Apparatus for producing metal powder and method for producing metal powder

Abstract

To provide an apparatus producing metal powder and a method for producing metal powder that allow production of fine metal powder with reduced generation of irregularly-shaped particles.SOLUTION: An apparatus for producing metal powder comprises: a supply unit having a discharge port and supplying a molten metal from the discharge port; a main body unit that is provided below the supply unit and includes a flow passage through which the molten metal supplied from the supply unit passes, and an orifice that sprays a fluid in a conical shape converging below the flow passage; and a suction pipe that is provided below the main body unit, has a tubular shape extending in a vertical direction, and brings the molten metal that has passed through the flow passage and the fluid sprayed from the orifice into contact with each other inside. An apex angle of the fluid sprayed in the conical shape is 5° or more and less than 10°, and a maximum negative pressure inside the flow passage or the suction pipe is 45 kPa or more and 100 kPa or less.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to a metal powder manufacturing apparatus and a metal powder manufacturing method.

Background Art

[0002] Patent Document 1 discloses a metal powder manufacturing apparatus having a supply unit that supplies molten metal, a flow path that is installed below the supply unit and through which the molten metal supplied from the supply unit can pass, and a nozzle that has an orifice formed at the lower end of the flow path and injects fluid into the flow path. In this manufacturing apparatus, molten metal is scattered by bringing the molten metal that has passed through the flow path into contact with the fluid ejected from the orifice, thereby manufacturing metal powder. According to such a manufacturing apparatus, fine metal powder with uniform particle size can be efficiently manufactured.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] In recent years, with the miniaturization of metal powder, control of the particle shape has become important. In particular, there is a demand for an apparatus capable of manufacturing metal powder in which the generation of particles with different shapes is suppressed.

Means for Solving the Problems

[0005] The metal powder manufacturing apparatus according to an application example of the present invention has a discharge port and a supply unit that supplies molten metal from the discharge port, a main body portion that is provided below the supply unit and has a flow path through which the molten metal supplied from the supply unit passes, and an orifice that injects fluid in a conical shape that converges below the flow path, A suction pipe provided below the main body portion and having a tubular shape extending in the vertical direction, is provided with, the molten metal that has passed through the flow path and the fluid ejected from the orifice are configured to contact each other inside the suction pipe, the apex angle of the fluid ejected in a conical shape is 5° or more and less than 10°, the maximum negative pressure inside the flow path or the suction pipe is 45 kPa or more and 100 kPa or less.

[0006] The method for manufacturing metal powder according to an application example of the present invention is, in a reduced-pressure space that extends in the vertical direction and in which a negative pressure of 45 kPa or more and 100 kPa or less is formed, by bringing into contact a fluid ejected downward in a conical shape so that the apex angle becomes 5° or more and less than 10° with droplets of molten metal to be dropped, the droplets are cooled and solidified.

Brief Description of the Drawings

[0007]

Figure 1

Figure 2

Figure 3

Figure 4

Embodiments for Carrying Out the Invention

[0008] Hereinafter, the metal powder manufacturing apparatus and the metal powder manufacturing method of the present invention will be described in detail with reference to the accompanying drawings.

[0009] 1. First Embodiment FIG. 1 is a schematic diagram (longitudinal sectional view) showing a metal powder manufacturing apparatus 1 according to a first embodiment. FIG. 2 is a partially enlarged view of FIG. 1.

[0010] The metal powder manufacturing apparatus 1 shown in Fig. 1 is an apparatus that atomizes molten metal Q to produce metal powder R. The metal powder manufacturing apparatus 1 includes a supply unit 2 that supplies molten metal Q, a main body unit 3 provided below the supply unit 2, a suction pipe 7 provided below the main body unit 3, and an exhaust pump 8.

[0011] 1.1. Supply Unit The supply unit 2 stores molten metal Q and supplies the 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 discharge port 23. The storage unit 22 contains molten metal Q obtained by melting the raw material of the metal powder R to be manufactured.

[0012] Further, the discharge port 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 discharge port 23 and is supplied to the main body unit 3.

[0013] 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, an orifice 34, and an exhaust pipe 36.

[0014] The flow path 31 is a through hole that vertically penetrates between the upper surface 301 and the lower surface 302 of the main body unit 3 along the central axis O shown in Fig. 1. The molten metal Q supplied from the supply unit 2 passes through this flow path 31. The fluid storage unit 32 stores water S (fluid) supplied from a water source (not shown). The orifice 34 injects the water S stored in the fluid storage unit 32 toward the flow path 31. When the water S is injected from the orifice 34, the flow of the injected water S draws the air above the flow path 31 into the flow path 31. As a result, a downward air flow F is generated in the flow path 31.

[0015] The constituent material of the main body unit 3 is not particularly limited, and examples include iron-based alloys such as stainless steel and carbon steel, aluminum-based alloys, titanium-based alloys, and the like.

[0016] 1.2.1. Flow Path The flow path 31 shown in Fig. 1 has a circular shape (planar view shape) centered on the central axis O when viewed from above. The central axis O is parallel to the vertical line. Note that the circular shape may be an elliptical shape or an oval shape, but is preferably a perfect circle. Also, a polygon may be adopted instead of the circular shape.

