JPH0575803B2 - - Google Patents

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention provides
This invention relates to a method for producing Nd alloy flakes by supplying molten Nd alloy to the outer peripheral surface of a cooling drum and rapidly cooling and solidifying it.

[Conventional technology]

BACKGROUND ART The method of producing metal ribbon by rapidly solidifying molten metal has attracted attention for its advantages following the development of amorphous alloys, and is now 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. 5, and proposed a pouring container in Japanese Patent Application No. 333289/1989. 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. In addition,
In order to uniformly cool the molten metal 44 by the cooling drum 47, a polishing roll 52 and a brush roll 53 are provided upstream of the position where the paddle 48 is formed.

The flakes 49 collected in the flake chamber 51 are
After removing the granulated iron, it is crushed to a predetermined size.
Becomes magnetic material.

[Problem to be solved by the invention]

In this flake manufacturing apparatus, in order to manufacture flakes 49 with a predetermined crystal structure, it is necessary to maintain the paddle 48 stably on the outer peripheral surface of the cooling drum 47 and to keep the cooling conditions of the molten Nd alloy constant. be. Therefore, it is required that the molten Nd alloy flow flowing out from the injection nozzle 41 provided at the lower part of the pouring container 40 be supplied to the outer peripheral surface of the cooling drum 47 in a rectified state with a constant thickness.

However, Nd contained in the molten metal flow has an extremely high affinity for oxygen, and the injection nozzle 41
The injection port, the process from the injection nozzle 41 to the cooling drum 47, the outer peripheral surface of the cooling drum 47, etc. are easily oxidized. When such oxidation occurs, the supply of molten metal to the cooling drum 47 becomes uneven.
Alternatively, the oxide acts as a heat insulating material between the cooling drum 47 and the paddle 48, locally reducing the heat extraction ability of the cooling drum 47. In order to prevent oxidation of this molten Nd alloy, flakes are manufactured in a reduced pressure atmosphere replaced with an inert atmosphere such as argon.

However, conventional atmosphere control is based on the prevention of oxidation of general molten metal.
It does not take into account phenomena specific to Nd alloys.
Therefore, oxidation of the molten Nd alloy jetted from the jet nozzle 41 to the cooling drum 47 cannot be completely prevented. As a result, it is still inevitable that the flow of the molten metal becomes unstable, and the generated oxides adversely affect the cooling conditions on the outer peripheral surface of the cooling drum 47.

Therefore, the present invention suppresses oxidation of the Nd alloy by adjusting the atmospheric pressure and oxygen partial pressure in consideration of the characteristics of the Nd alloy, and allows the flow of the molten Nd alloy under uniform and stable conditions. The purpose is to supply Nd alloy flakes to the outer peripheral surface of the cooling drum and produce excellent quality Nd alloy flakes.

[Means to solve the problem]

In order to achieve the object, the present invention injects molten Nd alloy from an injection nozzle onto the outer peripheral surface of a cooling drum to rapidly cool and solidify it to produce flakes.
At least the atmosphere in contact with the Nd alloy molten metal flow and the cooling drum is a reduced pressure inert atmosphere, and further, assuming that the atmospheric pressure of the atmosphere is P and the oxygen partial pressure is Po ₂ , P = 0.5 to 0.05 atm, Po ₂ ≦1.2×
10 ⁻⁵ atm (preferably Po ₂ ≦9.0×10 ⁻⁶ atm),
Po ₂ ≦ (26.3P−1.0)×10 ⁻⁶ (preferably, Po ₂ ≦
(19.5P−0.75)×10 ^-6 ).

[Effect]

When the flow of molten Nd alloy is sent to the outer circumferential surface of the cooling drum where it is rapidly cooled and solidified into flakes in a reduced pressure atmosphere replaced with an inert gas such as argon, the molten Nd alloy is oxidized. The proportion of In addition, due to the reduced pressure in the working atmosphere,
Atmospheric gas, which causes air pockets, is less likely to be drawn in between the paddle formed on the outer circumferential surface of the cooling drum and the cooling drum. For this reason, the atmospheric pressure P is maintained at 0.5 to 0.05 atm. When this atmospheric pressure P exceeds 0.5 atm,
Oxidation of the molten metal and gas entrainment can be seen. Conversely, 0.05
Reducing the pressure from atmospheric pressure has problems in terms of equipment configuration, workability, etc. Furthermore, it becomes difficult to suppress the oxygen partial pressure caused by trace amounts of oxygen contained in argon gas and trace amounts of oxygen released from equipment members such as refractories to a range that does not cause an oxide film to appear in the jet stream.

However, simply maintaining the atmospheric pressure P in the range of 0.5 to 0.05 atm still does not prevent oxidation of the molten Nd alloy. According to research by the present inventors, oxidation in a reduced pressure atmosphere is
It was discovered that this problem is unique to Nd alloys, which have a large affinity for oxygen.

