JPS60138008A - Production of metallic powder - Google Patents

Abstract

PURPOSE:To reduce metallic powder which is less oxidized and has an excellent grain size distribution and particle shape by blowing an inert gas in the form of liquid to the molten metal flowing in an inert atmosphere at a specific ratio and recovering the molten metal in the powder state. CONSTITUTION:The molten metal 2 contained in a melting furnace 1 is dropped through the central hole of an atomizer nozzle 3 into an atomizing tank 4. The molten metal is pulverized by the jet 5 of a liquid gas (>=one kind among liquid nitrogen, liquid argon and liquid helium) ejected from the same nozzle 3 in the mid-way of said dropping. The weight ratio of the liquid gas with respect to the metal 2 is made >=0.3%. The pulverized particles are quickly cooled and solidified and dropped into a cooling medium 6 (water, oil, etc.) in the tank 4. The liquefied gas is separated from the powder by a solid-liquid separator 7 after cooling and the powder is contained in a product tank 8. The metallic powder contg. less impurities is thus obtd.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to a method for producing gold B powder by liquid atomization.

(Prior Art) Conventionally, a technique for producing metal powder by impinging a jet of gas, water, or oil as an atomizing medium on a molten metal stream is well known as the so-called atomization method.

A gas atomization method (hereinafter referred to as a gas atomization method) uses a gas as an atomization medium, and in that case, if an inert gas or a reducing gas is used as an atomization medium, powder with a low oxygen content can be produced. However, since the cooling rate with gas cooling is slow, it takes a relatively long time for the molten metal to cool down to the recovered powder. It becomes something big. In addition, since the spray medium is a gas and has a small mass per unit area, it is difficult to form powder.

On the other hand, in the water atomization method using water as the atomizing medium, the cooling rate is high, the powder has an irregular shape suitable for powder compaction, and the crystal grains are fine, but oxidation of the powder during atomization treatment is unavoidable. A subsequent reduction step is essential. In particular, C
In the case of powders containing easily oxidizable metals such as r, Mn, Ti, Nb, and V, it is difficult to reduce them.

Incidentally, recently, an oil atomization method using oil as a spray medium has been proposed. This method uses oil as a spray medium, so the cooling rate is high, the particle shape obtained is irregular, and the oxygen content is low. When metals that tend to form carbides are included, carbides are likely to be formed, making it difficult to remove the carbon in subsequent steps.

As described above, the various conventional atomization methods are not necessarily satisfactory, and today, there is a need in the industry for a method for producing metal powder that has the following advantages.

(1) A manufacturing method that does not contain oxygen or carbon as impurities.

This is to prevent impurities from being mixed in during the atomization process that would particularly reduce the strength of the final product after powder molding. Incidentally, the inclusion of small amounts of inert components such as N2, Ar, and lle poses fewer problems than the above-mentioned elements, so although small amounts of inert components are unavoidable, it is desirable that they be as small as possible.

(2) A manufacturing method having a cooling rate at least higher than the gas atomization method, preferably at a cooling rate comparable to the current water atomization method or oil atomization method.

This is because the cooling rate should be fast so that the uniform dispersion of precipitates due to rapid solidification, which is one of the characteristics of the powder method, which is a type of metal forming method, can be fully utilized.

(3) A manufacturing method capable of producing powders ranging from fine powders as fine as those produced by the current water atomization method and oil atomization method to powders as fine as those produced by gas atomization methods.

This is because it is necessary to have a wide range of particle size distribution, from coarse to fine, in order to accommodate various uses, and being able to do so is effective in increasing the economic efficiency of the manufacturing method.

(4) A manufacturing method that can produce a wide range of powders from spherical to irregular shapes depending on the atomization conditions.

Since the shape may range from irregular to spherical depending on the purpose, it is essential to be able to produce both irregularly shaped and spherical powders in order to increase the economic efficiency of the production method.

(Object of the invention) Thus, the object and intention of the present invention is to achieve the above-mentioned (1).
An object of the present invention is to provide a method for producing metal powder that can satisfy all of the requirements in (4).

