JPH01247509A - Production of metal sphere - Google Patents

Abstract

PURPOSE:To stably produce metal spheres having a large diameter by a rotating electrode method by increasing the pressure of He or Ar used as atmospheric gas and specifying the distance of scattering of drops of a melt from the periphery of an electrode as stock. CONSTITUTION:When metal spheres having a large diameter of >=110mum are produced by a plasma arc rotating electrode method, He or He-based mixed gas under >=1 atm, Ar or Ar-based mixed gas under >=1.1 atm is used as atmospheric gas and the distance of scattering of drops of a melt from the periphery of an electrode as stock is regulated to >=1.3m. This regulation is performed by controlling the speed ot rotation of the electrode, electric current and voltage for plasma arc and the distance between electrodes so as to prevent the projection of the molten end of the electrode as stock and the formation of a locally deep molten part.

Description

Detailed Description of the Invention [Field of Industrial Application] The present invention relates to a method for producing granules by a rotating electrode method, and more specifically, the present invention relates to a method for producing granules using a rotating electrode method. It lies in the manufacturing method necessary to obtain it.

[Conventional technology]

Rotating polarity is a well-known technique for producing powders. In other words, in this method, the material to be powdered is made into a round bar in appearance, and this is rotated at high speed around its cylindrical axis.
It is melted from one end by a heat source such as a plasma arc,
In this method, the melt is scattered around by centrifugal force, solidifying during flight to obtain spherical powder. The rotating electrode method is generally well known as a method for producing metal powder, but since it is a method with high production costs, it has rarely been adopted for industrial production of powder.

The present inventors took advantage of the advantages of the powder obtained by the rotating electrode method: uniform particle size, high sphericity, and minimal chemical contamination.
On the other hand, we have been searching for ways to contribute to cost reduction. As one of these ring technologies, the present invention opens the door for the rotating electrode method, which was a method for manufacturing powder, to be used for manufacturing granules as well.

That is, in the rotating electrode method, the higher the rotation speed of the material electrode, the smaller the average particle size of the powder obtained.

Powder used in powder metallurgy processing such as HIP and sintering generally aims to have a particle size of 50 μm or less, so it is used at high rotational speeds or circumferential speeds of 30.0 OOrpn+ or higher or 2,800 M/min or higher. There are many things. In the production of these powders, the melt is scattered from the material electrode,
Although there is no need to give special consideration to the time or flight distance required for the particles to solidify, and the atmospheric composition and atmospheric pressure that are related to the cooling rate, the present invention aims to
If it is intended to obtain particle sizes of 0 μm or more, special conditions must be defined for the cooling of the particles.

The powder and granules used as catalysts in chemical reactions are well-flowing spheres with a diameter of 100 μm in order to improve circulation, recovery, and regeneration within the reactor, as well as the penetration of gas and liquid involved in the reaction.
Particles with a larger particle size are required. Furthermore, when mixed with resin and molded into machine parts, spherical and large-diameter particles are desired in order to improve moldability, wear resistance, and lubricity of the product.

In addition, when coating the surface of surgical implant materials such as artificial bone or tooth root material with powder or granules by sintering, etc., approximately 1.
Forming pores of 50 μm or more improves the compatibility of bones and meat with living organisms, so spheres with a uniform particle size of several 100 μm or more are desirable.

[Problem to be solved by the invention]

However, despite the above-mentioned requirements for metal balls, the objective is to obtain metal balls with high uniformity of ball diameter and ball diameter and high sphericity.

[Means to solve the problem]

The present invention uses a plasma arc rotating electrode method to produce a 100μ
In order to manufacture large-diameter metal spheres with a diameter of m or more, one of the constituent requirements is to increase the cooling rate of the flying droplets by increasing the pressure of the atmospheric gas. There is a big difference in the cooling rate of droplets when using argon and helium as the atmospheric gas, and helium can achieve a faster cooling rate. Furthermore, depending on the purpose of manufacturing the metal sphere, it may be possible to mix hydrogen gas into the atmospheric gas, which can slightly increase the cooling rate of the droplets.

Even if the atmospheric gas and pressure described above are used, in order to obtain the large-diameter metal sphere that is the object of the present invention, the inner wall of the manufacturing equipment must be set above a certain value from the surface of the electrode material to provide a sufficient flight distance. In this case, non-spherical particles are formed due to the relationship between the collision force and the high-temperature deformation force of the particles after solidification. However, if one were to try to obtain an infinitely long flight distance, the device would become unnecessarily large and uneconomical. In addition, even if we only aim for long flight distances, as mentioned above, the conditions for producing large diameter particles are on the low rotational speed side, so the centrifugal force during the flight of the droplets is insufficient, and collisions and mergers of particles occur. It is necessary to increase the gas pressure to enhance the cooling effect. Therefore, the present invention provides a method for manufacturing a metal sphere using a plasma arc rotating electrode, in which the atmosphere is helium at 1 atm or more or a mixture of helium and other gases mainly consisting of helium, or argon at 1° or more at 1 atm or mainly argon. It is characterized in that it is mixed with other gases, and the flight distance of the droplets from the outer periphery of the electrode material is 1.3M or more.

[Effect]

Regarding the atmospheric gas, which is one of the constituent elements of the present invention, for helium or a gas mainly composed of helium, 1
Atmospheric pressure or higher. The higher the pressure of the gas, the better the cooling effect of the droplets, but compared to argon, the cooling effect of helium is greater even at the same pressure, and in practical terms, if it is 1 atm, the flight distance of the droplets will be extra long. There is no need,
For practical purposes, 1.3M is sufficient. Same as this 1.
When using argon as the atmospheric gas with a droplet flight distance of 3M, a minimum of 1.1 atm is required; if it is lower than that, the particles may be deformed when they collide with the inner wall, or particles may collide in some areas. Merged particles become visible. Figure 1 shows the numbers in Table 1 shown below.

