阅读说明：本技术 金属铸块的制造方法 (Method for manufacturing metal ingot ) 是由 舟金仁志 滨荻健司 于 2018-04-13 设计创作，主要内容包括：提供一种能够抑制炉床内的熔液所含有的杂质向铸锭混入的金属铸块的制造方法。一种金属铸块的制造方法,其使用包括电子枪和用于贮存金属原料的熔液的炉床的电子束熔炼炉,其中,向沿着用于贮存所述金属原料的熔液的炉床的第2侧壁配置的供给线的位置供给所述金属原料。对在所述熔液的表面中沿着所述供给线配置且配置于比所述供给线靠所述炉床的中央部侧的位置的第1照射线照射第1电子束。由此,使所述第1照射线处的所述熔液的表面温度(T2)比所述炉床内的所述熔液的整个表面的平均表面温度(T0)高,在所述熔液的表层中形成自所述第1照射线朝向所述供给线的第1熔液流。(Provided is a method for producing a metal ingot, which can suppress impurities contained in a melt in a hearth from being mixed into an ingot. A method for manufacturing a metal ingot, using an electron beam melting furnace including an electron gun and a hearth for holding a melt of a raw metal material, wherein the raw metal material is supplied to a position along a supply line arranged along a 2 nd side wall of the hearth for holding the melt of the raw metal material. The method includes irradiating a 1 st irradiation beam, which is arranged along the supply line on the surface of the melt and is arranged closer to the center portion side of the hearth than the supply line, with a 1 st electron beam. Thereby, the surface temperature (T2) of the melt at the 1 st irradiation line is made higher than the average surface temperature (T0) of the entire surface of the melt in the hearth, and the 1 st melt flow from the 1 st irradiation line toward the supply line is formed in the surface layer of the melt.)

1. A method for producing a metal ingot, which comprises producing a metal ingot containing at least one metal element selected from the group consisting of titanium, tantalum, niobium, vanadium, molybdenum and zirconium in a total amount of 50 mass% or more, using an electron beam melting furnace comprising an electron gun capable of controlling the irradiation position of an electron beam and a hearth for holding a melt of a metal raw material,

a 1 st side wall among a plurality of side walls of a hearth for storing a melt of the metal raw material is a side wall provided with a lip for flowing the melt in the hearth to a mold, a 2 nd side wall is at least 1 side wall other than the 1 st side wall,

supplying the metal raw material to a position of a supply line arranged along an inner side surface of the 2 nd side wall on a surface of the melt,

irradiating a 1 st irradiation beam which is arranged along the supply line on the surface of the melt and is arranged closer to the center portion side of the hearth than the supply line with a 1 st electron beam,

the 1 st irradiation line is irradiated with the 1 st electron beam so that a surface temperature (T2) of the melt at the 1 st irradiation line is higher than an average surface temperature (T0) of the entire surface of the melt in the hearth, and a 1 st melt flow is formed in a surface layer of the melt from the 1 st irradiation line toward the supply line.

2. The method of manufacturing a metal ingot according to claim 1,

a temperature gradient DeltaT/L represented by the following formula (A) is-2.70 or more,

ΔT/L＝(T2-T1)/L…(A)，

t1: the surface temperature of the melt at the supply line,

t2: the surface temperature of the melt at the 1 st irradiation line,

l: the distance between the 1 st irradiation line on the surface of the molten liquid and the supply line,

the unit of the delta T/L is K/mm, the unit of the T1 and the unit of the T2 is K, and the unit of the L is mm.

3. The method of manufacturing a metal ingot according to claim 2,

the delta T/L is more than 0.00,

forming the 1 st molten metal flow on the surface layer of the molten metal, the 1 st molten metal flow traversing the supply line from the 1 st irradiation line toward the inner side surface of the 2 nd side wall,

the unit of the delta T/L is K/mm.

4. The method of manufacturing a metal ingot according to any one of claims 1 to 3, wherein,

the metal raw material is melted in a raw material supply unit, and the melted metal raw material is dropped from the raw material supply unit to a position of the supply line of the melt in the hearth.

5. The method of manufacturing a metal ingot according to any one of claims 1 to 4, wherein,

in the surface of the melt, both ends of the 1 st irradiation line are positioned further outward in the extending direction of the supply line than both ends of the supply line.

6. The method of manufacturing a metal ingot according to any one of claims 1 to 5, wherein,

forming a 2 nd molten liquid flow toward the lip in a band-shaped region between the supply line and the 1 st irradiation line,

irradiating the 2 nd molten stream point with a 2 nd electron beam.

7. The method of manufacturing a metal ingot according to claim 6,

the 2 nd electron beam is irradiated to the 2 nd molten metal stream point at a position of an irradiation point disposed at an end portion of the band-shaped region on the lip portion side.

8. The method of manufacturing a metal ingot according to any one of claims 1 to 7, wherein,

irradiating a No. 2 irradiation beam, which is arranged on the surface of the melt so as to block the lip and has both ends positioned in the vicinity of the No. 1 side wall, with a No. 3 electron beam.

9. The method of manufacturing a metal ingot according to any one of claims 1 to 8, wherein,

the metal material contains 50 mass% or more of titanium element.

Technical Field

The present invention relates to a method for producing a metal ingot in which a metal raw material is melted by an electron beam melting method.

Background

Ingots (ingots) of pure titanium, titanium alloys, or the like are produced by melting a titanium raw material such as titanium sponge or titanium scrap. Examples of the technique for melting a metal raw material such as a titanium raw material (hereinafter, also simply referred to as "raw material") include a vacuum arc melting method, a plasma arc melting method, and an electron beam melting method. Among them, in the Electron Beam melting method, a solid raw material is melted by irradiating the raw material with an Electron Beam in an Electron Beam melting furnace (hereinafter, referred to as "EB furnace"). In order to prevent energy dissipation of the electron beam, melting of the raw material by irradiation of the electron beam in the EB furnace is performed in a vacuum chamber. Molten titanium (hereinafter, also referred to as "melt") as a raw material to be melted is refined in a hearth and then solidified in a mold (die) to form an ingot of titanium. In the electron beam melting method, the irradiation position of the electron beam as a heat source can be accurately controlled by electromagnetic force, and therefore, heat can be sufficiently supplied to the melt in the vicinity of the mold. Therefore, the ingot can be produced without deteriorating the surface quality of the ingot.

The EB furnace generally includes a raw material supply unit for supplying a raw material such as titanium sponge, 1 or more electron guns for melting the supplied raw material, a hearth (e.g., a water-cooled copper hearth) for storing the molten raw material, and a mold for cooling the molten titanium flowing from the hearth to form an ingot. EB furnaces are roughly classified into two types according to the structure of the hearth. Specifically, the EB furnace includes, for example, an EB furnace 1A including a melting hearth 31 and a refining hearth 33 as shown in fig. 1, and an EB furnace 1B including only a refining hearth 30 as shown in fig. 2.

The EB furnace 1A shown in FIG. 1 includes a raw material supply unit 10, electron guns 20a to 20e, a melting hearth 31, a refining hearth 33, and a mold 40. The solid raw material 5 fed from the raw material supply unit 10 into the melting hearth 31 is irradiated with electron beams by the electron guns 20a and 20b, and the raw material 5 is melted into a melt 5 c. The raw material (melt 5c) melted in the melting hearth 31 flows to the refining hearth 33 communicating with the melting hearth 31. In the refining hearth 33, the electron guns 20c and 20d irradiate the melt 5c with electron beams, thereby maintaining the temperature of the melt 5c or raising the temperature of the melt 5 c. Thereby, impurities and the like contained in the melt 5c are removed to refine the melt 5 c. Then, the refined melt 5c flows into the die 40 from the lip 33a provided at the end of the refining hearth 33. The melt 5c is solidified in the mold 40 to produce an ingot 50. The hearth including the melting hearth 31 and the refining hearth 33 as shown in fig. 1 is also referred to as a long hearth.

On the other hand, the EB furnace 1B shown in fig. 2 includes raw material supply units 10A and 10B, electron guns 20A to 20D, a refining hearth 30, and a mold 40. Such a hearth including only the refining hearth 30 is also referred to as a short hearth, relative to the long hearth shown in fig. 1. In the EB furnace 1B using a short hearth, the solid raw material 5 placed on the raw material supply parts 10A and 10B is directly irradiated with an electron beam by the electron guns 20A and 20B to be melted, and the melted raw material 5 is dropped from the raw material supply parts 10A and 10B into the melt 5c of the refining hearth 30. Thus, in the EB furnace 1B shown in fig. 2, the melting hearth 31 shown in fig. 1 can be omitted. In the refining hearth 30, the electron gun 20C irradiates the entire surface of the melt 5C with an electron beam over a wide range, thereby maintaining the temperature of the melt 5C or increasing the temperature of the melt 5C. Thereby, impurities and the like contained in the melt 5c are removed to refine the melt 5 c. Then, the refined melt 5c flows into the mold 40 from the lip 36 provided at the end of the refining hearth 30, and an ingot 50 is produced.

Here, when an ingot is produced by the electron beam melting method described above using a hearth and a mold, if impurities are mixed into the ingot, the ingot is broken. Therefore, it is desired to develop an electron beam melting technique capable of avoiding impurities from being mixed into the melt flowing from the hearth into the mold. The impurities are mainly mixed into the raw material, and are classified into two types, HDI (High Density impurities) and LDI (Low Density impurities). HDI is an impurity containing, for example, tungsten as a main component, and has a higher specific gravity than molten titanium. On the other hand, LDI is an impurity mainly containing titanium nitride or the like. The inside of LDI is porous, and therefore the specific gravity of LDI is smaller than that of molten titanium.

A solidified layer in which molten titanium in contact with the hearth is solidified is formed on the inner surface of the water-cooled copper hearth. This solidified layer is called skull. Since HDI among the impurities has a high specific gravity, HDI is precipitated in the molten metal (molten titanium) in the hearth and is fixed to and captured by the surface of the skull, and thus the possibility of mixing into the ingot is low. On the other hand, since the specific gravity of LDI is smaller than that of molten titanium, most of LDI is suspended on the surface of the melt in the hearth. While LDI is suspended on the surface of the melt, nitrogen diffuses and LDI is melted in the melt. In the case of using the long hearth shown in fig. 1, since the residence time of the melt in the long hearth can be extended, impurities such as LDI can be easily melted in the melt as compared with the case of using the short hearth. On the other hand, in the case of using the short hearth shown in fig. 2, the residence time of the melt in the short hearth is shorter than that in the long hearth, and therefore the possibility that the impurities in the short hearth are not melted in the melt is higher than that in the long hearth. In addition, LDI having a high nitrogen concentration has a high melting point, and therefore has a very low possibility of melting into a melt during the residence time of a normal operation.

Here, for example, patent document 1 discloses an electron beam melting method of metallic titanium: the electron beam is scanned in the direction opposite to the flow direction of the melt toward the mold on the surface of the melt in the hearth, and the average temperature of the melt in the region adjacent to the melt discharge port in the hearth is set to be equal to or higher than the melting point of impurities. In the technique described in patent document 1, the electron beam is scanned in a zigzag pattern in a direction opposite to the flow direction of the melt, and the impurities suspended on the surface of the melt are pushed back to the upstream side, thereby preventing the impurities from flowing into the downstream die.

