WO1999033598A1

WO1999033598A1 - Method of producing metal powder

Info

Publication number: WO1999033598A1
Application number: PCT/JP1998/005867
Authority: WO
Inventors: Masato Kikukawa; Shigemasa Matsunaga; Tsuneta Inaba; Osamu Iwatsu; Tohru Takeda
Original assignee: Fukuda Metal Foil & Powder Co., Ltd.
Priority date: 1997-12-25
Filing date: 1998-12-24
Publication date: 1999-07-08

Abstract

A method of producing metal powder by spraying a cooling liquid to a molten metal flowing down, characterized in that the cooling liquid is continuously discharged towards the molten metal flow passing through a ring-like nozzle from the ring-like nozzle so disposed as to encompass the molten metal flow so that the cooling liquid encompasses the molten flow in the shape of a hyperboloid of one sheet. This invention can efficiently produce metal powder which is very fine and pseudo-spherical and moreover has a small width of particle distribution.

Description

Description: Gold powder production method

The present invention relates to a method for producing a metal powder, and more particularly, to a method for producing a metal powder that is fine, pseudo spherical, and has a narrow particle size distribution. Conventional technology

The shape and shape distribution of metal powders for manufacturing products such as injection molding materials, magnetic materials, and conductive materials have a significant effect on the characteristics of products manufactured using them, resulting in higher quality. In order to manufacture such products, it is necessary to use metal powder that is fine, pseudo-spherical and has a narrow particle size distribution.

There are many techniques for producing metal powders in the past, but the atomizing method of producing a metal powder by spraying a cooling medium (spraying medium) onto a molten metal stream is known as the ^ method of efficiently producing metal powders. I have. Generally, the atomization method using a gas as a cooling medium is called a gas atomization method, and the atomization method using a liquid as a cooling medium is called a liquid atomization method. As the gas atomization method, for example, a method using a nozzle described in U.S. Pat. No. L659.291 and U.S. Pat. No. 3,235.783 is known. Such a gas jet by the gas atomization method is not visible, but when confirmed by the shurilen method, the gas jet discharged from the nozzle is monotonically expanding. This is probably because the gas jet, which is a compressible fluid, adiabatically expands as soon as it comes out of the nozzle. This adiabatic expansion sharply lowers the energy density of the gas jet, so the gas atomization method can efficiently produce fine gold powder. It ’s difficult to humiliate, The resulting metal powder has a broad particle size distribution. In addition, since the gas jet easily entrains the ambient gas, the gas atomization method has a problem of blowing up molten metal.However, the gas used as a cooling medium has a relatively low cooling capacity. Therefore, the molten metal droplets dispersed by the gas jet are spheroidized by surface tension and then solidified. Therefore, the metal powder obtained by the gas atomization method has a relatively pseudospherical shape.

The nozzles described in the above-mentioned U.S. Pat.No. 1,659,291 and U.S. Pat. As a result, the gas jet discharged from the nozzle is displaced in the same direction with respect to the center of the nozzle. It is thought that this displacement suppresses ^ Lh of the molten metal by entraining gas jet force <atmospheric gas. As the liquid atomization method, a V-jet type liquid atomization method (FIG. 4 (a) or FIG. 4 (b)) in which a liquid jet is linearly collided, a ring: ^ a single point collision of the liquid jet discharged from the nozzle 15 Conical jet-type liquid atomization method (Fig. 4 (c)) or pencil jet-type liquid atomization method (Fig. 4 (d)) in which a liquid jet emitted from a pencil jet type nozzle part 14 collides at a single point. Have been. Since the cooling medium of the liquid atomization method is an incompressible fluid, the energy density of the liquid jet for dispersing the molten metal stream 6 is much larger than the energy density of the gas jet. Therefore, according to the liquid atomization method, finer metal powder can be obtained than in the case of the gas atomization method.

In the conventional liquid atomization method involving linear collision or single point collision, the dispersed molten metal droplet before solidification concentrates near the collision part of the liquid jet and the liquid jet. Cooling suddenly due to intense contact with Therefore, the dispersed molten metal droplet force, the metal powder obtained to contact and stick in a tuft The end contains coarse particles, is irregularly shaped, and has a wide particle size distribution 0

Therefore, when pseudo-spherical metal powder is required, or when metal powder with a narrow particle size distribution is required, it is necessary to further perform separation treatment and mechanical treatment, which increases the production cost. Would. Various improvements have been attempted in the past to solve the above-mentioned problem s in the liquid atomization method.

