JP2979986B2 - Metal continuous casting apparatus and continuous casting method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention makes it possible to produce slabs free of surface defects and to perform high-speed casting when continuously solidifying molten metal to produce slabs. The present invention relates to a casting apparatus and a casting method capable of performing continuous casting with a plurality of strands without using.

[0002]

2. Description of the Related Art The most common continuous casting method for steel is to supply molten steel through a submerged nozzle into a water-cooled mold, add a lubricant onto the surface of the molten steel (fluid surface), and vibrate the mold. In this method, the lubricant is easily infiltrated into the gap between the slab and the mold and solidified. In this case, a defect called an oscillation mark inevitably occurs on the surface layer of the slab due to mold vibration (hereinafter referred to as oscillation).

[0003] The mechanism of the formation of the mark is that the tip of the solidified shell falls due to positive pressure generated in the lubricant during a period in which the lowering speed of the mold is higher than the drawing speed (hereinafter referred to as a negative period), and the rising period of the mold. It has been confirmed that the molten steel overflows onto the solidified shell tip due to negative pressure in the lubricant during the positive period (hereinafter referred to as a positive period) or the shell tip is bent toward the mold.

[0004] As a continuous casting method without using an immersion nozzle and an oscillation, there is a type in which a tundish and a mold are directly connected. In this method, the hot water supply speed is reduced, which is advantageous for inclusion floating. However, even in this method, oxidation and nitridation on the refractory surface occur due to shell growth from the refractory side at a portion where the molten metal, the mold and the tundish refractory come into contact (hereinafter referred to as a triple point), and intermittent withdrawal occurs. This results in a systematically discontinuous intermittent withdrawal mark. In addition, solidification shell restraint is likely to occur due to solidification of the solidified shell at the triple point, causing breakout due to solidified shell breakage, which is an obstacle to operational stability and high-speed casting.

For such a reason, Japanese Patent Application Laid-Open No. Hei.
42, JP-A-4-138843, JP-A-5-13843
In the continuous casting method in which molten metal is supplied into a mold and continuously solidified, a portion where the molten metal starts to solidify,
There is disclosed a method in which an AC electromagnetic field is applied to a so-called initial solidification portion to suppress surface layer defects such as oscillation marks and intermittently drawn marks of a slab and improve operation stability.

[0006] The applicant of the present invention has disclosed in Japanese Patent Application Laid-Open No. Hei 4-138844 or Japanese Patent Application Laid-Open No. Hei 6-39449, as shown in FIG. An energizing coil connected to a high-frequency power source is arranged on the outer periphery of the mold within the range, and a continuous casting apparatus and a casting method for applying a high-frequency current to this coil have been proposed.

FIG. 6 is a view showing the above-mentioned continuous casting apparatus. FIG. 6A is a longitudinal sectional view of a main part, and FIG. 6B is a horizontal sectional view of the same. Reference numeral 1 denotes a mold, 1a denotes a segment portion of the mold 1, 1b denotes a cooling water inlet, 1c denotes a slit, 2 denotes an energizing coil, 2a denotes a cooling water inlet of the energizing coil 2, 3 denotes an immersion nozzle, 4 denotes molten metal, and 5 denotes a molten metal. Solidified shell, 6 is a lubricant, 6
-1 indicates a solidifying lubricant, and F indicates an electromagnetic force.

The presence of the slit 1c of the mold 1 as shown in the figure makes it possible to apply a high-frequency electromagnetic field to the molten metal 4 in the mold. The electromagnetic force F acts in the molten metal 4 by the high-frequency electromagnetic field. However, at a high frequency, the electromagnetic force F acts only on the surface layer of the slab because the electromagnetic penetration thickness is small. This electromagnetic force (because it becomes a pressure force, hereinafter referred to as magnetic pressure) F
, It is possible to obtain a stable swelling of the molten metal surface and to secure the angle θ shown in the figure, and the inflow of the lubricant 6 is promoted. Further, the generation of the oscillation mark can be suppressed by controlling the growth of the tip of the solidified shell 5 by the induction heating effect on the surface layer of the slab, and the slab without the oscillation mark defect on the surface layer can be manufactured.

