JPH05117724A - Production of metal powder - Google Patents

Abstract

(57) [Summary] [PROBLEMS] To provide a metal powder production method capable of controlling blow-up even when atomizing is performed at an arbitrary spraying angle of 30 to 80 °. [Constitution] In the gas atomizing method, if the pressure in the nozzle box is P ₁ , the pressure in the spray chamber is P ₂ , and the pressure difference (P ₁ -P ₂ ) is ΔP, ΔP is 10 mmHg or more, A method for producing a metal powder, characterized in that the inside of the spray chamber is kept in a constant negative pressure state with respect to the inside of the nozzle box at a constant value within ± 10% at 400 mmHg or less.

Description

Detailed Description of the Invention

[0001]

FIELD OF THE INVENTION The present invention relates to an atomizing method for producing powder from molten metal.

[0002]

2. Description of the Related Art With the recent development of powder metallurgy, methods for producing a molding from powder have been diversified. One of the atomizing methods for producing the raw material powder is that most alloy compositions can be produced, and the shape of the powder from spherical powder to irregularly shaped powder can be controlled relatively easily by selecting the atomizing medium used for atomizing. .. In order to increase the pulverization energy efficiency of this atomizing method, it is most effective to shorten the distance from the spray medium ejecting from the spray nozzle to the collision with the molten metal. In order to shorten this distance, the length from the spray nozzle ejection port to the molten metal can be shortened, and the ring nozzle that is structurally relatively simple and can eject the spray medium from the entire circumference is It is considered to be optimal for effectively using energy. The ring nozzle referred to here is a type of nozzle that has a jet port arranged so as to surround the molten metal flow, and the space above and below the nozzle can be separated by a spray form of a spray medium, and the shape of the jet port is Not limited. The nozzle forms a spray foam that is or has the shape of an inverted cone or an inverted polygonal pyramid. Hereinafter, the apex angle of this spray foam will be referred to as the spray angle.

However, in the case of atomizing with this ring nozzle, a phenomenon called "blowing up" occurs in the conventional method when the spraying angle is around 30 ° or more, and it is impossible to continuously perform atomizing by closing the nozzle. Becomes
The main reason for this is that an upward velocity is generated in the spray medium by increasing the spray angle. The angle at which this blow-up begins to occur is about 45 for those that eject the spray medium from two directions and form a V-shaped spray foam.
In contrast, the ring nozzle has a small angle of about 30 °. This is because the atomizing medium concentrates from all directions,
As the spray medium increases in thickness toward the center,
This is because the vicinity of the spray foam is in a vacuum state, and the actual collision angle is larger than that of forming the V-shaped spray foam.

The atomizing angle discussed above is easy to measure in the case of atomizing using a liquid as the atomizing medium and difficult to measure in the case of gas atomizing. It is generated regardless of the gas. That is, when the atomization angle is increased in both the liquid atomization and the gas atomization, blow-up always occurs in the usual method.

The above is the case where the pressure inside the chamber and the inside of the nozzle box are maintained at substantially the same pressure. For example, the nozzle box has no communication holes for other than the ring nozzle and the molten metal nozzle, and the spray medium is Needless to say, atomization cannot be performed at all even if the inside of the nozzle box is greatly decompressed by the jetting action of the jet as soon as it is ejected from the ring nozzle, even if the angle is less than 30 °.

In addition, Japanese Patent Publication No. 53-33109 and Japanese Patent Publication No. 55-1325
It is necessary to circulate the gas in the chamber and the nozzle box so that the pressure in the nozzle box is almost the same as the pressure in the chamber as shown in No. 2, when performing atomization with the ring nozzle, it is the minimum in both gas atomization and liquid atomization. Although it is necessary, it is not possible to perform highly efficient atomization of about 30 ° or more. That is, in the case of using the conventional technique in which the pressure inside the nozzle box and the inside of the chamber are almost the same, blow-up occurs when the spray angle is about 30 ° or more.

