Cold rolling equipment, steel plate manufacturing equipment, cold rolling method, and steel plate manufacturing method

Abstract

To provide a cold rolling facility capable of suppressing brittle-cracking during rolling by suppressing deformation of a workpiece, a steel sheet manufacturing facility, a cold rolling method, and a steel sheet manufacturing method.SOLUTION: The cold rolling facility comprises: one or more cold rolling mills that spray coolants toward a work roll and a metal steel strip and cold-roll the metal steel strip; a plurality of rolls provided closer to the upstream side of the metal steel strip in a conveying direction than the cold rolling mills and fed for conveying the metal steel strip; and a control device that controls an elevation difference among the rolls. The control device controls the rolls so that the metal steel strip can be lower toward the downstream side in the conveying direction on the upstream side of at least some of the cold rolling mills including an uppermost rolling mill provided on the uppermost upstream side.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present disclosure relates to cold rolling equipment, steel plate manufacturing equipment, a cold rolling method, and a steel plate manufacturing method. [Background technology]

[0002] Steel sheets containing silicon, such as electrical steel sheets, have low toughness and are prone to brittle fracture during rolling. Generally, the higher the silicon content in a steel sheet, the lower its ductile-brittle transition temperature tends to be. One way to prevent brittle fracture is to heat the steel sheet to above its ductile-brittle transition temperature before rolling.

[0003] In steel plate rolling equipment, such as tandem mills, coolant is sprayed toward the area where the work rolls and steel plate meet to improve the lubrication of the steel plate during rolling and prevent thermal deformation of the work rolls. As a result, the sprayed coolant bounces off the work rolls and flows over the steel plate toward the entry side. If the steel plate is heated before rolling, the coolant flowing toward the entry side (coolant liquid) will lower the steel plate temperature.

[0004] The slower the line speed, the longer the length of coolant that stays on the steel plate in the longitudinal direction. Also, as the line speed increases, the force that draws the coolant into the steel plate increases, so the length of coolant that stays on the plate tends to decrease. Therefore, when the line speed is slow, the steel plate cools down to the same temperature as the coolant even if it is preheated.

[0005] For example, Patent Document 1 discloses a technique of providing a draining device that blows draining air onto the upper roll of a rolling mill to prevent coolant sprayed onto the upper roll from falling onto the strip and causing a drop in the temperature of the strip.

[0006] In order to solve the problem of insufficient lubrication of the steel sheet that occurs in the draining device of Patent Document 1, for example, Patent Document 2 discloses a technique in which a small amount of emulsion is supplied to the steel sheet at a high concentration.

[0007] On the other hand, in the rear stands of a multi-stage rolling mill, the temperature of the steel sheet rises due to heat generated during rolling, but if the temperature is too high, the amount of heat input to the work rolls increases during rolling, resulting in the formation of thermal crown on the work rolls.The formation of thermal crown deteriorates the rolled shape of the steel sheet.

[0008] In particular, when the rolling speed increases, the amount of heat input per unit time increases, the thermal crown grows further, and the rolled shape of the steel sheet deteriorates. [Prior art documents] [Patent documents]

[0009] [Patent Document 1] Japanese Patent Application Laid-Open No. 2000-271614 [Patent Document 2] Japanese Patent Application Laid-Open No. 2006-272382 Summary of the Invention [Problem to be solved by the invention]

[0010] However, although providing the draining device described in Patent Document 1 is effective in suppressing a drop in the strip temperature, it causes poor lubrication of the steel strip, making it prone to seizure.

[0011] In the case of Patent Document 2, the emulsion is supplied to the steel sheet at the entry side of the rolling mill, and the steel sheet is cooled by the emulsion riding on it, thereby decreasing the temperature of the steel sheet.

[0012] In the rear stands of a multi-stage rolling mill, if the steel sheet temperature is too high due to heat generated during rolling, the steel sheet temperature will be reduced by coolant liquid adhesion, and the amount of heat input to the work rolls can be reduced. However, if the rolling speed is high, the liquid adhesion length will be short, and the cooling effect will be small.