Disclosure of Invention

Problems to be solved by the invention

However, in the method described in patent document 1, since the electron beam is scanned in a direction opposite to the flow direction of the melt, there is a possibility that the impurities pass through to a position on the downstream side of the irradiation position of the electron beam where the melt flows. Further, the flow of the melt toward the die is accelerated at a position downstream of the position of irradiation of the electron beam, and the residence time of the melt in the hearth may be shortened, thereby reducing the removal rate of impurities. Further, if the impurities are located on the downstream side of the irradiation position of the electron beam in the flow of the melt, the risk of the impurities flowing out to the die along with the flow of the melt increases. For the above reasons, there is a possibility that impurities contained in the melt in the hearth, particularly LDI suspended on the surface of the melt 5c, flow out from the hearth to the mold and mix into the ingot formed by the mold. Therefore, a method for producing a metal ingot is desired in which impurities such as LDI are prevented from flowing out from a hearth to a mold, and the impurities are prevented from being mixed into an ingot.

The present invention has been made in view of the above problems, and an object of the present invention is to provide a novel and improved method for producing a metal ingot, which can suppress impurities contained in a melt in a hearth from being mixed into an ingot.

Means for solving the problems

In order to solve the above-mentioned problems, according to an aspect of the present invention,

a method for producing a metal ingot, which comprises producing a metal ingot containing at least one metal element selected from the group consisting of titanium, tantalum, niobium, vanadium, molybdenum and zirconium in a total amount of 50 mass% or more, using an electron beam melting furnace comprising an electron gun capable of controlling the irradiation position of an electron beam and a hearth for holding a melt of a metal raw material,

a 1 st side wall among a plurality of side walls of a hearth for storing a melt of the metal raw material is a side wall provided with a lip for flowing the melt in the hearth to a mold, a 2 nd side wall is at least 1 side wall other than the 1 st side wall,

supplying the metal raw material to a position of a supply line arranged along an inner side surface of the 2 nd side wall on a surface of the melt,

irradiating a 1 st irradiation beam which is arranged along the supply line on the surface of the melt and is arranged closer to the center portion side of the hearth than the supply line with a 1 st electron beam,

the 1 st irradiation line is irradiated with the 1 st electron beam so that a surface temperature (T2) of the melt at the 1 st irradiation line is higher than an average surface temperature (T0) of the entire surface of the melt in the hearth, and a 1 st melt flow is formed in a surface layer of the melt from the 1 st irradiation line toward the supply line.

The temperature gradient DeltaT/L represented by the following formula (A) may be-2.70 [ K/mm ] or more.

ΔT/L＝(T2-T1)/L…(A)

T1: surface temperature [ K ] of the melt at the supply line

T2: surface temperature [ K ] of the melt at the 1 st irradiation line

L: distance [ mm ] between the 1 st irradiation line on the surface of the melt and the supply line

The DeltaT/L may be 0.00[ K/mm ] or more,

the 1 st molten metal flow is formed on the surface layer of the molten metal, from the 1 st irradiation line, across the supply line, and toward the inner side surface of the 2 nd side wall.

The metal raw material may be melted in a raw material supply unit, and the melted metal raw material may be dropped from the raw material supply unit to a position of the supply line of the melt in the hearth.

In the surface of the melt, both ends of the 1 st irradiation line may be positioned outside both ends of the supply line in the extending direction of the supply line.

In the band-shaped region between the supply line and the 1 st irradiation line, a 2 nd melt flow toward the lip may be formed,

irradiating the 2 nd molten stream point with a 2 nd electron beam.

The 2 nd electron beam may be irradiated to the 2 nd molten metal stream point at a position of an irradiation point disposed at an end portion of the band-shaped region on the lip portion side.

The 2 nd irradiation line may be arranged on the surface of the melt so as to block the lip portion and may be irradiated with the 3 rd electron beam, the 2 nd irradiation line having both ends positioned in the vicinity of the 1 st side wall.

The metal material may contain 50 mass% or more of titanium element.

ADVANTAGEOUS EFFECTS OF INVENTION

As described above, according to the present invention, impurities contained in the melt in the hearth can be prevented from being mixed into the ingot.

Drawings

Fig. 1 is a schematic view showing an electron beam melting furnace having a long hearth.

Fig. 2 is a schematic view showing an electron beam melting furnace having a short hearth.

Fig. 3 is a schematic view showing an electron beam melting furnace (short hearth) for carrying out the method of manufacturing a metal ingot according to embodiment 1 of the present invention.

Fig. 4 is a plan view showing an example of the irradiation line and the supply line of the hearth according to the embodiment.

FIG. 5 is a plan view showing an example of a melt flow formed by the method for producing an ingot of metal according to this embodiment.

Fig. 6A is a vertical cross-sectional view showing a flow state of the melt when the electron beam is not irradiated along the irradiation line as a comparative example of the embodiment.

Fig. 6B is a plan view showing a flow state of the melt when the electron beam is not irradiated along the irradiation line as a comparative example of the embodiment.

Fig. 7 is a vertical cross-sectional view showing the flow state of the melt when an electron beam is irradiated along an irradiation line in the method for producing a metal ingot according to the embodiment.

FIG. 8 is a plan view showing another example of the melt flow formed by the method for producing an ingot of metal according to this embodiment.

FIG. 9 is a plan view of a hearth showing another example of a melt flow formed by the method for producing an ingot of metal according to the embodiment.

Fig. 10 is a plan view of a hearth showing an example of a melt flow formed by the method for manufacturing a metal ingot according to the modification of the embodiment.

Fig. 11 is a plan view showing an example of a melt flow formed by the method for manufacturing a metal ingot according to the modification of the embodiment.

FIG. 12 is a plan view showing an example of a melt flow formed by the method for producing an ingot of metal according to embodiment 2 of the present invention.

Fig. 13 is a plan view of a hearth showing an example of a melt flow formed by the method for manufacturing a metal ingot according to the modification of the embodiment.

Fig. 14 is a plan view of a hearth showing an example of a melt flow formed by the method for manufacturing a metal ingot according to the modification of the embodiment.

FIG. 15 is a plan view showing an example of a melt flow formed by the method for producing an ingot of metal according to embodiment 3 of the present invention.

Fig. 16 is a plan view of a hearth showing an example of a melt flow formed by the method for manufacturing a metal ingot according to the modification of the embodiment.

Fig. 17 is a plan view showing the state of the hearths of comparative examples 1 and 2.

FIG. 18 is a flow chart showing the flow of the melt in example 1.

Fig. 19 is an explanatory diagram showing simulation results of example 1.

Fig. 20 is an explanatory diagram showing simulation results of example 2.

Fig. 21 is an explanatory diagram showing simulation results of example 3.

Fig. 22 is an explanatory diagram showing simulation results of example 4.

Fig. 23 is an explanatory diagram showing simulation results of example 5.

Fig. 24 is an explanatory diagram showing simulation results of example 6.

Fig. 25 is an explanatory diagram showing simulation results of example 7.

Fig. 26 is an explanatory diagram showing simulation results of comparative example 1.

Fig. 27 is an explanatory diagram showing simulation results of example 8.

Fig. 28 is an explanatory diagram showing simulation results of example 9.

Fig. 29 is an explanatory diagram showing simulation results of example 10.

Fig. 30 is an explanatory diagram showing simulation results of example 11.

Fig. 31 is an explanatory diagram showing simulation results of example 12.

Fig. 32 is an explanatory diagram showing the simulation result of comparative example 2.

Detailed Description

Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings. In the present specification and the drawings, the same reference numerals are given to components having substantially the same functional configuration, and redundant description is omitted.

[ 1] embodiment 1]

First, a method for producing a metal ingot according to embodiment 1 of the present invention will be described.

[1.1. Structure of Electron Beam melting furnace ]

First, the structure of an electron beam melting furnace for carrying out the method for producing a metal ingot according to the present embodiment will be described with reference to fig. 3. Fig. 3 is a schematic diagram showing the structure of an electron beam melting furnace 1 (hereinafter referred to as "EB furnace 1") according to the present embodiment.

As shown in fig. 3, the EB furnace 1 includes a pair of raw material supply units 10A and 10B (hereinafter, may be collectively referred to as "raw material supply unit 10"), a plurality of electron guns 20A to 20E (hereinafter, may be collectively referred to as "electron guns 20"), a refining hearth 30, and a mold 40. As described above, the EB furnace 1 of the present embodiment includes only 1 refining hearth 30 as a hearth, and this hearth structure is referred to as a short hearth. The method of producing a metal ingot of the present invention can be suitably applied to an EB furnace 1 with a short hearth as shown in fig. 3, but can also be applied to an EB furnace 1A with a long hearth as shown in fig. 1.

The refining hearth 30 (hereinafter referred to as "hearth 30") is a device for refining the melt 5c while storing the melt 5c of the raw metal material 5 (hereinafter referred to as "raw material 5") and removing impurities in the melt 5 c. The hearth 30 of the present embodiment is constituted by a water-cooled copper hearth having a rectangular shape, for example. A lip 36 is provided on a side wall of one end in the longitudinal direction (Y direction) of the hearth 30. The lip 36 is an outlet for discharging the melt 5c in the hearth 30 to the mold 40.

The mold 40 is a device for cooling and solidifying the melt 5c of the raw material 5 to produce a metal ingot 50 (e.g., an ingot of titanium or a titanium alloy). The mold 40 is made of, for example, a water-cooled copper mold having a rectangular tubular shape. The mold 40 is disposed below the lip 36 of the hearth 30, and cools the melt 5c flowing from the upper hearth 30. As a result, the melt 5c in the mold 40 gradually solidifies as it flows downward of the mold 40, and a solid ingot 50 is formed.

The raw material supply unit 10 is a device for supplying the raw material 5 to the hearth 30. The raw material 5 is, for example, a titanium raw material such as titanium sponge or titanium scrap. In the present embodiment, for example, as shown in fig. 3, a pair of raw material supply portions 10A and 10B are provided above a pair of long side walls of the hearth 30. Solid raw materials 5 supplied from the outside are placed on the raw material supply units 10A and 10B, and the raw materials 5 are irradiated with electron beams from the electron guns 20A and 20B.

In this way, in the present embodiment, in order to supply the raw material 5 to the hearth 30, the raw material 5 is melted by irradiating the solid raw material 5 with an electron beam in the raw material supply portion 10, and the melted raw material 5 (molten metal) is dropped from the inner edge portion of the raw material supply portion 10 into the melt 5c in the hearth 30. That is, the raw material 5 is melted outside the hearth 30 in advance, and then the molten metal is dropped into the melt 5c in the hearth 30 to supply the raw material 5 to the hearth 30. Thus, a dropping line indicating a position where the molten metal drops from the raw material supply unit 10 onto the surface of the melt 5c in the hearth 30 corresponds to a supply line 26 (see fig. 4) described later.

The method of supplying the raw material 5 is not limited to the above dropping example. For example, the solid raw material 5 may be directly charged into the melt 5c in the hearth 30 from the raw material supply unit 10. The charged solid raw material 5 is melted in the high-temperature melt 5c and added to the melt 5 c. In this case, an input line indicating a position where the solid raw material 5 is input to the melt 5c in the hearth 30 corresponds to a supply line 26 (see fig. 4) described later.

