Method for producing metal powder

Abstract

The present invention addresses the problem of providing a method for producing a metal powder that makes it possible to improve yield when producing a metal powder which has a small particle size. This method for producing a metal powder comprises a continuous downward flow step and a downward flow suspension step. The continuous downward flow step is for causing a molten metal obtained by melting a metal raw material to flow downward continuously. The downward flow suspension step is for stopping the downward flow of the molten metal. In this method for producing a metal powder, the continuous downward flow step and the downward flow suspension step are repeated alternately.

Description

Metal powder manufacturing method

[0001] The present invention relates to a method for producing metal powders such as titanium powder and titanium alloy powder.

[0002] Gas atomization is known as one method for producing metal powders such as titanium powder and titanium alloy powder. In a typical gas atomization method for producing metal powder, a metal raw material held in a crucible is heated by an appropriate heating means to form a molten metal (hereinafter sometimes referred to as "molten metal"), which is then allowed to flow downward and atomized by blowing high-velocity gas onto it to form fine particles (hereinafter sometimes referred to as "powder processing") (see, for example, Japanese Patent Laid-Open No. 08-199207).

[0003] Japanese Patent Application Publication No. 08-199207

[0004] However, in conventional methods for producing metal powders using gas atomization, in order to obtain metal powders for specific applications, it is sometimes necessary to classify the obtained metal powders and select only metal powders with small particle sizes. For this reason, the yield of producing small particle size metal powders using conventional gas atomization methods has never been high.

[0005] An object of the present invention is to provide a method for producing metal powder that can improve the yield when producing metal powder with a small particle size.

[0006] The method for producing metal powder according to the present invention includes a continuous flowing step and a flow stopping step. Here, the continuous flowing step is a step of continuously flowing molten metal obtained by melting a metal raw material, and the flow stopping step is a step of stopping the flow of the molten metal. In the method for producing metal powder according to the present invention, the continuous flowing step and the flow stopping step are alternately repeated.

[0007] As a result of extensive research by the present inventors, it was found that by alternately repeating the continuous flow-down process and the flow-down stop process, it was possible to obtain metal powder having a smaller particle size than metal powder produced by conventional gas atomization. Therefore, when the metal powder obtained by the metal powder production method of the present invention is classified, the yield of metal powder with a small particle size increases. Therefore, the metal powder production method of the present invention can improve the yield when producing small particle size metal powder.

[0008] Furthermore, it is preferable that the metal powder obtained by the above-mentioned method for producing a metal powder has a D90 of less than 89 μm. Note that D90 here refers to the particle size that constitutes 90% of the cumulative particle size from the smallest particle in the cumulative particle size distribution of the powder.

[0009] Furthermore, it is preferable that the D50 of the metal powder obtained by the above-mentioned metal powder manufacturing method is in the range of 20 μm to 42 μm. Here, D50 refers to the particle size that is 50% by volume from the small particle side in the cumulative particle size distribution of the powder. Also, D10 refers to the particle size that is 10% by volume from the small particle side in the cumulative particle size distribution of the powder.

[0010] Furthermore, in the above-described method for producing metal powder, it is preferable that the flow rate of the molten metal is controlled by a high-frequency heating coil. The high-frequency heating coil is preferably controlled by current control. In this case, it is preferable that the magnitude of the current used in the flow-stopping step is in the range of 10% to 60% of the current used in the continuous flow-down step.

[0011] According to the above configuration, the Joule heat applied to the metal raw material by the electromagnetic induction heating of the high-frequency heating coil can be adjusted by controlling the current, and therefore, by controlling the magnitude of the current flowing through the high-frequency heating coil, the time for which the molten metal continuously flows down and the time for which the molten metal stops flowing down can be controlled.

[0012] Additionally, the above-described method for producing metal powder may further include an intermittent flowing step in which the molten metal is intermittently flowed down. The amount of the molten metal flowing down in the intermittent flowing step is preferably within a range of more than 0% and not more than 20% of the amount of the molten metal flowing down in the continuous flowing step. In such a case, the time for which the molten metal is intermittently flowed down (the time for which the intermittent flowing step is performed) is preferably within a range of 0 to 1 second.

