JPH091289A - Method for casting al or al alloy in electromagnetic field - Google Patents

Abstract

PURPOSE: To improve the surface quality of a cast block by preventing the nonuniformity of thickness of a surface oxidation film layer and the local crack on the surface oxidation film layer. CONSTITUTION: In a casting method of Al in an electromagnetic field, a pouring nozzle 7 for flowing out molten Al and an electromagnetic coil 3 so as to surround this pouring nozzle 7 are arranged, and while holding the molten Al flowed out from the pouring nozzle 7 to a columnar state by electromagnetic force generated with an electromagnetic coil 3, the side surface of molten metal 2 held to this columnar state is cooled with cooling medium to form the cast block and this cast block is drawn downward to cast Al. Then, a shifting magnetic field generating means 1 is arranged just above the surface of molten metal 2 held to the columnar state and circular flow (a) in the horizontal direction is given on the upper surface layer of the molten metal 2 held to the columnar state by this shifting magnetic field generating means 1.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention holds an Al or Al alloy melt in a columnar shape inside an electromagnetic coil by an electromagnetic force generated by the electromagnetic coil and cools it to form an ingot, and the ingot is drawn downward. TECHNICAL FIELD The present invention relates to an electromagnetic field casting method for Al or Al alloy to be cast by casting, and particularly to an electromagnetic field casting method for Al or Al alloy which improves the quality of the ingot surface.

[0002]

2. Description of the Related Art As one of the methods for casting Al or an Al alloy (hereinafter represented by Al), a semi-continuous casting method called an electromagnetic field casting method is carried out. This method is
A pouring nozzle from which the molten metal flows out and an electromagnetic coil are arranged so as to surround the pouring nozzle, and the Al molten metal flowing out from the pouring nozzle is held in a non-contact columnar shape by the electromagnetic force generated by the electromagnetic coil. On the other hand, the side surface of the molten metal held in a columnar shape (hereinafter referred to as molten metal column) is cooled with a cooling medium to form an ingot, and this ingot is drawn downward and cast. With such an electromagnetic field casting method, it is said that a relatively smooth ingot surface can be obtained, the omission of the chamfering step before rolling and reduction of the chamfering amount can be achieved, and it is also structurally excellent. In recent years, particular attention has been paid to the production of such ingots.

When an ingot is cast from the molten aluminum by the above electromagnetic field casting method, an oxide film layer is formed on the upper surface of the molten aluminum column, and this oxide film layer is constantly formed on the peripheral portion during casting due to the flow of the molten aluminum. It moves to form the surface layer of the ingot. However, especially when casting a rectangular ingot, since the distance from the pouring nozzle is not equal all around,
The movement of the oxide film layer on the upper surface is not always uniform and smooth, and the oxide film layer tends to locally grow thick and locally form large cracks. Then, gas and inclusions separated and floated from the molten Al tend to stagnate in the lower part of the thickly grown oxide film layer, and vertical streak defects start from there. Further, the cracks in the oxide film layer tend to be the starting points of ingot cracks. Therefore, the presence of the above-mentioned defects due to the oxide film layer not only impairs the appearance of the ingot to be obtained, but is also unfavorable in terms of surface quality, and is a feature of the ingot to be obtained by electromagnetic field casting. Omission of the cutting process and reduction of the amount of chamfering will not be achieved.

[0004]

For these reasons, various electromagnetic field casting techniques for improving the quality of the surface of the ingot have been proposed so far. As such a method, for example, a frame weir is disposed near the outer periphery of the surface of the molten Al column to control the movement of the oxide film (see, for example, Japanese Patent Publication No.
-40210 gazette), the upper surface of the molten metal column is covered with conductive slag or flux, and the molten metal column is sealed by disposing a shell weir near the outer peripheral surface to generate oxides in the molten metal column. A method of controlling the growth (see, for example, Japanese Patent Publication No. 59-35708), a cover member is arranged so as to surround the upper and lower portions of the molten metal column, and an inert gas is introduced into the cover member so that the surface of the molten metal column is covered. A method for controlling oxide formation / growth (for example, Japanese Patent Laid-Open No. 1-12
7143 gazette)).

However, according to the above method, the movement of the oxide film from the inside to the outside of the frame weir cannot be completely suppressed and controlled, and the nonuniformity of the oxide film formed on the outside of the frame weir is eliminated. I can't do it either. In the above method, there is a problem that the apparatus structure becomes complicated, maintenance becomes complicated, cost is increased, and slag and flux are entrained in the ingot. In the above method, unless a highly pure inert gas is used,
It is not possible to exert the sealing effect on the surface of the molten metal column,
There is a problem in that the use of high-purity inert gas causes high cost.