In order to perform the electron beam melting method, the electron gun 20 irradiates the raw material 5 or the melt 5c with an electron beam. As shown in fig. 3, the EB furnace 1 of the present embodiment includes, for example, electron guns 20A and 20B for melting the solid raw material 5 supplied to the raw material supply section 10, an electron gun 20C for keeping the temperature of the melt 5C in the hearth 30, an electron gun 20D for heating the upper melt 5C in the mold 40, and an electron gun 20E for suppressing the outflow of impurities from the hearth 30. The electron guns 20A to 20E can control the irradiation positions of the electron beams. Therefore, the electron guns 20C and 20E can irradiate the desired position on the surface of the melt 5C in the hearth 30 with the electron beam.

The electron guns 20A and 20B irradiate the solid raw material 5 placed on the raw material supply unit 10 with electron beams, thereby heating and melting the raw material 5. The electron gun 20C irradiates an electron beam to a wide range of the surface of the melt 5C in the hearth 30, thereby heating and maintaining the melt 5C at a predetermined temperature. The electron gun 20D irradiates the surface of the melt 5c in the mold 40 with an electron beam, thereby heating the upper melt 5c in the mold 40 to maintain a predetermined temperature so as to prevent the upper melt 5c from solidifying. The electron gun 20E intensively irradiates an irradiation beam 25 (see fig. 4) on the surface of the melt 5c in the hearth 30 to prevent impurities from flowing out from the hearth 30 to the mold 40.

As described above, the present embodiment is characterized in that the irradiation beam 25 on the surface of the melt 5c is intensively irradiated with an electron beam (line irradiation) using, for example, an electron gun 20E to prevent the outflow of impurities, and the details thereof will be described later. In the EB furnace 1 of the present embodiment, as shown in fig. 3, the electron gun 20E for the beam irradiation is provided independently of the other electron guns 20A to 20D. Thus, the irradiation with the electron gun 20E can be continued while the raw material 5 is melted by the other electron guns 20A to 20D and the melt 5c is kept warm, and therefore, the surface temperature of the melt 5c at the position of the irradiation with the line can be prevented from decreasing. However, the present invention is not limited to this example. For example, the electron gun 20E for irradiation with the setting line may be omitted by irradiating the electron beam with the control beam 25 using one of the existing electron guns 20A and 20B for melting the raw material and the existing electron guns 20C and 20D for keeping the melt warm. This reduces the number of electron guns installed in the EB furnace 1, reduces the facility cost, and makes it possible to effectively use the existing electron guns.

[1.2. outline of method for producing Metal ingot ]

Next, an outline of the method for producing a metal ingot according to the present embodiment will be described with reference to fig. 3 to 5. Fig. 4 is a plan view showing an example of the irradiation line 25 and the supply line 26 of the hearth 30 of the present embodiment. FIG. 5 is a plan view showing an example of a melt flow formed by the method for producing an ingot of metal according to the present embodiment. The top views of the hearth 30 in fig. 4 and 5 correspond to the hearth 30 of the EB furnace 1 in fig. 3.

The problem to be solved by the method for producing a metal ingot of this embodiment is to suppress impurities contained in a molten metal (melt 5c) obtained by melting a solid raw material 5 from flowing from a hearth 30 into a mold 40 and to suppress the impurities from being mixed into the ingot 50 when producing the ingot 50 of a metal such as pure titanium or a titanium alloy. The problem to be solved by the method for producing a metal ingot according to the present embodiment is, in particular, to suppress LDI, which is a specific gravity smaller than that of a molten titanium (molten titanium), from among impurities contained in a titanium raw material, from being mixed into an ingot 50 of titanium or a titanium alloy, for the titanium raw material as a metal raw material. The titanium or titanium alloy referred to herein is a metal containing 50 mass% or more of titanium as an element.

In order to solve this problem, in the method of manufacturing a metal ingot according to the present embodiment, as shown in fig. 4, the raw material 5 is supplied to the melt 5c in the hearth 30 at the position of the supply line 26 adjacent to the long side walls 37A and 37B of the hearth 30. Then, the irradiation beam 25 adjacent to the supply line 26 is intensively irradiated with an electron beam on the surface of the melt 5c stocked in the hearth 30.

The supply line 26 (corresponding to "supply line" in the present invention) is an imaginary line showing a position where the raw material 5 is supplied from the outside of the hearth 30 to the melt 5c in the hearth 30. The supply line 26 is disposed along the inner surfaces of the side walls 37A and 37B of the hearth 30 on the surface of the melt 5 c.

In the present embodiment, as shown in fig. 3, the molten raw material 5 is dropped onto the hearth 30 from the inner edge portion of the raw material supply portion 10 disposed above the side walls 37A and 37B on the long sides of the hearth 30. Therefore, the supply line 26 is positioned below the inner edge of the raw material supply portion 10 on the surface of the melt 5c in the hearth 30, and has a linear shape extending along the inner surfaces of the side walls 37A and 37B. The supply line 26 may not be strictly linear as long as it is linear extending along the inner surfaces of the side walls 37A, 37B, 37C of the hearth 30, and may be, for example, a broken line, a dot line, a curved line, a wavy line, a zigzag line, a double line, a belt, a broken line, or the like.

The irradiation line 25 (corresponding to the "1 st irradiation line" of the present invention) is a virtual line showing a trajectory of a position on the surface of the melt 5c in the hearth 30 where an electron beam (corresponding to the "1 st electron beam" of the present invention) is intensively irradiated. The irradiation line 25 is arranged on the surface of the melt 5c along the supply line 26 of the raw material 5. The irradiation line 25 may not be strictly linear as long as it is linear extending along the supply line 26, and may be, for example, a broken line, a dot line, a curved line, a wavy line, a zigzag line, a double line, a belt, a broken line, or the like.

Here, the arrangement of the irradiation line 25 and the supply line 26 will be described in more detail. As shown in fig. 4, the rectangular hearth 30 of the present embodiment has 4 side walls 37A, 37B, 37C, and 37D (hereinafter, may be collectively referred to as "side walls 37"). The pair of side walls 37A and 37B facing each other in the X direction constitute a pair of long sides of the hearth 30, and are parallel to the longitudinal direction (Y direction) of the hearth 30. The pair of side walls 37C and 37D facing each other in the Y direction form a pair of short sides of the hearth 30, and are parallel to the width direction (X direction) of the hearth 30.

A lip 36 for discharging the melt 5c in the hearth 30 to the die 40 is provided on one side wall 37D of the short side. On the other hand, the lips 36 are not provided on the other 3 side walls 37A, 37B, and 37C than the side wall 37D. Therefore, the side wall 37D corresponds to the "1 st side wall" provided with the lip, and the side walls 37A, 37B, and 37C correspond to the "2 nd side wall" not provided with the lip 36.

In the example shown in fig. 4, two linear supply lines 26 and 26 parallel to each other are arranged on the surface of the melt 5c in the hearth 30. Two linear irradiation lines 25, 25 parallel to each other are arranged inside the supply lines 26, 26 (on the central portion side in the width direction (X direction) of the hearth 30). The supply lines 26 and 26 are disposed along the inner surfaces of two side walls 37A and 37B (2 nd side wall) of the 4 side walls of the hearth 30 at positions separated by a predetermined distance L1 from the inner surfaces toward the center portion side in the width direction (X direction) of the hearth 30. The irradiation lines 25, 25 are disposed along the supply lines 26, 26 at positions separated by a predetermined distance L from the supply lines 26, 26 toward the center portion side in the width direction of the hearth 30.

In the present embodiment, the irradiation beam 25 on the surface of the melt 5c is intensively irradiated with an electron beam, so that a special temperature gradient is formed on the surface of the melt 5c in the hearth 30, and the flow of the melt 5c is controlled. Here, the temperature distribution of the surface of the melt 5c in the hearth 30 will be described.

In the electron beam melting method, in order to prevent solidification of the melt 5C in the hearth 30, for example, the electron gun 20C uniformly irradiates the heat-retaining irradiation region 23 occupying a wide range on the surface of the melt 5C with an electron beam, thereby retaining the melt 5C in the hearth 30. By irradiation of the electron beam for heat retention, the entire melt 5c stored in the hearth 30 is heated to maintain an average surface temperature T0 (hereinafter referred to as "melt surface temperature T0") of the entire surface of the melt 5c at a predetermined temperature. The melt surface temperature T0 is, for example, 1923K (melting point of titanium alloy) to 2323K, preferably 1973K to 2273K.

In the present embodiment, in the raw material supply unit 10, the electron guns 20A and 20B irradiate the solid raw material 5 with the electron beams to melt the raw material 5, and the molten metal having a high temperature thus melted is dropped to the position of the supply line 26 of the melt 5c in the hearth 30, thereby supplying the raw material 5 to the hearth 30. Therefore, impurities such as LDI contained in the raw material 5 are present in the vicinity of the supply line 26 in the melt 5c in the hearth 30 in a large amount. Since the high-temperature molten metal is continuously or discontinuously supplied to the supply line 26, a high-temperature region having a surface temperature T1 higher than the molten surface temperature T0 is formed in the vicinity of the supply line 26 (see the region S1 in fig. 6A and 7). The surface temperature T1 of the melt 5c at the supply line 26 (hereinafter referred to as "raw material supply temperature T1") is substantially the same as the temperature of the molten metal dropping from the raw material supply portion 10 to the hearth 30 and is higher than the melt surface temperature T0 (T1 > T0). The raw material supply temperature T1 is, for example, 1923K to 2423K, preferably 1973K to 2373K.

In the method for producing a metal ingot according to the present embodiment, in addition to the irradiation of the heat-retaining irradiation region 23 of the melt 5c with the electron beam for heat retaining, the irradiation beam 25 on the surface of the melt 5c is intensively irradiated with the electron beam by the electron gun 20E. Specifically, the position of irradiation with the electron beam of the electron gun 20E is moved on the irradiation line 25 on the surface of the melt 5 c. By the concentrated irradiation of the electron beam with the control beam 25, a high temperature region having a surface temperature T2 higher than the melt surface temperature T0 is formed in the vicinity of the irradiation beam 25 (see a region S2 in fig. 7). The surface temperature T2 of the melt 5c at the irradiation line 25 (hereinafter referred to as "line irradiation temperature T2") is higher than the melt surface temperature T0 (T2 > T0). In order to more reliably suppress the outflow of impurities, the radiation temperature T2 is preferably higher than the raw material supply temperature T1 (T2 > T1 > T0). The radiation temperature T2 is, for example, 1923K to 2473K, preferably 1973K to 2423K.

As described above, in the method for producing a metal ingot according to the present embodiment, the irradiation line 25 on the surface of the melt 5c is intensively irradiated with the electron beam, so that not only the high-temperature region of the melt 5c is formed in the vicinity of the supply line 26 but also the high-temperature region of the melt 5c is formed in the vicinity of the irradiation line 25. As a result, as shown in fig. 5, a melt flow 61 (corresponding to the "1 st melt flow" in the present invention) from the irradiation line 25 toward the supply line 26 can be forcibly formed in the surface layer of the melt 5 c. In particular, the temperature of the melt 5c can be maintained higher than T0 at any position of the irradiation line 25, and the formed melt flow 61 can be stably maintained.

