Method for producing aluminum ingot

Abstract

To suppress the generation of an abnormal structure by refining a crystal grain size, to reduce the macroscopic segregation of a solute element and to suppress the cracking of an ingot by imparting a proper flow to molten metal in a process for producing the ingot.SOLUTION: In the method for producing the aluminum cast block by using a spout 4 and a float 7 and pouring molten metal 2 into a die 1 from the spout 4 through the float 7, the solidified molten metal is drawn so that the flowing speed of the molten metal 2 flowing out from the float 4 into the die 1 becomes ≥ 0. 05m / sec.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a method for producing an aluminum ingot, and more particularly to a method for producing an aluminum ingot that can reduce macroscopic segregation of solute elements, refine crystal grain size, suppress the occurrence of abnormal structures, and suppress ingot cracking by imparting appropriate fluidity to a molten metal. [Background technology]

[0002] For example, sputtering targets are required to have a chemical composition that contains few impurities, to be free of foreign matter such as non-metallic inclusions, to have a low rate of defects such as voids, and to have uniform and fine crystal grain sizes across the entire sputtering surface, and similar properties are also required of the ingots that are the raw materials for such targets.

[0003] When manufacturing a sputtering target, raw materials meeting a specified purity are first melted so as not to be contaminated by other metal elements. Next, the composition is adjusted by adding specified metals to the molten metal, and the molten metal is then subjected to a slag removal process to remove foreign matter such as non-metallic inclusions and a degassing process to remove hydrogen gas. The molten metal is then passed through a filter to remove foreign matter before being poured into a casting machine.

[0004] The molten metal is cooled in a casting machine and solidified into a cylindrical or rectangular prism to obtain an ingot, which is the raw material. The ingot is then subjected to predetermined plastic working and heat treatment to obtain a sputtering target.

[0005] Furthermore, the crystal grains of the sputtering target are controlled in the processes of plastic working and heat treatment. The finer the crystal grain size of the ingot, the easier this control becomes, and simplifying the processes of plastic working and heat treatment also enables cost reduction.

[0006] In the chemical composition of ingots, which are the raw materials for sputtering targets, the impurity content is low and the frequency of solidification nuclei during the solidification process is low, so the crystal grain size tends to become coarse and abnormal structures such as feathery crystals occur frequently. Furthermore, the components contained are subject to strict regulations, and the addition of metals and their compounds, which are often used as refiners in general alloy ingots, is not permitted.

[0007] However, it is known that the coarse grain size and the presence of abnormal structures in the ingot, which is the material for the sputtering target, have adverse effects such as poor deformation and uneven structure during the plastic processing of the sputtering target, and that they cause solidification stress to concentrate during the solidification process of the ingot, which can lead to ingot cracking. Therefore, in order to improve the quality of sputtering targets, it is necessary to prevent the occurrence of abnormal structures and reduce the grain size.

[0008] In addition, in casting, when a molten metal containing solute elements is solidified, redistribution of the solute occurs, resulting in micro- and macro-segregation of the solute elements. Among these, macro-segregation of the solute elements in particular not only deteriorates the properties of the sputtering target, but can also cause cracking of the ingot. Therefore, reducing the macro-segregation of the solute elements can increase the success rate of the casting process.

[0009] It is already known that the above problems can be improved by mechanically or electromagnetically agitating the molten metal near the solidification interface during the casting process, and one such method has been proposed, for example, in Patent Document 1, entitled "Method for continuous casting of aluminum alloy."

[0010] This conventional "aluminum alloy continuous casting method" employs a combination of ultrasonic vibration and electromagnetic stirring, which applies a time-varying magnetic field to oscillate the molten metal. These methods are used to generate a molten metal flow with a vector parallel to the solidification interface, and processing is performed. Note that ultrasonic vibration is used in the hope of increasing the number of crystal nuclei (solidification nuclei) by applying impact and pressure, rather than generating a molten metal flow with a vector parallel to the solidification interface, as shown in Patent Document 2. [Prior art documents] [Patent documents]

[0011] [Patent Document 1] Japanese Patent Application Publication No. 8-238539 [Patent Document 2] Japanese Patent Application Laid-Open No. 2012-45558 Summary of the Invention [Problem to be solved by the invention]

[0012] However, when molten metal is stirred by electromagnetic stirring, even if a molten metal flow including a vector parallel to the solidification interface is generated, feathery crystals may actually occur, and the effect of reducing the crystal grain size to suppress the occurrence of abnormal structures or the effect of reducing the macroscopic segregation of solute elements to suppress ingot cracking cannot be said to be sufficient, and sufficient quality of ingots cannot be consistently obtained.

