JP7789554B2 - Apparatus, method, and program for manufacturing metal ingots - Google Patents

Description

One embodiment of the present invention relates to an apparatus, method, and program for producing ingots of metals such as titanium.

One method for producing metal ingots is the melting and casting method. In this method, raw materials such as powder, pellets, wire, sponge, briquette, plate, or billet of a metal or alloy are melted to produce a liquid metal (molten metal), which is then poured into a mold and solidified to produce an ingot that reflects the shape of the mold. For example, Patent Document 1 discloses that a cylindrical titanium alloy ingot can be produced by irradiating the raw material titanium alloy with an electron beam to form a molten metal, which is then poured into a cylindrical mold and cooled.

Japanese Patent Application Laid-Open No. 2020-204055

One embodiment of the present invention aims to provide a novel apparatus and method for producing ingots of metal or alloy, and a program for executing this method. For example, one embodiment of the present invention aims to provide an apparatus and method for selectively producing and providing high-quality metal ingots by applying a melting and casting method, and a program for executing this method.

One embodiment of the present invention is an apparatus for producing metal ingots. The apparatus includes a chamber, a hearth, a mold, an imaging device, and a control device. The hearth is disposed within the chamber and receives raw material containing metal. The mold is also disposed within the chamber and is poured with molten metal formed in the hearth. The imaging device is disposed outside the chamber and configured to capture video images of the mold. The control device is configured to distinguish between molten metal and solid metal based on the captured video images.

One embodiment of the present invention is a method for manufacturing metal ingots using the above-mentioned apparatus.

That is, the above manufacturing method includes melting raw materials containing metal in a hearth placed inside a chamber to form a molten metal, pouring the molten metal into a mold inside the chamber, capturing video images of the mold using an imaging device installed outside the chamber, and distinguishing between the molten metal and solid metal based on the video images.

One embodiment of the present invention is a program. This program is configured to cause a control device connected to an imaging device provided in a manufacturing apparatus for producing metal ingots by pouring molten metal into a mold to acquire video images of the mold via the imaging device and to distinguish between molten metal and solid metal based on the acquired video images.

One embodiment of the present invention is a computer-readable storage medium on which the above program is recorded.

1 is a block diagram of a metal ingot manufacturing apparatus according to an embodiment of the present invention; 1 is a schematic end view of an apparatus for producing a metal ingot according to one embodiment of the present invention; 1 is a schematic end view of an apparatus for producing a metal ingot according to one embodiment of the present invention; 1 is a schematic top view of an apparatus for manufacturing a metal ingot according to an embodiment of the present invention; 1 is a flowchart illustrating a method for manufacturing a metal ingot according to one embodiment of the present invention. 1 is a schematic perspective view illustrating a method for manufacturing a metal ingot according to an embodiment of the present invention. 1 is a schematic perspective view illustrating a method for manufacturing a metal ingot according to an embodiment of the present invention. 1 is a schematic perspective view illustrating a method for manufacturing a metal ingot according to an embodiment of the present invention. 1A to 1C are schematic diagrams illustrating a method for manufacturing a metal ingot according to one embodiment of the present invention. 1A to 1C are schematic diagrams illustrating a method for manufacturing a metal ingot according to one embodiment of the present invention. 1A to 1C are schematic diagrams illustrating a method for manufacturing a metal ingot according to one embodiment of the present invention. 1A to 1C are schematic diagrams illustrating a method for manufacturing a metal ingot according to one embodiment of the present invention. 1A to 1C are schematic diagrams illustrating a method for manufacturing a metal ingot according to one embodiment of the present invention. 1A to 1C are schematic diagrams illustrating a method for manufacturing a metal ingot according to one embodiment of the present invention. 1A to 1C are schematic diagrams illustrating a method for manufacturing a metal ingot according to one embodiment of the present invention. FIG. 4 is a schematic diagram showing an evaluation area and sub-areas in an embodiment.

Each embodiment of the present invention will be described below with reference to the drawings, etc. However, the present invention can be embodied in various forms without departing from the spirit of the invention, and should not be construed as being limited to the description of the embodiments exemplified below.

In order to clarify the explanation, the drawings may show the width, thickness, shape, etc. of each part schematically compared to the actual embodiment, but this is merely an example and does not limit the interpretation of the present invention. In this specification and each drawing, elements with the same function as those explained in the previous drawing may be given the same reference numeral, and duplicate explanations may be omitted. When describing part of a reference numeral, a lowercase letter is added to the reference numeral. When describing multiple elements with the same or similar structure to distinguish them from each other, a hyphen and a natural number are added after the reference numeral. When describing multiple elements with the same or similar structure collectively, only the reference numeral is used.

Here, dissolution refers to the phenomenon in which gas, liquid, and solid mix in a liquid to form a uniform liquid phase, but in the following description, it is used as a term that also encompasses melting, the phenomenon in which a solid changes into a liquid.

1. Metal Ingot Manufacturing Apparatus 1-1. Overview First, a manufacturing apparatus 100 according to one embodiment of the present invention will be described. The manufacturing apparatus 100 is an apparatus for manufacturing elemental metal or alloy ingots (hereinafter, elemental metal ingots and alloy ingots will be collectively referred to as metal ingots) using a melting and casting method. It is configured to heat and melt a raw material containing a metal (a zero-valent metal) by supplying thermal energy, and then pour the resulting molten metal into a mold. The molten metal is cooled in the mold to produce a metal ingot. The raw material is heated using a heat source. Examples of heat sources include an electron gun and a plasma torch. In the former case, thermal energy is supplied by an electron beam emitted from the electron gun, and in the latter case, thermal energy is supplied by an arc discharge emitted from a plasma torch. The former method is called electron beam melting and casting, and the latter method is called plasma arc melting and casting. Below, we will describe electron beam melting and casting, which uses an electron gun as a heat source. However, one embodiment of the present invention can also be applied to plasma arc melting and casting, which uses a plasma torch as a heat source.

