JPH0649512A - Device for producing gas-atomized metal powder - Google Patents

Abstract

PURPOSE:To prevent blocking and to impart a strong pulverizing action by forming an upper jet between the intersections of a molten metal nozzle and a lower jet and intercepting the blowing up due to a crushing effect by the lower jet. CONSTITUTION:An upper gas jet 5G from an upper gas ejection nozzle 3 and a lower gas jet 6G from a lower gas ejection nozzle 4 are ejected into a molten metal M flowing down from a molten metal nozzle 1 to powder the molten metal M. At this time, the solid part 5B of the nozzle is formed in the upper ejection nozzle 3 at regular intervals to generate a jet-free part in the circumferential direction of the gas jet 5G. Consequently, the blowing up of fine powder due to the strong powdering effect of the lower jet 6G is intercepted, blocking is prevented, and the molten metal pieces weakly crushed by the upper jet 5G is strongly crushed by the lower inverted-conical high-speed gas jet 6G.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an apparatus for producing metal powder by a gas jet, which is generally called a gas atomizing method.

[0002]

2. Description of the Related Art A high-speed gas is injected into a vertically flowing columnar molten metal flow, which is finely divided and crushed.
The gas atomization method for producing a fine metal powder by cooling is a spherical shape close to a true sphere, and since a high-purity metal powder with less surface oxidation can be obtained, the metal powder according to the present method has a characteristic of high purity. In addition, it has excellent filling properties and fluidity, and is used not only in general metallurgical applications but also in very wide fields such as painting. However, the particle size of the metal powder produced by the gas atomization method generally shows a wide distribution from several μm to about 1 mm, and for example, the yield of fine powder particles of 45 m or less, which is commonly used for sintering, is a mass-scale equipment. At present, it is low. As a manufacturing technique for obtaining fine powder particles, increasing the gas flow rate to the molten metal and increasing the gas injection pressure can be mentioned, but since the manufacturing cost increases in mass production equipment,
These must be fully considered.

The gas atomizing nozzle of the gas atomizing method is roughly classified into a freefall type and a confined type, and an annular type, a pencil type, a V type and the like are used respectively. The free-fall type is a type that obtains metal powder by injecting a high-speed gas into the free stream of the molten metal, and is excellent in mass productivity, but the distance from the gas injection port to the intersection with the molten metal stream is relatively large. Since it is long, the gas flow velocity is attenuated and the pulverization efficiency is reduced, which is disadvantageous for producing fine powder particles. On the other hand, in the confined type, the injection gas from a nozzle provided directly above the molten metal flow collides with the molten metal flow after passing through a narrow space immediately after the molten metal flows out, so that the gas flow velocity is not attenuated and the grinding efficiency is improved. Since it is high, it is advantageous for producing fine powder particles. However, the so-called blocking phenomenon, in which the molten metal is blown up by the generation of the backflow region having the upward velocity component due to the generation of the dynamic pressure at the time of collision of the jet gas, and this is adhered and deposited on the molten metal nozzle and the gas injection port to block them, There is a problem that such trouble frequently occurs.

In order to effectively obtain fine powder particles, nozzles are installed in multiple stages so that jets collide with a vertically flowing molten metal stream or its spray body stream at two or more locations in the vertical direction. Is known. That is, for the purpose of producing fine powder particles, a method of providing two or more gas injection nozzles in the vertical direction and injecting high-speed gas from the nozzles in each step (JP-A-60-190502), or a two-stage fluid In an injection nozzle, an atomizing fluid ejecting nozzle device that prevents re-aggregation of metal particles atomized in the upper stage and narrows the particle size distribution width in the lower stage (Japanese Patent Laid-Open No. 1-16270)
No. 4) and the like, as a method of avoiding blocking and making particles finer, two pairs of pencil type fluid jet nozzles are concentrically arranged so as to face each other, and a horizontal distance is maintained at a constant jet intersection angle. There is proposed a method (Japanese Patent Application Laid-Open No. 1-219110) in which nozzles are provided in multiple stages by changing the temperature distribution and the jet intersections are distributed within a range of 2 to 5 times the molten metal flow diameter.