[0017] The flow path 31 shown in Fig. 1 has an inner diameter gradually decreasing portion 33 whose inner diameter gradually decreases downward from the upper surface 301. The velocity (flow velocity) of the air flow F drawn into the flow path 31 increases when passing through the inner diameter gradually decreasing portion 33. As the flow velocity increases, the pressure in the flow path 31 decreases. And before and after passing through the inner diameter minimum portion 331 where the inner diameter is the smallest, the flow velocity becomes the maximum. When the air flow velocity reaches the maximum, the pressure inside the flow path 31 also particularly decreases at the inner diameter minimum portion 331 or on the downstream side thereof.

[0018] Also, the inner diameter of the flow path 31 becomes larger again below the inner diameter minimum portion 331. For this reason, the air drawn into the flow path 31 is depressurized further after the pressure is released after passing through the inner diameter minimum portion 331.

[0019] The molten metal Q supplied to the flow path 31 passes through the low-pressure portion formed in the flow path 31 in this way. Then, the surrounding pressure becomes lower than the cohesive force with which the molten metal Q tends to aggregate, and the molten metal Q splits and scatters. As a result, the molten metal Q becomes a large number of droplets Q1. Note that in Fig. 1, it is illustrated as if the droplets Q1 are generated in the flow path 31, but the metal powder manufacturing apparatus 1 may be configured to generate the droplets Q1 below the flow path 31.

[0020] 1.2.2. Fluid storage part The fluid storage part 32 is provided inside the main body part 3 and stores the water S (fluid) supplied from the water source. Then, it supplies the water S to the orifice 34. The orifice 34 is continuously open in the circumferential direction on the side surface of the flow path 31 as will be described later. Therefore, the fluid storage part 32 that supplies the water S to this orifice 34 is also preferably arranged annularly along the circumferential direction of the flow path 31. Thereby, the water S can be supplied to the orifice 34 with uniform pressure.

[0021] 1.2.3. Orifice The orifice 34 is open along the circumferential direction of the flow path 31. That is, the orifice 34 shown in FIG. 1 forms an annular shape centered on the central axis O of the flow path 31. When the water S (fluid) is ejected from such an orifice 34, the ejected water S converges downward and forms a conical fluid jet S1 with the top S2 facing downward. When the droplet Q1 contacts this fluid jet S1, the droplet Q1 is cooled and solidified. Thereby, the metal powder R is obtained. The obtained metal powder R is collected in a container (not shown) provided below the metal powder manufacturing apparatus 1.

[0022] Note that a cylindrical member (not shown) may be provided below the discharge port 23. In this case, the molten metal Q discharged from the discharge port 23 is supplied to the main body part 3 through the inside of the cylindrical member. Thereby, since the molten metal Q discharged in a thin line shape is less likely to bend on the way, the molten metal Q easily flows down along the central axis O. As a result, the molten metal Q can be evenly split, and the generation of coarse and irregularly shaped particles can be suppressed.

[0023] Also, the fluid ejected from the orifice 34 may be a gas, but is preferably a liquid such as water S. Since the liquid has a larger heat capacity than the gas, the droplet Q1 can be rapidly cooled. Thereby, oxidation of the metal powder R can be suppressed and coarsening of the crystal particle size can be suppressed.

[0024] The opening of the orifice 34 is annular and is located below the minimum inner diameter portion 331. As a result, the water S jetted annularly from the orifice 34 can form a continuous conical fluid jet S1, which has the effect of efficiently pushing down the air in the flow path 31 downward. Thereby, the flow path 31 can be further depressurized.

[0025] The ring diameter φ34 of the opening (the water S jet port) of the orifice 34 shown in FIG. 2 is preferably larger than the inner diameter φ331 of the minimum inner diameter portion 331. According to such a configuration, the fluid jet S1 can be formed by the water S jetted from the orifice 34 without disturbing the air flow F passing through the minimum inner diameter portion 331.

[0026] 1.2.4. Exhaust pipe The exhaust pipe 36 shown in FIG. 1 is provided in the main body portion 3 and is a pipe connecting the inner surface of the flow path 31 and the outside. One end of the exhaust pipe 36 opens near the minimum inner diameter portion 331. The other end of the exhaust pipe 36 is connected to the exhaust pump 8. By the operation of the exhaust pump 8, the flow path 31 is depressurized to a lower pressure through the exhaust pipe 36.

[0027] The number of the exhaust pipes 36 may be one or a plurality. In the latter case, the openings at one end of the exhaust pipes 36 may be arranged at equal intervals along the circumferential direction centered on the central axis O. Thereby, the depressurized state of the flow path 31 can be equalized, so that finer metal powder R with fewer irregular shapes (higher circularity of the particle image) can be efficiently manufactured.

[0028] Note that the exhaust pipe 36 may be provided as necessary and may be omitted. In that case, the exhaust pump 8 is also omitted similarly.

[0029] 1.3. Suction pipe The suction pipe 7 shown in Fig. 1 is provided vertically below the main body 3. The suction pipe 7 extends in the vertical direction and has a cylindrical (tubular) shape centered on the central axis O. The planar shape of the suction pipe 7 may be circular centered on the central axis O or polygonal. The suction pipe 7 prevents the scattering of the metal powder R that falls downward.

[0030] Also, the suction pipe 7 is preferably airtightly connected to the lower surface 302 of the main body 3. Thereby, the inflow of outside air into the suction pipe 7 can be suppressed. As a result, the contact of the outside air with the droplets Q1 and the metal powder R can be suppressed, and the unintended cooling of the droplets Q1 and the oxidation of the metal powder R can be suppressed.

