JP7040340B2 - Continuous casting equipment and rolling method - Google Patents

Description

The present invention relates to a continuous casting facility and a rolling method.

In the twin-drum type continuous casting device, a metal molten metal storage unit is formed by a pair of cooling drums for continuous casting (hereinafter, also referred to as "cooling drums") and side dams arranged horizontally facing each other. A pair of cooling drums is rotated to cast a thin-walled slab (hereinafter referred to as "slab") from the molten metal stored in the slab (for example, Patent Document 1). When the molten metal is stored in the molten metal storage section, the cooling drums are rotated downward from above, and the molten metal is solidified and grown on the peripheral surface of the cooling drum and sent downward as slabs. The slabs sent out from the cooling drum are sent out horizontally by a pinch roll and adjusted to a desired plate thickness by a downstream in-line mill. The slab whose thickness has been adjusted by the in-line mill is wound into a coil by a winding device installed downstream of the in-line mill.

In such a twin-drum type continuous casting apparatus, the cooling drum is generally at a low temperature before the start of casting, and when the casting is started, the temperature rises due to contact with the molten metal. Further, the cooling drum is cooled from the inner surface by a cooling medium (for example, cooling water) so as not to exceed a predetermined temperature. Hereinafter, the period during which the temperature of the cooling drum reaches a predetermined temperature and becomes constant is defined as the steady casting period, the arbitrary time point of the steady casting period is defined as the steady casting, and the temperature of the cooling drum during the steady casting period is defined as the steady temperature. .. The state of the steady casting period is called the steady state.

The profile of the cooling drum changes over time from the start of casting to the steady state. Therefore, the profile of the cooling drum is set so that the plate profile (plate crown) of the slab at the time of steady casting becomes a desired plate profile.

Further, in such a twin-drum type continuous casting apparatus, a dummy sheet (not shown) is used at the start of casting. The tip of this dummy sheet is set in a coil winder, and the tail end of the dummy sheet is set so as to be sandwiched between twin roll drums.

The molten metal, which is the tip of the slab, first cools and hardens, and then bonds with the tail end of the dummy sheet described above. After that, the cooling drum rotates, and the slabs combined with the dummy sheet are sequentially supplied to the casting coil. The plate thickness of the joint portion of the dummy sheet is much thicker than the plate thickness of the slab. This thick part is also called a hump. If the hump is strongly pressed or rolled with a pinch roll or an in-line mill, meandering or plate breakage will occur. It starts from.

A scale is formed on the slab conveyed to the entry side of the rolling mill having an in-line mill after casting, and the composition, thickness, etc. of the scale differ depending on the steel type of the slab or the slab temperature on the entry side of the rolling mill. A part of this scale may peel off from the slab and adhere to the surface of the work roll when the slab is pressed down by an in-line mill. The scale adhering to the surface of the work roll is pressed down at the contact surface where the work roll and the backup roll come into contact, and is pressure-bonded to the surface of the work roll. This crimped scale may react with the surface of the slab during rolling of the slab to further grow and grow. In addition, the scale that has grown to some extent may fall off from the surface of the work roll. Such a large scale grows, and deteriorates the surface quality of the rolled slab, or bites into the surface of the slab and causes surface defects.

When such surface defects occur in the slab, it is necessary to perform over-pickling to perform unnecessarily hot pickling in the pickling in the next step. In the over-pickling, for example, the pickling speed is reduced to perform the pickling, so that the productivity is lowered and the plate thickness is reduced by the over-pickling, so that the yield is lowered. As described above, when per-pickling is performed in order to improve the surface quality of the slab caused by the scale adhesion in the rolling mill, the manufacturing cost increases and the yield decreases.

In order to solve the decrease in productivity and yield due to such scale, the scale on the surface of the slab is removed before the scale is compressed by the in-line mill, and the scale attached to the work roll is removed. Is effective.

For example, Patent Document 2 discloses a technique using a descaler that injects water onto the surface of a slab at high speed as a method of removing scale on the surface of the slab. Further, Patent Document 3 discloses a technique for removing scale of a slab using a grinding brush. Further, Patent Document 4 discloses a method using a brush as a method for removing the scale adhering to the surface of the work roll.

Japanese Unexamined Patent Publication No. 2000-343103 Jitsufuku No. 5-39701 Gazette Jikkensho 58-147614 Japanese Unexamined Patent Publication No. 2010-184254 Japanese Patent No. 5433794

However, although the method described in Patent Document 2 is effective in removing scale from the slab or work roll surface, high-pressure water is used to remove scale from the strip surface or work roll surface using water. It is necessary to inject, which increases the equipment cost. Further, in the method of removing the scale of the slab surface or the work roll using a grinding brush or the like as described in Patent Documents 3 and 4, the grinding brush or the like is worn, so the grinding brush or the like is frequently replaced. There is a need. Further, since the grinding brushes and the like described in Patent Documents 3 and 4 are relatively large with respect to the rolling apparatus, there is a space limitation when applied to a work roll.

Further, for example, Patent Document 5 discloses a technique for cleaning a rolling roll with a cavitation nozzle in a tempering rolling mill. However, even if the cavitation nozzle disclosed in Patent Document 5 is applied to the continuous casting facility as it is, the rolling roll is not sufficiently cooled, so that a thermal crown may be generated on the work roll and the plate shape may be disturbed. ..

Therefore, the present invention has been made in view of the above problems, and an object of the present invention is due to the scale adhering to the work roll when slabs are manufactured by the twin drum type continuous casting apparatus. It is an object of the present invention to provide new and improved continuous casting equipment and casting methods capable of reducing surface quality defects of slabs.

