A structure of a ladle shroud for reducing turbulence intensity in a tundish area and a design method thereof

Abstract

The present application relates to the technical field of steel metallurgy continuous casting process, and particularly relates to a long ladle shroud structure for reducing turbulence intensity of a tundish and a design method thereof. The present application is directed to the problem of strong turbulence and slag entrapment of molten steel in the tundish after the molten steel enters the tundish during the ladle pouring process. From the design perspective of controlling the fluid passing area and the outlet flow rate, a long ladle shroud outlet structure for reducing the turbulence intensity of the tundish impact area during the ladle pouring process and a design method thereof are provided. The long ladle shroud designed by using the method can effectively slow down the flow rate of the molten steel under the condition of the same static pressure by increasing the outlet area, so as to achieve the purpose of reducing the turbulence intensity of the molten steel in the tundish, prevent the molten steel from entrapment of slag, and improve the pouring stability.

Description

Technical Field

[0001] This invention relates to the field of continuous casting technology in iron and steel metallurgy, specifically to a long nozzle structure and design method for reducing turbulence intensity in the tundish. Background Technology

[0002] With users' increasing demands for steel quality, smelting steel with low inclusion content and high cleanliness has become a key focus of steelmaking science and technology research. A ladle is a container for molten steel, and the ladle nozzle is a device installed between the bottom outlet of the ladle and the tundish. The smelted molten steel is transported to the tundish through the ladle's outlet.

[0003] Turbulence is a ubiquitous fluid motion in nature, generated when fluids flow at high speeds. Compared to laminar flow, the fundamental characteristic of turbulence lies in its random vortex structure and the random motion of these vortices within the fluid. Therefore, turbulence can cause the exchange and pulsation of momentum, energy, and concentration between adjacent fluid layers.

[0004] The long nozzle of a steel ladle is typically a vertical tubular device made of corrosion-resistant refractory material. Its upper end, shaped like a bowl, connects to the bottom outlet of the ladle to ensure full contact with the outlet. The lower part is a straight tube, with the bottom outlet connecting to the tundish. During casting, the ladle is placed above the tundish, and the molten steel flowing from the ladle is transported into the tundish through the long nozzle using gravitational potential energy. Due to the high pressure of the molten steel, gravitational potential energy is converted into kinetic energy, creating severe turbulence upon entering the ladle. This causes intense disturbance to the molten steel in the tundish, resulting in slag entrainment, secondary oxidation, and severely affecting the cleanliness of the molten steel.

[0005] To suppress turbulence and reduce its impact on molten steel in the tundish, existing technologies typically employ turbulence suppressors, which involve installing a basin-shaped container below the long nozzle. This reduces turbulence by using the method of canceling out the inflow with the return flow, thus limiting the range of turbulence's influence on the molten steel in the tundish.

[0006] However, existing technologies have the following problems:

[0007] 1. The long nozzle of the steel ladle is a vertical tubular structure. The molten steel entering the tundish flows at a fast speed, rushing straight to the bottom of the ladle and then spreading outwards. The streams that turn up along the ladle wall can easily cause "red eyes" on the surface of the molten steel in the tundish, resulting in secondary oxidation of the molten steel and slag entrapment.

[0008] 2. Existing turbulence suppressors can reduce turbulence to a certain extent and limit its range of influence, but they cannot completely solve the turbulence problem. After the molten steel enters the tundish, it rushes straight to the bottom of the ladle. The strong impact energy of the molten steel returns to the liquid surface, which will still cause turbulence and slag entrainment, forming "red eyes" near the long nozzle, causing secondary oxidation of the molten steel.

[0009] 3. Existing turbulence suppressors are expensive and costly to use. After the refractory material of the suppressor is corroded, it can easily contaminate the molten steel. Summary of the Invention

[0010] The technical problem to be solved by the present invention is to provide a long nozzle structure and design method for reducing the turbulence intensity in the tundish, which can effectively reduce the turbulence intensity in the tundish impact zone, prevent slag entrapment in molten steel, and improve casting stability, in order to address the shortcomings of the prior art.

