JP3171723B2 - Vertical continuous casting method and apparatus for metal - Google Patents

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 and apparatus for a metal, and more particularly to a method for improving the quality of an ingot by preventing oxidation of a molten metal.

[0002]

2. Description of the Related Art Ingots for rolling, extruding and forging non-ferrous metals, particularly aluminum and its alloys, are mostly produced by continuous casting, especially vertical continuous casting. One of the methods is so-called DC casting, in which a molten metal is supplied into a vertically open mold from a molten metal nozzle above the mold, and the amount of molten metal is controlled by a float type molten metal distribution device arranged on the molten metal in the mold. This is a casting method in which a solidified shell is formed by removing heat from the inner wall of the mold, and the ingot is drawn out while spraying a coolant from the lower part of the mold to completely solidify. At this time, in order to reduce friction between the mold and the ingot, a lubricant is previously applied to the inner surface of the mold or continuously supplied during casting.

One of the problems with this method is that since the surface of the molten metal in the mold is in contact with the atmosphere, in the case of a highly reactive molten metal, it reacts with oxygen in the atmosphere on the surface of the molten metal in the mold to form an oxide. Is generated. If the generated oxide is mixed into the surface of the ingot or inside the ingot, not only will the ingot quality significantly deteriorate, but if the amount of oxide is too large, the cooling of the ingot will be uneven, so the molten metal will not be able to solidify completely Hot water leaks from the lower part of the mold, making casting impossible. Particularly, in the case of a highly reactive Al-Li alloy melt, the formation of oxides is remarkable, and casting in an air atmosphere is impossible.

Another problem is that in the case of a highly reactive molten metal such as an Al-Li alloy molten metal, the lubricating oil reacts with the molten metal to generate smoke. When smoke is generated, the casting operation is very difficult or impossible at all because the level of the molten metal in the mold cannot be monitored.

[0005] Although the above two problems can be solved by themselves, each solution exacerbates other problems. That is, if a transparent enclosure is provided above the mold in order to suppress the reaction with the atmosphere and the inside is replaced with an inert gas, the generated smoke cannot be discharged, so that the inside cannot be monitored at all. Conversely, if an air current is generated on the surface of the molten metal in order to efficiently discharge smoke, even if it is an inert gas air flow, the air is entrained, so the contact efficiency between the molten metal and the air is increased and oxide generation is promoted. .

[0006]

SUMMARY OF THE INVENTION It is an object of the present invention to suppress the oxidation reaction by protecting the surface of a molten metal in a mold with an inert gas, and to suppress the smoke generated by the reaction between the lubricating oil and the molten metal. It is an object of the present invention to provide a vertical continuous casting method and an apparatus thereof capable of monitoring the inside by discharging the gas continuously.

[0007]

That is, the method of the present invention comprises:
A molten metal is supplied from above into a vertically opened cylindrical mold via a lubricant, a coolant is injected and solidified, the solidified ingot is drawn into a lower pit, and the pit is forcibly exhausted. In such a vertical continuous casting method, an inert gas is introduced into the upper surface of the molten metal at a flow rate sufficient to discharge smoke generated by a reaction between the lubricant and the molten metal, and the upper surface of the molten metal is forcibly evacuated and the upper surface of the molten metal is removed. A positive pressure state is maintained, and exhaust is performed into the pit.

[0008] The apparatus of the present invention also comprises a cylindrical mold which is opened up and down, a cooling device which injects a coolant into the molten metal supplied from above into the mold to solidify the molten metal, and Atmosphere having a drawing cylinder, a pit provided with an exhaust device for accommodating the ingot to be drawn therein and forcibly exhausting the internal atmosphere, and further having an inlet and an exhaust port for the inert gas which cover the upper surface of the molten metal. A cover is provided, and an exhaust port is communicated with the pit, and the exhaust amount is controlled so as to maintain the inside of the atmosphere cover at a more positive pressure than the inside of the pit, At this time, it is effective to form a part of the atmosphere cover with a transparent material.