[0031] Furthermore, by providing the suction pipe 7, the flow path 31 and the inside of the suction pipe 7 form a continuous space, and it becomes easier to further reduce the pressure in the flow path 31. Hereinafter, this space is referred to as a "decompression space". By reducing the pressure in the decompression space, the molten metal Q can be split more finely, and metal powder R with a small particle size can be manufactured.

[0032] The inner diameter φ7 of the suction pipe 7 shown in Fig. 2 is preferably 1.0 times or more and 4.0 times or less, more preferably 1.1 times or more and 2.0 times or less, the ring diameter φ34 of the opening (the injection port of water S) of the orifice 34. Thereby, while sufficiently dispersing the droplets Q1, the pressure in the decompression space can also be sufficiently reduced. As a result, the molten metal Q is split more finely, and the heat insulation around the droplets Q1 is improved. As a result, metal powder R that is finer, has fewer irregular shapes, and has suppressed oxidation can be efficiently manufactured.

[0033] The ring diameter φ34 of the opening of the orifice 34 is appropriately set according to the production amount of the metal powder R per unit time, the supply amount of the molten metal Q, etc. As an example, it is preferably 100 mm or more and 800 mm or less.

[0034] In addition, if the inner diameter φ7 of the suction pipe 7 is less than the lower limit value, the liquid droplets Q1 cannot be sufficiently dispersed, and there is a risk that irregularly shaped particles may be generated or the particle size cannot be made sufficiently small. On the other hand, if the inner diameter φ7 of the suction pipe 7 exceeds the upper limit value, the pressure in the decompression space may not be sufficiently reduced. For this reason, there is a risk that the particle size of the metal powder R cannot be made sufficiently small. Also, if the pressure in the decompression space is not sufficiently reduced, the cooling of the liquid droplets Q1 may proceed rapidly and solidify without being sufficiently spheroidized. In this case, the roundness of the particle image may decrease.

[0035] The length L7 of the suction pipe 7 is not particularly limited, but is preferably 1500 mm or more, more preferably 2000 mm or more and 4000 mm or less, and even more preferably 2200 mm or more and 3500 mm or less. By setting the length L7 of the suction pipe 7 within the above range, the pressure in the decompression space can be sufficiently reduced. As a result, the molten metal Q is split more finely and the heat insulation around the liquid droplets Q1 is improved. As a result, finer metal powder R with fewer irregular shapes can be efficiently produced.

[0036] In addition, if the length L7 of the suction pipe 7 is less than the lower limit value, the liquid droplets Q1 cannot be sufficiently dispersed, and there is a risk that irregularly shaped particles may be generated or the particle size cannot be made sufficiently small. On the other hand, if the length L7 of the suction pipe 7 exceeds the upper limit value, since it takes time until it escapes from the suction pipe 7, there is a risk that the distance between the particles of the metal powder R cannot be sufficiently ensured. In this case, the cooling rate of the metal powder R decreases and it is likely to oxidize. Also, there is a risk of increasing the size of the metal powder manufacturing apparatus 1.

[0037] When cutting along a cross-sectional plane perpendicular to the central axis O of the suction pipe 7, the cross-sectional shape is preferably constant along the central axis O, but may change midway. For example, the cross-sectional shape may increase similarly downward.

[0038] Also, the suction pipe 7 is preferably a straight pipe along the central axis O, but may be bent midway.

[0039] 1.4. Exhaust pump The exhaust pump 8 shown in Fig. 1 is not particularly limited as long as it is a pump capable of reducing the pressure in the flow path 31. For example, various vacuum pumps can be mentioned. Examples of the vacuum pump include a reciprocating pump, a rotary pump, a mechanical pump, and a fluid-operated pump.

[0040] 1.5. Vertex angle of fluid In Fig. 2, let the vertex angle of the conical fluid jet S1 be θ. The vertex angle θ of the fluid jet S1 is set to be 5° or more and less than 10°, preferably 6° or more and 9° or less, and more preferably 7° or more and 8° or less. By setting the vertex angle θ within the above range, the position of the top S2 in the vertical direction can be optimized. As a result, the time until the droplet Q1 collides with the fluid jet S1 can be optimized. As a result, the time for the droplet Q1 to be spheroidized can be ensured, and metal powder R with few irregular shapes can be produced. In addition, the pressure in the suction pipe 7 can be sufficiently reduced, the molten metal Q can be split more finely, and fine metal powder R can be produced. Furthermore, since the time until the droplet Q1 is cooled and solidified can be optimized, metal powder R with a small oxygen content and suppressed crystal growth can be obtained. Therefore, when the molten metal Q is made of a raw material for soft magnetic powder, soft magnetic powder with high magnetic permeability can be produced. In addition, since the crystal particle size in the powder can be reduced, soft magnetic powder with low coercive force can be produced.

[0041] Note that when the apex angle θ is below the lower limit value, the top S2 of the fluid jet S1 drops too much, so that the time until the droplet Q1 and the fluid jet S1 collide becomes too long. For this reason, the time until cooling becomes long, the oxygen content of the metal powder R increases, and crystal growth tends to proceed. Then, in the case of the soft magnetic powder, the magnetic permeability is low due to the oxygen content, and the coercive force is high due to the crystal particle size. On the other hand, when the apex angle θ exceeds the upper limit value, the top S2 of the fluid jet S1 rises too much, so that the time until the droplet Q1 and the fluid jet S1 collide becomes too short. For this reason, the time until cooling becomes short, and irregularly shaped particles are generated or the spheroidization of the particles becomes insufficient. Also, the pressure in the reduced-pressure space cannot be sufficiently reduced, making it difficult to manufacture fine metal powder R.

