JPH10291054A - Mold for continuous casting - Google Patents

Abstract

PROBLEM TO BE SOLVED: To eliminate an air-gap developed between a mold and cast slab (solidified shell) with the solidified shrinkage and the transformation shrinkage in a continuous casting of a metal, to increase the solidified shell thickness by improving the cooling speed between the mold and the cast slab and to improve the productivity and the product quality of the continuous casting by reducing bulging and breakout. SOLUTION: In the mold for continuously casting the metal, slits 6 for jetting high pressure gas, having the shape of arc-state or projecting curve-state to the outer side at the lower part of the gas spouting hole 6 on the whole periphery or at least on the wide surfaces at the lower part of the mold 1, or the shape inclining the angle of the gas spouting hole 6 in the cast advancing direction to the inner wall surfaces of the mold or the both constitutions. Further, desirably, the curvature radius of the arc part is made to three or more times of the jetting hole thickness and the angle of the gas jetting hole is made to <=60 deg. to constitute the gas spouting hole.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a mold for continuous casting of metal such as steel, which is excellent in mold-to-slab cooling or lubricating properties.

[0002]

2. Description of the Related Art In a conventional continuous casting method of steel using a fixed mold, casting is performed with a structure as shown in FIG. The molten steel 2 in contact with the water-cooled mold 1 via the lubricating powder 4 at the upper part of the mold starts to solidify and is drawn out in the casting direction while growing. Normally, lubricating powder 4 is applied while vibrating the mold to prevent seizure between mold 1 and slab 3.
Is supplied between the mold and the slab.

[0003] The solidified shell 3 undergoing solidification and growth forms an air gap 8 between the mold and the slab due to solidification shrinkage and shrinkage due to δ-γ transformation. The presence of the air gap 8 reduces the cooling rate in the lower part of the mold, which is one of the factors that hinders the growth of the solidified shell. If the air gap generated on the wide surface and the narrow surface of the mold is completely eliminated, the solidified shell after passing through the mold can be thickened, and defects and breakout due to bulging can be reduced.

As a method of eliminating the air gap, a method of tapering the narrow or wide surface of the mold so as to become narrower downward or a method of mechanically pressing the wide or narrow surface is used. It is not possible to completely eliminate air gaps across all steel grades. In the latter method, a mechanical mechanism is expensive.

The present invention is characterized in that a high-pressure gas is blown between a mold and a slab and a gas flow flowing in a casting direction is formed by utilizing a Coanda effect described later to control an air gap. This was not possible with the gas blowing method (Japanese Patent Publication No. 57-124555). The reason is that, as shown in FIG. 3, the molten steel 2 has a hydrostatic pressure 9 (P + ρgh; P: static pressure, ρ: density, g:
This is because a distribution of gravity acceleration (h: molten steel depth) is generated, and the blown gas 5 flows from a higher hydrostatic pressure 9 to a lower hydrostatic pressure 9, thereby forming a flow in a direction opposite to the casting direction.
That is, the blown gas 5 disturbs the initially solidified portion, which makes it difficult to obtain a slab having a stable shape.

Next, the Coanda effect will be described. The Coanda effect is a principle that a fluid flows along a wall under predetermined conditions, and is widely used in air conditioners, gas turbine engines, and the like for the purpose of forming a flow along a wall by bending a blowing angle. In order to induce the Coanda effect, 1) the shape of the outlet is a two-dimensional slit, and 2) the radius of the arc at least three times the thickness of the outlet at the outlet in the direction in which the flow is to be truly bent. It is good to secure the conditions such as 3) tilting the blowout angle in the direction to be bent, etc. (Reference: Mitsubishi Heavy Industries Technical Report Vo)
l.26, No.3 (1989) p206).