[0013] 1 is a diagram showing the configuration of a gas atomizing device suitable for carrying out the present invention.

[0014] REFERENCE SIGNS LIST 1 Metal raw material 2 High frequency heating coil 3 Molten metal (molten metal) 4 Gas nozzle 5 Atomizing gas 6 Atomizing powder 100 Gas atomizing device

[0015] The method for producing metal powder according to the embodiment of the present invention includes a continuous flow-down process and a flow-down stop process. The continuous flow-down process is a process for continuously flowing down molten metal obtained by melting a metal raw material, and the flow-down stop process is a process for stopping the flow of the molten metal. In the method for producing metal powder according to the embodiment of the present invention, the continuous flow-down process and the flow-down stop process are alternately repeated. A gas atomizing apparatus 100 used to carry out the method for producing metal powder according to the embodiment of the present invention will now be described with reference to FIG. 1 .

[0016] In the gas atomizing apparatus 100 according to the embodiment of the present invention, first, a metal raw material 1 such as titanium powder or titanium alloy powder is continuously or intermittently melted to produce molten metal 3. Here, the metal raw material 1 is melted by electromagnetic induction heating using a high-frequency heating coil 2, as shown in FIG. 1 . The magnitude of Joule heat applied to the metal raw material 1 by this electromagnetic induction heating is controlled by the magnitude of the current passed through the high-frequency heating coil 2. That is, the larger the magnitude of the current passed through the high-frequency heating coil 2, the greater the Joule heat applied to the metal raw material 1, and vice versa. In this case, the greater the Joule heat applied to the metal raw material 1, the greater the amount of molten metal 3 flowing down, and vice versa.

[0017] In the metal powder manufacturing method according to the embodiment of the present invention, the magnitude of the current used in the flow-down stopping step is preferably within a range of 10% to 60% of the current used in the continuous flow-down step. In this case, the Joule heat applied to the metal raw material 1 is reduced in the flow-down stopping step, and the temperature of the metal raw material 1 drops below its melting point, causing the metal raw material 1 to solidify. As a result, by appropriately changing the magnitude of the current passed through the high-frequency heating coil 2, it is possible to switch from the continuous flow-down step to the flow-down stopping step and from the flow-down stopping step to the continuous flow-down step.

[0018] In the method for producing a metal powder according to an embodiment of the present invention, the time for which the molten metal is continuously allowed to flow (the time for which the continuous flow-down step is performed) is preferably in the range of 1 to 5 seconds, more preferably in the range of 1 to 3 seconds. Also, the time for which the flow-down of the molten metal is stopped (the time for which the flow-down stopping step is performed) is preferably in the range of 1 to 5 seconds, more preferably in the range of 1 to 3 seconds.

[0019] Furthermore, when switching from the continuous flow-down process to the flow-down stop process, or when switching from the flow-down stop process to the continuous flow-down process, an intermittent flow-down process may be performed between one process and the other. Note that intermittent flow-down can also be referred to as dripping. In such cases, the amount of molten metal 3 flowing down in the intermittent flow-down process is preferably within a range of more than 0% and not more than 20% of the amount of molten metal 3 flowing down in the continuous flow-down process. Note that the time during which the molten metal is intermittently flowed (the time during which the intermittent flow-down process is performed) is preferably within a range of 0 seconds to 1 second, and more preferably 0 seconds (i.e., when switching from the continuous flow-down process to the flow-down stop process, or when switching from the flow-down stop process to the continuous flow-down process, it is more preferable not to perform the intermittent flow-down process).

