JP2017164756A - Agitation rotor and manufacturing method for aluminum alloy billet using the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an agitation rotor for easily obtaining an aluminum alloy billet constituted of a microcrystal grain structure and a manufacturing method for an aluminum alloy billet using the same.SOLUTION: An agitation rotor 5 immersed in molten metal 10 consisting of an aluminum alloy to agitate the molten metal 10 in a casting mold 3 used for the continuous casting of an aluminum alloy billet 1 comprises a rotary shaft 51 and a screw 50 provided on the rotary shaft 51. The screw 50 has a plurality of body blades 52 spirally formed by projecting radially outward from the rotary shaft 51 and a plurality of bottom edge blades 53 formed by projecting downward from the bottom edge 523 of each of the body blades 52.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a stirring rotor and a method for producing an aluminum alloy billet using the same.

  Generally, billets used for extruded products of aluminum alloys, forged products, and the like are manufactured by a vertical semi-continuous casting method, similar to slabs used for plate products and the like. In order to suppress cracks generated in billets of aluminum alloy, improve hot workability, increase the strength of the final product, etc., it is desirable to refine crystal grains in the cast structure.

Conventionally, as a method for refining crystal grains of an aluminum alloy ingot, a method of adding a refining agent such as Al-Ti-B or Al-Ti-C to a molten metal (hereinafter referred to as a conventional method) is generally used. Has been done. In the case of the conventional method, it is known that intermetallic compound particles such as TiB ₂ , Al ₃ Ti, and TiC contained in the refining agent serve as the nucleus of the crystal grain, and the more the nucleus of this crystal grain, the finer the grain structure. Yes.

  However, in the case of the conventional method, when a certain amount or more of the micronizing agent is added, the crystal grains are not only further refined but also become constant, and intermetallic compound particles are aggregated to become inclusions. There is a problem that the quality of the alloy ingot and the final product is deteriorated.

  Thus, several methods other than the conventional method (addition of a finer) have been proposed as methods for refining crystal grains of an aluminum alloy ingot. For example, Patent Documents 1 and 2 propose a method of applying ultrasonic waves to the molten metal, Patent Document 3 proposes a method of applying electromagnetic vibration to the molten metal, and Patent Document 4 proposes a method of applying continuous inversion vibration to the molten metal. . Patent Document 5 discloses that the molten metal is stirred using a stirring device.

JP-A-2-247314 JP 2004-209487 A JP 2004-306116 A JP 2002-361400 A JP 2012-167868 A

  However, the method for refining crystal grains of an aluminum alloy ingot by applying ultrasonic waves in Patent Documents 1 and 2 and applying electromagnetic vibration in Patent Document 3 is effective for relatively small ingots having a diameter of about 100 mm. However, as the ingot becomes larger in size, it becomes more difficult to obtain a uniform fine grain structure from the surface layer to the center. That is, it becomes difficult to refine the structure of the central part of the ingot.

  Therefore, in the ingot size used for industrial products that are actually produced, a coarse crystal grain structure is formed in the central portion where the cooling rate is slow, and cracks are likely to occur, making it difficult to apply. In addition, in the case of an ingot in which such a coarse crystal grain structure is formed, expected hot workability, mechanical properties, and the like cannot be sufficiently obtained.

  In addition, the crystal grain refining method of the aluminum alloy ingot by applying continuous inversion vibration described in Patent Document 4 has a problem that it is not suitable for continuous casting because the molten metal cannot be continuously supplied into the mold during casting.

  As described above, in the methods of applying ultrasonic waves, applying electromagnetic vibration, and applying continuous reversal vibration described in Patent Documents 1 to 4, in an aluminum alloy ingot for mass production, the crystal grain refinement of the ingot structure can be achieved. Is difficult.

  Moreover, the stirring apparatus of the said patent document 5 is an apparatus for suppressing the stirring nonuniformity of a molten metal, and aims at disperse | distributing the additive added to a molten metal uniformly. Moreover, the homogenization of the molten metal by stirring does not necessarily contribute to the refinement of crystal grains of the aluminum alloy ingot.

  The present invention has been made in view of such a background, and provides a stirring rotor for easily obtaining an aluminum alloy billet having a fine and uniform crystal grain structure and a method for producing an aluminum alloy billet using the same. .

  A stirring rotor according to one aspect of the present invention is a stirring rotor for immersing in a molten metal made of an aluminum alloy and stirring the molten metal in a mold used for continuous casting of an aluminum alloy billet. A shaft portion, and a screw portion provided on the rotation shaft portion. The screw portion protrudes radially outward from the rotation shaft portion and is formed in a spiral shape, and each of the body blade portions A plurality of lower end blade portions that protrude downward from the lower end.

