Micro-metal ball manufacturing device

Abstract

To provide a micro-metal sphere manufacturing apparatus capable of stably producing micro-metal spheres with high precision and small variations in sphere diameter. [Solution] The micro-metal ball manufacturing apparatus 1 has a crucible 20 for containing molten metal M and a cooling tower 30 connected vertically to the crucible 20. An orifice 40 is provided at the bottom 24 of the crucible 20, connecting the crucible 20 and the cooling tower 30. The crucible 20 has a pressurized gas supply means 70 for supplying pressurized gas G1. The micro-metal ball manufacturing apparatus 1 has an excitation rod 54 that extends from outside the crucible 20 through the inside of the molten metal M to just before the orifice 40, and a vibrator 53 that is positioned outside the crucible 20 and vibrates the excitation rod 54 in the axial direction. The cooling air blowing means 70 blows cooling air around the entire circumference of the exposed part of the vibrator 53.

Description

Technical Field

[0001] The present invention relates to a micro metal sphere manufacturing apparatus.

Background Art

[0002] Micro metal spheres such as solder balls used for joining electronic elements of semiconductor devices and rigid balls for micro ball bearings used for micromachines, etc., are required to have high sphericity and small variation in ball diameter (narrow particle size distribution). As a method for manufacturing such micro metal spheres, pressure is applied to molten metal in a crucible, and the molten metal is discharged into a cooling tower from an orifice provided at the bottom of the crucible. A method of separating the discharged molten metal into micro metal spheres by the vibration of a vibration rod is known (for example, see Patent Document 1). According to such a manufacturing method, it becomes possible to form micro metal spheres with high sphericity.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] Incidentally, the size (sphere diameter) of the microscopic metal spheres depends on the diameter of the orifice, the pressure applied to the molten metal in the crucible, the amplitude of the excitation rod, and the vibration frequency. The excitation rod is vibrated axially by an oscillator such as a piezoelectric element or a magnetostrictive element. These oscillators have temperature characteristics. For example, when the oscillator gets hot, the amplitude decreases and the sphere diameter becomes smaller. Since the excitation rod is immersed in the molten metal, it becomes the same temperature as the molten metal. The oscillator is located on the outside of the crucible. However, heat from the molten metal is conducted to the oscillator connected to the excitation rod. Furthermore, the oscillator generates heat itself through vibration. Due to these factors, the oscillator becomes hot, or temperature differences occur depending on the part of the oscillator, causing fluctuations in amplitude and vibration frequency. Therefore, it is difficult to stably manufacture microscopic metal spheres of the desired diameter.

[0005] Therefore, the present invention was made to solve these problems and aims to realize a micro-metal sphere manufacturing apparatus that can stably produce micro-metal spheres with high precision and small variation in sphere diameter. [Means for solving the problem]

[0006] [1] The present invention provides a micro-metal ball manufacturing apparatus comprising: a crucible for containing molten metal; a cooling tower connected vertically to the crucible; an orifice provided at the bottom of the crucible and connecting the crucible and the cooling tower; a pressurized gas supply means for supplying pressurized gas to the crucible; an excitation rod extending from outside the crucible through the inside of the molten metal to just before the orifice; a vibrator positioned outside the crucible and vibrating the excitation 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 vibrator.

[0007] [2] In the micrometal ball 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 ball manufacturing apparatus of the present invention, it is preferable that the crucible further has a lid member that airtightly fixes the internal space containing the molten metal, the vibrating rod has a flange portion that protrudes outward in the outer direction between the vibrator and the lid member, and a ring-shaped rigid first shim plate and an elastic second shim plate are laminated and interposed between the flange portion and the lid member, through which the shaft portion of the vibrating rod passes.

[0009] [4] In the micrometal sphere manufacturing apparatus of the present invention, it is preferable that the orifice is formed on an orifice plate made of a precious stone.

[0010] [5] In the micrometal ball manufacturing apparatus of the present invention, the crucible has a heater for generating the molten metal, and the heater consists of a first heater positioned around the side wall of the crucible and a second heater positioned around the outer circumference of the orifice plate at the bottom, and the crucible is preferably embedded to the extent that at least the second heater enters the interior of the cooling tower.

