Composite electromagnetic stirring device for high-pulling-speed continuous casting billet

Abstract

The invention provides a composite electromagnetic stirring device for a high-pulling-speed continuous casting billet, and belongs to the technical field of steel continuous casting equipment. The traveling wave magnetic field generating device is used for enabling the molten steel to move longitudinally; the spiral magnetic field normalizing device is annular and located between the rotating magnetic field generating device and the traveling wave magnetic field generating device, and the rotating magnetic field generating device and the traveling wave magnetic field generating device are fixedly connected with the front face and the back face of the annular spiral magnetic field normalizing device through a first connecting part and a second connecting part. The ratio of the cross sectional area of any connecting part to the annular area of the spiral magnetic field normalizing device is not larger than 5%. By arranging the spiral magnetic field normalizing device with the specific size, the magnetic flux density of the spiral area and the rotating area is increased, the penetrating power is high, and compared with the prior art, the penetrating depth can be increased by at least 50%.

Description

Technical Field

[0001] This invention belongs to the technical field of steel continuous casting equipment, specifically relating to a composite electromagnetic stirring device for high-speed continuous casting billets. Background Technology

[0002] Electromagnetic stirring technology plays a crucial role in improving the equiaxed grain ratio of continuously cast billets, refining the solidification structure, reducing billet segregation, improving inclusion distribution, and promoting compositional homogenization. The working principle of electromagnetic stirring is that the alternating magnetic field excited by electromagnetic stirring penetrates into the molten steel. The induced current interacts with the magnetic field in the molten steel to generate an electromagnetic force, thereby propelling the molten steel. Therefore, based on the form of the magnetic field excited by electromagnetic stirring, it can be classified into: DC magnetic field, rotating magnetic field, traveling wave magnetic field, and spiral magnetic field electromagnetic stirring, etc.

[0003] In recent years, the demand for high-efficiency continuous casting has led to varying degrees of quality problems in special steels at high casting speeds, such as central porosity, shrinkage cavities, and segregation. While conventional electromagnetic stirring with a rotating magnetic field can partially improve these quality issues through optimized installation and operating parameters, it cannot completely solve them. The main reason is that rotary stirring can only achieve strong two-dimensional stirring on the cross-section of the billet, and the electromagnetic force is mainly concentrated near the surface of the billet, making it difficult to penetrate into the core. Therefore, the molten steel in the core of the billet is essentially not stirred, failing to completely resolve internal quality problems. In some cases, excessive stirring can even result in a bright white band of negative solute element segregation appearing at one-quarter of the billet's length.

[0004] Existing technologies propose using composite stirring technology to solve billet quality problems. Two technical approaches exist: one is a composite electromagnetic stirrer with multiple magnetic field types and stirring functions. While this type of stirrer offers multiple magnetic field types and stirring functions, it can only output one magnetic field type during execution. For example, Chinese invention patent CN101700477B discloses a rotating magnetic field and a traveling wave magnetic field, but the excitation coil of the rotating magnetic field is placed before or after the excitation coil of the traveling wave magnetic field. In actual execution, the coil at the front end magnetically shields the magnetic field of the coil at the rear end, resulting in low stirring efficiency. The other approach uses a combination of traveling wave and rotating magnetic fields, such as Chinese invention patent CN109158563B, which discloses an electromagnetic stirrer for continuous casting crystallizers with a composite magnetic field. The traveling wave magnetic field generator is placed above the rotating magnetic field generator. This approach installs the electromagnetic stirrer in the continuous casting crystallizer area. Because the spiral magnetic field uses a superposition of traveling wave and rotating magnetic fields, the spiral magnetic field strength is low and cannot effectively penetrate the billet, thus failing to effectively stir the molten steel. Summary of the Invention

[0005] To address the aforementioned problems, this invention provides a composite electromagnetic stirring device for high-speed continuous casting billets. By setting a spiral magnetic field conditioning device of a specific size, the magnetic flux density in the spiral and rotating regions is increased, and the penetration capability is strong. Compared with the prior art, the penetration depth can be increased by at least 50%.