FIG. 6 is a diagram for explaining the oxidation state under this reduced pressure atmosphere. The molten Nd alloy 44 injected from the injection nozzle 41 becomes a jet stream 54 and reaches the outer peripheral surface of the cooling drum 47 . At this time, a sheath-like oxide film 55 may be formed around the jet stream 54 . When the sheath-like oxide film 55 is formed, the flow resistance of the jet flow 54 flowing down inside the sheath increases, and combined with the high viscosity of the molten Nd alloy, the flow rate and thickness of the jet flow 54 decrease. decreased and a normal paddle is not formed. Furthermore, the sheath-like oxide film 55 grows further and in extreme cases may reach the outer circumferential surface of the cooling drum 47, resulting in no puddles being formed at all and no healthy flakes being produced.

Further, even if it does not reach the outer circumferential surface of the cooling drum 47, a part of the sheath-shaped oxide film 55 may be separated by the flow energy of the jet stream 54 and sent to the outer circumferential surface of the cooling drum 47 together with the molten Nd alloy. be. A portion of the separated oxide film then enters between the paddle 48 and the cooling drum 47, reducing the ability of the cooling drum 47 to remove heat. The intrusion of this oxide film irregularly disturbs the cooling conditions on the outer peripheral surface of the cooling drum 47, making it impossible to obtain flakes of consistent quality.

The inventors of the present invention have inferred the reason why such a sheath-shaped oxide film 55 is formed as follows. That is, since the atmosphere around the jet stream 54 is at a reduced atmospheric pressure P, the molten Nd alloy is in a state where it is easy to evaporate. This evaporation occurs more actively as the atmospheric pressure P approaches a vacuum, and the surface of the jet stream 54 becomes active. Moreover, since Nd has an extremely high affinity for oxygen, it preferentially reacts with oxygen in the atmosphere, becomes an oxide immediately after evaporation, and remains around the jet stream 54. This tendency can be seen, for example, in crucibles, etc.
One of the reasons is that the surface area of the jet stream 54 is much larger than in the case where molten Nd alloy is held, so the chances of reaction between Nd and oxygen are increased. Furthermore, since new surfaces of molten Nd alloy are formed one after another, the amount of molten Nd alloy that takes part in the reaction is large. As a result, it was inferred that a sheath-shaped oxide film 55 as shown in the figure was formed.

Therefore, based on this assumption, the sheath-shaped oxide film 55
In order to suppress the formation of , the relationship between the partial pressure Po ₂ of oxygen contained as an impurity in the atmospheric gas and the atmospheric pressure P was investigated. As a result, it was clarified that the relationship shown in FIG. 1 was established between the two regarding the presence or absence of oxide film formation. That is, even if the oxygen partial pressure Po ₂ is constant, depending on the atmospheric pressure P, the sheath-like oxide film 55 may or may not be formed around the jet 54. Further, even if the atmospheric pressure P is constant, an oxide film is likely to be formed when the oxygen partial pressure Po _{2 is high, and no oxide film is formed when the oxygen partial pressure Po 2} is low. They also found that the presence or absence of this oxide film formation can be clearly differentiated by Po ₂ ≦ (26.3P − 1.0) × 10 ^-6 , preferably Po ₂ ≦ (19.5P − 0.75) × 10 ^-6 . .

Note that it is necessary to maintain the oxygen partial pressure Po ₂ at 1.2×10 ⁻⁵ atmosphere or less, preferably at 9.0×10 ⁻⁶ or less. The original purpose of reduced pressure operation is to suppress the formation of air pockets and to produce flakes that are uniformly cooled. However, as shown in FIGS. 3 and 4, as the atmospheric pressure in the flaking chamber is lowered, the coarse grain area ratio decreases and the magnetic property values of the flakes improve. Here, the magnetic property value is (BH) _nax ≧10MGOe for a bonded magnet with a specific gravity of 6.0.
Although the target is 9.0 MGOe, it can be used without any major problems.

Here, if the atmospheric pressure is 0.5 atm or less, it can be seen from FIG. 3 that it is possible to manufacture a bonded magnet of approximately 9.0 MGOe. When this atmospheric pressure is 0.5 atm, the condition that no oxide film is generated in the jet flow is the first condition.
From the figure and Fig. 2, Po ₂ ≦ (26.3P−1.0)×10 ^-6 ,
Preferably, Po ₂ ≦(19.5P−0.75)×10 ⁻⁶ , and each oxygen partial pressure is Po ₂ ≦1.2×10 ⁻⁵ atm, preferably Po ₂ ≦9.0×10 ⁻⁶ atm. .

Based on this knowledge, when producing flakes by supplying molten Nd alloy to the outer circumferential surface of a cooling drum and rapidly cooling and solidifying it while controlling the atmospheric pressure P and oxygen partial pressure _Po2 , a sheath-shaped oxide film is formed. 55 was not observed, and the flow rate and thickness of the jet stream 54 were stable. As a result, the cooling conditions on the outer peripheral surface of the cooling drum 47 are stabilized, and the quality of the obtained flakes becomes constant.

