JP4877514B2 - Manufacturing method of sintered ferrite magnet - Google Patents

Description

The present invention relates to a method for manufacturing a sintered ferrite magnet .

In the production of a bipolar anisotropic cylindrical ferrite sintered magnet (hereinafter simply referred to as a ferrite sintered magnet ) based on a conventional compression molding method, a ferrite filled in a required mold in order to enhance the magnetic field orientation. It is common to use as a starting material a sintered magnet powder obtained by pulverizing a preform that has been preliminarily shaped while applying a magnetic field into granules (hereinafter referred to as magnetic field granules). Is.
Then, the granule material is filled in a mold, and is molded into a predetermined shape by applying pressure while applying a magnetic field, so that a molded body is formed by performing so-called molding in a magnetic field, which is fired and sintered with ferrite. I'm getting a magnet .

In such a sintered ferrite magnet , it is always required to improve the magnetic characteristics.
When forming a ferrite sintered magnet having a large ratio (L / R) of the height dimension (L) in the compression direction (L) to the outer diameter (R) (for example, 2.0 or more), In terms of filling properties, magnetic field orientation, and the like, it is difficult to manufacture in an industrially stable state, and a technique capable of stably manufacturing this is always desired.

On the other hand, in the case of using as a raw material a material obtained by crushing a preform formed by applying a magnetic field to a sintered ferrite magnet powder into a magnetic field granule material, the preliminary molding is a dry process. It is shaping | molding, the density of a preforming body shall be 42 to 51% of theoretical density, and the method of making the particle | grain ratio of 75 micrometers or less contained in a magnetic-field granule material 10 wt% or less (for example, refer patent document 1). In addition, efforts have been made to satisfy the above-described requirements by means of devising the magnetic field orientation direction (see, for example, Patent Document 2).

Japanese Patent Laid-Open No. 11-273939 JP 2004-296849 A

As described above, a device using a ferrite sintered magnet is always required to have high performance. For example, it is required to improve the properties of sintered ferrite magnets having various forms such as a dipole anisotropy or a ring magnet having polar anisotropy used in a motor.
Then, an object of this invention is to provide the manufacturing method of the ferrite sintered magnet which can further improve the magnetic characteristic of the ferrite sintered magnet manufactured using a magnetic field granule material.

For this purpose, the method for producing a sintered ferrite magnet according to the present invention includes an additive addition step of adding and dispersing octanoic acid and / or hexanoic acid as a first additive to a raw material powder of a sintered ferrite magnet. The raw material powder in which the first additive is dispersed is pressure-formed while applying a magnetic field, and a preforming step for obtaining a preform, a crushing step for crushing the preform and obtaining a granule, It is characterized by comprising a main forming step of pressing the granule while applying a magnetic field to obtain a main formed body, and a firing step of baking the main formed body to obtain a fired body.
The first additive is for increasing the orientation of the raw material powder in the pre-forming step and the main forming step, and by adding this, the orientation of the raw material powder in the pre-forming step and the main forming step is increased. Thus, the magnetic properties of the obtained sintered ferrite magnet can be improved.
At this time, it is preferable to add 0.05 to 0.20 wt% of the first additive with respect to the raw material powder. If the added amount is small, the effect is small, and if the added amount is excessively large, the effect is large, but the strength of the molded body is reduced, leading to the occurrence of cracks in the molded body after the main molding.
Such a 1st additive is added in the state heated more than melting | fusing point of the 1st additive. When the first additive is in a molten state, the viscosity resistance is reduced, so that the orientation of the raw material powder can be further increased.
In addition, it is also preferable to perform the steps from the additive addition step to the main forming step while maintaining the temperature at or above the melting point of the first additive.
Furthermore, the 2nd additive different from a 1st additive can also be added at an additive addition process. The second additive is for reducing the friction between the mold used in the main molding step and the raw material powder.

According to the present invention, by adding octanoic acid or hexanoic acid as the first additive, the orientation of the raw material powder can be improved, and a sintered ferrite magnet having higher magnetic properties can be obtained. It becomes.

