Metal powder producing apparatus and metal powder producing method

A metal powder producing apparatus includes a molten metal supply unit, a cylinder body, and a cooling liquid introduction unit. The molten metal supply unit discharges a molten metal. The cylinder body is capable of being formed with a layer of a cooling liquid for cooling the molten metal on an inner circumference surface of the cylinder body. The cooling liquid introduction unit supplies the cooling liquid to an upper inside of the cylinder body. The inner circumference surface of the upper inside of the cylinder body has a substantially elliptical shape.

BACKGROUND OF THE INVENTION

The present invention relates to a metal powder producing apparatus and a metal powder producing method.

For example, as shown in Patent Document 1, a metal powder producing apparatus for producing a metal powder using a so-called gas atomization method and a producing method using the apparatus are known. The conventional apparatus includes a molten metal supply container for discharging a molten metal, a cylinder body provided below the molten metal supply container, and a cooling liquid introduction unit for forming a flow of a cooling liquid for cooling the molten metal discharged from the molten metal supply container along an inner circumference surface of the cylinder body.

The cooling liquid introduction unit forms a cooling liquid layer by spraying a cooling liquid toward a tangent direction of the inner circumference surface of the cooling cylinder body and flowing the cooling liquid down while circling it along the inner circumference surface of the cooling container. When the cooling liquid layer is used, it is expected to rapidly cool a molten drop and produce a metal powder having a high functionality.

In the conventional metal powder production, however, a molten drop may be cooled insufficiently rapidly, and there is a need for apparatus and method capable of producing a higher-quality metal powder.Patent Document 1: JPH1180812 (A)

BRIEF SUMMARY OF THE INVENTION

The present invention has been achieved under such circumstances. It is an object of the present invention to provide a metal powder producing apparatus capable of producing a higher quality metal powder and a producing method for the metal powder.

To achieve the above object, a metal powder producing apparatus according to the present invention comprises:a molten metal supply unit for discharging a molten metal;a cylinder body capable of being formed with a layer of a cooling liquid for cooling the molten metal on an inner circumference surface of the cylinder body; anda cooling liquid introduction unit for supplying the cooling liquid to an upper inside of the cylinder body,wherein the inner circumference surface of the upper inside of the cylinder body has a substantially elliptical shape.

In the metal powder producing apparatus according to the present invention, it is possible to form the cooling liquid layer flowing in a substantially elliptical spiral manner along the inner circumference surface of the cylinder body. The molten metal drop can be cooled more rapidly by spraying the molten metal drop against the cooling liquid layer. The flow speed of the elliptical spiral cooling liquid is faster on the short diameter side of the ellipse and slower on the long diameter side of the ellipse, and the molten metal drop sprayed against the cooling liquid layer is flowed in the cooling liquid layer together with the cooling liquid while changing the flow speed.

Since the molten metal drop flows in the cooling liquid layer together with the cooling liquid while changing the flow speed, the vapor film around the molten metal drop, which is considered to be generated immediately after the contact with the cooling liquid, is easily peeled from the molten metal drop, and the rapid cooling effect of the molten metal drop in the cooling liquid layer is enhanced. A metal powder having good amorphousness and magnetic characteristics even with a fine particle size can be produced by rapidly cooling the molten metal drop in such a manner.

Preferably, the cooling liquid introduction unit includes a cooling liquid discharge port for discharging the cooling liquid, supplied from outside the cylinder body, in a spiral orbit flow along the inner circumference surface from an upper part of the cylinder body. In this configuration, the cooling liquid discharge port can form the cooling liquid layer in an elliptical spiral manner from the upper portion of the cylinder body toward the lower portion of the cylinder body along the inner circumference surface, the rapid cooling effect of the molten metal drop in the cooling liquid layer is enhanced, and a metal powder having good amorphousness and magnetic characteristics even with a fine particle size can be obtained.

