JP5200796B2 - Method of imparting swirl to molten metal flow - Google Patents

Description

  The present invention is a swirl flow forming mechanism inside a molten metal injection process utilizing a difference in height, such as injection of molten metal from a ladle to a tundish in continuous casting, and a plurality of blades around a dome part. The present invention relates to a method for removing non-metallic inclusions in molten metal using a cylindrical injection tube having a dome blade.

  As a method of injecting molten metal from a container arranged at the top to a container arranged at the bottom, such as pouring molten metal from a ladle into a tundish in continuous casting, it has been conventionally injected. A method using a tube is adopted.

  FIG. 1 is a longitudinal sectional view of a conventional injection tube. The injection tube 1 is a structure made of a cylindrical refractory having a uniform inner diameter, the inner diameter d11 is about 300 to 1500 mm, and the length L10 is about 500 to 1500 mm. In FIG. 1, the seal ring 11 which is a seal structure arrange | positioned at the upper end of the injection tube 1 is shown collectively.

  FIG. 2 is a partial configuration diagram of a continuous casting apparatus showing a situation in which molten metal is injected from a ladle into a tundish using a conventional injection tube and continuous casting is performed. As shown in the figure, in the method using the injection tube, the cylindrical injection tube 1 is installed in the tundish lid 5 so that the lower end of the tube is immersed in the molten metal 72 in the tundish 4. A ladle nozzle 61 provided at the lower portion of 6 is brought into close contact with the upper end of the injection tube 1 through a seal ring 11 and the inside of the injection tube 1 is filled with an inert gas 8 such as Ar. Then, the molten metal 71 in the ladle 6 is injected as a molten metal injection flow 7 from the ladle nozzle 61 so as to strike the molten metal 72 in the injection tube 1. The molten metal 72 injected into the tundish 4 is injected into the mold 13 via the immersion nozzle 12 provided at the bottom of the tundish 4 and is pulled down and solidified while being cooled, The slab 14 is obtained.

  In the method using an injection tube, when the falling flow from the ladle is struck against the molten metal surface, the inert gas in the atmosphere is entrained, and the inert gas such as Ar entrained is non-metallic intervening in the molten metal. Since an upward flow is formed while trapping an object, it is effective for cleaning the molten metal.

  In order to improve the effect of cleaning molten metal in a method using an injection tube, the present inventors have provided a swirl flow forming mechanism inside the injection tube and the inner diameter of the lower portion of the injection tube in Patent Documents 1 and 2. Has been proposed to provide a swirl to the molten metal.

  By imparting swirl to form a swirl flow, mixing of the inert gas and the molten metal is promoted, and the non-metallic inclusions in the molten metal are easily trapped by the inert gas, thereby cleaning the molten metal. The effect can be improved.

JP-A-2005-254245 (Claims and paragraphs [0038] to [0040]) JP 2007-44731 A (claims, paragraphs [0041] and [0042])

  There have been two problems with the conventional method of imparting swirl to the molten metal by providing a swirl flow forming mechanism inside the injection tube. The first problem is that the swirling speed of the molten metal is insufficient, and the cleaning effect of the molten metal cannot be sufficiently improved. The second problem is that the molten metal dropped from the ladle into the injection pipe collides with the swirl flow forming mechanism and jumps upward, and a large amount of molten metal accumulates and overflows in the injection pipe. It is possible to cause

  The present invention has been made in view of the above problems, and in the injection pipe used when injecting molten metal from a ladle into a tundish, the swirling speed of the molten metal is increased to improve the cleaning effect. At the same time, it is an object to provide a method for imparting swirl to a molten metal flow that can prevent the molten metal from jumping or overflowing.

  In order to achieve the above object, the inventors of the dome blade, which is a swirl flow forming mechanism having a plurality of blades around the dome portion, by a continuous casting test of molten steel and a numerical analysis using a computer. The shape was examined.

  As a result, in order to achieve the above object, it is effective to make the blade of the dome blade have a specific shape, and an area within the injection tube that can hold a sufficiently high molten metal is necessary above the blade. The knowledge that it is.

  This invention is made | formed based on said knowledge, The summary exists in the rotation provision method to the following molten metal flow.

In injecting the molten metal in the container, a body portion, located in the lower portion of the body portion, the refractory steel injection tube and a reduced inside diameter portion having a portion where the inner diameter is reduced toward the top to bottom, A dome blade is installed above the inner diameter reducing portion to impart a swirl to the molten metal passing between the blades of the dome blade, and the inner diameter reducing portion of the injection tube located downstream of the blade. A method of imparting swirl to a molten metal flow that increases the flow velocity of the swirl flow of molten metal, wherein the dome blade is disposed at a central portion in the radial direction and has a dome shape having a convex dome shape and the dome portion The dome portion has a thickness of 10 to 150 mm, the blade has a thickness of 10 to 50 mm, and the wing has a thickness of 10 to 150 mm. Is but angle between the horizontal plane, the are from the top of the blade decreases towards the lower part and the side surface of the dome portion, is surrounded with the vane adjacent to each other, by the inner wall of the injection tube body portion the flow path of the previous SL molten metal forms, the difference between the outer radius of the outer radius of the dome portion of the dome blades in horizontal cross-section of the dome blade decreases towards the bottom from the top of the channel, it Along with this, the cross-sectional area in the horizontal cross section of the flow path is also reduced , and the blades constituting the dome blade have one or more cubic curved surfaces, two or more quadratic curved surfaces, three or more planes, or these The first angle that the blade makes with the horizontal plane in an arbitrary vertical cross section is the maximum at the upper end of the blade and the minimum at the lower end of the blade. The first angle is 25 to 90 ° at the upper end of the blade and 5 to 45 ° at the lower end, and a radial line that is a straight line passing through the center of the injection tube in an arbitrary horizontal cross section and the blade Is the smallest at the connection point of the blade with the dome, and is the largest at the outer periphery of the blade, and the second angle at the upper end of the blade is the dome. The method for imparting swirl to the molten metal flow, characterized in that the angle is 0 to 45 ° at the connection point with the part and 30 to 80 ° at the outer peripheral part of the blade .