[0009]

In order to suppress the oxidation reaction on the surface of the molten metal in the mold, it is necessary to replace the upper surface of the mold with an inert gas. For reliable atmosphere control, a cover must be further provided on the upper surface of the mold, and the inside of the cover must be an inert gas atmosphere. Part of the cover is made of a transparent material so that the inside can be monitored.

However, the provision of the cover makes it impossible to discharge the generated smoke. In order to solve this problem, the cover may be provided with an inlet and an outlet for an inert gas so that the inside of the cover is ventilated by the inert gas flow.

[0011] However, in order to provide sufficient ventilation, the flow rate of the inert gas also increases, and accordingly, the pressure inside the cover increases as the gas flow rate increases. In the case of vertical continuous casting, particularly so-called DC casting, there is always a partial gap between the inner surface of the mold and the ingot. Inert gas flows out from the gap with the lump to the lower part of the mold. When the gas flows out in this way, an inert gas film is formed unevenly in the gap between the coolant injected from the lower end of the mold and the ingot, and the ingot quality is deteriorated due to uneven solidification. In addition, cracks are generated in the ingot, and finally molten metal that cannot be solidified leaks from the lower part of the mold, and casting becomes impossible.

In order to prevent the pressure inside the cover from increasing while increasing the flow rate of the inert gas, it is conceivable to increase the size of the exhaust port. However, when the exhaust port is enlarged, a problem arises in that a backflow of the outside air occurs, and further, a problem arises in that the flow rate of the inert gas needs to be increased. An extreme increase in the flow rate of the inert gas is not only uneconomical, but also causes a decrease in the temperature of the molten metal in the mold, which must be appropriately controlled for maintaining the quality of the ingot.

As another means for preventing the pressure inside the cover from increasing, forcible exhaustion from an exhaust port can be considered. However, in order to keep the pressure inside the cover appropriate and constant, it is necessary to strictly control the flow rate balance between the amount of the inactive gas and the amount of the exhaust gas, which is extremely difficult. That is, if the amount of exhaust gas exceeds the amount of inert gas inflow, the inside of the cover becomes negative pressure. In such a case, the coolant penetrates into the upper portion of the mold from the gap between the inner surface of the mold and the ingot, and the coolant and the molten metal come into direct contact with each other.

Therefore, in order to solve these problems, the balance between the flow rate of the inert gas and the flow rate of the exhaust gas is ensured so that the inside of the cover is stably maintained at a slight positive pressure while securing the required flow rate of the inert gas. Must be controlled.

By the way, in a vertical continuous casting facility, particularly a so-called DC casting facility, an ingot to be produced is almost always drawn into a pit provided below a mold. In most cases, the coolant used for continuous casting is water or some aqueous solution, and a large amount of water vapor is generated in contact with the high-temperature ingot.

The present inventors paid attention to the forced exhaust in the pit. That is, it has been found that the exhaust amount can be automatically controlled by guiding the exhaust pipe of the exhaust port provided in the cover for controlling the atmosphere into the pit. This is because the inside of the cover communicates with the pit that is forcibly exhausted, so the inside of the cover can not be negative pressure than the outside, especially the pit below the mold, and the inert gas flows into the cover This is because a slight positive pressure is maintained outside, especially in the pit below the mold. By using the forced exhaust in the pit in this way, while securing the required inert gas flow rate,
The inside of the cover can be stably ventilated to a slight positive pressure, and the present invention has been completed.

[0017]

BRIEF DESCRIPTION OF THE DRAWINGS FIG. FIG. 1 is an explanatory view of one embodiment of the apparatus according to the present invention in a continuous casting state. The melt passes through the tapping nozzle (1)
While controlling the amount of hot water by the float type molten metal distribution device (2),
It is supplied to the upper and lower open mold (3). The coolant is guided to a coolant chamber (4) in the mold (3) through a coolant supply pipe (not shown), and is further injected into the ingot (6) through the slit (5) to form the ingot (6). Is pulled out into the lower pit (9) by the cylinder (8) together with the base (7).
In order to reduce the friction between the mold and the ingot, a lubricant is applied to the inner surface of the mold in advance, or is continuously supplied from the lubricant supply port (10) during casting.

