JP2006100292A - Dust core manufacturing method and dust core manufactured thereby - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a dust core appropriate to an apparatus in which a hysteresis loss is required to be small in a transformer, a reactor or the like thereof, and a magnetic saturation characteristic is required to be linear, and to provide a manufacturing method therefor. <P>SOLUTION: The mixture of a soft magnetic metal powder having two particle size distributions and an organic material binder, or a soft magnetic metal powder having two particle size distributions coated with the organic binder on the surface thereof is contained in a mold, vibrated, pressure-molded at a pressure in the range of 10 to 100 MPa, and heated with a temperature at which the organic matter binder thermally decomposes, or a lower temperature. The dust core provided by this way is molded without the soft magnetic metal powder being largely deformed by an applied pressure, thus the hysteresis loss does not increase. In addition, since the effect of having two particle size distributions without increasing the applied pressure and the effect of vibration enable the high density filling as well as enlarging the density of the core which is completed by the vibration filling, neither the saturation magnetization nor magnetic permeability does not significantly decrease. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a magnetic powder core suitable for an apparatus such as a transformer, a reactor, etc., which requires a characteristic with low hysteresis loss and a linear magnetic saturation characteristic, and a method for manufacturing the same.

  Conventionally, the magnetic core has a shape that suppresses a decrease in magnetic properties due to an eddy current in the core generated in the thickness direction by overlapping silicon steel plates or the like. However, recently, there is a method of manufacturing a dust core in which soft magnetic powder and an insulating binder are mixed and pressed to form due to the complicated magnetic characteristics and shape. By this means, various soft magnetic metal powders can be used, and magnetic cores having the desired magnetic properties have been obtained.

  Already, for reducing the core loss, it is known that when the crystal grains of the soft magnetic powder used in the dust core are coarsened, the hysteresis loss of the dust core due to the decrease in coercive force is reduced. It is also known that the use of a fine soft magnetic powder is effective in reducing the overcurrent loss of the dust core. Therefore, the soft magnetic powder to be used is preferably a fine one with coarse crystal grains. And the means to add elements, such as S, Te, Se, is disclosed to soft magnetic metal powder as a countermeasure against the oxide inclusion at the time of powder manufacture (refer to patent documents 1).

  In addition, in a method of manufacturing a powder magnetic core by compacting and heating a powder obtained by mixing soft magnetic powder and resin powder, the resin powder is 5% by volume of powder having a median diameter of 50 μm or less with respect to the soft magnetic powder. The following is preferred. That is, non-magnetic resin fine powder exists between the soft magnetic powders, and the soft magnetic powders can maintain uniform insulation. Such uniformity suppresses heat generation due to eddy currents in use in a high frequency region, and can extend the life (see Patent Document 2).

  Furthermore, for Ni-based magnetic alloys with excellent magnetic flux saturation density, DC superposition characteristics, etc., even with Fe-Al-Si-based alloys, if the alloy powder is heat-treated in advance to improve the crystallinity, it will be higher than Ni-based alloys. There are also examples in which the magnetic flux saturation density and the DC superimposition characteristics were obtained (see Patent Document 3).

In addition, when a soft magnetic material powder is molded and compressed at a high pressure using a mold or the like, and then subjected to a heat treatment such as a sintering process, oxygen enters into the powder and the magnetic properties deteriorate. is there. For this reason, countermeasures have been taken, such as forming an Al oxide layer on the powder surface using an alloy that adds Al in the composition of the soft magnetic metal powder. However, since Al is contained, the magnetic flux saturation density is low and the DC superimposition characteristic is also low. Therefore, the amounts of Al and Si added to the soft magnetic metal alloy are specified, and the heat treatment temperature is also specified. Since oxide layers are formed on the surface of the soft magnetic material, when these are pressure-molded, the magnetic saturation density is larger than that of the ferrite sintered material, so that a large current can be achieved ( (See Patent Document 4).
JP2003-257722, (0005-0006) JP 2004-146804 A, (0015-0016) JP 2004-214418 A, (0008) JP 2004-128327 A, (0004-0005), (0010)

  In the preceding examples as described above, the material to be used has a characteristic, and the finished core has a characteristic in each material or composition / structure. And the characteristic as a magnetic core is improved.

  In a reactor that stores magnetic energy, magnetic characteristics such as low iron loss, unsaturation characteristics, and direct current superposition characteristics are required instead of magnetic characteristics such as high permeability and low iron loss required for motors and the like. In order to meet this requirement, it is technical that the coercive force of the constituent magnetic material is small and the hysteresis loss is small, and the permeability is constant at the operating point in the BH curve, that is, the BH curve is linear and is not easily saturated. It becomes a solution target.

