JPH04276006A - Production of metal powder - Google Patents

Abstract

PURPOSE:To easily produce a metal powder having a specified particle size in high yield by detecting the flow rate of a falling molten metal from the change in the level of the molten metal in a tundish and fixing the ratio of the jetting flow rate of an atomizing medium to that of the molten metal. CONSTITUTION:The molten metal 2 in a tundish 1 is dropped from a nozzle 3 as a molten metal flow 8. The jet 5 of an atomizing medium from the ejection nozzle 12 of a nozzle device 4 is let to strike against the molten metal flow 8 in a atomizing chamber 6, and the molten metal flow 8 is powdered to obtain a metal powder. In this production of the metal powder, the level of the molten metal 2 in the tundish 1 is detected by a detector 28, a pressure control valve 27 is adjusted by a flow controller 29 based on the information to change the flow rate of the jet 5, hence the ratio of the flow rate of the jet to that of the molten metal is fixed, and powdering is performed. In this case, a jet curtain inverse-conically rotated is formed, plural powder recovery devices are provided through a switching valve, and the temp. of the molten metal is preferably kept constant.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing metal powder by an atomization method, in which the resulting metal powder has a narrow particle size distribution and a uniform particle size.

0002

2. Description of the Related Art The so-called atomization method, in which molten metal is pulverized with an atomization medium such as gas or water, is widely used as a method for industrially producing metal powder in large quantities at low cost. As shown in Fig. 7, the atomization method involves storing a molten metal 2 to be powdered in a tundish 1, allowing the molten metal to flow down from a molten metal nozzle 3 attached to the bottom of the tundish 1, and placing the molten metal at the bottom of the tundish 1. Nozzle device 4
In this method, the jets 5 of the atomizing medium injected from the atomizing chamber 6 cross each other in the atomizing chamber 6, and the molten metal flow 8 is pulverized at the intersection, thereby producing metal powder. An annular distribution chamber 10 is formed inside the main body 9 of the nozzle device 4, and the atomized medium that is pressure-fed to the distribution chamber 10 from the supply pipe 11 is sent to the injection nozzle 12 provided on the lower surface of the main body 9.
The jet 5 is ejected from the jet 5 to form a jet curtain having a V-shaped cross section or an inverted conical shape. 13 is a powder collection container.

[0003] Depending on the purpose of the metal powder, for example, in the case of powder for thermal spraying, the particle size is limited to a range of 10 to 45 μm, for example, depending on the ability of the thermal spraying equipment in terms of powder feedability and the density of the formed film. Powder is required. In the future, when manufacturing highly functional powder products in other fields as well, there is a tendency for the particle size distribution of the powder to be often required to have a narrow range.

In this case, when the same metal is atomized using the same nozzle for ejecting the atomizing medium, the particle size of the powder is adjusted based on the temperature of the molten metal, the diameter of the molten metal nozzle, and the injection pressure of the atomizing medium (jet speed and jet flow rate). This is done by changing operating conditions such as (changes at the same time). The average particle size of the obtained powder changes with the injection pressure, but if other conditions are constant, the particle size distribution is almost the same.

[0005]

[Problems to be Solved by the Invention] The current atomization method for adjusting the particle size distribution of powder has the following problems. ■The flow rate of the molten metal is determined by the height of the molten metal in the tundish, the diameter of the molten metal nozzle, and the molten metal temperature.
Since the molten metal height and molten metal temperature change during atomization, the molten metal flow rate changes accordingly. Therefore, when the flow rate of the atomizing medium is constant, the ratio of the flow rate of the molten metal to the flow rate of the atomizing medium changes, so that the particle size distribution of the obtained powder is broadened. ■If the pressure of the atomizing medium is increased for pulverization, the molten metal tends to blow up and the pulverization phenomenon of the molten metal becomes unstable, so the particle size distribution of the obtained powder broadens and becomes coarse powder or acicular powder. There are many cases, making classification difficult. ■The change in the ratio of the molten metal flow rate to the atomizing medium flow rate immediately after the start of atomization is extremely drastic compared to the above-mentioned ratio until the end of atomization, and furthermore, the powdering phenomenon immediately after atomization is extremely unstable. The particle size distribution of the powder is broadened.

