JP2004273471A - Component with core and its manufacturing method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To prevent the cracking of the core of an electronic component, such as the transformer, reactor, etc., having a core. <P>SOLUTION: In the core of the electronic component, an insulating tap 16 having a substrate 16a coated with an adhesive 16b is wound around middle legs 21c and 22c. The middle legs 21c and 22c with the insulating tape 16 wound thereon are inserted into the cavity 32 of a coil bobbin 12 around which primary and secondary windings 13 and 14 are wound. A transformer 1 is impregnated with varnish 17 after the coil bobbin 12 is inserted into the cavity 32 and the varnish 17 is dried and hardened. The adhesion between the coil bobbin 12 and middle legs 21c and 22c is prevented by the insulating tape 16. The external force applied to the core 11 generated when the varnish 17 is dried and hardened, is buffered by the elasticity of the adhesive 16b applied to the insulating tape 16. <P>COPYRIGHT: (C)2004,JPO&NCIPI

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a cored component capable of preventing core cracking and a method for manufacturing the same.
[0002]
[Prior art]
There are electrical components having a core such as a transformer and a reactor.
For example, a transformer includes a ferrite core, a coil bobbin, and a winding.
The ferrite core includes two pairs of core members, and the core members have magnetic legs. The middle foot is usually provided with a gap for adjusting the inductance.
[0003]
To form a transformer, a coil bobbin around which a winding is wound is set on a core member, and the two core members are combined. The coil bobbin is arranged so as to surround the outer periphery of the core member.
[0004]
The thus assembled transformer is impregnated with varnish for insulation, heat radiation, and suppression of beat noise. The impregnated varnish is dried and cured by heat treatment at 90 to 120 ° C. As the varnish cures, the transformer is cooled to room temperature.
[0005]
The transformer thus formed has a problem such as occurrence of a core crack. This core crack is caused by the mechanical strength of the ferrite core and the external force applied to the core.
[0006]
That is, the ferrite core is a sintered product of ferrite and has low mechanical strength. When the transformer is heated during the varnish impregnation, the core and the coil bobbin expand together during the heating. Since the thermal expansion coefficient of the coil bobbin is larger than the thermal expansion coefficient of the core, the coil bobbin expands more than the core. If there is no clearance in the axial direction of the core of the core between the core and the coil bobbin, an external force is applied to the core so that the coil bobbin pushes the core in the axial direction of the magnetic leg.
[0007]
When impregnated with a liquid varnish, the varnish enters the gap between the core and the coil bobbin. When the varnish cures during heating, the core and the coil bobbin may be adhered by the varnish. Since the difference in thermal expansion coefficient between the core and the coil bobbin is large, when the transformer is cooled in this state, an external force is applied to the core. Such external force causes a core crack.
[0008]
Since such a heat history occurs not only at the time of manufacturing the transformer but also at the time of operating the transformer, the core crack may occur at the time of operating the transformer.
[0009]
In the conventional cored parts, the following measures are taken to prevent core cracking. First, the bobbin length is made shorter than the core length, and a clearance is provided. Second, the material of the coil bobbin has a coefficient of thermal expansion substantially equal to that of the ferrite core. Third, after impregnation and curing, a varnish having relatively flexibility is selected and used. Fourth, the curing temperature after impregnation is lowered, the curing time is lengthened, and the external force applied to the core of the coil bobbin is reduced.
[0010]
However, such measures limit the design of the bobbin, the selection of the bobbin material, and the varnish to be used, and also cause the disadvantage that the impregnation hardening time is prolonged and the productivity is reduced.
In order to prevent the varnish from entering between the center foot of the core and the coil bobbin, an additional member is attached to the base of the center foot of the core (for example, see Patent Document 1).
[0011]
[Patent Document 1]
JP-A-8-321423 (page 3-5, FIG. 2)
[0012]
[Problems to be solved by the invention]
However, even if such measures are taken, the additional member may not be able to prevent the varnish from entering, and if the varnish enters between the coil bobbin and the core, similarly, an external force is applied to the core, and Cracks will occur.
