Metal powder manufacturing method

Abstract

To provide a metal powder manufacturing method that can produce metal powder of a target particle size with high yield. [Solution] A method for producing metal powder by spraying a coolant in an inverted cone shape from a nozzle of a cylindrical main body and flowing molten metal down from above the main body toward a liquid film formed thereon, thereby scattering the molten metal into fine droplets and cooling and solidifying the droplets, wherein the ring diameter of the nozzle is 55 mm or more and 135 mm or less, the flow rate of the coolant is WM [L / min], the ring diameter of the nozzle is φ [mm], WM / φ is 6.0 or more and less than 10.0, the thickness of the liquid film is 50 μm or more and 140 μm, the negative pressure inside the main body is 70 kPa or more, and the airflow rate of the gas drawn into the main body from above is 0.15 m 3 A method for producing metal powder characterized by having a rate of / s or higher.

Description

[Technical Field]

[0001] This invention relates to a method for producing metal powder. [Background technology]

[0002] Patent Document 1 discloses a method for producing metal powder by atomization, characterized in that the downward flow of molten metal is passed through the center of a nozzle through which gas flows, the molten metal is split by the gas near the nozzle outlet, and then the split molten metal is further split into smaller pieces by a liquid ejected in an inverted cone shape.

[0003] Furthermore, in Example 1 of Patent Document 1, the diameter of the slit of the inverted cone-shaped nozzle that ejects the liquid is 55 mm, the apex angle of the liquid jet is 30°, the water flow rate is 390 L / min, and the water pressure is 950 kgf / cm². 2 It is disclosed that the pressure is 93.2 MPa, the minimum pressure inside the nozzle is 160 Torr, and the average particle size of the resulting metal powder is 16.7 μm.

[0004] This method for producing metal powder makes it possible to manufacture fine, spherical metal powder with a low oxygen content. [Prior art documents] [Patent Documents]

[0005] [Patent Document 1] International Publication WO99 / 11407 Specification [Overview of the project] [Problems that the invention aims to solve]

[0006] The particle size of metal powder is selected according to its application, therefore, metal powder manufacturing methods require the production of metal powders of various particle sizes with high yield. In particular, in recent years, there has been a growing demand for finer metal powders. However, conventional metal powder manufacturing methods have not been able to adequately meet these demands.

[0007] Therefore, the challenge is to realize a metal powder manufacturing method that can produce metal powder of the target particle size with high yield. [Means for solving the problem]

[0008] The metal powder production method according to an application example of the present invention is: A method for producing metal powder by spraying a cooling liquid in an inverted cone shape from a nozzle of a cylindrical body, and then flowing molten metal down from above the body toward the liquid film formed, thereby scattering the molten metal into fine droplets, and then cooling and solidifying the droplets, The ring diameter of the aforementioned injection nozzle is 55 mm or more and 135 mm or less. When the flow rate of the coolant is WM [L / min] and the ring diameter of the injection port is φ [mm], WM / φ is 6.0 or more and less than 10.0, The thickness of the liquid film is 50 μm or more and 140 μm. The negative pressure inside the main body is 70 kPa or more. The amount of gas drawn into the main body from above is 0.15 m³. 3 It is / s or greater. [Brief explanation of the drawing]

[0009] [Figure 1] This is a schematic diagram (vertical cross-sectional view) showing a metal powder manufacturing apparatus, which is an example of an apparatus used in the metal powder manufacturing method according to the embodiment. [Figure 2] Figure 1 is a partially enlarged view of the metal powder manufacturing apparatus shown. [Figure 3] Table 1 shows the configuration of the metal powder manufacturing method for samples No. 1 to 16 and the evaluation results of the manufactured metal powders. [Figure 4] Table 2 shows the configuration of the method for manufacturing metal powders of Sample Nos. 17 to 24 and the evaluation results of the manufactured metal powders.

Embodiments for Carrying Out the Invention

[0010] Hereinafter, the method for manufacturing metal powders according to the present invention will be described in detail based on the preferred embodiments shown in the accompanying drawings.

[0011] 1. Metal Powder Manufacturing Apparatus FIG. 1 is a schematic diagram (vertical cross-sectional view) showing a metal powder manufacturing apparatus 1 which is an example of an apparatus used in the method for manufacturing metal powders according to the embodiment.

[0012] The metal powder manufacturing apparatus 1 shown in FIG. 1 is an apparatus for pulverizing molten metal Q into powder by an atomizing method to manufacture metal powder R. The metal powder manufacturing apparatus 1 includes a supply unit 2 for supplying molten metal Q, a main body unit 3 provided below the supply unit 2, an upper pipe 4 provided above the main body unit 3, and a suction pipe 7 provided below the main body unit 3.

[0013] 1.1. Supply Unit The supply unit 2 stores molten metal Q and supplies molten metal Q toward the main body unit 3 at a predetermined supply rate. The supply unit 2 shown in FIG. 1 is a container 21 having a storage unit 22 and a molten metal outlet 23. The storage unit 22 stores molten metal Q obtained by melting the raw material of the metal powder R to be manufactured.