In swirl applying method to this molten metal stream, the cross-sectional area of the injection tube in a horizontal cross-section of said injection tube main body, the remaining area obtained by subtracting the projected area of the dome blade to the horizontal cross section, It is preferable that the area is 20% or less of the projected area of the dome blade because the molten metal can be efficiently turned. Further, it is preferable to allow a sphere having a diameter of 40 mm to pass through the molten metal flow path because blockage of the flow path by non-metallic inclusions can be prevented.

  Furthermore, the position of the upper limit of the molten metal surface height of the molten metal that can be retained in the injection tube main body is 400 mm or more upward from the upper end of the blade of the dome blade. It is preferable for preventing overflow. The injection tube main body has an inner diameter of 300 to 1500 mm, the inner diameter reduction portion has a minimum inner diameter of 60 to 300 mm, and the ratio of the inner diameter reduction portion to the outer diameter of the dome blade is 1/15 to 1 / 3, and the length of the portion in which the inner diameter of the inner diameter reduced portion is the above ratio is 0.5 to 4.0 times the minimum inner diameter, the solidified metal contained in the molten metal or It is preferable from the viewpoint of preventing the injection tube from being blocked by non-metallic inclusions and efficiently imparting swirl.

  Further, in the inner diameter reduced portion of the injection tube, from the inner wall of the portion where the ratio of the inner diameter of the inner diameter reduced portion to the outer diameter of the dome blade is 1/15 to 1/3, the flow rate is 1 to 50 NL / min. An inert gas is preferably blown in order to efficiently capture non-metallic inclusions by bubbles.

  In this specification and the like, the “dome-shaped shape” means a round roof shape or an umbrella shape whose diameter increases from the upper part toward the lower part, and means a shape having an opening on the bottom surface like a bell.

The “cross-sectional area of the injection tube” means the area of the portion surrounded by the inner wall of the injection tube in the horizontal cross section. The “radial width of the injection pipe in the horizontal cross section of the molten metal flow path” means the difference between the outer radius of the dome blade and the outer radius of the dome portion in the horizontal cross section of the dome blade.

  In addition, “quadratic surface” means a curved surface drawn as a locus when a curved line drawn on a plane is linearly moved. For example, a rectangular paper is kept parallel to a pair of opposite sides. An example is a curved surface obtained when bent as it is. “Cubic surface” means a curved surface that can be drawn by moving a curve in a curved line, and examples thereof include a spherical surface and terrain irregularities.

  According to the swirl imparting method to the molten metal flow of the present invention, non-metallic inclusions are removed by efficiently forming a swirl flow while preventing the injected molten metal from jumping and overflowing, and The cleaning effect can be improved. Moreover, the removal effect of nonmetallic inclusions can be further improved by combining inert gas blowing or the like.

As described above, the method for imparting swirl to the molten metal flow according to the present invention includes a main body portion and a portion that is located at a lower portion of the main body portion and has an inner diameter that decreases from the upper portion toward the lower portion when the molten metal is injected into the container. In a refractory injection pipe having an inner diameter reduced portion having a dome blade above the inner diameter reduced portion, to provide a swirl to the molten metal passing between the blades of the dome blade, A method for imparting swirl to a molten metal flow that increases the flow velocity of the swirl flow of the molten metal at an inner diameter reduced portion of the injection pipe located downstream of the blade, wherein the dome blade is disposed at the center in the radial direction The dome portion has an upward convex dome shape and a refractory having a shape having a plurality of blades in the radially peripheral portion of the dome portion, and the thickness of the dome portion is 10 to 150 mm. There, the thickness of the blade is 10 to 50 mm, the angle of the blade makes with the horizontal plane is reduced toward the lower portion from the upper portion of the wing, and a side surface of the dome portion, adjacent to each other said blade, said enclosed by the inner wall of the injection tube body portion flow path before Symbol molten metal is formed, the difference in outer radius of the outer radius of the dome portion of the dome blades in horizontal cross-section of the dome blade Decreases from the upper part to the lower part of the flow path, and accordingly, the cross-sectional area of the horizontal cross section of the flow path also decreases , and the blades constituting the dome blade include one or more cubic curved surfaces It has a shape of two or more quadric surfaces, three or more planes, or a combination of these, and the first angle that the blades make with the horizontal plane in any vertical section is at the upper end of the blades The largest and smallest at the lower end of the vane, the first angle being 25-90 ° at the upper end of the vane and 5-45 ° at the lower end, in any horizontal cross section The second angle formed by the radial line, which is a straight line passing through the center of the injection tube, and the blade is minimum at the connection point of the blade with the dome portion, and is maximum at the outer peripheral portion of the blade. The second angle at the upper end of the blade is 0 to 45 ° at the connection point with the dome, and 30 to 80 ° at the outer periphery of the blade . This is a turning imparting method. Hereinafter, the swirl imparting method to the molten metal flow of the present invention will be described in detail.

  FIG. 3 is a configuration diagram of a continuous casting apparatus showing a situation in which continuous casting is performed using the swirl imparting method to the molten metal flow of the present invention. The continuous casting apparatus shown in FIG. 3 has the same configuration as that of the continuous casting apparatus shown in FIG. 2 except for the configuration of the injection tube, and substantially the same parts are denoted by the same reference numerals.

  In FIG. 3, the molten metal 71 in the ladle 6 is injected into the tundish 4 as a molten metal injection flow 7 through a ladle nozzle 61 attached to the bottom of the ladle 6. The molten metal 72 injected into the tundish 4 is further injected into the mold 13 via the immersion nozzle 12 provided at the bottom of the tundish 4 and is drawn out below the mold 13 while being cooled and solidified. Thus, the slab 14 is obtained.

