Patent Publication Number: US-2021178478-A1

Title: Metal powder manufacturing device, and crucible apparatus and molten metal nozzle for metal powder manufacturing device

Description:
TECHNICAL FIELD 
     The present invention relates to a metal powder manufacturing device in which a fluid is sprayed to an atomization tank-side end part of a molten metal nozzle to cause the high-pressure fluid to collide against a melting metal flowing downward from the molten metal nozzle, thereby manufacturing a fine particulate form metal (metal powder), and a crucible apparatus and a molten metal nozzle for the metal powder manufacturing device. 
     BACKGROUND ART 
     As a method for manufacturing a fine particle form metal (metal powder) from a melting metal, there are atomizing methods including a gas atomizing method and a water atomizing method. In the gas atomizing method, a molten metal is allowed to flow downward through a molten metal nozzle at a lower part of a solution tank in which the melting metal is stored, and an inert gas is sprayed to the molten metal from a plurality of gas spraying nozzles disposed in the periphery of the molten metal nozzle. The flow of the melting metal from the molten metal nozzle is divided by the inert gas flow from the gas spraying nozzles into a plurality of fine metal droplets, which falls within an atomization tank, to be solidified while being spheroidized by surface tension. As a result, a spherical metal powder is recovered by a collection hopper at a bottom part of the atomization tank. 
     For example, JP-2016-211027-A discloses a metal powder manufacturing device including: a crucible that is provided at an upper part of an atomization chamber (atomization tank) and holds a molten metal; an atomizing nozzle (molten metal nozzle) that is connected to a bottom part of the crucible and allows the molten metal to fall into the atomization chamber while spraying the inert gas to the molten metal; a plurality of inert gas nozzles (spraying nozzles) that spray a high-pressure inert gas to the molten metal flowing downward through the atomizing nozzle to form a multiplicity of fine metal droplets; a gas introduction port and a gas discharge port for gas replacement in the atomization chamber; and a second gas introduction port for giving a gas for establishing an oxidizing atmosphere and/or a nitriding atmosphere in the atomization chamber. 
     PRIOR ART DOCUMENT 
     Patent Document 
     Patent Document 1: JP-2016-211027-A 
     SUMMARY OF THE INVENTION 
     Problem to be Solved by the Invention 
     In recent years, the need has been increasing for a metal powder having a particle diameter smaller than that of a metal powder conventionally demanded for an atomizing method, inclusive of, for example, a material for a metal three-dimensional printer for forming a metal of a desired shape by stacking a large amount of metal particles. While the particle diameter of conventional metal powders for use in powder metallurgy, welding and the like is on the order of 70 to 100 μm, the particle diameter of the metal powder for use in the three-dimensional printer is very fine, for example, on the order of 20 to 50 μm. 
     Incidentally, the molten metal nozzle of a metal powder manufacturing device based on the atomizing method includes an orifice part which is a part for controlling the flow rate of a molten metal and is a part thinnest (smallest) in inside diameter. Besides, the molten metal nozzle is generally manufactured from a single material. For example, a comparatively soft material such as boron nitride (BN) has resistance to a shock form thermal stress (thermal shock) due to a sudden temperature change upon pouring of a molten metal, and, therefore, is accompanied by little fear of molten metal leakage. However, since such a material is liable to be abraded by contact with the molten metal, continued use thereof enlarges the diameter of the orifice part, the flow rate of the molten metal increases from an initial value, and the particle diameter of the metal powder may be thereby enlarged. In contrast, a comparatively hard material such as a ceramic is excellent in abrasion resistance, and has such a characteristic that the diameter of the orifice part can be maintained even when the orifice part makes contact with the molten metal repeatedly; since the material is liable to be damaged by thermal shock upon pouring of the molten metal, it is difficult to overcome the fear of molten metal leakage. 
     In addition, the types of the atomization nozzle of the metal powder manufacturing method based on the atomizing method include a free fall type which is excellent in mass-producibility but poor in fine particle formation property, and a confined type which is excellent in fine particle formation property but poor in mass-producibility. In the case of manufacturing the very fine metal powder as aforementioned, it is preferable to utilize the latter, confined type. A confined type atomization nozzle has a gas spraying nozzle for pulverizing the melting metal by spraying a high-pressure gas to the tip end of the molten metal nozzle, and the gas sprayed from the gas spraying nozzle cools the tip end of the molten metal nozzle. Therefore, in the confined type atomization nozzle, thermal stress distribution in the molten metal nozzle is liable to be uneven as compared to the free fall type, thus countermeasure against thermal shock is more important than in the prior art. 