[0013] Increasing the coolant flow rate will improve the cooling capacity, and increasing the liquid length will further improve the cooling capacity. However, this requires upgrading the pump, reviewing the diameter of the coolant supply pipe, and reviewing the size of the circulation tank.

[0014] The present disclosure has been made in view of the above-mentioned problems, and aims to provide cold rolling equipment, steel plate manufacturing equipment, cold rolling method, and steel plate manufacturing method that can suppress deformation of work rolls and suppress brittle cracking during rolling. [Means for solving the problem]

[0015] (1) A cold rolling facility according to an embodiment of the present disclosure includes: The rolling mill comprises one or more cold rolling mills that spray coolant toward work rolls and a metal steel strip to cold roll the metal steel strip, a plurality of rolls that are provided upstream of the one or more cold rolling mills in the conveying direction of the metal steel strip and are used to convey the metal steel strip, and a control device that controls the height difference between the plurality of rolls, The control device controls the multiple rolls upstream of at least a portion of the one or more cold rolling mills, including the most upstream rolling mill located on the most upstream side, so that the metal steel strip is positioned lower toward the downstream side in the conveying direction.

[0016] (2) As an embodiment of the present disclosure, in (1), The control device sets the inclination angle of the metal steel strip relative to the biting portion of the one or more cold rolling mills, upstream of at least a portion of the one or more cold rolling mills including the most upstream rolling mill, based on at least one of the steel type of the metal steel strip, the line speed, the coolant injection flow rate, the temperature of the metal steel strip, and the target temperature of the metal steel strip.

[0017] (3) As an embodiment of the present disclosure, in (2), The control device controls the rolls so that the tilt angle is equal to or greater than 2° and equal to or less than 10°.

[0018] (4) As an embodiment of the present disclosure, in any one of (1) to (3), The one or more cold rolling mills are plural, The control device controls the multiple rolls upstream of at least a portion of the one or more cold rolling mills, including the most downstream rolling mill located on the most downstream side, so that the metal steel strip is positioned higher downstream in the conveying direction.

[0019] (5) A cold rolling facility according to an embodiment of the present disclosure includes: The rolling mill comprises one or more cold rolling mills that spray coolant toward work rolls and a metal steel strip to cold roll the metal steel strip, a plurality of rolls that are provided upstream of the one or more cold rolling mills in the conveying direction of the metal steel strip and are used to convey the metal steel strip, and a control device that controls the height difference between the plurality of rolls, The control device controls the multiple rolls upstream of at least a portion of the one or more cold rolling mills, including the most downstream rolling mill located on the most downstream side, so that the metal steel strip is positioned higher downstream in the conveying direction.

[0020] (6) As an embodiment of the present disclosure, in (5), The control device sets the inclination angle of the metal steel strip relative to the biting portion of the one or more cold rolling mills, upstream of at least a portion of the one or more cold rolling mills including the most downstream rolling mill, based on at least one of the steel type of the metal steel strip, the line speed, the coolant injection flow rate, the temperature of the metal steel strip, and the target temperature of the metal steel strip.

[0021] (7) As an embodiment of the present disclosure, in (6), The control device controls the rolls so that the tilt angle is greater than or equal to -10° and less than or equal to -2°.

[0022] (8) A steel sheet manufacturing equipment according to an embodiment of the present disclosure includes: The cold rolling equipment comprises any one of (1) to (7) and equipment for cutting the metal steel strip.

