Title of invention: Manufacturing method of slabs and continuous casting equipment
Technical field
[0001]
　The present invention relates to a method for producing a slab and a continuous casting facility.
　The present application claims priority based on Japanese Patent Application No. 2018-037945 filed in Japan on March 2, 2018, the contents of which are incorporated herein by reference.
Background technology
[0002]
　In the twin drum type continuous casting apparatus, a metal molten metal storage portion is formed by a pair of cooling drums for continuous casting (hereinafter referred to as "cooling drums") and a pair of side dams arranged horizontally facing each other, and the metal molten metal is formed. 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 storage portion (for example, Patent Document 1). When the molten metal is stored in the molten metal storage section, the cooling drums are rotated in opposite directions, 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.
[0003]
　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, any time during 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 a steady state.
[0004]
　The profile of the cooling drum changes with the elapsed 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.
[0005]
　Further, in such a twin drum type continuous casting apparatus, a dummy sheet 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.
[0006]
　The molten metal, which is the tip of the slab, first cools and hardens, and then combines with the tail end of the dummy sheet described above. After that, the cooling drum rotates and is 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 portion is also referred to as a hump. If the hump is strongly pressed or rolled with a pinch roll or in-line mill, meandering or plate breakage will occur.Therefore, this part should have a large gap between the upper and lower pinch rolls and the work roll of the in-line mill (roll gap). , Pass the pinch roll and in-line mill without compressive force on the hump. After the hump has passed through the pinch roll, the flying touch of the pinch roll is started. The flying touch of the in-line mill depends on the shape control ability of the in-line mill, but if the shape control ability of the in-line mill is insufficient after the hump passes through the in-line mill, the flying touch is started after the steady state is reached. It is rolled so that the output side plate thickness of the in-line mill reaches the target value. After the hump has passed through the in-line mill, if the shape control capability of the in-line mill is sufficient, the flying touch is started from the state before the steady state, and the in-line mill is rolled so that the outer plate thickness reaches the target value. To.
[0007]
　For the purpose of improving cooling efficiency or casting stability, for example, a concave shape is formed on the surface of the cooling drum of such a twin drum type continuous casting apparatus as described in Patent Document 2. It is dimple-processed. Since the molten metal enters the dimples and hardens, protrusions formed by the dimples (hereinafter, may be simply referred to as "protrusions") are formed on the surface of the slab after the cooling drum. As described in Patent Document 3, the shape of this protrusion can be determined with priority given to the stability of casting.
[0008]
　When a slab having such protrusions is rolled with an in-line mill, the protrusions may be folded. In general, the larger the value of the ratio of the height of the protrusion to the width of the protrusion (the height of the protrusion / the width of the protrusion), and the higher the reduction rate of the in-line mill, the more easily the protrusion is bent. Here, with reference to FIG. 1, a protrusion d1 in which folding occurs and a protrusion d10 in which folding does not occur will be described. FIG. 1 is a conceptual diagram showing a fold of a protrusion formed on a slab. FIG. 1 shows two protrusions d1 and d10 having different ratios of the height b of the protrusions and the width a of the protrusions. The ratio of the height b and the width a of the protrusion d1 is larger than the ratio of the height b and the width a of the protrusion d10.
[0009]
　The protrusion d1 having a large ratio of the height b to the width a is likely to break when the slab is rolled with an in-line mill. The oxide scale c1 on the surface of the slab may be bitten into the folded portion e in which the protrusion d1 is folded. On the other hand, the protrusion d10 having a small ratio of the height b to the width a is unlikely to break even when rolled by an in-line mill. Therefore, unlike the protrusion d1, the fold portion e is not generated in the slab, and the oxide scale c1 on the surface of the slab is not bitten.
[0010]
　The oxide scale on the surface of the slab is removed in the next pickling step. However, the oxide scale c1 bitten in the folded portion e of the slab cannot be sufficiently removed by ordinary pickling. Therefore, when the slab is rolled to a thinner predetermined plate thickness after the pickling step, the oxide scale is exposed on the surface of the slab and the surface texture of the slab deteriorates, and the surface of the slab after rolling is deteriorated. Defects may become apparent.
[0011]
　In order to remove the oxide scale caught in the fold portion e of the slab, in order to dissolve the fold portion e of the protrusion by pickling, it takes more than twice the normal pickling time. Assuming that a fold portion having the same depth is generated, the pickling capacity is halved or less even if simply considered. Therefore, the productivity is significantly reduced. In addition, it is difficult to judge whether or not the oxide scale is bitten by the folds of the protrusions on the slab to which the scale is attached before pickling. To make a judgment, the slab is cut out separately and an observation sample It is necessary to create and observe the cross section. Therefore, in the pickling step, from the viewpoint of quality assurance, a method such as overmelting the slab has been taken in order to surely remove the oxidation scale.
Prior art literature
Patent documents
[0012]
Patent Document 1: Japanese Patent Application Laid-Open No. 2000-343103
Patent Document 2: Japanese Patent Application Laid-Open No. 5-285601
Patent Document 3: Japanese Patent Application Laid-Open No. 4454868
Non-patent literature
[0013]
Non-Patent Document 1: "Theory and Practice of Plate Rolling" by The Iron and Steel Institute of Japan, published by The Iron and Steel Institute of Japan, 1984, p. 22-23, p. 195,
Outline of the invention
Problems to be solved by the invention
[0014]
　However, if over-melting is performed to prevent surface defects of the slab, quality deterioration can be prevented, but manufacturing cost increases and yield decreases.
[0015]
　Therefore, the present invention has been made in view of the above problems, and an object of the present invention is generated when a slab having protrusions formed by a twin-drum type continuous casting apparatus is rolled by an in-line mill. It is an object of the present invention to provide a method for producing a slab and a continuous casting facility capable of preventing the folding of the protruding protrusion without impairing the productivity.