  As a countermeasure, in order to lower the magnetic permeability of the core material, there is a treatment such as notching a part of the core and sandwiching a nonmagnetic material in the part, but generally, as in the above-mentioned patent document, An insulating material is mixed with the soft magnetic metal powder to reduce the magnetic permeability of the entire core and improve the magnetic saturation characteristics.

  In addition, when an insulating material is added to a soft magnetic metal powder and compressed to increase the density and form the desired shape, a large pressure is required. Due to this large pressure, the soft magnetic metal powder is physically strained. It was found that the hysteresis loss of the molded core was increased. In order to remove this distortion after molding, it is necessary to mold at a temperature of 700 ° C. or higher. However, unless the insulating material is an oxide as in Patent Document 4, an organic binder is usually used, and at most 500 ° C. The temperature is the limit. Therefore, in the core using such an organic binder, the hysteresis loss cannot be improved.

The present invention provides a powder magnetic core having improved hysteresis loss by improving a method for producing a powder magnetic core produced using a soft magnetic metal powder and an organic binder.
The means is that a soft magnetic metal powder having two particle size distributions and an organic binder or a soft magnetic metal powder having two particle size distributions coated with an organic binder on the surface is placed in a mold, and vibration is applied. It is characterized by being pressure-molded in a range of ˜100 MPa and heating at a temperature lower than the thermal decomposition temperature of the organic binder.
The magnetic powder core produced in this way is molded without the soft magnetic metal powder being subjected to large distortions due to the applied pressure, so that the hysteresis loss is not increased. In addition, even if the applied pressure is not increased, high density packing can be achieved by the effect of having two particle size distributions and the effect of vibration, and the density of the core obtained by filling by vibration can be increased. There is no decline.

  When the vibration is applied, mechanical vibration may be used. However, since it is sufficient to apply vibration only to the molding material put in the mold, it is preferable to apply ultrasonic vibration in the mold.

  Further, the soft magnetic metal powder to be used is preferably a spherical powder which is easily dispersed uniformly by vibration, and atomized powder is particularly preferably used.

  The organic binder can be preferably used as long as the material has good heat resistance, but it is preferable to use a thermosetting resin that exhibits high electrical resistance when converted into a resin.

  The organic binder may be mixed with a soft magnetic metal powder in the form of a powder, but it may be subjected to vibration in the mold and may become non-uniform. It is preferable to take means for coating the metal powder.

  With the production method according to the present invention, the powder magnetic core can be adjusted in desired properties depending on the kind and amount of soft magnetic metal powder and resin binder used. In particular, the magnetic characteristics can be adjusted without being limited by hysteresis loss. In addition, the powder magnetic core produced according to the present invention maintains the linearity of the BH curve up to a high magnetic flux, and is therefore preferably used for equipment that converts a large current.

  In the manufacturing method according to the present invention, the point to be noted is that it takes measures that combine the distortion to the workpiece due to relatively light compression and the improvement of the filling density of the workpiece by applying vibration in advance. It is in. A workpiece having a sufficient density can be obtained in spite of relatively light pressurization by preliminarily filling the workpiece with a honey-comb filled state by vibration during molding. By sufficiently increasing the density, the magnetic permeability is not significantly reduced. On the other hand, mild pressurization requires only a slight strain on the soft magnetic metal powder, and as a result, a reduction in hysteresis loss can be prevented. The applied pressure is in the range of 10 to 100 MPa, and if it is less than 10 MPa, it may be a condition that cannot be molded depending on the properties of the workpiece. On the other hand, if it exceeds 100 MPa, the strain on the soft magnetic metal powder in the workpiece increases, and the hysteresis loss may increase.

  In order to increase the packing density, it is preferable to use a soft magnetic metal powder having two particle size distributions. Here, having two particle size distributions means having two peak values when the particle size distribution of the powder is measured. That is, it means that it is composed of two types of particles having different average particle diameters. In the case of having a uniform particle size, there are many gaps at the time of close-packing, and it is preferable to combine a coarse diameter and a fine diameter to fill the gap. In order to increase the packing density, the coarse diameter particle size is preferably a combination of 1.5 to 3 times the fine diameter particle size, and the coarse diameter amount is 1. It may be in the range of 5 to 2.5 times. That is, a soft magnetic metal powder having two particle size distributions of a soft magnetic metal powder having a coarse average particle diameter and a soft magnetic metal powder having a fine average particle diameter is used. The relationship is slightly different depending on the particle size distribution, but the average particle size in the particle size distribution may be a relationship between the coarse diameter and the fine diameter.

