KR20060042348A - Fluid control device and the method using electro-magnetic braking principle - Google Patents

Abstract

The present invention relates to a method of controlling the flow of molten steel by using electromagnetic force to improve the quality of the product produced in the continuous casting process of steel mill, more specifically, the inert gas under the two immersion nozzles through the immersion nozzle In the continuous casting process, a weak magnetic field is formed for the excessively rising part of the molten steel to weaken the rising flow, and in the part where excessive cooling occurs to weaken the flow, the magnetic field strength is strongly applied to suppress the subcooling. The present invention relates to a flow control device using the electromagnetic braking principle and a method thereof, by which the flow in the width direction of the hot water surface is appropriately distributed to improve the surface quality of the cast steel.

The flow control device according to the present invention by controlling the flow form in the continuous casting mold through the above process to reduce the mixing of the mold powder and the non-metallic inclusions and inert gas bubbles in the molten steel to improve the surface quality is good It has the advantage of being able to produce continuous cast slabs.

Continuous casting, molten steel, flow rate, electromagnetic field, core, coil

Description

Fluid Control Device and the Method Using Electro-Magnetic Braking Principle}             

1 is a schematic diagram of a conventional generally used continuous casting process.

2A-2E are cross-sectional views illustrating flow patterns occurring in a mold of a continuous casting process using various conventional methods.

3A and 3B are cross-sectional views and perspective views, respectively, of the electromagnetic flow control device according to the present invention, and FIGS. 3C and 3D are cross-sectional views and perspective views showing the shapes of the upper and lower electromagnets of the electromagnetic flow control device, respectively.

4A to 4B are graphs showing a distribution change of a magnetic field according to the related art and the present invention in three dimensions.

5A to 5B are graphs simulating flow rate distribution according to the magnetic field ratios of FIGS. 6A to 6B.

6A to 6B are tables showing the result of reducing the defect factor accumulated on the surface as a result of applying the flow control device according to the present invention.

Figures 7a to 7b are impurities under the surface layer of the slab according to the strength of the upper and lower magnetic field, using a statistical analysis method at the optimum conditions of use, when using the conventional apparatus and the flow control apparatus according to the present invention, respectively A box plot showing the degree of

* Explanation of symbols for the main parts of the drawings

2: ladle 4: tundish

6: immersion nozzle 8: mold

10: mold powder 12: discharge flow

14: upward flow 16: downward flow

18: bubble rise 20: electromagnetic core

22: ideal flow by the core 24: electromagnetic lower core

26: electromagnetic upper core 28: superconducting magnet

32: lower coil 34: upper coil

36: Water Jacket 38: Current Control Device

50: upper electromagnet 60: lower electromagnet

72: minimum value 74: maximum value

76: median 78: first quartile

80: third quartile 82: mean

84: 25-75% quartile

The present invention relates to a method of controlling the flow of molten steel by using electromagnetic force to improve the quality of the product produced in the continuous casting process of steel mill, more specifically, the inert gas under the two immersion nozzles through the immersion nozzle In the continuous casting process, a weak magnetic field is formed for the excessively rising part of the molten steel to weaken the rising flow, and in the part where excessive cooling occurs to weaken the flow, the magnetic field strength is strongly applied to suppress the subcooling. Therefore, the present invention relates to a flow control apparatus and a method using an electromagnetic braking principle that can distribute the flow in the width and direction of the hot water surface appropriately to improve the surface quality of the cast steel.

The flow control device is capable of producing a continuous casting cast with good surface quality by reducing the mixing of the mold powder and the non-metallic inclusions and inert gas bubbles in molten steel by appropriately controlling the flow pattern in the continuous casting mold. Has

1 is a schematic diagram of a conventional continuous casting process that is commonly used.

Referring to FIG. 1, the conventional continuous casting is cooled while the molten steel exiting the ladle 2 flows into the mold 8 through the submerged entry nozzle 6 in the tundish 4. This begins and the surface of the cast piece is formed. Thus most of the surface quality is determined in the mold 8.

FIG. 2A is a cross-sectional view showing a general flow pattern occurring in a mold of a continuous casting process, FIG. 2B is a cross-sectional view showing the installation position of the core of the flow control apparatus using initial electromagnetic braking and the flow thereof, and FIG. 2C Figure 2 is a cross-sectional view showing the flow according to the flow control device designed to solve the problem of the initial electromagnetic flow control device, Figure 2d is a flow control device of the electromagnetic braking type in the mold having two pairs of cores FIG. 2E is a cross-sectional view showing the shape of a core of a flow control apparatus of an electromagnetic braking method using a superconducting method.

