JP6064539B2 - Powder core powder manufacturing method and dust core powder - Google Patents

Description

  The present invention relates to a method for producing a dust core powder for producing a dust core having a high magnetic flux density and low iron loss, and to a dust core powder.

Magnetic cores used in motors and transformers are required to have high magnetic flux density and low iron loss. Conventionally, a laminate of electromagnetic steel sheets has been used as such a magnetic core, but in recent years, a dust core has attracted attention as a magnetic core material for motors.
The greatest feature of the dust core is that a three-dimensional magnetic circuit can be formed. In other words, electromagnetic steel sheets form magnetic cores by stacking, so there is a limit to the degree of freedom of shape. However, dust cores are formed by pressing soft magnetic particles with insulation coating, so there is only a mold. There is no restriction on the shape, and it is possible to obtain a degree of freedom in shape that exceeds that of the electromagnetic steel sheet.
In addition, in the case of electromagnetic steel sheets, since the steel sheet surfaces are insulated, the magnetic properties are different between the steel plate surface direction and the surface vertical direction, and the magnetic properties in the surface vertical direction are inferior. . On the other hand, the dust core is suitable for use in a three-dimensional magnetic circuit because each particle is covered with an insulating coating and has uniform magnetic characteristics in all directions. In addition to the superiority in such characteristics, press molding with a dust core has a short process and a high yield compared to the stacking process of steel sheets, so the cost is combined with the low price of the raw material powder. It is expected to take advantage of

  As mentioned above, the dust core is an indispensable material for designing a three-dimensional magnetic circuit and is excellent in cost performance. In recent years, the viewpoints of miniaturization of motors, rare earth free, cost reduction, etc. Therefore, research and development of motors having a three-dimensional magnetic circuit using a dust core have been actively conducted.

  Here, two of the magnetic properties most required for a soft magnetic material for motors are high magnetic flux density and low iron loss. In order to increase the magnetic flux density, it is preferable that the components of the powder are high purity and the crystal structure inside the powder is coarse. As a result, the powder is softened, and a high compact density is obtained, so that the magnetic flux density is improved. Moreover, in order to reduce iron loss, it is preferable that the component of the powder is high purity, the crystal structure inside the powder is coarse, and the filling rate (apparent density) of the powder into the mold is high. . This reduces the amount of strain accumulated during molding and reduces iron loss. Note that increasing the purity of the component also has the effect of reducing iron loss by cleaning the structure and facilitating magnetization.

  In order to meet the above-described requirements, for example, in Patent Document 1, atomized iron powder to which Nb and Ti are added is heat-treated in a reducing atmosphere at 800 ° C. to 900 ° C., and then for the purpose of coagulating and separating the powder as much as possible. A technique is disclosed in which mechanical pulverization is performed so as not to add strain, and when there is a concern about introduction of strain, a strain removing heat treatment is performed and an insulating coating is applied to obtain powder for a dust core. This technology combines technology equivalent to high purity of components that coagulates and precipitates solute elements harmful to magnetic properties by adding Nb and Ti, and technology for straining iron powder by heat treatment after grinding. However, since no attempt has been made to increase the filling rate into the mold, that is, to increase the apparent density, there is room for improvement in order to obtain excellent magnetic properties. In addition, “mechanical pulverization for the purpose of agglomeration and separation of powder” is performed, but such pulverization is generally performed using an impact pulverizer such as a hammer mill. However, in order to increase the apparent density by pulverization, it is necessary to positively introduce a certain shear strain to the powder. In mechanical pulverization that does not add the strain as much as possible, a dust core having a low iron loss is required. It was difficult to get.

  Moreover, in patent document 2 and patent document 3, the technique which improves an apparent density by performing crushing with a rotary crusher with respect to water atomized iron powder is disclosed. However, since the techniques described in Patent Document 2 and Patent Document 3 are performed under a condition in which a very large strain is introduced into the powder, the crystal structure inside the powder after strain relief annealing is refined. There is a disadvantage that the loss increases.