[0013] In addition, electromagnetic stirring requires expensive equipment and a large amount of electricity, resulting in high costs. Furthermore, a magnetic circuit must be built into the casting machine, and when multiple ingots are cast simultaneously, as is often done in the production of ingots for sputtering targets, sufficient clearance is required to prevent magnetic interference, which creates a problem of large equipment size. For these reasons, it has been difficult to add molten metal stirring functionality to existing equipment.

[0014] The present invention has been devised in view of the above points, and has an object to provide a method for producing an aluminum ingot that can reduce macroscopic segregation of solute elements by imparting appropriate flow to the molten metal, refine the crystal grain size, suppress the occurrence of abnormal structures, and suppress ingot cracking. [Means for solving the problem]

[0015] [1] In order to achieve the above object, the method for producing an aluminum ingot of the present invention uses a spout that pours molten aluminum into a mold, and a float that floats on the surface of the molten metal poured into the mold and controls the amount of molten metal poured from the spout in accordance with the up and down movement of the molten metal surface, and is a method for producing an aluminum ingot in which the molten metal is poured from the spout through the float into the mold, and the solidified molten metal is withdrawn so that the flow rate of the molten metal flowing from the float into the mold is 0.05 m / sec or more.

[0016] According to the method for producing an aluminum ingot of the present invention, the solidified molten metal is withdrawn so that "the flow rate of the molten metal flowing from the float into the mold is 0.05 m / sec or more." The flow of the molten metal in the mold promotes the generation of crystal grains due to the stirring effect of the flow that includes a vector perpendicular to the solidification interface, and grain growth that causes the crystal grain size to become coarse and the growth of abnormal structures are suppressed. That is, the solidification interface is subjected to a predetermined pressure by the flow of the flowing molten metal, thereby suppressing grain growth that causes coarsening of the crystal grain size and the growth of abnormal structures.

[0017] Furthermore, because the flow velocity of the molten metal flowing from the float into the mold is 0.05 m / sec or more, the stirring effect of the flow, which includes a vector perpendicular to the solidification interface, also solves the problem of macroscopic segregation of solute elements.

[0018] Furthermore, this flow of the molten metal is effective in refining the crystal grain size, and the crystal grain size can be refined without adding a refiner (such as titanium or boron).

[0019] Incidentally, "aluminum" here includes both "pure aluminum (including high-purity aluminum)" and "aluminum alloys." Therefore, "aluminum ingot" includes both "aluminum made of pure aluminum (including high-purity aluminum)" and "aluminum alloy."

[0020] [2] The present invention also provides a method for producing an aluminum ingot, which uses a spout for pouring molten aluminum into a mold and a float that floats on the surface of the molten metal poured into the mold and controls the amount of molten metal poured from the spout in accordance with the up and down movement of the molten metal surface, and which pours the molten metal from the spout into the mold via the float, and which withdraws the solidified molten metal so that the molten metal flowing out of the float into the mold exerts a flow on the solidification interface with a velocity component of 0.05 m / sec or more in a direction perpendicular to the solidification interface.

[0021] According to the method for producing an aluminum ingot of the present invention, the solidified molten metal is withdrawn so that "the molten metal flowing from the float into the mold causes a flow on the solidification interface with a velocity component of 0.05 m / sec or more in a direction perpendicular to the solidification interface." The stirring effect of the flow, which includes a vector perpendicular to the solidification interface, causes the flow of the molten metal in the mold to promote the generation of crystal grains, and suppresses grain growth that causes coarsening of the crystal grains and the growth of abnormal structures. That is, the solidification interface is subjected to a predetermined pressure by the flow of the flowing molten metal, thereby suppressing grain growth that causes coarsening of the crystal grain size and the growth of abnormal structures.

[0022] Furthermore, because the velocity component perpendicular to the solidification interface is 0.05 m / sec or more, the stirring effect of the flow, which includes a vector perpendicular to the solidification interface, also solves the problem of macroscopic segregation of solute elements.

[0023] Furthermore, this flow of the molten metal is effective in refining the crystal grain size, and the crystal grain size can be refined without adding a refiner (such as titanium or boron).

