JP2007332406A - Method for forming fine powder by using rotary crucible, and apparatus therefor - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method for producing a powder which comprises fine particles with uniform sizes, and has a narrow width in a particle diameter distribution, with excellent mass-productivity, and to provide an apparatus therefor. <P>SOLUTION: This apparatus has a rotary container having a heated cylindrical crucible 10 with a bottom. The production method comprises the steps of: supplying a molten metal (A) to the bottom surface in the vicinity of the rotation axis of the rotary container: applying 100% of the centrifugal force onto the molten metal to press the molten metal to the inner wall surface of the crucible; scatter-spraying the molten metal into an atmospheric gas such as argon gas, helium gas, nitrogen gas and air from crucible apertures by using the centrifugal force, while keeping the quantity balance between the sprayed metal and the continuously-supplied molten metal; and thereby producing a superfine powder (B) having uniform particle sizes. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a metal powder, metal powder, metal powder for thermal metallurgy, magnetic material, spherical metal powder for thermal spraying, metal powder for conductive paste, solder ball, and regenerator material for magnetic refrigerator, etc. The present invention relates to a method for producing spherical fine particles applicable to a wide range of inorganic and organic substances used in foods, pharmaceuticals, chemical industries, and the like, and a centrifugal spray device thereof.

  As a method for forming a metal or alloy into a spherical powder, various centrifugal spraying methods are known in addition to a rotating consumable electrode method, a droplet dropping spraying method, a gas atomizing method, a water atomizing method, and the like. However, the powder particle size in these methods is generally widely distributed over several μm to several 100 μm, and there are restrictions on the control of the particle size produced, and there are problems in productivity, There are many challenges. Among them, the centrifugal spray method has been tried many because it has a good controllability of operating parameters and can relatively obtain a spherical powder.

  The centrifugal spraying method in the prior art is, for example, a disk with a flat surface as a rotating body, a disk with irregularities (Patent Documents 1 and 2), or a dish with a dent on the top of the disk ( Patent Document 4), on the contrary, has been proposed in which various processes are added in consideration of pouring and scattering of the target raw material, using a circular plate as a basic shape, such as an umbrella having an upper portion inclined.

  However, in these methods, depending on the wettability between the molten metal and the rotating body and the pouring position, a slip occurs between the molten metal and the rotating body due to an abrupt speed difference. As a result, the centrifugal force generated by the high-speed rotation reaches the outer periphery of the rotating body without being able to sufficiently act on the molten metal and is scattered in the atmosphere, so that sufficient atomization of the spray cannot be realized. As a solution to this problem, there is a combination of centrifugal spraying and gas spraying (Patent Document 4). However, this technique cannot greatly compensate for the disadvantages of conventional gas spraying, and the particle size distribution of the produced powder. Can not reduce the spread of. In addition, a large amount of atomizing gas is required, which is not economically advantageous.

JP2006-2176 / S Science JP2002-317212 / Sanei Kasei Co., Ltd. Patent 3511082 / NIMS JP 10-85583 / Dowa iron powder Patent No. 3270713 / Japanese material JP 05-171228 / Shin-Etsu JP 07-224305 / Fukuda Metal

  However, it is difficult to control the particle size distribution of the particles such as the metal to be manufactured, and the particle size distribution of the particles such as the manufactured metal is generally wider than the required particle size distribution. For this reason, in order to obtain particles having a required particle size distribution, the produced particles having a wide particle size distribution are spheroidized. However, the current yield is very poor. Therefore, it has an adverse effect on the productivity and, in turn, the production cost of powders of metals and the like, and is the biggest bottleneck in the production of powders of metals and the like.

  The present invention has been made in view of the above-described circumstances, and a method for producing a powder capable of producing a powder composed of fine particles having a narrow particle size distribution and a uniform particle size with good mass productivity. And an object to provide an apparatus.

  The raw material molten metal is supplied to the bottom surface in the vicinity of the center of the rotation axis of a rotating cylindrical vessel with a heated bottomed cylindrical crucible, and the molten metal is pressed against the inner wall of the crucible by causing 100% of the centrifugal force to act on the molten metal. Ultra fine powder with a uniform powder size is produced by spraying from an opening of the crucible into an atmospheric gas such as argon, helium, nitrogen, and air by centrifugal force so as to balance the molten metal supplied.