[0009] However, when casting is performed with a plurality of strands in the continuous casting apparatus, a single high-frequency power supply supplies a high-frequency current to a current-carrying coil of one strand, and the number of high-frequency power supplies is equal to the number of strands. We need to prepare. Normally, even a single high-frequency power supply requires a considerable amount of equipment space, and it is difficult to secure a large space at the actual operation site, and there is a problem in terms of equipment space and equipment cost. Furthermore, running a plurality of high-frequency power supplies results in a considerable increase in power consumption.

JP-A-3-13354 proposed by the present applicant
In the continuous casting method in which the tundish and the mold are directly connected to each other, the above-described facility and power problems still remain when casting is performed using a plurality of strands.

The method disclosed in Japanese Patent Application Laid-Open No. 5-285598 is
In a structure in which the mold and the tundish are directly connected, the mold is a horizontal continuous casting method in which the mold is composed of conductive segments, and an energizing coil for a high-frequency current is arranged on the outer periphery of the mold, and the high-frequency current is applied to the coil. In this method, the high-frequency current does not always flow, but the high-frequency electromagnetic field is intermittently generated using a high-frequency pulse electromagnetic field induction device to generate a magnetic pressure sufficient to hold the static pressure of the molten metal in a pulsed manner. Apply. By this, the frictional force of drawing can be reduced. However, also in this method, when casting is performed with a plurality of strands, similarly, a high-frequency pulse current is applied to a current-carrying coil of one strand by one high-frequency pulse electromagnetic field induction device. Therefore, the conditions become worse in terms of equipment space and energy efficiency.

[0012]

SUMMARY OF THE INVENTION The present invention has been made in view of the above-mentioned problems, and an object of the present invention is to provide a high-frequency power supply device with a high-frequency power supply for each energizing coil of a continuous casting apparatus having a plurality of strands. By applying current under appropriate conditions, we can manufacture slabs without oscillation marks or intermittent withdrawal marks on the slab surface layer, as well as equipment space,
It is an object of the present invention to provide a continuous casting apparatus and a continuous casting method that can achieve a reduction in equipment cost and power saving.

[0013]

The gist of the present invention is as follows.
(1) A continuous casting apparatus for metal and (2) a continuous casting method using the same.

(1) A plurality of slits provided along the casting direction near the solidification start point of the molten metal of the metal water-cooled mold divide the mold wall in the vicinity thereof into segments, and both ends of the upper and lower portions of the segment Alternatively, only the lower end is connected and electrically short-circuited, and in a continuous casting apparatus of a plurality of strands in which a coil for supplying a high-frequency current is wound coaxially with the axis of the mold within a slit area on the outer periphery of the mold, each of the energized coils is A continuous casting apparatus for metal, comprising one power supply unit for supplying a high-frequency current.

(2) In the casting using the metal continuous casting apparatus of the above (1), a high-frequency current is sequentially and intermittently applied to a current-carrying coil of each strand by using a single power-supply device for supplying a high-frequency current. A continuous casting method for a metal, characterized in that the metal is cast while applying a high-frequency electromagnetic field intermittently in a continuous casting apparatus for each strand while energizing the metal with a shift.

In the above (2), during the period in which the high-frequency electromagnetic field is intermittently applied, in the case where oscillation is used, the intermittent extraction is performed without using the oscillation at the beginning of the negative period of the oscillation or the beginning of the positive period. In this case, it is desirable to set the initial stage of the drawing start.

[0017]

The configuration example of the mold and the energizing coil for each strand in the continuous casting apparatus of the present invention is basically the same as that shown in FIG. However, the upper end of the mold may not have a slit, and the segments may be connected to each other at the upper and lower ends of the segment and electrically short-circuited.
In this mold, since the upper end is also connected, the strength shortage of the mold can be compensated, and effects such as deformation of the mold due to heat or the like and prevention of intrusion of molten steel into the slit can be obtained.

