JP6325790B2 - Powder magnetic core and manufacturing method thereof - Google Patents

Description

  The present invention relates to a dust core for a reactor suitable for a power factor improving apparatus for improving the power factor of electric power supplied from an AC power source, and a method for manufacturing the same.

  In recent years, energy-saving and environmental problems are increasing, and some of the vehicles powered by electricity such as plug-in hybrid vehicles and electric vehicles have been put into practical use. It is expected that

  Plug-in hybrid vehicles and electric vehicles include a charging device for charging an in-vehicle battery from a commercial power outlet provided at home. And in order to charge a vehicle-mounted battery using AC100V or AC200V household outlet, the AC / DC converter for converting an alternating voltage (AC) into the direct current voltage for a battery is needed.

  In such an AC / DC converter, in order to improve charging efficiency and harmonic countermeasures, a power factor improvement circuit using a step-up chopper is disclosed, and a step-up reactor is used. The step-up chopper type power factor correction circuit is operated by high-frequency switching at 30 kHz to 100 kHz in order to reduce the size of the entire circuit. However, since the high-frequency current is superimposed on the step-up reactor, the iron loss that is a loss of the reactor As a result, the efficiency of the reactor is reduced, and the heat generation of the reactor is a problem.

  In order to solve the problem of reactor iron loss, soft magnetic materials with low iron loss characteristics at high frequencies are generally used for reactor cores, and powders such as dust cores with good high frequency characteristics are used. A magnetic core having a structure compacted by a molding press is used.

  As materials having good iron loss characteristics, oxide soft magnetic materials such as ferrite, and alloy-based soft magnetic materials such as Fe-Si-Al alloys and amorphous metals are used. Such a magnetic material has low iron loss characteristics even in a high frequency region, but has a tendency to have a low saturation magnetic flux density. In addition, when used as a dust core, the hardness of magnetic particles is higher than that of pure iron, so the molding density during dusting is lower than the true density, and the saturation magnetic flux density of the compact further decreases. It becomes a trend.

  When the saturation magnetic flux density of the magnetic core is lowered, the magnetic permeability of the magnetic core when current is superimposed on the reactor is lowered, so that the inductance value of the reactor is lowered as the current is increased. Therefore, in order to secure an inductance value, the size of the magnetic core is increased, and the size of the reactor is increased. Further, since the total length of the winding is increased by increasing the size of the magnetic core, the DC resistance is increased and the copper loss is increased. As a result, the copper loss increases despite the iron loss being suppressed, and the merit of using the alloy-based soft magnetic material is reduced. In addition, the alloy-based soft magnetic material is expensive because the price of the magnetic particles is higher than that of the pure iron-based soft magnetic material.

  On the other hand, the pure iron-based soft magnetic materials shown in Patent Document 1 and Patent Document 2 are known to have a high density of magnetic flux and a high density of compacted powder because the hardness of magnetic particles tends to be low.

JP 2006-233295 A JP 2010-043361 A JP 2006-206948 A

  Although the inductance value of the pure iron core shown in the prior art as described above tends not to decrease even with a large current, the iron loss characteristic at a high frequency shows a high value, so that it is used for a high frequency circuit such as a power factor correction circuit. It was in a situation where it could not be used. In particular, in this type of application, since the commercial voltage of 100 to 240 V is applied as the input voltage, the core loss of the reactor iron core is remarkably increased, and the conventional dust core cannot be used.

  Although a proposal focusing on the quality factor has been made as in Patent Document 3, it has been simply stated that “the smaller the average particle size, the higher the frequency characteristic of the initial permeability μi extends to a high frequency and the higher the quality factor value. Only ". Therefore, in the prior art, different quality factor values are generated even when the average particle diameter is the same, and the average particle diameter is the same when the powder magnetic core is obtained by pressing the soft magnetic powder. In the case of soft magnetic powder containing large-sized particles, the problem that the quality count value varies even if the average particle size is equal cannot be solved.