[0005]

It is considered that the above-mentioned proposed gas atomizing methods are insufficient for producing fine powder particles of 45 μm or less with a good yield and preventing the trouble of blocking phenomenon. That is, after the high-speed gas is injected from the injection nozzle, the longer the injection distance is, the more the flow velocity is attenuated, and the sufficient crushing ability cannot be obtained (Japanese Patent Laid-Open No.
219110), insufficient means for avoiding the blocking phenomenon (JP-A-60-190502, JP-A-1-162704), and the fact that the pulverizing effect balance is not sufficiently taken into consideration in the multi-stage nozzle. Is. Therefore, the present invention, as a method for producing fine powder particles with good yield and preventing blocking, has achieved an effective fine pulverization effect by primary coarse pulverization and secondary fine pulverization of a multi-stage jet method, while preventing the blocking phenomenon. An object of the present invention is to provide a gas atomized metal powder manufacturing apparatus.

[0006]

The present invention is a multi-stage jet method using at least two stages using upper and lower jets. By effectively distributing the roles of the jets to each other, it is possible to prevent blocking and increase the fine powder. Achieving yield is achieved.

That is, according to the present invention, a fine metal powder for injecting a high-speed gas jet from the periphery of a vertically flowing molten metal flow or a spray body flow thereof is collided downward at a plurality of positions in the vertical direction. In the manufacturing apparatus, the upper jet that collides with the molten metal flow or the spray body flow at a specific vertical position has a collision effect around the center line of the molten metal flow or the spray body flow as compared with other portions. A gas spray metal powder production apparatus having a lacking portion, wherein the lower jet that collides at a position below the specific vertical position has an inverted conical shape with the collision position as an apex. .

[0008]

When the present inventor intends to produce a fine powder with a high yield by injecting a plurality of stages of high-speed jets from the periphery of the flowing molten metal flow, the jet in the lower stage is compared with that in the upper stage. It was found from various experiments that it should be remarkably powerful. That is, the metal melt that has once been made into droplets is stable due to the action of surface tension, and its diameter is small, so that a large relative velocity (in the multistage jet method, due to the upper jet in a multistage jet method) The primary droplet has acquired a large downward velocity by collision with the upper jet, and this minute velocity also has the effect of reducing the relative velocity with the lower jet, which also has a downward velocity). It will not re-divide unless it is done. In order to realize a strong crushing force for the lower jet, the present invention adopts an inverted cone shape having a vertex directly below the generation point of the molten metal spray body. It was found that this inverted conical jet is suitable as a lower jet in the multi-stage jet method because it has less momentum diffusion and can easily realize a very large velocity gradient.

In the present invention, the upper jet has the advantages of the conventional confined type as it is, and it is possible to suppress the occurrence of blocking phenomenon. It has a shielding effect against blowing up caused by a strong collision effect. That is, in general, the gas atomizing method powders the molten metal stream 24 flowing down from the molten metal holding container 23 by the high-speed gas 25 jetted from the gas jet nozzle 22 as shown in FIG. In order to efficiently carry out the production of fine powder, FIG.
A confined type gas injection nozzle as shown in FIG. In this nozzle, a vigorous circulating motion occurs in a narrow space surrounded by the melt nozzle 31, the gas injection nozzle body 32 and the high speed gas jet 33.

That is, the gas in the space is given a downward velocity due to the high-speed gas 33 and its inducing action in the outer peripheral portion, and expands under the influence of the thermal energy of the molten metal flow in the central portion, whereby A circulation action occurs, and as a result, a large blow-up action occurs with respect to the flowing molten metal flow. Due to this blowing-up action, there is a blocking phenomenon in which the scattered fragments of the molten metal flow adhere to and accumulate on the molten metal nozzle 31 to hinder the downward flow of the molten metal flow, or adhere to and accumulate on the gas injection nozzle 32 to impede the injection of high-speed gas. Occur. Although this blocking phenomenon is infrequent, it may occur even when the injection gas pressure and the injection angle are unbalanced even in the free fall type.