The continuous casting apparatus of the present invention has a plurality of strands, each of which has the structure shown in FIG. 6, and a high-frequency current is applied to each energizing coil provided in the apparatus.
And a power switching device for sequentially and intermittently energizing the energizing coils of each strand.

With such a configuration, it is possible to operate each energizing coil of a plurality of strands with only one high-frequency power supply device, and it is possible to simultaneously reduce the equipment space and equipment cost and save power. it can.

Next, a method for supplying a high-frequency current and a mechanism for improving surface defects such as an oscillation mark and an intermittent extraction mark by applying an electromagnetic field will be described with reference to FIGS.

FIG. 1 is a schematic diagram for explaining a method of energizing each energizing coil of a three-strand continuous casting apparatus by one high-frequency power supply device. As shown, one high-frequency power supply device 7 is connected to the current-carrying coils 2-1, 2-2 and 2-3 via one power supply switching device 8. Further, a speed detector 9 having a function of detecting a speed difference between the oscillation cycle speed of the mold and the speed of drawing the slab is connected to the power supply switching device 8.

The high-frequency power supply 7 is always in a state in which a high-frequency current can be continuously supplied, and is first connected to the first power supply coil 2-1 to supply power. After a lapse of a certain time, the power supply switching device 8 switches to and connects to the second energizing coil 2-2 to energize the second coil. After a certain time has elapsed, the third energizing coil 2-3 is similarly energized. Thereafter, the first energizing coil 2-1 is switched and connected again, and a high-frequency current is sequentially and intermittently applied to each energizing coil in the order of 1 → 2 → 3 → 1 → 2 → 3 → 1. The power supply switching device 8 sets the timing of power supply switching by sequence control that receives a signal from the speed detector 9.

FIG. 2 shows that the method of energizing each energizing coil of a three-strand continuous casting apparatus by one high-frequency power supply apparatus is applied to intermittent drawing in a direct connection type continuous casting apparatus that does not use an immersion nozzle or oscillation. It is a schematic diagram explaining a case. Note that the power supply device and the like are omitted in FIG. 2 and have the same configuration as that of FIG. In the case of the intermittent extraction, the high-frequency current is supplied by detecting the rising of the extraction speed by the speed detector 9 as shown in FIG.

The cycle of power supply switching, that is, the cycle of applying a high-frequency electromagnetic field, is set in accordance with the cycle of mold oscillation or intermittent drawing of each strand, and in order to apply a high-frequency electromagnetic field to each strand sequentially and intermittently, The drive system such as the oscillation and the intermittent withdrawal (withdrawal-stop timing) is set by shifting the phase.

Next, the period of the drive system for improving the properties of the surface layer of the slab and the desirable timing of the application of the electromagnetic field will be described with reference to FIGS.

FIG. 3 is a longitudinal sectional view of a mold and a main part in the mold for explaining a casting state during an oscillation negative period when an oscillation method is used when the mold and the tundish are not directly connected using an immersion nozzle. As shown in the drawing, in the method in which the mold and the tundish are not directly connected, the tip of the solidified shell 5 is prevented from falling down due to the positive pressure in the lubricant 6 during the oscillation negative period, which causes the generation of an oscillation mark. As shown in FIGS. 1 and 2, the magnetic pressure F is applied to the initially solidified portion at the beginning of the oscillation negative period, thereby expanding the flow path of the lubricant 6 to reduce the positive pressure in the lubricant 6, thereby reducing the oscillation. Suppress marks.

FIG. 4 is a longitudinal sectional view of a mold and a main part of the mold for explaining a casting state during an oscillation positive period when the mold and the tundish are not directly connected.

As shown in the figure, the lubricant 6 during the oscillation positive period causing the generation of the oscillation mark is provided.
In order to suppress the overflow of the molten metal 4 onto the solidified shell 5 due to the negative pressure in the inside, and to prevent the tip of the solidified shell 5 from being drawn to the mold side by the negative pressure in the lubricant 6, the oscillation positive period By applying the magnetic pressure F at the beginning of the process, the flow path of the lubricant 6 is enlarged to reduce the negative pressure in the lubricant 6 and suppress the oscillation mark.