Another object of the present invention is to use a spray medium that has completely different properties from water, oil, or various gases conventionally used, and to produce metal 15) powder that is less oxidized and has an excellent particle size distribution and particle shape. An object of the present invention is to provide a method for manufacturing.

(Summary of the Invention) As a result of many years of research, the present inventors have hereby found that liquid nitrogen, liquid argon, liquid helium, and other undisturbed gases in a liquid state (these are collectively referred to herein as All of the above requirements are met by using liquefied gas (called "liquefied gas") in a liquid state, spraying an appropriate amount of it in a jet stream toward the molten metal stream, and recovering the powder without introducing any impurities. The present invention was completed by discovering that

Thus, the present invention provides at least one member selected from the group consisting of liquid nitrogen, liquid argon, and liquid helium toward the flow of molten metal flowing down under an inert atmosphere in a weight ratio relative to the flow rate of the molten metal. This method of producing metal powder is characterized in that the molten metal is recovered in a powder state by spraying in a jet form at a liquefied gas flow rate ratio of 0.3 or more.

The molten metal may be a single metal or an alloy, such as steel, and is not particularly limited.

The metal thus powdered according to the present invention may be cooled in a container isolated from the atmosphere using the same coolant as the spray medium, or may be cooled with water or oil.

As a further alternative, the metal powdered according to the invention may be cooled with water in a container isolated from the atmosphere and then treated to remove water by vacuum dehydration or solvent washing. Furthermore, the product may be cooled with oil instead of water, deoiled if necessary in a solid-liquid separator, and then treated to be degreased by solvent washing and heating in a non-oxidizing atmosphere.

(Aspects of the Invention) The reasons for limiting each treatment step in the present invention as described above are as follows.

In the present invention, at least one selected from the group consisting of liquid nitrogen, liquid Arbon, and liquid helium is used as the atomizing medium, because all of these are inert elements and liquids. by.

First, since it is inert, there are no impurities mixed in that would particularly reduce the strength of the product during atomization. Unlike the water atomization method and oil atomization method, oxygen and carbon are not mixed in, and the cooling rate is faster than the gas atomization method.
, total, lie gas, etc. are extremely rare.

Furthermore, since it is a liquid, its mass per unit volume and specific heat are much larger than those of gas, and in addition, there is also the heat removal effect due to the latent heat of vaporization accompanying evaporation that occurs during powdering, and the cooling rate is lower than that of the gas atomization method. is significantly faster than.

Comparing the water atomization method, oil atomization method, and the method of the present invention with respect to the cooling rate, the mass and specific heat of the spray media of each method are approximately the same. In the case of the present invention, although the temperature of the liquid of the spray medium itself is low, the latent heat of vaporization is small, so the cooling rate is about the same under the same atomization conditions.

As mentioned above, since the liquid gas used in the sixth aspect of the present invention has a mass close to that of oil and water, the required mass flow rate for obtaining fine powder can be easily obtained. Regarding the shape, in the case of the present invention, the quality of the spray medium, cold performance, and 11 performance are both close to those of the water and oil atomization methods.
5) can be molded.

The reason for setting the liquid gas flow rate/molten metal flow rate at the time of atomization to a weight ratio of 0.3 or more is as follows.

When pulverizing a molten metal flow with liquefied gas, the first thing that needs to be done is that if the liquefied gas flow rate is too small compared to the molten metal flow rate, not only will the pulverization be insufficient, but the particles that have been pulverized will stick to each other. That's true. The condition is that the liquefied gas flow N/
It has been experimentally found that a molten metal flow rate of 0.3 or more by weight is required. Generally, it is sufficient if it is 0.3 or more,
It can be appropriately selected depending on the particle size distribution of the target powder. Hereinafter, this flow rate ratio (weight) of liquid gas to molten metal will be simply referred to as the "atomization ratio" for convenience.

The invention will now be further explained in connection with the drawings.

FIG. 1 is a flowchart 1 showing the basic steps of the method according to the present invention.

FIG. 2 is an explanatory diagram schematically showing an example of a device used in the present invention.