Means to solve problems
[0016]
(1) In the first aspect of the present invention, a metal molten metal storage portion is formed by a pair of cooling drums having dimples formed on the surface and a pair of side dams, and the metal molten metal is melted while rotating the pair of cooling drums. A twin-drum type continuous casting device for casting slabs having protrusions formed by the dimples from molten metal stored in a storage unit, and a twin-drum type continuous casting device arranged on the downstream side of the twin-drum type continuous casting device to cool the slabs. An in-line mill that is arranged on the downstream side of the cooling device and performs 1-pass rolling of the slab with a work roll with a rolling reduction of 10% or more, and an in-line mill that is arranged on the downstream side of the in-line mill and the casting. It is a method of manufacturing a slab by a continuous casting facility equipped with a winding device for winding a piece into a coil, and is a measured value of rolling load and advanced rate when the slab is rolled using a rolling analysis model. The friction coefficient is calculated from the above, the lubrication conditions during rolling of the slab are controlled so that the friction coefficient falls within a predetermined range, and the deformation resistance model based on the Orowan theory and Shida's approximation formula is used as the rolling analysis model. When the friction coefficient is calculated from the measured values ​​of the rolling load and the advanced rate using the formula, the predetermined range is 0.15 or more and 0.25 or less.
(2) In the method for producing a slab according to the above (1), the height of the protrusion may be 50 μm or more and 100 μm or less.
(3) In the method for producing a slab according to (1) or (2) above, the lubrication condition is the amount of lubricating oil supplied to at least one of the work roll or the cast slab. You may.
(4) In the second aspect of the present invention, a metal molten metal storage portion is formed by a pair of cooling drums having dimples formed on the surface and a pair of side dams, and the metal molten metal is formed while rotating the pair of cooling drums. A twin-drum type continuous casting device for casting slabs having protrusions formed by the dimples from molten metal stored in a storage unit, and a twin-drum type continuous casting device arranged on the downstream side of the twin-drum type continuous casting device to cool the slabs. An in-line mill that is arranged on the downstream side of the cooling device and performs 1-pass rolling of the slab with a work roll with a rolling reduction of 10% or more, and an in-line mill that is arranged on the downstream side of the in-line mill and the casting. Actual measurement of the rolling load and advanced rate using a winding device that winds the pieces into a coil, a measuring device that measures the rolling load and advanced rate of the slab rolled by the in-line mill, and a rolling analysis model. A lubrication control device that calculates the friction coefficient from the value and controls the lubrication conditions during rolling of the slab so that the friction coefficient falls within a predetermined range is provided, and the Rowan theory and Shida are provided as the rolling analysis model. Continuous casting equipment whose predetermined range is 0.15 or more and 0.25 or less when the friction coefficient is calculated from the measured values ​​of the rolling load and the advanced rate using the formula of the deformation resistance model based on the approximate formula of. Is.
(5) In the continuous casting equipment according to (4) above, the height of the protrusion may be 50 μm or more and 100 μm or less.
(6) In the continuous casting facility according to (4) or (5) above, the lubrication control device calculates the supply amount of lubricating oil required to control the friction coefficient and supplies it to the in-line mill. A friction coefficient adjuster for controlling the supply of lubricating oil may be provided.
Effect of the invention
[0017]
　According to the means described above, it is possible to prevent the protrusions from being folded when the slab having the protrusions formed by the twin-drum type continuous casting apparatus is rolled by the in-line mill without impairing the productivity. ..
A brief description of the drawing
[0018]
[Fig. 1] Fig. 1 is a conceptual diagram showing a fold of a protrusion formed by dimples.
FIG. 2 is a diagram showing a twin-drum type continuous casting facility according to an embodiment of the present invention.
FIG. 3 is a detailed view of an in-line mill of a twin-drum type continuous casting facility according to the same embodiment.
[Fig. 4] Fig. 4 is a schematic view of protrusions formed by dimples.
[Fig. 5] Fig. 5 is a table showing the relationship between the coefficient of friction and protrusions.
FIG. 6 is a flowchart showing an example of a control flow of lubrication conditions.
Mode for carrying out the invention
[0019]
　Preferred embodiments of the present invention will be described in detail with reference to the 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.
[0020]
　<1. Overview> The
　present inventor makes it possible to prevent breakage of protrusions when rolling a slab having protrusions formed by dimples manufactured by a twin drum type continuous casting facility with an in-line mill. I studied the manufacturing method diligently. As a result, when rolling the slab with an in-line mill, the friction coefficient is calculated from the measured values ​​of the rolling load and the advanced rate using the rolling analysis model, and the slab is adjusted so that the friction coefficient falls within a predetermined range. I came up with a method to control the lubrication conditions during rolling. By controlling the lubrication conditions of the slab so that the coefficient of friction falls within a predetermined range, it is possible to prevent the protrusions formed on the surface of the slab from breaking without impairing productivity.
[0021]
　<2. Manufacturing Process>
　First, with reference to FIG. 2, an outline of a manufacturing process for manufacturing a slab according to an embodiment of the present invention will be described. FIG. 2 is an explanatory diagram showing a schematic configuration of a manufacturing process of a slab (thin-walled slab) according to the present embodiment.
[0022]
　As shown in FIG. 2, the continuous casting equipment 1 according to the present embodiment includes, for example, a tundish (storage device) T, a double drum type continuous casting device 10, an antioxidant device 20, a cooling device 30, and a second. The pinch roll device 40 of 1, the in-line mill 100, the second pinch roll device 60, and the take-up device 70 are provided.
[0023]
　(Twin-drum type continuous casting device) As
　shown in FIG. 2, the twin-drum type continuous casting device 10 is arranged on both sides of a pair of cooling drums 10a and 10b and a pair of cooling drums 10a and 10b in the axial direction, for example. It is provided with a pair of side dams (not shown). The pair of cooling drums 10a and 10b and the side weir form a molten metal storage unit 15 for storing the molten metal supplied from the tundish T. The twin drum type continuous casting apparatus 10 casts slabs from the molten metal stored in the molten metal storage unit 15 while rotating the pair of cooling drums 10a and 10b in opposite directions.
