Micro-metal ball manufacturing device

Abstract

To provide a minute metal ball manufacturing device capable of stably manufacturing minute metal balls with high precision and small variations in ball diameter. [Solution] The micro metal sphere manufacturing apparatus (1) has a crucible (20) that contains molten metal (M) and a cooling tower (30) that is connected vertically to the crucible (20). An orifice (40) that connects the crucible (20) to the cooling tower (30) is provided in the bottom (24) of the crucible (20). The crucible (20) has a pressurized gas supply means (70) that supplies pressurized gas (G1). The micro metal sphere manufacturing apparatus (1) has a vibrating rod (54) that extends from the outside of the crucible (20) through the inside of the molten metal (M) to a position close to the orifice (40), and an oscillator (53) that is disposed outside the crucible (20) and vibrates the vibrating rod (54) in the axial direction. A cooling air blowing means (70) blows cooling air around the entire circumference of the exposed portion of the oscillator (53).

Description

[Technical Field]

[0001] The present invention relates to an apparatus for manufacturing minute metal spheres. [Background technology]

[0002] Microscopic metal spheres, such as solder balls used to bond electronic elements in semiconductor devices and hard balls for microscopic ball bearings used in micromachines, are required to have high sphericity and small variance in diameter (narrow particle size distribution). One method for manufacturing such microscopic metal spheres involves applying pressure to molten metal in a crucible and discharging the molten metal into a cooling tower through an orifice provided at the bottom of the crucible. A known method is to separate the discharged molten metal into microscopic metal spheres by vibrating a vibrating rod (see, for example, Patent Document 1). This manufacturing method makes it possible to mold microscopic metal spheres with high sphericity. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Laid-Open No. 2001-226705 Summary of the Invention [Problem to be solved by the invention]

[0004] The size (diameter) of the microscopic metal spheres depends on the diameter of the orifice, the pressure applied to the molten metal in the crucible, and the amplitude and vibration frequency of the vibrating rod. The vibrating rod is vibrated axially by a vibrator such as a piezoelectric element or a magnetostrictive element. These vibrators have temperature characteristics. For example, as the vibrator heats up, the amplitude decreases and the diameter of the spheres decreases. The vibrating rod is immersed in the molten metal, so it has the same temperature as the molten metal. The vibrator is located outside the crucible. However, heat from the molten metal is conducted to the vibrator connected to the vibrating rod. Furthermore, the vibrator itself generates heat as it vibrates. These factors can cause the vibrator to heat up, or temperature differences can occur at different locations on the vibrator, resulting in fluctuations in the amplitude and vibration frequency. Therefore, it is difficult to consistently produce microscopic metal spheres of the desired diameter.

[0005] Therefore, the present invention has been made to solve these problems, and aims to realize a micro metal sphere manufacturing device that can stably manufacture micro metal spheres with high precision and small variations in sphere diameter. [Means for solving the problem]

[0006] [1] The micro metal sphere manufacturing apparatus of the present invention is characterized by comprising: a crucible for containing molten metal; a cooling tower connected vertically to the crucible; an orifice provided at the bottom of the crucible connecting the crucible and the cooling tower; a pressurized gas supply means for supplying pressurized gas to the crucible; a vibrating rod extending from the outside of the crucible through the inside of the molten metal to the immediate vicinity of the orifice; an oscillator arranged outside the crucible for vibrating the vibrating rod in the axial direction; and a cooling air blowing means for blowing cooling air around the entire circumference of the exposed portion of the oscillator.

[0007] [2] In the micro metal sphere manufacturing apparatus of the present invention, it is preferable that the crucible and the cooling tower are detachably fixed to each other.

[0008] [3] In the micro-metal sphere manufacturing apparatus of the present invention, it is preferable that the crucible further has a lid member that hermetically secures the internal space that contains the molten metal, and that the vibration rod has a flange portion that protrudes outwardly between the vibrator and the lid member, and that a ring-shaped rigid first shim plate and an elastic second shim plate, through which the shaft portion of the vibration rod passes, are stacked and interposed between the flange portion and the lid member.

[0009] [4] In the micro-metal sphere manufacturing device of the present invention, the orifice is preferably formed in an orifice plate made of precious stone.

[0010] [5] In the micro-metal sphere manufacturing apparatus of the present invention, the crucible has a heater for producing the molten metal, and the heater is composed of a first heater arranged around the side wall of the crucible and a second heater arranged in a position surrounding the outer periphery of the bottom orifice plate, and it is preferable that the crucible is buried at least to a position where the second heater enters the interior of the cooling tower.

[0011] [6] In the micro metal sphere manufacturing apparatus of the present invention, it is preferable that the cooling tower further has a heating gas supply pipe that blows heating gas onto the molten metal in the form of columnar droplets immediately after being discharged from the orifice, and that the heating gas supply pipe is positioned so that the heating gas can be heated to a temperature at which the micro metal spheres can be separated from the columnar droplets by radiant heat from the second heater.

[0012] [7] The micro metal sphere manufacturing apparatus of the present invention preferably further comprises a charging means having an electrode portion for applying an electric repulsive force to the micro metal spheres dropping from the crucible into the cooling tower.

