JPH07315917A - Method for firing ferrite core and ferrite core obtained by the method - Google Patents

Abstract

(57) [Abstract] [PROBLEMS] To provide a method for firing a ferrite core and a ferrite core obtained by the method, which can prevent deformation of a molded body during firing. [Structure] By pressing the ferrite powder,
A ferrite core firing method for obtaining a ferrite core by firing, on a firing furnace material 1, a molded body 3 molded in a substantially flat shape having a slit hole 4 in the center thereof.
The central part of the is baked in the non-contact state with the baking furnace material 1. For example, a concave portion 2 is formed in the firing furnace material 1, and the concave portion brings the molded body 3 into a non-contact state.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION The present invention relates to a flat cable E
The present invention relates to a method for firing a ferrite core used for MI (electromagnetic interference) measures and a ferrite core obtained by the method.

[0002]

2. Description of the Related Art Conventionally, as a ferrite core for EMI countermeasures, a flat cable ferrite core called a flat core has been known. This ferrite core 20
7 is formed into a flat shape as shown in FIG. 7, and a flat cable 25 is inserted into a slit hole 24 provided in the center of the flat cable 25 for use.

By the way, this ferrite core 20 is
Ferrite powder containing e ₂ O ₃ as a main component is pressure-molded in a cavity of a mold to form a compact 23 as shown in FIG.
To mold. The slit hole 24 is formed in the center of the molded body 23. And this molded body 2
The ferrite core 20 is manufactured by arranging the lower surface 23b of No. 3 in the sagger 21 as a firing furnace material and firing at a high temperature of several thousand and several hundred degrees C. in a firing furnace (not shown). The bowl 21 is usually made of porous mullite ceramics, and the inside thereof is covered with alumina powder 26 or alumina beads (not shown).

[0004]

However, this firing method has a problem that the molded body is easily deformed during firing. That is, when the alumina powder 26 is spread, a local load is applied to the molded body 23 due to the unevenness and the inclination generated in the sagger 21 by the alumina powder 26. Even when the alumina beads are spread, unevenness due to the overlapping of the beads may occur, or the molded body 2
The particles 3 move on the spherical beads due to the contraction during firing and come into contact with another molded body 23 to stick to each other.

As a result, at the time of firing, the lower surface 23b side of the slit hole 24 of the molded body 23, that is, the alumina powder 2
The load and resistance act on the contact surface side with 6 or the like, the entire circumference of the molded body 23 is not uniformly contracted, and the ferrite core 20 after firing is
However, for example, the upper surface side shrinks too much and the width becomes narrower, and the lower surface side shrinks less and the width becomes wider. As a result, the flat cable 2 is deformed due to the deformation of the slit hole 24.
5 cannot be inserted into the slit hole 24, or the outer shape is deformed, so that the ferrite core 20 does not fit in the case of the apparatus. Therefore, the dimensional inspection is performed after firing, and the defective product is discarded. Is the actual situation.

The present invention has been made in view of the above circumstances, and an object thereof is to provide a method for firing a ferrite core capable of preventing deformation of a molded body during firing, and a ferrite core obtained by the method. To do.

[0007]

In order to achieve the above object, a method of firing a ferrite core according to claim 1 is a method of press-molding ferrite powder so that a substantially flat surface is formed so as to have a slit hole in the center. In the method of firing a ferrite core, the shaped body is fired on a firing furnace material to obtain a ferrite core.In the firing method of the ferrite core, the central portion in the longitudinal direction is fired in a non-contact state with the firing furnace material. It is characterized by A firing method according to a second aspect is characterized in that a recess is formed on the upper surface side of the firing furnace material, and the molded body is brought into a non-contact state with the firing furnace material by the recess.

The ferrite core according to claim 3 is
A ferrite core obtained by firing a ferrite powder under pressure into a substantially flat shape having a slit hole in the center by firing on a firing furnace material. And a concave portion is formed on the contact surface side with.

[0009]

According to the method of firing a ferrite core according to claim 1, first, a molded body formed into a substantially flat shape is placed so that the central portion in the longitudinal direction thereof is not in contact with the firing furnace material. And bake. Since the central portion of the molded body does not receive load or resistance on the upper and lower surfaces and can be contracted almost freely, the upper and lower surfaces of the molded body contract uniformly during firing, and for example, the width of the slit hole is Deformation such as extremely narrowing is prevented. Further, in the firing method according to the second aspect, the central portion in the longitudinal direction of the molded body can be brought into a non-contact state with the firing furnace material by the recess formed in the firing furnace material.