[0024]
　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 whose axial center is slightly recessed. Further, the first cooling drum 10a and the second cooling drum 10b are configured so that the intervals between the cooling drums 10a and 10b can be adjusted according to the plate thickness or the internal quality of the slab S to be manufactured. 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. The cooling drums 10a and 10b can be cooled by circulating the cooling medium inside the cooling drums 10a and 10b. Further, dimples are formed on the surfaces of the cooling drums 10a and 10b.
[0025]
　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 the steady state is 30 μm (initial). Has been processed). Further, the dimples may have a length of 1.0 mm to 2.0 mm in the rolling direction and a depth of 50 μm to l00 μm. That is, the length of the protrusions formed by the dimples in the rolling direction may be 1.0 mm to 2.0 mm, and the height of the protrusions formed by the dimples may be 50 μm or more and 100 μm or less. The outer diameter, drum body length (width), and dimple shape of the pair of cooling drums 10a and 10b are not limited to this.
[0026]
　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 larger 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. In rolling in the in-line mill 100, a rolling start method called flying touch is performed, in which the hump starts rolling after passing through the in-line mill 100. By such a rolling start method, the slab S from the tip end portion of the slab S to the flying touch start portion remains in the cast state.
[0027]
　(Antioxidant device) The
　antioxidant device 20 is a device that performs a process for preventing the surface of the slab S immediately after casting from being oxidized to generate scale. In the antioxidant device 20, the amount of oxygen can be adjusted by, for example, nitrogen gas. The antioxidant device 20 is preferably applied as necessary in consideration of the steel type of the slab S to be cast.
[0028]
　(Cooling device) The
　cooling device 30 is a device arranged on the downstream side of the twin-drum type continuous casting device 10 and cools the slab S whose surface has been subjected to the antioxidant treatment by the antioxidant device 20. The cooling device 30 includes, for example, a plurality of spray nozzles (not shown), and sprays cooling water from the spray nozzles to the surfaces (upper surface and lower surface) of the slab S according to the steel type to generate the slab S. Cooling.
[0029]
　A pair of feed rolls 87 may be arranged between the antioxidant device 20 and the cooling device 30. The pair of feed rolls 87 do not roll the slab S, but sandwich the slab S by a pressing device (not shown), and the slab S between the pair of cooling drums 10a and 10b and the feed roll 87. While measuring the loop length of, a horizontal conveying force is applied to the slab S so that the loop length becomes 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.
[0030]
　(First Pinch Roll Device)
　The first pinch roll device 40 is a pinch roll device arranged on the entry side of the inline mill 100. The first pinch roll device 40 does not roll the slab S, but includes an upper pinch roll 40a and a lower pinch roll 40b, a housing, a roll chock, a rolling load detecting device, and a pressing device (first pinch roll device). Anything other than 40 is not shown.) And. The upper pinch roll 40a and the lower pinch roll 40b each have a hollow flow path formed therein, and are configured so that a cooling medium (for example, cooling water) can flow. The first pinch roll device 40 can be cooled by circulating the cooling medium.
[0031]
　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 pressing device (not shown). .) Is connected.
[0032]
　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 pressing device, the pressing 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 in-line mill 100. Further, the slab S in the pair of pinch rolls 40a and 40b and the in-line mill 100 so that the tension generated in the slab S between the first pinch roll device 40 and the in-line mill 100 becomes a preset tension. The moving speed of is controlled. Further, the tension of the slab S between the first pinch roll device 40 and the in-line mill 100 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.
[0033]
　(In-line mill) The in-
　line mill 100 is a rolling apparatus arranged on the downstream side of the cooling device 30 and the first pinch roll device 40 and rolling the slab S for one pass to make the slab S a desired plate thickness. .. In the present embodiment, the in-line mill 100 is configured as a quadruple rolling mill. That is, the in-line mill 100 includes a pair of work rolls 101a and 101b and backup rolls 102a and 102b arranged above and below the work rolls 101a and 101b. In addition, "1 pass rolling" means that a slab S having a plate thickness of a slab S that has passed through the continuous casting apparatus 10 is rolled once with an in-line mill 100 to obtain a desired plate thickness on the exit side of the in-line mill. It means that it is plastically deformed to have.
[0034]
　In the in-line mill 100, by rolling the slab S at a rolling reduction of 10% or more for one pass, the slab S can be made into a desired plate thickness without impairing productivity. The reduction rate is preferably 15% or more, and more preferably 20% or more.
　The upper limit of the rolling reduction should not be particularly limited, but if the rolling reduction in 1-pass rolling is excessively high, the protrusions may be folded even if the friction coefficient is controlled as described later. is there. Therefore, the upper limit of the reduction rate is preferably 40% or less, and more preferably 35% or less.
　The reduction rate (r) is defined by the following equation.
　r = {(Hh) / H} × 100 (%)
　Here, H (mm) is the plate thickness of the slab S before rolling, and h (mm) is the plate thickness of the slab S after rolling. Is.
[0035]
　As the in-line mill 100, for example, work rolls 101a and 101b having a roll diameter of 400 mm and backup rolls 102a and 102b having a roll diameter of 1200 mm may be used. The body length of each roll may be the same, for example, 2000 mm.
[0036]
　In addition to the above configuration, the in-line mill 100 is provided with equipment for supplying lubricating oil to at least one of the work roll and the slab, and can control the lubricating conditions and the like. A detailed description of the supply of lubricating oil will be described later.
