JPS6210743B2 - - Google Patents

Description

[Detailed description of the invention] The present invention relates to a horizontal continuous casting method.

In conventional horizontal continuous equipment, in order to prevent molten metal from flowing out between the tundish nozzle made of refractory material and the water-cooled mold,
The tandate nozzle and the mold were fixedly attached to each other. The other portions of the tundish nozzle adjacent to the water-cooled mold are cooled and form a solidified shell at the molten metal contact area, which is stuck to the tundish nozzle. Furthermore, since the molten metal enters the pores of the refractory material constituting the tundish nozzle and solidifies as it is, the adhesion force increases.
Therefore, when the cast body is pulled out, the solidified shell sometimes ruptures and a so-called breakout occurs.

In the prior art to solve this problem, a non-porous silicon nitride ring or boron nitride ring with excellent lubricity is hermetically connected between the tundish nozzle and the mold. These silicon nitride rings and boron nitride rings have a short lifespan and are expensive. However, although the use of these materials has the effect of alleviating the sticking of the tundish nozzle and the solidifying shell, it is not possible to completely avoid the sticking of the mold tube and the solidifying shell.
As seen in the figure, intermittent withdrawal is inevitable.

In order to solve these drawbacks of the prior art, an electromagnetic field generating means that generates a higher magnetic flux density at the bottom than at the top of the molten metal is placed near the boundary between the tundish nozzle and the mold. Horizontal continuous casting equipment that constricts near the boundary has been proposed (Japanese Patent Application No. 56-94333, Japanese Unexamined Patent Publication No. 1983-1999).
Publication No. 209752). By squeezing the molten metal in this way, the molten metal does not come into contact with the tundish nozzle, and the solidified shell is prevented from sticking to the tundish nozzle as described above.
Continuous extraction becomes possible. Furthermore, since it is not necessary to fix the tundish nozzle and the mold, it is possible to vibrate the mold, which also prevents the coagulation shell from sticking to the tundish nozzle or the mold. This is also the case in Utility Model Application No. 52-160615 and Japanese Patent Application Publication No. 53-76130.

In such prior art, no consideration is given to the waveform of the AC power that energizes the electromagnetic field generating means, and therefore there is a problem in that the efficiency is low.

An object of the present invention is to provide an improved horizontal continuous casting method that efficiently generates electromagnetic force for squeezing molten metal.

The present invention provides a means for detecting the level of molten metal in the tundish, a coil is placed near the boundary between the tundish nozzle and the mold, and the coil is excited by alternating current power to generate the electromagnetic force. The current that excites the coil by squeezing the molten metal has a waveform whose time rate of change is small when the current increases and becomes large when the current decreases, and the coil increases the electromagnetic force when the level increases, This horizontal continuous casting method is characterized by adjusting the supplied power to reduce the electromagnetic force when the metal falls.

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is an overall system diagram of an embodiment of the present invention. In this horizontal continuous casting equipment, a tundish 1 is provided with a heating device 2 for stabilizing the temperature of molten metal 12 supplied from a ladle 8. The cast body 4 from the mold 3 is
The ingots 9 are drawn from the cooling zone 5 by a drawing device 6 and cut by a cutting device 7 to obtain ingots 9. This ingot 9 is placed on the roller table 1
Carried by 0.

FIG. 2 is an enlarged sectional view of the vicinity of the mold 3. The tundish 1 is lined with a refractory material 11 and stores molten metal 12. A tundish nozzle 14 made of a refractory material is fixed to the tundish 1 by a mounting hardware 13. The mold 3 has a cooling liquid passage 15 in which a copper mold tube 33 is liquid cooled, and a passage 16 for the cast body 4 of the mold 3 is coaxially continuous with the tundish nozzle 14 . This mold 3 is fixed to a tundish nozzle 14. Near the boundary 17 between the tundish nozzle 14 and the mold 3, an electromagnetic field generating means 18 is provided which is comprised of a coil surrounding the boundary 17 and is energized by alternating current power. Due to the electromagnetic field of the electromagnetic field generating means 18, the molten steel passing near the boundary 17 is reduced in diameter and squeezed inward in the radial direction for reasons described later in connection with FIG. Therefore, near the boundary 17, molten steel is prevented from coming into contact with the portion of the tundish nozzle 14 closer to the mold 3. Therefore, tandate nozzle 1
This prevents the solidified shell from sticking to the cast body 4, making it possible to draw out the cast body 4 continuously or intermittently.

The electromagnetic field generating means 18 includes a first coil 34 surrounding the vicinity of the boundary 17 and a second coil 35. The coil wires of both coils 34 and 35 are wound around the tundish nozzle 14 and a portion of the mold 3 with a gap in the radial direction.