[0024] In this way, the present invention [1] [2] reduces the macroscopic segregation of solute elements by improving the flow of the molten metal, refines the crystal grain size, and suppresses the occurrence of abnormal structures and cracks in the ingot.

[0025] [3] In the method for producing an aluminum ingot of the present invention, it is preferable to withdraw the solidified molten metal at a speed of 38 mm / min or more and 140 mm / min or less.

[0026] In this case, the occurrence of abnormal structures can be sufficiently suppressed, and the solidification of the molten metal is unlikely to progress to the float portion (the float is less likely to be cast-in). In addition, the occurrence of cracks in the ingot can also be sufficiently suppressed.

[0027] On the other hand, if the casting is withdrawn at a speed of "less than 38 mm / min," the flow of the molten metal will be insufficient (the flow rate and volume of the molten metal flowing from the float into the mold will be insufficient, and the velocity component perpendicular to the solidification interface will be insufficient), increasing the frequency of feathery crystals. Also, if the casting is withdrawn at a speed of "less than 38 mm / min," the solidification of the molten metal will progress to the float, increasing the possibility that the float will be surrounded by the casting.

[0028] Furthermore, if the drawing speed exceeds 140 mm / min, the possibility of cracking of the ingot increases.

[0029] [4] In the method for producing an aluminum ingot of the present invention, the lower end of the spout is preferably located at a height of 35 mm to 50 mm above the lower end of the mold.

[0030] In this case, the occurrence of abnormal structures can be sufficiently suppressed, and the solidification of the molten metal is unlikely to progress to the float portion (the float is unlikely to be cast-in).

[0031] On the other hand, if the height is "less than 35 mm," the float will be too close to the solidification interface (the float will be located closer to the solidification interface than the spout), and the solidification of the molten metal will progress to the float part, increasing the possibility that the float will be cast-in.

[0032] Furthermore, if the height exceeds 50 mm, the ingot, once it comes into contact with the mold and begins to solidify, shrinks and separates from the mold. After that, the time period during which cooling is ineffective until it is directly cooled by water is too long, which increases the peripheral structure (the structure that is cut and removed), resulting in a decrease in yield.

[0033] [5] In the method for producing an aluminum ingot of the present invention, it is preferable that the float has an outer diameter that is 70% or more and 80% or less of the diameter of the mold, and that the float has an insertion hole through which the spout is inserted and has a diameter that is 125% or more and 145% or less of the outer diameter of the spout.

[0034] In this case, the area of ​​the molten metal surface exposed to air is reduced, suppressing the generation and mixing of oxides. In addition, the buoyancy (surface tension) that the float receives from the molten metal can be increased, and there is no interference with the spout, which is expected to improve the float's ability to follow the molten metal surface.

[0035] On the other hand, if the outer diameter of the float is "less than 70%" of the mold diameter, the contact area with the molten metal is too small, so buoyancy does not work in parts of the float far from the center of gravity, and there is a risk that the float's vibration-damping effect will be difficult to obtain. Also, if it is "less than 70%," the contact area between the molten metal and the air is too large, which increases the generation and contamination of oxides.

[0036] Furthermore, if the outer diameter of the float is "more than 80%" of the diameter of the mold, it becomes difficult to visually check the bottom metal placed in the mold at the start of casting (when withdrawal begins), which makes it more likely that the timing of the start of casting (when withdrawal begins) will vary. If the timing of starting casting is too early (if withdrawal starts too early), there will not be enough molten metal in the base metal, which will result in "overflow," where the molten metal escapes before solidifying.If the timing of starting casting is too late (if withdrawal starts too late), the molten metal will completely solidify in the mold, resulting in "hanging," where the ingot hangs in the mold.

[0037] Furthermore, if the diameter of the insertion hole is "less than 125%" of the outer diameter of the spout, there is a risk that it will interfere with the spout when the molten metal surface rises and falls, reducing the float's ability to follow the molten metal surface.

[0038] Also, if the diameter of the insertion hole is "more than 145%" of the outer diameter of the spout, the horizontal movement of the float becomes excessive, drawing in the oxide film on the molten metal surface and increasing the likelihood of foreign matter being contained in the aluminum ingot. Furthermore, if the outer diameter of the spout is "more than 145%," the float will deviate from its center position (normal position), causing problems such as uneven temperature distribution of the molten metal in the mold, the bottom of the float hitting the solidification interface and becoming engulfed in the cast, and uneven flow velocity of the molten metal.

