JPH0575804B2 - - Google Patents

Description

[Detailed description of the invention]

[Industrial Application Field] The present invention is applicable to the production of Nd alloy flakes by injecting molten Nd alloy onto the outer peripheral surface of a cooling drum from a pouring container placed in an inert atmosphere such as argon gas. The present invention relates to an outer circumferential surface adjustment method and apparatus for online finishing the outer circumferential surface to a state suitable for flake generation. [Prior Art] The method of manufacturing a metal ribbon by rapidly solidifying molten metal has attracted attention for its advantages with the development of amorphous alloys, and has been in the spotlight as a means for developing new materials. This technology for producing metal ribbon using the rapid solidification method involves spraying a high-temperature molten material onto the outer surface of a cooling drum that is rotating at high speed and rapidly cooling it to produce an amorphous or near-crystalline material. . When using this technology, machining is difficult.
For example, ribbons of materials that cannot be cold rolled can be obtained directly from molten metal. Furthermore, it is possible to transform a high-temperature phase into an amorphous state at room temperature, which is impossible with ordinary cooling means. On the other hand, as a technique for manufacturing Nd--Fe--B permanent magnets by the rapid solidification method, there are methods introduced in Japanese Patent Application Laid-Open Nos. 57-210934 and 60-9852. In addition, many similar methods have been reported as research results by universities, companies, etc. However, all of the conventional techniques are laboratory-scale, in which a small amount of the alloy is melted in a quartz crucible and rapidly solidified. Therefore, the present inventors developed an apparatus having the equipment configuration shown in FIG. 4, and proposed a pouring container in Japanese Patent Application No. 333829/1983. In this device, the inside of the device main body 31 is divided into a melting chamber 32 and a flaking chamber 33, each of which is separated by a vacuum exhaust device 3.
Connected to 4. A melting container 36 equipped with a high-frequency coil 35 is tiltably arranged in the melting chamber 32 . A bellows 38 is attached to a partition wall 37 that partitions the melting chamber 32 and the flaking chamber 33, and a funnel 39 and a pouring container 40 are attached to the bellows 38. An injection nozzle 41 is provided at the lower end of the pouring container 40, and a high-frequency coil 42 for maintaining the main body of the pouring container 40 and the injection nozzle 41 at a predetermined temperature is arranged around them.
In order to efficiently heat the pouring container 40 by the high frequency coil 42, a graphite block 43 is interposed between the pouring container 40 and the high frequency coil 42. In addition, a graphite block 43 and a high frequency coil 4
2, an outer crucible 45 is placed between the pouring container 40 and
support. After melting a predetermined amount of Nd-Fe-B alloy raw material in the melting container 36, by tilting the melting container 36, the molten Nd alloy 44 is poured from the melting container 36 through the funnel 39 into the pouring container 40. Transfer to.
Note that the inside of the dissolution chamber 32 is opened or sealed by opening and closing the dissolution chamber door 46. The molten metal 44 supplied to the pouring container 40 is sprayed onto the outer peripheral surface of the cooling drum 47 from the injection nozzle 41 located at the bottom of the pouring container 40 . The molten metal 44 forms a puddle 48 on the outer peripheral surface of the cooling drum 47,
The flakes 4 are removed by removing heat through the cooling drum 47.
Fly as 9. The flakes 49 are collected in a flake chamber 51 via a duct 50. The flakes 49 collected in the flake chamber 51 are crushed into a predetermined size after removing the iron particles, and become a magnet material. [Problem to be solved by the invention] The molten Nd alloy jetted from the jet nozzle 41 is
A paddle 48 is formed on the outer peripheral surface of the cooling drum 47,
It is rapidly cooled and solidified. At this time, if the flow of the molten metal, the atmospheric pressure, the outer circumferential surface of the cooling drum 47, etc. change irregularly, atmospheric gas is likely to be caught between the paddle 48 and the outer circumferential surface of the cooling drum 47. FIG. 5 is a diagram for explaining the entrainment of atmospheric gas and the occurrence of defects caused by it. That is, the Nd alloy molten metal flow 52 jetted from the jet nozzle 41 forms a paddle 48 on the outer peripheral surface of the cooling drum 47 . At this time, the Nd alloy molten metal flow 52
