JP3372861B2 - Heat-resistant screen for continuous casting of aluminum or aluminum alloy - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention is intended to remove oxides and the like contained in the molten aluminum or aluminum alloy and to mitigate the jet flow from the immersion nozzle when continuously casting aluminum or aluminum alloy. In particular, the present invention relates to a container-shaped heat-resistant screen which is disposed on the upper part of the mold so as to cover the tip of the immersion nozzle.

[0002]

2. Description of the Related Art FIG. 3 is a sectional view for explaining a DC casting method which is a general continuous casting method for aluminum or aluminum alloy.

A cylindrical water-cooled mold 53 opened vertically is used for the DC casting, and an aluminum melt or an aluminum alloy melt (hereinafter, sometimes referred to as Al melt) 58 adjusted to a desired composition is used. The water is supplied from the upper gutter 50 or the tundish into the water-cooled mold 53 through the immersion nozzle 51. At this time, a heat resistant screen 52 is disposed between the immersion nozzle 51 and the mold 53. The heat-resistant screen 52 is the same as the A from the immersion nozzle 51.
l The molten metal 58 is relaxed, and the high-temperature Al molten metal 58 near the nozzle 51 and the low-temperature Al molten metal 58 near the ingot 57.
It has a function of preventing the mixing with the above, and additionally filtering out oxides and the like formed on the surface of the molten metal.

Then, the Al molten metal 58 is cooled by the mold 53 to solidify it, and the lower bottom metal 56 is lowered (arrow A) to solidify the solidified ingot 57 into the water-cooled mold 5.
3 is pulled out from below, and is thus semi-continuously cast. The water-cooled mold 53 has a cooling water 54 circulating therein.
The cooling water 54 is discharged from the lower part of the mold 53 (arrow C) to further cool the ingot 57. The line B in the drawing represents the solidification interface, and the ingot 57 is on the drawing side (lower side) of the line B.
The molten metal injection side (upper side) is the molten metal pool.

The heat resistant screen 52 is generally made of a coarse mesh sheet made of glass fiber, and FIG. 4 is a perspective view showing the heat resistant screen, which is a rectangle with an open upper part. It is a box-shaped heat resistant screen 70 (conventional example). Such a rectangular heat resistant screen is used when casting with a mold having a rectangular cross section.

In addition, as a heat-resistant screen, a screen partially provided with a molten metal impervious portion has been proposed, and Japanese Patent Application Laid-Open No. 9-141393 discloses an open upper part as shown in a perspective view of FIG. In the rectangular box-shaped heat-resistant screen, the entire side surface 61 of the short side is used as a molten metal passage portion, while the central portion 63a of the side surface portion 63 of the long side is a molten metal non-passage portion, both end portions 6
3b is used as a molten metal passage portion, and similarly, a center portion 62a of a bottom surface portion (a surface on the ingot drawing side) 62 is a molten metal non-passage portion, and both end portions 62b are molten metal passage portions (conventional example). .

The heat-resistant screen of the conventional example has a shape similar to that of a mold having a rectangular cross section, and the molten metal jet from the dipping nozzle is applied to the non-passing portion of the bottom center portion 62a to flow in the lateral direction (horizontal direction). The direction is changed, and the long side surface 63
By directing the molten aluminum toward the non-passing portion of the central portion 63a, the flow velocity is relaxed to prevent a direct impact on the side wall surface of the mold, while the side surface portion 61 on the short side and the side surface on the long side in the vicinity thereof are prevented. Good outflow from the end 63b and the bottom end 62b.

In continuous casting using a mold having a rectangular cross section, in the case of the above-mentioned conventional heat-resistant screen having a coarse mesh, the molten metal ejected from the dipping nozzle is near the mold wall on the short side, that is, the end in the longitudinal direction. Since it takes a long time to reach the portion, the temperature distribution becomes non-uniform, and the ingot surface may be cracked or the like. However, the heat-resistant screen of the above-mentioned conventional example is designed to flow mainly from the short side surface 61. Therefore, the molten metal is promoted to reach the above-mentioned hard-to-reach areas and the Al molten metal is uniformly supplied into the mold. Therefore, the temperature distribution of the molten metal in the mold becomes uniform, and casting with no surface defects occurs. It is designed so that a lump can be obtained.