FIG. 5 is a longitudinal sectional view of a mold and a main part in the mold for explaining a casting state when the mold and the tundish are directly connected. In the continuous casting apparatus having a structure in which the mold and the tundish are directly connected, as shown in the figure, the growth of the solidified shell 5 from the side of the tundish refractory 10 at the triple junction directly connected causes flaws (intermittent pulling) on the surface layer of the slab. Mark) occurs. Further, since the solidified shell 5 is easily restrained at the triple point, a breakout due to breakage of the solidified shell 5 is easily caused.

Therefore, as shown in FIGS. 2 and 5, a high-frequency electromagnetic field is generated intermittently so as to coincide with the start time of the intermittent drawing, and the magnetic pressure F is applied intermittently. As a result, the contact pressure between the solidified shell 5 or the molten metal 4 and the mold is instantaneously reduced at the triple point, so that the drawing force (frictional force) at the start of drawing can be considerably small, and the solidified shell 5
Is less likely to occur, and high-speed casting can be achieved.

By applying the high-frequency electromagnetic field as described above,
Since the induction heating effect can be obtained in addition to the action by the magnetic pressure described above, the immersion nozzle method can achieve slow cooling casting even in a steel type in which non-uniform solidification easily occurs, such as peritectic steel. Further, in the direct connection type continuous casting method, the growth of the solidified shell from the tundish refractory at the triple junction can be suppressed, and the depth of the intermittently drawn mark can be reduced.

The frequency of the high-frequency current applied to the coil is
It is desirable to set the range from 1 kHz to several hundred kHz so as to obtain the effect of stabilization of the mold surface and induction heating.

In addition, any of the above-mentioned functions and effects is not affected by the cross-sectional shape and the drawing direction of the mold, but is achieved in an arbitrary mold shape and drawing direction.

[0034]

【Example】

(Comparative Example) A continuous casting apparatus using a single-strand oscillation and immersion nozzle having a current-carrying coil and a slit connected to one high-frequency power supply,
A casting experiment was conducted by continuously supplying a high-frequency current to the current-carrying coil, and the occurrence of oscillation marks was observed. The specifications of the continuous casting apparatus used and the casting conditions are as follows.

Number of strands: 1 Mold dimensions: inner diameter 200 mmφ, wall thickness 30 mm, length 700 mm Mold slit: width 0.25 mm, length 125 mm, number 45 Oscillation: stroke 6 mm, 140 cpm Immersion nozzle: inner diameter 30 mmφ energizing coil Dimension: inner diameter 250 mmφ, outer diameter 265 mmφ Cross section: 15mm × 15mm Number of turns: 5 High frequency current effective value: 14000 AT High frequency current frequency: 25 kHz High frequency power supply Number of units: 1 Power output: 300 kW Cast molten steel Composition of (peritectic steel): C = 0.12%, Si = 0.2
%, Mn = 0.6%, P = 0.035%, S = 0.015%, Fe =
Remainder Cast molten steel temperature: 1610 ° C Lubricant components: SiO ₂ = 39.4%, CaO = 35.3%, Al ₂ O _{3
= 7.1%, Fe 2 0 3} = 1.0%, Na 2 0 = 5.4%, MgO = 4.
3%, F = 6.8%, F.I. C = 1.0%, B ₂ O ₃ = 0.9% Casting speed: 2.0 m / min Casting time: 10 minutes As a result of observing the obtained slab, the depth of the oscillation mark was 120 μm on average and no high-frequency electromagnetic field was applied. It was considerably improved compared to the depth of 500 μm. The steel used in this test is a type of steel in which surface cracks (longitudinal cracks) are likely to occur due to uneven growth of the solidified shell on the slab surface. It turned out that it was.

However, when considering the continuous casting of three strands with three high-frequency power units, the power output is 90
This requires power as large as 0 kW, and the installation space for the power supply equipment is considerably large.

(Example 1 of the present invention) In the method of the present invention in which a high-frequency electromagnetic field is sequentially and intermittently applied at the beginning of a negative period of oscillation, a single high-frequency power supply is used to energize a current-carrying coil of a three-strand mold. An experiment of casting was performed, and the state of generation of oscillation marks was observed.

