JP3124217B2 - Flow controller for molten metal - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION The present invention relates to a method for agitating and driving a molten metal by an electromagnet arranged opposite to an upper surface of the molten metal,
Further, the present invention relates to an electromagnetic stirrer having a function of applying braking to a downward flow of the molten metal by another electromagnet disposed below the meniscus with the molten metal interposed therebetween.

[0002]

2. Description of the Related Art In continuous casting, for example, molten steel is poured into a mold from a tundish, and the molten steel is drawn from the mold wall while being gradually cooled. If the temperatures on the mold wall surfaces at the same height are not uniform, surface cracks and shell ruptures are likely to occur. In order to improve this, conventionally, molten steel was placed in a mold parallel to its upper surface using a linear motor.
Proposal of flow driving along the mold wall surface (for example,
228645) or a proposal to reduce inclusions contained in molten steel by applying a brake to the molten steel flow flowing into the mold from the pouring nozzle 30 (for example, Japanese Patent Laid-Open No.
-258442).

Although the flow driving of molten steel disclosed in Japanese Patent Application Laid-Open No. 1-228645 has a certain effect, the circulating flow along the mold wall surface is disturbed by the flow of molten steel flowing into the tundish through the injection nozzle. . For this type of flow driving, a linear motor type electromagnet in which an electric coil is wound around each of a plurality of magnetic poles arranged along the long side of the mold is used. Bundled into
The phase and the phase of the three-phase power supply are connected in units bundled into each phase of the three-phase power supply having a phase shift of 120 °, and the voltage and / or frequency of the three-phase power supply is adjusted by an inverter or a cycloconverter. Speed is obtained.

FIG. 10A is a vertical sectional view of a mold, and FIG. 10B is a plan view of the upper surface (meniscus) of molten steel in the mold from above the mold. As shown by a solid arrow in FIG.
The molten steel flows into the mold through 9 and generates a molten steel flow,..., In the direction of the short side of the mold and slightly downward, and this flows on the short side of the mold, partly upward and others downward. The molten steel flow flowing upward generates a surface flow toward the nozzle 30 at the meniscus as shown by a solid line arrow in FIG. This surface flow tends to entrain the powder on the meniscus. On the other hand, when the molten steel changes to a solid, a gas (bubbles) such as CO is generated. In addition, if the molten steel stays in a part of the inner surface of the mold, the powder is likely to remain in the molten steel, and furthermore, it tends to cause seizure which causes breakout. In order to prevent these, it is preferable to form a stable rectification on the surface layer.

Therefore, conventionally, as shown in FIG. 13 (b), the linear motors 3RF and 3RL facing the outer surface of the mold along the long side of the mold are required to respond to the surface flow caused by the surface flow. An electromagnetic driving force in the direction indicated by the dotted arrow in FIG. 10B is applied to the molten steel, and the circulating flow along the mold inner wall 1 as shown by the two-dot chain arrow in FIG. About to happen. Due to this circulation flow, the floating of bubbles is promoted, powder is not entrained in the molten steel, the inner surface of the mold near the surface layer is wiped cleanly, and the stagnation of the molten steel is eliminated.

On the other hand, in an "electromagnetic brake device" proposed in Japanese Patent Application Laid-Open No. 3-258442, a pair of electromagnets having a width substantially equal to the width of the long side of the mold are opposed along the long side of the mold. It is installed and direct current flows through the electric coil.
The molten steel flowing in the constant magnetic field (DC magnetic field) generated by the electromagnet generates an electromotive force according to Fleming's right-hand rule, and a current circulating in the magnetic flux flows. The braking force acts to stop the flow, which brakes the downward molten steel flow shown in FIG. 10 (a), and suppresses the sinking of the inclusions accompanying the molten steel flow downward. .

[0007]

By the way, for example, FIG.
As shown in FIG. 3 (a), if one of the molten steel flows flowing out of the two outlets 19 of the pouring nozzle 30 into the space inside the mold is strong, and the other is weak, that is, if the symmetry is lost, this is accompanied by this. As for the surface flow, as shown in FIG. 13B, the surface flow (the molten steel flow side) located above the outflow port where the molten steel flow is weak is weakened.

[0008] Such turbulence (deviation) of the molten steel flow causes a high-temperature part and a low-temperature part in the molten steel MM in the mold. In other words, the temperature is high in a place where the molten steel flow is strong, and the temperature is low in a place where the flow is weak. If the temperatures on the mold wall surfaces at the same height are not uniform, surface cracks and shell ruptures are likely to occur.

Although the non-uniformity of temperature can be avoided to some extent by the molten steel driving by the linear motor, the pouring nozzle 3
The outflow characteristics of the outflow port 19 during the pouring change due to the adhesion of steel to the outflow port 19 during pouring, and when this change is made, particularly when the outflow characteristic difference between the two outflow ports becomes large, a considerable temperature deviation occurs. Further, a part of the molten steel flowing into the mold from the pouring nozzle 30 is directed downward as described above. However, the molten steel flow flowing downward, the inclusions intrude deep into the mold and are trapped inside the slab, This is a quality problem.

