JPH05138320A - Method for pouring molten metal into mold for continuous casting - Google Patents

Abstract

PURPOSE:To prevent the clogging of an immersion nozzle by conducting electric current into a control coil provided near a suction hole of the immersion nozzle and holding molten metal stream with the generated electromagnetic force. CONSTITUTION:Induction current generated by conducting the electric current is caught with a transmitting coil 10 and a receiving coil 11 embedded near the suction hole and at the lower part in the immersion nozzle 4, the conductive current into the control coil 7 so as to keep gap between the molten metal stream near the suction hole and the inner wall of the nozzle to the suitable range. Then, by action of the electromagnetic force generated with this current conduction, the molten metal stream near the suction hole is suitably kept. By this method, the clogging of the immersion nozzle can be prevented.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for pouring molten metal into a continuous casting mold, and more particularly to a method for pouring molten metal into a wide mold such as a slab mold by a dipping nozzle.

[0002]

2. Description of the Related Art In the continuous casting method, molten metal (molten metal) is poured into a cylindrical mold having openings at the top and bottom, and the water is cooled by contacting it with the inner wall of the mold which is cooled by water, and the outside is covered with a solidified shell. Obtained cast slab, further cooling while continuously pulling it from the lower opening of the mold, cut into a predetermined size after solidification has progressed to the inside, the material in the post-process such as rolling It is a method of obtaining a product slab that becomes

Pouring of molten metal into the mold (pouring) is performed through a pouring nozzle extending from a tundish which is arranged above the casting mold and stores the molten metal. 2. Description of the Related Art An immersion nozzle has been widely used in which the tip of the mold is immersed in a molten metal that remains inside a mold for a predetermined length to prevent contact between the molten metal flowing inside and the outside air.

[0004]

By the way, in the pouring of the casting mold for continuous casting performed as described above, the base metal of the molten metal flowing inside the immersion nozzle and the alumina contained in the molten metal adhere to the inner wall. There is a problem of accumulation and clogging of the flow path, so-called nozzle clogging, and the nozzles and tundish are forced to be replaced frequently in order to continue the operation, which is a factor that hinders the productivity of the continuous casting method. Is becoming

The nozzle clogging is apt to occur at a portion where the molten metal flow is stagnant, and is particularly remarkable in the vicinity of the opening end (suction port) of the immersion nozzle inside the tundish, and for a wide slab. The dipping nozzle for pouring molten metal into the mold is provided with a plurality of discharge ports that open toward both sides in the width direction of the mold, and the molten metal flowing inside changes the flow direction toward both discharge ports. Therefore, remarkable nozzle clogging also occurs near these discharge ports.

As conventional measures against such nozzle clogging, a method of pouring molten metal while blowing argon gas into the immersion nozzle, and a method of pouring molten metal while heating the immersion nozzle (Japanese Patent Laid-Open No. 54-6816). Gazette). However, all of these methods are intended for the middle part of the immersion nozzle, whereas as described above, the actual nozzle clogging is concentrated near the suction port on the proximal side and the discharge port on the distal side, It is difficult to effectively eliminate these nozzle clogging.

Further, Japanese Patent Laid-Open No. 60-250862 discloses a method of preventing nozzle clogging near the suction port. This method applies a high-frequency current to a coil provided near the suction port, and the action of a magnetic field generated inside the nozzle by this causes the flow of the molten metal, which is a conductor, to be kept floating from the inner wall of the nozzle. It is intended to prevent the occurrence of nozzle clogging by pouring molten metal to eliminate direct contact between the inner wall of the nozzle and the molten metal.

However, in carrying out this method, the gap between the inner wall of the nozzle and the molten metal differs depending on the amount of molten metal poured into the mold, the amount of storage inside the tundish, the inner diameter of the nozzle, etc. However, it is difficult to always ensure a proper gap during operation, and in reality, contact of the molten metal with the inner wall of the nozzle occurs, and there is a drawback that the occurrence of nozzle clogging cannot be prevented.