Other casting conditions and equipment specifications were the same as those of the above comparative example, and the electromagnetic field application conditions were as follows.

Number of strands: 3 Number of high-frequency power supplies Number of power supplies: 1 Power supply output: 300 kW Applied time: Initial period of negative period of oscillation Switching frequency: 140 cpm (2.33 Hz) (same cycle as oscillation, but 1 cycle of oscillation cycle As a result of observing the obtained cast slab, the surface layer of the cast slab obtained by the continuous caster with three strands was cast by applying a high-frequency electromagnetic field constantly. Compared with the surface properties of the piece, there was no inferiority, the oscillation mark was reduced, and it was confirmed that the oscillation mark could be suppressed by applying the intermittent electromagnetic field. Further, by applying a high-frequency electromagnetic field to the initially solidified portion, uneven growth of the solidified shell could be suppressed, and a cast without cracks was obtained.

The improvement of the oscillation mark has the same effect as the case where the high-frequency electromagnetic field is always applied. On the other hand, the power consumption of the high-frequency power source is equivalent to three strands for three high-frequency power devices. This is reduced to one third as compared with the case where the current is supplied to the current supply coil, and a great power saving is achieved. Since only one device is required for the power supply equipment, a large installation space is not required.

(Example 2 of the present invention) In the method of the present invention in which a high-frequency electromagnetic field is sequentially and intermittently applied at the beginning of a positive period of oscillation, a single high-frequency power supply is used to apply a current to each energizing coil of a three-strand mold. An experiment of casting by energizing was performed, and the state of generation of oscillation marks was observed. Other casting conditions and device specifications were the same as those of Example 1 of the present invention, and the electromagnetic field application conditions were as follows.

High frequency power supply Number of units: 1 Power supply output: 300 kW Application timing: Initial period of positive period of oscillation Switching frequency: 140 cpm (2.33 Hz) (same cycle as oscillation, but 1 cycle for one strand in switching cycle) As a result of observing the obtained cast slab, the same results as those of Example 1 of the present invention described above were obtained in both the oscillation mark and the power consumption of the cast slab. As a result, it was confirmed that the same effect as that of Example 1 of the present invention can be obtained also by the method of intermittently applying the high-frequency electromagnetic field at the beginning of the oscillation positive period.

(Example 3 of the present invention) A high-frequency electromagnetic field is produced by using a vertical continuous casting apparatus in which a three-strand tundish having slits, a refractory, and a mold are directly connected to an energizing coil and a slit connected to one high-frequency power supply apparatus. In the method of the present invention, in which a single high-frequency power supply device is used to energize each energizing coil of a three-strand mold and casting is performed, and the pulling force is measured by the method of the present invention in which a single high-frequency power supply device is applied intermittently at the beginning of the intermittent extraction period. At the same time, the occurrence of intermittent withdrawal marks was observed. The casting conditions, equipment specifications and electromagnetic field application conditions were as follows.

Number of strands: 3 Mold dimensions: Inner diameter 200 mmφ, wall thickness 30 mm, length 700 mm Mold slit: width 0.25 mm, length 125 mm, number of 45 Energized coils Dimensions: inner diameter 250 mmφ, outer diameter 265 mmφ Cross section: 15mm × 15mm Number of turns: 5 Effective frequency of high-frequency current: 14000 AT High-frequency current frequency: 25 kHz High-frequency power supply Number of units: 1 Power output: 300 kW Composition of cast molten steel: C = 0.45%, Si = 0.2%, Mn = 0.
7%, P = 0.025%, S = 0.008%, Fe = balance Cast molten steel temperature: 1600 ° C Casting speed: 2.0 m / min Intermittent drawing: 90 cpm Casting time: 10 minutes Electromagnetic field application timing: Initial drawing in intermittent drawing period Switching frequency: 90 cpm (1.5 Hz) (same cycle as oscillation, but 1/3 applied to one strand during switching cycle, 2/3 stop) Pulling force is measured by installing a strain gauge on dummy bar head. It was measured. In the comparison of the drawing force values, the case where the high-frequency electromagnetic field was intermittently applied was significantly reduced compared to the case where the high-frequency electromagnetic field was not applied, and was comparable to the case where the high-frequency electromagnetic field was not always applied. .