[0023] (9) A cold rolling method according to an embodiment of the present disclosure includes: A cold rolling method carried out in cold rolling equipment including one or more cold rolling mills that spray coolant toward work rolls and a metal steel strip to cold roll the metal steel strip, a plurality of rolls that are provided upstream of the one or more cold rolling mills in a conveying direction of the metal steel strip and are used to convey the metal steel strip, and a control device that controls a height difference between the plurality of rolls, The control device includes a step of controlling the multiple rolls upstream of at least a portion of the one or more cold rolling mills, including the most upstream rolling mill located most upstream, so that the metal steel strip is lowered toward the downstream side in the conveying direction.

[0024] (10) A cold rolling method according to an embodiment of the present disclosure includes: A cold rolling method carried out in cold rolling equipment including one or more cold rolling mills that spray coolant toward work rolls and a metal steel strip to cold roll the metal steel strip, a plurality of rolls that are provided upstream of the one or more cold rolling mills in a conveying direction of the metal steel strip and are used to convey the metal steel strip, and a control device that controls a height difference between the plurality of rolls, The control device includes a step of controlling the multiple rolls upstream of at least a portion of the one or more cold rolling mills, including the most downstream rolling mill located at the most downstream side, so that the metal steel strip is positioned higher downstream in the conveying direction.

[0025] (11) A method for manufacturing a steel sheet according to an embodiment of the present disclosure includes: The method includes the step of carrying out the cold rolling method of (9) or (10) and cutting the metal steel strip. [Effects of the Invention]

[0026] According to the present disclosure, it is possible to provide cold rolling equipment, steel plate manufacturing equipment, cold rolling method, and steel plate manufacturing method that can suppress deformation of work rolls and suppress brittle cracking during rolling. [Brief explanation of the drawings]

[0027] [Figure 1]FIG. 1 is a diagram illustrating a configuration example of a cold rolling mill included in a cold rolling facility according to an embodiment of the present disclosure. [Figure 2] FIG. 2 is a diagram illustrating a configuration example of a cold rolling mill included in the cold rolling facility according to an embodiment of the present disclosure. [Figure 3] FIG. 3 is a diagram for explaining the change in temperature of a metal steel strip in cold rolling equipment. DETAILED DESCRIPTION OF THE INVENTION

[0028] Hereinafter, cold rolling equipment, steel plate manufacturing equipment, cold rolling method, and steel plate manufacturing method according to an embodiment of the present disclosure will be described with reference to the drawings.

[0029] First, with reference to FIG. 3, an example of temperature change of a metal steel strip in cold rolling equipment will be described. In the example of FIG. 3, the cold rolling equipment includes a heating device, multiple rolls, and first to fourth cold rolling mills. The first to fourth cold rolling mills are heated by the heating device and cold roll the metal steel strip transported by the multiple rolls. The cold rolling equipment includes, in order from upstream to downstream in the transport direction of the metal steel strip, a heating device, a first cold rolling mill, a second cold rolling mill, a third cold rolling mill, and a fourth cold rolling mill. The cold rolling equipment may constitute part of a steel plate manufacturing equipment. The steel plate manufacturing equipment may further include equipment for cutting the metal steel strip, for example, downstream of the fourth cold rolling mill, to cut out steel plates of a desired size.

[0030] Each of the first to fourth cold rolling mills is equipped with a coolant header (see Figure 1) that sprays coolant toward the work rolls and the metal steel strip. The coolant is a liquid, for example, a mixture of rolling oil and water, and is sprayed to ensure lubrication and cool the work rolls.

[0031] If a certain temperature is not maintained when a metal steel strip is inserted into a cold rolling mill, there is a risk of brittle fracture. Examples of steel sheets manufactured using manufacturing facilities that include cold rolling equipment include electrical steel sheets. Typically, electrical steel sheets have a ductile-brittle transition temperature of 70 to 80°C, so they are heated to a temperature above the ductile-brittle transition temperature (e.g., 200 to 500°C) before being inserted into the rolling equipment and rolled. However, the temperature of the steel sheet decreases due to the rolling oil used during rolling, and if the temperature of the metal steel strip (hereinafter also referred to as "strip temperature") when inserted into the cold rolling mill falls below the ductile-brittle transition temperature, fracture is likely to occur. In cold rolling equipment, the strip temperature can sometimes drop lower than expected depending on the amount of rolling oil present.

