JPH06297100A - Vertical type continuous casting method for metal and device therefor - Google Patents

Abstract

PURPOSE:To stably produce a sound cast billet even in the case of molten metal having strong oxidizing property by forcedly evacuating the upper surface of the molten metal and covering with inert gas held under the positive pressure condition, in a vertical continuous casting method drawing the solidified cast billet downward. CONSTITUTION:The molten metal 16 is supplied into a cylindrical mold 3 opening the upper and the lower parts from the upper part and the solidified cast billet 6 is drawn downward. The upper surface of the molten metal is forcedly evacuated and covered with the inert gas held under the positive pressure condition. Further, in this apparatus, a cooling device 4 for solidifying the molten metal 16 by injecting coolant, a cylinder 8 for drawing the cast billet 6 downward and a pit 9 accommodating the drawn cast billet 6 in the inner part thereof and providing an evacuating device 15 for evacuating the inner part atmosphere are provided. Further, an atmospheric cover 11 for covering the upper surface part of the molten metal and is provided with a flowing inlet 12 and a gas exhaust pipe 14 for inert gas is arranged, and this gas exhaust pipe 14 is communicated with the pit. By this method, the oxidation of molten metal is prevented and the quality of a cast billet can be improved.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for vertical casting of metal and its apparatus, and more particularly to improving the quality of ingot by preventing the oxidation of molten metal.

[0002]

Most of the ingots for rolling, extrusion and forging of non-ferrous metals, especially aluminum and its alloys, are manufactured by a continuous casting method, especially a vertical continuous casting method. One of the methods is so-called DC casting, in which the molten metal is supplied into the upper and lower open molds from the molten metal nozzle above, and the amount of molten metal is controlled by a float type molten metal distributor arranged on the molten metal in the mold. Meanwhile, it is a casting method in which the solidified shell is formed by removing heat from the inner wall of the mold, and the ingot is pulled out while injecting the coolant from the lower part of the mold to completely solidify. At this time, in order to reduce the friction between the mold and the ingot, the lubricant is applied to the inner surface of the mold in advance or continuously supplied during casting.

One of the problems of 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 oxides. Is generated. If the produced oxide mixes on the surface of the ingot or inside the ingot, not only will the quality of the ingot be significantly deteriorated, but if the amount of oxide is too large, the ingot will be cooled unevenly and the molten metal will not be able to solidify. Molten metal leaks from the bottom of the mold, making casting impossible. In particular, in the case of an Al-Li alloy melt having a very strong reactivity, 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 melt such as an Al-Li alloy melt, the lubricating oil reacts with the melt to generate smoke. When smoke is generated, the casting operation is very difficult or even impossible because the surface of the molten metal in the mold cannot be monitored.

Although the above two problems may be solved by themselves, each solution makes other problems more serious. That is, if a transparent enclosure is provided on the upper part of the mold in order to suppress reaction with the atmosphere and the interior is replaced with an inert gas, the smoke produced cannot be discharged, and the interior cannot be monitored at all. On the contrary, if an air flow is generated on the surface of the molten metal in order to efficiently discharge smoke, the atmosphere will be involved even if it is an inert gas stream, so the efficiency of contact between the molten metal and the atmosphere will be increased, and oxide formation will be promoted. .

[0006]

An object of the present invention is to suppress the oxidation reaction by protecting the surface of the molten metal in the mold with an inert gas and to effectively produce smoke produced by the reaction between the lubricating oil and the molten metal. The object of the present invention is to provide a vertical continuous casting method and apparatus capable of monitoring the inside by discharging the material.

[0007]

[Means for Solving the Problems] That is, according to the method of the present invention, a molten metal is supplied from above into a cylindrical mold that is open vertically.
In a vertical continuous casting method in which a solidified ingot is drawn downward, the molten metal upper surface is forcibly evacuated and covered with an inert gas that is maintained in a positive pressure state.

Further, the apparatus of the present invention comprises a cylindrical mold which is opened up and down, a cooling device which injects a cooling agent into a molten metal which is supplied into the mold from above and solidifies the molten metal, and an ingot is moved downward. Atmosphere cover having a cylinder for drawing out and a pit equipped with an exhaust device for accommodating the ingot to be drawn out and exhausting the internal atmosphere, and further having an inlet for inert gas and an exhaust port for covering the upper surface of the molten metal Is provided, and the exhaust port is communicated with 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. In order to reliably control the atmosphere, it is necessary to further provide a cover on the upper surface of the mold and make the inside thereof an inert gas atmosphere. Part of the cover is made of transparent material so that the inside can be monitored.

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

However, in order to perform sufficient ventilation, the flow rate of the inert gas also increases, so that the pressure inside the cover rises as the gas flow rate increases. In vertical continuous casting, especially in so-called DC casting, there is always a partial gap between the inner surface of the mold and the ingot, but when the pressure inside the cover, that is, the molten metal surface in the mold increases, the inner surface of the mold and the casting The inert gas flows out to the lower part of the mold through the gap with the lump. When the gas flows out in this way, an inert gas film is unevenly formed in the gap between the coolant injected from the lower end of the mold and the ingot, and the ingot quality deteriorates because the solidification becomes uneven. Moreover, cracks occur in the ingot, and the molten metal that does not solidify finally leaks from the lower part of the mold, making casting impossible.