When the electromagnetic brake device is used alone, the symmetry that flows from the pouring nozzle 30 into the casting mold,
Alternatively, even if the effect of speed uniformity on the asymmetric molten steel flow is recognized, when used together with a molten steel driving device in a mold using a linear motor or the like, the molten steel flow (circulation flow) by the driving device is also braked. I will. That is, the electromagnetic brake
The key is to apply a braking force to the molten steel moving in a constant magnetic field to be applied.
In addition, the braking force acts on the surface flow.

SUMMARY OF THE INVENTION It is a first object of the present invention to prevent seizure of a slab to a mold and to prevent inclusions from being mixed into the slab, and an inner surface of the slab near a meniscus of molten steel in the mold. The second object is to effectively drive and drive the molten steel along the path and to suppress and uniform the downward flow, and the third object is to rectify and uniform the surface flow to strongly suppress the downward projecting flow. I do.

[0012]

According to the present invention, there is provided a molten metal flow control device comprising a plurality of four mold pieces, each of which is a quadrilateral, enclosing a molten metal along a first long piece (5F). The first set of electromagnet cores (10) arranged opposite to the upper surface of the molten metal near the first long piece (5F) and the first short piece (6R), and each slot for exciting this. A first set of electromagnets (LM) consisting of a combination of a plurality of electric coils (1Aa to 2Ca) inserted into
F); a plurality of slots are distributed along the second long piece (5L) of the mold piece, and are arranged opposite to the upper surface of the molten metal near the second long piece (5L) and the second short piece (6L). A second set of electromagnets (L) consisting of a combination of the second set of electromagnet cores (20) and a plurality of electric coils (4Ab to 5Cb) inserted into each slot to excite them.
ML); The first set of electromagnets (LMF) applies thrust in the direction along the first long piece (5F) to the upper surface of the molten metal, and the second set of electromagnets (LML) follows the second long piece (5L). AC voltage with a phase difference to give directional thrust to the upper surface of the molten metal is applied to each of the electric coils (1Aa-2Ca, 4Ab-5Cb) of the first and second sets of electromagnets (LMF, LML) A first pair of energizing means (20F1, 20L2); and a pair of at least one pair of magnetic poles (4AF, 4AL) opposed to each other under the meniscus of the mold piece with a molten metal interposed therebetween to excite them. A third electromagnet (4), which is a combination of electric coils (4CF, 4CL), and a third energizing means (20 V) for applying a current to the electric coil to apply a braking force to the molten metal.
D); In addition, in order to facilitate understanding, in parentheses, the symbols of the corresponding elements of the embodiment shown in the drawings and described below,
Added for reference.

According to this, looking down from above the mold,
There is a pair of electromagnets (LMF, LML) in at least one of two diagonal directions in a rectangular space surrounded by mold pieces (5F, 6L, 5L, 6R). The pair of electromagnets (LMF, LML) is used for injection nozzle (3
Since the thrust (indicated by a dotted arrow in FIG. 2) is applied to the molten metal in a direction opposite to the surface flow of the molten metal that appears due to the projecting flow of 0),
A relatively uniform surface flow is formed as shown by a solid line arrow in FIG. 2, and as a result, a stable circulating flow is obtained at a relatively constant speed as shown by a two-dot chain line arrow in FIG. .
As a result, the floating of bubbles is promoted, powder is not entangled in the molten metal, the inner surface of the mold near the surface layer is wiped cleanly, and the stagnation of the molten metal is eliminated. Further, as shown in FIG. 10A, molten metal (MM) is continuously supplied to the mold from the injection nozzle (30), and a part of the molten metal (MM) projects downward. A braking force is applied to the downward protruding flow by the set of electromagnets (4), and the protruding flow is suppressed. Therefore, the intrusion (entry) of foreign matter (inclusions) into the slab due to the projected flow of the molten metal (MM) is suppressed, and the internal quality of the slab is improved.

[0014]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The preferred embodiment of the present invention is a means for detecting the temperature distribution of a short piece of a mold (S31 to S3n, S41 to S4n);
The control means (43) gives an energization command for giving a high thrust to the molten metal near the location where the temperature is high to the first set of first and second energization means (20F1, 20L2). Thereby, a high thrust acts on the molten steel having a high temperature, a uniform surface circulation flow is generated, and the stirring effect is high, so that the temperature uniforming effect is high.

The relative relationship between the downward projecting flow component of the molten steel flow injected into the mold and the temperature of the mold piece, that is, if the flow velocity of the molten steel exiting from the nozzle is high, the flow that causes the surface flow,
The rise in mold strip temperature means an increase in the descending outflow component, because the downflow is strong, resulting in a high mold strip temperature and a strong downspout. The temperature distribution detecting means (S31 to S3n, S41 to S4n) detects this mold short piece, and the control means (43) issues an energization command to give a high braking force when the mold short side temperature is high. 20VD), whereby the third set of electromagnets (4) applies a high braking force to the downwardly projecting molten steel flow.

The increase in the braking force strongly dampens the downwardly projecting molten steel flow, thereby suppressing the intrusion (intrusion) of foreign matter (inclusions) into the slab and improving the internal quality of the slab.

Other objects and features of the present invention will become apparent from the following description of embodiments with reference to the drawings.