The melt flow 61 can control the flow of impurities such as LDI, which are present in the vicinity of the supply line 26 in a large amount, and prevent the impurities from flowing toward the lip 36. Specifically, by the melt flow 61, impurities such as LDI suspended on the surface of the melt 5c in the region near the supply line 26 can be moved toward the side walls 37A and 37B of the hearth 30 and captured by the skull 7 formed on the inner side surfaces of the side walls 37A and 37B. Further, the irradiation of the electron beam with the reference beam 25 to increase the beam irradiation temperature T2 can promote the melting of titanium nitride or the like, which is a main component of LDI, of the melt 5c suspended near the irradiation beam 25.

As described above, in the method for producing a metal ingot according to the present embodiment, the irradiation lines 25, 25 positioned closer to the center portion side (inner side) of the hearth 30 than the supply lines 26, 26 are irradiated with electron beams. Thereby, a high temperature region of the melt 5c is formed in the vicinity of the irradiation line 25, and the melt flow 61 from the high temperature region is shielded so that impurities such as LDI present in the vicinity of the supply line 26 flow toward the side walls 37A, 37B and do not flow toward the lip 36. Therefore, the outflow of the impurities from the hearth 30 to the mold 40 can be suppressed.

[1.3. flow of melt by irradiation with light ]

Next, the flow of the melt 5c in the hearth 30 by the irradiation of the electron beam is described in more detail with reference to fig. 5 to 7. Fig. 6A and 6B are a vertical sectional view and a plan view of a hearth showing a flow state of the melt 5c when the electron beam 25 is not irradiated as a comparative example of the present embodiment. FIG. 7 is a vertical cross-sectional view of a hearth showing a flow state of a melt 5c when an electron beam 25 is irradiated with a reference beam in the method for producing a metal ingot according to the present embodiment.

As described above, in the present embodiment, the raw material supply portions 10A and 10B are disposed above the long side walls 37A and 37B of the hearth 30, respectively, and the electron guns 20A and 20B irradiate the solid raw material 5 on the raw material supply portions 10A and 10B with the electron beams to melt the raw material 5. The molten raw material 5 is dropped from the raw material supply portions 10A and 10B to the supply lines 26 and 26 of the melt 5c in the hearth 30. In this way, in the present embodiment, the molten metal of the raw material 5 is dropped to supply the raw material 5 to the hearth 30. In this regard, the supply line 26 of the present embodiment corresponds to a virtual line (drop line) indicating a position on the surface of the melt 5c where the molten metal of the raw material 5 is dropped.

The melt 5c stored in the hearth 30 is refined while staying in the hearth 30, and then flows out from the lip 36 and is discharged to the die 40. As shown in fig. 5, a melt flow 60 flowing in the longitudinal direction (Y direction) of the hearth 30 is formed from the vicinity of one side wall 37C toward the lip 36 at the center in the width direction (X direction) in the hearth 30. The melt flow 60 causes the melt 5c stored in the hearth 30 to flow out from the lip 36 toward the die 40.

As shown in fig. 5 to 7, a solidified layer (referred to as "skull 7") in which the melt 5c is solidified is formed on the inner surface and the bottom surface of the side wall 37 of the hearth 30. By storing the melt 5c in the hearth 30, impurities contained in the melt 5c can be removed by the skull 7 and the like. The impurities are classified into HDI (not shown) having a higher specific gravity than the melt 5c and LDI8 having a lower specific gravity. Since HDI having a high specific gravity is settled in the melt 5c and fixed to the skull 7 formed on the bottom surface of the hearth 30, the HDI is less likely to flow out from the lip 36 to the mold 40. On the other hand, most of LDI8 having a low specific gravity floats on the surface of the melt 5c and flows along the surface layer of the melt 5 c. Therefore, it is preferable to control the surface flow of the melt 5c so as to avoid the LDI8 suspended in the melt 5c of the hearth 30 from flowing out from the lip 36 toward the mold 40.

Here, in the method of manufacturing a metal ingot according to the present embodiment, the irradiation lines 25, 25 located inside the supply lines 26, 26 are intensively irradiated with electron beams on the surface of the melt 5c in the hearth 30. As a result, marangoni convection occurs due to the temperature gradient of the surface of the melt 5c, and as shown in fig. 5 and 7, a surface layer flow (1 st melt flow 61) of the melt 5c from the irradiation line 25 toward the supply line 26 is formed in the surface layer of the melt 5 c. As a result, LDI8 present in the vicinity of supply line 26 in a large amount flows toward side walls 37A and 37B of hearth 30 adjacent to supply line 26 and is captured by skull 7 formed on the inner side surfaces of side walls 37A and 37B. The principle is explained in detail below.

When a temperature gradient is created at the surface of a fluid, the surface tension of the fluid also creates a gradient, thus creating convection of the fluid. This convection of fluid is referred to as marangoni convection. When the fluid is molten titanium or a molten titanium alloy, marangoni convection flows from a high-temperature region to a low-temperature region of the fluid. This is because molten titanium and molten titanium alloys have a property of reducing the surface tension at a high temperature.

Here, as a comparative example of the present embodiment, as shown in fig. 6A, a case is considered in which the temperature of the molten metal dropped onto the supply line 26 (raw material supply temperature T1) is higher than the molten metal surface temperature T0 already stored in the hearth 30 without irradiating the irradiation with the electron beam with the irradiation beam 25. In this case, a region S1 near the supply line 26 where the molten raw material 5 (molten metal) is dropped is a high temperature region having a higher temperature than the molten metal 5c in the other regions. Therefore, as shown in fig. 6A, the melt 5c in the region S1 flows from the supply line 26 in both directions of the central portion and the side wall 37B in the width direction (X direction) of the hearth 30, and therefore melt flows 62 and 63 are formed on the surface layer of the melt 5 c.

Then, as shown in fig. 6A and 6B, LDI8 contained in the molten metal dropped onto supply line 26 flows toward the center in the width direction (X direction) of hearth 30 with melt flow 62, and flows toward side wall 37B of hearth 30 with melt flow 63. As shown in fig. 6B, the melt flows 62 and 62 from the pair of left and right supply lines 26 and 26 toward the center of the hearth 30 collide with the center of the hearth 30 in the width direction, and a melt flow 60 is formed toward the lip 36 along the longitudinal direction (Y direction) of the hearth 30. As a result, the LDI8 suspended in the melt 5c also flows toward the lip 36 along with the melt flow 60, and flows out from the lip 36 toward the die 40. Therefore, in order to avoid the outflow of impurities such as LDI8 from the lip 36 to the die 40, it is preferable to control the surface flow of the melt 5c so that the LDI8 present near the supply line 26 flows toward the center in the width direction of the hearth 30 along with the melt flow 62 shown in fig. 6A and 6B.

In the present embodiment, as shown in fig. 5 and 7, the irradiation line 25 positioned closer to the center of the hearth 30 than the supply line 26 is intensively irradiated with the electron beam. Thereby, the surface temperature T2 of the melt 5c in the region S2 near the irradiation line 25 is increased, and a temperature gradient is generated in the surface temperature of the melt 5c in the strip-shaped region S3 between the irradiation line 25 and the supply line 26. As a result, marangoni convection (the 1 st molten metal flow 61) of the molten metal 5c from the irradiation line 25 toward the inner surfaces of the side walls 37A and 37B is generated in the surface layer of the molten metal 5 c. With this melt flow 61, it is possible to perform shielding so as to forcibly flow the LDI8 present in suspension on the surface of the melt 5c near the supply line 26 toward the side walls 37A, 37B without flowing toward the lip 36. Therefore, LDI8 contained in the molten metal dropped to the supply line 26 in the region between the irradiation line 25 and the side walls 37A, 37B flows toward the side walls 37A, 37B in accordance with the molten metal flow 61, and adheres to and is captured by the skull 7 formed on the inner side surfaces of the side walls 37A, 37B.

The flow of the melt 5c caused by the above-described line irradiation will be described in more detail. Fig. 5 and 7 show the flow of the melt 5c when the surface temperature T2 (line irradiation temperature T2) of the melt 5c at the irradiation line 25 is higher than the surface temperature T1 (raw material supply temperature T1) of the melt 5c at the supply line 26.

As described above, when the molten metal 5c is molten titanium, marangoni convection flows from the high-temperature region to the low-temperature region of the molten metal 5 c. When the electron beam is intensively irradiated with the reference beam 25, the region S2 near the irradiation beam 25 irradiated with the electron beam is heated to become a high temperature region. Thus, marangoni convection occurs from this region S2 toward the low-temperature region of its periphery. As a result, as shown in fig. 7, a melt flow 64 heading from the irradiation line 25 toward the widthwise central portion of the hearth 30 and a melt flow 61 heading from the irradiation line 25 across the supply line 26 toward the side wall 37B are formed in the surface layer of the melt 5 c. On the other hand, in the deep layer of the melt 5c, a melt flow 65 is formed from the side wall 37B at the end in the width direction (X direction) of the hearth 30 toward the central portion of the hearth 30.

Here, it is preferable that a temperature distribution in which the line irradiation temperature T2 is higher than the raw material supply temperature T1 and the surface temperature of the melt 5c continuously decreases from the irradiation line 25 to the supply line 26 is formed in the surface layer of the melt 5 c. By realizing this temperature distribution, as shown in fig. 7, a melt flow (corresponding to the melt flow 62 in fig. 6A and 6B) from the supply line 26 toward the central portion of the hearth 30 is not formed in the surface layer of the melt 5c, and the melt flow 61 from the irradiation line 25 toward the supply line 26 can cross the supply line 26 and reach the inner surface of the side wall 37B.

As a result, as shown in fig. 7, the LDI8 staying near the supply line 26 does not flow toward the center of the hearth 30 because the molten metal flow 61 flows from the region S1 near the supply line 26 toward the side wall 37B. Furthermore, LDI8 contained in the molten metal dropped onto supply line 26 temporarily diffuses from supply line 26 to both sides in the width direction (X direction) due to the influence of collision with the surface of molten metal 5c during dropping. However, thereafter, the melt flow 61 is forced to flow from the region S1 near the supply line 26 toward the side wall 37B.

Normally, the distance L1 between the supply line 26 from which the raw material 5 is dropped and the side wall 37B is small. Therefore, when the LDI8 suspended near the supply line 26 is moved toward the side wall 37B of the hearth 30 by the melt flow 61, the LDI8 easily adheres to the skull 7 formed on the inner surface of the side wall 37B. Therefore, by forming the molten metal flow 61 on the surface layer of the molten metal 5c by the irradiation of the electron beam, the LDI8 suspended in the region S1 near the supply line 26 can be efficiently captured and removed by the skull 7 on the inner surface of the side wall 37B.

The mixing source of LDI8 suspended in the melt 5c in the hearth 30 is molten metal dropped from the outside into the hearth 30, and at least a part of LDI8 contained in the molten metal dropped into the supply line 26 is melted in the melt 5c or attached to the skull 7 while staying in the hearth 30. Therefore, it is considered that LDI8 suspended in the melt 5c is substantially absent in the region other than the vicinity of the supply line 26. Therefore, as shown in fig. 7, there is substantially no LDI8 suspended in the region S2 near the irradiation line 25 irradiated with the electron beam in a concentrated manner, and the molten metal flow 64 from the region S2 toward the central portion in the width direction of the hearth 30 does not include the LDI 8. As shown in fig. 5, the X-direction melt flow 64 changes its direction at the center of the hearth 30 in the width direction to the Y-direction melt flow 60 toward the lip 36, and LDI8 is not included in the melt flow 60. Therefore, there is no problem even if the melt flow 60 is caused to flow directly from the lip 36 toward the die 40.

