Electromagnetic flow control method for reducing inclusions in small-size cast billet

Abstract

An electromagnetic flow control method for reducing inclusions in a small-size cast billet. During continuous casting of the small-size cast billet, an electromagnetic stirring device having a Z-direction electromagnetic force is provided at a mold (3) and is capable of controlling the flow of molten steel in the mold, and carrying out Z-direction acceleration on a peripheral region of the molten steel while promoting circumferential rotational stirring of the molten steel in the mold. The method can reduce the impingement depth of the molten steel from a submerged entry nozzle in the mold, thereby having positive effects on promoting the flotation of the inclusions and improving the quality of the cast billet.

Description

Electromagnetic flow control method for reducing inclusions in small size casting billets TECHNICAL FIELD

[0001] The present application relates to the field of electromagnetic metallurgy, in particular to an electromagnetic flow control method for reducing inclusions in small size casting billets. BACKGROUND

[0002] The role of the crystallizer in continuous casting is to receive the molten steel flowing out of the tundish. The flow field of the molten steel in the crystallizer not only has an important influence on the behavior of the steel-slag interface in the crystallizer, but also has a great influence on the solidification heat transfer of the casting billet. Since the solidification front is constantly scoured by the molten steel flow in varying degrees, the quality of the molten steel flow in the crystallizer directly affects the surface quality and internal quality of the casting billet.

[0003] The impact depth of the straight water nozzle molten steel directly affects the floating of inclusions, and further affects the quality of the casting billet. The flow of the molten steel in the crystallizer is related to many parameters such as the casting speed, the size of the casting billet, the structure size of the submerged water nozzle, and the water nozzle immersion depth. How to take measures to control the flow of the molten steel to reduce the inclusions in the casting billet has become a research hotspot in the field of continuous casting.

[0004] The technology of electromagnetic flow control (including electromagnetic stirring, electromagnetic braking, etc.) is currently widely used in the continuous casting process. For example, a "electromagnetic stirring type flow control crystallizer" disclosed in Chinese patent application No. CN1266759A, a "molten steel flow control method and flow control device in a crystallizer and a manufacturing method of a continuous casting product" disclosed in Chinese patent application No. CN1638893A, and a "molten steel flow field dynamic control device in a continuous casting crystallizer" disclosed in Chinese patent application No. CN101185957A. Among them, electromagnetic braking is to suppress the flow of the molten steel in the crystallizer by using the principle that the flowing metal melt is subjected to force in the magnetic field, so as to slow down the impact of the molten steel flow and promote the floating of inclusions. However, the manufacturing cost of the electromagnetic braking equipment is high, and the operation and maintenance cost is also high. Although electromagnetic stirring is an effective method for controlling fluid flow and improving ingot structure without pollution, the electromagnetic stirring used in the crystallizer at present is mainly to accelerate the circumferential movement of the molten steel. If the stirring intensity is too high, it will affect the fluctuation of the liquid surface, and if the stirring intensity is too low, it will not be able to achieve the purpose of improving the mass transfer and heat transfer of the molten steel in the crystallizer and promoting the floating of inclusions. In the preparation of small square billets and round billets, the electromagnetic stirrer is generally installed in the middle and lower part of the crystallizer, mainly to reduce the influence of electromagnetic stirring on the fluctuation of the molten steel liquid surface.

[0005] In addition to the application in the crystallizer, the electromagnetic flow control technology can also be applied at the water gap, such as the electromagnetic rotational flow water gap system based on big data and artificial intelligence disclosed in the Chinese patent application with the publication number CN115709279A, the electromagnetic rotational flow water gap for continuous casting disclosed in the Chinese patent application with the publication number CN103203450A, etc. The electromagnetic rotational flow water gap can effectively reduce the impact depth of the molten steel and plays an important role in reducing the inclusion content of the casting blank, but is not widely used due to the limitation of the cooling condition.

[0006] The flow vector diagram of the molten steel in the crystallizer of the small-size casting blank (including square blank and round blank) on the longitudinal throwing surface is shown in Fig. 1. As can be seen from the figure, the Z-direction flow velocity of the molten steel below the straight water gap 1 is very large. Taking the square blank continuous casting with the cross-sectional size of 180 mm as an example, when the pulling speed is 1.9 m / min, the Z-direction flow velocity of the molten steel at the center position of the stirrer (0.6 m away from the meniscus of the crystallizer) can reach 11 m / min. Without electromagnetic stirring, the Z-direction velocity of the molten steel at the center of the crystallizer 1.2 m away from the meniscus can still reach 3 m / min. The inclusions will enter the deep part of the liquid cavity with the high-speed molten steel, which makes it difficult to float up.

