JP2005238276A - Electromagnetic-stirring casting apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To enlarge electromagnetic force to be given to molten metal 8 under state of holding the input power into an electromagnetic-stirring unit according to a kind of the cast molten metal without machining long sidewall copper plates and/or back plates of the copper plates or without deteriorating the strength of the mold without arranging any slit, and to restrain the input power into the electromagnetic stirring unit 5 under state of holding the electromagnetic force to be given to the molten metal. <P>SOLUTION: In an electromagnetic-stirring casting apparatus for molten metal composed of a mold for continuously casting the molten metal, constituted of a pair of long sidewalls and a pair of short sidewalls facing each other, and a pair of linear motor type electromagnetic-stirring units disposed at the outside of the mold along the long sidewalls near the position in the mold height direction, at which the molten metal in this mold is started to solidify, these pair of linear motor type electromagnetic-stirring apparatuses generate the shifting magnetic fields advanced in mutually reverse direction to the long sidewalls in the mold to circulatively stir the molten metal in the mold, and the distance between the upper end of iron cores in the pair of linear motor type electromagnetic-stirring units and the upper end of the long side walls, is ≥100 mm. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a metal continuous casting facility, and more particularly to an electromagnetic stirring device capable of obtaining a high quality cast piece by swirling and stirring molten metal injected into a mold by a moving magnetic field.

In a continuous casting facility for metal, molten metal is injected into a mold from an immersion nozzle, and a slab whose surface is solidified is drawn out from the mold to cast a slab. During slab casting, the molten metal in the mold is made to flow, thereby preventing non-metallic inclusions from being trapped particularly near the surface of the slab and the temperature of the molten metal before and after the solidification start point is uniform. In this way, solidification is uniformly promoted, and the effect of preventing surface cracks and shell breakage can be obtained. Electromagnetic force is used as means for generating a flow in the molten metal in the mold, and a pair of linear motor electromagnetic stirring devices are installed outside the long side wall of the mold as means for applying electromagnetic force to the molten metal. .
With regard to the electromagnetic stirrer, by providing a flow rate that does not hinder the casting operation to the molten metal before and after the solidification start point so as to reach every corner of the slab mold cross section, It has been disclosed and put into practical use that the generation can be prevented over the entire surface including the short side of the mold, thereby preventing the entrainment of powder or the non-uniform distribution of powder on the molten metal surface, and the non-uniformity of powder flow (Patent Document) 1).

In addition, linear motor type electromagnetic force generators are installed along both long sides of the mold so that the thrust in the mold long side direction is opposite to each other at the position above the immersion nozzle in the mold of the immersion nozzle. It has been disclosed and put into practical use that powder casting is possible by arranging and providing the center of the linear motor core (iron core) near the hot water surface (Patent Document 2).
Note that the powder is a sprayed material to be sown on the surface of the molten metal for the purpose of lubrication of the mold and slab, prevention of temperature drop of the molten metal, prevention of reoxidation, adsorption of inclusions in the molten metal, and the like. .
As shown in FIG. 1, as is clear from the descriptions in Patent Document 1 and Patent Document 2, the position at which the electromagnetic force is applied to the molten metal 8, that is, the vertical installation position of the linear motor electromagnetic stirring device 5 is Since it is in the vicinity of the surface 18 (the upper surface of the molten metal), the upper half of the long side mold 1 is positioned in a normal continuous casting apparatus.
As shown in FIG. 2, in the linear motor electromagnetic stirring device 5, an iron core 6 is arranged outside the long mold side wall 1 along the long mold direction. A plurality of coils 7 are wound around the iron core 6 in a plane perpendicular to the mold long side wall 1. Each coil 7 is supplied with U, V, and W phase currents that are shifted by 120 degrees by a three-phase AC power source (not shown), so that the comb teeth of the iron core 6 facing the outside of the long side mold 1 are A moving magnetic field is generated toward the molten metal 8 and an eddy current flows in the molten metal 8 due to the magnetic field. The electromagnetic force that stirs the molten metal by the interaction of the moving magnetic field (vector) and the eddy current (vector). Occurs as the outer product of each vector.

