Gas atomization apparatus

Abstract

To provide a gas atomization apparatus which can suppress blockage of a molten metal nozzle without depending on the structure of the molten metal nozzle and excessive heating of molten metal.SOLUTION: A gas atomization apparatus 1 includes a hollow cylindrical cylinder 21, a hollow chamber 22 which is connected to one end of the cylinder 21 and where the cylinder 21 and an internal space are communicated with each other, an atomization unit 5 mounted on the other end of the cylinder 21, and an exhaust device 6 capable of exhausting air in internal spaces of the chamber 22 and the cylinder 21 so that the pressure is variable, wherein the atomization unit 5 includes a tundish 4 for storing molten metal, a molten metal nozzle 31 for discharging the molten metal in the tundish 4 into the cylinder, and a gas nozzle 32 which is arranged integrally with the molten metal nozzle 31, and jets gas to the molten metal discharged from the molten metal nozzle 31, and a cross-sectional area of the internal space perpendicular to an axial direction of the cylinder 21 is smaller than the chamber 22 in the cylinder 21.SELECTED DRAWING: Figure 2

Description

[Technical field]

[0001] The present invention relates to a gas atomizing device, and more particularly to a gas atomizing device equipped with a confined type gas atomizing nozzle. [Background technology]

[0002] There is a high demand for metal powder materials as raw materials for powder metallurgy and additive manufacturing. Gas atomization is widely used as one of the methods for producing metal powder materials. In the gas atomization method, gas is injected from a gas nozzle into the molten metal discharged from a molten metal nozzle, and the molten metal is turned into fine droplets, which are solidified to form metal powder. In particular, by using a confined gas atomization nozzle in which a molten metal nozzle and a gas nozzle are integrally provided and the discharge position of the molten metal and the injection position of the gas are close to each other, the crushing energy given to the molten metal by the injected gas can be increased, and fine metal powder can be produced with high efficiency. A confined gas atomization nozzle is disclosed in, for example, Patent Document 1 below. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] JP 2002-069512 A Summary of the Invention [Problem to be solved by the invention]

[0004] In a gas atomizing device equipped with a confined gas atomizing nozzle, high-temperature molten metal is quenched by high-pressure gas injection in the immediate vicinity of the molten metal nozzle. Therefore, the tip of the molten metal nozzle is excessively cooled by the injection gas, so that the molten metal in the molten metal nozzle solidifies, and the molten metal nozzle may be clogged by the solidified metal. In particular, inclusions in the molten metal are likely to accumulate in the molten metal nozzle and cause clogging. As a means for preventing such clogging of the molten metal nozzle, the above-mentioned Patent Document 1 forms the nozzle hole cross-sectional area of ​​the molten metal nozzle to be the smallest at the molten metal inlet. However, it is desirable to configure the gas atomizing device so that the clogging of the molten metal nozzle can be avoided even without using such a molten metal nozzle with a special structure. In addition, even if a gas atomizing nozzle with a special structure that makes clogging less likely to occur is used, it is difficult to completely avoid clogging of the molten metal nozzle, and it is preferable to adjust the conditions for gas atomization when the molten metal nozzle is about to be clogged so that the clogging of the molten metal nozzle can be avoided.

[0005] One method to avoid clogging of the molten metal nozzle by adjusting the conditions for gas atomization is to heat the molten metal to a high temperature in a tundish that stores the molten metal to be supplied to the molten metal nozzle. However, when the molten metal is heated to a high temperature, the materials that make up the tundish and molten metal nozzle, including refractories, can deteriorate. The deterioration of the materials shortens the lifespan of the tundish and molten metal nozzle.

[0006] The problem to be solved by the present invention is to provide a gas atomizing device that can suppress clogging of the molten metal nozzle without relying on the structure of the molten metal nozzle or excessive heating of the molten metal. [Means for solving the problem]

[0007] In order to solve the above problems, a gas atomizing device according to the present invention has the following configuration. [1] The gas atomization device of the present invention comprises a hollow cylindrical cylinder, a hollow chamber connected to one axial end of the cylinder and having an internal space interconnected with the cylinder, an atomization unit attached to the other axial end of the cylinder, and an exhaust device capable of evacuating the chamber and the internal space of the cylinder at a variable pressure, wherein the atomization unit comprises a tundish for storing molten metal, a molten metal nozzle for ejecting the molten metal in the tundish toward the inside of the cylinder, and a gas nozzle disposed integrally with the molten metal nozzle for injecting gas into the molten metal ejected from the molten metal nozzle, and the cross-sectional area of ​​the internal space perpendicular to the axial direction of the cylinder is smaller in the cylinder than that of the chamber.

