Electromagnetic flow control device and method for slab continuous casting nozzle

Abstract

According to the slab continuous casting water gap electromagnetic flow control device and method, static magnetic fields are arranged on the outer side of a slab continuous casting submersed water gap above a molten steel meniscus in a slab continuous casting crystallizer, and the arrangement modes of the static magnetic fields include the single magnetic field mode and the double magnetic field mode; in the single magnetic field form, a static magnetic field is perpendicular to the center line of the submersed nozzle, namely the static magnetic field is perpendicular to the gravity action direction; the static magnetic field is generated by at least two magnetic field generators which are arranged on the two sides of the submersed nozzle and distributed in an axial symmetry mode. The magnetic field generator is of an annular structure and surrounds the submersed nozzle and the magnetic field generator by a circle; the static magnetic field is perpendicular to the center line of the submersed nozzle, namely the static magnetic field is perpendicular to the gravity action direction; the static magnetic field is generated by at least two magnetic field generators which are arranged on the two sides of the submersed nozzle and distributed in an axial symmetry mode. The static magnetic field forms a closed loop after passing through the two C-shaped magnet yokes, and the C-shaped magnet yokes are symmetrically arranged along the submersed nozzle axis. And the C-shaped magnet yoke is made of a magnetic conductive material.

Description

Technical Field

[0001] The invention relates to continuous casting technology, and in particular to an electromagnetic flow control device and method for a slab continuous casting water nozzle. Background Art

[0002] The crystallizer is the heart of continuous casting. The flow state of molten steel in the crystallizer directly determines the final quality of the continuous casting product. In the production process, technical means are usually required to optimize the flow field of molten steel in the crystallizer to avoid slag rolls, liquid level fluctuations, and excessive impact of steel flow. Additional technical means are required to optimize the flow field of the crystallizer in production. The methods for optimizing the flow field of the crystallizer can usually be divided into two types: passive and active.

[0003] The passive type is mainly achieved through optimization of the immersed nozzle structure, inclination angle, etc.

[0004] The active type is mainly achieved by applying an external field, such as electromagnetic swirl nozzle, electromagnetic stirring of the crystallizer and electromagnetic braking. Electromagnetic stirring drives the molten steel to rotate through electromagnetic force. The rotating molten steel plays a scouring role at the solidification front, thereby taking away the inclusions and bubbles at the solidification front and promoting floating and removal, and finally improving the surface quality of the continuous casting billet. Electromagnetic braking is a technology that reduces the absolute flow velocity of the flowing molten steel by applying a static magnetic field to the flowing molten steel through the induced Lorentz force. When the static magnetic field acts below the nozzle, the impact depth of the molten steel can be reduced, which is conducive to the floating of inclusions and bubbles; when the static magnetic field acts on the meniscus, it can stabilize the liquid level fluctuation and reduce slag rolls.

[0005] In the actual production process of slab continuous casting, the flow field in the crystallizer is extremely complex and constantly changes during the entire continuous casting process. For example, bias flow often occurs during continuous casting, that is, the flow rate of the molten steel on both sides of the nozzle is quite different, resulting in an asymmetric phenomenon in which the flow rate on one side is faster and the other side is slower. Similarly, local excessive flow or eddy currents are prone to occur near the meniscus. Electromagnetic stirring or electromagnetic braking, as a technical means to optimize and control the flow field of the crystallizer, has been widely used in actual production.

[0006] However, a large number of production practices have shown that the use of a single electromagnetic technology cannot adapt to the improvement of the mold flow field under complex working conditions such as changes in casting speed, and more advanced flow field control devices and methods are needed.

[0007] In recent years, electromagnetic flow control methods for submerged nozzles have emerged. For example, Chinese patents CN1768984A and CN104028717A respectively proposed a method for controlling the flow of molten steel by using an electromagnetic swirl nozzle. This method uses the electromagnetic force generated by alternating magnetic field induction to act on liquid steel, causing the molten steel to rotate during injection into the crystallizer, thereby improving the crystallizer flow field. This method can play a certain role for conventional casting speeds of 1.2 to 1.4 m / min, but it is difficult to achieve the effect under high casting speeds above 1.8 m / min. Summary of the invention

[0008] The purpose of the present invention is to provide an electromagnetic flow control device and method for a slab continuous casting water nozzle. By applying electromagnetic braking technology to an immersed water nozzle, the braking force generated by the electromagnetic braking reduces the flow rate of the molten steel stream, thereby changing the flow field in the crystallizer, reducing the impact depth of the molten steel and the liquid level fluctuation, and ultimately achieving the effect of improving the surface quality of the ingot.

