JP5113413B2 - Aluminum ingot casting method - Google Patents

Description

  The present invention relates to a casting method for an aluminum ingot, and a casting apparatus used for the casting method, in which an aluminum ingot useful as a rolling material such as a reflector, a sputtering target material, and an electrode foil of an electrolytic capacitor is semi-continuously cast. About.

  Conventionally, high-purity aluminum plates and foils have been used for reflectors, sputter target materials, electrolytic capacitor electrode foils, and the like. Plates and foils used for these applications are required to have uniform surface treatability, crystal orientation, recrystallized grain size, and the like. The characteristics of such plates and foils are mainly controlled in a homogenization process and a rolling process performed subsequent to the casting process of the ingot material, but are also affected by the uniformity of the ingot used as a raw material.

  The high-purity aluminum ingot used as a raw material is manufactured by various casting methods, but the casting method using a water-cooled vertical semi-continuous casting mold is the most common. More specifically, molten aluminum is supplied from the top to a cylindrical mold having a hollow portion having a quadrangular prism shape that is open at the top and bottom, and is primarily cooled through the casting wall with cooling water supplied into the cylinder around the mold. , By casting the cooling water obliquely downward from the lower end of the mold, the molten aluminum is solidified by secondary cooling, and continuously drawn out from the lower part, thereby casting the ingot to a certain length. This is a so-called semi-continuous casting method. In this case, a mold made of a metal such as copper or aluminum is usually used from the viewpoint of thermal conductivity.

However, when the above-described conventionally known water-cooled vertical semi-continuous casting mold is used, the temperature of the molten metal gradually decreases from the primary cooling, and a certain amount of time is required until it is forcibly cooled and solidified by the secondary cooling. It will take. In other words, the cooling of the molten metal proceeds slowly, and as a result, the macrostructure and microstructure near the casting surface that are directly water-cooled by secondary cooling become finer, and the macrostructure and microstructure of the ingot center portion. Tended to lead to inhomogeneities of roughening. Such non-uniformity adversely affects the crystal orientation in the width direction and thickness direction of the plate or foil, the recrystallized grain size, surface treatment properties, etc. when the obtained aluminum ingot is used as a plate material or foil material. And reduce the product yield.
In addition, when the above-described conventionally known water-cooled vertical semi-continuous casting mold is used, there is a problem that the sliding property between the metal constituting the mold and the molten aluminum is insufficient. If the molten aluminum does not slide smoothly, there is a problem that the solidified part does not fall during casting.

Therefore, until now, the surface of the mold is roughened (see Patent Document 1), or a plurality of grooves 20 are provided in the casting direction (advancing direction of the molten metal) as shown in FIG. A metal mold has been proposed in which the contact surface with the metal is reduced, thereby providing the mold with heat insulation to suppress the temperature drop of the molten metal in the primary cooling and to improve the sliding property of the molten aluminum. It was.
JP 55-64950 A

  However, with the conventional metal mold, the slipperiness of the molten aluminum is considerably improved, but the thermal insulation performance is still not satisfactory until the uniformity of the macrostructure and microstructure of the resulting ingot is reached. The situation was not reached.

  Accordingly, an object of the present invention is to provide a casting method for an aluminum ingot and the casting method capable of semi-continuously casting an aluminum ingot excellent in uniformity of a macro structure and a microstructure from the vicinity of the surface to the inside. It is to provide a casting apparatus to be used.

  As a result of intensive research to solve the above-mentioned problems, the present inventors have found that a part of the inner surface of the mold that comes into contact with the molten aluminum in semi-continuous casting of an aluminum ingot using a water-cooled vertical semi-continuous casting mold. Is used instead of a graphite plate, the temperature of the molten aluminum supplied to the mold (casting temperature) is set to 760 ° C. or higher, and the amount of cooling water is 25 L / kg-Al or more. It has been found that by using more than before, an ingot having a uniform macrostructure and microstructure from the surface to the inside can be semi-continuously cast.

  That is, by using a mold in which a part of the inner surface of the mold that is in contact with the molten aluminum is replaced with a graphite plate, the molten aluminum is ensured to be slidable, and at the same time, a more reliable heat insulating property is exhibited and the molten metal is cast. It is possible to avoid excessive deprivation of the heat of the molten metal in the region in contact with. When a high-temperature molten metal is supplied to such a mold, the molten metal is rapidly cooled from a high-temperature state at once by cooling water that is poured obliquely downward from the lower end of the mold while maintaining the high temperature. The When solidified by such rapid cooling, the difference between the cooling rate inside the ingot and the cooling rate near the surface can be kept small, and as a result, the macrostructure and the microstructure can be made uniform. The present invention has been completed based on these findings.

The present invention has the following configuration.
(1) Supplying molten aluminum from the upper part to the hollow part of a cylindrical water-cooled vertical semi-continuous casting mold having a hollow part that has a rectangular column shape with an open top and bottom, solidified with cooling water, In a method of semi-continuously casting an aluminum ingot by continuously pulling out from the lower part, at least half of the casting direction of the side surface in contact with the hollow portion to which the molten aluminum is supplied is composed of a graphite plate. And the temperature of the molten aluminum supplied to the mold is 760 ° C. ( excluding the mold whose entire side surface contacting the hollow portion to which the molten aluminum is supplied is made of a graphite plate). A casting method for an aluminum ingot, characterized in that the cooling water is discharged at a rate of 25 L / kg-Al or more from the slit at the bottom of the mold.
(2) The method for casting an aluminum ingot according to (1), wherein the graphite plate is not disposed at a corner of a hollow portion having a quadrangular prism shape.
(3) The method for casting an aluminum ingot according to (1) or (2), wherein the casting speed is 55 mm / min or less.
(4) A casting apparatus for use in the method for casting an aluminum ingot according to any one of (1) to (3), wherein the cylindrical water cooling has a hollow portion having a quadrangular prism shape with the top and bottom open. A vertical semi-continuous casting mold, a spout hanging from above near the center axis of the mold, a flow dividing plate horizontally disposed near the lower end of the spout, and a bottom block positioned so as to be movable up and down below the mold More than half of the casting direction of the side surface in contact with the hollow portion to which the molten aluminum is supplied (excluding the entire side surface in contact with the hollow portion to which the molten aluminum is supplied). An apparatus for casting an aluminum ingot, characterized by comprising a plate made of graphite.
(5) The aluminum ingot casting apparatus according to (4), wherein the graphite plate is not disposed in a corner portion of a hollow portion having a quadrangular prism shape.
(6) The apparatus for casting an aluminum ingot according to (4) or (5), wherein the graphite plate is configured to be detachable.
In addition, the aluminum in this specification includes various aluminum alloys as well as pure aluminum.

  According to the present invention, an effect that semi-continuous casting of an aluminum ingot having excellent macro structure and micro structure uniformity from near the surface to the inside can be obtained. Furthermore, if the macrostructure of the resulting aluminum ingot is uniform, there is an advantage that uniform recrystallization characteristics can be obtained in the homogenization process. In addition, if the microstructure of the resulting aluminum ingot is uniform, the solute elements are likely to be uniformly solid-dissolved during the homogenization process, and the homogenization process temperature can be lowered and the processing time can be shortened. This is also advantageous in terms of energy costs.

Hereinafter, an embodiment of a casting apparatus of the present invention will be described with reference to the drawings.
FIG. 1 is a schematic view showing a vertical section of an embodiment of a casting apparatus of the present invention that can be preferably used in the method for casting an aluminum ingot of the present invention, and FIG. 2 is a mold in the apparatus shown in FIG. 3 is a partially enlarged vertical sectional view of FIG. 3, and FIG. 3 is a sectional view of the mold 3 in the apparatus shown in FIG.

  As shown in FIG. 1, the apparatus 1 includes a cylindrical water-cooled vertical mold 3 having a hollow portion 2 having a quadrangular prism shape that is open at the top and bottom, and a spout hanging from above near the center axis of the mold 3. 4, a flow dividing plate 5 disposed horizontally near the lower end of the spout 4, and a bottom block 6 positioned so as to be movable up and down below the mold 3. Further, on the outer side below the spout 4, A rectangular float 7 that floats on the supplied molten aluminum M is disposed. In addition, the hollow part 2 exhibits a rectangle by planar view as shown in FIG. 3, and usually has a size of about 300 to 600 mm on the short side and about 1000 to 2000 mm on the long side.