[0009]

However, when the amount of molten Al supplied from the immersion nozzle 51 becomes large, the heat-resistant screen of the above-mentioned conventional example causes uneven supply to the mold, as will be described in detail below. Therefore, there is a problem that the molten metal flow is disturbed and stable casting becomes difficult.

FIG. 7 is a diagram showing the flow of molten metal when a rectangular box-shaped heat-resistant screen which is designed to flow out mainly from the side surface on the short side is used, and is a cross section viewed from the long side of the mold. FIG. 6 is a perspective view showing a heat-resistant screen 80 used in simulating the molten metal flow. As shown in FIG. 6, the heat-resistant screen 80 has a short-side side surface portion 81.
Is the molten metal passage portion, the entire long side surface 83 is the molten metal non-passage portion, the central portion 82a of the bottom surface portion 82 is the molten metal non-passage portion, and both end portions 82b are the molten metal passage portion.

In FIG. 7, a large amount of molten Al 58 ejected from the immersion nozzle 51 is transferred to the mold 5 through the heat resistant screen 80.
As shown in FIG. 7, the molten aluminum 58 reaches the mold wall on the short side on the short side, while it reaches the bottom side of the heat-resistant screen 80 with a delay. The flow is uneven. Such molten metal flow causes the high temperature molten metal to hit the portion where the initial solidified shell, which is the outermost surface of the ingot, is formed. This causes the problem of frequent vertical cracks and breakouts that progress to. Such a phenomenon is that the average residence time of the molten aluminum in the heat resistant screen is 30 seconds.
It appears remarkably when the flow rate is large as follows.

The contour lines in the figure are heat-resistant screens 80.
The time required for the molten Al 58 flowing out from the above to reach the location is shown.

On the other hand, even when the conventional heat-resistant screen having a coarse mesh is used, it is difficult to uniformly supply the molten metal into the mold.

FIG. 8 shows the conventional heat-resistant screen 70.
FIG. 5 is a diagram showing a molten metal flow when (see FIG. 4) is used,
Similar to FIG. 7, it is a cross section viewed from the long side of the mold, and shows a state in which the Al molten metal 58 ejected from the immersion nozzle 51 is supplied into the mold 53 via the heat resistant screen 70. The contour lines in the figure indicate the heat-resistant screen 70 as described above.
The time required for the molten Al 58 flowing out from the above to reach the location is shown.

In the conventional heat-resistant screen 70 having a coarse mesh on all sides, the most molten metal flows out from the four corners (see FIG. 4).
(Refer to arrow D), but on the other hand, it also flows out from the whole. Therefore, as shown in FIG. 8, a non-uniform molten metal flow centered on the outflow from the corner portion and a non-uniform temperature distribution are obtained. Therefore, solidification progresses unevenly, causing a problem of cracking and breakout.

Therefore, the present invention has been made in view of the above problems. Even if the average flow rate of the molten aluminum in the heat-resistant screen is 30 sec. It is an object of the present invention to provide a heat-resistant screen capable of achieving a uniform molten metal flow inside and obtaining a homogeneous ingot without cracks or breakouts.

[0017]

A heat-resistant screen for continuous casting according to the present invention is a container-shaped heat-resistant screen which is immersed in a molten metal in a mold in a continuous casting apparatus for aluminum or aluminum alloy, wherein the heat-resistant screen has melt-passability. Has a good part and a part with low melt permeability,
80% or more of the area of the screen constituting the bottom surface of the heat-resistant screen is a portion having a good melt-passing property, and 90% or more of the area of the screen constituting the side surface of the heat-resistant screen is the passage of the molten metal. The main point is that it is a low-quality part.