On the other hand, since the nozzle clogging near the discharge port is caused by the change in the flow direction at the tip of the nozzle, the entire nozzle tip surface is used as the discharge port and the molten metal flow is made linear. Will be alleviated. However, when using such an immersion nozzle, the flow of pouring reaches the deep part of the mold, and as a result of being difficult to float on the surface of the molten metal retained in the mold, the surface temperature of the retained molten metal decreases, and at the surface However, there is a problem in that the quality of the product slab is deteriorated due to the impeding of the skinning and the poor slag formation of the powder supplied to the surface.

The present invention has been made in view of the above circumstances, and when pouring molten metal into a wide mold such as a mold for continuous casting, particularly a mold for slabs, by using an immersion nozzle, clogging occurs in each part of the nozzle. It is an object of the present invention to provide a pouring method capable of effectively avoiding the above and maintaining a good pouring state for a long period of time.

[0011]

According to a first aspect of the present invention, there is provided a continuous casting mold pouring method for pouring molten metal into a continuous casting mold by a dipping nozzle extending from a tundish above the casting mold. In the method of pouring, a control coil is provided around the suction port of the immersion nozzle that opens inside the tundish, and an electromagnetic force toward the center of the suction port is generated by energizing the control coil. The molten metal flow in the vicinity is held with a gap between it and the inner wall of the immersion nozzle, and a pair of coils is embedded in the vicinity of the suction port and at a position separated by a predetermined length below the suction port. A low-frequency exciting current is passed through the coil to generate a magnetic field, and the induced current induced in the other coil by the magnetic field is detected, and the phase difference and / or the intensity difference between the induced current and the exciting current is detected. Detected and the detection result Based calculates the size of the gap, the and controlling the energization of the control coil to maintain the result of the calculation to a predetermined target value.

Further, the method for pouring the molten metal for the continuous casting mold according to the second aspect of the present invention is a method for injecting the molten metal into the continuous casting mold by a dipping nozzle extending from a tundish above the casting mold. While using a dipping nozzle equipped with a discharge port in which the entire front end portion is opened inside the mold,
A coil is embedded in the mold so as to face the lower portion of the discharge port,
The coil is energized to generate an upward electromagnetic force to dampen the flow of molten metal flowing out from the discharge port.

[0013]

In the first aspect of the present invention, the energy of the magnetic field generated by passing the exciting current to one of the pair of coils (transmitting coil) embedded near and below the suction port of the immersion nozzle is immersed. The peripheral wall of the nozzle, the molten metal inside the nozzle, and the induced current that propagates through the gap between them and induces the other (reception coil) include the phase delay and the phase lag depending on the difference in the propagation path of the magnetic field. Utilizing the fact that the strength decreases, the size of the gap is calculated from the phase difference and / or the strength difference between the exciting current and the induced current, and the energizing current of the control coil is controlled to keep this result at a predetermined value. By doing so, an appropriate gap is always maintained between the flow of molten metal near the suction port and the inner wall of the immersion nozzle, and the occurrence of nozzle clogging near the suction port is avoided.

Further, in the second aspect of the present invention, while the nozzle clogging on the discharge side is alleviated by using the immersion nozzle having the discharge port opened on the entire front end portion, it is exposed to the lower part of the discharge port. The upward electromagnetic force generated by energizing the coil brakes the flow of the molten metal flowing downward from the discharge port and converts it upward, facilitating the floating to the surface of the molten metal inside the mold, and Prevents deterioration of product slabs by eliminating obstruction and poor powder slag formation.

[0015]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below in detail with reference to the drawings showing the embodiments. FIG. 1 is a schematic diagram showing an implementation state of a method for pouring a continuous casting mold according to the present invention (hereinafter referred to as the method of the present invention).