In the design of a built-in air conditioner such as a wall-mounted air conditioner, on the other hand, conditioned air is blown into a room under conditions that do not induce the above-mentioned Coanda effect so as to prevent a wall-adhering jet due to the Coanda effect from deteriorating the heating efficiency. [Ref: Mitsubishi Heavy Industries Technical Report Vol.26,
No. 3 (1989) p206]. In addition, there is a method of using a Coanda spiral nozzle as an optical fiber wiring technology, forcing supply air to flow through one opening of the nozzle, and supplying the optical fiber from the other opening, and this method also has the above-mentioned Coanda effect. It has been successfully used (Reference: Turbomachinery, Vol. 22, No. 4, 56, (1994)).

[0008]

SUMMARY OF THE INVENTION The present invention has been made to solve such a problem, and uses the Coanda effect to form a gas flow in the casting direction to reduce the pressure between the mold and the slab. To provide a continuous casting mold suitable for high-speed casting at a low cost.

[0009]

SUMMARY OF THE INVENTION In order to solve the above-mentioned problems, the gist of the present invention is to provide a continuous casting mold for a metal, in which a high-pressure gas cut horizontally over the entire lower part of the mold or at least over a wide surface. A slit for blowing is provided, and the shape of the flow path of the high-pressure gas reaching the slit is configured to generate a Coanda effect. This eliminates the air gap generated between the slabs, enhances the heat removal capability of the mold, and enables high-speed casting.

As a configuration for effectively generating the Coanda effect, the shape of the flow path of the high-pressure gas reaching the slit is such that the shape in the casting progress direction near the slit is an arc shape or an outwardly convex curved shape. The radius is at least three times the width of the high-pressure gas flow path.

Further, as another configuration, the flow path of the high-pressure gas reaching the slit is inclined toward the casting direction, and the angle inclined toward the casting direction is 60 degrees.
Degrees or less.

As still another configuration, a configuration combining the above two, that is, the flow path of the high-pressure gas reaching the slit is inclined toward the casting progress direction, and the angle inclined toward the casting direction is further reduced. Less than 60 degrees,
In addition, the shape of the flow path in the vicinity of the slit in the casting direction is a circular arc or an outwardly convex curve, and the radius of curvature is set to be three times or more the width of the high-pressure gas flow path.

[0013]

BEST MODE FOR CARRYING OUT THE INVENTION The metal to which the present invention is applied is steel, aluminum, titanium or the like, but it is particularly preferable to apply it to continuous casting of steel. A method for controlling an air gap in continuous casting using the fixed mold of the present invention will be described with reference to the drawings. In the present invention, as shown in FIG.
Is blown, and the gas 5 flows in the casting direction, so that the space behind the gas 5 is reduced or evacuated. Here, the inner surface of the lower part of the mold refers to the inner surface of the mold near the exit in the direction of casting, and a slit cut horizontally at 20 cm or less from the lower end of the mold is provided, and the Coanda effect of the high-pressure gas blown out therefrom is used. Things. The distance from the lower end is preferably shorter as the distance from the meniscus to the slit becomes the effective cooling length, but may be limited by the blowing high-pressure gas flow path, the interaction with the mold cooling water, and the like. It is also possible to adopt a mode in which a short mold having a slit for blowing out high-pressure gas is placed below the conventional mold while the conventional mold is kept as it is.

First, a method for forming an appropriate gas flow will be described. FIG. 3 shows the behavior when the gas 5 is blown into the mold 1-cast piece 3 with a normal nozzle (a straight slit nozzle having a gas blowing angle of 90 degrees with respect to the inner surface of the mold). The distribution of the hydrostatic pressure 9 is on the molten steel side, and the hydrostatic pressure is higher vertically downward, and the same hydrostatic pressure is applied to the thin solidified shell in the mold. When the gas 5 is blown through the slit, the gas has a property of flowing from a higher hydrostatic pressure to a lower hydrostatic pressure, and thus flows in a direction opposite to the casting direction. For this reason, the gas disturbs the solidified shell in the initial solidification part and comes into direct contact with the molten steel, so that the operation becomes impossible.

In the present invention, in order to make up for such a drawback and to make the gas flow properly in the casting direction, FIG.
As shown in FIG. 5 or FIG. 6, a unique shape processing is added to the slit 6.