The present invention has been made in order to solve the technical problems in the prior art, and its object is to prevent uneven thickness of the surface oxide film layer and local cracks in the surface oxide film layer. It is intended to provide an electromagnetic field casting method of Al or Al alloy which can prevent and achieve improvement of the surface quality of the ingot.

[0007]

In order to achieve the above object, the electromagnetic field casting method of Al or Al alloy according to the present invention comprises:
A pouring nozzle from which Al or Al alloy molten metal flows out, and an electromagnetic coil is arranged so as to surround the pouring nozzle, and the Al or Al alloy molten metal flowing out from the pouring nozzle is pillared by an electromagnetic force generated by the electromagnetic coil. While holding
In the electromagnetic field casting method of Al or Al alloy in which the side surface of the molten metal held in this column shape is cooled by a cooling medium to form an ingot, and the ingot is drawn downward and cast, the surface of the molten metal held in the column shape A moving magnetic field generating means is provided immediately above, and a horizontal swirling flow is applied to the upper surface layer of the molten metal held in a columnar shape by the moving magnetic field generating means.

In the above-mentioned electromagnetic field casting method of Al or Al alloy, the swirling flow in the horizontal direction may be applied intermittently, or it may be applied by reversing periodically. Good.

In addition, in the electromagnetic field casting method of Al or Al alloy described above, the amount of 200 to 200
A moving field of 300 gauss may be applied to provide a horizontal swirling flow.

[0010]

In the present invention, a horizontal swirling flow is imparted to the Al melt in the upper surface layer of the molten metal column by the moving magnetic field generating means provided directly above the surface of the molten metal column held by electromagnetic force. As a result, the oxide film layers generated on the surface of the molten metal column are shredded one after another and swirl on the surface of the molten metal. Microscopically, the oxide film layer thus shredded will have uneven thickness and minute cracks, but the swirling flow causes the oxide film layer to move relatively uniformly to the periphery. Since the surface layer of the ingot is formed, when viewed macroscopically over the entire circumference of the ingot, the thickness fluctuation of the oxide film layer in the initial stage forming the ingot surface layer is small and there is no local stagnation of gas or inclusions. In addition to the above, it is possible to make the cracks of the oxide film fine so as not to be a starting point of the ingot crack.

The horizontal swirling flow may be a continuous one-way flow, but an intermittent flow or a flow in which the flow direction is periodically reversed can be used. By doing so, the oxide film layer generated on the surface of the molten metal column can be shredded more finely, which makes it possible to further reduce the thickness variation of the oxide film layer in the initial stage of forming the ingot surface layer and to reduce the oxidation. The cracks in the coating can also be made finer than the starting point of ingot cracking.

In order to fully enjoy the above-mentioned effects, the horizontal swirling flow imparted to the molten metal should be at a position relatively shallower than the upper surface of the molten metal column and at a flow velocity that does not significantly disturb the flow. For this purpose, the magnetic flux density applied by the moving magnetic field generating means is preferably 200 to 300 gauss. Furthermore, it is desirable that the horizontal swirl flow is generated on the molten metal surface portion immediately before solidification, that is, on the side surface of the molten metal column. Therefore, the moving magnetic field generating means should be provided directly above the outer peripheral side of the upper surface of the molten metal column as much as possible. .

[0013]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a schematic plan view of an electromagnetic field casting apparatus to which the electromagnetic field casting method according to the present invention is applied, and FIG.
-A sectional view, in which, 1 is a moving magnetic field generator, 2 is a molten metal column, 3 is an electromagnetic coil, 4 is an ingot, 5 is a magnetic field shielding screen, 6 is a cooling medium, and 7 is a pouring nozzle. Show. The electromagnetic field casting apparatus shown in FIGS. 1 and 2 is for manufacturing a rectangular ingot.

The Al melt 8 which has been melted in a melting furnace (not shown) and which has undergone the steps of adjusting alloy components, degassing, removing inclusions, etc., is surrounded by the pouring nozzle 7 and the electromagnetic coil 3. The area is poured. An electromagnetic force from the electromagnetic coil 3 acts on the poured Al molten metal 8 so that the molten molten aluminum 8 is held in a non-contact state within the region, the molten metal column 2 is formed, and is sequentially cooled by a cooling medium 7 such as water to solidify. Then, ingot 4 is formed. At this time, a horizontal swirl flow a is imparted to the upper surface layer of the molten metal column 2 by the moving magnetic field generation device 1 arranged immediately above the upper surface of the molten metal column 2, and the swirl flow a causes the swirl flow a of the molten metal column 2. The oxide film layer generated on the surface is shredded one after another and swirls on the surface of the molten metal.