[0014] Further, the molten metal outlet 23 is provided at the bottom of the container 21. The molten metal Q stored in the storage unit 22 naturally falls in a thin line through this molten metal outlet 23 and is supplied to the main body unit 3.

[0015] 1.2. Main Body Unit The main body unit 3 is provided vertically below the supply unit 2. The main body unit 3 shown in FIG. 1 has a flow path 31, a fluid storage unit 32, and an orifice 34 (injection port).

[0016] The flow path 31 is a through-hole that runs vertically between the upper surface 301 and the lower surface 302 of the main body 3 along the central axis O shown in Figure 1. In other words, the main body 3 is cylindrical in shape, with the flow path 31 running through its interior. Molten metal Q supplied from the supply unit 2 passes through this flow path 31.

[0017] The fluid storage section 32 is a space for storing water S (coolant) supplied from a water source (not shown).

[0018] The orifice 34 is a slit that injects water S stored in the fluid reservoir 32 toward the flow path 31. When water S is injected from the orifice 34, the flow of the injected water S draws air above the flow path 31 into the flow path 31. This creates a downward airflow F in the flow path 31.

[0019] The constituent material of the main body 3 is not particularly limited, but examples include stainless steel, iron-based alloys such as carbon steel, aluminum-based alloys, titanium-based alloys, etc.

[0020] 1.2.1. Flow Channel The shape of the channel 31 shown in Figure 1, when viewed from above (plan view), is a circle centered on the central axis O. The central axis O is parallel to the vertical line. The circle may also be an ellipse or an oblong, but a perfect circle is preferred. Alternatively, a polygon may be used instead of a circle.

[0021] The flow path 31 shown in Figure 1 has an inner diameter reduction section 33 in which the inner diameter gradually decreases from the upper surface 301 downwards. The velocity (flow rate) of the airflow F drawn into the flow path 31 increases as it passes through the inner diameter reduction section 33. As the flow rate increases, the pressure in the flow path 31 decreases. The flow rate is maximized before and after passing through the inner diameter minimum section 331, where the inner diameter is smallest. When the air flow rate is maximized, the pressure inside the flow path 31 also decreases particularly at or downstream of the inner diameter minimum section 331.

[0022] The molten metal Q supplied to the channel 31 passes through the low-pressure region formed in the channel 31 in this manner. As a result, the surrounding pressure becomes lower than the cohesive force that would cause the molten metal Q to concentrate, and the molten metal Q splits and scatters. This causes the molten metal Q to become numerous droplets Q1. In Figure 1, droplets Q1 are shown to be generated in the channel 31, but the metal powder manufacturing apparatus 1 may be configured to generate droplets Q1 below the channel 31.

[0023] 1.2.2. Fluid Storage Section The fluid reservoir 32 is located inside the main body 3 and stores water S (coolant) supplied from the water source. It then supplies water S to the orifice 34. As will be described later, the orifice 34 has a continuous opening in the circumferential direction on the side of the flow path 31. Therefore, the fluid reservoir 32 that supplies water S to the orifice 34 is preferably arranged in an annular shape along the circumferential direction of the flow path 31. This allows water S to be supplied to the orifice 34 at a uniform pressure.

[0024] 1.2.3. Orifice The orifice 34 opens along the circumferential direction of the flow path 31. In other words, the orifice 34 shown in Figure 1 is an annular shape centered on the central axis O of the flow path 31. When water S (coolant) is injected from such an orifice 34, the injected water S converges downwards, forming a liquid film S1 that is conical (inverted cone) in shape with its apex S2 pointing downwards. When a droplet Q1 of molten metal Q comes into contact with this liquid film S1, the droplet Q1 is cooled and solidifies. This yields metal powder R. The obtained metal powder R is collected in a container (not shown) located below the metal powder manufacturing apparatus 1.

[0025] A cylindrical member (not shown) may be provided below the molten metal outlet 23. In this case, the molten metal Q discharged from the molten metal outlet 23 is supplied to the main body 3 through the inside of the cylindrical member. This makes it less likely for the molten metal Q discharged in a thin wire to bend along the way, allowing the molten metal Q to flow down along the central axis O. As a result, the molten metal Q can be evenly divided, and the generation of coarse and irregularly shaped particles can be suppressed.

[0026] Furthermore, the coolant injected from the orifice 34 may be a gas, but it is preferable that it be a liquid such as water S. Because liquids have a larger heat capacity than gases, they can rapidly cool the droplet Q1. This suppresses oxidation of the metal powder R and also suppresses the coarsening of the crystal particle size.

[0027] The opening of the orifice 34 is annular and located below the minimum inner diameter portion 331. As a result, the water S injected annularly from the orifice 34 can form a continuous conical liquid film S1, which effectively pushes the air in the flow path 31 downwards. This allows for further depressurization of the flow path 31.