  The mold 3 has a shape having a cooling water hollow portion 8 having a square cross section outside the hollow portion 2. A slit 9 is formed obliquely downward at the lower end of the hollow portion 2, and the cooling water W supplied to the hollow portion 8 is poured obliquely downward with respect to the molten aluminum M below the hollow portion 2. Can be done.

  The mold 3 includes a graphite plate 10 on a side surface in contact with the hollow portion 2, that is, a part of a contact surface with the molten aluminum M. For example, as shown in FIG. 2, the graphite plate 10 is provided with a space for mounting the graphite plate 10 from the side surface in contact with the hollow portion 2 of the mold 3 to the upper portion thereof, and the graphite plate is provided in the space. 10 is fitted, and the lid member 11 fitted in the upper part thereof is fixed with a bolt 12 so as to be detachable. As described above, if the graphite plate 10 is detachable, even if the graphite plate 10 is damaged due to contact with the solidified molten aluminum M or the like and is worn out or deteriorated, maintenance such as replacement can be easily performed. The advantage of becoming is obtained.

  The graphite plate 10 is preferably not disposed at the corner 2 'of the hollow portion 2 having a quadrangular prism shape, as shown in FIG. As a result, the molten aluminum M supplied to the hollow portion 2 is in a state where it is in contact with the mold 3, so that only the corner portion is not subjected to the heat insulating effect and solidifies slightly. When drawn downward, the molten aluminum M can be kept in a relatively stable shape without leaking from the corner portion of the mold 3, and as a result, it can be drawn at a desired casting speed. In this case, the corners of the ingot C to be obtained tend to have a non-uniform macrostructure and microstructure as compared with other parts. By removing it as an end, the adverse effect can be eliminated.

  The material of the part other than the graphite plate 10 (including the lid member 11) among the constituent members of the mold 3 is not particularly limited, and is generally composed of a metal such as copper or aluminum, but it is lightweight and It is preferable that it is made from aluminum at the point which is excellent in stain resistance.

  Next, an embodiment of a casting method for an aluminum ingot according to the present invention will be described. In this embodiment, by using the apparatus 1 shown in FIG. 1 described above, the molten aluminum M is supplied to the hollow portion 2 from the upper portion, solidified by the cooling water W, and continuously pulled out from the lower portion, An aluminum ingot is cast semi-continuously.

  When supplying the molten aluminum M, the bottom block 6 is arranged in advance under the hollow portion 2 of the mold 3. In this state, molten aluminum M made of aluminum that has been refined by removing impurities in advance or appropriately mixed with necessary elements is poured from the spout 4 and collided with the flow dividing plate 5, so that the molten metal M enters the hollow portion 2. Supply radially. At this time, by arranging the float 7, a certain amount of the molten metal M is uniformly filled in the hollow portion 2. The bottom block 6 is filled with the supplied molten aluminum M in the hollow portion 2 and lowered downward.

  The temperature (casting temperature) of the molten aluminum M supplied to the mold 3 is important to be 760 ° C. or higher, and preferably 780 ° C. or higher. When the casting temperature is less than 760 ° C., the temperature gradient when the molten metal M is cooled by the addition of cooling water is reduced (in other words, it is not rapidly cooled), and the macro structure and the microstructure are not sufficiently uniformized. It becomes.

On the other hand, the cooling water hollow portion 8 of the mold 3 is continuously supplied with cooling water W at a predetermined flow rate from a cooling water supply hole (not shown), and is discharged obliquely downward from the slit 9 at the lower end of the mold 3. Let
The amount of the cooling water W to be discharged from the slit 9 below the mold 3 is 25 L / kg-Al or more (25 L or more per 1 kg of molten aluminum M supplied into the hollow portion 2). Preferably, it is 30 L / kg-Al or more. When the amount of the cooling water W is less than 25 L / kg-Al, the temperature gradient when the molten metal M is cooled is reduced (in other words, it is not rapidly cooled), and the macro structure and the microstructure are not sufficiently uniformized. It becomes.

  As described above, by setting the casting temperature and the discharge amount of the cooling water W within the above ranges, the molten metal M sequentially supplied into the hollow portion 2 is hardly deprived of heat (however, in actuality, it is heated The solidified layer of about several millimeters for maintaining the shape of the molten metal M is formed only on the surface due to slight heat dissipation that naturally occurs in an environment where heat is not kept), the contact area with the mold 3, that is, the hollow portion After passing through 2, the cooling water W poured obliquely downward from the slit 9 at the lower end of the mold 3 is rapidly cooled from the temperature at the time of supply, and rapidly solidifies from the outer surface to the inside. When solidified in this way, ingots C are sequentially formed below the solidification interface K shown in FIG.

