JPH04325605A - Method for controlling apparent density of metal powder produced by liquid atomization - Google Patents

Abstract

PURPOSE:To quantitative control the apparent density of a metal powder without changing the grain size and distribution by adjusting the flow rate of the gas passing in the vicinity of the injection port of a jet injection nozzle. CONSTITUTION:A falling flow 2 of molten steel is injected from a tundish 1. A water jet 3 is injected from a water jet injection nozzle 4 of inner diameter 1D, concentrated at the point (f) of intersection and collided to atomizer the falling flow 2 of molten steel. The flow rate of the gas is fluctuated for each atomization in the vicinity of the nozzle 4. The flow rate of the gas is intentionally controlled to control the apparent density of the steel powder. The gas pressure at the injection port of the water jet 3 is measured to obtain the gas flow rate, and the flow rate is controlled by adjusting the flow rate of the gas to be delivered by a blower 6.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method of controlling apparent density when producing metal powder by atomizing a molten metal injection stream with a liquid jet.

0002

2. Description of the Related Art A liquid atomization method using a liquid as a jet medium has been widely adopted on an industrial scale as an efficient method for producing metal powder. Metal powder produced by the liquid atomization method is refined and melted in a ladle or a ladle of molten metal in a converter, open hearth, arc furnace, induction melting furnace, resistance heating furnace, or melting furnace that uses plasma, electron beam, laser, etc. as a heat source. The molten metal is poured into the tundish through a tub or directly, and allowed to flow vertically downward from a molten metal nozzle with a hole diameter of approximately 1 to 100 mmφ provided at the bottom of the tundish, and 2000 kgf/ The falling flow of molten metal is pulverized by spraying a liquid jet at a flow rate of up to 40 m3/min under a pressure of up to about cm2, followed by deliquification, drying, sieving, and reduction and softening as necessary. It is manufactured through various steps of annealing, crushing, and sieving. Apparent density is one of the most important properties in the production and use of metal powders. For example, the apparent density of metal powder for powder metallurgy when it is filled into a mold greatly affects fluidity, compressibility, formability, sinterability, and mechanical and physical properties of the sintered material. Therefore, it is necessary to select the apparent density of metal powder depending on the intended use, and it is important for metal powder manufacturers to have manufacturing technology that strictly controls the apparent density according to requirements.

Generally, methods for controlling the apparent density of metal powder in the liquid atomization method include controlling the pressure and flow rate at which the liquid jet is injected, the distance from the injection port to the powdering point, and the angle between the molten metal injection flow and the liquid jet. There are methods such as adjusting the injection flow rate and physical properties of molten metal, but these methods have the problem that not only the apparent density but also the particle size and particle size distribution vary greatly.

On the other hand, in Japanese Patent Publication No. 1967-1967,
A method is disclosed for adjusting the apparent density of, for example, water atomized stainless steel powder by adjusting the temperature of water, which is a liquid medium. However, in the case of continuous mass production equipment that repeatedly uses water for atomization, this method has a problem in that equipment costs and running costs are too high to accurately control the temperature of a large amount of water.

Furthermore, Japanese Patent Application Laid-Open No. 63-183109 discloses that atomized metal particles and a spray medium are mixed in a mixing chamber provided with an impactor at the lower part of a liquid injection nozzle to produce, for example, water-atomized copper particles. An apparatus for reducing the apparent density of powder is disclosed. However, this device is not only limited to the two conditions of "with" and "without" a mixing chamber with an impactor installed, but also quantifies the structure and specifications of the mixing chamber with an impactor installed, and can freely handle metals. It is difficult to control the apparent density of the powder.

[0006] Also, in Japanese Patent Application Laid-Open No. 1-246305,
In an atomization method using a V-shaped liquid jet, in which spray medium liquid is sprayed into opposing left and right flat plates and collided so that the cross section becomes V-shaped, the width of the spray medium is By narrowing the width of the jet at the intersection where the left and right jets collide, for example, water atomized high-speed steel powder (JIS SKH57) can be produced.
A method for lowering the apparent density of is disclosed. but,
This method has the problem that in order to adjust the apparent density of metal powder, a large number of liquid injection nozzles with tapered injection ports with narrower injection tip openings must be manufactured and replaced each time. be.

[0007]

Problem to be Solved by the Invention The present invention solves the above-mentioned problems, and without significantly changing the particle size and particle size distribution.
This was done in order to provide a method for easily and quantitatively controlling the apparent density of metal powder.

[0008]

[Means for Solving the Problems] The present invention provides a liquid atomization method for producing metal powder by adjusting the flow rate of gas passing through an injection nozzle toward an intersection point where liquid jets intensively collide with each other. This is a method for controlling the apparent density of liquid atomized metal powder, which controls the apparent density of metal powder.

[0009]

[Operation] When the particle size is the same, the apparent density of the metal powder depends on the shape of the metal powder. The shape of the metal powder produced by liquid atomization is highly irregular as the molten metal stream is crushed by the liquid jet. If it solidifies as it is, the apparent density will be significantly lower, but it generally does not solidify immediately and requires time to remove heat until it reaches the freezing point in order to transfer heat from the molten metal droplets to the liquid medium. During this time, the molten metal droplets become spherical due to surface tension, and in this process, the apparent density increases. As a result of intensive research into these phenomena during liquid atomization, the inventor of the present invention found that during liquid atomization, the molten metal droplets are highly heated and a vapor film of the liquid medium is formed around them, and this vapor film is transferred from the molten metal droplets to the liquid medium. They also found that this vapor film changes with the flow rate of gas passing through the injection nozzle, changing the rate of heat transfer.