     The present invention has been made in consideration of the aforementioned circumstances. It is an object of the present invention to provide a metal power manufacturing device including a confined type atomization nozzle having resistance to thermal shock and excellent in abrasion resistance, and a crucible apparatus and a molten metal nozzle for the metal power manufacturing device. 
     Means for Solving the Problem 
     In order to achieve the above object, the present invention provides a metal powder manufacturing device including: an atomization tank; a crucible in which a melting metal is stored; a molten metal nozzle that allows the melting metal stored in the crucible to flow downward into the atomization tank; and a fluid spraying nozzle including a plurality of spraying holes that spray a fluid to an atomization tank-side end part of the molten metal nozzle to pulverize the melting metal flowing downward from the molten metal nozzle, in which the molten metal nozzle includes a molten metal nozzle body, and an orifice part having an inside diameter equal to or smaller than an inside diameter of the molten metal nozzle body, and a material of the orifice part is harder than a material of the molten metal nozzle body. 
     Advantages of the Invention 
     According to the present invention, it is possible to provide a metal powder manufacturing device including a confined type atomization nozzle having resistance to thermal shock and excellent in abrasion resistance, and a crucible apparatus and a molten metal nozzle for the metal powder manufacturing device. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is an overall configuration view of a metal powder manufacturing device according to a first embodiment in which a solution tank according to the present invention is depicted in section. 
         FIG. 2  is a sectional view of a gas sprayer and a crucible apparatus provided in the metal powder manufacturing device according to the first embodiment of the present invention. 
         FIG. 3  is a perspective view of the gas sprayer provided in the metal powder manufacturing device according to the first embodiment of the present invention. 
         FIG. 4  is a sectional view of a crucible apparatus provided in the metal powder manufacturing device according to the first embodiment of the present invention. 
         FIG. 5  is a sectional view of the crucible apparatus formed from a material that is sensitive to thermal shock (hard material). 
         FIG. 6  is a sectional view of a crucible apparatus in which a molten metal nozzle formed of a material poor in abrasion resistance (soft material) is used. 
         FIG. 7  is a table depicting the combination of materials of a molten metal nozzle body and an orifice part of the crucible apparatus provided in the metal powder manufacturing device according to the first embodiment of the present invention. 
         FIG. 8  is a sectional view of a crucible apparatus and a stopper of a metal powder manufacturing device according to a second embodiment of the present invention. 
         FIG. 9  is a sectional view of a crucible apparatus of a metal powder manufacturing device according to a third embodiment of the present invention. 
         FIG. 10  is a sectional view of a crucible apparatus of a metal powder manufacturing device according to a fourth embodiment. 
         FIG. 11  is a sectional view of the crucible apparatus and a stopper of the metal powder manufacturing device according to the fourth embodiment of the present invention. 
         FIG. 12  is a sectional view of a crucible apparatus provided in a metal powder manufacturing device according to another embodiment. 
     
    
    
     MODES FOR CARRYING OUT THE INVENTION 
     Embodiments of the present invention will be described below using the drawings. 
     —Overall Configuration of Metal Powder Manufacturing Device— 
       FIG. 1  is an overall configuration view of a gas atomizing device as a metal powder manufacturing device according to an embodiment of the present invention,  FIG. 2  is a sectional view of a crucible apparatus and a gas sprayer according to the gas atomizing device of  FIG. 1 , and  FIG. 3  is a perspective view of the gas sprayer. In  FIG. 1 , the gas atomizing device includes a solution tank  1 , a gas sprayer  2 , a spray gas supply pipe (spray fluid supply pipe)  3 , an atomization tank  4 , a collection hopper  5 , and an exhaust pipe  6 . 
     The solution tank  1  is a hermetically sealed vessel (closed chamber) held in a vacuum atmosphere or an inert gas atmosphere, and accommodates a crucible apparatus  10  therein. The crucible apparatus  10  has, as illustrated in  FIG. 2 , a crucible  11  in which a molten metal (melting metal)  8  (see  FIG. 2 ) obtained by melting a solid metal (dissolved material) by heating is stored, and a plurality of molten metal nozzles  12  (in the illustrated example, two molten metal nozzles) that allows the molten metal  8  stored in the crucible  11  to flow downward into the atomization tank  4 . 
