed control device 10. This makes it possible to suppress warping from before the finishing stage by simply changing the operating conditions without making additional capital investment in the roll peripheral speed control device 10.

[0028] Conventionally, the roll peripheral speed control device 10 controls all the rough rolling stands R1 to R2 in the rough rolling mill 3. n The peripheral speeds of the upper work roll 3a and the lower work roll 3b of each of the rough rolling stands R are set and controlled to roll peripheral speed settings determined by the size and steel type of the hot rolled steel strip SP to be manufactured. n-1 The rolling speed of the slab S by the rolling stand R is the same as that of the rough rolling stand R downstream of the slab S. n The upstream rough rolling stand R n-1 and downstream roughing stand R n The rolling speed of the slab S by both the upstream roughing stand R and the upstream roughing stand R is the same as that of the slab S by both the upstream roughing stand R and the upstream roughing stand R. n-1 and downstream roughing stand R n The peripheral speeds of the upper work roll 3a and the lower work roll 3b are controlled.

[0029] On the other hand, in this embodiment, the roll peripheral speed control device 10 is n-2 The peripheral speeds of the upper work roll 3a and the lower work roll 3b of each of the above are controlled by setting them to roll peripheral speed settings determined by the size and steel type of the hot rolled steel strip SP to be rolled, as in the past. n-1 and downstream roughing stand R n Regarding the roll peripheral speed control device 10, the leading end of the slab S is located in the upstream rough rolling stand R n-1 Before being caught in the rough rolling stand R n-1The peripheral speeds of the upper work roll 3a and the lower work roll 3b are set to values ​​1 to 5% slower than the roll peripheral speed setting value, and the rough rolling stand R n The peripheral speeds of the upper work roll 3 a and the lower work roll 3 b are set to the roll peripheral speed setting value. n-1 After being bitten into the rough rolling stand R n When the material is caught in the roughing stand R n-1 The peripheral speeds of the upper work roll 3a and the lower work roll 3b are set (returned) to the roll peripheral speed setting value, and the downstream rough rolling stand R n The peripheral speed of the upper work roll 3a and the lower work roll 3b is maintained at the roll peripheral speed setting value. n-1 The rolling speed of the slab S by the rolling stand R is the same as that of the rough rolling stand R downstream of the slab S. n The upstream rough rolling stand R n-1 and downstream roughing stand R n The rolling speed is controlled to be 1 to 5% slower than the rolling speed of the slab S by both.

[0030] Here, the tip of the slab S is in the upstream rough rolling stand R. n-1 Before being caught in the rough rolling stand R n-1 The reason why the peripheral speeds of the upper work roll 3a and the lower work roll 3b are set to values ​​1 to 5% slower than the roll peripheral speed setting value will be explained. n-1 If the peripheral speeds of the upper work roll 3a and the lower work roll 3b are made slower than a value that is 5% slower than the roll peripheral speed setting value, the leading end of the slab S will not be able to move downstream of the rough rolling stand R n The moment the material was bitten into the rough rolling stand R n In addition, the load on the downstream roughing stand R may become too large. n The tensile force applied to the slab S may become excessively large, which may result in a poor width of the rough bar B after rough rolling.

[0031] On the other hand, the upstream rough rolling stand Rn-1 If the peripheral speed of the upper work roll 3a and the lower work roll 3b is made faster than a value that is 1% slower than the roll peripheral speed setting value, the leading end of the slab S will n If the roll bite is unstable, the slab S may not be able to apply the appropriate tension to the slab S at the moment it bites into the roll, and the leading edge of the slab S may warp. n-1 Before being caught in the rough rolling stand R n-1 The peripheral speeds of the upper work roll 3a and the lower work roll 3b are set to a value 1 to 5% slower than the set value of the roll peripheral speed, and more preferably, the peripheral speeds are set to a value 2.5% to 3.5% slower than the set value of the roll peripheral speed.