[0018]

FIG. 1 shows a linear motor L according to an embodiment of the present invention.
1 shows a longitudinal section of a continuous casting mold provided with MF (first set of electromagnets), LML (second set of electromagnets) and electromagnetic brake 4 (third set of electromagnets). Molten steel is injected into the mold from above through an injection nozzle 30 (not shown) downward (in the vertical direction z), and the meniscus (surface) of the molten steel MM is covered with powder PW. The mold is cooled by a water box (not shown) and cooling water flowing through a water flow path in the mold, and the molten steel MM gradually solidifies from the surface in contact with the mold, and the slab SB is continuously drawn out. As it is poured, there is always molten steel MM in the mold. Two linear motors LM are provided at upper positions of the molten steel MM so as to face the meniscus.
F and LML are provided, and these apply an electromagnetic force to a portion (surface layer area) immediately below the meniscus of the molten steel MM. An electromagnetic brake 4 is provided near the lower part of the mold, and applies an electromagnetic force (braking force) to the downward flow of molten steel. In the mold, the magnetic flux applied to the molten steel by the linear motors LMF and LML substantially does not reach the molten steel at the level of the electromagnetic brake 4.
Conversely, the magnetic flux applied by the electromagnetic brake 4 to the molten steel substantially does not reach the surface layer of the molten steel.

FIG. 2 shows a plane (upper surface) of the mold shown in FIG. The illustration of the electromagnetic brake 4 is omitted. In FIG. 2, 5F and 5L are first and second long pieces of a continuous casting mold, 6R and 6L are first and second short pieces, and molten steel is passed through an injection nozzle 30 in a space surrounded by these.
Injection is performed from the front side of the paper to the back side (from the top to the bottom in the vertical direction z). Each piece (5F, 5L, 6R, 6L)
Is a copper plate (1F, 1L, 3R, 3L) backed by a non-magnetic stainless steel plate (2F, 2L, 4R, 4L). In this embodiment, in order to drive the molten steel in the portion (surface layer area) immediately below the meniscus in the mold from the right to the left (in the direction from + y to -y) along the long piece 5L by a three-phase linear motor type electromagnet. In addition, first and second electromagnets LMF and LML are arranged on the opposing lines with the injection nozzle 30 as the center, facing the upper surface of the molten steel in the mold (5F, 5L, 6R, 6L).

FIG. 4 shows an enlarged cross section taken along the line II-II of FIG. 1, that is, a cross section of the electromagnetic brake 4 cut horizontally. The electromagnetic brake 4 applies an electromagnetic force to the molten steel passing below the mold, and applies a braking force to the molten steel downward projecting flow. The electromagnetic brake 4 is disposed so as to horizontally sandwich the mold at the lower part of the mold. Referring to FIG. 4, the electromagnet of the electromagnetic brake 4 has a width substantially equal to the width of the mold long pieces 5F and 5L. The magnetic poles 4AF and 4AL are provided facing each other with the mold long pieces 5F and 5L interposed therebetween, and the coils 4CF and 4AL are provided on the outer periphery of the magnetic poles.
CL is wound. Also, the left and right yoke 4BL, 4BR
The right and left magnetic poles are connected to form a closed magnetic path. Therefore, the electromagnetic brake 4 applies a magnetic field between the magnetic poles 4AF and 4AL in the horizontal direction (x-axis direction in FIG. 4), and the molten steel MM descends (z-axis direction) in this horizontal magnetic field. Since the molten steel as a conductor crosses the horizontal magnetic field, a braking force is applied to the molten steel to stop the movement.

FIG. 3A shows a first set of electromagnets LMF.
2 shows an enlarged vertical cross section (enlarged cross section taken along line 2A-2A in FIG. 2).
In this embodiment, the electromagnet core 10 has six slots, each of which has an electric coil 1Aa to 2Ca.
Is inserted. The electromagnet core 10 and the electric coils 1Aa to 2Ca are cooled and covered with a heat-resistant cover, but the cooling structure and the cover are not shown. The electromagnet core 10 is in a comb shape having slots on the lower surface, an electric coil is inserted into each slot, a magnetic pole is provided between the slots, and the lower end surface thereof is a continuous casting mold (5F, 5L,
6R, 6L). The electric coil is wound around the core 10. FIG. 3 (b)
Next, an enlarged vertical section of the second electromagnet LML (2B-2B in FIG. 2)
(Enlarged section taken along line). The second electromagnet LMF is also the first electromagnet L
It has the same structure as the ML, and its electric coil is also a body winding.

The linear motors LMF and LML are for applying a thrust indicated by dotted arrows in FIG. 2 to the molten steel MM. In this embodiment, the first linear motor LMF and the second linear motor LML To generate different thrusts,
A different level of current is applied to each linear motor. This content will be described later.