[1.4. arrangement of irradiation lines ]

Next, the arrangement of the irradiation lines 25 irradiated with the electron beams intensively will be described in more detail.

In the method of manufacturing a metal ingot according to the present embodiment, as shown in fig. 4, the irradiation lines 25, 25 arranged on the central portion side in the width direction (X direction) of the hearth 30 with respect to the supply lines 26, 26 are intensively irradiated with electron beams. Here, the supply line 26 is a virtual line showing a position where the molten metal of the raw material 5 is dropped onto the melt 5c of the hearth 30, and the irradiation line 25 is a virtual line corresponding to an irradiation locus of the electron beam of the electron gun 20E for line irradiation.

From the viewpoint of reliably preventing the outflow of impurities by the line irradiation, it is preferable that the supply lines 26 and 26 have a straight shape substantially parallel to the inner side surfaces of the pair of long side walls 37A and 37B of the hearth 30. Preferably, the irradiation line 25 has a straight line shape substantially parallel to the supply line 26.

Here, "substantially parallel" includes not only a case where both are strictly parallel (the angle difference is 0 °), but also a case where the angle difference is equal to or smaller than a predetermined angle. As a specific example, the effect of the present invention can be obtained if the difference in angle between the supply line 26 and the inner surfaces of the side walls 37A and 37B of the hearth 30 is 6 ° or less. However, the supply line 26 is not limited to this, if it is too close to the side walls 37A and 37B, specifically, to about 5mm, and the supply of the molten metal is obstructed. Further, if the angle difference between the irradiation line 25 and the supply line 26 is 4 ° or less, the effect of the present invention can be expected. However, the irradiation line 25 is not limited to this, if it is too close to the supply line 26, specifically, to about 5mm, and the formation of the melt flow 61 described later is hindered.

In the method of manufacturing a metal ingot of the present embodiment, as shown in fig. 5, the irradiation beam 25 is intensively irradiated with an electron beam, thereby generating a marangoni convection (molten metal flow 61) from the irradiation beam 25 toward the supply line 26. Then, the melt flow 61 pushes back the melt flow 62 from the supply line 26 toward the center of the hearth 30 toward the side walls 37A and 37B of the hearth 30. At this time, it is preferable to appropriately set the arrangement of the supply line 26 and the irradiation line 25 so as to avoid the melt flow 62 from the supply line 26 toward the central portion of the hearth 30 from flowing toward the central portion of the hearth 30 through the irradiation line 25.

In the present embodiment, as shown in fig. 4, the supply line 26 is set to be linear and substantially parallel to the inner surfaces of the long side walls 37A and 37B of the hearth 30, and the irradiation line 25 is set to be linear and substantially parallel to the supply line 26. Thus, regardless of the position of the hearth 30 in the longitudinal direction (Y direction), the distance L1 between the inner surface of the side wall 37A or 37B and the supply line 26 is substantially constant, and the distance L between the irradiation line 25 and the supply line 26 is substantially constant. Therefore, the melt flow 61 in the X direction from the irradiation line 25 toward the supply line 26 is formed substantially uniformly in the longitudinal direction (Y direction) of the hearth 30. This makes it possible to uniformly suppress the melt flow 62 from the supply line 26 toward the center of the hearth 30 by the melt flow 61 over the entire range of the supply line 26 in the Y direction. Therefore, the melt flow 62 can be more reliably prevented from flowing toward the center in the width direction (X direction) of the hearth 30 beyond the irradiation line 25.

Next, the distance L between the irradiation line 25 and the supply line 26 will be described. As shown in fig. 5, the irradiation line 25 is disposed at a position separated by a predetermined distance L from the supply line 26 between the supply line 26 and the widthwise central portion of the hearth 30. The distance L is generally determined by the raw material supply temperature T1, the irradiation conditions of the electron beam to be irradiated to the irradiation line 25, and the like, and is preferably 5mm to 35mm, for example. Accordingly, the LDI8 staying near the supply line 26 can be appropriately flowed to the side walls 37A and 37B by the melt flow 61 from the irradiation line 25 and captured by the skull 7.

When the distance L is less than 5mm, the irradiation line 25 is too close to the feeding line 26, and the high temperature region S2 shown in fig. 7 overlaps with the high temperature region S1. Therefore, it is difficult to form the melt flow 61 from the irradiation line 25 toward the supply line 26, and the LDI8 near the supply line 26 may flow toward the lip 36. On the other hand, when the distance L is more than 35mm, the melt flow 61 from the irradiation line 25 toward the supply line 26 is weakened before reaching the supply line 26. Therefore, it is difficult to cause the LDI8 near the supply line 26 to flow to the side walls 37A, 37B, and there is a possibility that the LDI8 flows toward the lip 36 in the band-shaped area S3 between the irradiation line 25 and the supply line 26. Therefore, in order to appropriately push back the melt flow 62 by the melt flow 61, the distance L is preferably 5mm or more and 35mm or less.

As shown in fig. 4 and 5, the irradiation line 25 is preferably longer than the supply line 26, and both ends of the irradiation line 25 are preferably disposed at positions outside the supply line 26 in the extending direction (outside the hearth 30 in the longitudinal direction (Y direction) in the illustrated example) from both ends of the supply line 26. Thus, the irradiation line 25 widely covers the supply line 26 in the Y direction, and therefore the melt flow 62 directed from the supply line 26 in the X direction can be suppressed from bypassing both ends of the irradiation line 25 in the Y direction and flowing toward the center of the hearth 30.

[1.5 setting of Electron Beam for radiation ]

Next, setting of an electron beam for irradiation of a ray (1 st electron beam) which is irradiated with the irradiation ray 25 in a concentrated manner will be described.

As described above, in order to push back the melt flow 62 (see fig. 6A and 6B) from the supply line 26 toward the side wall 37B of the hearth 30 by the melt flow 61 (see fig. 7) from the irradiation line 25, it is preferable to appropriately set irradiation conditions such as the heat transfer amount, the scanning speed, and the heat flux distribution of the electron beam for line irradiation.

The heat transfer amount [ W ] of the electron beam is a parameter that affects the temperature rise of the melt 5c at the irradiation line 25 and the flow rate of the marangoni convection (melt flow 61) generated by the temperature rise. When the heat transfer amount of the electron beam is small, the melt flow 61 stronger than the melt flow 62 from the supply line 26 cannot be formed. Therefore, the larger the heat transfer amount of the electron beam, the more ideal it is, for example, 0.15 to 0.60[ MW ].

The scanning speed [ m/s ] of the electron beam is a parameter that affects the flow velocity of the melt stream 61. When the irradiation beam 25 irradiates the electron beam, the irradiation beam 25 on the surface of the melt 5c is repeatedly scanned by the electron beam emitted from the electron gun 20E. If the scanning speed of the electron beam is slow, a position where the electron beam is not irradiated for a long time is generated on the irradiation line 25. The surface temperature of the melt 5c at the position where the electron beam is not irradiated decreases rapidly, and the flow velocity of the melt flow 61 generated from the position decreases. Thus, it is difficult to suppress the melt flow 62 from the supply line 26 by the melt flow 61, and the possibility that the melt flow 62 passes through the irradiation line 25 becomes high. Therefore, it is preferable that the scanning speed of the electron beam is as high as possible, for example, 1.0 to 20.0[ m/s ].

The heat flux distribution of the surface of the melt 5c caused by the electron beam is a parameter that affects the amount of heat transfer applied from the electron beam to the melt 5 c. The heat flux distribution corresponds to the size of the pinch of the electron beam. As the electron beam is narrowed, a sharp heat flux distribution can be given to the melt 5 c. The heat flux distribution on the surface of the melt 5c is represented by, for example, the following formula (1) (see, for example, non-patent document 1). The following formula (1) represents that the heat flux exponentially decays according to the distance from the center of the electron beam.

[ number 1]

∫∫_{all surface}q dxdy＝Q...(2)

Here, (x, y) represents the position on the surface of the melt, (x)₀，y₀) Represents the electron beam center position, and σ represents the standard deviation of the heat flux distribution. As shown in the above equation (2), the heat transfer amount Q of the electron gun is set to the sum of the heat fluxes Q on the surfaces of all the melts 5c in the hearth 30. The above-described parameters may be set by, for example, obtaining a value at which the melt flow 62 from the supply line 26 toward the central portion of the hearth 30 can flow toward the side walls 37A, 37B of the hearth 30 by the marangoni convection generated by the irradiation of the electron beam with the reference beam 25 by a thermal flow simulation or the like.

At this time, if the flow velocity of the melt flow 61 from the irradiation line 25 toward the supply line 26 is larger than the flow velocity of the melt flow 62 from the supply line 26 toward the center portion of the hearth 30, the melt flow 62 can be more reliably blocked by the melt flow 61, and the melt flow 62 can be pushed back toward the inner side surfaces of the side walls 37A, 37B of the hearth 30.

Here, as shown in fig. 7, the irradiation conditions of the electron beam for the line irradiation may be set so that the temperature of the high temperature region S2 in the vicinity of the irradiation line 25 (the line irradiation temperature T2) is higher than the temperature of the high temperature region S1 in the vicinity of the supply line 26 (the raw material supply temperature T1). Thus, the temperature difference between the line irradiation temperature T2 and the melt surface temperature T0 can be made larger than the temperature difference between the raw material supply temperature T1 and the melt surface temperature T0, and therefore the melt flow 61 from the irradiation line 25 toward the supply line 26 can be strengthened.

Further, irradiation conditions such as the heat transfer amount, the scanning speed, and the heat flux distribution of the electron beam for the line irradiation are restricted by the specifications of the apparatus for irradiating the electron beam. Therefore, when the irradiation conditions of the electron beam are set, it is preferable to increase the heat transfer amount as much as possible, increase the scanning speed as much as possible, and narrow the heat flux distribution (reduce the beam convergence of the electron beam) as much as possible within the range of the equipment specifications. The irradiation of the electron beam with the irradiation beam 25 may be performed by 1 electron gun, or may be performed by a plurality of electron guns. The electron gun for the line irradiation described here may be the electron gun 20E (see fig. 3) dedicated to the line irradiation, or may be used in combination with other applications such as the electron guns 20A and 20B for melting raw materials and the electron guns 20C and 20D for keeping the melt warm (see fig. 3).

[1.6. temperature gradient. DELTA.T/L ]

Next, referring to fig. 5, 8, and 9, the influence of the temperature gradient Δ T/L between the irradiation line 25 and the supply line 26 on the flow of the melt 5c in the hearth 30 will be described.

The intensity of the molten metal flow 61 from the irradiation line 25 toward the supply line 26 changes according to the temperature gradient Δ T/L between the irradiation line 25 and the supply line 26. Here, the temperature gradient DeltaT/L [ K/mm ] is represented by the following formula (A).

