Method for correcting mold of VAR furnace and method for manufacturing titanium-based ingot

Abstract

To provide a method for correcting a mold of a VAR furnace and a method for manufacturing a titanium-based ingot that can address waviness in a cylindrical part caused by thermal history and suppress the occurrence of situations in which the mold must be destroyed.SOLUTION: A method for correcting a mold 2 of a VAR furnace 1 according to the present invention includes the steps of: stepwise moving a mold correction device 6 from the upper side to the lower side inside a cylindrical part 20 of the mold 2; and pressing the inner surface of the cylindrical part 20 by the mold correction device 6 at each height position of the stepwise movement. A method for manufacturing a titanium-based ingot according to the present invention includes the steps of: repeatedly performing melting and manufacture of a titanium-based ingot using the VAR furnace 1; and correcting the mold 2 of the VAR furnace 1 using the aforementioned method.SELECTED DRAWING: Figure 6

Description

Technical Field

[0001] The present invention relates to a method for modifying a mold of a Vacuum Arc Remelting (VAR) furnace (hereinafter referred to as "VAR furnace") used for melting and manufacturing titanium-based ingots, and a method for manufacturing titanium-based ingots.

Background Art

[0002] Patent Document 1 below discloses a mold correction device having a substrate, a plurality of slide plates slidably disposed outward from the central portion of the substrate on the upper surface of the substrate, a pressing member for moving the slide plates from the central portion outward and inward from the outside, and a driving means for moving the pressing member in the vertical direction. By moving the plurality of slide plates outward from the central portion of the substrate by the driving means and the pressing member, the inner surface of the mold is pressed directly or via a spacer to correct the deformation of the mold. Further, in Patent Document 1, after ingot production, a so-called "hot top" operation of repeatedly performing arc discharge again to heat the top of the ingot in the mold is described, and it is proposed to correct the upper inner surface of the cylindrical portion (cylindrical main body) of the mold by the mold correction device.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] The mold has a cylindrical part with openings at the upper and lower sides respectively, and is repeatedly exposed to high temperatures (temperatures exceeding about 1668°C, the melting point of titanium) during ingot production and room temperature. Due to this thermal history, the cylindrical part may undulate (bend irregularly). The protrusion of the cylindrical part caused by the hot top occurs at the upper part of the cylindrical part, while the undulation due to the thermal history occurs in a wider range than that used for ingot casting of the cylindrical part. If the protrusion of the cylindrical part inward due to this undulation is large, the produced ingot cannot be taken out of the mold, and ultimately the mold may be destroyed, resulting in manufacturing defects. In the invention described in Patent Document 1, although the correction of the inner surface of the upper part of the cylindrical part caused by the hot top is considered, the undulation of the cylindrical part due to the thermal history is not addressed, and there is room for improvement.

[0005] The present invention has been made to solve the above problems, and one of its purposes is to provide a method for correcting a mold of a VAR furnace and a method for manufacturing a titanium-based ingot that can address the undulation of the cylindrical part due to the thermal history and suppress the occurrence of situations where the mold must be destroyed.

Means for Solving the Problems

[0006] The method for correcting a mold of a VAR furnace according to the present invention is, in one embodiment, a method for correcting a mold of a VAR furnace. The mold has a cylindrical part with openings at the upper and lower sides respectively, and a detachable bottom that closes the lower opening of the cylindrical part. The mold correction device is gradually moved from the upper side to the lower side inside the cylindrical part, and at each height position of the gradual movement, the inner surface of the cylindrical part is pressed by the mold correction device.

[0007] The method for manufacturing a titanium-based ingot according to the present invention is, in one embodiment, including repeatedly melting and manufacturing a titanium-based ingot in a VAR furnace, and correcting the mold of the VAR furnace by the above method.

Effects of the Invention

[0008] According to an embodiment of the method for modifying a mold of a VAR furnace and the method for manufacturing a titanium-based ingot of the present invention, the mold modification device is gradually moved from the upper side to the lower side inside the cylindrical portion, and at each height position of the gradual movement, the inner surface of the cylindrical portion is pressed by the mold modification device. Therefore, it is possible to cope with the undulation of the cylindrical portion due to the thermal history and suppress the occurrence of a situation where the mold must be destroyed.

Brief Description of the Drawings

[0009]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Figure 6

Figure 7

Embodiments for Carrying Out the Invention

[0010] Hereinafter, embodiments for carrying out the present invention will be described with reference to the drawings. The present invention is not limited to each embodiment, and components can be deformed and embodied without departing from the gist thereof. Further, various inventions can be formed by appropriately combining a plurality of components disclosed in each embodiment. For example, some components may be deleted from all the components shown in the embodiment. Furthermore, components of different embodiments may be appropriately combined.

[0011] FIG. 1 is a flowchart showing a method for manufacturing a titanium-based ingot according to an embodiment of the present invention, and FIG. 2 is an explanatory view showing a VAR furnace 1 used in the manufacturing method of FIG. 1. As shown in FIG. 1, the method for manufacturing a titanium-based ingot according to the present embodiment includes repeatedly melting and manufacturing a titanium-based ingot in a VAR furnace 1 (see FIG. 2) (step S1), and modifying a mold 2 (see FIG. 2) of the VAR furnace 1 (step S2). The titanium-based ingot includes a pure titanium ingot and a titanium alloy ingot. The modification of the mold 2 is carried out by the method for modifying the mold 2 of the VAR furnace 1 according to the embodiment of the present invention described later.