In order to solve the above problems, according to a certain viewpoint of the present invention, a metal molten metal storage portion is formed by a pair of cooling drums and a side dam, and the pair of the cooling drums are rotated and stored in the metal molten metal storage portion. A rolling mill having a twin-drum type continuous casting device for casting the molten metal and an in-line mill which is deployed on the downstream side in the casting direction of the twin-drum type continuous casting device and rolls a pair of work rolls from the cast pieces. A winding device, which is deployed on the downstream side of the rolling device in the rolling direction and winds the rolled slab into a coil, is provided, and the rolling device cools the work roll on the inline mill entry side. An inlet cooling nozzle for discharging the cooling water to be rolled and a drain plate provided between the inlet cooling nozzle and the slab to prevent the cooling water from falling onto the slab are provided. On the outlet side of the inline mill, an outlet cooling nozzle that discharges cooling water for cooling the work roll from the roll bite outlet along the rotation direction of the work roll, and an aerial cavitation jet toward the work roll. A continuous casting facility is provided in which a cavitation nozzle for injecting is sequentially deployed.

The injection amount of the aerial cavitation jet is controlled based on the slab thermometer provided on the entry side or the exit side of the rolling apparatus and measuring the surface temperature of the slab and the measured value of the slab thermometer. It may be provided with a control device for rolling out.

Further, in order to solve the above problems, according to another viewpoint of the present invention, it is a method of rolling a slab cast by a continuous casting facility, in which the continuous casting facility includes a pair of cooling drums and a side dam. A twin-drum type continuous casting device for forming a molten metal storage section and casting the molten metal stored in the molten metal storage section while rotating the pair of cooling drums, and a casting direction of the twin-drum type continuous casting device. A rolling apparatus having an in-line mill that is deployed on the downstream side and rolls cast slabs with a pair of work rolls, and a rolling slab that is deployed on the downstream side in the rolling direction of the rolling apparatus and winds the rolled slabs in a coil shape. A winding device is provided, and on the entry side of the in-line mill of the rolling apparatus, a drain plate is provided between the entry-side cooling nozzle and the slab, and the entry-side cooling nozzle is transferred to the work roll. Cooling water is discharged to the work roll, and on the outlet side of the inline mill, the outlet cooling nozzle and the cavitation nozzle, which are sequentially arranged along the rotation direction of the work roll from the roll bite outlet, are used on the work roll. On the other hand, there is provided a method for rolling a slab, in which cooling water is discharged from the outlet cooling nozzle and the slab is rolled while injecting an aerial cavitation jet from the cavitation nozzle.

The injection amount of the aerial cavitation jet may be controlled based on the temperature of the slab on the entry side or the exit side of the rolling apparatus.

With the above configuration, while cooling the work roll with the cooling nozzle, the scale adhering to the surface of the work roll is efficiently removed by the aerial cavitation jet by utilizing the volume change of the work roll due to the cooling of the work roll.

As described above, according to the present invention, when a slab is manufactured by a twin-drum type continuous casting apparatus, it is possible to reduce the surface quality defect of the slab due to the scale adhering to the work roll.

It is sectional drawing which shows the continuous casting equipment which concerns on embodiment of this invention. It is a figure which shows the detail of the rolling apparatus which concerns on the same embodiment. It is a figure which shows the arrangement of the cavitation nozzle in the rolling apparatus which concerns on the comparative example of the same embodiment. It is a figure which showed the relationship between the plate temperature of the slab which concerns on the comparative example of the same embodiment, and the injection pressure of a cavitation nozzle. It is a figure which shows the deployment of each structure in the rolling mill which concerns on the same embodiment. It is a figure which shows the deployment of each structure in the rolling mill which concerns on the comparative example of the same embodiment. It is a figure which shows the deployment of each structure in the rolling mill which concerns on the comparative example of the same embodiment. It is a figure which shows the deployment of each structure in the rolling mill which concerns on the comparative example of the same embodiment.

Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings. In the present specification and the drawings, components having substantially the same functional configuration are designated by the same reference numerals, so that duplicate description will be omitted.

(1. Shard manufacturing process)
First, with reference to FIG. 1, an outline of a manufacturing process for manufacturing a slab according to an embodiment of the present invention will be described. FIG. 1 is an explanatory diagram showing a schematic configuration of a manufacturing process of a slab (thin-walled slab) according to the present embodiment.

As shown in FIG. 1, in the slab manufacturing process 1 according to the present embodiment, for example, a tundish (storage device) T, a double-drum type continuous casting facility 10, an antioxidant device 20, a cooling device 30, and the like. It includes a first pinch roll device 40, a rolling device 5 including an in-line mill 50, a second pinch roll device 60, and a winding device 70.

(Double drum type continuous casting equipment)
As shown in FIG. 1, the twin-drum type continuous casting apparatus 10 includes, for example, a pair of cooling drums 10a and 10b and side weirs (not shown) arranged on both sides of the pair of cooling drums 10a and 10b in the axial direction. And. The pair of cooling drums 10a and 10b and the side weir constitute a molten metal storage unit 15 for storing the molten metal supplied from the tundish T.

The pair of cooling drums 10a and 10b includes a first cooling drum 10a and a second cooling drum 10b. The first cooling drum 10a and the second cooling drum 10b have a concave profile with a slightly recessed center in the axial direction. Further, the first cooling drum 10a and the second cooling drum 10b are configured so that the distance between the first cooling drum 10a and the second cooling drum 10b can be adjusted according to the plate thickness or the internal quality of the slab S to be manufactured. ing. The first cooling drum 10a and the second cooling drum 10b are configured so that a cooling medium (for example, cooling water) can flow inside. By circulating a cooling medium inside the first cooling drum 10a and the second cooling drum 10b, the first cooling drum 10a and the second cooling drum 10b can be cooled. Further, the surfaces of the first cooling drum 10a and the second cooling drum 10b are dimple-processed.