The method of the present invention generally includes a liquefied gas atomization step in which the liquid gas is atomized at a liquid gas flow rate/molten metal flow rate ratio (gravity 1) of 0.3 or more; vJ:11 It consists of a cooling process of cooling the shattered powder and a separation process of the coolant used for cooling.

To explain this in detail, as shown in Fig. 1, the molten metal that has been cleaved into the target components in the raw material melting and refining stage I is then sent to the liquefied gas atomizing stage II, where the atomization ratio is 0.3 or more, preferably 0.8. Under the above conditions, a jet flow of liquefied gas collides downstream to powder the molten metal. The shape and particle size distribution of the final product of the metal powdered in this way
Depending on the ingredients contained, etc., the product is sent to either the liquefied gas cooling stage (2), the water cooling stage (2), or the oil cooling stage (2).

As described above, cooling means include cooling methods using liquefied gas and cooling methods using water and oil. There are vacuum degassing methods, solvent cleaning methods, heating methods in a non-oxidizing atmosphere, etc. corresponding to each cooling method.

The vacuum degassing method is a method in which the coolant deposited at the end of the process is removed by vacuum suction at room temperature or while being slightly heated, and the purpose is to remove moisture without oxidizing it. The solvent cleaning method is a method of removing the coolant by washing the coolant with a solvent that has a lower boiling point and has no adverse effects.
) was first washed with benzene C6I16 (boiling point 80°C, 5°C), and then washed with ethyl ether (02H5)20 (boiling point 34.6°C), and the last adhering ethyl ether was removed by natural evaporation and degassing evaporation. This is the way to do it. The method of heating in a non-oxidizing atmosphere is a method of removing the coolant by heating the powder to a temperature higher than the boiling point of the attached coolant in an inert gas or reducing gas atmosphere.

In this way, as shown in FIG. 1, the product is made into a finished product after passing through the cooling step (1) in liquefied gas and then leaving it as it is or going through the vacuum degassing step (15). The powder that has passed through the underwater cooling step (2) may be made into a finished product after passing through the solid-liquid separation step (2) as needed or by passing through the vacuum degassing step (2) or the solvent washing step (2) as described above.

Furthermore, the powder that has passed through the oil cooling step (■) may be processed as a finished product after passing through a solid-liquid separation step (■) as required, or after passing through the aforementioned solvent washing step (■) or non-oxidizing atmosphere heating step (■).
Ru.

FIG. 2 schematically shows an example of an apparatus for carrying out the method according to the present invention.

As shown in the figure, the molten metal 2 accommodated in the melting furnace or tumbler 1 flows down through the center hole of the atomizer nozzle 3 and falls into the atomizing tank 4. On the way, the molten metal 2 is also liquefied which is spouted from the atomizer nozzle 3. It is pulverized by the gas jet 5. The powdered particles are rapidly cooled and solidified and fall into the cooling medium 6 in the atomization tank 4.

This cooling medium 6 may be the same substance as the spray medium, that is, ltX gas, or may also be water or oil.

Alternatively, depending on the type of metal to be powdered, no cooling medium may be used. This cooling medium is selected based on the melting point of the metal to be treated, the desired properties of the metal, etc. The illustrated example is an example in which the same liquefied gas as the spray medium is used as the coolant.

After cooling, the powder is transferred to solid-liquid separator 7 along with some liquefied gas.
It is separated from the liquefied gas and stored in the product tank 8. Further, the fine powder flowing into the exhaust gas system together with the liquefied gas evaporated during atomization is stored in the product tank 8 through the cyclone 9. During atomization, the powder flowing into the overflow tank 10 together with the overflowing liquefied gas is stored in the product tank 8 either through the solid-liquid separator 7 or as it is, depending on the situation.

The flow of liquid gas in the illustrated example is as follows.