[0037]
　(Second Pinch Roll Device)
　The second pinch roll device 60 is arranged on the outlet side of the inline mill 100. Like the first pinch roll device 40, the second pinch roll device 60 does not roll the slab S, but has an upper pinch roll, a lower pinch roll, a rolling load detecting device, and a pressing device (second). (Except for the pinch roll 60), none of them are shown.) The upper pinch roll and the lower pinch roll each have a hollow flow path formed inside, 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 a roll diameter of 400 mm and a roll body length (width) of 2000 mm, for example. 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 arranged between the in-line mill 100 and the second pinch roll device 60.
[0038]
　(Winling device) The
　winding device 70 is a device arranged on the downstream side of the in-line mill 100 and the second pinch roll device 60 and winds the slab S in a coil shape. A deflector roll 89 is arranged between the second pinch roll device 60 and the take-up device 70.
[0039]
　<3. Control of equipment configuration and lubrication conditions> When
　rolling a slab with protrusions with an in-line mill, if the protrusions are broken, surface defects will occur. Therefore, as a result of studies to prevent the occurrence of protrusion folds, the inventor of the present application changes the presence or absence of protrusion folds according to the friction coefficient between the slab and the work roll in the in-line mill. I got the finding. Then, based on this knowledge, he came up with the idea of ​​controlling the coefficient of friction between the slab and the work roll by controlling the lubrication conditions during rolling with an in-line mill to prevent the occurrence of bending of protrusions. Hereinafter, the control of the lubrication condition for preventing the protrusion of the slab from being broken by controlling the lubrication condition at the time of rolling the slab by the in-line mill will be described in detail. In addition, here, as an example of controlling the lubricating condition, an example of controlling the supply amount of lubricating oil will be described.
[0040]
　(3-1. Details of Configuration of
　Inline Mill ) In explaining the control of the lubrication condition at the time of rolling by the inline mill 100, the details of the inline mill 100 in the present embodiment will be described with reference to FIG. FIG. 3 is a detailed view of the in-line mill 100.
[0041]
　The in-line mill 100 includes a pair of work rolls 101a and 101b, and backup rolls 102a and 102b arranged above and below the work rolls 101a and 101b.
[0042]
　Cooling water supply nozzles 103a, 103b, 104a, 104b are provided before and after the rolling direction of the in-line mill 100, and cooling water is supplied to the work rolls 101a, 101b. The work rolls 101a and 101b are cooled by the cooling water. Further, draining plates 106a, 106b, 107a, 107b are provided between the cooling water supply nozzles 103a, 103b, 104a, 104b and the slab S so that the cooling water does not come into contact with the slab.
[0043]
　Lubricating oil supply nozzles 105a and 105b for supplying lubricating oil to at least one of the work roll surface and the slab are installed between the draining plates 107a and 107b installed on the inlet side of the in-line mill 100 and the slab S. To. In the description of the present embodiment, the lubricating condition is controlled by controlling the amount of lubricating oil supplied by these lubricating oil supply nozzles 105a and 105b.
[0044]
　The lubricating oil supplied from the lubricating oil supply nozzles 105a and 105b is stored in the lubricating oil tank 115. The lubricating oil may be, for example, an emulsion lubricating oil produced by heating and stirring water mixed in the lubricating oil tank 115 and rolling lubricating oil. The produced emulsion lubricating oil is sent by the pump P, passes through the pipe, and is supplied from the lubricating oil supply nozzles 105a and 105b.
[0045]
　The lubricating oil may be only rolling lubricating oil without containing a diluent such as water. Further, the hot water and the rolling lubricating oil may be stored in separate tanks, individually supplied into the pipe from each storage location, and then mixed and sheared to obtain an emulsion lubricating oil. As a method of supplying only the lubricating oil by the lubricating oil supply nozzles 105a and 105b, the lubricating oil itself may be sprayed onto the work roll, for example, as in air atomization. Further, solid lubricating oil may be supplied to the slab. When the temperature of the slab on the rolling mill inlet side changes by changing the supply amounts of the lubricating oil supply nozzles 105a and 105b, casting on the rolling mill inlet side even if the supply amounts of the lubricating oil supply nozzles 105a and 105b are changed. The temperature of the slab may be controlled by the cooling control of the cooling device 30 so that the temperature of the piece does not change. In the present embodiment, the continuous casting facility in which the cooling water supply nozzles 104a and 104b, the drain plates 106a and 106b, and the lubricating oil supply nozzles 105a and 105b are provided on the inlet side of the rolling mill is shown, but the cooling water supply nozzle 104a, 104b and drain plates 106a and 106b are not essential and may be omitted.
[0046]
　Here, when controlling the lubricating condition by supplying the lubricating oil, it is necessary to measure various parameters at the time of rolling and control the lubricating condition. Therefore, for example, a measuring device 110 that measures information necessary for controlling the lubrication conditions and a lubrication control device 120 that controls the lubrication conditions of the in-line mill 100 are provided.
[0047]
　The measuring device 110 includes a load cell 111 and a plate speedometer 112. The measuring device 110 actually measures various values ​​necessary for controlling the lubrication conditions. The load cell 111 is deployed on the roll chock of the upper backup roll 102a and measures the rolling load. The plate speedometer 112 is provided on the exit side of the rolling mill and measures the plate speed (V 0 ) of the slab . As the plate speedometer 112, for example, a non-contact type speed measuring device may be used.
[0048]
　The lubrication control device 120 includes a work roll (WR) speed converter 121, a calculator 122, a friction coefficient calculator 123, and a friction coefficient regulator 124. The lubrication control device 120 controls the lubrication conditions by calculating the friction coefficient μ based on the values ​​detected and calculated by the measuring device 110. WR rate conversion unit 121, the rotation speed of the motor 116, the work roll speed (V using a reduction gear (not shown.) The ratio by the work roll diameter R is calculated). The calculator 122 calculates the advanced rate (fs) from the plate speed and work roll speed of the slab. The calculator 122 calculates the advanced rate (fs) from the following equation (1). That is, the computing unit 122, the plate velocity (V o ) and the work roll speed (V R seek) based on the forward slip (fs).
　f S = (V O / V R -1) × 100 · · · (1)
[0049]
　The friction coefficient calculator 123 calculates the friction coefficient μ based on the advanced rate (fs) calculated by the calculator 122 and the rolling load. Then, the friction coefficient adjuster 124 calculates the supply amount of the lubricating oil required to control the friction coefficient μ using the calculated friction coefficient μ. The friction coefficient adjuster 124 further controls the pump P so as to supply the amount of lubricating oil required to control the calculated friction coefficient μ, and controls the supply of the lubricating oil supplied to the in-line mill 100. .. In this way, the lubrication conditions are controlled by using the measuring device 110 and the lubrication control device 120.