In the figure, reference numeral 1 denotes a cylindrical continuous casting mold having upper and lower openings. The molten metal 3 stored in the tundish 2 arranged above the mold 1 is poured into the mold 1 through a dipping nozzle 4 extending below the tundish 2. Is a slab 5 that is cooled while contacting with the water-cooled inner wall of the mold 1 while staying inside the mold 1, and becomes a slab 5 that is coated on the outside with a solidification shell 5a. Is continuously pulled out. The suction port 4a of the immersion nozzle 4 which is opened on the bottom surface of the tundish 2 is opened and closed by raising and lowering a stopper 6 having its tip facing the upper part of the tundish 2, so that the pouring amount to the mold 1 is adjusted. ..

The suction port is provided outside the upper part of the immersion nozzle 4.
A control coil 7 is provided so as to surround the periphery of 4a. The control coil 7 is connected to a high-frequency oscillator 70, is excited by energization of a high-frequency current output from the oscillator 70, and forms a magnetic field having a strength corresponding to the energization amount,
An electromagnetic force toward the center is applied to the molten metal 3 flowing inside the immersion nozzle 4 to maintain the flow of the molten metal 3 with the inner wall of the immersion nozzle 4 with a gap.

Further, the suction port is provided on the peripheral wall of the immersion nozzle 4.
A transmitter coil 10 is embedded in the vicinity of 4a, and a receiver coil 11 is embedded below the transmitter coil 10 at an appropriate distance. Transmit coil 10
Is connected to the low-frequency oscillator 12 and is excited by the energization of a low-frequency current, which is the output of the oscillator 12, to form a magnetic field around it. The energy of this magnetic field propagates as described later and reaches the receiving coil 11, and the induced current induced in the receiving coil 11 by this is given to the phase difference detector 14 via the amplifier 13.

The phase difference detector 14 includes the low frequency oscillator 12
Is also given, the phase difference detector 14 obtains the phase difference between the exciting current applied to the transmitter coil 10 and the induced current induced in the receiver coil 11, and controls this result by arithmetic control. Output to section 15.

As will be described later, the phase difference between the exciting current and the induced current, which is the output of the phase difference detector 14, will be
It corresponds to the size of the gap generated between the inner wall of the immersion nozzle 4 and the molten metal 3 inside it between the buried positions 0 and 11. The calculation control unit 15 calculates the size of the gap using the output of the phase difference detector 14, outputs the calculation result to the display unit 16 and displays the calculation result on the display unit 16 in advance. The target value is compared with the set target value, and a control signal is issued to the high frequency oscillator 70 connected to the control coil 7 based on the comparison result.

This control signal increases the energization amount to the control coil 7 when the calculation result is below the target value, and conversely decreases the energization amount to the control coil 7 when it exceeds the appropriate value. The increase or decrease in the amount of electricity supplied to the control coil 7 increases or decreases the electromagnetic force applied toward the center of the molten metal 3 flowing inside the immersion nozzle 4, and the flow of the molten metal 3 and the inner wall of the immersion nozzle 4 are increased or decreased. When the calculation of the size of the gap is correctly performed by the calculation control unit 15, the gap between the inner wall near the suction port 4a and the flow of the molten metal 3 has an appropriate width. Therefore, the contact between the two can be completely cut off, and the occurrence of nozzle clogging near the suction port 4a can be avoided.

The calculation in the calculation control unit 15 is performed according to the principle described below. FIG. 2 is an explanatory diagram of this principle. The magnetic field generated by the transmission coil 10 in response to the energization of the exciting current as described above is the first path through which the magnetic field directly propagates on the peripheral wall of the immersion nozzle 4, the immersion nozzle, as indicated by the white arrow in these drawings. 4 passes through the second path propagating through the gap A between the inner surface of the peripheral wall of No. 4 and the molten metal 3 and the third path propagating inside the molten metal 3 to reach the receiving coil 11, and an induced current is applied to the receiving coil 11. Induce.

At this time, the first path, that is, the immersion nozzle 4
The magnetic field directly propagating through the peripheral wall of the is greatly attenuated in energy, and becomes a negligible level when the separation distance between the transmitting coil 10 and the receiving coil 11 exceeds a predetermined length. When comparing the magnetic field energy propagating through the second path formed of the gap A which is a non-conductor and the magnetic field energy propagating through the third path formed of the molten metal 3 which is a conductor, the former is compared with the latter. Since the phase delay is small, the phase delay of the induced current induced in the receiving coil 11 by both of these propagations decreases as the width of the gap A forming the second path increases.

