KR20020095213A - Method and apparatus for producing amorphous metal - Google Patents

Abstract

A method for producing an amorphous metal, which comprises feeding a molten metal (1) into a liquid cooling medium (4) in such a manner as to cause the boiling through spontaneous formation of vapor bubble nuclei, thereby cooling the molten metal (1) rapidly while forming fine particles thereof utilizing the pressure wave induced by the boiling, to yield fine amorphous metal particles; and an apparatus for practicing the method which comprises a material feeding means (3), a cooling section (2) which introduces the cooling medium (4) in an amount being small and sufficient to cool and solidify the fed molten metal (1) and cools the molten metal (1) rapidly while forming fine particles thereof utilizing the pressure wave induced by the boiling caused through spontaneous formation of vapor bubble nuclei, to yield fine amorphous metal particles, and a recovering means (5) for recovering the fine amorphous metal particles from in the cooling medium (4). The method allows the production of an amorphous metal using a material from which conventional methods and apparatus have not been able to produce an amorphous metal, and also the production of amorphous metal particles having a size of from sub-micron order to 100 microns order, especially a few microns, which has not been achieved by conventional methods and apparatus, in good yield and in a large amount.

Description

Amorphous metal production method and apparatus {METHOD AND APPARATUS FOR PRODUCING AMORPHOUS METAL}

Conventional amorphous metal production methods include liquid quenching. The liquid quenching method involves melting and ejecting a liquid metal into a refrigerant, and cooling and solidifying the molten metal at a rate of 10 ⁴ to 10 ⁵ K / s to produce an amorphous metal. The liquid quenching method includes various methods such as a gas spraying method, a single roll method, and a double roll method, but among them, a liquid such as water is used as the refrigerant as a method for increasing the cooling rate relatively. Centrifugal methods are widely known.

In this centrifugal cooling, the coolant 101 is used as the coolant, and as shown in FIG. 14, the molten metal 103 is continuously continuous during the flow of the coolant 101 circulating at high speed in the rotary drum 102. It is executed by blowing out.

When the molten metal 103 is injected into the cooling water 101, a vapor film is formed around the molten metal 103 immediately after the injection. In the state where the surface of the molten metal 103 is covered with the vapor film by the boiling of the film, cooling of the molten metal 103 is gentle, so that the molten metal 103 is strongly injected into the cooling water 101 and the cooling water 101 By supplying the gas at high speed, a speed difference is generated between them, forcibly destroying the vapor film. The cooling water 101 and the molten metal 103 are brought into direct contact with each other so that the cooling rate is increased by the normal boiling cooling (consistant nuclear boiling occurring on the molten metal surface) or convective cooling. Since these ordinary boiling cooling or convective cooling have a poor cooling efficiency unless the relative speed of the refrigerant is fast, the cooling water 101 flows with respect to the molten metal 103 at a speed of, for example, 3 to 12 m / s.

However, in heat transfer by boiling or convective cooling, the heat flux between the molten metal and the two coolants is limited to the limit heat flux even at maximum, so the cooling rate can be made large in principle. none. For this reason, the cooling rate is 10 ^4-10 _5, and K / s is limited, there is a definite metal that can be amorphous.

It is an object of the present invention to provide an amorphous metal production method and apparatus capable of solidifying molten metal at a very high cooling rate capable of amorphizing even a metal that cannot be conventionally amorphous. In addition, the present invention makes it possible to easily produce 100 µm orders, particularly several micrometers of amorphous metal fine particles, from sub-µm orders that could not be realized in conventional methods and apparatuses. Moreover, an object of this invention is to provide the manufacturing method and apparatus in which a success rate is favorable in high yield, and a large amount of amorphous metal microparticles are obtained.

The present invention relates to a method and apparatus for producing amorphous metals. In more detail, this invention relates to the amorphous metal manufacturing method and manufacturing apparatus which use liquid, such as water, as a refrigerant.

1 is a flowchart illustrating a method of manufacturing an amorphous metal of the present invention.

2 is a conceptual diagram illustrating an amorphous metal manufacturing apparatus of the present invention.

3 is a conceptual view showing a state in which the swirl flow guide wire is disposed in the mixing nozzle.

4 is a cross-sectional view illustrating a connection relationship between a mixing nozzle and a swirl recovery nozzle.

5 is a conceptual diagram illustrating a first modification of the amorphous metal production apparatus of the present invention.

6 is a conceptual diagram illustrating a state in which molten metal joins a flow of a refrigerant.

7 is a conceptual diagram illustrating a second modification of the amorphous metal production apparatus of the present invention.

8 is a conceptual diagram illustrating a third modification of the amorphous metal production apparatus of the present invention.

9 is a conceptual diagram illustrating a fourth modification of the amorphous metal production apparatus of the present invention.

10 is a conceptual diagram showing a fifth modification of the amorphous metal production apparatus of the present invention.

11 is a graph showing a relationship between a supply method of molten metal in a refrigerant and a particle size distribution of molten metal atomized by the method.

12 is a graph showing particle size distribution of metal fine particles produced by changing molten metal temperature.

Figure 13 is a graph comparing the cooling rate of the cooling method of the present invention and the conventional cooling method.

14 is a conceptual diagram showing a cooling process of a conventional centrifugal method.

In order to achieve the above object, the amorphous metal production method of the present invention is to supply molten metal to a liquid refrigerant, cause boiling by spontaneous nucleation, and atomize the molten metal using the pressure wave to simultaneously cool and solidify it. . That is, according to the present invention, by controlling the amounts of the supplied molten metal and the refrigerant in a small amount, as the safe and small-scale vapor explosion is continuously generated, the molten metal is rapidly cooled while being atomized and amorphous. In this amorphous production method, it is more preferable to form a stable vapor film covering the molten metal in the refrigerant, and to disintegrate it by condensation. More preferably, it is supplied to a refrigerant | coolant by dripping molten metal.

A vapor film is formed by the evaporation of the refrigerant by receiving the heat of the molten metal around the molten metal supplied in the refrigerant. This vapor film is maintained by thermal equilibrium between evaporation that proceeds by receiving heat from the molten metal and cooling by the refrigerant, but when the temperature of the molten metal decreases, the thermal equilibrium collapses and condenses (voluntary collapse). Or collapses due to external factors such as pressure waves, velocity differences between the molten metal and the refrigerant, and contact with other materials. In the case of condensation, at the same time, the collapse of the vapor membrane takes place at the entire surface. Therefore, the entire surface of the molten metal is simultaneously brought into contact with the refrigerant, causing boiling by spontaneous nucleation around the particles of the molten metal.