The general flow form is an upward flow in which the molten steel 12 discharged from the immersion nozzle 6 hits the wall of the mold 8 and is directed toward the hot water surface where the mold powder 10 is in contact with the molten steel as shown in FIG. 2A. (14) and the upstream flow (18) around the immersion nozzle generated by buoyancy of the inert gas blown in the immersion nozzle (6) to prevent clogging of the nozzle and the downflow (16) to enter the inside of the cast steel Is formed.

At this time, most of the surface defects appearing in the cast steel is commonly known to be located within a few mm from the surface, and considering the cooling conditions in the mold (8), most of the hot water surface and the discharge flows 12 and the cross section of the mold (8) The cause of the surface defects is created between the hitting parts.

In order to solve the problems similar to the above, in the related art, a technique of mainly improving the quality of the cast steel by appropriately changing the discharge angle of the immersion nozzle 6 is used. That is, when the amount of the downstream 16 increases and the amount of the upstream 14 decreases, and a large number of defects are caused by the upstream 14, the discharge angle is increased, and the temperature of the hot water surface is low, so that the supercooling is performed. In the case where a large number of defects occur, a method of improving the quality by reducing the discharge angle has been used.

However, in the conventional technique of reducing the surface defect by adjusting the discharge angle as described above, when the amount of the upward flow 14 is reduced, the heat supplied to the hot water surface is reduced by that much, so the problem of subcooling reappears. In addition, when increasing the amount of the upward flow 14, the problem of incorporation of the mold powder 10 still remains. In addition, the flow pattern is changed according to the casting speed, casting width, immersion depth, and the amount of inert gas used to prevent the blockage of the nozzle. In this way, the corresponding factors are changed during the casting process, so that the fixed discharge angle Techniques for reducing defects using the immersion nozzle 6 have been limited.

As described above, there is a limit to the method of reducing defects using only the immersion nozzle 6, and as shown in FIG. 2B, an electromagnetic braking device using the electromagnetic braking principle where the discharge stream 12 passes directly under the immersion nozzle 6 ( EMBR: Electro Magnetic Brake Ruler (20) has been proposed to reduce the flow rate by the Lorentz force generated by the relationship between the flow of the molten steel and the magnetic field (Sweden Patent SE 8,003,695, US Patent US) 4,495,984). However, when this technique was practically applied, the quality improvement effect was inadequate due to the occurrence of the abnormal flow 22, which bypasses the portion of the braking force instead of decreasing the flow velocity as expected.

In order to solve the above problem, as shown in FIG. 2C, a pair of electromagnetic lower cores 24 are disposed horizontally under the immersion nozzle 6 to distribute a magnetic field in a horizontal direction so that braking force can be operated over the entire width of the cast steel. A method of making this has been suggested (Sweden patent SE 9,100,184: US patent US 5,404,933).

However, in this method, the braking force is applied to the entire downstream 16 so that the upstream 14 is increased instead of the downstream 16, so that the mold surface 10 becomes unstable in the case of high speed casting. The problem that the occurrence of defects due to the mixing of is increased.

In order to solve the above-mentioned surface instability, in addition to the electromagnetic lower core 24 of the lower part of the immersion nozzle 6 as shown in FIG. A method for stabilizing the hot water surface has been devised by confining the discharge flows 12 between 24 and 26 (Japanese Patent Laid-Open No. 2-284750).

However, such a method distributes the same magnetic field in the vertical direction by the upper and lower electromagnetic cores 24 and 26, and increases the strength of the magnetic field to reduce the downflow 16, so that the upflow 14 The same magnetic field strength is applied, and excessively reducing the upward flow 14 rising to the hot water surface causes the problem that the heat supply of the hot water surface is cut off and supercooling occurs. In addition, the bubble rising flow 18 is more formed near the immersion nozzle 6 by the inert gas introduced to prevent the clogging of the nozzle, the flow phenomenon is reversed, thereby promoting an unstable flow phenomenon in the mold 8 The effect was negligible in reducing defects.

As another approach of flow control using electromagnetic, 6.0 ton / min is applied to the entire mold 8 on the left and right sides of the immersion nozzle 6 by using a superconductive magnet 28 as shown in FIG. The purpose was to achieve quality improvement under the above high discharge amount.

