JP2025025723A - Roll peripheral speed control device, roll peripheral speed control method, and hot rolled steel strip manufacturing method - Google Patents

Abstract

The present invention provides a roll peripheral speed control device, a roll peripheral speed control method, and a hot-rolled steel strip manufacturing method that can suppress warping from occurring before the pre-finishing stage simply by changing operating conditions without requiring additional capital investment.
[Solution] When a slab S is rough rolled by a rough rolling mill 3 consisting of multiple rough rolling stands R ₁ to R _n , including an upstream rough rolling stand R _n-1 and a downstream rough rolling stand R _n capable of tandem rolling, a roll peripheral speed control device 10 controls the peripheral speeds of the work rolls 3 a, 3 b of the upstream rough rolling stand R _{n-1 and} the downstream rough rolling stand R _n so that the rolling speed of the slab S by only the upstream rough rolling stand R n- ₁ is slower than the rolling speed of the slab S by both the upstream rough rolling stand R _n-1 and the downstream rough rolling stand R _n after the slab S is bitten into the downstream rough rolling stand R n.
[Selected Figure] Figure 1

Description

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

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

In the continuous hot rolling that produces such hot-rolled steel strips, shape defects such as "warping" at the tip of the rolled material can occur at each stand of the roughing mill and the finishing mill. If upward warping occurs at the tip of the rolled material, it can 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 cases, rolling for the subsequent cycle must be stopped, resulting in a significant loss of operational productivity.

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 producing 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 correcting the warp of the rough bar using a first warp correction device, and then finish-correcting the warp of the rough bar using a second warp correction 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.

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 for reducing the tip upward warpage of a hot-rolled steel sheet in hot finish rolling shown in Patent Document 2, when hot finish rolling a steel sheet using a finishing mill consisting of multiple horizontal rolling mills, performs horizontal rolling to the product thickness by using at least one or more horizontal rolling mills preferentially from the front stage, 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 horizontal rolling mill at the last stage among the front stage horizontal rolling mills that performed horizontal rolling to the product thickness, and hot finish rolling is performed.

This reduces the amount of upward warping of the hot-rolled steel sheet at the exit of the finishing rolling mill, and suppresses problems with coiling on the coiler and variations in the cooling rate within the steel sheet during water cooling after finishing rolling.

JP 2004-351484 A JP 2015-42410 A

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 manufacturing method of the hot rolled steel strip shown in Patent Document 1, in addition to the roughing mill, the induction heating device, and the finishing rolling mill, the first and second warping correction devices are required, which poses a problem of high capital investment costs.

In addition, in the case of the method for reducing the upward warpage at the tip end of a hot-rolled steel sheet in hot finish rolling shown in Patent Document 2, it is possible to suppress the warpage at the horizontal rolling mill on the rear stage of the finishing mill, but it is not possible to deal with the warpage before the horizontal rolling mill on the rear stage of the finishing mill including the roughing mill.
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.

In order to solve the above problems, one aspect of the present invention is a roll peripheral speed control device that controls the peripheral speed 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 device is that it controls the peripheral speed 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.

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 speed of each 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 the gist of the method is to control the peripheral speed of each 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.

In addition, a method for producing a hot-rolled steel strip according to another aspect of the present invention includes a rough rolling process in which, 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 circumferential speed of the work rolls of the upstream rough rolling stand and the downstream rough rolling stand are controlled using the above-mentioned roll circumferential speed control method to rough roll the slab.

The roll peripheral speed control device, roll peripheral speed control method, and hot-rolled steel strip manufacturing method of the present invention make it possible to suppress warping before the pre-finishing stage by simply changing the operating conditions, without making any additional capital investments.

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. 2 is a flowchart for explaining a process flow in the roll peripheral speed control device shown in FIG. 1 . 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. 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. 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. 1 is a graph showing a 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.

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.

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.