[0050]
　(3-2. Relationship between the occurrence of folds of protrusions and the coefficient of friction) When
　rolling a slab with protrusions with the in-line mill 100 shown in FIG. For rolling, the lubrication conditions during rolling are controlled by an in-line mill. In this embodiment, such lubrication conditions are controlled by controlling the coefficient of friction between the slab and the work roll.
[0051]
　The folds of the protrusions are caused by the deformation in the roll bite that occurs when the slab is rolled, and are greatly affected by the shearing force of the surface layer in the roll bite. Here, the shearing force is calculated by multiplying the compressive stress (rolling load) in the roll bite and the friction coefficient μ. In an in-line mill that rolls slabs cast by a twin-drum casting device, it is basically rolled without changing its conditions such as steel type, rolling speed, and tension, and the rolling reduction ratio is also the same. Therefore, although the values ​​of these parameters cannot be changed, the shearing force of the surface layer in the roll bite in the in-line mill can be changed by adjusting the friction coefficient μ. Therefore, the inventor of the present application has investigated an appropriate range of the friction coefficient μ during rolling, which can prevent the protrusions of the slab from folding.
[0052]
　In defining the range of friction coefficient at which the protrusions of the slab do not fold, the width of the protrusions and the height of the protrusions were changed to verify the fold state of the protrusions of the slab after rolling. The results will be described with reference to FIGS. 4 and 5. In this verification, as shown in FIG. 4, the width A of the protrusion D was changed to 1 to 3 mm and the height B was changed to 50 to 200 μm, and the shape conditions of the five protrusions were set. Then, the slabs on which these protrusions were formed were rolled by changing the friction coefficient μ between 0.10 and 0.33. The friction coefficient μ is a value calculated using a rolling analysis model based on the rolling conditions shown below. In this verification, the Orowan theory and the deformation resistance model based on Shida's approximation were used as the rolling analysis model.
[0053]
　The rolling of the slab in this verification was carried out in the slab manufacturing process having the same configuration as in FIG. The slab used had a plate thickness of 2 mm and a plate width of 1200 mm, and was ordinary steel. The acceleration rate of the cooling drum from the start of casting was 150 m / min / 30 seconds, 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. In this verification, the slab was rolled with ordinary steel, but the type of steel to be rolled is not limited to ordinary steel.
[0054]
　Further, in the in-line mill 100, a slab having a plate temperature of 1000 ° C. was rolled for one pass at a rolling reduction of 30%, and the plate thickness of the slab on the exit side of the in-line mill was 1.4 mm. Rolling with the in-line mill 100 was started after the dummy sheet passed through the in-line mill 100 and the plate crown of the slab became 150 μm or less. In this verification, rolling with the in-line mill 100 was started 15 seconds after the start of casting. As the rolling lubricating oil, a lubricating oil (melting point 0 ° C.) based on a synthetic ester (hindered complex ester) was supplied by an air atomizing method.
[0055]
　In FIG. 5, the evaluation of the steel sheet under five conditions in which the width A and the height B of the protrusions are changed in the friction coefficient range of 0.10 to 0.33 is described. In the evaluation, steel sheets that were unstable during rolling or had protrusions folds were indicated by x. In addition, no defects during rolling such as unstable rolling were confirmed, and steel sheets with no protrusions and no folds were marked with ◯.
[0056]
　With reference to the evaluation of FIG. 5, it was found that when the friction coefficient μ exceeds 0.25, the protrusion D is folded regardless of the shape of the protrusion. When the friction coefficient μ is 0.15 or more and 0.25 or less, the protrusion D disappears and folds occur regardless of the shape of the protrusion width A and height B in any of the conditions 1 to 5. There was no. When the friction coefficient μ was less than 0.15, the protrusions disappeared, but the friction coefficient was small, and slippage occurred during rolling due to excessive lubrication, resulting in unstable rolling. In addition, excessive lubrication may occur because the supply amount of lubricating oil is larger than necessary. In this case, the basic unit of lubricating oil deteriorates and the manufacturing cost of slabs increases. .. In the range where the friction coefficient μ exceeded 0.25, the protrusion D was bent. From these results, the specified range of the friction coefficient μ is set to the range of 0.15 to 0.25.
[0057]
　Based on the above, in the in-line mill 100 according to the present embodiment, the lubrication conditions during rolling are controlled by setting the specified range of the friction coefficient μ to 0.15 or more and 0.25 or less, thereby preventing the protrusions of the slab from breaking. In the conventional equipment, lubricating oil is not supplied, and water lubrication that also serves as roll cooling is performed. In the case of water lubrication, the friction coefficient is high, and when the friction coefficient is calculated using the actual measurement values ​​of the rolling load and the advanced rate using the deformation resistance model formula based on the Orowan theory Shida's approximation formula as the rolling analysis model, the friction coefficient is 0.3. It was in the range of about 0.4.
[0058]
　(3-3. Lubrication Condition Control Method)
　Hereinafter, a lubrication condition control method in which the friction coefficient μ of the in-line mill 100 is within a specified range will be described with reference to FIG. FIG. 6 is a flowchart showing a control method of lubrication conditions according to the present embodiment.