[0028] 1.3. Upper pipe The upper pipe 4 shown in Figure 1 is located vertically above the main body 3. The upper pipe 4 extends vertically and has a cylindrical (tubular) shape centered on the central axis O. The plan view shape of the upper pipe 4 may be a circle centered on the central axis O, or it may be a polygon. The upper pipe 4 protects the molten metal Q flowing down toward the main body 3 and regulates the airflow F toward the main body 3. This stabilizes the negative pressure formed inside the main body 3.

[0029] The upper end of the upper pipe 4 may be closed, but it is open in Figure 1. By leaving it open, the airflow F can be optimized.

[0030] The lower end of the upper pipe 4 is connected to the main body 3. This allows the inside of the upper pipe 4 to communicate with the flow path 31 of the main body 3, thereby regulating the airflow F into the flow path 31, stabilizing the negative pressure, and suppressing the scattering of water droplets S rising from the liquid film S1. As a result, regardless of the amount of molten metal Q supplied to the flow path 31, droplets Q1 with little variation in particle size can be formed, and cooling can be performed uniformly.

[0031] 1.4. Suction pipe The suction pipe 7 shown in Figure 1 is located vertically below the main body 3. The suction pipe 7 extends vertically and has a cylindrical (tubular) shape centered on the central axis O. The plan view shape of the suction pipe 7 may be a circle centered on the central axis O, or it may be a polygon. The suction pipe 7 prevents the scattering of metal powder R falling downwards.

[0032] Furthermore, it is preferable that the suction pipe 7 is airtightly connected to the lower surface 302 of the main body 3. This prevents outside air from flowing into the suction pipe 7. As a result, contact of outside air with the droplets Q1 and metal powder R is suppressed, thereby preventing unintended cooling of the droplets Q1 and oxidation of the metal powder R.

[0033] Furthermore, the inclusion of the suction pipe 7 creates a continuous space between the flow path 31 and the inside of the suction pipe 7, making it easier to further reduce the pressure in the flow path 31. Hereinafter, this space will be referred to as the "reduced pressure space." As the pressure in the reduced pressure space decreases, the molten metal Q is broken down into finer particles, making it possible to produce metal powder R with a smaller particle size.

[0034] The cross-sectional shape when the suction pipe 7 is cut by a plane perpendicular to the central axis O is preferably constant along the central axis O, but it may change along the way. For example, the cross-sectional shape may increase proportionally downwards.

[0035] Furthermore, the suction pipe 7 is preferably a straight pipe along the central axis O, but it may be bent in the middle.

[0036] 2.Metal powder manufacturing method Next, a metal powder manufacturing method according to an embodiment will be described.

[0037] In the metal powder manufacturing method according to this embodiment, water S (cooling liquid) is sprayed in an inverted cone shape from the orifice 34 (injection port) of the cylindrical main body 3 to form a liquid film S1 onto which molten metal Q is flowed down from above the main body 3. This causes the molten metal Q to be scattered into fine droplets Q1, and the droplets Q1 are cooled and solidified to produce metal powder R.

[0038] Such a metal powder manufacturing method satisfies the following five elements (a) to (e).

[0039] (a) The ring diameter of orifice 34 is between 55 mm and 135 mm. (b) When the flow rate (volume) of water S (coolant) is WM [L / min] and the ring diameter of orifice 34 is φ [mm], then WM / φ is 6.0 or more and less than 10.0. (c) The thickness t of the liquid film S1 is 50 μm or more and 140 μm. (d) The negative pressure NP inside the main body 3 is 70 kPa or more. (e) The airflow AM of the air (gas) drawn into the main body 3 from above is 0.15 m³ 3 / s or greater

[0040] By having the five elements (a) to (e) described above, metal powder R of the target particle size can be produced in high yield. In other words, when producing metal powder R by supplying molten metal Q stored in the storage section 22 to the flow channel 31, even if the supply amount is changed according to the target particle size, variations in particle size can be suppressed. In particular, even with the fine particle sizes that are generally produced by the water atomization method, variations in particle size can be suppressed. As a result, metal powder R can be produced in high yield. The following explains the five elements (a) to (e) mentioned above.

[0041] 2.1.(a) Ring diameter of the orifice Figure 2 is a partially enlarged view of the metal powder manufacturing apparatus 1 shown in Figure 1.

[0042] Element (a) specifies that the ring diameter φ of the orifice 34 shown in Figure 2 is 55 mm or more and 135 mm or less. Preferably, the ring diameter φ is 60 mm or more and 115 mm or less, and more preferably 70 mm or more and 100 mm or less. By setting the ring diameter φ of the orifice 34 within the above range, the negative pressure NP and the water volume WM can be optimized, respectively. This allows for a sufficiently high cooling rate of the droplet Q1 while achieving appropriate particle size refinement of the droplet Q1. As a result, droplet Q1 with little particle size variation can be formed regardless of the amount of molten metal Q supplied to the flow path 31, and cooling can be performed uniformly. This makes it possible to produce metal powder R of the desired particle size in high yield.