The boiling by this spontaneous nucleation starts boiling from inside the refrigerant. In order for nuclear boiling to occur in water, it is necessary to overcome the surface tension of water and a refrigerant and generate bubble nuclei, and the starting temperature condition at that time is the spontaneous nucleation temperature, for example, 313 ° C under one atmosphere of water. Therefore, if the interfacial temperature when the vapor film collapses and the molten metal is in direct contact with the refrigerant is higher than the spontaneous nucleation temperature, bubble nuclei are formed in the refrigerant, and once the bubble nuclei are formed, they can evaporate at 100 ° C. One after another, steam gathers here to make an explosive boiling. Since steam generation by spontaneous nucleation is rapid and involves generation of pressure waves, the particles of molten metal are forcibly broken and pulverized and atomized by the pressure waves. In particular, when the vapor film collapses due to condensation, since a high pressure wave is uniformly applied to all the particles of the molten metal, it can be efficiently atomized without leaving a large lump. At the same time, the atomized molten metal is further cooled faster because its specific surface area becomes larger. And it cools and solidifies by latent heat transfer. Since the atomization of the molten metal further increases its specific surface area to increase the cooling rate, this results in positive feedback that further increases evaporation from the refrigerant and creates a larger pressure wave, thereby facilitating atomization and at the same time. It cools rapidly. By the experiments of the present inventors, it was confirmed that the cooling rate at this time was a speed which greatly exceeded 10 ⁷ K / s in which even the material which could not be amorphous by the conventional method could be amorphous.

Moreover, the amorphous metal manufacturing method of this invention supplies in a refrigerant | coolant by dripping a molten metal. In this case, most of the dropped molten metal is involved in spontaneous nucleation, thereby facilitating efficient atomization and cooling of the metal particles. In order to obtain high efficiency (particulation and cooling rate), it is preferable that the melt droplet diameter is small, for example, several hundred micrometers, most preferably in the form of a mist, and contacting the refrigerant. In this case, a specific surface area becomes large, atomization advances further and a cooling rate rises dramatically.

Moreover, in the amorphous metal manufacturing method of this invention, a refrigerant | coolant adds a salt. In this case, the salt is present around the vapor film that dissolves and covers the molten metal, and since the water molecules present in it are relatively small, condensation usually occurs, although evaporation from the refrigerant side becomes difficult, It is thought to be directed in the direction of condensation. Therefore, even if the molten metal is a substance in which spontaneous vapor film collapse is difficult to occur, for example, aluminum, the collapse of the vapor film can be promoted and the boiling caused by spontaneous nucleation can be promoted. In addition, even in the case of a material having a high melting point and a high initial temperature, it is difficult for spontaneous vapor film decay to take place due to the time taken for the vapor film to condense, but even in this case, the salt in the refrigerant promotes the collapse of the vapor film and causes spontaneous nucleation. Promotes boiling by

In the amorphous metal production method of the present invention, it is preferable that the molten metal and the refrigerant are supplied and mixed in the same direction and at a small speed difference. In addition, it is preferable to form a flow of the refrigerant having a region falling in the substantially vertical direction, and supply molten metal to the falling region of the refrigerant flow by free fall or by jet injection. In this case, the molten metal supplied to the refrigerant is supplied in the flow of the refrigerant with little change in the direction of the flow thereof, so that the molten metal does not receive a large shear force from the flow of the refrigerant. For this reason, steam destruction by external factors can be prevented, and spontaneous collapse by condensation can be achieved, and boiling by spontaneous nucleation can be generated around the particles at about the same time. Here, high-speed boiling, that is, boiling by spontaneous nucleation, causes hot molten metal and cold refrigerant to come into contact with each other, and when the interfacial temperature becomes higher than the spontaneous nucleation temperature, this becomes an initiation condition and bubbles nucleus are generated. If the relative speed difference between the refrigerant and the refrigerant is sufficiently low, it grows, causing high-speed boiling, that is, boiling by spontaneous nucleation. If the flow rate (relative velocity) of the refrigerant relative to the molten metal is too fast, boiling due to spontaneous nucleation does not occur, or even slightly occurs, it is cooled and disappears without growth. Therefore, it is preferable to make the speed of molten metal and the flow rate of a refrigerant | coolant match substantially. For example, the speed difference between the refrigerant in the refrigerant and the molten metal is more preferably 1 m / s or less. In this case, the shear force which a molten metal receives from the flow of a refrigerant | coolant can further be suppressed.

Moreover, the amorphous metal manufacturing method of this invention is made to irradiate an ultrasonic wave before molten metal contacts a refrigerant | coolant. In this case, since the refrigerant can be supplied from the droplets of the molten metal to a certain degree, the specific surface area of the molten metal is increased to participate in the vapor explosion as a whole, so that atomization is further promoted, and the cooling rate can be further improved. have.

In addition, the molten metal may be oxidized if it comes into contact with air before being supplied into the refrigerant. Oxidation of the molten metal changes the properties of the metal, and since the oxide film does not adhere uniformly, atomization and cooling do not occur at the same time in the portion where the oxide film is attached and in the portion that does not adhere. For this reason, steam explosion cannot be utilized well and the efficiency of atomization falls. Therefore, the amorphous metal manufacturing method of this invention is made to supply to a refrigerant | coolant, preventing the oxidation of molten metal.

In addition, the amorphous metal manufacturing apparatus of the present invention is a material supply means for supplying molten metal while controlling its supply amount, and a small amount of small amount supplied from the material supply means by introducing a small amount of refrigerant sufficient to cool and solidify the molten metal. And a cooling unit which rapidly mixes with the molten metal to generate boiling by spontaneous nucleation, and rapidly cools and amorphizes the molten metal by atomizing the resulting pressure wave, and a recovery means for recovering the amorphous metal from the refrigerant. Doing.

In the case of this apparatus, only by freely dropping the molten metal, it is rapidly cooled while being atomized by boiling by spontaneous nucleation in the refrigerant, thereby producing an amorphous metal. Then, the solidified amorphous metal particles can be recovered only by separating them from the refrigerant. Therefore, it is not necessary to drive a spray nozzle or rotating drum of a complicated structure at high speed or a power part accompanying it, so that the installation cost is low, the durability is excellent, and there is little risk of failure.