[0013]
The present invention has been made in view of such conventional problems, and an object of the present invention is to provide a cored component capable of preventing core cracking and a method of manufacturing the same.
[0014]
[Means for Solving the Problems]
In order to achieve this object, the cored component according to the first aspect of the present invention includes:
A core having magnetic legs;
Cushioning material covering the magnetic legs,
A coil bobbin arranged to surround the outer periphery of the cushioning material;
It is configured with.
[0015]
The coil bobbin has a larger coefficient of thermal expansion than the core,
It is preferable that the buffer has elasticity enough to reduce an external force from the coil bobbin to the magnetic leg to less than the mechanical strength of the core.
[0016]
It is preferable that the cushioning material covers substantially the entire outer periphery of the magnetic leg, or covers the outer periphery of the magnetic leg with a width shorter than the axial length of the magnetic leg.
[0017]
The cored component may be one in which an impregnating material is inserted in a gap between the outer periphery of the cushioning material and the coil bobbin.
[0018]
The method for manufacturing a cored component according to the second aspect of the present invention includes:
Covering the magnetic legs of the core with a cushioning material,
Arranging a coil bobbin on the outer periphery of the cushioning material.
[0019]
A step of impregnating an impregnating material between the cushioning material and the coil bobbin arranged on the outer periphery of the cushioning material,
Heating and curing the impregnating material;
A step of cooling the core, the buffer, the coil bobbin, and the impregnating material while buffering an external force from the coil bobbin to the magnetic leg through the cured impregnating material with the cushioning material. May be further provided.
[0020]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, a cored component according to an embodiment of the present invention will be described with reference to the drawings.
In the present embodiment, the cored component will be described as a transformer having a ferrite core.
[0021]
FIG. 1 shows the configuration of the transformer according to the present embodiment.
The transformer 1 according to the present embodiment includes a core 11, a coil bobbin 12, a primary winding 13, a secondary winding 14, an interlayer paper 15, an insulating tape 16, and a varnish 17. Have been.
[0022]
The core 11 is for forming a closed magnetic path, and is configured by combining a core member 21 and a core member 22. A sintered product formed by sintering ferrite is used for the core members 21 and 22. The expansion coefficient of this ferrite is about 9 to 15 × 10 ⁻⁶ (cm / cm / ° C.).
[0023]
The core 11 is a so-called EE-type core, and the core members 21 and 22 have, for example, alphabetical cross sections when the core members 21 and 22 are cut along the magnetic path as shown in FIG. Is used.
[0024]
The core member 21 includes magnetic legs 21a and 21b and a middle leg 21c. The middle leg 21c is shorter than the magnetic legs 21a and 21b to form an air gap. The middle foot 21c is shortened by cutting or the like.
[0025]
The core member 22 similarly includes magnetic legs 22a and 22b and a middle leg 22c. However, unlike the core member 21, the magnetic legs 22a and 22b and the middle leg 22c have the same length.
[0026]
The core 11 is formed by combining the core member 21 and the core member 22 such that the end surfaces of the magnetic legs 21a and 21b of the core member 21 and the end surfaces of the magnetic legs 22a and 22b of the core member 22 are in close contact with each other. As a result, a closed magnetic path is formed.
[0027]
As shown in FIG. 3, when the core member 21 and the core member 22 are combined, the middle foot 21c of the core member 21 is shorter than the magnetic legs 21a and 21b. A gap is formed between them. This gap becomes the air gap 11a. The air gap 11a adjusts the BH characteristics of the core 11 and makes the core 11 less likely to be magnetically saturated. Instead of an air gap formed by cutting the core, a gap member made of paper, a plastic film, mica or the like can be inserted.
[0028]
Returning to FIG. 1, the coil bobbin 12 is arranged on the outer periphery of the middle foot 21c and the middle foot 22c. This coil bobbin 12 is for forming a primary winding 13 and a secondary winding 14. The coil bobbin 12 is formed of, for example, a phenolic resin (Phenolic Plastic) or an ABS resin (Acrylonitrile Butadiene Styrene Resin). The linear expansion coefficient of the phenolic resin is larger than the linear expansion coefficient of the ferrite, and is approximately 2.0 to 4.0 × 10 ⁻⁵ (cm / cm / ° C.). The linear expansion coefficient of the ABS resin is also larger than the linear expansion coefficient of the ferrite, and is approximately 8.0 × 10 ⁻⁵ (cm / cm / ° C.).
