JPS6241287B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a method for producing metal powder. Methods for mass production of metal powder include mechanical crushing, spraying, reduction, etc., but all of them have drawbacks such as being time-consuming and requiring complicated equipment. The purpose of the present invention is to provide a method for easily producing metal powder using simple equipment, which has a surface layer with low wettability to molten metal, and has a surface layer of 2m/
A method for producing metal powder, which comprises dropping molten metal onto the surface of a roll rotating at a circumferential speed of seconds or more via a nozzle, dividing the molten metal into fine molten metal droplets, and solidifying the molten metal. While the roll is rotating, move the roll and the nozzle in the axial direction of the roll by 0.01mm/
The present invention relates to a method for producing metal powder that is relatively moved at a speed of more than a second. In the present invention, molten metal is dropped onto the surface of a roll rotating at high speed, and cavitation is generated by applying negative pressure to the molten metal at a circumferential speed of the roll that is significantly faster than the falling speed. Breaks the molten metal into fine droplets and solidifies the metal into a fine powder. The above roll has a surface that is difficult for molten metal to adhere to.
In order to be able to instantly split into fine particles and release them, it is necessary that the material is made of a material that has low wettability to molten metal, in other words, it is difficult to wet, or at least the surface layer must be made of a material that has low wettability. Graphite or TiN, Si ₃ N ₄ , SiC,
Those made of ceramics such as Al ₂ O ₃ or those having these layers on the surface are suitable. Also, the number of rolls may be one, or two rolls facing each other with a narrow roll interval may be used. In the former case, the molten metal comes into contact with the surface of the roll rotating in the falling direction, and the action of the centrifugal force is effectively absorbed. In order to prevent the molten metal droplets from scattering over a wide area, it is preferable to cause the molten metal to fall close to the tangential direction of the roll surface. For this purpose, it is preferable to supply the molten metal to the roll via a nozzle. In the latter case, if molten metal is supplied near the roll gap, it will easily create negative pressure between the surfaces of the rolls rotating at high speed while facing each other while passing through the narrow roll gap, causing cavitation. Due to the centrifugal force of the rolls, it is easily and finely divided and released. The distance between both rolls is 0.3mm
The following will have a great effect. If the two rolls have the same diameter and the same circumferential speed, they will be ejected in a direction perpendicular to the line connecting the centers of both rolls, which is convenient for storing metal powder. When the roll supplies molten metal in a continuous manner falling onto a certain circumference of the surface, the surface layer is made of graphite or ceramic, which has low heat conductivity and is brittle, as described above, so cavitation is difficult. It will become damaged as it twists. To prevent such damage to the roll, the position where the molten metal falls on the roll surface is constantly changed. That is,
The roll and the nozzle are moved relative to each other in the axial direction of the roll while the roll is rotating. If the moving speed is 0.01 mm/sec or more, damage to the roll can be prevented. In this case, the roll may be moved or the nozzle may be moved, but it is advantageous to move the nozzle together with the crucible containing the molten metal because the mechanism for movement can be simplified. Next, embodiments of the present invention will be described with reference to the accompanying drawings. A crucible 1 contains molten metal 2, and the molten metal is supplied from a sprue at the bottom of the crucible through a nozzle 3 to a roll 4 provided below. The roll 4 is designed to be rotated at high speed by a drive device (not shown), and the nozzle 3 is preferably externally cooled by a water cooling jacket 5 to prevent it from melting. The crucible 1 is moved at low speed in the axial direction of the rolls 4 or 4a, 4b by a drive device (not shown). As described above, FIG. 1 shows an example in which one roll 4 is used, and FIG. 2 shows an example in which a pair of two rolls 4a and 4b are used. In both cases, a is a vertical cross-sectional view parallel to the roll axis, and b is a vertical cross-sectional view perpendicular to the roll axis. The molten metal 2 is broken into fine molten metal droplets 6 by hitting the surface of the roll 4 or passing through the gap between the rolls 4a and 4b, solidified into fine metal powder 7, and stored in a container 8. An experiment was conducted to produce pure iron powder using the apparatus shown in Figure 2. However, crucible 1 and nozzle 3 are made of quartz and are integrally formed.
The height of the cylindrical part of is 380 mm, its inner diameter is 100 mm, the height of nozzle 3 is 10 mm, and its inner diameter is 0.8 mm, and the total height of crucible 1 and nozzle 3 is 400 mm. Also, the wall thickness is 20mm. Rolls 4a and 4b are each made of alloy tool steel SKD61.
(For hot molds) A 1mm thick graphite coating layer is provided on the surface of the roll, with a diameter of 80mm and a roll gap of 0.1mm. 5 kg of molten pure iron 2 heated to 1700°C is placed in the crucible 1, and the moving speed of the crucible 1 in the axial direction of the rolls 4a and 4b is kept constant at 0.01 mm/sec. Then, the circumferential speed of the rolls was changed (the circumferential speeds of rolls 4a and 4b were the same), and pure iron powder was produced. The results of measuring the major axis and minor axis of the obtained pure iron powder particles are shown in Table 1 below.

[Table] From this experimental result, it can be seen that when the peripheral speed of the roll is lower than 2 m/sec, the pure iron powder particles become elongated. In addition, when the circumferential speed of the roll is 2 m/sec or more, the difference between the major axis and the minor axis of the particles becomes very small.
Powder particles with a nearly spherical shape are obtained. Next, under the above experimental conditions, rolls 4a, 4
Pure iron powder was produced by keeping the circumferential speed of b constant at 10.5 m/sec and changing the moving speed of the crucible 1 in the axial direction of the roll. The obtained pure iron powder particles were measured in the same manner as described above, and the results are shown in Table 2 below.

[Table] From this result, when the moving speed of the crucible relative to the roll is smaller than 0.01 mm/sec, pure iron powder particles become elongated, but when the above moving speed is 0.01 mm/sec or more, the long and short diameters of the particles become elongated. The difference was very small, and powder particles close to spherical were obtained. Note that if a metal rotating body that rotates at high speed is provided below the roll and the molten metal droplets are made to collide with the surface of the metal rotating body, the solidification rate becomes faster and metal powder with a fine structure can be obtained. . As explained above, when using the method of the present invention, metal powder can be continuously obtained with simple operations without the need for complicated equipment.

[Brief explanation of the drawing]

Fig. 1 is a diagram schematically showing the main part of an embodiment of the method of the present invention, and Fig. 2 is a similar drawing showing an embodiment in the case of two rolls, in which a is parallel to the roll axis. A vertical cross-sectional view, b, is a vertical cross-sectional view perpendicular to the roll axis. 1... Crucible, 2... Molten metal, 3... Nozzle, 4... Roll, 4a, 4b... Roll pair, 5
...cooling jacket, 6...molten metal droplets, 7...
...Metal powder, 8... Container.

Claims (1)

[Claims] 1 The molten metal is supplied dropwise through a nozzle onto the surface of a roll that has a surface layer with low wettability to the molten metal and is rotating at a circumferential speed of 2 m/s or more, thereby turning the molten metal into fine particles. A method for producing metal powder that is divided into molten metal droplets and solidified, the roll and the nozzle being relatively moved in the axial direction of the roll at a speed of 0.01 mm/sec or more while the roll is rotating. Method for producing metal powder.