There are no restrictions on the metals that can be used with the manufacturing apparatus 100, and it can handle raw materials containing a variety of metals, such as titanium, copper, nickel, aluminum, zirconium, hafnium, tungsten, molybdenum, tantalum, or alloys containing metals selected from these metals. There are also no restrictions on the shape of the raw materials, and raw materials can be in powder, pellet, rod, wire, or plate form, as well as metal scrap, which is a by-product of metal cutting and contains a mixture of raw materials of various shapes. The density of the raw materials is also arbitrary. For example, when using raw materials containing titanium, sponge titanium produced by the reduction of titanium tetrachloride, as exemplified by the Kroll process or Hunter process, can be used. Note that metals containing titanium include not only pure titanium, but also titanium alloys such as titanium-aluminum alloys.

Figure 1 is a block diagram of the manufacturing apparatus 100, and Figure 2 is a schematic end view of the manufacturing apparatus 100. As shown in Figure 1, the manufacturing apparatus 100 includes a melting furnace 110 and a control device 160. The control device 160 may be connected to the melting furnace 110 or at least one component (described below) provided in the melting furnace 110 via an application programming interface (not shown), and may be configured to control all or part of the functions of the melting furnace 110. Alternatively, the control device 160 and the melting furnace 110 may be independent devices that are not connected to each other.

1-2. Melting Furnace As shown in FIG. 2 , the melting furnace 110 primarily comprises a chamber 112 providing a space for melting and solidifying the raw materials, a hearth 120 installed within the chamber 112, a mold 124, one or more electron guns 140, one or more electron guns 142, and an imaging device 150 installed outside the chamber 112. The melting furnace 110 may further include a drum feeder 114 filled with metal-containing raw materials 104, an exhaust device (vacuum pump) 116 for reducing the pressure inside the chamber 112, and a vibrating feeder 118 for transporting the raw materials 104 supplied from the drum feeder 114 to the hearth 120. The exhaust device 116 creates a reduced pressure atmosphere of 0.01 Pa or less inside the chamber 112, making it possible to handle highly reactive metals, such as titanium, which readily reacts with oxygen and nitrogen in the molten state. The vibrating feeder 118 is installed so that the hearth 120 side is lower than the drum feeder 114 side and is connected to a vibrating device (not shown). Therefore, for example, the drum feeder 114 can be rotated to supply the raw material 104 to the vibrating feeder 118 , and the vibrating feeder 118 can be vibrated to transport the raw material 104 to the hearth 120 .

The electron gun 140 is a heat source that supplies thermal energy to the raw material 104 supplied to the hearth 120. Although not shown, the electron gun 140 basically comprises a filament for generating thermoelectrons and a magnet for deflecting the electron beam. By controlling the magnetic field of the magnet, the irradiation direction of the electron beam can be controlled, allowing the electron beam to be scanned over the hearth 120. The energy supplied by the electron beam melts the metal contained in the raw material 104, forming molten metal 106.

The hearth 120 is configured to hold the raw materials 104 and the molten metal, and to supply the molten metal to the mold 124. For this reason, although not shown in FIG. 2, the hearth 120 is provided with a spout that overlaps with the mold 124 for pouring the molten metal 106 into the mold 124. The hearth 120 may also be configured to receive molten raw materials above it. Furthermore, a skull 122 may be formed on the hearth 120 in advance by melting and solidifying the metal contained in the raw materials. The skull 122 also functions as a flow path for the molten metal 106, but a portion of it may also be re-melted to function as a supply source for the molten metal 106.

The mold 124 is a container that receives the molten metal 106 formed in the hearth 120 and is positioned below the spout of the hearth 120. There is no limit to the number of molds 124; one or more molds 124 may be positioned within the chamber 112. The number of spouts on the hearth 120 may be equal to or greater than the number of molds 124. The mold 124 is constructed using a metal with high thermal conductivity, such as copper. Optionally, the mold 124 may have a flow path 126 for cooling the mold 124. The molten metal 106 poured into the mold 124 can be effectively cooled by circulating a cooling medium through the flow path 126, such as water, glycols such as ethylene glycol and propylene glycol, alcohols such as ethanol and isopropanol, fluorine-containing compounds such as tetradecafluorohexane and perfluoro-2-butyltetrahydrofuran, silicone oil, or aromatic compounds that are solid at room temperature, such as a mixture of biphenyl and diphenyl ether.

There are no restrictions on the shape of the mold 124, and the horizontal cross-sectional shape of the mold 124, more specifically, the shape of the inner wall in the horizontal cross-section, may be polygonal, such as rectangular, or may be circular. By using a mold 124 having an inner wall with a rectangular or circular horizontal cross-section, rectangular parallelepiped and cylindrical metal ingots 108 can be obtained, respectively. Furthermore, the horizontal cross-section of the inner wall of the mold 124 may be elliptical, or may be composed of straight lines and curves. There are also no restrictions on the size of the mold 124, and it may be appropriately set so that the area of the horizontal cross-section is, for example, between 1,500 ^cm2 and 15,000 ^cm2 .

A dovetail 128, which functions as a bottom cover, is provided at the bottom of the mold 124, and a withdrawal mechanism (not shown) is connected to the dovetail 128. A starting block 130, also known as a stub, may be formed on the dovetail 128. The starting block 130 contains metal contained in the raw material 104 to be cast, and is formed by pouring molten metal 106 onto the dovetail 128 and then solidifying it.

A withdrawal mechanism (not shown) is connected to the starting block 130 either directly or via the dovetail 128. The molten metal 106 poured into the mold 124 begins to solidify from the dovetail 128 side or the starting block 130 side. Therefore, by using the withdrawal mechanism to withdraw the dovetail 128 and/or starting block 130 downward from the mold 124 (see the straight arrow in Figure 2), the portion of the molten metal 106 that has solidified within the mold 124 can be obtained as a metal ingot 108. Note that the starting block 130 may be integrated with the molten metal 106 as it solidifies, forming part of the metal ingot 108. Alternatively, the starting block 130 may be cut and removed after the metal ingot 108 has been cast.

