JP2008240059A - Method for producing metal powder - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method for producing metal powder, in which the metal powder having desired grain size distribution and average grain diameter can be stably obtained. <P>SOLUTION: In the method for producing metal powder where a molten metal is continuously fed to the surface of a disk rotating at a high speed, and is atomized by centrifugal force, so as to be powdered, in the process where the disk is rotated at a prescribed speed of revolution for obtaining metal powder with the desired average grain diameter, so as to continuously produce the metal powder, on the condition that the speed of revolution of the disk is within the range of ±10% of the prescribed speed of revolution, control is performed either the speed of revolution of the disk is lowered in accordance with the lowering of the rate of coarse powder in the obtained metal powder or the speed of revolution of the disk is raised in accordance with the raise of the rate of the coarse powder in the obtained metal powder. <P>COPYRIGHT: (C)2009,JPO&INPIT

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 found that the above object is achieved by controlling the number of revolutions of the disk during the production according to the change 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 diameter, the rotational speed of the disk is within ± 10% of the predetermined rotational speed. As a condition, control is performed to lower the rotational speed of the disk according to the decrease in the coarse powder rate of the obtained metal powder, or to increase the rotational speed of the disk according to the increase of the coarse powder ratio of the obtained metal powder. It is characterized by that.

  Further, in the method for producing metal powder of the present invention, in controlling the number of revolutions of the disk, the number of revolutions of the disk at the start of spraying is set to a number of revolutions faster than the predetermined number of revolutions, and the coarse powder rate of the obtained metal powder The rotational speed of the disk is lowered below the rotational speed of the disk at the start of spraying, and then the rotational speed of the disk is increased according to the increase in the coarse powder rate of the obtained metal powder. Is preferred.

  Further, after the spraying starts, when the coarse powder ratio becomes less than a predetermined value, the rotational speed of the disk is lowered below the rotational speed of the disk at the start of spraying, and then the coarse powder ratio exceeds the predetermined value. Then, the rotational speed of the disk may be increased.

  Further, 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 rotation speed, and the rotation speed of the disk is controlled at a predetermined timing after the start of spraying according to the measurement result. May be.

  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]) and the like, the larger the number of revolutions of the disk, the smaller the particle size of the obtained metal powder, and the smaller the number of revolutions of the disk, the more obtainable metal powder. 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 change in the coarse powder rate, the rotational speed of the disk is controlled within a range of ± 10% with respect to the predetermined rotational speed.

  Specifically, the number of revolutions of the disk is decreased in accordance with the decrease in the coarse powder rate of the obtained metal powder, on condition that the number of revolutions of the disk is within ± 10% of the predetermined number of revolutions. Alternatively, control is performed to increase the rotational speed of the disk in accordance with the increase in the coarse powder rate of the obtained metal powder.

  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 the continuous production is based on the predetermined rotational speed, the coarse powder rate generated when continuous production is continued by controlling the rotational speed under specific conditions. Since the change can be suppressed and 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 recognized at each size level are regarded as coarse powder 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 conventional metal powder production method by centrifugal spraying, the disk temperature is low with respect to the melt temperature and the wettability to the melt is poor at the initial stage of spraying. Therefore, although the coarse powder rate is high, the present inventors have found that since the disk temperature rises with time, the wettability to the molten metal is improved and the coarse powder rate decreases with time.

  In addition, after the coarse powder rate has decreased over time in this way, the coarse powder rate becomes almost constant for a while, but the present inventors have also found that the coarse powder rate increases with the passage of time thereafter. . 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.

  Thus, since it has been found that the particle size distribution changes with time, in the present invention, control is performed to lower or increase the disk rotation speed in accordance with the change with time of the coarse powder rate of the obtained metal powder. Thus, the coarse powder rate is controlled, 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 controlling the number of revolutions of the disk according to the coarse powder rate of the obtained metal powder, the coarse powder rate of the metal powder can be adjusted within a predetermined range, and the particle size distribution can be controlled and stabilized. Therefore, metal powder having a desired particle size distribution and average particle size can be stably obtained.

  For example, at the start of spraying, the disk is rotated at a rotational speed faster than a predetermined rotational speed for obtaining metal powder having a desired average particle diameter, and the disk is rotated according to the decrease in the coarse powder rate of the obtained metal powder. By decreasing the number below the number of rotations of the disk at the start of spraying, the decrease in the coarse powder rate is suppressed.

  Thereafter, the increase in the coarse powder rate is suppressed by increasing the number of revolutions of the disc in accordance with the increase in the coarse powder rate due to wear deterioration of the disc. Thereby, a coarse powder rate can be stabilized continuously and the metal powder which has a desired particle size distribution and an average particle diameter can be obtained stably.

  When the rotational speed of the disk is lowered below the rotational speed of the disk at the start of spraying in accordance with the decrease in the coarse powder rate of the metal powder, it is preferably lowered to a predetermined rotational speed. Therefore, in that case, the rotational speed of the disk is increased to a state exceeding a predetermined rotational speed as the coarse powder rate increases.

  Further, for the increase in the coarse powder rate at the initial stage of spraying due to an increase in the temperature of the disk, a means of controlling the temperature of the disk can be considered, but according to the manufacturing method of the present invention, the temperature of the disk is considered. Regardless, the desired coarse powder rate can be achieved.