Further, according to the ferrite core of the third aspect, the recess is formed in advance on the lower surface which is the contact surface of the molded body with the firing furnace material. By this recess, the molded body is baked in a non-contact state with the firing furnace material during firing, deformation of the molded body is prevented, and a ferrite core with extremely few dimensional defects is obtained.

[0011]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described in detail below with reference to the drawings. 1 to 3 show a firing furnace material capable of carrying out the firing method of a ferrite core according to the present invention, FIG. 1 is a perspective view thereof, FIG. 2 is a sectional view thereof, and FIG. ing. The firing furnace material 1 is made of alumina, for example, and is formed into a substantially plate shape. The firing furnace material 1 has a width L on the upper surface 1a side.
The groove-shaped recess 2 is formed along the longitudinal direction. On both left and right sides of the recess 2 along the longitudinal direction, a step portion 1c lower than the upper surface 1a is formed. This step 1
The plurality of molded bodies 3 are placed on the stepped portion 1c while the molded bodies 3 are aligned by c.

The molded body 3 is molded by press-molding a ferrite powder containing Fe ₂ O ₃ as a main component in a cavity of a mold (not shown). As shown in FIGS. Has a flat irregular shape with a length W (however W >> T) and a height H. A slit hole 4 having a width t and a length w is formed in the center of the molded body 3. Then, the lower surface 3b of the molded body 3 is placed on the stepped portion 1c of the firing furnace material 1, and in the firing furnace (not shown) as in the conventional case, a temperature of several thousand and several hundred degrees C.
By firing at a high temperature, the ferrite core 20 as shown in FIG. 7 is manufactured. The size of the molded body 3 is set large in advance by the amount of shrinkage due to firing.

FIG. 4 shows the results of a specific embodiment of the firing method according to the present invention. In this example,
The respective dimensions of the molded body 3 are set as follows. External dimensions: length W = 60 mm, width T = 7.5 mm,
Height H = 14 mm Dimensions of Slit Hole 4: Length w = 52 mm, Width t = 1.
65 mm

The width L of the recess 2 of the firing furnace material 1 (see FIG.
(Refer to FIG. 3), the dimension d1 of the portion having the widest width t and the dimension d2 of the portion having the narrowest width t of the molded body 3 after firing, that is, the slit holes 4 of the ferrite core 20 are measured. From the difference between the dimensions d1 and d2, the deformation amount d (d =
The result of calculating d1-d2) is shown in the graph of FIG. That is, in the graph of FIG. 4, the horizontal axis represents the ratio of the width L of the recess 2 of the firing furnace material 1 to the length w of the slit hole 4 (w / L × 100%, hereinafter referred to as the dimensional ratio w / L). And the vertical axis represents the deformation amount d of the slit hole 4.

As is apparent from this graph, the dimensional ratio w
When / L is approximately 50% or more, the deformation amount is 0.1 mm or less. It has been confirmed that if the deformation amount d is 0.1 mm or less, there is no problem in actual use. Regarding the upper limit of the dimensional ratio w / L, the shrinkage rate of the molded body 3 is 1
Since it is about 5%, it is preferably 85% or less in order to prevent the molded body 3 after firing from falling into the concave portion 2. Therefore, the optimum dimensional ratio w / L is 50% or more and 85% or less.

As described above, in the above embodiment, since the lower surface 3b of the central portion of the slit hole 4 of the molded body 3 is not in contact with the firing furnace material 1, when the molded body 3 contracts by firing, It receives almost no local load or resistance and shrinks almost freely. As a result, the molded body 3 contracts substantially uniformly over the entire outer periphery thereof, the deformation amount d becomes extremely small, and the deformation of the molded body 3 which is a problem in practical use is prevented. As a result, in the dimensional inspection of the ferrite core 20 after firing, the defect rate can be significantly reduced, and the product yield is improved.

Further, the lower surface 3 of both end portions in the longitudinal direction of the molded body 3
b is securely supported by the step portion 1c of the firing furnace material 1 to prevent movement during firing, and the adjacent molded bodies 3 contract in the respective separating directions. To be prevented. Furthermore, as in the conventional case, the bowl 21
The work of laying the alumina powder 26 and the alumina beads inside is unnecessary, and the firing work becomes easy.