The organic binder can be mixed with the soft magnetic metal powder as it is, or the organic binder can be used in a state where the organic binder is coated on the soft magnetic metal powder in advance.
When the organic binder is mixed with the soft magnetic metal powder and molded, it is preferable to use the organic binder in a fine powder form. In particular, among the two particle size distributions of the soft magnetic powder, a particle size distribution having an average system equivalent to or less than a particle size distribution having a fine diameter is preferable. When the organic binder is in the form of a solution or in the form of a liquid resin, the filling with respect to vibration in the mold becomes smooth, which is more preferable.

  When the organic binder is coated on the soft magnetic metal powder in advance and put into a mold, it can be molded smoothly without worrying about segregation. Further, the molding can be performed with the ratio of the soft magnetic metal powder and the organic binder almost adjusted. The coating means will be described later.

As the vibration means, mechanical vibration is sufficient, but it is preferable to apply vibration using ultrasonic waves in order to fill the workpiece close to the honey filling. By using ultrasonic waves, it is only necessary to vibrate only the inside of the mold, and energy that is efficient and easily close-packed can be applied.
In the mechanical vibration, vibration with an excitation force of 10 N to 500 N and a vibration frequency of about 100 Hz to 200 Hz is sufficient. In the case of exciting with ultrasonic waves, a sufficient effect is exhibited at a frequency of 20 kHz to 50 kHz and an applied power of 20 W to 200 W.

The soft magnetic metal powder used in the present invention is a powder having two particle size distributions as described above. However, when the shape is spherical or elliptical, the fluidity in the mold is good and the pressure is small. Is preferable because high honey can be filled. Ideally, an organic binder fills the gaps between these spheres.
A powder in which the soft magnetic metal powder is nearly spherical is an atomized powder. In particular, gas atomized powder is preferable because it is close to a true sphere.

As the soft magnetic metal powder, a soft magnetic metal or an alloy thereof having characteristics according to the purpose of use can be used. In particular, an Fe-M (M = 0 to 10% by weight) alloy powder or an amorphous powder is used. preferable. Here, the M is at least one selected from the element symbols B, N, Al, Si, P, Ti, Mn, Co, Ni, Cu, Zr, and Nb.
Of these, all of the element symbols have a soft magnetism improving effect, and as a result, the saturation magnetization characteristics are improved. Further, when the element symbols N, Al, Si, P, Ti, Co, and Ni are selected, the coercive force and the magnetic strain are reduced, so that the effects of low iron loss and low noise can be obtained. Amorphization can be promoted by selecting element symbols B, P, Nb, and Zr. This amorphization may improve the magnetic characteristics. By including this element, amorphous can be obtained by atomization. In order to reduce the hardness of the powder itself and make it difficult to store molding strain, it is preferable to select from element symbols Mn, Cu, and Al.
The substantial average diameter of these soft magnetic metal powders is preferably in the range of 50 to 300 μm. This average diameter means the average diameter of the powder having the coarse particle size distribution. If it is less than 50 μm, fine particles are present on average, so that the coercive force is increased, which is not preferable. On the other hand, if it exceeds 300 μm, eddy currents are likely to be generated in the grains, and the high-frequency magnetization characteristics are degraded.

As the organic binder, it is not preferable to change the shape after being molded once, so it is preferable to select a thermosetting resin. The form before mixing is a fine powder, a liquid resin state, or a resin solution. In particular, it is preferable that the organic binder is pre-coated on the soft magnetic metal powder because segregation does not occur even when mixed or vibration is applied.
Among thermosetting resins, when uncured, there is fluidity at the time of molding, and it is possible to fill between metal powders, and those that have low thermal shrinkage at the stage of curing have excellent dimensional stability, and after curing Those having high strength are preferably selected. Examples thereof include phenolic resins, epoxy resins, silicone resins, polyimide resins, and the like.

The amount of the organic binder with respect to the soft magnetic metal powder is preferably 5 to 30% by volume, can maintain a high electric resistance, and has a large saturation magnetic flux (1.5 T or more). If it is less than 5% by volume, the electric resistance tends to be insufficient. If it exceeds 30% by volume, the saturation magnetic flux tends to decrease. However, in the case of a sintered soft magnetic core, it is produced at 10% by volume or less, and in the case of extrusion molding, it is often produced at 30% by volume or more.
In addition, in order to avoid agglomeration of the soft magnetic metal powder, it is preferable to add a dispersant treatment such as an organic or inorganic coupling agent during mixing.