  The stirring rotor includes a rotating shaft portion and a screw portion having a plurality of main body blade portions and a plurality of lower end blade portions. Therefore, by rotating the stirring rotor and forcibly stirring the molten metal in the mold, a large molten metal flow (melt flow) can be generated in the mold. In particular, by providing the screw portion with a plurality of lower end blade portions in addition to the plurality of main body blade portions, it is possible to generate a hot water flow in the casting direction, that is, downward in the mold.

  As a result, a molten metal flow is generated toward the entire solidification interface, particularly the solidification interface near the center of the solidification shell (the portion of the solidification interface that is located closest to the casting direction, that is, the lower side). collide. The crystals generated at the solidification interface are released from the solidification shell by the molten metal flow generated at the solidification interface, circulate in the molten metal, and are trapped and solidified again by the solidification shell. Without solidifying, a fine cellular structure is maintained. Therefore, an aluminum alloy billet composed of a finer and more uniform crystal grain structure than conventional can be cast.

  A method for producing an aluminum alloy billet according to another aspect of the present invention is a method for producing an aluminum alloy billet using the stirring rotor, wherein the stirring rotor is immersed in a molten metal in the mold, and the center in the mold is obtained. The aluminum alloy billet is cast while rotating the stirring rotor disposed in the section and stirring the molten metal.

  In the method for producing the aluminum alloy billet, the molten metal in the mold is forcibly stirred using the stirring rotor, so that a large hot water flow can be generated in the mold. In particular, by providing a plurality of lower end blade portions in addition to the plurality of main body blade portions in the screw portion of the stirring rotor, it is possible to generate a hot water flow in the casting direction, that is, downward. Thereby, the hot water flow can be generated toward the entire solidification interface, particularly the solidification interface in the vicinity of the center of the solidification shell (the portion of the solidification interface located closest to the casting direction, that is, the lower side). As a result, as described above, an aluminum alloy billet having a finer and more uniform crystal grain structure than conventional can be cast.

It is a partial cross-section explanatory drawing which shows the manufacturing method of the rotor for stirring and the aluminum alloy billet using the same in embodiment. It is a perspective view which shows the rotor for stirring in embodiment. It is a side view which shows the rotor for stirring in embodiment. It is a bottom view which shows the rotor for stirring in embodiment. It is a bottom view which shows the rotor for stirring in embodiment.

  Hereinafter, embodiments of the present invention will be described. In addition, this invention is not limited to the following embodiment, It cannot be overemphasized that it can implement with a various aspect in the range which does not deviate from the summary of this invention.

  The stirring rotor can be applied to, for example, continuous casting of an aluminum alloy billet using a hot top casting method or the like, specifically, immersed in a molten metal made of an aluminum alloy supplied into a mold, It can be used when the molten metal is stirred by rotating.

  Moreover, the number of main body blade | wing parts and a lower end blade | wing part will be limited if the molten metal can be stirred and a hot water flow (especially downward hot water flow) can be generated toward a solidification interface from a screw part. It is not a thing.

  Moreover, each lower end blade | wing part may be protruded and formed below from the whole lower end of each main body blade | wing part. In this case, a good hot water flow can be generated from the screw portion toward the solidification interface.

  Moreover, each lower end blade | wing part may be further extended in the radial direction inner side to the lower end of the rotating shaft part. For example, a stirring blade may not be provided immediately below the rotating shaft. In this case, a non-flow region (so-called dead zone) in which no molten metal flow is formed is formed immediately below the rotating shaft portion. Therefore, by forming each lower end blade portion at the above position, the downward hot water from the screw portion toward the solidification interface (especially the solidification interface near the center of the solidification shell) can be obtained even immediately below the rotation shaft portion. A flow can be generated.

  Each lower end blade portion is formed to protrude from the lower end of each main body blade portion in a direction parallel to the central axis of the rotation shaft portion, and the thickness of each lower end blade portion is the thickness of the lower end of each main body blade portion. 10 to 30 mm may be sufficient as the height of each lower-end blade | wing part. In this case, it is possible to generate a good downward hot water flow from the screw portion toward the solidification interface.

  When each lower end blade part is not formed so as to protrude from the lower end of each main body blade part in a direction parallel to the central axis of the rotating shaft part, a sufficient amount of hot water flows downward from the screw part toward the solidification interface. For example, the grain structure of the center part of the aluminum alloy billet is less likely to be refined and homogenized, and the grain structure may be larger than the grain structure other than the center part. is there.

  When the height of the lower end blade portion is less than 10 mm, there is a possibility that a hot water flow downward from the screw portion toward the solidification interface cannot be sufficiently generated. On the other hand, when the height of the lower end blade portion exceeds 30 mm, the rotational torque of the stirring rotor is increased and stable rotation is not performed, and the hot water flow is deteriorated. As a result, the crystal grain structure of the aluminum alloy billet, particularly There is a risk that the crystal grain structure in the center is not refined or uniformized.

  The height of each lower end blade part greatly affects the improvement in the flow rate of the hot water flow from the screw part toward the solidification interface. The optimum height of each lower end blade portion for sufficiently obtaining such action and effect depends on the diameter (billet diameter) of the aluminum alloy billet. For example, the height of each bottom blade may be 10 mm when the billet diameter is 350 mm, and 20 mm when the billet diameter is 500 mm. Thereby, the optimal downward hot water flow which goes to a solidification interface from a screw part can be generated.

  In addition, if the thickness of each lower end blade part is the same as the thickness of the lower end of each main body blade part, it becomes easy to produce the screw part. However, if the thickness can withstand stirring of the molten metal, each main body blade The thickness may not be the same as the thickness of the lower end of the part. Moreover, the thickness of each lower end blade part has little influence on the hot water flowability, that is, the downward hot water flow from the screw part toward the solidification interface.

  In addition, the inclination angle θ of the lower surface of each main body blade portion with respect to a plane orthogonal to the central axis of the rotation shaft portion may be 45 ° or more and less than 60 °, and the height of each main body blade portion may be tan θ. In this case, a good hot water flow can be generated from the screw portion toward the solidification interface.

  Note that the inclination angle θ is an angle formed by a plane orthogonal to the central axis of the rotating shaft portion and the lower surface of each main body blade portion, and the lower surface of the main body blade portion is opposite from the solidified shell side (lower side) ( It is an inclination angle that rises toward the upper side. The lower surface of the main body blade portion is a surface on the solidified shell side of the main body blade portion. By setting the tilt angle θ to the specific range, a good hot water flow can be generated from the screw portion toward the solidification interface.

  When the inclination angle θ is less than 45 °, the amount of molten metal captured by the main body blade is small, and the flow of hot water near the solidification interface is reduced. There is a risk that miniaturization and uniformity will be insufficient. On the other hand, when the inclination angle θ exceeds 60 °, the ratio of the hot water flow toward the inner wall surface of the mold is increased, and the hot water flow near the solidification interface is reduced, so that the liberation of crystals from the solidification interface is promoted. Therefore, there is a possibility that the crystal grains are not sufficiently refined and uniformized.

  Moreover, the screw part may be comprised with the refractory material which consists of graphite or a ceramic. In this case, heat resistance and durability can be sufficiently ensured even when used in a high-temperature molten metal. As the refractory material made of ceramic, for example, a silicon nitride material or the like can be used. In addition, even if the material which comprises a screw part is other than the said refractory material, if it can be used in molten metal and a screw part can be shape | molded in a desired shape, it will not be limited at all.

  The aluminum alloy billet manufacturing method can be applied to, for example, a hot top casting method and the like, and a stirring rotor (specifically, a molten metal made of an aluminum alloy supplied in a mold is disposed in the center of the mold). Is cooled and solidified while stirring by rotating the screw part), and an aluminum alloy billet is continuously cast. Here, the center portion in the mold refers to the center (center) portion inside the mold in the casting direction, that is, the direction (horizontal direction) orthogonal to the vertical direction.

  Further, the outer diameter of the screw part is ½ or more of the inner diameter of the mold and less than the inner diameter of the header arranged above the mold, and the lower end position of the outer end part of each lower end blade part is in the vertical direction. It may be an intermediate position between the upper end position of the mold and the solidification interface in the mold or an upper side thereof. In this case, the rotation of the stirring rotor (specifically, the screw part) can generate a good hot water flow from the screw part toward the solidification interface, thereby further promoting the liberation of crystals from the solidification shell. . Thereby, the effect of making the crystal grains finer and uniform can be further enhanced.

  Here, the header is a member that is disposed on the upper side of the mold, stores the molten metal, and supplies the molten metal into the mold. For example, a space for storing molten metal (a hot water reservoir) is formed in the header, and the header and the mold are communicated with each other. Moreover, the outer end part of each lower end blade | wing part means the edge part of the radial direction outer side of each lower end blade | wing part. The lower end position of the outer end portion of each lower end blade portion refers to the lowest end position of the outer end portion of each lower end blade portion. The solidification interface in the mold refers to the interface between the molten metal (liquid) and the solidified shell (solid) in the mold.

  When the outer diameter of the screw part is less than ½ of the inner diameter of the mold, the outer diameter of the screw part becomes smaller than the inner diameter of the mold, so that it is difficult to generate a uniform hot water flow throughout the mold. Become. Further, when the outer diameter of the screw part is equal to or larger than the inner diameter of the header, it becomes difficult to put in and out the stirring rotor (specifically, the screw part) in the casting mold.

  When the lower end position of the outer end portion of each lower end blade is below the intermediate position between the upper end position of the mold in the vertical direction and the solidification interface in the mold (solidified shell side), the screw part becomes the solidified shell. There is a possibility that the rotation of the stirring rotor (specifically, the screw portion) may be suppressed.