Here, the amount of molten metal and the refrigerant to be supplied is reduced to a small amount, so that the boiling by spontaneous nucleation is generated to generate a pressure wave that is large enough to atomize the molten metal dropped in the refrigerant, and thus, It is possible to prevent the pressure wave generated by boiling from becoming larger than necessary, thereby preventing the occurrence of large-scale steam explosion. In addition, even if a large amount of molten metal is leaked by breaking down the material supply means by setting the amount of the refrigerant to be stopped in the cooling section to an amount that loses control by the material supply means and does not cause massive vapor explosion even when molten metal is supplied at once. It does not cause a massive vapor explosion leading to an accident.

Moreover, in the amorphous metal manufacturing apparatus of this invention, a material supply means adds a molten metal to a refrigerant | coolant. Therefore, most of the dropped molten metal is involved in spontaneous nucleation, which promotes atomization of the molten metal droplets and at the same time promotes cooling.

Moreover, the salt used is the refrigerant | coolant used by the amorphous metal manufacturing apparatus of this invention. In this case, even in the case of a substance in which spontaneous vapor film collapse is unlikely to occur, such as aluminum, which has conventionally been said to not cause a vapor explosion, the vapor film collapse can be promoted and spontaneous nucleation can cause boiling. Therefore, it is possible to realize amorphousization of materials which have been difficult to atomize conventionally, such as aluminum.

In addition, the amorphous metal manufacturing apparatus of the present invention forms a flow of the refrigerant having a region falling in the vertical direction in the free space, and supplies the molten metal to the flow drop region of the refrigerant by free fall to form a cooling unit. have. In this case, spontaneous vapor film collapse can be caused without imparting shear force due to the flow of the coolant to the molten metal, so that efficient atomization can be performed and the cooling unit itself is structurally unnecessary. Therefore, it is low cost and there are few accidents and troubles.

Moreover, the amorphous metal manufacturing apparatus of this invention is provided with the ultrasonic irradiation means which irradiates an ultrasonic wave with respect to a molten metal between a material supply means and a refrigerant | coolant. Therefore, the droplet of the molten metal refined to some extent by the ultrasonic irradiation means which is a refinement | miniaturization means can be supplied to a refrigerant | coolant. Therefore, the atomization of the molten metal in the refrigerant can be further promoted, and the cooling rate thereof can be further improved. Further, since the micronization technique by ultrasonic irradiation has already been established, the primary atomization of molten metal is realized safely and simply.

Moreover, the amorphous metal manufacturing apparatus of this invention is provided with the oxidation prevention means which prevents the oxidation of the molten metal supplied from a material supply means to a cooling part. Therefore, the molten metal can be brought into contact with the refrigerant without being oxidized, so that boiling due to spontaneous nucleation can easily occur. Moreover, the droplet of molten metal can be prevented from scattering around the cooling part.

EMBODIMENT OF THE INVENTION Hereinafter, the structure of this invention is demonstrated in detail according to the best form shown in drawing.

An example of the amorphous metal manufacturing method of this invention is shown in FIG. 1, and an example of the amorphous metal manufacturing apparatus of this invention is shown in FIGS. This manufacturing apparatus introduces a material supply means 3 for supplying the molten metal 1 while controlling its supply amount, and a refrigerant 4 for cooling and solidifying the molten metal 1 to be supplied from the material supply means 3. A cooling unit 2 mixed with the molten metal 1 and rapidly cooled and amorphous while being atomized by boiling by spontaneous nucleation, and recovery means 5 for recovering amorphous metal fine particles from the refrigerant 4 Equipped.

The material supply means 3 is comprised by the crucible 7 provided with the heater 6 for heat insulation, for example. The crucible 7 includes a stopper 8 for opening and closing a hot water outlet 7a formed on the bottom surface, and a thermocouple for measuring the temperature of the molten metal 1 in the crucible 7. (9) is provided. The stopper 8 moves up and down by an actuator (not shown) to control or completely stop the amount of molten metal 1 falling from the hot water outlet 7a. The supply of the molten metal 1 increases the atomization efficiency and does not cause a large-scale vapor explosion leading to an accident, and it is preferable to keep it as small as possible and to increase the specific surface area. Therefore, in the present embodiment, for example, several drops of about g are allowed to drop freely in the shape of beads, but the present invention is not particularly limited thereto. It is preferable to make it small, for example, it is a several hundred micrometers, most preferably in a mist form, and it is made to contact a refrigerant | coolant.

In the case of this embodiment, the cooling part 2 is comprised from the nozzle (henceforth a mixing nozzle) 2 of the structure which makes the molten metal 1 and the coolant 4 always cool, and let it pass. The mixing nozzle 2 which is this cooling part is provided just below the tap opening 7a of the crucible 7 so as to receive the molten metal 1 dropped from the crucible 7. The distance between the hot water outlet 7a of the crucible 7 and the liquid level of the refrigerant 4 in the mixing nozzle 2 is preferably as short as possible, for example, preferably about 30 mm or less. . As a result, the collision force between the molten metal droplet and the refrigerant is reduced, so that the molten metal droplet can be smoothly accommodated in the refrigerant and can be dropped together with the refrigerant without destroying the vapor film covering the droplet, thereby forming a stable vapor film and condensing it. Spontaneous collapse caused by spontaneous collapse can cause boiling by spontaneous nucleation.

Here, in the mixing nozzle 2 as the cooling section, a molten metal 1 sufficient to rapidly boil (rapid evaporation phenomenon) due to spontaneous nucleation and rapidly cool the molten metal 1 at a rate necessary for amorphousization while atomizing the molten metal 1. It is required to secure the contact time between and the refrigerant 4. Accordingly, the mixing nozzle 2 of the present embodiment has a cylindrical shape, for example, and a swirling nozzle 10 for injecting water as the coolant 4 is connected to the circumferential wall thereof. Two swinging nozzles 10 are employed, and are connected to the upper part of the mixing nozzle 2 at 180 ° intervals so as to be tangential to the inner circumferential surface of the mixing nozzle 2 as shown in FIG. 4. Here, it is preferable that there is no flow of refrigerant and water to cause steam explosion. Therefore, in order to increase the residence time in the mixing nozzle 2 without making a speed difference between the molten metal 1 and the refrigerant 4, a coil-shaped swirling flow guide wire ( 11) is provided from the injection port of the revolving nozzle 10 to the outlet of the lower end of the mixing nozzle to assist in the formation of the swirl flow, and the swirling flow continues to the lower part of the mixing nozzle 2 according to the guide wire 11. Therefore, the water and refrigerant 4 injected from the two swirling nozzles 10 flow down while turning along the inner circumferential surface of the mixing nozzle 2 together with the droplets of the molten metal 1 (slewing). Classification). As a result, the contact time between the molten metal and the refrigerant is lengthened so that the time until the molten metal cools and boils (rapid evaporation phenomenon) due to vapor film collapse and subsequent spontaneous nucleation is ensured.