  The molten metal injection flow 7 entrains the inert gas 8 blown into the injection tube for the purpose of adjusting the atmosphere in the main body of the injection tube 1 indicated by 1A in FIG. There are suspended inert gas bubbles. The molten metal injection flow 7 is given a flow velocity component (swirl) in the circumferential direction inside the injection tube 1 while passing through the dome blade 2 disposed inside the main body 1A of the injection tube 1, and the swirl flow It flows down while forming. The molten metal injection flow 7 is arranged at the lower part of the main body 1A and flows down to the inner diameter reduced portion 1B having an inner diameter reduced from that of the main body 1A. Here, the circumferential flow velocity is further accelerated to generate a strong swirl flow. Form.

  Thus, by forming the swirl flow, the inert gas blown from the inert gas blowing portion 3 of the inner diameter reducing portion 1B becomes minute bubbles. Furthermore, the bubbles moving across the molten metal injection flow 7 toward the center of the swirling flow by the action of centrifugal force (centripetal force for low density phases) capture non-metallic inclusions and reduce the inner diameter reduced portion 1B. It flows out to the tundish 4 from the lower end.

  The bubbles that have captured the nonmetallic inclusions float on the liquid surface of the molten metal 72 in the tundish 4, so that the nonmetallic inclusions are separated from the molten metal 72 and the molten metal 72 is cleaned. In addition, the minute bubbles generated by the separation action of the low specific gravity substance based on the centrifugal force capture non-metallic inclusions on the way of rising in the tundish 4, so that the molten metal 72 is also cleaned.

1. About Dome Blade FIGS. 4 to 7 are a general view, a plan view, a bottom view, and a side view of a dome blade used in the method for imparting swirl to a molten metal flow according to the present invention, respectively. The dome blade 2 is a refractory structure, and includes a central dome portion 21 and a plurality of blades 22 provided around the dome portion 21 as shown in these drawings. The dome blade 2 is fixed inside the injection tube 1 and imparts angular momentum to the molten metal passing through the flow path 23 between the adjacent blades 22 to form a swirling flow.

1-1. About the dome part The dome part 21 has a dome-like shape with the center protruding upward, and has an opening (recessed part) 21a on the bottom surface like a bell as shown in FIG. Such a shape of the dome portion 21 is suitable for withstanding the load of the molten metal injected from above the dome blade 2 and guides the injected molten metal from the center side of the injection tube 1 to the inner wall side. Thus, the swirling flow velocity can be increased in the vicinity of the inner wall of the injection tube 1 in combination with the shape of the blades 22, which is suitable for imparting a large angular momentum to the molten metal. Moreover, it is more preferable that the diameter of the dome portion 21 is larger toward the lower side from the viewpoint of forming a swirl flow having a large swirl radius and imparting a large angular momentum to the molten metal.

  The thickness of the dome portion 21 is defined as 10 to 150 mm. This is because the strength is insufficient when the thickness is less than 10 mm. In addition, when the thickness exceeds 150 mm or when the dome portion 21 has a solid structure having a flat bottom surface, it not only causes an increase in mass more than necessary, but also weakens against thermal shock.

  The dome portion 21 desirably has a larger wall thickness in the upper portion than other portions in order to enhance durability against wear by the molten metal that collides. Specifically, it is desirable that the maximum thickness of the upper part is 20 to 100 mm and the thickness of other parts is 10 to 50 mm. Here, the upper part of the dome part 21 is a part exposed above the blades 22 in the side view of FIG. 7, and a part located on the center side of the blades 22 in the plan view of FIG. Point to.

1-2. About the blades The blades 22 of the dome blade 2 are provided around the dome portion 21 from the viewpoint of giving a large angular momentum to the molten metal, that is, the position where the radius of the swirling flow of the molten metal can be increased, that is, the outer periphery of the dome blade 2. This is because it is effective to rotate the molten metal on the side.

  Also, the provision of a plurality of blades 22 is because the flow velocity of the swirling flow formed by one blade 22 is not uniform in the circumferential direction, and the strength of the dome blade 2 and the load caused by the molten metal flow are circumferential. This is because of the bias. The number of blades 22 is preferably 4-10.

  The thickness of the blade 22 is defined as 10 to 50 mm. This is because the strength is insufficient when the thickness is less than 10 mm. Further, if the thickness exceeds 50 mm, not only the mass is increased more than necessary and the flow path 23 is decreased, but also the thermal shock is weakened. Here, the thickness of the blade 22 refers to the thickness in a direction perpendicular to the surface (flow path forming surface) of the blade 22.

  Further, the angle formed by the blade 22 with the horizontal plane changes so as to decrease from the upper portion to the lower portion of the blade 22, and the outer surface of the dome portion 21, the blade 22 adjacent to each other, and the main body portion 1 </ b> A of the injection tube 1. The radial width of the injection tube 1 in the horizontal cross-section of the molten metal flow path surrounded by the inner wall of the molten metal decreases from the upper part to the lower part of the flow path. The cross sectional area in the horizontal cross section is also reduced. In FIG. 5 and FIG. 6, a part of the flow path 23 formed between the adjacent blades 22 among the flow paths is indicated by hatching.

  By adjusting the angle formed by the blades 22 with the horizontal plane and the flow path 23 of the molten metal as described above, the injected molten metal 7 is easily accumulated in the flow path 23 formed between the adjacent blades 22. The flow rate of the molten metal 7 impinged on the blades 22 is reduced by the accumulated molten metal, so that the molten metal can be prevented from jumping up and the safety of the operation can be improved.

  Further, when reducing the radial width of the injection pipe 1 in the molten metal flow path, the position of the wall on the injection pipe center side of the flow path from the upper side to the lower side increases from the center side of the injection pipe 1 to the outer side. It is preferable to form so as to move. By configuring in this way, the center of the flow path can be moved outward from the upper part toward the lower part, the radius of the swirling flow can be increased, and a larger angular momentum can be imparted to the molten metal. This can be realized by making the diameter of the dome part 21 increase from the upper part toward the lower part.