     The gas sprayer  2  is an apparatus that sprays a high-pressure fluid (in the present embodiment, an inert gas) to atomization tank  4 -side end parts of the plurality of molten metal nozzles  12  (also referred to as tip end parts of the molten metal nozzles  12 ), and pulverizes the molten metal flow (melting metal)  8   a  flowing downward from the molten metal nozzles  12  into a multiplicity of fine particles, to thereby atomize the melting metal into the atomization tank  4  (see  FIG. 2 ). The gas sprayer  2  includes a plurality of spraying nozzles (also referred to as fluid spraying nozzles or gas spraying nozzles)  22  that sprays an inert gas  7  to the atomization tank  4 -side end parts  12   b  of the plurality of molten metal nozzles  12 , gas flow channels  23  that supplies the inert gas  7  to the plurality of spraying nozzles  22 , and molten metal nozzle insertion holes  24  in which the molten metal nozzles  12  are inserted. The plurality of spraying nozzles  22  include a plurality of spraying holes  21  arranged in an annular pattern in the periphery of each of the plurality of molten metal nozzles  12 , and spray the inert gas  7  to the atomization tank  4 -side end part  12   b  of each molten metal nozzle  12 . 
     Herein, the molten metal nozzles  12  and the spraying nozzles  22  including the plurality of spraying holes  21  provided in the periphery of the molten metal nozzles  12  are generically referred to as atomization nozzles  25 . The atomization nozzle  25  in the present embodiment is a so-called confined type nozzle in which opening ends of a plurality of spraying holes  21  are disposed such as to surround the periphery of a tip end part of the molten metal nozzle  12 , and a gas is sprayed from the plurality of spraying holes  21  (spraying nozzles  22 ) to the tip end part of the molten metal nozzle  12  to generate fine particles of metal. The confined type nozzle is characterized in that since the distance from the spraying holes  21  to the molten metal flow is very small, attenuation of the gas velocity until collision against the molten metal flow is small, which is excellent in fine particle formation property. In addition, as depicted in  FIGS. 2 and 3 , the metal powder manufacturing device according to the present embodiment includes two atomization nozzles  25 . The plurality of atomization nozzles  25  include one molten metal nozzle  12  and the spraying nozzle  22  including a plurality of spraying holes  21  provided in the periphery of the molten metal nozzle  12 . Note that the illustration is merely an example, and the number of the atomization nozzles  25  may be one, or may be three or more. 
     The spray gas supply pipe  3  is a piping for injecting an inert gas into the gas sprayer  2 , and is connected to the gas flow channels  23  in the gas sprayer  2 . 
     The atomization tank  4  is a vessel held in an inert gas atmosphere, and is a vessel in which the liquid metal of the fine particle form (metal particles)  8   b  atomized by the gas sprayer  2  is solidified by rapid cooling during falling. Note that the atomization tank  4  is a cylindrical vessel having the same diameter at upper and intermediate parts, but its lower part is tapered such that the diameter decreases in going closer to the collection hopper  5  from the viewpoint of ease of recovery of the metal powder. 
     The collection hopper  5  is an apparatus for recovering the powdery solid metal solidified during falling in the atomization tank  4 , and is provided at a bottom part of the atomization tank  4 . 
     The exhaust pipe  6  is a piping for discharging the inert gas filling up the atomization tank  4  and the collection hopper  5  from the collection hopper  5 , and is connected to the collection hopper  5 . 
     —Gas Sprayer  2 — 
     The gas sprayer  2  is provided with molten metal nozzle insertion holes  24  as two cylindrical through-holes, and each of the two molten metal nozzles  12  are inserted in each of the two molten metal nozzle insertion holes  24 . The molten metal  8  in the solution tank  1  flows down through holes  12   a  inside the molten metal nozzles  12  as a molten metal flow  8   a , and is discharged into the atomization tank  4 . As the minimum inside diameter of the molten metal nozzle  12  (the diameter of the orifice part  12   d  described later) that contributes to the magnitude of the diameter of the molten metal  8  made to flow downward to the gas sprayer  2 , a value smaller than a conventional value, for example, a value of equal to or smaller than 3 mm can be selected. 
