JPS61194104A - Method for atomizing molten metal - Google Patents

Abstract

PURPOSE:To atomize stably and efficiently a large amount of molten metal by obliquely spouting two fan- or trough-shaped jets of fluid having concaved upper sides downward from confronting positions and by feeding a downward flow of molten metal to the intersection of the jets. CONSTITUTION:Atomizing medium nozzles 7, 7 are placed opposite to each other, and fan-shaped jets 8, 8 of fluid having concaved upper sides are obliquely spouted downward from the nozzles 7, 7. Though the intersection 8b of the jets 8, 8 is a straight line when it is seen from a position right above it, both ends of the intersection 8b are positioned above the central part when the intersection 8b is seen from the side, and a conical part is formed at the central part. A downward flow 5 of molten metal is then fed to the central part of the intersection 8b. The molten metal is atomized by contact with the atomizing fluid as shown by a symbol 2b.

Description

DETAILED DESCRIPTION OF THE INVENTION (Industrial Application Field) The present invention relates to a method for producing metal powder, and more particularly to a method for atomizing molten metal for producing metal powder using a liquid atomizing medium.

(Prior Art) Conventionally, as a method for producing metal powder, the C1 atomization method, that is, the molten metal atomization method in which powder is obtained by atomizing and cooling molten metal by spraying a high-speed atomizing medium, has been used in the production of a wide range of molten metal powders. ing.

According to the molten metal atomization method, if the metal is meltable,
It is possible to powderize almost any metal, the alloy composition can be freely selected, and metal powder can be produced in large quantities at relatively low cost.

There are cases where a liquid is used as an atomizing medium for atomizing and cooling molten metal, and there are cases where a gas is used, but generally a liquid is often used when producing metal powder for powder metallurgy. This is because while the powder injected with gas is spherical, the powder obtained with liquid has a complex shape that looks like a combination of small spheres, which makes it difficult to obtain a compact by molding. This is because the strength of the green compact is increased, making it extremely suitable as a metal powder for powder metallurgy.

Furthermore, when a liquid spray method is used, it is easy to increase the speed of the Kurape spray medium jet when a gas is used. Therefore, it is relatively easy to atomize the metal powder.

Furthermore, the method of using C water as the atomizing medium is an excellent method in which a large amount of powder can be produced at low cost, and is generally used.

As mentioned above, by using a liquid spray medium, it is possible to inexpensively and efficiently produce metal powder for powder metallurgy, which has an appropriate particle size of 80 to 825 mesh (5% or more) and has excellent compressibility, formability, and sinterability. be able to. In the liquid atomization method, which is typified by the water atomization method, a molten metal stream is bombarded with a high-speed plate-shaped or droplet spray medium of several tens of degrees to aOO'l/sea from the surroundings, and the molten metal is pulverized into fine particles. As the spray medium or metal droplets collide with each other and are cooled, a metal powder with a fine and complex shape is obtained.

In general, the main factors that determine the properties of the resulting metal powder are the shape of the spray medium jet that is ejected from the spray medium nozzle and comes into contact with the molten metal stream, i.e. the spray form, the velocity of the jet, and the feed rate of the molten metal. It is recognized that Especially if the spray foam is not appropriate.
Even if you increase the jet velocity or reduce the molten metal supply rate, fine powder may not be obtained.
Therefore, proper control of the spray form is an important condition in producing metal powder by the atomization method.

As mentioned above, research on spray foam, which is most important in producing metal powder using an atomization method, has been actively conducted for a long time, and various spray foams have been proposed and implemented in the past. Among these conventionally known spray foams, the characteristics and problems of one type of spray foam will be described below.

A first horizontal flat spray form is shown in FIG.

In this spray form, the spray medium jet has a horizontal plane shape as shown by 11, and the molten metal flow 5 is allowed to flow down perpendicularly to the horizontal plane spray medium jet 11. Since it is the simplest shape, nozzle fabrication is easy. This spray form has been used for a long time because it is easy to use, the height of the spray tank is low, and misalignment of the molten metal flow is not a problem, making it relatively easy to obtain powder in equipment manufacturing and operation. It's faded. However, the molten metal that comes into contact with the spray medium that moves horizontally at high speed in the form of a flat plate scatters upward over a wide range without making sufficient contact with the spray medium, and is cooled by the atmosphere during flight, causing coarse particles to form. This is not suitable for producing gold powder for powder metallurgy with a good yield.

