JPH0271505A - Manufacture of permanent magnet flake - Google Patents

Abstract

PURPOSE:To realize high performance by controlling the following conditions: a spouting condition to spout a molten metal at a uniform velocity; a material of a roll for molten-metal cooling use; a surface roughness of the roll; the number of revolutions of the roll; a gap between a nozzle and the surface of the roll; an angle of inclination of the nozzle; an atmospheric gas inside a chamber. CONSTITUTION:The following conditions shall be set: regarding a differential pressure to control a spouting velocity of a molten metal, an initial differential pressure of 0.3 to 0.5kg/cm<2>; a middle differential pressure of 0.05 to 0.2kg/cm<2>; after the middle differential pressure has reached this differential pressure, the differential pressure is increased continuously to 0.2 to 0.4kg/cm<2>; a spouting angle of the molten metal is 2 to 10 deg. with reference to a perpendicular line; a distance at which the molten metal comes into contact with a roll is within a range of 0 to 12mm from the center of the roll to the side of its direction of rotation; a gap between the surface of the roll and a nozzle is 8 to 30mm; a shifting velocity of a flake on the surface of the roll is 20 to 30m/sec; a ratio of a volume velocity of a spout to a velocity of rotation of the roll is within a range of 0.06 to 0.10; a degree of vacuum inside a chamber before a spouting operation is 100 to 450mmHg; an atmospheric gas is a mixed gas of Ar and He; its mixture ratio is at Ar (50 to 70%) : He (30 to 50%). Thereby, it is possible to manufacture a flake whose magnetic characteristic is excellent and whose yield is good.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a method for obtaining Nd-based permanent magnet flakes using a rapid cooling method.

(Prior Art) Since the development of amorphous materials, the rapid cooling method has attracted attention for its manufacturing advantages and has been in the spotlight in the field of new material development. This manufacturing method involves spraying a substance in a liquid state onto rolls rotating at high speed and rapidly solidifying it to obtain an amorphous or nearly crystalline substance. According to this method, materials that have poor machinability and cannot be subjected to plastic working such as cold rolling can be made into thin strips. Furthermore, it is possible to transform a high-temperature phase into amorphous material at room temperature, which cannot be achieved using normal cooling methods.

The manufacturing technology of amorphous alloys using the ultra-quenching method is widely used because it is suitable for mass production in single rolls. Conventional techniques for this method include Japanese Patent Publication No. 60-9852;
It is described in Japanese Patent Publication No. 61-5821. Nd
In order to create permanent magnets with good magnetic properties by the rapid cooling method, it is necessary to have a surface shape with fewer irregularities and scratches on the surface of the flakes and appropriate cooling during production. In order to satisfy these conditions, conventional general manufacturing methods are insufficient and a new method must be developed. The problems with the conventional method are described below.

■The method of ejecting molten metal in the conventional method is to apply pressure from the top of the molten metal or to maintain a constant pressure difference (or pressure) between the top and bottom.
Because the liquid is ejected, the potential energy of the liquid level is
In other words, the Torricelli effect makes uniform jetting impossible. Here, differential pressure refers to the difference in pressure between the upper and lower sides of the nozzle hole. If the ejection speed is not constant, the thickness of the flakes cannot be controlled, and since the cooling rate by the rolls is constant, there will be a difference in the degree of cooling in the thickness direction. The magnetic properties of flakes are determined by their composition and grain size. Therefore, there is a problem in that the crystal grain size is determined by the thickness of the flakes and the magnetic properties vary.

■If the nozzle is perpendicular to the roll surface and the gap between the nozzle and the roll surface is several millimeters or more, as the roll rotates, the atmospheric gas comes into direct contact with the bottom of the nozzle, which cools the nozzle and prevents the flow of molten metal from the nozzle hole. As the flow is gradually contracted, the amount of ejection decreases. Due to this influence, the thickness of the flakes fluctuates and the magnetic properties become uneven. Even if the gap between the nozzle and the roll surface is set to 1++un or less so that the cooling of the atmospheric gas can be ignored, it is difficult to produce well-shaped flakes because Nd-based molten metal has a high surface tension and easily adheres to surrounding objects. . As described above, in the case of a vertical nozzle, there is a drawback that the temperature decreases significantly due to cooling by atmospheric gas, and the ejection amount cannot be controlled at a constant level. When the gap between the nozzle and the roll surface is set to 15 mm or less, the turbulence of the paddle due to instantaneous fluctuations in the amount of ejection causes the molten metal to scatter, adhere to surrounding objects, and deteriorate the subsequent flake shape. If the gap is 30 mm or more, the molten metal ejected from the nozzle hole will be in a widening state, and may become granular just before contacting the roll. In such a state, the kinetic energy of the molten metal is dispersed, so no puddles are formed on the roll, and flakes with non-uniform shape and thickness are produced. Particularly in the case of continuous production for 10 minutes or more, losses due to this adhesion and non-uniformity are significant.