FIG. 5A shows electric coils 1Aa to 2Ca and 4Ab of the linear motors LMF and LML shown in FIG.
5Cb and the connection with the power supply circuit are shown. FIG. 5B shows the electric coil connection of the electromagnetic brake 4 and the connection with the power supply circuit. The connection between the linear motors LMF and LML shown in FIG. 5A is of two poles (N = 2), and a three-phase alternating current (M = 3) is supplied to the electric coil.
For example, the electric coils 1Aa to 2Ca are arranged in the order of u, u, V, V, w, w, U, U, v,
v, W, and W. “U” represents the U-phase normal-phase energization of three-phase alternating current (current energization as it is), “u” represents the U-phase reverse-phase energization (energization 180 degrees out of phase with the U-phase), and the electric coil “U” ] Is applied with a U phase at the beginning of the winding, whereas the electric coil "u" is applied with a U phase at the end of the winding.
It means that a phase is applied. Similarly, “V” indicates V-phase positive-phase energization of three-phase AC, “v” indicates V-phase negative-phase energization,
“W” indicates the W-phase positive-phase energization of the three-phase AC, and “w” indicates the W-phase reverse-phase energization. Terminals U11, V shown in FIG.
11 and W11 are power supply connection terminals of the electric coils 1Aa to 2Ca of the first linear motor LMF, and a terminal U1
2, V12 and W12 are power connection terminals of the electric coils 4Ab to 5Cb of the second linear motor LML.

FIG. 5B shows the electric coil connection of the electromagnetic brake 4 and the magnetic poles formed thereby. DC is supplied to the electric coils 4CF and 4CL from a DC power supply 20VD to apply a magnetic field in a certain direction to the molten steel in the mold, but as seen from the arrangement structure of the electromagnetic brake 4, a direction perpendicular to the long side of the mold is obtained. A uniform horizontal magnetic field is applied to (x).

FIG. 6 shows a configuration of a first set of first power supply circuits 20F1 for supplying a three-phase alternating current to the electric coils 1Aa to 2Ca of the first linear motor LMF. The three-phase AC power supply (three-phase power line) 21 has a thyristor bridge 22A1 for DC rectification.
Is connected, and its output (pulsating flow) is
It is smoothed by A1 and the capacitor 26A1. The smoothed DC voltage is applied to a power transistor bridge 27A1 for forming a three-phase AC, and the U-phase of the three-phase AC output from the power transistor bridge 27A1 is connected to a power connection terminal U11 shown in FIG.
Phase to the power connection terminal V11 and W phase to the power connection terminal W
11 is applied.

The electric coil 1A of the first linear motor LMF
a to 2Ca, a coil voltage command value VdcA1 for generating a thrust indicated by a dotted arrow in FIG. 2 is given to a phase angle α calculator 24A1, and the phase angle α calculator 24A1 outputs a conduction phase angle α corresponding to the command value VdcA1. (Thyristor trigger-phase angle) is calculated, and a signal representing this is supplied to the gate driver 23A1. The gate driver 23A1 starts the phase count of the thyristor of each phase from the zero cross point of each phase and triggers conduction at the phase angle α. As a result, the DC voltage indicated by the command value VdcA1 is applied to the transistor bridge 27A1. On the other hand, the three-phase signal generator 31A1 outputs the frequency specified by the frequency command value Fdc (50 in this embodiment).
Hz), and generates a constant-voltage three-phase AC signal,
Give to A1. A triangular wave generator 30A1 supplies a constant voltage triangular wave of 3 KHz to the comparator 29A1. When the U-phase signal is at a positive level, the comparator 29A1 is at a high level H (transistor on) when the level is equal to or higher than the level of the triangular wave provided by the triangular wave generator 30A1, and at a low level L (transistor off) when the level is lower than the level of the triangular wave. Signal of U
To the positive section of the phase (to the U-phase positive voltage output transistor)
When the U-phase signal is at a negative level, a high-level signal is output when the U-phase signal is below the level of the triangular wave provided by the triangular-wave generator 30A1, and when the U-phase signal exceeds the level of the triangular wave, a low-level signal is output. , To the U-phase negative section (to the U-phase negative voltage output transistor). The same applies to the V-phase signal and the W-phase signal. The gate driver 28A1 energizes each transistor of the transistor bridge 27A1 in response to the signals addressed to each phase, positive and negative sections.

Thus, the power supply connection terminal U11 has 3
A U-phase voltage of phase alternating current is output, a similar V-phase voltage is output to a power supply connection terminal V11, and a similar W-phase voltage is output to a power supply connection terminal W11. The level between -k is determined by the coil voltage command value VdcA1.
In this embodiment, the frequency of the three-phase voltage is a frequency command value F
It is 50 Hz by dc. That is, 50 Hz of the peak voltage value (thrust) specified by the coil voltage command value VdcA1
3 and the first three-phase AC voltage shown in FIG.
It is applied to the electric coils 1Aa to 2Ca of the linear motor LMF.

FIG. 7 shows the electric coil 4 of the second linear motor.
The structure of the 1st set 1st power supply circuit 20L2 which flows three-phase alternating current to Ab-5Cb is shown. The configuration of the power supply circuit 20L2 is the same as that of the above-described 20F1, but the coil voltage command value (VdcB2) is different.

That is, the coil voltage command value VdcB2 at which the electric coils 4Ab to 5Cb of the second linear motor LML generate a thrust indicated by the dotted arrow in FIG.
4B2. These coil voltage command values Vdc
A1 (FIG. 6) and the coil voltage command value VdcB2 (FIG. 7) are output from the computer 43 shown in FIG.
Give to 0F1 and 20L2.

