JP2008240060A - Method for producing metal powder - Google Patents

Abstract

The present invention provides a metal powder production method capable of stably obtaining metal powder having a desired particle size distribution and average particle size.
In a metal powder manufacturing method in which molten metal is continuously supplied onto a disk rotating at a high speed and sprayed by centrifugal force to form powder, the disk is used to obtain metal powder having a desired average particle diameter. In the course of continuously producing metal powder by rotating at a predetermined rotational speed, the rotational speed of the disk is increased from the predetermined rotational speed in accordance with an increase in the coarse powder rate of the obtained metal powder.
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Description

  The present invention relates to a method for producing metal powder, and more particularly to a production method capable of continuously producing metal powder having a stable particle size distribution and average particle size.

  As a typical manufacturing method of metal powder such as solder powder used for joining electronic parts, etc., a metal melt (hereinafter referred to as “molten metal”) flows out from the pores and nitrogen gas or the like is allowed to act on it. Examples thereof include a gas spraying method in which powder is dispersed and powdered, and a centrifugal spraying method in which molten metal is supplied onto a disk rotating at a high speed and sprayed by centrifugal force to be powdered. The former gas spraying method tends to have a wide particle size distribution, and the latter centrifugal spraying method has a narrower particle size distribution, so the centrifugal spraying method is suitable for the production of metal powder (see Patent Document 1). In this centrifugal spraying method, in order to produce a metal powder having a desired average particle diameter, the production conditions such as the number of revolutions of the disk per minute (hereinafter simply referred to as “the number of revolutions”) and the material are usually determined. Manufactured by fixing to things. However, it is difficult to continuously obtain a metal powder having a desired particle size distribution in a stable state even if the manufacturing conditions such as the rotational speed of the disk are set to a predetermined value in order to obtain a metal powder having a desired average particle diameter. there were.

JP-A-6-340905 (paragraph numbers [0002], [0003], etc.)

  An object of this invention is to provide the manufacturing method of the metal powder which has the desired particle size distribution and can obtain the metal powder with few coarse powders stably in view of the situation mentioned above.

  As a result of intensive studies to achieve the above object, the present inventors have achieved the above object by increasing the number of revolutions of the disk during the production according to the increase in the coarse powder rate of the obtained metal powder in the centrifugal spray method. It has been found that this has been achieved, and the present invention has been completed.

  That is, the metal powder production method of the present invention is a metal powder production method in which molten metal is continuously supplied onto a disk rotating at a high speed and sprayed by centrifugal force to form powder. In the course of continuously producing metal powder by rotating at a predetermined rotational speed to obtain a metal powder having a particle size, the rotational speed of the disk is set to the predetermined speed according to an increase in the coarse powder rate of the obtained metal powder. It is characterized by being increased from the rotational speed.

  In the metal powder manufacturing method of the present invention, after the start of spraying, when the coarse powder ratio exceeds a predetermined value, the rotational speed of the disk may be increased above the predetermined rotational speed.

  Furthermore, in the method for producing metal powder of the present invention, the change over time in the coarse powder rate is measured in advance under the production conditions in which the disk is rotated at the predetermined rotation speed, and after spraying is started according to the measurement result. The rotational speed of the disk may be increased from the predetermined rotational speed at a predetermined timing.

  According to the method for producing metal powder of the present invention, it is possible to continuously produce metal powder having a stable coarse powder rate and a stable particle size distribution and average particle size.

Hereinafter, the present invention will be described in detail based on embodiments.
The metal powder production method of the present invention relates to a centrifugal spray method in which a metal melt (molten metal) is supplied onto a disk rotating at a high speed and sprayed by centrifugal force to obtain a metal powder. In the centrifugal spraying method, the particle size of the obtained metal powder changes according to the rotational speed of the disk. As described in Japanese Patent Application Laid-Open No. 2002-317212 (paragraph [0009]), the particle size of the obtained metal powder becomes smaller as the rotational speed of the disk becomes larger, and the metallic powder obtained as the rotational speed of the disk becomes smaller. The particle size of becomes larger. Therefore, the number of rotations of the disk is usually set to a predetermined value according to the desired average particle diameter of the metal powder.

  In the conventional production of metal powder, it has been considered that a metal powder having a desired average particle diameter can be stably obtained if the number of revolutions of the disk is kept constant. As a result, a stable metal powder was not obtained.

  On the other hand, in the method for producing metal powder of the present invention, in order to obtain metal powder having a desired particle size, the disk is rotated at a predetermined rotational speed to continuously produce metal powder. According to the increase in the coarse powder rate, the rotational speed of the disk is increased from the predetermined rotational speed. Specifically, the disk is rotated at a predetermined rotation speed for obtaining metal powder having a desired average particle diameter, and then the rotation speed of the disk is increased when the coarse powder rate of the obtained metal powder increases.

  In the present specification, as described above, the operation of “rotating the disk at a predetermined rotational speed for obtaining metal powder having a desired average particle diameter” is performed according to the average particle diameter of the desired metal powder. Although the rotational speed is set to a predetermined numerical value and the metal powder is continuously manufactured, the predetermined rotational speed can be determined according to the metal powder to be manufactured. For example, when producing solder powder having an average particle diameter of 10 to 70 μm, the predetermined disk rotation speed is set within the range of 20000 to 100000 rpm, and when producing copper powder having an average particle diameter of 20 to 40 μm, the predetermined disk rotation speed is set to It may be within the range of 70000-100,000 rpm, and in any case, it may be adjusted according to the temperature, composition, etc. of the molten metal.

  In the method for producing metal powder of the present invention, although continuously produced based on the predetermined rotational speed, by increasing the rotational speed, it is possible to suppress an increase in the coarse powder rate that occurs when continuous production is continued, Further, since the amount of fine powder smaller than the average particle diameter hardly changes, metal powder having a stable particle size distribution and average particle diameter can be continuously produced.

  In addition, the coarse powder rate as used in the field of this invention is a weight ratio which occupies the whole particle | grains of a particle | grain (coarse powder) whose particle size is a predetermined value or more, and if metal powder is solder powder, it is prescribed in JIS Z 3284. Particles having a particle size equal to or larger than the limit particle size at which a content of 1% by mass or less is observed at each size level are regarded as coarse particles. Specifically, an appropriate sieve is used according to the size. For example, the size above 3 μm is measured at 63 μm at size level 3, 45 μm at size level 4 and 38 μm at size level 5, and the ratio in the total amount of particles is determined. What is necessary is just to calculate. In addition, when controlling the solder powder to an average particle size other than the above standard, or when controlling a metal powder other than the solder powder, the particles of 1.5 times or more the average particle size are regarded as coarse powder particles, The coarse powder rate is calculated in the same manner as the powder example.

  Regarding the relationship between the coarse powder rate and the elapsed time, in the metal powder production method by the centrifugal spray method generally performed conventionally, the coarse powder rate is not stable and the coarse powder rate increases with the passage of time, As a result, the present inventors have found that the particle size distribution changes with time. This phenomenon is caused by the deterioration of the disk due to the erosion of the disk due to the molten metal and the formation of a product generated between the disk material and the molten metal, and the molten metal scatters from the middle of the disk without reaching the end of the disk. This is presumed to be the cause.

  Therefore, in the present invention, the coarse powder rate is controlled by increasing the disk rotation speed according to the change with time of the coarse powder rate of the obtained metal powder, and the particle size distribution and the average particle size are stabilized. Therefore, even if it manufactures continuously for a long time, the metal powder which has a desired particle size distribution and an average particle diameter can be manufactured stably. In other words, by increasing the rotational speed of the disk according to the coarse powder rate, the coarse powder rate of the metal powder can be adjusted to a predetermined value or less, and the particle size distribution can be controlled and stabilized, so that the desired particle size can be obtained. Metal powder having a distribution and average particle diameter can be obtained stably.

  In order to prevent wear and deterioration of the disc, it is conceivable to make the disc hard and excellent in wear resistance. However, depending on the components of the molten metal used in the production, the disc has poor wetting, and the resulting metal powder This causes a problem that the particle size of the metal becomes coarse and metal powder having a low coarse powder rate cannot be obtained. On the other hand, according to the manufacturing method of the metal powder of this invention, such a problem does not arise.

  As described above, according to the method for producing metal powder of the present invention, the coarse powder rate is stabilized by increasing the number of revolutions of the disk during the production according to the change in coarse powder rate with time, and the particle size distribution and A metal powder having a stable average particle diameter can be continuously produced. In addition, since the coarse powder rate is stable, even if metal powder is produced continuously for a long time, the desired metal powder production yield per batch is high, compared to the conventional production method in which the coarse powder rate fluctuates, Manufacturing efficiency is excellent.

  By the way, the timing for increasing the rotational speed of the disk and the increasing rate of the rotational speed are appropriately determined according to the coarse powder ratio of the metal powder. Therefore, by performing a test operation at a predetermined disk rotation speed for obtaining metal powder having a desired average particle diameter, and measuring the change over time in the coarse powder rate of the obtained metal powder in advance, the rotation speed increasing step is performed. You may determine the time to perform and the raise rate of rotation speed. In addition, it is preferable that the raise rate of rotation speed shall be about 1 to 10% with respect to the predetermined rotation speed for obtaining the metal powder of a desired average particle diameter. If it is this range, it can prevent that the individual particle size of the metal powder obtained does not deviate from a desired average particle size. The rate of increase of the rotational speed is more preferably about 3 to 8% with respect to the predetermined rotational speed, and the coarse powder rate and the particle size distribution can be adjusted more effectively if performed within this range. Further, the step of increasing the rotational speed of the disk may be performed once or a plurality of times, and the rotational speed of the disk may be increased stepwise or gradually. Of course, rather than measuring the change over time of the coarse powder rate in advance, the coarse powder rate of the obtained metal powder is measured at a predetermined timing, and depending on the measurement result, for example, the coarse powder rate has a predetermined value. When exceeding, the rotational speed of the disk may be increased. The predetermined value of the coarse powder ratio that serves as a reference for increasing the number of revolutions can be appropriately set from the target coarse powder ratio.

  The method for producing metal powder of the present invention can be applied to various metals and alloys including copper, for example, solder powder. Specifically, for example, solder powder containing lead such as the widely known Sn—Pb series, Sn—Pb—Ag series, Sn—Ag series, Sn—Cu—Ag series, Sn—Zn—Bi, etc. It can be applied to the production of solder powder such as solder powder (lead-free solder powder) that does not contain lead, such as Sn-based, Sn-Bi-based, and Sn-Sb-based.

  Although the average particle diameter of the metal powder to manufacture is not specifically limited, For example, it is 10-70 micrometers. In addition, in this invention, an average particle diameter is the numerical value which measured the average particle diameter with the dry laser diffraction particle size measuring apparatus (The Nikkiso Co., Ltd. make, Aerotrack SPR).

  The centrifugal spraying device used for manufacturing may be a general device used for the centrifugal spraying method. The material of the disk may be a general one, and examples thereof include carbon, ceramics, Ti, Au, Ni, and Fe-based alloys. Specifically, for example, carbon steel (SS) and stainless steel (SUS) are used. Can be used. Further, the size and shape of the disc are not particularly limited, and for example, various shapes such as a disk shape, a cone shape, and a V shape can be used.

  There is no particular limitation on the method of supplying the molten metal to the disk, and it may be dropped or flowed down. Further, the supply amount and the supply speed are not particularly limited, but the molten metal is preferably dropped onto a disk rotating at 5 to 100 kg / hour.

  An example of a centrifugal spray apparatus to which the method for producing metal powder of the present invention can be applied will be described with reference to FIG. FIG. 1 is a schematic sectional view of a centrifugal spray device. As shown in FIG. 1, the centrifugal spraying apparatus 10 has a chamber 12 in which a spraying chamber 11 is formed. A disk 14 connected to a motor 13 and rotated at a high speed by the drive thereof is an upper portion in the chamber 12. It is provided near the part. A molten metal holding part 16 for holding a molten metal (metal melt) 15 is provided at the ceiling of the chamber 12. The molten metal 15 is melted into an ingot or the like in the melting furnace 17 and introduced into the molten metal holding unit 16. The molten metal holding part 16 has a molten metal supply part 18 for supplying the molten metal 15 onto the disk 14 at the bottom. The molten metal holding part 16 and the molten metal supply part 18 are communicated with each other through a through hole 19, and the molten metal holding part 16 and the disk 14 are dropped through the through hole 19 so that the molten metal 15 is dropped onto the disk 14. Has been placed. A metal powder recovery unit 20 that recovers the manufactured metal powder is disposed on the bottom surface of the chamber 12.

  An example of a method for producing metal powder by the centrifugal spray device 10 will be described below. First, the chamber 12 is evacuated, and the chamber 12 is filled with an inert gas such as nitrogen or argon. And the molten metal 15 which melt | dissolved raw materials, such as a metal ingot, in the melting furnace 17 at the temperature about 1-100 degreeC higher than the melting | fusing point is hold | maintained at the molten metal holding part 16. FIG. The molten metal 15 is dropped on the center of the rotating disk 14. The molten metal 15 dropped on the disk 14 is sprayed and scattered as a molten liquid 21 from the end side of the disk 14 by centrifugal force. The splashed droplets 21 are cooled by the inert gas in the chamber 12, become powder 22, drop and accumulate on the bottom surface of the chamber 12, and are collected by the metal powder collecting unit 20. In the present invention, the coarse powder rate of the powder (metal powder) 22 collected by the metal powder collection unit 20 is grasped over time, and the rotational speed of the disk 14 is increased according to the coarse powder rate.

