JPH11179490A - Vertical type continuous casting method for al or al alloy slab - Google Patents

Abstract

PROBLEM TO BE SOLVED: To reduce the warp in the bottom part of a slab and the constriction in the short length part at the initial stage of casting by executing the cooling with the ordinary laminar flow and spraying, etc., in two stages of the direct cooling just below a mold and the cooling with the secondary cooling device below the mold and specifying injecting positions of the cooling water into the slab. SOLUTION: Molten Al or Al alloy is supplied from the upper part of the mold opened at the upper surface and the lower surface and cooled and solidified in the mold and also, continuously, draw out from the lower end of the mold to cast the slab having rectangular cross section. At this time, at least at the initial stage of casting, together with the direct injection of the cooling water from the lower end of the mold, the cooling with the injection of secondary cooling water in the secondary cooling device arranged below the mold is executed and also, the conical bottom or the hitting position onto the slab surface of the secondary cooling water from the secondary cooling device is regulated to the lower position in the range of 10-120 mm from the position directly hit with the cooling water from the lower end of the mold.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a vertical continuous casting method for Al (aluminum) or Al alloy (hereinafter simply referred to as "Al") slabs, and more particularly, to a semi-continuous Al slab having a rectangular cross section. The present invention relates to a technique for preventing troubles such as ingot cracking and molten metal leakage at the early stage of casting in casting.

[0002]

2. Description of the Related Art As shown in FIG. 2, semi-continuous casting of an Al slab uses a mold 24 having a rectangular opening 23 formed by a long side 21 and a short side 22. Injecting the molten metal M in a state where the lower opening is closed by the bottom 25, cooling and solidifying with the cooling water 27 directly from the inner wall surface 26 of the mold and the lower end of the mold, and continuously lowering the bottom 25. It is performed by FIG. 2 is an explanatory view showing a cross section of the left half from the center of the long side of the mold portion for explaining the semi-continuous casting method of the Al slab. Show.

In the semi-continuous casting of the Al slab, immediately after the casting is started (see FIG. 2A), the slab S is formed by cooling the molten metal M poured into the mold 24 from the inner wall surface 26 and the bottom 25 of the mold. At the time when the base 25 is lowered and the slab S is completely removed from the mold 24 (see FIG. 2B).
In, rapid cooling of the slab S by the direct cooling water 27 from the lower end of the mold is started. As described above, since the cooling of the slab S is discontinuous in the early stage of the casting, the slab S
Then, a rapid thermal stress is generated, the slab S is deformed, and the bottom 28 of the slab S is warped and the short portion 29 is narrowed as shown in FIG. In particular, when the size of the slab S is large, or when the aspect ratio between the short portion 29 and the long portion 30 of the slab S is large, the deformation becomes large, and
A gap 31 is formed between 24 and the slab S, and there is a danger of molten metal leaking from the gap 31 or molten metal leaking due to re-melting of the solidified shell. If the strength of the solidified shell during deformation is insufficient, cracks may occur in the bottom 28 of the slab S.

[0004] As a method of solving the above-mentioned problems in the early stage of casting, there are a method of mixing a gas into cooling water directly from a lower end of a mold,
Intermittent direct supply of cooling water, mist cooling by direct cooling water mist, method of optimizing the shape of the base, heat insulating material is installed on the inner wall surface of the mold, and the ingot (slab) ) And a method of removing from the mold (Japanese Patent Laid-Open No.
No. 7947) has been proposed.

[0005]

The method of mixing gas directly into the cooling water from the lower end of the mold and the method of intermittently supplying the direct cooling water can continuously control the cooling capacity for the slab, and are extremely Although these methods are excellent, they are not easy to introduce into actual operation due to reasons such as the need for some initial investment and the required cleanliness of cooling water. In addition, the method of performing mist cooling by directly converting the cooling water into mist is expected to complicate the equipment, and is considered to be difficult to apply to actual operation. In addition, the method of optimizing the shape of the base and the method of installing the heat insulating material on the inner wall surface of the mold can be easily introduced and have a certain effect, so that it can be effectively utilized. Compared with the method of mixing gas into cooling water,
The effect is relatively small, and when the slab size is large, the above-mentioned problems cannot be completely solved.

