JPH02247307A - Manufacture of nd alloy flake - Google Patents

Abstract

PURPOSE:To stably manufacture Nd alloy flakes having excellent quality by making treating atmosphere the reduced pressure atmosphere of inert gas adjusted to the prescribed value of oxygen partial pressure at the time of manufacturing the flakes by injecting the molten Nd alloy on surface of a rotated cooling drum. CONSTITUTION:The molten Nd alloy 44 is injected on the outer surface of the cooling drum 47 rotating at high speed as injecting stream 54 from injecting hole of an injecting nozzle 41 under inert gas atmosphere of Ar, etc., and rapidly cooled on surface of the cooling drum 47, and after forming paddles 48, they are discharged as the flakes 49. In this case, as the molten Nd alloy is easily oxidized, sheath-like oxide film 55 is generated at outer face of the injecting stream 54 and supplying rate of the molten Nd alloy to the cooling drum 47 comes to imbalance. In order to prevent this, the pressure P of Ar gas atmo sphere on the surface of cooling drum 47 is controlled to 0.5 - 0.05atm. and also the partial pressure Po2 of O2 in Ar atmosphere is controlled to <=1.2X10<-5>atm. and by keeping the relation of Po2<=(26.3P-1.0)X10<-6> between Po2 and P, the Nd alloy flake having excellent quality is stably manufactured.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention involves supplying molten Nd alloy to the outer peripheral surface of a cooling drum in an inert atmosphere such as argon gas, and producing Nd alloy flakes by rapid cooling and solidification. Regarding the method.

[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 No. 57-210934, Japanese Patent Application Laid-Open No. 60-9852, etc. 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 inventors of the present invention developed an apparatus having the equipment configuration shown in Fig. 5, and submitted a proposal regarding a pouring container in a patent application filed in 1986-3.
I went with No. 33289. 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 connected to a vacuum evacuation device 34. A melting container 36 equipped with a high-frequency coil 35 is tiltably arranged in the melting chamber 32 .

A partition wall 37 that partitions the melting chamber 32 and the flaking chamber 33
A bellows 38 is attached to the bellows 38.
A funnel 39 and a pouring container 40 are attached to.

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 addition, the pouring container 4 by the high frequency coil 42
A graphite block 43 is interposed between the pouring container 40 and the high-frequency coil 42 in order to efficiently heat the melt.

Furthermore, an outer crucible 45 is disposed between the graphite block 43 and the high-frequency coil 42 to support the pouring container 40.

After melting a predetermined amount of Nd-Fe-B alloy raw material in the melting container 36, by tilting the melting container 36, the Nd-Fe-B alloy raw material is melted.
The d-alloy melt 71h44 is transferred from the melting container 36 to the pouring container 40 via the funnel 39. Note that the inside of the dissolution chamber 32 is opened or sealed by opening and closing the dissolution chamber door 46.

The melt supplied to the pouring container 40! 44 is sprayed onto the outer peripheral surface of the cooling drum 47 from the spray nozzle 41 located at the bottom of the pouring container 40. The molten metal 44 forms a puddle 48 on the outer circumferential surface of the cooling drum 47, and flies off as flakes 49 by removing heat through the cooling drum 47. This flake 4
9 are collected in a flake chamber 51 via a duct 50.

In order to uniformly cool the melt 844 by the cooling drum 47, a Kenreki roll 52 is installed upstream of the position where the paddle 48 is formed.
and a brush roll 53.

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]

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 rectifying shape having a certain thickness.

However, Nd contained in the molten metal flow has an extremely high affinity for oxygen and is easily oxidized at the injection port of the injection nozzle 41, in the process from the injection nozzle 41 to the cooling drum 47, on the outer peripheral surface of the cooling drum 41r, etc. 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 7 and the paddle 48, locally reducing the heat extraction ability of the cooling drum 1. In order to prevent oxidation of this molten Nd alloy, the flake manufacturing apparatus is operated in a reduced pressure atmosphere substituted with F, such as argon, or an active atmosphere.

However, conventional atmosphere control is based on the prevention of oxidation of molten metal, and does not take into account the phenomenon unique 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 molten metal flow 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 cools the molten Nd alloy flow under uniform and stable conditions. The purpose is to supply Nd alloy flakes to the outer peripheral surface 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 onto the outer circumferential surface of the cooling drum from an injection nozzle to rapidly cool and
When solidifying to produce flakes, at least the atmosphere in contact with the molten Nd alloy flow and the cooling drum is both a reduced pressure inert atmosphere, and the atmospheric pressure of the atmosphere is P1, the oxygen partial pressure is PO□, P=0.5~0.05
Atmospheric pressure, Po, ≦·1,2XIO−′ atmosphere (preferably Pa, ≦9. OX 10−′ atmosphere).

po,≦(26,3P-1,0) X 10-' (preferably Po,≦(19,5P-0,75) x
10-').

[Effect]

When a flow of molten Nd alloy is sent to the outer peripheral surface of a cooling drum, where it is rapidly cooled and solidified into flakes in a reduced pressure atmosphere substituted with an inert gas such as argon, Nd
The rate of oxidation of the molten alloy decreases. Further, by reducing the pressure of the working atmosphere, atmospheric gas that 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 are observed. On the other hand, reducing the pressure below 0.05 atm poses 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 construction materials 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 under reduced pressure is caused by nitrogen, which has a large affinity for oxygen.
It was discovered that this problem is unique to d alloys.

FIG. 6 is a diagram for explaining the oxidation state under this reduced pressure atmosphere. Nd injected from the injection nozzle 41
The molten alloy 44 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-shaped 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 are increased. decreases 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 peripheral 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 peripheral surface of the cooling drum 47 together with the molten Nd alloy. 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 penetration 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, Nd
The molten alloy is in a state where it easily evaporates. This evaporation occurs more actively as the atmospheric pressure P approaches a vacuum, and the jet flow 540
The surface becomes active. Furthermore, since Nd 2 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 is also due to the fact that the surface area of the jet stream 54 is much larger compared to, for example, a case where the molten Nd alloy is held in a crucible, etc., which increases the chance of reaction between Nd and oxygen. There is one. Also, one after another, N
As a new surface of the d-alloy molten metal is formed, N that participates in the reaction
The amount of molten d alloy is also large. As a result, it was inferred that a sheath-shaped oxide film 55 as shown in the figure was formed.

Based on this speculation, the relationship between the partial pressure P~ of oxygen contained as an impurity in the atmospheric gas and the atmospheric pressure P was investigated in order to suppress the formation of the sheath-like oxide film 55. 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 is - constant, the sheath-shaped oxide film 55 may or may not be formed around the jet stream 54 depending on the atmospheric pressure I). Further, even if the atmospheric pressure P is constant, an oxide film is likely to be formed when the oxygen partial pressure PO2 is high, and no oxide film is formed when the oxygen partial pressure PO2 is low. The presence or absence of this oxide film formation is determined by P
o, ≦(26,3P , -1,0)
It was found that a clear division can be made with a boundary of 10".

Nao, W! Elementary partial pressure Pa2It, original Temo 1.2810-
It is necessary to maintain the pressure below the atmospheric pressure, preferably below 9.0XlO-@. The original purpose of reduced pressure operation is to suppress the formation of air pockets and produce flakes that cool evenly. However, as shown in Figures 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) for a bonded magnet with a specific gravity of 6.0.
,,,≧10 M G Oe is the first goal, but ≧
9. OMGOe can also 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 a bonded magnet of approximately 9.0 MGOe can be manufactured. When the atmospheric pressure is 0.5 atm, the conditions under which no oxide film is generated in the jet flow are as follows from Figures 1 and 2.
P02≦(26,3P −1,0) x, IO−′ Preferably Po,≦(19,5P −0,75) x 10
~6, and each oxygen partial pressure is Po, ≦
1.2 x 10-' atmospheres, preferably Po2≦9.
OX 10-'atmosphere.

Based on this knowledge, atmospheric pressure P and oxygen partial pressure Po
When producing flakes by supplying the molten Nd alloy to the outer peripheral surface of the cooling drum and rapidly cooling and solidifying it while controlling the It became 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 to the oxygen partial pressure PO2, there is also water vapor pressure that adversely affects the jet flow. This water vapor is generated by evaporation of water contained in the coil 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 (Nd 12 atomic%) heated to 1430°C
.

Co5 atomic%, B66 atomic%, SiO, 3 atomic%, A
The molten metal (1093 atomic %, Fe balance amount) was supplied from the injection nozzle 41 to the cooling drum 47 using the apparatus shown in FIG. At this time, the flaking chamber 33 in which the cooling drum 47 was placed was maintained at a reduced atmospheric pressure P. Also, oxygen partial pressure PO□ at each atmospheric pressure P
We made various changes to investigate the formation of oxide films. The results are part 2! ! Shown in I. As is clear from FIG. 2, it can be seen that the lower the atmospheric pressure P is, the more necessary it is to lower the oxygen partial pressure Pa in order to prevent the formation of an oxide film.

Flakes 49 manufactured by rapidly cooling and solidifying the molten Nd alloy 44 in this atmosphere are bonded to a resin bond with a specific gravity of 6.0.
Molded into a kg/cd magnet. When the maximum energy product (BH) of the obtained magnet was measured, the third
As shown in the figure, it was found that the magnetic properties of the magnet changed depending on the atmospheric conditions. That is, compared to magnets obtained from flakes produced under atmospheric pressure P and oxygen partial pressure Po2 in the oxide film formation region, under atmospheric conditions that do not form an oxide film! i! The magnet obtained from the leftover flakes has a significantly higher maximum energy product (BH)...
It shows that it is high.

Furthermore, 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. These coarse grains appear white when the free surface of the flake is taken in an enlarged photograph, so the area ratio of the 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 magnets with excellent magnetic properties,
These coarse particles 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 particles is significantly reduced, and the produced flakes have a high The yield was such that it could be used as a material for magnets.

〔Effect of the invention〕

As explained above, in the present invention, the oxygen partial pressure P
By producing flakes from molten Nd alloy in an atmosphere where O ing. Therefore, the molten Nd alloy jetted from the jet 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. Furthermore, since the flow of the molten Nd alloy is stable, troubles such as nozzle clogging do not occur, and workability is improved.

[Brief explanation of drawings]

Figure 1 shows the relationship between atmospheric pressure P and oxygen partial pressure PO2 that affect oxide film formation, Figures 2 to 4 are graphs specifically showing the effects of the present invention, and Figure 5 shows the relationship between atmospheric pressure P and oxygen partial pressure PO2 that affect the formation of an oxide film. FIG. 6 shows the overall structure of the flake production equipment, and is a diagram for explaining problems during flake production. 41: Injection nozzle 44: Nd alloy molten metal 47
: Cooling drum 48: Paddle 4 flakes
54: Jet flow 55: Sheath-shaped oxide film

Claims (1)

[Claims] 1. When producing flakes by injecting 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 depressurized 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)×1
A method for producing Nd alloy flakes, characterized by maintaining a relationship of 0^-6.