As described above, as a method for avoiding blow-up and allowing atomization, in gas atomization, the actual spray angle is reduced to 30 ° or less by a guide or the like, or the gas is rotated to form a focal point. The method of atomizing without doing is generally performed. Therefore, it is difficult to say that the gas pulverization energy of the general gas is sufficiently utilized, and there are problems that the atomization pressure of the gas is increased more than necessary and that a large amount of gas needs to be used. ..

[0008]

SUMMARY OF THE INVENTION The present invention has been made to remedy the above-mentioned drawbacks of the known conventional methods, in which the upward direction of the atomizing medium is increased by increasing the geometrical atomizing angle which is considered to be the root cause of blow-up. Speed generation, gas atomization,
Regardless of liquid atomization, the pressure difference between the upper and lower sides of the spray foam formed by the atomizing medium ejected from the atomizing nozzle, that is, the pressure difference ΔP between the pressure P ₁ inside the nozzle box 4 and the pressure P ₂ inside the atomizing chamber 5. The present invention has been completed by finding that it is possible to control blow-up even when atomizing is performed at an arbitrary spraying angle of 30 to 80 ° by changing the pressure difference ΔP.

[0009]

The present invention is an atomizing method in which a molten metal is flowed down and pulverized by a spray nozzle using a gas as a spray medium, and an atomizing chamber connected to a spray chamber 5 is used. By exhausting the inside of 5 and circulating all or part of the exhausted gas into the nozzle box 4, it surrounds the ring nozzle 7, communicates with the spray chamber 5 through the ring nozzle 7, and the vicinity of the ring nozzle 7. Let P _{1 be} the pressure in the nozzle box 4 that shuts off the air from the outside air, P ₂ be the pressure in the spray chamber 5, and ΔP be the pressure difference (P ₁ -P ₂ ).
It is a constant value within ± 10% at 10 mmHg or more and 400 mmHg or less, and is a method for producing a metal powder, characterized in that the inside of the spray chamber 5 is kept in a constant negative pressure state with respect to the inside of the nozzle box 4.

[0010]

The method of the present invention will be described below with reference to the drawings. FIG. 1 shows an example of an atomizing apparatus to which the method of the present invention is applied, using nitrogen as a spray medium. The high-pressure spray medium supplied from the spray medium introduction pipe 6 and ejected from the ring nozzle 7 forms an inverted conical spray foam 8. The spray foam 8 becomes a jet 9 in which the atmospheric gas in the spray chamber 5 is entrained and spreads in the spray chamber 5. The external exhaust device pipe 13 communicates with the external exhaust device to exhaust the inside of the spray chamber 5. Further, the atmospheric gas circulation pipe 12 circulates the atmospheric gas and adjusts the pressure inside the nozzle box 4 and the spray chamber 5.
The pressure inside is monitored by a pressure gauge 10.

First of all, the atomizing is performed by the pipe 13 for the external exhaust device.
Fully or half-open the valve provided in the, atmosphere gas introduction pipe 11, atmosphere gas circulation pipe 12, powder drain pipe 14
After fully closing the valve provided in, the operation of the external exhaust device connected to the external exhaust device pipe 13 is started, and the pressure inside the nozzle box and the spray chamber 5 is reduced. In addition,
It is effective to install a device for collecting fine powder between the external exhaust device pipe 13 and the external exhaust device in order to protect the exhaust device and prevent satellite powder from being generated.
At this time, by using the reduced pressure in the nozzle box 4 and the spray chamber 5, the atmospheric gas is introduced from the atmospheric gas introduction pipe 11 so that the nozzle box 4 and the spray chamber 5 are
Can be replaced with the atmosphere gas, and when the replacement is completed, the valve provided in the atmosphere gas introduction pipe 11 is fully closed to shut off the atmosphere.