The present invention has been made based on the above-mentioned circumstances, and an object of the present invention is to provide a vertical Al or Al alloy slab capable of reducing the warpage of the slab bottom and the constriction of the short part in the early stage of casting. A continuous casting method is provided.

[0007]

Means for Solving the Problems As a result of intensive studies to achieve the above object, it has been found that without mixing gas directly into the cooling water, intermittent supply of the direct cooling water or mist formation,
Cooling by ordinary laminar flow or spraying is performed in two stages: direct cooling directly below the mold and cooling by a secondary cooling device below the mold, and by adjusting the injection position of the same cooling water to the slab, And found that a great effect was obtained, and completed the present invention.

That is, according to the present invention, a molten metal of Al or an Al alloy is supplied from above a mold having open upper and lower surfaces, cooled and solidified in the mold, and continuously drawn from the lower end of the mold. In the vertical continuous casting method for casting a slab having a rectangular cross section, at least in the initial stage of casting, in conjunction with direct cooling water jetting from the lower end of the mold,
While cooling by jetting secondary cooling water from the secondary cooling device arranged below the mold, the position of the secondary cooling water from the secondary cooling device that hits the bottom or slab surface is directly from the lower end of the mold. A vertical continuous casting method of an Al or Al alloy slab, which is located below a position where cooling water is applied within a range of 10 to 120 mm.

[0009] In the vertical continuous casting method for Al or Al alloy slab according to the present invention, the heat insulating material is provided in a state where the base is inserted in the mold before the start of casting.
It may be affixed to the inner wall surface of the mold with a length of at least half of the long side centered on the long side center and a height of 40 to 150 mm.

Hereinafter, the present invention will be described in detail. As described above, the deformation of the slab in the early stage of casting is caused by the thermal stress generated by rapid cooling at the start of direct cooling in the early stage of casting. Reduce the cooling changes
There are two methods of increasing the deformation resistance when a thermal stress is generated.

The method of mixing gas into cooling water, the method of intermittently supplying cooling water, the method of performing mist cooling, and the like, all of which have been considered to have a large effect of suppressing slab deformation, have been described above. Based on this idea, the cooling efficiency is greatly reduced in the early stage of casting. Therefore, the solidified shell formed in the early stage of casting is very thin, and there is a danger of molten metal leakage when the casting conditions are changed or when some abnormality such as clogging of the cooling water ejection hole occurs.

Therefore, in the present invention, based on the above idea, at least at the initial stage of casting, the secondary cooling from the secondary cooling device disposed below the mold is performed together with direct cooling water jetting from the lower end of the mold. While performing cooling by water jetting, the position where the secondary cooling water from the secondary cooling device hits the bottom or the surface of the slab is 10 to 120 mm below the position where the cooling water hits directly from the lower end of the mold. It was done. In this case, the base and the slab before coming out of the mold are cooled by the cooling from the secondary cooling device below the mold as compared with the conventional method. Therefore, at the start of casting, the temperature of the slab itself in the vicinity of the direct cooling water injection position at the lower part of the mold is reduced, so that rapid cooling at the start of direct cooling is reduced, and the conventional method is used in the vicinity of the slab bottom. The solidified shell is formed thicker than in the case of only cooling from the lower end of the mold, the deformation resistance against the warpage of the slab bottom increases, and the constriction is reduced simultaneously with the warpage of the slab bottom. Further, since the warpage and constriction of the slab bottom are reduced in this manner, the risk of cracking of the slab bottom and / or leakage of molten metal can be reduced, and improvement in yield and productivity can be expected.

In order to effectively obtain the above-mentioned effects, the position where the secondary cooling water from the secondary cooling device hits the base or the surface of the slab is 10 times shorter than the position where the cooling water directly hits from the lower end of the mold. It is preferable that the distance be within the range of 120 mm. The reason is that if it is less than 10 mm, the form of cooling is almost the same as the case of cooling only from the lower end of the conventional mold, the thermal stress is not relaxed, the thickness of the solidified shell is not increased, On the other hand, 1
If it exceeds 20 mm, the influence on the cooling near the cooling point from below the mold will be small, and the thermal stress at the time of warpage of the bottom of the slab will not be sufficiently relaxed, and the solidification shell formation near the bottom will be insufficient. This is because

Further, in the present invention, in a state where the base is inserted into the mold before the start of casting, the heat insulating material is provided with a length of at least half of the long side centered on the center of the long side, Moreover, it may be attached to the inner wall surface of the mold at a height of 40 to 150 mm. By attaching the heat insulating material in this way, it is possible to delay the timing of the thermal stress caused by the direct cooling water by the height of the heat insulating material. Since the coated lower part of the slab can be sufficiently cooled, the thermal stress at the bottom of the slab can be reduced, and the thickness of the solidified shell near the bottom of the slab can be increased at the time of thermal stress generation, Paragraph number [0
012] (such as an increase in deformation resistance against warpage of the slab bottom) can be more effectively obtained. However, if the length of the heat insulating material attached to the inner wall of the mold is less than half of the long side centered on the center of the long side, or if the height is less than 40 mm, the thermal stress is relaxed and the thickness of the solidified shell is reduced. The effect on the expansion of the size cannot be expected, and the meaning of sticking is lost. On the other hand, when the height exceeds 150 mm, there is a case where a problem occurs in installation on the inner wall surface of the mold, which is not preferable.
Therefore, the heat insulating material is more preferably at least half the length of the long side centered on the center of the long side, and 40 to 100
It is good to stick on the inner wall of the mold at the height of mm.

As the heat insulating material, a filter-like refractory fiber cloth generally called glass cloth having an opening ratio of about 30%, an aluminum foil, or the like is used.
Any material can be used as long as it has a heat insulating effect and can be attached to a mold.

[0016]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 shows Al or Al according to the present invention.
It is explanatory drawing which shows the left half from the center of the long side part of the casting mold part to which the vertical continuous casting method of the alloy slab was applied, a shows the state immediately after casting start, b shows the state of the early stage of casting. In the figure, 1 indicates a mold and 2 indicates a secondary cooling device.

The mold 1 has a rectangular opening 5 formed by a long side 3 and a short side 4. The long side 3 and the short side 4
A cooling water passage 7 for cooling the inner wall surface 6 is provided inside, and a jet hole 9 for the cooling water 8 is directly provided at a lower end of the inner wall surface 6.
Is open.

The secondary cooling device 2 includes a rectangular ring-shaped header 10 provided so as to surround the slab S drawn from the mold 1, and a nozzle 11 provided on the header 10 toward the surface of the slab S. It is comprised including. And
When the method of the present invention is applied, the header 10 is such that the position where the secondary cooling water 12 ejected from the nozzle 11 hits the surface of the slab S is higher than the position where the cooling water 8 directly from the mold 1 hits.
It is provided so as to be adjusted downward by a distance L (10 to 120 mm).

Therefore, in the above configuration, the lower opening of the mold 1 is closed by the bottom base 13, so that the cooling water 8 is jetted directly together with the cooling in the mold and the secondary cooling water 12 is jetted from the secondary cooling device 2. When the injection of the molten metal M into the mold 1 is started while performing, the base 13 and the slab S before exiting from the mold 1 are cooled by the cooling from the secondary cooling device 2 as compared with the conventional method. Since the temperature in the vicinity of the bottom of the slab S before exiting the mold 1 is reduced, the rapid cooling by the direct cooling water 8 and the secondary cooling water 12 from the secondary cooling device 2 is reduced, and the slab S is cooled. The solidified shell near the bottom also
It is generated thicker than in the case of only cooling from the lower end of the conventional mold, the deformation resistance against the warpage of the bottom of the slab S is increased, the constriction is reduced at the same time as the warpage of the bottom of the slab S, and there is a danger of molten metal leakage and the like. Reduced.

In the above structure, a heat insulating material 14 may be attached along the inner wall surface 6 of the mold 1 as shown by a two-dot chain line in FIG. 1A. Even if the heat insulating material 14 is attached in this manner, the heat insulating material 14 is sufficiently cooled, so that the thickness of the solidified shell of the slab S can be increased at the time of thermal stress generation by the direct cooling water 8 and the mold 1, the heat insulating material 14 can alleviate rapid cooling by the direct cooling water 8 and the secondary cooling water 12 from the secondary cooling device 2;
[019] The effects described in [19] can be obtained more effectively.