In the present embodiment, the first cooling drum 10a and the second cooling drum 10b are set so that, for example, the outer diameter is 800 mm, the drum body length (width) is 1500 mm, and the plate crown of the slab S in a steady state is 30 μm (initial). Has been processed). Further, the dimple shape may have a major axis of 1.5 mm and a depth of 100 μm. Needless to say, the outer diameter, drum body length (width), and dimple shape of the pair of cooling drums 10a and 10b are not limited to these.

In the twin drum type continuous casting apparatus 10, a dummy sheet (not shown) is connected to the tip of the slab S to start casting. A dummy bar (not shown) having a thickness thicker than that of the slab S is provided at the tip of the dummy sheet, and the dummy sheet is guided by the dummy bar. Further, a hump (not shown) thicker than the plate thickness of the slab S is formed at the connection portion between the tip of the slab S and the dummy sheet. Rolling in the inline mill 50 is started after the protrusion 12 has passed through the inline mill 50. This rolling method is also referred to as flying touch.

(Antioxidant device)
The antioxidant device 20 is a device for performing a process for preventing the surface of the slab S immediately after casting from being oxidized to generate scale. In the antioxidant device 20, for example, the amount of oxygen can be adjusted by nitrogen gas. The antioxidant device 20 is preferably applied as necessary in consideration of the steel type of the slab S to be cast.

(Cooling system)
The cooling device 30 is a device that cools the slab S whose surface has been subjected to the antioxidant treatment by the antioxidant device 20. The cooling device 30 is provided with, for example, a plurality of spray nozzles (not shown), and the cooling water is ejected from the spray nozzles to the surface (upper surface and lower surface) of the slab S according to the steel type to produce the slab S. Cooling.

A pair of feed rolls 87 may be provided between the antioxidant device 20 and the cooling device 30. The pair of feed rolls 87 sandwich the slab S by a reduction device (not shown), and measure the loop length of the slab S between the pair of cooling drums 10a and 10b and the feed roll 87. A horizontal transport force is applied to the slab S so that the loop length is constant. The feed roll 87 is composed of, for example, a pair of rolls having a roll diameter of 200 mm and a roll body length (width) of 2000 mm.

(First pinch roll device)
The first pinch roll device 40 is a pinch roll device deployed on the entrance side of the inline mill 50. The first pinch roll device 40 is not shown except for the upper pinch roll 40a and the lower pinch roll 40b, the housing, the roll chock, the rolling load detecting device, and the rolling device (other than the first pinch roll device 40). ) And. Each of the upper pinch roll 40a and the lower pinch roll 40b has a hollow flow path formed therein, and is configured so that a cooling medium (for example, cooling water) can flow. By circulating the cooling medium, the first pinch roll device 40 can be cooled.

The upper pinch roll 40a and the lower pinch roll 40b may have, for example, a roll diameter of 400 mm and a roll body length (width) of 2000 mm. The upper pinch roll 40a and the lower pinch roll 40b are arranged via a roll chock in the housing and are rotationally driven by a motor (not shown). Further, the upper pinch roll 40a is connected to a pass line adjusting device (not shown) via an upper rolling load detecting device (not shown), and the lower pinch roll 40b is connected to a rolling device (not shown). .) Is connected.

In the first pinch roll device 40 having such a configuration, when the lower pinch roll 40b is pushed up toward the upper pinch roll 40a by the reduction device, the reduction load applied to the upper pinch roll 40a and the lower pinch roll 40b is detected. , Tension is generated in the slab S between the first pinch roll device 40 and the straightening device (not shown). Further, the slab S in the pair of pinch rolls 40a and 40b and the inline mill 50 so that the tension generated in the slab S between the first pinch roll device 40 and the inline mill 50 becomes a preset tension. The moving speed of is controlled. Further, the tension in the slab S between the first pinch roll device 40 and the straightening device is detected by the tension roll 88a. A position detecting device 41 for detecting the position of the slab may be provided on the upstream side of the first pinch roll.

(Rolling equipment)
The rolling apparatus 5 includes an in-line mill 50, a cooling nozzle, a draining plate, and a cavitation nozzle.

The in-line mill 50 is a rolling mill that rolls the slab S to make the slab S a desired plate thickness. In this embodiment, the in-line mill 50 is configured as a quadruple rolling mill. That is, the in-line mill 50 includes a pair of work rolls 51a and 51b, and backup rolls 52a and 52b arranged above and below the work rolls 51a and 51b.

The cooling nozzle discharges cooling water to the work rolls 51a and 51b to cool the work rolls 51a and 51b. The draining plate is provided so that the cooling water discharged from the cooling nozzle does not come into contact with the slab. The cavitation nozzle, for example, injects a high-pressure liquid such as water onto the work roll to generate cavitation and remove foreign matter adhering to the work roll. Details regarding the positional relationship between the cooling nozzle, the draining plate, and the cavitation nozzle with respect to the inline mill 50 in the rolling apparatus 5 and cavitation will be described later.

(Second pinch roll device)
The second pinch roll device 60 is deployed on the outlet side of the inline mill 50. Like the first pinch roll device 40, the second pinch roll device 60 includes an upper pinch roll and a lower pinch roll, a rolling load detecting device, and a rolling device. The upper pinch roll and the lower pinch roll each have a hollow flow path formed therein, and are configured so that a cooling medium (for example, cooling water) can flow. The pinch roll can be cooled by circulating the cooling medium. The upper pinch roll and the lower pinch roll may have, for example, a roll diameter of 400 mm and a roll body length (width) of 2000 mm. Further, the upper pinch roll and the lower pinch roll are arranged via a roll chock in the housing and are rotationally driven by a motor (not shown). A tension roll 88b is provided between the in-line mill 50 and the second pinch roll device 60.

