JPH08155603A - Method for continuously casting molten metal - Google Patents

Abstract

PURPOSE: To improve the quality of the surface of a cast slab by independently and suitably controlling both of the lubrication between a mold and the cast slab and the temp. of the molten metal in the mold. CONSTITUTION: Electromagnetic force is given in the perpendicular plane with a linear electromagnetic coil 3 giving the fixed cycle to the vertical direction and arranged so as to surround the mold 1 to the water cooling mod 1 for pouring the molten metal 2 together with the lubricator 5 to execute a continuous casting. In this method, two kinds of AC current having different frequencies are applied in single or supposed condition to an electromagnetic coil 3.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a continuous casting method for molten metal, and more particularly to a continuous casting method capable of obtaining a slab of good quality.

[0002]

2. Description of the Related Art For example, in the case of continuous casting of steel, molten steel is injected into a mold having a water-cooled structure and a lubricant (powder) is added to the surface of the molten steel so that the mold is vertically vibrated at a constant cycle. However, the molten steel was solidified from the periphery of the molten steel and pulled out downward to obtain a slab. During this casting, in order to obtain a slab with good surface properties, a single-phase electromagnetic coil is arranged around the position corresponding to the molten steel meniscus portion of the mold, and a pinch force is applied to the molten steel by the electromagnetic force, A technique is widely known in which a lubricant is smoothly introduced between a cast piece and a mold by raising the surface of the molten steel (see Japanese Patent Publication No. 57-21408).

When a single-phase alternating current is applied to the electromagnetic coil that surrounds this conventional mold to exert a pinch force to bend the meniscus upwardly convexly, this bulge is generated in the molten metal. It is generated by the interaction between the induced current and the magnetic field, but the induced current also produces Joule heat at the same time. Therefore, the molten metal has two effects: a contact pressure lowering effect with the mold and a temperature increasing effect. Such effects are governed by the frequency of the electromagnetic field.

However, the frequency applied to the conventional electromagnetic coil is about 60 Hz, and once it is set, this frequency is continuously maintained without changing during operation. Therefore, even if the rise of the meniscus is satisfied, As the temperature rise is insufficient, it was not possible to exert both effects at the same time.

[0005]

DISCLOSURE OF THE INVENTION The present invention independently and properly controls both the lubrication between the mold and the slab and the temperature of the molten metal in the mold, thereby achieving the optimum meniscus swelling. It is an object of the present invention to provide a continuous casting method for molten metal capable of achieving a state and inputting a target amount of heat and improving the quality of the surface of a slab.

[0006]

SUMMARY OF THE INVENTION The gist of the present invention is to vertically oscillate a water-cooled mold in which molten metal is injected together with a lubricant by vertically oscillating a fixed period and to vertically arrange a solenoid electromagnetic coil surrounding the mold. In a method for continuously casting molten metal by applying an electromagnetic force in a plane, continuous casting of molten metal is characterized in that two kinds of alternating currents having different frequencies are applied to the electromagnetic coil individually or in an overlapping manner. On the way.

In the above method, the superposed value of the low frequency electromagnetic force and the high frequency electromagnetic force is set to a constant value,
It is preferable that the amount of heat supplied to the molten metal be adjusted independently of the rise of the molten metal meniscus portion by changing the value of the current supplied to both.

[0008]

The function of the present invention will be described in detail below. In FIG.
Reference numeral 1 is a rectangular cross-section mold which is vertically vibrated at a constant cycle and is constructed in a water-cooled structure, 2 is a molten metal which is injected into the mold through a nozzle, and 3 is a molten metal which surrounds the mold 1 and which is in the mold 2. A single-phase electromagnetic coil for applying an electromagnetic force having a component in the vertical plane to the electromagnetic coil 4 is an AC power supply for applying an alternating current having two kinds of high and low frequencies f ₁ and f ₂ to the electromagnetic coil 3. Reference numeral 5 is a lubricant to be put on the molten metal, and 6 is a solidified shell. The arrow A indicates the direction of the electromagnetic force generated by the coil, and the arrow B indicates the direction of the stirring flow generated in the molten metal by the electromagnetic force.

Further, FIG. 2 shows that the above-mentioned two types of frequencies f ₁ ,
A circuit diagram for superimposing an alternating current having f ₂ is shown, which is conventionally known. This circuit rectifies three-phase AC and generates a DC voltage, and then generates an arbitrary waveform voltage between terminals U and V using an arbitrary signal given by a signal generator. Frequencies f ₁ and f ₂
Is applied between UVs.