Preferably, the cooling liquid discharge port is formed in a substantially elliptical shape over a circumference direction of the cylinder body. The cooling liquid discharge port may be continuously formed in a substantially elliptical shape over the circumferential direction of the cylinder body or may be formed intermittently over the circumferential direction of the cylinder body by, for example, providing the cooling liquid discharge port with a reinforcing member. When the cooling liquid discharge port is continuously formed over the circumferential direction of the cylinder body, it is easy to form the cooling liquid layer of the cooling liquid flowing in an elliptical spiral manner along the inner circumference surface of the cylinder body.

Preferably, the cooling liquid introduction unit includes a frame for changing a flow of the cooling liquid from outside toward inside to a flow of the cooling liquid along the inner circumference surface of the cylinder body, and the frame includes a substantially elliptical inner frame piece having a diameter smaller than that of the inner circumference surface of the cylinder body. In this configuration, a substantially elliptical cooling liquid discharge port can be formed between the inner frame piece and the inner circumference surface of the cylinder body. As a result, the cooling liquid flowing in an elliptical spiral manner along the inner circumference surface of the cylinder body can be discharged from the cooling liquid discharge port.

Preferably, the frame defines an inside space disposed inside the cylinder body to receive the cooling liquid from the outside to the inside of the cylinder body, and the inside space is formed in a substantially elliptical shape along the inner circumference surface. In this configuration, the cooling liquid can form an elliptical flow along the inner circumference surface in the inside space. When the cooling liquid is discharged downward along the core axis of the cylinder body along the inner circumference surface, an elliptical spiral cooling liquid layer can be formed smoothly along the inner circumference surface.

Preferably, the cooling liquid introduction unit includes an outside formation member for forming an outside space for temporarily storing the cooling liquid, the outside formation member is formed outside the cylinder body, and the outside space is formed in a substantially elliptical shape. In this configuration, the cooling liquid is introduced into the inside of the cylinder body while circling in an elliptical manner in the outside space, and it is easy to smoothly form the cooling liquid layer of the cooling liquid flowing in an elliptical spiral manner along the inner circumference surface of the cylinder body.

Preferably, the cooling liquid discharge port is formed between the inner circumference surface of the cylinder body and the inner frame piece. The inner circumference surface of the cylinder body may be an inner circumference surface of an auxiliary cylinder body. Preferably, a lower end of a passage portion connecting between the outside space and the inside space of the cooling liquid introduction unit is disposed above along the core axis.

Preferably, a center of an ellipse defined by the inner circumference surface is displaced so as to be inclined to a vertical line toward a lower part of the cylinder body. In this configuration, the cooling liquid of the cooling liquid layer formed along the inner circumference surface flows while drawing an elliptical spiral orbit and being inclined to the vertical direction. Thus, the distance of the elliptical spiral through which the cooling liquid flows can be increased. When the molten metal is sprayed downward in the vertical direction, the molten metal drop easily enters the cooling liquid layer without disturbing the cooling liquid flow, and the droplets are easily smoothly cooled.

Preferably, a ratio of a long diameter to a short diameter in an ellipse defined by the inner circumference surface is 1.04 or more and 3.00 or less. In this configuration, it is easy to form a cooling liquid layer with a uniform thickness while changing the flow speed of the cooling liquid.

A ring may be formed in a substantially elliptical shape along the inner circumference surface at the lower portion of the cylinder body. In this configuration, the ring controls the cooling liquid flow toward the direction along the core axis of the cylinder body, and it is easy to maintain a constant thickness of the cooling liquid layer of the cooling liquid flowing in an elliptical spiral manner along the inner circumference surface of the cylinder body.

To achieve the above object, a metal powder producing method according to the present invention comprises steps of:forming a layer of a cooling liquid whose flow speed changes along an inner circumference surface of a cylinder body;discharging a molten metal from a molten metal supply unit toward the layer of the cooling liquid; andflowing the molten metal together with the cooling liquid while changing their flow speed.

In this configuration, the rapid cooling effect of the molten metal drop is enhanced, and a metal powder having good amorphousness and magnetic characteristics even with a fine particle size can be produced.

Preferably, the layer of the cooling liquid is formed by flowing the cooling liquid in a substantially elliptical spiral manner along the inner circumference surface. In this configuration, the molten metal droplet flows along the inner circumference surface while changing the flow speed together with the cooling liquid, and the rapid cooling effect of the molten metal drop can be enhanced.

