JP7266009B2 - atomizing device - Google Patents

Description

The present invention relates to an atomizer for producing fine metal powder.

One of the methods for producing fine metal powder is the atomization method. In the atomizing method, high-pressure gas or water is injected into the molten metal flowed down from a nozzle to pulverize the metal flow, which is then cooled and solidified to be pulverized. As an atomizing apparatus for producing metal powder by such a method, molten metal melted in a melting furnace is supplied to a container such as a tundish, and the molten metal is allowed to flow down through a nozzle provided at the bottom of the container. In addition to this device, there is a device in which a nozzle is provided at the bottom of an induction heating furnace and the molten metal melted in the induction heating furnace flows directly down from the nozzle. In such an induction heating furnace, a graphite crucible is used as an electrically conductive crucible (see, for example, Patent Document 1).

When the metal powder is produced by the atomizer, if the temperature of the molten metal drops before it flows out of the nozzle, the nozzle hole may be blocked by the solidified metal. In particular, when the hole diameter of the nozzle is reduced in order to produce finer metal powder, the problem of clogging due to solidified metal becomes greater.

Therefore, an atomizing device having a nozzle made of graphite has also been proposed (see, for example, Patent Document 2). Since graphite has a high thermal conductivity, heat transfer from the heated graphite crucible raises the temperature of the nozzle, thereby suppressing a decrease in the temperature of the molten metal flowing out from the nozzle. In addition, the graphite nozzle can also be induction-heated by the coil for induction-heating the graphite crucible.

However, since graphite has low resistance to molten metal, if the nozzle is made of graphite, there is a problem that the nozzle is worn out by the flowing molten metal. Furthermore, since graphite is easily oxidized, the surface becomes brittle due to oxidation, which further reduces the resistance to molten metal. If the nozzle is worn out by the outflow of the molten metal, the hole diameter of the nozzle is enlarged, and the metal powder cannot be made finer. Therefore, there has been a demand for an atomizer that has a high resistance to molten metal, suppresses enlargement of the hole diameter, and suppresses a decrease in the temperature of the molten metal that flows out from the nozzle.

JP-A-10-030103 Japanese Patent Application Laid-Open No. 2006-002176

Therefore, in view of the above circumstances, it is an object of the present invention to provide an atomizing device that has high resistance to molten metal, suppresses enlargement of the hole diameter, and suppresses a decrease in the temperature of the molten metal that flows out from the nozzle. and

In order to solve the above problems, the atomizing device according to the present invention includes:
"An atomizing device in which a molten metal contained in an induction-heated graphite crucible is flown out from a nozzle provided at the bottom of the crucible, and high-pressure gas or high-pressure water is injected into the flowing out molten metal,
The nozzle is made of oxide ceramics, and
a graphite heating block surrounding a portion of the nozzle protruding from the bottom of the crucible;
The heating block is in contact with all of the outer peripheral surface of the nozzle except for the crucible contact surface that is in contact with the crucible,
The nozzle and the heating block are in the interior space of the coil for inductively heating the crucible.

In the atomizer of this configuration, since the nozzle is made of oxide ceramics, it has a high resistance to molten metal, and unlike graphite, there is no problem of deterioration due to oxidation. Despite these advantages, oxide ceramic nozzles have low thermal conductivity, so that heat is difficult to transfer from the heated crucible, and there is a risk that the temperature of the outflowing molten metal will drop.

To solve this problem, in this configuration, a nozzle and a graphite heating block are arranged in the internal space of a coil for induction heating (electromagnetic induction heating, high-frequency induction heating) of the crucible, and the nozzle heats the crucible from the bottom of the crucible. The protruding part is surrounded by a heating block. When a current is applied to the coil to inductively heat the graphite crucible, the graphite heating block is heated along with the crucible. This heats the nozzles surrounded by the heating block. Therefore, by preheating the nozzle with the heating block before the molten metal flows out from the nozzle, it is possible to suppress the decrease in the temperature of the molten metal flowing out from the nozzle.