[0006] To achieve the above objectives, the technical solution adopted by the present invention is as follows: This invention provides a composite electromagnetic stirring device for high-speed continuous casting billets, comprising: a rotating magnetic field generator for causing molten steel to rotate; a traveling wave magnetic field generator for causing molten steel to move longitudinally; and a spiral magnetic field straightening device, wherein the spiral magnetic field straightening device is annular and located between the rotating magnetic field generator and the traveling wave magnetic field generator. The rotating magnetic field generator and the traveling wave magnetic field generator are fixedly connected to the front and back sides of the annular spiral magnetic field straightening device through a first connecting part and a second connecting part. The ratio of the cross-sectional area of ​​any connecting part to the annular area of ​​the spiral magnetic field straightening device is not greater than 5%. The inner dimension of the annular spiral magnetic field straightening device is not greater than the inner dimension of the rotating magnetic field generator or the traveling wave magnetic field generator. The thickness of the annular spiral magnetic field straightening device is not less than 1 / 3 and not greater than 2 / 3 of the gap between the rotating magnetic field generator and the traveling wave magnetic field generator.

[0007] Furthermore, the gap between the spiral magnetic field conditioning device and the traveling wave magnetic field generator is smaller than the gap between the spiral magnetic field conditioning device and the rotating magnetic field generator.

[0008] Furthermore, the rotating magnetic field generating device includes: an annular yoke; a first magnetic core, the first magnetic core being used to wind a rotating magnetic field coil, the first magnetic core having a rectangular cross-section perpendicular to its own axis and extending from the inner wall of the annular yoke, the number of the first magnetic cores being 3N and uniformly arranged on the inner wall of the annular yoke, where N is a positive integer; and a first connecting portion being fixedly connected to one end of the annular yoke.

[0009] Furthermore, the traveling wave magnetic field generating device includes: a frame, the frame including two concentrically arranged annular structures of the same size and a second magnetic core disposed between the two annular structures, the number of the second magnetic cores being 3M and evenly arranged around the annular structures, where M is a positive integer, the second magnetic cores being used to wind a traveling wave magnetic field coil; and a second connecting part being fixedly connected to one end of the annular structure.

[0010] Furthermore, the projection of the adjacent first magnetic core on the plane of the ring structure is symmetrical to the projection of the adjacent second magnetic core on the plane of the ring structure, and the projection length of the second magnetic core extends beyond the projection of the middle position of the two adjacent first magnetic cores on the plane of the ring structure.

[0011] Furthermore, the projected length of the second magnetic core does not exceed the projection of the length of the two adjacent first magnetic cores at 3 / 5 of the length onto the plane of the ring structure.

[0012] Furthermore, the inner diameter of the spiral magnetic field straightening device is smaller than the inner diameter of the annular structure, and the outer diameter of the spiral magnetic field straightening device is larger than the outer diameter of the annular structure.

[0013] Furthermore, the spiral magnetic field straightening device is used to isolate the rotating magnetic field generator and the traveling wave magnetic field generator. It is provided with through holes, which are respectively provided at corresponding positions on the inner and outer sides of the second magnetic core. At least one of the through holes corresponding to each second magnetic core corresponds to the middle position of the adjacent second magnetic core.

[0014] Furthermore, the spiral magnetic field straightening device is annular, with one side being planar and the other side having a diverging protrusion centered on the annulus, and the side with the protrusion is adjacent to the traveling wave magnetic field generating device.

[0015] Furthermore, the dimensions of the protrusion satisfy the following conditions: ; Where r is the ratio of the height of the protrusion to the thickness of the spiral magnetic field straightening device, x1 is the distance between the spiral magnetic field straightening device and the rotating magnetic field generator, and x2 is the distance between the traveling wave magnetic field generator and the spiral magnetic field straightening device. and For correction factor, It is the angle of the gap between two adjacent protrusions.

[0016] The beneficial effects of the technical solution provided by the embodiments of the present invention include: First, when a rotating magnetic field generator and a traveling wave magnetic field generator are set up sequentially, a problem arises: the spiral magnetic field is formed by superimposing the rotating magnetic field generator and the traveling wave magnetic field generator. Since the superposition position is relatively far from the rotating magnetic field generator and the traveling wave magnetic field generator, the generated spiral magnetic field has a low magnetic flux density, making it difficult to stir the molten steel at the dendrite front at the solidification end (e.g., with a liquid phase fraction of 10%). This is also the reason why the invention patent with publication number CN109158563B applies this technology to a crystallizer. Second, the rotating magnetic field generator and the traveling wave magnetic field generator influence each other, resulting in severe distortion of the superimposed magnetic field and increased eddy current losses due to their superposition. Therefore, the present invention sets up a spiral magnetic field straightening device between the rotating magnetic field generator and the traveling wave magnetic field generator to improve the magnetic flux density of the spiral magnetic field. The flux density and strength can effectively stir the solidification end of a 350mm diameter billet; however, simply adding a spiral magnetic field straightening device cannot reduce power consumption. Therefore, this invention limits the ratio of the cross-sectional area of ​​any connection to the annular area of ​​the spiral magnetic field straightening device to no more than 5%, to avoid interference between the magnetic flux conducted by the connection and the magnetic field induced by the rotating magnetic field generator and the traveling wave magnetic field generator in the spiral magnetic field straightening device. Finally, this invention limits the thickness of the annular spiral magnetic field straightening device to no less than 1 / 3 and no more than 2 / 3 of the gap between the rotating magnetic field generator and the traveling wave magnetic field generator. This serves to isolate the rotating magnetic field generator and the traveling wave magnetic field generator, and the thickness and shape of the spiral magnetic field straightening device also affect the magnetic flux density. Through the above improvements, this invention achieves a spiral magnetic field penetration of up to 350mm under the same energy consumption, greatly improving the quality of the billet. Attached Figure Description