[0012] With reference to FIG. 2, the melting and manufacturing of the titanium-based ingot will be described in more detail. As shown in FIG. 2, a mold 2 is disposed in the VAR furnace 1. The mold 2 is usually a copper container or crucible. The mold 2 of the present embodiment has a cylindrical portion 20 having openings at the upper and lower portions, respectively, and a detachable bottom portion 21 that closes the lower opening of the cylindrical portion 20.

[0013] The cylindrical portion 20 is a cylindrical member extending in the height direction H of the mold 2. The cylindrical portion 20 may be provided with an upper flange 200U and a lower flange 200L extending radially outward from the outer peripheral surface of the cylindrical portion 20. The upper flange 200U may be disposed at the upper end of the cylindrical portion 20, and the lower flange 200L may be disposed at the lower end of the cylindrical portion 20.

[0014] The inner peripheral surface 201 of the cylindrical portion 20 may include a main inner peripheral surface 201a and a lower inner peripheral surface 201b. The main inner peripheral surface 201a may extend in the height direction H from the upper end of the cylindrical portion 20. In the height direction H of the mold 2, the extension length of the main inner peripheral surface 201a is longer than the extension length of the lower inner peripheral surface 201b. The extension length of the main inner peripheral surface 201a may occupy most of the total length of the cylindrical portion 20 in the height direction H, and may be 90% or more of the total length of the cylindrical portion 20. The diameter of the main inner peripheral surface 201a may be uniform in the height direction H of the mold 2. The diameter of the main inner peripheral surface 201a may sometimes be simply referred to as the inner diameter of the mold 2. The inner diameter of the mold 2 may be 750 mm or more. The inner diameter of the mold 2 may be 850 mm or more, 1000 mm or more, or 1250 mm or more. The lower inner peripheral surface 201b may extend in the height direction H from the lower end of the cylindrical portion 20. The diameter of the lower inner peripheral surface 201b is wider than the diameter of the main inner peripheral surface 201a. A stepped portion 201c extending in the radial direction of the mold 2 is formed between the lower inner peripheral surface 201b and the main inner peripheral surface 201a.

[0015] The bottom portion 21 may have a small-diameter portion 210 and a large-diameter portion 211 having an outer diameter larger than that of the small-diameter portion 210. The small-diameter portion 210 may be disposed above the large-diameter portion 211. The small-diameter portion 210 may be coaxially disposed with the large-diameter portion 211. The small-diameter portion 210 is inserted into the inside of the cylindrical portion 20 along the lower inner peripheral surface 201b. The tip of the small-diameter portion 210 abuts against the stepped portion 201c, and the upper surface of the large-diameter portion 211 abuts against the lower surface of the lower flange 200L. Although not shown, the bottom portion 21 can be attached to the lower part of the cylindrical portion 20 by fastening the large-diameter portion 211 to the lower flange 200L with a fastening member such as a bolt.

[0016] In a state where the bottom portion 21 is attached to the lower part of the cylindrical portion 20, a region from the upper surface position of the bottom portion 21 to a portion close to the upper end position of the cylindrical portion 20 becomes an area where an ingot can be formed. The upper surface position of the bottom portion 21 may be the position of the stepped portion 201c. The upper surface position of the bottom portion 21 or the position of the stepped portion 201c is called the inner bottom position of the mold 2, and the height from the inner bottom position of the mold 2 to the upper end position of the cylindrical portion 20 may be simply called the inner height of the mold 2. The inner height of the mold 2 may be 2500 mm or more, 3000 mm or more, 4000 mm or more, or 5000 mm or more. Note that the upper end position of the ingot cast in the mold 2 may be below the upper end position of the cylindrical portion 20 and may vary as appropriate depending on the manufacturing conditions.

[0017] A cooling jacket 3 may be attached to the outer periphery of the mold 2. The mold 2 may be cooled during the melting production of the titanium-based ingot. The cooling jacket 3 may be a water-cooled jacket.

[0018] The melting production of the titanium-based ingot may include a primary melting for producing a primary ingot 4a using the consumable electrode 4 as a raw material, and at least one secondary melting for producing a cast ingot 5a using the raw material ingot 5 as a raw material after the primary melting. Note that the primary ingot 4a and the cast ingot 5a may be collectively referred to as an ingot.

[0019] The consumable electrode 4 used in the first melting may be formed by welding and joining a plurality of briquettes manufactured by press-molding sponge titanium (and alloy raw materials if necessary) into a columnar shape. In the first melting, the primary ingot 4a is manufactured by vacuum arc melting. That is, after arranging the mold 2 and the consumable electrode 4 in the VAR furnace 1, the inside of the VAR furnace 1 is maintained at a vacuum of about 0.001 Torr. With the tip of the suspended consumable electrode 4 placed inside the mold 2, an arc is generated from the consumable electrode 4, and the consumable electrode 4 is melted by the heat. The melted consumable electrode 4 accumulates as molten metal inside the mold 2. As the melting of the consumable electrode 4 progresses, the molten metal level rises. The primary ingot 4a is formed by sequentially solidifying the molten metal inside the mold 2. That is, the primary ingot 4a is sequentially grown upward from the bottom 21 side inside the mold 2.