[0011] To solve the above-mentioned technical problems, the technical solution adopted by the present invention is as follows:

[0012] I. A steel ladle long nozzle structure for reducing turbulence intensity in the tundish

[0013] A long nozzle structure for a steel ladle to reduce turbulence intensity in an tundish includes, from top to bottom, an upper port 1, a pipe body 2, and a molten steel outlet 3. The top of the upper port 1 is connected to the steel ladle, and the bottom of the molten steel outlet 3 is connected to the tundish. The bottom of the molten steel outlet 3 is hemispherical, and a circular central hole 4 is opened in the center of the hemisphere. Multiple vertical openings 7 are evenly opened circumferentially on the sidewall of the molten steel outlet 3. The multiple vertical openings 7 are connected to the circular central hole 4 through multiple slits 5. A coating layer 6 is provided on the outside of the sidewall of the molten steel outlet 3.

[0014] Preferably, the upper port 1 is a bowl-shaped port, and the tube body 2 is made of refractory material.

[0015] Preferably, the lengths of the slit 5 and the vertical opening 7 satisfy the following formula:

[0016] L 1n +L 2n <H m

[0017] In the formula, L 1n Let L be the length of the nth vertical opening 7. 2n H is the length of the slit 5 connected to the nth vertical opening 7. m This refers to the depth to which the molten steel is immersed in the tundish when using a long nozzle.

[0018] Preferably, the areas of the plurality of slits 5 are all equal, and the total area of ​​the plurality of slits 5 is greater than the area of ​​the circular central hole 4.

[0019] Preferably, the total area S of the plurality of slits 5 and the circular central hole 4 satisfies the following formula:

[0020]

[0021] In the formula, Re0 is the preset Reynolds number for laminar flow of molten steel, Q is the volume coefficient of molten steel in the long nozzle, ρ is the density of molten steel, η is the dynamic viscosity coefficient of molten steel, and d is the characteristic dimension of the inner cavity of the tundish.

[0022] Preferably, the cladding layer 6 is made of sheet metal, and the melting point R0 of the sheet metal is higher than the temperature T1 of the molten steel in the ladle and lower than the temperature T2 of the molten steel in the tundish.

[0023] II. A design method for long nozzles in steel ladles to reduce turbulence intensity in tundishes

[0024] Based on the same inventive concept, this invention also provides a design method for a long nozzle structure of a steel ladle to reduce the turbulence intensity of the tundish as described above, specifically including the following steps:

[0025] S1. Based on experimental data, determine the maximum Reynolds number Re when the molten steel in the tundish is in a laminar flow state. max ;

[0026] S2, based on the maximum Reynolds number Re during the laminar flow state. max Calculate the maximum molten steel flow velocity v at the outlet of the long nozzle. max The specific formula is as follows:

[0027]

[0028] In the formula, ρ is the density of molten steel, η is the dynamic viscosity coefficient of molten steel, and d is the characteristic dimension of the inner cavity of the tundish.

[0029] S3, increase the outlet area of ​​the long nozzle, specifically by uniformly opening multiple vertical openings along the circumference of the side wall of the molten steel outlet, and opening multiple corresponding slits on the bottom hemisphere of the molten steel outlet, so that each vertical opening is connected to the original circular central hole at the bottom of the molten steel outlet through the corresponding slit.

[0030] S4, limiting the outlet flow velocity of the long nozzle, specifically based on the maximum molten steel flow velocity v. max Determine the number N of slits and the total area S of the slits and the circular central hole;

[0031] S5, with sheet metal covering the outside of the steel outlet sidewall.

[0032] Furthermore, in step S3, the lengths of the slit and the vertical opening satisfy the following formula:

[0033] L 1n +L 2n <H m

[0034] In the formula, L 1n Let L be the length of the nth vertical opening.2n H is the length of the slit connected to the nth vertical opening. m This refers to the depth to which the molten steel is immersed in the tundish when using a long nozzle.

