JP6559930B2 - Simple evaluation method for dust cores - Google Patents

Description

  The present invention relates to a dust core simple evaluation method for evaluating insulation and heat resistance of a dust core formed by compression-molding soft magnetic powder coated with an insulation film.

  In recent years, magnetic cores of electromagnetic parts such as stators and rotors in motors used in alternating current, especially reactors used in boosters for inverters and converters in hybrid vehicles, etc., have recently been compressed by compacting soft magnetic powder. Magnetic cores are increasingly used.

  A soft magnetic powder coated with an insulating film is used as the raw material powder for the dust core. The insulation film is formed on the surface of the raw material powder to suppress the eddy current loss of the powder magnetic core. If the insulation by this insulation film is insufficient, eddy current loss, which is one of iron loss, increases. End up. Further, even if the heat resistance due to the insulating film is insufficient, eddy current loss increases after strain relief annealing.

  As shown in FIG. 2, the eddy current loss generated in the powder magnetic core includes soft magnetic powder 1, that is, an intra-particle eddy current loss 6 generated in a particle and an inter-particle eddy current loss generated across a plurality of particles. There are seven. The intra-particle eddy current loss 6 is an inevitable loss, but the inter-particle eddy current loss 7 is a loss that can be suppressed by covering the soft magnetic powder 1 with the insulating film 2. Thus, the insulating film 2 is formed so as to cover the surface of the soft magnetic powder 1 that is the raw material powder in order to suppress the interparticle eddy current loss 7 among the eddy current losses.

  However, if the insulation or heat insulation by the insulating film 2 is insufficient, an inter-particle eddy current is generated, and when this eddy current is generated, the eddy current loss increases rapidly, so that the soft magnetic powder 1 is coated. The reliable formation of the insulating film 2 is a particularly important condition for producing a dust core.

  For this reason, in manufacturing the dust core, it is examined that the insulating film 2 covering the soft magnetic film 1 has insulation and heat resistance to such an extent that the interparticle eddy current loss 7 can be suppressed. However, it is common to evaluate the insulation and heat resistance of the dust core by measuring the eddy current loss directly.

  In order to measure the eddy current loss, as shown in FIG. 4, a ring-shaped dust core test piece 3 is prepared, and the winding core 8 is applied to the dust core test piece 3 to obtain a vortex as a measurement sample. Current loss is measured. However, for the production of the measurement sample, cotton tape or vinyl tape, which is an insulating material, is provided on the surface of the dust core test piece 3 so that the ring-shaped dust core test piece 3 and the winding 8 are not short-circuited. It is necessary to wind winding 8 after winding. In addition, the winding 8 includes two types of windings 8 of an excitation winding 8a and a detection winding 8b, and the winding 8 is prevented from short-circuiting the excitation winding 8a and the detection winding 8b. However, it is necessary to coat with an insulating material, and the present situation is that preparation of a measurement sample for measuring eddy current loss is very complicated.

  As described above, the conventional methods for measuring eddy current loss that are currently being carried out require a very complicated operation such as winding or covering with an insulating material to prepare a measurement sample. At present, the measurement is often performed at the minimum, and the development of a simple evaluation method for evaluating the insulation and heat resistance of the insulating film covering the soft magnetic film is awaited. .

  Patent Document 1 describes that in an inductance element, it is necessary to stabilize an inductance change (frequency characteristic) with respect to a frequency change, and Patent Document 2 is covered with an insulating film. As a result, good direct current superposition characteristics can be obtained by maintaining a sufficient gap between the soft magnetic powder particles. Furthermore, it is described that the direct current superimposition characteristic is evaluated by the rate of decrease in inductance.

JP-A-9-35937 JP 2013-138159 A

  The present invention has been made as a solution to the above-mentioned conventional problems, and it is possible to easily evaluate the insulation and heat resistance of a dust core by an insulating method rather than directly measuring eddy current loss. It is an object of the present invention to provide a simple evaluation method of a dust core that can be used.

  The simple evaluation method of a dust core of the present invention is a simple evaluation method of a dust core for evaluating the insulation and heat resistance of the insulation core in a dust core formed by compression molding a soft magnetic powder coated with an insulation film. In the above, a rod-shaped dust core test piece is inserted into a coil, and alternating currents of two different frequencies (hereinafter, Inductance of the dust core test piece at each frequency is measured by flowing each current), and the insulation and heat resistance by the insulating film are determined from the rate of decrease in inductance between the two frequencies. It is a simple evaluation method of a dust core characterized by evaluating.