[0039] [6] In the method for producing an aluminum ingot of the present invention, the purity of the aluminum can be 99.99 wt% or more.

[0040] In the case of high-purity aluminum, such as aluminum with a purity of 99.99 wt% or more, it is difficult to add a refiner (for example, titanium or boron). However, in the present invention, refinement of the crystal grain size is realized without adding a refiner, and therefore, refinement of high-purity aluminum is possible. [Effects of the Invention]

[0041] The present invention can provide a method for producing an aluminum ingot that can reduce the crystal grain size of the ingot to suppress the occurrence of abnormal structures, reduce macroscopic segregation of solute elements, and suppress ingot cracking. [Brief explanation of the drawings]

[0042] [Figure 1] FIG. 1 is a schematic diagram illustrating a casting machine used in the method for producing an aluminum ingot of the present invention. [Figure 2] FIG. 2 is a schematic diagram for explaining a float. [Figure 3] 5A and 5B are schematic diagrams for explaining the rising and falling movements of the float. [Figure 4] FIG. 2 is a schematic diagram for explaining the movement of a float. [Figure 5] FIG. 10 is a schematic diagram for explaining the solidification interface when the withdrawal speed is high. DETAILED DESCRIPTION OF THE INVENTION

[0043] Hereinafter, a mode for carrying out the invention (hereinafter referred to as "embodiment") will be described.

[0044] [About the casting machine] FIG. 1 is a schematic diagram illustrating a casting machine used in the method for producing an aluminum ingot of the present invention. The casting machine shown here has a vertical mold 1 with a jacket structure. A trough 3 is provided above the mold 1, through which molten metal 2 passes, and the molten metal 2 carried by the trough 3 passes through a tubular spout 4 made of refractory material and is supplied (pouring) into the mold 1. The molten metal 2 poured into the mold 1 solidifies as heat is removed by cooling water 5 (reference numeral 6 in Fig. 1 indicates solidified solid aluminum).

[0045] Then, the solidified ingot 6 is pulled out (pulled down) downward while the molten metal 2 is continuously poured from above, thereby carrying out continuous casting.

[0046] Here, the molten metal 2 carried by the trough 3 is located above the mold 1, so gravity causes it to flow endlessly into the mold 1. Therefore, a float 7 is used to properly control the amount of molten metal flowing in.

[0047] [About floats] As shown in FIG. 2, the float 7 has a float plate portion 71 and an adjustment plate portion 72. The float plate portion 71 has a disk shape as a whole, and is made of a refractory material (such as calcium silicate) with a specific gravity smaller than that of molten aluminum.

[0048] 1 indicates the outer diameter of the float plate portion 71, and the outer diameter R is set to be 75% of the outer diameter Ro of the mold 1.

[0049] Furthermore, an insertion hole 73 is provided in the center of the float plate portion 71, penetrating the front and back surfaces of the float plate portion 71. The symbol r in Fig. 2 indicates the diameter (inner diameter) of this insertion hole 73, and the diameter r is set to 135% of the outer diameter of the spout 4.

[0050] The spout 4 is inserted (loosely inserted) into the insertion hole 73, forming a predetermined gap between it and its inner surface, and the float plate portion 71 is configured to be able to move relative to the spout 4 in the axial direction while the spout 4 remains inserted into the insertion hole 73.

[0051] Here, because the spout 4 has a tapered shape, the relative size (135%) of the diameter of the insertion hole 73 based on the outer diameter of the spout 4 varies depending on the position of the float 7 (height of the molten metal surface), but the diameter of the insertion hole 73 is formed so that the relative size is 135% assuming that the "downward force exerted by the molten metal flow on the float 7 (pressure due to the molten metal flow)" and the "upward force exerted by the molten metal in the mold (buoyancy and surface tension)" are balanced and the molten metal surface does not rise and fall. Note that even if the molten metal surface rises and falls, the relative size is between 125% and 145%.

[0052] In addition, a peripheral wall portion 75 is formed around the entire back surface of the float plate portion 71 (the lower surface in Figure 1) so as to surround the insertion hole 73, and two connecting members 76 are provided on the back surface of the peripheral wall portion 75 (the surface opposite to the float plate portion 71).