[0042] Also, let the length of the fluid jet S1 be LS1. The length LS1 is the vertical length from the lower surface 302 of the main body 3 to the top S2. This length LS1 is preferably shorter than the length L7 of the suction pipe 7. Thereby, since the metal powder R can be manufactured in the suction pipe 7, it becomes easier to suppress the oxidation of the metal powder R.

[0043] Furthermore, the length LS1 is preferably 10% or more and 50% or less of the length L7, and more preferably 20% or more and 40% or less. Thereby, the top S2 of the fluid jet S1 will be located in the upper half range of the suction pipe 7. In this case, the metal powder R immediately after manufacturing will fall in the suction pipe 7 for a while. For this reason, oxidation of the metal powder R can be suppressed. Also, since the top S2 is in this position, the reduced-pressure state in the reduced-pressure space becomes stable over time. Thereby, since the splitting state of the molten metal Q also becomes stable, generation of coarse particles can be suppressed.

[0044] Note that when the length LS1 is below the lower limit value, the suction pipe 7 becomes excessively long, which may lead to an increase in the size of the metal powder manufacturing apparatus 1. On the other hand, when the length LS1 exceeds the upper limit value, the reduced-pressure state in the reduced-pressure space becomes unstable over time, which may increase the content rate of coarse and irregularly shaped particles. Also, there is a possibility that the metal powder R is likely to be oxidized.

[0045] 1.6. Negative pressure in the reduced-pressure space The reduced-pressure space formed by the continuity of the flow path 31 and the inside of the suction pipe 7 is reduced in pressure to a pressure lower than the atmospheric pressure by the exhaust by the exhaust pump 8 or the formation of the fluid jet S1. The maximum negative pressure in the reduced-pressure space is set to be 45 kPa or more and 100 kPa or less, preferably 50 kPa or more and 95 kPa or less, and more preferably 60 kPa or more and 90 kPa or less. If the maximum negative pressure in the reduced-pressure space is within the above range, the molten metal Q can be split more finely, and the generation of irregular shapes can be suppressed. In addition, the heat insulation around the droplet Q1 is ensured, and the oxidation of the metal powder R is suppressed.

[0046] Note that if the maximum negative pressure in the reduced-pressure space is below the lower limit value, the pressure reduction and heat insulation become insufficient, so that fine metal powder R cannot be manufactured. In addition, there is a risk that the metal powder R is likely to be oxidized. On the other hand, if the maximum negative pressure in the reduced-pressure space exceeds the upper limit value, the pressure change width in the reduced-pressure space becomes large. In this case, the molten metal Q will be split violently, and coarse particles are likely to be generated. Since it takes time for the coarse particles to be spheroidized, as a result, the metal powder R is likely to contain irregularly shaped particles.

[0047] Note that the part where the maximum negative pressure in the reduced-pressure space is located may be located in the flow path 31 or may be located in the suction pipe 7, but usually it is located near the minimum inner diameter part 331. For this reason, the maximum negative pressure in the reduced-pressure space is obtained as the pressure measured near the minimum inner diameter part 331. Note that the maximum negative pressure may be estimated based on the measured value of the pressure measured at other parts and the pressure distribution calculated by the pressure distribution simulation, and the estimated value may be used as the maximum negative pressure.

[0048] 1.7. Method for manufacturing metal powder Next, the method for manufacturing metal powder according to the first embodiment will be described. In the following description, a method using the above-described metal powder manufacturing apparatus 1 will be described as an example.

[0049] In the method for manufacturing metal powder, first, molten metal Q is prepared. The molten metal Q is prepared by melting raw materials in the supply unit 2.

[0050] The temperature of the molten metal Q (casting temperature) only needs to be equal to or higher than the melting point of the raw materials, but it is preferably 200°C or more and 400°C or less higher than the melting point of the raw materials, more preferably 215°C or more and 350°C or less higher, and even more preferably 230°C or more and 300°C or less higher. Thereby, the viscosity of the molten metal Q is optimized, and metal powder R that is finer and has fewer irregularly shaped particles can be manufactured.

[0051] Note that if the temperature of the molten metal Q is lower than the lower limit value, the viscosity of the molten metal Q increases, so it may be difficult to manufacture fine metal powder R. Also, the content rate of irregularly shaped particles may increase. On the other hand, if the temperature of the molten metal Q exceeds the upper limit value, special heat resistance is required in the supply unit 2, so it may be difficult to stably hold the molten metal Q.

[0052] The prepared molten metal Q is discharged through the discharge port 23 and supplied to the main body portion 3. The inner diameter of the discharge port 23 (nozzle diameter) affects the production amount, particle size, roundness, etc. of the metal powder R per unit time in order to determine the outer diameter of the flowing molten metal Q. The inner diameter φ23 of the discharge port 23 is preferably 2.0 mm or more and 6.0 mm or less, more preferably 2.5 mm or more and 5.5 mm or less, and even more preferably 3.0 mm or more and 5.0 mm or less. If the inner diameter φ23 of the discharge port 23 is within the above range, metal powder R that is fine, has a high roundness, and has a small amount of oxygen can be manufactured.