  For example, instead of the above-mentioned mold 3, when using a metal mold with a groove as shown in FIG. 4 which has been widely used conventionally, the molten metal M begins to be gradually cooled from the contact area with the mold. The solidification interface at which the molten metal M changes to the ingot C is gradually lowered from the contact area with the mold as shown by a broken line K ′ in FIG. 1, and then cooled by the cooling water W and extends toward the center. The vicinity of the part is the lowest pointed shape. Even when the mold 3 is used, when the casting temperature and the discharge amount of the cooling water W are out of the above ranges, the starting point of the solidification interface is in direct contact with the molten metal M. Although it decreases from the vicinity of the surface (casting surface), the temperature gradient at the time of cooling is smaller than in the case of the casting method of the present invention, so the shape of the solidification interface is also the sharpest shape near the center. . On the other hand, according to the casting method of the present invention, the solidification interface K gradually decreases from the portion where the cooling water W at the lower end of the mold 3 is poured as shown in FIG. It will draw a flat line. Thereby, the aluminum ingot C excellent in the uniformity of the macro structure and the microstructure from the surface vicinity to the inside is obtained.

  When the formed ingot C is continuously pulled out from the lower portion by the bottom block 6, the lowering speed of the bottom block 6, that is, the casting speed is preferably 55 mm / min or less, more preferably 40 to 50 mm / min. It is good to do. If the casting speed is faster than the above range, the uniformity of the macro structure and the microstructure may be reduced, or the molten metal M may leak during casting. On the other hand, if the casting speed is too slow, production efficiency is lowered, which is not preferable.

EXAMPLES Hereinafter, although an Example demonstrates this invention in detail, this invention is not limited to a following example.
Example 1
2000 kg of high-purity aluminum purified in three layers in an aluminum melting furnace was melted, and the composition was adjusted to Si: 10 ppm, Fe: 7 ppm, Cu: 33 ppm to obtain a molten aluminum. While maintaining this molten aluminum at 790 ° C., as shown in FIGS. 1 to 3, an aluminum water-cooled vertical semi-continuous casting mold partially equipped with a graphite plate (the dimension of the mold 3 is a depth). (Length in casting direction): 100 mm (inside, graphite plate: 50 mm), long side of hollow part 2: 1000 mm (inside, graphite plate: 960 mm), short side of hollow part 2: 400 mm (inside, Graphite plate: 360 mm)) (casting temperature 790 ° C.), cooling water is discharged from the slit at the bottom of the mold at 30 L / kg-Al, solidified, and drawn from the bottom at 50 mm / min (casting speed 50 mm / min) Thus, an ingot material having a length of 2000 mm was obtained.

(Comparative Example 1)
Instead of the mold used in Example 1, as shown in FIG. 4, an aluminum water-cooled vertical semi-continuous casting mold with fine grooves having grooves of 0.8 mm in width and 0.5 mm in depth at intervals of 1.3 mm Ingot material having a length of 2000 mm was obtained in the same manner as in Example 1 except that cooling water was discharged from the slit at the bottom of the mold at 20 L / kg-Al and solidified.

(Comparative Example 2)
Instead of the mold used in Example 1, as shown in FIG. 4, an aluminum water-cooled vertical semi-continuous casting mold with a rough groove having grooves with a width of 2 mm and a depth of 0.5 mm at intervals of 5 mm was used for casting. An ingot material having a length of 2000 mm was obtained in the same manner as in Example 1 except that the temperature was set to 740 ° C. and cooling water was discharged from the slit at the bottom of the mold at 20 L / kg-Al and solidified.

  The uniformity of the macro structure and the microstructure in the aluminum ingot obtained in the above Examples and Comparative Examples was evaluated by the following methods. The results are shown in Table 1.