[0053] Similarly to the float plate portion 71, the adjustment plate portion 72 has an overall disk shape and is made of a refractory material (such as calcium silicate) with a specific gravity lower than that of molten aluminum. Furthermore, the adjustment plate portion 72 is formed so that its outer diameter is larger than the diameter of the insertion hole 73 and smaller than the outer diameter of the float plate portion 71.

[0054] The adjustment plate portion 72 is connected to the connecting member 76 so as to be spaced apart from the float plate portion 71 by a predetermined distance and so as to be positioned coaxially with the float plate portion 71 (so as to be positioned directly below the insertion hole 73).

[0055] [Regarding adjustment of pouring amount] The float 7 configured in this manner floats on the surface of the molten metal 2 in the mold 1, and the molten metal 2 supplied from the spout 4 flows into the mold 1 through the gap between the adjustment plate portion 72 and the peripheral wall portion 75 (the gap between the connecting members 76).

[0056] Here, if the molten metal level rises due to an excess supply of molten metal 2, as shown in Figure 3(a), the float 7 rises along with the molten metal level, bringing the spout 4 and the adjustment plate portion 72 closer to each other (in some cases, the spout 4 and the adjustment plate portion 72 come into contact, and the adjustment plate portion 72 blocks the hole in the spout 4), and the amount of molten metal 2 poured (supplied) decreases.

[0057] On the other hand, when the molten metal level drops due to a shortage of supply of the molten metal 2, the float 7 drops along with the molten metal level, as shown in Figure 3(b), causing the spout 4 and the adjustment plate portion 72 to separate (the gap between the spout 4 and the adjustment plate portion 72 becomes larger), and the amount of molten metal 2 poured (supplied) increases.

[0058] In this way, by using the float 7 to vary the gap between the spout 4 and the adjustment plate portion 72 according to the height of the molten metal 2 surface in the mold, the amount of molten metal 2 poured (supplied) from the spout 4 is adjusted, and the molten metal surface is controlled to a predetermined height.

[0059] [Minimizing float movement] However, when the molten metal level changes, turbulence occurs due to the change in the flow rate of the molten metal, which can cause the formation of oxides that are entrained in the molten metal and then mixed into the ingot.

[0060] In addition, the flow of the molten metal 2 supplied from the spout 4 changes when it collides with the float 7, forming a flow with a specific direction and speed that flows into the mold. However, if there are areas in the mold where the flow velocity is low, problems such as large crystal grains in the ingot or abnormal crystal structure can easily occur.

[0061] Therefore, it is important to minimize the movement of the float 7 during casting. The movements of the float can be broadly divided into three types: (1) horizontal movement (see Figure 4(a)), (2) vertical movement (see Figure 4(b)), and (3) rotation around a horizontal axis (see Figure 4(c)).

[0062] (horizontal movement) Horizontal movement can be suppressed by reducing the diameter of the insertion hole 73 and causing it to interfere with the spout 4. Reducing the diameter of the insertion hole 73 also has the effect of reducing the area where the molten metal surface comes into contact with the atmosphere. However, if the diameter of the insertion hole 73 is made too small, it may interfere with the spout 4 when the molten metal surface rises and falls, reducing the float 7's ability to follow the molten metal surface. Therefore, in this embodiment, the diameter (inner diameter) r of the insertion hole 73 is set to 135% of the outer diameter of the spout 4.

[0063] (Vertical movement) Ideally, vertical movement should keep the molten metal surface from moving up and down, but the next most effective way to suppress turbulence is for the float to move so that its relative position to the molten metal surface remains constant.In other words, to prevent the float 7 from being overwhelmed by the flow of molten metal and moving below the molten metal surface when the flow rate supplied from the spout 4 increases, or to prevent the float 7 from moving above the molten metal surface due to buoyancy when the flow rate supplied from the spout 4 decreases, the "downward force exerted on the float 7 by the molten metal flow (pressure due to the molten metal flow)" and the "upward force exerted by the molten metal 2 in the mold (buoyancy, surface tension)" must be balanced. Therefore, in this embodiment, the outer diameter R of the float plate portion 71 is set to 75% of the outer diameter Ro of the mold 1.