[0053] In addition, if the inner diameter φ23 of the discharge port 23 is less than the lower limit value, the molten metal Q flowing down is likely to be cooled, which may lead to an increase in the oxygen content of the metal powder R or a decrease in the roundness. On the other hand, if the inner diameter φ23 of the discharge port 23 exceeds the upper limit value, it becomes difficult to finely and evenly split the molten metal Q. Then, coarse and irregularly shaped particles are likely to be generated, which may lead to a decrease in the roundness of the metal powder R. Also, in the case of soft magnetic powder, since the crystal particle size tends to be large in coarse particles, there is a possibility that the coercive force increases.

[0054] When the molten metal Q supplied to the main body 3 passes through a reduced-pressure space that is reduced in pressure to a pressure (negative pressure) of 45 kPa or more and 100 kPa or less, it splits into droplets Q1. The reduced-pressure space is a space composed of the flow path 31 and the inside of the suction pipe 7 continuous therewith. The flow path 31 has an inner diameter gradually decreasing portion 33 whose inner diameter gradually decreases downward. The inner diameter gradually decreasing portion 33 is provided above the opening of the orifice 34 (the injection port of water S). When the molten metal Q is allowed to flow down through the inner diameter gradually decreasing portion 33, the molten metal Q splits, and finer droplets Q1 are generated. The droplet Q1 collides with a fluid jet S1 having a conical shape with an apex angle θ of 5° or more and less than 10°, and the metal powder R is produced.

[0055] According to the metal powder manufacturing method as described above, it is possible to manufacture the metal powder R that is fine and in which the generation of irregularly shaped particles is suppressed.

[0056] The ratio of irregularly shaped particles in the metal powder R can be quantified by measuring the average roundness. The average roundness of the metal powder R manufactured by the above manufacturing method is preferably 0.82 or more, more preferably 0.84 or more and 0.95 or less, and even more preferably 0.87 or more and 0.95 or less. Thereby, the metal powder R excellent in fluidity and fillability can be obtained. In particular, when the metal powder R is a soft magnetic powder, a soft magnetic powder capable of manufacturing a green compact with a high green density can be obtained.

[0057] The average roundness of the metal powder R is measured as follows. 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. As the image processing software, for example, the image analysis type particle size distribution measurement software "Mac-View" manufactured by Mountech Co., Ltd. is used. Note that the imaging magnification is adjusted so that 50 or more and 100 or less particles are captured in one image. Then, a plurality of images are acquired so that 300 or more particle images can be obtained.

[0058] Next, using the software, the circularity of 300 or more particle images is calculated, and the average value is obtained. The obtained average value becomes the average circularity of the metal powder R. Note that when the circularity is e, the area of the particle image is S, and the perimeter length of the particle image is L, the circularity e is obtained by the following formula. e = 4πS / L 2

[0059] 2. Second Embodiment Next, the metal powder manufacturing apparatus according to the second embodiment will be described.

[0060] FIG. 3 is a schematic diagram (longitudinal sectional view) showing a part of the metal powder manufacturing apparatus 1 according to the second embodiment. FIG. 4 is a partial enlarged view of FIG. 3. Note that in FIGS. 3 and 4, the illustration of some configurations is omitted.

[0061] Hereinafter, the second embodiment will be described. In the following description, the description will focus on the differences from the first embodiment, and the description of the same matters will be omitted. Note that in FIG. 3, the same matters as those in the first embodiment are denoted by the same reference numerals.

[0062] The metal powder manufacturing apparatus 1 shown in FIG. 3 is the same as the metal powder manufacturing apparatus 1 shown in FIG. 1, except that it has a reduced diameter portion 5 provided in the flow path 31.

[0063] The reduced-diameter portion 5 is provided in the flow path 31 and partially constricts the inner diameter of the flow path 31. That is, by providing the reduced-diameter portion 5, the rate of gradual decrease in the inner diameter in the inner-diameter gradually decreasing portion 33 will change abruptly. As a result, the flow velocity of the air drawn into the flow path 31 will increase abruptly in the reduced-diameter portion 5. As a result, the molten metal Q can be split into finer particles, and finer metal powder R can be produced.

[0064] The change in the rate of gradual decrease in the inner diameter due to the reduced-diameter portion 5 can be represented by the angle of the inner wall surface of the flow path 31. That is, the reduced-diameter portion 5 is continuous from the inner wall surface of the flow path 31 and has a surface that bends inward. This makes it possible to abruptly change the flow velocity of the air.

[0065] In FIG. 4, the angle formed by the inner wall surface of the flow path 31 and the surface of the reduced-diameter portion 5 is designated as α. Hereinafter, this angle will be referred to as the "reduced-diameter angle α". The smaller the reduced-diameter angle α, the more abrupt the change in the rate of gradual decrease in the inner diameter. On the other hand, the closer the reduced-diameter angle α is to 180°, the smaller the change in the rate of gradual decrease in the inner diameter.

[0066] The reduced-diameter angle α is preferably 100° or more and 165° or less, more preferably 120° or more and 160° or less, and even more preferably 130° or more and 155° or less. When the reduced-diameter angle α is within the above range, the change in the rate of gradual decrease in the inner diameter is optimized, and the flow velocity of the air can be increased further. As a result, the reduced-pressure space can be further depressurized, and both the refinement and spheroidization of the produced metal powder R can be achieved. It also contributes to suppressing the oxygen content and crystal particle size of the metal powder R.

