An electromagnetic flow control device and method for slab continuous casting nozzles

Abstract

An electromagnetic flow control device and method for slab continuous casting nozzles includes: a static magnetic field arranged outside the slab continuous casting submerged entry nozzle above the meniscus of the molten steel in the slab continuous casting mold; the static magnetic field can be arranged in two ways: a single magnetic field and a double magnetic field; in the single magnetic field form, the static magnetic field is perpendicular to the centerline of the submerged entry nozzle, i.e., perpendicular to the direction of gravity; the static magnetic field is generated by at least two magnetic field generators arranged axially symmetrically on both sides of the submerged entry nozzle; the magnetic field generator is a ring structure surrounding the submerged entry nozzle and the magnetic field generators; in the double magnetic field form, the static magnetic field is perpendicular to the centerline of the submerged entry nozzle, i.e., perpendicular to the direction of gravity; the static magnetic field is generated by at least two magnetic field generators arranged axially symmetrically on both sides of the submerged entry nozzle; the static magnetic field forms a closed loop after passing through two C-shaped magnetic yokes, the C-shaped magnetic yokes being arranged axially symmetrically along the submerged entry nozzle; the C-shaped magnetic yokes are made of magnetically conductive material.

Description

Technical Field

[0001] This invention relates to continuous casting technology, and in particular to an electromagnetic flow control device and method for slab continuous casting nozzles. Background Technology

[0002] The crystallizer is the heart of continuous casting, and the flow state of the molten steel within it directly determines the final quality of the continuously cast product. During production, technical means are typically employed to optimize and control the molten steel flow field within the crystallizer, preventing phenomena such as slag entrapment, liquid level fluctuations, and excessively deep steel flow impact. Additional technical methods are needed to optimize and control the crystallizer flow field during production, and these methods can generally be categorized into two types: passive and active.

[0003] Passive systems are mainly achieved through optimizations such as submersible nozzle structure and tilt angle.

[0004] Active methods primarily achieve this through the application of external fields, such as electromagnetic vortex nozzles, electromagnetic stirring in the crystallizer, and electromagnetic braking. Electromagnetic stirring uses electromagnetic force to drive the molten steel to rotate. The rotating molten steel acts as a scouring agent at the solidification front, carrying away inclusions and bubbles and promoting their flotation and removal, ultimately improving the surface quality of the continuously cast billet. Electromagnetic braking, on the other hand, applies a static magnetic field to the flowing molten steel, using the induced Lorentz force to reduce its absolute flow velocity. When the static magnetic field acts below the nozzle, it reduces the impact depth of the molten steel, facilitating the flotation of inclusions and bubbles; when the static magnetic field acts on the meniscus, it stabilizes the liquid surface fluctuations and reduces slag entrainment.

[0005] In the actual production process of slab continuous casting, the flow field inside the crystallizer is extremely complex and constantly changes throughout the entire casting process. For example, flow deviation often occurs during continuous casting, meaning that there is a significant difference in the flow velocity of the molten steel on both sides of the nozzle, resulting in an asymmetry where one side has a faster flow velocity and the other side has a slower flow velocity. Similarly, localized excessively high flow velocities or eddies can easily occur near the meniscus. Electromagnetic stirring or electromagnetic braking, as technical means to optimize and control the flow field in the crystallizer, has been widely used in actual production.

[0006] However, extensive production practice has shown that using a single electromagnetic technology is insufficient to improve the flow field of the crystallizer under complex operating conditions such as changes in pulling speed, and more advanced flow field control devices and methods are needed.

[0007] In recent years, electromagnetic flow control methods for submerged entry nozzles have emerged. For example, Chinese patents CN1768984A and CN104028717A propose methods for controlling molten steel flow using electromagnetic vortex nozzles. These methods utilize electromagnetic force generated by alternating magnetic fields to act on the molten steel, causing it to rotate during injection into the crystallizer, thereby improving the flow field within the crystallizer. This method is effective for conventional casting speeds of 1.2–1.4 m / min; however, its effectiveness is limited at high casting speeds above 1.8 m / min. Summary of the Invention

[0008] The purpose of this invention is to provide an electromagnetic flow control device and method for slab continuous casting nozzles. By applying electromagnetic braking technology to the submerged entry nozzle, the braking force generated by the electromagnetic braking reduces the flow velocity of the molten steel stream, thereby changing the flow field inside the crystallizer, reducing the impact depth of the molten steel and the fluctuation of the liquid surface, and ultimately improving the surface quality of the cast billet.