     The gas sprayer  2  has the high-pressure inert gas  7  (hereinafter referred to as high-pressure gas) injected thereinto from the spray gas supply pipe  3  connected to a gas suction hole (not illustrated) provided in a side surface, and sprays the high-pressure gas as an oriented spray gas jet (spray gas  7   a ) through the spray nozzle  22  (spraying holes  21 ) provided at a cylindrical bottom surface. The spray gas  7   a  is sprayed to the molten metal flow  8   a  made to flow downward from the molten metal nozzle  12 . The molten metal flow  8   a  is pulverized into a multiplicity of fine particles  8   b  by collision on a reverse conical fluid film formed by the spray gas  7   a  in the vicinity of a focus of the spray gas  7   a  sprayed from the spraying nozzle  22 . The metal made into mist-like fine particles  8   b  by the spray gas  7   a  from the spraying nozzle  22  is solidified by rapid cooling during falling in the atomization tank  4 , and is recovered by the collection hopper  5  as a multiplicity of metal powders. 
     First Embodiment 
     Details of the configuration of the molten metal nozzle  12  of the crucible apparatus  10  in the metal powder manufacturing device according to a first embodiment of the present invention will be described below using the drawings. 
       FIG. 4  is a sectional view of the crucible apparatus  10  according to the first embodiment. Note that while the case where the crucible apparatus  10  is provided with the two molten metal nozzles  12  has been described in the description of the overall configuration of the metal powder manufacturing device conducted above using  FIGS. 2 and 3 , a case where the crucible apparatus  10  is provided with one molten metal nozzle  12  will be described in the following, for simplification of description. In addition, the same parts as those in the preceding figures are denoted by the same reference characters as used above and their descriptions may be omitted (the same applies also to the figures hereinbelow). 
     The crucible apparatus  10  of  FIG. 4  is provided with the crucible  11  and the molten metal nozzle  12 . The crucible  11  is an apparatus in which a melting metal (molten metal  8 ) obtained by melting a solid metal (dissolved material) by heating is stored, and is preferably formed from a material excellent in heat resistance, for example, alumina (aluminum oxide), magnesia (magnesium oxide), or zirconia (zirconium oxide). A bottom surface of the crucible  11  is formed with a nozzle fixing hole  11   a  that is a through-hole into which the molten metal nozzle  12  is inserted for fixation. 
     The molten metal nozzle  12  is an apparatus for allowing the molten metal (melting metal)  8  stored in the crucible  11  to flow downward into the atomization tank  4 , and is fixed to the crucible  11  by an adhesive or the like in a state in which its upper end part (base end part) is inserted in the nozzle fixing hole  11   a.    
     In addition, the molten metal nozzle  12  includes a molten metal nozzle body  12   c , and the orifice part  12   d  having an inside diameter equal to or smaller than the inside diameter of the molten metal nozzle body  12   c . The orifice part  12   d  and the molten metal nozzle body  12   c  are formed from different materials, and the material of the orifice part  12   d  is harder than the material of the molten metal nozzle body  12   c . In other words, the orifice part  12   d  is formed from a material relatively harder than the material of the molten metal nozzle body  12   c , and the molten metal nozzle body  12   c  is formed from a material relatively softer than the material of the orifice part  12   d.    
     The molten metal nozzle body  12   c  is a cylindrical nozzle having an upper end part (base end part) inserted and fixed in the nozzle fixing hole  11   a  of the crucible  11 , and is formed from a material relatively soft and having resistance to thermal shock compared with the material of the orifice part  12   d , for example, silicon nitride, boron nitride, silica or the like. The molten metal nozzle body  12   c  depicted in  FIG. 4  has a tip end part sharpened in a reverse truncated conical shape, but the shape of the tip end part of the molten metal nozzle body  12   c  is not limited to this shape. 
     The orifice part  12   d  is an annular member that has an inside diameter equal to or smaller than the inside diameter of the molten metal nozzle body  12   c  for controlling the flow rate of the molten metal  8 , and that is fixed to the inside of the molten metal nozzle body  12   c  by an adhesive or the like. The orifice part  12   d  is formed from a material relatively harder and better in abrasion resistance than the material of the molten metal nozzle body  12   c , for example, alumina, zirconia, silicon carbide or the like. 