[0008] [2] In the above aspect [1], the gas atomizing apparatus further has an exhaust control unit, and the exhaust control unit controls the output of the exhaust device and adjusts the pressure in the internal space based on at least one of the temperature of the molten metal in the tundish and the particle size of the metal powder to be produced.

[0009] [3] In the above aspect [2], the exhaust control unit may perform control to reduce the pressure in the internal space when the temperature of the molten metal in the tundish is lower than a reference value.

[0010] [4] In the above aspect [2] or [3], the exhaust control unit may be configured to control the pressure in the internal space to be higher as the particle size of the metal powder to be produced becomes smaller.

[0011] [5] In any one of the above aspects [1] to [4], the cylinder may be attached to the chamber so as to be movable back and forth along the axial direction, and the atomizing unit may be detachable from the cylinder.

[0012] [6] In any one of the above aspects [1] to [5], a gas atomizing nozzle equipped with the molten metal nozzle and the gas nozzle may be fixed to the tundish to form the atomizing unit. Effect of the Invention

[0013] In the gas atomizing device according to the present invention having the configuration of [1] above, the exhaust device can evacuate the internal space of the chamber and the cylinder at a variable pressure. The pressure in the hollow part of the cylinder, which is the space facing the tip of the molten metal nozzle, is determined by the balance between the gas injection from the gas nozzle and the exhaust by the exhaust device. By increasing the output of the exhaust device and lowering the pressure in the internal space of the cylinder, the discharge speed of the molten metal from the molten metal nozzle can be increased. Therefore, when the molten metal nozzle is about to be clogged due to solidification of the molten metal, the output of the exhaust device can be increased to increase the discharge speed of the molten metal from the molten metal nozzle and increase the amount of heat supplied to the tip of the molten metal nozzle, thereby suppressing the progress of the blockage of the molten metal nozzle.

[0014] Here, in the gas atomizing device according to the present invention, the cross-sectional area of ​​the internal space of the cylinder is smaller than the cross-sectional area of ​​the internal space of the chamber. Therefore, compared to the inside of the chamber in the case where a cylinder with such a small cross-sectional area is not provided and the molten metal is directly discharged into the chamber, the pressure inside the cylinder changes over a wide range due to the injection of gas from the gas nozzle and the exhaust by the exhaust device. In addition, the pressure inside the cylinder can be sensitively changed by adjusting the output of the exhaust device. Therefore, when the molten metal nozzle is about to be blocked due to solidification of the molten metal, the pressure inside the cylinder can be significantly reduced by increasing the output of the exhaust device, and the progress of the blockage of the molten metal nozzle can be strongly suppressed. In this way, according to the gas atomizing device according to the present invention, the blockage of the molten metal nozzle can be suppressed by utilizing the pressure change inside the cylinder without using a special structure of the molten metal nozzle or excessive heating of the molten metal.

[0015] On the other hand, by lowering the output of the exhaust device, the pressure inside the cylinder can be increased. In the gas atomization process, by increasing the pressure in the space into which the molten metal is discharged and decreasing the discharge speed of the molten metal, the particle size of the produced metal powder can be reduced. By utilizing the fact that the pressure inside the cylinder can be changed over a wide range and sensitively by adjusting the output of the exhaust device, the particle size of the produced metal powder can be controlled over a wide range. In particular, by lowering the output of the exhaust device, fine metal powder can be produced with high efficiency.

[0016] In the above aspect [2], the exhaust control unit controls the output of the exhaust device based on at least one of the temperature of the molten metal in the tundish and the particle size of the metal powder to be produced. The progress of clogging of the molten metal nozzle depends greatly on the temperature of the molten metal in the tundish, and as described above, the progress of clogging of the molten metal nozzle can be suppressed by controlling the pressure in the cylinder. Similarly, the particle size of the produced metal powder can be controlled by controlling the pressure in the cylinder. Therefore, by controlling the output of the exhaust device and controlling the pressure in the cylinder using at least one of the temperature of the molten metal in the tundish and the particle size of the metal powder to be produced as an index, it is possible to effectively suppress clogging of the molten metal nozzle and produce metal powder having a desired particle size.