[0020] In the method for producing metal powder according to the embodiment of the present invention, the time required to switch from the continuous flow-down process (via the intermittent flow-down process) to the flow-down stop process is preferably within a range of 2 to 11 seconds, more preferably within a range of 2 to 6 seconds. Also, the time required to switch from the flow-down stop process (via the intermittent flow-down process) to the continuous flow-down process is preferably within a range of 2 to 11 seconds, more preferably within a range of 2 to 6 seconds.

[0021] In the method for producing metal powder according to the embodiment of the present invention, the flow rate of the molten metal 3 in the continuous flow-down step is preferably in the range of 6 cm / min to 20 cm / min. Furthermore, the flow rate of the molten metal 3 in the intermittent flow-down step is preferably in the range of more than 0 cm / min to 20 cm / min. Furthermore, the flow rate of the molten metal 3 in the flow-down stop step is 0 cm / min (i.e., the flow of the molten metal 3 is stopped in the flow-down stop step). The flow rate of the molten metal 3 can be appropriately adjusted by adjusting the amount of atomizing gas 5 injected.

[0022] Next, in the gas atomization apparatus 100 according to the embodiment of the present invention, the molten metal 3 flowing continuously or intermittently is atomized by argon gas (atomization gas 5) sprayed toward the molten metal 3 from a gas nozzle 4 installed below the high-frequency heating coil 2. The atomized molten metal 3 then solidifies to obtain a metal powder (atomized powder 6). The D50 of the resulting metal powder (atomized powder 6) is preferably in the range of 20 μm to 42 μm, more preferably in the range of 20 μm to 40 μm, even more preferably in the range of 20 μm to 38 μm, even more preferably in the range of 25 μm to 38 μm, and particularly preferably in the range of 32 μm to 38 μm. The D90 of the resulting metal powder (atomized powder 6) is preferably less than 89 μm, more preferably 85 μm or less, even more preferably 80 μm or less, and particularly preferably 76 μm or less. In this case, the lower limit of D90 is not particularly limited, but is preferably 50 μm, more preferably 55 μm, even more preferably 60 μm, particularly preferably 65 μm, and most preferably 66 μm.

[0023] EXAMPLES In the following, examples and comparative examples are shown to explain the present invention in more detail, but the present invention is not limited to these examples.

[0024] 1. Continuous Flow-Down Process In a gas atomizing apparatus 100 shown in FIG. 1, a rod-shaped metal raw material 1 made of Ti-6Al-4V (hereinafter referred to as "titanium alloy") was inserted into a high-frequency heating coil 2. Thereafter, a current of 400 A was continuously applied to the high-frequency heating coil 2 for 5 seconds to melt the metal raw material 1 and obtain molten metal 3, which was then allowed to flow down at a rate of 8 cm / min. Argon gas was then introduced through a gas nozzle 4 shown in FIG. 1 at a flow rate of 16 Nm. ３ The spray was performed at a flow rate of 1 / min.

[0025] 2. Flow-Down Stopping Step Five seconds after starting to pass a current of 400 A through the high-frequency heating coil 2 in the continuous flow-down step described above, the magnitude of the current passing through the high-frequency heating coil 2 was changed to 200 A, and current was continued to pass through the high-frequency heating coil 2 for five seconds. During this time, the flow-down of the molten metal 3 stopped. Note that it took 0.6 seconds from when the magnitude of the current passing through the high-frequency heating coil 2 was changed to 200 A until the flow-down of the molten metal 3 completely stopped. In other words, this 0.6 second period corresponds to the intermittent flow-down step. The flow rate of the molten metal 3 during this intermittent flow-down step was 1.5 cm / min.