[0007] SUMMARY

[0008] The application provides an electromagnetic flow control method for reducing the inclusions of small-size casting blank. An electromagnetic stirring device with Z-direction electromagnetic force is developed on the basis of the principle of electromagnetic fluid mechanics, which can control the flow of the molten steel in the crystallizer, promote the circumferential rotational stirring of the molten steel in the crystallizer, accelerate the Z-direction of the molten steel edge, reduce the impact depth of the molten steel in the straight water gap of the crystallizer, and promote the floating of the inclusions and improve the quality of the casting blank.

[0009] In order to achieve the above purpose, the application adopts the following technical scheme:

[0010] An electromagnetic flow control method for reducing the inclusions of small-size casting blank, in which an electromagnetic stirring device with Z-direction electromagnetic force is arranged at the crystallizer during the continuous casting process of the small-size casting blank, which can perform circumferential rotational stirring of the molten steel in the crystallizer, accelerate the Z-direction of the molten steel edge, reduce the impact depth of the molten steel in the straight water gap of the crystallizer, and promote the floating of the inclusions.

[0011] Further, the small-size casting blank is small square blank or round blank.

[0012] Further, the electromagnetic stirring device with Z-direction electromagnetic force is a ring-shaped electromagnetic stirrer; the ring-shaped electromagnetic stirrer is composed of a power supply device, an electromagnetic induction device and a cooling device; the electromagnetic induction device comprises a yoke group and a coil; the yoke group is composed of a yoke back, a plurality of yokes and yoke ends; the yoke back is annular; the plurality of yokes are evenly arranged on the inner side of the yoke back in the circumferential direction; the coil is correspondingly sleeved on the yoke; the plurality of yoke ends are connected to the yoke back through corresponding yokes; the yoke end is arranged obliquely relative to the plane where the yoke axis is located; the oblique angle is θ.

[0013] Further, in the ring-shaped electromagnetic stirrer, the pole pair number of the coil is 2, 3, 4, 6 or 8.

[0014] Further, the electromagnetic stirring device with Z-direction electromagnetic force is composed of a plurality of plate-shaped electromagnetic stirrers which are evenly distributed along the circumference of the crystallizer; the plate-shaped electromagnetic stirrer is composed of a power supply device, an electromagnetic induction device and a cooling device; the electromagnetic induction device comprises a yoke group and a coil; the yoke group is composed of a yoke back and a yoke; the yoke back is plate-shaped; the plurality of yokes are evenly arranged on the yoke back in the longitudinal direction; the coil is correspondingly sleeved on the yoke; each plate-shaped electromagnetic stirrer is arranged obliquely relative to the cross section of the crystallizer; the oblique angle is 90-θ.

[0015] Further, θ=10°-70°.

[0016] An electromagnetic flow control method for reducing inclusions of small-size cast slabs, the specific operation process is as follows:

[0017] 1) The electromagnetic stirring device with Z-direction electromagnetic force is installed outside the copper plate of the crystallizer and in the cooling cavity, or is installed outside the crystallizer and is equipped with a separate water cooling system;

[0018] 2) The electromagnetic stirring device with Z-direction electromagnetic force is powered through the power supply device; the electromagnetic stirring current is 10A-1000A; the electromagnetic stirring frequency is 1-12Hz;

[0019] 3) The water cooling device is started before continuous casting starts;

[0020] 4) After the casting speed of the cast slab is stable, the power supply of the electromagnetic stirring device is turned on; the molten steel in the crystallizer is circumferentially stirred according to the set electromagnetic stirring current and electromagnetic stirring frequency; and the edge of the molten steel is accelerated in the Z direction;

[0021] 5) After continuous casting is completed, the power supply of the electromagnetic stirring device is disconnected; and the water cooling device is turned off when the ambient temperature is lower than 50℃.

[0022] Compared with the prior art, the beneficial effects of the present application are:

[0023] 1) Based on the principle of electromagnetic fluid mechanics, the electromagnetic stirring device with Z-direction electromagnetic force is developed, which can control the flow of molten steel in the crystallizer, promote the circumferential rotation stirring of molten steel in the crystallizer, accelerate the Z-direction of the edge of the molten steel, reduce the impact depth of the straight water nozzle in the crystallizer, and promote the floating of inclusions and improve the quality of the casting blank.