Referring to FIG. 3, when an excitation current flows through the coil wire of second coil 35 in the direction of arrow 36, a magnetic field is generated in the direction of arrow 37. When the exciting current increases along the curve 61 of FIG. 3a, an eddy current flows in the molten metal 12 in the direction of the arrow 38, which is opposite to the exciting current of the arrow 36. According to Fleming's left-hand rule, the molten metal 12
is acted upon by an electromagnetic force directed toward its center.
On the other hand, if the exciting current decreases along the curve 62 of FIG. 3a, the eddy current 38 will be in the opposite direction and will exert a spreading force on the molten steel. In order to suppress this force from acting on the molten steel as much as possible, the excitation current waveform is distorted as illustrated in FIG. This current waveform has a small rate of change over time when increasing, as indicated by reference numeral 61. With such an excitation waveform, it is possible to absorb the components in the region of the curve 62 by making the bobbin of the coil 35 or the tundish nozzle mounting bracket 13 in FIG. 2 made of copper or the like with low electrical resistivity. be.
As a result, when the time average of one cycle is taken, a drawing force acts on the molten steel as shown in FIG. 3a and 2.

Furthermore, in FIG. 3a, the excitation current is curve 6
In the region along lines 2 and 62', the molten steel flows in the opposite direction to the arrow 38 in FIG. 3, so a negative squeezing force acts on the surface of the molten steel. Curves 62, 6 with large changes in current value
As for the induced current in the region 2', the greater the change in the excitation current, the more easily the molten steel is absorbed by the mold wall, etc. Therefore, by shortening the regions of the curves 62, 62' shown in FIG. 3A, the induced current absorbing plate 18' provided inside the electromagnetic field generating means 18 is unnecessary. The induced current absorbing plate 18' actively absorbs the induced current in the area of curves 62 and 62'.

In this way, the diameter of the molten metal 12 is reduced near the boundary 17. This also applies to the other first coil 34.

FIG. 4 shows the pressure distribution of static pressure acting on the molten metal 12 passing through the tundish nozzle 14 and the mold 3, the static pressure compensating force acting on the molten steel surface by the first coil 34 and the second coil 35, and diameter reduction. Shows force distribution. When the axis-perpendicular cross section of the tundish nozzle 14 and the mold 3 is rectangular, the molten metal 12 stored in the tundish 1 acts on the surface layer of the molten metal near the boundary with the tundish nozzle 14 and the mold 3. The static pressure distribution is shown by line a in FIG. In addition, the distribution of the static pressure compensation force acting on the surface layer of the molten metal is shown in Figure 4-1.
It is shown by line b. The first coil 34 generates a magnetic force to compensate for the static pressure shown in FIG.
The static pressure compensating force P1 in FIG. 42 is the sum of the pressure Pat acting on the upper surface of the surface layer of the molten steel and the diameter reducing force Pα. The axis of this first coil 34 coincides with the axes of the tundish nozzle 14 and the mold 3. Furthermore, this second coil 35 is used to compensate for the unbalanced static pressure shown in FIG.
The axis of the coil is eccentrically arranged above the axes of the tundish nozzle 14 and the mold 3. Therefore, in the molten metal 12 near the boundary 17, a larger magnetic flux density is generated in the lower part of the molten metal 12 than in the upper part.

The function of the second coil 35 will be explained with reference to FIG. FIG. 5 1 is a front view of the second coil 35 viewed from the axial direction, and FIG. 5 2 shows the distribution of magnetic flux density in a cross section AA passing through the axis 39. Referring to this drawing, as the second coil 35 deviates from the axis 39 in the radial direction, the second coil 35
It can be seen that the magnetic flux density within 5 becomes large. The axis 39 of the second coil 35 is located above the axes of the tundish nozzle 14 and the mold 3,
Therefore, a large electromagnetic force acts on the lower part of the molten metal 12, and as a result, an electromagnetic force resisting the pressure shown in FIG. 4 acts on the molten metal 12, compensating for the differential pressure between the upper and lower surfaces of the molten metal. Ru. Furthermore, the cross-sectional shape of the reduced diameter portion 19 of the molten metal 12 perpendicular to the drawing direction 45 is similar to and concentric with the cross-sectional shape of the mold tube 33.

The inner diameter of the casting passage 16 of the mold 3 is made smaller along the front of the drawing direction of the casting 4 in accordance with the amount of shrinkage of the casting as it solidifies in order to equalize cooling within the mold.