[0032] On the other hand, if the strip temperature is high when the strip bites, breakage can be prevented, but due to factors such as heat generated during rolling, the strip temperature can become even higher in the downstream rolling passes.If the strip temperature is higher than expected, thermal crown on the work rolls can grow, which can cause shape defects in the metal steel strip after rolling.

[0033] The graph in the lower part of Figure 3 shows the temperature change of a metal steel strip. The vertical axis represents the temperature of the metal steel strip, and the horizontal axis represents the cold rolling equipment in the upper part of the figure and the corresponding position in the manufacturing process. The coolant sprayed in the first through fourth cold rolling mills bounces off the work rolls and flows over the metal steel strip toward the inlet (upstream) side, resulting in coolant entrainment. The length of the coolant entrainment in the longitudinal direction (conveyance direction) of the metal steel strip increases with slower line speeds, and decreases with faster line speeds due to the increased force of the steel sheet drawing in the coolant. In cold rolling equipment, the metal steel strip is rolled and elongated in the longitudinal direction by the rolling mills, so the line speed increases from the upstream cold rolling mill to the downstream cold rolling mill. In the example in Figure 3, the length of the coolant entrainment increases in the first and second cold rolling mills, which have relatively slow line speeds, causing the temperature of the metal steel strip to drop below the optimal temperature (below the ductile-brittle transition temperature). In addition, in the fourth cold rolling mill, which has a relatively fast line speed, the length of the coolant liquid is short, and processing heat and other factors accumulate during rolling, causing the temperature of the work roll to rise above the shape defect temperature, which causes the metal steel strip to become deformed.

[0034] As will be described below, the cold rolling equipment according to this embodiment can adjust the length of coolant liquid on the strip by setting the tilt angle of the metal steel strip relative to the engagement portion of the cold rolling mill upstream of each cold rolling mill based on the results of measurements such as the strip temperature, as shown in the lower diagram of Figure 3. By adjusting the length of coolant liquid on the strip, the temperature of the metal steel strip is kept within the optimum temperature range, which suppresses deformation of the work rolls and brittle cracking during rolling.

[0035] FIG. 1 is a diagram showing an example of the configuration of a cold rolling mill included in the cold rolling equipment according to this embodiment. The cold rolling equipment includes one or more cold rolling mills that spray coolant toward work rolls and a metal steel strip to cold roll the metal steel strip, a plurality of rolls that are provided upstream of the cold rolling mills in the conveying direction of the metal steel strip and are used to convey the metal steel strip, and a control device that controls the height difference between the plurality of rolls. The number of cold rolling mills included in the cold rolling equipment is not particularly limited, but this embodiment will be described assuming that there are four cold rolling mills, as shown in FIG. 3. FIG. 1 shows an enlarged view of one of the plurality of cold rolling mills included in the cold rolling equipment.

[0036] As shown in FIG. 1, the height of each of the multiple rolls on the entry side of a cold rolling mill can be adjusted using a lifting device. The lifting device may be, for example, a screw jack, but is not limited to a specific device. The control device controls the height difference between the multiple rolls by using a control signal to control the lifting device to raise and lower the rolls. In the example shown in FIG. 1, the control device controls the multiple rolls so that the metal steel strip is lowered toward the downstream side in the conveying direction. The angle of the entry side metal steel strip relative to the horizontal direction of the cold rolling mill's bite is defined as the inclination angle. In the example shown in FIG. 1, the control device controls the inclination angle to be positive. When the inclination angle is positive, coolant that bounces off the work rolls and flows over the metal steel strip toward the entry side (upstream side) returns to the bite side of the cold rolling mill due to the inclination. This reduces the coolant liquid runoff length. Therefore, the control device can increase the temperature of the metal steel strip at the entry side of a cold rolling mill, where the temperature of the metal steel strip has dropped below the optimal temperature, by controlling the metal steel strip to be lowered toward the downstream side in the conveying direction. Generally, the coolant layer length increases at the inlet side of the most upstream rolling mill, which is located at the most upstream side, and the temperature of the metal steel strip drops below the optimum temperature. Therefore, the control device may control the upstream side of one or more cold rolling mills, including the most upstream rolling mill, so that the metal steel strip is lowered toward the downstream side in the conveying direction. In the example of Figure 3, the control device raises and lowers the inlet rolls of the first cold rolling mill (the most upstream rolling mill) and the second cold rolling mill so that the inclination angle is positive, thereby shortening the coolant layer length and raising the temperature of the metal steel strip to within the optimum temperature range.

