JPS63241104A - Production of fine spherical metal powder - Google Patents

Abstract

PURPOSE:To efficiently form fine and spherical metal powder by specifying the flow rate of liquid and the crossing angle of a pair of planar liquid sprays facing each other at the time of pulverizing a perpendicularly falling molten metal by the above-mentioned liquid sprays. CONSTITUTION:The molten metal 3 housed in a crucible 1 is dropped from a small hole 2 in the bottom of the crucible 1 perpendicularly into a tank 5. The high pressure and high velocity liquid is sprayed in the form of a flat plate from a pair of opposed nozzle tips 9 of a nozzle device 4 to pulverize the molten metal 3 at the crossed part thereof. The liquid flow rate per unit in the section perpendicular to the flow of the respective liquid sprays in the part where the liquid sprays cross with each other is set at <=55kg/sec.m (the lower limit is about 40kg/sec.m) and the crossing angle 10 of the liquid sprays is set at >=25 deg. (the upper limit is about 60 deg.). The finely pulverized and cooled metal powder is suspended into the liquid in the tank 5 and is separated and recovered by a solid-liquid separator 7. The fine particles having about <=250mu diameter and about <=70X average diameter are thereby obtd.

Description

DETAILED DESCRIPTION OF THE INVENTION (Industrial Application Field) The present invention relates to a method for producing spherical fine metal powder, and in particular a method for producing spherical fine metal powder, in which molten metal is crushed by a pair of flat liquid sprays that are injected in opposition to each other. This invention relates to a method for producing powder.

(Prior Art) Conventionally, fine metal powders in the form of Ly are used in the field of powder metallurgy, including powder filling into capsules, such as III' (hot isostatic pressing) and CIP (cold isostatic pressing). There are gas atomization methods, vacuum atomization methods, and rotating electric bridge methods as methods for producing spherical fine metal powder, which has been in increasing demand in recent years as a material and as a raw material for injection molding, powder spraying, etc., but the cost is high. , each has its own problems in terms of productivity.

In the gas atomization method, a high-speed inert gas is injected into a molten metal stream to crush and cool the molten metal stream to obtain powder.
The high-pressure inert gas used as the propellant is expensive, and the price of the powder is also high. In the vacuum gas atomization method, molten metal is ejected into a high vacuum tower, but in the zero-rotation electrode method, which requires a large vacuum container and requires high equipment costs, the end of a metal cylinder rotating at high speed is heated with plasma or arc. Powder is obtained by melting and scattering using centrifugal force, but productivity is low and the powder is expensive.

The atomization method using liquids such as water and oil as a propellant is widely practiced and the powder price is considerably lower than the above three methods, but the shape of the powder produced is irregular and spherical. No powder was obtained.

Japanese Patent Publication No. 43-6389 describes an example using an annular nozzle, but it is possible to make the powder particles spherical or irregular by adjusting the speed of water, which is the atomizing medium. is disclosed.

In other words, spherical particles can be obtained even with liquid atomization if the water flow rate is low and the water is cooled slowly.

The diameter is 30μ, the apparent density is 3.25g/cd, and the diameter is 10
One with the same density of 3.0 g/cd was obtained at 0 μm. However, under these conditions, the yield of fine powder was extremely low (which was an industrial problem).

(Problems to be Solved by the Invention) An object of the present invention is to provide a method for efficiently producing spherical and fine metal powder by an atomization method using a liquid as an atomizing medium.

(Means for Solving the Problems) It is well known that metal powder produced by the atomization method tends to become spherical powder as the molten metal flow is pulverized and cooled more slowly until it solidifies. On the other hand, in the conventional liquid atomization method, the cooling rate is high and the resulting powder exhibits an irregular shape, but it is possible to obtain spherical metal powder by slowing down the cooling rate in some way.

However, apart from large particles, fine particles cannot be made fine unless the spray medium is applied to the molten metal stream at high speed; however, when the spray medium is sprayed at such high speeds, they are easily quenched. Spheroidization is difficult. The finer the particles, the more pronounced the quenching effect becomes, and the more difficult it becomes to spheroidize.