[0021]

[Embodiment] JIS3004 is used by using the mold having the structure shown in FIG.
Melting and casting alloy, thickness 600mm x width 1500 x length 1000mm
Slab was manufactured. The casting speed was 30 mm / min at the beginning of casting (up to 200 mm in length), and 50 mm / min during steady state thereafter. In the example using a heat insulating material, glass cloth (opening area 20%) was used as the heat insulating material.

Table 1 shows the distance (distance L) between the lower end of the casting mold and the injection position from the lower part of the casting mold to the ingot, the conditions for attaching the heat insulating material, and the casting results. The overlap distance between the base and the base when the base is set in the mold before the start of casting is 10 mm
In addition, the heat insulating material was stuck so that the lower end hit the edge of the bottom stand. In addition, the amount of warpage and the amount of necking were measured at the site shown in FIG. 3 on the obtained slab bottom.

[0023]

[Table 1]

As is clear from Table 1, the distance L in Comparative Example 1 was as short as 5 mm, so that immediately after the mold was removed from the mold, the sudden cooling by the direct cooling water from the mold and the secondary cooling water from the secondary cooling device occurred. Upon cooling, the amount of warpage and constriction of the slab was large, cracks were found at the bottom, and minute leakage of hot water was found at the short part of the slab. In Comparative Example 4, the distance L = 15
Because of the long length of 0 mm, the cooling of the mold and the bottom base until the mold exits is insufficient, and rapid cooling by direct cooling water from the mold immediately after exiting the mold adds a large amount of slab warpage and constriction. And a small leak of water in the short part of the slab. In Comparative Example 6, as in Comparative Example 1, the distance L was reduced to 5 mm, and a heat insulating material was attached to the mold.
Although the warp amount and constriction of the slab were smaller than those of the slab, the absolute amount was still large, and a minute leak of hot water was observed in a short portion of the slab. In contrast to such comparative examples, all of Examples 2, 3 and 5 of the present invention were small in the amount of warpage and constriction of the slab, and neither cracks at the bottom nor leakage of the molten metal were observed, and the casting was successfully performed.

[0025]

As described above, according to the present invention, the Al
Or according to the vertical continuous casting method of the Al alloy slab, warpage of the bottom of the slab, constriction can be reduced, with it, cracking of the slab is reduced, and improvement in yield can be expected,
The danger of molten metal leakage at the beginning of casting is reduced, and safety and productivity can be improved.

[Brief description of the drawings]

FIG. 1 is an explanatory view showing a cross section of a left half from a center of a long side portion of a mold portion to which a vertical continuous casting method of an Al or Al alloy slab according to the present invention is applied. This shows the initial state of casting.

FIG. 2 is an explanatory view showing a cross section of a left half from a center of a long side of a mold portion for explaining a conventional semi-continuous casting method of an Al slab. Is shown.

FIG. 3 is an explanatory view of warpage of a slab bottom portion and constriction of a short portion.

[Explanation of symbols]

1: Mold 2: Secondary cooling device
3: Long side 4: Short side 5: Opening
6: Inner wall 7: Cooling water passage 8: Direct cooling water
9: Vent hole 10: Header 11: Nozzle 1
2: Cooling water 13: Bottom stand 14: Insulating material L: Distance (distance) between the direct cooling water from the lower end of the mold and the secondary cooling water from the secondary cooling device on the bottom or slab surface M: Molten metal S: Slab

Claims (2)

[Claims] 1. A molten metal of Al or an Al alloy is supplied from above a mold having open upper and lower surfaces, cooled and solidified in the mold, and continuously drawn out from the lower end of the mold to form a rectangular cross section. In the vertical continuous casting method for casting a slab, at least at the initial stage of casting, in combination with direct cooling water injection from the lower end of the mold, cooling by secondary cooling water injection from a secondary cooling device disposed below the mold. And the position where the secondary cooling water from the secondary cooling device hits the bottom or the surface of the slab is 10 to 120 mm below the position where the cooling water hits directly from the lower end of the mold. Vertical continuous casting method of Al or Al alloy slab to be used. 2. In the vertical continuous casting method of Al or Al alloy slab according to claim 1, in a state where the base is inserted in the mold before the start of casting, the heat insulating material is applied to the center of the long side portion. At least half of the long side as the center,
A attached to the inner wall of the mold at a height of 40 to 150 mm
Vertical continuous casting method for 1 or Al alloy slab.