DETAILED DESCRIPTION OF THE INVENTION

Hereinafter, the present invention is described based on the embodiments shown in the figures.

First Embodiment

As shown inFIG.1A, a metal powder producing apparatus10according to an embodiment of the present invention is an apparatus for turning a molten metal21into powder by an atomization method (gas atomization method) so as to obtain a metal powder constituted from multiple metal particles. The apparatus10includes a molten metal supply unit20and a cooling unit30disposed below the metal supply unit20in the vertical direction. In the figures, the vertical direction is the direction along the Z-axis.

The molten metal supply unit20includes a heat resistance container22for containing the molten metal21. A heating coil24is disposed at the outer circumference of the heat resistance container22, and the molten metal21contained in the container22is heated and maintained in a molten state. A molten metal discharge port23is formed at the bottom of the container22, and the molten metal21is discharged as a molten metal drop21afrom the molten-metal discharge port23toward an inner circumference surface33of the cylinder body32constituting the cooling unit30.

A gas spray nozzle26is disposed around the molten-metal discharge port23at the outer side of the outer bottom wall of the container22. The gas spray nozzle26is provided with a gas spray port27. A high pressure gas is sprayed from the gas spray port27toward the molten metal drop21adischarged from the molten metal discharge port23. The high pressure gas is sprayed diagonally downward from the entire circumference of the molten metal discharged from the molten metal discharge port23, and the molten metal drop21ais formed into multiple liquid drops and moved toward the inner circumference surface33at the upper inside of the cylinder body32along the gas flow.

The molten metal21may include any elements and can be, for example, at least one selected from Ti, Fe, Si, B, Cr, P, Cu, Nb, and Zr. Since these elements are highly active, the molten metal21including these elements is easily oxidized to form an oxide film by contact with the air for a short period of time and is difficult to be fine. In the metal powder producing apparatus10, as mentioned above, since an inactive gas is employed as the gas sprayed from the gas spray port27of the gas spray nozzle26, even the molten metal21, which is easily oxidized, can be easily turned into powder.

The gas sprayed from the gas spray port27is preferably an inactive gas, such as nitrogen gas, argon gas, and helium gas, or a reducing gas, such as ammonia decomposition gas, but may be the air if the molten metal21is a metal that hardly oxidize.

In the present embodiment, at least the inner circumference surface33at the upper inside (the portion to which the molten metal drop21ais supplied) of the cylinder body32shown inFIG.1Ahas a substantially elliptical shape in an inclined cross section (e.g., a cross section substantially perpendicular to the Z-axis) at an angle θ1 to a core axis O of the cylinder body32. The angle θ1 can be expressed as θ1=(90 degrees−θ2), assuming that the core axis O of the cylinder body32is inclined to the Z-axis at an angle θ2.

In the cross section inclined at the angle θ1 to the core axis O of the cylinder body32, preferably, the major axis of the ellipse of the inner circumference surface33corresponds with the inclined direction of the core axis O of the cylinder body32to the Z-axis (vertical line). That is, preferably, the cylinder body32is configured so that the major axis of the ellipse is included in a plane including the core axis O of the cylinder body32and the Z-axis intersecting the core axis O.

For example, as shown inFIG.3A, the cylinder body32configured in this manner can be manufactured from a cylindrical member32ahaving a circular inner circumference surface of a cross section perpendicular to the core axis O. That is, the cylinder body32shown inFIG.1can be formed by horizontally cutting the upper and lower portions of the cylindrical member32awith the core axis O of the cylindrical member32ainclined at a predetermined angle θ2 to the vertical direction (Z-axis direction). In the present embodiment, the inner circumference surface33of the cylinder body32has a substantially elliptical inner circumference surface33of the same size continuously formed along the core axis O in a cross section inclined to the core axis O at the angle θ1.

