JP3257222B2 - Curved mold for continuous casting of metal - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an internal water-cooled slit mold used for continuous casting of metal utilizing electromagnetic force, and more particularly to a mold applicable to a curved continuous caster.

[0002]

2. Description of the Related Art In continuous casting of metal, for example, steel,
Usually, a powder or granular lubricant called a powder is put on a molten metal containing a meniscus in a mold and operated. Part of the powder is melted and flows into the space between the mold and the slab, and plays a role of preventing seizure and lubrication between the two and mitigating rapid cooling of the slab.

[0003] In order to ensure an appropriate powder inflow amount corresponding to the casting conditions, it is necessary to use a lubricant having physical properties suitable for the casting conditions at the time of operation. At the time of high-speed casting, a special lubricant is used. Further, a minute vertical vibration called oscillation is applied to the mold to promote the flow of the lubricant. However, the minute vibrations may cause periodic lateral folds called oscillation marks on the slab surface to cause surface defects.

Therefore, several methods have been proposed for controlling the amount of powder inflow using electromagnetic force. In these methods, an electromagnetic force is applied to the meniscus portion of the molten metal in contact with the mold to bend the meniscus and promote powder inflow into the gap between the surface of the slab and the inner surface of the mold. In addition, in the continuous casting method in which an electromagnetic force is applied to the vicinity of the initial solidified portion, in addition to the powder inflow control effect by controlling the shape of the meniscus, the effect of slow cooling near the initial solidified portion by high-frequency induction heating, and the oscillation mark Is obtained.

Japanese Patent Application Laid-Open No. 52-32824 proposes a mold in which an energizing coil is embedded inside a mold insulated with a refractory so as to surround the inner wall of the mold. A method is disclosed in which the meniscus is curved by supplying the powder to promote the inflow of powder. However, in this method, since a low-frequency alternating current passes through the inside of the mold, there is a problem that the powder is caught in the molten metal. Further, since the magnetic field is attenuated on the long side of the thin slab, there is a problem that the electromagnetic effect cannot be expected.

In the casting method disclosed in JP-A-64-83348, a meniscus is formed by supplying a pulse-like current to a current-carrying coil using an apparatus similar to that of JP-A-52-32824. By vibrating and periodically changing the gap with the inner surface of the mold, the powder can flow between the solidified shell and the mold without using oscillation. However, this method can be applied to the method disclosed in Japanese Patent Application Laid-Open No. 52-32824, but the magnetic field is greatly attenuated by the mold, and it is difficult to obtain a sufficient electromagnetic force.

Further, Japanese Patent Application Laid-Open No. 2-274351 discloses a method of supplying a low-frequency current instead of a pulse current to a device similar to the above, but this still has the above-described problem.

Accordingly, the present applicant has specially described a method in which a slit is provided in the upper portion of a mold around which an energizing coil is circulated, and a secondary induction current is generated in a molten metal in the mold to effectively apply an electromagnetic force. It was proposed in Japanese Unexamined Patent Publication No. Hei 4-138883. As shown in this publication, when a slit is provided in a mold, a mold structure in which a cooling water hole is formed in each segment (hereinafter, referred to as a “mold segment”) divided by adjacent slits is required. In addition, if the top of the mold is divided into a number of segments by slits,
In a structure in which cooling water holes are provided to supply cooling water from below and discharge it from above, the structure of the cooling water outlet attached to the upper part of the mold not only makes it difficult to install an energizing coil, but also Since the attenuation becomes large, it is necessary to provide two holes for the cooling water in the forward path and the return path, and to drain the water downward.

It is appropriate to drill a cooling water hole using a drill, considering the difficulty and accuracy of the processing and the processing cost. And, in drilling, the cooling water hole must be a straight round hole. On the other hand, in order to suppress the loss of the primary induction current induced in the mold and apply an effective electromagnetic force to the molten metal, it is necessary to reduce the thickness of the mold.

In order to apply the above-mentioned slit mold to a curved continuous casting machine, the above-mentioned straight cooling water hole must be formed in a curved thin-walled mold segment. However, when two cooling water holes are formed in a thin mold, the holes interfere with each other and a normal cooling structure cannot be obtained. Further, the thickness between the inner wall of the mold and the hole is reduced, so that the hole is easily damaged, and the life of the mold is shortened. Due to the problem of construction of such a cooling structure, a curved mold with a slit has not yet been put to practical use.