[0011] [6] In the micro-metal sphere manufacturing apparatus of the present invention, the cooling tower further comprises a heating gas supply pipe for blowing heating gas onto the molten metal, which is in the form of columnar droplets immediately after being discharged from the orifice, and the heating gas supply pipe is preferably positioned to raise the heating gas to a temperature at which it is possible to separate the micro-metal spheres from the columnar droplets by the radiant heat of the second heater.

[0012] [7] Preferably, the micrometal ball manufacturing apparatus of the present invention further includes a charging means equipped with an electrode for applying an electrical repulsive force to the micrometal balls that are dropped from the crucible into the cooling tower.

[0013] [8] In the micrometal sphere manufacturing apparatus of the present invention, it is preferable that the electrode portion is spaced apart to the side in the discharge direction of the columnar droplet immediately after it has been discharged from the orifice, and is positioned opposite to the columnar droplet on either side.

[0014] [9] Preferably, the micrometal sphere manufacturing apparatus of the present invention further includes a stroboscope and a camera positioned inside the cooling tower opposite each other with the falling micrometal spheres in between, wherein the stroboscope emits light in synchronization with the vibration of the oscillator, and the camera is capable of imaging at least two micrometal spheres in the process of falling.

[0015]

[10] In the micrometal ball manufacturing apparatus of the present invention, it is preferable that the pressurized gas is a mixture of an inert gas and a reducing gas.

[0016]

[11] In the micrometal ball manufacturing apparatus of the present invention, it is preferable that the gas supplied by the gas supply pipe is a mixture of an inert gas and a reducing gas.

[0017]

[12] In the micrometal ball manufacturing apparatus of the present invention, the cooling tower further comprises a cooling gas supply means for supplying a cooling gas to the interior, and it is preferable that the cooling gas is an inert gas. [Effects of the Invention]

[0018] The manufacturing of micro-metal spheres using the micro-metal sphere manufacturing apparatus described above begins by ejecting molten metal from a crucible through an orifice using the pressure of a pressurized gas and the vibration of an excitation rod. Immediately after ejection from the orifice, the molten metal forms columnar droplets, which are then separated into micro-metal spheres and fall due to the vibration of the excitation rod, which is excited by a vibrator. The diameter of the micro-metal spheres depends mainly on the diameter of the orifice, the pressure applied to the molten metal in the crucible, and the amplitude and vibration frequency of the vibrator (excitation rod). The diameter of the orifice and the pressure applied to the molten metal in the crucible can be easily controlled during the manufacturing process. However, heat from the molten metal is conducted to the vibrator connected to the excitation rod. Furthermore, the vibrator generates heat itself through vibration. As a result, the vibrator becomes hot, or temperature differences may occur depending on the part of the vibrator, causing fluctuations in amplitude and vibration frequency.

[0019] Therefore, the micro metal sphere manufacturing apparatus blows cooling air over the entire circumference of the exposed vibrator by means of the cooling air supply means. By doing so, it is possible to suppress the rise in the temperature of the vibrator and the temperature difference due to the parts of the vibrator, so that it becomes possible to suppress fluctuations in the amplitude and vibration frequency of the vibrator, and it becomes possible to stably manufacture micro metal spheres with high precision and small variations.

Brief Description of the Drawings

[0020] [Figure 1] It is an explanatory diagram showing an example of the configuration of the micro metal sphere manufacturing apparatus 1.

Embodiments for Carrying Out the Invention

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

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

[0023] The micro metal sphere manufacturing apparatus 1 is composed of a crucible 20 and a cooling tower 30. The crucible 20 and the cooling tower 30 are connected in the vertical direction. The crucible 20 contains molten metal M. In this example, a metal block (not shown) is put into the crucible 20 and melted. However, it is also possible to adopt a configuration in which 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 at the bottom 24 of the crucible 20.

[0024] The crucible 20 is a cylindrical airtight container, with a first heater 22 disposed around the side wall portion 21 and a second heater 23 disposed on the outer surface of the bottom portion 24. The first heater 22 and the second heater 23 melt a metal mass (not shown) introduced into 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 to manage the temperature of the molten metal M.