Therefore, from this point of view, the present inventors have repeatedly investigated various means for making the powder produced finer in the atomization method and for slowing down the cooling rate. The present invention was completed based on the knowledge that when pulverized metal powder is slowly cooled in a spray medium mist, it is possible to obtain a spherical powder.

Here, the gist of the present invention is to provide a method for producing metal powder by pulverizing vertically flowing molten metal by a pair of flat liquid sprays that are injected in opposition and cooling the liquid spray. The liquid flow rate per unit width in the cross section perpendicular to the flow of each liquid spray at the intersection thereof is 55 kg/sec.- or less, and the intersection angle of these liquid sprays is 25'' or more. This is a method for producing fine spherical metal powder.

According to the invention, after pulverizing the molten metal stream in this way,
In a preferred embodiment of the slow cooling method, a liquid spray is injected obliquely downward from a pair of liquid injection ports installed opposite to each other. The spray pattern can be flat, band-shaped, or fan-shaped.The molten metal stream flows down toward the area where the two sprays intersect and collide, where it is crushed. However, just before this collision zone, the fluid flow rate per unit width passing through the cross section perpendicular to the flow direction of each spray is 55 kg/5 ec.
- less than or equal to 25″ and also the intersection angle of the liquid spray is 25″
By doing so, the injected liquid spray spreads in the form of a mist over almost the entire area within the intersection angle of both sprays in the downstream part of the collision area, that is, below, and the metal powder passes through this after being crushed. is slowly cooled and becomes spherical.

Moreover, the powder obtained by colliding the flat spray as described above is quite fine, and the average particle size is 1/3 that of conventional methods using, for example, an annular nozzle. There is.

Incidentally, the fluid flow rate per unit width in the present invention as described above is considerably lower than that in the general liquid atomization method. 70μ-
The following fine particles can be obtained, and they can also be slowly cooled, resulting in an unexpected effect.

(Operation) Next, the present invention will be described in more detail with reference to the accompanying drawings.

FIG. 1 is a schematic diagram of a metal powder manufacturing apparatus using a liquid atomization method according to the present invention.

In the figure, molten metal 3 is housed in a crucible 1 and flows out from a small hole 2 at the bottom of the crucible 1. A high-pressure, high-speed liquid is injected from the nozzle device 4 toward the flow of molten metal to crush it. The finely pulverized and cooled metal powder is suspended in the liquid in the tank 5, sent from the outlet 6 to the solid-liquid separator 7, separated from the liquid of the spray medium, and recovered. The shape of the spray can be easily changed by changing the nozzle tip attached to the socket 8 whose length can be freely adjusted to m.

FIG. 2 is a schematic diagram schematically showing how two sprays collide. As already mentioned, the shape of the spray at this time may be one that spreads out in a belt shape or one that spreads out in a fan shape.In short, it is sufficient that the shape is a flat plate.The intersection angle 10 of the two sprays is: 259 or more, preferably 60° or less from the viewpoint of stable operation, and liquid vL
In the case of a mouse, the flow rate per unit width of light is 55 kg/see・1 or less, but generally in the field of powder metallurgy, the lower limit of the liquid flow rate in such a case is 40 kg/sec-m, so in the present invention, the flow rate is considerably lower. It will be low.

In spite of such a small flow rate, according to the present invention, considerably fine particles can be obtained, and the reason is considered to be as follows.

In other words, in the annular nozzle disclosed in Japanese Patent Publication No. 43-6389, the dynamic pressure of the water is weakened by the adjustment guide, but in the type shown in Figure 2, the dynamic pressure of the liquid remains high and is allowed to collide with the molten steel flow. This is because the molten metal flow directly collides with the molten metal flow.

After the two sprays collide, they become mist and disperse, so even the fine particles are not rapidly cooled as mentioned above, and are cooled for a sufficient amount of time to become spheroidal. Become.

Next, the present invention will be further explained by examples.