[0013] [8] In the micro-metal sphere manufacturing device of the present invention, it is preferable that the electrode portion is spaced apart to the side of the ejection direction of the columnar droplet immediately after being ejected from the orifice, and is positioned opposite the columnar droplet with the columnar droplet in between.

[0014] [9] In the micro metal ball manufacturing device of the present invention, it is preferable that the cooling tower further has a stroboscope and a camera arranged opposite each other on either side of the falling micro metal balls, the stroboscope emitting light in synchronization with the vibration of the vibrator, and the camera being capable of capturing images of at least two micro metal balls as they fall.

[0015]

[10] In the micro metal sphere manufacturing apparatus of the present invention, the pressurized gas is preferably a mixture of an inert gas and a reducing gas.

[0016]

[11] In the micro metal sphere manufacturing apparatus of the present invention, the gas sent from the gas supply pipe is preferably a mixture of an inert gas and a reducing gas.

[0017]

[12] In the micro metal sphere manufacturing apparatus of the present invention, it is preferable that the cooling tower further has a cooling gas supply means for supplying a cooling gas therein, and the cooling gas is an inert gas. [Effects of the Invention]

[0018] The manufacturing process for micro-metal spheres using the micro-metal sphere manufacturing device described above begins by ejecting molten metal from a crucible through an orifice using the pressure of a pressurized gas and the vibration of a vibrating rod. The molten metal immediately after ejection from the orifice becomes a columnar droplet, which then separates into micro-metal spheres and falls due to the vibration of the vibrating rod, which is excited by an oscillator. The diameter of the micro-metal spheres depends primarily on the diameter of the orifice, the pressure applied to the molten metal in the crucible, and the amplitude and vibration frequency of the oscillator (vibrating rod). It is easy to control the variations in the diameter of the orifice and the pressure applied to the molten metal in the crucible during the manufacturing process. However, heat from the molten metal is conducted to the oscillator connected to the vibrating rod. Furthermore, the oscillator itself generates heat as it vibrates. This can cause the oscillator to heat up, or temperature differences can occur in different parts of the oscillator, resulting in fluctuations in the amplitude and vibration frequency.

[0019] Therefore, the micro metal sphere manufacturing device uses a cooling air supply means to blow cooling air over the entire exposed circumference of the vibrator, which suppresses temperature rises in the vibrator and temperature differences between different parts of the vibrator, thereby suppressing fluctuations in the vibrator's amplitude and vibration frequency, enabling the stable manufacture of micro metal spheres with high precision and minimal variation. [Brief explanation of the drawings]

[0020] [Figure 1] 1 is an explanatory diagram showing an example of the configuration of a minute metal sphere manufacturing device 1. FIG. DETAILED DESCRIPTION OF THE INVENTION

[0021] Hereinafter, the minute metal sphere manufacturing apparatus 1 and the method for manufacturing minute metal spheres 10 of the present invention will be described with reference to FIG.

[0022] (Configuration of micro metal sphere manufacturing device 1) FIG. 1 is an explanatory diagram showing an example of the configuration of a micro metal sphere manufacturing apparatus 1. The micro metal sphere manufacturing apparatus 1 described in this example is suitable for manufacturing micro metal spheres 10 having a diameter of 100 μm or less, for example, several tens of μm. However, the micro metal sphere manufacturing apparatus 1 can also be used for spheres having a diameter of 100 μm or more. FIG. 1 shows an enlarged view of the micro metal spheres 10.

[0023] The micro metal sphere manufacturing device 1 comprises a crucible 20 and a cooling tower 30. The crucible 20 and the cooling tower 30 are connected vertically. The crucible 20 contains molten metal M. In this example, a metal block (not shown) is placed inside the crucible 20 and melted. However, it is also possible to configure the crucible 20 so that the molten metal M melted outside the crucible 20 is supplied to the crucible 20. The molten metal M discharged from the crucible 20 is separated into micro metal spheres 10 inside the cooling tower 30. The crucible 20 and the cooling tower 30 are connected by an orifice 40 provided in the bottom 24 of the crucible 20.

[0024] The crucible 20 is a cylindrical airtight container, and has a first heater 22 disposed around a sidewall 21 and a second heater 23 disposed on the outer surface of a bottom 24. The first heater 22 and the second heater 23 melt a metal lump (not shown) placed inside the crucible 20 to form molten metal M, and maintain the temperature of the molten metal M. The temperature of the molten metal M is detected by a temperature sensor (not shown) disposed inside the crucible 20, and the detected value is sent to the control device 70. The control device 70 controls the first heater 22 and the second heater 23 based on the detected value, and manages the temperature of the molten metal M.

