JPH01246307A - Manufacture of fine metal particle having non-porosity - Google Patents

Abstract

PURPOSE:To stably manufacture fine metal particle having nonporosity and small particle size at good yield by pouring molten metal into a tundish having fine hole at bottom part and giving the specific vibration to the whole tundish. CONSTITUTION:The molten metal is poured into the tundish having fine hole at the bottom part. Successively, the vibration containing vertical component having >=30times/sec number of the vibration and >=0.1mm amplitude is given to the whole tundish. By this method, the molten metal is forcedly flowed out from the above fine hole and also cut into piece and dripped. This dropped molten drips are cooled and solidified into the water vessel arranged at lower part and collected. By this method, the fine metal particle having non-porosity and <=about 2mm particle size and narrow particle size distribution is stably obtd. at high yield.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention relates to a method for producing poreless metal fine particles used for powder metallurgy, brazing, shot peening, and the like.

[Conventional Method] Conventionally, the method for manufacturing fine metal particles is based on a gas or water atomization method, similar to the method for manufacturing metal powder. In this method, the molten metal stream from the pores at the bottom of the tundish is atomized by a high-pressure gas stream or high-pressure water stream, granulated, and then classified to obtain fine metal particles of a predetermined particle size. However, the metal fine particles obtained by this method include many particles with pores inside, and a complicated sorting process is required to obtain pore-free fine particles. Furthermore, since the metal particles obtained by the atomization method have a wide range of particle sizes, the classification yield for obtaining the targeted fine particles is quite low.

As mentioned above, there is a drawback that the yield of non-porous fine particles obtained by the atomization method is significantly lowered by the above-mentioned classification and sorting.

In addition, as a method for manufacturing metal shot, JP-A-61-11
As disclosed in No. 7205, (1) A large number of pores are provided at the bottom of the tundish to narrow the molten metal flow.

■Depending on the target shot particle size, the pore size and the size of the tundish are determined. Controls the hot water head.

■ Move the entire tundish horizontally or rotate it to apply shearing force to the molten metal flow, making the molten metal flow a discontinuous flow.

■Discontinuous molten metal droplets are dropped into water and solidified to form a shot.

There is a method. In this method, the obtained metal particles have few internal pores, and metal particles having a target particle size can be produced at a relatively high yield. However, this method is suitable for producing coarse particles with a shot particle size of 2 to 5IIIm, and in order to produce fine particles with a particle size of about 2IIIm or less, which is the objective of the present invention, it is necessary to The pore size must be further reduced. For this reason, the molten metal does not flow out properly from the pores, or even if it does flow out, it is extremely unstable, making stable production impossible.

[Problem that the invention seeks to solve]

The present invention aims to solve the above-mentioned drawbacks of the conventional methods, and provides a method that can produce fine metal particles with a high yield (and stability) without pores and with a particle size of about 2 mm or less. That is.

[Means to solve the problem]

The present invention involves flowing molten metal into a tundish having a highest point at the bottom, and passing the molten metal through the tundish at a frequency of 30 vibrations/
Non-porous metal fine particles characterized by applying vibrations containing a vertical component of sec or more and amplitude 0.1 ma+ or more to force the molten metal to flow out from the pores at the bottom of the tundish, split it in the vertical direction, and cause it to drip. This is a manufacturing method.

[Effect]

Next, the reason for limiting the method to the method of the present invention will be described.

One of the objectives of the present invention is to obtain pore-free metal particles.

The present inventors investigated a method for producing metal particles by an atomization method, and as a result, it was found that the generation mechanism of pore particles is generally as follows.

That is, in the initial stage of the process in which the sprayed molten particles solidify while flying through the gas, there is a period when only the surface layer of the particles solidifies, while the inside remains in a molten state.

When the particle flight speed is high in this state, negative pressure is generated on the back side of the flying particles (rearward in the direction of flight), and this negative pressure draws the molten metal inside the particles to the outside of the particles, resulting in secondary spraying. . As a result, molten particles with a particle size of 0.2 am or more, where voids are formed inside and void particles remain on the outside, are likely to undergo the above-mentioned surface solidification and internal melting state. Moreover, the larger the particle size, the smaller the degree of deceleration of the initial velocity given during atomization, so when maintaining high-speed flight, the generation rate of void particles is much higher than with fine metal powder.