The means for supplying lubricant will be explained with reference to FIG. A ring-shaped header 41 is formed in the tundish nozzle 14. A nozzle 42 is formed in this header 41 so as to face inward in the radial direction of the tundish nozzle 14 . This header 41
A lubricant 46 is pumped through a conduit 43. The nozzle 42 is located at a position forward in the drawing direction 45 from a position 44 where the molten metal 12 leaves the tundish nozzle 14 . The lubricant 46 is CaO,
The main ingredients are powders of SiO ₂ and Al ₂ O ₃ , as well as pure iron,
It is made by mixing powder with good electrical conductivity such as Co. In the lubricant 46 mixed with powder having good electrical conductivity, an electromagnetic force directed inward in the radial direction of the tundish nozzle 14 and the mold 3 acts on the powder having good electrical conductivity. This ensures that the lubricant 46 adheres to the entire outer circumferential surface of the reduced diameter molten metal 12. Therefore, the lubricity with the portion where the diameter-reduced molten metal 12 first comes into contact with the casting passageway 16 is improved. The lubricant 46 may be made of rapeseed oil as a main component, with powder of pure iron, cobalt, etc. mixed therein.

In such horizontal continuous casting equipment, it is assumed that the level l (see FIG. 2) of the molten metal 12 in the tundish 1 fluctuates. When the level 1 is displaced upward, that is, when the amount of molten metal 12 stored in the tundish 1 becomes large, the static pressure acting on the surface layer of the molten metal 12 near the boundary 17 becomes large. Therefore, when the electromagnetic force by the first coil 34 of the electromagnetic field generating means 18 is constant, the rate at which the diameter of the molten metal 12 is reduced decreases, and the diameter of the reduced diameter portion 19 falls along the imaginary line in FIG.
It becomes large as shown by 0. In accordance with the diameter expansion of the reduced diameter portion 19, the separation start position 44 is displaced forward in the drawing direction 45, and the contact start position 47 of the molten metal 12 with the inner surface of the mold tube 33 is moved backward in the drawing direction 45. Displace. Further, when the level l is displaced downward, that is, when the amount of molten metal 12 stored in the tundish 1 becomes small, the static pressure acting on the surface layer of the molten metal 12 near the boundary 17 becomes small. Become. Correspondingly, the reduced diameter portion 19 is reduced in diameter as shown by the imaginary line 21, the separation start position 44 is displaced rearward along the pull-out direction 45, and the contact start position 47 is displaced forward along the pull-out direction 45.

When the separation start position 44 and the contact start position 47 are displaced in accordance with the fluctuation of the level l, the solidification thickness of the molten metal changes in accordance with the change in the length of the cooling zone in the mold 3, resulting in a homogeneous casting. There is a risk that it will not be possible to obtain a piece and that the nozzle 42 will become clogged with the molten metal 12.

Therefore, in the present invention, a change in the level l of the molten metal 12 in the tundish 1 is detected, and the power supplied to the first coil 34 is changed according to the change in the level l, so that the separation start position 44 and the contact start position are 47 is held at a preset constant position. That is, when the level 1 increases, the electromagnetic force of the first coil 34 is increased, and when the level 1 decreases, the supplied power is adjusted to decrease the electromagnetic force of the first coil 34.

Referring again to FIGS. 1 and 2, in order to perform the above-described adjustment, in this embodiment a television camera 2 is used to detect the level l in the tundish 1.
2 is provided. This television camera 22 images the inside of the tundish 1 through an opening 23 formed in the upper part of the tundish 1, and the level l detected by this television camera 22 is given to a control device 24. The control device 24 controls the power supply 25 for supplying power to the electromagnetic field generating means 18 to adjust the supplied power in accordance with fluctuations in the level l. Also, the tandate nozzle 1 of mold 3
A position detection means 26 for detecting a contact start position 47 is provided in a portion closer to 4. The contact start position 47 is detected by the position detecting means 26, and the amount of supplied power is adjusted so that the contact start position 47 is at a predetermined constant position.

Referring to FIG. 6, the position detecting means 26 includes a plurality of thermocouples 27, 28, 29, and 30, for example, four in the figure, which are provided at intervals in the axial direction within the mold tube 33, for example. molten metal 12
When the thermocouples 27 contact the inner surface of the mold tube 33, the temperature at the contact position increases.
30, the position of the thermocouple that detected the highest temperature becomes the contact start position.