[0025] An orifice plate 41 with an orifice 40 opened is fixed to the bottom portion 24 of the crucible 20. The crucible 20 and the cooling tower 30 are connected through the orifice 40. The orifice plate 41 is formed of a precious stone such as diamond, sapphire or ruby. It should be noted that artificial precious stones can be adopted for these precious stones. As the material of the orifice plate 41, metal or ceramic is also conceivable, but it is preferable to adopt the above precious stones with excellent heat resistance and durability. Further, when the diameter of the fine metal balls 10 is several tens of μm, the diameter (hole diameter) of the orifice 40 is set smaller than the diameter of the fine metal balls 10. It is difficult to open an orifice 40 with a diameter of several tens of μm and a smooth inner surface in metal or ceramic, but it is possible to easily open the orifice 40 with a precious stone.

[0026] The inner surface of the bottom portion 24 of the crucible 20 is formed in a funnel shape, so that the molten metal M can easily flow toward the orifice 40. The upper opening of the crucible 20 is airtightly sealed by a lid member 25. The lid member 25 is detachably fixed to the crucible 20 during the introduction and maintenance of the metal mass, which is the raw material of the fine metal balls 10. A pressurized gas supply port 26 for supplying a pressurized gas G1 is provided in the side wall portion 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 composition of the pressurized gas G1 is designed to prevent 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 finished product, the minute metal spheres 10.

[0028] The temperature of the pressurized gas G1 is such that it 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] An excitation means 50 is mounted on the upper part of the lid member 25 as shown in the figure. The excitation means 50 is attached to an excitation means support plate 52 which is fixed to the upper ends of a plurality of support columns 51 erected on the lid member 25. The excitation means 50 consists of a vibrator 53 and an excitation rod 54. The vibrator 53 can be, for example, a piezoelectric element or a magnetostrictive element, but it is preferable to use a laminated piezoelectric element that has a wide range of amplitude and vibration frequency adjustment and can obtain a large amplitude. The vibrator 53 is driven and controlled by a control device 70.

[0030] The vibrator 53 is fixed to the vibration means support plate 52. The vibration rod 54 is fixed in series with the vibrator 53 in the direction of vibration, and vibrates axially in accordance with the vibration of the vibrator 53, thereby exciting the molten metal M in the direction of the orifice. The vibration rod 54 consists of a shaft portion 55 that penetrates the lid member 25 from the connection point with the vibrator 53 toward the inside of the crucible 20, and a flange portion 56 that protrudes outward between the vibrator 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 just before the orifice 40. It is preferable to align the axial centers of the vibrator 53, the vibration rod 54, and the orifice 40.

[0031] Between the flange portion 56 formed on the vibration rod 54 and the lid member 25, a ring-shaped first shim plate 57 and a second shim plate 58 are interposed in a stacked state. The first shim plate 57 is a rigid metal plate that can be easily inserted into and removed from the shaft portion 55 of the vibration rod 54. The second shim plate 58 is molded from a rubber-based or resin material that has elasticity and resilience that does not hinder 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 for the micro-metal spheres 10 will be described later, but the diameter of the micro-metal spheres 10 depends on the hole 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 excitation rod 54 (vibrator 53). Incidentally, the crucible 20 and cooling tower 30 are periodically cleaned and maintained. At this time, the excitation rod 54 is disassembled from the crucible 20, and the distance d between the tip of the excitation rod 54 and the orifice 40 (orifice plate 41) may change. Even if the pressure, amplitude and vibration frequency are constant, the diameter of the micro-metal spheres 10 will change if the distance d changes. In other words, the distance d affects the reproducibility of the sphere diameter. Therefore, multiple types of first shim plates 57 with different thicknesses are prepared, and the first shim plates 57 are replaced to ensure the reproducibility of the distance d during disassembly and reassembly.

[0033] The excitation means 50 includes a cooling air blowing means 59 that blows cooling air G2 onto the transducer 53. The cooling air blowing means 59 blows cooling air G2 onto the transducer 53 from a cooling air blowing pipe 60. In the example shown in Figure 1, two cooling air blowing pipes 60 are provided. The two cooling air blowing pipes 60 are positioned opposite each other, with the transducer 53 in between. The two cooling air blowing pipes 60 allow cooling air G2 to be blown uniformly over the entire exposed outer circumference of the transducer 53. Note that as long as the entire transducer 53 can be cooled uniformly, there may be one cooling air blowing pipe 60, or three or more may be arranged. The amount of air blown by the cooling air blowing means 59 is controlled by the control device 70.