[0009] To achieve the above objectives, the technical solution of the present invention is as follows:

[0010] Besides factors such as steel purity, pouring temperature, casting speed, cooling intensity, and argon flow rate, the surface quality of continuously cast billets is significantly influenced by the use of electromagnetic stirring / electromagnetic braking. A key function of electromagnetic stirring / electromagnetic braking within the crystallizer is to alter the flow rate and direction of the molten steel through electromagnetic force. This improves the uniformity of the solidified shell, reduces the likelihood of inclusions and bubbles being trapped at the solidification front, and promotes their upward movement, ultimately improving surface quality. Simultaneously, the electromagnetic force also leads to more uniform steel temperature and can appropriately increase the equiaxed crystal ratio. Therefore, electromagnetic flow control technology has become a crucial core technology for high-quality, high-efficiency production of slab continuously cast billets.

[0011] In the continuous casting process of slabs, molten steel enters the continuous casting mold through a submerged entry nozzle. After impacting the narrow face of the mold, the molten steel flows in both upward and downward directions, thus forming two circulating flows within the mold. The size and local velocity of these two circulating flows have a crucial impact on the slab quality. Generally speaking, a stable and moderate flow velocity distribution is beneficial to production, but it is difficult to detect and control in real time during actual production, especially since flow deviation often occurs during the casting process.

[0012] Therefore, based on the above-mentioned characteristics of the flow field in the crystallizer, a static magnetic field can be applied before the molten steel enters the crystallizer. The Lorentz force induced in the static magnetic field by the flowing molten steel can be used to reduce the flow velocity of the molten steel, thereby controlling the flow state of the molten steel in the crystallizer and forming an ideal flow field distribution.

[0013] This invention improves the flow field state within the slab continuous casting mold by applying a static magnetic field to the submerged entry nozzle and adjusting the magnitude of the electromagnetic braking force according to the specific conditions during the continuous casting process. This reduces the flow velocity of molten steel entering the mold through the submerged entry nozzle, thereby improving the quality of the cast slab.

[0014] Specifically, the electromagnetic flow control device for slab continuous casting nozzles of the present invention includes,

[0015] A static magnetic field is arranged outside the slab continuous casting submersible nozzle above the meniscus of the molten steel in the slab continuous casting mold. The static magnetic field can be arranged in two ways: a single magnetic field or a dual magnetic field.

[0016] Single magnetic field configuration: The static magnetic field is perpendicular to the centerline of the submersible nozzle, i.e., the static magnetic field is perpendicular to the direction of gravity; the static magnetic field is generated by at least two magnetic field generators arranged on both sides of the submersible nozzle and distributed axially symmetrically; the magnetic field generator is a ring structure that surrounds the submersible nozzle and the magnetic field generator; the magnetic field generator is made of magnetically conductive material.

[0017] Dual magnetic field configuration: The static magnetic field is perpendicular to the centerline of the immersion nozzle, i.e., the static magnetic field is perpendicular to the direction of gravity; the static magnetic field is generated by at least two magnetic field generators arranged on both sides of the immersion nozzle and distributed axially symmetrically, the magnetic field generators adopt C-shaped magnetic yokes, and the two C-shaped magnetic yokes form a closed loop; preferably, the C-shaped magnetic yokes are made of magnetically conductive material.

[0018] The static magnetic field is located between the meniscus of the molten steel and the bottom surface of the tundish in the slab continuous casting crystallizer.

[0019] Preferably, the magnetic field generator is a permanent magnet or is made of a magnetically conductive material surrounded by multiple turns of copper wire.

[0020] Preferably, the magnetic field generator is a ring-shaped magnetic yoke that surrounds the immersion nozzle and the magnetic field generator and is connected and fixed together.

[0021] Preferably, the maximum magnetic induction intensity B1 of the static magnetic field is between 0.05T and 0.5T.