Hereinafter, the present invention will be described in detail based on embodiments shown in the accompanying drawings.
FIG. 1 is a diagram for explaining an outline of a sintered ferrite magnet in the present embodiment.
As shown in FIG. 1, a ferrite magnet (ferrite sintered magnet) 10 has an outer cylindrical shape, and a hole 11 extending in the axial direction is formed at the center thereof, and has a ring-shaped cross section. The ferrite magnet 10 can have a ratio (L / R) of a dimension (L) in the height direction to an outer diameter (R) of, for example, 2.0 or more.
Such a ferrite magnet 10 constitutes a magnet or the like incorporated in a motor for a water pump such as a washing machine or a dishwasher by inserting and fixing a rotation shaft (not shown) in the hole 11.

Such a ferrite magnet 10 is mainly composed of a ferrite having a hexagonal crystal structure, and at least one element selected from Sr, Ba, Ca, and Pb, which always contains Sr, is A, and a rare earth element At least one element selected from (including Y) and Bi, wherein La is essential and R is Co, or Co and Zn are M, and A, R, Fe and M are Contains,
Equation _{(1) A 1-x R} x (Fe 12-y M y) z O 19 (x, y, z is the number of moles)
When
0.04 ≦ x ≦ 0.5
0.04 ≦ y ≦ 0.5
0.7 ≦ z ≦ 1.2
1 ≦ (x / y)
It is preferable that

Now, such a ferrite magnet 10 is manufactured through the following processes.
FIG. 2 is a diagram showing an example of the flow of the manufacturing process of the ferrite magnet 10 in the present embodiment. In addition, it cannot be overemphasized that the manufacturing process of the ferrite magnet 10 shown in this Embodiment is only an example, and can change suitably.

(Raw material composition production process)
As shown in FIG. 2, in order to manufacture the ferrite magnet 10, first, raw material powders are mixed at a predetermined blending ratio (step S101). As the raw material powder, for example, Fe ₂ O ₃ powder, SrCO ₃ powder, SiO ₂ powder, and CaCO ₃ powder are used. Fe ₂ O ₃ powder and SrCO ₃ powder are weighed so that Fe and Sr have a predetermined ratio (molar ratio), and then a predetermined amount of SiO ₂ powder and CaCO ₃ powder are added to this mixture to obtain a raw material composition Get.

(Calcination process)
The obtained raw material composition is wet-mixed with an attritor or the like for a predetermined time, granulated and dried, and then calcined at a predetermined temperature for a predetermined time to obtain a calcined body (step S102).

(Crushing process)
Next, the obtained calcined body is pulverized to a submicron size through a coarse pulverization process and a fine pulverization process to obtain a fine pulverized powder composed of ferrite particles (step S103).
In the coarse pulverization step, the calcined body is coarsely pulverized with a roller mill or the like. Thereafter, as an additive for improving the magnetic characteristics of the coarsely pulverized calcined body, for example, Fe ₂ O ₃ powder, La (OH) ₃ powder, Co ₃ O ₄ powder, SiO ₂ powder, CaCO ₃ Add powder and pulverize with an attritor. Note that water or the like can be used as a dispersion medium for the fine pulverization.

  Thereafter, the solid content concentration is adjusted by dehydrating the finely pulverized slurry, and this is dried by an annealing kiln or the like (step S104).

(Additive addition / dispersion process)
Additives are added to the obtained dry powder, and these are dispersed and mixed with a Henschel mixer or the like (step S105).
As an additive added here, the 1st additive for improving the orientation of the particle | grains at the time of preforming is added. Furthermore, it is preferable to add a second additive for reducing friction between the magnetic material and the mold during magnetic field molding and suppressing the biting of the magnetic material to the mold.
Here, octanoic acid and hexanoic acid can be used as the first additive.
And it is preferable that the addition amount of a 1st additive shall be 0.05 wt% or more. As the amount of the first additive added is increased, the effect of improving the orientation is enhanced. However, as the amount of the additive is increased, the formability in the formed body (main forming) is reduced, leading to the occurrence of cracks and the like. Accordingly, the upper limit of the amount of the first additive is preferably 0.2 wt%. That is, the preferable addition amount of the first additive is 0.05 to 0.2 wt%, more preferably 0.10 to 0.15 wt%.