FIG. 8 shows an electric coil 4C of the electromagnetic brake 4.
5 shows a configuration of a second set of power supply circuits 20VD for supplying a direct current to F and 4CL. A thyristor bridge 22D1 for DC rectification is connected to the three-phase AC power supply (three-phase power line) 21,
The output (pulsating current) is smoothed by the inductor 25D1 and the capacitor 26D1. The smoothed DC voltage is applied to the terminals 4P and 4M of the electromagnetic brake shown in FIG.

Electric coils 4CF, 4C of electromagnetic brake 4
L is a coil voltage command value VdcD3 for generating a braking force for suppressing the downflow of molten steel is given to a phase angle α calculator 24D1, and the phase angle α calculator 24D1 determines a conduction phase angle corresponding to the command value VdcD3. .alpha. (thyristor trigger-phase angle) is calculated, and a signal representing this is supplied to gate driver 23D1. The gate driver 23D1 starts the phase count of the thyristor of each phase from the zero cross point of each phase and triggers conduction at the phase angle α. Thereby, the power supply circuit 20
The DC voltage indicated by the command value VdcD3 is output to the terminal VD of VD. This coil voltage command value VdcD3 is provided from a computer 43 shown in FIG. FIG. 9 shows the backs of the mold short pieces 6L and 6R shown in FIG. These short pieces 6L, 6R include thermocouples S31 to S3n and S41.
To S4n are arranged at regular intervals in a row in the slab drawing direction (height direction; vertical direction), and each thermocouple penetrates the backing stainless steel plate and is slightly inside the copper plate (the surface in contact with the molten steel). Part) temperature. That is, the signal processing circuits 41A and 41B generate an analog signal (detection signal) representing the temperature detected by the thermocouple and supply the analog signal to the analog gate 42.

The computer 43 includes an analog gate 42.
Of the thermocouples S31 to S3n and S41
To S4n are sequentially A / D converted and read, and the highest temperature value Tm1L1 and the next highest temperature value Tm2L1 among the detected temperatures of the thermocouples S31 to S3n are extracted by the high temperature value extraction processing 44, and , The highest temperature value Tm1R1 and the next highest temperature value Tm2R1 among the detected temperatures of the thermocouples S41 to S4n. Then, the representative temperature (Tm1L1-Tm2L1) × 0.7 + Tm2L1 of the short piece 6L is calculated, and the representative temperature (Tm1R1-Tm2R1) × 0.7 + Tm2R1 of the short piece 6R is calculated.

For controlling the flow velocity of the surface layer flow of the molten steel, the difference between the two, ie, the representative temperature difference between the short pieces 6R and 6L (Tm1R1-Tm2R1) × 0.7 + Tm2R1− (Tm1L1-Tm2L1) × 0.7−Tm2
By calculating L1, VdcA1 = (representative temperature difference × A) + B (A and B are coefficients) and VdcB2 = − (representative temperature difference × A) + B are calculated. When the representative temperature difference is a negative value (the temperature of the short piece 6L is higher), VdcA1 =
-(Absolute value of representative temperature difference x A) + B is calculated and Vdc
B2 = (absolute value of representative temperature difference × A) + B.

VdcA1 is the electric coil 1A on the short piece 6R side.
a to 2Ca (first linear motor LMF; FIG. 2) are current level (thrust) command values, and VdcB2 is a short piece 6L.
Side electric coils 4Ab to 5Cb (second linear motor LM
L; a current level (thrust) command value for FIG. 2).
These command values are such that the representative temperature difference is a positive value ((a) in FIG. 13).
When the temperature of the short piece 6R is higher due to the unbalanced flow as shown in FIG. 1), the electric coil 1 of the first linear motor LMF
The three-phase AC current level flowing through Aa to 2Ca is increased to apply a strong thrust (dotted arrow in FIG. 11B), and the three-phase AC current level flowing through the electric coils 4Ab to 5Cb of the second linear motor LML is reduced. Conversely, when the representative temperature difference is a negative value (the temperature of the short piece 6L is higher), the three-phase AC current level flowing through the electric coils 4Ab to 5Cb of the second linear motor LML is increased. This means that a strong thrust (dotted arrow in FIG. 11C) is applied to reduce the three-phase AC current level flowing through the electric coils 1Aa to 2Ca of the first linear motor LMF to weaken the thrust.

In order to control the flow velocity of the downflow of molten steel, the sum of the two, that is, the sum of the representative temperatures of the short sides 6L and 6R (Tm1L1-Tm2L1) × 0.7 + Tm2L1 + (Tm1R1-Tm2R1) × 0.7 + Tm2
R1 is calculated, and VdcD3 = representative temperature sum × C is calculated (C
Is a coefficient). If VdcD3 is large, that is, one or both of the short piece temperatures are high, it means that the flow velocity of the molten steel descending flow (protruding flow) is high, and the time required for floating the inclusions becomes insufficient. Therefore, the level of the direct current flowing through the electric coils 4CF and 4CR of the electromagnetic brake 4 is increased to increase the braking force applied to the descending flow, and the descending speed of the descending flow is limited (the descending flow is made uniform) to remove the inclusions. Promote ascent. Since the braking force applied to the molten steel is higher as the flow velocity of the molten steel is higher, the higher the descending flow, the stronger the braking force acts, and the lowering of the velocity is large, the flow velocity of the descending flow is uniform, and the DC current level is increased. By doing so, the uniformization and the suppression of the flow velocity act strongly.