When the flow rate and thickness of the paddle 4, the surface condition of the cooling drum 47, the atmospheric pressure of the flaking chamber 33, etc. change, the paddle 4
8 and the outer peripheral surface of the cooling drum 47 varies. Due to this variation in the contact angle θ, atmospheric gas 53 is drawn between the paddle 48 and the outer peripheral surface of the cooling drum 47. The entrained atmospheric gas 53 expands by receiving heat from the molten Nd alloy, forming an air pocket 54. This air pocket 54 acts as a kind of heat insulating layer and prevents the cooling drum 47 from removing heat from the flow of molten Nd alloy. Therefore, air pocket 5
The portion where No. 4 is formed undergoes slow cooling, which is different from the cooling conditions for the molten Nd alloy in other portions. FIG. 6 shows a ribbon 55 produced under such contact conditions. A depression 57 is formed on the drum surface 56 on the side that is in contact with the cooling drum 47 due to the air pocket 54 . In addition, in the part where the depression 57 occurs, the molten Nd alloy is cooled without contacting the cooling drum 47, so it is slowly cooled and the coarse particles 5
8 grows on the free surface 59 side. If the amount of coarse particles 58 generated increases, when an Nd--Fe--B permanent magnet is manufactured from the obtained flakes 49, it will not be possible to obtain a permanent magnet with high magnetic properties (BH) _nax . Therefore, in order to suppress the generation of air pockets 54 which are the cause of coarse grains 58, the Nd alloy molten metal flow 52 having a uniform flow rate and thickness is transferred to the cooling drum 4.
Various measures are required, such as ejecting the cooling drum 47, controlling the atmospheric pressure with high precision, and maintaining uniform surface properties of the cooling drum 47. However, even with these measures, air pockets 54
It is difficult to completely suppress the occurrence of Therefore, even if air pockets occur, the present invention suppresses the slow cooling phenomenon caused by air pockets by making the air pockets fine, thereby producing flakes of excellent quality with fewer coarse particles. The purpose is to [Means for Solving the Problems] In order to achieve the object, the method for adjusting the outer circumferential surface of a cooling drum for producing Nd alloy flakes of the present invention,
When producing flakes by injecting molten Nd alloy from a pouring container onto the outer peripheral surface of a cooling drum in an inert atmosphere and rapidly cooling and solidifying it, the area ratio of coarse particles in the produced flakes is 20% or less, preferably 15%. As described below, the method is characterized in that fine irregularities are formed on the outer circumferential surface of the cooling drum using a brush roll that is opposed to the outer circumferential surface of the cooling drum on the upstream side of the supply position of the Nd alloy. Further, the outer circumferential surface adjusting device of the present invention is an apparatus for producing flakes by injecting molten Nd alloy from a pouring container onto the outer circumferential surface of a cooling drum in an inert atmosphere to rapidly cool and solidify the Nd alloy supply position. The cooling drum is characterized in that a polishing roll and then a brush roll are arranged to face the outer circumferential surface of the cooling drum in this order on the upstream side. [Function] In the present invention, fine irregularities are formed on the surface of the cooling drum, and the molten Nd alloy is brought into contact with this surface. Therefore, minute gaps due to these unevenness occur over the entire surface between the cooling drum surface and the molten Nd alloy. Therefore, even if atmospheric gas is drawn into the interface between the surface of the cooling drum and the molten Nd alloy, the atmospheric gas will not form large air pockets where it collects locally.
Dispersed as fine bubbles. As a result, the molten Nd alloy is rapidly cooled and solidified under uniform cooling conditions without the aforementioned slow cooling phenomenon becoming apparent. The flakes obtained in this way have few coarse grains and excellent magnetic properties (BH) _nax .
This is the material used to manufacture B-series permanent magnets. Next, features of the present invention will be specifically explained with reference to the drawings. FIG. 1 shows the main parts of an outer circumferential surface adjusting device according to the present invention. Molten Nd alloy 2 accommodated in pouring container 1 is heated by high frequency coil 3 and maintained at a predetermined temperature (1430 to 1450°C). A spray nozzle 4 is provided at the bottom of the pouring container 1, and the molten Nd alloy 2 is passed from the spray nozzle 4 to a cooling drum 5.