[0022] The present invention also provides a method for electromagnetic flow control of slab continuous casting nozzles, which includes the following steps:

[0023] 1) A static magnetic field generator is arranged outside the slab continuous casting submersible nozzle above the meniscus of the molten steel in the slab continuous casting mold. The arrangement of the static magnetic field is as follows:

[0024] Single magnetic field form: The static magnetic field is perpendicular to the center line of the submersible nozzle, that is, the static magnetic field is perpendicular to the direction of gravity; the static magnetic field is generated by at least two magnetic field generators arranged on both sides of the submersible nozzle and distributed axially symmetrically.

[0025] Dual magnetic field configuration: The static magnetic field is perpendicular to the centerline of the submersible nozzle, i.e., the static magnetic field is perpendicular to the direction of gravity; the static magnetic field is generated by at least two magnetic field generators arranged on both sides of the submersible nozzle and distributed axially symmetrically; the magnetic field generator is a ring structure that surrounds the submersible nozzle and the magnetic field generator; the magnetic field generator is made of magnetically conductive material.

[0026] The maximum magnetic induction intensity B1 of the static magnetic field is 0.05 to 0.5 T;

[0027] The average magnetic induction intensity B2 within the effective area of ​​the static magnetic field satisfies:

[0028] B2×A≥8e -4 (Tm 2 )

[0029] B2 is the average magnetic flux density of the static magnetic field, in tons (T).

[0030] A represents the effective area of ​​the static magnetic field acting on the molten steel, in meters (m²). 2 .

[0031] Preferably, the magnetic field generator is a permanent magnet or is made of a magnetically conductive material surrounded by multiple turns of copper wire.

[0032] Preferably, the magnetic field generator is a ring-shaped magnetic yoke that surrounds the immersion nozzle and the magnetic field generator and is connected and fixed together.

[0033] Preferably, the static magnetic field forms a closed loop after passing through two C-shaped magnetic yokes, and the C-shaped magnetic yokes are arranged symmetrically along the immersion nozzle axis; preferably, the C-shaped magnetic yokes are made of magnetically conductive material.

[0034] Preferably, multiple static magnetic fields are arranged simultaneously along the axial direction of the immersion nozzle.

[0035] In response to the characteristics of the flow field in the slab continuous casting crystallizer, a static magnetic field is applied to the outside of the submerged entry nozzle, and the flow velocity of the molten steel inside the submerged entry nozzle is reduced by adjusting the electromagnetic braking parameters online. This improves the flow field of the molten steel inside the crystallizer, reduces the capture probability of inclusions, bubbles and other impurities at the solidification front, and achieves the goal of improving the surface quality of the cast slab.

[0036] Controlling the flow of molten steel within the nozzle using a vortex nozzle is a common method for altering the flow field in a crystallizer. This method applies a rotating stirring magnetic field to the molten steel within the nozzle, creating a circumferential stirring force, thereby changing the flow state of the molten steel after entering the crystallizer. However, due to the simultaneous effect of gravity on the molten steel, the downward impact velocity of the molten steel is not reduced after the rotating stirring action.

[0037] The static magnetic field proposed in this invention, when applied to the nozzle, generates a Lorentz force through the movement of molten steel cutting the magnetic lines of force. This force acts in the opposite direction to the movement of the molten steel, thereby reducing the impact velocity of the molten steel. This effect is particularly pronounced under high casting speeds above 1.8 m / min, facilitating the flotation of inclusions within the molten steel and ultimately improving the surface quality of the cast billet.

[0038] The beneficial effects of this invention are:

[0039] The use of electromagnetic flow control technology to improve the flow field in slab continuous casting molds has been validated in production, and electromagnetic stirring technology for molds has been widely applied in major steel mills in China. However, due to the complex and variable actual production conditions, a single, stable electromagnetic technology is no longer sufficient to meet the demands of high-quality and high-efficiency continuous casting production. Particularly under high casting speeds, to obtain high-quality continuously cast slabs, a static magnetic field needs to be applied within the mold to reduce the impact depth of molten steel and meniscus fluctuations. On the other hand, to further improve the surface quality of the cast slab, electromagnetic stirring with a traveling wave magnetic field is usually required to improve the flow state of molten steel within the mold. Therefore, under high casting speeds, simultaneously applying a static magnetic field and an alternating magnetic field within the mold places stringent requirements on electromagnetic parameters and production processes, resulting in a very narrow process window and demanding high operational standards in actual production.

