JP7808445B2 - Base plate, melting and casting device, and ingot manufacturing method - Google Patents

Description

This invention relates to a base plate, a melting and casting apparatus, and a method for manufacturing ingots.

To produce ingots of titanium-based materials such as pure titanium and titanium alloys, raw materials may be melted, for example, in an electron beam melting furnace or a plasma arc melting furnace to produce a molten metal, which is then poured into a continuous casting mold.

In the continuous casting mold, the molten metal is cooled and solidified from the bottom side to form an ingot material, which is then continuously pulled out of the mold. This produces ingots that are cylindrical or prismatic with a polygonal cross section. Prismatic ingots include slabs with a rectangular cross section that can be subjected to hot rolling.

A base plate is placed at the bottom of the continuous casting mold to cool the molten metal and hold the ingot material. A removal mechanism such as a removal rod is attached to the back side of the base plate, opposite the ingot material side. For example, by moving the base plate via this removal rod, the ingot material held by the base plate can be removed from the continuous casting mold.

Patent Document 1 describes an electron beam melting furnace that "forms ingots of predetermined dimensions by depositing metal material heated and melted by an electron beam on the upper surface of an ingot base, cooling and solidifying the molten metal material using cooling molds arranged around the ingot base, and sequentially pulling downward connecting fittings attached and fixed to the bottom surface of the ingot base; characterized in that a fixing plate for fixing the connecting fittings to the ingot base is attached to the bottom surface of the ingot base, and this fixing plate is fixed to the outer periphery of the bottom surface of the ingot base by multiple fixing means arranged around its periphery."

Patent Document 2 also describes a metal melting apparatus that includes a hearth for melting raw metal and a mold into which the molten metal is poured to produce a metal ingot, the metal melting apparatus being characterized in that a base for extracting the ingot is provided at the bottom of the mold, a recess is provided at an arbitrary position on the surface of the base, and the portion of the base surface surrounding the recess is inclined toward the recess.

Japanese Patent Application Laid-Open No. 2000-274957 International Publication No. 2007/052433

The continuous casting process described above sometimes uses a base plate made of copper or a copper alloy, which has an internal coolant flow path for a cooling medium such as water and has excellent thermal conductivity. Using copper or a copper alloy for the base plate that comes into contact with the ingot material is considered appropriate because it allows the heat from the molten metal and ingot material to be quickly removed, allowing the outer shape of the ingot material to be quickly formed.

To create such a base plate, for example, multiple holes may be formed by drilling multiple times from the side of a copper or copper alloy plate member toward the inside. Then, by inserting and welding a copper or copper alloy blocking member into the opening on the side, the opening can be blocked, creating a refrigerant flow path formed by combining the multiple holes inside.

However, copper and copper alloys have extremely high thermal conductivity, and heat diffusion makes preheating unstable, making welding difficult. For this reason, weld defects such as blowholes are likely to occur at the welded joints between copper or copper alloy plate members and blocking members. If a base plate with a poor weld is used in continuous casting, the cooling water or other refrigerant flowing through the refrigerant flow path will become contaminated with the ingot material, resulting in contamination of the final ingot with oxygen and other substances. In light of the difficulty of welding copper and copper alloys described above, holes have traditionally been drilled from the sides of the copper or copper alloy plate members to the inside in order to reduce the weld area.

Furthermore, repeated use of a copper or copper alloy base plate can cause deformation such as warping of the peripheral edges due to thermal expansion and contraction. In this case, it can become difficult to secure the base plate to the extraction rod, and it may even become unusable.

Neither Patent Document 1 nor Patent Document 2 pays any attention to this issue.

The object of this invention is to provide a base plate, a melting and casting apparatus, and an ingot manufacturing method that can suppress refrigerant leakage from the internal refrigerant flow path and that is less likely to deform even when used repeatedly in continuous casting.