However, due to the characteristics of the superconducting magnet, it can be used only at cryogenic temperatures, and due to the cores arranged left and right as shown in FIG. (JP 1996-7004658).

The present invention has been proposed to solve the above problems, the present invention is an object to control the flow near the water surface in the method of injecting inert gas inside the immersion nozzle while using a two-hole immersion nozzle in the continuous casting process By using a pair of electromagnets and using a non-uniform magnetic field strength in the width direction, a weak magnetic field is formed where a flow of water is required, and a flow is generated. The present invention provides a flow control apparatus using an electromagnetic braking principle that can improve the surface quality of a cast steel by appropriately distributing the flow in the width direction of the hot water surface by reducing the flow by applying a strong force.

By using the above apparatus, the flow rate in the mold can be controlled effectively so that the flow rate of the hot water surface is present over a large area, so that the flow rate distribution can be made more uniform, so that defects such as inclusions on the surface of the cast steel, mold powder, and bubbles can be obtained. Factors can be reduced, suppress subcooling and prevent inclusions from accumulating.

In order to achieve the above object, the present invention proposes a flow control apparatus using the electromagnetic braking principle.

In order to control the flow by using an electromagnetic force in the continuous casting process, the present invention, a pair of upper electromagnets opposed to the upper portion of the mold outer peripheral surface, and the lower portion of the mold outer peripheral surface corresponding to the lower portion of the mold immersion nozzle, the upper portion, It has a pair of lower electromagnets that act independently of the electromagnets.

Preferably, the current intensity applied to the upper and lower electromagnets can be adjusted differently, and the magnetic field strength of the upper electromagnet is kept smaller than the magnetic field strength of the lower electromagnet.

In addition, the upper electromagnet includes a core and a coil wound around the core, the surface of the upper electromagnet core facing the mold has a convex shape in the middle, and the lower electromagnet has a coil wound around the core and the core. And the surface facing the mold of the lower electromagnet core has a concave shape in the middle. The upper and lower electromagnets may be connected to yokes that are separated from each other or formed of a material having a magnetic permeability similar to air.

Hereinafter, with reference to the accompanying drawings, the most preferred embodiment of the present invention will be described in detail as follows.

3A and 3B are a longitudinal sectional view and a perspective view, respectively, of the electromagnetic flow control apparatus according to the present invention.

3A and 3B, the electromagnetic flow control apparatus according to the present invention faces a pair of upper electromagnets 50 positioned opposite to the upper part of the mold outer peripheral surface and a lower part of the mold outer peripheral surface corresponding to the lower part of the mold immersion nozzle. It can be seen that it consists of two pairs of independent electromagnets, each positioned and including a pair of lower electromagnets 60 acting independently of the upper electromagnets.

In the present invention, the core 26 of the upper electromagnet 50 and the core 24 of the lower electromagnet 60 are separated or connected to yokes made of a material having a magnetic permeability similar to air. Make sure that the and magnetic fields work together as much as possible. Coils 32 and 34 are wound on the outside of each core of the upper and lower electromagnets to form a magnetic field, and the outside of each coil is also equipped with a facility for cooling the coils.

In addition, the upper coil 34 and the lower coil 32 are each provided with a current control device 38 for supplying a current to adjust the intensity of the electromagnetic field. Accordingly, the present invention can form a magnetic field of different intensities by supplying current to the upper coil 34 and the lower coil 32 separately, and thus can be independently adjusted.

3C and 3D are cross-sectional views and perspective views showing the shape of the upper electromagnet and the lower electromagnet of the electromagnetic flow control device.

3C and 3D, the flow of molten steel introduced through the immersion nozzle 6 in the continuous casting process using the two-hole nozzle is discharged from the immersion nozzle 6 as shown in FIGS. 2A to 2E. Bubble rises generated near the immersion nozzle 6 due to the buoyancy of the upflow 14 and the downflow 16 generated after hitting the wall of the mold 8 and the inert gas generated to prevent nozzle clogging ( 18). In particular, in the case of the bubble rise (18) generated by the above inert gas is most often floated within the range from 300 mm to the immersion nozzle (6), which causes the mold powder 10 is mixed while the hot water surface is disturbed Situations often occur, and many defects occur in this area. Therefore, in order to prevent defects occurring in this part, a braking force should be applied to the upward flow 14 generated by buoyancy.