  In addition, for the increase in coarse powder rate due to disc wear deterioration, etc., a means of making the disc hard and excellent in wear resistance so as not to cause wear degradation of the disc can be considered, but it is used for manufacturing. Depending on the composition of the molten metal, poor wetting of the disk occurs, the particle size of the obtained metal powder becomes coarse, and there is a problem that metal powder with 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 controlling 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, Production efficiency is remarkably excellent.

  By the way, the timing for increasing or decreasing the rotational speed of the disk and the increasing or decreasing 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, the rotation speed is increased or increased by measuring the change over time in the coarse powder ratio of the obtained metal powder. You may determine the time to descend | decrease and the ratio of the raise or fall of rotation speed.

  The rate of increase or decrease in the rotational speed is within a range of ± 10% with respect to a predetermined rotational speed for obtaining metal powder having 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 or decrease in 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.

  The process of increasing or decreasing the rotational speed of the disk may be performed once or multiple times. However, as described above, the coarse powder ratio decreases at the initial stage of spraying, and then the coarse powder ratio increases. Therefore, the rotational speed of the disk is decreased. After that, it is preferable to increase the rotational speed of the disk. Further, the rotational speed of the disk may be increased or decreased stepwise, or may be gradually increased or decreased. 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 after the start of spraying is If it becomes less than the predetermined value, the rotational speed of the disk is lowered below the rotational speed of the disk at the start of spraying to the above-mentioned predetermined rotational speed, and then the rotational speed of the disk is set to the predetermined speed when the coarse powder ratio exceeds the predetermined value. You may make it raise from the rotation speed of. The predetermined value of the coarse powder rate that serves as a reference for decreasing or increasing the rotational speed can be appropriately set from the target coarse powder rate.

  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 the present invention, the average particle diameter is a numerical value obtained by measuring the average particle diameter with a dry laser diffraction particle size measuring apparatus (manufactured by Nikkiso Co., Ltd., 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 controlled according to the coarse powder rate.

  As described above, in the production method of the present invention, the change in the coarse powder rate is measured over time by measuring the coarse powder rate of the produced metal powder or by measuring in advance under the same conditions. While grasping, the rotational speed of the disk is controlled according to the coarse powder rate, so that the coarse powder rate of the obtained metal powder can be reliably stabilized, and metal powder with stable particle size distribution and average particle size can be obtained. It can be manufactured 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, Number of revolutions: Start spraying at 44000 rpm, descend to 42000 rpm 10 hours after starting spraying, and 42000 rpm until 40 hours after spraying (invoice) (Equivalent to “predetermined number of revolutions” in item 1) After 40 hours from the start of spraying, the molten metal feed rate was increased to 44000 rpm.
Atmosphere ... under nitrogen atmosphere

(Comparative Example 1)
The same operation as in Example 1 was performed except that the disk rotation speed was not 44,000 rpm but maintained at 42000 rpm. 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 in which the disk rotation speed was changed from 44000 rpm → 42000 rpm → 44000 rpm, the coarse powder rate was stable within a range of about 30 to 35%, and the coarse powder rate was 40% throughout the entire process. The following solder powder was obtained. On the other hand, in Comparative Example 1 in which the disk rotation speed was made constant, the coarse powder rate decreased with the passage of time in the initial stage of spraying, but then the coarse powder rate increased and exceeded 40%, and after 55 hours, it became about 55%. Until now. 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 55 hours had elapsed, the disk was scraped, compound formation and deposit formation occurred, and the disk was worn out. From this result, according to the production method of the present invention, it was found that the particle size distribution can be stabilized because the coarse powder rate is stable even if the disk is worn and deteriorated.

It is a figure which shows the outline of a centrifugal sprayer. 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 (4)

  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. In the course of continuously producing metal powder by rotating the number, the rotational speed of the disk is within the range of ± 10% of the predetermined rotational speed, the coarse powder rate of the obtained metal powder A method for producing metal powder, characterized in that control is performed to lower the number of rotations of the disk in accordance with the lowering or to increase the number of rotations of the disk in accordance with an increase in the coarse powder rate of the obtained metal powder.   The control of the number of revolutions of the disk is such that the number of revolutions of the disk at the start of spraying is faster than the predetermined number of revolutions, and the number of revolutions of the disk is set according to the decrease in the coarse powder rate of the obtained metal powder. 2. The control according to claim 1, wherein the control is performed such that the rotational speed of the disk is decreased below the rotational speed of the disk at the start of spraying, and then the rotational speed of the disk is increased in accordance with an increase in the coarse powder rate of the obtained metal powder. Metal powder manufacturing method.   After the start of spraying, when the coarse powder ratio becomes less than a predetermined value, the rotational speed of the disk is lowered below the rotational speed of the disk at the start of spraying, and then when the coarse powder ratio exceeds the predetermined value, 3. The method for producing metal powder according to claim 2, wherein the rotational speed of the disk is increased.   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 rotation speed, and the rotation speed of the disk is controlled at a predetermined timing after the start of spraying according to the measurement result. The method for producing metal powder according to claim 2.

Images