In the present embodiment, as shown inFIG.2B, a ratio (L3/L2) of a long diameter L3to a short diameter L2in the elliptical shape appearing in each horizontal cross section of the inner circumference surface33of the cylinder body32is preferably 1.01 or more and 3.00 or less, more preferably 1.04 or more and 2.00 or less, and particularly preferably 1.04 or more and 1.30 or less. In this configuration, it is easy to form a cooling liquid layer with a uniform thickness while changing the flow speed of the cooling liquid (e.g., cooling water). For example, when L3/L2is 1.04 to 3.00, the speed ratio (maximum speed/minimum speed) of the flow speed of the cooling liquid can be changed to about 1.07 to 1.33, although changed depending on the flow speed, fluid pressure, thickness, etc. of the cooling liquid layer.

As shown inFIG.1A, a discharge port34is provided below along the core axis O of the cylinder body32. The discharge port34can discharge the metal powder contained and flowed in the cooling liquid layer50to the outside together with the cooling liquid. The inner diameter of the inner circumference surface of the discharge port34may be smaller than the inner diameter of the inner circumference surface33of the cylinder body32and preferably continuously becomes smaller from the inner circumference surface33of the cylinder body32toward the inner circumference surface of the discharge port34. The horizontal cross section of the inner circumference surface of the discharge port34is not necessarily elliptical and may be circular. Preferably, the horizontal cross section of the inner circumference surface33of the cylinder body32is an ellipse of the same size from the upper part of the cylinder body32toward the discharge port34along the core axis O.

A cooling liquid introduction unit36is provided at the upper portion along the core axis O of the cylinder body32. As shown inFIG.1B, the cooling liquid introduction unit36includes a frame38and an outer formation member (outer-frame formation member)45. The outer formation member45may be formed integrally with the cylinder body32or may be formed separately from the cylinder body32and attached to the cylinder body32.

The outer formation member45defines an outside space44on the outside of the inner circumference surface33at the upper portion of the cylinder body32. Moreover, an auxiliary cylinder body40is mounted on the inner circumference surface of the upper portion of the cylinder body32. The auxiliary cylinder body40may be the upper end opening edge of the cylinder body32itself. In the illustrated example, however, the auxiliary cylinder body40is formed separately from the cylinder body32and mounted on the inner circumference surface of the upper portion of the cylinder body32. The inner circumference surface of the auxiliary cylinder body is preferably flush with the inner circumference surface33of the cylinder body32, but may be different.

The frame38may be formed integrally with the cylinder body32, but is preferably formed separately from the cylinder body32and includes an inner frame piece39adisposed on the inner side of the inner circumference surface of the cylinder body32and a frame support piece39bintersecting the inner frame piece39aat a predetermined angle. As shown inFIG.1C, the frame support piece39bis a plate piece having a substantially elliptical ring shape, and the inner frame piece39ahas a substantially elliptical cylindrical shape with a center axis Oa inclined at an angle θ1 from the substantially elliptical central opening edge of the frame support piece39b(to the direct axis of the ellipse).

The core axis Oa of the inner frame piece39ashown inFIG.1Ccorresponds with the core axis O of the cylinder body32shown inFIG.1A, and the horizontal cross section of the outer circumference surface of the inner frame piece39ahas a similar elliptical shape with an inner diameter smaller than that of the ellipse of the horizontal cross section of the inner circumference surface33of the cylinder body32shown inFIG.1A(or the inner circumference surface of the auxiliary cylinder body40). That is, the outer circumference surface of the inner frame piece39ahas a diameter smaller than that of the inner circumference surface33of the cylinder body32(or the inner circumference surface of the auxiliary cylinder body40) and is parallel thereto.

As shown inFIG.1A, the outer diameter portion of the frame support piece39bis attached to the upper end of the outer formation member45or the upper end of the cylinder body32. Instead, the outer diameter portion of the frame support piece39bmay be formed integrally with the upper end of the outer formation member45or the upper end of the cylinder body32. The inner diameter portion of the frame support piece39band the inner frame piece39adefine an inside space46on the inner side of the inner circumference surface33at the upper portion of the cylinder body32together with the inner circumference surface of the cylinder body32, the inner circumference surface of the auxiliary cylinder body40, and/or the inner circumference surface of the outer formation member45.

