JPH02101103A - Method and apparatus for atomizing molten metal - Google Patents

Abstract

PURPOSE:To manufacture powder having the aimed particle size at good accuracy and high yield by arranging concentric groove at peripheral part of a disk, supplying molten metal into this groove and rotating the disk at high speed. CONSTITUTION:The concentric groove 3 to the rotating axis is arranged at the peripheral part of the rotation disk 1 rotated at high speed with a motor 6. The molten metal 2 is supplied into the groove 3. The molten metal 2 is not solidified on the disk 1, but splashed toward horizontal direction to make the powder 4. By this method, the molten metal is put on the rotating movement as the molten state without forming sticking material on the disk 1 and dropping the molten metal 2. Therefore, while securing the stable driving of the rotation device, the powder having the aimed particle size can be obtd.

Description

[Detailed Description of the Invention] [Industrial Field of Application] The present invention is a method of supplying molten metal onto a rotating disk and applying centrifugal force to it for the production of metal powder used as a raw material for molding machine parts or as a paint mixture. to spray the molten metal. The present invention relates to a so-called centrifugal atomization method and its apparatus.

[Prior Art] Centrifugal spraying is a process in which a disk with a flat surface is rotated at high speed around a vertical or nearly vertical axis of rotation, and a molten material (such as metal) adjusted to a desired composition at high temperature is produced. By pouring the molten metal (hereinafter referred to as molten metal) onto the −E surface of the disk, a centrifugal force is generated in the molten metal on one disk and this is sprayed. , it cools down and becomes a powder while scattering in the gas phase. This technology, for example,
1209, Special Publication Showa 62-202. Tokuko Sho 62-202
45.

Here, in order to obtain a high yield of fine powder, it is necessary to apply a high centrifugal force to the molten metal, and the means to achieve this are: ■ Increasing the rotation speed, ■ Increasing the disk diameter and moving around the disk where the circumferential speed is high. Possible methods include spraying in the area. Among these, regarding (2), in general, it is necessary to make the rotating body smaller and lighter in order to achieve mechanically stable high-speed rotation. By the way, here,
There is no point in reducing the diameter of the disc. Therefore, in effect,
It is extremely important to realize the above item (■).

However, it has been thought that it is difficult to produce fine powder in high yield using this centrifugal spraying method. This is because if it is supplied near the periphery of one disc, good centrifugal spray conditions will not occur.

According to experiments by the present inventors, when high-temperature molten metal is supplied near the periphery of a disk, most of the molten metal does not ride the rotational motion of the disk and rolls out of the disk as particles with a diameter of several 1111. drop down. Therefore, if the temperature of the molten metal is lowered slightly, at high speed rotation, the molten metal droplets will partially adhere to the disk surface and form fine protrusions, and the molten metal that is subsequently supplied will not reach the disk surface. The protrusions are thrown away and the molten metal does not reach the original rotating surface of the disk. On the other hand, when the rotational speed is not so fast, the molten metal rides on the rotating disk, but because the temperature is low, it becomes a solidified substance and rises on the disk. In this way, when molten metal is supplied near the periphery of the disk, the molten metal either rolls down without riding the rotating motion of the disk, or even if it does, it is rapidly cooled and becomes solidified, resulting in a good centrifugal spray condition. It can't be achieved.

However, if the molten metal is supplied near the center of one disk, a centrifugal spray state can be produced. If molten metal is supplied near the center of the disk, the following will occur on the surface of the molten metal near the center of the disk. Since new molten metal flows into the molten metal, even if it adheres to the lower layer of the disk-shaped molten metal or the surface of the disk, the surface side remains in a good molten state. For this reason, the molten metal that is subsequently supplied is not thrown away and forms a liquid film on the disk surface, which spreads toward the periphery due to the action of centrifugal force. Here, if the diameter of the disk is about 40 to 50 mm, good spraying is possible.