[0037] Here, the control device may set the tilt angle of the first cold rolling mill to the same tilt angle as that of the second cold rolling mill, or may set a different tilt angle. The control device may set the tilt angle upstream of one or more cold rolling mills, including the most upstream rolling mill, based on at least one of the steel grade of the metal steel strip, the line speed, the coolant injection flow rate, the temperature of the metal steel strip, and the target temperature of the metal steel strip. The control device may set the tilt angle of the first cold rolling mill (the most upstream rolling mill) based on, for example, the temperature of the metal steel strip and the target temperature of the metal steel strip. Furthermore, the control device may set the tilt angle of the second cold rolling mill so that the tilt angle is smaller than the tilt angle of the first cold rolling mill, based on, for example, differences in line speed, etc.

[0038] It is preferable that the control device controls the multiple rolls so that the inclination angle is 2° or more and 10° or less. As shown in the experimental examples described below, if the inclination angle is less than 2°, the degree of reduction in the length of the coolant liquid layer is small and the effect of temperature rise is small. Also, if the inclination angle is greater than 10°, smooth transport of the metal steel strip may be hindered. If the inclination angle is 5° or more, it is possible to reduce the length of the coolant liquid layer by 50% or more. Therefore, the control device may control the multiple rolls so that the inclination angle is 5° or more and 10° or less.

[0039] Here, the length of the inclined portion should be a certain length, because if it is too short, the coolant may ride over the inclined portion. The length of the inclined portion is preferably 1 m or more, for example. Furthermore, an upper limit may be set for the length of the inclined portion due to facility constraints. The length of the inclined portion is preferably 3 m or less, for example.

[0040] Fig. 2 is a diagram showing another example of the configuration of a cold rolling mill included in the cold rolling facility according to this embodiment. The cold rolling facility includes one or more cold rolling mills, a plurality of rolls, and a control device, similar to Fig. 1. Fig. 2 will be described assuming that it shows an enlarged view of one of a plurality of cold rolling mills included in the same cold rolling facility as Fig. 1.

[0041] As in Figure 1, the height of each of the multiple rolls on the entry side of a cold rolling mill can be adjusted using an elevator. In the example of Figure 2, the control device controls the multiple rolls so that the metal steel strip is positioned higher toward the downstream side in the conveying direction. That is, in the example of Figure 2, the control device controls the rolls so that the inclination angle is negative. If the inclination angle is negative, the coolant that bounces off the work rolls and flows over the metal steel strip toward the entry side (upstream side) extends further upstream due to the inclination. This allows the coolant liquid to be longer. Therefore, the control device can lower the temperature of the metal steel strip by controlling the metal steel strip to be positioned higher toward the downstream side in the conveying direction at the entry side of a cold rolling mill where the temperature of the metal steel strip has risen above the shape defect temperature. Generally, at the entry side of the most downstream rolling mill, the coolant liquid is shorter, and processing heat and other factors accumulate during rolling, causing the temperature of the metal steel strip to rise above the shape defect temperature. Therefore, the control device may control the upstream side of one or more cold rolling mills, including the most downstream rolling mill, so that the metallic steel strip is positioned higher downstream in the conveying direction. In the example of Fig. 3, the control device raises or lowers the entry roll of the fourth cold rolling mill (the most downstream rolling mill) so that the inclination angle is negative, thereby increasing the length of the coolant liquid layer and lowering the temperature of the metallic steel strip to within the optimum temperature range.