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 the heating furnace 2, a rough rolling process in which the heated slab S is roughly rolled to a predetermined thickness in the rough rolling mill 3 to form a rough bar B, a finish rolling process in which the roughly rolled rough bar B is finish rolled in the finish rolling mill 4 to form a hot-rolled steel strip SP of a predetermined thickness, a cooling process in which the hot-rolled steel strip SP is cooled in the cooling device 5, and a winding process in which the cooled hot-rolled steel strip SP is wound up by the winding device 7.

Here, the roughing mill 3 is provided with a plurality of roughing rolling stands R ₁ to R _n (1 to n: n is any integer of 2 or more) arranged in order from the upstream side to the downstream side in the conveying direction (rolling direction). Among the plurality of roughing rolling stands R ₁ to R _n , the two upstream roughing rolling stands R _{n -1} and the downstream roughing rolling stand R _n on the most downstream side have a short distance between _them , and are roughing rolling stands capable of tandem rolling. In other words, when the leading end of the slab S is bitten into the downstream roughing rolling stand R _n , the slab S is also bitten into the upstream roughing rolling stand R _n-1 , and the slab S is rolled by both the upstream roughing rolling stand R _n-1 and the downstream roughing rolling stand R _n . Each of the plurality of rough rolling stands R ₁ to R _n includes 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.

The finishing mill 4 is equipped with a plurality of (1 to N: N is any integer of 2 or more) finishing rolling stands F ₁ to F _N arranged in order from the upstream side to the downstream side in the conveying direction (rolling direction). Each of the plurality of finishing rolling stands F ₁ to F _N is equipped 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.

In the hot rolling line 1, when the slab S is roughly rolled by the roughing mill 3 consisting of multiple roughing stands R _{1 to} R _n , a roll peripheral speed control device 10 is provided for controlling all the peripheral speeds of the upper work rolls 3a and the lower work rolls 3b of the multiple roughing stands R 1 to R _n in the roughing mill 3, including the peripheral speeds of the upper work rolls 3a and the lower work rolls 3b of the two upstream roughing stands R n- ₁ on the most downstream side and the downstream roughing stand R _n . The detailed processing of the roll peripheral speed control device 10 will be described later.

A host computer 11 is connected to the roll peripheral speed control device 10. The host computer 11 sends to the roll peripheral speed control device 10 information such as 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, the roll peripheral speed setting values of the upper work roll 3a and the lower work roll 3b in each rough rolling stand R ₁ to _Rn determined from the size and steel type of the hot rolled steel strip SP to be produced, and the diameters of the upper work roll 3a and the lower work roll 3b in each rough rolling stand R ₁ to _Rn .

In the continuous hot rolling for producing such hot rolled steel strip SP, the tip of the material to be rolled (slab S, rough bar B) may be "warped" in each of the rough rolling stands R ₁ to R _n of the rough rolling mill 3 and each of the finishing rolling stands F ₁ to F _N of the finishing rolling mill 4. If the tip of the material to be 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, the rolling of the subsequent cycle must be stopped, and the operational productivity is significantly impaired.

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 biting 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 biting 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 in the longitudinal direction on the upper surface side of the steel sheet SS, and a compressive stress 23 acts in the longitudinal direction on the lower surface side of the steel sheet SS. 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 on which 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 on which the compressive stress 23 acts. Since the forward advance speed on the upper surface side of the steel plate SS is slow and the forward advance speed on the lower surface side of the steel plate SS is fast, upward camber occurs in the steel plate SS after rolling.

On the other hand, as shown in Figure 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. As the steel sheet SS bends upward, a tensile stress 22 acts in the longitudinal direction on the lower surface side of the steel sheet SS, and a compressive stress 23 acts in the longitudinal direction on the upper surface side of the steel sheet SS. Due to the stress distribution in the thickness direction within 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 lower surface side of the steel sheet SS on which the tensile stress 22 acts. Conversely, the forward forward ratio during rolling increases and the forward forward speed increases on the upper surface side of the steel sheet SS on which the compressive stress 23 acts. Because the forward speed on the bottom surface of the steel plate SS is slow and the forward speed on the top surface of the steel plate SS is fast, downward warping occurs in the steel plate SS after rolling.