For example, there is an attempt to reduce the apex of the focal point of the V-jet

. It was thought that this reduced the collision energy of the liquid jet and reduced the deformation of the dispersed molten metal droplets.In practice, however, such an improvement would make the shape of the gold powder sufficiently pseudo-spherical It was difficult. Also, the energy loss increased as the distance from the nozzle to the collision point increased, and the resulting metal powder was coarse and the particle size distribution became wider.

Further, for example, Japanese Patent No. 552253 (Japanese Patent Publication No. 43-6389), Japanese Patent Publication No. 3-55522 and Japanese Patent Publication No. 2-56403 describe improvements of a conical jet type liquid atomizing method. In addition, the invention described in Japanese Patent Publication No. 2-56403 is a technology for generating a liquid jet by injecting a cooling liquid from a tangential direction and a normal direction of a nozzle. Under such conditions, only coarse powder and metal powder can be obtained. Technical issues

The present invention develops a new liquid jet having a form different from that of a conventional liquid jet, and applies the special liquid jet to a liquid atomization method to thereby obtain a conventional liquid jet. It is an object of the present invention to provide a technology capable of efficiently producing a finer, pseudospherical, and narrower particle size distribution metal powder than the atomization method. Solution

The inventor of the present application has conducted various studies to solve the above-described problems, and as a result, in a metal powder manufacturing method of manufacturing a metal powder by spraying a cooling liquid onto a flowing molten metal stream, the cooling liquid includes the molten metal stream. (Molten gold that has passed through the annular nozzle from the annular nozzle provided to surround it)! The above problem is solved by a method for producing a metal powder characterized by being continuously discharged so as to surround the molten metal flow in a single-leaf curved surface toward the flow. Look at it.

Next, the present invention will be described in more detail. Description of the drawings

FIG. 1 is a transverse sectional view (a) and a longitudinal sectional view (b) of an operating state of an annular nozzle attached to a metal powder production apparatus of the present invention.

FIG. 2 is a perspective view conceptually showing a one-lobe hyperboloid liquid jet discharged from the annular nozzle shown in FIG.

FIG. 3 is an electron micrograph of a metal powder produced according to the present invention and the prior art.

FIG. 4 is a view showing a conventional liquid atomizing method. FIG. 1 shows an embodiment of an annular nozzle 1 for carrying out the method for producing metal powder of the present invention. FIG. 1 (a) is a cross-sectional view of the annular nozzle, and FIG. It is a longitudinal cross-sectional view. The annular nozzle 1 shown in FIG. 1 is attached to a metal powder production apparatus such that the flowing molten metal stream 6 passes through the hole 2 of the annular nozzle.

The annular nozzle 1 has an inlet 3, a swirl chamber 4, and an annular slit 5. The coolant injected from the inlet 3 swirls inside the swirl chamber 4 and then passes through the hole 2. The molten metal is discharged from the ring-shaped slit 5 toward the molten metal flow. Next, this annular nozzle 1 Will be described in more detail.

Since the inlet 3 is provided along the diagonal of the swirl chamber 4 of the present nozzle, the coolant can be injected into the swirl chamber 4 at a high pressure. To turn. It is sufficient for the annular nozzle of the present invention to have at least one inlet, but in the present embodiment, two inlets are provided so that the coolant can be introduced at a high E. The inlet is not necessarily formed along the tangential direction of the swirl chamber, but may be formed in the normal direction of the swirl chamber.

The swirling chamber 4 is formed so as to surround the periphery of the hole 2 of the annular nozzle 1. Therefore, the cooling liquid injected into the swirling chamber 4 is discharged after swirling the periphery of the molten metal flow 6 passing through the litter section 2 in advance. The outer peripheral portion in the swirling chamber 4 has a cavity region 7 free from obstacles so that the coolant injected from the inlet spreads throughout the swirling chamber. Therefore, the coolant can be injected into the annular nozzle at a high pressure.

A plurality of guide wings 8 are provided inside the above-mentioned hollow area 内 in the swirl chamber 4. The guide vanes 8 serve to stabilize the flow of the coolant and to guide the coolant further inward while swirling. Then, the coolant is discharged from each part of the annular slit 5 formed along the inner surface of the hole 2 at a substantially uniform pressure. In addition, in addition to or instead of the above-mentioned guide vanes, a passage or a groove for turning the coolant into the swirl chamber is provided. It may be rotated in the evening or the like.

