JPH01219109A - Production of fine powder by gas atomization - Google Patents

Abstract

PURPOSE:To efficiently atomize a molten material by spouting gas on the molten material flowing down from a vessel as insufficiently expanded jets and by causing the vibration of pressure in the collision region. CONSTITUTION:High pressure gas 7 is spouted from the nozzle tips 6 of the body 2 of an atomizing nozzle at a high speed and collided against a molten material 4 flowing down from the opening 5 of a vessel 3. By the collision, the molten material is atomized and cooled to form fine powder. At this time, nozzle tips widened toward the ends are used as the nozzle tips 6 and the ratio So/Sr (throat ratio) of the cross-sectional area So of the outlet end B of each of the tips 6 to that Sr of the narrowest part A of the passage 9 in each of the tips 6 is properly selected. The gas 7 is spouted as insufficiently expanded jets and these jets do not diffuse, maintain the high speed and atomize the molten material 4. In the collision region, the material 4 is further atomized by the vibration of the pressure of the jets and the vibration of the speed.

Description

Detailed Description of the Invention (Field of Industrial Application) The present invention produces fine powder using a gas atomization method, in which a high-temperature molten material is made to flow down in the form of a rod or plate, and then a high-velocity gas collides with the material to atomize it. The present invention relates to a method for manufacturing.

(Prior art) The gas atomization method involves making a molten material such as metal flow down in the form of a rod or plate, and colliding it with a gas jet sprayed at a certain angle against the flow of the molten material. This is a method for producing a large amount of fine powder of metal or alloy by pulverizing a molten material and cooling it at the same time.

By the way, as a method of obtaining fine particles by this gas atomization method, there is a method of obtaining fine powder by injecting extremely high-pressure gas and colliding the ultrahigh-speed gas flow with a molten metal flow (Japanese Patent Laid-Open No. 61-266506). , or■50kg10
A method of obtaining fine metal powder by injecting a high-speed gas flow using ordinary high-pressure gas of up to 4 degrees (Japanese Patent Publication No. 62-24481)
No. 1) 1 or ■ A method of colliding an ultrasonically vibrating gas flow with a molten metal flow to pulverize it to obtain powder (D, H, Ro
and H, Sunwoo: 1983 Annu, P.
oder Metal, Conf, Proc.

(1984) P, 109-124), etc. have been proposed.

(Problem to be Solved by the Invention) However, the method disclosed in Japanese Patent Application Laid-open No. 61-266506 mentioned above (1) deals with very high pressure gas, so it is industrially difficult to use equipment costs, maintenance management costs, and operating costs. Since both are livestock, there are many problems that need to be resolved in implementation.

In addition, the method disclosed in Japanese Patent Publication No. 62-24481 (■) uses a large amount of gas (about INn? gas/1 kg material).
and the resulting powder also has an average particle size of 50 to 10
It's as big as 0 meshes.

Furthermore, the method (2) has a higher ratio of gas flow rate to metal flow rate, 3.
The result was that the relationship with the powder amount of 25 mensius or less was on a straight line, and the effect of ultrasonic atomization was not apparent.

The present invention was made in view of the above-mentioned problems, and aims to produce spherical fine powder with the smallest possible particle size at low cost and in large quantities by a gas atomization method using high-pressure gas at normal pressure (50 kg/cd or less). The aim is to provide a method that can be used.

(Means for Solving the Problems) As a result of various research and experiments, the present inventors found that: (1) When ejecting high-pressure gas into a low-pressure chamber using a flared-out nozzle tip to obtain a supersonic airflow, the flared-out nozzle tip When the ratio of the cross-sectional area of the outlet to the cross-sectional area of the throat portion is set to a predetermined value or less depending on the gas pressure and gas type, an underexpanded jet in which the pressure and flow velocity oscillate in the flow direction from the nozzle tip exit can be obtained; ■When such an underexpanded jet collides with the flowing molten material, the molten material is pulverized by the high-speed airflow, and the oscillation of the pressure of the airflow and the resulting oscillation of the flow velocity have the effect of further atomizing the material. I found out.