[0042] Here, the control device may set the tilt angle upstream of one or more cold rolling mills including the most downstream rolling mill based on at least one of the steel grade of the metal steel strip, line speed, coolant spray flow rate, temperature of the metal steel strip, and target temperature of the metal steel strip. The control device may set the tilt angle of the fourth cold rolling mill (the most downstream rolling mill) based on, for example, the temperature of the metal steel strip and the target temperature of the metal steel strip. Furthermore, the control device may calculate an optimal coolant liquid run-on length based on, for example, the steel grade of the metal steel strip, line speed, and coolant spray flow rate, and set the tilt angle of the fourth cold rolling mill so that the coolant liquid run-on length matches the calculated value.

[0043] It is preferable that the control device controls the multiple rolls so that the inclination angle is greater than -10° and less than -2°. As shown in the experimental examples described below, if the inclination angle is greater than -2°, the degree of extension of the coolant liquid layer length is small and the effect of temperature reduction is small. Also, if the inclination angle is greater than -10°, smooth transport of the metal steel strip may be hindered. If the inclination angle is less than -3°, the coolant liquid layer length may be increased by more than three times. Therefore, the control device may control the multiple rolls so that the inclination angle is greater than -10° and less than -3°.

[0044] Here, the type of cold rolling mill included in the cold rolling equipment is not limited. The cold rolling mill may be, for example, a multi-stage rolling mill or a reversing rolling mill. Also, different types of cold rolling mills may be included. Even when the cold rolling mill is a reversing rolling mill, it is sufficient to set the tilt angle to adjust the length of coolant liquid so that the temperature of the metal steel strip is within the optimum range.

[0045] The cold rolling equipment may also have a limiting mechanism to prevent the tilt angle from exceeding a predetermined angle range (e.g., −10° to 10°). The limiting mechanism may be, for example, a mechanical stopper, or a device that limits the range of motion of the lifting device based on a signal from a detection device such as a proximity switch.

[0046] As described above, the cold rolling equipment according to this embodiment is used as part of a steel sheet manufacturing facility. The cold rolling equipment control device can also execute a cold rolling method, including a step of controlling multiple rolls upstream of one or more cold rolling mills, including the most upstream rolling mill, so that the metal steel strip is lowered toward the downstream side in the conveying direction. The cold rolling equipment control device can also execute a cold rolling method, including a step of controlling multiple rolls upstream of one or more cold rolling mills, including the most downstream rolling mill, so that the metal steel strip is higher toward the downstream side in the conveying direction. The steel sheet manufacturing facility can also execute a steel sheet manufacturing method, including a step of executing the cold rolling method and cutting the metal steel strip.

[0047] As described above, the cold rolling equipment, steel sheet manufacturing equipment, cold rolling method, and steel sheet manufacturing method according to the present embodiment adjust the coolant liquid length and keep the temperature of the metal steel strip within the optimum temperature range by using the above-mentioned configuration or steps, thereby suppressing deformation of the work rolls and preventing brittle cracking during rolling.

[0048] Although embodiments of the present disclosure have been described with reference to the drawings, it should be noted that those skilled in the art would readily be able to make various modifications or alterations based on the present disclosure. For example, functions included in each component may be rearranged so as not to cause logical inconsistencies, and multiple components may be combined or separated into one. The embodiments of the present disclosure may also be realized as a program executed by a processor included in an apparatus or as a storage medium on which a program is recorded. It should be understood that these are also encompassed within the scope of the present disclosure.