[0024] 2) Under the same electromagnetic stirring condition, the electromagnetic stirring device with Z-direction electromagnetic force is more beneficial to the floating of inclusions compared with the traditional electromagnetic stirring device, and can effectively improve the floating removal efficiency of inclusions.

[0025] 3) The electromagnetic stirring device with Z-direction electromagnetic force has simple structure, long service life, easy processing and manufacturing, low maintenance cost, and remarkable application effect, and has important significance for the development of high-quality steel. BRIEF DESCRIPTION OF DRAWINGS

[0026] Fig. 1 is a flow vector diagram of molten steel in a small-size casting blank crystallizer on a longitudinal projection plane.

[0027] Fig. 2 is a schematic diagram of the generation principle of the Z-direction electromagnetic force.

[0028] Fig. 3 is a schematic diagram of the structure of the ring-shaped electromagnetic stirrer.

[0029] Fig. 4 is a schematic diagram of the structure of the plate-shaped electromagnetic stirrer.

[0030] Fig. 1 is a flow vector diagram of molten steel in a small-size casting blank crystallizer on a longitudinal projection plane. DETAILED DESCRIPTION

[0031] The specific embodiments of the present application will be further described below in combination with the drawings:

[0032] As can be seen from Fig. 1, the Z-direction flow rate of the molten steel inside is large, and the flow rate of the molten steel near the crystallizer, i.e. the edge of the molten steel, is low. Therefore, combined with the principle of electromagnetic fluid mechanics, if the electromagnetic skin effect can be fully utilized, the Z-direction flow rate of the edge of the molten steel is increased by using electromagnetic flow control technology, and the high-speed impact of the liquid cavity is suppressed, which can provide favorable conditions for the floating of inclusions.

[0033] The principle of generating Z-direction electromagnetic force is shown in Fig. 2. The moving direction of magnetic field is consistent with the direction of electromagnetic force. When the magnetic yokes are parallel to each other, the electromagnetic force is directed from the magnetic yoke A to the magnetic yoke B, as shown in Fig. 2(a). When the gap between the magnetic yoke A and the magnetic yoke B is at an angle θ with the vertical direction (Z-direction), the electromagnetic force F also has a corresponding angle θ. At this time, according to the vector rule, the electromagnetic force can be decomposed into the horizontal electromagnetic force FR and the vertical electromagnetic force FT. The horizontal electromagnetic force FR is equivalent to the rotating stirring force, and the vertical electromagnetic force FT is the traveling wave magnetic field stirring force, which can push the metal liquid in the Z-direction to accelerate, i.e. the Z-direction electromagnetic force described in the application. The numerical calculation results show that when the inclination angle of the gap between the magnetic yokes is 30°, the Z-direction electromagnetic force generated by the spiral electromagnetic stirrer can reach more than 60% of the horizontal electromagnetic force. If the Z-direction flow rate needs to be increased, the θ angle can be further increased under the condition that the space environment permits.

[0034] According to the different spatial structures of the billet crystallizer and the round billet crystallizer, the application designs two electromagnetic stirring devices capable of generating Z-direction electromagnetic force, one is a ring-shaped electromagnetic stirrer, and the other is a plate-shaped electromagnetic stirrer.

[0035] A conventional electromagnetic stirrer generally consists of a power supply system, an electromagnetic induction system and a cooling system. The electromagnetic induction system is composed of a magnetic yoke and a coil wrapped around the magnetic yoke. The cooling system is used to cool the coil and the core to prevent them from being damaged due to overheating. The ring-shaped electromagnetic stirrer described in the application consists of a power supply device, an electromagnetic induction device and a cooling device, etc. The electromagnetic induction device is composed of a magnetic yoke 7 and a coil 4 wrapped around the magnetic yoke 7. The magnetic yoke 7 includes a magnetic yoke back 6 and a magnetic yoke end 5 connected to each other. The magnetic yoke end 5 is arranged at an inclination with respect to the horizontal plane, and the inclination angle is θ.