Optionally, the chamber 112 may include a cooling pipe 134 for cooling the metal ingot 108. The cooling pipe 134 is arranged to surround the starting block 130 and the resulting metal ingot 108. Like the mold 124, the cooling pipe 134 preferably contains a metal with high thermal conductivity, such as copper. The cooling pipe 134 may also be provided with a flow path 136 for circulating a cooling medium.

Unlike electron gun 140, electron gun 142 is positioned so that it irradiates the molten metal 106 in mold 124 with an electron beam. By positioning electron gun 142, the temperature of molten metal 106 can be adjusted and the solidification rate can be controlled. In addition, if a deposit (described below) unintentionally falls into the molten metal in mold 124, electron gun 142 can also be used to melt the deposit. Like electron gun 140, electron gun 142 also has a filament and a magnet. By controlling the magnetic field of the magnet, it is possible to selectively irradiate any target, including molten metal 106, with an electron beam.

Examples of the imaging device 150 include an imaging device including a charge-coupled device (CCD) or a complementary metal-oxide semiconductor (CMOS) device. The imaging device 150 is positioned to capture moving images of the top surface of the mold 124. More specifically, it is positioned to capture moving images of the entire mold 124 and the molten metal 106 within the mold 124. Therefore, the imaging device 150 can be positioned in advance to include the evaluation area and even sub-areas described below. The imaging device 150 may also be positioned so that it can simultaneously capture images of the wall surface and spout of the hearth 120 facing the mold 124. This makes it possible to simultaneously capture moving images of the mold 124, the molten metal 106 within the mold 124, and a portion of the hearth 120 during the manufacturing process of the metal ingot 108.

The moving image acquired by the imaging device 150 is composed of multiple frame images. In other words, the imaging device 150 continuously acquires frame images, which are still images, and the multiple frame images obtained compose a single moving image. There are no restrictions on the interval between frame images (frame interval), and it may be selected appropriately from a range of, for example, 0.1 seconds (10 frame images acquired per second) to 10 seconds (0.1 frame images acquired per second). Note that the moving image only needs to include multiple frame images used to distinguish between molten metal and solid metal. The moving image may also include frame images other than the multiple frame images used to distinguish between molten metal and solid metal, for example, when the brightness of the frame images has been adjusted.

Figure 3A shows a schematic end view of the imaging device 150 and its vicinity. An opening may be formed in the top of the chamber 112, and a window 152 may be provided in the opening. The window 152 may include one or more of glass, quartz glass, and lead glass, and may be, for example, a laminate of quartz glass and lead glass. The imaging device 150 may be positioned so that it can capture an image of the top surface of the mold 124 through the window 152.

The position where the opening is provided can be set arbitrarily. However, when the raw material 104 is melted in the chamber 112, some of the metal may evaporate, resulting in metal deposition on the inner walls of the chamber 112 or the inside of the window 152. Metal evaporating from the molten metal is particularly likely to deposit at positions that overlap the mold 124 vertically. For this reason, as shown in FIG. 2, it is preferable to provide the opening at a position that does not overlap the mold 124 or hearth 120 vertically. Therefore, it is preferable that the imaging device 150 is also positioned so that it does not overlap the mold 124 or hearth 120, and that it captures an image through the opening from an oblique direction relative to the mold 124 (see FIG. 3A). In other words, it is preferable to position the imaging device 150 so that the optical axis of the lens of the imaging device 150 is tilted from the vertical direction.

As shown in Figures 3A and 3B, an adhesion prevention plate 154 overlapping the window 152 may be provided in the chamber 112 in any configuration. The adhesion prevention plate 154 is a metal plate having an approximately circular shape. By providing the adhesion prevention plate 154, metal vapor is prevented from adhering to the window 152, thereby preventing metal deposition and maintaining the transparency of the window 152 for an extended period of time. To enable the imaging device 150 to capture images of the mold 124, one or more openings 154a may be provided in the adhesion prevention plate 154, which may be rotated by a motor (not shown). The shape of the opening 154a may also be arbitrary, as long as it is formed so that the mold 124 can be captured when the opening 154a and the imaging device 150 overlap. For example, the opening 154a may be circular or rectangular. If multiple openings 154a are provided, they may be arranged in any configuration, for example, symmetrically about the center of the adhesion prevention plate 154. Alternatively, multiple openings 154a may be arranged at equal intervals along the rotation direction of the attachment prevention plate 154. The imaging device 150 is configured to capture a frame image when the openings 154a overlap with the imaging device 150. The openings 154a may be slits.

As an optional configuration, a nozzle 156 for spraying an inert gas such as argon or helium onto the inside of the window 152 may be provided in the chamber 112 in addition to or instead of the adhesion prevention plate 154 (Figure 2). The nozzle 156 is connected to an inert gas supply source (not shown) provided outside the chamber 112. When the raw materials are melted, supplying inert gas from the inert gas supply source to the inside of the window 152 prevents metal vapor from adhering to the window 152, thereby maintaining the transparency of the window 152.

Although not shown, a gas inlet may also be provided for introducing an inert gas into the chamber 112. An inert gas supply source is also connected to the gas inlet.

The control device 160 is a computer having communication and calculation functions, and may be a notebook or desktop computer, or may be a portable communication terminal such as a tablet computer. The control device 160 is connected to the chamber 112 or all or part of the components provided in the chamber 112 (e.g., the electron gun 142, the imaging device 150, etc.) via an external network such as the Internet or an internal network such as a LAN (Local Area Network).