As will be described later in detail, the present inventors' investigation revealed that if there is a gap between the outer peripheral surface of the nozzle and the heating block, the nozzle cannot be effectively heated by the heating block. On the other hand, in this configuration, the heating block is in contact with all of the outer peripheral surfaces of the nozzle except for the crucible contact surface that is in contact with the crucible. can be effectively heated.

The atomizing device according to the present invention, in addition to the above configuration,
``The outer shape of the nozzle is an inverted cone whose outer diameter gradually decreases from the upstream end to the downstream end, and does not have a stepped portion where the outer diameter changes discontinuously.'' be able to.

As will be described later in detail, the present inventors have found that if the nozzle has a step portion in which the outer diameter changes discontinuously, cracks are likely to occur in that portion. It is thought that this is because the oxide ceramics forming the nozzle has low thermal conductivity and low thermal shock resistance, and thermal stress concentrates on the corners of the stepped portions. On the other hand, the nozzle of this configuration has an inverted conical shape in which the outer diameter gradually decreases from the upstream end to the downstream end, and does not have a stepped portion. The occurrence of

The atomizing device according to the present invention, in addition to the above configuration,
"The crucible is mounted and supported on the heating block."

Since the heating block of this configuration supports and mounts the crucible, it is a fairly large block and has a large heat capacity. Therefore, even if the conditions for starting and stopping the outflow of molten metal and the conditions for induction heating change, the temperature of the heating block is less likely to change, and the temperature of the nozzle heated by the heating block is less likely to change. This further reduces the risk of cracks and other defects occurring in the nozzle due to thermal shock.

As described above, according to the present invention, it is possible to provide an atomizing device that has a high resistance to molten metal, suppresses enlargement of the hole diameter, and suppresses a decrease in the temperature of the molten metal that flows out from the nozzle. can.

1(a) is a longitudinal sectional view of an atomizing device according to an embodiment of the present invention, and (b) is an enlarged sectional view along AA and BB. 2 is a graph showing changes in the temperature of molten metal and the temperature of the nozzle when the output to the coil is gradually increased in the atomizer of FIG. 1. FIG. (a) A vertical cross-sectional view of an atomizing device of a comparative example, and (b) an enlarged cross-sectional view between CC and DD. 7 is a graph showing changes in the temperature of the molten metal and the temperature of the nozzle when the output to the coil is changed for the atomizer of the comparative example.

An atomizing device 1 according to a specific embodiment of the present invention will be described below with reference to the drawings. The atomizing device 1 includes a crucible 10, a coil 40 for induction heating the crucible 10, a nozzle 20 provided at the bottom of the crucible 10, a heating block 30 for heating the nozzle 20, and a melt flowing out from the nozzle 20. An injection device (not shown) that injects high-pressure gas or high-pressure water onto the metal, and a lower container (not shown) that receives the metal powder generated by cooling and solidifying the metal flow finely pulverized by the high-pressure gas or high-pressure water. is the main configuration.

The crucible 10 is made of graphite and is a cylindrical container with an open bottom. A nozzle 20 is provided at the bottom of the crucible 10 . The nozzle 20 is made of oxide ceramics and has a cylindrical shape. The upstream end 21 is located in the inner space of the crucible 10 and the bottom of the crucible 10 is positioned so that the molten metal contained in the crucible 10 flows out from the nozzle hole 25 . , and the downstream end 22 protrudes from the bottom of the crucible 10 . The outer shape of the nozzle 20 is an inverted conical shape in which the outer diameter gradually decreases from the upstream end 21 to the downstream end 22, and does not have a step portion in which the outer diameter changes discontinuously. . At the upstream end 21 of the nozzle 20, the nozzle hole 25 has a large diameter, and at the downstream end 22, the diameter is reduced to form a small hole 25n.

The portion of nozzle 20 protruding from the bottom of crucible 10 is surrounded by a heating block 30 made of graphite. The heating block 30 is in contact with the entire outer peripheral surface of the nozzle 20 except for the crucible contact surface 24 which is in contact with the crucible 10 . In other words, no gap exists between the outer peripheral surface of the nozzle 20 and the heating block 30 .