As the second additive, it can be used SiO _2, calcium stearate, sublimation binder (camphor), or the like.

  Here, the first additive is preferably added in a liquid state at the time of addition in order to improve dispersibility and adhesion to the dry powder. Therefore, it is preferable to add the first additive in a state heated to the melting point or higher. Further, in the subsequent steps, the mixed powder in which the first additive and the second additive are dispersed in the dry powder so that the first additive is kept in a liquid state until the main forming step described later, It is preferable to heat above the melting point of one additive. For this purpose, it is preferable to control the temperature of the mixed powder by providing a heater or the like in each step.

(Micronization process)
Subsequently, the mixed powder is atomized by an atomizer or the like (step S106).

(Preliminary molding process)
Then, the pulverized powder is preformed while applying a predetermined magnetic field. At this time, the magnetic field to be applied is a direction parallel to the pressurizing direction, so-called longitudinal magnetic field shaping (step S107).

(Crushing process)
The obtained preform is crushed to obtain a magnetic granule (step S108). For this purpose, it is preferable to perform crushing by passing the preform through a screen mesh having openings of a predetermined size.

(Main molding process)
Using this magnetic granule material, molding is performed in a magnetic field to obtain a ring-shaped molded body (step S109). At this time, it is preferable that the obtained molded body has a density within a preset range.
In the magnetic field forming, so-called transverse magnetic field forming in a direction perpendicular to the pressing direction is applied, and a magnetic field having a predetermined strength is applied.

(Baking process, processing process)
The molded body thus produced is fired under predetermined conditions to obtain a sintered body (step S110). Next, the ferrite magnet 10 is obtained by processing the sintered body into a predetermined dimension (step S111).

  In the present invention, since the first additive for improving the orientation of the particles is added prior to the preforming step, the orientation of the magnetic granule material in the preforming step can be improved. it can. Moreover, by making the addition amount within an appropriate range, it is possible to obtain high magnetic characteristics while avoiding an increase in the occurrence of defects such as cracks without impairing moldability.

As the raw material powder, for example, Fe ₂ O ₃ powder, SrCO ₃ powder, SiO ₂ powder, and CaCO ₃ powder are used. From these raw material powders, Fe ₂ O ₃ powder and SrCO ₃ powder were weighed so that the molar ratio Fe / Sr between Fe and Sr was 7.1, and 0.12 wt% of SiO ₂ powder was further added to this mixture. Then, 0.17 wt% of CaCO ₃ powder, 0.15 wt% of BaO powder and 0.1 wt% of Al ₂ O ₃ powder were added to obtain a raw material composition. This raw material composition was wet mixed with an attritor for 1 hour, dried and sized, and then calcined at 1330 ° C. for 2 hours.

After roughly pulverizing the calcined body with a roller mill, La ₂ CO ₃ powder is 2.7 wt%, CoO powder is 0.85 wt%, SiO ₂ powder is 0.45 wt%, CaCO ₃ powder is 1.35 wt%, BaO 0.15 wt% of the powder and 0.1 wt% of the Al ₂ O ₃ powder were added, and pulverization was performed with an attritor so that the specific surface area (BET) was 6.5 m ² / g. Note that water was used as a dispersion medium for the fine pulverization. The ferrite composition at this time is Sr _0.792 La _0.208 Fe _11.84 Co _0.162 O ₁₉ .

  The solid content concentration was adjusted to 77 wt% by dehydrating the finely pulverized slurry, and this was dried at 350 ° C. to reduce the water concentration to 0.3 wt% or less.