[0032] Here, if the rolling speed of the slab S is SV (mpm), the peripheral speed of the upper work roll 3a and the lower work roll 3b is RV (mpm), the rotation speed of the upper work roll 3a and the lower work roll 3b is N (rpm), and the diameter of the upper work roll 3a and the lower work roll 3b is D (mm), the following equation holds: SV=RV=π D N / 1000 The roll peripheral speed control device 10 receives information on the roll peripheral speed setting value (RV) and information on the diameter (D) of each of the top work rolls 3a and bottom work rolls 3b from the host computer 11, calculates the rotation speed (N) of each of the top work rolls 3a and bottom work rolls 3b based on the above formula, and controls the rotation speed of each of the top work rolls 3a and bottom work rolls 3b with the calculated rotation speed (N) of each of the top work rolls 3a and bottom work rolls 3b. n-1When the circumferential speeds of the upper work roll 3a and the lower work roll 3b are set to a value that is 1 to 5% slower than the roll circumferential speed set value, the roll circumferential speed control device 10 calculates a value that is 1 to 5% slower than the roll circumferential speed set value (RV) obtained from the host computer 11, and calculates the rotation speed (N) of each of the upper work roll 3a and the lower work roll 3b based on the above formula from this calculated slower value and information on the diameter (D) of each of the upper work roll 3a and the lower work roll 3b, and controls the rotation speed of each of the upper work roll 3a and the lower work roll 3b using the calculated rotation speed (N) of each of the upper work roll 3a and the lower work roll 3b.

[0033] In this embodiment, the above-mentioned upstream roughing stand R capable of tandem rolling is n-1 and downstream roughing stand R n The control of the peripheral speeds of the upper work roll 3a and the lower work roll 3b is performed when the set thickness of the hot rolled steel strip SP to be manufactured is 15 mm or more. The reason is that when the set thickness of the hot rolled steel strip SP to be manufactured is 15 mm or more, warping is likely to occur at the tip.

[0034] In addition, the roll peripheral speed control device 10 constantly grasps the position of the slab S in the transport direction, that is, the position of the leading end of the slab S in the transport direction, based on tracking information from transport rollers (not shown) in the hot rolling line 1. Next, the flow of processing in the roll peripheral speed control device 10 will be described with reference to Fig. 2. Fig. 2 is a flowchart for explaining the flow of processing in the roll peripheral speed control device.

[0035] First, in step S1, the roll peripheral speed control device 10 judges whether the set thickness of the hot rolled steel strip SP is 15 mm or more based on information on the size of the hot rolled steel strip SP to be manufactured from the host computer 11. The reason is that, as described above, when the set thickness of the hot rolled steel strip SP to be manufactured is 15 mm or more, warping is likely to occur at the leading end, and in this case, the roll peripheral speed control method according to this embodiment is particularly effective.

[0036] If the judgment result in step S1 is YES (if the set thickness of the hot rolled steel strip SP is 15 mm or more), proceed to step S2, and if the judgment result is NO (if the set thickness of the hot rolled steel strip SP is less than 15 mm), proceed to step S3. In step S3, the roll peripheral speed control device 10 controls all of the rough rolling stands R1 to R n The peripheral speeds of the upper work roll 3a and the lower work roll 3b are set to the roll peripheral speed setting value. The roll peripheral speed setting value is input from the host computer 11 to the roll peripheral speed control device 10, and as described above, is a constant determined by the size and steel type of the hot rolled steel strip SP to be manufactured. At this time, the roll peripheral speed setting value RV (mpm) and the peripheral speeds of each rough rolling stand R1 to R2 from the host computer 11 are input to the roll peripheral speed control device 10. n Based on the information on the diameter D (mm) of the upper work roll 3a and the lower work roll 3b, the roll peripheral speed control device 10 calculates the peripheral speed of each rough rolling stand R1 to R2 from the formula RV=π·D·N / 1000. n The rotation speed N (rpm) of the upper work roll 3a and the lower work roll 3b is calculated, and the calculated rotation speed N (rpm) is n The control values ​​for the rotational speeds of the upper work roll 3a and the lower work roll 3b are set as follows.