1-3. About the angle of the blades The shape of the blade 22 is the angle θ shown in FIG. 7 and the angle φ shown in FIG. 5, that is, the angle θ formed by the blade 22 with a horizontal plane in an arbitrary vertical section and the center of the injection tube 1 in an arbitrary horizontal cross section. It is preferable that the angle φ formed by the radial line that is a straight line passing through (substantially the same as the center of the dome blade 2 in this embodiment) and the blade 22 satisfy the following condition. The angle θ and the angle φ are defined on the upper surface side (concave surface side) of the blade 22 that has a great influence on the flow of the molten metal. Here, the angle θ is based on the horizontal plane, and the vertical downward direction is the positive direction. The angle φ is based on the outward direction of the radial line, and the turning direction of the molten metal is the positive direction. Note that the angle θ shown in FIG. 7 is viewed from an oblique direction and does not show an accurate angle.

  The angle θ is maximum at the upper end of the blade 22 and is minimum at the lower end of the blade 22, and the angle φ is minimum at the connection point of the blade 22 with the dome portion 21, and at the outer peripheral portion of the blade 22. The maximum is preferred. In this case, the angle θ is preferably 25 to 90 ° at the upper end of the blade 22 and 5 to 45 ° at the lower end. Further, the angle φ at the upper end of the blade 22 is preferably 0 to 45 ° at the connection point with the dome portion 21, and preferably 30 to 80 ° at the outer peripheral portion of the blade 22. The blade 22 having a shape satisfying this condition can be obtained by combining one or more cubic curved surfaces, two or more quadric curved surfaces, three or more flat surfaces, or a combination of these surfaces. From the viewpoint of forming a smoother surface, it is most preferable that the blade 22 is composed of one cubic curved surface.

  The angle θ is maximized at the upper end of the blade 22 and minimized at the lower end, as described above, by reducing the cross-sectional area of the flow path 23 from the upper part toward the lower part to form a pool of molten metal. This is to suppress the scattering of the molten metal injection flow hitting the lower part of the metal. Further, as the angle θ is closer to a right angle at the upper end of the blade 22, that is, as the vicinity of the upper end of the blade 22 is closer to the vertical, scattering when the injected molten metal hits the upper portion of the blade 22 is suppressed. Further, the smaller the angle θ is at the lower end of the blade 22, that is, the stronger the swirling flow is as the vicinity of the lower end of the blade 22 is closer to the horizontal.

  The preferable range of the angle θ at the upper end of the blade 22 is defined as 25 to 90 ° because the injected molten metal tends to be scattered when the angle θ is less than 25 ° at the upper end of the blade 22. Also, if the angle θ exceeds 90 °, there is no meaning from the viewpoint of swirling flow formation, and it becomes a factor that hinders swirling flow formation. That is, when the angle θ is 90 °, the vertical injection flow hardly hits the upper surface of the blade 22 and the upper surface of the lower surface (back surface), so the angle θ at the upper end of the blade 22 is 90 from the viewpoint of molten metal scattering. When the angle θ is more than 90 °, the vertical injection flow hits the back side, which is counterproductive. A more preferable range of the angle θ at the upper end of the blade 22 is 45 to 90 °.

  Although the preferable range of the angle θ at the lower end of the blade 22 is defined as 5 to 45 °, the smaller the angle θ at the lower end of the blade 22, the stronger the turning can be imparted. This is because the flow path 23 is narrowed by being too long in the circumferential direction. Further, when the angle θ exceeds 45 °, it is difficult to impart sufficient swirl to the molten metal. A more preferable range of the angle θ at the lower end of the blade 22 is 10 to 30 °.

  The reason why the angle φ is minimized at the connection point with the dome portion 21 of the blade 22 and maximized at the outer peripheral portion of the blade 22 is that the molten metal at the center portion of the injection tube 1 is the dome portion at the center of the dome blade 2. After hitting 21, the flow toward the peripheral blades 22, that is, the radially outward flow from the center portion to the peripheral portion of the injection tube 1, has a flow velocity component in the circumferential direction smoothly along the blades 22. This is because the swirl can be efficiently imparted to the molten metal. That is, by guiding the flow of the molten metal in this way, the kinetic energy of the molten metal flow can be efficiently converted into angular kinetic energy.

  In order to guide the molten metal flow in this way, the shape of the projection of the blade 22 projected on the plan view is such that the angle φ shown in the plan view of FIG. 5 is small on the center side of the dome blade 2 and gradually moves toward the outer peripheral side. It is desirable to have a curved shape so as to increase.

  The angle φ at the upper end of the blade 22 is defined as 0 to 45 ° at the connection point with the dome portion 21, that is, the center side of the dome blade 2, when the angle φ is smaller than 0 ° in this portion. This is because the inclination is opposite to the swirling direction of the molten metal flow, and the swirling flow is weakened. If the angle φ is larger than 45 °, the radial flow from the center portion to the peripheral portion of the injection tube 1 from the dome portion 21 toward the blade 22 is suddenly changed in the circumferential direction. It is because it becomes a factor which becomes impossible to give efficient turning by the factor of scattering of this, and the generated energy loss.

  The reason why the angle φ at the upper end of the blade 22 is defined as 30 to 80 ° at the outer peripheral portion of the blade 22 is that when the angle φ is smaller than 30 ° in this portion, the melting from the central portion of the injection tube 1 toward the peripheral portion is performed. This is because the action of changing the direction of the metal flow to the circumferential direction is small, and the swirl cannot be efficiently imparted to the molten metal. Further, if the angle φ is larger than 80 °, the blades 22 become too long in the circumferential direction, and the flow path 23 of the molten metal formed between the blades 22 adjacent to each other becomes narrow. In this case, if the thickness of the blade 22 is reduced, the flow path 23 can be secured, but in this case, there is a problem that the strength of the blade 22 is lowered.

1-4. About the unoccupied ratio of the dome blade in the horizontal cross section in the injection pipe In the horizontal cross section of the main body portion 1A of the injection pipe 1, the remainder obtained by subtracting the projected area of the dome blade 2 on the horizontal cross section from the cross sectional area of the injection pipe 1 The ratio of the area to the projected area of the dome blade 2 is defined as the unoccupied ratio of the dome blade in the horizontal cross section in the injection tube. In the present embodiment, the non-occupancy ratio of the dome blade is preferably 20% or less, and more preferably 10% or less.