  According to the present invention, since the molten metal droplets scattered from the opening end of the upper end surface of the crucible have a uniform velocity distribution, a powder consisting of fine particles with a narrow particle size distribution width and uniform particle size is obtained. It is done. And since a powder is formed, keeping the flow rate of the molten metal of a nozzle constant, a powder can be manufactured continuously and favorable productivity is obtained.

  Embodiments of the present invention will be described below with reference to the accompanying drawings. An outline of the centrifugal spray device and a high-speed rotating crucible structure are shown in FIGS. FIG. 1 is an overall view of the apparatus. FIG. 2 shows the structure around the rotating crucible and the behavior of the molten metal to be poured.

  The centrifugal spraying apparatus includes a melting furnace 2 inside the container 1, loads a raw material to be melted from the raw material additional apparatus 3 into the melting furnace 2, and heats to form a molten metal A. Then, the molten metal A is transferred to a holding furnace (tundish) 4 and poured from the nozzle 5 onto the bottom surface of the bottomed cylindrical crucible 10. The crucible 10 is provided with a heat insulating material 12 around the crucible 10 and accommodated in a heat-resistant metal crucible receiver 13 and can be rotated at high speed by a drive mechanism. The heat-resistant metal crucible receiver 13 is provided with fins 14 for cooling. The holding furnace (tundish) 4 and the nozzle 5 are provided with high-frequency induction heating coils 15 and 16 for keeping the molten metal warm. An energization resistance heating device may be used.

  An induction coil 16 is arranged on the outer surface of the pouring nozzle 5, and a heating sleeve 17 is installed on the inner and outer surfaces of the induction coil and on the lower part of the nozzle, and the inner surface and the bottom surface of the pouring nozzle and the crucible are heated by radiation.

In the present invention, the molten metal A is poured into the vicinity of the center of the crucible 10 rotating at a high speed, and the molten metal A is pressed against the inner wall of the crucible by centrifugal force, and the liquid film state is ensured at a stretch and the atmosphere is formed at a high speed. The rapidly cooled solidified powder B is produced by atomization by collision with He gas, Ar gas, N ₂ gas or the like. The produced coagulated powder B is continuously loaded into a container 6 provided at the lower part of the container 1.

  The greatest merit of the powder production according to the present invention is that the molten metal A is formed in a liquid film shape on the inner wall of the crucible 10 by centrifugal force. The degree is greatly increased. That is, in the prior art, ensuring wettability with the target metal was a big problem in disc material selection, whereas in the present invention, for the above-mentioned reason, the reactivity in the molten state with the target metal is simply. Only the viewpoint needs to be considered. Furthermore, in the case of a disk that rotates at a high speed, as a condition to be provided as a material, it is indispensable to secure mechanical strength that can withstand centrifugal force. It is possible to make the crucible receiver 13 made of heat-resistant metal bear mechanical strength, and the characteristics required for the crucible 10 are greatly relieved from this viewpoint.

  Further, the molten metal A poured into the vicinity of the crucible bottom center while being controlled to have a predetermined hot water supply speed by the control device installed at the upper end of the nozzle instantaneously becomes a thin liquid film, and the crucible bottom is moved to the crucible bottom. It flows toward the side wall surface, rises along the crucible side wall surface while being balanced by the centrifugal force with respect to the supply amount, and scatters from the opening into the gas atmosphere. Therefore, it is possible to insert a pouring nozzle having a heating mechanism inside the crucible, and the heating device can be used not only for the nozzle but also for heating the crucible.

  The melt raw material melted and adjusted in the high frequency induction furnace 2 or the like is set at the bottom of the tundish through a holding furnace held at a high temperature using means such as high frequency induction or the tundish (intermediate vessel) 4. From the hot water pouring nozzle 5, hot water is poured at a predetermined hot water supply speed onto the bottom surface at the center of the crucible 10 rotating at high speed. The pouring position may be gradually changed / moved from the center of the crucible toward the radial direction at a predetermined speed in order to prevent the pouring part from being locally melted. However, in order to avoid a sudden difference in rotational speed when the molten metal to be poured falls from the center of the crucible as it moves away from the center of the crucible, the distance that can be moved is within about 1/2 of the crucible radius. It is preferable to fit in.