[0034] As previously described, the diameter of the micro-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 excitation rod 54 (vibrator 53). The amplitude and vibration frequency of the vibrator 53, such as a piezoelectric element or magnetostrictive element, fluctuate with temperature changes, which can cause the diameter of the micro-metal spheres 10 to fluctuate. Furthermore, if the vibrator 53 is driven continuously, its own temperature will rise. Therefore, the temperature rise of the vibrator 53 can be suppressed by blowing cooling air G2 onto it. Also, if temperature differences occur in different parts of the vibrator 53, for example, radial vibration may occur in the excitation rod 54 in addition to axial vibration, which can 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 circumference where the vibrator 53 is exposed, it is possible to prevent temperature differences from occurring in different parts of the vibrator 53.

[0035] The temperature of the oscillator 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 it may be cooled by a chiller or the like before being 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 its upper opening is airtightly sealed by a lid member 31. The crucible 20 is embedded in the cooling tower 30 to a position where at least 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. Alternatively, a flange may be provided on the lid member 31 of the cooling tower 30, and the crucible 20, which cooperates with the flange 28, may be fixed to the cooling tower 30. Other means of attachment and detachment may be used to fix the crucible 20 to the cooling tower 30. 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 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 onto the minute metal spheres 10 by the vibration of the vibration rod 54. Furthermore, it is preferable to use a mixture of an inert gas and a reducing gas for the heating gas G3 in order to prevent oxidation of the surface of the columnar droplets 11, which would hinder their separation onto the 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 positioned immediately adjacent 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 at room temperature. However, it may be preheated to a predetermined temperature by the heating gas supply means 34. The inside of the cooling tower 30 is filled with cooling gas G4 that cools the tiny metal spheres 10 that separate from the columnar molten droplets 11 and fall, so the temperature of the heating gas G3 may decrease, but the temperature can be maintained by the radiant heat of the second heater 23. The temperature of the columnar molten droplets 11 is detected by a temperature sensor (not shown) positioned immediately adjacent to the columnar molten 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 airflow rate of the heating gas G3 as appropriate.

[0039] An electrode section 35 is positioned laterally and spaced apart from the discharge direction of the columnar molten droplet 11 immediately after it is discharged from the orifice 40. In the example shown in Figure 1, the electrode section 35 is positioned opposite the columnar molten droplet 11 (facing each other). The electrode section 35 becomes positively high-potential due to the voltage supplied from the charging means 36. The negative potential of the charging means 36 is connected to the molten metal M in the crucible 20. The space between the electrode section 35 and the columnar molten droplet 11 is a mixed gas of cooling gas G4 mainly composed of heating gas G3, and since this mixed gas can be considered a dielectric, the columnar molten droplet 11 becomes negatively potential. That is, the minute metal spheres 10 separated from the columnar molten droplet 11 become negatively potential, and electrical repulsion prevents the minute metal spheres 10, which are still at a high temperature, from joining together.

[0040] The electrode section 35 extends to include the columnar droplet 11 and the minute metal spheres 10 immediately after they have been separated from the columnar droplet 11 into a solid. The two electrode sections 35 are positioned opposite each other at the same distance from the columnar droplet 11. Therefore, the attractive forces of the two opposing electrode sections 35 on the minute metal spheres 10 are opposite to each other and cancel each other out. Also, because the falling speed of the minute metal spheres 10 is fast, the minute metal spheres 10 pass through the electrode section 35 before they are attracted to and reach the electrode section 35. Therefore, the minute metal spheres 10 are not attracted to the electrode section 35. Note that because the attractive force of the two electrode sections 35 on the minute metal spheres is small, the distance between the electrode section 35 and the columnar droplet 11 does not need to be exactly the same. The electrode section 35 may also be cylindrical with the columnar droplet 11 at its center.

[0041] The columnar droplets 11 are separated into tiny metal spheres 10 by the vibration of the vibration rod 54. The cooling tower 30 has a cooling gas supply pipe 37 at the bottom that supplies cooling gas G4. The cooling gas G4 is an inert gas (e.g., N2) that cools the tiny 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. Based on the detected value, the control device 70 controls the cooling gas supply means 38 that supplies the cooling gas, and adjusts the temperature and airflow rate of the cooling gas G4 as appropriate.

