JPS583904A - Manufacture of expanded metallic granule - Google Patents

Abstract

PURPOSE:To obtain expanded metallic granules with low apparent specific gravity by dispersing a molten metal contg. a dissolved gas in an evacuated atmosphere and by cooling the dispersed metal with oil or water. CONSTITUTION:A molten metal or alloy M contg. a dissolved hydrogen-base gas is allowed to flow down to a dispersing and solidifying apparatus 20 kept in an evacuated state. The molten metal M is received in a perforated plate or a net body 23 and dispersed as liq. droplets. By spraying oil or water on the droplets during free dropping from a blowpipe 24, the contained gas is absorbed and dissolved, and the droplets are expanded, cooled, and solidified. Thus, expanded metallic granules with low apparent specific gravity are obtd.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for producing foamed metal particles or alloy particles (herein simply referred to as "metal particles"), which forms slimy bubbles and has a solid apparent specific gravity of a single particle. The present invention relates to a method for producing foamed metal particles that are significantly lighter than the true specific gravity of the particles.

The foamed metal particles produced according to the present invention can be used as a lightweight material for various purposes, for example, by using the foamed metal particles as a raw material alone or by combining them with other binders, fillers, etc., and sintering or molding them. It can be used for insulation, waterproofing, soundproofing, vibration absorption, filter media, heat exchange, catalysts, etc.

Various methods have been proposed for the production of porous metal materials.Among them, the method of foaming the molten metal when it cools and solidifies is to add a special hydrogen-absorbing metal or a pyrolyzable foaming agent to the molten metal. There are methods of treating the molten metal by adding it or by spraying a water stream in a special manner. On the other hand, when producing a relatively large metal block, for example, in PJJ construction, making it a porous body causes the formation of bubbles due to the deviation of free gas and buoyancy due to the temperature distribution and liquid pressure difference during cooling and solidification.
It is known that it is extremely difficult to make the distribution uniform throughout, and it is also difficult to increase the bubble volume ratio, which is practically impossible.

Therefore, an object of the present invention is to provide a method for mass-producing foamed metal particles in a relatively simple and easy manner without using a special blowing agent or jetting water in a special manner. It is about providing.

Since the metal particles obtained by the method of the present invention have a bubble volume ratio of each single particle as described below, the metal particles can be used for various purposes even in their original state. If the cell volume ratio is adjusted and this material is collectively molded by sintering etc., the constituent single grains themselves not only have air bubbles and have a light specific gravity, but also intergranular voids are added, so the porosity as a whole is significantly reduced. It has the advantage of being able to easily and reliably produce a porous structural material SI that is high, lightweight, and uniform.

Therefore, in the present invention, as a result of examining various conditions for manufacturing this type of foamed metal particle material, the following points were adopted as the basic technical idea.

First, molten metal generally dissolves and absorbs gases such as hydrogen, and the amount increases as the temperature rises, but during cooling and assimilation, the solubility of these gases suddenly decreases, and the supersaturated gas is absorbed. Since they tend to be liberated, this phenomenon is utilized.

That is, molten metal that has mainly dissolved and absorbed gases such as hydrogen, and if necessary, foamed molten metal that has sufficiently absorbed these gases.

Second, even if you use a molten metal that has dissolved and absorbed the gases mentioned above, when it is cooled and solidified, as in casting under general atmospheric pressure, the free gas will be extracted and a so-called vinyl hole or blowhole will be formed. As mentioned above, it is difficult to form bubbles at a constant large volume ratio.

Therefore, in order to increase the amount of free gas by lowering the equilibrium saturation solubility when the molten metal is cooled and solidified, and to expand its volume, the atmospheric pressure when the molten metal is cooled and solidified must be considerably reduced. .