[0059]
　[S100: Pretreatment] When the
　amount of lubricating oil supplied to the work roll is controlled as a lubrication condition and the friction coefficient is within the specified range, first, in the target equipment, that is, the in-line mill 100 shown in FIG. The supply amount of the lubricating oil is changed to obtain the relationship between the supply amount of the lubricating oil and the friction coefficient μ (S100).
[0060]
　(Method of calculating the coefficient of friction)
　First, a method of calculating the coefficient of friction will be described. The coefficient of friction μ can be calculated using a rolling analysis model. The value of the friction coefficient μ differs slightly depending on the rolling analysis model used. Here, as a rolling analysis model, for example, the Orowan theory disclosed in Non-Patent Document 1 is used to calculate the friction coefficient μ. Further, as the formula of the deformation resistance model, the approximate formula of Shida also disclosed in Non-Patent Document 1 is used.
[0061]
　In the rolling analysis model, the roll diameter, tension, rolling load, plate thickness, rolling speed, etc. can be measured at the time of rolling and can be treated as known numbers. Therefore, if two independent values ​​are used, the coefficient of friction and the deformation resistance can be calculated as a coupled problem. Therefore, for example, in the rolling analysis model in which the measured values ​​of the rolling load and the advanced rate are substituted and the rolling analysis model in which the calculated values ​​of the rolling load and the advanced rate are substituted, the deformation resistance and the friction coefficient are changed so that both values ​​match. The friction coefficient μ can be obtained by performing the calculation.
[0062]
　In this embodiment, the Orowan theory and the formula of the deformation resistance model based on Shida's approximate formula are used as the rolling analysis model, but the present invention is not limited to this example, and the friction coefficient μ can be obtained by using another rolling analysis model. You may ask.
[0063]
　Further, the friction coefficient μ and the forward slip (f S since there is a strong correlation with) the friction coefficient μ and the forward slip was determined by rolling the analysis model of the (f S using the data group representing the relationship between), ) and may create an approximate expression for obtaining the frictional coefficient μ and a rolling load. For example, approximate expression for calculating the coefficient of friction μ is, forward slip (f S using) and rolling load (p), it can be expressed as the following equation (2). If necessary, a table may be prepared according to the steel type, plate thickness, and rolling temperature.
[0064]
　μ = a · f S + b · p + c ... (2)
[0065]
　The constants a, b and c of the approximate expression represented by the equation (2) may be obtained by multiple regression analysis. By using this approximate equation, forward slip to be measured during rolling (f S it is possible to obtain the friction coefficient μ using only)
[0066]
　(Relationship between friction coefficient and lubricating oil supply amount)
　Next, the relationship between the friction coefficient and the lubricating oil supply amount required when controlling the lubricating conditions by changing the lubricating oil supply amount from the friction coefficient is obtained. Regarding the relationship between the friction coefficient μ and the lubricating oil supply amount Q, in general, when the lubricating oil supply amount increases, the friction coefficient μ tends to decrease significantly at the initial stage when the lubricating oil supply is started, and then. There is a tendency for the change in the coefficient of friction μ to decrease. From this, the relationship between the friction coefficient μ and the lubricating oil supply amount Q can be expressed by, for example, a cubic approximation formula, that is, the following formula (3).
[0067]
　μ = a · Q 3 + b · Q 2 + c · Q + d ... (3)
[0068]
　The constants a, b and c of the approximate expression (3) may be obtained by using, for example, multiple regression analysis. The lubricating oil supply amount Q refers to the supply amount of the net lubricating oil supplied to at least one unit surface area of ​​the work roll or the slab. In the case of the emulsion lubricating oil, the diluted water content or the like is diluted. Does not contain solvent.
[0069]
　In step S100, in the target equipment, the supply amount of the lubricating oil is changed in a steady state, the rolling load (p) at each lubricating oil supply amount is acquired by the load cell, and the plate speed (plate speed) is obtained by the calculator 122. V o ) and the work roll speed (V R ) based on the forward slip Request (fs). Then, the friction coefficient calculator 123 calculates the friction coefficient at each lubricating oil supply amount from the rolling load and the advanced rate, for example, by using the above equation (2). When the relationship between a plurality of lubricating oil supplies and the friction coefficient is acquired, for example, the relationship between the lubricating oil supply amount represented by the above approximate equation (3) and the friction coefficient μ can be obtained using these data. Will be done. Based on the relationship between the supply amount of the lubricating oil acquired in step S100 and the friction coefficient μ, the supply amount of the lubricating oil in the in-line mill 100 in the actual operation is controlled.
[0070]
　[S102 to S116: Lubrication condition control in
　actual operation ] The supply amount of lubricating oil in the in-line mill 100 in actual operation is controlled based on the relationship between the friction coefficient μ acquired in step S100 and the lubricating oil supply amount Q. Will be done.
[0071]
　First, when the rolling of the slab by the in-line mill 100 is started, the rolling load is detected by the load cell 111 arranged in the roll chock of the upper backup roll (step S102). At this time, the WR speed converter 121 detects the rotation speed of the motor 116 that rotates the work rolls 101a and 101b, and calculates the work roll speed based on the rotation speed of the motor 116, the ratio by the speed reducer, and the work roll diameter. (Step S104). Further, at this time, the plate speed of the slab S is detected by the plate speedometer 112 arranged on the outlet side of the in-line mill 100 (step S106). In FIG. 6, the steps S102, S104, and S106 are shown in this order, but these processes are performed in parallel.
[0072]
　Next, the advance rate is calculated by the calculator 122 using the work roll speed calculated in step S104 and the plate speed measured in step S106 (step S108). Then, the friction coefficient μ is calculated by the friction coefficient calculator 123 based on the detected and calculated rolling load and the advanced rate (step S110). The coefficient of friction μ may be calculated using, for example, the above equation (2).