As described above, for example, when the protruding flow shown in FIG. 10A is substantially symmetrical with respect to the nozzle 30, the temperatures of the short pieces 6R and 6L become substantially the same, and the surface flow becomes the same as that of FIG. 2 and the solid arrow in FIG. 2, the nozzle 30 is symmetrical. In this case, VdcA1 = VdcB2, and the electric coils 1Aa to 2Ca on the short piece 6R side and the electric coil 4Ab on the short piece 6L side
To 5Cb are substantially equal, and the first linear motor
The motor LMF and the second linear motor LML are shown in FIGS.
As shown by the dotted arrow in (b), a thrust having substantially the same strength and opposite directions is applied to the molten steel. Thereby, the actual surface flow of the molten steel becomes a difference indicated by a two-dot chain line in FIG.
The flow velocity distribution shown by the two-dot chain line in FIG. Thereby, the floating of bubbles is promoted, the powder is not entrained in the molten steel, the inner surface of the mold near the surface layer is wiped clean, and the stagnation of the molten steel is eliminated.
That is, the temperature distribution of the molten steel is made uniform, and seizure of the molten steel is suppressed.

As shown in FIG. 13 (a), when the protruding flow toward the short piece 6R is strong and the protruding flow toward the short piece 6L is weak, the temperature of the short piece 6R increases and the temperature of the short piece 6L decreases. As shown by solid arrows in FIG. 13B, the surface flow between the nozzle 30 and the short piece 6R is strong and the surface flow between the nozzle 30 and the short piece 6L is weak. In this case, VdcA1> VdcB2. The energization level of the electric coils 1Aa to 2Ca on the short piece 6R side is high, and the energization level of the electric coils 4Ab to 5Cb on the short piece 6L side is low. The first linear motor LMF has a strong thrust and the second linear motor has a strong thrust. LML gives weak thrust to molten steel. As a result, FIG.
(B), the first linear motor L
The MF gives strong thrust to the second linear motor LML and the second linear motor LML gives weak thrust to the molten steel.

As a result, a circulating flow shown by a two-dot chain line in FIG. In this case, the circulating flow has a high speed on the high-temperature short piece 6R side and a low-speed on the low-temperature short piece 6L side. The high temperature molten steel on the short piece 6R side is conveyed to the low temperature short piece 6L side to reduce the temperature difference. Due to this circulation flow, the floating of bubbles is promoted, powder is not entrained in the molten steel, the inner surface of the mold near the surface layer is wiped cleanly, and the stagnation of the molten steel is eliminated.
That is, the temperature distribution of the molten steel is made uniform, and seizure of the molten steel is suppressed.

Conversely, when the protruding flow toward the short piece 6R is weak and the protruding flow toward the short piece 6L is strong, the temperature of the short piece 6R is reduced and the temperature of the short piece 6L is increased, and the surface flow is generated between the nozzle 30 and the short piece 6R. The surface flow is weak, and the surface flow between the nozzle 30 and the short piece 6L becomes strong, in this case, VdcA1 <Vdc
B2, the electric coils 1Aa to 2Ca on the short piece 6R side
Of the electric coil 4Ab ~ of the short piece 6L side
The 5Cb energization level increases, and the first linear motor LM
F gives a weak thrust and the second linear motor LML gives a strong thrust to the molten steel. As a result, the first linear motor LMF exerts a weak thrust, as indicated by a dotted arrow in FIG.
The second linear motor LML gives a strong thrust to the molten steel.

As a result, a circulating flow shown by a two-dot chain line in FIG. In this case, the circulating flow has a low speed on the low temperature short piece 6R side and a high speed on the high temperature short piece 6L side. The high-temperature molten steel on the short piece 6L side is conveyed to the low-temperature short piece 6R side to reduce the temperature difference. Due to this circulation flow, the floating of bubbles is promoted, powder is not entrained in the molten steel, the inner surface of the mold near the surface layer is wiped cleanly, and the stagnation of the molten steel is eliminated.
That is, the temperature distribution of the molten steel is made uniform, and seizure of the molten steel is suppressed.

When the flow of molten steel flowing downward from the outlet 19 shown in FIG. 10A is strong, the temperature of the two short pieces of the mold becomes higher, and the representative temperature sum detected by the two short pieces increases. Therefore, the voltage command value VdcD3 to the power supply circuit 20VD increases, and the DC voltage applied to the electromagnetic brake 4 increases. As a result, the braking force of the electromagnetic brake 4 against the molten steel descending flow in the mold increases, and the molten steel descending speed decreases. When the molten steel flow going downward from the outlet 19 shown in FIG. 13A is stronger than the molten steel flow, the temperature of the mold short piece 6R becomes higher, and the sum of the representative temperatures detected by the two short pieces rises. The voltage command value VdcD3 to the circuit 20VD increases, and the DC voltage applied to the electromagnetic brake 4 increases. As a result, the braking force of the electromagnetic brake 4 against the molten steel descending flow in the mold increases, and the molten steel descending speed decreases. When the molten steel flow is stronger than the molten steel flow, the temperature of the mold short piece 6L becomes higher and the representative temperature sum detected by both short pieces increases, so that the voltage command value VdcD3 to the power supply circuit 20VD increases, and The DC voltage applied to the key 4 increases. As a result, the braking force of the electromagnetic brake 4 against the molten steel descending flow in the mold increases, and the molten steel descending speed decreases. That is, a protruding downward flow is prevented, the time required for floating the inclusions to the meniscus is secured, and a product with improved internal quality can be manufactured.