The control valve 12 is provided in the piping part of the turning water nozzle 10, and the flow velocity and flow volume of the turning flow in the mixing nozzle 2 can be adjusted. The flow rate of the refrigerant 4 is such that it does not collapse the vapor film generated by the mixing with the molten metal 1, and it is possible to form a swirl flow so that it can be stopped in the mixing nozzle 2 for some time. The speed is adjustable. If the flow rate of the coolant 4 is too fast, grooves are formed in the vortex of the coolant 4 or the surface of the water in the center of the mixing nozzle 2, so that they interfere with the spontaneous collapse of the metal droplet 1. The flow velocity of) is preferably about 1 m / s or less, preferably about 1 m / s or less, so as not to cause vortex or water grooves. In addition, although not shown in the drawing, it is preferable to provide a cooler or the like for cooling the refrigerant in a supply system for circulating and supplying the refrigerant.

Thus, by forming the swirl flow of the coolant 4 in the mixing nozzle 2, the coolant 4 can be stopped and placed in the mixing nozzle 2 over a certain time. For this reason, the quantity of the refrigerant | coolant 4 to be used can be reduced, and a large-scale vapor explosion does not generate | occur | produce.

The inner diameter of the mixing nozzle 2 is sufficiently larger than the droplet diameter of the molten metal 1 and small enough to form a smoothly flowing swirl flow. For example, the inner diameter is about 2 to 8 mm or more and about 25 mm or less. The amount of the refrigerant 4 orbiting in the mixing nozzle 2 is a sufficient amount to fill all the surroundings of the molten metal droplets dropped on the mixing nozzle 2, for example, a volume of at least five times or more relative to the metal droplets. The coolant 4 is supplied. At the same time, it is preferable that the refrigerant 4 is small enough so that the crucible 7 is broken so that the molten metal 1 falls in the mixing nozzle 2 at once but does not cause a large-scale vapor explosion. In the experiment conducted by the present inventors, it is preferable that the amount of the refrigerant gathered at once in the mixing nozzle 2 is, for example, about 100 ml or less.

When the molten metal 1 is in direct contact with the coolant 4, the heat insulating heater is maintained at a temperature at which the interface temperature between the molten metal and the coolant is equal to or higher than the spontaneous nucleation temperature, preferably higher than the spontaneous nucleation temperature. It is heated by 6). The temperature of the molten metal 1 is, for example, below the temperature at which the vapor film collapses, i.e., the film boiling lower limit temperature, when the refrigerant 4 is in direct contact with the refrigerant 4. This film boiling lower limit temperature is prescribed | regulated by the temperature of a molten metal and a refrigerant | coolant when there is no external force at all.

The refrigerant 4 may be a liquid that can come into contact with the molten metal to be amorphous and cause boiling by spontaneous nucleation, and thus, for example, water, liquid nitrogen, organic solvents such as methanol and ethanol, or other liquids may be used. Preferably, water having excellent economy and safety is generally used. The selection of the coolant 4 is determined according to the material of the molten metal 1. For example, when the molten metal 1 has a low melting point such as gallium, liquid nitrogen is employed as the refrigerant 4. In addition, when the molten metal 1 is a substance in which spontaneous vapor film collapse such as aluminum, iron or zinc is difficult to occur, for example, salts such as sodium chloride, potassium chloride, calcium chloride, or the like may be used. It is preferable to add to. For example, in the case of using zinc as the molten metal 1, by using an aqueous sodium chloride solution as the refrigerant 4, spontaneous vapor film collapse can be caused to cause vapor explosion. In the case of using a Fe-Si alloy, for example, as the molten metal 1, spontaneous vapor film collapse occurs by using a 25 wt% calcium chloride aqueous solution that is saturated enough as the refrigerant 4, for example. The Fe-Si alloy may be vapor exploded. Moreover, even when using a thing with a high melting point as the molten metal 1, it is preferable to add a salt to the refrigerant | coolant 4. As a salt to be added in this case, use of calcium chloride, sodium chloride, potassium sulfate, sodium sulfate, calcium nitrate is possible, for example. Of course, it is, of course, preferable to select and use a salt of a kind that does not react with the molten metal. Moreover, it is preferable to use seawater as the refrigerant | coolant 4 containing a salt.

The addition of the salt to the coolant 4 causes the ions to interfere and evaporate from the coolant side because the water molecules present therein are relatively small so that the salt is present around the vapor film that dissolves and covers the molten metal. In spite of the difficulty, condensation usually occurs, so it is thought to be directed toward the condensation as a whole. Therefore, it is possible to promote vapor membrane collapse.

The recovery means 5 is a filter, for example. In this embodiment, two-stage filters 5a and 5b are used to recover the fine particles of amorphous metal having a predetermined particle diameter. The first stage filter 5a uses a rougher eye than the target particle size, and the second stage filter 5b uses a finer eye than the target particle size. Then, the fine particles of the amorphous metal captured by the second stage filter 5b through the first stage filter 5a are recovered as a product. In addition, the amorphous metal collected by the first stage filter 5a is returned to the crucible 7 and melted again, which is then subjected to the refinement treatment.

In this manufacturing apparatus, a small spontaneous nucleation that is not connected by an accident is caused to boil, and the molten metal 1 dropped in the refrigerant 4 is atomized using a pressure wave generated accordingly, and at the same time, rapidly It is cooled and made to be amorphous. In this embodiment, the amount of the refrigerant introduced into the mixing nozzle 2 is made as small as possible, and the supply amount is controlled in a small amount in a state where the specific surface area is as large as possible for the molten metal 1, By adjusting the contact amount between the molten metal 1 and the refrigerant 4, the boiling by spontaneous nucleation is suppressed to a predetermined scale. For example, the molten metal 1 is dropped dropwise by several grams, and the amount of the refrigerant 4 swirling in the mixing nozzle 2 is about 100 ml to prevent a large-scale vapor explosion from occurring. .