That is, by adjusting the flow rate of the gas passing through this injection nozzle, the rate of heat transfer from the molten metal droplets to the liquid medium can be changed, and the shape of the metal powder during solidification, as well as the apparent density of the metal powder, can be changed. I learned that it is possible to do this. The present invention is based on the above findings, and since the apparent density of the metal powder is controlled by adjusting the flow rate of gas passing through the injection nozzle, the apparent density of the metal powder can be easily varied over a wide range. can be controlled quantitatively and quantitatively.

[0011]

EXAMPLES The present invention will be explained based on examples in which molten steel and water are used as the molten metal and liquid medium, respectively. FIG. 1 shows a conceptual cross-sectional view of a water atomization device (example) for implementing the present invention. A falling stream 2 of molten steel is injected from a tundish 1. The water jet 3 colliding intensively at the intersection f has an inner diameter I
It is injected from the water jet nozzle 4 of D to atomize the falling flow 2 of molten steel. This atomized water flow passes through the discharge pipe 5 at the bottom of the water jet nozzle 4 to the spray tank (
(not shown). On the other hand, water jet nozzle 4
The space between the tundish 1 and the tundish 1 above it is not normally sealed, but in order to prevent oxidation of the molten steel, N2, Ar
In some cases, it is sealed with an inert gas such as When sealing with an inert gas, a blower 6 blows the inert gas around the falling flow 2 of molten steel.

[0012] When molten steel is atomized with a high-pressure water jet, a suction airflow is usually generated near the water jet injection nozzle, but the diameter of the molten steel flow, the atomization conditions,
The flow rate of this gas varies with each atomization, depending on the positional relationship between the injection nozzle and the tundish, the status of the seal gas, and other factors. It is an object of the present invention to control the apparent density of steel powder by intentionally controlling the flow rate of this gas. The flow rate of this gas is determined by measuring the atmospheric pressure Nm at the injection port position of the water jet 3 (lower surface of the water jet nozzle), and can be controlled by adjusting the flow rate of the gas sent by the blower 6. To prevent oxidation of molten steel, an inert gas such as N2 or Ar is used as the gas to be fed, but in the case of simply adjusting the flow rate, air may be used.

Table 1 shows that C; 0.
10% by weight (hereinafter abbreviated as %), Si; 0.015%, M
n; 0.15%, P; 0.015%, S; 0.015%
, Ni; 0.010%, Cr; 0.040%, Mo; 0
．． The water atomization conditions for spraying molten steel with 0.010% and the remainder consisting of unavoidable impurities and the characteristics of the steel powder obtained by spraying are shown below. In this case, N2 was used as the seal gas.

[0014]

[Table 1]

[0015] Steel powder produced by water atomization was dehydrated and dried at 200°C in an N2 atmosphere, and its properties were then measured. The median diameter was determined from the particle size distribution of the sieving method. Moreover, the apparent density was determined by the measuring method of JIS Z2504. Example No. As shown in Figures 1 to 7, the apparent density of the water-atomized steel powder can be adjusted to 3.10 to 3.10 by adjusting the flow rate of the N2 air that passes through the injection nozzle without changing the particle size of the water-atomized steel powder.
It can be adjusted significantly up to 3.81g/cm3. Comparative example No. 9 is Example No. This is the case where the water temperature is high among the water atomization conditions 3, and the apparent density is high because the water temperature is high. In this way, the increase in the atomized water temperature and the increase in the apparent density of the iron powder was determined by the increase in the atomization water temperature. 8
By decreasing the N2 airflow as shown in
Example No. without changing the particle size. The apparent density can be controlled to be the same as that of 3. In contrast, comparative example No. 10-1
As shown in 3, when the apparent density of water atomized steel powder is adjusted by adjusting the water pressure, water volume, molten steel pouring amount, and molten steel temperature, the particle size will vary.

[0016]

According to the method of the present invention, as described above, by adjusting the flow rate of gas passing near the jet nozzle injection port, the particle size and particle size distribution of metal powder can be easily observed without changing it. The hanging density can be controlled.

[Brief explanation of drawings]

FIG. 1 is a schematic cross-sectional view of an apparatus for carrying out the invention.

[Explanation of symbols]

1 Tundish 2 Falling flow of molten steel 3 Water jet 4 Water jet nozzle 5 Discharge pipe 6 Blower 7 Adjustment valve 8 Pneumatic tube 9 Metal powder 10 Liquid level f Intersection of water jets ID Inner diameter of water jet nozzle Nm Water jet nozzle position

Claims (1)

[Claims] Claim 1: In a liquid atomization method for producing metal powder, the apparent density of the metal powder obtained is adjusted by adjusting the flow rate of gas passing through the injection nozzle toward the intersection point where the liquid jets collide intensively with each other. A method for controlling the apparent density of metal powder by liquid atomization, characterized by controlling the apparent density of metal powder.