[0009] To achieve the above object, the technical solution of the present invention is:

[0010] The surface quality of continuous casting billets is related to the purity of molten steel, pouring temperature, billet drawing speed, cooling intensity, argon flow rate, etc., and the use of electromagnetic stirring / electromagnetic braking is crucial. An important function of using electromagnetic stirring / electromagnetic braking in the crystallizer is to change the flow rate and flow direction of molten steel through the action of electromagnetic force, improve the uniformity of the solidified billet shell, reduce the probability of inclusions and bubbles being captured at the solidification front, promote the floating of inclusions and bubbles, and ultimately improve the surface quality; at the same time, through the action of electromagnetic force, the temperature of molten steel becomes more uniform, and the equiaxed crystal ratio can be appropriately increased. Therefore, electromagnetic flow control technology has become a key core technology for high-quality and high-efficiency production of slab continuous casting billets.

[0011] During the slab continuous casting process, the molten steel enters the continuous casting mold through the submerged nozzle. After impacting the narrow surface of the mold, the molten steel flows in the upper and lower directions, forming two upper and lower circulations in the mold. The size of these two circulations and the local flow rate have a crucial impact on the quality of the slab. Generally speaking, a stable and moderate flow rate distribution is beneficial to production, but it is difficult to detect and control in real time during the actual production process, especially when biased flow often occurs during the casting process.

[0012] To this end, based on the above-mentioned characteristics of the crystallizer flow field, a static magnetic field can be applied before the molten steel enters the crystallizer, and the Lorentz force induced by the flowing molten steel in the static magnetic field 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 pattern.

[0013] The present invention applies a static magnetic field to an immersed nozzle, adjusts the magnitude of the electromagnetic braking force according to specific conditions in the continuous casting process, reduces the flow velocity of molten steel in the immersed nozzle entering the crystallizer, thereby improving the flow field state in the slab continuous casting crystallizer and ultimately improving the quality of the cast billet.

[0014] Specifically, the electromagnetic flow control device for slab continuous casting nozzle of the present invention comprises:

[0015] A static magnetic field is arranged outside the slab continuous casting submerged nozzle above the meniscus of the molten steel in the slab continuous casting crystallizer. The static magnetic field arrangement modes include: single magnetic field form and double magnetic field form; among which,

[0016] Single magnetic field form: the static magnetic field is perpendicular to the center line 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 in an axisymmetric manner; the magnetic field generator is a ring structure, surrounding the immersion nozzle and the magnetic field generator; the magnetic field generator is made of magnetic conductive material;

[0017] Dual magnetic field form: the static magnetic field is perpendicular to the center line of the immersed water outlet, that is, the static magnetic field is perpendicular to the direction of gravity; the static magnetic field is arranged on both sides of the immersed water outlet and generated by at least two magnetic field generators axially symmetrically distributed, and the magnetic field generator adopts a C-shaped yoke, and two C-shaped yokes form a closed loop; preferably, the C-shaped yoke is made of magnetic conductive material.

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

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

[0020] Preferably, the magnetic field generator is a circular magnetic yoke surrounding the immersion water outlet and the magnetic field generator and 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 a slab continuous casting nozzle, which comprises the following steps:

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

[0024] Single magnetic field form: the static magnetic field is perpendicular to the center line of the submerged 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 submerged nozzle and distributed in an axisymmetric manner;

[0025] Double magnetic field form: the static magnetic field is perpendicular to the center line of the immersion nozzle, that is, the static magnetic field is perpendicular to the direction of gravity; the static magnetic field is arranged on both sides of the immersion nozzle and generated by at least two magnetic field generators that are axially symmetrically distributed; 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 magnetic conductive material;

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

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

[0028] B2×A≥8e -4 (Tm 2 )

[0029] B2 is the average magnetic induction intensity of the static magnetic field, unit is T;

[0030] A is the effective area of ​​the static magnetic field acting on the molten steel, unit: m 2 .

[0031] Preferably, the magnetic field generator is made of a permanent magnet, or is made of a plurality of turns of copper wire wrapped around a magnetic conductive material.

[0032] Preferably, the magnetic field generator is a circular magnetic yoke surrounding the immersion water outlet and the magnetic field generator and connected and fixed together.

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

[0034] Preferably, a plurality of static magnetic fields are arranged simultaneously along the axial direction of the submerged water nozzle.