  In addition, when manufacturing the powder magnetic body core of this invention, the annealing process after shaping | molding is required besides the said characteristic. In the annealing treatment, it is preferable that the temperature is higher than the temperature at which the organic binder is cured, and the temperature is lower than the temperature at which the organic binder is degraded due to thermal decomposition. Annealing removes uncured organic substances and the like, so that the stability as the core is increased.

Here, there are various means for coating the soft magnetic metal powder with the organic binder, and preferred means are described below.
(Treatment of the dispersant) The treatment of the dispersant can be omitted, but in order to ensure the uniform dispersibility of the soft magnetic metal powder, the treatment is better. In addition, when a liquid such as a liquid resin or a resin solution is selected as the organic binder and an organic or inorganic coupling agent is used, it is mixed in advance with the organic binder and mixed with the soft magnetic metal powder.
In particular, the coupling agent may be applied to the soft magnetic metal powder as a base treatment, dried, and then treated with an organic binder. Here, the coupling agent can be selected from commercially available ones, and the amount of the coupling agent can be used based on the specifications.

  As another dispersant treatment, there is a chemical conversion treatment method. In the chemical conversion treatment method, an amorphous passive state is formed on the surface of the soft magnetic metal powder by adding the soft magnetic metal powder to the acidic compound solution to improve the compatibility with the organic binder. Depending on the type of metal to be treated, the acidic compound solution usually used includes acids such as phosphoric acid and boric acid and metal compounds such as element symbols Fe, Zn, Mn, Al, and Ca. Forms an amorphous passive state on the surface.

  Still another dispersant treatment is a sol-gel method. This means is a method in which a precursor such as an alkoxide of a dispersion to be coated is made into a solution, and a soft magnetic metal powder is added thereto to deposit the dispersion on the metal surface. The alkoxide hydrolyzes on the metal surface, thereby depositing a dispersion on the metal surface.

  (Processing of resin binder). Even if the dispersant is not treated, mixing is possible depending on the type and properties of the organic binder, but by coating the organic binder uniformly on the surface of the soft magnetic metal powder, a more uniform and stable core is formed. it can. Moreover, since the quantity of the organic binder with respect to soft-magnetic metal powder can be adjusted, it is preferable.

  When an organic or inorganic coupling agent is used as the dispersant, the coupling agent selectively adheres to the surface of the soft magnetic metal powder even when mixed with a liquid organic binder in advance. There is no need to process. When a powdered organic binder is used, the two-stage treatment is preferably performed. The two-stage treatment method is also applied when the dispersant treatment is performed using the chemical conversion treatment method or the sol-gel method.

  In order to coat the liquid organic binder onto the soft magnetic metal powder, a liquid organic binder is applied to the powder, and the organic binder is deposited on the surface of the powder by drying or heating. Can be achieved. In particular, when a soft magnetic metal powder treated with a dispersant is used, the organic binder and the soft magnetic metal powder are familiar, so that they can be applied uniformly and the coating after drying can be easily made uniform.

  As described above, the mixing of the soft magnetic metal powder and the organic binder can be accurately performed if the soft magnetic metal powder is coated with the organic binder in advance before being put into the mold. This is a preferable method because segregation due to vibrations of the material can be suppressed.

Claims (8)

  A mixture of soft magnetic metal powder having two particle size distributions and an organic binder, or a soft magnetic metal powder having two particle size distributions coated with an organic binder on the surface is placed in a mold, and a vibration is applied thereto. A method for producing a powder magnetic core, which is formed by pressing at a temperature below the thermal decomposition temperature of the organic binder.   The method for manufacturing a powder magnetic core according to claim 1, wherein the vibration means is based on ultrasonic vibration.   The method for producing a powder magnetic core according to claim 1 or 2, wherein the soft magnetic metal powder has a spherical or elliptical shape.   The method for producing a powder magnetic core according to any one of claims 1 to 3, wherein the soft magnetic metal powder uses atomized powder.   The method for producing a magnetic powder core according to any one of claims 1 to 4, wherein the organic binder uses a thermosetting resin.   6. The method for producing a magnetic powder core according to claim 1, wherein the organic binder is coated on the soft magnetic metal powder in advance.   A magnetic powder core produced by using the method according to claim 1.   The powder magnetic core according to claim 7, comprising a soft magnetic metal powder having two particle size distributions and 5 to 30% by volume of a thermosetting resin.