Moreover, this manufacturing apparatus is equipped with the oxidation prevention means 14 which prevents the oxidation of the molten metal 1 supplied from the material supply means 3 to the mixing nozzle 2 at least. Moreover, in some cases, oxidation prevention means for covering the entire manufacturing apparatus including the crucible 7 with an inert atmosphere is provided so that the molten metal is not oxidized while being stored in the crucible 7. This oxidation prevention means 14 uses an inert gas, for example, and provides the casing 15 which isolate | separates the space between the tap opening 7a of the crucible 7 and the mixing nozzle 2 from the outside at least, The inert gas is filled therein, and the molten metal droplets are installed to drop in the inert atmosphere. As an inert gas, argon etc. are used, for example.

Using the apparatus comprised as mentioned above, the microparticles | fine-particles of an amorphous metal can be manufactured as follows.

First, a predetermined amount of refrigerant 4 is supplied into the mixing nozzle 2 from the two swinging nozzles 10 to form a swirling flow falling in a spiral shape. In addition, the molten metal 1 in the crucible 7 is heated and kept to a temperature at which the interface temperature between the molten metal and the refrigerant when the direct contact with the refrigerant 4 is sufficiently higher than the spontaneous nucleation temperature.

In this state, the stopper 8 of the material supply means 3 is raised to cause the molten metal in the crucible 7 to drop freely in a drop shape by dropwise (step S21). When the molten metal 1 collides with the refrigerant 4 in the mixing nozzle 2, the molten metal 1 is dispersed in the refrigerant 4 with the force of collision, and then covered with a film of steam generated due to film boiling due to the high temperature of the molten metal. It will be in a rough mixing state (step S22).

The vapor film is generated around the molten metal 1 by receiving the heat of the molten metal 1 and evaporating the refrigerant and water. This vapor film is maintained because the thermal balance between evaporation proceeding by receiving heat from the molten metal 1 and cooling by the refrigerant is achieved. However, when the temperature of the molten metal decreases, the thermal equilibrium collapses and condenses. That is, collapse of the vapor film occurs (step S 23). And this condensation usually takes place at the same time in full view. Therefore, because the entire surface of the molten metal 1 is in contact with the refrigerant at the same time, and the interface temperature thereof becomes equal to or higher than the spontaneous nucleation temperature, the spontaneous nucleation is caused by the spontaneous nucleation in the refrigerant 4 which is the low temperature side liquid around the molten metal particles. Boiling occurs (step S24). Boiling by spontaneous nucleation causes rapid evaporation and rapidly expands the vapor bubble to generate high pressure waves. Since this pressure wave propagates at a very high speed and acts uniformly on the whole particle | grains of molten metal, particle | grains are forcibly broken by the pressure wave, it grind | pulverizes, and atomizes (step S25). At the same time, the specific surface area is increased by atomization, further increasing the cooling rate. It also increases the evaporation from the refrigerant and generates further pressure waves by developing into vapor film formation, vapor film collapse, and boiling by spontaneous nucleation.

Therefore, when the vapor film is broken by the dispersed particles, the pressure waves generated thereafter reach other particles and cause boiling by spontaneous nucleation. And since the specific surface area of the molten metal becomes larger and the cooling becomes faster, it takes positive feedback, which further increases evaporation from the refrigerant, which also creates a pressure wave, thereby facilitating atomization and rapidly cooling. . Therefore, the molten metal is efficiently atomized without leaving a large mass, and is rapidly cooled and amorphous at a rate exceeding 10 ⁷ K / s significantly.

Here, since the molten metal 1 is atomized using a pressure wave generated from a spontaneous nucleation bubble of several nm and is rapidly cooled by boiling, it is easily available as fine particles having a size from a subm order to 100 m order. It can manufacture. In addition, it is possible to realize the production of fine particles having a size not obtained in the conventional method of several μm, particularly about 3 μm, which was difficult to realize in the conventional amorphous metal production method and apparatus. And since this atomization does not leave a big lump by atomizing the whole simultaneously, the success rate is favorable. In addition, since particle size distribution is concentrated, fine particles of a preferable diameter are obtained in large quantities. And in this case, the atomization efficiency (particulation ratio) per unit mass can be made favorable. In addition, as the atomization progresses, the specific surface area increases, and the cooling rate is further increased.

In addition, the present manufacturing apparatus atomizes the molten metal only by freely dropping, for example, dropping the molten metal into the refrigerant falling in the mixing nozzle 2, and rapidly cools as it becomes amorphous. Like the gas spraying method, the apparatus is excellent in durability without burdening the nozzle, and long-term operation is possible. In addition, since the structure of the device is simple, the manufacturing cost of the device can be reduced at a low cost.

In addition, the amorphous metal fine particles and the refrigerant 4 fall while turning inside the mixing nozzle 2, and the refrigerant 4 passes through the first stage filter 5a and the second stage filter 5b and passes through the tank ( 13) Come back inside The amorphous metal fine particles are captured by the first stage filter 5a or the second stage filter 5b.

According to the experiments of the inventors, the molten metal (Al ₈₉ -Si ₁₁ alloy) of about 1500 DEG C is melted by continuously dropping 100 ml of refrigerant into the mixing nozzle 2 which turns 100 ml of the refrigerant at a flow rate of about 1 m / s as droplets of about 8 mm in diameter. The metal was solidified by rapid cooling at a rate significantly above 10 ⁷ K / s while atomizing the metal.

In addition, in the above-mentioned embodiment, although the cooling part comprised by the mixing nozzle 2 was mentioned as the example, it is not limited to this. For example, the cooling part 2 may be comprised by the flow of the refrigerant | coolant discharged to a free space. For example, although not shown in the figure, nozzles for allowing the refrigerant to flow out around the tap opening 7a of the crucible 7 may be arranged side by side in the vertical direction downward to flow the molten metal and the refrigerant in the same direction. In this case, since there is almost no speed difference between the molten metal and the refrigerant, and no shear force is required to collapse the vapor film, spontaneous collapse of the vapor film occurs uniformly, and the efficiency of atomization is good.