Vertical cracking or breakout of the ingot occurs when the molten metal flow in the mold becomes non-uniform as described above and a thin portion is formed in the solidified shell. Therefore, as a result of simulating the fluidity and temperature distribution of the molten metal using various heat resistant screens, the present inventors did not cause the molten metal to flow out so much in the side surface portion of the heat resistant screen as described above, and mainly melted the molten metal in the bottom portion If it is made to flow out, in the case of a large flow rate (the average residence time of the molten aluminum in the heat-resistant screen is 30 sec.
It has been found that even in the case of the following flow rate), the molten metal can be uniformly supplied into the mold and the molten metal flow can be satisfactorily adjusted, so that an ingot without cracks or breakouts can be obtained. .

Examples of the portion having a low melt passing property include a fine mesh sheet made of glass fiber and a heat-resistant sheet having no eyes (blinds) at all. , A coarse mesh sheet made of glass fiber, and the like.

Further, in the present invention, it is preferable that the opening ratio of the portion having good melt passing property is 12.5% or more and the opening ratio of the portion having low melt passing property is 6% or less. With such an opening ratio, the molten metal passes well in the portion having the opening ratio of 12.5% or more, while the molten metal hardly passes in the portion having the opening ratio of 6% or less, and the molten metal flow is well controlled. It has been confirmed by experiments that this is possible. More preferably, the opening ratio of the portion having a good melt passing property is 25% or more. Further, it is more preferable that the opening ratio of the portion having a low melt passing property is 1% or less.

If the opening ratio is too large in the portion where the melt flowability is good, oxides and the like cannot be removed by filtration, and the jet flow from the immersion nozzle is hardly alleviated. Since it will flow out to the outside as it is, and it will adversely affect the flow of the molten metal in the mold. Therefore, the opening ratio of the portion having good molten metal passage property is preferably 65% or less, more preferably 36%.
% Or less. Further, in the case where the portion having a good molten metal passage property is made of a mesh sheet made of glass fiber, the aperture ratio is 65% or less from the viewpoint of exerting sufficient strength to withstand the dynamic pressure of the Al molten metal. preferable.

Further, in the present invention, the portion having a good molten metal passage property is a mesh sheet having a pore diameter of 1 mm or more,
It is preferable that the portion having a low melt-permeable property is a mesh sheet having a pore diameter of 0.5 mm or less. As described above, it has been confirmed by experiments that the molten metal passes well when the hole diameter is 1 mm or more, and it is difficult to pass the molten metal when the hole diameter is 0.5 mm or less. More preferably, the hole diameter of the portion having good melt passing property is 2 mm or more, and the hole diameter of the portion having low melt passing property is 0.2 mm or less.

In addition, the upper limit of the pore size in the portion where the melt passability is good is 4 from the viewpoint of the filtration removal action of the heat resistant screen and the jet flow relaxation action of the dipping nozzle, as described above.
The thickness is preferably mm or less, and more preferably 3 mm or less.

[0024]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 is a perspective view showing an example of a heat-resistant screen 10 according to the present invention. The heat-resistant screen 10 has a rectangular box shape with an open upper part, and its short sides. Both the side surface portion 11 and the long side surface portion 13 are made of a glass fiber fine mesh sheet having a hole diameter of 0.5 mm and a hole pitch of 2 mm. On the other hand, the bottom end 1 of the bottom 12
2b is composed of a glass fiber coarse mesh sheet having a hole diameter of 1 mm and a hole pitch of 3 mm, and the bottom center portion 12a of the bottom part 12 is made of a glass fiber fine particle having a hole diameter of 0.5 mm and a hole pitch of 2 mm as in the above. It is composed of mesh sheets. The bottom surface end portion 12b occupies 86% of the bottom surface portion area when both end portions 12b are combined, and the remaining 14% area is the bottom surface central portion 12a.

Al molten metal does not pass through the portion of the fine mesh sheet, while the portion of the coarse mesh sheet is A.
The molten metal can pass through well, so that the heat-resistant screen 10 allows the molten aluminum to pass mainly through the bottom portion 12.

