JPH0686512A - Method of producing motor permanent magnet - Google Patents

Abstract

PURPOSE:To provide a method of producing a motor permanent magnet having high connection strength with a rotor over a wide range from ordinary temperature to high temperature. CONSTITUTION:A production method is such that a casting ingot of a permanent magnet is contacted with a rotor member each other to make hot working so that magnetic anisotropy occurs and, at the same time, that they are formed together as a unit by diffused connection of surfaces.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing a permanent magnet for a motor, and more particularly to a method for producing a permanent magnet for a motor in which a magnet member and a rotor member are integrated.

[0002]

2. Description of the Related Art Motors have been used as a power source for various devices in the past, but their applications have expanded greatly with the recent development of electronic and mechanical technologies. , For example, machine tools such as drills, lathes, milling machines, electric appliances such as fans, fan heaters, dryers, ventilation fans, AV equipment such as VCRs and CD players, toys such as models, electric wheelchairs and electric vehicles, etc. There is.

As a typical example of the motor, there is a segment type motor as shown in FIG. The segment type motor has a cylindrical rotor 7 made of a material containing iron, nickel, or cobalt as a main component around a shaft 8, and a plurality of arc segment type magnets 9 are provided in a body portion of the rotor 7. Have in parallel. Conventionally, in such a segment type motor, the magnet 9 and the rotor 7 have been bonded to each other on the bonding surface 9a using an epoxy adhesive. This is because the method of directly joining the magnet and the rotor by welding or the like is not suitable because it changes the properties of the magnet, and it is costly to perform complicated processing for engaging the rotor with the rotor. In addition, it is very difficult and, on the other hand, when the magnet is subjected to complicated processing, the strength of the magnet is significantly reduced and the magnet becomes brittle.

However, when the rotor and the magnet are joined together by using an epoxy adhesive, there is a big drawback that the joining strength is low. Specifically, it has a maximum tensile strength of about 1.5 kgf / mm ^{2 at} room temperature (25 ° C) and a maximum tensile strength of about 0.4 kgf / mm ^{2 at} high temperature (100 ° C). is there. In addition, since the joining conditions are strict and the management is difficult, the variations in the joining strength of the product become large and the reliability becomes poor.

The motor manufactured by the above method needs to have a high safety factor, and the upper limit of centrifugal force has to be set low. Therefore, the rotation speed of the motor is suppressed. Further, in order to obtain reliability, it is necessary to improve the joint strength between the rotor and the magnet in terms of motor design, for example, by attaching a cover made of SUS around the magnet or winding a reinforcing fiber. It was A motor having a magnet to which a cover or a reinforcing fiber is attached as described above has a large cost and a heavy weight.

In recent years, as motors have become smaller, lighter and more efficient, higher motor speeds have been demanded.

Therefore, an object of the present invention is to provide a method for producing a permanent magnet for a motor, which has a large bonding strength with a rotor over a wide range from room temperature to high temperature.

[0008]

As a result of earnest research in view of the above object, the inventors of the present invention produced a cast ingot of a magnet material, and brought the ingot into contact with a rotor member to perform hot working. If it is integrated together with magnetic anisotropy, the joining strength between the magnet member and the rotor member will be great,
It was discovered that the accuracy was high. Further, it was discovered that the permanent magnet for a motor manufactured in this way can be firmly joined to the rotor at low cost. The present invention is based on the above findings.

That is, the method of the present invention for producing a permanent magnet for a motor causes magnetic anisotropy by bringing the cast ingot of the permanent magnet and the rotor member into contact with each other and performing hot working. At the same time, it is characterized in that they are integrated by diffusion bonding at the interface.

[0010]

In the permanent magnet for a motor according to the present invention, since the magnet material and the rotor member are integrated by diffusion bonding, the bonding strength is large as compared with the case where they are bonded by an epoxy adhesive, and even at high temperature. The joint strength does not decrease. Since the permanent magnet for a motor manufactured in this way has a rotor member, it can be welded in joining with a rotor, and the welding does not deteriorate the magnetic characteristics of the magnet portion. Moreover, since complicated processing can be performed, joining with high strength can be performed at low cost.

[0011]

The production of permanent magnets for motors according to the method of the present invention will be described in detail below. FIG. 1 is a flow chart showing a manufacturing process of a motor permanent magnet using the method of the present invention.