     The orifice part  12   d  of  FIG. 4  is a cylindrical member (tubular member) having an outside diameter substantially equal to the inside diameter of the molten metal nozzle body  12   c , and is fixed to the inside of the molten metal nozzle body  12   c . An atomization tank  4 -side end part (lower end part), in the axial direction, of the orifice part  12   d  is located above an atomization tank  4 -side end part (lower end part), in the axial direction, of the molten metal nozzle body  12   c , and a crucible  11 -side end part (upper end part) in the axial direction of the orifice part  12   d  is located below a crucible  11 -side end part (base end part or upper end part), in the axial direction, of the molten metal nozzle body  12   c.    
     In general, a softer material tends to have resistance to thermal shock, and a harder material tends to be better in abrasion resistance. Therefore, a material relatively softer than the orifice part  12   d  is preferably utilized as the material of the molten metal nozzle  12   c , and a material relatively harder than the molten metal nozzle  12   c  is preferably utilized as the material of the orifice part  12   d . More specifically, a material having a thermal shock resistance by falling in water (JIS R1648) of equal to or more than 500° C. is preferably utilized as the material of the molten metal nozzle body  12   c , and a material having a Vickers hardness (JIS R1610) of equal to or more than 10 GPa is preferably utilized as the material of the orifice part  12   d .  FIG. 7  sets forth examples of the combination of the materials of the molten metal nozzle body  12   c  and the orifice part  12   d  that satisfy this condition. In other words, examples of preferred combination of the materials of the molten metal nozzle body  12   c  and the orifice part  12   d  include silicon nitride and zirconia (Example 1), silicon nitride and alumina (Example 2), silicon nitride and silicon carbide (Example 3), boron nitride and zirconia (Example 4), boron nitride and alumina (Example 5), boron nitride and silicon carbide (Example 6), silica and zirconia (Example 7), silica and alumina (Example 8), and silica and silicon carbide (Example 9). 
     —Conventional Problems— 
     Here, the problem involved in the conventional molten metal nozzle will be confirmed, and, thereafter, the effect of the metal powder manufacturing device according to the present embodiment will be described.  FIG. 5  is an illustration of a problem when the molten metal nozzle is manufactured by use of a single material (for example, a ceramic) that is hard and excellent in abrasion resistance but is poor in thermal shock resistance, and  FIG. 6  is an illustration of a problem when the molten metal nozzle is manufactured by using a single material (for example, boron nitride) that is soft and excellent in thermal shock resistance but is poor in abrasion resistance. 
     In general, the molten metal nozzle of a metal powder manufacturing device based on an atomizing method is manufactured from a single material. For example, a comparatively soft material such as boron nitride (BN) has resistance to a shock-form thermal stress (thermal shock) due to a sudden temperature change upon pouring of the molten metal, and, therefore, there is no fear of molten metal leakage. However, since the material is liable to be abraded by contact with the molten metal, continued use thereof may result in an enlargement of the diameter of the orifice part (the inside diameter  12   a  of the molten metal nozzle body), as depicted in  FIG. 6 , and an increase in the molten metal flow rate from an initial value, whereby the particle diameter of the metal powder may be enlarged. In contrast, a comparatively hard material such as a ceramic is excellent in abrasion resistance, and is characterized in that the diameter of the orifice part can be maintained even upon repeated contact with the molten metal. However, the material is liable to be damaged by thermal shock upon pouring of the molten metal, and it is difficult to overcome a fear of generation of molten metal leakage due to damage of the molten metal nozzle as depicted in  FIG. 5 . In addition, when not a free fall type atomization nozzle but a confined type atomization nozzle including a gas spraying nozzle for pulverizing a melting metal by spraying a high-pressure gas to the tip end of the molten metal nozzle is utilized as the atomization nozzle of the metal powder manufacturing device by the atomizing method, the gas sprayed from the gas spraying nozzle cools the tip end of the molten metal nozzle. For this reason, in the confined type atomization nozzle, the distribution of thermal stress in the molten metal nozzle is liable to be uneven as compared to the free fall type atomization nozzle, thus countermeasure against thermal shock is more important than in the prior art. 