(Winling device)
The winding device 70 is a device that is deployed on the outlet side of the second pinch roll device 60 and winds the slab S in a coil shape. A deflector roll 89 is deployed between the second pinch roll device 60 and the take-up device 70. The schematic configuration of the manufacturing process of the slab (thin-walled slab) according to the present embodiment has been described above.

(2. Scale removal in rolling mill)
(2-1. Configuration of rolling mill)
Next, with reference to FIG. 2, the positional relationship of the in-line mill, the cooling nozzle, the draining plate, and the cavitation nozzle constituting the rolling apparatus 5 of the above-mentioned continuous casting facility will be described. FIG. 2 is a diagram showing the positional relationship between the in-line mill, the cooling nozzle, the draining plate, and the cavitation nozzle of the rolling apparatus 5. The cooling nozzle, the draining plate, and the cavitation nozzle are arranged line-symmetrically with respect to the slab S, for example.

As shown in FIG. 2, on the inlet side of the in-line mill 50 of the rolling apparatus 5, two inlet cooling nozzles 130c and 130d that discharge cooling water for cooling the work roll 51a to the upper work roll 51a. Are sequentially deployed along the rotation direction of the work roll 51a. Similarly, on the lower work roll 51b, two inlet cooling nozzles 130g and 130h for discharging cooling water for cooling the work roll 51b to the lower work roll 51b are included in the work roll 51b. It is deployed along the direction of rotation.

A draining plate 120f is provided between the inlet cooling nozzle 130d and the slab S on the upper side of the slab S, and between the inlet cooling nozzle 130h and the slab S on the lower side of the slab S. Is equipped with a drainer plate 120e. By deploying the draining plates 120f and 120e, it is possible to prevent the cooling water discharged by the inlet cooling nozzles 130c, 130d, 130g and 130h from falling onto the slab S and the cooling water from being applied to the slab. The temperature drop of the slab S due to the cooling water is suppressed to prevent the rolling conditions from changing.

In this example, two cooling nozzles on the entrance side are provided on the upper side and two cooling nozzles on the lower side of the slab, but the number of cooling nozzles on the entrance side is two on the upper side and two on the lower side, respectively. Not limited to this, at least one or more may be provided on each of the upper side and the lower side.

On the outlet side of the in-line mill 50, there is an outlet cooling nozzle 130a that discharges cooling water for cooling the work roll 51a from the roll bite outlet along the rotation direction of the work roll 51a with respect to the upper work roll 51a. , A cavitation nozzle 110a for injecting an aerial cavitation jet toward the work roll 51a is sequentially deployed. Similarly, the outlet cooling nozzle 130e for discharging the cooling water for cooling the work roll 51b from the roll bite outlet to the lower work roll 51b along the rotation direction of the work roll 51b, and the work roll 51b. A cavitation nozzle 110b for injecting an aerial cavitation jet toward the air is sequentially deployed.

Here, the cavitation nozzle will be described. The cavitation nozzles 110a and 110b inject an aerial cavitation jet toward the work rolls 51a and 51b, respectively, and remove the scale adhering to the work rolls 51a and 51b.

An aerial cavitation jet contains a bubble-like gas phase in a liquid phase, and the impact force generated when the gas phase moves to the liquid phase is used to remove scale adhering to the work roll surface. It is a jet. In order to generate this cavitation jet, the cavitation nozzles 110a and 110b inject a low-speed jet into the atmosphere and inject a high-speed jet into the center of the low-speed jet to generate a gas phase in the liquid phase. By this method, a gas phase like bubbles is generated in the liquid phase, and the impact force when the gas phase causes a phase change in the liquid phase is used to remove the scale adhering to the surface of the slab. Water is mainly used as the liquid used for this aerial cavitation jet, but the liquid is not limited to this example and may be appropriately determined according to the scale type, steel type and the like.

The cavitation nozzles 110a and 110b are provided on the outlet side of the inline mill 50 as described above. With this arrangement, foreign matter including scale attached to the work roll is removed before being crimped between the work rolls 51a and 51b and the backup rolls 52a and 52b.

Further, the closer the cavitation nozzles 110a and 110b are to the backup rolls 52a and 52b, the higher the scale removal efficiency. This is because the closer to the backup roll 52a, the larger the difference between the maximum temperature and the minimum temperature of the work roll, the higher the cooling rate of the work roll 51a on the slab S, and the larger the volume change of the work roll, so that the scale is easily peeled off. It is thought that it will be. Therefore, the cavitation nozzles 110a and 110b may be deployed near the backup rolls 52a and 52b. A description of the volume change and scale of the work roll will be described later.

On the upper side of the slab S on the outlet side of the in-line mill 50, a drainer plate 120b is further arranged between the slab S and the outlet cooling nozzle 130a. The draining plate 120b prevents the slab S from being exposed to cooling water. Further, a draining plate 120a is provided between the cavitation nozzle 110a and the outlet cooling nozzle 130a. The draining plate 120a prevents the cooling water discharged from the outlet cooling nozzle 130a from moving to the cavitation nozzle 110a side along with the rotation of the work roll 51a.

These draining plates 120a and 120b do not necessarily have to be deployed in the rolling apparatus 5, and the presence or absence of deployment may be determined as appropriate. However, when the cooling water discharged from the outlet cooling nozzle 130a moves along the rotation direction of the work roll 51a, the collision of the aerial cavitation jet ejected from the cavitation nozzle 110a with the work roll 51a adheres to the work roll 51a. It will be hindered by the cooling water, and the scale removal effect will be reduced. Therefore, it is desirable to deploy the drainer plate 120a.