[0073]
　Next, the friction coefficient adjuster 124 calculates the amount of lubricating oil supplied. The friction coefficient adjuster 124 first obtains the difference Δμ between the friction coefficient μ calculated in step S110 and the target friction coefficient μ aim (step S112). Here, the target friction coefficient μ aim is set to a value in the range of 0.15 to 0.25. For example, in rolling with an actual machine, an error may occur between the actual friction coefficient and the calculated friction coefficient μ due to the influence of control error or measurement error. Thereby, in order to surely prevent the actual friction coefficient from being out of the specified range of the friction coefficient, the target friction coefficient μ aim may be set from a range in which the specified range is further narrowed. When the specified range of the friction coefficient is 0.15 or more and 0.25 or less as in the present embodiment, the target friction coefficient μ aim may be set to 0.20, for example.
[0074]
　Next, the friction coefficient adjuster 124 adjusts the lubricating oil corresponding to the difference Δμ calculated in step S112 based on the relationship between the known friction coefficient μ acquired in advance in step S100 and the lubricating oil supply amount Q. The amount (hereinafter, also referred to as “lubricating oil adjustment amount ΔQ”) is calculated (step S114).
[0075]
　As the relationship between the friction coefficient μ and the lubricating oil supply amount Q, for example, when the equation (3) is acquired, the change in the friction coefficient μ when the lubricating oil supply amount changes by ΔQ from a certain lubricating oil supply amount Q 0. the amount [Delta] [mu v is expressed by the following equation (4).
[0076]
　Δμ v = dμ / dQ · ΔQ
　　　= (3a · Q 0 2 + 2b · Q 0 + c) ΔQ ··· (4)
[0077]
　From the above equation (4), the amount of lubricating oil supplied (that is, the amount of lubricating oil supplied) ΔQ to be adjusted is calculated by the difference Δμ between the friction coefficient μ calculated in step S112 and the target friction coefficient μ aim .
[0078]
　Then, the friction coefficient adjuster 124 adjusts the currently set lubricating oil supply amount Q by the lubricating oil adjustment amount ΔQ according to the difference Δμ between the friction coefficient μ and the target friction coefficient μ aim, and adjusts the lubricating oil supply amount. Change to Q + ΔQ (step S116). The friction coefficient adjuster 124 controls the pump P so that the amount of lubricating oil supplied by the lubricating oil supply nozzles 105a and 105b becomes the amount of lubricating oil supplied Q 0 + ΔQ. As a result, the friction coefficient μ becomes the target friction coefficient μ aim .
[0079]
　The processes of steps S102 to S116 are repeated during rolling of the slab (S118). When the rolling of the slab is completed (step S118 / Yes), the control of the lubrication condition in the in-line mill 100 is completed. On the other hand, if the slab is being rolled (step S118 / No), the process is restarted from step 202 for detecting the rolling load by the load cell, and the process up to step S116 for adjusting the lubricating oil supply amount is repeated. Will be done.
[0080]
　The method of controlling the lubrication conditions according to the present embodiment has been described above. In the present embodiment, the amount of lubricating oil supplied to the work roll has been described, but the lubricating condition is not limited to the amount of lubricating oil supplied as long as the friction coefficient μ can be changed. For example, the lubricating conditions may be controlled by other methods such as the type of lubricating oil, the ratio of lubricating oil and water in the emulsion lubricating oil, and the supply temperature of the lubricating oil.
[0081]
　For example, the lubricating oil in the present embodiment may be a synthetic ester or a synthetic ester mixed with vegetable oil as a base oil. Further, if necessary, a solid lubricant or an extreme pressure additive may be added. If the pour point of the lubricating oil is 0 ° C. or higher, the lubricating oil solidifies in winter, so that the pour point of the lubricating oil is preferably less than 0 ° C.
Example
[0082]
　In order to confirm the effect of the present invention, the presence or absence of breakage of the protrusions of the slab formed by the dimples is checked by using the same equipment as the continuous casting equipment 1 according to the present embodiment shown in FIG. investigated. In both Examples and Comparative Examples, slabs having protrusions having a width of 2 mm and a height of 130 μm in the rolling direction were used.
[0083]
　This example was carried out in the manufacturing process of a slab having the same structure as that of FIG. In this embodiment, ordinary steel having a plate thickness of 2 mm and a plate width of 1200 mm was used. The acceleration rate of the cooling drum from the start of casting was 150 m / min / 30 seconds, 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. In this embodiment, the slab was rolled with ordinary steel, but the type of steel to be rolled is not limited to ordinary steel.
[0084]
　Further, in the in-line mill, a slab having a plate temperature of 1000 ° C. was rolled for one pass at a rolling reduction of 30%, and the plate thickness of the slab on the exit side of the in-line mill was 1.4 mm. Rolling in the in-line mill was started after the dummy sheet passed through the in-line mill and the plate crown of the slab became 150 μm or less. In this verification, rolling with an in-line mill was started 15 seconds after the start of casting. As the rolling lubricating oil, a lubricating oil (melting point 0 ° C.) based on a synthetic ester (hindered complex ester) was supplied by an air atomizing method.
[0085]
　In this example, the coefficient of friction μ was obtained by measuring the rolling load (p) and the advanced ratio (fs) during rolling and using the above formula (2). In this embodiment, the lubricating oil is derived from the above formula (4) based on the relationship between the friction coefficient μ obtained by the above formula (2), the friction coefficient μ expressed by the above formula (3), and the lubricating oil supply amount Q. The adjustment amount ΔQ was calculated, the supply amount of the lubricating oil was controlled, and the supply amount of the lubricating oil was controlled with a target friction coefficient of μaim 0.21. As a result, the slab was rolled so that the friction coefficient μ was in the range of 0.19 to 0.23. The rolled slab was pickled in a pickling step, and then multi-passed to a plate thickness of 0.2 mm with a Zenzimer rolling mill having a diameter of 60 mm. In the pickling step, 10 μm of smelting was performed.