[0040] The present invention proposes applying a static magnetic field at the nozzle position to reduce the impact velocity of molten steel, creating better conditions for controlling the electromagnetic parameters of the crystallizer flow field, effectively expanding the process adjustment window, and facilitating stable production operation.

[0041] By utilizing the device and parameter control method of this invention, the flow field state of the crystallizer can be effectively improved by controlling the flow rate of molten steel in the submerged nozzle under different real-time flow field conditions, especially under high casting speed conditions, thereby achieving a better electromagnetic flow control effect and ultimately obtaining high-quality continuous casting billets. Attached Figure Description

[0042] Figure 1 This is a schematic diagram of Embodiment 2 of the present invention;

[0043] Figure 2 This is a top view of Embodiment 2 of the present invention;

[0044] Figure 3 This is a top view of the static magnetic field of Embodiment 2 of the present invention;

[0045] Figure 4 for Figure 3 AA section view;

[0046] Figure 5 This is a front view of the static magnetic field of Embodiment 1 of the present invention;

[0047] Figure 6 for Figure 5 Top view. Detailed Implementation

[0048] The present invention will be further described below with reference to the embodiments and accompanying drawings.

[0049] See Figures 1-6 The electromagnetic flow control device for slab continuous casting nozzles of the present invention comprises,

[0050] A static magnetic field 3 is arranged outside the slab continuous casting submersible nozzle 2 above the meniscus of the molten steel in the slab continuous casting crystallizer 1. The static magnetic field 3 can be arranged in two ways: a single magnetic field or a double magnetic field.

[0051] Single magnetic field configuration: The static magnetic field 3 is perpendicular to the centerline of the submersible inlet 2, i.e., the static magnetic field 3 is perpendicular to the direction of gravity; the static magnetic field 3 is generated by two magnetic field generators 4 arranged symmetrically on both sides of the submersible inlet 2; for example... Figure 3 , Figure 4 As shown;

[0052] The magnetic field generator 5 is a ring structure that surrounds the immersion nozzle 2 and the magnetic field generator 4; the magnetic field generator 5 is made of magnetically conductive material.

[0053] Dual magnetic field configuration: The static magnetic field 3 is perpendicular to the centerline of the submersible inlet 2, i.e., the static magnetic field 3 is perpendicular to the direction of gravity; the static magnetic field 3 is generated by two magnetic field generators 4 arranged symmetrically on both sides of the submersible inlet 2; the static magnetic field 3 forms a closed loop after passing through two C-shaped magnetic yokes, the C-shaped magnetic yokes being arranged symmetrically along the axis of the submersible inlet 2; the C-shaped magnetic yokes are made of magnetically conductive material, such as... Figure 5 , Figure 6 As shown.

[0054] Preferably, the magnetic field generator 4 is a permanent magnet or is made of a magnetically conductive material surrounded by multiple turns of copper wire.

[0055] Preferably, the magnetic field generator 5 is a ring-shaped magnetic yoke that surrounds the immersion nozzle 2 and the magnetic field generator 4 and is connected and fixed together.

[0056] Preferably, the maximum magnetic induction intensity B1 of the static magnetic field is between 0.05T and 0.5T.

[0057] Preferably, multiple static magnetic fields are arranged simultaneously along the axial direction of the water inlet.

[0058] Example 1

[0059] The continuous casting speed is 1.6 m / s, the width is 1650 mm, and the thickness is 230 mm; the steel grade produced is IF steel plate, and the nozzle insertion depth (i.e., the distance from the meniscus to the upper edge of the nozzle) is 210 mm.

[0060] During production, molten steel flows out of the nozzle and rapidly impacts the narrow face of the crystallizer, forming an upward backflow and a downward impinging flow. The maximum velocity of the downward impinging flow at the solidification front reaches 0.5 m / s.

[0061] To address these operating conditions, a static magnetic field is applied 100 mm above the meniscus on the outside of the submerged entry nozzle. This static magnetic field employs a dual-magnetic-field configuration, achieved by winding multiple turns of copper wire around a pair of C-shaped magnetic yokes and applying direct current. The resulting DC magnetic field forms a closed loop along the C-shaped yokes and passes through the molten steel in the submerged entry nozzle. During the injection of the molten steel into the crystallizer, it passes through the aforementioned static magnetic field twice, generating a Lorentz force. The direction of this Lorentz force is opposite to the direction of the molten steel flow, thereby slowing down the flow rate of the molten steel.