However, in order to apply strong centrifugal force, the diameter of the disk was changed to 6h.
Problems arise when the diameter is increased to m, 70 mm, or larger. If the diameter of the disk is large, the molten metal that spreads into a film due to the action of centrifugal force at the beginning of the molten metal supply will solidify before reaching the outer periphery of the disk, adhere to and stack on the disk, and prevent scattering and atomization. does not reach the state. After a certain amount of solidified material is formed on the disk, some of the molten metal that is subsequently supplied does not solidify and flies out from the disk as fine droplets in the horizontal direction, creating a good spray condition. That too is only for a short period of time. This is because, during this time, the solidified material on the disk is gradually increasing in size, and eventually due to the weight imbalance, the solidified material will be separated from the disk due to violent vibrations. As the solidified material separates, the spray state disappears and the disc returns to a stable rotating state, but the molten metal that is then supplied is newly attached to and stacked on the disc, a phenomenon that is repeated periodically.

Here, the droplets fly out from the outer periphery of the solidified material stacked on the disk. The size of the coagulum increases in the latter half of the centrifugal spray stage, and as a result of the increased peripheral velocity, the particle size of the powder produced also increases due to the growth of the coagulum.
It changes with the cycle of withdrawal.

[Problems to be Solved by the Invention] As mentioned above, in the conventional centrifugal spraying method using a flat disk, the molten metal has to be supplied near the center of the disk, so it is difficult to obtain a high yield of fine powder. Moreover, even in this method of pouring the powder into the center, (1) the rotation becomes unstable due to the presence of solidified matter, and (2) the yield of powder decreases due to the formation of solidified matter. (2) The particle size of the powder produced depends on the size of the coagulum, making it difficult to control the particle size.

Regarding this centrifugal spraying method, see Utility Model Publication No. 1209/1983.

A technique has been disclosed in which a concave locking portion is provided in the center of the disk to prevent the solidified material from separating. However, as long as a coagulum is formed, the weight imbalance is unavoidable and increases over time, which places a large load on the rotating shaft. Therefore, this method can only be applied to centrifugal spraying at a lower rotational speed than conventional methods. Conventionally, continuous operation up to a certain level of high speed rotation was possible because this solidified material was periodically separated.

In order to fundamentally solve the above problems, it is necessary to use a method that is completely different from conventional methods and sprays the material in a molten state without forming a solidified material on the disk. Furthermore, in order to obtain fine powder, it is necessary to realize a state in which the molten metal always pops out from the periphery of the disk. The present invention is based on this technical idea.

[Means for Solving the Problems] The means of the present invention is characterized by: (1) providing concentric grooves in the peripheral portion of the disk; (2) supplying molten metal into the grooves;
In addition, (j) it is preferable to supply the molten metal at a sufficiently high temperature so that it does not solidify before it is ejected from the groove to the outside of the disk.

Conventionally, in order to place molten metal on a high-speed disk, the disk was cooled and a portion of the molten metal adhered to the disk surface, or the disk shape was designed to prevent the molten metal from separating on the assumption that it would solidify. Disclosed. According to conventional thinking, the disk shape presented here is extremely unstable. I mean,
This shape intentionally limits the molten metal to the periphery, but if a solidified material were to suddenly form at the periphery of the disk, it would not be possible for the gravity to be balanced. However, the truth is quite the opposite. The shape of the disk presented here was conceived based on the basic premise of spraying molten metal onto the disk without solidifying it, and is a method that fundamentally solves the problems of the conventional centrifugal spraying method. It is.

[Operations] Below, we will explain the significance of providing a groove concentric with the disk in the peripheral area of the disk and supplying the molten metal there.

First, by limiting the presence of the same root-like molten metal to the periphery, the molten metal does not spread into a film and forms a puddle. At this time, the contact area between the molten metal and the disk surface and between the molten metal and the gas phase is limited to a small size, and the temperature of the molten metal is maintained at a good level.