  Moreover, it is preferable that the whole screw part is arrange | positioned in the casting_mold | template. In this case, the above-described effect of refining and homogenizing the crystal grains can be sufficiently obtained by rotation of the stirring rotor (specifically, the screw portion).

  Further, the molten metal may be stirred by rotating the stirring rotor at a rotational speed of 170 to 400 rpm. In this case, the rotation of the stirring rotor (specifically, the screw part) can generate a good hot water flow from the screw part toward the solidification interface, thereby further promoting the liberation of crystals from the solidification shell. . Thereby, the effect of making the crystal grains finer and uniform can be further enhanced.

  When the rotation speed of the stirring rotor is less than 170 rpm, the molten metal flow in the mold becomes small, so that the release of crystals from the solidified shell is not promoted, and the refinement and homogenization of crystal grains may be insufficient. There is. On the other hand, when the rotation speed of the stirring rotor exceeds 400 rpm, the molten metal surface (the surface of the molten metal) becomes a mortar-like vortex state, and the contact area between the molten metal and the atmosphere decreases, and the molten metal temperature decreases. Oxide is likely to be generated, and this oxide may be caught in the aluminum alloy billet.

  The stirring rotor can be rotated in any direction as long as the stirring rotor is rotated to stir the molten metal so that a hot water flow (especially downward hot water flow) can be generated from the screw portion toward the solidification interface. It is not limited.

  The manufacturing method of the said aluminum alloy billet is applicable to casting of the billet (aluminum alloy billet) which consists of aluminum alloys, such as JIS standard 1000, 2000, 3000, 5000, 6000, 7000 series, for example. In particular, a 7000 series aluminum alloy having a wide temperature range of the solid-liquid coexisting phase has a large crystal grain refinement / homogenization effect.

Next, embodiments of the present invention will be described with reference to the drawings.
Specifically, as shown in FIGS. 1 to 4, the stirring rotor 5 and the method for manufacturing the aluminum alloy billet 1 using the same will be described in detail below.

  In this embodiment, the aluminum alloy billet 1 is cast by a hot top casting method using the casting apparatus 2 shown in FIG. In the present embodiment, the casting direction Z shown in FIG. 1 indicates the casting direction in the vertical direction. In addition, the arrow which shows the direction attached | subjected to FIG. 1 is described in order to make it easy to understand the relationship between each figure. The present invention is not limited to the direction given in FIG.

  The casting apparatus 2 includes a mold 3 for casting an aluminum alloy billet having a predetermined shape, a header 4 disposed immediately above the mold 3, and a stirring rotor 5 for stirring the molten metal 10 made of an aluminum alloy. I have.

  The mold 3 is formed in a cylindrical shape (annular shape). The inner side of the mold 3 is circular in the cross section orthogonal to the axial direction (vertical direction). On the lower end portion of the inner wall surface 31 of the mold 3, a diameter-expanded surface 311 having an gradually increasing inner diameter is formed. The inner diameter A of the mold 3 is the inner diameter of the upper part (the part in which the inner side of the mold 3 is filled with the molten metal 10) with respect to the part where the expanded surface 311 is formed. The inner diameter A of the mold 3 is constant in the axial direction (vertical direction).

  The header 4 is formed in a cylindrical shape. The header 4 is made of a calcium silicate refractory material. The header 4 has a circular shape inside the header 4 in a cross section orthogonal to the axial direction (vertical direction). A hot water reservoir 40 that stores the molten metal 10 is formed in the header 4. The inner diameter B of the header 4 is the inner diameter of the portion where the hot water reservoir 40 is formed. The inner diameter B of the header 4 is constant in the axial direction (vertical direction). The inner diameter B of the header 4 is smaller than the inner diameter A of the mold 3.

  A molten metal supply part 49 for supplying the molten metal 10 to the hot water reservoir 40 is connected to the header 4. The molten metal 10 is supplied from the molten metal supply unit 49 to the hot water reservoir 40 in the header 4. The lower end opening 42 of the header 4 and the upper end opening 32 of the mold 3 communicate with each other in the vertical direction. The molten metal 10 is supplied from the hot water reservoir 40 in the header 4 into the mold 3 through the lower end opening 42 of the header 4 and the upper end opening 32 of the mold 3.

  As shown in FIGS. 2 to 4, the stirring rotor 5 includes a rod-shaped rotating shaft portion 51 and a screw portion 50 provided on the rotating shaft portion 51 for stirring the molten metal 10. The screw part 50 has four main body blade parts 52 and four lower end blade parts 53. The outer diameter D (FIG. 4) of the screw part 50 is not less than ½ of the inner diameter A (FIG. 1) of the mold 3 and less than the inner diameter B (FIG. 1) of the header 4. The rotating shaft portion 51 and the screw portion 50 (the main body blade portion 52 and the lower end blade portion 53) are made of graphite.