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

As a method of applying tension to the slab S as the material to be rolled, as shown in Fig. 5, in an upstream rough rolling stand Rn _-1 and a downstream rough rolling stand _Rn capable of tandem rolling, the rolling speed of the slab S by only the upstream rough rolling stand Rn _-1 is slower than the rolling speed of the slab S by both the upstream rough rolling stand Rn _-1 and the downstream rough rolling stand _Rn , and tension is applied to the slab S at the moment of being bitten by the downstream rough rolling stand _Rn . If the rolling speed of the slab S by only the upstream rough rolling stand Rn _-1 is the same as the rolling speed of the slab S by both the upstream rough rolling stand Rn _-1 and the downstream rough rolling stand _Rn , tension cannot be applied to the slab S at the moment of being bitten by the downstream rough rolling stand _Rn . As a result, as shown on the left side of Figure 5, buckling occurs when the slab S is bitten between the upper work roll 3a and the lower work roll 3b, the roll bite becomes unstable, and upward and downward warping occurs in the slab S (rough bar B) after rolling.

For this reason, in this embodiment, the peripheral speeds of the upper work roll 3a and the lower work roll 3b of each of the upstream roughing stand Rn _-1 and the downstream roughing stand _Rn are controlled by the above-mentioned roll peripheral speed control device 10 so that the rolling speed of the slab S by only the upstream roughing stand Rn _{-1 is} slower than the rolling speed of the slab S by both the upstream roughing stand Rn _- 1 and the downstream roughing stand _Rn after the slab S is bitten into the downstream roughing stand Rn. This makes it possible to suppress warping before the pre-finishing stage by simply changing the operating conditions without making additional capital investment in the roll peripheral speed control device 10.

Conventionally, the roll peripheral speed control device 10 has set and controlled the peripheral speeds of the upper work rolls 3a and the lower work rolls 3b of all roughing stands R ₁ to R _n in the roughing mill 3 to roll peripheral speed set values determined by the size and steel type of the hot-rolled steel strip SP to be manufactured. Therefore, conventionally, the peripheral speeds of the upper work rolls 3a and the lower work rolls 3b of the upstream roughing stand R _{n -} 1 and the downstream roughing stand R _n have been controlled so that the rolling speed of the slab S by only the upstream roughing stand R _n-1 is the same as the rolling speed of the slab S by both the upstream roughing stand R _n-1 and the downstream roughing stand R _n after the slab S is bitten into the downstream roughing stand R n.

On the other hand, in this embodiment, the roll peripheral speed control device 10 controls the peripheral speeds of the upper work roll 3a and the lower work roll 3b of each of the upstream roughing stands R ₁ to R _n-2 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 rolled, as in the past. On the other hand, for the upstream roughing stand R _n-1 and the downstream roughing stand R _n 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 R _{n- 1 to a value 1 to 5% slower than the roll peripheral speed set value before the leading end of the slab S is bitten into the upstream roughing stand R n-} 1, and sets the peripheral speeds of the upper work roll 3a and the lower work roll 3b of the downstream roughing stand R _n to the roll peripheral speed set value. Then, when the leading end of the slab S is bitten by the rough rolling stand R _n-1 on the upstream side and then bitten by the rough rolling stand R _n on the downstream side, the roll peripheral speed control device 10 sets (returns) the peripheral speed of the upper work roll 3a and the lower work roll 3b of the rough rolling stand R _n-1 on the upstream side to the roll peripheral speed set value, and maintains the peripheral speed of the upper work roll 3a and the lower work roll 3b of the rough rolling stand R _n on the downstream side at the roll peripheral speed set value. As a result, the roll peripheral speed control device 10 controls the rolling speed of the slab S by only the rough rolling stand R _n-1 on the upstream side to a speed 1 to 5 _% slower than the rolling speed of the slab S by both the rough rolling stand R _n-1 on the upstream side and the rough rolling stand R _n on the downstream side after the slab S is bitten by the rough rolling stand R n on the downstream side.