     —Effect— 
     In view of such a problem, in the metal powder manufacturing device according to the present embodiment that is configured as aforementioned, the molten metal nozzle  12  includes the molten metal nozzle body  12   c  and the orifice part  12   d  having an inside diameter equal to or smaller than the inside diameter of the molten metal nozzle body  12   c , and the material of the orifice part  12   d  is selected to be harder than the material of the molten metal nozzle body  12   c . With the molten metal nozzle  12  formed in this way, the member disposed in an environment of friction with the molten metal flow  8   a  during metal powder manufacture is mainly the orifice part  12   d  which is comparatively hard and excellent in abrasion resistance, thus the inside diameter of the orifice part  12   d  can be prevented from being enlarged even upon continued use, and it is easy to maintain the diameter of the molten metal flow  8   a . In addition, since the orifice part  12   d  is covered by, and located inside of, the molten metal nozzle body  12   c , the orifice part  12   d  does not make direct contact with the gas sprayed from the spraying nozzle  22 , and since the orifice part  12   d  is disposed in an environment of being heated mainly by only the molten metal flow  8   a , thermal stress distribution is more uniformized and possibility of damage can be reduced as compared to the prior art. In contrast, since the molten metal nozzle body  12   c  is formed of a material which is comparatively soft and excellent in thermal shock resistance, the molten metal nozzle body  12   c  is not easily damaged even when utilized in an environment of being able to perform heat exchange with both a comparatively low temperature matter such as the gas from the spraying nozzle  22  and the inert gas in the atomization tank  4  and a comparatively high temperature matter such as the molten metal in the crucible  11  and the molten metal flow in the molten metal nozzle  12 . Therefore, according to the present embodiment, thermal shock resistance and abrasion resistance of the confined type atomization nozzle (molten metal nozzle) can be enhanced, whereby a metal powder having a stable particle diameter distribution can be manufactured in a continued manner. 
     Particularly, in the present embodiment, an atomization tank  4 -side end part (lower end part), in the axial direction, of the orifice part  12   d  is located above an atomization tank  4 -side end part (tip end part or lower end part), in the axial direction, of the molten metal nozzle body  12   c ; therefore, the orifice part  12   d  can be prevented from being cooled by the gas sprayed from the spraying nozzle  22 , whereby the possibility of damaging of the orifice part  12   d  by thermal shock can be lowered. In addition, a crucible  11 -side end part (upper end part), in the axial direction, of the orifice part  12   d  is located below a crucible  11 -side end part (base end part or upper end part), in the axial direction, of the molten metal nozzle body  12   c ; therefore, the orifice part  12   d  can be prevented from being heated by the molten metal which is at the highest temperature in the crucible  11 , whereby the possibility of damaging of the orifice part  12   d  by thermal shock can be lowered. 
     Note that a minimum inside diameter of the orifice part  12   d  may be coincident with a minimum inside diameter of the molten metal nozzle body  12   c . When the molten metal nozzle  12  is configured in this way, although there is a possibility that the molten metal nozzle body  12   c  makes contact with the molten metal flow  8   a  and is abraded in the beginning of use, the contact with the molten metal flow  8   a  is not generated after the abrasion proceeds to a certain extent, with the result that the minimum inside diameter of the orifice part  12   d  can become smaller than the minimum inside diameter of the molten metal nozzle body  12   c.    
     Second Embodiment 
     Next, a metal powder manufacturing device according to a second embodiment of the present invention will be described below using the drawings. 
       FIG. 8  is a sectional view of a crucible apparatus of the metal powder manufacturing device according to the second embodiment. The present embodiment differs from the first embodiment in that the metal powder manufacturing device (crucible apparatus  10 ) further includes a stopper  13  which is supported such as to be movable upward and downward within the crucible  11 , makes contact with a crucible  11 -side end part  12   e  of the molten metal nozzle body  12   c  at a lowered position, and closes a crucible  11 -side opening  12   f  of the molten metal nozzle  12 , and that the material of the stopper  13  is harder than the material of the molten metal nozzle body  12   c  (the material of the molten metal nozzle body  12   c  is softer than the material of the stopper  13 ). 