Thirdly, when the target coagulated mass is made into a relatively large mass,
This point was also mentioned above, but even if the volume ratio of bubbles could be increased, it would be difficult to make the formation distribution uniform throughout, so dispersing the molten metal that has dissolved and absorbed the gas,
If the droplet is cooled in a free-falling state with a relatively small diameter, it will be able to cool under the liquid pressure caused by the slight surface tension in an almost weightless state.
Combined with the effect of the second term for each dispersed particle, it becomes easy to uniformly form bubbles with a large volume ratio, and the dispersed particles
When the foam expands, it takes on a spherical shape due to surface tension.

In other words, molten metal is cooled and solidified in a dispersed state as droplets.

Next, an explanation will be given with reference to FIG. 1 of the accompanying drawings, in which an example of an apparatus for carrying out the method of the present invention based on the second concept is shown.

This device basically consists of: 5- a molten metal forming section 10 that melts raw metal or alloy; a dispersion and coagulation container 20 that disperses and solidifies the molten metal from the molten metal forming section to form metal foam particles;
It consists of a discharge section 30 for removing the formed metal foam particles. The molten metal forming section 10 includes a crucible 1 loaded with raw materials.
1, a heating furnace 12 in which a heating coil 121 is embedded for heating the crucible and converting the raw material in the crucible into molten metal M;
A hermetically sealed seat 13 and a heat insulating pedestal 14 are provided. A tapping hole 111 is formed at the bottom of the crucible 11, and this tapping hole is closed when the molten metal M is accommodated, and is opened when the molten metal M is tapped. Furthermore, a high thermometer 15 is attached to the crucible 11 to confirm melting of the raw material and to adjust the heating temperature of the crucible by the heating coil 121.

The molten metal forming section 10 is configured as described above, but if the raw metal or alloy is separately prepared for melting in a melting furnace, a simple molten metal receiving roll 1 may be used instead of the crucible 11.

A conduit 21 equipped with a valve 21.1 is provided at a suitable location of the dispersion coagulation vessel 20, for example at the top of the outer wall, and this conduit 21 is connected to a vacuum pump (not shown).
The interior of the container 20 is maintained in a reduced pressure state. Since the pressure inside the container 20 is displayed on the pressure gauge 22,
By reading this and operating the valve 201, the container 2
The reduced pressure state inside 0 can be adjusted.

If the hole diameter of the tapping hole 111 of the crucible 11 is small, it is possible to form the molten metal into droplets while flowing down inside the dispersion and coagulation container 20 under reduced pressure without using any special members.
If the hole diameter of 1] is made small, it will be easy to squeeze out the hole, which will cause problems in the work. For this reason, even if the hole diameter of the tapping hole 111 is made relatively large, the molten metal M flowing down can be dispersed and not form drops, and an auxiliary member can be provided. For this purpose, minutes! 'fIi
A perforated plate or mesh body (hereinafter referred to as a first perforated plate) 23 is provided inside the coagulation container 20 and at a position close to the upper lid 201 thereof. The molten metal M, which has passed through the perforated plate 23 and has become droplet-like, becomes spherical due to its surface tension, cools while falling in the dispersion and coagulation container 20, releases supersaturated gas, becomes foamed and solidified metal particles, and is dispersed. The oil or water dispersion deposits at the bottom of the coagulation vessel 20, but is used to contact the tapped molten metal, especially the droplet-shaped molten metal, to absorb and dissolve gas through a decomposition reaction, and to promote cooling of the foamed metal particles generated. It can also be provided on the outer wall 202 of the coagulation vessel 20.

The discharge section 30 for taking out the foamed metal particles accumulated at the bottom of the dispersion and coagulation container 20 is a chute equipped with a two-stage sealed opening/closing door 31 and 32, as shown in the figure. It is preferable that the leakage of outside air into the tank is prevented as much as possible.

The method of the invention will now be explained in more detail with reference to an example carried out using the apparatus shown in FIG. 1 and using aluminum as the metal raw material.

Example 1 First, a tapping hole 11175 was drilled in three holes in the crucible 11.
The temperature was maintained at 0°C, and it was designated as molten metal M. At this time, if the raw aluminum contains oil, moisture, corrosion, etc., the molten metal M dissolves and absorbs gases mainly composed of hydrogen, but if necessary, it catalytically decomposes with the molten metal M to mainly generate hydrogen. For example, oil, ammonium carbonate, The gas is dissolved and absorbed into the molten metal M by adding a water-containing powder flux or by other appropriate methods.