Here, the reason for setting the peripheral speed of the upper work roll 3a and the lower work roll 3b of the upstream roughing rolling stand R _{n -1} to a value 1 to 5% slower than the roll peripheral speed setting value before the leading end of the slab S is bitten into the upstream roughing rolling stand R n-1 will be explained. If the peripheral speed of the upper work roll 3a and the lower work roll 3b of the upstream roughing rolling stand R _n-1 is set to a value slower than 5% slower than the roll peripheral speed setting value, the load on the downstream roughing rolling stand R _n may become too large at the moment when the leading end of the slab S is bitten into the downstream roughing rolling stand R _n . In addition, the tensile force on the slab S by the downstream roughing rolling stand R _n may become excessive, and the width of the rough bar B after rough rolling may become poor.

On the other hand, if the circumferential speed of the upper work roll 3a and the lower work roll 3b of the upstream roughing rolling stand R _{n -1} is set to a value that is 1% slower than the roll circumferential speed setting value, the slab S cannot be given an appropriate tension at the moment when the leading end of the slab S is bitten into the downstream roughing rolling stand R _n, and the biting of the roll bite is unstable, which may cause the leading end of the slab S to warp. For this reason, the circumferential speed of the upper work roll 3a and the lower work roll 3b of the upstream roughing rolling stand R _n-1 is set to a value that is 1 to 5% slower than the roll circumferential speed setting value before the leading end of the slab S is bitten into the upstream roughing rolling stand R n-1. It is more preferable to set the circumferential speed to a value that is 2.5 to 3.5% slower than the roll circumferential speed setting value.

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 is established.
SV=RV=π・D・N/1000
The roll peripheral speed control device 10 receives information on the roll peripheral speed set value (RV) and information on the diameter (D) of each of the upper work rolls 3a and the lower work rolls 3b from the host computer 11, calculates the rotation speed (N) of each of the upper work rolls 3a and the lower work rolls 3b based on the above formula, and controls the rotation speed of each of the upper work rolls 3a and the lower work rolls 3b using the calculated rotation speed (N) of each of the upper work rolls 3a and the lower work rolls 3b. In addition, when the circumferential speeds of the upper work roll 3a and the lower work roll 3b of the upstream roughing rolling stand R _n-1 are set to a value 1 to 5% slower than the roll circumferential speed set value, the roll circumferential speed control device 10 calculates a value 1 to 5% slower than the roll circumferential speed set value (RV) obtained from the upper computer 11, and calculates the rotation speed (N) of each of the upper work rolls 3a and the lower work rolls 3b based on the above formula from this calculated slower value and information on the diameter (D) of each of the upper work rolls 3a and the lower work rolls 3b, and controls the rotation speed of each of the upper work rolls 3a and the lower work rolls 3b using the calculated rotation speed (N) of each of the upper work rolls 3a and the lower work rolls 3b.

In this embodiment, the peripheral speeds of the upper work roll 3a and the lower work roll 3b of the upstream roughing roll stand Rn _-1 and the downstream roughing roll stand _Rn capable of tandem rolling are controlled when the set thickness of the hot rolled steel strip SP to be produced is 15 mm or more. This is because warping is likely to occur at the leading end when the set thickness of the hot rolled steel strip SP to be produced is 15 mm or more.

In addition, the roll peripheral speed control device 10 always grasps the position of the slab S in the transport direction, i.e., 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 flow chart for explaining the flow of processing in the roll peripheral speed control device.

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 for this is that, as mentioned 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 tip, and in this case, the roll peripheral speed control method according to this embodiment is particularly effective.