[0062] The maximum magnetic induction intensity B1 at the center of the static magnetic field is 0.12 T, and the average magnetic induction intensity B2 is 0.09 T; the effective area of ​​the static magnetic field is A, which is 0.01 m². 2 The product of the static magnetic field and the effective area is: B × A = 9e -4 (Tm 2 ).

[0063] By implementing the above-mentioned electromagnetic flow control of the submerged nozzle, the flow rate of molten steel entering the crystallizer through the tundish is effectively controlled, thereby reducing the impact velocity of the outflow stream from the nozzle. On the one hand, this reduces the impact depth of the molten steel stream, with the maximum impact velocity decreasing from 0.5 m / s to 0.2 m / s; on the other hand, it also reduces the surface fluctuation of the meniscus.

[0064] Example 2

[0065] The continuous casting speed is 1.8 m / s, the width is 1450 mm, and the thickness is 230 mm; the steel grade produced is IF steel plate, and the nozzle insertion depth (i.e., the distance from the meniscus to the upper edge of the nozzle) is 210 mm.

[0066] During production, molten steel flows out of the nozzle and rapidly impacts the narrow face of the crystallizer, forming an upward backflow and a downward impinging flow. The maximum velocity of the downward impinging flow at the solidification front reaches 0.6 m / s.

[0067] To address these operating conditions, a static magnetic field is applied 100 mm above the meniscus on the outside of the submerged entry nozzle. This static magnetic field is a single magnetic field. Specifically, multiple turns of copper wire are wound around a pair of magnetically conductive materials, and a direct current is applied. The resulting DC magnetic field passes through the molten steel in the submerged entry nozzle. As the molten steel is injected into the crystallizer, it passes through this static magnetic field, generating a Lorentz force. The direction of this Lorentz force is opposite to the direction of the molten steel flow, thus slowing down the flow rate. The pair of magnetically conductive materials are connected by a circular magnetic yoke around the submerged entry nozzle to form a closed magnetic field loop.

[0068] The maximum magnetic induction intensity B1 at the center of the static magnetic field is 0.15 T, and the average magnetic induction intensity B2 is 0.12 T; the effective area of ​​the static magnetic field is A, which is 0.02 m². 2 The product of the static magnetic field and the effective area is: B × A = 2.4e -3 (Tm 2 ).

[0069] By implementing the above-mentioned electromagnetic flow control of the submerged nozzle, the flow rate of molten steel entering the crystallizer through the tundish is effectively controlled, thereby reducing the impact velocity of the outflow stream from the nozzle. On the one hand, this reduces the impact depth of the molten steel stream, with the maximum impact velocity decreasing from 0.6 m / s to 0.2 m / s; on the other hand, it also reduces the surface fluctuation of the meniscus.

[0070] In summary, the online control method for static magnetic field parameters provided by this invention can optimize the flow state of molten steel in the crystallizer. Combined with the application of electromagnetic stirring and electromagnetic braking technologies in the crystallizer, high-quality continuously cast billets can ultimately be obtained.

[0071] With users' increasing demands for steel product quality, and enterprises' own inherent requirements for efficient production, higher demands are being placed on the control of the flow field in slab crystallizers. The immersion-type nozzle magnetic field flow control device and method designed in this invention are flexible and controllable, with low difficulty in actual processing, manufacturing, and implementation. The equipment is easy to install and replace, and is expected to have a wide range of applications.

Claims

1. An electromagnetic flow control device for slab continuous casting nozzles, characterized in that, include, A static magnetic field is arranged outside the slab continuous casting submersible nozzle above the meniscus of the molten steel in the slab continuous casting crystallizer. The static magnetic field is located between the meniscus of the molten steel in the slab continuous casting crystallizer and the bottom surface of the continuous casting tundish. The static magnetic field can be arranged in two ways: single magnetic field and dual magnetic field. Single magnetic field configuration: The static magnetic field is perpendicular to the centerline of the submersible nozzle, that is, the static magnetic field is perpendicular to the direction of gravity; the static magnetic field is generated by at least two magnetic field generators arranged on both sides of the submersible nozzle and distributed axially symmetrically; the magnetic field generator is a ring structure that surrounds the submersible nozzle and the magnetic field generator; the magnetic field generator is made of magnetically conductive material. Dual magnetic field configuration: The static magnetic field is perpendicular to the centerline of the immersion nozzle, that is, the static magnetic field is perpendicular to the direction of gravity; the static magnetic field is generated by at least two magnetic field generators arranged on both sides of the immersion nozzle and distributed axially symmetrically, the magnetic field generators adopt C-shaped magnetic yokes, and the two C-shaped magnetic yokes form a closed loop.

