JP2021167456A - Atomizer - Google Patents

Abstract

To provide an atomizer which has high resistance to molten metal, suppresses expansion of hole diameter, and suppresses lowering of temperature of molten metal flowing out from a nozzle.SOLUTION: In an atomizer 1, molten metal housed in a graphite crucible 10 subjected to induction heating is made to flow out from a nozzle 20 provided at the bottom of the crucible, and high pressure gas or high pressure water is jetted to the flowing molten metal. The atomizer includes a heating block 30 made of graphite having a nozzle made of oxide ceramics and surrounding a portion protruding from the bottom of the crucible in the nozzle. The heating block is in contact with all of the outer peripheral surfaces of the nozzle except for the crucible contact surface 24 in contact with the crucible, and the nozzle and the heating block are in the internal space of a coil 40 for inductively heating the crucible.SELECTED DRAWING: Figure 1

Description

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

The atomization method is one of the methods for producing fine metal powder. In the atomizing method, the metal flow is finely pulverized by injecting high-pressure gas or water onto the molten metal flowing down from the nozzle, and then pulverized by cooling and solidifying. As an atomizing device 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 the device, there is a device in which a nozzle is provided at the bottom of the induction heating furnace to allow molten metal melted in the induction heating furnace to flow directly 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 producing metal powder by an atomizing device, if the temperature of the molten metal drops before it flows out from the nozzle, the nozzle hole may be blocked by the solidified metal. In particular, if the pore size of the nozzle is reduced in order to make the produced metal powder finer, the problem of clogging due to the solidified metal becomes greater.

Therefore, an atomizing device in which the nozzle is 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 causes the nozzle to become hot, and it is possible to suppress a decrease in the temperature of the molten metal flowing out from the nozzle. In addition, the graphite nozzle can also be induced and heated by the coil for inducing and 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 by the molten metal that flows out. Furthermore, since graphite is easily oxidized, the surface becomes brittle due to oxidation, and the resistance to molten metal is further lowered. When the nozzle is worn due to the outflow of the molten metal, the pore diameter of the nozzle is enlarged and the metal powder cannot be miniaturized. Therefore, there has been a demand for an atomizing device that has high resistance to molten metal, suppresses the expansion of the pore diameter, and suppresses a decrease in the temperature of the molten metal flowing out from the nozzle.

Japanese Unexamined Patent Publication No. 10-030103 Japanese Unexamined Patent Publication No. 2006-002176

Therefore, in view of the above circumstances, it is an object of the present invention to provide an atomizing apparatus which has high resistance to molten metal, suppresses expansion of pore diameter, and suppresses decrease in temperature of molten metal flowing out from a nozzle. Is to be.

In order to solve the above problems, the atomizing device according to the present invention
"An atomizing device in which molten metal housed in an induction-heated graphite crucible is discharged from a nozzle provided at the bottom of the crucible, and high-pressure gas or high-pressure water is injected onto the flowing molten metal.
The nozzle is made of oxide ceramics and
The nozzle is provided with a graphite heating block that surrounds a portion of the nozzle that protrudes from the bottom of the crucible.
The heating block is in contact with all of the outer peripheral surfaces of the nozzle except the crucible contact surface that is in contact with the crucible.
The nozzle and the heating block are in the internal space of the coil that induces and heats the crucible. "

In the atomizing apparatus having this configuration, since the nozzle is made of oxide ceramics, it has high resistance to molten metal, and unlike graphite, there is no problem of deterioration due to oxidation. Although it has such an advantage, the nozzle made of oxide ceramics has a low thermal conductivity, so that it is difficult to transfer heat from the heated crucible, and the temperature of the molten metal to be discharged may decrease.

In response to such a problem, in this configuration, a nozzle and a heating block made of graphite are arranged in the internal space of the coil for inductive heating (electromagnetic induction heating, high frequency induction heating) of the crucible, and the nozzle is used from the bottom of the crucible. The protruding part is surrounded by a heating block. When an electric current is passed through the coil to induce and heat the graphite crucible, the graphite heating block is heated together with the crucible. As a result, the nozzle surrounded by the heating block is heated. Therefore, by preheating the nozzle with a heating block prior to flowing out the molten metal from the nozzle, it is possible to suppress a decrease in the temperature of the molten metal flowing out from the nozzle.

As will be described in detail later, the present inventors have found that if there is a gap between the outer peripheral surface of the nozzle and the heating block, the heating block cannot effectively heat the nozzle. On the other hand, in this configuration, since the heating block is brought into contact with all of the outer peripheral surfaces of the nozzle except the crucible contact surface that is in contact with the crucible, the nozzle is provided by the induction-heated heating block. Can be effectively heated.