In the above-described embodiment, the temperature of the short pieces 6R and 6L is detected by a thermocouple, and the strength (flow velocity) of the surface flow and the descending flow is determined in accordance with the strength of the protruding flow from the injection nozzle 30 into the mold. Electromagnetic thrust for detecting and generating a stable circulating flow or descending flow is applied to molten steel by the first linear motor LMF, the second linear motor LML, and the electromagnetic brake 4. However, for example, using a flow rate sensor as shown in FIG.
Surface flow Vsa at the position of spa and surface flow Vs at the position of Vspb
b, or the lowering speed Vva of the Vvsa position in FIG.
And the lowering speed Vvb of the Vvsb position may be detected, and the current level index values VdcA1, VdcB2, and VdcD3 may be respectively controlled.

In the above-described embodiment, a pair of linear motors LMF and LML is used. In the second embodiment of the present invention, two pairs are used as shown in FIG. It may be arranged. In this case, the first pair of linear motors LMF
1 and LML1 control the power supply level in the same manner as the LMF and LML of the above-described embodiment, but the second pair of linear motors LM
F2, LML2, as indicated by the dotted arrow in FIG. 12B, reverse the thrust direction to that of the first pair, and furthermore, the increase and decrease of the energization level with respect to the detected temperature are the same as those of the first pair. However, since the thrust direction is the same as the direction of the surface flow generated by the nozzle injection flow, the thrust value (power supply level) is set smaller than that of the first pair. According to the second embodiment, the surface circulation flow (FIG.
The flow rate of 0 (b) shown by a two-dot chain line) can be made higher than in the first embodiment.

Therefore, the temperature of the molten steel in the surface layer can be made more uniform. Since the descending flow partially increases as the flow velocity in the surface layer increases, the energizing level of the electromagnetic brake 4 is also increased.

[Brief description of the drawings]

FIG. 1 is a longitudinal sectional view showing a section of a continuous casting mold to be controlled according to a first embodiment of the present invention.

FIG. 2 is a plan view showing a configuration of a mold and a linear motor portion of FIG.

FIG. 3 (a) shows a linear motor LMF 2 shown in FIG.
FIG. 3 is an enlarged cross-sectional view taken along line A-2A, and FIG. 2 (b) is an enlarged cross-sectional view taken along line 2B-2B of the linear motor LML shown in FIG.

FIG. 4 is an enlarged cross-sectional view of the electromagnetic brake 4 shown in FIG.

FIG. 5 is an electric circuit diagram showing connection of the electric coils shown in FIGS. 2 and 3.

FIG. 6 is an electric circuit diagram showing a first set of first power supply circuits for applying a three-phase AC voltage to electric coils of the first set of linear motors LMF shown in FIG. 2;

FIG. 7 is an electric circuit diagram showing a first set of second power supply circuits for applying a three-phase alternating current to electric coils of a second set of linear motors LML shown in FIG. 2;

8 is an electric circuit diagram showing a second set of power supply circuits for applying a DC voltage to the electric coil of the electromagnetic brake 4 shown in FIG.

9 is a block diagram showing the backs of the short pieces 6L and 6R of the casting mold shown in FIG. 2, the electric circuit connected to the thermocouples provided on them, and the output of the computer 43.

10A is a cross-sectional view of molten steel in a mold, and FIG. 10B is a plan view showing a surface layer flow in a meniscus of the molten steel in the mold.

FIG. 11 (a) is a plan view showing the upper surface of molten steel in a mold,
(B) and (c) are plan views showing surface flows (dotted arrows) induced in the molten steel in the mold by the linear motors LMF and LML.

FIG. 12 (a) is a plan view showing a surface flow caused by injection of molten steel from a pouring nozzle in a meniscus of molten steel in a mold, and FIG. 12 (b) is a surface flow to be generated in a second embodiment of the present invention. Is a plan view indicated by a dotted arrow, and (c) is a plan view indicated by a solid line arrow indicating the Bertle sum of the surface flow generated by the injection of molten steel from the pouring nozzle and the surface flow generated by the thrust of the linear motor of the second embodiment. is there.

FIG. 13A is a cross-sectional view of molten steel in a mold, and FIG. 13B is a plan view showing a surface flow (by molten steel injection) in a meniscus of the molten steel in the mold and an arrangement of a conventional linear motor.