[0037] Then, when step S3 is completed, the process in the roll peripheral speed control device 10 is terminated. On the other hand, in step S2, the roll peripheral speed control device 10 controls the rough rolling stands R1 to R n-2 The peripheral speeds of the upper work roll 3a and the lower work roll 3b are set to the roll peripheral speed setting value. n-1 and downstream roughing stand R n In the case of slab S, the tip of the slab is located upstream of the rough rolling stand R. n-1 Before being caught in the rough rolling stand R n-1 The peripheral speeds of the upper work roll 3a and the lower work roll 3b are set to values ​​1 to 5% slower than the roll peripheral speed setting value, and the rough rolling stand R n The peripheral speeds of the upper work roll 3a and the lower work roll 3b are set to the roll peripheral speed setting values.

[0038] The roll peripheral speed control device 10 is a rough rolling stand R n-1 The peripheral speeds of the upper work roll 3a and the lower work roll 3b are determined based on the roll peripheral speed setting value RV (mpm) obtained from the host computer 11 and the rough rolling stand R n-1 Based on the information on the diameter D (mm) of the upper work roll 3a and the lower work roll 3b, and the deceleration rate α, the rough rolling stand R is calculated from the formula (1-α)RV=π·D·N / 1000. n-1 The rotation speed N (rpm) of the upper work roll 3a and the lower work roll 3b is calculated. Then, the calculated rotation speed N (rpm) is n-1 The control value of the rotational speed of the upper work roll 3a and the lower work roll 3b is set as the rotational speed control value of the upper work roll 3a and the lower work roll 3b. Here, α is the deceleration rate as described above, and in this embodiment, it is a value between 1% and 5%. n The peripheral speeds of the upper work roll 3a and the lower work roll 3b are determined by the roll peripheral speed setting value RV (mpm) and the rough rolling stand R n Based on the information on the diameter D (mm) of the upper work roll 3a and the lower work roll 3b, the rough rolling stand R is calculated from the formula RV=π·D·N / 1000. n The rotation speed N (rpm) of the upper work roll 3a and the lower work roll 3b is calculated. Then, the calculated rotation speed N (rpm) is n The control values ​​for the rotational speeds of the upper work roll 3a and the lower work roll 3b are set as follows.

[0039] Next, in step S4, the roll peripheral speed control device 10 detects whether the leading end of the slab S is in the downstream rough rolling stand R n At this time, the roll peripheral speed control device 10 grasps the position of the leading end of the slab S on the basis of tracking information from a transport roller (not shown) in the hot rolling line 1. If the result of the judgment in step S4 is YES (the leading end of the slab S is in the downstream rough rolling stand R nIf the result of the determination is NO (if the leading end of the slab S is caught in the rough rolling stand R n If the bit is not caught in the bit line, the determination in step S4 is repeated.

[0040] In step S5, the roll peripheral speed control device 10 detects whether the leading end of the slab S is in the downstream rough rolling stand R n When the material is caught in the roughing stand R n-1 The peripheral speeds of the upper work roll 3a and the lower work roll 3b are set to the roll peripheral speed setting value, and the rough rolling stand R n The peripheral speeds of the upper work roll 3a and the lower work roll 3b are maintained at the roll peripheral speed setting values.

[0041] Then, when step S3 is completed, the process in the roll peripheral speed control device 10 is terminated. In this way, according to the roll peripheral speed control device 10 and the roll peripheral speed control method according to the present embodiment, the upstream rough rolling stand R capable of tandem rolling is n-1 and downstream roughing stand R n Roughing stands R1 to R2 each having a n When the slab S is roughly rolled by the rough rolling mill 3 consisting of the rough rolling stand R n-1 The rolling speed of the slab S by the rolling stand R is the same as that of the rough rolling stand R downstream of the slab S. n The upstream rough rolling stand R n-1 and downstream roughing stand R n The rolling speed of the slab S by the upstream roughing stand R is slower than that of the upstream roughing stand R. n-1 and downstream roughing stand R n The peripheral speeds of the upper work roll 3a and the lower work roll 3b are controlled.