[0020] The raw material ingot 5 used in at least one second melting may be the primary ingot 4a manufactured in the first melting in the second melting performed immediately after the first melting, and may be the cast ingot 5a manufactured in the previous second melting in the second melting after the second time. For example, in the second second melting, it may be the cast ingot 5a manufactured in the first second melting. Also in the second melting, the cast ingot 5a is manufactured by vacuum arc melting. That is, after arranging the mold 2 and the raw material ingot 5 in the VAR furnace 1, the inside of the VAR furnace 1 is maintained at a vacuum of about 0.001 Torr. With the tip of the suspended raw material ingot 5 placed inside the mold 2, an arc is generated from the raw material ingot 5, and the raw material ingot 5 is melted by the heat. The melted raw material ingot 5 accumulates as molten metal inside the mold 2. As the melting of the raw material ingot 5 progresses, the molten metal level rises. The cast ingot 5a is formed by sequentially solidifying the molten metal inside the mold 2. That is, the cast ingot 5a is sequentially grown upward from the bottom 21 side inside the mold 2.

[0021] The more the number of meltings is increased, the more the impurities in the ingot decrease and the purity increases. Performing two or more second meltings is advantageous for manufacturing a high-purity titanium ingot.

[0022] The mold 2 is repeatedly exposed to high temperatures (temperatures exceeding about 1668°C, the melting point of titanium) and room temperature during ingot production. Due to this thermal history, the cylindrical portion 20 may undulate (bend irregularly). Undulation due to thermal history occurs in a wide range used for ingot casting. That is, undulation due to thermal history occurs in the region affected by the heat of the molten metal of the melted consumable electrode 4 or the raw material ingot 5, and occurs in at least a part of the region where the molten metal generated from the consumable electrode 4 or the raw material ingot 5 comes into contact. More specifically, undulation due to thermal history can occur in at least a part from the inner bottom position of the mold 2 to the upper end position of the primary ingot 4a or the cast ingot 5a. If the protrusion of the cylindrical portion 20 inward due to this undulation is large, the produced ingot cannot be removed from the mold 2, and ultimately the mold 2 may be destroyed, resulting in a manufacturing defect.

[0023] As shown in FIG. 1, while repeatedly melting and manufacturing a titanium-based ingot in the VAR furnace 1, when the inner diameter of the mold 2 is measured and it is determined that the inner diameter of the mold 2 has fluctuated by a predetermined amount or more, the mold 2 may be corrected. That is, repeatedly melting and manufacturing a titanium-based ingot in the VAR furnace 1 having the configuration shown in FIG. 2 (step S1 in FIG. 1) may include melting and manufacturing a titanium-based ingot in the VAR furnace 1 and measuring the inner diameter of the mold 2, and determining whether correction of the mold 2 is necessary based on the measurement result.

[0024] The mold 2 to be corrected may be at least one of the primary melting mold used for primary melting and the secondary melting mold used for secondary melting.

[0025] Here, on the surface or outer peripheral surface of the primary ingot 4a produced by the primary melting (the surface that becomes the contact surface with the inner peripheral surface 201 of the cylindrical portion 20 of the primary melting mold), a sponge shape remains to some extent. On the other hand, on the surface or outer peripheral surface of the cast ingot 5a produced by the secondary melting (the surface that becomes the contact surface with the inner peripheral surface 201 of the cylindrical portion 20 of the secondary melting mold), the sponge shape hardly remains and tends to become a smooth curved surface. Therefore, the contact area between the primary ingot 4a and the cylindrical portion 20 of the primary melting mold is relatively small, and the undulation due to the thermal history in the cylindrical portion 20 of the primary melting mold is relatively small. On the other hand, the contact area between the cast ingot 5a and the cylindrical portion 20 of the secondary melting mold is relatively large, and the undulation due to the thermal history in the cylindrical portion 20 of the secondary melting mold is relatively large. For this reason, it is preferable to target the secondary melting mold used in the secondary melting for correction.

[0026] Next, FIG. 3 is an explanatory diagram showing an example of a method for measuring the inner diameter of the mold 2 in FIG. 2. FIG. 3(a) is an explanatory diagram showing the inner diameter measurement positions when the mold 2 is viewed in a plane, and FIG. 3(b) is an explanatory diagram showing the inner diameter measurement positions when the mold 2 is viewed in a cross section.

[0027] The inner diameter of the mold 2 can be measured by any method, but it may be measured by the method as shown in FIG. 3. That is, as shown in FIG. 3(a), the inner diameter of the mold 2 may be measured in two directions (A-C position and B-D position) perpendicular to each other. Also, in the two perpendicular directions, as shown in FIG. 3(b), the inner diameter of the mold 2 may be measured at a plurality of positions spaced apart in the height direction H of the mold 2. The plurality of positions spaced apart in the height direction H of the mold 2 may be positions at a predetermined interval such as 200 mm or the like with reference to the inner bottom position of the mold 2.