[0035] Furthermore, in step S4, the total area S of the slit and the circular central hole satisfies the following formula:

[0036]

[0037] In the formula, Re0 is the preset Reynolds number for laminar flow of molten steel, Q is the volume coefficient of molten steel in the long nozzle, ρ is the density of molten steel, η is the dynamic viscosity coefficient of molten steel, and d is the characteristic dimension of the inner cavity of the tundish.

[0038] Furthermore, in step S5, the melting point R0 of the sheet metal material satisfies the following formula:

[0039] T1 < R0 < T2

[0040] In the formula, T1 is the temperature of the molten steel in the ladle, and T2 is the temperature of the molten steel in the tundish.

[0041] Compared with the prior art, the present invention has the following main advantages:

[0042] 1. This invention determines the maximum molten steel flow velocity at the long nozzle outlet based on the maximum Reynolds number when the molten steel in the tundish is in a laminar flow state. By increasing the molten steel outlet area by opening multiple vertical openings and slits at the long nozzle outlet of the ladle, the molten steel flow velocity at the outlet is limited, thereby effectively reducing the turbulence intensity in the tundish impact zone, preventing slag entrapment, and improving casting stability.

[0043] 2. The long nozzle structure of the ladle designed in this invention has a total steel outlet area that is more than twice the area of ​​the original circular central hole. Under the same static pressure, the outlet steel flow velocity can be reduced by more than 50%. At the same time, due to the small and long slit width and large contact area with the steel, the flow velocity of the steel flowing into the tundish can be further reduced, thereby reducing the Reynolds number of the molten steel in the tundish.

[0044] 3. The present invention covers the outer wall of the molten steel outlet of the long nozzle with sheet metal material, which can prevent the molten steel from scattering at the opening before the long nozzle is immersed into the tundish. At the same time, the melting point of the sheet metal material is lower than the temperature of the molten steel in the tundish. After the formal pouring begins, the sheet metal melts, causing the molten steel to flow out from the vertical opening, which can significantly reduce the molten steel flow rate and thus effectively reduce the occurrence rate of defects such as inclusions and slag in the tundish. Attached Figure Description

[0045] Figure 1 This is a schematic diagram of the long nozzle structure of the ladle in an embodiment of the present invention;

[0046] Figure 2 This is a bottom view of the long nozzle of the ladle in an embodiment of the present invention;

[0047] Figure 3 This is a flowchart of the design method for the long nozzle of the ladle in an embodiment of the present invention.

[0048] In the diagram: 1. Upper port; 2. Pipe body; 3. Molten steel outlet; 4. Circular central hole; 5. Slit; 6. Coating layer; 7. Vertical opening. Detailed Implementation

[0049] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the invention. Furthermore, the technical features involved in the various embodiments of this invention described below can be combined with each other as long as they do not conflict with each other.

[0050] It should be noted that, depending on the implementation needs, the various steps / components described in this application can be broken down into more steps / components, or two or more steps / components or parts of the operation of steps / components can be combined into new steps / components to achieve the purpose of this invention.

[0051] Example 1: This example provides a long nozzle structure for a steel ladle to reduce turbulence intensity in the tundish, such as... Figures 1-2 As shown, from top to bottom, there is an upper port 1, a pipe body 2, and a molten steel outlet 3. The top of the upper port 1 is connected to a steel ladle, and the bottom of the molten steel outlet 3 is connected to an intermediate ladle. The bottom of the molten steel outlet 3 is hemispherical, and a circular central hole 4 is opened in the center of the hemisphere. Multiple vertical openings 7 are evenly opened in the circumferential direction on the side wall of the molten steel outlet 3. The multiple vertical openings 7 are connected to the circular central hole 4 through multiple slits 5. A cladding layer 6 is provided on the outside of the side wall of the molten steel outlet 3.

[0052] Furthermore, the upper port 1 is specifically a bowl-shaped port, and the tube body 2 is specifically made of refractory material.