As shown in the block diagram of FIG. 1, the control device 160 includes a control unit 162 that controls the operation of the control device 160, as well as an input unit 164, output unit 166, transceiver unit 168, memory unit 170, audio output unit 172, input port 174, and other components controlled by the control unit 162. The memory unit 170 stores a basic application program for operating the control device 160, as well as a program for implementing the manufacturing method for metal ingot 108 described below. The control unit 162 includes a processor such as a central processing unit (CPU), and controls various processes executed by the control device 160 by running the basic application program and the above programs stored in the memory unit 170. The input unit 164 is a user interface used to input commands and information to the control device 160, and typically includes a keyboard, touch panel, mouse, or a combination of these. The output unit 166 provides various data stored in the memory unit 170 as images or printed matter, and is an output device such as a display device such as a liquid crystal display device or an organic electroluminescent display device, or a printer. The transceiver 168 has the function of communicating with the melting furnace 110 or components provided therein via a network. For example, the transceiver 168 may be configured to receive images captured by the imaging device 150 and transmit signals to components provided in the chamber 112, such as the electron guns 140 and 142. The audio output unit 172 is a speaker capable of generating various sounds. The input port 174 is a wired interface that can be physically connected to the imaging device 150 or a storage medium, such as a memory card, attached to the imaging device 150. Even if the control device 160 and the melting furnace 110 are not connected, the captured video images can be read and stored in the storage unit 170 by connecting the imaging device 150 or a storage medium to the control device 160 via the input port 174.

The block diagram in FIG. 1 shows an example in which the drum feeder 114, exhaust device 116, vibrating feeder 118, electron guns 140 and 142, and image capture device 150 provided in the melting furnace 110 are all controlled by the control device 160. However, the control device 160 does not need to control all of these components; for example, it may be configured to control and operate only the image capture device 150. Alternatively, the control device 160 may be connected only to the image capture device 150 and configured to receive or store video image data captured by the image capture device 150 and process that data. In this case, other components, such as the drum feeder 114, vibrating feeder 118, exhaust device 116, extraction mechanism (not shown), and electron guns 140 and 142, may be controlled and operated by a control system independent of the control device 160. Alternatively, as described above, the control device 160 may be independent and not connected to the melting furnace 110. In this case, video images captured by the image capture device 150 are input to the control device 160 via the input port 174.

As described above, during the process of manufacturing metal ingots 108 using the melting and casting method, metal may gradually evaporate from the high-temperature molten metal 106 in the hearth 120 or mold 124. When the metal vapor adheres to the sidewalls of the hearth 120, the ceiling, or the inner walls of the chamber 112, it cools and the metal precipitates and deposits. These deposits are solid metal, unlike the liquid molten metal 106, and are called deposits. As the deposit deposition progresses, it may fall into the molten metal 106 in the mold 124 or hearth 120. If the fallen deposit remelts, it mixes uniformly with the molten metal 106, resulting in a metal ingot 108 with uniform density and composition. However, if the deposit does not completely melt, it remains solid during the cooling process of the molten metal 106, and the molten metal 106 solidifies, incorporating the deposit. The density of the deposit is lower than the density of the metal ingot 108 obtained when the molten metal 106 solidifies. As a result, the trapped deposits create locally low-density defects in the metal ingot 108. These defects are called low-density inclusions (LDIs). If LDIs are present in the metal ingot 108, they appear as surface defects after the metal ingot 108 is rolled, causing fatal defects in the material. Furthermore, it is not always easy to determine whether LDIs are present inside the metal ingot 108 after it has been manufactured.

As described in detail below, by using the manufacturing apparatus 100, deposits can be easily and quickly detected during the manufacturing process of metal ingots 108 using the melting and casting method. Therefore, even if deposits are mixed into the molten metal 106, their behavior can be tracked in detail, and the effects of the deposits can be reliably understood. As a result, metal ingots 108 that contain or are likely to contain LDI can be removed, making it possible to reliably secure and provide only non-defective metal ingots 108.

2. Metal Ingot Manufacturing Method Hereinafter, a description will be given of a metal ingot manufacturing method using the manufacturing apparatus 100. Fig. 4 is a flowchart showing an example of a metal ingot manufacturing method according to an embodiment of the present invention.

2-1. Formation of Molten Metal from Raw Materials First, the atmosphere in the chamber 112 is adjusted appropriately. For example, the exhaust device 116 may be used to reduce the pressure in the chamber 112. When using raw materials 104 containing a metal that exhibits high reactivity in a molten state, such as titanium, it is preferable to adjust the pressure in the chamber 112 to 0.001 Pa to 0.005 Pa. When using raw materials 104 containing a metal that exhibits low reactivity in a molten state, the atmosphere in the chamber 112 may be air, or may be an inert gas introduced through a gas inlet.

Next, the raw material 104 is introduced from the drum feeder 114 into the vibrating feeder 118 (S1, Figure 2). For example, the drum feeder 114 filled with the raw material 104 can be used, and the drum feeder 114 can be rotated to drop the raw material 104 into the vibrating feeder 118 (see the curved arrow in Figure 2). The vibrating feeder 118 is equipped with a vibrating device (not shown), and the vibration of the vibrating feeder moves the raw material 104 towards the hearth 120, where it is ultimately supplied into the hearth 120.

Then, one or more electron guns 140 are used to scan an electron beam over the hearth 120 so that the raw material 104 is irradiated with the electron beam. This melts the metal contained in the raw material 104, forming the molten metal 106 (S2). When a certain amount of the molten metal 106 has accumulated, it flows out of the spout of the hearth 120 and is poured into the mold 124 (S3). The rate at which the molten metal 106 is supplied to the mold 124 can be adjusted by appropriately controlling the amount of raw material 104 supplied and the intensity of the electron beam. Note that a dovetail 128 may be placed at the bottom of the mold 124 before the molten metal 106 is poured into the mold 124. Alternatively, the dovetail 128 and a starting block 130 formed on top of it may be placed (see Figure 2), or the starting block 130 alone may be placed instead of the dovetail 128. When the starting block 130 is placed, the molten metal 106 solidifies and becomes integrated with the starting block 130 to form a metal ingot 108.

The electron beam emitted from the electron gun 142 may also be scanned over the surface of the molten metal 106 supplied to the mold 124. The solidification rate can be adjusted by appropriately controlling the intensity and scanning speed of the electron beam from the electron gun 142.