2. The electromagnetic flow control device for slab continuous casting nozzles as described in claim 1, characterized in that, The C-shaped magnetic yoke is made of magnetically conductive material.

3. The electromagnetic flow control device for slab continuous casting nozzles as described in claim 1, characterized in that, The magnetic field generator is a permanent magnet or is made of a magnetically conductive material surrounded by multiple turns of copper wire.

4. The electromagnetic flow control device for slab continuous casting nozzles as described in claim 1, characterized in that, The magnetic field generator is a ring structure that surrounds the immersion nozzle and the magnetic field generator; the magnetic field generator is made of magnetically conductive material.

5. The electromagnetic flow control device for slab continuous casting nozzles as described in claim 1, characterized in that, The maximum magnetic induction intensity B1 of the static magnetic field is between 0.05T and 0.5T.

6. The electromagnetic flow control device for slab continuous casting nozzles as described in claim 1 or 5, characterized in that, Multiple static magnetic fields are simultaneously arranged along the axial direction of the water inlet.

7. A method for electromagnetic flow control of slab continuous casting nozzles, characterized in that, Includes the following steps: A static magnetic field generator is arranged outside the slab continuous casting submersible nozzle above the meniscus of the molten steel in the slab continuous casting crystallizer. The static magnetic field can be arranged in two ways: single magnetic field or dual magnetic field. Single magnetic field configuration: The static magnetic field is perpendicular to the centerline of the submersible nozzle, that is, the static magnetic field is perpendicular to the direction of gravity; the static magnetic field is generated by two magnetic field generators arranged on both sides of the submersible nozzle and distributed axially symmetrically; the magnetic field generator is a ring structure that surrounds the submersible nozzle and the magnetic field generator; the magnetic field generator is made of magnetically conductive material. Dual magnetic field configuration: The static magnetic field is perpendicular to the centerline of the submersible inlet, that is, the static magnetic field is perpendicular to the direction of gravity; the static magnetic field is generated by two magnetic field generators arranged on both sides of the submersible inlet and distributed axially symmetrically. The maximum magnetic induction intensity B1 of the static magnetic field is 0.05 to 0.5 T; The static magnetic field is located between the meniscus of the molten steel and the bottom surface of the tundish in the slab continuous casting crystallizer. The average magnetic induction intensity B2 within the effective area of ​​the static magnetic field satisfies: B2×A≥8e -4 (T.m 2 ) B2 is the average magnetic flux density of the static magnetic field, in tons (T). A represents the effective area of ​​the static magnetic field acting on the molten steel, in meters (m²). 2 .

8. The method for electromagnetic flow control of slab continuous casting nozzles as described in claim 7, characterized in that, The magnetic field generator uses a permanent magnet or is made of a magnetically conductive material surrounded by multiple turns of copper wire.

9. The method for electromagnetic flow control of slab continuous casting nozzles as described in claim 7, characterized in that, The magnetic field generator is a ring structure that surrounds the immersion nozzle and the magnetic field generator; the magnetic field generator is made of magnetically conductive material.

10. The method for electromagnetic flow control of slab continuous casting nozzles as described in claim 7, characterized in that, when When the static magnetic field is arranged in a dual magnetic field configuration, the static magnetic field forms a closed loop through two C-shaped magnetic yokes, and the C-shaped magnetic yokes are arranged symmetrically along the immersion nozzle axis.

11. The method for electromagnetic flow control of slab continuous casting nozzles as described in claim 10, characterized in that, The C-shaped magnetic yoke is made of magnetically conductive material.

12. The method for electromagnetic flow control of slab continuous casting nozzles as described in claim 7, characterized in that, Multiple static magnetic fields are simultaneously arranged along the axial direction of the immersion nozzle.

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