[0042] This allows the downstream roughing stand R n At the moment of being bitten by the rolling mill, tension can be applied to the slab S, and the slab S is moved downstream by the rough rolling stand R. nThis prevents buckling from occurring when the slab is bitten into the roll bite, stabilizes the biting of the roll bite, and prevents the slab S (rough bar B) from warping upward or downward after rolling. Here, with the existing roll peripheral speed control device 10, warping from before the finishing stage can be suppressed simply by changing the operating conditions without making additional capital investments.

[0043] In addition, according to the roll peripheral speed control device 10 and the roll peripheral speed control method of the present embodiment, the leading end of the slab S is moved to the upstream rough rolling stand R n-1 Before being caught in the rough rolling stand R n-1 The peripheral speeds of the upper work roll 3a and the lower work roll 3b are set to values ​​1 to 5% slower than the roll peripheral speed setting value, and the rough rolling stand R n The peripheral speeds of the upper work roll 3a and the lower work roll 3b are set to the roll peripheral speed setting value. Then, the leading end of the slab S is moved to the downstream rough rolling stand R n When the material is caught in the roughing stand R n-1 The peripheral speeds of the upper work roll 3a and the lower work roll 3b are set to the roll peripheral speed setting value, and the rough rolling stand R n The peripheral speeds of the upper work roll 3a and the lower work roll 3b are maintained at the roll peripheral speed setting values.

[0044] This allows the upstream roughing stand R n-1 The rolling speed of the slab S by the rolling chisel is defined as the rolling speed of the slab S by the rough rolling stand R n The upstream rough rolling stand R n-1 and downstream roughing stand R n The rolling speed of the slab S can be controlled to be 1 to 5% slower than that of the slab S by both of the above. In addition, according to the roll peripheral speed control device 10 and the roll peripheral speed control method according to the present embodiment, when the set thickness of the hot rolled steel strip SP to be produced is 15 mm or more, n-1 The rolling speed of the slab S by the rolling stand R is the same as that of the rough rolling stand R downstream of the slab S. n The upstream rough rolling stand R n-1and downstream roughing stand R n The rolling speed of the slab S by the upstream roughing stand R is slower than that of the upstream roughing stand R. n-1 and downstream roughing stand R n The peripheral speeds of the upper work roll 3a and the lower work roll 3b are controlled.

[0045] As a result, for materials having a set thickness of 15 mm or more for hot-rolled steel strip SP, which is prone to upward warping at the tip, the existing roll peripheral speed control device 10 can appropriately suppress warping before the pre-finishing stage by simply changing the operating conditions without making any additional capital investment. In addition, according to the method for producing a hot-rolled steel strip according to this embodiment, the upstream rough rolling stand R capable of tandem rolling is n-1 and downstream roughing stand R n Roughing stands R1 to R2 each having a n When the slab S is rough-rolled by the rough rolling mill 3 consisting of the above-mentioned roll peripheral speed control method, n-1 and downstream roughing stand R n The process includes a rough rolling step in which the slab S is rough rolled by controlling the peripheral speeds of the upper work roll 3a and the lower work roll 3b.

[0046] This makes it possible to produce hot rolled steel strips SP that are free from damage caused by contact with equipment inside the rolling mill due to warping, without impairing operational productivity. Although the present embodiment has been described above, the present invention is not limited to this embodiment and various modifications and improvements can be made. For example, the roll peripheral speed control device 10 controls all of the rough rolling stands R1 to R n It is not always necessary to control the peripheral speeds of the upper work roll 3a and the lower work roll 3b. n-1 , R n The peripheral speeds of the upper work roll 3a and the lower work roll 3b are controlled, and the other rough rolling stands R1 to R n-2The peripheral speeds of the upper work roll 3a and the lower work roll 3b may be controlled by another roll peripheral speed control device provided separately.

[0047] In addition, multiple rough rolling stands R1 to R n In this case, the upstream roughing stand and the downstream roughing stand capable of tandem rolling are R n-1 and R n Instead, the rough rolling stand R k and R k+1 (k is an arbitrary integer from 1 to n-1), the roll peripheral speed control device 10 is k The rolling speed of the slab S by the rolling stand R is the same as that of the rough rolling stand R downstream of the slab S. k+1 The upstream rough rolling stand R k and downstream roughing stand R k+1 The rolling speed of the slab S by the upstream roughing stand R is slower than that of the upstream roughing stand R. k and downstream roughing stand R k+1 It is only necessary to control the peripheral speeds of the upper work roll 3a and the lower work roll 3b.