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

As will be described in detail later, it has been found by the present inventors that if the nozzle has a stepped portion whose outer diameter changes discontinuously, cracks are likely to occur in that portion. It is considered that this is because the oxide ceramics constituting the nozzle have low thermal impact resistance due to their low thermal conductivity, and the thermal stress is concentrated on the corners of the stepped portion. 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, so that a crack due to concentration of thermal stress occurs. The occurrence of is suppressed.

The atomizing device according to the present invention has the above configuration in addition to the above configuration.
It can be said that "the crucible is placed and supported on the heating block".

Since the heating block of this configuration is a block on which a crucible is placed and supported, it is a fairly large block and has a large heat capacity. Therefore, even if the conditions such as the start and stop of the outflow of the molten metal and the conditions of the induction heating change, the temperature of the heating block does not change easily, and the temperature of the nozzle heated by the heating block does not change easily. As a result, the possibility of defects such as cracks occurring in the nozzle due to thermal shock is further reduced.

As described above, according to the present invention, it is possible to provide an atomizing apparatus having high resistance to molten metal, suppressing expansion of pore diameter, and suppressing a decrease in temperature of molten metal flowing out from a nozzle. can.

(A) A vertical sectional view of an atomizing device according to an embodiment of the present invention, and (b) an enlarged sectional view between AA and BB. FIG. 5 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 gradually increased for the atomizing device of FIG. 1. (A) is a vertical cross-sectional view of the atomizing device of the comparative example, and (b) is an enlarged cross-sectional view between CC and DD. It is a graph which showed the change of the temperature of molten metal and the temperature of a nozzle when the output to a coil was changed about the atomizing apparatus of a comparative example.

Hereinafter, the atomizing device 1 according to a specific embodiment of the present invention will be described with reference to the drawings. The atomizing device 1 includes a crucible 10, a coil 40 for inducing and 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 melting flowing out from the nozzle 20. An injection device that injects high-pressure gas or high-pressure water onto metal (not shown) and a lower container that receives metal powder generated by cooling and solidifying a metal stream pulverized by high-pressure gas or high-pressure water (not shown). Is the main configuration.

The crucible 10 is made of graphite and is a bottomed cylindrical container that opens upward. A nozzle 20 is provided at the bottom of the crucible 10. The nozzle 20 is formed of oxide ceramics in a cylindrical shape, and the upstream end 21 is located in the internal space of the crucible 10 in order to allow the molten metal contained in the crucible 10 to flow out from the nozzle hole 25, and the bottom of the crucible 10 is formed. The downstream end 22 side 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 is gradually reduced from the upstream end 21 to the downstream end 22, and the shape 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 narrowed to form a pore 25n.

A portion of the nozzle 20 protruding from the bottom of the crucible 10 is surrounded by a graphite heating block 30. The heating block 30 is in contact with all of the outer peripheral surfaces of the nozzle 20 except the crucible contact surface 24, which is in contact with the crucible 10. That is, there is no void between the outer peripheral surface of the nozzle 20 and the heating block 30.

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

When an electric current is passed through the coil 40 with the metal contained in the crucible 10, the metal is melted by induction heating. A stopper 60 is inserted inside the crucible 10 in order to open and close the nozzle hole 25 and adjust the amount of molten metal flowing out 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 the lower end, and the head portion 61 can close the nozzle hole 25 at the upstream end 21 of the nozzle 20. When the stopper 60 is raised to open the nozzle hole 25, the molten metal flows into the nozzle hole 25 and flows out from the pore 25n as a thin metal flow. The outflow amount of the molten metal can be adjusted by 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 high resistance to molten metal, and unlike graphite, there is no problem of deterioration due to oxidation.

The 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 in the internal space of the coil 40. Therefore, by passing an electric current through the coil 40 to induce and heat the crucible 10, the heating block 30 is also induced and heated together with the crucible 10, and the nozzle 20 is heated by the heated block 30. Therefore, by preheating the nozzle 20 with the heating block 30 prior to flowing the molten metal through the nozzle hole 25, it is possible to suppress a decrease in the temperature of the molten metal flowing out from the nozzle hole 25.