As shown inFIG.1B, the outer formation member45defines the outside space44on the outer side of the inner circumference surface33at the upper portion of the cylinder body32together with the cylinder body32(including the auxiliary cylinder body40). The inside space46is located radially on the inner side of the outside space and communicates with the outside space44via a passage portion42. The upper end of the auxiliary cylinder body40or the cylinder body32is located between the outside space44and the inside space so that the passage portion42is formed at or near the top of the outside space44along the core axis O of the cylinder body32.

In the present embodiment, the outside space44is formed in a substantially elliptical ring shape continuing horizontally on the outside of the inner circumference surface33of the cylinder body32. The inside space46is formed in a substantially elliptical ring shape continuing horizontally along the inner circumference surface33on the inside of the inner circumference surface33of the cylinder body32. Likewise, the passage portion42is also formed in a substantially elliptical ring shape continuing horizontally. A vertical width W1along the core axis O of the passage portion42is smaller than a vertical width W2in the core axis direction of the outside space44. Preferably, W1/W2is ½ or less.

A cooling liquid supply line37for introducing a cooling liquid is attached to the radially outer side of the outer formation member45. Preferably, a connection port from the supply line37to the outside space44is located below the passage portion42along the core axis O.

In the outside space44, preferably, the cooling liquid flowing from the supply line37goes from the bottom to the top of the outside space and enters the inside space46from the passage portion42. In addition, preferably, the lower end of the inner frame piece39afor defining the inside space46is located below the passage portion42along the core axis O. A cooling liquid discharge port52is formed between the lower end of the inner frame piece39aand the inner circumference surface33(including the inner circumference surface of the auxiliary cylinder body40) of the cylinder body32. As shown inFIG.1C, the lower end of the inner frame piece39adefines a substantially elliptical opening on the horizontal plane.

The inner diameter of the cooling liquid discharge port52corresponds with the outer diameter of the inner frame piece39a, and the outer diameter of the cooling liquid discharge port52corresponds with the inner circumference surface of the cylinder body32(the inner diameter of the auxiliary cylinder body40). Preferably, the cooling liquid discharge port52is formed in a substantially elliptical ring shape continuing along the circumferential direction in the horizontal cross section.

The cooling liquid discharge port52is connected to the inside space46, and the cooling liquid in the inside space46is blown out in an elliptical spiral manner from the cooling liquid discharge port52toward the inner circumference surface33of the cylinder body32. In the present embodiment, the radial width of the cooling liquid discharge port52is not limited, but corresponds with the thickness of the cooling liquid layer50of the cooling liquid flowing along the inner circumference surface of the cylinder body32and is determined in relation to it.

As shown inFIG.1A, the axial length L1of the inner frame piece39ais a length covering the width W1in the core axis O of the passage portion42shown inFIGS.1B and1sdetermined so that the cooling liquid discharge port52is formed on the upstream side of the contact position between the molten metal discharged from the molten metal supply unit20and the cooling liquid layer50. Moreover, as shown inFIG.1A, the axial length L1of the inner frame piece39ais determined so that the liquid surface of the cooling liquid layer50having a sufficient axial length L0is exposed on the inner circumference surface33of the cylinder body32.

Preferably, the length L0along the core axis O of the cooling liquid layer50exposed inside is 5 to 500 times larger than the axial length L1of the inner frame piece39a. The inner diameter (short diameter of the ellipse) of the inner circumference surface33of the cylinder body32is not limited, but is preferably 50 to 500 mm.

In the present embodiment, the cooling liquid supply line37may be connected in the tangential direction of the cooling liquid introduction unit36. The cooling liquid can enter the inside of the outside space44from the cooling liquid supply line37so as to rotate around the core axis O in an elliptical spiral manner. The cooling liquid entered in the inside of the outside space44in a spiral manner passes through the passage portion42and enters the inside of the inside space46in a spiral manner.

In the present embodiment, in the cooling liquid introduction unit36, the cooling liquid is temporarily stored in the outside space44disposed outside the cylinder body32. The outside space44is formed in a substantially elliptical shape. In this configuration, the cooling liquid is introduced into the inside space46while circling in an elliptical manner in the outside space44.