A draining plate 120c is provided between the slab S and the outlet cooling nozzle 130e on the lower side of the slab S on the outlet side of the inline mill 50, as on the upper side of the slab S. The draining plate 120c prevents the slab S from being exposed to cooling water. Further, a draining plate 120d is provided between the cavitation nozzle 110b and the outlet cooling nozzle 130e. The draining plate 120d prevents the cooling water discharged from the outlet cooling nozzle 130e from moving to the cavitation nozzle 110b side along with the rotation of the work roll 51b.

These draining plates 120c and 120d do not necessarily have to be deployed in the rolling apparatus 5, and the presence or absence of deployment may be determined as appropriate. However, when the cooling water discharged from the outlet cooling nozzle 130e moves along the rotation direction of the work roll 51b, the collision of the aerial cavitation jet ejected from the cavitation nozzle 110b with the work roll 51b adheres to the work roll 51b. It will be hindered by the cooling water, and the scale removal effect will be reduced. Therefore, it is desirable to deploy the drainer plate 120d.

A slab thermometer 180 for measuring the surface temperature of the slab S is provided on the outlet side of the rolling apparatus 5. In FIG. 2, the slab thermometer 180 is provided on the exit side of the rolling apparatus 5, but the present invention is not limited to this example and may be provided on the entry side of the rolling apparatus 5. By providing the slab thermometer 180 on the entry side of the rolling apparatus 5, it is possible to set an appropriate injection amount of the aerial cavitation jet for the slab S to be rolled. The slab thermometer 180 measures the surface temperature of the slab S and outputs the measured value to the control device 190.

The control device 190 controls the injection amount of the aerial cavitation jet. The injection amount of the aerial cavitation jet is controlled, for example, by adjusting the injection pressure at the time of injection from the cavitation nozzle, the flow rate of the fluid, and the like. The control device 190 controls the injection amount of the aerial cavitation jet based on the measured value of the slab thermometer 180, so that the rolling apparatus 5 has an appropriate injection amount of the aerial cavitation jet according to the temperature of the slab. The scale can be removed at. Specifically, the control device 190 receives the input of the temperature of the slab S measured by the slab thermometer 180, and is input from the relationship between the temperature and the pressure set in advance based on an experiment or the like. The injection pressure corresponding to the temperature is obtained, and the injection pressure of the fluid supplied to the cavitation nozzles 110a and 110b is controlled so as to be the injection pressure.

(2-2. Control of injection amount of aerial cavitation jet)
Here, the result of investigating the relationship between the injection pressure of the aerial cavitation jet injected from the cavitation nozzle 110a and the temperature on the inlet side of the rolling mill is shown. In this survey, as shown in FIG. 3, the survey was conducted with a rolling apparatus equipped with a cavitation nozzle 110a on the outlet side of the inline mill 50. The distance between the tip of the cavitation nozzle 110a and the surface of the work roll 51a was set to 50 mm. Although only the upper side of the slab S is shown in FIG. 3, the configuration of the upper side of the slab shown in FIG. 3 is provided line-symmetrically with respect to the slab on the lower side of the slab S. The injection pressure of the aerial cavitation jet was changed from 10 MPa to 60 MPa, and the carbon steel temperature on the rolling mill entry side was changed from 800 ° C. to 1100 ° C., and the surface of the work roll 51a and the surface of the plate after rolling were investigated. As the rolling apparatus, work rolls 51a and 51b having a roll diameter of 400 mm and backup rolls 52a and 52b having a roll diameter of 1200 mm were used. The body length of each roll was, for example, 2000 mm. Further, the steel type of the slab S was carbon steel, the plate width was 1200 mm, and the plate thickness was 2 mm.

The results of this survey are shown in FIG. FIG. 4 is a diagram showing the relationship between the plate temperature of the slab and the injection pressure of the aerial cavitation jet. In FIG. 4, those in which no abnormality such as surface defects was confirmed on the work roll surface and the plate surface after rolling are indicated by ◯, and those in which abnormalities were confirmed on the work roll surface and the plate surface after rolling are indicated by ×.

From FIG. 4, it can be seen that if the injection pressure of the aerial cavitation jet is 50 MPa or more, no abnormalities such as surface defects occur on the work roll surface and the plate surface after rolling even if the plate temperature is changed from 800 ° C. to 1100 ° C. Further, as the plate temperature becomes higher in the high temperature range, the injection pressure of the aerial cavitation jet required to prevent surface defects and the like from occurring on the work roll surface and the plate surface after rolling decreases. It is considered that this is because the higher the temperature of the work roll when the scale adheres to the work roll, the higher the linear expansion coefficient.

The work roll reaches the highest temperature when it comes into contact with the slab S, is then cooled by the cooling water discharged from the cooling nozzle, and after contacting the backup roll, the temperature of the work roll until it comes into contact with the slab S again. Is declining. The higher the temperature of the slab S, the higher the temperature of the work roll in contact with the slab S. Therefore, the scale adheres to the work roll in a state where the linear expansion rate of the work roll is high when the temperature of the slab S is high. After that, when the work roll is cooled, the work roll contracts, and the higher the temperature of the slab S when it comes into contact with the work roll, the higher the cooling rate of the work roll, so that the volume or length of the work roll changes significantly. , The scale is easily peeled off from the work roll surface. For this reason, the higher the temperature of the slab S, the larger the difference in the linear expansion coefficient of the work roll, and the easier the scale peeling. Therefore, even when the injection pressure of the aerial cavitation jet is low, after rolling. It is considered that no abnormality such as surface defects occurs in the slab S of.

Further, the higher the injection pressure of the aerial cavitation jet, the larger the change width of the plate temperature, the more the scale can be removed. However, from the viewpoint of manufacturing cost, it is preferable to control the injection amount of the aerial cavitation jet according to the plate temperature because the electric power cost is increased by keeping the injection pressure of the aerial cavitation jet high. For example, when the injection pressure of the aerial cavitation jet drops from 50Mpa to 30Mpa, the required power drops to about 70% of the pressure at 50Mpa.