[0017] To more clearly illustrate the technical solutions in the embodiments of the present invention, the accompanying drawings used in the description of the embodiments will be briefly introduced below. Obviously, the accompanying drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0018] Figure 1 A schematic diagram of the composite electromagnetic stirring device after removing the outer shell, provided in an embodiment of the present invention; Figure 2 A schematic diagram of the composite electromagnetic stirring device provided in an embodiment of the present invention; Figure 3 A schematic diagram of a rotating magnetic field generating device provided in an embodiment of the present invention; Figure 4 A schematic diagram of a traveling wave magnetic field generating device provided in an embodiment of the present invention; Figure 5This is a cross-sectional view of the composite electromagnetic stirring device provided in an embodiment of the present invention; Figure 6 This is a schematic diagram of the through-hole location provided in an embodiment of the present invention; Figure 7 This is a schematic diagram of another spiral magnetic field straightening device provided in an embodiment of the present invention; Figure 8 The image shows a cross-sectional view of the billet prepared in Example 1 of the present invention, where a is a cross-sectional dimension of 350 mm and b is a cross-sectional dimension of 450 mm. Figure 9 This is a cross-sectional view of the billet prepared in Example 4 of the present invention; Figure 10 This is a cross-sectional view of the billet prepared in Comparative Example 1 of the present invention; Figure 11 This is a cross-sectional view of the billet prepared in Comparative Example 2 of the present invention.

[0019] Reference numerals: 01, Upper housing; 04, Lower housing; 03, Outer housing; 02, Inner housing; 05, Cooling water inlet; 06, Cooling water outlet; 07, Wiring part; 08, Mounting part; 080, Mounting plane; 081, Snap-fit ​​part; 1, Rotating magnetic field generator; 10, Ring-shaped yoke; 11, First magnetic core; 12, Rotating magnetic field coil; 2, Traveling wave magnetic field generator; 20, Circular ring structure; 21, Second magnetic core; 22, Traveling wave magnetic field coil; 3, Spiral magnetic field straightening device; 30, Through hole; 40, First connecting part; 41, Second connecting part. Detailed Implementation

[0020] To make the objectives, technical solutions, and advantages of the present invention clearer, the present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments.

[0021] This invention provides a composite electromagnetic stirring device for high-speed continuous casting billets, such as... Figure 1As shown, the device includes: a rotating magnetic field generator 1 for inducing rotational motion in molten steel; a traveling wave magnetic field generator 2 for inducing longitudinal motion in molten steel; and a spiral magnetic field straightening device 3. The spiral magnetic field straightening device 3 is annular and located between the rotating magnetic field generator 1 and the traveling wave magnetic field generator 2. The rotating magnetic field generator 1 and the traveling wave magnetic field generator 2 are fixedly connected to the annular spiral magnetic field straightening device 3 via a first connecting part 40 and a second connecting part 41 on their opposite sides. The ratio of the cross-sectional area of ​​any connecting part to the annular area of ​​the spiral magnetic field straightening device 3 is not greater than 5%. The inner dimension of the annular spiral magnetic field straightening device 3 is not greater than the inner dimension of either the rotating magnetic field generator 1 or the traveling wave magnetic field generator 2. The thickness of the annular spiral magnetic field straightening device 3 is not less than 1 / 3 and not greater than 2 / 3 of the gap between the rotating magnetic field generator and the traveling wave magnetic field generator. Preferably, the thickness of the spiral magnetic field straightening device is 10mm-20mm.

[0022] It should be noted that the "gap" in this invention refers to the shortest distance between the devices, and the devices are connected at a fixed interval through the first connecting part 40 and the second connecting part 41. Preferably, in order to achieve the goal that "the ratio of the cross-sectional area of ​​any connecting part to the annular area of ​​the spiral magnetic field straightening device 3 is not greater than 5%", a spiral and nut connection method is used for fixed connection, with a high pulling speed of 1.6-2.5 m / min.