[0086]
　On the other hand, in the comparative example, the same rolling as in the example was performed without supplying the lubricating oil, and then the pickling was performed in the pickling step, and then the same rolling as in the example was performed. The coefficient of friction μ at this time was 0.38 when calculated using the Orowan theory and the deformation resistance model formula based on Shida's approximate formula as a rolling analysis model. Further, in the pickling step, 10 μm of smelting was performed.
[0087]
　A combination of Examples and Comparative Examples was rolled for 50 coils, and the surface of the slab after rolling was observed by a Zenzimer rolling mill. As a result of surface observation, no surface defects were confirmed in the slabs in the examples. On the other hand, in the comparative example, surface defects were confirmed in the slab. When the same rolling was performed again under the conditions of the comparative example, it was confirmed that 30 μm of welding was required in the pickling step in order to eliminate the surface defects. That is, it was confirmed that in the comparative example, it is necessary to perform melt milling three times as much as in the example on the slab. From these results, it is possible to prevent the occurrence of bending of protrusions by appropriately controlling the range of the friction coefficient μ when rolling the slab, and further to improve the pickling efficiency three times as much as the conventional technique. all right.
[0088]
　From the above, when manufacturing slabs with a twin-drum type continuous casting facility, it is possible to prevent the protrusions on the surface of the slab from folding during rolling, improve pickling efficiency, and then perform rolling in the next process. It was confirmed that the surface defects that become apparent can be prevented and the manufacturing cost can be reduced.
[0089]
　Although preferred embodiments of the present invention have been described in detail with reference to the accompanying drawings, the present invention is not limited to such 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.
Industrial applicability
[0090]
　According to the present invention, it is possible to prevent the protrusions from being broken when rolling a slab having protrusions formed by a twin-drum type continuous casting apparatus with an in-line mill without impairing productivity. A method for producing a slab and a continuous casting facility can be provided.
Description of the sign
[0091]
　1 Continuous casting equipment
　10 Double drum type continuous casting equipment
　10a, 10b Cooling drum
　15 Metal molten metal storage part
　20 Antioxidant device
　30 Cooling device
　40 First pinch roll device
　40a, 40b Pinch roll
　41 Position detection device
　60 Second pinch roll Device
　70 Winding device
　88a, 88b Tension roll
　100 In-line mill
　101a, 101b Work roll
　102a, 102b Backup roll
　103a, 103b, 104a, 104b Cooling water supply nozzle
　105a, 105b Lubricating oil supply nozzle
　106a, 106b, 107a, 107b Drain plate
　110 Measuring device
　111 Load cell
　112 Plate speedometer
　115 Lubrication oil tank
　116 Motor
　120 Lubrication control device
　121 WR speed converter
　122 Calculator
　123 Friction coefficient calculator
　124 Friction coefficient adjuster
The scope of the claims
[Claim 1]
　A metal molten metal storage portion is formed by a pair of cooling drums having dimples formed on the surface and a pair of side dams, and the dimples are used from the metal molten metal stored in the metal molten metal storage portion while rotating the pair of cooling drums. A twin-drum type continuous casting device for casting a slab having a formed protrusion, a
　cooling device arranged on the downstream side of the twin-drum type continuous casting device and cooling the slab, and a
　cooling device on the downstream side of the cooling device. An in-line mill that is arranged and rolls the slab with a work roll for 1-pass rolling with a rolling reduction ratio of 10% or more,
　and a winding device that is arranged on the downstream side of the in- line mill and winds the slab in a coil shape.
It is a method of manufacturing a slab by a continuous casting facility equipped with a
　rolling analysis model , in which a friction coefficient is calculated from actual measurement values ​​of a rolling load and an advanced rate when the slab is rolled, and the friction coefficient is predetermined. The lubrication conditions during rolling of the slab are controlled so as to fall within the range
　of A
method for producing a slab , which comprises 0.15 or more and 0.25 or less in the predetermined range when the friction coefficient is calculated from an actually measured value .
[Claim 2]
　The
method for producing a slab according to claim 1, wherein the height of the protrusion is 50 μm or more and 100 μm or less .
[Claim 3]
　The
method for producing a slab according to claim 1 or 2, wherein the lubricating condition is a supply amount of lubricating oil supplied to at least one of the work roll or the cast slab.
[Claim 4]
　A metal molten metal storage portion is formed by a pair of cooling drums having dimples formed on the surface and a pair of side dams, and the dimples are used from the metal molten metal stored in the metal molten metal storage portion while rotating the pair of cooling drums. A twin-drum type continuous casting device for casting a slab having a formed protrusion, a
　cooling device arranged on the downstream side of the twin-drum type continuous casting device and cooling the slab, and a
　cooling device on the downstream side of the cooling device. An in-line mill that is arranged and rolls the slab with a work roll for 1-pass rolling with a rolling reduction of 10% or more,
　and a winding device that is arranged on the downstream side of the in- line mill and winds the slab in a coil shape.
　Using a measuring device that measures the rolling load and advanced rate of the slab rolled by the in-line mill and a
　rolling analysis model, the friction coefficient is calculated from the measured values ​​of the rolling load and advanced rate, and the friction coefficient is calculated. It
is equipped with a lubrication control device that controls the lubrication conditions during rolling of the slab so as to fall within a predetermined range, and
　uses the Orowan theory and the deformation resistance model formula based on Shida's approximate formula as the rolling analysis model.
A continuous casting facility characterized in that the predetermined range is 0.15 or more and 0.25 or less when the friction coefficient is calculated from the measured values ​​of the rolling load and the advanced rate .
[Claim 5]

The continuous casting facility according to claim 4, 　wherein the height of the protrusion is 50 μm or more and 100 μm or less .
[Claim 6]
　The lubrication control device is
characterized by including a friction coefficient adjuster that calculates the supply amount of the lubricating oil required to control the friction coefficient and controls the supply of the lubricating oil to be supplied to the in-line mill. , The continuous casting equipment according to claim 4 or 5.