[0049] In the above embodiment, a cold rolling facility including four cold rolling mills has been described with reference to Figure 3, but the number of cold rolling mills included in the cold rolling facility is not limited. For example, the cold rolling facility may include only one cold rolling mill, and the control device may only control the multiple rolls so that the metal steel strip is lowered toward the downstream side in the conveying direction, or control the multiple rolls so that the metal steel strip is higher toward the downstream side in the conveying direction. Furthermore, when the cold rolling facility includes multiple cold rolling mills, each of the cold rolling mills provided in between, excluding the most upstream and most downstream rolling mills, may be adjusted by the control device to have a positive inclination angle, a negative inclination angle, or no inclination angle adjustment may be performed.

[0050] The effects of the present disclosure will be specifically explained below based on examples (experimental examples), but the present disclosure is not limited to these examples.

[0051] (Example) Using the cold rolling equipment described in the above embodiment, rolling experiments were carried out to check whether seizure and sheet breakage occurred after rolling. The cold rolling equipment used was equipped with four cold rolling mills as shown in Figure 3. The compositions (mass%) of the steel types A to C tested are as shown in Table 1. In Table 1, "Bal." indicates that the remainder is Fe.

[0052] [Table 1]

[0053] A rolling experiment (first experiment) was conducted with the inclination angle varied from 0° to 10°. In the first experiment, the inclination angle of the first cold rolling mill (No. 1std), the most upstream rolling mill, was varied. The coolant flow rate was 100 to 300 L / min. The initial temperature of the steel plate (metal strip) being passed through was 200°C. The steel plate (metal strip) size was 1000 mm wide and 2.0 mm thick. The line speed was 15 mpm or 100 mpm. The thickness of the plate was set to 2.0 mm to 1.2 mm by rolling in the first cold rolling mill. The coolant used was a mixture of 5% rolling oil and 95% pure water. The coolant temperature was 60°C.

[0054] Table 2 shows the results of the first experiment. Under condition No. 1, the coolant liquid length was less than 100 mm, but seizure occurred. Under condition No. 5, no seizure occurred, but the coolant liquid length was long at 600 mm, and the strip temperature at the entry side dropped by 140°C from the initial temperature to 60°C, resulting in strip fracture. Nos. 3 and 4 were the results of inclining the pass line, but no seizure occurred in either case. Furthermore, under Nos. 3 and 4, the strip temperature at the entry side was over 80°C, exceeding the ductile-brittle transition temperature, and no strip fracture occurred.

[0055] Other results are shown in Table 2. In the comparative example, the inclination angle was 0°, and sheet breakage occurred with a high probability. From the inventive examples in Table 2, it was found that when the initial temperature of the steel sheet (metallic steel strip) is 200°C, the prevention effect of sheet breakage can be further enhanced by inclining the pass line and setting the inclination angle of the most upstream rolling mill to 5° or more. This result is thought to be similar for cold rolling mills installed intermediately, where the temperature of the steel sheet (metallic steel strip) on the entry side is below the ductile-brittle transition temperature.

[0056] [Table 2]

[0057] Furthermore, using the cold rolling equipment described in the above embodiment, rolling experiments were carried out to check whether shape defects occurred after rolling. The cold rolling equipment used was equipped with four cold rolling mills as shown in Figure 3. The compositions (mass%) of the steel types A to C used as the test pieces are shown in Table 1.

[0058] The rolling experiment (second experiment) was conducted with the tilt angle varied from 0° to -10°. In the second experiment, the tilt angle of the fourth cold rolling mill (No. 4std), the most downstream rolling mill, was varied. The coolant flow rate was 2000 to 3000 L / min. The initial temperature of the steel plate (metal strip) was 300°C. The steel plate (metal strip) size was 1000 mm wide and 2.0 mm thick. The line speed was 1000 to 1500 mpm. The thickness of the plate was set to 0.4 to 0.3 mm by rolling on the fourth cold rolling mill. The coolant used was a mixture of 5% rolling oil and 95% pure water. The coolant temperature was 60°C.