Since the shredded oxide film layer moves relatively uniformly to the peripheral portion by the swirling flow a to form the surface layer of the ingot 4, the initial surface of the ingot surface layer is formed. The thickness variation of the oxide film layer can be made small, the gas and inclusions are not locally stagnate, and the oxide film becomes fine so that cracks of the oxide film do not become the starting points of ingot cracks, and an ingot with good surface quality can be obtained.

Using the electromagnetic field casting apparatus shown in FIGS.
A molten aluminum-Mg alloy (JIS 5182 alloy) was subjected to a moving magnetic field having a frequency of 60 Hz and a magnetic flux density of 0 to 500 Gauss to form a rectangular ingot having a thickness of 600 mm and a width of 1200 mm. At this time, the casting speed was 75 mm / min, and the pouring temperature was 700 ° C., which was constant. Table 1 shows the results of evaluation of the surface properties of the obtained ingot by the number of vertical line defects formed on the surface, the average depth thereof, and the variation in the thickness of the ingot.

[0017]

[Table 1]

Since the Al-Mg alloy has a strong oxidizing power of Mg as an alloying component, it tends to form a thick oxide film layer on the surface of the molten metal, and the thickness of this oxide film layer is increased by the conventional electromagnetic field casting method. There was a tendency for wrinkle-like vertical line defects to occur on the rolling surface on the side surface of the ingot due to unevenness of movement and movement speed, but as is clear from Table 1, according to the present invention, vertical line defects are significantly improved. I understand that it will be done. However, when the magnetic flux density is strong, the swirling flow velocity of the molten metal becomes fast, the flow is disturbed, and this tends to cause ingot thickness variation, while when the magnetic flux density is weak, the effect of the horizontal swirling flow cannot be obtained, Longitudinal streak defects appear. Therefore, the magnetic flux density applied to the molten metal is 2
00-300 gauss is preferred.

[0019]

As described in detail above, the Al according to the present invention
Alternatively, according to the electromagnetic field casting method of an Al alloy, surface defects such as vertical streak defects and ingot cracks generated on the surface of the Al or Al alloy ingot can be significantly reduced, and an ingot with excellent surface quality can be manufactured. Became. As a result, the surface before being rolled can be flattened or the amount of chamfered can be reduced, and the yield can be significantly improved.

[Brief description of the drawings]

FIG. 1 is a schematic plan view of an electromagnetic field casting apparatus to which an electromagnetic field casting method according to the present invention is applied.

FIG. 2 is a sectional view taken along line AA of FIG.

[Explanation of symbols]

1: Moving magnetic field generator 2: Molten metal column
3: Electromagnetic coil 4: Ingot 5: Magnetic field shielding screen
6: Cooling medium 7: Pouring nozzle 8: Al molten metal
a: Horizontal swirling flow

Claims (4)

[Claims] 1. A pouring nozzle through which Al or Al alloy molten metal flows out, and an electromagnetic coil surrounding the pouring nozzle, and the electromagnetic coil generates Al or Al alloy molten metal flowing out from the pouring nozzle. Electromagnetic field casting method of Al or Al alloy in which an ingot is formed by cooling the side surface of the molten metal held in a column shape with a cooling medium while holding it in a column shape by an electromagnetic force In the above, a moving magnetic field generating means is provided immediately above the surface of the molten metal held in the columnar shape, and a horizontal swirling flow is applied to the upper surface layer of the molten metal held in the columnar shape by the moving magnetic field generating means. Electromagnetic field casting method of Al alloy. 2. The electromagnetic field casting method of Al or Al alloy according to claim 1, wherein a horizontal swirling flow is intermittently applied. 3. The electromagnetic field casting method of Al or Al alloy according to claim 1, wherein the horizontal swirling flow is periodically reversed and imparted. 4. Al or Al according to claim 1, 2 or 3.
In the electromagnetic field casting method of an alloy, an electromagnetic field casting method of Al or Al alloy in which a moving magnetic field of 200 to 300 Gauss is applied to the upper surface layer of the molten metal held in a column shape to impart a horizontal swirling flow.