  The present invention has been proposed to solve the above-described problems of the prior art. An object of the present invention is to provide a powder magnetic core having a good inductance DC superposition characteristic suitable for a reactor through which a relatively large current flows, such as an in-vehicle charger, and a method for manufacturing the same in a power factor correction circuit. And

The dust core and the manufacturing method thereof according to the present invention are characterized by having the following configuration.
(1) Pure iron powder treated with an opening of 70 μm or less, preferably 50 μm or less, and an insulating resin are mixed to form an insulating coating around the pure iron powder.
(2) The pure iron powder on which the insulating coating is formed is pressure-molded into a predetermined shape with a lubricant added.
(3) The molded body is heated in a non-oxidizing atmosphere and annealed.
(4) In performing the pressure molding process, when the insulating coating formed on the surface of the pure iron powder constituting the molded body gave a current of 100 kHz to the reactor using the completed powder magnetic core, The quality factor is maintained at 10 or more, preferably 20 or more.

  In the present invention, the annealing temperature is preferably 600 to 650 ° C. A silicone-based resin can be used as the insulating resin. In one embodiment of the present invention, in the pressure molding process, the collapse of the insulating coating formed on the surface of the pure iron powder constituting the compact is within a range of 100 μm or less from the surface of the compact. By controlling the surface roughness of the sliding surface with the molded body on the mold surface of the molded body, the quality factor can be increased to 10 or more, and the collapse of the insulating coating can be made within 100 μm from the surface of the molded body.

  According to the present invention, it is possible to manufacture an inexpensive dust core with low reactor loss by using pure iron powder, and to determine from the surface by using the quality factor for determining the characteristics of the dust core. Therefore, it is possible to easily determine the degree of collapse of the insulating coating inside the dust core.

The graph which shows the relationship between the sieve opening of a pure iron powder and the reactor loss in the reactor which uses the powder magnetic core of embodiment of this invention. The graph which shows the relationship between the quality factor and reactor loss in the reactor which uses the powder magnetic core of embodiment of this invention.

  Hereinafter, embodiments of the present invention will be specifically described.

(1) Pure iron powder In this embodiment, in order to improve the high-frequency characteristic of the iron loss, which is a disadvantage of the pure iron-based magnetic material, the sieve opening is 70 μm or less, preferably 50 μm or less.

  Iron loss can be broadly divided into hysteresis loss and eddy current loss, but in high frequency applications, the effect of eddy current loss increases. Therefore, a material with a smaller ratio of eddy current loss is better for the core of the reactor. Eddy current loss is expressed by the following theoretical formula.

Pce∝ (D · f · B) ^ 2 / ρ
Pce: Eddy current loss D: Particle size of magnetic particle f: Circuit driving frequency B: Operating magnetic flux density ρ: Electric resistivity

  As described above, the eddy current loss decreases as the electrical resistivity of the magnetic particles increases and as the particle size of the magnetic particles decreases. Here, since the eddy current loss is proportional to the square of the particle diameter of the magnetic particles, the contribution of the particle diameter is considered to be large. Therefore, by controlling the particle size of the magnetic particles, it is possible to provide a reactor suitable for high frequency while being a pure iron-based soft magnetic material. In the present embodiment, since the particle size of the pure iron powder is determined not by the average particle size but by the opening of the sieve, large-diameter particles that cause an increase in iron loss of 70 μm or more do not exist in the pure iron powder.

(2) Insulating film Silicone resin can be used as the insulating film. Silicone resin forms a resin layer on the particle surface of pure iron powder, ensuring electrical insulation between particles, enhancing shape retention during molding, and further strengthening the strength of the molded body after annealing It shall be

  Silicone resins are roughly classified into heat-curing types that condense and cure by heat and room-temperature curing types that cure at room temperature. In the present embodiment, a thermosetting silicone resin in which a functional group reacts by heating and crosslinking by a siloxane bond (—Si—O—Si— bond) proceeds to cause condensation / curing is preferable. The transformation temperature at which the silicone resin softens varies depending on the type of silicone resin, and thus cannot be specified unconditionally, but is about 70 to 300 ° C. By heating to this temperature, the silicone resin adhering to the particle surface of the pure iron powder becomes a hard silicone resin film.