[0036] As shown in Fig. 3, in the ring-shaped electromagnetic stirrer described in the application, six coils 4 are arranged in two groups (i.e. the number of pole pairs is 3). The phase difference of the current of each group of coils is 120°. By passing three-phase alternating current, electromagnetic stirring can be achieved. The ring-shaped electromagnetic stirrer can also be powered by two-phase electricity. In this case, the structure needs to be changed accordingly, such as using coils with a number of pole pairs of 4 or 8, etc. As shown in Fig. 3, by inclining the magnetic yoke end 5 by an angle θ, a relatively strong Z-direction thrust can be generated locally, while the circumferential stirring effect is not affected. The size of the angle θ can be 10°-70°, which can be designed according to the specific needs during continuous casting.

[0037] As shown in Fig. 4, the plate-shaped electromagnetic stirrer is used in the small square billet or round billet crystallizer, and 3-8 plate-shaped electromagnetic stirrers are arranged uniformly in the circumferential direction of the crystallizer 3 to form a set of electromagnetic stirring devices for forming effective circumferential electromagnetic stirring effect. The formed electromagnetic stirring device can stir the steel liquid 2 in the circumferential direction. The angle between the plate-shaped stirrer and the horizontal plane is 90-θ, and the angle θ is 10°-70°. The angle θ is designed according to the specific needs during continuous casting, and the size of the angle θ directly affects the size of the local Z-direction electromagnetic force.

[0038] The structure and size of the electromagnetic stirring device with Z-direction electromagnetic force are not much different from those of the conventional electromagnetic stirring device, so in the actual use process, the conventional electromagnetic stirring device for the crystallizer can be completely replaced; compared with the conventional electromagnetic stirring device, the electromagnetic stirring device with Z-direction electromagnetic force not only has circumferential stirring effect, but also can accelerate the Z-direction of the edge of the steel liquid, thereby reducing the impact depth of the straight water gap 1 on the steel liquid 2 in the crystallizer 3, and improving the floating removal efficiency of the inclusions.

[0039] The specific use method of the electromagnetic stirring device with Z-direction electromagnetic force is as follows:

[0040] 1. The electromagnetic stirring device with Z-direction electromagnetic force is installed outside the crystallizer copper plate and in the cooling cavity, or is installed outside the crystallizer, and a separate water cooling system is provided; the provided water cooling system ensures that the temperature of the coil and the core in the electromagnetic stirring device is not more than 50℃;

[0041] 2. The electromagnetic stirring device with Z-direction electromagnetic force is powered by a separate power supply system, and the current can be 10A-1000A according to the number of turns and the diameter specification of the coil; the power frequency is 0-10Hz, and the corresponding process parameters are selected on site according to the actual production situation.

[0042] 3. Before continuous casting starts, the water cooling system is turned on to ensure that the electromagnetic stirring device works normally;

[0043] 4. After the casting speed is stable, the power supply of the electromagnetic stirring device is connected, and the molten steel in the crystallizer is stirred according to the set electromagnetic stirring current and frequency, and the edge of the molten steel is accelerated in the Z-direction;

[0044] 5. After continuous casting is completed, the power supply of the electromagnetic stirring device is turned off first, and the water cooling system is turned off after the ambient temperature is lower than 50℃.

[0045] According to the detection, when the electromagnetic stirring device with Z-direction electromagnetic force is used to apply rotating electromagnetic stirring to the crystallizer, the Z-direction speed of the steel flow center at a distance of 1.2m from the meniscus of the crystallizer is 1.5m / min under the influence of centrifugal flow.

[0046] In order to more directly embody the present application, the embodiments of the present application are further described in conjunction with the examples. The following examples are merely the preferred embodiments of the present application, but the scope of protection of the present application is not limited thereto, and any person skilled in the art can obviously obtain the technical solutions within the technical scope disclosed by the present application, including simple changes or equivalent replacements, which are within the scope of protection of the present application.

[0047] Example 1

[0048] In the round billet continuous casting process with a diameter of 200 mm, a ring-shaped electromagnetic stirrer (structure as shown in Fig. 3) is arranged in the crystallizer, and the parameters of the ring-shaped electromagnetic stirrer are shown in Table 1.

[0049] Table 1. Parameters of the ring-shaped electromagnetic stirrer

[0050] In the continuous casting process of the present example, the input frequency of the ring-shaped electromagnetic stirrer is 1.5 Hz, the input current is 200 A, and the continuous casting steel grade is 45 steel.