In the method of the present invention, it is preferable to use, as the magnet member, an R-Fe-B type magnet (here, R represents a rare earth element such as praseodymium or neodymium) having excellent magnetic properties. This R-Fe-B system permanent magnet material can be manufactured as follows.

First, the raw materials are mixed in step (a). In this type of permanent magnet, the phase exhibiting magnetic properties (main phase) is R ₂ Fe ₁₄ B. In the method of the present invention, the raw materials are basically mixed so as to match this composition, but in reality, the addition amounts of the rare earth elements, iron and boron are set to R ₂ Fe in consideration of the ease of pressure molding. _It is preferable to adjust appropriately from the composition of _14B .

Further, in the present invention, other elements may be blended for the purpose of improving the magnetic properties of the finally obtained magnet. For example, a transition metal element such as Co, Cu, Nb or V can be added. These transition metal elements are Co
Can replace up to 50 atom% of Fe, and the others can be compounded to replace up to 3 atom% of Fe.

It is also possible to add an element of Group 3B of the periodic table, such as Al or Ga. These Group 3B elements can be mixed so as to replace up to 1.5 atom% of B.

When a raw material mixture containing the above elements is obtained,
Next, in step (b), this is heated and melt mixed.
This melt mixing must be performed in an inert gas atmosphere for the purpose of preventing oxidation. Specifically, the raw material mixture is
_It is placed in a crucible such as ₂ O ₃ and vacuumed once, and then an inert gas such as high-purity argon gas is introduced and heated and melted.

In the present invention, the heat-melted raw material mixture is used for casting to produce an ingot. Here, in order to make the finally obtained permanent magnet for a motor magnetically excellent in characteristics, the manufacturing conditions of the ingot are as follows: (1) pouring surface cross-sectional area of the ingot, (2) in the ingot The volume fraction of columnar crystals, (3) average cooling rate after ingot casting, (4) ingot volume, and (5) average particle diameter of main phase particles in the ingot are preferably as follows. However, it is not necessary to satisfy all the conditions in (1) to (5), and when one condition is prioritized, the ranges in other conditions may change with a certain width.

(1) Ingot pouring surface cross-sectional area When the raw material mixture is heated and melted into a uniform state,
As (c), the melt is poured into a mold as shown in FIG. As the mold, it is preferable to use a mold made of a material such as Cu-Be, pure Cu, and stainless steel. 25 magnets obtained
The cross-sectional area of the pouring surface is 20 cm in order to have the characteristics above MGOe.
Casting is performed at ² or less. It is particularly preferably 0.5 to 16 cm ² . Here, the cross-sectional area of the pouring surface in the mold,
When the volume of the cast ingot is V and the average height of the cast ingot is h, it is defined by the cross-sectional area (A) = V / h of the pouring surface. At this time, the cross section of the cast ingot is preferably a rectangle whose shortest side is in the range of 0.4 to 4 cm.

(2) Volume of columnar crystals in ingot
The volume fraction of the columnar crystals in the rate of the ingot is 40% or more. If the volume fraction of columnar crystals is less than 40%, the volume fraction of equiaxed crystals will increase, and there will be a magnetic difference in height inside the magnet obtained after hot working. Can't get The volume fraction of columnar crystals is 40 to 10
Magnet obtained if the 0% (BH) _{ma x} is equal to or greater than 25 MGOe. In order to adjust the volume fraction to the above range, the temperature of the mold is set to 200 ° C. or lower in the step (c). Mold temperature is 20
Above 0 ° C, the volume fraction of columnar crystals formed in the ingot becomes less than 40%.

(3) Rapid cooling is performed as an average cooling rate step (d) after ingot casting . The rapid cooling can be performed by bringing the cooling medium into contact with the side surface of the mold. By this quenching, fine crystal nuclei (which become the nuclei of columnar crystals formed in the material in the heat treatment described later) consisting of the ferromagnetic main phase are formed in the material. Average cooling rate is 5 ℃ /
It is preferably not less than sec, especially 5 to 200 ° C./sec. If it is less than 5 ° C / sec, the obtained magnet cannot have characteristics of 25MGOe or more. Further, at 200 ° C./sec, the upper limit value of 35 MGOe is reached, so it is not preferable in terms of cost to set the cooling rate higher than that. The average cooling rate can be calculated by measuring the cooling curve with a thermocouple.