After the molten metal 106 is poured, the dovetail 128 and/or starting block 130 is slid downward to withdraw the metal ingot 108 from the mold 124. The withdrawal speed may be set appropriately within the range of, for example, 0.5 t/h to 4 t/h. In this way, the metal ingot 108 can be obtained.

2-2. Acquisition of Moving Images To detect deposits, moving images of the mold 124 are acquired using the imaging device 150. As described above, the imaging device 150 is preferably positioned in advance so that it does not overlap the hearth 120 or the mold 124 in the vertical direction and can capture images from an oblique direction relative to the surface of the molten metal 106 (see FIGS. 2 and 3A). In this case, if the inner wall of the mold 124 has a rectangular shape in top view, as shown in FIG. 5A, the imaging device 150 may be positioned so that the optical axis of its lens intersects or is perpendicular to the short side of the mold 124, or so that it intersects or is perpendicular to the longitudinal direction of the mold 124, as shown in FIG. 5B. The imaging device 150 is positioned so that moving images of at least the entire surfaces of the mold 124 and the molten metal 106 can be acquired, and preferably is further positioned so that the spout 120a of the hearth 120 and/or the side wall 120b on the mold 124 side are included in the moving images (see FIG. 6). In addition, when multiple molds 124 are placed in the chamber 112, an imaging device 150 corresponding to each mold 124 may be used, or a single imaging device 150 may be used to capture moving images of multiple molds 124.

Capturing moving images can begin at any timing; for example, it may begin after irradiation of the electron beam from the electron gun 142 has begun, after the molten metal 106 has formed in the mold 124, or after the dovetail 128 and/or starting block 130 has begun to be removed from the mold 124. Furthermore, to prevent halation, irradiation of the electron beam from the electron gun 142 may be temporarily stopped when acquiring each frame image.

As described above, a moving image is composed of multiple frame images, which are still images captured continuously. Each frame image is captured as a set of combinations of coordinates and grayscale data for data points arranged in a matrix of multiple columns and rows. Each data point is expressed as a grayscale selected from a total of 256 grayscales, ranging from the darkest grayscale 0 to the brightest grayscale 255. When this image is displayed on a display device, each data point corresponds to a pixel, and the grayscale is expressed as brightness. In other words, the image of the mold 124 or molten metal 106 is viewed on the display as a collection of pixels providing 256 different levels of brightness.

Before acquiring the frame images to be evaluated later, the brightness of the frame images is adjusted using the aperture of the imaging device 150, a neutral density filter (ND filter), or the like (S4). Specifically, brightness is adjusted so that the average gradation of the data points corresponding to the molten metal 106 in each frame image falls within a certain range (reference gradation). The reference gradation may be appropriately selected, for example, from the range of 120 to 200 gradations. As described above, in the melting and casting process, metal vapor is generated from the molten metal 106 and accumulates to form a deposit. However, if the deposit adheres to the imaging window 152 and clouds the window 152, the amount of light passing through the window 152 gradually decreases. This can result in a gradational decrease in the overall moving image, resulting in a degradation of image quality. Furthermore, as described below, the deposit is represented in the frame images as a lower-gradation area compared to the molten metal 106. Therefore, by adjusting the brightness before acquiring the frame images and ensuring that the gradation of the data points corresponding to the molten metal 106 is at a certain level or above, it is possible to prevent a decrease in the quality of the frame images and more reliably detect deposited matter as a collection of data points with low gradation. Brightness adjustment may be performed each time a frame image is acquired, or for each set of multiple frame images. Alternatively, brightness adjustment may be performed at regular intervals. Furthermore, the average gradation may be the average of the gradations of the data points corresponding to the evaluation area, which will be described later. Furthermore, the average gradation may be acquired when there is no deposited matter.

After brightness adjustment, a frame image is acquired (S5). The frame image is stored permanently or temporarily in the memory unit 170 via the transceiver unit 168 of the control device 160.

Assuming that moving images can be acquired to distinguish between the molten metal 106 and solid metal, and further between the molten metal 106 and deposition material, the above-mentioned steps of positioning the imaging device 150, adjusting the brightness of the frame images, and forming the molten metal 106 in the mold 124 may be performed in any order. Therefore, moving images may be acquired in an order other than the flowchart shown in Figure 4. For example, the following order may be applied: positioning the imaging device 150 in a predetermined position, forming the molten metal 106 in the mold 124, adjusting the brightness of the frame images, starting to acquire frame images to be used for the above-mentioned identification, and starting to pull out the ingot.

2-3. Distinguishing between molten metal and deposited material Subsequently, each frame image is processed to distinguish between the molten metal 106 and deposited material.

(1) Selection of Evaluation Area: First, an evaluation area is selected in each frame image (S6). The selection of the evaluation area can be performed as needed, for example, by the operator, or a predetermined range may be selected as the evaluation area in consideration of the relationship between the control device 160 and the image capture device 150. As described above, in the melting and casting process, steam is generated from the molten metal to form a deposit. Some of the steam also accumulates on the inner and upper surfaces of the mold 124, forming relatively small metal lumps, as shown in the enlarged view in FIG. 6 . Metal lumps may also be formed when a portion of the molten metal 106 is ejected by the electron beam irradiated onto the molten metal 106 in the mold 124 and adheres to and solidifies on the upper and inner surfaces of the mold 124. Such small metal lumps are called "molten metal deposits" 182 and are distinguished from deposits. To selectively detect deposits 180 without detecting "molten metal deposits" 182, it is preferable to select the evaluation area by excluding areas where "molten metal deposits" 182 may occur. 7A , among the areas in which the molten metal 106 is displayed, an area that is at least a certain distance d away from the inner wall of the mold 124 is selected as the evaluation area 184. The distance d may be selected, for example, from a range of 10 mm to 30 mm. Alternatively, an area that is centered on the molten metal 106 and has an area that is 70% to 90% of the area of the molten metal 106 may be selected as the evaluation area 184. By selecting the evaluation area 184 in this manner, detection noise caused by the mold 182 can be eliminated. Note that, because the imaging device 150 often captures moving images in a fixed state, the selection of the actual evaluation area can be determined in conjunction with the placement of the imaging device 150.