FIG. 4 is a vertical sectional view perpendicular to the inner surface of the mold according to the present invention. It has a slit 6 for blowing out high-pressure gas which is cut horizontally on at least the entire circumference of the inner surface of the lower part of the mold or at least on the wide surface 11. As shown in FIG. 5 (a), the slit 6 provided on the entire periphery of the lower part of the mold refers to a slit 6 which is horizontally cut so as to be connected to two wide surfaces 11 and two narrow surfaces 12 of the inner surface of the mold in a circumferential manner. . In addition, the slit provided only on the wide surface refers to the slit 6 cut horizontally only on the two wide surfaces 11 on the inner surface of the mold as shown in FIG. The shape of the high-pressure gas flow path connected to the slit 6 in the vicinity of the slit in the casting direction is preferably three times or more the width of the high-pressure gas flow path 10 (d in FIGS. 4, 6, and 7). By forming an arc shape having a radius of curvature R or an outwardly convex curved shape, a Coanda effect is induced, and gas is caused to flow in the casting direction in spite of the hydrostatic pressure distribution. In this case, in order to make the Coanda effect more likely to occur, the Reynolds number Re (=
Ud / ν) is preferably 2000 or more. Also,
It may be a smooth curved surface whose curvature radius is gradually changed as long as the radius of curvature satisfies the above condition as an outwardly convex curved shape, or a set of flat surfaces obtained by approximating the curved surface to a polyhedron.

FIG. 6 is a vertical sectional view perpendicular to the inner surface of the mold according to the third and fourth aspects of the present invention.
The high pressure gas flow path 10 leading to the casting is inclined at an angle of 60 degrees or less in the casting direction with respect to the inner surface of the mold, thereby forming a gas flow in the casting direction. Note that the inclination angle indicates θ shown in FIG. In this case, when the conditions described in claims 1 and 2 are not used together, the inclination angle of the flow path is set to 30 degrees or less, and the Reynolds number Re is set to 2000.
It is preferable to make the above.

FIG. 7 is a diagram showing the present invention described in claims 5 and 6, which is a combination of the above two methods. Next, the supply pressure of the high-pressure gas 5 will be described. As shown in FIG. 7, when the distance between the slit position and the lower end of the mold is L (cm), the hydrostatic pressure difference between the slit and the lower end of the mold acting when the air gap completely disappears is (L / 14).
8) (atm), the gas supply pressure must be equal to or higher than the sum of (L / 148) (atm) to the total pressure loss of the gas flow path system.

Under the above conditions, a high-pressure gas is blown from the inner surface of the lower part of the mold to the slab 3 so as to generate the Coanda effect, thereby forming a gas flow flowing in the casting direction.
By forming a vacuum or decompression point between the slabs 3,
By sucking the slab 3 toward the mold and bringing it into close contact with the mold 1, it is possible to eliminate the air gap or to control the air gap thickness.

In the air gap control means of the present invention, the air gap is controlled at low cost by using the Coanda effect of the blown gas to control the air gap without adding an expensive mechanical mechanism to the fixed mold. It is intended to reduce product defects due to bulging and reduction in productivity due to breakout, which are problems in operation.

[0021]

Embodiment 1 An embodiment of the present invention described in claim 6 is shown in Table 1.
Shown in

[Table 1]

Hereinafter, continuous casting of steel was performed under the operating conditions shown in Table 1. First, in order to determine whether or not the air gap disappeared, the degree of scratches on the inner surface of the mold after casting was observed. As a result, in the conventional operation, no scratch was observed from the middle to the lower part of the mold except for the vicinity of the meniscus, which was a trace of the contact between the slab 3 and the mold 1, indicating the presence of the air gap 8 (see FIG. 2). On the other hand, scratches were observed on the inner surface of the mold after casting using the method and apparatus of the present invention from the meniscus to the lower portion of the mold. This suggests that the air gap could be eliminated in the present invention.