[0023] This invention first sets up a rotating magnetic field generator and a traveling wave magnetic field generator sequentially. However, a problem arises: the spiral magnetic field is formed by superimposing the rotating and traveling wave magnetic field generators. Because the superposition location is relatively far from the rotating and traveling wave magnetic field generators, the generated spiral magnetic field has a low magnetic flux density, making it difficult to stir the molten steel at the dendrite front of the solidification end (e.g., with a liquid phase concentration of 10%). This is why the invention patent with publication number CN109158563B applies this technology to a crystallizer. Secondly, the rotating and traveling wave magnetic field generators interfere with each other, resulting in severe distortion of the superimposed magnetic field and increased eddy current losses due to their superposition. Therefore, this invention sets up a spiral magnetic field straightening device between the rotating and traveling wave magnetic field generators to improve the magnetic flux density and intensity of the spiral magnetic field, which can address the issue of... Effective stirring is achieved at the solidification end of the 350mm diameter billet. However, simply adding a spiral magnetic field straightening device cannot reduce power consumption. Therefore, this invention limits the ratio of the cross-sectional area of ​​any connection to the annular area of ​​the spiral magnetic field straightening device to no more than 5%, to avoid interference between the magnetic flux conducted by the connection and the magnetic field induced by the rotating magnetic field generator and the traveling wave magnetic field generator in the spiral magnetic field straightening device. Finally, this invention limits the thickness of the annular spiral magnetic field straightening device to no less than 1 / 3 and no more than 2 / 3 of the gap between the rotating magnetic field generator and the traveling wave magnetic field generator. This serves to isolate the rotating magnetic field generator and the traveling wave magnetic field generator, and the thickness and shape of the spiral magnetic field straightening device also affect the magnetic flux density. Through the above improvements, this invention achieves a spiral magnetic field penetration of up to 350mm under the same energy consumption, greatly improving the quality of the billet.

[0024] Optionally, the composite electromagnetic stirring device of the present invention includes a housing, such as... Figure 2 As shown, it includes an upper shell 01, a lower shell 04, an outer shell 03, and an inner shell 02. The inner shell 02 is made of stainless steel, while the upper shell 01, lower shell 04, and outer shell 03 are preferably made of pure copper to avoid magnetic leakage. The outer shell has three openings, namely a cooling water inlet 05, a cooling water outlet 06, and a wiring part 07.

[0025] Specifically, the gap between the spiral magnetic field straightening device and the traveling wave magnetic field generating device is smaller than the gap between the spiral magnetic field straightening device and the rotating magnetic field generating device. Due to the special structure of the rotating magnetic field generating device and the traveling wave magnetic field generating device in this invention, in order to straighten the superimposed spiral magnetic field, the installation position of the spiral magnetic field straightening device is set according to the characteristics of the two magnetic field generating devices, which can further improve the straightening of the magnetic field and increase the penetration distance. Preferably, 0.05 ≤ ≤0.15, where x1 is the distance between the helical magnetic field conditioning device and the rotating magnetic field generator, and x2 is the distance between the traveling wave magnetic field generator and the helical magnetic field conditioning device. It is the absolute value of the difference between x1 and x2.

[0026] like Figure 3 As shown, the rotating magnetic field generating device 1 includes: an annular yoke 10; a first magnetic core 11, which is used to wind a rotating magnetic field coil 12. The first magnetic core 11 has a rectangular cross-section perpendicular to its own axis and extends from the inner wall of the annular yoke. The number of the first magnetic cores is 3N and they are evenly arranged on the inner wall of the annular yoke, where N is a positive integer. The first connecting part 40 is fixedly connected to one end of the annular yoke 10. During use, the first magnetic core 11 is approximately perpendicular to the axis of the continuously cast billet.

[0027] Preferably, in the cross-sectional direction, the ratio of the arc length occupied by the first magnetic core within the annular yoke to the arc length occupied by the gap between two adjacent first magnetic cores within the annular yoke is not less than 1 and not greater than 1.4.

[0028] To avoid magnetic leakage and facilitate housing installation, the rotating magnetic field generator 1 has a mounting part 08 attached to the side away from the spiral magnetic field straightening device 3. The mounting part 08 has a mounting plane 080 for fixed connection with the upper housing 01, and also includes a snap-fit ​​part 081 for snapping onto the inner wall of the annular yoke. The mounting part 08 is made of pure copper and completely shields the first connecting part 40, i.e. the exposed bolts and nuts, which are fixedly installed on the annular yoke.