As a result, it was confirmed that even when the high-frequency electromagnetic field was intermittently applied, the restraint of the shell due to the solidification of the shell on the tundish refractory at the triple junction was suppressed, and stable extraction was possible.

Observation of the obtained slab shows that the depth of the intermittently drawn mark on the surface layer is comparable to the case where a high-frequency electromagnetic field is always applied, and the surface grinding amount in the next step is reduced, which can contribute to an improvement in yield. Was.

The power consumption of the high frequency power supply is 1/1/3 of the power consumption of three high frequency power supplies when three current supply coils are energized.
3 to achieve power saving.

[0048]

According to the present invention, by appropriately energizing each energizing coil of a continuous casting apparatus having a plurality of strands with one high-frequency power supply apparatus, equipment costs and installation space can be reduced, and power consumption can be reduced. At the same time, a slab excellent in surface layer properties can be obtained.

[Brief description of the drawings]

FIG. 1 is a schematic view for explaining a method of sequentially and intermittently energizing each energizing coil for three strands by one high-frequency power supply device.

FIG. 2 is a schematic diagram illustrating a case where the apparatus of FIG. 1 is applied to intermittent drawing without using a dipping nozzle or oscillation.

FIG. 3 is a longitudinal sectional view of a main part for explaining an effect of applying an electromagnetic field in an initial stage of an oscillation negative period.

FIG. 4 is a longitudinal sectional view of a main part for explaining an effect of applying an electromagnetic field in an initial period of an oscillation positive period.

FIG. 5 is a longitudinal sectional view of a main part for explaining an effect of applying an electromagnetic field at an initial stage of a drawing period at the time of intermittent drawing in a direct connection type continuous casting method.

FIG. 6 is a view showing a casting apparatus disclosed in Japanese Patent Application Laid-Open No. 4-138843. (a) is a longitudinal sectional view of a main part, and (b) is a horizontal sectional view.

[Explanation of symbols]

1: Template, 1a: Segment part of template, 1b:
Cooling water inlet, 1c: slit, 2: energizing coil,
2a: cooling water inlet, 3: immersion nozzle 4: molten metal, 5: solidified shell, 6: lubricant,
6-1: solidifying lubricant, 7: high frequency power supply, 8: power supply switching device, 9: speed detector,
10: Tundish refractory, F: Electromagnetic force (magnetic pressure),
θ: Angle between solidified shell and solidified lubricant

──────────────────────────────────────────────────続 き Continuation of the front page (56) References JP-A-4-200849 (JP, A) JP-A-7-266004 (JP, A) JP-A-5-15949 (JP, A) JP-A-4-199 138843 (JP, A) JP-A-5-146854 (JP, A) JP-A-62-197253 (JP, A) JP-A-7-335381 (JP, A) (58) Fields investigated (Int. Cl. ⁶ , DB name) B22D 11/00 B22D 11/04 311 B22D 11/10 350 B22D 27/02

Claims (2)

(57) [Claims] 1. A mold wall in the vicinity thereof is divided into segments by a plurality of slits provided along a casting direction near a solidification start point of a molten metal of a metal water-cooled mold, and both ends of upper and lower portions of the segment or Only the lower end is connected and electrically short-circuited.In a continuous casting apparatus of a multi-strand in which a coil for supplying a high-frequency current is wound coaxially with the axis of the mold within a slit area on the outer periphery of the mold, a high-frequency A continuous casting apparatus for metal, comprising one power supply unit for supplying a current. 2. A casting using a continuous casting apparatus for metal according to claim 1, wherein a single high-frequency power supply device is used to apply high-frequency current to a current-carrying coil of each strand sequentially and intermittently with a phase shift. A continuous casting method for a metal, wherein casting is performed while applying a high-frequency electromagnetic field intermittently in a continuous casting apparatus for each strand.