In the present embodiment, since the lower end of the passage portion42is formed above the lower end of the outside space44, the cooling liquid is once lifted upward while circling in an elliptical spiral manner in the outside space44and enters the inside space46via the passage portion42. Since the cooling liquid entering the inside space46located at the upper inside of the cylinder body32passes through the passage portion42, the flow speed of the cooling liquid increases, and the cooling liquid collides with the inner frame piece39aof the inside space46so as to change its flow direction.

The cooling liquid passing through the passage portion42provided at the upper part of the cylinder body32and entering the inside of the inside space46in an elliptical spiral manner changes its flow downward along the inner frame piece39a(along the core axis O). The frame support piece39bblocks the upward flow of the cooling liquid. The cooling liquid forms an elliptical ring flow along the inner circumference surface33around the core axis O in the inside space46. Moreover, gravity acts downward along the inner circumference surface33(along the core axis O), and the cooling liquid is discharged from the cooling liquid discharge port52along the inner circumference surface33so as to flow in a substantially elliptical spiral orbit due to the synergistic effect with gravity. The cooling liquid discharged from the cooling liquid discharge port52forms the cooling liquid layer50in which the cooling liquid flows in an elliptical spiral manner with a substantially constant thickness along the inner circumference surface33.

In the present embodiment, as shown inFIG.1A, since the cooling liquid is supplied from the cooling liquid introduction unit36to the inner circumference surface33formed in an ellipse shape at the upper inside of the cylinder body32, the cooling liquid can form the cooling liquid layer50flowing in a substantially elliptical spiral manner along the inner circumference surface33of the cylinder body32. The molten metal drop21a, which is a droplet of the molten metal21, can be cooled more rapidly by spraying the molten metal drop21aonto the inner liquid surface of the cooling liquid layer50. As shown inFIG.2AandFIG.2B, the flow speed of the elliptical spiral cooling liquid is faster on the short diameter side of the ellipse and slower on the long diameter side of the ellipse, and the molten metal drop21asprayed against the cooling liquid layer50is flowed in the cooling liquid layer50together with the cooling liquid while changing the flow speed.

Since the molten metal drop21aflows in the cooling liquid layer50together with the cooling liquid while changing the flow speed, the vapor film around the molten metal drop21a, which is considered to be generated immediately after the contact with the cooling liquid, is easily peeled from the molten metal drop21a, and the molten metal drop21ais easily rapidly cooled by the cooling liquid layer50. A metal powder having good amorphousness and magnetic characteristics even with a fine particle size can be produced by rapidly cooling the molten metal drop21ain such a manner.

In the present embodiment, as shown inFIG.1A, the cooling liquid discharge port52is continuously formed in a substantially elliptical shape over the circumferential direction of the cylinder body32, but may be formed intermittently over the circumferential direction of the cylinder body32by, for example, providing the cooling liquid discharge port52with a reinforcing member. When the cooling liquid discharge port52is continuously formed over the circumferential direction of the cylinder body32, it is possible to form the cooling liquid layer50of the cooling liquid flowing in an elliptical spiral manner along the inner circumference surface33of the cylinder body32.

In the present embodiment, as shown inFIG.1A, the cooling liquid introduction unit36can form a substantially elliptical cooling liquid discharge port52between the inner frame piece39aand the inner circumference surface33of the cylinder body32. As a result, the cooling liquid flowing in an elliptical spiral manner along the inner circumference surface33of the cylinder body32can be discharged from the cooling liquid discharge port52.

In the present embodiment, as shown inFIG.1A, the center of the ellipse formed by the inner circumference surface33is displaced so as to be inclined at an angle θ2 to the vertical line (Z-axis) toward the lower part of the cylinder body32. As shown inFIG.2A, the cooling liquid of the cooling liquid layer50formed along the inner circumference surface33flows while drawing an elliptical spiral orbit and being inclined to the vertical direction (gravity direction).