  Each main blade 52 is formed in a plate shape. Each main body blade part 52 protrudes radially outward from the rotating shaft part 51 and is formed in a spiral shape. The four main body blade portions 52 are arranged at equal intervals in the circumferential direction. The upper surface 521 and the lower surface 522 of each main body blade portion 52 are inclined with respect to a plane (orthogonal plane 511) orthogonal to the central axis 510 of the rotation shaft portion 51. Of the two main surfaces of the main body blade portion 52, the surface facing the upper side (header 4 side) is the upper surface 521, and the surface facing the lower side (solidified shell 11 side) is the lower surface 522. The inclination angle θ of the lower surface 522 of each main body blade 52 with respect to the orthogonal plane 511 is 45 ° or more and less than 60 °. The vertical height C (FIG. 3) of each main body blade portion 52 is a product of the radius D / 2 of the screw portion 50 and tan θ.

  Each lower end blade portion 53 is formed to project downward from the entire lower end 523 of each main body blade portion 52. Each lower end blade portion 53 is formed to protrude from the lower end 523 of each main body blade portion 52 in a direction parallel to the central axis 510 of the rotation shaft portion 51. Each lower end blade portion 53 is continuously formed radially outward from the rotating shaft portion 51 to the outer end position of the lower end 523 of each main body blade portion 52. The thickness F (FIG. 4) of each lower end blade portion 53 is the same as the thickness of the lower end 523 of each main body blade portion 52. Here, the thickness of the lower end 523 of each main body blade portion 52 refers to the thickness of the lower end 523 of each main body blade portion 52 in a direction orthogonal to the vertical direction. The height in the vertical direction of each lower end blade portion 53 is 10 to 30 mm.

  As shown in FIG. 1, a screw portion 50 of the stirring rotor 5 is disposed at the center of the mold 3. In addition, the center part in the casting_mold | template 3 means the center (center) part inside a casting_mold | template 3 in the direction (horizontal direction) orthogonal to an up-down direction. The screw portion 50 of the stirring rotor 5 is disposed through the header 4 and inserted into the mold 3 from the upper end opening 32 of the mold 3. The entire screw portion 50 is disposed in the mold 3.

  The lower end position E of the outer end portion of each lower end blade portion 53 is an intermediate position between the upper end position E1 of the mold 3 and the solidification interface 110 (E2 in FIG. 1) in the vertical direction or above (the header 4). Side). That is, the distance from the upper end position E1 in the mold 3 in the vertical direction to the lower end position E of the outer end of each lower end blade portion 53 is the solidification interface 110 in the mold 3 from the upper end position E1 of the mold 3 in the vertical direction (see FIG. 1 or less of the distance to E2). The solidification interface 110 is a boundary surface between the molten metal 10 (liquid) and the solidification shell 11 (solid) in the mold 3. The solidification interface 110 is positioned downward (deeper) from the outer peripheral portion of the solidified shell 11 toward the central portion.

  In manufacturing (casting) the aluminum alloy billet 1 by the hot top casting method using the casting apparatus 2 having the above configuration, as shown in FIG. The cylindrical aluminum alloy billet 1 is cast while the molten metal 10 in the mold 3 is forcibly agitated by the screw portion 50 arranged in the above. The stirring rotor 5 is continuously rotated at a constant rotational speed within a range of 170 to 400 rpm.

  By forcibly stirring the molten metal 10 in the mold 3 by the rotation of the stirring rotor 5 (specifically, the screw portion 50), a large molten metal flow (flow of the molten metal 10) is generated in the mold 3. The crystals generated at the solidification interface 110 by the hot water flow by the stirring are released from the solidification shell 11 and circulate in the molten metal 10, and the surrounding solidification shell is maintained in a state where a fine cellular structure is maintained before grain growth. 11 is trapped and solidified. Thereby, the aluminum alloy billet 1 having a fine crystal grain structure is cast.

  Further, since the stirring rotor 5 having the screw portion 50 having the shape shown in FIGS. 2 to 4 is used and the inclination angle θ of the lower surface 522 of the main body blade portion 52 of the screw portion 50 is within the specific range, the stirring rotor When 5 is viewed from above, the stirring rotor 5 is rotated clockwise (in the positive direction).

  As a result, the molten metal 10 in the mold 3 flows from the central part in the mold 3 (from the screw part 50) toward the solidification interface 110 and collides with the solidification interface 110, and then rises along the inner wall surface 31 of the mold 3. Then, it flows again from the central portion in the mold 3 toward the solidification interface 110. And when the molten metal 10 collides with the solidification interface 110, the release | extrication from the solidification shell 11 of the crystal | crystallization produced | generated in the solidification interface 110 is accelerated | stimulated, and the crystal grain refinement effect is produced. In particular, the screw portion 50 is provided with a lower end blade portion 53, and this molten metal flow is guided to the solidification interface 110, particularly the solidification interface 110 near the center of the solidification shell 11, thereby producing an aluminum alloy billet having a fine and uniform structure. Can be obtained.