The heating block 30 is a large block placed on a furnace bottom 50 made of a refractory material. The heating block 30 also rests and supports the crucible 10 thereon. A furnace bottom opening 50h is formed in the furnace bottom portion 50, and the fine holes 25n of the nozzle 20 face the furnace bottom opening 50h. The heating block 30 placed on the furnace bottom 50 and the crucible 10 placed on the heating block 30 are surrounded by a furnace wall 51 made of a refractory material. The coil 40 is wound around the furnace wall 51 , and the nozzle 20 and the heating block 30 are both in the interior space of the coil 40 .

When a current is passed through the coil 40 while the metal is contained inside the crucible 10, the metal is melted by induction heating. A stopper 60 is inserted into the crucible 10 in order to open and close the nozzle hole 25 and adjust the flow rate of the molten metal through the nozzle hole 25 . The stopper 60 is a long rod-shaped member having a hemispherical or spindle-shaped head portion 61 formed at its lower end. When the stopper 60 is lifted to open the nozzle hole 25, the molten metal flows into the nozzle hole 25 and flows out as a thin metal stream from the hole 25n. The flow rate of molten metal can be adjusted by adjusting the degree to which the nozzle hole 25 is opened by the head portion 61 .

Since the nozzle 20 is made of oxide ceramics, it has a high resistance to molten metal, and unlike graphite, there is no problem of deterioration due to oxidation.

A portion of the nozzle 20 protruding from the bottom of the crucible 10 is surrounded by a heating block 30, and the heating block 30 is made of graphite. Both the heating block 30 and the nozzle 20 are then in the interior space of the coil 40 . Therefore, by applying current to the coil 40 to induction-heat the crucible 10 , the heating block 30 is induction-heated together with the crucible 10 , and the nozzle 20 is heated by the heating block 30 having a high temperature. Therefore, by preheating the nozzle 20 with the heating block 30 before the molten metal flows through the nozzle hole 25, the temperature of the molten metal flowing out from the nozzle hole 25 can be suppressed from decreasing.

Actually, using the atomizer 1 of this embodiment, a test was conducted in which the molten metal in the crucible 10 flowed out from the nozzle 20, and the temperature of the molten metal and the temperature of the nozzle 20 were measured. Magnesia-stabilized zirconia was used as oxide ceramics constituting the nozzle 20 . Pure silver was used as the metal to be dissolved. The temperature of the nozzle 20 is measured by a thermocouple placed in the middle of the outer peripheral surface of the nozzle 20 (point P1 in FIG. 1), and the temperature of the molten metal is measured by a thermocouple placed at the tip of the head portion 61 of the stopper 60. bottom.

FIG. 2 shows changes in the temperature of the nozzle 20 and the temperature of the molten metal when the power (output) supplied to the coil 40 is gradually increased. As the output to the coil 40 increases, the temperature of the nozzle 20 and the temperature of the molten metal also rise. It can be seen that the nozzle 20 is sufficiently heated by heating. Further, when the output to the coil 40 is interrupted (illustration, arrow X), the temperature of the molten metal drops, while the temperature of the nozzle 20 hardly changes. This is because the heating block 30 is large enough to support the crucible 10 and has a large heat capacity. It is considered that the temperature of the nozzle 20 in which the nozzle 20 is present is also less likely to change.

Observation of the nozzle 20 after the temperature measurement revealed no defects such as cracks.

In addition, a test was conducted in which a series of operations of induction heating by turning on the output to the coil 40, outflow of the molten metal from the nozzle 20, and turning off the output to the coil 40 were repeated. No defect such as generation was confirmed.