[0017] In the above aspect [3], the exhaust control unit controls the pressure in the internal space to be lowered when the temperature of the molten metal in the tundish is lower than a reference value. Since the lower the temperature of the molten metal in the tundish, the more likely it is that the molten metal nozzle will become clogged due to solidification of the molten metal, by controlling the exhaust device to increase its output and lower the pressure in the cylinder, the progress of the clogging of the molten metal nozzle can be effectively suppressed.

[0018] In the above aspect [4], the exhaust control unit controls the pressure in the internal space to be higher as the grain size of the metal powder to be produced becomes smaller. The higher the pressure in the cylinder and the slower the discharge speed of the molten metal, the finer the metal powder with a smaller grain size can be produced. Therefore, by controlling the output of the exhaust device to be lowered and the pressure in the cylinder to be higher as the grain size of the metal powder to be produced becomes smaller, it is possible to obtain the intended fine powder.

[0019] In the above embodiment [5], the cylinder is attached to the chamber so that it can move back and forth. Then, after replacing the atomizing unit, the cylinder can be brought into close contact with the atomizing unit by moving the cylinder forward toward the atomizing unit. By bringing the cylinder into close contact with the atomizing unit, the airtightness of the space inside the cylinder is increased, and the pressure inside the cylinder can be easily changed over a wide range. In addition, by utilizing the movement of the cylinder back and forth, the workability of operations involving the attachment and detachment of the atomizing unit to and from the cylinder, such as replacement of the atomizing unit, is improved.

[0020] In the above embodiment [6], a gas atomizing nozzle equipped with a molten metal nozzle and a gas nozzle is fixed to a tundish to form an atomizing unit. In this case, the entire atomizing unit can be attached and detached to the cylinder as a whole, and maintenance of the gas atomizing device can be easily performed. In particular, when the cylinder can be moved forward and backward with respect to the chamber, the atomizing unit can be easily attached and detached by utilizing the forward and backward movement of the cylinder. [Brief description of the drawings]

[0021] [Figure 1] 1 is a schematic diagram showing an outline of a gas atomizing device according to one embodiment of the present invention. [Diagram 2] FIG. 2 is an enlarged cross-sectional view showing the vicinity of a cylinder of the gas atomizing device. [Diagram 3](a) is a graph showing the time variations of the exhaust blower output, the discharge speed of the molten alloy, and the gas / metal ratio when the gas atomizer is operated while controlling the exhaust blower output. (b) shows the relationship between the exhaust blower output and the discharge speed ratio of the molten metal, which is obtained from the results of (a). DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0022] Hereinafter, a gas atomizing device according to one embodiment of the present invention will be described with reference to the drawings.

[0023] [Outline of gas atomization equipment] Fig. 1 shows a schematic configuration of a gas atomizing device 1 according to one embodiment of the present invention. Fig. 2 shows an enlarged view of a cylinder 21 and the surrounding area of ​​the gas atomizing device 1. Hereinafter, directions such as up and down will follow the directions shown in Figs.

[0024] The gas atomizing apparatus 1 according to this embodiment includes a furnace body 2 consisting of a chamber 22 and a cylinder 21, an atomizing unit 5, and an exhaust blower 6 as an exhaust device. The gas atomizing apparatus 1 further includes, optionally, a temperature measuring unit 81 and an exhaust control unit 82. The atomizing unit 5 includes a gas atomizing nozzle 3 in which a molten metal nozzle 31 and a gas nozzle 32 are integrally arranged, and a tundish 4. In the illustrated embodiment, two gas atomizing nozzles 3 are provided.

[0025] The furnace body 2 is a component that forms the outer shell of the gas atomizing device 1, and includes a chamber 22 and a cylinder 21. The chamber 22, which is the main body of the furnace body 2, is configured as a hollow container. The cylinder 21 also forms part of the outer shell of the gas atomizing device 1, and is configured as a hollow cylindrical component. In the illustrated embodiment, the cylinder 21 is configured as a cylindrical component, and the axial direction is aligned in the vertical direction.

[0026] At the lower end of the cylinder 21, the chamber 22 is connected to the cylinder 21 to form the furnace body 2, and the internal spaces of the cylinder 21 and the chamber 22 are mutually connected. In detail, at the upper end of the chamber 22, a hollow cylindrical neck 221 whose inner diameter is formed slightly larger than the outer diameter of the cylinder 21 is provided, and a part of the lower end side of the cylinder 21 is inserted into the neck 221 of the chamber 22. An O-ring seal 23 is disposed between the neck 221 of the chamber 22 and the cylinder 21, sealing the gap between the cylinder 21 and the chamber 22. The cylinder 21 is attached to the chamber 22 so as to be movable forward and backward along the axial direction. That is, the cylinder 21 can move up and down in the vertical direction. The up and down movement of the cylinder 21 can be driven by an actuator (hydraulic or air type) not shown, and can be fixed in a state where it is raised and lowered to a desired height.