An electromagnetic coil 3 surrounding the mold 1 as shown in FIG.
In case of arranging, as described above, the molten metal 2 corresponding to this coil position has a pinch force and a temperature increasing effect. In the present invention, the alternating-current power supply for this electromagnetic coil is configured so that alternating currents having two kinds of frequencies f ₁ and f ₂ are simultaneously superposed or individually flowed. Therefore, if the heads (static pressure reduction margins) generated by the frequencies f ₁ and f ₂ are H ₁ and H ₂ and the generated Joule heats are Q ₁ and Q ₂ , for a mold of a predetermined size, the desired head (H )
And the Joule heat (Q) can be independently reached to the target value by selecting f ₁ and f ₂ and adjusting the strength thereof. Although the target head varies depending on the metal, in the case of steel, it is generally in the range of 10 mm to 50 mm, and the target temperature depends on the degree of superheat of molten metal, but the liquidus temperature of steel + 10 ° C to 3
It is in the range of 0 ° C.

For example, high and low frequencies having a difference as the above two kinds of frequencies are used, and a superposed value of an electromagnetic force of a low frequency and an electromagnetic force of a high frequency is constantly set as a required molten metal head supporting pressure, By appropriately changing the value of the current supplied to both frequencies, that is, changing the power ratio, the amount of heat input to the molten metal can be adjusted independently of the rise of the molten metal meniscus portion. Therefore, by such independent adjustment, it becomes easy to maintain the rise of the meniscus portion within a range where no defect occurs, and at the same time, maintain the temperature of the meniscus portion within a range where a low temperature or a high temperature defect does not occur.

[0012]

【Example】

Casting conditions-Casting material: Normal steel aluminum killed material-Mold size: 150mmφ x 800mmh-Nozzle: 1 hole downward-Mold vibration: Stroke 6mm, cycle 180cpm
(3 Hz) lubricants Main characteristics _{C-CaO-SiO 2 -Al 2} O 3 -NaF
System ・ Viscosity 2 Poise Electromagnetic force condition ・ Coil: Coil top end level (Mold top -100
mm), coil height 200 mm below the level
Up to magnetic field Single-phase AC 60Hz generation head 30mm (this is a), single-phase AC, 60Hz and 300Hz superposition, synthetic head 30mm, power ratio 1: 1, 1: 2, 1:
3 levels of 3 (these 3 levels are b, c and d respectively)

As a result of casting under the above conditions, the change in meniscus temperature measurement value of molten steel is shown in FIG. 3, and the slab surface defect index comparison is shown in FIG. From FIG. 3, it can be seen that (a) has a low superheat degree, (d) has a too high superheat degree, and (b) and (c) show the most preferable temperatures. In addition, from FIG. 4A, the meniscus temperature is too low to cause defects such as powder trapping and deckle (a state where small lumps are formed), and FIG. 4D is too high to cause defects such as bleeding.
It was found that in (b) and (c), such a slab with few such defects was obtained and a satisfactory slab was obtained.

[0014]

As described above, according to the casting method of the present invention, since it is possible to apply two kinds of alternating currents having different frequencies to the electromagnetic coil for applying an electromagnetic force to the molten metal, the molten metal meniscus portion is applied. It is possible to always apply the optimum pinch force and superheat degree corresponding to the casting conditions.
Thereby, both the contact pressure between the mold and the slab and the temperature of the molten metal in the mold can be appropriately controlled independently, and thus a slab with excellent surface quality can be manufactured.

[Brief description of drawings]

FIG. 1 is a schematic cross-sectional view of a mold portion for explaining the method of the present invention.

FIG. 2 is a circuit diagram of a two-frequency AC power source used in the present invention.

FIG. 3 is a diagram showing changes in meniscus temperature measurement values in Examples of the present invention together with Comparative Examples.

FIG. 4 is a diagram showing a slab surface defect index in an example of the present invention together with a comparative example.

[Explanation of symbols]

 1 Mold 2 Molten Metal 3 Electromagnetic Coil 4 Power Supply 5 Lubricant 6 Solidification Shell

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Kenzo Sawada Kenzo Sawada 20-1 Shintomi, Futtsu City, Chiba Nippon Steel Corporation Corporate Technology Development Division

Claims (2)

[Claims] 1. A molten metal in which a water-cooled mold for injecting molten metal together with a lubricant is vertically vibrated with a constant period and an electromagnetic coil is provided to surround the mold to apply an electromagnetic force in a vertical plane. 2. The method for continuous casting of molten metal, wherein two kinds of alternating currents having different frequencies are applied to the electromagnetic coil individually or in a superimposed manner. 2. The amount of heat supplied to the molten metal is set to be a swelling of the molten metal meniscus portion by setting the superposition value of the low frequency electromagnetic force and the high frequency electromagnetic force to be constant and changing the supply current value to both. The continuous casting method according to claim 1, which comprises independently adjusting.