ΔT/L＝(T2-T1)/L…(A)

T1: the surface temperature (raw material supply temperature) [ K ] of the melt 5c at the supply line 26

T2: the surface temperature (line irradiation temperature) [ K ] of the melt 5c at the irradiation line 25

L: distance [ mm ] between irradiation line 25 and supply line 26 on the surface of melt 5c

The temperature gradient DeltaT/L is preferably at least-2.70 [ K/mm ] (DeltaT/L. gtoreq. -2.70K/mm), more preferably at least 0.00[ K/mm ] (DeltaT/L. gtoreq.0.00K/mm). This enables the melt flow 61 to be appropriately formed from the irradiation line 25 toward the supply line 26. Therefore, in the band-shaped region S3 between the irradiation line 25 and the supply line 26, the flow of the foreign matter such as LDI8 suspended near the supply line 26 toward the lip 36 can be suppressed, and the amount of the foreign matter flowing out from the lip 36 can be appropriately suppressed. The reason for this will be described in detail below.

(1) Case where "Δ T/L.gtoreq.0.00

First, referring to FIG. 5, a case where the temperature gradient Δ T/L is 0.00[ K/mm ] or more will be described. In this case, the irradiation temperature T2 is sufficiently high to be not lower than the raw material supply temperature T1 (T2. gtoreq.T 1 > T0), and Δ T/L is also sufficiently high.

Therefore, as shown in fig. 5, in the belt-shaped area S3 between the irradiation line 25 and the supply line 26, the melt flow 61 from the irradiation line 25 toward the supply line 26 is more advantageous than the melt flow 62 from the supply line 26 toward the irradiation line 25 (see fig. 6A and 6B). Therefore, the melt flow 61 can be appropriately formed from the irradiation line 25 across the supply line 26 toward the inner side surfaces of the side walls 37A, 37B. Therefore, the molten metal flow 61 allows the LDI8 near the supply line 26 to flow appropriately toward the side walls 37A and 37B, and is reliably captured and removed by the skull 7 on the inner side surfaces of the side walls 37A and 37B (see fig. 7). Accordingly, when Δ T/L is not less than 0.00K/mm, the outflow of impurities such as LDI8 from the lip 36 can be appropriately suppressed, and therefore, the outflow of impurities from the lip 36 can be greatly reduced to, for example, 0.1% or less, as compared with the case where the electron beam is not irradiated with the irradiation beam 25. Here, the amount of impurities (mass) contained in the melt 5c flowing out from the lip 36 per unit time is counted and compared with the amount of impurities flowing out.

(2) "-2.70. ltoreq. DELTA.T/L < 0.00

Next, with reference to FIG. 8, a case where the temperature gradient DeltaT/L is-2.70 [ K/mm ] or more and less than 0.00[ K/mm ] will be described. In this case, the irradiation temperature T2 is higher than the melt surface temperature T0 (T2 > T0), but is lower than the raw material supply temperature T1, and Δ T/L is also less than zero.

Therefore, as shown in fig. 8, in a band-shaped area S3 between the irradiation line 25 and the supply line 26, the melt flow 62 from the supply line 26 toward the irradiation line 25 is equal to the melt flow 61 from the irradiation line 25 toward the supply line 26. Therefore, the melt flow 66 may be formed in the Y direction toward the lip 36 in the strip-shaped region S3. However, since the melt flow 62 from the supply line 26 can be suppressed by the melt flow 61 from the irradiation line 25, the melt flow 62 can be prevented from flowing toward the center in the width direction of the hearth 30 beyond the irradiation line 25. The LDI8, the entry of which into the center portion is stopped, moves in the belt-like region S3 with the melt flow 66 and gradually advances toward the lip 36. The strip-shaped region S3 is interposed between the supply line 26 having a temperature T1 and the irradiation line 25 having a temperature T2, and therefore the temperature of the strip-shaped region S3 is higher than that of T0. Thus, a portion of LDI8 melts during being located within banded region S3. Accordingly, since the flow-out of the impurities such as LDI8 from the lip 36 can be suppressed when Δ T/L is ≧ 2.70, the flow-out amount of the impurities from the lip 36 can be reduced to, for example, 1% or less, as compared with the case where the electron beam is not irradiated with the irradiation beam 25.

(3) Case of "DeltaT/L < -2.70

Next, with reference to FIG. 9, a case where the temperature gradient Δ T/L is less than-2.70 [ K/mm ] will be described. In this case, the irradiation temperature T2 is significantly lower than the raw material supply temperature T1 (T1 > T2 > T0), and Δ T/L is also a negative value that is significantly reduced. Therefore, depending on the irradiation position (position in the Y direction) of the electron beam irradiated with the reference beam 25, there is a possibility that a position where the melt flow 61 directed from the irradiation line 25 toward the supply line 26 is formed and a position where the melt flow 61 directed from the irradiation line 25 toward the supply line 26 is not formed are generated.

Specifically, as shown in fig. 9, both the melt flow 61 heading from the irradiation line 25 toward the supply line 26 and the melt flow 62 heading from the supply line 26 toward the irradiation line 25 are formed in the belt-shaped region S3 between the irradiation line 25 and the supply line 26. In addition, a region S31 where the molten metal flow 61 is equal to the molten metal flow 62 and a region S32 where the molten metal flow 62 is more dominant than the molten metal flow 61 are mixed according to the irradiation position of the electron beam irradiated with the reference beam 25. That is, there are also cases where: in a region S31 where the line irradiation temperature T2 is high due to being close to the irradiation position of the electron beam moving on the irradiation line 25, the molten metal flow 61 is equal to the molten metal flow 62, but in a region S32 where the line irradiation temperature T2 is relatively low due to being far from the irradiation position of the electron beam, the molten metal flow 61 of sufficient intensity is not formed.

Therefore, in the band-shaped region S3 between the irradiation line 25 and the supply line 26, there is a possibility that the melt flow 66 toward the lip 36 or the melt flow 67 flowing from the supply line 26 across the irradiation line 25 toward the center portion side in the width direction of the hearth 30 is formed. Thus, there is a risk that: LDI8 residing near supply line 26 flows out of lip 36 with melt stream 66 or melt stream 67.

However, even in the case of Δ T/L < -2.70, the melt flow 62 from the supply line 26 can be suppressed to some extent by the melt flow 61 from the irradiation line 25. Therefore, the LDI8 entering the central portion of the hearth 30 in the width direction and stopped by the melt flow 61 is gradually melted while staying in the belt-shaped region S3. Accordingly, since the flow of the impurities such as LDI8 near the supply line 26 toward the lip 36 can be suppressed to some extent, the amount of the impurities flowing out of the lip 36 can be reduced to, for example, 5% or less, compared to the case where the electron beam 25 is not irradiated.

From the above, in order to form an appropriate melt flow 61 by the irradiation with a ray and reduce the amount of impurities flowing out, the temperature gradient Δ T/L is preferably-2.70 [ K/mm ] or more, and more preferably 0.00[ K/mm ] or more. In order to obtain the temperature gradient Δ T/L in the appropriate numerical range, irradiation conditions of the electron beam for line irradiation (for example, a heat transfer amount, a scanning speed, a heat flux distribution, and the like of the electron beam), temperatures T0, T1, and T2 of the melt 5c, arrangement of the irradiation line 25 and the supply line 26, a distance L, L1, and the like may be appropriately set.

From the viewpoint of suppressing the amount of impurities flowing out, the larger the temperature gradient Δ T/L, the better. However, the upper limit value of the temperature gradient Δ T/L is restricted by the specifications of the apparatus to which the electron beam is irradiated. Due to the restrictions of the equipment specifications, the upper limit value of the temperature gradient Δ T/L is, for example, preferably 64.0[ K/mm ] or less, and more preferably 10.0[ K/mm ] or less.

[1.7. modified example ]

Next, a modification of embodiment 1 will be described. In the above embodiment, an example in which the pair of irradiation lines 25 and 25 parallel to the side walls 37A and 37B and the supply lines 26 and 26 in the longitudinal direction (Y direction) of the hearth 30 are arranged as shown in fig. 4 is described. However, the present invention is not limited to this example. The irradiation lines 25 and the supply lines 26 may be arranged along any 1 or more than two side walls 37A, 37B, and 37C (2 nd side wall) other than the side wall 37D (1 st side wall) provided with the lip 36, and the number, direction, and the like of the irradiation lines 25 and the irradiation lines 25 are not limited to the example of fig. 4.

For example, there are also cases where: as shown in fig. 10, the raw material 5 is supplied to the hearth 30 along 1 linear supply line 26 substantially parallel to the side wall 37C on one short side of the hearth 30. In this case, the irradiation line 25 may be arranged along the supply line 26 at a position closer to the center portion side in the longitudinal direction (Y direction) of the hearth 30 than the supply line 26. When the melt flow 61 is formed from the irradiation line 25 toward the short side wall 37C, impurities near the supply line 26 can be captured and removed by the skull 7 on the inner surface of the side wall 37C.

In addition, there are also cases where: as shown in fig. 11, 1 supply line 26 in japanese コ shape is arranged along a pair of long side walls 37A and 37B and 1 short side wall 37C, and the raw material 5 is supplied to the hearth 30 along the supply line 26. In this case, 1 irradiation line 25 shaped like japanese コ may be arranged along the supply line 26 at a position closer to the center portion side in the longitudinal direction (Y direction) and the width direction (X direction) of the hearth 30 than the supply line 26. When the melt flow 61 is formed from the irradiation line 25 toward the long side walls 37A and 37B and the short side wall 37C, impurities near the supply line 26 can be captured and removed by the skull 7 on the inner side surfaces of the side walls 37A, 37B, and 37C.

Further, although not shown, the side wall of the hearth may have a curved shape such as an elliptical shape or a prolate circular shape. In this case, the curved supply line 26 and the irradiation line 25 may be arranged along the side wall of the curved hearth.

[1.8. summary ]

The method for producing a metal ingot according to embodiment 1 of the present invention is described above. In the present embodiment, the irradiation line 25 is arranged along the supply line 26 at a position closer to the center portion side in the width direction of the hearth 30 than the supply line 26, and the electron beam is irradiated intensively to the irradiation line 25. As a result, as shown in fig. 5, 8, 9, and the like, a high-temperature region is formed near the irradiation line 25, and a melt flow 61 from the irradiation line 25 toward the supply line 26 can be formed. Therefore, the molten metal flow 61 can prevent diffusion of impurities such as LDI8 suspended on the surface of the molten metal 5c near the supply line 26. This can prevent impurities from flowing out of the lip 36 of the hearth 30 into the mold 40 and mixing into the ingot 50.

By setting Δ T/L to be equal to or greater than 0.00, as shown in fig. 5, when the melt flow 61 is formed to flow from the irradiation line 25 over the supply line 26 toward the side walls 37A, 37B of the hearth 30, the impurities can be made to flow toward the side walls 37A, 37B of the hearth 30 and fixed to the skull 7 on the inner side surface. This can more reliably prevent impurities from flowing out of the lip 36 of the hearth 30 into the mold 40 and mixing into the ingot 50.

Further, by setting Δ T/L to ≧ 2.70, as shown in FIG. 8, the melt flow 62 from the supply line 26 can be suppressed by the melt flow 61 from the irradiation line 25. Therefore, impurities such as LDI8 suspended on the surface of the melt 5c near the supply line 26 can be prevented from flowing toward the center in the width direction of the hearth 30 beyond the irradiation line 25 with the melt flow 62. This makes it possible to accumulate and melt impurities such as LDI8 in the high-temperature strip-shaped region S3, and therefore outflow of the impurities from the lip 36 can be appropriately suppressed.