[0027] The cylinder 21 and the chamber 22 have different cross-sectional areas. That is, in a cross section perpendicular to the axial direction (up-down direction) of the cylinder 21, the cross-sectional area of ​​the internal space of the cylinder 21 is smaller than that of the chamber 22. The specific cross-sectional areas of the chamber 22 and the cylinder 21 are not particularly specified, but from the viewpoint of fully obtaining the effect of providing the cylinder 21 with a smaller cross-sectional area as described later, it is preferable that the cross-sectional area of ​​the internal space of the cylinder 21 is 0.3% or more and 30% or less of the cross-sectional area of ​​the internal space of the chamber 22. Furthermore, it is preferable that the volume of the cylinder 21 is smaller than the volume of the chamber 22.

[0028] An exhaust blower 6 is connected to the chamber 22 as an exhaust device. The exhaust blower 6 exhausts the internal space of the chamber 22 and the internal space of the cylinder 21 that communicates with the chamber 22. The exhaust blower 6 can change its output, and by changing the output, it is possible to exhaust the internal space of the furnace body 2 consisting of the chamber 22 and the cylinder 21 at a variable pressure. In other words, by increasing the output of the exhaust blower 6, it is possible to increase the exhaust speed and lower the pressure in the internal space of the furnace body 2. The exhaust device is not limited to the exhaust blower, and various exhaust devices can be used as long as they can exhaust (reduc) the internal space of the furnace body 2 at a variable pressure. In detail, the exhaust blower 6 is arranged by branching a path from the bottom of the chamber 22 to a cyclone 71 that classifies the produced metal powder and a hopper 72 that accumulates the classified metal powder.

[0029] The atomizing unit 5 is a unit that ejects molten metal to atomize it, and is attached to the upper end of the cylinder 21 of the furnace body 2. As described above, the atomizing unit 5 includes the molten metal nozzle 31, the gas nozzle 32, and the tundish 4. The molten metal nozzle 31 and the gas nozzle 32 are integrally arranged to form a confined gas atomizing nozzle 3. The tundish 4 is configured as a container capable of storing molten metal, and is arranged with its bottom in close contact with the upper end of the cylinder 21. In detail, a bottom plate 41 attached to the bottom surface of the tundish 4 is arranged in close contact with the upper end surface of the cylinder 21, with an O-ring seal 24 appropriately sandwiched therebetween.

[0030] The molten metal nozzle 31 has a nozzle hole 311 through which the molten metal can pass. The base end of the molten metal nozzle 31 is attached to the bottom of the tundish 4, and the nozzle hole 311 is connected to the space inside the tundish 4. The tip side of the molten metal nozzle 311 protrudes toward the hollow part of the cylinder 21, and the molten metal inside the tundish 4 can be discharged from the tip of the molten metal nozzle 31 toward the hollow part of the cylinder 21. The gas nozzle 32 is configured as a member having a gas injection port surrounding the outer periphery of the tip of the molten metal nozzle 31, and can inject inert gas supplied from a gas supply source (not shown) at high pressure. The gas injected from the gas nozzle 32 is injected from obliquely above toward the area immediately below the tip of the molten metal nozzle 31.

[0031] The atomizing unit 5 is attached to the cylinder 21 at a bottom plate 41 provided on the bottom surface of the tundish 4, but is preferably detachable from the cylinder 21. Furthermore, it is preferable that the gas atomizing nozzle 3 equipped with the molten metal nozzle 31 and the gas nozzle 32 is fixed to the tundish 4 to constitute the atomizing unit 5. In other words, it is preferable that the entire atomizing unit 5 can be attached and detached as a whole to the cylinder 21 while the gas atomizing nozzle 3 remains fixed integrally to the tundish 4.