If the judgment result of 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 sets the peripheral speeds of the upper work rolls 3a and the lower work rolls 3b of all the rough rolling stands _R1 to _Rn to a 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 is a constant determined by the size and steel type of the hot rolled steel strip SP to be manufactured, as described above. At this time, based on the roll peripheral speed set value RV (mpm) and information on the diameter D (mm) of the upper work roll 3a and bottom work roll 3b of each roughing rolling stand R ₁ to _Rn from the host computer 11, the roll peripheral speed control device 10 calculates the rotation speed N (rpm) of the upper work roll 3a and bottom work roll 3b of each roughing rolling stand R ₁ to _Rn from the formula RV = π · D · N / 1000, and sets the calculated rotation speed N (rpm) as the control value for the rotation speed of the upper work roll 3a and bottom work roll 3b of the roughing rolling stands R ₁ to _Rn .

After 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 sets the peripheral speeds of the upper work roll 3a and the bottom work roll 3b of the roughing stands R ₁ to R _n-2 to the roll peripheral speed set value. Also, for the upstream roughing stand R _n-1 and the downstream roughing stand R _n capable of tandem rolling, the roll peripheral speed control device 10 sets the peripheral speeds of the upper work roll 3a and the bottom work roll 3b of the upstream roughing stand R _{n -1} to a value 1 to 5% slower than the roll peripheral speed set value before the leading end of the slab S is bitten into the upstream roughing stand R n-1, and sets the peripheral speeds of the upper work roll 3a and the bottom work roll 3b of the downstream roughing stand R _n to the roll peripheral speed set value.

The roll peripheral speed control device 10 calculates the rotation speed N (rpm) of the upper work roll 3a and the lower work roll 3b of the roughing stand R _{n-1 on} the upstream side from the formula (1-α)RV=π·D·N/1000 based on the roll peripheral speed setting value RV (mpm) acquired from the host computer 11, the diameter D (mm) of the upper work roll 3a and the lower work roll 3b of the roughing stand R _n-1 from the host computer 11, and the information of the deceleration rate α. Then, the calculated rotation speed N (rpm) is set as the control value of the rotation speed of the upper work roll 3a and the lower work roll 3b of the roughing stand R _n-1 . Here, α is the deceleration rate as described above, and in this embodiment, it is a value between 1% and 5%. Furthermore, with regard to the circumferential speeds of the upper work roll 3a and the bottom work roll 3b of the roughing stand _Rn on the downstream side, the roll circumferential speed control device 10 calculates the rotational speed N (rpm) of the upper work roll 3a and the bottom work roll 3b of the roughing stand _Rn from the formula RV=π·D·N/1000 based on the roll circumferential speed set value RV (mpm) and information on the diameter D (mm) of the upper work roll 3a and the bottom work roll 3b of the roughing stand _Rn obtained from the host computer 11. Then, the calculated rotational speed N (rpm) is set as the control value for the rotational speeds of the upper work roll 3a and the bottom work roll 3b of the roughing stand _Rn .

Next, in step S4, the roll peripheral speed control device 10 judges whether or not the leading end of the slab S is caught 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 from tracking information from a conveying roller (not shown) in the hot rolling line 1.
If the judgment result of step S4 is YES (if the leading end of the slab S is bitten by the downstream rough rolling stand _Rn ), proceed to step S5, and if the judgment result is NO (if the leading end of the slab S is not bitten by the downstream rough rolling stand _Rn ), the judgment of step S4 is repeated.

In step S5, when the leading end of the slab S is bitten into the downstream roughing rolling stand R _n , the roll peripheral speed control device 10 sets the peripheral speeds of the upper work roll 3 a and the lower work roll 3 b of the upstream roughing rolling stand R _n-1 to the roll peripheral speed set value, and maintains the peripheral speeds of the upper work roll 3 a and the lower work roll 3 b of the downstream roughing rolling stand R _n at the roll peripheral speed set value.