As described above, the coolant is guided toward the annular slit 5 while swirling in the swirl chamber 4, and the inside of the swirl chamber 4 gradually becomes narrower as approaching the annular slit 5. As a result, the cooling liquid is discharged from the annular slit 5 as a high-speed liquid jet. If the liquid jet is released toward the molten gold flow passing through the hole 2, the position of the annular slit is not limited to the inner surface of the hole, but may be on the lower surface of the annular nozzle 1. It may be formed. Further, the present invention is not limited to a circular annular slit as shown in the drawings, but may have other shapes (for example, an elliptical shape or a rectangular shape). Etc.) may be used. The liquid jet 13 discharged from the annular nozzle 1 has a single-leaf hyperboloid 9 as shown in FIG. In order to facilitate understanding, a virtual line 10 indicating the discharge direction of the liquid jet discharged from each part of the annular slit 5 is described in the one-lobe hyperboloid liquid jet shown in FIGS. 1 and 2. Have been. According to the present invention, the liquid jets 13 (imaginary lines 10) discharged from the respective portions of the annular slit 5 approach each other once, but flow so as to be crowded without colliding with each other. Form. The method for producing metal powder of the present invention is not limited to a method using an annular nozzle having a swirling chamber 4 and an annular slit 5 as shown in FIG. For example, the outlets of a plurality of pencil jet type nozzle parts 14 are arranged in an annular shape along the annular slit 5 in FIG. 1, and the liquid from each pencil jet type nozzle part along the imaginary line 10 is shown. The jet may be emitted in a one-lobe hyperboloid. In this case, a plurality of pencil jet type nozzle parts arranged in a ring form the ring nozzle of the present invention. The use of the metal powder manufacturing apparatus having the annular nozzle 1 as described above makes it possible to efficiently produce a finer, pseudo-spherical, and narrower particle size distribution metal powder than the conventional liquid atomization method. .

Without being bound by any particular consideration, according to the present invention, it is considered that the metal powder is produced as follows. According to the present invention, the liquid jet is discharged in a one-lobe hyperboloidal shape as described above. However, since this liquid jet is composed of an incompressible fluid, the energy density is high, and the liquid jet is in the middle. It can flow stably all the time without colliding with each other The pressure inside the one-hyperboloid formed by the high-speed liquid jet decreases rapidly as it approaches the constriction. Therefore, the molten metal flow

When the molten metal 6 flows down toward the constricted portion 11 of the one-lobe hyperboloid, the molten metal flow 6 is regularly and continuously dispersed with uniform energy until passing through the constricted portion 11, and the fine molten metal flows. Drops.

Then, the dispersed molten gold droplets solidify into gold m powder, or in the present invention, these molten metal droplets can be solidified gently without contacting each other. In other words, even if the molten metal droplets become fine as described above, if the molten metal droplets come into contact with each other before solidification, the resulting gold powder becomes an irregular shape. In the present invention, by providing the constricted portion 11, the molten metal droplet can pass through the constricted portion and move to the lower part of the one-lobe hyperboloid without contacting each other. Moreover, the molten metal droplet before solidification according to the present invention is essentially one-lobe hyperbolic; it is relatively slowly cooled without traversing, so that it becomes a sphere due to surface tension.

In this regard, there is a significant difference from the conventional liquid atomization method in which the dispersed molten metal droplets come into contact with each other near the collision portion of the liquid jet, and are rapidly cooled by violent contact intersection with the liquid jet. I do.

In summary, according to the present invention, the molten gold droplets which are finely dispersed regularly and continuously at a uniform energy by the liquid jet are solidly and gently solidified without contacting each other. Therefore, it is considered that the present invention can efficiently produce a finer, pseudospherical, and narrower particle size distribution metal powder than the conventional method. In the present invention, the flow rate of the liquid jet 13 is not particularly limited, but is not less than 10 Om / sec, more preferably not less than 130 m / sec, most preferably not less than I5 Om / sec, and more preferably Is preferably 20 m / sec or more.

The pressure inside the constricted part 11 of the liquid jet is 50 to 750 mmHg with respect to the atmospheric pressure. The pressure is reduced to 100 to 750 mmHg, and optimally to 150 to 700 tnmHg (that is, 1 to 5 (h ^-750 mmHg, more preferably to 100 to ^ 750 mmHg, optimally to 0 to Because the vapor pressure of the liquid exists, for example, when using water at normal temperature (2 O'C) as the cooling liquid, the pressure inside the constricted section should be large. It is difficult to reduce the pressure to 75 O mmHg or more with respect to the atmospheric pressure.In the present invention, the discharge direction of the liquid jet is not particularly limited as long as the liquid jet is discharged in a one-lobe hyperboloidal shape. However, preferably, the liquid jet is discharged at a descent angle 0 and a swirl angle ω described below.