     The stopper  13  is a rod-shaped member of a heat-resistant hard material (for example, a ceramic) extending substantially in the vertical direction, and a driving mechanism (not illustrated) for moving the stopper  13  upward and downward is attached to the stopper  13 . When the stopper  13  is moved downward by the driving mechanism to bring the tip end (lower end) of the stopper  13  into contact with the crucible  11 -side end part  12   e  of the molten metal nozzle body  12   c  (the base end part of the molten metal nozzle body  12   c ), the crucible  11 -side opening  12   f  of the molten metal nozzle  12  is closed, and flow-out of the molten metal  8  in the crucible  11  is stopped. Conversely, when the stopper  13  is moved upward by the driving mechanism to space the tip end of the stopper  13  from the crucible  11 -side opening  12   f  of the molten metal nozzle  12 , the crucible  11 -side opening  12   f  of the molten metal nozzle  12  is opened into the crucible  11 , thus the molten metal in the crucible  11  can be made to flow downward into the molten metal nozzle  12 . 
     In the metal powder manufacturing device (the crucible apparatus  10 ) according to the present embodiment configured as aforementioned, the material of the molten metal nozzle body  12   c  is a material (for example, silicon nitride) softer than the material of the stopper  13 , and, therefore, the crucible  11 -side end part  12   e  of the molten metal nozzle body  12   c  (the base end part of the molten metal nozzle body  12   c ) can easily make close contact with the tip end (lower end) of the stopper  13  making contact therewith, thus the molten metal  8  in the crucible  11  can be prevented from leaking into the molten metal nozzle  12 . 
     Note that in the present embodiment, the material of the molten metal nozzle body  12   c  is softer than the material of the stopper  13 , and the stopper  13  is brought into contact with the crucible  11 -side end part  12   e  of the molten metal nozzle  12 , to thereby close the crucible  11 -side opening  12   f  of the molten metal nozzle  12 . Alternatively, the material of the stopper  13  may be softer than the material of the orifice part  12   d , and the stopper  13  may be brought into contact with a crucible  11 -side end part  12   g  of the orifice part  12   d , to thereby close the crucible  11 -side opening  12   f  of the molten metal nozzle  12 . In addition, while the shape of the lower end of the stopper  13  depicted in  FIG. 8  has a rectangular section, the shape of the lower end of the stopper may be a curved line-shaped section or may be a shape having other section. 
     Third Embodiment 
     Next, a metal powder manufacturing device according to a third embodiment of the present invention will be described below using the drawings. 
       FIG. 9  is a sectional view of a crucible apparatus  14  of the metal powder manufacturing device according to the third embodiment. The present embodiment differs from the first embodiment mainly in that an orifice part  15   a  is a member that is coated in an annular shape on an inside surface of a molten metal nozzle body  12   c.    
     Examples of a method of manufacturing a molten metal nozzle  15  including the orifice part  15   a  in such a film form include a method in which a material comparatively harder and better in abrasion resistance than the material of the molten metal nozzle body  12   c  of the first embodiment is applied or sprayed to the inner peripheral surface of the molten metal nozzle body  12   c . In the other points, the present embodiment is the same as the first embodiment. In other words, the molten metal nozzle  15  according to the present embodiment includes the molten metal nozzle body  12   c  formed of a material having resistance to thermal shock, and the orifice part  15   a  formed of a material which is high in hardness and excellent in abrasion resistance, like in the first embodiment. 
     When the molten metal nozzle  15  is formed in this way, an effect that the molten metal nozzle  15  can be easily manufactured can be exhibited, in addition to the effect of the first embodiment. 
     Fourth Embodiment 
     Next, a metal powder manufacturing device according to a fourth embodiment of the present invention will be described below using the drawings. 
       FIG. 10  is a sectional view of a crucible apparatus  16  of the metal powder manufacturing device according to the fourth embodiment. The present embodiment differs from the first embodiment mainly in that an orifice part  17   b  is located above a molten metal nozzle body  17   a , and is supported by an upper end part (a crucible  11 -side end part (upper end surface)) of the molten metal nozzle body  17   a . In other words, as depicted in  FIG. 10 , the upper end part of the molten metal nozzle body  17   a  and the orifice part  17   b  are inserted in a nozzle fixing hole  11   a  of the crucible  11 , the upper end part of the molten metal nozzle body  17   a  is fixed to the nozzle fixing hole  11   a  of the crucible  11  by an adhesive or the like, and a lower end part of the orifice part  17   b  is supported by the upper end part of the molten metal nozzle body  17   a . Note that the orifice part  17   b  has an inside diameter equal to or smaller than the inside diameter of the molten metal nozzle body  17   a , and is formed of a material harder and better in abrasion resistance than the material of the molten metal nozzle body  12   c , like the orifice part  12   d  in the first embodiment. 