[0043] Furthermore, if the ring diameter φ falls below the lower limit, the water flow rate WM cannot be sufficiently increased, and the negative pressure NP cannot be sufficiently secured. As a result, the molten metal Q may not be sufficiently refined, or the cooling rate of the droplet Q1 may be insufficient. On the other hand, if the ring diameter φ exceeds the upper limit, the negative pressure NP may not be sufficiently secured, or unevenness may occur in the airflow rate AM within the flow path 31. As a result, the molten metal Q may not be sufficiently refined, or unevenness may occur in the cooling rate of the droplet Q1, leading to variations in particle size.

[0044] The ring diameter φ of the orifice 34 refers to the diameter of the portion of the orifice 34 that opens into the flow path 31. Specifically, when the main body 3 shown in Figure 2 is viewed from below, the opening of the orifice 34 appears ring-shaped. The ring diameter φ is the midpoint between the inner diameter and the outer diameter of this ring-shaped opening.

[0045] 2.2.(b) Relationship between water flow rate WM and ring diameter φ Element (b) specifies that the ratio WM / φ of the water flow rate WM [L / min] to the ring diameter φ [mm] of the orifice 34 is 6.0 or more and less than 10.0. Furthermore, the ratio WM / φ is preferably 6.5 or more and 9.5 or less, and more preferably 7.0 or more and 9.0 or less. By keeping the ratio WM / φ within the above range, the balance between the ring diameter φ of the orifice 34 and the water flow rate WM can be optimized. As a result, droplets Q1 with little variation in particle size can be formed regardless of the amount of molten metal Q supplied to the flow path 31, and cooling can be performed uniformly. In addition, by keeping the ratio WM / φ within the above range, the negative pressure NP inside the main body 3 and the airflow rate AM of the air drawn into the main body 3 from above can be optimized. As a result, metal powder R of the desired particle size can be produced in high yield.

[0046] Furthermore, if the ratio WM / φ falls below the lower limit, the water volume WM is insufficient relative to the ring diameter φ, resulting in insufficient negative pressure NP or uneven airflow AM within the flow path 31. This can lead to insufficient refinement of the molten metal Q or uneven cooling of droplets Q1, causing variations in particle size. On the other hand, if the ratio WM / φ exceeds the upper limit, the water volume WM becomes excessive relative to the ring diameter φ, causing the injected water S to easily become airborne, hindering the refinement and cooling of the molten metal Q. This can result in insufficient refinement of the molten metal Q or uneven cooling of droplets Q1, causing variations in particle size.

[0047] 2.3.(c) Thickness t of liquid film S1 Element (c) specifies that the thickness t of the liquid film S1 is 50 μm or more and 140 μm or less. Furthermore, the thickness t of the liquid film S1 is preferably 60 mm or more and 130 mm or less, and more preferably 70 mm or more and 120 mm or less. By setting the thickness t within the above range, the water flow rate WM can be optimized, and thus the negative pressure NP and airflow rate AM can be optimized, respectively. This allows for a moderate degree of miniaturization of the droplets Q1 while sufficiently increasing the cooling rate of the droplets Q1. As a result, regardless of the amount of molten metal Q supplied to the flow path 31, droplets Q1 with little variation in particle size can be formed and cooled uniformly.

[0048] Furthermore, if the thickness t of the liquid film S1 falls below the lower limit, the negative pressure NP and airflow AM will be insufficient. On the other hand, if the thickness t of the liquid film S1 exceeds the upper limit, the water flow rate WM tends to become excessive, hindering the refinement and cooling of the molten metal Q. The thickness t of the liquid film S1 is determined as the thickness of the opening of the orifice 34.

[0049] 2.4.(d) Negative pressure NP inside the main body 3 Element (d) specifies that the negative pressure NP inside the main body 3 is 70 kPa or more. Furthermore, the negative pressure NP is preferably 75 kPa or more and 150 kPa or less, and more preferably 80 kPa or more and 140 kPa or less. By keeping the negative pressure NP within the above range, the molten metal Q can be finely milled. In addition, oxidation of the molten metal Q can be suppressed, making it easier to maintain a constant viscosity of the molten metal Q and suppressing variations in particle size.

[0050] Furthermore, if the negative pressure NP falls below the lower limit, the negative pressure NP becomes too high (too low), making it difficult to maintain, resulting in insufficient refinement of the molten metal Q or variations in particle size. On the other hand, if the negative pressure NP exceeds the upper limit, the negative pressure NP becomes insufficient, resulting in insufficient refinement of the molten metal Q or variations in particle size.

[0051] The negative pressure NP is measured by a negative pressure gauge 81 shown in Figure 1. The negative pressure gauge 81 shown in Figure 1 has a negative pressure measuring unit 812 and a measuring pipe 814. The measuring pipe 814 is positioned so that one end is located near the top S2 of the water S and the other end is located outside the suction pipe 7. The negative pressure measuring unit 812 is connected to the other end of the measuring pipe 814. This allows the negative pressure measuring unit 812 to measure the negative pressure inside the suction pipe 7.