[0048] Furthermore, the control of the roll peripheral speed by the roll peripheral speed control device 10 of the present invention is not limited to when the set thickness of the hot rolled steel strip SP to be produced is 15 mm or more, but can also be applied when the set thickness of the hot rolled steel strip SP is less than 15 mm. EXAMPLES

[0049] In order to verify the effect of the present invention, the peripheral speeds of the upper work roll 3a and the lower work roll 3b in the roughing stands R1 to R5 were controlled by the roll peripheral speed control devices of the comparative example and the present invention example to produce hot rolled steel strips SP, and the amount of upward camber of the target material was measured at the delivery side of the finishing rolling stand F1 in the finishing mill 4. The plate thicknesses of the produced hot rolled steel strips SP were 15 mm, 18 mm, and 25 mm, which are 15 mm or more at which upward camber is likely to occur.

[0050] In the comparative example roll peripheral speed control device, all of the peripheral speeds of the upper work rolls 3a and the bottom work rolls 3b of each of the multiple rough rolling stands R1 to R5 in the rough rolling mill 3 were set and controlled to roll peripheral speed setting values ​​determined by the size and steel type of the hot-rolled steel strip SP to be produced. In contrast, the roll peripheral speed control device 10 of the present invention controls the peripheral speeds of the upper work roll 3a and the lower work roll 3b of each of the roughing stands R1 to R3 by setting them to roll peripheral speed set values ​​determined by the size and steel type of the hot rolled steel strip SP to be manufactured. On the other hand, for the upstream roughing stand R4 and the downstream roughing stand R5 capable of tandem rolling, the roll peripheral speed control device 10 sets the peripheral speeds of the upper work roll 3a and the lower work roll 3b of the upstream roughing stand R4 to a value 3% slower than the roll peripheral speed set value before the leading end of the slab S is bitten into the upstream roughing stand R4, and sets the peripheral speeds of the upper work roll 3a and the lower work roll 3b of the downstream roughing stand R5 to the roll peripheral speed set value. Then, when the leading end of the slab S is bitten into the downstream rough rolling stand R5, the roll circumferential speed control device 10 sets (returns) the circumferential speed of the upper work roll 3a and the lower work roll 3b of the upstream rough rolling stand R4 to the roll circumferential speed set value, and maintains the circumferential speed of the upper work roll 3a and the lower work roll 3b of the downstream rough rolling stand R5 at the roll circumferential speed set value.

[0051] FIG. 6 shows the measurement results of the amount of upward camber of the target material at the delivery side of the finishing rolling stand F1 in the finishing mill 4 for the produced hot rolled steel strips SP having thicknesses of 15 mm, 18 mm, and 25 mm. As shown in Figure 6, when hot-rolled steel strip SP was produced using the roll peripheral speed control device of the present invention, it was confirmed that the amount of upward warping of the target material at the exit side of the finishing rolling stand F1 was reduced compared to when hot-rolled steel strip SP was produced using the roll peripheral speed control device of the comparative example, regardless of whether the hot-rolled steel strip SP had a thickness of 15 mm, 18 mm, or 25 mm. [Explanation of symbols]

[0052] 1. Hot rolling line 2 Furnace 3 Roughing mill 3a Upper work roll 3b Lower work roll 3c Upper backup roll 3d Lower Backup Roll 4 Finishing rolling mill 4a Upper work roll 4b Lower work roll 4c Upper backup roll 4d Lower backup roll 5 Cooling device 6 Pinch Roll 7 Winding device 10 Roll peripheral speed control device 11 Upper computer 21a Upper work roll 21b Lower work roll 22 Tensile Stress 23 Compressive Stress B Coarse bar F1~F N Finishing Rolling Stand R1~R n Roughing Stand S slab SP hot rolled steel strip SS steel plate