  The reason why the above range is preferable is that when the non-occupancy ratio of the dome blade in the horizontal cross section in the injection pipe is increased, the flow path vertically flowing without being swirled by the blades 22 of the dome blade 2 is expanded. This is because the swirl cannot be efficiently imparted to the molten metal.

  In addition, when the blades 22 adjacent to each other of the dome blade 2 are projected onto the horizontal cross section, if they overlap each other, the total area of the overlapping portions is 20% or less of the projected area of the dome blade 2. It is preferably 10% or less. This is because if the area of the portion where the blades 22 overlap is large, the flow resistance of the molten metal passing between the blades 22 increases, and the swirl cannot be efficiently imparted to the molten metal.

1-5. Molten Metal Channel A molten metal channel is formed in a region surrounded by the outer surface of the dome 21, the blades 22 adjacent to each other, and the inner wall of the main body 1 </ b> A of the injection tube 1. The flow path of the molten metal is preferably formed so that a sphere having a diameter of at least 40 mm can pass through so that a lump of non-metallic inclusions flowing together with the molten metal can pass through without clogging.

2. FIG. 8 is a longitudinal sectional view of the injection tube according to the present invention. In general, the injection tube is a cylindrical refractory structure as shown in FIG. On the other hand, as shown in FIG. 8, the injection tube 1 according to the present invention includes an upper body portion 1A and a lower inner diameter reduction portion 1B, and an inner diameter reduction portion inside the main body portion 1A of the injection tube 1. A dome blade 2 is disposed above 1B.

  The main body 1A has a cylindrical shape with a constant inner diameter. An overflow hole 9, which is a through hole, is provided on the upper wall surface of the main body 1 </ b> A, and an overflow rod 10 is provided on the outer surface of the main body 1 </ b> A so as to be connected to the overflow hole 9. The overflow hole 9 defines the upper limit position of the molten metal surface height that can be retained in the injection tube 1 and the molten metal surface height should rise abnormally. Even when the molten metal overflows from the overflow hole 9, it is safely discharged from the overflow bowl 10.

  The inner diameter reducing portion 1B has a shape having an inner diameter that is the same as that of the main body portion 1A at the upper end and a portion in which the inner diameter decreases downward. An inert gas blowing portion 3 is provided on the inner surface of the narrow-diameter portion located below the inner-diameter reduced portion 1B, which will be described later 2-3. Will be described in detail.

2-1. About the hot water reservoir region The region from the upper end of the blade 22 provided in the dome blade 2 to the lower end of the overflow hole 9 inside the injection pipe 1 is an area where molten metal can be retained (hereinafter referred to as “hot water reservoir region”). It is also called). The height L11 of the hot water reservoir region is preferably 400 mm or more, and more preferably 600 mm or more. When the height L11 of the hot water reservoir region is less than 400 mm, the molten metal is removed from the upper portion of the main body portion 1A of the injection pipe 1 when the molten metal surface height of the molten metal staying in the injection pipe 1 fluctuates during operation. This is because there is a danger of overflowing. Although the upper limit value of the height L11 of the hot water reservoir region is not particularly defined, about 1000 mm or 1500 mm is a substantial upper limit value from the viewpoint that the injection tube 1 is not unnecessarily enlarged.

  The upper limit position of the hot water reservoir region is the lower end of the overflow hole 9 in the injection pipe 1 shown in FIG. However, when the possibility of an abnormal rise in the hot water level in the injection pipe 1 is sufficiently small, the upper end of the injection pipe 1 may be set as the upper limit position of the hot water storage area without providing the overflow hole 9. Further, a portion having a low height may be provided at a part of the upper end of the injection tube 1, and an overflow rod may be connected to this portion. When the overflow hole 9 is provided on the side surface of the main body 1A of the injection pipe 1, the overflow hole 9 is refractory during normal operation from the viewpoint of maintaining the atmosphere adjusting effect and the air blocking effect inside the injection pipe 1 by the inert gas. It is desirable to close with a cloth or the like.

2-2. About the dimension of a main-body part and an internal diameter reduction part 300-1500 mm is preferable and, as for the internal diameter d11 of the main-body part 1A of the injection tube 1, 400-1000 mm is more preferable. The minimum inner diameter d12 of the inner diameter reduction portion 1B is preferably 60 to 300 mm, and the ratio of the minimum inner diameter d12 to the outer diameter of the dome blade 2, that is, the drawing ratio is preferably 1/15 to 1/3. More preferably, the minimum inner diameter d12 is 80 to 150 mm, and the drawing ratio is 1/10 to 1/4.

  The reason why the dimensions of the injection tube 1 are defined in this way is that the solidified metal or nonmetal contained in the molten metal if the inner diameter d11 of the main body 1A and the minimum inner diameter d12 of the inner diameter reduced portion 1B are less than the lower limit of the above range. This is because there is a high possibility that the injection tube 1 is blocked by inclusions. In addition, when the inner diameters of the main body 1A and the inner diameter reduction part 1B exceed the upper limit of the above range, the injection tube 1 becomes larger than necessary, leading to an increase in cost.

  Moreover, it is preferable that the drawing ratio is 1/15 to 1/3. If the drawing ratio is smaller than 1/15, the molten metal level of the molten metal staying in the injection pipe 1 increases, This is because the height L11 of the reservoir region is insufficient for the length defined in the present invention, and when the throttle ratio is larger than 1/3, the flow velocity of the obtained swirling flow is insufficient.

  Of the inner diameter reduced portion 1B, a length L12 in the vertical direction of a portion 1C (hereinafter referred to as a “narrow diameter portion”) having a drawing ratio of 1/15 to 1/3 (more preferably 1/10 to 1/4). However, 0.5 to 4.0 times the minimum inner diameter d12 of the inner diameter reduced portion 1B is preferable, and 0.8 to 2.5 times is more preferable.

  The reason for defining the dimensions of the inner diameter reduced portion 1B and the narrow diameter portion 1C in this way is that bubbles or owing to centrifugal force (centripetal force for low density phases) acting in the swirling flow obtained when this portion is too short. This is because the length of the region where the non-metallic inclusions collide and coalesce is insufficient, and the cleaning effect using the swirl flow is reduced. On the other hand, if this portion is too long, the flow velocity of the swirling flow is attenuated by the frictional resistance with the inner wall surface of this portion, and also in this case, the cleaning effect using the swirling flow is reduced.

