TECHNICAL FIELD

The present disclosure relates to an apparatus for producing a metal powder and a method of producing a metal powder.

BACKGROUND ART

As a method of producing a metal powder, a gas atomizing method of injecting a high-pressure gas into a molten metal that is supplied downwardly to produce a metal powder or a water atomizing method of injecting high-pressure water into a molten metal that is supplied downwardly to produce a metal powder has been known. As a method of producing a metal powder using the gas atomizing method, a method of injecting a high-pressure gas into a molten metal that is supplied downwardly, dividing (firstly pulverizing) the molten metal into fine droplets, thrusting the divided droplets into a revolving water flow, and dividing (secondly pulverizing) and cooling the droplets into fine droplets has been known (for example, Japanese Patent Application Laid-Open (JP-A) No. H10-121115, JP-A No. H11-43707, JP-A No. H11-80812, and JP-A No. 2010-90410).

In the method of producing a metal powder described in the above patent documents, for example, a metal powder having a fine particle size is produced by flowing cooling water downward with revolving the cooling water to form a revolving water flow along an inner peripheral wall of a cylindrical pulverization cooling cylinder whose axis line is inclined relative to a vertical direction, thrusting droplets, which was firstly divided (firstly pulverized) with a high-pressure gas, into the revolving water flow together with a gas flow, and secondly dividing (secondly pulverizing) and cooling the droplets.

SUMMARY OF INVENTION

In the method of producing a metal powder described in the above patent documents, since a temperature of the high-pressure gas (atomized gas) injected into the molten metal is extremely lower than that of the molten metal, the molten metal is pulverized while being cooled. For this reason, the molten metal is pulverized while a viscosity of the molten metal increases, and even if an injected gas pressure is increased, it is difficult to pulverize the molten metal more finely. That is, there is a limit in obtaining a metal powder having a finer particle size.

In the method of producing a metal powder described in the above patent documents, since the firstly divided droplets are thrust into the revolving water flow together with the high-pressure gas that was spread due to an injection angle, there is variation in a distance (time) until the droplets are thrust into the revolving water flow. Since the firstly divided droplets are thrust into the revolving water flow while being cooled with the high-pressure gas, if there is variation in a distance (time) until the firstly divided droplets are thrust into the revolving water flow, there is variation in quality of the metal powder, for example, amorphization of the metal powder, which is affected by a cooling rate of the droplets.

The disclosure has been made in view of the above-described problems, and an object of the present disclosure is to provide an apparatus for producing a metal powder and a method of producing a metal powder that are capable of obtaining a metal powder having a fine particle size of excellent quality.

An apparatus for producing a metal powder according to a first aspect includes: a supply unit that downwardly supplies a molten metal; a combustion flame injection unit that convergently injects a supersonic combustion flame from a combustion flame injection port to a molten metal supplied from the supply unit and jets the convergent combustion flame as a focused jet flow directly downward; and a pulverization device having a pulverization cooling cylinder that forms a revolving water flow along an inner peripheral wall of the pulverization cooling cylinder, which has an axis line that is inclined relative to a vertical direction, and that thrusts the focused jet flow inflowing from an upper opening into the revolving water flow. A convergence position of the combustion flame is in an open space above the opening.

According to the apparatus for producing a metal powder according to the first aspect, the supersonic combustion flame from the combustion flame injection port is convergently injected to the molten metal supplied from the supply unit, and as a result, a combustion flame gas can convergently collide with the molten metal. As a result, the supplied molten metal is pulverized by a high collision energy of a supersonic gas. The molten metal is pulverized while being heated by the combustion flame, that is, while being reduced in viscosity, and as a result, the metal powder having a fine particle size can be easily obtained.

According to the apparatus for producing a metal powder according to the first aspect, the supplied molten metal is pulverized (firstly pulverized) at the convergence position of the combustion flame to form the droplets, and a temperature of the droplets becomes higher than that of the molten metal and the droplets can move by being carried on the focused supersonic jet flow. As a result, an inertia force acts on massive droplets, a large velocity difference between the droplets and the focused jet flow occurs, and the firstly pulverized droplets are elongated and are subjected to a tearing force, until the droplets reach the revolving water flow, and re-pulverized (secondly pulverized), and as a result, the metal powder having a finer particle size can be obtained.