Claims

1. A roll peripheral speed control device for controlling the peripheral speeds of work rolls of each of the upstream rough rolling stand and the downstream rough rolling stand when rough rolling a slab using a rough rolling mill having a plurality of rough rolling stands including an upstream rough rolling stand and a downstream rough rolling stand capable of tandem rolling, comprising: A roll peripheral speed control device characterized by controlling the peripheral speeds of the work rolls of the upstream rough rolling stand and the downstream rough rolling stand so that the rolling speed of the slab by only the upstream rough rolling stand is slower than the rolling speed of the slab by both the upstream rough rolling stand and the downstream rough rolling stand after the slab is bitten into the downstream rough rolling stand.

2. 2. The roll circumferential speed control device according to claim 1, characterized in that before the leading end of the slab is engaged in the upstream roughing rolling stand, the circumferential speed of the work roll of the upstream roughing rolling stand is set to a value that is 1 to 5% slower than the roll circumferential speed set value, and the circumferential speed of the work roll of the downstream roughing rolling stand is set to the roll circumferential speed set value, and when the leading end of the slab is engaged in the downstream roughing rolling stand, the circumferential speed of the work roll of the upstream roughing rolling stand is set to the roll circumferential speed set value, and the circumferential speed of the work roll of the downstream roughing rolling stand is maintained at the roll circumferential speed set value.

3. 2. A roll peripheral speed control device as described in claim 1, characterized in that when the set thickness of the hot-rolled steel strip to be produced is 15 mm or more, the peripheral speeds of the work rolls of the upstream rough rolling stand and the downstream rough rolling stand are controlled so that the rolling speed of the slab by only the upstream rough rolling stand is slower than the rolling speed of the slab by both the upstream rough rolling stand and the downstream rough rolling stand after the slab is bitten into the downstream rough rolling stand.

4. A method for controlling the peripheral speed of a work roll of each of the upstream roughing stand and the downstream roughing stand when rough rolling a slab using a roughing mill having a plurality of roughing stands including an upstream roughing stand and a downstream roughing stand capable of tandem rolling, comprising: A roll peripheral speed control method, characterized in that the peripheral speeds of the work rolls of the upstream rough rolling stand and the downstream rough rolling stand are controlled so that the rolling speed of the slab by only the upstream rough rolling stand is slower than the rolling speed of the slab by both the upstream rough rolling stand and the downstream rough rolling stand after the slab is bitten into the downstream rough rolling stand.

5. 5. The roll circumferential speed control method according to claim 4, characterized in that before the leading end of the slab is engaged in the upstream roughing rolling stand, the circumferential speed of the work roll of the upstream roughing rolling stand is set to a value 1 to 5% slower than the roll circumferential speed set value, and the circumferential speed of the work roll of the downstream roughing rolling stand is set to the roll circumferential speed set value, and when the leading end of the slab is engaged in the downstream roughing rolling stand, the circumferential speed of the work roll of the upstream roughing rolling stand is set to the roll circumferential speed set value, and the circumferential speed of the work roll of the downstream roughing rolling stand is maintained at the roll circumferential speed set value.

6. The roll peripheral speed control method according to claim 4, characterized in that, when the set thickness of the hot-rolled steel strip to be produced is 15 mm or more, the peripheral speeds of the work rolls of the upstream roughing rolling stand and the downstream roughing rolling stand are controlled so that the rolling speed of the slab by only the upstream roughing rolling stand is slower than the rolling speed of the slab by both the upstream roughing rolling stand and the downstream roughing rolling stand after the slab is bitten into the downstream roughing rolling stand.

7. 7. A method for producing a hot-rolled steel strip, comprising: a rough rolling step of rough rolling a slab by using a rough rolling mill consisting of a plurality of rough rolling stands, each of which includes an upstream rough rolling stand and a downstream rough rolling stand capable of tandem rolling, to control the peripheral speeds of the work rolls of the upstream rough rolling stand and the downstream rough rolling stand by using the roll peripheral speed control method according to any one of claims 4 to 6.

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