(4) Volume of Ingot Once the ingot is obtained by the step (d), it is released from the mold (step
(e)) and machine to the required size (cross-sectional area: 0.2 to 20 cm ² ) by mechanical cutting and polishing. The volume of cast ingot and 0.1 cm ³ or more, particularly preferably in the 0.1 ~1000cm ^3. If an ingot with such a size is used, the finally obtained magnet will have characteristics of 25 MGOe or more. When an ingot larger than 1000 cm ³ is used, the volume fraction of equiaxed crystals increases when cast. If necessary, degreasing is performed using acetone or the like. .

[0022] (5) a heat treatment for a plurality of ingots obtained in an average particle size above the main phase particles in the ingot (step (f)
)I do. By this heat treatment, α-Fe in the ingot
Disappears and the ferromagnetic main phase (Pr ₂ Fe ₁₄ B) crystallizes out. The heat treatment must be performed in a vacuum of 5.0 × 10 ^-4 Torr or less or in an inert gas. The average particle size of the main phase particles in the ingot is 15 μm or less, and particularly preferably 1 to 15 μm. According to the research conducted by the present inventors, if the average particle size is within the above range, the finally obtained permanent magnet (BH)
_max is 25 MGOe or more. In order to obtain such a magnet, the heat treatment time is preferably about 1 to 10 hours, and the heat treatment temperature is preferably 600 to 1100 ° C. In addition, the particle diameter in the present invention is measured by a direct intersection method.

After the heat treatment, as shown in FIG. 3, the cast ingot 1 and the rotor member 2 are superposed and inserted into the mold 3 (step
(g)). In the present invention, the "rotor member" refers to a member that is joined to a magnet member and that is joined to the rotor as a substrate material of the magnet member.

Considering the strength after joining to the magnet member, the rotor member is usually made of a metal such as iron, iron-nickel system or iron-cobalt system which is easy to weld and work, preferably S10C or the like. Use mild steel. The height of the rotor member 2 is preferably 10% to 200% of the height of the ingot. If it exceeds 200%, the weight is unnecessarily increased, while if it is less than 10%, welding becomes difficult and the magnet member is damaged. Also, complicated processing becomes very difficult.

On the upper part of the cast ingot 1, a mold 5 is placed so that the obtained magnet has a desired shape. The molds 3 and 5 are preferably made of ceramics such as alumina (Al ₂ O ₃ ).

Next, in step (h), the ingot 1 and the rotor member 2 placed in the mold 3 are hot worked by the upper and lower punches 4 of alumina to magnetically anisotropy and diffusion bond them. This hot working is preferably carried out under the following conditions: (a) working temperature, (b) strain rate, (c) working rate, and (d) average working pressure. However, it is not necessary to satisfy all the conditions in (a) to (d), and when one condition is prioritized, the ranges under other conditions may change with a certain width. When pressure is applied in one direction under these conditions, the ingot easily plastically deforms. During the plastic deformation, each component element diffuses to achieve magnetic anisotropy of the ingot 1, and at the same time, the interface 6a between the ingot 1 and the rotor member 2 is completely joined to obtain the motor permanent magnet 6. You can

(B) Working temperature Hot working is preferably carried out within a temperature range of 800 to 1140 ° C. Α-Fe precipitates at temperatures higher than 1140 ° C,
The (BH) _max of the resulting magnet is below 25 MGOe. Also, if hot working is performed at a temperature lower than 800 ° C, the mechanical strength is reduced. Specifically, the tensile strength is 0.4 kgf / mm ² or less at 100 ° C.

(B) Strain rate The strain rate in hot working is preferably 0.0001 to ¹ sec ^-1 . In order for the finally obtained magnet to obtain a coercive force of 10 kOe or more, the strain rate must be 0.0001 sec ^-1 or more. To obtain a tensile strength of 0.4 kgf / mm ² or more at 100 ° C, the strain rate must be Must be less than 1 sec ^-1 .
This is because if the strain rate exceeds 1 sec ^-1 , the diffusion of each component element does not proceed sufficiently and a uniform member cannot be obtained, so that sufficient strength cannot be obtained. Here, as shown in FIG. 3, the strain rate is ΔL = L−L ′ when the object (ingot) having the height L is pressed in one direction to have the height L ′, and the strain rate (S ) = (ΔL / L) / time required for processing (se
c), the dimension is [sec ^-1 ].
Is. Therefore, for example, the strain rate S when an object with a height of 40 mm is processed to a height of 10 mm in 20 minutes is S = (30
/ 40) / 20 x 60 = 6.25 x 10 ^-4 / sec.