High pressure (10 to 500 atmospheres) by high pressure pump for liquid gas
The liquefied gas passes through the atomizer nozzle 3,
It flows down into the atomization tank 4. Next, it flows into the atomization tank 4 through the same pre-caulked pipe and is mixed with the coolant 6 which is the same liquefied gas stored therein, and the part that flows out to the overflow tank 10 and the part that remains in the tank are collected by the solid-liquid separator 7. It is further divided into a portion that becomes a gas during the Amize treatment and is sent to a gas liquefaction system 12 through a compressor 11 after passing through a cyclone 9 through an exhaust gas system.

The liquefied gas discharged from the overflow tank 10 and the solid-liquid separation tank 7 is also sent to the gas liquefaction system 12 through the pump 13. The liquefied gas, which is recycled into a liquid state in the liquefaction system 12 and from which impurities have been removed, is sent together with new liquefied gas for replenishment to the atomizer nozzle 3 again as an atomizing medium by a high-pressure pump 14. In the figure, the symbol "Q" indicates a powder cutting device.

Next, the present invention will be further explained in connection with examples.

Inkool 71 according to the method of the present invention under the conditions shown below.
8 composition alloy powder is shown in Figure 2, the same 5 kg/ch
Manufactured using large-scale experimental equipment. As the liquefied gas used, liquid nitrogen was used only as shown in Table 1.

The same liquid nitrogen as the spray medium in Table 1 was used as the cooling medium, and liquid nitrogen and moisture adhering to the powder were removed by a solvent cleaning method using benzene and ethyl ether.

The properties of the powder obtained in this example are shown in Tables 2 and 3. Table 2 shows the alloy composition, and Table 3 shows the particle size distribution.

Table 2 Table 3 ■ According to the results of microscopic examination of the injected powder 15), a slightly irregular shape similar to that of powder obtained by oil atomization was obtained. A solidification structure corresponding to a cooling rate of 102 to 103°C/sec was also obtained. Note that the cooling rate in the gas atomization method is usually 10°C/sec.

As is clear from the above results, according to the present invention, all of the following conditions can be satisfied.

(i) Less contamination of impurities.

(11) The cooling rate is sufficiently fast.

(iii) Particle size distribution is comparable to powder obtained by water atomization method or gas atomization method, and is sufficiently finer than powder obtained by gas atomization method.

(1v) Irregular shapes can also be obtained.

In this example, 50Cr-5ONi alloy powder was produced according to Example 1.

The liquefied gas used was liquid argon in the amount shown in Table 4.

As the cooling medium in Table 4, an organic solvent with a low melting point was used, and the removal of the adsorbed solvent was carried out by a vacuum degassing method.

The powder properties obtained in this example are shown in Tables 5 and 6.

Table 5 shows the alloy composition, and Table 6 shows the particle size distribution. Comparing the composition of the molten metal and the composition of each powder (U), they are almost the same composition, and it is clear that according to the present invention, there is virtually no contamination of C, O, N, etc. be.

According to the results of microscopic observation of the obtained metal 15) powder in Table 6, in Case 1, the shape was close to spherical, as in the case of the gas atomization method, and in Case 2, the shape was close to irregular. It's iq. Also, regarding the solidification structure, the cooling rate is 10℃/
sec or more has been obtained.

As is clear from the above results, according to the present invention, the following conditions can be satisfied.

(i) Less contamination of impurities.

(ii) The cooling rate is also higher than that of the gas atomization method.

(iii) Particle size distribution can also be controlled by changing the flow rate of liquid argon.

(1v) Shapes can range from irregular shapes to spherical powders.

[Brief explanation of drawings]

1 is a flowchart of a method according to the invention; and FIG. 2 is a schematic illustration of an apparatus implementing the invention. 1: Melting furnace 2: Molten metal 3: Atomizer nozzle 4: Atomizing tank 5; Liquid gas jet 6: Coolant

Claims (1)

[Claims] towards the flow of molten metal flowing down under an inert atmosphere.
At least one selected from the group consisting of liquid nitrogen, liquid argon, and liquid helium is sprayed in a jet form at a liquefied gas flow rate ratio of 0.3 or more by weight to the flow rate of the molten metal, so as to produce the molten metal. A method for producing metal powder, which comprises recovering metal powder in a powdered state.