[0025] An orifice plate 41 with an orifice 40 is fixed to the bottom 24 of the crucible 20. The crucible 20 and the cooling tower 30 are connected by the orifice 40. The orifice plate 41 is made of a precious stone such as diamond, sapphire, or ruby. These precious stones may also be artificial precious stones. While metals and ceramics may be used as the material for the orifice plate 41, it is preferable to use the above-mentioned precious stones, which have excellent heat resistance and durability. Furthermore, when the diameter of the minute metal spheres 10 is set to several tens of micrometers, the diameter (hole diameter) of the orifice 40 is set to be smaller than the diameter of the minute metal spheres 10. While it is difficult to open an orifice 40 with a diameter of several tens of micrometers and a smooth inner surface in metal or ceramic, it is easy to open the orifice 40 in a precious stone.

[0026] The inner surface of the bottom 24 of the crucible 20 is formed in a funnel shape, which allows the molten metal M to easily flow toward the orifice 40. The upper opening of the crucible 20 has the internal space airtight sealed by a lid member 25. The lid member 25 is removably fixed to the crucible 20 when adding metal ingots, which are the raw material for the minute metal spheres 10, or when performing maintenance. A pressurized gas supply port 26 for supplying pressurized gas G1 is provided on the side wall 21 of the crucible 20. The pressurized gas supply port 26 is connected to a pressurized gas supply means 27.

[0027] The pressurized gas G1 is a mixture of an inert gas (e.g., N2) and a reducing gas (e.g., H2). The pressurized gas G1 has a composition that prevents oxidation of the molten metal M inside the crucible 20. This prevents clogging of the orifice 40 due to oxidation of the molten metal M, and makes it possible to improve the sphericity of the microscopic metal spheres 10, which are the finished product.

[0028] The temperature of the pressurized gas G1 is a temperature that does not lower the temperature of the molten metal M inside the crucible 20. The pressurized gas G1 pressurizes the inside of the crucible 20 to a pressure that allows the molten metal M to be discharged from the orifice 40. The pressure and temperature of the pressurized gas supply means 27 are controlled by the control device 70.

[0029] A vibration means 50 is attached above the cover member 25 in the figure. The vibration means 50 is attached to a vibration means support plate 52 fixed to the upper tips of multiple support columns 51 erected on the cover member 25. The vibration means 50 is composed of a vibrator 53 and a vibration rod 54. For example, a piezoelectric element or a magnetostrictive element can be used as the vibrator 53, but it is preferable to use a laminated piezoelectric element which has a wide adjustment range for amplitude and vibration frequency and can obtain a large amplitude. The vibrator 53 is driven and controlled by a control device 70.

[0030] The oscillator 53 is fixed to the oscillator support plate 52. The oscillator rod 54 is fixed in series with the oscillator 53 in the vibration direction and vibrates in the axial direction following the vibration of the oscillator 53, vibrating the molten metal M in the direction of the orifice. The oscillator rod 54 is composed of a shaft portion 55 that penetrates the lid member 25 from the connection portion with the oscillator 53 toward the inside of the crucible 20, and a flange portion 56 that protrudes outward between the oscillator 53 and the lid member 25. Inside the crucible 20, the shaft portion 55 passes through the inside of the molten metal M and extends to the immediate vicinity of the orifice 40. It is preferable to align the axial centers of the oscillator 53, the oscillator rod 54, and the orifice 40.

[0031] A ring-shaped first shim plate 57 and a second shim plate 58 are stacked and interposed between the flange 56 formed on the vibration rod 54 and the lid member 25. The first shim plate 57 is a rigid metal plate that can be easily inserted into and removed from the shaft 55 of the vibration rod 54. The second shim plate 58 is molded from a rubber-based material or a resin material that has elasticity and resilience that does not interfere with the vibration of the vibration rod 54. The second shim plate 58 functions as a gasket to maintain the airtightness of the crucible 20.

[0032] The manufacturing method of the minute metal spheres 10 will be described later. The diameter of the minute metal spheres 10 depends on the diameter of the orifice 40, the pressure applied to the molten metal M in the crucible 20, and the amplitude and vibration frequency of the vibrating rod 54 (vibrator 53). The crucible 20 and cooling tower 30 are periodically cleaned and maintained. During this process, the vibrating rod 54 is disassembled from the crucible 20, which may change the distance d between the tip of the vibrating rod 54 and the orifice 40 (orifice plate 41). Even if the pressure, amplitude, and vibration frequency are constant, a change in the distance d will change the diameter of the minute metal spheres 10. In other words, the distance d affects the reproducibility of the diameter. Therefore, a plurality of first shim plates 57 with different thicknesses are prepared, and the first shim plates 57 are interchangeable to ensure the reproducibility of the distance d during disassembly and reassembly.

[0033] The vibration means 50 has a cooling air blowing means 59 that blows cooling air G2 onto the vibrator 53. The cooling air blowing means 59 blows cooling air G2 onto the vibrator 53 from a cooling air blowing duct 60. In the example shown in FIG. 1, two cooling air blowing ducts 60 are provided. The two cooling air blowing ducts 60 are arranged at positions opposite each other with the vibrator 53 in between. The two cooling air blowing ducts 60 allow the cooling air G2 to be blown uniformly over the entire exposed outer periphery of the vibrator 53. Note that as long as the entire vibrator 53 can be uniformly cooled, one cooling air blowing duct 60 may be provided, or three or more cooling air blowing ducts 60 may be provided. The amount of air blown by the cooling air blowing means 59 is controlled by a control device 70.