FIG. 2 is a diagram showing the flow of molten metal when the above heat-resistant screen 10 is used. It is a cross section as seen from the long side of the mold in the same manner as above, in which the Al molten metal 58 ejected from the immersion nozzle 51 is It is supplied into the mold 53 through the heat resistant screen 10. The contour lines in the figure represent the time taken for the molten Al 58 flowing out of the heat-resistant screen 10 to reach the location, as in the above case. Further, the molten metal flow shown in FIG. 2 has an average residence time 3 of the Al molten metal in the heat-resistant screen.
A case of a large flow rate of 0 sec. Or less is shown.

As can be seen from FIG. 2, when the heat-resistant screen 10 of the present invention is used, the molten aluminum flows in parallel from top to bottom (from the immersion nozzle side to the ingot drawing side). There is. In the heat-resistant screen 10 of the present invention, the molten aluminum does not directly flow out in the lateral direction, but the bottom end portion 1
It is considered that the molten metal flowing out from 2b wraps around to the side surface as shown by arrow E. That is, a molten metal flow that collides with the inner wall of the mold does not occur, and the molten metal flows in a gentle flow, and the circulated Al molten metal is gradually downward in parallel without being disturbed. Therefore, a thin portion does not occur in the initial solidified shell, and the temperature distribution is uniform, so that stable casting is possible, and therefore, there is no defect such as cracking or breakout, and an ingot with good internal quality can be obtained.

Moreover, the heat-resistant screen 10 of the present invention is used when the amount of molten metal supplied is small (for example, Al in the heat-resistant screen).
It has been confirmed that even when the average residence time of the molten metal is 40 sec.), The molten metal flow can be well controlled and a homogeneous ingot can be obtained.

Incidentally, as shown in FIG. 1, it is preferable that the center of the bottom portion is a portion having a low melt-permeable property, because the influence of the jet flow from the immersion nozzle on the outside of the screen can be further mitigated. All of the bottom surface may be a portion having good melt passing property, and the jet flow from the dipping nozzle is moderated by the heat resistant screen having good melt passing property.

<Experiment> Aluminum was cast using the heat-resistant screens shown in FIGS. The molten metal impervious portion of the heat-resistant screen shown in FIG. 6 is composed of a glass fiber fine mesh sheet having a hole diameter of 0.5 mm and a hole pitch of 2 mm as in the heat-resistant screen of FIG. 1, and the molten metal passage portion has a hole diameter of 1 mm and a hole pitch. It is composed of a 3 mm glass fiber coarse mesh sheet, and the molten metal impervious portion (fine mesh sheet) of the bottom portion 82 is 43% of the area of the bottom portion 82. The heat-resistant screen shown in FIG. 4 was composed of a glass fiber coarse mesh sheet having a hole diameter of 1 mm and a hole pitch of 3 mm on the entire surface.

A JIS standard 3004 aluminum alloy is used as a raw material metal for casting, and a mold size is 600 mm × 1500 m.
m, cooling water temperature: 25 ℃, heat-resistant screen size: length 250mm
× width 700 mm × immersion depth 100 mm (volume 17.5 liters), molten aluminum temperature: 700 ° C., molten metal supply rate from the immersion nozzle 45 liters / min., Casting speed: 50 mm / min. The molten metal supply rate from the immersion nozzle is 45 liters / min.
Is the average residence time of the molten aluminum in the heat-resistant screen 23
Corresponds to sec.

As a result of casting, the heat-resistant screen 1 shown in FIG.
When 0 was used, a molten metal flow state was uniform as shown in FIG. 2, and the frequency of cracking of the obtained aluminum ingot was 0.1% or less.

When the heat-resistant screen 70 shown in FIG. 4 was used, the molten metal flow state shown in FIG. 8 was obtained, and the frequency of cracking of the obtained aluminum ingot was about 3%. In this way, the frequency of ingot cracking is high because the high temperature molten metal flows in the upper part of the mold where the initial solidified shell is generated.
It is considered that this is because the initial solidified shell was thinned.