[0067] If the reduced-diameter angle α is less than the lower limit value, the change in the rate of gradual decrease in the inner diameter becomes excessive, and there is a risk that the air flow F will be obstructed. Then, the flow velocity may decrease, and there is a risk that the reduced-pressure space cannot be sufficiently depressurized. On the other hand, if the reduced-diameter angle α exceeds the upper limit value, the change in the rate of gradual decrease in the inner diameter becomes insufficient. Then, there is a risk that it will be difficult to further depressurize the reduced-pressure space compared to the case where the reduced-diameter portion 5 is not provided.

[0068] The reduced-diameter portion 5 may be fixed to the flow path 31, but it is preferably detachable. Thereby, according to the type of the metal powder R to be manufactured, it is possible to select whether or not to attach the reduced-diameter portion 5. As a result, it is possible to realize the metal powder manufacturing apparatus 1 capable of forming an optimal reduced-pressure space according to the type of the metal powder R to be manufactured. In addition, since the reduced-diameter portion 5 can be replaced due to wear or the like, it is possible to realize the metal powder manufacturing apparatus 1 that can stably obtain the above-described effects at low cost over a long period of time.

[0069] The constituent material of the reduced-diameter portion 5 is not particularly limited, and examples thereof include iron-based alloys such as stainless steel and carbon steel, aluminum-based alloys, titanium-based alloys, and the like. Also in the second embodiment as described above, the same effects as those of the first embodiment can be obtained.

[0070] 3. Effects exhibited by the above embodiment The metal powder manufacturing apparatus 1 according to the above embodiment includes a supply unit 2, a main body unit 3, and a suction pipe 7. The supply unit 2 has a discharge port 23 and supplies the molten metal Q from the discharge port 23. The main body unit 3 is provided below the supply unit 2 and has a flow path 31 and an orifice 34. The flow path 31 allows the molten metal Q supplied from the supply unit 2 to pass through. The orifice 34 injects water S (fluid) in a conical shape that converges below the flow path 31. The suction pipe 7 is provided below the main body unit 3 and has a tubular shape extending in the vertical direction.

[0071] Such a metal powder manufacturing apparatus 1 is configured such that the molten metal Q that has passed through the flow path 31 and the water S injected from the orifice 34 come into contact with each other inside the suction pipe 7. In addition, the apex angle θ of the water S (fluid jet S1) injected in a conical shape is 5° or more and less than 10°. Further, the maximum negative pressure (the maximum negative pressure in the reduced-pressure space) inside the flow path 31 or the suction pipe 7 is 45 kPa or more and 100 kPa or less.

[0072] According to such a configuration, it is possible to realize a metal powder manufacturing apparatus 1 capable of manufacturing the metal powder R that is fine and in which the generation of irregularly shaped particles is suppressed. Further, according to this metal powder manufacturing apparatus 1, it is possible to manufacture the metal powder R with a small amount of oxygen and suppressed crystal growth.

[0073] Further, it is preferable that the length L7 of the suction pipe 7 is set such that the top S2 of the water S (fluid) jetted in a conical shape is located within the upper half range of the suction pipe 7.

[0074] According to such a configuration, oxidation of the metal powder R can be suppressed. Further, since the top S2 is at this position, the reduced pressure state in the reduced pressure space becomes stable over time. As a result, the splitting state of the molten metal Q also becomes stable, so that generation of coarse particles can be suppressed.

[0075] Further, it is preferable that the length L7 of the suction pipe 7 is 1500 mm or more. According to such a configuration, the pressure in the reduced pressure space can be sufficiently reduced. As a result, the molten metal Q is split more finely and the heat insulation around the droplet Q1 is improved. As a result, it is possible to efficiently manufacture a finer metal powder R with fewer irregular shapes.

[0076] Further, the flow path 31 may have a shape in which the inner diameter gradually decreases downward. According to such a configuration, the flow velocity of the air drawn into the flow path 31 can be increased. And, along with the increase in the flow velocity, the pressure in the flow path 31 can be reduced. As a result, the molten metal Q can be split to generate a large number of droplets Q1, and finally, a fine metal powder R can be manufactured.

[0077] Further, in the metal powder manufacturing apparatus 1 according to the above embodiment, the orifice 34 is located below the minimum inner diameter portion 331 (the portion with the minimum inner diameter) of the flow path 31 and has an annular opening. The ring diameter φ34 of this opening is larger than the inner diameter φ331 of the minimum inner diameter portion 331.

[0078] According to such a configuration, the water S jetted annularly from the orifice 34 forms a continuous conical fluid jet S1, and efficiently pushes down the air in the flow path 31 downward. Further, the water S jetted from the orifice 34 can form the fluid jet S1 without disturbing the air flow F passing through the minimum inner diameter portion 331. Thereby, the pressure in the flow path 31 can be further reduced.

[0079] Further, the metal powder manufacturing apparatus 1 according to the embodiment has a reduced diameter portion 5. The reduced diameter portion 5 is provided in the flow path 31 and partially constricts the inner diameter of the flow path 31.

[0080] According to such a configuration, the flow velocity of the air drawn into the flow path 31 rapidly increases at the reduced diameter portion 5. As a result, the molten metal Q can be split more finely, and finer metal powder R can be manufactured.