As shown in FIG. 1 and FIG. 2, a long-side mold 1 of a continuous casting mold provided with an electromagnetic stirring device 5 is provided with a copper plate 3 having a thickness of several tens of mm on the inner side and a cooling water channel (not shown) on the outer side, thereby deforming the copper plate. It consists of a back plate 4 having a thickness of several tens of millimeters for suppression, and the back plate 4 has a structure that also serves as a storage box for the electromagnetic stirring device 5 (Patent Document 3).
Since the copper plate 3 and the back plate 4 have relatively good electrical conductivity, the induced current easily flows straight in both metals, and an induced current loss occurs. For this reason, in order to reduce the induced current loss in the mold body as much as possible and further increase the effectiveness of electromagnetic stirring, the copper plate 3 and / or the back plate 4 constituting the mold long side 1 is provided with a copper plate. 3 and / or a continuous casting mold of molten metal 8 is proposed and practiced by reducing at least one low electrical conductive layer in the thickness direction of the back plate 4 to reduce the loss (Patent Document 4).
JP 55-64953 A Japanese Patent Laid-Open No. 56-41054 JP 2002-321040 A JP-A-7-148553

However, in order to implement the invention of Patent Document 4, it is necessary to process the copper plate 3 and / or the back plate 4, but in reality, the processing is not easy. Moreover, when the low electrical conductive layer provided in the copper plate 3 and / or the back plate 4 is a slit (groove), the strength of the copper plate 3 and / or the back plate 4 is reduced, and the molten metal can be cast stably. It may not be possible and will be a problem.
In the present invention, the electric power supplied to the electromagnetic stirrer 5 can be changed depending on the type of molten metal to be cast without processing the copper plate 3 and / or the back plate 4 and without reducing the strength of the mold without providing a slit. The electromagnetic force applied to the molten metal 8 is increased while keeping it constant, or the electric power applied to the electromagnetic stirring device 5 is suppressed while the electromagnetic force applied to the molten metal 8 is maintained at a required strength. An object of the present invention is to provide an electromagnetic stir casting apparatus that enables the above.

The first invention for solving the above problems is
A continuous casting mold composed of a pair of opposed long side walls and a pair of short side walls, and a position in the mold height direction where the molten metal in the mold starts to solidify, along the long side wall, outside the mold Molten metal electromagnetic stir casting apparatus comprising a pair of linear motor electromagnetic stirrers that are installed and generate a moving magnetic field that travels in opposite directions relative to the long side of the mold to swirl and stir the molten metal in the mold In
In the pair of linear motor electromagnetic stirring apparatuses, the distance between the upper end of the iron core and the upper end of the long side wall is 100 mm or more.
Furthermore, the second invention
A continuous casting mold composed of a pair of opposed long side walls and a pair of short side walls, and a position in the mold height direction where the molten metal in the mold starts to solidify, along the long side wall, outside the mold Molten metal electromagnetic stir casting apparatus comprising a pair of linear motor electromagnetic stirrers that are installed and generate a moving magnetic field that travels in opposite directions relative to the long side of the mold to swirl and stir the molten metal in the mold In
The installation position in the mold height direction in the pair of linear motor electromagnetic stirrers is variable, and the distance between the upper end of the iron core and the upper end of the long side wall in the linear motor electromagnetic stirrer is 100 mm or more. It is the electromagnetic stirring casting apparatus of the featured molten metal.

  According to the present invention, the electric power supplied to the electromagnetic stirrer 5 can be changed depending on the type of molten metal to be cast without processing the copper plate 3 and / or the back plate 4 and without lowering the strength of the mold without providing a slit. The electromagnetic force applied to the molten metal 8 is increased while keeping it constant, or the electric power applied to the electromagnetic stirring device 5 is suppressed while the electromagnetic force applied to the molten metal 8 is maintained at a required strength. Thus, an electromagnetic stir casting apparatus with better energy efficiency than before can be realized.

The linear motor electromagnetic stirring device 5 shown in FIG. 2 generates a moving magnetic field for the purpose of stirring the molten metal 8 in the mold. The generated moving magnetic field passes through the long side mold 1 composed of the copper plate 3 and the back plate 4 and reaches the molten metal 8. At this time, since the eddy current flows in the direction of suppressing the moving magnetic field inside the copper plate 3 and the back plate 4, the moving magnetic field reaching the molten metal 8 is attenuated.
When the moving magnetic field reaches the molten metal 8, an eddy current is generated so as to go around the magnetic field lines. An electromagnetic force for stirring the molten metal is generated as an outer product of the vectors by the interaction between the generated eddy current (vector) and the moving magnetic field (vector). Since the magnitude and direction of the electromagnetic force is determined by the outer product of the vectors, the electromagnetic force is reduced when the moving magnetic field is attenuated. It is generally known that when the copper plate is thinned by cutting or the like, the attenuation of the moving magnetic field is reduced, so that the electromagnetic force is increased.
The electromagnetic force generated in the molten metal has all six components in the upper, lower, left, and right directions, but in the range from the front of the electromagnetic stirrer to about 15 mm from the copper plate necessary for stirring the molten metal in the mold. 3, most of the electromagnetic force 9 acting on the molten metal 8 is a component in the casting width direction 10.