After extensive research, the inventors came up with the idea of constructing a base plate by pressure-welding a copper or copper alloy plate portion and a steel plate portion. By forming a groove for a refrigerant flow path on the back side of the copper or copper alloy plate portion, which is positioned with its front surface facing the ingot material, and providing an inlet and outlet that connect to the refrigerant flow path in the steel plate portion, which is placed on top of that back side, it is possible to eliminate welds in the copper or copper alloy plate portion. Furthermore, by fastening the copper or copper alloy plate portion and the steel plate portion together using pressure welding such as explosive welding, the high-strength steel plate portion adheres sufficiently to the copper or copper alloy plate portion, thereby suppressing deformation of the base plate even when it is used repeatedly in continuous casting.

The base plate of this invention is located on the bottom side of the continuous casting mold, holds the ingot material formed within the mold, and is used to withdraw the ingot material from the mold. It is equipped with a copper or copper alloy plate portion with its front surface facing the ingot material and a groove for a refrigerant flow path formed on its back surface, and a steel plate portion press-welded to the back surface of the copper or copper alloy plate portion, and both the inlet and outlet ports communicating with the refrigerant flow path are provided in the steel plate portion.

In the above-mentioned base plate, a groove is preferably formed on the joining surface of the steel plate portion facing the copper or copper alloy plate portion, and the refrigerant flow path is preferably defined by the groove in the copper or copper alloy plate portion and the groove in the steel plate portion.

In this case, it is preferable that the steel plate portion has a plate-shaped component with a through hole formed therethrough in the plate thickness direction, and a lid-shaped component that fits into the plate-shaped component from the back side opposite the joining surface, covering the through hole and defining the groove portion.

It is preferable that the inlet and outlet of the above-mentioned base plate open on the back surface of the steel plate portion, opposite the joining surface on the copper or copper alloy plate portion side.

It is preferable that the corners between the bottom surface and inner surface of the groove portion of the copper or copper alloy plate portion of the base plate be formed into curved surfaces.

It is preferable that the copper or copper alloy plate portion of the above-mentioned base plate is a single piece.

In the above-mentioned base plate, the copper or copper alloy plate portion may have a recess on the surface that is used to hold the ingot material.

The melting and casting apparatus of this invention comprises any of the above-described base plates, a continuous casting mold, and an electron beam melting furnace or a plasma arc melting furnace.

The ingot manufacturing method of this invention involves using the above-mentioned melting and casting apparatus to withdraw the ingot material from the continuous casting mold while cooling it.

The base plate of this invention has the advantage of being able to prevent refrigerant leakage from the internal refrigerant flow path and is less likely to deform even when used repeatedly in continuous casting.

1 is a cross-sectional view schematically showing a melting and casting apparatus in which a base plate according to an embodiment of the present invention can be used. FIG. 2 is a perspective view of the base plate of FIG. 1; FIG. 3 is a partial cross-sectional perspective view of the base plate of FIG. 2; FIG. 10 is a partial cross-sectional perspective view of a base plate according to another embodiment. FIG. 10 is a partial cross-sectional perspective view of a base plate according to yet another embodiment. 3 is a cross-sectional view showing a part of the base plate of FIG. 2 along the plate thickness direction. FIG. 2 is a partially cross-sectional perspective view schematically showing a base plate of the embodiment. FIG. 10 is a partially cross-sectional perspective view schematically showing a base plate of a comparative example. 10A and 10B are diagrams showing coolant flow paths provided in base plates of an example and a comparative example.

Hereinafter, an embodiment of the present invention will be described in detail.
A base plate 11 according to one embodiment of the present invention is used in a melting and casting apparatus 1 as shown in FIG. 1 . The melting and casting apparatus 1 shown in FIG. 1 includes a melting furnace 21 that melts raw material Ms, including titanium sponge, to form molten metal Mm, a continuous casting mold 31 that converts the molten metal Mm into ingot material Mi, and finally forms an ingot, and a base plate 11 disposed on the bottom side of the continuous casting mold 31. Note that the location of the base plate 11 can be changed as appropriate as long as it can hold the ingot material Mi. In the illustrated example, the base plate 11 is disposed inside the bottom side of the continuous casting mold 31. Alternatively, a base plate 11 having a surface Sf area larger than the cross-sectional area of the interior of the bottom side of the continuous casting mold 31 may be disposed outside the bottom side of the continuous casting mold 31.