[0081] Further, the reduced diameter portion 5 may be detachable from the flow path 31. According to such a configuration, depending on the type of the metal powder R to be manufactured, it is possible to select whether or not to attach the reduced diameter portion 5. As a result, it is possible to realize the metal powder manufacturing apparatus 1 capable of forming an optimal decompression space according to the type of the metal powder R to be manufactured. Further, since the reduced diameter portion 5 can be replaced due to wear or the like, it is possible to realize the metal powder manufacturing apparatus 1 capable of stably obtaining the above-described effects at low cost over a long period of time.

[0082] Further, the inner diameter φ23 of the discharge port 23 is preferably 2.0 mm or more and 6.0 mm or less.

[0083] According to such a configuration, it is possible to manufacture fine metal powder R with high roundness and a small amount of oxygen.

[0084] Further, the fluid jetted from the orifice 34 is preferably a liquid. According to such a configuration, since the heat capacity of the liquid is larger than that of the gas, the liquid droplet Q1 can be rapidly cooled. Thereby, oxidation of the metal powder R can be suppressed, and coarsening of the crystal particle size can be suppressed.

[0085] Further, in the method for producing metal powder according to the above embodiment, in a reduced-pressure space that extends in the vertical direction and in which a negative pressure of 45 kPa or more and 100 kPa or less is formed, water S (fluid) is jetted downward in a conical shape so that the apex angle θ is 5° or more and less than 10°. The liquid droplet Q1 of the molten metal Q to be dropped is brought into contact with the water S to cool and solidify the liquid droplet Q1.

[0086] According to such a configuration, it is possible to produce the metal powder R that is fine and in which generation of irregularly shaped particles is suppressed. Further, it is possible to produce the metal powder R with a small amount of oxygen and suppressed crystal growth.

[0087] Further, the temperature of the molten metal Q is preferably 200°C or more and 400°C or less higher than the melting point of the raw material.

[0088] According to such a configuration, the viscosity of the molten metal Q is optimized, and it is possible to produce the metal powder R that is finer and has fewer irregularly shaped particles.

[0089] Further, in the method for producing metal powder according to the above embodiment, the molten metal Q is caused to flow down so as to pass through a flow path 31 provided above the injection port of the water S (fluid) and having an inner diameter that gradually decreases downward. According to such a configuration, the molten metal Q is split, and finer liquid droplets Q1 are generated.

[0090] Further, in the method for producing metal powder according to the above embodiment, metal powder R having an average circularity of 0.82 or more is produced. According to such a configuration, metal powder R excellent in fluidity and filling property can be obtained.

[0091] As described above, the metal powder manufacturing apparatus and the metal powder manufacturing method of the present invention have been described with reference to the illustrated embodiments. However, the present invention is not limited thereto. For example, the metal powder manufacturing apparatus of the present invention may be one to which an arbitrary component is added with respect to the above-described embodiment. Further, the metal powder manufacturing method of the present invention may be one to which a process for an arbitrary purpose is added with respect to the above-described embodiment.

Example

[0092] Next, specific examples of the present invention will be described. 4. Production of Metal Powder First, the raw material of the Fe-based soft magnetic material was melted in the supply unit of the metal powder manufacturing apparatus to obtain molten metal. Next, the obtained molten metal was supplied from the supply unit toward the main body unit to produce metal powder. The configuration of the metal powder manufacturing apparatus and the manufacturing conditions of the metal powder are as shown in Tables 1 to 3. In Tables 1 to 3, the metal powder produced by the metal powder manufacturing apparatus and the metal powder manufacturing method corresponding to the present invention is referred to as "Example", and the metal powder produced by the metal powder manufacturing apparatus and the metal powder manufacturing method not corresponding to the present invention is referred to as "Comparative Example".

[0093] 5. Evaluation of Metal Powder The following measurements or evaluations were performed on the metal powders of each Example and each Comparative Example. The measurement results and evaluation results are shown in Tables 1 to 3.

[0094] 5.1. Average Particle Diameter D50 The average particle diameter D50 was measured for the metal powders of each Example and each Comparative Example. The average particle diameter D50 refers to the particle diameter at which the cumulative frequency is 50% from the smaller diameter side in the volume-based cumulative particle size distribution of the metal powder obtained using a laser diffraction particle size distribution measuring device.

[0095] 5.2. Tap Density The tap density was measured for the metal powders of each Example and each Comparative Example. The tap density was measured as follows.

[0096] First, the metal powder was treated with a coupling agent. Phenyltrimethoxysilane was used as the coupling agent. Next, the tapped density of the treated metal powder was measured using a powder property evaluation apparatus. As the powder property evaluation apparatus, Hosokawa Micron Corporation's Powder Tester (registered trademark) PT-X was used.

[0097] 5.3. Oxygen content For the metal powders of each example and each comparative example, the oxygen content was measured. The measurement of the oxygen content was carried out in accordance with the general rules for the oxygen determination method of metallic materials specified in JIS Z 2613:2006. Also, as the measuring apparatus, LECO Corporation's oxygen / nitrogen / hydrogen analyzer, ONH836, was used.

[0098] 5.4. Specific surface area For the metal powders of each example and each comparative example, the specific surface area was measured. The specific surface area was measured by the BET method. As the measuring apparatus, BET type specific surface area measuring apparatus HM1201-010 manufactured by Mountech Co., Ltd. was used, and the amount of the sample was set to 5 g.