The obtained dry powder, 0～0.3Wt% octanoic acid as the first additive, the SiO ₂ after adding 0.11 wt%, and mixed for 5 minutes in a Henschel mixer as a second additive, The mixed powder was pulverized twice using an atomizer. At this time, a screen having a hole diameter of 0.5 mm was arranged in the atomizer.
About the octanoic acid added at this time, the temperature was made into melting | fusing point (16.7 degreeC) or more.

About the powder obtained above, the bulk density was measured.
The results are shown in Table 1.

  As shown in Table 1, the larger the amount of octanoic acid added, the larger the bulk density, suggesting that the powder fluidity is increased by the addition of octanoic acid.

  Subsequently, the obtained powder was pressure-molded while applying a magnetic field to obtain a preform, and then the preform was crushed to obtain a granule. This granule was pressure-molded while applying a magnetic field to obtain a cylindrical shaped body having a height of 15 mm and a diameter of 30 mm. A magnetic field was applied at an intensity of 850 kA / m in the same direction as the pressing direction.

  The formed body was fired at 1230 ° C. for 1 hour to obtain a sintered body. Next, the sintered body was processed to a height of 10 mm to obtain a magnet body.

  The magnetic properties of this magnet body were examined. The results are as shown in Table 1 and FIG.

As shown in Table 1 and FIG. 3, the greater the amount of octanoic acid added, the better the orientation in molding in a magnetic field. Here, the orientation is a ratio B ₀ / J _m of the magnetic flux density B ₀ when the magnetic field H = 0 with respect to the maximum magnetic flux density J _m in the BH curve.

Now, to the dry powder obtained in the same manner as in Example 1, octanoic acid was added as shown in Table 2 as the first additive, and SiO ₂ as the second additive was added in an amount of 0.00. After adding 11 wt% and mixing with a Henschel mixer for 5 minutes, the mixed powder was pulverized twice using an atomizer. At this time, a screen having a hole diameter of 0.5 mm was arranged in the atomizer.

The powder obtained above was preformed by applying a magnetic field in the same direction as pressing. By preforming, a preform having a compact density of 2.35 to 2.7 g / cm ³ was obtained. The dimensions of the preform were 60 mm × 12 mm. Moreover, the magnetic field applied at the time of preforming is 800 kA / m.

  And the obtained preform was pulverized through a screen having an aperture of 0.345 mm to obtain a magnetic granule material.

  Using this magnetic granule material, molding was performed in a magnetic field to obtain a cylindrical molded body having a height of 15 mm and a diameter of 30 mm. The molding density (dp) is as shown in Table 2. A magnetic field was applied at a strength of 850 kA / m in a direction parallel to the pressing direction.

  The formed body was fired at 1230 ° C. for 1 hour to obtain a sintered body. Firing was performed in two ways: firing in an electric furnace and firing in a gas furnace. Next, the sintered body was processed to a height of 10 mm to obtain a magnet body.

  And the magnetic characteristic was measured about this magnet body. The results are shown in Table 2 and FIG.

  As shown in Table 2 and FIG. 4, it can be understood that the residual magnetic flux density Br and the orientation Br / Jm are improved as the additive amount of the first additive is 0.05 wt% or more and the additive amount is increased.

The dry powder obtained in the same manner as in Example 1, 0.11 wt% octanoic acid as the first additive, and the SiO ₂ was added 0.11 wt% as a second additive. Further, for comparison, a material in which the same amount of SiO ₂ was added as the second additive without adding the first additive was prepared.
The obtained mixed powder was mixed with a Henschel mixer for 5 minutes, and then pulverized twice using an atomizer. At this time, a screen having a hole diameter of 0.5 mm was disposed in the atomizer.

Using the powder obtained as described above, molding in a magnetic field similar to that in Example 1 was performed to obtain a cylindrical molded body having a diameter of 30 mm, a height of 15.5 mm, and a molded body density of 2.76 g / cm ^3. Produced. At this time, the material temperature at the time of magnetic field forming was set to four types of 10 ° C, 15 ° C, 22 ° C, and 34 ° C.
In each case where the material temperature during magnetic field molding was 10 to 34 ° C., the strength of the obtained molded body was measured using a tablet tester. The results are shown in Table 3 and FIG.