[Explanation of symbols]

1: inner wall of mold 4: electromagnetic brake 10: first linear motor core 20: second linear motor core 19: outlet 30: injection nozzle 43: computer 1Aa to 2Ca: first linear motor Electric coils 4Ab to 5Cb: electric coils of the second linear motor 1F, 1L, 3L, 3R: copper plates 2F, 2L, 4L, 4R: non-magnetic stainless steel plates 4AF, 4AL: electromagnetic brake cores 4BF, 4BL : Electromagnetic brake / yoke 4CF, 4CL: Electromagnetic brake coil 5F, 5L: Long piece 6R, 6L: Short piece 20F1, 20L2, 20VD: Power supply circuit 3RF, 3RL, LMF, LML: Linear motor MM : Molten steel PW: Powder SB: Cast slab S31 ~ S3n, S41 ~ S4n:
Thermocouple U11, V11, W11 / U12, V12, W12, 4P, 4M: Power supply connection terminal

────────────────────────────────────────────────── ─── Continuation of the front page (56) References JP-A-7-290214 (JP, A) JP-A-7-256412 (JP, A) JP-A-7-246445 (JP, A) JP-A-7-290 241649 (JP, A) JP-A-61-140355 (JP, A) JP-A-3-258442 (JP, A) JP-A-1-228645 (JP, A) JP-A 8-197196 (JP, A) JP-A-8-243698 (JP, A) JP-A-8-108257 (JP, A) JP-A-7-246444 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) B22D 11/115 B22D 11/04 311 B22D 11/16 B22D 11/16 104

Claims (5)

(57) [Claims] A plurality of slots are distributed along a first long piece of four mold pieces on each side of a quadrilateral surrounding a molten metal, wherein a plurality of slots are distributed near the first long piece and the first short piece. A first set of electromagnets comprising a combination of a first set of electromagnet cores disposed opposite to the upper surface of the molten metal and a plurality of electric coils inserted into respective slots to excite the cores; A plurality of slots are distributed along the strip, and a second set of electromagnet cores disposed opposite to the upper surface of the molten metal near the second long piece and the second short piece, and inserted into each slot to excite the core. A second set of electromagnets composed of a combination of a plurality of electric coils; the first set of electromagnets provides a thrust in a direction along the first long piece to the upper surface of the molten metal, and the second set of electromagnets along the second long piece. AC voltages having a phase difference for applying a thrust in the directional direction to the upper surface of the molten metal are applied to the first set and the second set. A first set of energizing means for applying to each of the electric coils of the electromagnet; and at least one pair of opposed magnetic poles with a molten metal interposed therebetween under the meniscus of the mold piece, and electricity for exciting the magnetic poles. A molten metal flow control device, comprising: a third set of electromagnets formed of a combination of coils; and a second set of energizing means for applying a current to the electric coils to apply a braking force to the molten metal. 2. A plurality of slots distributed along a first long piece of four mold pieces on each side of a quadrilateral surrounding a molten metal, wherein a plurality of slots are distributed near the first long piece and the first short piece. A first electromagnet composed of a combination of a first electromagnet core opposed to the upper surface of the molten metal and a plurality of electric coils inserted into each slot to excite the first electromagnet core; a direction in which the first electromagnet core is along the first long piece Applying an AC voltage having a phase difference for applying the thrust to the upper surface of the molten metal to each of the electric coils of the first electromagnet.
Energizing means; a second electromagnet core having a plurality of slots distributed along the second long piece of the mold piece and disposed opposite to the upper surface of the molten metal near the second long piece and the second short piece, and exciting the second electromagnet core A second electromagnet composed of a combination of a plurality of electric coils inserted into each slot to perform the operation; an alternating current having a phase difference so that the second electromagnet core gives a thrust in a direction along the second long piece to the upper surface of the molten metal. Second energizing means for applying a voltage to each of the electric coils of the second electromagnet; and at least one pair of magnetic poles opposed to each other with a molten metal interposed below the meniscus of the mold piece. A flow control device for molten metal, comprising: a third electromagnet formed by a combination of electric coils for applying a current to apply a braking force to the molten metal to the electric coil; 3. The flow of molten metal of the molten metal surrounded by the mold pieces, directly below the first and second electromagnet cores, resulting from the injection of new molten metal from the injection nozzle into the molten metal surrounded by the mold pieces. Means for measuring the strength; and when the flow of molten metal directly below the first electromagnet core is stronger than that immediately below the second electromagnet core, the current level of the electric coil of the first electromagnet is increased via the first and second energizing means. Raise the current level of the electric coil of the second electromagnet, and vice versa, decrease the current level of the electric coil of the first electromagnet, raise the current level of the electric coil of the second electromagnet, and increase the first and / or second electromagnet core 3. The molten metal flow control device according to claim 2, further comprising: thrust control means for increasing the current level of the electric coil of the third electromagnet via the third energizing means when the molten metal flow immediately below is strong. 4. The measuring means is a temperature sensor for detecting the temperature of the first and second short pieces; the thrust control means is configured to detect the temperature of the electric coil of the first electromagnet when the first short piece is higher in temperature than the second short piece. Increasing the current level and decreasing the current level of the electric coil of the second electromagnet, and vice versa, decreasing the current level of the electric coil of the first electromagnet and increasing the current level of the electric coil of the second electromagnet; The molten metal flow control device according to claim 3, wherein the current level of the electric coil of the third electromagnet is increased when the two short pieces are at a high temperature, and the current level of the electric coil of the third electromagnet is decreased when the two short pieces are hot. 5. The temperature sensor of each short piece includes a plurality of temperature detecting elements distributed in the direction of drawing the slab; the thrust control means picks out the high temperature detected by them and outputs it to each short piece. The molten metal flow control device according to claim 4, wherein the temperature is a representative temperature.