[0051] According to the simulation results, under the same continuous casting process conditions, when there is no electromagnetic stirring, the Z-direction velocity of the steel flow center at a distance of 1.2 m from the meniscus of the crystallizer reaches 3 m / min. When the conventional electromagnetic stirring device is used, the Z-direction velocity at this position is 2.1 m / min; and when the ring-shaped electromagnetic stirrer of the present application is used, the Z-direction velocity at this position is reduced to 1.1 m / min.

[0052] Through statistical analysis of the inclusions in the cast billet, after the ring-shaped electromagnetic stirrer with Z-direction electromagnetic force is used in the present example, the number of inclusions greater than 30 μm in the cast billet is reduced by 30% compared with the number of inclusions in the cast billet using the conventional electromagnetic stirring device.

[0053] Example 2

[0054] In the square billet continuous casting process with a cross-sectional size of 150 x 150 mm, a plate-shaped electromagnetic stirrer (4 groups are uniformly distributed along the circumference of the crystallizer) as shown in Fig. 4 is used for production test. The parameters of the plate-shaped electromagnetic stirrer are shown in Table 2.

[0055] Table 2. Parameters of the plate-shaped electromagnetic stirrer

[0056] In the continuous casting process of the present example, the input frequency of the plate-shaped electromagnetic stirrer is 1.2 Hz, the input current is 240 A, and the continuous casting steel grade is 70 steel.

[0057] ​By statistical analysis of the inclusions in the casting blank, the number of inclusions greater than 30 μm in the casting blank after the plate-shaped electromagnetic stirrer with Z-direction electromagnetic force is adopted is reduced by 25% compared with the number of inclusions in the casting blank after the traditional electromagnetic stirring device is adopted.

[0058] The above merely provides the preferred embodiments of the present application, but the protection scope of the present application is not limited thereto, and any skilled person in the art can make equivalent substitutions or changes according to the technical solutions and the inventive concept of the present application within the technical range disclosed by the present application, which should be covered within the protection scope of the present application.

Claims

1. An electromagnetic flow control method for reducing inclusions in a small size strand, characterized by, In a small-size casting process, an electromagnetic stirring device with Z-direction electromagnetic force is arranged at a crystallizer to rotate and stir the molten steel in the crystallizer in a circumferential direction and accelerate the molten steel at the edge in the Z direction, so as to reduce the impact depth of the molten steel at the straight nozzle in the crystallizer and promote the floating of inclusions.

2. An electromagnetic flow control method for reducing inclusions in a small-size casting strand according to claim 1, characterized in that, The small-size casting is a small square billet or a round billet.

3. The electromagnetic flow control method of claim 1, wherein, The electromagnetic stirring device with Z-direction electromagnetic force is a ring-shaped electromagnetic stirrer, which is composed of a power supply device, an electromagnetic induction device and a cooling device.

4. An electromagnetic flow control method for reducing inclusions in a small-size casting strand according to claim 3, characterized in that, In the ring-shaped electromagnetic stirrer, the pole pair number of the coil is 2, 3, 4, 6 or 8.

5. The electromagnetic flux control method of reducing inclusions in a small size strand as claimed in claim 1, wherein, The electromagnetic stirring device with Z-direction electromagnetic force is composed of a plurality of plate-shaped electromagnetic stirrers which are uniformly distributed along the circumference of the crystallizer.

6. An electromagnetic flow control method for reducing inclusions in a small-size casting billet according to claim 3 or 5, characterized in that, θ=10°-70°.

7. The electromagnetic flux control method of reducing inclusions in a small size strand as claimed in claim 1, wherein, The specific operation process is as follows: 1) The electromagnetic stirring device with Z-direction electromagnetic force is installed outside the copper plate of the crystallizer and in the cooling cavity, or is installed outside the crystallizer and is equipped with a separate water cooling system; 2) The electromagnetic stirring device with Z-direction electromagnetic force is powered by the power supply device, and the electromagnetic stirring current is 10A-1000A; the electromagnetic stirring frequency is 1-12Hz; 3) The water cooling device is started before the continuous casting starts; 4) After the casting speed of the casting billet is stabilized, the power supply of the electromagnetic stirring device is turned on, and the molten steel in the crystallizer is circumferentially stirred according to the set electromagnetic stirring current and electromagnetic stirring frequency, while the edge molten steel is accelerated in the Z direction; 5) After the continuous casting is completed, the power supply of the electromagnetic stirring device is turned off, and the water cooling device is turned off after the ambient temperature is lower than 50℃. ​

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