Therefore, a preliminary test using the same kind of metal as the immersion nozzle 4 and the molten metal 3 was carried out, and the gap A between them was obtained.
The phase difference generated in each case is checked by changing the width of each of the values, and if the result is stored in the arithmetic control unit 15, the arithmetic control unit
In 15, the output of the phase difference detector 14 obtained during the operation of the continuous casting equipment is used, and the size of the gap generated between the inner wall of the immersion nozzle 4 and the flow of the molten metal 3 in the vicinity of the suction port 4a. Can be calculated.

The above principle is based on Japanese Patent Application No.
It is based on the "method for measuring the interplanar gap of a metal body" proposed in No. 298536. In the method of the present invention, it is possible to know the gap between the inner wall near the suction port 4a and the flow of the molten metal 3 online. As a result, the electromagnetic force applied to the molten metal 3 toward the center is increased or decreased based on this result, so that the molten metal can be poured with the gap maintained at an appropriate width, and nozzle clogging near the suction port 4a can be prevented. Occurrence is almost completely avoided. The appropriate width of the gap needs to be at least 1.0 mm or more, preferably 1.5 mm or more.

When the separation distance between the transmission coil 10 and the reception coil 11 is set so that the propagation energy of the first path is sufficiently small, the electromagnetic force generated by the immersion nozzle 4 generated in the reception result of the reception coil 11 is generated. Since such influences are eliminated, the burying depth of the transmitting coil 10 and the receiving coil 11 from the inner wall surface of the immersion nozzle 4 can be set appropriately, and both coils 10, 11
It is possible to prevent damage due to heat radiation from the molten metal 3 having a high temperature.

Further, the induced current induced in the receiving coil 11 is also reduced in intensity according to the difference in the propagation path of the magnetic field energy described above. Therefore, instead of the phase difference detector 14, an intensity difference detector is used. Alternatively, the output of this may be used to calculate the gap width.

On the other hand, as shown in FIG. 1, the immersion nozzle 4 is provided with a discharge port 4b formed by opening the entire front end (lower end) thereof, and the discharge port is formed on the short side of the mold 1. 4b
A coil 8 is buried at a position slightly lower than. This coil 8 is connected to a high frequency oscillator 80,
Is excited by the energization of a high-frequency current, which is the output of, to form a magnetic field having a strength corresponding to this energization amount, and an upward electromagnetic force is applied to the molten metal 3 inside the mold 1.
Energization of the coil 8 is always performed at a constant level during the operation of the continuous casting equipment.

Thus, the flow of the molten metal 3 flowing down inside the immersion nozzle 4 flows downward from the discharge port 4b opening at the tip of the immersion nozzle 4, and is shown by a dashed arrow in the figure. As a result, the electromagnetic force in the upward direction accompanying the energization of the coil 8 acts as a braking force that obstructs the penetration of the molten metal 3 flowing out from the discharge port 4b. The flow is converted into an upward flow as indicated by the arrow in the figure, and quickly rises to the surface of the molten metal 3 that remains inside the mold 1.

That is, by adopting the immersion nozzle 4 having the discharge port 4b opened at the entire tip, it is possible to prevent the occurrence of nozzle clogging in the vicinity of the discharge port 4b. The problem, that is, the inhibition of skinning on the surface of the molten metal 3 inside the mold 1 and the poor slag formation of the powder 9 supplied to the surface of the molten steel 2 is caused by the action of electromagnetic force generated by energizing the coil 8. Since the problem is solved, it is possible to prevent the nozzle clogging on the discharge side without deteriorating the quality of the product slab.

Finally, in order to investigate the effect of the method of the present invention as described above, the method of the present invention and the conventional method are used in a one-point straightening type continuous casting facility with a bending radius of 10 m for producing a slab of a size of 1600 w × 200 t. The continuous casting test was conducted under the same conditions, and the results of comparing the two will be described. The casting speed was 3.0 m / min, and the material used in the test was a low carbon material having the composition shown in Table 1.