Next, the vacuum pump was operated in advance to reduce the pressure in the container 20 to % atm based on the value indicated by the pressure gauge 22 through the conduit 21, and the tap hole 11 was opened to tap the hot water.

The foamed aluminum particles that are dispersed, cooled, foamed, solidified, and deposited at the bottom of the container 20 are removed from the closed door 3 of the discharge chute 33.
1 and 32 were opened and closed alternately and taken out.

The obtained foamed aluminum particles have a well-shaped spherical shape except for some deformed lumps, and almost all of the air bubbles are closed pores that do not open to the outside, so they float well even when placed in water, and their appearance does not change. The specific gravity was 1 or less.

Their properties are shown in Table 1.

9- (Table 1) The particle structure (appearance and cross-sectional structure) of the obtained foamed aluminum grains is shown in the photographs (1.5 times magnification) in place of drawings in Figures 2a and 2b.
It was as shown in

According to this practical test, the particle size when the molten aluminum M flowing out from the tapping hole 1]1 becomes dispersed droplets is as follows.
The pore size of foamed aluminum particles has a large influence on the pore size, and therefore, although it also depends on the degree of foaming, the particle size of foamed aluminum particles is basically determined by the tapping hole]
It has been found that if the diameter of the hole is small, the molten aluminum M is easily squeezed by dross generated by oxidation, making the work unstable.

In addition, the occurrence of deformed lumps, which were thought to be caused by the coalescence of droplets once flowing down, was observed, so the following improvements were implemented to prevent these.

Example 2 The hole diameter of the tapping hole 111 was expanded compared to that of Example 1, and the diameter of the tapping hole 111 was expanded to 7
mm, in order to alleviate the effect of constriction, while dispersing outflow holes with a hole diameter of 3 mm with a hole spacing larger than the hole diameter,
A dispersion plate 23 made of stainless steel plate with several perforations is placed in the container 2.
0, and the other conditions were carried out in the same manner as in Example 1. Although the average apparent specific gravity was almost the same as in the previous example, the occurrence of deformed lumps was hardly observed in the particle size distribution. , the maximum outer diameter became less than about 8 mm, the incidence of deformed lumps decreased, and the average outer diameter became about 4.5 mm. This is considered to be due to the effect of the dispersion outflow holes bored in the bottom plate of the dispersion plate 23 at a distance. Although the dispersion plate 23 is made of stainless steel plate in this example, it can also be made of other metals or inorganic non-metals.

The outflow hole of the dispersion plate 23 also tends to be narrowed depending on its hole diameter and the properties of the molten metal M. Therefore, to prevent this as much as possible, it is necessary to preheat before starting the work, or to further evacuate the air in the container 20 in advance, for example. It is effective to replace the gas with nitrogen or other inert gas and then reduce the pressure.

In the method of the above embodiment, the particle size of the aluminum foam obtained is controlled by the outflow hole diameter of the dispersion plate 23 when the foaming rate is the same, so if finer particles are desired, the outflow hole is made smaller. do it.

Note that various known mechanical methods and devices have been proposed as means for dispersing the molten metal into droplets, such as using a rotating body, and it is of course possible to apply them as appropriate.

As an experiment to prove the method of the present invention, for example, when dry chlorine gas was blown into molten aluminum to degas absorbed gases such as hydrogen, it was found that almost no foaming occurred even if the aluminum was then simply cooled and solidified under reduced pressure. Also, when the gas-absorbing molten metal was dispersed and solidified at atmospheric pressure, no foaming phenomenon as in the case of the present invention was observed.

That is, it was confirmed that uniformly foaming and solidifying dispersed droplets of molten aluminum containing gas bubbles with a large volume ratio has a remarkable characteristic effect of the present invention.