[0011]

SUMMARY OF THE INVENTION An object of the present invention is to provide a curved mold having a slit for use in a curved continuous casting machine, which has a normal mold cooling ability, a long mold life, and a molten metal in the mold. An object of the present invention is to provide a mold to which an electromagnetic force can be effectively applied to produce a slab having good surface properties stably at a high speed.

[0012]

The gist of the present invention resides in the following molds.

As shown in FIG. 2, a curved mold having an internal water cooling structure having a plurality of slits 2 extending parallel to the casting direction near a free surface of a molten metal 9 in the mold, wherein adjacent slits of the curved mold are provided. A cooling water return hole 5 and a small-diameter cooling water outward pipe 4 inserted in the cooling water return hole are provided inside the mold segment 3 divided by Curved mold for casting.

As shown in FIG. 3, the mold is configured as one curved mold by combining a plurality of short curved molds (for example, 1A and 1B), and at least the uppermost short curved mold (1A ) Is a curved mold for continuous casting of metal having the structure described above.

[0015]

The most significant feature of the curved casting mold for continuous casting of the present invention (hereinafter referred to as "curved casting mold" or simply "mold") is as follows.
The cooling structure in the curved mold segment is of a double type that can be accurately machined by simple construction. Hereinafter, the structure of the mold of the present invention and its effects will be described with reference to the drawings.

FIG. 1 is a partially cutaway perspective view of the mold of the present invention. Although this mold is slightly curved as shown in FIG. 2, the mold is not shown in FIG. 1 in order to clearly show the cooling structure.

As shown, the curved mold 1 of the present invention includes:
A cooling water return hole 5 is provided in the mold segment 3, and a cooling water outward pipe 4 is inserted inside the cooling water return hole 5. That is, the cooling structure has a double structure of the forward path and the return path, and the cooling water is supplied from below the forward path pipe 4 and flows upward as indicated by the arrow.
It reverses and descends the return hole 4 and is discharged from below (see FIG. 2).

First, one cooling water return hole 5 may be formed in each mold segment 3. Since this hole may extend straight in the longitudinal direction of the mold as shown in FIG. 2, it can be accurately machined by simple drilling. A small-diameter outward pipe (for example, a copper pipe) 4 capable of keeping a sufficient distance from the inner wall thereof is provided inside the return hole 5.
Is inserted. In addition, the structure of the cooling supply port and the discharge port may be a conventionally well-known one.

In the mold of the present invention having the above-described structure, the two holes are too close to each other and short-circuited in the middle of the water channel, as in the case of providing two holes for the outward and return holes of the cooling water. It is possible to avoid such a situation that the thickness between the inner wall of the mold and the hole becomes extremely thin.

Accordingly, this mold has a normal cooling capacity,
It will have a long mold life.

In order to prevent the cooling water outgoing pipe 4 from vibrating inside the hole and deforming under the high water pressure of the supply water, spacers 6 are provided at several places in the height direction between the returning water hole 5 and the hole. It is desirable to insert and fix. In addition, since the straight cooling water return hole 5 is formed in the curved mold, the wall thickness between the inner wall of the mold and the cooling water return hole is slightly deviated in the height direction. There is no practical problem because it has no effect.

Next, some embodiments in which the curved mold of the present invention is applied to a curved continuous casting machine will be described.

FIG. 2 shows an example of a curved continuous casting machine to which the mold of the present invention is applied. (A) is a cross-sectional view taken along the line AA 'in FIG. (B), the left half of (b) is a vertical cross-sectional view of BO in FIG. It is.

As shown in the figure, a high frequency energizing coil 7 is wound several turns around a portion corresponding to a vicinity of a molten metal meniscus 10 of a mold 1 having an internal double water cooling structure having a plurality of slits 2 in a casting direction. I have. A molten metal 9 is supplied into the mold 1 from an immersion nozzle 8, and a powdery or granular powder 13 is put on the molten metal 9, and a part of the powder 13 is heated by the molten metal 9 and melted. powder
A part of 14 flows into the gap between the mold 1 and the solidified shell 11.