[0029] like Figure 4 As shown, the traveling wave magnetic field generating device 2 includes: a frame, the frame comprising two concentrically arranged annular structures 20 of the same size and a second magnetic core 21 disposed between the two annular structures 20, the number of the second magnetic cores 21 being 3M and uniformly arranged around the circumference of the annular structures 20, where M is a positive integer, the second magnetic cores being used to wind a traveling wave magnetic field coil 22, and the second connecting part 41 being fixedly connected to one end of the annular structure 20. It can be seen that the winding axis of the traveling wave magnetic field coil 22 is parallel to the axis of the composite electromagnetic stirring device.

[0030] It should be noted that the first magnetic core and the second magnetic core in the embodiments of the present invention are formed by pressing silicon steel sheets.

[0031] It should be noted that the values ​​of N and M in this invention satisfy N / M=2. The main reason for limiting the values ​​of N and M is to ensure compatibility between them to avoid backflow and to ensure good magnetic field relay.

[0032] Furthermore, the projection of the adjacent first magnetic core 11 onto the plane of the ring structure is symmetrical to the projection of the adjacent second magnetic core 21 onto the plane of the ring structure, and the projection length of the second magnetic core 21 extends beyond the projection of the midpoint of the two adjacent first magnetic cores 11 onto the plane of the ring structure, as shown below. Figure 5 As shown, the projections of the midpoints of two adjacent first magnetic cores 11 onto the plane of the annular structure are P1 and P2, respectively. The projections of adjacent second magnetic cores 21 onto the plane of the annular structure are S1 and S2. It can be seen that the projected length of the second magnetic core 21 extends beyond the projection of the midpoints of the two adjacent first magnetic cores 11 onto the plane of the annular structure; that is, the line segment P1P2 is within the line segment S1S2. Preferably, the ratio of the lengths of P1P2 to S1S2 is not less than 0.8.

[0033] The projected length of the second magnetic core 21 does not exceed the projection of 3 / 5 of the length of the two adjacent first magnetic cores 11 onto the plane where the ring structure is located.

[0034] The reason for limiting the relative positions of the first and second magnetic cores is to determine how to match the rotating magnetic field and the traveling wave magnetic field. For example, in the rotating magnetic field, the magnetic flux is relatively small at the gap between two adjacent first magnetic cores, which easily generates eddy currents and reduces the stirring effect of the molten metal. In the traveling wave magnetic field, the magnetic field between two second magnetic cores is relatively weak, which easily generates edge backflow R1. This application reduces losses such as backflow and eddy current by matching the first and second magnetic cores. Specifically, for the gap of the rotating magnetic field, the traveling wave magnetic field generates a pulling effect on the molten metal flow, reducing the eddy current phenomenon. For the gap of the traveling wave magnetic field, the spiral magnetic field generated by the combination of the rotating magnetic field and the traveling wave magnetic field is used to make the molten steel spiral, which hinders the formation of backflow.

[0035] Specifically, the inner diameter of the spiral magnetic field straightening device is smaller than the inner diameter of the ring structure, and the outer diameter of the spiral magnetic field straightening device is larger than the outer diameter of the ring structure. This is to isolate the traveling wave magnetic field generator and the rotating magnetic field generator as much as possible, avoiding mutual interference between the magnetic fields generated by the two. At the same time, the spiral magnetic field straightening device enhances the penetrating power of the spiral magnetic field.

[0036] In another preferred embodiment, such as Figure 1 As shown, the spiral magnetic field straightening device 3 is used to isolate the rotating magnetic field generating device 1 and the traveling wave magnetic field generating device 2. It is provided with a through hole 30, which is provided corresponding to the second magnetic core. The through holes 30 are respectively provided at corresponding positions on the inner and outer sides of the second magnetic core, and at least one of the through holes corresponding to each second magnetic core corresponds to the middle position of two adjacent second magnetic cores.

[0037] Specifically, the spiral magnetic field conditioning device is used to isolate the rotating magnetic field generator and the traveling wave magnetic field generator. This isolation can be complete, such as by sealing the spiral magnetic field conditioning device with the inner shell 02 and the outer shell 03 to isolate the rotating magnetic field generator and the traveling wave magnetic field generator, or by having the spiral magnetic field conditioning device cooperate with the inner shell and the outer shell to obstruct the flow of the cooling medium. It is provided with through holes, the function of which is to allow the cooling medium to flow.