The present invention has been made based on this knowledge, and in the gas atomization method in which the flowing molten material is pulverized by injecting high-velocity gas and colliding with the molten material, the surroundings of the flowing molten material are The gist of this is to inject an underexpanded jet from the collision area to oscillate the total pressure in the collision area.

(Function) In the present invention, the reason why the total pressure is oscillated in the region of collision with the molten material is based on the experimental results of the present inventors. That is, as shown in FIG. 3, when such total pressure vibrations are applied and the total amplitude of the total pressure vibrations increases, the average diameter of the generated particles rapidly decreases.

The total amplitude of the total pressure vibration is preferably 15 kPa, more preferably 50 kPa or more.

According to the method of the present invention described above, by making the injected gas into a supersonic underexpanded jet, there is very little entrainment of surrounding atmospheric gas in the section until the center flow velocity of this jet reaches the sonic velocity. The jet flow maintains a high velocity and maintains the shape of the nozzle exit. Therefore, if this material is made to collide with the flow of molten material, it will be finely pulverized by the high velocity air flow.

In addition, after the jet velocity attenuates below the speed of sound, the jet flow spreads by incorporating the surrounding atmosphere and the flow velocity decreases further, but in this case as well, the velocity decreases only small because it diffuses after approaching the flow of the molten material. The flow rate is higher than that of conventional jet flow, and it has a pulverization effect.

Furthermore, in addition to the pulverization caused by the collision of high-velocity gas, the pressure and flow velocity of the jet oscillate in the region of collision with the molten material, so the split particles are affected by the oscillations of gas pressure and flow velocity. Since a corresponding acceleration can be applied, it is possible to further split the molten particles and obtain a fine powder.

(Example) ,・The method of the present invention will be explained below based on the attached drawings.

FIG. 1 is a schematic diagram showing an embodiment of an apparatus for carrying out the method of the present invention. In the figure, 1 is a powder recovery tank, and a 7 Tomize nozzle main body 2 is installed in the upper part of the powder recovery tank 1. There is. For example, at the center of the atomizing nozzle body 2, an opening 5 for flowing down the molten material 4 in the molten material container 3 provided above the atomizing nozzle body 2 is provided. Through this, the molten material 4 is fed into the powder recovery tank 1 in the required amount.

Reference numeral 6 denotes nozzle chips disposed around the aperture 5 of the atomizing nozzle body 2, for example, at 8 equal parts, and these nozzle tips are used to collect the molten material that is injected into the powder recovery tank l through the atomization nozzle body 2. The molten material 4 is pulverized and cooled by blowing high-pressure gas 7 such as Ar gas against collision with the molten material 4 to produce fine powder. Note that this fine powder is separated from the injection gas and recovered in the solid-gas separator 8, while the gas is released.

By the way, in the method of the present invention, the nozzle chip 6 used is one with a flared shape as shown in FIG.
The left end in the figure is connected to the atomizing nozzle main body 2, and the atomizing nozzle main body 2 is connected to a high-pressure gas supply chamber (not shown), and the right end of the nozzle chip 6 is supplied with a high-pressure gas 7 of Ar at a supply chamber pressure of 4 MPa, for example. It erupts.

In the present invention, the high-pressure gas 7 ejected from the nozzle chip 6 needs to be an underexpanded jet, so the cross-sectional area So of the outlet end B of the nozzle chip 6 and the minimum cross-sectional area of the flow path 9 in the nozzle chip 6 The ratio of the cross-sectional area S of part A to So/St
(hereinafter referred to as "throat ratio") is important.

Table 1 below shows the results when fine powder was manufactured by the fine powder manufacturing apparatus shown in FIG. 1 using the flared nozzle tip 6 shown in FIG. 2. The various dimensions of the nozzle tip 6 are shown in Table 2, and the manufacturing conditions are shown in Table 1.
It is also shown in the table.