[0052] 2.5.(e) Airflow AM In element (e), the airflow rate AM of the air (gas) drawn into the interior from above the main body 3 is 0.15 m³. 3 It is specified that the airflow rate must be at least / s. Furthermore, the airflow rate AM is preferably 0.15 m³. 3 / s or more 0.80m 3 / s or less, more preferably 0.17m3 0.75 m or more 3 and preferably 0.20 m or less, and more preferably 3 0.70 m or more 3 and 0.70 m or less. By setting the air volume AM within the above range, unevenness in the air volume AM can be suppressed, and unevenness in the cooling rate of the droplets Q1 can be suppressed. As a result, while stabilizing the negative pressure NP, it is possible to suppress the splashing of the water S rising from the liquid film S1. Thereby, regardless of the amount of the molten metal Q supplied to the flow path 31, droplets Q1 with little variation in particle size can be formed and cooled evenly.

[0053] When the air volume AM is less than the lower limit value, since the air volume AM is insufficient, the negative pressure NP is also insufficient. For this reason, the refinement of the molten metal Q becomes insufficient or the particle size varies. On the other hand, when the air volume AM exceeds the upper limit value, the unevenness of the air volume AM becomes large, and a large amount of droplets of the water S splash from the liquid film S1, so the unevenness of the cooling rate of the droplets Q1 becomes large. As a result, the particle size of the molten metal Q varies.

[0054] The air volume AM is measured by the air volume meter 82 shown in FIG. 1. The air volume meter 82 shown in FIG. 1 includes a differential pressure gauge 822 and a Pitot tube 824. The Pitot tube 824 is disposed so as to penetrate the upper tube 4 and has a total pressure measurement hole and a static pressure measurement hole (not shown). The total pressure measurement hole is located inside the upper tube 4 and is open so as to face the air flow F. On the other hand, the static pressure measurement hole is located inside the upper tube 4 and is open so as to be orthogonal to the air flow F. The differential pressure gauge 822 obtains the difference (dynamic pressure) between the total pressure measured through the total pressure measurement hole and the static pressure measured through the static pressure measurement hole, and obtains the wind speed [m / s] based on this dynamic pressure and the air density. The air density is 1.293 [kg / m 3 . Then, the air volume AM is obtained as the product of the obtained wind speed [m / s] and the effective area (cross-sectional area) [m 2 of the flow path 31.

[0055] 2.6. Focal length L As shown in FIG. 2, the vertical length from the orifice 34 (injection port) to the top S2 of the liquid film S1 is referred to as the "focal length L".

[0056] In the metal powder manufacturing method according to the embodiment, the focal length L is preferably 90 mm or more, more preferably 90 mm to 1200 mm, even more preferably 120 mm to 900 mm, and particularly preferably 140 mm to 700 mm. By setting the focal length L within the above range, the negative pressure NP and airflow rate AM can be stabilized, so that metal powder R of the target particle size can be manufactured with a higher yield. In addition, since time can be secured until the droplet Q1 contacts the liquid film S1, it is easier to make the droplet Q1 spherical. Therefore, metal powder R with high circularity can be manufactured.

[0057] Furthermore, if the focal length L falls below the lower limit, the space for dispersing and cooling the droplet Q1 becomes smaller, which may lead to the generation of irregularly shaped particles or a large variation in particle size. In addition, the circularity of the manufactured metal powder R may decrease. On the other hand, if the focal length L exceeds the upper limit, the suction tube 7 becomes too long, which may prevent sufficient distance between the particles of the manufactured metal powder R, potentially reducing the cooling rate.

[0058] 2.7. Area A of liquid film S1 The liquid film S1 formed by the injection of water S forms an inverted cone with a base that is a circle with a diameter equal to the ring diameter φ and a height equal to the focal length L along the central axis O. When this inverted cone is cut by a plane containing the central axis O, the area of ​​the isosceles triangle that appears on the cut surface is defined as "Area A of the liquid film S1".

[0059] In the metal powder manufacturing method according to this embodiment, the area A of the liquid film S1 is preferably 2000 mm². 2 The above is 100,000. 2 The following, more preferably 5000 mm 2 Over 50,000 mm 2 The following, and more preferably 8000 mm 2 More than 30000mm 2The following is achieved: By keeping the area A of the liquid film S1 within the aforementioned range, sufficient volume of space for splitting and cooling the molten metal Q formed by the liquid film S1 can be secured. As a result, regardless of the amount of molten metal Q supplied to the flow path 31, droplets Q1 with little variation in particle size can be formed and cooled uniformly.

[0060] Furthermore, if the area A of the liquid film S1 falls below the lower limit, the space for dispersing and cooling the droplet Q1 becomes smaller, which may lead to the generation of irregularly shaped particles or large variations in particle size. On the other hand, if the area A of the liquid film S1 exceeds the upper limit, the ring diameter φ becomes excessively large, which may result in insufficient negative pressure NP or uneven airflow AM within the flow path 31.

[0061] 2.8. Water pressure (WP) In the metal powder manufacturing method according to this embodiment, the water pressure WP (pressure of water S) is preferably 30 MPa to 200 MPa, more preferably 50 MPa to 150 MPa, and even more preferably 70 MPa to 120 MPa. If the water pressure WP is within the above range, the thickness t of the liquid film S1 and the amount of water WM can be optimized within the above range.