  Since the siloxane bond progresses as the temperature rises, the silicone resin coating undergoes high-temperature heat treatment such as annealing, so that partial crosslinking is changed to total crosslinking, and the coating strength is improved. In addition, since this silicone resin film is excellent in heat resistance, it is not destroyed even if high temperature heating such as annealing is performed on the compacted powder magnetic core, and the cross-linking proceeds further, and particles of pure iron powder The bond between them is strengthened

  The type of silicone resin varies depending on the application, such as resin-based, silane compound-based, rubber-based silicone, silicone powder, organically modified silicone oil, or composites thereof.

  In the present invention, a resin-based silicone resin for coating, that is, a straight silicone resin composed only of silicone is preferable. This is because the reactivity with the fatty acid described later is good. Straight silicone resins are preferred from the viewpoints of heat resistance, weather resistance, moisture resistance, electrical insulation, and ease of coating.

  As the silicone resin, a methylphenyl silicone resin in which a functional group on Si is a methyl group or a phenyl group is generally used. In the present invention, any silicone resin may be used. Furthermore, in this invention, you may use the silicone resin which mixed the 2 or more types of silicone resin from which a kind, molecular weight, and a functional group differ in a suitable ratio.

  The adhesion amount of the silicone resin coating is preferably adjusted to 0.01 to 1.0% by mass with respect to the pure iron powder. When the content is less than 0.01% by mass, the insulation is inferior and the electrical resistance is lowered. On the other hand, if it is added in an amount of more than 1.0% by mass, the powder after heat drying tends to be lumpy, and the molded product after compression molding is affected by the springback because the thickness of the silicone resin attached around the powder is large It expands and it is difficult to achieve high density, and cracks are likely to occur.

(3) Lubricating resin As the lubricating resin, stearic acid and metal salts thereof and waxes such as ethylene bisstearamide can be used. Specific examples include ethylene bisstearamide, lithium stearate, and aluminum stearate. By mixing these, it is possible to improve the sliding between the powders, so that the density during mixing can be improved and the molding density can be increased. Furthermore, it is possible to reduce the punching pressure of the upper punch during molding and to prevent the vertical stripes on the core wall surface from being generated due to the contact between the mold and the powder.

  The amount of the lubricating resin added is preferably about 0.1 wt% to 1.0 wt%, and generally about 0.5 wt% with respect to the pure iron powder. If it is less than this, a sufficient effect cannot be obtained, and if it is more than this, there arises a problem that the magnetic characteristics are deteriorated due to the decrease in the maximum magnetic flux density due to the density decrease and the increase in hysteresis loss.

(4) Quality factor The dust core of the present embodiment is characterized in that the quality factor of the reactor is 10 or more, preferably 20 or more in a state where a current of 100 kHz is applied.

  If the magnetic particles are damaged when the magnetic particles are compression-molded, the insulating coating layer applied around the magnetic particles may be destroyed. When the insulating coating layer is destroyed, the magnetic particles come into contact with each other, and even if pure iron-based magnetic particles having a small angle and particle diameter are used, the iron loss increases and the reactor loss increases. It will be. In evaluating the quality of the insulating coating layer, it is easy to discriminate using a quality factor.

The quality factor in the reactor is expressed by the following formula: Q = (2 · π · f · L) / Rac
Q: Quality factor,
L: Reactor inductance,
f: circuit drive frequency,
Rac: AC resistance

  In the above formula, AC resistance is a parameter including DC resistance and iron loss. Since the quality factor tends to decrease as the iron loss increases, it is possible to evaluate the reactor loss. The reason for the evaluation based on the quality factor instead of the AC resistance is that the absolute value of the loss increases as the reactor capacity increases, making it difficult to relatively determine the quality of the material itself.