The electromagnetic force in the casting width direction 10 has two components in the same direction as the moving direction of the moving magnetic field and in the opposite direction. With these two components, since the magnitude of the moving direction component of the moving magnetic field is greater than the magnitude of the opposite direction component, the molten metal 8 is consequently stirred in the same direction as the moving magnetic field.
The electromagnetic force of the moving direction component of the moving magnetic field is the outer product of the magnetic field (vector) of the casting thickness direction component and the eddy current (vector) of the casting direction component. As shown in FIG. Follow. On the other hand, the electromagnetic force in the opposite direction is the outer product of the magnetic field of the casting direction component and the eddy current of the casting thickness direction component, and its direction also follows Fleming's left-hand rule.
Now, the difference in electromagnetic force depending on the shape of the mold wall will be described. The electromagnetic force is represented by the symbol F, the magnetic flux density by the symbol B, the eddy current density by the symbol I, and the casting width direction is represented by X, the casting thickness direction is represented by Y, and the casting direction is represented by Z and the subscript. The electromagnetic force in the direction is expressed by equation (1). However, in the casting width direction, the moving direction of the moving magnetic field is positive.
F _X = B _Y × I _Z −B _Z × I _Y (1)

FIG. 5 shows an eddy current distribution when the vertical position of the electromagnetic stirring device relative to the mold is changed. By means for moving the iron core position 17 of the electromagnetic stirring device downward, eddy currents easily flow in the vicinity of the iron core position 17 in the molten metal.
FIG. 6 shows the eddy current distribution when the height of the mold is changed. By means for extending the copper plate length upward, the eddy current 16 easily flows in the vicinity of the iron core position 17 of the electromagnetic stirrer installed in the upper part of the mold.
Since the thickness of the long side copper plate 3 does not change, the eddy current density in the casting width direction (X) 10 and the casting direction (Z) 12 increases. Due to this influence, the magnetic field in the casting thickness direction (Y) 11 and the magnetic field in the casting direction (Z) 12 are attenuated, and the values of the first term on the right side and the second term on the right side of Equation (1) are both reduced.
At this time, since the attenuation of the second term on the right side is larger than that on the first term on the right side of the formula (1), the difference is that the casting width direction electromagnetics in the molten metal in the front surface of the electromagnetic stirring device contributing to the swirling stirring force _{F X} becomes larger.

FIG. 7 shows a schematic view of the experimental system in which the electromagnetic force in the mold is measured as seen from the side of the mold. A frame 20 was assembled on the long-side mold 1 into which molten metal was not injected, and a brass plate 19 was suspended from the frame with a wire 21. The brass plate 19 is 100 mm higher than the thickness of the iron core 6 of the electromagnetic stirring device 5, and the height of the brass plate 19 and the thickness center of the iron core 6 are the same height 22 with the length of the wire 21. It adjusted so that it might become.
FIG. 8 is a view of the experimental system as viewed from above the mold. The brass plate 19 was adjusted to be hung so that the front surface of the iron core 6 of the electromagnetic stirrer 5 and the position of about 15 mm from the long side copper plate 3 were. Further, the brass plate 19 having the same width as the iron core 6 was used.

By applying a three-phase alternating current to the coil 7 of the electromagnetic stirrer 5 with respect to the brass plate arranged at the position shown in FIGS. 7 and 8, a moving magnetic field is applied to the brass plate 19. Eddy currents are generated in the brass plate. An electromagnetic force is generated by the interaction between the moving magnetic field (vector) and the eddy current (vector), and the brass plate 19 suspended by the wire 21 moves the moving magnetic field in the same manner as when the molten metal is present in the mold. It moves in the same casting width direction 10 as the direction.
As described above, a spring balance (not shown) is prepared on the side opposite to the direction in which the brass plate 19 moves, and the balance is attached to the brass plate 19, so that the force of moving the brass plate, that is, the electromagnetic stirring device 5. The electromagnetic force acting on the brass plate was measured.