In the apparatus for producing a metal powder according to the first aspect, the convergence position of the combustion flame is in an open space above the opening of the pulverization cooling cylinder. As a result, the distance from the convergence position of the combustion flame to the revolving water flow becomes long, the time of the secondary pulverization becomes long, and the droplets are easily spheroidized, and as a result, the metal powder that is close to a sphere and has a fine particle size can be obtained.

By configuring the convergence position of the combustion flame in the open space above the opening of the pulverization cooling cylinder, a smoother airflow is formed around an upstream portion of the focused jet flow, and thus a generation of a negative pressure is suppressed. As a result, the focused jet flow is suppressed from unstably vibrating due to being pulled by the negative pressure, which is irregularly generated. It is possible to obtain the metal powder having a fine particle size in which the variation in the quality of the metal powder that is caused by the secondary pulverization, for example, the spread of the particle size distribution, is suppressed.

By increasing the distance from the convergence position of the combustion flame to the revolving water flow of the pulverization cooling cylinder, the droplets stay in the high-temperature combustion flame for a long time. As a result, the gas entangled in the droplets during the firstly pulverization or the gas generated in the droplets is easily discharged to the outside of the droplets, and the metal powder having a fine particle size in which the number of internal pores is small can be obtained.

Since the droplets stays in the high-temperature combustion flame for a long time, even if other droplets come into contact with a droplet, these droplets are easily united into one droplet. This makes it difficult to form a metal powder in a state referred to as a so-called “satellite” in which fine metal particles adhere to the metal particles, and as a result, it is possible to obtain the metal powder having a fine particle size and excellent fluidity.

In the apparatus for producing a metal powder according to the first aspect, the supersonic combustion flame is convergently injected from a fuel flame injection port to a supplied molten metal. Due to the characteristics of the supersonic gas flow, the convergent combustion flame is jet linearly vertically downward as the focused supersonic jet flow. As a result, the variation in the distance (time) from the firstly pulverization of the molten metal to the thrusting of the molten metal into the revolving water flow, that is, variation of the distance (time) of the secondly pulverization is suppressed, and as a result, it is possible to obtain the metal powder having a fine particle size in which the variation in the quality of the metal powder that is affected by the secondary pulverization, for example, the spread of the particle size distribution, is suppressed.

In the apparatus for producing a metal powder according to the first aspect, the re-pulverization (thirdly pulverization) can be performed by the impact when the droplets that are secondly pulverized by the focused jet flow thrust into the revolving water flow or by the impact when the droplets flowing by being carried in the revolving water flow collide with the inner wall of the pulverization cooling cylinder. As a result, the metal powder having a finer particle size can be obtained.

According to the apparatus for producing a metal powder according to the first aspect, the droplets that are secondly pulverized can be cooled by thrusting into the revolving water flow together with the focused jet flow in which the high-temperature combustion flame is focused. That is, the droplets that is secondly pulverized can thrust into the revolving water flow while being heated by the combustion flame and maintained at a high temperature. As a result, it is possible to obtain the metal powder having a fine particle size in which the cooling variation of the droplets is suppressed, and the variation in the quality of the metal powder, such as the stable amorphization, is suppressed. The quality of the metal powder is affected by the cooling rate of the droplets.

As described above, according to the apparatus for producing a metal powder according to the first aspect, it is possible to obtain the metal powder having a fine particle size of excellent qualities such as sphericity and favorable fluidity of the metal powder, poreless inside the powder, the particle size distribution in which the spread of the distribution is suppressed, and the stable amorphization.

According to an apparatus for producing a metal powder according to a second aspect, in the apparatus for producing a metal powder according to the first aspect, the convergence position of the combustion flame is above the axis line of the pulverization cooling cylinder.

According to the apparatus for producing a metal powder according to the second aspect, even if an inner diameter of the pulverization cooling cylinder decreases, the distance from the convergence position of the combustion flame to the revolving water flow can be long, that is, the time of the secondary pulverization can be long. As a result, the metal powder having a fine particle size can be obtained even with a simpler apparatus having the small inner diameter of the pulverization cooling cylinder and a small capacity of a water supply source for generating the revolving water flow.