Therefore, the manufacturing cost can be reduced by adjusting the injection pressure of the aerial cavitation jet to an appropriate value according to the plate temperature. Further, by controlling the injection pressure of the aerial cavitation jet, it is possible to extend the life of parts and the like used for the cavitation nozzle, rather than maintaining the injection pressure at the maximum. As described above, it is preferable to control the injection pressure of the aerial cavitation jet from the viewpoint of equipment maintenance and economy. Furthermore, the composition and thickness of the scale change according to the plate temperature. As described above, it is preferable to control the injection pressure of the aerial cavitation jet from the viewpoint of scale.

As shown in FIG. 4, the relationship between the plate temperature and the appropriate injection pressure differs depending on the steel type of the slab S, the atmosphere of the cooling device in the continuous casting facility, and the like, and may be appropriately obtained by experiments in advance. When rolling the slab S, an approximate curve L showing a limit curve showing no surface defects on the slab S and the work roll as shown in FIG. 4 is obtained, and in the control device 190, the approximate curve L is determined by the plate temperature. The injection pressure may be controlled so as not to be lower than the injection pressure indicated by. Further, instead of controlling the injection pressure, a plurality of cavitation nozzles having different nozzle diameters may be provided and the cavitation nozzles to be used may be switched so that the injection amount of the cavitation jet can be changed even with the same injection pressure.

By controlling the configuration of the rolling apparatus described above and the injection amount of the aerial cavitation jet in the rolling apparatus, the slabs produced by the twin-drum continuous casting facility adhere to the work roll when rolled by an in-line mill. It is possible to reduce surface quality defects of slabs caused by the scale of rolling.

In order to confirm the effect of the present invention, the slab is rolled using a rolling apparatus in which the cavitation nozzles are arranged in the positional relationship shown in FIG. 2 and a rolling apparatus in which the cavitation nozzles are arranged at other positions. Surface defects were confirmed. A description will be given with reference to FIGS. 3 and 5A to 5D. 3 and 5A to 5D show the configuration of the rolling apparatus only on the upper side in the vertical direction with respect to the slab S, and show the positional relationship of each configuration of the in-line mill, the cooling nozzle, the draining plate, and the cavitation nozzle. There is. A similar configuration is provided in line symmetry with the slab S on the lower side in the vertical direction from the slab S. First, the configuration arrangement of the rolling mill will be described with reference to each figure. In the rolling apparatus shown in FIG. 5A, the cavitation nozzle is arranged in the same manner as the cavitation nozzle of the present invention described with reference to FIG.

(Example 1)
FIG. 5A shows a rolling apparatus similar to that of FIG. 2, and is a view showing the upper side of the slab S. In the rolling apparatus 5 shown in FIG. 5A, two inlet cooling nozzles 130c and 130d for discharging cooling water for cooling the work roll 51a are workpieces on the inlet side of the inline mill 50 with respect to the upper work roll 51a. A draining plate 120f is arranged along the rotation direction of the roll 51a and prevents the cooling water from being applied to the slab S between the inlet cooling nozzle 130d and the slab S. On the outlet side of the in-line mill 50, the outlet cooling nozzle 130a for discharging the cooling water for cooling the work roll 51a and the aerial cavitation jet toward the work roll 51a are injected to the upper work roll 51a. The cavitation nozzle 110a and the cavitation nozzle 110a are sequentially arranged from the roll bite outlet along the rotation direction of the work roll 51a. A draining plate 120a is provided between the cavitation nozzle 110a and the outlet cooling nozzle 130a, and a draining plate 120b is provided between the outlet cooling nozzle 130a and the slab S. This rolling apparatus is referred to as Example 1.

(Comparative Example 1)
In the rolling apparatus shown in FIG. 5B, two inlet cooling nozzles 130c and 130d for discharging cooling water for cooling the work roll 51a to the upper work roll 51a are provided on the inlet side of the inline mill 50. A draining plate 120f is provided between the inlet cooling nozzle 130d and the slab S, which is arranged along the rotation direction of the 51a and prevents the cooling water from being applied to the slab S. On the outlet side of the in-line mill 50, there is a cavitation nozzle 110a that injects an aerial cavitation jet toward the work roll 51a with respect to the upper work roll 51a, and outlet cooling that discharges cooling water that cools the work roll 51a. The nozzles 130b and the nozzles 130b are sequentially arranged from the roll bite outlet along the rotation direction of the work roll 51a. A draining plate 120a is provided between the cavitation nozzle 110a and the outlet cooling nozzle 130b, and a draining plate 120b is provided between the cavitation nozzle 110a and the slab S. This rolling apparatus will be referred to as Comparative Example 1.

(Comparative Example 2)
In the rolling apparatus shown in FIG. 5C, on the outlet side of the in-line mill 50, two outlet cooling nozzles 130a and 130b that discharge cooling water for cooling the work roll 51a to the upper work roll 51a are provided on the work roll. It is deployed along the direction of rotation of 51a. A drainer plate 120a is provided between the outlet side cooling nozzle 130a and the outlet side cooling nozzle 130b, and a drainer plate 120b is provided between the outlet side cooling nozzle 130a and the slab S. On the entrance side of the in-line mill 50, an aerial cavitation jet is jetted from the contact point between the work roll 51a and the backup roll 52a toward the work roll 51a along the rotation direction of the work roll 51a. The cavitation nozzle 110a to be used and the inlet cooling nozzle 130d for discharging the cooling water for cooling the work roll 51a are sequentially arranged. A draining plate 120f is provided between the inlet cooling nozzle 130d and the slab S. This rolling apparatus will be referred to as Comparative Example 2.