  Further, in the simple evaluation method of the dust core of the present invention, the electrical resistance and the iron loss of the dust core test piece are measured in advance, the electrical resistance, the eddy current loss obtained from the iron loss, and the It is preferable to evaluate the insulation and heat resistance of the insulating film by obtaining a calibration curve from the relationship with the inductance reduction rate and determining the threshold value of the inductance reduction rate.

  According to the simple evaluation method of a dust core of the present invention, the insulation and heat resistance of an insulation film of a dust core can be directly measured using a measurement sample that involves a very complicated operation for preparation. Instead, it can be easily evaluated by a simple method of measuring inductance by inserting a simple bar-shaped dust core test piece into a spirally wound coil.

It is a perspective view which shows the state which is measuring the inductance by applying the simple evaluation method of the dust core of this invention. It is explanatory drawing which shows the intra-particle eddy current loss which generate | occur | produces in the particle | grains of a soft magnetic powder, and the inter-particle eddy current loss which generate | occur | produces over several particle | grains. It is a graph which shows the relationship between the inductance and frequency in a dust core. It is a perspective view which shows the state which is measuring the eddy current loss using a ring-shaped dust core test piece. It is a graph which shows the relationship between the electrical resistance of a powder magnetic core test piece measured in the Example, and an eddy current loss. It is a graph which shows the relationship between the electrical resistance of the powder magnetic core test piece measured in the Example, and the decreasing rate of an inductance. It is a graph which shows the relationship between the fall rate of the inductance of a powder magnetic core test piece measured in the Example, and an eddy current loss.

  In order to produce a dust core industrially, it is necessary to inspect the insulation treatment process and to inspect the product to evaluate that the insulating film has sufficient insulation and heat resistance. In the conventional method of directly measuring eddy current loss when evaluating the insulation and heat resistance of a dust core insulation film, the sample is prepared by winding or covering with an insulating material. The present inventors have been able to evaluate the insulation and heat resistance of the dust core with an insulating film by a simple method using a test piece having a simple structure. With the aim of finding out, we studied diligently, research and experimentation.

  As a result, a rod-shaped dust core test piece is inserted into a spirally or spirally wound coil, and two different frequency currents satisfying certain conditions are applied to the dust core test piece, respectively. By measuring the inductance of the powder magnetic core test piece at each frequency, the inductance reduction rate between the two types of frequencies is obtained, and from the inductance reduction rate, the insulation core of the powder magnetic core is used. The inventors have found that insulation and heat resistance can be easily evaluated by a simple method, and completed the present invention.

It is known that the inductance L decreases from a certain frequency when the frequency is increased. For example, as shown in FIG. 3, a dust core A having poor insulation and heat resistance is insulated. As compared with the dust core B having high heat resistance and heat resistance, the inductance L decreases from a low frequency. Each inductance L is measured by flowing currents of a low frequency f ₁ and a high frequency f ₂ that satisfy a certain condition through the powder magnetic core test piece 3, and the rate of decrease thereof is evaluated. It can be evaluated whether or not has sufficient insulation and heat resistance.

  Hereinafter, the present invention will be described in more detail based on embodiments shown in the accompanying drawings.

FIG. 1 shows a state where an inductance is measured by an LCR meter 5 connected to a coil 4 using a dust core test piece 3 by applying the dust core simple evaluation method of the present invention. A powder magnetic core test piece 3 compression-molded into a rod shape is inserted into the center of a coil 4 wound in a spiral shape or a spiral shape, and in this state, currents of two different frequencies which will be described later are respectively supplied to the powder magnetic core. The respective inductances L are measured with an LCR meter 5 connected in sequence to the test piece 3 and connected to the coil 4. Based on the measured inductances Lf ₁ and Lf ₂ at _two different frequencies f ₁ and f ₂ , the reduction rate of the inductance L is obtained from the equation (Lf ₁ −Lf ₂ ) / Lf ₁ × 100 (FIG. 3). See). Although details will be described in the embodiment, eddy current loss can be assumed from the rate of decrease of the inductance L. Details of the two types of currents flowing through the dust core test piece 3 will be described later. Incidentally, it can be said that when the decrease rate of the inductance L is small, the electrical resistance is large, and when the decrease rate of the inductance L is large, the electrical resistance is small.

  In addition, as long as the shape of the powder magnetic core test piece 3 is a rod shape, it may be any shape such as a prismatic shape, a cylindrical shape, a strip shape, or the like. Moreover, the dust core test piece 3 is produced by compression-molding the soft magnetic powder 1 covered with the insulating film 2 as shown in FIG. 2 in the same manner as a normal dust core.