Next, the amount of bulging generated in the slab between the rolls under the mold was measured. Table 2 shows a comparison between the conventional operation and the operation based on the present invention. In the casting using the mold of the present invention as compared with the casting using the conventional mold, the bulging amount at the lower part of the mold was reduced to about ２〜 to ３, and the effectiveness of the present invention was confirmed.

[0024]

[Table 2]

[0025]

As described above, according to the continuous casting mold of the present invention, the air gap can be controlled in accordance with the type of cast steel by performing low-cost processing in the continuous casting mold of steel. Defects and breakouts can be reduced.

[Brief description of the drawings]

FIG. 1 shows a schematic diagram of air gap control using the present invention.

FIG. 2 shows a schematic view of an air gap generated by conventional casting.

FIG. 3 is a schematic view showing a case where air is blown by a conventional nozzle.

FIG. 4 is a schematic view of a vertical section perpendicular to the inner surface of the mold of the first mold of the present invention.

FIG. 5 is a diagram schematically showing a state in which a slit for blowing out high-pressure gas from the inner surface of the mold of the present invention is cut. (A) has slits on the entire surface, and (b) has slits only on the wide surface.

FIG. 6 is a schematic view of a vertical section perpendicular to the inner surface of the mold of the second mold of the present invention.

FIG. 7 shows a schematic view of a vertical cross section perpendicular to the inner surface of the mold of the second mold of the present invention.

[Description of Signs] 1 mold 2 molten steel 3 cast piece (or solidified shell) 4 powder 5 gas 6 gas discharge slit 7 air pocket 8 air gap 9 molten steel hydrostatic pressure 10 high pressure gas flow path 11 mold wide surface 12 mold narrow surface

────────────────────────────────────────────────── ───

[Procedure amendment]

[Submission date] October 21, 1997

[Procedure amendment 1]

[Document name to be amended] Statement

[Correction target item name] 0021

[Correction method] Change

[Correction contents]

[0021]

Embodiment 1 An embodiment of the present invention described in claim 6 is shown in Table 1.
Shown in

[Table 1]

Claims (6)

[Claims] 1. A mold for continuous casting of metal, comprising a high-pressure gas blowing slit cut horizontally over at least the entire lower part of the mold, or at least over a wide surface, and perpendicular to the inner surface of the high-pressure gas flow path leading to the slit. A casting mold for continuous casting of metal, which has a vertical cross-sectional shape and a shape in the direction of casting in the vicinity of a slit of a flow path is an arc shape or a curved shape protruding outward. 2. The curvature radius of a curved portion having a circular arc shape or an outwardly projecting shape in the vicinity of the slit of the high-pressure gas flow path in the casting direction is at least three times the width of the high-pressure gas flow path. The mold for continuous casting of metal according to claim 1, wherein: 3. A casting mold for continuous casting of metal, comprising a slit for blowing high-pressure gas, which is horizontally cut at least on the entire periphery of the lower portion of the casting mold or at least over a wide surface, and a flow path of the high-pressure gas reaching the slit is directed in a casting direction. A mold for continuous casting of metal, characterized by being inclined toward. 4. The mold for continuous casting of metal according to claim 3, wherein an angle of the flow path of the high-pressure gas inclined toward a casting direction is 60 degrees or less. 5. A mold for continuous casting of metal, comprising a high-pressure gas blowing slit cut horizontally over at least the entire periphery of the lower portion of the mold or at least over a wide surface, and a flow path of the high-pressure gas reaching the slit is formed in the casting direction. A casting mold for continuous casting of metal, wherein the casting mold is inclined toward the flow path and has a shape of a circular arc or an outwardly convex curved shape in the vicinity of a slit of the flow path. 6. The flow path of the high-pressure gas, wherein an angle of the flow path of the high-pressure gas inclined toward the casting direction is not more than 60 degrees, and the shape of the high-pressure gas in the casting direction near the slit of the flow path is arc-shaped or convex outward. The mold for continuous casting of metal according to claim 5, wherein the radius of curvature of the curved portion is at least three times the width of the flow path of the high-pressure gas.