JP2011-202213 JP-A 64-21001 JP 4-48001

As described above, in the prior art, it has been difficult to obtain soft magnetic iron powder having a high magnetic flux density and a low iron loss after molding.
An object of the present invention is to provide a powder for a dust core that is provided with a high magnetic flux density and low iron loss characteristics to a dust core after molding, and a method for producing the same.

  Based on the above three prior arts, the inventors have an iron-based soft material that has high apparent density and purity, excellent compressibility, and excellent magnetic properties (high magnetic flux density, low iron loss). Studies have been conducted on the production method of magnetic powder. As a result, the components were purified by hydrogen reduction at a high temperature, and the apparent density of the powder aggregated by the high temperature hydrogen reduction was recovered and further increased in the subsequent pulverization and pulverization processes. Less strain loss annealing is performed to release the strain introduced in the powder while preventing powder aggregation, and finally the insulation coating is applied to the powder, resulting in low iron loss and high magnetic flux density after molding. Has succeeded in obtaining an iron-based soft magnetic powder capable of imparting a high temperature.

That is, the gist of the present invention is as follows.
1. A method for producing an iron-based soft magnetic powder for a dust core,
Obtaining an iron-based soft magnetic powder by an atomizing method;
A reduction heat treatment step of heat-treating the iron-based soft magnetic powder in a hydrogen atmosphere at 950 ° C. or higher;
A pulverization step for pulverization after the reduction heat treatment step;
A crushing step of crushing the powder after the crushing step by applying a shearing force by a rotating body;
A strain relief heat treatment step of performing a strain relief heat treatment at a temperature of 500 ° C. or more and less than 900 ° C. after the crushing step;
Including a step of applying an insulation coating of 0.05 mass% or more and less than 0.3 mass% to the surface of the powder after the distortion removing heat treatment step,
The powder for a dust core, wherein the crushing step is performed under a condition that a product of a peripheral speed (m / s) of the rotating body and a crushing time (s) is 1000 m or more and 22000 m or less. Manufacturing method.

2. A powder for a dust core obtained by the production method according to 1 above.

3. The powder for a dust core according to 2, wherein the C content is 0.003 mass% or less and the O content is 0.1 mass% or less.

4). 4. The powder for a dust core according to 2 or 3, wherein the apparent density is 4.0 g / cm ³ or more.

  ADVANTAGE OF THE INVENTION According to this invention, the powder for powder magnetic cores which makes the shape | molded powder magnetic core high magnetic flux density and low iron loss can be provided.

Hereinafter, the present invention will be specifically described.
The iron-based soft magnetic powder used as a raw material for the powder for a dust core of the present invention is obtained by an atomizing method. Here, the reason for limiting to the atomization method is that the powder obtained by the oxide reduction method or the electrolytic deposition method has a low apparent density, so that even if it is pulverized, a sufficient effect of improving the apparent density is obtained. It is because it is not possible. As long as the atomizing method is used, any kind of gas, water, gas + water, centrifugal, etc. may be used. However, in view of practical use, it is preferable to use a water atomizing method that can produce a large amount of powder at a time and is most excellent in terms of cost.

  The composition of the soft magnetic powder may be anything that contains iron as a main component. Such soft magnetic powders include pure iron, Fe—Si, Fe—Cr, Fe—Co, Fe—Al, Fe—Ni, Fe—Si—Al, Fe—Ni—Co, and the like. In particular, it is preferable to use a pure iron powder that is inexpensive and easy to manufacture by the water atomization method. When pure iron powder is used, inevitable impurities include C ≦ 1.0 mass%, O ≦ 1.0 mass%, Al ≦ 0.01 mass%, Si ≦ 0.03 mass%, Mn ≦ 0.1 mass%, and Cr ≦ 0.05 mass%. Permissible.