2-3. Inert gas blowing portion An inert gas blowing portion 3 is provided on the inner wall of the narrow diameter portion 1 </ b> C of the injection tube 1. An inert gas is introduced into the inert gas blowing section 3 from the outside of the injection pipe 1 through an inert gas introduction path (not shown) provided in the pipe wall of the injection pipe 1. When an inert gas is blown into the swirling flow formed in the dome blade 2 from the inert gas blowing portion 3 of the narrow diameter portion 1C, many small bubbles are generated. These bubbles play a role of a filter that traps non-metallic inclusions when moving in the central direction while traversing the swirling flow of the molten metal by centrifugal force.

  In order to increase the ratio of the bubble filter to the horizontal cross section of the narrow-diameter portion 1C, the inert gas blowing portion 3 is preferably provided on the entire circumference of the inner wall of the narrow-diameter portion 1C. Further, the inert blowing part may be constituted by pores having a diameter of about 0.3 to 1.5 mm, which are provided in the inner wall of the narrow diameter part 1C. You may comprise with a porous refractory.

  In addition, since the smaller the diameter of the generated bubbles, the more advantageous for trapping inclusions, the inert gas blowing portion 3 is provided at the smallest inner diameter portion, which is the portion where the swirl flow velocity is the largest in the narrow diameter portion 1C. Is preferred.

  The flow rate of the inert gas blown from the inert gas blowing section 3 is preferably 1 to 50 NL / min. This is because if the flow rate is less than 1 NL / min, the total amount of bubbles is insufficient and the action of capturing non-metallic inclusions is reduced. On the other hand, if it exceeds 50 NL / min, the ratio of bubbles in the molten metal is increased, the flow resistance of the molten metal is increased, and more energy than necessary to make the molten metal flow (heads inside and outside the injection tube 1). This is because a difference is necessary.

3. FIG. 9 to FIG. 12 are an outline view, a plan view, a bottom view, and a side view of another dome blade used in the method of imparting swirl to the molten metal flow according to the present invention, respectively. . The dome blade 2 has a shape having ten blades 22.

  The dome blade 2 shown in FIGS. 4 to 7 has a shape in which the lower end of the dome portion 21 and the lower end of the blade 22 are on the same plane, but the shape of the blade 22 is described in the means for solving the above problems. 9 to 12, the lower end of the blade 22 may be in a shape positioned below the bottom surface of the dome portion as long as the specified condition is satisfied.

  FIG. 13 is a cross-sectional view of an injection tube used in the method for imparting swirl to a molten metal flow according to the present invention, in which another dome blade is disposed. As shown in FIG. 13, as long as the shapes of the inner diameter reduced portion 1 </ b> B and the narrow diameter portion 1 </ b> C satisfy the above-described conditions, the seal ring 11 is disposed on the upper portion of the injection tube 1 and overflows to the wall surface of the injection tube 1. It is good also as a form which does not provide the hole 9. FIG.

  In order to confirm the effect of the present invention, the following continuous casting test was performed, and the properties of the obtained cast pieces were evaluated.

1. Casting conditions Casting method: Casting with a curved 4-strand continuous casting machine.
Steel type: Al killed steel having the composition shown in Table 1 below.
Molten steel temperature: The temperature in the tundish was set to 1550 to 1600 ° C.
Ladle capacity: 200t.
Tundish capacity: 20t.
Ar gas blowing rate for atmosphere adjustment: 1000 NL / min
Ar gas injection rate for capturing non-metallic inclusions: 5 NL / min
Slab size: 410 mm thick x 530 mm wide.
Slab drawing speed: 0.5 m / min.

2. Shape of Injection Pipe and Dome Blade Example 1 of the present invention uses the injection pipe having the shape shown in FIG. 8 in which the dome blade having the shape shown in FIGS. 4 to 7 is installed, and uses the continuous casting apparatus having the configuration shown in FIG. Carried out. Moreover, Example 2 of this invention was implemented using the injection tube of the shape shown in FIG. 13 which installed the dome blade of the shape shown in FIGS. The continuous casting apparatus used in Example 2 of the present invention has the same configuration as the continuous casting apparatus shown in FIG. 3 except for the injection tube and the dome blade. In the comparative example, an injection tube having the shape shown in FIG. 1 was used, and the continuous casting apparatus shown in FIG. 2 was used. The dimensions of the injection tube are as shown in Table 2 below, and the dimensions of the dome blade are as shown in Table 3 below.

<Invention Example 1>
In Example 1 of the present invention, a domed blade, which is a swirl flow forming mechanism made of alumina-magnesia refractory, was formed in an injection pipe made of alumina-graphitic refractory that was formed by isostatic pressing.

  The injection tube has an overall height L10 of 1200 mm, an inner diameter d11 of the main body portion of 480 mm, and a wall thickness of 40 mm. An overflow hole having a diameter of 120 mm was provided in the upper part of the main body. The minimum inner diameter d12 of the inner diameter reduction portion is 96 mm, and the outer diameter of the minimum inner diameter portion is 160 mm. The ratio of the minimum inner diameter d12 of the inner diameter reduction portion to the outer diameter d21 of the dome blade of 480 mm is 1/5, which is in the range of 1/15 to 1/3. Of the reduced inner diameter portion, the length L12 of the narrow diameter portion, which is a portion whose inner diameter is 1/15 to 1/3 of the outer diameter of the dome blade, that is, 32 to 160 mm, is 200 mm, and the minimum inner diameter d12 is 2.1. And is in the range of 0.4 to 4.0 times. In FIG. 8, a portion whose inner diameter is 1/3 of the outer diameter of the dome blade is shown as d13. Twelve inert gas blowing holes for capturing non-metallic inclusions having a diameter of 0.5 mm were provided equally in the circumferential direction 130 mm above the molten metal outlet at the lower end of the injection tube.