[0062] Furthermore, if the water pressure WP falls below the lower limit, the water flow rate WM may decrease or become unstable depending on the thickness t of the liquid film S1. On the other hand, if the water pressure WP exceeds the upper limit, the water flow rate WM may become excessive or unstable depending on the thickness t of the liquid film S1.

[0063] 2.9. Vertex angle θ In the metal powder manufacturing method according to the embodiment, the apex angle θ (angle of the apex S2 of the liquid film S1) shown in Figure 2 is preferably 3° to 60°, more preferably 5° to 50°, and even more preferably 7° to 30°. By setting the apex angle θ within the above range, sufficient volume of space for splitting and cooling the molten metal Q formed by the liquid film S1 can be secured. As a result, regardless of the amount of molten metal Q supplied to the flow path 31, droplets Q1 with little variation in particle size can be formed and cooled uniformly. In addition, since time can be secured before the droplet Q1 contacts the liquid film S1, it is easier to make the droplet Q1 spherical. For this reason, metal powder R with high circularity can be manufactured.

[0064] Furthermore, if the apex angle θ falls below the lower limit, the space for dispersing and cooling the droplet Q1 becomes smaller, which may lead to the generation of irregularly shaped particles or large variations in particle size. On the other hand, if the apex angle θ exceeds the upper limit, the area A of the liquid film S1 becomes excessively large, which may result in insufficient negative pressure NP or uneven airflow AM within the flow path 31.

[0065] 2.10.Casting temperature The casting temperature (temperature of the molten metal Q) should be above the melting point of the raw material, but it is preferably 200°C to 400°C higher than the melting point of the raw material, more preferably 215°C to 350°C higher, and even more preferably 230°C to 300°C higher. This optimizes the viscosity of the molten metal Q, enabling the production of metal powder R with less variation in particle size and fewer irregularly shaped particles.

[0066] Furthermore, if the casting temperature falls below the lower limit, the viscosity of the molten metal Q increases, which may make it difficult to produce fine metal powder R, increase particle size variation, or result in a large number of irregularly shaped particles. On the other hand, if the casting temperature exceeds the upper limit, special heat resistance is required in the supply unit 2, which may make it difficult to stably hold the molten metal Q. In addition, there is a risk of increased particle size variation.

[0067] 2.11. Nozzle diameter As shown in Figure 1, the prepared molten metal Q is discharged from the molten metal outlet 23 and supplied to the main body 3. The inner diameter φ23 (nozzle diameter) of the molten metal outlet 23 determines the outer diameter of the flowing molten metal Q, and thus affects the amount of metal powder R produced per unit time and its particle size. The inner diameter φ23 of the molten metal outlet 23 is preferably 1.0 mm or more and 6.0 mm or less, more preferably 1.5 mm or more and 5.5 mm or less, and even more preferably 2.0 mm or more and 5.0 mm or less. If the inner diameter φ23 of the molten metal outlet 23 is within the above range, the target particle size can be easily adjusted while suppressing variations in particle size. Specifically, reducing the nozzle diameter tends to result in a smaller target particle size of metal powder R, while increasing the nozzle diameter tends to result in a larger target particle size of metal powder R. The target particle size can also be adjusted by other parameters, such as negative pressure NP and airflow rate AM.

[0068] Furthermore, if the nozzle diameter of the molten metal outlet 23 falls below the lower limit, the molten metal Q flowing down becomes more easily cooled, which may lead to increased particle size variation or a decrease in the circularity of the metal powder R. On the other hand, if the nozzle diameter of the molten metal outlet 23 exceeds the upper limit, it becomes difficult to finely and uniformly split the molten metal Q. This may result in the generation of coarse and irregularly shaped particles, which may lead to increased particle size variation or a decrease in the circularity of the metal powder R.

[0069] 2.12.Representative particle size Typical particle sizes of the metal powder R produced include particle sizes D10, D50, and D90.

[0070] Particle size D10 is the particle size when the cumulative frequency of the metal powder R is 10% from the smallest diameter side, based on the volume-based particle size distribution obtained using a laser diffraction particle size distribution analyzer.

[0071] Particle size D50 is the particle size when the cumulative frequency of the smallest diameter particles is 50% when the particle size distribution is obtained on a volume basis using a laser diffraction particle size distribution analyzer for the metal powder R.

[0072] Particle size D90 is the particle size of metal powder R when the cumulative frequency is 90% from the smallest diameter side, based on the volume-based particle size distribution obtained using a laser diffraction particle size distribution analyzer.

[0073] The particle size D10 of the metal powder R is not particularly limited, but is, for example, 1.0 μm or more and 7.0 μm or less.

[0074] The particle size D50 of the metal powder R is not particularly limited, but is, for example, 5.0 μm or more and 20.0 μm or less.

[0075] The particle size D90 of the metal powder R is not particularly limited, but is, for example, 20.0 μm or more and 45.0 μm or less.