In the conventional operation, the inflow of powder depends only on micro-vibration caused by mold oscillation. However, in the continuous casting machine using the mold of the present invention, when a high-frequency current is applied to the energizing coil 7, the molten metal 9
An electromagnetic field is effectively applied in the vicinity of the initial solidified portion (the upper end of the solidified shell 11), and the molten metal meniscus 10 is bent by the action of the electromagnetic force. At that time, the gap between the surface of the molten metal and the mold is large and deep, so that the inflow of the molten powder 14 can be promoted. Furthermore, Joule heat generated by the induced current generated in the molten metal relaxes the cooling, that is,
A slow cooling effect is obtained, and effects of improving surface properties such as preventing cracks on the slab surface and reducing oscillation marks are obtained.

In the case of the immersion nozzle hot water supply system, the molten metal 9 existing on the front surface of the slit 2 is removed by the action of the electromagnetic force in addition to the low static pressure of the molten metal in the initial solidification part. It is possible to avoid a situation in which the resin is melted and solidified in the slit to cause a restrictive breakout. However, if the jug becomes a problem,
The slit may be filled with an insulating refractory such as silicon nitride. Further, since the inflow of the molten powder can be controlled by controlling the shape of the molten metal meniscus, it is not necessary to selectively use the powder in the initial casting period and the stationary casting period or to use a special powder at the time of high-speed casting. Further, at the time of high-speed casting, the powder is liable to be cut, and as a result, the slab of the slab may be baked into the mold, and further, a breakout due to the baking may occur. Since the flow rate can be controlled and further promoted, breakout during high-speed casting can also be prevented.

FIG. 3 shows an example of a curved continuous casting machine to which a mold combining a short mold, which is one of the molds of the present invention, is applied. (A) is a cross-sectional view taken along the line AA 'of (b),
The left half of (b) is a B-O longitudinal sectional view of FIG. (A), and the right half is a B'-O 'longitudinal sectional view of the same.

As shown in the figure, when the radius of curvature of the curvature of the casting machine is small, it is difficult to form cooling water holes over the entire length of the casting mold. Therefore, a plurality of short casting molds, for example, the upper casting mold 1A and the lower casting mold Combine with 1B and join by bolting etc. to form one curved mold. And the upper mold 1A
Only the double cooling structure described above may be adopted. In this case, the lower mold 1B may have a conventional tubular structure that is easy to manufacture. Although the mold in FIG. 3 is a combination of two short molds, it may be a combination of three or more molds. In that case, at least the uppermost mold has a double cooling structure.

If the combination curved mold having the structure shown in FIG. 3 is used, the perforation distance of the cooling water return hole 5 of the upper mold 1A may be short, and the machining is easy and the reliability in accuracy is improved. further,
Even when the mold becomes worn out and becomes unusable, only the upper mold 1A needs to be replaced, which is advantageous from the viewpoint of operation maintenance. The operation and effect of this mold are the same as those described in FIG.

Although the cross-sectional shape of the mold has been described above, it may be rectangular, square, or the like.

[0031]

Example 1 A round-section slab was manufactured using the curved continuous casting machine shown in FIG. The equipment specifications and operating conditions are as follows.

Casting mold: copper diameter 150mm, wall thickness 30mm, length 750mm, radius of curvature 10m Slit: 150mm x 32, width 0.2mm, filled with silicon nitride Cooling structure: cooling water return hole 12mmφ, Cooling water outgoing pipe (copper) 8 mmφ × 1 mm t The distance between the inner surface of the mold and the cooling water return hole is about 10 mm Cooling condition: Water volume 800 liter / min Electricity coil: Outer diameter 30 mm, wall thickness 2 mm, number of windings 2, frequency
35 KHz current effective value 9000 AT Steel type: JIS S45C (Chemical composition is as shown in Table 1) Casting speed: 3.5 m / min Powder: Chemical composition is as shown in Table 2

[0033]

[Table 1]

[0034]

[Table 2]

While supplying molten steel having the composition shown in Table 1 from the immersion nozzle into the mold, a powder for continuous casting having the composition shown in Table 2 was poured into the surface of the molten steel. It was drawn at a speed of min for 10 minutes and cast. Despite the high speed casting, the slab drawing was performed smoothly and there was no trouble such as breakout. Although there were several small jugs on the slab surface, there were no casting problems. In addition, no surface defects such as cracks and flaws, and no center segregation were observed, and extremely good cast pieces were obtained.