  In order to sufficiently coarsen the crystal structure in the powder during the finish heat treatment described later, it is preferable to use a powder having an average particle diameter of 100 μm or more. Here, the average particle diameter is the median diameter D50 of the cumulative weight distribution. The median diameter D50 can be determined by measuring the particle size distribution using a sieve defined in JIS Z8801-1. That is, when the average particle size is less than 100 μm, the crystal structure in the powder is not sufficiently coarsened, and the hysteresis loss after the dust core molding is increased. Therefore, it is preferable to use a powder having an average particle size of 100 μm or more.

Further, the apparent density of the powder is preferably higher, and it is better to use a powder having a density of 3.5 g / cm ³ or more. Here, the apparent density is an index indicating the degree of powder filling rate and can be measured by a test method defined in JIS Z2504. That is, when the apparent density is less than 3.5 g / cm ^3, it becomes difficult to obtain a powder having an apparent density of 4.0 g / cm ³ or more after pulverization. The apparent density after crushing needs to be 4.0 g / cm ³ or more as described later.

The obtained iron-based soft magnetic powder is subjected to particle size distribution adjustment as necessary. Specifically, fine powder of 45 μm or less is removed. Thereby, it becomes easy to set the average crystal grain size to 50 μm or more in a subsequent process.
In addition, as a method for adjusting the particle size distribution, there is a sieving method using a sieve defined in JIS Z8801-1.

Next, a reduction heat treatment is performed in a hydrogen atmosphere. The purpose of this reduction heat treatment is to reduce the amount of C in the powder, to reduce the amount of O, and to coarsen the crystal grains.
That is, C increases the hardness and coercive force of the powder, leading to a decrease in compressibility at the time of molding and an increase in iron loss of the dust core, so 0.003 mass% or less, and further 0.002 mass% or less. preferable. O exists in an oxide state on the powder surface, and this oxide causes an increase in iron loss of the dust core. Therefore, it is preferably 0.1 mass% or less, more preferably 0.08 mass% or less.

  In addition, if the crystal structure in the powder is fine, the compressibility of the powder is reduced and the iron loss of the dust core is increased as in the case where the amount of C is large. Therefore, the crystal structure in the powder is preferably coarse, and the average crystal grain size is preferably 50 μm or more. The upper limit of the average crystal grain size is not particularly required, but the upper limit is naturally limited by the particle size of the powder.

Here, the average crystal grain size in the present invention can be determined by the following method.
First, iron powder, which is the object to be measured, is mixed with a thermoplastic resin powder to obtain a mixed powder, and then the mixed powder is charged into an appropriate mold, heated to melt the resin, and then solidified by cooling. Let it be a contained resin solid. Next, after cutting the iron powder-containing resin solid material with a suitable cross section, polishing and corroding the cut surface, observe the cross-sectional structure of the iron powder particles using an optical microscope or scanning electron microscope (100 times) And / or image. For a given grain in the field of view, five lines are drawn across the grain. At this time, the lines are made non-parallel, and are drawn so as to cross the vicinity of the center of the particle. A crystal grain size is obtained by dividing the total length of the lines contained in the grains by the number of grains traversed by each line. By measuring the crystal grains as described above with 10 or more powders per field of view and 4 fields or more, crystal grains of at least 40 powders are measured.

  In order to obtain a powder according to the above-mentioned C amount and O amount and the average crystal grain size, it is necessary to perform the above reduction heat treatment at 950 ° C. or higher. This is because when the temperature is lower than 950 ° C., the amount of C and O is reduced and the crystal grain size is not sufficiently increased. On the other hand, the upper limit is preferably set to 1100 ° C. or lower in order to prevent excessive aggregation of the powder.

  Furthermore, the treatment time is preferably 60 to 120 minutes. That is, if the treatment time is less than 60 minutes, the reduction of the amount of C and O and the coarsening of the crystal grain size become insufficient, while if the treatment time exceeds 120 minutes, the powder aggregation proceeds. This is because the load of crushing and crushing in the subsequent process increases.

  For example, a hydrogen atmosphere is preferable as the reducing atmosphere in the reduction heat treatment. In this hydrogen atmosphere, the first half is wet hydrogen having a dew point of 60 ° C. or lower, the second half is dry hydrogen, and the heat treatment in the first half wet hydrogen atmosphere is preferably half or less of the total heat treatment time. This is because a wet hydrogen atmosphere is necessary for decarburization, but when the wet hydrogen atmosphere is introduced excessively, the amount of O increases. The reason why the wet hydrogen atmosphere is the first half is that decarburization is performed in the first half, thereby reducing the influence of suppressing the crystal grain growth during the heat treatment by C.

  The iron powder subjected to the reduction heat treatment is strongly bonded. Therefore, it is necessary to perform pulverization and crushing in order to break up the aggregation of the powder. First, the purpose of pulverization is to reduce the load on the apparatus in the subsequent pulverization, and any conditions and techniques may be used as long as the powder aggregation can be solved to some extent, but at least 500 μm after pulverization. It is preferable to carry out in accordance with conditions such that the following particles have a mass ratio of 80% or more of the total. As an apparatus for performing this pulverization, there are a hammer mill and a jaw crusher. Further, when there are particles having a particle diameter of 500 μm or more after pulverization, it is preferable to remove them. In addition, as a method for removing particles having a particle size of 500 μm or more, there is a sieving method using a sieve defined in JIS Z8801-1.

It is important to crush after this crushing. The main purpose of crushing is to improve the apparent density of the powder, and it is preferable to obtain an apparent density of at least 4.0 g / cm ³ or more by crushing. This is because if it is less than 4.0 g / cm ³ , a large amount of strain is introduced into the powder at the time of molding, so that iron loss increases.

For this purpose, it is necessary to use an apparatus capable of applying a strong shearing force to each powder, instead of using an impact-type pulverizing apparatus such as the apparatus used in pulverization. As an apparatus for performing such crushing, an apparatus that gives a strong shearing force to the powder by a rotating body (feather or rotor) such as a Henschel mixer, a pulverizer, an impeller mill, or a high speed mixer is suitable.
However, if an excessive shear force is applied, a large amount of strain is introduced into the powder, and recrystallization occurs during the subsequent strain relief annealing, leading to the disadvantage that the crystal grains become finer. Therefore, the crushing step is preferably performed under the condition that the integral of the peripheral speed of the rotating body and the processing time (peripheral speed (m / s) × processing time (s)) is 1000 m or more and 22000 m or less. That is, if the integrated amount is less than 1000 m, it is difficult to obtain the above-mentioned apparent density of 4.0 g / cm ³ or more. On the other hand, if it exceeds 22000 m, a large amount of strain is introduced into the powder and iron loss increases. Because. Here, the peripheral speed of the rotating body refers to the peripheral speed at the outermost peripheral edge of the rotating body. Note that the number of rotating bodies is not particularly limited. For example, the number of rotating blades may be arbitrary.

  Next, a strain removing heat treatment is performed in order to release the strain introduced into the powder after crushing. By releasing the strain, iron loss after molding is reduced and compressibility is improved. The strain relief heat treatment is preferably performed at a temperature and a time at which the powder does not aggregate, and is preferably less than 900 ° C. and 90 minutes or less. Further, since the strain is not released if the temperature is too low, it is carried out at 500 ° C. or higher. Similarly, when the treatment time is short, the distortion is not released, and therefore it is preferable to carry out the treatment in 10 minutes or more.

After the strain relief heat treatment, an insulating coating is applied to the powder. Insulation coating is performed to prevent an increase in iron loss after molding of the dust core. The insulating coating may be anything as long as it can maintain insulation even after molding of the dust core, and as such an insulating coating, a glassy insulating amorphous material based on silicone resin, metal phosphate or metal borate is used. Layers, metal oxides such as MgO, forsterite, talc and Al ₂ O ₃ , or crystalline insulating layers based on SiO ₂ .
In addition, it is preferable that the coating amount of insulation coating shall be the range of 0.05-0.3 mass% with the whole powder. This is because if the coating amount is less than 0.05 mass%, the coating becomes non-uniform, resulting in a decrease in insulation. On the other hand, if the coating amount exceeds 0.3 mass%, the ratio of the powder for the dust core in the dust core becomes large. This is because the density of the molded body is significantly reduced.

Hereinafter, the present invention will be specifically described based on examples.
(Reduction heat treatment process)
As a sample, water atomized iron powder having a particle size distribution by sieving of 45 to 250 μm, an average particle size D50 of 120 μm, and an apparent density of 3.8 g / cm ³ was used. Here, a sieve defined in JIS Z8801-1 was used for sieving and particle size distribution measurement for determining D50. The apparent density was determined by the test method specified in JIS Z2504. The amounts of C and O of the powder before the heat treatment were C: 0.163 mass% and O: 0.298 mass%. Table 1 shows the results of heat treatment of the obtained powder under five conditions. All the heat treatments were carried out in a hydrogen atmosphere, from a temperature rise to a holding time of 10 minutes with wet hydrogen having a dew point of 60 ° C. and the remaining time with dry hydrogen. Further, unavoidable impurities other than C and O were not more than the prescribed amount described above for all samples.

  From Table 1, in symbols 3, 4 and 5 satisfying the conditions of the present invention, the C content, the O content and the crystal grains were values suitable for obtaining good magnetic properties. Further, by increasing the heat treatment temperature or lengthening the heat treatment time, the amount of C and O is further reduced, the crystal grain size is further coarsened, and the powder is preferable for obtaining excellent iron loss.

Subsequently, the powder subjected to the above reduction heat treatment was pulverized by a hammer mill. The average particle diameter D50 after pulverization was 107 μm. For some powders (except branch No. C), crushing with a high speed mixer (Fukae Powtech Co., Ltd., LFS-GS-2J type), rotating blade peripheral speed: 10 m / s and processing time: 30 min. That is, it was carried out at peripheral speed x processing time = 18000m. This crushing resulted in an apparent density of 4.1 g / cm ³ . Further, a part of the crushed sample was subjected to strain relief heat treatment. The conditions for strain relief heat treatment are as shown in Table 2.

In Table 2, samples other than branch number C could be easily crushed by hand after the strain-removing heat treatment. Therefore, the resin coating, molding, and magnetic measurement in the subsequent process were not performed. All samples except branch number C were subjected to an insulating coating (insulating coating amount: 0.25 mass%) with silicone resin. Here, the silicone resin is dissolved in toluene to prepare a resin diluted solution with a resin content of 1.0 mass%, and then the powder and the resin diluted solution are mixed so that the resin addition ratio to the powder is 0.25 mass%. And dried in air. A coated iron-based soft magnetic powder was obtained by performing a resin baking process at 200 ° C. for 120 minutes in the air after drying. These powders were molded at a molding pressure of 1470 MPa (15000 kgf / cm ² ) and die lubrication to produce ring-shaped test pieces having an outer diameter of 38 mm, an inner diameter of 25 mm, and a height of 6 mm.
The prepared test piece was heat-treated at 700 ° C. for 45 minutes in nitrogen. Then, winding was performed (primary volume 100 turns, secondary volume 100 turns), magnetic flux density (10000 A / m, measured with Metron Giken DC magnetometer) and iron loss (1.0 T, 400 Hz, Metron Giken) Measured with a high-frequency iron loss measuring apparatus). The measurement results are shown in Table 3.

  In Example 1 described above, the acceptance criteria are set such that the magnetic flux density is the same level (≧ 1.50 T) as that of the above-described Patent Document 1, and the iron loss is less than that of Patent Document 1 (≦ 40.0 W / kg). ) From Table 3, 3-D, 3-E, 3-F, 3-G, 4-D, 4-E, 4-F, 4-G, 5-D, 5-E, 5- Both F and 5-G have acceptable magnetic properties. On the other hand, some of the other conditions (comparative examples) have iron loss satisfying the acceptance criteria, but all of the magnetic flux densities did not meet the acceptance criteria.

(Insulation coating)
With respect to Sample 5-D of Example 1, samples having various insulation coating amounts were produced. The molding conditions, the heat treatment conditions after molding, and the magnetic measurement conditions are the same as those in Example 1. The results are shown in Table 4.

  From Table 4, 5-D-3 to 5-D-6 included in the range of the insulation coating amount of 0.05 to 0.3 mass% had a magnetic flux density of more than 1.50 T and an iron loss of less than 40.0 W / kg. . Among them, 5-D-3 and 5-D-4, whose insulation coating amounts are 0.05 mass% and 0.10 mass%, have a magnetic flux density exceeding 1.6 T, and have extremely excellent magnetic characteristics. On the other hand, 5-D-1 with no insulation coating and 5-D-2 with an insulation coating amount of 0.03 mass% were too high to be measured, and the insulation coating amount was 0.35 mass%. The magnetic flux density of -D-7 and 5-D-8, which was 0.50 mass%, was lower than 1.50T.

  About the powder of the symbol 5 of Table 1 of Example 1, after grind | pulverizing with a hammer mill, the conditions of the crushing by a high speed mixer (FFS Kyushu LFS-GS-2J type) were changed variously, and the powder Was made. Table 5 shows the crushing conditions and the apparent density after crushing.

These powders were subjected to heat treatment for strain relief at 800 ° C. for 60 minutes. After the strain relief heat treatment, an insulating coating (insulating coating amount: 0.25 mass%) with silicone resin was applied. Here, the silicone resin is dissolved in toluene to prepare a resin diluted solution with a resin content of 1.0 mass%, and then the powder and the resin diluted solution are mixed so that the resin addition ratio to the powder is 0.25 mass%. And dried in air. A coated iron-based soft magnetic powder was obtained by performing a resin baking process at 200 ° C. for 120 minutes in the air after drying. These powders were molded at a molding pressure of 1470 MPa (15000 kgf / cm ² ) and die lubrication to produce ring-shaped test pieces having an outer diameter of 38 mm, an inner diameter of 25 mm, and a height of 6 mm.
The prepared test piece was heat-treated at 700 ° C. for 45 minutes in nitrogen. After that, winding was performed (primary volume 100 turns, secondary volume 100 turns), magnetic flux density (10000 A / m, measured with a DC magnetometer manufactured by Metron Giken) and iron loss (1.0 T, 400 Hz, made by Metron Giken) Measured with a high-frequency iron loss measuring apparatus). The measurement results are shown in Table 6.

  In this example, the same acceptance criteria as in Examples 1 and 2 were used. Moreover, about the magnetic flux density, all samples other than 5-1 reached the acceptance standard. From Tables 5 and 6, those satisfying the condition of the present invention, peripheral speed x treatment time of 22000 m or less, had an iron loss of 40.0 W / kg or less and met the acceptance criteria. On the other hand, the sample with a peripheral speed × processing time exceeding 22000 m, which is out of the scope of the invention, has an increased iron loss although the apparent density is high. In particular, symbols 5-13 and 5-15 are about 30 to 50% larger than the other examples.

Claims (1)

A method for producing an iron-based soft magnetic powder for a dust core,
Obtaining an iron-based soft magnetic powder by an atomizing method;
A reduction heat treatment step of heat-treating the iron-based soft magnetic powder in a hydrogen atmosphere at 950 ° C. or higher;
A pulverization step for pulverization after the reduction heat treatment step;
A crushing step of crushing the powder after the crushing step by applying a shearing force by a rotating body;
A strain relief heat treatment step of performing a strain relief heat treatment at a temperature of 500 ° C. or more and less than 900 ° C. after the crushing step;
Including a step of applying an insulation coating of 0.05 mass% or more and less than 0.3 mass% to the surface of the powder after the distortion removing heat treatment step,
The powder for a dust core, wherein the crushing step is performed under a condition that a product of a peripheral speed (m / s) of the rotating body and a crushing time (s) is 1000 m or more and 22000 m or less. Manufacturing method.