Accordingly, the upper core 26 forms a relatively strong magnetic field near the immersion nozzle 6 than both ends, and strongly brakes the bubble rise 18 caused by the inert gas to stabilize the hot water surface. It has the shape of the convex core 26. The convex shape of the center of the upper core 26 has the weakest magnetic field at both ends, and the weak magnetic field in the middle induces an appropriate upward flow 14 near the wall of the mold 8 to suppress subcooling. And prevents the accumulation of inclusions.                     

In contrast, the lower core 24 has a concave shape in the center and convex toward both ends. The magnetic field formed by the lower core 24 prevents the non-metallic inclusions contained in the molten steel discharged from the immersion nozzle 6 from reaching deep inside the cast steel, thereby improving the internal quality of the cast steel. In addition, it is possible to reduce the force that the discharge flow 12 of the immersion nozzle 6 directly impinges on the short side to prevent the slab burst phenomenon due to the re-melting phenomenon of the slab.

In particular, the maximum magnetic field strength is formed near the short sides of the mold, which are both ends of the lower core 24, and the flow is lowered along the down stream 16 by weakening the strength of the magnetic field to the maximum at the center of the lower core 24. When it comes up again, it aims at accelerating the separation of the inclusions by weakening the braking force.

Therefore, in the present invention, the magnetic field strength of the center portion is maintained larger than the magnetic field strengths of both ends at the bath surface, and the magnetic field strength of the center portion is kept smaller than the magnetic field strengths of both ends at the lower part of the immersion nozzle, and the inclusions on the surface of the cast steel Or defects such as mold powder and bubbles can be greatly reduced.

4A to 4B are graphs showing the results of measuring the magnetic field strength as a result of testing the flow control apparatus according to the present invention in actual equipment.

4A to 4B are measured while varying the intensity of the magnetic field applied to the upper core 26 while the magnetic field strength applied to the lower core 24 is fixed after the flow control device according to the present invention is installed. . The above experiments allowed the independent adjustment of the upper and lower magnetic field intensities by fixing the intensity of the lower current applied to the lower core 24 and changing the intensity of the upper current applied to the upper core 26. In this experiment, the depth direction experiment of magnetic field strength measured the magnetic field strength from 0 mm to 1000 mm from the water surface, and the width direction experiment of magnetic field strength from 0 mm to 800 mm radius from the center of the water surface. Intensity was measured.

First, referring to FIG. 4A, when looking at the distribution of the magnetic field in the depth direction by the upper core 26, the magnetic field strength at the top of the bath surface is about 100 mT, and the strength of the magnetic field decreases closer to the bottom away from the top. In the bottom part, the magnetic field intensity is about 67 mT and the magnetic field distribution is formed to have an intensity of about 67% of the central magnetic field strength.

Referring to FIG. 4B, the magnetic field distribution in the width direction by the upper core 26 has a magnetic field strength of about 140 mT at the center, and a magnetic field strength of about 85 mT toward the end, far from the mold center. As the intensity increases, the strength of the magnetic field decreases, and at the end, the magnetic field distribution is formed to have an intensity of about 60% of the central magnetic field strength.

5A to 5B are graphs illustrating a distribution change of a magnetic field according to a conventional invention and the present invention in three dimensions, and FIGS. 6A to 6B are simulations of a flow velocity distribution according to a ratio of magnetic fields of FIGS. 5A to 5B. The graph is shown.

First, FIG. 5A illustrates a case where the intensity ratios of the upper magnetic field and the lower magnetic field are 1: 1 to form magnetic fields having the same size, and FIG. 6B illustrates the upper magnetic field and the lower magnetic field according to the present invention. Using a flow control device with adjustable size, the intensity ratio of the upper magnetic field and the lower magnetic field is 0.5: 1, and the distribution of the magnetic field when the strength of the upper magnetic field is 50% of the lower magnetic field is shown.

In FIG. 6A, when using a conventional method as illustrated in FIG. 5A, when a strong electromagnetic field is applied to control the flow flowing downward, a strong magnetic field of the same size is also applied on the surface of the molten steel, thereby preventing the molten steel from rising to the surface of the molten iron. As a result, only bubbles rise by the inert gas appear to exist. As a result, the portion of the surface of the cast steel has a high defect factor, such as inclusions on the surface of the cast steel, mold powder, and bubbles.

However, when the ratio of the upper magnetic field and the lower magnetic field is adjusted as shown in FIG. 5B, it can be seen that the flow velocity of the tap surface exists over a large area as shown in FIG. 6B, and the flow velocity distribution is also more uniform. Accordingly, it can be seen that defect factors such as inclusions on the surface of the cast steel, mold powder, bubbles, etc. are greatly reduced than in the case of using the conventional invention of applying the existing magnetic field of the same intensity.

