JPH0217457Y2 - - Google Patents

Description

[Detailed Description of the Invention] [Industrial Application Field] This invention relates to a ferrite magnetic core used for adjusting the inductance of a coil.

[Conventional technology]

As shown in FIGS. 5 to 7, the ferrite magnetic core has a cylindrical main body 1 with a threaded groove on its circumferential surface 2, and a slotted hole 3 on its end surface for inserting the tip of a rotating tool such as a screwdriver. It is something that In the conventional ferrite magnetic core, the slot 3 has a rectangular planar shape and a horizontal cross-sectional shape.

[Problem that the invention attempts to solve]

This conventional ferrite magnetic core has a problem in that the torque strength is weak when the tip of a screwdriver or the like is inserted into the slot 3 and rotated, and it is relatively easily broken from the corner part of the slot 3. It has been pointed out.

The main cause of this is thought to occur in the manufacturing process as follows. That is, in the mass production process of ferrite magnetic cores, ferrite powder is pressure-molded using a rotary press. At this time, as shown in FIG. 8, ferrite powder a is
It is fed along a circular trajectory b while being held by a horizontally rotating table 4. On the other hand, the punch 5 for forming this is attached to the rotary table 4.
The pressure roller 6 is placed above (or below) and is pressed down by a pressure roller 6 having a horizontal rotation axis. Therefore, at the place where the pressure roller 6 contacts the head of the punch 5 in an uneven manner, due to a deviation between the above-mentioned locus b and the rotational direction of the pressure roller 6, a deviation in the line of action of the pressure roller 6 with respect to the punch 5, etc. A rotational force acts on the punch 5 in the direction of the arrow. Then, a twisting force is applied to the ferrite powder a by the punch 5 during molding, and this causes minute cracks to occur in the molded product, particularly at the corners of its slots.

Stress tends to concentrate at the corners of the slot holes, and the minute cracks mentioned above occur, so in order to adjust the inductance of the coil, the ferrite magnetic core was screwed into the screw hole of the coil bobbin. When rotating with a screwdriver, etc., the corners of the slot 3 are likely to be damaged. Such damage will occur more frequently if the corner of the driver tip becomes worn and the tip of the driver starts to slip against the slot 3 during rotation.

This idea was made to solve the above-mentioned problems with conventional ferrite magnetic cores, and while maintaining the basic shape of the conventional slot into which the tip of a screwdriver etc. can be inserted,
By adopting a special shape for the slot, the purpose is to provide a ferrite magnetic core with higher torque strength than conventional ones.

[Means to solve the problem]

Hereinafter, the configuration of this invention will be explained in detail based on FIGS. 1 to 3.

The slot 13 of the ferrite magnetic core 11 necessarily has a planar shape and a horizontal cross-sectional shape close to a rectangle because the tip of a rotating tool such as a screwdriver is inserted into the slot 13 . In this invention, while maintaining this basic shape, two opposing surfaces of the slot 13 are formed by planes 14, 14 consisting of long sides,
The other two opposing surfaces are formed by arcuate surfaces 15, 15 shorter than the plane 14.

The arcuate surfaces 15, 15 are preferably concentric with the circumferential surface 12, and from the arcuate surfaces 15, 15, the flat surface 14,
It is preferable that the portion following 14 be continuous with a smooth curved surface and have no corners. In addition, this slot 1
3 is usually formed so that the opening side is wide and the opening becomes narrower toward the back so that the tip of a screwdriver or the like can be easily inserted.

[Effect]

In the ferrite magnetic core according to this invention, the slot 13
The intersecting angle between the planes 14, 14 and the arcuate surfaces 15, 15 is simpler than in the case of a conventional rectangular slot. Therefore, the unevenness in the molding density of the raw material is reduced, and the molding density between the arcuate surfaces 15, 15 and the circumferential surface 12 is increased. From this point of view, even if the punch 5 of the rotary press rotates during molding and excessive weight is applied to the flat surfaces 14, 14 of the slot 13, the distortion inside the molded product can be suppressed to a small level, and the occurrence of minute cracks can be prevented. can do. In addition, stress concentration at the corners of the slot becomes less likely.

〔Example〕

Next, an example of this invention will be described in order to confirm the above-mentioned effect.

Fe-Ni-Zn-based ferrite powder was pressure-molded using a rotary press at a pressure of Iton/cm ² . This molded body has a cylindrical shape with a diameter of 3.2 mm and a length of 6 mm, and slots with a depth of 1.4 mm are provided on both end faces.
This slot has a planar shape and a horizontal cross-sectional shape that are close to rectangular, and its long side is formed by a flat surface, and its short side is formed by an arcuate surface including a concentric circle with the circumferential surface. Also, the opening of this slot is wide and gradually narrows as it goes deeper.

After this compact was sintered by firing in a tunnel furnace, thread grooves were cut into the circumferential surface to produce a ferrite magnetic core as shown in FIGS. 1 to 3.

When the tip of a screwdriver was inserted into the slot 13 of these 250 ferrite magnetic cores and the torque strength was measured by applying twist, the results were as shown on the left side of FIG. 4. That is, in these samples, the torque strength was distributed in the range of 500 to 1000 g·cm, and was particularly concentrated in the range of 700 to 800 g·cm.

[Comparative example]

For comparison with the above examples, ferrite magnetic cores as shown in FIGS. 5 to 7 were manufactured from Fe--Ni--Zn based ferrite powder using the same method. The slot 3 of this ferrite magnetic core has four plane surfaces surrounding it, and its planar shape and horizontal cross-sectional shape are completely rectangular.

When the torque strength of 250 of these ferrite magnetic cores was measured in the same manner as in the above example, the results were as shown on the left and right sides of FIG. 4. That is,
In these samples, the torque strength is between 200 and 600
It was distributed in the g·cm range, and was particularly concentrated in the range of 300 to 500 g·cm.

[Effect of idea]

As explained above, with this invention, it is possible to maintain the basic shape of the conventional slotted hole, which is close to a rectangle, while preventing the reduction in torque strength of the ferrite magnetic core due to minute cracks that occur during molding. . Therefore, it is possible to improve the torque strength, and at the same time, it is convenient because the same tools such as a screwdriver that have been used in the past can be used.

[Brief explanation of the drawing]

FIG. 1 is a plan view of a ferrite magnetic core showing an embodiment of this invention, FIG. 2 is a cross-sectional view taken along the line A-A in FIG. 1, and FIG. 3 is a cross-sectional view taken along the line B-B in FIG. FIG. 4 is a graph showing the results of the torque test of the above example and its comparative example, FIG. 5 is a plan view showing a conventional example of a ferrite magnetic core, and FIG. 6 is a cross section taken along the line A-A in FIG. Figure 7 is a sectional view taken along line B-B in Figure 5, and Figure 8 is
The figure is an explanatory diagram of a press device showing an outline of the pressure forming process of a ferrite magnetic core, and A is a side view;
Figure B is a plan layout. 11...Main body, 12...Surrounding surface, 13...Slot hole,
14...Flat surface, 15...Circular surface.

Claims (1)

[Scope of utility model registration request] In a ferrite magnetic core, a threaded groove is provided on the outer circumferential surface 12 of a cylindrical main body 11 made of ferrite, and a slot 13 having a four-sided opening on at least one end face is provided, and one of the slots 13 is opposed to the other. A ferrite magnetic core characterized in that one surface facing the other is formed by a flat surface 14, and the other opposing surface is formed by an arcuate surface 15.