(C) Working Rate The working rate in hot working is preferably 30% or more. If the processing rate is lower than 30%, the anisotropy under plastic deformation does not proceed sufficiently, so the residual magnetic flux density, which is a guide for the anisotropy, does not improve, and the (BH) _max value is
This is because it is not possible to obtain the characteristics of 25 MGOe or more. If the processing rate is 10% or less, the diffusion under plastic deformation does not proceed sufficiently, resulting in a significant decrease in strength and
It is impossible to obtain a tensile strength of 0.4 kgf / mm ² or more. Here, as shown in FIG. 3, when the object (ingot) having the height L is pressed in one direction to have the height L ′, the processing rate is ΔL = L−L ′, and the processing rate (P ) = (ΔL / L) × 100.

(D) Average processing pressure The average processing pressure in hot working is 5 to 50,000 kg.
/ cm ² is preferable. When hot working is performed at an average working pressure outside that range, the (BH) _{max of the} resulting magnet
The value cannot get the characteristic more than 25MGOe.

The hot working is performed in a vacuum of 2 × 10 ^-3 Torr or less or in an inert gas such as argon gas in order to prevent the material from being oxidized.

After this hot working, the obtained magnet material is cooled at a cooling rate of 2 ° C./sec (step (i)) to obtain a desired permanent magnet for a motor.

FIG. 4 shows a state in which the obtained motor permanent magnet is joined to the rotor by welding. Since each permanent magnet 6 is welded to the rotor 7 at the joint surface 6b, the joint strength is very high. Further, since the welding is performed on the rotor member of the motor permanent magnet 6, the magnetism of the magnet member is not changed.

The permanent magnet for the motor may be joined to the rotor as shown in FIG. A plurality of recesses are formed in the body of the rotor 7, and the recesses widen toward the bottom surface. On the other hand, the permanent magnet 6 is processed into a shape with a wide hem so as to match the shape of the recess formed in the rotor 7. By driving the permanent magnet 6 from the side surface of the rotor 7 in the direction indicated by the arrow, the permanent magnet 6 and the rotor 7 are meshed and firmly joined. The permanent magnet 6 thus bonded does not come off due to its centrifugal force even if the rotor 7 rotates. In this embodiment, since it is not necessary to perform complicated processing on the magnet member, the cost can be suppressed and the processing can be easily performed.

Further, the method is not limited to the above method, and the permanent magnet and the rotor are threaded and joined by screws.
Various methods are possible.

Example 1 As a starting material, electrolytic iron having a purity of 99.9% or more, purity 99.0%
Using the above praseodymium, crystal boron with a purity of 99.0% or more, pure copper with a purity of 99.5% or more, and gallium with a purity of 99.5% or more, the composition is Pr ₁₉ Fe ₇₄ B ₅ Cu _1.5 Ga _0.5 , and the total amount is 50 g. And mixed.

The above mixture was placed in an alumina crucible, the atmosphere was once set to a vacuum of 2 × 10 ^-4 Torr or less, and then high frequency heating was performed under an argon gas pressure of 26 cmHg. 1500 ° C
And held for 5 minutes to obtain a melt.

Next, the obtained melt was kept at 1400 ° C.,
This was poured into a pure copper mold shown in FIG. At this time,
The mold temperature is 25 ° C and the cross-sectional area of the pouring surface is 2.23 cm.
^{It was 2} (4.05 cm x 0.55 cm). Immediately after this casting,
The side surface of the mold was rapidly cooled at an average cooling rate of 20 ° C / sec. Then, let it cool and ingot from the mold (40.5 mm × 5.2 mm ×
30mm) was taken out. The obtained ingot is degreased and washed with acetone, and then 40 mm × by machining and polishing.
The size was 5 mm x 24 mm.