  The dome blade has an overall outer diameter d21 of 475 mm that combines the dome portion and the blades. The dome has a uniform outer diameter d22 of 305 mm and a thickness of 20 mm at the lower end with the largest outer diameter. Around the dome portion, eight blades having a cubic curved surface, a thickness of 20 mm, and a height h21 of 140 mm are equally arranged. The height of the lower end of the blade is the same as the height of the lower end of the dome, and the height of the upper end of the blade is 60 mm lower than the height of the upper end of the dome (h22).

  The radial width of the injection tube in the horizontal cross section of the molten metal channel formed between adjacent blades and between the dome blade and the injection tube decreases from the top to the bottom of the channel, Along with this, the cross-sectional area in the horizontal cross section of the flow path has also decreased.

  In addition, the angle θ between the blade and the horizontal plane in an arbitrary vertical section is maximum at the upper end of the blade and minimum at the lower end of the blade. The angle θ is 90 ° at all points on the upper end of the blade, and is approximately 20 ° at the lower end, although it is slightly different between the connection point side with the dome portion and the outer peripheral portion.

  The angle φ formed between the radial line that is a straight line passing through the center of the injection tube and the blade in any horizontal cross section is the smallest at the connection point with the dome portion of the blade and the largest at the outer peripheral portion of the blade. . The angle φ at the upper end of the blade is 20 ° at the connection point with the dome, and 60 ° at the outer periphery of the blade.

  The unoccupied ratio of the dome blade in the horizontal cross section in the injection tube is 0.2%, which satisfies the condition of 20% or less.

  In addition, as shown in FIG. 6, a sphere having a diameter of 40 mm can pass through the flow path of the molten metal even at the lower end portion of the blade having the narrowest interval between adjacent blades.

<Invention Example 2>
In Example 2 of the present invention, a dome blade, which is a swirl flow forming mechanism made of magnesia-alumina refractory, was formed inside an injection pipe made of magnesia-graphite refractory that was press-formed by hydrostatic pressure.

  The injection tube has an overall height L10 of 1100 mm, an inner diameter d11 of the main body portion of 540 mm, and a wall thickness of 30 mm. The minimum inner diameter d12 of the inner diameter reduction portion is 110 mm, and the outer diameter of the minimum inner diameter portion is 180 mm. The ratio of the minimum inner diameter of the inner diameter reduced portion with respect to the outer diameter of the dome blade of 540 mm is 1 / 4.9, which is in the range of 1/15 to 1/3. Of the inner diameter reduced portion, the length L12 of the narrow diameter portion, which is the portion whose inner diameter is 1/15 to 1/3 of the outer diameter of the dome blade, that is, 36 to 180 mm is 220 mm, which is 2.0 times the minimum inner diameter. It is.

  Further, the distance L11 from the upper end of the blade of the dome blade to the upper limit of the hot water reservoir region of the injection tube main body is 380 mm, and a seal ring having a height L20 of 330 mm is placed on the upper portion of the injection tube. It is fixed with.

  The dome blade has an overall outer diameter d21 of 535 mm that combines the dome portion and the blades. The dome portion has an outer diameter d22 of 376 mm at the lower end portion having the largest outer diameter, and a uniform thickness of 50 mm. On the periphery of the dome portion, 10 blades having a thickness of 20 mm and a height h21 of 155 mm, each having a cubic curved surface, are equally arranged. The height of the upper end of the wing is 65 mm lower than the height of the upper end of the dome (h22), and the height of the lower end of the wing is 70 mm lower than the height of the lower end of the dome (h23).

  The radial width of the injection tube in the horizontal cross section of the molten metal channel formed between adjacent blades and between the dome blade and the injection tube decreases from the top to the bottom of the channel, Along with this, the cross-sectional area in the horizontal cross section of the flow path has also decreased.

  Further, the angle θ is maximum at the upper end of the blade and is minimum at the lower end of the blade. The angle θ at the upper end of the blade is 60 ° at the maximum at the connection point with the dome portion and 35 ° at the outer peripheral portion. The angle θ at the lower end of the blade is 40 ° at the maximum at the connection point with the dome portion and 20 ° at the outer peripheral portion.

  The angle φ is minimum at the connection point with the dome portion of the blade and is maximum at the outer peripheral portion of the blade. The angle φ at the upper end of the blade is 0 ° at the connection point with the dome, and 10 ° at the outer periphery of the blade.

  Further, as shown in FIG. 11, a sphere having a diameter of 40 mm can pass through the flow path of the molten metal even at the lower end portion of the blade having the narrowest interval between adjacent blades.

<Comparative example>
The injection tube used in the comparative example is a cylindrical tube made of an alumina-graphitic refractory that has been subjected to isostatic pressing, and does not have a swirl flow forming mechanism. As for the shape, the inner diameter d11 is 480 mm, the total height L10 is 860 mm, and the wall thickness is 30 mm. By placing a seal ring with a height L20 of 210 mm on the top of the injection tube, the injection flow was blocked from the atmosphere.

3. Test results Using the casting apparatus of Example 1 of the present invention, while pouring molten steel from the ladle into the tundish, Ar gas for atmosphere adjustment was 1000 NL / min in the space above the injection pipe, and the inert gas at the lower end of the injection pipe Ar gas for capturing non-metallic inclusions was blown from the blow hole at a flow rate of 5 NL / min to cast Al killed steel having the composition shown in Table 1 above. Further, Al killed steel having the same composition was cast while blowing Ar gas for adjusting the atmosphere at a flow rate of 1000 NL / min into the space above the injection pipe using the casting apparatus of the comparative example.

  Inclusion concentrations in these Al killed steels were evaluated by measuring the total oxygen concentration for samples cut from the slab. The sample was cut out as a pin sample having a diameter of 3 mm from the top side 1/4 thickness and 1/2 width position of the continuous casting machine in the cross section of the slab.

  As a result, when the total oxygen concentration of the slab obtained in the comparative example that does not use the swirl flow is set to 100, the total oxygen concentration of the slab obtained in the present invention example 1 is significantly reduced to 75. Thus, the effect of cleaning the molten metal by the swirl imparting method to the molten metal flow of the present invention could be confirmed.