When the heat-resistant screen 80 shown in FIG. 6 was used, the molten metal flow state shown in FIG. 7 was obtained, and the frequency of cracking of the obtained aluminum ingot was about 4%. It is considered that the reason why the occurrence of ingot cracking is high is that the high-temperature molten metal flows into the upper part of the mold where the initial solidified shell is generated, and the initial solidified shell is thinned.

As described above, the heat-resistant screen according to the present invention has been specifically described with reference to the drawings showing an embodiment, but the present invention is not limited to the illustrated examples, and the present invention is not limited thereto.
It is also possible to make appropriate modifications and implement them within a range that is compatible with the gist of the above and below, and all of them are included in the technical scope of the present invention.

For example, a glass fiber mesh sheet having a hole diameter of 4 mm and a hole pitch of 5 mm may be used as the coarse mesh sheet of the portion having a good molten metal passage property.

[0037]

EFFECTS OF THE INVENTION The heat-resistant screen according to the present invention achieves uniform melt flow in the mold even when the average molten metal residence time in the heat-resistant screen is a large flow rate of 30 sec. It is possible to obtain a homogeneous ingot without defects such as cracks and breakouts.

[Brief description of drawings]

FIG. 1 is a perspective view showing an example of a heat-resistant screen according to the present invention.

FIG. 2 is a view showing a molten metal flow when the heat resistant screen shown in FIG. 1 is used.

FIG. 3 is a sectional view for explaining a DC casting method of aluminum.

FIG. 4 is a perspective view showing a conventional heat-resistant screen whose entire surface is composed of a coarse mesh.

FIG. 5 is a perspective view showing a conventional heat-resistant screen partially provided with a molten metal impermeability portion.

FIG. 6 is a perspective view showing a heat-resistant screen which is designed to mainly flow out from a short-side side surface portion.

FIG. 7 is a diagram showing a molten metal flow when the heat-resistant screen shown in FIG. 6 is used.

FIG. 8 is a view showing a molten metal flow when the heat-resistant screen shown in FIG. 4 is used.

[Explanation of symbols]

10,52,70,80 Heat resistant screen 11, 61, 81 Short side surface 12, 62, 82 Bottom part 12a, 62a, 82a Bottom center part 12b, 62b, 82b Bottom end 13, 63, 83 Long side surface 50 upper gutter 51 immersion nozzle 53 Water-cooled mold 54 Cooling water 56 bottom 57 Ingot 58 Al molten metal 63a Long side side center part 63b Long side side end

─────────────────────────────────────────────────── ─── Continuation of the front page (56) Reference JP-A-9-141393 (JP, A) JP-A-11-156487 (JP, A) JP-A-58-212846 (JP, A) JP-A-2- 211937 (JP, A) JP 62-207542 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) B22D 11/103 B22D 11/00 B22D 11/04 311 B22D 11/049

Claims (3)

(57) [Claims] 1. A container-shaped heat-resistant screen which is immersed in a molten metal in a mold in a continuous casting apparatus for aluminum or aluminum alloy, wherein the heat-resistant screen has a portion having a good molten metal passage property and a portion having a low molten metal passage property. 80% or more of the area of the screen that constitutes the bottom surface of the heat-resistant screen is a portion having good melt passage properties, and 90% or more of the area of the screen that constitutes the side surface of the heat-resistant screen is the molten metal. A heat-resistant screen for continuous casting of aluminum or aluminum alloy, which is a portion having low permeability. 2. The aluminum or aluminum alloy according to claim 1, wherein the opening ratio of the portion having good melt passage is 12.5% or more, and the opening ratio of the portion having low melt passage is 6% or less. Heat resistant screen for continuous casting. 3. The hole having a hole diameter of 1 is a portion having good molten metal passage properties.
The heat-resistant screen for continuous casting of aluminum or an aluminum alloy according to claim 1 or 2, wherein the heat-resistant screen is a mesh sheet having a diameter of 0.5 mm or more, and the portion having a low melt permeability is a mesh sheet having a hole diameter of 0.5 mm or less.