[0035] According to the characteristics of the flow field of the slab continuous casting crystallizer, a static magnetic field is applied to the outside of the submerged nozzle, and the flow rate of the molten steel in the submerged nozzle is reduced by adjusting the size of the electromagnetic braking parameters online, thereby improving the flow field of the molten steel in the crystallizer and reducing the capture probability of impurities such as inclusions and bubbles at the solidification front, thereby achieving the purpose of improving the surface quality of the casting.

[0036] Using a swirl nozzle to control the flow of molten steel in the nozzle is a common method to change the flow field of the crystallizer. This method applies a rotating stirring magnetic field to the molten steel in the nozzle and forms a circumferential stirring force, thereby changing the flow state of the molten steel after entering the crystallizer. However, due to the gravity that the molten steel is also subjected to, the downward impact speed of the molten steel after the rotating stirring action is not weakened.

[0037] After the static magnetic field proposed by the present invention acts on the nozzle, the Lorentz force generated by the movement of the molten steel cutting the magnetic lines of force is opposite to the movement direction of the molten steel, thereby slowing down the impact speed of the molten steel. In particular, it can play a good deceleration effect under the condition of a high pulling speed of more than 1.8m / min, thereby facilitating the floating of inclusions in the molten steel and ultimately improving the surface quality of the ingot.

[0038] Beneficial effects of the present invention:

[0039] The use of electromagnetic flow control technology to improve the flow field of slab continuous casting crystallizer has been verified in production, especially the crystallizer electromagnetic stirring technology has been widely used in major domestic steel mills. However, due to the complex and changeable actual production conditions, the use of a single stable electromagnetic technology has been difficult to meet the needs of high-quality and high-efficiency continuous casting production. Especially under high pulling speed conditions, in order to obtain high-quality continuous casting billets, it is necessary to apply a static magnetic field in the crystallizer to reduce the impact depth of the molten steel and the fluctuation of the meniscus. On the other hand, in order to further improve the surface quality of the billet, it is usually necessary to improve the flow state of the molten steel in the crystallizer through traveling wave magnetic field electromagnetic stirring. Therefore, under high pulling speed conditions, the simultaneous application of static magnetic field and alternating magnetic field in the crystallizer puts forward strict requirements on electromagnetic parameters and production processes. The process window is very narrow, and the actual production process has high requirements for operation.

[0040] The static magnetic field is applied at the water inlet position proposed by the present invention, which slows down the impact speed of the molten steel, creates better conditions for controlling the electromagnetic parameters of the crystallizer flow field, effectively expands the process adjustment window, and facilitates stable production operation.

[0041] By utilizing the device and parameter control method of the present invention, the flow field state of the crystallizer can be effectively improved by controlling the flow rate of the molten steel in the submerged nozzle according to different real-time flow field states, especially under high pulling speed conditions, to achieve a better electromagnetic flow control effect, and ultimately obtain high-quality continuous casting billets. BRIEF DESCRIPTION OF THE DRAWINGS

[0042] Figure 1 is a schematic diagram of embodiment 1 of the present invention;

[0043] Figure 2 is a top view of embodiment 1 of the present invention;

[0044] Figure 3 A top view of the static magnetic field of Example 1 of the present invention;

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

[0046] Figure 5 It is a front view of the static magnetic field of Example 2 of the present invention;

[0047] Figure 6 for Figure 5 Top view of the . DETAILED DESCRIPTION

[0048] The present invention will be further described below in conjunction with the embodiments and drawings.

[0049] See also Figure 1 to Figure 6 The electromagnetic flow control device for slab continuous casting nozzle of the present invention comprises:

[0050] A static magnetic field 3 is arranged outside the slab continuous casting submerged nozzle 2 above the meniscus of the molten steel in the slab continuous casting crystallizer 1. The static magnetic field 3 is arranged in the following ways: single magnetic field form and double magnetic field form; wherein,

[0051] Single magnetic field form: the static magnetic field 3 is perpendicular to the center line of the immersion nozzle 2, that is, the static magnetic field 3 is perpendicular to the direction of gravity; the static magnetic field 3 is arranged on both sides of the immersion nozzle 2 and is generated by two magnetic field generators 4 that are axially symmetrically distributed; Figure 3 , Figure 4 As shown;

[0052] The magnetic field generator 5 is an annular structure, surrounding the submerged water inlet 2 and the magnetic field generator 4; the magnetic field generator 5 is made of magnetic conductive material;

[0053] Double magnetic field form: the static magnetic field 3 is perpendicular to the center line of the immersion nozzle 2, that is, the static magnetic field 3 is perpendicular to the direction of gravity; the static magnetic field 3 is arranged on both sides of the immersion nozzle 2 and is generated by two magnetic field generators 4 that are axially symmetrically distributed; the static magnetic field 3 forms a closed loop after passing through two C-shaped magnetic yokes, and the C-shaped magnetic yokes are arranged axially symmetrically along the immersion nozzle 2; the C-shaped magnetic yoke is made of magnetic conductive material, such as Figure 5 , Figure 6 shown.