  Since the quality factor includes an inductance parameter, it is possible to make a pass / fail judgment on the loss of the iron core regardless of the capacity of the reactor, which is an effective means. The reason for selecting 100 kHz in the evaluation of the quality factor is that the iron loss tends to be higher at higher frequencies, so the iron loss ratio is much greater than the DC resistance loss in the vicinity of 100 kHz, and the core material is evaluated. This is because the DC resistance loss can be ignored.

  The quality of the insulating coating layer cannot be easily determined simply by observing the surface of the molded dust core. That is, even if the insulating resin coating covering the pure iron powder exposed on the surface of the dust core is crushed, the depth of about 100 μm to 40 μm from the surface (2 to 3 particles of pure iron powder) Loss of iron loss is small. However, if the insulation coating is crushed to a particle with a depth greater than this, the iron loss increases and the reactor loss increases. However, even if the molded powder magnetic core is observed from the outside, the insulation depth can be increased. It cannot be determined whether the film layer is defective.

  Therefore, in the present embodiment, a reactor is manufactured with the completed dust core, and the loss coefficient Q in the reactor is measured, so that the insulation coating of pure iron powder is crushed to what depth of the dust core. It is determined whether or not.

  In this embodiment, “smashing of insulating coating” refers to insulation performance required between adjacent pure iron powders due to loss of insulating coating formed around pure iron powder particles, thinning of the insulating coating, etc. The state that cannot be secured. Crushing of the insulating coating layer of the dust core occurs when the dust core is subjected to molding pressure and heat treatment, and when the dust core formed from the inside of the mold is taken out. Occurs on the sliding surface with the mold surface.

  Although the collapse of the insulating coating that occurs when the molded body is removed from the mold can be suppressed by the addition of the lubricating resin, sliding with the molded body of the mold results from repeated use of the same mold. One reason is that fine scratches (irregularities) are generated on the surface, and the scratches cause the insulating coating on the surface of the pure iron powder to be crushed when the compact is pressed and taken out. In this embodiment, a reactor is manufactured using a dust core obtained when the number of pressurization / removal times reaches a certain value, and the life of the mold is determined by measuring its quality factor. You can also. Thus, in this embodiment, the process which maintains a quality factor to 10 or more is realizable by performing the surface roughness management of the sliding surface with the molded object in the metal mold | die surface.

(6) Manufacturing method The powder magnetic core of this embodiment is manufactured as follows.

(6-1) Insulating film forming step Pure iron powder and an insulating material such as silicone resin are mixed for about 15 minutes using, for example, a granulating mixer.

  To the mixture of pure iron powder and insulating material, 0.1 to 1.0 wt% of a lubricious resin is added to pure iron and further mixed. It is also possible to mix the insulating material and the lubricating resin simultaneously.

(6-2) Molding step In the molding step, the mixture to which the binder resin has been added is filled in a mold and pressure-molded. In that case, the mold temperature is preferably room temperature, but may be in the range up to 80 ° C. That is, the normal temperature here means a range from 5 ° C. to 35 ° C., but may be a range from 5 ° C. to 80 ° C. The molding pressure is, for example, 800 to 1700 MPa.

(6-3) Heat treatment step The heat treatment for the molded body is performed, for example, at a temperature of 600 ° C to 650 ° C in a non-oxidizing atmosphere such as an inert gas such as 100% nitrogen gas or a hydrogen gas.

  The heat treatment step is performed for the purpose of removing residual strain and residual stress in the molded body. As a result, the coercive force and hysteresis loss of the dust core can be reduced. The residual strain removed in the heat treatment step may be strain accumulated in the metal powder before the forming step.