[0099] 5.5. Coercive force For the metal powders of each example and each comparative example, the coercive force was measured. The coercive force was measured using a vibrating sample magnetometer. The maximum applied magnetic field when measuring the coercive force was set to 15 kOe.

[0100] 5.6. Average circularity For the metal powders of each example and each comparative example, the average circularity was measured. The measuring method is as described above.

[0101] 5.7. Comprehensive evaluation For the metal powders of each example and each comparative example, the results of the above evaluations were comprehensively evaluated with reference to the following evaluation criteria.

[0102] A: The average particle size D50 is 15.0 μm or less, the tapped density is 4.5 g / cm 3 or more, and the average circularity is 0.85 or more B: The average particle size D50 is 15.0 μm or less, the tapped density is 4.3 g / cm3 The above, and the average circularity is 0.82 or more (excluding A) C: The average particle size D50 is more than 15.0 μm, or the tap density is less than 4.3 g / cm 3 or the average circularity is less than 0.82

[0103]

Table 1

[0104]

Table 2

[0105]

Table 3

[0106] From the evaluation results shown in Tables 1 to 3, the following matters were recognized. · By using a metal powder manufacturing apparatus in which the apex angle θ of the fluid jet S1 and the negative pressure in the reduced pressure space are each set within a predetermined range, it was found that it is possible to manufacture metal powder that is fine and in which the generation of irregularly shaped particles is suppressed (with good tap density and average circularity). · By optimizing parameters such as the length L7 of the suction pipe, the nozzle diameter (inner diameter of the discharge port 23), the diameter reduction angle α, and the difference between the casting temperature and the melting point, it was found that it is possible to manufacture metal powder in which fineness and spheroidization are achieved while low oxygenation, magnetization of coercive force, etc. are achieved.

Explanation of symbols

[0107] 1... Metal powder manufacturing apparatus, 2... Supply section, 3... Main body section, 5... Reducing diameter section, 7... Suction pipe, 8... Exhaust pump, 21... Container, 22... Storage section, 23... Discharge port, 31... Flow path, 32... Fluid storage section, 33... Inner diameter gradually reducing section, 34... Orifice, 36... Exhaust pipe, 301... Upper surface, 302... Lower surface, 331... Minimum inner diameter section, O... Central axis, Q... Molten metal, Q1... Droplet, R... Metal powder, S... Water, S1... Fluid jet, S2... Top, α... Reducing diameter angle, θ... Apex angle, φ23... Inner diameter, φ331... Inner diameter, φ34... Ring diameter, φ7... Inner diameter

Claims

1. It has a discharge port, a supply unit that supplies molten metal from the discharge port, a main body portion provided below the supply unit, having a flow path through which the molten metal supplied from the supply unit passes, and an orifice that injects fluid in a conical shape and converges below the flow path, a suction pipe provided below the main body portion and having a tubular shape extending in the vertical direction, and is provided with the molten metal that has passed through the flow path and the fluid ejected from the orifice are configured to come into contact with each other inside the suction pipe, the apex angle of the fluid ejected in a conical shape is 5° or more and less than 10°, A metal powder manufacturing apparatus, characterized in that the maximum negative pressure inside the flow path or the suction pipe is 45 kPa or more and 100 kPa or less.

2. The metal powder manufacturing apparatus according to claim 1, wherein the length of the suction pipe is set such that the top of the fluid ejected in a conical shape is located within the upper half range of the suction pipe.

3. The metal powder manufacturing apparatus according to claim 1 or 2, wherein the length of the suction pipe is 1500 mm or more.

4. The metal powder manufacturing apparatus according to claim 1 or 2, wherein the flow path has a shape in which the inner diameter gradually decreases downward.

5. The orifice is located below the minimum part of the inner diameter of the flow path and has an annular opening, The metal powder manufacturing apparatus according to claim 4, wherein the ring diameter of the opening is larger than the inner diameter of the minimum part.

6. The metal powder manufacturing apparatus according to claim 4, further comprising a reduced-diameter portion provided in the flow path for partially narrowing the inner diameter of the flow path.

7. The metal powder manufacturing apparatus according to claim 6, wherein the reduced-diameter portion is detachable from the flow path.

8. The metal powder manufacturing apparatus according to claim 1 or 2, wherein the inner diameter of the discharge port is 2.0 mm or more and 6.0 mm or less.

9. The metal powder manufacturing apparatus according to claim 1 or 2, wherein the fluid ejected from the orifice is a liquid.

10. A method for manufacturing metal powder, characterized in that, in a reduced-pressure space extending in the vertical direction and having a negative pressure of 45 kPa or more and 100 kPa or less, a fluid ejected downward in a conical shape so that the apex angle is 5° or more and less than 10° is brought into contact with droplets of molten metal to be dropped, thereby cooling and solidifying the droplets.

11. The method for manufacturing metal powder according to claim 10, wherein the temperature of the molten metal is 200°C or more and 400°C or less higher than the melting point of the raw material.

12. The method for manufacturing metal powder according to claim 10 or 11, wherein the molten metal is caused to flow down so as to pass through a flow path provided above the ejection port of the fluid and having a gradually decreasing inner diameter downward.

13. The method for manufacturing metal powder according to claim 10 or 11, wherein metal powder having an average circularity of 0.82 or more is manufactured.

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