[0029]
As shown in FIG. 4, the coil bobbin 12 has a cylindrical shape, and includes a body 31, a cavity 32, flanges 33 a and 33 b, and pins 34. The cavity 32 is for passing the middle foot 21c of the core member 21 and the middle foot 22c of the core member 22.
[0030]
The axial length of the coil bobbin 12 passing through the cavity 32 is set to be shorter than the sum of the length from the root to the tip of the magnetic leg 21a and the length from the root to the tip of the magnetic leg 22a. Thereby, a clearance is formed between the core 11 and the coil bobbin 12 in the axial direction passing through the cavity 32 of the coil bobbin 12. The size of the clearance is set according to the difference between the thermal expansion of the coil bobbin 12 and the thermal expansion of the core 11.
[0031]
Returning to FIG. 1, the primary winding 13 and the secondary winding 14 are wound on the coil bobbin 12. The primary winding 13 is a winding for exciting the core 11. The secondary winding 14 is a winding for outputting a voltage generated by a change in the magnetic flux density due to a change in the current flowing through the primary winding 13. The primary winding 13 and the secondary winding 14 are wound via an interlayer paper 15 for insulation in order to improve the coupling property.
[0032]
The insulating tape 16 is a sheet member having an insulating property, and is wound around the outer circumference of the middle feet 21 c and 22 c and inside the cavity 32 of the coil bobbin 12. The insulating tape 16 is obtained by applying an adhesive 16b to a base material 16a, and the insulating tape 16 is attached to the outer periphery of the middle feet 21c and 22c by the adhesive 16b.
[0033]
The base material 16a is for preventing the coil bobbin 12 from directly adhering to the outer peripheral surfaces of the middle feet 21c and 22c by the varnish 17, and for maintaining insulation between the middle feet 21c and 22c and the coil bobbin 12. is there.
[0034]
The pressure-sensitive adhesive 16 b is used to reduce external force applied to the core 11 from the coil bobbin 12 via the cured varnish 17. For this reason, in order to reduce external force, an adhesive having elasticity as well as viscosity is used as the adhesive 16b. Since the adhesive 16b has elasticity, the insulating tape 16 functions as a cushioning material.
[0035]
As the insulating tape 16, a polyester base 16a and an adhesive 16b made of an elastic acrylic adhesive are used as easily available ones. The thickness of the base material 16a is 0.020 mm or more, and the thickness of the adhesive 16b is 0.015 mm or more.
[0036]
The insulating tape 16 is wound around the outer circumference of the middle feet 21c and 22c several times. The number of turns is determined by the distance between the middle feet 21c and 22c and the inner circumference of the cavity 32 of the coil bobbin 12, and the degree of elasticity of the adhesive 16b for reducing external force from the coil bobbin 12 to the middle feet 21c and 22c. is there.
[0037]
In other words, the number of turns is such that it enters the gap between the middle feet 21c and 22c and the cavity 32 of the coil bobbin 12, and the external force from the coil bobbin 12 to the middle feet 21c and 22c causes the mechanical strength of the core 11 due to the elasticity of the adhesive 16b. The number of turns is less than the number of turns.
[0038]
The varnish 17 is impregnated mainly to maintain insulation between the core 11 and the coil bobbin 12. The varnish 17 is made of a heat-resistant alkyd resin, an unsaturated polyester resin, an epoxy resin, or the like.
[0039]
The varnish 17 is initially in a liquid state at room temperature, and is dried and cured by being kept at about 90 to 120 ° C. for a predetermined time. Once cured, the varnish 17 remains cured without becoming liquid even at room temperature. The varnish 17 shrinks during drying and curing.
[0040]
Next, a method for manufacturing the transformer 1 according to the present embodiment will be described.