[0076] For example, a particle size distribution measuring device is the Microtrac HRA9320-X100 manufactured by Nikkiso Co., Ltd.

[0077] 2.13. Circularity The circularity of the metal powder R can be quantified by the average circularity of the particle image. The average circularity of the metal powder R is preferably 0.82 or higher, more preferably 0.84 or higher, and even more preferably 0.87 or higher.

[0078] The average circularity of the metal powder R is measured as follows:

[0079] First, an image (secondary electron image) of the metal powder R is captured using a scanning electron microscope (SEM). Next, the obtained image is loaded into image processing software. For example, image processing software such as "Mac-View," an image analysis-based particle size distribution measurement software manufactured by Mountec Co., Ltd. is used. The imaging magnification is adjusted so that 50 to 100 particles are captured in each image. Then, multiple images are acquired so that a total of 300 or more particle images are obtained.

[0080] Next, the circularity of over 300 particle images is calculated using software, and the average value is determined. The resulting average value becomes the average circularity of the metal powder R. Note that the circularity is denoted as e, and the area of ​​the particle image is denoted as S. R Let L be the perimeter of the particle image. R In this case, the degree of circularity e can be calculated using the following formula. e=4πS R / L R 2

[0081] 3. Effects achieved by the above embodiment The metal powder manufacturing method according to the above embodiment involves injecting water S (coolant) in an inverted cone shape from an orifice 34 (injection port) of a cylindrical main body 3 to form a liquid film S1. Molten metal Q is then flowed down from above the main body 3 towards this film, scattering the molten metal Q into fine droplets, and then cooling and solidifying the droplets Q1 to produce metal powder R. In this metal powder manufacturing method, the ring diameter of the orifice 34 is 55 mm or more and 135 mm or less. Also, when the flow rate of water S is WM [L / min] and the ring diameter of the orifice 34 is φ [mm], WM / φ is 6.0 or more and less than 10.0. Furthermore, the thickness t of the liquid film S1 is 50 μm or more and 140 μm. Also, the negative pressure NP inside the main body 3 is 70 kPa or more. Furthermore, the airflow rate AM of the air (gas) drawn into the main body 3 from above is 0.15 m 3 It is / s or greater. With this configuration, metal powder R of the target particle size can be produced in high yield.

[0082] In the metal powder manufacturing method according to the above embodiment, it is preferable that the focal length L (vertical length from the orifice 34 (injection port) to the top S2 of the liquid film S1) is 90 mm or more.

[0083] With this configuration, the negative pressure NP and airflow AM can be stabilized, allowing for the production of metal powder R with the target particle size in higher yield. Furthermore, sufficient time can be ensured for the droplet Q1 to contact the liquid film S1, making it easier to achieve spherical droplet Q1. Therefore, metal powder R with high circularity can be produced.

[0084] In the metal powder manufacturing method according to the above embodiment, the area A of the liquid film S1 is 2000 mm². 2 The above is 100,000. 2 The following is preferable:

[0085] With this configuration, sufficient volume of space can be secured for the liquid film S1 to split and cool the molten metal Q. As a result, regardless of the amount of molten metal Q supplied to the flow path 31, droplets Q1 with little variation in particle size can be formed and cooled uniformly.

[0086] In the metal powder manufacturing method according to the above embodiment, it is preferable that the water pressure WP of the water S (cooling liquid) is 30 MPa or more and 200 MPa or less.

[0087] With this configuration, the thickness t of the liquid film S1 and the water volume WM can be adjusted to an optimal range.

[0088] In the metal powder manufacturing method according to the above embodiment, it is preferable that the apex angle θ of the liquid film S1 is 3° or more and 60° or less.

[0089] With this configuration, sufficient volume of space is secured for the liquid film S1 to split and cool the molten metal Q. As a result, droplets Q1 with little variation in particle size can be formed regardless of the amount of molten metal Q supplied to the flow path 31, and cooling can be performed uniformly. In addition, sufficient time is secured for the droplets Q1 to come into contact with the liquid film S1, making it easier to make the droplets Q1 spherical. Therefore, metal powder R with high circularity can be manufactured.

[0090] Although the metal powder manufacturing method according to the present invention has been described above in the illustrated embodiments, the present invention is not limited thereto. For example, the metal powder manufacturing method according to the present invention may have additional steps added to the above embodiments for any purpose.

[0091] Furthermore, potential applications of the manufactured metal powder R include, for example, powder metallurgy, magnetic elements, fillers, thermal spray materials, and additive manufacturing. [Examples]

[0092] Next, specific embodiments of the present invention will be described. 4. Manufacturing of metal powders First, precipitation-hardening stainless steel SUS630 (17-4PH) raw material was melted in the supply section of the metal powder manufacturing apparatus to obtain molten metal. Next, the obtained molten metal was supplied from the supply section to the main body to produce metal powder. In this metal powder manufacturing method, the configuration was changed as shown in Tables 1 and 2. In Tables 1 and 2, metal powder manufacturing methods with different configurations are designated as Samples No. 1 to 24. Of these, metal powders produced by the metal powder manufacturing method and its manufacturing method corresponding to the present invention are designated as "Examples," and metal powders produced by the metal powder manufacturing method and its manufacturing method that do not correspond to the present invention are designated as "Comparative Examples."