FIG. 7 is a simplified block diagram showing the configuration of the control device 24. The detected value of level l by the television camera 22 is sent to the arithmetic unit 4 via an amplifier 48.
given to 9. This arithmetic unit 49 includes a comparator 5
The comparator 50 receives signals from the setter 51 and the position detecting means 26. That is, the setting device 51 outputs a signal corresponding to the predetermined contact start position 47, and the signal from the position detection means 26 and the setting device 51
The comparator 50 compares the output signal with the output signal. The arithmetic unit 49 performs arithmetic operations in response to the signal from the amplifier 48 and the signal from the comparator 51, and the adjustment unit 75 adjusts the power supplied by the power source 25 based on the arithmetic values.

In this way, the power supplied to the first coil 34 is controlled so that the contact start position 47 is at a preset constant position. Therefore, the contact start position 47 and the separation start position 44 are constant positions regardless of the level l, and the length of the cooling zone of the molten metal 12 in the mold 3 is constant, so that the solidified thickness does not change and a good slab is produced. can be used.
Further, the nozzle 42 is prevented from being blocked by the molten metal 12. Moreover, since the cross-sectional shape of the reduced diameter portion 19 is substantially similar to and concentric with the cross-sectional shape of the mold tube 33, the amount of variation in the contact start position 47 on each surface such as the upper and lower surfaces is suppressed to a small level, and disturbances in the cooling conditions are prevented. Become as small as possible.

In addition, in order to suppress fluctuations in the level l as much as possible, the ladle 8 (first
The driving section 32 may be controlled to drive the sliding gate 31 provided at the bottom of the device (see figure). In this way, the flow rate of the molten metal 12 flowing into the tundish 1 from the ladle 8 is controlled, and fluctuations in the level 1 are suppressed as much as possible.

As another embodiment of the present invention, the position detection means 26
Alternatively, instead of the thermocouples 27 to 30 described above, a plurality of temperature-sensitive magnetic bodies may be provided, or the contact start position 47 may be detected by γ rays or the like. Note that if the magnetic field force is large enough to affect the detection of the contact position, the power supply to the electromagnetic force generating coil may be stopped for a very short time at the position where the current value is 0, and the detection may be performed during that time. good.

As a further embodiment of the present invention, a load cell 5 as shown in FIG. 8 is used instead of the television camera 22.
2 may be provided. That is, one end portion of the support hardware 55 is supported by a pin by a support column 54 erected on the pedestal 53 . The other end of this support hardware 55 is connected to a support protrusion 56 provided on the tundish 1.
The other end is received by the load cell 52 on the pedestal 57. By doing so, the amount of molten metal 12 stored in the tundish 1 is detected by the load cell 52. Therefore, the electromagnetic force of the first coil 34 can be changed in accordance with the change in the storage amount, that is, the change in the static pressure near the boundary 17, as in the previous embodiment.

As still another embodiment of the present invention, as shown in FIG. load cell 60
You may also receive it at

FIG. 10 is a sectional view of another embodiment of the invention. The nozzle hole 61 of the tundish 1 is provided with a sliding gate 62 for blocking and outflowing the molten metal 12.
2 is driven by a driving cylinder 63. Near the end of the tundish nozzle 14 closer to the mold 3, an electromagnetic field generating means 64, which is formed by winding a wire around the tundish nozzle 14, is arranged. Due to the electromagnetic force generated by the electromagnetic field generating means 64, the molten metal 12 flowing within the tundish nozzle 14 is constricted inward in the radial direction. mold 3
has an inner diameter larger than the outer diameter of the tundish nozzle 14. Near the end face of the mold 3 facing the tundish nozzle 14 at the boundary 17 between the tundish nozzle 14 and the mold 3, another electromagnetic field generating means 65 is arranged in a plane substantially perpendicular to the drawing direction. Each electromagnetic field generating means 64, 6
Induced current absorbing plates 64' and 65' are arranged inside the 5.

FIG. 11 shows the molten metal 12 near the boundary 17.
It is a figure showing the static pressure distribution which acts on the surface layer part of. Static pressure acts on the surface layer of the molten metal 12, which increases toward the bottom. Therefore, as shown in FIG. 12, if an electromagnetic field generating means 64 having a shape almost symmetrical to a curve 67 showing the static pressure distribution in FIG. 11 with respect to the center position 66 of the molten metal 12 is arranged, the distribution of electromagnetic force The result is as shown by curve 69 in FIG. In other words, an inwardly concave electromagnetic force distribution is obtained on both sides of the molten metal 12. If the static pressure shown in FIG. 11 is compensated for by the electromagnetic force given by such a curve 69, the diameter-reduced portion 19 will have a laterally expanded diameter. Therefore, if the shape of the electromagnetic field generating means 64 is made to be slightly concave inward from both sides of the curve, the electromagnetic force distribution at that time will be the curve 70 shown by the broken line.
becomes. This curve 70 is similar to the curve 67 showing the static pressure distribution in FIG.
The distance between the tundish nozzle 9 and the inner surface of the tundish nozzle 14 can be made substantially uniform in the circumferential direction.