[0059] Table 3 shows the results of the second experiment. When the tilt angle was 0° and the strip temperature at the entry side was 250°C, the coolant liquid length was 400 mm and quarter elongation (defective shape) occurred. When the tilt angle was -2° and the strip temperature at the entry side was 250°C, the coolant liquid length was 1500 mm and quarter elongation did not occur.

[0060] Other results are shown in Table 3. In the comparative example, the tilt angle was 0°, and shape defects occurred with a high probability. From the inventive examples in Table 3, it was found that when the initial temperature of the steel plate (metal steel strip) is 300°C, the prevention effect of shape defects can be improved by tilting the pass line to prevent shape defects by setting the tilt angle of the most downstream rolling mill to -2° or less. It is thought that this result will also be applicable to cold rolling mills that are installed intermediately and in which the temperature of the steel plate (metal steel strip) on the inlet side is equal to or higher than the shape defect occurrence temperature.

[0061] [Table 3]

Claims

1. The rolling mill comprises one or more cold rolling mills that spray coolant toward work rolls and a metal steel strip to cold roll the metal steel strip, a plurality of rolls that are provided upstream of the one or more cold rolling mills in the conveying direction of the metal steel strip and are used to convey the metal steel strip, and a control device that controls the height difference between the plurality of rolls, The one or more cold rolling mills are plural, the control device controls the rolls upstream of a portion of the one or more cold rolling mills, including the most upstream rolling mill, so that the metal steel strip is positioned lower toward the downstream side in the conveying direction in order to shorten the length of the coolant liquid on the metal steel strip; The control device is a cold rolling equipment that controls the multiple rolls upstream of a portion of the one or more cold rolling mills, including the most downstream rolling mill located on the most downstream side, so that the metal steel strip is positioned higher toward the downstream side in the conveying direction in order to increase the length of the coolant liquid carried.

2. 2. The cold rolling facility according to claim 1, wherein the control device sets an inclination angle of the metal steel strip with respect to a biting portion of the one or more cold rolling mills upstream of the one or more cold rolling mills based on at least one of the steel type of the metal steel strip, the line speed, the coolant injection flow rate, the temperature of the metal steel strip, and the target temperature of the metal steel strip.

3. 3. The cold rolling facility according to claim 2, wherein the control device controls the rolls so that the inclination angle is 2° or more and 10° or less for some of the one or more cold rolling mills including the most upstream rolling mill.

4. The cold rolling facility according to claim 2, wherein the control device controls the plurality of rolls so that the inclination angle is −10° or more and −2° or less for some of the one or more cold rolling mills including the most downstream rolling mill.

5. A steel plate manufacturing facility comprising: the cold rolling facility according to any one of claims 1 to 4; and a facility for cutting the metal steel strip.

6. A cold rolling method carried out in cold rolling equipment including one or more cold rolling mills that spray coolant toward work rolls and a metal steel strip to cold roll the metal steel strip, a plurality of rolls that are provided upstream of the one or more cold rolling mills in a conveying direction of the metal steel strip and are used to convey the metal steel strip, and a control device that controls a height difference between the plurality of rolls, The one or more cold rolling mills are plural, a step in which the control device controls the plurality of rolls upstream of a portion of the one or more cold rolling mills, including the most upstream rolling mill provided at the most upstream side, so that the metal steel strip is positioned lower toward the downstream side in the conveying direction in order to shorten the length of coolant liquid on the strip; A cold rolling method comprising: the control device controlling the plurality of rolls upstream of a portion of the one or more cold rolling mills, including the most downstream rolling mill located at the most downstream side, so that the metal steel strip is positioned higher downstream in the conveying direction in order to increase the length of the coolant liquid carried.

7. 7. A method for producing a steel sheet, comprising the steps of: carrying out the cold rolling method of claim 6; and cutting the metal strip.

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