(2) Detection of Deposit and Identification of Frame Image Then, as schematically shown in FIG. 7B , the gradations of the data points constituting the evaluation region (hereinafter referred to as evaluation region data points DP) are calculated, and data points _DP2 below a certain gradation (threshold gradation) are identified from among them. The threshold gradation is appropriately selected from gradations lower than the above-mentioned average gradation, for example, from a range of 40 gradations or lower or 70 gradations or lower. The lower limit of the threshold gradation may be, for example, 0 gradation or 10 gradation. The deposit 180 is clearly recognized as dark compared to the molten metal 106 even when viewed visually, and as described above, the deposit 180 is also represented as an extremely dark region compared to the molten metal 106 in the moving image. Therefore, the data point _DP1 exceeding the threshold gradation and the data point _DP2 constituting the low gradation region below the threshold gradation can be determined to be data points constituting the molten metal 106 and the deposit 180, respectively. Furthermore, false detection (noise) can be reduced by setting the average gray level and the threshold gray level with a certain degree of difference therebetween.

Next, it is determined whether the area of the low-gradation region in the evaluation region of each frame image is equal to or greater than a certain threshold (S8). Specifically, the ratio of the number of data points _DP2 to the number of evaluation region data points DP is calculated, and if this ratio is equal to or greater than a certain threshold (hereinafter referred to as the area threshold), it is determined that the deposit 180 has been detected. The area threshold may be selected, for example, from a range of 0.0005 or greater. By setting the area threshold within the above range, it is possible to eliminate low-gradation regions resulting from image capture errors, molded deposits 182 that have separated from the mold 124, and deposits 180 that are so small that they can quickly dissolve in the molten metal 106. In other words, it is possible to prevent false detections and overdetections, accurately distinguish between the molten metal 106 and the deposits 180, and selectively and reliably detect the deposits 180 to be tracked.

If the ratio is equal to or greater than the area threshold in each frame image, it is suggested that a deposit 180 to be tracked is present. In this case, the frame image is identified (S9). There is no limitation on the identification method. For example, frame numbers may be assigned sequentially to all frame images included in one video, and the frame number corresponding to the ratio equal to or greater than the area threshold may be stored in the storage unit 170. At this time, a warning sound may be emitted from the audio output unit 172, or an alert may be displayed on the display device constituting the output unit 166. Furthermore, a figure enclosing data points _DP2 that are equal to or less than the threshold gradation may be displayed on the display device.

After determining whether or not deposition material 180 is present, if casting is not complete, steps S4 to S9 are repeated. A single moving image is composed of multiple frame images captured up until the end of casting. In another embodiment, the acquisition of moving images up to the end of casting may be performed first, and the presence or absence of deposition material 180 may be determined for the multiple frame images of the acquired moving image. If the acquisition of moving images is performed first, it is preferable to adjust the brightness (S4). As described above, the acquisition of moving images and the determination of the presence or absence of deposition material 180 may be performed simultaneously, or may be performed at different times as appropriate.

(3) Verification of the Casting Process Next, the casting process is verified based on the acquired moving images. This verification process may be performed when the frame images are identified, or after one moving image is acquired.

If there is no frame image identified as containing a deposit 180 in a single video image acquired during the casting of the metal ingot 108, it is determined that no deposit has occurred on the surface of the molten metal 106 in the mold 124, or that even if it has occurred, it is negligible to the extent that it does not significantly affect the quality of the metal ingot 108.

On the other hand, if one or more frame images are identified as containing the deposition material 180 in a single video, the video images following the identified frame image are analyzed to track the behavior of the deposition material 180 (S10). If it is confirmed that the deposition material 180 has completely dissolved in the molten metal 106, it is determined that the deposition material 180 is negligible and does not significantly affect the quality of the resulting metal ingot 108. Alternatively, if it is confirmed that the deposition material 180 does not mix with the molten metal 106 and remains attached to components of the melting furnace 110, such as the mold 124 and hearth 120, until the end of casting, it can also be determined that the deposition material 180 has not been incorporated into the metal ingot 108.

However, if it is determined that the deposit 180 did not completely dissolve in the molten metal 106 and that the molten metal 106 solidified while the deposit 180 was being absorbed into the molten metal 106 while maintaining a solid state, it is determined that the resulting metal ingot 108 is highly likely to contain LDI. In this case, measures can be taken, such as excluding the resulting metal ingot 108 from shipment or reusing it as raw material 104 (S11).

As such, according to a manufacturing method according to one embodiment of the present invention, during the process of manufacturing a metal ingot 108 by melting and casting, it is possible to distinguish between the deposit 180 and the molten metal 106 based on a moving image of the molten metal 106 in the mold 124, and to detect the deposit 180 that needs to be tracked in order to maintain the quality of the metal ingot 108. Furthermore, by tracking the deposit 180, it is possible to select appropriate measures for the metal ingot, and therefore, by applying this manufacturing method, it is possible to selectively provide high-quality metal ingots 108.

2-4. Modifications In this manufacturing method, the evaluation region 184 may be divided into multiple regions (subregions), and the deposition material 180 and the molten metal 106 may be identified for each subregion ( S7 in FIG. 4 ). There are no limitations on the division method. For example, as shown in FIGS. 8A and 8B , the evaluation region 184 may be divided so that multiple subregions (four subregions 184-1 to 184-4 in this example) are aligned in the longitudinal direction of the mold 124 or in a direction perpendicular to the longitudinal direction. The subregions may have the same area or shape. Alternatively, as shown in FIG. 9A , the evaluation region 184 may be divided so that the area or shape of at least one subregion (subregion 184-3 in this example) is different from the area or shape of the other subregions (subregions 184-1 and 184-2 in this example). Furthermore, as shown in FIG. 9B , the evaluation region 184 may be divided so that at least two subregions partially overlap each other. In the example shown in FIG. 9B , subregions 184-1 to 184-3 partially overlap each other.