A part of the heat of the molten metal is transmitted to the surface of the disk, and the temperature of the surface of the disk is increased by heating the disk surface temperature above the melting point of the molten metal, or by supplying the molten metal directly into the grooves around the periphery. The heat of the molten metal is limited to a narrow range, and the required portion of the disk surface is efficiently heated with a small amount of heat from the molten metal. Furthermore, for a rotating disk, there is a swirling airflow that is sucked in from above toward the center of the disk and ejected toward the periphery along the surface of the disk. By making it lower than the surface, the cooling effect caused by this swirling airflow can be avoided. The first effect of this groove is the multiple molten metal heat retention function described above.

Furthermore, once a puddle is formed, the subsequently supplied molten metal is sucked into the puddle and does not splash or roll out. Of course, if the outer wall of the groove or the molten metal splashes, it will directly stop it on the disk, but more importantly, the molten metal will be injected into the thick film of molten metal formed by the shape of the groove. In other words, the splashing of the molten metal is suppressed. This effect of smoothly capturing the supplied molten metal onto the rotating disk is the second effect of this groove.

The outer wall of the groove directly prevents the molten metal from falling and generates a large centrifugal force on the molten metal as it rotates at high speed.

[Example] Figure 1 shows the situation of the present invention. Reference numeral 1 denotes a rotating disc rotated by an electric motor 6, and molten metal 2 is supplied into a groove 3 provided around the disc. The molten metal jumps out horizontally and becomes powder 4 without solidifying on the disk. The height of the outer portion of the groove may be equal to or less than the reference surface of the disk. Note that 5 is a heat insulating film provided to cover the surface of the disk l.

Figure 2 shows the situation of the conventional method. The molten metal 2 is supplied near the center of the rotating disk 1, or the molten metal 2 is
becomes a solidified material 7, and then the molten metal or the solidified material jumps out horizontally and becomes a powder 4.

An example in which aluminum is sprayed using the method shown in FIG. 1 (present invention) and FIG. 2 (conventional method) will be described. The molten metal supply conditions were a temperature of 1000° C. and a supply rate of 300 g/min, and the condition of the obtained powder is as shown in Table 1. Here, the powder yield is the ratio of powder of 300μI or less to the amount of molten metal supplied,
Whether it is solidified into a disc or particles that have fallen from the disc, it is removed from this. This ratio is about twice that of the conventional 351, which is a significant improvement. Further, it is recognized that there is a regular relationship between the particle size of the powder obtained by water splashing (average value of powder of 300 μm or less) and the rotational speed of the disk, as shown in FIG. Using these results, it is possible to efficiently produce powder with a target particle size.

Table [Effects of the Invention] As stated above, in the conventional centrifugal spraying method using a flat disk, if the molten metal is supplied to the peripheral area, it is not possible to satisfactorily place the molten metal on the rotating disk, so it is unavoidable. A method is used in which the molten metal is dropped near the center, and in that case, it is sprayed on top of the solidified material that is formed periodically.
- Rotation becomes unstable due to coagulum; - Powder yield decreases due to coagulum formation; - Particle size of the produced powder depends on the size of coagulum, making it difficult to control particle size. There was a problem.

According to the present invention, it is possible to rotate the molten metal without forming deposits on the base or causing the molten metal to fall, thereby ensuring stable continuous rotation of the rotating device. It has now become possible to obtain powder with the target particle size with high precision and high yield.

[Brief explanation of the drawing]

FIG. 1 is a diagram showing the method of the present invention, FIG. 2 is a diagram showing the conventional method, and FIG. 3 is an example of the results obtained by the present invention, showing the relationship between the rotational speed of the disk and the powder particle size. 1... Rotating disc, 2... Molten metal, 3... Groove provided on the outer periphery of the disc 1, 5... A heat insulating film covering the surface of the disc 1.

Claims (1)

[Claims] 1. In a method in which molten metal is supplied onto a disk rotating at high speed and is dispersed and atomized by centrifugal force, a concentric groove is provided on the periphery of the disk, and the molten metal is A molten metal spraying method characterized by supplying. 2. A molten metal spraying device characterized in that a groove concentric with the rotating shaft is provided on the upper surface of the rotating disk.