In view of the above, in the present invention, the dynamic pressure caused by the jet-induced gas flow, which is the main factor of the blocking phenomenon, at the lower end portion 35 in the closed space mutually or by collision with the molten metal is By providing a weak portion, that is, a portion having a weak gas curtain action, a dynamic pressure is released from this portion to suppress the upward flow. Part of the escaped flow is discharged by the suction effect of the lower jet. As described above, the blocking phenomenon can be effectively avoided. In addition, an inflow corresponding to this escape occurs in the upper part of the closed space, but since there is almost no molten metal splash in this part, no blocking occurs due to this inflow.

The molten metal fragments crushed by the high-speed gas jet injected from the upper gas injection nozzle are not completely solidified and are cooled and solidified while the fragments are flying by the gas flow. This solidification time varies depending on the initial crushing state (crushed particle size, molten metal temperature), material type (melting point, specific heat, density), gas conditions (flow rate, flow rate, gas pressure, gas type), but is generally 10 ⁴ -10 Cooling / solidification is completed at the solidification rate of ⁷ ° K / sec. If a crushing force is further applied during the flight in the non-solidified state, the molten metal fragments are finely crushed, and at the same time, the molten metal fragments are rapidly cooled and fly to complete the solidification to produce fine metal powder.

However, as described above, even if a plurality of gas jets are simply jetted, the molten metal flow is not always effectively made into fine powder. The pulverizing ability of the gas jet is mainly determined by the gas flow velocity, and the kinetic energy increases as the flow velocity increases, and the pulverizing ability improves. However, using the upper jet and the lower jet as separate gas sources is disadvantageous in terms of the structure of the nozzle and the gas supply system, and the pressure energy held by the gas is converted into velocity energy with high efficiency. For this purpose, it is desirable to use Laval nozzles (end-spreading nozzles) regardless of the upper and lower sides. In this case, the upper and lower jets have substantially the same flow velocity. Therefore, in this case, the lower jet should have a larger flow rate than the upper jet. Further, it is preferable that the energy is concentrated on both the upper and lower sides by using an inverted cone shape. Of course, by setting the relative position of the lower jet just below the intersection of the upper jets, the blocking phenomenon is avoided, and the weak flow crushing of the first stage and the strong crushing of the second stage are realized, and the fine metal powder is improved. It can be manufactured stably at a high rate.

Although the present invention has been described above using the upper and lower jets, the present invention is not limited to this. In order to obtain a sharp powder particle size distribution and to suppress the tendency of the blocking phenomenon to occur due to the increase of the cone apex angle for the purpose of stronger crushing effect of the lower jet, in addition to the upper jet, by adding the same thing, etc. The number of stages can be increased to 3 or even more.

[0015]

EXAMPLE Using the gas injection nozzle shown in FIG.
2.2 About C-4Cr-12W-9Mo-5V-12Co-Fe molten metal,
An atomizing experiment was conducted. In FIG. 1 (a), in the injection gas 5G, as shown in FIG. 1 (b), the nozzle-free portions 5B are circumferentially arranged at intervals of 60 ° at 120 ° intervals (axial symmetry). Causes a jet-missing part.
Gas can flow freely through this lacking part,
High pressure is prevented from being generated in the lower part of the closed space (35 in FIG. 3), the blocking phenomenon due to the blowing phenomenon is prevented, and the metal powder can be stably manufactured. In this embodiment, since the upper jet is also a conical jet, it has a great crushing effect even at a small gas flow rate, and since it is axisymmetric, there is no change in the center of the spray body flow, and its central part and the lower jet. It prevents the displacement from the top.

The spraying conditions of the present invention are shown in Table 1,
The results are summarized in comparison with the method using the one-step confined type (conventional method 1) and the method using the two-step freefall type (conventional method 2). The average particle size shown at the bottom is
As the particle size normally used as gas atomized powder,
-100mesh (149 μm or less) is a value measured for particles.
From this table, it can be seen that the method of the present invention can produce a metal powder of fine powder particles clearly compared with the conventional method, and can stably produce the metal fine powder without causing a trouble such as a blocking phenomenon.