[0064] (rotation with horizontal axis) Regarding rotation about a horizontal axis, if the center of gravity of the float 7 is away from the molten metal surface (for example, if it is located below the molten metal surface), when the float 7 is subjected to a slight vibration, the center of gravity of the float 7 acts as the point of action, with the part of the float 7 located at the molten metal surface as the fulcrum, and a rotational moment is applied to the entire float 7. To suppress this, it is important to move the center of gravity closer to the fulcrum, which is near the molten metal surface. Therefore, in this embodiment, the diameter of the adjustment plate portion 72 and the peripheral wall portion 75 is made smaller than that of the float plate portion 71, and the corners of the connecting member 76 are removed (chamfered), thereby increasing the mass of the upper portion and moving the center of gravity closer to the surface of the molten metal.

[0065] [Optimization of effective mold length] In the process of manufacturing high-purity aluminum ingots into target material, a process of cutting the outer periphery of the ingot is sometimes incorporated. This is to prevent a large discrepancy in the sputtering rate (film formation ability) when used as a target material, because the outer structure of the ingot produced by the semi-continuous casting method is significantly different from the inner structure. The discrepancy between the outer structure and the inner structure is particularly pronounced in high-purity aluminum, which cannot be doped with titanium or other elements that have a grain refinement effect.

[0066] Furthermore, the outer periphery of the cut-off ingot is difficult to reuse as a raw material due to contamination with iron and other components, which leads to increased costs (deterioration of yield) for the target material.

[0067] Here, the molten metal 2 begins to solidify when it comes into contact with the mold 1, and solidification is completed by the cooling water 5 that is discharged from the bottom of the mold 1. If the point where the molten metal 2 comes into contact with the mold 1 is defined as the "primary cooling starting point," and the point where the cooling water 5 is discharged is defined as the "secondary cooling starting point," then the thickness of the peripheral structure will change depending on the distance between the "primary cooling starting point" and the "secondary cooling starting point" (hereinafter, this distance will be referred to as the "effective mold length"). That is, when the effective mold length is long, solidification begins the moment the molten metal 2 touches the mold 1, and solidification shrinkage occurs, causing the ingot to separate from the mold 1, creating an area where cooling is ineffective (an air gap), during which the structure at the periphery thickens. Therefore, the shorter the effective mold length, the thinner the structure at the periphery can be.

[0068] On the other hand, if the effective mold length is short (excessively short), the distance from the surface of the molten metal 2 to the solidification interface becomes small, increasing the possibility (risk) of the float 7 coming into contact with the solidification interface, and as a result, increasing the possibility that the float 7 will be cast-in. In addition, if the quenching time is too short, the ingot skin becomes thin, and the skin may be broken by the pressure of the molten metal 2, resulting in a casting failure. Considering these points, there is a minimum required height for the effective mold length, and casting must be carried out under conditions that do not fall below this height.

[0069] Among the factors that determine the effective mold length, the height from the "bottom end of mold 1" to the "bottom end of spout 4" is particularly important. This is because the molten metal level does not rise above the point where the float 7 contacts the bottom end of the spout 4 (more specifically, where the adjustment plate portion 72 contacts). Therefore, the closer the bottom end of the spout 4 is to the bottom end of the mold 1, the closer the upper limit of the molten metal level becomes to the bottom end of the mold 1, which means that the effective mold length becomes shorter.

[0070] Taking these points into consideration, in this embodiment, the spout 4 is positioned so that its lower end (the lower end of the spout 4) is 40 mm high from the lower end of the mold 1 (the height indicated by the symbol X in Figure 1). That is, the spout 4 is provided so that its lower end is located at a height of 40 from the lower end of the mold 1 to satisfy the minimum required length of the effective mold length.

[0071] Furthermore, when the spout 4 is positioned so that its lower end is 40 cm above the lower end of the mold 1, the float 7 will be located at a height of 5 mm to 15 mm above the solidification interface. That is, the distance between the rear surface of the adjusting plate portion 72 and the solidification interface is located at a height of 5 mm or more and 15 mm or less.

[0072] [Removal of solidified molten metal] In this embodiment, the solidified ingot 6 is withdrawn at a rate of 38 to 140 mm / min. By withdrawing at this speed, a predetermined gap is maintained between the spout 4 and the adjustment plate portion 72, and the molten metal 2 supplied from the spout 4 to the float 7 flows into the mold 1 through the gap between the connecting members 76.