[0038] Furthermore, to improve the cooling effect, this invention features a special design for the coil windings and the through-holes used to transport the cooling medium. Specifically, for the same magnetic core, the rotating magnetic field coil 12 and the traveling wave magnetic field coil 22 employ multiple coils, with gaps between them. These gaps are designed to allow the coolant to flow in a turbulent manner, thereby increasing heat transfer efficiency. The gaps are at least 2 mm. Each second magnetic core has three traveling wave magnetic field coils wound around it, and similarly, the first magnetic core has three rotating magnetic field coils wound around it. Regarding the design of the through-holes, as shown... Figure 6 As shown, on one side of the traveling wave magnetic field generator, the through-hole 30 is located on the helical magnetic field straightening device, and is located inside and outside the projection of the second magnetic core onto the helical magnetic field straightening device. The projection of the traveling wave magnetic field coil 22 onto the helical magnetic field straightening device covers the through-hole 30. Preferably, for each second magnetic core, six through-holes are provided, with three located inside the projection of the second magnetic core onto the helical magnetic field straightening device and three located outside the projection of the second magnetic core onto the helical magnetic field straightening device. One through-hole is located radially through the middle position of the second magnetic core, and the positions of the other two holes satisfy the following: the angle α between the radial line connecting the two holes and the radial line connecting the middle position of the second magnetic core, and the angle β between the radial line connecting the middle position of the second magnetic core and the radial line connecting the edge position of the second magnetic core, where 1 / 3β≤α≤2 / 3β. Preferably, the inner through-hole and the outer through-hole are on the same radial line.

[0039] Specifically, such as Figure 7 As shown, the spiral magnetic field straightening device is ring-shaped, with one side being planar and the other side having a diverging protrusion centered on the ring. The side with the protrusion is adjacent to the traveling wave magnetic field generator 2.

[0040] The dimensions of the protrusion satisfy the following conditions: ; Where r is the ratio of the height h of the protrusion to the thickness of the spiral magnetic field straightening device, x1 is the distance between the spiral magnetic field straightening device and the rotating magnetic field generator, and x2 is the distance between the traveling wave magnetic field generator and the spiral magnetic field straightening device. and For correction factor, This refers to the angle between two adjacent protrusions. (In an embodiment of the invention) The value ranges from 0.5 to 0.6. The value should be between 2.4 and 2.5. (Preferred value) The value of is no greater than 15%.

[0041] This invention employs multi-phase power supply control, allowing individual control of each coil within the composite electromagnetic stirrer. During control, each coil is identified and connected to one phase of the power supply. The number of connected coils corresponds to the number of phases of the power output. By setting the phase angle φ of the power supply, the output current phase at any output port of the multi-phase power supply can be arbitrarily adjusted. Through multi-phase power supply output control, the magnetic field generated by the stirrer is adjusted.

[0042] Both the traveling wave magnetic field generating device and the rotating magnetic field generating device are powered by three-phase alternating current.

[0043] The three-phase alternating current supplied to the traveling wave magnetic field generating device and the rotating magnetic field generating device has different frequencies and intensities.

[0044] The technical solution provided by this invention is applicable to steel grades that exhibit segregation during solidification, especially medium and low carbon steel and low alloy steel. For illustration, the embodiments of this invention use circular continuously cast billets with cross-sectional dimensions of 350mm and 450mm (diameter). The composite electromagnetic stirring device provided by this invention is installed at the end of solidification (liquidity 10%), and the casting speed is 2.5m / min. Specifically, Q235 steel is used. To characterize the provided high-speed continuously cast billet using the composite electromagnetic stirring device, the microstructure of the billet is observed, and the grade of central shrinkage cavity is analyzed. The classification of central shrinkage cavity grades adopts the YB / T4002-2013 standard.

[0045] To better illustrate the embodiments of the present invention, the present invention will be further described in detail below through specific examples.

[0046] Example 1 This invention provides a composite electromagnetic stirring device for high-speed continuous casting billets, wherein the thickness of the spiral magnetic field conditioning device is 10 mm, and the gap between the spiral magnetic field conditioning device and the traveling wave magnetic field generator is 20 mm. The distance between the spiral magnetic field conditioning device and the rotating magnetic field generator is 5.5 mm, and the distance between the traveling wave magnetic field generator and the spiral magnetic field conditioning device is 4.5 mm.

[0047] The spiral magnetic field straightening device is ring-shaped and has no protrusions.

[0048] A current of 500A and 5Hz is passed through the composite electromagnetic stirring device.

[0049] The prepared slab, such as Figure 8As shown in Figure a, measurements show that a circular continuously cast billet with a cross-sectional dimension of 350 mm does not have a central shrinkage cavity; as shown in Figure a. Figure 8 As shown in b, the central shrinkage grade of a circular continuously cast billet with a cross-sectional dimension of 450mm is 0.1.