In the present invention, the descending angle 0 and the turning angle ω are defined as follows. First, the velocity V of the liquid jet is defined as the velocity component V _x in the tangential direction of the annular slit (X-axis direction in Fig. 4), the velocity component V in the normal direction of the circular slit (Y-axis direction in Fig. 4), , And the velocity component V, in the vertical direction (the z-axis direction in Fig. 3). Here, the turning angle ω is defined as an angle formed by the resultant force of V _x and V, with respect to the y-axis. The descending angle 0 is defined as the angle formed by the resultant force of V _y and V, with respect to the z-axis.

The turning angle ω is 1 ° 30 °, and 3 ° ≤ω≤20. Optimally, it is preferable that 5 ° ≤ ω ≤ 20 °. The descent angle 0 is 5 ° 60

°, and even 7. ≤ 0 ≤ 5 5. Optimally, it is preferable that 8 ° ≤ 0≤ 40 °. Particularly good metal powders are obtained when the liquid jet is discharged at a swirl angle ω and a descent angle 0 within the above ranges. In the present invention, the amount of coolant (ie, liquid jet) released per unit time with respect to the amount of molten metal flowing down per unit time is not particularly limited, and can be set arbitrarily. , (Flow rate of molten gold): (coolant discharge rate) is preferably 1: 2 to 100, more preferably 1: 3 to 50, and most preferably 1: 5 to 30. ing. By setting the discharge amount of the cooling liquid within the above range, good metal powder can be efficiently produced with energy saving. The present invention can be applied to any metal including a metal element, a metal compound, an alloy and an intermetallic compound. Further, according to the present invention, it is possible to produce a metal powder having desired characteristics by setting atomizing conditions according to the characteristics of a metal.

Preferred examples of the metal powder obtained by the present invention are described below. Unless otherwise specified, the following features describe gold-extended powders having a particle size of not more than one stroke selected according to JIS Z-8801 after using the liquid atomizing method of the present invention.

(1) The relative apparent density of the metal powder obtained by the present invention is preferably 28% or more, more preferably 30 or more, and optimally 32% or more.

(2) The relative tab density of the metal powder obtained by the present invention is preferably 45% or more, more preferably 50% or more, and most preferably 55% or more.

3) The median diameter of the metal powder is preferably 50 πι or less, more preferably 35 m or less, optimally 25 // m or less, and most optimally 15 / m or less.

場合 When the metal powder has a median diameter of 25 m or less, the following fine powder having a specific particle size is contained in a predetermined ratio.

1) It contains at least 20% by weight, preferably 40% by weight or more, and most preferably 45% by weight or more of fine powder having a particle size of less than \ 0 fim.

2) At least 3% by weight, preferably at least 10% by weight, and optimally at least 18% by weight of fine powder having a particle size of 5 μιη or less.

場合 When the median diameter of the metal powder is less than m, fine powder having the following specific particle size is contained at a predetermined ratio.

1) Fine powder having a diameter of IQ um or less is preferably at least 35% by weight or more. More than 45% by weight, optimally more than 50% by weight.

2) Contains at least 10% by weight, preferably at least 10% by weight, and optimally at least 20% by weight of a powder having a particle size of 5 or less.

3) Fine powder having a particle size of 1 μm or less is contained at least 0.01% by weight or more, preferably 0.05% by weight or more, and most preferably 0.1% by weight or more.

金属 The geometric standard deviation of the metal powder obtained by the present invention is preferably 3.0 or less, more preferably 2.5 or less, and most preferably 2.3 or less. The width of the particle size distribution can be evaluated by the geometric standard deviation.

The specific surface area of the metal powder obtained by the present invention is preferably 4000 cm ² / g or less, more preferably 3000 cmVg or less, and most preferably 2500 cm ² / g or less. Example

Next, the present invention will be described in more detail based on examples. The following examples are recognized by the inventor at the time of filing as being the best embodiment, but the present invention is not limited thereto. Water was used as a coolant to produce metal powders of Cu, Cu-10n alloy, Cr-Ni-Mo alloy and Fe-Si.-Co alloy. Metal powders were produced using various atomizing conditions according to the present invention (Examples 1 to 8).

In addition, metal powder was manufactured according to the conventional method using a conventional nozzle for generating a conical jet (Comparative Examples 1 to 8). Table 1 shows these atomizing conditions.