[0032]

The method of the present invention in this test is conducted in the central portion of the immersion nozzle 4 by energizing the control coil 7.
It was carried out under the condition that a magnetic field varying before and after 7,000 gauss was generated, and by energizing the coil 8 embedded in the mold 1, a constant magnetic field of 4500 gauss was generated at the opening position of the discharge port 4b.

FIG. 3 shows how the nozzle opening changes with time according to the method of the present invention and the conventional method. The vertical axis of this figure shows the nozzle opening, and the horizontal axis shows the number of operations performed without replacing the tundish 2 and the immersion nozzle 4 at the bottom of the tundish 2, that is, the so-called consecutive number. As shown in this figure, in the conventional method, in order to maintain a predetermined casting speed (3.0 m / min) in the middle of the fourth continuous casting, the nozzle opening started to increase and before the sixth continuous casting was completed. While the nozzle opening exceeded 80%, it became difficult to control after that and the operation had to be stopped.
In the method of the present invention, it can be seen that even in the 7th continuous casting, the predetermined casting speed can be maintained and the nozzle clogging hardly occurs by the molten metal and the nozzle cross-sectional area ratio that are substantially the same as in the 1st continuous casting.

FIG. 4 shows the results of comparison of the inclusion states of inclusions in the slab obtained by the method of the present invention and the conventional method. This comparison is based on a value (inclusion index) obtained by counting the number of inclusions by microscopic inspection of samples of the same size taken at the same cross-sectional position of both slabs and converting this to the number per fixed area. It was carried out, and the superiority of the method of the present invention is clear from this figure.

This is because the amount of inclusions such as alumina adhered to the inner wall of the dipping nozzle 4 is small, and these deposits are released and flow into the mold 1 together with the molten metal 3 in the cast piece 5 that is pulled out from the mold 1. It is less likely to be mixed in the water, and the immersion nozzle 4
The flow of the molten metal 3 flowing into the mold 1 is changed upward by the action of the magnetic field formed by the coil 8 facing the discharge port 4b of the above, and inclusions mixed in the molten metal 3 stay in the mold 1. This is because it floats on the surface of the molten metal 3 and is captured by the powder 9 that covers the surface. That is, the method of the present invention has the additional effect of increasing the cleanliness of the product slab.

Further, in order to obtain an appropriate value of the size of the gap between the inner wall of the immersion nozzle 4 and the molten metal 3 inside thereof, the strength of the magnetic field formed by energizing the control coil 7 is changed to various values. A test for measuring the thickness of the deposit on the inner wall of the dipping nozzle 4 was performed by carrying out one charge operation while maintaining gaps of different sizes. The result is shown in FIG.

From this figure, when the gap between the inner wall of the dipping nozzle 4 and the molten metal 3 inside the dipping nozzle 4 is 1.0 mm or less, the thickness of the deposit is large and it is of little use in eliminating the nozzle clogging. On the other hand, it can be seen that when the gap is 1.0 mm or more, the thickness of the deposit is drastically reduced. This is because even in the magnetic field formed by energizing the control coil 7, when the gap is 1.0 mm or less, the molten metal 3 does not have a perfect rod shape and is not retained, and a local bulge occurs to cause an immersion nozzle. This is because contact with the inner wall of No. 4 occurs.

That is, in order to effectively prevent the nozzle clogging, it is necessary to secure a gap of at least 1.0 mm or more, preferably 1.5 mm or more in order to avoid the contact, and in the method of the present invention, the arithmetic control unit. By setting the target value to be compared with the calculation result of 15 to 1.5 mm or more and controlling the energization of the control coil 7 to maintain this target value, it is possible to maintain an appropriate gap and effectively prevent nozzle clogging. Can be prevented.