Here, the melting furnace 21 can be an electron beam melting furnace (so-called EB furnace) or a plasma arc melting furnace, etc. In the illustrated example, the melting furnace 21 as an electron beam melting furnace is configured to include one or more electron guns 22 that irradiate the raw material Ms with an electron beam to melt the raw material Ms, a hearth 23 that stores or flows the molten metal Mm obtained by melting the raw material Ms with the electron gun 22, and a feeder 24 that is used to feed the raw material Ms into the hearth 23.

1 shows one hearth 23, multiple hearths may be provided. The hearth may include a dispensing hearth, in which case multiple continuous casting molds may be provided according to the number of pouring ports provided in the dispensing hearth.
1 shows one feeder 24 as an example, multiple feeders may be provided, since rod-shaped raw materials may be extended to above the upstream side of the hearth and irradiated with an electron gun to form a molten metal.

Here, the continuous casting mold 31 has a casting space of the desired shape formed inside, into which molten metal Mm is poured from the hearth 23 of the melting furnace 21. A base plate 11 is disposed on the bottom side of the interior (the lower side in Figure 1). When molten metal Mm is poured from the hearth 23 into the continuous casting mold 31, the molten metal Mm cools and solidifies on the base plate 11, becoming ingot material Mi, which is held by the base plate 11 on its surface Sf side.

A withdrawal rod 41 is connected to the back surface Sb of the base plate 11. When molten metal Mm is poured from the hearth 23 into the continuous casting mold 31, the molten metal Mm cools and solidifies from the inner surface of the continuous casting mold 31 and the surface Sf of the base plate 11, and ingot material Mi begins to form. This ingot material Mi is held by the base plate 11 on the surface Sf side. By moving the base plate 11 holding the ingot material Mi downward via the withdrawal rod 41, the ingot material Mi that is being formed can be withdrawn from the continuous casting mold. This allows for the continuous casting and production of long ingots made of pure titanium, titanium-based titanium alloys, or other materials.

In this embodiment, as shown in Figures 2 and 3, the base plate 11 includes a copper or copper alloy plate portion 12 with its surface Sf facing the ingot material Mi, and a steel plate portion 13 press-welded to the back surface Sr of the copper or copper alloy plate portion 12. The copper or copper alloy plate portion 12 and the steel plate portion 13 are bonded together by pressure welding (i.e., solid-state welding). By pressing the steel plate portion 13, which has higher strength than copper or copper alloy, to the copper or copper alloy plate portion 12, the steel plate portion 13 suppresses deformation such as warping caused by thermal expansion and contraction of the copper or copper alloy plate portion 12 during repeated use of the base plate 11. Conventional base plates made entirely of copper or copper alloy can warp around their edges when repeatedly used in continuous casting, but this embodiment prevents such defects from occurring.

If the copper or copper alloy plate portion 12 and the steel plate portion 13 were fixed together using bolts or fittings rather than pressure welding, the adhesion between them would be insufficient, and deformation of the copper or copper alloy plate portion 12 may not be suppressed.

Methods for pressure welding the copper or copper alloy plate portion 12 and the steel plate portion 13 include gas pressure welding, friction welding, resistance welding, diffusion bonding, ultrasonic pressure welding, pressure welding using a rolling mill or the like, and explosive welding. Among these, explosive welding is preferred because the pressure-welded portion between the components exhibits a fine wavy shape, increasing the bonding area. When a cross section along the thickness direction of a base plate 11 in which the copper or copper alloy plate portion 12 and the steel plate portion 13 are pressure-welded by explosive welding is observed, the bonded interface between the copper or copper alloy plate portion 12 and the steel plate portion 13 exhibits a wavy, ripple-like shape.