Next, the effect in the manufacturing method of the stirring rotor 5 of this embodiment and the aluminum alloy billet 1 using the same will be described.
The stirring rotor 5 of this embodiment includes a rotating shaft portion 51 and a screw portion 50 having a plurality of main body blade portions 52 and a plurality of lower end blade portions 53. Therefore, by rotating the stirring rotor 5 and forcibly stirring the molten metal 10 in the mold 3, a large molten metal flow (flow of the molten metal 10) can be generated in the mold 3. In particular, by providing the screw portion 50 with a plurality of lower end blade portions 53 in addition to the plurality of main body blade portions 52, it is possible to generate a hot water flow in the casting direction Z, that is, downward.

  As a result, the solidification interface 110 as a whole, particularly the solidification interface 110 near the center of the solidification shell 11 (the portion of the solidification interface 110 located closest to the casting direction Z, that is, the lower side (near the deepest position G of the solidification interface 110)). A hot water flow is generated toward the surface, and the molten metal 10 collides with the entire solidification interface 110. The crystals generated at the solidification interface 110 are released from the solidification shell 11 by the molten metal flow generated at the solidification interface 110, circulate in the molten metal 10, and are captured and solidified by the solidification shell 11 again. Since it is short, it does not grow and solidifies while maintaining a fine cellular structure. Therefore, the aluminum alloy billet 1 having a finer and more uniform crystal grain structure than conventional can be cast.

  Each lower end blade portion 53 is formed to protrude downward from the entire lower end 523 of each main body blade portion 52. Therefore, a good hot water flow from the screw part 50 toward the solidification interface 110 can be generated.

  Each lower end blade portion 53 is formed so as to protrude from the lower end 523 of each main body blade portion 52 in a direction parallel to the central axis 510 of the rotating shaft portion 51, and the thickness of each lower end blade portion 53 is determined by each main body blade portion 53. It is the same as the thickness of the lower end 523 of the blade | wing part 52, and the height of each lower end blade | wing part 53 is 10-30 mm. Therefore, a good downward hot water flow from the screw part 50 toward the solidification interface 110 can be generated.

  In addition, the inclination angle θ of the lower surface 522 of each body blade portion 52 with respect to a plane (orthogonal plane 511) orthogonal to the central axis 510 of the rotation shaft portion 51 is 45 ° or more and less than 60 °, and the height of each body blade portion 52 is high. Is tan θ. Therefore, a good hot water flow from the screw part 50 toward the solidification interface 110 can be generated.

  Moreover, the screw part 50 is comprised with the refractory material which consists of graphite. Therefore, even when used in the high-temperature molten metal 10, heat resistance and durability can be sufficiently ensured. In addition, the screw part 50 may be comprised with the refractory material which consists of ceramics (for example, silicon nitride type material etc.). In this case, the same effect as described above can be obtained.

  In the manufacturing method of the aluminum alloy billet 1 of this embodiment, the molten metal 10 in the mold 3 is forcibly stirred using the stirring rotor 5, so that a large hot water flow can be generated in the mold 3. In particular, by providing the screw portion 50 of the stirring rotor 5 with the plurality of lower end blade portions 53 in addition to the plurality of main body blade portions, it is possible to generate a hot water flow in the casting direction Z, that is, downward in the mold. it can. As a result, the solidification interface 110 as a whole, particularly the solidification interface 110 near the center of the solidification shell 11 (the portion of the solidification interface 110 located closest to the casting direction Z, that is, the lower side (near the deepest position G of the solidification interface 110)). A hot water flow can be generated toward As a result, as described above, the aluminum alloy billet 1 having a finer and more uniform crystal grain structure than conventional can be cast.

  Further, the outer diameter D of the screw portion 50 is ½ or more of the inner diameter A of the mold 3 and less than the inner diameter B of the header 4 disposed on the upper side of the mold 3. Further, the lower end position E of the outer end portion of each lower end blade portion 53 is above the intermediate position between the upper end position E1 of the mold 3 and the solidification interface 110 (E2 in FIG. 1) in the mold 3 in the vertical direction. Therefore, by rotating the stirring rotor 5 (specifically, the screw portion 50), a good hot water flow is generated from the screw portion 50 toward the solidification interface 110, and the liberation of crystals from the solidification shell 11 is further promoted. Can do. Thereby, the effect of making the crystal grains finer and uniform can be further enhanced.