After step S3 is completed, the process in the roll peripheral speed control device 10 is terminated.
Thus, according to the roll peripheral speed control device 10 and roll peripheral speed control method of this embodiment, when a slab S is roughly rolled by a rough rolling mill 3 consisting of a plurality of rough rolling stands R ₁ to R _n , including an upstream rough rolling stand R _n-1 and a downstream rough rolling stand R _n capable of tandem rolling, the peripheral speeds of the upper work roll _{3 a and the lower work roll 3 b of each of the upstream rough rolling stand R n -1} and the downstream rough rolling stand R _n are controlled so that the rolling speed of the slab S by only the upstream rough rolling stand R _n-1 is slower than the rolling speed of the slab S by both the upstream rough rolling stand R _n-1 and the downstream rough rolling stand R _n after the slab S is bitten into the downstream rough rolling stand R n.

This allows tension to be applied to the slab S at the moment of being bitten by the downstream rough rolling stand _Rn , prevents buckling when the slab S is bitten by the downstream rough rolling stand _Rn , stabilizes the biting of the roll bite, and prevents the slab S (rough bar B) from warping upward or downward after rolling. Here, in the existing roll peripheral speed control device 10, warping before the pre-finishing stage can be suppressed only by changing the operating conditions without making additional capital investment.

Moreover, according to the roll peripheral speed control device 10 and the roll peripheral speed control method of this embodiment, before the leading end of the slab S is bitten into the upstream rough rolling stand R _n-1 , the peripheral speeds of the upper work roll 3a and the bottom work roll 3b of the upstream rough rolling stand R _n-1 are set to a value 1 to 5% slower than the roll peripheral speed set value, and the peripheral speeds of the upper work roll 3a and the bottom work roll 3b of the downstream rough rolling stand R _n are set to the roll peripheral speed set value. Then, when the leading end of the slab S is bitten into the downstream rough rolling stand R _n , the peripheral speeds of the upper work roll 3a and the bottom work roll 3b of the upstream rough rolling stand R _n-1 are set to the roll peripheral speed set value, and the peripheral speeds of the upper work roll 3a and the bottom work roll 3b of the downstream rough rolling stand R _n are maintained at the roll peripheral speed set value.

This makes it possible to control the rolling speed of the slab S by only the upstream rough rolling stand R _n-1 to a speed that is 1 to 5% slower than the rolling speed of the slab S by _both the upstream rough rolling stand R _n-1 and the downstream rough rolling stand R _n after the slab S is bitten into the downstream rough rolling stand R n.
Furthermore, according to the roll peripheral speed control device 10 and the roll peripheral speed control method of this embodiment, when the set thickness of the hot-rolled steel strip SP to be manufactured is 15 mm or more, the peripheral speeds of the upper work roll 3 a and the lower work roll 3 _b of each of the upstream rough rolling stand R _{n-1 and} the downstream rough rolling stand R n are controlled so that the rolling speed of the slab S by only the upstream rough rolling stand R _{n- 1} is slower than the rolling speed of the slab S by both the upstream rough rolling stand R n-1 and the downstream rough rolling stand R _n after the slab S is bitten into the downstream rough rolling stand R n.

As a result, for hot-rolled steel strip SP manufactured with a set thickness of 15 mm or more, which is prone to upward warping at the tip, warping can be appropriately suppressed from before the finishing stage by simply changing the operating conditions in the existing roll peripheral speed control device 10, without making any additional capital investment.
Furthermore, according to the method for producing a hot-rolled steel strip according to this embodiment, when a slab S is roughly rolled by a rough rolling mill 3 consisting of a plurality of rough rolling stands R ₁ to R _n, each of which is provided with an upstream rough rolling stand R _n-1 and a downstream rough rolling stand R _n capable of tandem rolling, the method includes a rough rolling step in which the circumferential speeds of the upper work roll 3 a and the lower work roll 3 b of each of the upstream rough rolling stand R _n-1 and the downstream rough rolling stand R _n are controlled using the above-mentioned roll peripheral speed control method to roughly roll the slab S.

