JPH0575801B2 - - Google Patents

Description

[Detailed Description of the Invention] [Industrial Field of Application] The present invention supplies a Nd alloy melted in a melting vessel placed in an inert atmosphere such as argon gas to the outer peripheral surface of a cooling drum to rapidly cool and cool it. The present invention relates to a method of controlling atmospheric pressure when forming flakes by solidification.

[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. 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. 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, the injection pressure of the molten Nd alloy flowing out from the injection nozzle 41 is affected by the difference in atmospheric pressure between the melting chamber 32 and the flaking chamber 33, and by the pressure of the molten Nd alloy injected into the pouring container 40.
It tends to fluctuate depending on the static pressure of the molten Nd alloy. If this injection pressure fluctuates, the flow state of the molten Nd alloy supplied from the injection nozzle 41 to the outer peripheral surface of the cooling drum 47 will change irregularly, making it impossible to obtain flakes 49 that have received a predetermined cooling effect.

If the atmospheric pressure is simply controlled so as to offset this variation in injection pressure, inert gas such as argon will be entrained in the flow of molten Nd alloy supplied from the injection nozzle 41 to the outer peripheral surface of the cooling drum 47. The entrained inert gas is transferred to the cooling drum 47 and paddle 48.
A heat insulating layer is formed between the Nd alloy and the molten Nd alloy.
It delays solidification and forms a structure with coarse grains.
Furthermore, if an attempt is made to eliminate the influence of fluctuations in the static pressure of the molten metal using only the atmospheric pressure in the flaking chamber, the jet flow sent to the cooling drum 47 will not be constant, and flakes will be produced under unstable conditions. Moreover, since coarsening of crystal grains occurs irregularly, the yield of flakes 49 used as Nd--Fe--B permanent magnets having high magnetic property values decreases.

Therefore, the present invention independently controls the atmospheric pressure in the melting chamber and the flaking chamber, thereby supplying the molten Nd alloy from the injection nozzle to the cooling drum at a constant injection pressure, and reducing the atmosphere in the flaking chamber. The purpose is to prevent atmospheric gas from being entrained between the outer peripheral surface of the cooling drum and the molten Nd alloy by controlling the pressure so that there is no fluctuation in pressure.

[Means to solve the problem]

In order to achieve the objective, the atmospheric pressure control method of the present invention transfers molten Nd alloy from a melting container placed in a melting chamber to a pouring container, and then transfers the molten Nd alloy to a flaking chamber located below the melting chamber. When producing flakes by injecting the molten Nd alloy onto the outer circumferential surface of the cooling drum from an injection nozzle provided at the bottom of the pouring container and rapidly cooling and solidifying it, both the melting chamber and the flaking chamber are in a vacuum chamber. An active atmosphere is created, and the atmospheric pressure in the melting chamber is controlled so as to offset fluctuations in the static pressure of the molten Nd alloy in the electric pouring container, and the injection pressure of the molten Nd alloy flowing out from the injection nozzle is set to 0.2 to 0.4. It is characterized in that the atmospheric pressure in the flaking chamber is finely adjusted within a range of Kg/cm ² and within a range of 0.05 to 0.5 atm.

[Effect]

In the present invention, as shown in FIG. 1, equipment is used in which the melting chamber 32 and the flaking chamber 33 are connected to vacuum evacuation devices 1 and 2 each having an atmospheric pressure control mechanism. Note that it is also possible to control the atmospheric pressures of the melting chamber 32 and the flaking chamber 33 with a single evacuation device by adjusting the valve opening, supplying argon, or the like. And dissolution chamber 3
The atmospheric pressure in the flaking chamber 33 is independently controlled by the evacuation device 1, and the atmospheric pressure in the flaking chamber 33 is independently controlled by the evacuation device 2. Further, the bellows 38 is designed to prevent atmospheric gas from diffusing between the melting chamber 32 and the flaking chamber 33.
An O-ring 3 is used to seal the space between the molten metal and the pouring container 40. In addition, in the same figure, parts corresponding to those shown in FIG. 4 are indicated by the same reference numbers.

The atmospheric pressure in the melting chamber 32 is controlled so that the injection pressure P of the molten Nd alloy flowing out from the injection nozzle 41 toward the cooling drum 47 is constant. This injection pressure is the sum of the difference between the atmospheric pressure P ₂ in the melting chamber 32 and the atmospheric pressure P ₃ in the flaking chamber 33, and the static pressure of the Nd alloy poured into the pouring container 40. changes approximately in proportion to the meniscus level of the Nd alloy in the pouring vessel 40. Therefore, the meniscus is detected using, for example, gamma rays, and the molten metal static pressure _P1 is calculated from the detected value. Then, the differential pressure ΔP (=
P−P ₁ +P ₃ ) is calculated, and the atmospheric pressure P ₂ in the melting chamber 32 is changed by an amount corresponding to this pressure difference ΔP.
As a result, the injection pressure P of the molten Nd alloy is always maintained constant.

The atmospheric pressure _P3 in the flaking chamber 33 is controlled to be low and with little fluctuation in order to minimize the occurrence of air pockets caused by the entrainment of argon gas between the outer periphery of the cooling drum 47 and the paddle 48. be done. From this point of view, the appropriate range of atmospheric pressure _P3 is 0.05 to 0.5 atm. Atmospheric pressure _P3 is 0.5
If the pressure is higher than the atmospheric pressure, more argon gas will be entrained, making it easier to form air pockets, that is, flakes with many coarse particles, and the magnetic properties will deteriorate. vice versa,
When the atmospheric pressure P ₃ becomes less than 0.05 atm, an oxide film is likely to be formed in the jet flow, a phenomenon in which the condition of the jet flow deteriorates, and normal flakes cannot be obtained.
The reason for this reduction in pressure is unknown in detail, but
It is thought that the evaporation rate of the highly reactive active Nd alloy increases as the pressure decreases, and the surface of the jet becomes more active, reacting with the small amount of oxygen contained in the atmosphere and forming an oxide film. It will be done.

On the other hand, in order to ensure an appropriate injection speed for each nozzle, the target injection pressure P varies depending on the size of the nozzle hole diameter. For example, when using a nozzle with a small nozzle hole, increasing the injection pressure P,
To lower the injection pressure P when a nozzle with a large nozzle hole diameter is used. The nozzle used for spraying the Nd alloy has a nozzle hole diameter of 0.7 to 1.2 mm. This nozzle hole diameter is 0.7mm
The guideline for injection pressure P is 0.4Kg/cm ² when the diameter is 1.2mm.
The approximate injection pressure P is 0.2Kg/cm ² when the diameter is 0.2Kg/cm 2 . For these reasons, the upper limit of the injection pressure P is set to 0.4.
Kg/cm ² , and the lower limit is 0.2Kg/cm ² .

On the other hand, the atmospheric pressure _P3 in the flake chamber 51 is 0.05~
Finely adjusted in a range of 0.5 atm. When the atmospheric pressure _P3 is within this range, the water flows down from the injection nozzle 41.
No air pockets are generated between the molten Nd alloy and the outer peripheral surface of the cooling drum 47 due to the entrainment of inert gas, and uniform contact between the molten Nd alloy and the cooling drum 47 is ensured. Therefore,
The molten Nd alloy is cooled and solidified under certain conditions.
Since the flakes 49 have a predetermined structure, the manufacturing yield is improved. Therefore, it is necessary to finely adjust the atmospheric pressure _P3 within the range of 0.05 to 0.5 atm.

In order to prevent foreign matter such as dust floating in the melting chamber 32 from entering the pouring container 40 via the funnel 39, it is preferable to attach the lid 4 to the funnel 39 so that it can be opened and closed. Furthermore, when starting pouring, operating conditions vary, and flakes or granulated iron are likely to be formed due to insufficient cooling or excessive cooling. Therefore, it is preferable to provide a damper 5 in the middle of the duct 50 in order to separate the flakes, granulated iron, etc. formed at this initial stage from the product. By switching the damper 5, flakes, granulated iron, etc. produced under unstable conditions are guided to a separately arranged collection chamber (not shown).
When the steady state is reached, the flakes 49 are introduced into the flake chamber 51. As a result, flakes 49 of excellent quality are stored in the flake chamber 51.

〔Example〕

Nd alloy heated to a temperature of 1430℃ (Nd 12 atomic%,
Co5 atomic%, B6 atomic%, Si0.3 atomic%, Al0.3 atomic%, Fe balance) molten metal is poured into a pouring container 40 from a melting container 36 placed in a melting chamber 32 with an atmospheric pressure of P ₂ =0.4 atm. The molten metal was poured onto the outer peripheral surface of the cooling drum 47 from an injection nozzle 41 with a nozzle hole diameter of 0.9 mm provided at the bottom of the molten metal pouring container 40. The pouring container 40 has a cross section with an inner diameter of 180 mm and an effective height of 390 mm.
I used the one from Molten Nd alloy was poured into this pouring container 40 with the upper limit height of the meniscus set to 180 mm. The meniscus level of the poured Nd alloy molten metal was measured using a γ-ray level meter, and the molten metal static pressure P ₁ was calculated from the measured value.

FIG. 2 is a graph showing the relationship between the meniscus level and the molten metal static pressure P ₁ at this time. In this way, depending on the meniscus level, the injected Nd
The molten metal static pressure P ₁ applied to the molten alloy varies. This fluctuation is caused by the injection pressure P ejected from the injection nozzle 41.
This causes fluctuations in the Therefore, the molten metal static pressure P ₁
The atmospheric pressure in the melting chamber 32 is adjusted so as to offset fluctuations in
_P2 was controlled. As a result, the injection pressure P of the molten Nd alloy showed a substantially constant value (0.30 Kg/cm ² ).

On the other hand, the atmospheric pressure P ₃ in the flaking chamber 33 is 0.2
The atmospheric pressure was maintained at a constant value. The atmospheric pressure P ₃ is
For example, when a sudden pressure change occurs in the flaking chamber 33, such as when a sudden pressure drop occurs due to the expansion of argon gas in the chamber at the start of injection, the flaking chamber atmospheric pressure control device immediately stabilizes the pressure. pressure and is maintained at that value.

By controlling the atmospheric pressure, the molten Nd alloy is injected into the cooling drum 47 from the injection nozzle 41 in a rectified stream having a constant thickness, and is uniformly cooled on the outer peripheral surface of the cooling drum 47. As a result, as shown in FIG. 3, the magnetic properties of the Nd-Fe-B permanent magnet were high, and the yield of flakes was improved. The yield in FIG. 3 is expressed as the ratio of magnet powder having the characteristics shown in the figure to the Nd alloy raw material.

On the other hand, the melting chamber 32 and the flaking chamber 33
By controlling only the atmospheric pressure, the injection pressure can be kept as low as 0.3.
In the comparative example in which flakes were produced while maintaining the temperature at Kg/cm ² , the flow rate of the Nd alloy supplied to the outer circumferential surface of the cooling drum 47 varied greatly, and the thickness of the molten metal flow was not determined. As a result, insufficient cooling or overcooling occurs, and even in a steady state, cooling conditions become uneven due to air pockets, and coarse crystal grains, amorphous particles, iron particles, etc. are mixed into the resulting flakes. The ratio was high, and both the magnetic property value and the yield were low.

〔Effect of the invention〕

As explained above, in the present invention, the atmospheric pressure in the melting chamber and the flaking chamber are controlled independently, and the molten Nd alloy is injected from the injection nozzle while canceling out fluctuations in the static pressure of the molten metal. By maintaining the pressure constant, flakes are produced under uniform cooling conditions and without generating air pockets due to entrainment of atmospheric gas. As a result, the generation of coarse crystal grains, amorphous grains, granular iron, etc. is suppressed, and flakes having a predetermined crystal structure are manufactured at a high yield.

[Brief explanation of drawings]

Figure 1 shows a flake production facility in which the atmospheric pressures of the melting chamber and the flaking chamber are independently controlled;
3 and 3 are graphs specifically showing the effects of the present invention, and FIG. 4 shows a flake manufacturing apparatus that does not perform independent atmospheric pressure control. 1: Vacuum exhaust device, 2: Vacuum exhaust device, 3: O
Ring, 4: Lid, 5: Damper, 32: Melting chamber, 33: Flaking chamber, 36: Melting container, 4
0: Pouring container, 47: Cooling drum, 48: Paddle.

Claims (1)

[Claims] 1 From the melting container placed in the melting chamber to the pouring container
The molten Nd alloy is transferred, and the molten Nd alloy is injected from an injection nozzle provided at the bottom of the pouring container onto the outer peripheral surface of a cooling drum placed in a flaking chamber located below the melting chamber to rapidly cool and solidify the molten Nd alloy. When producing flakes, both the melting chamber and the flaking chamber are set in a reduced pressure inert atmosphere, and the atmosphere in the melting chamber is adjusted so as to offset fluctuations in the static pressure of the molten Nd alloy in the pouring container. By controlling the pressure, the injection pressure of the molten Nd alloy flowing out from the injection nozzle was set to 0.2
-0.4 Kg/ ^cm2 , and finely adjusting the atmospheric pressure in the flaking chamber in the range of 0.05 to 0.5 atm.