[0032] The temperature measuring unit 81 is a member capable of measuring the temperature of the molten metal in the tundish 4. For example, the temperature measuring unit 81 may be provided as a thermocouple attached to the tundish 4. The temperature measuring unit 81 such as a thermocouple may be of a wired type that reads the temperature value, but when the atomizing unit 5 is detachable from the cylinder 21, it is preferable to use a temperature measuring unit 81 that is capable of wireless communication. In that case, it is preferable to configure the temperature measured by the temperature measuring unit 81 so that it can be read by an external device such as an exhaust control unit 82 via wireless communication.

[0033] The exhaust control unit 82 is composed of a calculation and control device such as a CPU, and can control the output of the exhaust blower 6. The exhaust control unit 82 may control the output of the exhaust device based on at least one of the temperature of the molten metal in the tundish 4 measured by the temperature measurement unit 81 and the particle size of the metal powder to be produced in the gas atomizing device 1. When controlling the output of the exhaust blower 6, the exhaust control unit 82 may also take into consideration other conditions related to the production of metal powder, such as the component composition of the molten metal.

[0034] In the gas atomizing device 1, when producing metal powder, the internal space of the furnace body 2 is evacuated in advance by the exhaust blower 6. Then, molten metal is poured into the tundish 4 and discharged from the molten metal nozzle 31. At the same time, high-pressure gas is ejected from the gas nozzle 32 and sprayed onto the molten metal discharged from the molten metal nozzle 31. The molten metal is then pulverized into fine droplets by the sprayed gas. The fine droplets are cooled and solidified while passing through the cylinder 21, forming fine powder of metal. The formed metal powder passes through the cylinder 21 and reaches the chamber 22, where the atomizing gas and the metal powder are separated by the cyclone 71 connected to the chamber 22, and the metal powder is accumulated in the hopper 72.

[0035] In this way, the exhaust blower 6 continues to evacuate the internal space of the furnace body 2 while the metal powder is being produced, and the output of the exhaust blower 6 is controlled by the exhaust control unit 82. The output of the exhaust blower 6 may be controlled so as not to change from an initially set state, or may be controlled to change midway according to the progress of the production of the metal powder. The gas atomizing device 1 according to this embodiment controls the discharge speed of the molten metal from the molten metal nozzle 31 by the pressure in the internal space of the cylinder 21. Next, the control of the pressure in the internal space of the cylinder 21 by controlling the output of the exhaust blower 6 and the phenomena caused by this will be described in detail.

[0036] [Effect of pressure inside the cylinder] In the gas atomizing device 1 according to this embodiment, the gas atomizing nozzle 3 including the molten metal nozzle 31 and the gas nozzle 32 is attached facing the upper end of the cylinder 21, and the discharge speed of the molten metal from the molten metal nozzle 31 is affected by the pressure in the internal space of the cylinder 21. The lower the pressure (back pressure) in the internal space of the cylinder 21, the stronger the molten metal is sucked out from the molten metal nozzle 31, and the greater the discharge speed of the molten metal.

[0037] The pressure in the internal space of the cylinder 21 is determined as a balance between the pressure rise caused by the ejection of high-pressure gas from the gas nozzle 32 and the pressure drop caused by exhausting the gas by the exhaust blower 6, and the higher the output of the exhaust blower 6, the lower the pressure in the cylinder 21. Although the internal spaces of the cylinder 21 and the chamber 22 are connected together, the supply of high-pressure gas from the gas nozzle 32 is performed locally at the upper part of the cylinder 21, so the internal pressures of the cylinder 21 and the chamber 22 are not necessarily the same. In particular, in the gas atomizing device 1 according to this embodiment, the cross-sectional area of ​​the internal space perpendicular to the axial direction of the cylinder 21 is smaller in the cylinder 21 than in the chamber 22. Therefore, the cylinder 21 is more significantly affected by the pressure rise caused by the ejection of high-pressure gas from the gas nozzle 32 and the pressure drop caused by the exhaust blower 6. As a result, the pressure in the internal space of the cylinder 21 fluctuates over a larger pressure range than the pressure in the internal space of the chamber 22 when the cylinder 21 is not provided. Therefore, the pressure inside the cylinder 21 can be changed over a wide range by adjusting the output of the exhaust blower 6. That is, the amount of pressure drop when the output of the exhaust blower 6 is increased and the amount of pressure rise when the output of the exhaust blower 6 is decreased become large. In addition, when the output of the exhaust blower 6 is changed, the pressure inside the cylinder 21 changes sensitively.