  The molten metal poured into the bottom of the crucible moves to the crucible side wall surface by centrifugal force, and then the molten metal behavior in centrifugal casting gradually increases the melt thickness at the crucible side wall surface by the molten metal poured continuously. The crucible side wall surface rises in a liquid film state while receiving a strong centrifugal force in the same manner as in FIG. As soon as the melt in the liquid film state reaches the upper end of the opening of the crucible 10, it is scattered at high speed in the atmosphere by the energy accumulated by being released from the centrifugal force, and is atomized along with the sudden frictional collision with the atmospheric gas. To do. Thus, in the present invention, 100% of the centrifugal force acts on the molten liquid film existing on the side wall surface of the crucible, and there is a slip between the disk and the liquid film as in the conventional centrifugal spraying by rotating the disk. In addition, it is not affected by the material and shape of the rotating disk, which has been a problem from the viewpoint of wettability with a liquid film in the prior art.

  As mentioned above, since the kinetic energy of the molten metal accumulated by centrifugal force is released at a stretch in the crucible opening, the scattering velocity distribution at the time of scattering from the crucible opening end is a velocity distribution in a very narrow range, As a result, the powder produced by the method and apparatus of the present invention has a very uniform size distribution in principle, and the shape of the powder has a very high concentricity because solidification is completed in the droplet state. can get.

In general centrifugal spraying, since the state of the liquid film immediately before spraying determines the spray size, in the present invention, the hot water supply speed Q (cc / cc), which is a factor governing the liquid film thickness immediately before leaving the rotating crucible in the present invention. Q / r ² n is defined from min), crucible radius r (cm), and rotational speed n (min ^-1 ).

Operational parameters, while corresponding to the powder size and production rate desired, in accordance with the optimization of the crucible diameter, it is possible to change to the rotational speed from 2000min- ¹ 50000min- ^1.
Now, with a hot water supply speed of 10 kg / min while giving a rotation of 2000 min- ¹ using a crucible with a radius of 2.5 cm for pure copper, if the density of molten pure copper is 7.8 g / cm ³ , Q / r The value of ² n is 0.10 (cm). Similarly, for a hot water supply speed of 0.1 kg / min and a crucible with a radius of 25 cm and a rotational speed of 20000 min- ¹ , the value of Q / r ² n is 1.0 × In the case of 10 ⁻⁶ (cm) and the same hot water supply speed of 0.1 kg / min and a crucible with a radius of 16 cm and a rotational speed of 50000 min- ¹ , the value of Q / r ² n is 1.0 × 10 ⁻⁶ (cm )

From these, the relationship between the hot water supply speed Q (cc / min) for producing fine metal powder while controlling the liquid film thickness, the crucible radius r (cm), and the crucible rotation speed n (min- ¹ ) is as follows. It has been found that it is sufficient to control the range of the equation.
1.0 × 10 ^-6 ≦ Q / r ² n ≦ 1.0 × 10 ^-1

  The method for heating the crucible is not limited to high frequency induction heating. That is, when heating at a relatively low temperature is sufficient, radiation heating with an infrared lamp is possible. Similarly, when a conductive material is possible as a crucible material, the rotating shaft is placed on the outer periphery of the crucible or at the bottom of the crucible bottom. It is possible to arrange a permanent magnet separated and fixed and to heat by eddy current generated with the crucible rotation by induction with the permanent magnet.

Next, several examples and comparative examples will be described.
Example 1:
In the argon gas atmosphere container of about 1 atm, the following rotating body was installed for the purpose of rotating spray. First, a carbon crucible having an inner diameter of 85 mm and a depth of 65 mm was used as a rotating crucible. On the outer periphery of the crucible, a heat insulating structure was formed with porous ceramics mainly composed of zirconia having a thickness of 8 mm. These rotating bodies are stored inside a crucible receiver formed of Inconel 600. Also, on the outer periphery of the crucible receiver, fins with a blade thickness of 1.5 mm and a depth of 6 mm are processed at a pitch of 8 mm in the crucible height direction for the purpose of cooling. The thickness of the fin becomes thinner as it goes away from the outer cylinder surface of the crucible for weight reduction.

After melting 10 kg of pure copper on the inner surface of the crucible arranged in this way with a high frequency induction furnace, it rotates at 35000 min- ¹ from a pouring nozzle having an opening with a diameter of 1.0 mm set at the bottom of the holding furnace (tundish) The hot water was poured almost at the center of the crucible at a rate of about 1 kg per minute. The pouring nozzle is made of carbon and has an opening of 1.0 mm in diameter only 10 mm from the tip of the nozzle, and the upper part (tundish side) has a cylindrical shape with an inner diameter of 10 mm. In this example, after the hot water was supplied to the holding furnace, the raw material was additionally charged into the melting furnace, the next heat was melted, and a total operation of 3 heats was performed.