The amount of electricity supplied to the control coil 7 differs depending on the cross-sectional area of the immersion nozzle 4, more specifically, the cross-sectional area of the flow of the molten metal 3 flowing inside the immersion nozzle 4. Table 2 shows the results of examining the required amount of magnetic field strength at the center of the immersion nozzle 4. The energization amount of the control coil 7 may be set based on the energization amount required to obtain the magnetic field strength shown in Table 2.

[0041]

[0042]

As described in detail above, in the method of the present invention, one of a pair of coils buried near the suction port of the immersion nozzle and below the suction port is used as a transmission coil, and the other is used as a reception coil. By capturing the induced current induced in the latter by the propagation of the energy of the generated magnetic field, the size of the gap between the molten metal flow in the vicinity of the suction port and the inner wall of the immersion nozzle is determined, and this result is maintained within an appropriate range. In order to maintain the flow of the molten metal around the suction port by controlling the amount of electricity supplied to the control coil around the suction port and the action of the electromagnetic force generated by this energization, the inner wall of the immersion nozzle around the suction port is controlled. It is possible to avoid contact of the molten metal with the molten metal, and to prevent the occurrence of nozzle clogging near the suction port.

Further, by energizing the coil embedded in the mold so as to face the discharge port of the immersion nozzle, an upward electromagnetic force is generated, and the flow of the molten metal flowing out from the discharge port is braked and converted to the upward direction. It is possible to use the immersion nozzle provided with a discharge port that opens to the entire front end portion without deteriorating the quality of the product slab, and prevent nozzle clogging on the discharge side.

That is, according to the method of the present invention, it is possible to effectively prevent the nozzle clogging that occurs during the operation of continuous casting equipment on both the suction side and the discharge side, and maintain a good pouring state for a long period of time. As a result, the present invention has excellent effects such that productivity can be significantly improved by reducing the frequency of replacement of the tundish and the immersion nozzle.

[Brief description of drawings]

FIG. 1 is a schematic view showing an implementation state of a method of the present invention.

FIG. 2 is an explanatory diagram of a calculation principle of a gap size.

FIG. 3 is a diagram showing a result of comparison of changes in nozzle opening with time between the method of the present invention and the conventional method.

FIG. 4 is a diagram showing a result of comparing inclusion states of inclusions in a slab obtained by the method of the present invention and the conventional method.

FIG. 5 is a diagram showing a correlation between magnetic field strength and the amount of deposits.

[Explanation of symbols]

 1 mold 2 tundish 3 molten metal 4 immersion nozzle 4a suction port 4b discharge port 7 control coil 8 coil 10 transmission coil 11 reception coil 12 low frequency oscillator 14 phase difference detector 15 arithmetic control unit 70 high frequency oscillator 80 high frequency oscillator

Claims (2)

[Claims] 1. A method of injecting molten metal into a continuous casting mold by means of an immersion nozzle extending from a tundish above the mold, wherein a control coil is provided in the vicinity of the suction port of the immersion nozzle opening inside the tundish. Around the suction coil, an electromagnetic force directed toward the center of the suction port is generated by energizing the control coil, and the flow of molten metal in the vicinity of the suction port is held with a gap between it and the inner wall of the immersion nozzle. , A pair of coils are embedded in the vicinity of the suction port and at a position separated by a predetermined length below the suction port, a low-frequency exciting current is passed through one coil to generate a magnetic field, and the magnetic field causes the other The induced current induced in the coil is captured, the phase difference and / or the intensity difference between the induced current and the exciting current is detected, and the size of the gap is calculated based on the detection result. Keeping the result at the specified target value Pouring method of continuous casting mold, characterized by controlling the energization of the control coil so. 2. A method for injecting molten metal into a casting mold for continuous casting by means of a dipping nozzle extending from a tundish above the casting mold, wherein the casting mold is provided with a discharge port having the entire front end opened. A dipping nozzle is used, a coil is embedded in the mold so as to face the lower portion of the discharge port, and an upward electromagnetic force is generated by energizing the coil to brake the flow of the molten metal flowing out from the discharge port. The method for pouring a continuous casting mold according to claim 1, characterized in that.