  Further, the molten rotor 10 is stirred by rotating the stirring rotor 5 at a rotational speed of 170 to 400 rpm. Therefore, by rotating the stirring rotor 5 (specifically, the screw portion 50), a good hot water flow is generated from the screw portion 50 toward the solidification interface 110, and the liberation of crystals from the solidification shell 11 is further promoted. Can do. Thereby, the effect of making the crystal grains finer and uniform can be further enhanced.

  In this embodiment, as shown in FIG. 4, each lower end blade portion 53 of the screw portion 50 is formed so as to protrude radially outward from the rotating shaft portion 51. As shown, each lower end blade portion 53 may extend radially inward to the lower end of the rotating shaft portion 51. That is, it is good also as a structure by which each lower end blade | wing part 53 is provided also under the rotating shaft part 51. FIG. In the example of FIG. 5, the four lower end blade portions 53 are configured to merge directly below the rotating shaft portion 51.

  By setting it as such a structure, it can suppress that the non-flow area | region (what is called a dead zone) in which a molten metal flow does not arise immediately under the rotating shaft part 51 is formed. Therefore, a good downward hot water flow can be generated directly from the screw portion 50 toward the solidification interface 110 (particularly, the solidification interface 110 near the center of the solidification shell 11) just below the rotation shaft portion 51.

  Examples of the present invention will be described below in comparison with comparative examples to demonstrate the effects of the present invention. These examples show one embodiment of the present invention, and the present invention is not limited to these examples.

  First, a plurality of aluminum alloy billets (samples 1 to 20) shown in Table 1 below were manufactured by the hot top casting method using the above-described casting apparatus (see FIG. 1). Specifically, a molten metal in which an aluminum alloy having a predetermined alloy composition was melted was caused to flow down from the header of the casting apparatus into the mold to cast an aluminum alloy billet.

  At this time, an agitation rotor (see FIGS. 2 to 5) was inserted into the mold from above the header, and the aluminum alloy billet was cast while rotating the rotor at a predetermined rotational speed to agitate the molten metal. The casting speed, the amount of cooling water, etc. were set within the range of the conditions that have been implemented conventionally. Sample 17 was not mechanically stirred using a stirring rotor.

  Here, “Alloy No.” in Table 1 is the type of aluminum alloy. “Size” represents the outer diameter of the cast aluminum alloy billet in inches. “Addition of finer agent” refers to continuous addition of a finer agent such as an Al—Ti—B system or an Al—Ti—C system into a molten metal.

  The “material” of the stirring rotor in Table 1 refers to the material of the stirring rotor. “Position” is the ratio of the distance from the upper end position in the mold in the vertical direction to the lower end position of the outer end of the lower end blade part relative to the distance from the upper end position of the mold in the vertical direction to the solidified shell interface in the mold. . The “outer diameter ratio” is the ratio of the outer diameter of the stirring rotor to the inner diameter of the mold. The “inclination angle” is an inclination angle θ (see FIGS. 1 and 3) of the lower surface of the main body blade portion with respect to a plane (orthogonal plane) orthogonal to the central axis of the stirring rotor. “Rotation speed” is the rotation speed of the stirring rotor. The “rotation direction” is the rotation direction when the stirring rotor is viewed from above.

  Further, the “height” of the lower end blade portion of the stirring rotor in Table 1 is the height in the vertical direction of the lower end blade portion. The “length ratio” of the lower end blade portion is a ratio of the radial length of the lower end blade portion to the radial length of the lower end of the main body blade portion. The base point of the length in the radial direction of the lower end blade portion is the outer end in the radial direction of the lower end blade portion.

  The inner diameter of the header used in each sample shown in Table 1 is 223 mm for an aluminum alloy billet having an outer diameter of 9 inches, 349 mm for an aluminum alloy billet having an outer diameter of 14 inches, and 501 mm for an aluminum alloy billet having an outer diameter of 20 inches. .

  Next, the crystal grain structure of the manufactured aluminum alloy billet was observed, and the average crystal grain size was measured. Specifically, the crystal grain structure of the center part of the aluminum alloy billet and the intermediate part between the center part and the surface layer (hereinafter referred to as “D / 4 part”) was observed, and the average crystal grain size was measured. In the case of an aluminum alloy billet, the D / 4 part is generally known as a position showing average characteristics, and is for evaluating the effect of the present invention.

  The average crystal grain size of the target aluminum alloy billet was obtained by mechanically polishing a cross section parallel to the casting direction, performing polarization etching, and observing three visual fields at 50 times with an optical microscope. And the average crystal grain diameter was measured using the area measurement method with respect to these photographs. Note that the observation field of view contained 100 or more crystal grains.

Table 1 shows the measurement results of the average crystal grain size of each manufactured aluminum alloy billet.
Samples 1 to 9 have a smaller average crystal grain size of the aluminum alloy billet and a smaller difference in average crystal grain size between the central part and D / 4 part than sample 17 which was not mechanically stirred by the stirring rotor. It was found that the fine grain structure was obtained. Moreover, when the stirring rotor which does not have a lower end blade | wing part like the sample 10 was used, the average crystal grain diameter of the center part of aluminum alloy billet became coarse, and sufficient refinement | miniaturization effect was not acquired.