In addition, according to the method for manufacturing a metal ingot of the present embodiment, it is not necessary to change the shape of the conventional hearth 30, and therefore, the method can be easily performed and requires no special maintenance.

In the conventional method for producing an ingot of titanium or a titanium alloy, usually, HDI is fixed to a skull formed on the bottom surface of a hearth by allowing a molten metal to stay on the hearth for a long time, LDI is melted in the molten metal, and impurities are removed. Therefore, conventionally, a long hearth has been generally used in order to secure the residence time of the melt in the hearth. However, according to the present embodiment, even when the residence time of the melt in the hearth is relatively short, impurities can be appropriately removed, so that a short hearth can be used. Therefore, the running cost of the EB furnace 1 can be reduced by using a short hearth in the EB furnace 1. Further, if a short hearth is used, the yield of the ingot 50 can be improved without recycling the skull 7 remaining on the hearth.

[ 2] embodiment 2]

Next, a method for producing a metal ingot according to embodiment 2 of the present invention will be described.

[2.1. outline of method for producing Metal ingot ]

First, an outline of a method for producing a metal ingot according to embodiment 2 will be described with reference to fig. 12. FIG. 12 is a plan view showing an example of a melt flow formed by the method for producing an ingot of metal according to embodiment 2.

As shown in fig. 12, the method for producing a metal ingot according to embodiment 2 is characterized in that, in order to further reduce the amount of impurities flowing out of the hearth 30, an electron beam for melting (corresponding to "2 nd electron beam" in the present invention) of impurities is spot-irradiated to a molten metal flow 66 (corresponding to "2 nd molten metal flow" in the present invention) flowing in a strip-shaped region S3 between the irradiation line 25 and the supply line 26 in addition to the irradiation (line irradiation) of the electron beam by the reference beam 25 in embodiment 1.

In embodiment 2, the irradiation line 25 is irradiated with an electron beam, so that a high temperature region S2 is formed near the irradiation line 25 to form a molten metal flow 61 from the irradiation line 25 toward the supply line 26. Thereby, the flow of the melt 5c is controlled between the irradiation line 25 and the side wall 37 of the hearth 30, and the flow of impurities such as LDI8 suspended near the supply line 26 toward the lip 36 is restricted. In embodiment 2 as well, when the molten metal flow 61 is formed from the irradiation line 25 toward the side walls 37A and 37B, the LDI8 staying near the supply line 26 can be captured and removed by the skull 7 formed on the inner side surfaces of the side walls 37 of the hearth 30.

In this regard, in embodiment 1, as described with reference to fig. 5, when the temperature gradient Δ T/L between the irradiation line 25 and the supply line 26 is sufficiently large (for example, when Δ T/L ≧ 0.00), the melt flow 61 heading from the irradiation line 25 toward the supply line 26 crosses the supply line 26 and reaches the side walls 37A and 37B. By the strong melt flow 61, the LDI8 suspended near the supply line 26 is caused to flow to the inner side surfaces of the side walls 37A and 37B and captured by the skull 7 formed on the inner side surfaces, and the outflow of impurities such as LDI8 from the lip 36 can be appropriately suppressed.

However, as described with reference to fig. 8 and 9, in the case where the temperature gradient Δ T/L is small (for example, in the case where Δ T/L < 0.00), the melt flow 61 from the irradiation line 25 toward the supply line 26 is relatively weak, and it is difficult to push back the melt flow 62 from the supply line 26 toward the irradiation line 25. Therefore, as shown in fig. 8, the melt flow 66 in the Y direction toward the lip 36 is formed in the band-shaped region S3 between the irradiation line 25 and the supply line 26. In this case, there is a risk that: the impurities such as LDI8 flow toward the lip 36 with the melt flow 66, and flow out from the lip 36 toward the die 40.

In embodiment 2, as shown in fig. 12, an electron beam is intensively irradiated (spot irradiation) to the irradiation spot 27 of the belt-like region S3 disposed between the irradiation line 25 and the supply line 26. Thereby, the electron beam is irradiated to the molten metal flow 66 point flowing toward the lip 36 in the band-shaped region S3. Therefore, the surface temperature of the melt 5c can be locally raised at the position of the irradiation point 27, and impurities such as LDI8 contained in the melt flow 66 can be melted and removed from the melt 5 c. This can more reliably prevent impurities such as LDI8 from flowing out of the lip 36 toward the die 40.

[2.2. Point irradiation temperature ]

LDI8 is formed of titanium nitride or the like, and the melting point of titanium nitride is higher than that of pure titanium. Therefore, when the melt surface temperature T0 is relatively low, even when titanium, which is the main component of the melt 5c, is melted, titanium nitride, which is the component of LDI8, does not melt and tends to remain as a granular solid. Here, the irradiation spot 27 is intensively irradiated with the electron beam, and the surface temperature T3 of the melt 5c (hereinafter referred to as "spot irradiation temperature T3") at the irradiation spot 27 is greatly increased as compared with the melt surface temperature T0. This makes it possible to melt titanium nitride into the melt 5c and diffuse nitrogen, thereby changing titanium nitride into titanium, while keeping the spot irradiation temperature T3 higher than the melting point of titanium nitride, for example. Therefore, the LDI8 contained in the melt flow 66 passing through the irradiation point 27 can be reliably melted and removed from the melt 5 c. The melting point of titanium nitride varies depending on the nitrogen concentration, and for example, when the nitrogen concentration is 1.23 to 4 mass%, the melting point of titanium nitride is 2300K.

The spot irradiation temperature T3 is, for example, 2300K to 3500K, preferably 2400K to 2700K. Preferably, the spot irradiation temperature T3 is higher than the raw material supply temperature T1 and the line irradiation temperature T2 (T3 > T1 and T3 > T2). Thus, even when the LDI8 is not melted and remains in a solid state when the raw material 5 is melted in the raw material supply portion 10 (raw material supply temperature T1) or irradiated with a ray (ray irradiation temperature T2), the LDI8 can be heated at the higher spot irradiation temperature T3, and thus the LDI8 can be more reliably melted.

[2.3. position of irradiation Point ]

First, the position of the irradiation point 27 in the Y direction is explained. Preferably, as shown in fig. 12, the irradiation spot 27 is disposed at or near the end portion on the lip 36 side in the belt-like region S3 between the irradiation line 25 and the supply line 26. The melt flow 66 flowing toward the lip 36 in the strip-shaped region S3 flows out of the strip-shaped region S3 from the end of the strip-shaped region S3 on the lip 36 side. Therefore, the LDI8 included in the melt flow 66 flowing in the strip-shaped region S3 passes through the end portion of the strip-shaped region S3 on the lip 36 side. Therefore, it is preferable that the irradiation spot 27 is disposed at the end portion of the band-shaped region S3 on the lip 36 side, and the electron beam is intensively irradiated to the irradiation spot 27. This can more reliably melt and remove most or all of the LDI8 flowing toward the lip 36 with the melt flow 66 flowing in the strip-shaped region S3 at the position of the irradiation spot 27.

Next, the position of the irradiation point 27 in the X direction will be described. The irradiation spot 27 is disposed between the irradiation line 25 and the supply line 26. The distance L2 between the irradiation point 27 and the supply line 26 is appropriately set in accordance with the raw material supply temperature T1, the line irradiation temperature T2, the irradiation conditions of the line irradiation and the point irradiation, and the like, but the distance L2 is preferably about half the distance L between the irradiation line 25 and the supply line 26. Accordingly, the irradiation spot 27 can be appropriately disposed at the position of the melt flow 66 flowing in the belt-shaped area S3 between the irradiation line 25 and the supply line 26, and thus the LDI8 included in the melt flow 66 can be efficiently melted and removed.

In the example of fig. 12, only 1 irradiation spot 27 is disposed at the end portion of each strip-shaped region S3 on the lip 36 side, and the electron beam is irradiated to the molten metal flow 66 at one point. However, the present invention is not limited to this example, and any position on the surface of the melt 5c through which impurities such as LDI8 pass may be spot-irradiated. For example, a plurality of irradiation points 27 may be separately arranged in the band-shaped region S3, and the molten metal flow 66 may be irradiated with electron beams at a plurality of positions. Further, as long as the molten metal flow 66 in the strip-shaped region S3 can be spot-irradiated, the electron beam may be spot-irradiated at an arbitrary position (for example, at the center portion in the Y direction, or at the upstream side or the downstream side in the Y direction of the center portion) in the strip-shaped region S3. Further, not only the inner point of the band-shaped region S3 but also the outer point of the band-shaped region S3 may be irradiated with an electron beam toward the molten metal stream point of the lip 36 or the peripheral point of the lip 36.

[2.4 setting of Electron Beam for Point irradiation ]

In embodiment 2, as described above, the flow path (molten metal flow 66) of the LDI8 is formed in the strip-shaped area S3 between the irradiation line 25 and the supply line 26, the irradiation spot 27 is disposed so as to block the flow path, and the electron beam is irradiated intensively to the irradiation spot 27. Thereby, the spot irradiation temperature T3 at the irradiation spot 27 is maintained at a high temperature, and the LDI8 in the melt flow 66 toward the lip 36 can be more reliably melted. When the molten metal 5c is molten titanium, the LDI8 contained in the molten titanium can be reliably melted by maintaining the spot irradiation temperature T3 measured by the radiation thermometer at 2400K or higher, for example.

In addition, if the spot irradiation temperature T3 can be maintained within the predetermined temperature range, the electron beam for spot irradiation that melts impurities such as LDI8 may be continuously irradiated to the irradiation spot 27 or may be intermittently irradiated. In addition, irradiation conditions such as the heat transfer amount, scanning speed, and heat flux distribution of the electron beam for spot irradiation are restricted by the specifications of the apparatus for irradiating the electron beam. Therefore, when the irradiation conditions of the electron beam are set, it is preferable to increase the heat transfer amount of the electron beam as much as possible, increase the scanning speed as much as possible, and narrow the heat flux distribution as much as possible (reduce the beam convergence of the electron beam) within the range of the equipment specifications.

The irradiation of the electron beam to the irradiation spot 27 may be performed by 1 electron gun, or may be performed by a plurality of electron guns. Further, it is preferable that the electron gun for spot irradiation is used in combination with the electron gun 20E for line irradiation (see fig. 3). This reduces the number of electron guns installed in the EB furnace 1, reduces the facility cost, and makes it possible to effectively use the existing electron guns. However, the present invention is not limited to this example, and an electron gun for spot irradiation may be used as a dedicated spot irradiation electron gun (not shown), or may be used as an electron gun for other purposes such as electron guns 20A and 20B for melting raw materials and electron guns 20C and 20D for keeping molten metal warm (see fig. 3).

[2.5. modified example ]

Next, a modification of embodiment 2 will be described. In the above embodiment, an example in which two strip-shaped regions S3, S3 substantially parallel to the side walls 37A, 37B in the longitudinal direction (Y direction) of the hearth 30 are arranged as shown in fig. 12 is described. However, the present invention is not limited to this example. The strip-shaped regions S3 may be disposed along any 1 or more than two side walls 37A, 37B, 37C (2 nd side wall) other than the side wall 37D (1 st side wall) provided with the lip 36, and the number, direction, shape, and the like of the strip-shaped regions S3 are not limited to the example of fig. 12.