The present invention has been made in view of these problems, and it is an object of the present invention to provide a method for producing powder with a narrow particle size distribution during atomization and easily obtaining a high yield of metal powder within a predetermined particle size range. .

[0007]

[Means for Solving the Problems] The manufacturing method of the present invention, which has been made to achieve the above object, includes applying a jet of atomizing medium injected from an injection nozzle to a molten metal flow flowing down from a tundish in an atomization chamber. In a method for manufacturing metal powder by pulverizing a molten metal flow, a molten metal surface position detector is provided to detect the molten metal surface position in a tundish, and the jet flow rate is determined based on the molten metal surface position information from the detector. The structure of the invention is to perform powdering while keeping the ratio of jet flow rate and molten metal flow rate constant by changing the ratio.

At this time, a plurality of jets are injected below the injection nozzle and in contact with an imaginary concentric circle around the vicinity of the molten metal flow to form an inverted cone-shaped jet curtain, and the jets approach each other. It is preferable to flow the molten metal into the formed intersection area and pulverize it. Further, a powder collection container having two storage parts and a switching valve for selectively using one of the storage parts is provided in the atomization chamber,
It is preferable to collect the powder obtained at the initial stage of powdering into one storage section, and then operate the switching valve to collect the powder into the other storage section.

Furthermore, a temperature raising means for raising the temperature of the molten metal in the tundish and a temperature detector for detecting the temperature of the molten metal are provided, and the temperature raising means is operated based on the temperature information from the detector, and the tundish is heated. It is best to keep the temperature of the molten metal contained in the dish constant and powder it.

0010

[Operation] By changing the injection pressure and/or flow rate of the jet while measuring the molten metal level position (molten metal height) in the tundish with a detector (level meter), the ratio of jet flow rate and molten metal flow rate is kept the same. It can be adjusted to become. Therefore, by performing such an operation during atomization, the molten metal flow flowing down from the tundish can be easily powdered to have a predetermined particle size distribution and a predetermined particle size.

Furthermore, when a plurality of jets are injected below the injection nozzle and in contact with an imaginary concentric circle around the vicinity of the molten metal flow to form an inverted conical jet curtain, the jets approach each other. The intersection area formed is
Since the centers of high-energy jets do not interfere with each other, upward flow of the atomized medium is less likely to occur. Therefore, by allowing the molten metal to flow down the intersection area, the blow-up of the droplets is reduced and the operation is stabilized, so the width of the particle size distribution of the powder produced under the specified pressure and flow rate is narrowed. . The individual jets constituting the jet curtain are:
Since the jet is twisted from above to below around the molten metal flow and appears to be swirling, the curtain will be referred to as a swirling jet curtain hereinafter. In addition, in a conventional inverted cone-shaped jet curtain (non-swirling jet curtain), the centers of the jets intersect at the apex of the cone, and the centers interfere with each other, resulting in an upward flow of the atomizing medium and the formation of droplets. blow-up is likely to occur, and operations tend to become unstable.

Furthermore, by using a powder collection container with a switching valve, it is possible to remove the powder obtained during the unstable period of powderization immediately after atomization, thereby obtaining powder with a particle size distribution in an extremely narrow range. be able to. Since the reduction in powder yield due to removal is for a short period of 5 seconds or less, the reduction in powder yield is about several kg, so it is not a problem in a large amount of atomization. Rather, the classification operation to remove initial acicular powder and adhesion of coarse powder is troublesome, and irregularly shaped powder may be mixed into the product, causing quality problems. From this point of view, when the above collection container is used, the operation is simple and the spread of particle size can be easily suppressed.

Furthermore, by operating the temperature raising means based on the molten metal temperature information from the temperature sensor and keeping the molten temperature in the tundish constant, it is easy to control the production of powder with an extremely narrow particle size distribution. Become. That is, when atomizing a large amount, the atomization time reaches several tens of minutes, but during this time the temperature of the molten metal in the tundish decreases. When the temperature of the molten metal approaches its melting point, the physical properties of the molten metal, such as surface tension and viscosity, change significantly in accordance with the temperature change. Therefore, when atomizing under such temperature changes, the state of pulverization of the molten metal by the jet changes significantly. However, broadening of the particle size range of the resulting powder is unavoidable. By keeping the temperature of the molten metal constant, the above-mentioned broadening of the particle size distribution can be easily avoided.