[0053] Furthermore, the lengths of the slit 5 and the vertical opening 7 satisfy the following formula:

[0054] L 1n +L 2n <H m

[0055] In the formula, L 1n Let L be the length of the nth vertical opening 7. 2n H is the length of the slit 5 connected to the nth vertical opening 7. m This refers to the depth to which the molten steel is immersed in the tundish when using a long nozzle.

[0056] Furthermore, the areas of the plurality of slits 5 are all equal, and the total area of ​​the plurality of slits 5 is greater than the area of ​​the circular central hole 4.

[0057] The Reynolds number, also known as the Reynolds dimensionless number, is a dimensionless number used to determine the flow state of viscous fluids. Its formula is:

[0058]

[0059] Where v is the fluid velocity (m / s), ρ is the density of molten steel (kg / m3), η is the dynamic viscosity coefficient of molten steel (Ns / m2), and d is the characteristic dimension (m).

[0060] The Reynolds number can be used to distinguish whether a fluid flow is laminar or turbulent. A small Reynolds number means that the viscous forces between the fluid particles are dominant, and the fluid particles flow regularly parallel to the inner wall of the pipe, exhibiting laminar flow. A large Reynolds number means that inertial forces are dominant, and the fluid exhibits turbulent flow.

[0061] In this example, the intermediate package Reynolds number Re < 2000 indicates laminar flow, Re = 2000 to 4000 indicates transitional flow, and Re > 4000 indicates turbulent flow.

[0062] In traditional steel metallurgical fluid containers, the Re is much greater than 4000, so the flow state is turbulent. This application starts from the direction of reducing the turbulence intensity, and minimizes the outlet flow velocity v and increases the outlet cross-sectional area, which can effectively reduce the turbulence intensity of molten steel entering the tundish.

[0063] Therefore, the total area S of the plurality of slits 5 and the circular central hole 4 satisfies the following formula:

[0064]

[0065] In the formula, Re0 is the preset Reynolds number for laminar flow of molten steel, Q is the volume coefficient of molten steel in the long nozzle, ρ is the density of molten steel, η is the dynamic viscosity coefficient of molten steel, and d is the characteristic dimension of the inner cavity of the tundish.

[0066] Furthermore, the cladding layer 6 is specifically made of sheet metal, and the melting point R0 of the sheet metal is higher than the temperature T1 of the molten steel in the ladle and lower than the temperature T2 of the molten steel in the tundish.

[0067] Example 2: This example uses a double-strand tundish for slabs, with a capacity of 60 tons, an inner diameter of 95mm for the long nozzle, and an outlet area of ​​70.85cm². 2 During normal pouring, the sprue is immersed to a depth of 350mm.

[0068] The design method of the steel ladle long nozzle structure of the present invention is as follows: In order to meet the uniformity of its unidirectional flow, it is designed with 4 slits, each 12mm wide and 300mm long, with the outlet diameter reduced to 70mm, and the slit area is covered with 0.5mm thick iron sheet.

[0069] Actual result: Total export area 182.47 cm² 2 Compared with the original total export area, it increased by 157.3%, the export flow velocity decreased significantly, the "red-eye" phenomenon in the long water outlet impact zone basically disappeared, and its use effect was tracked. Under the condition that other processes remained unchanged, the incidence of defects such as inclusions and slag entrapment decreased from 2.6% to 2.3%.

[0070] Example 3: This example uses a single-strand tundish for thin slab continuous casting. The tundish capacity is 45 tons, its long nozzle inner diameter is 80 mm, and its outlet area is 50.24 cm². 2 During normal pouring, the sprue should be immersed to a depth of 300mm.

[0071] The design method of the long nozzle structure of the steel ladle of the present invention is as follows: In order to meet the uniformity of its unidirectional flow, it is designed with 3 slits, the slits are 12mm wide and 250mm long, the outlet diameter is reduced to 50mm, and the slit area is covered with 0.5mm thick iron sheet.