is sprayed onto the outer circumferential surface of the The molten Nd alloy 2 forms a puddle 6 at the injection position, and is rapidly cooled and solidified by the cooling drum 5 to become flakes 7. The cooling drum 5 is rotating in the direction shown by the arrow, and the paddle 6
It contacts the polishing roll 8 and then the brush roll 9 on the upstream side. The polishing roll 8 removes attached foreign matter such as fine flakes, base metal, scum, and dust, and makes the outer circumferential surface of the cooling drum 5 a clean metal surface. This polishing roll 8 rotates the cooling drum 5 under stable conditions and applies a pressing force from above to produce the flakes 7.
It is preferable to press it against the outer peripheral surface of the cooling drum 5 at about 0.3 to 0.7 kg/cm ² . This pressing force is 0.3Kg/
If it is less than cm ² , a sufficient cleaning effect cannot be obtained, and the outer circumferential surface of the cooling drum 5 is carried to the injection position with some foreign matter remaining. Conversely, the pressing force is 0.7Kg/cm ²
If it exceeds this, flaws will occur in the cooling drum 5, and the polishing roll 8 will be severely damaged and lose its shape, and not only will it no longer function properly, but even worse, bad flakes will be formed. Moreover, the braking force increases, and the rotation of the cooling drum 5 becomes unstable. In addition, the polishing roll 8
As the material, nylon or the like containing SiC-based abrasive grains is used. A brush roll 9 is then pressed against the cleaned outer circumferential surface of the cooling drum 5 to form fine mat-like irregularities. Due to this surface roughening, numerous fine gaps are formed between the paddle 6 and the outer circumferential surface of the cooling drum 5, and large air pockets 54 as explained in FIG. 5 are not generated. In addition, since there are countless protrusions on the roughened circumferential surface of the cooling drum 5 that serve as starting points for solidification of the molten Nd alloy 2,
The contact surface area with the cooling drum 5 increases, the cooling effect increases, and a large number of crystal nuclei are generated. As a result, the flakes 7 have a fine structure in which the proportion of coarse grains 58 is suppressed. At this time, the flakes 7 are produced by forming fine irregularities on the outer peripheral surface of the cooling drum 5 so that the area ratio of coarse particles in the produced flakes 7 is 20% or less, preferably 15% or less. Ta
The magnetic properties (BH) _nax of Nd-Fe-B permanent magnets are significantly improved. Incidentally, the term "coarse grains" in the present invention refers to a coarse solidified structure formed above the air pocket 57 shown in FIG. 6, and refers to the size of the solidified structure, not the size of the crystals. The area ratio of these coarse grains can be determined by taking a photo of the free surface of the flake magnified approximately 30 times.
The area of the white part on the photograph is measured and expressed as a percentage (%) of the entire photograph. The reason these coarse grains appear white in photographs is because the coarse grains are slowly cooled, making the flakes thinner and creating dents, where the light that shines on them reflects diffusely and becomes white. It's for a reason. On the other hand, normally cooled areas are uniformly cooled and have a fine structure, so there is no diffuse reflection of light and they appear as black areas on photographs. As a result of measurements, it was found that flakes with this coarse grain structure had inferior coercive force compared to other flakes. On the other hand, the flakes exhibiting high magnetic properties had a uniform fine crystal grain size of 20 to 100 nm. This is said to be the reason why Nd-Fe-B magnets have a large coercive force.
This supports the prediction that the single magnetic domain grain size of Nd ₂ Fe ₁₄ B is about 0.3 μm. As the material of the brush roll 9, flexible, elastic, hard stainless steel, SS41 class ordinary steel, brass, etc. are used. If the wire is planted too roughly, there will be less pine flaws and less effect on fine flake formation. Also, when the wires are closely planted, problems with pine flaws do not occur, but it becomes difficult to manufacture brushes. Further, as the diameter of the wire becomes thicker, the planting density can be lowered. However, if it is too thick, the pine flaws will become larger and deeper, creating the opposite effect of increasing air pockets. This rubbing of the brush roll 9 forms irregularities on the outer circumferential surface of the cooling drum 5 that are effective for producing fine flakes. Table 1 shows the material, wire diameter, planting density, etc. of the wire planted in the brush roll 9 that are effective in forming fine flakes.