Next, a high pressure atomizing medium is ejected from the ring nozzle 7. Here, a part of the exhaust gas from the external exhaust device is circulated through the atmospheric gas circulation pipe 12. The balance can be recycled as a gas for atomization. As a result, the pressure in the nozzle box 4 becomes higher than the pressure in the spray chamber 5. At this time, assuming that the pressure in the nozzle box 4 is P ₁ , it is desirable to keep P ₁ at atmospheric pressure or slightly lower than atmospheric pressure for flowing down the molten metal. It is also possible to adjust the amount of molten metal flow down by adjusting P ₁ .

As described above, the pressure in the spray chamber 5 is reduced by the external exhaust device. If the pressure in the spray chamber 5 is P ₂ and (P ₁ -P ₂ ) is ΔP, this differential pressure The optimum value of ΔP varies depending on the spray medium flow rate, spray angle, and spray pressure, but a pressure difference of about 10 mmHg or more is required to achieve a spray angle of 30 ° or more at a pressure of ² kgf / cm ² or more. .. At this time, in order to obtain the required ΔP, it is necessary to have an exhaust device with a sufficient exhaust volume. Generally, in gas atomization, the flow rate of the gas used is as high as 10 m ³ / min or more, so it is difficult to exhaust the inside of the chamber during spraying with a small fan, blower, etc. until it is sufficiently decompressed. In this case, it is necessary to increase the exhaust amount or to operate several exhaust devices in parallel. Even in this case, since spray foam 8 itself is a gas, it is practically difficult to obtain a ΔP of 400 mgHg or more. If the differential pressure ΔP thus obtained is too large with respect to the optimum value, the actual spray angle is reduced and a spray foam in which a large amount of atmospheric gas is entrained is produced, resulting in a decrease in spray efficiency. On the contrary, if it is small, blow-up occurs and atomization becomes impossible.

After setting P ₁ , P ₂ and ΔP to the values that allow stable atomization as described above, the stopper 1 is pulled up and melted from the bottom orifice of the tundish 2 to the center of the ring nozzle 7. Atomize by flowing down metal. When you start atomizing, P ₁ and P ₂ change considerably. This is mainly because the molten metal flows down, so that its volume increases, and the amount of heat of the molten metal heats the inside of the spray chamber 5 to increase the pressure. Further, in order to adjust the atmosphere, the valve of the atmosphere gas introduction pipe 11 may be opened to introduce the atmosphere gas. Due to these reasons, nozzle box 4 and spray chamber 5
If the pressure changes, the valves of the atmosphere gas circulation pipe 12 and the external exhaust device pipe 13 are adjusted to adjust the circulation amount so that ΔP is within ± 10% of the optimum value. This △ P
If the change is ± 10% or more, stable and highly efficient atomization may not be performed due to occurrence of blow-up or a substantial decrease in spray angle. In addition, the fact that such adjustment is possible can also cope with the change in ΔP generated during atomization due to changes in the temperature of the spray medium, changes in the melt flow rate, and other causes. Further, it is also effective to facilitate the control by automatically controlling this valve control.

The powder obtained by atomization is deposited in the lower part of the spray chamber 5 and is recovered by opening the valve provided in the powder discharge pipe 14. As described above in detail, in the method of the present invention, the pressure in the nozzle box 4 is
Let P _{1 be} the pressure in the spray chamber 5 and P ₂ be the pressure difference Δ
P (P ₁ -P ₂ ) is maintained at a constant value within ± 10% when the pressure is 10 mmHg or more and 400 mmHg or less, and the pressure P ₂ in the spray chamber 5 is a constant negative value with respect to the pressure P ₁ in the nozzle box 4. By maintaining the pressure state, it becomes possible to continuously perform highly efficient and stable gas atomization at a spraying angle of 30 to 80 °, which could not be performed conventionally.