[0042] Furthermore, 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 surface oxidation is prevented. For the micro-metal spheres 10 to separate from the columnar droplets 11 and be recovered in a stable state, for example, when the micro-metal spheres 10 are 100 μm in size, the height of the cooling tower 30 will be about 1.5 m. Consequently, the volume of the cooling tower 30 will be large. Therefore, by changing the cooling gas G4 from a mixture containing an expensive reducing gas to a mixture containing only an inexpensive inert gas, it is possible to reduce costs.

[0043] The temperature of the cooling gas G4 may be at room temperature. Furthermore, the pressure inside the cooling tower 30 may be adjusted to be slightly higher than atmospheric pressure in order to appropriately manage the temperature gradient derived from the falling speed and temperature of the minute metal spheres 10 from the columnar molten droplets 11 to a stable state (a state where they do not deform upon falling). This allows for a lower height for the cooling tower 30.

[0044] The cooling tower 30 is positioned on either side of the columnar molten droplets 11, which fall to the surface of the columnar droplets 11, and includes a camera 43 and a stroboscope 44 for imaging the minute metal spheres 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 spheres 10 as they fall. The captured still image data is sent to the control device 70, where the sphere diameter is detected through image processing. The control device 70 then compares the detected sphere diameter with a preset target sphere diameter and adjusts the amplitude and vibration frequency of the oscillator 53 to correct the difference. Although not shown in the illustration, it is more preferable that the stroboscope 44 has a collimating lens and emits parallel light.

[0045] Furthermore, the diameter of the micro-metal spheres 10 can be determined by imaging two micro-metal spheres 10 falling in succession and detecting the distance between them. This is because it is known that there is a correlation between the distance between two micro-metal spheres 10 and their diameters, so it is possible to detect the diameter by formulating the relationship between distance and diameter into a mathematical equation during the preliminary manufacturing stage.

[0046] A non-magnetic collection receiver 45 for collecting the hardened micro-metal spheres 10 is located at the bottom of the cooling tower 30. Although not shown in the illustration, the cooling tower 30 has openings in the side wall 32 or bottom plate 46 for collecting the collection receiver 45. If the micro-metal spheres 10 are made of a non-magnetic material, when they are collected in the collection receiver 45, the micro-metal spheres 10 will spontaneously release their negative charge and become "uncharged".

[0047] (Method for manufacturing the micrometal spheres 10) Next, the method for manufacturing the micro-metal spheres 10 using the micro-metal sphere manufacturing apparatus 1 will be described. The method for manufacturing the micro-metal spheres 10 begins by melting a metal mass placed in a crucible 20 to form molten metal M. The molten metal M is then pressurized with pressurized gas G1, and high-frequency vibrations are applied from the vibrator 53 to the excitation rod 54, causing the molten metal M to be discharged from the orifice 40. The molten metal M discharged from the orifice 40 drips down in the form of columnar droplets 11. The columnar droplets 11 are separated into individual micro-metal spheres 10 by the vibrations applied from the excitation rod 54 and fall. As they fall down the cooling tower 30, the surface tension of the molten metal M causes them to become spherical and cool, forming micro-metal spheres 10 with high sphericity.

[0048] The diameter of the micro-metal spheres 10 is determined by key 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 excitation rod 54 and the orifice 40, and the amplitude and vibration frequency of the vibrator 53 (i.e., the excitation rod 54). These conditions must be combined appropriately and are pre-set during pre-manufacturing. The distance between the columnar droplet 11 and the electrode section 35, and the extension length of the electrode section 35 are also set to optimal conditions during pre-manufacturing, similar to the above conditions. Key conditions that fluctuate during manufacturing are detected by sensors and fed back to the control device 70, which then controls each of these key conditions.

[0049] The viscosity of the molten metal M is determined by the material and is affected by the melting temperature. Therefore, the internal temperature of the crucible 20 is constantly detected, and the first heater 22 and the 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 from the cross-sectional area and discharge speed of the columnar molten droplets 11. Since it is known that the pore diameter of the orifice 40 has a correlation with the sphere diameter of the minute metal spheres 10, it may be predetermined, or multiple orifice plates 41 with different pore diameters may be prepared in advance and replaced with the one with the optimal pore diameter.