[0038] As described above, the lower the pressure inside the cylinder 21, the higher the discharge speed of the molten metal. In the gas atomizing device 1 according to the present embodiment, the cross-sectional area of ​​the internal space of the cylinder is small, so that the pressure inside the internal space of the cylinder 21 can be changed over a wide range, and therefore the discharge speed of the molten metal can be easily increased significantly. By utilizing this, clogging of the molten metal nozzle 31 can be suppressed as follows.

[0039] In the confined type gas atomizing nozzle 3, high pressure gas is injected from the gas nozzle 32 to a position immediately adjacent to the tip of the molten metal nozzle 31 to atomize and cool the molten metal, so that the tip of the molten metal nozzle 31 is cooled by the gas. Then, the molten metal may solidify in the molten metal nozzle 31, causing clogging of the molten metal nozzle 31. In particular, inclusions contained in the molten metal are likely to cause clogging of the molten metal nozzle 31. However, in the gas atomizing device 1 according to the present embodiment, if the output of the exhaust blower 6 is increased and the pressure in the cylinder 21 is reduced when the molten metal nozzle 31 is about to be clogged, the discharge speed of the molten metal from the molten metal nozzle 31 increases. Then, the molten metal is discharged without stagnation at the tip of the molten metal nozzle 31. Furthermore, the supply rate of high-temperature molten metal from the tundish 4 to the molten metal nozzle 31 also increases, and the amount of heat supplied to the tip of the molten metal nozzle 31 increases, so that the metal material that has solidified or is about to solidify at the tip of the molten metal nozzle 31 can be melted and discharged from the tip. By utilizing these phenomena, the progress of blockage of the molten metal nozzle 31 can be suppressed by increasing the output of the exhaust blower 6.

[0040] When the temperature of the molten metal in the tundish 4 becomes low, the molten metal nozzle 31 is likely to be clogged, so the temperature of the molten metal in the tundish 4 is used as an index to suppress clogging by increasing the output of the exhaust blower 6. In other words, the exhaust control unit 82 may control the output of the exhaust blower 6 based on the temperature of the molten metal in the tundish 4 measured by the temperature measurement unit 81. For example, when the temperature measured by the temperature measurement unit 81 becomes lower than a predetermined reference value, the exhaust control unit 82 may increase the output of the exhaust blower 6 and perform control to reduce the pressure in the internal space of the furnace body 2. As a result, the pressure inside the cylinder 21 is significantly reduced, and the discharge speed of the molten metal increases, thereby suppressing the progress of clogging of the molten metal nozzle 31. In addition, in the early stage of the production of metal powder, immediately after the discharge of the molten metal from the molten metal nozzle 31 is started, the temperature of the molten metal discharged from the molten metal nozzle 31 is low, so the discharge speed is kept low, and the molten metal nozzle 31 is likely to be clogged. Therefore, after starting to discharge the molten metal, the output of the exhaust blower 6 is increased for a while to reduce the pressure inside the cylinder 21, and then the output of the exhaust blower 6 is reduced once the molten metal nozzle 31 has reached a sufficiently high temperature.

[0041] In this way, by providing the cylinder 21 with a small cross-sectional area of ​​the internal space in the furnace body 2 and changing the pressure inside the cylinder 21 by controlling the output of the exhaust blower 6, clogging of the molten metal nozzle 31 can be efficiently suppressed. In order to suppress clogging of the molten metal nozzle 31, it is not necessary to heat the molten metal to an excessively high temperature that would cause deterioration of the components of the atomizing unit 5, such as the refractory material of the tundish 4. In addition, it is not necessary to use a molten metal nozzle designed with a special structure to suppress clogging, such as that disclosed in Patent Document 1.

[0042] Furthermore, in the gas atomizing device 1 according to the present embodiment, not only can the clogging of the molten metal nozzle 31 be suppressed, but also the state of the produced metal powder can be controlled by utilizing the change in pressure in the cylinder 21 caused by controlling the output of the exhaust blower 6. In the gas atomizing process, the particle size of the produced metal powder tends to become smaller and the content of fine powder in the metal powder tends to become higher as the discharge speed of the molten metal is reduced and the mass flow ratio (gas / metal ratio) of the atomizing gas injected from the gas nozzle 32 to the molten metal discharged from the molten metal nozzle 31 is increased (the larger the mass flow rate of the gas is, the smaller the mass flow rate of the molten metal is). Therefore, in the gas atomizing device 1 according to the present embodiment, when the possibility of the clogging of the molten metal nozzle 31 occurring is low, such as when the temperature of the molten metal nozzle 31 is sufficiently high, the output of the exhaust blower 6 is reduced, the pressure in the cylinder 21 is increased, and the discharge speed of the molten metal is reduced, thereby producing metal powder with a small particle size.