[0054] Preferably, the magnetic field generator 4 is a permanent magnet or is made of a plurality of turns of copper wire wrapped around a magnetic conductive material.

[0055] Preferably, the magnetic field generator 5 is a circular magnetic yoke surrounding the immersion nozzle 2 and the magnetic field generator 4 and 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, a plurality of static magnetic fields are arranged simultaneously along the axial direction of the water inlet.

[0058] Example 1

[0059] The continuous casting speed is 1.6m / s, the width is 1650mm, and the thickness is 230mm; the steel type 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 210mm.

[0060] During the production process, the molten steel will quickly impact the narrow surface of the crystallizer after flowing out of the nozzle outlet, and form an upward counterflow and a downward impact flow. The maximum flow rate of the downward impact flow at the solidification front reaches 0.5m / s.

[0061] In view of this working condition, a static magnetic field is applied on the outside of the submerged nozzle, 100mm above the meniscus. The static magnetic field adopts a dual magnetic field form, that is, by winding multiple turns of copper wire on a pair of C-shaped magnetic yokes and passing direct current, the generated DC magnetic field forms a closed loop along the pair of C-shaped magnetic yokes and passes through the molten steel in the submerged nozzle. During the process of injecting the molten steel in the submerged nozzle into the crystallizer, it passes through the static magnetic field twice and generates Lorentz force. The direction of the Lorentz magnetic force is opposite to the flow direction of the molten steel, 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 0.12T, and the average magnetic induction intensity B2 is 0.09T; the effective area of ​​the static magnetic field A is 0.01m 2 ; The product of the static magnetic field and the effective action area is: B×A=9e -4 (Tm 2 ).

[0063] Through the implementation of the above-mentioned electromagnetic flow control of the submerged water nozzle, the flow rate of the molten steel entering the crystallizer through the tundish is effectively controlled, thereby reducing the impact speed of the water nozzle outflow stream. On the one hand, the impact depth of the molten steel stream is reduced, and the maximum impact speed is reduced from 0.5 / s to 0.2m / s; on the other hand, the liquid level fluctuation of the meniscus is also reduced.

[0064] Example 2

[0065] The continuous casting speed is 1.8m / s, the width is 1450mm, and the thickness is 230mm; the steel type 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 210mm.

[0066] During the production process, the molten steel will quickly impact the narrow surface of the crystallizer after flowing out of the nozzle outlet, and form an upward counterflow and a downward impact flow. The maximum flow rate of the downward impact flow at the solidification front reaches 0.6m / s.

[0067] In view of this working condition, a static magnetic field is applied on the outside of the immersion nozzle, 100mm above the meniscus, and the static magnetic field adopts a single magnetic field form. That is, by winding multiple turns of copper wire on a pair of magnetic conductive materials, and passing direct current, the generated DC magnetic field passes through the molten steel in the immersion nozzle. During the process of injecting the molten steel in the immersion nozzle into the crystallizer, the molten steel passes through the static magnetic field and generates Lorentz force. The direction of the Lorentz magnetic force is opposite to the flow direction of the molten steel, thereby slowing down the flow rate of the molten steel. The pair of magnetic conductive materials are connected by the annular magnetic yoke around the immersion nozzle to form a closed magnetic field loop.

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

[0069] Through the implementation of the above-mentioned electromagnetic flow control of the submerged water nozzle, the flow rate of the molten steel entering the crystallizer through the tundish is effectively controlled, thereby reducing the impact speed of the water nozzle outflow stream. On the one hand, the impact depth of the molten steel stream is reduced, and the maximum impact speed is reduced from 0.6 / s to 0.2m / s; on the other hand, the liquid level fluctuation of the meniscus is also reduced.

[0070] In summary, the static magnetic field parameter online control method provided by the present invention can optimize the flow state of molten steel in the crystallizer, and combined with the application of electromagnetic stirring and electromagnetic braking technology in the crystallizer, high-quality continuous casting billets can be finally obtained.