[0028] More specifically, the following procedure may be followed. That is, after the casting of the ingot is completed, the bottom part 21 is removed from the mold 2, and the cylindrical part 20 is laid down horizontally. While using an instrument such as a laser marking device, the height of the base between the upper part and / or the lower part of the cylindrical part 20 and the placement surface is adjusted so that the inner peripheral surface 201 of the cylindrical part 20 extends horizontally. For example, using a marker such as chalk, draw four vertical lines from the upper flange 200U to the inner bottom position of the mold 2, and write marks (A, B, C, D) for each vertical line. At this time, the four vertical lines are drawn at the positions where the surfaces orthogonal to each other and the inner peripheral surface 201 of the cylindrical part 20 intersect. Write marks at a pitch of 200 mm on each of the four vertical lines, and at the intersection of each vertical line and the mark, measure and record the inner diameter using an inside gauge (inside micrometer for measuring inner diameter). At this time, measure the inner diameter of the mold 2 in two directions (A - C position and B - D position) orthogonal to each other.

[0029] When the measured value of the inner diameter varies by a predetermined set amount or more from the initial inner diameter (or nominal inner diameter) of the mold 2, remove members such as a water-cooling guide attached to the cylindrical part 20, and perform correction (inner diameter correction) on the mold 2 or the cylindrical part 20. The set amount can be arbitrarily determined, but can be, for example, 7 mm or 10 mm, etc.

[0030] Next, with reference to FIGS. 4 and 5, a mold correction device 6 that can be used for correcting the mold 2 in the method for manufacturing a titanium-based ingot or the method for correcting the mold 2 of the VAR furnace 1 according to the present embodiment will be described. FIG. 4 is an explanatory view showing the mold correction device 6 in a closed state that can be used for correcting the mold 2 of FIG. 2, and FIG. 5 is an explanatory view showing the mold correction device 6 of FIG. 4 in an open state. (a) of FIGS. 4 and 5 shows the mold correction device 6 in a partial cross-section, and (b) of FIGS. 4 and 5 shows the mold correction device 6 in a plan view.

[0031] Any device may be used for correcting the mold 2, but for example, a mold correction device 6 as shown in FIGS. 4 and 5 may be used. Such a mold correction device 6 is also disclosed in Japanese Patent Application Laid-Open No. 2002-66693 by the present applicant.

[0032] As shown in FIGS. 4 and 5, the mold correction device 6 has a driving means 60, a pressing member 61, a substrate 62, a plurality of slide plates 63, and an attachment 64.

[0033] The driving means 60 is for moving the pressing member 61 up and down. The driving means 60 may be a fluid pressure cylinder and may have a main body 600 and an operating shaft 601 provided so as to be able to advance and retreat from the main body 600. The operating shaft 601 advances and retreats from the main body 600 in response to a fluid pressure such as hydraulic pressure, water pressure, or air pressure supplied to the main body 600.

[0034] The pressing member 61 is attached to the upper part of the operating shaft 601 of the driving means 60 and is configured to be able to advance and retreat together with the operating shaft 601. The pressing member 61 is a frustum-shaped member that tapers downward. More specifically, the pressing member 61 has a frustum shape with a square cross-section. A fitting groove 61a having a T-shaped cross-section is provided on the side surface of the pressing member 61.

[0035] The substrate 62 is disposed below the slide plate 63 and supports the slide plate 63. The substrate 62 may be supported by any configuration, but may be attached to the upper surface of the main body 600 of the driving means 60 as shown in the illustrated embodiment. The substrate 62 may be provided in an annular shape so as to surround the operating shaft 601. The substrate 62 may include a plurality of partial substrates spaced apart in the circumferential direction of the operating shaft 601. The upper surface 62a of the substrate 62 is an inclined surface that slopes downward as it moves away from the operating shaft 601.

[0036] The plurality of slide plates 63 are arranged side by side in the circumferential direction of the pressing member 61 so as to surround the pressing member 61. As particularly shown in FIGS. 4 and 5(b), corresponding to the pressing member 61 being in the shape of a frustum of a square pyramid in the illustrated embodiment, four slide plates 63 are provided. Each of the slide plates 63 is placed on the upper surface 62a of the substrate 62. The inner surface 63a of each of the slide plates 63 is an inclined surface inclined so as to approach the operating shaft 601 as it goes downward, and is adjacent to the side surface of the pressing member 61. A fitting rail 63b having a T-shaped cross section is provided on the inner surface 63a of each of the slide plates 63, and the fitting rail 63b is fitted into the fitting groove 61a on the side surface of the pressing member 61. The fitting rail 63b is provided so as to be able to advance and retreat within the fitting groove 61a. The outer peripheral surfaces 63c of the plurality of slide plates 63 may be arc-shaped so as to draw a single circle as a whole when viewed in plan.

[0037] As shown in FIG. 5, when the pressing member 61 is lowered according to the advancement and retreat of the operating shaft 601, each of the slide plates 63 projects outward in the radial direction of the operating shaft 601 while sliding on the upper surface 62a of the substrate 62. Thereby, the diameter of the circle drawn by the outer peripheral surfaces 63c of the plurality of slide plates 63 is expanded. This state of the mold correcting device 6 is called an open state.