〔Example〕

Using the apparatus shown in Figure 1, a temperature of 1430°C was
Flow rate of Nd alloy molten metal 2 is 8.0 from a 15-hole nozzle.
Kg/min, cooling drum 5 as a molten metal flow with a thickness of 0.9 mm
was injected. The cooling drum 5 is made of Cu99%,
Has a surface layer of 1% Cr alloy and has a thermal conductivity of 290Kcal/
m・hr・℃ was used, and it was rotated at a circumferential speed of 27.5 m/sec. A buff roll was used as the polishing roll 8, and it was pressed against the cooling drum 5 with a pressing force of 0.5 kg/cm ² . On the other hand, the brush roll 9 has a diameter of
Planting density of 0.06mm SUS304 stainless steel wire
Use seeds planted at 100 plants/cm ² and apply pressure
It was pressed against the cooling drum 5 at 0.25 kg/cm ² . FIG. 2 is a photograph of the drum surface and free surface of the flakes obtained under these conditions. As is clear from Figure a, which shows the drum surface, the depressions caused by the air pockets are finely dispersed over the entire surface of the drum. The free surface corresponding to this has a fine structure with few coarse grains and a substantially uniform grain size, as shown in Figure b. On the other hand, if the surface is not roughened by the brush roll 9, large depressions will occur on the drum surface of the flakes as shown in figure c, and there will be many dents on the free surface as shown in figure d. Coarse particles were detected. Specifically, the area ratio occupied by coarse particles is 25.1 when the brush roll 9 is not used.
%, but when the surface was roughened with brush roll 9, it decreased to 14.3%. The area ratio of the coarse particles can be adjusted by the material, diameter, planting density, pressing force, etc. of the wire planted on the brush roll 9. FIG. 3 is a graph showing the influence of this area ratio on the magnetic properties (BH) _nax of the product. As is clear from FIG. 3, when the area ratio of coarse grains is 20% or less, flakes with excellent magnetic properties of (BH) _nax 15MGOe or higher can be obtained. This is due to the roughening of the outer peripheral surface of the cooling drum 5 by the brush roll 9, which exerts a sufficient rapid cooling effect on the molten Nd alloy and forms fine crystal grains.
In addition, the yield of flakes used when the maximum energy product (BH) nax of the bonded magnet converted to a product with the target magnetic properties (specific gravity 6.01 g/cm ³ ) _nax ≧10.0 MGOe is calculated by this process. 83.2% to 89.4
%. [Effects of the Invention] As explained above, in the present invention, large air pockets caused by entrainment of atmospheric gas can be eliminated by roughening the outer circumferential surface of the cooling drum and then bringing it into contact with the molten Nd alloy. suppress the outbreak,
The flakes are manufactured under uniform cooling conditions. Therefore, the proportion of coarse grains is reduced, and flakes with a fine structure with excellent magnetic properties can be obtained.

[Brief explanation of the drawing]

Fig. 1 is a front view showing the main parts of the device used in the present invention, and Fig. 2 is a photograph showing the surface structure of the drum side and free side of the flakes obtained in the inventive examples and comparative examples, respectively. , FIG. 3 is a graph specifically showing the effect of surface roughening. On the other hand, the fourth
The figure shows the overall configuration of a conventional Nd alloy flake manufacturing apparatus, and FIGS. 5 and 6 are diagrams for explaining problems caused by atmospheric gas entrainment. 1: Pouring container, 2: Molten Nd alloy, 3: High frequency coil, 4: Injection nozzle, 5: Cooling drum, 6:
Paddle, 7: Flake, 8: Polishing roll, 9: Brush roll.

Claims (1)

[Claims] 1. When producing flakes by injecting molten Nd alloy from a pouring container onto the outer peripheral surface of a cooling drum in an inert atmosphere and rapidly cooling and solidifying it, the area ratio of coarse particles in the produced flakes is 20%. % or less, the Nd alloy flakes are characterized in that fine irregularities are formed on the outer circumferential surface of the cooling drum by a brush roll facing the outer circumferential surface of the cooling drum on the upstream side of the supply position of the Nd alloy. A method for adjusting the outer peripheral surface of a cooling drum for manufacturing. 2. In an apparatus for producing flakes by injecting molten Nd alloy from a pouring container onto the outer circumferential surface of a cooling drum in an inert atmosphere to rapidly cool and solidify it, a polishing roll is used upstream from the Nd alloy supply position, followed by a brush roll. An apparatus for adjusting an outer peripheral surface of a cooling drum for producing Nd alloy flakes, characterized in that the outer peripheral surface of the cooling drum is opposed to the outer peripheral surface of the cooling drum in this order.