[0093] Figure 3 is shown in Table 1, which illustrates the configuration of the metal powder manufacturing method for samples No. 1 to 16 and the evaluation results of the manufactured metal powders.

[0094] Figure 4 is shown in Table 2, which illustrates the configuration of the metal powder manufacturing method for samples No. 17 to 24 and the evaluation results of the manufactured metal powders.

[0095] Although not shown in Tables 1 and 2, the water pressure was set within the range of 70 to 120 MPa.

[0096] 5. Evaluation of metal powders The following measurements or evaluations were performed on the metal powders of each example and comparative example. The measurement and evaluation results are shown in Table 1 (Figure 3) and Table 2 (Figure 4).

[0097] 5.1. Representative particle size (particle size D10, D50, D90) The representative particle size was measured for the metal powders of each example and comparative example. The measurement results are shown in Tables 1 and 2.

[0098] 5.2. Target particle size The target particle size for each example and comparative example of the metal powder production method is shown in Tables 1 and 2. The target particle size was set based on the nozzle diameter and fine-tuned by negative pressure (NP). The nozzle diameter was adjusted within the range of 2.0 to 5.0 mm.

[0099] Furthermore, the yield of the target particle size, as shown in Tables 1 and 2, was evaluated. The yield of the target particle size was evaluated as follows:

[0100] First, the absolute value of the deviation between particle size D50 and the target particle size was calculated. The calculation results are shown in Tables 1 and 2 as "Deviation of particle size D50". Next, the deviation of particle size D50 was evaluated against the following evaluation criteria. The evaluation results are shown in Tables 1 and 2.

[0101] A: The displacement of particle size D50 is 1.0 μm or less. B: The displacement of particle size D50 is greater than 1.0 μm and less than or equal to 2.0 μm. C: The displacement of particle size D50 is greater than 2.0 μm.

[0102] 5.3. Mean Circularity The average circularity was measured for the metal powders of each example and comparative example. The measured average circularity was then evaluated against the following evaluation criteria. The evaluation results are shown in Tables 1 and 2.

[0103] A: The average circularity is 0.87 or higher. B: The average circularity is 0.82 or higher and less than 0.87. C: The average circularity is less than 0.82.

[0104] 5.4. Discussion Based on the evaluation results shown in Tables 1 and 2, the following points were observed.

[0105] It was found that by satisfying the aforementioned elements (a) to (e) in the metal powder manufacturing method, it is possible to manufacture metal powder of the desired particle size in high yield.

[0106] In the metal powder manufacturing method, it was found that by optimizing the apex angle θ of the liquid film S1 while satisfying elements (a) to (e), it is possible to manufacture metal powder with high circularity in high yield. [Explanation of Symbols]

[0107] 1…Metal powder manufacturing apparatus, 2…Supply unit, 3…Main unit, 4…Upper pipe, 7…Suction pipe, 21…Container, 22…Storage unit, 23…Molten metal outlet, 31…Flow path, 32…Fluid storage unit, 33…Inner diameter reduction unit, 34…Orifice, 81…Negative pressure gauge, 82…Air flow meter, 301…Top surface, 302…Bottom surface, 331…Minimum inner diameter, 812…Negative pressure measurement unit, 814…Measurement piping, 822…Differential pressure gauge, 824…Pitot tube, F…Airflow, L…Focal length, O…Central axis, Q…Molten metal, Q1…Droplet, R…Metal powder, S…Water, S1…Liquid film, S2…Top, θ…Top angle, φ…Ring diameter, φ23…Inner diameter

Claims

1. A method for producing metal powder by spraying a cooling liquid in an inverted cone shape from a nozzle of a cylindrical body, and then flowing molten metal down from above the body toward the liquid film formed, thereby scattering the molten metal into fine droplets, and then cooling and solidifying the droplets, The ring diameter of the aforementioned injection nozzle is 55 mm or more and 135 mm or less. When the flow rate of the coolant is WM [L / min] and the ring diameter of the injection port is φ [mm], WM / φ is 6.0 or more and less than 10.0, The thickness of the liquid film is 50 μm or more and 140 μm. The negative pressure inside the main body is 70 kPa or more. The amount of gas drawn into the main body from above is 0.15 m³. ３ A method for producing metal powder characterized by having a rate of / s or higher.

2. The method for producing metal powder according to claim 1, wherein the vertical length from the injection nozzle to the top of the liquid film is 90 mm or more.

3. The area of ​​the aforementioned liquid film is 2000 mm². ２ 100,000 mm ２ The method for producing metal powder according to claim 1 or 2, which is as follows:

4. The method for producing metal powder according to claim 1 or 2, wherein the water pressure of the cooling liquid is 30 MPa or more and 200 MPa or less.

5. The method for producing metal powder according to claim 1 or 2, wherein the apex angle of the liquid film is 3° or more and 60° or less.

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