Example 2:
For pure copper, we attempted further refinement at a casting rate of 1.0 kg / min for a nozzle diameter of 1.0 mmφ for a diameter of 200 mmφ crucible and a crucible rotation speed of 35000 min- ¹ . Compared with Example 1, since the crucible diameter is large, the centrifugal force received by the liquid film is also large, and the obtained particle size distribution has an average particle size less than half that of Example 1.

Example 3:
Using an alumina crucible, a powder production test was conducted on 95.75% Sn-3.5% Ag-0.75Cu alloy, which is a lead-free solder. As a result of testing under the test conditions as shown in Table 1, a powder having an average diameter of 10 μm could be produced.

Example 4:
Using an alumina crucible, a powder production test was conducted on 30% Ag-38% Cu-32% Zn alloy used for silver brazing. As a result of testing under the test conditions shown in Table 1, powder having an average diameter of 32 μm could be produced.

Example 5:
For stainless steel (SUS316L), a large diameter crucible was tested for the purpose of producing fine powder with high productivity. A magnesia crucible with a diameter of 500 mmφ and a depth of 120 mm was employed, spraying was performed at a pouring rate of 2.0 kg / min with a rotation speed of 2000 min- ¹ . The pouring nozzle diameter used was 1.5 mmφ, and the nozzle heating, crucible heating, and the structure around the crucible were similar to the series of examples corresponding to the crucible size. The size distribution of the produced powder was 5.2 μm in average particle size, 2.1 μm or less for a cumulative 10%, 4.2 μm or less for a cumulative 50%, and 7.8 μm or less for a cumulative 90%.

Comparative Example 1:
A spray test was conducted on Sn-Ag-Cu solder using a flat disk disc (diameter 120 mmφ manufactured by SUS304, thickness 23 mm) as found in the prior art instead of the crucible. In addition, all the rotating crucible peripheral structures used in Examples 1 to 5 were removed, and in order to avoid the solidification of the molten metal on the disk surface, a magnetic pole in the circumferential direction with the same diameter as the disk was placed on the back surface side of the disk. A 6-pole permanent magnet with alternating changes was placed, and the disk surface was heated to 430 ° C. while adjusting the distance from the disk. The permanent magnet is covered with a thin heat insulating sheet and is fixed separately from the rotating shaft. The test conditions are shown in Table 1. Although the produced powder had an average particle size of 85 μm, it had a very wide particle size distribution from a size of several microns to a maximum of 320 microns.

Comparative Example 2:
For the disk used in Comparative Example 1, the surface is processed into a spherical shape with a constant radius of 600 mmR, and the outermost peripheral part is raised by about 3 mm with respect to the center part of the flat plate, and the centrifugal force of the rotating disk is made into a molten liquid film as much as possible. The device which can be granted was performed. The test conditions were exactly the same as in Comparative Example 1, but the average particle size was 56 μm, and there were no giant particles as seen in Comparative Example 1, and a powder with a relatively narrow particle size distribution was obtained. This seems to be a result of comparatively sufficient application of centrifugal force to the molten metal relative to Comparative Example 1. However, looking at the overall particle size distribution, the average particle size is 74 μm, the cumulative 10% weight is 8 μm or less, the cumulative 50% weight is 68 μm or less, and the cumulative 90% weight is 145 μm or less. And a very wide size distribution.

  In addition, although it limited to manufacture of a metal powder in a present Example, it cannot be overemphasized that it is applicable also to a foodstuff, a pharmaceutical, a dye, a pigment, etc., when processing temperature is not high like metal, depending on the case. Since a crucible heating mechanism is not required, a simple rotating mechanism can be used. When a large powder size is required, a spherical powder can be produced with high productivity by using a crucible having a diameter larger than that of the crucible used in this embodiment.

  In addition, the heating means can perform energization resistance heating in addition to high-frequency induction heating. Furthermore, in general, there is concern about melting and wear of the crucible due to the molten metal in the pouring part, so if there is a margin in the crucible size, the pouring position is gradually moved in the radial direction of the crucible. A mechanism may be provided.