[0038] On the other hand, as shown in FIG. 4, when the pressing member 61 is raised according to the advancement and retreat of the operating shaft 601, each of the slide plates 63 is pulled back inward in the radial direction of the operating shaft 601 while sliding on the upper surface 62a of the substrate 62. Thereby, the diameter of the circle drawn by the outer peripheral surfaces 63c of the plurality of slide plates 63 is reduced. This state of the mold correcting device 6 is called a closed state.

[0039] The attachment 64 is a member having a predetermined thickness and shape, and is attached to the outer peripheral surface 63c of each slide plate 63. By changing the attachment 64 according to the size and inner surface shape of the mold 2, one mold correcting device 6 can be used for various molds 2.

[0040] Next, with reference to FIGS. 6 and 7, a method for modifying the mold 2 of the VAR furnace 1 according to an embodiment of the present invention will be described. FIG. 6 is an explanatory diagram showing a method for modifying the mold 2 of the VAR furnace 1 according to an embodiment of the present invention implemented in the modification (step S2) of the mold 2 in FIG. 1, and FIG. 7 is an explanatory diagram showing the relative rotation of the mold modification device 6 and the mold 2 at each height position in FIG. 6.

[0041] The method for modifying the mold 2 of the VAR furnace 1 according to the present embodiment includes stepwise moving the mold modification device 6 from the upper side to the lower side inside the cylindrical portion 20, and pressing the inner surface of the cylindrical portion 20 by the mold modification device 6 at each height position of the stepwise movement. By pressing the inner surface of the cylindrical portion 20 by the mold modification device 6 at each height position of the stepwise movement, the inner diameter of the mold 2 can be corrected over a wide area in the height direction H. Thereby, it is possible to cope with the undulation of the cylindrical portion 20 due to the thermal history and suppress the occurrence of a situation where the mold 2 has to be destroyed. Further, as a result of correcting the inner diameter of the mold 2, the mold 2 can be continuously used, and the number of uses or the life of the mold 2 can be increased. The two-dot chain line in FIG. 6 indicates the position where the mold modification device 6 is moved stepwise.

[0042] The mold modification device 6 may be moved inside the cylindrical portion 20 while being suspended by the suspension means 7. The suspension means 7 may include a suspension means 70 fixed to the mold modification device 6, a plurality of wires 71 attached to the suspension means 70, and a suspension hook 72 to which the wires 71 are hung. By moving the suspension hook 72 up and down by a driving device (not shown), the mold modification device 6 can be moved.

[0043] The mold correction device 6 in a closed state can be moved within the cylindrical portion 20. The inner diameter correction of the mold 2 by the mold correction device 6 can be carried out by setting the mold correction device 6 in an open state, that is, lowering the pressing member 61 and projecting the plurality of slide plates 63 radially outward. The outer peripheral surface 63c of the plurality of slide plates 63 may be directly pressed against the inner peripheral surface 201 of the cylindrical portion 20, or the attachment 64 attached to the outer peripheral surface 63c of the slide plate 63 may be pressed against the inner peripheral surface 201 of the cylindrical portion 20. After the inner diameter of the mold 2 is corrected once, the mold correction device 6 may be returned to the closed state.

[0044] The stepwise movement is performed so as to include the region where undulation due to the thermal history occurs, that is, the region where the molten metal of the consumable electrode 4 or the raw material ingot 5 melted within the mold 2 is in contact. In other words, the stepwise movement is performed from the upper end position of the primary ingot 4a or the cast ingot 5a to the inner bottom position of the mold 2. If necessary, the inner surface of the cylindrical portion 20 may be pressed by the mold correction device 6 even above the upper end position of the primary ingot 4a or the cast ingot 5a.

[0045] The stepwise movement may be performed within a range of 50 mm or more and 500 mm or less. That is, the mold correction device 6 may be moved in the height direction H by a distance within this range, and the inner diameter of the mold 2 may be corrected at that position. The total length of the slide plate 63 in the height direction H of the mold 2 may be about 700 mm. That is, the total length of the slide plate 63 in the height direction H may be equal to or greater than the moving distance of the mold correction device 6 in the height direction H. By performing the stepwise movement within the above range, the occurrence of regions where the inner diameter correction is not performed in the height direction H can be suppressed. Further, as shown in FIG. 5, when the mold correction device 6 is in the open state, the pressing member 61 is in contact with the lower part of the slide plate 63, and it is considered that the inner diameter correction of the mold 2 through the lower part of the slide plate 63 is reliable. By performing the stepwise movement within the above range, the inner diameter correction of the mold 2 can be performed more reliably. The stepwise movement may be performed at 200 mm so as to mainly use the range of 200 mm on the lower side of the slide plate 63 for the inner diameter correction of the mold 2. At this time, the mold correction device 6 may be moved stepwise with reference to the marks at a 200 mm pitch written at the time of inner diameter measurement. When the mold correction device 6 is moved stepwise at other intervals, other marks may be written on the inner peripheral surface 201 of the cylindrical portion 20.