In addition, as shown in FIG. 3, the base plate 11 is provided with a coolant flow path 14 through which a coolant such as cooling water flows to cool the molten metal Mm. In this embodiment, a groove 12a is formed on the back surface Sr of the copper or copper alloy plate portion 12, which is pressed against the steel plate portion 13, and the groove 12a is recessed from the back surface Sr and extends in an arbitrary shape on the back surface Sr. Furthermore, the steel plate portion 13 is formed on the joining surface Sp, which is pressed against the copper or copper alloy plate portion 12, with a groove 13a recessed from the joining surface Sp and extending in a shape corresponding to the groove 12a of the copper or copper alloy plate portion 12. When the copper or copper alloy plate portion 12 and the steel plate portion 13 are pressed against each other, the groove 12a and groove 13a come together, defining the coolant flow path 14.

Here, the inlet 13b and outlet 13c, which communicate with the refrigerant flow path 14 inside the base plate 11 and through which the refrigerant flows in and out of the refrigerant flow path 14, are both provided in the steel plate portion 13. The illustrated base plate 11 has only one inlet 13b and outlet 13c, but the number of inlet 13b and outlet 13c can be selected as appropriate. By forming a groove 12a for the refrigerant flow path 14 in the copper or copper alloy plate portion 12 and providing the inlet 13b and outlet 13c for the refrigerant flow path 14 in the steel plate portion 13, it is not necessary to drill holes in the copper or copper alloy plate portion 12 or to weld the openings formed by the drilling. For example, as in the illustrated embodiment, the copper or copper alloy plate portion 12 can be made into a single piece without any welds. This reduces welding defects caused by welding the copper or copper alloy plate portion 12, which is difficult to weld. As a result, leakage of coolant such as cooling water from the coolant flow path 14 due to poor welding is prevented, and contamination of the ingot with oxygen and other substances originating from the cooling water is suppressed.

Furthermore, by forming grooves 12a for the coolant flow paths 14 in the copper or copper alloy plate portion 12, the molten metal Mm in contact with the surface Sf of the copper or copper alloy plate portion 12 in the continuous casting mold 31 can be efficiently cooled by the coolant flowing through the coolant flow paths 14.

The inlet 13b and outlet 13c can also be provided on the outer peripheral surface of the steel plate portion 13, but in this embodiment, they are provided on the back surface Sb of the steel plate portion 13, opposite the joining surface Sp on the copper or copper alloy plate portion 12 side. This makes it easier to fit the base plate 11 and the continuous casting mold 31 together.

It is not necessary to provide a groove 13a in the steel plate portion 13. In the embodiment shown in Figure 4, the coolant flow path 14 is defined between a groove 12a formed on the back surface Sr of the copper or copper alloy plate portion 12 and the joining surface Sp of the steel plate portion 13. The steel plate portion 13 is provided with holes 13d extending in the plate thickness direction so that the inlet 13b and outlet 13c on the back surface Sb side each communicate with the groove 12a in the copper or copper alloy plate portion 12.

The steel plate portion 13 can also be constructed by combining multiple components. For example, in the embodiment shown in Figure 5, the steel plate portion 13 includes a plate-shaped component 13e and a lid-shaped component 13f fitted into the plate-shaped component 13e. The plate-shaped component 13e has a through-hole 13g that extends in a shape corresponding to the groove portion 13a and penetrates through its thickness. Meanwhile, the lid-shaped component 13f has a shape corresponding to the through-hole 13g of the plate-shaped component 13e and is fitted into the through-hole 13g from the back surface Sb side. Because the lid-shaped component 13f and the plate-shaped component 13e are both made of steel, they can be easily joined by welding. A groove portion 13a is defined between the through-hole 13g of the plate-shaped component 13e and the lid-shaped component 13f.

As shown in Figure 6, the grooves 12a formed in the copper or copper alloy plate 12 preferably have curved corners 12b between the bottom and inner surfaces of the grooves 12a. This reduces stress concentration at the corners 12b and prevents cracks from forming there.