  The soft magnetic powder 1 is a ferromagnetic metal powder. Specific examples thereof include pure iron powder, iron-based alloy powder (Fe—Al alloy, Fe—Si alloy, Sendust, Permalloy, etc.), amorphous powder, and the like. be able to. Such a soft magnetic powder 1 can be manufactured, for example, by reducing the fine particles by an atomizing method, and then reducing the fine particles.

  Further, as the insulating film 2 covering the surface of the soft magnetic powder 1, an inorganic material such as a phosphoric acid-based chemical film such as a phosphoric acid-based chemical film or a chromium-based chemical film, a low-melting glass film, a resin It is preferable to employ a film formed using. Examples of the resin include olefin resins such as silicone resin, phenol resin, epoxy resin, phenoxy resin, polyamide resin, polyimide resin, polyphenylene sulfide resin, styrene resin, acrylic resin, styrene / acrylic resin, ester resin, urethane resin, and polyethylene. Carbonate resins, ketone resins, fluororesins such as fluorinated methacrylate and vinylidene fluoride, engineering plastics such as PEEK, or modified products thereof can be used as the film.

  As described above, in the dust core simple evaluation method of the present invention, two kinds of currents of a predetermined frequency are passed through the dust core test piece 3, and the frequency ranges from 10 Hz to 1 MHz, and 100 Two different frequencies with a difference of twice or more are used. The range of 10 Hz to 1 MHz is an appropriate range for the frequency of the current flowing through the powder magnetic core test piece 3 used for the reactor and the like in terms of the frequency band of the powder magnetic core used and the configuration of the apparatus. However, if the difference between the frequencies of the two kinds of currents flowing through the dust core test piece 3 is too small, it is difficult to evaluate the insulation and heat resistance of the insulating film, assuming eddy current loss from the rate of decrease in inductance. The frequency difference between the two types of currents flowing through the dust core test piece 3 is 100 times or more. In addition, although the upper limit is not specifically described, since the frequency of the current passed through the dust core test piece 3 is in the range of 10 Hz to 1 MHz, it is 100,000 times.

  Moreover, the simple evaluation method of the dust core of the present invention can be prepared in advance by simply setting the test body by inserting the rod-like dust core test piece 3 into the center of the coil 4. As in the test using the conventional ring-shaped dust core test material shown in Fig. 4, the insulating material is wound around the dust core test material, and then the winding is applied. The present invention can be said to be an evaluation method excellent in work efficiency because it does not require a very complicated preparation work of covering.

  Note that the dust core has different frequency bands to be used, the absolute value of the inductance, and the rate of decrease of the inductance depending on the product or material to be mounted. Therefore, it is desirable to create a calibration curve and set the inductance threshold after evaluating the relationship between the inductance drop rate and eddy current loss in advance.

  Moreover, since the simple evaluation method of the dust core of the present invention is not a measurement performed in a closed circuit, it is assumed that the magnetic flux leaks to a space other than the magnetic core. For this reason, it is not preferable that a magnetic material exists around the measurement coil 4, and it is a requirement that no magnetic material exists within at least 50 cm around the coil 4.

  EXAMPLES Hereinafter, the present invention will be described more specifically with reference to examples. However, the present invention is not limited by the following examples, and the present invention is implemented with appropriate modifications within a range that can meet the gist of the present invention. These are all included in the technical scope of the present invention.

Pure iron powder (manufactured by Kobe Steel: Magmel (registered trademark) ML35N) was used as the soft magnetic powder, and a phosphoric acid-based chemical conversion film serving as an insulating film was formed on the surface thereof. In forming this phosphoric acid-based chemical conversion film, water: 50 parts by mass, NaH ₂ PO ₄ : 30 parts by mass, H ₃ PO ₄ : 10 parts by mass, (NH ₂ OH) ₂ · _{H 2 SO} 4: 10 parts by _{mass, Co 3 (PO 4) 2} : 10 parts by weight and mixed to stock, varying concentrations were diluted appropriately to 50 times with water in order to change the electrical resistance process The liquid was used. The phosphoric acid-based chemical film was formed on the surface of the pure iron powder by mixing 5 parts by mass of the treatment liquid with various concentrations with respect to 100 parts by mass of the pure iron powder and drying in the atmosphere at 200 ° C.