In addition, as shown in FIG. 5, a nozzle 32 for discharging the coolant 4 upward (or toward the horizontal direction although not shown) is provided, and the coolant 4 discharged from the nozzle 32 is provided. The molten metal 1 may be dropped and supplied to the region 31 where the flow direction is changed downward by the action of the gravity. By releasing the refrigerant 4 upwardly, the downward flow region 31f can be formed in the vicinity of the nozzle 32. In this case, since the downward flow region 31f in the substantially vertical direction of the flow 31 of the coolant 4 with respect to the supply direction A of the molten metal 1 is also in the vertical direction, the molten metal 1 dropped is It is supplied into the coolant 4 with almost no change in the flow direction, and the shear force received by the molten metal 1 from the flow of the coolant 4 can be suppressed small. In addition, by matching the falling speed of the molten metal 1 joining with the flow velocity of the coolant 4, the shear force which the molten metal 1 receives from the flow 31 of the coolant 4 can be further suppressed. That is, when the molten metal 1 is supplied into the flow 3l of the coolant 4, a vapor film is generated between the molten metal 1 and the coolant 4, but the vapor film is transferred to the flow 31 of the coolant 4. Rather than being broken by the shearing force produced by the condensation, the entire vapor film can be broken at once by condensation of the vapor film, and can be generated as a whole without limiting boiling due to spontaneous nucleation. In this case, the flow rate of the refrigerant 4 flowing out of the nozzle 32 is, for example, about 50 cm / s or less, more preferably about 20 cm / s, so that the refrigerant 4 and the molten metal 1 have almost no speed difference. The state can be realized, and the refrigerant 4 is likely to cause boiling by spontaneous nucleation. The release rate of the coolant is preferably as slow as possible, but if it is lower than about 20 cm / s, the flow as shown in FIG. By releasing the refrigerant from the side with respect to the supply direction of the molten metal, so-called parallel to form the downward flow region 31f in the flow 31 of the refrigerant in substantially the same direction in the direction in which the droplets of the molten metal are ejected (falling direction). In order to form the classification system, even if it does not arrange | position slightly upward like the nozzle 32 of FIG. 5, even if it arrange | positions horizontally or slightly downward, it can implement. In this case, the coolant can be released at a lower speed.

Also, the size of the flow 31 of the downward flow region 31f is, for example, 2 to 5 times larger than the size of the droplets or jets of the molten metal 1 to be supplied. It is preferable to set it as. The size of the flow 31 in the downward flow region 31f of the coolant 4 is twice the size of the droplet or jet size of the molten metal 1, so that the molten metal in the coolant 4 is set at this value. This is because the refrigerant 4 in an amount sufficient to generate boiling due to spontaneous nucleation can be secured around (1). In addition, the size of the flow 31 of the coolant 4 is 5 times or less the size of the droplets or jets of the molten metal 1 because the shear force acting on the molten metal 1 becomes larger than this. to be. That is, as shown by the solid line in FIG. 6, when the flow 31 of the coolant 4 is thin, the flow 37 that traverses until the molten metal 1 flows into the flow 31 is not much, but FIG. 6. As indicated by the dashed-dotted line in FIG. 2, when the flow 31 ′ of the refrigerant 4 becomes large, the flow 37 ′ that crosses until the molten metal 1 joins the flow 31 ′ increases, and more Because you will receive a lot of shear. That is, by setting the size of the flow 31 of the coolant 4 in the above-described range, the coolant 4 receives from the flow 31 of the coolant 4 while ensuring a sufficient amount of the coolant 4 around the molten metal 1. Shear force can be suppressed. Moreover, it is not necessary to necessarily install the nozzle 32 toward inclination upper direction, For example, you may provide the nozzle 32 toward horizontal or inclination downward.

In addition, as shown in FIG. 7, by flowing the coolant 4 on the curved guide 33, a flow 31 of the coolant 4 that changes in direction from a downward direction to a horizontal direction is formed. ) May be supplied to the molten metal 1 from the material supply means 3. In this way, the amount of the refrigerant 4 used in a small amount is sufficient, and a sufficient amount of the refrigerant 4 can be ensured around the molten metal 1.

8, the nozzle 32 which blows out the coolant 4 may be provided upward, and the molten metal 1 may be supplied from directly above this nozzle 32. As shown in FIG. By setting it as such a structure, the cooling part 2 which cools the molten metal 1 becomes simple and compact. For this reason, many nozzles 32 can be installed side by side in a small space, and the apparatus suitable for mass production can be provided. In other words, it is possible to mass-produce metal fine particles with less equipment investment.

As shown in FIG. 9, a plurality of nozzles 32 for injecting the coolant 4 toward the falling point of the molten metal 1 may be provided so as to surround the falling point. In FIG. 9, four nozzles 32 are provided at intervals of 90 ° in the circumferential direction. By jetting and hitting the coolant 4 of the same flow rate and the same flow rate from the four nozzles 32, the flow 3l of the coolant 4 is canceled, and the coolant 4 is formed to collect in the cooling unit 2. Can be. That is, by injecting the coolant 4 from the four nozzles 32 toward the falling point of the molten metal 1, the amount of the coolant sufficient to cause boiling by spontaneous nucleation around the supplied molten metal 1 (4) can be gathered, making amorphous of a metal fine particle favorable, and a microparticle yield improves. That is, the ratio of microparticles | fine-particles below a predetermined particle diameter can be enlarged, and the success rate of microparticle manufacture is improved. Further, by injecting the coolant 4 from the four nozzles 32 at a flow rate of, for example, 50 cm / s, the coolant 4 suitable for causing boiling by spontaneous nucleation can be collected.

In addition, as shown in FIG. 10, the molten metal 1 may be supplied into the pool 36 that flows in from the port 34 and flows out of the port 35. In this case, by forming the circumferential wall of the pool 36 to a certain height, all of the produced metal fine particles are recovered in the pool 36. For this reason, recovery of amorphous metal fine particles becomes easy.

Here, the influence of the difference in the mixing system of the refrigerant and the molten metal on the atomization will be described according to FIG. 11 and the effect of the difference in the molten metal temperature on the atomization according to FIG. 12.

11 shows particle size distribution of molten metal (tin) for three different contact modes of a refrigerant and molten metal. Water is used as the refrigerant, and the method of supplying the water is the flow of the refrigerant 31 in the direction parallel to that of the parallel flow shown in FIG. 5, that is, the supply direction of the molten metal 1 (31). Method of supplying the molten metal 1 to the collision fraction shown in FIG. 8, that is, the refrigerant ejected upwardly (hereinafter referred to as collision fraction) for the molten metal 1 falling directly above. Method of supplying molten metal to stream 31 of (4) (symbol B), molten metal 1 is supplied to the pool system shown in FIG. 10, that is, pool 36 filled with water in a vertical pipe having an inner diameter of 155 mm. Method (symbol C). The distance between the nozzle which dripped the molten metal 1, and the liquid level of the refrigerant | coolant 4 was 30 mm. In addition, the subcooling degree (initial subcooling degree in the method of FIG. 10) of the refrigerant | coolant 4 was 85K. In addition, the initial temperature of the molten metal (tin) 1 was 700 degreeC, and the droplet diameter was 3.2 mm.