The shape of the coolant flow path 14 is not particularly important, but a meandering shape that extends throughout the interior of the base plate 11 while curving or bending at multiple locations is preferable from the perspective of effectively cooling the molten metal Mm on the surface Sf side. In this embodiment, the coolant flow path 14 is configured to include at least grooves 12a formed on the copper or copper alloy plate portion 12 side, thereby achieving an excellent cooling effect on the surface Sf side. Furthermore, the steel plate portion 13 is also cooled by the coolant passing through the coolant flow path 14, making it easier to maintain the shape of the base plate 11.

In addition, a recess 15 used to hold the ingot material can be provided on the surface Sf of the copper or copper alloy plate portion 12. In the example shown, the opening of the recess 15 has a generally trapezoidal or other rectangular shape when viewed from above, and the space becomes wider as it approaches the depth due to its slope, but the shape of the recess 15 is not limited to this and can be modified as appropriate. During continuous casting, the molten metal Mm supplied from the hearth 23 into the continuous casting mold 31 enters the recess 15, and functions to catch and hold the ingot material Mi formed by cooling the molten metal Mm.

Of the base plates 11 described above, the base plate 11 shown in Figure 5 can be manufactured, for example, as follows. First, a flat copper or copper alloy plate member and a flat steel plate member are prepared. Next, the copper or copper alloy plate member and the steel plate member are pressure-welded together by explosive bonding or the like, and this serves as the base plate material. It is also possible to use a clad material in which a copper or copper alloy plate member and a steel plate member are already pressure-welded together.

Then, through holes 13g are formed in the steel plate member (base plate material) from the back side using cutting or other processing, and further processing is performed toward the back (interior) to form grooves 12a in the copper or copper alloy plate member. As a result, the steel plate member becomes the plate-shaped component 13e of the steel plate portion 13, and the copper or copper alloy plate member becomes the copper or copper alloy plate portion 12.

Furthermore, a separately prepared lid-shaped component 13f is then fitted into the through-hole 13g of the plate-shaped component 13e from the back side of the base plate material, and the lid-shaped component 13f and the plate-shaped component 13e are joined by welding or the like. In this way, the base plate 11 is produced.

Here, the detailed description has been given using as an example a base plate 11 whose out-of-plane contour shape is a perfect circle, ellipse, oval, or the like, and whose outer shape is essentially a disk. However, the shape of the base plate 11 can be changed as appropriate to match the shape of the ingot to be produced by continuous casting and the shape of the continuous casting mold 31. Although not shown in the figures, it may also be a plate-shaped base plate whose out-of-plane contour shape is a rectangle or other polygon.

Although not shown, the base plate may be a split type in which some components in a plan view can be detached from the remaining components. In this case, after continuous casting, the base plate holding the ingot on the surface side can be split and the individual components disassembled, allowing the ingot to be easily separated from the surface of the base plate. In this case, it is sufficient that at least one of the split components of the base plate has the above-mentioned configuration in which a copper or copper alloy plate portion and a steel plate portion are pressed together. All of the split components of the base plate may have this configuration. It is preferable that the refrigerant flow path 14 is not exposed on the opposing surfaces of the components that make up the base plate (in other words, the refrigerant flow path is contained within each component and does not extend between the components).

The steel plate portion 13 may be made of stainless steel, carbon steel, or the like. If the copper or copper alloy plate portion 12 is made of a copper alloy, it may be made of a high-copper alloy, for example. This high-copper alloy contains alloying elements, and may have a copper content of 96% by mass or more, for example.

Next, we created a prototype base plate of this invention and confirmed its effectiveness, which we will explain below. However, this explanation is for illustrative purposes only and is not intended to be limiting.

In the example, as shown in Figure 7, a base plate was used in which a stainless steel plate portion and a copper plate portion were explosively welded together. This base plate had a refrigerant flow path defined inside by grooves provided in the copper plate portion and the steel plate portion, with the inlet and outlet provided on the back surface of the steel plate portion. Furthermore, as shown in Figure 5, the steel plate portion was composed of a plate-shaped component and a lid-shaped component.