Dividing the evaluation area 184 into multiple sub-areas and distinguishing between the deposit 180 and the molten metal 106 in each sub-area makes it possible to narrow the range of false detections. In other words, sub-areas other than those in which false detections persist can be continuously monitored for the presence or absence of falling deposits. Deposits behave in a variety of ways. For example, some deposits 180 fall when they reach a certain size, while others hang down from the sidewalls of the hearth 120 or the ceiling of the chamber 112. In the latter case, the deposit 180 remains in the space above the mold 124 for a long period of time. In the latter case, the deposit 180 does not fall into the molten metal 106, but is recorded as a low-gradation data point _DP2 in the moving image, resulting in a false detection. If the evaluation area 184 were not divided, it would be necessary to track the behavior of the deposit 180 for all frame images in which the deposit 180 was falsely detected. On the other hand, dividing the evaluation area 184 into multiple sub-areas increases the area in which false detections do not occur, thereby ensuring a range in which normal inspection is possible.

Furthermore, in this manufacturing method, a correction may be made in the calculation of the ratio of the number of data points _DP2 to the number of evaluation area data points DP, taking into account the inclination of the imaging direction. As described above, in order to minimize the influence of metal vapor deposition during melting and casting, it is preferable that the window 152 and the imaging device 150 for acquiring moving images are positioned so as not to overlap the hearth 120 or the mold 124 in the vertical direction. For this reason, moving images are acquired from a direction oblique to the mold 124. In moving images, objects closer to the imaging device 150 appear larger than objects located further away. Therefore, as schematically shown in FIG. 10 , even if there are deposition objects 180 having exactly the same shape and area, the data points _DP2 corresponding to deposition objects 180 located farther from the imaging device 150 (farther in the horizontal direction) will be fewer than the data points _DP2 corresponding to deposition objects 180 located closer to the imaging device 150 (closer in the horizontal direction). As a result, depending on the distance from the imaging device 150 to the mold 124 and the imaging direction, the distance from the imaging device 150 has a significant effect on the detection of the deposition material 180.

To eliminate such effects and detect deposition material 180 with higher accuracy, the area threshold may be corrected according to the distance from the imaging device 150. For example, the area threshold may be reduced as the distance from the imaging device 150 increases. More specifically, when dividing the evaluation region 184, the correction may be performed for each subregion. For example, as shown in FIG. 9B, if the evaluation region 184 is divided into three subregions 184-1 to 184-3 and subregion 184-3 is closest to the imaging device 150, the largest area threshold may be set for subregion 184-3, and the same area threshold may be set for subregions 184-1 and 184-2 that are smaller than the area threshold for subregion 184-3. Furthermore, the area threshold may be reduced for each subregion as the distance from the imaging device 150 increases. Furthermore, when a single imaging device 150 is used to capture moving images of multiple molds 124, or when the imaging device 150 is positioned so that it intersects or is perpendicular to the longitudinal direction of the molds 124, the area threshold may be changed not only in the depth direction of the moving images, but also in the left-right direction.

Conventionally, when manufacturing metal ingots using the melting and casting method, the presence or absence of deposits was confirmed by visually observing the mold throughout the manufacturing process. However, it is impossible to accurately predict the timing and location of deposit fall or the size of the deposit in advance. Furthermore, the melting rate and settling rate of the deposit into the molten metal vary greatly depending on the size and density of the deposit and the temperature of the molten metal. For these reasons, visual detection not only places a heavy burden on the worker, but also carries the risk of overlooking deposits falling into the molten metal, creating a demand for a more accurate detection method. By applying a manufacturing apparatus and manufacturing method according to one embodiment of the present invention, deposits can be detected more reliably, and the time of their occurrence can be instantly identified from the frame number. Furthermore, the behavior of the deposit can be confirmed from video images taken after the deposit occurs, making it easy to determine the presence or absence of LDI in the metal ingot. This makes it possible to selectively provide non-defective metal ingots.

3. Program A manufacturing method according to one embodiment of the present invention can be implemented by the manufacturing apparatus 100 described above and a program installed in its control device 160. Thus, one embodiment of the present invention is a program for causing the control device 160 to execute some or all of the processes from S1 to S9 described above to manufacture a metal ingot by a melting and casting method.

A computer-readable recording medium on which this program is recorded also constitutes an embodiment of the present invention. Examples of computer-readable recording media include magnetic media such as hard disks, flexible disks, and magnetic tapes, optical media such as CD-ROMs and DVDs, magneto-optical media such as floptical disks, and hardware devices configured to store and execute the program, such as ROM, RAM, and flash memory. The program includes not only machine code such as that generated by a compiler, but also high-level language code executed by a server using an interpreter or the like. The program is installed from the computer-readable medium into storage unit 170. The program may also be downloadable from a network to storage unit 170.

This example describes the results of producing a titanium ingot using a manufacturing method according to one embodiment of the present invention.

The melting furnace used was the melting furnace 110 shown schematically in Figure 2. Metal pieces containing titanium sponge were continuously fed from the drum feeder 114 via the vibrating feeder 118 to the hearth 120, and an electron beam was irradiated from an electron gun 140 (Ardennes, model EH-800V) positioned above the hearth 120 to form the molten metal 106. The molten metal 106 was poured into a mold 124, the horizontal cross section of whose inner wall was rectangular (1100 mm long x 250 mm wide), with one short side positioned below the hearth 120. Electron beam irradiation of the molten metal 106 was then initiated using an electron gun 142 (Ardennes, model EH-800V) positioned above the mold 124. The dovetail 128 was then lowered.