7A to 7B illustrate the use of the impurities below the surface layer of the slab according to the strength of the upper and lower magnetic fields, using statistical analysis at the optimum conditions of use, when using the conventional apparatus and the flow control apparatus according to the present invention, respectively. Boxplot showing the degree.                     

The box plot shows the Minimum (72), Maximum (74), Median (76), First Quartile (78), and Third Quartile of the data. (80) is a graph showing the distribution form of data as a graph, and especially, a graph that presents an objective criterion for outliers, and is a statistical graph commonly used when comparing two or more data.

Referring to FIG. 7A in more detail, in the case of using the flow control apparatus according to the present invention, the average 82 of defects such as inclusions and mold powder at both ends in the width direction is about 0.0068, and 25 The interquartile range (84) between% and 75% is about 0.0067, with an average (82) of the defect factor using the conventional method (82) of about 0.0375, and the interquartile range (84) between 25% and 75%. It can be seen that is significantly reduced by about five times compared to about 0.0436.

Similarly, referring to FIG. 7B, in the case of using the flow control apparatus according to the present invention, the average 82 of defect factors such as inclusions and mold powder accumulated in the center portion in the width direction is about 0.0065, and is 25% to 75%. The interquartile range 84 is about 0.0058, the mean 82 of defect factors using the conventional method is about 0.0155, and the quartile range 84 between 25% and 75% is about 0.0161. It can be seen that the reduction is about 2 times or more.

Therefore, when using two independent pairs of electromagnets according to the present invention, when the magnetic field of the independent strength is formed, it can be seen that there is an effect of reducing the defect factors such as inclusions, mold powder, bubbles, etc. on the surface of the cast steel.

As mentioned above, although this invention was demonstrated in detail using the preferable Example, the scope of the present invention is not limited to a specific Example and should be interpreted by the attached Claim. In addition, those skilled in the art should understand that many modifications and variations are possible without departing from the scope of the present invention.

As described above, the present invention, in the continuous casting process using a two-hole immersion nozzle while using an inert gas in the inside of the immersion nozzle to use the two independent pair of electromagnets in order to control the flow near the water surface and the width direction By using a method that uses a non-uniform magnetic field strength, a weak magnetic field is generated where a flow surface is needed, and a flow is generated.In the part where the flow is to be weakened, the magnetic field strength is strongly applied to reduce the flow surface. By appropriately distributing the flow in the width direction has the effect of improving the surface quality of the cast.

By using the system as described above, the flow velocity in the mold can be controlled effectively so that the flow velocity of the hot water surface exists over a large area so that the flow velocity distribution can be made more uniform, so that defects such as inclusions on the surface of the cast steel, mold powder, and bubbles can be obtained. Factors can be reduced, have a great effect in suppressing supercooling and preventing inclusions from accumulating.

Claims (8)

A pair of upper electromagnets opposed to the upper part of the mold outer peripheral surface, And a pair of lower electromagnets opposed to the lower part of the mold outer peripheral surface corresponding to the lower part of the mold immersion nozzle and acting independently of the upper electromagnet. The method according to claim 1, Flow control device having a different current strength applied to the upper and lower electromagnets. The method according to claim 2, Flow control apparatus using electromagnetic braking principle that the magnetic field strength of the upper electromagnet is kept smaller than the magnetic field strength of the lower electromagnet. The method according to any one of claims 1 to 3, The upper electromagnet includes a core and a coil wound around the core, and a surface of the upper electromagnet core facing the mold has a convex shape in the middle. The method according to any one of claims 1 to 3, The lower electromagnet includes a core and a coil wound around the core, and a surface of the lower electromagnet core facing the mold has a concave shape in the middle. The method according to any one of claims 1 to 3, The upper and lower electromagnets each include a core and a coil wound around the core, the face of the upper electromagnet core facing the mold has a convex shape in the middle, and the face of the lower electromagnet core facing the mold has a concave shape in the middle. Flow control device with The method according to any one of claims 1 to 3, The upper and lower electromagnets are flow control device using the electromagnetic braking principle is separated from each other. The method according to any one of claims 1 to 3, The upper and lower electromagnets are flow control devices using electromagnetic braking principles connected by yokes formed of a material having a magnetic permeability similar to air.

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