  Further, in this embodiment, the electromagnetic flow control method is incorporated in the pouring flow control, but a stopper method immersed in a holding furnace (tundish) may be adopted.

  Although one embodiment of the present invention has been described so far, it is needless to say that the present invention is not limited to the above-described embodiment, and may be implemented in various forms within the scope of the technical idea.

1 is an overall view of a powder production apparatus according to an embodiment of the present invention. It is the figure which showed the behavior of the structure around a rotation crucible, and the molten metal poured.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Container 2 Melting furnace 3 Raw material replenishment apparatus 5 Pouring nozzle 6 Container 10 Cylindrical crucible 12 with a bottom Insulating material 13 Heat-resistant metal crucible receiver 14 Fins 15 and 16 High-frequency induction heating coil 17 Heating sleeve A Raw material melt B Rapid Cold solidified powder (powder)

Claims (14)

Heating organic or inorganic materials to form molten materials,
Rotate the bottomed cylindrical crucible at high speed along the rotation center axis,
Pouring the molten material from a pouring nozzle onto the bottom of the crucible,
A fine powder forming method using a rotating crucible, characterized in that fine powder is formed by centrifugal spraying from the open end of the crucible.   2. The fine powder molding method using a rotating crucible according to claim 1, wherein the center axis of the crucible is aligned with the rotating shaft, and the crucible opening is set vertically upward.   3. The fine powder molding method using a rotating crucible according to claim 1 or 2, wherein the inner wall of the crucible in the depth direction is set to an upper or lower wide diameter within ± 10 degrees with respect to the vertical direction.   4. A fine powder molding method using a rotating crucible according to claim 1, 2, or 3, comprising a rotating body having a heat insulating material on the outer side of the crucible and a crucible holder made of a heat-resistant metal on the outer periphery thereof.   5. The fine powder molding method using a rotating crucible according to claim 1, wherein the crucible is heated to a temperature equal to or higher than a melting temperature of the material to be sprayed.   Claims 1, 2, 3, 4, and 5 using a ceramic crucible, a heat insulating material on its outer periphery, and a heat-resistant metal crucible holder that can withstand centrifugal force at high speed rotation on its outer periphery. A fine powder molding method using a rotating crucible characterized by comprising:   Claims 1, 2, 3, 4, 5, and 6 are arranged such that a hot water pouring nozzle is placed around the rotation center axis and a high-frequency induction heating coil or an energizing resistance heating device is arranged on the outer periphery so as to be inserted into the crucible. Then, a fine powder molding method using a rotating crucible, characterized by heating a pouring nozzle and a crucible.   Claims 1, 2, 3, 4, 5, 6, and 7, wherein an induction coil is disposed on the outer surface of the pouring nozzle, and a heating sleeve is disposed on the inner and outer surfaces of the induction coil and on the lower portion of the nozzle, A fine powder molding method using a rotating crucible, wherein the inner surface and bottom surface of the crucible are heated by radiation.   9. The fine powder molding method using a rotating crucible according to claim 1, 2, 3, 4, 5, 6, 7, and 8, wherein a cooling fin is attached to the outer periphery of the refractory metal crucible receiver. In claims 1, 2, 3, 4, 5, 6, 7, 8, and 9, the volume hot water supply speed Q, the crucible radius r, and the crucible rotation speed n are controlled within the ranges of the following equations, where Q is [ cc / min], r is [cm], and n is [min- ¹ ]. A fine powder molding method using a rotating crucible.

  2. The fine powder molding method using a rotating crucible according to claim 1, wherein the crucible is made of ceramics, high-strength molded carbon, or metal.   2. The fine powder molding method using a rotating crucible according to claim 1, wherein the pouring nozzle is disposed in a region within a half radius from the rotation center of the crucible.   2. The fine powder molding method using a rotating crucible according to claim 1, wherein the molten material is poured while ensuring a laminar state having a circular or elliptical cross section with a diameter of 0.3 mm to 5.0 mm from the pouring nozzle. A cylindrical crucible with a bottom;
A drive device for rotating the crucible at a high speed along the rotation center axis;
A pouring nozzle for pouring molten material on the bottom of the crucible,
A fine powder molding apparatus using a rotating crucible, wherein the molten material is centrifugally sprayed from the open end of the crucible to form a fine powder.

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