[0050] Example 2 This invention provides a composite electromagnetic stirring device for high-speed continuous casting billets, wherein the thickness of the spiral magnetic field conditioning device is 15mm, and the gap between the spiral magnetic field conditioning device and the traveling wave magnetic field generator is 45mm. The distance between the spiral magnetic field conditioning device and the rotating magnetic field generator is 24mm, and the distance between the traveling wave magnetic field generator and the spiral magnetic field conditioning device is 21mm.

[0051] The spiral magnetic field straightening device is ring-shaped and has no protrusions.

[0052] A current of 500A and 5Hz is passed through the composite electromagnetic stirring device.

[0053] Measurements showed that the circular continuous casting billet with a cross-sectional dimension of 350 mm had no central shrinkage cavity; the central shrinkage cavity grade of the circular continuous casting billet with a cross-sectional dimension of 450 mm was 0.1.

[0054] Example 3 This invention provides a composite electromagnetic stirring device for high-speed continuous casting billets, wherein the thickness of the spiral magnetic field conditioning device is 20 mm, and the gap between the spiral magnetic field conditioning device and the traveling wave magnetic field generator is 30 mm. The distance between the spiral magnetic field conditioning device and the rotating magnetic field generator is 5.5 mm, and the distance between the traveling wave magnetic field generator and the spiral magnetic field conditioning device is 4.5 mm.

[0055] The spiral magnetic field straightening device is ring-shaped and has no protrusions.

[0056] A current of 500A and 5Hz is passed through the composite electromagnetic stirring device.

[0057] Measurements showed that the circular continuous casting billet with a cross-sectional dimension of 350 mm had no central shrinkage cavity; the central shrinkage cavity grade of the circular continuous casting billet with a cross-sectional dimension of 450 mm was 0.1.

[0058] Example 4 Unlike Example 1, in this example, the spiral magnetic field straightening device adopts a structure with divergent protrusions. The value is 5°, the distance between the spiral magnetic field conditioning device and the rotating magnetic field generator is 5.5 mm, and the distance between the traveling wave magnetic field generator and the spiral magnetic field conditioning device is 4.5 mm. The value is 0.5. The value is set to 2.5. After calculation, r is 0.11, which means the total thickness of the spiral magnetic field straightening device is 10mm and the height h of the protrusion is 1.1mm.

[0059] The prepared slab, such as Figure 9 As shown, through measurement, the circular continuous casting billet with a cross-sectional dimension of 350mm does not have a central shrinkage cavity; the circular continuous casting billet with a cross-sectional dimension of 450mm does not have a central shrinkage cavity.

[0060] Comparative Example 1 Unlike Example 1, the spiral magnetic field conditioning device is removed from the composite electromagnetic stirring device for high-speed continuous casting billets in this comparative example.

[0061] The prepared slab, such as Figure 10 As shown, measurements revealed that a circular continuously cast billet with a cross-sectional dimension of 350 mm had a central shrinkage cavity of grade 0.5.

[0062] Comparative Example 2 Unlike Example 1, this comparative example provides a composite electromagnetic stirring device for high-speed continuous casting billets, wherein the thickness of the spiral magnetic field conditioning device is 10 mm, and the gap between the spiral magnetic field conditioning device and the traveling wave magnetic field generator is 40 mm. The distance between the spiral magnetic field conditioning device and the rotating magnetic field generator is 18 mm, and the distance between the traveling wave magnetic field generator and the spiral magnetic field conditioning device is 15 mm.

[0063] The prepared slab, such as Figure 11 As shown, measurements revealed that a circular continuously cast billet with a cross-sectional dimension of 350 mm had a central shrinkage cavity of grade 0.2.

[0064] Comparative Example 3 Unlike Example 1, this comparative example provides a composite electromagnetic stirring device for high-speed continuous casting billets, wherein the thickness of the spiral magnetic field conditioning device is 10 mm, and the gap between the spiral magnetic field conditioning device and the traveling wave magnetic field generator is 13 mm. The distance between the spiral magnetic field conditioning device and the rotating magnetic field generator is 2 mm, and the distance between the traveling wave magnetic field generator and the spiral magnetic field conditioning device is 1 mm.

[0065] Measurements revealed that a 0.2-grade central shrinkage cavity existed in a circular continuously cast billet with a cross-sectional dimension of 350mm. The main reason for this was that the cooling medium transport process was obstructed, resulting in low electromagnetic stirring efficiency.