Example 1 Atomization of a molten metal stream according to the method of the invention was carried out using the apparatus shown in FIGS. 1 and 2. Molten metal is 5US316L, tapping temperature is 1500°C1 flow16.
It was 6 kg/min. The injection liquid was hydraulic oil, the flow rate was 200j'/min, and the pressure was 10 MPa.

At this time, we used a commercially available nozzle tip in which the spray pattern of the liquid spray is flat and fan-shaped when viewed from above, and the center angles of the fan-shape are 15°, 25°, 40", 50°, and 65".
By using a pair of each type of powder, the flow rate of the liquid per unit width of light passing through a cross section perpendicular to the flow direction of the liquid spray was varied, and the shape and appearance of the metal powder produced at that time was determined. Density and particle size were measured. Note that the intersection angle of both sprays was 40''.

The results are summarized in a graph in Figure 3.

The sphericity of the produced powder is determined by the appearance photograph of the powder and the apparent density (JI
It was determined by comparing the measured value of S Z 2504),
The higher the density, the closer the appearance is to a spherical shape, 5US316
In the case of L, when the apparent density was greater than 4.5 g/am3, it was considered to be spherical.

From the results shown in Figure 3, the flow rate per unit width of light is 55 kg.
It can be seen that spherical powder is produced when the ratio is smaller than /sec, m.

For reference, when using a circular nozzle as disclosed in Japanese Patent Publication No. 43-6389, the apparent density is 3.2 g/cmZ, as shown for reference in Figure 3. Regularly shaped powder was produced. The flow rate at this time is 2.8 kg
/sec.

In any of these cases, the average particle diameter is 70μ
-It was.

The relationship between the intersection angle of the liquid spray and the apparent density of the powder in this example is summarized in a graph in FIG. 4, where:
In order to maintain a constant distance along the spray flow between the tip of the nozzle tip and the molten metal flow, the length of the socket 8 shown in FIG. 1 was set to 11 nodes. The spray pattern seen from above was fan-shaped, and a nozzle tip with a center angle of 25'' was used.

From the results shown in Figure 4, it can be seen that the spray intersection angle needs to be 25" or more to obtain spherical powder. This is because when the spray intersection angle is small, the spatial density of the liquid mist increases. , this is interpreted to be because the powder is rapidly cooled.

Example 2 In this example, metal powder was produced by repeating Example 1, except that an NCF IB alloy similar to Inconel 600 M, which is a corrosion-resistant and heat-resistant superalloy, was used as the molten metal, and the molten steel temperature was 1430 ° C. .

At this time, the relationship between the flow rate per unit width of the liquid spray and the apparent density of the produced powder was determined, and the results are summarized in a graph in FIG.

In the case of FIG. 5, an apparent density of 4.8 g/cmff or more was considered to be spherical.

As is clear from the results shown in Figure 5, the appropriate spray flow rate is 55 kg/s in order to generate spherical powder.
It can be seen that the value is less than ec-m.

(Effects of the Invention) As detailed above, according to the present invention, powder having generally contradictory characteristics such as fineness and spherical shape can be realized by a relatively simple means of simply adjusting the atomization conditions. It must be said that the present invention has great significance in view of the current situation where spherical and fine particles are strongly desired.

[Brief explanation of drawings]

FIG. 1 is a schematic diagram of an apparatus for carrying out the method according to the invention; FIG. 2 is a schematic diagram showing an example of a spray pattern; and FIGS. 3 to 5 are embodiments of the invention. This is a graph summarizing the results.

Claims (1)

[Claims] In a method of manufacturing metal powder by pulverizing vertically flowing molten metal by a pair of flat liquid sprays that are injected in opposition to each other and cooling the metal powder, a molten metal that is vertically flowing down is crushed by a pair of flat liquid sprays that are injected in opposition to each other, and is cooled to produce metal powder. A method for producing fine spherical metal powder, characterized in that the liquid flow rate per unit width in a cross section is 55 kg/sec·m or less, and the intersection angle of these liquid sprays is 25° or more.