[0034] As described above, the diameter of the minute metal balls 10 depends on the diameter of the orifice 40, the pressure applied to the molten metal M in the crucible 20, and the amplitude and vibration frequency of the vibrating rod 54 (vibrator 53). The vibration amplitude and vibration frequency of the vibrator 53, such as a piezoelectric element or a magnetostrictive element, fluctuate with temperature changes, which can cause the diameter of the minute metal balls 10 to fluctuate. Furthermore, the temperature of the vibrator 53 increases when it is continuously driven. Therefore, the temperature increase of the vibrator 53 can be suppressed by blowing cooling air G2 onto the vibrator 53. Furthermore, if a temperature difference occurs within the vibrator 53 itself, for example, the vibrating rod 54 may vibrate radially in addition to axially, which may cause the discharge direction of the molten metal M discharged from the orifice 40 to become unstable. By uniformly blowing cooling air G2 over the entire outer periphery where the vibrator 53 is exposed, it is possible to prevent temperature differences from occurring depending on the location of the vibrator 53.

[0035] The temperature of the vibrator 53 should not fluctuate while the micro metal sphere manufacturing apparatus 1 is in operation. Therefore, the cooling air G2 may be at room temperature, or cooling air G2 cooled by a chiller or the like may be supplied.

[0036] Next, the configuration of the cooling tower 30 will be described. The cooling tower 30 is a cylindrical airtight container connected vertically below the crucible 20, and the upper opening is airtightly sealed by a lid member 31 to seal the internal space. The crucible 20 is buried inside the cooling tower 30 at least up to the position where the second heater 23 is located. In this example, the crucible 20 is detachably fixed to the lid member 31 of the cooling tower 30 using a flange 28 provided on the crucible 20. Note that a configuration may also be adopted in which a flange is provided on the lid member 31 of the cooling tower 30 and the crucible 20 is fixed to the cooling tower 30 in cooperation with the flange 28. The crucible 20 and the cooling tower 30 may be fixed to each other by a detachable means other than flange fixing. Note that the lid member 31 is detachably fixed to the cooling tower 30.

[0037] The cooling tower 30 has a heating gas supply pipe 33 that supplies a heating gas G3 to maintain the temperature of the molten metal M immediately after it is discharged from the orifice 40. The molten metal M becomes columnar droplets 11 immediately after it is discharged from the orifice 40. The heating gas G3 is a mixture of an inert gas (e.g., N2) and a reducing gas (e.g., H2). The heating gas G3 heats the columnar droplets 11 to a temperature at which they can be separated and dropped into minute metal spheres 10 by the vibration of the vibrating rod 54. Furthermore, it is preferable to use a mixture of an inert gas and a reducing gas as the heating gas G3 to prevent the surfaces of the columnar droplets 11 from oxidizing, which would hinder their separation into minute metal spheres 10, and to prevent deterioration of the sphericity of the minute metal spheres 10 due to oxidation.

[0038] The heating gas G3 is supplied from the heating gas supply means 34 via the heating gas supply pipe 33. The heating gas supply pipe 33 is disposed in close proximity to the second heater 23 so that the heating gas G3 is heated by the radiant heat of the second heater 23. In this configuration, the heating gas G3 supplied from the heating gas supply means 34 may be room temperature gas. However, the heating gas G3 may be preheated to a predetermined temperature by the heating gas supply means 34. The interior of the cooling tower 30 is filled with a cooling gas G4 that cools the minute metal spheres 10 that separate from the columnar droplets 11 and fall. Therefore, although the temperature of the heating gas G3 may decrease, the temperature can be maintained by the radiant heat of the second heater 23. The temperature of the columnar droplets 11 is detected by a temperature sensor (not shown) disposed in close proximity to the columnar droplets 11, and the detected value is sent to the control device 70. The control device 70 controls the heating gas supply means 34 based on the detected value, and adjusts the flow rate of the heating gas G3 as appropriate.

[0039] An electrode unit 35 is disposed at a position spaced apart to the side of the columnar droplet 11 in the direction of discharge immediately after it is discharged from the orifice 40. In the example shown in FIG. 1 , the electrode units 35 are disposed at positions facing each other across the columnar droplet 11. The electrode units 35 are set to a positive high potential by a voltage supply from a charging means 36. The negative potential of the charging means 36 is connected to the molten metal M in the crucible 20. Between the electrode unit 35 and the columnar droplet 11 is a gas mixture consisting mainly of a heating gas G3 and a cooling gas G4. This gas mixture can be considered a dielectric, and therefore the columnar droplet 11 is at a negative potential. In other words, the minute metal spheres 10 separated from the columnar droplet 11 are at a negative potential, and the electrical repulsion prevents the minute metal spheres 10, still in a high temperature state, from coalescing.