■If the moving speed of the roll surface is the same as the rotational speed of the roll, and the moving speed is less than 15 m/sec, the puddles that should have been formed on the roll surface will bounce off, resulting in particles or particles of about 0.2 cm. It becomes thick flakes. This is a phenomenon due to the high ejection speed. Movement speed is 35a+
/sec or more, the molten metal will instantly solidify unless the ejection amount is supplied in a proportionate amount, producing flakes with irregular shapes and non-uniform magnetic properties. If the amount of ejection is small, there will be insufficient force to press the molten metal against the rolls, and the inertia of the rotation of the rolls will blow the molten metal away, reducing the amount of heat removed by the rolls and deteriorating the magnetic properties. In a laboratory scale of several logs or an intermittent quenching device that finishes in a few minutes, the speed is 15 m/sec or less, 35 m/sec.
Conventional methods can handle roll rotation speeds of c or more, but 1
If the production time is longer than 0 minutes, heat accumulation in the rolls will affect the cooling rate of the flakes, and the range of roll rotation speeds for obtaining a uniform crystal grain size will become narrower. This is because when a small amount of molten metal is rapidly cooled, most of the flakes become amorphous or have a fine crystal grain size close to that, regardless of the roll rotation speed.

■In the conventional method, there are examples in which the atmospheric gas in the room is an inert gas and the degree of vacuum is about 1 to 3 nmHg, but Nd-based materials easily react with other substances, and in particular, the influence of oxygen gas is large on the magnetic field. It is. Therefore, the conditions of high vacuum under an inert gas have the advantage that oxidation by oxygen is reduced, and heat conduction is less inhibited by the gas film between the roll surface and the flakes. However, the action of the gas that accompanies the rotation of the rolls is to press and mold the molten metal from above and from the left and right at a maximum of two lengths where the molten metal solidifies, and to cool the upper side of the flakes. Such an effect does not exist in the case of high vacuum. When the flakes are manufactured under a high degree of vacuum when carrying out the present invention, the shape of the flakes may be distorted, some portions may become extremely thick, and the magnetic properties will be worse than those produced under a low degree of vacuum. Furthermore, the temperature drop due to cooling of the nozzle bottom varies depending on the type of inert gas. In this case, He gas is more preferable than Ar. This is because there is a difference in gas density even at the same degree of vacuum. Ar gas is superior in the effect of forming the molten metal and the effect of cooling the upper side of the flakes by the gas flow described above. As described above, it is necessary to select an appropriate degree of vacuum and the type of atmospheric gas in consideration of the effects of the gas, and it is impossible to manufacture Nd-based materials with an optimum crystal grain size and a high yield using conventional methods.

[Problem to be solved by the invention]

SUMMARY OF THE INVENTION In view of the above-mentioned problems, an object of the present invention is to provide a method for manufacturing Nd-based permanent magnet flakes by a rapid cooling method, with a high yield of flakes with small variations in thickness and excellent magnetic properties. do.

(Means for solving problems) The gist of the present invention is as follows.

In the method of manufacturing Nd-based permanent magnet flakes by injecting molten metal from a molten metal supply container to a rotating cooling roll through a nozzle and appropriately cooling and solidifying the molten metal, , the initial differential pressure is 0.3
~0.5 kg/ci, medium-term differential pressure 0.05~0.2k
gZc After the main medium-term differential pressure reaches the above differential pressure, the differential pressure is continuously increased to 0.2 to 0.4 kg/cf using a three-stage differential pressure control method. The angle is 2 to 10 degrees with respect to the perpendicular, and the distance at which the ejected molten metal contacts the roll is in the range of 0 to 12 mm from the center of the roll in the rotation direction,
The gap between the roll surface and the nozzle is 8 to 30 mm, ■ The moving speed of flakes on the roll surface is 20 to 30 m/s.
ec, and the ratio of the volume velocity of the jet to the rotational speed of the rolls must be in the range of 0.06 to 0.10; ■The degree of vacuum in the room before the jet is 100 to 450 mmHg, and the atmospheric gas is Ar and A method for producing permanent magnet flakes, characterized in that a mixed gas of He has a mixing ratio of Ar (50 to 70%):He (30 to 50%).