For example, as shown in fig. 13, 1 linear supply line 26 and 1 irradiation line 25 may be arranged substantially parallel to the side wall 37C on one short side of the hearth 30, and a strip-shaped region S3 substantially parallel to the side wall 37C on the short side may be arranged between the supply line 26 and the irradiation line 25. In this case, two irradiation points 27, 27 may be disposed at both ends of the strip-shaped region S3 in the X direction, and the electron beams may be intensively irradiated to the melt flows 66, 66 flowing in the X direction in the strip-shaped region S3 at the two irradiation points 27, 27. This can melt LDI8 included in the melt flows 66, and therefore LDI8 can be prevented from bypassing both ends in the X direction of the irradiation line 25 and flowing toward the lip 36.

As shown in fig. 14, a supply line 26 and a radiation line 25 each having a shape of japanese コ may be arranged along the pair of long side walls 37A and 37B and the 1 short side wall 37C, and a band-shaped region S3 each having a shape of japanese コ may be arranged between the supply line 26 and the radiation line 25. In this case, two irradiation points 27, 27 may be disposed at both end portions of the strip-shaped region S3 shaped like japanese character コ on the lip 36 side, and the electron beams may be intensively irradiated to the melt flows 66, 66 flowing toward the lip 36 in the strip-shaped region S3 at the two irradiation points 27, 27. Accordingly, the LDI8 included in the molten metal flows 66, 66 can be melted, and therefore the LDI8 can be prevented from flowing toward the lip 36 through both ends of the japanese コ -shaped belt-shaped region S3.

[2.6. conclusion ]

The method for producing a metal ingot according to embodiment 2 of the present invention has been described above. In embodiment 2, the following effects are obtained in addition to the effects of embodiment 1 described above.

In embodiment 2, when the melt flow 66 is formed toward the lip 36 in the strip-shaped region S3 between the irradiation line 25 and the supply line 26, the melt flow 66 is intensively irradiated with the electron beam for melting of impurities at the irradiation point 27 disposed at one end or both ends of the strip-shaped region S3. Thus, before the impurities such as LDI8 contained in the melt flow 66 reach the lip 36 from the band-shaped region S3, the impurities can be melted and removed at the high-temperature irradiation point 27. This can more reliably prevent the impurities such as LDI8 from flowing out of the lip 36 toward the die 40.

In the above embodiment 1, depending on the apparatus specification and other constraints, when the line irradiation temperature T2 is lower than the raw material supply temperature T1, and when the temperature gradient Δ T/L between the supply line 26 and the irradiation line 25 is less than 0.00, the melt flow 66 directed toward the lip 36 may be formed in the band-shaped region S3, and the impurities may flow out toward the lip 36 along with the melt flow 66. Even in such a case, the method of manufacturing a metal ingot according to embodiment 2 is particularly useful because it can more reliably suppress the outflow of impurities to the lip portion 36.

[3 ] embodiment 3 ]

Next, a method for producing a metal ingot according to embodiment 3 of the present invention will be described.

[3.1. outline of method for producing Metal ingot ]

First, an outline of a method for producing a metal ingot according to embodiment 3 will be described with reference to fig. 15. FIG. 15 is a plan view showing an example of a melt flow formed by the method for producing an ingot of metal according to embodiment 3.

As shown in fig. 15, the method for producing a metal ingot according to embodiment 3 is characterized in that, in addition to the irradiation (line irradiation) of the electron beam along the irradiation line 25 (corresponding to the "1 st irradiation line" of the present invention) according to embodiment 1 described above, an electron beam (corresponding to the "3 rd electron beam" of the present invention) is irradiated to the irradiation line 28 (corresponding to the "2 nd irradiation line" of the present invention) disposed so as to block the lip 36, in order to further reduce the amount of impurities flowing out from the hearth 30.

In embodiment 3 as well, the irradiation line 25 is irradiated with an electron beam to form a high temperature region S2 near the irradiation line 25 and form a molten metal flow 61 from the irradiation line 25 toward the supply line 26. Thereby, the flow of the melt 5c is controlled between the irradiation line 25 and the side wall 37 of the hearth 30, and the flow of impurities such as LDI8 suspended near the supply line 26 toward the lip 36 is restricted. In embodiment 3 as well, if the melt flow 61 from the irradiation line 25 toward the side walls 37A and 37B can be formed, the LDI8 accumulated in the vicinity of the supply line 26 can be captured and removed by the skull 7 formed on the inner surface of the side wall 37 of the hearth 30.

However, as described with reference to fig. 8 and 9, in the case where the temperature gradient Δ T/L is small (for example, in the case where Δ T/L < 0.00, particularly Δ T/L < -2.70), the melt flow 61 from the irradiation line 25 toward the supply line 26 is relatively weak, and therefore the melt flow 62 from the supply line 26 toward the irradiation line 25 cannot be pushed back. Therefore, in the belt-shaped region S3 between the irradiation line 25 and the supply line 26, the melt flow 66 in the Y direction toward the lip 36 (see fig. 8) may be formed, or the melt flow 67 from the supply line 26 may flow toward the center of the hearth 30 beyond the irradiation line 25 (see fig. 9). In this case, there is a risk that: the LDI8 flows toward the lip 36 along with the melt flow 66 or the melt flow 67 and the melt flow 60, and flows out from the lip 36 toward the die 40.

In embodiment 3, as shown in fig. 15, the irradiation beam 28 is disposed on the surface of the melt 5c in the hearth 30 so as to block the lip 36, and the irradiation beam 28 is intensively irradiated with an electron beam (2 nd beam irradiation). Thereby, the surface temperature of the melt 5c is locally raised along the irradiation line 28, and a high temperature region is formed in the vicinity of the irradiation line 28. As a result, a melt flow 68 is formed from the vicinity of the irradiation line 28 in the direction opposite to the lip 36 on the surface layer of the melt 5c around the lip 36. The molten metal flow 68 can be prevented from flowing into the lip 36 by pushing back the molten metal flow 66 and the molten metal flow 60 containing impurities such as LDI 8. Since the pushed-back melt 5c remains in the hearth 30 for a long time, nitrogen is diffused and melted in the melt 5c over time and removed from impurities such as LDI8 contained in the melt 5 c.

Thus, in embodiment 3, as compared with embodiment 1, it is possible to more reliably prevent the impurities such as LDI8 from flowing out from the lip portion 36 to the die 40.

[3.2. position of irradiation line and irradiation temperature of irradiation line ]

The irradiation line 28 is a virtual line showing a locus of a position on the surface of the melt 5c in the hearth 30 where the electron beam is intensively irradiated. The irradiation line 28 is disposed on the surface of the melt 5c so as to surround the lip 36. Both ends of the irradiation line 28 are located in the vicinity of the inner side surfaces of the side walls 37D (1 st side wall) of the hearth 30. Here, "vicinity" means that the distance between both ends of the irradiation line 28 and the inner surface of the side wall 37 is in the range of 5mm or less. By disposing both ends of the irradiation line 28 in the vicinity of the side wall 37D, it is possible to appropriately suppress the impurities from flowing toward the lip 36 through the gap between both ends of the irradiation line 28 and the side wall 37D.

The irradiation line 28 in the example shown in fig. 15 is a V-shaped line, but may be, for example, an arc shape, an oval shape, another curved shape, japanese コ -shaped, U-shaped, wavy line, zigzag, double line, or band-shaped, as long as it is linear and arranged so as to surround the lip portion 36.

By irradiating the electron beam intensively along the irradiation line 28, a high temperature region having a surface temperature T4 higher than the melt surface temperature T0 is formed in the vicinity of the irradiation line 28 on the surface of the melt 5 c. Preferably, the surface temperature T4 of the melt 5c at the irradiation line 28 (hereinafter referred to as "2 nd irradiation temperature T4") is higher than the melt surface temperature T0 (T4 > T0) and higher than the raw material supply temperature T1 (T4 > T1 > T0). The 2 nd ray irradiation temperature T4 is, for example, 1923K to 2473K, preferably 1973K to 2423K.

[3.3 setting of Electron Beam for 2 nd ray irradiation ]

In embodiment 3, as shown in fig. 15, the irradiation line 28 surrounding the lip 36 is intensively irradiated with an electron beam, thereby forming a melt flow 68 directed from the irradiation line 28 to the side opposite to the lip 36. The periphery of the lip 36 is shielded by the melt flow 68 to prevent the melt flow containing impurities such as LDI8 from flowing into the lip 36. The electron beam for the 2 nd ray irradiation may be continuously irradiated with the irradiation ray 28 or intermittently irradiated, as long as the 2 nd ray irradiation temperature T4 can be maintained within a predetermined range. In addition, irradiation conditions such as the heat transfer amount, scanning speed, and heat flux distribution of the electron beam for the 2 nd ray irradiation are restricted by the specifications of the apparatus for irradiating the electron beam. Therefore, when the irradiation conditions of the electron beam are set, it is preferable to increase the heat transfer amount of the electron beam as much as possible, increase the scanning speed as much as possible, and narrow the heat flux distribution as much as possible (reduce the beam convergence of the electron beam) within the range of the equipment specifications.

The irradiation of the electron beam with the reference beam 28 (irradiation of the 2 nd beam) may be performed with 1 electron gun, or may be performed with a plurality of electron guns. Further, it is preferable that the 2 nd electron gun for the ray irradiation is used in combination with the above-described electron gun 20E for the ray irradiation (see fig. 3). This reduces the number of electron guns installed in the EB furnace 1, reduces the facility cost, and makes it possible to effectively use the existing electron guns. However, the present invention is not limited to this example, and the electron gun for the 2 nd ray irradiation may be the electron gun for the spot irradiation (not shown), or may be used in combination with other applications such as the electron guns 20A and 20B for melting the raw material and the electron guns 20C and 20D for keeping the melt warm (see fig. 3).

[3.4. modified example ]

Next, a modification of embodiment 3 will be described with reference to fig. 16. FIG. 16 is a plan view showing an example of a melt flow formed by the method for producing a metal ingot according to the modification of embodiment 3.

The method of manufacturing a metal ingot according to this modification is an example in which the spot irradiation according to embodiment 2 described above (see fig. 12 and the like) is further applied to the method of manufacturing a metal ingot according to embodiment 3 shown in fig. 15. As shown in fig. 16, in this modification, the line irradiation with the contrast ray 25 (embodiment 1), the spot irradiation with the contrast ray 27 (embodiment 2), and the 2 nd line irradiation with the contrast ray 28 (embodiment 3) are combined. Here, the arrangement of the irradiation line 25, the irradiation point 27, and the irradiation line 28 is adjusted so as not to interfere with each other.

With this combination, even with the line irradiation of embodiment 1 and the spot irradiation of embodiment 2, impurities such as LDI8 cannot be completely removed and some of the impurities flow toward the lip 36 along with the melt flow, and finally the impurities can be prevented from flowing into the lip 36 by the irradiation line 28 near the lip 36. This can further reliably prevent the foreign matter from flowing out from the lip 36 to the die 40.