[0040] The electrode unit 35 extends to a range that includes the columnar droplet 11 and the minute metal ball 10 immediately after it has separated from the columnar droplet 11 into a solid. The two electrode units 35 face each other at the same distance from the columnar droplet 11. Therefore, the forces with which the two opposing electrode units 35 attract the minute metal ball 10 are opposite to each other, and the attraction forces are canceled out. Furthermore, because the falling speed of the minute metal ball 10 is fast, the minute metal ball 10 passes through the electrode unit 35 before reaching the electrode unit 35. Therefore, the minute metal ball 10 is not attracted to the electrode unit 35. Note that, because the attraction forces of the two electrode units 35 toward the minute metal ball are small, the distances between the electrode units 35 and the columnar droplet 11 do not need to be exactly the same. The electrode unit 35 may be cylindrical, with the columnar droplet 11 at its center.

[0041] The columnar droplets 11 are separated into minute metal spheres 10 by the vibration of the vibrating rod 54. The cooling tower 30 has a cooling gas supply pipe 37 on the bottom side that supplies cooling gas G4. The cooling gas G4 is an inert gas (e.g., N2) that cools the minute metal spheres 10 and solidifies them so that they do not deform. The cooling gas G4 is supplied from a cooling gas supply means 38. The internal temperature of the cooling tower 30 is detected by a temperature sensor (not shown), and the detected value is sent to a control device 70. The control device 70 controls the cooling gas supply means 38 that supplies the cooling gas based on the detected value, and appropriately adjusts the temperature and air volume of the cooling gas G4.

[0042] The cooling gas G4 can also be a mixture of an inert gas (e.g., N2) and a reducing gas (e.g., H2). The micro metal spheres 10 do not need to contain a reducing gas, as long as they can prevent surface oxidation. For the micro metal spheres 10 to separate from the columnar droplets 11 and be recovered in a stable state as micro metal spheres 10, for example, the height of the cooling tower 30 must be approximately 1.5 m when the micro metal spheres 10 are 100 μm in size. This increases the volume of the cooling tower 30. Therefore, by using a mixture of cooling gas G4 containing an expensive reducing gas but using only an inexpensive inert gas, it is possible to reduce costs.

[0043] The temperature of the cooling gas G4 may be room temperature. The pressure inside the cooling tower 30 may be adjusted to be higher than atmospheric pressure in order to appropriately control the temperature gradient derived from the temperature and the falling speed of the minute metal balls 10 from the columnar droplets 11 until they become stable (a state where they are not deformed by falling). In this way, the height of the cooling tower 30 can be reduced.

[0044] The cooling tower 30 has a camera 43 and a stroboscope 44 arranged on either side of the minute metal balls 10 falling below the columnar droplets 11, for capturing images of the minute metal balls 10. The stroboscope 44 emits light in synchronization with the vibration frequency of the oscillator 53. The camera 43 captures still images of the minute metal balls 10 as they fall. The captured still image data is sent to a control device 70, which detects the ball diameter through image processing. The control device 70 then compares the detected ball diameter with a preset target ball diameter and adjusts the amplitude and vibration frequency of the oscillator 53 to correct the difference. Although not shown, the stroboscope 44 preferably has a collimating lens to emit parallel light.

[0045] The diameter of the minute metal balls 10 can be measured by capturing images of two consecutively falling minute metal balls 10 and detecting the distance between these minute metal balls 10. Since it is known that there is a correlation between the distance between two minute metal balls 10 and their diameter, it is possible to detect the diameter by formulating the relationship between the distance and the diameter in advance during the pre-manufacturing stage.

[0046] A non-magnetic collection receptacle 45 is disposed at the bottom of the cooling tower 30 to collect the hardened minute metal balls 10. Although not shown, the cooling tower 30 has an opening in the side wall 32 or bottom plate 46 for collecting the collection receptacle 45. If the minute metal balls 10 are made of a non-magnetic material, when they are collected in the collection receptacle 45, the negative charge of the minute metal balls 10 is naturally released, and they become "uncharged."

[0047] (Method of manufacturing minute metal balls 10) Next, a method for manufacturing minute metal spheres 10 using minute metal sphere manufacturing apparatus 1 will be described. In the method for manufacturing minute metal spheres 10, first, metal lump placed in crucible 20 is melted to form molten metal M, and molten metal M is pressurized with pressurized gas G1 while oscillator 53 applies high-frequency vibration to vibrating rod 54, causing molten metal M to be discharged from orifice 40. The molten metal M discharged from orifice 40 drips in the form of columnar droplets 11. The columnar droplets 11 are separated into individual minute metal spheres 10 by the vibration applied by vibrating rod 54, and fall. Then, as the molten metal M falls down cooling tower 30, the surface tension of the molten metal M causes it to become spherical, and it is cooled to form minute metal spheres 10 with high sphericity.

[0048] The diameter of the minute metal spheres 10 is determined by the main conditions, such as the melting temperature and viscosity of the molten metal M, the internal pressure of the crucible 20, the diameter of the orifice 40, the distance d between the vibrating rod 54 and the orifice 40, and the amplitude and vibration frequency of the vibrator 53 (i.e., the vibrating rod 54). These conditions must be appropriately combined, and the conditions are set in advance through pre-manufacturing or the like. Similarly to the above conditions, the distance between the columnar droplet 11 and the electrode part 35 and the extension length of the electrode part 35 are set to optimal conditions through pre-manufacturing or the like. Any changes in the main conditions during manufacturing are detected by sensors or the like and fed back to the control device 70, which then controls each main condition.