[0050] Furthermore, the amplitude and vibration frequency of the transducer 53 fluctuate due to temperature changes during operation of the micro-metal ball manufacturing apparatus 1. Therefore, temperature fluctuations can be suppressed by blowing cooling air G2 around the entire circumference of the exposed portion of the transducer 53.

[0051] The distance d between the vibration rod 54 and the orifice 40 does not fluctuate during the operation of the micro-metal ball manufacturing apparatus 1, but the crucible 20 and cooling tower 30 are disassembled for maintenance. At that time, the distance d may change. Therefore, a first shim plate 57 is interposed between the flange portion 56 of the vibration rod 54 and the lid member 25 of the cooling tower 30 to adjust the distance d to an initial setting value. Multiple first shim plates 57 with different thicknesses are prepared in advance and the distance d is adjusted by replacing them.

[0052] Molten metal M is discharged from the orifice 40 into the cooling tower 30 in the form of columnar droplets 11, and is separated into minute metal spheres 10 by high-frequency vibration of the excitation rod 54. The cooling tower 30 cools the separated minute metal spheres 10. Therefore, if the temperature of the columnar droplets 11 decreases, there is a risk that it will no longer be possible to separate them into minute metal spheres 10. To address this, heating gas G3 is heated by the second heater 23 and blown onto the columnar droplets 11 to maintain a temperature at which the columnar droplets 11 can be separated into minute metal spheres 10. Heating gas G3 is a mixture of an inert gas (e.g., N2) and a reducing gas (e.g., H2), which prevents oxidation of the columnar droplets 11.

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

[0054] The inside of the cooling tower 30 is filled with cooling gas G4 from below. Heated heating gas G3 is blown onto the columnar molten droplets 11 at the top of the cooling tower 30. Thus, a temperature gradient is formed where the temperature is high at the top of the cooling tower 30 and decreases towards the bottom. The tiny metal spheres 10 separated from the columnar molten droplets 11 become spherical at the top due to surface tension, and are cooled as they gradually fall downward, becoming tiny metal spheres 10 with high sphericity. The cooling gas G4 is an inert gas (e.g., N2), which prevents oxidation of the columnar molten droplets 11.

[0055] As explained above, the manufacturing method for the micro-metal spheres 10 appropriately combines 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 excitation rod 54 and the orifice 40, and the amplitude and vibration frequency of the vibrator 53 (i.e., the excitation rod 54). However, the diameter of the micro-metal spheres 10 may vary. Therefore, the manufacturing method for the micro-metal spheres 10 includes a step to detect the diameter of the spheres while they are separated from the columnar molten droplet 11 and falling. The diameter is measured using an optical system consisting of a stroboscope 44 and a camera 43. The camera 43 captures a still image of the falling micro-metal spheres 10, and the control device 70 calculates the diameter by image processing. The control device 70 adjusts the amplitude and vibration frequency of the vibrator 53 based on the difference between the actually measured diameter data and the target diameter. Furthermore, the control device 70 appropriately adjusts the pressure of the pressurized gas G1, the temperature of the molten metal M, the cooling air G2, and the temperature and airflow rate of the heating gas G3 based on the detected values.

[0056] As described 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 part of the vibrator 53. By blowing cooling air G2 onto the vibrator 53, the cooling air blowing means 59 can suppress the rise in temperature of the vibrator 53 and the temperature difference depending on the part of the vibrator 53. As a result, it is possible to suppress fluctuations in the amplitude and vibration frequency of the vibrator 53, and it becomes possible to stably manufacture micro-metal spheres 10 with high precision and small variation, that is, with a narrow particle size distribution.

[0057] The crucible 20 and the cooling tower 30 are detachably fixed to each other. This makes it possible to easily separate the crucible 20 and the cooling tower 30 for maintenance. The lid member 25 of the crucible 20 is also detachably fixed to the crucible 20. This makes it easy to load the metal ingots, which are the raw materials for the micro-metal spheres 10, into the crucible 20, and also makes it easy to perform maintenance such as internal cleaning. The lid member 31 of the cooling tower 30 is also detachably fixed to the cooling tower 30. This makes it easy to adjust the position of the electrode section 35, the relative positions of the camera 43 and stroboscope 44, and makes it easy to perform maintenance such as cleaning on the cooling tower 30.