[0072] Actual result: Total export area 109.63 cm² 2 Compared with the original total export area, it increased by 118.2%, the export flow velocity decreased significantly, the "red-eye" phenomenon in the long water outlet impact zone basically disappeared, and its use effect was tracked. Under the condition that other processes remained unchanged, the incidence of defects such as inclusions and slag entrapment decreased from 5.4% to 4.8%.

[0073] Example 4: Based on the same inventive concept, this example also provides a design method for a long nozzle structure of a steel ladle to reduce turbulence intensity in the tundish as described above, such as... Figure 3 As shown, the specific steps include the following:

[0074] S1. Based on experimental data, determine the maximum Reynolds number Re when the molten steel in the tundish is in a laminar flow state. max ;

[0075] S2, based on the maximum Reynolds number Re during the laminar flow state. max Calculate the maximum molten steel flow velocity v at the outlet of the long nozzle. max The specific formula is as follows:

[0076]

[0077] In the formula, ρ is the density of molten steel, η is the dynamic viscosity coefficient of molten steel, and d is the characteristic dimension of the inner cavity of the tundish.

[0078] S3, increase the outlet area of ​​the long nozzle, specifically by uniformly opening multiple vertical openings along the circumference of the side wall of the molten steel outlet, and opening multiple corresponding slits on the bottom hemisphere of the molten steel outlet, so that each vertical opening is connected to the original circular central hole at the bottom of the molten steel outlet through the corresponding slit.

[0079] S4, limiting the outlet flow velocity of the long nozzle, specifically based on the maximum molten steel flow velocity v. max Determine the number N of slits and the total area S of the slits and the circular central hole;

[0080] S5, with sheet metal covering the outside of the steel outlet sidewall.

[0081] Furthermore, in step S3, the lengths of the slit and the vertical opening satisfy the following formula:

[0082] L 1n +L 2n <H m

[0083] In the formula, L 1n Let L be the length of the nth vertical opening. 2n H is the length of the slit connected to the nth vertical opening. m This refers to the depth to which the molten steel is immersed in the tundish when using a long nozzle.

[0084] Furthermore, in step S4, the total area S of the slit and the circular central hole satisfies the following formula:

[0085]

[0086] In the formula, Re0 is the preset Reynolds number for laminar flow of molten steel, Q is the volume coefficient of molten steel in the long nozzle, ρ is the density of molten steel, η is the dynamic viscosity coefficient of molten steel, and d is the characteristic dimension of the inner cavity of the tundish.

[0087] Furthermore, in step S5, the melting point R0 of the sheet metal material satisfies the following formula:

[0088] T1 < R0 < T2

[0089] In the formula, T1 is the temperature of the molten steel in the ladle, and T2 is the temperature of the molten steel in the tundish.

[0090] In summary:

[0091] 1. This invention determines the maximum molten steel flow velocity at the long nozzle outlet based on the maximum Reynolds number when the molten steel in the tundish is in a laminar flow state. By increasing the molten steel outlet area by opening multiple vertical openings and slits at the long nozzle outlet of the ladle, the molten steel flow velocity at the outlet is limited, thereby effectively reducing the turbulence intensity in the tundish impact zone, preventing slag entrapment, and improving casting stability.

[0092] 2. The long nozzle structure of the ladle designed in this invention has a total steel outlet area that is more than twice the area of ​​the original circular central hole. Under the same static pressure, the outlet steel flow velocity can be reduced by more than 50%. At the same time, due to the small and long slit width and large contact area with the steel, the flow velocity of the steel flowing into the tundish can be further reduced, thereby reducing the Reynolds number of the molten steel in the tundish.

[0093] 3. The present invention covers the outer wall of the molten steel outlet of the long nozzle with sheet metal material, which can prevent the molten steel from scattering at the opening before the long nozzle is immersed into the tundish. At the same time, the melting point of the sheet metal material is lower than the temperature of the molten steel in the tundish. After the formal pouring begins, the sheet metal melts, causing the molten steel to flow out from the vertical opening, which can significantly reduce the molten steel flow rate and thus effectively reduce the occurrence rate of defects such as inclusions and slag in the tundish.