[0043] For example, the gas atomizing device 1 may be configured so that the exhaust control unit 82 controls the output of the exhaust blower 6 based on the particle size of the metal powder to be produced. In other words, the smaller the particle size of the metal powder to be produced, the more the exhaust control unit 82 controls to reduce the output of the exhaust blower 6 and increase the pressure in the internal space of the furnace body 2. This increases the pressure inside the cylinder 21 and reduces the discharge speed of the molten metal, resulting in the production of fine metal powder.

[0044] In the gas atomizing device 1 according to the present embodiment, a confined type gas atomizing nozzle 3 that injects gas in the immediate vicinity of the position where the molten metal is discharged is used, and fine metal powder is more easily obtained than in the case of using a free-fall type gas atomizing device that injects gas at a position far away from the tip of the molten metal nozzle. By combining this confined type gas atomizing nozzle 3 and carrying out the refinement of metal powder by controlling the output of the exhaust blower 6, fine metal powder can be produced with high yield and productivity. As described above, the confined type gas atomizing nozzle 3 is more likely to cause clogging of the molten metal nozzle 31 than the free-fall type due to its structure, but if the suppression of clogging by controlling the output of the exhaust blower 6 is performed in combination with the control of particle size, a further high effect can be obtained in improving the yield and productivity in the production of fine metal powder.

[0045] In this embodiment, as described above, the cross-sectional area of ​​the internal space of the cylinder 21 is made small to increase the range of pressure changes inside the cylinder 21, but the change in internal pressure of the chamber 22 is not as large as that of the cylinder 21. Therefore, the chamber 22, which occupies a large volume, does not need to be made of a thick material or have ancillary equipment so as to withstand large pressure changes.

[0046] [Using the rising and falling of cylinders] As described above, in the gas atomizing device 1 according to this embodiment, the cylinder 21, whose internal space has a cross-sectional area smaller than that of the chamber 22, is provided together with the variable-output exhaust blower 6, so that the discharge speed of the molten metal from the molten metal nozzle 31 can be controlled by utilizing the pressure change inside the cylinder 21. Furthermore, by making the cylinder 21 capable of ascending and descending relative to the chamber 22, the effect of pressure control inside the cylinder 21 can be further enhanced by utilizing the ascending and descending of the cylinder 21.

[0047] The atomizing unit 5 includes the tundish 4, which is a heavy and voluminous member, and it may be difficult to arrange the atomizing unit 5 in the correct position above the thin cylinder 21 and to attach the atomizing unit 5 without creating a gap between the bottom surface (bottom plate 41) of the tundish 4 and the upper end surface of the cylinder 21. Therefore, if the atomizing unit 5 is attached by raising the cylinder 21 and pressing it against the bottom plate 41, a gap is less likely to be created between the tundish 4 and the cylinder 21. This improves the airtightness of the cylinder 21, and makes it easier to control the pressure inside the cylinder 21 sensitively over a wide pressure range by controlling the output of the exhaust blower 6.

[0048] In addition, the atomizing unit 5 needs to be attached to and detached from the furnace body 2 in order to change the metal material used, or to perform maintenance on components such as refractories. By utilizing the lifting and lowering of the cylinder 21, the convenience of the work involved in attaching and detaching the atomizing unit 5 can be improved. For example, the atomizing unit 5 is placed with the cylinder 21 lowered, and then the cylinder 21 is raised, so that the atomizing unit 5 can be easily attached to a predetermined position relative to the cylinder 21. Furthermore, when the cylinder 21 is subsequently raised, the cylinder 21 can be brought into close contact with the bottom plate 41 at the bottom of the tundish 4 as described above, thereby improving the airtightness of the cylinder 21.

[0049] The ease of attachment / detachment and maintenance of the atomizing unit 5 can be further improved by previously fixing the gas atomizing nozzle 3 to the tundish 4 and integrating the atomizing unit 5 as a whole. Furthermore, if a temperature measuring unit 81 capable of wireless communication is used, it becomes possible to attach and detach the atomizing unit 5 to and from the cylinder 21 without attaching and detaching wiring for the temperature measuring unit 81. EXAMPLES

[0050] Examples of the present invention are shown below. However, the present invention is not limited to these examples. Here, it was verified whether it is possible to actually control the discharge speed of the molten metal by controlling the output of the exhaust blower.