[0017]

[Table 1]

In the conventional method 1, the results are obtained by performing atomization by arraying and jetting pencil type jets on an inverted cone. Approximately 20 seconds after the start of atomization, the molten metal nozzle was blocked due to blocking, and the solidified mass of molten metal was also attached in the vicinity of the gas injection slit. Conventional method 2
Is an example of performing atomization by injecting V-type jets in two stages. In the free-wall type atomizing system represented by the V-type jet, blocking is less likely to occur, but the distance from the jet injection port to the intersection with the molten metal flow is long, and therefore the gas flow velocity decay is unavoidable. . Therefore, the actual situation is that the particle size of the generated powder does not become so small even if the two-stage injection is performed.

The results shown in the present inventions 1 and 2 are that the upper jet is provided with a lacking portion of a gas curtain through which gas can freely flow, so that an upward flow that causes blocking is suppressed and blocking is prevented. I was able to. Further, since it is a confined type, the attenuation of the gas flow velocity is small, so atomization is carried out by fully utilizing the kinetic energy of the gas jet. Further, since the lower jet crushes the unsolidified crushed pieces crushed by the upper jet with the gas having a higher speed and a larger flow rate than the upper jet, fine powder is generated. The jet angle of the upper and lower jets is 5 to 15 ° to reduce the apex angle of the lower jet in order to enhance the suction effect on the lower jet. The particle size of 2 is slightly coarser than that of Example 1, but this is because the focal length between the upper jet and the lower jet is slightly larger and the pulverization by the lower jet did not contribute effectively. .

[0020]

INDUSTRIAL APPLICABILITY The present invention prevents the blocking phenomenon by forming the upper jet between the intersection of the molten metal nozzle and the lower jet to block the blow-up caused by the strong crushing effect of the lower jet. In addition, it realizes a grinding mode in which the molten fragment weakly crushed by the upper jet is strongly crushed by the lower conical high-speed gas jet in the lower stage, which prevents the blocking phenomenon and the strong fine crushing action which cannot be obtained by the conventional technology. Compatibility can be achieved.

[Brief description of drawings]

FIG. 1 is a schematic view showing an example of a gas atomized metal powder production apparatus according to the present invention. (A) is sectional drawing, (b) is a figure which shows the upper jet injection form example.

FIG. 2 is a schematic diagram showing an example of a general gas atomizing apparatus.

FIG. 3 is a schematic view of a confined type gas injection nozzle in the related art.

[Explanation of symbols]

1,31 Molten metal nozzle, 2 Gas injection nozzle body, 3
Upper gas injection nozzle, 4 Lower gas injection nozzle, 5G Upper gas jet, 5B Upper gas jet lacking part, 7 Primary crushed fragment, 8 Secondary crushed metal powder, 21 Gas atomizing tank, 22 Gas injection nozzle, 23 Molten metal holding container, 24 ，
34 molten metal flow, 25, 33 gas jet, 32 gas injection nozzle, 35 lower part of closed space

Claims (3)

[Claims] 1. An apparatus for producing fine metal powder, in which a high-speed gas jet is jetted from the surroundings of a vertically flowing molten metal flow or its atomized body flow, as if it collides downward at a plurality of positions in the vertical direction. In the above, the upper jet that collides with the molten metal flow or the spray body flow at a specific vertical position is a portion where the collision effect is insufficient around the center line of the molten metal flow or the spray body flow compared to other portions. And a lower jet that collides at a position lower than the specific vertical position has an inverted conical shape with the collision position as an apex. 2. An inverted cone having an upper jet having a center line of the molten metal flow or its atomized body flow as an axis and a collision point with the molten metal as an apex, and having a portion lacking the flow symmetrically with respect to the axis. An apparatus for producing a gas atomized metal powder, characterized in that 3. The upper jet and the lower jet both use a pressure chamber formed so as to surround the molten metal flow as a common source, and the lower jet has a larger flow rate than the upper jet. The gas atomized metal powder production apparatus according to claim 1 or 2.