When the mold long side 1 having a width of 2000 mm, a height of 900 mm, and a thickness of 250 mm is constituted by a long side copper plate 3 having a thickness of 25 mm and a long side back plate 4 having a thickness of 60 mm, the length and conductivity of the long side copper plate are passed through the coil 7. The electromagnetic force acting on the brass plate was measured with the upper end of the iron core 6 of the electromagnetic stirrer 5 at two positions 80 mm and 130 mm from the upper end of the long side copper plate 3 with the current value and the like kept constant.
As shown in FIG. 9, when the electromagnetic stirrer was separated from the upper end of the copper plate by 50 mm, a result that the spring balance was pulled with a large force could be obtained, and the effect of the present invention could be confirmed.
Further, as shown in FIG. 10, the electromagnetic force acting on the brass plate when the distance from the upper end of the long side copper plate 3 to the upper end of the iron core 6 of the electromagnetic stirrer was changed from 80 mm to 160 mm was measured. In FIG. 10, the horizontal axis represents the distance from the upper end of the long side copper plate 3 to the upper end of the iron core 6 of the electromagnetic stirrer, and the vertical axis represents the distance from the upper end of the long side copper plate 3 to the upper end of the iron core 6 of the electromagnetic stirrer. The electromagnetic force ratio based on the electromagnetic force acting on the brass plate when the distance is 80 mm is shown.
Usually, the electromagnetic stirrer is installed at a height near the molten metal surface. On the other hand, the upper end of the long side copper plate of the mold only needs to have a height that prevents the molten metal from overflowing from the mold, and may be about 80 mm or more as in this embodiment. As can be seen from FIG. 10, the distance between the upper end of the iron core of the electromagnetic stirrer and the upper end of the long side wall is preferably 100 mm or more and less than half the length of the long side copper plate.
On the other hand, in continuous casting equipment such as steel, a tundish with molten metal is installed at a position of several hundred mm or more on the mold, and the upper limit of the mold long side is determined by peripheral equipment such as tundish. It is done.

It is the figure which represented the position of the casting_mold | template, an electromagnetic stirring apparatus, and a molten metal from the side surface. It is the figure which represented the position of the casting_mold | template, an electromagnetic stirring apparatus, and a molten metal from the upper surface. It is a figure showing the stirring direction of a molten metal. It is a figure showing the left hand rule of Fleming. It is a figure showing eddy current distribution when the up-and-down position of an electromagnetic stirrer is changed to a mold. It is a figure showing eddy current distribution when changing mold length (copper board length). It is the figure which represented the measuring method of the electromagnetic force from the casting_mold | template side surface. It is the figure which represented the measuring method of the electromagnetic force from the casting_mold | template upper surface. It is a figure showing the measurement result of electromagnetic force. It is a figure showing the electromagnetic force ratio with respect to the distance from the upper end of a long side copper plate to the iron core upper end of an electromagnetic stirrer.

Explanation of symbols

1 Long edge mold
2 Short side mold
3 Long side copper plate
4 Long side back plate
5 Linear motor electromagnetic stirring device
6 Iron core
7 coils
8 Molten metal
9 Electromagnetic force acting on molten metal
10 Casting width direction
11 Casting thickness direction
12 Casting direction
13 Direction of current
14 Direction of magnetic field
15 Direction of electromagnetic force
16 Eddy current flow
17 Iron core position of electromagnetic stirrer
18 Hot water surface (upper surface of molten metal, meniscus)
19 Brass plate
20 Stand for hanging brass plate
21 Wire for hanging brass plate
22 Center of height of iron core and brass plate

Claims (2)

A continuous casting mold composed of a pair of opposed long side walls and a pair of short side walls, and a position in the mold height direction where the molten metal in the mold starts to solidify, along the long side wall, outside the mold Molten metal electromagnetic stir casting apparatus comprising a pair of linear motor electromagnetic stirrers that are installed and generate a moving magnetic field that travels in opposite directions relative to the long side of the mold to swirl and stir the molten metal in the mold In
The molten metal electromagnetic stirring casting apparatus, wherein the distance between the upper end of the iron core and the upper end of the long side wall in the pair of linear motor electromagnetic stirring apparatuses is 100 mm or more. A continuous casting mold composed of a pair of opposed long side walls and a pair of short side walls, and a position in the mold height direction where the molten metal in the mold starts to solidify, along the long side wall, outside the mold Molten metal electromagnetic stir casting apparatus comprising a pair of linear motor electromagnetic stirrers that are installed and generate a moving magnetic field that travels in opposite directions relative to the long side of the mold to swirl and stir the molten metal in the mold In
The installation position in the mold height direction in the pair of linear motor electromagnetic stirrers is variable, and the distance between the upper end of the iron core and the upper end of the long side wall in the linear motor electromagnetic stirrer is 100 mm or more. An electromagnetic stir casting apparatus for molten metal.

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