[0058] When the distance d between the tip of the vibration rod 54 and the orifice 40 changes, the diameter of the small metal sphere 10 changes. In maintenance of the crucible 20 and the cooling tower 30, even if the other conditions described above are kept constant, fluctuations in distance d affect the reproducibility of the sphere diameter. The vibration rod 54 is supported between the vibrator 53 and the lid member 31 of the cooling tower 30. Between the flange portion 56 of the vibration rod 54 and the lid member 31, a ring-shaped rigid first shim plate 57 and an elastic second shim plate 58 are interposed in a stacked state, through which the shaft portion 55 of the vibration rod 54 passes. 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, it is possible to ensure the reproducibility of the distance d.

[0059] Furthermore, the orifice 40 is formed on an orifice plate 41 made of a precious stone such as a diamond, sapphire, or ruby. By making the orifice plate 41 from a precious stone, it is possible to form an orifice 40 with a smooth inner surface for a micro-pore diameter, and furthermore, it is possible to improve the heat resistance and durability of the orifice 40.

[0060] The crucible 20 has a first heater 22 positioned around the side wall 21 and a second heater 23 positioned around the outer circumference of the orifice plate 41 at the bottom 24, which melts the metal mass (not shown) that is placed inside. The crucible 20 is then embedded until the second heater 23 enters the inside 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 molten 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 molten droplets 11 immediately after they are discharged from the orifice 40. The heating gas supply pipe 33 is positioned so that the heating gas G3 can be heated by the radiant heat of the second heater 23. This makes it possible to maintain the heating gas G3 at a temperature that allows for the separation of the minute metal spheres 10 from the columnar molten droplets 11, even inside the cooling tower 30.

[0062] The cooling tower 30 has a charging means 36 equipped with an electrode section 35 for applying an electrical repulsive force to the minute metal spheres 10 that are dropping (falling) from the crucible 20. The minute metal spheres 10 separated from the columnar molten droplets 11 are charged by the electrode section 35 and become negatively charged, and the electrical repulsive force prevents the minute metal spheres 10, which are still at a high temperature, from sticking together.

[0063] The electrode portion 35 is positioned laterally and spaced apart from the discharge direction of the columnar droplet 11 immediately after it is ejected from the orifice 40. It is also positioned within the continuous length range of the columnar droplet 11. This prevents the tiny metal spheres 10 that separate from the columnar droplet 11, become negatively charged, and fall, from being attracted to the positively charged electrode portion 35.

[0064] The cooling tower 30 has a stroboscope 44 and a camera 43 positioned opposite each other, flanking the falling minute metal sphere 10. The stroboscope 44 emits light in synchronization with the vibration of the oscillator 53, and the camera 43 captures still images of the falling minute metal sphere 10. The still image data is sent to the control device 70, where it can be detected as the sphere diameter through image processing. The control device 70 then compares the detected sphere diameter with a preset target sphere diameter and adjusts the amplitude and vibration frequency of the oscillator 53 to correct the difference. This makes it possible to stably manufacture minute metal spheres 10 with high precision and small variations in sphere diameter. The control device 70 also has a function to control the pressurized gas supply means 27 and the heating gas supply means 34 for sphere diameter management.

[0065] Furthermore, the pressurized gas G1 that pressurizes the inside of the crucible 20 is a mixture of an inert gas and a reducing gas. When the molten metal M oxidizes, its fluidity deteriorates, which can cause clogging of the orifice 40, or the sphericity of the tiny metal spheres 10 formed by surface tension may decrease. Therefore, by making the pressurized gas G1 a mixture of an inert gas and a reducing gas, it is possible to prevent the oxidation of the molten metal M.

[0066] For similar reasons, the heating gas G3 is a mixture of an inert gas and a reducing gas. This prevents oxidation of the columnar droplets 11 discharged from the crucible 20, and makes it possible to separate the minute metal spheres 10 and improve the sphericity of the minute metal spheres 10.

[0067] The cooling tower 30 has a cooling gas supply means 38 that supplies cooling gas G4 to its interior. By using an inert gas for the cooling gas G4, oxidation of the surface of the falling minute metal spheres 10 can be prevented.