[0049] Since the viscosity of the molten metal M is determined by the material and is influenced by the melting temperature, the internal temperature of the crucible 20 is constantly detected and the first heater 22 and second heater 23 are controlled to adjust the melting temperature. The pressure of the pressurized gas G1 and the amplitude and vibration frequency of the oscillator 53 are determined by finding an appropriate combination based on the cross-sectional area and discharge speed of the columnar droplets 11. Note that, since it is known that the hole diameter of the orifice 40 is correlated with the diameter of the minute metal spheres 10, the hole diameter may be determined in advance, or multiple orifice plates 41 with different hole diameters may be prepared in advance and replaced with one with the optimal hole diameter.

[0050] The amplitude and vibration frequency of the vibrator 53 fluctuate due to temperature changes during operation of the micro metal sphere manufacturing apparatus 1. Therefore, the temperature fluctuations of the vibrator 53 can be suppressed by blowing cooling air G2 around the entire periphery of the exposed part.

[0051] The distance d between the vibrating rod 54 and the orifice 40 does not change while the micro metal sphere manufacturing apparatus 1 is in operation, but it is disassembled for maintenance of the crucible 20 and the cooling tower 30. At that time, the distance d may change. Therefore, a first shim plate 57 is interposed between the flange 56 of the vibrating rod 54 and the lid member 25 of the cooling tower 30 to adjust the distance d to an initial setting value, and multiple first shim plates 57 with different thicknesses are prepared in advance and replaced to adjust the distance d.

[0052] Molten metal M is discharged from an orifice 40 into a cooling tower 30 in the form of columnar droplets 11, and is separated into minute metal spheres 10 by high-frequency vibration of a vibrating rod 54. The cooling tower 30 cools the separated minute metal spheres 10. Therefore, if the temperature of the columnar droplets 11 drops, they may no longer be able to separate into minute metal spheres 10. Therefore, a heating gas G3 is heated by a second heater 23 and sprayed onto the columnar droplets 11 to maintain the temperature at which the columnar droplets 11 can be separated into minute metal spheres 10. The heating gas G3 is a mixture of an inert gas (e.g., N2) and a reducing gas (e.g., H2), and prevents oxidation of the columnar droplets 11.

[0053] The minute metal spheres 10 separated from the columnar droplets 11 fall while being cooled in the cooling tower 30. When they first fall, the minute metal spheres 10, which are not sufficiently cooled, may come into contact and coalesce. However, by placing an electrode 35 on the side of the columnar droplets 11 and charging them with a high voltage of positive potential, the columnar droplets 11 are made negatively charged. The minute metal spheres 10 separated from the columnar droplets 11 repel each other, making it possible to prevent them from coalescing.

[0054] The interior of the cooling tower 30 is filled with cooling gas G4 from below. Heated heating gas G3 is sprayed onto the columnar droplets 11 at the top of the cooling tower 30. This creates a temperature gradient in which the temperature is higher at the top of the cooling tower 30 and lower toward the bottom. The minute metal spheres 10 separated from the columnar droplets 11 become spherical at the top due to surface tension and gradually cool as they fall downward, becoming minute metal spheres 10 with high sphericity. The cooling gas G4 is an inert gas (e.g., N2) and can prevent the columnar droplets 11 from oxidizing.

[0055] As described above, the method for producing minute metal spheres 10 appropriately combines the melting temperature and viscosity of molten metal M, the internal pressure of crucible 20, the diameter of orifice 40, the distance d between vibrating rod 54 and orifice 40, and the amplitude and vibration frequency of vibrator 53 (i.e., vibrating rod 54). However, the diameter of minute metal spheres 10 may vary. Therefore, the method for producing minute metal spheres 10 includes a step of detecting the diameter of the spheres as they separate from columnar droplet 11 and fall. The diameter is measured using optical means including stroboscope 44 and camera 43. Camera 43 captures a still image of the falling minute metal spheres 10, and control device 70 calculates the diameter through image processing. Control device 70 adjusts the amplitude and vibration frequency of vibrator 53 based on the difference between the actually measured diameter data and the target diameter. The control device 70 also adjusts the pressure of the pressurized gas G1, the temperature of the molten metal M, the temperatures and air volumes of the cooling air G2 and the heating gas G3, etc., based on the detected values.

[0056] As explained above, the micro metal sphere manufacturing apparatus 1 has a cooling air blowing means 59 that blows cooling air G2 around the entire circumference of the exposed portion of the vibrator 53. By blowing cooling air G2 onto the vibrator 53, the cooling air blowing means 59 can suppress the temperature rise of the vibrator 53 and the temperature difference between different parts of the vibrator 53. This makes it possible to suppress fluctuations in the amplitude and vibration frequency of the vibrator 53, and enables the stable manufacture of micro metal spheres 10 with high precision and small variation, i.e., a narrow particle size distribution.