First, the primary winding 13 and the secondary winding 14 are wound around the coil bobbin 12. The primary winding 13 is wound around the coil bobbin 12, the interlayer paper 15 is wound, and the secondary winding 14 is wound. Depending on the number of turns, the primary winding 13 and the secondary winding 14 are wound in layers. The ends of the wound primary winding 13 and secondary winding 14 are wound around pins 34 and fixed, for example, by soldering.
[0041]
Next, the insulating tape 16 is wound around the outer circumferences of the middle foot 21c of the core member 21 and the middle foot 22c of the core member 22 with the adhesive 16b inside. The wound insulating tape 16 adheres to the middle feet 21c and 22c.
[0042]
As described above, the number of turns of the insulating tape 16 enters the gap between the middle feet 21c and 22c and the cavity 32 of the coil bobbin 12, and the external force applied to the middle feet 21c and 22c causes the mechanical strength of the core 11 due to the elasticity of the adhesive 16b. The number of turns is such that the number of turns decreases to less than. The insulating tape 16 may be wound in such a number that the gap between the inner periphery of the cavity 32 of the coil bobbin 12 and the outer periphery of the middle feet 21c and 22c is filled.
[0043]
When the insulating tape 16 is wound, the middle leg 21 c of the core member 21 is inserted into the cavity 32 of the coil bobbin 12.
[0044]
Next, the core member 21 and the core member 22 are combined so that the end surfaces of the magnetic legs 21a and 21b and the end surfaces of the magnetic legs 22a and 22b are in close contact with each other. As a result, the core 11 is formed, and a closed magnetic path is formed.
[0045]
Also, since the middle leg 21c is shorter than the magnetic legs 21a and 21b, when the core member 21 and the core member 22 are combined, an air gap 11a is formed between the middle legs 21c and 22c.
[0046]
The transformer 1 assembled in this manner is impregnated with varnish. In this step, the transformer 1 is pre-heated and cooled, and then impregnated in a liquid varnish 17. The varnish 17 to be impregnated enters the gap between the coil bobbin 12 and the core 11. However, the adhesion of the varnish 17 to the outer peripheral surfaces of the middle feet 21 c and 22 c is prevented by the insulating tape 16.
[0047]
When the impregnation of the varnish 17 is performed, the surplus varnish 17 is dropped and a drying and curing process is performed. In this process, the transformer 1 is kept at about 90 to 120 ° C. for a predetermined time. By this process, the varnish 17 dries and hardens.
[0048]
The varnish 17 shrinks with drying and curing. In addition, the varnish 17 that has entered the gap between the coil bobbin 12 and the core 11 is also cured. However, since the coil bobbin 12 adheres to the insulating tape 16 when the varnish 17 is cured, it does not adhere to the outer peripheral surface of the core 11.
[0049]
When the drying and curing process is completed, the transformer 1 is cooled. When the transformer 1 is cooled, the coil bobbin 12 contracts more than the core 11 due to a difference in thermal expansion coefficient. Then, when the coil bobbin 12 contracts more than the core 11, an external force to the core 11 is generated. However, this external force is applied to the core 11 via the insulating tape 16, and is reduced by the elasticity of the adhesive 16b.
[0050]
The transformer 1 manufactured in this manner operates by being incorporated in a power supply device or the like. When a current flows through the primary winding 13 and the amount of current changes, the magnetic flux density changes and a voltage is generated at both ends of the secondary winding 14.
[0051]
When a current flows through the primary winding 13, the temperature of the transformer 1 rises. The temperature of the transformer 1 also rises due to the excitation of the core 11. When the transformer 1 operates in this manner, an external force to the core 11 is generated due to a rise and fall in temperature. However, the generated external force is similarly reduced by the elasticity of the adhesive 16b.
[0052]
As described above, according to the present embodiment, at the time of assembling the transformer 1, the insulating tape 16 on which the adhesive 16b is applied is wound around the outer circumference of the middle feet 21c and 22c. Then, the transformer 1 is impregnated in the varnish 17, and the varnish 17 is dried and hardened.