  As described above, in the manufacturing method of the present invention, while measuring the coarse powder rate of the manufactured metal powder, or by measuring the coarse powder rate in advance under the same conditions, the change in the coarse powder rate. Since the rotational speed of the disk is increased according to the coarse powder rate while grasping the time course, the coarse powder rate of the resulting metal powder can be stabilized, and the metal with stable particle size distribution and average particle size The powder can be produced continuously.

Hereinafter, the present invention will be further described in detail based on the following examples and comparative examples.
Example 1
Using the centrifugal spray device 10 shown in FIG. 1, solder powder was manufactured under the following manufacturing conditions so that solder powder with an average particle diameter of 40 μm was manufactured. At that time, the coarse powder rate of the solder powder recovered in the metal powder recovery unit 20 was measured over time. The measurement result of the coarse powder ratio of the solder powder with respect to the time from the start of spraying (spraying time) is shown in FIG. The solder powder particle size was measured using a dry laser diffraction particle size measuring device (Nikkiso Co., Ltd., Aerotrack SPR, gas pressure 0.05 MPa), and the solder powder having a particle size of 45 μm or more was sampled. The weight ratio in the total amount was defined as the coarse powder ratio.
<Production conditions>
Solder powder composition: Sn-8Zn-3Bi
Disc: Material: Carbon steel, Diameter: 32 mm, Shape: Disc shape, Rotational speed: 42000 rpm (corresponding to “predetermined rotational speed” in claim 1), and increased to 44000 rpm 40 hours after the start of spraying Supply amount of molten metal: 65 kg / hour, dripping melt temperature: 210 ° C
Atmosphere ... under nitrogen atmosphere

(Comparative Example 1)
The same operation as in Example 1 was performed, except that the disc rotation speed was not changed to 44000 rpm but maintained at 42000 rpm 40 hours after the start of spraying. The measurement result of the coarse powder ratio of the solder powder with respect to the spraying time is shown in FIG.

  As shown in FIG. 2, in Example 1 where the disk rotation speed was increased by 2000 rpm 40 hours after the start of spraying, the coarse powder rate was stabilized at the 30% level, and the coarse powder rate was 40% or less throughout the entire process. was gotten. On the other hand, in Comparative Example 1 in which the disk rotation speed was not increased, the coarse powder rate increased with the passage of time, and after 40 hours, the coarse powder rate rapidly increased and exceeded 40%, and after 60 hours, 70%. It became about%. Further, as described above, the amount of coarse powder was different between Example 1 and Comparative Example 1, but the amount of fine powder having a particle size smaller than 40 μm was hardly different between Example 1 and Comparative Example 1. It was. Therefore, it was found that in Example 1 in which the coarse powder rate was stably low, metal powder having a desired average particle diameter could be stably produced with less change in particle size distribution than in Comparative Example 1.

  In both Example 1 and Comparative Example 1, after 60 hours, the disk was scraped, compound formation and deposit formation occurred, and the disk was worn out. From this result, according to the manufacturing method of the present invention, it was found that the particle size distribution can be stabilized because the coarse powder rate is stable even when the disk is worn out.

It is a figure which shows the outline of a centrifugal spraying apparatus. It is a graph which shows the time-dependent change of the coarse powder rate of the solder powder of Example 1 and Comparative Example 1.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 Centrifugal spray apparatus 11 Spraying chamber 12 Chamber 13 Motor 14 Disk 15 Molten metal 16 Molten metal holding | maintenance part 17 Melting furnace 18 Molten metal supply part 19 Through-hole 20 Metal powder collection | recovery part 21 Molten droplet 22 Powder

Claims (3)

  In a method for producing a metal powder in which molten metal is continuously supplied onto a disk rotating at a high speed and sprayed by centrifugal force to form powder, the disk is rotated at a predetermined speed to obtain a metal powder having a desired average particle diameter. The metal powder is characterized in that the number of rotations of the disk is increased from the predetermined number of rotations in accordance with an increase in the coarse powder rate of the obtained metal powder during the continuous production of metal powder by rotating the number. Manufacturing method.   2. The method for producing metal powder according to claim 1, wherein after the start of spraying, when the coarse powder ratio exceeds a predetermined value, the rotational speed of the disk is increased above the predetermined rotational speed.   The change over time in the coarse powder ratio is measured in advance under the manufacturing conditions in which the disk is rotated at the predetermined rotational speed, and the rotational speed of the disk is set to the predetermined rotational speed at a predetermined timing after the start of spraying according to the measurement result. It raises rather than a number, The manufacturing method of the metal powder of Claim 1 characterized by the above-mentioned.

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