5 is a photograph of the appearance of a metal sphere obtained according to the present invention having a uniform particle size and high sphericity obtained in Example 5.

As exemplified above, a method of solidifying a controlled amount of molten metal in a gas is effective in producing spherical metal particles that are achieved by satisfying the conditions specified by the present invention in the rotating electrode method. The rotating electrode method is one such method.

Particularly in the case of this method, by controlling the melt shape in the electrode to a specific shape, the amount of flying droplets can be regulated and a uniform particle size can be obtained. This control involves controlling the rotational speed according to the specific gravity of the electrode material, the current and voltage of the plasma arc that is the melting heat source, and the distance between the electrodes to specific values to prevent the melting end surface of the material electrode from becoming convex and locally. By controlling the melt so as not to create deep penetration, the flow of the melt at the end face is kept constant and the release into the gas is controlled only at the outer periphery of the melt end face. Here, in order to obtain metal spheres of 100 μm or more as described above, it is necessary to keep the rotation speed of the electrode material low. For this reason, the melt particles separated from the electrode material collide with each other during flight and are likely to merge.

This phenomenon is particularly observed in particles of 100 μm or more, and FIG. 2 shows an example of No. 004 in Table 1. To prevent this, it is effective to speed up the cooling rate during flight. Moreover, when the particles become large, they collide with the inner wall of the manufacturing equipment, etc., forming deformed particles. An example of this is shown in Table 1.
o, 15 shown in Figure 3. Therefore, to prevent this, it is necessary to ensure a sufficient flight distance.

In order to maintain the surface activity of the sphere, like iron-based metal spheres,
When it is desired to make metal spheres in a slightly reducing atmosphere, it is effective to add a small amount of hydrogen to the gas. Furthermore, when it is desired to intentionally color the surface of a titanium ball, a very small amount of nitrogen may be added to the atmospheric gas. These additional gases are
Since a small amount is required for each purpose, it is not necessary to separately specify the atmospheric gas pressure or the flight distance of the droplets to substantially adjust the cooling rate of the droplets.

〔Example〕

Table 1 shows manufacturing conditions for manufacturing metal spheres of 100 μm or more using the rotating electrode method. The flying distance of a droplet at the knee is expressed as the straight-line distance from the outer periphery of the electrode material to the inner wall of the container through which the droplet is made to fly. In addition, the outer diameter of the electrode material is 30 mm, and the plasma arc current is 21 mm.
0 A and a voltage of 35 V were used, and changes in the distance between electrodes due to melting and consumption of the electrodes were maintained constant by detecting changes in voltage and automatically micro-controlling the entrance and exit of the plasma torch. The apparatus used in the example uses a cylindrical container 1 as shown in the outline in Fig. 4, and changes in droplet flight distance were investigated by using another adjustable inner wall 2 within the inner wall. did. In Fig. 4, l is the inner wall of the device, 2 is a variable inner diameter wall for reducing the flight distance of droplets, 3 is a pressure gauge for atmospheric gas, 4 is a round bar of electrode material, 5 is a plasma arc torch, and 6 is a A rotation drive device for the rotating electrode, and 7 a moving and holding device for the plasma arc torch.

Table 1 [Effects of the invention] In the field of so-called powder metallurgy, where metal powder is used as a material for molding by sintering or pressurization, the grain size is reduced and the crystal grain size is refined using the rapid cooling effect. However, in applications where powder is used as a powder, particles with a slightly larger diameter are often required. For example, what is shown in the embodiments of the present invention is used when it is made into a paste with flux during micro spot welding and used as an insert material, or when a paste-like brazing material is made into spherical particles, it becomes easier to handle. This makes it possible to use automatic machines.

In addition, when reacting with gas or liquid or using as a catalyst, the spherical shape and large diameter provide good fluidity, eliminating troubles such as clogging in the device and improving the permeability of the reaction fluid.

Plastics are used in rotating mechanical parts that are immersed in chemically highly reactive liquids, and chemically passive titanium alloy grains and the like are also mixed in to strengthen these materials and provide wear resistance. In this case as well, spherical, large-diameter particles are highly useful both for molding and for improving performance.

Metal particles suitable for these applications are too small to be produced by mechanical abrasion and insufficiently large to utilize conventional powder manufacturing methods.

The present invention uses the rotating electrode method, which has conventionally been thought to only be able to produce powder, to produce particles with a diameter of 100 μm or more, and in many cases 400 μm.
The present invention provides a technology for producing metal spheres with a stable particle size and shape.

[Brief explanation of the drawing]

Figure 1 is a photograph showing a metal sphere obtained by the present invention, Figure 2 is a photograph showing an example of particles colliding and merging, and Figure 3 is a photograph showing an example of particles colliding and merging together. A photograph showing an example of particles deformed by colliding with the inner wall of the apparatus; FIG. 4 is a schematic diagram of the apparatus for producing metal balls according to the present invention; Variable inner diameter wall, 3. atmospheric gas pressure gauge,
4. Electrode material round rod, 5. plasma arc torch. Applicant: Nippon Steel Welding Industry Co., Ltd. Representative Patent Attorney Minoru Aoyagi Day 1, Figure 2

Claims (1)

[Claims] 1. In the method for manufacturing metal spheres using a plasma arc rotating electrode, the atmosphere is helium at 1 atm or higher or a mixture of helium-based gases and other gases, or argon or other argon-based gases at 1.1 atm or higher. A particle size of 100, characterized in that it is mixed with a gas and the flying distance of the droplet from the outer periphery of the electrode material is 1.3M or more.
A method for manufacturing metal balls of μm or larger.