Next, an atomizing device 100 of a comparative example will be described. The atomizing device 100 of the comparative example differs from the atomizing device 1 of the embodiment in the external shape of the nozzle 120 and the heating blocks 130a and 130b, as shown in FIG. In the embodiment, the outer shape of the nozzle 20 is an inverted conical shape in which the outer diameter gradually decreases from the upstream end 21 to the downstream end 22, and has a step portion in which the outer diameter changes discontinuously. Nozzle 120 of the comparative example has an outer shape having a stepped portion 126 . Specifically, the outer diameter is gradually reduced from the upstream end 121 to the downstream end 122 halfway, and the outer diameter is constant from there to the downstream end 122, so that the outer diameter is discontinuous. It has steps 126 at changing positions. Further, in the embodiment, the heating block 30 was in contact with all of the outer peripheral surfaces of the nozzle 20 except for the crucible contact surface 24 in contact with the crucible 10, whereas in the comparative example the heating block , two annular heating blocks 130 a and 130 b having different inner diameters, and a gap exists between the heating blocks 130 a and 130 b and the nozzle 120 .

Regarding the atomizer 100 of the comparative example, changes in the temperature of the nozzle 120 and the temperature of the molten metal were measured when the output to the coil 40 was changed. The temperature of the nozzle 120 is measured by a thermocouple installed at a portion of the outer peripheral surface closer to the downstream end 122 than the stepped portion 126 (point P2 in FIG. 3). Measured by a thermocouple placed at the tip of 61. The measurement results are shown in FIG. In FIG. 4, arrows Y1 and Y2 indicate the time points at which metal (pure silver) is introduced into the crucible, and arrows Z1, Z2, and Z3 indicate the time points at which the molten metal (molten silver) is discharged from the pore 125n of the nozzle hole 125. ing.

In the comparative example, the temperature of the molten metal and the nozzle 120 also changed according to the output of the coil. It was 200° C. to 400° C. lower than the temperature of the metal. From this, it can be seen that in the comparative example, the nozzle 120 is not sufficiently heated by the induction heating of the heating blocks 130a and 130b. This is because although the heating blocks 130a and 130b surround the nozzle 120, they are not in contact with the outer peripheral surface of the nozzle 120, and there is a gap between the heating blocks 130a and 130b and the nozzle 120, that is, air with high heat insulation. This is thought to be due to the existence of a layer of

Moreover, when the nozzle 120 was observed after measuring the temperature, it was confirmed that cracks had occurred along the stepped portion 126 . It is believed that this is because the oxide ceramic (magnesia-stabilized zirconia) forming the nozzle 120 has a low thermal conductivity and a low thermal shock resistance, so thermal stress concentrates on the corners of the stepped portion 126 . rice field. Therefore, in order to suppress the occurrence of such cracks, it was considered effective to have a shape that does not have a step like the nozzle 20 of the embodiment.

As described above, the present invention has been described with reference to preferred embodiments, but the present invention is not limited to the above embodiments, and as shown below, various improvements can be made without departing from the scope of the present invention. and design changes are possible.

For example, in the above-described embodiments, the oxide ceramics constituting the nozzle was exemplified by magnesia-stabilized zirconia, but other materials such as calcia-stabilized zirconia, yttria-stabilized zirconia, alumina, mullite, and aluminum titanate are used. Oxide ceramics can be used without particular limitation.

1 atomizing device 10 crucible 20 nozzle 21 upstream end 22 downstream end 24 crucible contact surface 25 nozzle hole 30 heating block 40 coil 126 stepped portion

Claims (2)

An atomizing device in which molten metal contained in an induction-heated graphite crucible flows out from a nozzle provided at the bottom of the crucible, and high-pressure gas or high-pressure water is injected into the flowing out molten metal,
The nozzle is made of oxide ceramics, and
a graphite heating block surrounding a portion of the nozzle protruding from the bottom of the crucible;
The heating block is in contact with all of the outer peripheral surface of the nozzle except for the crucible contact surface that is in contact with the crucible,
The nozzle and the heating block are in the interior space of a coil for induction heating of the crucible,
The crucible is mounted and supported on the heating block
An atomizing device characterized by: The outer shape of the nozzle is an inverted conical shape in which the outer diameter gradually decreases from the upstream end to the downstream end, and does not have a step portion in which the outer diameter changes discontinuously. The atomizing device according to claim 1.

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