[0094] In the description of this invention, it should be noted that, unless otherwise explicitly specified and limited, the terms "connected" and "linked" should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral connection; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium. Those skilled in the art can understand the specific meaning of the above terms in this invention based on the specific circumstances.

[0095] In the description of this invention, unless otherwise stated, "several" means one or more; "multiple" means two or more; the terms "upper," "lower," "left," "right," "inner," "outer," etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the drawings, and are only for the convenience of describing this invention and simplifying the description, and are not intended to indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation, and therefore should not be construed as a limitation of this invention.

[0096] Those skilled in the art will readily understand that the above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A method for designing a structure of a ladle shroud for reducing the intensity of turbulence in a tundish region, characterized in that: The ladle shroud structure is sequentially provided with an upper port (1), a pipe body (2) and a molten steel outlet (3) from top to bottom, the top of the upper port (1) is connected with a ladle, and the bottom of the molten steel outlet (3) is connected with a tundish; the bottom of the molten steel outlet (3) is in a semispherical shape, a circular center hole (4) is arranged at the center of the semispherical shape, a plurality of vertical openings (7) are uniformly arranged on the side wall of the molten steel outlet (3) in a circumferential direction, the plurality of vertical openings (7) are respectively connected with the circular center hole (4) through a plurality of slits (5), and a cladding layer (6) is arranged on the outside of the side wall of the molten steel outlet (3). The design method comprises the following steps: S1, determining the maximum Reynolds number of the molten steel in the tundish in a laminar flow state through experimental data ; S2, the maximum Reynolds number at the time of the laminar flow state , the maximum molten steel flow rate v of the long nozzle molten steel outlet max , the specific formula is as follows: In the formula, is the density of the liquid steel, η is the dynamic viscosity coefficient of the liquid steel, and d is the characteristic size of the tundish cavity. S3, increasing the outlet area of the shroud, specifically, a plurality of vertical openings are uniformly arranged on the side wall of the molten steel outlet in a circumferential direction, and a plurality of corresponding slits are arranged on the semispherical bottom of the molten steel outlet, so that each vertical opening is connected with the original circular center hole of the bottom of the molten steel outlet through a corresponding slit; S4, limiting the outlet flow rate of the long nozzle, specifically according to the maximum molten steel flow rate v max determining the number N of the slits and the total area S of the slits and the circular hole; S5, cladding the outside of the side wall of the molten steel outlet with iron sheet material.

2. The design method of claim 1, wherein The upper port (1) is specifically a bowl-shaped port, and the pipe body (2) is specifically made of refractory material.

3. The method of claim 1, wherein In step S3, the lengths of the slits (5) and the vertical openings (7) satisfy the following formula: L 1n +L 2n <H m wherein L 1n is the length of the n-th vertical opening (7), L 2n is the length of the slit (5) associated with the n-th vertical opening (7), H m is the depth of immersion of the long nozzle into the bath of the tundish.

4. The method of claim 1, wherein, The areas of the plurality of slits (5) are equal, and the total area of the plurality of slits (5) is greater than the area of the circular center hole (4).

5. The method of claim 1, wherein In step S4, the total area S of the plurality of slits (5) and the circular center hole (4) satisfies the following formula: wherein is the preset Reynolds number of the laminar flow state of the liquid steel, Q is the volume coefficient of the liquid steel in the long nozzle, is the density of the liquid steel, η is the dynamic viscosity coefficient of the liquid steel, and d is the characteristic size of the inner cavity of the tundish.

6. The method of claim 1, wherein, The cladding layer (6) is specifically made of iron sheet material, and the melting point R0 of the iron sheet material is higher than the temperature T1 of the molten steel in the ladle and lower than the temperature T2 of the molten steel in the tundish.

7. The method of claim 1, wherein In step S5, the melting point R0 of the iron sheet material satisfies the following formula: T1 < R0 < T2 In the formula, T1 is the temperature of the molten steel in the ladle, and T2 is the temperature of the molten steel in the tundish.

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