[0066] Comparative Example 4 Unlike Example 1, in this comparative example, the ratio of the cross-sectional area of ​​any connection to the annular area of ​​the spiral magnetic field straightening device is 7%.

[0067] Measurements revealed that a circular continuously cast billet with a cross-sectional dimension of 350 mm had a central shrinkage cavity of grade 0.3.

[0068] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A composite electromagnetic stirring device for high-speed continuous casting billets, characterized in that, include: A rotating magnetic field generator is used to induce rotational motion in molten steel. A traveling wave magnetic field generator is used to induce longitudinal movement in molten steel. A spiral magnetic field straightening device is provided, wherein the spiral magnetic field straightening device is annular and located between the rotating magnetic field generator and the traveling wave magnetic field generator. The rotating magnetic field generator and the traveling wave magnetic field generator are fixedly connected to the front and back of the annular spiral magnetic field straightening device through a first connecting part and a second connecting part. The ratio of the cross-sectional area of ​​any connecting part to the annular area of ​​the spiral magnetic field straightening device is not greater than 5%. The inner dimension of the annular spiral magnetic field straightening device is not greater than the inner dimension of the rotating magnetic field generator or the traveling wave magnetic field generator. The thickness of the annular spiral magnetic field straightening device is not less than 1 / 3 and not greater than 2 / 3 of the gap between the rotating magnetic field generator and the traveling wave magnetic field generator.

2. The composite electromagnetic stirring device according to claim 1, characterized in that, The gap between the spiral magnetic field conditioning device and the traveling wave magnetic field generator is smaller than the gap between the spiral magnetic field conditioning device and the rotating magnetic field generator.

3. The composite electromagnetic stirring device according to claim 1, characterized in that, The rotating magnetic field generator includes: Ring-shaped yoke; The first magnetic core is used to wind a rotating magnetic field coil. The cross-section of the first magnetic core perpendicular to its own axis is rectangular and extends from the inner wall of the annular yoke. The number of the first magnetic cores is 3N and they are evenly arranged on the inner wall of the annular yoke, where N is a positive integer. The first connecting part is fixedly connected to one end of the annular yoke.

4. The composite electromagnetic stirring device according to claim 3, characterized in that, The traveling wave magnetic field generator includes: The frame includes two concentrically arranged circular ring structures of the same size and a second magnetic core disposed between the two circular ring structures. The number of the second magnetic cores is 3M and they are evenly arranged around the circumference of the circular ring structures, where M is a positive integer. The second magnetic cores are used to wind a traveling wave magnetic field coil. The second connecting part is fixedly connected to one end of the ring structure.

5. The composite electromagnetic stirring device according to claim 4, characterized in that, The projection of the adjacent first magnetic core on the plane of the ring structure is symmetrical to the projection of the adjacent second magnetic core on the plane of the ring structure, and the projection length of the second magnetic core extends beyond the projection of the middle position of the two adjacent first magnetic cores on the plane of the ring structure.

6. The composite electromagnetic stirring device according to claim 5, characterized in that, The projected length of the second magnetic core does not exceed the projection of the two adjacent first magnetic cores at 3 / 5 of their lengths onto the plane of the ring structure.

7. The composite electromagnetic stirring device according to claim 4, characterized in that, The inner diameter of the spiral magnetic field conditioning device is smaller than the inner diameter of the ring structure, and the outer diameter of the spiral magnetic field conditioning device is larger than the outer diameter of the ring structure.

8. The composite electromagnetic stirring device according to claim 7, characterized in that, The spiral magnetic field straightening device is used to isolate the rotating magnetic field generator and the traveling wave magnetic field generator. It is provided with through holes, which are respectively provided at corresponding positions on the inner and outer sides of the second magnetic core. At least one of the through holes corresponding to each second magnetic core corresponds to the middle position of the adjacent second magnetic core.

9. The composite electromagnetic stirring device according to claim 2, characterized in that, The spiral magnetic field straightening device is ring-shaped, with one side being planar and the other side having a radiating protrusion centered on the ring. The side with the protrusion is adjacent to the traveling wave magnetic field generating device.

10. The composite electromagnetic stirring device according to claim 9, characterized in that, The dimensions of the protrusion satisfy the following conditions: ； Where r is the ratio of the height of the protrusion to the thickness of the spiral magnetic field straightening device, x1 is the distance between the spiral magnetic field straightening device and the rotating magnetic field generator, and x2 is the distance between the traveling wave magnetic field generator and the spiral magnetic field straightening device. and For correction factor, It is the angle of the gap between two adjacent protrusions.

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