[0014]

DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 shows the main parts of an atomization facility for carrying out the present invention, and the same members as those in the prior art are designated by the same reference numerals. A heater 21 for heating the tundish 1 is provided between the tundish 1 and a cover 22, and a temperature detector 23 for detecting the temperature of the molten metal 2 in the tundish 1 is installed around the tundish 1. It is located at the top. Further, a temperature controller 24 is provided which receives a signal (information) from the temperature detector 23 and controls the output of the heater 21 so that the temperature reaches a preset temperature. On the other hand, a pressure control valve 27 is provided in the conduit 26 that supplies the atomizing medium to the nozzle device 4 , and a molten metal 2 level position detector 28 is provided above the tundish 1 . In addition, the signal from the molten metal level position detector 28 is received to calculate the molten metal flow rate corresponding to the molten metal level, and the jet is calculated based on the ratio between the preset molten metal flow rate and the jet flow rate (supply amount) of the atomizing medium. A flow rate control device 29 is provided that calculates the flow rate and outputs a valve throttle amount corresponding to the flow rate to the pressure control valve 27. Note that a flow control valve may be used instead of the pressure control valve 27.

[0015] Instead of controlling the heater, the amount of molten metal heated from the melting furnace poured into the tundish may be controlled by a temperature controller. The amount of injection can be easily controlled by the amount of tilting of the melting furnace. By using such a device, a constant hot water temperature is ensured regardless of the elapse of the atomizing operation time, and a jet flow rate is applied according to the molten metal flow rate regardless of a drop in the hot water level, so that it can be adjusted to changes in atomization conditions. It is possible to prevent the occurrence of variations in particle size distribution caused by this.

Although conventional nozzle devices can be used, by using a nozzle device that forms a swirling jet curtain, the atomized medium (gas) can be
It is possible to prevent the occurrence of an upward flow toward the molten metal nozzle side, thereby increasing the stabilization of atomization and narrowing the particle size distribution width. FIG. 2 shows an example of a nozzle device 4A for forming a swirling jet curtain, and the injection direction of the injection nozzle 12A is different from that of the conventional device. That is, the main body 9A
A plurality of injection nozzles 12A consisting of nozzle tips are attached to the lower surface of the nozzle at equal intervals on a concentric circle centered on the center line of the flow hole 15. Each injection nozzle 12A is
As shown in Figures 3 and 4, the nozzle center line is aligned with the molten metal flow 8.
It is attached so as to be oriented diagonally downward so as to be in contact with the circumference of an imaginary diameter D around the vicinity of the center,
The center line of each injection nozzle 12A is equidistantly offset from the center line of the molten metal flow (flow hole) in the horizontal direction at an angle of approximately a. In the figure, 16 indicates the outlet of the nozzle hole, and θ indicates the apparent intersection angle of the jet curtain with respect to the center line of the molten metal flow. Note that the injection nozzle is not limited to a nozzle chip having a nozzle hole, but may be one having a nozzle hole directly formed in the bottom wall of the main body.

At this time, the diameter D of the inscribed circle at the position where the center lines of each nozzle (that is, the center lines of the jets) are close to each other is expressed as D/d=1 to 5 (
It is preferable to set the center line of each nozzle so that it becomes 1 to 3). When D/d is less than 1, an upward gas flow tends to occur, and the operation tends to become unstable. On the other hand, if it exceeds 5, the gas flow velocity within the inscribed circle will decrease, which in turn will reduce the pulverization energy, making it easier to produce coarse powder, which will actually widen the width of the particle size distribution.

A good example of a powder collection container attached to the atomization chamber 6 is shown in FIG. The container 13A has two storage portions 33, 33 partitioned by a partition wall 32 inside the container body 31. Partition wall 3
A switching valve 35 is mounted on a horizontal shaft 34 extending horizontally along the upper edge of 2.
is attached, and the horizontal shaft 34 is pivotally supported on the side wall of the container body 31. A handle 36 for rotating the switching valve 35 is attached to the end of the horizontal shaft 34 on the outside of the container body 31. By rotating the handle 36, the switching valve 35 closes one of the accommodating sections 33, 33 defined on the left and right sides of the partition wall 32, and allows communication between the container opening and the other accommodating section.