[0026] The above-mentioned "continuous flow-down process" and "flow-down stopping process" were repeated to obtain a titanium alloy powder. The obtained titanium alloy powder was measured for D10, D50, and D90 using a laser diffraction particle size distribution analyzer (LA-750 manufactured by Horiba, Ltd.) (note that this measurement was performed under the conditions described below). The results were D10 of 17 μm, D50 of 38 μm, and D90 of 76 μm. The obtained titanium alloy powder was then classified using a vibrating sieve. The obtained titanium alloy powder was classified using a sieve with a mesh size of 105 μm (hereinafter referred to as "sieve 1"), a sieve with a mesh size of 55 μm (hereinafter referred to as "sieve 2"), and a sieve with a mesh size of 15 μm (hereinafter referred to as "sieve 3"). This classification yielded titanium alloy powder that passed through sieve 1 (hereinafter referred to as "Powder 1") and titanium alloy powder that passed through sieve 2 but did not pass through sieve 3 (i.e., remained on sieve 3) (hereinafter referred to as "Powder 2"). The yield of Powder 1 was then calculated using the weight of Powder 1 and the weight of the total titanium alloy powder obtained before classification. As a result, the yield of Powder 1 was 93%. Similarly, the yield of Powder 2 was 50%.

[0027] The measurement conditions for the laser diffraction particle size distribution measuring device (LA-750 manufactured by Horiba, Ltd.) were as follows:

[0028] Dispersion medium: sodium hexametaphosphate Particle refractive index: 3.0659 Dispersion medium refractive index: 1.3330

[0029] Titanium alloy powder was obtained under the same conditions as in Example 1, except that the duration of current flow through the high-frequency heating coil 2 during the continuous flow-down step and the flow-down stop step was changed to 2 seconds. The flow of molten metal 3 stopped during the 2-second continuous flow of 200 A current through the high-frequency heating coil 2 (the flow-down stop step). It took 0.4 seconds for the flow of molten metal 3 to completely stop after the magnitude of the current flowing through the high-frequency heating coil 2 was changed to 200 A. In other words, this 0.4-second period corresponds to the intermittent flow-down step. The flow rate of molten metal 3 during this intermittent flow-down step was 0.5 cm / min. The D10, D50, and D90 values ​​of the titanium alloy powder obtained by the same method as in Example 1 were measured. The D10 was 13 μm, the D50 was 32 μm, and the D90 was 66 μm. The obtained titanium alloy powder was then classified by the same method as in Example 1 to obtain Powders 1 and 2. Thereafter, the yield of Powder 1 was calculated in the same manner as in Example 1, and was found to be 95%. The yield of Powder 2 was 55%.

[0030] 1. Continuous Flow-Down Process A rod-shaped metal raw material 1 made of a titanium alloy was inserted into a high-frequency heating coil 2. Thereafter, a current of 270 A was continuously applied to the high-frequency heating coil 2 for 2 seconds to melt the metal raw material 1 and obtain a molten metal 3, which was then flowed down at a rate of 8 cm / min. Argon gas was then introduced at a flow rate of 16 Nm through a gas nozzle 4 shown in FIG. ３ The water was sprayed onto the molten metal 3 flowing down at a flow rate of 1 / min.

[0031] 2. Flow-Down Stopping Step Two seconds after starting to pass a 270 A current through the high-frequency heating coil 2 in the continuous flow-down step, a 270 A current was continued to pass through the high-frequency heating coil 2 for another two seconds to melt the metal raw material 1 and obtain molten metal 3, which was then allowed to flow down at a rate of 0 cm / min (i.e., the flow of the molten metal 3 was stopped). At this time, it took 0.4 seconds for the flow of the molten metal 3 to completely stop. That is, this 0.4 second period corresponds to the intermittent flow-down step. The flow rate of the molten metal 3 during this intermittent flow-down step was 0.5 cm / min.

[0032] Next, the D10, D50, and D90 of the titanium alloy powder obtained by the same method as in Example 1 were measured, and the results were D10: 15 μm, D50: 33 μm, and D90: 70 μm. The obtained titanium alloy powder was then classified by the same method as in Example 1 to obtain Powders 1 and 2. The yield of Powder 1 was then calculated by the same method as in Example 1, and was found to be 95%. The yield of Powder 2 was also found to be 55%.