  As shown in Table 1 and Table 2 below, Examples 1 to 6 and Comparative Examples 1 to 4 using pure iron powder having different sieve opening sizes as magnetic core materials, and Sendust as magnetic core materials were used. According to Comparative Example 3, a dust core was actually produced. Each powder magnetic core is provided with a primary winding (28 turns) and a secondary winding (28 turns), and a frequency is measured using a BH analyzer (Iwatori Measurement Co., Ltd .: SY-8232) which is a magnetic measurement device. The quality characteristics and iron loss were evaluated under the condition of 100 kHz and the maximum magnetic flux density Bm = 30MT, and the copper loss was evaluated under the condition of the rated current of 16 Arms.

  As shown in Table 1 and FIG. 1, the evaluation results confirmed that the reactor loss was small in Examples 1 and 2 in which the sieve opening was 50 μm or less and the quality factor of 100 kHz was 30 or more. . In this case, as shown in Comparative Example 2, even when the quality factor is 10 or more, when the sieve opening of pure iron powder (pure iron dust) is 75 μm, the iron loss particularly increases, and the entire loss Is also big. In the case of a powder magnetic core using the Sendust powder of Comparative Example 3, the quality factor is high and the iron loss is small even if the opening is 75 μm and the particle diameter is large, but it is more expensive and has a reactor structure than pure iron powder. There is a disadvantage that increases.

  As shown in Table 2 and FIG. 2, the iron loss is greatly increased in Comparative Examples 4 and 5 in which the quality factor of 100 kHz is less than 10 even if the sieve opening is 50 μm or less, and the quality factor is When it becomes 10 or more Examples 3-6, the reduction effect of an iron loss will be acquired. From these experimental results, it can be seen that a quality factor of 10 or more prevents the insulation coating on the surface of the dust core from being crushed and is effective in reducing iron loss. This tendency is particularly remarkable when the quality factor is 20 or more, and the effect of suppressing iron loss is great.

  As described above, when the opening of the sieving process is 50 μm or less, which corresponds to the bending point of the graph of FIG. 1, the reduction in iron loss is more effective. However, if the sieve opening does not reach 75 μm, specifically, as can be seen from the graph of FIG. 1, the total loss of the reactor is about 18.0 W even if the sieve opening is 70 μm. Therefore, in the present invention, the opening of the sieving process is set to 70 μm or less.

Claims (4)

Pure iron powder sieved with an opening of 70 μm or less and an insulating resin are mixed to form an insulating coating around the pure iron powder,
The pure iron powder on which the insulating coating is formed is pressure-molded into a predetermined shape with a lubricant added,
The molded body is heat-treated in a non-oxidizing atmosphere,
In the press molding process, when the insulating coating formed on the surface of the pure iron powder constituting the compact gives a current of 100 kHz to the reactor using the finished dust core, the quality factor is 10 A dust core characterized by being maintained in the above state. Pure iron powder sieved with an opening of 70 μm or less and an insulating resin are mixed to form an insulating coating around the pure iron powder,
The pure iron powder on which the insulating coating is formed is pressure-molded into a predetermined shape with a lubricant added,
The molded body is heat-treated in a non-oxidizing atmosphere,
A dust core in which the collapse of the insulating coating formed on the surface of pure iron powder constituting the compact is within a range of 100 μm or less from the surface of the compact during the pressure molding process. Pure iron powder treated with an opening of 70 μm or less and an insulating resin are mixed to form an insulating film around the pure iron powder,
Pure iron powder with an insulating coating formed is pressed into a predetermined shape with a lubricant added,
The molded body is heat-treated in a non-oxidizing atmosphere,
In performing the pressure molding treatment, when the insulating coating formed on the surface of the pure iron powder constituting the compact gives a current of 100 kHz to the reactor using the finished powder magnetic core, the quality factor thereof Is maintained at 10 or more. The said heat processing are performed at 600 to 650 degreeC, The manufacturing method of the powder magnetic core of Claim 3 characterized by the above-mentioned.