  Thereafter, the soft magnetic powder on which the insulating film is formed is compacted to form a ring-shaped dust core test piece (φ45 × φ33 × 5 t: unit mm) and a prismatic dust core test piece ( 12.7 × 31.75 × 5t: unit mm).

  The electrical resistance and iron loss (eddy current loss) are measured using a ring-shaped dust core test piece 3 as shown in FIG. 4, and the inductance L is measured using a prismatic dust core test piece 3. It was measured. As shown in FIG. 1, the inductance L is measured by inserting a prismatic dust core test piece 3 into the center of a coil 4 in which a litz wire is wound (number of turns 100), and an LCR meter 5 is inserted into the coil 4. The LCR meter 5 was used to measure the inductance L when currents having a frequency of 100 Hz and 100 kHz were passed.

From the inductance L _{100 Hz} when a current of 100 Hz was passed and the inductance L _{100 kHz} when a current of 100 kHz was passed, a reduction rate L _D (unit%) of the inductance L was determined based on the following formula.
L _D = (L _{100 Hz−} L _{100 kHz} ) / L _{100 Hz} × 100

  FIG. 5 shows the relationship between the electrical resistance (unit μΩ · m) and the eddy current loss (unit W / kg) obtained in each measurement, and the reduction rate (unit%) of the electrical resistance (unit μΩ · m) and the inductance L. 6 shows the relationship between the rate of decrease in inductance L (unit%) and the eddy current loss (unit W / kg). FIG.

  According to the relationship between the electrical resistance and the eddy current loss shown in FIG. 5, it can be seen that the eddy current loss rapidly increases when the electrical resistance decreases to some extent. 6 also shows the same tendency as the relationship between the electrical resistance and eddy current loss shown in FIG. 5, and the contents shown in FIGS. This suggests that there is a correlation between the rate of decrease of inductance L and eddy current loss.

  FIG. 7 shows the relationship between the decrease rate of the inductance L and the eddy current loss. As the decrease rate of the inductance L increases, the eddy current loss increases, and a positive correlation exists between the decrease rate of the inductance L and the eddy current loss. I understand that there is. Further, since the value of the eddy current loss hardly changes when the decrease rate of the inductance L is 3% or less, the value of the eddy current loss is an inevitable loss in the particles, which is an inevitable loss generated in the soft magnetic powder. It can be said. That is, in the case of ML35N, if the rate of decrease of the inductance L is 3% or less, all eddy current loss can be regarded as intra-particle eddy current loss, and by setting 3% as a threshold, Insulation and heat resistance can be evaluated.

DESCRIPTION OF SYMBOLS 1 ... Soft magnetic powder 2 ... Insulating film 3 ... Powder magnetic core test piece 4 ... Coil 5 ... LCR meter 6 ... Intraparticle eddy current loss 7 ... Interparticle eddy current loss 8 ... Winding 8a ... Excitation winding 8b ... Detection Winding wire

Claims (2)

In a simple evaluation method of a dust core for evaluating insulation or heat resistance of the insulation core in a dust core formed by compression molding a soft magnetic powder coated with an insulation film,
Insert a rod-shaped dust core test piece into the coil,
The inductance of the dust core test piece at each frequency is measured by flowing alternating currents of two different frequencies with a difference of 100 times or more in the range of 10 Hz to 1 MHz to the dust core test piece. A simple evaluation method for a dust core, wherein the insulation or heat resistance of the insulating film is evaluated from the rate of decrease in inductance between the two types of frequencies. Families Ku step previously measured electric resistance and the eddy current loss of the powder magnetic core specimen,
Creating a calibration curve indicating the relationship between the decrease rate of the inductance and the eddy current loss from the relationship between the electrical resistance and the eddy current loss, and the relationship between the electrical resistance and the decrease rate of the inductance;
In the calibration curve, the first region where the value of the eddy current loss does not change with respect to the increase in the inductance reduction rate is considered that the eddy current loss is all in-particle eddy current loss, and the inductance reduction rate. The second region in which the eddy current loss increases as the eddy current loss increases, the eddy current loss evaluation step that considers that the eddy current loss is superimposed on the interparticle eddy current loss in addition to the intraparticle eddy current loss;
A threshold value determining step for determining a reduction rate of the inductance at a position where the first region and the second region of the calibration curve intersect as a threshold value of the reduction rate of the inductance;
Have
The simple evaluation method of a dust core according to claim 1, wherein the insulation or heat resistance of the insulating film is evaluated depending on whether the rate of decrease in inductance is equal to or less than the threshold value .

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