In the comparative example, as shown in Figure 8, a base plate made entirely of copper was used. This base plate had a refrigerant flow path inside, which was formed by drilling holes from the surrounding side surfaces toward the inside and welding a blocking member to the opening on the side surface.

In addition, each base plate has a serpentine coolant flow path formed inside, as shown by the dashed line in Figure 9, and a recess, as shown in Figure 2, is provided on the surface facing the ingot material.

Using each of the above base plates, more than 150 titanium ingots were produced for each of the examples and comparative examples in a melting and casting apparatus equipped with an electron beam melting furnace and a continuous casting mold.

In the comparative example, cooling water leaked from the refrigerant flow path three times immediately after the base plate began to be used. Including these leaks, the leaks occurred in 0.2% of the ingots produced. Furthermore, in the comparative example, in nearly 100% of the ingots produced, the base plate warped by approximately 4.5 to 5.0 mm at the periphery compared to the center, necessitating replacement.

On the other hand, in the example, the occurrence rate of cooling water leakage from the refrigerant flow path was 0 (zero)%. Furthermore, no warping of the base plate occurred.

From the above, it has been found that this invention can suppress refrigerant leakage from a base plate having a refrigerant flow path inside, and also has the effect of making it less likely to deform even when used repeatedly in continuous casting.

REFERENCE SIGNS LIST 1 Melting and casting apparatus 11 Base plate 12 Copper or copper alloy plate portion 12a Groove portion 12b Corner portion 13 Steel plate portion 13a Groove portion 13b Inlet 13c Outlet 13d Hole portion 13e Plate-shaped component 13f Lid-shaped component 13g Through-hole 14 Coolant flow path 15 Recess 21 Melting furnace 22 Electron gun 23 Hearth 24 Feeder 31 Continuous casting mold 41 Drawing rod Ms Raw material Mm Molten metal Mi Ingot material Sf Front surface Sb Back surface Sr Back surface Sp Joining surface

Claims (11)

A plate-like base plate is located on the bottom side of a continuous casting mold in the production of titanium-based ingots, and is used to hold an ingot material formed in the continuous casting mold and to extract the ingot material from the continuous casting mold,
a copper or copper alloy plate part arranged so that its front surface faces the ingot material and having a groove part for a coolant flow path formed on its back surface, the groove part extending on the back surface ; and a steel plate part pressure-welded to the back surface of the copper or copper alloy plate part,
a base plate in which both an inlet and an outlet communicating with the refrigerant flow path are provided in the steel plate portion; a groove is formed on the joining surface of the steel plate portion on the side of the copper or copper alloy plate portion,
2. The base plate according to claim 1, wherein the coolant flow path is defined by the groove in the copper or copper alloy plate portion and the groove in the steel plate portion. The base plate of claim 2, wherein the steel plate portion comprises a plate-shaped component having a through hole formed therethrough in the plate thickness direction, and a lid-shaped component fitted to the plate-shaped component from the back side opposite the joining surface, covering the through hole and defining the groove portion. The base plate according to any one of claims 1 to 3, wherein the inlet and outlet are open on the back surface of the steel plate portion opposite the joining surface on the copper or copper alloy plate portion side. A base plate according to any one of claims 1 to 4, wherein the corner between the bottom surface and inner surface of the groove of the copper or copper alloy plate portion is formed into a curved surface. The base plate according to any one of claims 1 to 5, wherein the copper or copper alloy plate portion is a single piece. The base plate according to any one of claims 1 to 6, wherein the copper or copper alloy plate portion has a recess on the surface thereof that is used to hold an ingot material. The base plate according to any one of claims 1 to 7, wherein a pull-out rod is connected to the back surface of the base plate. A melting and casting apparatus comprising the base plate according to any one of claims 1 to 8, a continuous casting mold, and an electron beam melting furnace or a plasma arc melting furnace. The melting and casting apparatus of claim 9, further comprising a pull rod connected to the back surface of the base plate. A method for producing an ingot, in which an ingot material is withdrawn from a continuous casting mold while being cooled using the melting and casting apparatus described in claim 9 or 10.