[0033] Comparative Example 1 A rod-shaped metal raw material 1 made of a titanium alloy was inserted into a high-frequency heating coil 2. Thereafter, a current of 270 A was continuously passed through the high-frequency heating coil 2 to melt the metal raw material 1 and obtain a molten metal 3, which was then allowed to flow downward at a rate of 8 cm / min. Argon gas was then introduced at a flow rate of 16 Nm through a gas nozzle 4 shown in FIG. ３ The titanium alloy powder was obtained by spraying at a flow rate of 1 / min (i.e., the flow stopping step in the example was not performed). The D10, D50, and D90 of the titanium alloy powder obtained by the same method as in Example 1 were measured, and found to be D10 of 20 μm, D50 of 45 μm, and D90 of 90 μm. The resulting titanium alloy powder was then classified by the same method as in Example 1 to obtain Powders 1 and 2. The yield of Powder 1 was then calculated by the same method as in Example 1, and was found to be 90%. The yield of Powder 2 was also found to be 40%.

[0034] (Comparative Example 2) Titanium alloy powder was obtained under the same conditions as Comparative Example 1, except that the magnitude of the current flowing through the high-frequency heating coil 2 was changed to 400 A. The D10, D50, and D90 of the titanium alloy powder obtained using the same method as in Example 1 were measured, and found to be D10 of 18 μm, D50 of 43 μm, and D90 of 89 μm. The resulting titanium alloy powder was then classified using the same method as in Example 1 to obtain Powders 1 and 2. The yield of Powder 1 was then calculated using the same method as in Example 1, and was found to be 93%. The yield of the titanium alloy powder in Powder 2 was 43%.

[0035] The results obtained in Examples 1 to 3 are shown in Table 1, and the results obtained in Comparative Examples 1 and 2 are shown in Table 2.

[0036]

[0037]

[0038] (Summary) As is clear from Table 1, the titanium alloy powders obtained in Examples 1-3, in which the continuous flow-down process and the stop-flow-down process were alternately repeated, had a D90 of 66 μm or more and 76 μm or less, and a D50 of 32 μm or more and 38 μm or less. Furthermore, the yield of the titanium alloy powder (Powder 1) that passed through Sieve 1 in Examples 1-3 was equal to or greater than the yield of Powder 1 in Comparative Examples 1 and 2 (see Tables 1 and 2). Furthermore, the yield of the titanium alloy powder (Powder 2) that passed through Sieve 2 but not Sieve 3 (i.e., remained on Sieve 3) in Examples 1-3 was higher than the yield of Powder 2 in Comparative Examples 1 and 2 (see Tables 1 and 2). From all of the above facts, it was suggested that in the method for producing metal powders such as titanium powder and titanium alloy powder according to the present invention, by alternately repeating the continuous flow-down step and the flow-down stop step, titanium alloy powder having a D90 of less than 89 μm can be obtained, titanium alloy powder having a D50 of 32 μm or more and 38 μm or less can be obtained, and the yield of Powder 2 can be increased.

Claims

1. A method for producing metal powder comprising: a continuous flowing down process for continuously flowing down a molten metal obtained by melting a metal raw material; and a flow stopping process for stopping the flow of the molten metal, the continuous flowing down process and the flow stopping process being alternately repeated.

2. The method for producing a metal powder according to claim 1, wherein the metal powder has a D90 of less than 89 μm.

3. The method for producing metal powder according to claim 1, wherein the metal powder has a D50 in the range of 20 μm or more and 42 μm or less.

4. A method for producing metal powder as described in any one of claims 1 to 3, wherein the amount of the molten metal flowing down is controlled by a high-frequency heating coil, the high-frequency heating coil is controlled by current control, and the magnitude of the current used in the flow stopping process is within the range of 10% or more and 60% or less of the current used in the continuous flowing down process.

5. The method for producing metal powder as set forth in claim 4, further comprising an intermittent flowing process for causing the molten metal to flow intermittently, wherein the amount of the molten metal flowing in the intermittent flowing process is within the range of more than 0% and not more than 20% of the amount of the molten metal flowing in the continuous flowing process.

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