According to an apparatus for producing a metal powder according to a third aspect, in the apparatus for producing a metal powder according to the second aspect, the convergence position of the combustion flame is above a virtual horizontal plane passing through an upper end edge of the pulverization cooling cylinder.

In the apparatus for producing a metal powder according to the third aspect, an airflow flows almost uniformly around an upstream portion of the focused jet flow from all sides, and a smooth airflow is formed around the upstream portion of the focused jet flow. As a result, since the generation of the negative pressure around the upstream portion of the focused jet flow is further suppressed and thus the vibration of the focused jet f low is further suppressed, it is possible to obtain the metal powder having a fine particle size in which the variation in the quality of the metal powder that is affected by the secondary pulverization, for example, the spread of the particle size distribution, is suppressed

According to an apparatus for producing a metal powder according to the fourth aspect, in the apparatus for producing a metal powder according to any one of the first to third aspects, the convergence position is in a range of 15 to 120 mm from the lower end of the combustion flame injection port.

According to an apparatus for producing a metal powder according to a fifth aspect, in the apparatus for producing a metal powder according to any one of the first to fourth aspects, an inclination angle of the axis line of the pulverization cooling cylinder with respect to the vertical direction is from 10° to 55°, and the tip of the combustion flame injection port is above the virtual horizontal plane passing through the upper end edge of the pulverization cooling cylinder.

In a method of producing a metal powder according to a sixth aspect, a supersonic combustion flame is convergently injected into a molten metal that is downwardly supplied, the convergent combustion flame is jetted directly below as the focused jet flow, the focused jet flow thrusts into the revolving water flow formed along an inner peripheral surface of a pulverization cooling cylinder, which has an axis line that is inclined relative to a vertical direction, and the convergence position of the combustion flame is in an open space above the revolving water flow.

According to a method of producing a metal powder according to a seventh aspect, in the method of producing a metal powder according to the sixth aspect, the convergence position of the combustion flame is above the axis line of the pulverization cooling cylinder.

According to a method of producing a metal powder according to an eighth aspect, in the method of producing a metal powder according to the seventh aspect, the convergence position of the combustion flame is above a virtual horizontal plane passing through an upper end edge of the pulverization cooling cylinder.

According to a method of producing a metal powder according to a ninth aspect, in the method of producing a metal powder according to any one of the sixth to eighth aspects, an airflow flows into the upstream portion of the focused jet flow from all sides.

According to a method of producing a metal powder according to a tenth aspect, in the method of producing a metal powder according to any one of the sixth to ninth aspects, the inclination angle of the axis line of the pulverization cooling cylinder with respect to the vertical direction is from 10° to 55°, and the tip of the combustion flame injection port that injects the combustion flame is above the virtual horizontal plane passing through the upper end edge of the pulverization cooling cylinder.

In a method of producing a metal powder according to an eleventh aspect, the method includes: a first pulverizing step of convergently injecting a supersonic combustion flame into a downwardly supplied molten metal and firstly pulverizing the molten metal to form molten droplets; a second pulverizing step of jetting the combustion flame as a focused jet flow including the firstly pulverized droplets directly downward, moving the firstly pulverized droplets in the focused jet flow, which has a relatively fast speed, and secondly pulverizing the droplets to form smaller molten droplets; and a third pulverizing step of thrusting the focused jet flow including the secondly pulverized droplets into a revolving water flow and thirdly pulverizing and cooling the focused jet flow to make a metal powder smaller than the secondly pulverized droplets.

According to a method of producing a metal powder according to a twelfth aspect, in the method of producing a metal powder according to the eleventh aspect, the airflow equally flows into an upstream portion of the focused jet flow from all sides.

The actions and effects of the sixth to eighth aspects overlap with the actions and effects of the first to third aspects, and a description thereof will not be repeated.

According to the apparatus for producing a metal powder and the method of producing a metal powder of the disclosure, it has an effect that the metal powder having the fine particle size of excellent quality can be obtained.