  According to the swirl imparting method to the molten metal flow of the present invention, the non-metallic inclusions are removed by efficiently forming the swirl flow while preventing the injected molten metal from jumping or overflowing, and the molten metal is removed. It can be cleaned very effectively. Moreover, the removal effect of nonmetallic inclusions can be further improved by combining inert gas blowing or the like. As a result, the method of imparting swirl to the molten metal flow according to the present invention is widely used as an economical method capable of obtaining a high-quality slab having high cleanliness by using simple equipment. Applicable.

It is a longitudinal cross-sectional view of the conventional injection tube. It is a partial block diagram of the continuous casting apparatus which shows the condition which inject | pours a molten metal from a ladle to a tundish using the conventional injection pipe, and performs continuous casting. It is a block diagram of the continuous casting apparatus which shows the condition which performs continuous casting using the rotation provision method to the molten metal flow of this invention. It is a general-view figure of the dome blade used in the turning imparting method to the molten metal flow according to the present invention. It is a top view of the dome blade used in the turning imparting method to the molten metal flow according to the present invention. It is a bottom view of the dome blade used in the turning imparting method to the molten metal flow according to the present invention. It is a side view of the dome blade used in the turning imparting method to the molten metal flow according to the present invention. It is a longitudinal cross-sectional view of the injection pipe used in the swirling imparting method to the molten metal flow according to the present invention. It is a general-view figure of another dome blade used in the rotation provision method to the molten metal flow which concerns on this invention. It is a top view of another dome blade used in the turning imparting method to the molten metal flow according to the present invention. It is a bottom view of another dome blade used in the turning imparting method to the molten metal flow according to the present invention. It is a side view of another dome blade used in the turning imparting method to the molten metal flow according to the present invention. It is a longitudinal cross-sectional view of another injection pipe used in the swirling imparting method to the molten metal flow according to the present invention.

Explanation of symbols

1: injection tube, 1A: body portion, 1B: inner diameter reduced portion, 1C: narrow diameter portion,
2: Dome blade, 21: Dome, 21a: Opening 22: Blade,
23: flow path, 3: inert gas blowing part, 4: tundish,
5: Tundish lid, 6: Ladle, 61: Ladle nozzle, 7: Molten metal injection flow,
71: Molten metal, 72: Molten metal, 8: Atmosphere adjusting inert gas,
9: Overflow hole, 10: Overflow rod, 11: Seal ring,
12: immersion nozzle, 13: mold, 14: slab

Claims (6)

In injecting the molten metal into the container, in the injection tube made of a refractory, comprising a main body portion and an inner diameter reduced portion located at the lower portion of the main body portion and having a portion whose inner diameter decreases from the upper portion toward the lower portion, A dome blade is installed above the inner diameter reduced portion, and a swirl is imparted to the molten metal passing between the blades of the dome blade, and the molten metal is melted in the inner diameter reduced portion of the injection pipe located downstream of the blade. A method of imparting swirl to a molten metal flow that increases the flow velocity of the metal swirl flow,
The dome blade is composed of a dome portion having a convex dome-like shape disposed at a center portion in the radial direction and a refractory having a shape having a plurality of blades in the radial peripheral portion of the dome portion,
The wall thickness of the dome is 10 to 150 mm, the thickness of the blade is 10 to 50 mm, and the angle formed by the blade with the horizontal plane decreases from the top to the bottom of the blade, and and the side surface of the dome portion, the vanes adjacent the flow path of the previous SL molten metal is surrounded by the inner wall of the injection tube body portion is formed with one another, of the dome blades in horizontal cross-section of the dome blade The difference between the outer radius and the outer radius of the dome portion decreases from the upper part to the lower part of the flow path, and accordingly, the cross-sectional area in the horizontal cross section of the flow path also decreases .
The blades constituting the dome blade have one or more cubic curved surfaces, two or more secondary curved surfaces, three or more planes, or a combination of these,
The first angle that the blade makes with the horizontal plane in any vertical cross section is maximum at the upper end of the blade and minimum at the lower end of the blade,
The first angle is 25-90 ° at the upper end of the blade and 5-45 ° at the lower end,
The second angle formed between the radial line, which is a straight line passing through the center of the injection tube in any horizontal cross section, and the blade is the smallest at the connection point between the blade and the dome, and the outer periphery of the blade. The largest in the department,
The second angle at the upper end of the blade is 0 to 45 ° at the connection point with the dome, and 30 to 80 ° at the outer periphery of the blade . A turning method. The remaining area obtained by subtracting the projected area of the dome blade on the horizontal cross section from the cross-sectional area of the injection pipe in the horizontal cross section of the injection pipe main body is 20% or less of the projected area of the dome blade. The method for imparting swirl to the molten metal flow according to claim 1 . The method for imparting swirl to a molten metal flow according to claim 1 or 2 , characterized in that a sphere having a diameter of 40 mm can pass through the molten metal flow path. The upper limit position of the molten metal surface height of the molten metal that can be retained in the injection pipe main body is 400 mm or more upward from the upper end of the blade of the dome blade. The method of imparting swirl to the molten metal flow according to any one of to 3 . The inner diameter of the injection tube main body is 300 to 1500 mm, the minimum inner diameter of the inner diameter reduction part is 60 to 300 mm, and the ratio of the minimum inner diameter of the inner diameter reduction part to the outer diameter of the dome blade is 1/15 to 1/3. , and the to any one of claims 1 to 4, the inner diameter of the inner diameter reduction portion, wherein the length of the vertical portion is the above ratio is 0.5 to 4.0 times the minimum inner diameter A method of imparting swirl to the molten metal flow described. Inactive at a flow rate of 1 to 50 NL / min from the inner wall of the inner diameter reduced portion of the injection tube where the ratio of the inner diameter of the inner diameter reduced portion to the outer diameter of the dome blade is 1/15 to 1/3. 6. A method for imparting swirl to a molten metal flow according to claim 5 , wherein gas is blown.

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