[0057] The crucible 20 and the cooling tower 30 are detachably fixed. This allows the crucible 20 and the cooling tower 30 to be separated for easy maintenance. In addition, the lid member 25 of the crucible 20 is detachably fixed to the crucible 20. This allows the crucible 20 to easily be charged with metal ingots, which are the raw material for the micro metal spheres 10, and to easily perform maintenance such as cleaning the interior. In addition, the lid member 31 of the cooling tower 30 is detachably fixed to the cooling tower 30. This allows the cooling tower 30 to easily adjust the position of the electrode unit 35, adjust the relative positions of the camera 43 and the stroboscope 44, and to easily perform maintenance such as cleaning.

[0058] When the distance d between the tip of the vibrating rod 54 and the orifice 40 changes, the diameter of the minute metal balls 10 also changes. Even if the other conditions described above are kept constant, fluctuations in the distance d during maintenance of the crucible 20 or the cooling tower 30 can affect the reproducibility of the ball diameter. The vibrating rod 54 is supported between the vibrator 53 and the lid member 31 of the cooling tower 30. A ring-shaped rigid first shim plate 57 and an elastic second shim plate 58, through which the shaft 55 of the vibrating rod 54 passes, are stacked and interposed between the flange 56 of the vibrating rod 54 and the lid member 31. Therefore, by preparing multiple types of first shim plates 57 with different thicknesses and replacing the first shim plate 57 with one of the appropriate thickness, the reproducibility of the distance d can be ensured.

[0059] The orifice 40 is formed in an orifice plate 41 made of a precious stone such as diamond, sapphire, or ruby. By using a precious stone for the orifice plate 41, it is possible to form an orifice 40 with a small hole diameter and a smooth inner surface, and further to improve the heat resistance and durability of the orifice 40.

[0060] The crucible 20 has a first heater 22 arranged around the sidewall 21 and a second heater 23 arranged at a position surrounding the outer periphery of the orifice plate 41 at the bottom 24, and melts the metal pieces (not shown) that are introduced into the crucible 20. The crucible 20 is buried up to a position where the second heater 23 enters the interior of the cooling tower 30. The heating of the heating gas G3 by radiant heat from the second heater 23 makes it possible to maintain the columnar droplets 11 discharged from the orifice 40 at a temperature at which they can be separated into minute metal spheres 10.

[0061] The cooling tower 30 has a heating gas supply pipe 33 that blows heating gas G3 onto the columnar droplets 11 immediately after they are discharged from the orifice 40. The heating gas supply pipe 33 is disposed at a position where the temperature of the heating gas G3 can be increased by radiant heat from the second heater 23. This makes it possible to maintain the heating gas G3 at a temperature that allows the minute metal spheres 10 to be separated from the columnar droplets 11, even inside the cooling tower 30.

[0062] Cooling tower 30 has charging means 36 equipped with electrode portion 35 for applying an electric repulsive force to minute metal spheres 10 dripping (falling) from crucible 20. Minute metal spheres 10 separated from columnar droplet 11 are charged by electrode portion 35 to a negative potential, and the electric repulsive force prevents minute metal spheres 10, which are still in a high temperature state, from coalescing together.

[0063] The electrode part 35 is disposed at a position spaced apart from the side of the columnar droplet 11 in the direction of discharge immediately after it is discharged from the orifice 40. The electrode part 35 is also disposed within the continuous length range of the columnar droplet 11. This prevents the minute metal balls 10 that separate from the columnar droplet 11 and fall while being negatively charged from being attracted to the electrode part 35, which is at a positive potential.

[0064] The cooling tower 30 has a stroboscope 44 and a camera 43 arranged opposite each other across the falling micro-metallic balls 10. The stroboscope 44 emits light in synchronization with the vibration of the oscillator 53, and the camera 43 captures still images of the micro-metallic balls 10 as they fall. The still image data is sent to the control device 70, where it can be detected as the ball diameter through image processing. The control device 70 then compares the detected ball diameter with a preset target ball diameter and adjusts the amplitude and vibration frequency of the oscillator 53 to correct for the difference. This enables the stable production of micro-metallic balls 10 with high precision and minimal diameter variation. The control device 70 also has the function of controlling the pressurized gas supply means 27 and the heating gas supply means 34 for ball diameter management.

[0065] The pressurized gas G1 that pressurizes the inside of the crucible 20 is a mixture of an inert gas and a reducing gas. If the molten metal M oxidizes, its fluidity may deteriorate, causing clogging of the orifice 40, and the sphericity of the microscopic metal spheres 10 formed by surface tension may decrease. Therefore, by using a mixture of an inert gas and a reducing gas as the pressurized gas G1, it is possible to prevent oxidation of the molten metal M.

[0066] For the same reason, the heating gas G3 is a mixture of an inert gas and a reducing gas, which prevents oxidation of the columnar droplets 11 discharged from the crucible 20 and improves the separation of the minute metal spheres 10 and the sphericity of the minute metal spheres 10.