     According to the present embodiment, the orifice part  17   b  is supported by the upper end part of the molten metal nozzle body  17   a , and, therefore, the orifice part  17   b  can be prevented from dropping off from a molten metal nozzle  17 . Note that it is natural that the molten metal nozzle  17  in the present embodiment can exhibit an effect similar to the effect of the molten metal nozzle  12  in the first embodiment. 
     Note that the orifice part  17   b  may be fixed to the nozzle fixing hole  11   a  of the crucible  11  or the upper end part of the molten metal nozzle body  17   a  by an adhesive or the like, or the fixation by an adhesive or the like may be avoided and the orifice part  17   b  may be attachable to and detachable from the nozzle fixing hole  11   a  of the crucible  11  or the upper end part of the molten metal nozzle body  17   a . In the latter case, it is easy to exchange to an orifice part  17   b  different in inside diameter according to the particle diameter of the metal powder desired, and, therefore, the efficiency of manufacturing metal powders of different particle diameters can be enhanced. 
     In addition, a stopper  18  of a material softer than the material of the orifice part  17   b , as described in  FIG. 11 , may be additionally provided to the metal powder manufacturing device in the present embodiment. The stopper  18  can make contact with a crucible  11 -side end part  17   c  of the orifice part  17   b , and can close a crucible  11 -side opening  17   d  of the molten metal nozzle  17 . In this case, since the material of the stopper  18  is a material (for example, silicon nitride) softer than the material of the orifice part  17   b , the tip end (lower end) of the stopper  18  can make close contact with the crucible  11 -side end part  17   c  of the orifice part  17   b  making contact therewith, and can prevent the molten metal  8  in the crucible  11  from leaking through the contact part. 
     &lt;Others&gt; 
     The present invention is not limited to the above-described embodiments, but includes various modifications within such ranges as not to depart from the gist of the invention. For example, the present invention is not limited to a configuration including all the configurations described in each of the above embodiments, but includes a configuration in which part of the configurations is omitted. In addition, a part of the configuration according to an embodiment may be added to or used to substitute the configuration according to other embodiment. 
     While a case where one molten metal nozzle  12  is provided at the bottom surface of the crucible  11  has been described in the above-described embodiments, the number of the molten metal nozzles  12  provided at the bottom surface of the crucible  11  is not limited to one, but may be two or may be three or more. In this case, the plurality of spraying nozzles  22  are provided in each of the peripheries of the molten metal nozzles  12 ,  15 , and  17 , and spray a spray gas  7   a  to the molten metal flow  8   a  flowing downward from each of the molten metal nozzles  12 . 
     In addition, while an example in which the molten metal nozzle  12 ,  15 ,  17  is inserted and fixed in the nozzle fixing hole  11   a  of the crucible  11  has been depicted, the molten metal nozzle  12 ,  15  may be fixed to the bottom surface of the crucible  19  by an adhesive or the like such that a through-hole  19   a  and the inside of the molten metal nozzle  12 ,  15  communicate with each other, as depicted in  FIG. 12 . 
     Besides, while the so-called gas atomizing device in which a gas (inert gas  7 ) is sprayed from the spraying nozzle  22  has been described above, the present invention is applicable to any atomizing device in which a fluid is sprayed, inclusive of a water atomizing device in which water (liquid) is sprayed from the spraying nozzle  22 , and is applicable further to a disk atomizing device. 
     DESCRIPTION OF REFERENCE CHARACTERS 
     
         
           1 : Solution tank 
           2 : Gas sprayer 
           3 : Spray gas supply pipe 
           4 : Atomization tank 
           5 : Collection hopper 
           6 : Exhaust pipe 
           7 : Inert gas 
           7   a : Spray gas 
           8 : Molten metal 
           8   a : Molten metal flow 
           8   b : Fine particles 
           10 : Crucible apparatus 
           11 ,  19 : Crucible 
           11   a : Nozzle fixing hole 
           12 ,  15 ,  17 : Molten metal nozzle 
           12   c ,  17   b : Molten metal nozzle body 
           12   d ,  15   a ,  17   a : Orifice part 
           13 ,  18 : Stopper 
           21 : Spraying hole 
           22 : Spraying nozzle 
           24 : Molten metal nozzle insertion hole 
           25 : Atomization nozzle