Thus, the distance of the elliptical spiral through which the cooling liquid flows can be increased on condition that the length in the Z-axis is constant. When the molten metal is sprayed in the gravity direction against one end along the long diameter of the ellipse of the inner circumference surface33of the cylinder body32, the molten metal drop21aeasily enters the inner circumference surface33(cooling liquid layer50) of the cylinder body32from the upper end opening of the cylinder body32, and the droplets can be cooled smoothly.

In the above-mentioned embodiment, the horizontal cross section of the inner circumference surface33of the cylinder body32is an ellipse of the same size from the upper portion of the cylinder body32toward the discharge port34along the core axis O, but the horizontal cross section of the inner circumference surface33of the cylinder body32has a substantially elliptical shape at least in the upper portion of the cylinder body32and may have a shape changing in the middle toward the discharge port34along the core axis O, for example, gradually changing from a substantially elliptical shape to a substantially circular shape (or another shape).

In the horizontal cross section of the inner circumference surface33of the cylinder body32, a ratio (L3/L2) of a long diameter L3to a short diameter L2in an ellipse is preferably constant from the upper portion of the cylinder body32toward the discharge port34along the core axis O, but may be changed. For example, the ratio (L3/L2) may be changed so as to be smaller, larger, or alternately smaller or larger from the upper portion of the cylinder body32toward the discharge port34along the core axis O.

In the horizontal cross section of the inner circumference surface33of the cylinder body32, the direction of the long diameter of the ellipse may be changed gradually from the upper portion of the cylinder body32toward the discharge port34along the core axis O. For example, the direction of the long diameter of the ellipse may correspond with the inclination direction of the core axis O of the cylinder body32in the upper portion of the cylinder body32, and the direction of the long diameter of the ellipse may be changed so as to be substantially perpendicular to the inclination direction of the core axis O of the cylinder body32in the lower portion of the cylinder body32.

In the present embodiment, the predetermined angle θ2 of the core axis O of the cylinder body32to the vertical direction is not limited, but is preferably 5 to 45 degrees. In such an angle range, the molten metal drop21afrom the molten metal discharge port23can be easily discharged against the cooling liquid layer50formed on the inner circumference surface33of the cylinder body32.

In the present embodiment, the cooling liquid introduction unit36is formed so that the frame support piece39bis horizontal, but the present invention is not limited to this as long as the cooling liquid introduction unit36is configured so as to discharge the cooling liquid layer50in an elliptical spiral manner.

Second Embodiment

As shown inFIG.4, a metal powder producing apparatus110and a metal powder producing method according to another embodiment of the present invention are similar to those of First Embodiment except for the following respects. The common members are provided with the common names and references. The common respects are not partly described.

A ring35is fixed on the downstream side of the inner circumference surface33of the cylinder body32constituting the cooling unit30. The ring35functions as a weir (or baffle plate) on the downstream side of the cooling liquid layer50on the inner circumference surface33of the cylinder body32. Since the flow in the direction of the core axis O is blocked by the ring35, the cooling liquid layer50has a predetermined thickness and flows over the ring35to the lower portion of the cylinder body32. Since the ring35is provided on the downstream side of the cooling liquid layer50, the ring35controls the flow of the cooling liquid in the direction along the core axis O of the cylinder body32, and it is easy to maintain a constant thickness of the cooling liquid layer50.

In the present embodiment, the ring35is attached at an angle θ1 to the core axis O of the cylinder body32and formed in an elliptical ring shape along the inner circumference surface33of the cylinder body32. The radial thickness of the ring35corresponds with the radial thickness of the cooling liquid layer50and is preferably substantially the same as the radial width of the discharge port52.

The present invention is not limited to the above-mentioned embodiments and may variously be modified within the scope of the present invention.

For example, unlike the above-mentioned embodiments, instead of the cylindrical member32α having the circular inner circumference surface33perpendicular to the core axis O shown inFIG.3A, the cylinder body32may be an elliptical cylindrical member previously having a substantially elliptical cross section of the inner circumference surface perpendicular to the core axis O as shown inFIG.3B.