Actually, using the atomizing device 1 of the present embodiment, a test was conducted in which the molten metal in the crucible 10 was discharged 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 the oxide ceramics constituting the nozzle 20. The metal to be dissolved was sterling silver. The temperature of the nozzle 20 is measured by a thermocouple installed at an intermediate portion (point P1 in FIG. 1) on the outer peripheral surface of the nozzle 20, and the temperature of the molten metal is measured by a thermocouple arranged 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 electric power (output) supplied to the coil 40 is gradually increased. As the output to the coil 40 increases, both the temperature of the nozzle 20 and the temperature of the molten metal rise, but the temperature of the nozzle 20 is about 100 ° C. higher than that of the molten metal, and the temperature of the heating block 30 is induced. It can be seen that the nozzle 20 is sufficiently heated by heating. Further, when the output to the coil 40 is momentarily interrupted (in the figure, arrow X), the temperature of the molten metal is lowered, while the temperature of the nozzle 20 is hardly changed. This is because the heating block 30 is large enough to support the crucible 10 and has a large heat capacity, so that the temperature of the heating block 30 is unlikely to change even if the conditions of induction heating are slightly changed, and by extension, the heating block 30 heats the crucible. It was considered that the temperature of the crucible 20 was also unlikely to change.

When the nozzle 20 was observed after the temperature was measured, no defects such as cracks were confirmed.

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

Next, the atomizing device 100 of the comparative example will be described. The difference between the atomizing device 100 of the comparative example and the atomizing device 1 of the embodiment is the outer shape of the nozzle 120 and the aspects of 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 is gradually reduced from the upstream end 21 to the downstream end 22, and has a step portion in which the outer diameter changes discontinuously. On the other hand, the nozzle 120 of the comparative example has an outer shape having a step portion 126. Specifically, the outer diameter is gradually reduced from the upstream end 121 to the downstream end 122, and the outer diameter is constant from there to the downstream end 122, so that the outer diameter is discontinuous. The step portion 126 is provided at a changing position. Further, in the embodiment, the heating block 30 is in contact with all of the outer peripheral surfaces of the nozzle 20 except the crucible contact surface 24 which is in contact with the crucible 10, whereas the heating block of the comparative example is in contact with all of the outer peripheral surfaces. It is composed of two annular heating blocks 130a and 130b having different inner diameters, and a gap exists between the heating blocks 130a and 130b and the nozzle 120.

For the atomizing device 100 of the comparative example, the changes in the temperature of the nozzle 120 and the temperature of the molten metal when the output to the coil 40 was changed were measured. The temperature of the nozzle 120 is measured by a thermocouple installed on the outer peripheral surface on the downstream end 122 side (point P2 in FIG. 3) from the step portion 126, and the temperature of the molten metal is measured by the head portion of the stopper 60 as in the embodiment. It was 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 when the metal (pure silver) was charged into the crucible, and arrows Z1, Z2 and Z3 indicate the time when the molten metal (molten silver) was discharged from the pores 125n of the nozzle hole 125. ing.

In the comparative example as well, the temperatures of the molten metal and the nozzle 120 change according to the output of the coil, and the temperature of the nozzle 120 becomes high when the molten metal flows out, but the temperature of the nozzle 120 melts throughout the entire process. 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 do not contact 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, highly heat-insulating air. It was thought that this was due to the existence of this layer.

Further, when the nozzle 120 was observed after the temperature was measured, it was confirmed that cracks were generated along the step portion 126. It is considered that this is because the oxide ceramics (magnesia-stabilized zirconia) constituting the nozzle 120 have low thermal conductivity and low thermal shock resistance, so that thermal stress is concentrated on the corners of the step 126. rice field. Therefore, in order to suppress the occurrence of such cracks, it is considered effective to have a shape having no step portion like the nozzle 20 of the embodiment.

Although the present invention has been described above with reference to preferred embodiments, the present invention is not limited to the above embodiments, and as shown below, various improvements are made without departing from the gist of the present invention. And the design can be changed.

For example, in the above embodiment, the case where the oxide ceramics constituting the nozzle are magnesia-stabilized zirconia is illustrated, but other examples such as calcia-stabilized zirconia, yttria-stabilized zirconia, alumina, mulite, 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 Steps

Claims (3)

An atomizing device in which molten metal housed in an induction-heated graphite crucible is discharged from a nozzle provided at the bottom of the crucible, and high-pressure gas or high-pressure water is injected onto the flowing molten metal.
The nozzle is made of oxide ceramics and
The nozzle is provided with a graphite heating block that surrounds a portion of the nozzle that protrudes from the bottom of the crucible.
The heating block is in contact with all of the outer peripheral surfaces of the nozzle except the crucible contact surface that is in contact with the crucible.
The atomizing device, wherein the nozzle and the heating block are located in an internal space of a coil that induces and heats the crucible. The outer shape of the nozzle is an inverted conical shape in which the outer diameter is gradually reduced from the upstream end to the downstream end, and is characterized by not having a step portion in which the outer diameter changes discontinuously. The atomizing device according to claim 1. The atomizing device according to claim 1 or 2, wherein the crucible is placed and supported on the heating block.

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