(Comparative Example 3)
In the rolling apparatus shown in FIG. 5D, on the outlet side of the inline mill 50, two outlet cooling nozzles 130a and 130b for discharging cooling water for cooling the work roll 51a to the work roll 51a rotate the work roll 51a. Deployed along the direction. A drainer plate 120a is provided between the outlet side cooling nozzle 130a and the outlet side cooling nozzle 130b, and a drainer plate 120b is provided between the outlet side cooling nozzle 130a and the slab S. On the entrance side of the in-line mill 50, cooling water for cooling the work roll 51a is discharged from the contact point between the work roll 51a and the backup roll 52a along the rotation direction of the work roll 51a. A side cooling nozzle 130c and a cavitation nozzle 110a for injecting an aerial cavitation jet toward the work roll 51a are sequentially arranged. A draining plate 120f is provided between the cavitation nozzle 110a and the slab S. This rolling apparatus will be referred to as Comparative Example 3.

(Comparative Example 4)
In the rolling apparatus shown in FIG. 3, a cavitation nozzle 110a is provided on the outlet side of the inline mill 50. In the rolling apparatus shown in FIG. 3, neither a cooling nozzle nor a draining plate is provided. This rolling apparatus will be referred to as Comparative Example 4.

(Comparative Example 5)
Although not shown, the rolling apparatus in which the cooling water nozzle is provided instead of the cavitation nozzle 110a of the rolling apparatus shown in the first embodiment is referred to as Comparative Example 5.

Using the rolling apparatus described above, slabs were manufactured in the slab manufacturing process having the same configuration as in FIG. 1. The slab used in this example was carbon steel having a plate thickness of 2 mm and a plate width of 1200 mm. In this embodiment, carbon steel is used, but the steel type of the slab is not limited to this example. The acceleration rate of the cooling drum from the start of casting was 150 m / min / 30 sec, and the rotation speed of the cooling drum in the steady state was 150 m / min. The initial profile of the cooling drum was processed so that the plate crown of the slab was 43 μm in a steady state. Further, in the rolling apparatus, the plate temperature of the slab was set between 980 and 1150 ° C., and rolling was performed with a rolling reduction of 30% by an in-line mill. The plate thickness of the slab on the exit side of the inline mill after rolling was 1.4 mm. Rolling in the in-line mill was started 15 seconds after the start of casting after the dummy sheet had passed and the plate crown of the slab became 150 μm or less.

In this embodiment, a cubic function that approximates the limit curve by a cubic equation is calculated from the relationship between the plate temperature on the entrance side of the rolling mill and the injection pressure of the aerial cavitation jet shown in FIG. 4, and the cubic equation is calculated. Incorporated the function into the controller. Then, the rolling was performed by controlling the injection amount of the aerial cavitation jet within the range where the surface of the work roll and the slab S was not defective by the control device incorporating the cubic function.

Carbon steel was rolled with 100 coils, a plate temperature of 1000 ° C., and a rolling reduction of 30% by the rolling apparatus of Example 1 and Comparative Examples 1 to 5 described above. After rolling 100 coils of the slab, the surface of the work roll after casting was photographed, and the area ratio of the foreign matter adhering to the surface of the work roll was obtained by image processing. Here, as a reference for determining the area ratio of foreign matter, the slab is rolled by the rolling apparatus of Comparative Example 5, and the area of the foreign matter adhering to the surface of the work roll is set to 1 by the rolling apparatus. The area ratio of foreign matter in the slabs of the example and other comparative examples was determined. In the rolling by the rolling apparatus of Comparative Example 5, rolling was performed so that the injection amount of the cavitation nozzle 110a shown in the first embodiment and the discharge flow rate of the cooling water nozzle arranged in place of the cavitation nozzle 110a were the same.

In Example 1, the area ratio of the foreign matter was 0, and the adhesion of the foreign matter was not confirmed.

In Comparative Example 1, the area ratio of the foreign matter was 0.09. In Comparative Example 2, the area ratio of the foreign matter was 0.41. In Comparative Example 3, the area ratio of the foreign matter was 0.42.

In the rolling apparatus of Comparative Example 4 in which the cooling nozzle and the draining plate were not provided, the area ratio of the foreign matter was 0.08. In the rolling of Comparative Example 4, since the work roll was not cooled, a thermal crown was generated, the plate shape of the slab S was disturbed, and stable rolling could not be performed.

The results of Example 1 and Comparative Example 1 show the results when the cavitation nozzle is deployed on the outlet side of the inline mill. As for the position of the cavitation nozzle, the cavitation nozzle of Example 1 is arranged at a position closer to the backup roll than that of Comparative Example 1. Comparing the area ratios of the foreign substances of Example 1 and Comparative Example 1, they were 0 and 0.09, respectively, and it was confirmed that the closer the cavitation nozzles were deployed to the backup roll, the lower the area ratio of the foreign substances.

It is considered that this is because the work roll is cooled as it is closer to the backup roll, and the scale is more easily peeled off as the cavitation nozzle is placed closer to the backup roll. The work roll reaches the highest temperature when it comes into contact with the slab S, is then cooled by the cooling water discharged from the cooling nozzle, and after contacting the backup roll, the temperature of the work roll until it comes into contact with the slab S again. Is declining. Therefore, the scale adheres to the work roll in a state where the linear expansion rate of the work roll is high. After that, when the work roll is cooled, the work roll contracts. On the outlet side of the inline mill, the closer the work roll is to the backup roll, the cooler the temperature of the work roll, the greater the change in volume or length of the work roll, and the easier it is for scale to peel off the surface of the work roll. Therefore, in Example 1, it is considered that the scale was efficiently removed and the area ratio of the foreign matter decreased as the deployment position of the cavitation nozzle was closer to the backup roll.