By using the powder collection container 13A, the powder produced during the unstable period of powdering immediately after the start of atomization and the powder produced in a stable state can be transferred through the switching valve 35 and the handle 36. By rotating the powder, it can be collected into each of the two storage sections 33, 33, preventing mixing of the two and easily obtaining powder with a narrow distribution width. Next, specific examples are listed.

[0020] Under the atomization conditions shown in Table 1, Fe-4
．． 5% carbon steel powder was produced. The diameter of the molten metal nozzle was 3.5φmm in both the example and the conventional example.

[0021]

[Table 1] As a result, the average particle diameter and geometric standard deviation of the obtained powder are shown in Table 2, and the particle size distribution is shown in FIG.

[0022]

[Table 2] From Table 2, it was confirmed that the average particle size of the powders of the examples was equal to or smaller than that of the conventional example, and the standard deviations were all small.

[0023]

According to the method of the present invention, the particle size distribution of powder can be easily narrowed by keeping the ratio of jet flow rate and molten metal flow rate constant during atomization. At this time, by forming a swirling jet curtain with a jet of the atomizing medium, blowing up of the molten metal, which occurs when using a non-swirling jet curtain in which the jets collide, is reduced.
By stabilizing the operation and stabilizing powdering, it is possible to narrow the width of the particle size distribution of the powder produced under a predetermined pressure and flow rate.

Furthermore, by using a powder collection container with a switching valve, powder obtained during the unstable period of powdering immediately after atomization can be removed, and powder with a particle size distribution in an extremely narrow range can be easily obtained. be able to. moreover,
By keeping the temperature of the molten metal in the tundish constant, powder with an extremely narrow particle size distribution can be easily produced.

[Brief explanation of the drawing]

FIG. 1 is a sectional view of essential parts of an atomization device for carrying out the present invention.

FIG. 2 is a sectional view of a nozzle arrangement for forming a swirling jet curtain.

FIG. 3 is a plan view showing a state where injection nozzle center lines intersect.

FIG. 4 is a side view of the same.

FIG. 5 is a sectional view of a powder collection container equipped with a switching valve.

FIG. 6 is a graph showing powder particle size distribution of Examples.

FIG. 7 is a cross-sectional explanatory diagram of the atomization device.

[Explanation of symbols]

1 Tundish 2 Molten metal 5 Jet 6 Atomization chamber 8 Molten metal flow 12 Injection nozzle 12A injection nozzle 13 Powder collection container 13A Powder collection container 23 Temperature detector 28 Hot water level position detector 35 Switching valve

Claims (4)

[Claims] Claim 1: A method for producing metal powder by applying a jet of atomizing medium injected from an injection nozzle to a molten metal stream flowing down from a tundish in an atomizing chamber, thereby pulverizing the molten metal stream and producing metal powder. A hot water level position detector is provided to detect the hot water level position, and the flow rate of the jet is changed based on the hot water level position information from the detector to perform powdering while keeping the ratio of the jet flow rate and the molten metal flow rate constant. A method for producing metal powder, characterized in that: 2. A plurality of jets are injected below the injection nozzle so as to touch an imaginary concentric circle around the vicinity of the molten metal flow to form an inverted cone-shaped jet curtain, and the jets are formed close to each other. 2. The method for producing metal powder according to claim 1, wherein a flow of molten metal is flowed down into the intersection area where the metal powder is pulverized. 3. A powder collection container having two storage parts and equipped with a switching valve for selectively using one of the storage parts is provided in the atomization chamber, and the powder obtained at the initial stage of powdering is collected in one of the storage parts. 2. The method for producing metal powder according to claim 1, wherein the powder is collected in a storage part, and then the switching valve is operated to collect the powder in the other storage part. 4. Temperature raising means for raising the temperature of the molten metal in the tundish and a temperature detector for detecting the temperature of the molten metal are provided, and the temperature raising means is operated based on temperature information from the detector, and the tundish is heated. 2. The method for producing metal powder according to claim 1, wherein the molten metal contained in the dish is pulverized at a constant temperature.