In the embodiment shown inFIG.3A, the inner circumference surface33inclined to the core axis O is formed in an elliptical shape by cutting the cylindrical member32a. As shown inFIG.3B, however, a cylindrical member previously having an elliptical cross section of the inner circumference surface33perpendicular to the core axis O may be employed. In First Embodiment mentioned above, as shown inFIG.2A, an elliptical spiral flow is formed in which the center of the ellipse horizontal around the Z-axis changes along the core axis O of the cylinder body. In the present embodiment, however, an elliptical spiral flow is formed in which the center of the ellipse perpendicular to the core axis O along the inner circumference surface33of the cylinder body moves along the core axis O.

EXAMPLES

Hereinafter, the present invention is described based on more detailed examples, but the present invention is not limited to the examples.

EXAMPLES

A metal powder composed of Fe—Co—Si—B—P—Cu (Experiment No. 9) was produced using a metal powder producing apparatus10having an angle θ2 of 15 degrees and a L3/L2of 1.04. Moreover, a metal powder composed of Fe—Co—Si—B—P—Cu (Experiment No. 11) was produced using a metal powder producing apparatus10having an angle θ2 of 40 degrees and a L3/L2of 1.30.

In each experiment, the melting temperature was 1500° C., the gas spray pressure was 5 MPa, and the type of gas used was Argon. As the spiral flow condition, the pump pressure was 7.5 kPa. In the examples, it was possible to produce a metal powder having an average particle size of 24.9 to 26.2 μm, being comparatively small in each composition, and having a small variation. The average particle size was measured using a dry particle size distribution measuring device (HELLOS). Also, the crystal structure analysis of the metal powders produced by Experiment Nos. 7 to 14 was evaluated by a powder X-ray diffraction method. In the examples, amorphous metal powders were produced. The magnetic characteristics of the metal powders were measured by a coercivity (Oe) using an He meter. The results are shown in Table 1. Also, the thickness of the cooling liquid layer50was 30 mm, and the unevenness of the thickness in the core axis O direction was small.

When the L3/L2was 1.04, the speed ratio (maximum speed/minimum speed) of the flow speed of the cooling liquid was about 1.07. When the L3/L2was 1.10, the speed ratio of the flow speed of the cooling liquid was about 1.16. When the L3/L2was 1.30, the speed ratio of the flow speed of the cooling liquid was about 1.20.

Reference Examples

Metal powders (Experiment Nos. 1 to 6) were produced and evaluated similarly to the examples, except for, as shown inFIG.5AandFIG.5B, having a circular cross section (L3/L2=1.00) perpendicular to the core axis O of the inner circumference surface33of the cylinder body32and using a metal powder producing apparatus in which the lower end of the inner frame piece39aof the cooling liquid introduction port defined a circular opening in a cross section perpendicular to the core axis O so that the cooling liquid discharge port52had a circular shape. Table 1 shows the results.

Comparing the examples with the reference examples in Table 1, as for the magnetic characteristics of the metal powders, the coercivity of the examples was smaller than that of the reference examples in a similar composition, and the magnetic characteristics of the examples were excellent. This result indicates that the magnetic characteristics were excellent despite the same pump pressure and the same flow amount of the cooling water as in the reference examples and is considered to be due to the following phenomenon.

In the metal powder producing apparatus of the reference examples, as shown inFIG.5AandFIG.5B, the cooling liquid flowing on the inner circumference surface forms a circular spiral cooling liquid layer. Thus, the flow speed of the cooling liquid on the inner circumference surface is considered to be substantially constant (the speed ratio of the flow speed of the cooling liquid is approximately 1.00). On the other hand, in the examples, as shown inFIG.2AandFIG.2B, the cooling water forms a substantially elliptical spiral cooling liquid layer50. In the elliptical spiral cooling liquid layer50, the flow speed is slower on the long diameter side and faster on the short diameter side, and the flow speed changes. Thus, the molten metal droplet sprayed against the cooling liquid layer50flows while changing the flow speed together with the cooling liquid layer. The vapor film around the droplet considered to be generated immediately after contact with the cooling liquid is easily peeled from the droplet due to the change in flow speed. This is because the rapid cooling effect of the droplet in the cooling liquid layer is enhanced.

DESCRIPTION OF THE REFERENCE NUMERICAL