Place the second V-shaped flat spray form into the 9th and 10th
As shown in the figure. This spray form is formed by two planar spray medium jets 12 and 18 tilting downward at opposite positions and intersecting each other below, and the intersection I!
The molten metal flow 5 is caused to flow down into the center of the pipe 14.

This v1J! ! The flat spray form differs from the horizontal flat spray 7 ohm in that there are fewer metal droplets that fly upwards without sufficient contact with the spray medium, and the metal droplets that fly upwards come into contact with the spray medium again. Atomized. Moreover, compared to the CSV type flat flat spray form horizontal flat spray 7 ohm, the expansion of the particle size distribution due to the scattering of metal droplets is suppressed, and a high spray efficiency can be obtained.

In order to obtain a v-shaped flat spray form, the spray form shown in Figure 9 is obtained by making the slit-shaped nozzles face each other, and the spray form shown in Fig. 10 is obtained by making the slit-shaped spray nozzles face each other. is obtained. When using a fan-shaped spray nozzle, a relatively simple nozzle header can be used, and the spray device can be easily obtained. .

However, since this V-shaped flat spray is a combination of sprays from two directions, the width of the spray must be widened in order for the spray medium to catch the metal droplets scattered in the direction of the intersecting line of the spray medium. The disadvantage is that it does not. However, when the width of the spray is widened, it is necessary to increase the flow rate of the spray medium, but the end of the spray
This only acts to re-micronize the scattered metal droplets, does not significantly contribute to spraying, and has a problem in that the efficiency of using the spray medium is low.

In view of the various problems mentioned above, an inverted conical spray form as shown in FIG. 11 has been proposed.・.

This sprayform is generally obtained by means of an annular slit nozzle, which directs the molten metal stream into a focal point 16 of an inverted conical spray medium jet 15.

Since the spray medium jet 15 is concentrated at the focal point 16, there is sufficient contact between the molten metal and the spray medium, and even if metal droplets are scattered in all directions due to contact with the spray medium, these metal droplets will not fall. Almost all of the liquid is atomized again as it comes into contact with the atomizing medium again. Therefore, the inverted conical spray foam can be said to be an excellent spray foam with less generation of coarse particles.

However, the spacing between the annular slits used to generate the inverted conical spray form is narrow, and high-precision machining is required to obtain the appropriate spacing. In addition to applying force in the direction in which the C slit expands, it is also affected by the spray medium supply piping.
There is a problem in that it is difficult to maintain a stable and uniform slit interval.

Therefore, in order to stably obtain a uniform spray medium film using the C1 annular slit nozzle, Japanese Patent Publication No. 43-688
As described in Publication No. 9, it becomes necessary to improve the internal structure.

As described above, the annular slit nozzle has the drawback that it is difficult to form a uniform spray medium jet film, and the nozzle structure becomes complicated.

In addition, when the molten metal flow 5 deviates from the focal point 16 where all the spray medium is concentrated, the spray medium and the molten metal droplets collide with each other, causing the inverted cone-shaped spray 7 ohm to move upward, that is, toward the annular slit nozzle. Another disadvantage is that metal droplets are easily blown up, and in severe cases, they adhere and accumulate inside the nozzle, making it difficult to continue spraying.

Furthermore, even with similar spray forms, the same amount of water per unit of molten metal, and the same spraying medium velocity, the smaller the sprayform, that is, the shorter the length of the spraying medium jet, the faster the melting velocity of the spraying medium. Since there is little attenuation and expansion before colliding with metal, the energy of the spray medium effectively works for atomization and atomization is possible.

Therefore, when it is desired to obtain a large amount of fine metal powder, an excellent method is to flow a large number of molten metal streams and atomize each molten metal stream with a small spray of 7 ohms.

However, in practice it is not easy to direct the molten metal stream to the focal point of each of a large number of spray forms, especially in the case of inverted conical sprays. In other words, due to thermal expansion of the tundish holding the molten metal, the position of the molten metal 4 downstream nozzle provided at the bottom of the tundish may shift from the position of the spray form, and the inverted conical In the case of a spray form, it is difficult to direct a separate stream of metal to each focal point, since it is necessary to direct a stream of molten metal to each focal point.