  As shown in Table 3 and FIG. 5, it can be seen that the strength of the compact is increased by about 25% by setting the material temperature at the time of magnetic field molding to the melting point (16.7 ° C.) or higher of octanoic acid.

To the dry powder obtained in the same manner as in Example 1, octanoic acid was added as a first additive while being changed to 0.1 to 0.3 wt% as shown in Table 4, the SiO ₂ was added 0.11 wt% as an additive.
The obtained mixed powder was mixed with a Henschel mixer for 5 minutes, and then pulverized twice using an atomizer. At this time, a screen having a hole diameter of 0.5 mm was disposed in the atomizer.

Using the powder obtained as described above, molding in a magnetic field similar to that in Example 3 was performed to obtain a cylindrical molded body having a diameter of 30 mm, a height of 15.5 mm, and a molded body density of 2.76 g / cm ^3. Produced. At this time, the material temperature at the time of magnetic field shaping was set to two types of 12 ° C. and 33 ° C.
In each case, the strength of the resulting molded body was measured with a tablet tester.

  Furthermore, the obtained molded body was fired under the same conditions as in Example 1 to obtain a sintered body. And the orientation degree (Br / Jm) of the obtained sintered compact was measured and compared. The results are shown in Table 4 and FIG.

  As shown in Table 4 and FIG. 6, when the material temperature at the time of magnetic field molding is set to be equal to or higher than the melting point of octanoic acid (material temperature 12 ° C. → 33 ° C.), the strength of the compact is increased and Br / Jm is also improved. I understand that. However, in any case, when the amount of octanoic acid added becomes 0.3 wt%, the strength of the molded body decreases. Therefore, the amount of octanoic acid added is preferably 0.2 wt% or less.

It is a figure which shows the ferrite magnet in this Embodiment. It is a figure which shows the manufacturing process of a ferrite magnet. (A) is a figure which shows the relationship between the addition amount of octanoic acid and residual magnetic flux density in Example 1, (b) is a figure which shows the relationship between the addition amount of octanoic acid and orientation. (A) is the relationship between the amount of octanoic acid added, the crushed particle size and the residual magnetic flux density in Example 2, and (b) is the relationship between the amount of octanoic acid added, the crushed particle size and orientation. FIG. FIG. 6 is a diagram showing the relationship between the temperature of the first additive and the strength of the molded body in Example 3. It is a figure which shows the relationship between the temperature of the 1st additive in Example 4, molded object strength, and orientation.

Explanation of symbols

10. Ferrite magnet (ferrite sintered magnet)

Claims (5)

An additive addition step of adding and dispersing octanoic acid and / or hexanoic acid as a first additive to the raw material powder of the sintered ferrite magnet ;
The raw material powder in which the first additive is dispersed is pressure-molded while applying a magnetic field to obtain a preform, and a preforming step,
Crushing the preformed body to obtain a granule; and
The granule is pressure-molded while applying a magnetic field, and a main molding step for obtaining a main molded body,
And firing the main forming body, and a sintering step to obtain a fired body
Said 1st additive is added in the state heated more than melting | fusing point of said 1st additive , The manufacturing method of the ferrite sintered magnet characterized by the above-mentioned. The method for producing a ferrite sintered magnet according to claim 1, wherein 0.05 to 0.20 wt% of the first additive is added to the raw material powder. 3. The method for producing a sintered ferrite magnet according to claim 1 , wherein the steps from the additive adding step to the main forming step are performed while maintaining a temperature equal to or higher than the melting point of the first additive. 4. The ferrite according to any one of claims 1 to 3, wherein the first additive is for increasing the orientation of the raw material powder in the preforming step and the main forming step. Manufacturing method of sintered magnet . In the additive addition step, a second additive different from the first additive is added,
5. The ferrite according to claim 1, wherein the second additive is for reducing friction between a mold used in the main forming step and the raw material powder. 6. Manufacturing method of sintered magnet .

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