<Macro-structure crystal grain size>
A sample cut by a cross section orthogonal to the casting direction (solidification direction) of the ingot is immersed in aqua regia (hydrochloric acid: nitric acid (weight ratio) = 3: 1) at 25 ° C. for 3 to 10 minutes, Etching was performed so that a macro structure appeared in the cross section. This macrostructure is visually observed, the macrostructure crystal grain size near the casting surface and the macrostructure crystal grain size inside the ingot are counted by counting the number (X) of crystal grains crossing a straight line having a length of 250 mm. Calculated based on the formula. When counting crystal grains, in the vicinity of the casting surface, which is relatively fine, the counting is performed at a portion located 15 mm from the casting surface (in other words, a straight line with a length of 250 mm is 15 mm from the casting surface over the entire length. The value is set as a representative value. On the other hand, in the ingot, which is a coarse particle, counting is performed at three portions located inside 50 mm, 100 mm, and 150 mm from the casting surface (in other words, a straight line having a length of 250 mm to be counted is 50 mm from the casting surface over the entire length. , 100 mm, and 150 mm), and the average value thereof was used as a representative value.
Macrostructure crystal grain size (mm) = 250 mm / number (X)

<Microstructure spacing>
By sequentially emery polishing, buffing, and electrolytic polishing on a sample cut in a cross section parallel to the casting direction (solidification direction) of the ingot, and then etching with a 5% NaOH aqueous solution at 50 ° C. for 5 minutes. The microstructure appeared in the cross section. In this microstructure, a plurality of cells generated in parallel with the casting direction are observed by removing the portion where impurities are concentrated by etching. This microstructure was observed with a 50-fold metal microscope, and the interval between the cells in which the cells were observed in parallel in the microstructure (cell interval of the microstructure) was measured.

It is the schematic which shows one Embodiment of the casting apparatus of this invention which can be preferably used for the casting method of the aluminum ingot of this invention in a vertical cross section. FIG. 2 is a vertical cross-sectional view showing a partially enlarged mold 3 in the apparatus shown in FIG. 1. It is sectional drawing when the casting_mold | template 3 in the apparatus shown in FIG. 1 is cut | disconnected by XX cross section. It is the schematic which looked at the partial vertical cross-section of the conventional grooved metal water-cooled vertical semi-continuous casting mold.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Apparatus 2 Hollow part 3 Water-cooling vertical mold 4 Spout 5 Dividing plate 6 Bottom block 7 Float 8 Cooling water hollow part 9 Slit 10 Graphite plate 11 Lid member 12 Bolt M Aluminum molten W Cooling water C Aluminum ingot

Claims (6)

To the hollow part of the cylindrical water-cooled vertical semi-continuous casting mold having a hollow part that has a rectangular column shape that is open at the top and bottom, molten aluminum is supplied from the upper part and solidified by cooling water. In a method of semi-continuously casting an aluminum ingot by pulling out from the lower part,
A mold in which at least half of the casting direction of the side surface in contact with the hollow portion to which the molten aluminum is supplied is made of a graphite plate (however, the entire side surface in contact with the hollow portion to which the molten aluminum is supplied is graphite. excluding mold that consists of manufacturing of the plate.) with use, the temperature of the molten aluminum is supplied to the mold and 760 ° C. or higher, and, emitting at the cooling water from the mold bottom of the slit 25L / kg-Al or The casting method of the aluminum ingot characterized by the above-mentioned.   The method for casting an aluminum ingot according to claim 1, wherein the graphite plate is not disposed at a corner of a hollow portion having a quadrangular prism shape.   The method for casting an aluminum ingot according to claim 1 or 2, wherein the casting speed is 55 mm / min or less. It is a casting apparatus used for the casting method of the aluminum ingot in any one of Claims 1-3, Comprising: The cylindrical water-cooled vertical semi-continuous casting mold which has the hollow part which exhibited the square pillar shape which opened up and down A spout hanging from above near the center axis of the mold, a flow dividing plate horizontally disposed near the lower end of the spout, and a bottom block positioned so as to be movable up and down below the mold. Of these, 1/2 or more in the casting direction of the side surface in contact with the hollow part to which the molten aluminum is supplied (except for the entire side surface in contact with the hollow part to which the molten aluminum is supplied) is composed of a graphite plate . An apparatus for casting an aluminum ingot, characterized in that:   The apparatus for casting an aluminum ingot according to claim 4, wherein the graphite plate is not disposed at a corner of a hollow portion having a quadrangular prism shape.   6. The apparatus for casting an aluminum ingot according to claim 4, wherein the graphite plate is configured to be detachable.

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