During the above operation, the series of steps from S4 to S9 described above were repeated. As shown in Figure 2, the imaging device 150 (Keyence CMOS camera, model CA-H500C) was positioned so as not to overlap the mold 124 in the vertical direction, and images were taken from the short side of the mold 124 opposite the hearth 120 (see Figure 6). Images were acquired through the window 152 while rotating the adhesion prevention plate 154.

The brightness adjustment in step S4 was performed so that the gradation of the molten metal 106 in the mold 124 was in the range of 120 to 200. Of the obtained frame images, the area within 10 mm of the inner wall of the mold 124 was excluded, and the remaining area was set as the evaluation area 184. Furthermore, as shown in FIG. 9B, the evaluation area 184 was divided into three sub-areas 184-1 to 184-3, and the moving images were evaluated. As shown in FIG. 11, the sub-area 184-3 is on the opposite side of the hearth 120 and is the area closest to the imaging device 150. The width W of the sub-area 184-3 was 230 mm, and the length _l3 was 650 mm. The sub-area 184-1 is located on the hearth 120 side and on one of the long sides. In contrast, the sub-area 184-2 is located on the hearth 120 side and on the other long side. The widths w ₁ and w ₂ of the sub-regions 184-1 and 184-2 were both 140 mm, and the lengths l ₁ and l ₂ were both 550 mm. As can be seen from Figure 11, the three sub-regions 184-1 to 184-3 partially overlap one another.

The threshold gradation for determining the presence or absence of deposition material 180 was set to the 60th gradation. The area threshold in step S8 was set so that deposition material 180 equivalent to a size of 50 mm square in each sub-region could be detected. Specifically, the area thresholds for sub-regions 184-1 to 184-3 were set to 0.017, 0.016, and 0.013, respectively.

A total of 18 titanium ingots were produced under the above conditions. During the casting process, 15 deposits 180, each measuring 50 mm square, were detected. The behavior of each deposit 180 was examined based on captured video images. It was determined that none of the deposits 180 affected the properties of the titanium ingots, and all of the titanium ingots were of good quality.

In this way, by applying the manufacturing method according to an embodiment of the present invention, it is not necessary to continuously visually observe the mold 124 during the long-term casting process. Instead, the behavior of the deposition material can be reliably understood by analyzing the video images from the frame image in which the deposition material 180 of a predetermined size is detected onward. Therefore, this manufacturing method makes it possible to effectively utilize the human resources required for quality control of metal ingots.

Based on the above-described embodiments of the present invention, those skilled in the art may add or remove components or modify designs, or add or omit processes or change conditions as appropriate, and these modifications are within the scope of the present invention as long as they maintain the essence of the present invention. Even if there are other effects and advantages different from those achieved by the aspects of the above-described embodiments, those that are clear from the description in this specification or that would be easily predictable by a person skilled in the art are naturally considered to be achieved by the present invention.

100: Manufacturing equipment, 104: Raw material, 106: Molten metal, 108: Metal ingot, 110: Melting furnace, 112: Chamber, 114: Drum feeder, 116: Exhaust device, 118: Vibration feeder, 120: Hearth, 120a: Spout, 120b: Side wall, 122: Skull, 124: Mold, 126: Flow path, 128: Dovetail, 130: Starting block, 134: Cooling pipe, 136: Flow path, 140: Electron gun, 14 2: electron gun, 150: imaging device, 152: window, 154: adhesion shield, 154a: opening, 156: nozzle, 160: control device, 162: control unit, 164: input unit, 166: output unit, 168: transmitting/receiving unit, 170: memory unit, 172: audio output unit, 174: input port, 180: deposition material, 182: casting, 184: evaluation area, 184-1: sub-area, 184-2: sub-area, 184-3: sub-area, 184-4: sub-area

Claims (12)

Includes a melting furnace and control device,
The melting furnace is
chamber,
a hearth disposed within the chamber for receiving a metal-containing feedstock;
a mold disposed within the chamber and into which the molten metal formed in the hearth is poured; and an imaging device disposed outside the chamber and configured to capture a moving image of the mold, the imaging device being connected to the control device,
The apparatus for manufacturing metal ingots, wherein the control device is configured to identify the solid metal produced from the molten metal and the metal vapor in the moving image based on the moving image. The device described in claim 1, wherein the imaging device does not overlap the mold in the vertical direction. The apparatus of claim 1, wherein the imaging device is positioned to acquire the moving images through a window provided in the chamber. The device described in claim 1, wherein the moving image includes a portion of the hearth. the moving image is composed of a plurality of frame images,
The apparatus according to claim 1 , wherein the imaging device acquires the plurality of frame images under conditions in which an average gray level of data points corresponding to the molten metal in each of the plurality of frame images falls within a certain range of gray levels. The control device, for each of the plurality of frame images constituting the moving image,
selecting data points having a gradation equal to or less than a first threshold as low-gradation data points from a plurality of evaluation area data points constituting an evaluation area inside the mold; and identifying the frame image when a ratio of the number of the low-gradation data points to the number of the evaluation area data points is equal to or greater than a second threshold.
The apparatus of claim 1 configured to perform: The control device, for each of the plurality of frame images constituting the moving image,
selecting, for each of a plurality of sub-regions obtained by dividing the evaluation region inside the mold, data points having a gradation equal to or less than a first threshold as low gradation data points from a plurality of evaluation region data points constituting the plurality of sub-regions; and identifying the frame image when, in at least one of the plurality of sub-regions, the ratio of the number of low gradation data points to the number of evaluation region data points is equal to or greater than a second threshold.
The apparatus of claim 1 configured to perform: The device described in claim 7, wherein the multiple sub-regions partially overlap each other. The apparatus of claim 7, wherein the second threshold decreases for each subregion as the distance between the mold and the imaging device increases. The device described in claim 6 or 7, wherein the evaluation area is at least 10 mm away from the inner wall of the mold. A method for manufacturing metal ingots using the apparatus described in claim 1. The control device according to claim 1,
a program for causing the program to execute the following: acquiring a moving image of the mold via the imaging device; and distinguishing between the molten metal and the solid metal based on the moving image.