The electromagnetic field generating means 65 is formed to extend in the radial direction near the end face of the mold 5 facing the tundish nozzle 14. This electromagnetic field generating means 65 is constructed by winding a wire around the axis of the mold 3. When a current flows through the strands of the electromagnetic field generating means 65 perpendicular to the page of FIG. 10 and toward the back of the page, the molten metal 12 in the mold 3 flows toward the front of the page of FIG. Eddy currents are generated, indicated by reference numeral 71, and a magnetic field is generated in the direction of arrow 72. Therefore, the molten metal 12 in the mold 3
, an electromagnetic force indicated by an arrow 73 directed forward in the drawing direction 45 is generated. Moreover, the electromagnetic field generating means 65
As it goes downward, it is inclined forward in the drawing direction 45 by an angle θ with respect to a horizontal line that coincides with the axis of the mold 3. As a result, the molten metal 1 in the mold 3
2 will be given a larger electromagnetic force at the bottom than at the top. Therefore mold 3
The molten metal 12 within maintains a plane substantially perpendicular to the drawing direction 45. Therefore, the solidification conditions at the position 47 where the molten metal 12 contacts the inner circumferential surface of the mold 3 are uniform throughout the circumferential direction. In this way, the contact length of the molten metal 12 within the mold 3, that is, the cooling capacity, does not differ between the upper and lower positions, and a uniform cooling effect can be obtained.

Even in this embodiment, by adjusting the power supplied to the electromagnetic field generating means 64 and 65 in response to fluctuations in static pressure near the boundary 17, the contact start position 47 and the separation start position 44 can be kept at approximately constant positions. can be maintained.

Note that in the present invention, the position detecting means 26 is not an essential requirement, and the position detecting means 26 may be omitted in some cases.

As described above, according to the present invention, a coil disposed near the boundary between the tundish nozzle and the mold is excited by AC power to squeeze the molten metal, and the current that excites the coil is Since the waveform has a waveform in which the rate of change is small when the current increases and becomes large when the current decreases, it is possible to reduce the negative squeezing force acting on the molten metal as much as possible. This makes it possible to efficiently squeeze the molten metal.

Further, in the present invention, the level of molten metal in the tundish is detected by the detection means, and when this level rises, the electromagnetic force generated by the coil is increased, and when the level falls, the electromagnetic force is decreased. Since the diameter of the molten metal is adjusted as follows, the rate at which the diameter of the molten metal is reduced can be kept almost constant, and therefore the position 44 where the molten metal peels off from the tundish nozzle and the point where the molten metal starts contacting the inner surface of the mold tube. This makes it possible to keep the position 47 constant. As a result, the length of the cooling zone within the mold becomes constant, and therefore the solidification heat of the molten metal becomes constant, achieving the excellent effect that a homogeneous slab can be obtained.

[Brief explanation of the drawing]

FIG. 1 is an overall system diagram of an embodiment of the present invention, FIG. 2 is an enlarged sectional view of the vicinity of the mold 3, FIG. 3 is a perspective view for explaining the principle of reducing the diameter of the molten metal 12, and FIG. Figure 3a is a diagram showing the relationship between exciting current and aperture force. FIG. 4 is a cross-sectional view for explaining the force acting on the molten metal whose diameter is reduced, and FIG. 5 is a cross-sectional view of the second coil 35.
6 is an enlarged sectional view of the position detection means 26, FIG. 7 is a simplified block diagram showing the configuration of the control device 24, and FIG. 8 is another embodiment of the present invention. 9 is a front view of still another embodiment of the present invention, FIG. 10 is a sectional view of another embodiment of the present invention, and FIG. 11 is a static pressure distribution near the boundary 17. FIG. 12 is a distribution diagram showing electromagnetic force. 3...mold, 12...molten metal, 14...
Tandate nozzle, 18, 64, 65... Electromagnetic field generating means, 26... Position detecting means, 44...
Separation start position, 47...Contact start position, 52,6
0...Load cell.

Claims (1)

[Claims] 1. A means for detecting the level of molten metal in the tundish is provided, a coil is disposed near the boundary between the tundish nozzle and the mold, and the coil is excited by alternating current power, and the electromagnetic The current that squeezes the molten metal by force and excites the coil has a waveform whose time rate of change is small when the current increases and becomes large when the current decreases, and the coil increases the electromagnetic force when the level increases. , a horizontal continuous casting method characterized by adjusting the supplied power to reduce the electromagnetic force when the level drops.