On the other hand, in Comparative Example 2 and Comparative Example 3, the area ratios of the foreign matter are 0.41 and 0.42, respectively, and the cavitation nozzle is provided on the in-line mill entry side rather than the in-line mill exit side. It was found that the area ratio of foreign matter was high. It is considered that this is because the scale attached to the work roll was crimped by coming into contact with the backup roll, and the scale could not be removed even by injecting an aerial cavitation jet.

From the above, it was found that the rolling apparatus of Example 1 showing the arrangement of the cavitation nozzles of the present invention is remarkably effective in removing foreign substances including scales.

In the above, it was confirmed that the area ratio of foreign matter on the surface of the work roll changes depending on the arrangement position of the cavitation nozzle. Next, the effect of the rolling control of the present invention was confirmed with respect to the control of the injection amount of the aerial cavitation jet injected from the cavitation nozzle.

In this embodiment, in addition to the above embodiment, the rolling apparatus shown in Example 1 is used to change the cooling conditions so that the temperature of the slab is from 900 ° C to 150 ° C, and rolling is performed. The surface of the slab after rolling was observed.

(Example 2)
In Example 2, the injection amount of the aerial cavitation jet was not controlled according to the plate temperature of the slab.

(Example 3)
In Example 3, rolling was performed by controlling the injection pressure of the aerial cavitation jet according to the plate temperature of the slab, and the surface of the work roll after rolling was observed.

In Example 2, the higher the temperature of the cooled work roll, the more foreign matter may adhere to the surface of the work roll. On the other hand, in Example 3 in which the injection pressure of the cavitation nozzle was controlled, no foreign matter adhered to the surface of the work roll even when the temperature of the cooled work roll was on the high temperature side. It is considered that this is because when the plate temperature changes, the work roll temperature until the air cavitation jet is injected into the work roll differs, and the ease of scale peeling changes. The higher the temperature of the cooled work roll, the smaller the volume change of the work roll, so that the scale is less likely to peel off.

That is, in Example 2, since the injection amount of the aerial cavitation jet was constant, it is considered that the scale remained on the work roll surface and foreign matter was confirmed when the temperature of the work roll where the scale was difficult to peel off was high. .. On the other hand, in Example 3, since the injection amount of the aerial cavitation jet is changed according to the plate temperature, the volume change of the work roll is small and the scale is difficult to peel off, so that the aerial cavitation jet is injected. It is probable that the scale could be removed by increasing the amount.

From the above, it has been confirmed that the present invention can reduce the surface quality defects of the slabs caused by the scale adhering to the work roll when the slabs manufactured by the twin drum type continuous casting equipment are rolled by an in-line mill. Was done. If surface quality defects can be reduced, it is not necessary to perform over-pickling in the next pickling step, and the manufacturing cost due to over-pickling can be reduced.

Although the preferred embodiments of the present invention have been described in detail with reference to the accompanying drawings, the present invention is not limited to these examples. It is clear that a person having ordinary knowledge in the field of technology to which the present invention belongs can come up with various modifications or modifications within the scope of the technical ideas described in the claims. , These are also naturally understood to belong to the technical scope of the present invention.

110a, 110b Cavitation nozzle 120a, 120b, 120c, 120d, 120e, 120f Drainer plate 130a, 130e Outlet side cooling nozzle 130c, 130d, 130g, 130h Inside cooling nozzle 180 Shard thermometer 190 Control device

Claims (4)

A twin-drum type continuous casting device that forms a molten metal storage unit by a pair of cooling drums and a side weir and casts the molten metal stored in the molten metal storage unit while rotating the pair of cooling drums.
A rolling apparatus having an in-line mill for rolling a pair of work rolls of cast pieces, which is deployed on the downstream side in the casting direction of the twin-drum type continuous casting apparatus.
A winding device deployed on the downstream side of the rolling device in the rolling direction and winding the rolled slab into a coil, and a winding device.
Equipped with
The rolling mill
On the entry side of the inline mill,
An inlet cooling nozzle that discharges cooling water that cools the work roll,
A draining plate provided between the inlet cooling nozzle and the slab to prevent the cooling water from falling onto the slab is provided.
On the exit side of the inline mill, from the roll bite outlet along the rotation direction of the work roll,
An outlet cooling nozzle that discharges cooling water that cools the work roll,
A continuous casting facility that sequentially deploys a cavitation nozzle that injects an aerial cavitation jet toward the work roll. A slab thermometer provided on the entry side or the exit side of the rolling mill to measure the surface temperature of the slab, and a slab thermometer.
The continuous casting facility according to claim 1, further comprising a control device for controlling the injection amount of the aerial cavitation jet based on the measured value of the slab thermometer. A rolling method for slabs cast by continuous casting equipment.
The continuous casting facility
A twin-drum type continuous casting device that forms a molten metal storage unit by a pair of cooling drums and a side weir and casts the molten metal stored in the molten metal storage unit while rotating the pair of cooling drums.
A rolling apparatus having an in-line mill, which is deployed on the downstream side in the casting direction of the twin-drum type continuous casting apparatus and rolls the cast pieces by a pair of work rolls.
A winding device, which is deployed on the downstream side in the rolling direction of the rolling device and winds the rolled slab into a coil, is provided.
On the entry side of the inline mill of the rolling mill,
With the draining plate installed between the inlet cooling nozzle and the slab, the cooling water is discharged from the inlet cooling nozzle to the work roll.
On the exit side of the inline mill,
Using the outlet cooling nozzles and the cavitation nozzles sequentially arranged along the rotation direction of the work roll from the roll bite outlet,
Cooling water is discharged from the outlet cooling nozzle to the work roll.
A method for rolling a slab, in which the slab is rolled while injecting an aerial cavitation jet from the cavitation nozzle. The method for rolling a slab according to claim 3, wherein the injection amount of the aerial cavitation jet is controlled based on the temperature of the slab on the entry side or the exit side of the rolling apparatus.

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