From FIG. 11, when the droplet of molten metal l is brought into contact with the equilibrium fractionation (in the case of symbol A), atomization of the molten metal 1 is most promoted, and then the droplet of molten metal 1 is dropped in the pool 36. It was found that the atomization efficiency was good in the order of the method (in the case of reference C) and the method of contacting the droplet of the molten metal 1 with the collision classification (in the case of the reference B). It is considered as follows that the method using the equilibrium classification has the best atomization efficiency. In other words, when the molten metal 1 is supplied to the equilibrium fractionation, the molten metal 1 can be joined to the flow 31 of the coolant 4 without changing the flowing direction thereof. Therefore, the shear force which the molten metal 1 receives from the flow 31 of the refrigerant | coolant 4 can be suppressed the smallest. Thus, it is considered that boiling due to spontaneous nucleation is most likely to occur and grow stably, and most of the droplets of the molten metal 1 can be involved in the vapor explosion. In the case of dropping the droplets of the molten metal 1 into the pool 36, since the substantial subcooling degree of the refrigerant 4 in contact with the subsequent droplets decreases, atomization of the molten metal 1 is performed. I don't think it was promoted. On the other hand, in the method of bringing the droplet of molten metal 1 into contact with the jetting fraction, the lower part of the droplet serving as the collision surface is atomized by vapor explosion, but in other parts, it is difficult to be amorphous by normal nuclear boiling or convective cooling. Was found by observation.

In FIG. 12, the particle size distribution obtained by contacting a refrigerant | coolant and molten tin droplet in the parallel sorting system with the best atomization efficiency is shown for every molten tin temperature. As the initial molten tin temperature rises, atomization is promoted. This is considered to be because the larger the enthalpy difference to the solidification point during direct contact, the higher the steam explosion generation pressure and the smaller the viscosity coefficient. However, as the temperature rises, the effect of these on atomization becomes small. In addition, since the steam explosion does not occur due to the spontaneous collapse of the vapor film at a certain temperature or higher, it is considered that the optimum temperature exists in the atomization.

From these results, it became clear that the optimum initial temperature exists for atomization, and that the atomization is most promoted by the entire droplet being involved in the vapor explosion in the contact mode where the relative velocity with the refrigerant is small.

In addition, by using a material that is not in an amorphous (-Si ₈₉ Al ₁₁ alloy), an amorphous metal exemplary production process of the invention, and dendritic crystals (dendrite) it was confirmed as follows for the cooling rate by the observations. Here, the initial temperature of this molten metal is about 1000 degreeC, the droplet diameter is 6 mm, and it makes it collide with the aqueous solution surface of 150 mm vertically downward. Initial subcooling temperature was 85K. It is known that the combination of aluminum and water does not cause spontaneous vapor explosion. In the present invention, Al-Si is vapor-exploded to obtain a powder by using a 25 wt% aqueous calcium chloride solution as a vapor explosion accelerator.

In order to measure the cooling rate, Al-Si powder atomized by vapor explosion was polished, etched with aqua regia, and dendritic crystals were observed with a metal microscope. As an example, the average dendrite-arm spacing of the average dendritic crystal at the center of a relatively large powder (particle diameter of 1 mm) was 0.83 µm. According to the correlation for Al ₈₉ -Si ₁₁ , the cooling rate is estimated to be 2.0 x 10 ⁵ K / s. Moreover, although the observation of the powder of several micrometers considered to be high cooling rate was observed, since the dark space | interval of dendritic crystal | crystallization was short, meaningful measurement was impossible with a metal microscope.

In Fig. 13, the cooling rate achieved by the present method and apparatus is tested and the results are shown. In addition, in the figure, it compares with the gas spray method and the SWAP method which has the highest cooling rate now as a general cooling system. The SWAP method uses convective cooling and, of course, the present method has the highest cooling rate.

Experimental condition:

Molten Metals: Al ₈₉ -Si ₁₁

Refrigerant: 20w% calcium chloride aqueous solution

Molten Metal Temperature: 1500 ℃

Refrigerant Temperature: 20 ℃

Mixing system: System for injecting molten metal into the aqueous solution of beads

Molten Metal Droplet Diameter: 8mm

Cooling Rate Estimation: Darkness of Dendritic Crystals

According to the experimental results of FIG. 13, the present invention shows that a cooling rate of one order or more higher than that of the swap method, which is said to have the highest speed in the past, is obtained, and that the material can be amorphous even if it has not been previously amorphous. Suggests.

According to the above-described amorphous metal production method and apparatus, by cooling the molten metal 1 using boiling heat transfer by spontaneous nucleation, the cooling rate can be made very large as compared with the conventional method. For this reason, since the cooling rate required for amorphousization is large, it becomes possible to amorphousize the material which cannot be manufactured by the conventional method. In addition, since the cooling rate required for amorphization is large, it is possible to reduce the amount of the additive to a material which had previously required to add an additive that suppresses crystal nucleation in order to be amorphous. Can be. Usually, these additives are expensive rare earths, and since the use of expensive rare earths can be suppressed, it contributes greatly to manufacturing cost reduction. Moreover, when the molten metal 1 is an aluminum alloy etc., the density at the time of making it amorphous can be made small by reducing the quantity of an additive.

In addition, since the amorphous metal to be produced is obtained as fine particles of submicron to 100 탆 order, an amorphous bulk material can be obtained by mechanical alloying, extrusion forming, and powder compaction. For example, the iron core of the transformer can be made of amorphous metal. Background Art Conventionally, it has been known that the iron core of a transformer can be made amorphous metal to significantly reduce no-load damage, thereby improving the energy saving effect. However, in order to use an amorphous metal as the iron core of a transformer, an amorphous thin plate having a sheet thickness of 50 to 100 µm and a plate width of 150 mm or more is required, and development of a manufacturing technique capable of producing a homogeneous and mass production is required. Conventionally, the above-mentioned amorphous thin plate is manufactured by repeatedly bonding a very thin tape-shaped amorphous metal produced by the liquid quenching method, and used as an iron core of a transformer. For this reason, the manufacturing cost of an iron core becomes very high. However, by producing the amorphous metal in the form of fine particles and producing the thin plate by powder molding as a raw material according to the present invention, it becomes possible to manufacture the amorphous thin plate at low cost, thereby lowering the manufacturing cost of the transformer.