[0053]
Therefore, when the varnish 17 is impregnated, the insulating tape 16 adheres to the middle feet 21c and 22c, so that adhesion between the outer peripheral surfaces of the middle feet 21c and 22c and the coil bobbin 12 is avoided. The external force generated when the varnish 17 is dried and hardened is buffered by the elasticity of the adhesive 16b. As a result, the external force applied to the middle feet 21c and 22c is reduced, and the core can be prevented from cracking.
[0054]
Further, the insulating tape 16 is an easily available and inexpensive one that is always used as long as it is an electric component having a core such as the transformer 1 and the reactor. In addition, all that is required is to wind the insulating tape 16 around the middle feet 21c and 22c. For this reason, the measures for preventing core cracking can be performed at low cost and with a simple operation.
[0055]
Further, in order to prevent the core from cracking, there is no need to use a special material for the coil bobbin 12, use a special material for the varnish 17, or change the varnish impregnation process. Can be suppressed. In addition, core cracking can be prevented without impairing productivity.
[0056]
In carrying out the present invention, various modes are conceivable, and the present invention is not limited to the above embodiments.
For example, in the above embodiment, the insulating tape 16 is wound around both cores of the middle feet 21c and 22c so as to cover almost the entire surface. However, as shown in FIG. 5, the insulating tape 16 may be wound so as to cover only one of the cores 22 c, not both cores.
[0057]
In addition, as shown in FIG. 6, the insulating tape 16 may be wound so as to cover one of the cores, ie, the middle foot 21c. In this manner, the external force of the coil bobbin 12 is similarly attenuated only by winding the insulating tape 16 around one of the outer circumferences of the middle feet 21c and 22c.
[0058]
In the above-described embodiment, the cored component has been described as a transformer. However, the cored component is not limited to this, and may be, for example, a choke coil or the like.
[0059]
The core members 21 and 22 are not limited to EE-type cores, and EI-type cores having an E-shaped cross section and an I-shaped cross section can be used. Further, the core members 21 and 22 may be EER-type cores in which the cross sections of the middle legs 21c and 22c are round.
[0060]
【The invention's effect】
As described above, according to the present invention, a core crack can be prevented.
[Brief description of the drawings]
FIG. 1 is a cross-sectional view illustrating a configuration of a transformer according to an embodiment of the present invention.
FIG. 2 is a perspective view showing a core member of FIG. 1;
FIG. 3 is a cross-sectional view of a core having an air gap.
FIG. 4 is a perspective view showing the coil bobbin of FIG. 1;
FIG. 5 is a sectional view showing an application example of a transformer.
FIG. 6 is a sectional view showing an application example of a transformer.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 Transformer 12 Coil bobbin 13 Primary winding 14 Secondary winding 16 Insulating tape 16a Base material 16b Adhesive 17 Varnish 11 Core 21, 22 Core members 21c, 22c Midfoot

Claims (6)

A core having magnetic legs;
Cushioning material covering the magnetic legs,
A coil bobbin arranged to surround the outer periphery of the cushioning material;
Configured with
A part with a core, characterized in that: The coil bobbin has a larger coefficient of thermal expansion than the core,
The buffer has elasticity enough to reduce an external force from the coil bobbin to the magnetic leg to less than the mechanical strength of the core.
The component with a core according to claim 1, wherein: The cushioning material covers substantially the entire outer periphery of the magnetic leg, or covers the outer circumference of the magnetic leg with a width shorter than the axial length of the magnetic leg so as to make one round.
The cored component according to claim 1, wherein: An impregnating material was inserted in the gap between the outer periphery of the cushioning material and the coil bobbin,
The component with a core according to any one of claims 1 to 3, wherein: Covering the magnetic legs of the core with a cushioning material,
Arranging a coil bobbin on the outer periphery of the cushioning material,
A method for manufacturing a cored component. A step of impregnating an impregnating material between the cushioning material and the coil bobbin arranged on the outer periphery of the cushioning material,
Heating and curing the impregnating material;
A step of cooling the core, the buffer, the coil bobbin, and the impregnating material while buffering an external force from the coil bobbin to the magnetic leg through the cured impregnating material with the cushioning material. Further equipped with
The method for manufacturing a component with a core according to claim 5, wherein:

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