Table 2 Nozzle chin pros are all minimum part A as shown in Table 2 above.
They are manufactured so that the diameter of the tubes is φ1■l, so that when injected at the same pressure, the gas flow rate is the same. Note that the distance between the geometric focal point 10 (see FIG. 1 (b)) and the exit end B of the nozzle tip 6 is 25 m.

As shown in Table 1, the diameter of the powder particles produced when gas injection is performed using the method of the present invention is the same as that of the conventional method (Conventional Example 1.
It is 1/3 to 1/4 smaller than the case of 2).

Figure 4 shows that the nozzle tip shown in Figure 2 and Table 2 above is attached to the atomizing nozzle main body 2 shown in Figure 1, and the
These are the results of measuring the total pressure along the central axis of the nozzle tip by injecting high-pressure gas 7 under the conditions shown in the table. geometric focus 1
It is known from other photographs that most of the molten material 4 is powdered at approximately 51 points above and below 0, so we measured the pressure vibration on the central axis of the nozzle tip 6, and The total amplitude of pressure oscillations in the five regions above and below the focal point 10 was measured.

In addition, the relationship between the total amplitude of pressure vibration on the central axis and the diameter of the produced powder particles is as shown in Figure 3 above.
It has been found that pressure vibrations in the area (3) are effective in pulverizing the powder.

That is, by appropriately selecting the throat ratio So/St of the nozzle tip 6 as in the method of the present invention, the high-pressure gas 7 ejected from the nozzle tip 6 is formed into an underexpanded jet, thereby preventing the jet from diffusing and achieving a high flow velocity. The holding length becomes longer, and the molten material 4 can be finely pulverized. In addition, in the present invention, the molten material 4 can be further finely pulverized due to the vibration of the jet pressure and the vibration of the flow velocity in the collision area with the molten material 4.

(Effects of the Invention) As explained above, according to the method of the present invention, by making the injected gas into a supersonic underexpanded jet, in the section until the center flow velocity of this jet reaches the sonic velocity, the surrounding atmospheric gas Since there is very little entrainment, the jet flows in the same nozzle shape while maintaining a high flow velocity. Therefore, if this material is made to collide with the flow of molten material, it will be finely pulverized by the high velocity air flow.

In addition, after the jet velocity attenuates below the speed of sound, the jet flow spreads by incorporating the surrounding atmosphere and further reduces the flow velocity, but in this case as well, the speed decrease is small because it diffuses after approaching the flow of molten material. The flow rate is higher than that of conventional jet flow, and it has a pulverization effect.

Furthermore, in addition to the pulverization due to the collision of high-velocity gas, there are oscillations in the pressure of the jet and oscillations in the flow velocity in the region of collision with the molten material, so the split particles have an acceleration that corresponds to the gas pressure and flow velocity fluctuations. can be added, thereby further splitting the molten particles to obtain fine powder.

That is, according to the present invention, fine spherical powder can be produced in large quantities at low cost using high pressure gas that can be generated using ordinary industrial equipment. Therefore, it can be supplied as injection molding powder, sintering aid, etc.

[Brief explanation of the drawing]

Figure 1 (a) is a schematic explanatory diagram of the gas atomizing device used in the uninvented method, (b) is an enlarged view of the atomizing nozzle body, Figure 2 is an enlarged vertical cross-sectional view of the nozzle tip, and Figure 3 is the total pressure A diagram showing the relationship between the total amplitude of vibration and the average diameter of generated particles,
FIG. 4 is a diagram showing the relationship between the distance from the nozzle tip outlet and the total pressure on the jet center axis. 4 is a molten material, 6 is a nozzle tip, and 7 is a high pressure gas. Figure 3 @ Figure 4

Claims (1)

[Claims] (1) In the gas atomization method, which atomizes the flowing molten material by injecting high-velocity gas and causing the material to collide, an underexpanded jet is injected from around the flowing molten material to reach the collision area. A method for producing fine powder using a gas atomization method characterized by oscillating the total pressure.