Further, in order to confirm the slow cooling effect, FeS was added to the molten steel during casting, the slab was subjected to sulfur printing, and the solidification coefficient k was calculated from the growth degree of the solidified shell. ^0.5 . In the conventional operation in which no slit mold is used and no electromagnetic force is applied, k is about 22 mm / min ^0.5 .

Further, in order to confirm the effect of promoting powder inflow, the thickness of the lubricant recovered from the slab surface after casting was measured and found to be 1.37 mm on average (about 0.96 mm in the conventional operation described above). The oscillation mark was greatly reduced, and the mark depth was measured to be 0.07 mm on average (0.12 mm in the conventional operation described above).

[0038]

Example 2 A round section cast piece was manufactured using a curved continuous caster shown in FIG. The equipment specifications are as follows. Other conditions were the same as in Example 1.

Casting mold: Inner diameter 150 mm, radius of curvature 8.2 m Upper mold: 450 mm in length, slit part thickness 30 mm Lower mold: 300 mm in length Cooling structure: Upper mold: Same as in Example 1.

Lower mold: Conventional tubular structure (copper plate thickness: 10 mm, gap between inner surface of mold and cooling water channel: 5 mm) Cooling condition: Water volume of upper mold: 800 L / min Water volume of lower mold: 1000 L / min In the example, since the radius of curvature of the curvature is smaller than that of the first embodiment, a combination mold of two short molds was used. The cast slab obtained after casting was almost the same as that obtained in Example 1, and very good cast slabs were produced stably and at high speed.

[0041]

According to the present invention, a cooling structure for a curved mold segment having a slit can be formed accurately with a simple construction. Therefore, normal mold cooling can be performed and the life of the mold can be extended. By using this mold, electromagnetic casting using a curved mold with a slit, which has been difficult in the past, can be put to practical use. In addition, since an electromagnetic field can be effectively applied to the molten metal in the mold, it is possible to control the powder inflow and perform slow cooling casting by heating even in a curved continuous casting machine, thereby stabilizing and speeding up casting and reducing slabs. The surface properties can be improved.

[Brief description of the drawings]

FIG. 1 is a partially cutaway perspective view of a curved mold with a slit of the present invention.

FIGS. 2A and 2B show an example of a curved continuous casting machine to which the curved mold with a slit of the present invention is applied, wherein FIG.
The left half of A 'is a cross-sectional view of B', and the left half of (b) is a vertical cross-sectional view of BO in FIG.

3A and 3B show an example of a curved continuous casting machine to which the combined curved mold of the present invention is applied, wherein FIG. 3A is a cross-sectional view taken along the line AA ′ in FIG. 3B, and FIG. ) FIG.
The right half is a B'-O 'longitudinal sectional view.

Continuation of the front page (56) References JP-A-54-35127 (JP, A) JP-A-56-141945 (JP, A) JP-A-4-220141 (JP, A) JP-A-55-68157 (JP, A) JP-A-4-162939 (JP, A) JP-A-4-333351 (JP, A) JP-A-4-138843 (JP, A) JP-A-5-38555 (JP, A) 5-15949 (JP, A) JP-A-52-32824 (JP, A) JP-A-64-83348 (JP, A) JP-A-2-274351 (JP, A) JP-A-4-162940 (JP, A A) Japanese Unexamined Patent Publication No. 3-133542 (JP, A) Japanese Utility Model Application No. Sho 61-153267 (JP, U) Japanese Utility Model Application No. 54-82021 (JP, U) Japanese Utility Model Application No. 5-76653 (JP, U) Japanese Utility Model Application Sho 62 -20746 (JP, U) JP-B-57-21408 (JP, B2) (58) Fields investigated (Int. Cl. ⁷ , DB name) B22D 11/055 B22D 11/043 B22D 11/11

Claims (2)

(57) [Claims] 1. A curved mold having an internal water-cooling structure having a plurality of slits extending parallel to a casting direction near a free surface of a molten metal in a mold, wherein the mold segment is divided by adjacent slits of the curved mold. Has a cooling water return hole,
A curved casting mold for continuous casting of metal, comprising: a cooling water outgoing pipe having a small diameter inserted in the cooling water return hole. 2. A mold wherein a plurality of short curved molds are combined to constitute one curved mold, wherein at least the uppermost short curved mold has the structure according to claim 1. Curved mold for continuous casting of metal.