In addition, in order to increase the amount of gas absorbed and dissolved in molten aluminum in the form of dispersed droplets in a container, it is also possible to decompose it by contacting it with water or oil, absorb mainly hydrogen, and then cool, foam, and solidify it. In this case, in order to maintain the reduced pressure inside the container as much as possible, oil or water is sprayed onto the droplets using pressure spraying instead of air spraying, or the droplets are dropped directly into these liquids, allowing them to cool and solidify. Even if this was done, a certain degree of foaming effect could be observed as long as the pressure was reduced. Therefore, it should be noted that these additional processes also fall within the scope of the present invention.

The following description of the embodiments is for aluminum, but the present invention mainly dissolves and absorbs gases such as hydrogen in a high-temperature molten state, and upon cooling and solidification, significantly reduces the saturation solubility of the gas to create supersaturation. The steel that releases the
Of course, the present invention can also be applied to general pure metals and alloys, including non-ferrous copper and nickel, with similar effects.

13- The cell volume ratio of a single foamed metal particle is controlled by the amount of gas dissolved in the molten metal, and increases as the humidity of the molten metal increases and the atmospheric pressure in the vessel during dispersion cooling and solidification decreases. .

However, in the case of extreme foaming, the cell volume ratio is 7.
In some cases, the cell volume ratio is about 5% or more, but if the cell volume ratio is increased too much, a part of the outer shell is likely to break and become open cells.

Therefore, when the purpose is to produce foamed metal particles with closed cells, it is necessary to take various conditions such as metal properties into consideration, conduct a test, and determine the cell volume ratio by taking the results into consideration.

On the other hand, foamed metal particles with open cells are also suitable for special purposes, and in that case, they should be actively produced as appropriate.

If the present invention is appropriately applied and carried out, it is possible to produce foamed metal particles with any cell volume ratio, but if the cell volume ratio is too small, the effect will be weak, and generally, if the cell volume ratio is at least 20%, the effect will not be effective. appear.

Furthermore, although the particle size of a single particle depends on the characteristics of the metal, if large size particles are intended, deformed lumps are likely to occur, and the particle size distribution will also be biased.

Therefore, the diameter may vary slightly depending on the metal type, or the diameter is generally 15 mm or less, which is relatively easy to manufacture.

Although the foamed metal particles produced by the invention are spherical, it is of course possible to use the metal material by compressing it and processing it into a flat shape if necessary. .

[Brief explanation of drawings]

In the accompanying drawings, Figure 1 is a longitudinal sectional view schematically showing an example of an apparatus suitable for carrying out the method of the present invention, and Figures 2a and 2b are enlarged views showing the particle structure of foamed metal particles produced by the method of the present invention. FIG. 2a shows the external structure, and FIG. 2b shows the cross-sectional structure of foamed metal particles pressed into a synthetic resin body and cut. Molten metal・・・・・・・・・・・・・・・M Dispersion and coagulation container・・・・・・・・・・・・20 mesh plate or mesh body・・・・・・・・・・・・・・・23 Blow pipe for oil or water spray・・・・・・・2415-

Claims (4)

[Claims] (1) A molten metal or alloy containing dissolved gas, mainly hydrogen, is caused to flow down as droplets into a dispersion solidification device maintained under reduced pressure, and these droplets are granulated by their surface tension and then cooled and solidified. A method for producing foamed metal particles, which is characterized by foaming them under the pressure of dissolved gas liberated as a result of the process, thereby forming seed spherical metal particles with a diameter of 15 zm or less and having bubbles with a volume ratio of 20% or more inside. (2) The manufacturing method according to claim 1, characterized in that the molten metal flowing down within the dispersion and coagulation device is once received by a perforated plate or a mesh body and dispersed into droplets. (3) The manufacturing method according to claim 1 or 2, characterized in that oil or water is sprayed during free falling of the droplet-shaped molten metal to absorb and dissolve gas, foam, and cool and solidify. (4) The method according to any one of claims 1 to 3, characterized in that the droplet-shaped molten metal is dropped into oil or water, absorbs and dissolves gas, and is foamed and solidified by cooling. Manufacturing method.