Next, these ingots were treated with 1 × 10 ^-4 Torr.
Heat treatment was performed in the following vacuum. In this heat treatment, (1) the temperature was raised from room temperature to 850 ° C over 30 minutes, (2) the temperature was maintained at 850 ° C for 8 hours, and then (3) cooled down to 500 ° C over 1 hour.
The average particle size of the main phase particles of the obtained ingot was 9 μm.

As shown in FIG. 3, the ingot and the rotor member made of S10C were inserted into a mold made of alumina, and an arch mold made of alumina was placed on top of the mold.
In a vacuum of × 10 ^-3 Torr or less, and at a temperature of 1090 ° C, pressure was applied in the direction of the arrow in Fig. 3 by the upper and lower punches of alumina at an average processing pressure of 500 kg / cm ² . At this time, the ingot was compressed from a height of 24 mm to a height of 6 mm over 20 minutes. That is, the processing rate of the height of the ingot was 75%, and the strain rate was 6.25 × 10 ⁻⁴ / sec. The size of the rotor member was 40 mm × 5 mm × 10 mm.

After cooling, the obtained permanent magnet was cut into a size of 40 mm × 5 mm × 5 mm so as to include the bonding interface.
In the same way, a total of 20 permanent magnets were manufactured, and 25 ℃ and 100 ℃
A tensile strength test was conducted at two different temperatures in the direction perpendicular to the bonding interface. Table 1 shows the average value of the tensile strength measured at each temperature and the standard deviation.

Comparative Example 1 Only an ingot obtained in the same manner as in Example 1 was hot-worked under the same conditions as in Example 1. The obtained permanent magnet was cut into a size of 40 mm × 5 mm × 5 mm and bonded to a rotor member having a size of 40 mm × 5 mm × 10 mm by an epoxy adhesive. S10C was used for the rotor member and was used for the epoxy adhesive.

Twenty permanent magnets were produced in the same manner, and a tensile strength test was conducted in the same manner as in Example 1. Table 1 shows the average values of the measured tensile strengths and the standard deviations at each temperature.

Table 1 25 ° C. 100 ° C. Average value ⁽¹⁾ Standard deviation ⁽¹⁾ Average value ⁽¹⁾ Standard deviation ⁽¹⁾ Example 1 2.1 0.4 2.0 2.0 0.4 Comparative example 1 1.5 0.9 0.4 0.2

Table 1 Note (1): The unit is kgf / mm ² .

As is apparent from Table 1, the permanent magnet according to the present invention has a high temperature (1 ° C.) even at room temperature (25 ° C.) as compared with the conventional method using an epoxy adhesive.
It can be seen that the film has a high tensile strength even at 00 ° C. Further, there was little variation in tensile strength at room temperature, and the variation did not change even at high temperature.

[0047]

As described above in detail, according to the method of the present invention, it is possible to manufacture a permanent magnet for a motor having a high joint strength between the magnet member and the rotor member and having a high accuracy. Further, the permanent magnet for a motor manufactured in this manner can be firmly bonded to the rotor easily at low cost, has little variation as a product, and has extremely high reliability.

The motor using the permanent magnet for a motor according to the present invention can achieve high rotation speed, light weight, and high efficiency.

[Brief description of drawings]

FIG. 1 is a flowchart showing a process of manufacturing a permanent magnet for a motor.

FIG. 2 is a view showing a mold for casting an ingot.

FIG. 3 is a schematic view showing a state in which an ingot and a rotor member are pressure-formed in one direction during hot working.

FIG. 4 is a view showing a state in which a motor permanent magnet is joined to a rotor by welding.

FIG. 5 is a view in which each of the permanent magnets for a motor and the rotor is processed so as to mesh with each other.

FIG. 6 is a diagram showing a rotor portion of a conventional segment type motor.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Casting ingot 2 Rotor member 3, 5 type 4 Punch 6 Permanent magnet for motor according to the present invention 6a Joining interface 6b Welded portion 7 Rotor 8 Shaft 9 Conventional permanent magnet for motor 9a Joining surface

Claims (1)

[Claims] 1. A method for producing a permanent magnet for a motor, wherein a cast ingot of the permanent magnet and a rotor member are brought into contact with each other to perform hot working, thereby causing magnetic anisotropy and forming an interface. A method characterized by integrating by diffusion bonding of.