[0067] The cooling tower 30 has a cooling gas supply means 38 for supplying a cooling gas G4 therein. By using an inert gas as the cooling gas G4, the surfaces of the falling minute metal balls 10 can be prevented from being oxidized.

[0068] According to the minute metal sphere manufacturing device 1 described above, it is possible to stably manufacture minute metal spheres 10 with high precision and small variations in sphere diameter. [Explanation of symbols]

[0069] REFERENCE SIGNS LIST 1...micro metal sphere manufacturing apparatus, 10...micro metal sphere, 11...columnar droplet, 20...crucible, 21, 32...side wall portion, 22...first heater, 23...second heater, 24...bottom portion of crucible, 25, 31...lid member, 26...pressurized gas supply port, 27...pressurized gas supply means, 28...flange, 30...cooling tower, 33...heating gas supply pipe, 34...heating gas supply means, 35...electrode portion, 36...charging means, 37...cooling gas supply Supply pipe, 38...cooling gas supply means, 40...orifice, 41...orifice plate, 43...camera, 44...stroboscope, 53...vibrator, 54...vibration rod, 55...shaft portion, 56...flange portion, 57...first shim plate, 58...second shim plate, 59...cooling air blowing means, 60...cooling air blowing pipe, 70...control device, G1...pressurized gas, G2...cooling air, G3...heating gas, G4...cooling gas, M...molten metal

Claims

1. a crucible for containing molten metal; a cooling tower vertically connected to the crucible; an orifice provided at the bottom of the crucible and communicating the crucible with the cooling tower; a pressurized gas supply means for supplying pressurized gas to the crucible; a vibration rod extending from the outside of the crucible through the inside of the molten metal to a position immediately adjacent to the orifice; an oscillator arranged outside the crucible and vibrating the vibration rod in the axial direction; a cooling air blowing means for blowing cooling air around the entire periphery of the exposed portion of the vibrator; have, A micro metal sphere manufacturing device.

2. 2. The micro metal sphere manufacturing apparatus according to claim 1, The crucible and the cooling tower are detachably fixed to each other. A micro metal sphere manufacturing device.

3. 2. The micro metal sphere manufacturing apparatus according to claim 1, The crucible further includes a cover member for sealingly fixing an internal space for accommodating the molten metal, the vibration rod has a flange portion extending in an outer circumferential direction between the vibrator and the cover member, a first shim plate having a ring shape and having rigidity, through which a shaft portion of the vibration rod passes, and a second shim plate having elasticity are stacked and interposed between the flange portion and the cover member; A micro metal sphere manufacturing device.

4. 2. The micro metal sphere manufacturing apparatus according to claim 1, The orifice is formed in an orifice plate made of precious stone. A micro metal sphere manufacturing device.

5. 2. The micro metal sphere manufacturing apparatus according to claim 1, the crucible has a heater for producing the molten metal; the heater comprises a first heater disposed around the side wall of the crucible and a second heater disposed at a position surrounding the outer periphery of the bottom orifice plate; The crucible is immersed at least to a position where the second heater enters the interior of the cooling tower. A micro metal sphere manufacturing device.

6. 6. The micro metal sphere manufacturing apparatus according to claim 5, the cooling tower further includes a heating gas supply pipe for blowing a heating gas onto the molten metal in the form of columnar droplets immediately after being discharged from the orifice; the heating gas supply pipe is disposed at a position where the heating gas can be heated to a temperature at which minute metal spheres can be separated from the columnar droplets by radiant heat from the second heater. A micro metal sphere manufacturing device.

7. 2. The micro metal sphere manufacturing apparatus according to claim 1, The cooling tower further includes a charging means having an electrode portion for applying an electric repulsive force to the minute metal balls dropping from the crucible into the cooling tower. A micro metal sphere manufacturing device.

8. 8. The micro metal sphere manufacturing apparatus according to claim 7, the electrode portions are spaced apart from each other on either side of the ejection direction of the columnar droplet immediately after being ejected from the orifice, and are arranged at positions facing each other with the columnar droplet in between. A micro metal sphere manufacturing device.

9. 2. The micro metal sphere manufacturing apparatus according to claim 1, The cooling tower further includes a stroboscope and a camera disposed opposite each other with the falling minute metal balls interposed therebetween, the stroboscope emits light in synchronization with the vibration of the vibrator; The camera is capable of capturing an image of the minute metal balls while they are falling. A micro metal sphere manufacturing device.

10. 2. The micro metal sphere manufacturing apparatus according to claim 1, The pressurized gas is a mixture of an inert gas and a reducing gas. A micro metal sphere manufacturing device.

11. 7. The micro metal sphere manufacturing apparatus according to claim 6, The heating gas sent by the heating gas supply pipe is a mixed gas of an inert gas and a reducing gas. A micro metal sphere manufacturing device.

12. 2. The micro metal sphere manufacturing apparatus according to claim 1, The cooling tower further includes a cooling gas supply means for supplying a cooling gas therein, The cooling gas is an inert gas. A micro metal sphere manufacturing device.

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