At this time, an atmosphere cover (11) is installed on the upper surface of the mold (3), and an inert gas is introduced from an inert gas inlet (12) of the cover (11) to thereby form the cover (11). The inside is made into an inert gas atmosphere to prevent oxidation of the molten metal (16) surface. Also, to be able to monitor the inside of the mold,
The upper surface of the cover (11) is made of a transparent monitoring window (13). Further, an exhaust pipe (14) for forced exhaust is provided at the other end of the cover (11) so that smoke generated by the reaction between the lubricating oil and the molten metal is ventilated, and the exhaust pipe (14) is guided into the pit.

The forced exhaust in the cover (11) is performed simultaneously with the exhaust in the pit by the forced exhaust duct (15) in the pit (9). For this reason, the inside of the cover (11) cannot have a negative pressure more than the outside, especially in the pit below the mold (3). Further, since an inert gas flows into the inside of the cover (11), the outside (particularly, the mold (3)) can be reduced. Some positive pressure is maintained than the lower part of (). As described above, stable atmosphere control and stable casting conditions can be maintained by stable pressure control inside the cover (11).

AA8090 alloy having a size of 150 mm × 350 mm was cast by the apparatus of the present invention shown in FIG. 1 under the conditions shown in Table 1. The AA8090 alloy contains about 2.5% of Li and has a very strong oxidizing property, and is therefore an optimal alloy for confirming the effects of the present invention. As Comparative Example 1, the same conditions as in the present invention were used,
An example in which casting was carried out with only the exhaust in the pit stopped is shown, and the same conditions as those of the present invention example were used as Comparative Example 2, but after the inside of the cover was replaced with Ar, the inert gas inlet and the exhaust port were also closed, and ventilation in the mold was performed. Stop casting. Continuous casting was performed using these casting apparatuses, and the results are shown in Table 2.

[0021]

[Table 1]

[0022]

[Table 2]

From Table 2, according to the present invention, a sound ingot could be produced, while in Comparative Examples 1 and 2, ingot production itself was impossible, and even ingot quality could not be compared.

[0024]

According to the present invention, there is a remarkable effect that a sound ingot can be stably produced by continuous casting even if the molten metal is highly oxidizable. The present invention is not limited to the device shown in the embodiment, but is applicable to any device having the same concept.

[Brief description of the drawings]

FIG. 1 is an explanatory diagram showing an embodiment of the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Hot-water supply nozzle 2 Floating-type molten metal distribution device 3 Top and bottom open mold 4 Coolant room 5 Slit 6 Ingot 7 Bottom stand 8 Cylinder 9 Pit 10 Lubricating oil supply port 11 Atmospheric cover 12 Inert gas inlet 13 Monitoring window 14 Exhaust pipe 15 Forced exhaust duct 16 molten metal

Continuation of the front page (58) Field surveyed (Int. Cl. ⁷ , DB name) B22D 11 / 047,11 / 106,11 / 11 B22D 23/00

Claims (3)

(57) [Claims] 1. A molten metal is supplied from above through a lubricant into a cylindrical mold opened vertically and solidified by spraying a coolant, and the solidified ingot is drawn into a lower pit. In the vertical continuous casting method in which the inside is forcibly evacuated, an inert gas is introduced into the pit at a flow rate sufficient to discharge smoke generated by the reaction between the lubricant and the molten metal on the upper surface of the molten metal. A vertical continuous casting method for metal, wherein the upper surface of the molten metal is forcibly evacuated and the upper surface of the molten metal is maintained at a positive pressure. 2. A cylindrical mold that is opened up and down, a cooling device that injects a coolant into a molten metal supplied from above into the mold to solidify the molten metal, a cylinder that pulls out the ingot downward, A pit provided with an exhaust device for accommodating the ingot to be accommodated therein and forcibly exhausting the internal atmosphere, and further provided with an atmosphere cover which covers the upper surface of the molten metal and has an inlet and an outlet for an inert gas, and A vertical continuous casting apparatus for metal, wherein an exhaust port is communicated with the pit, and an exhaust amount is controlled so that the inside of the atmosphere cover is maintained at a more positive pressure than the inside of the pit. 3. The vertical continuous casting apparatus according to claim 2, wherein a part of said atmosphere cover is formed of a transparent material.