[0071] With the continuous improvement of users' requirements for the quality of steel products and the inherent requirements of enterprises for efficient production, higher requirements are put forward for the control of the flow field of the slab crystallizer. The submerged nozzle magnetic field flow control device and method designed by the present invention are flexible and controllable, the actual processing, manufacturing and implementation of the device are not difficult, the equipment is easy to install and replace, and it is expected to have a wide range of application prospects.

Claims

1. An electromagnetic flow control device for a slab continuous casting nozzle, characterized in that: include, A static magnetic field is arranged outside the slab continuous casting submerged nozzle above the meniscus of the molten steel in the slab continuous casting crystallizer. The static magnetic field is arranged in the following ways: single magnetic field form and double magnetic field form; wherein, in the single magnetic field form: the static magnetic field is perpendicular to the center line of the submerged nozzle, that is, the static magnetic field is perpendicular to the direction of gravity; the static magnetic field is arranged on both sides of the submerged nozzle and is generated by at least two magnetic field generators that are axially symmetrically distributed; the magnetic field generator is an annular structure that surrounds the submerged nozzle and the magnetic field generator; the magnetic field generator is made of magnetic conductive material; Dual magnetic field form: the static magnetic field is perpendicular to the center line of the immersed water outlet, that is, the static magnetic field is perpendicular to the direction of gravity; the static magnetic field is arranged on both sides of the immersed water outlet and generated by at least two magnetic field generators axially symmetrically distributed, and the magnetic field generator adopts a C-shaped yoke, and two C-shaped yokes form a closed loop; preferably, the C-shaped yoke is made of magnetic conductive material.

2. The electromagnetic flow control device for slab continuous casting nozzle according to claim 1, characterized in that: The magnetic field generator is a permanent magnet or is made of a plurality of turns of copper wires surrounding a magnetic conductive material.

3. The electromagnetic flow control device for slab continuous casting nozzle according to claim 1, characterized in that: The magnetic field generator is a circular ring-shaped magnetic yoke surrounding the immersion water inlet and the magnetic field generator, which are connected and fixed together.

4. The electromagnetic flow control device for slab continuous casting nozzle according to claim 1, characterized in that: The maximum magnetic induction intensity B1 of the static magnetic field is between 0.05T and 0.5T.

5. The electromagnetic flow control device for slab continuous casting nozzle according to claim 1 or 4, characterized in that: The static magnetic field is arranged in plurality along the axial direction of the water inlet.

6. A method for electromagnetic flow control of a slab continuous casting nozzle, characterized in that: The steps include: 1) A static magnetic field generator is arranged outside the slab continuous casting submerged nozzle above the meniscus of the molten steel in the slab continuous casting crystallizer. The static magnetic field is arranged as follows: Single magnetic field form: the static magnetic field is perpendicular to the center line of the immersion 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 immersion nozzle and distributed axially symmetrically; the magnetic field generator is a ring structure, surrounding the immersion nozzle and the magnetic field generator; the magnetic field generator is made of magnetic conductive material; Double magnetic field form: the static magnetic field is perpendicular to the center line of the submerged 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 submerged nozzle and distributed in an axisymmetric manner; The maximum magnetic induction intensity B1 of the static magnetic field is 0.05-0.5T; 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 average magnetic induction intensity B2 in the effective action area of ​​the static magnetic field satisfies: B2×A≥8e -4 (T.m 2 ) B2 is the average magnetic induction intensity of the static magnetic field, unit is T; A is the effective area of ​​the static magnetic field acting on the molten steel, unit: m 2 .

7. The method for electromagnetic flow control of a slab continuous casting nozzle as claimed in claim 6, characterized in that: The magnetic field generator is made of a permanent magnet or a magnetic conductive material surrounded by multiple turns of copper wire.

8. The method for electromagnetic flow control of a slab continuous casting nozzle as claimed in claim 6, characterized in that: The magnetic field generator is a circular ring-shaped magnetic yoke surrounding the immersion water inlet and the magnetic field generator, which are connected and fixed together.

9. The method for electromagnetic flow control of a slab continuous casting nozzle as claimed in claim 6, characterized in that: The static magnetic field forms a closed loop after passing through two C-shaped yokes, and the C-shaped yokes are symmetrically arranged along the axis of the immersion nozzle; preferably, the C-shaped yokes are made of magnetic conductive material.

10. The method for electromagnetic flow control of a slab continuous casting nozzle as claimed in claim 6, characterized in that: The static magnetic field is arranged in plurality along the axial direction of the submerged water nozzle.

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