It should be noted that the shapes of the molded body 3 and the firing furnace material 1 in the above embodiment are merely examples, and for example, the width t of the slit hole 4 of the molded body 3 is set to be relatively large with respect to the length w. Alternatively, the step portion 1c of the firing furnace material 1 may be eliminated and the molded body 3
May be placed on the upper surface 1a, or both ends of the recess 2 in the longitudinal direction may be flush with the upper surface 1a.

5 and 6 show an embodiment of a ferrite core obtained by the firing method according to the present invention. This ferrite core is characterized in that the recess 12 is formed in the lower surface 13b of the slit hole 14 of the molded body 13. The molded body 13 is fired as follows. That is, a recess (not shown) is formed in a mold (not shown) corresponding to the lower surface 13b of the molded body 13, and the molded body 13 is pressure-molded by this mold.

As a result, the recess 12 is formed in the lower surface 13b of the molded body 13, and the molded body 13 is placed, for example, on the sagger 21 in which the alumina powder 26 or alumina beads similar to the conventional one is spread. Bake. Concavities and convexities such as the alumina powder 26 are absorbed by the concave portions 12 and do not come into contact with the molded body 13. The depth h of the recess 12 (see FIG. 5) is preferably 0.1 mm or more. Even with such a configuration, the central portion of the lower surface 13b of the molded body 13 in the longitudinal direction does not contact the sagger 21, the deformation of the molded body 13 during firing is prevented, and a ferrite core with extremely few dimensional defects is provided. can get.

In each of the above embodiments, the recess 2 or the recess 12 is formed in the firing furnace material 1 or the molded body 3 so as to be in a non-contact state.
It goes without saying that various modifications can be made without departing from the gist of the present invention, such as forming recesses in both of them and making them in a non-contact state.

[0022]

As described in detail above, in the method for firing a ferrite core of the present invention and the ferrite core obtained by the method, the central portion in the longitudinal direction of the molded body is in a non-contact state with the firing furnace material. By firing, it is possible to prevent deformation of the molded body during firing.

[Brief description of drawings]

FIG. 1 is a perspective view of a firing furnace material capable of carrying out a ferrite core firing method according to the present invention.

FIG. 2 is a sectional view of the same.

FIG. 3 is a plan view of the main part of the same.

FIG. 4 is a graph showing the results of deformation amount of the specific example.

FIG. 5 is a side view of a ferrite core according to the present invention.

FIG. 6 is a bottom view of the same.

FIG. 7 is a perspective view showing an example of how to use the ferrite core according to the present invention.

FIG. 8 is a perspective view of a bowl in which a conventional ferrite core firing method can be implemented.

[Explanation of symbols]

 1 --- Baking furnace material 1a --- top surface 1c --- step portion 2 --- recessed portion 3 --- Molded body 3b ... ・ Lower surface 4 ・ ・ ・ ・ ・ ・ Slit hole 12 ・ ・ ・ ・ ・ ・ Recessed portion 13 ・ ・ ・ ・ Molded body 13b ・ ・ ・ ・ ・ ・ Lower surface 14・ ・ ・ ・ ・ ・ ・ ・ ・ Slit hole 20 ・ ・ ・ ・ ・ ・ Ferrite core 21 ・ ・ ・ ・ ・ ・ ・ Vase (firing furnace material) 23 ・ ・ ・ ・ ・ ・ Molded body 24 ・ ・ ・ ・ ・..Slit holes 25 ........ Flat cable 26 ........ Alumina powder

Claims (3)

[Claims] 1. A ferrite core obtained by press-molding a ferrite powder, which is molded into a substantially flat shape having a slit hole in the center thereof, and is fired on a firing furnace material to obtain a ferrite core. In the firing method, the molded body is fired at a central portion in a longitudinal direction thereof in a non-contact state with the firing furnace material. 2. The firing of a ferrite core according to claim 1, wherein a recess is formed on the upper surface side of the firing furnace material, and the molded body is brought into a non-contact state with the firing furnace material by the recess. Method. 3. A ferrite core obtained by firing a ferrite powder into a substantially flat shape having a slit hole in the center by firing on a firing furnace material. A ferrite core characterized in that a concave portion is formed on the contact surface side of the molded body with the firing furnace material.