In addition, things that have a negative impact on the jet flow include:
In addition to the oxygen partial pressure Po ₂ there is water vapor pressure. This water vapor is generated by the evaporation of moisture contained in the coin cement holding the coil 42 for heating the injection nozzle 41, the pouring container 40, and the like. Therefore, it is preferable to sufficiently pre-dry these devices.

〔Example〕

Nd alloy heated to a temperature of 1430℃ (Nd 12 atomic%,
The molten metal (Co5 atomic%, B6 atomic%, Si0.3 atomic%, Al0.3 atomic%, Fe balance amount) is transferred from the injection nozzle 41 to the cooling drum 47 using the device shown in FIG.
supplied. At this time, the flaking chamber 33 in which the cooling drum 47 was placed was maintained at a reduced atmospheric pressure P. In addition, the oxygen partial pressure Po ₂ at each atmospheric pressure P was variously changed, and the occurrence of an oxide film was investigated. The results are shown in FIG. As is clear from Fig. 2, the lower the atmospheric pressure P, the more
It can be seen that lowering the oxygen partial pressure Po ₂ is necessary to prevent oxide film formation.

Flakes 49 produced by rapidly cooling and solidifying the molten Nd alloy 44 in this atmosphere were molded into a magnet with a specific gravity of 6.0 Kg/cm ³ by resin bonding. When the maximum energy product (BH) _nax of the obtained magnet was measured, it was found that the magnetic properties of the magnet changed depending on the atmospheric conditions, as shown in FIG. That is, compared to magnets obtained from flakes produced under atmospheric pressure P and oxygen partial pressure Po ₂ in the oxide film forming region, magnets obtained from flakes produced under atmospheric conditions that do not form an oxide film. The magnets shown here exhibit significantly higher maximum energy products (BH) _nax .

Further, when observing the flakes formed on the outer circumferential surface of the cooling drum 47, it was found that the proportion of coarse particles that do not exhibit high magnetic properties varies greatly depending on the atmospheric pressure P, as shown in FIG. Incidentally, the coarse grains in FIG. 4 refer to the coarse solidified structure generated above the air pocket, and indicate the size of the solidified structure, not the crystal size. This coarse grain is
When the free surface of a flake is taken in an enlarged photograph, it appears white, so the area ratio of coarse grains can be determined from this photograph. As a result of measurements, it was found that the coercive force in this coarse grained portion was significantly inferior to that in other finely structured portions.

Therefore, when manufacturing a magnet with excellent magnetic properties, these coarse grains are removed from the magnet material, resulting in a decrease in yield. On the other hand, when flakes are produced by reducing the atmospheric pressure P under the conditions specified in the present invention, the proportion of coarse grains is significantly reduced, and 90% of the produced flakes are
With this high yield, it could be used as a material for magnets.

〔Effect of the invention〕

As explained above, in the present invention, by producing flakes from a molten Nd alloy in an atmosphere where the oxygen partial pressure Po ₂ is controlled in relation to the atmospheric pressure P, Nd with a high oxygen affinity is released into the atmosphere. It also prevents it from reacting with the small amount of oxygen present in it. Therefore, the molten Nd alloy ejected from the injection nozzle is supplied to the outer peripheral surface of the cooling drum without forming an oxide film, and is rapidly cooled and solidified into flakes under stable cooling conditions. Therefore, the quality of the obtained flakes is stabilized, and the yield of flakes used to manufacture magnets with required magnetic properties is also improved. Also, Nd
Since the flow of the molten alloy is also stable, troubles such as nozzle clogging do not occur, and workability is also good.

[Brief explanation of the drawing]

Figure 1 shows the relationship between atmospheric pressure P and oxygen partial pressure Po ₂ that affect oxide film formation, and Figures 2 to 4
The figure is a graph specifically expressing the effects of the present invention.
The figure shows the overall structure of Nd alloy flake manufacturing equipment.
FIG. 6 is a diagram for explaining problems during flake production. 41: Injection nozzle, 44: Nd alloy molten metal, 4
7: cooling drum, 48: paddle, 49: flake, 54: jet stream, 55: sheath-shaped oxide film.

Claims (1)

[Claims] 1. When producing flakes by injecting the molten Nd alloy from an injection nozzle onto the outer peripheral surface of the cooling drum and rapidly cooling and solidifying it, at least the molten Nd alloy flow and the atmosphere in contact with the cooling drum are both in a reduced pressure inert atmosphere. Further, when the atmospheric pressure of the atmosphere is P and the oxygen partial pressure is Po ₂ , P = 0.5 to 0.05 atm, Po ₂ ≦1.2 × 10 ^-5 atm, Po ₂ ≦ (26.3P − 1.0) ×
A method for producing Nd alloy flakes characterized by maintaining a relationship of 10 ^-6 .