Therefore, it is conceivable to enlarge the exhaust port in order to prevent the pressure inside the cover from rising while the flow rate of the inert gas is increased. However, if the exhaust port is enlarged, there is a problem that a backflow of outside air occurs, and further, there is a problem that inertness requires an increase in flow rate. Then, the extreme increase in the flow rate of the inert gas is not only uneconomical, but also causes a decrease in the melt temperature in the mold that must be properly controlled to maintain the quality of the ingot.

Further, as another means for preventing the pressure increase inside the cover, forced exhaust from the exhaust port can be considered. However, in order to keep the pressure inside the cover appropriate and constant, the flow rate balance between the inflowing inert gas amount and the exhaust gas amount must be strictly controlled, which is extremely difficult. That is, if the exhaust amount exceeds the inert gas inflow amount, the inside of the cover becomes negative pressure. In such a case, the coolant penetrates into the upper part of the mold through 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, possibly causing an explosion, which is extremely dangerous.

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

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

The present inventors have paid attention to the forced exhaust in the pit. That is, it was found that the exhaust amount can be automatically controlled by introducing the exhaust pipe of the exhaust port provided in the atmosphere control cover into the pit. This is because the inside of the cover communicates with the pit that is forcibly evacuated, so the inside of the cover cannot become a negative pressure than the outside, especially inside the pit below the mold, and the inert gas flows into the cover. Therefore, 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 necessary inert gas flow rate,
It has become possible to ventilate the inside of the cover in a stable manner so as to have a slight positive pressure, thus completing the present invention.

[0017]

Embodiments will be described below with reference to embodiments shown in the drawings. FIG. 1 is an explanatory view of one embodiment of the apparatus according to the present invention in a continuous casting state. The molten metal passes through the tap nozzle (1),
While controlling the amount of molten metal discharged by the float type molten metal distributor (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), further injected through a slit (5) to the ingot (6), and the ingot (6). Is pulled out into the lower pit (9) by the cylinder (8) together with the base (7).
Further, 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 lubricating oil 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 port (12) of the cover (11) to cover the cover (11). The inside is made an inert gas atmosphere to prevent the surface of the molten metal (16) from being oxidized. Also, in order to be able to monitor the inside of the mold,
The upper surface of the cover (11) is a monitoring window (13) made of a transparent material. 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 of the lubricating oil and the molten metal is ventilated, and the exhaust pipe (14) is introduced 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 from the outside, especially from the inside of the pit below the mold (3), and since the inert gas flows into the inside of the cover (11), the outside, especially the mold (3) ) A slight positive pressure is maintained than the lower part. Thus, stable pressure control inside the cover (11) enables reliable atmosphere control and stable maintenance of casting conditions.

Using the apparatus of the present invention shown in FIG. 1, an AA8090 alloy having a size of 150 mm × 350 mm was cast under the conditions shown in Table 1. The AA8090 alloy contains Li in an amount of about 2.5% and has an extremely strong oxidative property, and is therefore an optimum alloy for confirming the effect of the present invention. As Comparative Example 1, under the same conditions as those of the present invention,
An example in which only the exhaust in the pit is stopped and casting is performed is shown. Further, as Comparative Example 2, under the same conditions as in the example of the present invention, after the inside of the cover is replaced with Ar, the inert gas inlet port and the exhaust port are closed to ventilate the mold. Stopped and casted. Continuous casting was performed using these casting devices, and the results are shown in Table 2.

[0021]

[Table 1]

[0022]

[Table 2]

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

[0024]

EFFECTS OF THE INVENTION According to the present invention, even a molten metal having a strong oxidizing property has a remarkable effect that a sound ingot can be stably produced by continuous casting. The present invention is not limited to the device shown in the embodiment, but can be applied to any device having a similar idea.

[Brief description of drawings]

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

[Explanation of symbols]

 1 Hot-water Nozzle 2 Float-type Molten Metal Distributor 3 Vertical Open Mold 4 Coolant Chamber 5 Slit 6 Ingot 7 Bottom Stand 8 Cylinder 9 Pit 10 Lubricant Supply Port 11 Atmosphere Cover 12 Inert Gas Inlet 13 Monitoring Window 14 Exhaust Pipe 15 Forced exhaust duct 16 Molten metal

Claims (3)

[Claims] 1. In a vertical continuous casting method in which a molten metal is supplied from above into a vertically open cylindrical mold and a solidified ingot is drawn out downward, the molten metal upper surface is forcibly exhausted and kept in a positive pressure state. A vertical continuous casting method for metal, which is characterized in that it is covered with the inert gas. 2. A cylindrical mold opened vertically, a cooling device for injecting a cooling agent into a molten metal supplied from above into the mold to solidify it, a cylinder for pulling out an ingot downward, and a withdrawal. A pit having an exhaust device for accommodating the ingot to be exhausted therein and for exhausting the internal atmosphere, and further, providing an atmosphere cover having an inflow port and an exhaust port for the inert gas, which covers the upper surface of the molten metal, and A vertical vertical metal casting apparatus having an exhaust port communicating with the inside of the pit. 3. The vertical continuous casting apparatus according to claim 2, wherein a part of the atmosphere cover is made of a transparent material.