[For production]

Hereinafter, the present invention will be explained in detail using the drawings.

(2) Fig. 1 shows a method of controlling differential pressure according to the present invention.

The present invention employs the following means for the purpose of uniform jetting.

In other words, a high differential pressure is initially applied to prevent the nozzle from clogging and the molten metal is spouted out, and then the differential pressure is temporarily lowered to a predetermined pressure (this is called the mid-term differential pressure) in order to suppress the sudden spouting of the molten metal, and the predetermined pressure is reached. This is a three-stage differential pressure control method that realizes uniform jetting by increasing the differential pressure by the decrease in potential energy of the rear liquid level height and the nozzle contraction caused by the atmospheric gas.

The initial differential pressure is set higher than the normal differential pressure to prevent blockage when ejecting molten metal from the nozzle. Upper limit of 0.5kg/
If the differential pressure exceeds afl, the amount of molten metal ejected will increase, making it impossible to produce flakes with good quality by splashing on the roll. When the differential pressure reaches the lower limit of 0.3 kg/ci without a groove, there is a high probability that a part of the nozzle will become clogged or that the amount of ejection will decrease. Therefore, the range of initial differential pressure that can obtain a good jetting speed without clogging the nozzle is 0.3 to 0.5 kg/c-f.
It is IT.

Once ejected due to the initial pressure difference, the ejection speed is high and the flakes become thick, making it impossible to obtain good magnetic properties. Therefore, the medium-term differential pressure is lowered in as short a time as possible (several seconds) to obtain flakes with an appropriate thickness. During these few seconds, there is enough pressure due to the height of the molten metal to reach 0.
At over 2 kg/c11T, the ejection speed is high and the flakes are still thick, and at less than 0.05 kg/c11, the flakes become small and thin.

The appropriate range of medium-term differential pressure is 0.05 to 0.2 kg/c+f
It is.

For the purpose of uniform jetting, the differential pressure in the latter stage is continuously increased to compensate for the decrease in the liquid level, that is, the Torricelli effect and the contracted flow due to the drop in nozzle temperature. The optimum range for obtaining a constant thickness is 0.2 to 0.4 kg/
cffl.

FIG. 2 shows the differential pressure (pressure) of the conventional method when molten Nd-based permanent magnet is cast. FIG. 3 is a comparison of ejection time and ejection amount between the conventional method and the present invention. In the conventional method, the jetting amount decreases due to the synergistic effect of the late Torricelli effect and the contraction of flow due to the decrease in nozzle temperature.

In the three-stage differential pressure control system of the present invention, linear in time,
That is, uniform ejection is achieved, and the flakes have a shape with a constant thickness and width. FIG. 4 shows the relationship between flake thickness and magnetic properties. Flakes with a certain range of thickness exhibit the best magnetic properties. The present invention can produce flakes with a thickness within this optimum range by combining various conditions mainly using a three-stage differential pressure control method.

■In order to smoothly eject molten metal from the nozzle and produce well-shaped flakes, the nozzle should be ejected at an angle of 2 to 10 degrees to the perpendicular to the roll (hereinafter referred to as an inclined nozzle) rather than perpendicular to the roll surface. This will result in fewer paddle disturbances and flakes with a stable aspect ratio (ratio of flake width to thickness).

If ejected vertically, a paddle will not form unless the kinetic energy of the ejected water exceeds a certain level.

With weak kinetic energy that does not result in the formation of puddles, the molten metal is splashed by the rolls and cannot be cooled properly; that is, it is slowly cooled, the crystal grain size increases, and the magnetic properties deteriorate. In the case of a vertical nozzle, the bottom of the nozzle comes into direct contact with the gas flow caused by the rotation of the rolls, so there is a drawback that the temperature decreases significantly and the amount of ejection cannot be controlled at a constant level.

In the case of the inclined nozzle according to the invention, the bottom of the nozzle is not in direct contact with the gas flow, so that the temperature drop is small.

If the angle of inclination is less than 2 degrees, which is close to vertical, it will still be affected by the gas flow. If the temperature exceeds 10 degrees, there is no problem with spouting, but the position where the molten metal contacts the roll surface, that is, the distance from the center of the roll, becomes longer, and the contact time becomes shorter by that distance, making it impossible for the flakes to cool properly. However, the magnetic properties deteriorate. Therefore, the optimum range of the inclination angle is 2 to 10 degrees.

FIG. 5(a) shows a vertical nozzle and an inclined nozzle.

Table 1 shows a comparison of the ejection speeds of the vertical nozzle and the inclined nozzle under the same conditions. From now on, there is no need for statistical testing, and the inclined nozzle has better average values and degree of dispersion. Additionally, as a secondary effect, when the nozzle is tilted, when the kinetic energy is below a certain level, the molten metal flows smoothly along the roll even if no puddles are formed, producing flakes with a good shape with few irregularities and scratches. Can be done. Therefore, the inclined nozzle has the effect of causing the molten metal to flow out smoothly along the roll, making it possible to constantly produce flakes that have a good shape and are properly cooled.

Further, the position where the spouted molten metal contacts the roll surface is in the range of 0 to 12IIIffl from the center of the roll. If the contact distance is greater than this, the cooling zone from the roll will become shorter and proper cooling will not occur. Table 2 shows a comparison of magnetic properties depending on the contact distance of the molten metal from the center of the roll.
When the gap between the nozzle and the roll surface is small, a particularly high differential pressure is applied at the beginning of jetting, so the molten metal scattered from the roll surface adheres to the nozzle heater, and this deposit solidifies.
This inhibits subsequent flake production. Therefore, the gap must be at least 8M or more. It is safe to make the gap larger to prevent this initial adhesion, but if the gap exceeds 30M, the ejected flow tends to become clear when it comes into contact with the rolls, which may cause pores in the manufactured flakes or uneven thickness. There will be more uniform items. Therefore, the gap should be 8 mm or more and 30 mm or less.

(2) Figure 6 shows the relationship between roll rotation speed and flake thickness at a constant ejection speed. This figure shows that it is possible to control the thickness of the flakes by changing the number of rotations of the rolls. FIG. 7 is an example of the relationship between roll rotation speed and magnetic properties. When rotating at low speed, underquench occurs and the magnetic properties are not good. In the case of high-speed rotation, it becomes amorphous, and its magnetic properties will not be restored unless it is heat treated. Naturally, if the nozzle hole diameter and differential pressure, which affect the amount of ejection, differ, the amount of ejection will vary and the roll rotation speed must be matched.
In the range of 0, no heat treatment step is required.

Flakes with optimal magnetic properties are produced within the range of 20 to 30 m/sec in terms of roll rotational speed.

(2) Figure 8 shows the relationship between the temperature drop at the bottom of the nozzle and the type of atmospheric gas. This causes a difference in the temperature drop due to cooling of the nozzle bottom. In this case, Ile gas is more desirable than Ar. FIG. 9 shows the relationship between the degree of vacuum and magnetic properties. In a vacuum range of 100 to 450 mmHg, Ar gas is superior in forming the molten metal and cooling the upper side of the flakes by the gas flow accompanying the rotation of the rolls. As described above, it is necessary to select an appropriate degree of vacuum and the type of atmospheric gas in consideration of the effects of the gas.

In the present invention, Ar and He gases are mixed in consideration of their advantages, and the relationship between the degree of vacuum and the magnetic properties is determined. The results are shown in FIG. One of the advantages over using one type of gas alone is that the inhibition of heat conduction by the film between the roll and the flakes is improved compared to using Ar gas alone. That is, the total heat conduction due to the film between the roll and the flake is about 1710 lle. The shaping of the molten metal by the gas flow and the cooling effect on the upper side of the flakes were improved compared to He gas alone.

〔Example〕

Table 3 shows a comparison between the production conditions according to the present invention and the production conditions according to the conventional method, which are substantially the same.

Table 4 shows a comparison of the magnetic properties of flakes produced under production conditions according to the present invention and conventional production conditions.

It can be seen from Table 4 that the manufacturing conditions of the present invention are superior to the conventional method.

〔Effect of the invention〕

In the quenching method, a substance in a liquid state is sprayed onto rolls rotating at high speed and rapidly solidified to obtain an amorphous or nearly crystalline substance. What is important is how stable the puddles formed on the rolls can be until solidification. The shape and size of this paddle determines the flake shape (thickness and width). The flake shape and its composition are factors that determine the quality of magnetic properties. Therefore, the crystal structure of the composition and the size of the crystal grain size are factors in determining the quality of the magnetic properties. The purpose of quenching materials other than magnet materials is to create completely amorphous particles without crystal grains within the flakes. When magnet materials are produced into flakes with an amorphous or nearly amorphous fine crystal structure, a heat treatment process is required to obtain the optimum crystal grain size. The effect of heat treatment is to grow these fine crystals to an appropriate grain size, but
There are also reactions that reduce the magnetic properties of the flakes, which already have optimal crystallization during quenching. In particular, the decrease in intrinsic coercive force is remarkable. Comparing the sorted flakes produced by rapid cooling and the same flakes heat-treated, the sorted ones have better magnetic properties.

The present inventors investigated the jetting conditions for spouting the molten metal at a uniform speed, the material of the roll for cooling the molten metal, the surface roughness of the roll, the number of rotations of the roll, the gap between the nozzle and the roll surface, the inclination angle of the nozzle, the atmospheric gas in the room, etc. By controlling various conditions, we have completed a method for producing high-performance permanent magnet flakes without a heat treatment process. Optimum magnetic properties for the composition can be obtained if the produced flakes do not need to be heat treated. Also, since no heat treatment equipment is required, it is economical and labor-saving, contributing to cost reduction.

[Brief explanation of the drawing]

FIG. 1 is a diagram showing an example of the three-stage differential pressure control method of the present invention;
Fig. 2 is a diagram showing a conventional differential pressure control method, Fig. 3 is a diagram showing the relationship between ejection time and ejection amount by comparing the conventional method and the three-stage differential pressure control method of the present invention, and Fig. 4 is a diagram showing a flake control method. A diagram showing the relationship between thickness and magnetic properties. Figure 5 is a diagram comparing a conventional vertical nozzle (a) and an inclined nozzle (b) according to the present invention. Figure 6 is a diagram showing the relationship between roll rotation speed and flake thickness. Figure 7 is a diagram showing the relationship between roll rotation speed and magnetic properties, Figure 8 is a diagram showing the relationship between the temperature drop at the bottom of the nozzle depending on the type of atmospheric gas, and Figure 9 is a diagram showing the relationship between indoor vacuum and magnetic properties. A diagram showing the relationship between the characteristics, Figure 10, shows the indoor atmosphere between Ar and ll.
FIG. 3 is a diagram showing the relationship between e and magnetic properties in a mixed gas.

Claims (1)

[Claims] A method for producing Nd-based permanent magnet flakes by spraying the molten metal from a molten metal supply container through a nozzle onto a rotating cooling roll and appropriately cooling and solidifying the molten metal, comprising: The differential pressure that controls the jetting speed is 0 when the initial differential pressure is 0.
．． 3-0.5kg/cm^2, medium-term differential pressure 0.05-0
．． 2 kg/cm^2, and after the medium-term differential pressure reaches the above differential pressure, it is a three-stage differential pressure control method that continuously increases the differential pressure to 0.2 to 0.4 kg/cm^2, (2) The ejection angle of the molten metal is 2 to 10 with respect to the perpendicular to the roll.
(3) The distance that the ejected molten metal contacts the roll is in the range of 0 to 12 mm from the center of the roll in the direction of rotation, and the gap between the roll surface and the nozzle is 8 to 30 mm. (3) Roll Movement speed of surface flakes is 20-30m
/sec, and the ratio of the volume velocity of the jet to the rotational speed of the roll should be in the range of 0.06 to 0.10, (4) The degree of vacuum in the room before the jet is 100 to 450 mmHg.
A method for producing permanent magnet flakes, characterized in that the atmospheric gas is a mixed gas of Ar and He, and the mixing ratio is Ar (50-70%):He (30-50%).