In addition, the amorphous bulk material thus obtained is heated to crystallization near the melting point, whereby a high-strength polycrystal (nanocrystalline material) can be obtained because the crystal grain size is small.

In addition, although the form mentioned above is an example of the preferable aspect of this invention, various deformation | transformation is possible in the range which does not deviate from the summary of this invention, without being limited to this. For example, in the above description, the inside of the casing 15 is set as an inert gas atmosphere as the anti-oxidation means 14, but instead of being made into an inert gas atmosphere, a reducing gas atmosphere such as hydrogen or carbon monoxide is used, or The inside of the casing 15 may be depressurized to a vacuum state having a low oxygen concentration. In addition, by reducing the pressure inside the casing 15, the boiling by spontaneous nucleation can be made small, and the metal droplet 1 is more easily atomized. Moreover, you may install the whole apparatus in inert gas atmosphere or reducing gas atmosphere, or you may install in the pressure-reduced casing.

Further, the molten metal 1 may be refined by applying an external force in advance and supplied to the coolant 4. For example, by providing a means for miniaturizing the molten metal 1 between the material supply means 3 and the refrigerant 4, the fine particles of the molten metal 1 can be made to a certain degree and then supplied into the refrigerant 4. Can be. In this case, since the molten metal 1 is refined to some extent by the refinement means and then supplied to the refrigerant, the specific surface area is increased, so that the production and cooling of the vapor film becomes more efficient. Thereafter, boiling occurs by spontaneous nucleation in the refrigerant 4, and the molten metal 1 can be further atomized by the pressure wave generated by the boiling. For this reason, the atomization of the molten metal 1 in the refrigerant 4 can be further promoted, and the cooling rate thereof can be further improved. As a refining means for atomizing the molten metal 1, for example, application of an ultrasonic irradiation technique already established as a refining technique is preferable, and as shown in FIG. 5, between the material supply means 3 and the refrigerant 4. Ultrasonic irradiation apparatus 16 may be provided in the apparatus, and ultrasonic waves of about 10 kHz to 10 MHz may be irradiated to the molten metal 1 dropped from the material supply means 3. Moreover, the use of the apparatus which refine | miniaturizes the molten metal 1 by forming an electric field in the space which the molten metal 1 passes is also possible. And it is thought that it is appropriate to refine the molten metal 1 immediately after the molten metal 1 is discharged from the material supply means 3.

In addition, in the above description, although the molten metal 1 was supplied by dropping the molten metal 1 from the tap opening 7a of the crucible 7, the molten metal 1 was jet-shaped from the tap opening 7a. You may make it blow out. In this case, it is necessary to be thin in shape and small in quantity.

In addition, in the present embodiment, spontaneous collapse due to condensation has been mainly described for the collapse of the vapor membrane, but in some cases, the vapor membrane may be broken due to external factors. For example, an ultrasonic irradiation device for irradiating ultrasonic waves of about 10 kHz to 10 MHz with respect to the mixing nozzle 2 constituting the cooling unit or the flow of the coolant is provided, and the vapor film covering the droplets around the molten metal in the coolant is collapsed early. It is also possible to directly contact the droplets of the molten metal and the refrigerant at a higher temperature to cause boiling by spontaneous nucleation with good efficiency. It is preferred for amorphous metals with high melting points. In this case, since it is to be broken from one direction, in other areas, for example, the other side, for example, the vapor film does not break or spontaneously generates spontaneous nucleation with good efficiency even if it breaks, so that the whole portion is left without being particulate. In order not to generate | occur | produce, it is preferable to consider that a steam film | membrane breaks in multiple directions.

Claims (17)

A molten metal is supplied to a liquid refrigerant, causing boiling by spontaneous nucleation, rapidly cooling and amorphous while atomizing the molten metal using the pressure wave to form amorphous metal fine particles. . The method of claim 1, A stable vapor film covering the molten metal in the refrigerant is formed, and the vapor film is collapsed by condensation. The method of claim 1, And supplying the molten metal to the refrigerant by dropping the molten metal. The method of claim 1, And the molten metal is supplied to the refrigerant in the form of a mist. The method of claim 1, The refrigerant is a method of producing an amorphous metal, characterized in that the salt is added. The method of claim 1, And the molten metal and the refrigerant are supplied at a small speed difference in the same direction to be mixed. The method of claim 6, A flow of a coolant having a region falling in the vertical direction is formed, and the molten metal is supplied to the dropping region of the coolant flow by free fall. The method of claim 1, Ultrasonic radiation is irradiated before the molten metal reaches the refrigerant. The method of claim 1, A method for producing an amorphous metal, characterized in that the supply to the refrigerant while preventing the oxidation of the molten metal. The method of claim 1, And a velocity difference between the refrigerant and the molten metal in the refrigerant is 1 m / s or less. A material supply means for supplying the molten metal while controlling the supply amount; A small amount of refrigerant is introduced to cool the solidified metal and mixed with a small amount of the molten metal supplied from the material supply means to generate boiling by spontaneous nucleation, and the pressure wave generated thereby A cooling unit which rapidly cools and amorphizes the molten metal to obtain fine particles; Recovery means for recovering the amorphous metal fine particles from the refrigerant An apparatus for producing an amorphous metal, characterized in that it comprises a. The method of claim 11, And the material supply means is dropping the molten metal onto the refrigerant. The method of claim 11, The refrigerant is an amorphous metal production apparatus, characterized in that the salt is added. The method of claim 11, And the cooling unit forms a flow of the refrigerant having a region falling in the vertical direction in the free space, and supplies the molten metal to the falling region of the refrigerant flow by free fall. The method of claim 11, Ultrasonic irradiation means for irradiating an ultrasonic wave with respect to the said molten metal between the said material supply means and the said refrigerant | coolant of the said cooling part, The amorphous metal manufacturing apparatus characterized by the above-mentioned. The method of claim 11, And an oxidation preventing means for preventing oxidation of molten metal supplied from the material supply means to the cooling part. The amount of the coolant stopped in the cooling unit is an amount that does not cause a large-scale vapor explosion even if the molten metal is supplied at once by losing control in the material supply means.