  In Samples 1 to 9, since the “height” and “length ratio” of the lower end blade portion of the stirring rotor are within a favorable range, the average crystal grain size is small by mechanical stirring, and the central portion and D / 4 portion The difference in average crystal grain size was small, and a fine crystal grain structure was obtained. On the other hand, when the “length ratio” of the lower end blade part is small (the radial length of the lower end blade part is short) like the sample 11, the sample is lower when the “height” of the lower end blade part is low like the sample 12. It was found that when the “height” of the lower end blade portion is high as in FIG. 13, the average crystal grain size becomes coarse and a fine crystal grain structure cannot be obtained.

  In Samples 1 to 9, since the “inclination angle” of the main body blade portion of the stirring rotor is within a favorable range, the average crystal grain size is small by mechanical stirring, and the average crystal grain size of the central part and D / 4 part The difference was small and a fine grain structure was obtained. On the other hand, it was found that when the “tilt angle” of the main body blade portion was outside the preferred range as in Samples 14 and 15, the average crystal grain size was coarse and a fine crystal grain structure could not be obtained.

  Since Samples 1 to 9 use graphite as the “material” of the stirring rotor, the stirring of the molten metal with the stirring rotor can be performed continuously and stably, and an aluminum alloy billet having a fine grain structure is obtained. . On the other hand, when cast iron is used as the “material” of the stirring rotor as in sample 16, the main body blade portion and the lower end blade portion of the stirring rotor are melted by the molten metal heat, and sufficient mechanical stirring cannot be performed. It was.

  When the “outer diameter ratio” of the stirring rotor is small as in the sample 18 or when the “rotation speed” of the stirring rotor is low as in the sample 19, the average crystal grain size becomes coarse, and the fine grain structure It was found that could not be obtained. In addition, when the “rotation speed” of the stirring rotor is high as in the case of the sample 20, there is a problem that the molten metal scatters on the surface of the molten metal or the solidified shell at the bottom of the mold is broken and the molten metal leaks. Stable casting was not possible.

  DESCRIPTION OF SYMBOLS 1 ... Aluminum alloy billet, 3 ... Mold, 5 ... Stirring rotor, 10 ... Molten metal, 50 ... Screw part, 51 ... Rotating shaft part, 52 ... Main body blade part, 53 ... Lower end blade part, 523 ... Lower end (Main body blade part) Bottom edge)

Claims (8)

In a mold used for continuous casting of an aluminum alloy billet, it is immersed in a molten metal made of an aluminum alloy, and is a stirring rotor for stirring the molten metal,
A rotating shaft,
A screw part provided on the rotating shaft part,
The screw portion includes a plurality of main body blade portions that are spirally formed to protrude radially outward from the rotating shaft portion, and a plurality of lower end blade portions that are formed to protrude downward from the lower ends of the main body blade portions. A stirring rotor.   2. The stirring rotor according to claim 1, wherein each of the lower end blade portions protrudes downward from the entire lower end of each of the main body blade portions.   Each lower end blade portion is formed to project from the lower end of each main body blade portion in a direction parallel to the central axis of the rotation shaft portion, and the thickness of each lower end blade portion is determined by the thickness of each main body blade portion. 3. The stirring rotor according to claim 1, wherein the lower end blade portion has a height of 10 to 30 mm.   The inclination angle θ of the lower surface of each main body blade portion with respect to a plane orthogonal to the central axis of the rotation shaft portion is 45 ° or more and less than 60 °, and the height of each main body blade portion is the radius D of the screw portion. The stirring rotor according to claim 1, which is a product of / 2 and tan θ.   The said screw part is a rotor for stirring of any one of Claims 1-4 comprised by the refractory material which consists of graphite or a ceramic. A method for producing an aluminum alloy billet using the stirring rotor according to any one of claims 1 to 5,
An aluminum alloy in which the agitating rotor is immersed in the molten metal in the mold and the aluminum alloy billet is cast while the molten rotor is agitated by rotating the agitating rotor disposed in the center of the mold. Billet manufacturing method.   The outer diameter of the screw part is ½ or more of the inner diameter of the mold and less than the inner diameter of the header arranged on the upper side of the mold, and the lower end position of the outer end part of each lower end blade part is The manufacturing method of the aluminum alloy billet of Claim 6 which is the intermediate position of the upper end position of the said casting_mold | template in the direction and the solidification interface in this casting_mold | template, or its upper side.   The manufacturing method of the aluminum alloy billet according to claim 6 or 7, wherein the stirring rotor is rotated at a rotational speed of 170 to 400 rpm to stir the molten metal.

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