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

[0069] 1...Micrometal sphere manufacturing apparatus, 10...Micrometal sphere, 11...Columnar droplet, 20...Crucible, 21,32...Side wall, 22...First heater, 23...Second heater, 24...Bottom 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 section, 36...Charging means, 37...Cooling gas supply G1...Cooling gas supply means, 38...Orifice, 41...Orifice plate, 43...Camera, 44...Stroboscope, 53...Vibrator, 54...Excitation rod, 55...Shaft, 56...Flange, 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 connected vertically to the crucible, An orifice is 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, An excitation rod extending from the outside of the crucible through the inside of the molten metal to just before the orifice, A vibrator is positioned outside the crucible and vibrates the excitation rod in the axial direction, A cooling air blowing means for blowing cooling air over the entire circumference of the exposed portion of the vibrator, Possesses, A device for manufacturing micro-metal spheres characterized by the following features.

2. In the apparatus for manufacturing minute metal spheres according to claim 1, The crucible and the cooling tower are detachably fixed to each other. A device for manufacturing micro-metal spheres characterized by the following features.

3. In the apparatus for manufacturing minute metal spheres according to claim 1, The crucible further includes a lid member that securely fastens the internal space containing the molten metal, The vibration rod has a flange portion that protrudes outward in the outer direction between the vibrator and the cover member, Between the flange portion and the cover member, a ring-shaped, rigid first shim plate and an elastic second shim plate are laminated and interposed, through which the shaft portion of the vibration rod passes. A device for manufacturing micro-metal spheres characterized by the following features.

4. In the apparatus for manufacturing minute metal spheres according to claim 1, The orifice is formed in an orifice plate made of a precious stone. A device for manufacturing micro-metal spheres characterized by the following features.

5. In the apparatus for manufacturing minute metal spheres according to claim 1, The crucible has a heater for generating the molten metal, The heater consists of a first heater positioned around the side wall of the crucible and a second heater positioned around the outer circumference of the orifice plate at the bottom. The crucible is buried at least to the extent that the second heater enters the interior of the cooling tower. A device for manufacturing micro-metal spheres characterized by the following features.

6. In the apparatus for manufacturing minute metal spheres according to claim 5, The cooling tower further includes a heating gas supply pipe for blowing heating gas onto the molten metal, which is in the form of columnar droplets immediately after being discharged from the orifice. The heating gas supply pipe is positioned to raise the heating gas to a temperature at which it is possible to separate the minute metal spheres from the columnar molten droplets by the radiant heat of the second heater. A device for manufacturing micro-metal spheres characterized by the following features.

7. In the apparatus for manufacturing minute metal spheres according to claim 1, The system further includes a charging means equipped with an electrode for applying an electrical repulsive force to minute metal spheres that drip from the crucible onto the cooling tower. A device for manufacturing micro-metal spheres characterized by the following features.

8. In the apparatus for manufacturing minute metal spheres according to claim 7, The electrode portions are spaced apart to the side in the direction of discharge of the columnar droplet immediately after it is discharged from the orifice, and are positioned opposite each other with respect to the columnar droplet. A device for manufacturing micro-metal spheres characterized by the following features.

9. In the apparatus for manufacturing minute metal spheres according to claim 1, The cooling tower further includes a stroboscope and a camera positioned opposite each other, with a falling minute metal sphere in between. The stroboscope emits light in synchronization with the vibration of the oscillator, The camera is capable of imaging the minute metal sphere in the process of falling. A device for manufacturing micro-metal spheres characterized by the following features.

10. In the apparatus for manufacturing minute metal spheres according to claim 1, The aforementioned pressurized gas is a mixture of an inert gas and a reducing gas. A device for manufacturing micro-metal spheres characterized by the following features.

11. In the apparatus for manufacturing minute metal spheres according to claim 6, The heating gas supplied by the heating gas supply pipe is a mixture of an inert gas and a reducing gas. A device for manufacturing micro-metal spheres characterized by the following features.

12. In the apparatus for manufacturing minute metal spheres according to claim 1, The cooling tower further includes a cooling gas supply means for supplying cooling gas to the interior, The cooling gas is an inert gas. A device for manufacturing micro-metal spheres characterized by the following features.

Images