[0051] [Test Method] As shown in Figures 1 and 2, a gas atomization device was prepared by attaching an atomization unit equipped with a confined type gas atomization nozzle to a furnace body. The furnace body had a chamber and a cylinder whose internal space had a smaller cross-sectional area than the chamber. A variable output exhaust blower was attached to exhaust the internal space of the furnace body.

[0052] Metal powder was produced using the gas atomization device. An Fe-based alloy was used as the raw material molten metal. When producing the metal powder, the exhaust blower was first operated at 100% output, and after the molten metal started to be discharged from the molten metal nozzle, the output of the exhaust blower was gradually reduced. In addition, during the production of the metal powder, the discharge speed of the molten metal was evaluated based on the weight of the metal powder produced in a certain period of time, and the gas / metal ratio was evaluated based on the mass of the metal powder produced in a certain period of time and the gas flow rate used for gas atomization.

[0053] [Test Results] Figure 3(a) shows the results of recording the time changes of the discharge speed of the molten metal and the gas / metal ratio, along with the output of the exhaust blower. It can be seen that the discharge speed of the molten metal tends to decrease as the output of the exhaust blower is reduced, except for the region where the discharge speed increases rapidly immediately after the start of the discharge of the molten metal. In addition, the gas / metal ratio increases as the discharge speed decreases. Furthermore, Figure 3(b) plots the relationship between the output of the exhaust blower and the discharge speed ratio of the molten metal, as read from Figure 3(a). Here, the discharge speed ratio is the discharge speed of the molten metal, with the value at 60% of the blower output being set to 1. Figure 3(b) confirms that the discharge speed ratio of the molten metal increases linearly as the output of the exhaust blower increases.

[0054] The above results are interpreted as meaning that by lowering the output of the exhaust blower, the pressure inside the cylinder increases, and the discharge speed of the molten metal is suppressed. It is also shown that by controlling the output of the exhaust blower, it is possible to control the discharge speed of the molten metal by utilizing the change in the pressure inside the cylinder, thereby suppressing clogging of the molten metal nozzle and controlling the particle size of the metal powder.

[0055] Although the embodiments of the present invention have been described above, the present invention is not particularly limited to these embodiments and various modifications can be made. [Explanation of symbols]

[0056] 1 Gas atomizing device 2 Furnace body 21 Cylinder 22 Chamber 3 Gas atomizing nozzle 31 Molten metal nozzle 32 Gas nozzle 4 Tundish 5 Atomization Unit 6 Exhaust blower (exhaust device) 81 Temperature measurement section 82 Exhaust control section

Claims

1. A hollow cylindrical cylinder; a hollow chamber connected to one axial end of the cylinder and having an internal space mutually communicating with the cylinder; an atomizing unit attached to the other end of the cylinder in the axial direction; an exhaust device capable of evacuating the chamber and the internal space of the cylinder at a variable pressure; the atomizing unit includes a tundish that stores a molten metal, a molten metal nozzle that discharges the molten metal in the tundish toward the inside of the cylinder, and a gas nozzle that is disposed integrally with the molten metal nozzle and that injects gas into the molten metal discharged from the molten metal nozzle; A gas atomizing device, wherein a cross-sectional area of ​​the internal space perpendicular to the axial direction of the cylinder is smaller in the cylinder than that of the chamber.

2. The gas atomizing device further includes an exhaust control unit, 2. The gas atomizing apparatus according to claim 1, wherein the exhaust control unit controls an output of the exhaust device and adjusts a pressure in the internal space based on at least one of a temperature of the molten metal in the molten metal nozzle and a particle size of the metal powder to be produced.

3. 3. The gas atomizing device according to claim 2, wherein the exhaust control unit performs control to reduce the pressure in the internal space when the temperature of the molten metal in the molten metal nozzle is lower than a reference value.

4. 3. The gas atomizing device according to claim 2, wherein the exhaust control unit performs control so as to increase the pressure in the internal space as the particle size of the metal powder to be produced decreases.

5. The cylinder is attached to the chamber so as to be movable back and forth along the axial direction, 5. The gas atomizing device according to claim 1, wherein the atomizing unit is detachable from the cylinder.

6. 6. The gas atomizing apparatus according to claim 5, wherein a gas atomizing nozzle including the molten metal nozzle and the gas nozzle is fixed to the tundish to form the atomizing unit.

Images