[0073] Here, when the solidified ingot 6 is withdrawn at "38 to 140 mm / min", the flow rate of the molten metal 2 flowing from the float 7 into the mold 1 is 0.05 m / sec or more. Furthermore, due to the molten metal flowing from the float 7 into the mold 1, the velocity component in the direction perpendicular to the solidification interface is 0.05 m / sec or more.

[0074] When the solidified ingot 6 is withdrawn at a rate of "less than 38 mm / min," the molten metal surface rises more than in the present embodiment, the gap between the spout 4 and the adjustment plate portion 72 becomes smaller, and the amount of molten metal 2 supplied from the spout 4 to the float 7 decreases. Therefore, the amount of molten metal flowing from the float 7 into the mold 1 through the gaps between the connecting members 76 also decreases, and the flow rate becomes less than 0.05 m / sec. In addition, the velocity component perpendicular to the solidification interface becomes less than 0.05 m / sec. Therefore, the flow of the molten metal 2 becomes insufficient, and the frequency of occurrence of feathery crystals increases.

[0075] Furthermore, if the solidified ingot 6 is pulled out at a speed of "less than 38 mm / min," the solidification interface and the float 7 will be too close to each other, and the solidification of the molten metal 2 will progress to the float 7, increasing the possibility that the float 7 will be cast in.

[0076] On the other hand, when the solidified ingot 6 is withdrawn at a rate of "more than 140 mm / min," the molten metal 2 is cooled from the region in contact with the mold 1, and as shown by the symbol Z in FIG. 5, the center of the solidification interface becomes deep (the symbol Y in FIG. 5 corresponds to the present embodiment), and the concentration of solidification stress at the center of the solidification interface increases the frequency of ingot cracking. In addition, as the center of the solidification interface becomes deeper, the velocity component in the direction perpendicular to the solidification interface becomes less than 0.05 m / sec, which may result in insufficient flow of the molten metal 2 and increase the frequency of feathery crystals (risk).

[0077] Taking these points into consideration, in this embodiment, the solidified ingot 6 is pulled out at a speed of "38 to 140 mm / min."

[0078] [effect] In the method for manufacturing an aluminum ingot to which the present invention is applied, the effective mold length is optimized to minimize the structure of the outer periphery of the ingot 6, thereby improving the yield.

[0079] Furthermore, by optimizing the positions of the spout 4 and the float 7 and optimizing the withdrawal speed, a predetermined pressure is applied to the solidification interface by the flowing molten metal, which makes it possible to refine the crystal grain size of the ingot and suppress the occurrence of abnormal structures. Furthermore, it is possible to reduce the macroscopic segregation of solute elements and also suppress cracking of the ingot. [Explanation of symbols]

[0080] 1. Mold 2 Molten metal 3. Gutter 4 spout 5 Cooling water 6 Ingot 7. Float 71 Float plate part 72 Adjustment plate section 73 Insertion hole 75 Peripheral wall part 76 Connecting member

Claims

1. A spout for pouring molten aluminum into the mold; a float that floats on the surface of the molten metal poured into the mold and controls the amount of molten metal poured from the spout in accordance with the up and down movement of the molten metal surface, and the molten metal is poured from the spout into the mold via the float, so that the flow rate of the molten metal flowing from the float into the mold is 0.05 m / sec or more, The solidified molten metal is extracted. A method for manufacturing aluminum ingots.

2. A spout for pouring molten aluminum into the mold; a float that floats on the surface of the molten metal poured into the mold and controls the amount of molten metal poured from the spout in accordance with the up and down movement of the molten metal surface, and the molten metal is poured from the spout into the mold via the float, The molten metal flowing out from the float into the mold causes a flow on the solidification interface having a velocity component of 0.05 m / sec or more in a direction perpendicular to the solidification interface, The solidified molten metal is extracted. A method for manufacturing aluminum ingots.

3. The solidified molten metal is Pull out at 38mm / min or more and 140mm / min or less The method for producing an aluminum ingot according to claim 1 or 2.

4. The spout is The lower end is located at a height of 35 mm to 50 mm from the lower end of the mold. The method for producing an aluminum ingot according to claim 1 or 2.

5. The float is Its outer diameter is 70% or more and 80% or less of the diameter of the mold, and The spout is inserted through an insertion hole having a diameter of 125% to 145% of the outer diameter of the spout. The method for producing an aluminum ingot according to claim 1 or 2.

6. The purity of the aluminum is 99.99 wt% or more. The method for producing an aluminum ingot according to claim 1 or 2.

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