This makes it possible to produce hot-rolled steel strip SP that is 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 does not necessarily need to control the peripheral speeds of the top work rolls 3a and bottom work rolls 3b of all roughing stands R ₁ to R _n. It may be possible to control the peripheral speeds of the top work rolls 3a and bottom work rolls 3b only of roughing stands R _n-1 and R _n capable of tandem rolling, and control the peripheral speeds of the top work rolls 3a and bottom work rolls 3b of the other roughing stands R ₁ to R _n-2 by another roll peripheral speed control device provided separately.

Furthermore, when, among a plurality of rough rolling stands R ₁ to R _n , the upstream rough rolling stand and the downstream rough rolling stand capable of tandem rolling are not R _n-1 and R _n but rough rolling stands R _k and R _k+1 (k is any integer from 1 to n-1), the roll peripheral speed control device 10 only needs to control the peripheral speeds of the upper work roll 3 a and the lower work roll 3 b of the upstream rough rolling stand R _k and the downstream rough rolling stand R _{k +1 so that the rolling speed of the slab S by only the upstream rough rolling stand R k is} slower than the rolling speed of the slab S by both the upstream rough rolling stand R _k and the downstream rough rolling stand R _{k+1 after the slab S is bitten into the downstream rough rolling stand R k+1} .

In addition, 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 manufactured 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.

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.

In the roll peripheral speed control device of the comparative example, the peripheral speeds of all of the upper work rolls 3a and the lower 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 was bitten into the downstream roughing rolling stand _R5 , the roll peripheral speed control device 10 set (returned) the peripheral speeds of the upper work roll _3a and the lower work roll 3b of the upstream roughing rolling stand R4 to the roll peripheral speed set value, and maintained the peripheral speeds of the upper work roll _3a and the lower work roll 3b of the downstream roughing rolling stand R5 at the roll peripheral speed set value.

FIG. 6 shows the measurement results of the amount of upward camber of the target material at the delivery side of the finish rolling stand _F1 in the finish rolling 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 thickness of the hot rolled steel strip SP was 15 mm, 18 mm, or 25 mm.

REFERENCE SIGNS LIST 1 hot rolling line 2 heating furnace 3 roughing mill 3a upper work roll 3b lower work roll 3c upper backup roll 3d lower backup roll 4 finishing 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 host computer 21a upper work roll 21b lower work roll 22 tensile stress 23 compressive stress B rough bar F ₁ to F _N finishing rolling stand R ₁ to R _n rough rolling stand S slab SP hot rolled steel strip SS steel plate

Claims (7)

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. The roll circumferential speed control device according to claim 1, characterized in that before the leading edge of the slab is engaged in the upstream rough rolling stand, the circumferential speed of the work roll of the upstream rough 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 rough rolling stand is set to the roll circumferential speed set value, and when the leading edge of the slab is engaged in the downstream rough rolling stand, the circumferential speed of the work roll of the upstream rough rolling stand is set to the roll circumferential speed set value, and the circumferential speed of the work roll of the downstream rough rolling stand is maintained at the roll circumferential speed set value. The roll peripheral speed control device according to claim 1, characterized in that when the set thickness of the hot-rolled steel strip to be manufactured 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. 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. The roll circumferential speed control method according to claim 4, characterized in that before the leading edge of the slab is engaged in the upstream rough rolling stand, the circumferential speed of the work roll of the upstream rough 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 rough rolling stand is set to the roll circumferential speed set value, and when the leading edge of the slab is engaged in the downstream rough rolling stand, the circumferential speed of the work roll of the upstream rough rolling stand is set to the roll circumferential speed set value, and the circumferential speed of the work roll of the downstream rough rolling stand is maintained at the roll circumferential speed set value. 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 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. A method for producing a hot-rolled steel strip, comprising the steps of: rough rolling a slab using a rough rolling mill consisting of multiple rough rolling stands, each of which includes an upstream rough rolling stand and a downstream rough rolling stand capable of tandem rolling; controlling the peripheral speed of the work rolls of the upstream rough rolling stand and the downstream rough rolling stand using the roll peripheral speed control method according to any one of claims 4 to 6 to roughly roll the slab;

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