The pressure in the constriction was measured using a pipe with a cross-sectional area of 20 mm or less of the cross-sectional area in the constriction. A pressure gauge is connected to one opening of the pipe. Then, the pipe was inserted from above along the central axis 12 of the one-lobe hyperboloid such that the other opening of the pipe was positioned inside the constricted portion 11. Also The velocity of the liquid jet was calculated from the cooling injection pressure measured at the inlet 3 by using Bernoulli's theorem.

Analytical tests were performed on the metal powders having a particle size equal to or less than 1 face selected according to J 1 SZ8801 for the analytical items described in Table 1. The results of the analysis are also shown in Table 1. In addition, these analyzes were performed by the following means.

• The apparent density was measured in accordance with ISO-3923.

'Tap density was measured according to IS〇-3953.

-Relative apparent density was calculated according to (apparent density)） (true density) × 100.

• The relative tap density was calculated based on (tap density) x 10 (true density) x 100.

• The median diameter was measured using a laser diffraction scattering method (volume) using a micro track manufactured by Nikkiso Co., Ltd.

-The content of fine powder having a diameter of 10 m, 5 m and 1 / m or less in the metal powder was measured by using a laser diffraction scattering method (volume%).

• The geometric standard deviation was calculated according to the cumulative 50% diameter Z cumulative .87% in the median diameter measurement results.

-The specific surface area was measured according to the BET method of the gas phase adsorption method.

• The oxygen content was measured according to the non-dispersive infrared absorption method.

• Yield is the percentage of the metal powder having a particle size of 45 / m or less in the metal powder having a particle size of 1 mm or less selected according to J ISZ8801.

'Electron micrographs were taken using a scanning microscope manufactured by Hitachi, Ltd.

From the analysis results shown in Table 1, when compared with the same type of metal powder, the present invention It is thought that there is an effect. The apparent density and tap density of the metal powder according to the present invention are higher than those of the comparative example, and the relative apparent density and relative evening density of the metal powder according to the present invention are higher than those of the comparative example. This indicates that the metal powder produced according to the present invention is more pseudospherical than the metal powder produced according to the conventional method. The median diameter of the metal powder according to the invention is smaller than in the comparative example. This indicates that the metal powder obtained by the present invention is finer than the metal powder of the comparative example. It has been confirmed that the metal powder according to the present invention contains more fine powder than the metal powder according to the conventional method. In particular, the metal powder according to the present invention is significantly different from the metal powder of the comparative example in that the metal powder contains a through powder of 1 m or less within a range that can be confirmed by a laser diffraction scattering method. The geometric standard deviation of the metal powder according to the invention is smaller than in the comparative example. This indicates that the width of the abundance distribution of the metal powder obtained by the present invention is narrower than that of the metal powder of the comparative example. The oxygen content of the metal powder according to the present invention is smaller than that of the comparative example. This is considered to be because the metal powder of the present invention has a pseudospherical shape, so that the surface contact is small and oxidation is difficult. The yield according to the invention is higher than in the comparative example. This is considered to be because according to the present invention, the molten metal stream is regularly and continuously dispersed by the liquid jet, and the dispersed molten metal is cooled slowly without contacting each other. From the _t electron micrograph, it is clear that the edges of the metal powder of the present invention have been removed, and that the metal powder of the present invention is more pseudospherical than the metal powder of the comparative example.

Claims

Claims A method for producing a metal powder by spraying a cooling liquid onto a flowing molten metal flow to produce a metal powder,

The cooling liquid is continuous from an annular nozzle provided to surround the molten metal flow toward the molten metal flow passing through the annular nozzle so as to surround the molten metal flow in a single-blade hyperbolic shape. A method for producing metal powder, characterized in that the metal powder is released to the atmosphere.

The method according to claim 1, wherein the cooling liquid is discharged from the ring-shaped nozzle at a rate of 10 Om / sec or more.

The cooling liquid is discharged such that the turning angle ω is 1 ° ≤ω ^ 30 ° and the descending angle 0 is 5 ° ≤ Θ ^ 60 °. the method of.

A metal powder produced by the method according to any one of claims 1 to 3, having a median diameter of 50 m or less, a geometric standard deviation of 3.0 or less, and a pseudospherical shape. A metal powder characterized in that:

A metal powder manufacturing apparatus S provided with an annular nozzle for spraying a cooling liquid onto the flowing molten metal,

The annular nozzle is arranged so as to surround the molten metal flow, the annular nozzle includes a swirl chamber for swirling the coolant around the molten metal flow, and the swirl chamber swirled in the swirl chamber. An annular slit for discharging a coolant toward the molten metal stream,

The metal powder producing apparatus according to claim 1, wherein the coolant discharged from the annular slit surrounds the molten metal stream in a one-lobe hyperbolic shape.