[0016]

[Examples and Comparative Examples] The pressure in the nozzle box 4 obtained when nitrogen was used as the atomizing medium by the apparatus shown in FIG.
The relationship between the differential pressure △ P and (P ₁ -P ₂₎ and sprayable region P ₁ and the pressure P ₂ in the spray chamber 5 shown in Figure 2. At this time, the spray pressure is 4 kgf / cm ² , and the flow rate is 16 Nm ³ / min, which is constant. The areas that can be sprayed are the shaded areas and the dotted areas in the figure. With the conventional method, the differential pressure ΔP is almost 0 mmHg, so
At °, blowing up occurs and atomization is not possible, but differential pressure △
As P is increased, atomization can be performed at a larger angle. However, at the same spray angle, the differential pressure Δ
Even if P is made too large, the spray foam spreads, the spray energy decreases, and the gas suction amount increases, resulting in atomization with low efficiency. That is, FIG. 2 shows that in actual atomization, it is necessary to control the differential pressure ΔP at least within the range of the diagonal line according to the spray angle. That is, it can be seen that the spray angle and the differential pressure ΔP have optimum ranges. Also, not limited to liquid and gas,
If the differential pressure ΔP is made extremely large, the molten metal may be dispersed by the sucked gas and adhere to the nozzle inlet, making it impossible to continue atomizing. However, the method of the present invention makes it possible to arbitrarily control the conditions under which atomization can be stably and continuously performed within the range of 30 to 80 °.

Next, nitrogen was used as the atomizing medium and Cu-10% was added to the molten metal.
Spraying angle using Sn is 80 °, spraying pressure 4kgf / cm ² , flow rate 16N
Atomization was performed at m ³ / min and a differential pressure of 120 mmHg. As a comparative example, the spray angle was changed by the conventional method with a differential pressure ΔP of 0 mmHg.
Atomization was performed at 30 °. The results are shown in Table 1.

[0018]

[Table 1]

As shown in Table 1, the method of the present invention enables atomization with a large spraying angle and a high spraying efficiency, and the difference is clearly shown in the -100mesh recovery rate and the particle size distribution. Moreover, the recovery rate of -100mesh of gas atomized was close to that of liquid atomized. As can be understood from the above description, the method of the present invention enables high atomization angle gas atomization that could not be conventionally performed by blowing up, fundamentally solves blowing up, and is particularly useful as a method for enabling stable powder production. It is valid.

[0020]

As described in detail above, according to the present invention, the atomizing angle in the high atomizing angle in the gas atomizing is maintained by keeping the pressure difference ΔP between the nozzle box and the atomizing chamber at a constant value for atomizing. It is an industrially useful invention that solves blow-up and enables atomization with high spray efficiency.

[Brief description of drawings]

FIG. 1 is an example of an apparatus using the method of the present invention.

[Fig. 2] Nozzle box 4 when nitrogen is used as the atomizing medium
The pressure difference between the internal pressure P ₁ and the spray chamber 5 pressure P ₂ △
It shows the relationship between P and the sprayable range.

[Explanation of symbols] 1 stopper 2 intermediate tundish 3 molten metal 4 nozzle box 5 spray chamber 6 spray medium introduction pipe 7 ring nozzle 8 spray foam 9 jet 10 pressure gauge 11 atmosphere gas introduction pipe 12 atmosphere gas circulation pipe 13 for external exhaust device Piping 14 Powder discharge pipe

Claims (1)

[Claims] 1. An atomizing method in which molten metal is flowed down and pulverized by a spray nozzle using a gas as a spray medium, the inside of the spray chamber 5 is exhausted by using an exhaust device connected to the spray chamber 5, and the exhaust gas is exhausted. By circulating all or part of the generated gas into the nozzle box 4, it surrounds the ring nozzle 7, communicates with the atomizing chamber 5 through the ring nozzle 7, and
The pressure inside the nozzle box 4 that shuts off the vicinity of the
Let P _{1 be} the pressure in the spray chamber 5 and P ₂ be the pressure difference (P _1-
If (P ₂ ) is ΔP, ΔP is a constant value within ± 10% when it is 10 mmHg or more and 400 mmHg or less, and the inside of the spray chamber 5 should be kept at a constant negative pressure state with respect to the inside of the nozzle box 4. A method for producing a metal powder, comprising: