JPH0348241B2 - - Google Patents

Description

[Detailed description of the invention]

[Industrial Application Field] The present invention relates to a method for manufacturing a Fe-Si-Al alloy dust core. [Prior art] Fe-Si-Al alloy powder magnetic cores have been used in electronic devices because they exhibit stable high magnetic permeability in high frequency bands, along with iron powder magnetic cores and Fe-Ni alloy powder magnetic cores. These coils have been used as high-impedance coils to attenuate high-frequency noise generated from power supplies, that is, noise that travels back and forth between power supply lines and is called normal mode. The Fe-Si-Al alloy powder magnetic core has superior high-frequency characteristics than the iron powder magnetic core, and is particularly excellent in DC superposition characteristics, and does not contain effective raw materials such as Ni and Mo. Since it is cheaper than powder magnetic core, demand has been gradually increasing in recent years. Conventionally, Fe-Si-Al alloy powder magnetic cores are made by melting an ingot, diffusion annealing it to reduce the segregation of Al and Si, and then coarsely pulverizing it. It has been manufactured by coating the powder surface with an inorganic insulating material, compacting it, and heating it. [Problems to be solved by the invention] However, in the process of pulverizing the ingot as described above, the entire process of manufacturing, annealing, and pulverizing the ingot is long, and the cost of raw material powder for force compaction is high. The current situation is that the Fe-Si-Al alloy powder magnetic core itself is expensive, and its widespread use as a chiyoke coil is restricted. The present invention was made in view of the above circumstances, and is based on new findings regarding the relationship between the properties of powder particles and the magnetic properties of a powder magnetic core. The purpose is to provide an inexpensive Fe-Si-Al alloy powder magnetic core. [Means for Solving the Problems] The present invention is based on new knowledge regarding the relationship between the powder morphology and particle size and the magnetic properties of the dust core, which will be described later. In order to obtain a Fe-Si-Al alloy powder magnetic core, a molten Fe-Si-Al alloy is directly poured into a liquid to produce shot- or flat-shaped coarse powder with an average particle size of 20 mm or less, and then The average particle size obtained by further pulverizing the coarse powder is within the range of 40 to 110 μm, and the apparent density is
It has been found that it is effective to use a powder having a weight of 2.6 to 3.8 g/cm ³ as a raw material powder. Note that the Fe-Si-Al alloy here refers to an alloy known as a so-called sendust alloy, which is mainly composed of 4 to 13% Si, 4 to 7% Al, and the balance is Fe, with other unavoidable impurities. , refers to a high magnetic permeability alloy that optionally contains 5% or less of additional elements. [Operation] First, one of the findings newly discovered by the present inventors will be explained. In powder magnetic cores, it is most important that the effective magnetic permeability remains stably high and approximately constant up to a high frequency band. For this purpose, in Fe-Si-Al alloy powder magnetic cores, the surfaces of powder particles are coated with an inorganic insulating material such as water glass and then pressure-formed to create a state in which the particles are insulated to a certain degree. This is used as a magnetic core, which is then heat treated to obtain the above characteristics. The reason why a heat-resistant inorganic material is used instead of an organic material for the surface insulation of the powder particles is to enable the final heat treatment. According to the inventors, the biggest factor influencing the value of effective magnetic permeability and its frequency characteristics is
(A) Particle morphology and (B) particle size. Regarding (A), even if the particles are covered with an insulating film, if the particles are pressed against each other during molding, the film is likely to be destroyed and the insulation will deteriorate, and the higher the frequency of the alternating magnetic field, the more likely eddy currents will flow. , the effective permeability decreases. Therefore, from the viewpoint of frequency characteristics, the particle shape is required to be difficult to cause dielectric breakdown due to local pressure bonding. That is, if the particle surface is disordered and has an irregular shape, dielectric breakdown will easily occur during molding, and spherical particles with a smooth surface are most preferable. Therefore, the apparent density of the powder decreases as the shape becomes more irregular, so it is desirable that the apparent density as a shape parameter be high. However, magnetic permeability is also a parameter for the density of the powder magnetic core, and in the case of perfectly spherical particles with the highest apparent density, they are consolidated by point contact, so the density of the compact is rather low, and the demagnetizing field The coefficient becomes high, making it somewhat difficult to achieve high magnetic permeability. Therefore, there is a trade-off between increasing the frequency at which the effective permeability begins to decrease by maintaining good insulation and increasing the initial DC effective permeability by increasing the density of the compact. , there is a need to strike a balance. For this purpose, there is a suitable range for the apparent density of the powder. On the other hand, from the viewpoint of (B), if the powder particles are too coarse, eddy currents are likely to occur due to the alternating magnetic field.
There is an upper limit to the particle size because the frequency characteristics of effective magnetic permeability are likely to deteriorate and the strength of the compact is reduced. On the other hand, if the particles are too fine, the compressibility of the powder particles decreases and the initial (DC) magnetic permeability decreases, so there is a lower limit to the particle size. Based on the above findings, the present inventors have developed Fe-Si-Al
The optimum apparent density and particle size of the powder particles for the alloy powder magnetic core were defined, and the conditions for producing powder within the defined range at a low cost were further investigated. That is, a molten Fe-Si-Al alloy is directly poured into a liquid to produce shot-like or flat-shaped coarse powder with an average particle size of 20 mm or less, and then the coarse powder is further crushed. The average particle size obtained is 40~
It was discovered that a powder magnetic core using powder having a diameter of 110 μm and an apparent density of 2.6 to 3.8 g/cm ³ has excellent properties and can be manufactured at a lower cost than before, and the present invention has been completed. The present invention will be explained in more detail below. First, the reason why the upper limit of the average particle size was set to 110 μm will be described. Figure 1 shows 5.5%Al-9.5%Si-residue Fe with approximately the same apparent density as 3.4±0.1g/ ^cm3 and different average particle sizes.
This figure shows the dependence of the high-frequency characteristics of magnetic permeability on the average particle size of a dust core made of alloy powder. After adjusting the particle size, the powder was annealed at 900℃ in a hydrogen stream.
The powder surface was coated with 0.8% by weight of water glass as a solid content, and the outer diameter was 28mm and the inner diameter was 15mm under a pressure of 20ton/ ^cm3 .
After forming into a ring shape with a height of 8 mm, it was annealed at 700°C in the air. The magnetic permeability of this molded body was measured using an impedance meter. μe13M/μe10K on the vertical axis in FIG. 1 is the ratio of the effective magnetic permeability μe13M at 13 MHz to the effective magnetic permeability μe10K at 10 KHz, and was used as a measure of the high frequency characteristics of magnetic permeability. 1st
From the figure, the larger the average particle size, the more μe13M/
It can be seen that as μe10K decreases, the frequency characteristics deteriorate. In particular, when the average particle size exceeds 110 μm, μe13M/μe10K falls below 0.4, resulting in significant deterioration. Therefore, the upper limit of the average particle size was set to 110 μm.
In addition, when the average particle size exceeded 130 μm, the strength of the molded product was low and it was impossible to handle it. Next, the reason for setting the lower limit of the average particle size to 40 μm will be explained. FIG. 2 shows the dependence of the effective magnetic permeability μe10K at 10 KHz on the average particle size of a molded body manufactured by the same method as used in FIG. 1. μe10K increases as the particle size increases, but Fe
It can be seen that in order to obtain the minimum μe10K of 70 required for a -Si-Al alloy dust core, the average particle size must be 40 μm or more. Next, the reason for setting the lower limit of the apparent density to 2.6 g/cm ³ will be described. Figure 3 shows that the average particle size is 70±
5.5% Al−, which is approximately equal to 5μm and has a different apparent density.
This figure shows the apparent density dependence of the frequency characteristics of a dust core made of 9.5% Si-remaining Fe alloy powder. The method of manufacturing the magnetic core is the same as in the case of FIGS. 1 and 2. Irregularly shaped powders with lower apparent density
μe13M/μe10K is low and frequency characteristics are poor.
As mentioned in Fig. 1, the required value of μe13M/μe10K was set to 0.4, and the lower limit of the apparent density was set to 2.6. Furthermore, the reason for setting the upper limit of the apparent density to 3.8 g/cm ³ will be described. Figure 4 uses the same powder as in Figure 3, with a length of 40 mm.
This is the result of measuring the transverse rupture strength of a molded body having a width of 10 mm and a height of 7 mm. The transverse rupture strength of a molded body of powder with a higher apparent density, that is, a powder having a smaller contact area between particles and less entanglement, has a lower transverse rupture strength. Fe-Si-Al alloys have low plastic deformability;
Therefore, the strength of the compacted compact is lower than that of iron or Fe-Ni alloy compacts, but it must have a strength of at least 0.2 kg/mm ² so that it can be handled at least on an automatic press forming line. . From this point of view, the upper limit of the apparent density of the powder is set at 3.8 g/cm ³ . As shown in Figures 1 to 4, in order to obtain a dust core with stable magnetic permeability and frequency characteristics, the average particle size is 40 to 110 μm, and the apparent density is 2.6 to 3.8 g/ ^cm3. It is clear that the powder is of practical use. Naturally, the magnetic permeability and its frequency characteristics change depending on the pressure when the powder is compacted, but in the case of Fe-Si-Al alloy, the permeability is 15 tons/
It is difficult to obtain a magnetic permeability of 70 or higher without a molding pressure of cm ² or higher. Furthermore, the molding pressure is currently limited to about 25 ton/cm ² even if it is increased to the maximum due to limitations on mold life. from 15
Even if the molding pressure changes up to about 25 ton/cm ² , the effects on the characteristics of the particle size and apparent density of the powder particles as described above do not change as a whole. In order to obtain powder having the particle size and apparent density specified above at a low cost, the present inventors focused on a method of producing powder directly from molten metal and conducted various studies. As a result, the molten metal of the Fe-Si-Al alloy is passed through a nozzle to form a molten metal flow, which is then directly flowed into a stationary or stirred liquid to produce shot- or flat-shaped coarse powder with an average particle size of 20 mm or less. It has been found that the desired powder can be obtained at a low cost by manufacturing and then further finely pulverizing the coarse powder.
In this coarse powder production method, the cooling liquid used is preferably water in view of ease of post-treatment, but is not particularly limited. The final target particle size after pulverization is 40 to 110 μm, which is smaller than that of coarse powder, which is on the order of 20 mm or less, so there are no restrictions on the shape of coarse powder, but the shape obtained is similar to that of a sphere in a static bath. It was found that it had a nearly shot shape, and that it tended to become flat when agitation was applied. In addition, when water remained in the dissolved raw material or when the molten metal had a high H ₂ content, it was likely to become shot-like, and an aqueous solution of a highly viscous substance such as glycerin also tended to become shot-like. The reason why the average particle size of the coarse powder was set to 20 mm or less will be explained. Figure 5 shows how the μe10K of the Fe-Si-Al alloy powder magnetic core changes depending on the particle size of the coarse powder produced by the production method of the present invention and the ingot produced by the prior art. be. That is, coarse powders and ingots of various initial particle sizes were ground to produce powders with average particle sizes of 100±5 μm and 45±5 μm. The apparent density is approximately equal to 3.3±0.2 g/cm ³ . All ingots, including ingots, were crushed to the above specifications without being subjected to diffusion annealing to prevent Al and Si polarization, and then annealed in a hydrogen stream and water glass.
A powder magnetic core was obtained by insulation treatment at 0.8% by weight and pressure molding at 20 tons/cm ² . In Figure 5, the curve shows an average particle size of 100±5μm,
is the μe10K of the magnetic core made of pulverized powder of 45±5 μm. According to this, it can be seen that when diffusion annealing is not performed in the initial coarse powder and ingot state, the smaller the initial particle size, the higher the μe10K.
On the premise of omitting diffusion annealing at around 1000℃, the fifth
In the figure, the particle size of the initial coarse powder with almost no μe10K deterioration is 20 mm or less. Therefore, the average particle size of the coarse powder was defined as 20 mm or less. In the coarse powder production method of the present invention, the nozzle diameter for stably passing the molten metal is determined by Fe-Si-Al
In the case of alloys, the diameter is 3mm even if the molten metal temperature is around 1600℃.
The above is necessary. Therefore, although it varies depending on the cooling conditions, it is easy to make the particle size of the obtained coarse powder 20 mm or less. It is advantageous to make the particle size even smaller from the perspective of crushing efficiency, and by applying an inert gas flow of several kg/cm ² to several tens of kg/cm ² to the molten metal from the side or diagonally, the molten metal can be crushed. It is effective to promote scattering. As described above, since the coarse powder of the present invention has a higher solidification and cooling rate than conventional ingots, there is no segregation of Al or Si, and therefore high-temperature annealing is not required at all. Not only does ingot annealing become unnecessary, but it is also easier to crush. The method of pulverizing the coarse powder is not particularly limited, and a wide variety of methods can be applied. For example, after coarsely pulverizing the powder using a roller mill, hammer mill, etc. to obtain a powder of several 100 μm, the desired particle size and apparent density can be obtained using a vibration mill, attritor, ball mill, jet mill, etc. In devices such as vibrating mills and attritors that require high energy input, it is possible to obtain the desired powder in one pulverization process, depending on the pulverization conditions. The method for manufacturing the Fe-Si-Al alloy powder of the present invention has been described above, but the method of flowing the molten alloy into a cooling liquid bath involves manufacturing an ingot, then diffusion annealing it, and performing several steps. This is an epoch-making method that significantly shortens the process and saves energy compared to the conventional process of grinding in the process, reducing the cost of raw material powder. Hereinafter, specific contents of the present invention will be further explained with reference to Examples. [Example] Example 1 5.5% Al-9.5% Si-residue dissolved in Ar atmosphere
Molten Fe at 1600°C was poured into a still water tank through a nozzle with a diameter of 5 mm to form shot-like powder with an average particle size of 10 mm. -50 by stamp mill
After pulverizing to mesh, it was dry-pulverized using a vibrating mill. By controlling the vibration frequency, amplitude, grinding media and powder filling rate, the average particle size is 80 μm and the apparent density is 3.30.
A powder of g/cm ³ was obtained. This powder was strain-removed in a hydrogen stream at 900℃ for 1 hour, the surface was insulated with 0.5, 1.0, and 1.5wt% water glass, and then pressure molded at a pressure of 20ton/ ^cm2. Then, a powder magnetic core was obtained by heat treatment at 700°C for 0.5 hours. μe10K and μe13M/μe10K of the powder magnetic core thus obtained are shown in Table 1, and the high magnetic permeability is stable up to the high frequency band.

[Table] Example 2 5.5% Al-9.5% Si-residue dissolved in Ar atmosphere
Fe molten metal at 1600℃ is flowed down through a 5mmφ nozzle, and the molten metal is flowed diagonally upward.
The molten metal was scattered by applying an Ar gas flow at a pressure of 10 Kg/cm ² and a flow rate of 15 min from a 45° direction, and the scattered molten metal was cooled in a stirred water tank. The average particle size of the obtained coarse powder was 2.5 mm. This coarse powder is processed by a hammer mill to obtain an average particle size of
After pulverizing to 600 μm, dry pulverization was performed using a vibrating mill to an average particle size of 76 μm. By controlling the vibration frequency, amplitude, grinding media and powder filling rate, the average particle size is 51μ
A powder with an apparent density of 3.62 g/cm ³ was obtained. This powder was strain-removed in a hydrogen stream at 900℃ for 1 hour, the surface was insulated with 0.5, 1.0, and 1.5wt% water glass, and then pressure molded at a pressure of 20ton/ ^cm2. Then, a powder magnetic core was obtained by heat treatment at 700°C for 0.5 hours. μe10K and μe13M/μe10K of the powder magnetic core thus obtained are shown in Table 1, and the high magnetic permeability is stable up to the high frequency band.

[Table] [Effects of the invention] As is clear from the above, the Fe-Si-Al of the present invention
The method for producing powder magnetic cores made from alloy alloys is the most suitable method for producing powder magnetic cores that exhibit stable high magnetic permeability over a high frequency range, and is a conventional method for producing powder magnetic cores that produce molten ingots, undergo annealing, and then This method provides a powder magnetic core that is cheaper than the method of manufacturing a powder magnetic core using powder obtained by pulverization, and has great industrial value.

[Brief explanation of drawings]

Figure 1 is a correlation diagram between the average particle size of powder and the frequency characteristics of magnetic permeability, Figure 2 is a diagram of the correlation between the average particle size of powder and magnetic permeability, and Figure 3 is the frequency characteristic of apparent density and magnetic permeability of powder. FIG. 4 is a correlation diagram between the apparent density of powder and transverse rupture strength, and FIG. 5 is a correlation diagram between initial coarse powder particle size and magnetic permeability.

Claims (1)

[Claims] 1 Fe-Si-Al alloy powder is coated with an inorganic insulating material and then heat-treated after pressure molding.
In the manufacturing method of Si-Al alloy dust core, Fe
- A shot-like or flat-shaped coarse powder with an average particle size of 20 mm or less is produced by directly flowing a molten Si-Al alloy into a liquid, and then the coarse powder is further pulverized. A method for producing an Fe-Si-Al alloy powder magnetic core, characterized in that powder having an average particle size of 40 to 110 μm and an apparent density of 2.6 to 3.8 g/cm ³ is used.