From the above, it can be assumed that in order to obtain non-porous metal particles, the flight speed of the molten particles should be made as slow as possible. A method for slowing down the flight speed of molten metal particles is to allow the molten metal particles to fall naturally. Therefore, the present inventors created pores at the bottom of the tundish,
We investigated a method of injecting molten metal into it and letting it fall naturally. As a result, it was found that the metal particles obtained by this method had almost no pores inside, as expected.611 L'2
It was done.

In addition, in this method, in order for the falling particles to solidify completely,
Since a fairly long distance is required, the height of the device must be increased considerably. Therefore, in order to prevent the height of the device from becoming too high, we decided to collect the particles after the surface of the particles had solidified to some extent, then dropped them into water to completely solidify them. It was found that this method also produced metal grains with almost no internal pores.

Next, another object of the present invention is to enable fine metal particles of approximately 2 mm or less to be produced in a high yield (and stably). An experiment was conducted in which a pore with a diameter of
Below φ, the flow of molten metal becomes unstable, especially at 2
It was observed that the outflow of molten metal often stopped when the temperature was below mn+φ.

In addition, as a result of investigating the relationship between the metal particle diameter (Dp) obtained by this method and the pore diameter (Do), it was found that Do < Dp
<3D.

It turned out to be.

Although the particle size of the metal particles mentioned above is narrower than that of the atomization method, there is still some spread. Also,
Since the minimum diameter at which molten metal can stably flow out from the pores at the bottom of the tundish is 3 mm + φ, the smallest metal particles obtained by this method are about 3 to 91, which is the target particle size of 2 mm. Fine grains smaller than φ cannot be obtained.

Therefore, the present inventors investigated conditions under which molten metal could be stably flowed out even if the pore diameter at the bottom of the tundish was 2 wa+φ or less, and fine particles could be obtained.

First, let's consider the conditions under which the outflow of molten metal stops when the pore diameter is made smaller. In the model shown in Figure 1,
When considering the equilibrium state at the limit pore diameter Dc at which the molten metal flows out or stops, the force F that tries to cause the molten metal to flow out is equal to the viscous resistance force R with the side surface of the pore where the molten metal attempts to flow out. It is equal to the resultant force of T and the surface tension T of the molten metal formed at the bottom of the pore. That is, F = R1T −−−−−−−−−−−...−1−
−−−■ holds true. Here, F=πDc”hρg ・−・■ R−νπDc l −−−−−−・−・−・■, T=
TπDc ゛−−−−−−−−−−−−■ρ: Specific gravity of molten metal g: Acceleration of gravity S: Viscous resistance force per unit length with the pore side surface T: At the bottom peripheral surface of the pore Since the surface tension per unit length of
By substituting , ■ into the equation 0 and sorting it out, hρ g is obtained. In the equation 0, g is a constant. Also, once the material of the molten metal is determined, C, T, and δ are also constants, so Dc
In order to reduce , there is no choice but to reduce r or increase h. However, to do the above,
There is a practical limit due to the strength of the tundish, and in reality, Dc is around 2 m-φ. It is not possible to reduce Dc to 2III-φ or less, that is, to stably flow out the molten metal with a pore diameter of 2+mφ or less.

Next, in Equation 0, note that Dc is inversely proportional to the downward acceleration component g.
If it can be made larger, it should be possible to make Dc smaller, that is, to stably flow out the molten metal with a pore diameter of 21II11φ or less. Based on the above, let's consider applying vibrations that include a vertical component. To facilitate analysis, radius a and acceleration ω in the vertical plane
The acceleration component at time t in the vertical direction when given equal daily motion is dt''. Since this is added to g in the above equation 0, the time when given the vibration of vertical circular motion is The apparent equilibrium pore diameter Dct at time t is hρ.Here, the apparent equilibrium pore diameter Dct does not actually exist, and the apparent equilibrium pore diameter Dct at time t is D.
When Oct is equal to Dc, it means that an equilibrium state is maintained, and when Oct is thicker than Dc, the molten metal will flow out, and when Oct is smaller than Dc, the molten metal will stop flowing out.

Therefore, by selecting a and ω such that aω22g, it is possible to obtain the following equation. That is, the molten metal can flow out at time t, and stop flowing out at time t2. In other words, as shown in FIG. 2, a forced outflow effect and a vertical breaking force act repeatedly on the molten metal at a constant cycle of ω/2π. As a result, a certain amount of molten metal is forced out of the pores, broken up and dripped. Therefore, the particle sizes of the resulting fine particles are very uniform. Furthermore, even if the pore size is constant, the targeted fine particle size can be controlled by changing the vibration frequency. In Figure 3, the pore diameter is 1.5 mmφ, the vibration width is 0.211II11, and the vibration direction is 30.
The figure shows the particle size distribution of pure copper grains obtained when the vibration frequency is kept constant (relative to the horizontal plane) and the vibration frequency is varied.

As shown in Figure 3, as the frequency increases,
Although the particle size of the obtained pure copper grains shifts to the finer side, it can be seen that the particle size is uniform around a certain particle size at any frequency.

In the present invention, the frequency of vibration is 30 times/sec or more, the amplitude is 0.
The reason why vibrations are limited to those containing a vertical component of 1 mm or more is that the effect of vibration cannot be changed below this value.

This means that the acceleration component of the vibration in the vertical direction is determined by the equation 0, and its maximum value is determined by aω2. Therefore, aω” = −(2πf)2 ・・・−・■X: amplitude f: frequency, so in formula ■, x-0,01(ca+), f=
When 30 (1/5 ec) is substituted, aω""=177 (cm/sec"), which is obvious from the fact that this is not a very large value compared to g=980 (cm/sec").

Above, for convenience of explanation, we have only mentioned circular motion of vibrations that include vertical components, but the vibration waveform is not particularly limited; for example,
Exactly the same effect can be obtained by applying vibration in a pulsed waveform, triangular waveform, or sawtooth waveform.

In addition, the upper limit of the frequency and amplitude depends on the material of the tanditshu,
The upper limit is not specified because it is determined by the thickness, that is, the strength of the tundish, or the limits of the vibration source and auxiliary equipment, etc., and is not based on the essential technical idea of the present invention.

Examples of the present invention and comparative examples are shown below.

[Example/Comparative example]

An experiment was conducted to produce fine particles from molten nickel wax (BNi-2). Table 1 shows the method of the present invention (Nllll-4)
and a comparative example under conditions outside the range of the method of the present invention (Nα5~
Regarding 7), the conditions and results are shown below.

In this manufacturing experiment, the inner diameter of the tundish was 50n+mφ.
An alumina crucible with a depth of 150 mm was used, and one pore was provided at the center of the bottom. As the vibration source, an electromagnetic vibrator was used for Nos. 1 to 6, and a mechanical drive device was used for No. 7. Molten nickel solder (BNi-2) was heated in advance to 1400"C in an Ar atmosphere in an electric furnace and poured into a tundish. The amount of molten metal poured was adjusted so that the head of the molten metal was maintained at about 100 am.

The droplets that dripped from the pores at the bottom of the crucible were cooled and collected in a water tank provided below. Here, the distance between the bottom of the crucible and the water surface of the tank was approximately 1n+.

As is clear from Table 1, the method of the present invention can stably produce fine particles of 8 to 16 meshes and shows a high yield, whereas the method with the conditions shown in the comparative example It is either not possible at all, or it is very unstable even if it is possible.
It can be seen that the yield is also extremely low.

Further, nickel solder (BNi
-2) When the cross section of 8 to 16 mesh fine grains was examined, almost no internal pores were observed.

〔Effect of the invention〕

As described above in the Examples, the method of the present invention can stably produce non-porous fine particles at a high yield, which has not been possible using conventional techniques.

Therefore, its economic effect is extremely large.

[Brief explanation of the drawing]

Fig. 1 is a schematic diagram showing that molten metal is in an equilibrium state in a tundish, Fig. 2 is a schematic diagram showing the generation of molten metal fine particles by the method of the present invention, and Fig. 3 is a schematic diagram showing the particle size of the fine particles obtained by the present invention. This is an example showing the relationship between distribution and frequency.

Claims (1)

[Claims] (1) Inject molten metal into a tundish with pores at the bottom, and apply vibrations to the entire tundish at a frequency of 30 times/se.
A non-porous metal pore characterized by applying vibrations including a vertical component with a vibration width of 0.1 mm or more and forcing the molten metal to flow out from the pores at the bottom of the tundish, dividing it in the vertical direction, and causing it to drip. Method of manufacturing grains.