[0046] As described above, it is considered that the inner diameter correction of the mold 2 through the lower part of the slide plate 63 is reliable. By moving the mold correction device 6 stepwise from the upper side to the lower side, the inner diameter correction of the mold 2 through the lower part of the slide plate 63 can be sequentially performed, and the correction accuracy can be improved.

[0047] The pressing of the inner surface of the cylindrical portion 20 by the mold correction device 6 may be performed with the bottom portion 21 removed from the cylindrical portion 20. Thereby, the inner diameter correction of the mold 2 can be more reliably performed up to the inner bottom position of the mold 2 and its periphery. Removing the bottom portion 21 from the cylindrical portion 20 is particularly useful in the mode where the pressing portion, that is, the slide plate 63, is disposed on the upper portion of the mold correction device 6, as shown in FIG. 6. Further, a fluid pressure supply source 65 may be connected to the main body 600 through the opening below the cylindrical portion 20. Although not shown in detail, the cylindrical portion 20 is suspended in the air by being hooked to a jig. A space is provided below the cylindrical portion 20.

[0048] The amount of pressing the inner surface of the cylindrical portion 20 by the mold correction device 6 (the amount of inner diameter correction) corresponds to the amount of horizontal movement of the slide plate 63 of the mold correction device 6. The amount of movement of the slide plate 63 has a directly proportional relationship with the stroke amount of the operating shaft 601 of the mold correction device 6, and the stroke amount of the operating shaft 601 can be confirmed by a digital counter.

[0049] It is preferable to suppress the amount of inner diameter correction in one pressing to a predetermined amount or less, for example, about 3 mm or less. By suppressing it to a predetermined amount or less, a large driving force is not required, and an increase in the size of the mold correction device 6 can be avoided. Also, if the correction amount in one pressing is large, the difference in the thickness of the cylindrical portion 20 in the height direction H becomes large, the amount of strain introduced due to the correction work becomes large, and as a result, damage such as cracks is likely to be formed in the cylindrical portion 20. To ensure the final amount of inner diameter correction, the movement of the mold correction device 6 from the upper side to the lower side may be repeated. That is, the mold correction device 6 that has reached the lower end may be returned to the upper side, and the correction work may be performed again from the upper side. For example, when the amount of inner diameter correction at each height position is set to about 3 mm in the process of lowering the mold correction device 6 once from the upper side to the lower side, an inner diameter correction of around 10 mm can be performed by repeating the movement of the mold correction device 6 from the upper side to the lower side 3 to 4 times.

[0050] When using the mold correction device 6 as in this embodiment, by opening the mold correction device 6 once, the inner diameter of the mold 2 can be corrected in four directions. However, there is a gap between the slide plates 63 with respect to the circumferential direction CD (see FIG. 7) of the cylindrical portion 20. As shown in FIG. 7, the method for correcting the mold 2 of the VAR furnace 1 according to this embodiment may further include pressing the inner surface of the cylindrical portion 20 with the mold correction device 6 at each height position of the stepwise movement, and then relatively rotating the mold correction device 6 and the mold 2 by a predetermined amount in the circumferential direction CD of the cylindrical portion 20, and pressing the inner surface of the cylindrical portion 20 again with the mold correction device 6. By rotating the mold correction device 6 and / or the mold 2 to press the inner surface of the cylindrical portion 20, the inner diameter correction of the mold 2 can be performed more uniformly with respect to the circumferential direction CD of the cylindrical portion 20. The rotation of the mold correction device 6 and / or the mold 2 and the pressing of the inner surface of the cylindrical portion 20 may be performed multiple times. The mold correction device 6 may be rotated with the mold 2 fixed.

[0051] The amount of rotation of the mold correction device 6 and / or the mold 2 for one rotation may be less than 90° with respect to the circumferential direction CD of the cylindrical portion 20. The amount of rotation for one rotation may be 10° or more and 70° or less, and may be 15° or more and 50° or less. In the aspect shown in FIG. 7, the mold correction device 6 is rotated by 30° at a time with the mold 2 fixed.

[0052] The number of rotations at each height position may be 2 or more and 5 or less. By setting the number of rotations to 2 or more, the inner diameter correction of the mold 2 can be performed more uniformly in the circumferential direction CD of the cylindrical portion 20. By setting the number of rotations to 5 or less, a balance can be achieved between the uniformity of the inner diameter correction of the mold 2 and the working efficiency.

[0053] To summarize the above, in the method for correcting the mold 2 of the VAR furnace 1 of this embodiment, the inner diameter of the mold 2 may be corrected as follows. - Align the height position of the mold correction device 6 inside the cylindrical portion 20. - Project the slide plate 63 of the mold correction device 6 radially outward and press the inner surface of the cylindrical portion 20 through the slide plate 63, and then pull the slide plate 63 radially inward. - Rotate the mold correction device 6 and the mold 2 relative to each other, and after rotation, press the inner surface of the cylindrical portion 20 via the slide plate 63. Multiple rotations and presses may be performed. - Move the mold correction device 6 downward by a predetermined amount. After the movement, press the inner surface of the cylindrical portion 20 via the slide plate 63, rotate the mold correction device 6 and the mold 2 relative to each other, and press the inner surface of the cylindrical portion 20 via the slide plate 63 after rotation. Perform this sequentially until the inner bottom position of the mold 2. - If necessary, move the mold correction device 6 from the upper side to the lower side of the cylindrical portion 20 a plurality of times.

[0054] As described above, the preferred embodiments of the present invention have been described in detail with reference to the accompanying drawings, but the present invention is not limited to such examples. It is obvious that those having ordinary knowledge in the technical field to which the present invention pertains can conceive of various modification examples or correction examples within the scope of the technical idea described in the claims, and it is naturally understood that these also belong to the technical scope of the present invention.

Example

[0055] Hereinafter, the present invention will be described more specifically by way of examples. The present invention is not limited to these examples.

[0056] (Example 1) The inventor used the mold 2, which is a mold for secondary melting with an inner diameter of 1000 mm and a height of 3800 mm, 200 times in the production of titanium-based ingots, and then measured the inner diameter of the mold 2.

[0057] The inner diameter was measured by the method described with reference to Fig. 3. That is, after removing the bottom 21 from the mold 2 after ingot casting, the cylindrical portion 20 was laid on its side, and while using a laser marking device, the height of the base between the upper and / or lower portions of the cylindrical portion 20 and the placement surface was adjusted so that the inner peripheral surface 201 of the cylindrical portion 20 extended horizontally. Four vertical lines were drawn from the upper flange 200U to the inner bottom position of the mold 2 with chalk, and marks (A, B, C, D) were written for each vertical line. At this time, the four vertical lines were drawn at the positions where the surfaces orthogonal to each other and the inner peripheral surface 201 of the cylindrical portion 20 intersect. Marks at 200 mm pitch were written on each of the four vertical lines, and the inner diameter was measured and recorded using an inside gauge (inside calipers) at the intersection points of each vertical line and the marks. At this time, the inner diameter of the mold 2 was measured in two directions (A - C position and B - D position) orthogonal to each other. The measurement results of the inner diameter are shown in Table 1 below. Also, after implementing the method for modifying the mold 2 of the VAR furnace 1 according to the embodiment of the present invention, the inner diameter of the mold 2 was measured again. The results are also shown in accordance with Table 1.

[0058]

Table 1

[0059] In Table 1, "measurement position" indicates the inner diameter measurement position of the mold 2 with the inner bottom position of the mold 2 as the reference (0th position, 0 mm position). The inner diameter is measured at 200 mm pitch upward from the inner bottom position of the mold 2. "Reference value" indicates the initial inner diameter (or nominal inner diameter) of the mold 2. "A - C" and "B - D" indicate the inner diameter measurement positions in two orthogonal directions as shown in Fig. 3. "Value before modification" indicates the inner diameter measurement value before implementing the method for modifying the mold 2 of the VAR furnace 1 according to the embodiment of the present invention, and "after modification" indicates the inner diameter measurement value after implementing the method for modifying the mold 2 of the VAR furnace 1 according to the embodiment of the present invention.

[0060] In the column of "Before correction value", "レ" indicates that the decrease in the inner diameter measurement value from the reference value is less than 1 mm, "!" indicates that the decrease in the inner diameter measurement value from the reference value is 1 mm or more and 5 mm or less, and "×" indicates that the decrease in the inner diameter measurement value from the reference value exceeds 5 mm. The arrow in the column of "After correction" indicates the variation tendency of the inner diameter measurement value from the "Before correction value". The underline in the columns of "Before correction value" and "After correction" indicates the minimum value of the inner diameter measurement value.

[0061] As shown in Table 1, when mold 2 was used 200 times in the production of titanium ingots, the maximum protrusion amount into the inside of the cylindrical portion 20 was 9.9 mm (the second position of the B-D inner diameter). In this state, if mold 2 is continuously used, there is a risk that the produced titanium ingots cannot be taken out of mold 2, so it was decided to correct mold 2.

[0062] The mold correction device 6 was gradually moved from the upper side to the lower side inside mold 2, and the inner surface of the cylindrical portion 20 was pressed by the mold correction device 6 three times at each height position. As a result, the maximum protrusion amount into the inside of the cylindrical portion 20 could be reduced to 0.8 mm (the 19th position of the A-C inner diameter). The time required for this correction was 7 hours. In addition, since the mold correction device 6 was rotated 30° twice at each height position, the inner surface was pressed three times at each height position.

[0063] (Example 2) The inventor measured the inner diameter of mold 2, which is a mold for secondary melting with an inner diameter of 750 mm and a height of 4200 mm, after using it 200 times in the production of titanium-based ingots, and performed the method for correcting mold 2 of VAR furnace 1 according to the embodiment of the present invention to correct the inner diameter of mold 2. The maximum protrusion amount inside the cylindrical portion 20 before correction was 13.3 mm. In this state, if mold 2 is continuously used, there is a risk that the produced titanium-based ingot cannot be taken out from mold 2, so it was decided to correct mold 2. After replacing the attachment 64 with one suitable for mold 2 having an inner diameter of 750 mm, the mold correction device 6 was gradually moved from the upper side to the lower side under the same conditions as in Example 1, and the inner surface of the cylindrical portion 20 was pressed by the mold correction device 6 at each height position for 7 rounds. As a result, the maximum protrusion amount inside the cylindrical portion 20 could be reduced to 0.9 mm. The time required for this correction was 10 hours.

[0064] From these results, it was confirmed that the method for correcting mold 2 of VAR furnace 1 according to the embodiment of the present invention can cope with the undulation of the cylindrical portion 20 due to the thermal history and can suppress the occurrence of a situation where mold 2 has to be destroyed.

[0065] Note that the invention described in this specification can also be described as follows. [1] A method for correcting a mold of a VAR furnace, wherein the mold has a cylindrical portion having openings at the upper and lower sides respectively, and a detachable bottom for closing the lower opening of the cylindrical portion. The mold correction device is gradually moved from the upper side to the lower side inside the cylindrical portion, and at each height position of the gradual movement, the inner surface of the cylindrical portion is pressed by the mold correction device. including A method for correcting a mold of a VAR furnace. [2] After pressing the inner surface of the cylindrical portion by the mold correction device at each height position of the gradual movement, the mold correction device and the mold are relatively rotated by a predetermined amount in the circumferential direction of the cylindrical portion, and further including pressing the inner surface of the cylindrical portion again by the mold correction device. The method for correcting the mold of a VAR furnace according to claim 1. [3] The number of rotations at each height position is 2 or more and 5 or less. The method for correcting the mold of a VAR furnace according to claim 2. [4] The stepwise movement is performed within a range of 50 mm or more and 500 mm or less. The method for correcting the mold of a VAR furnace according to any one of claims 1 to 3. [5] The mold is a mold for secondary melting. The method for correcting the mold of a VAR furnace according to any one of claims 1 to 4. [6] The inner diameter of the mold is 750 mm or more. The method for correcting the mold of a VAR furnace according to any one of claims 1 to 5. [7] The pressing of the inner surface of the cylindrical portion by the mold correction device is performed in a state where the bottom portion is removed from the cylindrical portion. The method for correcting the mold of a VAR furnace according to any one of claims 1 to 6. [8] A method for manufacturing a titanium-based ingot, comprising: repeating the melting and manufacturing of a titanium-based ingot in a VAR furnace, and correcting the mold of the VAR furnace by the method according to any one of claims 1 to 7. A method for manufacturing a titanium-based ingot, including the above steps. [9] The melting and manufacturing of the titanium-based ingot includes: primary melting for manufacturing a primary ingot using a consumable electrode as a raw material, and after the primary melting, at least one secondary melting for manufacturing a cast ingot using a raw material ingot as a raw material. The mold is at least one of a primary melting mold used in the primary melting and a secondary melting mold used in the secondary melting. The method for manufacturing a titanium-based ingot according to claim 8.

Explanation of reference numerals

[0066] 1: VAR furnace 2: Mold 20: Cylindrical part 21: Bottom 4: Consumable electrode 5: Raw material ingot 6: Mold correction device

Claims

1. A method for modifying a mold of a VAR furnace, wherein the mold has a cylindrical portion having openings at the upper and lower portions respectively, and a detachable bottom for closing the lower opening of the cylindrical portion. Moving a mold correction device step by step from the upper side to the lower side inside the cylindrical portion, and pressing the inner surface of the cylindrical portion by the mold correction device at each height position of the step-by-step movement. Including A method for modifying a mold of a VAR furnace.

2. At each height position of the step-by-step movement, after pressing the inner surface of the cylindrical portion by the mold correction device, rotating the mold correction device and the mold relative to each other by a predetermined amount in the circumferential direction of the cylindrical portion, and further pressing the inner surface of the cylindrical portion by the mold correction device. The method for modifying a mold of a VAR furnace according to Claim 1.

3. The number of rotations at each height position is 2 or more and 5 or less. The method for modifying a mold of a VAR furnace according to Claim 2.

4. The step-by-step movement is performed within a range of 50 mm or more and 500 mm or less. The method for modifying a mold of a VAR furnace according to Claim 1.

5. The mold is a mold for secondary melting. The method for modifying a mold of a VAR furnace according to Claim 1.

6. The inner diameter of the mold is 750 mm or more. The method for modifying a mold of a VAR furnace according to Claim 1.

7. Pressing the inner surface of the cylindrical portion by the mold correction device is performed in a state where the bottom is removed from the cylindrical portion. The method for modifying a mold of a VAR furnace according to Claim 1.

8. A method for manufacturing a titanium-based ingot, including Repeatedly melting and manufacturing a titanium-based ingot in a VAR furnace, and Modifying the mold of the VAR furnace by the method according to any one of Claims 1 to 7. Including, a method for manufacturing a titanium-based ingot.

9. The melting and manufacturing of the titanium-based ingot includes Primary melting for manufacturing a primary ingot using a consumable electrode as a raw material, and After the primary melting, at least one secondary melting for manufacturing a cast ingot using a raw material ingot as a raw material, and The mold is at least one of a primary melting mold used in the primary melting and a secondary melting mold used in the secondary melting. The method for manufacturing a titanium-based ingot according to Claim 8.

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