In addition, in the case of an inverted conical spray form, as mentioned above, metal droplets tend to scatter upwards, and when making an inverted conical spray form small, it is structurally necessary to The pores become particularly small. Therefore, the nozzle hole is likely to be clogged due to upward scattering of metal droplets due to defocus, making it difficult to continuously produce metal powder.

Compared to a cone-point or inverted conical spray form, in a V-shaped spray form, the intersection of the spray medium is a line rather than a point, so it is not a big problem for the molten metal flow to deviate from the center of the intersection line in the cross direction. There is an advantage.

(1 point while the invention is trying to solve) As mentioned above, the important point in the method of manufacturing metal powder by colliding a high-speed jet of atomizing medium with a molten metal stream, turning it into droplets and cooling it, is , the point is to select a suitable spray 7 ohm, which has a short jet length of the atomizing medium and prevents the metal droplets from dispersing outside the spray so that the metal droplets flying from the impact point can be crushed again. It is desirable that the shape is such that two or more streams of molten metal can be sprayed at the same time. However, as mentioned above, conventionally;
Each spray form has its advantages and disadvantages, and a 7 ohm spray that satisfies the above conditions has not been obtained.
When producing a large amount of powder inexpensively and efficiently using the molten metal Ff4=a method, there are problems such as generation of coarse particles, loss of spray energy, and low production speed.

(Means for Solving the Problems) In view of the above-mentioned problems, the present invention provides a method that makes it possible to stably and efficiently atomize a large amount of molten metal using 14 jet nozzles with a simple structure. with the purpose of providing
According to the present invention, the fan-shaped or trough-shaped liquid jets 211 having a concave curved surface on the upper side are made to face each other and are inclined downward.
The molten metal is atomized by flowing down onto the intersection line of these liquid jets.

(Function) According to the present invention, a spray form having a linear intersection formed by two fan-shaped or trough-shaped jets having a concave curved surface on the upper side is formed, and this spray form is formed by a molten metal flow and a liquid jet. The molten metal droplets scattered upward from the collision point contact again when they fall, and have the effect of pulverizing these molten metal droplets. is formed in a linear shape, so when two or more molten metal streams are made to flow down from the same molten metal holding container and each of these metal streams is atomized,
There is no problem even if the position of the molten metal flowing nozzle changes slightly due to thermal expansion or the like.

(Embodiment) FIG. 1 shows an example of an apparatus for carrying out the present invention, in which C, 1 is a ladle, and 2 is a tundish-like tundish for receiving and holding molten metal 8 from the ladle 1. In the illustrated example, in the metal holding container, two molten metal flow nozzles 4, 4 are arranged in parallel at the bottom of the tundish 2, and two molten metal flows 5, 4 are installed in parallel.
5 is caused to flow down, and spray medium nozzles 7 provided in spray medium headers 6 and 6 are disposed on both sides of each molten metal stream 5 as shown in FIG. Curved surface 8a
The fan-shaped liquid jets 8, 8 having the following characteristics are injected at a downward angle to the molten metal flow 5, and the linear intersection of these liquid jets 8, 8 or the center of the intersection line 8b is injected as shown in FIG. 2(a). It is configured to cause a molten metal flow 5 to flow down as shown in FIG. Thereby, the liquid jets 8, 8 collide with the molten metal stream 5, the molten metal is atomized, cooled and solidified, and metal powder is formed in the spray tank 9 and deposited therein as shown at 10.

Since the liquid jet 8 has an upward concave curved surface, its intersection @sb
When viewed from directly above, it is a straight line as shown in Figure 2(a), but when viewed from the side, as shown in Figures 2 (middle) and (C), both ends of the intersection line 8b of the liquid jet 8 are in the center. It is located at a higher position and has a mortar shape in the vicinity where the molten metal flow 5 flows down.

Therefore, similar to the traditional inverted conical spray form,
The metal droplets scattered above °C by the spray liquid are also shown in Figure 2 (
As shown in 2b in 0), the particles are atomized by contact with the spray liquid.

As described above, the spray foam according to the present invention, like the conventional inverted conical spray foam, is an excellent 7-ohm spray that makes it easy to obtain fine powder with less generation of coarse particles.

Further, according to the present invention, the complexity of the spray nozzle, which is a problem with conventional inverted conical spray forms, can be avoided, especially when using the fan-shaped liquid jet shown in FIG. In addition, when using a gutter-like liquid jet as shown in Figure 4, the odor (C) also sludges at the end of the slit.
It is possible to prevent the expansion of [, and the slit interval is unlikely to fluctuate, making stable spraying possible.

Furthermore, the spray form of the present invention can simultaneously unite two or more molten metal streams 5 as shown in FIG. 5, similar to the conventional V-shaped spray form.

FIG. 6 shows a spray medium nozzle 7 that can be used to obtain a fan-shaped jet with a concave upper side as shown in FIG. 3, and '7a indicates the nozzle opening. FIG. 7 also shows a spray medium nozzle 7 that can be used to obtain a trough-like jet with a concave upper side as shown in FIG.

As mentioned above, conventional inverted conical layer spray forms are difficult to focus, and metal droplets are particularly prone to flying upwards when the molten metal stream is defocused, making it difficult to focus multiple molten metal streams in a series. Although it is difficult to atomize using a spray medium nozzle of It is a straight line, and even if the C molten metal flow deviates on this straight line, it will not cause a major hindrance to spraying.

Alternatively, it is possible to spray two or more molten metal streams at the same time by installing as shown in FIG. Therefore, 'C1; shorten the length of the jet of the tributary medium, that is,
It is possible to produce a large amount of powder in a short time under conditions that allow fine powder to be obtained.

The cross-sectional shape of the fan-shaped or trough-shaped jet according to the present invention preferably has an arc angle α (see FIG. 2) of 20° to 120°. The reason for this is that when the arc angle α is smaller than 20', the height at both ends of the intersection line is low, which is the feature of the present invention.
It is difficult to catch the metal droplets scattered in the direction of the intersection line of the medium, and the effect of the present invention cannot be obtained. Also, if the angle is larger than 120°, the bowl-shaped part becomes deep and collides at the end of the intersection line. This is because there is a problem in that the 7 ohm spray at the center is likely to be disturbed by the spray medium droplets, which may prevent stable spraying.

Further, it is desirable that the angle β (see FIG. 2) between the 7-ohm molten metal stream and the spray medium jet according to the present invention is 8° or more, preferably 2O2 or more. The reason for this is that, as mentioned above, the particle size of the powder produced by the atomization method depends on the velocity of the atomized liquid jet in the shear direction relative to the molten metal flow;
Therefore, in order to produce powder with a high yield, it is desirable that the angle be large, and if the angle β is smaller than 8°, it will be difficult to obtain fine powder even if the flow rate is increased. However, if the angle β between the molten metal flow and the atomized liquid jet becomes too large, the molten metal droplets generated by the collision with the atomized liquid jet tend to scatter upward, so the It is necessary to select the angle.

(Effects of the Invention) According to the present invention, it is possible to stably and efficiently atomize a large amount of molten metal into atomized particles.

[Brief explanation of the drawing]

Fig. 1 is a diagrammatic longitudinal cross-sectional view of a molten metal atomizing device showing one embodiment of the present invention, Fig. 2 is an explanatory diagram of the action of a 7 ohm fan-shaped spray according to the present invention, and Fig. 8 is a diagram of the present invention. FIG. 4 is a perspective view of a trough-like spray form according to the present invention; FIG. 5 is a perspective view showing a plurality of fan-shaped spray forms arranged in a row; FIG. 6 is a perspective view of a fan-shaped spray form according to the invention; Figure 7(a) is a perspective view of the spray medium nozzle used to form a 7-ohm spray; Figure 7(a) is a bottom view of the spray medium nozzle used to form a 7-ohm gutter spray; The plan view and FIGS. 8 to 11 are perspective views of a conventional spray foam. 1... Ladle 2... Tundish 3... Molten metal 4... Nozzle for molten metal flow 5... Molten metal flow 6... Spray medium header 7... Spray medium nozzle 8...・Liquid jet 9... Spray tank 10... Metal powder Fig. 2 (ab (1)) (C) Fig. 3 Fig. 4 b Fig. 5 Fig. 7 (a) (1D)

Claims (1)

[Claims] 1. Two fan-shaped or gutter-shaped liquid jets with a concave curved surface on the upper side are injected downward at opposing positions, and the molten metal flow is caused to flow down on the intersection line of these liquid jets to form a mist of molten metal. A molten metal atomization method characterized by: